Esterification of isocyanide carboxylic acids and hydrolysis of their esters

Abstract

The naturally occurring isocyanide carboxylic acids dermadin (1; R=H) and 3-[3-isocyano-(Z)-cyclopent-2-enylidene]propionic acid (2; R = H) have been esterified in 45–70% yields by reaction with alcohols and phenols in the presence of dicyclohexylcarbodi-imide and a trace of 4-dimethylaminopyridine. The phenyl esters are hydrolysed in methyl alcohol–carbonate buffer pH 10 to the parent isocyanide acids with retention of full biological activity, in ca. 60% yield. The isocyano esters have been characterised as their stable crystalline [Rh(η⁵-C₅Me₅)(SCN)₂] complexes, most of which have sharp, characteristic melting points.