bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereoselective Synthesis of myo‐, neo‐, L‐chiro, D‐chiro, allo‐, scyllo‐, and epi‐Inositol Systems via Conduritols Prepared from p‐Benzoquinone
Authors: Podeschwa Michael , Plettenburg Oliver , vom Brocke Jochen , Block Oliver , Adelt Stephan , Altenbach Hans‐Josef 
Published: May 2003

AbstractA practical route is described for the flexible preparation of a wide variety of inositol stereoisomers and their polyphosphates. The potential of this approach is demonstrated by the synthesis of myo‐, L‐chiro‐, D‐chiro‐, epi‐, scyllo‐, allo‐, and neo‐inositol systems. Optically pure compounds in either enantiomeric form can be prepared from p‐benzoquinone via enzymatic resolution of a derived conduritol B key intermediate. High‐performance anion‐exchange chromatography with pulsed amperometric detection permits inositol stereoisomers to be resolved and detected with high sensitivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Solvent and Temperature Effects on Diastereofacial Selectivity: Amines as Co‐Solvents in n‐Butyllithium Addition to α‐Chiral Aldehydes
Authors: Cainelli Gianfranco , Giacomini Daria , Galletti Paola , Quintavalla Arianna 
Published: May 2003

AbstractTemperature‐dependent selectivity in nucleophilic additions to α‐chiral aldehydes is affected by solvent mixtures. In this context, we investigated the effect on diastereoselectivity of tertiary amines as co‐solvents. Addition of 5 mol% of an amine to hexane strongly influences the anti/syn ratio in the additions of nBuLi to 2‐phenylpropanal and to (2S)‐2‐[(tert‐butyl)dimethylsilyloxy]‐2‐propanal. In these hexane/amine mixtures as reaction solvents, we observed diastereoselectivities higher than those obtained in hexane. In the corresponding Eyring plots of ln(anti/syn) against the reciprocal temperature, we observed inversion temperatures (Tinv), these generally occurring at higher temperatures in the hexane/amine mixtures than in pure hexane. The presence of the inversion temperatures confirms that these tertiary amines take part in the solvation of the starting aldehyde, thus contributing to a solvent effect on facial selectivity. In some cases, the differential entropy of activation is the predominant factor in differentiating the diastereoselectivity among these hexane/amine mixtures. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Stereochemistry of Polyethylated Aromatic Systems
Authors: Marks Vered , Gottlieb Hugo E. , Biali Silvio E. 
Published: May 2003

AbstractHexaethylbenzene adopts a conformation with the ethyl groups perpendicular to the aromatic ring and oriented in a fully alternated up‐down arrangement. The synthesis, stereochemistry and rotational barriers of systems possessing two polyethylaryl rings in spatial proximity (e.g., decaethylbiphenyl, octaethylbiphenylene) are reviewed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of Ruthenium‐Labelled Tripeptoids with Alternating Amide and Diaryl Ether Bonds
Authors: Leone‐Stumpf Danielle , Lindel Thomas 
Published: May 2003

AbstractFree‐amino forms of 4‐O‐methyldopamine and 4‐O‐methyltyramine react as nucleophiles in a chemoselective manner with [RuCp]+‐complexed p‐substituted chloroarenes. As a consequence, it is not necessary to use protecting groups for the synthesis of peptoids with alternating amide and diaryl ether bonds. [RuCp]+‐labelled diaryl ether tripeptoids containing DOPA‐ and tyrosine‐derived subunits have been assembled as model compounds. The purification of the charged complexes was conveniently achieved employing aminopropyl‐functionalised silica as a stationary phase. The free‐amino form of tripeptoid 2 resembles the ABB′ partial structure of the macrocyclic bastadins, biologically active natural products from the marine sponge Ianthella. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Knoevenagel Adducts from Reactions between Glutaconate Moieties and Aldehydes and Their Adducts with Primary Amines and Enamines
Authors: Giral Angela Lopez , Mahuteau‐Betzer Florence , Gateau‐Olesker Alice , Marazano Christian 
Published: May 2003

AbstractEvaluation of an hypothesis regarding the biomimetic synthesis of manzamine alkaloids from the stepwise condensation of malonate, aldehydes and primary amine derivatives is presented. The first part of this study was concentrated on the Knoevenagel reaction, with various aldehydes, of glutaconaldehydes 7 and their ester analogues 17 and 23, in order to prepare stable derivatives of dienes 8. This reaction, previously reported to work only with salicylaldehyde and glutaconic esters, appeared to be difficult to control in the case of the glutaconaldehyde derivative 7a, but was successful when starting from esters 17 and 23. This result allowed the preparation of new dienes 21, 22a−c, and 25. The second part of this paper reports preliminary results concerning the reactivity of diene 21 towards primary amines and aldehyde equivalents. Dienals such as 21 were found to react with primary amines to afford 1,2‐dihydropyridines such as 26 or 27. Diene 21 was also shown to give diastereoisomeric cycloadducts 30 or 32 with enamines or oxazolidine derivatives. The cycloadducts 30 were finally shown to react with n‐butylamine in acidic medium to give rearranged cyclopentenes 36 and 37. Although the synthesis of derivatives such as 9 or 10, corresponding to the AB ring system of manzamine A, by this approach have yet to be successful, the reported results reveal some new aspects of this multicomponent chemistry, some features of which are related to polyketide‐type condensations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Val‐Ala Dipeptide Isosteres by Hydrocyanation of α′‐Amino α,β‐Unsaturated Ketones − Control of Stereoselectivity by the N‐Protecting Group
Authors: Benedetti Fabio , Berti Federico , Garau Gianpiero , Martinuzzi Ivan , Norbedo Stefano 
Published: May 2003

AbstractThree diastereoisomeric hydroxyethylene isosters of the Val‐Ala dipeptide were synthesized from α,β‐unsaturated ketones 1 derived from N‐Boc‐ and N,N‐dibenzyl‐L‐valine. The enones were hydrocyanated with diethylaluminum cyanide to give the corresponding β‐cyano ketones with the stereoselectivity depending on the protecting group. N‐Boc protected enone 1a gave a 1:1 mixture of anti and syn adducts 4a, 5a while the corresponding N,N‐dibenzyl compound 1c gave a 6:1 mixture of anti, syn adducts 4c, 5c. Borohydride reduction of the resulting cyano ketones is also controlled by the protecting group, resulting in opposite stereoselectivities for N‐Boc and N,N‐dibenzyl compounds. The cyano alcohols thus obtained were converted, in several steps, into two series of enantiomerically pure hydroxyethylene isosters of the Val‐Ala dipeptide. In the first series the hydroxy group and the N‐terminal of the isoster are internally protected through the formation of an oxazolidine; in the second series the hydroxy group and the C‐terminal are protected as lactone. Two oxazolidines (28, 29), corresponding to syn,syn and syn,anti 4‐hydroxy‐5‐amino acid isosters, and three lactones (23−25), corresponding to syn,syn, syn,anti, and anti,anti isosters were obtained by this approach. (© Wiley‐VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and Molecular Modeling Studies of SYNPHOS®, a New, Efficient Diphosphane Ligand For Ruthenium‐Catalyzed Asymmetric Hydrogenation
Authors: Paule Sébastien Duprat de , Jeulin Séverine , Ratovelomanana‐Vidal Virginie , Genêt Jean‐Pierre , Champion Nicolas , Dellis Philippe 
Published: May 2003

AbstractA new, optically active, atropisomeric diphosphane ligand, (2,3,2′,3′‐tetrahydro‐5,5′‐bi(1,4‐benzodioxin)‐6,6′‐diyl)bis‐(diphenylphosphane) (SYNPHOS®), has been synthesized, characterized, and used in ruthenium‐catalyzed asymmetric hydrogenations. This new ligand has been compared with other atropisomeric diphosphanes (BINAP and MeO‐BIPHEP) with respect to their dihedral angles calculated by molecular modeling and the enantioselectivity of their ruthenium‐mediated hydrogenation reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Substrates for Investigation of DNA Polymerase Function: Synthesis and Properties of 4′‐C‐Alkylated Oligonucleotides
Authors: Detmer Ilka , Summerer Daniel , Marx Andreas 
Published: May 2003

AbstractIn addition to their potential as diagnostic and therapeutic agents, modified oligonucleotides have also been shown to be highly valuable tools for examination of complex biological processes. Carefully designed nucleotide analogues have therefore found considerable application in investigations of DNA polymerase function and mechanism. To examine the contribution of primarily steric constraints on DNA polymerase selectivity, we have developed a new functional strategy based on the use of modified nucleotide analogues that differ primarily in their steric demand. Here we report the efficient synthesis of modified thymidine analogues bearing 4′‐alkyl groups with varying steric demand, the effects of 4′‐alkylation on sugar puckering, and the incorporation of these analogues into oligonucleotides by use of automated solid‐phase DNA synthesis. We also studied the pairing properties of 4′‐alkylated oligonucleotide duplexes in relation to those of their natural counterparts under a range of buffer conditions. In general, our studies indicate that 4′‐alkylation of thymidines has little effect on nucleoside and oligonucleotide conformation. These results have relevance to the previously reported action of 4′‐alkylated nucleotides and oligonucleotides as probes of DNA polymerase function and mechanism. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Theoretical Studies on Cycloaddition Reactions of 2‐Azaallene Cations with Isocyanates
Authors: Yang Si‐Ya , Sun Cheng‐Ke , Fang De‐Cai 
Published: May 2003

AbstractThe mechanisms of cycloaddition reactions between 2‐azaallene cations and isocyanates have been explored at the B3LYP/6‐31G* level. It is found that [2+2] or [2+4] cycloaddition reactions can take place via an intermediate when 2‐azaallene cations react with 1 or 2 equiv. of isocyanates. The effects of substituents are also reported in the present paper, and the results obtained indicate that electron‐attracting groups on 2‐azaallene cations favor the reaction, and electron‐donating groups on 2‐azaallene cations hinder the reaction. Substituents on isocyanates have the opposite effects. These results have been rationalized with FMO interaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Development of a Functionalizable External β‐Turn Mimic Based on a cis‐Fused 1,7‐Naphthyridine Scaffold
Authors: Rombouts Frederik J. R. , Borggraeve Wim M. De , Delaere David , Froeyen Matheus , Toppet Suzanne M. , Compernolle Frans , Hoornaert Georges J. 
Published: May 2003

AbstractAn intramolecular Diels−Alder strategy using 2(1H)‐pyrazinones was applied to generate a substituted perhydro‐1,7‐naphthyridine ring system that served as a scaffold to construct the type VI β‐turn mimic 2, featuring a cis‐amide linkage between the central i+1 and i+2 residues. The synthesis permits mimicking of the amino acid side chains of the central dipeptide, a unique feature for external‐turn mimics. Modeling studies indicated that the cis‐fused bicyclic system adopts a conformation suitable for induction of a β‐turn when the angular position 8a bears a non‐H substituent. Extensive NMR analysis of an 8a‐methyl derivative 25 confirmed its β‐turn‐inducing properties in various solvents, including water. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Structures of Saturated 5H‐Pyrrolo[1,2‐a][3,1]benzoxazin‐1(2H)‐ones Prepared from 4‐Oxopentanoic Acid and Cyclic Amino Alcohols
Authors: Kivelä Henri , Klika Karel D. , Szabó Angela , Stájer Géza , Pihlaja Kalevi 
Published: May 2003

AbstractSaturated heterocycles containing two condensed heterocyclic rings and a carbo(bi)cyclic ring have been prepared by the reaction of 4‐oxopentanoic acid (1) with (bi)cyclic amino alcohols. 5H‐Pyrrolo[1,2‐a][3,1]benzoxazin‐1(2H)‐ones 2−5 were formed in the reaction of 1 with trans‐ or cis‐2‐(hydroxymethyl)cyclohexylamines or ‐cyclohexenylamines. With di‐endo‐ or di‐exo‐3‐aminobicyclo[2.2.1]hept‐2‐yl‐ or ‐hept‐5‐en‐2‐ylmethanols, 1 yielded the corresponding derivatives 6−9 that are methylene‐bridged in the cyclohexane or cyclohexene rings. The stereoselectivity of the syntheses were high; only for 5, 7 and 9 were both C‐3a epimers produced in observable amounts. The structures were established by means of NMR spectroscopic methods by applying standard pulse techniques. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of Nitrile Oligomers through Multiple Anion Capture Reactions of Allene Dianions
Authors: Langer Peter , Döring Manfred , Seyferth Dietmar , Görls Helmar 
Published: May 2003

AbstractDomino reactions between 1,1‐dilithio‐3,3‐diphenylallene and nitriles resulted in the formation of products containing up to four nitrile molecules, representing the highest number to date of nitrile molecules involved in the formation of unambiguously characterized oligomers. The unusual domino process reported constitutes a new method for the synthesis of imidazoles. The solid‐state structures of the sterically encumbered products were studied by crystal structure analyses. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Efficient Large‐Scale Synthesis of Picolinic Acid‐Derived Nickel(II) Complexes of Glycine
Authors: Ueki Hisanori , Ellis Trevor K. , Martin Collin H. , Soloshonok Vadim A. 
Published: May 2003

AbstractAn efficient, large‐scale method for the preparation of 2‐[N‐(α‐picolyl)amino]acetophenone (PAAP) and 2‐[N‐(α‐picolyl)amino]benzophenone (PABP), the hitherto unknown 4‐methyl‐2‐[N‐(α‐picolyl)amino]benzophenone (4‐Me‐PABP) and 4‐nitro‐2‐[N‐(α‐picolyl)amino]benzophenone (4‐NO2‐PABP), and their corresponding NiII complexes with glycine is described. The key step of the method is the formation of the mixed anhydrides derived from o‐picolinic acid and ethyl chloroformate or p‐toluenesulfonyl chloride. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Di‐ and Trispirocyclopropanated Tetrahydropyridinones
Authors: Gensini Martina , Kozhushkov Sergei I. , Frank Daniel , Vidović Denis , Brandi Alberto , Meijere Armin de 
Published: May 2003

AbstractA variety of spirocyclopropane‐annelated tetrahydropyridinones of types 14/15 and 18/19 have been prepared in good yields (68−80%) by means of 1,3‐dipolar cycloadditions between nitrones 25, 31, and 34 and cyclopropylidenespiropentane (7) and 7‐cyclopropylidenedispiro[2.0.2.1]heptane (8), with subsequent thermal rearrangement. While the overall reactions of nitrones 25 and 31 with 7‐cyclopropylidenedispiro[2.0.2.1]heptane (8) occurred with the commonly observed regioselectivity (i.e., the initially formed cycloadducts of type 12/13 rearranged to give compounds 29, 30, and 33 as major products), the reactions of 31 and 34 with cyclopropylidenespiropentane (7) and of 34 with 7‐cyclopropylidenedispiro[2.0.2.1]heptane (8) showed an opposite trend. Thermal rearrangement of compound 27 gave a mixture of pyridinone 29 and ring‐opened product 30 (19 and 58% yields, respectively). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A New and Expedient Diastereoselective Synthesis of α‐(Hydroxyamino)phosphonates and α‐Aminophosphonates by Silyl Triflate Promoted Diethyl Phosphite Addition to Chiral N‐Benzyl Nitrones
Authors: De Risi Carmela , Perrone Daniela , Dondoni Alessandro , Pollini Gian Piero , Bertolasi Valerio 
Published: May 2003

AbstractAn efficient methodology for the synthesis of α‐aminophosphonates has been developed taking advantage of the tert‐butyldimethylsilyl triflate activated addition of diethyl phosphite to N‐benzyl nitrones derived from chiral α‐alkoxy and α‐(Boc‐amino) aldehydes. The stereoselective carbon− phosphorus bond‐forming reaction proceeded smoothly to give α‐(hydroxyamino)phosphonate intermediates as the primary adducts, which were subsequently converted into the corresponding polyhydroxylated α‐amino‐ and α,β‐diaminophosphonates by conventional reductive processes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Conjugate Addition of Phenols to 2‐Nitrogalactal − Synthesis of O‐(2‐Acetamido‐2‐deoxygalactosyl)tyrosine
Authors: Khodair Ahmed I. , Winterfeld Gottfried A. , Schmidt Richard R. 
Published: May 2003

Abstract2‐Nitrogalactal derivative 1 afforded 2‐deoxy‐2‐nitrogalactopyranosides on treatment with phenol and substituted derivatives under base catalysis. Transformation of the nitro group into the amino and the acetamido groups and O‐deprotection could readily be performed, thus providing aryl 2‐acetamido‐2‐deoxygalactopyranosides 5 and 6 in high yields and with good stereoselectivities. The same reaction sequence could also be successfully applied to N‐Boc‐protected tyrosine methyl ester, to afford the O‐galactopyranonsyl tyrosine derivative 10. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Photochromic Properties of Perhydro‐ and Perfluorodithienylcyclopentene Molecular Switches
Authors: Jong Jaap J. D. de , Lucas Linda N. , Hania Ralph , Pugzlys Audrius , Kellogg Richard M. , Feringa Ben L. , Duppen Koos , Esch Jan H. van 
Published: May 2003

AbstractVarious substituted phenylthienyl perhydro‐ and perfluorocyclopentenes have been synthesized in order to compare their spectroscopic and photochromic properties. The difference in the electron densities of the central cyclopentene moieties in the perhydrocyclopentene and perfluorocyclopentene molecular switches has only a small effect on the absorption maxima of the electronic spectra, but causes some subtle changes in substituent and solvatochromic effects. The photochromic behaviour is remarkably similar, and both type of switches combine excellent quantum yields (0.6) with high degrees of photoconversion (> 0.85). The main difference is the lower photochemical and thermal stability of the perhydrocyclopentene molecular switches. It is concluded that in most studies the perhydrocyclopentenes are an excellent alternative for the perfluorocyclopentenes, while the perfluorocyclopentenes might be better suited for applications such as data storage, which depend critically on fatigue resistance and thermal stability. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cycloaddition Behavior of 1,2‐Thiaphospholes: Reactions with Diazocumulenes and with Cyclopentadiene
Authors: Kerth Jochen , Jikyo Tamaki , Maas Gerhard 
Published: May 2003

Abstract1,2‐Thiaphospholes 3a,b react with (1‐diazo‐2‐oxoalkyl)silanes 1a−c to form [1,2]thiaphospholo[2′,3′:3,4][1,3]diphospholo[1,5‐b][1,2]thiaphosphole systems 4 with cis‐anti‐cis configuration of the tricyclic framework. They are accompanied by small amounts of compounds 5 that are presumably the cis‐syn‐cis isomers of 4, and 6‐alkylidene‐1‐phospha‐2‐thiabicyclo[3.1.0]hex‐3‐enes 6. It is likely that these reactions proceed by [3+2] cycloaddition of diazocumulenes, which coexist with diazo compounds as minor equilibrium components, at the P=C bond of the heterophospholes, followed by N2 elimination and formation of short‐lived 2‐alkylidene‐1,2(λ5)thiaphospholes. The latter can either add to excess thiaphosphole to form the tricyclic products or undergo electrocyclization to form bicyclic alkylidenephosphiranes. Thiaphosphole 3a does not seem to react directly with cyclopentadiene in a [4+2] or [2+4] cycloaddition. Reaction with excess cyclopentadiene at 120 °C yields the polycyclic compounds 15 and 16, which are likely to arise from a Diels−Alder reaction of 3a, reacting as a heterodiene, with the cyclopentadiene dimer. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The First, General, Highly Efficient Method for Preparing Tetrasubstituted Epoxides Using HOF·CH3CN
Authors: Rozen Shlomo , Golan Elizabeth 
Published: May 2003

AbstractTetrasubstituted epoxides, and especially electron‐depleted ones, generally are difficult to prepare. HOF·CH3CN complex, probably the best oxygen transfer agent known today, epoxidizes tetrasubstituted alkenes at 0 °C in a matter of minutes or less in excellent yields. HOF·CH3CN complex is very easy to prepare by bubbling diluted fluorine (commercial) through aqueous acetonitrile. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cover Picture: Substrates for Investigation of DNA Polymerase Function: Synthesis and Properties of 4′‐C‐Alkylated Oligonucleotides (Eur. J. Org. Chem. 10/2003)
Authors: Detmer Ilka , Summerer Daniel , Marx Andreas 
Published: May 2003

AbstractThe cover picture shows the design and structures of 4′‐C‐alkylated thymidines. These modified nucleosides were synthesized and subsequently incorporated into oligonucleotides to probe inherent properties of the DNA double helix (left‐hand) side) and DNA polymerases in their interplay with their DNA substrates (right‐hand side). Details are discussed in the article by I. Detmer, D. Summerer and A. Marx on p. 1837 ff.
Voltametric and Flow Injection Determination of Oxytetracycline Residues in Food Samples Using Carbon Fiber Microelectrodes
Authors: Agüí L. , Guzman A. , Pedrero M. , Yáñez‐Sedeño P. , Pingarrón J. M. 
Published: May 2003

AbstractA voltammetric method for the determination of the antibiotic oxytetracycline (OTC) in food samples is reported. Carbon fiber microelectrodes (CFMEs), which allow voltammetric measurements to be performed in a small volume (1 mL) of the analyte extract from the samples, are employed. Repeatable electroanalytical responses were obtained with no need of applying cleaning treatments to the CFME. Under the optimized square‐wave conditions, a linear calibration plot for OTC was obtained in the 1.0×10−6–1.0×10−4 mol L−1 range, with a detection limit of 2.9×10−7 mol L−1 (150 ng mL−1) OTC. The determination of OTC by a flow‐injection method with amperometric detection using a homemade flow cell specially designed to work with CFMEs, was also evaluated using pure acetonitrile as the carrier. The SW voltammetric method was applied to the determination of OTC in spiked milk and eggs samples, at 100 ng mL−1 and 200 ng g−1 levels, respectively. The procedure involved the extraction of the analyte in ethyl acetate, evaporation of the solvent and reconstitution of the residue in acetonitrile −5.0×10−4 mol L−1 tetrabutylammonium perchlorate medium. Recoveries of 96±8 and 91±8% were obtained for milk and eggs, respectively, by applying the standard additions method.