RESUMO
The wobble uridine of certain bacterial and mitochondrial tRNAs is modified, at position 5, through an unknown reaction pathway that utilizes the evolutionarily conserved MnmE and GidA proteins. The resulting modification (a methyluridine derivative) plays a critical role in decoding NNG/A codons and reading frame maintenance during mRNA translation. The lack of this tRNA modification produces a pleiotropic phenotype in bacteria and has been associated with mitochondrial encephalomyopathies in humans. In this work, we use in vitro and in vivo approaches to characterize the enzymatic pathway controlled by the Escherichia coli MnmE*GidA complex. Surprisingly, this complex catalyzes two different GTP- and FAD-dependent reactions, which produce 5-aminomethyluridine and 5-carboxymethylamino-methyluridine using ammonium and glycine, respectively, as substrates. In both reactions, methylene-tetrahydrofolate is the most probable source to form the C5-methylene moiety, whereas NADH is dispensable in vitro unless FAD levels are limiting. Our results allow us to reformulate the bacterial MnmE*GidA dependent pathway and propose a novel mechanism for the modification reactions performed by the MnmE and GidA family proteins.
Assuntos
Proteínas de Escherichia coli/metabolismo , Escherichia coli/enzimologia , GTP Fosfo-Hidrolases/metabolismo , RNA de Transferência/metabolismo , Uridina/análogos & derivados , Biocatálise , Cromatografia Líquida de Alta Pressão , Cromatografia em Camada Fina , Escherichia coli/genética , Proteínas de Escherichia coli/genética , Evolução Molecular , Flavina-Adenina Dinucleotídeo/metabolismo , GTP Fosfo-Hidrolases/genética , Glicina/metabolismo , Complexos Multienzimáticos/metabolismo , NAD/metabolismo , Transferases de Grupo de Um Carbono , Compostos de Amônio Quaternário/metabolismo , RNA de Transferência/química , RNA de Transferência de Lisina/química , RNA de Transferência de Lisina/metabolismo , Uridina/biossíntese , Uridina/químicaRESUMO
A small library of compounds with an oxa(thia)zole scaffold and structural diversity in both positions 2 and 5 has been synthesized. Double acylation of a protected glycine affords intermediate alpha-amido-beta-ketoesters, which in turn can be dehydrated to afford 1,3-oxazoles or reacted with Lawesson's reagent to furnish 1,3-thiazoles. This procedure was designed with its adaptation to fluorous techniques in mind. Thus, when a protected glycine with a fluorous tag in the ester moiety is used as a starting material, the synthesis can be easily completed without column chromatography purification of intermediate compounds with good to excellent yields, thus affording a suitable entry to the preparation of small libraries of these bioactive compounds. The prepared oxa(thia)zoles were assayed for their antibacterial activity, and several of them were active against Staphylococcus aureus.
Assuntos
Antibacterianos/síntese química , Azóis/síntese química , Bibliotecas de Moléculas Pequenas/síntese química , Antibacterianos/farmacologia , Azóis/farmacologia , Azóis/uso terapêutico , Avaliação Pré-Clínica de Medicamentos , Testes de Sensibilidade Microbiana , Sondas Moleculares/síntese química , Soluções , Staphylococcus aureus/efeitos dos fármacosRESUMO
A range of partially modified retro (PMR) psi[NHCH(2)] peptide mimetics containing a hydrolytically stable CH(2)CH(CF(3))CO unit have been synthesized. The first kind of peptidomimetics is obtained from the highly efficient aza-Michael addition of different amines to alpha-trifluoromethyl acrylamide acceptors. Subsequent deprotection of the amino group furnishes the key common intermediate for the synthesis of other families of peptidomimetics: dipeptides, tripeptides, peptidomimetics containing a urea moiety, and structures containing two units of alpha-trifluoromethyl-beta(2)-alanine. Finally, a conformational study of several of the newly synthesized peptidomimetics, performed with the aid of X-ray analysis and NMR techniques, shows a beta-turn-like conformation for the structures both in the solid state and in solution.
Assuntos
Acrilamidas/química , Alanina/análogos & derivados , Compostos Aza/química , Compostos de Flúor/síntese química , Peptídeos/síntese química , Alanina/síntese química , Alanina/química , Cristalografia por Raios X , Compostos de Flúor/química , Espectroscopia de Ressonância Magnética , Conformação Molecular , Peptídeos/química , SoluçõesRESUMO
Oxidation reactions are of fundamental importance in nature, and are key transformations in organic synthesis. The development of new processes that employ transition metals as substrate-selective catalysts and stoichiometric environmentally friendly oxidants, such as molecular oxygen or hydrogen peroxide, is one of the most important goals in oxidation chemistry. Direct oxidation of the catalyst by molecular oxygen or hydrogen peroxide is often kinetically unfavored. The use of coupled catalytic systems with electron-transfer mediators (ETMs) usually facilitates the procedures by transporting the electrons from the catalyst to the oxidant along a low-energy pathway, thereby increasing the efficiency of the oxidation and thus complementing the direct oxidation reactions. As a result of the similarities with biological systems, this can be dubbed a biomimetic approach.
Assuntos
Peróxido de Hidrogênio/química , Metais/química , Compostos Orgânicos/química , Oxigênio/química , Biomimética , Catálise , Transporte de Elétrons , OxirreduçãoRESUMO
An efficient method for the preparation of beta,gamma-unsaturated delta-lactones has been developed. The starting materials for the synthesis of these compounds are allene-substituted malonates which undergo gold-catalyzed cyclization by means of nucleophilic attack of the ester moiety on the allene. It is worth mentioning that this is the first example where an ester group attacks as a nucleophile in a gold-catalyzed transformation of allenes.
RESUMO
[reaction: see text] An efficient and convenient two-step synthesis of new fluorinated uracils is described. The first step involves the condensation of an ester enolate with a fluorinated nitrile to furnish fluorinated beta-enamino esters. In turn, these compounds react with organic isocyanates or isothiocyanates to give C-6 fluorinated uracils or thiouracils, respectively, in excellent yields. This synthesis has been successfully adapted to solid-phase conditions with high diversity, thereby facilitating the creation of small (thio)uracil libraries.
Assuntos
Hidrocarbonetos Fluorados/síntese química , Soluções/química , Uracila/análogos & derivados , Uracila/síntese química , Hidrocarbonetos Fluorados/química , Isocianatos/química , Isotiocianatos/química , Estrutura Molecular , Nitrilas/químicaRESUMO
[reaction: see text] A simple, asymmetric synthesis of tetramic acid derivatives is described in this paper. The key step is a carbonyl transfer from carbonyldiimidazole (CDI) to alpha-diimines (I) to form N-alkyl-4-alkylamino-5-methylenepyrrol-2-ones (II). In turn, these compounds can be easily transformed into tetramic acid derivatives (III) in two additional steps.
RESUMO
A series of potentially biologically active fluorinated uracil derivatives has been prepared in three steps from oxazolines and fluorinated nitriles with good chemical yields.
Assuntos
Uracila/análogos & derivados , Antimetabólitos/síntese química , Hidrocarbonetos Fluorados/química , Nitrilas/química , Oxazóis/química , Uracila/síntese químicaRESUMO
The diastereoselective synthesis of cyclic beta,beta-difluorinated alpha-amino acid derivatives bearing a quaternary stereocenter is described. The process relies on the chemo- and diastereoselective addition of allylic organometallic reagents to fluorinated alpha-imino esters and a subsequent ring-closing metathesis reaction (RCM). Complete selectivity in the nucleophilic addition was achieved with (R)-phenylglycinol methyl ether as a chiral auxiliary. The resulting amino acids were introduced into peptide chains, which could facilitate the preparation of potentially bioactive dipeptide derivatives. In addition, the solution synthesis of these cyclic fluorinated alpha-amino acids was successfully adapted to solid-phase and fluorous-phase techniques. The reaction times and final deprotection were clearly more favorable in the latter, in which a fluorous trimethylsilylethanol (TMSE) tag was used. The tag was then easily removed upon treatment with TBAF in a high-yield transesterification process.
Assuntos
Aminoácidos Cíclicos/síntese química , Compostos de Flúor/síntese química , Aminação , Aminoácidos Cíclicos/química , Ésteres/química , Compostos de Flúor/química , Iminas/química , Estrutura Molecular , Prótons , Soluções , EstereoisomerismoRESUMO
Aza-Michael additions of alpha-amino esters to fluorinated acceptors take place in a highly stereoselective manner, to give partially modified Psi[NHCH2]retropeptides incorporating a hydrolytically stable trifluoroalanine mimic. The reaction mechanism has been investigated experimentally and theoretically, in order to explain the effect of the trifluoromethyl group on the reactivity and the origins of the experimentally observed stereocontrol. The reaction is a two-step process, involving a tandem aza-Michael addition followed by a stereoselective hydrogen transfer. Both steps are base-catalyzed. The high level of stereocontrol is the result of a combination of electrostatic interactions and steric effects.
Assuntos
Acrilamida/química , Flúor/química , Espectroscopia de Ressonância Magnética , Espectrometria de Massas , Modelos Moleculares , EstereoisomerismoRESUMO
Two families of bicyclic fluorinated uracils have been prepared starting from a gem-difluorinated unsaturated nitrile, by means of a ring-closing metathesis reaction to form the new ring, which is fused at the C-5/C-6 or N-1/C-6 positions of the uracil moiety. The selective formation of olefin regioisomers in the metathesis process can be controlled according to the reaction conditions (catalyst, solvent, and temperature). The acaricidal activities of the resulting compounds have also been investigated.