| Abstract: | The racemization of the penultimate residue of the tripeptide prepared from Boc-d -Phe-d -Phe and free glycine in an aqueous mixed solvent system was examined. An HPLC method was developed to quantitate the amount of product with inverted stereochemistry, starting material, and other biproducts of the reaction. Depending on coupling conditions, the amount of inversion varied from less than 0.5 to nearly 25%. Using near optimal conditions (20% aqueous dioxane, 0.05 m reactants, 5°) two peptides were successfully synthesized in good yield with an acceptable extent of racemization. After recrystallization these peptides contained 0.1-0.2% diastereomer and were recovered in 70-74% yield. Such a prodedure could be useful for the incorporation of radiolabeled amino acids at the carboxyterminus of a peptide where minimal handling of radiolabeled intermediates is desirable. |
