Synthesis of various kinds of isoflavones, isoflavanes, and biphenyl- ketones and their 1,1-diphenyl-2-picrylhydrazyl radical-scavenging activities

Abstract

Forty-eight kinds of isoflavones (8), thirty-one isoflavanes (9), and forty-seven biphenyl-ketones (10, 10') were synthesized from eleven kinds of substituted phenols (11) and six phenylacetic acids (12). Among them, seventy-five compounds are new. The radical scavenging activities of these compounds were evaluated using 1,1- diphenyl-2-picrylhydrazyl (DPPH) at pH 6.0. We found that thirty-nine out of forty-three compounds having a catechol moiety on either the A- or the B-ring exhibited a high activity (ED 50=12-54 μM) similar to that of catechin. In these cases, the remaining part of their structure seemed to have little effect on their activity. Many 6- or 8-hydroxyisoflavanes (9E-I) and their biphenyl-ketone derivatives (10E-H) also showed a high activity (ED 50=<50 μM), while all of their corresponding isoflavones (8E-I) were not active at all. The 7-hydroxyisoflavanes having either an additional hydroxyl group at the C5-position (9D) or a methoxy group at the C6-position (9J) presented a high activity (ED 50=26-32 μM). This study suggests that natural isoflavones have the possibilities of exhibiting antioxidant activities through the hydroxylation at the C6-, C8-, or C3'-position or the formation of the isoflavanes (9) and/or the biphenyl-ketone derivatives (10') by metabolism or biotransformation. © 2009 Pharmaceutical Society of Japan.