Magterpenes A–C: Three Meroterpenoids with an Unprecedented 6/6/6/6/6 Polycyclic Skeleton Extracted from Magnolia officinalis Rehd. et Wils

Magterpenes A–C (1–3), three unprecedented meroterpenoids featuring a unique 6/6/6/6/6 polycyclic skeleton, were isolated from the ethanol extract of Magnolia officinalis Rehd. et Wils. The compounds were obtained as racemic mixtures that were completely resolved through chiral columns. Their structures were elucidated by extensive analyses of one-dimensional (1D) and 2D nuclear magnetic resonance, high-resolution electrospray ionization mass spectrometry, chemical calculations of 1H/13C NMR, and electronic circular dichroism calculations. The compounds were constructed via two Diels–Alder reactions in the proposed biosynthetic pathway. All isolates were evaluated for their nephroprotective and hepatoprotective activities. The results demonstrated that (+)-1 and (−)-1 possessed promising nephroprotective activities in a dose-dependent manner, while (−)-2 and (+)-3 exhibited moderate hepatoprotective activities.