Anti-tyrosinase, antioxidant, and antibacterial activities of novel 5-hydroxy-4-acetyl-2,3-dihydronaphtho[1,2-b]furans.

Novel 5-hydroxy-4-acetyl-2,3-dihydronaphtho[1,2-b]furans (7a-k) were synthesized using ceric ammonium nitrate (CAN)-catalyzed formal [3 + 2] cycloaddition. Synthesized compounds were evaluated for their tyrosinase inhibitory, antioxidant, and antibacterial activities. A modified spectrophotometric method using l-DOPA as substrate was used to determine tyrosinase inhibitory activities, and a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay was used to evaluate antioxidant properties. Antibacterial activities against gram-negative Escherichia coli (KCTC-1924) and gram-positive Staphylococcus aureus (KCTC-1916) were evaluated using the disc diffusion technique. Of the synthesized compounds, 7b with a 4-acetyl and an electron-enriched dihydronaphthofuran ring showed the highest tyrosinase-inhibition activity (IC50 = 8.91 μg/mL), which was comparable with that of standard kojic acid (IC50 = 10.16 μg/mL), potent antioxidant activity (IC50 = 3.33 μg/mL), which was comparable with that of BHT (IC50 = 34.67 μg/mL), and excellent antibacterial activities (MICs: 0.50 μg/mL against E. coli and S. aureus strains). A mechanistic analysis of 7b demonstrated that its tyrosinase inhibitory activity was reversible and competitive. Compounds 7c and 7d showed potent antioxidant activities (IC50: 6.30 and 5.01 μg/mL), and compound 7d also exhibited potent inhibitory activity against E. coli with a MIC of 0.5 μg/mL. Furthermore, compounds 7a, 7e, 7f, and 7i showed potent antibacterial activities against S. aureus with MICs of 0.5 μg/mL, which was comparable to that of ampicillin (MIC = 0.5 μg/mL).