Synthesis of heterobifunctional poly(ethylene glycol) with a reducing monosaccharide residue at one end.

A new synthetic method for a heterobifunctional poly(ethylene glycol) (PEG) having a monosaccharide moiety at one end was created. PEG with a reducing monosaccharide residue at the alpha-end, which is linked to a defined position of the sugar molecule, could be prepared via the anionic polymerization of ethylene oxide (EO) initiated with a potassium alkolate of a protected monosaccharide such as 1,2;5,6-di-O-isopropylidene-D-glucofuranose (DIGL), 1,2;3,4-di-O-isopropylidene-D-galactopyranose (DIGA), and 1,2-O-isopropylidene-3,5-O-benzylidene-D-glucofuranose (IBGL). The resulting PEGs possess the corresponding sugar molecule at the alpha-chain end and a hydroxyl group at the omega-chain end. The omega-chain end could be converted to several functional groups such as allyl, amino, and hydroxycarbonyl groups in high yield. Such heterobifunctional PEGs possessing a reducing monosaccharide residue at the alpha-end are one of the promising tools for bioconjugate chemistries.