Photochemical Identification of Auxiliary Severe Acute Respiratory Syndrome Coronavirus 2 Host Entry Factors Using µMap.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the infectious agent of the COVID-19 pandemic, remains a global medical problem. Angiotensin-converting enzyme 2 (ACE2) was identified as the primary viral entry receptor, and transmembrane serine protease 2 primes the spike protein for membrane fusion. However, ACE2 expression is generally low and variable across tissues, suggesting that auxiliary receptors facilitate viral entry. Identifying these factors is critical for understanding SARS-Cov-2 pathophysiology and developing new countermeasures. However, profiling host-virus interactomes involves extensive genetic screening or complex computational predictions. Here, we leverage the photocatalytic proximity labeling platform µMap to rapidly profile the spike interactome in human cells and identify eight novel candidate receptors. We systemically validate their functionality in SARS-CoV-2 pseudoviral uptake assays with both Wuhan and Delta spike variants and show that dual expression of ACE2 with either neuropilin-2, ephrin receptor A7, solute carrier family 6 member 15, or myelin and lymphocyte protein 2 significantly enhances viral uptake. Collectively, our data show that SARS-CoV-2 synergistically engages several host factors for cell entry and establishes µMap as a powerful tool for rapidly interrogating host-virus interactomes.

The Application of Pulse Radiolysis to the Study of Ni(I) Intermediates in Ni-Catalyzed Cross-Coupling Reactions.

Here we report the use of pulse radiolysis and spectroelectrochemistry to generate low-valent nickel intermediates relevant to synthetically important Ni-catalyzed cross-coupling reactions and interrogate their reactivities toward comproportionation and oxidative addition processes. Pulse radiolysis provided a direct means to generate singly reduced [(dtbbpy)NiBr], enabling the identification of a rapid Ni(0)/Ni(II) comproportionation process taking place under synthetically relevant electrolysis conditions. This approach also permitted the direct measurement of Ni(I) oxidative addition rates with electronically differentiated aryl iodide electrophiles (kOA = 1.3 × 104-2.4 × 105 M-1 s-1), an elementary organometallic step often proposed in nickel-catalyzed cross-coupling reactions. Together, these results hold implications for a number of Ni-catalyzed cross-coupling processes.

Searching for an ideal SERM: Mining tamoxifen structure-activity relationships.

The repurposing of old drugs for new treatments has recently garnered increased attention in the face of new diseases and declining productivity of the pharmaceutial industry. This report draws attention to potential opportunities hiding in plain sight within the SAR of off-patent drugs. Herein we explore the untapped potential of Selective Estrogen Receptor Modulators (SERMs). SERMs are a class of molecules that have been highly influential in the treatment of estrogen receptor-positive breast cancers. However, the most commonly prescribed SERM, tamoxifen, has been found to increase the risk of endometrial cancer. Another SERM, raloxifene, does not increase incidence of endometrial cancer, but has been abandoned as a breast cancer treatment. We report the design, synthesis, and evaluation of an unexplored tamoxifen substitution pattern which mimics the geometry of raloxifene to confer its favorable pharmacodynamics. This substitution pattern was found to maintain excellent binding affinity to estrogen receptor-α.

Mechanistic Analysis of Metallaphotoredox C-N Coupling: Photocatalysis Initiates and Perpetuates Ni(I)/Ni(III) Coupling Activity.

The combined use of reaction kinetic analysis, ultrafast spectroscopy, and stoichiometric organometallic studies has enabled the elucidation of the mechanistic underpinnings to a photocatalytic C-N cross-coupling reaction. Steady-state and ultrafast spectroscopic techniques were used to track the excited-state evolution of the employed iridium photocatalyst, determine the resting states of both iridium and nickel catalysts, and uncover the photochemical mechanism for reductive activation of the nickel cocatalyst. Stoichiometric organometallic studies along with a comprehensive kinetic study of the reaction, including rate-driving force analysis, unveiled the crucial role of photocatalysis in both initiating and sustaining a Ni(I)/Ni(III) cross-coupling mechanism. The insights gleaned from this study further enabled the discovery of a new photocatalyst providing a >30-fold rate increase.

Transient Absorption Spectroscopy Offers Mechanistic Insights for an Iridium/Nickel-Catalyzed C-O Coupling.

We report mechanistic insights into an iridium/nickel photocatalytic C-O cross-coupling reaction from time-resolved spectroscopic studies. Using transient absorption spectroscopy, energy transfer from an iridium photocatalyst to a catalytically relevant Ni(II)(aryl) acetate acceptor was observed. Concentration-dependent lifetime measurements suggest the mechanism of the subsequent reductive elimination is a unimolecular process occurring on the long-lived excited state of the Ni(II) complex. We envision that our study of the productive energy-transfer-mediated pathway would encourage the development of new excited-state reactivities in the field of metallaphotocatalysis that are enabled by light harvesting.

Decarboxylative Hydroalkylation of Alkynes.

The merger of open- and closed-shell elementary organometallic steps has enabled the selective intermolecular addition of nucleophilic radicals to unactivated alkynes. A range of carboxylic acids can be subjected to a CO2 extrusion, nickel capture, migratory insertion sequence with terminal and internal alkynes to generate stereodefined functionalized olefins. This platform has been further extended, via hydrogen atom transfer, to the direct vinylation of unactivated C-H bonds. Preliminary studies indicate that a Ni-alkyl migratory insertion is operative.

Tumor Immune Cell Targeting Chimeras (TICTACs) For Targeted Depletion of Macrophage-Associated Checkpoint Receptors.

Immune cells in the tumor microenvironment are not only powerful regulators of immunosuppression and tumorigenesis, but also represent a dominant cell type, with tumor-associated macrophages (TAMs) comprising up to 50% of total cell mass in solid tumors. Immunotherapies such as immune checkpoint inhibitors (ICIs) derive their efficacy from this cancer-immune cell interface, however, immune-related adverse events resulting from systemic blockade remain a significant challenge. To address this need for potent, yet highly tumor-specific immunotherapies, we developed Tumor-Immune Cell Targeting Chimeras (TICTACs), antibody conjugates that are capable of selectively depleting immune checkpoint receptors such as SIRPa from the surface of TAMs. These chimeric molecules consist of a synthetic glycan ligand that binds the C-type lectin CD206, a well-established TAM marker, conjugated to a non-blocking antibody that binds but does not inhibit the checkpoint receptor. By engaging CD206, which constitutively recycles between the plasma membrane and early endosomes, TICTACs facilitate robust removal of the checkpoint receptors from the surface of CD206high macrophages, while having no effect on CD206low macrophages. By decoupling antibody selectivity from its blocking function, we present a new paradigm for developing highly tumor-specific immunotherapies.

Discovery of an Atropisomeric PI3Kß Selective Inhibitor through Optimization of the Hinge Binding Motif.

A series of PI3Kß selective inhibitors derived from a novel 4-(1H-benzo[d]imidazol-1-yl)quinoline chemotype has been rationally designed. Crucial to achieving the desired selectivity over the other class I PI3K isoforms, including the challenging δ-isoform, was the identification of a subset of substituted pyridine hinge binders. This work led to the discovery of (P)-14, a highly selective and orally bioavailable PI3Kß inhibitor displaying an excellent pharmacokinetic profile in addition to great cellular potency in various PTEN-deficient tumor cell lines. Results from a dog toxicology study revealing structure-related, off-target ocular toxicity are also briefly discussed.

Atropisomerism by Design: Discovery of a Selective and Stable Phosphoinositide 3-Kinase (PI3K) ß Inhibitor.

Atropisomerism is a type of axial chirality in which enantiomers or diastereoisomers arise due to hindered rotation around a bond axis. In this manuscript, we report a case in which torsional scan studies guided the thoughtful creation of a restricted axis of rotation between two heteroaromatic systems of a phosphoinositide 3-kinase (PI3K) ß inhibitor, generating a pair of atropisomeric compounds with significantly different pharmacological and pharmacokinetic profiles. Emblematic of these differences, the metabolism of inactive ( M)-28 is primarily due to the cytosolic enzyme aldehyde oxidase, while active ( P)-28 has lower affinity for aldehyde oxidase, resulting in substantially better metabolic stability. Additionally, we report torsional scan and experimental studies used to determine the barriers of rotation of this novel PI3Kß inhibitor.