Synthesis and inhibitory effect on platelet aggregation of 2-phenyl-1(2H)-phthalazinone derivatives.

2-Phenyl-1 (2H)-phthalazinone derivatives (4) were synthesized by the reactions of corresponding o-phthalaldehydic acids (5) with phenylhydrazine derivatives. The preparation of 5 was carried out by decarboxylation of keto-carboxylic acids (6) or hydroxylation of phthalides (8) via their bromo derivatives (9). The derivatives (4) were tested for inhibitory activity on platelet aggregation. None of them showed any appreciable effect on platelet aggregation induced by adenosine diphosphate. Several compounds (4l, 4m, 16a, and 16c), however, effectively inhibited platelet aggregation induced by arachidonic acid.