the present invention relates to compounds of the formula wherein r 1 , r 2 , r 3 , r 4 , r 5 , r 6 , r 7 , r 8 , a , x and y are defined as in the specification , to pharmaceutical compositions containing them and to their medicinal use . the compounds of the invention are useful in the treatment or alleviation of inflammation and other inflammation associated disorders , such as arthritis , colon cancer , and alzheimer &# 39 ; s disease in mammals , preferably humans , dogs , cats and livestock animals .