Poly(gamma-glutamic acid) esters with reactive functional groups suitable for orthogonal conjugation strategies
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Abstract
We report on a series of novel poly(c-glutamic acid)
(PGGA) esters, in which the chemical structure and composition,
and the molecular weight are systematically changed. Modification
of PGGA of microbial origin, used either as the sodium salt or
in the free acid form, by means of alkylation with highly reactive
bromides under SN2 conditions, affords copolymers with an
essentially random microstructure. These reaction conditions are
applied iteratively to achieve full esterification, obtaining allyl or
propargyl ester functionalities within the polymer backbone,
diluted with inert functional groups, such as benzyl, ethyl, or hexyl
ester functionalities. The copolymers have been characterized
regarding their chemical structure and thermal and bulk properties
using nuclear magnetic resonance, thermogravimetry, differential
scanning calorimetry, and X-ray diffraction techniques. We demonstrate
that allyl and propargyl ester groups can be efficiently
transformed using click chemistries, such as thiol-ene or copper(I)-
catalyzed azide–alkyne cycloaddition reactions; such efficient
conjugation strategies will be required to transformthe native bacterial
biopolymer into a material with tailored properties for bulk
scale or biomedical applications.Peer Reviewe