bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of 1‐(m‐Hydroxybenzyl)‐Substituted 1,2,3,4‐Tetrahydroisoquinoline‐3‐carboxylic Acid Derivatives as Opioid Peptide Mimetics − Unexpected Amide Bond Cleavages under Mild Conditions
Authors: Mannekens Els , Crisma Marco , Van Cauwenberghe Sylvia , Tourwé Dirk 
Published: August 2003

AbstractN‐Glycyl‐(1R,3S)‐1‐(m‐hydroxybenzyl)‐1,2,3,4‐tetrahydroisoquinoline‐3‐carboxylic acid (Tic) was prepared as a Tyr‐Tic dipeptide mimetic for exploration of its potential as a delta opioid receptor selective ligand. The compound was successfully obtained by a stereoselective synthesis starting from L‐Tic. In the course of the reactions, unusual peptide bond cleavages were observed under mild conditions, and reaction mechanisms have been proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Versatile Route to Functionalized Dilactones as Monomers for the Synthesis of Poly(α‐hydroxy) Acids
Authors: Leemhuis Mark , van Steenis Jan Hein , van Uxem Michelle J. , van Nostrum Cornelus F. , Hennink Wim E. 
Published: August 2003

AbstractA synthetic pathway to functionalized six‐membered dilactones structurally analogous to lactide is described. Through the use of orthogonal protecting groups, the synthesis of functionalized dilactones was performed in a straightforward way by cyanuric chloride‐mediated cyclization of the corresponding linear α‐hydroxy acid dimers. The synthesis of three different dilactones − methylglycolide, benzyloxymethylglycolide, and 2‐benzyloxymethyl‐5‐methylglycolide − by the same procedure demonstrated the versatility of this route. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
One‐Pot Synthesis of 6‐Hydroxyisochromans: The Example of Demethyl‐oxa‐coclaurine
Authors: Guiso Marcella , Bianco Armandodoriano , Marra Carolina , Cavarischia Claudia 
Published: August 2003

AbstractUsing a modified oxa‐Pictet Spengler reaction that we recently described, we synthesized 6‐hydroxy‐isochromans and their 7‐hydroxy derivatives. The successful one step synthesis did not require protecting groups and provided high yields. The obtainment of 1‐(4′‐hydroxybenzyl)‐6,7‐dihydroxyisochroman (1) indicates that this protocol can be used to synthesize oxygenated analogues of benzyl‐tetrahydroisoquinoline alkaloids, such as demethyl‐coclaurine (2). This methodology could provide a general procedure for the synthesis of hydroxyisochromans. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Solvolysis of Some Arenediazonium Salts in Binary EtOH/H2O Mixtures under Acidic Conditions
Authors: Pazo‐Llorente Román , Bravo‐Díaz Carlos , González‐Romero Elisa 
Published: August 2003

AbstractWe have determined the product distribution, the rate constants for dediazoniation product formation, and the solvolytic rate constants for 2‐, 3‐, and 4‐methylbenzenediazonium ions (2‐, 3‐, and 4‐MBD, respectively) loss in acidic ethanol/water mixtures over the whole composition range by a combination of spectrophotometric (UV/Vis) and high performance liquid chromatography (HPLC) measurements. The observed rate constants (kobs) for substrate loss are equal to those for product formation, and they remain essentially constant (2‐MBD) with changing solvent composition but increase by a factor of ≈︁2 (4MBD) on going from water to 100% EtOH. Up to four dediazoniation products − cresols (ArOH), chlorotoluene (ArCl), methylphenetole (ArOEt), and toluene (ArH) − were detected, depending on the solvent composition; the major dediazoniation products were the ArOH and ArOEt derivatives. The product selectivity (S) of the reaction towards nucleophiles is low and essentially constant with changing solvent composition, and good linear correlations between log kobs and YCl (solvent ionizing power) were observed for the three ArN2+ ions. All data are consistent with the rate‐determining formation of an aryl cation, which reacts immediately with available nucleophiles. The data suggest that the distribution of neutral and anionic nucleophiles in the neighborhood of the ground state arenediazonium ion remains essentially unchanged upon dediazoniation, the observed product distribution reflecting the concentrations of nucleophiles in their immediate environment (i.e., in the first solvation shells of the arenediazonium ions). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Choice of Phosphane Reagent in Fukuyama−Mitsunobu Alkylation: Intramolecular Selectivity Between Primary and Secondary Alcohols in the Preparation of Asymmetric Tetraamine Building Blocks for Synthesis of Philanthotoxins
Authors: Olsen Christian A. , Jørgensen Malene R. , Witt Matthias , Mellor Ian R. , Usherwood Peter N. R. , Jaroszewski Jerzy W. , Franzyk Henrik 
Published: August 2003

AbstractPhilanthotoxin‐433 (PhTX‐433) is a polyamine wasp toxin that antagonizes certain ionotropic receptors noncompetitively. Four analogues of PhTX‐433, C‐methylated in the polyamine chain, were synthesized from (RS)‐1,3‐butanediol, two diamine building blocks, and an activated/protected tyrosine derivative. Use of a phosphane reagent more bulky than trimethylphosphane gave a high intramolecular selectivity between primary and secondary hydroxy groups in the Fukuyama−Mitsunobu reaction. Thus, trimethylphosphane proved to be the only phosphane reagent that enabled alkylation of 2‐nitrobenzenesulfonamides with a wide range of secondary alcohols, whereas tributylphosphane was selective for primary alcohol groups. This selectivity was utilized to obtain orthogonally protected, asymmetric, branched tetraamines, employed for solution‐phase synthesis of philanthotoxin analogues. The branched philanthotoxin analogues thus obtained were tested in an electrophysiological assay using rat brain ionotropic glutamate receptors expressed in Xenopus laevis oocytes. Their potencies proved to be similar to the corresponding nonbranched analogues. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Manipulating L‐Aspartic and L‐Glutamic Acids − Diastereoselective Synthesis of Enantiopure β‐Amino‐γ‐hydroxy Acids and γ‐Amino‐δ‐hydroxy Acids
Authors: Andrés José M. , Muñoz Eva M. , Pedrosa Rafael , Pérez‐Encabo Alfonso 
Published: August 2003

AbstractEnantiopure (3S,4R)‐ and (3S,4S)‐3‐amino‐4‐hydroxyhexanoic acids and (4S,5R)‐ and (4S,5S)‐4‐amino‐5‐hydroxyheptanoic acid derivatives have been prepared by stereodivergent synthesis from L‐aspartic and L‐glutamic acids, respectively. The stereochemistry at the carbon atom attached to the amino group was determined from the starting material, but the configuration at C‐4 or C‐5 is controlled by diastereoselective alkylation with diethylzinc or ethylmagnesium bromide. The protection of the carboxylic group as OBO orthoester improved the yields in the final products. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of the Tetracyclic Bis(acetal) Lactone Portion of Saudin
Authors: Labadie Guillermo R. , Luna Liliana E. , Gonzalez‐Sierra Manuel , Cravero Raquel M. 
Published: August 2003

AbstractTwo synthetic approaches towards the synthesis of the tetracyclic lactone 4, containing the caged bis(acetalic) backbone of Saudin, were explored. Both sequences included the utilization of the known epoxy‐acetal 3, prepared stereoselectively by means of an intramolecular radical cyclization, as the common key intermediate, allowing total control over the relative stereochemistry of four consecutive chiral centers. Oxidative degradation with ruthenium dioxide and unsymmetrical ozonolysis reactions provided the new two key synthons in each synthetic route. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Dimethoxydimethylsilane from Silicon Atoms and Dimethyl Ether: A Combined Matrix‐Spectroscopic and Density Functional Theory Study
Authors: Maier Günther , Glatthaar Jörg 
Published: August 2003

AbstractThe reaction between silicon atoms and dimethyl ether (6) has been studied in an argon matrix at 10 K and in solid dimethyl ether (6) at temperatures up to 80 K. In the initial step, a triplet n‐adductT‐5is formed between a silicon atom and6. The next step needs photochemical activation. Depending on the relative dimethyl ether/argon ratio, the photoproduct is either dimethylsilanone (1) or singlet methoxymethylsilylene (S‐2), which, in the presence of an excess of6, exists as a dimethyl ether complex8of silyleneS‐2.Longer irradiation transforms dimethyl ether addition compoundsS‐8‐t/S‐8‐cinto dimethoxydimethylsilane (7). If irradiation is applied directly during cocondensation of silicon atoms with6, the only detectable products are8and7. Upon further irradiation of the pure dimethyl ether matrix, the rest of8is also photoisomerized, and dimethoxydimethylsilane (7) is observed exclusively. The structural elucidation of all new species is based on comparison of the experimental observations with density functional theory calculations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Some Key Experimental Features of a Modular Synthesis of Heparin‐Like Oligosaccharides
Authors: Paz José‐Luis de , Ojeda Rafael , Reichardt Niels , Martín‐Lomas Manuel 
Published: August 2003

AbstractThe key features of a modular n+2 strategy for a completely stereoselective synthesis of oligosaccharides containing the GlcN−IdoA repeating unit of the major sequence of heparin are presented and discussed in detail. These key features include the regio‐ and stereoselective synthesis of disaccharide building blocks and the reactivity of building blocks in the modular assembly process. The synthetic strategy, the effectiveness of which has previously been demonstrated by the total synthesis of four hexasaccharides and two octasaccharides, allows the size and the charge distribution of the target oligosaccharide fragments to be controlled. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003
Synthesis and Structural Characterization of PNA‐DNA Quadruplex‐Forming Chimeras
Authors: Esposito Veronica , Randazzo Antonio , Messere Anna , Galeone Aldo , Petraccone Luigi , Giancola Concetta , Piccialli Gennaro , Mayol Luciano 
Published: August 2003

AbstractThe synthesis and structural characterization of four PNA‐DNA chimeras − 5′TGGG3′‐t (C1), 5′TGG3′‐gt (C2), t‐5′GGGT3′ (C3) and tg‐5′GGT3′ (C4), where lower and upper case letters indicate PNA and DNA residues, respectively − are reported. The oligomers were synthesized through the use of commercially available Bhoc/Fmoc PNA monomers and 3′‐ or 5′‐phosphoramidite nucleosides as building blocks. All the molecules were studied by 1H NMR, CD and UV spectroscopy and by molecular modelling. The CD spectra and NMR spectroscopic data of C1 and C3 are typical of quadruplexes involving four parallel strands. Moreover, the UV melting profiles indicate that their thermal stabilities are quite similar to that observed for the reference quadruplex [d(TGGGT)]4. The 1H NMR spectra of C2 and C4 show that these oligomers are not able to fold into a single, well defined species. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Oligo(1,4‐phenylenepyrazole‐3,5‐diyl)s
Authors: Meier Herbert , Hormaza Angelina 
Published: August 2003

AbstractThe bifunctional nucleophile methylhydrazine reacts in an alkaline medium in a regioselective mode with chalcones to yield 2‐pyrazolines, which can be oxidized by DDQ to the corresponding 1H‐pyrazoles. From oligo(chalcone)s this reaction yields cross‐conjugated compounds with an alternating sequence of 1,4‐disubstituted benzene rings and 3,5‐disubstituted 1H‐pyrazole rings. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Highly Enantioselective Rhodium‐Catalyzed Hydrogenation of 2‐(2‐Methoxy‐2‐oxoethyl)acrylic Acid − A Convenient Access of Enantiomerically Pure Isoprenoid Building Blocks
Authors: Ostermeier Markus , Brunner Bernhard , Korff Christian , Helmchen Günter 
Published: August 2003

AbstractAsymmetric catalytic hydrogenation of 2‐(2‐methoxy‐2‐oxoethyl)acrylic acid (5) to give (2S)‐4‐methoxy‐2‐methyl‐4‐oxobutanoic acid [(S)‐6] was studied. An enantiomeric excess of 99.7% ee was achieved with a catalyst formed in situ from [Rh(COD)2]BF4 and the chiral phosphite L2 in 1,2‐dichloroethane as solvent. In addition, enzyme‐catalyzed semi‐saponification of dimethyl 2‐methylsuccinate was investigated. Mono ester (S)‐6 was transformed into a few compounds which can serve as C5‐building blocks in natural product syntheses. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Effect of Ring Size on Catenane Synthesis
Authors: Duda Stefan , Godt Adelheid 
Published: August 2003

AbstractThe synthesis of a [2]catenane with 87‐membered rings was improved and extended to [2]catenanes with 63‐ and 147‐membered rings. One of the key features is the carbonate linkage between phenols with tolane substituents in the 2‐ and 6‐positions, which serves as a covalent template for the geometrical arrangement of a macrocycle and a ring precursor. Subsequent cyclization of the threaded ring precursor gives the precatenane as the main product, and this is converted into the catenane by carbonate hydrolysis. As well as the precatenane, its dumbbell shaped isomer is formed in the cyclization step. From the known conformation of the templating carbonate moiety and the strong dependence of the ratio of precatenane and dumbbell on the ring size, the dumbbell's origin is attributed to the conformational flexibility of the large rings and not to geometrical ambiguity of the carbonate moiety. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Atroposelectivity of Reactions of Benzylic Metalated Thiobenzamides and Thionaphthamides
Authors: Ach David , Reboul Vincent , Metzner Patrick 
Published: August 2003

AbstractN,N‐Dialkyl‐2‐methylbenzenecarbothioamides and naphthalenecarbothioamides were prepared by thionation of amides with Lawesson’s reagent under unusual conditions. Their axial chirality was evidenced. Benzylic deprotonation of thioamides bearing N,N‐diisopropyl groups with sec‐butyllithium was selective. The resulting anions were reacted with prochiral electrophiles (aromatic aldehydes, an unsaturated aldehyde or ketone, and an imine) to afford diastereomeric adducts (up to 88:12 dr). This is the first report on atroposelective C−C bond formation in the benzylic position of thioamides. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Inside Protonation of 1,8‐Diazabicyclo[6.6.n]alka‐4,11‐diynes
Authors: Balalaie Saeed , Kunze Andreas , Gleiter Rolf , Rominger Frank , Geis Sibylle , Oeser Thomas 
Published: August 2003

AbstractProtonation of 1,8‐diazabicyclo[6.6.3]heptadeca‐4,11‐diyne (4a), 1,8‐diazabicyclo[6.6.4]octa‐deca‐4,11‐diyne (4b), 1,8‐diazabicyclo[6.6.5]nonadeca‐4,11‐diyne (4c), and 1,8‐diazabicyclo[6.6.6]eicosa‐4,11‐diyne (4d) was achieved by treatment of 4a−4d with strong acids. Monoprotonation products were isolated in all cases, while for 4b and 4c diprotonation products were also obtained. X‐ray investigations show inside protonation for the mono‐ and diprotonation products. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Solid‐Phase Synthesis of a Phytoalexin Elicitor Pentasaccharide Using a 4‐Azido‐3‐chlorobenzyl Group as the Key for Temporary Protection and Catch‐and‐Release Purification
Authors: Egusa Kenji , Kusumoto Shoichi , Fukase Koichi 
Published: August 2003

AbstractA phytoalexin elicitor pentasaccharide of the rice blast disease fungus, Pyricularia oryzae, was synthesized by a new route involving a solid‐phase method, in which a 4‐azido‐3‐chlorobenzyl (ClAzb) group was used for temporary protection of the hydroxy functions and catch‐and‐release purification. Thioglycosides possessing the ClAzb group were used as glycosyl donors and a macroporous polystyrene as a solid support. The saccharide chain was elongated by repeating a set of reactions: removal of the ClAzb group, glycosylation and capping of the unglycosylated hydroxy groups. Cleavage from the solid support by treatment with sodium methoxide afforded a crude pentasaccharide possessing the ClAzb group as a tag. The pentasaccharide was then purified by a catch‐and‐release procedure based on the specific reaction between the azido group and a solid‐supported phosphane. The final deprotection of all benzyl‐type protective groups gave the desired phytoalexin elicitor pentasaccharide 1 in overall 15% yield (from a solid‐supported monosaccharide 4, average yield of 81% for each of a total of nine steps). The characteristic peaks of the azido group in the infrared spectrum were also useful for monitoring reactions in the solid phase. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cover Picture: Pyrrolo‐Tetrathiafulvalenes and Their Applications in Molecular and Supramolecular Chemistry (Eur. J. Org. Chem. 17/2003)
Authors: Jeppesen Jan O. , Becher Jan 
Published: August 2003

AbstractThe cover picture shows the molecular structure (center) of the parent pyrrolo‐tetrathiafulvalene, which has been incorporated into a number of molecular and supramolecular systems, such as cyclophanes (upper right), rotaxanes (lower right), porphyrins (lower left), and calixpyrroles (upper left). The synthesis and physical properties of the parent pyrrolo‐tetrathiafulvalenes, followed by a journey through their applications in macrocyclic, molecular, and supramolecular chemistry, are described in the Microreview by J. O. Jeppesen and J. Becher on p. 3245 ff.
A two‐dimensional proteome map of Shigella flexneri
Authors: Liao Xiang , Ying Tianyi , Wang Hengliang , Wang Jie , Shi Zhaoxing , Feng Erling , Wei Kaihua , Wang Yuelan , Zhang Xuemin , Huang Liuyu , Su Guofu , Huang Peitang 
Published: August 2003

AbstractShigella flexneri is a Gram‐negative facultatively intracellular pathogen responsible for bacillary dysentery in humans. In this study, extracellular proteins from the culture medium and whole cell proteins in cellular extracts of S. flexneri 2a strain 2457T were examined by two‐dimensional (2‐D) gel electrophoresis using immobilized pH gradient (IPG) technology. Proteins were identified by matrix‐assisted laser desorption/ionization‐mass spectrometry (MALDI‐MS) in combination with Mascot search program. In total, among the 488 proteins spots processed, 388 proteins were identified. The identified proteins represented 169 genes. By comparing results of Mascot search against databases of Escherichia coli and genomes of S. flexneri 2a, one S. flexneri‐specific protein was identified and one possible gap was found in 2457T genome sequences. Although this proteome map is still incomplete, it is already a useful reference for future studies involving pathogenicity, vaccine development, design of novel antibacterial drugs, etc. Proteome maps and a table of all identified proteins are available on the internet at www.proteomics.com.cn.
Dimorphic Alu element located between the TFIIH and CDSN genes within the major histocompatibility complex
Authors: Dunn David S. , Inoko Hiditoshi , Kulski Jerzy K. 
Published: August 2003

AbstractMost Alu members of the large SINE family are fixed within the human genome but some younger mobile members are dimorphic, that is, they are either present or absent in the genome. Four different dimorphic Alu insertions have been identified and characterized previously within the class I region of the major histocompatibility complex (MHC). Here we report on (i) the identification and characterization of a new dimorphic Alu insertion, AluyTF, located between the transcription factor II H (TFIIH) and corneodesmosin (CDSN) genes within a region of the MHC that is telomeric of the human leukocyte antigen type B (HLA‐B) locus and centromeric of the HLA‐A locus, (ii) the haplotypic relationships between the AluyTF dimorphism and the HLA‐A and ‐B loci within a panel of 48 IHW cell‐lines representing at least 36 different HLA class I haplotypes, (iii) the AluyTF genotype, allele and haplotype frequencies present in the Australian caucasian and Japanese populations, and (iv) the frequency of association between the AluTF dimorphisms and HLA‐A and ‐B alleles in 108 Australian caucasians and 99 Japanese. The AluyTF insertion was present at 27% in the IHW cell lines, and the gene frequency was 0.107 and 0.083 in the Australian caucasian and Japanese population, respectively. The Alu haplotype frequencies constructed from four different dimorphic Alu loci including AluyTF within the MHC were not significantly different (p > 0.05) between the two populations. There were no significant associations between the Alu insertion and either the HLA‐A or ‐B alleles except for a moderately strong association with HLA‐A29 in the Australians (71.7%). This polymorphic AluyTF element, along with the four other previously described polymorphic Alu elements within the class I region of the MHC, will be useful lineage and linkage markers in human population studies and for elucidating the evolution of HLA class I haplotypes.
Capillary electrophoresis of trace metals in highly saline physiological sample matrices
Authors: Riaz Asif , Kim Bojeong , Chung Doo Soo 
Published: August 2003

AbstractTrace metal ions in highly saline samples such as urine were determined with capillary electrophoresis (CE) without desalting or off‐line preconcentration. By mixing with a dye, 4‐(2‐pyridylazo) resorcinol (PAR), the metal ions were converted into anionic complexes having strong absorbance near 500 nm. A large volume of the metal‐PAR complex sample solution injected into a coated capillary was stacked isotachophoretically and separated under a reverse potential. The salt anion (chloride) and PAR in the sample matrix acted as the leading and terminating electrolytes, respectively. In a sample containing a 250 mM NaCl matrix, more than 400‐fold enhancement in the absorbance detector response was realized compared to the normal CE injection mode. Combination of the dye complexation and isotachophoretic stacking provided excellent detection limits (S/N = 3) for three trace metal ions in the low ppb range (Fe2+, 0.7 ppb, Ni2+, 0.4 ppb; Zn2+, 1.2 ppb) with absorbance detection. The migration time reproducibility was excellent (relative standard deviations: standard samples < 1%, urine samples ∼1%). The proposed method is convenient and fast, and the sample analysis can be completed within 20 min.
A simple polyacrylamide gel electrophoresis procedure for separation of polyamidoamine dendrimers
Authors: Sharma Ajit , Mohanty Dillip K. , Desai Ankur , Ali Riaz 
Published: August 2003

AbstractA simple, inexpensive, and rapid electrophoresis technique was developed for use as a routine tool for evaluating purity of polyamidoamine (PAMAM) dendrimers. A variety of factors influencing migration of generations 0–7 dendrimers on nongradient polyacrylamide gels were evaluated. The low generation dendrimers were found to be very sensitive to diffusion during or after electrophoresis. The proposed method incorporates steps that minimize diffusion, in order to obtain improved resolution and sensitivity, especially for the lower‐molecular‐weight dendrimers. This was accomplished by inclusion of a dendrimer fixation step with glutaraldehyde and performing the electrophoresis separation, fixation, staining, and destaining at 4°C. PAMAM dendrimer separation was studied under basic and acidic conditions. Electrophoresis under acidic conditions gave increased resolution and sensitivity over separation at alkaline pH. Oligomers and trailing generations could be clearly separated and visualized under these conditions. The smallest PAMAM dendrimer, generation 0, was visible at 1.5 μg under the optimized acidic conditions. With slight modifications, this technique should be applicable to separation of other water‐soluble dendrimers.