Pyrido [2, 3-d] pyrimidinedione derivatives form a class of fused heterocyclic compounds which reveal interesting pharmacological and biological properties [2]. Isoxazoloand oxadiazoloheterocycles in the quinoline and pyrimidine series were investigated thoroughly in the last decades and many representatives were found to show biological activities [3-7]. These findings prompted us to study the combination of these two biological interesting ...