Design, synthesis and biological evaluation of novel chalcone-derived thioxopyridine and pyrazolopyridine compounds as antimicrobial agents

The present work deals with the synthesis of some new chalcone, 2- thioxopyridine,2-methylthiopyridine, 2-hydrazinopyridine and 3-amino-1 H -pyrazolo[3,4- b ]pyridine derivatives containing biologically active substituents. The starting material of the present study was synthesis of the 2-cyanoethanethioamide from malononitrile using a modified Brunskill procedure, followed by the synthesis of the 1,3-diarylprop-2-en-1-one (chalcone) from a ketone and an aldehyde. 2 - Thioxopyridines were obtained through Michael addition of α,β-unsaturated ketones with 2-cyanothioacetamide to afford the non-isolable intermediates 8 & 9 followed by cyclization and subsequent dehydration and dehydrogenation of the cyclized product to give compound 4-(furan-2-yl)-6-(4- methoxyphenyl)-2-thioxo-1,2-dihydropyridine-3-carbonitrile which was reacted with methyl iodide in methanolic sodium methoxide to afford the corresponding 4-(furan-2-yl)-6-(4-methoxyphenyl)-2-(methylthio) pyridine-3-carbonitrile , which was reacted with hydrazine hydrate to give the corresponding 2-hydrazinopyridines, which cyclized to afford the corresponding 3-aminopyrazolo[3,4- b ]pyridine derivatives and were characterized by FT-IR, 1 H-NMR, 13 C-NMR and MS spectral studies. All the newly synthesized compounds were evaluated for their in vitro antibacterial activity against S. aureus as example of Gram-positive bacteria and E. coli as example of Gram-negative bacteria. They were also evaluated for their in vitro antifungal potential effect against C. albicans . The zone of inhibition was measured using the well diffusion assay, and the results indicated that compounds 3, 5, 10 and 13 showed potential antibacterial and antifungal effects.