Comparative antiaggregatory activity in human platelets of a benzopyranone aci-reductone, clofibric acid, and a 2,3-dihydrobenzofuran analogue.

A synthetic method for the preparation of aci-reductone 6-chloro-3,4-dihydroxy-2H-1-benzopyran-2-one (3) from 5-chlorosalicylate is presented. In human platelets, the benzopyranone derivative 3, clofibric acid (1), and the 2,3-dihydrobenzofuran analogue 4 inhibited aggregation and serotonin secretory responses to adenosine diphosphate (ADP) with a rank order of potency 3 greater than or equal to 4 greater than 1. Only analogues 3 and 4 consistently blocked the aggregatory responses (greater than 50%) to arachidonic acid (AA) and U46619, a thromboxane A2 agonist. Further, the rank order of inhibitory potency against U46619-induced serotonin secretion was 4 greater than 3 greater than 1. Benzopyranone 3 is of interest since it was the most potent inhibitor of thrombin-induced [3H]AA release (3 much greater than 4 = 1) and more potent than 1 or 4 for the blockade of the ADP- or AA-mediated pathway of platelet aggregation.