Six new triterpenoids (1-6) and the previously known penasterone, acetylpenasterol, and ergosta-4,24(28)-dien-3-one were isolated from a Penares 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 (1-4) 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 2. The isolated triterpenoid 6 was cytotoxic against human leukemia HL-60 cells (IC₅₀ = 9.7 μM).
