Novel cathepsin k and l inhibitors

The present invention relates to a cathepsin K inhibitor comprising or consisting of Formula (I) (X1)(X2)(X3)(X4)(Y)(X5)(X6)(X7) Formula (I), wherein (X1) is the amino acid K; (X2) is an amino acid selected from R and W, and is preferably R; (X3) is an amino acid selected from R and W, and is preferably R; (X4) is the amino acid L; (X5) is an amino acid selected from Y, V and W, and is preferably V or Y, and is most preferably V; (X6) is an amino acid selected from I, M, L, W and R, and is preferably I, L or W; and is most preferably I; (X7) is an amino acid selected from H, W, A T, R; and is preferably H or R, and is most preferably R; and (Y) is a Michael acceptor. The present invention also relates to a cathepsin L inhibitor comprising or consisting of Formula (II) (X1)(X2)(X3)(X4)(Y)(X5)(X6)(X7) Formula (II), wherein (X1) is the amino acid K; (X2) is the amino acid R; (X3) is an amino acid selected from R, L and M, and is preferably L; (X4) is an amino acid selected from L, W, F and Y, and is preferably W; (X5) is an amino acid selected from V, H and R, and is preferably V; (X6) is an amino acid selected from M, L, I, W and R, and is preferably L; (X7) is an amino acid selected from W, A T, R; and is preferably W; and (Y) is a Michael acceptor.