bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of an Optically Active Decahydro‐6‐isoquinolone Scaffold with a Quaternary Stereocenter
Authors: Christoffers Jens , Scharl Heiko , Frey Wolfgang , Baro Angelika 
Published: June 2004

AbstractA straightforward synthesis of optically active decahydro‐6‐isoquinolone derivative 3, containing a quaternary stereocenter, is reported. The starting (R)‐configured enantiopure enone 2, which is readily accessible through a copper‐catalyzed, L‐valine amide mediated Michael reaction and a subsequent Robinson annulation, was hydrogenated with Pd/C in iPrOH to give the decahydroisoquinolone 4. Treatment of 4 with ethyleneglycol in the presence of PPTS yielded the dioxolane‐protected derivative 7. A sequence of ester reduction with LiAlH4 and subsequent Ley oxidation of the resulting primary alcohol 10 accomplished the synthesis. Enantiomerically pure aldehyde 3, with three groups for further functionalization, was thus obtained in 63% overall yield. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
4H‐Imidazoles and Imidazoles from Anionic and Dipolar Electrocyclization Reactions of 2,4‐Diazapenta‐1,3‐dienes
Authors: Habersaat Nils , Fröhlich Roland , Würthwein Ernst‐Ulrich 
Published: June 2004

Abstract1‐Amino‐2,4‐diazapenta‐1,3‐dienes 5 are synthesized by the activation of N‐acylamidines 2 with trifluoromethanesulfonic anhydride and subsequent condensation with amino compounds 4. When the amino compounds 4 possess electron‐withdrawing substituents (e.g. alkoxycarbonyl groups, fluorenyl derivatives) this condensation leads instead to 4H‐imidazoles 6 and imidazoles 7. These reactions are considered to be 1,5‐dipolar electrocyclization reactions of 1,5‐dipoles that are tautomers of the 2,4‐diazapenta‐1,3‐dienes 5. Deprotonation of 5b,f by the use of strong organic bases yields the corresponding imidazoles 7b,c after amine elimination during the anionic 1,5‐electrocyclization reaction. Results of quantum chemical model calculations (RHF, MP2, SCS‐MP2, G3, DFT) performed on the parent 2,4‐diazapentadienyl anion 9a, its lithium compound 9a‐Li, the corresponding 1,5‐dipole 12 and their substituted derivatives are in accordance with the suggested reaction mechanism. X‐ray data are given for the 2,4‐diazapenta‐1,3‐dienes 5a·F3CSO3H, 5c, 5d·F3CSO3H, 5e,f and the spirocyclic 4H‐imidazole derivatives 6b−d. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Thienodolin
Authors: Engqvist Robert , Javaid Atif , Bergman Jan 
Published: June 2004

AbstractWe report a total synthesis of the alkaloid thienodolin (1a), as well as its 5‐chloro isomer 1b and its unsubstituted analogue 1c, in three steps from the corresponding oxindoles 8a−c. The preparation was achieved through an initial Vilsmeier−Haack−Arnold reaction (chloro‐formylation) followed by protection at the indole nitrogen, creation of the fused thiophene ring by nucleophilic substitution at the 2‐position and an intramolecular cyclization using mercaptoacetamide. This gave 1a, 1b and 1c in total yields of 42%, 35% and 37%, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Interchangeable PEG‐Supported Synthesis of Peptide‐Oligonucleotide Chimeras
Authors: Adamo Ilaria , Ballico Maurizio , Campaner Pietro , Drioli Sara , Bonora Gian Maria 
Published: June 2004

AbstractA procedure has been developed for the preparation of peptide‐PEG‐oligonucleotide conjugates: the two sequences were synthesized at the extremities of the same commercial high‐molecular‐weight polyethylene glycol (PEG) starting both from the peptide as well as from the oligonucleotide component. The commercial PEG was modified at its terminal hydroxyl functions with two orthogonal protecting groups (DMT and Fmoc). The selective removal of those groups allowed the synthesis of the chimeras following two different, interchangeable strategies. Comparison of the final conjugates suggested that their production was equally effective. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Facile Cleavage of Si−C Bonds during the Sol‐Gel Hydrolysis of Aminomethyltrialkoxysilanes − A New Method for the Methylation of Primary Amines
Authors: Adima Augustin , Bied Catherine , Moreau Joël J. E , Wong Chi Man Michel 
Published: June 2004

AbstractThe reaction of chloromethyltriethoxysilane with (1R,2R)‐bis(methylamino)cyclohexane (1) afforded the corresponding bis‐silylated compound 2. The sol‐gel hydrolysis of 2 did not give the expected bridged silsesquioxane owing to quantitative Si−C‐bond cleavage. Instead, silica and (1R,2R)‐bis(dimethylamino)cyclohexane (3) were obtained. This reaction was exploited to propose a new route for the methylation of amines. Such methylation reaction of amines could be extended to other amines and provides a new method for the selective monomethylation of primary amines. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Metabolites of the Ah Receptor Ligand 6‐Formylindolo[3,2‐b]carbazole
Authors: Wahlström Niklas , Romero Ivan , Bergman Jan 
Published: June 2004

AbstractSynthesis of the five mono‐ and di‐hydroxylated metabolites of the aryl hydrocarbon receptor high affinity ligand 6‐formylindolo[3,2‐b]carbazole is described. The structures of the metabolites were unequivocally established as 2‐hydroxy‐, 8‐hydroxy‐, 2,10‐dihydroxy‐, 4,8‐dihydroxy‐ and 2,8‐dihydroxyindolo[3,2‐b]carbazole‐6‐carboxaldehyde. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
A Mechanistic Rationale for the Mode Selectivity in the Intramolecular Cyclization of Ethylene‐Tethered Iminoketenimines: [2+2] versus [4+2] Stepwise Cycloadditions
Authors: Alajarín Mateo , Sánchez‐Andrada Pilar , Vidal Angel , Tovar Fulgencio 
Published: June 2004

AbstractA stepwise mechanism, via a zwitterionic intermediate, has been established by ab initio and DFT calculations for the intramolecular cyclization of N‐(3‐azabut‐3‐enyl)ketenimine into its corresponding [2+2] cycloadduct. The control of the mode selectivity ([2+2] versus [4+2] cycloaddition) in the intramolecular cyclization of C‐vinyl‐N‐(iminoethylene)ketenimines, which favors the [4+2] cycloadducts, also has been rationalized by comparing the energies calculated for both reaction pathways; the results have been confirmed by a quantitative kinetic analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Incorporation of Diarylbutylamine Pharmacophore into Indeno‐ or Naphtho[1,2‐b]pyran Ring Systems
Authors: Maertens Faye , Toppet Suzanne , Compernolle Frans , Hoornaert Georges J. 
Published: June 2004

AbstractVarious conformationally constrained forms of the diarylbutylamine pharmacophore were accessed by incorporating it into heterocyclic ring systems, i.e., indeno[1,2‐b]furan, indeno[1,2‐b]pyran, naphtho[1,2‐b]furan, and benzo[h]chromene. These compounds were formed by epoxidation of 2‐alkenyl‐substituted 1‐indanols or 1‐naphthalenols. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
First Total Synthesis of Naturally Occurring (−)‐Nitidon and Its Enantiomer
Authors: Bellina Fabio , Carpita Adriano , Mannocci Luca , Rossi Renzo 
Published: June 2004

AbstractThe first total synthesis of naturally occurring (−)‐nitidon and its enantiomer is reported. The best of the routes investigated for preparation of these enantiomerically pure compounds involves a modification of the Cadiot−Chodkiewicz reaction and the Sharpless asymmetric epoxidation of an (E)‐2‐ene‐4,6‐diyn‐1‐ol as key steps and proceeds in five steps and 18% overall yield. Both enantiomers of nitidon and some related 6‐(1,3‐diyn‐1‐yl)‐2H‐pyran‐2‐ones have been found to exhibit significant cytotoxic activity against human cancer cell lines in vitro. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Phenylacetylene Dendrimers Having Sterically Congested Diazo Units and Characterization of Their Photoproducts
Authors: Itoh Tetsuji , Maemura Toshiyuki , Ohtsuka Yusuke , Ikari Yoshiyuki , Wildt Holger , Hirai Katsuyuki , Tomioka Hideo 
Published: June 2004

AbstractThe compound (4‐tert‐butyl‐2,6‐dimethylphenyl)(2,4,6‐tribromophenyl)diazomethane (1a), a precursor for persistent triplet carbene, was found to be stable enough to survive Sonogashira coupling reaction conditions to give (4‐tert‐butyl‐2,6‐dimethylphenyl)(2,6‐dibromo‐4‐ethynylphenyl)diazomethane (2a). The diazomethane 2a was used as a starting compound for synthesis of phenylacetylene dendritic molecules having peripheral diazo groups by the convergent method. Thus, tridendrons with peripheral groups bearing 3 (3a), 6 (6a), and 12 (8a) diazo units were prepared, in which diazo groups were introduced so as to generate polycarbenes in a ferromagnetic fashion. In order to characterize the spin states of carbenes generated by the photolysis of these dendrimers, the magnetic susceptibility of the photoproducts was measured. Although the data for the photoproduct of the tris(diazo) compound were fitted with S = 2.5, those for the photoproducts of hexakis and dodecakis(diazo) compounds were fitted with S = 1.62, a value that is much smaller than the theoretically predicted value and even smaller than that of triscarbene. The results are interpreted in terms of the disjoint‐nondisjoint concept. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004
X‐ray Crystal Structure Study of Sterically Congested Diphenyldiazomethanes
Authors: Iikubo Takashi , Itoh Tetsuji , Hirai Katsuyuki , Takahashi Yasutake , Kawano Masaki , Ohashi Yuji , Tomioka Hideo 
Published: June 2004

AbstractX‐ray crystallographic structures were determined for five diphenyldiazomethanes (DDMs) with various ortho substituents, namely, bis(2,4,6‐trichlorophenyl)diazomethane, bis(2,4,6‐tribromophenyl)diazomethane, bis(4‐tert‐butyl‐2,6‐dibromophenyl)diazomethane, (4‐tert‐butyl‐2,6‐dimethylphenyl)(2,4,6‐tribromophenyl)diazomethane, and [4‐tert‐butyl‐2,6‐bis(trifluoromethyl)phenyl](4‐tert‐butyl‐2,6‐dibromophenyl)diazomethane, and for bis(4‐bromophenyl)diazomethane, a DDM with no ortho substituents. The correlation between the structural parameters, the ESR zero‐field splitting (ZFS) parameters and the lifetimes of the triplet diphenylcarbenes (DPCs) generated from these diazo compounds was examined. It is noted that as ortho substituents are introduced onto the phenyl rings of the DDMs, the interplanar angle between the two phenyl rings increases, while the angle of the diazo carbon changes very little. DDM 6‐N2, from which the longest‐lived triplet carbene is generated, is shown to have the largest interplanar angle of the DDMs examined. The bond distances between the aromatic carbons and the ortho substituents as well as the van der Waals radii of the substituents were also examined. These studies do not provide a quantitative correlation between the structural parameters of the precursor DDMs and the ZFS parameters and lifetimes of their photoproducts, triplet DPCs, but show how steric shielding of the ortho substituents affects the structures and stabilities of triplet DPCs. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Cover Picture: Fluorescence Assay and Screening of Epoxide Opening by Nucleophiles (Eur. J. Org. Chem. 12/2004)
Authors: Badalassi Fabrizio , Klein Gérard , Crotti Paolo , Reymond Jean‐Louis 
Published: June 2004

AbstractThe cover picture shows blue‐fluorescent enzyme assays. The intense blue fluorescence of umbelliferone is readily detected under UV illumination (356 nm) when this fluorescent product is released from non‐fluorescent ether precursors. This fluorescent signal is the key to a number of high‐throughput enzyme assays, usually in a 96‐well microtiter‐plate format as shown. Fluorescence enzyme assays involving epoxide opening reactions with nucleophiles are discussed in the article by J.‐L. Reymond et al. on page 2557 ff.
A staggered conservative scheme for every Froude number in rapidly varied shallow water flows
Authors: Stelling G. S. , Duinmeijer S. P. A. 
Published: June 2004

AbstractThis paper proposes a numerical technique that in essence is based upon the classical staggered grids and implicit numerical integration schemes, but that can be applied to problems that include rapidly varied flows as well. Rapidly varied flows occur, for instance, in hydraulic jumps and bores. Inundation of dry land implies sudden flow transitions due to obstacles such as road banks. Near such transitions the grid resolution is often low compared to the gradients of the bathymetry. In combination with the local invalidity of the hydrostatic pressure assumption, conservation properties become crucial. The scheme described here, combines the efficiency of staggered grids with conservation properties so as to ensure accurate results for rapidly varied flows, as well as in expansions as in contractions. In flow expansions, a numerical approximation is applied that is consistent with the momentum principle. In flow contractions, a numerical approximation is applied that is consistent with the Bernoulli equation. Both approximations are consistent with the shallow water equations, so under sufficiently smooth conditions they converge to the same solution. The resulting method is very efficient for the simulation of large‐scale inundations. Copyright © 2003 John Wiley & Sons, Ltd.
Computation of strongly swirling confined flows with cubic eddy‐viscosity turbulence models
Authors: Yang Xiaodong , Ma Huiyang 
Published: June 2004

AbstractAn investigation on the predictive performance of four cubic eddy‐viscosity turbulence models for two strongly swirling confined flows is presented. Comparisons of the prediction with the experiments show clearly the superiority of cubic models over the linear k–εmodel. The linear k–εmodel does not contain any mechanism to describe the stabilizing effects of swirling motion and as a consequence it performs poorly. Cubic models return a lower level of Reynolds stresses and the combined forced‐free vortex profiles of tangential velocity close to the measurements in response to the interaction between swirl‐induced curvature and stresses. However, a fully developed rotating pipe flow is too simple to contain enough flow physics, so the calibration of cubic terms is still a topic of investigation. It is shown that explicit algebraic stress models require fewer calibrations and contain more flow physics. Copyright © 2003 John Wiley & Sons, Ltd.
Verification testing in computational fluid dynamics: an example using Reynolds‐averaged Navier–Stokes methods for two‐dimensional flow in the near wake of a circular cylinder
Authors: Richmond‐Bryant Jennifer 
Published: June 2004

AbstractVerification testing was performed for various Reynolds‐averaged Navier–Stokes methods for uniform flow past a circular cylinder at Re= 5232. The standard and renormalized group (RNG) versions of the k–ε method were examined, along with the Boussinesq, Speziale and Launder constitutive relationships. Wind tunnel experiments for flow past a circular cylinder were also performed to obtain a comparative data set. Preliminary studies demonstrate poor convergence for the Speziale relationship.Verification testing with the standard and RNG k–ε models suggests that the simulations exhibit global monotonic convergence for the Boussinesq models. However, the global order of accuracy of the methods was much lower than the expected order of accuracy of 2. For this reason, pointwise convergence ratios and orders of accuracy were computed to show that not all sampling locations had converged (standard k–ε model: 19% failed to converge; RNG k–ε model: 14% failed to converge). When the non‐convergent points were removed from consideration, the average orders of accuracy are closer to the expected value (standard k–ε model: 1.41; RNG k–ε model: 1.27). Poor iterative and global grid convergence was found for the RNG k–ε/Launder model. The standard and RNG k–ε models with the Boussinesq relationship were compared with experimental data and yielded results significantly different from the experiments. Copyright © 2003 John Wiley & Sons, Ltd.
A discontinuous Galerkin method/HLLC solver for the Euler equations
Authors: Remaki Malika , Habashi Wagdi G. 
Published: June 2004

AbstractThis paper proposes a fully three‐dimensional non‐linear Euler methodology for solving aerodynamic and acoustic problems in the presence of strong shocks and rarefactions. It uses a discontinuous Galerkin method (DGM) within the element, and a Riemann solver (HLLC) at the boundaries to propagate rarefactions while preserving the entropy condition and capturing shocks with no spurious oscillations. This approach is thought to marry the best aspects of finite element and finite volume methods, achieving conservation while not requiring the solution of a large matrix. Examples in which shock and rarefaction waves are well captured are presented and the propagation of acoustic pulses is well demonstrated. Copyright © 2003 John Wiley & Sons, Ltd.
Efficient solution of the steady‐state Navier–Stokes equations using a multigrid preconditioned Newton–Krylov method
Authors: Syamsudhuha  , Silvester David J. 
Published: June 2004

AbstractAn inexact Newton's method is used to solve the steady‐state incompressible Navier–Stokes equations. The equations are discretized using a mixed finite element approximation. A new efficient preconditioning methodology introduced by Kay et al. (SIAM J. Sci. Comput., 2002; 24: 237–256) is applied and its effectiveness in the context of a Newton linearization is investigated. The original strategy was introduced as a preconditioning methodology for discrete Oseen equations that arise from Picard linearization. Our new variant of the preconditioning strategy is constructed from building blocks consisting of two component multigrid cycles; a multigrid V‐cycle for a scalar convection–diffusion operator; and a multigrid V‐cycle for a pressure Poisson operator. We present numerical experiments showing that the convergence rate of the preconditioned GMRES is independent of the grid size and relatively insensitive to the Reynolds number. Copyright © 2003 John Wiley & Sons, Ltd.
Postradiotherapy surveillance practice for head and neck squamous cell carcinoma—too much for too little?
Authors: Schwartz David L. , Barker Jerry , Chansky Kari , Yueh Bevan , Raminfar Leila , Drago Pamela , Cha Christine , Austin‐Seymour Mary , Laramore George E. , Hillel Allen D. , Weymuller Ernest A. , Wallner Kent E. 
Published: June 2004

AbstractIntroduction.Limited information is available regarding surveillance patterns after head and neck cancer radiotherapy. We cataloged follow‐up for a specified patient cohort treated at three neighboring university, community, and Veterans Administration institutions.Methods.One hundred fifteen patients were treated with curative intent between 1994–1998 with definitive or postoperative radiotherapy for newly diagnosed squamous cell carcinoma of the oral cavity, oropharynx, larynx, or hypopharynx. One hundred patients had continuous follow‐up at their treating institution and were included for analysis. Median follow‐up until disease recurrence or censorship was 28.5 months.Results.Median follow‐up frequency was 5.7 visits/year and was highly variable. Although visit frequency correlated with disease stage and the presence of high‐risk disease features, this association was lost when patients with early recurrences were removed from analysis. Procedure and test utilization closely mirrored visit frequency, resulting in a wide range of estimated yearly charges ($0–15,668/year; median, $1,772/year). Actuarial 3‐year overall survival for the study group was 71%. Eighty‐six percent (19 of 22) of potentially salvageable locoregional failures were discovered secondary to symptomatic complaint rather than by test results. Disease failure, whether detected by symptom or testing, predicted for poor survival (22% at 24 months after recurrence).Conclusions.Postradiotherapy surveillance for head and neck cancer is inconsistently pursued. A proven correlation between intensive follow‐up and improved patient survival is lacking. Surveillance directed by patient symptoms should be investigated as an alternative approach. © 2003 Wiley Periodicals, Inc. Head Neck 25: 000–000, 2003
Rim versus sagittal mandibulectomy for the treatment of squamous cell carcinoma: Two types of mandibular preservation
Authors: Guerra Mario Fernando Muñoz , Campo Francisco J. Rodríguez , Gías Luis Naval , Pérez Jesús Sastre 
Published: June 2004

AbstractBackground.The role of conservative mandibulectomy for patients with bone invasion from squamous cell carcinoma remains poorly defined. However, marginal mandibular resection is biomechanically secure in its design while maintaining the mandibular continuity. This procedure has proven to be a successful method of treating squamous cell carcinoma with limited mandibular involvement.Purpose.The purpose of this study was to analyze our results after the use of a marginal technique for the treatment of oral and oropharyngeal cancer and to compare two types of mandibular conservative procedures: rim resection versus sagittal inner mandibulectomy.Methods.A retrospective review of a cohort of 50 patients (global group) who underwent mandibular conservative resection for previously untreated squamous cell carcinoma was performed. Two subgroups were considered: rim group (n= 37) and sagittal group (n= 13). Clinical evaluation and preoperative radiologic studies were the means used to evaluate bony invasion and to decide on the extent of mandibulectomy. The treatment outcome after these two types of mandibular resection was calculated and compared using analysis by the Pearson χ2test, logistic regression model for multivariate analysis, and the Kaplan‐Meier method to determine survival.Results.In the sagittal group, specimens from 2 patients (11.7%) demonstrated tumor invasion on decalcified histologic examination, whereas the rim group showed 11 cases (29.7%) with bone invasion. Local recurrence was observed in the follow‐up of 10 patients. No statistical relationship was found between the presence of histologic bone invasion and the risk of local recurrence. The size of bone resection >4 cm (p= .002) and tumor invasion of surgical margins (p= .039) were found to be associated with increased local recurrence rates. In multivariate analysis, lymph node affectation significantly correlated with histologic mandibular involvement (p= .02). In the global group, the 5‐year observed survival rate was 56.97%. Overall survival and rate of recurrence were comparable in both groups. In the global group, tumor infiltration beyond the surgical margin was statistically related with poor survival (p= .01).Conclusions.Analysis of this series disclosed that marginal mandibulectomy is effective in the control of squamous cell carcinomas that are close to or involving the mandible. In carefully selected patients, sagittal bone resection seems to be as appropriate as rim resection in the local control of these tumors. © 2003 Wiley Periodicals, Inc. Head and Neck 25: 000–000, 2003