Antioxidative principles from peanut hulls

Inhibition of Cu⁺²/O₂-induced low density lipoprotein (LDL) lipid peroxidation-guided fractionation and separation resulted in the isolation of six flavonoids as the active principles from peanut (Arachis hypogaea L.) hulls. Their structures were characterized as 3',4',5,7-tetrahydroxy-8-(3- methylbut-2-enyl)flavone (1), chrysoeriol (2), 4',5-dihydroxy-3'-methoxy- 2'',2''-dimethylpyrano[5'',6'':7:8]flavone (3), 4',5,7-trihydroxy-3'-methoxy- 8-(3-methylbut-2-enyl)flavone (4), luteolin (5) and eriodictyol (6) by spectroscopic methods. Compounds 1, 2, 5 and 6 had more potent activities, and their IC₅₀ values were 4.5, 2.6, 1.7 and 1.5 μM, respectively. Flavones with an isopentenyl substitution at C-8 were less potent. Flavonoids having an ortho-dihydroxy on the B-ring showed stronger activity than the same skeleton compound with a methoxy substituent at C-3'. The antioxidant potency of flavanone (6) was higher than flavone (5).