MAHESH JASEJA, RABINDRA N. REJ, FRANCOIS SAURIOL, and ARTHUR S. PERLIN. Can. J. Chem. 67, 1449 (1989).Nuclear magnetic resonance spectroscopic evidence is presented in characterizing three new structurally modified forms of heparin. One of these, polymer M-I, represents a conversion of about two-thuds of the a-L-iduronic acid 2-sulfate residues (1) into residues of a 2,3-anhydro derivative (3), through the action of sodium hydroxide. The formation of 3 is attributed to a base-catalysed displacement of the sulfate group of 1 by an intramolecular attack of 0 -3 on C-2. In more concentrated sodium hydroxide solution, heparin is transformed almost quantitatively into polymer M-11, which differs from it in having residues of (non-sulfated) a-L-iduronic acid (4) in place of 1. It is likely that 3 is an intermediate, and that a selective nucleophilic attack of hydroxide ion at C-2 accounts for the ido configuration in 4. The third modification, giving polymer M-111, is induced when a neutral or weakly alkaline solution of M-I is heated at 70°C or above, which promotes a different stereochemistry in the hydrolysis of the 2,3-oxirane ring of 3. Hence, in contrast to residues of 4 in M-11, most of the uronic acid residues of M-I11 appear to have the alternate, a-L-galacto, configuration. As shown by a comparison of beef lung and hog mucosal heparin, the rate at which M-I is converted into M-111 is facilitated by the higher level of structural heterogeneity in the mucosal heparin. Whereas the formation of M-I, -II, and -1II is accompanied by only moderate depolymerization, these novel polymers retain little of the anti-coagulant and anti-XA activities of the unmodified heparin.Key words: NMR spectroscopy, heparin, desulfation, anhydroaldoside, base-catalysed displacement. On prCsente les spectres de rdsonance magnCtique nuclCaire de trois nouvelles formes d'hCparine modifiCes structuralement. Dans l'une d'elles, le polymkre M-I, environ les deux tiers des rCsidus sulfates de I'acide a-L-iduronique (1) ont Ct C transformCs en rCsidu du dCrivC dthydro-2,3 (3) sous I'action de l'hydroxyde de sodium. On attribue la formation du dCrivC 3 au dCplacement, catalysk par une base, du groupe sulfate du composC 1 par suite d'une attaque intramolCculaire de I'oxygkne en position 3 (0-3) sur le carbone en position 2 (C-2). Dans une solution plus concentrke d'hydroxyde de sodium, I'hCparine se transforme presque quantitativement en polymkre M-11 qui difEre de I'hCparine par la prksence de rksidus (non sulfatks) de l'acide a-L-iduronique (4) au lieu du composC 1. I1 est comrnunCment admis que le compost! 3 est un intermkdiaire, et qu'une attaque nucltophile sklective de I'ion hydroxyde en C-2 est responsable de la configuration ido dans le composC 4. La troisikme modification, conduisant au polymkre M-111, est obtenue par chauffage B 70°C ou au-dessus d'une solution neutre ou faiblement alcaline du polymkre M-I, ce qui favorise une sterkochimie diffkrente dans I'hydrolyse du cycle oxyrane-2,3 du compost 3. Cependant, contrairement au rCsi...

Dendroaspin is a short chain neurotoxin homologue from the venom of Elapidae snakes, which lacks neurotoxicity. Unlike neurotoxins, it contains an Arg-Gly-Asp-(RGD)-motif and functions as an inhibitor of platelet aggregation and platelet adhesion with comparable potency to the disintegrins from the venoms of Viperidae. We have determined the structure of dendroaspin in solution using NMR spectroscopy. The structure contains a core similar to that of short chain neurotoxins, but with a novel arrangement of loops and a solvent-exposed RGD-motif. Dendroaspin is thus an integrin antagonist with a well defined fold different from that of the disintegrins, based on the neurotoxin scaffold.

The use of two-dimensional NMR techniques and spin simulation afforded a detailed set of chemical shift and spin-spin coupling data for the main tautomeric forms of D-frUCtose in dimethyl sulfoxide and aqueous solutions. Differences in Vicinal coupling parameters for &D-frUCtOfWanOSe in the two solvents are taken as evidence that this tautomer incorporates intramolecular hydrogen bonding in dimethyl sulfoxide, which helps to account for its excep tional prominence in this solvent. The enhanced proportion of a-D-frUCtOfIIratIose in dimethyl sulfoxide over that in water also receives comment. Also described are corresponding data from NMR measurements on the tautomeric equilibria of disaccharides that contain a D-fruCtose reducing-end residue, and of the homomorphic ketose, Lgufacto-2-heptulose, i.e. structurally related compounds that may entail different kinds of hydrogen-bonding possibilities. Evidence indicating the presence of extensive inter-residue hydrogen bonding within the individual tautomers of the disaccharide turanose is provided by the pattern of hydroxyl proton chemical shifts in dimethyl sulfoxide.

As part of a program to investigate the origins of peptide-carbohydrate mimicry, the conformational preferences of peptides that mimic the group B streptococcal type III capsular polysaccharide have been investigated by NMR spectroscopy. Detailed studies of a dodecapeptide, FDTGAFDPDWPA, a molecular mimic of the polysaccharide antigen, and two new analogs, indicated a propensity for ␤-turn formation. Different ␤-turn types were found to be present in the trans and cis (Trp-10 -Pro-11) isomers of the peptide: the trans isomer favored a type I ␤-turn from residues Asp-7-Trp-10, whereas the cis isomer exhibited a type VI ␤-turn from residues Asp-9 -Ala-12. The interaction of the dodecapeptide FDT-GAFDPDWPA with a protective anti-group B Streptococcus monoclonal antibody has also been investigated, by transferred nuclear Overhauser effect NMR spectroscopy and saturation-transfer difference NMR spectroscopy (STD-NMR). The peptide was found to adopt a type I ␤-turn conformation on binding to the antibody; the peptide residues (Asp-7-Trp-10) forming this turn are recognized by the antibody, as demonstrated by STD-NMR experiments. STD-NMR studies of the interactions of oligosaccharide fragments of the capsular polysaccharide have also been performed and provide evidence for the existence of a conformational epitope.

. Can. J. Chem. 65, 1384 (1987). The structures of the two major saponins isolated from the starfish Asterias forbesi have been deduced totally by nuclear magnetic resonance methods applied to the undegraded molecules. The structure of forbeside A, 6a-0-{P-D-galactopyranosyl- [Traduit par la revue]In view of the widespread interest (1) in the biological functions, toxicity, and pharmacology of starfish saponins (asterosaponins), we recently embarked on structural studies on the asterosaponins of Asterias forbesi. This is a common species on the Atlantic seaboard and, in particular, in the Bay of Fundy.Shimizu (2) reported antiviral activity in three glycosidic substances (probably asterosaponins) from A. forbesi, and Goldsmith and Carlson (3) demonstrated that analgesic, hypotensive, and anti-inflammatory properties were associated with asterosaponins from this species. An antimitotic substance from the ovaries of'A. forbesi reported by Heilbrunn et al. (4) in 1954 was possibly an asterosaponin.Previous chemical studies on A . forbesi have been limited to the structures of the steroidal products of hydrolysis of its asterosaponin mixture. Shimizu (5) isolated 3P,6a-dihydroxy5a-pregn-9(11)-en-20-one (asterone) from the hydrolysate, and ApSimon et al. (6) reported asterone and the corresponding trio1 (asterogenol) from hydrolysed asterosaponin from the same organism.A methanol extract of specimens collected in Passamaquoddy Bay (August 1984) was chromatographed on an Amberlite XAD2 column to yield a crude saponin-containing fraction, the chlorofonn/methanol (6:4) soluble portion of which was subjected to preparative layer chromatography (plc) on silica gel to provide three fractions, which, after further purification on reversed phase plc and high performance liquid chromatography (hplc), yielded four pure saponins that were designated forbesides A, B, C, and D (-2:3: 1:l). This paper deals with the structures of A and B, which were deduced entirely by nuclear magnetic resonance methods.One-dimensional nuclear magnetic resonance (nmr) methods have yielded limited information for the determination of complete structure and stereochemistry of complex saponins. No systematic method for complete structural analysis has resulted, largely because of the severe resolution problems encountered, since most oligosaccharide proton signals fall within a 2-ppm chemical shift range and substantial overlap of multiplets occurs.In view of this, it has generally been necessary to resort to permethylation and hydrolysis experiments to determine the sugar sequence and the sites of interglycosidic linkage (7-1 1).The whole process is somewhat tedious and also consumes saponin, which is often very difficult to separate and purify and may be better employed in biological evaluation experiments.These difficulties can be overcome by the use of modem high field 2D nmr experiments. The critical requirement is the unambiguous assignment of 'H resonances, especially in the oligosaccharide portion. We have used two-dimensional (2D) nuclear pr...