Acquiring a Prognostic Power in Co₂(CO)₆‑Mediated, Cobaltocene-Induced Radical Dimerizations of Propargyl Triflates

Cobalt-complexed propargyl triflates can be generated <i>in situ</i> from methyl propargyl ethers and triflic anhydride and then reduced with cobaltocene to topologically and functionally diverse 1,5-alkadiynes. The electronic effect of an α-substituent is shown to attenuate the ionic nature of an α-C–OTf bond and thus its reducibility with cobaltocene. The powerful π-donors, such as phenyl, naphthyl, alkenyl, alkynyl, and alkoxy groups, provide the ionicity of α-C–OTf bonds and make them suitable recipients for a single-electron delivery from cobaltocene. σ-Donors (alkyl groups), a H atom, and σ/π-acceptors (ester groups) do not sufficiently stabilize propargyl cations, maintaining the covalent nature of α-C–OTf bonds and making them resistant toward the reducing agent. A newly acquired ability to differentiate between the α-C–OTf bonds is used in polyethers for the regioselective reduction and radical dimerization in select propargylic positions, thus paving the way for a long sought after radical-ionic α,α′-functionalization in propargyl systems. Heterolytic bond dissociation energy (BDE) values are used to quantitate the impact of alpha substituents, to identify the “ionic” and “covalent” domains for electronically diverse propargyl triflates (ionic: BDE_het 238–271 kcal/mol; covalent: BDE_het 277–315 kcal/mol), and also to make predictions for new types of substituents and new classes of organic compounds

Assembling Contiguous Quaternary Carbon Atoms: Regio- and Stereoselective Rearrangements in Cobalt-Directed Radical Reactions of 1,4-Enynes

Radical coupling reactions of Co₂(CO)₆-complexed 1,4-enynes occur in a regio- and stereoselective fashion, providing access to 3<i>E</i>,7<i>E</i>-decadiene-1,9-diynes in excellent yields (84–99%). The formation of contiguous quaternary carbon atoms follows a tandem allylic rearrangement that projects an original reaction site gamma to the metal core. Propargyl alcohols with an α-alkenyl group as a substituent are treated with HBF₄, followed by the reduction of the highly conjugated propargyl cations with zinc. The scope of the reaction is expanded to include 1,4-enyne complexes with cyclic and acyclic substituents gamma to the metal core, as well as aliphatic and aromatic substituents attached to the acetylenic termini. The alternative design includes relocation of the cation generation siteα-to-γprior to the reduction step, employing either the cation isolation technique with HBF₄ or an <i>in situ</i> generation of ionic propargyl triflates with Tf₂O. Retention of the reaction site in 1,3-enynes is observed in both γ-alcohols and γ-Me ethers, affording respective γ,γ-radical dimers in excellent yields (98–99%)

Acquiring a Prognostic Power in Co₂(CO)₆‑Mediated, Cobaltocene-Induced Radical Dimerizations of Propargyl Triflates

Cobalt-complexed propargyl triflates can be generated <i>in situ</i> from methyl propargyl ethers and triflic anhydride and then reduced with cobaltocene to topologically and functionally diverse 1,5-alkadiynes. The electronic effect of an α-substituent is shown to attenuate the ionic nature of an α-C–OTf bond and thus its reducibility with cobaltocene. The powerful π-donors, such as phenyl, naphthyl, alkenyl, alkynyl, and alkoxy groups, provide the ionicity of α-C–OTf bonds and make them suitable recipients for a single-electron delivery from cobaltocene. σ-Donors (alkyl groups), a H atom, and σ/π-acceptors (ester groups) do not sufficiently stabilize propargyl cations, maintaining the covalent nature of α-C–OTf bonds and making them resistant toward the reducing agent. A newly acquired ability to differentiate between the α-C–OTf bonds is used in polyethers for the regioselective reduction and radical dimerization in select propargylic positions, thus paving the way for a long sought after radical-ionic α,α′-functionalization in propargyl systems. Heterolytic bond dissociation energy (BDE) values are used to quantitate the impact of alpha substituents, to identify the “ionic” and “covalent” domains for electronically diverse propargyl triflates (ionic: BDE_het 238–271 kcal/mol; covalent: BDE_het 277–315 kcal/mol), and also to make predictions for new types of substituents and new classes of organic compounds

The Influence of Programmed Cell Death in Myeloid Cells on Host Resilience to Infection with Legionella pneumophila or Streptococcus pyogenes

Pathogen clearance and host resilience/tolerance to infection are both important factors in surviving an infection. Cells of the myeloid lineage play important roles in both of these processes. Neutrophils, monocytes, macrophages, and dendritic cells all have important roles in initiation of the immune response and clearance of bacterial pathogens. If these cells are not properly regulated they can result in excessive inflammation and immunopathology leading to decreased host resilience. Programmed cell death (PCD) is one possible mechanism that myeloid cells may use to prevent excessive inflammation. Myeloid cell subsets play roles in tissue repair, immune response resolution, and maintenance of homeostasis, so excessive PCD may also influence host resilience in this way. In addition, myeloid cell death is one mechanism used to control pathogen replication and dissemination. Many of these functions for PCD have been well defined in vitro, but the role in vivo is less well understood. We created a mouse that constitutively expresses the pro-survival B-cell lymphoma (bcl)-2 protein in myeloid cells (CD68(bcl2tg), thus decreasing PCD specifically in myeloid cells. Using this mouse model we explored the impact that decreased cell death of these cells has on infection with two different bacterial pathogens, Legionella pneumophila and Streptococcus pyogenes. Both of these pathogens target multiple cell death pathways in myeloid cells, and the expression of bcl2 resulted in decreased PCD after infection. We examined both pathogen clearance and host resilience and found that myeloid cell death was crucial for host resilience. Surprisingly, the decreased myeloid PCD had minimal impact on pathogen clearance. These data indicate that the most important role of PCD during infection with these bacteria is to minimize inflammation and increase host resilience, not to aid in the clearance or prevent the spread of the pathogen

Epithelium intrinsic vitamin A signaling co-ordinates pathogen clearance in the gut via IL-18.

Intestinal epithelial cells (IECs) are at the forefront of host-pathogen interactions, coordinating a cascade of immune responses to protect against pathogens. Here we show that IEC-intrinsic vitamin A signaling restricts pathogen invasion early in the infection and subsequently activates immune cells to promote pathogen clearance. Mice blocked for retinoic acid receptor (RAR) signaling selectively in IECs (stopΔIEC) showed higher Salmonella burden in colonic tissues early in the infection that associated with higher luminal and systemic loads of the pathogen at later stages. Higher pathogen burden in stopΔIEC mice correlated with attenuated mucosal interferon gamma (IFNγ) production by underlying immune cells. We found that, at homeostasis, the intestinal epithelium of stopΔIEC mice produced significantly lower amounts of interleukin 18 (IL-18), a potent inducer of IFNγ. Regulation of IL-18 by vitamin A was also observed in a dietary model of vitamin A supplementation. IL-18 reconstitution in stopΔIEC mice restored resistance to Salmonella by promoting epithelial cell shedding to eliminate infected cells and limit pathogen invasion early in infection. Further, IL-18 augmented IFNγ production by underlying immune cells to restrict pathogen burden and systemic spread. Our work uncovers a critical role for vitamin A in coordinating a biphasic immune response to Salmonella infection by regulating IL-18 production by IECs

Infection of macrophages with <i>L</i>. <i>pneumophila</i> or <i>S</i>. <i>pyogenes</i> results in increased apoptotic cell death.

<p>Measurement of active caspase-3/7, using cell event reagent in BMDMs infected with <i>L</i>. <i>pneumophila</i> (A) or <i>S</i>. <i>pyogenes</i> (B). Percent of caspase-3/7 BMDMs at titrated MOIs of <i>L</i>. <i>pneumophila</i> (C) or <i>S</i>. <i>pyogenes</i> (D). Data shown is representative of at least 3 independent experiments with n = 3–4 per experiment. The mean values are displayed. * denotes P value ≤ 0.05. ** denotes P value ≤ 0.001.</p

Overexpression of bcl-2 rescues other myeloid cell types from etoposide-induced cell death.

<p>Effect of bcl-2 transgene on etoposide-induced caspase-3/7 activation in bone marrow derived DCs (BMDC) (A), neutrophils (B), and resident peritoneal macrophages (C), as measured by staining of activated caspase-3/7 and sytox. Peritoneal apoptosis is quantified in (D). These data are representative of at least 3 independent experiments with n = 3–4 per experiment. The mean values are displayed. * denotes P value ≤ 0.05.</p

Overexpression of bcl-2 rescues other myeloid cell types from <i>L</i>. <i>pneumophila</i>-induced cell death.

<p>Caspase-activation is measured in BMDC from CD68(bcl2)tg mice and littermate controls after infection with <i>L</i>. <i>pneumophila</i>. A representative staining is shown in (A), and the amount of apoptotic cells is quantified in (B). Caspase-activation is measured in alveolar macrophages from CD68(bcl2)tg mice and littermate controls after infection with <i>L</i>. <i>pneumophila</i>. A representative staining is shown in (C), and the amount of apoptotic cells is quantified in (D). Caspase-activation is measured in neutrophils from CD68(bcl2)tg mice and littermate controls after infection with <i>L</i>. <i>pneumophila</i>. A representative staining is shown in (E), and the amount of apoptotic cells is quantified in (F). These data are representative of at least 3 independent experiments with n = 3–4 per experiment. The mean values are displayed. * denotes P value ≤ 0.05.</p

Cytokine production from myeloid cells after infection with <i>S</i>. <i>pyogenes</i>.

<p>Production of IL-6 and TNF<b>α</b> was measured by intracellular staining. Grey shaded histograms are uninfected and <i>S</i>. <i>pyogenes</i> infected are depicted with solid black lines. Representative staining of DCs is shown in (A), and the percent of cells expressing cytokines is shown in (B top), and the MFI is shown in (B bottom). Representative staining of macrophages is shown in (C), and the percent of cells expressing cytokines is shown in (D top), and the MFI is shown in (D bottom). Ex vivo isolated macrophages from the spleens of CD68(bcl2)tg and littermate mice infected with <i>S</i>. <i>pyogenes</i> were stained intracellular for TNF<b>α</b> (E). These data are representative of at least 3 independent experiments with n = 3–4 per experiment. The mean values are displayed. * denotes P value ≤ 0.05.</p