– Prostaglandin D2 (PGD2) is a primary enzymatic prostaglandin derived from PGH2 and is abundantly produced in the cerebrospinal fluid (CSF) by the lipocalin-type PGD synthase, and peripherally by myeloid cells such as mast cells and basophils via a hematopoietic-type PGD synthase. PGD2 is chemically unstable and presents challenges for use and analysis due to its brief in vivo half-life. Δ12-PGD2, an initial decomposition product of PGD2, acts as an intermediate in the pathway to Δ12-PGJ2, a cyclopentenone prostaglandin known for its antimitotic and carcinogenic properties. The metabolism of Δ12-PGD2 involves the addition of thiol nucleophiles, a common pathway for many cyclopentenone prostaglandins.