bluuebunny/crossref_metadata_2025_split huggingface dataset:
A convenient synthesis of a lipopeptide containing a diacylglycerol moiety: Preparation of a potential inhibitor of protein kinase C
Authors: de Bont H. B. A. , van Boom J. H. , Liskamp R. M. J. 
Published: September 2010

AbstractThe synthesis of a dimyristoylglycerol peptide is reported. Starting from 1,2‐diisopropylidene‐sn‐glycerol, a 1,2‐dimyristoyl‐sn‐glycerol derivative has been synthesized which has been coupled to an immobilized peptide. After deprotection and cleavage from the resin, a diacylglycerol‐moiety‐containing lipopeptide was obtained which can be considered as a potential inhibitor of protein kinase C.
A preliminary appraisal of selected problems in computer‐assisted organic synthesis
Authors: Hippe Z. S. , Fic G. , Mazur M. 
Published: September 2010

AbstractSome basic problems of contemporary computer‐assisted organic synthesis are briefly dealt with. The discussion (led from the point of view of computer science) mainly concerns the question of a solution space in organic synthesis and methods of artificial intelligence used to search it. Some features of systems assisting in organic synthesis, regarded as dedicated expert systems, are also commented on. An interactive strategy for development of an optimum synthetic tree is proposed. Finally, expected future trends in computer‐assisted organic synthesis and simulation (modeling) of organic reactions are briefly summarized.
Synthesis of mitosenes from N‐aryl‐2‐(diphenylphosphinyl)pyrrolidines
Authors: van der Gen A. , Zorgdrager J. , van der Steeg M. , Schreurs H. 
Published: September 2010

AbstractA new route for the construction of the mitosene skeleton was developed using 2‐(diphenylphosphinyl)pyrrolidine (2) and 2‐methoxy‐3‐methyl‐1,4‐benzoquinone (3) as starting materials. Regioselective oxidative addition of 2 to 3 gave 5‐substituted pyrrolidinylbenzoquinone 4. Protection of the quinone function by reduction, followed by in‐situ reaction with benzyl bromide, gave the bis‐benzylated product 5. Using a recently developed route to pyrrolo[1,2‐a]indoles, 5 was converted into the protected mitosenes 8. Debenzylation and subsequent oxidation of 8 produced the mitosenes 1 in good yields.
Synthesis of chiral 4‐pyrazolol derivatives starting from D‐glucose
Authors: de Wit D. , van Unen L. M. A. , van Rantwijk F. , Maat L. , Kieboom A. P. G. 
Published: September 2010

AbstractThe condensation of protected and unprotected 3‐ketoglucose (1) with hydrazines to 4‐pyrazolols has been investigated. 3‐ (5) and 5‐(D‐erythro‐1,2,3‐trihydroxypropyl)‐4‐pyrazolol (4) were obtained from 1 in high yield, as a mixture of these two isomers. A regioselective route starting from protected 1 in two steps yielded a mixture of diastereomers as a result of epimerization in the side chain.
Mechanism of enantioselective ester cleavage by histidine‐containing peptides at a micellar interface. 2. Effect of changing peptide chain length
Authors: Cleij Marco C. , Drenth Wiendelt , Nolte Roeland J. M. 
Published: September 2010

AbstractChiralp‐nitrophenyl esters derived from the amino acid phenylalanine are cleaved by various histidine‐containing tripeptides and higher oligopeptides as catalysts at a micellar interface. It is assumed that the oligopeptides adopt an internally hydrogen‐bonded C7conformation when they dissolve into the micellar hydrocarbon phase. Chiral recognition is attributed to the formation of a hydrogen bond in the micellar hydrocarbon phase between one enantiomer of the ester and the peptide. It is important for the activity that the imidazolyl NH moiety of the His residue remains in the aqueous phase. The hydrophilic/hydrophobic balance, which determines the location of each of the amino acid residues of the peptide in the two‐phase system, can be controlled by varying the length and stereochemistry of the peptide chain and by attaching hydrophobic groups. The most selective catalyst is a tripeptide with the structure C4H9OC(O)‐L‐Phe‐L‐His‐L‐Leu. It cleaves thep‐nitrophenyl esters of N‐protected L‐ and D‐phenylalanine with an enantioselective ofkI/kD≈︁ 40. Further lengthening of the peptide chain with L‐Leu and L‐Ala residues and lengthening of the N‐protecting group of the catalyst decreases the enantioselectivity down tokI/kD≈︁ 6 for the penta‐peptide C12H25OC(O)‐L‐Phe‐L‐His‐(L‐Leu)3. The origin of these effects is discussed.
Synthesis of 20‐oxo steroids
Authors: van Leusen Daan , van Echten Erik , van Leusen Albert M. 
Published: September 2010

AbstractThe synthesis is described of a series of eighteen 16‐dehydro‐20‐isocyano‐20‐sulfonylpregnanes (5 and 8–14) by C‐20 alkylation of 17‐[isocyano(sulfonyl)methylene]androstanes 1–3. The geminal isocyano and sulfonyl groups at C‐20 (compounds 5, 8–14) are removed by acid hydrolysis to provide a new entry into 20‐oxo steroids (6, 15–19). The C‐20 alkylation also includes halomethylation and alkoxymethylation to form 21‐halo‐ and 21‐alkoxy‐16‐dehydro‐20‐oxopregnanes, respectively. As an attractive alternative to acid hydrolysis, the isocyano group is first oxidized with Pb(OAc)4 to an isocyanato group prior to hydrolysis (of the geminal isocyanato and sulfonyl groups) to the same 20‐oxo steroids. The latter conversion is carried out under non‐acidic conditions at room temperature in a slurry of alumina in dichloromethane.
Supramolecular encapsulation of C60 in a water soluble calixarene; A core‐shell charge transfer complex
Authors: Williams René M. , Verhoeven Jan W. 
Published: September 2010

AbstractA calix[8]arene derivative has been found to form a water soluble complex with fullerene‐C60, but not with C70, which allows extraction of C60 from e.g. toluene into the aqueous phase. Charge transfer character of the complex is evident from strong charge transfer absorption around 440 nm measured in water. Molecular modeling calculations indicate a core‐shell structure for the complex.
Synthesis and spectroscopy of nine isomeric methylacephenanthrylenes
Authors: Mulder Patrick P. J. , Boere Ben B. , Baart Arthur , Cornelisse Jan , Lugtenburg Johan 
Published: September 2010

AbstractThe synthesis of nine isomeric methyl‐substituted acephenanthrylenes is described. Three different approaches were used. 1‐, 2‐, And 6‐methylacephenanthrylene (1a, 1c and 1f) were prepared by formylation of acephenanthrene (2) and 4,5,7,8,9,10‐hexahydroacephenanthrylene (17), followed by Wolff‐Kishner reduction and dehydrogenation. 4‐, 5‐, 7‐ And 10‐methylacephenanthrylene (1d, 1e, 1g and 1j) were synthesized by treating the corresponding acephenanthrenones with methyllithium, followed by dehydration and, in the case of 1g and 1j, dehydrogenation. 8‐ And 9‐methylacephenanthrylene (1h and 1i) were prepared by a Haworth synthesis starting with the reaction of methylsuccinic anhydride with acenaphthene. The spectroscopic properties of acephenanthrylene and its methyl derivatives were investigated with mass spectrometry, 1H NMR and UV‐VIS spectroscopy. According to the 1H NMR spectra, steric hindrance between the methyl group and nearby protons decreases in the following order: 1, 10 > 6 > 7 > 3 > 4, 5, 8, 9.
CCK‐A Agonists: Endeavours involving structure‐activity relationship studies
Authors: Hermkens Pedro H. H. , Ottenheijm Harry C. J. , van der Werf‐Pieters Jane M. L. , Broekkamp Chris L. E. , de Boer Thijs , van Nispen Jan W. 
Published: September 2010

AbstractThe design cycle of peptidomimetics having CCK‐A agonistic activity is discussed. The phases of this strategic approach are discussed briefly and results obtained either in our laboratories or by other groups are elaborated in this framework.Most of the CCK‐A agonists prepared until recently still consist of six or more amino acid residues. Several conclusions can be drawn from studies in which one single amino acid has been exchanged against other residues. Studies involving the exchange of Tyr(SO3H) (amino acid 2) indicate that rather than the presence of the aromatic ring, the correct positioning of an acidic function is responsible for activity. The third amino acid (Met) probably acts as spacer residue. Amino acid 4 (Gly) can only be exchanged by D‐amino acids containing small side chains (D‐Ala). Replacement of Trp (amino acid 5) almost always results in decrease of actvity. Changes in position 6 indicate that the side‐chain is involved in hydrophobic interactions with the receptor site and replacement of Asp (amino acid 7) demonstrates that the acidic function of the side chain is of importance for activity. The aromatic ring of amino acid 8 (Phe) may be substituted by a bulky alkyl or cycloalkyl moiety without considerable loss of activity.Isosteric replacements of protease‐sensitive amide bonds enhancing the metabolic stability are permitted.Two new classes of cyclic peptides were found with conserved CCK‐A activity. A start has been made with these peptides to determine the active CCK‐A topology by means of molecular modeling and NMR studies.
Conformational analysis of 1‐arylpiperazines and 4‐arylpiperidines
Authors: Dijkstra Gerard D. H. 
Published: September 2010

AbstractA conformational analysis of 1‐arylpiperazines and 4‐arylpiperidines is presented using molecular‐mechanics and semi‐empirical calculations. It has been found that electronic effects of substituents on the aryl ring determine the conformational behaviour of 1‐arylpiperazines. Steric effects play a minor role. Electron‐withdrawing substituents on the aryl moiety increase the conjugation between the anilino nitrogen lone pair and the π electrons of the aryl group and direct the orientation between the aryl and heterocycle towards the same plane. Electron‐releasing substituents have the opposite effect and reduce the energy difference between a coplanar and perpendicular orientation between the rings. 4‐Arylpiperidines prefer a perpendicular orientation between the rings.
Electrochemistry of potentially bioreductive alkylating quinones. Part 4. Qualitative and quantitative structure‐activity relationships of aziridinylquinones
Authors: Driebergen R. J. , Moret E. E. , Janssen L. H. M. , Beijnen J. H. , Holthuis J. J. M. , Kelder S. J. Postma , Verboom W. , Reinhoudt N. D. , Lelieveld P. 
Published: September 2010

AbstractThe concept of bioreductive alkylation as a mechanism of action of aziridinylquinoid anticancer agents has been investigated. The influence of quinone substituents on quinone reduction, on protonation of the aziridines prior to and following quinone reduction and on partitioning properties of the compound was examined. Parameters obtained from a combined electrochemical, chemical‐stability and lipophilicity study describing these processes were determined and correlated quantitatively in a Hansch‐type QSAR study with biological data obtained from three experimental tumor models. Poor quantitative correlations between cytotoxicity in a L1210 clonogenic assay and the parameters were obtained. Good linear relationships, however, between antitumor activity in vivo (vs. L1210 leukemic mice and vs. B16 melanoma‐bearing mice) and the lipophilic properties of the quinone were found. These relationships, showing a negative correlation between antitumor activity and lipophilicity, can be used to predict the activity of new, unknown compounds. No trend was evident between antitumor activity and other parameters, although some indications for potential importance of electronic and steric properties of the substituents and of their ability to form hydrogen bonds were found.
Synthesis of dicyclopenta‐fused derivatives of phenanthrene
Authors: Mulder Patrick P. J. , Boere Ben B. , Cornelisse Jan , Lugtenburg Johan 
Published: September 2010

AbstractThe synthesis of cyclopent[hi]acephenanthrylene (CPAP), a dicyclopenta‐fused derivative of phenanthrene, is described. The 4,5‐dihydro and 4,5,6,7‐tetrahydro derivatives of CPAP were also prepared. These novel compounds are characterized by means of 1H‐NMR, UV‐VIS and mass spectrometry.
Macrocyclic carriers in supported liquid membranes
Authors: van Straaten‐Nijenhuis Wilma F. , de Jong Feike , Reinhoudt David N. 
Published: September 2010

AbstractMacrocyclic receptor molecules can be designed to selectively bind a variety of host molecules, including metal cations and neutral molecules. This property can be uniquely exploited in separation processes, by using these compounds as carriers in transport through liquid membranes.The various types of liquid membrane systems are briefly discussed, and the attractive features of the supported (by a microporous polymer film) liquid membrane (SLM) are explained. The mechanical stability of the SLMs is dependent on several factors, including the type of polymer support, membrane solvent, and hydrophobicity of the carrier used.The rates and selectivity of transport are discussed in terms of membrane geometry, membrane solvent type, structure and concentration of the carrier, and the type and concentration of cations, and anions in both the source and receiving phases. Existing mathematical models in which these parameters have been incorporated, are compared with experimental data. Apart from a concentration gradient of the metal cation over the membrane, other driving forces, such as anion concentration, proton counter‐transport and redox‐active transport, are discussed.
Convergent functional groups XIV. Synthesis and binding studies of new molecular clefts for recognition and catalysis
Authors: Pieters Roland J. , Rebek Julius 
Published: September 2010

AbstractTwo new molecular clefts have been synthesized, both containing an adenine receptor portion and a metal‐binding site. The binding of adenine derivatives was evaluated in CDCl3, acetone‐d6 and water using NMR titrations. Base‐paired hydrogen‐bonded complexes are formed in all three solvents, but structural differences in the complexes are also observed. The CuII binding ability was established using UV spectroscopy.
Alkali‐metal‐ion‐assisted BAL2 cleavage of 2‐(methoxycarbonyl)‐1,3‐xylylene‐18‐crown‐5 by benzenemethanethiolate anion
Authors: Cacciapaglia R. , Mandolini L. , Castelli V. Van Axel 
Published: September 2010

AbstractBAL2 demethylation of 2‐(methoxycarbonyl)‐1,3‐xylylene‐18‐crown‐5 by benzenemethanethiolate anion in dimethylformamide (+ 1.6M water) at 35°C is significantly promoted by alkali‐metal counterions, the efficiency order being Na+ > K+ > Cs+ > Li+. The contrasting behaviour of the model compound, methyl 2,6‐dimethylbenzoate, whose demethylation reaction is in fact slightly inhibited by metal ions, points to the crucial role played by the polyether bridge of the crown ether substrate. In line with previous work from this laboratory, selective transition‐state stabilisation in the metal‐ion‐promoted cleavage of the crown‐ether substrate is ascribed to a favourable combination of electrostatic binding of the metal ions with the negative charge being transferred from the nucleophile to the convergent methoxycarbonyl group and coordinative binding to the neutral donors of the polyether bridge.
The effect of chemical structure upon the thermodynamics of micellization of model alkylarenesulphonates. Prediction of micellar properties with the Poisson‐Boltzmann model
Authors: Bijma Koos , Engberts Jan B. F. N. 
Published: September 2010

AbstractThis paper describes how the theory of the “dressed micelle”, which is based on the nonlinear Poisson‐Boltzmann equation, can be used to calculate a number of thermodynamic quantities for micellization of sodium p‐alkylbenzenesulphonates. From the Gibbs energy of micellization, the enthalpy of micelle formation is calculated and compared with calorimetric enthalpies. A number of other thermodynamic quantities, such as the degree of counterion binding, the electrostatic surface potential of a micelle, and the entropy of micelle formation, have also been calculated as a function of temperature and surfactant structure and, where possible, compared with experimental data. In general, the calculated thermodynamic parameters obtained using the model show the same trend with respect to temperature and structure as the experimental quantities. The absolute values, however, differ from the experimental quantities. Finally a comparison is made between the Poisson‐Boltzmann model, the phase‐separation model and the mass‐action model.
X‐ray structure of a molecular basket. Origin of its poor binding properties
Authors: Martens C. F. , Sijbesma R. P. , Gebbink R. J. M. Klein , Nolte R. J. M. , Spek A. L. 
Published: September 2010

AbstractX‐ray analysis and 1H‐NMR data in solution show that the entrance of the cavity of receptor 1c is blocked by benzyl groups, preventing the binding of substrate molecules.
Preparation and characterization of novel cage‐type cyclophanes having a helically twisted and cylindrical internal cavity
Authors: Murakami Yukito , Hayashida Osamu , Matsuura Sadahiko 
Published: September 2010

AbstractAn asymmetric character of the internal cavities provided by novel cage‐type cyclophanes, two triaza[3.3.3]paracyclophanes linked with three chiral bridging components, was clarified by means of circular dichroism (CD) spectroscopy and a computer‐aided molecular modeling study based on molecular mechanics conformational search.
Programmed antibodies as tailor‐made catalysts
Authors: Pandit Upendra K. 
Published: September 2010

AbstractAntibodies raised against stable transition‐state analogues of specific reactions act as catalysts for the same reactions. Catalytic antibodies have been developed for a variety of reaction types. These include: hydrolysis of carbonates, esters, amides and phosphates, transacylation, cleavage of ethers and acetals, sigmatropic rearrangement, cis‐trans isomerization, 4 + 2 cycloaddition, β‐elimination, photochemical cycloaddition and photo‐induced cleavage and decarboxylation. Strategies have been evolved for constructing antibody active sites incorporating metal ions and organic cofactors. These extend the scope of designed antibody catalysts. The chiral nature of the antibody pocket induces enantioselectivity in the catalyzed reaction in several cases. The concept of antibody catalysis opens up the principal possibility of designing tailor‐made catalysts for any pre‐selected reaction.
Multinuclear‐magnetic‐resonance study of the coordination of aluminium (III)‐aldarate complexes with calcium(II) in aqueous solution
Authors: Venema F. R. , Peters J. A. , van Bekkum H. 
Published: September 2010

AbstractThe coordination of aluminium(III)‐aldarate complexes with calcium(II) in aqueous solution has been investigated with the use of 1H‐, 13C‐, 17O‐, and 27Al‐NMR spectroscopy. Xylarate and mannarate adopt, in the presence of AlIII and CaII, 1:2 AlIII‐ligand complexes with tetrahedrally coordinated AlIII. The AlIII‐xylarate complex binds one, whereas the mannarate complex binds two CaII ions. Arabinarate and glucarate give 2:2 AlIII‐ligand complexes with tetrahedrally coordinated AlIII, which bind one and two CaII ions, respectively. The CaII sites of all the complexes contain free carboxylate groups and, additionally, AlIII‐bonded (hydr)oxy or free α‐hydroxy groups.
Perception and generalization of protective groups in the COSYMA system
Authors: Hamm P. , Ellermann L. , Jauffret P. , Kaufmann G. 
Published: September 2010

AbstractA new approach to computer‐assisted design of organic synthesis is proposed with the COSYMA system. This system was described in a previous paper. It is based on adaptation of a registered synthesis strategy to the structure of a new target molecule. An improvement to the COSYMA system founded on the perception of protection and deprotection reactions, is presented in this paper. The aim is to increase the performance of the system, to enable a clearer display with more complete results.
Reaction of C60 and C70 with ozone at different temperatures
Authors: Heymann Dieter , Chibante L. P. Felipe 
Published: September 2010

AbstractThe reactions of C60 and C70, dissolved in toluene, with ozone at 100, 23.5, 0. ‐ 16, and ‐ 78°C are reported. Both fullerenes are transformed swiftly at all of these temperatures. Both fullerenes form monoxides, dioxides and possibly higher oxides. The ratio of the rate parameters for the transformations of the two fullerenes change only slightly in the above temperature range. C60, however, is transformed about 40% faster than C70. The maximum yields of C60O, C60O2 and C70O increase at higher temperature.
Synthesis and exploratory photophysical investigation of donor‐bridge‐acceptor systems derived from N‐substituted 4‐piperidones
Authors: Scherer T. , Hielkema W. , Krijnen B. , Hermant R. M. , Eijckelhoff C. , Kerkhof F. , Ng A. K. F. , Verleg R. , van der Tol E. B. , Brouwer A. M. , Verhoeven J. W. 
Published: September 2010

AbstractWe report a two‐step synthesis for N‐aryl‐ and N‐alkyl‐substituted 4‐piperidones, in which the N substituent can easily be varied. A number of intramolecular donor‐acceptor systems was synthesized from these piperidones by conversion of the carbonyl functionality. The influence of the N‐aryl donor on the electronic absorption and fluorescence spectra was investigated systematically. It was concluded that some systems can be used as efficient fluorescent probes with a high sensitivity for solvent polarity.
Preparation of dyes derived from Eriochrome Red B and Acid Alizarin Violet N soluble in organic solvents
Authors: Katritzky Alan R. , Rachwal Bogumila , Rachwal Stanislaw , Smith Terrance P. , Macomber David W. 
Published: September 2010

AbstractBoth hydroxy groups of Eriochrome Red B are protected by acetylation and the sulfonic acid group is converted to the sulfonyl chloride with phosphorus pentachloride. Reaction with dibutylamine orN‐butylbenzeneethanamine followed by the deprotection gives red azo dyes7aor7b, readily soluble in chloroform and toluene. A similar procedure applied to Acid Alizarin Violet N gives only a multicomponent mixture. Friedel‐Crafts reaction between dibutylsulfamoyl chloride and 2‐nitrophenol givesN,N‐dibutyl‐4‐hydroxy‐3‐nitrobenzenesulfonamide (11). Reduction of the nitro group gives amine14which is diazotized and coupled with 2‐naphthol to give the required dye13giving deep‐red solutions in methanol, chloroform and acetone.
Electrophilic substitution of two monohomoperylenes and perylene
Authors: Cerfontain Hans , Koeberg‐Telder Ankie , Lerch Ulrike 
Published: September 2010

AbstractVarious types of electrophilic substitution of monohomoperylene(1)and its 11,11‐difluoro derivative(2)have been studied,viz. Bromination, nitration, acylation, formylation and sulfonation. Bromination withN‐bromosuccinimide (NBS) of1in dichloromethane leads to initial substitution mainly at the α positions 2 and 10,i.e., of the annuleno moiety, followed by further substitution of the β positions 4 and 8 of the same moiety, and of the α positions 2′ and 10′ of the naphthaleno moiety. Reaction of1with 5.0 mol‐equiv. of NBS yields 2,4,8,10,2′‐pentabromo‐1in 46% yield.Sulfonation of1with SO3in dichloromethane using 1.2 mol‐equiv. of dioxane as reactivity moderator leads to the formation of1‐2‐sulfonic acid (1‐2‐S),1‐2,10‐S2, and the intermediate σ complex6. Sulfonation of the 11,11‐difluoro derivative2leads to the formation of2‐2‐S,2‐2,10‐S2and 2‐2,10‐disulfonic anhydride(7), together with small amounts of2‐2,2′‐S2or/and2‐2,10′‐S2. The other types of electrophilic substitution of1and2studied were found to proceed similarly, in that the initial substitution occurs at the 2‐position and the subsequent one at the 10‐position,i.e., perito the primarily introduced substituent.The chemical behaviour (i.e., the substitution pattern and relative reactivity) of the two monohomoperylenes1and2have been compared with that of 1,6‐methano[10]annulene(3), its 11,11‐difluoro derivative(4), and perylene (5). For example, the sulfonation reactivity ratio of the naphthalene to the [10]annuleno moiety is significantly greater for2than1, as predicted on the basis of the higher sulfonation reactivity of3compared to4.