The kinetic resolution of the α,β-unsaturated vicinal diols 3 has been investigated by irreversible transesterification in organic media and by hydrolysis of the corresponding diacetates 6 (Scheme. 1
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Scheme. 1. Synthesis and kinetic resolution of the diols 3a–e and their corresponding diacetates 6a–e). The best results were obtained in the hydrolysis of the diacetates with the lipase CAL-B from Candida antarctica as a catalyst. 相似文献
A Ni8 cluster and a Ni10 cluster were successfully acquired by regulating the ligands. The metallic core of Ni8 cluster is comprised of two centrosymmetric cubanes Ni4(µ3-O)3(µ6-O). Interestingly, the mat? ligand was introduced into the synthesis of Ni8 cluster and a new tetrahedral Ni10 cluster was isolated. 相似文献
Using the chiral ligands LSS (+)-4,5-pinene bipyridine and LRR (−)-4,5-pinene bipyridine (Scheme 1), two novel Eu(III)-based complexes with the formula [Eu(DBM)3L] (LSS in 1, LRR in 2, DBM = dibenzoylmethanate) have been successfully synthesized and characterized by X-ray single crystal determination and spectroscopic methods. The crystal structure analysis of 1 and 2 reveal that they crystallize in the chiral space group P21 of the monoclinic system. The central Eu(III) ion is eight-coordinated in a geometrical environment intermediate between a square antiprism and a dodecahedron. The CD spectra reflect that complexes 1 and 2 are enantiomers. When ground in daylight, complexes 1 and 2 exhibit brilliant triboluminescence at room temperature. 相似文献
Amides of 9-amino(9-deoxy)epicinchonine have been used as chiral base catalysts to induce asymmetry in enantioselective decarboxylation reactions. To understand the reaction mechanism and to optimize the bases by variation of the amide substituents, a detailed knowledge of their preferred conformation is necessary. The conformations were investigated by 1H NMR spectroscopy, X-ray analysis and semi-empirical molecular orbital calculations. Principally, cinchona alkaloids may adopt four different conformations (Fig. 1
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Figure 1. Schematic drawings illustrating the two closed and open conformations of 9-amino(9-deoxy)epicinchonine derivatives), of which openb and openb′ are preferred by 2-ethoxy-N-(9-deoxyepicinchonine-9-yl)benzamide 2 in solution. AM1 Calculations confirm these results, and the small energy barrier between the two open conformations explains their simultaneous existence in solution. Crystal structure analyses of various amides show open conformations in the solid state. Local minimum energy conformations were found for open conformations of the compound 2 protonated at the quinuclidine system, which is the active species in the enantioselective decarboxylation reaction. 相似文献
Highlights? A lipid-based probe, lipid 1, for continuous monitoring of endocytosis in live cells is reported ? Lipid 1 was shown to report only on new endocytic events ? Lipid 1 reports on the rate of endocytosis ? Cancerous and noncancerous cell lines from the same patient have different endocytosis rates 相似文献
Synopsis: This mini review presents recent advances and our comments on the research subject of graphene-conducting polymer nanocomposite-based supercapacitors. We emphasize material design, controlled assembly and nanoscale engineering of relevant composites, and their applications in flexible and bendable supercapacitors.
Highlights? A dimerization-dependent red fluorescent protein (ddRFP) was engineered ? ddRFP fluorogenesis results from modulation of pKa and quantum yield ? ddRFP-based biosensors exhibit reversible intensiometric responses ? ddRFP-based biosensors can detect Ca2+ dynamics and caspase-3 activity in live cells 相似文献
The density functional theory (DFT) calculations were used to study the effects of PCP ancillary ligands on the relative stabilities of hydrido amido complexes and ammonia coordination complexes. Calculations on the four compounds 1a, 1b, 2a and 2b containing PCP ligands with t-butyl groups on P atoms showed that 1b is more stable than 1a and 2a is more stable than 2b. Calculations also showed that the relative energies of hydrido amido complexes with respect to the isomeric ammonia coordinated complexes vary with the different substituent groups (R = H, Me and tBu) on the P atoms of the PCP ligands. An alternative method to study the ligand effects introduced by different substituents on the P atoms is to vary the nuclear charge on the P atoms of PCP ligand. The relative energies were predicted to decrease with the nuclear charge of the P atoms on the PCP ligands, which indicates that increasing the electron donating ability tend to favor the hydrido amido complexes over the ammonia coordination complexes:
The oxalato-bridged dicopper(II) complexes [Cu2(μ-ox)(LRR)2(H2O)2(ClO4)2] (1),[Cu2(μ-ox)(LRR)2(CH3COCH3)2(ClO4)2](1a),[Cu2(μ-ox)(LSS)2(H2O)2(ClO4)2] (2) and [Cu2(μ-ox)(LRR)(LSS)2(CH3COCH3)2(ClO4)2] (3) [LRR = (8R,10R)-(-)-[4,5]-pineno2,2′-bipyridine,LSS = (8S,10S)-(+)-[4,5]-pineno-2,2′-bipyridine;ox2= oxalate] were first prepared.A possible mechanism for the formation of the chial dicopper(II) complexes was proposed.Based on elemental analysis,conductance measurement,UV-Vis spectra,CD spectra and X-ray single-crystal diffraction,the oxalato-bridged structures of 1 and 2 were deduced to adopt two Cu(II) ions and the bridged oxalate lying in the nearly same plane.The crystal structures of 1a and 3 reveal that the coordination geometry around each Cu(II) ion is an elongated and distorted octahedron and two axial solvent molecules and two perchlorate ions are anti to each other respectively in both binuclear molecules.The solution CD spectra of 1 and 2 in the visible d-d range show very weak Cotton effects with peaks at 588 and 779 nm,which are approximately of mirror image,suggesting the optical activities may be derived from the vicinal effects of the chiragenic centers at the pinene group of LRR and LSS,respectively.Complex 1 has been characterized by variable-temperature magnetic susceptibility and the data was least-square fitted to the Blenaey-Bowers equation.The exchange integral J was found to be -338.41(4) cm-1,indicating a strong antiferromagnetic interaction between two copper(II) ions. 相似文献
Highlights? S1P1 antagonists were designed and optimized ? NIBR-0213 is a highly potent and selective S1P1 antagonist ? NIBR-0213 induces long lasting reduction of lymphocyte counts in blood ? NIBR-0213 has comparable efficacy to fingolimod (FTY720) in a mouse EAE model 相似文献
Highlights? JadG catalyzes the oxidative C-C bond B ring cleavage of dehydrorabelomycin ? JadG needs FMNH2 or FADH2 as cofactors ? JadY is a flavin reductase that could supply FMNH2 or FADH2 for JadG 相似文献
Resolution of racemic 1,2-diphenyl-1,2-ethanediamine was performed through recrystallization of its diastereomeric adducts 2a,b with N*-chiral ortho-palladated complex (SCRN)-1. The structure and absolute configuration of the less soluble (SCRN,SS)-2a diastereomer was determined by X-ray diffraction. The complex has an unusual dimeric structure with a palladacycle:diamine ratio of 2:3; the association of 2a with an additional diamine molecule of the same (SS) absolute configuration is achieved due to hydrogen bonds between the coordinated and solvate diamine. 相似文献
Highlights? Fluorescent saxitoxins synthesized as imaging agents for sodium ion channels (NaVs) ? Electrophysiology and confocal imaging establish potency and selectivity of NaV probes ? Single-molecule and super-resolution imaging reveal subdiffraction NaV distributions ? Dynamic motions of NaVs measured in specific membrane regions in live cells 相似文献
Cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 (1) is capable of reacting with ethanol to form a 1:1 complex, {[(o-C6F4Hg)3](EtOH)} (2), having a pyramidal structure. The ethanol molecule in 2 is coordinated through the oxygen atom to all Hg atoms of the macrocycle. The interaction of 1 with THF followed by drying of the product obtained in vacuum also gives the corresponding pyramidal 1:1 complex {[(o-C6F4Hg)3](THF)} (3). However, when a THF solution of 1 is slowly concentrated to a small volume and the resulting crystals are not dried, three cocrystallized adducts, viz., {[(o-C6F4Hg)3](THF)2} (4), {[(o-C6F4Hg)3](THF)3} (5) and {[(o-C6F4Hg)3](THF)4} (6), containing two, three and even four THF molecules, respectively, are produced. Complex 4 has a bipyramidal structure. Complexes 5 and 6 are also characterized by the presence of a bipyramidal fragment formed by two coordinated THF species. The topological analysis of the DFT-calculated function of the electron density distribution in the crystals of 2 and 3 revealed the critical points (3, −1) on each of the three Hg···O lines, which is in accord with the X-ray diffraction data indicating on the presence of the triply coordinated Lewis base molecule in both adducts. If a THF solution of 1 is held for a month at 20 °C on air under stirring, a sandwich complex of 1 with previously unknown bis-2,2′-tetrahydrofuryl peroxide (THFPO) is formed. The THFPO ligand in this sandwich, {[(o-C6F4Hg)3]2(THFPO)} (7), provides all its four oxygen atoms for the bonding to the molecules of 1. Two of these oxygen atoms, belonging to the tetrahydrofuryl moieties, are cooperatively bound each by three Hg atoms of the neighbouring macrocyclic unit whereas two others, belonging to the peroxide group, coordinate to a single Hg atom of the adjacent macrocycle. 相似文献
Highlights? Purification of Plasmodium proteasomes and labeling with an activity-based probe ? Identification of an epoxyketone-based inhibitor with parasite-specific toxicity ? Demonstration that Plasmodium is sensitive to partial inhibition of its proteasome ? Determination of key parameters for selective parasite killing with proteasome inhibitors 相似文献
The reactions of three-mercury anticrown (o-C6F4Hg)3 (1) with acetoacetic ester (AE), malonic ester (ME), and malonodinitrile (MN) afford 1: 1 complexes {[(o-C6F4Hg)3](AE)} (3), {[(o-C6F4Hg)3](ME)} (4), and {[(o-C6F4Hg)3](MN)} (5). The structures of complexes 3–5 were determined by X-ray diffraction analysis. Complex 3 has a discrete structure in the solid state, whereas complexes 4 and 5 form in the crystal extended stacks representing polydecker sandwiches with alternating molecules of 1 and ME or MN. According to the X-ray diffraction and IR spectral data, the molecule of AE in complex 3 is in the keto form. 相似文献
Highlights? Molecular basis for the biosynthesis of a fatal food toxin revealed ? Functional genetics by λ Red recombination in the pathogen Burkholderia gladioli ? Stereochemistry of modular bongkrekic acid PKS decoded ? β-Branching and six-electron methyl oxidation lead to tricarboxylic fatty acid 相似文献
Highlights? Phylogenomics can be used to predict cognate ligands for TetR-family regulators ? KijR (SCO7719) regulates kijX (SCO7720) in response to the antibiotic kijanimicin ? kijX encodes a kijanimicin-resistance determinant ? KijX is a glycosyl hydrolase and inactivates kijanimicin through deglycosylation 相似文献
The title compounds were prepared by heating solutions of ester protected amino acids (H-l-Ala-OEt, H-β-Ala-OEt, H-l-Val-OMe, GABA-OMe, H-l-Asp(OMe)-OMe) and glyoxal in the presence of M(CO)4(pip)2 (M=Mo, W). The resulting novel complexes, M(CO)4(dab-xxx-OR) (dab=diazabutadiene), contain an N,N′-diimine ligand and were characterized by 1H- and 13C-NMR, IR, and UV-vis measurements. The low energy band in the visible portion of the electronic spectrum is assigned to a MLCT transition and exhibits solvatochromism. The valine, alanine and aspartic ester derivatives have C2 symmetry resulting from the C2 symmetry of the ligand. The reaction of the alanine and aspartic amino esters in the presence of NEt3 produces diastereomeric mixtures caused by racemization at the amino acid α-carbon. Racemization is not observed during the formation of the valine derivatives. The crystal structures of (R,S)-Mo(CO)4(dab-asp(OMe)-OMe) (5-RS), and (S,S)-Mo(CO)4(dab-asp(OMe)-OMe) (5-SS), were determined. The structure of 5-RS confirms that racemization at the α-carbon occurred. 5-SS has C2 symmetry. 相似文献
The manipulation of the enone moiety associated with the biomass-derived, homochiral and now abundant compound levoglucosenone (1) is described. While the trichloroacetimidates derived from the allylic alcohols 3 and 4 failed to engage in Overman-type rearrangements, certain ester derivatives reacted in the presence of Pd[0]-catalysts to give regio-isomeric mixtures of β,γ-unsaturated malonates or ketones, the structures of which were confirmed by single-crystal X-ray analyses. In other sequences involving 1,3-transposition reactions, an operationally simple means for converting compound 1 into isolevoglucosenone (2) is described.
