Abstract
A study of the preparation of carbobenzoxy‐dipeptide p‐nitrophenyl esters revealed that partial racemization may occur depending on the structure of the dipeptide derivative used. Whereas carbobenzoxy‐S‐benzyl‐L‐cysteinyl‐L‐tyrosine yielded an optically pure ester employing the sulfite method, the synthesis of the ester of carbobenzoxy‐L‐tyrosine by various methods proceeded with partial racemization. The optically pure carbobenzoxy‐L‐seryl‐L‐tyrosine p‐nitrophenyl ester was obtained by condensation of carbobenzoxy‐L‐serine with p‐nitrophenyl L‐tyrosinate.