bluuebunny/crossref_metadata_2025_split huggingface dataset:
Peptide‐Cavitands Based on Resorc[4]arenes − Synthesis and Structure
Authors: Berghaus Carsten , Feigel Martin 
Published: July 2003

AbstractAmino acids and peptides were coupled to the four aminomethyl groups of the bridged resorc[4]arene 2, resulting in peptide cavitands 3 of the general structure 2 [−Aa1‐[Aa2‐[Aa3]]−N(H)R]4. These compounds contain either four amino acids (3a−3d: Aa1 = Gly, Val, Leu or Phe, R = H; 3e, 3f: Aa1 = Gly or Val, R = Z), four dipeptides (3g−3l: Aa1 = Gly, Aa2 = Gly, Val, Leu, Phe, Lys(Boc) or Pro, R = Z), four tripeptides (3m, 3n: Aa1 = Gly, Aa2 = Val, Aa3 = Val or Met, R = Z) or four β‐Ala dipeptides (3o, 3p: Aa1 = β‐Ala, Aa2 = Val or Leu, R = Z). The dipeptide and tripeptide cavitands 3g−3n, which have a glycine bonded to the resorcarene core, form stable inclusion complexes with acetonitrile in chloroform solution. The free energy of complexation exceeds −5.9 kcal mol−1. The exchange between complexed and free acetonitrile molecules is slow on the NMR spectroscopic time scale (298 K). NMR spectroscopic data suggest that the peptides in the acetonitrile complexes of 3g−3n form a cyclic array of hydrogen bonds at the upper rim involving the glycine CO and NH groups. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Recent Developments in the Ring‐Chain Tautomerism of 1,3‐Heterocycles
Authors: Lázár László , Fülöp Ferenc 
Published: July 2003

AbstractSome important results from the past seven years on the ring‐chain tautomerism of 1,3‐heterocycles are reviewed, including substituent effects on the tautomeric equilibria and synthetic applications of this phenomenon. The structures and reactivities of numerous five‐ and six‐membered, saturated, N‐unsubstituted 1,3‐X,N‐heterocycles (X = O, S, NR) can be characterized by the ring‐chain tautomeric equilibria of the 1,3‐X,N‐heterocycles and the corresponding Schiff bases; this is often exploited advantageously in different areas of organic synthesis, and also in physical, medicinal and peptide chemistry. The selectivity of certain transformations can be explained on the basis of the ring‐chain tautomeric equilibration of the intermediates, followed by a shift in the equilibrium. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of Dihalo‐Substituted Analogues of Tröger’s Base from ortho‐ and meta‐Substituted Anilines
Authors: Hansson Anna , Jensen Jacob , Wendt Ola F. , Wärnmark Kenneth 
Published: July 2003

AbstractFor the first time, ortho‐ and meta‐halo‐substituted anilines were successfully condensed with formaldehyde to dihalo‐substituted analogues of Tröger’s base. By using paraformaldehyde and TFA, yields of 2−85% of these potential supramolecular building blocks were obtained. Even the inconceivable achievement of condensing anilines unsubstituted in para‐position to analogues of Tröger’s base was successful. Adding our present results to our previous, makes it now possible to synthesize analogues of Tröger’s base halo‐substituted in almost any desired position in each of its two aromatic rings. In addition the first X‐ray structure of a dihalo‐substituted analogue of Tröger’s base, 3,9‐dibromo‐4,10‐dimethyl‐6H,12H‐5,11‐methanodibenzo[b,f][1,5]diazocine (17), is presented. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of 2,6‐Disubstituted Piperidine‐Bearing α‐Amino Acid Side‐Chains
Authors: Boeglin Damien , Heitz Annie , Martinez Jean , Fehrentz Jean‐Alain 
Published: July 2003

AbstractA straightforward synthesis of 2,6‐disubstituted piperidines bearing α‐amino acid side‐chains was developed. Synthesis was based on a Horner−Wadsworth−Emmons condensation of a β‐ketophosphonate derived from an α‐amino acid residue with a β‐homologated aldehyde of anN‐protected amino acid residue. The generated α‐β unsaturated ketones were then reduced, deprotected, and cyclized in a hydrogenation/hydrogenolysis one‐pot procedure to yield piperidine moieties. Introduction of a new conformational restriction in the obtained molecules allowed total assignment of the stereocenters by NMR experiments. This assignment allowed us to propose a mechanistic pathway during the cyclization process, explaining the loss of exocyclic carbon‐center configuration. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Efficient Generation of β‐L‐Rhamnosidic Linkages by the 2‐Ulosyl Donor Approach: Synthesis of a Trisaccharide with a Central β‐L‐Rhamnose Unit
Authors: Lichtenthaler Frieder W. , Metz Thomas 
Published: July 2003

AbstractPractical procedures for the production of variously blocked 6‐deoxy‐α‐L‐arabino‐2‐ketohexosyl bromides from L‐rhamnose have been developed. These compounds are highly useful as indirect β‐L‐rhamnosyl donors: they undergo β‐specific glycosidations under Koenigs‐Knorr conditions, and the 2‐keto group of the resulting 6‐deoxy‐β‐L‐hexosiduloses is reduced with high β‐L‐rhamno selectivity. The straightforward application of this 2‐ulosyl donor approach for the synthesis of β‐L‐rhamnose‐containing di‐ and trisaccharides is demonstrated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Sterically Hindered Cyclic Diynes − Syntheses and Structures
Authors: Schaefer Carsten , Gleiter Rolf , Rominger Frank 
Published: July 2003

AbstractThe synthesis of three 14‐membered ring systems 8a−8c with the 1,3,8,10‐tetraoxa‐2,9‐disilacyclotetradeca‐5,12‐diyne skeleton is described. In all three ring systems the α‐positions are substituted with gem‐dimethyl and/or gem‐diphenyl groups. Structural investigations on 8a and 8c reveal a chair like conformation of the central ring with parallel alkyne units. For 8b the voluminous phenyl groups cause a twist‐chair and a twist‐boat conformation. Columnar structures were encountered for 8a in the solid state. Reactions with octacarbonyldicobalt yield for 8a mono‐ and biscomplexation (12, 13). For 8b only the mono complexation product 14 was isolated. For 8c the bis(hexacarbonyldicobalt) complex 15 was obtained. X‐ray investigations revealed columnar structures in the solid state for 12, 13, and 15. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
C‐Glycosidations of a 2‐Ketohexosyl Bromide with Electrophilic, Radical, and Nucleophilic Anomeric Carbons
Authors: Lichtenthaler Frieder W. , Lergenmüller Matthias , Schwidetzky Sabine 
Published: July 2003

AbstractThe susceptibility of acylated 2‐ketohexosyl halides to C‐homologation is demonstrated with the easily accessible tri‐O‐benzoyl‐α‐D‐arabino‐hexos‐ulosyl bromide 1 as the model compound. C‐Glycosidation with an electrophilic anomeric carbon requires prior carbonyl protection, to avoid carbonyl addition by the C‐nucleophile, for example, as the cyanohydrin. Silver triflate‐promoted reaction with the silylenol ether of acetophenone then efficiently yields the β‐phenacyl product. With thermal (AIBN) or photochemical induction, 1 smoothly generates an anomeric radical − comparatively electrophilic, due to its capto‐dative substitution − which exclusively traps hydrogen in the presence of tributyltin and electron‐deficient alkenes. With allyltributylstannanes, however, it reacts with high stereoselectivity to afford α‐C‐allyl glycosiduloses. The α‐bromoketone functionality in ulosyl bromide 1 is susceptible to Reformatsky conditions: treatment with zinc‐copper couple readily generates the 1,2‐enolate, a most simple anomeric nucleophile, which effectively adds to aldehydes to give α‐C‐hydroxyalkyl glycosiduloses or α‐C‐disaccharides (with sugar aldehydes) with a high degree of double stereoselection. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Novel Promising Benzoazacrown Ethers as a Result of Ring Transformation of Benzocrown Ethers: Synthesis, Structure, and Complexation with Ca2+
Authors: Gromov Sergey P. , Dmitrieva Svetlana N. , Vedernikov Artem I. , Kuz’mina Lyudmila G. , Churakov Andrey V. , Strelenko Yuri A. , Howard Judith A. K. 
Published: July 2003

AbstractA series of promising benzoazacrown ethers with the nitrogen atom conjugated with the benzene ring were synthesized using a novel synthetic procedure based on stepwise transformation of the macroheterocycle. The structures and spectral properties of the resulting benzoazacrown ethers and their complexes with Ca2+ were studied by X‐ray diffraction and 1H, 13C, and 15N NMR spectroscopy including the 2D NOESY technique. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A New Versatile Synthesis of Macrotricyclic Tetraazacycloalkane‐Based Ligands from Bis‐aminal Derivatives
Authors: Develay Stéphanie , Tripier Raphaël , Chuburu Françoise , Le Baccon Michel , Handel Henri 
Published: July 2003

AbstractA new powerful synthesis of symmetrical (two‐step) or dissymmetrical (three‐step) macrotricyclic cyclen‐ or cyclam‐based ligands is reported. In this procedure, the starting materials are bis‐aminals derived from condensation of cyclen or cyclam with glyoxal. The two macrocyclic subunits are linked by two aromatic spacers through nitrogen atoms. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Syntheses and Structures of Imidazole Analogues of Lissoclinum Cyclopeptides
Authors: Haberhauer Gebhard , Rominger Frank 
Published: July 2003

AbstractThe syntheses of the cyclic peptides 3−7, which contain imidazole units in their backbones and resemble naturally occurring marine cyclopeptides such as westiellamide and ascidiacyclamide, are described. Structural investigations on the trimer 3 reveal a molecular triangle conformation with all lone pairs of the imidazole nitrogen atoms and the hydrogen atoms of the secondary amides directed to the center of the macrocycle. The structures of the tetramers 4 and 6 display distorted molecular square conformations with the heterocycles (4) and the αCH groups (6) placed at the corners of the rectangle, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of 1‐ and 3‐Nitrobenzo[a]pyrene
Authors: Dyker Gerald , Kadzimirsz Daniel , Thöne Andreas 
Published: July 2003

AbstractThe synthesis of the important carcinogens 1‐nitrobenzo[a]pyrene and 3‐nitrobenzo[a]pyrene was achieved in four steps starting from the parent compound. A hexyl ester functionality was introduced as a removable blocking group, controlling the regioselectivity of the synthesis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of Benzo[a]pyren‐6‐yl‐Substituted Carboxylic Acids
Authors: Dyker Gerald , Kadzimirsz Daniel 
Published: July 2003

AbstractThe title compounds were synthesized from benzo[a]pyrene in three to four steps, depending on the chain length of the carboxylic acid. After iodination, alkanone chains were introduced by special Heck reactions. Transformation into carboxylic acids was achieved by haloform reaction and by Willgerodt−Kindler reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of “Garner” Aldehyde‐Derived Cyclopropylboronic Esters
Authors: Pietruszka Jörg , Witt Andreas , Frey Wolfgang 
Published: July 2003

AbstractThe “Garner” aldehyde has been used as a common intermediate for the preparation of the corresponding alkyne 7 and the alkenylboronic esters 12−16 (24−80%). Diastereoselective cyclopropanation afforded cyclopropylboronic esters 17−20 (60−84%, dr 22:78 to 92:8), the configurations of which were determined by chemical correlation (cyclopropanols 22), X‐ray structural analysis (of 21a), and characteristic NMR spectroscopic data. The protected amino alcohols 23−26 and amino acids 27 have been synthesised from the cyclopropylboronic esters 19 by oxidation, Matteson homologation or Suzuki coupling. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Reactions of a Stable (Phosphanyl)(silyl)carbene with Aliphatic Aldehydes: [2+1] versus [2+2] Addition to a Carbonyl Group
Authors: Illa Ona , Gornitzka Heinz , Branchadell Vicenç , Baceiredo Antoine , Bertrand Guy , Ortuño Rosa M. 
Published: July 2003

AbstractThe reactions between the stable (phosphanyl)(silyl)carbene 1 and different aliphatic aldehydes have been investigated for the first time. Results reveal that two competitive processes take place. The kinetically most favorable one is a concerted [2+1] cycloaddition to carbonyl leading to oxiranes as single diastereomers, with the trans arrangement of the alkyl and phosphoranyl groups, as the major products. Simultaneously, a [2+2]‐like addition provides short‐lived oxaphosphetene intermediates that rapidly evolve to the corresponding olefins with E stereochemistry, which are the thermodynamically most stable compounds. DFT calculations establish the mechanism for both processes and a rationale for the observed diastereoselectivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Self‐Terminating Radical Oxygenations: Probing of the Scope of the Concept by Use of Various Organic O‐Centered Radicals
Authors: Jargstorff Christian , Wille Uta 
Published: July 2003

AbstractAddition of various organic O‐centered radicals XO• {i.e. (alkoxycarbonyl)oxyl radicals, ROC(O)O•, [(alkoxycarbonyl)acyl]oxyl radicals, ROC(O)C(O)O•, (carbamoyl)oxyl radicals, R2NC(O)O•, alkoxyl radicals, RO•, and nitroxyl radicals, R2NO•} to alkynes initiates an oxidative radical cyclization cascade, which is terminated by release of a C‐ or N‐centered radical X•. This finding clearly highlights the generality of the recently discovered concept of self‐terminating radical oxygenations, through which C≡C triple bonds may be converted into carbonyl groups under very mild reaction conditions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Novel Chiral Amide Hosts Derived from Mandelic Acid: A Marked Difference in Inclusion Abilities between Host Stereoisomers
Authors: Tanaka Koichi , Hiratsuka Takaichi , Urbanczyk‐Lipkowska Zofia 
Published: July 2003

AbstractNovel chiral amide host compounds (2−8) have been synthesized from mandelic acid (1). A marked difference between the inclusion properties of analogous isomers such as 5 and 6 was observed. Host compounds 4 and 5 showed a relatively high chiral recognition in the optical resolution of guest compounds by inclusion crystallization. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cover Picture: Sterically Hindered Cyclic Diynes − Syntheses and Structures (Eur. J. Org. Chem. 16/2003)
Authors: Schaefer Carsten , Gleiter Rolf , Rominger Frank 
Published: July 2003

AbstractThe cover picture shows on the left‐hand side a sterically hindered cyclic diyne and its synthesis. The packing of the molecules in the crystal is depicted in the center. Within the crystal weak intermolecular interactions were found that are illustrated on the right‐hand side. For more details on the synthesis of sterically hindered cyclic diynes and their reactivity towards octacarbonyldicobalt as well as the solid‐state structures of the diynes and their products, see the article by R. Gleiter et al. on p. 3051 ff.
ADV measurements of velocity distributions in a gravel‐bed flume
Authors: Ferro Vito 
Published: July 2003

AbstractVelocity measurements carried out by an acoustic doppler velocimeter (ADV) in a rectangular laboratory ﬂume having a gravel bed are presented. The velocity proﬁles are measured in six verticals of the channel cross‐section having an increasing distance (from 4 to 38·5 cm) from the ﬂume wall. The experimental runs are carried out for ﬁve different bed arrangements, characterized by different concentrations of coarser elements, and for the two conditions of small‐ and large‐scale roughness. For both hydraulic conditions, the velocity measurements are ﬁrst used to test the applicability of the Dean proﬁle and of the logarithmic proﬁle corrected by a divergence function proposed in this paper. Then, for each value of the depth sediment ratio h/d84, the non‐dimensional friction factor parameter is calculated by integration of the measured velocity distributions in the different verticals of the cross‐section. Finally a semi‐logarithmic ﬂow resistance equation is empirically deduced. Copyright © 2003 John Wiley & Sons, Ltd.
A casting procedure for reproducing coarse‐grained sedimentary surfaces
Authors: Buffin‐Bélanger Thomas , Reid Ian , Rice Stephen , Chandler Jim H. , Lancaster Jill 
Published: July 2003

AbstractIn the ﬁeld, the measurement of near‐bed hydraulics remains problematic. Greater precision is possible in the laboratory, but, in the case of gravels, it is difﬁcult to create a water‐worked channel‐bed that is realistic enough to replicate faithfully the conditions found in nature. In this paper, a technique to reproduce coarse‐grained sedimentary fabrics of large areal extent is described. It involves moulding natural river‐bed surfaces from which facsimiles are cast. Remarkably realistic casts with dimensions of 1 m by 2 m have been produced and their quality assessed using spatial data derived using automated digital photogrammetry. The casts reproduce the prototype surfaces with errors at millimetre scale (0·5 per cent of the microrelief). The technique has facilitated the introduction of sedimentary surfaces that incorporate natural, complex structures of grains up to cobble size into experimental channels where detailed studies of near‐bed hydraulics can be carried out. Copyright © 2003 John Wiley & Sons, Ltd.
Evolution and inheritance of a rock coast: western Galicia, northwestern Spain
Authors: Blanco Chao R. , Costa Casais M. , Martínez Cortizas A. , Pérez Alberti A. , Trenhaile A. S. 
Published: July 2003

AbstractThere is increasing evidence that shore platforms and other elements of rock coasts may be inherited, at least in part, from interglacial stages when sea level was similar to today's. Most of this evidence, which includes ancient beaches and datable terrestrial deposits, has been obtained from areas of resistant, slowly eroding rock, where the platforms often appear to be much too wide to have developed since the sea reached its present level. It is much more difﬁcult to demonstrate that inheritance has occurred in areas of weaker rock, which generally lack any datable material. The coast of western Galicia in northwestern Spain has shore platforms in igneous and metamorphic rocks that were deeply weathered during the Tertiary. These platforms are closely associated with ancient beaches from the last interglacial stage, and associated periglacial and ﬂuvio‐nival deposits that covered and fossilized most of the Eemian platforms and cliffs during the late middle and late Weichselian glacial stage. The sedimentary processes and the thickness and facies of the sediments were determined by the height, aspect and gradient of the coastal mountains, and their distance from the coast. Radiocarbon dating, sedimentary analysis and platform morphology indicate that the shore platforms of Galicia have been inherited from at least the last interglacial stage. They were fossilized in places beneath thick Weichselian deposits and then exhumed during the Holocene transgression. The abundant evidence for inheritance in Galicia has important implications for other coasts in fairly weak rocks where such evidence is generally lacking. Copyright © 2003 John Wiley & Sons, Ltd.
Stem mechanics, functional anatomy and ecology ofAlnus viridisandAlnus glutinosa
Authors: Brüchert F. , Gallenmüller F. , Bogenrieder A. , Speck T. 
Published: July 2003

AbstractMechanical properties, the internal stem structure and the wood anatomy of stems ofAlnusglutinosafrom the Black Forest and of two populations ofAlnusviridisfrom the Black Forest and from the Swiss Alps are compared as to their ecological significance. The mechanical bending properties are characterised by the parameters “flexural stiffness” (Estruct·Iax) and “structural modulus of elasticity” (Estruct). The structural modulus of elasticity increases significantly for all three populations during the first years of growth and becomes approximately constant in stems being five years old and older. These ontogenetic variations of the bending mechanical properties are affected by changes of the internal stem structure, i.e. by changes of the amount and distribution of plant tissues with different mechanical properties within the cross section, described by the axial second moment of area (Iax) which weights the position of the tissues by their distance to the neutral plane. The contribution of bending‐stiff wood towards the axial second moment of area increases during the first years of growth whereas the contribution of the more bending flexible bark decreases. With further increasing age, i.e. in five years old and older stems, the distribution of tissues remains approximately constant as do the mechanical properties. Comparing the different species or populations, respectively, the interspecific difference betweenA.glutinosaandA.viridisfrom the same regional origin (Black Forest) are much smaller than the intraspecific differences between the twoA.viridispopulations from the Black Forest and from the Alps. Significant differences between the two species from the Black Forest are only found in the structural modulus of elasticity of 5–7 year old stems. In contrary, in most ontogenetic stages significant differences are found in all tested mechanical and anatomical parameters betweenA.viridisfrom the Black Forest andA.viridisfrom the Alps. The differences may be due to the different environmental conditions in high elevated sites in the Alps compared to lower sites in the Black Forest. However, the observed differences may also originate from a genetic differentiation into two different ecotypes inA. viridis.
Cotyledon morphology: an aid in identification of Ipomoea taxa (Convolvulaceae)
Authors: Ogunwenmo K. O. 
Published: July 2003

AbstractMorphometric and qualitative characters of matured cotyledons of 18 taxa of Ipomoea were assessed to determine their value for identification at seedling stage. The characters examined include cotyledon colour, texture, indumentum, basal‐apical notch distance, shape and dimensions. A key for the identification of the taxa based on these characters is presented.
The hairs of Plantago reniformisBeck, section EremopsylliumPilg. (Plantaginaceae)
Authors: Andrzejewska‐Golec E. 
Published: July 2003

AbstractThe paper is a continuation of the investigations on the hairs in representatives of family Plantaginaceae. It regards monotypic section Eremopsyllium Pilg. separated by Pilger from sectio Lamprosantha Decne. According to Rahn and Rønsted it is incorrect. In Plantago reniformis headed hairs typical of the family Plantaginaceae are present. They are plesiomorphic hairs with one celled stalk and head divided vertically into two cells. Headless hairs also are similar to hairs in subgenus Plantago sensu Rahn.
Revision of the subgenus Wichuraea (M.Roemer) Baker of BomareaMirbel (Alstroemeriaceae)
Authors: Hofreiter A. , Tillich H.‐J. 
Published: July 2003

AbstractThe subgenus Wichuraea of Bomarea (Alstroemeriaceae) was last revised by Baker (1888) as part of his revision of the genus Bomarea. Since then the number of validly published names has increased from seven to recently 50, indicating an urgent need for further revision. Extensive field studies in Peru (A. Hofreiter) and depth investigation of herbarium material have led to new insights into the subgenus. As a result a number of Bomarea species formerly placed under Wichuraea are relocated to another subgenus, a large number of names are placed into synonymy and one species, Bomarea vargasii Hofreiter sp. nova, and one subspecies, Bomarea andimarcana subsp. andimarcana Hofreiter comb. nov. und B. andimarcana subsp. densifolia Hofreiter comb. nov., are newly described. A key to the 16 species is given. Field studies revealed that even taxonomically valuable characters can be remarkably variable, even within a single population. This has demonstrably resulted in a high degree of taxa instability in the group. The typical habit and its variability, preferred habitats and the geographical distribution of each species is presented.