N-(2-((2-(1H-indol-3-yl)ethyl)carbamoyl)phenyl)furan-2-carboxamide

Abstract

In the present study, we describe the synthesis of N-(2-((2-(1H-indol-3-yl)ethyl)carbamoyl)phenyl)furan-2-carboxamide via a two-step reaction sequence. Initially, isatoic anhydride was reacted with tryptamine to afford the corresponding intermediate, which was subsequently subjected to acylation using furan-2-carbonyl chloride. The final product was comprehensively characterized by melting point analysis, ¹H and ¹³C NMR, HSQC, IR, and MS spectrometry. The combined spectroscopic and analytical data unequivocally confirm the successful synthesis and structural integrity of the target compound.

1. Introduction

The structure–activity relationship is crucial in designing bioactive compounds. Rational drug design, particularly molecular hybridization, integrates pharmacophoric elements from multiple active molecules into a single structure to improve therapeutic efficacy, selectivity, and multi-target activity. This research aims to create a new hybrid molecule with pharmacophoric patterns from tryptamine, isatoic anhydride, and furan-2-carbonyl chloride. Tryptamine (Figure 1) is an indole-based compound characterized by a fused bicyclic structure consisting of a pyrrole ring and a benzene ring, with an ethylamine side chain terminating in a primary amino group attached at the third position of the indole nucleus [1].

The amine group’s strong interaction with pyrrole resulted in a stiff chemical potential that exhibits biological activity, extending the drug’s action. As a monoamine alkaloid, tryptamine functions similarly to a neurotransmitter and is also utilized as a hallucinogenic substance. Despite having an agonistic effect on 5-hydroxytryptamine receptors, tryptamine’s significant cytotoxicity makes it an antitumor drug. Because of its strong pharmacological indices, it is also used to treat obesity and migraines, such as sumatriptan (Figure 2) [2,3].

The increased reactivity of this heterocyclic structure, which is especially vulnerable to electrophilic substitution reactions, is advantageous to the thriving chemistry of indole functionalization [4]. Due to its structural versatility and biological relevance, the indole framework often serves as a key pharmacophore involved in receptor–ligand interactions [5]. Tryptamine and its derivatives have demonstrated a wide range of pharmacological activities, including antimigraine, antitumor, antihistaminic, antifungal, antibacterial, antioxidant, anti-HIV, anticonvulsant, anti-inflammatory, and analgesic effects. Additionally, they have been reported to be helpful in the treatment of a number of neurological and psychiatric conditions, including Alzheimer’s disease [6,7,8]. As physiologically active indole alkaloids, tryptamines are being thoroughly investigated as neuromodulators [9].

An adaptable chemical precursor for a wide range of materials and medications is isatoic anhydride. The reactivity of the heterocyclic ring is determined by its chemistry; nucleophilic attack opens the ring, while electrophilic assault functionalizes the amide-like and benzenic moiety [10].

Because of its physicochemical characteristics and reactivity qualities, isatoic anhydride is a special substance in organic synthesis. It has been widely employed in the industrial sector for the production of paints, perfumes, agrochemicals, desiccants, and pharmaceuticals. Additionally, it has been utilized as a starting material for the production of antimicrobials and for clinical diagnostics in biological research. Fluorescent labeling of mRNA and tRNA and the production of heterocyclic compounds such as quinazolinones, quinazolones, benzimidazolones, phthalimides, pyrroloquinazolones, and quinazolinediones both use isatoic anhydrides as an intermediate [11,12]. Also, isatoic anhydride and its derivatives, with their aminophilic reactivity, have been used in lysine ligation and as a drug delivery route to release doxorubicin into cancer cells [13,14].

Furans are structural motifs in natural substances such as pheromones, polyether antibiotics, and furanoterpenes [15]. The furan moiety, an electron-rich system, has the potential to modify protein molecules due to its physiological activity and its ability to form hydrogen bonds with various biological enzymes [16,17]. The nonpolar aromatic nature of furan derivatives and the presence of ether oxygen make them a special type of chemical in medicinal chemistry. By improving the pharmacokinetic properties of the parent compounds, these derivatives maximize their solubility and bioavailability [18]. Numerous drugs for a variety of medical disorders contain furan derivatives, including muscle relaxants, anti-inflammatory, antihypertensive, antiarrhythmic, antimicrobial, anti-aging, antiulcer agents, antihistamines, anticholinergics, antiparkinsonian agents, antidiuretics, and sickle cell inhibitors [19].

The reported hybrid molecule is of scientific interest due to the rational incorporation of pharmacophoric moieties derived from tryptamine, isatoic anhydride, and furan-2-carbonyl chloride. This approach aligns with contemporary drug design strategies aimed at enhancing therapeutic efficacy, selectivity, and multi-target potential, thereby underscoring the relevance of this hybrid molecule as a promising scaffold for future pharmacological development.

2. Results and Discussion

In this work, we describe the successful synthesis of N-(2-((2-(1H-indol-3-yl)ethyl)carbamoyl)phenyl)furan-2-carboxamide 5 via a two-step reaction sequence (Scheme 1 and Scheme 2).

In the first place, a mixture of isatoic anhydride 1 and tryptamine 2 dissolved in dichloromethane was stirred 12 h at rt. The resulting solution was filtered on neutral Al₂O₃ and concentrated.

Intermediate 3 is a known compound and has been reported previously [20,21].

The obtained N-(2-(1H-indol-3-yl)ethyl)-2-aminobenzamide 3 was subjected to acylation with furan-2-carbonyl chloride (Scheme 2).

The reaction was initiated by the addition of furan-2-carbonyl chloride 4 (1 mmol) to a stirred solution of N-(2-(1H-indol-3-yl)ethyl)-2-aminobenzamide 3 (1 mmol) in dichloromethane. After 10 min of pre-stirring, trimethylamine (1.5 mmol) was added dropwise to the reaction mixture. The progress of the reaction was monitored by thin-layer chromatography (TLC). After 30 min, the appearance of a product spot with an R_f value of 0.48 confirmed the formation of the desired hybrid compound.

The structure of the synthesized compound was confirmed through comprehensive spectral analysis, including ¹H and ¹³C NMR, HSQC, IR, and mass spectrometry. The collected data clearly support the successful formation of the target molecule. In the ¹³C NMR spectrum, the signal for the carbon adjacent to the NH group is obscured by the solvent peak (Figures S2 and S3 in the Supplementary File); however, HSQC analysis confirmed its presence (Figure S4 in the Supplementary File).

3. Materials and Methods

All reagents and chemicals were obtained from commercial sources (Sigma-Aldrich S.A. and Riedel-de Haën, Sofia, Bulgaria) and used as received without further purification. Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker Avance Neo 400 spectrometer (BAS-IOCCP—Sofia; Bruker, Billerica, MA, USA), operating at 400 MHz for ¹H and 101 MHz for ¹³C. All spectra were acquired in DMSO-d₆, with chemical shifts (δ) referenced to tetramethylsilane (TMS, δ = 0.00 ppm) and coupling constants (J) reported in hertz (Hz). NMR experiments were performed at ambient temperature (approximately 295 K). The HSQC analysis was performed using a compact NMR spectrometer, Magritek Spinsolve 80 (University of Plovdiv, Faculty of Chemistry, Plovdiv; Magritek, Wellington, New Zealand), operating at a proton frequency of 80 MHz. Melting points were measured using a Boetius hot-stage apparatus (Plovdiv University; Boetius, Germany) and are reported uncorrected. Infrared (IR) spectra were recorded on a Bruker Alpha II FT-IR spectrometer (Plovdiv University; Bruker, Billerica, MA, USA). High-resolution mass spectrometry (HRMS) analyses were carried out using a Q Exactive Plus spectrometer equipped with a heated electrospray ionization (HESI-II) source (Thermo Fisher Scientific, Bremen, Germany) and interfaced with a Dionex Ultimate 3000RSLC UHPLC system (Thermo Fisher Scientific, Waltham, MA, USA). Thin-layer chromatography (TLC) was performed on 0.2 mm silica gel 60 plates (Fluka, Merck KGaA, Darmstadt, Germany).

Synthesis

Synthesis of N-(2-(1H-indol-3-yl)ethyl)-2-aminobenzamide 3

A solution of isatoic anhydride 1 (0.163 g, 1 mmol) and tryptamine 2 (0.160 g, 1 mmol), previously dissolved in dichloromethane (30 mL), was stirred at ambient temperature for 12 h. Upon completion of the reaction, the mixture was filtered through a column of neutral alumina (Al₂O₃), and the solvent was removed under reduced pressure. The resulting product, a previously reported compound, was obtained in sufficient purity and was used directly in the subsequent synthetic step without further purification.

Synthesis of N-(2-((2-(1H-indol-3-yl)ethyl)carbamoyl)phenyl)furan-2-carboxamide 5

A solution of N-(2-(1H-indol-3-yl)ethyl)-2-aminobenzamide 3 (1.0 mmol, 0.279 g) in dichloromethane (30 mL) was prepared, followed by the addition of an equimolar amount of furan-2-carbonyl chloride 4 (1.0 mmol, 0.1305 g). After stirring the reaction mixture for 10 min at room temperature, triethylamine (1.2 mmol, 1.67 mL) was added dropwise. The reaction was allowed to proceed for an additional 30 min. Upon completion, the reaction mixture was washed successively with dilute hydrochloric acid, saturated aqueous sodium carbonate, and brine. The organic phase was separated, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The crude product was purified by short-column chromatography on neutral aluminum oxide (Al₂O₃) using CH₂Cl₂ as the eluent to afford the desired hybrid compound.

N-(2-((2-(1H-indol-3-yl)ethyl)carbamoyl)phenyl)furan-2-carboxamide 5

White solid (m.p.155–157 °C), yield 94% (0.312 g), R_f = 0.48 (diethyl ether/petroleum = 4/1 v/v), ¹H NMR (400 MHz, DMSO) δ 12.53 (s, 1H), 10.83 (s, 1H), 8.98 (t, J = 5.6 Hz, 1H), 8.61 (dd, J = 8.4, 1.2 Hz, 1H), 8.00 (dd, J = 1.8, 0.8 Hz, 1H), 7.80 (dd, J = 8.0, 1.5 Hz, 1H), 7.59 (d, J = 7.9 Hz, 1H), 7.55 (ddd, J = 8.6, 7.3, 1.5 Hz, 1H), 7.35 (dt, J = 8.1, 0.9 Hz, 1H), 7.25 (dd, J = 3.5, 0.9 Hz, 1H), 7.22 (d, J = 2.4 Hz, 1H), 7.19 (ddd, J = 7.9, 7.3, 1.2 Hz, 1H), 7.08 (ddd, J = 8.1, 7.0, 1.2 Hz, 1H), 6.99 (ddd, J = 8.0, 7.0, 1.1 Hz, 1H), 6.74 (dd, J = 3.5, 1.7 Hz, 1H), 3.62 (dt, J = 13.0, 7.4 Hz, 2H), 3.01 (t, J = 7.5 Hz, 2H). ¹³C NMR (101 MHz, DMSO) δ 168.75, 156.13, 148.13, 146.54, 139.31, 136.72, 132.57, 128.63, 127.75, 123.28, 123.16, 121.42, 120.86, 120.68, 118.72, 115.66, 113.09, 112.20, 111.87, 40.68, 25.24. IR (KBr) ν_max., cm⁻¹: 3351, 3310 ν (N-H), 1664 ν (C=O), 1520 δ (N-H) + δ (C-N). Electrospray ionization (ESI) m/z calculated for [M + Na]⁺ C₂₂H₁₉N₃NaO₃⁺ = 396.1319 found 396.1373 (mass error ∆m = 13.6 ppm).