Monosaccharides tetroses

The simple sugars or monosaccharides are polyhydroxy aldehydes or ketones, and belong to Solubility Group II. They are termed tetroses, pentoses, hexoses. etc. according to the number of carbon atoms in the long chain constituting the molecule, and aldoses or ketoses if they are aldehydes or ketones. Most of the monosaccharides that occur in nature are pentoses and hexoses. 

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-... 

Monosaccharides are those carbohydrates that cannot be hydrolyzed into simpler carbohydrates They may be classified as trioses, tetroses, pentoses, hex-oses, or heptoses, depending upon the number of carbon atoms and as aldoses or ketoses depending upon whether they have an aldehyde or ketone group. Examples are listed in Table 13-1. 

As demonstrated by MacMillan and coworkers, a-oxygenated aldehydes are very good reaction partners in the aldehyde-aldehyde crossed-aldol reaction. The products are tetroses, and one further aldol step affords a range of hexoses, i.e. differentially protected monosaccharides, in a two-step synthesis (Scheme 20) [203],... 

Depending on the number of carbon atoms present, monosaccharides are classihed as triose, tetrose, pentose or hexose, containing three, four, five or six carbon atoms, respectively. Glucose is a hexose as it contains six carbon atoms. Sometimes, monosaccharides are classified more precisely to denote the functional group as well as the number of carbon atoms. For example, glucose can be classified as an aldohexose, as it contains six carbon atoms as well as an aldehyde group. 

Monosaccharides with four, five, six, and seven carbon atoms in their backbones are called, respectively, tetroses, pentoses, hexoses, and heptoses. There are aldoses and ketoses of each of these chain lengths ... 

To be consistent with the relationship between a mono- and a disaccharide, some authorities do not term a tetrose or a pentose a monosaccharide. By combining the aid- and ket- prefixes, certain compounds then may be called aldohcxoses. such as glucose and galactose, or ketohexoses. such as fructose and sorbose. 

Monosaccharides, also called simple sugars, are classified by the number of carbon atoms (triose, tetrose, pentose, and so on) and by the nature of the carbonyl group (aldose or ketose). 

The resulting furfurals then can undergo a series of complicated polymerization reactions. Hodge (8) reported that these reactions include hydrolytic fission, fission of 2-ketoses, dehydration of triose, dismutation of biose, trioses, and tetroses, self- and cross-condensations of aldehydes and ketones, reversion of aldoses and ketoses to various oligosaccharides, dimerization of monosaccharides, cyclodehydration of aldoses followed by polymerization, and finally, the enolization and dehydration of formed oligosaccharides. 

Tetrose (Section 27.2) A monosaccharide containing four carbons. 

Monosaccharides carbohydrates that cannot be hydrolyzed (split, with the addition of HjO) into simpler carbohydrates. Typically, they contain 3,4,5, or 6 carbons (trioses, tetroses, pentoses, hexoses). Glucose (fig. 3.1) as well as fructose and galactose are examples of hexoses. 

There are many publications and comprehensive handbooks on the thin-layer chromatography (TLC) of carbohydrates (e.g., Refs. 1 and 2). The reason is their great importance in life science and the great diversity of cases monosaccharide, disaccharide, trisaccharide, oligosaccharide, polysaccharide, aldose, ke-tose, triose, tetrose, pentose, hexose, as well as reducing and nonreducing sugars. In addition, when extracted from natural products or produced by fermentation, carbohydrates are accompanied by many impurities. That is why separation methods are used predominantly for their analysis. 

Carbohydrates form a class of compounds of carbon with hydrogen and oxygen. The name comes from the chemical formulas of these compounds, which can be written C (H20) suggesting a hydrate of carbon. Simple sugars, or monosaccharides, are carbohydrates with the chemical formula C H2 0 . Sugars with three, four, five, and six carbon atoms are called trioses, tetroses, pentoses, and hexoses, respectively. 

Lower monosaccharides, i.e., aldo- and keto-bioses, -trioses, and -tetroses, do not exist naturally in a free state. Glyceroaldehyde and hydroxyacetone in phospho-rylated forms are the products of alcoholic fermentation and glycolytic sequence. Erythrose and erythrulose also appear in phosphorylated forms in the pentose cycle of glucose, while ketopentose-ribulose can be found as its phosphate ester (Table 5.1). 

Monosaccharides bearing an aldehyde are known as aldoses, whereas those bearing a ketone are known as ketoses. Sugars bearing three, four, five and six carbon atoms are known as trioses, tetroses, pentoses and hexoses, respectively. 

The forms of glucose in aqueous solution are quite complex and small proportions exist as furanose structures. These arise from the reaction between the OH group at C-4 and the aldehyde group in aldoses. The five-membered ring system is quite stable but pyranose forms are favoured over furanose forms by most monosaccharides notable exceptions are the ketohexose fructose and the aldopentose ribose. Too much strain would be involved in reducing bond angles to produce smaller rings, so trioses and tetroses do not form intermolecular cyclic systems. 

Monosaccharides may be called trioses, tetroses, pentoses, hexoses, heptoses, or octoses, depending on whether they have 3, 4, 5, 6, 7, or 8 carbons, respectively, in them. 

The R-S nomenclature, which is an absolute naming scheme, is shown in Figure 9.6. It is commonly used by organic chemists, but is rarely used by biochemists since it is difficult to apply to molecules, such as tetroses, pentoses, hexoses, etc., which may have more than one chiral carbon. The predominant monosaccharides found in nature have the D configuration. 

A monosaccharide can be a polyhydroxy aldehyde such as D-glucose or a polyhydroxy ketone such as o-liructose. Polyhydroxy aldehydes are called aldoses ( aid is for aldehyde ose is the suffix for a sugar), whereas polyhydroxy ketones are called ketoses. Monosaccharides are also classified according to the number of carbons they contain Monosaccharides with three carbons are trioses, those with four carbons are tetroses, those with five carbons are pentoses, and those with six and seven carbons are hexoses and heptoses, respectively. A six-carbon polyhydroxy aldehyde such as o-glucose is an aldo-hexose, whereas a six-carbon polyhydroxy ketone such as o-fructose is a ketohexose. 

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