Improvement of the synthesis of poly(L-cystyl-L-cystine): A new biodegradable polymer

A new synthesis of poly(L-cystyl-L-cystine) by using N,N'-bis(trimethylsilyl)cystine dibenzyl ester is described. The polycondensation of the latter with N,N'-bis(benzyloxycarbonyl)cystine bis(pentafluorophenyl) ester allowed us to obtain polymers having higher molar masses (28 700 instead of 14 000 g/mol) and improved properties compared with earlier methods. The partial as well as complete deprotection of the polymer using a new method, generally used in peptide chemistry, is also described.