Synthesis and inhibitory effect on platelet aggregation and antihypertensive activity of 1-hydroxy-2,5-dihydro-1H-imidazole-2-carboxylic acid 3-oxides, 1,3-dihydroxyimidazolidine-2-carboxylic acids, and 1,4-dihydroxy-2,3-piperazinediones.

The reaction of 1,2-hydroxylamino-oximes 1 with pyruvic or glyoxylic acid and of 1,2-bishydroxylamines 4 with glyoxylic acid resulted in 2,5-dihydro-1H-imidazole-2-carboxylic acid 3-oxides 2 and 2-imidazolidinecarboxylic acids 5, respectively. It was found that hydroxylamino acids 2 and 1,4-dihydroxy-2,3-piperazinediones 7 showed marked inhibitory effect on platelet aggregation. 1-Hydroxy-2-methyl-1,5,6,7,8,8a-hexahydro-2H,4H-cycloheptimidazole -2-carboxylic acid 3-oxide 2e exhibited antihypertensive activity.