Xylose preparation

Originally obtained as a sirup, the carefully purified 2,3-dimethyl-D-xylose prepared from esparto xylan4(b) and pear cell-wall xylan6 has now been obtained crystalline.6 16 ... 

Enzymic syntheses are considered next. Xylitol is a substrate for sheep-liver L-iditol dehydrogenase, a NAD-linked enzyme. 1-Deoxy-D-xylitol, prepared by Raney nickel reduction of D-xylose diethyl dithioacetal in a 27% overall yield from D-xylose, was also reported31 to be a substrate, although with a higher Km and lower Vmax. The product was assumed to be l-deoxy-D-f/ireo-pentulose because of the appearance of a yellowish fluorescent spot when a chromatogram was sprayed with acidic 3,5-aminobenzoic acid, resembling that formed from 1 -deoxyfructose. There was no more-rigorous characterization. 

Triazoline imino sugar derivatives 297 that are prospective glycosidase inhibitors have been prepared as single diastereomers in high yield via an lAOC reaction of in situ generated azido alkene 296 (Eq. 32) [78]. m-CPBA oxidation of the dithioacetal groups in the 0-acetylated 5-azido-5-deoxydibenzyl dithio-acetal of o-xylose or D-ribose 294 to the bis-sulfone 295, followed by loss of HOAc between C-1 and C-2 provided the lAOC precursor 296. 

From L-arabinose, carba-sugars of the a-D-gluco and h-altro types were prepared from D-arabinose, carba-a-L-mannopyranose from D-ribose, that of the fi-L-manno modification from D-xylose, those of the -L-gluco and a-D-altro forms and, from D-glucose, those of the P-L-allo a-L-... 

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... 

SPS could be degraded by the cruder, aaikalus preparation Pectinex Ultra-SP, giving a product consisting mostly of the monomeric sugars xylose, galactose, fucose, arabinose and... 

Xylose-rich pectic polysaccharide was extracted from defatted and protein-free cell wall preparation (5) using HCl solution (pH 1.6) at 85° C for 4 h. The extract was adjusted to pH 5.0 with ammonia, concentrated on a rotary evaporator under reduced pressure at 40°C, and precipitated with 5 volumes of 96% ethanol. After washing twice with 80% ethanol and drying in an air circulated oven at 40°C for 2 h, the pellet was ledissolved with distilled water and then precipitated with 4 vols 96% ethanol. Before the pellet was gently ground, the precipitated pellet was washed twice with 70% ethanol and dried at 40 ° in an air circulated oven for 16 h. The resultant white powder was labelled "xylose-rich pectic polysaccharide" and stored in a refrigerator. 

The nomenclature adopted in the designation of the analogs of L-ascorbic acid is based for convenience upon the name of the sugar from which the osone was prepared. For example, D-xylose (XVIII)... 

C. Moreau, R. Durand, D. Peyron, J. Duhamet, and P. Rivalier, Selective preparation of furfural from xylose over microporous solid acid catalysts, Ind. Crops Prod., 7 (1998) 95-99. 

Weidenhagen46 obtained L-xylosone in 60% yield on oxidizing L-xylose by his modification of the copper acetate method.46 This method was employed by Salomon, Bums and King63 in the preparation of C14-labeled ascorbic acid and by Hamilton and Smith69 in the preparation of isoascorbic acid. 

Pursuing the synthesis of angelmicin B, Mootoo prepared the tricyclic intermediate fragment 93 from D-xylose derivative 90 (Fig. 31).46... 

The D-xyloketose was prepared by autoclaving at 120° a 10% solution of D-xylose for 45 minutes in the presence of 0.2 M phosphate buffer, pH 6.8. Most of the unreacted D-xylose was separated by crystallization, leaving a sirup consisting chiefly of D-xyloketose. 

Relatively pure xylan isolated from the holocellulose of aspen (Populus) wood is said to contain 85% of xylose residues.78 One of the characteristic properties of xylan is its ease of hydrolysis. Because it hydrolyzes much more readily than cellulose, mild acid treatment may be employed to bring about preferential hydrolysis of xylan from plant material. Xylose is ordinarily prepared in the laboratory by direct sulfuric acid hydrolysis of the native xylan in ground corn cobs.74 Hydrolysis in hydrochloric acid proceeds rapidly, but decomposition to furfural also occurs to some extent.76 A commercial method for the production of D-xylose from cottonseed hulls76 and straw77 and from corn cobs17 78 has been described. 

The availability, in gram quantities, of the fluorinated carbohydrates thus far synthesized has also made possible their use as starting materials for the synthesis of other analogs and intermediates for example, the preparation of 3,5-dideoxy-3,5-difluoro-D-xylose from 3-deoxy-3-fluoro-D-xylose,88 which is itself preparable from 3-deoxy-3-fluoro-l,2-0-isopropylidene-a-D-glucofuranose. Electrolytic oxidation of 3-deoxy-3-fluoro-D-glucose afforded, after treatment with an acidic... 

Both L-gulose12,13 (9) and D-gulose (d-9, see Ref. 10) have been oxidized with bromine to L- or D-gulonic acid, respectively (see Scheme 1). L-Gulose (9) has been prepared by a number of different procedures. Schemes 2 and 3 show two early procedures that afforded L-gu-lose, but the overall yields were low (<30%). In the first procedure12 (see Scheme 2), D-glucitol (10) was converted into 2,4-O-benzylidene-D-glucitol (11), which was then oxidized with lead tetraacetate to 2,4-O-benzylidene-L-xylose (12). Nitromethane was added to 12 to afford crystalline 13 in 50% yield. Hydrolysis of 13 provided 14, which was treated with sodium hydroxide, followed by sulfuric acid, to afford 9, which was isolated in 52% yield as the 2-benzyl-2-phenylhydrazone. 

Methods for the preparation of L-idonic acid and L-xylose were discussed in Ref. 1. 

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