Synthesis and investigation of the stability of esters of 6′-carbamoylmethylthio-5′-cyano-1′,4′-dihydro-3,4′-and-4,4′-bipyridine-3′-carboxylic acids 1. Esters of 6′-carbamoylmethylthio-5′-cyano-1′,4′-dihydro-3,4′-bipyridine-3′-carboxylic acids

Esters of 6′-carbamoylmethylthio-5′-cyano-1′,4′-dihydro-3,4′-bipyridine-3′-carboxylic acids are obtained by the alkylation of piperidinium 3′-alkoxycarbonyl-5′-cyano-1′,4′-dihydro-3,4′-bipyridine-6′-thiolates with iodoacetamide. For an HPLC study of the stability of solutions of the abovementioned 1,4-dihydrobipyridines (solution pH 2.3–9.0) the appropriate esters of 6′-carbamoylmethylthio-5′-cyano-3,4′-bipyridine-3′-carboxylic acids and esters of 8-cyano-5-methyl(or phenyl)-3-oxo-7-pyridin-3-yl-2,3-dihydro-7H-thiazolo3,2-a]pyridine-6-carboxylic acids were synthesized as reference compounds. Analysis by HPLC was carried out under conditions of reverse-phase chromatography. It was shown that solutions of the investigated compounds in a mixture of acetonitrile and phosphate buffer (pH 3.0–5.0) were stable for 1 month on storage protected from light. Under the action of light in all the solutions investigated irrespective of pH the formation occurs of the corresponding esters of 6′-carbamoylmethylthio-5′-cyano-3,4′-bipyridine-3′-carboxylic acids. The presence of esters of 8-cyano-5-methyl(or phenyl)-3-oxo-7-pyridin-3-yl-2,3-dihydro-7H-thiazolo3,2-a]pyridine-6-carboxylic acids (no more than 4%) was detected only in 0.1% solutions of phosphoric acid (pH 2.3) under conditions of storage of the latter protected from light. A series of as yet unidentified products was detected in solutions of pH 7.0–9.0. Dedicated to E. Lukevics on his 70th birthday __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 59–68, January, 2007.