Dipeptidyl peptidase IV (DPP-IV)-inhibiting compounds are provided that have formula I: wherein n is 1 to 3; X is CH2; S; O; CF2 or C(CH3)2; Z is H; halogen; hydroxyl; (C1-6)alkoxy; (C1-12)alkyl; (C3-12)cycloalkyl; phenyl; or heteroaryl; where the phenyl and heteroaryl groups are optionally mono- or independently plurisubstituted with R7; optionally, X together with an adjacent ring carbon and Z form a fused cyclopropyl; and optionally, one of the bonds in the ring containing X is a double bond; and CRiRii, R1, R2, R3, R4 and R5 are as described herein.