Potent and selective inhibitor of phosphatidyl-inositol 3-kinase. Active in purified preparations and cytosolic fractions(IC50 = 5nM) and is highly cell permeable. Covalently binds to PI 3-kinase and is selective, inhibiting other kinases such as PI 4-kinase and myosin light chain kinase at concentrations 100-fold higher than that required for inhibition of PI 3-kinase.