- Phytoalexins from Thlaspi arvense, a wild crucifer resistant to virulent Leptosphaeria maculans: Structures, syntheses and antifungal activity
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Phytoalexins are inducible chemical defenses produced by plants in response to diverse forms of stress, including microbial attack. Our search for phytoalexins from cruciferous plants resistant to economically important fungal diseases led us to examine s
- Pedras,Chumala,Suchy
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- Thermodynamics of phenylacetamides synthesis: Linear free energy relationship with the pK of amine
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The effective equilibrium constants K′C expressed through the total concentrations of the reagents for the synthesis of N-phenylacetyl-derivatives in aqueous medium from phenylacetic acid and various primary amino compounds have been determined with penicillin acylase as a catalyst. Broad specificity of penicillin acylase (EC 3.5.1.11) to amino components made possible to investigate the acylation of primary amines with different structures and physicochemical properties. Analysis of different components of the effective standard Gibbs energy change ΔGC o′ has revealed favorable thermodynamics for the synthesis of phenylacetamides from unionized substrates forms, however the ionization of reactants carboxy and amino groups in aqueous solutions pushes the equilibrium position to the hydrolysis especially in case of highly basic amines. A linear correlation between the standard Gibbs energy change for amide bond formation from the unionized reagents species and the basicity of amino group was observed: ΔGTo=-3.56pKamine+7.71(kJ/mol). The established linear free energy relationship (LFER) allows to predict the thermodynamic parameters for direct condensation of phenylacetic acid with any amine of known pK. Condensation of phenylacetic acid and amines with pK value within 1.5-8.5 was shown to be thermodynamically favorable in homogeneous aqueous solution. .
- Guranda, Dorel T.,Ushakov, Gennadij A.,Yolkin, Petr G.,Svedas, Vytas K.
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- Copper-catalyzed cross-coupling of O -alkyl hydroxamates with aryl iodides
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N-Aryl-O-alkylhydroxamic acid derivatives were prepared by copper-catalyzed cross-coupling of hydroxamates with aryl iodides. The reaction conditions are compatible with standard hydroxy-protecting groups on the hydroxylamine moiety and are applicable to
- Kukosha, Tatyana,Trufilkina, Nadezhda,Belyakov, Sergey,Katkevics, Martins
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supporting information; experimental part
p. 2413 - 2423
(2012/09/07)
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- Investigating N-methoxy-N′-aryl ureas in oxidative C-H olefination reactions: An unexpected oxidation behaviour
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Herein, we report a urea derived directing group for mild and highly selective oxidative C-H bond olefination. Subsequent intramolecular Michael addition affords dihydroquinazolinones in good yields. The N-O bond of the urea substrate exhibits superior oxidative behaviour compared to a variety of other external oxidants. The Royal Society of Chemistry 2011.
- Willwacher, Jens,Rakshit, Souvik,Glorius, Frank
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supporting information; experimental part
p. 4736 - 4740
(2011/08/06)
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- Three-component condensations of aldehydes with N-methoxycarboxamides
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The first condensations of N-methoxycarboxamides (component A) with aliphatic acetals (component B) are described. Depending upon the conditions, the hemiaminal type products (AB) can usually be isolated. Conducting the condensations with 2 equiv of acetal affords β-(N-methoxy)amido aldehydes (type ABB products). A condensation using anisole (component C) afforded a product of type ABC.
- Marson, Charles M.,Pucci, Sabrina
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p. 9007 - 9010
(2007/10/03)
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- Total synthesis of HUN-7293
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The first total synthesis of the cyclic heptadepsipeptide HUN-7293 (1), a potent inhibitor of cell adhesion molecule expression exhibiting anti-inflammatory properties, is detailed. The most effective approach relied on an unusually efficient macrocyclization with the formation of the MLEU3 - LEU4 secondary amide that potentially benefits from intramolecular H-bonding preorganization of the acyclic substrate. The requisite linear depsipeptide was convergently assembled with the late stage introduction of the linking ester enlisting a Mitsunobu esterification that occurs with inversion of the DGCN α-center permitting the utilization of a readily available L-amino acid precursor to the D α-hydroxy carboxylic acid residue. An alternative and similarly attractive approach of direct macrolactonization of a substrate necessarily incorporating a D-DGCN subunit proved viable albeit less effective. Biological evaluation in cellular assays for vascular adhesion molecule expression confirmed that synthetic HUN-7923 (1) is essentially indistinguishable from the naturally occurring cyclodepsipeptide.
- Boger, Dale L.,Keim, Holger,Oberhauser, Berndt,Schreiner, Erwin P.,Foster, Carolyn A.
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p. 6197 - 6205
(2007/10/03)
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- Mild hydrolysis or alcoholysis of amides. Ti(IV) catalyzed conversion of primary carboxamides to carboxylic acids or esters
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Reaction of primary amides (e.g., 1a or 6-13) or O-methylhydroxamates (1b and 1c) with a catalytic amount of TiCI4 and one equivalent of aqueous HCI converts these compounds in good yields to carboxylic esters (when an alcohol is used as solvent) or to carboxylic acids (when 9:1 dioxane:H2O is used as solvent). These conversions are chemoselective for primary amides: mono- and dialkyl amides are not affected by the reaction conditions. The hydrolysis conditions described do not compromise the stereochemical integrity of an adjacent chiral center. This is exemplified by the hydrolysis of naproxen amide (34) to naproxen (33) without detectable racemization as determined by chiral HPLC.
- Fisher,Caroon,Stabler,Lundberg,Zaidi,Sorensen,Sparacino,Muchowski
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p. 142 - 145
(2007/10/02)
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- O-Methylarenehydroxamates as Ortho-Lithiation Directing Groups. Ti(III)-Mediated Conversion of O-Methyl Hydroxamates to Primary Amides
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Reaction of O-methyl benzohydroxamates 2a-c with sec-butyllithium in the presence of TMEDA at -40 deg C regiospecifically generates the highly reactive N,ortho-dilithiated species (e.g. 3).These dilithio species react avidly with a wide spectrum of electrophilic reagents, including alkyl halides, givind adducts which on reduction with TiCl3 are converted into ortho-substituted primary benzamides in excellent yields.Ortho lithiation of O-methyl benzohydroxamates is thus formally equivalent to ortho lithiation of primary benzamides themselves.The utility of these synthetic operations is enhanced by the well-known facility with wich the primary amide moiety can be transformed into other useful functional groups.The conversion of O-methyl hydroxamates to primary amides is shown to be general, as exemplified by transformation of 14a-f to 15a-f.O-Methyl-2-methylbenzohydroxamate (4a) undergoes regiospecific dilithiation on nitrogen and on the methyl group when treated with sec-butyllithium at -70 deg C.These dilithio species react with DMF or "Weinreb-type" amides to give condensation products wich cyclize to N-methoxyisoquinolin-1(2H)-ones under mildly acidic conditions.Removal of the N-methoxy moiety under conditions analogous to those used for O-methyl benzohydroxamate provides N-unsubstituted isoquinolin-1(2H)-ones with high overall efficiency.This process is exemplified by the synthesis of isoquinolin-1(2H)-one 9a, its 3-n-butyl congener 9b, and the tricyclic isoquinolin-1(2H)-ones 20a and 20b from O-methyl 2-methylbenzohydroxamate (4a).
- Fisher, Lawrence E.,Caroon, Joan M.,Jahangir,Stabler, S. Russell,Lundberg, Scott,Muchowski, Joseph M.
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p. 3643 - 3647
(2007/10/02)
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- Electrophilic Aromatic Substitution with N-Methoxy-N-acylnitrenium Ions Generated from N-Chloro-N-methoxyamides: Syntheses of Nitrogen Heterocyclic Compounds Bearing a N-Methoxyamide Group
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N-Methoxy-N-acylnitrenium ions (II), generated by treatment of N-chloro-N-methoxyamides with silver carbonate in trifluoroacetic acid, react with arenes to give N-aryl-N-methoxyamides in good yields.In the case of the intramolecular cyclization of N-chloro-N-methoxy-2-phenylacetamides, the mode of cyclization is highly dependent on the nature of ortho or para substituent groups.Nitrenium ions II can primarily attack three positions (C-1, C-2, and C-6) of a phenyl ring.Normally II attack C-6.On the other hand, when the ortho position was occupied with a substituent group, II attacked both C-2 and C-6, in the former case followed by a 1,2-substituent migration, which was proved by a deuterium labeling experiment.Especially, when a methoxy group is substituted on ortho or para position, II attack C-1 due to the effect of the electron-releasing methoxy group to give spiro dienone compounds 39.A general discussion of the utility and mechanistic details of these reactions is presented.
- Kawase, Masami,Kitamura, Takahiro,Kikugawa, Yasuo
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p. 3394 - 3403
(2007/10/02)
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- N-ALKOXY-N-ACYLNITRENIUM IONS IN INTRAMOLECULAR AROMATIC ADDITION REACTIONS
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N-alkoxy-N-acylnitrenium ions are generated by treatment of N-alkoxy-N-chloroamides with silver ions in ethereal solvents.These intermediates readily cyclise onto aromatic nuclei on alkoxy side-chains to give benzoxazines and benzoxazepines and on the acyl side-chains to give γ, δ and ε benzolactams.Spirane products are formed by ipso addition when a 4-methoxy substituent is present on the side-chain aromatic rings.The yields and regioselectivities of these reactions have been ascribed to different transition structures for cyclisation onto the acyl and alkoxy side-chains which involve respectively an exocyclic and endocyclic N-O ?-bond.Evidence for this exeptionally high ?-bond character has been obtained from MNDO calculations which predict a ?-bond order of 0.9 and a rotational barrier of 29.7 kcalmol-1
- Glover, Stephen A.,Goosen, Andre,McCleland, Cedric W.,Schoonraad, Johan L.
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p. 2577 - 2592
(2007/10/02)
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