Synthesis of poly(ethylene glycol)-tethered poly(propylene fumarate) and its modification with GRGD peptide

Abstract

Poly(ethylene glycol) (PEG), a highly biocompatible hydrophilic polyether, was tethered to poly(propylene fumarate) (PPF), a biodegradable polyester. To avoid change in molecular weight distribution of PPF, end hydroxyl groups of PPF were reacted with bis-carboxymethyl PEG after being treated with thionyl chloride. New end carboxyl groups of the PEG-tethered PPF were further reacted with N-hydroxysuccinimide (NHS) in the presence of dicyclohexylcarbodiimide (DCC) to couple bioactive molecules. Glutamine and glycine–arginine–glycine–aspartic acid (GRGD) were attached to the PEG-tethered PPF in 50mM phosphate buffer of pH of 7.4.Tethering PEG to PPF, activation of the PEG-tethered PPF with NHS, and coupling of peptide and amino acid were characterized by proton nuclear magnetic resonance (1H-NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and gel permeation chromatography (GPC). The 1H-NMR spectrum of PEG-tethered PPF showed significant PEG proton peaks at 3.5ppm. The GPC chromatogram of PEG-tethered PPF showed significant increase in molecular weight of the polymer without noticeable unreacted PEG. Characteristic proton peaks of glutamine and GRGD also were observed in proton NMR spectra after the modification of PEG-tethered PPF. The carbonyl stretching bands of amide bonds (amide I bands) were observed in the IR spectra of modified PEG-tethered PPF with glutamine and GRGD. Glutamine and GRGD were coupled to the PEG-tethered PPF with yields of 90 and 99%, respectively, as determined by trinitrobenzene sulfonic acid (TNBS) analysis. The proposed method also will be valuable for the preparation of a triblock copolymer with PEG end blocks and the coupling of biologically active molecules.