Gombaspiroketals A–C, Sesterterpenes from the Sponge <i>Clathria gombawuiensis</i>

Abstract

Gombaspiroketals A–C (<b>1</b>–<b>3</b>), tetracyclic sesterterpenes of a novel skeletal class, were isolated from the Korean marine sponge <i>Clathria gombawuiensis</i>. On the basis of the combined spectroscopic analyses, the structures of these compounds were determined to be highly rearranged sesterterpene spiroketal methoxyacetals (<b>1</b> and <b>2</b>) and a corresponding hemiacetal (<b>3</b>). The relative and absolute configurations were assigned by NOESY analysis and ECD calculations, respectively. These compounds exhibited moderate cytotoxicities and antibacterial activities