The discovery of asunaprevir (BMS-650032, 24) is described. This tripeptidic acylsulfonamide inhibitor of the NS3/4A enzyme is currently in phase III clinical trials for the treatment of hepatitis C virus infection. The discovery of 24 was enabled by employing an isolated rabbit heart model to screen for the cardiovascular (CV) liabilities (changes to HR and SNRT) that were responsible for the discontinuation of an earlier lead from this chemical series, BMS-605339 (1), from clinical trials. The structure-activity relationships (SARs) developed with respect to CV effects established that small structural changes to the P2* subsite of the molecule had a significant impact on the CV profile of a given compound. The antiviral activity, preclincial PK profile, and toxicology studies in rat and dog supported clinical development of BMS-650032 (24).

The discovery of BMS-605339 (35), a tripeptidic inhibitor of the NS3/4A enzyme, is described. This compound incorporates a cyclopropylacylsulfonamide moiety that was designed to improve the potency of carboxylic acid prototypes through the introduction of favorable nonbonding interactions within the S1' site of the protease. The identification of 35 was enabled through the optimization and balance of critical properties including potency and pharmacokinetics (PK). This was achieved through modulation of the P2* subsite of the inhibitor which identified the isoquinoline ring system as a key template for improving PK properties with further optimization achieved through functionalization. A methoxy moiety at the C6 position of this isoquinoline ring system proved to be optimal with respect to potency and PK, thus providing the clinical compound 35 which demonstrated antiviral activity in HCV-infected patients.

The discovery of a back-up to the hepatitis C virus NS3 protease inhibitor asunaprevir (2) is described. The objective of this work was the identification of a drug with antiviral properties and toxicology parameters similar to 2, but with a preclinical pharmacokinetic (PK) profile that was predictive of once-daily dosing. Critical to this discovery process was the employment of an ex vivo cardiovascular (CV) model which served to identify compounds that, like 2, were free of the CV liabilities that resulted in the discontinuation of BMS-605339 (1) from clinical trials. Structure-activity relationships (SARs) at each of the structural subsites in 2 were explored with substantial improvement in PK through modifications at the P1 site, while potency gains were found with small, but rationally designed structural changes to P4. Additional modifications at P3 were required to optimize the CV profile, and these combined SARs led to the discovery of BMS-890068 (29).

The design and synthesis of potent, tripeptidic acylsulfonamide inhibitors of HCV NS3 protease that contain a difluoromethyl cyclopropyl amino acid at P1 are described. A cocrystal structure of with a NS3/4A protease complex suggests the presence of a H-bond between the polarized C-H of the CHF moiety and the backbone carbonyl of Leu135 of the enzyme. Structure-activity relationship studies indicate that this H-bond enhances enzyme inhibitory potency by 13- and 17-fold compared to the CH and CF analogues, respectively, providing insight into the deployment of this unique amino acid.

Long-acting (LA) human immunodeficiency virus-1 (HIV-1) antiretroviral therapy characterized by a ≥1 month dosing interval offers significant advantages over daily oral therapy. However, the criteria for compounds that enter clinical development are high. Exceptional potency and low plasma clearance are required to meet dose size requirements; excellent chemical stability and/or crystalline form stability is required to meet formulation requirements, and new antivirals in HIV-1 therapy need to be largely free of side effects and drug–drug interactions. In view of these challenges, the discovery that capsid inhibitors comprising a quinazolinone core tolerate a wide range of structural modifications while maintaining picomolar potency against HIV-1 infection in vitro, are assembled efficiently in a multi-component reaction, and can be isolated in a stereochemically pure form is reported herein. The detailed characterization of a prototypical compound, GSK878, is presented, including an X-ray co-crystal structure and subcutaneous and intramuscular pharmacokinetic data in rats and dogs.