Spiroconyone B and C, Two Rearranged Cholestane Steroids with Spiro[4.5]decane and Oxaspiro[4.5]decane Scaffolds from <i>Patiria pectinifera</i>

Spiroconyone B (<b>1</b>) and C (<b>2</b>), two unique steroids bearing rare spiro[4.5]decane and oxaspiro[4.5]decane scaffolds, along with four analogues (<b>3</b>-<b>6</b>) were isolated from the sea star <i>Patiria pectinifera</i>. Structures were established by comprehensive spectroscopic analysis, quantum-chemical nuclear magnetic resonance calculations, electronic circular dichroism data, and single-crystal X-ray diffraction. Compounds <b>1</b>, <b>4</b>, and <b>5</b> exhibited cytotoxicity toward HL-60 cells with IC₅₀ values of 7.6 ± 0.3, 3.6 ± 0.1, and 6.0 ± 0.5 μM, respectively. Flow cytometry indicated that <b>4</b> induced G₂/M phase arrest, and annexin V/PI assays showed dose-dependent increases in the level of total apoptosis for <b>1</b> and <b>4</b>. Western blotting revealed downregulation of cyclin B1 and cdc2 (CDK1) by <b>4</b>; both <b>1</b> and <b>4</b> decreased Bcl-2 and increased Bax, consistent with mitochondria-mediated apoptosis. Network pharmacology, supported by mechanistic assays, further suggested the engagement of the PI3K/Akt pathway by <b>4</b>.