Synthesis of sequential polypeptides containing <scp>L</scp>‐β‐3,4‐dihydroxyphenyl‐α‐alanine (DOPA) and <scp>L</scp>‐lysine

Abstract

Abstract Six different sequential polypeptides with the repeating units L ‐lysyl‐ L ‐DOPA, L ‐DOPA‐ L ‐lysine, L ‐lysyl‐ L ‐lysyl‐ L ‐DOPA, L ‐DOPA‐ L ‐DOPA‐ L ‐lysine, L ‐lysyl‐ L ‐lysyl‐ L ‐lysyl‐ L ‐DOPA, and L ‐DOPA‐ L ‐DOPA‐ L ‐DOPA‐ L ‐lysine have been synthesized by solution polymerization of the p ‐nitrophyenyl esters of the corresponding di‐, tri‐, and tetrapeptides. The O , O ′‐dimethyl and N ‐ε‐2‐chlorobenzyloxycarbonyl groups were used to protect side chains of L ‐DOPA and L ‐lysine. The monomers for the polytripeptides and polytetrapeptides were prepared by stepwise elongation, using the dicyclohexylcarbodiimide coupling method. Moderately high molecular weight sequential polypeptides were obtained. The addition of 1‐hydroxybenzotriazole increased their molecular weights, but not so effectively. The protected groups of the side chains were removed simultaneously by use of boron tribromide in chloroform. Water‐soluble sequential polypeptides containing L ‐DOPA were obtained.