Bioactive Dimeric Tetrahydroxanthones with 2,2′- And 4,4′-Axial Linkages from the Entomopathogenic FungusAschersonia confluens

Abstract

Thirteen tetrahydroxanthone dimers,atrop-ascherxanthone A (1), ascherxanthones C-G (2-6), and confluxanthones A-G (7-13), were isolated from the entomopathogenic fungusAschersonia confluensBCC53152. The chemical structures were determined based on analysis of NMR spectroscopic and mass spectrometric data. The absolute configurations of compounds1and7were confirmed by single-crystal X-ray diffraction experiments, while the configurations of other compounds were assigned based upon evidence from NOESY and NOEDIFF experiments, modified Mosher’s method, and ECD spectroscopic data together with biogenetic considerations. Compounds1,3-5,7-11, and13showed antimalarial activity againstPlasmodium falciparum(K1, multidrug-resistant strain) (IC500.6-6.1 μM), antitubercular activity againstMycobacterium tuberculosisH37Ra (MIC 6.3-25.0 μg/mL), and cytotoxicity against NCI-H187 (IC500.5-3.5 μM) and Vero (IC500.9-6.1 μM) cells. All tested compounds except for compound9exhibited cytotoxicity against KB cells (IC501.3-9.7 μM).