4-(METHYLTHIO)PHENYL AND 4-(METHYLSULFONYL)PHENYL ESTERS IN PREPARATION OF PEPTIDES AND POLYPEPTIDES . SYNTHESIS OF PROTECTED HEPTAPEPTIDE (A82-A88) OF BOVINE CHYMOTRYPSINOGEN A

The syntheses of some N-t-butyloxycarbonyl-L-amino acid pentachlorophenyl esters, prepared for facile peptide synthesis, are described. Their use is illustrated by the synthesis of the protected tripeptide N,N'-dicarbobenzoxy-L-lysyl-L-leucyl-e-N-carbobenzoxy-n-lysine 4-(methylthio)pheny 1 ester which corresponds to the sequence (A82-A84) of bovine chymotrypsinogen A. Oxidation of this tripeptide derivative yielded the protected tripeptide 4-(methylsulfonyl)phenyl activated ester without rupture of the protecting groups or peptide bonds. By a similar method the protected tetrapeptide L-isoleucyl-L-alanyl-e-N-carbobenzoxy-L-lysyl-n-valine 4-(methylthio)-phenyl ester hydrochloride, sequence A85-A88 of the same material, was prepared. The protected heptapeptide sequence (A82-A88) of bovine chymotrypsinogen A, N,N'-dicarbobenzoxy-L-lysyl-L-leucyl-e-N-carbobenzoxy-Llysyl-L-isoleucyl-L-alanyl-e-N-carbobenzoxy-L-lysyl-L-valine 4-(methylthio )phenyl ester, was obtained by coupling the protected tripeptide (A82-A84) with the tetrapeptide derivative (A82-A88) through the 4-(methylsulfonyl)-phenyl activated ester. © 1968, American Chemical Society. All rights reserved.