Synthesis of the carboxy-terminal octapeptide of cholecystokinin (CKK-8) based on incorporation of O4-sulfotyrosine by enzymatically catalyzed formation of peptide bonds

Abstract

Papain-catalyzed condensation of sodium salt of tert-butyloxycarbonyl-β-tert-butyloxyaspartyl-O4-sulfotyrosine (fragment 1-2) with methionyl-glycyl-tryptophyl-methionyl-aspartyl-phenylalanine amide (fragment 3-8) has been elaborated. Deprotection of the thus-obtained octapeptide afforded CCK-8 which exhibited full biological activities. Benzyloxycarbonylaspartyl-phenylalanine amide (fragment 7-8) was prepared using thermolysin without protecting the aspartic acid side chain. Attempted condensation of tert-butyloxycarbonylmethionyl-glycyl-tryptophan (fragment 3-5) with methionyl-aspartyl-phenylalanine amide (fragment 6-8), catalyzed by α-chymotrypsin, subtilisin or proteinase K, afforded the product (fragment 3-8) in only low yields. Further use of proteolytic enzymes for preparing other peptide fragments of the CCK-8 molecule without side chain protection is investigated.