Tooniliatone A (1), a novel limonoid with an unprecedented 6/5/6/5 tetracarbocyclic skeleton was isolated from Toona ciliata Roem. var. yunnanensis. Its rearranged ring-seco backbone was proposed to biosynthetically originate from co-isolated known toonacilin (3) via a rare electron-deficient alkene electrophilic cyclization and 1,2-alkyl shift sequence. The acid-catalyzed biomimetic conversion of 3 not only successfully afforded 1 but also another novel 6/5/6/5 tetracarbocyclic skeleton, tooniliatone B (2). The priority of 2 in this biomimetic conversion, the existence of 1 and the absence of 2 in the crude extract suggested the biosynthetic selectivity of 1 from 3. The divergent biomimetic sequence, based on a carbocation from an epoxide moiety, provided an inspiration for constructing complex polycyclic carbon skeletons.

中文翻译：

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重排柠檬苦素，具有来自香椿的独特6/5/6/5四碳环骨架和仿生结构差异

从Toona ciliata Roem中分离出Tooniliatone A（1），它是一种具有前所未有的6/5/6/5四碳环骨架的新型柠檬苦素。变种 云南。其重排环-开环的主链被提出生物合成从共分离已知toonacilin（起源3）经由一种罕见的缺电子烯烃电环化和1,2-烷基移位序列。酸催化的仿生转化3不仅成功提供了1，而且还提供了另一个新颖的6/5/6/5四碳环骨架，tooniliatone B（2）。在此仿生转换中优先级为2的存在1和2的粗提物中不存在表明1从3的生物合成选择性。基于环氧化物部分的碳正离子的不同的仿生序列为构建复杂的多环碳骨架提供了灵感。