Mitochondrial complex II (CII) is an emerging target for numerous human diseases. Sixteen analogues of the CII inhibitor natural product atpenin A5 were prepared to evaluate the structure-activity relationship of the C-5 pyridine side chain. The side chain ketone moiety was determined to be pharmacophoric, engendering a bioactive conformation. One analogue (16c) displayed CII IC50 = 64 nM, retained selectivity for CII over mitochondrial complex I (>156-fold) and possessed a ligand-lipophilicity efficiency of 5.62, desirable metrics for a lead compound. This derivative and other highly potent complex II inhibitors possess potent and selective anti-proliferative activity in multiple human prostate cancer cell lines under both normoxia and hypoxia, acting to inhibit mitochondrial electron transport.

Alzheimer’s disease (AD) is the most common dementia affecting one in nine people over 65. Only a handful of small-molecule drugs and the anti-β amyloid (Aβ) antibody aducanumab are approved to treat AD. However, they only serve to reduce symptoms of advanced disease. Novel treatments administered early in disease progression before the accumulation of Aβ and tau reaches the threshold where neuroinflammation is triggered and irreversible neuronal damage occurs are more likely to provide effective therapy. There is a growing body of evidence implying that mitochondrial dysfunction occurs at an early stage of AD pathology. The mitochondrial enzyme amyloid-binding alcohol dehydrogenase (ABAD) binds to Aβ potentiating toxicity. Moreover, ABAD has been shown to be overexpressed in the same areas of the brain most affected by AD. Inhibiting the Aβ–ABAD protein–protein interaction without adversely affecting normal enzyme turnover is hypothesized to be a potential treatment strategy for AD. Herein, we conduct structure–activity relationship studies across a series of functionalized allopurinol derivatives to determine their ability to inhibit Aβ-mediated reduction of estradiol production from ABAD. The lead compound resulting from these studies possesses potent activity with no toxicity up to 100 μM, and demonstrates an ability to rescue defective mitochondrial metabolism in human SH-SY5Y cells and rescue both defective mitochondrial metabolism and morphology ex vivo in primary 5XFAD AD mouse model neurons.