The iridium‐catalysed borylation of aromatic C−H bonds has become the preferred method for the synthesis of aromatic organoboron compounds. The reaction is highly efficient, tolerant of a broad range ...of substituents and can be applied to both carbocyclic and heterocyclic substrates. The regioselectivity of C−H activation is dominated by steric considerations and there have been considerable efforts to develop more selective processes for less constrained substrates. However, most of these have focused on benzenoid‐type substrates and in contrast, heteroarenes remain much desired but more challenging substrates with the position and/or nature of the heteroatom(s) significantly affecting reactivity and regioselectivity. This review will survey the borylation of heteroarenes, focusing on the influence of steric and electronic effects on regiochemical outcome and, by linking to current mechanistic understandings, will provide insights to what is currently possible and where further developments are required.
Which C−H bond? The iridium‐catalysed C−H borylation reaction is a powerful method for the preparation of aromatic organoboronate esters. Sterically regulated regioselectivity dominates carbocyclic aromatic C−H borylation. In contrast, heterocyclic aromatics display a much greater influence from electronic effects. In this review, examples of heterocyclic C−H borylation are surveyed, and the origins of heterocyclic C−H borylation regioselectivities discussed.
We investigated dopaminergic and cholinergic correlates of gait speed in Parkinson disease (PD) and non-PD control subjects to test the hypothesis that gait dysfunction in PD may result from ...multisystem degeneration.
This was a cross-sectional study. Subjects with PD but without dementia (n = 125, age 65.6 ± 7.3 years) and elderly subjects without PD (n = 32, age 66.0 ± 10.6 years) underwent ¹¹Cdihydrotetrabenazine dopaminergic and (11)Cmethyl-4-piperidinyl propionate acetylcholinesterase PET imaging, and cognitive and clinical testing, including an 8.5-m walk in the dopaminergic "off" state. The fifth percentile of cortical cholinergic activity in the elderly without PD was used to define normal-range activity in the subjects with PD.
Normal-range cortical cholinergic activity was present in 87 subjects with PD (69.6%). Analysis of covariance using gait speed as the dependent variable demonstrated a significant model (F = 6.70, p < 0.0001) with a significant group effect (F = 3.36, p = 0.037) and significant slower gait speed in the low cholinergic PD subgroup (0.97 ± 0.22 m/s) with no significant difference between the normal-range cholinergic PD subgroup (1.12 ± 0.20 m/s) and control subjects (1.17 ± 0.18 m/s). Covariate effects were significant for cognition (F = 6.58, p = 0.011), but not for striatal dopaminergic innervation, sex, or age.
Comorbid cortical cholinergic denervation is a more robust marker of slowing of gait in PD than nigrostriatal denervation alone. Gait speed is not significantly slower than normal in subjects with PD with relatively isolated nigrostriatal denervation.
A copper-mediated nucleophilic radiofluorination of aryl- and vinylstannanes with 18FKF is described. This method is fast, uses commercially available reagents, and is compatible with both ...electron-rich and electron-deficient arene substrates. This method has been applied to the manual synthesis of a variety of clinically relevant radiotracers including protected 18FF-phenylalanine and 18FF-DOPA. In addition, an automated synthesis of 18FMPPF is demonstrated that delivers a clinically validated dose of 200 ± 20 mCi with a high specific activity of 2400 ± 900 Ci/mmol.
A copper-mediated radiofluorination of aryl- and vinylboronic acids with K18F is described. This method exhibits high functional group tolerance and is effective for the radiofluorination of a range ...of electron-deficient, -neutral, and -rich aryl-, heteroaryl-, and vinylboronic acids. This method has been applied to the synthesis of 18FFPEB, a PET radiotracer for quantifying metabotropic glutamate 5 receptors.
A practical, rapid, and highly regioselective Cu-catalyzed radiofluorination of (mesityl)(aryl)iodonium salts is described. This protocol utilizes 18FKF to access 18F-labeled electron-rich, ...-neutral, and -deficient aryl fluorides under a single set of mild conditions. This methodology is applied to the synthesis of protected versions of two important radiotracers: 4-18Ffluorophenylalanine and 6-18FfluoroDOPA.
The last 2-3 years have seen numerous relationships develop between organometallic chemists, fluorine chemists and PET Centers around the world. These collaborations have led to the development of ...many new strategies for the late-stage introduction of fluorine-18 into complex bioactive molecules. In this perspective we highlight recent developments and key milestones since 2011.
In this perspective we highlight recent developments and key milestones in "late-stage fluorination" since 2011.
Little is known about the relative contributions of multisystem degenerative processes across the spectrum of predemented cognitive decline in Parkinson disease (PD).
To investigate the relative ...frequency of caudate nucleus dopaminergic and forebrain cholinergic deficits across a spectrum of cognitively impaired patients with PD to explore their relative, individual, and combined contributions to cognitive impairment in PD.
A cross-sectional study at an academic movement disorders clinic that included a predominantly nondemented cohort of 143 patients with PD. The mean (SD) age of patients was 65.5 (7.4) years and the mean (SD) Hoehn and Yahr stage was 2.4 (0.6).
Binary classification of carbon 11-labeled 11CPMP acetylcholinesterase and caudate nucleus 11CDTBZ monoaminergic positron-emission tomography imaging based on normative data. The frequency of significant degenerative processes based on normative values was determined for consecutive intervals of cognitive impairment, ranging from no or minimal (z > -0.5) to more severe (z ≤ -2) cognitive impairment.
Across the spectrum from minimal (z > -0.5) to more severe (z ≤ -2) global cognitive impairment scores, caudate nucleus dopaminergic denervation was relatively frequent in individuals with minimal or no cognitive changes (51.1%) and increased in patients with more severe cognitive impairments (χ2 = 12.8; P = .01). Cortical cholinergic denervation frequency increased monotonically with increasing cognitive impairment from 24.7% (z > -0.5) to 85.7% (z ≤ -2); χ2 = 23.2; P = .001). Eighty-seven percent of patients with neocortical cholinergic deficits had caudate nucleus dopaminergic deficits. Multiple regression analysis (F = 7.51; P < .001) showed both independent cognitive predictions for caudate nucleus dopaminergic (F = 7.25; P = .008) and cortical cholinergic (F = 7.50; P = .007) degenerations as well as interaction effects (F = 5.40; P = .02).
Cortical cholinergic denervation is a major neurodegeneration associated with progressive declines across the spectrum of cognitive impairment in PD and typically occurs in the context of significant caudate nucleus dopaminergic denervation. Our findings imply that dopaminergic and cholinergic degenerations exhibit both independent and interactive contributions to cognitive impairment in PD.
The pathophysiology of postural instability in Parkinson's disease remains poorly understood. Normal postural function depends in part on the ability of the postural control system to integrate ...visual, proprioceptive, and vestibular sensory information. Degeneration of cholinergic neurons in the brainstem pedunculopontine nucleus complex and their thalamic efferent terminals has been implicated in postural control deficits in Parkinson's disease. Our aim was to investigate the relationship of cholinergic terminal loss in thalamus and cortex, and nigrostriatal dopaminergic denervation, on postural sensory integration function in Parkinson's disease. We studied 124 subjects with Parkinson's disease (32 female/92 male; 65.5 ± 7.4 years old; 6.0 ± 4.2 years motor disease duration; modified Hoehn and Yahr mean stage 2.4 ± 0.5) and 25 control subjects (10 female/15 male, 66.8 ± 10.1 years old). All subjects underwent (11)C-dihydrotetrabenazine vesicular monoaminergic transporter type 2 and (11)C-methylpiperidin-4-yl propionate acetylcholinesterase positron emission tomography and the sensory organization test balance platform protocol. Measures of dopaminergic and cholinergic terminal integrity were obtained, i.e. striatal vesicular monoaminergic transporter type 2 binding (distribution volume ratio) and thalamic and cortical acetylcholinesterase hydrolysis rate per minute (k3), respectively. Total centre of pressure excursion (speed), a measure of total sway, and sway variability were determined for individual sensory organization test conditions. Based on normative data, principal component analysis was performed to reduce postural sensory organization functions to robust factors for regression analysis with the dopaminergic and cholinergic terminal data. Factor analysis demonstrated two factors with eigenvalues >2 that explained 52.2% of the variance, mainly reflecting postural sway during sensory organization test Conditions 1-3 and 5, respectively. Regression analysis of the Conditions 1-3 postural sway-related factor R(2)adj = 0.123, F(5,109) = 4.2, P = 0.002 showed that decreased thalamic cholinergic innervation was associated with increased centre of pressure sway speed (β = -0.389, t = -3.4, P = 0.001) while controlling for covariate effects of cognitive capacity and parkinsonian motor impairments. There was no significant effect of cortical cholinergic terminal deficits or striatal dopaminergic terminal deficits. This effect could only be found for the subjects with Parkinson's disease. We conclude that postural sensory integration function of subjects with Parkinson's disease is modulated by pedunculopontine nucleus-thalamic but not cortical cholinergic innervation. Impaired integrity of pedunculopontine nucleus cholinergic neurons and their thalamic efferents play a role in postural control in patients with Parkinson's disease, possibly by participating in integration of multimodal sensory input information.
Positron (β(+)) emission tomography (PET) is a powerful, noninvasive tool for the in vivo, three-dimensional imaging of physiological structures and biochemical pathways. The continued growth of PET ...imaging relies on a corresponding increase in access to radiopharmaceuticals (biologically active molecules labeled with short-lived radionuclides such as fluorine-18). This unique need to incorporate the short-lived fluorine-18 atom (t1/2 = 109.77 min) as late in the synthetic pathway as possible has made development of methodologies that enable rapid and efficient late stage fluorination an area of research within its own right. In this review we describe strategies for radiolabeling with fluorine-18, including classical fluorine-18 radiochemistry and emerging techniques for late stage fluorination reactions, as well as labeling technologies such as microfluidics and solid-phase radiochemistry. The utility of fluorine-18 labeled radiopharmaceuticals is showcased through recent applications of PET imaging in the healthcare, personalized medicine and drug discovery settings.
The general corrosion and stress corrosion cracking behaviors of the nickel-base Alloy 600 in the primary high temperature aqueous coolants of light water cooled and moderated nuclear power reactors ...are reviewed. The compatible welding Alloys 182 and 82 as well as the high strength, precipitation hardened analogue, Alloy X-750, are also included. The emphasis is on what is known of the underlying science of these degradation phenomena rather than on the associated engineering consequences and remedies.
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