Aldopentoses

An aldopentose is a pentose that is also an aldose. A pentose is a sugar or saccharide containing five carbon atoms. An aldose is any of a class of monosaccharides having an aldehyde or hemiacetal functional group. The aldopentoses have three chiral centers and therefore eight different (2^3) stereoisomers are possible. These stereoisomers include D-Arabinose, L-Arabinose, D-Lyxose, L-Lyxose, D-Ribose, L-Ribose, D-Xylose, and L-Xylose. These compounds are optically active, with stereogenic centers at carbons-2,3, & 4. The stereochemistry of the stereoisomers is shown below.

Arabinose gets its name from arabic gum, from which it was first isolated. In synthetic biology, arabinose is often used as a one-way or reversible switch for protein expression under the P_bad promoter in E. coli.

Lyxose is a C'-2 carbon epimer of the sugar Xylose. It occurs only rarely in nature, for example, as a component of bacterial glycolipids.

Ribose forms part of the backbone of RNA. It is related to deoxyribose, which is found in DNA. Phosphorylated derivatives of ribose such as ATP and NADH. Such derivatives play central roles in metabolism. 

Xylose gets its name from wood, from which the sugar was first isolated. In animal medicine, xylose is used to test for malabsorption. If xylose is detected in blood and/or within the next few hours after consumption, it has been absorbed by the intestines.

Stereochemistry of Aldopentose stereoisomers

References: http://www.chem.ucla.edu/harding/IGOC/A/aldopentose.html

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