RESUMO
Achieving site selectivity in C-H functionalization reactions is a significant challenge, especially when the target C-H bond is distant from existing functional groups. Coordination of a functional group to a metal is often a key driving force and control element in many important reactions including asymmetric hydrogenation, epoxidation and lithiation. Exploitation of this effect has led to the development of a broad range of directed C-H activation reactions. However, these C-H activation methods are limited to proximal C-H bonds, which are spatially and geometrically accessible from the directing functional group. The development of meta-selective C-H functionalizations remains a significant challenge. We recently developed a U-shaped template that can be used to overcome this constraint and have shown that it can be used to selectively activate remote meta-C-H bonds. Although this approach has proved to be applicable to various substrates and catalytic transformations, the need for a covalently attached, complex template is a substantial drawback for synthetic applications. Here we report an alternative approach employing norbornene as a transient mediator to achieve meta-selective C-H activation with a simple and common ortho-directing group. The use of a newly developed pyridine-based ligand is crucial for relaying the palladium catalyst to the meta position by norbornene after initial ortho-C-H activation. This catalytic reaction demonstrates the feasibility of switching ortho-selectivity to meta-selectivity in C-H activation of the same substrate by catalyst control.
Assuntos
Carbono/química , Hidrogênio/química , Alquilação , Amidas/química , Catálise , Halogênios/química , Ligantes , Norbornanos/química , Paládio/química , Piridinas/químicaRESUMO
A fungal pigment, hypocrellin D (1), together with three known perylenequinone derivatives hypocrellin A (2), B (3) and C (4), was isolated from the fruiting bodies of Shiraia bambusicola. Its structure was elucidated on the basis of spectral data including 2D NMR experiments. Hypocrellin D (1) significantly inhibited the growth of tumor cell lines Bel-7721, A-549 and Anip-973 with IC50 values of 1.8, 8.8, 38.4 microg/ml, respectively.
Assuntos
Antibióticos Antineoplásicos/isolamento & purificação , Ascomicetos/metabolismo , Perileno/análogos & derivados , Pigmentos Biológicos/isolamento & purificação , Antibióticos Antineoplásicos/química , Antibióticos Antineoplásicos/farmacologia , Linhagem Celular Tumoral , Humanos , Perileno/química , Perileno/isolamento & purificação , Perileno/farmacologia , Pigmentos Biológicos/química , Pigmentos Biológicos/farmacologiaRESUMO
Nine new acetylenic acids, gallicynoic acids A-I ( 1- 9), have been isolated from a culture of the basidiomycete Coriolopsis gallica. The structures of 1- 9 were elucidated on the basis of spectroscopic and chemical means.
Assuntos
Alcinos/isolamento & purificação , Basidiomycota/química , Alcinos/química , China , Ésteres , Estrutura MolecularRESUMO
Four new natural products possessing vibralactone skeleton, 1,5-secovibralactone (1), vibralactone B (2), vibralactone C (3) and acetylated vibralactone (4), together with known compound vibralactone (5), had been isolated from cultures of the basidiomycete Boreostereum vibrans. The structures of 1-4 were elucidated on the basis of spectroscopic methods. The absolute configuration of 1 was suggested to be S by computational methods.
Assuntos
Basidiomycota/química , Lactonas/química , Acetilação , Cromatografia por Troca Iônica , Meios de Cultura , Etanol , Fermentação , Espectroscopia de Ressonância Magnética , Solventes , Espectrometria de Massas por Ionização por Electrospray , Espectrofotometria Infravermelho , Espectrofotometria UltravioletaRESUMO
A new phenyl-ethanediol, (1S)-(4-acetylphenyl)-1, 2-ethanediol (1), and a new natural product, (1S)-(3-ethenylphenyl)-1, 2-ethanediol (2), were isolated from the culture broth of the basidiomycete Boletus edulis together with three related known compounds, 1-(4-ethylphenyl)-1, 2-ethanediol (3), 1-(3-ethylphenyl)-1, 2-ethanediol (4) and 1-(3-formylphenyl)-ethanone (5). Their structures were elucidated by spectroscopic methods including extensive 2D-NMR techniques.