Arthur S. Perlin

High-field, 13C-N.M.R. spectroscopy of β-d-glucans, amylopectin, and glycogen

Abstract 13 C-N.m.r. spectra of several d -glucans, recorded at 100 MHz, have afforded information about structural detail not previously accessible at lower frequencies. Spectra of (1→4)- and (1→3)-linked β- d -glucans of oats, barley, and lichenan of Iceland moss demonstrate the presence, in each, of three, non-equivalent, 4- O -substituted residues, that the ratio of these to 3- O -substituted residues averages 2.4–2.5, and hence that the patterns of repeating sequences in the three polymers are essentially the same. A comparison of wheat amylopectin with a minor, amylopectin-like fraction of wheat starch indicates that they are strictly analogous in basic structure, and differ only in that the average length of branches in the minor fraction is 20–25% shorter. By combining the advantages of high-field operation with the use of dimethyl sulfoxide as solvent, a large number of distinctive resonances have been observed, representing end-units, branch-points, and residues adjacent to branch-points. Accordingly, these signals are even more prominent in the spectrum of glycogen, reflecting the higher incidence of branching in this polymer. At 100 MHz, the excellent resolution and sensitivity afforded constitute a potent basis for assessing the purity of polysaccharide preparations, as illustrated with wheat amylose and barley β- d -glucans.

Evidence for a (1→4)-linked 4-O-(α-L-idopyranosyluronic acid 2-sulfate)-(2-deoxy-2-sulfoamino-D-glucopyranosyl 6-sulfate) sequence in heparin : Long-range H-H coupling in 4-deoxy-hex-4-enopyranosides

Abstract A disaccharide produced from heparin by Flavobacterium heparinum is shown to be an elimination product having the probable structure 1 ; namely, 4- O -(4-deoxy-α- L - threo -hex-4-enopyranosyluronic acid 2-sulfate)-(2-deoxy-2-sulfoamino- D -glucopyranose 6-sulfate). Since 1 accounts for about three-quarters of the heparin used, its formation, taken together with other evidence available, indicates that the heparin molecule is composed largely of a repeating sequence of (1→4)-linked 4- O -(α- L -idopyranosyluronic acid 2-sulfate)-(2-deoxy-2-sulfoamino-α- D -glucopyranosyl 6-sulfate) biose residues. The anomeric configuration of the unsaturated uronic acid residue of 1 was deduced primarily from the fact that the olefinic 4-proton is long-range coupled with H-2 of the same residue. Thus, H-4-H-2 coupling appears to be general in 4-deoxy-α- L - threo -hex-4-enopyranose derivatives, but does not occur in the β-anomers. Among the compounds examined were unsaturated oligosaccharides from chondroitin 4-sulfate and pectin, and some monosaccharide 4-deoxy-hex-4-enopyranosides. Synthesis of the anomeric methyl 2,3-di- O -acetyl-4-deoxy-6- aldehydo - L - threo -hex-enodialdo-1,5-pyranosides by methyl sulfoxide oxidation-base-catalyzed elimination is described.

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.

Synthesis and 13C N.M.R. spectrum of D-glucose-3-d. bond-polarization differences between the anomers of D-glucose

Abstract D -Glucose- 3-d ( 1 ) has been synthesized by reactions involving, as the key step, conversion of 1,2:5,6-di- O -isoproylidene-3- O -tosyl-α- D -allofuranose- 3-d into 3- O - bensoyl-1,2:5,6-di- O -isopropylidene-α- D -glucofuranose- 3-d . Compound 1 , together with D -glucose- 5-d and D -glucose 5,6,6-d 3 , have facilitated the assignment of signals in the 13 C and 1 H n.m.r. spectra of αβ- D -glucose; the 220-MHz p.m.r. spectrum of the latter is described. A comparison of 13 C and 1 H chemical shifts for α- and β- D -glucose, and of the corresponding hydroxyl-proton reonances, shows that there is a widespread difference between the anomers in the polarization of their various bonds. That is, inversion of the anomeric hydroxyl group from an equatorial to an axial orientation is associated with a uniform increase in shielding of 13 C, derease in shielding of the appended proton, and increase in shielding of the hydroxyl proton, at all positions except 4 and 6, which remain virtually unaffected.

Catalysis by mercuric ion of reactions of glycals with water

Abstract In the presence of mercuric sulfate, 3,4,6-tri- O -acetyl- d -glucal ( 4 ), dissolved in 1,4-dioxane-dilute sulfuric acid at room temperature, is rapidly and quantitatively converted into 4,6-di- O -acetyl-2,3-dideoxy- aldelhydo d - erythro - trans -hex-2-enose ( 8 ). With acetone as the organic component of the solvent, this product is accompanied by the 5,6-di- O -acetyl isomer ( 10 ). The corresponding, α,β-unsaturated aldehydes ( 12 and 13 ; 15 ) are formed in an analogous way from 3,4,6-tri- O -acetyl- d -galactal ( 11 ) and 3,4-di- O -acetyl- d -arabinal ( 14 ). Similarly, instead of hydration, d -glucal ( 1 ) and d -galactal undergo elimination catalyzed by mercuric ion and acid to yield 2-( d - glycero -1,2-dihydroxyethyl)furan ( 3 ) as the sole product. Possible mechanisms for these transformations are discussed.

Infrared absorption and raman scattering of sulfate groups of heparin and related glycosaminoglycans in aqueous solution

Abstract The i.r. spectra for aqueous solutions of sulfated glycosaminoglycans and model compounds in the transmittance “window” region of the solvent (1400-950 cm −1 ) are dominated by the strong and complex absorption centered at ∼1230 cm −1 and associated with the antisymmetric stretching vibrations of the SO groups. Primary and secondary O -sulfate groups absorb at somewhat higher frequencies (1260-1200 cm −1 ) than N -sulfates (∼1185 cm −1 ). Each sulfate band lends itself to quantitative applications, especially within a given class of sulfated polysaccharide. Laser-Raman spectra of heparin and model compounds have been obtained in aqueous solution and in the solid state. The most-prominent Raman peak (at ∼1060 cm −1 ) is attributable to the symmetrical vibration of the SO groups, with N -sulfates emitting at somewhat lower frequencies (∼1040 cm −1 ) than O -sulfates. The Raman pattern in the 950-800 cm −1 region (currently used in the i.r. for distinguishing between types of sulfate groups) also involves vibrations that are not localized only in the COS bonds.

A 13C-n.m.r. spectral study of chondroitin sulfates A, B, and C: evidence of heterogeneity

Chondroitin sulfates A, B, and C produce well-resolved 13C-n.m.r. spectra which allow for a more complete characterization than that available from their p.m.r. spectra. The 13C data fully support earlier evidence as to the main structural features of these glycosaminoglycans, but they also show that many chondroitin preparations are substantially heterogeneous in composition. Thus, spectra of chondroitin A and C have the appearance of composites representative of both types of polymer: specimens of A may contain 25% of the C-type of structural sequence, and C,30% of the A-type of sequence; 10-20% of unidentified constituents, including a residue bearing a 6-sulfate group, are present in the specimens of chondroitin B. Chemical-shift and 1JC-H values found for the L-iduronic acid residues of chondroitin B, as well as the effect of gadolinium nitrate on the relaxation properties of its 13C nuclei, indicate that this moiety possesses the alpha configuration and favors the 1C4(L) conformation. Corresponding data for the acetamidodeoxy-D-galactose and D-glucuronic acid residues of the chondroitins are consistent with the beta-anomeric configuration and 4C1(D) conformation in all instances.

13C-n.m.r. spectroscopy of cellulose ethers

Abstract Characteristics of the 13 C-n.m.r. spectra of cellulose ethers (methyl, carboxymethyl, and hydroxyethyl) have been examined at 22.6 MHz. Partial depolymerization with acid or cellulase proved to be a requisite preliminary step. Strong deshielding of 13 C nuclei bearing alkoxyl groups was clearly evident in these spectra, which permitted an assessment of the degree of substitution at individual positions of the d -glucose residues. Better resolved spectra, and more-detailed structural analyses, were afforded by complete hydrolysates of the polymers. The findings are wholly consistent with data obtained for these derivatives by other methods, showing that the reactivities of the hydroxyl groups of cellulose are OH-2>OH-6 ⪢ OH-3. It is also shown that reducing-end residues liberated during enzymic hydrolysis of the cellulose derivatives are not substituted at the 2-position.

Synthesis of glycosyl halides and glycosides via 1-O-sulfonyl derivatives

Abstract The reaction of an aldose derivative containing a free anomeric hydroxyl group with trifluoromethanesulfonic anhydride or methanesulfonic anhydride, in the presence of halide ion and s -collidine, furnishes a glycosyl halide; if an alcohol is then introduced, glycoside synthesis is effected in an overall, “one-pot” reaction. Several α- d -glucopyranosides, including disaccharides, have been prepared in high yield by using 2,3,4,6-tetra- O -benzyl- d -glucose as the aldose, and generating the corresponding glycosyl bromide(s) in situ . As a halide-exchange step is incorporated in the reaction sequence, orthoacetate formation was favored in reactions of 2,3,4,6-tetra- O -acetyl- d -glucose, such as occurs with per- O -acetylglycosyl halides. Methanesulfonic anhydride promotes glycosidation or orthoester formation in the absence of halide ion, as well as in its presence, whereas formation of an intermediate glycosyl halide appears to be necessary in order to moderate the more vigorous reactions of the trifluoro derivative. The analogous reaction of methanesulfonyl chloride with an aldose provides a ready route to glycosyl chlorides. Under the conditions employed for these various syntheses, acid-sensitive protecting groups may be used, including cyclic and acyclic acetals and O -trityl substituents.

Methyl α- and β-D-idopyranosiduronic acids synthesis and conformational analysis

Abstract Methyl α- and β- D -idopyranosiduronic acid have been synthesized by catalytic oxidation of the corresponding D -idopyranosides, and each has been characterized as a crystalline brucinium salt. Proton and 13 C magnetic resonance data indicate that, in solution, the α anomer adopts a conformation represented mainly by the C1 ( D ) form and the β anomer favors this conformation almost exclusively. Possible relationships between these findings and the conformation of α- L -idopyranosyluronic acid residues in heparin and dermatan sulfate are discussed, as well as the optical rotations of these polymers.