Chitosan N-sulfate. A water-soluble polyelectrolyte.

Chitosans having degrees of acetylation (da) of 0.04, 0.10, and 0.22, respectively, were N-sulfated under a variety of reaction conditions. The derivatives obtained ranged in degree of sulfation (ds) from 0.4 to 0.86 (+/-0.05). All were soluble in water, and the rheological properties of their solutions varied markedly with da and ds values. Both ionic strength and pH had an effect on their solubility properties, and also on interactions that they exhibited with O-(carboxymethyl)cellulose, xanthan gum, and heparin. Being compatible with other polyelectrolytes such as these, the chitosan derivatives may be useful in some aqueous formulations.

Evidence of a selective free radical degradation of heparin, mediated by cupric ion.

A free radical reaction generated by a mixture of Cu2+, hydrogen peroxide, and ascorbate causes an abrupt reduction in the anti Xa activity of heparin by about one-half, and in molecular weight by about one-third. The product, which has the characteristics of a "low molecular weight" heparin, differs little in constitution from the intact heparin, on the basis of NMR evidence that includes data for fractions of the polymers. The free radical attack appears to occur adjacent to, rather than directly upon, some residues of alpha-L-iduronic acid 2-sulfate. Substitution of the Cu2+ with Fe2+, results in a less selective alteration of the heparin. Dermatan sulfate undergoes more extensive degradation than heparin with the Cu-reagent, although its anti Xa a potency is less drastically reduced. Overall, the results are more consistent with a high degree of regioselectivity in the interaction between heparin and Cu2+ ion, than with a delocalized counter-ion interaction.

Regioselectivity in the sulfation of some chemically-modified heparins, and observations on their cation-binding characteristics.

Two modified forms of heparin, polymers A and B, have been prepared, one containing residues of nonsulfated alpha-L-idopyranosyluronic acid (3) and the other residues of alpha-L-galactopyranosyluronic acid (7), in place of the normal alpha-L-idopyranosyluronic acid 2-sulfate (1). In addition, both A and B contained 2-acetamido-2-deoxy-alpha-D-glucopyranosyl 6-sulfate residues (6) in place of the corresponding N-sulfated residues (2) of the original heparin. These polymers were subjected to sulfation under various conditions. Examination of the products by NMR spectroscopy showed that polymer A was sulfated initially at position-3 of residue 3, and that slower substitution occurred at position-3 of 6. By contrast, polymer B exhibited low regioselectivity, as sulfation occurred with about equal facility at positions-2 and -3 of 7, and -3 of 6. The sulfation products had no significant anti Xa activity. Based on the paramagnetic effects of Cu2+ and chemical shift displacements induced by Ca2+, NMR spectroscopy was used to compare cation-binding properties of A and B with those of heparin. In contrast to heparin, which forms a complex with Cu2+ detectable at a level of < 10(-3) mol per dimeric unit of the polymer, neither A nor B exhibited an interaction with the cation. However, polymer A was found to bind Ca2+, in this respect being distinct from the related modification, 1-->6, which contains a 2-sulfate group in 1, as well as from polymer B.

Adverse effects of alkali and acid on the anticoagulant potency of heparin, evaluated with methyl 2-deoxy-2-sulfamino-alpha-D-glucopyranoside 3-sulfate as a model compound.

A variety of chemical modifications can induce a reduction in the anticoagulant activity of heparin. Among such modifications are the removal in alkaline solution of the 2-O-sulfonate group of alpha-L-idopyranosyluronic acid 2-sulfate residues (1) and, in a weakly acidic medium, of the N-sulfonate group of residues of 2-deoxy-2-sulfamino-alpha-D-glucopyranose 6-sulfate (2). This study examined the possibility that the losses in anticoagulant potency are related to a concomitant removal of the 3-O-sulfonate group of residues of 2-deoxy-2-sulfamino-alpha-D-glucopyranose 3,6-disulfate (6) in the AT-III binding site. It entailed a synthesis of methyl 2-deoxy-2-sulfamino-alpha-D-glucopyranoside 3-sulfate (7), as a model compound that was subjected to both the strongly alkaline and weakly acidic conditions appropriate for the modification of residues 1 and 2, respectively. The 3-sulfate group of 7 was found to be highly stable in both environments. This indicated that the adverse effects that these conditions have on the anticoagulant properties of heparin are not specifically associated with the 3-sulfate substituent of residues of 6 in the polymer.

Single optical fibre transducer for pressure measurement.

In a single optical fibre transducer, light is injected into a fibre through a fibre optic coupler, located at some distance from the distal end of the fibre. Injected light travels toward the front face of the fibre, where it exits in the shape of a cone. then, after reflection from a reflective surface, it is readmitted into the same fibre. The reflected beam of light travels back through the coupler, exits through the distal end of the fibre and illuminates the photosensitive area of a photo diode, where it is converted to an electrical current. Depending on which one of the parameters is allowed to vary the amount of the returning light, one can build a variety of different sensors. Among them are: linear/angular displacement sensors and their derivatives such as pressure or force sensors; transmittance sensors such as turbidity and chemical sensors; reflectance sensors such as temperature sensors, optical encoders and scanners, colourometric and other types of chemical sensors. In the case of the single optic fibre transducer (SOFT) made by Pearl Instruments (Chicago, II, USA), the reflective surface is made of a thin metal foil with 6 microns thickness and 1.25 mm diameter. Optical fibres are pf the multimode type with 55 microns diameter. Their numerical aperture is equal to 0.66. The SOFT head is 1.25 mm in diameter and has an overall length of 50 cm. The disposable part of the system contains the head, fibre, protective sheathing and plug. Its operating range is -15 to +300 mmHg, and +25 to +45 degrees C, and its resolution is +/- 1 mmHg.

Regioselectivity in the sulfation of dermatan sulfate and methyl 4,6-O-benzylidene-alpha-D-idopyranoside.

The sulfation of dermatan sulfate by SO3-trimethylamine in N,N-dimethylformamide led to substitution initially at HO-6 of residues of 2-acetamido-2-deoxy-beta-D-galactopyranosyl 4-sulfate (1), to produce the 4,6-disulfate (6). When this step reached a level of greater than 50%, sulfation occurred with equal facility at HO-2 and HO-3 of residues of alpha-L-idopyranosyluronic acid (2), giving rise to a mixture of 2-,3-, and 2,3-disulfates. An analogous substitution pattern was observed for HO-2 and -3 of a simpler idopyranose unit, in the sulfation of methyl 4,6-O-benzylidene-alpha-D-idopyranoside (12). This lack of regioselectivity in the reaction of 2 (and 12) contrasts markedly with the high affinity of the reagent for HO-3 of residues of alpha-L-idopyranosyluronic acid present in a modified form of heparin. It is attributed to a difference between the two polymers in the relative orientation of their neighboring amino sugar residues, whereby there is an unobstructed access of the reagent in one instance, and hindrance of HO-2 selectively in the other. Enzymolysis by chondroitinase ABC was found to yield unsaturated disaccharide containing residues of 4,6-disulfate, as well as larger fragments containing unsaturated glycosyl groups derived from L-idopyranosyluronic acid 2-sulfate, evidence of a relatively broad enzyme specificity. The presence of extra sulfate groups in dermatan sulfate did not enhance its weak antithrombotic activity, as measured by anti Xa assay, in disagreement with earlier reports.

A novel method for differentiating dextran sulfate from related sulfated polysaccharides.

A method is described for unequivocal identification of dextran sulfate, based on combined chemical desulfation and dextranase enzymolysis of dextran sulfate moieties to isomaltose, a specific indicator of dextran-type precursors. The method was developed using high-resolution (300 MHz) 1H NMR spectroscopy for assurance of the molecular transformations, identification, and estimation of the hydrolysis products. Overall conversion of approximately 80% of highly sulfated and moderately sulfated dextran sulfates was realized. Both 2-D 1H and 13C NMR spectra of a dextran sulfate (MW 500,000) clarified the extent of sulfation (75%) at C-4 and confirmed that sulfation at positions C-2 and C-3 was virtually complete. Estimation of the hydrolysis products (isomaltose, major; alpha-D-glucose, minor) is not restricted to 1H NMR now that the desulfation-enzymolysis methodology has been established; rather, it can be performed using HPLC or GLC (with derivatization).

Characterization and differentiation of some complex dextran sulfate preparations of medicinal interest.

Dextran sulfate samples from different sources were examined by 1H and 13C NMR spectroscopy to differentiate the samples on the basis of extent and sites of sulfation. The anomeric (H-1) signal proved to be a good indicator ranging from no sulfation (as in dextran) to virtually complete sulfation at positions 2 and 3, whereas the relative intensity of the H-4 signal afforded a measure, conversely, of the degree of sulfation at position 4. Three different dextran sulfate tablet formulations were found by NMR to contain similar dextran sulfate material that was characterized by a high degree of sulfation at positions 2 and 3. Position 4 of dextran appears to be less readily amenable to substitution. Quasi-elastic light scattering (QELS) analysis of aqueous dispersions of the bulk dextran sulfate samples and formulated tablets permitted additional particle size and homogeneity differentiation. None of the dextran sulfate materials showed either anti-factor Xa activity or marked anticoagulant activity.

Sulfation of some chemically-modified heparins. Formation of a 3-sulfate analog of heparin.

A modified form of heparin containing residues of nonsulfated alpha-L-idopyranosyluronic acid (7) in place of the normal 2-sulfate (1) was sulfated with sulfur trioxide-trimethylamine in dimethylformamide at 0 and 25 degrees. Examination of the reaction products by n.m.r. spectroscopy showed that sulfation occurred selectively at C-3 of residue 7, to give a new polymer that may be described as a 3-sulfate analog of heparin. A slower substitution reaction led subsequently to sulfation at C-3 of 2-deoxy-2-sulfamino-alpha-D-glucopyranosyl 6-sulfate residues (2), although this was accompanied by partial N-desulfation of 2. An analogous pattern of O-sulfation-N-desulfation was observed for the residues of 2 in two other modified heparins, one containing residues of 2,3-anhydro-alpha-L-gulopyranosyluronic acid and the other residues of alpha-L-galactopyranosyluronic acid, in place of residues of 1. The galacto diastereomer exhibited relatively low regioselectivity, as it was found to be sulfated at C-2 or C-2.3, or both. Selective resulfation of free amino groups gave the products that were examined for anticoagulant activity and susceptibility to enzymolysis by heparinase. Antithrombin-binding affinity measurements were also carried out. Although none of the materials had significant anti-Xa activity, nor were they affected by heparinase, their patterns of binding to antithrombinagarose were not dissimilar to that of heparin.

Marked stereoselectivity in the binding of copper ions by heparin. Contrasts with the binding of gadolinium and calcium ions.

Heparin forms a complex with cupric ion (Cu2+) at a level of less than or equal to 10(-3) mol of the metal ion per dimeric unit of the polymer, as evidenced by paramagnetic relaxation effects on its 1H- and 13C-n.m.r. spectra. No interaction occurred with heparin derivatives modified either by desulfation of the residues of alpha-L-iduronic acid 2-sulfate, or by hydrolysis of the sulfamino group of the residues of 2-deoxy-2-sulfamino-alpha-D-glucose 6-sulfate, although binding was induced by N-acetylation of the latter derivative. Under the same experimental conditions, no alternative type of glycosyluronic acid structure tested, including the other glycosaminoglycans, showed significant relaxation enhancement by Cu2+. These results are in contrast to those obtained with gadolinium ion (Gd3+), another paramagnetic probe, or with calcium ion (Ca2+), which promotes chemical-shift displacements. The binding selectivities of those two cations are much broader than that of Cu2%, although they also differ notably in their relationship to the structure of heparin.

Formation of disaccharides related to heparin and heparan sulfate by chemical modification of maltose.

Maltose has been converted into 4-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-L-idopyranuronic acid, 4-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-D-glucopyranose, and 4-O-alpha-D-glucopyranosyl-L-idopyranose, the first two disaccharides being related structurally to biose sequences in heparin and heparan sulfate. Used as the starting material was a major product of the kinetic acetonation of maltose, namely, 2,3:5,6-di-O-isopropylidene-4-O-(4,6-O-isopropylidene-alpha-D-glucopyran osyl)-aldehydo-D-glucose dimethyl acetal. It was subjected to a sequence of transformation that included the introduction of a 2'-amino-2'-deoxy function into the glucosyl group, the inversion of C-5 in the glucose residue to give the L-ido configuration, oxidation at position 6, and cyclisation of the acyclic dimethyl acetal to give the desired pyranuronic acid. In the formation of the latter, the 5-O-levulinoyl substituent was found to be less prone to acyl migration to O-6 than more conventional ester groups. The relative acid labilities of the O-isopropylidene and dimethyl acetal groups are compared, and conformations of the acyclic residues of some disaccharide derivatives are discussed.

Physicochemical characterization of the First World Health Organization International Standard for low molecular weight heparin derivatives.

High-field (300 MHz) 1H NMR spectral analysis and particle size distribution analysis employing the quasielastic light scattering (QELS) technique were performed on samples of the 1st International Standard for low molecular weight (LMW) heparin derivatives recently selected by the World Health Organization (WHO). We propose that the results of these analyses, which showed that the material is highly homogeneous in particle size and retains spectral features characteristic of its porcine mucosal origin, form an appropriate basis for physicochemical comparison between the "Standard" and other LMW heparin preparations.

Chemical composition, particle size range, and biological activity of some low molecular weight heparin derivatives.

Several low molecular weight (LMW) heparin sodium derivatives from different sources, as well as some related regular heparin sodium preparations, were examined for chemical composition by high field (300 MHz) 1H NMR spectroscopy, for particle size range by quasi-elastic light scattering (QELS) methods, and for anti-coagulation potency and anti-factor Xa activity by the standard U.S. Pharmacopeial assays described for regular heparin. The NMR spectra provided insight into possible modes of depolymerization used to generate the LMW heparins, as well as into the presence of dermatan sulfate or other chemical contaminants. The QELS analysis permitted the heparin preparations to be characterized and compared by virtue of their distinctive particle size distributions.

Heparin in molluscs: chemical, enzymatic degradation and 13C and 1H n.m.r. spectroscopical evidence for the maintenance of the structure through evolution.

The structural features and anticoagulant activity of heparins isolated from three species of molluscs (Anomalocardia brasiliana, Donnax striatus and Tivela mactroides) are reported. It is shown by chemical analyse, type of products formed by action of heparinase and heparitinase II, anticoagulant activity, 13C and 1H n.m.r. spectroscopy, that the mollusc heparins are virtually indistinguishable from heparins present in mammalian tissues. These data, taken as a whole, suggest that heparin has maintained its main structural features through evolution. The implications of these findings are discussed.

Nuclear magnetic resonance spectra of heparin in admixture with dermatan sulfate and other glycosaminoglycans. 2-D spectra of the chondroitin sulfates.

Characteristics of the 1H-n.m.r. spectra of heparin admixed with other glycosaminoglycans are described with respect to the identification of the latter as possible contaminants of pharmaceutical heparins. Chemical shift differences are sufficiently large, particularly with the aid of resolution enhancement, to allow for the detection of dermatan sulfate, chondroitin 4- or 6-sulfate, hyaluronic acid, or heparan sulfate as a minor constituent in the presence of heparin. The acetamidomethyl resonance region (delta 1.95-2.15) is especially useful in this context, both for identification and quantitative estimation. Whereas dermatan sulfate is a common contaminant of pharmaceutical heparin preparations, in some instances comprising 10-15 percent of the polymer mixture, the other glycosaminoglycans, by contrast, were not detected in such preparations. Two-dimensional heterocorrelation and homo-correlation n.m.r. experiments have provided 1H- and 13C-chemical shift data that complete or verify (or both) previous information available for heparin, dermatan sulfate, and chondroitin 4- and 6-sulfates (chondroitins A and C).

Monitoring the purity of pharmaceutical heparin preparations by high-field 1H-nuclear magnetic resonance spectroscopy.

High-field (300 MHz) 1H NMR spectral analyses are reported for various sodium or calcium heparin products available on the Canadian market. Dermatan sulfate (chondroitin sulfate B) was detected as a contaminant in virtually all of these products. Its content varied among the suppliers from less than 1 to 15%, and also over nearly the same range within the groups of heparin preparations of particular suppliers. No correlation was found between in vitro biological activities (potency and anti-factor Xa by the USP tests) and the levels of dermatan sulfate found. Other components, or unlisted constituents, detected in some preparations were paramagnetic metal ions, polyols, and lidocaine.

A relationship between 13C-chemical-shift displacements and counterion-condensation theory, in the binding of calcium ion by heparin.

Characteristics of the interaction between heparin and calcium ion in the presence of sodium ion have been examined by monitoring the 13C-chemical shift changes as a function of the calcium ion concentration and the total ionic strength. The results indicated that the association between the polyanion and the divalent cation is a delocalized process, as opposed to one involving specific binding. The correspondence found between chemical shift and the number of Ca2+ ions bound per charged group, as derived from the Manning counterion-condensation model, showed that the stoichiometry is not a constant quantity but, rather, varies throughout the titration, and approaches a limiting value of 2 at high dilution. Additional measurements of T1 and line-width were consistent with an intramolecular order-disorder conformational process induced by the binding of calcium ion. Moreover, binding does not occur or is relatively weak with N-desulfated heparin, or chondroitin 4-sulfate and 6-sulfate, each of which possesses fewer sulfate groups than heparin. These differences serve to emphasize the importance of the charge-density parameter in the control of counterion condensation according to the Manning model, and suggest that the spacing between the negatively charged groups is an associated factor.