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-β-D-glucopyranoside (2), (2S)-8-formyl-6-methylnaringenin (3), and (2S)-8-formyl-6-methylnaringenin 7-O-β-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 IC50 values of 22.8 and 27.1 μM, respectively.