Development of the Large-Scale Synthesis of Tetrahydropyran Glycine, a Precursor to the HCV NS5A Inhibitor BMS-986097.

An efficient large-scale synthesis of acid 1, a penultimate precursor to the HCV NS5A inhibitor BMS-986097, along with the final API step are described. Three routes were devised for the synthesis of 1 at the various stages of the program. The third generation route, the one that proved scalable and is the main subject of this paper, features a one-step Michael addition of t-butyl 2-((diphenylmethylene)amino)acetate (24) to (E)-benzyl 4-(1-hydroxycyclopropyl)but-2-enoate (28) followed by cyclization and chiral separation to form 27c, the core skeleton of cap piece 1. The epimerization and chiral resolution of 27c followed by further synthetic manipulations involving the carbamate formation, lactone reduction and cyclization, afforded cyclopropyl pyran 1. A detailed study of diphenylmethane deprotection via acid hydrolysis as well as a key lactone to tetrahydropyran conversion, in order to avoid a side reaction that afforded an alternative cyclization product, are discussed. This synthesis was applied to the preparation of more than 100 g of the final API BMS-986097 for toxicology studies.

Discovery and development of hepatitis C virus NS5A replication complex inhibitors.

Lead inhibitors that target the function of the hepatitis C virus (HCV) nonstructural 5A (NS5A) protein have been identified by phenotypic screening campaigns using HCV subgenomic replicons. The demonstration of antiviral activity in HCV-infected subjects by the HCV NS5A replication complex inhibitor (RCI) daclatasvir (1) spawned considerable interest in this mechanistic approach. In this Perspective, we summarize the medicinal chemistry studies that led to the discovery of 1 and other chemotypes for which resistance maps to the NS5A protein and provide synopses of the profiles of many of the compounds currently in clinical trials. We also summarize what is currently known about the NS5A protein and the studies using NS5A RCIs and labeled analogues that are helping to illuminate aspects of both protein function and inhibitor interaction. We conclude with a synopsis of the results of notable clinical trials with HCV NS5A RCIs.

Hepatitis C virus NS5A replication complex inhibitors: the discovery of daclatasvir.

The biphenyl derivatives 2 and 3 are prototypes of a novel class of NS5A replication complex inhibitors that demonstrate high inhibitory potency toward a panel of clinically relevant HCV strains encompassing genotypes 1-6. However, these compounds exhibit poor systemic exposure in rat pharmacokinetic studies after oral dosing. The structure-activity relationship investigations that improved the exposure properties of the parent bis-phenylimidazole chemotype, culminating in the identification of the highly potent NS5A replication complex inhibitor daclatasvir (33) are described. An element critical to success was the realization that the arylglycine cap of 2 could be replaced with an alkylglycine derivative and still maintain the high inhibitory potency of the series if accompanied with a stereoinversion, a finding that enabled a rapid optimization of exposure properties. Compound 33 had EC50 values of 50 and 9 pM toward genotype-1a and -1b replicons, respectively, and oral bioavailabilities of 38-108% in preclinical species. Compound 33 provided clinical proof-of-concept for the NS5A replication complex inhibitor class, and regulatory approval to market it with the NS3/4A protease inhibitor asunaprevir for the treatment of HCV genotype-1b infection has recently been sought in Japan.

Hepatitis C virus NS5A replication complex inhibitors. Part 6: Discovery of a novel and highly potent biarylimidazole chemotype with inhibitory activity toward genotypes 1a and 1b replicons.

A medicinal chemistry campaign that was conducted to address a potential genotoxic liability associated with an aniline-derived scaffold in a series of HCV NS5A inhibitors with dual GT-1a/-1b inhibitory activity is described. Anilides 3b and 3c were used as vehicles to explore structural modifications that retained antiviral potency while removing the potential for metabolism-based unmasking of the embedded aniline. This effort resulted in the discovery of a highly potent biarylimidazole chemotype that established a potency benchmark in replicon assays, particularly toward HCV GT-1a, a strain with significant clinical importance. Securing potent GT-1a activity in a chemotype class lacking overt structural liabilities was a critical milestone in the effort to realize the full clinical potential of targeting the HCV NS5A protein.

HCV NS5A replication complex inhibitors. Part 4. Optimization for genotype 1a replicon inhibitory activity.

A series of symmetrical E-stilbene prolinamides that originated from the library-synthesized lead 3 was studied with respect to HCV genotype 1a (G-1a) and genotype 1b (G-1b) replicon inhibition and selectivity against BVDV and cytotoxicity. SAR emerging from an examination of the prolinamide cap region revealed 11 to be a selective HCV NS5A inhibitor exhibiting submicromolar potency against both G-1a and G-1b replicons. Additional structural refinements resulted in the identification of 30 as a potent, dual G-1a/1b HCV NS5A inhibitor.

Characterizations of HCV NS5A replication complex inhibitors.

The hepatitis C virus NS5A protein is an established and clinically validated target for antiviral intervention by small molecules. Characterizations are presented of compounds identified as potent inhibitors of HCV replication to provide insight into structural elements that interact with the NS5A protein. UV-activated cross linking and affinity isolation was performed with one series to probe the physical interaction between the inhibitors and the NS5A protein expressed in HCV replicon cells. Resistance mapping with the second series was used to determine the functional impact of specific inhibitor subdomains on the interaction with NS5A. The data provide evidence for a direct high-affinity interaction between these inhibitors and the NS5A protein, with the interaction dependent on inhibitor stereochemistry. The functional data supports a model of inhibition that implicates inhibitor binding by covalently combining distinct pharmacophores across an NS5A dimer interface to achieve maximal inhibition of HCV replication.

HCV NS5A replication complex inhibitors. Part 2: investigation of stilbene prolinamides.

In a previous disclosure,(1) we reported the dimerization of an iminothiazolidinone to form 1, a contributor to the observed inhibition of HCV genotype 1b replicon activity. The dimer was isolated via bioassay-guided fractionation experiments and shown to be a potent inhibitor of genotype 1b HCV replication for which resistance mapped to the NS5A protein. The elements responsible for governing HCV inhibitory activity were successfully captured in the structurally simplified stilbene prolinamide 2. We describe herein the early SAR and profiling associated with stilbene prolinamides that culminated in the identification of analogs with PK properties sufficient to warrant continued commitment to this chemotype. These studies represent the key initial steps toward the discovery of daclatasvir (BMS-790052), a compound that has demonstrated clinical proof-of-concept for inhibiting the NS5A replication complex in the treatment of HCV infection.

Discovery of potent hepatitis C virus NS5A inhibitors with dimeric structures.

The exceptional in vitro potency of the hepatitis C virus (HCV) NS5A inhibitor BMS-790052 has translated into an in vivo effect in proof-of-concept clinical trials. Although the 50% effective concentration (EC(50)) of the initial lead, the thiazolidinone BMS-824, was ~10 nM in the replicon assay, it underwent transformation to other inhibitory species after incubation in cell culture medium. The biological profile of BMS-824, including the EC(50), the drug concentration required to reduce cell growth by 50% (CC(50)), and the resistance profile, however, remained unchanged, triggering an investigation to identify the biologically active species. High-performance liquid chromatography (HPLC) biogram fractionation of a sample of BMS-824 incubated in medium revealed that the most active fractions could readily be separated from the parental compound and retained the biological profile of BMS-824. From mass spectral and nuclear magnetic resonance data, the active species was determined to be a dimer of BMS-824 derived from an intermolecular radical-mediated reaction of the parent compound. Based upon an analysis of the structural elements of the dimer deemed necessary for anti-HCV activity, the stilbene derivative BMS-346 was synthesized. This compound exhibited excellent anti-HCV activity and showed a resistance profile similar to that of BMS-824, with changes in compound sensitivity mapped to the N terminus of NS5A. The N terminus of NS5A has been crystallized as a dimer, complementing the symmetry of BMS-346 and allowing a potential mode of inhibition of NS5A to be discussed. Identification of the stable, active pharmacophore associated with these NS5A inhibitors provided the foundation for the design of more potent inhibitors with broad genotype inhibition. This culminated in the identification of BMS-790052, a compound that preserves the symmetry discovered with BMS-346.

The synthesis and evaluation of a novel class of (E)-3-(1-cyclohexyl-1H-pyrazol-3-yl)-2-methylacrylic acid hepatitis C virus polymerase NS5B inhibitors.

Herein we report the identification and evaluation of a novel series of (E)-3-(1-cyclohexyl-1H-pyrazol-3-yl)-2-methylacrylic acid derivatives identified from a deannulation study performed on the reported benzimidazole NS5B inhibitor, 1. This resulted in the identification of (E)-3-(2-(4-((4'-cyano-4-(4-hydroxypiperidine-1-carbonyl)biphenyl-2-yl)methoxy)phenyl)-1-cyclohexyl-1H-imidazol-4-yl)-2-methylacrylic acid (11) as a potent inhibitor of NS5B. Potential pathways for the further optimization of this series are suggested.

Inhibitors of HCV NS5A: From Iminothiazolidinones to Symmetrical Stilbenes.

The iminothiazolidinone BMS-858 (2) was identified as a specific inhibitor of HCV replication in a genotype 1b replicon assay via a high-throughput screening campaign. A more potent analogue, BMS-824 (18), was used in resistance mapping studies, which revealed that inhibitory activity was related to disrupting the function of the HCV nonstructural protein 5A. Despite the development of coherent and interpretable SAR, it was subsequently discovered that in DMSO 18 underwent an oxidation and structural rearrangement to afford the thiohydantoin 47, a compound with reduced HCV inhibitory activity. However, HPLC bioassay fractionation studies performed after incubation of 18 in assay media led to the identification of fractions containing a dimeric species 48 that exhibited potent antiviral activity. Excision of the key elements hypothesized to be responsible for antiviral activity based on SAR observations reduced 48 to a simplified, symmetrical, pharmacophore realized most effectively with the stilbene 55, a compound that demonstrated potent inhibition of HCV in a genotype 1b replicon with an EC50 = 86 pM.

Identification of hepatitis C virus NS5A inhibitors.

Using a cell-based replicon screen, we identified a class of compounds with a thiazolidinone core structure as inhibitors of hepatitis C virus (HCV) replication. The concentration of one such compound, BMS-824, that resulted in a 50% inhibition of HCV replicon replication was approximately 5 nM, with a therapeutic index of >10,000. The compound showed good specificity for HCV, as it was not active against several other RNA and DNA viruses. Replicon cells resistant to BMS-824 were isolated, and mutations were identified. A combination of amino acid substitutions of leucine to valine at residue 31 (L31V) and glutamine to leucine at residue 54 (Q54L) in NS5A conferred resistance to this chemotype, as did a single substitution of tyrosine to histidine at amino acid 93 (Y93H) in NS5A. To further explore the region(s) of NS5A involved in inhibitor sensitivity, genotype-specific NS5A inhibitors were used to evaluate a series of genotype 1a/1b hybrid replicons. Our results showed that, consistent with resistance mapping, the inhibitor sensitivity domain also mapped to the N terminus of NS5A, but it could be distinguished from the key resistance sites. In addition, we demonstrated that NS5A inhibitors, as well as an active-site inhibitor that specifically binds NS3 protease, could block the hyperphosphorylation of NS5A, which is believed to play an essential role in the viral life cycle. Clinical proof of concept has recently been achieved with derivatives of these NS5A inhibitors, indicating that small molecules targeting a nontraditional viral protein like NS5A, without any known enzymatic activity, can also have profound antiviral effects on HCV-infected subjects.

3-[(5-Chloro-2-hydroxyphenyl)methyl]-5-[4-(trifluoromethyl)phenyl ]-1,3,4-oxadiazol-2(3H)-one, BMS-191011: opener of large-conductance Ca(2+)-activated potassium (maxi-K) channels, identification, solubility, and SAR.

Compound 8a (BMS-191011), an opener of the cloned large-conductance, Ca2+-activated potassium (maxi-K) channel, demonstrated efficacy in in vivo stroke models, which led to its nomination as a candidate for clinical evaluation. Its maxi-K channel opening properties were consistent with its structural topology, being derived by combining elements from other known maxi-K openers. However, 8a suffered from poor aqueous solubility, which complicated elucidation of SAR during in vitro evaluation. The activity of 8a in in vivo stroke models and studies directed toward improving its solubility are reported herein. Enhanced solubility was achieved by appending heterocycles to the 8a scaffold, and a notable observation was made that inclusion of a simple amino group (anilines 8k and 8l) yielded excellent in vitro maxi-K ion channel opening activity and enhanced brain-to-plasma partitioning compared to the appended heterocycles.

Dihydropyridine neuropeptide Y Y1 receptor antagonists 2. bioisosteric urea replacements.

Structure-activity studies around the urea linkage in BMS-193885 (4a) identified the cyanoguanidine moiety as an effective urea replacement in a series of dihydropyridine NPY Y(1) receptor antagonists. In comparison to urea 4a (K(i)=3.3 nM), cyanoguanidine 20 (BMS-205749) displayed similar binding potency at the Y(1) receptor (K(i)=5.1 nM) and full functional antagonism (K(b)=2.6 nM) in SK-N-MC cells. Cyanoguanidine 20 also demonstrated improved permeability properties in Caco-2 cells in comparison to urea 4a (43 vs 19 nm/s).

Novel openers of Ca2+-dependent large-conductance potassium channels: symmetrical pharmacophore and electrophysiological evaluation of bisphenols.

Electrophysiological evaluation of symmetrical analogues of the known maxi-K opener NS-004 (1) led to the discovery of bisphenols 2a, 3a and 4a as openers of cloned maxi-K channels expressed in oocytes.

4,5-diphenyltriazol-3-ones: openers of large-conductance Ca(2+)-activated potassium (maxi-K) channels.

A series of diphenyl-substituted heterocycles were synthesized and evaluated by electrophysiological techniques as openers of the cloned mammalian large-conductance, Ca(2+)-activated potassium (maxi-K) channel. The series was designed from deannulation of known benzimidazolone maxi-K opener NS-004 (2) thereby providing an effective template for obtaining structure-activity-related information. The triazolone ring system was the most studied wherein 4,5-diphenyltriazol-3-one 6d (maxi-K = 158%) was identified as the optimal maxi-K channel opener.