New Cytotoxic Norditerpenes from the Australian Nudibranchs Goniobranchus Splendidus and Goniobranchus Daphne

This study reports the isolation and characterisation of six new metabolites with ‘gracilin’-type carbon skeletons and of aplytandiene-3 from the Australian nudibranch Goniobranchus splendidus. The structure of gracilin G is revised, and the C-6 configuration deduced by comparison of calculated 3JC/H values with values measured using the EXSIDE pulse sequence. A lactone isolated from Goniobranchus daphne contains a rearranged spongionellin-type skeleton. Screening of selected metabolites revealed significant cytotoxicity against a HeLa S3 cell line by five of the new terpenes.