Synthesis of oxygen‐18 isotope labeled amino acids and dipeptides and its effects on carbon‐13 NMR

Abstract

Abstract Oxygen‐18 isotope labeled at the carboxyl group of glycine, L‐alanine and L‐proline were synthesized by acid catalyzed exchange or acid hydrolysis of respective methyl ester derivatives of amino acids in HC1/H 2 18 O. Quantitative enrichment of glycine was achieved by the acid hydrolysis of amino acetonitrile in H 2 18 O. In order to conserve the isotopic enrichment [ 18 O] dipeptides were synthesized by solid phase method. [ 18 O] isotope effects on [ 13 C] NMR of carboxylic carbon of amino acids and carbonyl carbon of peptides was observed. The [ 18 O] isotopic shifts observed for the carboxylic carbon of singly and doubly [ 18 O] labeled amino acids showed that the [ 18 O] isotope effect is additive.