Thielavin A and B, new inhibitors of prostaglandin biosynthesis produced by Thielavia terricola

Two potent inhibitors of prostaglandin biosynthesis, thielavin A (C31H34O10) and B (C29H30O10), were isolated from cultures of Thielavia terricola. Both of these compounds were shown to be structurally related to depsides, thus consisting of three hydroxybenzoic acid groups. Concentrations required for 50% inhibition of the conversion of 14C-arachidonic acid into prostaglandins F2 alpha plus E2 by microsomes of ram seminal vesicles were 12 microM for thielavin A and 9 microM for thielavin B, respectively. Of the enzymatic steps involved in prostaglandin synthesis, thielavin A specifically inhibited the conversion of arachidonic acid into prostaglandin H2, while prostaglandin E2 synthesis from the endoperoxide was the most sensitive to thielavin B. Thromboxane A2 synthesis from prostaglandin H2 in bovine platelet microsomes were inhibited by 50% at concentrations of 150 and 350 microM of thielavin A and B, respectively. Thielavin B was significantly effective on carrageenan-induced oedema of rats when administered intravenously but on on oral administration. The anti-inflammatory activity was not detectable with thielavin A either on intravenous injection or on oral administration.