Studies Of The Secondary Metabolites From A Mangrove Brguiera Sexangula Var. Rhynchopetala Fungus

Mangrove forests as a special population grow in tropical and subtropical coast intertidal zone,including many living creatures which constitute the unique ecosystems.Due to unique growth environment,making the mangrove is rich in many special endophytic microorganisms.These unique microbial can produce some secondary metabolites with unique structure and activity.Medicinal mangrove endophytic fungi have become an important source of active marine natural products.Brguiera sexangula var.Rhynchopetala is endemic medicinal mangrove in Hainan province.And it often used in the treatment of malaria in the folk.The literature showed that the extract of mangrove has antitumor activity and antimicrobial activity.Currently,there have some literatures about the study of the chemical ingredients in B.sexangula var.Rkynchopetala.But there have no literatures about the study of the endophytic fungi.This study provides the theoretical basis for antitumor and antibacterial drug research.And it has great significance for protecting and reusing the resource of mangrove plants.In this study,125 microorganisms were isolated from the B.sexangula var.Rhynchopetala,which was collected from the South China Sea.Under the bioassay guided and HPLC-MS screening,an epiphytic fungus of Stemphylium sp.33231 was selected for fermentation.The secondary metabolites were isolated by column chromatography on Sephadex LH-20,silica gel and HPLC,and identified by spectroscopy of 1D-NMR,2D-NMR,MS,UV,IR,CD,X-ray and chemical methods.Forty-two compounds(1-42)were isolated and puried from the endophytic fungus Stemphylium sp.33231,including 13 new compounds.More than 7 structural types were found,including 28 anthraquinones,5 nitrogen-containing,2 pyrones,1 chromone,1 lactone,2 steroids,and 1 lipid.The absolute configuration of 1,3 and 4 were determined by single-crystal X-ray diffraction of their derivatives(la,3b and 4a).The absolute configuration of 17-19,22-24 were determined by single-crystal X-ray diffraction.The absolute configuration of 10 was assigned by CD spectroscopy.Five derivatives of compound 13(13a-13e)have been prepared by acetylation,bromobenzene formyl,and bromine for further research on structure and activity relationships.The biological assayes including cytotoxic activity antibacterial activity and brine shrimp lethality were used to find active compounds.Compounds 3,5,17-19,34 and 37 exhibited cytotoxic activity against A549 cell lines.Compounds 14,17,19 exhibited a broad spectrum antibacterial activity and 18 exhibited antibacterial activity against S.aureus with MIC value 2.07μM.Only 2 displayed a moderate lethality effect.