Synthesis of novel Schiff base benzamides via ring opening of thienylidene azlactones for potential antimicrobial activities

3-Hydrazinyl-3-oxo-1-(thiophen-2-yl)prop-1-en-2-yl]benzamide (4) is identified as a key intermediate for the synthesis of some new 3-[aryl substituted hydrazinyl]-3-oxo-1-(thiophen-2-yl)prop-1-en-2-yl]benzamide (Schiff base compounds) (5a–5o). The nucleophilic attack of hydrazine hydrate on 2-phenyl-4-(thiophen-2-ylmethylidene)-1,3-oxazol-5(4H)-one (3) results in the breaking of heterocyclic 1,3-oxazol-5(4H)-one with the formation of compound (4). It contains a new bonding site for further nucleophilic attack of substituted aldehyde, resulting in the formation of an imine. Structures of newly synthesized compounds were established by IR, ¹H NMR, ¹³C NMR, mass spectra and elemental analysis. Newly formed compounds were evaluated for their preliminary in vitro antibacterial and antifungal activity. From the activity studies, it was observed that, among all the derivatives, 5a, 5b, 5d, 5e 5f, 5g, and 5h showed potent antimicrobial activity. The time–kill study report of the most active compound 5e exhibited 100% growth inhibition of Candida albicans at 2 h and Pseudomonas aeroginosa at 4 h. From the in silico molecular docking studies, it was observed that compounds 5k and 5f best fit into the receptors, methionine tRNA synthase from Escherichia coli and glucosamine-6-phosphate enzymes from E. coli, respectively. The compound 5e also showed moderate binding capacity to the respective targets.