Compounds of the formula II: ##STR00001## wherein R.sup.2 is the side chain of leucine, isoleucine, cyclohexylglycine, O-methyl threonine, 4-fluoroleucine or 3-methoxyvaline; R.sup.3 is H, methyl or F; Rq is trifluoromethyl and Rq' is H or Rq and Rq' define keto; Q is a p-(C.sub.1-C.sub.6alkylsulphonyl)phenyl- or an optionally substituted 4-(C.sub.1-C.sub.6alkyl)piperazin-1-yl-thiazol-4-yl- moiety have utility in the treatment of disorders characterized by inappropriate expression or activation of cathepsin K, such as osteoporosis, osteoarthritis, rheumatoid arthritis or bone metastases.