bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nouvelles synthèses de systèmes bihétérocycliques II. Cycloaddition dipolaire‐1,3 et condensation de carbène sur des triazépines‐1,2,4
Authors: Hasnaoui A. , El Messaoudi M. , Lavergne J.‐P. 
Published: September 2010

AbstractThe condensation of mesitonitrile and dichlorocarbene in aqueous medium to 1,2,4‐triazepines has been studied. In all cases this cycloaddition is peri and regiospecific. Compounds with the unknown ring systems isoxazolo[5,4‐e]‐1,2,4‐triazepine and azirino[2,1‐g]‐1,2,4‐triazepine have been synthesized. The structural elucidation of these products was accomplished by spectral evidences.
The chemistry of small‐ring compounds. Part 48. Oxidation of cyclopropylidenecycloalkanes with singlet oxygen
Authors: van den Heuvel C. J. M. , Steinberg H. , de Boer Th. J. 
Published: September 2010

AbstractCyclopropylidenecyclohexane undergoes the ene reaction with singlet oxygen. The migrating allylic hydrogen originates exclusively from the cyclohexane ring and therefore the hydroperoxy group becomes attached to the cyclopropane ring. Since the O ‐ O bond in cyclopropyl peroxy systems is weak, the reaction product undergoes homolysis even at − 50°C and this also triggers rupture of the small ring.The resulting radical pair, consisting of 7 and the hydroxyl radical, recombines to form unsaturated β‐hydroxy ketone 8 and the di‐α, β‐unsaturated ketone 9 (cf. Scheme 2).As a model for a cyclopropylidenecycloalkane containing no active allylic hydrogen, the adamantyl derivative 10 was subjected to photo‐oxidation. In this case, the product is lactone 11 (yields in Table I), formed by early ring enlargement, i.e. before O ‐ O rupture, as outlined in Scheme 4.The zwitter ion 15a isomerises to the key intermediate carbonyl oxide 17 and, as a result of the presence of the cyclobutane ring, this can rearrange to lactone 11 in various ways (cf. Scheme 5 and 6). By photo‐oxygenation in 18O‐labelled acetone, zwitter ion 17 is trapped by the solvent as an unstable ozonide which decomposes with formation of 18O‐labelled lactone (Scheme 7). Photo‐oxygenation in the presence of TCNE gives exclusively ketone 12 by deoxygenation of 17 (Scheme 4).
Mechanistic photochemical studies on the 1,3‐acyl shift and oxa‐di‐π‐methane rearrangement of two β,γ·γ′,δ′‐dienones
Authors: Koppes Margareth J. C. M. , Cerfontain Hans 
Published: September 2010

AbstractThe photochemical rearrangement of the two 2‐(2‐alkenyl)‐2‐(1‐cyclopentenyl)cyclopentanones (E)‐1aand (E)‐2ahave been studied under conditions of both direct (λ 300 nm) and tripletsensitized irradiation in order to determine the applicability of 2‐alkenyl moieties as intramolecular quenchers of the lowest excited triplet states of the β,γ‐enone chromophore.The β,γ·γ′,δ′‐dienone (E)‐1a, upon direct irradiation, exhibits a reversible 1,3‐acyl shift (1,3‐AS) leading to an eventual photostationary state {[(E)‐1a]/[(E)‐1b]}pss= 4.0 ± 0.8, whereas triplet photosensitization of (E)‐1agives the ODPM isomer (E)‐1c. Both processes occur without (E)‐(Z) isomerization of the 2‐butenyl side‐chain. Direct irradiation of (E)‐2ayields, albeit very inefficiently, the 1,3‐AS compound (E)‐2b(Φ < 0.001) as the primary product which, upon electronic excitation, forms, in competing reactions, (E)‐2a(Φ = 0.18) and (Z)‐2b(Φ = 0.035). Upon triplet photosensitization of both (E)‐2aand (E)‐2b, only (E)‐(Z) isomerization of the styryl side‐chain is observed. The eventual photostationary state in the direct irradiation equals {[(E)‐2a]/[(Z)‐2a]/[(E)‐2b]/[(Z)‐2b]}pss=(33± 1)/(33 ± 1)/(17 ± 1)/(17 ± 1).The differences in photochemical behaviour of the β,γ·γ′,δ′‐dienone substrates and their 1,3‐AS products are discussed with special emphasis being placed upon the triplet energies of the 2‐alkenyl chromophores relative to those of the β,γ‐enone chromophores and the occurrence of CT interaction which enhances the internal conversion of theS1(nπ*) states of the β,γ‐enone chromophores.
Photochemical synthesis of 5‐alkylpyrimidine nucleosides
Authors: Hassan Mohamed E. 
Published: September 2010

Abstract5‐Alkylpyrimidine nucleosides, bearing different functional groups attached to the newly formed carbon chains at C‐5, were synthesized via a photocoupling reaction. 5‐(2‐Hydroxyethyl)uridine and its derivatives were obtained from the reaction of uridine (U) or 2′‐deoxyuridine (DU) with 2‐iodoethanol. Trimethylsilyl derivatives of 5‐iodouridine (IU) and 5‐iodo‐2′‐deoxyuridine (IDU), when treated with methyl acrylate, gave methyl 3‐(5‐uridinyl)propenoate and methyl 3‐(2′‐deoxy‐5–uridinyl) propenoate, respectively, which, upon catalytic hydrogenation, afforded 5‐[2‐(methoxy‐carbonyl)ethyl]uridine and its 2‐deoxyuridine analogue. IU and IDU also gave 5‐(2‐cyano‐ethenyl(uridine and its 2′‐deoxyuridine analogue, when treated with acrylonitrile. The latter compounds gave the corresponding 5‐(2‐cyanoethyl) nucleosides when subjected to catalytic hydrogenation.
Synthesis and properties of nitro derivatives of 2‐tert‐butyl‐ and 2,7‐di‐tert‐butylpyrene
Authors: Rodenburg L. , Brandsma R. , Tintel C. , van Thuijl J. , Lugtenburg J. , Cornelisse J. 
Published: September 2010

AbstractNitration of 2‐tert‐butyl‐ and 2,7‐di‐tert‐butylpyrene affords molecules with severely hindered nitro groups. A nitro group ortho to a tert‐butyl group is twisted at least 82° out of the plane of the aromatic nucleus. The lack of interaction between the hindered nitro group and the aromatic system is reflected in the chemical behaviour, as well as in the spectroscopic properties, of these nitro derivatives.Upon fragmentation in the mass spectrometer, the tert‐butyl group is always replaced by a hydrogen atom. Nitro groups are only replaced by a hydrogen atom if they are ortho to a tert‐butyl group.
Synthesis of the mirror image of the RNA fragment D‐CAAGG: A model compound to study interactions between oligonucleotides of opposite handedness
Authors: Visser G. M. , van Westrenen J. , van Boom J. H. , van Boeckel C. A. A. 
Published: September 2010

AbstractThe pentamer L‐CAAGG was prepared starting from properly protected β‐L‐ribonucleosides via a phosphotriester approach. The identity and chiral purity of the pentamer were established by 1H NMR and CD spectroscopy, respectively.
Conformational analysis of synthetic heparin‐like oligosaccharides containing α‐L‐idopyranosyluronic acid
Authors: van Boeckel C. A. A. , van Aelst S. F. , Wagenaars G. N. , Mellema J.‐R. , Paulsen H. , Peters T. , Pollex A. , Sinnwell V. 
Published: September 2010

AbstractHigh‐field NMR spectroscopy of synthetic heparin‐like di‐ and trisaccharides has afforded a complete set of inter‐proton‐coupling data on α‐L‐idopyranosyluronic acid, which have been used for conformational analysis. These data lead to the conclusion that α‐L‐iduronic acid may display considerable conformational freedom including 1C4, 4C1 and 2S0 (e.g. compound 1) conformers.The 2‐O‐sulphate substituent at iduronic acid tends to stabilize the 1C4 conformation (e.g. compounds 2 and 4). In addition carbohydrate substituents at position 4 hinder the 4C1 conformation (e.g. compound 3a,b versus 1).Furthermore, the conformation of α‐L‐idopyranosyluronic acid 2‐sulphate is affected seriously by the substituent at position 2 of the non‐reducing glucosamine residue. Thus the presence of an ammonium group (i.e. compound 7) leads to unexpected deformation of the 1C4 form of iduronic acid, whereas a sulphamino substituent at this position (e.g. compound 5a,b) brings about the 2S0 skew boat conformation.The iduronic acid moiety of a trisaccharide (compound 6), which represents a part of the anti‐thrombin III‐binding site of heparin, shows conformational preference for the 2S0 form in aqueous solution under low ionic conditions. However, increasing the ionic strength (e.g. 3 M NaCl) causes the conformational equilibrium to incline towards the 1C4 chair conformer. This feature may be indicative for the mechanism of conformational control as exerted by the AT‐III protein upon heparin binding.Several molecular models of preferred conformers have been constructed; Nuclear Overhauser Enhancement data, exo‐anomeric effect and Van der Waals interactions have been taken into account.
Synthesis and conformational analysis of an analogue of the antithrombin‐binding region of heparin: The role of the carboxylate function of α‐L‐idopyranuronate
Authors: van Boeckel C. A. A. , Lucas H. , van Aelst S. F. , van den Nieuwenhof M. W. P. , Wagenaars G. N. , Mellema J.‐R. 
Published: September 2010

AbstractAn analogue of the antithrombin‐III‐binding region of heparin has been synthesized. This analogue [GlcNSO3 (6‐OSO3)‐GlcU‐GlcNSO3 (3,6‐OSO3)‐Xyl(2‐OSO3)‐GlcNSO3 (6‐OSO3), i.e. compound 11] lacks the carboxylate function of the α‐L‐iduronic acid moiety, which implies that the 2‐O‐sulphated α‐L‐idopyranuronate unit is replaced by 2‐O‐sulphated β‐D‐xylopyranose. Compound 11 was prepared from fully protected pentasaccharide 10a, which was synthesized from two disaccharides (7 and 6b) and a monosaccharide (9). Synthesis of disaccharide 6b required preparation of a new, suitably protected xylopyranose‐building block: 2‐O‐acetyl‐ or 2‐O‐benzoyl‐3‐O‐benzyl‐4‐O‐levulinoyl‐α‐D‐xylopyranosyl fluoride 4a,b.High‐field NMR spectroscopy of compound 11 afforded a complete set of interproton coupling data and Nuclear Overhauser Enhancement data, which have been used for conformational analysis. It appears that β‐D‐xylopyranose in compound 11 adopts exclusively the 4C1 conformation, whereas it is known that α‐L‐idopyranuronate in the naturally occurring heparin fragment exhibits 2S0 and 1C4 conformations. Thus, the carboxylate function of α‐L‐idopyranuronate in the heparin fragment is an important conformational drive.Since neither compound 11 nor another analogue containing L‐idose (with similar conformational properties as the natural fragment) elicit AT‐III‐mediated activity, it is proposed that the carboxylate of idopyranuronate interacts with AT‐III to bring about the active conformation of the protease inhibitor.
Conformational analysis of three simple organosilicon compounds
Authors: Jenneskens Leonardus W. , Louwen Jaap N. , van den Berg Ellen M. M. , van Beuzekom Aart A. , Lugtenburg Johan 
Published: September 2010

AbstractThe 1H NMR spectra of 3‐(triethoxysilyl)propanenitrile (1), 3‐(trichlorosilyl)propanenitrile (2) and trichloropropylsilane (3) show that these systems are present to about 40% in the gauche conformer. For 1 and 3, the solvent dependence of the conformational equilibrium has also been studied. In more polar solvents, the more polar gauche conformers contribute to a greater extent to the equilibrium mixture. The results of MNDO calculations for these compounds are compared with the conclusions drawn from the NMRz measurements. The reliability of MNDO for the description of this type of organosilicon compound is described.
Mechanistic studies of the oxidative‐coupling polymerization of 2,6‐dimethylphenol. Part V: Effect of different copper counter‐ions on the structure of the copper complex, its catalytic activity and specificity for polymer formation
Authors: Viersen F. J. , Challa G. , Reedijk J. 
Published: September 2010

AbstractIn studying the mechanism of the oxidation coupling polymerization of 2,6‐dimethylphenol, the effect of the copper counter‐ion was also investigated. This polymerization is catalyzed by copper(II)‐amine complexes. In these experiments, tmed*** is used as amine ligand. The counter‐ions were divided into strongly coordinating (viz. Cl− and Br−), weakly coordinating (viz. NO3−) and non‐coordinating counter‐ions (viz. ClO4−, CF3SO3− and BF4−).Catalyst solutions, prepared from copper salts with coordinating counter‐ions, yield very high maximum activities at OH/Cu ≈︁ 1, whereas the non‐coordinating counter‐ions give much lower maximum reaction rates at OH/Cu ≈︁ 2 or higher. Copper‐amine complexes of weakly and non‐coordinating counter‐ions were found to yield hydroxo‐bridged complexes with a very low catalytic activity under all conditions. Due to this stable dihydroxo bridge and the absence of coordinating counter‐ions (Cl−, Br−) to replace them, only phenolate anion can readily attack this complex and occupy a coordination site at the expense of a coordinated OH− ion, thus explaining the optimum activity at an OH/Cu ratio of 2 or higher. However, even under these conditions, catalytic activity of these complexes is still low compared to catalysts prepared from CuCl2 or CuBr2, further suggesting that preformation of a chloro‐bridged or bromo‐bridged copper complex is beneficial. Thus, these experiments indicate that the active catalyst, or its precursor, is the chloro‐bridged, or bromo‐bridged, dinuclear copper complex with hydroxide acting as a co‐catalyst required for the formation of strongly coordinating phenolate anions.Although large differences in reactivity were observed, the product composition, i.e. the fraction polymer (by C‐O coupling) and diphenoquinone (DPQ, undesired side‐product formed by C‐C coupling), was not affected by the counter‐ion used, viz. 3.5% DPQ. These results are a further indication that specificity is not primarily determined by the catalyst structure.
Thermally Stable Arylpalladium Diamine Complexes as Versatile Precursors in Organopalladium Chemistry; Synthesis and X‐Ray Molecular Structure of PdIPh(tmeda) and its Conversion to PdMePh(tmeda) {tmeda = Me2N(CH2)2NMe2}
Authors: de Graaf Wim , van Wegen John , Boersma Jaap , van Koten Gerard , Spek Anthony L. 
Published: September 2010

AbstractThe new complex PdIPh(tmeda) (1) (tmeda = Me2N(CH2)2NMe2) was prepared by oxidative addition of iodobenzene to {bis(dibenzylideneacetone)}palladium(0) in the presence of tmeda and has been characterized by NMR spectroscopy and X‐ray crystallography. Treatment with MeLi affords the remarkably stable mixed diorgano species PdMePh(tmeda) (2). Both (1) and (2) are useful precursors to other organopalladium species by ligand exchange reactions.
Chemisorption and catalysis of zeolite‐entrapped palladium
Authors: Homeyer S. T. , Karpiński Z. , Sachtler W. M. H. 
Published: September 2010

AbstractThe chemisorption of H2and of CO and the catalysis of neopentane conversion have been studied on two groups of Y‐zeolite‐supported Pd samples. One group was prepared under conditions which result in the formation of “grape‐shaped” Pd particles filling adjacent supercages. In the second group, pretreatment conditions were chosen which yield isolated Pd particles of the size of the supercages. Both groups of Pd/NaY samples differ in adsorption of H2and CO; the COads/Hadsratios are in agreement with the different particle morphologies. The selectivity of neopentane conversion does not detectable depend on Pd morphology; however, the activation energy for reaction is significantly higher for the samples of the first group.
Preparation of optically pure 2‐aryl‐ and 2‐aryloxy‐propionates by selective enzymatic hydrolysis
Authors: Mutsaers J. H. G. M. , Kooreman H. J. 
Published: September 2010

AbstractSelective enzymatic hydrolysis of racemic esters is an attractive method for the resolution of 2‐aryl‐ and 2‐aryloxy‐propionates. The non‐steroidal antiinflammatory drugs, naproxen, ibuprofen, flurbiprofen and the herbicides, fluazifop and diclofop, can be obtained in high optical purity with the aid of carboxylesterase NP. This enzyme was brought to high production levels by cloning it into Bacillus subtilis 1‐85. The unfavourable influence of a non‐specific lipase, present in the wild type rain, was also completely eliminated by cloning. The ability of the esterase under application conditions was greatly improved by chemical modification, the be results being obtained with formaldehyde, glutaraldehyde and glyoxal.
Biocatalytic production of hydroxylated aromatic and alicyclic compounds: Products derived from tetralin
Authors: Sikkema Jan , de Bont Jan A. M. 
Published: September 2010

AbstractBiological hydroxylation is an area with many opportunities for the production of fine chemicals. Especially for the production of hydroxylated aromatic and alicyclic compounds, the specificity and mildness of biocatalysis can be beneficial. 1,2,3,4‐Tetrahydronaphthalene (Tetralin) is a bicyclic aromatic compound, consisting of an aromatic and an alicyclic moiety. The biological oxidation of this compound provides an interesting model reaction, because different sites of initial attack are possible. Eight rains of bacteria that utilize tetralin as sole source of carbon and energy have been teed for the formation and accumulation of interesting oxidation products. Accumulation of oxidation products characteristic of both the oxidation of the aromatic and the alicyclic moiety has been demonstrated. Two rains, aCorynebacteriumand anAcinetobacterhave been studied in more detail.CorynebacteriumC125 starts with initial attack on the aromatic ring by a dioxygenase type of enzyme resulting in the formation of acis‐dihydro diol that is chemically dehydrated to a phenol in an acid environment.AcinetobacterT5 starts with oxidation of the benzylic carbon atom, resulting in the formation of an alcohol, that is further oxidized via a ketone.
Molecular recognition of neutral molecules by rigid binaphthyl metalloclefts: Synthesis, complexation and calculations
Authors: van Doorn Arie R. , Rushton David J. , Verboom Willem , Reinhoudt David N. , Bos Marinus 
Published: September 2010

AbstractThe binaphthyl metallocleft 2 in which an electrophilic uranyl cation is immobilized was synthesized by reaction of 1,2‐benzenediamine and aldehyde 5. According to 1H‐NMR spectroscopy, 2 is formed as a mixture of meso and racemic diastereomers (ratio 1:0.85). The complexation of 2 with pyridine, (iso)quinoline, acridine, benzylamine, and 1‐naphthalenemethanamine was investigated. The association constants of the complexes with aromatic amines vary from 3.5 · 102 to 3.6 · 106 M−1 (meso‐2) and 1.5 · 102 to 1.0 · 106 M−1 (racemic‐2). The higher stability of the complexes with meso‐2 is in agreement with the results of molecular mechanics calculations.
Chemical modification of azasugars, inhibitors of N‐glycoprotein‐processing glycosidases and of HIV‐I infection: Review and structure‐activity relationships
Authors: van den Broek L. A. G. M. , Vermaas D. J. , Heskamp B. M. , van Boeckel C. A. A. , Tan M. C. A. A. , Bolscher J. G. M. , Ploegh H. L. , van Kemenade F. J. , de Goede R. E. Y. , Miedema F. 
Published: September 2010

AbstractThe synthesis of a series of analogues of the α‐glucosidase inhibitor 1‐deoxynojirimycin (dNM, 1) and of the α‐mannosidase inhibitor 1‐deoxymannojirimycin (dMM, 3) is described. The ability of dNM, dMM and a series of N‐alkylated dNM and dMM derivatives to interfere with biosynthesis, transport and maturation of the glycoprotein α1‐antitrypsin in human hepatoma HepG2 cells and with the syncytium‐inducing capacity of HIV‐infected cells was investigated. A strong correlation was observed between α‐glucosidase inhibition found in HepG2 cells and antiviral activity in HIV‐I‐infected cells. N‐Butyl‐ (35), N‐pentyl‐ (38), N‐benzyl‐ (41) and N‐decyl‐dNM (47) showed high activity in both assays. N‐Decyl‐dNM was active at 0.01 mM but showed drug‐related cell toxicity at concentrations exceeding 0.1 mM. Branching of the N‐alkyl side chain reduced the activity of dNM derivatives considerably. N‐Benzyl‐6‐O‐butyryl‐dNM (42) and N‐decyl‐6‐O‐benzoyl‐dNM (48) showed activity comparable to that of N‐benzyl‐dNM (41) and N‐decyl‐dNM (47), respectively. None of the dMM analogues prevented HIV‐induced syncytia formation. The 3‐hydroxyl group in dNM and in dMM plays a crucial role in the interaction of these drugs with the corresponding processing glycosidases: 3‐O‐methyl‐dNM (49) and 3‐O‐methyl‐dMM (56) were inactive in both assays. The plasma membrane constitutes a permeability barrier for castanospermine (CAS, 2), but not for dNM, since the activity of CAS in streptolysin‐O‐permeabilized HepG2 cells was significantly higher than that in intact HepG2 cells. Finally, an overview is given of structures, other than the many N‐substituted derivatives that were described, related to dNM and dMM that have appeared in the literature in recent years.
Synthesis and characterization of isotopically labelled drugs
Authors: Kaspersen Frans M. , Vader Jan F. , Funke Carel W. , Sperling Eric M. G. 
Published: September 2010

AbstractThe article describes approaches for the synthesis and analysis of isotopically (2H,3H,13C,14C,35S) labelled drugs necessary for the development of a pharmacologically active compound into a registered drug.Special features such as isotope effects, radiolysis and3H NMR spectra are discussed.
The synthesis and properties of some long‐chain alkyl‐D‐glucofuranosidurono‐6,3‐lactones, D‐glucofuranosides and derivatives thereof
Authors: Raaijmakers Harry W. C. , Zwanenburg Binne , Chittenden Gordon J. F. 
Published: September 2010

AbstractSeveral long‐chain alkyl‐D‐glucofuranosidurono‐6,3‐lactones were synthesized by the acid‐catalysed glycosidation of glucurono‐6,3‐lactone. The alkyl β‐D‐glucofuranosidurono‐6,3‐lactones were reacted with sodium borohydride to give the corresponding alkyl β‐D‐glucofuranosides, and with 2‐aminoethanol andN,N‐dimethylethanediamine to give the corresponding alkyl‐N‐(2‐hydroxyethyl)‐β‐D‐glucofuranosiduronamides and alkyl‐N‐[2‐(dimethylamino)ethyl]‐β‐D‐glucofuranosiduronamides, respectively. The dodecyl‐N‐[2‐(dimethylamino)ethyl]‐β‐D‐glucofuranosiduronamides were quaternized with iodomethane to give the ammonium iodides. These new compounds, and some representative derivatives, were characterised by1H‐ and13C‐NMR spectroscopy. The physical properties (liquid‐crystal behaviour, surface tension, CMC) of some of these compounds were also determined.
Steroid cyclophanes as artificial receptors embedded in synthetic bilayer membranes: Aggregation behavior and molecular recognition
Authors: Murakami Yukito , Kikuchi Jun‐Ichi , Inada Masahiko , Miura Hideaki , Suehiro Kazuaki , Hayashida Osamu 
Published: September 2010

AbstractTwo steroid cyclophanes, having individually L‐lysine and L‐aspartate residues as connector units interposed between a 1,6,20,25‐tetraaza[6.1.6.1]paracylophane skeleton and four cholate moieties, were designed and synthesized. The cationic steroid cyclophane, having L‐lysine residues, binds anionic and non‐ionic guests very efficiently, while it has no capacity to bind a guest with a positive charge in aqueous solution. On the other hand, the anionic steroid cyclophane, bearing L‐aspartate residues, shows good binding affinity toward hydrophobic guests in aqueous solution regardless of their charged states. Aggregate morphology of the cationic and anionic peptide lipids, involving an L‐alanine residue interposed between a charged head moiety and a hydrophobic double‐chain segment, in the sonicated vesicular state was not perturbed significantly upon formation of hybrid assemblies with the steroid cyclophanes in 2.5 mol%. Even though the anionic bilayer vesicle interacts only weakly with anionic guests, the corresponding hybrid assembly formed with the cationic steroid cyclophane is capable of marked molecular recognition of anionic guests, along with shape‐sensitive discrimination, through electrostatic and hydrophobic interactions in aqueous solution. In a similar manner, the cationic bilayer membrane alone is incapable of binding a cationic guest. However, the guest‐binding ability is not much enhanced in the presence of the anionic steroid cyclophane. Consequently, the cationic steroid cyclophane can act as an efficient cell‐surface receptor model for anionic guests while the anionic steroid cyclophane is not a good receptor model when both are embedded in bilayer membranes.