- InCl3 immobilized in ionic liquids: A novel and recyclable catalytic system for tetrahydropyranylation and furanylation of alcohols
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A mild and highly efficient method has been developed for the protection of hydroxyl compounds as tetrahydropyranyl and furanyl ethers using a catalytic amount of indium trichloride immobilized in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid under mild conditions. A wide range of functional and protecting groups such as THP, TBDMS, TBDPS, PMB, MOM ethers, acetonides, olefins and epoxides are compatible with ionic liquids. Monoprotection of diols has also been achieved using this novel procedure.
- Yadav, Jhillu Singh,Reddy, Basi V. Subba,Gnaneshwar, Dughani
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Read Online
- Microwave-mediated selective monotetrahydropyranylation of symmetrical diols catalyzed by iodine
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Selective protection of one hydroxyl group as its tetrahydropyranyl ether in 1, n-symmetrical diol is achieved by iodine-catalyzed reaction of the diol with dihydropyranyl ether under microwave irradiation.
- Deka,Sarma
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Read Online
- Selective monotetrahydropyranylation of 1,n-diols catalyzed by aqueous acids
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1,n-Diols with 3-12 carbon atoms gave selectively the corresponding monotetrahydropyranyl ethers in higher yields than 80% in the reaction catalyzed by hydrogen ion in the water layer which is in contact with DHP-toluene or DHP-hexane layer. (C) 2000 Elsevier Science Ltd.
- Nishiguchi,Hayakawa,Hirasaka,Saitoh
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- Highly Selective Monotetrahydropyranylation of Symmetrical Diols Catalysed by a Strongly Acidic Ion-exchange Resin
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Several primary and secondary symmetrical diols, ranging from propane-1,3-diol to decane-1,10-diol, are selectively monoprotected by monotetrahydropyranyl ether formation catalysed by a strongly acidic ion-exchange resin (Dowex 50x x 2, 50-100 mesh) in a 3,4-dihydro-2H-pyran-hydrocarbon mixture.
- Nishiguchi, Takeshi,Kuroda, Masahumi,Saitoh, Masahiko,Nishida, Akiko,Fujisaki, Shizuo
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- Synthesis and characterization of hexadecadienyl compounds with a conjugated diene system, sex pheromone of the persimmon fruit moth and related compounds
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Hexadecadien-1-ol and the derivatives (acetate and aldehyde) with a conjugated diene system have recently been identified from a pheromone gland extract of the persimmon fruit moth (Stathmopoda masinissa), a pest insect of persimmon fruits distributed in
- Nishida, Takanobu,Vang, Le Van,Yamazawa, Hiroyuki,Yoshida, Ryuji,Naka, Hideshi,Tsuchida, Koji,Ando, Tetsu
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- Preparation of monotetrahydropyranylated short-chain symmetrical diols
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Efficient and robust methods for the monoprotection of 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol as THP ethers have been developed. The preparation of 4-(tetrahydro-pyran-2-yloxy)-butan-1-ol from 1,4-butanediol and 5-(tetrahydro-pyran-2-yloxy)-pentan-1-ol from 1,5-pentanediol was accomplished using a two-phase system composed of CH2Cl2. 3,4-dihydro-2H-pyran, and aqueous 0.1 N HCL. Preparation of 3-(tetrahydro-pyran-2-yloxy)-propan-1-ol from 1,3-propanediol was accomplished using a water-free biphasic mixture composed of 1,3-propanediol, catalytic pyridinium p-toluenesulfonate, 3,4-dihydro-2H-pyran, and 25% ether in hexane. The compounds are very useful three- to five-carbon homologating agents.
- Petroski, Richard J.
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- Photochemical E(trans)-Z(cis) isomerization in 9-anthraceneacrylic esters
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Several (1-6) 9-anthraceneacrylic esters were synthesized in order to study photochemical E(trans)-Z(cis) isomerization. All of the compounds 1-6 underwent selective E-to-Z isomerization upon direct excitation (> 400 nm) in organic solvents, leading to the formation of a thermodynamically less stable Z isomer over 96%. Triplet sensitized isomerization selectively produces the Z-to-E isomer in over 98%. The higher quantum yield of isomerization observed in the triplet-sensitized Z-to-E isomerization process informs us that a "quantum chain" process is in operation. Fluorescence data generated on all compounds indicate that the E-to-Z isomerization process involves a charge-transfer or polar singlet excited state.
- Reddy, Majjigapu Janaki Ram,Srinivas, Uppalanchi,Srinivas, Kolupula,Reddy, Vummadi Venkat,Jayathirtha Rao, Vaidya
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- A palladium/chiral amine co-catalyzed enantioselective dynamic cascade reaction: Synthesis of polysubstituted carbocycles with a quaternary carbon stereocenter
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Polysubstituted 5- and 6-membered carbocycles were synthesized by the title reaction. The one-pot dynamic relay process generates four new stereocenters, including a quaternary carbon center, in a highly enantioselective fashion (99.5:0.5→99:0.5 e.r.) by using a simple combination of palladium and chiral amine co-catalysts. Copyright
- Ma, Guangning,Afewerki, Samson,Deiana, Luca,Palo-Nieto, Carlos,Liu, Leifeng,Sun, Junliang,Ibrahem, Ismail,Cordova, Armando
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Read Online
- Drastic fluorine effect: Complete reversal of the selectivity in the Au-catalyzed hydroalkoxylation reaction of fluorinated haloalkynes
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The gold-catalyzed hydration reaction of haloalkynes is highly regioselective producing 2-halomethylketones as the sole products. Herein, we document a drastic fluorine effect where the reaction of 1-halo-3,3-difluoroalkynes as substrates leads to a complete reversal of selectivity and produces 3,3-difluoroesters as the unique products.
- Cloutier, Mélissa,Mamone, Marius,Paquin, Jean-Fran?ois
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supporting information
p. 5969 - 5972
(2020/06/04)
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- Condensed tricyclic compound and applications in medicines
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The invention relates to a condensed tricyclic compound and applications in medicines, particularly to applications of the condensed tricyclic compound as drugs for treating and/or preventing hepatitis B, specifically to a compound represented by general
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Paragraph 0670; 0672-0674
(2020/04/02)
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- Au-catalyzed intramolecular hydroalkoxylation of gem-difluorinated alkynols
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The intramolecular hydroalkoxylation of gem-difluorinated alkynols was found possible under Au catalysis, allowing for the preparation of a series of fluorinated heterocycles. The nature of the solvent was found to be especially critical in the cyclizatio
- Hamel, Jean-Denys,Paquin, Jean-Fran?ois
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- Remote Cooperative Group Strategy Enables Ligands for Accelerative Asymmetric Gold Catalysis
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An accelerative asymmetric gold catalysis is achieved for the first time via chiral ligand metal cooperation. An asymmetrically positioned remote amide group in the designed chiral binaphthyl-based ligand plays the essential role of a general base catalyst and selectively accelerates the cyclizations of 4-allen-1-ols into one prochiral allene face. The reactions are mostly highly enantioselective with achiral substrates, and due to the accelerated nature of the catalysis catalyst loadings as low as 100 ppm are allowed. With a pre-existing chiral center at any of the backbone sp3-carbons, the reaction remained highly efficient and most importantly maintained excellent allene facial selectivities regardless of the substrate stereochemistry. By using different combinations of ligand and substrate enantiomers, it is now possible to access all four stereoisomers of versatile 2-vinyltetrahydrofurans with exceedingly high selectivity. The underpinning design of this chemistry reveals a novel and conceptually distinctive strategy to tackle challenging asymmetric gold catalysis, which to date has relied on decelerative asymmetric steric hindrance approaches.
- Wang, Zhixun,Nicolini, Corrado,Hervieu, Cedric,Wong, Yuk-Fai,Zanoni, Giuseppe,Zhang, Liming
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supporting information
p. 16064 - 16067
(2017/11/22)
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- SUBSTITUTED BRIDGED UREA ANALOGS AS SIRTUIN MODULATORS
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The present invention relates to novel substituted bridged urea analog compounds of Formula (I) or pharmaceutically acceptable salts thereof, corresponding pharmaceutical compositions, processes for making and use of such compounds, alone or in combination with other therapeutic agents, as Sirtuin Modulators useful for increasing lifespan of a cell, and for use in treating and/or preventing a wide variety of diseases and disorders, which include, but are not limited to, for example, diseases or disorders related to aging or stress, diabetes, obesity, neurodegenerative diseases, cardiovascular disease, blood clotting disorders, inflammation, cancer, and/or flushing as well as diseases or disorders that would benefit from increased mitochondrial activity.
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Page/Page column 252-253
(2016/06/15)
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- PROCESSES AND INTERMEDIATES FOR PREPARING α,ω-DICARBOXYLIC ACID-TERMINATED DIALKANE ETHERS
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The present disclosure provides a process for the preparation of compounds of formula (III), compounds of formula (V), and corresponding salts of formula (IV). The compounds made by the methods and processes of the invention are particularly useful for ad
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Paragraph 00329; 00382; 00383
(2016/06/06)
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- TETRASUBSTITUTED ALKENE COMPOUNDS AND THEIR USE
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Disclosed herein are compounds, or pharmaceutically acceptable salts thereof, and methods of using the compounds for treating breast cancer by administration to a subject in need thereof a therapeutically effective amount of the compounds or pharmaceutically acceptable salts thereof. The breast cancer may be an ER-positive breast cancer and/or the subject in need of treatment may express a mutant ER-α protein.
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Page/Page column 66
(2016/12/22)
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- Synthesis of cycloalkanone-fused cyclopropanes by Au(I)-catalyzed oxidative ene-yne cyclizations
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Au(I)-catalyzed oxidative cyclizations that successfully convert 1,5-ene-ynes and a 1,6-ene-yne to the corresponding cycloalkanone-fused cyclopropanes are described. This Au(I)-catalyzed oxidative cyclization can be effectively applied to various substrat
- Uetake, Yuta,Niwa, Takashi,Nakada, Masahisa
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supporting information
p. 6847 - 6850
(2015/01/09)
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- Polystyrene-supported GaCl3: A new, highly efficient and recyclable heterogeneous Lewis acid catalyst for tetrahydropyranylation of alcohols and phenols
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A new, simple and highly chemoselective method for tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-pyran (DHP) in the presence of polystyrene-supported gallium trichloride (PS/GaCl3) as a highly active and reusable heterogeneous Lewis acid catalyst at room temperature is presented.
- Rahmatpour, Ali
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p. 66 - 71,6
(2012/12/11)
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- Preparation of highly hindered polyenes with tert-butyl groups in internal positions
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The conjugated tetraenes 3 and 4 a-c have been prepared and shown to possess an orthogonal structure. This was not only demonstrated by their spectroscopic properties and X-ray structural analysis of solid representatives (e.g., 4 a-c) but also by the res
- Betz, Markus,Hopf, Henning,Ernst, Ludger,Jones, Peter G.,Okamoto, Yoshio
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scheme or table
p. 231 - 247
(2011/03/19)
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- Anodic oxidation: An attractive alternative to CAN-mediated cleavage of para-methoxyphenyl ethers
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para-Methoxyphenyl (PMP) ether is a very convenient protecting group for the alcohol function; however, its cleavage requires strong oxidative conditions. In this field, the use of powerful eerie ammonium nitrate has been widely described, despite the fac
- Vaxelaire, Carine,Souquet, Florence,Lannou, Marie-Isabelle,Ardisson, Janick,Royer, Jacques
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supporting information; experimental part
p. 3138 - 3140
(2009/12/05)
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- Bifunctional inhibitors of mevalonate kinase and mevalonate 5-diphosphate decarboxylase
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A bifunctional inhibitor of mevalonate kinase and mevalonate 5-diphosphate decarboxylase was synthesized. Both enzymes are in the cholesterol biosynthetic pathway and play an important role in regulating cholesterol biosynthesis. The molecule may become a
- Qiu, Yongge,Li, Ding
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p. 1013 - 1016
(2007/10/03)
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- Silica-gel-supported aluminium chloride: A stable, efficient, selective, and reusable catalyst for tetrahydropyranylation of alcohols and phenols
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A simple, effective, and highly chemoselective method to form 2-tetrahydropyranyl ethers of alcohols and phenols in the presence of silica-gel-supported aluminium chloride as a heterogeneous Lewis acid catalyst is described. The catalyst can be easily recovered and reused without appreciable change in its efficiency. Copyright Taylor & Francis Group, LLC.
- Borujeni, Kaveh Parvanak
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p. 2705 - 2710
(2007/10/03)
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- A highly efficient synthetic protocol for tetrahydropyranylation/ depyranylation of alcohols and phenols
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Bismuth(III) nitrate pentahydrate [Bi(NO3)3· 5H2O] is found to be an effective catalyst for both tetrahydropyranylation and depyranylation of alcohols and phenols. Some of the major advantages of this protocol are: non-aqueous workup, good yields, the involvement of a less-expensive and nontoxic catalyst, and compatibility in the presence of a large number of other protecting groups. Notably, isopropylidene, benzylidene, and thioacetal groups are also unaffected under the experimental conditions. Remarkably, a selective mono-protection of diols and primary alcohols can be achieved chemoselectively by employing the same catalyst. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
- Khan, Abu T.,Ghosh, Subrata,Choudhury, Lokman H.
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p. 4891 - 4896
(2007/10/03)
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- Synthesis of medium- and large-sized lactones in an aqueous-organic biphasic system
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(Chemical Equation Presented) Saving solvent: An aqueous-ethyl acetate biphasic system allows an efficient synthesis of medium- and large-sized lactones by an intramolecular Tsuji-Trost reaction (see scheme, n = 1-5). The macrocyclization protocol does not require a large quantity of solvents or a slow-addition technique.
- Kinoshita, Hidenori,Shinokubo, Hiroshi,Oshima, Koichiro
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p. 2397 - 2400
(2007/10/03)
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- Total synthesis of bidensyneosides A2 and C: Remarkable protecting group effects in glycosylation
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Bidensyneosides are a group of five recently identified polyacetylenic glucosides from Bidens parviflora WILLD, a traditional Chinese medicinal plant that contains rich bioactive natural products. It was shown that bidensyneosides inhibited both histamine
- Gung, Benjamin W.,Fox, Ryan M.
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p. 9405 - 9415
(2007/10/03)
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- Silyl group deprotection by Pd/C/H2. A facile and selective method
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An easy, high yield, RT, short-reaction-time Pd/C hydrogenation of silyl groups is described. This includes TES, TPS, TBS, TBDMS, TIPS, and TBDPS. The relative selectivity of the process has been investigated and we can show, for example, that TES, TPS, TBS, and TBDMS removal can be performed in the presence of TIPS and TBDPS.
- Kim, Seongjin,Jacobo, Sheila Marie,Chang, Chih-Tsung,Bellone, Sophie,Powell, William S.,Rokach, Joshua
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p. 1973 - 1976
(2007/10/03)
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- Chemoselective tetrahydropyranylation of alcohols and phenols using polystyrene supported aluminium chloride as a catalyst
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A simple, efficient and highly chemoselective method for tetrahydropyranylation of alcohols and phenols has been developed by their reaction with 3,4-dihydro-2H-pyran at room temperature in the presence of a catalytic amount of polystyrene supported AlCl3. The method is also highly selective for monoprotection of symmetrical diols.
- Tamami, Bahman,Parvanak Borujeny, Kaveh
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p. 715 - 718
(2007/10/03)
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- Simple, facile and highly selective tetrahydropyranylation of alcohols using silica chloride
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A simple and efficient process for tetrahydropyranylation of alcohols has been developed by reacting with dihydropyran at room temperature in presence of catalytic amount of silica chloride. The process is highly selective for monoprotection of the hydroxyl groups of symmetric diols.
- Ravindranath,Ramesh,Das
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p. 1777 - 1778
(2007/10/03)
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- An efficient synthesis of trans-γ-oxo-α,β-unsaturated carboxylic acids, the intermediates for patulolide A and pyrenophorin
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An efficient synthesis of intermediates for macrolide antifungals patulolide A 14 and pyrenophorin 16 are described with the key steps involving (i) coupling of the alkyl lithium with α,β-unsaturated aldehyde 8, (ii) the oxidation of the cis-trans mixture
- Davis,Bhalerao,Vittal Rao
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p. 656 - 661
(2007/10/03)
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- Synthesis of achiral, but unsymmetric, seven-membered rhodium(I)-chelates for hydrogenation in the chiral environment of alkyl polyglucoside micelles
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Chiral rhodium(I) chelates containing a seven-membered ring are well-known active catalysts for the asymmetric hydrogenation of amino acid precursors. A high conformational flexibility allows their enantioselectivity to be strongly influenced by modifiers. Now we show the nature of the counter-ions to have a large influence in apolar solvents. In addition, the presence of micelle forming alkyl polyglycosides as amphiphiles causes a remarkable increase in the enantiomeric excess (%ee). However, on achiral catalysts this enantioselectivity inducing effect scarcely exceeds the standard deviation for the gas chromatographic determination of the enantiomeric ratio. This is also true for the application of unsymmetric P,P′-ligands such as 3-phosphinopropyl-phosphinites or butane-1,4-diyl-bis(phosphines) carrying different P′-aryl groups, for which synthetic routes are given.
- Fehring,Kadyrov,Ludwig,Holz,Haage,Selke
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p. 120 - 129
(2007/10/03)
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- Design and synthesis of macro-heterocycles structurally related to tirofiban
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Sequences of nine and four steps were designed to yield two tirobifan related macrocycles by SN2 macrocyclization. The cyclic compounds contain the amino acid tyrosine, one insaturation and are either 18- or 20-membered rings. All the reaction conditions are very mild and the overall yields indicate that the results depend a lot on the structure of the targets and on the length of the reaction sequence. (C) 2000 Published by Elsevier Science Ltd.
- Ramaseshan, Mahesh,Robitaille, Martin,Ellingboe, John W.,Dory, Yves L.,Deslongchamps, Pierre
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p. 4737 - 4742
(2007/10/03)
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- Synthesis, CoMFA analysis, and receptor docking of 3,5-diacyl-2,4- dialkylpyridine derivatives as selective A3 adenosine receptor antagonists
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3,5-Diacyl-2,4-dialkyl-6-phenylpyridine derivatives have been found to be selective antagonists at both human and rat A3 adenosine receptors (Li et al. J. Med. Chem. 1998, 41, 3186-3201). In the present study, ring- constrained, fluoro, hydroxy, and other derivatives in this series have been synthesized and tested for affinity at adenosine receptors in radioligand binding assays. K(i) values at recombinant human and rat A3 adenosine receptors were determined using [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)- 5'-N-methylcarbamoyladenosine). Selectivity for A3 adenosine receptors was determined vs radioligand binding at rat brain A1 and A(2A) receptors, and structure-activity relationships at various positions of the pyridine ring (the 3- and 5-acyl substituents and the 2- and 4-alkyl substituents) were probed. At the 5-position inclusion of a β-fluoroethyl (7) or a γ- fluoropropyl ester (26) was favorable for human A3 receptor affinity, resulting in K(i) values of 4.2 and 9.7 nM, respectively, while the pentafluoropropyl analogue was clearly less potent at human A3 receptors. At the 2-, 3-, and 4-positions, fluoro or hydroxy substitution failed to enhance potency and selectivity at human A3 receptors. Several analogues were nearly equipotent at rat and human A3 receptors. To further define the pharmacophore conformationally, a lactam, a lactone, and thiolactones were tested in adenosine receptor binding. The most potent analogue in this group was compound 34, in which a thiolactone was formed between 3- and 4-positions and which had a K(i) value of 248 nM at human A3 receptors. Using affinity data and a general pharmacophore model for A3 adenosine receptor antagonists recently proposed, we applied comparative molecular field analysis (CoMFA) to obtain a three dimensional quantitative structure-activity relationship for pyridine derivatives, having good predictability (r2(pred) = 0.873) for compounds in the test set. A rhodopsin-based model of the human As receptor was built, and the pyridine reference ligand 2,3,4,5-tetraethyl-6-phenyl- pyridine-3-thiocarboxylate-5-carboxylate (MRS 1476) was docked in the putative ligand binding site. Interactions between receptor transmembrane domains and the steric and the electrostatic contour plots obtained from the CoMFA analysis were analyzed.
- Li, An-Hu,Moro, Stefano,Forsyth, Nancy,Melman, Neli,Ji, Xiao-Duo,Jacobson, Kenneth A.
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p. 706 - 721
(2007/10/03)
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- A key intermediate towards oxylipins. A formal synthesis of (12S)-HETE and (12S)-LTB4
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A key intermediate in the synthesis of various oxylipins, the optically active (3S,5Z)-3-methoxymethoxyundec-5-en-1-yne, has been obtained in 11 steps starting from propane-1,3-diol, with an overall yield of 14%.
- Benkouider, Abdelhamid,Pale, Patrick
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p. 104 - 105
(2007/10/03)
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- Selective monotetrahydropyranylation of symmetrical diols catalyzed by ion-exchange resins
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Primary and secondary symmetrical diols with 2-10 carbon atoms gave selectively monotetrahydropyranyl ethers in the reaction catalyzed by wet sulfonic acid-type ion-exchange resins in 3,4-dihydro-2H-pyran (DHP)/toluene or DHP/hexane. The yields of the monoethers were higher than 80% while those of the corresponding diethers were lower than 5%. In these reactions the rate of the formation of the diethers did not increase much even after most of the diols had been consumed. In the reaction of 1,10-decanediol in DHP/hexane, the yields of the monoether were increased by the addition of DMF or DMSO. Each diol was found to have a particular DHP/hydrocarbon ratio that gave the highest selectivity for the monoether. Generally, the larger the number of carbon atoms of the diols, the smaller the ratio of DHP in the solvents to give high selectivity for the monoether. This method of the selective etherification is quite simple and practical.
- Nishiguchi, Takeshi,Fujisaki, Shizuo,Kuroda, Masahumi,Kajisaki, Kohtaro,Saitoh, Masahiko
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p. 8183 - 8187
(2007/10/03)
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- A mild, efficient, and selective method for the desilylation of more common trialkylsilyl ethers by cerium(III) chloride heptahydrate and sodium iodide in acetonitrile
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Treatment of trialkylsilyl ethers with cerium(III) chloride heptahydrate and sodium iodide in acetonitrile provides a simple, convenient, and chemoselective process for desilylation, and the parent alcohol was obtained in high yield. The trialkylsilyl ethers have been cleaved selectively in the presence of acetate, benzyl and tetrahydropyranyl ethers.
- Bartoli, Giuseppe,Bosco, Marcella,Marcantoni, Enrico,Sambri, Letizia,Torregiani, Elisabetta
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p. 209 - 211
(2007/10/03)
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- Hemiaminal generated by hydration of ketone-based nitrone as an N,O-centered nucleophile in organic synthesis
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Isoxazolidines that are useful precursors for β-amino acids have been prepared relying on intermolecular amino Michael addition-intramolecular S(N)2 displacement employing hydroxylamine or hydrate of ketone-based nitrone as an N- and O-centered binucleophile.
- Ishikawa, Teruhiko,Nagai, Keita,Senzaki, Mami,Tatsukawa, Akiko,Saito, Seiki
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p. 2433 - 2448
(2007/10/03)
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- Selective acceleration for deprotection of benzyl ethers with ti-HMS
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Ti-HMS, a Ti-loaded hexagonal mesoporous silica, was found to accelerate deprotection of benzyl ethers under hydrogenolytic conditions with palladium catalyst. Such acid-sensitive functional groups as silyl ether and acetal moieties in the molecule were little affected by Ti-HMS, which possesses Lewis acid sites due to Ti-atom.
- Itoh, Akichika,Kodama, Tomohiro,Maeda, Shiro,Masaki, Yukio
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p. 9461 - 9464
(2007/10/03)
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- Studies on the transannular Diels-Alder reaction of 15-membered macrocyclic trienes containing a trans-trans diene. Part I: Synthesis and isomerization of various model cyclopentadecatrienes
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The transannular Diels-Alder reaction of 15-membered macrocyclic trienes with a trans-trans-cis (TTC) olefin geometry can lead to A.B.C. tricyclic products of trans-syn-trans (TST) and cis-syn-cis (CSC) stereochemistry whereas the TTT isomers can p
- Hall, Dennis G.,Mueller, Renate,Deslongchamps, Pierre
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p. 1675 - 1694
(2007/10/02)
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- Highly Selective Monoetherification of Symmetrical Diols Catalysed by Metallic Sulfate Supported on Silica Gel
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Several symmetrical primary and secondary diols from C2 to C16 have been protected in high selectivity by tetrahydropyranyl ether formation catalysed by metallic sulfates supported on silical gel.This selective etherification is simple and practical.The s
- Nishiguchi, Takeshi,Kawamine, Katsumi,Ohtsuka, Tomoko
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p. 153 - 156
(2007/10/02)
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- PEPTIDE BOND FORMATION USING AN ENZYME MIMICKING APPROACH
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A man-made enzyme-model based on a concerted proton transfer step (bifunctional catalysis) which mimics the corresponding step in non-ribosomal peptide synthesis was developed.Important features of the model are the following: (a) a bifunctional acid-base catalyst for the thiolester aminolysis rate acceleration, (b) two thiol-containing arms mimicking the "swinging arms" of the enzyme, and (c) symmetry elements so that the process can be iterated with consequent formation of the polypeptide chain.Peptide bond formation was obtained by intramolecularly catalyzed thiolester aminolysis to give 5 in 80percent isolated yield (Scheme IV, V) and with at least a 103-fold rate acceleration in comparison with the corresponding non catalyzed process (4 -> 6)(Scheme IV, Table 1).The reaction is also 4-20 times faster than the analogous process 4 -> 6 run in the presence of 0.1M external catalyst (Et3N-ButCOOH or 2-Pyridone).Important structural and reaction parameters are discussed.A second intramolecular aminolysis reaction gave tripeptide 8 in lower yield (35percent) because of higher steric congestion in the transition state.
- Gennari, Cesare,Molinari, Francesco,Piarulli, Umberto,Bartoletti, Marcella
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p. 7289 - 7300
(2007/10/02)
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- A Specific and Efficient Synthesis of (+/-)-Dihydrocorynantheol
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A specific and efficient synthesis of (+/-)-dihydrocorynantheol (1) is reported.Starting with the easily accessible imine (3), ring D was built via stereoselective reaction with the lactone (4a), thus providing the complete carbon skeleton of (1); subsequ
- Danieli, Bruno,Lesma, Giordano,Palmisano, Giovanni,Tollari, Stefano
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p. 1237 - 1240
(2007/10/02)
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- Difunctionalized Trans-2,5-Disubstituted Pyrrolidine (Azethoxyl) Nitroxide Spin-Labels
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The synthesis of two short-chain trans-2,5-difunctionalized azethoxyl nitroxide spin-labels, dinitrile 12 and dicarboxylic acid 14, is described.The trans stereochemistry of 12 and 14 was established by conversion of 12 to a diastereomeric mixture of N-hydroxy esters 13, which was analyzed by NMR spectroscopy.
- Keana, John F. W.,Seyedrezai, Seyed E.,Gaughan, Glen
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p. 2644 - 2647
(2007/10/02)
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- General Synthetic Route to Hexaamine Macrocycles
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A general synthetic route has been developed for the preparation of hexaamine macrocycles containing two diethylenetriamine units joined by aliphatic hydrocarbon bridges of varying length.By use of this method, the new 20-, 22-, and 24-membered polyamines
- Martin, Andrea E.,Bulkowski, John E.
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p. 415 - 418
(2007/10/02)
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