Antioxidative flavonoids from Cleistocalyx operculatus buds.

Four new flavonoids, 3'-formyl-4',6',4-trihydroxy-2'-methoxy-5'-methylchalcone (1), 3'-formyl-6',4-dihydroxy-2'-methoxy-5'-methylchalcone 4'-O-beta-D-glucopyranoside (2), (2S)-8-formyl-6-methylnaringenin (3), and (2S)-8-formyl-6-methylnaringenin 7-O-beta-D-glucopyranoside (4) were isolated from the buds of Cleistocalyx operculatus (Myrtaceae). The structures of the new metabolites (1-4) were determined on the basic of spectroscopic analyses including 2 dimensional NMR. Compounds 1 and 3 exhibited 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity with IC(50) values of 22.8 and 27.1 microM, respectively.