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

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posted on 28.12.2016, 00:00 by Ji-Qin Hou, Cui Guo, Jian-Juan Zhao, Qi-Wei He, Bao-Bao Zhang, Hao Wang
Frutescone A–G [(16), (+)-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 47 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.