Two Antimicrobial Heterodimeric Tetrahydroxanthones with a 7,7′-Linkage from Mangrove Endophytic Fungus Aspergillus flavus QQYZ

Mangrove endophytic fungi represent significant and sustainable sources of novel metabolites with unique structures and excellent biological activities, attracting extensive chemical investigations. In this research, two novel heterodimeric tetrahydroxanthones, aflaxanthones A (1) and B (2), dimerized via an unprecedented 7,7′-linkage, a sp(3)-sp(3) dimeric manner, were isolated from the mangrove endophytic fungus Aspergillus flavus QQYZ. Their structures were elucidated through high resolution electrospray ionization mass spectroscopy (HRESIMS) and nuclear magnetic resonance (NMR) spectroscopy, the absolute configurations of them were determined by a single-crystal X-ray diffraction combined with calculated electronic circular dichroism (ECD) spectra and a 1D potential energy scan. These compounds were evaluated for antifungal activities in vitro and exhibited broad-spectrum and potential antifungal activities against several pathogenic fungi with minimum inhibitory concentration (MIC) values in the range of 3.13–50 μM. They also performed moderate antibacterial activities against several bacteria with MIC values in the range of 12.5–25 μM. This research enriched the resources of lead compounds and templates for marine-derived antimicrobial drugs.