In chemistry, a pentose is a monosaccharide (simple sugar) with five carbon atoms. The chemical formula of many pentoses is , and their molecular weight is 150.13 g/mol.
Pentoses are very important in biochemistry. Ribose is a constituent of RNA, and the related molecule, deoxyribose, is a constituent of DNA. Phosphorylated pentoses are important products of the pentose phosphate pathway, most importantly ribose 5-phosphate (R5P), which is used in the synthesis of nucleotides and nucleic acids.
Like some other monosaccharides, pentoses exist in two forms, open-chain (linear) or closed-chain (cyclic), that easily convert into each other in water solutions.
The ring closure converts the carbonyl carbon into a chiral center, which may adopt either of two configurations, depending on the position of the new hydroxyl. Therefore, each linear form can produce two distinct closed forms, identified by prefixes "α" and "β".
Deoxypentoses
The one deoxypentose has two total stereoisomers.
{| class="wikitable skin-invert-image"
|-align="center"
| 150px<br /><br /><small>D</small>-Deoxyribose
|-align="center"
| 150px<br /><br /><small>L</small>-Deoxyribose
|}
Properties
In the cell, pentoses have a higher metabolic stability than hexoses.
A polymer composed of pentose sugars is called a pentosan.
Tests for pentoses
The most important tests for pentoses rely on converting the pentose to furfural, which then reacts with a chromophore. In Tollens' test for pentoses (not to be confused with Tollens' silver-mirror test for reducing sugars), the furfural ring reacts with phloroglucinol to produce a colored compound; in the aniline acetate test with aniline acetate; and in Bial's test, with orcinol. In each of these tests, pentoses react much more strongly and quickly than hexoses.