New diastereomeric bis-sesquiterpenes from Hainan marine sponges Axinyssa variabilis and Lipastrotethya ana.

Three unprecedented diastereoisomeric dimers, cis-dimer A (1), cis-dimer B (2) and trans-dimer C (3), exhibiting a bis-bisabolene skeleton, and a new sesquiterpene, dehydrotheonelline (4), their potential precursor, have been isolated from the South China Sea sponges Axinyssa variabilis and Lipastrotethya ana, along with known related sesquiterpenes. The structure of the novel molecules has been determined by extensive NMR spectral analysis.