Iridium-catalyzed hydroacylation reactions of C1-substituted oxabenzonorbornadienes with salicylaldehyde: an experimental and computational study.

An experimental and theoretical investigation on the iridium-catalyzed hydroacylation of C1-substituted oxabenzonorbornadienes with salicylaldehyde is reported. Utilizing commercially available [Ir(COD)Cl]2 in the presence of 5 M KOH in dioxane at 65 °C, provided a variety of hydroacylated bicyclic adducts in up to a 95% yield with complete stereo- and regioselectivity. The mechanism and origins of selectivity in the iridium-catalyzed hydroacylation reaction has been examined at the M06/Def2TZVP level of theory. The catalytic cycle consists of three key steps including oxidative addition into the aldehyde C-H bond, insertion of the olefin into the iridium hydride, and C-C bond-forming reductive elimination. Computational results indicate the origin of regioselectivity is involved in the reductive elimination step.

Depletion of Pax7+ satellite cells does not affect diaphragm adaptations to running in young or aged mice.

KEY POINTS: Satellite cell depletion does not affect diaphragm adaptations to voluntary wheel running in young or aged mice. Satellite cell depletion early in life (4 months of age) has minimal effect on diaphragm phenotype by old age (24 months). Prolonged satellite cell depletion in the diaphragm does not result in excessive extracellular matrix accumulation, in contrast to what has been reported in hind limb muscles. Up-regulation of Pax3 mRNA+ cells after satellite cell depletion in young and aged mice suggests that Pax3+ cells may compensate for a loss of Pax7+ satellite cells in the diaphragm. Future investigations should focus on the role of Pax3+ cells in the diaphragm during adaptation to exercise and ageing. ABSTRACT: Satellite cell contribution to unstressed diaphragm is higher compared to hind limb muscles, which is probably attributable to constant activation of this muscle to drive ventilation. Whether satellite cell depletion negatively impacts diaphragm quantitative and qualitative characteristics under stressed conditions in young and aged mice is unknown. We therefore challenged the diaphragm with prolonged running activity in the presence and absence of Pax7+ satellite cells in young and aged mice using an inducible Pax7CreER -R26RDTA model. Mice were vehicle (Veh, satellite cell-replete) or tamoxifen (Tam, satellite cell-depleted) treated at 4 months of age and were then allowed to run voluntarily at 6 months (young) and 22 months (aged). Age-matched, cage-dwelling, Veh- and Tam-treated mice without wheel access served as activity controls. Diaphragm muscles were analysed from young (8 months) and aged (24 months) mice. Satellite cell depletion did not alter diaphragm mean fibre cross-sectional area, fibre type distribution or extracellular matrix content in young or aged mice, regardless of running activity. Resting in vivo diaphragm function was also unaffected by satellite cell depletion. Myonuclear density was maintained in young satellite cell-depleted mice regardless of running, although it was modestly reduced in aged sedentary (-7%) and running (-19%) mice without satellite cells (P < 0.05). Using fluorescence in situ hybridization, we detected higher Pax3 mRNA+ cell density in both young and aged satellite cell-depleted diaphragm muscle (P < 0.05), which may compensate for the loss of Pax7+ satellite cells.

Mutations M287L and Q266I in the glycine receptor α1 subunit change sensitivity to volatile anesthetics in oocytes and neurons, but not the minimal alveolar concentration in knockin mice.

BACKGROUND: Volatile anesthetics (VAs) alter the function of key central nervous system proteins but it is not clear which, if any, of these targets mediates the immobility produced by VAs in the face of noxious stimulation. A leading candidate is the glycine receptor, a ligand-gated ion channel important for spinal physiology. VAs variously enhance such function, and blockade of spinal glycine receptors with strychnine affects the minimal alveolar concentration (an anesthetic EC50) in proportion to the degree of enhancement. METHODS: We produced single amino acid mutations into the glycine receptor α1 subunit that increased (M287L, third transmembrane region) or decreased (Q266I, second transmembrane region) sensitivity to isoflurane in recombinant receptors, and introduced such receptors into mice. The resulting knockin mice presented impaired glycinergic transmission, but heterozygous animals survived to adulthood, and we determined the effect of isoflurane on glycine-evoked responses of brainstem neurons from the knockin mice, and the minimal alveolar concentration for isoflurane and other VAs in the immature and mature knockin mice. RESULTS: Studies of glycine-evoked currents in brainstem neurons from knockin mice confirmed the changes seen with recombinant receptors. No increases in the minimal alveolar concentration were found in knockin mice, but the minimal alveolar concentration for isoflurane and enflurane (but not halothane) decreased in 2-week-old Q266I mice. This change is opposite to the one expected for a mutation that decreases the sensitivity to volatile anesthetics. CONCLUSION: Taken together, these results indicate that glycine receptors containing the α1 subunit are not likely to be crucial for the action of isoflurane and other VAs.

Chemistry of Unsymmetrical C1-Substituted Oxabenzonorbornadienes.

Oxabenzonorbornadiene (OBD) is a useful synthetic intermediate, which can be readily activated by transition metal complexes with great face selectivity due to its dual-faced nature and intrinsic angle strain on the alkene. To date, the understanding of transition-metal catalyzed reactions of OBD itself has burgeoned; however, this has not been the case for unsymmetrical OBDs. Throughout the development of these reactions, the nature of C1-substituent has proven to have a profound effect on both the reactivity and selectivity of the outcome of the reaction. Upon substitution, different modes of reactivity arise, contributing to the possibility of multiple stereo-, regio-, and in extreme cases, constitutional isomers, which can provide unique means of constructing a variety of synthetically useful cyclic frameworks. To maximize selectivity, an understanding of bridgehead substituent effects is crucial. To that end, this review outlines hitherto reported examples of bridgehead substituent effects on the chemistry of unsymmetrical C1-substituted OBDs.

[(1R*,3S*,4S*)-3-(2-Hy-droxy-benzo-yl)-1,2,3,4-tetra-hydro-1,4-ep-oxy-naphthalen-1-yl]methyl 4-nitro-benzoate.

The relative stereo- and regiochemistry of the racemic title compound, C25H19NO7, were established from the crystal structure. The fused benzene ring forms dihedral angles of 77.3 (1) and 60.3 (1)° with the hy-droxy-substituted benzene ring and the nitro-substituted benzene ring, respectively. The dihedral angle between the hy-droxy-substituted benzene ring and the nitro-substituted benzene ring is 76.4 (1)°. An intra-molecular O-H⋯O hydrogen bond closes an S(6) ring. In the crystal, weak C-H⋯O hydrogen bonds connect the mol-ecules, forming layers parallel to (100). Within these layers, there are weak π-π stacking inter-actions with a ring centroid-ring centroid distance of 3.555 (1) Å.

Differential requirement for satellite cells during overload-induced muscle hypertrophy in growing versus mature mice.

BACKGROUND: Pax7+ satellite cells are required for skeletal muscle fiber growth during post-natal development in mice. Satellite cell-mediated myonuclear accretion also appears to persist into early adulthood. Given the important role of satellite cells during muscle development, we hypothesized that the necessity of satellite cells for adaptation to an imposed hypertrophic stimulus depends on maturational age. METHODS: Pax7CreER-R26RDTA mice were treated for 5 days with vehicle (satellite cell-replete, SC+) or tamoxifen (satellite cell-depleted, SC-) at 2 months (young) and 4 months (mature) of age. Following a 2-week washout, mice were subjected to sham surgery or 10 day synergist ablation overload of the plantaris (n = 6-9 per group). The surgical approach minimized regeneration, de novo fiber formation, and fiber splitting while promoting muscle fiber growth. Satellite cell density (Pax7+ cells/fiber), embryonic myosin heavy chain expression (eMyHC), and muscle fiber cross sectional area (CSA) were evaluated via immunohistochemistry. Myonuclei (myonuclei/100 mm) were counted on isolated single muscle fibers. RESULTS: Tamoxifen treatment depleted satellite cells by ≥90% and prevented myonuclear accretion with overload in young and mature mice (p < 0.05). Satellite cells did not recover in SC- mice after overload. Average muscle fiber CSA increased ~20% in young SC+ (p = 0.07), mature SC+ (p < 0.05), and mature SC- mice (p < 0.05). In contrast, muscle fiber hypertrophy was prevented in young SC- mice. Muscle fiber number increased only in mature mice after overload (p < 0.05), and eMyHC expression was variable, specifically in mature SC+ mice. CONCLUSIONS: Reliance on satellite cells for overload-induced hypertrophy is dependent on maturational age, and global responses to overload differ in young versus mature mice.

The effects of potassium and muscle homogenate on proprioceptive responses in crayfish and crab.

Proprioception of limbs and joints is a basic sensory function throughout most of the animal kingdom. It is important to understand how proprioceptive organs and the associated sensory neurons function with altered environments such as increased potassium ion concentrations ([K+]) from diseased states, ionic imbalances, and damaged tissues. These factors can drastically alter neuronal activity. To assess this matter, we used the chordotonal organ in a walking leg of a blue crab (Callinectes sapidus) and the muscle receptor organ of the crayfish (Procambarus clarkii). These organs serve as tractable models for the analysis of proprioception. The preparations can help serve as translational models for these effects, which may be observed in other invertebrate species as well as mammalian species (including humans). When extracellular potassium concentration ([K+]o) is increased to 20 mM in both preparations, mixed results are observed with activity increasing in some preparations and decreasing in others after mechanical displacement. However, when [K+]o is increased to 40 mM, activity drastically decreases in all preparations. Additionally, proprioceptor sensory activity declines upon exposure to a diluted muscle homogenate, which contains a host of intracellular constituents. The robust effects of altered [K+] on proprioception in these models illuminate the potential detriments on neuronal function in cases of severe tissue damage as well as altered [K+]o.