Search For New Antineoplastic Substances From Marine-derived Fungi

Thousands of new compounds have been isolated from marine organisms since the symposium entitled 'Drugs from the sea' in 1967.Most of them are structurally unique and show significant biological activity.Many researchers believe that these bioactive compounds are actually produced by 'symbiotic' microorganisms.Therefore,chemical studies of marine microorganisms have been a hotspot in the area of marine natural products in the past several years.Effective bioassay systems are important in searching for new bioactive natural products.Pyricularia oryzae model is such a screening method that depends on detecting deformation of mycelia germinated from conidia of P.oryzae P-2b. Kinds of antimitotic and antifungal compounds,such as rhizoxin,fusarielin A and phomopsidin,were found using this screening system.In order to search for new antimitotic and antifungal substances from marine-derived fungi,we apply this method as a primarily screening system and guided the purification process.During the systemmetric chemical research on the 10 bioactive fungus out of 1012 tested one,we obtained forty metabolites and thirty two of them were identified as paxilline(1),paspaline(2),emeniveol(3),12-demethylpaspaline-11-ene(4), 13-desoxypaxilline(5),emindole SB(6),paspaline B(7),β-PC-M6(8),pyrenocine A(9), pyrenocine C(10),pyrenocine E(11),zearalenone(12),8'-hydroxyzearalenone(13), 5'-hydroxyzearalenol(14),zearalenol(15),5'-hydroxyzearalenone(16),7'-dehydrozearalenone (17),fusarielin A(18),fusarielin B(19),fusarielin C(20),fusarielin E(21), 5-(acetyloxy)-1,5-dihydro-2H-pyrrol-2-one(22),fusapyrone(23),deoxyfusapyrone(24), asteltoxin(25),cycloechinulin(26),penicillic acid(27),4-hydroxymellein(28),α,β-dehydrocurvularin(29),terrein(30),ascochlorin(31) and mycophenolic acid(32), respectively.Coumpounds 4,14,16,and 21 are new compounds,and the single crystal X-ray diffraction analysis of 13-desoxypaxilline(5) and 5'-hydroxyzearalenol(14) was obtained firstly.It is the first isolation of emeniveol(3) from the genus Penicillium,and 5-(acetyloxy)-1,5-dihydro-2H-pyrrol-2-one(22) from natural source.We thus provided more evidence of the proposed biosynthetic pathway of the neurotoxin paxilline(1),and made some modifications to the proposed biosynthesis scheme based on chemical identification of those related metabolites 1-8.Activity experiments showed that compound 18 induced significant morphalogical abnormality of the conidia and mycelia of P.oryzae P-2b by curling effect,and inhibited the growth of them with minimum inhibition concentration(MIC) of 12.5μg/mL;compounds 1, 2,6,21,and 23-24 caused weak curling deformation,with MIC of 1.6,3.1,3.1,50,12.5 and 1.6μg/mL,respectively;compounds 3-5,7,9,11-13,16-17,20,22,25,and 27-32 showed no deformation effect,and the MIC values were between 0.31-400μg/mL;other compounds showed little effect against P.oryzae P-2b.Compounds 9-11,18-19,and 21 were shown to induce neuronal differentiation in rat PC12 cells,while compounds 1-8 and 20 showed cytotoxic activity against rat PC12 cells.The bioactivity of those compounds against P.oryzae P-2b in our study was in accordance with the antifungal or cytotoxic effects reported by other researchers,thus the P. oryzae model was proved to be efficient in guiding the seperation of bioactive metabolites from marine-derived fungi.