Antioxidant phenolic glycoside and flavonoids from Pieris japonica

A new phenolic glycoside, benzyl 2-hydroxy-4-O-β-D-glucopyranosyl-benzoate (1), along with nine known flavonoids, epicatechin-(2 → O → 7,4 → 8)-ent-epicatechin (2), bis-8,8'-catechinylmethane (3), quercetin (4), quercetin-3-O-α-L-arabinfuranoside (5), quercetin-3-O-α-L-rhamnopyranoside (6), astilbin (7), engeletin (8), (2S,3R)-ent-catechin (9), and 2',4-dihydroxy-4'-methoxy-6'-O-β-D-glucopyranosyl dihydrochalcone (10), was isolated from the flowers of Pieris japonica. Their structures were elucidated on the basis of MS, 1D NMR, and 2D NMR techniques. This paper describes the isolation, structural elucidation as well as in vitro antioxidant activity of these compounds.