PYRAZOLO[3,4-B]PYRIDINE COMPOUND, AND ITS USE AS A PDE4 INHIBITOR

The invention provides a compound of formula (I) or a salt thereof: wherein R2 is H, C1-3alkyl, n-butyl, C1-2fluoroalkyl, cyclopropyl, cyclobutyl, (cyclopropyl)methyl-, -CN, or -CH2OH; R3 is inter alia optionally substituted C4-7cycloalkyl or an optionally substituted heterocyclic group (aa), (bb) or (cc); Ra is H, methyl or ethyl; Rb is H or methyl; R4 is H, methyl, ethyl, n-propyl, -C(O)-Me, or -C(O)-C1fluoroalkyl; and R5 is: -C(O)-(CH2)n-Ar, -C(O)-Het, -C(O)-C1-6alkyl, -C(O)-C1 fluoroalkyl, -C(O)-(CH2)2-C(O)-NR15bNR15b, -C(O)-CH2-C(O)-NR15bNR15b, -C(O)-NR15b-(CH2)m1-Ar, -C(O)-NR15b-Het, -C(O)-NR15b-C1-6alkyl, -C(O)-NR5aR5b, -S(O)2-(CH2)m2-Ar, -S(O)2-Het, -S(O)2-C1-6alkyl, or -CH2-Ar; or R4 and R5 taken together are -(CH2)p1-, -(CH2)2-X5-(CH2)2-, -C(O)-(CH2)p2-, -C(O)-N(R15)-(CH2)p3-; or NR4R5 is of sub-formula (y), (y1), (y2) or (y3). The invention provides the use of the compounds as inhibitors of phosphodiesterase type IV (PDE4) and/or for the treatment and/or prophylaxis of inflammatory and/or allergic diseases such as COPD and the like.