A slurry of phenoxypyruvic acid (1.8 g) (prepared by the condensation of ethyl phenoxyacetate with diethyl oxalate, followed by acid catalyzed hydrolysis and decarboxylation) and L-alanyl-L-proline (0.37 g) in 10 ml of water is adjusted to pH 7 with dilute NaOH. The mixture is treated with NaBH3CN (0.18 g) and allowed to stir at room temperature for 5 days. On the second and third days additional ketoacid (0.9 g) and sodium cyanoborohydride (0.18 g) are added. The product is adsorbed on strong acid ion-exchange resin and eluted with 2% pyridine in water to yield, after freeze-drying, 0.5 g of N-(1-carboxy-2-phenoxyethyl)-L-alanyl-L-proline. The nmr is consistent with structure. The mass spectrum shows a peak at 479 for the silylated molecular ion minus methyl (494-15).
