bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enantioselective Synthesis of (R)‐(+)‐Pulvilloric Acid
Authors: Rödel Thomas , Gerlach Hans 
Published: July 2007

AbstractThe fungal metabolite (R)‐(+)‐pulvilloric acid [(+)‐1] was synthesized for the first time. Reaction of the Grignard reagent of 5 with 2‐pentyloxirane (S)‐(−)‐4 in the presence of 1,5‐cyclooctadienecopper(I) chloride as the catalyst led to (S)‐(+)‐6. The enantiomer (S)‐(−)‐4 was prepared from dimethyl L‐malate via the dioxolane (S)‐(+)‐3. The alcohol (S)‐(+)‐6 was transformed into (R)‐(−)‐6 via the benzoate (R)‐(−)‐7 by a Mitsunobu reaction. Hydrogenolysis of (−)‐6 gave the resorcyl alcohol (R)‐(+)‐2. The remaining steps to produce (R)‐(+)‐1 from (+)‐2 required carboxylation to (R)‐(−)‐8, formylation and in situ ring closure with triethyl orthoformate to furnish the required quinomethide structure. Application of the same reactions to (S)‐(+)‐6 afforded (S)‐(−)‐1 via the intermediates (S)‐(−)‐2 and (S)‐(+)‐8. With (±)‐6 as starting material (±)‐2, (±)‐8 and (±)‐1 were prepared.
Side‐Chain Modifications of C60 via Activation of the Easily Accessible Fulleromalonic Acid C61(COOH)2
Authors: Lamparth Iris , Schick Georg , Hirsch Andreas 
Published: July 2007

AbstractSide‐chain modifications of fullerenes can be achieved starting from the malonic acid 2, which is easily accessible by saponification of the corresponding diethyl malonate adduct 1 and is therefore an ideal building block for side chain chemistry on fullerenes. Coupling reactions are carried out via the synthesis of the fullerene active ester 4, which is formed by the reaction of the malonic acid 2 with N‐hydroxysuccinimide. During this reaction the malonic acid undergoes decarboxylation, yielding an acetic acid derivative instead of a malonic system. The active ester 4 is isolable and represents an ideal building block for fullerene chemistry. Sidechain modifications can also be carried out as one‐step reactions by preparing 4 in situ. We have performed coupling reactions with various compounds containing primary or secondary amino groups.
Rearrangements of 2‐ and 3‐Furfurylidene
Authors: Albers Reinhard , Sander Wolfram 
Published: July 2007

AbstractThe photo‐ and thermochemistry of diazo(2‐furyl)methane (3) and diazo(3‐furyl)methane (6) was investigated using the matrix isolation technique. Photolysis of 3 results in the formation of (Z)‐pent‐2‐en‐4‐yn‐1‐al (2) in a clean reaction, in agreement with the observation of Shechter et al. Photolysis or pyrolysis of diazo compound 6 yields (s‐Z)‐(α‐formyl)methylenecyclopropene (s‐Z‐13) as the only detectable product. Carbene 14 and cyclopropene 15 are proposed as intermediates, but not stable under the reaction conditions and thus not directly observed. The reaction sequence 6→13 provides a novel and simple route to methylenecyclopropenes.
The Photoaddition of Pyrroles to Arylethenes and Arylethynes
Authors: Austin Mark , Covell Christopher , Gilbert Andrew , Hendrickx Ramon 
Published: July 2007

AbstractThe photochemical reactions of styrene, (E)‐stilbene, phenyl‐ethyne, and diphenylethyne with pyrrole and N‐methylpyrrole have been investigated. The pyrroles quench the fluorescence of the phenylethenes and phenylethynes efficiently and broad structureless emissions attributed to exciplexes are observed from the N‐methylpyrrole systems. Substituted pyrroles (1:1 and 2:1 adducts) are formed from irradiation of the phenylethenes with pyrrole, and 2‐styrylpyrroles result from the phenylethynes. Styrene, but none of the other arenes, undergoes photoaddition to N‐methylpyrrole in the presence of 10% acetic acid.
Centrohexacyclic or “K5” Molecules: Development of a Growing Family of Topologically Nonplanar Organic Compounds
Authors: Kuck Dietmar 
Published: July 2007

AbstractThis article gives a comprehensive review of the synthetic development of centrohexacyclic organic compounds (“centrohexacyclanes”) during the past decade. With their unique feature of having a molecular constitution that corresponds to the complete graph K5, centrohexacyclanes represent the majority of the rare class of topologically nonplanar compounds. Starting from the few previously known organic, element–organic and inorganic K5 compounds, the syntheses of various organic centrohexacyclanes are discussed, based mainly on three different strategies that have emanated from the chemistry of centropolyindanes: the propellane, fenestrane, and “broken fenestrane” routes. In addition, the first results of some targeted transformations of centrohexaindane, the Td‐symmetrical hexabenzoannelated centrohexaquinane, are presented.
Stereoselective Synthesis of Alcohols, L. Synthesis and Conformational Studies of 1,5‐Dioxa‐cis‐decalin
Authors: Hoffmann Reinhard W. , Münster Ingo 
Published: July 2007

Abstractcis‐2‐Vinyltetrahydropyran‐3‐ol (6) is accessible by a selective intramolecular allylboration reaction. Compound 6 was converted into 1,4‐dioxa‐cis‐decaline (4) and cis‐syn‐cis‐perhydrotrioxaanthracene 32; heterocycles with fused tetrahydropyran rings. These ring systems populate predominantly the conformation in which the oxygen atoms are in a gauche arrangement. The tricycle 31 is a rigid derivative of 14‐crown‐3 and, as in the case of 12‐crown‐3, it forms complexes with lithium ions in acetonitrile.
Selective CC Bond Cleavage of Quaternary β‐Amino Aldehydes and β‐Amino Ketones by Sodium–Amide‐Induced Grob‐Type Fragmentation
Authors: Mölm Detlef , Risch Nikolaus 
Published: July 2007

AbstractQuaternary β‐amino aldehydes and β‐amino ketones are cleaved in a Grob‐type fragmentation induced by nucleophilic attack of NH2− on the carbonyl group of 3, to yield new carbonyl derivatives 4 and alkenes 5, and unsaturated amides 6, respectively.
Application of Vicarious Nucleophilic Substitution in Organic Synthesis
Authors: Ma̧kosza Mieczyslaw , Wojciechowski Krzysztof 
Published: July 2007

AbstractVicarious Nucleophilic Substitution (VNS) provides the possibility of the replacement of hydrogen atoms in electrophilic arenes with α‐functionalized alkyl substituents. This review focuses on the transformations of products obtained by VNS, particularly into heterocyclic compounds. In addition, some characteristic features of the VNS mechanism are briefly described.
Utilization of Industrial Waste Materials, 11. Synthesis of New, Chiral β‐sec‐Amino Alcohols – Diastereodivergent Addition of Grignard Reagents to α‐Amino Aldehydes Based on the (all‐R)‐2‐Azabicyclo[3.3.0]octane System
Authors: Wilken Jörg , Thorey Claire , Gröger Harald , Haase Detlev , Saak Wolfgang , Pohl Siegfried , Muzart Jacques , Martens Jürgen 
Published: July 2007

AbstractNew, chiral β‐sec‐amino alcohols (αR,βR)‐11a–13a, (αS,βR)‐11b–17b, (αS,βS)‐11c, 12c, 15c, 17c and (αR,βS)‐11d, 12d, 15d, 17d have been synthesized from the enantiomerically pure amine (all‐R)‐1a via diastereomeric, N‐tert‐butoxycarbonyl‐protected aldehydes 3. Grignard additions proceed in fair yields with a high degree of diastereofacial stereoselection (diastereomeric ratios dr up to ⩾ 95:5) with non‐chelation control, generally in favor of the anti‐(erythro) structures. A mechanistic interpretation of the stereochemical course of this reaction is presented. The stereodifferentiating ability of selected stereoisomeric (erythro)‐ and (threo)‐amino alcohol structures were tested in homogeneous catalysis, e.g. in two model reactions (optical purities up to 95%).
Cyclopropyl Building Blocks for Organic Synthesis, 42. An Unprecedented Mode of Ring Opening of Methylenecyclopropane Moieties – Reactions of Methylenecyclopropanecopper Reagents with an Electrophilic Glycine Equivalent
Authors: Kozhushkov Sergei I. , Brandl Melanie , Yufit Dmitrii S. , Machinek Reinhard , de Meijere Armin 
Published: July 2007

AbstractThe reactions of ethyl 2‐acetoxy‐2‐diphenylmethyleneaminoacetate (1) with organocopper reagents derived from bicyclopropylidene (2) and methylenecyclopropane (3) are accompanied by an unusual mode of opening of one three‐membered ring to give 4‐methylene‐1,2,3,4‐tetrahydropyridine derivatives 8a, 9 in good yields. The cuprate derived from methylenespiropentane (4) reacts with 1 to yield both the normal substitution product 14 (37%) as well as the rearrangement product 15 (34%), while the simple cyclopropylcuprate undergoes substitution to give the protected cyclopropylglycine 16 (75%) without rearrangement. The tetrahydropyridine 8a shows an interesting tautomerism in solution. The 4‐cyclopropylidenetetrahydropyridine 15 undergoes an unusual dehydrodimerization to produce two separable rotamers, C2‐19 and C1‐19, via 18.
Photoinduced Electron‐Transfer in Porphyrin‐quinone Cyclophanes, 15. Distance Dependence of Photoinduced Electron‐Transfer: Syntheses and Structures of Naphthalene‐Spacered Porphyrin‐Quinone Cyclophanes
Authors: Staab Heinz A. , Feurer Achim , Krieger Claus , Kumar A. Sampath 
Published: July 2007

AbstractSyntheses, conformational and structural analyses of porphyrin‐quinone cyclophanes 2 with naphthalene‐spacers are presented and the findings are compared with data for previously investigated analogous benzene‐spacered compounds 1. In combination with data for the biphenylene‐ and anthracene‐spacered porphyrin‐quinone cyclophanes 3 and 4, to be published in following papers, the results reported herein allow some appraisal to be made of the distance dependences of photoinduced electron‐transfer from porphyrin to quinone units.
Some Reactions of the Chloromethyl trans‐β‐Styryl Sulfone Carbanion
Authors: Ma̧kosza Mieczyslaw , Krylova Irina 
Published: July 2007

AbstractThe chloromethyl trans‐β‐styryl sulfone carbanion reacts with benzaldehyde and acrylonitrile under phase‐transfer catalysis conditions to give 2‐phenyl‐3‐(trans‐β‐styrylsulfonyl)oxirane and bis(2‐cyanoethyl)chloromethyl trans‐β‐styryl sulfone, respectively, and with nitroarenes to form the products of vicarious nucleophilic substitution of hydrogen.
On the Oxidation of Bridged 1‐Naphthylamine and Aniline Derivatives – Formation of Substituted Quinoline and Benzo[c,d]indole Derivatives
Authors: Kanitz Andreas , Hartmann Horst 
Published: July 2007

AbstractThe bridged aniline or 1‐naphthylamine derivatives 8–10 react with nitrous acid in the presence of perchloric acid to give the bridged diphenoquinone diiminium salts 12·2 HClO4, 17·2 HClO4, 19·2 HClO4 and 23. The same products are obtained from these substrates upon their reaction with hydrogen peroxide. Upon treatment of the bridged diphenoquinone diiminium salts 12·2 HClO4 and 23 with base, a disproportionation reaction occurs resulting in the formation of the corresponding benzidine derivatives 13 and 26 and, following a multistep process, the quinoline derivatives 15 and 25 are obtained. Analogously, the 1,2‐dihydrobenzo[c,d]indole hydroperchlorate 10·HClO4 is transformed into the bridged benzidine derivative 21 and the bis(benzo[c,d]indol‐6‐yl) hydroperchlorate 20·HClO4. Furthermore, as a result of an oxidation process initiated by the protonated species of the corresponding indaminium salts, condensation of N,N‐dimethyl‐4‐nitrosoaniline (27) with the bridged aniline or naphthylamine derivatives 8a–8c leads to the N′‐(6‐quinolyl)‐substituted N,N‐dimethylbenzoquinone bis(iminium) salts 29a–28c rather than the corresponding indaminium salts 28a–28c.
Biologically Active Metabolites from Fungi, 10. Generation of the Palmarumycin Spiroacetal Framework by Oxidative Cyclization of an Open Chain Metabolite from Coniothyrium palmarum
Authors: Krohn Karsten , Beckmann Karsten , Aust Hans‐Jürgen , Draeger Siegfried , Schulz Barbara , Busemann Stefan , Bringmann Gerhard 
Published: July 2007

AbstractThe first “open chain” representative of the palmarumycins, the biaryl ether 1, was isolated from Coniothyrium palmarum. Phenol oxidation of 1 with silver oxide as a model for a biosynthetic step yielded 4 with the usual spiroacetal structure of the palmarumycins. The absolute (S)‐configuration of 4 (and thus of 1) was determined by quantumchemical CD calculations.
Kinetics of the Acid‐Catalysed Reaction of Cyclohexene with Hydrogen Peroxide: Mechanistic Aspects of the “In Situ” Activation of H2O2
Authors: Vayssié Stéphane , Elias Horst 
Published: July 2007

AbstractThe kinetics of the reaction of cyclohexene (CH) with an excess of H2O2 in acetonitrile (AN) at 293 K was studied at variable concentrations of H2O2 (1.7–13 M), water (1.6–13 M), acids HX (0.2–1.4 M), and salts NaX (0–1.7 M), with HXHClO4, H2SO4, HNO3, HPF6, p‐toluenesulfonic acid (TSAH), acetic acid (AH), trifluoroacetic acid (TFAH), and benzeneseleninic acid (BSAH). The solvent polarity parameter ET(30) of AN/water mixtures was determined. The oxidation of CH by H2O2, monitored by gas chromatography, was found to be acid‐catalysed. The detailed investigation of the systems CH/HClO4/AN and CH/TSAH/AN showed that the reaction is first‐order in CH according to [CH][CH]0 exp(–kexp·t). At [H2O2] ⩽ 3 M, the experimental rate constant kexp could be approximated by kexp = k0[H2O2] + k·[H2O2]·[HX]2· [X−]tot·[H2O]−2, with k0 = (0.93 ± 0.7)·10−5 M−1s−1 and k = (9.65 ± 0.20)·10−3 M−2s−1 for HClO4 and k = (5.96 ± 0.10)·10−3 M−2s−1 for TSAH ([X−]tot = [NaX] + [HX]). GC analysis of the HClO4‐catalysed reaction showed that trans‐cyclohexane‐1,2‐diol (CHD) is a reaction product. The order of catalytic activity of the various acids HX, as derived from the size of kexp obtained under standard conditions, was found to be: AH ≪ HNO3 < TFAH < TSAH < HClO4 < HPF6 < H2SO4 < BSAH. A mechanistic interpretation is presented and the synthetic potential of the acid‐catalysed oxidation of olefins by H2O2 is discussed.
3D 1H MRSI of brain tumors at 3.0 tesla using an eight‐channel phased‐array head coil
Authors: Osorio Joseph A. , Ozturk‐Isik Esin , Xu Duan , Cha Soonmee , Chang Susan , Berger Mitchel S. , Vigneron Daniel B. , Nelson Sarah J. 
Published: July 2007

AbstractPurposeTo implement proton magnetic resonance spectroscopic imaging (1H MRSI) at 3 Tesla (3T) using an eight‐channel phased‐array head coil in a population of brain‐tumor patients.Materials and MethodsA total of 49 MRI/MRSI examinations were performed on seven volunteers and 34 patients on a 3T GE Signa EXCITE scanner using body coil excitation and reception with an eight‐channel phased‐array head coil. 1H MRSI was acquired using point‐resolved spectroscopy (PRESS) volume selection and three‐dimensional (3D) phase encoding using a 144‐msec echo time (TE).ResultsThe mean choline to N‐acetyl aspartate ratio (Cho/NAA) was similar within regions of normal‐appearing white matter (NAWM) in volunteers (0.5 ± 0.04) and patients (0.6 ± 0.1, P = 0.15). This ratio was significantly higher in regions of T2‐hyperintensity lesion (T2L) relative to NAWM for patients (1.4 ± 0.7, P = 0.001). The differences between metabolite intensities in lesions and NAWM were similar, but there was an increase in SNR of 1.95 when an eight‐channel head coil was used at 3T vs. previous results at 1.5T.ConclusionThe realized increase in SNR means that clinically relevant data can be obtained in five to 10 minutes at 3T and used to predict the spatial extent of tumor in a manner similar to that previously used to acquire 1.5T data in 17 minutes. J. Magn. Reson. Imaging 2007;26:23–30. © 2007 Wiley‐Liss, Inc.
Optically Driven Encapsulation Using Novel Polymeric Hollow Shells Containing an Azobenzene Polymer
Authors: Bédard Matthieu , Skirtach Andre G. , Sukhorukov Gleb. B. 
Published: July 2007

AbstractA novel method of macromolecule encapsulation using micron‐sized polymeric shells constructed with a photoactive azobenzene containing polyelectrolyte is discussed. Fluorescently labeled dextran molecules were encapsulated using light to remotely shrink and change the wall permeability of new polymeric hollow shells. We observed that the proportion of shells with dye encapsulated increased along with the duration of irradiation. Electron microscopy imaging illustrated significant changes in the surface roughness of shells after being exposed to light. Finally, this new system was shown to possess a high thermal stability.magnified image
Influence of perfusion on high‐intensity focused ultrasound prostate ablation: A first‐pass MRI study
Authors: Wiart Marlène , Curiel Laura , Gelet Albert , Lyonnet Denis , Chapelon Jean‐Yves , Rouvière Olivier 
Published: July 2007

AbstractOur aim was to evaluate the influence of regional prostate blood flow (rPBF) on high‐intensity focused ultrasound (HIFU) treatment outcome. A total of 48 patients with clinically localized prostate cancer were examined by dynamic contrast‐enhanced (DCE)‐MRI prior to HIFU therapy. A prostate‐specific antigen (PSA) nadir threshold of 0.2 ng/ml was used to define the populations of responders and nonresponders. A dedicated tracer kinetic model, namely “monoexponential plus constant” (MPC) deconvolution, was implemented to provide quantitative estimates of rPBF. The results were compared with those obtained by semiquantitative (steepest slope, mean gradient) and quantitative (Fermi deconvolution) approaches. Of the four methods studied, quantitative rPBF obtained by MPC deconvolution proved the most sensitive to the perfusion changes encountered in this study. Furthermore, blood‐flow values obtained with MPC deconvolution in the prostate and muscle (12 ± 8 and 5 ± 3 ml/min/100 g, respectively) were in good agreement with literature data. The mean pretreatment rPBF obtained with MPC deconvolution was significantly higher in nonresponders compared to responders (16 ± 9 vs. 10 ± 6 ml/min/100 g), suggesting a correlation between baseline perfusion and treatment outcome. The present work describes and validates the use of dynamic MRI to estimate rPBF in patients, which in the future may help to refine the conduct of HIFU therapy. Magn Reson Med 58:119–127, 2007. © 2007 Wiley‐Liss, Inc.
Vapor pressure apparatus: Semi‐micro
Authors: Bonhorst Carl W. , Althouse P. M. , Triebold H. O. 
Published: July 2007

SummaryAn apparatus is described for the determination of vapor pressures on small amounts of pure substances with an accuracy of ±0.1 mm. Use is made of the increase in resistance to gas flow which accompanies decrease in diameter of a capillary.
Protein conformations and their stability
Authors: Pace C. N. 
Published: July 2007

AbstractOur understanding of the conformations of proteins and their stability has increased substantially in recent years. A reaction of considerable interest is native (N) ⇌ denatured (D) where N is the globular, native state of the protein which is now well defined as a result of numer‐ous structural determinations by X‐ray diffraction studies, and D represents unfolded, denatured states of the protein whose structure depends on the denaturant used to promote unfolding. Through experimental studies much is known about the kinetics, thermody‐namics, and mechanism of this reaction. For example, it is known that the free energy change for this reaction under physiological conditions, ΔGD, is between 3 and 15 kcal/mol for a fairly wide range of globular proteins. Thus, the globular conformation which is absolutely essential for the biological function is only marginally stable. In addition, these ΔGD values are remarkably sensitive to small changes in the structure of the protein. It has been shown that single amino acid substitutions can dramatically increase or decrease ΔGD values and some substitutions surely lead to unfolding of the polypeptide chain. Most chemical alterations in the structure of a protein, e.g., cleavage of a peptide bond, or modification of an amino acid side chain, lead to decreases, often sizable, in the confor‐mational stability. The remarkably low conformational stability of globular proteins is important, in part, because many properties of the protein, e.g., solubility and proteolytic digestibility, change sub‐stantially when the protein unfolds. Recent developments in these areas of interest to protein chemists and food scientists are illus‐trated and discussed.
Interactions between sodium tetradecyl sulfate and a series of homogeneous polyoxyethyleneglycol‐ n‐ dodecyl ethers
Authors: Meguro Kenjiro , Kanbe Tetsuya , Esumi Kunio 
Published: July 2007

AbstractThe surface tensions of a mixed system of sodium tetradecyl sulfate (STS) and a series of polyoxyethyleneglycol‐n‐dodecyl ethers (nED) were measured at temperatures of 30 and 40 C, respectively. When the STS concentration was fixed, the surface tension curves of the mixed system showed a flat portion in the range of which the mixed micelles would be formed. With a decrease of the added STS concentration, the length of the flat portion in these curves decreased gradually, and finally disappeared in the presence of 0.05 mM STS. Furthermore, when the concentration of STS was fixed at 1.0 mM, which is below the critical micelle concentration (CMC), the flat portion length in the surface tension curves de‐creased with decreasing ethylene oxide chain length in nED and with increasing temperature. The influence of increment of temper‐ature was comparable to that for reducing the length of ethylene oxide chain in nED.
Biodegradation of sodium alkyl poly(oxyalkylene)sulfates
Authors: Yoshimura K. , Masuda F. 
Published: July 2007

AbstractThe biodegradability of sodium alkylpoly(oxyalkylene)sulfates was studied under aerobic conditions by oxygen consumption, total organic corbon (TOC) and methylene blue active substance (MBAS) measurements. MBAS of linear alkylpoly(oxyalkylene)sulfates with propylene oxide (APS) or ethylene oxide (AES) disappeared within 5 days, whereas AES with branched alkyl chains were degraded less than linear AES. APS with propylene oxide from 1 to 3 mol showed BOD/ThOD values of more than 40% after 6 days. Therefore, these surfactants are considered to be readily biodegradable. In comparison to the biodegradability of APS and AES, the existence of propylene oxide groups resulted in a slight decreasing in oxygen consumption and TOC removal. Linear APS with PO of 1~3 mol were degraded according to Swisher's distance principle up to a C16 alkyl chain length. That is, increasing distance principle up to a C16 alkyl chain length. That is, increasing distance between sulfate and chain end increased the rate of biodegradation of these surfactants. Furthermore, from the biodegradation test of35S‐C12E3S, it is suggested that the initial step of biodegradation is attack on the terminal methyl group.
Desorption of soy oil lutein from rice hull cristobalite with polar solvents
Authors: Proctor Andrew , Palaniappan Sevugan 
Published: July 2007

AbstractThe effectiveness of sequential isopropanol/hexane washes of increasing polarity for desorbing soy oil pigment (lutein) from alkaline and acid rice hull ash was studied. Increasing the polarity promoted desorption of pigment. However, the amount of pigment desorbed with each extraction decreased after washing with 2% isopropanol. More lutein was desorbed as the amount of adsorbed lutein increased. Desorption from acid ash was greater than that from alkaline ash, which may be due to the absence of potassium from acid ash. The data suggest that the adsorption sites, occupied by lutein, are not all equally accessible to isopropanol, probably because of the irregular structure of the ash.