Compound of formula (I) or a pharmaceutically-acceptable salt thereof, formula (I) wherein Ar is optionally substituted phenyl; R.sup.1 is selected from: formula a) or b) (wherein is a single or double bond); R.sup.5, R.sub.6, R.sub.7 and R.sup.8 are for or alkyl; R.sup.4 is selected from hydrogen, (3-4C)cycloalkyl and optionally substituted (1-4C)alkyl; R.sup.10 is for example selected from hydrogen, (1-4C)alkyl, (3-6C)cycloalkyl(1-4C)alkyl, hydroxy(1-4C)alkyl, (1-4C)alkoxy, aryl(1-4C)alkyl; Y is carbon and Ring A is optionally substituted phenylene; or each Y may independently be carbon or nitrogen and Ring A is optionally substituted 5- or 6-membered, heteroarylene ring; R.sup.11 is selected from hydrogen and optionally substituted phenyl; p is independently at each occurrence 0, 1 or 2; are described. Processes for making such compounds and their use as DPP-IV inhibitors in the treatment of diabetes are also described.