An ethyl acetate-soluble extract of Chorizanthe diffusa was found to exhibit significant antioxidant activity, as judged by scavenging stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals and inhibition of 12- O -tetradecanoylphorbol 13-acetate (TPA)-induced free radical formation with cultured HL-60 cells. Bioassay-directed fractionation of this extract using the DPPH antioxidant assay as a monitor led to the isolation of five structurally related flavonoids ( 1 − 5 ), including the novel compound 5,8,3‘,4‘,5‘-pentahydroxy-3,7-dimethoxyflavone ( 1 ). Isolates 1 − 5 demonstrated varying degrees of antioxidant or antimutagenic activity. Two of the compounds, 5,7,3‘,4‘-tetrahydroxy-3-methoxyflavone ( 2 ) and quercetin ( 4 ), were subsequently found to inhibit carcinogen-induced preneoplastic lesions in a mouse mammary organ culture model. Inhibitory activity of this type is known to correlate with cancer chemopreventive effects in full-term models of tumorigenesis.
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Chung et al. (1998) studied this question.
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