A new furanosesterterpene from the South African nudibranch Hypselodoris capensis and a dictyoceratida sponge.

The known cytotoxic, linear beta-substituted sesterterpenes (18R)-variabilin (1) and 22-deoxyvariabilin (4) and a new variant, 22-deoxy-23-hydroxymethylvariabilin (5), were isolated from the endemic South African nudibranch Hypselodoris capensis together with the known ichthyotoxic sesquiterpenes nakafuran-8 (2) and -9 (3). One of H. capensis' dietary sponges, a Fasciospongia sp. collected simultaneously with the nudibranchs, yielded sesterterpenes 1, 4, and 5 and the ubiquitous prenylated furan derivative, furospinosulin-1 (7).