Monanchosterols A and B, Bioactive Bicyclo[4.3.1]steroids from a Korean Sponge <i>Monanchora</i> sp.

Chemical investigation of a Korean marine sponge, <i>Monanchora</i> sp., led to the isolation of three new steroids (<b>1</b>–<b>3</b>). Compounds <b>1</b> and <b>2</b>, designated as monanchosterols A and B, respectively, represent the first examples of steroids possessing the bicyclo[4.3.1] A/B ring system from a natural source. Compounds <b>1</b>–<b>3</b> were investigated for their anti-inflammatory activity by evaluating their inhibitory effects on the mRNA expression of IL-6, TNF-α, and COX-2 in the LPS-stimulated murine RAW264.7 macrophage cells. Compounds <b>2</b> and <b>3</b> exhibited significant inhibitory effects on the mRNA expression of IL-6 without notable cytotoxicity to the cells in a dose-dependent manner