bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enantioselective enzymatic catalysis.:2. Applicability of methods for enantiomeric ratio determinations
Authors: Bert J. , van Tol A. , Jongejan Jaap A. , Geerlof Arie , Duine Johannis A. 
Published: September 2010

AbstractThree methods for the determination of the enantiomeric ratio, E, of enantioselective, Michaelis‐Menten‐type enzymes have been investigated with respect to accuracy, using the method of propagation of standard deviation. In addition, estimations of standard deviations of E were obtained from simulations and representative experiments. The coefficient of variation (γE) achieved in the values derived from the kinetic parameters of the enantiomers (method I) does not depend on the absolute value of E. With initial‐rate measurements on mixtures of enantiomers at a fixed concentration of substrates (method II), the accuracy depends on the characteristics of the system, i.e., kinetic parameters, concentration and enantiomeric purity of the substrates, whereas with end‐point analysis (method III) the value of E is the crucial factor. Accurate estimates (γE< 0.1) of E can be obtained with method I, and for E < 30 also with method III.As well as the aspect of accuracy, the methods have different intrinsic merits which can also be relevant in making a choice: method I gives information on the reaction mechanism; method II is well suited for screening purposes; method III is attractive for applied studies as it mimics a preparative process. In view of these complementary capabilities, an adequate set of tools seems to be available now for fundamental and applied studies on enantioselectivity.
Conversion of D‐ribo‐3‐hexosulose into D‐ribulose and D‐erythronic acid in aqueous medium
Authors: de Wit D. , van Rantwijk F. , Maat L. , Kieboom A. P. G. 
Published: September 2010

AbstractThe decomposition of D‐ribo‐3‐hexosulose in water, studied by HPLC, gave D‐ribulose (60‐65%) and D‐erythronic acid (20%), both isolated by column chromatography. D‐Ribulose was characterized using LC‐MS and NMR. From the latter technique, the ratio of three isomeric structures was determined. D‐Erythronic acid was characterized by NMR.
Hydride transfer reactions of benzylic alcohols catalyzed by acid faujasites
Authors: Climent María J. , Corma Avelino , García Hermenegildo , Iborra Sara , Primo Jaime 
Published: September 2010

AbstractReaction of five benzylic alcohols in solution at 78°C has been performed in the presence of a series of HY zeolites at three different levels of Na+ ‐to‐NH4+ exchange (HY‐21, HY‐50 and HY‐100) and framework Si‐to‐Al ratio (HY‐100, HY‐200 and HY‐400). Dehydration to form a CC double bond is the main primary process for 1‐phenyl‐ and 1,1‐diphenylethanol. Nevertheless, the initial alkenes are unstable, giving rise to the corresponding phenylethanes and, in the case of styrene, also to dimers. In contrast, benzyl alcohol and diphenylmethanol gave equimolar amounts of phenylmethanes and phenyl ketones, by an intermolecular hydride transfer not observed under conventional homogeneous acid catalysis. This process was found to be highly demanding from the point of view of the acid strength of the sites involved. Finally, triphenylmethanol showed a remarkable reluctance to undergo any change, although small amounts of triphenylmethane, benzophenone and 9‐phenyl‐9‐hydroxyfluorene were detected after long reaction times.
Calix (aza‐)crowns as potential ionophores for divalent and trivalent cations
Authors: Ostaszewski Ryszard , Stevens Tieme W. , Verboom Willem , Reinhoudt David N. , Kaspersen Frans M. 
Published: September 2010

AbstractA series of calix (aza‐)crowns 6a‐f and 11a,b has been prepared by reaction of either calix dimethyl ester 4 or calix diacid dichloride 10 with an appropriate diamine. The complexation with both di‐ and trivalent cations has been qualitatively studied using fast‐atom bombardment mass spectrometry.
Mechanism of the reaction of carbodiimides with carboxylic acids
Authors: Schotman A. H. M. 
Published: September 2010

AbstractThe kinetic parameters of the reaction of diphenylcarbodiimide with various carboxylic acids have been determined at a temperature interval of 20‐160°C.The classical scheme for the reaction of carbodiimides with carboxylic acids is extended. It has been found that, at high temperatures, amides and isocyanates are the end products of the reactions. N‐Acylureas, initially formed from aromatic carbodiimides and carboxylic acids, dissociate into isocyanates and amides at temperatures above 60°C. N‐Acylureas formed by the reaction of carboxylic acids with aliphatic carbodiimides prove to be more stable: their dissociation temperature is about 50°C higher. Both the formation and dissociation of N‐acylureas are much faster when the parent acid is stronger.
Chemistry of indoles carrying basic functions. I. Transformation of hydroxyindolones into indoles
Authors: Moldvai István , Gács‐Baitz Eszter , Szántay Csaba 
Published: September 2010

Abstract3‐Hydroxy‐3‐[(2‐ and 4‐pyridyl)methyl]‐1H‐indol‐2‐ones (1, 12) have been reduced with NaBH4/MeOH/t‐BuOH. After acidic treatment, 2‐ and 3‐substituted indoles (2, 11 and 13, 14, respectively) were obtained. The intermediates 3 and 4 of the rearrangement were isolated and the effect of the pyridylmethyl groups on the rearrangement has also been established.
The preparation and reactions of 2‐halogenoethyl β‐L‐arabinopyranosides
Authors: Hough Leslie , McCarthy Karl C. , Richardson Anthony C. 
Published: September 2010

AbstractAcid‐catalysed reaction of L‐arabinose with 2‐chloroethanol, 2‐bromoethanol or 2‐iodoethanol at 50‐60 °C, afforded the highly crystalline 2‐haloethyl β‐L‐arabinopyranosides in 20%, 86% and 23% yields respectively, which each crystallised out directly from the reaction mixtures. Following O‐acetylation of 2‐bromoethyl β‐L‐arabinopyranoside, the bromo substituent underwent substitution by various nucleophilic anions (N3−, NCS−, AcS−, BzO−) to give the appropriate acetylated functionalised glycosides. O,S‐Deacetylation of 2‐(acetylthio)ethyl 2,3,4‐tri‐O‐acetyl‐β‐L‐arabinoside afforded 2‐mercaptoethyl β‐L‐arabinopyranoside, but deblocking of the 2‐thiocyanatoethyl 2,3,4‐tri‐O‐acetyl‐P‐L‐arabinoside in the same way afforded the thiol as a minor product, with the derived disulphide and methylthio derivatives as the major products. The origin of these compounds is discussed. Reaction of the 2‐bromoethyl arabinoside with base afforded the as‐fused bicycle 1,2‐O‐ethylene‐β‐L‐arabinopyranose in high yield. Acetonation and subsequent oxidation of the 2‐azidoethyl arabinoside gave the 2‐ketone, reductive amination of which led to the trans‐fused bicycle 2‐amino‐2‐deoxy‐1,2‐O, N‐ethylene‐β‐L‐ribose. Chlorination of 2‐chloroethyl β‐L‐arabinopyranoside with triphenylphosphine/carbon‐tetrachloride, followed by treatment with base afforded 3,4‐anhydro‐1,2‐O‐ethylene‐β‐L‐arabinopyranoside, ring‐opening of which by azide proceeded regiospecifically to give the 4‐azido‐D‐xylo isomer, which was reduced to the amine.
Gas‐phase pyrolysis of coumaran and 2,3‐dimethylcoumaran
Authors: van Meurs Marcel , Arends Isabel W. C. E. , Louw Robert , Mulder Peter 
Published: September 2010

AbstractPyrolysis of coumaran, 2,3‐dihydrobenzofuran,(Ia) at ca. 700°C leads to the isomeric o‐vinylphenol Ila and some benzofuran IIIa. The 2,3‐dimethyl derivative Ib ‘directly’ gives IIIa in a relatively easy double homolytic de‐methylation reaction (2).
Recent developments in polymer synthesis
Authors: Mijs W. J. , Addink R. 
Published: September 2010

AbstractRecent developments in polymer synthesis are reviewed, especially those methods that lead to well defined structures: group‐transfer polymerization, living cationic and anionic polymerization from cyclic and acyclic monomers using new initiating systems, metathesis polymerizations with new catalysts. Pseudo‐living radical polymerizations, leading to new block copolymers and new mechanisms of radical ring opening, leading to new polymers and copolymers are included. From the field of stepwise polymerization, new developments in phase‐transfer catalysis and activated polycondensation mechanisms are described. New polymer architecture, important for modern applications in new materials is represented by the section on liquid‐crystalline polymers.
13C NMR microstructure determinations of low‐density polyethylene homopolymers and copolymers
Authors: Randall J. C. , Ruff C. J. , Kelchtermans M. 
Published: September 2010

AbstractLow‐density polyethylenes, prepared by free radical processes in high‐pressure reactors, are dendritic polymers with complex microstructures. Both long‐ and short‐chain aliphatic branches are produced by Roedel intramolecular and intermolecular chain‐transfer reactions during free‐radical processes. Unlike catalytically produced linear low‐density polyethylenes, high‐pressure free‐radical polymerization processes possess the capability for incorporating polar comonomers, which leads to copolymers, such as poly(ethylene‐co‐vinylacetate), poly(ethylene‐co‐acrylic acid), poly‐(ethylene‐co‐methylacrylate), etc. Although it is not often discussed, these comonomer units can also be involved in Roedel intramolecular and intermolecular chain‐transfer reactions either as terminal units or as sites for chain‐transfer during a ‘backbiting’ step. These additional reactions lead to even more complex structures. In this study, the various ways comonomer units can be incorporated into low‐density polyethylene chains, as a consequence of Roedel chain‐transfer chemistry, are identified and the microstructures are given in terms of aliphatic branching as well as type and amount of comonomer structures. This leads to more complete structural determinations that yield results consistent with the melting behavior and that are useful in establishing structure‐property relationships.
Review of 1H‐ and 13C‐NMR spectroscopy of (meth)acrylate (co)polymers
Authors: Gaur H. Angad 
Published: September 2010

AbstractA review of 1H‐ and 13C‐NMR investigation of (meth)acrylate homo‐ and copolymers and of (meth)acrylate‐styrene copolymers is presented. The results obtained by these techniques are discussed in terms of compositional and stereo‐conformational sequence distributions. Topics also covered are 2D NMR and computational techniques.
(1R)‐ and (1S)‐5‐demethyl‐8,16‐methanobacteriorhodopsin and its properties. The synthesis and spectroscopy of 5‐demethyl‐8,16‐methanoretinal in optically active and isotopic forms
Authors: Spijker‐Assink M. B. , Robijn G. W. , Ippel J. H. , Lugtenburg J. , Groen B. H. , van Dam K. 
Published: September 2010

Abstract(All‐E)‐5‐demethyl‐8,16‐methanoretinal was prepared in both optical antipodes (1R and 1S), as well as in their 9‐Z and 13‐Z forms. The interaction of the 1R and 1S forms with bacterioopsin shows that there is a clear chiral recognition on the formation of the bacteriorhodopsin analogues, reflected in the rate of binding and ϵmax values. The two bacteriorhodopsins with optically active chromophores have an identical λmax value and show the same efficiency of the light‐driven proton pump. The absence of the 5‐methyl group leads to a 50% lower proton‐pump efficiency than the native system. In addition, for the racemic 5‐demethyl‐8,16‐methanoretinal, the 5‐2H, 7‐2H, 5,7‐2H2 and 5,7,16a,16a‐2H4 isotopomers in the various isomeric forms all‐E, 9‐Z and 13‐Z were also prepared.
Near absolute regio‐, diastereo‐, and enantioselectivity in a palladium: Catalyzed alkylation using an uncommon chiral auxiliary
Authors: Sjouken Ronald , Ebens Rijko , Kellogg Richard M. 
Published: September 2010

AbstractCondensation of R‐(+)‐1‐(2‐chlorophenyl)‐2,2‐dimethyl‐propan‐1,3‐diol (2) with a derivative (1) of 1‐formylcyclohexene substituted in the 3‐position with an acetoxy group proceeded with absolute stereospecificity at the acetal center. Catalytic alkylation of the π‐allyl complex obtained upon reaction with Pd with the anion of dimethylmalonate proceeded at the 3‐position of the cyclohexyl ring with complete stereocontrol.
Synthesis of β‐amino α‐hydroxy carboxylic esters from oxiranecarboxylic esters
Authors: Legters Johan , van Dienst Erik , Thijs Lambertus , Zwanenburg Binne 
Published: September 2010

Abstract3‐Aryl‐3‐azido‐2‐hydroxypropanoic esters, prepared from the corresponding 3‐aryl‐oxirane‐2‐carboxylic esters by ring opening with sodium azide, were reduced with tin(II) chloride dihydrate in methanol to give 3‐amino‐3‐aryl‐2‐hydroxypropanoic esters in good yields. Under these conditions, halogen substituents in the aromatic rings were not affected. The nitro group, however, was partially reduced to the amino group. Treatment of aliphatic oxirane‐2‐carboxylic esters with acetonitrile in the presence of boron trifluoride etherate led to regiospecific formation of 2,4‐dialkyl‐2‐oxazoline‐5‐carboxylic esters, resulting from reaction of the nitrile at C3. Acidic hydrolysis of these oxazoline‐5‐carboxylic esters gave the corresponding 3‐(acylamino)‐2‐hydroxy carboxylic esters. With these two complementary methods, both aryl‐ and alkyl‐substituted β‐amino α‐hydroxy acid derivatives are accessible.
Solid‐phase synthesis of oligodeoxynucleotides containing 4‐alkoxythymidine residues
Authors: Roelen H. C. P. F. , Brugghe H. F. , van den Elst H. , van der Marel G. A. , van Boom J. H. 
Published: September 2010

AbstractImmobilized and fully protected oligodeoxynucleotides containing a 4‐(1,2,4‐triazolyl)‐thymidine residue at a predetermined position were prepared according to a well‐established phosphite triester methodology using 2‐cyanoethyl phosphoramidites of a 4‐(1,2,4‐triazolyl)‐substituted thymidine and standard protected nucleosides. Treatment of the immobilized oligomer with methanol, ethanol or n‐propanol in the presence of DBU at 50°C gave the corresponding oligonucleotides containing 4‐methoxy, 4‐ethoxy‐ or 4‐n‐propoxythymidine residue.
Some new cationic di‐ and tricarbonyl complexes of technetium(I)
Authors: Castro H. H. Knight , Hissink C. E. , Teuben J. H. , Vaalburg W. , Panek K. 
Published: September 2010

AbstractSome new low‐valent, cationic complexes of technetium‐99 have been prepared. Oxidation of Tc2(CO)10 (1) with NOPF6 in acetonitrile gave [Tc(CH3CN)(CO)5]PF6 (2) quantitatively. This complex constitutes a useful precursor for cationic carbonyl complexes, as exemplified by a variety of reactions with bi‐ and tridentate ligands from which air‐stable, water‐soluble complexes of type [LTc(CO)3]+ (L = 1,4,7‐triazacyclononane, 1,4,7‐trimethyl‐1,4,7‐triazacyclononane and 1,4,7‐trithiacyclononane) have been isolated and characterized. A series of mixed complexes of technetium(I) of general formula {Tc(N,N)[P(OR)3]2(CO)2}PF6 (N,N = 2,2′‐bipyridine, 4,4′‐dimethyl‐2,2′‐bipyridine and R = methyl, isopropyl) has also been prepared.
Reductive cleavage of the carbonphosphorus bond with alkali metals. III. Reactions of arylalkylphosphines
Authors: van Doorn Johannes A. , Meijboom Nico 
Published: September 2010

AbstractThe reductive cleavage of phenylalkylphosphines Ph2PR, PhPR2 (R = Bu, iPr) with Na/NH3 is unselective: both phenyl and alkyl groups can be cleaved and Birch reduction may occur. Reaction of Ph2tBuP gives a high yield of diphenylphosphide. Polar groups (CO2Na, SO3,Na) at the ω position of primary alkyl groups may lead to an increase in selectivity; Birch reduction is suppressed and a functionalised secondary phosphide is obtained.From diarylbenzyl‐ and diarylallylphosphines, the benzyl and allyl groups are selectively removed; Ar2PH and ArRPH are formed in high yield after hydrolytic work‐up unless the aryl group bears F, CF3, or (CH3)2N substituents. From the reaction mixture of Ph2PCH2Ph we have isolated 1,2‐ ‐diphenylethane.2‐Methoxyphenyl and 2,6‐dimethoxyphenyl groups are selectively removed from Ar2BuP, ArPhBuP and Ar2P(CH2)3PAr2, forming ArBuPH, PhBuPH and ArP(H)(CH2)3(H)PAr, respectively. A double‐cleavage reaction of Ar2RP may occur in low yield. 2,6‐(Dimethoxyphenyl‐dibutylphosphine gives dibutylphosphine in moderate yield. When compounds with a 2,6‐dimethoxyphenyl moiety are allowed to react with Li/THF, removal of a methyl group leads to novel phosphinophenols. It is concluded that cleavage of alkyl groups R selectively occurs when R° is relatively stable (tBu, PhCH2 > iPr > Bu).
Sulfonation of anisole, phenol, toluene and related alkyl and alkoxy derivatives with SO3. The influence of the solvent system on the reactivity and the sulfonic acid product distribution
Authors: Ansink Harold R. W. , Cerfontain Hans 
Published: September 2010

AbstractThe reactions of anisole (1), phenol (2), the alkoxy‐ and alkylphenyl ethers 3–11, toluene (12) and the o‐dialkylbenzenes 13–15 with sulfur trioxide in dichloromethane or trichlorofluoromethane have been studied. Our results have been compared with those obtained with the same substrates upon reaction with SO3 in nitromethane and dioxane. We show that ortho substitution is enhanced for sterically unhindered phenyl ethers and phenols due to complex formation between SO3 and the C(sp2)‐bonded oxygen when dichloromethane is used as solvent instead of nitromethane or dioxane. This is mainly as a result of intramolecular SO3, transfer from the oxygen to the ortho carbon and subsequent conversion of the resulting σ‐complex into the ortho sulfonic acid.
Synthesis of phosphatidylinositol analogs containing sulfonylmethylene or methyleneoxy linkages
Authors: Elie C. J. J. , Brounts D. M. , Dreef C. E. , van der Marel G. A. , van Boom J. H. 
Published: September 2010

AbstractAlkylation of the α‐lithio anion of 2,3,4,5,6‐penta‐O‐benzyl‐myo‐inositol 1‐(methanesulfonate) with 1,2‐O‐isopropylidene‐sn‐glycerol 3‐(trifluoromethanesulfonate) gave, after removal of the acetonide function followed by palmitoylation and finally hydrogenolysis of the benzyl protecting groups, the racemic phosphatidylinositol analog 3. The methyleneoxy‐containing inositol phospholipid 4 was prepared by iodonium‐ion‐assisted condensation of 1,2‐O‐isopropylidene‐3‐(methylthiomethyl)‐sn‐glycerol with 2,3,4,5,6‐penta‐O‐benzyl‐myo‐inositol, and subsequent removal of all protecting groups.
Computer‐executed synthesis planning, a progress report
Authors: Dogane I. , Takabatake T. , Bersohn M. 
Published: September 2010

AbstractWe describe the Sumitomo Chemical Company computer program, which designs synthetic routes for organic molecules, without consulting a user. There are only approximately 2500 reactions stored in the program. Significant advances in the automation of reaction input are presented. We also give some examples of synthetic routes proposed by the program, one being an enantiospecific and stereospecific route for the synthesis of the antibiotic chloramphenicol.
Erythronolide B: Analysis of the synthesis pathway proposed by the Lilith program
Authors: Baumer Luca , Compagnari Ilaria , Sala Giordano , Sello Guido 
Published: September 2010

AbstractComputer‐Assisted Organic Synthesis (CAOS) has become a common tool in synthesis pathway design. Many different approaches exist, each giving suggestions for the exploration of the synthetic space. Validation of the proposed solutions can be done both by using different programs and by experimental realization of the synthesis. To this end, a molecule of medium complexity, erythronolide B, has been used to make a three‐way comparison using results obtained by the program LHASA, in the laboratory, and by the program Lilith. The importance of using different sources in studying a synthesis pathway is discussed, with respect to achieving the best result from each approach. The high level of convergence in the syntheses proposed by the Lilith program is the most interesting characteristic of the program's results. Moreover, reproduction of the syntheses proposed by the other approaches guarantees the applicability of the Lilith program to real synthetic problems. A brief outline of the Lilith program is included.
Some recent progress in the development of the LHASA computer system for organic synthesis design: Starting‐material‐oriented retrosynthetic analysis
Authors: Johnson A. Peter , Marshall Chris , Judson Philip N. 
Published: September 2010

AbstractOne of the strategies used by chemists when designing retrosynthetic routes is to direct them towards particular starting materials which have been chosen because they have structural similarities to the target compounds. This paper illustrates uses of the starting‐material strategy in the LHASA program. To apply the strategy, LHASA must be able to select potential starting materials, perceive how they map onto the target compound, recognise the structural changes implied by the mapping if the target structure is to be converted retrosynthetically into that of the starting material, find chemical reactions that can bring about the changes and decide upon the order in which they should be done.
Lewis‐acid‐induced reactions of α‐methoxyglycinamide derivatives with silyl enol ethers. Formation of 3‐amino‐2‐pyrrolidinones and 3‐amino‐2‐pyrrolinones
Authors: Roos Eric C. , Hiemstra Henk , Speckamp W. Nico , Kaptein Bernard , Kamphuis Johan , Schoemaker Hans E. 
Published: September 2010

AbstractIn order to develop an expedient synthetic route to γ‐oxo‐α‐aminocarboxamides, five different α‐(alkoxycarbonyl)amino‐α‐methoxyacetamides were subjected to borontrifluoride‐etherate‐mediated reactions with one silyl ketene acetal and four silyl enol ethers. Reactions of primary and secondary amides did not lead to the desired CCbond formation. Reactions of the tertiary N,N‐dimethylamide gave the expected γ‐oxo‐α‐aminocarboxamides. The reaction of an N‐methoxy‐N‐trimethylsilylcarboxamide with the ketene acetal also proceeded normally. However, the initial products of the latter amide with silyl enol ethers reacted further by cyclization, respectively, to give a cyclic N‐ methoxy‐N‐acyliminium intermediate. Depending on structural features of the enol ether used, this iminium intermediate suffered either proton loss and isomerization to give protected 3‐amino‐1‐methoxy‐δ3‐pyrrolin‐2‐ones, or underwent a second coupling with the enol ether to give protected 3‐amino‐1‐methoxypyrrolidin‐2‐ones.
Synthesis of a highly unsaturated fatty acid moiety of lipo oligosaccharides determining host‐specificity in rhizobium
Authors: Verduyn R. , Lagas R. M. , Dreef C. E. , van der Marel G. A. , van Boom J. H. 
Published: September 2010

AbstractThe phosphonate ethyl 6‐(diethylphosphono)‐2E,4E‐hexadienoic acid is a suitable synthon for the highly stereoselective preparation of 2E,4E,6E,11Z‐octadecatetraenoic acid and its 2E,4E,6E‐ analog.
Synthesis, characterization and metal‐uptake behaviour of pyrazole ligands immobilized on silica
Authors: Verweij P. D. , Haanepen M. J. , de Ridder J. J. , Driessen W. L. , Reedijk J. 
Published: September 2010

AbstractThe novel didentate ligand 2‐(3,5‐dimethyl‐1‐pyrazolyl)ethylamine (Naed) and the tridentate ligand bis[2‐(3,5‐dimethyl‐1‐pyrazolyl)ethyl] amine (ddaH) were immobilized onto silica by two different methods. The first method involves the coupling of the ligand to silica, previously modified with (3‐glycidyloxypropyl)trimethoxysilane (GLYMO). The second method involves the coupling of the ligand to the oxirane ring of GLYMO in a homogeneous reaction, followed by grafting onto silica, yielding the highest ligand concentrations on the silica (about 0.3 mmol/g silica). With the first method, only part of the epoxy group reacts with the ligand. With Naed, tertiary amines are also formed through reaction of the primary amine group of the ligand with two epoxy groups.These new ion‐exchange materials selectively adsorb Cu2+ (maximum capacity 0.11–0.26 mmol Cu2+ per gram of ion exchange) at pH > 2 from aqueous solutions containing a mixture of the bivalent metal ions, Cu2+, Cd2+, Zn2+, Ni2+ and Co2+. For products containing the didentate ligand Naed as the chelating group, the metal‐ion capacity decreases rapidly with decreasing pH, while the Cu2+ ‐uptake capacity for the product containing the tridentate ligand ddaH is comparatively high at low pH.