Novel purine derivatives, production and use thereof as medicaments

The invention relates to novel purine derivatives of the general formula in which R1 to R4 are defined as mentioned in the claims, the tautomers, the stereoisomers, the mixtures thereof, the prodrugs thereof and the salts thereof, particularly the physiologically acceptable salts with inorganic or organic acids or bases, which have valuable pharmacological properties, particularly an inhibitory effect on the activity of the enzyme dipeptidyl peptidase-IV (DPP-IV), their preparation, their use for the prevention or treatment of diseases or conditions, the activity associated with an increased DPP-IV, or which can be prepared by reduction of the DPP-IV prevented or alleviated activity, particularly diabetes mellitus of type I or type II, a compound of general formula (I) or a physiologically acceptable salt thereof containing drugs as well as processes for their preparation.