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. The compounds are useful in treating PI 3-kinase-dependent conditions including cardiovascular diseases such as coronary artery occlusion, stroke, acute coronary syndrome, acute myocardial infarction, vascular restenosis, atherosclerosis, and unstable angina; respiratory diseases such as asthma, chronic obstructive pulmonary diseases (COPD), and bronchitis; inflammatory disorders, neoplasms including cancers such as glioma, prostate cancer, small cell lung cancer, and breast cancer, and diseases linked to disordered white blood cell function, such as autoimmune and inflammatory diseases.