Synthesis of 3,5-disubstituted pyridines as antimicrobial agents.

3,5-Diacetylpyridine (1) reacted with hydroxylamine hydrochloride, thiourea or phenylhydrazine affording the corresponding carbaldoximo- (2) aminothiazolyl-(3) and phenylhydrazono- (4) derivatives, respectively. Cyclization of 4 by the action of PPA or thionyl chloride afforded the corresponding indolyl- (5) and thiadiazolyl-(6) derivatives. Condensation of 1 with aldehydes yielded bis-(beta-acryloyl) derivatives 7, which on further treatment with malononitrile or ethyl cyanoacetate afforded cyanopyridines of the types 8 and 9. The latter was successfully utilized in the synthesis of thieno[2,3-b]pyridines 13. Some of the obtained compounds showed remarkable antimicrobial activity comparable to oxytetracycline.