Osides

The numbering scheme used for nucleosides maintains the independence of the two structural units The pyrimidine or purine is numbered m the usual way So is the car bohydrate except that a prime symbol ( ) follows each locant Thus adenosine is a nude oside of D nbose and 2 deoxyadenosine is a nucleoside of 2 deoxy d ribose... 

Treatment of methyl 2-azido-4,6-0-benzylidene-2-deoxy-a-D-altro-pyranoside (128) (42) with 121 followed by refluxing and processing afforded a chloro derivative as a sirup in 70% yield (46, 49). Reduction of this product with an excess of Raney-nickel in methanol containing acetic anhydride afforded a crystalline product, m.p. 179°C., which is formulated as the d-manno analog 131. The actual product is most likely methyl azido-4,6-0-benzylidene-3-chloro-2,3-dideodxy - a - d - mannopyran-oside (130) resulting from attack of chloride ion at C-3 with inversion of configuration in the intermediate 129. Had the chlorination proceeded... 

Glycosides are named by first citing the alkyl group and then replacing the -ose ending of the sugar with -oside. Like all acetals, glycosides are stable to neutral water. They aren t in equilibrium with an open-chain form, and they don t show mutarotation. They can, however, be converted back to the free monosaccharide by hydrolysis with aqueous acid (Section 19.10). 

The names of the individual compounds of this type are formed by replacing (a) the -ose of the systematic or trivial name of the aldose by -uronic acid , (b) the -oside of the name of the glycoside by -osiduronic acid or (c) the -osyl of the name of the glycosyl group by -osy luronic acid . The carbon atom of the (potential) aldehydic carbonyl group (not that of the carboxy group as in normal systematic nomenclature [13,14]) is numbered 1 (see 2-Carb-2.1, note 1). 

Before 1983, branched-chain sugars had not been found in bacterial polysaccharides, but there are now five examples belonging to this class. The LPS from Coxiella burned phase I contains both 6-deoxy-3-C-methyl-L-gulose (L-virenose) as pyranoside (12) and 3-C-(hydroxymethyl)-L-lyxose as furan-oside (13). Another 6-deoxy-3-C-methylhexose, having the manno configuration, is a component of the Nitrobacter hamburgiensis 0-antigen. ... 

As we have seen above, anthocyanins comprise an aglycone fraction commonly known as anthocyanidin and a frequently acylated osidic substituent. This characteristic leads to two different approaches for the analysis of these pigments (1) a direct anthocyanin analysis without a hydrolysis stage requiring identification of a number of molecules (several hundreds in the plant kingdom) or (2) an analysis of the anthocyanidin fraction only after hydrolysis of the anthocyanins present in the medium. 

P212121 Z = 4 D, = 1.413 R = 0.041 for 3,165 intensities. Thepyran-oside conformation is 4C1, with Q = 58 pm, 6 = 5°. The primary alcohol group is gauche-trans. The linkage-bond torsion-angles are O-5-C-l-0-1 -C-7 = — 87°, C-1-0-1-C-7-0-7 = — 67°. The two rings of the monoterpene moiety are inclined to each other, with C-C-C-C torsion-angles, about the common bond, of 149 and —97°. 

M. Quirasco, A. Lopez-Munguia, V. Pelenc, M. Remaud, F. Paul, and P. Monsan, Enzymatic production of glucooligosaccharides containing a-(1 —> 2) osidic bonds. Potential application in nutrition, Ann. NY Acad. Sci., 750 (1995) 317-320. 

A one-pot, high-yielding synthesis of 1,2,3,4,6-penta-(9-acetyl-/ -D-( 1 -2H)glucopyranose (127) from tetra-O-acetyl-D-glucono-1,5-lactone (126) has been reported (172). Sodium borodeuteride reduction of 126, followed by in situ acetylation, gave the readily isolated and crystalline 127. The crystalline 2,4-dinitrophenyl 2,3,4,6-tetra-0-acetyl-/ -D-(l-2H)glucopyran-oside (128) was subsequently obtained from 127. 

The study of monosaccharides subjected to conditions of methanolysis is considered for two reasons. First, the decomposition of monosaccharides is indicative of the decomposition of monosaccharides liberated during methanolysis second, the ratio of methyl glycosides of a particular standard monosaccharide is the same for the same monosaccharide released during methanolysis (for a particular set of methanolysis conditions), provided that the concentration of sugars is relatively low. Up to four methyl glycosides (the a and )8 anomers of the pyranoside and furan-oside forms) of a particular monosaccharide may be formed the acyclic dimethyl acetal is an additional possibility. The ratios of methyl glycosides of 10 monosaccharides subjected to methanolysis with M hydrogen chloride for 24 h at 80° has been reported. Similar information is also available in another study."... 

The cyclic hemiacetal and hemiketal forms of monosaccharides are capable of reacting with an alcohol to form acetals and ketals (see Section 7.2). The acetal or ketal product is termed a glycoside, and the non-carbohydrate portion is referred to as an aglycone. In the nomenclature of glycosides we replace the suffix -ose in the sugar with -oside. Simple glycosides may be synthesized by treating an alcoholic solution of the monosaccharide with an acidic catalyst, but the reaction mixture usually then contains a mixture of products. This is an accepted problem with many carbohydrate reactions it is often difficult to carry out selective transformations because of their multifunctional nature. 

Reaction of glucose with methanol and gaseous HCl yields four acetal products, the a- and P-pyran-osides and a- and P-furanosides, which may be separated. The pyranosides are the predominant components, and the major product is the a-pyran-oside. This is perhaps unexpected, in that the P-pyranoside has ah its substituents equatorial. 

Toxicity. Atractyloside, a diterpenoid glycoside that occurs naturally in plants, may be present at levels as high as 600 mg/kg of dried plant material. Gonsumption of plants containing atractyloside or carboxyatractyl-oside has caused fatal renal proximal tubule necrosis and/or centrilobular hepatic necrosis in man and farm animals. Although pure atractyloside and crude plant extracts disrupt carbohydrate homeostasis and induce similar pathophysiological lesions in the kidney and liver, it is also possible that the toxicity of atractyloside may be confounded by the presence of other natural constituents in plants. Atractyloside competitively inhibits the adenine nucleoside... 

Fluorination of a nucleoside concerns either the base or the furanose moiety. This chapter mostly focuses on nucleosides that are fluorinated on the furanose osidic moiety. A short summary of nucleosides that are fluorinated on the base moiety is given at the end of this section, and a more extensive overview is given in Chapter 7 (enzyme inhibitors). 

A.3 Synthesis from Non-Osidic Precursors Some total syntheses of trifluoromethylated sugars have been described, starting from non-acidic precursors, fluorinated or not. 

Figure 6.38 Synthesis of trifluoromethyl sugars through trifluoromethylation of non-osidic...

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