| Abstract |
In order to search for new bioactive compounds, we have investigated the secondary metabolites of the soft coral Scleronephthya gracillimum, the red alga Laurencia brongniartii and the brown alga Homoeostrichus formosana. Chemical constituents from the organic extracts of S. gracillimum, fourteen new pregnane-type steroids 1, 4, 5, 7−15, 16, 17, and a new diterpenoid 3-methyl-5-(10′-acetoxy-2′,6′,10′- trimethylundecyl)-2- penten-5-olide 18, including three known pregnane-type steroids 2, 3, 6 have been isolated. In addition, a novel polybrominated indole derivative 20 and eleven known metabolites 19, 21−30 were isolated from the acetone extracts of L. brongniartii. Furthermore, one novel meroditerpenoid-related natural product 31, one semi-synthesis through acetylated derivative of 31 (compound 36), along with four known compounds 32−35 were isolated for the first time from Homoeostrichus formosana. The structures of the isolated metabolites were elucidated through extensive spectroscopic methods, in particular 1D and 2D NMR experiments. The absolute configurations of sugar moieties in steroidal glycosides 9−12 were determined by HPLC analysis of the o-tolylthiocarbamate derivatives of the liberated sugars hydrolysed from these steroidal glycosides. Moreover, the absolute configurations of 2 were established by application of the modified Mosher’s method. Compounds 1−4, 9−11, 15−17, 19−25, 27−32 and 34−36 have been exhibited cytotoxicity toward a limited panel of cancer cell lines. Compounds 1, 4, 8, 14, 16–19, 25 and 28–30 were found to display significant in vitro anti-inflammatory activity in LPS-stimulated RAW 264.7 macrophage cells by inhibiting the expression of the iNOS protein. Compounds 1, 4, 8, 13, 14, 16–18, 28, and 29 also could effectively reduce the level of the COX-2 protein. Moreover, 19 were exhibited antibacterial activity against Enterobacter aerogenes (ATCC13048), Salmonella enteritidis (ATCC13076), and Serratia marcescens (ATCC25419), and compounds 28 and 29 showed activity against Serratia marcescens. Compound 32 has been exhibited remarkable inhibitory effects on superoxide anion generation and elastase release by human neutrophils. Compound 35 showed moderately inhibitory effects on superoxide anion generation and the elastase release by human neutrophils. Interestingly, compound 31 was exhibited mild activity to enhance human neutrophils superoxide anion generation and elastase release. According to the initial analysis of compounds 31–36 were assayed for antibacterial acticity against Bacillus cereus (ATCC14579), Staphylococcus aureus (ATCC9144), Salmonella typhimurium (ATCC14028), Pseudomonas aeruginosa (ATCC 27853), Serratia marcescens (ATCC25419) and Yersinia enterocolitica (ATCC23715), 31 exhibited against all six pathogens and compounds 32, 35 and 36 significantly inhibit the activity of P. aeruginosa. |
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