Methyl pentoses

Hydrangea paniculata Sieb. (bark) D-galactose, L-arabinose and methyl pentose 78... 

Gelidium pacificum Okam. Chrondus ocellatus Holmes D-galactose D-galactose, methyl pentose, 2-keto-hexonic acid (7), sulfate, D- and irerythrose 111... 

Allylic esters of fluoroacetic acid were used in the Ireland silyl ketene acetal rearrangement procedures by the Welch group at Albany [164]. For example, Eq. (53) shows a highly diastereoselective rearrangement which formed an early stage in syntheses of 2,3-dideoxy-2-fluoro-3-C-methyl pentose nucleosides [165, 166]. If a stereoselective synthesis of a functionalised monofluorocompound is... 

Figure 5.1.7 shows the ESI-MS/MS spectra of the compounds solasteroside A and ruberoside E. Both compounds have the molecular mass, m/z 1223, in deuterated solvents and show identical MS/MS fragments at m/z 1075, 927, 779 and 645, corresponding to the sequential loss of three methyl pentoses and one pentose. Nevertheless, mass spectrometry yields the information... 

In the hydrolysis of the methyl pentosan, the methyl group remains attached to the pentose ring, thus leading to methyl pentose, but it must be noted that the methyl group can be attached at the 5-position or at the 1-position of the pentose ring. Thus, when the methyl pentose is dehydrated by acid catalysis, the result is either 5-methyl furfural or furyl methyl... 

Figure 38. The Formation of 5-Methyl Furfural from 5-Methyl Pentose.

Figure 39. The Formation of Furyl Methyl Ketone from 1-Methyl Pentose.

These observations of demethylation and 2-furaldehyde formation led ineluctably to the conclusion that lime-water had caused these methylated pentoses to form (by probable loss of 1 mole of methanol per mole) substances which were exceedingly easily converted, by further loss of 2 moles of methanol per mole, to 2-furaldehyde in acid solution. Accordingly, Lewis proposed the following scheme [shown with 2,3,4-tri-O-methyl-D-xylose (XIX) as the starting substance] for this sequence of reactions. 

D-ribose and L-rhamnose, a methylated pentose, are present at concentrations below 100 mg/1. 

The metabolic-synthesis of 4-amino sugars is widespread in the microorganisms and takes place via CDP-sugars. In many cases the sugars involved are 6-deoxy hexoses (i.e. C-methyl pentoses) and again the initial formation of a 4-oxo-sugar intermediate is required. The formation of 6-deoxy-4-oxo-sugars is discussed below. 

Neutral monosaccharides, uronic acids, hexosa-mines, and sialic (neurominic acids) are identified and determined by specific colorimetric reactions. The principle behind the techniques rests on the condensation of the degraded products of the neutral monosaccharides (hexose, pentose and methyl pentose) by sulfuric acid with anthrone, cysteine hydrochloride, orcinol, and phenol reagents. Uronic acids may be determined by colorimetric and manometric procedures. While sialic acids are determined after chemical/enzymatic hydrolysis, gravimetric and Van-Soest detergent based methods are used to determine cellulose, hemicellulose, and fiber. 

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