Synthesis of Some New Pyridine-2,6-carboxamide-derived Schiff Bases as Potential Antimicrobial Agents

A series of pyridine-bridged 2,6-bis-carboxamide Schiff's bases has been prepared starting from 2,6-pyridinedicarbonyl dichloride (1) and L-alanine or 2-methyl-alanine methyl ester. The coupling of acid chloride 1 with L-alanine methyl ester hydrochloride -or 2-methylalanine methyl ester hydrochloride gave the corresponding 2,6-bis- carboxamide pyridine methyl esters 2a,b. Hydrazonolysis of 2 with hydrazine hydrate afforded the corresponding bis-hydrazides 3a,b. Treatment of 3a,b with appropriate aromatic or heterocyclic aldehydes afforded the corresponding pyridine-bridged 2,6-bis-carboxamide Schiff's bases 4a-f and 5a-f, respectively. The newly synthesized compounds 2-5 were screened for their bactericidal and fungicidal activities. Many of the obtained compounds exhibited significant antimicrobial activity, comparable to streptomycin and fusidic acid, which were used as reference antibiotic drugs.