Monitoring Drug Self-Aggregation and Potential for Promiscuity in Off-Target In Vitro Pharmacology Screens by a Practical NMR Strategy

A simple NMR assay was applied to monitor the tendency of compounds to self-aggregate in aqueous media. The observation of unusual spectral trends as a function of compound concentration appears to be signatory of the formation of self-assemblies. ¹H NMR resonances of aggregating compounds were sensitive to the presence of a range of molecular assemblies in solution including large molecular-size entities, smaller multimers, and mixtures of assembled species. The direct observation of aggregates via unusual NMR spectra also correlated with promiscuous behavior of molecules in off-target in vitro pharmacology assays. This empirical assay can have utility for predicting compound promiscuity and should complement predictive methods that principally rely on the computing of descriptors such as lipophilicity (cLogP) and topological surface area (TPSA). This assay should serve as a practical tool for medicinal chemists to monitor compound attributes in aqueous solution and various pharmacologically relevant media, as demonstrated herein

Compound Aggregation in Drug Discovery: Implementing a Practical NMR Assay for Medicinal Chemists

The pharmaceutical industry has recognized that many drug-like molecules can self-aggregate in aqueous media and have physicochemical properties that skew experimental results and decisions. Herein, we introduce the use of a simple NMR strategy for detecting the formation of aggregates using dilution experiments that can be performed on equipment prevalent in most synthetic chemistry departments. We show that ¹H NMR resonances are sensitive to large molecular-size entities and to smaller multimers and mixtures of species. Practical details are provided for sample preparation and for determining the concentrations of single molecule, aggregate entities, and precipitate. The critical concentrations above which aggregation begins can be found and were corroborated by comparisons with light scattering techniques. Disaggregation can also be monitored using detergents. This NMR assay should serve as a practical and readily available tool for medicinal chemists to better characterize how their compounds behave in aqueous media and influence drug design decisions

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

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

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 1<i>H</i>-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

Discovery of the First Thumb Pocket 1 NS5B Polymerase Inhibitor (BILB 1941) with Demonstrated Antiviral Activity in Patients Chronically Infected with Genotype 1 Hepatitis C Virus (HCV)

Combinations of direct acting antivirals (DAAs) that have the potential to suppress emergence of resistant virus and that can be used in interferon-sparing regimens represent a preferred option for the treatment of chronic HCV infection. We have discovered allosteric (thumb pocket 1) non-nucleoside inhibitors of HCV NS5B polymerase that inhibit replication in replicon systems. Herein, we report the late-stage optimization of indole-based inhibitors, which began with the identification of a metabolic liability common to many previously reported inhibitors in this series. By use of parallel synthesis techniques, a sparse matrix of inhibitors was generated that provided a collection of inhibitors satisfying potency criteria and displaying improved in vitro ADME profiles. “Cassette” screening for oral absorption in rat provided a short list of potential development candidates. Further evaluation led to the discovery of the first thumb pocket 1 NS5B inhibitor (BILB 1941) that demonstrated antiviral activity in patients chronically infected with genotype 1 HCV

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, <b>27</b>) to the first thumb pocket 1 NS5B inhibitor to demonstrate antiviral activity in genotype 1 HCV infected patients, BILB 1941 (<b>1</b>). Cell-based replicon potency was significantly improved through electronic modulation of the p<i>K</i>_a of the carboxylic acid function of the lead molecule. Subsequent ADME-PK optimization lead to <b>27</b>, a predicted low clearance compound in man. The preclinical profile of inhibitor <b>27</b> is discussed, as well as the identification of a genotoxic metabolite that led to the discontinuation of the development of this compound