Seven new briarane diterpenoids, gemmacolides G-M (1-7), were isolated together with two known analogues, juncin O and junceellolide C, from the South China Sea gorgonian Dichotella gemmacea. The structures of the new compounds were elucidated by detailed analysis of spectroscopic data and comparison with reported data. In an in vitro bioassay, these compounds exhibited different levels of growth inhibition activity against A549 and MG63 cells. In particular, compound 4 was more active than the positive control adriamycin against A549 cells. Compounds 4 and 7 also exhibited weak antimicrobial activity against the bacterium Bacillus megaterium and the fungus Septoria tritici, respectively.

Two new prenylgermacrane-type diterpenoids, lobophytumins A and B (1 and 2), two new prenyleudesmane-type diterpenoids, lobophytumins C and D (3 and 4), and two new spatane-type diterpenoids, lobophytumins E and F (5 and 6), were isolated from the Hainan soft coral Lobophytum cristatum Tixier-Durivault. Their structures, including relative configuration, were elucidated by detailed analysis of spectroscopic data and by comparison with related known compounds. In addition, the absolute configuration of lobophytumin C (3) was tentatively assigned by comparing its specific rotation with that of the closely related model compound (-)-β-selinene (8). On the basis of biogenetic considerations, the absolute configurations of lobophytumins A, B, and D-F were also tentatively suggested. This is the first report of spatane-type diterpenoids from a soft coral source. The present work supports Faulkner's proposal of prenylgermacrene as the precursor of many diterpenes. In a bioassay, lobophytumins C and D (3 and 4) showed weak in vitro cytotoxicities against the tumor cell lines A-549 and HCT-116.

Ten new cembrane-based diterpenes, locrassumins A–G (1–7), (–)-laevigatol B (8), (–)-isosarcophine (9), and (–)-7R,8S-dihydroxydeepoxysarcophytoxide (10), were isolated from a South China Sea collection of the soft coral Lobophytum crassum, together with eight known analogues (11–18). The structures of the new compounds were determined by extensive spectroscopic analysis and by comparison with previously reported data. Locrassumin C (3) possesses an unprecedented tetradecahydrobenzo[3,4]cyclobuta[1,2][8]annulene ring system. Compounds 1, 7, 12, 13, and 17 exhibited moderate inhibition against lipopolysaccharide (LPS)-induced nitric oxide (NO) production with IC50 values of 8–24 μM.

Nineteen metabolites with diverse structures, including the rare pyrroloindoline alkaloid verrupyrroloindoline (1), the unprecedented highly fused benzosesquiterpenoid verrubenzospirolactone (2), the new asteriscane-type sesquiterpenoid 10-deoxocapillosanane D (3), and the two new cyclopentenone derivatives (4S*,5S*)-4-hydroxy-5-(hydroxymethyl)-2,3-dimethyl-4-pentylcyclopent-2-en-1-one (4) and (S)-4-hydroxy-5-methylene-2,3-dimethyl-4-pentylcyclopent-2-en-1-one (5), were isolated from a South China Sea collection of the soft coral Sinularia verruca. Eleven previously described marine metabolites (7−15, 18, and 19) were also obtained as well as three new EtOH-adduct artifacts (6, 16, and 17). The structures of the new compounds were elucidated by extensive spectroscopic analysis and by comparison with previously reported data. Compounds 4, 5, and 16 showed protection against the cytopathic effects of HIV-1 infection with EC 50 values of 5.8−34 μM, and 4, 6, and 16 exhibited inhibition against LPS-induced NO production with IC 50 values of 24−28 μM. S oft corals of the genus Sinularia (family Alcyoniidae) are commonly distributed in the tropical coral reef systems of the world and are well known for being a rich source of biologically active secondary metabolites. In the past several decades, more than 50 Sinularia species have been chemically investigated, resulting in the discovery of hundreds of secondary metabolites including sesquiterpenoids, diterpenoids, polyhydroxylated steroids, cyclopentenones, and butenolides.

A floristic study of the marine plants and algae at Luhuitou reef, Sanya Bay, Hainan Island, China, was conducted during the rainy (October 2008 and November 2010) and dry seasons (April 2009 and February 2012). Specimens were collected in the upper subtidal zone (from 0.5 to 3 m depth at low tide). A total of 156 taxa were collected, including 143 macrophyte species (90%), 12 blue–green algal species (10%), and the seagrass, Thalassia hemprichii. The most diverse group was the Rhodophyta (79 taxa or 55%), followed by the Chlorophyta (38 taxa or 25%) and then the Phaeophyceae (26 taxa or 20%). In the upper subtidal zone, macroalgae formed two types of communities: polydominant communities of turf-forming algae and monodominant and bidominant communities of foliose or fleshy algae. Seasonal changes occurred in the dominant species, which appear to be caused by periodic annual events of thalli detachment and subsequent community succession. In spite of heavy pollution from dissolved inorganic nitrogen and phosphorus in Sanya Bay, the subtidal flora has not undergone any dramatic changes in species numbers or composition and is similar to that of unpolluted regions in the Indo-Pacific.

Chemical investigation of the ethanol extract of soft coral Sinularia sp. collected from the South China Sea led to the isolation of three new polyoxygenated sterols, (3S,23R,24S)-ergost-5-ene-3β,23α,25-triol (1), (24S)-ergostane-6-acetate-3β,5α,6β,25-tetraol (2), (24S)-ergostane-6-acetate-3β,6β,12β,25-tetraol (3) together with three known ones (4–6). The structures, including relative configurations of the new compounds (1–3), were elucidated by detailed analysis of spectroscopic data (IR, UV, NMR, MS) and by comparison with related reported compounds. The absolute configuration of 1 was further determined by modified Mosher’s method. Compound 5 exhibited moderate cytotoxicity against K562 cell line with an IC50 value of 3.18 μM, but also displayed strong lethality toward the brine shrimp Artemia salina with a LC50 value of 0.96 μM.

Four new steroids, named 7-dehydroerectasteroid F (1), 11α-acetoxyarmatinol A (2), 22,23-didehydroarmatinol A (3), and 3-O-acetylhyrtiosterol (4), together with 11 previously described analogues, were isolated from a South China Sea collection of the soft coral Dendronephthya gigantea. The structures of the new steroids were elucidated by comprehensive spectroscopic analysis and by comparison with previously reported data. Compound 1 showed potent protection against H 2 O 2 -induced oxidative damage in neuron-like PC12 cells by promoting nuclear translocation of Nrf2 and enhancing the expression of HO-1. 1 represents the first steroid-type antioxidant from marine organisms.

Eight new marine steroids, characterized by either the presence of an aromatic ring or a cross-conjugated dienone system in ring A, were isolated from the Hainan soft coral Dendronephthya studeri Ridley. Their structures were elucidated on the basis of detailed spectroscopic analysis and by comparison of their NMR data with those reported in the literature.