a compound for therapeutic use , of the formula wherein r 1 is aryl or heteroaryl optionally substituted with r 5 ; r 2 is h , alkyl or ch 2 oh or forms part of a ring with r 4 ; r 3 is h , alkyl or ch 2 oh or forms part of a ring with r 4 ; r 4 is h , alkyl or ch 2 ; and r 5 is alkyl , cf 3 , oh , oalkyl , ocoalkyl , conh 2 , cn , halogen , nh 2 , no 2 , nhcho , nhconh 2 , nhso 2 me , conh 2 , or some ; or a salt thereof .