Of D-mannose

D (+) Galactose is a constituent of numerous polysaccharides It is best obtained by acid hydrolysis of lactose (milk sugar) a disaccharide of d glucose and d galactose L (—) Galactose also occurs naturally and can be prepared by hydrolysis of flaxseed gum and agar The principal source of d (+) mannose is hydrolysis of the polysaccharide of the ivory nut a large nut like seed obtained from a South American palm... 

It IS not possible to tell by inspection whether the a or p pyranose form of a par ticular carbohydrate predominates at equilibrium As just described the p pyranose form IS the major species present m an aqueous solution of d glucose whereas the a pyranose form predominates m a solution of d mannose (Problem 25 8) The relative abundance of a and p pyranose forms m solution depends on two factors The first is solvation of the anomeric hydroxyl group An equatorial OH is less crowded and better solvated by water than an axial one This effect stabilizes the p pyranose form m aqueous solution The other factor called the anomeric effect, involves an electronic interaction between the nng oxygen and the anomeric substituent and preferentially stabilizes the axial OH of the a pyranose form Because the two effects operate m different directions but are com parable m magnitude m aqueous solution the a pyranose form is more abundant for some carbohydrates and the p pyranose form for others... 

Treatment of D mannose with methanol in the presence of an acid catalyst yields four iso menc products having the molecular formula C7H14O6 What are these four products ... 

StmcturaHy, guar gum comprises a straight chain of D-mannose with a D-galactose side chain on approximately every other mannose unit the ratio of mannose to galactose is 2 1 (53). Guar gum has a molecular weight on the order of 220,000 (54). 

The reversible reactions are initiated by an equilibrium between neutral and ionized forms of the monosaccharides (see Fig. 6). The oxyanion at the anomeric carbon weakens the ring C-O bond and allows mutarotation and isomerization via an acyclic enediol intermediate. This reaction is responsible for the sometimes reported occurrence of D-mannose in alkaline mixtures of sucrose and invert sugar, the three reducing sugars are in equilibrium via the enediol intermediate. The mechanism of isomerization, known as the Lobry de Bruyn-... 

Walden inversion on C2 has occurred in one of these sequences if in the first, then chitose, chitonic acid and isosaccharic acid have the configuration of D-mannose if in the second, i. e., in the deamination of 2-amino-D-gluconic acid, then chitaric acid and epi-isosaccharic acid are... 

Varying proportions of D-mannose and of the rarely occurring D-form of arabinose are obtained76 on hydrolysis of the polysaccharide of tubercle bacillus (Mycobacterium tuberculosis) strain H-37, whereas the poly-... 

Aspinall, G. 0., The Methyl Ethers of Hexuronie Acids, IX, 131-148 Aspinall, G. 0., The Methyl Ethers of D-Mannose, VIII, 217-230... 

Di(2,3,4,6-tetra-0-acetyl-b-D-mannopyranosyl)-l,2,5-oxadiazole 2-oxide has been synthesized from D-mannose by a route, involving as the key step, dimerization of mannopyranosyl nitrile oxide. Three methods have been used for the generation of the nitrile oxide isocyanate-mediated dehydration of nitro-methylmannose derivative, treatment of aldoxime with aqueous hypochlorite and base-induced dehydrochlorination of hydroximoyl chloride. D-gluco, D-galacto, D-xylo and L-fucopyranosyl analogs has been prepared similarly. The structure of D-mannose-derived 1,2,5-oxadiazole 2-oxide has been established by X-ray crystallography (478). 

The conversion of D-mannose (20) into L-gulose (9) was reported by Evans and Parrish,15 and is shown in Scheme 4. D-Mannose (20) was converted into 21 by condensation with acetone, methanol, and 2,2-di-methoxypropane in the presence of an acid, and mild hydrolysis of 21 afforded 22. Methanesulfonylation of 22 provided 23, which was transformed into 24 with sodium acetate in refluxing N,N-dimethyl-formamide. The overall yield of 24 from D-mannose was >50%. Base hydrolysis, followed by acid hydrolysis, afforded L-gulose (9). 

Hodosi, G. Kovac, P., Manipulation of free carbohydrates via stannylene acetals. Preparation of beta-per-O-acyl derivatives of D-mannose, L-rhamnose, 6-0-trityl-D-talose, andD-lyxose. Carbohydr. Res. 1997,303, 239-243. 

These properties of the enzyme are good for the production of D-mannose from P-mannan in the presence of the P-mannanase described above. 

Removal of the a-hydrogen in o-glucose leads to enolization (we have omitted the enolate anion in the mechanism). Reversal of this process allows epimerization at C-2, since the enol function is planar, and a proton can be acquired from either face, giving D-mannose as well as o-glucose. Alternatively, we can get isomerization to o-fmctose. This is because the intermediate enol is actually an enediol restoration of the carbonyl function can, therefore, provide either a C-1 carbonyl or a C-2 carbonyl. The equilibrium mixture using dilute aqueous sodium hydroxide at room temperature consists mainly of o-glucose and o-fructose, with smaller amounts of D-mannose. The same mixture would be obtained... 

De Armas and co-workers [67] chose the epoxide 122, a derivative of D-mannose, as their starting material for what they claim a formal synthesis of (+)-preussin (Scheme 30, PMB=para-methoxybenzyl). In 14 steps and 8%... 

This enzyme [EC 5.3.1.7] catalyzes the interconversion of D-mannose and D-fructose. Both D-lyxose and D-rham-nose can act as substrates as well. 

This enzyme [EC S.4.2.8] catalyzes the interconversion of D-mannose 1-phosphate and D-mannose 6-phosphate. Either D-mannose 1,6-bisphosphate or D-glucose 1,6-bis-phosphate can act as the cofactor. 

M. Rizzotto, M. Frascaroli, S. Signorella, and L. Sala, Oxidation of D-mannose and L-rhamnose by Cr (VI) in aqueous acetic acid medium, Polyhedron, 15 (1996) 1517-1523. 

The oxime of D-lyxose has not been prepared, but L-rhamnose oxime (XX) with ithe same spatial configuration about carbon atoms 2, 3 and 4 reacts in an open-chain form when submitted to mild acetylation, and gives only the nitrile this reactivity is confirmed when the oxime is submitted to mild propionylation, for only the hexapropionyl-aWe%do-L-rhamnose oxime is produced and that in high yield. As already mentioned, the oximes of D-mannose (XXI), and D-gala-L- reawno-heptose (XXII),having the same configuration as rhamnose about carbon atoms 2, 3 and 4, react in a similar manner. 

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