The first highly enantioselective intermolecular (4 + 2) cycloaddition between allenes and dienes is reported. reaction provides good yields of optically active cyclohexenes featuring diverse substitution patterns up to three stereocenters. Key the success process use newly designed axially chiral N-heterocyclic carbene-gold catalysts.

In this paper, a novel three-dimensional (3-D) space-vector algorithm for four-leg multilevel converters is presented. It can be applied to active power filters or neutral-current compensator applications mitigating harmonics and zero-sequence components using abc coordinates (referred from now on paper as natural coordinates). This technique greatly simplifies the selection of 3-D region where given voltage vector supposed found. Compared three-level modulation three-leg converters, does...

IL-2 was shown to induce phosphatidylinositol-3-kinase activity in the CTLL-2 murine lymphocyte line. Tyrosine phosphorylation of demonstrated by immunoabsorption with antiphosphotyrosine antibody and coincident activation an IL-2R-associated tyrosine kinase. Half-maximal this enzyme, cell proliferation, occurred at 30 pM IL-2. Incubation cells genistein, a selective kinase inhibitor, blocked IL-2-dependent receptor-associated activities, suggesting that phosphorylation-dependent is...

The existence of an intracellular phospholipase A2 (PLA2) involved in the production 1-O-alkyl-sn-glycero-3-phosphocholine and free arachidonic acid has been repeatedly postulated. Using 1-O-hexadecyl-2-[3H]arachidonoyl-sn-glycero-3-phosphocholine as a substrate series conventional high-pressure liquid chromatographic techniques, we have purified PLA2 from soluble fraction differentiated human monocytic U937 cells. enzyme nearly 2000-fold to homogeneity. molecular mass 56 kDa, under reducing...

Studies of the specificity phospholipases Az (PLAzs) for different substrates have usually been carried out in vesicles or mixed micelles, where differences shape, size, charge formed with phospholipids may give misleading results.Another factor is binding enzyme to phospholipid surface, which has recently addressed using an anionic phospholipid, dimyristoylan-glycero-3-phosphomethanol (DMPM) some extracellular PLAzs were shown bind a very high affinity (Jain, M. K., and Berg, 0. G .(1989)

Previous studies using phospholipid mixed vesicles have demonstrated that several types of phospholipase A2 (PLA2) enzymes exhibit different selectivity for fatty acids at the sn-2 position, type chemical bond sn-1 position or phosphobase moiety sn-3 phospholipids. In present study, we utilized natural mammalian membranes from U937 monocytes to determine whether two purified 14 kDa PLA2 isoenzymes (Type I, Type II) and a partially 110 substrate certain these studies, arachidonic acid (AA)...

A straightforward and atom-economical enantioselective approach to highly substituted tetrahydropyrans is reported. The process, which consists of an intermolecular gold-catalyzed [2+2+2] cycloaddition between allenamides, alkenes, aldehydes, efficiently catalyzed by both phosphoramidite- chiral N-heterocyclic carbene-gold catalysts, occurs with complete chemoselectivity regioselectivity, moderate diastereoselectivity, very good enantioselectivities.

The selective Suzuki cross-coupling of 1,3-dichloroisoquinoline with 2-substituted 1-naphthylboronic acids/esters followed by construction the imidazo[1,5-b]isoquinoline ring and alkylation constitutes a straightforward route to imidazolium salts fused into an axially chiral biaryl skeleton. Metalation these azolium afforded corresponding NHC silver complexes, which were used as carbene transfer agents for synthesis Au(I) derivatives.

The AuI-catalyzed reaction between terminal alkynes and aromatic haloalkynes proceeds through divergent pathways depending on the nature of catalyst counteranion. Thus, cationic complexes containing strongly basic NHC ligands noncoordinating anions such as BArF4 catalyze cis haloalkynylation alkyne, whereas introduction a weakly triflate counteranion results in stereoselective hydroalkynylation haloalkyne, yielding haloenyne products good yields complete trans selectivity. Experimental...

Primary cultures of [3H]arachidonic acid-prelabeled mouse peritoneal macrophages were stimulated with the physiologic agonists zymosan and Con A. The cells released a large quantity labeled compounds into extracellular medium. When preincubated for 10 min PMA at concentrations from to 1000 ng/ml, zymosan- A-stimulated compound release was greatly enhanced. also potentiated arachidonic acid when calcium ionophore A23187. However, under same conditions, treatment blocked agonist-...

We have studied the capacity of human neutrophils to release arachidonic acid from diacylglycerol, employing 1-stearoyl-2-[1-14C]arachidonoyl-sn-glycerol and 1-[1-14C]stearoyl-2-arachidonoyl-sn-glycerol as exogenous substrates. found that is removed diacylglycerol by sequential action two enzymes. First, sn-1 position split 1-diacylglycerol lipase activity, then, released resulting 2-monoacylglycerol a lipase. The specific activity lipase, using 2-[1-14C]arachidonoyl-sn-glycerol substrate,...

Neutral, C2-symmetric S/C/S ligands based on N-heterocyclic carbenes and thioether functionalities were incorporated into transition metal complexes characterised by two direct metal-stereogenic sulfur bonds. This new ligand design was applied to 1,3-dipolar cycloadditions as the first example of use silver in asymmetric catalysis.

The benzoannulation of the most common families aromatic NHCs, imidazol-2-ylidenes and 1,2,4-triazol-3-ylidenes, results in heterobicyclic imidazo[1,5-a]pyridin-3-ylidenes ('s) [1,2,4]triazolo[4,3-a]pyridin-3-ylidenes ('s), characterized by a bridged N atom. These are versatile platforms that offer multiple possibilities for modulation steric electronic properties carbene ligand and/or organocatalyst, also diverse opportunities introduction several types chiralities. In this paper different...

Attaining and maintaining the Official Tuberculosis Free status continues to be a challenge when several domestic wild hosts contribute maintenance of Mycobacterium tuberculosis complex (MTC). Local hotspots are sometimes identified in cattle low-prevalence regions. We have, therefore, studied one such hotspot depth order produce an epidemiological diagnosis. Host population size MTC prevalence were estimated selected wildlife livestock, while on-cattle environmental DNA detection was...

Modulable monosulfonyl squaramides have been shown to exert activation of gold(I) chloride complexes through H-bonding in an intermolecular way. Combinations (PPh3)AuCl or IPrAuCl and optimal sulfonyl squaramide cocatalyst bearing two 3,5-bis(trifluoromethyl)phenyl groups efficiently catalyzed diverse heterocyclizations a cyclopropanation reaction, avoiding all cases undesired side reactions. Computational studies indicate that the Au-Cl bond breaks by transligation triple ternary complex...

Orthogonal and modular templating is an effective basis for the preparation of biologically active annonaceous acetogenin 10-hydroxyasimicin (1). The versatile tartrate-derived 2,3-butanediacetal building block together with a highly diastereoselective hetero-Diels–Alder approach to butenolide unit were usefully employed in this novel synthetic route.

Abstract The selective N‐oxidation of the most nucleophilic amino nitrogen atom in hydrazides is central to development an unprecedented methodology for cleavage their NN bonds under oxidative conditions. Treatment a series 1 – 9 with peracids such as magnesium monoperoxyphtalate hexahydrate (MMPP ⋅ 6 H 2 O) or meta ‐chloroperbenzoic acid ( m ‐CPBA) afforded corresponding amides 10 16 good‐to‐excellent yields (80–92 %). extension carbamate‐like substrates 17 and 18 was also investigated,...

According to a chiral memory protocol, glycolic acid equivalent, the butane-2,3-diacetal-desymmetrized glycolate 2, is obtained from 3-halopropane-1,2-diols 1. Compound 2 new and effective building block for synthesis of mono- dialkylated α-hydroxy acids 3, which constitute biologically pharmacologically important structural motif.

A versatile methodology for the nucleophilic formylation and cyanation of conjugated enones is reported. The procedure based on use formaldehyde dimethylhydrazone, which, acting as a neutral formyl anion equivalent, adds to preformed trialkylsilyl−enone complexes. Both 4-(silyloxy)-3-enal hydrazones 3 or deprotected 4-oxo aldehyde monohydrazones 4 can be obtained products depending quenching conditions. In full analogy, an asymmetric version reaction using chiral SAMP-hydrazone synthon has...

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTEnantioselective Nucleophilic Formylation and Cyanation of Conjugated Enones via Michael Addition Formaldehyde SAMP-HydrazoneJose-María Lassaletta, Rosario Fernández, Eloísa Martín-Zamora, Elena DíezView Author Information Departamento de Química Orgánica Facultad Química, Universidad Sevilla Apartado Correos No. 553 E-41071, Seville, Spain Cite this: J. Am. Chem. Soc. 1996, 118, 29, 7002–7003Publication Date (Web):July 24, 1996Publication...

Enantiopure N,N-dialkylhydrazones 3 smoothly react with N-benzyloxycarbonyl-N-benzyl glycine as an aminoketene precursor to afford trans-3-amino-4-alkylazetidin-2-ones 4 single diasteromers. As exception, hydrazone 3f (R = OBn) affords cis-(3R,4R)-4f under modified conditions. N-N Bond cleavage of cycloadducts afforded free azetidinones 5 in high yields. [structure: see text]

The preparation of butane-2,3-diacetal protected glycolic acid and related systems is described together with highly selective alkylation reactions (R,R) (S,S) butanediacetal acid. These compounds are readily deprotected to give enantiopure alpha-hydroxyacids, alpha-hydroxyesters or alpha-hydroxyamides by suitable choice conditions.

The synthesis of 1-alkyl-1,2,4-triazolium salts containing chiral 4-dialkylamino substituents was accomplished by selective alkylation at N-1 the corresponding 4-(dialkylamino)-1,2,4-triazoles. latter were synthesized reaction N,N-dimethylformamidazine dihydrochloride with N,N-dialkylhydrazines in pyridine. Alternatively, 4-[(2S,5S)-2,5-diphenylpyrrolidin-1-yl]-1-phenyl-1,2,4-triazolium perchlorate performed 3-phenyl-1,3,4-oxadiazolium (2S,5S)-1-amino-2,5-diphenylpyrrolidine. These...

The formal insertion of alkenes into aromatic chloro- and bromoalkynes takes place under cationic gold catalysis. This haloalkynylation reaction can be performed with cyclic, gem-disubstituted monosubstituted alkenes, using BINAP, triazolo[4,3-b]isoquinolin-3-ylidene ligands or SPhos, respectively. products were isolated in moderate to excellent yields complete diastereo- regioselectivity; the halogen atom bonding more substituted carbon alkene. Preliminary experiments showed that...

Formaldehyde dialkylhydrazones behave as neutral d1 synthons in their uncatalyzed reaction with trifluoromethyl ketones (see reaction). Both racemic and optically pure 1,2-adducts were obtained good yields. Efficient deprotection of the hydrazone moiety afforded interesting fluorinated quaternary compounds such 1 2.