Magterpenoids A–C, Three Polycyclic Meroterpenoids with PTP1B Inhibitory Activity from the Bark of Magnolia officinalis var. biloba

Magterpenoid A (1), possessing a rare 4,6,11-trioxatricyclo­[5.3.1.01,5]­undecane framework with an irregular monoterpenoid moiety, magterpenoid B (2), with an unprecedented 6/6/6/6 polycyclic skeleton, and magterpenoid C (3), a novel terpenoid quinone with a C6–C3 unit, were isolated from the bark of Magnolia officinalis var. biloba. Plausible biogenetic pathways of 1-3 are presented. Compounds 1 and 3 exhibited significant PTP1B inhibitory activities with IC50 values of 1.44 and 0.81 μM, respectively.