Six new acetylenic compounds, 1, 7–11, were isolated from the marin sponge Pellina triangulata. Structures were established using NMR spectroscopy and chemical degradation. Collisional activation decomposition (CAD) tandem mass spectrometry of the lithium adducts of the acetylenic compounds was applied to ascertain if charge-remote fragmentation would yield definitive information regarding the site of internal unsaturation in these polyfunctional compounds. Pellynic acid ( 1) inhibited inosine monophosphate dehydrogenase (LMPDH) in vitro. Six new acetylenic compounds, 1, 7–11, were isolated from the marine sponge Pellina triangulata. Structures were established using NMR spectroscopy, chemical degradation, and collisional activation decomposition (CAD) tandem mass spectrometry. Pellynic acid (1) inhibited IMPDH.