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1.
Molecules ; 26(7)2021 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-33804954

RESUMO

A new class of bis-cyclometalated iridium(III) catalysts containing two inert cyclometalated 6-tert-butyl-2-phenyl-2H-indazole bidentate ligands or two inert cyclometalated 5-tert-butyl-1-methyl-2-phenylbenzimidazoles is introduced. The coordination sphere is complemented by two labile acetonitriles, and a hexafluorophosphate ion serves as a counterion for the monocationic complexes. Single enantiomers of the chiral-at-iridium complexes (>99% er) are obtained through a chiral-auxiliary-mediated approach using a monofluorinated salicyloxazoline and are investigated as catalysts in the enantioselective conjugate addition of indole to an α,ß-unsaturated 2-acyl imidazole and an asymmetric Nazarov cyclization.

2.
Elife ; 102021 04 06.
Artigo em Inglês | MEDLINE | ID: mdl-33820602

RESUMO

Bacteria carry antibiotic resistant genes on movable sections of DNA that allow them to select the relevant genes on demand.


Assuntos
Bactérias , Integrons , Antibacterianos/farmacologia , Bactérias/efeitos dos fármacos , Bactérias/genética , Resistência Microbiana a Medicamentos/efeitos dos fármacos
3.
Artigo em Inglês | MEDLINE | ID: mdl-33270000

RESUMO

Transposons are genetic elements that change their intracellular genomic position by transposition and are spread horizontally between bacteria when located on plasmids. It was recently discovered that transposition from fully heterologous DNA also occurs in the course of natural transformation. Here, we characterize the molecular details and constraints of this process using the replicative transposon Tn1 and the naturally competent bacterium Acinetobacter baylyi. We find that chromosomal insertion of Tn1 by transposition occurs at low but detectable frequencies and preferably around the A. baylyi terminus of replication. We show that Tn1 transposition is facilitated by transient expression of the transposase and resolvase encoded by the donor DNA. RecA protein is essential for the formation of a circular, double-stranded cytoplasmic intermediate from incoming donor DNA, and RecO is beneficial but not essential in this process. Absence of the recipient RecBCD nuclease stabilizes the double-stranded intermediate. Based on these results, we suggest a mechanistic model for transposition during natural transformation.

4.
Org Lett ; 22(16): 6653-6656, 2020 08 21.
Artigo em Inglês | MEDLINE | ID: mdl-32806187

RESUMO

A ring-closing aminooxygenation of alkenes with N-benzoyloxycarbamates occurs with very high diastereoselectivity (typically >20:1 d.r.) and very high enantioselectivity (up to 99% ee). The reaction is catalyzed by a recently developed chiral-at-metal ruthenium complex at catalyst loadings of 0.5-1.0 mol %. The reaction is proposed to proceed through a ruthenium nitrenoid intermediate that depending on the nature of the substrate undergoes either an aminooxygenation (1,2-disubstituted alkenes) or stops at the stage of the aziridination (trisubstituted alkenes), which can then be ring opened with benzoic acid. The resulting chiral cyclic carbamates can be hydrolyzed under basic conditions to provide versatile chiral 2-amino-1,3-diols with vicinal stereocenters.

5.
Org Lett ; 22(15): 6127-6131, 2020 08 07.
Artigo em Inglês | MEDLINE | ID: mdl-32662272

RESUMO

An enantioselective total synthesis of the natural product (-)-preussochromone A is reported. The tricyclic thiopyrane skeleton could be assembled via Lewis acid-mediated cycloisomerization of a precursor with a 2-thiochromenone substructure and an α-ketoester moiety. The chromenone core was synthesized by cyclization of a dithioketene acetal and oxidation to a 2-sulfonylchromenone to set up the subsequent thia-Michael-retro-Michael addition of an aliphatic thiol producing the highly oxidized side chain.

6.
Acta Crystallogr E Crystallogr Commun ; 76(Pt 4): 477-480, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32280487

RESUMO

The title crystal structure is assembled from the superposition of two mol-ecular structures, (E)-1-(5-chloro-thio-phen-2-yl)-3-(3-methyl-thio-phen-2-yl)prop-2-en-1-one, C12H9ClOS2 (93%), and (Z)-1-(5-chloro-thio-phen-2-yl)-3-(3-methyl-thio-phen-2-yl)prop-1-en-1-ol, C12H11ClOS2 (7%), 0.93C12H9ClOS2·0.07C12H11ClOS2. Both were obtained from the reaction of 3-methyl-thio-phene-2-carbaldehyde and 1-(5-chloro-thio-phen-2-yl)ethanone. In the extended structure of the major chalcone component, mol-ecules are linked by a combination of C-H⋯O/S, Cl⋯Cl, Cl⋯π and π-π inter-actions, leading to a compact three-dimensional supra-molecular assembly.

7.
Chem Sci ; 10(37): 8634-8641, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31803437

RESUMO

The 8-aminoquinoline (8AQ) directed C(sp3)-H functionalization was applied in the synthesis of ß-arylated tryptophan derivatives. The laborious protecting group reorganization towards α-amino acids compatible for solid phase peptide synthesis (SPPS) was cut short by the transformation of the directing group into an activated amide, which was either used directly in peptide coupling or in the gram scale synthesis of storable Fmoc-protected amino acids for SPPS. In this work, directed C-H activation and nonplanar amide chemistry complement each other for the synthesis of hybrids between phenylalanine and tryptophan with restricted side chain mobility.

8.
J Am Chem Soc ; 141(48): 19048-19057, 2019 12 04.
Artigo em Inglês | MEDLINE | ID: mdl-31751132

RESUMO

A new class of chiral ruthenium catalysts is introduced in which ruthenium is cyclometalated by two 7-methyl-1,7-phenanthrolinium heterocycles, resulting in chelating pyridylidene remote N-heterocyclic carbene ligands (rNHCs). The overall chirality results from a stereogenic metal center featuring either a Λ or Δ absolute configuration. This work features the importance of the relative metal-centered stereochemistry. Only the non-C2-symmetric chiral-at-ruthenium complexes display unprecedented catalytic activity for the intramolecular C(sp3)-H amidation of 1,4,2-dioxazol-5-ones to provide chiral γ-lactams with up to 99:1 er and catalyst loadings down to 0.005 mol % (up to 11 200 TON), while the C2-symmetric diastereomer favors an undesired Curtius-type rearrangement. DFT calculations elucidate the origins of the superior C-H amidation reactivity displayed by the non-C2-symmetric catalysts compared to related C2-symmetric counterparts.

9.
Acta Crystallogr E Crystallogr Commun ; 75(Pt 9): 1357-1361, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-31523466

RESUMO

The synthesis, crystal structure and structural motif of two thio-phene-based cyano-acrylate derivatives, namely, ethyl (E)-2-cyano-3-(3-methyl-thio-phen-2-yl)acrylate (1), C11H11NO2S, and ethyl (E)-2-cyano-3-(thio-phen-2-yl)acrylate (2), C10H9NO2S, are reported. Derivative 1 crystallized with two independent molecules in the asymmetric unit, and derivative 2 represents a new monoclinic (C2/m) polymorph. The mol-ecular conformations of 1 and the two polymorphs of 2 are very similar, as all non-H atoms are planar except for the methyl of the ethyl groups. The inter-molecular inter-actions and crystal packing of 1 and 2 are described and compared with that of the reported monoclinic (C2/m) polymorph of derivative 2 [Castro Agudelo et al. (2017 ▸). Acta Cryst. E73, 1287-1289].

10.
Chemistry ; 25(67): 15333-15340, 2019 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-31541505

RESUMO

A new class of bis-cyclometalated rhodium(III) catalysts containing two inert cyclometalated 6-tert-butyl-2-phenyl-2H-indazole ligands and two labile acetonitriles is introduced. Single enantiomers (>99 % ee) were obtained through a chiral-auxiliary-mediated approach using a monofluorinated salicyloxazoline. The new chiral-at-metal complex is capable of catalyzing the visible-light-induced enantioselective α-cyanoalkylation of 2-acyl imidazoles in which it serves a dual function as the chiral Lewis acid catalyst for the asymmetric radical chemistry and at the same time as the photoredox catalyst for the visible-light-induced redox chemistry (up to 80 % yield, 4:1 d.r., and 95 % ee, 12 examples).

11.
Angew Chem Int Ed Engl ; 58(41): 14462-14466, 2019 10 07.
Artigo em Inglês | MEDLINE | ID: mdl-31469211

RESUMO

3-(2-Formylphenyl)-1-pyrazol-1-yl-propenones undergo an asymmetric photorearrangement to benzo[d]cyclopropa[b]pyranones with up to >99 % ee, which is catalyzed by a bis-cyclometalated rhodium catalyst in the presence of visible light. Mechanistic experiments and DFT calculations support a mechanism in which a photoexcited catalyst/substrate complex triggers an intramolecular hydrogen-atom transfer followed by a highly stereocontrolled hetero-Diels-Alder reaction. In this reaction scheme, the rhodium catalyst fulfills multiple functions by 1) enabling visible-light π→π* excitation of the catalyst-bound enone substrate, 2) facilitating the hydrogen-atom transfer, and 3) providing the asymmetric induction for the hetero-Diels-Alder reaction.

12.
Org Lett ; 21(11): 4365-4369, 2019 06 07.
Artigo em Inglês | MEDLINE | ID: mdl-31140814

RESUMO

Methyl (α-naphthyl) acrylates bearing an ortho-substituent with a hydrogen atom produce naphthocyclobutenes upon Ir(Fppy)3-mediated photosensitization. This reaction can be described as a carbon analogue of the Norrish-Yang reaction: upon triplet excitation of the acrylate a 1,5-HAT results in a 1,4-diradical which forms the cyclobutene. Diastereoselectivities up to >20:1 were observed for the ring-closure reaction.

13.
Org Lett ; 21(11): 4374-4377, 2019 06 07.
Artigo em Inglês | MEDLINE | ID: mdl-31135164

RESUMO

An efficient, stereoselective synthesis of the natural product (-)-preussochromone D is reported. The tricyclic skeleton was assembled by a diastereoselective intramolecular aldol addition of a chromanone to an α-ketoester. Further key steps are an asymmetric 1,4-addition of diisopropenyl zinc to a chromenone and an intermolecular diastereoselective aldol addition of methyl diazoacetate to an aldehyde. The diazo group was oxidized to generate the α-ketoester while oxidative side reactions at the chromanone could be prevented by the use of a difluoromethyl ether as a protecting group.

14.
J Am Chem Soc ; 141(11): 4569-4572, 2019 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-30839201

RESUMO

A new class of chiral iron catalysts is introduced that contains exclusively achiral ligands with the overall chirality being the result of a stereogenic iron center. Specifically, iron(II) is cis-coordinated to two N-(2-pyridyl)-substituted N-heterocyclic carbene (PyNHC) ligands in a bidentate fashion in addition to two monodentate acetonitriles, and the dicationic complex is complemented by two hexafluorophosphate ions. Depending on the helical twist of the PyNHC ligands, the metal center adopts either a Λ or Δ absolute configuration. Importantly, the two PyNHC ligands are constitutionally and configurationally inert, while the two acetonitriles are labile and allow asymmetric transition metal catalysis. This is demonstrated with an enantioselective Cannizzaro reaction (96% yield, 88% ee) and an asymmetric Nazarov cyclization (89% yield, >20:1 dr, 83% ee).

15.
Org Lett ; 21(3): 785-788, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-30648874

RESUMO

A stereoselective synthetic approach to the natural product (+)-nivetetracyclate A is reported. The tetracyclic skeleton was assembled in a convergent manner by an alkylation to a diarylmethane and subsequent Friedel-Crafts acylation. Further key steps are an asymmetric Sharpless epoxidation and the boron trifluoride-mediated diastereoselective rearrangement of an epoxy alcohol to a ß-hydroxy aldehyde. Optimized timing for the deprotection step and the chemo- and stereoselective Noyori -transfer hydrogenation of a 1,4-diketone allowed the late stage introduction of the C4 stereocenter.

16.
Chem Sci ; 10(41): 9483-9492, 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-32055322

RESUMO

A new generation of carbodiphosphoranes (CDPs), incorporating pyrrolidine, tetramethylguanidine, or tris(dimethylamino)phosphazene as substituents is introduced as the most powerful class of non-ionic carbon superbases on the basicity scale to date. The synthetic approach as well as NMR spectroscopic and structural characteristics in the free and protonated form are described. Investigation of basicity in solution and in the gas phase by experimental and theoretical means provides the to our knowledge first reported pK BH + values for CDPs in the literature and suggest them as upper tier superbases.

17.
Angew Chem Int Ed Engl ; 58(4): 1088-1093, 2019 01 21.
Artigo em Inglês | MEDLINE | ID: mdl-30475437

RESUMO

An enantioselective ring-closing C(sp3 )-H amination of 2-azidoacetamides is catalyzed by a chiral-at-metal ruthenium complex and provides chiral imidazolidin-4-ones in 31-95 % yield, with enantioselectivities of up to 95 % ee, and at catalyst loadings down to 0.1 mol % (turnover number (TON)=740). To our knowledge, this is the first example of a highly enantioselective C(sp3 )-H amination with aliphatic azides. Mechanistic experiments reveal the importance of the amide group, which presumably enables initial bidentate coordination of the 2-azidoacetamides to the catalyst. DFT calculations show that the transition state leading to the major enantiomer features a better steric fit and favorable π-π stacking between the substrate and the catalyst framework.

18.
ChemSusChem ; 12(1): 320-325, 2019 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-30324685

RESUMO

Chiral-at-metal bis-cyclometalated iridium(III) complexes are introduced as a new class of chiral catalysts for the reaction of epoxides with CO2 to form cyclic carbonates under conditions of kinetic resolution. Reactions are typically performed at room temperature in the presence of 1 mol % of iridium catalyst and 1.5 mol % of tetraethylammonium bromide as the nucleophilic cocatalyst to provide selectivity factors of up to 16.6. A variety of monosubstituted epoxides, including styrene epoxide, epoxides with aliphatic side chains, glycidyl ethers, and a glycidyl ester, are found to be suitable substrates. No polymerization side reaction is observed for any of the investigated substrates.

19.
Org Biomol Chem ; 16(35): 6586-6599, 2018 09 11.
Artigo em Inglês | MEDLINE | ID: mdl-30168830

RESUMO

Herein, we present a series of isomerically pure, peripherally alkyl substituted, soluble and low aggregating azaphthalocyanines as well as their new, smaller hybrid homologues, azasubphthalocyanines. The focus lies on the effect of the systematically increasing number of aza building blocks [-N[double bond, length as m-dash]] replacing the non-peripheral [-CH[double bond, length as m-dash]] units and their influence on the physical and photophysical properties of these chromophores. The absolute and relative HOMO-LUMO energies of azaphthalocyanines were analyzed using UV-Vis and CV and compared to the density functional theory calculations (B3LYP, TD-DFT). The lowering of the HOMO level is revealed as the determining factor for the trend in the adsorption energies by electronic structure analysis. Crystals of substituted subphthalocyanines, N2-Pc*H2 and N4-[Pc*Zn·H2O], were obtained out of DCM. For the synthesis of the valuable tetramethyltetralin phthalocyanine building block a new highly efficient synthesis involving a nearly quantitative CoII catalyzed aerobic autoxidation step is introduced replacing inefficient KMnO4/pyridine as the oxidant.

20.
Chemistry ; 24(67): 17686-17690, 2018 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-30264911

RESUMO

Disclosed herein is a visible light mediated cyclization of methyl (α-naphthyl) acrylates and heteroaromatic analogues yielding substituted acenaphthenes and azaacenaphthenes. This highly functional-group-tolerant transformation was put to the test in an enantioselective formal synthesis of delavatine A. Mechanistic details were elucidated by DFT-calculations revealing an unusual intramolecular H-transfer mediated by a primary amine. The generality of this transformation enables a novel synthetic strategy of five membered ring annulation at an advanced stage, allowing reliance upon naphthalene chemistry up to the point of acenaphthene construction.

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