THROMBOXANE A(2) BIOSYNTHESIS INHIBITORS - SYNTHESIS AND EVALUATION OF PYRAZOLOTRIAZINYL ALKANOIC ACIDS

A novel series of (6-aryl-4-oxo-pyrazolo 2,3-d] [1,2,5] triazin-3-yl) alkanoic acids was synthesized and evaluated in vitro as thromboxane A (2) (TXA(2)) biosynthesis inhibitors. The experiments were carried out using arachidonic acid (32.8 mu M) as a substrate and horse platelet microsomes (HPM) as sources of TXA(2) synthetase. TXB(2), a stable bre akdown product of TXA(2), was determined by radioimmunoassays (RIA). T he substances under study, at concentrations ranging from 1.10(-6) M t o 1.10(-4)M, significantly inhibited the biosynthesis of TXA(2) in vit ro. This activity was found to be dose-dependent, the potency of which could be related to structural features of the molecules. Compound 3b , bearing a butanoic side chain in the 3-position and a 4-chloro pheny l ring in the 6-position of the bicyclic system, was the most active d erivative in in vitro enzyme inhibition (ID50 = 2.81 x 10(-5) M). Comp arison of the spatial configurations of prostaglandin H-2 (PGH(2)) and 3b displayed a good correlation between essential structural moieties of both molecules. In addition, a conceptual model for the PGH(2) and TX synthetase interactions was applied to compound 3b.