RESUMEN
α-Alkylation of a ß-keto ester is a frequently used reaction for carbon-carbon bond formation. However, extension to a stereoselective reaction remains a significant challenge, because the product easily racemizes under acidic or basic conditions. Here, we report a hybrid system consisting of Pd and Ru complexes that catalyzes the asymmetric dehydrative condensation between cinnamyl-type allylic alcohols and ß-keto esters. α-Non-substituted ß-keto ester can be allylated to afford an α-mono-substituted product with high regio-, diastereo-, and enantioselectivity. No epimerization occurs owing to the nearly neutral conditions, which is achieved by a rapid proton transfer from Pd-enolate formation to Ru π-allyl complex formation. Four diastereomers can be synthesized on demand by changing the stereochemistry of the Pd or Ru complex. Eight stereoisomers with three adjacent stereogenic centers can be synthesized by employing diastereoselective reduction of the ketone in the products. The formal synthesis of (+)-pancratistatin demonstrates the utility of the reaction.
Asunto(s)
Ésteres , Protones , Carbono , Catálisis , Ésteres/química , Cetonas , EstereoisomerismoRESUMEN
To elucidate the reaction mechanism and the origin of the enantioselectivity of the asymmetric dehydrative cyclization of allyl alcohol to cyclic ether catalyzed by a Cp-ruthenium complex and a chiral pyridinecarboxylic acid, (R)-X-Naph-PyCOOH, density functional theory (DFT) calculations were performed. According to the DFT calculations, the rate-determining step is the dehydrative σ-allyl formation step with ΔG = 18.1 kcal mol-1 at 80 °C. This agrees well with the experimental data (ΔG = 19.01 kcal mol-1 at 80 °C). The DFT result showed that both hydrogen and halogen bonds play a key role in the high enantioselectivity by facilitating the major R,SRu-catalyzed reaction pathway via a σ-allyl Ru intermediate to generate the major (S)-product. In contrast, the reaction is sluggish in the presence of the diastereomeric R,RRu catalyst with an apparent activation energy of 33.1 kcal mol-1; the minor (R)-product is formed via a typical π-allyl Ru intermediate and via a minor pathway for the cyclization step. In addition, the calculated activation Gibbs free energies, 14.4 kcal mol-1 for I < 16.8 kcal mol-1 for Br < 18.1 kcal mol-1 for Cl, reproduced the observed halogen-dependent reactivity with the (R)-X-Naph-PyCOOH ligands. The origin of the halogen trend was clarified by a structural decomposition analysis.
RESUMEN
Asymmetric Pd-catalyzed Tsuji-Trost-type allylation is an important catalytic reaction toward chiral natural and unnatural product syntheses. We successfully modified a desalt-type reaction using allyl ester or halide to a dehydrative one using allylic alcohol via the establishment of two redox-mediated donor acceptor bifunctional catalyst systems. These systems were cationic CpRu-Cl-Napy-PyCOOH and cationic CpRu-Naph-diPIM-dioxo-iPr/p-TsOH and were designed on the basis of the soft ruthenium and hard Brønsted acid combined catalyst concept. The complementary use of the two chiral catalysts for dehydrative asymmetric allylation expands the application scope facilitating the utilization of both aliphatic and aromatic allylic alcohols with various nucleophiles in the substrate. In this account, the design, synthesis, and application of these catalysts were reported.
RESUMEN
A cationic CpRu/halogen/Brønsted acid hybrid catalyst (Râ¯cat) with the axially chiral Cl-Naph-PyCOOH ligand (naph = naphthyl, py = pyridine) is highly efficient for dehydrative cyclization of pyrroles to construct 1,2-fused-2-allylated pyrroles that, so far, have not been achieved. The mechanistic study has implied that hydrogen and halogen bonds play a key role for facilitating the R,SRu-catalyzed reaction pathway via a σ-allyl intermediate and that the diastereomeric R,RRuâ¯cat slowly gives the minor enantiomer via a π-allyl intermediate.
RESUMEN
A convenient synthetic route to α,α-difluoroalkylphosphonates is described. Structurally diverse aldehydes are condensed with LiF2CP(O)(OCH2CHâCH2)2. The resultant alcohols are captured as the pentafluorophenyl thionocarbonates and efficiently deoxygenated with HSnBu3, BEt3, and O2, and then smoothly deblocked with CpRu(IV)(π-allyl)quinoline-2-carboxylate (1-2 mol %) in methanol as an allyl cation scavenger. These mild deprotection conditions provide access to free α,α-difluoroalkylphosphonates in nearly quantitative yield. This methodology is used to rapidly construct new bis-α,α-difluoroalkyl phosphonate inhibitors of PTPIB (protein phosphotyrosine phosphatase-1B).
Asunto(s)
Compuestos Alílicos/química , Hidrocarburos Fluorados/farmacología , Organofosfonatos/farmacología , Proteína Tirosina Fosfatasa no Receptora Tipo 1/antagonistas & inhibidores , Rutenio/química , Catálisis , Humanos , Hidrocarburos Fluorados/síntesis química , Hidrocarburos Fluorados/química , Estructura Molecular , Organofosfonatos/síntesis química , Organofosfonatos/química , Proteína Tirosina Fosfatasa no Receptora Tipo 1/metabolismoRESUMEN
Aryl bromides 2a and 2b bearing an alkynyl substituent in the o-position reacted with n-butyllithium and 1-benzylpiperidin-4-one in a one-pot Domino reaction to form ester 3 and aldehyde 5, respectively. Enantiomeric alcohols (R)-8 and (S)-8 were obtained by conjugate NaBH4 reduction of α,ß-unsaturated ester 3 in the presence of chiral cocomplexes (R,R)-10 and (S,S)-10. Starting from orthoester 2a, the precursors (R)-8 and (S)-8 for the synthesis of fluspidine enantiomers (R)-1/[18F](R)-1 and (S)-1/[18F](S)-1 were obtained in only two reaction steps without additional steps for N-protection in an atom-economic manner in 95.6% ee and 97.2% ee, respectively.
Asunto(s)
Benzofuranos/química , Benzofuranos/síntesis química , Piperidinas/química , Piperidinas/síntesis química , Tomografía de Emisión de Positrones , Receptores sigma/metabolismo , Benzofuranos/metabolismo , Técnicas de Química Sintética , Ligandos , Piperidinas/metabolismo , Estereoisomerismo , Receptor Sigma-1RESUMEN
A ZnII complex of a C2 -chiral bisamidine-type sp2 N bidentate ligand (LR ) possessing two dioxolane rings at both ends catalyzes a highly efficient quinone asymmetric Diels-Alder reaction (qADA) between o-alkoxy-p-benzoquinones and 1-alkoxy-1,3-butadienes to construct highly functionalized chiral cis-decalins, proceeding in up to a >99:1 enantiomer ratio with a high generality in the presence of H2 O (H2 O:ZnII =4-6:1). In the absence of water, little reaction occurs. The loading amount of the chiral ligand can be minimized to 0.02â mol % with a higher Zn/LR ratio. This first success is ascribed to a supramolecular 3D arrangement of substrates, in which two protons of an "H2 O-ZnII " reactive species make a linear hydrogen bond network with a dioxolane oxygen atom and one-point-binding diene; the ZnII atom captures the electron-accepting two-points-binding quinone fixed on the other dioxolane oxygen atom via an n-π* attractive interaction. The mechanisms has been supported by 1 Hâ NMR study, kinetics, X-ray crystallographic analyses of the related ZnLR complexes, and ligand and substrate structure-reactivity-selectivity relationship.
RESUMEN
The core skeleton of phalarine was rapidly synthesised through novel palladium-catalysed dearomative spirocyclisation and a palladium-catalysed Wacker-carbonylative cyclisation cascade. The two key steps allowed for the efficient construction of a tricyclic propeller skeleton bearing contiguous tetrasubstituted carbon centres, within 3 steps from a topologically planar precursor.
RESUMEN
A CuII complex of bisamidine ligand L S catalyzes the Friedel-Crafts (FC) reaction of indole with trifluoropyruvate with high generality, yielding the highly enantiomerically enriched FC adduct. Electron-rich indoles have high reactivity due to a dual activation mechanism showing second-order kinetics for CuII, whereas indoles with a soft substituent at C(4) proceed at a rate that is three orders of magnitude lower via a coordination mechanism, which reverses the sense of enantioselectivity.
RESUMEN
The total synthesis of 4-methylenegermine is described.
Asunto(s)
Cevanas/síntesis química , Acetatos , Estructura Molecular , Plantas Medicinales , EstereoisomerismoRESUMEN
Intracellular pathogens belonging to the genus Leishmania have developed effective strategies that enable them to survive within host immune cells. Immunostimulatory compounds that counteract such immunological escape mechanisms represent promising treatment options for diseases. Here, we demonstrate that a lipopeptidephosphoglycan (LPPG) isolated from the membrane of a protozoan parasite, Entamoeba histolytica (Eh), shows considerable immunostimulatory effects targeted against Leishmania (L.) major, a representative species responsible for cutaneous leishmaniasis (CL). Treatment led to a marked reduction in the number of intracellular Leishmania parasites in vitro, and ameliorated CL in a mouse model. We next designed and synthesized analogs of the phosphatidylinositol anchors harbored by EhLPPG; two of these analogs reproduced the anti-leishmanial activity of the native compound by inducing production of pro-inflammatory cytokines. The use of such compounds, either alone or as a supportive option, might improve the currently unsatisfactory treatment of CL and other diseases caused by pathogen-manipulated immune responses.
Asunto(s)
Antiprotozoarios/síntesis química , Antiprotozoarios/farmacología , Entamoeba histolytica/química , Glucolípidos/síntesis química , Glucolípidos/farmacología , Leishmania/efectos de los fármacos , Animales , Antiprotozoarios/química , Supervivencia Celular/efectos de los fármacos , Glucolípidos/química , Hemólisis , Humanos , Leishmaniasis Cutánea/tratamiento farmacológico , Leishmaniasis Cutánea/inmunología , Leishmaniasis Cutánea/metabolismo , Leishmaniasis Cutánea/parasitología , Estructura MolecularRESUMEN
A new enantioselective catalysis has been developed for the one-step construction of methylene-bridged chiral modules of 1,2- and 1,3-OH and/or NH function(s) from δ- or λ-OH/NHBoc-substituted allylic alcohols and "H2CâO"/"H2CâNBoc". A protonic nucleophile, either in situ-generated CH2OH or CH2NHBoc, is intramolecularly allylated to furnish eight possible 1,2- or 1,3-O,O, -O,N, -N,O, and -N,N chiral modules equipped with an ethenyl group in high yields and enantioselectivities. The utility of this method has been demonstrated in the five-step synthesis of sphingosine.
RESUMEN
Targeting CCR2 and CCR5 receptors is considered as promising concept for the development of novel antiinflammatory drugs. Herein, we present the development of the first probe-dependent positive allosteric modulator (PAM) of CCR5 receptors with a 2-benzazepine scaffold. Compound 14 (2-isobutyl-N-({[N-methyl-N-(tetrahydro-2H-pyran-4-yl)amino]methyl}phenyl)-1-oxo-2,3-dihydro-1H-2-benzazepine-4-carboxamide) activates the CCR5 receptor in a CCL4-dependent manner, but does not compete with [3H]TAK-779 binding at the CCR5. Furthermore, introduction of a p-tolyl moiety at 7-position of the 2-benzazepine scaffold turns the CCR5 PAM 14 into the selective CCR2 receptor antagonist 26b. The structure affinity and activity relationships presented here offer new insights into ligand recognition by CCR2 and CCR5 receptors.
Asunto(s)
Benzazepinas/farmacología , Receptores CCR2/antagonistas & inhibidores , Receptores CCR5/metabolismo , Benzazepinas/síntesis química , Benzazepinas/química , Relación Dosis-Respuesta a Droga , Humanos , Ligandos , Estructura Molecular , Relación Estructura-Actividad , Células Tumorales CultivadasRESUMEN
Chiral spirocarbocyclic skeletons are ubiquitous in natural products. An intramolecular Tsuji-Trost (T-T) α-allylation of simple cyclic ketones is a reasonable approach to construct chiral spriocarbocyclic motifs; however, it has been a challenging approach despite many excellent intermolecular examples. For the first time, this has been achieved by a Ru/H+ combined catalyst that dehydratively cyclizes racemic allylic alcohols comprising a simple ketone via simultaneous activation of the C=O and OH groups. This chiral technology facilitates the construction of various spirocarbocycles containing two contiguous spiro all-carbon quaternary and tertiary stereocenters. Among four possible stereoisomers, one stereoisomer can be selectively produced in high yield, enhancing the feasibility of the T-T strategy, particularly in the synthesis of spirocarbocycles.
Asunto(s)
Complejos de Coordinación/química , Compuestos Heterocíclicos/síntesis química , Rutenio/química , Compuestos de Espiro/síntesis química , Catálisis , Compuestos Heterocíclicos/química , Concentración de Iones de Hidrógeno , Estructura Molecular , Compuestos de Espiro/química , EstereoisomerismoRESUMEN
The influence of an F-atom in the side chain of benzo[7]annulen-7-amines on the affinity towards GluN2B subunit containing NMDA receptors and the selectivity over related receptors was investigated. The synthesis of 5a and 5b was performed by reductive amination of the ketone 6 with primary alkanamines 14a and 14b bearing an F-atom in ß-position. The GluN2B affinities of non-fluorinated and fluorinated ligands 4 and 5 are almost identical. The low impact of the F-atom on GluN2B affinity was unexpected, as it influences several chemical and physicochemical properties of the ligands. However, introduction of the F-atom led to reduced selectivity over σ receptors. Whereas 5a and 5b display still a 2-3-fold preference for GluN2B over σ1 receptors, they show almost the same affinity to GluN2B and σ2 receptors.
RESUMEN
Optically pure hinckdentine A was synthesized on a 300 mg scale via an asymmetric catalysis-based strategy. The key steps to the first asymmetric synthesis involved (i) enantioselective dearomative cyclization of an achiral N-acyl indole that allowed for the efficient construction of the key polycyclic indoline intermediate with a crucial tetrasubstituted stereogenic carbon center, (ii) Beckmann fragmentation-mediated ring expansion, (iii) rearrangement-based introduction of an anilinic nitrogen atom, (iv) regioselective tribromination, and (v) final closure of the cyclic amidine moiety.
Asunto(s)
Quinazolinas/química , Catálisis , Ciclización , Lactamas/química , Estructura Molecular , Paladio/química , EstereoisomerismoRESUMEN
A general synthetic methodology toward the erythrina alkaloids has been developed. Inspired by a proposed biosynthetic mechanism, the medium-sized chiral biaryl lactam was asymmetrically transformed into the common core A-D rings by a stereospecific singlet oxygen oxidation of the phenol moiety, followed by a transannular aza-Michael reaction to the dienone functionality. The late-stage manipulation of the oxidation and oxygenation states of the functional groups on the peripheral moieties enabled the flexible syntheses of the erythrina alkaloids.
RESUMEN
Tsuji-Trost-type asymmetric allylation of carboxylic acids has been realized by using a cationic CpRu complex with an axially chiral picolinic acid-type ligand (Cl-Naph-PyCOOH: naph = naphthyl, py = pyridine). The carboxylic acid and allylic alcohol intramolecularly condense by the liberation of water without stoichiometric activation of either nucleophile or electrophile part, thereby attaining high atom- and step-economy, and low E factor. This success can be ascribed to the higher reactivity of allylic alcohols as compared with the allyl ester products in soft Ru/hard Brønstead acid combined catalysis, which can function under slightly acidic conditions unlike the traditional Pd-catalyzed system. Detailed analysis of the stereochemical outcome of the reaction using an enantiomerically enriched D-labeled substrate provides an intriguing view of enantioselection.
Asunto(s)
Compuestos Alílicos/síntesis química , Ácidos Carboxílicos/química , Lactonas/síntesis química , Compuestos Alílicos/química , Lactonas/química , Conformación Molecular , Compuestos Organometálicos/química , Rutenio/químicaRESUMEN
The combination of a Goodwin-Lions-type chiral N4 ligand, (R)-Ph-BINAN-H-Py ((R)-3,3'-diphenyl-N(2),N(2')-bis((pyridin-2-yl)methyl)-1,1'-binaphthyl-2,2'-diamine; L), with Ru(π-CH2C(CH3)CH2)2(cod) (A) (cod = 1,5-cyclooctadiene) catalyzes the hydrogenation of acetophenone (AP) to (R)-1-phenylethanol (PE) with a high enantiomer ratio (er). Almost no Ru complex forms, with A and L remaining intact throughout the reaction while generating PE quantitatively according to [PE] = k(obs)t(2). An infinitesimal amount of reactive and unstable RuH2L (B) with C2-Λ-cis-α stereochemistry is very slowly and irreversibly generated from A by the action of H2 and L, which rapidly catalyzes the hydrogenation of AP via Noyori's donor-acceptor bifunctional mechanism. A CH-π-stabilized Si-face selective transition state, CSi, gives (R)-PE together with an intermediary Ru amide, D, which is inhibited predominantly by formation of the Ru enolate of AP. The rate-determining hydrogenolysis of D completes the cycle. The time-squared term relates both to the preliminary step before the cycle and to the cycle itself, with a highly unusual eight-order difference in the generation and turnover frequency of B. This mechanism is fully supported by a series of experiments including a detailed kinetic study, rate law analysis, simulation of t/[PE] curves with fitting to the experimental observations at the initial reaction stage, X-ray crystallographic analyses of B-related octahedral metal complexes, and Hammett plot analyses of electronically different substrates and ligands in their enantioselectivities.