Synthesis of some new 1,2,4-triazoles starting from isonicotinic acid hydrazide and evaluation of their antimicrobial activities

5-Pyridin-4-yl-1,3,4-oxadiazole-2-thiol (2) was obtained from the reaction of isonicotinic acid hydrazide with carbon disulfide in basic media and converted into 4-amino-5-pyridin-4-yl-4H-1,2,4-triazole-3-thiol (5) by the treatment with hydrazine hydrate. The synthesis of 3 and 6 was performed from the reaction of 2 and 5 with ethyl bromide. The treatment of 5 with 4-fluorobenzaldehyde or indol-3-carbaldehyde resulted in the formation of 4-[(arylmethylene)amino]-5-pyridin-4-yl-4H-1,2,4-triazole-3-thiols (7a and 7b). The reactions of 2, 5 and 7a with some primary and secondary amines in the presence of formaldehyde afforded the corresponding Mannich bases, 4a, 4b, 9a-9c and 8.