Three units of malonate react with a hydroxybenzoic acid (C6-C1). Benzophenones may be converted by oxidative rings closure into xanthones.
Several xanthones that possess antidepressant activity inhibit monoamine oxidases. These compounds have in vitro cytotoxicity and in vivo antitumor activity. Xanthones kill microbes, improve depression, stimulate the production of urine and improve the function of the heart.
Xanthones derivatives occur in a number of higher plant families and fungi. Some fungal species are well known as sources of xanthone derivatives, for example, Penicilium raistrickii G. Sm, Phomopsis sp, and Humicola sp.
Biology of xanthones