Syntheses of (3R)-[4,4,4-D-3]-L-valine, [N-15]-L-isoleucine and [N-15]-allo-isoleucine from homochiral 2-alkylated carboxylic acids are described, The approach involves a one-carbon homologation of the carboxylic acid to give the corresponding beta-substituted alpha-keto ester which is converted directly to the alpha-amino acid in a one-pot procedure involving two enzyme catalysed reactions (Candida cylindracea lipase to hydrolyse the ester and leucine dehydrogenase to catalyse the reductive amination of the ketone). This strategy may be simply adapted for the selective labelling of each site of the L-amino acid.