a compound of formula wherein r a , r b , x , and y are as defined herein , or a tautomer , stereoisomer , or salt thereof , particularly a physiologically acceptable salt thereof . in addition , pharmaceutical compositions comprising an effective amount of a compound of formula , methods for the treatment or prophylaxis of benign or malignant tumors , diseases of the airways and lungs , polyps , diseases of the gastrointestinal tract , bile duct , gall bladder , kidneys , and skin , and methods for making compounds of formula are disclosed .