Two different types of azide functionalized magnetite@silica nanoparticles are synthesized, which are ideally suited as inexpensive supports for catalysts and reagents as demonstrated with the grafting of copper(II)‐azabis(oxazoline) complexes via a copper(I) catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The potential of the immobilized complexes as catalysts is tested in the desymmetrization of racemic 1,2‐diols through asymmetric benzoylation. Compared to azabis(oxazolines) “clicked” to common polymeric supports such as MeOPEG or Merrifield resin, Fe3O4@SiO2 proves to be superior with respect to activity and selectivity, as exemplified by employing the catalysts in up to five runs with consistent high activity and selectivity. Recycling of the catalysts is achieved quantitatively by magnetic decantation.
Phosphorus dendrimer immobilized azabis(oxazoline) ligands can be efficiently synthesized up to the third generation with 48 ligand molecules being attached to the periphery using click chemistry. The so-assembled macromolecules were evaluated in copper(II)-catalyzed asymmetric benzoylations, showing good yields and enantioselectivities. Moreover, the copper(II)-catalysts could be readily recovered and reused in several cycles. The globular structure of the dendritic ligands seems to prevent interference of the triazole moieties in the catalysis, contrasting MeOPEG or polystyrene bound ligands of the same type.
Objective. We undertook this study to examine the effects of estradiol on chondrogenesis of human bone marrow-derived mesenchymal stem cells (MSCs), with consideration of sex-dependent differences in cartilage repair.Methods. Bone marrow was obtained from the iliac crest of young men. Density-gradient centrifugation-separated human MSCs proliferated as a monolayer in serum-containing medium. After confluence was achieved, aggregates were created and cultured in a serum-free differentiation medium. We added different concentrations of 17-estradiol (E2)
[Structure: see text] Simple bis(oxazoline) ligands, especially azabis(oxazolines), can catalyze the copper-catalyzed addition of indoles to benzylidene malonates in up to >99% ee, provided that excess of chiral ligand is avoided. The paradigm followed in many asymmetric catalyses that an excess of chiral ligand with respect to the metal should improve enantioselectivity because a background reaction by free metal is suppressed, is not applicable here, which might call for revisiting some of the many copper(II)-bis(oxazoline)-catalyzed processes known.
Simple bis(oxazoline) ligands, especially azabis(oxazolines), can promote the copper(II)-catalyzed Michael addition of indoles to benzylidene malonates with up to >99 % ee (ee=enantiomeric excess), provided that the ligand/metal ratio is tuned meticulously with particular regard to the electronic properties of the substrate. Despite a common paradigm followed in many asymmetric catalyses, an excess of chiral ligand is not always beneficial. In fact any excess of ligand has to be avoided to reach excellent enantioselectivities when electron-rich benzylidene malonates are used. On the contrary, malonates carrying an electron-withdrawing group require an excess of ligand for an optimum ee value. A correlation of optical yields versus the sigma(I) values of several para substituents shows a sigmoid trajectory. In the presence of an additive, such as triflate, the significance of the ligand/metal ratio vanishes and very good enantioselectivities are achieved at any rate--no matter whether electron-donating or withdrawing substituents are present.
Over the years, organic synthesis has witnessed several improvements through the development of new chemical transformations or more efficient reagents for known processes. Likewise, technological advances, aiming at speeding up reactions and facilitating their work-up, have established themselves in academic as well as in industrial laboratories. In this Minireview, we highlight very recent developments in flow chemistry, focusing on organometallic reagents and catalysts. First, we describe reactions with homogeneous catalysts immobilized on different support materials using the concept of packed bed reactors. In the last chapter, we will discuss applications that utilize organometallic reagents.
17β-Estradiol (E2) exerts rapid non-genomic vascular effects through activation of its plasma membrane receptors. We tested the hypothesis that E2 induces vasorelaxation through activation of the G-protein-coupled receptor 30 (GPR30) in rat aorta. Rat aortic rings were mounted in organ baths and subjected to contraction followed by relaxation. Whether endothelium was intact or denuded, both E2 and G1, a GPR30 agonist, induced vasorelaxation in concentration-dependent manners. Although G15, a specific GPR30 antagonist, blocked G1-induced vasorelaxation, it did not block E2-induced vasorelaxation. In conclusion, 17β-estradiol induces vasorelaxation in a GPR30-independent manner in rat aorta.
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