Antioxidant phenylacetic acid derivatives from the seeds of Ilex aquifolium.

Reversed-phase preparative HPLC analysis of the methanol extract of the seeds of Ilex aquifolium afforded two antioxidant phenylacetic acid derivatives, 2,4-dihydroxyphenylacetic acid (1) and 2,4-dihydroxyphenylacetic acid methyl ester (2). The structures were determined by spectroscopic methods. In the DPPH assay for antioxidant activity, the IC(50) values of 1 and 2 were 1.50 x 10(-3) and 2.55 x 10(-3) mg mL(-1), respectively, compared to 2.88 x 10(-5) mg mL(-1) of quercetin, a natural antioxidant.