Monosaccharides dihydroxyacetone

All the monosaccharides except dihydroxyacetone contain one or more asymmetric (chiral) carbon atoms and thus occur in optically active isomeric forms (pp. 17-19). The simplest aldose, glyceraldehyde, contains one chiral center (the middle carbon atom) and therefore has two different optical isomers, or enantiomers (Fig. 7-2). 

The simplest carbohydrates, sometimes referred to as monosaccharides, or sugars, are either polyhydroxyaldehydes (aldoses) or polyhydroxyketones (ketoses). They can be derived from polyalcohols (polyols) by oxidation of one carbinol group to a carbonyl group. For example, the simple three-carbon triol, glycerol, can be converted either to the aldotriose, glyceraldehyde, or to the ketotriose, dihydroxyacetone, by loss of two hydrogens (fig. 12.1). 

Fructose 1,6-biphosphate aldolase from rabbit muscle in nature reversibly catalyzes the addition of dihydroxyacetone phosphate (DHAP) to D-glyceraldehyde 3-phosphate. The tolerance of this DHAP-dependent enzyme towards various aldehyde acceptors made it a versatile tool in the synthesis of monosaccharides and sugar analogs [188], but also of alkaloids [189] and other natural products. For example, the enzyme-mediated aldol reaction of DHAP and an aldehyde is a key step in the total synthesis of the microbial elicitor (—)-syringolide 2 (Fig. 35a) [190]. 

Fig. 11-17 The conversion of the monosaccharide fructose into the glycolytic intermediates dihydroxyacetone phosphate and glyceraldehyde 3-phosphate.

All carbohydrates have common names. The simplest aldehyde, glyceraldehyde, and the simplest ketone, dihydroxyacetone, are the only monosaccharides whose names do not end in the suffix -ose. ( The prefix D- is explained in Section 27.2C.)... 

The family of D-ketoses, shown in Figure 27.5, is formed from dihydroxyacetone by adding a new carbon (bonded to H and OH) between C2 and C3. Having a carbonyl group at C2 decreases the number of stereogenic centers in these monosaccharides, so that there are only four D-ketohexoses. The most common naturally occurring ketose is D-fructose. 

Monosaccharides, the simplest carbohydrates, are aldehydes or ketones that have two or more hydroxyl groups the empirical formula of many is (C-H20) , literally a "carbon hydrate." Monosaccharides are important fuel molecules as well as building blocks for nucleic acids. The smallest monosaccharides, for which n = 3, are dihydroxyacetone and eland 1-glyceraldehyde. 

Enzymes turned out to be very helpful in the de novo synthesis of certain monosaccharides. Generally, two chiral carbonyl compounds are combined in an aldol-type reaction. In carbohydrate metabolism, aldolases catalyze the condensation of dihydroxyacetone phosphate (DHAP) and aldehydes to higher sugar components. To date, about thirty aldolases have been classified, but only... 

Monosaccharides are identified by their carbonyl functional group (aldehyde or ketone) and by the number of carbon atoms they contain. The simplest monosaccharides are the two trioses glyceraldehyde (an aldotriose) and dihydroxyacetone (aketotriose). Four-, five-, six-, and seven-carbon-containing monosaccharides are called tet-roses, pentoses, hexoses, and heptoses, respectively. Structures of some monosaccharides are shown in Figure 9-1. All monosaccharides, with the exception of dihydroxyacetone, contain at least one asymmetrical or chiral carbon atom, and therefore two or more stereoisomers are... 

Polyhydroxy Aldehydes and Ketones Carbohydrates are a class of organic biopolymers which consist of polyhydroxy aldehydes and ketones, their derivatives and polymers. Other terms for carbohydrates include sugars and saccharides. A single monomer unit is called a monosaccharide several units are referred to as an oligosaccharide larger polymers are called polysaccharides. The simplest carbohydrates are glyceraldehyde and dihydroxyacetone. 

Monosaccharides can exist as aldehydes or ketones and are called aldoses or ketoses, respectively. For example, (Figure 9.3) shows the structures of glyceraldehyde, an aldo-triose, and dihydroxyacetone, a keto-triose. Glyceraldehyde and dihydroxyacetone have the same atomic composition, but differ only in the position of the hydrogens and double bonds. Moreover, they can interconvert via an enediol intermediate (Figure 9.4). When the structures of molecules are related in these ways, the molecules are called tautomers. 

Dihydroxyacetone phosphate-dependent aldolases (DHAP-aldolases) have been used widely for preparative synthesis of monosaccharides and sugar analogs (Fessner and Walter 1997 Wymer and Toone 2000 Silvestri et al. 2003). Among them, RAMA RhuA and FucA from E. coli are the most available aldolases, especially the former which was one of the first to be commercialized (Fessner and Walter 1997 Takayama et al. 1997). In many of the chemo-enzymatic strategies they are involved, the biocatalytic aldol addition to the configuration of the newly stereogenic centers is fixed by the enzyme. However, pertinent examples have been reported in which... 

A comprehensive review (260 refs.) on the synthesis of carbohydrates from noncarbohydrate sources covers the use of benzene-derived diols and products of Sharpless asymmetric oxidation as starting materials, Dodoni s thiazole and Vogel s naked sugar approaches, as well as the application of enzyme-catalysed aldol condensations. The preparation of monosaccharides by enzyme-catalysed aldol condensations is also discussed in a review on recent advances in the chemoenzymic synthesis of carbohydrates and carbohydrate mimetics, in parts of reviews on the formation of carbon-carbon bonds by enzymic asymmetric synthesis and on carbohydrate-mediated biochemical recognition processes as potential targets for drug development, as well as in connection with the introduction of three Aldol Reaction Kits that provide dihydroxyacetone phosphate-dependent aldolases (27 refs.). A further review deals with the synthesis of carbohydrates by application of the nitrile oxide 1,3-dipolar cycloaddition (13 refs.). ... 

The simplest monosaccharides are the compounds glyceraldehyde and dihydroxyacetone (see the following structures). Of these two compounds, only glyceraldehyde contains a chirality center. 

Trloses yceraldehyde and dihydroxyacetone. They contain 3 C-atoms and are the simplest monosaccharides Their phosphates are important metabolic intermediates (see Those phosphates). 

PoYSER and West [503] and Harris, Luscombe and Poyser [274] determined the relative activities of different carbohydrates injected locally in inhibiting the increase in vascular permeability caused by intradermally injected ovomucoid, dextran, dextrin, yeast mannan and z5miosan. With the exception of dihydroxyacetone, galactose, lactose, rhamnose and ribose many hexoses, pentoses, tricses and disaccharides were active. In a further study, Poyser and West [504] elucidated the structural and stereospecific features of topically administered sugars for potent inhibitory activity against intradermal responses to dextran. The monosaccharides most active as inhibitors contained the... 

Glyceraldehyde is a common name the lUPAC name for this monosaccharide is 2,3-dihydroxypropanal. Similarly, dihydroxyacetone is a common name its lUPAC name is 1,3-dihydroxypropanone. The common names for these and other monosaccharides, however, are so firmly rooted in the literature of organic chemistry and biochemistry that they are used almost exclusively to refer to these compounds. Therefore, throughout our discussions of the chemistry and biochemistry of carbohydrates, we use the names most common in the literature of chemistry and biochemistry. 

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