The spatially close and highly reactive ester appendages through the opening of A and B rings of prieurianin-type limonoids would further rearrange into diverse ring system via oxygen-bridges or new C–C bonds. In our current research, two limonoids with an unprecedented 7/6/5 tricyclic skeleton (1) and 2,6-dioxabicyclo[3.2.2]nonan-3-one caged ring A system (2), along with eight other new ones (3–10) were obtained from Aphanamixis polystachya and Aphanamixis sinensis, and the structure of 1 was confirmed by X-ray crystallographic diffraction. Meanwhile, a reliable solution based on biomimetic alkaline hydrolysis to build new oxygen-bridges via OH-1 was established to resolve the difficulties in the structural elucidation of prieurianin limonoids with broad or missing NMR signals and applied for the determination of 9 and 10. Moreover, the potential of Dieckmann reaction as a key biosynthetic step in the formation of C-3/C-6 bonds in the aphanamolide-type backbone was verified by chemical conversions of 13–16. These findings provided new ideas and perspectives for structural elucidation and chemical communication of prieurianin-type limonoids.

中文翻译：

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来自两个Aphanamixis物种的具有氧桥式笼状骨架的多样prieurianin型柠檬苦素：发现和仿生转化

通过Prieurianin型柠檬苦素类化合物A和B环的开放而在空间上紧密且具有高反应性的酯类附件会通过氧桥或新的CC键进一步重排成各种环系统。在我们当前的研究中，两个具有前所未有的7/6/5三环骨架的柠檬苦素（1）和2,6-二氧杂双环[3.2.2] nonan-3-笼状A环系统（2），以及另外八个新的（3-10）分别来自多形瓜（Aphanamixis polystachya）和中华密瓜（Aphanamixis sinensis），其结构1由X射线晶体衍射证实。同时，基于仿生碱水解的可靠解决方案可通过以下途径建立新的氧桥建立OH-1是为了解决宽泛的或缺少NMR信号的普eur素柠檬苦素类化合物在结构解析中的困难，并将其用于9和10的测定。此外，通过化学转化13–16验证了Dieckmann反应作为Aphanamolide型骨架中C-3 / C-6键形成的关键生物合成步骤的潜力。这些发现为Prieurianin型柠檬苦素的结构阐明和化学通讯提供了新的思路和观点。