Four Highly Oxygenated Sesquiterpenoids from the Fruits of <i>Illicium micranthum</i> Dunn

Four highly oxygenated sesquiterpenoids, illimicranolides A (1) and B (2), and illicinolides E (3) and F (4), were obtained from the fruits of Illicium micranthum Dunn, as well as one known analog, illicinolide B (5). The chemical structures of 1-4 were determined comprehensively by 1D (¹ H and ¹³ C) and 2D (HMBC, HSQC, ¹ H-¹ H COSY, and ROESY) NMR, and HR-ESI-MS data. Structurally, compound 1 was an unprecedented sesquiterpenoid with a 5/5/6/5-fused tetracyclic ring system and was the first seco-prezizaane sesquiterpenoid featuring a 11,8-γ-lactone ring. Compounds 3 and 4 were the fifth and sixth examples of illicinolide-type sesquiterpenoids. Moreover, compound 1 demonstrated neurotrophic activity of NGF-induced PC12 cells with differentiation rate of 10.34 % at a concentration of 10 μM.