3381-51-9Relevant articles and documents
Group 4 metallocene complexes bearing cholestanol-derived substituents at the Cp-rings-their synthesis and use in propene polymerization catalysis
Erker, Gerhard,Mollenkopf, Christoph
, p. 173 - 182 (1994)
Two series of Group 4 bent metallocene complexes bearing cholestanol-derived substituents at their Cp-rings have been prepared. 5α-Cholestan-3α-ol was converted to the 3α-mesylate.Nucleophilic substitution with CpNa, followed by deprotonation and treatment with ZrCl4(THF)2 gave bis5-5α-cholestan-3β-yl)cyclopentadienyl>zirconium dichloride 3β-5. 5α-Cholestan-3-one 6 was converted to the corresponding fulvene, methyl lithium was added and deprotonation and addition to ZrCl4(THF)2 furnished bis5-(3β-methyl-5α-cholestan-3α-yl)cyclopentadienyl>zirconium dichloride (11b).Treatment of the chiral Cp-substituted zirconocene dichlorides with a large excess of methyl alumoxane gave homogeneous Ziegler catalysts.Propene polymerization proceeded with overall stereochemical chain end control to give partly isotactic polypropylene.Keywords: Zirconium; Cholestanol; Polymerization
Predictable Selectivity in Remote C?H Oxidation of Steroids: Analysis of Substrate Binding Mode
Olivo, Giorgio,Capocasa, Giorgio,Ticconi, Barbara,Lanzalunga, Osvaldo,Di Stefano, Stefano,Costas, Miquel
supporting information, p. 12703 - 12708 (2020/06/02)
Predictability is a key requirement to encompass late-stage C?H functionalization in synthetic routes. However, prediction (and control) of reaction selectivity is usually challenging, especially for complex substrate structures and elusive transformations such as remote C(sp3)?H oxidation, as it requires distinguishing a specific C?H bond from many others with similar reactivity. Developed here is a strategy for predictable, remote C?H oxidation that entails substrate binding to a supramolecular Mn or Fe catalyst followed by elucidation of the conformation of the host-guest adduct by NMR analysis. These analyses indicate which remote C?H bonds are suitably oriented for the oxidation before carrying out the reaction, enabling prediction of site selectivity. This strategy was applied to late-stage C(sp3)?H oxidation of amino-steroids at C15 (or C16) positions, with a selectivity tunable by modification of catalyst chirality and metal.
Addressable Cholesterol Analogs for Live Imaging of Cellular Membranes
Rakers, Lena,Grill, David,Matos, Anna L.L.,Wulff, Stephanie,Wang, Da,B?rgel, Jonas,K?rsgen, Martin,Arlinghaus, Heinrich F.,Galla, Hans-Joachim,Gerke, Volker,Glorius, Frank
, p. 952 - 12,961 (2018/05/08)
Cholesterol is an essential component of most biological membranes and serves important functions in controlling membrane integrity, organization, and signaling. However, probes to follow the dynamic distribution of cholesterol in live cells are scarce and so far show only limited applicability. Herein, we addressed this problem by synthesizing and characterizing a class of versatile and clickable cholesterol-based imidazolium salts. We show that these cholesterol analogs faithfully mimic the biophysical properties of natural cholesterol in phospholipid mono- and bilayers, and that they integrate into the plasma membrane of cultured and primary human cells. The membrane-incorporated cholesterol analogs can be specifically labeled by click chemistry and visualized in live-cell imaging experiments that show a distribution and behavior comparable with that of endogenous membrane cholesterol. These results indicate that the cholesterol analogs can be used to reveal the dynamic distribution of cholesterol in live cells. Cholesterol is an important component of biological membranes, but probes recording its dynamic intracellular distribution are scarce. Rakers et al. developed cholesterol-derived imidazolium salts mimicking properties of natural cholesterol. Following specific labeling via click chemistry, one of the cholesterol analogs was shown to incorporate into cellular membranes equivalent to endogenous cholesterol.
