A new antibacterial quinolone derivative from the endophytic fungus Aspergillus versicolor strain Eich.5.2.2

Abstract

Fine chromatographic fractionation of the EtOAc (ethyl acetate) extract of a solid rice culture of the endophytic fungus Aspergillus versicolor strain Eich.5.2.2 from the petals of flowers of the Egyptian water hyacinth Eichhornia crassipes revealed the isolation of a new quinolone derivative (1) along with its known isomer aniduquinolone A (2). Structure elucidation of the isolated compounds was unambiguously determined through HRESIMS (High-Resolution Electrospray Ionization Mass Spectrometry) and extensive 1D and 2D NMR (Nuclear Magnetic Resonance) spectroscopy. The relative and absolute configurations of the new compound are deduced through ROESY (Rotational Overhauser Effect SpectroscopY), optical rotation as well as biogenetic consideration. Interestingly, the epimers (1/2) altogether exhibited a significant antibacterial activity against the bacterium Staphylococcus aureus (ATCC700699) with a MIC (Minimum Inhibitory Concentration) of 0.4 µg/mL and fortunately with no cytotoxic effects highlighting a specificity of the antibacterial effect.