N-(4-Methoxyphenethyl)-2-oxo-2H-chromene-3-carboxamide

Abstract

Herein, we present the synthesis of N-(4-methoxyphenethyl)-2-oxo-2H-chromene-3-carboxamide. The synthesized compound has been thoroughly characterized using melting point analysis, ¹H- and ¹³C-NMR spectroscopy, infrared spectroscopy, and mass spectrometry. The comprehensive data obtained from these techniques confirm the successful synthesis and structural integrity of the newly synthesized molecule.

1. Introduction

Coumarins are an important class of natural and synthetic compounds known for their diverse biological and pharmacological properties [1]. Found in plants, they exhibit anticoagulant [2], anti-inflammatory [3], antioxidant [4], antimicrobial [5], and anticancer [6] activities, making them valuable in medicine. Coumarins also play a significant role in cosmetics, fragrances, and as additives in food [7]. Their applications extend to agrochemicals, where they act as plant growth regulators and pest deterrents. The structural versatility of coumarins enables extensive chemical modifications, enhancing their potential for drug development and other industrial uses.

Functionalized coumarin 1 has been designed and synthesized as a potential anti-austerity agent to overcome cancer cells’ tolerance to nutrient starvation [8] (Figure 1).

Other similar structures have been studied for targeting acetylcholinesterase for Alzheimer’s disease. Namely, 2-Oxo-N-phenethyl-2H-chromene-3-carboxamide 2, N-(4-fluorophenethyl)-8-methoxy-2-oxo-2H-chromene-3-carboxamide 3, and a few other molecules have been examined theoretically using field-based 3D-QSAR, pharmacophore model-based virtual screening, molecular docking, MM/GBSA, ADME, and MD Simulation study, showing promising results [9].

A series of scopoletin derivatives were designed, synthesized, and biologically evaluated. All reported derivatives exhibit potent antiproliferative activities against human breast cancer cell lines MCF-7 and MDA-MB-231, and reduced cytotoxicity to human breast epithelial cell line MCF-10A compared to the lead compounds. The most potent compound (4) (Figure 2) possessed preferable antiproliferation against MCF-7 cells, which was stronger than doxorubicin in vitro [10].

Monoamine oxidases (MAOs) are crucial enzymes responsible for regulating and metabolizing major neurotransmitters like serotonin, norepinephrine, and dopamine. There are two primary isoforms: hMAO-A and hMAO-B, which play significant roles in neurological and psychiatric conditions [11].

Researchers have discovered that certain coumarin derivatives can effectively inhibit MAO enzymes. Specifically, 3-carboxamido-7-substituted coumarins have shown promising potential for selective MAO-B inhibition. The most effective compounds demonstrated selective inhibition of hMAO-B, enhanced activity with specific phenyl group substitutions, and improved potency with electron-withdrawing groups like fluorine [11].

The most notable compound in the study is N-(4-(methylsulfonyl)phenyl)-2-oxo-2H-chromene-3-carboxamide 5, with exceptional human MAO-B selectivity, and it contained a methanesulfonyl group at the 4′-position of the N-phenyl substituent, showing an incredibly low IC₅₀ value of 0.0014 µM (Figure 3).

Creating new, unreported coumarin derivatives is important because it can lead to discovering new medical treatments and finding better solutions for industrial problems. This research has great potential to bring innovative ideas and make a positive impact. Each new coumarin compound could open doors to treating diseases, improving health, and solving real-world challenges in unique ways.

2. Results and Discussion

Here, we present the successful synthesis of N-(4-methoxyphenethyl)-2-oxo-2H-chromene-3-carboxamide 8, as illustrated in Scheme 1. To achieve this, 2-(4-methoxyphenyl)ethan-1-amine 6 (1.2 mmol) was introduced into a solution of ethyl 2-oxo-2H-chromene-3-carboxylate 7 (1 mmol) in ethanol. The resulting mixture was stirred under reflux for 6 h. This reaction is known [12], but the obtained compound has not been reported previously.

The starting ethyl 2-oxo-2H-chromene-3-carboxylate 7 was obtained by us using the known procedure from [13,14], but instead of ethanol, we carried out the reaction in toluene for one hour under reflux. The procedure is explained in detail in the experimental section.

The structure of the newly synthesized hybrid molecule 8 was clearly confirmed using a combination of advanced techniques. Moreover, ¹H- and ¹³C-NMR spectroscopy provided important information about the arrangement and connections of hydrogen and carbon atoms.

The signals for the hydrogen atoms from the methylene groups appear at 2.79 and 3.53 ppm as a triplet and a quartet, respectively. The singlet for the methoxy group is observed at 3.71 ppm. The proton from the amino group appears as a triplet at 8.74 ppm. The CH proton from the heterocyclic ring in the coumarin molecule is observed at 8.87 ppm as a singlet.

In the ¹³C NMR spectrum, all carbon atoms are present, with the signals for the C=O groups appearing at 161.42 ppm (-O-(C=O) C) and 160.87 ppm (C=ONH), respectively. The methylene carbon atoms are observed at 41.41 ppm (NH-CH₂-CH₂-Ph) and 34.55 ppm (NH-CH₂-CH₂-Ph), while the methoxy carbon atom appears at 55.44 ppm. The carbon atoms from the aromatic region are also clearly identified.

Mass spectrometry accurately determined the molecular weight of the compound. Infrared (IR) spectroscopy identified key functional groups through their specific vibrational patterns. Together, these methods reliably confirmed the identity and structure of the molecule.

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. NMR spectral data were recorded on a Bruker Avance Neo 400 spectrometer (BAS-IOCCP—Sofia, Bruker, Billerica, MA, USA) operating at 400 MHz for ¹H NMR and 101 MHz for ¹³C NMR. Spectra were acquired in DMSO-d₆, with chemical shifts referenced relative to tetramethylsilane (TMS) (δ = 0.00 ppm) and coupling constants reported in Hz. NMR measurements were performed at room temperature (approximately 295 K). Melting points were determined using a Boetius hot stage apparatus and are reported uncorrected. IR spectra were measured on a Bruker Alpha II FT IR spectrometer (Bruker, Billerica, MA, USA). Mass spectrometry was performed using a Q Exactive Plus high-resolution mass spectrometer (HRMS) with a heated electrospray ionization source (HESI-II) from Thermo Fisher Scientific, Inc., Bremen, Germany, coupled with a Dionex Ultimate 3000RSLC ultrahigh-performance liquid chromatography (UHPLC) system (Thermo Fisher Scientific, Inc., Waltham, MA, USA). Thin-layer chromatography (TLC) was carried out on 0.2 mm Fluka silica gel 60 plates (Merck KGaA, Darmstadt, Germany).

3.1. Synthetic Procedures

3.1.1. Synthesis of Ethyl 2-Oxo-2H-chromene-3-carboxylate 7

A 250 mL round-bottom flask was charged with 5 mmol (610 mg) of salicylaldehyde, 5 mmol (800.8 mg) of malonic ester, 0.5 mL of piperidine, one drop of glacial acetic acid, and 70 mL of toluene. The flask was subsequently connected to a reflux condenser equipped with a Dean–Stark apparatus to facilitate the separation of water. The reaction mixture was heated under reflux for a duration of approximately one hour, during which the water and alcohol generated as byproducts were periodically removed. The toluene was then removed via simple distillation. The remaining residue in the flask was transferred to a beaker and subjected to cooling in an ice bath to induce precipitation. The resulting precipitate was separated by filtration. The yield of the isolated product ethyl 2-oxo-2H-chromene-3-carboxylate 7 was 84% (922.6 mg) and the melting point was 92–93 °C, which is consistent with the data reported in the literature [15,16].

3.1.2. Synthesis of N-(4-methoxyphenethyl)-2-oxo-2H-chromene-3-carboxamide 8

Furthermore, 2-(4-Methoxyphenyl)ethan-1-amine (1.2 mmol, 181.0 mg) was added to a solution of ethyl 2-oxo-2H-chromene-3-carboxylate (1 mmol, 218 mg) in 20 mL hot ethanol. The mixture was refluxed for 6 h to afford a white precipitate. The precipitates were filtered, recrystallized with ethanol, and dried under a vacuum to obtain N-(4-methoxyphenethyl)-2-oxo-2H-chromene-3-carboxamide 3 as a yellow solid in a 94% (303 mg) yield.

N-(4-methoxyphenethyl)-2-oxo-2H-chromene-3-carboxamide 8: Yellow solid (m.p. 165–167 °C), TLC R_f = 0.42 (diethyl ether: petrol = 3:1 v/v), ¹H NMR (400 MHz, DMSO), δ 8.87 (s, 1H, CH), 8.74 (t, J = 5.8 Hz, 1H, NH), 7.99 (dd, J = 7.8, 1.6 Hz, 1H, Ar), 7.75 (ddd, J = 8.7, 7.3, 1.6 Hz, 1H, Ar), 7.53–7.40 (m, 2H, Ar), 7.18 (d, J = 8.6 Hz, 2H, Ar), 6.87 (d, J = 8.6 Hz, 2H, Ar), 3.73 (s, 3H, OCH₃), 3.54 (q, J = 7.1 Hz, 2H, NHCH₂CH₂), 2.79 (t, J = 7.3 Hz, 2H, NHCH₂CH₂), ¹³C NMR (101 MHz, DMSO), δ 161.42 (-O-(C=O)C), 160.87 (C=ONH), 158.23 (Ar), 154.32 (Ar), 147.96 (Ar), 134.56 (Ar), 131.46 (Ar), 130.75 (Ar), 130.10 (Ar), 125.61 (Ar), 119.29 (PhCH=CH-C=O), 118.94 (Ar), 116.59 (Ar), 114.30 (PhCH=CH-C=O), 55.44 (OCH₃), 41.41 (NH-CH₂-CH₂-Ph), and 34.55 (NH-CH₂-CH₂-Ph). HRMS Electrospray ionization (ESI) m/z calculated for [M + H]⁺ C₁₉H₁₈NO₄⁺ = 324.1231, found 324.1224 (mass error ∆m = −2.16 ppm). IR (KBr) ν_max., cm⁻¹: 3347 ν(N-H), 1649 ν(C=O), 1531 δ(N-H) + δ(C-N), 1240 ν_as (C-O-C), and 1038 ν_s (C-O-C).