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Friedländer-Type Reaction of 4-Cholesten-3-one with 2′-Aminoacetophenone: Angular versus Linear Quinoline-Fused Steroids

Dipartimento di Scienze Fisiche e Chimiche, Università degli Studi di L’Aquila, Via Vetoio, 67100 Coppito, Italy
Dipartimento di Bioscienze e Tecnologie Agroalimentari e Ambientali, Università degli Studi di Teramo, Via R. Balzarini, 64100 Teramo, Italy
Author to whom correspondence should be addressed.
Molbank 2023, 2023(3), M1712;
Received: 22 July 2023 / Revised: 12 August 2023 / Accepted: 15 August 2023 / Published: 16 August 2023
(This article belongs to the Section Organic Synthesis)


To optimize the experimental conditions used for the Friedländer-type condensation, an angular fused 4-substituted quinoline steroid has been obtained in very high yield and regioselectivity using readily available 4-cholesten-3-one and 2′-aminoacetophenone. Moreover, by varying the reaction conditions and the catalyst, the corresponding linear regioisomer was also achieved with an acceptable isolated yield and high chemoselectivity. Both structures have been definitively elucidated via 2D-NMR and fully characterized.

1. Introduction

The quinoline nucleus is ubiquitous in nature and plays a significant role in the development of novel heterocyclic compounds that have important pharmacological features, such as antitumoral activities [1,2]. Over time, studies of the biological activity of quinoline derivatives on diverse cancer cell lines have revealed a wide range of action mechanisms, paving the way for the development of more effective quinoline-derived drugs [3,4]. Figure 1 depicts a non-exhaustive list of commercialized anticancer drugs that use the quinoline ring as their primary component.
In addition, the incorporation of the quinoline nucleus into the steroid nucleus [5] has emerged as a promising strategy for the identification of new antitumor agents (Figure 2) [6,7,8].
So far, the Friedlӓnder reaction has proved to be one of the most powerful methods of performing diversity-oriented synthesis of bioactive heterocyclic scaffolds based on the quinoline nucleus [9,10,11]. Indeed, the Friedlӓnder condensation of 2-formyl- or 2-acyl anilines with keto-steroids provided a simple way to achieve A-ring and D-ring-fused quinolines [12,13].
In this field, as part of our ongoing research into heterocyclic scaffolds that have potential biological activity, two members of our team successfully synthetized pyridines and quinolines via cascade amination/cyclization/aromatization reactions of propargylamine [14] or β-(2-aminophenyl)-α,β-ynones [15], with the ketones using metal or Brønsted acid catalysis, respectively. These methodologies also enabled access to linear and angular polycyclic steroidal derivatives using cholestanones or cholestenones, respectively, as reaction partners (Scheme 1).
Due to the importance of substituent and skeleton variations in drug design [16], we became interested in implementing the synthesis of fused quinoline steroids using readily available and inexpensive 2-acyl-substituted anilines as convenient alternative starting materials in Friedlӓnder-type condensation with α,β-unsaturated keto-steroids.
Here we report a preliminary optimization study of the model system 2′-aminacetophenone and 4-cholesten-3-one, which aimed to obtain novel 4-alkyl-substituted quinolines, as well as address the α/α’ regioselectivity issue.

2. Results and Discussion


Due to the possibility of forming two regioisomeric enamine intermediates (type A and B), the reaction between 2′-aminoacetophenone 1 and 4-cholesten-3-one 2 poses a regioselectivity issue, namely the competition between the condensations at the α and α’ positions (Figure 3) [17].
Thus, following our previous studies of this matter, we performed the reaction under a variety of experimental conditions, using both gold(III) catalysis and Brønsted acid catalysis. The effects of the catalytic loading, the nature of the solvent and the temperature were also investigated (Table 1).
Using previously reported conditions for sequential condensation/annulation reaction of active methylene ketones with 2-aminocarbonyls, the gold(III)-catalyzed reaction produced a mixture of angular and linear quinolines 3 and 4 in a 1:2 ratio with a modest overall yield of 40% after 24 h (entry 1). Despite the fact that 66% of the starting material 2 could be recovered when the reaction was terminated, NMR analysis of the crude after a shorter reaction time (5 h) revealed a comparable conversion of 2 (note c, entry 1). Due to the low regioselectivity, the catalyst loading was not further investigated.
An increase in the temperature resulted in a slight increase in overall yield (45%) and substantially unchanged regio- and chemo-selectivity (i.e., global quinoline-isolated yield vs. starting material conversion) (entry 2).
Moreover, 2D-NMR experiments performed using isolated products definitively disambiguated the structures of the two regioisomers. As detailed in the Supplementary Materials document, the key difference between the two types is the observation of NOE between vinylic H and the methyl group using the quinoline moiety in 3 vs. the lack of NOE between vinylic H and the same methyl group using quinoline 4, which, conversely, presents a strong transient NOE with methylene 1 (See Figure S22).
In contrast, substantial improvements in efficiency and overall yield were obtained when using p-toluenesulfonic acid monohydrate (p-TsOH·H2O) as the catalyst. In fact, under the conditions described in entry 3, the quinolines 3 and 4 were isolated in 60% and 30%, respectively.
A remarkable enhancement of the regioselectivity in favor of the angular quinoline was achieved using non-polar toluene as the solvent rather than polar protic EtOH, so much so that, with a stoichiometric amount of p-TsOH·H2O in toluene at 80 °C, the starting material 2 was completely converted within 5 h, and the angular quinoline 3 was isolated as a single regioisomer in nearly quantitative yield (entry 8).
A control experiment performed using NaAuCl4·2H2O in toluene confirmed the crucial effect of this solvent in preferentially directing the regioselectivity toward the angular quinoline. In fact, despite a poor overall yield of 15%, the regioisomer 3 was isolated in a large majority of cases (entry 9). In these cases, toluene strongly impacts the chemoselectivity of the reaction, probably due to the well-known sensitivity of the catalyst to aromatic compounds [18].

3. Materials and Methods

3.1. General Information

The reactions were monitored via thin layer chromatography (TLC) using Merck Silica Gel 60 F254 plates (Milan, Italy) and visualized through fluorescence quenching at 254 nm.
The purification of products was carried out via flash chromatography using silica gel 60. The NMR spectra were recorded via Bruker Avance 400 spectrometers (400 MHz, 1H; 101 MHz, 13C; 135 MHz DEPT) (Milan, Italy). Spectra were referenced to the residual CHCl3 (7.26 ppm, 1H; 77.00 ppm, 13C). A full characterization using the 2D-NMR spectra of both 3 and 4 can be found in the Supplementary Materials document.
Yields are given for isolated products. Purity was monitored via NMR spectra. High-resolution mass spectra (HRMS) were acquired using a Xevo G2-XS QTof (Waters Corporation, Milford, CT, USA). The samples were ionized in positive ion mode using an electrospray (ESI) ionization source. The IR spectra were recorded via a Perkin–Elmer spectrometer (Spectrum Two FT-IR) (Waltham, MA, USA) equipped with a universal attenuated total reflectance accessory (UATR). Optical rotations were measured using a ZUZI 412 Digital Polarimeter (tube length: 100 mm) (Auxilab, Navarra, Spain). Melting points were determined using STUART Melting Point Apparatus SMP30 (Vernon Hills, IL, USA).

3.2. Materials

All chemicals and solvents were obtained from commercial sources and used without further purification.

3.3. General Procedure for the Synthesis of Compound 3 and 4

A mixture of 2-Aminoacetophenone 1 (0.8 mmol, 108 mg, 97 µL and 2 equivalent), (+)-4-cholesten-3-one 2 (0.4 mmol and 154 mg) and p-TsOH·H2O (0.4 mmol, 76 mg and 1 equivalent) in Toluene (2 mL) was stirred at 80 °C for 5 h. After completion (reaction monitored via TLC eluting in pure CH2Cl2), the mixture was diluted using a saturated solution of NaHCO3 and extracted using CH2Cl2 (25 mL × 3). The combined organic layer was dried over anhydrous Na2SO4. After the removal of the solvent at reduced pressure, the crude product was purified via flash chromatography using silica gel eluting with n-hexane/CH2Cl2 mixtures (from 9:1 to pure CH2Cl2) to give 189 mg of (3R,3aR,5bR)-3a,5b,13-trimethyl-3-((R)-6-methylheptan-2-yl)-2,3,3a,4,5,5a,5b,6,7,15,15a,15b-dodecahydro-1H-cyclopenta[5,6]naphtho[2,1-a]acridine (3) as a white solid (yield 98%; mp 127.5–128.0 °C; [α]D= −10.78 (c 0.1 in CHCl3). IR (cm−1) 2944; 2920; 2866; 2845; 1452; 1380; 765).
1H NMR (400 MHz, CDCl3) δ 7.98 (dd, J = 12.2, 8.4 Hz, 2H); 7.62 (t, J = 7.5 Hz, 1H); 7.49 (t, J = 7.6 Hz, 1H); 5.60 (d, J = 3.3 Hz, 1H); 2.89–2.78 (m, 2H); 2.70 (s, 3H); 2.31 (dt, J = 17.5, 4.6 Hz, 1H); 2.19–2.05 (m, 2H); 1.94–0.99 (m, 21H); 0.93 (m, 12H) and 0.76 (s, 3H). 13C{1H} NMR (101 MHz, CDCl3) δ 161.3; 145.7; 139.8; 139.2; 132.4; 128.9; 128.6; 128.2; 128.1; 125.3; 124.4; 56.9; 56.3; 47.3; 42.6; 40.0; 39.5; 38.0; 36.2; 35.8; 34.6; 32.31; 32.30; 32.0; 28.3; 28.0; 24.2; 23.9; 23.7; 22.8; 22.6; 22.0; 18.7; 15.5 and 12.1. HRMS: m/z (MALDI-TOF) positive ion, which was calculated for C35H50N: [M + H]+ 484.3943, found: 484.3941 (see Supplementary Materials).
A mixture of 2-Aminoacetophenone 1 (0.44 mmol, 59 mg, 53 µL and 1.1 equivalent), (+)-4-cholesten-3-one 2 (0.4 mmol, 154 mg and 1.0 equivalent) and NaAuCl4·2H2O (0.02 mmol, 8 mg and 0.05 equivalent) in EtOH (2 mL) was stirred at 110 °C for 5 h. After completion (reaction monitored via TLC elution in pure CH2Cl2), the mixture was diluted using a saturated solution of NaHCO3 and extracted using CH2Cl2 (25 mL × 3). The combined organic layers were dried using anhydrous Na2SO4. After the removal of the solvent at reduced pressure, the crude was purified via flash chromatography (eluents: n-hexane/CH2Cl2 mixtures from 9:1 to pure CH2Cl2) to yield 30 mg of (1R,13aR,15aR)-12,13a,15a-trimethyl-1-((R)-6-methylheptan-2-yl)-2,3,3a,3b,4,5,13,13a,13b,14,15,15a-dodecahydro-1H-cyclopenta[5,6]naphtho[1,2-b]acridine (4) as a white solid (yield 30%; mp 136.3–138.8 °C; [α]D= 30.06 (c 0.02 in CHCl3). IR (cm−1): 2928; 2868; 1451; 1380; 761; 754.
1H NMR (400 MHz, CDCl3) δ 7.92 (dd, J = 22.8, 8.3 Hz, 2H); 7.56 (t, J = 7.6 Hz, 1H); 7.41 (t, J = 7.6 Hz, 1H); 6.45 (s, 1H); 3.26 (d, J = 15.3 Hz, 1H); 2.55 (s, 3H); 2.53–2.37 (m, 3H); 2.07 (t, J = 12.3 Hz, 1H); 1.91–0.98 (m, 21H); 0.97–0.82 (m, 12H) and 0.74 (s, 3H). 13C{1H} NMR (101 MHz, CDCl3) δ 156.7; 153.5; 146.5; 139.1; 129.2; 128.0; 127.6; 125.7; 125.1; 123.6; 123.4; 56.3; 56.1; 53.6; 42.7; 39.9; 39.5; 39.2; 38.8; 36.2; 36.1; 35.8; 31.7; 31.5; 29.7; 28.2; 28.0; 24.3; 23.9; 22.8; 22.6; 21.9; 18.7; 18.4; 13.4 and 11.9. HRMS: m/z (MALDI-TOF) positive ion, which was calculated for C35H50N: [M + H]+ 484.3943, found: 484.3945 (see Supplementary Materials).

4. Conclusions

In summary, we presented a direct means of accessing synthetically relevant fused angular- and linear 4-methyl-substituted quinoline derivatives of 4-cholesten-3-one. In addition to successfully adjusting the reaction parameters to maximize the yield of the angular regioisomer, the challenging linear derivative has been achieved in a significant isolated yield for the first time. The evaluation of the biological activity of both molecules will occur in due course in our laboratory.

Supplementary Materials

S1: NMR Spectra; S2: IR Spectra; S3: Mass Spectra; S4: 3 and 4 structure determination (2D-NMR spectra).

Author Contributions

Conceptualization, A.A.; investigation, C.M.; data curation and data analysis, C.M., V.M. and M.C.; 2D-NMR data curation and data analysis, M.C.; writing—original draft preparation, A.A.; writing—review and editing, L.P.; supervision, project administration, A.A. and L.P. All authors have read and agreed to the published version of the manuscript.


This research received no external funding.

Data Availability Statement

Not applicable.


L.P. gratefully acknowledges support provided by the European Union—NextGenerationEU project via the Italian Ministry of University and Research’s (MUR) National Innovation Ecosystem grant ECS00000041-VITALITY-CUP E13C22001060006.

Conflicts of Interest

The authors declare no conflict of interest.


  1. Kaur, K.; Kumar, N.; Singh, J.V.; Bedi, P.M.S.; Singh, H. Recent Development of Quinoline Derivatives as Anticancer Agents: 2015–2022. In Interdisciplinary Cancer Research; Springer: Cham, Switzerland, 2023; pp. 1–34. [Google Scholar] [CrossRef]
  2. Elebiju, O.F.; Ajani, O.O.; Oduselu, G.O.; Ogunnupebi, T.A.; Adebiyi, E. Recent advances in functionalized quinoline scaffolds and hybrids-Exceptional pharmacophore in therapeutic medicine. Front. Chem. 2023, 10, 1074331. [Google Scholar] [CrossRef] [PubMed]
  3. Ilakiyalakshmi, M.; Napoleon, A.A. Review on recent development of quinoline for anticancer activities. Arab. J. Chem. 2022, 15, 104168. [Google Scholar] [CrossRef]
  4. Concepción, A.; Fuertes, M.; Martín-Encinas, E.; Selas, A.; Rubiales, G.; Tesauro, C.; Knudssen, B.K.; Palacios, F. Novel topoisomerase I inhibitors. Syntheses and biological evaluation of phosphorus substituted quinoline derivates with antiproliferative activity. Eur. J. Med. Chem. 2018, 148, 225–237. [Google Scholar] [CrossRef]
  5. Hassner, A.; Haddalin, M.J. Synthesis of Quinolino Steroids. J. Org. Chem. 1962, 27, 1911–1914. [Google Scholar] [CrossRef]
  6. Ilovaisky, A.I.; Scherbakov, A.M.; Merkulova, V.M.; Chernoburova, E.I.; Shchetinina, M.A.; Andreeva, O.E.; Salnikova, D.I.; Zavarzin, I.V.; Terent’ev, A.O. Secosteroid–quinoline hybrids as new anticancer agents. J. Steroid Biochem. Mol. Biol. 2023, 228, 106245. [Google Scholar] [CrossRef] [PubMed]
  7. Yang, Y.-T.; Du, S.; Wang, S.; Jia, X.; Wang, X.; Zhang, X. Synthesis of new steroidal quinolines with antitumor properties. Steroids 2019, 151, 108465. [Google Scholar] [CrossRef] [PubMed]
  8. Gu, W.; Jin, X.-Y.; Li, D.-D.; Wang, S.-F.; Tao, X.-B.; Chen, H. Design, synthesis and in vitro anticancer activity of novel quinoline and oxadiazole derivatives of ursolic acid. Bioorg. Med. Chem. Lett. 2017, 27, 4128–4132. [Google Scholar] [CrossRef] [PubMed]
  9. Wu, L.-Q.; Ma, X.; Zhang, C.; Liu, Z.-P. Design, synthesis, and biological evaluation of 4-substituted-3,4-dihydrobenzo[h]quinoline-2,5,6(1H)-triones as NQO1-directed antitumor agents. Eur. J. Med. Chem. 2020, 198, 112396. [Google Scholar] [CrossRef] [PubMed]
  10. Costa, C.A.; Lopes, R.M.; Ferraz, L.S.; Esteves, G.N.N.; Di Iorio, J.F.; Souza, A.A.; De Oliveira, I.M.; Manarin, F.; Judice, W.A.S.; Stefani, H.A.; et al. Cytotoxicity of 4-substituted quinoline derivatives: Anticancer and antileishmanial potential. Bioorg. Med. Chem. 2020, 28, 115511. [Google Scholar] [CrossRef] [PubMed]
  11. Desroches, J.; Kieffer, C.; Primas, N.; Hutter, S.; Gellis, A.; El-Kashef, H.; Rathelot, P.; Verhaeghe, P.; Azas, N.; Vanelle, P. Discovery of new hit-molecules targeting Plasmodium falciparum through a global SAR study of the 4-substituted-2-trichloromethylquinazoline antiplasmodial scaffold. Eur. J. Med. Chem. 2017, 125, 68–86. [Google Scholar] [CrossRef] [PubMed]
  12. Rajendran, S.; Sivalingam, K.; Jayarampillai, R.P.K.; Wang, W.-L.; Salas, C.O. Friedlӓnder’s synthesis of quinolines as a pivotal step in the development of bioactive heterocyclic derivatives in the current era of medicinal chemistry. Chem. Biol. Drug Des. 2022, 100, 1042–1085. [Google Scholar] [CrossRef] [PubMed]
  13. Albuquerque, H.M.T.; Da Silva, R.N.; Pereira, M.; Maia, A.; Guieu, S.; Soares, A.R.; Santos, C.M.M.; Vieira, S.I.; Silva, A.M.S. Steroid–Quinoline Hybrids for Disruption and Reversion of Protein Aggregation Processes. ACS Med. Chem. Lett. 2022, 13, 443–448. [Google Scholar] [CrossRef] [PubMed]
  14. Abbiati, G.; Arcadi, A.; Bianchi, G.; Di Giuseppe, S.; Marinelli, F.; Rossi, E. Sequential Amination/Annulation/Aromatization Reaction of Carbonyl Compounds and Propargylamine: A New One-Pot Approach to Functionalized Pyridines. J. Org. Chem. 2003, 68, 6959–6966. [Google Scholar] [CrossRef] [PubMed]
  15. Marsicano, V.; Chiarini, M.; Marinelli, F.; Arcadi, A. Synthesis of Polycyclic Quinolines by Means of Brønsted Acid Mediated Reaction of β-(2-Aminophenyl)-α,β-Ynones with Ketones. Adv. Synth. Catal. 2019, 361, 2365–2370. [Google Scholar] [CrossRef]
  16. Bancet, A.; Raingeval, C.; Lomberget, T.; Le Borgne, M.; Guichou, J.-F.; Krimm, I. Fragment Linking Strategies for Structure-Based Drug Design. J. Med. Chem. 2020, 63, 11420–11435. [Google Scholar] [CrossRef]
  17. Diedrich, C.L.; Haase, D.; Saak, W.; Christoffers, J. Regioselectivity of Friedländer Quinoline Syntheses. Eur. J. Org. Chem. 2008, 2008, 1811–1816. [Google Scholar] [CrossRef]
  18. Li, Z.; Brouwer, C.; He, C. Gold-Catalyzed Organic Transformations. Chem. Rev. 2008, 108, 3239–3265. [Google Scholar] [CrossRef] [PubMed]
Figure 1. Selected therapeutic agents that have a quinoline nucleus.
Figure 1. Selected therapeutic agents that have a quinoline nucleus.
Molbank 2023 m1712 g001
Figure 2. Selected hybrid and fused steroidal quinolines tested for anticancer activity.
Figure 2. Selected hybrid and fused steroidal quinolines tested for anticancer activity.
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Scheme 1. Previous approaches to studying polycyclic pyridines and quinolines considered in this work.
Scheme 1. Previous approaches to studying polycyclic pyridines and quinolines considered in this work.
Molbank 2023 m1712 sch001
Figure 3. Reaction scheme and key spectral differences between regioisomers 3 and 4.
Figure 3. Reaction scheme and key spectral differences between regioisomers 3 and 4.
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Table 1. Friedlӓnder condensation of 2′-aminoacetophenone and 4-cholesten-3-one under various conditions.
Table 1. Friedlӓnder condensation of 2′-aminoacetophenone and 4-cholesten-3-one under various conditions.
EntryCatalyst (%)T (°C)SolventTime (h)2 a
Conversion (%) a
Yield (%) b
Yield (%) b
1 cNaAuCl4·2H2O (5%)80EtOH24541327
2NaAuCl4·2H2O (5%)110EtOH5621530
3p-TsOH·H2O (20%)110EtOH2Quantitative6030
4 dp-TsOH·H2O (20%)80Toluene245545Traces
5p-TsOH·H2O (20%)80Toluene488567Traces
6p-TsOH·H2O (20%)110Toluene5Quantitative767
7p-TsOH·H2O (1 eq)110Toluene5Quantitative8114
8 ep-TsOH·H2O (1 eq)80Toluene5Quantitative>98Traces
9NaAuCl4·2H2O (5%)110Toluene247512<3
(a) Conversion was calculated using recovered 4-cholesten-3-one. (b) Yield refers to isolated and chromatographically pure products. (c) 2/(3 + 4) NMR ratio calculated after 5 h at 80°C was 1:1. (d) In this entry, conversion of 2 and yield in 3 were estimated through 1H-NMR. (e) In this entry, 2.5 equivalent of 2′-aminoacetophenone 1 was used.
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MDPI and ACS Style

Momoli, C.; Morlacci, V.; Chiarini, M.; Palombi, L.; Arcadi, A. Friedländer-Type Reaction of 4-Cholesten-3-one with 2′-Aminoacetophenone: Angular versus Linear Quinoline-Fused Steroids. Molbank 2023, 2023, M1712.

AMA Style

Momoli C, Morlacci V, Chiarini M, Palombi L, Arcadi A. Friedländer-Type Reaction of 4-Cholesten-3-one with 2′-Aminoacetophenone: Angular versus Linear Quinoline-Fused Steroids. Molbank. 2023; 2023(3):M1712.

Chicago/Turabian Style

Momoli, Caterina, Valerio Morlacci, Marco Chiarini, Laura Palombi, and Antonio Arcadi. 2023. "Friedländer-Type Reaction of 4-Cholesten-3-one with 2′-Aminoacetophenone: Angular versus Linear Quinoline-Fused Steroids" Molbank 2023, no. 3: M1712.

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