Concise synthesis of quercetagetin (3,3ʹ,4ʹ,5,6,7-hexahydroxyflavone) with antioxidant and antibacterial activities

Abstract

Quercetagetin (3,3ʹ,4ʹ,5,6,7-hexahydroxyflavone) is a characteristic flavonol that has six hydroxy (–OH) group based on the chemical structure of the flavone backbone. Herein, we report a concise, efficient, and scalable synthesis of biologically important quercetagetin with antioxidant and antibacterial activities. The synthesis has been achieved in three steps from starting materials 1 and 2 in 27 % overall yield. The chemical structure of synthetic quercetagetin has been confirmed by 1H NMR, 13C NMR, and high-resolution mass spectrometry (HRMS) analyses. Antioxidant activity of synthetic quercetagetin and control compounds quercetin, butylated hydroxyanisole (BHA), and Trolox has been compared using DPPH and ABTS radical scavenging assays. The synthetic quercetagetin exhibits the highest antioxidant activity when compared with control compounds. Furthermore, the synthetic quercetagetin has displayed potent antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) strains with MIC value of 16 µg/mL when compared with standard antibiotic drugs Ampicillin and Kanamycin (with MIC values of >256 µg/mL). To distinguish bactericidal and bacteriostatic effects of synthetic quercetagetin, time-kill kinetic studies have been performed and the results exhibit that the synthetic quercetagetin possesses bacteriostatic action.