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Three new cembranoids (1–3) and a new casbanoid (4), along with three known analogues (5–7), have been isolated from the soft coral Sinularia nanolobata collected off Ximao Island. The structures, including the absolute configurations of new compounds, were established using extensive spectroscopic data analysis, time-dependent density functional theory/electronic circular dichroism (TDDFT-ECD) calculations, and the comparison with spectroscopic data of known compounds. In the in vitro bioassay, compounds 1 and 5 exhibited moderate cytotoxic activities against human erythroleukemia (HEL) cell lines, with IC50 values of 37.1 and 42.4 μM, respectively. [ABSTRACT FROM AUTHOR]

Nanolobatone A, featuring an unprecedented tricyclo[10.3.0.01,2]pentadecane carbon skeleton, along with four new polyoxygenated and four unusual endoperoxide‐bridged casbane‐type diterpenoids were isolated from the Hainan soft coral Sinularia nanolobata. The structures of the new compounds were established by extensive spectroscopic analysis, X‐ray diffraction analysis, and time‐dependent density functional theory/electronic circular dichroism calculations. A plausible biosynthetic pathway of new isolates was proposed. Bioassays revealed that nanolobatone A showed weak antibacterial activity against the Gram‐positive bacteria Streptococcus pyogenes. [ABSTRACT FROM AUTHOR]

A detailed chemical investigation of the nudibranch Glossodoris atromarginata collected from Weizhou Island, South China Sea, yielded a new spongian‐type diterpene 1, together with the four known‐related compounds 2–5. The structure of the new compound 1 was elucidated by the detailed spectroscopic analysis, the comparison of the spectroscopic data with the known diterpene isoagatholactone, and the 13C chemical shift calculation. In addition, evidence for the absolute stereochemistry of the known compound 2 was, for the first time, provided by the application of time‐dependent density functional theory electronic circular dichroism calculation. [ABSTRACT FROM AUTHOR]

• A series of polycyclic furanobutenolide-derived norcembranoids were obtained. • TDDFT-ECD and X-Ray diffraction analysis were employed to determine absolute configurations. • ECD spectra data were in agreement with the proposed empirical ECD helicity rule. • Potent immunosuppressive activities against T and/or B lymphocytes were observed. One new polycyclic furanobutenolide-derived norcembranoid, xiguscabrolide H (1), together with eleven known related norditerpenoids 2 – 12 were isolated from South China Sea soft corals Sinularia scabra and S. polydactyla , respectively. Among them, compounds 1 , 6 , 8 , and 12 were discovered from the former species, while compounds 2 – 5 , 7 , and 9 – 11 were obtained from the latter species. The structure of new compound 1 was elucidated by extensive spectroscopic analysis and by the comparison with the reported data. With the assistance of time-dependent density functional theory electronic circular dichroism (TDDFT-ECD) calculations, its absolute configuration was determined. Moreover, the absolute stereostructures of the known compounds 3 , 4 , and 9 – 12 , of which only relative configurations were assigned, were established for the first time by X-Ray diffraction analysis and TDDFT-ECD calculations, respectively. In bioassay, several isolates exhibited potent inhibitory effects on the ConA-induced T lymphocytes and/or LPS-induced B lymphocytes proliferation. [ABSTRACT FROM AUTHOR]