Isolation, Structures, and Biological Activities of Triterpenoids from a <i>Penares</i> sp. Marine Sponge

Six new triterpenoids (<b>1</b>–<b>6</b>) and the previously known penasterone, acetylpenasterol, and ergosta-4,24(28)-dien-3-one were isolated from a <i>Penares</i> sp. sponge collected from Vietnamese waters. Structures of the obtained compounds were established by extensive 1D and 2D NMR spectroscopy and mass spectrometry. Configurations of the triterpene epoxy lactones (<b>1</b>–<b>4</b>) were determined on the basis of NOESY and CD data and calculation of spin coupling constants and confirmed by X-ray crystallographic analysis of compound <b>2</b>. The isolated triterpenoid <b>6</b> was cytotoxic against human leukemia HL-60 cells (IC<sub>50</sub> = 9.7 μM).