In an effort to design inhibitors of human glutaminyl cyclase (QC), we have synthesized a library of N-aryl N-(5-methyl-1H-imidazol-1-yl) propyl thioureas and investigated the contribution of the aryl region of these compounds to their structure–activity relationships as cyclase inhibitors. Our design was guided by the proposed binding mode of the preferred substrate for the cyclase. In this series, compound 52 was identified as the most potent QC ...