New diarylheptanoids from Alnus japonica and their antioxidative activity

In the course of research oil the bioactive constituents of woody plants in the Cyugoku area of Japan, a methanol extract of the leaves of Alnus japonica were found to have strong antioxidative activity. Ethyl acetate soluble and n-buthanol soluble fractions of the methanol extract had a potent autioxidative effect. Both fractions were purified by silica gel column chromatography and HPLC using all ODS column to give four new diaryliheptanoids along with known diarylheptanoids and flavonoids. These new compounds were elucidated to be 7-(3,4-dihvdroxyphenyl)-5-hydroxy-1-(4-hydroxyphenyl)-3-heptanone-5-O-beta-(D)-xylopyranoside (1), 1-(3,4-dihydroxyphenyl)-5-hydroxy-7-(4-hydroxyphenyl)-3-heptanone-5-O-beta-(D)-xyloranoside (2), 1,7-bis-(3,4-dihydroxydroxyphenyl)-5-hydroxy-3-heptanone-5-O[2-(2-methylbutenoyl)]-beta-(D)-xylopyranoside (3) and 1,7-bis-(3,4-dihydroxyphenyl)-5-methoxy-3-heptanone (4) using spectral methods and especially H-1-, C-13-NMR and 2D-NMR measurements. The isolated compounds including their main constituent, oregonin (5), were tested for antioxidative activity. Some of these compounds having two catechol structures showed potent antioxidative activity. Compounds having one catechol structure showed moderate antioxidative activity, but a peracetate of 5 having no catechol structure exhibited no antioxidative activity. Thus the catechol structure of the diarylheptanoids is indispensable for antioxidative activity.