Abstract: Compounds of the general formula (I): ##STR1## in which: X denotes a hydrogen atom,Y denotes a hydrogen atom or a hydroxyl group or alternatively X and Y together denote an oxygen atom,T denotes a hydrogen atom or a lower alkyl group,Z denotes a hydrogen atom or alternatively Z forms a .pi. bond with Y, in which case X denotes a hydrogen atom,R denotes a hydrogen atom or a lower alkyl group,Ar denotes an aryl or heteroaryl or (lower alkyl)aryl group, such as pyrimidinyl, optionally substituted with a halogen atom, or a lower alkyloxy or alkyl group, themselves optionally substituted with one or more halogen atoms,their enantiomers, epimers and diastereoisomers, as well as their addition salts with a pharmaceutically acceptable acid.