RESUMO
We report the oxidative dimerization reaction of siloxydienes derived from simple enones that creates a new gamma-gamma (γ-γ) C-C bond using catalytic iron and benzoyl peroxide as the terminal oxidant in acetonitrile solvent at ambient temperature. The reaction shows a broad substrate scope including cyclic and acyclic siloxydienes derived from ketones, aldehydes, and esters, which are converted to 1,8-dicarbonyl compounds under mild catalytic reaction conditions in 19-89 % yield across 30 examples. The method is suitable for the coupling of sterically demanding carbon centers, including the formation of vicinal quaternary centers. Conceptually, the dienol ether serves as a precursor to a conjugated radical cation, which undergoes highly site selective γ-dimerization reactions. The γ-γ dimerization strategy is applied to the synthesis of a bioactive analogue of honokiol.
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We report a general, regioselective, and metal free γ-fluorination of α,ß-unsaturated carbonyls via silyl dienol ethers that are readily prepared from simple ketones and aldehydes. The transformation displays broad scope including 27 cyclic and acyclic siloxydienes providing γ-fluoro compounds in 28-91 % yield. Notably, the reported conditions are also suitable for the synthesis of challenging tertiary fluorides. The regioselectivity of the reaction was studied on a series of acyclic siloxydienes and was observed to be sensitive to the conformational flexibility of the substrate. Diversification of the γ-fluorocarbonyls demonstrates the promise of fluorine as a stereocontrol element.
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A general regio- and stereoselective γ-C-C bond formation is achieved using α-halocarbonyl compounds and dienol ethers via Cu(II) catalysis. This method constitutes a novel approach to the challenging 1,6-dioxygenation motif. A range of γ-substituted enones, including many bearing all-carbon quaternary centers, are available through a simple protocol under mild reaction conditions with superb functional group compatibility. Excellent stereoinduction is observed providing controlled access to challenging stereochemical arrays.
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A radical-based strategy for regioselective γ-C-C bond formation/oxa-conjugate addition, forming the tetrahydrobenzofuran core common to many bioactive natural products is described. The technique utilizes readily available enone derivatives and 1,3-dicarbonyl compounds as coupling partners in an oxidative formal [3+2] cycloaddition mediated by Mn(III) . The transformation delivers polycyclic products in good yields and proceeds with complete regiocontrol and excellent stereoselectivity. Sterically encumbered substrates are notably well-tolerated and bond formation occurs readily to form neopentyl and all-carbon quaternary centers in good yields. Several stereo- and chemoselective transformations of the products are described.
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An enantioconvergent catalytic process has the potential to convert a racemic starting material to a single highly enantioenriched product with a maximum yield of 100%. Three mechanistically distinct approaches to effecting enantioconvergent catalysis are identified, and recent examples of each are highlighted. These processes are compared to related, non-enantioconvergent methods.
RESUMO
Biologically active natural products often contain particularly challenging structural features and functionalities in terms of synthesis. Perhaps the greatest difficulties are those caused by issues of stereochemistry. A useful strategy for synthesizing such molecules is to devise methods of bond formation that provide opportunities for using enantioselective catalysis. In using this tactic, the desire for a particular target structure ultimately drives the development of catalytic methods. New enantioselective catalytic methods contribute to a greater fundamental understanding of how bonds can be constructed and lead to valuable synthetic technologies that are useful for a variety of applications.
Assuntos
Produtos Biológicos/química , Produtos Biológicos/síntese química , Carbazóis/síntese química , Carbazóis/química , Catálise , Diterpenos/síntese química , Diterpenos/química , Indanos/síntese química , Indanos/química , Alcaloides Indólicos/síntese química , Alcaloides Indólicos/química , Indolizinas/síntese química , Indolizinas/química , Lactamas/síntese química , Lactamas/química , Pirazinas/síntese química , Pirazinas/química , Fosfato de Sitagliptina , Compostos de Espiro/síntese química , Compostos de Espiro/química , Triazóis/síntese química , Triazóis/químicaRESUMO
National Institutes of Health (NIH)-sponsored screening centers provide academic researchers with a special opportunity to pursue small-molecule probes for protein targets that are outside the current interest of, or beyond the standard technologies employed by, the pharmaceutical industry. Here, we describe the outcome of an inhibitor screen for one such target, the enzyme protein phosphatase methylesterase-1 (PME-1), which regulates the methylesterification state of protein phosphatase 2A (PP2A) and is implicated in cancer and neurodegeneration. Inhibitors of PME-1 have not yet been described, which we attribute, at least in part, to a dearth of substrate assays compatible with high-throughput screening. We show that PME-1 is assayable by fluorescence polarization-activity-based protein profiling (fluopol-ABPP) and use this platform to screen the 300,000+ member NIH small-molecule library. This screen identified an unusual class of compounds, the aza-ß-lactams (ABLs), as potent (IC(50) values of approximately 10 nM), covalent PME-1 inhibitors. Interestingly, ABLs did not derive from a commercial vendor but rather an academic contribution to the public library. We show using competitive-ABPP that ABLs are exquisitely selective for PME-1 in living cells and mice, where enzyme inactivation leads to substantial reductions in demethylated PP2A. In summary, we have combined advanced synthetic and chemoproteomic methods to discover a class of ABL inhibitors that can be used to selectively perturb PME-1 activity in diverse biological systems. More generally, these results illustrate how public screening centers can serve as hubs to create spontaneous collaborative opportunities between synthetic chemistry and chemical biology labs interested in creating first-in-class pharmacological probes for challenging protein targets.
Assuntos
Hidrolases de Éster Carboxílico/antagonistas & inibidores , Inibidores Enzimáticos , Animais , Hidrolases de Éster Carboxílico/genética , Hidrolases de Éster Carboxílico/metabolismo , Avaliação Pré-Clínica de Medicamentos , Inibidores Enzimáticos/síntese química , Inibidores Enzimáticos/química , Inibidores Enzimáticos/farmacologia , Células HEK293 , Humanos , Camundongos , Camundongos Knockout , National Institutes of Health (U.S.) , Proteína Fosfatase 2/genética , Proteína Fosfatase 2/metabolismo , Estados UnidosRESUMO
Pd-catalyzed enantioselective alkylation in conjunction with further synthetic elaboration enables the formal total syntheses of a number of "classic" natural product target molecules. This publication highlights recent methods for setting quaternary and tetrasubstituted tertiary carbon stereocenters to address the synthetic hurdles encountered over many decades across multiple compound classes spanning carbohydrate derivatives, terpenes, and alkaloids. These enantioselective methods will impact both academic and industrial settings, where the synthesis of stereogenic quaternary carbons is a continuing challenge.
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MALDI-TOF MS is a powerful tool to analyze biomolecules owing to its soft ionization nature and generally results in simple spectra of singly charged ions. Moreover, implementation of the technology in imaging mode provides a means to spatially map analytes in situ. Recently, a new matrix, DBDA (N1,N4-dibenzylidenebenzene-1,4-diamine) was reported to facilitate the ionization of free fatty acids in the negative ion mode. Building on this finding, we sought to implement DBDA for MALDI mass spectrometry imaging studies in brain tissue and successfully map oleic acid, palmitic acid, stearic acid, docosahexaenoic acid and arachidonic acid using mouse brain sections. Moreover, we hypothesized that DBDA would provide superior ionization for sulfatides, a class of sulfolipids, with multiple biological functions. Herein we also demonstrate that DBDA is ideal for MALDI mass spectrometry imaging of fatty acids and sulfatides in brain tissue sections. Additionally, we show enhanced ionization of sulfatides using DBDA compared to three different traditionally used MALDI matrices. Together these results provide new opportunities for studies to measure sulfatides by MALDI-TOF MS including in imaging modes.
RESUMO
MALDI-TOF MS is a powerful tool to analyze biomolecules, owing to its soft ionization nature that generally results in simple spectra of singly charged ions. Implementation of the technology in the imaging mode provides a means to spatially map analytes in situ. Recently, a new matrix, DBDA (N1,N4-dibenzylidenebenzene-1,4-diamine) was reported to facilitate the ionization of free fatty acids in negative ion mode. Building on this finding, we sought to implement DBDA for MALDI mass spectrometry imaging studies in brain tissue and successfully map oleic acid, palmitic acid, stearic acid, docosahexaenoic acid, and arachidonic acid using mouse brain sections. Moreover, we hypothesized that DBDA would provide superior ionization for sulfatides, a class of sulfolipids with multiple biological functions. Herein, we also demonstrate that DBDA is ideal for MALDI mass spectrometry imaging of fatty acids and sulfatides in brain tissue sections. Additionally, we show enhanced ionization of sulfatides using DBDA compared with three different traditionally used MALDI matrices. Together these results provide new opportunities for studies to measure sulfatides by MALDI-TOF MS.
Assuntos
Ácidos Graxos , Sulfoglicoesfingolipídeos , Camundongos , Animais , Ácidos Graxos/análise , Sulfoglicoesfingolipídeos/análise , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz/métodos , ÍonsRESUMO
We use first principles quantum mechanics (density functional theory) to report a detailed reaction mechanism of the asymmetric Tsuji allylation involving prochiral nucleophiles and nonprochiral allyl fragments, which is consistent with experimental findings. The observed enantioselectivity is best explained with an inner-sphere mechanism involving the formation of a 5-coordinate Pd species that undergoes a ligand rearrangement, which is selective with regard to the prochiral faces of the intermediate enolate. Subsequent reductive elimination generates the product and a Pd(0) complex. The reductive elimination occurs via an unconventional seven-centered transition state that contrasts dramatically with the standard three-centered C-C reductive elimination mechanism. Although limitations in the present theory prevent the conclusive identification of the enantioselective step, we note that three different computational schemes using different levels of theory all find that inner-sphere pathways are lower in energy than outer-sphere pathways. This result qualitatively contrasts with established allylation reaction mechanisms involving prochiral nucleophiles and prochiral allyl fragments. Energetic profiles of all reaction pathways are presented in detail.
Assuntos
Carbono/química , Estereoisomerismo , TermodinâmicaRESUMO
Serine hydrolases are one of the largest and most diverse enzyme classes in Nature. Most serine hydrolases lack selective inhibitors, which are valuable probes for assigning functions to these enzymes. We recently discovered a set of aza-ß-lactams (ABLs) that act as potent and selective inhibitors of the mammalian serine hydrolase protein-phosphatase methylesterase-1 (PME-1). The ABLs inactivate PME-1 by covalent acylation of the enzyme's serine nucleophile, suggesting that they could offer a general scaffold for serine hydrolase inhibitor discovery. Here, we have tested this hypothesis by screening ABLs more broadly against cell and tissue proteomes by competitive activity-based protein profiling (ABPP), leading to the discovery of lead inhibitors for several serine hydrolases, including the uncharacterized enzyme α,ß-hydrolase domain-containing 10 (ABHD10). ABPP-guided medicinal chemistry yielded a compound ABL303 that potently (IC(50) ≈ 30 nM) and selectively inactivated ABHD10 in vitro and in living cells. A comparison of optimized inhibitors for PME-1 and ABHD10 indicates that modest structural changes that alter steric bulk can tailor the ABL to selectively react with distinct, distantly related serine hydrolases. Our findings, taken together, designate the ABL as a versatile reactive group for creating first-in-class serine hydrolase inhibitors.
Assuntos
Serina Endopeptidases/metabolismo , Inibidores de Serina Proteinase/farmacologia , beta-Lactamas/farmacologia , Ligação Competitiva/efeitos dos fármacos , Estrutura Molecular , Inibidores de Serina Proteinase/síntese química , Inibidores de Serina Proteinase/química , Estereoisomerismo , Relação Estrutura-Atividade , beta-Lactamas/químicaRESUMO
α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic ß-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center.
Assuntos
Compostos Alílicos/química , Carbonatos/química , Cetonas/química , Paládio/química , Alquilação , Catálise , Descarboxilação , Cetonas/síntese química , Ligantes , Estrutura Molecular , EstereoisomerismoRESUMO
A novel "non-aromatic pool" synthetic strategy for the synthesis of benzofuran-based natural products via oxidative haloaromatization of enones is reported. This approach is successfully applied in the first total synthesis of the natural product aspergillusene B. In comparison with a separately executed "aromatic pool" synthesis, the "non-aromatic pool" protocol demonstrates equivalent efficiency but offers a much higher degree of modularity.
Assuntos
Benzofuranos/química , Produtos Biológicos/síntese química , Cetonas/química , Produtos Biológicos/química , Halogenação , Estrutura Molecular , EstereoisomerismoRESUMO
General homogeneous conditions for the palladium-catalyzed synthesis of carbonyl compounds with tertiary carbon stereocenters at the alpha-position are reported. The highly reactive catalyst tolerates a variety of substrate substitution and functionality, and generates enantioenriched cyclic ketones from racemic allyl beta-ketoester starting materials.
Assuntos
Ácidos Carboxílicos/química , Paládio/química , Catálise , Espectroscopia de Ressonância Magnética , Prótons , EstereoisomerismoRESUMO
A short enantioselective formal synthesis of the antibiotic natural product platencin is reported. Key steps in the synthesis include enantioselective decarboxylation alkylation, aldehyde/olefin radical cyclization, and regioselective aldol cyclization.
RESUMO
A novel synthetic approach for the synthesis of bioactive phenolic natural products is reported. This strategy highlights the power of halogenative aromatization reactions recently developed in our group for preparing densely functionalized arenes in a controlled fashion. Five natural products related by an aromatic core and a farnesyl side chain are synthesized. In contrast to prior methods, this synthesis features high efficiency and generality that permits preparation of targets in gram-scale quantities.
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Carbonyl compounds bearing a γ-amino group are valuable pharmacologically active targets. Regioselective γ-C-N bond formation is achieved with simple enone substrates through controlled dienolate reactivity toward azodicarboxylate electrophiles. The amination reaction occurs readily with sterically demanding nucleophiles and is stereoselective.
Assuntos
Cetonas/química , Cetonas/síntese química , Aminação , Catálise , Técnicas de Química Combinatória , Estrutura Molecular , Nitrogênio/química , EstereoisomerismoRESUMO
A strategy for synthesis of γ-alkylated enones through oxidative coupling of siloxydienes and 1,3-dicarbonyl compounds is reported. This method is an interrupted form of our formal [3 + 2] cycloaddition method reported previously. The present work excels in generating all-carbon quaternary centers via C-C bond formation at the remote γ-site which is traditionally challenging to functionalize. Stereoselectivity and functional group tolerance are examined in complex systems. Double alkylation reactions are also described.
RESUMO
The polyhydroxyalkanes 1,6,11,16-hexadecanetetraol (1) and 2,7,12,17-octadecanetetraol (2) were synthesized utilizing the thiophene ring as a scaffold to affix the hydroxyalkyl chains by lithiation of the acidic alpha-hydrogens and subsequent desulfurization. Both compounds exhibited significant anesthetic potency, individually and in additivity studies with hexanol, using immobility in tadpoles as the phenotypic endpoint. These results, which contradict a protein-binding mechanism in which cutoff results from steric hindrance, are consistent with recent predictions of a membrane-mediated mechanism involving the lateral pressure profile.