The present invention relates to compounds of the formula (I) ##STR00001## wherein R.sup.1 and R.sup.2 are as defined in the description and claims, and pharmaceutically acceptable salts thereof. The compounds are useful for the treatment and/or prophylaxis of diseases which are associated with DPP-IV, such as diabetes, non-insulin dependent diabetes mellitus and/or impaired glucose tolerance, obesity, and/or metabolic syndrome or .beta.-cell protection.