Chemistry of xylopyranosides

Abstract

Xylose is one of the few monosaccharidic building blocks that are used by mammalian cells. In comparison with other monosaccharides, xylose is rather unusual and, so far, only found in two different mammalian structures, i.e. in the Notch receptor and as the linker between protein and glycosaminoglycan (GAG) chains in proteoglycans. Interestingly, simple soluble xylopyranosides can not only initiate the biosynthesis of soluble GAG chains but also function as inhibitors of important enzymes in the biosynthesis of proteoglycans. Furthermore, xylose is a major constituent of hemicellulosic xylans and thus one of the most abundant carbohydrates on Earth. Altogether, this has spurred a strong interest in xylose chemistry. The scope of this review is to describe synthesis of xylopyranosyl donors, as well as protective group chemistry, modifications, and conformational analysis of xylose.

Xylose: absorption, fermentation, and post-absorptive metabolism in the pig

“…Monogastric animals do not have endogenous enzymes capable of degrading xylan to release monomeric xylose for absorption in the small intestine; consequently, there was little need to develop efficient mechanisms for xylose metabolism. Furthermore, xylose is a rare carbohydrate in mammalian cells and so far is only found as a link between the protein and glycosaminoglycan chains of some proteoglycans and in the Notch receptor [ 1 ]. The Notch receptor is part of a highly conserved core signaling pathway required for various cell fate decisions at multiple stages of development [ 70 ].…”

“…The Notch receptor is part of a highly conserved core signaling pathway required for various cell fate decisions at multiple stages of development [ 70 ]. However, UDP-xylose, the activated precursor for xylose involvement in these structures, is synthesized from UDP-glucose and is not derived from dietary xylose sources [ 1 ]. As a result, the absence of an efficient or well-conserved pathway for xylose metabolism comes as no surprise because there has been no need.…”

“…Xylose, as a major constituent of plant xylan polymers, is one of the most abundant carbohydrates on the earth, second only to glucose [ 1 , 2 ]. This abundant pentose sugar, along with arabinose, makes up a majority of the hemicellulose backbone as arabinoxylan in the cell walls of cereal grains fed to pigs [ 3 ].…”

“…Cereal arabinoxylans (also known as pentosans) are composed of a linear β-1,4-linked xylose backbone which may be substituted at the 2’-OH and/or 3’-OH, generally with single arabinose residues (Fig. 1 ) [ 1 ]. In contrast to α-linked starch, which is hydrolyzed to glucose by endogenous enzymes, β-linkages in arabinoxylan and other non-starch polysaccharides (NSP) must be degraded by microbial enzymes.…”

A selective and mild glycosylation method of natural phenolic alcohols

“…The lack of selectivity at room temperature can be explained by a higher thermodynamic stability of the α-xylopyranosides compared to the corresponding β-xylopyranosides. Apparently, anomerisation of the kinetically formed β-anomer easily takes place under mild reaction conditions at ambient temperature [ 40 ], but it is suppressed by decreased temperature in combination with an appropriate promoter (ZnO–I 2 ). Moreover, this new promoter was successfully applied to the reactions of the corresponding acceptor and four other glycosyl bromides, i.e., D-glucosyl ( Table 1 , entries 4 and 9), D-galactosyl ( Table 1 , entry 13), lactosyl ( Table 1 , entry 17) and L-arabinosyl ( Table 1 , entry 19).…”