Abstract
A new series of N-{4-methyl-5-[4-(4-oxo-2-phenyl(1,3-thiazolidin-3-yl)]-5-sulfanyl(1,2,4-triazol-3-yl)-1,3-thiazol-2-yl }acetamide (7a-l) was synthesized in order to determine their antimicrobial activity and feasible structure–activity relationships. The compounds were synthesized in good yield and the structures of all newly synthesized compounds were established on the basis of their IR, 1HNMR, and elemental analysis. The synthesized compounds were tested in vitro antibacterial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi and antifungal activity against Aspergillus niger, Candida albicans by measuring the zone of inhibition in mm.
1. Introduction
Heterocycles bearing nitrogen, sulphur, and thiazole moieties constitute the core structure of a number of biologically interesting compounds. Literature survey shows that thiazole derivatives play a very important role in biological fields such as antimicrobial [1–4], antidiabetic [5], antiviral [6], anti-inflammatory [7], antituberculosis [8], and anticancer [9] activities. 1,2,4-Triazole is among the various heterocycles that have received the most attention during the last two decades as potential antimicrobial agents [10–13]. Schiff base has good antimicrobial [14], and antifungal [15] activity, and it can be prepared by the acid-catalysed reaction of aldehyde or ketone and amines [16]. Thiazolidin-4-one [17] derivatives are known to exhibit diverse bioactivities such as antidiarrheal [18], anticonvulsant [19], antimicrobial [20–22], antidiabetic [23], antihistaminic [24], anticancer [25, 26], anti-HIV [27], cyclooxygenase inhibitory [28], antiplatelet activating factor [29–31]. Hence, it is thought of interest to accommodate thiazolidin-4-one and 2-amino benzothiazole moieties in single molecular framework and screen them for their antimicrobial activity. Today, the trend in antimicrobial drug design [32] is to clubbing two or three heterocyclic molecules having different sites or mechanisms of action, and this initiated our construction of compounds containing thiazole, triazole, and thiazolidin-4-one ring systems in the same matrix to serve as a new scaffold towards the development of novel antimicrobial agents. In view of these data, we aimed the synthesis of thiazolyltriazole-substituted thiazolidin-4-one as antimicrobial agents.
2. Result and Discussion
In this present work, a series of new compounds was synthesized. Thus, starting from the ethyl 2-amino-4-methylthiazole-5-carboxylate 1 was synthesized as per reported procedure [33]. Ethyl 2-acetamido-4-methylthiazole-5-carboxylate (2), N-(5-(hydrazinecarbonyl)-4-methylthiazol-2-yl)acetamide (3), potassium dithiocarbazinate (4), N-(5-(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl)-4-methylthiazol-2-yl)acetamide (5), and N-(5-(4-(benzylideneamino)-5-mercapto-4H-1,2,4-triazol-3-yl)-4-methyl thiazol-2-yl)acetamide (6a–l) were prepared as per reported procedure [34]. The Schiff bases on cyclization with mercapto acetic acid in the presence of anhydrous 1,4-dioxane and triturated with an excess of 10% NaHCO3 solution furnished N-{4-methyl-5-[4-(4-oxo-2-phenyl(1,3-thiazolidin-3-yl)]-5-sulfanyl(1,2,4-triazol-3-yl)-1,3-thiazol-2-yl}acetamide (7a–l) as shown in Scheme 1. The structures of the various synthesized compounds were assigned on the basis of elemental analysis, IR, and 1HNMR spectral data. Spectral and analytical data of the title compounds (7a–l) are shown in Tables 1 and 2. The compounds are evaluated for their antimicrobial activity, and results are summaries in Table 3. From the antimicrobial screening, it was observed that all the compounds exhibited activity against all the organisms employed. Looking at the structure activity relationship, marked inhibition in bacteria was observed in the compounds bearing R = H–, 4-Cl–, 2-OH–, 4-OH–, 4-(CH3)2N–, 4-CH3– (7a, 7b, 7c, 7f, 7g, 7k) substitutions whereas compound (7d, 7e, 7h, 7i, 7j, 7l) showed moderate to good activity. Fungicidal screening data also revealed that compounds bearing R = H–, 4-Cl–, 4-(CH3)2N–, 3,4,5-(OCH3)3–, 4-Br–, 4-CH3– (7a, 7c, 7g, 7j, 7k) imparted maximum activity to the compounds, where as compounds (7b, 7d, 7e, 7f, 7h, 7i) showed moderate to good activity.
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3. Experimental Section
The melting points were recorded on electrothermal apparatus and are uncorrected. IR spectra were recorded in KBr on a Perkin-Elmer model-983. 1HNMR spectrum was recorded on Varian Mercury 300 MHz instrument using DMSO- as solvent (chemical shift in δ ppm), using TMS as internal standard. Elemental analysis was performed on a Heracus CHN analyzer. Analyses indicated by the symbols of the elements of functions were within ±/0.4% of the theoretical values.
Synthesis of N-{4-methyl-5-[4-(4-oxo-2-phenyl(1,3-thiazolidin-3-yl)]-5-sulfanyl(1,2,4-triazol-3-yl)-1,3-thiazol-2-yl}acetamide (7a). The compound 6a (0.01 mole) was refluxed with mercapto acetic acid (0.015 mole, 1.38 gm) in the presence of anhydrous 1,4-dioxane (25 mL) at 120°C for 10–12 hrs. The reaction mixture was then cooled and triturated with an excess of 10% NaHCO3 solution. The precipitate was formed; filtered, washed several times with water, and recrystallised in DMSO. Other thiazolidin-4-ones (7b–l) were obtained in similar manner.
4. Antimicrobial Activity
The synthesized compounds (7a–l) were screened for their in vitro antibacterial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhi and antifungal activity against Aspergillus niger, and Candida albicans by measuring the zone of inhibition in mm. The antimicrobial activity was performed by cup plate method [35–38] at concentration 100 μg/mL in DMSO and reported in Table 3 for antibacterial and antifungal activities. Nutrient agar was employed as culture medium, and DMSO was used as solvent control for antimicrobial activity. Penicillin and griseofulvin were used as standard for antibacterial and antifungal activities, respectively.
5. Conclusion
In continuation of our previous studies to find new agents against microbial infection, a series of N-{4-methyl-5-[4-(4-oxo-2-phenyl(1,3-thiazolidin-3-yl)]-5-sulfanyl(1,2,4-triazol-3-yl)-1,3-thiazol-2-yl}acetamide (7a–l)was synthesized and its antimicrobial activity was determined. The adopted method is simple, inexpensive, gave good yields. As we consider all results obtained from antibacterial and antifungal tests together we can say that entire compounds tested are active towards bacteria and fungi.
Acknowledgments
The authors express their sincere thanks to Ms. D. S. Ghorpade, Government College of Pharmacy, Amravati, for the biological activity data, and Head, SAIF, University of Pune, Pune for providing elemental, spectral data.