EFFICIENT SYNTHESIS OF NOVEL 3-[5-(1H-BENZIMIDAZOL-2-YLMETHANESULFONYL)-4-PHENYL-4H-(1,2,4)TRIAZOL-3-YL]-1H-(1,8)NAPHTHYRIDIN-4-ONE DERIVATIVES

of 1,4-dihydro-4-oxo-1,8-naphthyridine-3-carbohydrazide (4) with substituted phenyl isothiocyanates (5) in ethanol under reflux for 30 min gave thiosemicarbazide derivatives 6, which on cyclization in 2N NaOH under refluxing conditions for 1 h resulted in 3-(5-mercapto-4-phenyl-4H-1,2,4-triazol-3-yl)-1,8-naphthyridin-4(1H)-one (7). Alternatively, 7 could also be prepared from following sequence of reactions, i.e., 4 -> 8 -> 7. In another sequence of reactions, condensation of 7 with chloroacetic acid in dimethylformamide (DMF) and K2CO3 as a mild base at 120 degrees C for 2 h resulted in 2-((5-(1,4-dihydro-4-oxo-1,8-naphthyridin-3-yl)-4-phenyl-4H-1,2,4-triazol-3-yl) sulfanyl) acetic acid (10). The latter, on reaction with substituted o-phenylenediamine (11) in 6N HCl for 4 h yielded 3-(5-((1H-benzo[d]imidazol-2-yl) methylthio)-4-phenyl-4H-1,2,4-triazol-3-yl)-1,8-naphthyridin-4(1H)-one (12). Alternatively, 12 could also be prepared by reacting 7 with 13 in DMF and K2CO3 as a mild base at 120 degrees C for 2 h, followed by oxidation with H2O2 resulting in the corresponding sulfonyl derivatives 14.