Oxidative cyclization reagents reveal tryptophan cation-π interactions.

Methods for selective covalent modification of amino acids on proteins can enable a diverse array of applications, spanning probes and modulators of protein function to proteomics1-3. Owing to their high nucleophilicity, cysteine and lysine residues are the most common points of attachment for protein bioconjugation chemistry through acid-base reactivity3,4. Here we report a redox-based strategy for bioconjugation of tryptophan, the rarest amino acid, using oxaziridine reagents that mimic oxidative cyclization reactions in indole-based alkaloid biosynthetic pathways to achieve highly efficient and specific tryptophan labelling. We establish the broad use of this method, termed tryptophan chemical ligation by cyclization (Trp-CLiC), for selectively appending payloads to tryptophan residues on peptides and proteins with reaction rates that rival traditional click reactions and enabling global profiling of hyper-reactive tryptophan sites across whole proteomes. Notably, these reagents reveal a systematic map of tryptophan residues that participate in cation-π interactions, including functional sites that can regulate protein-mediated phase-separation processes.

Discovery of Potent Pyrazoline-Based Covalent SARS-CoV-2 Main Protease Inhibitors.

While vaccines and antivirals are now being deployed for the current SARS-CoV-2 pandemic, we require additional antiviral therapeutics to not only effectively combat SARS-CoV-2 and its variants, but also future coronaviruses. All coronaviruses have relatively similar genomes that provide a potential exploitable opening to develop antiviral therapies that will be effective against all coronaviruses. Among the various genes and proteins encoded by all coronaviruses, one particularly "druggable" or relatively easy-to-drug target is the coronavirus Main Protease (3CLpro or Mpro), an enzyme that is involved in cleaving a long peptide translated by the viral genome into its individual protein components that are then assembled into the virus to enable viral replication in the cell. Inhibiting Mpro with a small-molecule antiviral would effectively stop the ability of the virus to replicate, providing therapeutic benefit. In this study, we have utilized activity-based protein profiling (ABPP)-based chemoproteomic approaches to discover and further optimize cysteine-reactive pyrazoline-based covalent inhibitors for the SARS-CoV-2 Mpro. Structure-guided medicinal chemistry and modular synthesis of di- and tri-substituted pyrazolines bearing either chloroacetamide or vinyl sulfonamide cysteine-reactive warheads enabled the expedient exploration of structure-activity relationships (SAR), yielding nanomolar potency inhibitors against Mpro from not only SARS-CoV-2, but across many other coronaviruses. Our studies highlight promising chemical scaffolds that may contribute to future pan-coronavirus inhibitors.

An Activity-Based Oxaziridine Platform for Identifying and Developing Covalent Ligands for Functional Allosteric Methionine Sites: Redox-Dependent Inhibition of Cyclin-Dependent Kinase 4.

Activity-based protein profiling (ABPP) is a versatile strategy for identifying and characterizing functional protein sites and compounds for therapeutic development. However, the vast majority of ABPP methods for covalent drug discovery target highly nucleophilic amino acids such as cysteine or lysine. Here, we report a methionine-directed ABPP platform using Redox-Activated Chemical Tagging (ReACT), which leverages a biomimetic oxidative ligation strategy for selective methionine modification. Application of ReACT to oncoprotein cyclin-dependent kinase 4 (CDK4) as a representative high-value drug target identified three new ligandable methionine sites. We then synthesized a methionine-targeting covalent ligand library bearing a diverse array of heterocyclic, heteroatom, and stereochemically rich substituents. ABPP screening of this focused library identified 1oxF11 as a covalent modifier of CDK4 at an allosteric M169 site. This compound inhibited kinase activity in a dose-dependent manner on purified protein and in breast cancer cells. Further investigation of 1oxF11 found prominent cation-π and H-bonding interactions stabilizing the binding of this fragment at the M169 site. Quantitative mass-spectrometry studies validated 1oxF11 ligation of CDK4 in breast cancer cell lysates. Further biochemical analyses revealed cross-talk between M169 oxidation and T172 phosphorylation, where M169 oxidation prevented phosphorylation of the activating T172 site on CDK4 and blocked cell cycle progression. By identifying a new mechanism for allosteric methionine redox regulation on CDK4 and developing a unique modality for its therapeutic intervention, this work showcases a generalizable platform that provides a starting point for engaging in broader chemoproteomics and protein ligand discovery efforts to find and target previously undruggable methionine sites.

Direct Catalytic Decarboxylative Amination of Aryl Acetic Acids.

The decarboxylative coupling of a carboxylic acid with an amine nucleophile provides an alternative to the substitution of traditional organohalide coupling partners. Benzoic and alkynyl acids may be directly aminated by oxidative catalysis. In contrast, methods for intermolecular alkyl carboxylic acid to amine conversion, including amidate rearrangements and photoredox-promoted approaches, require stoichiometric activation of the acid unit to generate isocyanate or radical intermediates. Reported here is a process for the direct chemoselective decarboxylative amination of electron-poor arylacetates by oxidative Cu catalysis. The reaction proceeds at (or near) room temperature, uses native carboxylic acid starting materials, and is compatible with protic, electrophilic, and other potentially complicating functionality. Mechanistic studies support a pathway in which ionic decarboxylation of the acid generates a benzylic nucleophile which is aminated in a Chan-Evans-Lam-type process.

Direct Catalytic Enantioselective Benzylation from Aryl Acetic Acids.

We demonstrate that metal-catalyzed enantioselective benzylation reactions of allylic electrophiles can occur directly from aryl acetic acids. The reaction proceeds via a pathway in which decarboxylation is the terminal event, occurring after stereoselective carbon-carbon bond formation. This mechanistic feature enables enantioselective benzylation without the generation of a highly basic nucleophile. Thus, the process has broad functional group compatibility that would not be possible employing established protocols.

Decarboxylative Benzylation of Aryl and Alkenyl Boronic Esters.

The copper-catalyzed decarboxylative benzylation of aryl and alkenyl boronic esters with electron-deficient aryl acetates is reported. The oxidative coupling proceeds under mild, aerobic conditions and tolerates a host of potentially reactive electrophilic functional groups that would be problematic with traditional benzylation methods (aryl iodides and bromides, protic heteroatoms, aldehydes, Michael acceptors). A reaction pathway in which a benzylic nucleophile is generated by aryl acetate decarboxylation and in turn is intercepted by the catalyst to form diarylmethane products is supported by mechanistic studies.

Intermolecular Aminocarbonylation of Alkenes using Concerted Cycloadditions of Iminoisocyanates.

The aminocarbonylation of alkenes is a powerful method for accessing the ß-amino carbonyl motif that remains underdeveloped. Herein, the development of intermolecular aminocarbonylation reactivity of iminoisocyanates with alkenes is presented. This includes the discovery of a fluorenone-derived reagent, which was effective for many alkene classes and facilitated derivatization. Electron-rich substrates were most reactive, and this indicated that the LUMO of the iminoisocyanate is reacting with the HOMO of the alkene. Computational and experimental results support a concerted asynchronous [3 + 2] cycloaddition involving an iminoisocyanate, which was observed for the first time by FTIR under the reaction conditions. The products of this reaction are complex azomethine imines, which are precursors to valuable ß-amino carbonyl compounds such as ß-amino amides and esters, pyrazolones, and bicyclic pyrazolidinones. A kinetic resolution of the azomethine imines by enantioselective reduction (s = 13-43) allows access to enantioenriched products. Overall, this work provides a new tool to convert alkenes into ß-amino carbonyl compounds.

Ambient Decarboxylative Arylation of Malonate Half-Esters via Oxidative Catalysis.

We report decarboxylative carbonyl α-arylation by coupling of arylboron nucleophiles with malonic acid derivatives. This process is enabled by the merger of aerobic oxidative Cu catalysis with decarboxylative enolate interception reminiscent of malonyl-CoA reactivity in polyketide biosynthesis. This method enables the synthesis of monoaryl acetate derivatives containing electrophilic functional groups that are incompatible with existing α-arylation reactivity paradigms. The utility of the reaction is demonstrated in drug intermediate synthesis and late-stage functionalization.

Oxidative Coupling of Aryl Boron Reagents with sp(3)-Carbon Nucleophiles: The Enolate Chan-Evans-Lam Reaction.

Reported is a versatile new oxidative method for the arylation of activated methylene species. Under mild reaction conditions (RT to 40 °C), Cu(OTf)2 mediates the selective coupling of functionalized aryl boron species with a variety of stabilized sp(3) -nucleophiles. Tertiary malonates and amido esters can be employed as substrates to generate quaternary centers. Complementing either traditional cross-coupling or SN Ar protocols, the transformation is chemoselective in the presence of halogen electrophiles, including aryl bromides and iodides. Substrates bearing amide, sulfonyl, and phosphonyl groups, which are not amenable to coupling under mild Hurtley-type conditions, are suitable reaction partners.

Kinetic Resolution of Azomethine Imines by Brønsted Acid Catalyzed Enantioselective Reduction.

Azomethine imines are valuable substrates in asymmetric catalysis, and can be precursors to ß-amino carbonyl compounds and complex hydrazines. However, their utility is limited because complex and enantioenriched azomethine imines are often unavailable. Reported herein is a kinetic resolution of N,N'-cyclic azomethine imines by enantioselective reduction (s=13-43). This resolution was accomplished using a Brønsted acid catalyst, and represents the first example of the asymmetric reduction of azomethine imines. The pyrazolidinone product (up to 86 % ee) and the recovered azomethine imine (up to 99 % ee) can both be used to access the opposite enantiomers of valuable products.

Direct reversible decarboxylation from stable organic acids in dimethylformamide solution.

Many classical and emerging methodologies in organic chemistry rely on carbon dioxide (CO2) extrusion to generate reactive intermediates for bond-forming events. Synthetic reactions that involve the microscopic reverse-the carboxylation of reactive intermediates-have conventionally been undertaken using very different conditions. We report that chemically stable C(sp3) carboxylates, such as arylacetic acids and malonate half-esters, undergo uncatalyzed reversible decarboxylation in dimethylformamide solution. Decarboxylation-carboxylation occurs with substrates resistant to protodecarboxylation by Brønsted acids under otherwise identical conditions. Isotopically labeled carboxylic acids can be prepared in high chemical and isotopic yield by simply supplying an atmosphere of 13CO2 to carboxylate salts in polar aprotic solvents. An understanding of carboxylate reactivity in solution enables conditions for the trapping of aldehydes, ketones, and α,ß-unsaturated esters.

Coronary Artery Calcium and Long-Term Risk of Death, Myocardial Infarction, and Stroke: The Walter Reed Cohort Study.

OBJECTIVES: This study aimed to assess the long-term risk of death and atherosclerotic cardiovascular disease (ASCVD) outcomes, including stroke, in a real-world cohort that underwent coronary artery calcium (CAC) scoring. BACKGROUND: Large-scale, long-term studies assessing the independent relationship of CAC for prediction of ASCVD events, to include stroke, in young, low-risk patients are uncommon outside of the clinical trial setting. METHODS: A total of 23,637 consecutive subjects without ASCVD who underwent CAC scoring from 1997 to 2009 were studied. Subjects were assessed for myocardial infarction (MI), stroke, major adverse cardiovascular events (MACE) (e.g., MI, stroke, or cardiovascular death), and all-cause mortality. Outcomes were extracted from the Military Data Repository and the National Death Index and assessed using Cox proportional hazards models, controlling for baseline risk factors, atrial fibrillation, and competing mortality. RESULTS: Patients (mean age 50.0 ± 8.5 years) were followed over a median of 11.4 years. The relative adjusted subhazard ratio (aSHR) for CAC 1 to 100, 101 to 400, and >400 was 2.2, 3.8, and 5.9 for MI; 1.2, 1.4, and 1.9 for stroke; 1.4, 2.0, and 2.8 for MACE; and 1.2, 1.5 and 2.1 for death (p < 0.0001). The addition of CAC score to risk factors significantly improved the prognostic accuracy for all outcomes by the likelihood ratio test. Area under the curve increased from 0.658 to 0.738 for MI, 0.703 to 0.704 for stroke, 0.685 to 0.705 for MACE, and 0.759 to 0.767 for mortality. Among subjects without traditional risk factors (n = 6,208; mean age 43.8 ± 4.4 years), the presence of any CAC (>0; n = 848) was associated with an increased risk of MACE (aSHR: 1.67; 95% confidence interval: 1.16 to 2.39). CONCLUSIONS: CAC scoring significantly improved long-term prognostic accuracy for MACE events and mortality, irrespective of age and risk factors. These results support CAC screening for improving individual ASCVD risk assessment and prevention in low-risk, young adults.

Developing a Mobile Health Application to Assist With Clinic Flow, Documentation, Billing, and Research in a Specialty Clinic.

In specialty clinics, a staff physician is often required to direct patient flow through the clinic and performs all documentation for coding/billing. In response to the workload created by increased patient volume, many specialty clinics have implemented protocols for both disease treatment and coordination of clinic flow. In this article, we review the literature on using mobile technology to assist with patient care, clinic flow, disease treatment, and documentation/billing. We also describe the development and implementation of a mobile application in our pulmonary clinic designed to automate patient flow, assist the physician in documentation/billing, and gather research data including review of initial user data and lessons learned.

Expanding the limit of Pd-catalyzed decarboxylative benzylations.

The Pd-catalyzed decarboxylative cross-coupling of electron-deficient aryl acetates with aryl bromides is reported. The method widens the scope of benzylic partners that can undergo efficient reactivity from highly activated nitrophenylacetates established previously, to a diverse series of substrates bearing modestly stabilizing groups, allowing direct access to functionalized diarylmethanes. Mechanistic studies support the role of dienolates as key intermediates in the coupling process.

Z-Selective iridium-catalyzed cross-coupling of allylic carbonates and α-diazo esters.

A well-defined Ir-allyl complex catalyzes the Z-selective cross-coupling of allyl carbonates with α-aryl diazo esters. The process overrides the large thermodynamic preference for E-products typically observed in metal-mediated coupling reactions to enable the synthesis of Z,E-dieneoates in good yield with selectivities consistently approaching or greater than 90 : 10. This transformation represents the first productive merger of Ir-carbene and Ir-allyl species, which are commonly encountered intermediates in allylation and cyclopropanation/E-H insertion catalysis. Potentially reactive functional groups (aryl halides, ketones, nitriles, olefins, amines) are tolerated owing to the mildness of reaction conditions. Kinetic analysis of the reaction suggests oxidative addition of the allyl carbonate to an Ir-species is rate-determining. Mechanistic studies uncovered a pathway for catalyst activation mediated by NEt3.

Impact of Statins on Cardiovascular Outcomes Following Coronary Artery Calcium Scoring.

BACKGROUND: Compared with traditional risk factors, coronary artery calcium (CAC) scores improve prognostic accuracy for atherosclerotic cardiovascular disease (ASCVD) outcomes. However, the relative impact of statins on ASCVD outcomes stratified by CAC scores is unknown. OBJECTIVES: The authors sought to determine whether CAC can identify patients most likely to benefit from statin treatment. METHODS: The authors identified consecutive subjects without pre-existing ASCVD or malignancy who underwent CAC scoring from 2002 to 2009 at Walter Reed Army Medical Center. The primary outcome was first major adverse cardiovascular event (MACE), a composite of acute myocardial infarction, stroke, and cardiovascular death. The effect of statin therapy on outcomes was analyzed stratified by CAC presence and severity, after adjusting for baseline comorbidities with inverse probability of treatment weights based on propensity scores. RESULTS: A total of 13,644 patients (mean age 50 years; 71% men) were followed for a median of 9.4 years. Comparing patients with and without statin exposure, statin therapy was associated with reduced risk of MACE in patients with CAC (adjusted subhazard ratio: 0.76; 95% confidence interval: 0.60 to 0.95; p = 0.015), but not in patients without CAC (adjusted subhazard ratio: 1.00; 95% confidence interval: 0.79 to 1.27; p = 0.99). The effect of statin use on MACE was significantly related to the severity of CAC (p < 0.0001 for interaction), with the number needed to treat to prevent 1 initial MACE outcome over 10 years ranging from 100 (CAC 1 to 100) to 12 (CAC >100). CONCLUSIONS: In a largescale cohort without baseline ASCVD, the presence and severity of CAC identified patients most likely to benefit from statins for the primary prevention of cardiovascular diseases.

Implications of New Cholesterol Treatment Guidelines on Statin Utilization, Intensity, and Costs in Active Duty Service Members.

Background: The recommendations in the 2013 American College of Cardiology/American Heart Association (ACC/AHA) blood cholesterol guidelines expanded the indications and level of intensity of statin therapy for the primary prevention of cardiovascular disease. We assessed the treatment and cost implications of theseguidelines within a cohort of active duty service members. Methods: Using the military electronic medical record system, the Armed Forces Health Longitudinal Technology Application, we randomly selected 1,000 active duty persons aged 40 yr or older and reviewed their lipid profiles and medical records to identify risk factors for atherosclerotic cardiovascular disease. We compared the recommended cholesterol treatment under the new ACC/AHA guidelines versus the Third Adult Treatment Panel of the National Cholesterol Education Program. Findings: The mean age was 49 ± 7 yr, 36% were female, 22% were on baseline statin therapy (4% high intensity), and 13% were not at Third Adult Treatment Panel cholesterol goal. There was no difference in the proportion eligible for statin therapy between ACC/AHA and Third Adult Treatment Panel guidelines. Statin treatment under the ACC/AHA guideline resulted in a mean statin dose increase from 25 ± 20 mg to 36 ± 25 mg (p < 0.001) with an increase in those eligible for high-intensity statin therapy, 6% to 11% (p < 0.001). These changes translated to higher estimated yearly statin acquisition costs, $40,197 versus $52,527 per 1,000 patient-years of treatment (p < 0.001). Discussion: Within a low-risk active duty population over 40 yr, application of the 2013 ACC/AHA cholesterol treatment guidelines may not significantly increase those eligible for statins, but may increase statin treatment intensity and costs.

Promotion of noise-induced cochlear injury by toluene and ethylbenzene in the rat.

Ethylbenzene + toluene are known individually to have ototoxic potential at high exposure levels and with prolonged exposure times generally of 4-16 weeks. Both ethylbenzene + toluene are minor constituents of JP-8 jet fuel; this fuel has recently been determined to promote susceptibility to noise-induced hearing loss. Therefore, the current study evaluates the ototoxic potential of combined exposure to ethylbenzene + toluene exposure in a ratio calculated from the average found in three laboratories. Rats received ethylbenzene + toluene by inhalation and half of them were subjected simultaneously to an octave band of noise (OBN) of 93-95 dB. Another group received only the noise exposure which was designed to produce a small, but permanent auditory impairment while an unexposed control group was also included. In two separate experiments, exposures occurred either repeatedly on 5 successive days for 1 week or for 5 days on 2 successive weeks to 4000 mg/m(3) total hydrocarbons for 6 h based upon initial pilot studies. The concentration of toluene was 400 ppm and the concentration of ethylbenzene was 660 ppm. Impairments in auditory function were assessed using distortion product otoacoustic emissions and compound action potential testing. Following completion of these tests, the organs of Corti were dissected to permit evaluation of hair cell loss. The uptake and elimination of the solvents was assessed by harvesting key organs at two time points following ethylbenzene + toluene exposure from additional rats not used for auditory testing. Similarly, glutathione (GSH) levels were measured in light of suggestions that oxidative stress might result from solvent-noise exposures. Ethylbenzene + toluene exposure by itself at 4000 mg/m(3) for 6 h did not impair cochlear function or yield a loss of hair cells. However, when combined with a 93-dB OBN exposure combined solvent + noise did yield a loss in auditory function and a clear potentiation of outer hair cell death that exceeded the loss produced by noise alone. No evidence was found for a loss in total GSH in lung, liver, or brain as a consequence of ethylbenzene + toluene exposure.

JP-8 jet fuel can promote auditory impairment resulting from subsequent noise exposure in rats.

We report on the transient and persistent effects of JP-8 jet fuel exposure on auditory function in rats. JP-8 has become the standard jet fuel utilized in the United States and North Atlantic Treaty Organization countries for military use and it is closely related to Jet A fuel, which is used in U.S. domestic aviation. Rats received JP-8 fuel (1000 mg/m(3)) by nose-only inhalation for 4 h and half of them were immediately subjected to an octave band of noise ranging between 97 and 105 dB in different experiments. The noise by itself produces a small, but permanent auditory impairment. The current permissible exposure level for JP-8 is 350 mg/m(3). Additionally, a positive control group received only noise exposure, and a fourth group consisted of untreated control subjects. Exposures occurred either on 1 day or repeatedly on 5 successive days. Impairments in auditory function were assessed using distortion product otoacoustic emissions and compound action potential testing. In other rats, tissues were harvested following JP-8 exposure for assessment of hydrocarbon levels or glutathione (GSH) levels. A single JP-8 exposure by itself at 1000 mg/m(3) did not disrupt auditory function. However, exposure to JP-8 and noise produced an additive disruption in outer hair cell function. Repeated 5-day JP-8 exposure at 1000 mg/m(3) for 4 h produced impairment of outer hair cell function that was most evident at the first postexposure assessment time. Partial though not complete recovery was observed over a 4-week postexposure period. The adverse effects of repeated JP-8 exposures on auditory function were inconsistent, but combined treatment with JP-8 + noise yielded greater impairment of auditory function, and hair cell loss than did noise by itself. Qualitative comparison of outer hair cell loss suggests an increase in outer hair cell death among rats treated with JP-8 + noise for 5 days as compared to noise alone. In most instances, hydrocarbon constituents of the fuel were largely eliminated in all tissues by 1-h postexposure with the exception of fat. Finally, JP-8 exposure did result in a significant depletion of total GSH that was observable in liver with a nonsignificant trend toward depletion in the brain and lung raising the possibility that the promotion of noise-induced hearing loss by JP-8 might have resulted from oxidative stress.