Rhodomollacetals A–C, PTP1B Inhibitory Diterpenoids with a 2,3:5,6-Di-seco-grayanane Skeleton from the Leaves of Rhododendron molle

Three novel diterpenoids with an unprecedented 2,3:5,6-di-seco-grayanane carbon skeleton, rhodomollacetals A–C (1–3), are isolated from the leaves of Rhododendron molle. Their structures are elucidated by comprehensive spectroscopic techniques and single-crystal X-ray diffraction. Rhodomollacetal A (1) possesses a novel cis/cis/cis/cis-fused 6/6/6/6/5 pentacyclic ring system, featuring an unprecedented 11,13,18-trioxa-pentacyclo [8.7.1.15,8.02,8.012,17]­nonadecane scaffold. Compounds 2 and 3 have a rare 4-oxatricyclo­[7.2.1.01,6]­dodecane moiety and a 2,3-dihydro-4H-pyran-4-one unit. Compounds 1–3 showed moderate PTP1B inhibitory activities, and their molecular dockings were investigated.