ketodeoxynonulosonic

Ketodeoxynonulosonic acid refers to a subset of nonulosonic acids, a family of nine-carbon sugar acids that includes various biologically important members. The term describes 2-keto-3-deoxy-nonulosonic acids, in which a ketone resides at the C2 position and the C3 hydroxyl is absent. The best-characterized member is 2-keto-3-deoxy-D-glycero-D-galacto-nonulosonic acid (KDN).

Occurrence and structure: Ketodeoxynonulosonic acids occur in some bacteria and archaea, often as components of lipopolysaccharides or glycoproteins. They share a nine-carbon backbone but can differ in substituents and stereochemistry depending on the organism and derivative. They are distinct from other nonulosonic acids such as the eight-carbon KDO (keto-deoxyoctulosonic acid) and from the well-known sialic acids like N-acetylneuraminic acid (Neu5Ac).

Biosynthesis and variation: In bacteria that produce KDN, dedicated biosynthetic pathways assemble the nine-carbon sugar and introduce the keto and deoxy features. These pathways differ from those that synthesize Neu5Ac or KDO, and the responsible genes (variously described in different species) reflect the diversity of nonulosonic acid biosynthesis.

Biological relevance: Ketodeoxynonulosonic acids can be found on lipopolysaccharides or glycoproteins, where they may influence interactions with the host immune system. Their roles are organism-specific and not as universally essential as other sialic acids in vertebrates. Because of their diversity and occurrence in pathogenic bacteria, they are of interest in glycoscience and antimicrobial research.

Analytical notes: Characterization typically involves chromatographic separation and mass spectrometry, with structural confirmation by NMR in research settings.