Esterification of poly(γ-glutamic acid) (γ-PGA) mediated by its tetrabutylammonium salt

Poly(γ-glutamic acid) is a linear anionic biopolymer synthesized by bacterial fermentation from sustainable resources. Being water soluble, biodegradable, edible and non-toxic to humans and the environment, applications of γ-PGA are of interest in a broad range of industrial sectors. However, preparation of γ-PGA derivatives is plagued by several difficulties including its scarce solubility in organic solvents. We here report a γ-PGA derivatization procedure based on the use of its tetrabutylammonium salt. The modified solubility of γ-PGA provided by counterion exchange led to the synthesis of poly(α-ethyl-γ-glutamate), poly(α-benzyl-γ-glutamate) and poly(α-n-butyl-γ-glutamate) under smoother conditions and an almost complete functionalization degree.