Hispidanins A–D: Four New Asymmetric Dimeric Diterpenoids from the Rhizomes of Isodon hispida

Hispidanins A–D (1–4), four unprecedented asymmetric dimeric diterpenoids, were obtained from the rhizomes of Isodon hispida. Their structures were elucidated by extensive spectroscopic analysis (1D and 2D NMR, MS, UV, IR), as well as single-crystal X-ray diffraction analysis. Hispidanin B showed significant cytotoxicities against tumor cell lines SGC7901, SMMC7721, and K562, with IC50 values of 10.7, 9.8, and 13.7 μM, respectively.