Use of 2-hydroxyphenyl esters for a racemization-free synthesis of alternating diastereoisomeric poly-(γ-benzyl glutamate)s

Abstract

Poly-(γ-benzyl-D-glutamyl-γ-benzyl-L-glutamate) and its mirror image were prepared by polycondensation of the tetrapeptide 2-hydroxyphenyl esters. No racemization was detected by optical rotation measurements on the polymers dissolved in helicoclastic solvents. Fractionation of the crude polypeptides led to the pure α- and β-forms, characterized by their i.r. spectra and differing in their molecular weights. The α-form can undergo a transition to a new helical form, indicating that the optical purity of the residues is largely preserved during the synthesis. Poly-(γ-benzyl-L-glutamyl-γ-benzyl-D-glutamyl-γ-benzyl-L-glutamate) was prepared similarly.