Isosteric replacements for benzothiazoles and optimisation to potent Cathepsin K inhibitors free from hERG channel inhibition.

The discovery of nitrile compound 4, a potent inhibitor of Cathepsin K (Cat K) with good bioavailability in dog is described. The compound was used to demonstrate target engagement and inhibition of Cat K in an in vivo dog PD model. The margin to hERG ion channel inhibition was deemed too low for a clinical candidate and an optimisation program to find isosteres or substitutions on benzothiazole group led to the discovery of 20, 24 and 27; all three free from hERG inhibition.

A cryptic matrix targeting signal of the yeast ADP/ATP carrier normally inserted by the TIM22 complex is recognized by the TIM23 machinery.

The yeast ADP/ATP carrier (AAC) is a mitochondrial protein that is targeted to the inner membrane via the TIM10 and TIM22 translocase complexes. AAC is devoid of a typical mitochondrial targeting signal and its targeting and insertion are thought to be guided by internal amino acid sequences. Here we show that AAC contains a cryptic matrix targeting signal that can target up to two thirds of the N-terminal part of the protein to the matrix. This event is coordinated by the TIM23 translocase and displays all the features of the matrix-targeting pathway. However, in the context of the whole protein, this signal is 'masked' and rendered non-functional as the polypeptide is targeted to the inner membrane via the TIM10 and TIM22 translocases. Our data suggest that after crossing the outer membrane the whole polypeptide chain of AAC is necessary to commit the precursor to the TIM22-mediated inner membrane insertion pathway.

(1R,2R)-N-(1-cyanocyclopropyl)-2-(6-methoxy-1,3,4,5-tetrahydropyrido[4,3-b]indole-2-carbonyl)cyclohexanecarboxamide (AZD4996): a potent and highly selective cathepsin K inhibitor for the treatment of osteoarthritis.

Directed screening of nitrile compounds revealed 3 as a highly potent cathepsin K inhibitor but with cathepsin S activity and very poor stability to microsomes. Synthesis of compounds with reduced molecular complexity, such as 7, revealed key SAR and demonstrated that baseline physical properties and in vitro stability were in fact excellent for this series. The tricycle carboline P3 unit was discovered by hypothesis-based design using existing structural information. Optimization using small substituents, knowledge from matched molecular pairs, and control of lipophilicity yielded compounds very close to the desired profile, of which 34 (AZD4996) was selected on the basis of pharmacokinetic profile.

Pharmacokinetic benefits of 3,4-dimethoxy substitution of a phenyl ring and design of isosteres yielding orally available cathepsin K inhibitors.

Rational structure-based design has yielded highly potent inhibitors of cathepsin K (Cat K) with excellent physical properties, selectivity profiles, and pharmacokinetics. Compounds with a 3,4-(CH3O)2Ph motif, such as 31, were found to have excellent metabolic stability and absorption profiles. Through metabolite identification studies, a reactive metabolite risk was identified with this motif. Subsequent structure-based design of isoteres culminated in the discovery of an optimized and balanced inhibitor (indazole, 38).