Diclofenac-Based Hydrazones and Spirothiazolidinones: Synthesis, Characterization, and Antimicrobial Properties

We report here the synthesis, structural characterization, and biological evaluation of novel diclofenac-based hydrazone (4a-f) and spirothiazolidinone (5a-f, 6a-f) derivatives designed as potential antimicrobial agents. The compounds were evaluated in vitro for their antiviral activity against a wide spectrum of DNA and RNA viruses. They were further screened in vitro against different strains of bacteria and fungi. The hydrazone derivatives, 4a and 4c-f, were found to be active against herpesviruses (HSV-1, HSV-2, and HSV-1 TK^- ), vaccinia virus, and Coxsackie B4 virus, with EC₅₀ values between 6.6 µg/mL and 14.7 μg/mL, and the selectivity index values were greater than 10 for 4a and 4f. The newly synthesized compounds (4-6) were inactive against the bacterial and the fungal strains tested, at levels below 2500, 1250, or 625 μg/mL. Interestingly, the key intermediate 3 with a free hydrazide moiety displayed antifungal properties against Candida albicans and C. parapsilosis at MIC values of 4.88 µg/mL and 78.12 μg/mL, respectively.