Heparin oligosaccharide

The total synthesis of a series single glyco-mimetics of heparin was recently announced (169). One structurally optimized oligosaccharide heparin mimetic is 10 times more potent in vivo than both standard heparin and low molecular weight heparins and is also devoid of the undesired side effect, thrombocytopenia, that is associated with heparin treatment. Thus, chemical synthesis was employed to optimize the length and the charge of the synthetic oligosaccharides. 

In a synthetic series that explored chain length, it was clear that reducing the size to the minimum that still allowed thrombin inhibition was not sufficient to abolish the undesired interaction with PF4. The next step was to reduce the charge of the molecule for anti-thrombin, and that provided the structurally optimized oligosaccharide heparin mimetic. 

Indeed, the optimized oligosaccharide heparin mimetic has 10 times the antithrombotic potency relative to that obtained for heparin but is unable to activate platelets in the presence of plasma from patients with heparin-induced thrombocytopenia and is devoid of other side effects attributed to the anionic charges of heparin, such as hemorrhage. 

The identification of L-iduronic acid as the major glycuronic acid constituent of heparin proved to be a much slower process than the identification of the amino sugar residue. Although this compound was detected in acid hydrolyzates of heparin116117 and heparin oligosaccharides,118 its yield was usually poor, because of the drastic conditions used for the acid hydrolysis (which are known to lead to extensive destruction of uronic acid).119120 Also, L-iduronic acid escaped detection as L-idose in the hydrolyzates of carboxyl-reduced heparin, probably because L-idose is readily converted into 1,6-anhydro-L-idose under the usual hydrolytic conditions. 

Antithrombin, already mentioned in the context of heparin, is the most abundantly occurring natural inhibitor of coagulation. It is a single-chain 432 amino acid glycoprotein displaying four oligosaccharide side chains and an approximate molecular mass of 58 kDa. It is present in plasma at concentrations of 150 pig ml 1 and is a potent inhibitor of thrombin (factor Ha), as well as of factors IXa and Xa. It inhibits thrombin by binding directly to it in a 1 1 stoichiometric complex. 

L. M. Mallis, H. M. Wang, D. Loganathan, and R. J. Linhardt. Sequence Analysis of Highly Sulfated, Heparin-Derived Oligosaccharides Using Fast Atom Bombardment Mass Spectrometry. Anal. Chem., 61(1989) 1453-1458. 

The applicability of cITP-NMR for the analysis of trace impurities was demonstrated by the selective detection of 1.9 nmol of atenolol injected in a sample containing a 1000-fold excess of sucrose [100]. cITP-NMR has also been used for the analysis of a cationic neurotoxin present in a homogenate of the hypo-branchial gland of the marine snail Calliostoma canaliculatum [109]. Korir et al. [110] used an anionic cITP separation with online NMR detection to separate and identify nanomole quantities of heparin oligosaccharides. Although only a few cITP-NMR applications have appeared, the ability to selectively separate, concentrate, and detect charged analytes makes cITP-NMR a potentially powerful method for trace analysis. 

RJ Linhardt, T Toida. Heparin Oligosaccharides New Analogues Development and Applications. In ZJ Witczak, KA Nieforth. Carbohydrate as Drugs. New York Marcel Dekker, 1997, pp 277-341. 

I Capila, MJ Hernaiz, YD Mo, TR Mealy, B Campos, RJ Linhardt, BA Seaton. Annexin V-heparin oligosaccharide complex suggests heparan sulfate-mediated assembly on cell surface. Structure 9 57-64, 2001. 

The work on the first sulfated oligosaccharides was based on investigations of the polymeric heparinoids derivatives of heparin had been prepared to obtain information on the structural requirements of heparin for SMC antiproliferative activity. A clue for further studies was brought about by carboxyl-reduced sulfated heparin (CRS-heparin, 9) in which all carboxyl groups were reduced and... 

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