Pyrimidine derivatives have played an important role in the chemistry of biological systems. This review focuses on recent work of our studies on the synthesis and biological activity of fused pyrimidine derivatives including pyrido[4,3-d]pyrimidine-4(3H)-ones; 3,4-dihydro-pyrido[4,3-d]pyrimidine-8-carbonitriles; pyrazolo[3,4-b]pyrido[4,3-d]-pyrimidine-4-ones; thieno[3',2'-5,6]pyrido [4,3- d]pyrimidin-4(3H)-ones; 1,2,3-triazolo[4,5-d]pyrimidin-7-ones; 1,2,4-triazolo[1,5-a]pyrimidin-10(3H)-ones; thiazolo[4,5-d]pyrimidin- 4(3H)-ones and pyrazolo[...
