Isolation of Antioxidative Compounds from Brazilian Propolis: 3,4-Dihydroxy-5-prenylcinnamic Acid, a Novel Potent Antioxidant.

One new and 11 previously known antioxidative compounds were isolated from Brazilian propolis. The new compound was determined as 3,4-dihydroxy-5-prenylcinnamic acid (3-[3,4-dihydroxy-5-(3-methyl-2-butenyl)phenyl]-2-(E)-propenoic acid) by various physical analyses (MS, IR, 1 H-NMR, 13 C-NMR, and 2D-NMR). The inhibitory activity of each compound against peroxidation of linoleic acid in a micelle solution was measured. We found that the novel compound possessed the highest potency (IC50, 0.17 m M) among them and was more effective than butylated hydroxytoluene (BHT; IC50, 0.36 m M) under the experimental conditions employed. Among the isolated antioxidative compounds, 3,5-diprenyl-4-hydroxycinnamic acid (artepillin C; IC50, 0.44 m M) was found to be most abundant in Brazilian propolis.