- Steric and electronic factors influencing recognition by a simple, charge neutral norbornene based anion receptor
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Based on 1H NMR studies, subtle electronic factors rather than pre-organisation dictate the binding stoichiometry of the new, norbornene based, anion hosts 1 and 2 with acetate, however, the binding of dihydrogenphosphate appears to be based so
- Lowe, Adam J.,Dyson, Gail A.,Pfeffer, Frederick M.
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Read Online
- The synthesis of fluorinated endcaps: Part 1. the effect of C-7 fluorination on the base-catalyzed monohydrolysis of 5-norbornenyl-2,3-diesters
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In an attempt to improve the thermo-oxidative stability of aerospace polyimides, we have explored the preparation of 7-fluorinated nadic endcaps. The latter are 5-norbonenyl acid esters in a 2-endo,3-endo configuration, which is required for imidization. The most obvious precursor is the corresponding diester and, hence, we carried out a preliminary study of the saponification of the symmetric dimethyl esters of various 7-mono- and 7,7-disubstituted nadic acids (5-norbornenyl-2-endo,3-endo-dicarboxylic acids). These included the 7-fluoro (7c) and 7,7-difluoro (7e) derivatives, as well as the 7,7-diprotio (7a), 7-hydroxy (7b) and 7-oxo (7d) analogs for the purpose of comparison. Contrary to previous reports, and depending on the substitution pattern and the basic conditions used, various amounts of hydrolysis and configuration inversion were observed giving various yields of 2-endo,3-endo monoacid monoesters 8, 2-endo,3-exo monoacids monoester 13, 2-endo,3-endo diacids 6, and/or 2-endo,3-exo diacids 15. Interestingly, the inversion in configuration always occurred at C3-i.e., on the carbon α to the remaining ester-and the 2-exo,3-endo acid ester 14 was not observed. Overall, the order of increasing configuration inversion is dependant on the C7- substituent(s) with H2 2 7-substituent(s), which contribute(s) to the stability of the enolate formed at C3. These results require a novel synthetic approach to 7-fluorinated nadic endcaps.
- Rajsfus, David E.,Alter-Zilberfarb, Sari,Frimer, Aryeh A.
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Read Online
- Oxathiaborolium-Catalyzed Enantioselective [4 + 2] Cycloaddition and Its Application in Lewis Acid Coordinated and Chiral Lewis Acid Catalyzed [4 + 2] Cycloaddition
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The nascency of second-generation sulfur-stabilized borenium cations by halophilic Lewis acid SnCl4 leads to highly active chiral Lewis acids that are very effective catalysts for [4 + 2] cycloaddition. Oxathiaborolium pentachlorostannate (5-10 mol %) successfully catalyzed cycloaddition of various dienes and dienophiles to afford cycloadducts with excellent enantioselectivity (20 examples, up to 99% ee). This super Lewis acid also exhibited good enantioselectivity for the first Lewis acid coordinated and chiral Lewis acid catalyzed [4 + 2] cycloaddition to α,β-unsaturated mixed ester amide.
- Boobalan, Ramalingam,Chein, Rong-Jie
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supporting information
p. 6760 - 6764
(2021/09/11)
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- TETRACARBOXYLIC DIANHYDRIDE, CARBONYL COMPOUND, POLYIMIDE PRECURSOR RESIN, AND POLYIMIDE
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A tetracarboxylic dianhydride which is a compound represented by the following general formula (1): [in the formula (1), A represents one selected from the group consisting of optionally substituted divalent aromatic groups in each of which the number of carbon atoms forming an aromatic ring is 6 to 30, and Ras each independently represent a hydrogen atom or the like], wherein 60% by mass or more of a stereoisomer contained in the compound is an exo/exo type stereoisomer represented by a specific general formula.
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Paragraph 0086-0087
(2021/04/30)
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- Norbornane-based cationic antimicrobial peptidomimetics targeting the bacterial membrane
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The design, synthesis and evaluation of a small series of potent amphiphilic norbornane antibacterial agents has been performed (compound 10 MIC = 0.25 μg/mL against MRSA). Molecular modelling indicates rapid aggregation of this class of antibacterial agent prior to membrane association and insertion. Two fluorescent analogues (compound 29 with 4-amino-naphthalimide and 34 with 4-nitrobenz-2-oxa-1,3-diazole fluorophores) with good activity (MIC = 0.5 μg/mL against MRSA) were also constructed and confocal microscopy studies indicate that the primary site of interaction for this family of compounds is the bacterial membrane.
- Hickey, Shane M.,Ashton, Trent D.,Boer, Gareth,Bader, Christie A.,Thomas, Michael,Elliott, Alysha G.,Schmuck, Carsten,Yu, Heidi Y.,Li, Jian,Nation, Roger L.,Cooper, Matthew A.,Plush, Sally E.,Brooks, Douglas A.,Pfeffer, Frederick M.
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supporting information
p. 9 - 22
(2018/10/20)
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- Epimerization of Tertiary Carbon Centers via Reversible Radical Cleavage of Unactivated C(sp3)-H Bonds
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Reversible cleavage of C(sp3)-H bonds can enable racemization or epimerization, offering a valuable tool to edit the stereochemistry of organic compounds. While epimerization reactions operating via cleavage of acidic C(sp3)-H bonds, such as the Cα-H of carbonyl compounds, have been widely used in organic synthesis and enzyme-catalyzed biosynthesis, epimerization of tertiary carbons bearing a nonacidic C(sp3)-H bond is much more challenging with few practical methods available. Herein, we report the first synthetically useful protocol for the epimerization of tertiary carbons via reversible radical cleavage of unactivated C(sp3)-H bonds with hypervalent iodine reagent benziodoxole azide and H2O under mild conditions. These reactions exhibit excellent reactivity and selectivity for unactivated 3° C-H bonds of various cycloalkanes and offer a powerful strategy for editing the stereochemical configurations of carbon scaffolds intractable to conventional methods. Mechanistic study suggests that the unique ability of N3? to serve as a catalytic H atom shuttle is critical to reversibly break and reform 3° C-H bonds with high efficiency and selectivity.
- Wang, Yaxin,Hu, Xiafei,Morales-Rivera, Cristian A.,Li, Guo-Xing,Huang, Xin,He, Gang,Liu, Peng,Chen, Gong
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supporting information
p. 9678 - 9684
(2018/07/21)
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- Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions
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Grafting density and graft distribution impact the chain dimensions and physical properties of polymers. However, achieving precise control over these structural parameters presents long-standing synthetic challenges. In this report, we introduce a versatile strategy to synthesize polymers with tailored architectures via grafting-through ring-opening metathesis polymerization (ROMP). One-pot copolymerization of an ω-norbornenyl macromonomer and a discrete norbornenyl comonomer (diluent) provides opportunities to control the backbone sequence and therefore the side chain distribution. Toward sequence control, the homopolymerization kinetics of 23 diluents were studied, representing diverse variations in the stereochemistry, anchor groups, and substituents. These modifications tuned the homopolymerization rate constants over 2 orders of magnitude (0.36 M-1 s-1 homo -1 s-1). Rate trends were identified and elucidated by complementary mechanistic and density functional theory (DFT) studies. Building on this foundation, complex architectures were achieved through copolymerizations of selected diluents with a poly(d,l-lactide) (PLA), polydimethylsiloxane (PDMS), or polystyrene (PS) macromonomer. The cross-propagation rate constants were obtained by nonlinear least-squares fitting of the instantaneous comonomer concentrations according to the Mayo-Lewis terminal model. In-depth kinetic analyses indicate a wide range of accessible macromonomer/diluent reactivity ratios (0.08 1/r2 20), corresponding to blocky, gradient, or random backbone sequences. We further demonstrated the versatility of this copolymerization approach by synthesizing AB graft diblock polymers with tapered, uniform, and inverse-tapered molecular "shapes." Small-angle X-ray scattering analysis of the self-assembled structures illustrates effects of the graft distribution on the domain spacing and backbone conformation. Collectively, the insights provided herein into the ROMP mechanism, monomer design, and homo- and copolymerization rate trends offer a general strategy for the design and synthesis of graft polymers with arbitrary architectures. Controlled copolymerization therefore expands the parameter space for molecular and materials design.
- Chang, Alice B.,Lin, Tzu-Pin,Thompson, Niklas B.,Luo, Shao-Xiong,Liberman-Martin, Allegra L.,Chen, Hsiang-Yun,Lee, Byeongdu,Grubbs, Robert H.
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supporting information
p. 17683 - 17693
(2017/12/15)
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- Synthesis and evaluation of cationic norbornanes as peptidomimetic antibacterial agents
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A series of structurally amphiphilic biscationic norbornanes have been synthesised as rigidified, low molecular weight peptidomimetics of cationic antimicrobial peptides. A variety of charged hydrophilic functionalities were attached to the norbornane scaffold including aminium, guanidinium, imidazolium and pyridinium moieties. Additionally, a range of hydrophobic groups of differing sizes were incorporated through an acetal linkage. The compounds were evaluated for antibacterial activity against both Gram-negative and Gram-positive bacteria. Activity was observed across the series; the most potent of which exhibited an MIC's ≤ 1 μg mL-1 against Streptococcus pneumoniae, Enterococcus faecalis and several strains of Staphylococcus aureus, including multi-resistant methicillin resistant (mMRSA), glycopeptide-intermediate (GISA) and vancomycin-intermediate (VISA) S. aureus.
- Hickey, Shane M.,Ashton, Trent D.,Khosa, Simren K.,Robson, Ryan N.,White, Jonathan M.,Li, Jian,Nation, Roger L.,Yu, Heidi Y.,Elliott, Alysha G.,Butler, Mark S.,Huang, Johnny X.,Cooper, Matthew A.,Pfeffer, Frederick M.
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supporting information
p. 6225 - 6241
(2015/06/08)
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- Polyethylene as a Cosolvent and Catalyst Support in Ring-Opening Metathesis Polymerization
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Polyethylene oligomers (PEOlig) can be used as cosolvents and sometimes soluble catalyst supports in ring-opening metathesis polymerization (ROMP) reactions. As a catalyst support, this polyolefin serves as an N-heterocyclic carbene ligand for a ROMP catalyst, making it soluble at 70 °C and insoluble at room temperature. As a cosolvent, unfunctionalized PE oligomers facilitate quantitative separation of PEOlig-bound Ru-catalyst residues from polymer products. In these cases, the insolubility of the unfunctionalized polyethylene (Polywax) and its entrapment of the PEOlig-supported Ru residue in the product phase at room temperature afford ROMP products with Ru contamination lower than other procedures that use soluble catalysts. These separations require only physical processes to separate the product and catalyst residues - no additional solvents are necessary. Control experiments suggest that most (ca. 90%) of the Ru leaching that is seen results from Ru byproducts formed in the vinyl ether quenching step and not from the polymerization processes involving the PEOlig-supported Ru complex. (Chemical Equation Presented).
- Suriboot, Jakkrit,Hobbs, Christopher E.,Guzman, William,Bazzi, Hassan S.,Bergbreiter, David E.
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p. 5511 - 5516
(2015/09/02)
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- Palladium(0)-Catalyzed Methylcyclopropanation of Norbornenes with Vinyl Bromides and Mechanism Study
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An unusual methylcyclopropanation from [2 + 1] cycloadditions of vinyl bromides to norbornenes catalyzed by Pd(OAc)2/PPh3 in the presence of CH3ONa and CH3OH has been established. A methylcyclopropane subunit was installed by a 3-fold domino procedure involving a key protonation course. Preliminary deuterium-labeling studies revealed that the proton came from methyl of CH3OH and also exposed an additional hydrogen/deuterium exchange process. These two proton-concerned reactions were fully chemoselective.
- Mao, Jiangang,Xie, Hujun,Bao, Weiliang
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supporting information
p. 3678 - 3681
(2015/08/18)
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- Ionic liquids are compatible with on-water catalysis
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A major limitation of on-water catalysis has been the need for liquid reactants to enable emulsification. We demonstrate that ionic liquids are compatible with on-water catalysis, enabling on-water catalysed reactions for otherwise unreactive solid-solid systems. The unique solvation properties of ionic liquids dramatically expands the scope of on-water catalysis.
- Beare, Kaitlin D.,Yuen, Alexander K. L.,Masters, Anthony F.,Maschmeyer, Thomas,McErlean, Christopher S. P.
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supporting information
p. 8347 - 8349
(2013/09/23)
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- NOVEL HEPATITIS C VIRUS INHIBITORS
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The invention provides compounds of formula (I): wherein Rings A and A' are independently 5-membered optionally substituted aromatic heterocycles; Q is C(=O)NR1R1' or formula U is C(R4)2, O, S, S(=O)2, C(R4)2C(R4)2, CH2O, OCH2, CH2S, SCH2, CH2S(=O)2, S(=O)CH2 or C=C(Ru )2; X is CH2, CHR12, CR12R12, O, S, S(=O)2 or NRx; m is 0, 1, 2 or 3; n is 0, 1, 2 or 3; the other variables are as defined in the claims, which are of use in the treatment or prophylaxis of hepatitis C virus infection, and related aspects.
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Page/Page column 90
(2013/07/05)
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- Stabilization and controlled release of reactive molecules by solid-state van der waals capsules
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Control by encapsulation: A dimeric capsule assembled from a tripodal host by van der Waals forces can stabilize a series of reactive molecules, such as cyclopentadiene and trichlorosilane, in the crystalline state even under relatively harsh conditions. Moreover, these reactive molecules can be controllably released into liquid media for further chemical reaction by thermal programming, leaving the insoluble host molecules behind for easy separation and reuse (see scheme). Copyright
- Wei, Wei,Li, Wanlong,Li, Zhongfeng,Su, Weiping,Hong, Maochun
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p. 469 - 473
(2013/02/23)
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- A convenient procedure for bis-esterification of cyclic anhydrides
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Aromatic and aliphatic cyclic anhydrides are chemoselectively and conveniently transformed to the corresponding diesters by the use of DBU and appropriate alkyl/allyl halides. This bis-esterification reaction has been exemplified mostly with dimethyl esters. But in some cases, mixed dialkyl esters are also prepared.
- Jana, Amit Kumar,Karmakar, Raju,Dinda, Bidyut Kumar,Mitra, Prithiba,Ghosh, Ketaki,Karmakar, Rajdip,Mal, Dipakranjan
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p. 975 - 979
(2012/10/29)
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- Serendipitous and acid catalyzed synthesis of spirolactones
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Formation of three diasteroisomeric spirodilactones 14a-c and 11 has been reported from diester 13 and 9, respectively, under the influence of mineral acid.
- Kotha, Sambasivarao,Dipak, Mirtunjay Kumar,Mobin, Shaikh M.
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scheme or table
p. 4616 - 4619
(2011/06/27)
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- N-hexylpyridinium bis(trifluoromethylsulfonyl)imide and Lewis acids - Catalytic systems for Diels-Alder reaction
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A comparative study of the Diels-Alder reactions between cyclopentadiene (1) and dienophiles (2 a - c) in N-hexylpyridinium bis(trifluoromethylsulfonyl) imide in a temperature range of 20-45°C is reported. The reaction rate constants and activation energies were calculated. Moreover, the catalytic systems based on N-hexylpyridinium bis(trifluoromethylsulfonyl)imide and Lewis acids were tested as a reaction media to perform the Diels-Alder reaction. Yb, Y, Mg, Zn triflates and chlorides (0.005 to 0.1 mmol) were used as catalysts. The recycling of catalytic system consisted of YCI3 and ionic liquid was performed. Versita Sp. z o.o.
- Bittner, Bozena,Janus, Ewa,Milchert, Eugeniusz
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scheme or table
p. 192 - 198
(2012/04/04)
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- The mechanism of on-water catalysis
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Acid catalysis by interfacial water: A new mechanism is proposed for onwater catalysis, the acceleration of organic reactions when conducted in aqueous emulsions. It involves the protonation of a substrate by water, driven by the strong adsorption of hydroxide ions at aqueous interfaces with oils. This accounts for the specific role of water, and a deuterium isotope effect, at the interface, on reactions known to be acid-catalysed.
- Beattie, James K.,McErlean, Christopher S. P.,Phippen, Christopher B. W.
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supporting information; experimental part
p. 8972 - 8974
(2010/10/02)
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- Remote Exo/Endo selectivity in selective monohydrolysis of dialkyl bicyclo[2.2.1]heptane-2,3-dicarboxylate derivatives
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Figure presented High exo-facial selectivity was observed in the selective monohydrolysis of a series of near-symmetric diesters that possess an exo-ester group and an endo-ester group attached on a norbornane or norbornene skeleton. The selectivities were found to be clear-cut, although the reaction center in these reactions is one covalent bond distant from the norbornane or norbornene ring, where the difference of the environment between the exo face and endo face is therefore expected to be negligible. The effect of the co-solvent we studied earlier for the selective monohydrolysis reaction was also confirmed and contributed to improvement of the yields of the half-esters.
- Niwayama, Satomi,Cho, Hanjoung,Zabet-Moghaddam, Masoud,Whittlesey, Bruce R.
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supporting information; experimental part
p. 3775 - 3780
(2010/09/03)
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- Triethylsulfonium bistriflimide as the reaction medium in catalyzed and uncatalyzed cycloaddition [4 + 2]
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Triethylsulfonium bistriflimide, [S2.2.2][NTf2], has been tested and compared with other ionic liquids and molecular solvents as a medium in Diels-Alder reaction between cyclopentadiene and dimethyl maleate. Triflates and chlorides of different metals have been combined with [S 2.2.2][NTf2] and the catalytic activity of the systems formed have been determined. The effect of concentration of the catalysts in sulfonium ionic liquid and reactants on the yield and endo:exo ratio has been established. The representative catalyst-Yb(OTf)3?xH 2O in [S2.2.2][NTf2] has been examined in the reaction of cyclopentadiene with various dienophiles. The use of sulfonium ionic liquids permitted recycling the catalysts. For the best four catalytic systems, the products have been isolated.
- Janus, Ewa,Bittner, Bozena
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experimental part
p. 147 - 154
(2010/11/05)
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- Solvent-free Diels-Alder reactions of in situ generated cyclopentadiene
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A solvent-free Diels-Alder reaction was carried out by heating a mixture of dicyclopentadiene and a dienophile. Cyclopentadiene, formed in situ, reacted with the dienophile in a thermodynamically controlled reaction. Besides being solvent-free, the descri
- Huertas, David,Florscher, Melinda,Dragojlovic, Veljko
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experimental part
p. 91 - 95
(2010/04/22)
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- Structural elucidation of daphniacetal A, a new oxa-cage compound isolated from Daphniphyllum macropodum Miq.
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A new oxa-cage natural product daphniacetal A (1) was isolated from Daphniphyllum macropodum Miq. Its structure and relative configuration were established based on spectroscopic data and the single-crystal X-ray diffraction crystallography. Compound 1 was also synthesized for determination of its absolute configuration and evaluation of antioxidant effects.
- Kong, Ning-Chuan,Zhang, Yu,Gao, Suo,Lu, Yang,Zheng, Qi-Tai,Sun, Quan-Yun,Yang, Fu-Mei,Di, Ying-Tong,Hao, Xiao-Jiang
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body text
p. 957 - 959
(2009/05/27)
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- Biodegradable pyridinium ionic liquids: Design, synthesis and evaluation
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A range of ionic liquids (ILs) with a pyridinium cation were synthesised and their biodegradability was evaluated using the CO2 Headspace test (ISO 14593). ILs bearing an ester side chain moiety were prepared from either pyridine or nicotinic acid and showed high levels of biodegradation under aerobic conditions and can be classified as 'readily biodegradable'. In contrast, pyridinium ILs with alkyl side chains showed significantly lower levels of biodegradability in the same test. The utility of the biodegradable IL 6c as a reaction solvent for the Diels-Alder reaction was also investigated.
- Harjani, Jitendra R.,Singer, Robert D.,Garcia, M. Teresa,Scammells, Peter J.
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experimental part
p. 83 - 90
(2010/04/22)
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- Diels-Alder reaction in protic ionic liquids
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Protic imidazolium ionic liquids have been tested as reaction media in the Diels-Alder reaction between cyclopentadiene and two dienophiles (dimethyl maleate and methyl acrylate). Good conversions and endo/exo selectivities were achieved. The activation of the dienophile by hydrogen bonding with protic imidazolium ILs was demonstrated.
- Janus, Ewa,Goc-Maciejewska, Izabela,?ozyński, Marek,Pernak, Juliusz
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p. 4079 - 4083
(2007/10/03)
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- [2.2.1]-Bicyclic systems relevant to synthetic studies on CP-225,917 - Use of a new silylated cyclopentadiene
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The [2.2.1]-bicyclic ketone 6, a potential synthetic precursor to CP-225,917, was prepared by a sequence beginning with Diels-Alder reaction between dimethyl fumarate and the silylated cyclopentadiene 38. The adduct 40 was subjected to Tamao-Fleming oxidation, which converted it into alcohol 21. During the oxidation BF3·Et2O-AcOH was used instead of the more expensive BF3·2AcOH complex. Alcohol 21 was elaborated into 6, which carries one of the sidechains of CP-225,917, as well as other substituents that are appropriate for further elaboration.
- Clive, Derrick L.J.,Cheng, Hua,Gangopadhyay, Pulak,Huang, Xiaojun,Prabhudas, Bodhuri
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p. 4205 - 4221
(2007/10/03)
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- Lewis acid-promoted transesterification of N-acyl oxazolidinones under mild conditions
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N-Acyl oxazolidinones are smoothly converted to the corresponding esters by Lewis acid-promoted transesterification. Mild reaction conditions suppress epimerization or racemization of chiral substrates and allow acid-sensitive groups to survive.
- Orita, Akihiro,Nagano, Yoshifumi,Hirano, Junichi,Otera, Junzo
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p. 637 - 639
(2007/10/03)
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- Diels - Alder reactions of epoxybutene derivatives and subsequent synthetic manipulations of the cycloadducts
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Diels - Alder reactions between cyclopentadiene, cyclohexadiene, and a number of epoxybutene derivatives are reported. The endo diastereomer from the Diels - Alder reaction of cyclopentadiene with 2,5-dihydrofuran was functionalized by additional oxidative transformations.
- Franks, Marion A.,Hyatt, John A.,Welker, Mark E.
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p. 514 - 518
(2013/09/07)
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- Diels-Alder reactions in chloroaluminate ionic liquids: Acceleration and selectivity enhancement
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The utility of room temperature chloroaluminate ionic liquids as solvent and catalyst for the synthetically important Diels-Alder reaction was studied. The AlCl3-1-ethyl-3-methyl-1H-imidazolium chloride medium proved to be ideally suited for Diels-Alder reactions. Endo selectivity and rate enhancement were observed for the cyclopentadiene/methyl acrylate Diels- Alder reaction.
- Lee, Carlos W.
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p. 2461 - 2464
(2007/10/03)
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- The nature of lithium perchlorate and gallium chloride salt effect in cycloaddition reactions
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Comparing the acceleration effects of (4 + 2)-, (3 + 2)- and (2 + 2)-cycloaddition reactions in the presence of the salts of two types: gallium chloride in inert solvents and lithium perchlorate (LP) in diethyl ether (DE) it was observed that in the presence of GaCl3 the acceleration effect is approximately the same (104 times) for the studied reactions, while in LPDE medium for the same reactions strong increase (up to 104 times), weak increase or even decrease of the rate and equilibrium constants take place even with the common dienophile depending on the nature of the second reagent. it was suggested that the acceleration effect of cycloaddition reactions in the presence of such Lewis acids as aluminum, gallium or boron halides is due to the sharp increase of Π-acceptor properties of dienophiles and therefore increasing energy of orbital interaction, whereas LPDE medium demonstrates strong stabilization of static and/or dynamic polar forms and favors reactions with charge control.
- Shtyrlin, Yury G.,Murzin, Dmitry G.,Luzanova, Natalia A.,Iskhakova, Gulnara G.,Kiselev, Vladimir D.,Konovalov, Alexandr I.
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p. 2631 - 2646
(2007/10/03)
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- Cycloadditions with clays and alumina without solvents
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The utilization of unactivated K-10 montmorillonite or alumina for Diels-Alder reactions in the absence of solvents, either with symmetrically- or unsymmetrically-substituted carbonyl dienophiles, constitutes an environmentally-friendly alternative providing excellent selectivities under mild conditions.
- Avalos, Martin,Babiano, Reyes,Bravo, Jose L.,Cintas, Pedro,Jimenez, Jose L.,Palacios, Juan C.,Ranu, Brindaban C.
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p. 2013 - 2016
(2007/10/03)
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- Cyclopentanedi- and tricarboxylic acids as squalene synthase inhibitors: Syntheses and evaluation
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Based on earlier lead squalene synthase inhibitor A-87049 (3) and zaragozic acids, a series of cyclopentanedi- and tricarboxylic acids were synthesized and evaluated against the enzyme. Some exhibited good potency and SAR revealed the importance of conformation and substitution pattern of these synthetic inhibitors.
- Shen, Wang,Garvey, David S.,Cohen, Jerry,Stein, Herman,Rosenberg, Saul H.
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p. 891 - 896
(2007/10/03)
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- A C2-symmetric titanium(IV) complex as a Lewis acid promoter in Diels-Alder reaction
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3-Aza-3-benzyl-1,5-dihydroxy-1,5-diphenylpentane 1, a C2-symmetric diol has been prepared by the reaction of benzylamine and styrene oxide using a modified procedure. The corresponding titanium complex has been effectively utilised as a Lewis acid promoter in Diels-Alder reactions. The reactions are performed with cyclopentadiene and various dienophiles under different reaction conditions. The Diels-Alder adducts have been obtained in moderate to good yield and with high endo selectivity.
- Manickam,Sundararajan
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p. 1006 - 1011
(2007/10/03)
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- Optical Resolution of trans-Bicycloheptane-2,3-diamine: Chiral Recognition in the Crystal of its Complex with (2R,3R)-O,O'-Dibenzoyltartaric Acid
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The synthesis of trans-bicycloheptane-2,3-diamine (6c), its optical resolution via formation of its complex with (2R,3R)-O,O'-dibenzoyltartaric acid (-BTA), and the crystal structure determination of this complex by X-ray diffraction techniques are reported.The absolute configuration of 6c in the complex has been determined to be (S,S)-6c from the endowed chirality of -BTA, thus optical resolution of 6c is achieved.Crystal data for the (S,S)-6c*(-BTA) complex is reported: C25H28N2O8*2H2O, M = 520.54, monoclinic P21, a = 9.150(1), b = 8.581(1), c = 17.036(1) Angstroem, β = 103,30(1) deg, V = 1301(2) Angstroem3, Z = 2, R = 0.037.The crystal of the molecular complex is found to have a multilamellar structure partitioned by thin hydrogen bonded sheets containing complex ammonium-carboxylate-water hydrogen bonds.Attached on both sides of the sheet, monolayer templates with benzoyl groups of -BTA and bicycloheptane fragments of 6c stack with the next templates to form hydrophobic bilayers.In the monolayer template, a cavity is formed surrounded by two pairs of two benzoyl groups distinguished from each other by their orientations toward the hydrogen bond sheet.The cavity provides a final site for the chiral recognition of 6c.The (S,S)-enantiomer of 6c is probably distinguished from the (R,R)-enantiomer by the favourable orientation of bicycloheptane skeleton in the cavity.
- Hatano, Keiichiro,Takeda, Tadahiro,Saito, Reiko
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p. 579 - 584
(2007/10/02)
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- Enzymatic optical resolution of norbornanecarboxylic esters using Pig Liver Esterase
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The hydrolysis of a series of norbornane-type carboxylic esters catalyzed by pig liver esterase (PLE) has been investigated.It was found that an exo-ester function (syn to the C7 methylene group) is hydrolyzed with high preference.Enantioselective hydrolysis can be accomplished when a vicinal carbonyl-containing function (ester, formyl, acetyl) is present in a trans position with respect to the exo ester.The regiospecifity of the enzymatic hydrolysis has been used for the separation of exo/endo mixtures of the cycloadducts derived from cyclopentadiene and alkene esters.The regiospecifity and enantioselectivity of the enzymatic hydrolysis of norbornane-type esters were analyzed in terms of Tamm's substrate model and also by Griengl's method.
- Gastel, F. J. C. van,Klunder, A. J. H.,Zwanenburg, B.
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p. 175 - 184
(2007/10/02)
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- Cycloaddition reactions of dimethyl maleate and fumarate with cyclopentadiene on γ-alumina. Competing mechanisms for epimerization of the Diels-Alder adducts
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The Diels-Alder adducts, formed in the reaction of cyclopentadiene and dimethyl maleate and fumarate, epimerize on γ-alumina by competing mechanisms involving the retro-Diels-Alder reaction and enolates.
- Bains,Pagni,Kabalka
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p. 5663 - 5666
(2007/10/02)
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- Mild and highly selective ultrasound-promoted zinc/acetic acid reduction of C=C bonds in α,β-unsaturated γ-dicarbonyl compounds
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Sonication of various, α,β-unsaturated γ-diketones, quinones, α,β-unsaturated γ-diacids or γ-diesters with powdered zinc and acetic acid at room temperature results in selective reduction of the C=C bond in each case within ca. 5 minutes to 2.5 h and affords the corresponding reduction products in yields of 94-100%. Isolated (i.e., nonconjugated) C=C bonds are not affected by zinc/acetic acid under these conditions.
- Marchand,Reddy
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p. 198 - 200
(2007/10/02)
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- The Reaction of Wittig Reagents with Selenium. Formation of Selenoaldehydes
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The reaction of Wittig reagents with elemental selenium gave the corresponding selenoaldehydes which further reacted with other Wittig reagents to give the corresponding dimeric olefins in good yields.The selenoaldehydes formed afforded corresponding adducts by the reaction with dienes.These selenoaldehydes obtained by retro Diels-Alder reaction were also found to react with Wittig reagents to give the corresponding olefins in good yields.
- Okuma, Kentaro,Komiya, Yasuo,Kaneko, Isao,Tachibana, Yuji,Iwata, Eiji,Ohta, Hiroshi
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p. 1653 - 1657
(2007/10/02)
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- REDUCTION OF ENEDICARBOXYLATE COMPOUNDS WITH LOW VALENT TITANIUM
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The carbon-carbob double bonds of enedicarboxylate compounds can be reduced readily with TiCl4-LiAlH4-Et3N in THF.Other double bond of the enedicarboxylate does not react during the reduction process.
- Hung, Chi Wai,Wong, Henry N. C.
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p. 2392 - 2396
(2007/10/02)
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- STEREOSELECTIVE PIG LIVER ESTERASE-CATALYZED HYDROLYSIS OF RIGID BICYCLIC MESO-DIESTERS : PREPARATION OF OPTICALLY PURE 4,7-EPOXYTETRA- AND HEXA-HYDROPHTHALIDES.
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The bicyclic and rather rigid meso-diesters 1 - 3 have been found to be good substrates for pig liver esterase.The half-esters obtained have been converted to either one of the enantiomers of tricyclic lactones, of potential value for natural product synthesis.
- Bloch, R.,Guibe-Jampel, E.,Girard, C.
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p. 4087 - 4090
(2007/10/02)
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- SELECTIVE DIELS-ALDER REACTIONS IN AQUEOUS SOLUTIONS AND SUSPENSIONS
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Diels-Alder reactions show high endo/exo selectivities in aqueous suspensions.
- Breslow, Ronald,Maitra, Uday,Rideout, Darryl
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p. 1901 - 1904
(2007/10/02)
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- STEREOSELECTIVE ALKYLATION OF THE LITHIUM DI-ENOLATE OF BIS-2,3-CARBOMETHOXY BICYCLOHEPT-5-ENE. A CONVENIENT SYNTHESIS OF MONO- AND DISUBSTITUTED FUMARATE ESTERS.
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The diesters formed by a Diels-Alder reaction between cyclopentadiene and methyle maleate or fumarate give the same lithium dienolate which is stereoselectively mono- or dialkylated.The products obtained are good precursors for substituted fumarate esters.
- Girard, C.,Bloch, R.
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p. 3683 - 3686
(2007/10/02)
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- EIN BEITRAG ZUR STEREOSPEZIFITAET VON (4+2)-CYCLOADDITIONEN
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Addition of maleo-, fumaronitrile and maleic-, fumaric ester (with and without AlCl3) to cyclopentadiene are stereospecfic to a degree of higher than 99.8-99.98 percent.
- Prantl, B.,Eibler, E.,Sauer, J.
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p. 1139 - 1142
(2007/10/02)
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