The present invention relates to a compound The instant invention relates to a compound of formulae (I A), (I B), (X A), (X B), (Y A) or (Y B), wherein R' represents (formula) and R' represents hydrogen, hydroxy, C-Calkoxy, C-C-alkanoyloxy, or RRN-CO-O-, where R and R independently are C-Calkyl or phenyl which is unsubstituted or substituted by a substitutent selected from C-Calkyl, C-Calkoxy, halogen and trifluoromethyl and where R additionally is hydrogen； or R and R together represent C-Calkylene； in free form or in form of a pharmaceutically acceptable acid addition salt. Compounds of formulae (I A), (I B), (X A), (X B), (Y A) or (Y B) inhibit DPP-IV (dipeptidyl- peptidase-IV) activity. They are therefore indicated for use as pharmaceuticals in inhibiting DPP-IV and in the treatment of conditions mediated by DPP-IV, such as non-insulin- dependent diabetes mellitus, arthritis, obesity, osteoporosis and further conditions of impaired glucose tolerance.
