Synthesis and antibacterial activity of pyrazole and 1,3,4-oxadiazole derivatives of 2-phenyl-1,8-naphthyridine

2-Phenyl-1,8-naphthyridine-3-carboxylic acid hydrazide 2 reacts with acetyl acetone and ethyl acetoacetate to give 3,5-dimethyl-1-[(2-phenyl-1,8-naphth yridin-3-yl)carbonyl]pyrazole 3 and 3-methyl-1-[(2-phenyl-1,8-naphthyridin- 3-yl)-carbonyl]pyrazolin-5(4H)-one 4, respectively. The hydrazide 2 has bee n reacted with different acetophenones to yield the respective acetophenone 2-phenyl-1,8-naphthyridine-3-carbonylhydrazones 5, which on reaction with Vilsmeier-Haack reagent (DMF/POCl3) furnish the corresponding 3-(3-aryl-4-f ormylpyrazole-1-carbonyl)-2-phenyl-1,8-naphthyridines 6. On the other hand, interaction of 2 with different acid chlorides affords N-aroyl-N'-(2-pheny l-1,8-naphthyridine-3-carbonyl) hydrazines 7, which on treatment with POCl3 yield 3-(5-aryl-1,3,4-oxadiazol-2-yl)-2-phenyl-1,8-naphthyridines 8. These compounds have been characterized on the basis of elemental analyses, IR, H-1 NMR and MS. Compounds 6 and 8 have been tested for their antibacterial activity using streptomycin as a reference compound.