bluuebunny/crossref_metadata_2025_split huggingface dataset:
Xerostomia: 12‐Month changes in saliva production and its relationship to perception and performance of swallow function, oral intake, and diet after chemoradiation
Authors: Logemann Jeri A. , Pauloski Barbara Roa , Rademaker Alfred W. , Lazarus Cathy L. , Mittal Bharat , Gaziano Joy , Stachowiak Linda , MacCracken Ellen , Newman Lisa A. 
Published: May 2003

AbstractBackground.Previous investigators have found permanent changes in saliva production after chemoradiation but have not examined these in relation to swallowing measures, diet changes, and patient comfort over time.Methods.Thirty patients with advanced stage cancer of the oropharynx treated with chemoradiation were followed with videofluoroscopic swallow studies, a measure of stimulated total saliva production, a questionnaire of their perception of dry mouth, and a questionnaire on the nature of their oral intake at pretreatment until 12 months after treatment.Results.Saliva declined significantly from pretreatment to 12 months. Swallowing‐related complaints increased significantly over the 12 months, especially in patients with lower saliva weights. Diet choices increased over time after treatment, except crunchy foods. Swallow measures did not relate to saliva weight.Conclusions.Reduced saliva weight does not correlate with slowed or inefficient swallow. Instead, reduced saliva weight seems to change patients' perceptions of their swallowing ability and, on that basis, their diet choices. © 2003 Wiley Periodicals, Inc. Head Neck 25: 432–437, 2003
Malignant peripheral primitive neuroectodermal tumor‐peripheral neuroepithelioma of the head and neck: A clinicopathologic study of five cases and review of the literature
Authors: Nikitakis Nikolaos G. , Salama Andrew R. , O'Malley Bert W. , Ord Robert A. , Papadimitriou John C. 
Published: May 2003

AbstractBackground.The term primitive neuroectodermal tumor (PNET) encompasses a number of neoplasms of common neuroectodermal origin, but of variable clinical, histopathologic, ultrastructural, and molecular characteristics. Here, we focus on one particular member of the PNET family, the malignant peripheral PNET (pPNET) or peripheral neuroepithelioma of head and neck.Methods.Five patients diagnosed with malignant pPNET–peripheral neuroepithelioma of head and neck were included in the study. All existing literature was reviewed.Results.The diagnosis of malignant pPNET–peripheral neuroepithelioma of the head and neck was confirmed in all five cases. All patients are alive after treatment with a combination of therapeutic modalities; only one patient had metastatic disease develop. A literature review revealed another 38 reported cases.Conclusions.Malignant pPNET–peripheral neuroepithelioma should be included in the differential diagnosis of small, round, blue cell tumors of head and neck. A combination of multiple diagnostic modalities is essential for correct diagnosis, and multimodality treatment offers the best outcome. © 2003 Wiley Periodicals, Inc. Head Neck 25: 488–498, 2003
Efficacy of radiation therapy in the local control of desmoplastic malignant melanoma
Authors: Vongtama Roy , Safa Afshin , Gallardo David , Calcaterra Thomas , Juillard Guy 
Published: May 2003

AbstractBackground.Desmoplastic malignant melanoma (DMM) is a rare variant of malignant melanoma with high local recurrence rate after surgical excision. We performed a retrospective review to address the role of radiation therapy in local control of this tumor.Methods.Between 1976 and 1997, 44 patients with the pathologic diagnosis of DMM were registered at our tumor registry. Fourteen patients received postoperative RT, and one patient received preoperative RT. Three of the irradiated lesions had gross residual or positive surgical margins. Doses ranged from 44 to 66 Gy.Results.Sixty‐eight percent of DMM lesions occurred in the head and neck region. Forty‐eight percent (21 of 44) of patients experienced a local recurrence after initial excision (mean time to recurrence, 12 months). Local failure in head and neck was 46% (14 of 30). Clark level, primary site, and neurotropism did not predict local recurrence; the Clark level predicted distant metastasis. No viable tumor was found in the surgical specimen of the patient who received preoperative RT. None of 15 patients who received adjuvant irradiation had any additional recurrences (mean follow‐up, 64.7 months). By contrast, four of seven patients with history of recurrence who did not receive RT had local relapse (p = .005). The incidence of distant metastasis did not reach statistical significance between the irradiated and nonirradiated groups.Conclusions.The high rate of local recurrence of DMM after surgical resection is dramatically reduced by adjuvant radiation therapy. We recommend adjuvant postoperative radiation therapy as a part of treatment of DMM. © 2003 Wiley Periodicals, Inc. Head Neck 25: 423–428, 2003
Pentopyranosyl Oligonucleotide Systems. Communication No. 13
Authors: Jungmann Oliver , Beier Markus , Luther Anatol , Huynh Hoan K. , Ebert Marc‐Olivier , Jaun Bernhard , Krishnamurthy Ramanarayanan , Eschenmoser Albert 
Published: June 2003

AbstractAmong the members of a family of diastereoisomeric pentopyranosyl‐(4′→2′)‐oligonucleotide systems derived from D‐ribose, D‐xylose, L‐lyxose, and L‐arabinose, the α‐arabinopyranosyl system shows by far the strongest WatsonCrick base pairing. The system is, in fact, one of the strongest oligonucleotide‐type base‐pairing systems known. It undergoes efficient cross‐pairing with all the other members of the pentopyranosyl family, but not with RNA and DNA. The paper describes the synthesis and pairing of the properties of α‐L‐arabinopyranosyl‐(4′→2′)‐oligonucleotides.
Copper‐Binding Motifs: Structural and Theoretical Aspects
Authors: Kaufman Katz Amy , Shimoni‐Livny Liat , Navon Oshrit , Navon Nadav , Bock Charles W. , Glusker Jenny P. 
Published: June 2003

AbstractIn this paper, we report the results of a study involving the coordination geometries of CuI, CuII, and CuIII crystal structures in the Cambridge Structural Database, and on Cu binding sites in proteins taken from the Protein Data Bank. The motifs used to bind two bridged Cu ions are also described. In addition, we report the results of ab initio molecular‐orbital calculations performed on a variety of model CuI/CuII complexes (CuI/CuII⋅XnYm (X, Y=NH3, SH2); n+m=4; n=0–4) to provide data on the structural and energetic changes that occur in isolated complexes when the oxidation state of the Cu ion is changed from II to I while the coordination number is conserved. The use of such simple ligands in these calculations eliminates constraints on the geometric changes that may be imposed by more‐complicated ligands.
Dilemmas in Crystallization. The ‘Unusual' Behavior of trans‐1,5‐Dichloro‐9,10‐diethynyl‐9,10‐dihydroanthracene‐9,10‐diol and the More ‘Normal' Behavior of Its Pseudopolymorphs with Dipolar Aprotic Solvents
Authors: Banerjee Rahul , Desiraju Gautam R. , Mondal Raju , Batsanov Andrei S. , Broder Charlotte K. , Howard Judith A. K. 
Published: June 2003

AbstractThe compound trans‐1,5‐dichloro‐9,10‐diethynyl‐9,10‐dihydroanthracene‐9,10‐diol (DDDA) has an inversion center as the only molecular symmetry element and yet does not occupy an inversion center in the centrosymmetric space group that it adopts in the crystal structure. The reason for this very unusual occurrence is the crowded environment of the H‐bond donors and acceptors that leads to less than optimal H‐bonding. A centrosymmetric supramolecular synthon constituted with four Cl‐atoms in a planar array occupies an i site in the crystal, and this appears to provide a satisfactory alternative packing. Based on the hypothesis that H‐bonding is less than optimal in the crystal structure of DDDA, pseudopolymorphs were prepared with strongly H‐bond‐accepting solvents. The crystal structures of five of these solvates are described, wherein the DDDA molecule is able to occupy an i site and form strong and linear OH ⋅⋅⋅O H‐bonds with the solvent molecules. Competition experiments show that a smaller solvent molecule with a greater H‐bond‐accepting ability is included more readily and that the H‐bonds formed are correspondingly better.
Crystalline‐State Photoreaction of 1‐Azido‐2‐nitrobenzene – Direct Observation of Heterocycle Formation by X‐Ray Crystallography
Authors: Takayama Terufumi , Kawano Masaki , Uekusa Hidehiro , Ohashi Yuji , Sugawara Tadashi 
Published: June 2003

AbstractThe crystalline‐state photoreaction of 1‐azido‐2‐nitrobenzene (1) was investigated by a combination of X‐ray crystallography, IR spectroscopy, electron‐spin resonance (ESR), and by means of theoretical calculations. Upon low‐temperature (80 K) photolysis of 1, the formation of benzofuroxan (2) was directly observed by X‐ray single‐crystal analysis. ESR Measurements at 5 K suggested the presence of a triplet nitrene as an intermediate in the formation of the heterocycle. Temperature‐dependent IR spectroscopy also revealed that another intermediate, trans,trans‐1,2‐dinitrosobenzene, was produced at temperatures below 80 K.
Chiral Heterospirocyclic 2H‐Azirin‐3‐amines as Synthons for 3‐Amino‐2,3,4,5‐tetrahydrofuran‐3‐carboxylic Acid and Their Use in Peptide Synthesis
Authors: Stamm Simon , Linden Anthony , Heimgartner Heinz 
Published: June 2003

AbstractThe heterospirocyclic N‐methyl‐N‐phenyl‐5‐oxa‐1‐azaspiro[2.4]hept‐1‐e n‐2‐amine (6) and N‐(5‐oxa‐1‐azaspiro[2.4]hept‐1‐en‐2‐yl)‐(S)‐proline methyl ester (7) were synthesized from the corresponding heterocyclic thiocarboxamides 12 and 10, respectively, by consecutive treatment with COCl2, 1,4‐diazabicyclo[2.2.2]octane, and NaN3 (Schemes 1 and 2). The reaction of these 2H‐azirin‐3‐amines with thiobenzoic and benzoic acid gave the racemic benzamides 13 and 14, and the diastereoisomeric mixtures of the N‐benzoyl dipeptides 15 and 16, respectively (Scheme 3). The latter were separated chromatographically. The configurations and solid‐state conformations of all six benzamides were determined by X‐ray crystallography. With the aim of examining the use of the new synthons in peptide synthesis, the reactions of 7 with Z‐Leu‐Aib‐OH to yield a tetrapeptide 17 (Scheme 4), and of 6 with Z‐Ala‐OH to give a dipeptide 18 (Scheme 5) were performed. The resulting diastereoisomers were separated by means of MPLC or HPLC. NMR Studies of the solvent dependence of the chemical shifts of the NH resonances indicate the presence of an intramolecular H‐bond in 17. The dipeptides (S,R)‐18 and (S,S)‐18 were deprotected at the N‐terminus and were converted to the crystalline derivatives (S,R)‐19 and (S,S)‐19, respectively, by reaction with 4‐bromobenzoyl chloride (Scheme 5). Selective hydrolysis of (S,R)‐18 and (S,S)‐18 gave the dipeptide acids (R,S)‐20 and (S,S)‐20, respectively. Coupling of a diastereoisomeric mixture of 20 with H‐Phe‐OtBu led to the tripeptides 21 (Scheme 5). X‐Ray crystal‐structure determinations of (S,R)‐19 and (S,S)‐19 allowed the determination of the absolute configurations of all diastereoisomers isolated in this series.
Enantioselective Synthesis of Key Intermediates in a Novel Approach towards the Iboga‐Alkaloid Family
Authors: Höck Stefan , Borschberg Hans‐Jürg 
Published: June 2003

AbstractSignificant improvements in the realm of a recently disclosed, novel synthetic concept towards the Iboga alkaloid family are presented. The key step for the construction of the bicyclic aliphatic core consists of an intramolecular nitroneolefin 1,3‐dipolar cycloaddition reaction of a 1 : 1 mixture 15/16 yielding the two diastereoisomeric tricyclic isoxazolidine derivatives 17 and 18. The required nitrones were prepared from the readily available (S)‐hydroxylactone 6 in twelve steps with an overall yield of 15% (average: 83.5% per step). The relative configuration of the minor isomer was deduced unambiguously by single‐crystal X‐ray analysis of the derived tricyclic carbamate 21. As four out of five asymmetric centers in the pair 17/18 have opposite configuration, destruction of the one possessing the same absolute configuration transforms the original set of diastereoisomers into a pair of enantiomers. We verified this contention by oxidizing the two alcohols 20 and 22 to yield the two antipodal forms of ketone 23. The absence of significant amounts of by‐product and the high reproducibility of the crucial cycloaddition reaction represent marked improvements over our earlier attempts. In addition, the new route, which starts from L‐glutamate, should provide access to both naturally occurring antipodal series of the targeted alkaloid class.
The Yellow Polymorphs of Mercuric Iodide (HgI2)
Authors: Hostettler Marc , Birkedal Henrik , Schwarzenbach Dieter 
Published: June 2003

AbstractHgI2 crystallizes under ambient conditions from various solvents and by sublimation into three concomitant polymorphs whose colors are red, orange, and yellow. The orange and yellow phases are metastable and transform into the red phase when touched. A phase transition from red to yellow occurs at 400 K. The reverse transition from yellow to red shows a huge hysteresis. We established that the structures of the metastable yellowM phase (determined by single‐crystal X‐ray diffraction) and the high‐temperature yellowHT phase (determined by powder synchrotron X‐ray diffraction and second‐harmonic generation) are different, albeit closely related. Both show analogous packings of IHgI molecules, which are straight in the first and bent with an angle of ca. 160° in the second. The red and orange phases are tetrahedral semiconductor structures that sublime even at room temperature. The growth of the yellowM phase from 2‐chloroethanol and the kinetics of the reconstructive phase transition red to yellowHT and back were studied by optical microscopy, Raman spectroscopy in solution, luminescence, and powder synchrotron X‐ray diffraction as a function of time at various temperatures. Both yellow phases grow by accretion of HgI2 molecules, present in the solution or liberated from the red crystals, on the surface of the crystal. In contrast, the reverse transformation from yellow to red occurs in the bulk of the crystal, presumably by migration of Hg in the packing of I and subsequent rearrangement of I. The displacement parameters of Hg in both structures are considerably larger than those of I and apparently not dominated by disorder effects.
Chiral Amplification of Oligopeptides in the Polymerization of α‐Amino Acid N‐Carboxyanhydrides in Water
Authors: Hitz Thomas , Luisi Pier Luigi 
Published: June 2003

AbstractThis article is concerned with the chiral amplification of oligopeptides formed in the polymerization of chiral, nonracemic mixtures of the N‐carboxyanhydride (NCA) of Leu and Glu in aqueous solution. Labeling (deuteration) of one enantiomer and reversed‐phase and normal‐phase high‐performance liquid chromatography mass spectrometry (RP‐ and NP‐HPLC/MS, respectively) were used to determine the product distribution, both with respect to oligopeptide chain length and stereoisomer distribution. Starting the polymerization with an enantiomeric excess (ee) of 20% of the L‐enantiomer (L‐amino acid/D‐amino acid 6 : 4) leads to an ee of 73% at the level of the homochiral enantiomeric (Leu)5, and of 71% at the level of the homochiral enantiomeric (Glu)7. For the Leu system and in the presence of a solid support (quartz), the ee reached values of up to 100%. We argue that such amplification processes could be relevant for the chemical evolution towards single‐handedness.
From Hit to Lead: De Novo Design Based on Virtual Screening Hits of Inhibitors of tRNA‐Guanine Transglycosylase, a Putative Target of Shigellosis Therapy
Authors: Brenk Ruth , Gerber Hans‐Dieter , Kittendorf Jeffrey D. , Garcia George A. , Reuter Klaus , Klebe Gerhard 
Published: June 2003

AbstractShigellosis, a bacterial disease, causes the death of more than one million people per year. Extensive studies of Shigella flexneri have recognized tRNA‐guanine transglycosylase (TGT, EC 2.4.2.29) as one of the key enzymes involved in the regulation of bacterial virulence. Based on the crystal structure of the Zymomonas mobilis enzyme, we have embarked on the rational design of TGT inhibitors. Herein, we describe the structure‐based optimization of hits previously found by virtual screening (see Tables 1–3). For the pteridines, the most potent compound class discovered in a previous virtual screening run, a versatile synthesis could be established giving access to a broad range of substituted derivatives (see Scheme 5). The best ligand in this series, 14, exhibits a Ki=0.45 μM.
Reduction‐Labile Organo‐cob(III)alamins via Cob(II)alamin: Efficient Synthesis and Solution and Crystal Structures of [(Methoxycarbonyl)methyl]cob(III)alamin
Authors: Puchberger Michael , Konrat Robert , Kräutler Bernhard , Wagner Ulrike , Kratky Christoph 
Published: June 2003

AbstractAn efficient synthesis of Coβ‐[(methoxycarbonyl)methyl]cob(III)alamin (6) is reported as an example of a new method for the preparation of some easily reducible organo‐cob(III)alamins via the alkylation of cob(II)alamin. The procedure represents a considerable improvement compared to earlier methods that were based on an alkylation of cob(I)alamin. Thus, aquacob(III)alamin chloride (5+⋅Cl) was reduced to cob(II)alamin (4), either by controlled potential electrolytic reduction or with an excess of sodium formate as reducing agent. The solution of 4 was then treated with an excess of methyl bromoacetate while being reductively poised potentiostatically or kept reduced by the formate, to give crystalline 6 in a yield of up to 91%. The structure of 6 in aqueous solution was mainly established by the completely assigned 1H‐ and 13CNMR spectra (Table 1). The NOE data (Table 2) were best rationalized by the presence of a single main conformation of the (methoxycarbonyl)methyl ligand. Single crystals of 6 were obtained by crystallization from an aqueous solution, and the crystal structure was determined by X‐ray analysis at cryotemperatures. The NMR and crystallographic data of 6 indicated similar structures in aqueous solution and in the crystal with the (methoxycarbonyl)methyl ligand preferring a ‘southern' orientation in each case.
Structural Aspects of the β‐Polymorph of (E)‐4‐Formylcinnamic Acid: Structure Determination Directly from Powder Diffraction Data and Elucidation of Structural Disorder from Solid‐State NMR
Authors: Meejoo Siwaporn , Kariuki Benson M. , Kitchin Simon J. , Cheung Eugene Y. , Albesa‐Jové David , Harris Kenneth D. M. 
Published: June 2003

AbstractAmong the derivatives of (E)‐cinnamic acid for which the solid‐state photochemical properties have been studied, (E)‐4‐formylcinnamic acid (1) has already received much attention. Given the inability to prepare single crystals of the β‐polymorph of 1 that are of suitable size and quality for structural characterization by single‐crystal X‐ray diffraction, the structure of this material was determined directly from powder X‐ray‐diffraction data by means of the genetic‐algorithm technique for structure solution, followed by Rietveld refinement. High‐resolution solid‐state 13CNMR was also applied to elucidate details of structural disorder concerning the orientation of the formyl group, and provided independent support for the disorder model established form the Rietveld refinement. The reported structure establishes that the β‐phase of 1 is not structurally anomalous among photoreactive (E)‐cinnamic acid crystals, and finally resolves a long‐standing controversy concerning the structural properties of this material.
Structures of Four Crystal Forms of Decaplanin
Authors: Lehmann Christopher , Debreczeni Judit É. , Bunkóczi Gábor , Dauter Miroslawa , Dauter Zbigniew , Vértesy László , Sheldrick George M. 
Published: June 2003

AbstractThe glycopeptide antibiotic decaplanin (1; formerly known as MM 47761 and M86‐1410) crystallizes in two P21 and two P6122 crystal forms, each with four monomers in the asymmetric unit, with solvent contents varying from 48 to 69%. Although with ca. 600 unique atoms, the structures are larger than typical small molecules, one was solved by direct methods. The other three were solved by typical macromolecular methods: single‐wavelength anomalous diffraction (SAD) of the Cl‐atoms present naturally in the structure, multiple‐wavelength anomalous diffraction (MAD) at the Br absorption edge for a crystal soaked in NaBr solution, and molecular replacement. There is evidence of appreciable radiation damage with loss of 20–30% of the covalent and ionic halogens affecting the synchrotron datasets that may even have unintentionally facilitated the MAD structure solution. The structures contain the dimer units typical of antibiotics related to vancomycin, but, in addition, there are a variety of further intermolecular interactions responsible for the polymorphy leading to intertwined 61‐helices in two of the crystal forms. Except for the sugars and some sidechains, the conformations of the 16 independent monomers are very similar.
Glycosylidene Carbenes. Part 31
Authors: Bernet Bruno , Mangholz Sissi E. , Briner Karin , Vasella Andrea 
Published: June 2003

AbstractThe diastereoselectivity of the addition of NH3 and MeNH2 to glyconolactone oxime sulfonates and the structures of the resulting N‐unsubstituted and N‐methylated glycosylidene diaziridines wereThe 15N‐labelled glucono‐ and galactono‐1,5‐lactone oxime mesylates 1* and 9* add NH3 mostly axially (>3 : 1; Scheme 4), while the 15N‐labelled mannono‐1,5‐lactone oxime sulfonate 19* adds NH3 mostly equatorially (9 : 1; Scheme 7). The 15N‐labelled mannono‐1,4‐lactone oxime sulfonate 30* adds NH3 mostly from the exo side (>4 : 1; Scheme 9). The configuration of the N‐methylated pyranosylidene diaziridines 17, 18, 28, and 29 suggests that MeNH2 adds to 1, 9, 19, and 23 mostly to exclusively from the equatorial direction (>7 : 3; Schemes 5 and 8). The mannono‐1,4‐lactone oxime sulfonate 30 adds MeNH2 mostly from the exo side (85 : 15; Scheme 10), while the ribo analogue 37 adds MeNH2 mostly from the endo side (4 : 1; Scheme 10). Analysis of the preferred and of the reactive conformers of the tetrahedral intermediates suggests that the addition of the amine to lactone oxime sulfonates is kinetically controlled. The diastereoselectivity of the diaziridine formation is rationalized as the result of the competing influences of intramolecular H‐bonding during addition of the amines, steric interactions (addition of MeNH2), and the kinetic anomeric effect.The diaziridines obtained from 2,3,5‐tri‐O‐benzyl‐D‐ribono‐ and ‐D‐arabinono‐1,4‐lactone oxime methanesulfonate (42 and 48; Scheme 11) decomposed readily to mixtures of 1,4‐dihydro‐1,2,4,5‐tetrazines, pentono‐1,4‐lactones, and pentonamides.The N‐unsubstituted gluco‐ and galactopyranosylidene diaziridines 2, 4, 6, 8, and 10 are mixtures of two trans‐substituted isomers (S/R ca. 19 : 1, Scheme 2). The main, (S,S)‐configured isomers S are stabilised by a weak intramolecular H‐bond from the pseudoaxial NH to ROC(2). The diaziridines 12, derived from GlcNAc, cannot form such a H‐bond; the (R,R)‐isomer dominates (R/S 85 : 15; Scheme 3). The 2,3‐di‐O‐benzyl‐D‐mannopyranosylidene diaziridines 20 and 22 adopt a 4C1 conformation, which does not allow an intramolecular H‐bond; they are nearly 1 : 1 mixtures of R and S diastereoisomers, whereas the OH5 conformation of the 2,3:5,6‐di‐O‐isopropylidene‐D‐mannopyranosylidene diaziridines 24 is compatible with a weak H‐bond from the equatorial NH to OC(2); the (R,R)‐isomer is favoured (R/S ≥7 : 3; Scheme 6). The mannofuranosylidene diaziridine 31 completely prefers the (R,R)‐configuration (Scheme 9).