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1.
Nat Commun ; 11(1): 792, 2020 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-32034155

RESUMO

Acyclic contiguous stereocenters are frequently seen in biologically active natural and synthetic molecules. Although various synthetic methods have been reported, predictable and unified approaches to all possible stereoisomers are rare, particularly for those containing non-reactive hydrocarbon substituents. Herein, a ß-boronyl group is employed as a readily accessible handle for predictable α-functionalization of enolates with either syn or anti selectivity depending on reaction conditions. Contiguous tertiary-tertiary and tertiary-quaternary stereocenters are thus accessed in generally good yields and diastereoselectivity. Based on experimental and computational studies, mechanism for syn selective alkylation is proposed, and Bpin (pinacolatoboronyl) behaves as a smaller group than most carbon-centered groups. The synthetic utility of this methodology is demonstrated by preparation of several key intermediates for bioactive molecules.

2.
Chem Sci ; 10(28): 6828-6833, 2019 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-31391905

RESUMO

An unprecedented S8-catalyzed selective triple-cleavage of bromodifluoroacetamides is disclosed for the first time. Valuable 2-amido substituted benzimidazoles, benzoxazoles and benzothiazoles were obtained in good to excellent yields in a cascade protocol in this strategy. Mechanistic studies suggested that a C2 source was generated in situ by selective cleavage of three C-X bonds, including two inert C(sp3)-F bonds on bromodifluoroacetamides, while leaving C-C bonds intact. This strategy will undoubtedly further consummate the role of halo difluoro compounds and enrich both fluorine chemistry and pharmaceutical sciences.

3.
Org Lett ; 21(13): 4924-4928, 2019 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-31074630

RESUMO

DFT calculations are used to reveal the mechanism of Brønsted-base-mediated borylation of propynols. The reaction is predicted to go through a key intermediate of alkenylboronate. Therefore, the possible pathways involve two key steps, borylation and reductive dehydroxylation. The favored pathway for the generation of the alkenylboronate intermediate involves alkoxy exchange, methoxylation, electrophilic substitution, and protonation. Then, the final product is yielded by a second alkoxy exchange, intramolecular nucleophilic attack, ß-methoxy elimination, and protonation.

4.
Front Chem ; 7: 149, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30972320

RESUMO

Density functional theory (DFT) calculations have been performed to investigate the mechanism of alkaline-earth-metal-catalyzed hydroboration of pyridines with borane. In this reaction, the active catalytic species is considered to be an alkaline earth metal hydride complex when the corresponding alkaline earth metal is used as the catalyst. The theoretical results reveal that initiation of the catalytic cycle is hydride transfer to generate a magnesium hydride complex when ß-diimine alkylmagnesium is used as a pre-catalyst. The magnesium hydride complex can undergo coordination of the pyridine reactant followed by hydride transfer to form a dearomatized magnesium pyridine intermediate. Coordination of borane and hydride transfer from borohydride to magnesium then give the hydroboration product and regenerate the active magnesium hydride catalyst. The rate-determining step of the catalytic cycle is hydride transfer to pyridine with a free energy barrier of 29.7 kcal/mol. Other alkaline earth metal complexes, including calcium and strontium complexes, were also considered. The DFT calculations show that the corresponding activation free energies for the rate-determining step of this reaction with calcium and strontium catalysts are much lower than with the magnesium catalyst. Therefore, calcium and strontium complexes can be used as the catalyst for the reaction, which could allow mild reaction conditions.

5.
Org Lett ; 21(3): 593-597, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-30633534

RESUMO

An efficient method for preparing highly functionalized chiral nonspiro-phosphonylpyrazolines via an asymmetric formal 1,3-dipolar cycloaddition reaction of α-diazomethylphosphonate with activated, acyclic α,ß-unsaturated ketones, bearing an additional nitrile electron-withdrawing group, has been developed, utilizing an in situ generated chiral silver phosphate catalyst, affording excellent stereoselectivities (up to 98% ee, 99:1 dr) and yields (up to 95%). A stepwise mechanism is proposed based upon density functional M11 calculations.

6.
J Am Chem Soc ; 141(2): 961-971, 2019 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-30543293

RESUMO

A novel chiral phosphine-urea bifunctional ligand has been developed for Cu-catalyzed asymmetric 1,3-dipolar cycloaddition of iminoesters with methacrylonitrile, a long-standing challenging substrate in asymmetric catalysis. Distortion-interaction energy analysis based on density functional theory (DFT) calculations reveals that the distortion energy plays an important role in the observed enantioselectivity, which can be attributed to the steric effect between the phosphine ligand and the dipole reactant. DFT calculations also indicate that nucleophilic addition is the enantioselectivity-determining step and hydrogen bonding between the urea moiety and methacrylonitrile assists in control of the diastereo- and enantioselectivity. By a combination of metal catalysis and organocatalysis, excellent diastereo- and enantioselectivities (up to 99:1 diastereomeric ratio, 99% enantiomeric excess) as well as good yields are achieved. A wide range of substitution patterns of both iminoester and acrylonitrile is tolerated by this catalyst system, providing access to a series of highly substituted chiral cyanopyrrolidines with up to two quaternary stereogenic centers. The synthetic utility is demonstrated by enantioselective synthesis of antitumor agent ETP69 with a pivotal nitrile pharmacophore and an all-carbon quaternary stereogenic center.

7.
Org Lett ; 20(17): 5153-5157, 2018 09 07.
Artigo em Inglês | MEDLINE | ID: mdl-30141948

RESUMO

An efficient approach to tetrasubstituted alkenylboronates via a cascade borylation/B-O elimination of propynols and B2pin2 was disclosed. A series of tetrasubstituted alkenylboronates were readily furnished with this strategy in good yields, with further transformations leading to tetrasubstituted alkenes and ß-diketones demonstrating the synthetic potential of the alkenylboronates constructed by this strategy as versatile intermediates in organic synthesis.

8.
Acta Chim Slov ; 64(3): 633-637, 2017 09.
Artigo em Inglês | MEDLINE | ID: mdl-28862301

RESUMO

Two CuI complexes based on the π-conjugated tetrathiafulvalene-annulated phenanthroline ligands (TTF-Phen, L1 and L2), [CuI(Xantphos)(L1)]BF4 (1, Xantphos = 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene) and [CuI(Binap)(L2)]BF4 (2, Binap = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl), have been synthesized. They have been fully characterized, and their photophysical and electrochemical properties are reported together with those of L1 and L2 for comparison. Both CuI complexes show metal-to-ligand charge transfer (MLCT) absorption bands, whereas the 3MLCT luminescence is strongly quenched.

9.
J Fluoresc ; 26(1): 323-31, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-26555291

RESUMO

A series of new cyclometalated btp-based iridium(III) complexes with three different ancillary ligands, Ir(btp)2(bozp) (3a), Ir(btp)2(btzp) (3b) and Ir(btp)2(izp) (3c) (btp = 2-(benzo[b]thiophen-2-yl)pyridine, bozp =2-(benzo[d]oxazol-2-yl)phenol, btzp =2-(benzo[d]thiazol-2-yl)phenol, izp = 2-(2 H-indazol-2-yl)phenol), have been synthesized and fully characterized. The crystal structure of 3b has been determined by single crystal X-ray diffraction analysis. A comparative study has been carried out for complexes 3a - 3c by UV-vis absorption spectroscopy, photoluminescence spectroscopy, cyclic voltammetry and DFT calculations. This observation illustrates that the substitution of N or S in ancillary ligand can lead to a marked bathochromic shift of absorption and emission wavelengths. The spectroscopic characterisation of these complexes has been complemented by DFT and TD-DFT calculations, supporting the assignment of (3)MLCT/(3)LC to the lowest energy excited state.


Assuntos
Irídio/química , Compostos Organometálicos/química , Piridinas/química , Teoria Quântica , Tiofenos/química , Cristalografia por Raios X , Ligantes , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/síntese química
10.
Acta Chim Slov ; 62(4): 917-22, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26680720

RESUMO

A new bis-cyclometalated iridium(III) complex [Ir(dmabt)(2)(bipy)][PF(6)] (3) (dmabt = 4-(benzo[d]thiazol-2-yl)-N,N-dimethylaniline, bipy = 2,2'-bipyridine) has been synthesized and fully characterized. The complex 3 has been determined by X-ray structure analyses which shows that the central iridium(III) ion assumes distorted octahedral geometry. The photoluminescence spectrum exhibits orange emission maximum at 612 nm with quantum yield of 17% at 298 K. The frontier molecular orbital diagrams and the spin-allowed singlet-singlet electronic transitions of 3 have been calculated with density functional theory (DFT) and time-dependent DFT (TD-DFT), and the UV-Vis spectra are discussed based on the theoretical calculations.

11.
Biosci Trends ; 8(5): 260-5, 2014 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-25382442

RESUMO

This study aims to find an optimal method for modifying the neck of dental implants for gingival attachment through in vitro investigations of the biological features of various anodised TiO2 films. The titanium sheets were divided into four groups: a control group and three test groups classified according to the anodisation voltage (Group 150 V, Group 180 V or Group 200 V).The surface microstructure and crystal structure were observed using scanning electron microscopy and X-ray diffraction. The protein adsorption ability, antibacterial activity and cell adhesion ability were tested to examine the biological properties of the materials in vitro. Microscopic grooves were observed in the control group, whereas the test groups contained numerous pores. Group 180 V and Group 200 V showed higher protein adsorption ability (p < 0.05), whereas Group 150 V and Group 180 V exhibited better antibacterial activity (p < 0.05). Higher cell concentrations of L929 were observed in Group 180V and Group 200 V than in the other two groups (p < 0.05), which indicated that the TiO2 films formed at 180 V promote protein adsorption and enhance fibroblast growth while inhibiting bacterial adhesion. These results indicate that anodisation positively affects the formation of a biological seal in the neck region of dental implants.


Assuntos
Materiais Biocompatíveis/química , Implantes Dentários/efeitos adversos , Titânio/química , Adsorção , Animais , Antibacterianos/química , Materiais Biocompatíveis/efeitos adversos , Bioengenharia , Adesão Celular , Células Cultivadas , Implantes Dentários/microbiologia , Fibroblastos/citologia , Camundongos , Microscopia Eletrônica de Varredura , Porosidade , Propriedades de Superfície , Difração de Raios X
12.
Acta Chim Slov ; 61(4): 786-91, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25551718

RESUMO

Two new pi-conjugated pyridine-based tetrathiafulvalene derivatives, 2-(2- (4,5-bis(methylthio)-1,3-dithiol-2-ylidene)-6-phenyl-[1,3]dithiolo[4,5-b][1,4]dithiin-5-yl)pyridine (2a) and 3-(2-(4,5-bis(methylthio)-1,3-dithiol-2-ylidene)-6-(pyridin-2-yl) -[1,3]dithiolo[4,5-b][1,4]dithiin-5-yl)quinoline (2b), have been synthesized and characterized by 1H NMR, elemental analysis and mass spectroscopies. The compound 2a has also been studied by X-ray crystallography and theoretical calculations using density functional theory (DFT) framework with B3LYP/6-311+G(d,p) level of theory. Its crystal structure is triclinic system, space group P1-. The unit cell dimensions are: a = 8.813(3) Å, b = 11.082(3) Å, c = 12.620(4) Å, alfa = 88.805(5)°, beta = 80.440(5)°, gama = 75.680(5)°, V = 1177.3(6) Å3, Z = 2. The molecule exhibits one classical C-H···N intermolecular hydrogen bonds, two kinds of short intermolecular S···S interactions and two types of C-H···pi supramolecular interactions.

13.
J Prosthet Dent ; 110(5): 344-8, 2013 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-24084145

RESUMO

Because of the low bone quality in the posterior maxilla, edentulism in this area often results in a resorbed osseous structure and a pneumatized maxillary sinus, which makes dental implant surgery in the posterior maxilla a challenge. Two main surgical approaches are available for the sinus lift procedure: lateral and crestal. Improvement of the maxillary sinus floor elevation technique and increase in predictability are desirable. This article describes an innovative approach to maxillary sinus floor elevation with piezoelectric surgery and hydraulic pressure for xenograft and simultaneous implant placement in situations with insufficient residual alveolar bone.


Assuntos
Matriz Óssea/transplante , Implantação Dentária Endo-Óssea/métodos , Implantes Dentários , Xenoenxertos/transplante , Piezocirurgia/métodos , Levantamento do Assoalho do Seio Maxilar/métodos , Adulto , Idoso , Aumento do Rebordo Alveolar/instrumentação , Aumento do Rebordo Alveolar/métodos , Densidade Óssea/fisiologia , Substitutos Ósseos/uso terapêutico , Tomografia Computadorizada de Feixe Cônico/métodos , Feminino , Humanos , Complicações Intraoperatórias/prevenção & controle , Masculino , Maxila/cirurgia , Pessoa de Meia-Idade , Minerais/uso terapêutico , Mucosa Nasal/diagnóstico por imagem , Pressão , Levantamento do Assoalho do Seio Maxilar/instrumentação
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