A compound for therapeutic use, of the 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 or forms part of a ring with R.sub.4; R.sub.3 is H, alkyl or CH.sub.2OH or forms part of a ring with R.sub.4; R.sub.4 is H, alkyl or (when forming part of a ring with R.sub.2 or R.sub.3) CH.sub.2; and R.sub.5 is alkyl, CF.sub.3, OH, Oalkyl, OCOalkyl, CONH.sub.2, CN, halogen, NH.sub.2, NO.sub.2, NHCHO, NHCONH.sub.2, NHSO.sub.2Me, CONH.sub.2, or SOMe; or a salt thereof. ##STR00001##