Heparin optical rotation

A classical, and still most useful, physicochemical parameter for characterizing glycosaminoglycans is their specific optical rotation. For pure heparins from common sources, [a]80 = + 45 to + 53 ° (see Table II). The actual value depends on the relative proportions of monosaccharide constituents (that is, the L-idosyluronic acid residues make a less positive contribution than the n-glucosyluronic residues), and on the degree of sulfation of the preparation (that is, although sulfate groups may have little direct influence on the molecular rotation, they lower the value by acting as diluents ). 

Mucopolysaccharides are naturally occurring carbohydrate polymers containing glucosamine and usually a uronic acid share to some degree the properties listed for heparin and heparinoids less sulfur, much weaker metachromatic and anticoagulant activities, but show negative optical rotation, differ in solubility characteristics, aqueous solutions show considerable viscosity. 

Chondroitin 4-sulfate is easily differentiated from the sulfated polysaccharides of the heparin type by its negative optical rotation, and from dermatan sulfate (also called chondroitin sulfate B or /S-heparin) by the identification of L-iduronic acid in the latter. However, it is difficult to distinguish it from chondroitin 6-sulfate ( chondroitin sulfate C ), since the differences in optical rotation, solubility, and susceptibility to enzymic degradation between the two substances are minimal or non-existent. It is probable that studies made in the past with products isolated from incompletely characterized sources have dealt with mixtures of both chondroitin sulfates. 

Heparin in the acid state, and its amorphous sodium and potassium salts are very soluble in water, whereas its crystalline barium acid salt and its amorphous lead salt have a low solubility. In addition to the barium salt, other salts of heparin have a crystalUne appearance, for example those formed with piperidine, -pentylamine, and isopentylamine. Values of the optical rotation of the barium salt have been reported from -1-45 to -t-yo . 

The reaction of nitrous acid on ghicosamine containing p>olysaccharides was first studied on chitosan, which afforded 2,5-anhydro-O-maimose. The same result was obtained in the degradation of the methyl-2-amino-2-deoxy-a- or / -D-glucopyranoside. When applied to iSf-desulfated heparin, the rate of this reaction resembled more that of the a-anomer than that of the fi-anomer, thus establishing on a firmer basis the presence of the a-linkages, suggested by the positive optical rotation . 

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