Rh-POP Pincer Xantphos Complexes for C-S and C-H Activation. Implications for Carbothiolation Catalysis

The neutral Rh­(I)–Xantphos complex [Rh­(κ³-_P,O,P-Xantphos)­Cl]_<i>n</i>, <b>4</b>, and cationic Rh­(III) [Rh­(κ³-_P,O,P-Xantphos)­(H)₂]­[BAr^F₄], <b>2a</b>, and [Rh­(κ³-_P,O,P-Xantphos-3,5-C₆H₃(CF₃)₂)­(H)₂]­[BAr^F₄], <b>2b</b>, are described [Ar^F = 3,5-(CF₃)₂C₆H₃; Xantphos = 4,5-bis­(diphenylphosphino)-9,9-dimethylxanthene; Xantphos-3,5-C₆H₃(CF₃)₂ = 9,9-dimethylxanthene-4,5-bis­(bis­(3,5-bis­(trifluoromethyl)­phenyl)­phosphine]. A solid-state structure of <b>2b</b> isolated from C₆H₅Cl solution shows a κ¹-chlorobenzene adduct, [Rh­(κ³-_P,O,P-Xantphos-3,5-C₆H₃(CF₃)₂)­(H)₂(κ¹-ClC₆H₅)]­[BAr^F₄], <b>3</b>. Addition of H₂ to <b>4</b> affords, crystallographically characterized, [Rh­(κ³-_P,O,P-Xantphos)­(H)₂Cl], <b>5</b>. Addition of diphenyl acetylene to <b>2a</b> results in the formation of the C–H activated metallacyclopentadiene [Rh­(κ³-_P,O,P-Xantphos)­(ClCH₂Cl)­(σ,σ-(C₆H₄)­C­(H)CPh)]­[BAr^F₄], <b>7</b>, a rare example of a crystallographically characterized Rh–dichloromethane complex, alongside the Rh­(I) complex <i>mer</i>-[Rh­(κ³-_P,O,P-Xantphos)­(η²-PhCCPh)]­[BAr^F₄], <b>6</b>. Halide abstraction from [Rh­(κ³-_P,O,P-Xantphos)­Cl]_<i>n</i> in the presence of diphenylacetylene affords <b>6</b> as the only product, which in the solid state shows that the alkyne binds perpendicular to the κ³-POP Xantphos ligand plane. This complex acts as a latent source of the [Rh­(κ³-_P,O,P-Xantphos)]⁺ fragment and facilitates <i>ortho</i>-directed C–S activation in a number of 2-arylsulfides to give <i>mer</i>-[Rh­(κ³-_P,O,P-Xantphos)­(σ,κ¹-Ar)­(SMe)]­[BAr^F₄] (Ar = C₆H₄COMe, <b>8</b>; C₆H₄(CO)­OMe, <b>9</b>; C₆H₄NO₂, <b>10</b>; C₆H₄CNCH₂CH₂O, <b>11</b>; C₆H₄C₅H₄N, <b>12</b>). Similar C–S bond cleavage is observed with allyl sulfide, to give <i>fac</i>-[Rh­(κ³-_P,O,P-Xantphos)­(η³-C₃H₅)­(SPh)]­[BAr^F₄], <b>13</b>. These products of C–S activation have been crystallographically characterized. For <b>8</b> in situ monitoring of the reaction by NMR spectroscopy reveals the initial formation of <i>fac</i>-κ³-<b>8</b>, which then proceeds to isomerize to the <i>mer</i>-isomer. With the <i>para</i>-ketone aryl sulfide, 4-SMeC ₆H₄COMe, C–H activation <i>ortho</i> to the ketone occurs to give <i>mer</i>-[Rh­(κ³-_P,O,P-Xantphos)­(σ,κ¹-4-(COMe)­C₆H₃SMe)­(H)]­[BAr^F₄], <b>14</b>. The temporal evolution of carbothiolation catalysis using <i>mer</i>-κ³-<b>8</b>, and phenyl acetylene and 2-(methylthio)­acetophenone substrates shows initial fast catalysis and then a considerably slower evolution of the product. We suggest that the initially formed <i>fac</i>-isomer of the C–S activation product is considerably more active than the <i>mer</i>-isomer (i.e., <i>mer</i>-<b>8</b>), the latter of which is formed rapidly by isomerization, and this accounts for the observed difference in rates. A likely mechanism is proposed based upon these data

CD93-Signaling Regulates Self-Renewal and Proliferation of Chronic Myeloid Leukemia Stem Cells in Mice and Humans and Might be a Promising Target for Treatment

Background: The introduction of BCR/ABL-specific tyrosine kinase inhibitors (TKIs) more than two decades ago revolutionized chronic myelogenous leukemia (CML) therapy. The majority of CML patients treated with TKIs obtain durable cytogenetic and molecular responses. However, only a subgroup of these patients can successfully discontinue TKI therapy and maintain a treatment-free remission (Laneuville et al. 2011). TKI-resistant leukemia stem cells (LSCs) persist in the majority of patients at low levels over a prolonged period. These quiescent, self-renewing LSCs in the BM are the major cause of relapse after drug discontinuation (Holyoake et al, 2017). The selective elimination of LSCs requires the definition of unique signaling pathways that promote self-renewal of LSCs but not of normal HSCs. Based on the documented expression of CD93 on LSCs (Kinstrie et al, 2015), the aim of the present study was to investigate the role of the cell surface receptor CD93 in the regulation of self-renewal of human and murine CML LSCs and its contribution to disease development and progression. Methods and Results: We found CD93 expression on LSCs and leukemia progenitor cells but not on more differentiated leukemia granulocytes in a murine retroviral lineage-negative Sca-1+ c-kit+ (LSK) transduction/transplantation CML model. Next-generation sequencing analysis revealed that Cd93-/- LSCs have a silenced gene expression signature particularly in genes involved in the regulation of gene expression, stem cell maintenance and proliferation. Out of the 1120 genes differentially expressed between BL/6 and Cd93-/- LSCs, 1108 genes were down-regulated. In contrast, naïve BL/6 and Cd93-/- hematopoietic stem cells (HSCs) did not display a dysregulation in these pathways. Functionally, CD93-deficiency in LSCs resulted in impaired self-renewal, reduced LSC frequencies in vitro (at least by a factor of 100, P&amp;lt;0.001) and in the incompetence to induce and propagate CML in mice. To study whether CD93-signaling in LSCs relies on ligand-binding to the extracellular domain of CD93, we generated an extracellular domain deletion mutant of CD93 (mCd93intra). Comparable to transduction with full-length mCd93, the expression of Cd93intra restored colony formation of Cd93-/- LSCs in vitro, suggesting that the maintenance of LSC self-renewal is independent of ligand-binding to the extracellular domain of CD93. Furthermore, analysis of the sub-cellular localization of CD93 in CML cells using a lentiviral expression vector encoding for AcGFP1-N1-Cd93 demonstrated nuclear localization of the CD93 intracellular domain (ICD). SCY1 like pseudokinase 1 (SCYL1), a regulator of gene transcription, directly interacts with the highly charged juxta membrane domain of the cytoplasmic tail of CD93 (Bohlson et al, 2005). Silencing of Scyl1 significantly reduced colony formation of BL/6 but not Cd93-/- LSCs in vitro suggesting that the ICD of CD93 regulates gene transcription via Scyl1 in CML LSCs. To discover compounds that affect LSC function similarly as genetic CD93 blockade, we performed a compound screen using the FDA approved drug library V2. The antiemetic agent metoclopramide, which is widely used in clinical routine to reduce nausea in cancer patients, was one very promising candidate identified in the screen. Metoclopramide treatment reduced clonogenic potential of CD93-competent LSCs to comparable levels as CD93-deficient LSCs in vitro without further affecting colony formation of CD93-deficient LSCs. Analysis of LSCs from newly diagnosed CML patients similarly demonstrated that CD93-signaling induces the expression of genes associated with proliferation and stemness, resulting in an increased clonogenic potential in vitro. In addition, colony formation and re-plating capacity in semisolid cultures of human CD34+CD38- LSCs was significantly impaired by metoclopramide at a pharmacological concentration of 0.1mM compared to control treatment. Conclusions: Overall, these results indicate that CD93-siganling is an important regulator of stemness and proliferation of human and murine CML LSCs. Furthermore, this study identifies expression of CD93 by LSCs as promising novel target for the treatment of CML. Disclosures Baerlocher: Novartis: Research Funding. </jats:sec

Social pedagogical activities in the local municipality of Dubna small rural district for decreasing unjustified non-atendance

Diplomdarbs „Sociālpedagoģiskā darbība Dubnas pagasta pašvaldībā skolēnu neattaisnoto kavējumu novēršanā” pievērš uzmanību sociāli nozīmīgai problēmai. Diplomdarba mērķis ir raksturot sociālpedagoģisko darbību Dubnas pagastā un izstrādāt darba programmu ģimenēm skolēnu neattaisnoto kavējumu novēršanā, teorētiski to pamatot un veikt šīs programmas aprobācijas rezultātu analīzi. Diplomdarbā tiek aplūkota ģimenes, skolas un sabiedrības loma skolēnu neattaisnoto kavējumu novēršanā, kā arī izvērtētas pašvaldības iespējas izglītības apguves sekmēšanā. Darba praktiskajā daļā, pamatojoties uz veikto izpēti, ir analizēti skolēnu neattaisnoto skolas kavējumu iemesli Dubnas pagasta pašvaldībā un izstrādāta sociālpedagoģiska darbības programma ģimenēm skolēnu neattaisnoto kavējumu novēršanā. Izstrādātās programmas aprobācijas analīze liecina, ka savlaicīgi konstatēti problēmas cēloņi un pārdomāta sociālpedagoģiska darbība ģimenē, veicina pozitīvu darba rezultātu neattaisnoto skolas kavējumu novēršanā. Atslēgvārdi: skolēns, ģimene, vecāki, sociālpedagoģiskā darbība, pašvaldība.The diploma paper „Social pedagogical activities in the local municipality of Dubna small rural district for decreasing unjustified non-atendance” raises a socially significant problem. The objective of the diploma paper is to characterize social pedagogical activity in the local authority of Dubna rural district and work out a programme for decreasing unjustified non-attendance, substantiate it theoretically and analyze the results of approbation of the programme. In the diploma paper the role of family, school and society for decreasing unjustified non-atendance has been examined, as well as considered possibilities of the rural municipality to favour advancement. In the practical part of the diploma paper, basing on the research, causes of unjustified non-attendance in the local authority of Dubna rural distict are analysed and social pedagogical activity programme for families is developed for eliminating unjustified non-atendance. The analysis of the approbation of the developed programme testifies that duly established causes of the problem and deliberative social pedagogical activity facilitates a positive result of work in decreasing unjustified non-atendance. Key words: pupil, family, parents, social pedagogical activity, local authorit