Racemization in the synthesis of polytripeptide models of collagen

Racemization in the synthesis of tripeptide intermediates and their polymers was investigated, using L‐amino acid oxidase. Stepwise investigation of peptide intermediates showed no racemization during peptide coupling steps or deprotection of benzyl esters by hydrogenolysis. Saponification of one of the methyl esters produced some racemization. Preparation of active esters from N‐protected tripeptide acids containing optically active C‐terminal amino acid, with one exception, produced racemization. The fractionated polymers were found to contain less racemized amino acids than the crude products or starting monomeric tripeptides, indicating that the racemized sequences gave rise to lower molecular‐weight oligomers. The sequences investigated were ‐Pro‐Pro‐Ala‐, ‐Ala‐Pro‐Pro‐, ‐Val‐Pro‐Pro‐, ‐Pro‐Pro‐Leu‐, ‐Pro‐Gly‐Leu‐, ‐Pro‐Gly‐Phe‐, ‐Pro‐Gly‐Val‐, ‐Gly‐Val‐Pro‐, ‐Phe‐Pro‐Gly‐, ‐Leu‐Pro‐Gly‐, and Ile‐Pro‐Gly‐.