Expanding Ligand Space: Preparation, Characterization, and Synthetic Applications of Air-Stable, Odorless Di-tert-alkylphosphine Surrogates

The di-tert-alkylphosphino motif is common to many best-in-class ligands for late-transition-metal catalysis. However, the structural diversity of these privileged substructures is currently limited by the need to manipulate highly toxic, highly reactive reagents and intermediates in their synthesis. In response to this longstanding challenge, we report an umpolung strategy for the synthesis of structurally diverse di-tert-alkylphosphine building blocks via SN1 alkylation of in situ generated PH3 gas. We show that the products—which are isolated as air-stable, odorless phosphonium salts—can be used directly in the preparation of key synthetic intermediates and ligand classes. The di-tert-alkylphosphino building blocks that are accessible using our methodology therefore enable facile expansion of extant ligand classes by modification of a previously invariant vector; we demonstrate that these modifications affect the steric and electronic properties of the ligands and can be used to tune their performance in catalysis

Recording plasticity in neuronal activity in the rodent intrinsic cardiac nervous system using calcium imaging techniques

The intrinsic cardiac nervous system (ICNS) is composed of interconnected clusters of neurons called ganglionated plexi (GP) which play a major role in controlling heart rate and rhythm. The function of these neurons is particularly important due to their involvement in cardiac arrhythmias such as atrial fibrillation (AF), and previous work has shown that plasticity in GP neural networks could underpin aberrant activity patterns that drive AF. As research in this field increases, developing new techniques to visualize the complex interactions and plasticity in this GP network is essential. In this study we have developed a calcium imaging method enabling the simultaneous recording of plasticity in neuronal activity from multiple neurons in intact atrial GP networks. Calcium imaging was performed with Cal-520 AM labeling in aged spontaneously hypertensive rats (SHRs), which display both spontaneous and induced AF, and age-matched Wistar Kyoto (WKY) controls to determine the relationship between chronic hypertension, arrhythmia and GP calcium dynamics. Our data show that SHR GPs have significantly larger calcium responses to cholinergic stimulation compared to WKY controls, as determined by both higher amplitude and longer duration calcium responses. Responses were significantly but not fully blocked by hexamethonium, indicating multiple cholinergic receptor subtypes are involved in the calcium response. Given that SHRs are susceptible to cardiac arrhythmias, our data provide evidence for a potential link between arrhythmia and plasticity in calcium dynamics that occur not only in cardiomyocytes but also in the GP neurons of the heart

Understanding the role of Caspr2 in the developing cerebellum

Despite receiving renewed attention due to the revelation it is involved in higher cognitive functions, we still know little about how the cerebellum develops and operates. Studies suggest Contactin-associated protein-like 2 (Caspr2), a member of the Neurexin superfamily, has a cerebellar function. However, the cellular and molecular bases for this remain unknown. An initial assessment of the spatio-temporal expression pattern of Caspr2, using immunohistochemistry and biochemical fractionation, suggested that Caspr2 is expressed at specific synapses in the developing cerebellum. Little is known about the function of Caspr2 at synapses and so the Caspr2 domain exposed to the synaptic cleft, the Caspr2 extra-cellular domain (ECD), was focused on. The addition of recombinant Caspr2 ECD to organotypic cerebellar slice cultures prepared from Cntnap2-/- mice rescued a dendritic morphology defect observed in untreated cultures, suggesting Caspr2 affects cellular morphology during cerebellar development. To understand the molecular basis for this effect, a pull down assay was used to identify the synaptic binding partners of Caspr2. Unexpectedly, mass spectrometry analysis of this experiment revealed that the Ca2+ channel Inositol 3,4,5- trisphosphate receptor type I (IP3R1) is a cognate partner of Caspr2 at synapses in the developing cerebellum. Further biochemical assays revealed both that the Caspr2-IP3R1 interaction underlies the regulation of cellular morphology by Caspr2 and that Caspr2 may modulate cytoplasmic Ca2+ levels. Combined with data from co-immunoprecipitation assays suggesting that Caspr2 interacts with the IP3R1 poreforming domain, these data are consistent with Caspr2 acting via IP3R1 to regulate cellular morphology during cerebellar development, most likely by directly affecting the IP3R1 pore region environment. Together, these experiments therefore reveal novel cellular and molecular roles for Caspr2 in the developing cerebellum. As well as improving our understanding of the nervous system, knowledge such as this will likely be increasingly clinically relevant, given the previously overlooked links between the cerebellum and cognition.</p

Bismuth-Mediated α-Arylation of Acidic Diketones with ortho-Substituted Boronic Acids

The α-arylation of cyclic and fluoroalkyl 1,3-diketones is made challenging by the highly stabilized nature of the corresponding enolates, and is especially difficult for sterically demanding aryl partners. As a general solution to this problem, we report the Bi-mediated oxidative coupling of acidic diones and ortho-substituted arylboronic acids. Starting from a bench-stable bismacycle precursor, a sequence of B-to-Bi transmetallation, oxidation and C−C bond formation furnishes the arylated diones. Development of methodology that tolerates both sensitive functionality and steric demand is supported by interrogation of key reactive intermediates. Application of our strategy to cyclic diones enables the concise synthesis of important agrochemical intermediates which were previously prepared using toxic Pb reagents. This methodology also enables the first ever arylation of fluoroalkyl diones which, upon condensation with hydrazine, provides direct access to valuable fluoroalkyl pyrazoles

Bilayer-Mediated Structural Transitions Control Mechanosensitivity of the TREK-2 K2P Channel

The mechanosensitive two-pore domain (K2P) K(+) channels (TREK-1, TREK-2, and TRAAK) are important for mechanical and thermal nociception. However, the mechanisms underlying their gating by membrane stretch remain controversial. Here we use molecular dynamics simulations to examine their behavior in a lipid bilayer. We show that TREK-2 moves from the "down" to "up" conformation in direct response to membrane stretch, and examine the role of the transmembrane pressure profile in this process. Furthermore, we show how state-dependent interactions with lipids affect the movement of TREK-2, and how stretch influences both the inner pore and selectivity filter. Finally, we present functional studies that demonstrate why direct pore block by lipid tails does not represent the principal mechanism of mechanogating. Overall, this study provides a dynamic structural insight into K2P channel mechanosensitivity and illustrates how the structure of a eukaryotic mechanosensitive ion channel responds to changes in forces within the bilayer