SYNTHESIS AND BIOLOGICAL EVALUATION OF NOVEL COUMARIN DERIVATIVES AS POTENTIAL ANTIMICROBIAL AGENTS

Objective: Synthesize new series of 7-hydroxy-4-methylcoumarin and 7-alkoxy-4-methylcoumarin derivatives featuring thiosemicarbazone or thiazolidin-4-one moieties and to evaluate their antimicrobial activity against two strains of Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), two Gram-negative bacteria (Escherichia Coli and Pseudomonas aeruginosa), and Candida albicans.Methods: Preparation of the new coumarin derivatives was done by adopting Pechmann condensation and attaching different isothiocyanates to give coumarin-thiosemicarbazone hybrids. Thiosemicarbazones were cyclized into thiazolidine-4-ones using chloroacetic acid or diethyl bromo malonate.Results: Compounds VIb, Xb, XIVb, and XVc gave the highest inhibition zones (>20 mm) against Staphylococcus aureus. Their MIC (minimum inhibitory concentration) values ranging from 0.19-0.36 µg/ml were better than the reference drug tobramycin with MIC= 2µg/ml.Conclusion: The newly synthesized compounds with the 7-hydroxyl group showed better antimicrobial activity than those with the 7-alkoxy groups.Keywords: Coumarin, Thiosemicarbazones, Thiazolidin-4-ones, Antimicrobial activit