Mollanol A, a Diterpenoid with a New C‑Nor-D-homo­grayanane Skeleton from the Fruits of Rhododendron molle

Two new grayanoids, mollanol A (<b>1</b>) and rhodomollein XXV (<b>2</b>), were isolated from the fruits of Rhododendron molle. Their structures were elucidated by spectroscopic methods and X-ray diffraction analyses. Mollanol A (<b>1</b>) possesses a new C-nor-D-homo­grayanane carbon skeleton, while rhodomollein XXV (<b>2</b>) is the first example of an 11,16-epoxy­grayanane and features a caged oxa-tricyclo­[3.3.1.0^3.7]­nonane ring system. Plausible biogenetic pathways for <b>1</b> were proposed. Compound <b>1</b> exhibited transcriptional activation effects on the <i>xbp1</i> upstream promoter in IEC-6, 293T, and RAW264.7 cells