bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Structure of an Isomeric Pair of a (Tetraamine)copper(II) Compound in the solid state and in solution
Authors: Comba Peter , Hilfenhaus Peter , Nuber Bernhard 
Published: December 2004

AbstractThe template condensation of [Cu(3, 2, 3‐tet)]2+ (3, 2, 3‐tet = N, N″)‐(ethane‐1, 2‐diyl)propane‐1, 3‐diamine with CH2O and en (en = ethane‐1, 2‐diamine) affords the copper(II) compounds of two isomeric tricyclic ligands in high yield. The strikingly different UV/VIS and EPR spectroscopic behavior of these two compounds, [Cu(‘syn’‐L)](CIO4)2 and [Cu(‘anti’‐L)](ClO4)2 · 1/2 H2O (L = 1, 4, 8, 10, 13, 15‐hexaazatricyclo [13.3.1.14, 8]icosane), is analyzed by angular overlap model (AOM) calculations based on the experimentally determined solid‐state structures (powder spectra) and a combination of molecular mechanics and AOM calculations (MM‐AOM) for the solution‐structure behavior.
An unexpected transformation of benzyl carbamates into α‐azidobenzeneacetamides
Authors: Strässler Christoph , Heimgartner Heinz 
Published: December 2004

AbstractSuccessive treatment of benzyl carbamates 5 (Z‐protected secondary amines) with lithium diisopropylamide (LDA), diphenyl phosphorochloridate (DPPC1), and NaN3 yielded the corresponding ã‐azidobenzeneacetamides 6 in 45–50% yield (Schemes 2 and 3). In the case of Z‐protected diisopropylamine 5b, the phosphate 7 was isolated as a minor product. A reaction mechanism for this unexpected transformation is proposed in Scheme 4, the key step being the ring closure of a benzylic anion to give an oxirane intermediate B. In cursory experiments, it was demonstrated that ã‐azidobenzeneacetamides 6 can be used as 2‐phenylglycine synthons in the formation of dipeptides by using a phosphine‐mediated coupling (Scheme 5).
Synthesis and Evaluation of α‐Methylidene‐γ‐butyrolactone bearing flavone and xanthone moieties
Authors: Tzeng Cherngy‐Chyi , Zhao Yue‐Ling , Chen Yeh‐Long , Liou Shorong‐Shii , Wang Tai‐Chi , Chang Ya‐Ling , Teng Che‐Ming 
Published: December 2004

AbstractIn a search for inhibitors of platelet aggregation, a number of α‐methylidene‐γ‐butyrolactones 5 and 6 bearing flavone or xanthone moieties, respectively, were synthesized and evaluated for their antiplatelet activity against thrombin(Thr)‐, arachidonic‐acid(AA)‐, collagen(Col)−, and platelet‐activating‐factor(PAF)‐induced aggregation in washed rabbit platelets. These compounds were synthesized from 7‐hydroxyflavone (1) or 3‐hydroxyxanthone (2) via O‐alkylation (→ 3 and 4, resp.) and Reformatsky‐type condensation (Scheme). Most of the flavone‐containing α‐methylidene‐γ‐butyrolactones 5a–d showed potent antiplatelet effects on AA‐ and Col‐induced aggregation, while xanthone derivatives 6c–e were found to have the same pharmacological profile than aspirin in which only AA‐induced aggregation was inhibited (Table 1). However, 6c–e were approximately three to ten times more potent than aspirin (Table 2). For the vasorelaxing effects, 5a was the only compound which exhibited significant inhibitory activity on the high‐K+ medium, Ca2+‐induced vasoconstriction (Table3). Both 5a and 6a, with an aliphatic Me substituent at C(γ) of the lactone, were active against norepinephrine‐induced phasic and tonic constrictions while their γ‐aryl‐substituted counterparts 5b–f and 6b–f were inactive.
New Cyclophanes as Initiator Cores for the Construction of Dendritic Receptors: Host‐guest complexation in aqueous solutions and structures of solid‐state inclusion compounds
Authors: Wallimann Peter , Mattei Sebastiano , Seiler Paul , Diederich François 
Published: December 2004

AbstractCyclophanes 3 and 4 were prepared as initiator cores for the construction of dendrophanes (dendritic cydophanes) 1 and 2, respectively, which mimic recognition sites buried in globular proteins. The tetra‐oxy[6.1.6.1]paracyclophane 3 was prepared by a short three‐step route (Scheme 1) and possesses a cavity binding site shaped by two diphenylmethane units suitable for the inclusion of flat aromatic substrates such as benzene and naphthalene derivatives as was shown by 1H‐NMR binding titrations in basic D2O phosphate buffer (Table 1). The larger cyclophane 4, shaped by two wider naphthyl(phenyl)methane spacers, was prepared in a longer, ten‐step synthesis (Scheme 2) which included as a key intermediate the tetrabromocyclophane 5. 1H‐NMR Binding studies in basic borate buffer in D2O/CD3OD demonstrated that 4 is an efficient steroid receptor. In a series of steroids (Table 1), complexation strength decreased with increasing substrate polarity and increasing number of polar substituents; in addition, electrostatic repulsion between carboxylate residues of host and guest also affected the binding affinity strongly. The conformationally flexible tetrabromocyclophane 5 displayed a pronounced tendency to form solid‐state inclusion compounds of defined stoichiometry, which were analyzed by X‐ray crystallography (Fig. 2). 1,2‐Dichloroethane formed a cavity inclusion complex 5a with 1:1 stoichiometry, while in the 1:3 inclusion compound 5b with benzene, one guest is fully buried in the macrocyclic cavity and two others are positioned in channels between the Cyclophanes in the crystal lattice. In the 1:2 inclusion compound 5c, two toluene molecules penetrate with their aromatic rings the macrocyclic cavity from opposite sides in an antiparallel fashion. On the other hand, p‐xylene (= 1,4‐dimethylbenzene) in the 1:1 compound 5d is sandwiched between the cyclophane molecules with its two Me groups penetrating the cavities of the two macrocycles. In the 1:2 inclusion compound 5e with tetralin (= 1,2,3,4‐tetrahydronaphthalene), both host and guest are statically disordered. The shape of the macrocycle in 5a–e depends strongly on the nature of the guest (Fig. 4). Characteristic for these compounds is the pronounced tendency of 5 to undergo regular stacking and to form channels for guest inclusion; these channels can infinitely extend across the macrocyclic cavities (Fig. 6) or in the crystal lattice between neighboring cyclophane stacks (Fig. 5). Also, the crystal lattice of 5c displays a remarkable zig‐zag pattern of short Br…︁O contacts between neighboring macrocycles (Fig. 7).
New Anellation Methods for the Synthesis of 8H‐Heptaleno[1,10‐bc]furans,‐pyrroles, and ‐thiophenes
Authors: Hörndler Cornelia , Hansen Hans‐Jürgen 
Published: December 2004

AbstractHeptaleno[1,2‐c]furan‐6‐carbaldehydes such as 8 or their thiocarbaldehyde or iminomethyl derivatives easily undergo thermal cyclization, followed by a [1,5]‐H shift, to give the corresponding heptalenodifurans, thienoheptalenofurans, as well as furoheptalenopyrroles (cf. Schemes 2 and 3). Generation of the 6‐acetyl derivative of 8 from the corresponding secondary alcohol 15 with 1‐hydroxy‐1,2‐benziodoxol‐3(1H)‐one 1‐oxide (IBX) at 0° (cf. Scheme 4) leads directly to the formation of the cyclization product 16 which, upon standing at room temperature, undergoes the [1,5]‐sigmatropic H‐shift to the final difuran 17. 1‐Formylheptalene‐4,5‐dicarboxylates such as 9 can also be cyclized thermally, followed by the [1,5]‐H shift, to the corresponding 8H‐heptaleno[1,10‐bc]furan‐5,6‐dicarboxylate 11. On thiation with Lawesson′s reagent, 9 yields directly the corresponding heptalenothiophene 13 (cf. Scheme 3).
Distamycin‐NA: A DNA Analog with an Aromatic Heterocyclic Polyamide Backbone. Part 1. Synthesis and structural analysis of monomers and dimers containing the nucleobase uracil
Authors: Sauter Guido , Stulz Eugen , Leumann Christian 
Published: December 2004

AbstractThe synthesis of the monomeric building block 13 and its constitutional isomer 12 of a new type of DNA analog, distamycin‐NA, is presented (Schemes 1 and 2). This building block consists of a uracil base attached to a thiophene core unit via a biaryl‐like axis. Next to the biaryl‐like axis on the thiophene chromophore, a carboxy and an amino substituent are located allowing for oligomerization via peptide coupling. The proof of constitution and the conformational preferences about the biaryl‐like axis were established by means of X‐ray analyses of the corresponding nitro derivatives 10 and 11. Thus, the uracil bases are propeller‐twisted relative to the thiophene core, and bidentate H‐bonds occur between two uracil bases in the crystals. The two amino‐acid building blocks 12 and 13 were coupled to give the dimers 15 and 16 using dicyclohexylcarbodiimide (DCC) in THF/LiCl and DMF, respectively. While the dimer 15 showed no atropisomerism on the NMR time scale at room temperature, its isomer 16 occurred as distinct diastereoisomers due to the hindered rotation around its biaryl‐like axis. Variable‐temperature 1H‐NMR experiments allowed to determine a rotational barrier of 19 ± 1 kcal/mol in 16. The experimental data were complemented by AM1 calculations.
[2+3] Cycloadditions of Azomethine Ylides with 1,3‐Thiazole‐5(4H)‐thiones
Authors: Mlostoń Grzegorz , Linden Anthony , Heimgartner Heinz 
Published: December 2004

AbstractThermal reactions of 1,2,3‐trisubstituted aziridines 1 with 1,3‐thiazole‐5(4H)‐thiones 6 in toluene yielded, in general, a mixture of two diastereoisomeric spirocyclic [2+3] cycloadducts. The formation of these products can be explained by a stereoselective electrocyclic ring opening of 1 to give an azomethine ylide 2 as the reactive intermediate, which is trapped immediately by 6 via a stereoselective 1,3‐dipolar cycloaddition. Only in the case of trans‐dimethyl 1‐(4‐methoxyphenyl)aziridine‐2,3‐dicarboxylate (trans‐1a), four diastereoisomeric cycloadducts were formed (Scheme 4). This result is rationalized by an isomerization of the intermediate azomethine ylide cis‐2a to trans ‐2a.
Synthesis of Bridgehead‐Functionalized Bicyclo[3.2.1]octanes via intramolecular titanium‐ and tributylstannane‐induced pinacol coupling
Authors: Egger Anita , Hunziker Jürg , Leumann Christian , Rihs Grethy 
Published: December 2004

AbstractThe synthesis of the enantiomerically pure, bridgehead‐functionalized bicyclo[3.2.1]octanes 11 and 16, containing a conformationally fixed trihydroxypropyl (aminodihydroxypropyl) unit, as well as the X‐ray structure of 11 are described. These compounds are of interest as sugar surrogates in the preparation of DNA analogs. Compounds 11 and 16 became available in 10 and 12 steps, respectively, and in an overall yield of 11 and 4% from D‐arabinose via a highly stereoselective pinacol coupling as the key step.
Prenylated Flavanones from Monotes engleri: On‐line Structure Elucidation by LC/UV/NMR
Authors: Garo Eliane , Wolfender Jean‐Luc , Hostettmann Kurt , Hiller Wolf , Antus SÁNdor , Mavi Steven 
Published: December 2004

AbstractThe CH2Cl2 extract of Monotes engleri Gilg. (Dipterocarpaceae) showed antifungal activity against the yeast Candida albicans in our bioautographic TLC assays. After a first fractionation of the crude extract, the bioactivity was located in one of the fractions. To perform an efficient targeted isolation of the active compounds, LC/UV/MS and LC/UV/NMR analyses of the crude extract and the active fraction were performed. LC/UV/, LC/MS, and LC/NMR data (1D and 2D) allowed the identification of 1 as (2S)‐2,3‐dihydro‐5,7‐dihydroxy–{3‐hydroxy‐4‐[(3‐methylbut‐2‐enyl) oxy]phenyl}‐4H‐1‐benzopyran‐4‐one, a new prenylated flavanone, named monoteson A. Subsequent isolation of 1 has permitted the determination of its absolute configuration on the basis of CD measurements. Theree other prenylated flavanoes 2–4 were isolated from the same extract. Compound 3 was identified as 2‐ (3, 5‐dihydroxyphenyl) ‐2,3‐dihydro‐5, 7‐dihydroxy‐6, 8‐bis (3‐methylbut‐2‐enyl)‐4 H‐1‐benzopyran‐4‐one, another new natural product, named monotesone B. The structures of 2 and 4 were established as selinone and lonchocarpol A, respectively. The antifungal activity against Candida albicans was determined for all compounds.
Synthesis of Oligonucleotides Containing 2′‐Deoxyisoguanosine and 2′‐Deoxy‐5‐methylisocytidine Using Phosphoramidite Chemistry
Authors: Jurczyk Simona C. , Kodra Janos T. , Rozzell J. David , Benner Steven A. , Battersby Thomas R. 
Published: December 2004

AbstractThe synthesis of oligonucleotides containing 2′‐deoxy‐5‐methylisocytidine and 2′‐deoxyisoguanosine using phosphoramidite chemistry in solid‐phase oligonucleotide synthesis is described. Supporting previous observations, the N,N‐diisobutylformamidine moiety was found to be a far superior protecting group than N‐benzoyl for 2′‐deoxy‐5‐methylisocytidine. 2′‐Deoxy‐N2‐[(diisobutylamino)methylidene]‐5′‐(4,4′‐dimethoxytityl)‐5‐methylisocytidine 3′‐(2‐cyanoethyl diisopropylphosphoramidite) (1c) incorporated multiple consecutive residues during a standard automated synthesis protocol with a coupling efficiency > 99% according to dimethoxytrityl release. Extending coupling times of the standard protocol to ≥ 600s using 2′‐deoxy‐N6‐[(diisobutylamino)methylidene]‐5′‐O‐(dimethoxytrityl)‐O2‐(diphenylcarbamoyl)isoguanosine, 3′‐(2‐cyanoethyl diisopropylphosphoramidite) (7e) led to successful incorporation of multiple consecutive 2′‐deoxyisoguanosine bases with a coupling efficiency > 97% according to dimethoxytrityl release.
Antitumor Agents. Part 184. Syntheses and antitubulin activity of compounds derived from reaction of thiocolchicone with amines: Lactams, alcohols, and ester analogs of allothiocolchicinoids
Authors: Shi Qian , Chen Ke , Brossi Arnold , Verdier‐Pinard Pascal , Hamel Ernest , McPhail Andrew T. , Lee Kuo‐Hsiung 
Published: December 2004

Abstract7‐O‐Substituted analogs of deaminodeoxycolchinol thiomethyl ether were synthesized and evaluated for their inhibitory effects on tubulin polymerization in vitro. Ketone 9, a key compound in this study, was derived from thiocolchicone 6 by reaction with aniline. Reaction of compound 6 with MeNH2 or BuNH2 gave tetracyclic lactams 7 and 8, respectively. Optically active alcohols 11a and 11b were obtained from racemic 11 by chemical resolution including a separation of the comphanate diastereoisomers 12a and 12b, followed by basic hydrolysis. The (aR,7R)‐configuration of 12b was verified by X‐ray crystallographic analysis. Almost all racemic and optically active 7‐O‐acyl or 7‐O‐aroyl compounds had strong inhibitory effects on the tubulin polymerization reaction, with IC50 values from 1.7 to 5.1 μM. A few agents, such as the lactams 7 and 8, the camphanates 12a and 12b, the cyclohexanecarboxylates 19a and 19b, and, most notably, the (7S)‐benzoate 15a, had negligible effects on polymerization, yielding IC50 values greater than 40μM. Ketone 9 showed strong inhibition of tubulin polymerization comparable to that of thiocolchicone (6). Optically active alcohol 11a and acyl esters 13a and 14a with a (7S)‐configuration were more active than the (7R)‐esters 13b and 14b. However, the esters 15a–17a with a (7S)‐configuration were less active than the (7R)‐isomers 15b–17b, in which the (7R)‐benzoate 15b was at least 15‐fold more inhibitory than the (7S)‐isomer 15a. For the most part, the agents causing strongest inhibition of polymerization also caused the greatest inhibition of [3H]colchicine binding. NMR and optical rotatory data indicate that, in polar solvents, the equilibrium in esters with a 7‐O‐aroyl substituent, i.e., 15a,b, 16a,b, and 17a,b, is reversed from (aS) to (aR) or from (aR) to (aS), as compared to nonpolar solvents.
Synthesis of 1‐(1H‐Imidazol‐2‐yl)ethane‐1,2‐diol Derivatives: A novel class of protein kinase C inhibitors
Authors: Röhrle Andreas N. , Schmidhammer Helmut 
Published: December 2004

AbstractCompounds 6–13 were prepared starting from 1‐(triphenlymethyl)‐protected 1H‐imidazoles 14 and 15 in several steps. Lithiation with BuLi in THF followed by reaction with (triphenylmethoxy)acetaldehyde (16) afforded 17 and 18, respectively. O‐Methylation of 17 and 18 gave diethers 19 and 20, respectively. The N‐ and O‐trityl protecting groups of 17–20 were cleaved by acid treatment to give deprotected compounds 21–24. Acylation with equimolar amounts (for mono‐ or di‐O‐acylation) of the corresponding acyl chlorides yielded 1H‐imidazoles 6–13. Compounds 7, 8, 10, and 11 exhibited moderate protein kinase C inhibition.
Synthesis of Vitamin‐B12 Derivatives with Peripheral Tris(oxyethylene) Chains
Authors: Pfammatter Michael J. , Darbre Tamis , Keese Reinhart 
Published: December 2004

AbstractThe new derivatives 7a–c, of vitamin B12, with a peripheral tris(oxyethylene) chain linked to the corrin ring by an amide or ester group, are prepared, and their ligand‐exchange reactions are investigated. Upon reduction of the aqua‐cyano complexes 8a–c with NaBH4, cleavage of the ‘outer’ ester and amide group is observed.
Synthesis of Vitamin‐B12 Derivatives with an Electropolymerizable Side Chain
Authors: Otten Thomas , Darbre Tamis , Cosnier Serge , Abrantes Luisa , Correia Jorge , Keese Reinhart 
Published: December 2004

AbstractThree new derivatives of vitamin B12 with a pyrrole head group attached to the corrin ring have been prepared. Ligand‐exchange reactions and reduction provided reactive CoIII and CoII complexes. Their electro‐chemical properties and their potential for fixation at the surface of electrodes by electropolymerization were studied.
Glycosylidene Carbenes. Part 27. Glucosidation of titanium dioxide with 1‐aziglucoses: Preparation and characterization of modified titanium‐dioxide surfaces
Authors: Weber Martin , Vasella Andrea , Textor Marcus , Spencer Nicholas D. 
Published: December 2004

AbstractTitanium‐dioxide surfaces have been glycosylated with the benzyl‐, 4‐fluorobenzyl‐, and acetyl‐protected diazirines 1–3. The modified TiO2 surfaces were characterized by contact‐angle measurement, X‐ray photoelectron spectroscopy (XPES), and time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS). The main by‐products of the glucosidation (mostly azines and trehaloses) were identified. Their physisorption slightly reduces the efficiency of the glucosidation by 1 mM solution of 1 or 2 in CH2Cl2, but this influence is neutralized by repeating the glucosidation, or by using a 100 mM solution of the diazirines. The immobilized, acetylated glucosyl moieties were deacetylated in situ. Calculations based on the XPES peaks of Ti 2p and F 1s for the TiO2 surface modified with 2 indicated 1.5 ± 0.9 immobilized glucosyl moieties per nm2.
A Novel NO2/OH Exchange in α‐Nitro Ketones: A mechanistic investigation
Authors: Yurdakul Ayçil , Gurtner Christian , Jung Elena‐Silvia , Lorenzi‐Riatsch Annalaura , Linden Anthony , Guggisberg Armin , Bienz Stefan , Hesse Manfred 
Published: December 2004

AbstractThe reaction of α‐nitro ketones to the corresponding α‐hydroxy ketones under basic aqueous conditions, a novel transformation, was studied. The investigation revealed that the reaction is only possible with α‐nitro ketones that are CH‐acidic in the α′‐position and readily deprotonated under the reaction conditions. The NO2/OH exchange was established to proceed with retention of configuration at the stereogenic center, and labeling experiments have shown that the OH O‐atom originates, to a great extent, from the solvent. In particular, the stereochemical course of the reaction and the incorporation of external nucleophiles led us to propose a mechanism that involves neighboring‐group participation. The product formation is explained by a double SN2 reaction, which proceeds via a Favorskii‐like cyclopropanone intermediate.
Mechanical properties of hydrophilic copolymers of 2‐hydroxyethyl methacrylate with ethyl acrylate,n‐butyl acrylate, and dodecyl methacrylate
Authors: Kolařík Jan , Migliaresi Claudio 
Published: December 2004

AbstractCopolymers were prepared of 2‐hydroxyethyl methacrylate, which is strongly hydrophilic, with hydrophobic comonomers having a low glass transition temperature, i.e., ethyl acrylate, n‐butyl acrylate, and dodecyl methacrylate. The glass transition temperature, Tα (1 Hz), of polymers in the dry state (xerogels) was determined by means of dynamic mechanical measurements. The dependence of Tα on composition in all the three series of copolymers was described in terms of a one‐parameter equation. The equilibrium swelling of copolymers in water decreases more steeply than the weight fraction of 2‐hydroxyethyl methacrylate. When swollen in water to equilibrium, all copolymers with ethyl acrylate or n‐butyl acrylate are in the rubber‐like state; their tensile modulus E assumes values in the range 0.17–0.50 MPa. While poly(2‐hydroxyethyl methacrylate) has the modulus E = 0.39 MPa, the tensile strength σu = 0.32 MPa, and the strain‐at‐break ϵu = 1.81, for the weight fraction of the comonomer in the range 0.36 ⩽ w2 ≤ 0.56 it is possible to achieve σu and ≤ u lying in the respective ranges 0.7–0.9 MPa and 5–7. Copolymers with the dodecyl methacrylate content w2 < 0.2 or w2 > 0.8 are rubberlike, and at 0.30 ≤ w2 ≤ 0.62 they become leathery; the latter have the modulus E and strength σu within the ranges 12–32 and 3–4 MPa, respectively. The stress–strain curves of these copolymers evidence yielding and orientation hardening which have been tentatively explained by the nonhomogeneous composition and structure of the copolymers.
Preparation and strength of poly(ethylene terephthalate) fiber bundles for model synthetic tendons
Authors: Kolařík Jan , Vaníček Jiří , Migliaresi Claudio 
Published: December 2004

AbstractPoly(ethylene terephthalate) fibers suited for model synthetic tendons were prepared on a pilot‐plant scale by additional drawing (postdrawing) of commercial textile fibers texturized by false twist. The modified fibers have a tensile modulus of 7–9 GPa, a one‐minute creep modulus of 5–6 GPa, tensile strength 0.55–0.63 GPa, and strain at break of 16–19%. It is essential for their application in synthetic tendons that plastic deformation was reduced to about 0.5%, which could be completely eliminated by subsequent mechanical conditioning of fibers. Since the strength of model tendons consisting of 20 vol % of fibers and of a hydrogel matrix is primarily determined by the strength of the fibers, some aspects of the theory of strength of fiber bundles are briefly recapitulated. The prediction is compared with earlier experimental results obtained for the synthetic tendons. Such an approach, taking into account the fiberstrength distribution in the bundle, predicts a strength of model tendons lower by 20–40% than does the rule of mixtures.
Ultrathin coating of plasma polymer of methane applied on the surface of silicone contact lenses
Authors: Ho Chung‐Peng , Yasuda H. 
Published: December 2004

AbstractSilicone rubber has great advantages as a contact lens material because of its very high oxygen permeability, softness, and excellent mechanical strength and durability. Practical application is hampered by inherent characteristics of elastomers, i.e., high tackiness and highly hydrophobic surface properties. By applying a thin layer, e.g., 5 nm, of plasma polymer of methane, it was found that all these disadvantages can be eliminated without sacrificing high oxygen permeation rate, e.g., less than 15% reduction. Optimization of operational parameters to achieve this task has been investigated. It was also found that under optimum conditions the coating withstood severe and repeated flexing of the contact lens.