A Water-Soluble 5/14-Carbobicyclic Steroid with a <i>trans</i>-9,11-Epoxy Ring from the Marine Dinoflagellate <i>Amphidinium gibbosum</i>: Insights into Late-Stage Diversification of Steroids

Abstract

Gibbosterol A (1), a water-soluble 14-membered carbocyclic steroid with a twisted trans-9,11-epoxy ring, was discovered from the South China Sea dinoflagellate, Amphidinium gibbosum, together with its acid-induced cyclization product 2. It exhibits marked agonistic effects against human pregnane-X-receptor in a dose-dependent manner within the concentration range of 100 nM to 10 μM. Its 5/14-carbobicyclic nucleus is proposed to be originated from late-stage oxidative cleavage of the C5–C10 and C8–C9 bonds of β-sitosterol.

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