| This thesis consists of two chapters.The first chapter discusses the guanacastane-type diterpenes isolated from the rice fermentation of Psathyrella candolleana and their biological activities.The second chapter discusses the studies on the biosynthetic pathways of guanacastane-type diterpenes.The fungus Psathyrella candolleana belongs to the genus psathyrella of the family Psathyrellaceae.Previous chemical studies on this fungus have reported guanacastane-type diterpenoids,which contain a 5/7/6 tricyclic backbone.According to the literature,the guanacastane-type diterpenoids possess various bioactivities including antibacterial,and anticancer activities.In the current investigation,a total of 31 compounds have been isolated from the rice fermentation of P.candolleana.Their structures were established on the basis of extensive spectroscopic analysis(1D and 2D NMR,MS,UV,IR,and single crystal X-ray diffraction analyses).Of them,sixteen new guanacastane-type diterpenes including new carbon skeletons,as well as three ergosterols were identified.The isolated compounds were evaluated for their antibacterial and cytotoxic activities.Compounds 1,2and 21 exhibited antibacterial activities,and compounds 27 and 28 exhibited cytotoxic activities.Guanacastane diterpenes have attracted much attention due to their novel structure.However,the biochemical and genetic basis of its biosynthesis have remained obscure.In this study,we identified a candidate gene cluster,Psa,responsible for the biosynctehsis of guanacastane diterpenes by combination of genome sequencing,transcriptome sequencing,q RT-PCR and bioinformatic analysis.The function of diterpenece cyclase,Psa C,in the gene cluster was characterized by gene clone,heterologeous expression and in vitro enzymatic assays.The cyclized product of Psa C was elucidated by synthetic biology method.Thus,we proved Psa C is the diterpene cyclase responsible for the biosynthesis of guanacastane diterpenes. |
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