RESUMO
Electron-rich aryl bromides are rapidly converted to the corresponding lithium triarylmagnesiates with (n-Bu)3MgLi, which undergo efficient nickel-catalyzed Kumada-Corriu cross-coupling reactions with a variety of aryl and alkenyl bromides, chlorides, tosylates, and triflates.
RESUMO
Concise and protective group free syntheses of (±)-hamigeran B and (±)-4-bromohamigeran B are reported. The key reactions include an enone migration and a Diels-Alder cyclization to provide the requisite tricyclic skeleton.
Assuntos
Naftoquinonas/síntese química , Animais , Ciclização , Estrutura Molecular , Naftoquinonas/química , Poríferos/química , EstereoisomerismoRESUMO
A scalable synthesis of a potent renin inhibitor (1) is described. The absolute stereochemistry is set via an unprecedented diastereoselective Dieckmann cyclization directed by a remote chiral protecting group. This transformation enables preparation of chiral 1,3-[3.3.1]-diazabicyclononenes by desymmetrization of alkyl-esters, with selectivities ranging from 4 to 17:1.
Assuntos
Compostos Azo/síntese química , Compostos Bicíclicos Heterocíclicos com Pontes/síntese química , Inibidores de Proteases/síntese química , Inibidores de Proteases/farmacologia , Renina/antagonistas & inibidores , Tolueno/análogos & derivados , Compostos Azo/química , Compostos Bicíclicos Heterocíclicos com Pontes/química , Cristalografia por Raios X , Ciclização , Conformação Molecular , Estrutura Molecular , Inibidores de Proteases/química , Estereoisomerismo , Tolueno/síntese química , Tolueno/química , Tolueno/farmacologiaRESUMO
Cytochrome P450 monooxygenases (P450s) are important enzymes for generating some of the enormous structural diversity of plant terpenoid secondary metabolites. In conifers, P450s are involved in the formation of a suite of diterpene resin acids (DRAs). Despite their important role in constitutive and induced oleoresin defense, a P450 gene of DRA formation has not yet been identified. By using phylogenetic cluster analysis of P450-like ESTs from loblolly pine (Pinus taeda), functional cDNA screening in yeast (Saccharomyces cerevisiae), and in vitro enzyme characterization, we cloned and identified a multifunctional and multisubstrate cytochrome P450 enzyme, CYP720B1 [abietadienol/abietadienal oxidase (PtAO)]. PtAO catalyzes an array of consecutive oxidation steps with several different diterpenol and diterpenal intermediates in loblolly pine DRA biosynthesis. Recombinant PtAO oxidized the respective carbon 18 of abietadienol, abietadienal, levopimaradienol, isopimara-7,15-dienol, isopimara-7,15-dienal, dehydroabietadienol, and dehydroabietadienal with apparent Michaelis-Menten (K(m)) values of 0.5-5.3 muM. PtAO expressed in yeast also catalyzed in vivo oxidation of abietadiene to abietic acid, but with activity much lower than with abietadienol or abietadienal. Consistent with a role of DRAs in conifer defense, PtAO transcript levels increased upon simulated insect attack using methyl jasmonate treatment of loblolly pine. The multisubstrate, multifunctional P450 diterpene oxidase PtAO, in concert with expression of a family of single-product and multiproduct diterpene synthases, allows for formation of a diverse suite of DRA defense metabolites in long-lived conifers.