Polypeptides. Part XXII. The synthesis of peptides of α-benzylphenyl-. Alanine by the dicyclohexylcarbodi-imide method

Abstract

Dicyclohexylcarbodi-imide appears to be generally useful for the synthesis of protected dipeptides of α-benzyl-phenylalanine and for adding α-benzylphenylalanyl residues to the N-terminus of larger peptides. It is not, however, generally suitable for adding further amino-acid residues to peptides with an N-terminal α-benzylphenylalanyl residue or for coupling reactions using peptides with a C-terminal α-benzylphenylalanyl residue. Suitable N-protecting groups for α-benzylphenylalanyl peptides are benzyloxycarbonyl and o-nitrophenylsulphenyl. Ethyl esters are not suitable for C-protection, since they are difficult to hydrolyse owing to steric hindrance; 2-methylthioethyl esters are not subject to this and can be used successfully.

Syntheses of two protected peptides corresponding to sequences 6–9 and 1–4 in bradykinin are described.