Xylose methylation

DL-Dihydrostreptose and its ribo isomer were similarly obtained. Birch reduction of 2-methyl-3-furoic acid, followed by addition of methanol, bromination, and dehydrobromination, gave 402 as a mixture of the isomers. Hydroxylation of 402 with osmium tetraoxide-so-dium chlorate, and subsequent treatment with acetone-sulfuric acid afforded three isomeric acetals (403-405). The structures of these compounds were assigned on the basis of their H-n.m.r. spectra. In addition, the relationship between 403 and 404 was established by hydrolysis and reglycosidation. The methyl esters 403-405 were quantitatively reduced to the corresponding alcohols. The mixture of alcohols obtained from 403 and 404 was converted into crystalline 5-deoxy-3-C-(hydroxymethyl)-l,2-0-isopropylidene-a-DL-ribofuran-ose (406), which was compared directly with a sample prepared from D-xylose. Methyl 5-deox y-3-C-(hydroxy methyl)-2,3-O-isopropy lidene-/3-DL-lyxofuranoside (407), obtained by reduction of 405 with lithium aluminum hydride, was hydrolyzed with dilute hydrochloric acid, to give a,/3-DL-dihydrostreptose.2,ifi... 

Elimination of multiple peaks may also be achieved by conversion of a sugar into the dithioacetal or the nitrile. The suitability of the former type of derivative for g.l.c. appears to have been explored only in a model study on xylose methyl ethers. Lance and J. K. N. Jones also demonstrated that the acetylated nitriles derived from diese ethers give sharp, single peaks, and permit 2- and 3-0-methyl-i>-xylose to be distinguished from each other, a resolution not achieved by using alditol acetates. Nitriles have been used by Bouhours and Cheshire to demonstrate the occurrence of the same two xylose ethers in peat, and by Bacon and Cheshire to prove the natural existence of 3-O-methyl-D-galactose in leaves. 

The Oxidation of Some Carbohydrate Derivatives using Acetic Anhydride - Methyl Sulphoxide Mixtures and the Pfitzner-Moffat Reagent. Facile Synthesis of 3-Acetamido-3-deoxy-D-glucose and 3-Amino-3-deoxy-D-xylose, J. S. Brimacombe, J. G. H. Bryan, A. Husain, M. Stacey, and M. S. 

The NMR spectrum of the dry sample showed broad unresolved peaks that correspond to a typical mixture of 4-O-methyl-D-glucuronic acid, L-arabinose and D-xylose, and proteins (Oliveira et al., 2010) (Figure 5). 

D-Xylose, which is one of the most abundant sugars in plant polysaccharides, is a rare component of bacterial polysaccharides. It is found in the LPS of Type 1 Neisseria gonorrhoeae strain" GC 6. L-Xylose and its 3-methyI ether are components of the LPS of Pseudomonas maltophila strain NCTC 10257, and are j -pyranosidic. The d- and L-sugars, and different methyl ethers of these, have also been found in the LPS of some photosynthetic bacteria."... 

D-Xylose (b) D-Glucose (c) D-Galactose (d) Methyl D-Xyloside (e) Methyl D-Glucoside and (f) Methyl D-Galactoside. (Redrawn from Refs. 4 and 5.)... 

Spectrum (- -), and Fragment Circular Dichroism Spectra (—) for the Corresponding d-Xylose and the Addition of a Hydroxymethyl Group at C-S (a) a-o-Glucose (b) /3-D-Glucose (c) Methyl a-o-Glucopyranoside and (d) Methyl /8-D-Glucopyranoside. (Redrawn from Ref. 

Fig. 7.—Predicted (- -) and Fragment (—) Circular Dichroism Spectra /3-L-Arabinose Calculated from (a) a-D-Xylose, and (b) Methyl /3-L-Aiabinoside a-L-Arabinose Calculated from (c) j3-D-Xylose, and (d) Average Calculated for /3-L-Arabinose Methyl a-L-Arabinoside Calculated from (e) Methyl /3-D-Xyloside, and (f) Methyl /3-L-Arabinoside. (Redrawn from Ref. 6.)...

Analysis of the MHR by high-performance size-exclusion chromatography (HPSEC) revealed three distinct populations to be present, which were isolated on a preparative scale. The composition of the populations differed mainly in the relative proportion of rhamnose, xylose and the amount of methyl esters and acetyl groups, although the general characteristics were rather similar (Table 2). However, degradation studies with RGase showed that, in contrast... 

The glycosyl-residue compositions of the three purified fractions (Table 1) were very similar with a predominance of galacturonic acid, rhamnose and arabinose. The presence in the three purified fractions of the rare monosaccharides characteristic of RG-II (e.g. 2-( -methyl-L-fucose, 2-O-methyl-D-xylose, apiose, Kdo, Dha and aceric acid) was confirmed by GC-CIMS analysis. The molar ratios corresponded approximately to the known structure of the RG-II molecule (Figure 1) and to previously published data for RG-II from sycamore [26], rice [4], arabidospis leaves [8] and Pectinol [12]. 

RG-n, Rhamnogalacturonan II Kdo, 3-deoxy-D-manno-octulosonic acid Dha, 3-deoxy-D-/yxo-heptulosaric acid aceric acid, 3-C- carboxy-5-deoxy-L-xylose TMS, per-0-trimethylsilylated methyl glycosides. 

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