L -Arabinose

The reaction is used for the chain extension of aldoses in the synthesis of new or unusual sugars In this case the starting material l arabinose is an abundant natural product and possesses the correct configurations at its three chirality centers for elaboration to the relatively rare l enantiomers of glucose and mannose After cyanohydrin formation the cyano groups are converted to aldehyde functions by hydrogenation m aqueous solution Under these conditions —C=N is reduced to —CH=NH and hydrolyzes rapidly to —CH=0 Use of a poisoned palladium on barium sulfate catalyst prevents further reduction to the alditols... 

Similarly l gluconomtrile has been reduced to l glucose its yield was 26% from L arabinose)... 

Gum ghatti is the calcium and magnesium salt of a complex polysaccharide which contains L-arabinose, D-galactose, D-mannose, and D-xylose and D-glucuronic acid (48) and has a molecular weight of approximately 12,000. On dispersion in water, gum ghatti forms viscous solutions of viscosity intermediate between those of gum arabic and gum karaya. These dispersions have emulsification and adhesive properties equivalent to or superior to those described for gum arabic. 

A second approach for the synthesis of 6-formylpterin (23) involves the condensation of triamin opyrimidinone (10) with 5-deoxy-L-arabinose (26). The key diol is obtained in four steps starting from compound (10). Cleavage of the diol side chain is achieved either with periodate (39) or with lead(TV) (40) to furnish 6-formylpterin (23) in 45% overall yield. 

Most free pentoses, hexoses, and heptoses occur primarily in less strained pyranose rings, but the furanose ring is also quite important. The furanose ring is formed in the same way as the pyranose ring and also occurs in a and P forms. This is demonstrated with L-arabinose, which is commonly found in polysaccharides in the form of a-L-arabinofuranosyl units (see Fig. 2). 

The L-arabino-(4-0-methyl-D-glucurono)xylans are found in softwoods and annual plants. The L-arabinose is present primarily as a-L-arabinofuranosyl units, although P-L-arabinopyranosyl units may also be present. In either case, the arabinosyl units are often, but not always, present as single-unit side chains, as are the uronic acid units. 

B-L-Arabinose (natural) [87-72-9] M 150.1, m 158 , [a]o +104 (c 4, H2O after 24h). Crystd slowly twice from 80% aq EtOH, then dried under vacuum over P2O5. 

L-Monosaccharides do exist in nature, serving a few relatively specialized roles. L-Galactose is a constituent of certain polysaccharides, and L-arabinose is a constituent of bacterial cell walls. 

Method B (one-pot procedure)-. 5 g (33 mmol) of L-arabinose. 12 mL of ethanol and 4mL (36.7 mmol) of bcnzylaminc arc heated on a steam bath for 5 to 10 min to give a clear solution. After cooling, 2.5 mL of anliyd hydrogen cyanide are added. Spontaneous crystallization of the product begins within a few minutes. After cooling for 2 h with an ice-bath, the product is isolated by filtration and washed with ethanol yield 7.0-7.5g (79-85%) nip 129-131 C after recrystallization from ethanol mp 130-132 C. 

In 1947, L-rhamnose was first recognized by Stacey as a constituent of Pneumococcus Type II specific polysaccharide. This finding was confirmed, in 1952, by Kabat et al. and in 1955 again by Stacey when 2,4- and 2,5-di-O-methyl-L-rhamnose were synthesized and the former was shown to be identical with a di-O-methylrhamnose, obtained by hydrolysis of the methylated polysaccharide. This result indicated a pyranose ring structure for the rhamnose units in the polysaccharide. Announcement of the identification of D-arabinofuranose as a constituent of a polysaccharide from M. tuberculosis aroused considerable interest. The L-enantiomer had been found extensively in polysaccharides, but reports of the natural occurrence of D-arabinose had been comparatively rare. To have available reference compounds for comparison with degradation products of polysaccharides, syntheses of derivatives (particularly methyl ethers) of both d- and L-arabinose were reported in 1947. 

Such names as bacillosamine for 2,4-diamino-2,4,6-trideoxy-D-glucose and garosamine for 3-deoxy-4-C-methyl-3-methylamino-L-arabinose are not recommended, as they imply replacement of OH by NH2 in a nonexistent parent sugar. 

As an example for continuous process design, 2-keto-3-deoxy-D lycero-D-galacto-nonosouate (KDN) (S) has been produced on a 100-g scale from D-mannose and pyruvate using a pilot-scale EMR at a space-time yield of 375 gl d and an overall crystallized yield of 75% (Figure 10.6) [47]. Similarly, L-KDO (6) can be synthesized from L-arabinose [48]. 

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). 

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-... 

Five pentoses, namely, D-ribose, d- and L-arabinose, and D- and L-xylose, have been found in hydrolyzates of bacterial polysaccharides. D-Riboseisthe most common of these, and is a component of different LPS, capsular polysaccharides, and teichoic acid type of polymers. In all these polymers, it occurs as the /I-furanosyl group or residue. 

D-Arabinose occurs in arabinogalactans and arabinomannans elaborated by Mycobacterium species. When this had been determined, for example, for some arabinomannans, it was found to be furanosidic and a-linked. The arabinogalactan from Mycobacterium tuberculosis,however, contains both a- and y -linked D-arabinofuranosyl residues. It also occurs in the a-form in the LPS from Pseudomonas maltophila strain NCIB 9204. l-Arabinose is a component of the LPS from the purple, sulfur bacterium Chromatium vinosum. °... 

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