Sarcaglarone A, a lindenane–monoterpene heterodimer from the seeds of Sarcandra glabra

Three novel lindenane-monoterpene heterodimers with different skeleton types (1-3), together with a known analogue (4), were obtained from the seeds of Sarcandra glabra. Their structures were elucidated on the basis of comprehensive spectroscopic analyses, single crystal X-ray diffraction, and calculations of ECD. Sarcaglarone A (1) displayed an unprecedented monocyclic monoterpene moiety formed by a free-radical-mediated C1'-C5' bond formation reaction. 6α-Hydroxysarglaperoxide A (2) and 7'-oxyisosarcaglabrin A (3) are C₂₃ and C₂₅ terpenes formed by [2 + 2 + 2] cycloaddition and the Diels-Alder reaction, respectively. Their inhibitory activities against nitric oxide (NO) production were evaluated.