A compound that is useful for the treatment or prevention of a condition such as pain, that is associated with T-cell proliferation or that is mediated by pro- and/or anti-inflammatory cytokines, is of formula (I) wherein R.sub.1 is aryl or heteroaryl optionally substituted with R.sub.5; R.sub.2 is H, alkyl or CH.sub.2OH and can be part of a ring with R.sub.4; R.sub.3 is H, alkyl or CH.sub.2OH and can be part of a ring with R.sub.4; R.sub.4 is H or alkyl or CH.sub.2 (when forming part of a ring with R.sub.2 or R.sub.3); and R.sub.5 is alkyl, CF.sub.3, OH, Oalkyl, OCOalkyl, CONH.sub.2, CN, F, Cl, Br, I, NH.sub.2, NHCHO, NHCONH.sub.2, NHSO.sub.2alkyl, CONH.sub.2, SOMe, CH.sub.2OH or OCONalkyl.sub.2; or a salt thereof.