One-Step Semisynthesis of a Segetane Diterpenoid from a Jatrophane Precursor via a Diels–Alder Reaction

A novel segetane diterpenoid (1) and four jatrophane diterpenoids (2–5) were isolated from an acetone extract of Euphorbia peplus. Due to quantity limitations, we prepared 1 via a Diels–Alder reaction, an approach motivated by this compound’s biosynthetic pathway and successfully performed X-ray analysis of 1. Furthermore, in an in vitro activity test, 1 exhibited moderate anti-inflammatory activity, whereas both its precursor (2) and the relevant intermediate (2a, IC50 = 1.56 μM) exhibited significant anti-inflammatory activity.