A new approach to preparing synthetic forms of the anticoagulant heparin provides pure heptasaccharides with improved yields over previous approaches (Science, DOI: 10.1126/science.1207478). Heparin is a variably sulfated glycosaminoglycan that is currently isolated from pig intestines and used clinically to prevent blood clotting. It is difficult to synthesize, yet synthetic forms are desired to help address quality-control and safety concerns. Past synthetic tactics suffered from low yields and, in enzymatic approaches, poor structural control. Now, a group led by Robert J. Linhardt of Rensselaer Polytechnic Institute and Jian Liu of the University of North Carolina, Chapel Hill, has developed optimized pathways to make two heparin heptasaccharide sequences. The synthetic schemes start with a disaccharide obtained from fermentation and use a combination of bacterial enzymes and chemical synthesis steps to produce the products with roughly 40% overall yields. The products show in vitro anticoagulant activity and pharmacokinetic properties similar to GlaxoSmithKline’s synthetic heparin pentasaccharide, fondaparinux sodium (Arixtra). The new chemoenzymatic methods should help pave the way to industrial-scale synthesis of additional products, the researchers say.