Compounds of the formula II:
wherein
R
2
is the side chain of leucine, isoleucine, cyclohexylglycine, O-methyl threonine, 4-fluoroleucine or 3-methoxyvaline;
R
3
is H, methyl or F;
Rq is trifluoromethyl and Rq′ is H or Rq and Rq′ define keto;
Q is a p-(C
1
-C
6
alkylsulphonyl)phenyl- or an optionally substituted 4-(C
1
-C
6
alkyl)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.