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Article

Novel N-Arylsulfonylindoles Targeted as Ligands of the 5-HT6 Receptor. Insights on the Influence of C-5 Substitution on Ligand Affinity

1
Bioactive Heterocycles Synthesis Laboratory (BHSL), Departamento de Farmacia, Facultad de Química y de Farmacia, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Macul, Santiago 7820436, Chile
2
Instituto de Química y Bioquímica, Facultad de Ciencias, Universidad de Valparaíso, Avenida Gran Bretaña 1111, Valparaíso 2360102, Chile
3
Centro de Investigación Farmacopea Chilena (CIFAR), Universidad de Valparaíso, Santa Marta 183, Valparaíso 2360134, Chile
4
Drug Development Laboratory, Faculty of Chemical and Pharmaceutical Sciences, Universidad de Chile, Sergio Livingstone 1007, Santiago 8380492, Chile
5
Chemical Biology & Drug Discovery Lab, Escuela de Química y Farmacia, Facultad de Medicina y Ciencia, Universidad San Sebastián, Lota 2465, Providencia, Santiago 7510157, Chile
6
Centro Interdisciplinario de Neurociencias, Pontificia Universidad Católica de Chile, Marcoleta 391, Santiago 8330024, Chile
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Pharmaceuticals 2021, 14(6), 528; https://doi.org/10.3390/ph14060528
Submission received: 24 April 2021 / Revised: 27 May 2021 / Accepted: 28 May 2021 / Published: 1 June 2021
(This article belongs to the Special Issue Molecular Pharmacology of 5-HT Receptors)

Abstract

:
A new series of twenty-two C-5 substituted N-arylsulfonylindoles was prepared with the aim of exploring the influence of C-5 substitution on 5-HT6 receptor affinity. Eleven compounds showed moderate to high affinity at the receptor (Ki = 58–403 nM), with compound 4d being identified as the most potent ligand. However, regarding C-5 substitution, both methoxy and fluorine were detrimental for receptor affinity compared to our previously published unsubstituted compounds. In order to shed light on these observations, we performed docking and molecular dynamics simulations with the most potent compounds of each series (4d and 4l) and PUC-10, a highly active ligand previously reported by our group. The comparison brings about deeper insight about the influence of the C-5 substitution on the binding mode of the ligands, suggesting that these replacements are detrimental to the affinity due to precluding a ligand from reaching deeper inside the binding site. Additionally, CoMFA/CoMSIA studies were performed to systematize the information of the main structural and physicochemical characteristics of the ligands, which are responsible for their biological activity. The CoMFA and CoMSIA models presented high values of q2 (0.653; 0.692) and r2 (0.879; 0.970), respectively. Although the biological activity of the ligands can be explained in terms of the steric and electronic properties, it depends mainly on the electronic nature.

1. Introduction

The serotonergic system modulates a diverse variety of physiological functions, such as thermoregulation, sexual and aggressive behavior, learning and memory, endocrine and gastrointestinal functions, and food intake, among others [1]. In order to perform these different tasks, the neurotransmitter 5-hydroxytryptamine (5-HT) interacts with various receptor subtypes among which the 5-HT6 receptor (5-HT6R) is one of the most recently discovered, about a quarter of a century ago [2]. The 5-HT6R is involved in several physiological functions, such as learning, memory, and neurodevelopment, and diverse pathological states, such as eating disorders, anxiety, depression, addictive behavior, schizophrenia, epilepsy and Alzheimer’s disease [3,4,5,6,7,8]. 5-HT6 receptor ligands (specially antagonists) have been shown to have procognitive behavioral effects, making them potential cognitive enhancers in conditions associated with cognitive impairment, such as Alzheimer’s disease, schizophrenia, and autism spectrum disorder, among others [9,10,11,12,13].
To date, an overwhelming majority of 5-HT6 ligands, both agonists and antagonists, share the following structural features: a basic ionizable amine group (PI), a sulfonamide moiety as a hydrogen bond acceptor group (HBA) connected to a hydrophobic site (HYD) and a π-electron donor aromatic or heterocyclic ring (AR) [9,14]. However, a few reports claim that the PI pharmacophoric feature is not essential for receptor affinity [15,16]. In this context, and given our interest in exploring the limits of the -HT6 ligand pharmacophore, we have previously reported the design, synthesis and pharmacological evaluation of a number of extended and weakly basic N-arylsulfonylindole derivatives with moderate to high affinity and antagonistic profile toward the 5-HT6 receptor [17], where our structural scaffold could be regarded as a masked and extended N-arylsulfonyltryptamine, similar to MS-245 (Figure 1). In this work, the activity of the ligands was attributed to an additional hydrogen bond between the alcohol group and Asp106 (3.32) and to the interaction of the aromatic ring linked to piperazine with a second hydrophobic pocket, proposed from molecular docking studies.
Considering the excellent affinity presented by several 5-methoxy arylsulfonyltryptamines derivatives, similar to MS-245 [19,20], we decided to explore the influence of this substitution pattern on our structural scaffold. To have a comparative insight regarding the substitution on C-5 of the indole ring and ligand affinity, we also proposed the synthesis of analogs bearing fluorine as an electron-withdrawing atom. Therefore, in this work, we report the synthesis, affinity evaluation over the 5-HT6 receptor, molecular modeling of receptor–ligand interactions through molecular dynamic simulations, and 3DQSAR studies of twenty-two new N-arylsulfonylindole compounds with C-5 substitution.

2. Results and Discussion

2.1. Synthesis

The synthesis of the new N-arylsulfonylindoles targeting the 5-HT6 receptor (4av) was performed as is briefly described in Scheme 1 (for details, see the experimental section). First, the synthesis of C-5 substituted 3-bromoacetylindoles 1ab was performed following a previously reported method for benzenesulfonyltriptamines, which has already been used by our group with slight modifications [17,21,22]. Acylation was performed in a one-pot, two-step sequence, starting from adequately substituted commercial indoles (5-methoxyindole and 5-fluoroindole) and methyl magnesium bromide to provide the corresponding magnesium salts, followed by a transmetallation reaction with anhydrous zinc chloride. Then, the zinc salts were acylated using bromoacetyl chloride under an inert atmosphere to afford bromoacetylindoles 1ab in good yields.
The previously obtained 5-fluoro and 5-methoxy bromoacetylindoles 1ab were further protected with the appropriate aromatic sulfonyl chlorides under basic conditions to afford the corresponding C-5 substituted N-arylsulfonyl-3-bromoacetylindoles 2ai with moderate to good yields [17,23]. In the next step, the prepared haloketones were subjected to bromide displacement in a basic medium at room temperature with various arylpiperazines or morpholines to obtain the respective functionalized ethanones 3av in moderate to excellent yields [17,24]. Ketones obtained after the N-alkylation reaction described above were subsequently reduced with sodium borohydride in methanol to obtain the corresponding alcohols 4av as racemic mixtures. The structures and purity of the new compounds were confirmed through spectral (1H-NMR, 13C-NMR, IR, HRMS) and chromatographic (TLC) methods. The assignment of the signals from the NMR spectra of the synthesized compounds was carried out by analyzing the multiplicity of the signals and their corresponding coupling constants, and by comparison with the NMR spectra of the unsubstituted C-5 compounds previously reported by us.

2.2. Radioligand Binding Assays

Synthesized C-5 substituted N-arylsulfonylindole derivatives were tested in standard radioligand competition binding assays, using HEK-293 cell membranes expressing a recombinant human 5-HT6 receptor. The compounds were assayed as free bases at eight different concentrations in triplicate in order to obtain the dose response curves, determine the half maximal inhibitory concentration (IC50) values, and calculate the inhibitory constant (Ki) values for each one of them (Table 1). Additionally, the structures and Ki values of some unsubstituted derivatives previously reported by our research group are shown.
All tested compounds exhibited inhibition of [125I]-SB-258585 [26] binding to 5-HT6 receptors (radioligand displacement). Eleven of the twenty-two compounds showed an important binding affinity for the 5-HT6 receptor (equal or better than 400 nM of Ki). However, C-5 substitution, regardless of the substituent, was detrimental for affinity compared to our previous set of ligands within this structural framework [17].
In general, the series with a 5-methoxy substituent exhibited better affinity than the series with 5-fluorine (eight compounds with Ki values below 400 nM including four below 200 nM), even though the best compound of all series was the 5-fluoro derivative 4d with a Ki value of 58 nM. This ligand was the only compound that was better than the endogenous ligand 5-HT and it showed a Ki in the same order of magnitude as the most potent unsubstituted compounds PUC-7, PUC-10, and PUC-32 (See Figure 1 and Table 1). However, this result was not completely surprising given the substitution pattern of 4d, which is like PUC-10. The analogous 5-methoxy derivative 4l also exhibited a good affinity (Ki 160 nM), but lower than that of 4d and PUC-10. Both 4d and 4l ligands have a 2-methoxyphenyl group on Ar2, as do five other compounds (4a, 4i, 4j, 4r and 4u). All these seven ligands are included within the eleven most potent compounds. Thus, the 2-methoxyphenyl substitution in the piperazine ring was revealed as the best-performing group. These results are in agreement with our previous report of unsubstituted compounds [17]. A more specific comparison between both series of C-5 substituted ligands indicated that 5-methoxy derivatives were superior to 5-fluoro derivatives as is shown for the following pairs of ligands (except for the mentioned pair of molecules 4d v/s 4l): 4j v/s 4a (Ki: 289 nM v/s 390 nM); 4k v/s 4c (Ki: 403 nM v/s 12,515 nM); 4n v/s 4e (Ki: 153 nM v/s 801 nM); 4m v/s 4f (Ki: 247 nM v/s 683 nM); 4u v/s 4h (Ki: 270 nM v/s 850 nM); and 4r v/s 4i (Ki: 167 nM v/s 381 nM).
Regarding the Ar1 substitution pattern, in this work we only employed electron-rich rings, given that our previous results indicated that poor electron density rings were detrimental for affinity [17]. In this way, we confirmed our previous observations that the 1-naphthyl group is the best ring to be used as a hydrophobic region, given that three of the five best compounds bear this substitution in Ar1 (4d, 4l and 4n). Regarding the substitution in Ar1, we also observed that two of the five best compounds bear a 5-bromo-2-thiophenyl group (4r and 4s with Ki 167 nM and 130 nM respectively). This group follows the structural guidelines formulated in our previous work on the requirement of electron-rich aromatic or heteroaromatic groups in that position [27]. The affinities showed by derivatives bearing a 5-bromo-2-thiophenyl substitution at Ar1 are similar to those which possess the p-iodophenyl groups, although the first ones proved to be slightly potent compared to p-iodophenyl derivatives (4i v/s 4a; 4r v/s 4j and 4s v/s 4k). This result could suggest the existence of a halogen bond between these ligands and the active site of the receptor. It is noteworthy that a similar halogen bond interaction was previously described by López-Rodríguez in a series of dimethylaminoethyl-1H-benzimidazol-yl-aryl-sulfonamides in an analogous position (i.e., the halogen group is pending from an aryl group of the sulfonamide) [9]. It is worth mentioning that in our previous work on the matter, a derivative containing a p-iodophenyl group presented high affinity (PUC-7), equipotent with PUC-10, the most active compound of the series (see Figure 1) [17].
An interesting observation could be made by comparing these C-5 substituted derivatives with the corresponding unsubstituted derivatives that were previously reported (see Table 1). In addition to the lower activity found for compounds 4d and 4l when compared with PUC-10, both 4a and 4j exhibited decreased affinity at the 5-HT6 receptor of more than one order of magnitude compared to PUC-7. In addition, the fluorine derivative 4b exhibited ten times less affinity than its unsubstituted derivative PUC-9. Similarly, compound 4g showed half the affinity of its unsubstituted derivative PUC-12. On the other hand, the methoxylated derivative 4t had approximately eight times less affinity than PUC-22, the unsubstituted derivative. The ligand 4p (Ki = 2195 nM) was approximately four times less active than the unsubstituted PUC-24 (Ki = 479 nM). When comparing derivatives 4o (Ki = 972 nM) and PUC-32 (Ki = 13.6 nM), the same trend could be observed. Perhaps the only anomalous result in this trend was presented by the trio 4e, 4n and PUC-11. In this case, the fluorine-containing derivative was less potent than the unsubstituted derivative PUC-11 (Ki = 801 nM vs. 148 nM), but the methoxylated ligand 4n (Ki = 153 nM) was equipotent with PUC-11. Overall, the results seemed to indicate that whatever C-5 substitution is used, this is detrimental for affinity, and in the best case, it is not better than its absence. With the aim of attaining better knowledge about this behavior, we performed molecular docking studies and molecular dynamic simulations over the most potent ligand of this new series 4d, its methoxylated analog 4l and the best overall compound PUC-10.

2.3. Docking Studies

Previously, we reported PUC-10 as a high affinity antagonist of the 5-HT6 receptor (Ki = 14.6 nM) [17]. Compounds 4l and 4d correspond to the C-5 substituted methoxylated and fluorinated analogues of PUC-10. Although the affinity of both compounds was not completely abolished, 4d diminished its affinity by 4-fold (Ki = 58 nM) compared to PUC-10, whereas 4l diminished its affinity by a factor of 11 (Ki = 160 nM).
To gain further molecular insights, these compounds were docked into the 5-HT6 receptor model, and the R/S stereoisomers of each compound were analyzed separately. The results presented in Figure 2 show that molecules with the hydroxy group in the S configuration allowed the placement of the naphthalene ring into a cavity created between TMH-3 and 5, and the phenylpiperazinyl moiety oriented toward TMH-2 and 7 (Figure 2A). On the other hand, molecules in R conformation flipped their binding mode by 180 degrees, with the naphthalene ring extending toward TMH-2 and 7 regions and the phenylpiperazinyl moiety fitting within the cavity between TMH-3 and 5 (Figure 2B).
Although the crystal structure of the 5-HT6 receptor was still not available, efforts to describe the orthosteric binding pocket indicated that the key residues included: Asp106 (3.32), which assists in ligand recognition by forming a salt-bridge with charged ligands; Asn288 (6.55), which forms hydrogen bond interactions with HBAs in the ligand; Val107 (3.33), Cys110 (3.36), Ala192 (5.42), Ser193 (5.43) that surround the orthosteric binding pocket; and the hydrophobic cluster on TMH-6 comprised of Trp281 (6.48), Phe284 (6.51) and Phe285 (6.52) [29]. Arylindoles are reported to bind into the described pocket by inserting the indole nucleus into the hydrophobic cluster on TMH-6 with the aryl group extending between TMH-3 and TMH-5 and interacting with the surrounding residues Val107 (3.33) and Ala192 (5.42) [14]. Based on this literature evidence, we reasoned that S stereoisomers better fit the reported binding model of arylindoles in the 5-HT6 receptor. Moreover, considering the hydrophobic nature of the naphthalene ring, it is more reasonable for this moiety to plunge deeper inside the receptor rather than face toward the extracellular region (as in the case of R stereoisomers), where the binding pocket becomes more hydrophilic.
Molecules in the S configuration were further accommodated within the binding pocket by running short MD simulations. The trajectory was then clustered using cpptraj [30], and the final interactions of the ligand–receptor complex were analyzed through the PLIP web server (Figure 3) [31]. The key salt bridge between Asp106 (3.32) and the piperazinium cation was maintained for all three compounds. In addition, a hydrogen bond was established between Asp106 (3.32) and Tyr310 (7.42), which aided in the stabilization of the ligand. This interaction network between Asp106 (3.32), Tyr310 (7.42) and the ligand is present in many crystal structures of aminergic receptors and is thought to facilitate the interaction of the amine group of the ligand with the receptor [32]. Another common binding feature for all three compounds was the insertion of the naphthalene ring into the hydrophobic cavity between TMH-3 and TMH-5, thereby interacting with hydrophobic and aromatic side chains that included P161 (4.60), F188 (5.39), V107 (3.33) and A192 (5.42).
A difference in the established interactions involved the hydrogen bonding with residue Asn288 (6.55), which has been implicated as an important residue for 5-HT6 antagonist recognition [33]. In the case of PUC-10 and 4d (Figure 3A,B), the -OH group, which is in an alpha position to the indole ring, flipped its orientation to establish a hydrogen bond with Asn288 (6.55). However, in 4l (Figure 3C), this -OH group maintained an interaction with Asp106 (3.32) and did not interact directly with Asn288 (6.55). Regarding the indole ring, it is worth noting the depth that it reaches in each compound within the hydrophobic cluster of TMH-6. PUC-10 plunged the deepest into the pocket, followed by 4d and then by 4l (Figure 3); the magnitude was in accordance with Ki values.
The GPCRs activation mechanism involves the upward movement of TMH-6 toward the extracellular compartment; therefore, the interaction of antagonists with residues in this helix would be pivotal to stabilize the receptor in its inactive form [34]. That said, PUC-10 and 4d lowered the indole ring sufficiently to establish an edge-to-face π interaction with Phe285 (6.52) from TMH-6. This residue has been identified as important for antagonist binding through site-directed mutagenesis [33]. However, in the case of 4l, the methoxy substituent imposed steric hindrance, preventing sufficient lowering of the indole ring to establish a π-stacking with Phe285 (6.52). Instead, 4l interacted with the aromatic residue through the energetically weaker hydrophobic interaction. As for the case of 4d, electron withdrawing groups, such as -F, decreased the binding energy of the T-shape aromatic interactions when the group was substituted on the facial aromatic system [35]. Therefore, is it suggested that the interaction of 4d with Phe285 (6.52) should be weaker than that established by PUC-10 (Table 2, Table 3 and Table 4).

2.4. CoMFA and CoMSIA Studies

Quantitative structure–activity relationship (QSAR) studies allow systematizing the information of the main structural and physicochemical characteristics for a series of compounds, which are responsible for their biological activity. In this way, these studies minimize the error of a qualitative SAR analysis and allow the design of new compounds based on the information obtained.
In order to find the best models, a sequential search for the best field combinations for comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) was carried out (34 combinations of steric + electrostatic + hydrophobic + hydrogen-bond donor + hydrogen-bond acceptor; Table S1 in Supplementary Materials). The best models obtained are presented in Table 5.
As is shown in Table 5, both final models have a value of q2 > 0.5 and high r2test values (0.786 and 0.726 for CoMFA and CoMSIA respectively). An equilibrium can be seen in terms of the steric and electrostatic contributions to biological affinity. However, in both cases, the electrostatic contribution is higher. Thus, these properties can play a more important role in the affinity. To validate both models, a test set study was carried out for both models. In Table S2 of Supplementary Materials, we report the values of the external validation. In both cases, both models passed validation. Likewise, the experimental affinity values versus predicted values, in logarithmic scale (pKi = −logKi) for each compound according to the CoMFA and CoMSIA models, are also shown in Table S3 (Supplementary Material).
The CoMFA model presented 24 molecules with a negative residual (pKiexp − pKipred) and 22 with a positive residual, while CoMSIA presented 28 predictions with negative residual and 18 with positive residual. Therefore, the CoMFA model presents the best equilibrium in terms of predictive capability, while CoMSIA tends to overestimate prediction values. Figure 4A,B shows the distribution of experimental versus predicted values for CoMFA and CoMSIA. As can be seen in both cases, one compound deviated in more than one logarithmic unit in the predicted value of Ki (compound 4s, represented as a triangle). All other training and test set compounds had an adequate distribution along the y = x straight line. The best value fit was obtained for the CoMSIA model.
Unlike a 2D-QSAR, the results of a 3D-QSAR can be represented as contour maps around the molecules of the study. The analysis of the different colored polyhedrons around a molecule (e.g., the most active compound in the series) allows understanding the main characteristics that are favorable or unfavorable for affinity or biological activity. Figure 5 shows the results of the steric (Figure 5A,B) and electrostatic (Figure 5C,D) maps for CoMFA and CoMSIA over the most active compound of our synthetic series (derivative 4d).
The CoMFA steric contour map (Figure 5A) shows a green polyhedron in the phenyl-piperazine zone, that is, it is favorable for biological activity to use bulky substituents in that position. The less active compounds present a morpholino group instead of the aryl-piperazine fragment, which may partly explain the lower activity of these derivatives. CoMSIA steric contour map (Figure 5B) is consistent with this information but shows an additional green polyhedron close to the sulfonyl group region; therefore, the direct connection of bulky rings or alkyl groups to the nitrogen atom of the indole ring would be an interesting option to explore. Close to the hydroxyl group, both the CoMFA and CoMSIA steric contour maps (Figure 5A,B) show a yellow polyhedron, suggesting that the use of low-volume functional groups in that area is most appropriate. The elimination of the hydroxyl group could be evaluated, although there are additional electronic factors linked to this functional group. Finally, near the naphthyl ring, there is a set of yellow polyhedrons in CoMFA (Figure 5A) and a large yellow polyhedron in the steric map of CoMSIA (Figure 5B). Therefore, the insertion of bulky groups at positions 6 and 7 of the naphthyl group should be avoided. On the other hand, the electrostatic contour maps for CoMFA and CoMSIA (Figure 5C,D) are concordant. In both cases, a red polyhedron can be seen through the piperazine and indole connecting chain. In the case of CoMSIA, the red polyhedron is closer to the piperazine nitrogen atom 1 (N-1) (Figure 5D). Therefore, the insertion of groups favoring a higher charge density over this nitrogen atom would be favorable. This implies that increasing the basicity of such nitrogen atom would be favorable, which is consistent with our docking studies for the most active derivative 4d, where the nitrogen atom (N-1) of piperazine moiety mediates a key salt bridge with Asp106 (3.32). A red polyhedron over the hydroxyl group on CoMFA map (Figure 5C) indicates that the presence of an electronegative atom in that position would be beneficial. Another red polyhedron is seen close to the halogen of the indole ring. Complementary to this information, the CoMSIA electrostatic contour map (Figure 5D) shows a blue polyhedron in the indole ring. Therefore, the presence of electron-attracting groups on the indole scaffold would be beneficial for biological activity. Among them, it would be interesting to explore groups NO2, CF3, CN and COR among others. In Figure 6, we summarize the structure–activity relationships found in this study. With this information, new active molecules can be designed and synthesized in the future.

3. Materials and Methods

All organic solvents used for the synthesis were of analytical grade. All reagents used were purchased from Sigma-Aldrich (St. Louis, MO, USA), Merck (Kenilworth, NJ, USA) or AK Scientific (Union City, CA, USA) and were used as received. Melting points were determined on a Stuart Scientific SMP30 apparatus (Bibby Scientific Limited, Staffordshire, UK) and are uncorrected. NMR spectra were recorded on a Bruker Avance III HD 400 (Billerica, MA, USA) at 400.1 MHz for 1H, 100.6 MHz for 13C-NMR and 376.5 MHz for 19F-NMR using the solvent signal (CDCl3 or DMSO-d6) as reference. The chemical shifts are expressed in ppm (δ scale) downfield from tetramethylsilane (TMS). Multiplicity is given as follows: s, singlet; bs, broad singlet; d, doublet; t, triplet; td, triplet of doublets; m, multiplet. Coupling constants values (J) are given in Hertz. Atom numbering and, 1H and 13C NMR spectra of the final compounds are available in the ESI. High resolution mass spectra were obtained on mass spectrometer with flight time analyzer (TOF) and Triwave® system model SYNAPT™ G2 (WATERS, Milford, MA, USA), using atmospheric pressure ionization with electro spray (ESI+/−), Capillarity 3.0, source temperature 100 °C, desolvation temperature 500 °C. The IR spectra were obtained on a Bruker Vector 22 spectrophotometer (Billerica, MA, USA) using KBr discs. Column chromatography was performed on Merck silica gel 60 (70–230 mesh). Thin layer chromatographic separations were performed on Merck silica gel 60 (70–230 mesh) chromatofoils.

3.1. Synthetic Procedures

2-bromo-1-(5-fluoro-1H-indol-3-yl)ethan-1-one (1a)
To a solution of 5-fluoroindole (1 g, 7.40 mmol) in dry CH2Cl2 (30 mL) was added anhydrous zinc chloride (2.08 g, 15.25 mmol) under N2 atmosphere; immediately, methylmagnesium bromide 3 M (2.5 mL, 7.50 mmol) was slowly added over a 20 min period and the mixture was vigorously stirred for 2 h at room temperature. After this time, bromoacetyl chloride (0.84 mL, 9.65 mmol) was added in one portion and the mixture was stirred until the starting product disappeared upon checking TLC. The reaction was quenched by adding saturated ammonium chloride solution and extracted with CH2Cl2. The combined organic layers were dried with anhydrous sodium sulfate and the removal of the solvent afforded a residue, which was further purified by column chromatography on silica gel (CH2Cl2/ EtOAc 5:1) to give 929 mg of (1a) as a light brown solid. Yield: 49% mp: 200.5–200.9 °C; IR (KBr) cm−1: 3196, 2955, 1645, 1519, 1467 and 1168. 1H-NMR (400.1 MHz, DMSO-d6) δ (ppm): 12.28 (s, 1H, N-H), 8.54 (d, J = 3.1 Hz, 1H, H-2′), 7.83 (dd, J = 2.2 and 9.8 Hz, 1H, H-4′), 7.53 (dd, J = 4,6 and 8,8 Hz, 1H, H-7′), 7,10 (td, J = 2.4 and 9.3 Hz, 1H, H-6′), 4.65 (s, 2H, H-2). 13C-NMR (100.6 MHz, DMSO-d6) δ (ppm): 186.8, 159.2 (d, J = 235.1 Hz); 137.0, 133.7, 126.5 (d, J = 11.1 Hz), 114.1, 114.0, 111.8 (d, J = 26.0 Hz), 106.5 (d, J = 26.0 Hz), 33.7. HRMS calculated for C10H8BrFNO [M + H+]: 255.9768; Found: 255.9764.
2-bromo-1-(5-methoxy-1H-indol-3-yl)ethan-1-one (1b)
5-Methoxyindole (1.01 g, 6.80 mmol), anhydrous zinc chloride (1.85 g, 13.6 mmol), methylmagnesium bromide 3M (5 mL, 15.0 mmol) and bromoacetyl chloride (0.80 mL, 9.19 mmol) were reacted to give a residue, which was purified by column chromatography on silica gel using CH2Cl2/EtOAc 5:1 to afford 1.21 g of (1b) as a pale pink solid. Yield: 66% mp: 230–233 °C; IR (KBr) cm−1: 3193, 1643. 1H-NMR (400.1 MHz, DMSO-d6) δ (ppm): 12.07 (s, 1H, N-H); 8.38 (d, J = 3.2 Hz, 1H, H-2′); 7.67 (d, J = 2.0 Hz, 1H, H-4′); 7.40 (d, J = 8.8 Hz, 1H, H-7′); 6.88 (dd, J = 8.8 and 2.3 Hz,1H, H-6′); 4.85 (s, 2H, H-2); 3.79 (s, 3H, OCH3). 13C-NMR (100.6 MHz, DMSO-d6) δ (ppm): 186.4, 156.1, 135.2, 131.8, 126.6, 113.8, 113.5, 113.3, 103.3, 55.7 and 46.6. HRMS calculated for C11H11BrNO2 [M + H+]: 267.9968; Found: 267.9968.
General Procedure for 2-Bromo-1-(arylsulfonyl-1H-3-yl)ethanone Derivatives (2ai):
2-bromo-1-(5-fluoro-1-((4-iodophenyl)sulfonyl)-1H-indol-3-yl)ethan-1-one (2a)
In a round bottom flask under N2, 2-bromo-1-(5-fluoro-1H-indol-3-yl)ethan-1-one (1a) (2.0 g, 7.81 mmol), p-iodobenzenesulfonyl chloride (2.84 g, 9.39 mmol), DMAP (96 mg, 0.78 mmol), and triethylamine (1.6 mL, 11.53 mmol) were dissolved in 30 mL of dry CH2Cl2, and the solution was stirred at room temperature until the starting material disappeared upon checking TLC. The reaction mixture was quenched by dilution with CH2Cl2 (30 mL), and the organic extract was washed with 1N HCl (20 mL). The organic layer was dried over anhydrous Na2SO4 and filtered, and the solvent was removed under vacuum. The product was purified by silica gel column chromatography using CH2Cl2/hexane (2:1) to give 2.08 g of (2a) as light pink crystalline plates. Yield: 51% m.p.: 165.8–166.4 °C; IR (KBr) cm−1: 1683, 1378, 1192. 1H-NMR (400.1 MHz, DMSO-d6) δ (ppm): 8.24 (s, 1H, H-2′), 7.93 (dd, J = 8.9 and 2.5 Hz, 1H, H-4′), 7.80 (m, 3H, H-7′, H-3″ and H-5″), 7,56 (d, J = 8.5 Hz, 2H, H-2″ and H-6″), 7.08 (td, J = 8.9 and 2.6 Hz, 1H, H-6′), 4.45 (s, 2H, H-2). 13C-NMR (100.6 MHz, DMSO-d6) δ (ppm): 185.6, 159.8 (d, J = 243.8 Hz), 138.1, 135.6, 132.3, 129.9, 127.8, 127.1, 113.8, 113.6, 113.2 (d, J = 9.5 Hz), 108.1 (d, J = 25.6 Hz), 102.3 and 44.7. HRMS calculated for C16H11BrFINO3S [M + H+]: 521.8666; Found: 521.8673.
2-bromo-1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)ethan-1-one (2b)
2-Bromo-1-(5-fluoro-1H-indol-3-yl)ethan-1-one (1a) (920 mg, 3.60 mmol), naphthalenesulfonyl chloride (947 mg, 4.32 mmol), DMAP (44 mg, 0.36 mmol) and triethylamine (0.8 mL, 5.77 mmol) were reacted to give a crude mixture, which was purified by column chromatography on silica gel using CH2Cl2/hexane 2:1 to afford 675 mg of (2b) as pale pink crystalline plates. Yield: 42% m.p.: 176.5–177.7 °C; IR (KBr) cm−1: 1676, 1375, 1159. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.53 (d, J = 8.0 Hz, 1H, H-2″), 8.53 (s, 1H, H-2′), 8.31 (dd, J = 7.5 and 1.0 Hz, 1H, H-8″), 8.06 (d, J = 8.0 Hz, 1H, H-4′), 7.83–7.88 (m, 2H, H-4″ and H-5″), 7.63–7.57 (m, 2H, H-3″ and H-7′), 7.55–7.48 (m, 2H, H-6″ and H-7″), 6.96 (td, J = 9.0 and 2.5 Hz, 1H, H-6′), 4.47 (s, 2H, H-2). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 187.1, 161.0 (d, J = 244.6 Hz, 137.2, 134.7, 134.5, 132.5, 131.7, 130.0, 129.9, 129.0 (d, J = 11.1 Hz), 128.2, 128.1, 124.5, 123.5, 117.6 (d, J = 4.1 Hz), 114.8, 114.6, 114.5 (d, J = 9.4 Hz), 109.3 (d, J = 25.4 Hz) and 46.1. HRMS calculated for C20H14BrFNO3S [M + H+]: 445.9856; Found: 445.9854.
2-bromo-1-(5-fluoro-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)ethan-1-one (2c)
2-Bromo-1-(5-fluoro-1H-indol-3-yl)ethan-1-one (1a) (1.44 g, 5.63 mmol), p-methoxybenzenesulfonyl chloride (1.40 g, 6.76 mmol), DMAP (69 mg, 0.57 mmol) and triethylamine (1.2 mL, 8.65 mmol) were reacted to give a crude mixture, which was purified by column chromatography on silica gel using CH2Cl2/hexane 2:1 to afford 897 mg of (2c) as orange crystalline plates. Yield: 37% m.p.: 190.3–194.1 °C; IR (KBr) cm−1: 1672, 1379 and 1163. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.85 (s, 1H, H-2′), 7.96 (d, J = 9.0 Hz, 2H, H-2″ and H-6″), 7.88 (dd, J =9.1 and 4.3, 1H, H-4′), 7.83 (dd, J = 9.1 and 2.6 Hz, 1H, H-7′), 7.12 (td, J = 9.0 and 2.6 Hz, 1H, H-6′), 7.00 (d, 9.0 Hz, 2H, H-3″ and H-5″), 4.89 (s, 2H, H-2), 3.78 (s, 3H, OCH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 187.4, 164.7, 160.3 (d, J = 241.1 Hz), 135.8, 130.9, 130.0, 128.6 (d, J = 11.0 Hz), 127.9, 117.6, 115.3, 114.7 (d, J = 9.4 Hz), 114.0 (d, J = 25.7 Hz), 108.2 (d, J = 25.3 Hz), 56.1, 46.8. HRMS calculated for C17H14BrFNO4S [M + H+]: 425.9805; Found: 425.9798.
2-bromo-1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-fluoro-1H-indol-3-yl)ethan-1-one (2d)
2-Bromo-1-(5-fluoro-1H-indol-3-yl)ethan-1-one (1a) (1 g, 3.91 mmol), 5-bromothiophene-2-sulfonyl chloride (1.23 g, 4.69 mmol), DMAP (48 mg, 0.39 mmol) and triethylamine (0.8 mL, 5.77 mmol) were reacted to give a crude mixture, which was purified by column chromatography on silica gel using CH2Cl2/hexane (2:1) to afford 549 mg of (2d) as pale pink crystalline plates. Yield: 29%; m.p.: 171.0–174.6 °C; IR (KBr) cm−1: 1676, 1384, 1160, 1534, 1471, 1198. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.20 (s, 1H, H-2′), 7.94 (dd, J = 8.9 and 2.5 Hz, 1H, H-4′), 7.81 (dd, J = 9.1 and 4.3 Hz, 1H, H-7′), 7.48 (d, J = 4.1 Hz, 1H, H-2″), 7.11 (td, J = 8.9 and 2.6 Hz, 1H, H-6′); 6.99 (d, J = 4.1 Hz, 1H, H-3″), 4.47 (s, 2H, H-2). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 186.7, 160.9 (d, J = 243.4 Hz), 137.2, 134.8, 133.1, 130.9 (d, J = 16.8 Hz), 128.9 (d, J = 11.0 Hz), 124.1, 118.6 (d, J = 4.2 Hz), 115.0, 114.4, 114.3 (d, J = 9.5 Hz), 109.2 (d, J = 25.7 Hz), 45.8. HRMS calculated for C14H9Br2FNO3S2 [M + H+]: 479.8369; Found: 479.8363.
2-bromo-1-(1-((4-iodophenyl)sulfonyl)-5-methoxy-1H-indol-3-yl)ethan-1-one (2e)
2-Bromo-1-(5-methoxy-1H-indol-3-yl)ethan-1-one (1b) (1.06 g, 3.7 mmol), p-iodobenzenesulfonyl chloride (1.12 g, 4.1 mmol), DMAP (46 mg, 0.38 mmol) and triethylamine (0.6 mL, 4.32 mmol) were reacted to give a crude mixture, which was purified by column chromatography on silica gel using CH2Cl2 to afford 796 mg of (2e) as colorless crystalline plates. Yield: 40%; m.p.: 189.0–190.0 °C; IR (KBr) cm−1: 1681, 1378, 1132, 1053, 607, 586. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.44 (s, 1H, H-2′), 8.06 (d, J = 8.1 Hz; 2H, H-3″ and H-5″), 8.00–7.98 (m, 2H, H-4′ and H-7′), 7.22 (d, J = 8.1 Hz, 2H, H-2″ and H-6″), 7.01 (d, J = 9.1 Hz, 1H, H-6′), 4.77 (s, 2H, H-2), 3.04 (s, 3H, OCH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 186.9, 157.9, 139.0 (2C), 136.8, 132.3, 129.1, 128.7, 128.2 (2C), 118.4, 116.2, 113.9, 104.6, 102.9, 55.7, 45.9. HRMS calculated for C17H14BrINO4S [M + H+]: 533.8866; Found: 533.8862.
2-bromo-1-(5-methoxy-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)ethan-1-one (2f)
2-Bromo-1-(5-methoxy-1H-indol-3-yl)ethan-1-one (1b) (2.00 g, 7.5 mmol), naphthalenesulfonyl chloride (1.87 g, 8.2 mmol), DMAP (100 mg, 0.82 mmol) and triethylamine (1.1 mL, 7.93 mmol) were reacted to give a crude mixture, which was purified by column chromatography on silica gel using CH2Cl2 to afford 1.30 g of (2f) as a colorless crystalline plate. Yield: 38%; m.p.: 135.0–137.0 °C; IR (KBr) cm−1: 1656, 1372, 1165, 1027, 689. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.54 (d; J = 8.5 Hz, 1H, H-2″), 8.44 (s, 1H, H-2′), 8.26 (dd, J = 7.5 and 1.1 Hz, 1H, H-8″), 8.00 (d, J = 8.3 Hz, 1H, H-4″), 7.79 (d, J = 8.1 Hz, 1H, H-5″), 7.65 (d, J = 2.6 Hz, 1H, H-4′), 7.59–7.53 (m, 1H, H-3″), 7.53 (d, J = 9.2 Hz, 1H, H-7′), 7.47 (t, J = 7.81, 2H, H-7″ and H-6″), 6.81 (dd, J = 9.1 and 2.6 Hz, 1H, H-6′), 4.48 (s, 2H, H-2), 3.70 (s, 3H, OCH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 187.5, 158.5, 136.9, 134.7, 133.6, 132.8, 130.9, 129.9, 129.7, 129.5, 128.9, 128.3, 127.9, 124.5, 123.6, 117.7, 116.3, 114.2, 104.9, 56.1, and 46.3. HRMS calculated for C21H17BrNO4S [M + H+]: 458.0056; Found: 458.0063.
2-bromo-1-(5-methoxy-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)ethan-1-one (2g)
2-Bromo-1-(5-methoxy-1H-indol-3-yl)ethan-1-one (1b) (2.00 g, 7.5 mmol), p-methoxybenzenesulfonyl chloride (1.69 g, 8.2 mmol), DMAP (91 mg, 0.7 mmol) and triethylamine (1.2 mL, 8.65 mmol) were reacted to give a crude mixture, which was purified by column chromatography on silica gel using CH2Cl2 to afford 1.14 g of (2g) as pale brown crystalline plates. Yield: 35% m.p.: 173–176 °C; IR (KBr) cm−1: 1673, 1375 1166, 994 and 680. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.18 (s, 1H, H-2′), 7.78 (d, J = 9.0 Hz, 2H, H-2″), 7.72 (d, J = 9.1 Hz, 1H, H-7′), 7.69 (d, J = 2.6 Hz, 1H, H-4′), 6.91 (dd, J = 9.1 and 2.6 Hz, 1H, H-6′), 6.84 (d, J = 9.0 Hz, 2H, H-3″), 4.49 (s, 2H, H-2), 3.75 (s, 3H, 4″OCH3), 3.72 (s, 3H, 5′-OCH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 187.0, 164.5, 157.8, 132.6, 129.5 (2C), 129.2, 128.6, 128.4, 117.8, 115.9, 114.9 (2C), 104.4, 108.2, 55.8, 55.7, 45.9. HRMS calculated for C18H17BrNO5S [M + H+]: 438.0005; Found: 438.0012.
2-bromo-1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-methoxy-1H-indol-3-yl)ethan-1-one (2h)
2-Bromo-1-(5-methoxy-1H-indol-3-yl)ethan-1-one (1b) (632 mg, 2.4 mmol), 5-bromothiophene-2-sulfonyl chloride (1.07 g, 2.6 mmol), DMAP (30 mg, 0.25 mmol) and triethylamine (0.4 mL, 2.88 mmol) were reacted to give a crude mixture, which was purified by column chromatography on silica gel using CH2Cl2 to afford 312 mg of (2h) as a white crystalline plate. Yield: 30%; m.p.: 151.0–152.0 °C; IR (KBr) cm−1: 1656, 1390, 1169, 854, 688, 618. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.11 (s, 1H, H-2′), 7.73 (d, J = 9.0 Hz, 1H, H-7′), 7.72 (d, J = 2.7 Hz, 1H, H-4′), 7.46 (d, J = 4.1 Hz, 1H, H-3″), 6.99–6.94 (m, 2H, H-2″ and H-6′), 4.49 (s, 2H, H-2), 3.79 (s, 3H, 5′-OCH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 187.0, 158.1, 137.5, 134.6, 132.1, 131.0, 128.9, 128.8, 123.7, 118.8, 116.3, 114.0, 104.8, 55.8, and 45.9. HRMS calculated for C15H12Br2NO4S2 [M + H+]: 491.8569; Found: 491.8569.
2-bromo-1-(5-methoxy-1-tosyl-1H-indol-3-yl)ethan-1-one (2i)
2-Bromo-1-(5-methoxy-1H-indol-3-yl)ethan-1-one (1b) (623 mg, 2.3 mmol), p-toluensulfonyl chloride (687 mg, 3.4 mmol), DMAP (46 mg, 0.38 mmol) and triethylamine (0.35 mL, 2.52 mmol) were reacted to give a crude mixture, which was purified by column chromatography on silica gel using CH2Cl2-hexane (1:1) to afford 676 mg of (2i) as a white crystalline plate. Yield: 70%; m.p.: 182.0–183.0 °C; IR (KBr) cm−1: 1680, 1376, 1175, 891, 678. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.21 (s, 1H, H-2′), 7.74–7.67 (m, 4H, H-4′ and H-7′, H2″), 7.18 (d, J = 8.0 Hz, 2H, H-3″), 6.90 (d, J = 9.0 Hz, 1H, H-6′), 4.27 (s, 2H, H-2), 3.74 (s, 3H, 5′-OCH3), 2.26 (s, 3H, 4″-CH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 187.5, 158.2, 146.5, 134.7, 133.5, 130.7(2C), 129.7, 129.1, 127.6 (2C), 118.3, 116.4, 114.4, 104.9, 56.1, 31.9, 22.1. HRMS calculated for C18H17BrNO4S [M + H+]: 422.0056; Found: 422.0057.
General Procedure for 2-(4-(Aryl)piperazin-1-yl)-1-(1-arylsulfonyl-1H-indol-3-yl)ethanone Derivatives (3av):
1-(5-fluoro-1-((4-iodophenyl)sulfonyl)-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-one (3a)
To a solution of 1-(2-methoxyphenyl)-piperazine (208 mg, 1.08 mmol) and potassium carbonate (149 mg, 1.08 mmol) in acetone (30 mL) 2-bromo-1-(5-fluoro-1-((4-iodophenyl)sulfonyl)-1H-indol-3-yl)ethan-1-one (2a) (511 mg, 0.98 mmol) was added and the mixture was stirred for 24 h at room temperature. The reaction was stopped by dilution with water (30 mL) and the organic layer was extracted with CH2Cl2 (3 × 30 mL). The combined organic layers were dried with anhydrous sodium sulfate, and removal of the solvent under vacuum afforded a crude residue. The solid was purified by column chromatography on silica gel (CH2Cl2) to yield 240 mg of (3a) as an orange gel. Yield: 39% m.p.: 155 °C (dec); IR (KBr) cm−1: 1656, 1562, 1500, 1385, 1174, 1142, 1028, 736. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.77 (s, 1H, H-2′), 8.04 (dd, J = 9.1 and 2.6 Hz, 1H, H-4′), 7.87 (dd, J = 9.1 and 4.3 Hz, 1H, H-7′), 7.83 (d, J = 8.5 Hz, 2H, H-3″ and H-5″), 7.62 (d, J = 8.6 Hz, 2H, H-2″ and H-6″), 7.11 (td, J = 8.9 and 2.6 Hz, 1H, H-6′), 7.05–7.00 (m, 1H, H-5‴), 6.96 (d, J = 4.1 Hz, 2H, H-3‴ and H-4‴), 6.88 (d, J = 7.8 Hz, 1H, H-6‴), 3.87 (s, 3H, OCH3), 3.68 (s, 2H, H-2), 3.14 (bs, 4H, H-3⁗ and H-5⁗), 2.80 (bs, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.7, 161.1 (d, J = 242.5 Hz), 152.7, 141.5, 139.5, 137.5, 134.5, 131.1, 129.7 (d, J = 11.0 Hz), 128.5, 123.6, 121.5, 120.0 (d, J = 4.0 Hz), 118.6, 114.6 (d, J = 14.4 Hz), 114.4 (d, J = 1.5 Hz), 111.8, 109.6 (d, J = 25.5 Hz), 103.4, 67.5, 55.8, 54.2 (2C) and 51.1 (2C). HRMS calculated for C27H26FIN3O4S [M + H+]: 634.0667; Found: 634.0681.
1-(5-fluoro-1-((4-iodophenyl)sulfonyl)-1H-indol-3-yl)-2-(4-(pyridin-2-yl)piperazin-1-yl)ethan-1-one (3b)
1-(2-Pyridyl)-piperazine (406 mg, 2.49 mmol), potassium carbonate (344 mg, 2.49 mmol) and 2-bromo-1-(5-fluoro-1-((4-iodophenyl)sulfonyl)-1H-indol-3-yl)ethan-1-one (2a) (1.18 g, 2.26 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to obtain 615 mg of pure product (3b) as white crystalline plates. Yield: 45% m.p.: 133.1–135.7 °C; IR (KBr) cm−1: 1664, 1387 and 1146, 1595, 1538, 1171, 737. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.75 (s, 1H, H-2′), 8.23 (d, J = 4.3 Hz, 1H, H-3‴), 8.05 (dd, J = 9.0 and 2.3 Hz, 1H, H-4′), 7.89–7.87 (m, 1H, H-7′), 7.85 (d, J = 8.6 Hz, 2H, H-3″ and H-5″), 7.62 (d, J = 8.4 Hz, 2H, H-2″ and H-6″), 7.52 (t, J = 7.7 Hz, 1H, H-5‴), 7.13 (td, J = 8.9 and 2.4 Hz, 1H, H-6′), 6.69–6.65 (m, 2H, H-4‴ and H-6‴), 3.69 (s, 2H, H-2), 3.64–3.57 (m, 4H, H-3⁗ and H-5⁗), 2.75–2.69 (m, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 192.9, 160.7 (d, J = 242.7 Hz), 159.4, 148.0, 139.1 (2C), 137.6, 136.9, 134.0, 130.7, 129.2 (d, J = 11.1 Hz), 128.1 (2C), 119.5 (d, J = 4.2 Hz), 114.2 (d, J = 21.4 Hz), 114.0 (d, J = 4.9 Hz), 113.6, 109.2 (d, J = 25.5 Hz), 107.2, 103.1, 66.8, 53.3 (2C), 45.3 (2C). HRMS calculated for C25H23FIN4O3S [M + H+]: 605.0514; Found: 605.0522.
1-(5-fluoro-1-((4-iodophenyl)sulfonyl)-1H-indol-3-yl)-2-morpholinoethan-1-one (3c)
Morpholine (0.1 mL, 1.16 mmol), potassium carbonate (100 mg, 0.72 mmol) and 2-bromo-1-(5-fluoro-1-((4-iodophenyl)sulfonyl)-1H-indol-3-yl)ethan-1-one (2a) (340 mg, 0.65 mmol) were reacted to give an orange gel, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to obtain 190 mg of pure product (3c) as orange crystalline plates. Yield: 55%; m.p.: 139.7–141.1 °C; IR (KBr) cm−1: 1655, 1568, 1535, 1389, 1174, 1144, 738. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.59 (s, 1H, H-2′); 7.93 (dd, J = 9.1 and 2.6 Hz, 1H, H-4′); 7.82–7.75 (m, 3H, H-7′, H-3″ and H-5″); 7.56 (d, J = 9.0 Hz, 2H, H-2″ and H-6″); 7.03 (td, J = 8.9 and 2.6 Hz, 1H, H-6′); 3.75–3.67 (m, 4H, H-3⁗ and H-5⁗); 3.58 (s, 2H, H-2); 2.59–2.52 (m, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 192.5, 160.7 (d, J = 242.7 Hz), 139.1 (2C), 136.9, 133.7, 130.7, 129.1 (d, J = 11.0 Hz), 128.1 (2C), 119.5 (d, J = 4.2 Hz), 114.2 (d, J = 36.5 Hz), 114.1, 109.1 (d, J = 25.5 Hz), 103.1, 66.8 (2C), 66.7 and 53.8 (2C). HRMS calculated for C20H19FIN2O4S [M + H+]: 529.0089; Found: 529.0113.
1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-one (3d)
1-(2-Methoxyphenyl)-piperazine (428 mg, 2.22 mmol), potassium carbonate (307 mg, 2.22 mmol) and 2-bromo-1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)ethan-1-one (2b) (900 mg, 2.02 mmol) were reacted to give an orange gel, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to obtain 1.04 g of pure product (3d) as a yellowish gel. Yield: 93% m.p.: product in gel state °C; IR (KBr) cm−1: 1655, 1593, 1502, 1373, 1174, 1146. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.93 (s, 1H, H-2′); 8.56 (d, J = 8.6 Hz, 1H, H-2″); 8.28 (d, J = 6.8, 1H, H-8″); 8.02 (d, J = 8.2 Hz, 1H, H-4′); 7.94 (dd, J = 9.1 and 2.5 Hz, 1H, H-4″); 7.82 (d, J = 8.1 Hz, 1H, H-5″); 7.66 (dd, J = 9.1 and 4.3 Hz, 1H, H-7′); 6.98–6.93 (m, 2H, H-6′ and H-5‴); 6.88 (d, J = 4.2 Hz, 2H, H-3‴ and H-4‴); 6.81 (d, J = 7.9 Hz, 1H, H-6‴); 3.79 (s, 3H, OCH3); 3.65 (s, 2H, H-2); 3.07 (s, 4H, H-3⁗ and H-5⁗); 2.76 (s, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 192.9, 160.5 (d, J = 242.0 Hz), 152.3, 141.0, 136.7, 134.7, 134.4, 132.6, 130.8, 130.5, 129.6, 129.4, 128.9 (d, J = 11.2 Hz), 128.0, 127.6, 124.2, 124.1, 123.3 (d, J = 3.8 Hz), 121.0, 118.6 (d, J = 4.1 Hz), 118.4, 114.0 (d, J = 8.7 Hz), 113.7, 111.4, 109.0 (d, J = 25.5 Hz), 66.8, 55.4, 53.8 (2C) and 50.4 (2C). HRMS calculated for C31H29FN3O4S [M + H+]: 558.1857; Found: 558.1885.
1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-(4-(pyridin-2-yl)piperazin-1-yl)ethan-1-one (3e)
1-(2-Pyridyl)-piperazine (315 mg, 1.93 mmol), potassium carbonate (267 mg, 1.93 mmol) and 2-bromo-1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)ethan-1-one (2b) (780 mg, 1.75 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to obtain 528 mg of pure product (3e) as white crystalline plates. Yield: 57% m.p.: 173–175.7 °C; IR (KBr) cm−1: 1656, 1596, 1531, 1382, 1199, 1170. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 9.02 (s, 1H, H-2′), 8.64 (d, J = 8.7 Hz, 1H, H-2″); 8.38 (d, J = 7.5 Hz, 1H, H-8″); 8.25 (d, J = 4.6 Hz, 1H, H-4′); 8.10–8.06 (m, 1H, H-3‴); 8.04 (dd, J = 9.2 and 2.4 Hz, 1H, H-4″); 7.88 (d, J = 8.2 Hz, 1H, H-5″); 7.79 (dd, J = 9.1 and 4.3 Hz, 1H, H-7′); 7.64–7.58 (m, 2H, H-3″ and H-5‴); 7.56–7.51 (m, 2H, H-6″ and H-7″); 7.06 (td, J = 8.9 and 2.3 Hz, 1H, H-6′); 6.70–6.66 (m, 2H, H-4‴ and H-6‴); 3.67 (s, 2H, H-2); 3.58–3.53 (m, 4H, H-3⁗ and H-5⁗); 2.72–2.67 (m, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.1, 160.5 (d, J = 241.0 Hz, 1C), 159.4, 147.9, 137.6, 136.7, 134.6, 134.3, 132.5, 130.8, 130.5, 129.6, 129.4, 128.9 (d, J = 11.1 Hz), 127.9, 127.6, 124.2, 123.2, 118.6 (d, J = 4.2 Hz), 114.1 (d, J = 10.0 Hz), 113.9 (d, J = 26.0 Hz), 113.6, 109.0 (d, J = 25.4 Hz), 107.2, 67.1, 53.3 (2C) and 45.2 (2C). HRMS calculated for C29H26FN4O3S [M + H+]: 529.1704; Found: 529.1720.
1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-morpholinoethan-1-one (3f)
Morpholine (0.12 mL, 1.39 mmol), potassium carbonate (188 mg, 1.36 mmol) and 2-bromo-1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)ethan-1-one (2b) (550 mg, 1.23 mmol) were reacted to obtain a crude mixture, which was purified by column chromatography employing CH2Cl2/ethyl acetate 5:1 to yield 436 mg of (3f) as a yellow gel. Yield: 78% m.p.: 145–148 °C; IR (KBr) cm−1: 1665, 1587, 1535, 1361, 1171, 1155. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.96 (s, 1H, H-2′); 8.66 (d, J = 8.6 Hz, 1H, H-2″); 8.37 (d, J = 7.5 Hz, 1H, H-8″); 8.16 (d, J = 8.2, 1H, H-5″); 8.01 (dd, J = 9.1 and 2.4 Hz, 1H, H-4′); 7.94 (d, J = 8.1 Hz, 1H, H-4″); 7.74 (dd, J = 9.1 and 4.3 Hz, 1H, H-7′); 7.70–7.65 (m, 1H, H-3″); 7.62 (dd, J = 10.9 and 4.7 Hz, 2H, H-6″ and H-7″); 7.04 (td, J = 9.0 and 2.0 Hz, 1H, H-6′); 3.79–3.75 (m, 4H, H-3⁗ and H-5⁗); 3.66 (s, 2H, H-2); 2.63 (s, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 192.7, 160.5 (d, J = 242.0 Hz), 136.7, 134.4, 134.3 132.5, 130.8, 130.5, 129.6, 129.3, 128.8 (d, J = 11.0 Hz), 127.9, 127.6, 124.2, 123.2, 118.6 (d, J = 4.2 Hz), 114.0 (d, J = 1.8 Hz), 113.9 (d, J = 18.5 Hz), 108.9 (d, J = 25.5 Hz), 67.0, 66.8 (2C) and 53.8 (2C). HRMS calculated for C24H22FN2O4S [M + H+]: 453.1279; Found: 453.1312.
1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-(4-(pyrimidin-2-yl)piperazin-1-yl)ethan-1-one (3g)
1-(2-Pyrimidyl)-piperazine (146 mg, 0.89 mmol), potassium carbonate (123 mg, 0.89 mmol) and 2-bromo-1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)ethan-1-one (2b) (363 mg, 0.81 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 329 mg of (3g) as white crystalline plates. Yield: 77%; m.p.: 185.9–187.5 °C; IR (KBr) cm−1: 1659, 1585, 1544, 1359, 1169, 1147. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 9.02 (s, 1H, H-2′); 8.66 (d, J = 8.6 Hz, 1H, H-2″); 8.40–8.33 (m, 3H, H-3‴, H-5‴ and H-8″); 8.13 (d, J = 8.2 Hz, 1H, H-4′); 8.04 (dd, J = 9.1 and 1.9 Hz, 1H, H-4″); 7.92 (d, J = 8.1 Hz, 1H, H-5″); 7.76 (dd, J = 9.1 and 4.1 Hz, 1H, H-7′); 7.66 (t, J = 7.8 Hz, 1H, H-3″); 7.59 (m, 2H, H-6″ and H-7″); 7.06 (dt, J = 8.9 and 1.8 Hz, 1H, H-6′); 6.54 (s, 1H, H-4‴); 3.89 (s, 4H, H-3⁗ and H-5⁗); 3.69 (s, 2H, H-2); 2.67 (s, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.3, 160.9 (d, J = 241 Hz), 162.1, 158.1, 137.0, 134.9, 134.7, 133.0, 131.2, 130.8, 130.0, 129.7, 129.3 (d, J = 10.9 Hz), 128.4, 128.0, 124.6, 123.6, 119.0 (d, J = 4.0 Hz), 114.4 (d, J = 8.3 Hz), 114.1, 110.5, 109.4 (d, J = 25.6 Hz), 67.4, 53.8 (2C) and 44.0 (2C). HRMS calculated for C28H25FN5O3S [M + H+]: 530.1657; Found: 530.1700.
1-(5-fluoro-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-one (3h)
1-(2-Methoxyphenyl)-piperazine (448 mg, 2.32 mmol), potassium carbonate (321 mg, 2.32 mmol) and 2-bromo-1-(5-fluoro-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)ethan-1-one (2c) (900 mg, 2.11 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 7:1 to obtain 1.10 g of (3h) as an orange gel. Yield: 97%; m.p.: product in gel state; IR (KBr) cm−1: 1665, 1594, 1500, 1380, 1165, 1198. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.70 (s, 1H, H-2′); 7.93 (dd, J = 9.2 and 2.5 Hz, 1H, H-4′); 7.81–7.74 (m, 3H, H-7′, H-2″ and H-6″); 6.97, (td, J = 9.0 and 2.5 Hz, 1H, H-6′); 6.93–6.83 (m, 2H, H-3‴ and H-5‴); 6.83–6.74 (m, 2H, H-3″, H-5″, H-4‴ and H-6‴); 3.75 (s, 3H, 4″-OCH3); 3.64 (s, 3H, 2‴-OCH3); 3.60 (s, 2H, H-2); 3.04 (s, 4H, H-3⁗ and H-5⁗); 2.70 (s, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.3, 164.5, 160.5 (d, J = 241.5), 152.3, 141.1, 134.4, 130.8, 129.5, 129.1 (d, J = 11.0 Hz), 128.6, 123.1, 121.0, 118.9 (d, J = 4.2 Hz), 118.2, 115.0, 114.1 (d, J = 9.5 Hz), 113.8 (d, J = 25.9 Hz), 114.4, 108.8 (d, J = 25.4 Hz), 66.7, 55.7, 55.4, 53.7 (2C) and 50.6 (2C). HRMS calculated for C28H29FN3O5S [M + H+]: 538.1806; Found: 538.1825.
1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-fluoro-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-one (3i)
1-(2-Methoxyphenyl)-piperazine (432 mg, 2.24 mmol), potassium carbonate (310 mg, 2.24 mmol) and 2-bromo-1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-fluoro-1H-indol-3-yl)ethan-1-one (2d) (985 mg, 2.04 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to obtain 505 mg of (3i) as a light orange solid. Yield: 42%; m.p.: 104–107 °C; IR (KBr) cm−1: 1667, 1588, 1500, 1390, 1174, 1148. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.76 (s, 1H, H-2′); 8.07 (dd, J = 9.0 and 2.5 Hz, 1H, H-4′); 7.88 (dd, J = 9.1 and 4.3 Hz, 1H, H-7′); 7.54 (d, J = 4.0 Hz, 1H, H-3″); 7.14 (td, J = 8.9 and 2.5 Hz, 1H, H-6′); 7.03 (d, J = 4.6 Hz, 1H, H-2″); 6.99–6.86 (m, 4H, H-3‴, H-4‴, H-5‴ and H-6‴); 3.87 (s, 3H, 2‴-OCH3); 3.70 (s, 2H, H-2); 3.17 (s, 4H, H-3⁗ and H-5⁗); 2.81 (s, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.2, 160.8 (d, J = 242.6 Hz), 152.3, 141.1, 137.6, 134.5, 134.0, 131.0, 130.5, 129.4 (d, J = 11.0 Hz), 123.6, 123.1, 121.1, 119.8 (d, J = 4.2 Hz), 118.3, 114.1 (d, J = 9.5 Hz), 113.8 (d, J = 25.9 Hz), 111.3, 109.3 (d, J = 25.5 Hz), 67.0, 55.4, 53.8 (2C), 50.6 (2C). HRMS calculated for C25H24BrFN3O4S2 [M + H+]: 592.0370; Found: 592.0399.
1-(1-((4-iodophenyl)sulfonyl)-5-methoxy-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-one (3j)
1-(2-Methoxyphenyl)-piperazine (154 mg, 0.80 mmol), potassium carbonate (96 mg, 0.70 mmol) and 2-bromo-1-(1-((4-iodophenyl)sulfonyl)-5-methoxy-1H-indol-3-yl)ethan-1-one (2e) (370 mg, 0.69 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/AcOEt 5:1 to give 416 mg of (3j) as white crystalline plates. Yield: 93%; m.p.: 99–100 °C; IR (KBr) cm−1: 1663, 1386, 1215, 1176, 963, 585. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.57 (s, 1H, H-2′); 7.77 (d, J = 2.4 Hz, 1H, H-4′); 7.74 (d, J = 8.3, 2H, H-2″ and H-6″); 7.73 (d, J = 9.1 Hz, 1H, H-7′); 7.54 (d, J = 8.3 Hz, 2H, H-3″ and H-5″); 6.97–6.85 (m, 4H, H-6′, H-3‴, H-4‴ and H-5‴); 6.81 (d, J = 7.9 Hz, H-6‴); 3.80 (s, 3H, 5′-OCH3); 3.77 (s, 3H, 2‴-OCH3); 3.65 (s, 2H, H-2); 3.08 (bs, 4H, H-3⁗ and H-5⁗); 2.75 (bs, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.4, 157.8, 152.3, 141.0, 138.9 (2C), 137.2, 133.1, 129.1, 128.9, 128.1(2C), 123.2, 121.1, 119.7, 118.3, 115.8, 113.8, 111.3, 104.7, 102.7, 66.6, 55.7, 55.4, 53.8(2C), 50.6(2C). HRMS calculated for C28H29IN3O5S [M + H+]: 646.0867; Found: 646.0869.
1-(1-((4-iodophenyl)sulfonyl)-5-methoxy-1H-indol-3-yl)-2-morpholinoethan-1-one (3k)
Morpholine (0.1 mL, 1.16 mmol), potassium carbonate (83 mg, 0.6 mmol) and 2-bromo-1-(1-((4-iodophenyl)sulfonyl)-5-methoxy-1H-indol-3-yl)ethan-1-one (2e) (320 mg, 0.6 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 237 mg of (3k) as yellow crystalline plates. Yield: 73% m.p.: 163–166 °C; IR (KBr) cm−1: 1651, 1387, 1174, 1215, 1115, 863, 616. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.48 (s, 1H, H-2′); 7.76 (d, J = 8.5 Hz, 2H, H-2″ and H-6″); 7.74 (d, J = 2.6 Hz, 1H, H-4′); 7.71 (d; J = 9.1 Hz, 1H, H-7′); 7.53 (d, J = 8.3 Hz, 2H, H-3″ and H-5″); 6.90 (dd, J = 9.1 and 2.5 Hz, 1H, H-6′); 3.76 (s, 3H, 5′-OCH3); 3.70 (t, J = 4.6 Hz, 4H, H-3⁗ and H-5⁗); 3.57 (s, 2H, H-2); 2.53 (t, J = 4.4 Hz, 4H, H-2⁗ and H-6⁗).13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.0, 157.8, 138.9 (2C), 137.1, 132.7, 129.1, 128.9, 128.1 (2C), 119.7, 115.8, 113.8, 104.7, 102.8, 66.9 (2C), 66.7, 55.7, 53.8 (2C). HRMS calculated for C21H22IN2O5S [M + H+]: 541.0289; Found: 541.0305.
1-(5-methoxy-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-one (3l)
1-(2-Methoxyphenyl)-piperazine (119 mg, 0.62 mmol), potassium carbonate (86 mg, 0.62 mmol) and 2-bromo-1-(5-methoxy-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)ethan-1-one (2f) (284 mg, 0.62 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 269 mg of product (3l) as a brown-orange solid. Yield: 77%; m.p.: 78–80 °C; IR (KBr) cm−1: 1661, 1371, 1134, 1215, 1030. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.92 (s, 1H, H-2′); 8.67 (d, J = 8.7 Hz, 1H, H-2″); 8.32 (dd, J = 7.5 and 1.0 Hz, 1H, H-8″); 8.08 (d, J = 8.3 Hz, 1H, H-4″); 7,88 (d, J = 7.8 Hz, 1H, H-5″); 7.83 (d, J = 2.6, 1H, H-4′); 7.67 (d, J = 9.1 Hz, 1H, H-7′); 7.67–7.61 (m, 1H, H-3″); 7.58–7.52 (m, 2H, H-6″ and H-7″); 7.05–7.01 (m, 1H, H-5‴); 6.98–6.93 (m, 2H, H-3‴ and H-4‴); 6.91 (dd, J = 9.1 and 2.6 Hz, 1H, H-6′); 6.88 (d, J = 7.8 Hz, 1H, H-6‴); 3.87 (s, 3H, 5′-OCH3); 3.81 (s, 3H, 2‴-OCH3); 3.72 (s, 2H, H-2); 3.15 (bs, 4H, H-3⁗); 2.83 (bs, 4H, H-2⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.4, 157.6, 152.3, 141.1, 136.4, 134.3, 133.7, 132.8, 130.3, 129.5, 129.2, 129.1, 128.8, 128.0, 127.5, 124.2, 123.4, 123.1, 121.0, 118.7, 118.4, 115.5, 113.7, 111.3, 104.6, 66.8, 55.7, 55.4, 53.8 (2C), 50.5 (2C). HRMS calculated for C32H32N3O5S [M + H+]: 570.2057; Found: 570.2074.
1-(5-methoxy-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-morpholinoethan-1-one (3m)
Morpholine (0.1 mL, 1.16 mmol), potassium carbonate (97 mg, 0.7 mmol) and 2-bromo-1-(5-methoxy-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)ethan-1-one (2f) (320 mg, 0.7 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 319 mg of product (3m) as an orange solid. Yield: 98%; m.p.: 104–107 °C; IR (KBr) cm−1: 1657, 1366, 1173, 1216, 1116, 985. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.76 (s, 1H, H-2′); 8.58 (d, J = 8.6 Hz, 1H, H-2″); 8.23 (d, J = 7.5 Hz, 1H, H-8″); 8.03 (d, J = 8.2 Hz, 1H, H-4″); 7.83 (d, J = 8.1 Hz, 1H, H-5″); 7.72 (s, 1H, H-4′); 7.57 (d, J = 9.2 Hz, 1H, H-7′); 7.58–7.53 (m, 1H, H-3″); 7.53–7.46 (m, 2H, H-6″ and H-7″); 6.82 (dd, J = 9.1 and 1.9 Hz, 1H, H-6′); 3.72 (s, 3H, 5′-OCH3); 3.68 (t, J = 4.3 Hz, 4H, H-3⁗); 3.56 (s, 2H, H-2); 2.52 (t, J = 4.0 Hz, 4H, H-2⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.2, 157.6, 136.4, 134.3, 133.4, 132.8, 130.3, 129.5, 129.1, 129.1, 128.7, 127.9, 127.5, 124.2, 123.3, 118.7, 115.5, 113.7, 104.5, 66.9, 66.8(2C), 55.7, 53.9(2C). HRMS calculated for C25H25N2O5S [M + H+]: 465.1479; Found: 465.1488.
1-(5-methoxy-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-(4-(pyridin-2-yl)piperazin-1-yl)ethan-1-one (3n)
1-(2-Pyridyl)-piperazine (114 mg, 0.7 mmol), potassium carbonate (99 mg, 0.72 mmol) and 2-bromo-1-(5-methoxy-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)ethan-1-one (2f) (320 mg, 0.7 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 360 mg of product (3n) as a brown solid. Yield: 95%; m.p.: 109–112 °C; IR (KBr) cm−1: 1654, 1381, 1174, 1215, 855. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.81 (s, 1H, H-2′); 8.56 (d, J = 8.6 Hz, 1H, H-2″); 8.23 (d, J = 7.5 Hz, 1H, H-8″); 8.14 (d, J = 4.6 Hz, 1H, H-3‴); 7.96 (d, J = 8.2 Hz, 1H, H-4″); 7.79–7.73 (m, 2H, H-4′ and H-5″); 7.61 (d, J = 9.1 Hz, 1H, H-7′); 7.55–7.38 (m, 4H, H-6′, H-3″, H-6″ and H-7″); 6.83 (d, J = 7.4 Hz, 1H, H-5‴); 6.60–6.53 (m, 2H, H-6‴ and H-4‴); 3.73 (s, 3H, 5′-OCH3); 3.59 (s, 2H, H-2); 3.47 (t, J = 4.7 Hz, 4H, H-3⁗ and H-5⁗); 2.64–2.57 (t, J = 4.6 Hz, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.4, 159.4, 157.6, 148.0, 137.5, 136.4, 134.3, 133.6, 132.8, 130.3, 129.5, 129.2, 129.1, 128.8, 128.0, 127.5, 124.2, 123.3, 118.7, 115.5, 113.8, 113.5, 107.2, 104.6, 66.9, 55.7, 53.3(2), 45.2(2). HRMS calculated for C30H29N4O4S [M + H+]: 541.1904; Found: 541.1913.
1-(5-methoxy-1-tosyl-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-one (3o)
1-(2-Methoxyphenyl)-piperazine (154 mg, 0.8 mmol), potassium carbonate (110 mg, 0.8 mmol) and 2-bromo-1-(5-methoxy-1-tosyl-1H-indol-3-yl)ethan-1-one (2i) (338 mg, 0.8 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 264 mg of product (3o) as a yellow-orange solid. Yield: 62%; m.p.: 85–88 °C; IR (KBr) cm−1: 1663, 1377, 1173, 1241, 1029. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.57 (s, 1H, H-2′); 7.76–7.72 (m, 4H, H-2″, H-4′ and H-7′); 7.17 (d, J = 8.2 Hz, 2H, H-3″); 6.96–6.82 (m, 4H, H-3‴, H-4‴, H-5‴ and H-6′); 6.80 (d, J = 7.8 Hz, 1H, H-6‴); 3.79 (s, 3H, 5′-OCH3); 3.75 (s, 3H, 2‴-OCH3); 3.66 (s, 2H, H-2); 3.08 (bs, 4H, H-3⁗); 2.75 (bs, 4H, H-2⁗); 2.26 (s, 3H, 4″-CH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.4, 157.7, 152.3, 145.9, 141.1, 134.7, 133.3, 130.2 (2C), 129.1, 129.0, 127.1 (2C), 123.1, 121.0, 119.2, 118.3, 115.5, 113.9, 111.3, 104.5, 66.5, 55.7, 55.4, 53.7 (2C), 50.5(2C), 21.6. HRMS calculated for C29H32N3O5S [M + H+]: 534.2057; Found: 534.2076.
1-(5-methoxy-1-tosyl-1H-indol-3-yl)-2-(4-(pyridin-2-yl)piperazin-1-yl)ethan-1-one (3p)
1-(2-Pyridyl)-piperazine (89 mg, 0.55 mmol), potassium carbonate (76 mg, 0.55 mmol) and 2-bromo-1-(5-methoxy-1-tosyl-1H-indol-3-yl)ethan-1-one (2i) (230 mg, 0.54 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 269 mg of product (3p) as a yellow solid. Yield: 99%; m.p.: 144–147 °C; IR (KBr) cm−1: 1654, 1385, 1174, 1216, 857. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.64 (s, 1H, H-2′); 8.21 (d, J = 3.8 Hz, 1H, H-3‴); 7.89–7.82 (m, 4H, H-4′, H-7′ and H-2″); 7.49 (t, J = 7.7 Hz, 1H, H-5‴); 7.24 (d, J = 8.0 Hz, 2H, H-3″); 6.98 (d, J = 9.0 Hz, 1H, H-6′); 6.72–6.56 (m, 2H, H-4‴ and H-6‴); 3.84 (s, 3H, 5′-OCH3); 3.69 (s, 2H, H-2); 3.61 (bs, 4H, H-3⁗ and H-5⁗); 2.71 (bs, 4H, H-2⁗ and H-6⁗); 2.33 (s, 3H, 4″-CH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.8, 159.8, 158.1, 148.4, 146.3, 137.9, 135.0, 133.7, 130.6(2C), 129.5, 129.4, 127.5(2C), 119.6, 115.9, 114.3, 113.9, 107.5, 104.9, 67.0, 56.1, 53.7 (2C), 45.6 (2C), 22.0. HRMS calculated for C27H29N4O4S [M + H+]: 505.1904; Found: 505.1920.
1-(5-methoxy-1-tosyl-1H-indol-3-yl)-2-morpholinoethan-1-one (3q)
Morpholine (0.1 mL, 1.16 mmol), potassium carbonate (101 mg, 0.73 mmol) and 2-bromo-1-(5-methoxy-1-tosyl-1H-indol-3-yl)ethan-1-one (2i) (311 mg, 0.74 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 308 mg of product (3q) as a yellow solid. Yield: 97%; m.p.: 152–154 °C; IR (KBr) cm−1: 1663, 1377, 1174, 1216, 1086, 811. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.60 (s, 1H, H-2′), 7.97–7.73 (m, 4H, H-4′, H-7′, H-2″); 7.28 (d, J = 7.6 Hz, 2H, H-3″); 6.97 (d, J = 8.2 Hz, 1H, H-6′); 3.83 (s, 3H, 5′-OCH3); 3.78 (s, 4H, H-3⁗); 3.65 (s, 2H, H-2); 2.61 (bs, 4H, H-2⁗); 2.36 (s, 3H, 4″-CH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.5, 158.1, 146.3, 135.1, 133.5, 130.6(2C), 129.5, 129.4, 127.5(2C), 119.6, 115.9, 114.3, 104.9, 67.3 (2C), 67.1, 56.1, 54.2 (2C), 22,0. HRMS calculated for C22H25N2O5S [M + H+]: 429.1479; Found: 429.1494.
1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-methoxy-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-one (3r)
1-(2-Methoxyphenyl)-piperazine (116 mg, 0.6 mmol), potassium carbonate (84 mg, 0.61 mmol) and 2-bromo-1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-methoxy-1H-indol-3-yl)ethan-1-one (2h) (300 mg, 0.61 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 353 mg of product (3r) as a brown gel. Yield: 96%; m.p.: product in gel state; IR (KBr) cm−1: 1672, 1387, 1176, 1215, 858, 605. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.55 (s, 1H, H-2′); 7.80 (bs, 1H, H-4′); 7.74 (d, J = 9.1 Hz, 1H, H-7′); 7.44 (d, J = 4.0 Hz, 1H, H-4″); 6.97–6.83 (m, 5H, H-6′, H-3″, H-3‴, H-4‴, H-5‴); 6.80 (d, J = 7.9 Hz, 1H, H-6‴); 3.79 (s, 3H, 5′-OCH3); 3.78 (s, 3H, 2‴-OCH3); 3.63 (s, 2H, H-2); 3.09 (bs, 4H, H-3⁗ and H-5⁗); 2.74 (bs, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.6, 158.0, 152.3, 141.1, 137.9, 134.2, 132.9, 130.9, 129.3, 128.7, 123.2, 123.1, 121.0, 120.0, 118.3, 115.8, 113.9, 111.3, 104.9, 66.8, 55.7, 55.4, 53.8 (2C), 50.6 (2C). HRMS calculated for C26H27BrN3O5S2 [M + H+]: 604.0570; Found: 604.0565.
1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-methoxy-1H-indol-3-yl)-2-morpholinoethan-1-one (3s)
Morpholine (0.1 mL, 1.16 mmol), potassium carbonate (86 mg, 0.62 mmol) and 2-bromo-1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-methoxy-1H-indol-3-yl)ethan-1-one (2h) (300 mg, 0.61 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 277 mg of product (3s) as a yellow solid. Yield: 91%; m.p.: 130–133 °C; IR (KBr) cm−1: 1670, 1389, 1172, 1217, 1130, 854, 605. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.46 (s, 1H, H-2′); 7.77 (d, J = 2.7 Hz, 1H, H-4′); 7.73 (d, J = 9.1 Hz, 1H, H-7′); 7.45 (d, J = 4.1 Hz, 1H, H-4″); 6.96–6.92 (m, 2H, H-6′, H-3″); 3.78 (s, 3H, 5′-OCH3); 3.71 (t, J = 4.6 Hz, 4H, H-3⁗ and H-5⁗); 3.57 (s, 2H, H-2); 2.54 (t, J = 4.5 Hz, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.1, 158.0, 137.9, 134.3, 132.7, 130.9, 129.2, 128.7, 123.3, 120.0, 115.8, 113.9, 104.9, 66.9 (2C), 66.8, 55.7, 53.8 (2C). HRMS calculated for C19H20BrN2O5S2 [M + H+]: 498.9992; Found: 499.0013.
1-(5-methoxy-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)-2-morpholinoethan-1-one (3t)
Morpholine (0.1 mL, 1.16 mmol), potassium carbonate (97 mg, 0.7 mmol) and 2-bromo-1-(5-methoxy-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)ethan-1-one (2g) (307 mg, 0.7 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 305 mg of product (3t) as an orange gel. Yield: 98%; m.p.: product in gel state; IR (KBr) cm−1: 1656, 1382, 1164, 1215, 1114, 985. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.51 (s, 1H, H-2′) 7.79 (d, J = 8.9 Hz, 2H, H-2″ and H-6″); 7.75–7.71 (m, 2H, H-4′ and H-7′); 6.89 (dd, J = 9.1 and 2.5 Hz, 1H, H-6′); 6.80 (d, J = 8.9 Hz, 2H, H-3″ and H-5″); 3.75 (s, 3H, 5′-OCH3); 3.72 (s, 3H, 4″-OCH3); 3.70 (t, J = 4.5 Hz, 4H, H-3⁗ and H-5⁗); 3.57 (s, 2H, H-2); 2.53 (t, J = 4.4 Hz, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.1, 164.4, 157.6, 133.0, 129.4 (2C), 129.0, 129.0, 128.8, 119.0, 115.5, 114.8 (2C), 113.9, 104.5, 66.9 (2C), 66.6, 55.8, 55.7, 53.8 (2C). HRMS calculated for C22H25N2O6S [M + H+]: 445.1428; Found: 445.1443.
1-(5-methoxy-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-one (3u)
1-(2-Methoxyphenyl)-piperazine (135 mg, 0.7 mmol), potassium carbonate (98 mg, 0.71 mmol) and 2-bromo-1-(5-methoxy-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)ethan-1-one (2g) (307 mg, 0.7 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 362 mg of product (3u) as an orange-brown solid. Yield: 94%; m.p.: 73–76 °C; IR (KBr) cm−1: 1682, 1371, 1169, 1217, 985. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.59 (s, 1H, H-2′); 7.79 (d, J = 8.9 Hz, 2H, H-2″ and H-6″); 7.78–7.73 (m, 2H, H-7′, H-4′,); 6.96–6.76 (m, 7H, H-6′, H-3″, H-5″, H-3‴, H-4‴, H-5‴, H-6‴); 3.79 (s, 3H, 5′-OCH3); 3.76 (s, 3H, 2⁗-OCH3); 3.68 (s, 3H, 4″-OCH3); 3.63 (s, 2H, H-2); 3.07 (bs, 4H, H-3⁗ and H-5⁗); 2.72 (bs, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.6, 164.3, 157.6, 152.3, 141.2, 133.3, 129.4 (2C), 129.1, 129.0, 128.9, 123.1, 121.0, 119.1, 118.2, 115.5, 114.8 (2C), 113.9, 111.3, 104.5, 66.7, 55.7, 55.6, 55.4, 53.8 (2C), 50.6 (2C). HRMS calculated for C29H32N3O6S [M + H+]: 550.2006; Found: 550.2023.
1-(5-methoxy-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)-2-(4-(pyridin-2-yl)piperazin-1-yl)ethan-1-one (3v)
1-(2-Pyridyl)-piperazine (115 mg, 0.7 mmol), potassium carbonate (100 mg, 0.72 mmol) and 2-bromo-1-(5-methoxy-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)ethan-1-one (2g) (305 mg, 0.7 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 361 mg of product (3v) as a brown gel. Yield: 99%; m.p.: product in gel state; IR (KBr) cm−1: 1662, 1376, 1166, 1216, 980. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.56 (s, 1H, H-2′); 8.12 (d, J = 5.8 Hz, 1H, H-3‴); 7.80–7.72 (m, 4H, H-4′, H-7′, H-2″ and H-6″); 7.44–7.37 (m, 1H, H-5‴); 6.89 (dd, J = 9.1 and 2.6 Hz, 1H, H-6′); 6.81 (d, J = 8.9 Hz, 2H, H-3″ and H-5″); 6.60–6.53 (m, 2H, H-4‴, H-6‴); 3.76 (s, 3H, 5′-OCH3); 3.69 (s, 3H, 4″-OCH3); 3.61 (s, 2H, H-2); 3.52 (t, J = 4.9 Hz, 4H, H-3⁗ and H-5⁗); 2.63 (t, J = 4.9 Hz, 4H, H-2⁗ and H-6⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 193.3, 164.3, 159.4, 157.6, 148.0, 137.6, 133.2, 129.4 (2C), 129.0, 129.0, 128.8, 119.1, 115.5, 114.8 (2C), 113.9, 113.5, 107.1, 104.5, 66.5, 55.7, 55.7, 53.3 (2C), 45.2 (2C). HRMS calculated for C27H29N4O5S [M + H+]: 521.1853; Found: 521.1866.
General Procedure for 2-(4-(Aryl)piperazin-1-yl)-1-(1-arylsulfonyl-1H-indol-3-yl)ethanol Derivatives (4av)
1-(5-fluoro-1-((4-iodophenyl)sulfonyl)-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl) ethan-1-ol (4a)
To a solution of (3a) (214 mg, 0.34 mmol) in ethanol (30 mL) was added sodium borohydride (19 mg, 0.51 mmol) in one portion and the mixture was vigorously stirred at room temperature until the starting material was disappeared upon checking TLC. Adding water (30 mL) stopped the reaction. The organic phase was extracted with CH2Cl2 (3 × 30 mL). The combined organic layers were dried with anhydrous sodium sulfate, and the removal of the solvent under vacuum afforded a residue, which was further purified by column chromatography on silica gel using CH2Cl2/ethyl acetate 5:1 to give 69 mg of (4a) as pale-yellow crystalline plates. Yield: 32%; m.p.: 94.5–96.4 °C; IR (KBr) cm−1: 3423, 1500, 1468, 1375, 1175, 1137, 751. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 7.82 (dd, J = 9.0 and 4.3 Hz, 1H, H-4′); 7,70 (d, J = 8.5 Hz, 2H, H-3″ and H-5″); 7.49 (s, 1H, H-2′); 7.47 (d, J = 8.8 Hz, 2H, H-2″ and H-6″); 7.24 (dd, J = 8.8 and 2.0 Hz, 1H, H-7′); 7.00–6.97 (m, 1H, H-6′); 6.95–6.92 (m, 1H, H-5‴); 6.87–6.84 (m, 2H, H-3‴ and H-4‴); 6.80 (d, J = 7.8 Hz, 1H, H-6‴); 4.92 (dd, J = 9.4 and 3.9 Hz, 1H, H-1); 3.80 (s, 3H, OCH3); 3.07 (bs, 4H, H-3⁗ and H-5⁗); 2.92–2.85 (m, 2H, H-2a⁗ and H-6a⁗); 2.69–2.64 (m, 4H, H-2, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 159.9 (d, J = 241.0 Hz); 152.7, 141.4, 139.1 (2C), 137.9, 132.2, 130.6 (d, J = 10.0 Hz), 128.4 (2C), 124.9, 124.3 (d, J = 2.1 Hz), 123.6, 121.5, 118.7, 115.2 (d, J = 9.6 Hz), 113.5 (d, J = 25.8 Hz), 111.8, 106.9 (d, J = 24.3 Hz), 102.4, 64.2, 63.3, 55.8, 53.8 (2C), 51.1 (2C). HRMS calculated for C27H28FIN3O4S [M + H+]: 636.0824; Found: 636.0840.
1-(5-fluoro-1-((4-iodophenyl)sulfonyl)-1H-indol-3-yl)-2-(4-(pyridin-2-yl)piperazin-1-yl)ethan-1-ol (4b)
(3b) (556 mg, 0.92mmol) and sodium borohydride (52 mg, 1.38 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 197 mg of compound (4b) as an orange solid. Yield: 35%; m.p.: 135–137 °C; IR (KBr) cm−1: 3422, 1593, 1470, 1386, 1175, 1140, 735. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.20 (dd, J = 4.8 and 1.3 Hz, 1H, H-3‴); 7.90 (dd, J = 9.1 and 4.4 Hz, 1H, H-4′); 7.79 (d, J = 8.6 Hz, 2H, H-3″ and H-5″); 7.58–7.53 (m, 3H, H-2′, H-2″ and H-6″); 7.53–7.47 (m, 1H, H-5‴); 7.31 (dd, J = 8.8 and 2.5 Hz, 1H, H-7′); 7.05 (td, J = 9.0 and 2.5 Hz, 1H, H-6′); 6.69–6.61 (m, 2H, H-4‴ and H-6‴); 5.01 (dd, J = 10.2 and 3.3 Hz, 1H, H-1); 3.70–3.52 (m, 4H, H-3⁗ and H-5⁗); 2.92–2.84 (m, 2H, H-2a⁗ and H-6a⁗); 2.81–2.66 (m, 2H, H-2); 2.66–2.58 (m, 2H, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 159.7 (d, J = 240.0 Hz), 159.5, 148.1, 138.8 (2C), 137.7, 137.6, 131.9, 130.2 (d, J = 9.9 Hz), 128.1 (2C), 124.6, 123.9 (d, J = 4.1 Hz). 114.9 (d, J = 9.4 Hz), 113.8, 113.3 (d, J = 25.6 Hz), 107.3, 106.5 (d, J = 24.4 Hz), 102.1, 64.0, 63.1, 53.1 (2C), 45.4 (2C). 19F-NMR (376.5 MHz, CDCl3) δ (ppm): −118.75. HRMS calculated for C25H25FIN4O3S [M + H+]: 607.0671; Found: 607.0682.
1-(5-fluoro-1-((4-iodophenyl)sulfonyl)-1H-indol-3-yl)-2-morpholinoethan-1-ol (4c)
(3c) (175 mg, 0.33 mmol) and sodium borohydride (19 mg, 0.51 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 68 mg of compound (4c) as a pale-yellow gel. Yield: 39%; m.p.: product in gel state; IR (KBr) cm−1: 3423, 1567, 1469, 1375, 1176, 1115, 736. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 7.89 (dd, J = 9.1 and 4.4 Hz, 1H, H-4′); 7.79 (d. J = 8.4 Hz, 2H, H-3″ and H-5″); 7.58–7.51 (m, 3H, H-2′, H-2″ and H-6″); 7.28 (dd, J = 8.8 and 2.5 Hz, 1H, H-7′); 7.05 (td, J = 9.0 and 2.5 Hz, 1H, H-6′); 4.96 (dd, J = 8.3 and 5.5 Hz, 1H, H-1); 3.82–3.71 (m, 4H, H-3⁗ and H-5⁗); 2.80–2.70 (m, 2H, H-2a⁗ and H-6a⁗); 2.70–2.62 (m, 2H, H-2); 2.55–2.46 (m, 2H, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 159.7 (d, J = 240.9 Hz), 138.8 (2C), 137.6, 131.9, 130.2 (d, J = 9.9 Hz), 128.1 (2C), 124.6, 123.8 (d, J = 4.1 Hz), 114.9 (d, J = 9.4 Hz), 113.3 (d, J = 25.7 Hz), 106.5 (d, J = 24.3 Hz), 102.1, 67.1 (2C), 64.4, 62.9, 53.7 (2C). 19F-NMR (376.5 MHz, CDCl3) δ (ppm): −118.77. HRMS calculated for C20H21FIN2O4S [M + H+]: 531.0245; Found: 531.0253.
1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-ol (4d)
(3d) (601 mg, 1.1 mmol) and sodium borohydride (62 mg, 1.65 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 499 mg of compound (4d) as pale orange crystalline plates. Yield: 81%; m.p.: 181.1–183.2 °C; IR (KBr) cm−1: 3449, 1593, 1500, 1370, 1174, 1139. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.71 (d, J = 8.7 Hz, 1H, H-2″); 8.09–8.02 (m, 2H, H-4″ and H-8″); 7.89 (d, J = 8.1 Hz, 1H, H-5″); 7.81–7.75 (m, 2H, H-2′ and H-4′); 7.68–7.62 (m, 1H, H-7″); 7.57 (t, J = 7.5 Hz, 1H, H-6″); 7.50 (t, J = 7.9 Hz, 1H, H-3″); 7.34 (dd, J = 8.9 and 2.5 Hz, 1H, H-7′); 7.06–6.91 (m, 4H, H-6′, H-3‴, H-4‴ and H-5‴); 6.89 (d, J = 7.7 Hz, 1H, H-6‴); 5.01 (dd, J = 10.1 and 3.5 Hz, 1H, H-1); 3.88 (s, 3H, OCH3); 3.14 (bs, 4H, H-3⁗ and H-5⁗); 3.02–2.91 (m, 2H, H-2a⁗ and H-6a⁗); 2.83–2.65 (m, 4H, H-2, H-2b⁗ and H-6b⁗).13C-NMR (100.6 MHz, CDCl3) δ (ppm): 159.4 (d, J = 240.5 Hz), 152.4, 141.2, 135.7, 134.4, 134.0, 132.0, 129.8 (d, J = 10.1 Hz), 129.3 (d, J = 7.5 Hz), 129.0, 128.2, 127.4, 125.2, 124.2, 124.1, 123.3, 122.5 (d, J = 4.2 Hz), 121.2, 118.4, 114.7 (d, J = 9.4 Hz), 113.1, 112.8, 111.4, 106.5 (d, J = 24.3 Hz), 63.9, 63.1, 55.5, 53.5 (2C), 50.8 (2C). 19F-NMR (376.5 MHz, CDCl3) δ (ppm): −119.47. HRMS calculated for C31H31FN3O4S [M + H+]: 560.2014; Found: 560.2029.
1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-(4-(pyridin-2-yl)piperazin-1-yl)ethan-1-ol (4e)
(3e) (493 mg, 0.93 mmol) and sodium borohydride (53 mg, 1.40 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 99 mg of compound (4e) as an orange gel. Yield: 57%; m.p.: 112–114 °C; IR (KBr) cm−1: 3421, 1565, 1481, 1367, 1171, 1140. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8,70 (d, J = 8,7 Hz, 1H, H-2″); 8.21 (d, J = 3.9 Hz, 1H, H-3‴); 8.11–8.00 (m, 2H, H-4″ and H-8″); 7.87 (d, J = 8,2 Hz, 1H, H-5″); 7.81–7.74 (m, 2H, H-2′ and H-4′); 7.64 (t, J = 7.8 Hz, H1, H-7″); 7.55 (d, J = 7.5 Hz, 1H, H-6″); 7,49 (t, J = 7.9 Hz, 2H, H-3″ and H-5‴); 7.32 (dd, J = 8.9 and 2.6 Hz, 1H, H-7′); 6.98 (td, J = 9.0 and 2.6 Hz, 1H, H-6′); 6.70–6.60 (m, 2H, H-4‴ and H-6‴); 5.02 (dd, J = 10.4 and 3.4 Hz, 1H, H-1); 3.67–3.49 (bs, 4H, H-3⁗ and H-5⁗); 2.89–2.80 (bs, 2H, H-2a⁗ and H-6a⁗); 2.80–2,63 (m, 2H, H-2); 2.63–2.54 (m, 2H, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 159.5, 159.4 (d, J = 240.5 Hz), 148.1, 137.7, 135.8, 134.4, 133.9, 131.9, 129.7 (d, J = 10.0 Hz), 129.3 (d, J = 4.1 Hz), 129.0, 128.2, 127.4, 125.2, 124.2, 124.0, 122.4 (t, J = 4.2 Hz), 114.7 (d, J = 9.4 Hz), 113.7, 113.1, 112.8, 107.3, 106.4 (d, J = 24.3 Hz), 64.0, 63.2, 53.1 (2C), 45.4 (2C). 19F-NMR (376.5 MHz, CDCl3) δ (ppm): −119.40. HRMS calculated for C29H28FN4O3S [M + H+]: 531.1861; Found: 531.1868.
1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-morpholinoethan-1-ol (4f)
(3f) (360 mg, 0.80 mmol) and sodium borohydride (45 mg, 1.20 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 191 mg of compound (4f) as pale-yellow crystalline plates. Yield: 53%; m.p.: 164.1–165.8 °C; IR (KBr) cm−1: 3449, 1592, 1470, 1373, 1173, 1139. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.69 (d, J = 8.6 Hz, 1H, H-2″); 8.12–7.99 (m, 2H, H-4″ and H-8″); 7.88 (d, J = 8.1 Hz, 1H, H-5″); 7.81–7.72 (m, 2H, H-2′ and H-4′); 7.64 (t, J = 7.7 Hz,1H, H-7″); 7.56 (t, J = 7.5 Hz, 1H, H-6″); 7.49 (t, J = 7.9 Hz, 1H, H-3″); 7.30 (dd, J = 8.9 and 1.6 Hz, 1H, H-7′); 6.98 (td, J = 9.0 and 1.7 Hz, 1H, H-6′); 5.00 (dd, J = 9.9 and 3.5 Hz, 1H, H-1); 3.85–3.65 (m, 4H, H-3⁗ and H-5⁗); 3.37 (s, 1H, OH); 2.80–2.72 (bs, 2H, H-2a⁗ and H-6a⁗); 2.72–2.61 (m, 2H, H-2); 2.55–2.47 (bs, 2H, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 159.4 (d, J = 240,5 Hz), 135.8, 134.4, 134.0, 132.0, 129.7 (d, J = 9.9 Hz), 129.3 (d, J = 3.5 Hz), 129.0, 128.2, 127.5, 125.2, 124.2, 124.1, 122.2 (d, J = 4.2 Hz), 114.8 (d, J = 9.4 Hz), 113.1, 112.9, 106.4 (d, J = 24.4 Hz), 67.0 (2C), 64.4, 63.0, 53.7 (2C). 19F-NMR (376.5 MHz, CDCl3) δ (ppm): −119.42. HRMS calculated for C24H24FN2O4S [M + H+]: 455.1435; Found: 455.1440.
1-(5-fluoro-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-(4-(pyrimidin-2-yl)piperazin-1-yl)ethan-1-ol (4g)
(3g) (264 mg, 0.50 mmol) and sodium borohydride (28 mg, 0.75 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 220 mg of compound (4g) as a white-orange solid. Yield: 83%; m.p.: 100–103 °C; IR (KBr) cm−1: 3423, 1586, 1470, 1360, 1172, 1139. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.69 (d, J = 8.6 Hz, 1H, H-2″); 8.31 (d, J = 4.7 Hz, 2H, H-3‴ and H-5‴); 8.06 (d, J = 7,4 Hz, 1H, H-4″); 8.03 (d, J = 8.2 Hz, 1H, H-8″); 7.86 (d, J = 8.1 Hz, 1H, H-5″); 7.80–7.73 (m, 2H, H-2′ and H-4′); 7.66–7.60 (m, 1H, H-7″); 7.54 (t, J = 7.5 Hz, 1H, H-6″); 7.48 (t, J = 7.8 Hz, 1H, H-3″); 7.32 (dd, J = 8.9 and 2.4 Hz, 1H, H-7′); 6.97 (td, J = 9.0 and 2.4 Hz, 1H, H-6′); 6.49 (t, J = 4.7 Hz, 1H, H-4‴); 5.02 (dd, 10.3 and 3.0 Hz, 1H, H-1); 3.95–3.79 (m, 4H, H-3⁗ and H-5⁗); 2.84–2.71 (m, 3H, H-2a, H-2a⁗ and H-6a⁗); 2.64 (dd, J = 12.6 and 3.4 Hz, 1H, H-2b); 2.58–2.49 (m, 2H, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 161.7, 159.4 (d, J = 240.5 Hz), 157.8 (2C), 135.7, 134.3, 133.9, 131.9, 129.7 (d, J = 10.0 Hz), 129.3 (d, J = 2.4 Hz), 128.9, 128.2, 127.4, 125.1, 124.2, 124.0, 122.3 (d, J = 4.2 Hz); 114.7 (d, J = 9.4 Hz), 113.0, 112.8, 110.2, 106.4 (d, J = 24.3 Hz); 64.0, 63.2, 53.1 (2C), 43.8 (2C). 19F-NMR (376.5 MHz, CDCl3) δ (ppm): −119.38. HRMS calculated for C28H27FN5O3S [M + H+]: 532.1813; Found: 532.1830.
1-(5-fluoro-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-ol (4h)
(3h) (411 mg, 0.77 mmol) and sodium borohydride (44 mg, 1.16 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 308 mg of compound (4h) as a pale-yellow gel. Yield: 74%; m.p.: product in gel state; IR (KBr) cm−1: 3424, 1594, 1499, 1372, 1188, 1165, 803. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 7,93 (dd, J = 9.1 and 4.4 Hz, 1H, H-4′); 7.80 (d, J = 9.0 Hz, 2H, H-2″ and H-6″); 7.60 (s, 1H, H-2′); 7.33 (dd, J = 8.9 and 2.5 Hz, 1H, H-7′); 7.08–6.98 (m, 2H, H-6′ and H-5‴); 6.97–6.90 (m, 2H, H-3‴ and H-4‴); 6.90–6.84 (m, 3H, H-3″, H-5″ and H-6‴); 4.99 (dd, J = 10.1 and 3.6 Hz, 1H, H-1); 3.87 (s, 3H, 2‴-OCH3); 3.77 (s, 3H, 4″-OCH3); 3.14 (bs, 4H, H-3⁗ and H-5⁗); 3.01–2.90 (bs, 2H, H-2a⁗ and H-6a⁗); 2.82–2.63 (m, 4H, H-2, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 164.0, 159.4 (d, J = 240.1 Hz), 152.3, 141.1, 131.9, 130.1 (d, J = 9.9 Hz), 129.5, 129.2 (2C), 124.7, 123.2, 123.1 (d, J = 4.1 Hz), 121.1, 118.3, 114.8 (d, J = 9.4 Hz), 114.6 (2C), 112.8 (d, J = 25.6 Hz), 111.4, 106.3 (d, J = 24.3 Hz), 63.8, 63.0, 55.7, 55.5, 53.4 (2C), 50.8 (2C). 19F-NMR (376.5 MHz, CDCl3) δ (ppm): −119.47. HRMS calculated for C28H31FN3O5S [M + H+]: 540.1963; Found: 540.2001.
1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-fluoro-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-ol (4i)
(3i) (297 mg, 0.50 mmol) and sodium borohydride (28 mg, 0.75 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 215 mg of compound (4i) as a yellow gel. Yield: 72%; m.p.: product in gel state; IR (KBr) cm−1: 3422, 1594, 1500, 1381, 1173, 1138. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 7.90 (dd, J = 9.0 and 4.3 Hz, 1H, H-4′); 7.53 (s, 1H, H-2′); 7.41–7.32 (m, 2H, H-2″ and H-7′); 7.08 (td, J = 8.9 and 1.9 Hz, 1H, H-6′); 7.03–6.96 (m, 1H, H-5‴); 6.96–6.96 (m, 3H, H-3″, H-3‴ and H-4‴); 6.86 (d, J = 7.9 Hz, 1H, H-6‴); 5.00 (dd, J = 9.6 and 3.7 Hz, 1H, H-1); 3.85 (s, 3H, 2‴-OCH3); 3.12 (bs, 4H, H-3⁗ and H-5⁗); 2.99–2.87 (bs, 2H, H-2a⁗ and H-6a⁗); 2.81–2.63 (m, 4H, H-2, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 159.7 (d, J = 241.2 Hz), 152.3, 141.1, 138.3, 133.5, 131.7, 130.5, 130.4 (d, J = 10.0 Hz), 124.8 (d, J = 3.9 Hz), 124.3, 123.2, 122.1, 121.1, 118.3, 115.0 (d, J = 9.4 Hz), 113.2 (d, J = 25.6 Hz), 111.4, 106.7 (d, J = 24.4 Hz), 63.8, 63.0, 55.4, 53.4 (2C), 50.7 (2C). HRMS calculated for C25H26BrFN3O4S2 [M + H+]: 594.0527; Found: 594.0547.
1-(1-((4-iodophenyl)sulfonyl)-5-methoxy-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-ol (4j)
(3j) (416 mg, 0.60 mmol) and sodium borohydride (30 mg, 0.80 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 142 mg of compound (4j) as pale-brown crystalline plates. Yield: 31%; m.p.: 101–104 °C; IR (KBr) cm−1: 3406, 1372, 1221, 1174, 1029, 609. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 7.83 (d, J = 9.1 Hz, 1H, H-7′); 7.73 (d, J = 8.5 Hz, 2H, H-2″ and H-6″); 7.55–7.50 (m, 3H, H-2′, H-3″ and H-5″); 7.11 (d, J = 2.3 Hz, 1H, H-4′); 7.05–6.99 (m, 1H, H-5‴); 6.95–6.90 (m, 3H, H6′, H3‴, H4‴); 6.87 (d, J = 8.0 Hz, 1H, H6‴); 5.12 (dd, J = 9.3 and 3.2 Hz, 1H, H-1); 3.86 (s, 3H, 2‴-OCH3); 3.82 (s, 3H, 5′-OCH3); 3.18 (bs, 4H, H-3⁗ and H-5⁗); 3.05 (bs, 2H, H-2a⁗ and H-6a⁗); 2.91–2.80 (m, 4H, H-2, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 156.6, 152.3, 140.8, 138.6 (2C), 137.7, 130.2, 130.1, 128.1 (2C), 124.1, 123.8, 123.4, 121.2, 118.4, 114.6, 114.0, 111.4, 103.4, 101.8, 63.6, 63.0, 55.9, 55.5, 53.6 (2C), 50.3 (2C). HRMS calculated for C28H31IN3O5S [M + H+]: 648.1024; Found: 648.1040.
1-(1-((4-iodophenyl)sulfonyl)-5-methoxy-1H-indol-3-yl)-2-morpholinoethan-1-ol (4k)
(3k) (374 mg, 0.70 mmol) and sodium borohydride (31 mg, 0.80 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 173 mg of compound (4k) as orange crystalline plates. Yield: 44%; m.p.: 120–124 °C; IR (KBr) cm−1: 3423, 1374, 1225, 1175, 1115, 974, 614. 1H-NMR (400.1 MHz, DMSO-d6) δ (ppm): 7.96 (d, J = 8.1 Hz, 2H, H-2′’ and H-6′’); 7.81 (d, J = 9.0 Hz, 1H, H-7′); 7.65 (d, J = 8.1 Hz, 2H, H-3′’ and H-5′’); 7.59 (s, 1H, H-2′); 7.19 (s, 1H, H-4′); 6.96 (d, J = 9.0 Hz, 1H, H-6′); 5.32 (s, 1H, OH); 4.99 (s, 1H, H-1); 3.77 (s, 3H, 5′-OCH3); 3.56 (bs, 4H, H-3⁗ and H-5⁗); 2.71 (bs, 2H, H-2a⁗ and H-6a⁗); 2.61–2.44 (bs, 4H, H-2, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, DMSO-d6) δ (ppm): 156.4, 139.1 (2C), 136.9, 130.9, 129.7, 128.5 (2C), 127.0, 124.3, 114.6, 114.0, 104.2, 104.0, 66.4 (2C), 64.4, 63.7, 55.9, 54.0 (2C). HRMS calculated for C21H24IN2O5S [M+H+]: 543.0445; Found: 543.0453.
1-(5-methoxy-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-ol (4l)
(3l) (370 mg, 0.60 mmol) and sodium borohydride (30 mg, 0.80 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 175 mg of compound (4l) as brown crystalline plates. Yield: 47%; m.p.: 105–107 °C; IR (KBr) cm−1: 3423, 1362, 1221, 1172, 1026. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.73 (d, J = 8.7 Hz, 1H, H-2″); 8.01 (t, J = 7.2 Hz, 2H, H-4″ and H-8″); 7.87 (d, J = 8.1 Hz, 1H, H-5″); 7.73 (d, J = 7.9 Hz, 1H, H-7′); 7.72 (s, 1H, H-2′); 7.64 (t, J = 7.7 Hz, 1H, H-7″); 7.55 (t, J = 7.5 Hz, 1H, H-6″); 7.47 (t, J = 7.9 Hz, 1H, H-3″); 7.10 (d, J = 2.3 Hz, 1H, H-4′); 7.06–6.98 (m, 1H, H-5‴); 6.99–6.91 (m, 2H, H-3‴ and H-6′); 6.92–6.84 (m, 2H, H-4‴ and H-6‴); 5.05 (dd, J = 10.1 and 3.3 Hz, 1H, H-1); 3.88 (s, 3H, 2‴-OCH3); 3.80 (s, 3H, 5′-OCH3); 3.14 (bs, 4H, H-3⁗ and H-5⁗); 2.97 (bs, 2H, H-2a⁗ and H-6a⁗); 2.87–2.65 (m, 4H, H-2, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 156.3, 152.3, 141.1, 135.3, 134.3, 134.2, 130.3, 129.7, 129.1, 128.9, 128.7, 128.2, 127.2, 124.2, 124.1, 124.1, 123.2, 122.4, 121.0, 118.3, 114.4, 113.6, 111.3, 103.2, 63.8, 63.0, 55.8, 55.4, 53.4 (2C), 50.7 (2C). HRMS calculated for C32H34N3O5S [M+H+]: 572.2214; Found: 572.2227.
1-(5-methoxy-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-morpholinoethan-1-ol (4m)
(3m) (361 mg, 0.80 mmol) and sodium borohydride (35 mg, 0.90 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 234 mg of compound (4m) as white crystalline plates. Yield: 50%; m.p.: 190–192 °C; IR (KBr) cm−1: 3423, 1364, 1221, 1175, 1116, 1025. 1H-NMR (400.1 MHz, DMSO-d6) δ (ppm): 8.65 (d, J = 8.6 Hz, 1H, H-2″), 8.31–8.25 (m, 2H, H-4″ and H-8″); 8.08 (d, J = 8.1 Hz, 1H, H-5″); 7.89 (s, 1H, H-2′); 7.77–7.62 (m, 4H, H-7′, H-3″, H-6″ and H-7″); 7.19 (s, 1H, H-4′); 6.89 (d, J = 9.0 Hz, 1H, H-6′); 5.23 (bs, 1H, OH); 4.98 (bs, 1H, H-1); 3.74 (s, 3H, 5′-OCH3); 3.50 (s, 4H, H-3⁗ and H-5⁗); 2.71–255 (m; 2H, H-2a⁗ and H-6a⁗); 2.50–2.38 (m, 4H, H-2, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, DMSO-d6) δ (ppm): 156.1, 136.4, 134.3, 133.1, 130.5, 130.3, 129.9, 129.5, 129.4, 127.9, 127.6, 125.5, 125.1, 124.7, 123.8, 114.2, 113.8, 104.2, 66.7 (2C), 64.9, 64.0, 55.9, 54.2 (2C). HRMS calculated for C25H27N2O5S [M + H+]: 467.1635; Found: 467.1651.
1-(5-methoxy-1-(naphthalen-1-ylsulfonyl)-1H-indol-3-yl)-2-(4-(pyridin-2-yl)piperazin-1-yl)ethan-1-ol (4n)
(3n) (336 mg, 0.60 mmol) and sodium borohydride (28 mg, 0.70 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 286 mg of compound (4n) as a yellow gel. Yield: 63%; m.p.: product in gel state; IR (KBr) cm−1: 3422, 1362, 1218, 1171, 981. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.72 (d, J = 8.7 Hz; 1H, H-2″); 8.20 (d, J = 3.9 Hz, 1H, H-3‴); 8.00 (t, J = 7.0 Hz, 2H, H-4″ and H-8″); 7.84 (d, J = 8.1 Hz, 1H, H-5″); 7.73 (s, 1H, H-2′), 7.72 (d, J = 7.5 Hz, 2H, H-7′); 7.63 (t, J = 7.7 Hz, 1H, H-7″); 7.56–7,41 (m, 3H, H-3″, H-6″ and H-5‴); 7.11 (s, 1H, H-4′); 6.86 (d, J = 9.0 Hz, 1H, H-6′); 6.64 (d, J = 7.6 Hz, 2H, H-4‴, H-6‴); 5.09 (d, J = 9.8 Hz, 1H, H-1); 4.32 (bs, 1H, OH); 3.79 (s, 3H, 5′-OCH3); 3.69–3.36 (m, 4H, H-3⁗ and H-5⁗); 2.92–2.78 (m, 3H, H-2a and H-2a⁗ and H-6a⁗); 2.74–2.59 (m, 3H, H-2b and H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 159.3, 156.2, 148.0, 137.6, 135.4, 134.2, 134.1, 130.2, 129.6, 129.1, 129.0, 128.7, 128.1, 127.2, 124.2, 124.1, 124.1, 122.3, 114.4, 113.7, 113.7, 107.3, 103.2, 63.8, 63.1, 55.8, 53.0 (2C), 45.1 (2C). HRMS calculated for C30H31N4O4S [M + H+]: 543.2061; Found: 543.2065.
1-(5-methoxy-1-tosyl-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-ol (4o)
(3o) (250 mg, 0.50 mmol) and sodium borohydride (35 mg, 0.90 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 57 mg of compound (4o) as a pale-brown crystalline plate. Yield: 23%; 85–88 °C; IR (KBr) cm−1: 3423, 1369, 1222, 1171, 1029. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 7.87 (d, J = 9.0 Hz, 1H, H-7′); 7.73 (d, J = 8.2 Hz, 2H, H-2″ and H-6″); 7.53 (s, 1H, H-2′); 7.19 (d, J = 8.2 Hz, 2H, H-3″ and H-5″); 7.08 (d, J = 2.4 Hz, 1H, H-4′); 7.05–6.98 (m, 1H, H-5‴); 6.97–6.90 (m, 3H, H-6′, H-3‴, H-4‴); 6.87 (d, J = 7.9 Hz, 1H, H-6‴); 5.05 (dd, J = 10.0 and 3.4 Hz, 1H, H-1); 3.87 (s, 3H, 2‴-OCH3); 3.82 (s, 3H, 5′-OCH3); 3.16 (bs, 4H, H-3⁗ and H-5⁗); 3.00 (bs, 2H, H-2a⁗ and H-6a⁗); 2.90–2.67 (m, 4H, H-2, H-2b⁗ and H-6b⁗); 2.32 (s, 3H, 4″-CH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 156.4, 152.4, 145.0, 141.0, 135.3, 130.3, 130.1, 130.0 (2C), 126.9 (2C), 123.9, 123.3, 123.2, 121.2, 118.4, 114.7, 113.7, 111.4, 103.2, 63.8, 63.1, 55.9, 55.5, 53.5 (2C), 50.6 (2C), 21.6. HRMS calculated for C29H34N3O5S [M + H+]: 536.2214; Found: 536.2228.
1-(5-methoxy-1-tosyl-1H-indol-3-yl)-2-(4-(pyridin-2-yl)piperazin-1-yl)ethan-1-ol (4p)
(3p) (269 mg, 0.50 mmol) and sodium borohydride (24 mg, 0.60 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 286 mg of compound (4p) as pale-brown crystalline plates. Yield: 74%; 123–126 °C; IR (KBr) cm−1: 3423, 1369, 1219, 1171, 979. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.19 (dd, J = 4.8 and 1.3 Hz, 1H, H-3‴); 7.87 (d, J = 9.0 Hz, 1H, H-7′); 7.72 (d, J = 8.3 Hz; 2H, H-2″ and H-6″); 7.51 (s, 1H, H-2′); 7.51–7.45 (m, 1H, H-5‴); 7.18 (d, J = 8.2 Hz, 2H, H-3″ and H-5″); 7.07 (d, J = 2.4 Hz, 1H, H-4′); 6.92 (dd, J = 9.0 and 2.4 Hz, 1H, H-6′); 6.68–6.59 (m, 2H, H-4‴ and H6‴); 5.01 (dd, J = 10.2 and 3.1 Hz, 1H, H-1); 3.81 (s, 3H, 5′-OCH3); 3.66–3.49 (m, 4H, H-3⁗ and H-5⁗); 2.88–2.80 (m, 2H, H-2, H-2a⁗ and H-6a⁗); 2.80–2.65 (m, 2H, H-2); 2.63–2.55 (m, 2H, H-2b⁗ and H-6b⁗); 2.31 (s, 3H, 4″-CH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 159.5, 156.3, 148.1, 145.0, 137.6, 135.3, 130.3, 130.1, 129.9 (2C), 126.9 (2C), 123.9, 123.3, 114.7, 113.6 (2C), 107.2, 103.3, 63.8, 63.2, 55.8, 53.1 (2C), 45.4 (2C), 21.6. HRMS calculated for C27H31N4O4S [M + H+]: 507.2061; Found: 507.2064.
1-(5-methoxy-1-tosyl-1H-indol-3-yl)-2-morpholinoethan-1-ol (4q)
(3q) (327 mg, 0.80 mmol) and sodium borohydride (35 mg, 0.90 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 220 mg of compound (4q) as light brown crystalline plates. Yield: 67%; 130–133 °C; IR (KBr) cm−1: 3423, 1365, 1216, 1171, 1115, 830. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 7.86 (d, J = 9.0 Hz, 1H, H-7′); 7.72 (d, J = 8.3 Hz, 2H, H-2″ and H-6″); 7.50 (s, 1H, H-2′); 7.18 (d, J = 8.2 Hz, 2H, H-3″ and H-5″); 7.05 (d, J = 2.4 Hz, 1H, H-4′); 6.91 (dd, J = 9.0 and 2,.4 Hz, 1H, H-6′); 4.97 (dd, J = 9.9 and 3.6 Hz, 1H, H-1); 3.80 (s, 3H, 5′-OCH3); 3.78–3.69 (m, 4H, H-3⁗ and H-5⁗); 2.79–2.61 (m, 4H, H-2, H-2a⁗ and H-6a⁗); 2.53–2.42 (m, 2H, H-2b⁗ and H-6b⁗); 2.32 (s, 3H, 4″-CH3). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 156.3, 145.0, 135.3, 130.3, 130.1, 129.9 (2C), 126.9 (2C), 123.9, 123.1, 114.7, 113.6, 103.2, 67.1 (2C), 64.2, 63.0, 55.8, 53.7 (2C), 21.6. HRMS calculated for C22H27N2O5S [M + H+]: 431.1635; Found: 431.1635.
1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-methoxy-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-ol (4r)
(3r) (318 mg, 0.60 mmol) and sodium borohydride (24 mg, 0.80 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 260 mg of compound (4r) as a yellow gel. Yield: 75%; product in gel state; IR (KBr) cm−1: 3422, 1367, 1219, 1164, 1029. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 7.85 (d, J = 9.0 Hz, 1H, H-7′); 7.45 (s, 1H, H-2′); 7.39 (bs, 1H, H-2″); 7.13 (s, 1H, H-4′), 7.07–6.91 (m, 5H, H-6′, H-3″, H-3‴, H-4‴, H-5‴); 6.88 (d, J = 7.9 Hz, 1H, H-6‴); 5.05 (d, J = 8.4 Hz, 1H, H-1); 3.87 (s, 3H, 2‴-OCH3); 3.85 (s, 3H, 5′-OCH3); 3.70 (bs, 1H, OH); 3.16 (bs, 4H, H-3⁗ and H-5⁗); 3.00 (bs, 2H, H-2a⁗ and H-6a⁗); 2.88–2.61 (m, 4H, H-2, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 156.7, 152.3, 140.9, 138.6, 133.1, 130.5, 130.4, 130.0, 124.8, 123.5, 123.2, 121.7, 121.1, 118.3, 114.8, 113.9, 111.3, 103.6, 63.7, 63.0, 55.8, 55.4, 53.5 (2C), 50.6 (2C). HRMS calculated for C26H29BrN3O5S2 [M + H+]: 606.0727; Found: 606.0741.
1-(1-((5-bromothiophen-2-yl)sulfonyl)-5-methoxy-1H-indol-3-yl)-2-morpholinoethan-1-ol (4s)
(3s) (364 mg, 0.70 mmol) and sodium borohydride (33 mg, 0.90 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 231 mg of compound (4s) as orange crystalline plates. Yield: 45%; 52–55 °C; IR (KBr) cm−1: 3424, 1373, 1220, 1174, 1113, 866, 684. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 7.83 (d, J = 9.0 Hz, 1H, H-7′); 7.42 (s, 1H, H-2′); 7.38 (d, J = 3.8 Hz, 1H, H-2″); 7.10 (s, 1H, H-4′); 7.00–6.90 (m, 2H, H-6′ and H-3″); 5.05 (dd, J = 9.4 and 3.2 Hz, 1H, H-1), 4.31 (bs, 1H, OH); 3.83 (s, 3H, 5′-OCH3); 3.78 (bs, 4H, H-3⁗ and H-5⁗); 2.85–2.69 (m, 4H, H-2, H-2a⁗ and H-6a⁗); 2.63–2.52 (m, 2H, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 156.7, 138.5, 133.2, 130.5, 130.2, 129.9, 124.5, 123.5, 121.8, 114.8, 113.8, 103.5, 66.7 (2C), 64.0, 62.8, 55.8, 53.6 (2C). HRMS calculated for C19H22BrN2O5S2 [M+H+]: 501.0148; Found: 501.0168.
1-(5-methoxy-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)-2-morpholinoethan-1-ol (4t)
(3t) (377 mg, 0.80 mmol) and sodium borohydride (39 mg, 1.00 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 230 mg of compound (4t) as white crystalline plates. Yield: 44%; 64–67 °C; IR (KBr) cm−1: 3422, 1366, 1221, 1166, 1115, 1031. 1H-NMR (400.1 MHz, DMSO-d6) δ (ppm): 7.77 (d, J = 9.0 Hz, 2H, H-2″ and H-6″); 7.74 (d, J = 9.0 Hz, 1H, H-7′); 7.51 (s, 1H, H-2′); 7.10 (d, J = 2.3 Hz, 1H, H-4′); 6.99 (d, J = 9.0 Hz, 2H, H-3″ and H-5″); 6.87 (dd, J = 9.0 and 2.4 Hz, 1H, H-6′); 5.19 (bs, 1H, OH); 4.93–4.86 (m, 1H, H-1); 3.71 (s, 3H, 4″-OCH3); 3.69 (s, 3H, 5′-OCH3); 3.48 (bs, 4H, H-3″″ and H-5″″); 2.60 (bs, 2H, H-2a″″ and H-6a″″); 2.43 (bs, 4H, H-2, H-2b″″ and H-6b″″). 13C-NMR (100.6 MHz, DMSO-d6) δ (ppm): 163.6, 155.8, 130.3, 129.3, 129.0 (2C), 128.6, 125.8, 123.9, 114.9 (2C), 114.1, 113.3, 103.6, 66.1 (2C), 64.2, 63.4, 55.9, 55.5, 53.6 (2C). HRMS calculated for C22H27N2O6S [M+H+]: 447.1584; Found: 447.1582.
1-(5-methoxy-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethan-1-ol (4u)
(3u) (353 mg, 0.60 mmol) and sodium borohydride (29 mg, 0.80 mmol) were reacted to give a gel, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 185 mg of compound (4u) as a yellow gel. Yield: 61%; product in gel state; IR (KBr) cm−1: 3423, 1218, 1362, 1171, 1095. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 7.86 (d, J = 9.0 Hz, 1H, H-7′); 7.79 (d, J = 8.1 Hz, 2H, H-2″ and H-6″); 7.53 (s, 1H, H-2′); 7.10 (s, 1H, H-4′); 7.06–6.98 (m, 1H, H-5‴); 6.97–6.90 (m, 3H, H-3‴, H-6′ and H-4‴); 6.90–6.81 (m, 3H, H-6‴, H-3″ and H-5″); 5.22 (s, 1H, OH); 5.11 (d, J = 9.8 Hz, 1H, H-1); 3.86 (s, 3H, 2‴-OCH3); 3.82 (s, 3H, 4″-OCH3); 3.76 (s, 3H, 5′-OCH3); 3.18 (bs, 4H, H-3⁗ and H-5⁗); 3.04 (bs, 2H, H-2a″ and H-6a″); 2.96–2.72 (m, 4H, H-2, H-2b‴ and H-6b‴). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 163.7, 156.3, 152.3, 140.8, 130.2, 130.0, 129.6, 129.1 (2C), 123.9, 123.3, 123.1, 121.1, 118.3, 114.6, 114.5 (2C), 113.6, 111.3, 103.0, 63.7, 63.0, 55.8, 55.6, 55.4, 53.5 (2C), 50,2 (2C). HRMS calculated for C29H34N3O6S [M +H+]: 552.2163; Found: 552.2179.
1-(5-methoxy-1-((4-methoxyphenyl)sulfonyl)-1H-indol-3-yl)-2-(4-(pyridin-2-yl)piperazin-1-yl)ethan-1-ol (4v)
(3v) (351 mg, 0.70 mmol) and sodium borohydride (30 mg, 0.80 mmol) were reacted to give a solid, which was purified by column chromatography on silica gel using dichloromethane/ethyl acetate 5:1 to obtain 268 mg of compound (4v) as yellow crystalline plates. Yield: 67%; 97–100 °C; IR (KBr) cm−1: 3422, 1367, 1219, 1164, 979. 1H-NMR (400.1 MHz, CDCl3) δ (ppm): 8.19 (d, J = 2.3 Hz, 1H, H-3‴); 7.86 (d, J = 9.0 Hz, 1H, H-7′); 7.77 (d, J = 8.2 Hz, 2H, H-2″); 7.51 (s, 1H, H-2′); 7.50–7.44 (m, 1H, H-5‴); 7.08 (d, J = 2.3 Hz, H-4′); 6.92 (dd, J = 9.0 and 2.4 Hz, 1H, H-6′); 6.83 (d, J = 8.2 Hz, 2H, H-3″); 6.67–6.59 (m, 2H, H-4‴, H-6‴); 5.04 (d, J = 10.1 and 2.9 Hz, 1H, H-1); 3.81 (s, 3H, 5′-OCH3); 3.75 (s, 3H, 4″-OCH3); 3.67–3.50 (m, 4H, H-3⁗ and H-5⁗); 2.90–2.82 (m, 2H, H-2a⁗ and H-6a⁗); 2.82–2.66 (m, 2H, H-2); 2.66–2.57 (m, 2H, H-2b⁗ and H-6b⁗). 13C-NMR (100.6 MHz, CDCl3) δ (ppm): 163.8, 159.4, 156.3, 148.0, 137.7, 130.3, 130.1, 129.7, 129.1 (2C), 123.9, 123.1, 114.7, 114.5 (2C), 113.7, 113.6, 107.3, 103.2, 63.8, 63.2, 55.9, 55.7, 53.1 (2C), 45.3 (2C). HRMS calculated for C27H31N4O5S [M + H+]: 523.2010; Found: 523.2013.

3.2. Radioligand Binding Assay at the 5-HT6 Receptor

The affinity of compounds toward 5-HT6 receptor was evaluated utilizing membranes from HEK-293 cells expressing human 5-HT6 receptors and [125I]-SB-258585 as iodinated specific radioligand (4-iodo-N-[4-methoxy-3-(4-methyl-piperazin-1-yl)-phenyl]-benzenesulphonamide; Kd= 1.3 nM; 2200 Ci/mmol). Competitive inhibition assays were performed according to standard procedures. Briefly, fractions of 45 µL of diluted 5-HT6 membrane preparation were incubated at 27 ºC for 180 min with 25 µL of [125I]-SB-258585 (0.2 nM) and 25 µL of WGA PVT SPA beads (4mg/mL) in the presence of increasing concentrations (10−11 to 10−4M) of the competing drug (5 μL) or DMSO, in a final volume of 100 μL of assay buffer (50 mM Tris, 120 mM NaCl, pH 7.4). Nonspecific binding was determined by radioligand binding in the presence of a saturating concentration of 100 μM of clozapine. The binding of [125I]-SB-258585 to 5-HT6 receptors directly correlated to an increase in the signal that was read on Perkin Elmer Topcount NXT HTS. All compounds were tested at eight concentrations in triplicate. Clozapine was used as an internal standard for comparison. The data generated were analyzed using Prism software (GraphPad Inc). A linear regression line of data points was plotted from which the concentration of the competing ligand, which displaces 50% of the specific binding of the radioligand (IC50 value), was determined and the Ki value was calculated based upon the Cheng–Prusoff equation: Ki = IC50/(1 + L/KD), where L is the concentration of free radioligand used in the assay and KD is the dissociation constant of the radioligand for the receptor.

3.3. Docking and Molecular Dynamics (MD) Simulations Studies of Compounds 4d, 4l and PUC-10

The 5-HT6 receptor model previously reported by our group was used as a starting point [17]. Molecular docking was performed using OEDocking suite v3.3.0.3 (OpenEye Scientific Software, Inc., Santa Fe, NM, USA) [36]. First, the receptor was prepared using the MakeReceptor GUI v3.3.0.3: a box with dimensions 32 × 28 × 29 Å was generated covering key residues reported to be involved in ligand recognition, namely Asp106 (3.32), Val107 (3.33), Cys110 (3.36), Val189 (5.39), Ala192 (5.42). Ser193 (5.43), Thr196 (5.46), Trp281 (6.48), Phe285 (6.52) and Asn288 (6.55) [17,37]. A site shape potential was set up, obtaining an outer contour of 2611 Å; no constraints were defined. The ligands were constructed using MarvinSketch v19.18.0 (ChemAxon Ltd., Budapest, Hungary) and exported as SMILES. The stereocenters were enumerated using Flipper (part of OMEGA distribution) and multiconformer libraries of compounds were prepared using OMEGA v3.1.0.3 (OpenEye Scientific Software, Inc., Santa Fe, NM, USA) [38,39]. QUACPAC v2.0.0.3 (OpenEye Scientific Software, Inc., Santa Fe, NM, USA) was used to assign AM1BCC charges to the library of conformers [40,41,42]. Finally, compounds were docked using FRED v3.3.0.3 (OpenEye Scientific Software, Inc., Santa Fe, NM, USA) and the best-scoring conformation according to the ChemGauss4 score of each compound was extracted for further analysis [43,44,45]. Graphical representations of docking poses were generated using PyMOL v2.4.1 (Schrödinger, LLC, Cambridge, MA, USA).
For MD simulations, ligand–receptor complexes were inserted into the POPC membrane, solvated, and ionized up to a concentration of 0.15 M NaCl, using the Membrane Builder module from the CHARMM-GUI web server [46,47]. The protein orientation was defined based on the OPM database. The initial system size was about 100 × 100 × 120 Å and consisted approximately of 111,000 atoms. All MD simulations were performed using the NAMD package v2.14 [48]. The simulation systems were first relaxed with 2000 steps of minimization followed by gradual heating from 0 to 310 K by running short MD simulations of 500 steps every cycle. The systems were then fixed, except for the lipid tails, which were left to equilibrate for 250 ps. The simulation was switched to NPT conditions and was further equilibrated for 2.5 ns while constraining the protein with an initial force constant of 10 kcal/(mol·Å2) and gradually decreasing to 8, 6, 4, 2, 1, 0.5, 0.05 kcal/(mol·Å2) every 250 ps of the MD simulation. Finally, the systems were run without any constraints for 80 ns. Proteins, lipids, and ions were described by the CHARMM36 force field and the parameters for ligands were obtained using the antechamber option available in the Membrane Builder interface [49,50]. The Van der Waals interactions were calculated applying a cutoff distance of 12 Å and switching the potential from 10 Å. A timestep of 2 fs was used in the production phase and PME (Particle Mesh Ewald) was employed for the treatment of long-range electrostatic interactions [51]. The temperature was maintained at 310 K using Langevin dynamics. The Nose–Hoover–Langevin piston method was used to control the target pressure (1 atm) with the LangevinPistonPeriod set to 200 fs and LangevinPistonDecay set to 50 fs. The results were analyzed using Visual Molecular Dynamics (VMD) software and PyMOL suite [52,53]. The last 30 ns of each simulation was extracted for analysis and clustered using the hierarchical agglomerative algorithm available in cpptraj [30]. The representative frame of the most populated cluster was then analyzed using PLIP web server [31].

3.4. CoMFA and CoMSIA Studies

3.4.1. Selection of Conformers and Molecular Alignment

CoMFA and CoMSIA studies were performed with SYBYL-X v1.2 (Tripos International, St. Louis, MO, USA) software installed in a Windows 10 environment on a PC with an Intel Core i7 CPU. The alignment of the best docking poses was used as a basis for the formulation of the models. For the calculation of the potentials, each compound was assigned MMFF94 loads. The compounds were divided into training and test sets in order to test both the quality of the internal and external predictive capacities of the models. Fifteen compounds were used as test sets (equivalent to 32% of the total) and 32 compounds as training sets (equivalent to 68% of the total). The Ki values were converted to pKi (−logKi).

3.4.2. CoMFA and CoMSIA Field Calculation

To derive the CoMFA and CoMSIA descriptor fields, the aligned training set molecules were placed in a three-dimensional cubic lattice with a grid spacing of 2Å in the x, y, and z directions such that the entire set was included in it. The CoMFA steric and electrostatic field energies were calculated using a sp3 carbon probe atom with a Van der Waals radius of 1.52 Å and a charge of +1.0. The cut-off values for both steric and electrostatic fields were set to 30.0 kcal/mol. For CoMSIA analysis, the standard settings (probe with charge +1.0, radius 1Å, hydrophobicity +1.0, H-bond donating +1.0, and H-bond accepting +1.0 [54]) were used to calculate five different fields: steric, electrostatic, hydrophobic, donor, and acceptor. Gaussian-type distance dependence was used to measure the relative attenuation of the field position of each atom in the lattice and led to a much smoother sampling of the fields around the molecules when compared to CoMFA. The default value of 0.3 was set for attenuation factor α.

3.4.3. Internal Validation and Partial Least Squares (PLS) Analysis

PLS analysis was used to construct a linear correlation between the CoMFA and CoMSIA descriptors (independent variables) and the activity values (dependent variables) [55]. To select the best model, cross-validation analysis was performed using the leave-one-out (LOO) method (and sample distance PLS [SAMPLS]), which generated the square of the cross-validation coefficient (q2) and the optimum number of components (N). The non-cross validation was performed with a column filter value of 2.0 to speed up the analysis and reduce the noise. The q2, which is a measure of the internal quality of the models, was obtained according to the following Equation (1):
q 2 = 1 ( y i y p r e d ) 2 ( y i y ¯ ) 2
where y i , y ¯ , and y p r e d are the observed, mean, and predicted activity in the training set, respectively.

4. Conclusions

In this work, we reported the synthesis, biological evaluation, and modeling studies of novel N-arylsulfonyl indole derivatives as ligands of the 5-HT6 receptor. A convenient synthesis was achieved to readily access twenty-two novel diversely substituted derivatives of the extended indole-aryl piperazines. Fifteen of the tested compounds exhibited nanomolar affinity for the 5-HT6 receptor, with compound 4d being the most potent, having a Ki of 58 nM, which is better than the 5-HT endogenous ligand. Protein–ligand molecular dynamics simulations provided us a deeper insight about the influence of the 5-methoxy or 5-fluorine substitutions in the binding mode of the ligands, suggesting that these C-5 substitutions are detrimental to affinity due to them precluding the ligand from plunging inside the binding site. On the other hand, in the 3D-QSAR studies, the CoMFA and CoMSIA models presented high values of q2 (0.653; 0.692) and r2 (0.879; 0.970), respectively. The biological activity of the compounds can be explained based on the steric and electronic properties, but mainly on their electronic nature. The information gained in this study will allow the design of novel derivatives with improved activity.

Supplementary Materials

The following are available online at https://www.mdpi.com/article/10.3390/ph14060528/s1, 1H-NMR and 13C-NMR spectra of final compounds; high-resolution mass spectra of final compounds; radioligand binding studies, dose-response curves for final compounds; tables of QSAR, Tables S1–S3: CoMFA and CoMSIA data.

Author Contributions

G.R.-G. formulated the research idea, designed the synthetic routes of compounds, analyzed the data and wrote the manuscript; C.F.L. and Y.H.C. performed the bioinformatics studies (docking and MD simulations) and contribute to write the manuscript; compounds were synthesized, purified and characterized by G.R.-G. students G.V., L.A.-R. and D.E.-R.; J.M.-R. and D.C. contributed with the QSAR studies and manuscript preparation; D.V.-V. performed HRMS analysis. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Fondo Nacional de Desarrollo Científico y Tecnológico de Chile FONDECYT grant number 11121418 to Gonzalo Recabarren-Gajardo.

Data Availability Statement

Data is contained within the article and Supplementary Materials.

Acknowledgments

Gonzalo Recabarren-Gajardo thanks DIPOG from Facultad de Química y de Farmacia of Pontificia Universidad Católica de Chile for support through internal projects 3913-529-81 and 3913-541-81. Carlos F. Lagos thanks OpenEye Scientific Software, ChemAxon & Inte: Ligand GmbH for academic licenses of their software. Powered@NLHPC: This research was partially supported by the supercomputing infrastructure of the NLHPC (ECM-02). We acknowledge Benjamin Diethelm-Varela (Pharmacist) for his review of the English language of the manuscript.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

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Figure 1. Structures and inhibition constants (Ki) for 5-HT [18], MS-245 [19,20], and examples of our previously reported N-arylsulfonylindole antagonists over the 5-HT6 receptor [17].
Figure 1. Structures and inhibition constants (Ki) for 5-HT [18], MS-245 [19,20], and examples of our previously reported N-arylsulfonylindole antagonists over the 5-HT6 receptor [17].
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Scheme 1. Synthesis of derivatives 4av, reagents and conditions: a: (i) Anhydrous ZnCl2, dry CH2Cl2, CH3MgBr, rt, 2 h; (ii) BrCH2COCl, 12 h; (iii) NH4Cl sat.; b: ArSO2Cl, Et3N, DMAP, CH2Cl2, rt.; c: Arylpiperazines or morpholine, K2CO3, acetone, rt.; d: NaBH4/MeOH.
Scheme 1. Synthesis of derivatives 4av, reagents and conditions: a: (i) Anhydrous ZnCl2, dry CH2Cl2, CH3MgBr, rt, 2 h; (ii) BrCH2COCl, 12 h; (iii) NH4Cl sat.; b: ArSO2Cl, Et3N, DMAP, CH2Cl2, rt.; c: Arylpiperazines or morpholine, K2CO3, acetone, rt.; d: NaBH4/MeOH.
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Figure 2. FRED-obtained binding modes for compounds PUC-10 (sky-blue), 4d (deep salmon) and 4l (lemon) in (A) S conformation and (B) R conformation. Residues in orange depict the hydrophobic cluster in TMH-6 and TMH7 regions; yellow depicts residues in TMH-3 and TMH-5 surrounding the binding pocket, cyan depicts Asp106 (3.32) implicated in Scheme 288. (6.55) and Ser193 (5.43) implicated in hydrogen bond interactions (residues are also indicated under Ballesteros–Weinstein nomenclature [28]).
Figure 2. FRED-obtained binding modes for compounds PUC-10 (sky-blue), 4d (deep salmon) and 4l (lemon) in (A) S conformation and (B) R conformation. Residues in orange depict the hydrophobic cluster in TMH-6 and TMH7 regions; yellow depicts residues in TMH-3 and TMH-5 surrounding the binding pocket, cyan depicts Asp106 (3.32) implicated in Scheme 288. (6.55) and Ser193 (5.43) implicated in hydrogen bond interactions (residues are also indicated under Ballesteros–Weinstein nomenclature [28]).
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Figure 3. Binding modes obtained after MD simulation of compounds (A) PUC-10 (sky-blue), (B) 4d (deep salmon) and (C) 4l (lemon) depicted from the extracellular view. The 2D interaction plots were obtained with LigandScout v4.2 (Inte:Ligand GmbH).
Figure 3. Binding modes obtained after MD simulation of compounds (A) PUC-10 (sky-blue), (B) 4d (deep salmon) and (C) 4l (lemon) depicted from the extracellular view. The 2D interaction plots were obtained with LigandScout v4.2 (Inte:Ligand GmbH).
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Figure 4. Figure 4. Plots of experimental versus predicted pKi values for the training and test set molecules of (A) CoMFA and (B) CoMSIA. The only outlier compound (residual > 1.0) in both cases was compound 4s, represented as a triangle in the figure.
Figure 4. Figure 4. Plots of experimental versus predicted pKi values for the training and test set molecules of (A) CoMFA and (B) CoMSIA. The only outlier compound (residual > 1.0) in both cases was compound 4s, represented as a triangle in the figure.
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Figure 5. Graphics results of the CoMFA and CoMSIA studies. (A) CoMFA steric contour map for Table 4. 4d (pKi = 7.234) and (B) CoMSIA steric contour map. Green polyhedrons indicate that it is favorable for biological activity to use bulky substituents, while yellow polyhedrons indicate that it is not favorable. (C) CoMFA electrostatic contour map for the most active molecule 4d and (D) CoMSIA electrostatic contour map. Blue polyhedrons indicate that the presence of electron-deficient zones is favorable for activity, while red polyhedrons indicate that electron-rich zones are favorable.
Figure 5. Graphics results of the CoMFA and CoMSIA studies. (A) CoMFA steric contour map for Table 4. 4d (pKi = 7.234) and (B) CoMSIA steric contour map. Green polyhedrons indicate that it is favorable for biological activity to use bulky substituents, while yellow polyhedrons indicate that it is not favorable. (C) CoMFA electrostatic contour map for the most active molecule 4d and (D) CoMSIA electrostatic contour map. Blue polyhedrons indicate that the presence of electron-deficient zones is favorable for activity, while red polyhedrons indicate that electron-rich zones are favorable.
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Figure 6. The summary of the SAR founded in the 3D-QSAR study.
Figure 6. The summary of the SAR founded in the 3D-QSAR study.
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Table 1. 5-HT6 Binding affinity results for new N-arylsulfonylindole derivatives.
Table 1. 5-HT6 Binding affinity results for new N-arylsulfonylindole derivatives.
The General Structures of the Compounds
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CodeRAr1Ar2Ki (nM) aCodeRAr1Ar2Ki (nM) a
4aF4-I-Ph2-OMe-Ph3904qOMe4-Me-Ph-4024
4bF4-I-Ph2-py36294rOMe5-Br-2-thioph2-OMe-Ph167
4cF4-I-Ph-12,5154sOMe5-Br-2-thioph-130
4dFNaph2-OMe-Ph584tOMe4-OMePh-7490
4eFNaph2-py8014uOMe4-OMePh2-OMe-Ph270
4fFNaph-6834vOMe4-OMePh2-py2185
4gFNaph2-pyrim1444PUC7H4-I-Ph2-OMe-Ph18.4 b
4hF4-OMe-Ph2-OMe-Ph850PUC9H4-I-Ph2-py371 b
4iF5-Br-2-thioph2-OMe-Ph381PUC10HNaph2-OMe-Ph14.6 b
4jOMe4-I-Ph2-OMe-Ph289PUC11HNaph2-py148 b
4kOMe4-I-Ph-403PUC12HNaph2-pyrim603 b
4lOMeNaph2-OMe-Ph160PUC16H4-Me-Ph2-pyrim851 b
4mOMeNaph-247PUC22H4-OMePh-891 b
4nOMeNaph2-py153PUC24H4-Me-Ph2-py479 b
4oOMe4-Me-Ph2-OMe-Ph972PUC32H4-Me-Ph2-OMe-Ph13.6 b
4pOMe4-Me-Ph2-py21955-HT 75 [18]
a Displacement of [125I]-SB-258585 bound to cloned 5-HT6 human receptors stably expressed in HEK-293 cells. IC50 values (not shown) were determined in triplicate and Ki were calculated using Cheng–Prusoff equation [25]. In this assay, the IC50 value of Clozapine (Clz) was 12.4 nM; Ki = 11.9 nM. b Ki values for unsubstituted derivatives previously reported [17].
Table 2. Docking scoring and distance (in Å) of hydrophobic and salt bridge interactions established with residues within the binding site and compounds PUC10, 4d and 4l.
Table 2. Docking scoring and distance (in Å) of hydrophobic and salt bridge interactions established with residues within the binding site and compounds PUC10, 4d and 4l.
Hydrophobic Interactions
ResiduePUC104d4l
Ala83----3.98
Thr103--3.7--
Val1073.543.723.50
3.993.583.62
3.933.753.67
--3.78--
Pro1613.693.613.97
Ala1923.543.583.79
Phe284----3.55
Phe285----3.64
Phe3023.74----
Thr3063.74--3.97
Trp307----3.8
Salt Bridges
Asp1063.34.273.56
FRED ChemGauss 4 Score
−17.27−16.61−15.5
Table 3. π-stacking interactions established with residues within the binding site and compounds PUC10, 4d and 4l.
Table 3. π-stacking interactions established with residues within the binding site and compounds PUC10, 4d and 4l.
π-Stacking
CompoundResidueCentDistAngleOffsetType
PUC10Phe1884.6388.30.75T
--4.9388.461.88T
Phe2854.8987.81.62T
4dTrp1024.1528.791.44P
Phe1885.3774.160.98T
Phe2855.0978.611.34T
4lTrp1025.2978.411.23T
Phe1885.3484.211.27T
--5.3684.381.43T
Table 4. Hydrogen bond interactions established with residues within the binding site and compounds PUC10, 4d and 4l.
Table 4. Hydrogen bond interactions established with residues within the binding site and compounds PUC10, 4d and 4l.
Hydrogen Bonds
CompoundResidueDist_H-A Dist_D-ADon_Angle
PUC10Ser1933.183.51101.39
3.503.94109.52
4dThr1963.544.00114.16
Asn2881.632.63166.72
4lAsp1062.893.34109.58
Tyr3103.343.78104.37
Interactions calculated using the PLIP web server. Dist_H-A: Distance between H-bond hydrogen and acceptor atom. Dist_D-A: Distance between H-bond donor and acceptor atoms. Don_Angle: Angle at the donor.
Table 5. Statistical summary of the best models for CoMFA and CoMSIA.
Table 5. Statistical summary of the best models for CoMFA and CoMSIA.
Modelsq2NSEPr2ncvFSEEr2test% Contribution
StericElectrostatic
CoMFA-SE0.65320.4100.879101.2430.2430.78644.955.1
CoMSIA-SE0.69250.4090.970161.6240.1280.72639.260.8
q2 = the square of the LOO cross-validation (CV) coefficient; N = the optimum number of components; SEP = standard error of prediction; SEE is the standard error of estimation of non CV analysis; r2ncv is the square of the non CV coefficient; F is the F-test value; r2test is the regression coefficient for the molecules in the test set exclusively.
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Arrieta-Rodríguez, L.; Espinoza-Rosales, D.; Vera, G.; Cho, Y.H.; Cabezas, D.; Vásquez-Velásquez, D.; Mella-Raipán, J.; Lagos, C.F.; Recabarren-Gajardo, G. Novel N-Arylsulfonylindoles Targeted as Ligands of the 5-HT6 Receptor. Insights on the Influence of C-5 Substitution on Ligand Affinity. Pharmaceuticals 2021, 14, 528. https://doi.org/10.3390/ph14060528

AMA Style

Arrieta-Rodríguez L, Espinoza-Rosales D, Vera G, Cho YH, Cabezas D, Vásquez-Velásquez D, Mella-Raipán J, Lagos CF, Recabarren-Gajardo G. Novel N-Arylsulfonylindoles Targeted as Ligands of the 5-HT6 Receptor. Insights on the Influence of C-5 Substitution on Ligand Affinity. Pharmaceuticals. 2021; 14(6):528. https://doi.org/10.3390/ph14060528

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Arrieta-Rodríguez, Loreto, Daniela Espinoza-Rosales, Gonzalo Vera, Young Hwa Cho, David Cabezas, David Vásquez-Velásquez, Jaime Mella-Raipán, Carlos F. Lagos, and Gonzalo Recabarren-Gajardo. 2021. "Novel N-Arylsulfonylindoles Targeted as Ligands of the 5-HT6 Receptor. Insights on the Influence of C-5 Substitution on Ligand Affinity" Pharmaceuticals 14, no. 6: 528. https://doi.org/10.3390/ph14060528

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