Aldoses Polyhydroxyaldehydes

Trivial names are common in carbohydrate nomenclature. Fifteen of them form the basis of the systematic nomenclature. They are assigned to the simple aldoses (polyhydroxyaldehydes), from triose to hexoses. 

Aldoses polyhydroxyaldehydes, one of the two main subdivisions of the monosaccharides (the other is the ketoses see Carbohydrates). A. are characterized by a terminal aldehyde group -CHO, which is always given the number 1 in systematic nomenclature. The A. are formally derived from their simplest representative, glyceraldehyde, by chain extension. According to the number of carbon atoms in their chain, they are classified as trioses, tetroses, etc. The pentoses and hexoses are particularly important metaboli-cally. 

Carbohydrates (saccharides) are aliphatic polyhydroxyaldehydes (aldoses), polyhydroxyketones (ketoses), or compounds that can be hydrolyzed to them. The suffix -ose denotes this class of compounds. 

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). 

Monosaccharides, or simple sugars, are carbohydrates that cannot be hydrolyzed to simpler compounds. Figure 23-1 shows Fischer projections of the monosaccharides glucose and fructose. Glucose is a polyhydroxyaldehyde, and fructose is a polyhydroxy ketone. Polyhydroxyaldehydes are called aldoses (aid- is for aldehyde and -ose is the suffix for a sugar), and polyhydroxyketones are called ketoses (ket- for ketone, and -ose for sugar). 

Carbohydrates are either polyhydroxyaldehydes (aldoses, oses) or polyhydroxyke-tones (ketoses, uloses) there is an electron gap at their carbonyl carbon atom. Typically, aldehydes and ketones accept nucleophiles such as water to form hydrates or alcohols to form hemiketals (5.1 and 5.3) and hemiacetals (5.4 and 5.6), respectively. In pentoses, pentuloses, hexoses, hexuloses, and higher carbohydrates, one of the hydroxyl groups can play the role of internal nucleophile. Thus, open-chain structure (5.2 and 5.5) cyclizes into internal hemiacetals and ketals, all with either five- (5.1 and 5.3) or six- (5.4 and 5.6) membered cycles. 

Monosaccharides can be named on the basis of the functional groups they contain. A monosaccharide with a ketone (carbonyl) group is a ketose. If an aldehyde (carbonyl) group is present, it is called an aldose. Because monosaccharides also contain many hydroxyl groups, they are sometimes called polyhydroxyaldehydes or polyhydroxyketones. 

Aldehydes - Compounds RC(=0)H, in which a carbonyl group is bonded to one hydrogen atom and to one R group. [5] Aldoses - Aldehydic parent sugars (polyhydroxyaldehydes H[CH(0H)] C(=0)H, >1) and their intramolecular hemiac-etals. [5]... 

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