Pyrazolo[3,4-b]pyridine compounds, and their use as phosphodiesterase inhibitors

Abstract The invention relates to a compound of formula (I) or a salt thereof: Formula (I) wherein: R1 is C .4alkyl, C1.3fluoroalkyl or -(CH 2)20H; R2 is a hydrogen atom (H), methyl or Cifluoroalkyl; R3a is a hydrogen atom (H) or C1.3alkyl; R3 is optionally substituted 5 branched C3 .6 alkyl, optionally substituted C3.scycloalkyl, optionally substituted mono unsaturated-C 5.7cycloalkenyl, optionally substituted phenyl, or an optionally substituted heterocyclic group of sub-formula (aa), or (bb) or (cc) in which nI and n2 independently are I or 2; and Y is 0, S, SO 2 , or NR4, and wherein Het is of sub-formula (i), or (ii), or (iii), or (iv) or (v). The compounds are phosphodiesterase (PDE) inhibitors, in particular 10 PDE4 inhibitors. Also provided is the use of a compound of formula (I), or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for the treatment and/or prophylaxis of an inflammatory and/or allergic disease in a mammal such as a human, for example chronic obstructive pulmonary disease (COPD), asthma, or allergic rhinitis.