Synthesis and SAR investigation of natural phenylpropene-derived methoxylated cinnamaldehydes and their novel Schiff bases as potent antimicrobial and antioxidant agents

A series of cinnamyl compounds were synthesized from abundantly available methoxylated phenylpropenes and evaluated for their antimicrobial activity by the broth microdilution method against fourteen opportunistic bacterial and fungal human pathogens. Structure–activity relationship studies indicated that methylenedioxy cinnamaldehyde exhibited promising broad-spectrum activity against the tested microorganisms and hence was used as a lead structure to synthesize novel Schiff bases/heterocyclic compounds (23–33) under microwave irradiation. Out of these, thiazole-based Schiff bases have shown promising antibacterial activity against B. subtilis (26; MIC 0.12 mM), M. luteus (27; MIC 0.20 mM), and S. aureus (27; MIC 0.20 mM). Also, the compounds 23–33 were investigated for in vitro antioxidant activity using DPPH• assay where compound 28 showed a maximum of 80.71 % inhibition.