Efficient Synthesis of Nicotinic Acid Based Pseudopeptides Bearing an Amidoxime Function

Abstract

The synthesis of nicotinic acid based amino acid units bearing an amidoxime function on the pyridine ring has been developed. The starting 2-cyanonicotinic acid was efficiently coupled with methyl esters of l -α-amino acids to afford intermediate 2-cyanopyridin-3-yl-containing pseudopeptides together with the tautomeric methyl esters of (2 S )-2-(7-imino-5-oxo-5,7-dihydro-6 H -pyrrolo[3,4- b ]pyridin-6-yl)alkanoic acids. Regioselective pyrrolidine ring opening of these esters occurred upon hydroxylamine hydrochloride treatment, giving rise to the open-chain pyridin-3-yl 2-amidoxime pseudopeptides bearing the same structure as amidoximes obtained by direct hydroxyamination of the corresponding cyano esters.