Gas Chromatographic Investigation of Racemization during Peptide Synthesis

It is shown that the methyl esters of many diastereoisomeric N-trifluoroacetyldipeptides can be separated by gas chromatography on Golay columns. This makes it possible for the first time to carry out accurate quantitative investigations of recemization occurring during peptide synthesis without resort to measurements of optical rotation or enzymatic cleavage, and witout having to isolate the peptides. Some well-known methods of forming peptides were examined using the synthesis of the methyl ester of carbobenzoxy-L-valyl-L-valine as an example. The synthesis of the methyl ester of N-trifluoroacetyl-L-valyl-L-valine was investigated as a model for the linking of peptides. The influence on racemization of numerous factors was determined. General conclusions could be drawn regarding peptide synthesis.