<i>ent</i>-Kaurane-Based Diterpenoids, Dimers, and Meroditerpenoids from <i>Isodon xerophilus</i>
Jia-Meng Dai, Kun Hu, Bing‐Chao Yan, Xing‐Ren Li, Xiao‐Nian Li, Han‐Dong Sun, Pema‐Tenzin Puno
Abstract
Eight new diterpenoids (1–8) with varied structures were isolated from the aerial parts of Isodon xerophilus. Among them, xerophilsin A (1) was found to be an unusual meroditerpenoid representing a hybrid of an ent-kauranoid and a long-chain aliphatic ester, xerophilsins B–D (2–4) are dimeric ent-kauranoids, while xerophilsins E–H (5–8) are new ent-kauranoids. The structures of 1–8 were elucidated mainly through the analyses of their spectroscopic data. The absolute configurations of 2, 6, and 8 were confirmed by single-crystal X-ray diffraction, and the configuration of C-16 in 7 was established through quantum chemical calculation of NMR chemical shifts, as well as modeling of key interproton distances. Bioactivity evaluation of all isolated compounds revealed that 2, 3, and 5 inhibited NO production in LPS-stimulated RAW264.7 cells.