Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 116
Filtrar
1.
Chem Commun (Camb) ; 2021 Feb 23.
Artículo en Inglés | MEDLINE | ID: mdl-33620365

RESUMEN

By taking advantage of benzylidene succinimides as a new class of 3C synthons, a highly diastereo- and enantioselective tandem Mannich reaction/transamidation has been established by reacting them with cyclic trifluoromethyl N-acyl ketimines. Using a Cinchona alkaloid-derived squaramide as the catalyst, the tandem reaction proceeded smoothly under mild conditions and afforded a range of F3C-containing chiral polycyclic dihydroquinazolinones with excellent results (up to 99% yield, all cases >20 : 1 dr, up to 99% ee).

2.
J Org Chem ; 86(3): 2534-2544, 2021 Feb 05.
Artículo en Inglés | MEDLINE | ID: mdl-33423494

RESUMEN

A highly diastereo- and enantioselective cyclopropanation reaction of 3-acylcoumarins with 3-halooxindoles catalyzed by an organocatalyst through a [2 + 1] Michael/intramolecular cyclization process was developed. This scenario provides a facile strategy to access spirooxindole-cyclopropa[c]coumarin compounds bearing three continuous stereocenters, including two vicinal quaternary all-carbon stereocenters with high to excellent diastereo- and enantioselectivities. The HRMS study revealed the vital importance of the ammonium ylide intermediate in the catalytic process.

3.
J Org Chem ; 86(2): 1779-1788, 2021 Jan 15.
Artículo en Inglés | MEDLINE | ID: mdl-33377785

RESUMEN

An efficient decarboxylative [3 + 2] annulation reaction of ethynylethylene carbonates and azlactones has been developed with a copper salt as catalyst. This practical methodology gives access to a diverse library of γ-butyrolactones bearing α,ß-two vicinal quaternary carbon centers in good to high yields with good levels of diastereoselectivities (up to 98% yield, >95:5 dr). Preliminary trials on enantioselective variant with a chiral PyBox ligand provided chiral products in up to 71% ee. This synthetic method features mild reaction conditions, broad functional group tolerance, large-scale synthesis, and versatile products transformation. A plausible catalytic cycle for the protocol is proposed based on previous related studies and our experimental observations.

5.
Shanghai Kou Qiang Yi Xue ; 29(3): 312-315, 2020 Jun.
Artículo en Chino | MEDLINE | ID: mdl-33043351

RESUMEN

PURPOSE: To compare the aesthetic effects of all-ceramic micro-veneer and minimally invasive ultra-thin veneer in repairing deformed anterior teeth. METHODS: One hundred and twenty patients with deformed anterior teeth were selected for aesthetic restoration. According to the patient's personal condition, a suitable repair protocol was selected. Patients in the experimental group (60 cases) were repaired with all-ceramic micro-adhesive surface, while patients in the control group (60 cases) were treated with minimally invasive ultra-thin veneer. The US Public Health Administration's Evaluation Criteria (USPHS) scores were recorded and compared 6 months, 12 months, and 24 months after restoration. Statistical analysis was performed using SPSS 25.0 software package. RESULTS: There was no significant difference in the integrity, color, marginal closeness, translucency and marginal staining of the restorations between the two groups 24 months after operation (P>0.05). The satisfaction rate of the aesthetics of the experimental group was significantly lower than that of the control group (71.60% vs 93.83%, P<0.05). The incidence of complications such as broken, detached and secondary caries during the follow-up period was significantly lower in the experimental group than in the control group (1.23% vs 11.11%, P<0.05). CONCLUSIONS: The results showed that there is no significant difference in the success rate between the two methods. All-ceramic micro-veneer technique has good long-term effect, fewer complications, easy to collapse and stain the lip margin, but it has a small amount of teeth preparation and a low incidence of pulpitis in the later period. Minimally invasive super-thin veneer has high aesthetic value, so it is necessary to choose appropriate aesthetic repair methods according to the patients' needs.


Asunto(s)
Porcelana Dental , Coronas con Frente Estético , Cerámica , Color , Estética Dental , Humanos
6.
Chem Commun (Camb) ; 56(87): 13449-13452, 2020 Nov 11.
Artículo en Inglés | MEDLINE | ID: mdl-33043913

RESUMEN

A bifunctional thiourea-catalyzed asymmetric tandem α-functionalization/1,3-proton shift reaction of benzylidene succinimides with ß-trifluoromethyl enones has been developed. A series of F3C-containing chiral Rauhut-Currier type products were obtained in moderate to high yields (up to 98%) with excellent enantioselectivities (up to >99% ee). This represents the first example of benzylidene succinimides undergoing tandem α-functionalization/1,3-proton shift in catalytic enantioselective transformation.

7.
Chem Commun (Camb) ; 56(82): 12363-12366, 2020 Oct 21.
Artículo en Inglés | MEDLINE | ID: mdl-32930199

RESUMEN

The first organocatalytic diastereo- and enantioselective tandem sulfa-Michael/aldol reaction of 2-mercaptoindole-3-carbaldehydes and 2-mercaptobenzaldehydes with benzo[b]thiophene sulfones was developed. With multiple hydrogen-bonding thiourea as a catalyst, a wide range of polycyclic dihydrothiopyran-fused benzosulfolanes were smoothly obtained with excellent results (up to 99% yield, >20 : 1 dr and 99% ee) under mild reaction conditions.

8.
J Org Chem ; 85(18): 11812-11821, 2020 Sep 18.
Artículo en Inglés | MEDLINE | ID: mdl-32856456

RESUMEN

An unprecedented [4 + 2] annulation reaction between in situ formed azoalkenes and azlactones has been developed. This reaction provides a facile access to an array of 4,5-dihydropyridazin-3(2H)-one derivatives, which are very promising in medicinal applications as potential biologically active candidates. Notably, these dihydropyridazinones could also be synthesized via a one-pot reaction protocol by using the in situ formed azlactones from N-acyl amino acids and in situ generated azoalkenes from α-halogeno hydrazones. The potential applications of the methodology were also demonstrated by gram-scale experiments and the versatile conversions of the products into other nitrogen-containing compounds.

9.
Org Lett ; 22(18): 7088-7093, 2020 09 18.
Artículo en Inglés | MEDLINE | ID: mdl-32857519

RESUMEN

The first catalytic enantioselective dearomatization/rearomatization of 2-nitroindoles triggered by the Michael addition of 3-monosubstituted oxindoles was established. A wide range of 3-indolyl-3'-alkyloxindoles (up to 99% yield, 97% ee) and 3-indolyl-3'-aryloxindoles (up to 95% yield, 99% ee) were obtained by using an organocatalyst. This method provides an unprecedented strategy to access structurally diverse 3,3'-disubstituted oxindoles bearing a sterically congested triaryl-containing all-carbon quaternary stereocenter. The utility of this approach was verified by the formal synthesis of cyclotryptamine alkaloids.

10.
Virus Res ; 288: 198138, 2020 Oct 15.
Artículo en Inglés | MEDLINE | ID: mdl-32827625

RESUMEN

Human astroviruses (HAstVs) were first identified in 1975 and can be classified into three clades: classic HAstVs (HAstV 1-8), MLB (MLB1-3) and VA (VA1-5), with MLB and VA were newly identified. Recombination and a high mutation rate make HAstV as one of the rapidly evolving infectious agents. This study reported a novel identified recombinant human astrovirus (Y/1-CHN) and its long existence in two immunocompromised patients with diarrhea following allogeneic hematopoietic stem cell transplantation (allo-HSCT). The identified Yu/1-CHN genome contains 6801 base pairs encoding three open reading frames, with ORF1a best hit to the HAstV1 (Pune strain, 97 % nucleotide identity), while ORF1b and ORF2 best hit to HAstV-5 (DL30 strain, 99 % nucleotide identity). Possible recombination breakpoint was predicted to be located in the boundary of ORF1a and ORF1b. Different quasispecies were found in the host, and the dN/dS ratios of the S and P domains were determined to be 1.189 and 1.444, respectively, suggesting a positive selection existed. Fecal samples collected in different clinical phases from the two patients were all positive for Yu/1-CHN, suggesting a long existence of the virus in the host. It was indicated that immunocompromised patients may a reservoir for astrovirus, their excreta should be monitored even after discharge from hospital.

11.
Org Biomol Chem ; 18(24): 4560-4565, 2020 Jun 24.
Artículo en Inglés | MEDLINE | ID: mdl-32495795

RESUMEN

A catalyst-free and controllable reaction of isatin-derived para-quinone methides with sulfur ylides was developed. This protocol enables the divergent synthesis of two different valuable oxindole derivatives with a broad substrate scope and high stereoselectivities (up to >20 : 1 dr and only the (Z)-configuration).

12.
Artículo en Inglés | MEDLINE | ID: mdl-32394631

RESUMEN

A novel strategy for asymmetric Shono-type oxidative cross-coupling has been developed by merging copper catalysis and electrochemistry, affording C1-alkynylated tetrahydroisoquinolines with good to excellent enantioselectivity. The use of TEMPO as a co-catalytic redox mediator is crucial not only for oxidizing a tetrahydroisoquinoline to an iminium ion species but also for decreasing the oxidation potential of the reaction. A novel bisoxazoline ligand is also reported.

13.
Org Lett ; 22(8): 3114-3118, 2020 04 17.
Artículo en Inglés | MEDLINE | ID: mdl-32255357

RESUMEN

A sequential [4 + 2]/[2 + 1] annulation of α-aryl vinylsulfoniums with 2-aminochalcones and 2-(2-aminobenzylidene)-1H-indene-1,3(2H)-dione is reported that affords a series of cyclopropane-fused tetrahydroquinolines. The salient features of this novel and practical transformation include high efficiency, transition-metal-free nature, operational simplicity, and outstanding functional group tolerance.

14.
Chem Commun (Camb) ; 56(17): 2586-2589, 2020 Feb 28.
Artículo en Inglés | MEDLINE | ID: mdl-32016206

RESUMEN

An efficient enantioselective dearomatization of 2-nitrobenzofurans was realized via an organocatalyzed one-step Michael addition process. This method provides a facile strategy to access a range of structurally diverse 3,3'-disubstituted oxindoles, which feature an intriguing combination of two privileged motifs including 3-pyrrolyl-substituted-oxindoles and 2,3-dihydrobenzofurans substructures, in excellent results.

15.
Org Biomol Chem ; 18(5): 845-850, 2020 02 07.
Artículo en Inglés | MEDLINE | ID: mdl-31932837

RESUMEN

Coumarin-3-formylpyrazoles have been synthesized and applied as 3-carbon synthons in reaction with 3-hydroxyoxindoles by using DABCO as the catalyst. A range of structurally diverse spiro-fused pentacyclic spirooxindoles, bearing a spirooxindole-γ-lactone and a 3,4-dihydrocoumarin substructure, could be smoothly obtained in good to excellent yields (up to 99%) with excellent diastereoselectivities (all cases >20 : 1 dr). The asymmetric version of this tandem reaction was preliminarily investigated by using chiral organocatalysts.

16.
J Asian Nat Prod Res ; 22(9): 850-863, 2020 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-31345059

RESUMEN

Xanthohumol (XN) exerts a specific cytotoxicity in B16-F10 melanoma cells with cytoplasmic vacuoles formation. Further investigation showed XN inhibited cell proliferation in a time- and dose-dependent manner along with down-regulation of mitogen-activated protein kinase and up-regulation of the endoplasmic reticulum (ER) stress marker Bip, CHOP and protein ubiquitination, which was relieved by the ER-stress inhibitor 4-PBA. Whereas no early apoptosis characteristics was identified during XN induced cell death. [Formula: see text].


Asunto(s)
Estrés del Retículo Endoplásmico , Propiofenonas , Animales , Apoptosis , Muerte Celular , Línea Celular Tumoral , Flavonoides , Ratones , Estructura Molecular , Factor de Transcripción CHOP
17.
Chem Commun (Camb) ; 56(3): 439-442, 2020 Jan 02.
Artículo en Inglés | MEDLINE | ID: mdl-31825420

RESUMEN

An efficient asymmetric [4+2] cycloaddition of 1-((2-aryl)vinyl)naphthalen-2-ols and in situ generated ortho-quinone methides with chiral phosphoric acid as the catalyst was developed. This reaction enables the highly enantioselective synthesis of chiral polysubstituted chromanes bearing multiple contiguous stereogenic centers in excellent yields and stereoselectivities (up to 99% yield, >95 : 5 dr and >99% ee).

18.
Chem Commun (Camb) ; 55(58): 8478-8481, 2019 Jul 16.
Artículo en Inglés | MEDLINE | ID: mdl-31268101

RESUMEN

A highly enantioselective aza-Friedel-Crafts reaction of structurally new ketimines with indoles and pyrrole is developed by using a chiral phosphoric acid as the catalyst. This protocol enables the first enantioselective synthesis of isoquinoline-1,3(2H,4H)-dione derivatives in good to excellent yields (up to 99% yield) and excellent enantioselectivities (up to >99% ee).

19.
Chem Commun (Camb) ; 55(63): 9327-9330, 2019 Aug 14.
Artículo en Inglés | MEDLINE | ID: mdl-31313770

RESUMEN

A highly stereoselective sequential vinylogous aldol reaction/transesterification of methyl-substituted olefinic butyrolactones and isatins was developed. With this developed protocol, a series of chiral spirocyclic oxindole-dihydropyranones were obtained in good to excellent yields (73-99%) and enantioselectivities (71-97% ee).

20.
Org Lett ; 21(14): 5452-5456, 2019 Jul 19.
Artículo en Inglés | MEDLINE | ID: mdl-31251636

RESUMEN

Organocatalytic asymmetric dearomatization of 3-nitroindoles and 3-nitrobenzothiophenes by reaction with ethyl 4-mercapto-2-butenoate has been developed. A range of chiral tetrahydrothiopheneindolines and tetrahydrothiophenebenzothiophenes bearing three contiguous stereocenters are obtained in high yields with good diastereoselectivities and excellent enantioselectivities. This is the first example of thiol-triggered catalytic asymmetric dearomatization of 3-nitroindoles and 3-nitrobenzothiophenes.

SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA
...