Monosaccharides reaction

Monosaccharide Stereoisomers Cyclic Structure of Monosaccharides Reactions of Monosaccharides Important Monosaccharides... 

A similar rationale can be made for the 5-membered intermediate. The glucose derivative dehydrates to a 4-fiiranone. 4-Furanone is a relatively labile substance llich can be found only in monosaccharide reaction mixtures. In the fiiranoid structure which is derived from disaccharides, the bound sugar prevents this reaction and the molecule stabilizes itself by forming a 3-friranone (Figure 4). Recently we were able to isolate 3-fiiranone (7) and establish its structure by spectroscopic data (P). 

In NDP-sugar biosynthesis an initial glycosyl phosphate is formed through kinase-mediated phosphorylation of a monosaccharide. Reaction of the glycosyl phosphate with a nucleoside triphosphate (NTP) is then catalyzed by the corre-... 

Mono- and di saccharides are colourless solids or sjrrupy liquids, which are freely soluble in water, practically insoluble in ether and other organic solvents, and neutral in reaction. Polysaccharides possess similar properties, but are generally insoluble in water because of their high molecular weights. Both poly- and di-saccharides are converted into monosaccharides upon hydrolysis. 

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

Enantiomerically pure tetroses, pentoses, and hexoses have been synthesized by the following reaction sequence (A.W.M. Lee, 1982 S.Y. Ko, 1983), which is useful as a repetitive two-carbon hotnologi-.ation in total syntheses of higher monosaccharides and other polyhydroxy compounds (1) Wittig reaction of a protected hydroxy aldehyde with (triphenylphosphor-... 

When the 2-hydroxy group of a monosaccharide reacts with (diethylamino)sulfur trifluoride (DAST), quantitative and stereoselective rearrangements are observed (K.C Nico-laou, 1986). This reaction may simultaneously introduce fluorine to C-1 and a new oxygen, sulfur, or nitrogen residue to C-2 with inversion of configuration. 

Isomerization. Both the carbonyl group and the adjacent hydroxyl group are involved in isomerization of monosaccharides. This reaction can be catalyzed by either a base or an enzyme. By this reaction, an aldose is converted into another aldose and a ketose, and a ketose is converted into two... 

In a similar manner, ketones can react with alcohols to form hemiketals. The analogous intramolecular reaction of a ketose sugar such as fructose yields a cyclic hemiketal (Figure 7.6). The five-membered ring thus formed is reminiscent of furan and is referred to as a furanose. The cyclic pyranose and fura-nose forms are the preferred structures for monosaccharides in aqueous solution. At equilibrium, the linear aldehyde or ketone structure is only a minor component of the mixture (generally much less than 1%). 

Starch is stored in plant cells in the form of granules in the stroma of plas-tids (plant cell organelles) of two types chloroplasts, in which photosynthesis takes place, and amyloplasts, plastids that are specialized starch accumulation bodies. When starch is to be mobilized and used by the plant that stored it, it must be broken down into its component monosaccharides. Starch is split into its monosaccharide elements by stepwise phosphorolytic cleavage of glucose units, a reaction catalyzed by starch phosphorylase (Figure 7.23). This is formally an a(1 4)-glucan phosphorylase reaction, and at each step, the prod-... 

Thomson I Click Organic Interactive to predict products from reactions of simple monosaccharides. 

We saw in Section 25.6 that reaction of a monosaccharide with an alcohol yields a glycoside in which the anomeric -OH group is replaced by an -OR substituent. If the alcohol is itself a sugar, the glycosidic product is a disaccharide. 

Monosaccharides normally exist as cyclic hemiacetals rather than as open-chain aldehydes or ketones. The hemiacetal linkage results from reaction of the carbonyl group with an —OH group three or four carbon atoms away. A... 

Galactose, one of the eight essential monosaccharides (Section 25.7), is biosynthesized from UDP-glucose by galactose 4-epimerase, where UDP = uridylyl diphosphate (a ribonucleotide diphosphate Section 28.1). The enzyme requires NAD+ for activity (Section 17.7), but it is not a stoichiometric reactant. and NADH is not a final reaction product. Propose a mechanism. 

Glucosamine, one of the eight essential monosaccharides (Section 25.7), is biosjmthesized as its 6-phosphate derivative from fructose 6-phosphate by-reaction with ammonia. Propose a mechanism. 

Acetic anhydride, electrostatic potential map of, 791 reaction with alcohols, 807 reaction with amines, 807 reaction with monosaccharides, 988... 

---