Shishicrellastatins, inhibitors of cathepsin B, from the marine sponge Crella (Yvesia) spinulata

Two dimeric steroid derivatives, shishicrellastatin A (1) and B (2), have been isolated as cathepsin B inhibitors from the marine sponge Crella (Yvesia) spinulata. Their structures were determined by interpretation of spectroscopic data. Shishicrellastatins inhibit cathepsin B with an IC50 value of 8 μg/mL each.