Synthesis of Some 5-(substituted benzylidene-2, 4-dioxothiazolidin-3-yl) benzoic Acid Derivatives by Conventional and Microwave-assisted Methods and Evaluation of their Potential as Antimicrobial Agents

Abstract

<P>Background: Multiple antibiotic resistant bacteria represent a challenge in the treatment of infections. It is imperative, therefore, that new substances with antimicrobial properties should be searched to fight these microorganisms. Objective: A series of 5-benzylidene-2, 4-dioxothiazolidin-3-yl benzoic acid derivatives were synthesized and evaluated their antimicrobial potential. The compounds were synthesized by both conventional and microwave synthesizers. Methods: In this study, a series of 5-benzylidene-2, 4-dioxothiazolidin-3-yl benzoic acid derivatives were synthesized by Knoevenagel condensation of 2, 4-thiazolidinedione with substituted aryl aldehydes followed by substitution of 3-amino group with p-chlorobenzoic acid. All the synthesized compounds were characterized by spectral (FT-IR, mass and 1HNMR) and elemental analysis. The compounds were evaluated for their in-vitro antimicrobial activities against Gram-positive bacteria, Gram-negative bacteria and a fungal strain by agar well diffusion assay method and solid dilution method. Results: The compounds exhibited appreciable antimicrobial activity. Compound 4-(5-(2- chlorobenzylidene)-2, 4-dioxothiazolidin-3-yl)benzoic acid (3f) expressed potent antimicrobial activities against all of the microbial strains examined in this study with MIC values ranging between 0.6-0.8 µg/mL and diameter of the zone of inhibition between 17.2-19.5 mm at the concentration of 200 µg/mL. Conclusion: There was a marked decrease in the reaction time, under mild conditions through microwave synthesis wherein it presented a green approach towards syntheses of the thiazolidinedione derivatives. All compounds exhibited mild to moderate antimicrobial activity. The results of tested bioactive assay showed that the nature of the substituent on the phenyl ring significantly influenced the antimicrobial activity. Among the chloro, bromo and methoxy substituted derivatives, chloro derivative possessed the highest activity followed by bromo and then methoxy. The position of the substituents on the arylidene nucleus also affected the activity and it was found that generally ortho-substituted derivatives showed better antimicrobial activity than others.</P>