3.5. General Procedure to Determine the DPPH Radical Scavenging Activity

The radical scavenging activity of the prenylated compounds and starting materials towards the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical was measured as described [18], adapted to a screen to 96-well plates. Briefly, stock solutions of each compound were prepared in methanol at a 1-mM concentration (10 mL). Dilutions (1–200 µM) were prepared from the stock solutions. Methanol (90 µL), dilutions (150 µL), and DPPH (60 µL, Sigma–Aldrich) in methanol (0.5 mM), resulting in a final concentration of 0.1 mM of DPPH were added in a 96-well plate. Methanol was used as the blank sample. The mixtures were left for 30 min at room temperature, and the absorbances were then measured at 517 nm. Trolox was used as the standard antioxidant. The radical scavenging activity was calculated as follows: % Inhibition = [(blank absorbance − sample absorbance)/blank absorbance] × 100. The mean of three IC₅₀ (concentration causing 50% inhibition) values for each compound was determined graphically.