bluuebunny/crossref_metadata_2025 huggingface dataset:
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 compounds

We 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 Derivatives

5′‐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

Average 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

A 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

The 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)cyclohexanones

When 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‐Tetrahydroneopterins

Improved 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

The 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

The 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

The 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

The 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

A 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

The 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

From 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

Determination of Stability Constants in Ethanol for Li+‐selective Ionophores by Differential Vapour Pressure Osmometry

Stability 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

Compound (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

The 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

The 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

The 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

The 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

The 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

Oligothymidylates (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.
Mammalian alkaloids: Synthesis and O‐methylation of (S)‐ and (R)‐3′‐hydroxycoclaurine and their N‐methylated analogues with S‐adenosyl‐L‐[methyl‐14C]methionine in presence of mammalian catechol O‐methyltransferase
Authors: He Xiao‐Shu , Tadić Dragana , Brzostowska Malgorzata , Brossi Arnold , Bell Maureen , Creveling Cyrus
Published: December 2004

O‐Methylation of the optically active 3′‐hydroxycoclaurines 3a and 3b and of the N‐methylated analogs 5a,b with S‐adenosyl‐L‐[methyl‐14C]methionine in presence of mammalian COMT was investigated in vitro. The N‐unsubstituted (1S)‐ and (1R )‐isomers 3a and 3b, respectively, afforded almost equal amounts of the corresponding N‐norreticuline 4 and N‐nororientaline 19, besides two unknown by‐products (see Fig. and Table 1). The N‐methylated (1S)‐isoquinoline 5a, on the other hand, afforded largely (S)‐orientaline ((S)‐19), while an almost equal mixture of (R)‐reticuline (6b) and (R)‐orientaline ((R)‐19) was obtained from the (1R)‐enantiomer 5b. The isoquinolines 3a,b and 5a,b were prepared by a Bischler‐Napieralski cyclization yielding O‐benzyl‐protected isoquinoline 10 (Scheme 1). The optical resolution of 10 was accomplished with 2′‐bromotartranilic acid. The N‐methylated isoquinolines were prepared by N‐formylation of 10a,b and reduction of the formamides 13a,b with diborane (→ 14a,b). Deblocking of the benzyl‐ether moieties of 10a,b and 14a,b was accomplished by catalytic hydrogenation in presence of HCl, affording directly 3a,b·HCl and 5a,b·HCl, respectively.
Der ‘Push‐Pull’‐Effekt von ‘Push‐Pull’‐Oligoacetylenen. Eine 13C‐NMR‐Untersuchung
Authors: Neuenschwander Markus , Bartlome Andreas
Published: December 2004

The ‘Push‐Poll’ Effect of ‘Push‐Pull’ Oligoacetylenes. A 13C‐NMR Investigation

According to 13C‐chemicaI shifts of ‘push‐pull’ oligoacetylenes 1–4, the ‘push‐pull’ effect (i.e. π delocalization induced by ‘push‐pull’ substituents) rapidly decays in this series. To correct for other than π ‐charge‐density effects, Δδ values of symmetrically placed C‐atoms of the oligoacetylene chain are discussed. Stereoelectronic resteffects (SER) of the substituents on terminal C‐atoms of PP‐ketones 1a–3a and PP‐esters 1b–4b are estimated from the residual Δδ of the asymptotes of Fig. 3. Fig. 4 convincingly shows that Δδ values are dramatically decreasing with increasing number n of acetylene units between the push and pull substituents. Assignment problems of ‘push‐pull’ triacetylenes 3 have been solved by 13C labelling of the CO group of 3a.
Approaches to the synthesis of cytochalasans. Part 10. Cuprates as reagents for the formation of CC bonds
Authors: Matthes Michael , Tamm Christoph
Published: December 2004

Based upon our novel concept for the total synthesis of cytochalasans, the model lactams 2–9 were treated with Bu2Cu(CN)Li2. The results of these conversions vary much from those obtained with Ph2Cu(CN)Li2, demonstrating the uncertainty of predictions in cuprate chemistry. The bicyclic compound 20 was prepared in good yield. However, all attempts to convert p‐toluenesulfonate 20 into the Ph‐substituted derivative 21, an intermediate for the synthesis of cyiochulusm B(1), have failed so far.
Crystal Structure and ESR Study of a Bimetallic Copper/Iron Crown Ether Inclusion Complex
Authors: Chetcuti Peter A. , Liégard André , Rihs Grety , Rist Günther , Schweiger Arthur
Published: December 2004

Bimetallic inclusion complexes have been synthesized by a secondary coordination interaction between the guest complex [Fe(η5‐C5H5)(CO)2(NH3)][PF6] and copper(II) complex 1a or nickel(II) complex lb containing crown‐ether hosts. The X‐ray crystal‐structure analysis established that the Cu,Fe inclusion complex 2 crystallize as a centrosymmetric dimer with a CuCu separation of 3.73 Å and a novel out‐of‐plane CuN interaction. The magnetic parameters for 2 were obtained by ESR and ENDOR spectroscopy. ESR susceptibility measurements down to 6 K exclude the presence of any antiferromagnetic coupling interaction between the CuIIcenters of the dimer.
Heterocyclen aus Bis(alkoxycarbonyl)keten‐ethylen‐acetalen ( = Dialkyl‐2‐(1,3‐dioxolan‐2‐yliden)propan‐1,3‐dioate). Synthese und Eigenschaften einer neuen Klasse von Pyrazolium‐Betainen
Authors: Neidlein Richard , Schröder Günter , Krieger Claus , Kikelj Danijel
Published: December 2004

Heterocycles Starting from Bis(alkoxycarbonyl)ketene Ethylene Acetals ( = Dialkyl 2‐(1,3‐Dioxolan‐2‐ylidene)propane‐1,3‐dioate). Synthesis and Properties of a New Class of Pyrazolium Betaines

The readily available bis(alkoxycarbonyl)ketene ethylene acetals 1 react with bifunctional nucleophiles to give heterocycles 2–5 (Scheme 1). Their reactions with N,N‐dialkylhydrazines lead to the pyrazolium betaines 7a–f (Scheme 4). Cyclic N,N‐dialkylhydrazines give spiro compounds 7d–f. The reaction of thioketene acetal 12 and of the derivative 15 of methanetricarboxylic acid with N,N‐dimethylhydrazine results in the formation of 3‐(methylthio)‐ and 3‐methoxypyrazolium betaine 7g and 7h, respectively (Scheme 4). The chemical reactivity of the synthesized pyrazolium betaines 7 was tested. The structure of the 3‐(methylthio) derivative 7g was determined by X‐ray analysis.
The Diels‐Alder Chemoselectivity of 3,4,6,7‐Tetramethylidenebicyclo[3.2.1]octane‐2‐exo, 8‐syn‐diyl Derivatives
Authors: Claret François , Razaname Alain , Vogel Pierre
Published: December 2004

Strong dienophiles prefer to add onto the diene moiety attached at C(2),C(3) of 2,3,6,7‐tetramethylidenebicyclo[3.2.1]octane ((±)‐1; see Scheme 1), whereas in the case of 3,4,6,7‐tetramethylidenebicyclo[3.2.1]octane‐2‐exo,8‐syn‐diyl derivatives, the diene moiety at C(6),C(7) reacts faster than that at C(3),C(4), as long the bulk of the 8‐syn‐substituent is large enough (see Schemes 2 and 3).
Photolytic Reactions of (o‐Allylbenzyl)dicarbonyl(η5‐cyclopentadienyl)iron
Authors: Thoma Gebhard , Giese Bernd
Published: December 2004

Photolysis of (o‐allylbenzyl)dicarbonyl(η5‐cyclopentadienyl)iron (4) at 20° in CH2Cl2 leads to carbon‐monoxide loss followed by intramolecular complexation to [η2‐(o‐allylbenzyl)]carbonyl(η5‐cyclopentadienyl)iron (13). At 50° in C6D6, a photochemical rearrangement proceeds forming carbonyl (η5‐cyclopentadienyl){η3‐[3‐(2‐methylphenyl)allyl]}iron (17). Depending on the temperature, photolysis of 4 leads to intermolecular reactions at the benzylic or allylic position of the π complexes 13 and 17, respectively.
Confromational Studies on Peptides Containing Enantiometric α‐Methyl α‐Amino Acids. Part I. Differential conformational properties of (R)‐ and (S)‐2‐methylaspartic acid
Authors: Altmann Karl‐Heinz , Altmann Eva , Mutter Manfred
Published: December 2004

The conformational properties of four model peptides of the general formula Ac‐Tyr‐Xaa‐Yaa‐Zaa‐Ala‐Lys‐Glu‐ala‐Ala‐Glu‐Lys‐Ala‐Zaa‐Yaa‐Xaa‐Lys‐NH2 (Xaa‐Yaa‐Zaa = Ala‐Ala‐(R)‐Asp(2‐Me), 1; Ala‐Ala‐(S)‐Asp(2‐Me), 2; Ala‐Aib‐Asp, 3; Ala‐Ala‐Asp, 4; Asp(2‐Me) = 2‐methylaspartic acid; Aib = 2‐aminoisobutyric acid) were studied by CD spectroscopy in solution, to evaluate the helix‐inducing potential of enantiomerically pure 2‐methylaspartic acid as a function of its chirality at C(2). At neutral pH and 1°, all peptides exhibit significant helix formation in aqueous solution, the degree of helicity increasing in the order 4 3 ≈ 1. Lowering the pH to 2 results in a dramatic increase in helicity for peptide 1, while the diastereoisomeric peptide 2 now exists in a predominantly unordered conformation. Helix induction by protonated (R)‐Asp(2‐Me) exceeds Aib‐induced helix formation in peptide 3, and the helix content of 1 in aqueous solution at pH 2 is comparable to the degree of helicity in the strongly helix‐inducing solvent 2,2,2‐trifluoroethanol.
Ring‐Transformation von Imidazolidin–2,4‐dionen ( = Hydantoinen) zu 4H‐Imidazolen bei der Umsetzung mit 3‐(Dimethylamino)‐2,2‐dimethyl‐2H ‐azirin
Authors: Schläpfer‐Dähler Marlise , Mukherjee‐Müller Gabriele , Heimgartner Heinz
Published: December 2004

Ring Transformation of Imidazolidine‐2,4‐diones ( = Hydantoins) to 4H‐Imidazoles in the Reaction with 3‐(Dimethylamino)‐2,2‐dimethyl‐2H‐azirines

At ca. 70°, 3‐(dimethylamino)‐2,2‐dimethyl‐2H ‐azirine (1) and 5,5‐disubstituted hydantoins 4 in MeCN or i‐PrOH give 2‐(1‐aminoalkyl)‐5‐(dimethylamino)‐4,4‐dimethyl‐4H ‐imidazoles 5 in good yield (Scheme 2). These products are decarboxylated 1:1 adducts of 1 and 4. A reaction mechanism is suggested in analogy to the previously reported reactions of 1 and NH‐acidic heterocycles containing the CONHCONH moiety (Scheme 5). The formation of ureas 6 and 7 can be rationalized by trapping the intermediate isocyanate F by an amine. No reaction is observed between 1 and 1,5,5‐ or 3,5,5‐trisubstituted hydantoins in refluxing MeCN or i‐PrOH, but an N‐isopropylation of 1,5,5‐trimethylhydantoin (8b) occurs in the presence of morpholine (Scheme 3). The reaction of the bis(azirine)dibromozink complex 11 and hydantoines 4 in refluxing MeCN yields zink complexes 12 of the corresponding 2‐(1‐aminoalkyl)‐4H ‐imidazoles 5 (Scheme 4).
Synthesis and X‐Ray Structural Studies of ‘4,7,13‐Trioxa‐1,10‐diaza‐5,6‐benzocyclopentadecane‐2,9‐dione’ ( = 5,6,9,10‐Tetrahydro‐2H, 8H‐benzo[b][1,4,10]trioxa[7,13]diazacyclopentadecene‐311(4H,12H)‐dione) and ‘4,7,13,16‐Tetraoxa‐1,10‐diaza‐5,6‐benzocyclooctadecane‐2,9‐dione’ ( = 5,6,8,9,12,13‐Hexahydro‐2H,11H‐benzo[b][1,4,10,13]tetraoxa‐ [7,16]diazacyclooctadecene‐3,14(4H, 15H)‐dione)
Authors: Gluziński Przemyslaw , Jurczak Janusz , Krajewski Janusz W. , Sałański Piotr , Stankiewicz Tomasz , Urbańczyk‐Lipkowska Zofia , Armbruster Thomas , Bürgi Hans‐Beat
Published: December 2004

The molecular structures of the title compounds 3 and 5 were investigated by NMR and X‐ray structural methods. The NMR results suggest two equivalent halves for both molecules. The X‐ray study shows an approximate mirror plane for 3 and an approximate twofold axis for a significant portion of the macrocycle of 5.
1,3,5‐Triamino‐1,3,5‐trideoxy‐cis‐inositol, a New Ligand with a Remarkable Versatility for Metal Ions. Part 2. Safe and efficient ligand preparation and structure of the free ligand and the CoIII complex
Authors: Ghisletta Michele , Hegetschweiler Kaspar , Jalett Hans‐Peter , Gerfin Tobias , Gramlich Volker
Published: December 2004

A new, convenient, and safe route to 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol (taci) was investigated by hydrogenation of azo‐coupled derivatives of phloroglucinol. In the presence of acetic anhydride, the reduction of trisphenylazophloroglucinol (H2/Pd(5%) on C) resulted in the formation of tri‐, hexa‐, and nona‐acetylated derivatives of triaminophloroglucinol. All three compounds are air‐stable, colorless solids. However, the succeeding hydrogenation to the cyclohexane derivative failed. Trisodiumtris(p‐sulfonatophenylazo)phloroglucinol could be hydrogenated in a one‐pot reaction to the desired taci· 1.5H2SO4 using a Pt/Rh oxide as catalyst. taci provides two distinct chair conformations with either three amino or three hydroxy groups for metal binding. The unique metal‐binding properties are discussed in terms of minimal conformational changes required for coordination. Conformational analysis, based on X‐ray structural data of [BiCl6][H3(taci)] ·2 H2O (Pnma, a = 24.314 (5) Å, b = 10.215 (2) Å, c = 7.422 (8) Å, R = 5.8%) and [Co(taci)2(NO3)3]·2H2O (C2/c, a = 22.912 (8) Å, b = 8.942 (2) Å, c = 14.731 (3) Å, β = 128.66 (2)°, R = 4.9%) and the previously investigated [Cr(taci)2]3+ revealed an almost ideal chair conformation in all three molecules.
Protonic Quantum Correlations in the H‐Bond Dynamics of Nucleic Acids. Part 1. Conformational comparison of G‐C with Benner's κ‐π
Authors: Chatzidimitriou‐Dreismann C. Aris
Published: December 2004

A new base pair (called κ‐π) of Watson‐Crick type, with an H‐bond pattern different from that in A‐T and G‐C base pairs, has been recently synthesized by Benner and coworkers and shown to be stable and incorporable into duplex DNA and RNA by polymerases. This new base pair, which contains three H‐bonds, is compared with G‐C, in the framework of modern dynamical theory of quantum nonlocality and quantum correlations (also called Einstein‐Podolsky‐Rosen correlations). Connection with the traditional treatment of proton transfer in DNA base pairs, which uses the adiabatic approximation (thus considering the protons as classical particles), is explicitly made. As a result, the dynamics of the H‐bond pattern of G‐C is shown to exhibit a specific quantum‐mechanical phase stability (or: rigidity, stiffness), which is clearly missing in the case of κ‐π. This finding is discussed and illustrated, also in connection with recent quantum chemical calculations of proton transfers in DNA base pairs. Additionally, certain speculations concerning a probable ‘evolutionary advantage’ of G‐C with respect to κ‐π are shortly considered.
Paramagnetic Redox Stages of a Bisphane: An ESR and ENDOR Study
Authors: Gerson Fabian , Scholz Markus , De Meijere Armin , König Burkhard , Heinze Jürgen , Meerholz Klaus
Published: December 2004

Seven redox stages, the dication 12+, the radical cation \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{+}\kern-4pt {.}\kern-2pt }}$\end{document}, the neutral 1, the radical anion \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}, the dianion 12−, the radical trianion \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {3{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}\end{document}, and the tetraanion 14−, are indicated by cyclic voltammetry for the bisphane 1, in which the benzene decks of two lateral paracyclophane moieties are orthogonal to the plane of anthracene framework. In \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{+}\kern-4pt {.}\kern-2pt }}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}, the unpaired electron is accommodated into the central anthracene subsystem, and the same statement holds for the two positive or negative charges in 12+ and 12−. Formation of \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {3{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}\end{document} and 1− occurs through admission of additional electrons one‐by‐one into the two paracyclophane moieties flanking the doubly charged anthracene subsystem in 12−. The above‐postulated, successive release or uptake of electrons by the individual parts of the bisphane is in perfect accord with the hyperfine data determined by ESR and ENDOR spectroscopy for \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{+}\kern-4pt {.}\kern-2pt }}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {3{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}\end{document}, as well as for radical ions of suitable reference compounds.
Reactions of Carbonyl Group with Nitroso Compounds: Reaction of Formaldehyde with Substituted Nitrosobenzenes
Authors: Uršić Stanko
Published: December 2004

Formaldehyde reacts with substituted nitrosobenzenes giving the corresponding N‐phenylhydroxamic acids. A mechanism involving three sequential steps in this reaction is proposed. The first step is the nucleophilic attack of the nitroso group on the carbonyl group which leads to the formation of the unstable tetrahedral zwitterionic intermediate. This step is followed by the proton transfer to the zwitterionic intermediate to form more stable nitrosocarbinolic cation intermediate, which in the subsequent step undergoes the rate‐controlling elimination of proton from the C‐atom of nitrosocarbinolic group, leading to the final product, hydroxamic acid. The first and the second step appear to be reversible. The experimental evidence obtained, which is the basis for such a description of the investigated reaction, includes: (a) the order of reactivity of substituted nitrosobenzenes, as demonstrated by the plot of log kobs vs. σ Hammett parameters with slope of −1.74; (b) the observation of a general‐acid catalysis; (c) the observation of the inverse solvent deuterium isotope effect of ca. 1.8 in the reaction; (d) the observation of kinetic primary deuterium isotope effect of ca. 8 related to the ‘water’ reaction in the reactions of formaldehyde with substituted nitrosobenzenes; (e) the observation of general‐base catalysis in the reaction; (f) the observation of the kinetic primary deuterium isotope effect of ca. 2.1 for the acetate‐ion‐catalyzed reaction.
(o‐Hydroxyphenyl)methylphosphonic acids: Synthesis and potentiometric determinations of their pKa Values
Authors: Böhmer Volker , Vogt Walter , Chafaa Salah , Meullemeestre Jean , Schwing Marie‐José , Vierling François
Published: December 2004

(o‐Hydroxyphenyl)methylphosphonic acids are readily obtained from o‐(bromomethyl)‐ or o‐(hydroxymethyl)phenols and trialkyl phosphites. Subsequent hydrolysis leads to the corresponding phosphonic acids. For a series of such compounds, the pKa values have been determined by potentiometry. Their dependence on additional substituents in the aromatic ring is discussed in terms of electronic and steric effects.
Enantioselective Synthesis of α‐N‐Alkylamino Acids via Sultam‐Directed ‘Enolate’ Hydroxyamination
Authors: Oppolzer Wolfgang , Cintas‐Moreno Pedro , Tamura Osamu , Cardinaux Francis
Published: December 2004

Crystalline N‐hydroxyamino‐acid derivatives 4, readily available from non‐chiral acyl chlorides 2 and sultams 1, were treated with aldehydes in the presence of NaBH3CN to give N‐alkylhydroxylamines 5. N,O‐Hydrogenolysis of 5 and saponification of 6 furnished (S)‐N‐alkylamino acids 7 in high optical purity. Similarly, (R)‐N‐alkylamino acids 12 were obtained from the antipodal acylsultams 8.
Warum pentose‐und nicht hexose‐nucleinsäuren? Teil III. Oligo(2′,3′‐dideoxy‐β‐D‐glucopyranosyl) nucleotide (‘homo‐DNS’): Paarungesigenschaften
Authors: Hunziker Jürg , Roth Hans‐Jorg , Böhringer Markus , Giger Alfred , Diederichsen Ulf , Göbel Michael , Krishnan Ravichandran , Jaun Bernhard , Leumann Christian , Eschenmoser Albert
Published: December 2004

Why Pentose‐And Not Hexose‐Nucleic Acids? Part III. Oligo(2′,3′‐dideoxy‐β‐D‐glucopyranosyl)nucleotides. (‘Homo‐DNA’): Base‐Pairing Properties

Summary in collaboration with Prof. Dr. C. E. Wintner, Haverford College, Haverford, PA 19041‐1392.

The paper presents results of a comprehensive investigation on the pairing properties of homo‐DNA oligonucleotides, the preparation of which has been described in Part II of this series [2]. The investigation was carried out by using established methods described in the literature for the characterization of oligonucleotides in the natural series, such as determination of melting temperatures of oligonucleotide duplexes by temperature‐dependent of melting temperatures, determination of pairing stoichiometry by ratio‐dependent UV spectroscopy of binary mixtures of pairing partners, temperature‐dependent CD spectroscopy, gel electrophoresis under non‐denaturing conditions, and – in selected cases – 1H – and31P‐NMR spectroscopy.

The systematic comparison of the paring properties of homo‐DNA oligonucleotides with corresponding DNA nucleotides (up to dodecamers) indicates that homo‐DNA is a highly efficient, autonomous, artificial pairing system with a pairing behavior that is in part similar to, but also, in part, strikingly different from, the pairing behavior of DNA. The pairing properties established so far are listed below in a manner that reflects the sequence of subtitles in Chapt.2 of the text; they were determined under the conditions: H2O, 0.15M NaCl, 0.01M Tris‐HCl buffer, pH 7, oligonucleotide concentrations in the μM range, 1:1 ratio of single strands in the case of non‐selfcompementary sequences.
Transport Properties of H+‐Selective Membranes Containing Amine‐Derivative Ionophores and Mobile Sites
Authors: Nahir Tal M. , Buck Richard P.
Published: December 2004

Transport processes in plasticized PVC membranes containing the H+ chromoionophore ETH 5294 and additional tetraphenylborate‐type mobile sites were analyzed by employing the potential‐step method. Using chronoamperometry, impedance spectroscopy, and UV/VIS absorbance measurements, it is shown that the ionophore behaves as a carrier for protons, when the membranes are immersed between two aqueous solutions. It was possible to document the changes in the concentration profiles of both free ionophores and ionic species in some of the membranes. There is no evidence of proton hopping between the ionophores.
Zine Complexes of Cysteine, Histidine, and Derivatives Thereof: Potentiometric determination of their compositions and stabilities
Authors: Gockel Peter , Vahrenkamp Heinrich , Zuberbühler Andreas D.
Published: December 2004

The stabilities of Zn complexes of cysteine and histidine have been determined together with those with those of three derivatives of each n which one of their three donor functions (carboxyl, amino, and mercapto and imidazole, respectively) has been blocked. Using potentionmetric titrations of aqueous solutions, the 1:1 and 1:2 complexes of all for cysteine‐ and all four histidine‐derived ligands are observed among te various species present (ligands, 1:1 and 1:2 complexes, and protonatd derivatives thereof). All cysteine‐derived complexes are more stable than the corresponding histidine‐derived complexes by 1–2 orders of magnitude for the 1:1 composition and by 1–6 order of magnitude for the 1:2 composition. For the cysteine series, the sequence of stabilities is cysteine > cysteine ethyl ester ≫ N(α)‐acetylcysteine ≫ SMethylcysteine. For the histidine series, the corresponding sequence is histidine > histidine methyl ester > N,N (imidazole)‐dimethylhistidine > N(α)‐acetylhistidine. The order of stabilities can be explained by the relative strengths of the Zn–S vs. Zn–N coordination, y charge effects, and by chelate ring sizes.
Metal Complexes with Macrocylclic Ligands. Part XXXV. Stabilities of some bivalent metal‐ion complexes with 1,4,7‐triazacyclononane‐1‐acetie acid
Authors: Cai Hui‐Zhi , Kaden Thomas A.
Published: December 2004

The stability constants of the Mn2+, Zn2+, Ni2+, pb2+, and Cd2+ complexes with 1,4,7‐triazacylononane‐1‐acetic acid (noma) were determined at 25° and 0.5M (KNO3) by potentiometric titrations. The species [ML] and [ML(OH)] were found in al cases except for Ni2+, whereas [ML2] was only detected for Cd2+. For the complexes [ML], the order of stability is Mn2+ < Cd2+ < pb2+ < Zn2+ < Zn2+ < Ni2+ < Cu 2+, which is consisten with the Irvin‐Williams Series.
1,1′‐Disubstituted Ferrocene‐Containing Thermotropic Liquid Crystals of structure [Fe{(η5‐C5H4)COOC6H4XC6H4OCnH2n+1}2] (X  OOC or COO). Influence of the orientation of the central ester function on the mesogenic properties
Authors: Deschenaux Robert , Marendaz Jean‐Lue , Santiago Julio
Published: December 2004

The two series I and II of 1,1′ ‐disubstituted ferrocenes which differ by the direction of the ester function included in the rigid organic part were synthesized and their liquid crystal properties examined. These latter were found to be strongly dependent on the orientation of the connecting ester group and on the alkyl chain length.
Chemistry of (Carbonyl)(nitrosyl)[bis(phosphorus donor)]rhenium Complexes
Authors: Hund Hans‐Ulrich , Ruppli Urs , Berke Heinz
Published: December 2004

The chemistry of [Re(CO)(NO)L2] fragments (L  phosphorus donor) was explored. Starting from [Re(CO)5Cl] the synthesis of [Re2Cl2(μ‐Cl)2(CO)4(NO)2] (1) was accomplished via the preparation of [Et4N]2[Re2Cl2(μ‐Cl)2(CO)6] and nitrosylation of this compound with [NO][BF4]. Complex 1 was converted to [RecL2(CO)(NO)L2] complexes 2 (a L = (MeO)3P; b L = (EtO)3P; c L = (i‐PrO)3P; d L  Me3P; e L  Et3P; f L  Cy3P) by heating with L in MeCN. In the case of the reaction of L = (MeO)3P, a trisubstitued compound mer‐{ReCl2(NO)[P(OMe)3]3} 3 was also obtained. Replacement of the Cl ligands in 2a–e with Me groups was achieved by reacting them with MeLi in Et2O yielding cis, trans‐[Re(CO)(NO)Me2L2]complexes 4a–e. Reaction of 2a–e with Li[BHEt3] led to substitution of one Cl by an H ligand with formation of [ReCl(CO)H(NO)L2] compounds 5a–;e, displaying trans‐H,NO geometries. The hydride‐transfer agent Na[AlH2(OCH2CH2OCH3)2] transformed 2 into the cis‐dihydride systems [Re(CO)H2(NO)L2] 6a–f. Reductive carbonylation of 2a–d in the presence of Na/Hg and CO gave pentacoordinate [Re(CO)2(NO)L2] complexes 7b–d, and under comparable conditions the Cl substituents of 2b–f were replaced by tolane using Mg or t‐BuLi giving trigonal bipyramidal [Re(CO)(NO)L2(PhCCPh)] compounds 8b–f. Complexes 5c, 6a, and 8d were characterized by X‐ray crystal‐structure analysis.
Synthetische Analoga von niedermolekularen Spinnentoxinen mit Acyl‐polyamin‐Struktur
Authors: Fiedler Wolfgang J. , Guggisberg Armin , Hesse Manfred
Published: December 2004

Synthetic Analogues of Low‐Molecular‐Weight Acyl‐polyamine Spider Toxins

Low‐molecular‐weight spider and wasp toxins are selective inhibitors of glutamate receptors of the central nervous system and consist of a polyamine backbone and one or several carboxylic acids and/or amino acids linked by a peptide‐like bond. The syntheses of twelve analogues of spider and wasp toxins are described (10a–c, 15a–c, 20a–c, 25a–c) having the general structure of acyl, arylacyl, or heteroarylacyl → DL‐alanyl → ω‐aminoacyl → N1‐spermidine, with variation in the acyl and the ω‐aminoacyl part.