D-Arabinose, 3,5-di-O-methyl

When the effect of an organic solvent is combined with partial meth-ylation (see Section VI,1), the proportion of furanoses becomes most significant 2,3-di-O-methyl-D-galactose in dimethyl sulfoxide contains 38%, 2,3-di-O-methyl-D-arabinose 65%, and 2,3-di-O-methyl-D-altrose 80% of the furanose forms.87... 

Analysis of Freshly Cyclized 2,3-di-O-methyl-D-arabinose. The system 3,4-di-O-methyl-D-mannitol (2)—sodium metaperiodate meets the foregoing specifications. 3,4-Di-O-methylmannitol was rapidly cleaved by periodate to 2,3-di-O-methyl-D-arabinose (3), which is resistant to further oxidation (19). We prepared the crystalline / -anomer of this sugar (the a-anomer had previously been crystallized (20)) and showed that on a suitable GLC column the trimethylsilyl derivatives of the four ring forms could be separated (Figure 9). The individual peaks were characterized by preparative GLC and mass spectrometry. This allowed the analysis of the mixtures of anomeric forms generated in kinetic experiments (see p. 34). 

A melting point of 82°-83°C and [ ]D20 —85° - —100° were reported for 2,3-di-O-methyl-D-arabinose by Verheijden and Stoffyn (20). These authors preparation must have been largely or wholly an a-anomer, whereas ours is preponderantly ft. In view of the rarity of crystalline furanoses, it is presumed to be the / -pyranose, and in the PMR spectrum run at 0°C on a sample freshly dissolved in DoO the anomeric proton gave a signal, with the appearance of an unresolved doublet, at t 4.50. This chemical shift and a small value of Jit2, would be expected for H-l of a / -arabinopyranose in the 1C conformation. 

Similar products (but having R = /3-D-galactopyranosyl) were obtained from octa-O-acetyllactobiononitrile56 in 25% aqueous ammonia. The furanose structure of the monoamido derivative 61 (and that of its analog N-acetyl-3-0-/3-D-galactopyranosyl-D-arabinofuranosyl-amine56) was ascertained by methylation, hydrolysis, and identification of 2,5-di-O-methyl-D-arabinose. 

A series of polysaccharides have been isolated from the sea grass, Phyllos-padix torreyi, which are unusual in containing residues of o-apiose (2—28 One of these polysaccharides had the composition, L-rhamnose, L-arabinose, D-xylose, D-apiose, D-galactose, and D-mannuronic acid in the molar ratio 4 1 5 2 4 9. Of the D-apiose residues 80 % were oxidized by periodate and the major neutral sugar residues found in the hydrolysate of the methylated polysaccharide were 2,3,5-tri-O-methyl-L-arabinose, 2,5-di-O-methyl-L-arabinose, 3,4-di-O-methyl-L-rhamnose, 2,3-di-O-methyl-D-xylose, 2,3,6-tri-0-methyl-D-galactose, and 2,4-di-O-methyl-D-galactose in the ratio 1 1 6 6 3 3. 

U-Anhydrosugar derivatives which have a bicyclic skeleton corresponding to have been shown to undergo polymerization. 1,U-Anhydro-2,3-di-O-methyl-L-arabinose (l6) and 1,U-anhydro-2,3,6-tri-O-methyl-D-galactose (ij) yielded under the influence of Lewis acid initiators amorphous polymers containing both furanose and pyranose rings. 

In agreement with the earlier findings,126 approximately equimolecular proportions of 2,3,4,6-tetra-, 2,3,4-tri-, and 2,4-di-O-methyl-D-galacto-pyranose were isolated as the main products of hydrolysis of methylated e-galactan, but, in addition, small proportions of 2,3,4-tri-O-methyl-L-arabinose, 2,5-di-O-methyl-L-arabinose, and 2,4,6-tri- and 2-mono-0-methyl-D-galactose were found. Evidence in favor of partial structure XLI for the galactan framework was obtained by application to the polysac-... 

Mild, acid hydrolysis of European-larch arabinogalactan results in the formation of 3-0-/3-L-arabinopyranosyl-L-arabinose (XXXIX). 26 Although this disaccharide has been isolated as an acid-reversion product from L-arab-inose,131 it is accompanied under these conditions by two other arabinose-containing disaccharides, neither of which was detected in the larch polysaccharide hydrolyzate. Since hydrolysis of methylated -galactan gave approximately equimolar proportions of 2,3,4-tri-O-methyl-L-arabinose and 2,5-di-O-methyl-n-arabinose, traces of 2,3,5-tri-O-methyl-L-arabinose, and no mono-O-methyl-L-arabinose, it is clear that the L-arabinose units must arise from an arabinogalactan rather than from an arabinan, and that the majority of these must be present in 3-0-/3-L-arabinopyranosyl-L-arabino-furanose side-chains (XLV) linked, in some way as yet unknown, to the framework of D-galactose units (XLI). 

During the elucidation of the structure of mannosidostreptomycin by methylation. Fried and Stavely isolated two derivatives of a dimethyl ether of iV-methyl-L-glucosamine. In order to compare their physical constants with those of a known compound in the n-series. Fried and Walz prepared derivatives of 2-deoxy-3,6-di-0-methyl-2-methylamino-n-glucose. The addition of methylamine and hydrogen cyanide to 2,5-di-0-methyl-D-arabinose (prepared by the periodate oxidation of 3,6-di-O-methyl-D-glucose) was followed by hydrolysis, and jdelded a mixture of a dextro- and a levo-rotatory acid. The dextrorotatory product was con-... 

An L-arabino-D-galactan, in 2% yield, has been isolated from the fruits of Dillenia indica. From the results of partial acid hydrolysis and methylation analyses, when 2,6-di-O-methyl-D-galactose, 2,3,6-tri-O-methyl-D-galactose, 2,3,4,6-tetra-(9-methyl-D-galactose, and 2,3,5-tri-O-methyl-L-arabinose residues in the molar ratio 7 3 1 8 were identified, it was concluded that the polysaccharide was a (1- 4)-j3-D-galactan that contained L-arabinofuranose residues linked at 0-3 of some of the D-galactose residues in the main chain. 

S O-a B-Galdctopyranosyl-L-arabinose. Amorphous, [a] +152° (water) phenylosazone, m.p. 240°C. obtained by partial hydrolysis of Acacia cyanophylla gum 119). Hydrolysis of the methylated disaccharide gives 2,3,4,6-tetra-O-methyl-D-galactose and 2,4-di-O-methyl-L-arabinose. 

The capsular polysaccharide of Diplococcus pneumoniae has been shown to possess a linear pentasaccharide repeating unit containing residues of d-glucopyranosyluronic acid, o-galactofuranose, and L-rhamnopyranose (1 2 2). ° The presence of 2,3-linked D-galactofuranosyl residues in the polysaccharide of Klebsiella K41 has been confirmed by the characterization of 5,6-di-O-methyl-D-galactofuranose as a product in the methylation of the polysaccharide, and of the presence of L-arabinose in the Smith degradation... 

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