This invention relates to the discovery of substituted analogues of the selective platelet lowering agent anagrelide with reduced potential for cardiovascular side-effects which should lead to improved patient compliance and safety in the treatment of myeloproliferative diseases. More specifically, the present invention relates to certain imidazoquinazoline derivatives which have the general formula shown below wherein the substituents have the meanings defined in claim (I): and which have utility as platelet lowering agents in humans. The compounds of the present invention function by inhibiting megakaryocytopoeisis and hence the formation of blood platelets.
