Isolation and Absolute Configurations of Diversiform C, C and C Terpenoids from the Marine Sponge sp.

Chemical investigation of MeOH extract of a South China Sea sponge sp. yielded 15 terpenoids belonging to three different skeleton-types, including the unusual C -lactone norditerpenoids (⁻), the rare C pyridine meroterpenoid (), and the notable C manoalide-type sesterterpenoids (⁻, ⁻). Compounds ⁻ were initially obtained as enantiomers, and were further separated to be optically pure compounds (, , , , , , , , and ) by chiral HPLC, with a LiAlH₄ reduction aid for . Compounds / (a pair of inseparable enantiomers), , , , and were identified as new compounds, while / and / were obtained from a natural source and were determined for their absolute configurations for the first time. This is also the first time to encounter enantiomers of the well-known manoalide-type sesterterpenoids from nature. The structures with absolute configurations of the new compounds were unambiguously determined by comprehensive methods including HR-ESI-MS and NMR data analysis, optical rotation comparison, experimental and calculated electronic circular dichroism (ECD), and Mo₂(OAc)₄ induced circular dichroism (ICD) methods. The cytotoxicity of the isolates against selected human tumor cell lines was evaluated, however, the tested compounds showed no activity against selected cell lines.