Synthesis of sequential polypeptides containing L‐β‐3,4‐dihydroxyphenyl‐α‐alanine (DOPA) and L‐glutamic acid

Sequential polypeptides with the repeating units L ‐glutamyl‐ L ‐DOPA, L ‐DOPA‐ L ‐glutamyl‐ L ‐DOPA, L ‐glutamyl‐ L ‐glutamyl‐ L ‐DOPA, L ‐DOPA‐ L ‐DOPA‐ L ‐glutamyl‐ L ‐DOPA, and L ‐glutamyl‐ L ‐glutamyl‐ L ‐glutamyl‐ L ‐DOPA have been synthesized by solution polymerization of the p ‐nitrophenyl esters of the corresponding di‐, tri‐, and tetrapeptides. The O, O′‐dimethyl and γ‐methyl groups were used to protect side chains of L ‐DOPA and L ‐glutamic acid. 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 protected groups of the side chain were removed simultaneously by use of boron tribromide in chloroform. Trimethylphosphate‐soluble sequential polypeptides containing L ‐DOPA were obtained.