Timothy Stammers

Enantiomeric Atropisomers Inhibit HCV Polymerase and/or HIV Matrix: Characterizing Hindered Bond Rotations and Target Selectivity.

An anthranilic acid series of allosteric thumb pocket 2 HCV NS5B polymerase inhibitors exhibited hindered rotation along a covalent bond axis, and the existence of atropisomer chirality was confirmed by NMR, HPLC analysis on chiral supports, and computational studies. A thorough understanding of the concerted rotational properties and the influence exerted by substituents involved in this steric phenomenon was attained through biophysical studies on a series of truncated analogues. The racemization half-life of a compound within this series was determined to be 69 min, which was consistent with a class 2 atropisomer (intermediate conformational exchange). It was further found by X-ray crystallography that one enantiomer of a compound bound to the intended HCV NS5B polymerase target whereas the mirror image atropisomer was able to bind to an unrelated HIV matrix target. Analogues were then identified that selectively inhibited the former. These studies highlight that atropisomer chirality can lead to distinct entities with specific properties, and the phenomenon of atropisomerism in drug discovery should be evaluated and appropriately managed.

N-Acetamideindolecarboxylic acid allosteric ‘finger-loop’ inhibitors of the hepatitis C virus NS5B polymerase: discovery and initial optimization studies

SAR studies at the N(1)-position of allosteric indole-based HCV NS5B inhibitors has led to the discovery of acetamide derivatives with good cellular potency in subgenomic replicons (EC(50) <200 nM). This class of inhibitors displayed improved physicochemical properties and favorable ADME-PK profiles over previously described analogs in this class.

Conformation-Based Restrictions and Scaffold Replacements in the Design of Hepatitis C Virus Polymerase Inhibitors: Discovery of Deleobuvir (BI 207127)

Conformational restrictions of flexible torsion angles were used to guide the identification of new chemotypes of HCV NS5B inhibitors. Sites for rigidification were based on an acquired conformational understanding of compound binding requirements and the roles of substituents in the free and bound states. Chemical bioisosteres of amide bonds were explored to improve cell-based potency. Examples are shown, including the design concept that led to the discovery of the phase III clinical candidate deleobuvir (BI 207127). The structure-based strategies employed have general utility in drug design.

Structure-based design of novel HCV NS5B thumb pocket 2 allosteric inhibitors with submicromolar gt1 replicon potency: Discovery of a quinazolinone chemotype

We describe the structure-based design of a novel lead chemotype that binds to thumb pocket 2 of HCV NS5B polymerase and inhibits cell-based gt1 subgenomic reporter replicons at sub-micromolar concentrations (EC50<200nM). This new class of potent thumb pocket 2 inhibitors features a 1H-quinazolin-4-one scaffold derived from hybridization of a previously reported, low affinity thiazolone chemotype with our recently described anthranilic acid series. Guided by X-ray structural information, a key NS5B-ligand interaction involving the carboxylate group of anthranilic acid based inhibitors was replaced by a neutral two-point hydrogen bonding interaction between the quinazolinone scaffold and the protein backbone. The in vitro ADME and in vivo rat PK profile of representative analogs are also presented and provide areas for future optimization of this new class of HCV polymerase inhibitors.

Discovery of a novel series of non-nucleoside thumb pocket 2 HCV NS5B polymerase inhibitors.

A novel series of non-nucleoside thumb pocket 2 HCV NS5B polymerase inhibitors were derived from a fragment-based approach using information from X-ray crystallographic analysis of NS5B-inhibitor complexes and iterative rounds of parallel synthesis. Structure-based drug design strategies led to the discovery of potent sub-micromolar inhibitors 11a-c and 12a-c from a weak-binding fragment-like structure 1 as a starting point.

Molecular Dynamics Simulations and Structure-Based Rational Design Lead to Allosteric HCV NS5B Polymerase Thumb Pocket 2 Inhibitor with Picomolar Cellular Replicon Potency.

The design and preliminary SAR of a new series of 1H-quinazolin-4-one (QAZ) allosteric HCV NS5B thumb pocket 2 (TP-2) inhibitors was recently reported. To support optimization efforts, a molecular dynamics (MD) based modeling workflow was implemented, providing information on QAZ binding interactions with NS5B. This approach predicted a small but critical ligand-binding induced movement of a protein backbone region which increases the pocket size and improves access to the backbone carbonyl groups of Val 494 and Pro 495. This localized backbone shift was consistent with key SAR results and was subsequently confirmed by X-ray crystallography. The MD protocol guided the design of inhibitors, exploiting novel H-bond interactions with the two backbone carbonyl groups, leading to the first thumb pocket 2 NS5B inhibitor with picomolar antiviral potency in genotype (gt) 1a and 1b replicons (EC50 = 120 and 110 pM, respectively) and with EC50 ≤ 80 nM against gt 2-6.

Indole 5-carboxamide Thumb Pocket I inhibitors of HCV NS5B polymerase with nanomolar potency in cell-based subgenomic replicons (part 2): Central amino acid linker and right-hand-side SAR studies

In this part 2, new indole 5-carboxamide Thumb Pocket 1 inhibitors of HCV NS5B polymerase are described. Structure-activity relationships (SAR) were explored at the central amino acid linker position and the right-hand-side of the molecule in an attempt to identify molecules with a balanced overall profile of potency (EC(50)<100 nM), physicochemical properties and ADME characteristics.

Discovery of BI 207524, an indole diamide NS5B thumb pocket 1 inhibitor with improved potency for the potential treatment of chronic hepatitis C virus infection.

The development of interferon-free regimens for the treatment of chronic HCV infection constitutes a preferred option that is expected in the future to provide patients with improved efficacy, better tolerability, and reduced risk for emergence of drug-resistant virus. We have pursued non-nucleoside NS5B polymerase allosteric inhibitors as combination partners with other direct acting antivirals (DAAs) having a complementary mechanism of action. Herein, we describe the discovery of a potent follow-up compound (BI 207524, 27) to the first thumb pocket 1 NS5B inhibitor to demonstrate antiviral activity in genotype 1 HCV infected patients, BILB 1941 (1). Cell-based replicon potency was significantly improved through electronic modulation of the pKa of the carboxylic acid function of the lead molecule. Subsequent ADME-PK optimization lead to 27, a predicted low clearance compound in man. The preclinical profile of inhibitor 27 is discussed, as well as the identification of a genotoxic metabolite that led to the discontinuation of the development of this compound.

Anthranilic acid-based Thumb Pocket 2 HCV NS5B polymerase inhibitors with sub-micromolar potency in the cell-based replicon assay.

Optimization efforts on the anthranilic acid-based Thumb Pocket 2 HCV NS5B polymerase inhibitors 1 and 2 resulted in the identification of multiple structural elements that contributed to improved cell culture potency. The additive effect of these elements resulted in compound 46, an inhibitor with enzymatic (IC50) and cell culture (EC50) potencies of less than 100 nanomolar.

Aza follow-ups to BI 207524, a thumb pocket 1 HCV NS5B polymerase inhibitor. Part 1: Mitigating the genotoxic liability of an aniline metabolite.

A series of heterocyclic aza-analogs of BI 207524 (2), a potent HCV NS5B polymerase thumb pocket 1 inhibitor, was investigated with the goal to reduce the liability associated with the release of a genotoxic aniline metabolite in vivo. Analog 4, containing a 2-aminopyridine aniline isostere that is negative in the Ames test was identified, and was found to provide comparable GT1a/1b potency to 2. Although the cross-species PK profile, poor predicted human liver distribution of analog 4 and allometry principles projected high doses to achieve a strong antiviral response in patients, this work has provided a path forward toward the design of novel thumb pocket 1 NS5B polymerase inhibitors with improved safety profiles.