bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Radical Cations of 4,5,7,13,15,16‐Hexamethyl‐ and 4,5,7,8,12,13,15,16‐Octamethyl [2.2]paracyclophane
Authors: Gerson Fabian , Lopez Javier , Hopf Henning 
Published: December 2004

Abstract4,5,7,13,15,16‐Hexamethyl‐ (3) and 4,5,7,8,12,13,15,16‐octamethyl[2.2]paracyclophane (4) have been oxidized to their radical cations in solution under relatively mild conditions. Substantial hyperfine splittings in the ESR. spectra of 3⊕. and 4⊕. arise from the methyl protons, whereas those from methylene protons are very small. This result indicates that the ethano bridges, unlike the methyl substituents, are rather ineffective in delocalizing the positive charge in 3⊕. and 4⊕. It is in line with the interpretation proposed previously to rationalize the gas‐phase ionization potentials of multiply bridged [2N]cyclophanes and methyl derivatives of [2.2]paracyclophane. The π‐spin distributions in 3⊕. and 4⊕. are discussed in terms of a simple model in which the singly occupied orbitals are represented as the antibonding combinations of two benzene HOMO's.
Radicaux libres dérivés de sucres. V. Dérivés d'osamines N‐hydroxylées et composés voisins Communication préliminaire
Authors: Tronchet Jean M. J. , Schwarzenbach Dominique , Winter‐Mihaly Eva , Diamantides Charalambos , Likić Ubavka , Galland‐Barrera Griselda , Jorand Chantal , Pullie Kemal Deen , Ojha‐Poncet Joëlle , Rupp Joyce , Moret Gilles , Geoffrey Micjiel 
Published: December 2004

Free sugar radicals. V. Deoxyhydroxylaminosugar derivatives and related compoundsWe describe several synthetic routes to deoxyhydroxylaminosugar derivatives of the type Glyc‐N(OH)‐R where Glyc stands for a sugar moiety linked by any of its C‐atoms except the anomeric one and R for one of the following substituants: H‐atom, acyl, phosphoryl groups, aminoacid or sugar residues.Compounds of the above structure are potentially close analogs, homoisosteres, NOH replacing O, of biochemically important molecules. Under aerobic conditions, solutions of these derivatives contain minute concentrations of the corresponding nitroxide radicals which do not decrease significantly the resolution of the NMR. spectra but render these compounds usable as a new kind of spin labels. Spectroscopic properties (1H‐NMR., 13C‐NMR., ESR.) of some of these compounds are reported.
Stereospezifische Synthese des Cancerostatikums 5′‐Desoxy‐5‐fluor‐uridin (5‐DFUR) und seiner 5′ ‐deuterierten Derivate
Authors: Kiss Joseph , D'Souza Richard , Van Koeveringe Jan A. , Arnold Wolf 
Published: December 2004

Stereospecific Synthesis of the Anticancer Agent 5′‐Deoxy‐5‐fluorouridine and its 5′‐deuteriated Derivatives5′‐Deoxy‐5‐fluorouridine (5′‐DFUR) has been obtained in high yield and purity by Stereospecific condensation of the anomeric 5¨deoxy‐1,2,3‐tri‐ O‐acetyl‐D‐ribofu‐ranose with bis(trimethylsilylated)‐5‐fluorouracil in the presence of trimethylsilyl trifluoromethanesulfonate, and by subsequent cleavage of the acetate protecting groups. A minor by‐product of the synthesis, the α‐anomeric nucleoside is produced by a (β‐α)‐epimerization, a procedure which is catalyzed by trimethylsilyl trifluoromethanesulfonate.The corresponding 5′‐deuteriated, and 5′,5′‐dideuteriated nucleosides have also been synthesized using an analogous way.The synthesis of the sugar components of the latter nucleosides ‐ starting from D‐ribose, D‐xylose and D‐glucose ‐is also described.
Structural Characteristics of the Carboxylic Amide Group
Authors: Chakrabarti Pinakpani , Dunitz Jack D. 
Published: December 2004

AbstractAverage bond distances and bond angles as well as conformational preferences in the φ and ψ torsion angles of carboxylic amides with different substitution patterns have been derived by analyzing data from many crystal structures retrieved from the Cambridge Structural Database (CSD).
Total Synthesis of (±)‐3‐Deoxy‐7,8‐dihydromorphine, (±)‐4‐Methoxy‐N‐methylmorphinan‐6‐one and 2,4‐Dioxygenated (±)‐Congeners
Authors: Hsu Fu‐Lian , Rice Kenner C. , Brossi Arnold 
Published: December 2004

AbstractA total synthesis of racemic 3‐deoxy‐7,8‐dihydromorphine ((±)‐2) and 4‐me‐thoxy‐ALmethylmorphinan‐6‐one ((±)‐3) is described. The key intermediate was 2,4‐dihydroxy‐N‐formylmorphinan‐6‐one (11), obtained from 3,5‐dibenzyloxy‐phenylacetic acid (4) in 41.8% overall yield. Bromination of 11, and treatment with aqueous NaOH‐solution afforded, after N‐deblocking and reductive N‐methylation with concomitant removal of the aromatic bounded Br‐atom, the morphinanone 14. Elimination of the HO–C(2) group in 14 was accomplished by hydrogenolysis of its N‐phenyltetrazolyl ether 15, to give 3‐deoxy‐6,0‐didehydro‐7,8‐dihydromorphine (16). Reduction of 16 with L‐Selectride at low temperature provided (±)‐2 in high yield. The ether 15 directly afforded, under more vigorous reduction conditions, 4‐hydroxy‐N‐methylmorphinan‐6‐one (17). and after O‐methylation of 17, the methyl ether (±)‐3 was obtained. A (1:l)‐mixture of 4‐hydroxy‐2‐methoxy‐N‐methylmor‐phinan‐6‐one (28) and its 2‐hydroxy‐4‐methoxy isomer 30 svere obtained by Grewe‐cyclization of a mono‐methoxylated aromatic precursor similar to that which afforded 11. The 2,4‐dioxygenated N‐methylmorphinan‐6‐ones 29, 31 and 38 were also prepared and characterized.
Optically Active t‐Butyl 2‐(p‐Tolylsulfinyl)propionate and ‐butyrate: Synthesis and Reactivity in Aldol‐type Condensations
Authors: Solladié Guy , Matloubi‐Moghadam Firouz , Luttmann Claude , Mioskowski Charles 
Published: December 2004

AbstractThe syntheses of optically active t‐butyl 2‐(p‐tolylsulfinyl)propionate and ‐butyrate (2a and 2b, respectively) are described, and it is shown that aldol‐type condensation of the corresponding enolates is limited by steric hindrance. Optically active (2a) reacted, however, in high yield with aliphatic aldehydes and lead to 80% of asymmetric induction.
Asymmetrische Micheal‐Additionen. Praktisch vollständigdiastereo‐ und enantioselektive Alkylierungen des Enamins aus Cyclohexanon und Prolinylmethyläther.durch ω‐Nitrostyrole zu u‐2‐(l′‐Aryl‐2′‐nitroäthyl)cyclohexanonen
Authors: Blarer Stefan J. , Schweizer W. Bernd , Seebach Dieter 
Published: December 2004

Asymmetric Michael‐Additions Practically Completely Diastereo‐ and Enantloselective Alkylations of the Enamine from Cyclohexanone and Prolinyl Methyl Ether by ω‐Nitrostyrenes to Giveu2‐(1′‐Aryl‐2′‐nitroethyl)cyclohexanonesWhen the enamine(S)‐N‐(1′cyclohexenyl)‐2‐methoxymethyl‐pyrrolidine is added to 2‐aryl‐l‐nitroethylenes, only one of the four possible enantiomerically pure diastereomers is formed. Hydrolysis of the crude primary products furnishes α‐alkylated cyclohexanones of > 90% e. e. (3,Scheme 3). Their (2S,1′R)‐configuration was deduced by chemical correlation with l‐cyclohexyl‐l‐phenyl‐ethane and from an X‐ray crystal structure analysis of (−)‐(2R,3S,6′R1,l″S′)‐3‐methyl‐N‐[6′‐(2″‐nitro‐l″‐phenylethyl)‐l′‐cyclohexenyl]‐2‐phenylmorpholine (lla,Scheme 5andFig. 2). ‐ The relative topicity of reactant approach with the prolinol derivative (seeII) is specified aslkul‐l,4. The steric course and the mechanism of the reaction are discussed.
Über Pterinchemie. 85. Mitteilung. Polyacetylierte 5,6,7,8‐Tetrahydro‐D‐ und ‐L‐neopterine. Ein besonderer Fall von N(5)‐Alkylierung des 5,6,7,8‐Tetrahydroneopterin‐Gerüstes
Authors: Antoulas Syméon , Prewo Roland , Bieri Jost H. , Viscontini Max 
Published: December 2004

Polyacetylated 5,6,7,8‐Tetrahydro‐D‐ and L‐neopterins. A Special Case of N(5)‐Alkylation of 5,6,7,8‐TetrahydroneopterinsImproved conditions are reported for the preparation of the earlier described (6R)‐ and (6S)‐1′‐O,2′‐O,3′‐O,2‐N,5‐pentaacetyl‐5,6,7,8‐tetrahydro‐L‐neopterins, one of which could be obtained as pure crystals. Its structure, determined by X‐ray‐diffraction analysis, corresponds to the (6R)‐enantiomer. The method has also been used to make the corresponding D‐diastereoisomers. Further acetylation of (6RS)‐1′‐O,2′‐O,3′‐O,2‐N‐tetraacetyl‐5,6,7,8‐tetrahydro‐D‐neopterin under drastic conditions yields a mixture of several polyacetylated D‐neopterin derivatives and a polyacetylated ethyl‐tetrahydro‐D‐neopterin which was isolated in crystalline form and established by X‐ray‐diffraction analysis to be (6R)‐1′‐O,2′‐O,3′‐O,4‐O,2‐N,2‐N,8‐heptaacetyl‐5‐ethyl‐5,6,7,8‐tetrahydro‐D‐neopterin.
The Solid and Solution Conformations of (±)‐Corycavine
Authors: Kamigauchi Miyoko , Iwasa Kinuko , Takao Narao , Ishida Toshimasa , Inoue Masatoshi 
Published: December 2004

AbstractThe crystal structure of corycavine, a protopine‐type alkaloid, has been determined by X‐ray analysis. A conformational feature observed is the existence of a strong electrostade interaction between the N‐ and C‐atom at a distance of 2.618 Å. Such an interaction stabilizes the 10‐membered ring conformation of the structure. Analyses of NMR spectra indicate that corycavine has the same conformation in solution as in the crystal state.
Dimethylformamide‐Exchange Mechanism on Some First‐Row Divalent Transition‐Metal Ions
Authors: Cossy Cédric , Helm Lothar , Merbach André E. 
Published: December 2004

AbstractThe effect of temperature on the dimethylformamide exchange on Mn(DMF) and Fe(DMF) has been studied by 13C‐ and 17O‐NMR, respectively, yielding the following kinetic parameters: k298 equals; (2.2±0.2). 106 S−1, ΔH≠ = 34.6 ± 1.3 kJ mol−1, ΔS≠ = −7.4 ± 4.8 J K−1mol−1 for Mn2+ and K298 = (9.7 ± 0.2).105 S−1, Delta;H≠ = 43.0 ± 0.9 kJ mol−1, ΔS≠ = + 13.8 ± 2.8 J K−1mol−1 for Fe2+. The volumes of activation, ΔV≠ in cm3mol−1, derived from high‐pressure NMR on these metal ions, together with the previously published activation volumes for Co2+ and Ni2+ (+2.4 ± 0.2 (Mn2+), +8.5 ± 0.4 (Fe2+) +9.2 ± 0.3 (Co2+), + 9.1 ± 0.3 (Ni2+)) give evidence for a dissociative activation mode for DMF exchange on these high‐spin first‐row transition‐metal divalent ions. The small positive ΔV≠ value observed for DMF exchange on Mn2+ seems to indicate that a mechanistic changeover also occurs along the series, (probably from Id to D), as for the other solvents previously studied (Ia to Id, for H2O, MeOH, MeCN). This changeover is shifted to the earlier elements of the series, due to more pronounced steric crowding for dimethylformamide hexasolvates.
Inhibition of Electron‐Hole Recombination in Substitutionally Doped Colloidal Semiconductor Crystallites
Authors: Moser Jacques , Grätzel Michael , Gallay Roland 
Published: December 2004

AbstractThe subtitutional doping of 120‐Å‐ sized TiO2Particles with Fe(III)ions has a profound effect on the charge carrier recombination time in this colloidal semiconductor. In undoped particles, the mean lifetime of an electronhole pair isca.30 ± 15 ns. Doping with 0.5% Fe(III) drastically augments the charge‐carrier lifetime which is extended to minutes or hours. The slow character of the recombination dynamics in Fe(III)‐doped colloids was confirmed by laser photolysis using the characteristic optical of electrons in TiO2to monitor the time course of the reaction. EPR studies showed the Fe(III) ions to enter the host lattice on Ti(IV) sites, charge compensation taking place through the formation of oxygen vacancies. Valence‐band holes produced under band‐gap excitation react with these centers it the bulk forming Fe(IV), the conduction band electrons being trapped by Ti(IV) at the particle surface. Presumably, the spatial separation of the trapped electron and hole sites inhibits their recombination.
Synthesis and Formation of Ironcarbonyl Complexes of 3′,3′‐Dimethyl‐2,3,5,6‐tetramethylidenespiro[bicyclo[2.2.1]heptane‐7,2′‐oxirane]. Single‐Crystal and Molecular Structure of syn,exo2,3‐anti,endo5,6‐trans‐μ‐[(1r,2r,3s,4s,5s,6r)‐c,2,3,c‐η:c,5,6,c‐η‐(3′,3′‐dimethyl‐2,3,5,6,‐tetramethylidenespiro[bicyclo[2.2.1]heptane‐7,2′‐oxirane])]bis(tricarbonyliron)
Authors: Rubello Albino , Vogel Pierre , Chapuis Gervais 
Published: December 2004

AbstractThe 3′,3′–dimethyl‐2,3,5,6‐tetramethylidenespiro[bicyclo[2.2.1]heptane‐7,2′‐oxirane] (3) was derived from 6,6‐dimethylfulvene and maleic anhydride. Its reaction with 1 equiv. of ethylenetetracarbonitrile (TCNE) was not regioselective and gave a 1:1 mixture of the corresponding monoadducts 10 and 11. The rate constants of the Diels‐Alder additions of 10 and 11 to TCNE were significantly smaller than that of the reaction 3 + TCNE. Monocomplexation of 3 with Fe2(CO)9 was highly exo‐face selective giving a mixture of the corresponding monocomplexes 12(anti‐exo) and 13(syn‐exo). The latter were complexed with Fe2(CO)9 in a non‐stereoselective fashion, giving mixtures of the dicomplexes 14(anti‐exo, syn‐endo), 15(anti‐exo,syn‐exo), and 16(anti‐endo, syn‐exo). Exchange of the CO ligands was a faster process for the endo‐Fe(CO)3 moieties than for the exo‐Fe(CO)3 moieties. Line‐shape analysis of the 13C‐NMR spectrum of 15 established that one of the exo‐Fe(CO)3 groups in 15 rotates ca. 3 times as fast as the other Fe(CO)3 group at 40°. The structure of the anti‐endo, syn‐exo dicomplex 16 was determined by single‐crystal X‐ray diffraction studies.
A Regioselective Cyclohexannulation Procedure via Dienamine [4 + 2] Cycloaddition. Synthesis of Functionalised Decalins
Authors: Snowden Roger L. , Linder Simon M. , Wüst Manfred 
Published: December 2004

AbstractA regioselective cyclohexannulation procedure, whose key step involves the [4 + 2] cycloaddition of dienamines 12–24 with methyl acrylate, allows the conversion of cycloalkanones 1–11 to bicyclic dienoates 25 – 37. The chemistry of 26 is briefly examined and, in the context of organoleptic studies concerning functionalised 5,5,9‐tri‐methyldecalins, the transformation of 37 to ketones 44 and 46 as well as to acetates 53–56 is described.
Photochemical Reactions 150th Communication. Wavelength Dependence of the Photochemistry of 7‐Methyl‐β‐ionone
Authors: Mathies Peter , Nishio Takehiko , Frei Bruno , Jeger Oskar 
Published: December 2004

AbstractThe wavelength dependence of the photolysis of 7‐methyl‐β‐ionone ((E)‐1) was investigated. Irradiation of (E)‐1 with light of λ > 347 nm leads primarily to (E/Z)‐isomerization followed by transformation to the tricyclic enol ether 3 as the only secondary photoproduct. On photolysis of (E)‐1 with light of shorter wavelength (λ > 280 nm or λ = 254 nm), however, a series of other products was formed (via a) photocyclization of the dienone chromophore (→ 5), (b) photo‐enolization (→8), and (c) a 1,5‐sigmatropic H‐shift (→ (E/Z)‐7). For the structure elucidation of the new products, 7‐[13C]methyl‐β‐ionone ((E)‐[7‐methyl‐13C]‐1) was prepared and irradiated furnishing the corresponding 13C‐labelled photoproducts.
New Spirostaphyiotrichins from the Mutant Strain P 84 of Staphylotrichum coccosporum
Authors: Sandmeier Peter , Tamm Christoph 
Published: December 2004

AbstractFrom a mutant strain of S. coccosporum, the new spirostaphylotrichins E (2), F(3), G (4 or 5), H (5 or 4), I (6), K (7), L (8), M (9), and S (10) have been isolated. Their structures have been elucidated by spectroscopic methods (UV, IR, 1HNMR, 13CNMR, and MS), chemical transformations, and X‐ray analysis (3 and 7).
Bestimmung von Stabilitätskonstanten in Ethanol für Li+‐selektive Ionophore mittels differentieller Dampfdruckosmometrie
Authors: Bliggensdorfer René , Suter Gabriela , Simon Wilhelm 
Published: December 2004

AbstractDetermination of Stability Constants in Ethanol for Li+‐selective Ionophores by Differential Vapour Pressure OsmometryStability constants of some neutral carriers and their bridged isologues in interaction with Li+ and Na+ are determined by a differential vapour pressure osmometry method in ethanol utilizing Bjerrum formation curves. All ionophores studied induce high Li+ selectivity in solvent polymeric membranes.
(Benzo[4, 5]cyclohepta[l, 2‐b]thiophen‐4‐ylidene)acetic Acids: Novel Non‐ulcerogenic Antiinflammatory Agents
Authors: Bollinger Pietro , Cooper Philip , Gubler Hans U. , Leutwiler Albert , Payne Trevor 
Published: December 2004

AbstractCompound (Z)‐8a has been found to display interesting antiinflammatory activity. In order to prepare derivatives with a wide variety of substituents in the aromatic part of the molecule, a new synthesis of the key intermediates 9a‐g was developed starting from thiophene‐3‐carboxylic acid (11) and substituted benzyl bromides. The conversion of 9a‐g to 10a‐g follows a known procedure. Ketones 10a‐g, on reaction with alkyl (dialkoxy‐phosphoryl)acetate, followed by isomer separation and alkaline ester hydrolysis, yielded the desired derivatives (Z)‐8a‐g and (E)‐8a‐g. The biologically most interesting compound (Z)‐8a is currently undergoing clinical trials.
The Reactivity of the Pentacyano(η1‐Dioxygen)cobaltate(III) Ion in Aqueous Solution
Authors: Gubelmann Michel H. , Riittimann Stéphane , Bocquet Bernard , Williams Alan F. 
Published: December 2004

AbstractThe mononuclear η1‐dioxygen complex [Co(CN)5O2]3− (A) decomposes in aqueous solution to the hydroxo‐complex [Co(CN)5OH]3− (B) and the hydroperoxo complex [Co(CN)5CoO2N]3 (C). The mechanism involves partial dissociation of A to give [Co(CN)5]3− (E) which binds with unreacted A to give the η1:η1‐peroxo complex [(CN)5Co02Co(CN)5]6− (F) which is hydrolysed to B and C. The mechanism is supported by the effects of pH, dioxygen concentration, and ionic strength on the rate of decomposition, and by the trapping of oxidation products of E and F. Complex A reacts readily with reducing agents to give directly the hydroperoxo complex C.
Synthesis of Potential Glucosidase‐Inhibitors: D‐Xylopyranoside‐5‐spiro‐l′‐cyclopropanes
Authors: Huber Rolf , Molleyres Louis‐Pierre , Vasella Andrea 
Published: December 2004

AbstractThe synthesis of the D‐xylopyranose‐5‐spiro‐1′‐cyclopropane 5, its methyl α‐D‐glycoside 7 and its benzyl β‐D‐glycoside 13 from D‐glucose is described, and their conformation in solution is discussed. A Königs‐Knorr glycosidation of 10 reveals the ionic intermediate of a 1, 1‐(dibromocyclopropyl)carboxonium ion type to be stable against opening of the cyclopropane ring. Very weak inhibition of saccharase was observed for the α‐D‐configurated methyl glycoside 7, whereas the β‐D‐configurated benzyl glycoside 13 did not inhibit emulsin.
Synthesis of Pyrrolidine Analogues of N‐Acetylneuraminic Acid as Potential Sialidase Inhibitors
Authors: Czollner László , Kuszmann János , Vasella Andrea 
Published: December 2004

AbstractThe pyrrolidine derivatives 3, 4, and 5 were prepared from the methyl ester 7 of Neu2en5Ac via lie pyrrolidine‐borane adduct 33. They inhibit Vibrio cholerae sialidase competitively with Ki = 4. 4 10−3 M, 5. 3 10−3 M, and 4. 0 10−2 M, respectively. Benzylation of 7 gave the fully O‐benzylated 8 besides 9, 10, and 11. Ozonolysis and reduction with NaBH4 of 8 and 9 gave the 1, 4‐diols 12 and 15, the hydroxy acetates 13 and 16, and the furanoses 14 and 17 (Scheme 1), respectively. The diol 12 was selectively protected (→19→20→23) and transformed into the azide 27 by a Mitsunobu reaction. Selective base‐catalysed deprotection of the diacetate 22, obtained from 12, was hampered by an easy acetyl‐group migration. The mesylate 28 proved unstable. The azide 27 was transformed via 29 into the ketone 30 (Scheme 2). Hydrogenation of 30 gave the dihydropyrrole 31 and, hence, the pyrrole 32. The adduct 33 was obtained from 30 by a Staudinger reaction (→31) and reduction with LiBH4/HBF4. It was transformed into the pyrroudine 34. The structure of 34 was established by X‐ray analysis. Reductamination of the pyrrolidine‐borane adduct with glyoxylic acid gave 40 and, hence, 3. N‐Alkylation afforded 44 and, hence, the phosphonate 4. The acid 5 was obtained from 33 by acylation (→47) and deprotection (Scheme 4).
Phosphonic‐Acid Analogues of the N‐Acetyl‐2‐deoxyneiiraniinic Acids: Synthesis and Inhibition of Vibrio cholerae Sialidase
Authors: Wallimann Kurt , Vasella Andrea 
Published: December 2004

AbstractThe phosphonic acids 3 and 4 were prepared to compare their inhibitory activity on Vibrio cholerae sialidase with the one of the corresponding N‐acetyl‐2‐deoxyneuraminic acids 5 and 6. Thus, hydrogenation and benzylation of methyl N‐acetyl‐2,3‐didehydro‐2‐deoxyneuraminate (1MeNeu2en5Ac; 7) gave a mixture of the fully O‐benzylated benzyl and methyl esters 9 and 10, the partially O‐benzylated benzyl and methyl esters 11 and 12, and the fully O‐and N‐benzylated benzyl and methyl esters 13 and 14 (Scheme 1). Transesterification of 9 to 10 and hydrolysis of 10 gave the acid 15. Oxidative decarboxylation of 15 with Pb(OAc)4 gave a 1:9 mixture of the α‐and β‐D‐glycero‐D‐galacto‐acetates 16 and 17. Phosphonoylation of 17 with P(OMe)3 and Me3SiOTf gave a 1.3:1 mixture of the phosphonates 18 and 19, which were deprotected to give the (4‐acetamido‐2,4‐dideoxy‐D‐glycero‐α‐and β‐D‐galacto‐octopyranosyl)phosphonic acids 3 and 4, respectively. The acid 6 was obtained by epimerization of the tert‐butyl ester 23 with lithium N‐cyclohexylisoproylamide and deprotection. The phosphonic acids 3 (Ki 5.5 10‐5 M) and 4 (Ki 2.3.10−4 M) are stronger inhibitors of Vibrio cholerae sialidase than the anomeric N‐acetyl‐2‐deoxyneuraminic acids 5(Ki 2.3 10−3 M) and 6. Both 3 and 4 inhibit the Vibrio cholerae sialidase, while only the carboxylic acid 5, possessing an equatorial COOH group is an inhibitor.
Synthesis of 2‐Acetamido‐2‐deoxy‐D‐gluconhydroximolactone‐ and Chitobionhydroximolactone‐Derived N‐Phenylcarbamates, Potential Inhibitors of β‐N‐Acetylglucosaminidase
Authors: Beer Dieter , Maloisel Jean‐Luc , Rast Dora M. , Vasella Andrea 
Published: December 2004

AbstractThe N‐phenylcarbamate 7, derived from 2‐acetamido‐2‐deoxy‐D‐gluconhydroximo‐1,5‐lactone (3) and the analogous N‐phenylcarbamate 14, derived from chitobionhydroximo‐1,5‐lactone (10) have been prepared as potential inhibitors of β‐N‐acetylglucosaminidases. The unambiguous synthesis of the hydroximo‐1,5‐lactone 3 involves oxidation of the oxime 1, followed by deprotection with Na/NH3.
Carotinoide mit 7‐Oxabicyclo[2.2.1]heptyl‐Endgruppen. Teil I. Versuch einer Synthese von Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)‐3,6:3′,6′‐Diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotin‐5,5′‐diol)
Authors: Gmünder Michael Roman , Eugster Conrad Hans 
Published: December 2004

Carotenoids with 7‐Oxabicyclo[2,2.1]heptyl End Groups. Attempted Synthesis of Cycloviolaxanthin ( = (3S,5R,6S,3′S,5′R,6′R)‐3,6:3′,6′‐ Diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotin‐5,5′‐diol)Starting from our recently described synthon (+)‐24, the enantiomerically pure 3,6:4,5:3′,6′:4′,5′‐tetraepoxy‐4,5,4′,5′‐tetrahydro‐ε,ε‐carotene (34) and its 15,15′‐didehydro analogue 32 were synthesized in eleven and nine steps, respectively (Scheme 4). Chiroptical data show, in contrast to the parent ε,ε‐carotene, a very weak interaction between the chiral centers at C(5), C(5′), C(6), C(6′), and the polyene system. Diisobutylaluminium hydride reduction of 32 lead rather than to the expected 15,15′‐didehydro analogue 35 of Cycloviolaxanthin (8), to the polyenyne 36 (Scheme 5). We explain this reaction by an oxirane rearrangement leading to a cyclopropyl ether followed by a fragmentation to an aldehyd on the one side and an enol ether on the other (Scheme 6). This complex rearrangement includes a shift of the whole polyenyne chain from C(6), C(6′) to C(5), C(5′) of the original molecule.
Sequence‐Specific Spin Labeling of Oligothymidylates by Phosphotriester Chemistry
Authors: Duh Jauh‐Lin , Bobst Albert M. 
Published: December 2004

AbstractOligothymidylates (oligo(dT)'s) with the sequence‐specifically‐incorporated one‐atom‐tethered C(5)‐nitio‐xide‐labeled nucleoside 1 were synthesized by the phosphotriester method. Some modifications of the protocol were required to account for the chemical reactivity of the nitroxide, the stability of which was monitored during the synthesis by electron paramagnetic resonance (EPR) spectroscopy. The EPR specific activity (AEPR) of the FPLC‐purified nitroxide‐labeled oligomers was determined and found to be in agreement with enzymatically prepared spin‐labeled nucleic acids. Annealing the nitroxide‐labeled oligo(dT)'s to (dA)n or oligo(dA) resulted in different EPR‐lineshape changes suggesting a strong coupling of the short‐tethered nitroxide to global macro‐molecular motion.