Sequential polypeptides. Part I. Use of mono-esters of catechol in the synthesis of sequential polypeptides

Abstract

Benzyloxycarbonylpeptide 2-benzyloxyphenyl esters have been shown to be useful intermediates for the racemisation-free synthesis of sequential polypeptides. Simultaneous removal of the benzyloxycarbonyl and benzyl groups with hydrogen bromide in acetic acid (or, less satisfactorily, by hydrogenolysis) gives a peptide 2-hydroxyphenyl ester salt, which is not isolated but is polymerised immediately by triethylamine in dimethyl sulphoxide. Syntheses of poly(glycylglycyl-L-phenylalanine), poly-(β-alanyl-L-phenylalanine) and poly(glycyl-L-prolyl-L-alanine) are described as examples. In the last case the polymer (molecular weight by the Archibald method 1·20 ± 0·1 × 10⁴) had an optical rotation more than twice as great as a preparation of similar molecular weight obtained previously by use of a 4-nitrophenyl ester. Attempts to extend the versatility of the method by using alternative methods of blocking the phenolic group have so far proved fruitless.