New isomalabaricane triterpenes from the marine sponge Stelletta globostellata that induce morphological changes in rat fibroblasts

Three new isomalabaricane triterpenes, 29-hydroxystelliferin D (2), 3-epi-29-hydroxystelliferin E (3), and 3-epi-29-hydroxystelliferin A (4), were isolated from the marine sponge Stelletta globostellata. Their structures, including absolute stereochemistry, were determined on the basis of spectral data and chemical methods. Rat fibroblasts treated with 0.2 mu M of 2-4 exhibited unusual morphological characteristics, followed by death in 5 days.