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141.
The 1,3-dipolar cycloaddition reaction of unsymmetrically N-substituted and N-unsubstituted 1,3-oxazolium-5-olates with selected 3-substituted coumarins has been examined. Various types of pyrrole derivatives are isolated and their formation seems to be a function of the regio- and diastereochemistry of the initial cycloaddition step. 相似文献
142.
Diastereomers of 3-amino-2-hydroxy-6-methylheptanoic acid (AHMHA), a new amino acid unit in perthamides C and D, have been synthesized from commercially available 4-methylpentanol in a concise manner and 50% average overall yield. Comparison of the 1H and 13C NMR data, optical rotation data and Marfey’s analysis of the resulting isomers with the natural fragment unambiguously allowed the configurational assignment of the natural residue as (2R,3R). A structural revision of perthamides C and D is also reported. 相似文献
143.
Maria Laura Mercuri Paola Deplano Luca Pilia Angela Serpe Flavia Artizzu 《Coordination chemistry reviews》2010,254(13-14):1419-1433
Molecule-based materials are extremely versatile materials as they can be built from specifically designed building blocks with the desired size, shape, charge and electronic properties which determine their intermolecular interactions and, thus, their organization in the solid. The intermolecular interactions, therefore, in particular van der Waals interactions, π–π and π–d interactions, H-bonding, etc., play a crucial role in self-assembling these pre-designed molecular units and may provide a powerful way to afford layered mono- and multifunctional molecular materials with new or unknown physical properties. In this review the relationship between interaction modes and physical properties of organic/inorganic hybrids based on transition metal complexes with chalcogenolene ligands will be examined and an outlook will be proposed. With this goal, magnetic materials, highly conducting and metallic single-component materials containing dithiolene complex building blocks, multifunctional materials where the dithiolene complex is the magnetic or conducting component in addition to more complex systems involving other types of building block such as the metal oxalate complexes, will be discussed. 相似文献
144.
Giovanni Pellegrino Angelo Carotti Orazio Nicolotti Leonardo Pisani Angela Stefanachi Marco Catto 《Tetrahedron letters》2010,51(13):1702-7034
A small molecular library of 40 pyrimidine, pyrazole, and isoxazole derivatives, bearing structural features for a promising binding of therapeutically interesting enzymes, was designed and prepared. An efficient and straightforward solid phase synthesis was envisaged and carried out on a Rink amide resin. The assistance of microwave heating in any step reduced the reaction time, increased the reaction yields, and allowed an easy work-up and purification of the targeted compounds. 相似文献
145.
Carlo Bertucci Marco Pistolozzi Angela De Simone 《Analytical and bioanalytical chemistry》2010,398(1):155-166
Chirality plays a fundamental role in determining the pharmacodynamic and pharmacokinetic properties of drugs, and contributes significantly to our understanding of the mechanisms that lie behind biorecognition phenomena. Circular dichroism spectroscopy is the technique of choice for determining the stereochemistry of chiral drugs and proteins, and for monitoring and characterizing molecular recognition phenomena in solution. The role of chirality in our understanding of recognition phenomena at the molecular level is discussed here via several selected systems of interest in the drug discovery and development area. The examples were selected in order to underline the utility of circular dichroism in emerging studies of protein–protein interactions in biological context. In particular, the following aspects are discussed here: the relationship between stereochemistry and pharmacological activity—stereochemical characterization of new leads and drugs; stereoselective binding of leads and drugs to target proteins—the binding of drugs to serum albumins; conformational transitions of peptides and proteins of physiological relevance, and the stereochemical characterization of therapeutic peptides. 相似文献
146.
de Ceglie MC Musio B Affortunato F Moliterni A Altomare A Florio S Luisi R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(1):286-296
A highly stereo‐ and regioselective functionalisation of chiral non‐racemic aziridines is reported. By starting from a parent enantioenriched aziridine and finely tuning the reaction conditions, it is possible to address the regio‐ and stereoselectivity of the lithiation/electrophile trapping sequence, thereby allowing the preparation of highly enantioenriched functionalised aziridines. From chiral N‐alkyl trans‐2,3‐diphenylaziridines (S,S)‐ 1 a , b , two differently configured chiral aziridinyllithiums could be generated (trans‐ 1 a , b‐Li in toluene and cis‐ 1 a , b‐Li in THF), thus disclosing a solvent‐dependent reactivity that is useful for the synthesis of chiral tri‐substituted aziridines with different stereochemistry. In contrast, chiral aziridine (S,S)‐ 1 c showed a temperature‐dependent reactivity to give chiral ortho‐lithiated aziridine 1 c‐ ortho ‐Li at ?78 °C and α‐lithiated aziridine 1 c‐α‐Li at 0 °C. Both lithiated intermediates react with electrophiles to give enantioenriched ortho‐ and α‐functionalised aziridines. The reaction of all the lithiated aziridines with carbonyl compounds furnished useful chiral hydroxyalkylated derivatives, the stereochemistry of which was ascertained by X‐ray and NMR spectroscopic analysis. The usefulness of chiral non‐racemic functionalised aziridines has been demonstrated by reductive ring‐opening reactions furnishing chiral amines that bear quaternary stereogenic centres and chiral 1,2‐, 1,3‐ and 1,5‐aminoalcohols. It is remarkable that the solvent‐dependent reactivity observed with (S,S)‐ 1 a , b permits the preparation of both the enantiomers of amines ( 11 and ent‐ 11 ) and 1,2‐aminoalcohols ( 13 and ent‐ 13 ) starting from the same parent aziridine. Interestingly, for the first time, a configurationally stable chiral α‐lithiated aziridine ( 1 c‐α‐Li ) has been generated at 0 °C. In addition, ortho‐hydroxyalkylated aziridines have been easily converted into chiral aminoalkyl phthalans, which are useful building blocks in medicinal chemistry. 相似文献
147.
Shengyang Guan David C. Mayer Christian Jandl Sebastian J. Weishupl Angela Casini Alexander Pthig 《Molecules (Basel, Switzerland)》2021,26(15)
A new solvatomorph of [Au3(1-Methylimidazolate)3] (Au3(MeIm)3)—the simplest congener of imidazolate-based Au(I) cyclic trinuclear complexes (CTCs)—has been identified and structurally characterized. Single-crystal X-ray diffraction revealed a dichloromethane solvate exhibiting remarkably short intermolecular Au⋯Au distances (3.2190(7) Å). This goes along with a dimer formation in the solid state, which is not observed in a previously reported solvent-free crystal structure. Hirshfeld analysis, in combination with density functional theory (DFT) calculations, indicates that the dimerization is generally driven by attractive aurophilic interactions, which are commonly associated with the luminescence properties of CTCs. Since Au3(MeIm)3 has previously been reported to be emissive in the solid-state, we conducted a thorough photophysical study combined with phase analysis by means of powder X-ray diffraction (PXRD), to correctly attribute the photophysically active phase of the bulk material. Interestingly, all investigated powder samples accessed via different preparation methods can be assigned to the pristine solvent-free crystal structure, showing no aurophilic interactions. Finally, the observed strong thermochromism of the solid-state material was investigated by means of variable-temperature PXRD, ruling out a significant phase transition being responsible for the drastic change of the emission properties (hypsochromic shift from 710 nm to 510 nm) when lowering the temperature down to 77 K. 相似文献
148.
Angela Tuzi Anna Andolfi Alessio Cimmino Antonio Evidente 《Journal of chemical crystallography》2010,40(1):15-18
Abstract
The X-ray crystal structure of phyllostin (8-hydroxy-3-methyl-2-oxo-2,3,4a,5,8,8a-hexahydro-benzo[1,4]dioxine-6-carboxylic acid methyl ester) is reported. Phyllostin was recently and for the first time isolated, together with phytotoxin phyllostoxin and the phyllostictines A–D, from the culture filtrates of Phyllosticta cirsii, a fungal pathogen isolated from diseased Cirsium arvense leaves and evaluated as biocontrol agent of this noxious perennial weed. Phyllostin crystallizes in the monoclinic space group P21 with unit cell parameters: a = 8.371(2), b = 7.026(1), c = 9.918(1) ?, β = 92.013(8)°, Z = 2. The final refinement converged to R1 = 0.0530 for 1026 observed reflections having I > 2σ(I). In the molecule two trans joined six-membered rings are present. The cyclohexene ring adopts a half-chair conformation. The 2-oxo-1,4-dioxan ring adopts a distorted half-chair conformation. The relative stereochemistry of the four chiral centers turns out to be 3R,4aS,8R,8aS. In the crystal packing molecules form infinite chains through O–H···O intermolecular hydrogen bonds. Chains run along the crystallographic a axis forming layers of molecules stacking in the [0 1 0] direction. 相似文献149.
Stepped platinum surfaces can become hydrophobic when they are hydrogenated. Even though the Pt(533) and Pt(553) surfaces have similar geometries, the hydrophobicity on the deuterated surface is surprisingly different: on Pt(533) the surface is hydrophobic with water clustering at steps, whereas the entire surface is wet on Pt(553). 相似文献
150.
Minovich A Klein AE Janunts N Pertsch T Neshev DN Kivshar YS 《Physical review letters》2011,107(11):116802
We demonstrate experimentally the generation and near-field imaging of nondiffracting surface waves, plasmonic Airy beams, propagating on the surface of a gold metal film. The Airy plasmons are excited by an engineered nanoscale phase grating, and demonstrate significant beam bending over their propagation. We show that the observed Airy plasmons exhibit self-healing properties, suggesting novel applications in plasmonic circuitry and surface optical manipulation. 相似文献