Reduction, Mannich reaction, and antimicrobial activity evaluation of some new 1,2,4-triazol-3-one derivatives

Ethyl[4-arylmethyleneamino-3-(4-metylphenyl)-5-oxo-4,5-dihydro-1 H -1,2,4-triazole-1-yl] acetates (3a-e and 10a-d) were obtained starting from 4-amino-2,4-dihydro-3H -1,2,4-triazol-3-ones (1 and 9) in 2 steps. The treatment of 3a-e with NaBH4 resulted in the formation of 3 kinds of product incorporating carboxcilic acid (4a-c) or alcohol (5a-e) functionality. [4-{[(4-Methoxyphenyl) methylene] amino}- and 4-{[pyridin-4ylmethylene] amino}-3-(4-methylphenyl)-5-oxo-4,5-dihydro-1 H -1,2,4-triazole-1-yl] acetic acids (6a, 6e) were obtained by the hydrolysis of the corresponding esters (5a-5e). The treatment of 6a with NaBH4 caused the reduction of only the imine bond; the carboxyl group remained unchanged. Then this carboxylic acid was converted to the corresponding hydrazide (8) in 2 steps by reaction with ethanol and hydrazine hydrate, respectively. The synthesis of Mannich bases was performed by the reaction of the corresponding 1,2,4-triazoles containing an imine group (10a-d) with several primary or secondary amines including morpholine or piperazine nucleus.