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-1H -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-4- ylmethylene]amino}-3-(4-methylphenyl)-5-oxo-4,5-dihydro-1H -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. All newly synthesized compounds were screened for their antimicrobial activity. The antimicrobial activity study revealed that the Mannich bases (11-16) showed good activity against the test microorganisms as compared with ampicillin.