PMC

Pathway for the preparation of neoheparin.

Chemoenzymatic synthesis of heparin and heparin products. A. ultra-low molecular weight heparins; B. low molecular weight heparins; and C. bioengineered heparin.

Extractive preparation of heparin, HS and LMWHs. Typical process steps are shown the anion-exchange step is used in recovering GAG and the cation-exchange step is used in removing cationic impurities.

Structures of heparin and HS GAGs and their oligosaccharides. A. typical heparin and HS chains; B. typical low molecular weight heparin (enoxaparin) chains; and C. examples of ultra-low molecular weight heparins.

Preparation of ultra-low molecular weight heparin and low molecular weight heparin. A. Summary of a convergent multistep chemical synthesis of Arixtra® from cellobiose derivative (reagents not shown). B. Enzymatic and chemical depolymerization to prepare low molecular heparins from unfractionated heparin.

Biosynthesis of heparin/HS Synthesis begins with the stepwise addition of four monosaccharides (Xyl, Gal, Gal, and GlcA) to a serine residue of the core protein. Polymerization extends the chain by alternately adding GlcNAc and GlcA, and the chain is modified by epimerase and sulfotransferase enzymes to produce a variable structure, which includes high and low sulfated domains (NS and NA respectively) and antithrombin binding sites.

Bioactivities of heparin/HS. A. Anticoagulant activity of heparin- a pentasaccharide sequence in heparin induces a conformational shift in ATIII upon binding, which irreversibly binds thrombin, which also binds to heparin at an adjacent site, to inhibit coagulation. B. Role of HSPGs in infectious disease- Intracellular pathogens and viruses bind cell surface HSPGs to facilitate invasion or viral fusion. C. Role of HSPGs in leukocyte extravasation/metastasis- rolling along endothelial surface is mediated by selectin-HS binding, and chemokines bound to endothelial HSPGs attract the leukocyte to damaged tissue. Invasion requires heparanase activity to degrade HSPGs in the basement membrane. D. Role of HSPGs in angiogenesis-HSPGs stabilizes gradients of angiogenic factors (VEGF, PDGF, FGF2) to direct blood vessel formation.