Reinvestigating the synthesis and efficacy of small benzimidazole derivatives as presequence protease enhancers

Abstract Presequence protease (PreP) is a proteostatic enzyme that plays a key role in the maintenance of mitochondrial health. Defects in PreP stability are associated with neurological disorders in humans, and altered activity of this enzyme modulates the progress of Alzheimer's disease-like pathology in mice. As agonists that boost PreP proteolytic activity represent a promising therapeutic avenue, we sought to determine the structural basis for the action of benzimidazole derivatives (3c and 4c), first reported by Vangavaragu et al. (Eur. J. Med. Chem. 76 (2014) 506–516) that enhance the activity of PreP. However, we found the published procedure for the synthesis of 3c yielded aldimine A instead. We then developed an alternative synthesis and obtained 3c, termed compound C, and an alternative benzimidazole derivative, termed compound B. We tested compounds A, B and C for their ability to enhance the activities of human PreP. In contrast to the previous report, we observed that none of the compounds A, B, or C (3c) modulated the catalytic activity of human PreP. Here we report our findings on the mis-identification of the reported benzimidazoles and the lack of biological activity of such compounds on human PreP. Thus, PreP modulators for PreP-based therapies remain to be discovered.