bluuebunny/crossref_metadata_2025_split huggingface dataset:
Imidazole‐Analogues of 6‐Epicastanospermine and of 3,7a‐Diepialexine
Authors: Frankowski Andrzej , Seliga Czeslawa , Bur Daniel , Streith Jacques 
Published: December 2004

AbstractThe chiral bicyclic imidazol derivatives 7 and 8 were obtained from D‐glucose derivative 9 by a sequence of selective protection/deprotection and intramolecular SN2 reactions. Triols 7 and 8 are analogues of 6‐epica‐stanospermine (4) and of 3,7a‐diepialexine (6), respectively, and are potential glycosidase inhibitors. However, their anti‐HIV activity proved to be only marginal.
Regioselectivity, Stereoselectivity, and Isotopically Sensitive Branching in the Fe(I)‐Mediated Dehydrogenation of Octane‐1,8‐diol in the Gas Phase
Authors: Prüsse Tilmann , Fiedler Andreas , Schwarz Helmut 
Published: December 2004

AbstractRegio‐ and stereospecific labeling experiments are conducted to unravel the mechanistic features of the Fe+‐induced dehydrogenation of octane‐1,8‐diol in the gas phase. With regard to the regioselectivity, ca. 20% of molecular hydrogen originates from the C(3)/C(4) or the equivalent C(5)/C(6) positions. The remaining 80% are, provided by the C(4)/C(5) methylene units. The steps, preceding the reductive elimination of hydrogen, are irreversible, and the overall reaction follows a 1,2‐elimination mode. The loss of HD from C(3)/C(4) is associated with a kinetic isotope effect K/KHD = 1.68. Formation of D2 from the positions C(4)/C(5) has an isotope effect of K/K = 4.7; this figure is slightly dependent on the configuration at C(4)/C(5). Most interesting is the finding that the configuration at C(4)/C(5) in [4,5‐D2]octane‐1,8‐diol, i.e. 5c vs. 5d, plays a pivotal role in the dehydrogenation of the central C(4)/C(5) part. This unexpected and unprecedented result is explained in terms of conformational analysis. A staggered‐like conformation serves as a precursor to generate a trans‐fused bicyclic intermediate 6. It is this very intermediate from which most of the molecular hydrogen is eliminated. Of minor importance is the as‐fused chelate 7, which is formed from an eclipsed‐like conformation of the octane‐1,8‐diol/Fe+ complex. The contribution of 6 and 7 to the product formation is controlled by the relative configuration at the labeled positions C(4)/C(5). For the D,L‐form 5c, we estimate a ratio of ca. 9:1 for the contribution of 6 vs. 7; due to an isotope effect, this ratio drops to 1:85:1 for the meso‐form 5d. This finding constitutes the first example for the existence of isotopically sensitive branching (‘metabolic switching’) in gas‐phase organometallic chemistry.
CC Bond Formation via Carbon‐Centered Radicals Generated from Dicarbonyl(η5‐cyclopentadienyl) organoiron Complexes
Authors: Giese Bernd , Thoma Gebhard 
Published: December 2004

AbstractIrradiation of benzyldicarbonyl(η5‐cyclopentadienyl)iron complex (2) leads to hemolytic cleavage of the FeC bond. In the presence of activated alkenes, radical addition occurs and both saturated and unsaturated addition products 7–9 are formed. Photolysis of alkyliron complexes 2,3 and 20 in the presence of acrylonitrile leads to the same products as the irradiation of the respective acyliron complexes 28–30. This indicates that, under photolytical conditions, alkyl and acyl complexes are in equilibrium with each other.
Glycosylidene Carbenes. Part 4. Synthesis of Spirocyclopropanes from Acetamidoglycosylidene‐Derived Diazirines
Authors: Vasella Andrea , Witzig Christian , Husi René 
Published: December 2004

AbstractThe synthesis of the first glycosylidene‐derived 2‐acetamido‐2‐deoxydiazirine 4 from N‐acetylglucosamine 6 is described. Thus, 6 was transformed into the 3‐O‐mesylglucopyranoside 9 by glycosidation with allyl alcohol, benzylidenation, and mesylation (Scheme 2). Solvolysis of 9 gave the allopyranoside 10 which, upon benzylation and glycoside cleavage, yielded the hemiacetals 12. Using our established method (via the lactone oxime 14 and the diaziridines 16), 12 gave the diazirine 4. Thermolysis of this diazirine in the presence of i‐PrOH gave the dihydro‐1,3‐oxazole 5 (Scheme 1); in the presence of acrylonitrile, the four diastereoisomeric spirocyclopropanes 17–20 and the acetamidoallal 21 were obtained and separated by prep. HPLC (Scheme 3). Assignment of the configuration of 17–20 is based on NOE measurements and on the effect of diamagnetic anisotropy of the CN group. The ratio of the four cyclopropanes, which is in keeping with earlier results, is rationalized.
From 1‐(Silyloxy)Butadiene to 4‐Amino‐4‐Deoxy‐DL‐Erythrose and to 1‐Amino‐1‐Deoxy‐DL‐Erythritol Derivatives via Hetero‐Diels‐Alder Reactions with Acylnitroso Dienophiles
Authors: Defoin Albert , Pires Joaquim , Streith Jacques 
Published: December 2004

AbstractAcylnitroso dienophiles 4 reacted instantly with 1‐(silyloxy)butadiene 5α and led in good yield to the regioisomeric cycloadducts 6 (major) and 7 (minor; Scheme 2, Table 1). cis‐Hydroxylation of these primary cycloadducts with OsO4 (catalyst) occurred stereospecifically and in high yield (→8 and 9, resp.; Scheme 2). It was followed by reductive ring cleavage to give either 1‐amino‐1‐deoxy‐DL‐erythritol or 4‐amino‐4‐deoxy‐DL‐erythrose derivatives 10 and 14, respectively, depending on the nature of the reducing agent (Schemes 3 and 4).
2′‐Deoxyisoguanosine and Base‐Modified Analogues: Chemical and Photochemical Synthesis
Authors: Kazimierczuk Zygmunt , Mertens Ralf , Kawczynski Wieslaw , Seela Frank 
Published: December 2004

AbstractThe synthesis of 2′‐deoxyisoguanosine (2), and the pyrrolo[2,3‐d]pyrimidine and pyrazolo[3,4‐d]pyrimidine 2′‐deoxyribonucleosides 3 and 4 is described. Condensation of the imidazole precursor 5 with benzoyl isocyanate followed by reaction with ammonia gave 2. Its N(7) regioisomer was obtained from 6. Compound 2 was also prepared by the photochemically induced conversion of 2‐Chloro‐ and 2‐bromopurine 2′‐deoxyribofuranosides 9a and 10, respectively, in aqueous solution, The photo reaction was further used for the synthesis of the compounds 3 and 4 starting with the amino‐chloro‐2′‐deoxynucleosides 9b and 9c, respectively.
New Alkoxypyridine‐sulfonamides: Synthesis, Biological Evaluation, and Physicochemical Properties
Authors: Liegéois Jean‐François , Dive Georges , Dupont Léon , Delarge Jacques 
Published: December 2004

AbstractAs a further phanmacomodulation of benzamide derivatives, two structural modifications were introduced by synthesizing pyridinesulfonamides 5 and 6 (Scheme). The pharmacological profile of substituted benzamides such as metoclopramide (2) is not retained in the pyridine‐sulfonarm'des 6: the latter have very low toxicity but do not exhibit any affinity for D2 and 5‐HT2 receptors, and gastrointestinal prokinetic activity is weak (Table 3), Lipophilicity does not seem to be a determining factor for this lack of activity. A conformational analysis shows that the sulfonamide group in 6 is rather unfavorable for an intramolecular H‐bond formation when compared to the carboxamide group of, e.g., 2. Nevertheless, the interaction remains possible and leads to a stable conformation (Fig. 1, Table 5.) Moreover, the sp3 character of the sulfonamide N‐atom of 6 modifies the relative spatial orientation of one substituent in relation to each of the others. This feature seems to be more important for the observed very low activity than the H‐bond formation itself.
A Novel Synthesis of tert‐ Alkyl Sulfides
Authors: Katritzky Alan R. , Perumal Subbu , Kuzmierkiewicz Wojciech , Lue Ping , Greenhill John V. 
Published: December 2004

Abstracttert‐ Alkyl sulfides are conveniently prepared from α‐(1H‐benzotriazol‐1‐yl)alkyl sulfides by displacement of the 1H‐benzotriazol‐1‐yl group with Grignard reagents. The 1‐[α‐(alkylthio)alkyl]‐ and 1‐[α‐(arylthio)alkyl]‐1H‐benzotriazole intermediates are easily available by several routes: (i) displacement of the halogen from appropriate halides by sodium salts of thiols, (ii) condensation of 1H‐benzotriazole and thiols with carbonyl compounds, or (iii) lithiation of N‐substituted 1H‐benzotriazoles and subsequent treatment with electrophiles.
Photocycloaddition of Quinoxaline‐2(1H)‐thiones to Alkenes
Authors: Nishio Takehiko 
Published: December 2004

AbstractA synthetically useful CC bond formation involving the photochemical addition of quinoxaline‐2(1H)‐thiones to alkenes is described. Irradiation of the quinoxaline‐2(1H)‐thiones 1–4 in the presence of the alkenes 7 gave the 2‐(2′‐mercaptoalkyl)quinoxalines 8–11 in moderate‐to‐good yields via ring cleavage of an intermediate aminothietane with aromatization of the quinoxaline ring. The latter was formed by [2+2] photocycloaddition of the CS bond of the quinoxaline‐2(1H)‐thione and the CC bond of the alkene.
Regioselective Transformations of 2′,3′‐Seconucleosides into Anhydro Structures and Chiral Crown Ethers
Authors: Škarić Vinko , Čaplar Vesna , Škarić Đurđica , Žinić Mladen 
Published: December 2004

AbstractIntramolecular cyclisation of properly protected and activated derivatives of 2′,3′‐secouridine ( = 1‐{2‐hydroxy‐1‐[2‐hydroxy‐1‐(hydroxymethyl)ethoxy]‐ethyl}uracil; 1) provided access to the 2,2′‐, 2,3′‐, 2,5′‐, 2′,5′‐, 3′,5′‐, and 2′,3′‐anhydro‐2′,3′‐secouridines 5, 16, 17, 26, 28, and 31, respectively (Schemes 1–3). Reaction of 2′,5′‐anhydro‐3′‐O‐(methylsulfonyl)‐ (25) and 2′,3′‐anhydro‐5′‐O‐(methylsulfonyl)‐2′,3′‐secouridine (32) with CH2CI2 in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene generated the N(3)‐methylene‐bridged bis‐uridine structure 37 and 36, respectively (Scheme 3). Novel chiral 18‐crown‐6 ethers 40 and 44, containing a hydroxymethyl and a uracil‐1‐yl or adenin‐9‐yl as the pendant groups in a 1,3‐cis relationship, were synthesized from 5′‐O‐(triphenylmethyl)‐2′,3′‐secouridine (2) and 5′‐O,N6‐bis(triphenylmethyl)‐2′,3′‐secoadenosine (41) on reaction with 3,6,9‐trioxaundecane‐1,11‐diyl bis(4‐toluenesulfonate) and detritylation of the thus obtained (triphenylmethoxy) methylcompound 39 and 43, respectively (Scheme 4).
Cyclization of Hydroxyenol Ethers into Spiroacetals. Evidence for the position of the transition state and its implication on the stereoelectronic effects in acetal formation
Authors: Pothier Normand , Goldstein Solo , Deslongchamps Pierre 
Published: December 2004

AbstractAcid‐catalyzed cyclizations under thermodynamically and kinetically controlled conditions of the hydroxyenol ethers 18–21 are reported. Thermodynamically controlled cyclizations of 18, 19 and 21 produced only the more stable corresponding spiroacetals 22 and 27. Thermodynamically controlled cyclization of compound 20 produced a 1:1 mixture of non‐epimerisable spiroacetals 24 and 26. On the other hand, kinetically controlled cyclizations of the same four hydroxyenol ethers produced, along with the more stable spiroacetals mentioned above, the less stable spiroacetals 23, 25, and 28. These results show that the kinetically controlled cyclization takes place via an early transition state which produces a mixture of the less stable and the more stable isomers. These results are explained by an early transition state taking into account the principle of stereoelectronic control while following the antiperiplanar lone‐pair hypothesis (Bürgi‐Dunitz angle of attack of a nucleophile on a π system).
Channel‐Type Molecular Structures. Part 2. Synthesis of Bouquet‐Shaped Molecules Based on a β‐Cyclodextrin Core
Authors: Canceill Josette , Jullien Ludovic , Lacombe Liliane , Lehn Jean‐Marie 
Published: December 2004

AbstractA new series of channel‐type molecules presenting the features of potential transmembrane structures is described. They result from the grafting of amphiphilic side chains on a β‐cyclodextrin derivative 3 that constitutes the organizing core. They belong to the ‘bouquet’ family (B). Compounds bearing poly(oxyethylene) side chains, B16 and 17, and their polymethylene analogues B18 and 19, were synthesized. The properties investigated emphasize the suitability of such molecules to be incorporated into lipid bilayer membranes.
Tritium Labelling of Cyprodime ( = (—)‐17‐(Cyclopropylmethyl)‐4,14‐dimethoxymorphinan‐6‐one), a μ Receptor‐Selective Opioid Antagonist
Authors: Ötvös Ferenc , Tóth Géza , Schmidhammer Helmut 
Published: December 2004

AbstractThe preparation of [1‐3H]cyprodime (2), which has a specific activity of 31.6 Ci/mmol was carried out by catalytic tritiodehalogenation of 1‐bromocyprodime (3). Bromination of cyprodime was performed by using chloroperoxidase, KBr, and H2O2.
Highly Selective Benzylic CH Bond Activation of Toluene 1 by ‘Bare’ FeO+ in the Gas Phase. Short communication
Authors: Schröder Detlef , Florencio Helena , Zummack Waltraud , Schwarz Helmut 
Published: December 2004

AbstractThe reaction of FeO+ with toluene in the gas phase occurs at collision rate (kr = 1.36 × 10−9 cm3 molecule−1 s−1), and labeling experiments demonstrate that the total products due to CH bond activation involve to > 92% the benzylic position. In the ‘hydride’ abstraction process (formation of FeOH and C7H), the H‐atom originates elusively from the benzylic position to generate a benzyl cation, and an intramolecular kinetic isotope effect kH/kD = 1.75 has been obtained. There is no evidence for the existence of isotopically sensitive branching (‘metabolic switching’) in the system studied.
Magnetic Circular Dichroism and Electronic Spectra of Tropothione
Authors: Higashi Miwako , Yamaguchi Hiroyuki , Machiguchi Takahisa , Hasegawa Toshio , Baumann Harold 
Published: December 2004

AbstractThe magnetic circular dichroism (MCD) and electronic absorption spectra of tropothione have been measured. The circular‐dichroism (CD) spectrum of the β‐cyclodextrin complex with tropothione is also reported. The absorption bands of tropothione are assigned.
8‐Azaadenine 2′,3′‐Dideoxyribonucleosides: Synthesis via 1,2,3‐ triazolo[4,5‐d]pyrimidinyl anions
Authors: Seela Frank , Mersmann Karin 
Published: December 2004

AbstractThe 8‐azaadenine 2′,3′‐dideoxyribonucleosides 1–3 were synthesized via glycosylation of the 7‐methoxy‐ or 7‐amino‐3H‐1,2,3‐triazolo[4,5‐d]pyrimidinyl anion with 5‐O‐[(tert‐butyl)dimethylsilyl]‐2,3‐dideoxy‐D‐ glycero‐pentofuranosyl choride (6). As 6 was an anomeric mixture, anomeric glycosylation products were formed. Moreover, three regioisomers (N1, N2, and N3) were obtained in the case of the methoxy compound, but only two (N1 and N2) using 8‐azaadenine. They were characterized by 13C‐NMR and CD spectra. The N‐glycosylic bond of 8‐aza‐2′,3′‐dideoxyadenosine (1) was ca. 10 times more stable against acid than that of 2′,3′‐dideoxyadenosine. Compound 1 was deaminated by adenosine deaminase and showed inhibitory activity on HIV reverse transcriptase in form of its O‐5′‐triphosphate.
Glycosylidene Carbenes. Part 9. Regioselective glycosidation of diols and triols: Intra‐ and intermolecular hydrogen bonds
Authors: Uhlmann Peter , Vasella Andrea 
Published: December 2004

AbstractGlycosidation of the myo‐inositol derivatives 2 and 3 by the diazirine 1 yields 90% of a diastereoisomer pair of β‐D‐glycosides in a 1:1 ratio, i.e. 5/6 and 7/8, respectively (Scheme 1). The crystal structure of 3 shows a strong intramolecular H‐bond, which persists in solution, as indicated by FT‐IR and 1H‐NMR spectra. Yields and diastereoselectivity are lower for the glycosidation of 24 by 1 (Scheme 3). The resulting 1,2‐ and 1,4‐linked disaccharides 25–28 were isolated as their acetates 29–32. The previously determined crystal structure of 24 shows no intramolecular H‐bonds. The yield of the glycosidation of 24, but not of 3, depends upon the concentration, indicating that activation of 24 by intermolecular H‐bonds is required. Glycosidation of 2 and 3 with the trichloroacetimidate 14 gave mixtures of four (5,6,15, and 16), and six (7,8, and 17–20) disaccharides, respectively (Scheme 2).
Pyrazolo[3,4‐d]pyrimidine 2′ ‐Deoxy‐ and 2′,3′ ‐Dideoxyribonucleosides: Studies on the glycosylation of 4‐methoxypyrazolo[3,4‐d]pyrimidine
Authors: Seela Frank , Winter Holger , Möller Marianne 
Published: December 2004

AbstractThe glycosylation of the 4‐methoxypyrazolo[3,4‐d]pyrimidine (5) anion with 1‐halo‐2‐deoxyribose 6 in MeCN/TDA‐1 gives N2‐deoxynucleoside 9 (29%) together with N1‐isomer 7 (48%) and its anomer 8 (6%) [7]. The α‐D‐anomer 8 is not formed and the yield of the ß‐D‐anomer 7 increased to 62% when dimethoyethane is used as solvent and [18]crown‐6 as catalyst. Employing 1‐halo‐2,3‐dideoxyribose 10 instead of halogenose 6, the 2′,3′ ‐didexoynucleosides 12 and 14 were formed which desilylated (→ 1b and 2b) and converted into the ddI and ddA derivatives 3b (c7z8Idd), 15b (c7z8Add), and 17 (c7z8A′dd). Contrary to 7‐deazapurine nucleotides, the triphosphates of 3b and 15b showed on appreciable activity against HIV‐reverse transcriptase.
On the Novel Free Porphyrins Corallistin B, C, D, and E: Isolation from the demosponge Corallistes sp. of the Coral Sea and Reactivity of Their Nickel 55 (II) Complexes toward Formylating Reagents
Authors: D'Ambrosio Michele , Guerriero Antonio , Pietra Francesco , Debitus Cécile , Ribes Olivier 
Published: December 2004

AbstractReported here are the novel free porphyrins corallistin B, C, D, and E, isolated as methyl esters 2a, 3a, 4a, and 5a, respectively, from the sponge Corallistes sp. (Lithistida) collected at the basis of the south New Caledonian coral reef. A protocol is also established for formylation of their NiII complexes, which show a different reactivity pattern toward DMF/POCl3 from metal complexes of deuteroporphyrins. Together with corallistin A, Previously isolated as the methyl ester 1a, and the known deuteroporphyrin IX (isolated as 6a) also present in the sponge, the new corallistins, which may be thought to derive from protoporphyrin via heme, account for an amazing 60% of the EtOh extract from the sponge.
Die massenspektrometrische Wasserabspaltung aus makrocyclischen Amino‐ketonen
Authors: Benz Herbert , Hesse Manfred 
Published: December 2004

The Mass Spectral Loss of Water from Macrocyclic Amino‐ketonesMacrocyclic oxo‐lactams containing an N‐alkylamino side chain are stable natural products. Their electron‐impact mass spectra are characterized by intensive [M − H2O]+ signals, the molecular ion signal itself is missing. Under electrospray ionization conditions, on the other hand, the [M + 1]+ ion is the only detected signal. The loss of water is explained in terms of an internal (thermal) Schiff‐base formation, leading to a e.g. bicyclo[11.9.4]‐system. The alcohol corresponding to the macrocyclic ketones and/or lactams show an expected mass‐spectral behavior following well known rules.
Zur Herstellung von PQQ in kg‐Mengen
Authors: Martin Pierre , Steiner Eginhard , Auer Kurt , Winkler Tammo 
Published: December 2004

Preparation of PQQ in the kag ScaleThe improvement of the PQQ synthesis according to the method of Corey and Tramontano allows the preparation of the triester of this cofactor in the kg scale with an overall yield of 13% (average 78% per step), without a bottleneck in the sequence and with crystalline, analytically pure intermediates. The new purification of free PQQ from conc. H2SO4 is remarkable with respect to the application as well as to the stability of this natural product.
Das Diazo‐chinon von PQQ als mögliches Reagenz für die Kartierung von Chinoproteinen mittels Photoaffinitätsmarkierung
Authors: Martin Pierre , Winkler Tammo 
Published: December 2004

The Diazo‐quinone of PQQ as a Possible Reagent for Mapping Quinoproteins by Photo‐affinity LabelingPQQ is an organic redox cofactor found in a class of enzymes called quinoproteins. The synthesis and the photochemistry of the diazo‐quinones of PQQ and PQQ‐triester are described. The photogenerated Wolff‐rear‐rangement products have been caught with water and methanol as model nucleophiles. The products show a strong fluorescence. The diazoquinone of PQQ may be considered as possible reagent for mapping quinoproteins by photo‐affinity labeling.
Dehydroalanine‐Containing Peptides by AcOH‐Elimination from O‐Acetylserine Residuces with DBU/LiClO4 in Tetrahydrofuran
Authors: Sommerfeld Thimo L. , Seebach Dieter 
Published: December 2004

AbstractThe elimination of H2O from serine residues in peptides was found to be feasible by the following two steps: O‐acylation with AcCl/pyrideine in CH2Cl2 and treatment with an imidine base (DBU or DBN) in THF in the presence of large amounts of LiClO4 (10 examples). Other Li salts such as LiBr and LiCl can also be used. No epimerization of the amino acid residues in te peptide could be detected under these conditions. Thus, a simple method for the preparation of peptides with dehydroalanine residues in high yield, directly from serine‐containing precursors, is available.
Preparation and ESR‐Spectroscopical Investigation of Remarkably Persistent Oxoisobenzofuranyl Radicals
Authors: Kruppa Gary , Hug Paul , Liégard André , Rist Guenther , Nesvadba Petr 
Published: December 2004

AbstractThe synthesis of the diastereoisomeric 1,1′‐diaryl‐1,1′‐bi(isobenzofuran)‐3,3′(1H,1′H)‐diones 3a–d starting from the readily available 2‐aroylbenzoic acids 1a–d is described (Scheme 1). Of the colourless dimers 3a–d, only the sterically congested 3a and 3b dissociate at ambient temperature in solution to the deep red free 3‐oxoisobenzofuran‐1‐yl radicals 4a and 4b, respectively. The radicals 4a, b are extremely persistent in the absence of O2. The structures of these radicals are confirmed and the coupling constants assigned by ESR and ENDOR spectroscopy and computer simulation of their ESR spectra. The dissociation equilibrium constant at 20° in toluene for 3a is determined to be 1.18 · 10−5 M. By studying the steady‐state radical concentration as a function of temperature, the enthalpy and entropy changes for the homolytic dissociation of 3a are determined.
Conformational Analysis of Open‐Chain 1,2:3,4‐Diepoxides: Comparison of crystal structures, NMR data, and molecular‐orbital calculations
Authors: Bur Daniel , Nikles Martin , Séquin Urs , Neuburger Markus , Zehnder Margareta 
Published: December 2004

AbstractSeveral pairs of diastereoisomeric open‐chain 1,2:3,4‐diepoxides with different substitution patterns were prepared (see 3–9). As far as possible, crystal structures were determined to corroborate the relative configurations and to give insight into the solid‐state conformations of these compounds. The comparison with our earlier molecular‐orbital calculations and with 1H‐NMR measurements shows that the solid‐state conformations of eight out of the nine open‐chain 1,2:3,4‐diepoxides, whose crystal structures had been determined, correspond to minima on the calculated energy profiles for these compounds or for closely related derivatives. In solution, highly substituted diepoxides of the erythro‐series (e‐6, e‐7, e‐9) seem to prefer the same conformation as in the crystal. The solution conformations of all other diepoxides differ from the arrangement in the solid state.