Frutescone A–G, Tasmanone-Based Meroterpenoids from the aerial parts of Baeckea frutescens

Frutescone A–G [(1–6), (+)-7, (−)-7], a new group of naturally occurring tasmanone-based meroterpenoids, were isolated from the aerial parts of Baeckea frutescens L. Compounds 1 and 4 featured a rare carbon skeleton with an unprecedented oxa-spiro[5.8] tetradecadiene ring system, existing as two favored equilibrating conformers in CDCl3 solution, identified by variable-temperature NMR. The regioselective syntheses of 4–7 were achieved in a concise manner by a biomimetically inspired key hetero-Diels–Alder reaction “on water”. Compounds 1, 4, and 5 exhibited moderate cytotoxicities in vitro.Frutescone A–G [(1–6), (+)-7, (−)-7]是一类全新的天然存在的基于塔斯曼酮（tasmanone）的杂萜类（meroterpenoids）化合物，从岗松（Baeckea frutescens L.）的地上部分中分离得到。化合物1和4拥有罕见的碳骨架，其环系为前所未有的氧杂螺[5.8]十四二烯结构，在氘代氯仿（CDCl3）溶液中以两种优势平衡构象存在，该结论通过变温核磁共振（variable-temperature NMR）实验得以验证。通过仿生启发的关键杂狄尔斯-阿尔德反应，以简洁路线实现了化合物4至7的区域选择性合成。化合物1、4和5在体外实验中表现出中等强度的细胞毒性。