Isookanin shows strong diphenyl(2,4,6-trinitrophenyl)iminoazanium (DPPH) radical-scavenging activity with the IC50 value of 7.9 ± 0.53 μM. Isookanin is a potent inhibitor of α-amylase (IC50=0.447 mg/ml).
The chemical structures of these compounds were elucidated by extensive spectroscopic analysis and on the basis of their chemical reactivity. This work represents the first recorded example of the isolation of compounds 1??3, 6, 7, 9, 11, and 12 from C. tinctoria. Compounds 5??9 showed strong diphenyl(2,4,6-trinitrophenyl)iminoazanium (DPPH) radical-scavenging activity, with IC50 values of 3.35 ± 0.45, 9.6 ± 2.32, 4.12 ± 0.21, 6.2 ± 0.43, and 7.9 ± 0.53 μM, respectively. Compounds 2 and 8 exhibited angiotensin I-converting enzyme inhibitory activity, with IC50 values of 228 ± 4.47 and 145.67 ± 3.45 μM, respectively.