D-Xylopyranosyl

Certain cereal grains, especiaUy wheat and rye, contain hemicelluloselike arabinoxylans [9040-27-1], commonly caUed pentosans. Wheat flour pentosans are divided into two types water-soluble and water-insoluble arabinoxylans, which respectively constitute - 1.1 1.6% and 0.4—0.7% of the total flour. These polysaccharides have functional roles in dough development and baking performance. The water-soluble wheat-flour arabinoxylans consist of a (1 — 4)-linked chain of P-D-xylopyranosyl units substituted at 0-2 and/or 0-3 with single-unit a-L-arabinofuranosyl units. Preparations from each source consist of a family of molecules of various molecular weights and xyl ara ratios. 

Equilibrium constant not known in solution ctystalline form has all chlorines axial. TH-O-acetyl-p-D-xylopyranosyl chloride... 

Compounds in which conformational, rather than configurational, equilibria are influenced by the anomeric effect are depicted in entries 4—6. Single-crystal X-ray dilfiaction studies have unambiguously established that all the chlorine atoms of trans, cis, ira j-2,3,5,6-tetrachloro-l,4-dioxane occupy axial sites in the crystal. Each chlorine in die molecule is bonded to an anomeric carbon and is subject to the anomeric effect. Equally striking is the observation that all the substituents of the tri-0-acetyl-/ -D-xylopyranosyl chloride shown in entry 5 are in the axial orientation in solution. Here, no special crystal packing forces can be invoked to rationalize the preferred conformation. The anomeric effect of a single chlorine is sufficient to drive the equilibrium in favor of the conformation that puts the three acetoxy groups in axial positions. 

C -p-D-Xylopyranosyl-L-serine [(Xyl-)Ser] Glycosides can be named as substituents by the methods of 2-Carb-31. 

Glycosyl fluorides have also been prepared by treatment of per-O-acyl or partially 0-acylated sugars with hydrogen fluoride [liquid HF (for example, see Refs. 38 and 39) or HF in acetic acid or dichloromethane], as exemplified by 2,3,4-tri-O-benzyl-a-D-xylopyranosyl (18), a-D-glucopyranosyl (19), tetra-O-pivaloyl-a-D-glucopyranosyl (20), and 2,3,5-tri-O-acetyl-D-xylofur-anosyl fluorides (21) (see Table 1). Frequently, HF treatment - leads to... 

The Noyori procedure was applied to a total synthesis of baiyunoside, a sweet principle, using 2,3,4-tri-<9-benzyl-D-xylopyranosyl fluoride (18 see Table 1), and a synthesis of glycotriosyl ceramide. A model experiment for the synthesis, using 18, showed a solvent dependence for the a ratio of the products. In this case, the use of acetonitrile, oxolane, or ether gave the a anomer (1,2-a.v), and the use of toluene or hexane gave the P anomer (1,2-trans), preponderantly. 

D-glucopyranoside congeners, (Z)-3-hexenyl 6-0-(3-D-xylopyranosyl-(3-D-glucopyranoside (74), (Z)-3-hexenyl 6-0-a-L-arabinopyranosyl-(3-D-glucopyra-noside (75) and (Z)-3-hexenyl 6-0-a-L-rhamnopyranosyl-(3-D-glucopyranoside... 

Synthesis of n-hexyl fi-D-glucopyranoside (7) and n-hexyl 6-0-f3-D-xylopyranosyl-P-D-glucopyranoside (109)... 

Golden root (Roseroot, R. rosea L., Crassulaceae) has been used for a long time as a resource in Chinese traditional medicine to enhance the body s resistance against fatigue and to extend human life. Rosavin (121) was isolated as one of the chemical constituents of R. rosea by Kurkin et al. and 4-methoxycinnamyl 6-G-(a-L-arabinopyranosyl)-(3-D-glucopyranoside (122) and cinnamyl 6-0-(p-D-xylopyranosyl)-(3-D-glucopyranoside (123) were also isolated from an aqueous methanol extract of R. rosea by Ari et al. (Fig. 27). 

Lindberg and associates103 105 applied the Koenigs - Knorr procedure to the synthesis, from 138 and 139, of 3-0-/ -D-xylopyranosyl-L-serine103 (140), which constitutes the carbohydrate-protein linkage in such pro-... 

Tri-O-acetyl-a-D-xylopyranosyl bromide106 (138) and N-tosyl-L-serine methyl ester107 (139) were condensed in the presence of Drierite and silver oxide, and then the O-acetyl and methyl ester groups were removed by treatment with sodium hydroxide, and the N-tosyl group by means of sodium in liquid ammonia, to give 140. Synthesis of this compound has also been described by other workers108-110 and the a-D an-omer by Brendel and Davidson.108... 

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