Abstract: Morpholino-substituted pyridopyrimidine, quinolone, and benzopyranone derivatives inhibit phosphoinositide (PI) 3-kinase, an enzyme that regulates platelet-adhesion processes. As a consequence, the compounds in question have anti-thrombotic activity, as well as other pharmaceutical properties. The compounds claimed are represented by formula (I), (II) and (III). PI 3-kinase generates 3-phosphorylated PI second messengers which stimulate platelet adhesion under blood-flow conditions. Because platelet adhesion is a necessary step in the formation of a thrombus, inhibition by these compounds of PI 3-kinase under such conditions inhibits or prevents thrombus formation.