Identification and structural modification of ent-rosane diterpenoids from Euphorbia milii inhibiting RANKL-induced osteoclastogenesis

Phytochemical study on Euphorbia milii, a common ornamental plant, resulted in the identification of thirteen new ent-rosane diterpenoids (1–13), three new ent-atisane diterpenoids (14–16), and a known ent-rosane (17). Their structures were delineated using spectroscopic data, quantum chemical calculations, and X-ray diffraction experiments. Euphomilone F (1) represented a rare ent-rosane-type diterpenoid with a 5/7/6 skeleton. Euphoainoid G (8) was a rare rosane diterpenic acid. Compounds 9 and 10 carried infrequent tetrahydrofuran rings, and compounds 11–13 was 18-nor-ent-rosane diterpenoids. All isolates were evaluated for their inhibitory effects on RANKL-induced osteoclasts. Notably, compounds with aromatic ester groups (2–7) showed promising activities (IC50 < 10 μM), underscoring the significance of acylated A-ring moieties in the ent-rosane skeleton for anti-osteoclastogenesis. Thirteen synthetic derivatives were obtained through esterification of 17. Of these, compound 27 exhibited remarkable improvement, with an IC50 of 0.8 μM, more than a 12-fold increase in potency compared to the parent compound 17 (IC50 > 10 μM). This work presents a series of new ent-rosane diterpenoids with potential antiosteoporosis agents.