bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pheromonsynthesen ‐ Modellreaktionen zur Synthese von Polyether‐Antibiotika
Authors: Ireland Robert E. , Häbich Dieter 
Published: September 2007

AbstractEin allgemeines, konvergentes Schema zur Synthese von Spiroketalen wird vorgestellt. Die Hetero‐Diels‐Alder‐Reaktion zwischen einem exocyclischen Enolether 5 und einer α,β‐ungesättigten Carbonylverbindung führt zu Spiroalkenen 6. Diese lassen sich durch oxidative Ringkontraktion oder Reduktion zu 7 oder 8, den gemeinsamen Strukturelementen verschiedener Polyether‐Antibiotika und Insekteninhaltsstoffe, umsetzen. Modellreaktionen zu dieser Sequenz, ausgehend von 2‐Methylentetrahydropyran (14) und ‐furan (22), sowie die Synthesen der racem. Pheromone 2, 4 und 27 werden beschrieben.
Sterisch gehinderte Pyridiniumsalze, II1) Darstellung und Eigenschaften von 2,6‐Di‐tert‐butyl‐1‐methyl‐pyridiniumsalzen
Authors: Weber Horst , Pant Jahannes , Liedigk Mechthild , Wunderlich Hartmut 
Published: September 2007

AbstractDie Pyridiniumsalze 2a–c wurden erstmals durch Alkylierung der entsprechenden Pyridine 1 mit Fluorsulfonsäure‐methylester bei Atmosphärendruck dargestellt. Im Gegensatz zur seitherigen Auffassung besitzen sie keine außergewöhnlichen Eigenschaften; sie sind nicht unzersetzt sublimierbar. Die spektroskopischen Befunde werden eingehend diskutiert. Die Kristallstrukturen des Iodids und Perchlorats von 2a wurden mit Röntgenmethoden bestimmt. Die Kationen stimmen im Rahmen der Standardabweichungen überein und zeigen nur eine geringfügige Deformation des Pyridiniumrings.
Cycloadditions of Allyl Cations, 261) Norbornene Derivatives from Cyclopentadiene and 2,4‐Dimethyl‐3‐penten‐2‐ol in an Acidic Two Phase System. A Stepwise Diels‐Alder‐like Cyclization
Authors: Vathke‐Ernst Heidrun , Hoffmann H. M. R. 
Published: September 2007

Abstract2,4‐Dimethyl‐3‐penten‐2‐ol (1) and cyclopentadiene react in an acidic two phase system at 0‐25°C in several steps yielding epimeric norbornenylcarbinols (endo‐4 and exo‐4) and at least three isomeric allylcyclopentenols (2a, b, c), whereas allylcyclopentadienes (3a, b) and norbornene‐type olefins (endo‐5, exo‐5, and 6) are formed in traces under these conditions. All bicyclic products of this reaction were synthesized independently. On subjecting the pure product norbornenylcarbinols )endo‐4 and exo‐4) to the acidic, two phase reaction conditions at slightly elevated temperature, i. e. 50°C, some epimerization occurs and the norbornene‐type olefins (exo‐5, endo‐5, and 6) are mainly formed in addtion to allylcyclopentadienes (3a,b) allylcyclopentenols (2a, b, c), nortricyclic alcohol 7, and tricyclic ether 8. Independently, the forward reaction was traced by subjecting the isomeric allylcyclopentenols 2b, c to the acidic, two phase reaction conditions at 50°C: once again, endo/exo bicyclization gave the olefins 5 and 6 as well as alcohols 4 and 7 Hence, a stepwise Diels‐Alder‐like cyclization is proposed to account for the norbornenetype alcohols and bicyclic olefins, which are formed from the acid promoted reaction of cyclopentadiene and 1.
Synthesen biologisch wichtiger Kohlenhydrate, 241) Derivate des Sibirosamins (4,6‐Didesoxy‐3‐C‐methyl‐4‐methylamino‐D‐altropyranose) durch 4 → 2‐Chiralitätstransfer und vic. cis‐Oxyaminierung eines 3‐C‐Methyl‐hex‐3‐enopyranosids
Authors: Dyong Ingolf , Schulte Gerhard 
Published: September 2007

AbstractMethyl‐4‐O‐benzoyl‐2,6‐didesoxy‐3‐C‐methyl‐α‐D‐ribo‐hexopyranosid (14) liefert durch Eliminierung mit Thionylchlorid hoch selektiv das 3‐C‐verzweigte Hex‐2‐enopyranosid 15 bzw. 16 mit D‐erythro‐Konfiguration. 16 wird unter vollständiger Inversion an C‐4 zum D‐threo‐Phenylthioether 18 umgesetzt. Dessen Phenylsulfinyl‐Derivat 19 dient zum Aufbau des Chiralitätszentrums ans C‐2. [2,3]Sigmatrope Allylsulfoxid → Allylsulfenat‐Umlagerung führt unter 4 → 2‐Chiralitätstransfer (“selbst‐immolative” asymmetrische Synthese) zum Methyl‐2‐O‐acetyl‐3.4.6 tridesoxy‐3‐C‐methyl‐σ‐threo‐hex‐3‐enopyranosid (22). Sterische Kontrolle erlaubt die regio‐ und stereospezifische vic. cis‐Oxyaminierung zum Methyl‐2‐O‐acetyl‐4,6‐didesoxy‐3‐C‐methyl‐4‐(p‐tolylsulfonylamino)‐α‐pyranosid 23 mit D‐altro‐Konfiguration. Aus 23 wird das Methyl‐N‐acetyl‐α‐glycosid 28 der Titelverbindung, des Glycons des cytostatisch wirksamen Antibotikums Sibiromycin erhalten.
[Chlortris(dimethylamino)phosphonium]‐chlorosulfit, ein schonendes Kondensationsmittel bei Peptidsynthesen
Authors: Appel Rolf , Gläsel Ursula , Gläsel Volker Ingo 
Published: September 2007

[Chlorotris(dimethylamino)phosphonium] Chlorosulfite, a Versatile and Mild Condensation Reagent for the Synthesis of PeptidesThe title compound 5, which can be easily obtained from hexamethylphosphoric triamide (1) and thionyl chloride by catalysis of dimethylformamide, is succesfully applied as a mild condensation reagent for the synthesis of peptides.
Cycloadditions of Allyl Cations, 271) Dehydrative Cyclodimerization of 4‐Methyl‐3‐penten‐2‐ol‐in Two Phases. One‐Pot Preparation of Dimethylated Limonenes and α‐Terpineol
Authors: Vathke‐Ernst Heidrun , Hoffmann H. M. R. 
Published: September 2007

Cycloadditionen von Allyl‐Kationen, 271) Dehydrative Cyclodimerisierung von 4‐Methyl‐3‐penten‐2‐ol in zwei PhasenDehydrative Eintopfcyclodimerisierung von 4‐Methyl‐3‐penten‐2‐ol (1) in einem Gemisch aus wäβriger Toluosulfonsäure/Kohlenwasserstoff gibt dimethylierte Limonene 2a und c sowie dimethyliertes α‐Terpineol 3.
Synthese und Struktur von pentakoordinierten spirocyclischen Derivaten des Phosphors und Arsens
Authors: Roesky Herbert W. , Djarrah Habib , Amirzadeh‐Asl Djammschid , Sheldrick William S. 
Published: September 2007

Synthesis and Structure of Pentacoordinated Spirocyclic Derivatives of Phosphorus and ArsenicPhosphorus (2a,b) and arsenic 4 containing spirocyclic compounds have been synthesised from substituted ureas and halides of phosphorus and arsenic. On the basis of an X‐ray analysis of 2b it is demonstrated that λ5‐P compounds and not phosphonium salts were obtained.
Zur Umsetzung des Tricarbonyl(η4‐6,6‐diphenylpentafulven)eisens mit Nucleophilen
Authors: Eilbracht Peter , Henkes Erhard 
Published: September 2007

Conversion of Tricarbonyl(η4‐6,6‐diphenylpentafulvene)iron with NucleophilesTricarbonyl(η4‐6,6‐diphenylpentafulvene)iron (2a), reacts with methanol/methoxide to form the “metalloester” 7a via nucleophilic attack of the carbon monoxide ligand. This is contrary to an earlier report in which a bridged cyclopentadiene system 6 has been proposed as reaction product.
Polare und sterische Effekte bei Oxidationsreaktionen mit aliphatischen Persäuren
Authors: Schneider Hans‐Jörg , Becker Norman , Philippi Klaus 
Published: September 2007

Polar and Steric Effects in Oxidation Reactions with Aliphatic PeracidsEpoxidation rates of substituted peracids yield Taft reaction constants of p* = +2.0 and δ ≅ 0; the reaction order is secured and it is shown for in situ epoxidations that formation of the peracid is the slow step. α‐Halopercarboxylic acids are eletrophilic enough to oxidize paraffines selectively. Attempts to use hydrophobic interactions between (E)‐2‐octene and steroid carboxylic acids during in situ oxidations in protic solvents for asymmetric induction did not yield optical active compounds.
Verknüpfung von elektronenreichen Alkenen mit elektronenarmen Alkenen in Eintopfsynthesen
Authors: Giese Bernd , Heuck Klaus 
Published: September 2007

Coupling between Electron Rich Alkenes and Electron Deficient Alkenes in One‐Flask SynthesesElectron rich alkenes 4 with nucleophilic neighbouring groups X are coupled with acrylic ester to give the products 5 in one‐flask syntheses at room temperature.
Radikalionen, 451) Notiz zu Radikalanionen (H3C)2P‐substituierter Benzole
Authors: Kaim Wolfgang , Bock Hans 
Published: September 2007

Radical Ions, 451) Comment on Radical Anions of (H3C)2P‐substituted BenzenesAn ESR spectroscopic reinvestigation of the reduction of (H3C)2P‐substituted benzenes 1, 3, 5, 7 demonstrates that the corresponding phosphane oxide derivatives 2, 4, 6, 8 are more easily reduced, and that P‐aryl cleavage can occur under measurement conditions.
Distance Determination in Heterogeneous DNA Model Systems by Pulsed EPR
Authors: Ward Richard , Keeble David J. , El‐Mkami Hassane , Norman David G. 
Published: September 2007

AbstractMany biological systems, especially those based on nucleic acids, are structurally heterogeneous in solution. We demonstrate here the ability to measure multiple distances, of between 2 and 7 nm, from a heterogeneous mixture of double‐spin‐labeled DNA duplexes. We have constructed a DNA distance ruler based on the attachment of nitroxide spin labels to 2′‐amino‐modified nucleosides. The distribution of distances between the spin labels was obtained by Tikhonov regularization analysis of the dipolar coupling evolution data measured by using the electron paramagnetic resonance method, pulsed‐electron double resonance (PELDOR). Optimization of the conditions and techniques used in the preparation of the samples has allowed us to increase the sensitivity and reduce aggregation artifacts. As a result, we have been able to demonstrate deconvolution of distances from structurally heterogeneous samples and show the limits of the technique by examining data derived from up to five DNA duplexes, in a single mixture, in which the concentration of each species was as low as 5 μM.
LOX‐Induced Lipid Peroxidation Mechanism Responsible for the Detrimental Effect of Marine Diatoms on Zooplankton Grazers
Authors: Fontana Angelo , d'Ippolito Giuliana , Cutignano Adele , Romano Giovanna , Lamari Nadia , Massa Gallucci Alexia , Cimino Guido , Miralto Antonio , Ianora Adrianna 
Published: September 2007

AbstractSome marine diatoms negatively affect the reproduction of dominant zooplankton grazers such as copepods, thus compromising the transfer of energy through the marine food chains. In this paper, the metabolic mechanism that leads to diatom‐induced toxicity is investigated in three bloom‐forming microalgae. We show that copepod dysfunctions can be induced by highly reactive oxygen species (hROS) and a blended mixture of diatom products, including fatty acid hydroperoxides (FAHs); these compounds display teratogenic and proapoptotic properties. The process is triggered by the early onset of lipoxygenase activities that elicit the synthesis of species‐specific products, the basic structures of which were established (1–20); these compounds boost oxidative stress by massive lipid peroxidation. Our study might explain past laboratory and field results showing how diatoms damage zooplankton grazers even in the absence of polyunsaturated aldehydes, a class of molecules that has been formerly implicated in mediating the toxic activity of diatoms on copepods.
Interception of the Enzymatic Conversion of Farnesyl Diphosphate to 5‐Epi‐Aristolochene by Using a Fluoro Substrate Analogue: 1‐Fluorogermacrene A from (2E,6Z)‐6‐Fluorofarnesyl Diphosphate
Authors: Faraldos Juan A. , Zhao Yuxin , O'Maille Paul E. , Noel Joseph P. , Coates Robert M. 
Published: September 2007

AbstractTobacco 5‐epi‐aristolochene synthase (TEAS) catalyzes the MgII‐dependent cyclizations and rearrangements of (E,E)‐farnesyl diphosphate (PP) to the bicyclic sesquiterpene hydrocarbon via a tightly bound (+)‐germacrene A as a deprotonated intermediate. With the native enzyme, only a few percent of the putative germacrene A intermediate is released from the active site during the catalytic cycle. 6‐Fluorofarnesyl PP was designed and synthesized with the aim of arresting the cyclization–rearrangement mechanism en route to 5‐epi‐aristolochene. Indeed, incubation of (2E,6Z)‐6‐fluorofarnesyl PP with recombinant TEAS afforded (−)‐1‐fluororogermacrene A as the sole product in 58 % yield. Steady‐state kinetic experiments with farnesyl PP and the 6‐fluoro analogue showed that the overall catalytic efficiencies (kcat/Km) are essentially the same for both substrates. 1‐Fluorogermacrene A was characterized by chromatographic properties (TLC, GC), MS, optical rotation, UV, IR and 1H NMR data, and by heat‐induced Cope rearrangement to (+)‐1‐fluoro‐β‐elemene. 1H NMR spectra at room temperature revealed that this (E,E)‐configured fluorocyclodecadiene exists in solution as a 7:3 mixture of UU and UD conformers. 1‐Fluorogermacrene A underwent trifluoroacetic acid‐catalyzed cyclization to give three 1α‐fluoroselinene isomers at a rate estimated to be about 1000 times slower than that of the similar cyclization of (+)‐germacrene A to the parent selinenes.
Photooxidation of Guanine by a Ruthenium Dipyridophenazine Complex Intercalated in a Double‐Stranded Polynucleotide Monitored Directly by Picosecond Visible and Infrared Transient Absorption Spectroscopy
Authors: Elias Benjamin , Creely Caitriona , Doorley Gerard W. , Feeney Martin M. , Moucheron Cécile , Kirsch‐DeMesmaeker Andrée , Dyer Joanne , Grills David C. , George Michael W. , Matousek Pavel , Parker Anthony W. , Towrie Michael , Kelly John M. 
Published: September 2007

AbstractTransient species formed by photoexcitation (400 nm) of [Ru(dppz)(tap)2]2+ (1) (dppz=dipyrido[3,2‐a:2′,3′‐c]phenazine; tap=1,4,5,8‐tetraazaphenanthrene) in aqueous solution and when intercalated into a double‐stranded synthetic polynucleotide, [poly(dG‐dC)]2, have been observed on a picosecond timescale by both visible transient absorption (allowing monitoring of the metal complex intermediates) and transient infrared (IR) absorption spectroscopy (allowing direct study of the DNA nucleobases). By contrast with its behavior when free in aqueous solution, excitation of 1 when bound to [poly(dG‐dC)]2 causes a strong increase in absorbance at 515 nm due to formation of the reduced complex [Ru(dppz)(tap)2]+ (rate constant=(2.0±0.2)×109 s−1). The subsequent reformation of 1 proceeds with a rate constant of (1.1±0.2)×108 s−1. When the process is carried out in D2O, the rates of formation and removal of [Ru(dppz)(tap)2]+ are reduced (rate constants (1.5±0.3)×109 and (0.7±0.2)×108 s−1 respectively) consistent with proton‐coupled electron transfer processes. Picosecond transient IR measurements in the 1540–1720 cm−1 region in D2O solution confirm that the reduction of 1 intercalated into [poly(dG‐dC)]2 is accompanied by bleaching of IR ground‐state bands of guanine (1690 cm−1) and cytosine (1656 cm−1), each with similar rate constants.
Proton Activity Inside the Channels of Zeolite L
Authors: Albuquerque Rodrigo Q. , Calzaferri Gion 
Published: September 2007

AbstractThe proton activity inside the channels of zeolite L has been studied by investigating dye‐loaded zeolite L crystals under different conditions, such as water content, nature of the counterions, and nature of the solvent. The discussion is made within the frame of three types of dye‐loaded zeolite L systems, classified according to their ability to exchange matter (dyes, cations, solvent, and other small molecules) with the environment. The classification refers to dye‐loaded zeolites. The term “closed” and “semi‐open” characterize different possibilities of the channels to exchange small molecules, cations, and solvent molecules with the environment, but not dyes. The “open” systems also allow for dye exchange. UV‐visible and fluorescence spectroscopy have been used to observe the proton activity inside the zeolite L channels. The influence of the proton activity on the luminescence of encapsulated dyes is discussed, special attention being given to luminescence quenching by excited‐state protonation. Partially proton‐exchanged zeolite L can be a superacid, whereas for the M‐exchanged form (M: K+, Li+, Cs+, Mg2+, Ca2+) the pH ranges from about 2.5 to 3.5. For these last forms, the differences in pH are due to the acid–base reactions of the respective metal cations with water inside the zeolite. Finally, we describe an easy experimental procedure that can be used to tune the proton activity inside the zeolite L to a considerable extent.
Bisamides Derived from Azulene‐1,3‐ and ‐5,7‐dicarboxylic Acids as New Building Blocks for Anion Receptors
Authors: Zieliński Tomasz , Kȩdziorek Mariusz , Jurczak Janusz 
Published: September 2007

AbstractBisamides based on the azulene moiety were investigated as building blocks for anion receptors. In the course of these studies, derivatives of azulene‐1,3‐ and ‐5,7‐dicarboxylic acid were synthesized and thoroughly characterized. The anion affinities of the derivatives based on functionalization in the five‐membered ring and in the seven‐membered ring were determined by 1H NMR titration. The structural analysis of these building blocks was performed by X‐ray diffractometry, molecular modelling and 2D NMR spectroscopy. The five‐membered ring derivatives are easy to obtain, offer a binding site preorganized in the syn–syn conformation and bind anions with a strength similar to those of pyrrole‐based analogues. There is also strong evidence for aromatic CH⋅⋅⋅anion interactions. The ligands substituted at the 5‐ and 7‐positions offer a binding cleft with an uncommon geometry that originates from the seven‐membered ring and seems to be complementary to the chloride anion.
20‐(S)‐Camptothecin Analogues as DNA Topoisomerase I Inhibitors: A QSAR Study
Authors: Hansch Corwin , Verma Rajeshwar P. 
Published: September 2007

AbstractThe interest in the application of the quantitative structure–activity relationships (QSAR) has steadily increased in recent decades because it has repeatedly proven itself to be a low‐cost, high‐return investment. Potential use of QSAR models for screening of chemical databases or virtual libraries before their synthesis appears equally attractive to chemical manufacturers, pharmaceutical companies, and government agencies. We hope it may also be useful in the design and development of new camptothecin derivatives as DNA topoisomerase I (topo I) inhibitors. In this paper, two series of camptothecin derivatives were undertaken to correlate DNA topo I inhibition with their hydrophobic and steric properties, to understand their chemical–biological interactions. The resulting QSAR have shown that the inhibitory activity of camptothecin analogues4toward DNA topo I is mainly dependent on their hydrophobic and steric descriptors, whereas the same activity of 10,11‐methylenedioxy‐ camptothecin analogues5is largely dependent on their hydrophobicity at position‐7. Using internal [cross‐validation, quality factor (Q), Fischer statistics (F), and Y‐randomization tests] and external validation tests both of these QSAR models have been validated. Both series of these camptothecin derivatives are also filtered by Lipinski’s rule of five to check their oral bioavailability. On the basis of these QSAR models, five compounds (4‐35,4‐36,5‐20,5‐21, and5‐22) have been predicted that may be the next synthetic target. These molecules also fulfill the conditions of Lipinski’s rule of five.
A phase 3 randomized controlled trial of the efficacy and safety of atrasentan in men with metastatic hormone‐refractory prostate cancer
Authors: Carducci Michael A. , Saad Fred , Abrahamsson Per‐Anders , Dearnaley David P. , Schulman Claude C. , North Scott A. , Sleep Darryl J. , Isaacson Jeffrey D. , Nelson Joel B. ,   for the Atrasentan Phase III Study Group Institutions.
Published: September 2007

AbstractBACKGROUND.The objective of this study was to evaluate the efficacy and safety of atrasentan (Xinlay), a selective endothelin‐A receptor antagonist, in patients with metastatic hormone‐refractory prostate cancer (HRPC).METHODS.This multinational, double‐blind, placebo‐controlled trial enrolled 809 men with metastatic HRPC. Patients were randomized 1:1 to receive either atrasentan 10 mg per day or placebo. The primary endpoint was time to disease progression (TTP), which was determined according to radiographic and clinical measures. Analyses of overall survival and changes in biomarkers also were performed.RESULTS.Atrasentan did not reduce the risk of disease progression relative to placebo (hazards ratio, 0.89; 95% confidence interval, 0.76–1.04;P= .136). Most patients progressed radiographically at the first 12‐week bone scan without concomitant clinical progression. In exploratory analyses, increases from baseline to final bone alkaline phosphatase (BAP) and prostate‐specific antigen (PSA) levels were significantly lower with atrasentan treatment (P< .05 for each). The median time to BAP progression (≥50% increase from nadir) was twice as long with atrasentan treatment (505 days vs 254 days;P< .01). The delay in time to PSA progression did not reach statistical significance. Atrasentan generally was tolerated well, and the most common adverse events associated with treatment were headache, rhinitis, and peripheral edema, reflecting the vasodilatory and fluid‐retention properties of endothelin‐A receptor antagonism.CONCLUSIONS.Atrasentan did not delay disease progression in men with metastatic HRPC despite evidence of biologic effects on PSA and BAP as markers of disease burden. Cancer 2007. © 2007 American Cancer Society.
Increased risk of oral cancer in relation to common Indian mitochondrial polymorphisms and Autosomal GSTP1 locus
Authors: Datta Sayantan , Majumder Mousumi , Biswas Nidhan K. , Sikdar Nilabja , Roy Bidyut 
Published: September 2007

AbstractBACKGROUND.Polymorphisms at mitochondrial (mt) loci could modulate the risk of diseases including cancers. Here the mtDNA polymorphisms at 12,308 nucleotide pairs (np), 11,467 np, 10,400 np, and 10,398 np were studied to examine the association with the risk of oral cancer and leukoplakia, alone and in combination with polymorphisms at the GST loci.METHODS.Polymorphisms at mt loci were screened in 310 cancer, 224 leukoplakia, and 389 control individuals by polymerase chain reaction (PCR) restriction length polymorphism (RFLP) and most of the GST genotype data were taken from previously published reports. Data were analyzed to determine the risk of the diseases.RESULTS.The major allele, A, at 12,308 np on tRNALeu (CUN), increased the risk of cancer (odd ratio [OR] of 1.7; 95% confidence interval [95% CI], 1.1–2.6) but not that of leukoplakia. The same allele also appeared to increase the risk of cancer in smokers (OR of 4.0; 95% CI, 1.1–14.4), who are mostly males (OR of 1.8; 95% CI, 1.1‐3‐2), but not in smokeless tobacco users, who are mostly females. The major allele A at 11467 np demonstrated identical results as the major allele, A, at 12,308 np. The major alleles G at 10,398 np and T at 10,400 np (ie, M‐haplogroup) increased the risk of cancer significantly in smokers (OR of 2.6; 95% CI, 1.2–5.7 and OR of 2.4; 95% CI, 1.1–5.1, respectively). The risk‐risk genotype‐allele combination at GSTP1 and mt12308 np loci increased the risk of cancer (OR of 2.6; 95% CI, 1.4–4.9) when compared with the nonrisk‐nonrisk combination in leukoplakia patients.CONCLUSIONS.Polymorphisms at the mt loci alone and in combination with the risk genotype at GSTP1 increased the risk of oral cancer. Thus, risk genotypes from 2 different organelles may work in combination to increase the risk of oral cancer. Cancer 2007. © 2007 American Cancer Society.