Asymmetric insertion

Paramagnetic relaxation enhancement (PRE) approach was introduced for identifying the asymmetric insertion depths of membrane proteins in lipid bilayers. By applying Mn2+ ions on the outer but not the inner leaflet of lipid bilayers, the sidedness of protein residues in the lipid bilayer was determined. Protein-free lipid membranes with one-side Mn2+ bound surfaces exhibit... 

Copper complexes derived from bis(-2,6-dichlorophenyle-dene)-( 15,25)-1,2-diaminocyclohexane (11) catalyze various reactions such as Diels-Alder reaction, aziridination (eq 20), cyclopropanation, and silyl enol ether addition to pyruvate esters. Although the scope of these reactions may be sometimes limited, enantioselectivities are generally high. The same complex (with copper(I) salts) catalyzes the asymmetric insertion of silicon- hydrogen bond into carbenoids. ... 

The asymmetric insertion of a-diazoesters into the O—H bond of water provides an extremely simple approach for the synthesis of chiral a-hydroxyesters in an efficient and atom-economical way. The challenges of asymmetric O—H insertion of water are mainly attributed to two considerations first, the active metal carbene intermediates are generally sensitive to water and secondly, the small molecular structure of water makes chiral discrimination quite difficult. Zhou and co-workers discovered a highly enantioselective O—H insertion of water catalyzed by chiral spiro Cu [112] and Fe catalysts [111]. Under mild conditions, both Cu andFe complexes of ligand (S, 5,5)-23a... 

Transition metal catalyzed carbene insertion into the Si—H bond provides a direct and efficient method for the synthesis of organosilicon compounds. When chiral spiro diimine ligand (/ )-24a was applied in Cu-catalyzed asymmetric insertion of a-diazo-a-arylacetates with silanes, the Si—H insertion products were obtained in high yields (85-97%) and excellent enantioselectivities (90-99% ee) (Scheme 51) [26a],... 

Asymmetric insertion into X-H bonds is also possible. Enantioselective Si-H insertion reactions have also been achieved using the Rh2 (MEPY)4 catalyst (9.25). The enantioselectivity of Si-H insertion into the silane (9.113) was improved up... 

The ruthenium porphyrins, (TPP)RuCO and (TMP)RuCO catalyze carbene insertion into S - H bonds, leading to dialkyl and alkyl aryl sulfides using ethyl diazo acetate under mild conditions. The insertion process is regiospe-cific since dithiothreitol reacts to give the S - H insertion product without any trace of the ether compound (Scheme 18) [172]. With a homochiral porphyrin ruthenium complex, asymmetric insertions were obtained but with low enantioselectivities [191]. 

The first asymmetric insertion reactions of donor-donor carbenoids,i.e., those with no pendant electron-withdrawing groups, were reported. This process enabled the synthesis of densely substituted dihydrobenzo[6]furans with high levels of enantio- and diastereoselectivity (14JA15142). 

Scheme 10.18 Asymmetric insertion of diazoacetates into Si-H bonds catalyzed by dirhodium metallopeptides [103].

Budding Transition. In cells, the budding of vesicles from internal organel-lae or the plasma membrane is an ubiquitous process and a key process for cellular traffic. In case of giant lipid vesicles, asymmetric insertion of fluorescently labeled PEO with cholesteryl anchor groups into the outer monolayer lead to an increase of the spontaneous curvature and induced budding of starfish vesicles (136). The addition of the cholesteryl anchor increases both components of the effective spontaneous curvature Ado, the area difference, and the local spontaneous curvature as locally the membrane curves away from the polymer (147). 

Cyclobutane synthesis allows introduction of substituents on the cyclobutane ring in various patterns (Scheme 8.24) [55], Allyl bromide with boron trichloride and tri-ethylsilane yields the alkyldichloroborane 103, which is converted into pinacol (3-bro-mopropyl)boronate (104) and on to the cyano derivative 105 by standard methods. Transesterification of 105 and reaction with LiCHClj was used to make 100. However, 105 can be deprotonated and monoalkylated efficiently, and transesterification then yields 106. Transesterification with DICHED and asymmetric insertion of the CHCl group furnishes 107, which cyclizes to 108 or 109 with about the same 20 1 di-astereoselection as seen with the unsubstituted intermediate 100. The pattern of substitution shown by 111 was achieved via reaction of pinacol (bromomethyl)boronate (63) with lithioacetonitrile to form 110, which underwent chain extension and substitution in the usual manner. It was necessary to construct 110 in this way because substitution of a (p-haloalkyl)boronic acid is not possible. With R = H or CH3, substituents included Me, Bu, and OBn [55]. 

Wang, Y Guo, X. Tang, M. Wei, D. Theoretical Investigations toward the Asymmetric Insertion Reaction of Diazoester with Aldehyde Catalyzed by N-Protonated Chiral Oxazaborolidine Mechanisms and Stereoselectivity. /. Phys. Chem. A 2015,119,8422-8431. 

Gao, L. Kang, B. C. Ryu, D. H. Catalytic Asymmetric Insertion of Diazoesters into Aryl-CHO Bonds Highly Enantioselective Construction of Chiral All-Carbon Quaternary Centers. /. Am. Chem. Soc. 2013,135,14556-14559. 

Recent studies by Katz et al. (1977) have served to demonstrate a likely method for membrane glycoprotein synthesis—specifically, the insertion of the G protein of vesicular stomatitus virus (VSV) into pancreatic endoplasmic reticulum (PER). Their results are consistent with a scheme of membrane glycoprotein synthesis which postulates that the growing protein is extruded across the ER membrane with the amino terminus extruded first and is then translocated across the membrane. Asymmetric insertion, as well as glycosylation, requires the presence of membranes during protein synthesis, and glycosylation is restricted to the luminal surface of the ER. 

Katz, F. N., Rothman, J. E., Lingappa, V. R., Blobel, G., and Lodish, H. F., 1977, Membrane assembly in vitro Synthesis, glycosylation, and asymmetric insertion of a transmembrane protein, Proc. Natl. Acad. Sci. USA 74 3278. 

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