Polypeptide end-capping using functionalized isocyanates: Preparation of pentablock copolymers

The use of electrophiles (isocyanates, isothiocyanates, acid chlorides) to cap the N-terminal ends of polypeptides and the use of isocyanates to prepare poly(gamma-benzyl-L-glutamate) -b -(nonpeptide polymer) block copolymers are described. This chemistry was also used to prepare poly(ethylene glycol)-b-poly(gamma-benzyl-L-glutamate)-b-(polymer)-b-poly(gamma-benzyl-L-glutamate)-b-poly(ethylene glycol) pentablock copolymers, where polymer = polyoctenamer, poly(ethylene glycol), or poly(dimethylsiloxane). These alpha,omega-diamino-terminated polymers (polymer) were used to prepare difunctional macroinitiators for the living polymerization of gamma-benzyl-L-glutamic acid-N-carboxyanhydride (Glu NCA) to form triblock copolymers that were subsequently capped with isocyanate terminated poly(ethylene glycol) to give the pentablock copolymers. These methods allow the facile functionalization of the N-terminal ends of polypeptides from NCA polymerizations. They also were shown to allow the controlled preparation of "rod-coil" polypeptide - (nonpeptide polymer) multiblock architectures with good control over the chain lengths of the domains and without formation of homopolypeptide contaminants.