Preparation of cyclohexene isotopologues and stereoisotopomers from benzene.

The hydrogen isotopes deuterium (D) and tritium (T) have become essential tools in chemistry, biology and medicine1. Beyond their widespread use in spectroscopy, mass spectrometry and mechanistic and pharmacokinetic studies, there has been considerable interest in incorporating deuterium into drug molecules1. Deutetrabenazine, a deuterated drug that is promising for the treatment of Huntington's disease2, was recently approved by the United States' Food and Drug Administration. The deuterium kinetic isotope effect, which compares the rate of a chemical reaction for a compound with that for its deuterated counterpart, can be substantial1,3,4. The strategic replacement of hydrogen with deuterium can affect both the rate of metabolism and the distribution of metabolites for a compound5, improving the efficacy and safety of a drug. The pharmacokinetics of a deuterated compound depends on the location(s) of deuterium. Although methods are available for deuterium incorporation at both early and late stages of the synthesis of a drug6,7, these processes are often unselective and the stereoisotopic purity can be difficult to measure7,8. Here we describe the preparation of stereoselectively deuterated building blocks for pharmaceutical research. As a proof of concept, we demonstrate a four-step conversion of benzene to cyclohexene with varying degrees of deuterium incorporation, via binding to a tungsten complex. Using different combinations of deuterated and proteated acid and hydride reagents, the deuterated positions on the cyclohexene ring can be controlled precisely. In total, 52 unique stereoisotopomers of cyclohexene are available, in the form of ten different isotopologues. This concept can be extended to prepare discrete stereoisotopomers of functionalized cyclohexenes. Such systematic methods for the preparation of pharmacologically active compounds as discrete stereoisotopomers could improve the pharmacological and toxicological properties of drugs and provide mechanistic information related to their distribution and metabolism in the body.

Experiments and Direct Dynamics Simulations That Probe η2-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes.

Key steps in the functionalization of an unactivated arene often involve its dihaptocoordination by a transition metal followed by insertion into the C-H bond. However, rarely are the η2-arene and aryl hydride species in measurable equilibrium. In this study, the benzene/phenyl hydride equilibrium is explored for the {WTp(NO)(PBu3)} (Bu = n-butyl; Tp = trispyrazoylborate) system as a function of temperature, solvent, ancillary ligand, and arene substituent. Both face-flip and ring-walk isomerizations are identified through spin-saturation exchange measurements, which both appear to operate through scission of a C-H bond. The effect of either an electron-donating or electron-withdrawing substituent is to increase the stability of both arene and aryl hydride isomers. Crystal structures, electrochemical measurements, and extensive NMR data further support these findings. Static density functional theory calculations of the benzene-to-phenyl hydride landscape suggest a single linear sequence for this transformation involving a sigma complex and oxidative cleavage transition state. Static DFT calculations also identified an η2-coordinated benzene complex in which the arene is held more loosely than in the ground state, primarily through dispersion forces. Although a single reaction pathway was identified by static calculations, quasiclassical direct dynamics simulations identified a network of several reaction pathways connecting the η2-benzene and phenyl hydride isomers, due to the relatively flat energy landscape.

Teratoid Hepatoblastoma With Yolk Sac-Like and Neuroendocrine Elements.

Teratoid hepatoblastoma (HB) is a variant of mixed HB described as having a mixture of heterologous components. A 3-year-old boy presented for a liver transplant evaluation due to persistent HB. His liver was biopsied as well as a perirenal mass. Histologic examination demonstrated elements of yolk sac tumor and review of original resection showed a neuroendocrine component. This unique combination of histology has not been reported before in HB. Also, this case presents a unique diagnostic challenge as it presented with a metastasis containing yolk sac elements. Recognition and awareness of this histologic variant are important to accurately identify metastatic lesions.

Process mapping of the urgent red cell exchange procedure for patients with severe complications of sickle cell disease at a centralized hemapheresis service.

Sickle cell disease (SCD) patients require urgent red cell exchange (RCE) procedures for acute chest syndrome (ACS), demanding a coordinated effort of multiple clinical services. Execution of RCE is a multistep process from the time the procedure is requested to the time the procedure is initiated. A retrospective review of patients with SCD requiring urgent RCE for ACS and stroke from 2012 to 2017 was performed at a centralized hemapheresis service covering a multihospital healthcare system. A total of 30 urgent RCE procedures performed on 28 patients were evaluated. The time required for red blood cell (RBC) preparation was the longest step in the process (median 3.8 hours). Furthermore, RBC preparation time was longer for sickle cell patients with RBC alloimmunization compared with nonalloimmunized patients (8.6 vs 3.8 hours, P = .03). One mortality event occurred in Ab- group. This study identified potentially modifiable factors, which impact the time to implementation of RCE in one service area. It highlights the importance of a structured and coordinated approach for the efficient and timely delivery of this vital treatment modality.

Molybdenum-Promoted Synthesis of Isoquinuclidines with Bridgehead CF3 Groups.

The preparation of the complex MoTp(NO)(DMAP)(4,5-η2-(2-trifluoromethyl)pyridine) (DMAP = 4-(dimethylamino)pyridine; Tp = tris(pyrazolyl)borate) is described. The CF3 substituent is found to preclude κ-N coordination, allowing for direct coordination without protection of the nitrogen. The dihapto-coordinate complex can be isolated as a single diastereomer, methylated, and reacted with a range of nucleophiles. Oxidative decomplexation affords the free dihydropyridines in good yield (75-90%). As a demonstration of synthetic utility, a series of novel bridgehead CF3-substituted isoquinuclidines was prepared from these decomplexed dihydropyridines.

Highly Functionalized Cyclohexenes Derived from Benzene: Sequential Tandem Addition Reactions Promoted by Tungsten.

The dihapto-coordination of benzene to the π-basic fragment {TpW(NO)(PMe3)} (Tp = hydridotris(pyrazolyl)-borate) enhances the basicity of the arene ligand to the point that it can be protonated with a mild Brønsted acid (diphenylammonium triflate; p Ka ∼ 1). The resulting η2-benzenium complex reacts with a wide range of nucleophiles including protected enolates, cyanide, amines, methoxide, and aromatic nucleophiles to form 5-substituted 3,4-η2-1,3-cyclohexadiene complexes in good yield (42-70%). These coordinated dienes were successfully taken through a second protonation and nucleophilic addition with a similar scope of nucleophiles (54-80%). The resulting cis-3,4- and cis-3,6-disubstituted η2-cyclohexene complexes were prepared with high regio- and stereocontrol, as governed by the asymmetric nature of π-allyl intermediates. In some cases, a diene linkage isomerization from 3,4-η2 to 1,2-η2 could be effected with a redox catalyst, and reactions of the latter species led to cis-3,5-disubstituted cyclohexene products exclusively. Oxidative decomplexation afforded the free cyclohexene products in moderate yield (37-68%). Additionally, when a single enantiomer of the chiral dearomatization agent was used, the elaborated cyclohexenes were able to be synthesized in enantioenriched forms (86-90% enantiomeric excess). Full characterization of 40 new compounds is provided that includes two-dimensional NMR, IR, electrochemical and in some cases crystallographic data.

Molybdenum(0) Dihapto-Coordination of Benzene and Trifluorotoluene: The Stabilizing and Chemo-Directing Influence of a CF3 Group.

The preparation of the complexes TpMo(NO)(DMAP)(η2-PhCF3) (5) and TpMo(NO)(DMAP)(η2-benzene) (3) is described. The CF3 group is found to stabilize the metal-arene bond strength in 5 by roughly 3 kcal/mol compared to that in 3, allowing the large-scale synthesis and isolation of the trifluorotoluene analogue (5, 37 g, 70%). When a benzene solution of 5 is allowed to stand, clean conversion to the benzene analogue 3 occurs, and this complex may be precipitated from solution upon the addition of pentane and isolated. The trifluorotoluene complex is shown to be a synthetic precursor to functionalized cyclohexadienes: In solution, it selectively protonates at the ortho position, and the resulting η2-arenium species undergoes reactions with nucleophiles at the adjacent meta carbon. Thus, reactions of 5, triflic acid, and either N-methylpyrrole or 1-methoxy-2-methyl-1-(trimethylsilyloxy)-1-propene result in 5-substituted-1,3-cyclohexadienes after removal of the metal.

Tungsten-anisole complex provides 3,6-substituted cyclohexenes for highly diversified chemical libraries.

Medicinal chemists use vast combinatorial molecular libraries to develop leads for new pharmaceuticals. The syntheses of these compounds typically rely on coupling molecular fragments through atoms with planar (sp2) geometry. These so-called flat molecules often lack the protein binding site specificity needed to be an effective drug. Here, we demonstrate a coupling strategy in which a cyclohexene is used as a linker to connect two diverse molecular fragments while forming two new tetrahedral (sp3) stereocenters. These connections are made with the aid of a tungsten complex that activates anisole toward an unusual double protonation, followed by sequential nucleophilic additions. As a result, either cis- or trans-disubstituted cyclohexenes can be prepared with a range of chemical diversity unparalleled by other dearomatization methods.

The eIF4EBP-eIF4E axis regulates CD4+ T cell differentiation through modulation of T cell activation and metabolism.

CD4+ T cells are critical for adaptive immunity, differentiating into distinct effector and regulatory subsets. Although the transcriptional programs underlying their differentiation are known, recent research has highlighted the importance of mRNA translation in determining protein abundance. We previously conducted genome-wide analysis of translation in CD4+ T cells revealing distinct translational signatures distinguishing these subsets, identifying eIF4E as a central differentially translated transcript. As eIF4E is vital for eukaryotic translation, we examined how altered eIF4E activity affected T cell function using mice lacking eIF4E-binding proteins (BP-/-). BP-/- effector T cells showed elevated Th1 responses ex vivo and upon viral challenge with enhanced Th1 differentiation observed in vitro. This was accompanied by increased TCR activation and elevated glycolytic activity. This study highlights how regulating T cell-intrinsic eIF4E activity can influence T cell activation and differentiation, suggesting the eIF4EBP-eIF4E axis as a potential therapeutic target for controlling aberrant T cell responses.

The double protonation of dihapto-coordinated benzene complexes enables dearomatization using aromatic nucleophiles.

Friedel-Crafts Arylation (the Scholl reaction) is the coupling of two aromatic rings with the aid of a strong Lewis or Brønsted acid. This historically significant C-C bond forming reaction normally leads to aromatic products, often as oligomeric mixtures, dictated by the large stabilization gained upon their rearomatization. The coordination of benzene by a tungsten complex disrupts the natural course of this reaction sequence, allowing for Friedel-Crafts Arylation without rearomatization or oligomerization. Subsequent addition of a nucleophile to the coupled intermediate leads to functionalized cyclohexenes. In this work, we show that by coordinating benzene to tungsten through two carbons (dihapto-coordinate), a rarely observed double protonation of the bound benzene is enabled, allowing its subsequent coupling to a second arene without the need of a precious metal or Lewis acid catalyst.

η 2 Coordination of Electron-Deficient Arenes with Group 6 Dearomatization Agents.

The exceptionally π-basic metal fragments {MoTp-(NO)(DMAP)} and {WTp(NO)(PMe3)} (Tp = tris(pyrazolyl)borate; DMAP = 4-(N,N-dimethylamino)pyridine) form thermally stable η 2-coordinated complexes with a variety of electron-deficient arenes. The tolerance of substituted arenes with fluorine-containing electron withdrawing groups (EWG; -F, -CF3, -SF5) is examined for both the molybdenum and tungsten systems. When the EWG contains a π bond (nitriles, aldehydes, ketones, ester), η 2 coordination occurs predominantly on the nonaromatic functional group. However, complexation of the tungsten complex with trimethyl orthobenzoate (PhC(OMe)3) followed by hydrolysis allows access to an η 2-coordinated arene with an ester substituent. In general, the tungsten system tolerates sulfur-based withdrawing groups well (e.g., PhSO2Ph, MeSO2Ph), and the integration of multiple electron-withdrawing groups on a benzene ring further enhances the π-back-bonding interaction between the metal and aromatic ligand. While the molybdenum system did not form stable η 2-arene complexes with the sulfones or ortho esters, it was capable of forming rare examples of stable η 2-coordinated arene complexes with a range of fluorinated benzenes (e.g., fluorobenzene, difluorobenzenes). In contrast to what has been observed for the tungsten system, these complexes formed without interference of C-H or C-F insertion.

Intranasal immunization with influenza antigens conjugated with cholera toxin subunit B stimulates broad spectrum immunity against influenza viruses.

Frequent mutation of influenza viruses keep vaccinated and non-vaccinated populations vulnerable to new infections, causing serious burdens to public health and the economy. Vaccination with universal influenza vaccines would be the best way to effectively protect people from infection caused by mismatched or unforeseen influenza viruses. Presently, there is no FDA approved universal influenza vaccine. In this study, we expressed and purified a fusion protein comprising of influenza matrix 2 protein ectodomain peptides, a centralized influenza hemagglutinin stem region, and cholera toxin subunit B. Vaccination of BALB/c mice with this novel artificial antigen resulted in potent humoral immune responses, including induction of specific IgA and IgG, and broad protection against infection by multiple influenza viruses. Furthermore, our results demonstrated that when used as a mucosal antigen, cholera toxin subunit B improved antigen-stimulated T cell and memory B cell responses.