heptose

Heptose is a monosaccharide containing seven carbon atoms. Like other aldoses and ketoses, it can exist as multiple stereoisomers and as either an aldose or a ketose. The natural heptoses include sedoheptulose, an aldose, and various diastereomeric forms. In biochemical settings, several phosphorylated seven-carbon sugars play important roles.

Sedoheptulose-7-phosphate is an intermediate of the pentose phosphate pathway and, in photosynthetic organisms, the Calvin cycle. It can be converted through enzyme-catalyzed steps to other sugars and sugar phosphates used for nucleotide synthesis and one-carbon metabolism.

In bacteria, seven-carbon sugars are components of cell-surface glycans. Notably, heptose residues such as D-glycero-D-manno-heptose are found in the core region of lipopolysaccharides (LPS), where they contribute to membrane integrity and host interactions.

Chemical properties: Heptoses are highly water-soluble polyhydroxylated aldehydes or ketones. In solution they form cyclic hemiacetals with several possible ring sizes. They exhibit multiple chiral centers, giving rise to several D- and L- isomers; natural forms are often designated by specific stereochemical descriptors.

Summary: Heptose is a seven-carbon sugar occurring in limited natural forms, with sedoheptulose and its phosphates being central to metabolism, and with LPS-related heptoses playing roles in bacteria. They are studied in carbohydrate chemistry and biochemistry, with emphasis on their stereochemistry and biosynthetic pathways.