The present invention relates to compounds and compositions for treating diseases associated with cysteine protease activity. The compounds are reversible inhibitors of cysteine proteases S, K, F, L and B. Of particular interest are diseases associated with Cathepsin S. In addition this invention also discloses processes for the preparation of such inhibitors. (I) in which: A is a 6-membered ring optionally containing a double bond and optionally containing an oxygen atom or NR group in the ring;