Compounds of Formula IIwhereinR1a is H； and R1b is C1-C6alkyl, Carbocyclyl or Het； orR1a and R1b together define a saturated cyclic amine with 3-6 ring atoms；R2a and R2b are independently H, halo, C1-C4alkyl, C1-C4haloalkyl or C1-C4alkoxy, or R2a andR2b together with the carbon atom to which they are attached form a C3-C6cycloalkyl；R3 is a branched C5-C10 alkyl chain, C2-C4haloalkyl or —CH2C3-C7 cycloalkyl；R4′ is C1-C6alkyl, C1-C6haloalkyl or oxetany-3-yl.for use in the prophylaxis or treatment of a disorder characterised by inappropriate expression or activation of cathepsin S.
