New 5-methylisatin including thiocarbohydrazones: preparation, structure elucidation and antimicrobial activity

Abstract

New 5-methylisatin including thiocarbohydrazones (1–5) have been synthesized. The chemical structure of synthesized compounds was elucidated with IR, 1H NMR, 13C NMR spectroscopic methods, and elemental analysis. Moreover, the synthesized compounds have been screened for antimicrobial activity. Their antibacterial activities were tested against Gram-positive (Bacillus subtilis ATCC 6623, Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212), Gram-negative (Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 70060, Pseudomonas aeruginosa ATCC 27853), and fungal (Candida albicans ATCC 10231, Aspergillus niger ATCC 16404) microbial strains using the microdilution method. In the isatin series, particularly the compound 2 showed the best antimicrobial activity against E. faecalis strain with MIC values of 64 μg/mL compared to other compounds. This high activity of compound 2 is due to the presence of two electron-donating methoxy groups in its structure. The remaining substituted compounds have shown good and moderate antimicrobial activity compared to standard drugs. The results may provide insights into the target compounds' structure–activity relationships, which may facilitate the development of pharmacological and biological applications for the target compounds. Graphical abstract: New isatins bearing thiocarbohydrazone were synthesized. Structures of all compounds were elucidated with spectroscopic approaches. The antimicrobial activities of the tested compounds presented promising antimicrobial activity against the eight tested microorganisms. [Figure not available: see fulltext.]