Manadosterols A and B, Sulfonated Sterol Dimers Inhibiting the Ubc13–Uev1A Interaction, Isolated from the Marine Sponge Lissodendryx fibrosa

Two new dimeric sterols, manadosterols A (1) and B (2), were isolated from the marine sponge Lissodendryx fibrosa collected in Indonesia. The two compounds are comprised of two sulfonated sterol cores connected through the respective side chains. Manadosterols A (1) and B (2) inhibited the Ubc13-Uev1A interaction with IC50 values of 0.09 and 0.13 μM, respectively. They are the second and third natural compounds showing inhibitory activities against the Ubc13–Uev1A interaction and are more potent than leucettamol A (IC50, 106 μM), the first such inhibitor, isolated from another marine sponge.