A pair of novel bisheterocyclic quinoline-imidazole alkaloids, (+)- and (-)-spiroreticulatine (1), were isolated from the South China Sea sponge Fascaplysinopsis reticulata. The structures and absolute configurations were elucidated by comprehensive spectroscopic analysis, single-crystal X-ray diffraction, and quantum chemical calculation methods. Spiroreticulatine is the first example of a sponge-derived natural spiro quinoline-imidazole alkaloid that may derive from tryptophan and 1,3-dimethylurea. Compound 1 showed inhibitory activity on IL-2 production but inactive against normal tumor cell lines.
Three new sesquiterpenoids (sinuketal (1), sinulins A and B (2 and 3)) and two new cembranoids (sinulins C and D (4 and 5)), as well as eight known sesquiterpenoids (6–13) and eight known cembranoids (14–21), were isolated from the Xisha soft coral Sinularia sp. Their structures were elucidated by extensive spectroscopic analysis. Compound 1 possesses an unprecedented isopropyl-branched bicyclo [6.3.0] undecane carbon skeleton with unique endoperoxide moiety, and a plausible biosynthetic pathway of it was postulated. According to the reported biological properties of endoperoxide, the antimalarial, cytotoxic, antiviral, and target inhibitory activities of 1 were tested. Compound 1 showed mild in vitro antimalarial activity against Plasmodium falciparum 3D7, weak cytotoxic activities toward Jurkat, MDA-MB-231, and U2OS cell lines, inhibitory effects against influenza A viruses H1N1 and PR8, as well as mild target inhibitory activity against acetylcholinesterase. The other compounds were evaluated for cytotoxicities against HeLa, HCT-116, and A549 tumor cell lines and target inhibitory activities against protein tyrosine phosphatase 1B (PTP1B). Compound 20 exhibited cytotoxicities against HeLa and HCT-116, and compounds 5, 11, and 15 showed mild target inhibitory activities against PTP1B.
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