a compound of the formula ## str1 ## wherein n , x , r 3 , r 4 and ar are as defined above , useful in the treatment of a condition selected from the group consisting of arthritis , cancer , tissue ulceration , restenosis , periodontal disease , epidermolysis bullosa , scleritis and other diseases characterized by matrix metalloproteinase activity , aids , sepsis , septic shock and other diseases involving the production of tnf .