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Uncommon Diterpenoids from the South China Sea Soft Coral Sinularia humilis and Their Stereochemistry

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journal contribution
posted on 2021-01-26, 19:36 authored by Li-Li Sun, Wang-Sheng Li, Jie Li, Hai-Yan Zhang, Li-Gong Yao, Hui Luo, Yue-Wei Guo, Xu-Wen Li
The chemical investigation of the South China Sea soft coral Sinularia humilis has resulted in the isolation of a library of diverse diterpenoids, including four new cembranoids, namely, humilisins A–D (14), two new uncommon diterpenoids possessing a tetradeca­hydrocyclo­penta­[3′,4′]­cyclobuta­[1′,2′:4,5]­cyclonona­[1,2-b]­oxirene ring system, namely, humilisins E and F (5 and 6), and eight known related compounds (714). Humilisin A (1) is the first cembranoid with an ether linkage between C-3 and C-7. The structures and absolute configurations of 18 were determined by extensive spectroscopic data analyses, chemical reactions, and a series of quantum chemical calculations including quantum mechanical–nuclear magnetic resonance (QM-NMR), time-dependent density functional theory–electronic circular dichroism (TDDFT-ECD), and optical rotatory dispersion (ORD) methods. In bioassay, compound 6 displayed anti-inflammatory activity in lipopolysaccharide (LPS)-stimulated BV-2 microglia cells.