Synthesis of chitosan-graft-poly(sodium-l-glutamate) for preparation of protein nanoparticles

In this manuscript we have designed a synthetic approach for the preparation of a series of chitosan-graft-poly(l-glutamate) copolymers with different lengths of poly(l-glutamate) grafts. First, organosulfonic chitosan salt, soluble in DMSO, was prepared in order to effectively initiate ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydride. The chitosan-graft-poly(γ-benzyl-l-glutamate) copolymers were fully deprotected by applying tetrabutylammonium hydroxide. The molar mass characteristics and chemical composition of graft copolymers with various lengths of polypeptide grafts were determined by SEC-MALS, FT-IR and various NMR spectroscopic techniques. The synthesized chitosan-graft-poly(sodium-l-glutamate) copolymers were used in combination with trimethyl chitosan for the preparation of nanoparticles (NPs) of a recombinant granulocyte colony-stimulating factor (GCSF). The suspensions of NPs with typical average diameter of 200–300 nm were obtained with polydispersity index values below 0.26. The achieved loading efficiency was up to 95 % and the final loading of GCSF protein in NPs was up to 45 %. The time, temperature and pH stability of NPs was also studied.