Pharmaceutical Development Challenges in a Beyond Rule of Five Prodrug: Case Study of ABBV-167, Phosphate Prodrug of Venetoclax.

ABBV-167, a phosphate prodrug of BCL-2 inhibitor venetoclax, was recently progressed into the clinic as an alternative means of reducing pill burden for patients in high-dose indications. The dramatically enhanced aqueous solubility of ABBV-167 allowed for high drug loading within a crystalline tablet and, when administered in phase I clinical study, conferred venetoclax exposure commensurate with the equivalent dose administered as an amorphous solid dispersion. In enabling the progression into the clinic, we performed a comprehensive evaluation of the CMC development aspects of this beyond the rule of five (bRo5) prodrug. Adding a phosphate moiety resulted in excessively complex chemical speciation and solid form landscapes with significant physical-chemical stability liabilities. A combination of experimental and computational methods including microelectron diffraction (MicroED), total scattering, tablet colorimetry, finite element, and molecular dynamics modeling were used to understand CMC developability across drug substance and product manufacture and storage. The prodrug's chemical structural characteristics and loose crystal packing were found to be responsible for the loss of crystallinity during its manufacturing, which in turn led to high solid-state chemical reactivity and poor shelf life stability. The ABBV-167 case exemplifies key CMC development challenges for complex chemical matter such as bRo5 phosphate prodrugs with significant ramifications during drug substance and drug product manufacturing and storage.

Enabling, Decagram-Scale Synthesis of Macrocyclic MCL-1 Inhibitor ABBV-467.

ABBV-467 is a highly potent and selective MCL-1 inhibitor that was advanced to a phase I clinical trial for the treatment of multiple myeloma. Due to its large size and structural complexity, ABBV-467 is a challenging synthetic target. Herein, we describe the synthesis of ABBV-467 on a decagram scale, which enabled preclinical characterization. The strategy is convergent and stereoselective, featuring a hindered biaryl cross coupling, enantioselective hydrogenation, and conformationally preorganized macrocyclization by C-O bond formation as key steps.

Overcoming Bioavailability Challenges of Dasabuvir and Enabling a Triple-Combination Direct-Acting Antiviral HCV Regimen through a Salt of Very Weak Acid for Oral Delivery.

Dasabuvir is a non-nucleoside polymerase inhibitor for the treatment of hepatitis C virus (HCV) infection. It is an extremely weak diacidic drug (pKa = 8.2 and 9.2) and a prolific solvate former. Due to its exceedingly low aqueous solubility (≤0.127 µg/mL at pH 1-6.8, dose number of 1.31 × 104), crystalline dasabuvir free acid exhibited poor oral bioavailability in initial animal pharmacokinetic (PK) assessment. This necessitated the development of enabling formulation for human clinical studies to achieve the required therapeutic in vivo concentration of dasabuvir. While salt formation has been widely used to enhance the solubility and dissolution rate of solids, this approach has rarely been applied to develop oral solid dosage forms for acidic drugs as weak as dasabuvir due to concerns of rapid disproportionation and crystallization of its free acid. In this contribution, we detail our efforts in identifying dasabuvir monosodium monohydrate as a drug substance that is stable, manufacturable, and, most importantly, significantly enhances the dissolution and oral absorption of this poorly soluble drug. The oral delivery of dasabuvir through the salt approach has enabled the commercialization of the triple-combination direct-acting antiviral HCV regimen, Viekira Pak. The methodologies and solutions identified in targeted studies to overcome technical challenges encountered along the way (i.e., incorporation of polymers to inhibit crystallization and disproportionation and species mapping to enable salt manufacturing process, etc.) can be applied to other insoluble compounds.

Implications of the Conformationally Flexible, Macrocyclic Structure of the First-Generation, Direct-Acting Anti-Viral Paritaprevir on Its Solid Form Complexity and Chameleonic Behavior.

Direct-acting antiviral regimens have transformed therapeutic management of hepatitis C across all prevalent genotypes. Most of the chemical matter in these regimens comprises molecules well outside the traditional drug development chemical space and presents significant challenges. Herein, the implications of high conformational flexibility and the presence of a 15-membered macrocyclic ring in paritaprevir are studied through a combination of advanced computational and experimental methods with focus on molecular chameleonicity and crystal form complexity. The ability of the molecule to toggle between high and low 3D polar surface area (PSA) conformations is underpinned by intramolecular hydrogen bonding (IMHB) interactions and intramolecular steric effects. Computational studies consequently show a very significant difference of over 75 Å2 in 3D PSA between polar and apolar environments and provide the structural basis for the perplexingly favorable passive permeability of the molecule. Crystal packing and protein binding resulting in strong intermolecular interactions disrupt these intramolecular interactions. Crystalline Form I benefits from strong intermolecular interactions, whereas the weaker intermolecular interactions in Form II are partially compensated by the energetic advantage of an IMHB. Like Form I, no IMHB is observed within the receptor-bound conformation; instead, an intermolecular H-bond contributes to the potency of the molecule. The choice of metastable Form II is derisked through strategies accounting for crystal surface and packing features to manage higher form specific solid-state chemical reactivity and specific processing requirements. Overall, the results show an unambiguous link between structural features and derived properties from crystallization to dissolution, permeation, and docking into the protein pocket.

Synthesis and evaluation of 2'-dihalo ribonucleotide prodrugs with activity against hepatitis C virus.

Hepatitis C virus (HCV) nucleoside inhibitors have been a key focus of nearly 2 decades of HCV drug research due to a high barrier to drug resistance and pan-genotypic activity profile provided by molecules in this drug class. Our investigations focused on several potent 2'-halogenated uridine-based HCV polymerase inhibitors, resulting in the discovery of novel 2'-deoxy-2'-dihalo-uridine analogs that are potent inhibitors in replicon assays for all genotypes. Further studies to improve in vivo performance of these nucleoside inhibitors identified aminoisobutyric acid ethyl ester (AIBEE) phosphoramidate prodrugs 18a and 18c, which provide high levels of the active triphosphate in dog liver. AIBEE prodrug 18c was compared with sofosbuvir (1) by co-dosing both compounds by oral administration in dog (5 mg/kg each) and measuring liver concentrations of the active triphosphate metabolite at both 4 and 24 h post dosing. In this study, 18c provided liver triphosphate concentrations that were 6-fold higher than sofosbuvir (1) at both biopsy time points, suggesting that 18c could be a highly effective agent for treating HCV infected patients in the clinic.

Targeting lysine specific demethylase 4A (KDM4A) tandem TUDOR domain - A fragment based approach.

The tandem TUDOR domains present in the non-catalytic C-terminal half of the KDM4A, 4B and 4C enzymes play important roles in regulating their chromatin localizations and substrate specificities. They achieve this regulatory role by binding to different tri-methylated lysine residues on histone H3 (H3-K4me3, H3-K23me3) and histone H4 (H4-K20me3) depending upon the specific chromatin environment. In this work, we have used a 2D-NMR based fragment screening approach to identify a novel fragment (1a), which binds to the KDM4A-TUDOR domain and shows modest competition with H3-K4me3 binding in biochemical as well as in vitro cell based assays. A co-crystal structure of KDM4A TUDOR domain in complex with 1a shows that the fragment binds stereo-specifically to the methyl lysine binding pocket forming a network of strong hydrogen bonds and hydrophobic interactions. We anticipate that the fragment 1a can be further developed into a novel allosteric inhibitor of the KDM4 family of enzymes through targeting their C-terminal tandem TUDOR domain.

Pd-Catalyzed Synthesis of Aryl and Heteroaryl Triflones from Reactions of Sodium Triflinate with Aryl (Heteroaryl) Triflates.

A novel method for Pd-catalyzed triflination of aryl and heteroaryl triflates using NaSO2CF3 as the nucleophile is described. The combination of Pd2(dba)3 and RockPhos formed the most effective catalyst. A broad range of functional groups and heteroaromatic compounds were tolerated under the neutral reaction conditions. The order of reactivity ArOTf ≥ ArCl ≥ ArBr is consistent with transmetalation being a slow step of the reaction.

Ritonavir Form III: A New Polymorph After 24 Years.

Polymorphism occurs widely in pharmaceutical solids, and must be thoroughly studied during product development. Twenty-four years after ritonavir (RTV) Form II materialized, we report a new polymorph, Form III, discovered via melt crystallization. Form III has a unique PXRD pattern, Raman spectrum, lower melting point and heat of fusion, compared to the known polymorphs, Form I and Form II. It is the least stable form, monotropically, among the three polymorphs. Form III differs from Form I and Form II in molecular conformation and hydrogen bonding motifs in crystal lattice. Nucleation from RTV supercooled liquid is slow, and selected Form III exclusively. The discovery of RTV Form III demonstrates the importance of crystal nucleation studies. Crystallization from supercooled liquids should be incorporated as part of polymorph screening workflow.

Inhibiting Sublimation of Thymol by Cocrystallization.

A thymol:4,4'-dipyridyl (2:1) cocrystal (Form I) is reported to suppress thymol sublimation. The cocrystal was prepared via solution-mediated phase transformation and its structure is sustained by O-H (phenol) ··· N (pyridyl) hydrogen bonds between two individual components. A cocrystal polymorph (Form II) was formed via solid state transformation or via vapor phase upon heating. Using gravimetry analysis, it was demonstrated that cocrystal Form I decreased the sublimation rate of thymol by 38-fold. This study demonstrates that cocrystallization is an effective approach to reduce vapor pressure and sublimation of solids, thus achieving odor-masking.

Synthesis and SAR of 4-aminocyclopentapyrrolidines as N-type Ca²âº channel blockers with analgesic activity.

A novel 4-aminocyclopentapyrrolidine series of N-type Ca(2+) channel blockers have been discovered. Enantioselective synthesis of the 4-aminocyclopentapyrrolidines was enabled using N-tert-butyl sulfinamide chemistry. SAR studies demonstrate selectivity over L-type Ca(2+) channels. N-type Ca(2+) channel blockade was confirmed using electrophysiological recording techniques. Compound 25 is an N-type Ca(2+) channel blocker that produces antinociception in inflammatory and nociceptive pain models without exhibiting cardiovascular or motor liabilities.

Enabling Suzuki-Miyaura coupling of Lewis-basic arylboronic esters with a nonprecious metal catalyst.

The high cost and negative environmental impact of precious metal catalysts has led to increased demand for nonprecious alternatives for widely practiced reactions such as the Suzuki-Miyaura coupling (SMC). Ni-catalyzed versions of this reaction have failed to achieve high reactivity with Lewis-basic arylboron nucleophiles, especially pinacolboron esters. We describe the development of (PPh2Me)2NiCl2 as an inexpensive and air-stable precatalyst that addresses this challenge. Under activation by n-BuMgCl, this complex can catalyze the coupling of synthetically important heteroaryl pinacolborons with heteroaryl halides. Mildly basic conditions (aqueous K3PO4) allow the reaction to tolerate sensitive functional groups that were incompatible with other Ni-SMC methods. Experimental and computational studies suggest that catalyst inhibition by substitution of PPh2Me from Ni(ii) intermediates by Lewis basic reactants and products is disfavored relative to more commonly employed ligands in the Ni-SMC, which allows it to operate efficiently in the presence of Lewis bases such as unhindered pyridines.

Discovery of ABBV-3373, an Anti-TNF Glucocorticoid Receptor Modulator Immunology Antibody Drug Conjugate.

Using a convergent synthetic route to enable multiple points of diversity, a series of glucocorticoid receptor modulators (GRM) were profiled for potency, selectivity, and drug-like properties in vitro. Despite covering a large range of diversity, profiling the nonconjugated small molecule was suboptimal and they were conjugated to a mouse antitumor necrosis factor (TNF) antibody using the MP-Ala-Ala linker. Screening of the resulting antibody drug conjugates (ADCs) provided a better assessment of efficacy and physical properties, reinforcing the need to conduct structure-activity relationship studies on the complete ADC. DAR4 ADCs were screened in an acute mouse contact hypersensitivity model measuring biomarkers to ensure a sufficient therapeutic window. In a chronic mouse arthritis model, mouse anti-TNF GRM ADCs were efficacious after a single dose of 10 mg/kg i.p. for over 30 days. Data on the unconjugated payloads and mouse surrogate anti-TNF ADCs identified payload 17 which was conjugated to a human anti-TNF antibody and advanced to the clinic as ABBV-3373.

The effects of tautomerism on the nature of molecules in the solid state.

Tautomerism is a phenomenon well know to most chemists but frequently forgotten when chemistry leaves the bench and enters the computational realm. Through the examination of several examples from the crystallographic literature it can be clearly demonstrated that the tautomeric state of a molecules can strongly affect its nature.

Scalable synthesis and isolation of the four stereoisomers of methyl 1-amino-3-(4-bromophenyl)cyclopentanecarboxylate, useful intermediates for the synthesis of S1P1 receptor agonists.

The individual isomers of methyl 1-amino-3-(4-bromophenyl)cyclopentanecarboxylate are useful intermediates for the synthesis of S1P1 receptor agonists. Herein we describe a scalable synthesis and isolation of each of the four stereoisomers of this compound in gram quantities with >98% ee and de. The utility of this approach is demonstrated by the synthesis of ((1R,3R)-1-amino-3-(4-octylphenyl)cyclopentyl)methanol in 7 steps, 11% overall yield, and >98% ee and de.

Small Molecule IL-36γ Antagonist as a Novel Therapeutic Approach for Plaque Psoriasis.

IL-36 cytokines are pro-inflammatory members of the IL-1 family that are upregulated in inflammatory disorders. Specifically, IL-36γ is highly expressed in active psoriatic lesions and can drive pro-inflammatory processes in 3D human skin equivalents supporting a role for this target in skin inflammation. Small molecule antagonists of interleukins have been historically challenging to generate. Nevertheless, we performed a small molecule high-throughput screen to identify IL-36 antagonists using a novel TR-FRET binding assay. Several compounds, including 2-oxypyrimidine containing structural analogs of the marketed endothelin receptor A antagonist Ambrisentan, were identified as hits from the screen. A-552 was identified as a the most potent antagonist of human IL-36γ, but not the closely related family member IL-36α, was capable of attenuating IL-36γ induced responses in mouse and human disease models. Additionally, x-ray crystallography studies identified key amino acid residues in the binding pocket present in human IL-36γ that are absent in human IL-36α. A-552 represents a first-in-class small molecule antagonist of IL-36 signaling that could be used as a chemical tool to further investigate the role of this pathway in inflammatory skin diseases such as psoriasis.

Discovery and metabolic stabilization of potent and selective 2-amino-N-(adamant-2-yl) acetamide 11beta-hydroxysteroid dehydrogenase type 1 inhibitors.

Starting from a rapidly metabolized adamantane 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) inhibitor 22a, a series of E-5-hydroxy-2-adamantamine inhibitors, exemplified by 22d and (+/-)-22f, was discovered. Many of these compounds are potent inhibitors of 11beta-HSD1 and are selective over 11beta-HSD2 for multiple species (human, mouse, and rat), unlike other reported species-selective series. These compounds have good cellular potency and improved microsomal stability. Pharmacokinetic profiling in rodents indicated moderate to large volumes of distribution, short half-lives, and a pharmacokinetic species difference with the greatest exposure measured in rat with 22d. One hour postdose liver, adipose, and brain tissue 11beta-HSD1 inhibition was confirmed with (+/-)-22f in a murine ex vivo assay. Although 5,7-disubstitued-2-adamantamines provided greater stability, a single, E-5-position, polar functional group afforded inhibitors with the best combination of stability, potency, and selectivity. These results indicate that adamantane metabolic stabilization sufficient to obtain short-acting, potent, and selective 11beta-HSD1 inhibitors has been discovered.

Synthesis of novel and uniquely shaped 3-azabicyclo[4.2.0]octan-4-one derivatives by sequential Ugi/[2+2] ene-enone photocycloadditions.

[structure: see text]. We report a new methodology for the construction of novel and uniquely shaped 3-azabicyclo[4.2.0]octan-4-one derivatives by combining the Ugi multicomponent reaction with [2+2] enone-olefin photochemical transformations. The overall sequence is capable of creating up to five stereocenters; however, in most cases, only two diastereomers are observed.

Concise construction of novel bridged bicyclic lactams by sequenced Ugi/RCM/Heck reactions.

Herein we report a concise protocol for the diastereoselective synthesis of novel bridged bicyclic lactams from commercially available components by the sequence of Ugi, ring-closing metathesis (RCM), and Heck reactions. X-ray diffraction studies revealed that the bicyclic products contain varying degrees of pyramidalization of the bridgehead nitrogen atom.

A "hidden" co-crystal of caffeine and adipic acid.

Co-crystal formation between caffeine and adipic acid has been explored over the years without success; utilizing the newly developed co-crystal screening method, we have finally discovered this "hidden" caffeine and adipic acid co-crystal.