STUDIES ON THE PREPARATION OF BIOACTIVE LIGNANS BY OXIDATIVE COUPLINGREACTION .2. OXIDATIVE COUPLING REACTION OF METHYL (E)-3-(4,5-DIHYDROXY-2-METHOXYPHENYL)PROPENOATE AND LIPID-PEROXIDATION INHIBITORY EFFECTS OF THE PRODUCED LIGNANS

The oxidative coupling reaction of methyl (E)-3-(4,5-dihydroxy-2-metho xyphenyl)propenoate (10), obtainable from esculetin, has been studied using silver oxide and potassium hexacyanoferrate(III). The products w ere separated, after acetylation, by silica gel column chromatography. 1-Aryl-1,2-dihydronaphthalene derivative 12 was obtained as a major p roduct, accompanied by the benzo[kl]xanthene derivative 13. In the oxi dation with silver oxide, a benzodioxane compound 14a was produced add itionally in a minor amount. Thus, the course of the reaction differed notably from those of ferulic or caffeic acid derivatives. The compou nds 11, 12, 13 and 14a were tested for their inhibitory effects on lip id peroxidation in rat brain homogenate and rat liver microsomes. They showed activities more effective than that of idebenone in rat brain homogenate, and were found to be more potent than benzofuran lignans 4 and 5, and much more potent than (+/-)-alpha-tocopherol in rat liver microsomes.