Arabinose based

Bouquillon S (2011) D-Xylose and L-arabinose-based surfactants synthesis, reactivity and physico-chemical properties. C R Chim 114 716-725... 

The most useftil scaffolds would have modified functional groups such as -NH2, -SH, at C-5 and C-3 . Our laboratory is developing a new family of arabinose-based scaffolds with these functional groups at the above positions (Scheme 11). 

With tln(IV) chloride, benzylated glycofuranosyl acetates give anomeric carbonium ions which cause Friedel Crafts alkylation of 0 -2 benzyl substituents. Scheme 19 illustrates the reaction in the D-rlbose series the corresponding L-arabinose-based product was produced in 60 yield. 

Although the term nucleoside was once limited to the compounds in Table 28.2 and a few others, cunent use is more permissive. Pyrimidine derivatives of D-arabinose, for exfflnple, occur in the free state in certain sponges and are called spongonticleosides. The powerful antiviral drug ribavirin, used to treat hepatitis C and Lassa fever, is a synthetic nucleoside analog in which the base, rather than being a pyrimidine or purine, is a triazole. 

Ginsenan S-IIA, a polysaccharide fraction from the roots of P. ginseng is a potent inducer of IL-8 production by human monocytes and THP-1 cells, and this induction is accompanied by increased IL-8 mRNA expression. The polysaccharide appears from the structural feature to be a mixture of arabino-galactan type I and type II, based on the presence of 1,3-, 1,6-, 1,3,6-, 1,4-, and 1,4,6-galactose units as well as terminal arabinose and 1,5-, 1,3,5-, and 1,2,5-linked units. It also contains 1,4,6-linked glucose units that together with the 1,2,5-linked arabinose units are different from the units found in other ginseng polysaccharides and may thus be of importance for the activity [64]. 

Black pepper contains several polysaccharides of which one shows a strong effect as an immune enhancer based on the fact that the polymer is an anti-complementary polysaccharide. The polysaccharide has an Mw of approx. 40 kD. It is composed basically of rhamnose, arabinose, galactose and galac-turonic acid, and shows a high binding capacity for the Yariv reagent. This indicates that the side chain of the polymer is of the arabinogalactan type II, which is a common structure for several polysaccharides with an effect on the complement system [70]. 

Most of the structural and biochemical work related to KDO is based on the estimation of the compound or its derivatives by the periodate-thiobarbituric acid (TBA) assay in its various modifications. Indeed, KDO (see Fig. 3) was discovered9 through the formation of a characteristic, purple, TBA chromophore (Xmax 549 nm) from its 8-phosphate (2), which is the product of the condensation of D-arabinose 5-phosphate with enolpyruvate phosphate, catalyzed by 3-deoxy-8-0-phosphonooctulosonate synthetase (EC 4.1.2.16) (see Scheme 1 and Section V,2). 

Charon and Szabo17 demonstrated that chromophore 4 may be produced to a significant extent from a 5-O-substituted derivative of KDO (which does not contain a free diol grouping at C-4-C-5). These authors synthesized 3-deoxy-5-0-methyl-2-octulosonic acid (7 configuration at C-5-C-7, arabino at C-4, unknown) by the Comforth reaction18,19 from 4-0-formyl-2-0-methyl-D-arabinose (see Scheme 4 and Section IV,1). Compound 7 gave a millimolar extinction coefficient of 13 in the TBA assay (as compared to 92 5 for KDO). Based on this result, Charon and Szabo17 formulated for the TBA reaction of 5-0-... 

The transformation of L-arabinose (58) to lactone 57 was based on a route developed by Marquez and Sharma [51] Selective protection of the primary hydroxy group with TBDPSCl and oxidation of the lactol moiety with bromine afforded lactone 59. Subsequent selective deoxygenation a to the carbonyl group proceeded under Barton-McCombie conditions providing lactone 57 in 21% yield (Scheme 14). 

Figure 6.56 Saccharide-based epoxidizing organocatalysts derived from D-fructose (192 and 193) and L-arabinose (194).

Table 9 Influence of the nature and concentration of the base, and the reaction time on arabinose (15) conversion and the selectivity in water...

In 2008, the research group of Singh reported the synthesis of imidazohum-based ionic liquids in which the chiral moiety was constituted of a pentofuranoside unit [79]. The 2,3,5-tri-O-benzyl-D-arabinofuranose 45, easily prepared from commercial D-arabinose in 75% yield following known procedures, was transformed... 

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