Recent chemical and enzymatic approaches to the synthesis of glycosaminoglycan oligosaccharides

Glycosaminoglycans, highly charged polycarboxylated, polysulfated polysaccharides, are an important class of therapeutic agents and investigational drug candidates. Heparin has been widely used as a clinical anticoagulant for over 60 years. Low molecular weight heparins have begun to displace heparin and recently a synthetic heparin pentasaccharide was approved for clinical use in Europe. In addition to heparin (and the related heparan sulfate glycosaminoglycan), dermatan sulfate, chondroitin sulfate, hyaluronan and their derivatives are all in various stages of clinical evaluation. This review focuses on the chemical and chemoenzymatic synthesis of glycosaminoglycan oligosaccharides. Recent advances in functional group protection chemistry, conversion of D-gluco to L-ido or D-galacto configurations, glycosylation reactions and the preparation and use of novel starting materials in acidic oligosaccharide synthesis are discussed.