bluuebunny/crossref_metadata_2025_split huggingface dataset:
Total synthesis of (+)‐13‐ethyl‐3‐methoxygona‐1,3,5,9(11)‐tetraen‐17‐one via the tandem Claisen‐ene strategy
Authors: Groen‐Piotrowska E. M. , Groen M. B. 
Published: September 2010

AbstractA total synthesis of the title compound 2, a potential precursor of the progestagens desogestrel and 3‐ketodesogestrel, is described. The backbone of the steroid was assembled by condensation of 1,2‐dihydro‐4,7‐dimethoxynaphthalene (12) and [S‐(Z)]‐8,9‐dihydroxy‐7‐ethyl‐6‐nonen‐2‐ynoic acid methyl ester 9‐(tert‐butyldimethyl)silyl ether (11), prepared from [R‐(+ )]‐glyceraldehyde acetonide (4), and subsequent Claisen rearrangement. Heating of the resulting disecosteroid (14) at 170°C gave a 1:1 mixture of 9,11‐secosteroids, 15 and 16, having the 8α, 13β, 14α‐ and 8α, 13α, 14α‐configuration, respectively. The 13β‐epimer 15 was converted into 11‐bromo‐13‐ethyl‐3‐methoxy‐9,11‐secogona‐1,3,5(10)‐triene‐9,17‐dione (21), which reacted with triphenylphosphine under high pressure conditions (12 kbar, 55°C) to give the corresponding phosphonium salt 22. The intramolecular Wittig reaction of 22 proceeded with epimerization at C‐8 to give exclusively (8α)‐13‐ethyl‐3‐methoxygona‐1,3,5,9(11)‐tetraen‐17‐one (23) which, upon treatment with acid, isomerized to the title compound 2.
Synthesis of concave receptors derived from diphenylglycoluril
Authors: Sijbesma R. P. , Nolte R. J. M. 
Published: September 2010

AbstractImproved synthetic methods are described for the synthesis of concave receptor molecules. These receptors consist of a diphenylglycoluril unit, flanked by two aromatic moieties. The most versatile synthetic method consists of Lewis‐acid‐catalyzed reaction of a tetrakis(chloromethyl) derivative of diphenylglycoluril with the appropriate benzene or naphthalene derivative.
Case histories of peptidomimetics: Progression from peptides to drugs
Authors: Adang Anton E. P. , Hermkens Pedro H. H. , Linders Joannes T. M. , Ottenheijm Harry C. J. , van Staveren Catherina J. 
Published: September 2010

AbstractThere is a growing number of biologically active peptides which have potential for the development of new therapeutics. However, native peptides are only rarely directly usable as drugs, due to inherent limitations which include rapid proteolysis and metabolism, poor transport properties, rapid excretion by the liver and kidneys, and low oral activity. Furthermore, peptides are often aselective in their actions owing to their flexible structure. In efforts to address these limitations, peptides are modified into mimetics with specific physical, chemical and biological characteristics. These so‐called peptidomimetics are derived from peptides by partly or completely removing the amide bonds while retaining essential amino acid side chains in a defined, spatial relationship. They can be developed in a rational design cycle which starts either from a lead compound obtained in a screening programme or from the parent peptide. In the latter approach, which is the focus of this overview, first the smallest, active sequence is found, and the significance of each amino acid for the biological activity is determined. In the following steps the bioactive conformation is defined by the introduction of local and global constraints. In the final step the essential amino acid side chains are positioned onto a scaffold, preferably a small, polyfunctional ring of defined stereochemistry, using structural information obtained in earlier steps. Five examples of the application of the peptidomimetic design cycle in medicinal chemistry are described here, illustrating the progression from native peptides to therapeutically useful drugs.
Aggregation behaviour and copper‐binding properties of surfactants containing imidazole and pyrazole ligands
Authors: van Esch J.H. , Damen M. , Feiters M.C. , Nolte R.J.M. 
Published: September 2010

AbstractThe synthesis and aggregation behaviour of simple dialkylamine‐imidazole and dialkylamine‐pyrazole surfactants is described. In the presence of one equivalent of HCl the imidazole surfactants form stable vesicular dispersions. Addition of copper(II) dichloride to these dispersions leads to formation of metallo‐vesicles in which four imidazole groups are coordinated to one copper(II) ion. These metallo‐vesicles are unstable and are slowly converted into stacked bilayers, which precipitate. The pyrazole surfactants on the other hand do not form vesicles but give, with one molar equivalent of HCl, water‐insoluble stacked bilayers. The pyrazole moieties in these stacked bilayers do not coordinate copper(II) ions. This behaviour is most probably due to the formation of an intramolecular hydrogen bond in the mono‐protonated pyrazole surfactant molecule. The imidazole surfactants cannot form such a hydrogen bond.
Surface monolayers and aqueous bilayers of single‐chain ammonium amphiphiles which contain benzylideneaniline and salicylideneaniline units
Authors: Nishimi Taisei , Ishikawa Yuichi , Ando Reiko , Kunitake Toyoki 
Published: September 2010

AbstractThe assembling properties of single‐chain ammonium amphiphiles containing benzylideneaniline and salicylideneaniline units as rigid segments in the formation of aqueous bilayers, cast multi‐bilayers, and surface monolayers were studied. Electron microscopy indicated that aggregate morphologies observed in water, such as vesicles and fibers, were dependent on the nature of the aromatic unit and the alkyl‐chain length of the component amphiphiles. The patterns of molecular assembly in bilayers were examined by absorption spectroscopy of aqueous bilayers and X‐ray diffraction of cast multi‐bilayer films. The patterns were virtually identical to those of the corresponding azobenzene bilayers, and commonly determined by combinations of alkyl‐chain lengths. This alkyl‐chain combination was crucial for formation of stable surface monolayers.
Synthesis and photochemistry of (2S,4R)‐ and (2S,4R)‐1,2,3,4‐tetrahydro‐4‐ethyl‐1,1,4‐trimethyl‐3Z‐ethylidene‐2‐naphthalenols
Authors: Miesen F. W. A. M. , van Dongen J. L. J. , Meijer E. W. 
Published: September 2010

AbstractThe synthesis and photochemistry of optically pure (2S,4R)‐ and (2R,4R)‐1,2,3,4‐tetrahydro‐4‐ethyl‐1,1,4‐trimethyl‐3Z‐ethylidene‐2‐naphthalenols 10a and 11a are described. Naphthalenols 10a and 11a were prepared in seven steps from 2‐phenylbutanenitrile. Synthesis is mainly based upon acylation of isobutene by the optically active 2‐methyl‐2‐phenylbutanoyl chloride (5), and a Wittig reaction, while the ethylidene naphthalenones 8a and 9a are separated by HPLC. Under inert conditions, irradiation of both alcohols gives rise to E‐Z isomerization, followed by photodegradation reactions, leading to the formation of indane 12 by the elimination of formaldehyde. Irradiation of oxygenated solutions of 10a reveals a rapid photoaddition of oxygen to the double bond, leading to the stereo‐ and regioselective formation of hydroperoxide 13 and epoxy alcohol 15a, which hydrolyses on standing to triol 16a. The observed stereochemistry is explained by the stereoselective coordination of the hydroxyl group at the chiral allylic site with the attacking electrophilic oxygen. In the case of 11a a more complicated reaction mixture was obtained in which, analogously, the epoxy alcohol 15b and triol 16b were present. Semi‐empirical MNDO, AM1 and PM3 calculations revealed that, in the preferential ground state conformation, the hydroxyl group occupies an orthogonal position with respect to the exocyclic double bond. Fluorescence measurements revealed that the reactive state in the photochemistry of these naphthalenol systems under inert conditions is the triplet state. In the photoreactions of optically pure compounds 10a and 11a, we were unable to identify products analogous to 2, which are claimed to originate from the racemic precursors 1 via a planar 1,3 OH shift from a singlet (in the double bond) excited state. Clean photochemical reactions were observed only when 10a and 11a were irradiated in oxygenated solutions, resulting in stereo‐ and regiospecific photoproducts.
The fabrication of “high‐technology” catalysts
Authors: Ribeiro F.H. , Somorjai G.A. 
Published: September 2010

AbstractTo produce reaction products with 100% chemical selectivity, and to attain much higher turnover rates and number of turnovers, the development of new methods of catalyst preparation are necessary. Precise control of particle size, the separation between catalyst particles and their superior chemical and thermal stability must be achieved. To this end, five new methods of preparation of high‐technology catalysts are being studied. These are: (A) the method successfully used by W.M.H. Sachtler for metal particle deposition in zeolite cages, (B) the deposition of metal particles by atomic layer epitaxy, (C) controlled nucleation and growth of metal particles by substrate spinning, (D) deposition of metals on oxides by evaporation, (E) preparation of ordered metal arrays by electron‐beam lithography using microelectronic techniques. These different methods are described and discussed, and their present states of development are assessed.
Fano coupling in perturbed solid acid hydroxyls
Authors: van Santen R.A. 
Published: September 2010

AbstractA simple analytical expression for the Evans window in the infrared absorption spectrum of hydrogen‐bonded basic molecules in protonic zeolites is presented. The expression shows that the essential parameters are the position of the shifted “uncoupled” OH stretching frequency, its width, the position of the in‐plane bending overtone and the coupling of this mode with the OH stretching mode. Analysis of the Fermi resonances in the OH stretching band profile provides a method to determine whether adsorbed molecules are hydrogen bonded or protonated.
Molecular events on metal surfaces. FEM and FIM studies of metals and supported catalysts
Authors: Knor Z. 
Published: September 2010

AbstractThe application of field‐emission microscopy (FEM) and field‐ion microscopy (FIM) to surface studies related to catalysis (symmetry of atomic‐like states localized at the surface atoms of transition metals, spillover effect, dissipation of energy, etc.) is discussed together with a new approach to modeling of supported bimetallic catalysts in these devices.
Surface processes in the catalytic oxidative coupling of methane to ethane
Authors: Buyevskaya Olga , Wolf Dorit , Baerns Manfred 
Published: September 2010

AbstractRecent results on surface reaction steps in the oxidative coupling of methane (OCM) obtained from (1) transient experiments and (2) a microkinetic analysis are summarized. The interaction of methane and oxygen with MgO and Sm2O3 surfaces was investigated by applying H/D‐ and oxygen‐isotope‐exchange reactions. The role of short‐lived adsorbed oxygen species in methane activation and product formation over MgO and Sm2O3 catalysts is discussed. Furthermore, elementary reaction steps and their rate constants are derived for the oxidative conversion of methane to COx and ethane from kinetic data for different (CaO)x(CeO2)1−x catalysts; the rate constants are related to the solid's properties, i.e., electron and O2− conductivity.
Influence of chlorine and metal cation impurities in the CO hydrogenation over Pd/SiO2 and Rh/SiO2
Authors: Gloor A.P. , Prins R. 
Published: September 2010

AbstractCatalysts were prepared from ultra pure SiO2, Pd and Rh nitrates and chlorides, and by doping with Al, Fe, Na, K or Ca nitrate. The activities and selectivities of the Pd and Rh catalysts were investigated in CO hydrogenation at 553K, H2/CO = 2 or 3, and 2.5 or 4 MPa, respectively. Both the additives and the noble‐metal anions had a strong influence on the catalytic properties, even when no anions were present after catalyst preparation. These influences are due to dissolution of the metal additives by the aqueous noble‐metal salt solution during catalyst preparation, so that after reduction the additives end up in the vicinity of the metal particles. Chloride solutions extract the additives better from the catalyst support surface than nitrate solutions and therefore have a stronger influence on the catalytic properties, especially of SiO2‐supported catalysts.
The chelate effect in binding, catalysis, and chemotherapy
Authors: Breslow Ronald 
Published: September 2010

AbstractJacobus Henricus van't Hoff was in many senses the father of modern chemistry. It is a great honor to be invited to give this eighth van't Hoff lecture, and a great pleasure to visit the Netherlands again. Among his other contributions, van't Hoff made us aware of the importance of the three‐dimensional structure of chemical substances. In 1874 he was the first to explain optical isomerism and geometrical isomerism in organic chemistry, ruffling the feathers of older established chemists such as Kolbe.In this lecture, I will describe three studies in somewhat diverse areas ‐ binding, catalysis, and cancer chemotherapy ‐ that are related in the sense that they all involve the cooperative action of two groups of a molecule acting on a substrate. As will become clear, the three‐dimensional arrangement of these groups (“La chimie dans l'espace”) is a critical aspect of their effective cooperation.
Endohedral fullerene research
Authors: Holleman Iwan , Boogaarts Maarten G. H. , Meijer Gerard 
Published: September 2010

AbstractResearch on endohedral fullerenes has yielded unambiguous evidence for the existence of selected inside‐the‐cage complexes. Milligram quantities of purified samples of metallofullerenes have been produced, and characterized via techniques that selectively probe the endohedral guest. Experiments aimed at a detailed understanding of the molecular properties of the endohedral complexes as well as of the material properties of compounds containing endohedral fullerenes have just started.
Role of the stereochemistry of 3′‐fluoro‐3′‐deoxy analogues of 2‐5A in binding to and activation of mouse RNase L
Authors: Kalinichenko Elena N. , Podkopaeva Tatjana L. , Poopeiko Nicolai E. , Kelve Merike , Saarma Mart , Mikhailopulo Igor A. , van den Boogaart Jacquelien E. , Altona Cornelis 
Published: September 2010

AbstractThe synthesis of two sets of analogues of 2‐5A trimer containing 9‐(3‐fluoro‐3‐deoxy‐β‐D‐xylo‐furanosyl)adenine (AF) or 3′‐fluoro‐3′‐deoxyadenosine (AF) at different positions of the chain is described, along with the preparation of the corresponding 5′‐monophosphates and 5′‐diphosphorylated (core) trimers. The ability of each ribo and xylo isomeric pair of fluorodeoxy analogues of 2‐5A (i) to compete with p3(A2′p)3A3′[32P]pC3′p for binding to RNase L in L929 cell extracts, and (ii) to activate the partially purified RNase L from L929 cell extracts to hydrolyze poly(U)[3H], was compared to that of the related 3′‐deoxy analogue [Torrence et al., J. Biol. Chem. 263, 1131 (1988)] and the parent trimer, p3A3, using radiobinding and RNase L‐(2′,5′)pentaadenylate(core)‐agarose assays, respectively. Evidence is presented to show that the stereochemistry of the trimers plays an important role, specifically in the second process. The most striking observation is that, compared to 2‐5A, p3A(AF)A was found to be nine times more effective an activator of RNase L, whereas isomeric p3A(AF)A is 30 times less effective.
An abasic site induces a bulged conformation in the single‐stranded DNA trimer d(Ap(ab)pA). An NMR and model‐building study
Authors: van den Boogaart Jacquelien E. , Huige Cornelis J. M. , Boal Jila H. , Egan William , Altona Cornelis 
Published: September 2010

Abstract1′,2′‐Dideoxy‐D‐ribofuranose (ab), its 5′‐ and 3′‐phosphorylated analogues (ab5 and ab3), and the DNA trimer d(Ap(ab)pA) have been studied by means of proton NMR spectroscopy. These fragments are of interest as model compounds for abasic lesions occurring in vivo. All abasic sugars exhibit similar S‐type sugar conformations with populations of S‐conformer varying from 75% (in ab and ab5) to 83% (in ab3 and dab(2)), Ps ≈ 144° and Φs in the range from 30 to 33°. Having established the presence of mainly S‐type sugar, we could assign the H1′ and H1″ protons of all abasic residues stereospecifically on the basis of their respective vicinal coupling constants. The trimer exhibits considerable flexibility in the backbone. Moreover, chemical shifts as a function of temperature and chemical‐shift differences between abasic sugar protons in the trimer and in the abasic monomers point to the presence of a structure in which dab(2) is bulged out of the helix and the terminal residues stack on top of each other. Several models which fit the experimental data are presented.
Thionyl‐chloride‐pyridine‐mediated rearrangement of tertiary alcohols
Authors: Banerjee Ajoy K. , Vera William 
Published: September 2010

AbstractTertiary alcohols 5 and 8 undergo rearrangement on treatment with thionyl chloride and pyridine, yielding octahydronaphthalenes 6 and 9, respectively. Alcohol 12 under similar treatment affords a mixture of tetrahydronaphthalene 14 and diene 15, whereas alcohol 22 suffers no rearrangement but produces olefin 23.
Circular‐dichroism power of chiral, bridged, aromatic compounds. 7,8,15,16‐Tetrahydro‐7,15‐methanocycloocta[1,2‐a:5,6‐a′]dinaphthalene derivatives
Authors: Harada Nobuyuki , Hiyoshi Norie , Naemura Koichiro 
Published: September 2010

AbstractThe circular dichroism (CD) and UV spectra of chiral bridged aromatic compounds, 7,8,15,16−tetrahydro‐7,15‐methanocycloocta[1,2‐a:5,6‐a′]dinaphthalene‐8,16 ‐diol [(‐)‐1] and −8,16‐ dione [(‐)‐2], have been theoretically calculated by application of the π‐electron self‐consistent‐ field‐configuration‐interaction‐dipole‐velocity molecular orbital (SCF‐CI‐DV MO) method. The shape of component CD and UV bands was approximated by the Gaussian distribution method (A), or by employing the observed band shape of the UV spectra of model compounds (method B). The calculated CD and UV curves were in good agreement with the observed ones. For compound (7S,8R,15S,16R)‐(‐)‐1, method A: calcd. CD, λext 237.0 nm (Δϵ −319.2), 224.2 (+ 344.9), A = −664.1; obsd. CD, λext 233.0 nm (Δϵ −671.0), 222.3 (+ 194.6), A = −865.6. The calculated CD and UV spectral curves of compound 1 obtained by the application of method B were in excellent agreement with the observed ones: calcd. CD, λext 233.6 nm (Δϵ −740.8), 222.2 (+ 265.0), A = −1005.8; obsd. CD, λext 233.0 nm (Δϵ −671.0), 222.3 (+ 194.6), A = −865.6. For compound (7S,15S)‐(‐)‐2, method A: calcd. CD, λext 256.4 nm (Δϵ −69.4), 220.3 (+ 103.5); obsd. CD, λext 254.4 nm (Δϵ −89.0), 217.0 (+ 222.1). The absolute configurations of chiral, bridged aromatics (‐)‐1 and (‐)‐2 have thus been established.
Enzymatic ammoniolysis of amino acid derivatives
Authors: de Zoete M. C. , Ouwehand A. A. , van Rantwijk F. , Sheldon R. A. 
Published: September 2010

AbstractThe ammoniolysis of amino acid esters and their derivatives was performed with lipases and proteases yielding the corresponding amino acid amides with moderate to high enantioselectivity. Phenylglycine methyl ester racemized slowly under the reaction conditions.
The enantiomeric excess determination and dynamic behaviour of cyclic phosphoric acids used for resolution
Authors: Hulst Ron , Kruizinga Wim , Wynberg Hans , Feringa Ben L. , Kellogg Richard M. 
Published: September 2010

AbstractA method is presented to determine the enantiomeric excess (ee) of phosphoric acids 1, which are extensively used as resolving agents, by means of diastereomeric salt formation with chiral amines. The unexpected dynamic behaviour of these systems leads us to postulate a model, which we refer to as non‐reciprocal behaviour.
Induced chirality of guest molecules encapsulated into a dendritic box
Authors: Jansen Johan F. G. A. , de Brabander‐van den Berg Ellen M. M. , Meijer E. W. 
Published: September 2010

AbstractThe internal cavities of a dendritic box, constructed from poly(propylene imine) dendrimers and enantiomerically pure N‐tBOC‐L‐phenylalanine hydroxysuccinimide esters, possess distinct chiral properties as was demonstrated with the observation of induced optical activity of a variety of guests encapsulated in the box. This induced optical activity of guests is measured with CD (circular dichroism) spectroscopy and is remarkable as the optical activity of the amino acid outer shell itself is vanishingly small. Although small, the effects observed are significant in many cases, whilst in other cases the guests encapsulated do not show an induced CD. Indications for an enforced close proximity and some kind of ordering of guests is found by the observation of an exciton‐coupled CD spectrum in the case of four Bengal Rose molecules encapsulated in a single dendritic box. It is shown that the effects are dependent on the solvent used and the history of the sample. Therefore, the observation of induced optical activity can be used to study the mode of encapsulation of the guests into the box.
The synthesis of pure Amadori rearrangement products
Authors: Noomen S. N. , Breel G. J. , Winkel C. 
Published: September 2010

AbstractThe term “Maillard reaction” is used to describe a complex set of reactions in foods leading to flavour generation and non‐enzymatic browning. The first step in this process is the so‐called Amadori rearrangement: a reducing saccharide and a peptide fragment react to form an Amadori Rearrangement Product (ARP). To be able to do model studies on flavour generation, gram amounts of pure ARP are required. In the present study, glucose‐derived ARPs were synthesised from specifically protected and activated starting compounds. After deprotection and purification, pure ARPs were obtained. This is the first time that ARPs of dipeptides have been isolated.
Synthesis and aggregation behavior of 2‐(4‐butyloctyl) malonic acid in aqueous solution. The formation of physically and colloidally stable vesicles by a branched‐chain malonate
Authors: de Groot Rimke W. , Wagenaar Anno , Sein Arjen , Engberts Jan B. F. N. 
Published: September 2010

AbstractA new surfactant with a branched monoalkyl chain and a malonate headgroup has been synthesized: 2‐(4‐butyloctyl)malonic acid (BOMA). From the geometry of the surfactant, reflected in a packing parameter (P), it was anticipated that the surfactant would preferably aggregate in bilayers. This expectation was borne out in practice by the aggregation behavior, as studied by transmission electron microscopy (TEM) with negatively stained samples and freeze‐fracture samples of aqueous vesicle dispersions. The structure of the surfactant headgroup has been varied by changes in pH of the vesicle dispersions. Over a wide pH range (pH 2.8‐12.8) small unilamellar vesicles with a size of 20–50 nm were observed. Multilamellar vesicles were observed as well in the pH range 2.8–5.1. Phase‐penetration experiments using an optical polarization microscope showed the birth and growth of myelins and multilamellar vesicles over a pH range 1.5‐13.1. At pH < 2.8, a phase separation occured into a surfactant‐rich, optically isotropic phase and a surfactant‐lean phase. The physical and colloidal stability of the vesicular aggregates is high: up to one year as confirmed by TEM. The fusogenic properties of BOMA vesicles were examined. Upon the addition of Ca2+ ions, aggregates tended to become larger, but the formation of Ca2+ surfactant crystals was also observed.