Aldose A monosaccharide that contains

Aldose A monosaccharide that contains an aldehyde group. 

Monosaccharides that contain an aldehyde group are called aldoses, whereas those containing a ketone group are ketoses. Monosaccharides are also classified by the number of carbon atoms as trioses, tetroses, etc. objective 5 (Section 7.4), Exercise 7.22. Most natural monosaccharides belong to the d family. 

Monosaccharides containing three-, four-, five-, and six-carbon atoms are called trios-es, tetroses, pentoses, and hexoses, respectively. Monosaccharides that contain an aldehyde group on one carbon atom and a hydroxyl group on each of the other carbon atoms are called aldoses. Ketoses are monosaccharides that contain a ketone group on one carbon atom and a hydroxyl group on each of the other carbons. 

Carbohydrates are polyhydroxy aldehydes and ketones that are commonly known as sugars. A monosaccharide is a carbohydrate composed of one sugar unit and a disaccharide is a carbohydrate composed of two monosaccharide units. An oligosaccharide is composed of 2-10 monosaccharide units a polysaccharide is composed of 10 or more monosaccharide units. An aldose is a carbohydrate that contains an aldehyde unit and a ketose is a carbohydrate that contains a ketone unit. Monosaccharides are categorized by the total number of carbons in the structure triose, tetrose, pentose, hexose, etc. The d and 1 configurations of a monosaccharide are based on the Fischer projection of d-glyceraldehyde. A Fischer projection is an older representation of sugars. 

We restrict discnssion here to simple monosaccharides, i.e., polyhydroxy compounds that contain a carbonyl fnnctional gronp (Chap. 3). There are two series, the aldoses that contain an aldehyde group and... 

We will examine the products that would result from cleaving of all the possible combinations of bonds in a monosaccharide. We will do so by considering various subunits of the structme. However, all the subunits react, so we must analyze all carbon-carbon bonds and the attached functional groups to determine the products that can form. First, consider the subunit that contains a primary hydroxyl group. This structural feature exists at the highest numbered carbon atom of an aldose. The unit also occurs at C-1 and the highest numbered carbon atom of a ketose. 

The reduction of lactones of polyhydroxy carboxylic acids to the corresponding aldoses with sodium amalgam can be successfully achieved by electroreduction at a mercury cathode, provided that the catholyte contains salts of amalgam-forming metals. The electroreduction of the lactones of n-ribonic and n-arabinonic acids to n-ribose and n-arabinose, respectively, is performed at a mercury cathode, with sodium, potassium, or zinc sulfate (or their mixtures) as the catholyte, and platinum gauze as the anode, immersed in aqueous, 15% sulfuric acid. The electrolyzer compartments are separated by a diaphragm, and the electrolysis is performed with intensive stirring of the catholyte, which is maintained at a temperature of +5 to +12° and at a constant pH (adjusted by additions of dilute sulfuric acid). Yields of monosaccharide are increased by addition of boric acid to the reaction mixture. 

Although the early studies established the relationships and properties of the classic families of aldoses and ketoses, and their simple derivatives, some unusual monosaccharide structures were later encountered that were of importance in the biomedical area. The antiscorbutic vitamin isolated from paprika in 1928 by Szent-Gyorgi (40) and initially termed hexuronic acid was subsequently shown to be a six-carbon furanose lactone containing an enediol structure (Scheme 10)... 

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