Biological synthesis of monodisperse derivatives of poly(.alpha.,L-glutamic acid): model rodlike polymers

Abstract

Poly(α,L-glutamic acid) (PLGA) and its derivatives have played a central role in the physical chemistry and materials science of polymers. PLGA itself has been used in fundamental studies of the helix-coil transition and polyelectrolyte chemistry, and rodlike esters of PLGA-most notably poly(γ-benzyl α,L-glutamate) (PBLG)-have been shown to form liquid crystalline solutions and beautifully ordered monolayer films. The traditional synthetic route to PLGA and its esters involves the ring-opening polymerization of N-carboxy-α-amino acid anhydrides. This technique affords heterogeneous populations of chains characterized by relatively broad distributions of molecular weights, and subsequent conversion of PLGA esters to the parent acid can be accompanied by substantial racemization. The heterogeneity of the resulting products complicates the interpretation of their hydrodynamic, spectroscopic, and liquid crystalline behavior and limits the utility of these polymers in the design and synthesis of complex macromolecular architectures. We report herein a general biosynthetic route to monodisperse derivatives of PLGA, unique rodlike polymers. The method is illustrated by the synthesis of polymer 1.