Divergent Catalysis: Catalytic Asymmetric [4+2] Cycloaddition of Palladium Enolates.

An asymmetric decarboxylative [4+2] cycloaddition from a catalytically generated chiral Pd enolate was developed, forging four contiguous stereocenters in a single transformation. This was achieved through a strategy termed divergent catalysis, wherein departure from a known catalytic cycle enables novel reactivity of a targeted intermediate prior to re-entry into the original cycle. Mechanistic studies including quantum mechanics calculations, Eyring analysis, and KIE studies offer insight into the reaction mechanism.

Iridium-catalyzed asymmetric trans-selective hydrogenation of 1,3-disubstituted isoquinolines.

The development of the first asymmetric trans-selective hydrogenation of 1,3-disubstituted isoquinolines is reported. Utilizing [Ir(cod)Cl]2 and a commercially available chiral Josiphos ligand, a variety of differentially substituted isoquinolines are hydrogenated to produce enantioenriched trans-tetrahydroisoquinolines in good yield with high levels of enantioselectivity. Directing group studies demonstrate that the hydroxymethyl functionality at the C1 position is critical for hydrogenation to favor the trans-diastereomer. Preliminary mechanistic studies reveal that non-coordinating chlorinated solvents and halide additives are crucial to enable trans-selectivity.

Ir-Catalyzed Asymmetric Allylic Alkylation of Dialkyl Malonates Enabling the Construction of Enantioenriched All-Carbon Quaternary Centers.

An enantioselective iridium-catalyzed allylic alkylation of malonates with trisubstituted allylic electrophiles to form all-carbon quaternary stereocenters is reported. This reaction proceeds at ambient temperature and enables the preparation of a wide range of enantioenriched products in up to 93% yield and 97% ee. The quaternary products can be readily converted to several valuable building blocks such as vicinal quaternary products and ß-quaternary acids.

Systematic Study of the Glutathione Reactivity of N-Phenylacrylamides: 2. Effects of Acrylamide Substitution.

A comprehensive understanding of structure-reactivity relationships is critical to the design and optimization of cysteine-targeted covalent inhibitors. Herein, we report glutathione (GSH) reaction rates for N-phenyl acrylamides with varied substitutions at the α- and ß-positions of the acrylamide moiety. We find that the GSH reaction rates can generally be understood in terms of the electron donating or withdrawing ability of the substituent. When installed at the ß-position, aminomethyl substituents with amine pKa's > 7 accelerate, while those with pKa's < 7 slow the rate of GSH addition at pH 7.4, relative to a hydrogen substituent. Although a computational model was able to only approximately capture experimental reactivity trends, our calculations do not support a frequently invoked mechanism of concerted amine/thiol proton transfer and C-S bond formation and instead suggest that protonated aminomethyl functions as an electron-withdrawing group to reduce the barrier for thiolate addition to the acrylamide.

The development of a structurally distinct series of BACE1 inhibitors via the (Z)-fluoro-olefin amide bioisosteric replacement.

The (Z)-fluoro-olefin amide bioisosteric replacement is an effective tool for addressing various shortcomings of the parent amide. In an effort to fine tune ADME properties of BACE1 preclinical candidate AM-6494, a series of structurally distinct (Z)-fluoro-olefin containing analogs was developed that culminated in compound 15. Herein, we detail design considerations, synthetic challenges, structure activity relationship (SAR) studies, and in vivo properties of an advanced compound in this novel series of BACE1 inhibitors.

Enantioselective total synthesis of (-)-myrifabral A and B.

A catalytic enantioselective approach to the Myrioneuron alkaloids (-)-myrifabral A and (-)-myrifabral B is described. The synthesis was enabled by a palladium-catalyzed enantioselective allylic alkylation, that generates the C(10) all-carbon quaternary center. A key N-acyl iminium ion cyclization forged the cyclohexane fused tricyclic core, while vinyl boronate cross metathesis and oxidation afforded the lactol ring of (-)-myrifabral A. Adaptation of previously reported conditions allowed for the conversion of (-)-myrifabral A to (-)-myrifabral B.

Enantioselective synthesis of highly oxygenated acyclic quaternary center-containing building blocks via palladium-catalyzed decarboxylative allylic alkylation of cyclic siloxyketones.

The development of a palladium-catalyzed enantioselective decarboxylative allylic alkylation of cyclic siloxyketones to produce enantioenriched silicon-tethered heterocycles is reported. The reaction proceeds smoothly to provide products bearing a quaternary stereocenter in excellent yields (up to 91% yield) with high levels of enantioselectivity (up to 94% ee). We further utilized the unique reactivity of the siloxy functionality to access chiral, highly oxygenated acyclic quaternary building blocks. In addition, we subsequently demonstrated the utility of these compounds through the synthesis of a lactone bearing vicinal quaternary-trisubstituted stereocenters.

Iridium-Catalyzed Enantioselective and Diastereoselective Hydrogenation of 1,3-Disubstituted Isoquinolines.

The development of a general method utilizing a hydroxymethyl directing group for asymmetric hydrogenation of 1,3-disubstituted isoquinolines to provide chiral 1,2,3,4-tetrahydroisoquinolines is reported. The reaction, which utilizes [Ir(cod)Cl]2 and a commercially available chiral xyliphos ligand, proceeds in good yield with high levels of enantioselectivity and diastereo-selectivity (up to 95% ee and >20:1 dr) on a range of differentially substituted isoquinolines. Directing group studies demonstrate that the hydroxymethyl functional group at the C1-position is more efficient at enabling hydrogenation than other substituents, although high levels of enantioselectivity were conserved across a variety of polar and non-polar functional groups. By utilizing the generated chiral ß-amino alcohol as a functional handle, the synthetic utility is further highlighted via the synthesis of 1,2-fused oxazolidine, oxazolidinone, and morpholinone tetrahydroisoquinolines in one step. Additionally, a non-natural analog of the tetrahydroprotoberberine alkaloids was successfully synthesized.

Discovery of AM-6494: A Potent and Orally Efficacious ß-Site Amyloid Precursor Protein Cleaving Enzyme 1 (BACE1) Inhibitor with in Vivo Selectivity over BACE2.

ß-Site amyloid precursor protein cleaving enzyme 1 (BACE1) is an aspartyl protease that plays a key role in the production of amyloid ß (Aß) in the brain and has been extensively pursued as a target for the treatment of Alzheimer's disease (AD). BACE2, an aspartyl protease that is structurally related to BACE1, has been recently reported to be involved in melanosome maturation and pigmentation. Herein, we describe the development of a series of cyclopropylthiazines as potent and orally efficacious BACE1 inhibitors. Lead optimization led to the identification of 20, a molecule with biochemical IC50 BACE2/BACE1 ratio of 47. Administration of 20 resulted in no skin/fur color change in a 13-day mouse hypopigmentation study and demonstrated robust and sustained reduction of CSF and brain Aß40 levels in rat and monkey pharmacodynamic models. On the basis of a compelling data package, 20 (AM-6494) was advanced to preclinical development.

Discovery of a Covalent Inhibitor of KRASG12C (AMG 510) for the Treatment of Solid Tumors.

KRASG12C has emerged as a promising target in the treatment of solid tumors. Covalent inhibitors targeting the mutant cysteine-12 residue have been shown to disrupt signaling by this long-"undruggable" target; however clinically viable inhibitors have yet to be identified. Here, we report efforts to exploit a cryptic pocket (H95/Y96/Q99) we identified in KRASG12C to identify inhibitors suitable for clinical development. Structure-based design efforts leading to the identification of a novel quinazolinone scaffold are described, along with optimization efforts that overcame a configurational stability issue arising from restricted rotation about an axially chiral biaryl bond. Biopharmaceutical optimization of the resulting leads culminated in the identification of AMG 510, a highly potent, selective, and well-tolerated KRASG12C inhibitor currently in phase I clinical trials (NCT03600883).

Mechanistic Insights into the Racemization of Fused Cyclopropyl Isoxazolines.

Experimental and computational studies of the unexpected racemization of enantiopure fused cyclopropyl isoxazolines are reported. These studies offer insights into the mechanism of racemization, quantify the position of the transition state on the dipolar-diradical continuum, and establish a relationship between the structure and stability of this class of compounds. Experimental and computed energy barriers for racemization are also presented.

Discovery of N-(1-Acryloylazetidin-3-yl)-2-(1H-indol-1-yl)acetamides as Covalent Inhibitors of KRASG12C.

KRAS regulates many cellular processes including proliferation, survival, and differentiation. Point mutants of KRAS have long been known to be molecular drivers of cancer. KRAS p.G12C, which occurs in approximately 14% of lung adenocarcinomas, 3-5% of colorectal cancers, and low levels in other solid tumors, represents an attractive therapeutic target for covalent inhibitors. Herein, we disclose the discovery of a class of novel, potent, and selective covalent inhibitors of KRASG12C identified through a custom library synthesis and screening platform called Chemotype Evolution and structure-based design. Identification of a hidden surface groove bordered by H95/Y96/Q99 side chains was key to the optimization of this class of molecules. Best-in-series exemplars exhibit a rapid covalent reaction with cysteine 12 of GDP-KRASG12C with submicromolar inhibition of downstream signaling in a KRASG12C-specific manner.

Incorporation of a chiral gem-disubstituted nitrogen heterocycle yields an oxazolidinone antibiotic with reduced mitochondrial toxicity.

gem-Disubstituted N-heterocycles are rarely found in drugs, despite their potential to improve the drug-like properties of small molecule pharmaceuticals. Linezolid, a morpholine heterocycle-containing oxazolidinone antibiotic, exhibits significant side effects associated with human mitochondrial protein synthesis inhibition. We synthesized a gem-disubstituted linezolid analogue that when compared to linezolid, maintains comparable (albeit slightly diminished) activity against bacteria, comparable in vitro physicochemical properties, and a decrease in undesired mitochondrial protein synthesis (MPS) inhibition. This research contributes to the structure-activity-relationship data surrounding oxazolidinone MPS inhibition, and may inspire investigations into the utility of gem-disubstituted N-heterocycles in medicinal chemistry.

Discovery of TRPM8 Antagonist ( S)-6-(((3-Fluoro-4-(trifluoromethoxy)phenyl)(3-fluoropyridin-2-yl)methyl)carbamoyl)nicotinic Acid (AMG 333), a Clinical Candidate for the Treatment of Migraine.

Transient-receptor-potential melastatin 8 (TRPM8), the predominant mammalian cold-temperature thermosensor, is a nonselective cation channel expressed in a subpopulation of sensory neurons in the peripheral nervous system, including nerve circuitry implicated in migraine pathogenesis: the trigeminal and pterygopalatine ganglia. Genomewide association studies have identified an association between TRPM8 and reduced risk of migraine. This disclosure focuses on medicinal-chemistry efforts to improve the druglike properties of initial leads, particularly removal of CYP3A4-induction liability and improvement of pharmacokinetic properties. A novel series of biarylmethanamide TRPM8 antagonists was developed, and a subset of leads were evaluated in preclinical toxicology studies to identify a clinical candidate with an acceptable preclinical safety profile leading to clinical candidate AMG 333, a potent and highly selective antagonist of TRPM8 that was evaluated in human clinical trials.

Diastereoselective synthesis of fused cyclopropyl-3-amino-2,4-oxazine ß-amyloid cleaving enzyme (BACE) inhibitors and their biological evaluation.

The diastereoselective synthesis and structure activity relationship (SAR) of a series of fused cyclopropyl-3-amino-2,4-oxazine (2-oxa-4-azabicyclo[4.1.0]hept-3-en-3-amine)-containing BACE inhibitors is described. Through these efforts compound 2 was identified as a potent (cell IC50 = 15 nM) BACE inhibitor with acceptable ADME properties. When tested in vivo, compound 2 demonstrated a significant reduction of brain and cerebral spinal fluid (CSF) Aß40 levels (46% and 66%, respectively) in a rat pharmacodynamic study and thus represents a suitable starting point for the further development of in vivo efficacious compounds for the treatment of Alzheimer's disease.

Enantioselective Pd-Catalyzed Decarboxylative Allylic Alkylation of Thiopyranones. Access to Acyclic, Stereogenic α-Quaternary Ketones.

A catalytic, enantioselective decarboxylative allylic alkylation of 4-thiopyranones is reported. The α-quaternary 4-thiopyranones produced are challenging to access by standard enolate alkylation owing to facile ring-opening ß-sulfur elimination. In addition, reduction of the carbon-sulfur bonds provides access to elusive acyclic α-quaternary ketones. The alkylated products are obtained in up to 92% yield and 94% enantiomeric excess.

Development of 2-aminooxazoline 3-azaxanthene ß-amyloid cleaving enzyme (BACE) inhibitors with improved selectivity against Cathepsin D.

As part of an ongoing effort at Amgen to develop a disease-modifying therapy for Alzheimer's disease, we have previously used the aminooxazoline xanthene (AOX) scaffold to generate potent and orally efficacious BACE1 inhibitors. While AOX-BACE1 inhibitors demonstrated acceptable cardiovascular safety margins, a retinal pathological finding in rat toxicological studies demanded further investigation. It has been widely postulated that such retinal toxicity might be related to off-target inhibition of Cathepsin D (CatD), a closely related aspartyl protease. We report the development of AOX-BACE1 inhibitors with improved selectivity against CatD by following a structure- and property-based approach. Our efforts culminated in the discovery of a picolinamide-substituted 3-aza-AOX-BACE1 inhibitor absent of retinal effects in an early screening rat toxicology study.

The chemical biology of HNO signaling.

Nitroxyl (HNO) is a simple molecule with significant potential as a pharmacological agent. For example, its use in the possible treatment of heart failure has received recent attention due to its unique therapeutic properties. Recent progress has been made on the elucidation of the mechanisms associated with its biological signaling. Importantly, the biochemical mechanisms described for HNO bioactivity are consistent with its unique and novel chemical properties/reactivity. To date, much of the biology of HNO can be associated with interactions and modification of important regulatory thiol proteins. Herein will be provided a description of HNO chemistry and how this chemistry translates to some of its reported biological effects.

Telescoped Process to Manufacture 6,6,6-Trifluorofucose via Diastereoselective Transfer Hydrogenation: Scalable Access to an Inhibitor of Fucosylation Utilized in Monoclonal Antibody Production.

IgG1 monoclonal antibodies with reduced glycan fucosylation have been shown to improve antibody-dependent cellular cytotoxicity (ADCC) by allowing more effective binding of the Fc region of these proteins to T cells receptors. Increased in vivo efficacy in animal models and oncology clinical trials has been associated with the enhanced ADCC provided by these engineered mAbs. 6,6,6-Trifluorofucose (1) is a new inhibitor of fucosylation that has been demonstrated to allow the preparation of IgG1 monoclonal antibodies with lower fucosylation levels and thus improve the ADCC of these proteins. A new process has been developed to support the preparation of 1 on large-scale for wide mAb manufacture applications. The target fucosylation inhibitor (1) was synthesized from readily available d-arabinose in 11% overall yield and >99.5/0.5 dr (diastereomeric ratio). The heavily telescoped process includes seven steps, two crystallizations as purification handles, and no chromatography. The key transformation of the sequence involves the diastereoselective preparation of the desired trifluoromethyl-bearing alcohol in >9/1 dr from a trimethylsilylketal intermediate via a ruthenium-catalyzed tandem ketal hydrolysis-transfer hydrogenation process.