Novel synthesis of 2-oxo-4-phenyl-3-butynoic acid, a new inhibitor and alternate substrate of pyruvate decarboxylase

Article abstract of DOI:10.1021/jo00098a041

An improved method is reported for the synthesis of 2-oxo acids and is applied to the synthesis of 2-oxo-4-phenyl-3-butynoic acid. The compound is synthesized by reacting the N-methoxy-N-methylamide of monoethyloxalic acid with lithium phenylacetylide yielding ethyl 2-oxo-4-phenyl-3-butynoate (78% yield), followed by strictly pH-controlled hydrolysis to the free acid in nearly quantitative yield. The compound is shown to be a potent irreversible inhibitor of brewers' yeast pyruvate decarboxylase, in addition to producing both cis- and trans-cinnamic acids as products of turnover. The formation of these isomeric cinnamic acids can be rationalized if the thiamin diphosphate-bound α-carbanion/enamine intermediate resulting from decarboxylation is protonated at the side chain γ carbon to form two diastereomeric allenols, whose tautomerization and hydrolysis lead to the two products.