Synthesis of Novel Sulfonamide Derivatives Featuring 1-(Methylsulfonyl)-4-(2,3,4-Trimethoxybenzyl)Piperazine Core Structures

Abstract

Herein we report the synthesis of three novel sulfonamide derivatives of trimetazidine—medication primarily used to treat angina pectoris. The new compounds have been fully characterized with their melting point, ¹H- and ¹³C-NMR, UV, and mass spectrometry. The collected data confirm the successful synthesis and structural integrity of the new molecules.

1. Introduction

1-(2,3,4-Trimethoxybenzyl)-piperazine dihydrochloride (Figure 1), also known as trimetazidine dihydrochloride, is a safe and effective cellular anti-ischemic agent. This compound is a lipophilic weak base with low solubility in aqueous solutions. Trimetazidine is available on the market as a slightly hygroscopic white or off-white crystalline powder.

Trimetazidine therapy has been shown to have vasodilatory effects in individuals with heart disease, heart failure, and coronary artery conditions. Its beneficial effects may also extend to other ischemic organs, potentially through mechanisms such as reducing reactive oxygen species, altering cellular lipid composition, and inhibiting mitochondrial fatty acid oxidation [1].

Medications that promote carbohydrate oxidation also facilitate the oxidation of cardiac fatty acids, which, in the event of ischemia, reduces lactate production and elevates cellular pH. Trimetazidine, the first approved drug in this class, selectively inhibits 3-keto-acyl-CoA dehydrogenase, an enzyme involved in fatty acid β-oxidation, without impacting hemodynamics. For patients who do not respond to conventional therapy, trimetazidine is an excellent alternative to typical hemodynamic agents for relieving angina symptoms [2]. Furthermore, trimetazidine prevents oxidative damage to the mitochondrial membrane, which regulates metabolism in conditions such as ischemic heart disease, renal impairment, hepatic ischemia, and gastrointestinal disorders. In addition to its antinociceptive and potentially antidepressant properties, trimetazidine exhibits neuroprotective effects following cerebral injury. It reduces brain inflammation caused by lipopolysaccharides, promotes axonal regeneration, and protects against drug-induced oxidative damage to the hippocampus and experimental brain atrophy. In vivo experiments have shown that trimetazidine enhances brain glucose uptake and protects against cerebral ischemia–reperfusion injury [3].

Along with its positive properties, there are several factors that lead to limitations in its prescription. The European Medicines Agency has recommended that doctors restrict the use of trimetazidine-containing medications for treating angina pectoris. The drug should not be prescribed to patients with tinnitus, vertigo, or vision disturbances. Instead, it is advised as an add-on therapy for patients with stable angina pectoris who cannot tolerate first-line antianginal treatments. The agency also noted that a risk of movement disorders such as Parkinsonian symptoms, restless leg syndrome, tremors, and gait instability are associated with trimetazidine. The committee suggested implementing new contraindications and warnings to address the potential risks of these movement disorders [4].

Also, athletes have extended trimetazidine use into sports, employing it as a performance-enhancing substance. The drug’s capacity to boost endurance and delay fatigue made it appealing to competitors seeking an advantage. Because of these effects, trimetazidine has been classified as a metabolic modulator [1,5,6]. Recognizing the potential for misuse in sports, the World Anti-Doping Agency (WADA) added trimetazidine to its list of banned substances, effective 1 January 2014. Athletes caught using trimetazidine face penalties, including suspension and disqualification from competitions, as its use violates the principles of fair play and sports integrity. This ban highlights ongoing efforts to ensure a level playing field and safeguard the health and safety of athletes [7].

Sulfonamides, also known as sulfanilamides, represent a significant class of synthetic antimicrobial agents developed in the early 20th century. Their primary mechanism of action involves the inhibition of bacterial folic acid synthesis by acting as competitive antagonists of p-aminobenzoic acid (PABA), which is crucial for DNA production in bacteria. This action is mediated through their structural similarity to PABA, allowing sulfonamides to inhibit the enzyme dihydropteroate synthetase and ultimately leading to bacteriostatic effects rather than bactericidal ones [8].

Sulfonamides are characterized by their broad-spectrum antibacterial properties which are effective against various gram-positive and certain gram-negative bacteria, including Escherichia coli, Klebsiella, and Salmonella [9,10,11,12]. They are employed in the treatment of a range of infections, such as tonsillitis, urinary tract infections, and meningococcal meningitis [13,14]. Additionally, they exhibit activity against some fungi and protozoa, making them versatile in treating diverse infectious diseases [15,16].

The synthesis of hybrid molecules combining trimetazidine and sulfonamides represents a promising advancement in pharmaceutical development. Trimetazidine offers anti-ischemic, neuroprotective, and vasodilatory benefits, while sulfonamides provide broad-spectrum antibacterial action by inhibiting bacterial folic acid synthesis. Combining these drugs could enhance therapeutic outcomes by addressing both ischemic and infectious components of disease, potentially offering a multifaceted treatment approach. Hybrid molecules may also overcome the limitations and side effects of each individual drug, provide novel mechanisms of action, and broaden therapeutic applications [17]. This innovative strategy could improve the management of complex conditions involving ischemia and infections, potentially reducing the need for multiple medications and enhancing overall treatment efficacy.

2. Results and Discussion

We reported the successful synthesis of the following compounds: 1-(methylsulfonyl)-4-(2,3,4-trimethoxybenzyl)piperazine (3a), 1-(phenylsulfonyl)-4-(2,3,4-trimethoxybenzyl)piperazine (3b), and 1-(benzylsulfonyl)-4-(2,3,4-trimethoxybenzyl)piperazine (3c), as outlined in Scheme 1. These hybrid molecules were synthesized using a quick and efficient method described in the Materials and Methods section.

To achieve this, the corresponding sulfonyl chloride 2a–c (1 mmol) was added to a solution of trimetazidine 1 (1 mmol) in dichloromethane. The reaction mixture was stirred for ten minutes, then an excess of trimethylamine (1.5 mmol) was carefully added. After 30 min, TLC analysis confirmed the formation of the final products 3a–c. The structures of the three newly synthesized hybrid molecules were unequivocally confirmed using a comprehensive array of instrumental techniques. ¹H- and ¹³C NMR spectroscopy provided detailed information on the chemical shifts and connectivity of the hydrogen and carbon atoms, respectively (Figures S1–S6). UV spectroscopy offered insights into the to electronic transitions and absorbance characteristics of the molecules (Figures S7–S9). Mass spectrometry, with its high-resolution capabilities, further verified the molecular weights and composition of the compounds (Figures S10–S12). Collectively, these techniques conclusively established the identities and structures of the obtained molecules.

3. Materials and Methods

All reagents and chemicals were obtained from commercial sources (Sigma-Aldrich S.A., Wien, Austria 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 were reported uncorrected. Absorbance measurements were conducted with a Camspec M508 spectrophotometer (Spectronic CamSpec Ltd., Leeds, UK). 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, and 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).

Synthetic Procedure

A solution of trimetazidine 1 (1 mmol, 0.266 g) in dichloromethane (30 mL) was prepared, to which an equivalent amount of the corresponding sulfonyl chloride 2a–c (1 mmol) was added. After 10 min, triethylamine (1.2 mmol, 0.121 g) was introduced into the solution. Following a 30 min reaction period, the solution was sequentially washed with diluted hydrochloric acid, a saturated solution of Na₂CO₃, and brine. The combined organic layers were then dried over anhydrous Na₂SO₄, and the solvent was evaporated under reduced pressure. No additional purification steps were carried out. The reagents were combined and allowed to react at room temperature.

1-(Methylsulfonyl)-4-(2,3,4-trimethoxybenzyl)piperazine 3a: white solid (m.p. 125–127 °C), R_f = 0.4 (CH₂Cl₂:MeOH = 1:0.02 v/v), yield 93% (0.321 g), ¹H NMR (400 MHz, DMSO) δ 6.98 (d, J = 8.5 Hz, 1H), 6.77 (d, J = 8.6 Hz, 1H), 3.78 (s, 6H), 3.74 (s, 3H), 3.33 (s, 2H), 3.09 (t, J = 4.9 Hz, 4H), 2.86 (s, 3H), 2.46 (t, J = 5.0 Hz, 4H). ¹³C NMR (101 MHz, DMSO) δ 153.08, 152.52, 142.34, 125.18, 123.78, 108.04, 61.44, 60.75, 56.24, 55.93, 52.23, 46.01, 34.08. UV λmax, MeOH: 204 (ε = 102,000) nm, 226sh (ε = 32,600) nm. HRMS Electrospray ionization (ESI) m/z calculated for [M+H]⁺ C₁₅H₂₅N₂O₅S⁺ = 345.1479, found 345.1474 (mass error ∆m = −1.45 ppm).

1-(Phenylsulfonyl)-4-(2,3,4-trimethoxybenzyl)piperazine 3b: pale yellow oil, R_f = 0.5 (CH₂Cl₂:MeOH = 1:0.02 v/v), yield 95% (0.387 g), ¹H NMR (400 MHz, DMSO) δ 7.78–7.70 (m, 3H), 7.70–7.61 (m, 2H), 6.89 (d, J = 8.5 Hz, 1H), 6.72 (d, J = 8.6 Hz, 1H), 3.75 (s, 3H), 3.71 (d, J = 3.4 Hz, 6H), 3.34 (s, 2H), 2.88 (s, 4H), 2.43 (s, 4H). ¹³C NMR (101 MHz, DMSO) δ 153.02, 152.40, 142.23, 135.31, 133.72, 129.86, 128.05, 128.00, 125.08, 123.52, 108.03, 61.34, 60.73, 56.22, 55.66, 51.87, 46.46. UV λmax, MeOH: 204 (ε = 110,000) nm, 225sh (ε = 49,000) nm. HRMS Electrospray ionization (ESI) m/z calculated for [M+H]⁺ C₂₀H₂₇N₂O₅S⁺ = 407.1636, found 407.1628 (mass error ∆m = −1.96 ppm).

1-(Benzylsulfonyl)-4-(2,3,4-trimethoxybenzyl)piperazine 3c: white solid (m.p. 93–95 °C), R_f = 0.32 (CH₂Cl₂:MeOH = 1:0.02 v/v), yield 87% (0.368 g), ¹H NMR (400 MHz, DMSO) δ 7.46–7.31 (m, 5H), 6.96 (d, J = 8.5 Hz, 1H), 6.77 (d, J = 8.6 Hz, 1H), 4.41 (s, 2H), 3.78 (d, J = 3.3 Hz, 6H), 3.75 (s, 3H), 3.41 (s, 2H), 3.10 (t, J = 4.4 Hz, 4H), 2.38 (s, 4H). ¹³C NMR (101 MHz, DMSO) δ 153.10, 152.53, 142.33, 131.38, 129.91, 128.80, 128.63, 125.24, 123.69, 108.02, 61.43, 60.75, 56.24, 55.98, 54.61, 52.50, 46.01. UV λmax, MeOH: 204 (ε = 85,000) nm. HRMS Electrospray ionization (ESI) m/z calculated for [M+H]⁺ C₂₁H₂₉N₂O₅S⁺ = 421.1792, found 421.1785 (mass error ∆m = −1.66 ppm).