One of the principal nucleosides of DNA composed of cytosine and deoxyribose. A nucleoside consists of only a pentose sugar linked to a purine or pyrimidine base without a phosphate group.

(S)-3-Hydroxybutyric acid is a normal human metabolite that has been found elevated in geriatric patients remitting from depression.

2'-O-Methyladenosine, a methylated adenine residue is found in the urine of normals and adenosine deaminase deficient patients. It shows unique hypotensive activities.