NulOs or 9‑carbon non‑2‑ulosonic acids are a family of monosaccharides with a 9-carbon backbone. All representatives of this family are synthesised in unusual ways. They carry a noteworthy number of components on one monosaccharide. These include (1) negatively charged carboxylic acid, (2) a 3‑carbon glycerol-like side chain, and – optionally - (3) at least one amino group (Varki et al. 2015).
These molecules transmit information for glycan-protein, cell‑cell, and pathogen‑cell recognition. Because on vertebrate cells, these molecules occur in high density they use their electronegative charge to repel cell‑cell interactions, stabilise proteins, bind or transport ions (Varki et al. 2015). A well-known subclass of NulOs are sialic acids.