Synthesis of quinone and xanthone analogs of rhein

A new strategy based on carbonylation of aryl triflates has been developed to prepare 7-methyl rhein from emodin and new xanthone analogs of rhein. This approach avoids the oxidation step of methyl derivatives with toxic chromium salts. Although possessing the same structural arrangement of phenol and carboxylic acid functions as found in rhein, these new xanthone derivatives have no activity against IL-1. Thus, the quinone moiety of rhein appears to be essential for activity.