Synthesis of novel triazolothione,thiadiazole, triazole-functionalized furo/thieno[2,3-b]pyridine derivatives and their antimicrobial activity

A series of novel triazolothione, thiadiazole, triazole-functionalized furo/thieno2,3-b]pyridine derivatives 9a–l, respectively, were prepared starting from 2 (1H) pyridone 3 through selective O/S-alkylation followed by Thorpe–Ziegler cyclization to form furo/thieno2,3-b]pyridine derivatives 6. Compounds 6 on reaction with hydrazine hydrate resulted carbohydrazide derivatives 7 and further reacted with diverse substituted phenyl isothiocyanates to form phenyl hydrazine carbothiamide derivatives 8. Each compound 8 is independently reacted in presence of NaOH, H₂SO₄, and N₂H₄.H₂O to form triazolothione, thiadiazole, triazole-functionalized furo/thieno2,3-b]pyridine derivatives 9a–l, respectively. All the products 9a–l were screened against Gram +ve, Gram –ve bacteria and fungal strains. Compounds 9c–h showed high activity against Bacillus subtilis microbial-type culture collection (MTCC) 121 at <8.0 micromolar concentration. Promising compounds further screened for minimum bactericidal concentration against B. subtilis MTCC 121 using ciprofloxacin as standard and found to show very good activity. These compounds also screened for biofilm inhibition activity against B. subtilis MTCC 121 using erythromycin as standard and confirmed the high activity.