The invention relates to a compound of formula (I): Formula (I) or a pharmaceutically acceptable salt, solvate or polymorph thereof, including all tautomers and stereoisomers thereof, wherein A is heteraryl selected from 1 H-benzimidazolyl and imidazo[1,2-a]pyridine, and R1, R2, R3, R4 and R5 are as defined herein, as inhibitors of glutaminyl cyclase (QC, EC 2.3.2.5) and its isoenzyme glutaminyl-peptide cyclotransferase-like protein (QPCTL). QC and QPCTL catalyze the intramolecular cyclization of N-terminal glutamine residues into pyroglutamic acid (5-oxo-prolyl, pGlu*) under liberation of ammonia and the intramolecular cyclization of N-terminal glutamate residues into pyroglutamic acid under liberation of water.
