Isolation and characterization of 5-O-desmethyl kinanthraquinone B generated through O-methyltransferase gene disruption

Abstract 5- O -desmethyl kinanthraquinone B, a new kinanthraquinone analogue, was isolated from a kiqT1 disruptant. Its structure was elucidated by high-resolution electrospray ionisation mass spectrometry and nuclear magnetic resonance spectrometry and subsequently compared with the spectroscopic data of kinanthraquinone B. The newly isolated analogue exhibited antibacterial activity against Staphylococcus aureus , antimalarial activity against Plasmodium falciparum , and cytotoxicity toward HL-60 cells, with IC₅₀ values of 3.7, 5.5 and 11 μg/mL, respectively. Comparison of the biological activities of 5- O -desmethyl kinanthraquinone B and kinanthraquinone B indicated that methylation of the C-5 hydroxyl group reduced antibacterial activity and cytotoxicity with little effect on antimalarial activity.