The present invention provides a compound of formula (I) in which R1 is generally hydrogen or CF3, R2 is generally hydrogen, W is a cyclic amine, a heterocycle or a group L-Y—X where L-Y is a linking portion and X is generally an aromatic or non-aromatic heterocycle, alkyl or alkylcarbonyl and Z is generally a heterocycle such as 5-methylisoxazol-3-yl, and pharmaceutically acceptable salts thereof for enhancing cognition in conditions such as Alzheimer's Disease, pharmaceutical compositions comprising them, their use for manufacturing medicaments and methods of treatment using them