bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Thromboxane A2 Models from Glucose. II. Epoxidation Studies of Hex‐2‐enopyranosides
Authors: Cirelli Alicia Fernández , Moradei Oscar , Thiem Joachim 
Published: July 2007

AbstractThe synthesis of halohydrin 7, a potential precursor of the heterocyclic moiety of thromboxane A2 (TXA2) is described. Claisen‐Meerwein‐Eschenmoser rearrangement of hex‐3‐enopyranosides 4 and 8 yields the branched olefin sugars 5 and 9. Epoxidation studies with perbenzimidic acid (Payne's method) and m‐chloroperbenzoic acid (Anderson's method) were performed. Under treatment of the 2,3‐anhydrosugar 6 with LiBr, the epimeric halohydrins 7 and 10 were obtained in a ratio of 3:2.
Flexible Molecules with Defined Shape, VIII. Model Studies and Predictions for the Conformational Behavior of 2,4,6,n‐Polymethylated Alkane Derivatives
Authors: Hoffmann Reinhard W. , Göttlich Richard 
Published: July 2007

AbstractConformer equilibria of compounds having a single (6–8) or two (15–17) neighbouring dimethylpentane backbone segments have been studied. As in 2,4‐dimethylpentane, a biconformational situation prevails in each segment. The position of the local conformer equilibria were estimated from vicinal 3JH,H coupling constants between hydrogen atoms along the backbone. The position of the conformer equilibria were also calculated with the MM3* force field in good agreement with the experimental findings. A simple estimate of the position of the local conformer equilibria based on counting the number of the low energy diamond lattice type conformers available was used to discuss the conformer situation in molecules 18 and 19 possessing three adjacent dimethylpentane segments. The results were used to interprete the conformational behaviour of the more complex trimethoxyhexamethylpentadecene 2.
Interactions in Molecular Crystals, 123. Crystallization and Structure of Donor–Acceptor Complexes between Rigid or Conformationally Flexible Thio‐Crowns and Iodine
Authors: Bock Hans , Nagel Norbert , Seibel Andreas 
Published: July 2007

AbstractStudies of π and σ interactions in molecular crystals of donoracceptor complexes have stimulated interest in the crystallization and structure determination of {1,3,5‐trithiane…︁I2}, {1,5,8,12‐tetrathiocyclotetradecane…︁I2} and {1,4,7,10,13,16‐hexathiocyclooctadecane…︁(I2)3} in order to detect structural changes. The II bond lengths are stretched by up to 0.16 Å relative to the gas‐phase value and prove iodine to be the acceptor species. Additional distance data >S…︁I2 and II from the Cambridge Structural Database establish a nonlinear correlation. In contrast, bond lengths and bond angles of the sulphide donors remain largely unperturbed on complexation, even when considerable conformational changes are observed. For example, on addition of four iodine molecules, the rather flexible 18‐thio‐crown‐6 with a C2‐symmetric bowl‐shape is flattened to a Cs‐symmetric rectangle. The structural results complement those reported for stronger acceptor effects of metal cations.
Non‐Ionic Template Synthesis of Amide‐Linked Rotaxanes: Olefinic and Aliphatic Axle Building Blocks
Authors: Jäger Ralf , Baumann Sven , Fischer Marco , Safarowsky Oliver , Nieger Martin , Vögtle Fritz 
Published: July 2007

AbstractThe first synthesis of amide‐linked rotaxanes with non‐arene axle building blocks is reported. The threading synthesis of rotaxane 8 with olefinic fumaryl chloride proves that arene moieties are not necessary for non‐ionic template syntheses. Mass spectroscopic evidence of a rotaxane bearing an aliphatic axle, derived from succinic acid, revealed that hydrogen bonding, rather than π,π interactions, is the predominant template binding force. 1H‐NMR titration studies on the threading synthesis of these mechanically bonded molecules were carried out. The association constants measured suggest that the incorporation of the corresponding monoamide monochloride (cf. 7), rather than the incorporation of the diacid dichloride (cf. 5), plays the key role in these rotaxane syntheses. The X‐ray structural analysis of a semi axle (14) reveals hydrogen bonding patterns characteristic of diamides.
Radical Additions of Alkyl 2‐Haloalkanoates and 2‐Haloalkanenitriles to Alkenes Initiated by Electron Transfer from Copper in Solvent‐Free Systems
Authors: Metzger Jürgen O. , Mahler Ralf , Francke Gerald 
Published: July 2007

AbstractAlkyl 2‐iodoalkanoates 2, and 2‐iodoalkanenitriles 15 were added, with copper powder, to the 1‐alkenes 1a, e, f, and h, and to the alkenes 1b, c, d, and g with a 1,2‐dialkyl substituted double bond, to give, respectively, γ‐lactones and 4‐iodoalkanenitriles in very good yields. No solvent was used. The reaction is a free radical addition initiated by electron transfer from copper to the activated iodoalkane. Yields were lower using the respective bromo compounds. In situ formation of the iodo compounds, by addition of stoichiometric amounts of sodium iodide to the reaction mixture, gave improved yields. In the case of the methyl bromomalonates 6, the addition of sodium iodide proved to be unnecessary. The diastereoselectivity of the addition reaction by relative 1,3‐asymmetric induction was rationalized by consideration of the steric interactions of the substituents in the transition state which is formed in the process of iodine transfer to the chiral adduct radical.
Cytotoxic Triterpene Glycosides from Far‐Eastern Sea Cucumbers Belonging to the Genus Cucumaria
Authors: Drozdova Olga A. , Avilov Sergey A. , Kalinin Vladimir I. , Kalinovsky Anatoly I. , Stonik Valentin A. , Riguera Ricardo , Jiménez Carlos 
Published: July 2007

AbstractNew cytotoxic triterpene oligoglycoside disulfates, cucumariosides A3 (1) and A6‐2 (2), have been isolated from the sea cucumber Cucumaria japonica. The trisulfated cucumarioside A7‐3 (4) was found to be the major component in the glycoside fraction of Cucumaria miniata. The structures were assigned on the basis of extensive spectral data (NMR and MS), selective solvolysis of desulfated derivative 3 and other chemical evidence. The presence or absence of a carbonyl group at C‐16 of the aglycone and of sulfate groups at C‐6 of the glucose and 3‐O‐methylglucose units are interpreted in terms of the functional evolution of sea cucumbers in order to improve their defensive system. Both (1) and (2) are cytotoxic in vitro at IC50 = 1 μg/ml against a selection of five human and mice tumoral cell lines.
Diastereoselective Protonation of Chiral Enolates with Chelating Proton Donors under Reagent Control: Scope, Mechanism, and Applications
Authors: Krause Norbert , Ebert Sophia , Haubrich Andreas 
Published: July 2007

AbstractEndocyclic keto‐enolates of type 2 can be protonated under reagent control with high diastereoselectivities when chelating proton donors with a salicylate structure are used. The stereochemical course of these protonations is hardly affected by the ring size, the substitution pattern, and the presence of additional stereogenic centers in the enolate. The substrates can be prepared by conjugate cuprate addition as well as deprotonation; in the latter case, good diastereoselectivities are obtained by removal of competing proton sources and the inclusion of transmetalation steps. The chelate complex A serves as a mechanistic model that makes the usual trial and error search for stereoselective protonating agents unnecessary. The method is applied to stereoselective syntheses of a precursor for methyl epijasmonate and of the insect pheromone (2S,3S)‐diprionyl acetate.
Total Synthesis of (+)‐3‐Oxacarbacyclin 1. Retrosynthesis and Asymmetric Olefination through Horner–Wadsworth–Emmons, Peterson and Martin Reactions
Authors: Gais Hans‐Joachim , Schmiedl Gerhard , Ossenkamp Rainer K. L. 
Published: July 2007

AbstractThe asymmetric Horner–Wadsworth–Emmons (HWE) reaction of the prochiral ketones 8a/b with the phosphonoacetates 10a, ent‐10a, 10b and rac‐16, which contain 8‐phenylmenthol, 8‐phenylnormenthol and trans‐2‐(triphenylsilyl)‐cyclohexanol, respectively, as chiral auxiliaries, were studied. The HWE reaction of 8a with the phosphonoenolates Li‐10a/b at low temperatures gave the esters 7a/b and 11a/b in high yields with diastereoselectivities up to 97:3. The (E)‐configured esters 7a/b serve as starting material for the total synthesis of (+)‐3‐oxacarbacyclin. Similarly, the reaction of 8b with ent‐Li‐10a gave the esters ent‐7b and ent‐11b in a ratio of 95:5 in 82% yield. The olefination of 8b with rac‐16 afforded a mixture of the esters rac‐17 and rac‐18, of yet unassigned configuration, in a ratio of 70:30. The HWE reactions of 8a/b with Li‐10a, ent‐Li‐10a and rac‐Li‐10b show linear temperature–diastereoselectivity relationships. The stereochemical course of the HWE reactions can be understood in terms of a selective addition of the chiral (E)‐configured phosphonoenolate from its least hindered side to the ketone 8 at the convex side. The asymmetric Peterson reaction of 8b with the silyl enolate Li‐20 gave the esters ent‐7b and ent‐11b in a ratio of 89:11. The diastereomerically pure β‐hydroxy esters 22, rac‐25 and 27, which contain 8‐phenyl‐menthol, trans‐2‐(triphenylsilyl)cyclohexanol and 3‐{[(3,5‐dimethylphenyl)phenylsulfonyl]amino}isoborneol, respectively, as chiral auxiliaries, were prepared by a highly selective addition of the enolates Li‐21, rac‐Li‐24 and Li‐26 to the ketone 8b. The asymmetric Martin dehydration of 22, rac‐25 and 27 with the sulfurane 23 proceeds with stereoselectivities ranging from 82:18 to 99:1. Interestingly, the HWE, Peterson and Martin reactions involving 8‐phenylmenthol as the chiral auxiliary all proceed with the same sense of asymmetric induction.
Transitions of Electron Demand in Pericyclic Reactions: Normal, Neutral, and Inverse Diels–Alder Reactions of Polyhalogenated Cyclopentadienes
Authors: Eibler Ernst , Höcht Peter , Prantl Bernhard , Roßmaier Henry , Schuhbauer Hans Markus , Wiest Hubert , Sauer Jürgen 
Published: July 2007

AbstractNormal, neutral, and inverse‐type Diels‐Alder reactions can be observed in [4+2] cycloadditions of polyhalogenated cyclopentadienes 1a–1i with various aryl‐substituted cyclic and open‐chain dienophiles, and characteristic gradations of reactivity associated with the different mechanistic types are often displayed. Reaction rate constants and semiempirically derived HOMO and LUMO values for the reactants suggest that neutral [4+2] cycloadditions should be regarded as a transition between normal and inverse Diels‐Alder reactions.
Pheromone Synthesis, CLXXXVI. Synthesis of (1S,2R,5R)‐Bicolorin, the Aggregation Pheromone of Male Beech Bark Beetles (Taphrorychus bicolor), and Its (1R,2R,5S) Isomer
Authors: Takikawa Hirosato , Sano Satoshi , Mori Kenji 
Published: July 2007

Abstract(−)‐Bicolorin [(1S,2R,5R)‐(−)‐2‐ethyl‐1,5‐dimethyl‐6,8‐dioxabicyclo[3.2.1]octane (1)], the male‐produced pheromone of Taphrorychus bicolor, and its (1R,2R,5S) isomer 2 were synthesized by starting from (S)‐limonene oxide (3), employing osmium tetroxide catalyzed dihydroxylation of 7b as the key step.
Isofulminic Acid – Phantom or Reality?
Authors: Maier Günther , Bothur Axel , Eckwert Jürgen , Reisenauer Hans Peter , Stumpf Thomas 
Published: July 2007

AbstractThe complex photochemistry of matrix‐isolated dihaloformoximes 8a, 8b, and 8c, which are transformed upon irradiation into the new hydrogen‐bonded complexes HalCN…︁HOHal 10a–c′, identified by their IR spectra, has been unveiled. An earlier assignment of the experimental IR absorptions to isofulminic acid HONC (4) must be withdrawn. A competitive reaction to the formation of complexes 10a–c′ produces the hydrogen‐bonded complexes HalNCO/HHal 12a–c′, which can be regarded as intermediates on the photochemical pathway to the final product isocyanic acid HNCO (1), and are tentatively identified by their IR absorptions. Our findings are supported by deuteration experiments and theoretical calculations using the density functional method BLYP/6‐311G*.
Structure, Conformation, and Thermochemistry of Dimesityl Methanethial S‐oxide (Dimesityl Sulfine)
Authors: Kappert Wilhelm , Sander Wolfram , Landgrafe Claudia 
Published: July 2007

AbstractThe structure of dimesityl sulfine in solution and in the solid state was determined by NMR spectroscopy and X‐ray crystallography, respectively. In the crystal the two mesityl groups are twisted by approximately 60°, while in solution an averaged conformation with Cs symmetry is observed, with the anti mesityl ring located in the CSO plane and the syn mesityl ring perpendicular to the CSO plane. From the coalescence temperature Tc at 303 K, the free energy of activation for the rotation of the mesityl rings was estimated to be 14 ± 0.7 kcal/mol. At higher temperatures (140–185°C) dimesityl sulfine yields up to 95% 5,7‐dimethyl‐1‐mesityl‐benzo[c]thiophene.
Addition and Cyclization Reactions in the Thermal Conversion of Hydrocarbons with an Enyne Structure, 4. Formation and Rearrangements of Bicyclic C10H8 Aromatics from 1‐Phenyl‐1‐buten‐3‐yne
Authors: Schulz Kathrin , Hofmann Jörg , Zimmermann Gerhard 
Published: July 2007

AbstractThe thermal conversion of 1‐phenyl‐1‐buten‐3‐yne (1) into the cycloisomerization products naphthalene (2), azulene (3), and 1‐methylene‐1H‐indene (4) has been studied at temperatures between 550 and 1000°C, a reaction time of approximately 0.3 s at 13 Torr (FVP) and at low partial pressures in a quartz flow system. The results obtained by FVP as well as in the presence of chemically modified diluent gases suggest a predominance of unimolecular cycloisomerizations to 2 and 3 which are, however, always accompanied by radical cyclization reactions to 2 and 4 even under FVP conditions if temperatures above 550°C are applied.
Methylamination of Some 3‐Nitro‐1,8‐naphthyridines with Liquid Methylamine/Potassium Permanganate
Authors: Woźniak Marian , Grzegoz̊ek Maria , Surylo Piotr 
Published: July 2007

Abstract3‐Nitro‐1,8‐naphthyridines (1a–1h) are aminated, with a liquid methylamine solution of potassium permanganate (LMA/PP), to the corresponding 4‐methylamino‐substituted nitro compounds (3a–g). The intermediary 4‐methylamino‐σ‐adducts of some 3‐nitro‐1,8‐naphthyridines are detected by 1H‐NMR spectroscopy. Quantum chemical calculations show the reactions to be controlled by the interaction of the frontal molecular orbitals (FMO) of the reagents. Moreover, the heats of formation of the intermediary methylamino‐σ‐adducts of 1a and 1c–1h and transition states are calculated for the reactions studied. The agreement, between the calculated and observed results, is satisfactory for the reactions described.
Synthesis, Solvatochromism, and Molecular Structure of a New Pyridinium N+N− Betaine Dye
Authors: Milart Piotr , Stadnicka Katarzyna 
Published: July 2007

AbstractTwo methods for the synthesis of N‐[4‐(2,4,6‐triphenyl‐1‐pyridinio)phenyl]‐p‐toluenesulfonaminide (4), a new betaine dye with positive and negative charges at two nitrogen atoms separated by an aromatic ring, are described. 4 displays a negative solvatochromic effect slightly smaller than that observed for the standard betaine 1 [ET(30) scale]. X‐ray structure determination of crystals containing 4 and acetone solvate molecules in the molar ratio of 1:1 revealed that the geometry of the pyridinium moiety is strongly influenced by the negatively charged aminide nitrogen atom.
Morphology of the mammalian vestibulo‐ocular reflex: The spatial arrangement of the human fetal semicircular canals and extraocular muscles
Authors: Cox Philip G. , Jeffery Nathan 
Published: July 2007

AbstractThe vestibulo‐ocular reflex is the system of compensatory ocular movements in response to stimulation of the kinetic labyrinth seen in all vertebrates. It allows maintenance of a stable gaze even when the head is moving. Perhaps the simplest influence on the VOR is the spatial orientation of the planes of the semicircular canals relative to the extraocular muscles. It is hypothesized that the extraocular muscles are in parallel alignment with their corresponding semicircular canals in order to reduce the amount of neural processing needed and hence keep reflex times to a minimum. However, despite its obvious importance, little is known of this spatial arrangement. Moreover, nothing is known about any ontogenetic changes in the relative orientations of the extraocular muscles and semicircular canals. The morphologies of fetal and adult specimens of Homo sapiens were examined using magnetic resonance (MR) images. Three‐dimensional co‐ordinate data were taken from the images and used to calculate vector equations of the extraocular muscles and planes of best fit for the semicircular canals. The relative orientations of the muscles and canals were then calculated from the vectors and planes. It was shown that there are significant correlations between both the anterior and lateral semicircular canals and their corresponding extraocular muscles during ontogeny. In the case of the lateral canal with the medial rectus, the lateral canal with the lateral rectus, and the anterior canal with the inferior oblique, the trend is towards, though never reaching, alignment, whereas the anterior canal and the superior rectus muscle move out of alignment as age increases. Furthermore, it was noted that none of the six muscle‐canal pairs is in perfect alignment, either during ontogeny or in adulthood. It was also shown that the three semicircular canals are not precisely orthogonal, but that the anterior and posterior canals form an angle of about 85°, while the anterior and lateral canals diverge by ∼100°. Overall, it was shown that there is significant reorientation of the extraocular muscles and semicircular canals during ontogeny, but that, in most cases, there is little realignment beyond the fetal period. J. Morphol., 2007. © 2007 Wiley‐Liss, Inc.
Dynamic contrast‐enhanced magnetic resonance imaging of human melanoma xenografts with necrotic regions
Authors: Gaustad Jon‐Vidar , Benjaminsen Ilana C. , Ruud Else‐Beate M. , Rofstad Einar K. 
Published: July 2007

AbstractPurposeTo investigate whether high‐resolution images of necrotic regions in tumors can be derived from gadopentetate dimeglumine (Gd‐DTPA)‐based dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) series.Materials and MethodsE‐13 human melanoma xenografts were used as preclinical models of human cancer. DCE‐MRI was performed at a voxel size of 0.23 × 0.47 × 2.0 mm3 with the use of spoiled gradient recalled sequences. Tumor images of E · F (E is the initial extraction fraction of Gd‐DTPA and F is blood perfusion) and λ (the partition coefficient of Gd‐DTPA, which is proportional to extracellular volume fraction) were produced by subjecting DCE‐MRI series to Kety analysis, and these images were compared with histological preparations from the imaged slices.ResultsStrong correlations were found between fraction of necrotic tissue and fraction of voxels with λ > λL for λL values of 0.4 to 0.6. Binary λ images differentiating between λ values > λL and λ values < λL were found to mirror necrotic regions well in tumors with large necroses. However, necrotic foci that were small compared with the voxel size were not detectable.ConclusionClinically relevant images of necrotic tumor regions can be obtained for E‐13 melanomas by subjecting Gd‐DTPA‐based DCE‐MRI series to Kety analysis. J. Magn. Reson. Imaging 2007;26:133–143. © 2007 Wiley‐Liss, Inc.
Solitary fibrous tumor of the pleura: Apparent diffusion coefficient (ADC) value and ADC map to predict malignant transformation
Authors: Inaoka Tsutomu , Takahashi Koji , Miyokawa Naoyuki , Ohsaki Yoshinobu , Aburano Tamio 
Published: July 2007

AbstractSolitary fibrous tumors (SFTs) of the pleura are rare soft‐tissue tumors that are presumed to be of mesenchymal origin. Most SFTs are histologically benign, but up to 20% of SFTs may be malignant. In addition, malignant transformation may occur within histologically benign SFTs, though it is rare. However, it is difficult to diagnose malignant SFTs of the pleura by means of conventional computed tomography and magnetic resonance imaging (MRI). In this article we present the first case of malignant SFT of the pleura in an 81‐year‐old man in which the apparent diffusion coefficient (ADC) value and ADC map based on diffusion‐weighted MRI were very useful for identifying malignant transformation. J. Magn. Reson. Imaging 2007;26:155–158. © 2007 Wiley‐Liss, Inc.
Applications of multislice computed tomography in coronary artery disease
Authors: de Roos Albert , Kroft Lucia J.M. , Bax Jeroen J. , Geleijns Jacob 
Published: July 2007

AbstractMultislice computed tomography (MSCT) provides high accuracy for noninvasive assessment of coronary artery disease (CAD). The introduction of the latest computed tomography (CT) technology allows comprehensive evaluation of various aspects of CAD, including the coronary calcium score, coronary artery stenoses, bypass patency, and myocardial function. Other applications, such as plaque characterization, first‐pass perfusion imaging, and viability imaging using delayed contrast enhancement, are still under development and may demonstrate clinical utility in the future. Further improvements in CT hardware and imaging protocols are expected that may result in improved coronary artery imaging, new applications, and a significant reduction of radiation dose. J. Magn. Reson. Imaging 2007;26:14–22. © 2007 Wiley‐Liss, Inc.
Improved transverse relaxation rate measurement techniques for the assessment of hepatic and myocardial iron content
Authors: Song Ruitian , Cohen Alan R. , Song Hee Kwon 
Published: July 2007

AbstractPurposeTo develop and validate an optimized respiratory‐gated, gradient‐echo sampling of free induction decay and echo (GESFIDE) pulse sequence for the simultaneous measurement of R2, R2*, and R2′ in the liver or heart.Materials and MethodsFifteen subjects (12 thalassemia patients and three normal volunteers) were scanned using an optimized navigator‐gated GESFIDE pulse sequence for the measurement of R2, R2*, and R2′ in the liver and heart. For imaging the myocardium, dark‐blood preparation was used to suppress the blood signal to improve accuracy. The results were compared with those obtained from breath‐held GESFIDE and multi‐gradient‐echo (GRE) scans.ResultsGood agreement between breath‐held and navigator‐gated scans was found for R2, R2*, and R2′ values in the liver (slopes = 0.97–0.99, r = 0.997–0.998, P < 0.0001) and for R2* in the heart (slope = 1.02, r = 0.85, P < 0.0001). Both R2* and R2′ were closely correlated to R2 in the liver, with correlation factors of 0.998 and 0.994, respectively, but weaker correlations were observed in the heart (r = 0.72 for R2* vs. R2 and r = 0.51 for R2′ vs. R2).ConclusionThe improved sequence enables free‐breathing measurements of transverse relaxation rates of the myocardium and liver. The method precludes the need for multiple breath‐held scans and possible misregistration issues, and may prove most beneficial for imaging young children and patients who may have difficulty with prolonged or repeated breath‐holds. J. Magn. Reson. Imaging 2007;26:208–214. © 2007 Wiley‐Liss, Inc.