Variation among known kalihinol and new kalihinene diterpenes from the sponge Acanthella cavernosa

Seven new diterpene constituents were isolated from the sponge Acanthella cavernosa investigated from Fijian locations. Their structures were established based on a combination of spectroscopic data, x-ray crystallographic data and biogenetic arguments. These new diterpenes, of the kalihinane family, can be divided into the kalihinene (compounds 4 – 6) or the 6-hydroxy-kalihinene (compounds 7 – 10) frameworks. Also present were three known compounds, kalihinol A (1), isokalihinol F (2) and kalihinene (3). It is proposed that the kalihinane type diterpenes are a chemotaxonomic marker for A. cavernosa. Its diterpenes can be clustered into three biogenetic families based on the stereochemistry of the decalin ring forming process. The presence of different members of these biogenetic types might be used to chemically distinguish various populations of A. cavernosa. Its compounds, 1, 3 and 7 were major constituents in both the bulk collection extracted after collection and in 15 specimens held in a controlled aquaculture system for seven months before extraction. A subtle chemical difference could be discerned among these samples based on the content of compounds 1, 3 - 5 and 7.