4.5.1. DPPH Radical Scavenging Activity

A DPPH radical scavenging assay was carried out as previously reported [38]. Scavenging of 2,2-diphenyl-1-picryhydrazyl (DPPH) radicals by the acetone extract (AE) (50 μg of 2 mg/mL solution dissolved in DMSO) and compounds (**1**–**14**) (50 μg of 2 mg/mL solution dissolved in DMSO) was measured in 100 mM Tris-HCl buffer (pH 7.4) by recording the absorbance at 517 nm spectrophotometrically. Ascorbic acid (50 μg of 2 mg/mL solution

dissolved in DMSO) served as the standard. The results were expressed as %-scavenging and calculated by using the following formula: (Ac−At)/100 × Ac, where Ac was the absorbance of control and At was the absorbance of the test sample. Different concentrations of compounds were evaluated to obtain 50% scavenging activity (SC50). The SC50 was calculated based on the equation obtained from regression analysis.

#### 4.5.2. ABTS Radical Scavenging Activity

Scavenging of the 2,2 -azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS•+) was performed as per the earlier method [39]. Acetone extract (AE) (20 μg of 2 mg/mL solution dissolved in DMSO) and compounds (**1**–**14**) (20 μg of 2 mg/mL solution dissolved in DMSO) were incubated with ABTS•<sup>+</sup> solution in 6.8 mM phosphate buffer (pH 8.0) as described earlier. The discoloration of the ABTS•<sup>+</sup> solution was determined by measuring the absorbance at 734 nm spectrophotometrically. Ascorbic acid (20 μg of 2 mg/mL solution dissolved in DMSO) served as the standard. The activity was expressed as %-scavenging and calculated as follows: (Ac − At)/(100 × Ac), where Ac was the absorbance of control and At was the absorbance of the test sample. The SC50 of compounds was calculated as per the above formula.
