Microwave-assisted synthesis and antibacterial propensity of N′-s-benzylidene-2-propylquinoline-4-carbohydrazide and N′-((s-1H-pyrrol-2-yl)methylene)-2-propylquinoline-4-carbohydrazide motifs

Microwave-assisted approach was utilized as green approach to access a series of 2-propylquinoline-4-carbohydrazide hydrazone derivatives 10a-j of aromatic and heteroaromatic aldehydes in highly encouraging yields. It involved four steps reaction which was initiated with ring opening reaction of isatin in a basified environment and subsequent cross-coupling with pentan-2-one to produce compound 7. Esterification of 7 in acid medium led to the formation of compound 8 which was reacted with hydrazine hydrate to access 9 which upon microwave-assisted condensed with aromatic and heteroaromatic aldehydes furnished the targeted compounds 10a-j. The structures of 10a-j were confirmed by physico-chemical, elemental analyses and spectroscopic characterization which include UV, FT-IR, 1H and 13C NMR as well as DEPT-135. The targeted compounds 10a-j, alongside with gentamicin clinical standard, were investigated for their antibacterial efficacies using agar diffusion method. 2-Propyl-N′-(pyridine-3-ylmethylene) quinoline-4-carbohydrazide 10j emerged as the best antibacterial hydrazide-hydrazone with lowest MIC value of 0.39 ± 0.02 – 1.56 ± 0.02 µg/mL across all the organisms screened. Keywords: Pfitzinger synthesis, Microwave irradiation, Quinoline, Spectral study, Antibacterial