Chemical Investigations Of A Low-Temperature Adapted Phoma Sp. And Its EupA Disruption Mutant

Natural products are important sources of new drugs and lead compounds for therapeutics.Due to the vast diversity of fungi,fungal secondary metabolites play important roles in drug discovery and development.To date,many important medicines have been discovered either directly from fungi or derived from fungal secondary metabolites,such as penicillins,lovastatins,cyclosporin A,and fingolimod.Since it is increasingly difficult to discover new bioactive natural products from fungi residing in common ecological niches,those inhabiting unique environments(e.g.low-temperature habitats)have attracted much attention for the past decade.These fungi are more likely to produce structurally unique and biologically active secondary metabolites.The psychrotolerant fungi live in various low temperature environments,and gradually developed unique metabolism and defense system for survival.On the other hand,chemical investigations of this group of fungi remained underexplored,psychrotolerant fungi have huge potential in finding bioactive natural products,and even lead compounds for drug discovery.Based on the results from our prior chemical investigations of the fungal species isolated from various low-temperature environments,a strain of Phoma sp.isolated from a soil sample that was collected from the Qinghai-Tibetan plateau was chemically investigated,leading to the isolation of unique meroterpenoids with new skeletons,which showed potent antiproliferative effects against human tumor cell lines.To identify other minor active components and possible intermediates/precursors,the fungus was refermented in a larger scale on rice to afford a crude extract.The polyketide synthase gene eupA is a key gene for the biosynthesis of major secondary metabolites in the wild type strain(WT).By comparing the HPLC fingerprints of the eupA disruption mutant with those of WT,we found that the eupA disruption mutant(ΔeupA)produced a series of new compounds.The crude extracts prepared from frementation of WT and ΔeupA were subsequently fractionated by silica gel and/or Sephadex LH-20 column chromatography,and reversed-phase high performance liquid chromatography(RP HPLC)to afford 38 secondary metabolites,23 of which were new compounds.The structures of the new compounds were elucidated primarily by mass spectrometry(MS)and nuclear magnetic resonance(NMR)experiments,together with circular dichroism(CD)and X-ray diffraction analysis.Hypothetical biosynthetic pathways for some of the new compounds were proposed based on their chemical structures and biogenetic relationships.Two of the compounds isolated in the current work showed moderate cytotoxicity against human tumor cell lines.Chemical studies of the strain of Phoma sp.and its eupA disruption mutant notonly afforded a variety of new secondary metabolites,proposed their plausible biosynthetic pathways and mutual transformation relationships,and pave the way to further expore the biosynthetic pathways for the major secondary metabolites and to maximize the metabolic potential of the fungus.