bluuebunny/crossref_metadata_2025 huggingface dataset:
Models for the Active Center of Pterin‐Containing Molybdenum Enzymes: Crystal structure of a molybdenum complex with sulfur and pterin ligands
Authors: Fischer Berthold , Schmalle Helmut W. , Baumgartner Markus R. , Viscontini Max
Published: December 2004

The first crystal structure of a molybdenum complex 9 with a hydrogenated pterin and a sulfur ligand contributes to the discussion about the active center of molybdenum and tungsten enzymes containing a molybdopterin cofactor. Complex 9 was synthesized through a redox reaction of [MoVIO2 (LN‐S2)] (8; LN‐S2 = pyridine‐2, 6‐bis(methanethiolato)) with 5, 6, 7, 8‐tetrahydropterin (7). 2 HCl (H4Ptr.2 HCl). The complex crystallizes, with a non‐coordinating Cl‐atom acting as a counterion, in the monoclinic space group C2/c (No. 15) with cell dimensions a = 22.900(5), b = 10.716(2), c = 17.551(4) Å, β = 120.36(3)°, and Z = 8. We interpret 9 as [MoIVO(LN‐S2)(H+‐q‐H2Ptr)]Cl (q = quinonoid; H2Ptr = dihydropterin), i.e., a MoIV monooxo center coordinated by a pyridine‐2, 6‐bis(methanethiolato) ligand and a protonated dihydropterin. The spectroscopic properties of this new complex are comparable to those of other crystalline molybdenum complexes of hydrogenated pterins without additional S‐coordination. The slightly H2O‐soluble complex 9 reacts with the natural enzyme substrate DMSO very slowly, possibly due to the lack of easily dissociable ligands at the metal center.
6‐Azabicyclo[3.1.0]hex‐30‐en‐2‐ol Derivative, photochemically generated building blocks for bicyclic β‐lactams
Authors: Glarner Fabrice , Thornton Steven R. , Schärer Daniel , Bernardinelli Gérald , Burger Ulrich
Published: December 2004

The title compounds 4 are obtained by photolysis of simple N‐alkylpyridinium salts in H2O or alcohol. On reaction with [Fe2(CO)9] in THF, 4 gives bicyclic tricarbonyliron complexes 13a–d, which on oxidative decomplexation with ceric ammonium nitrate afford cis‐fused cyclopenteno‐β‐lactams 15a–d.
Metal Complexes with Macrocyclic Ligands. Part XLIII. Tetraazamacrocyclic nickel(II) and copper(II) complexes with aliphatic methylthio‐ and methoxy‐substituted pendant chains
Authors: Schmid Claudio L. , Neuburger Markus , Zehnder Margareta , Kaden Thomas A. , Bujno Krzysztof , Bilewicz Renata
Published: December 2004

The 14‐membered tetraazamacrocyclic Ni2+ and Cu2+ complexes of 4 (1, 4, 8‐trimethyl‐11‐[(2‐methylthio)ethyl]‐1, 4, 8, 11‐tetraazacyclotetradecane), 5. (1, 4‐dimethyl‐8, 11‐bis[2‐(methylthio)ethyl]‐l, 4, 8, 11‐tetraazacyclotetradecane), and 7 (1, 4, 8, ll‐tetrakis[2‐(methylthio)ethyl]‐1, 4, 8, 11‐tetraazacyclotetradecane), with pne, two, and four methylthio‐substituted pendant chains, respectively, and the Ni2+ complex of 6 (1, 4‐dimethyl‐8, 11‐bis (2‐methoxyethyl)‐1, 4, 8, 11‐tetraazacyclotetradecane), with two methoxy‐substituted pendant chains, were synthesized and their chemistry studied with regard to modelling F430. Solution spectra in H2O, MeCN, and DMF indicate participation of the side chain in metal coordination when the donor group is a thioether, whereas no coordination with the metal ion is observed with the ether group. Similarly the X‐ray structures of the thioether‐containing compounds [Ni(5)](ClO4)2, [Cu(5)](ClO4)2, and [Cu(7)](ClO4)2 show a coordination number of 5, whereas that of [Ni(6)](ClO4)2 with ether pendant chains, shows a coordination number of 4. Cyclic voltammetry of these complexes in MeCN reveals that Ni2+ is reversibly reduced to Ni+ between −0.64 and −0.77 V vs. SCE, the potential being influenced by the nature and number of the pendant chains. At more negative potentials, the thioether is cleaved, whereby a thiol is formed; the thiol is then oxidized at ca. + 0.8 V vs. SCE, when a glassy carbon electrode is used, or at ca. 0 V vs. SCE at a dropping Hg electrode. No cleavage of the ether bond in [Ni(6)](ClO4)2 is observed under similar conditions.
Palladium‐Catalysed Intramolecular Cyclisations of Olefinic Propargylic Carbonates and application to the diastereoselective synthesis of enantiomerically pure (−)‐α‐thujone
Authors: Oppolzer Wolfgang , Pimm Austen , Stammen Blanda , Hume W. Ewan
Published: December 2004

Intramolecular [Pd2(dba)3]/tri(2‐furyl)phosphine‐catalysed (dba = dibenzylideneacetone, PhCHCHCOCHCHPh) cyclisations of olefinic propargylic carbonates I provided alk‐1‐enyl‐(3‐aza)bicyclo[3.1.0]‐hexanes VIII in good yields. A palladium cascade sequence I → II → III → IV → VII → VIII is proposed. Furthermore, chiral propargylic carbonates such as 23, 24 and 25 allowed diastereoselective formation of bicyclo[3.1.0]hexanes 29, 30 and 31, respectively. The first diastereoselective synthesis of the monoterpene, (−)‐α‐thujone 40 illustrates the potential of the method.
Rogioldiol A, a new obtusane diterpene, and rogiolal, a degraded derivative, of the red seaweed Laurencia microcladia from II rogiolo along the coast of tuscany: A Synergism in Structural Elucidation
Authors: Guella Graziano , Pietra Francesco , Marchetti Fabio
Published: December 2004

The structure of rogioldiol A ((−)‐1), isolated from the red seaweed Laurencia microcladia, was determined. Employing the exciton‐coupling technique for rogioldiol A p‐bromobenzoate (2), the absolute configuration at C(9) of (−)‐1 was assigned, and, together with extensive NMR experiments, the absolute configuration at C(10) and preferred conformations of (−)‐1 were determined. The absolute configuration of the hetero‐substituted cyclohexane ring was deduced in analogy from the X‐ray structure of 4, a derivative of the aldehyde 3, which was isolated from the same seaweed and is believed to be a degradation product of (−)‐1.
C45‐ and C50‐Carotenoids Part7 Total synthesis of (all‐E,2R,6R,2′R,6′R)‐ and (all‐E,2R,6S,2′R,6′S)‐2,2′‐Bis(4‐hydroxy‐3‐methylbut‐2‐enyl)‐γ,γ‐carotene (sarcinaxanthin)
Authors: Lanz Marc , Bartels Birgit , Pfander Hanspeter
Published: December 2004

The synthesis of sarcinaxanthin ((2R,6R,2′R,6′R)‐1), a symmetrical C50‐carotenoid with two γ‐end groups, isolated from Sarcina lutea and from Cellulomonas biazotea as major pigment, was based on the strategy C20 + C10 + C20 = C50 using camphoric acid as starting material for the C20‐end group 3. The key step of the synthesis is a ring enlargement of the cyclopentane derivative 10 with 2,4,4,6‐tetrabromocyclohexa‐2,5‐dien‐1‐one (TBCO) to give the cyclohexane derivative 11 (Scheme 1). The spectroscopic data of the synthetic compound are in full agreement with the data of the isolated product and give the final proof for the (2R,6R,2′R,6′R) chirality of natural sarcinaxanthin.
Synthesis of Carotenoids in the Gliding Bacteria Taxeobacter: (all‐E,2′R)‐3‐deoxy‐2′‐hydroxyflexixanthin
Authors: Bireher Christof , Pfander Hanspeter
Published: December 2004

The c40‐carotenoid (all‐E, 2′R)‐deoxy‐2′‐hydroxyflexixanthin (=1′,2′‐dihydroxy‐3′,4′‐didehydro‐1′,2′‐dihydro‐β,ψ‐caroten‐4‐one;(2′R)‐2) was synthesized according to a C15 + C10 + C10 = C40 strategy. The chiral centre was introduced into the C10‐end group by the enantioselective Sharpless dihydroxylation. The four building blocks were coupled by applying four consecutive Witting reactions. By comparison of the CD spectra of the synthetic (2′R)‐2 with those of 2 isolated from the gliding bacteria Taxeobacter, the configuration of natural 2 was determined as (2′R).
Biosynthesis of cis‐Jasmone: a pathway for the inactivation and the disposal of the plant stress hormone jasmonic acid to the gas phase?
Authors: Koch Thomas , Bandemer Katja , Boland Wilhelm
Published: December 2004

Flowers of Jasminum rincospernum convert deuterium‐labeled jasmonic acid [2H5]‐4a and methyl 1,2‐didehy‐drojasmonate [2H4]‐8 into labeled cis‐jasmone [2H4]‐1. The labeling pattern of the resulting cis‐jasmone (1) is consistent with a Grob fragmentation of the didehydrojasmonic acid 8a by decarboxylation after protonation of the keto group. The pathway is also operative in leaves of several higher plants, including mono‐ and dicotyledonous specimens. In Lima beans besides cis‐jasmone (1) an equimolar mixture of trans‐ and cis‐isomers of methyl jasmonate (4) and epi‐4, is emitted after treatment with Jasmonic acid (4a). The relative ratio of 1 and 4/epi‐4 is critically dependent on the concentration of the administered jasmonic acid (4a) and the ambient temperature of the plant. Unlike 4a, the 1,2‐didehydrojasmonic acid (8a) is not able to induce volatile biosynthesis. Therefore, the transformation of 4a via 8 a into 1 appears to have a special importance for the irreversible inactivation and disposal of the plant stress hormone jasmonic acid to the gas phase and may serve, besides other modes of inactivation, as a shunt in case of high internal of the stress hormone 4a. The conversion of the biologically active jasmonic acid (4a) into the inactive and volatile cis‐jasmone (1) is the first example of a disposal of an inactive metabolite of a phytohormone to the gas phase as an infinite sink.
Investigation of the Chemo‐ and Stereoselectivity of the Ketene‐Claisen Rearrangement
Authors: Ernst Beat , Oehrlein Reinhold , Belluš Daniel , Gonda Jozef , Jeschke Rainer , Nubbemeyer Udo
Published: December 2004

A novel type of ketene‐Claisen rearrangement in which the precursor of the rearrangement is generated in situ by reaction of optically active allyl thioethers with dichloroketene is described. A characteristic feature of this rearrangement is the excellent chemoselectivity in favor of allyl thioethers vs. allyl ethers, i.e., exclusive chirality transfer of the allylic sulfur moiety is observed with 12, 13, and 25‐‐27. The cyclic, optically active allyl thioethers (+)‐(R)‐4 and (−)‐(S)‐4 and the open‐chain allyl thioethers 11‐‐13 rearrange with in situ generated dichloroketene to the optically active thioesters (−)‐(S)‐28, (+)‐(R)‐28, and 31‐33, respectively. A chirality‐transfer of > 99% in the cyclic cases (+)‐(R)‐4 and (−)‐(S)‐4, and 96‐‐98 % in the open‐chain cases 11‐‐13 is observed. Furthermore, the dichloroketene‐Claisen rearrangement is characterized by a high asymmetric 1,2‐induction. The chiral allylic sulfides 25‐‐27 give the optically active thioesters 36‐‐38 with a 1,2‐induction > 99% as determined by NMR‐shift experiments.
A Short Synthesis of the Factor‐Xa Inhibitor DX‐9065a using palladium‐catalyzed key steps
Authors: Kehr Christiane , Neidlein Richard , Engh Richard A. , Brandsretter Hans , Kucznierz Ralf , Leinert Herbert , Marzenell Klaus , Strein Klaus , Saal Wolfgang Von Der
Published: December 2004

We describe a new, efficient synthesis of DX‐9065a (4), a potent inhibitor of the blood coagulation enzyme factor Xa (fXa) which has previously been prepared in more than 20 steps. We saved approximately 10 steps starting with a Pd‐catalyzed cyanation of the triflate 10 of 7‐methoxynaphthalen‐2‐ol (9). After cleavage of the MeO group with boron tribromide, the triflate 6 was coupled to acrylate 5 in a Heck reaction (→3). The subsequent transformations led to DX‐9065 a.
Flash Photolysis of 5‐Methyl‐1,4‐naphthoquinone in Aqueous Solution: Kinetics and mechanism of photoenolization and of enol trapping
Authors: Chiang Yvonne , Kresge A. Jerry , Hellrung Bruno , Schünemann Patrick , Wirz Jakob
Published: December 2004

5‐Methyl‐1,4‐naphthoquinone (1) is a remarkable probe to study hydrogen and proton transfer reactions. The photoenol 4‐hydroxy‐5‐methylidene naphthalen‐1 (5H)‐one (2) is formed in the ground state within 2 ps of excitation and with a quantum yield of unity, presumably through a conical intersection of the S0 and S1 hypersurfaces. In aqueous acid, enol 2 is hydrated to 5‐(hydroxymethyl)naphthalene‐1,4‐diol 3 (X  OH, Scheme 1). The rate of hydration of 2 increases linearly with acid concentration from ca. 1.5 × 104 s−1 at pH 6 to reach a maximum value of 9 ×107 s−1 when the remaining carbonyl function is protonated, pKa(2+) = 1.1. Contrary to an earlier suggestion, the rate‐determining step in the acid‐catalyzed hydration of 2 is addition of water to the conjugate acid 2+. Pronounced acceleration of the decay rate of 2 by hydrazoic‐acid buffers indicates competitive trapping of 2+ by the azide ion. In neutral‐to‐weakly‐basic solutions, enol 2 reacts by ionization, pKa(2) = 6.5, and nearly diffusion‐controlled condensation of the carbanionic species 2− with quinone 1. Proto‐nation at the methylidene C‐atom does not compete measurably with protonation on carbonyl O‐atom, despite a Substsial thermodynamic basic for carbon Portoation of ca. 50 kJ mol−1 for 2 and 100 mol−1 for 2−.
Regioselective Enzyme‐Mediated Glycosylation of Natural Polyhydroxy Compounds. Part 1. Galactosylation of stevioside and steviolbioside
Authors: Danieli Bruno , Luisetti Monica , Schubert‐Zsilavecz Manfred , Likussar Werner , Steurer Sabine , Riva Sergio , Monti Daniela , Reiner Josef
Published: December 2004

Bovine β‐1,4‐galactosyltransierase is an efficient catalyst for the regioselective transfer of galactose from UPD‐galactose, generated in situ with the UDP‐glucose/UDP‐glucose‐4‐epimerase system, to the kaurane glycosides stevioside (1) and Steviolbioside (2), affording the corresponding galactosyl derivatives 3 and 4 in high yields. By a combination of 2D NMR techniques (COSY, TOCSY, ROESY, HMQC, and HMBC), the structure of the products is established as 13‐[(β ‐D‐galactopyranosyl‐(1 → 4)‐β‐D‐glucopyranosyl‐(1 → 2)‐ β ‐D‐glucopyranosyl)oxy]kaur‐16‐en‐19‐oic acid β ‐D‐glucopyranosyl ester (3) and 13‐[(β‐D‐galactopyranosyl‐(1 → 4)‐ β‐D‐glu‐copyranosyl‐(1 → 2)‐ β‐D‐glucopyranosyl)oxy]kaur‐16‐en‐19‐oic acid (4).
Topospecific Reactions of a [5.5.5.5]Fenestradiene with [Fe2(CO)9]
Authors: Wang Jing , Guidetti‐Grept Régine , Keese Reinhart , Stoeckli‐Evans Helen
Published: December 2004

N, N‐Dimethylformamide dimethyl acetal transforms an allylic OH group, which is part of a tetracyclic hydrocarbon in a unique elimination reaction into a [5.5.5.5]fenestradiene (2b → 4). In topologically selective reactions of this diene 4 with [Fe2(CO)9,], the [Fe(CO)4(η2‐diene)] and the [Fe(CO)3(η4‐diene)] complexes 8 and 9, respectively, are formed by complexation on one side of the diene moiety, whereas complexation on the other side leads to a [Fe(CO)2(Cp)] complex 10.
Synthesis of Vitamin B12 Derivatives with a Peripheral Metal Binding Site
Authors: Mayor Marcel , Scheffold Rolf , Walder Lorenz
Published: December 2004

The synthesis and structural characterization of the vitamin B12 derivatives 9 and 10 equipped with a peripheral EDTA (ethylenediaminetetraacetic acid) binding site is described. It is based on the condensation of an activated ester of cobester‐c‐acid with ethane‐1,2‐diamine or 2‐aminoethanol followed by acylation of the resulting amines with the monoanhydride 8 of EDTA. The title compounds 9 and 10 can be used as modifiers for metal oxide semiconductor electrodes and are potential precursors for the synthesis of bimetallic, supramolecular catalysts.
Substituent Effects on Fe+‐Mediated [4+2] Cycloadditions in the Gas Phase
Authors: Schroeter Katrin , Schalley Christoph A. , Schröder Detlef , Schwarz Helmut
Published: December 2004

The Fe+‐mediated [4+2] cycloaddition of dienes with alkynes has been examined by four‐sector ion‐beam and ion cyclotron resonance mass spectrometry. Prospects and limitations of this reaction were evaluated by investigating several Me‐substituted ligands. Me Substitution at C(2) and C(3) of the diene, i.e., 2‐methylbuta‐1,3‐diene, 2,3‐dimethylbuta‐1,3‐diene, hardly disturbs the cycloaddition. Similarly, variation of the alkyne by use of propyne and but‐2‐yne does not affect the [4+2] cycloaddition step, but allows for H/D exchange processes prior to cyclization. In contrast, Me substituents in the terminal positions of the diene moiety (e.g., penta‐1,3‐diene, liexa‐2,4‐diene) induce side reactions, namely double‐bond migration followed by [3+2] and [5+2] cycloadditions, up to almost complete suppression of the [4+2] cycloaddition for 2,4‐dimethylhexa‐2,4‐diene. Similarly, alkynes with larger alkyl substituents (pent‐1‐yne, 3,3‐dimethylbut‐1‐yne) suppress the [4 + 2] cycloaddition route. Stereochemical effects have been observed for the (E)‐ and (Z)‐penta‐1,3‐diene ligands as well as for (E,E)‐ and (E,Z)‐hexa‐2,4‐diene. A mechanistic explanation for the different behavior of the stereoisomers in the cyclization reaction is developed. Further, the regiochemical aspects operative in the systems ethoxyacetylene/pentadiene/Fe+ and ethoxyacetylcne/isoprene/Fe+ indicate that substituents avoid proximity.
Photolysis of Steroidal 20‐Aryl‐Substituted 11‐Nitrites
Authors: Kalvoda Jaroslav , Grob Jüren , Bjelakovíć Mira , Lorenc Ljubinka , Mihailovíć Mihailo Lj.
Published: December 2004

The two structurally similar 20‐phenyl‐ and 20‐(4‐methoxyphenyl)‐11‐(nitrosooxy)pregnan‐20‐ol derivatives 4 and 7 behave differently under photolytic conditions, the former nitrous acid ester affording, as a main product, the benzo‐fused hexacyclic compound 9, and the latter the 21‐nitro derivative 12. Mechanistic aspects of these transformations are discussed.
Synthesis of Unnatural Lipohilic N‐(9H‐Fluoren‐9‐ylmethoxy)carbonyl‐Substituted α‐Amino Acids and Their Incorporation into Cyclic RGD‐Peptides: A structure‐activity study
Authors: Koppitz Marcus , Huenges Martin , Gratias Rainer , Kessler Horst , Goodman Simon L. , Jonczyk Alfred
Published: December 2004

The αv/β3 integrin is implicated in human tumor metastasis and angiogenesis. It has been shown that structures of the sequence cyclo(‐Arg1‐Gly2‐Asp3‐D‐Phe4‐Xaa5‐) (I) and cyclo(‐Arg1‐Gly2‐Asp3‐Phe4‐D‐Xaa5‐) (II) bind with high affinity and the latter with high selectivity to this receptor. The residues Xaa and D‐Xaa accept a broad variety of amino acids. Here, we report on the synthesis, activities, and conformational analysis of cyclic Arg‐Gly‐Asp (RGD) peptides containing liophilic amino acids Xaa or D‐Xaa in position 5. For I, these were (2S)‐2‐aminohexadecanoic acid (Ahd) and N′‐hexadecylglycine (Hd‐Gly) and in II, D‐Ahd and Hd‐Gly, and, for control purposes, Ahd were incorporated (Fig. 1). The enantiomerically pure a‐amino acids were obtained by non‐enantioselective synthesis and subsequent enzymatic separation of isomers using acylase I (Scheme). Hd‐Gly was prepared in a modified procedure according to Stewart from ethyl bromoacetate and hexadecylamine (Scheme). The synthesis and physicochemical properties of the corresponding (9H‐fluoren‐9‐ylmethoxy)carbonyl (Fmoc) derivatives, compatible with solid‐phase peptide synthesis, are described. Structure elucidation by NMR reveals that the lipid modification has no significant impact on the template structures when incorporated into them. For peptides I with Xaa = Ahd or Hd‐Gly (1 or 2), a βII′/γ‐turn‐like arrangement with D‐Phe in i+1 position of the β‐turn is found. Peptides II with D‐Xaa = D‐Ahd or Hd‐Gly (3 or 4) exhibit a βII′/γ‐turn conformation with Gly in i+1 position of the β‐turn, whereas II with Ahd instead of D‐Xaa, i.e., lacking a D‐amino acid in position 4 or 5 (5). adopts no defined conformation. However, in assays of receptor specificity employing human αvv/β3 integrin, the compounds exhibit IC50 values ranging from nanomolar to less than millimolar. These results indicate that although the arrangement of the pharmacophoric groups is preserved in the target compounds, the biological activity is highly dependent on spatial requirements of the lipid anchor in the receptor binding pocket. Obviously, only certain positions do not affect the binding.
Studies on the Base‐Pairing Properties of N7‐(2‐Deoxy‐β‐D‐erythro‐pentofuranosyl)guanine (N7Gd)
Authors: Seela Frank , Leonard Peter
Published: December 2004

The base‐pairing properties of N7‐(2‐deoxy‐β‐D‐erythro‐pentofuranosyl)guanine (N7Gd; 1) are investigated. The nucleoside 1 was obtained by nucleobase‐anion glycosylation. The glycosylation reaction of various 6‐alkoxy‐purin‐2‐amines 3a‐i with 2‐deoxy‐3,5‐di‐O‐(4‐toluoyl)‐α‐D‐erythro‐pentofuranosyl chloride (8) was studied. The N9/N7‐glycosylation ratio was found to be 1:1 when 6‐isopropoxypurin‐2‐amine (3d) was used, whereas 6‐(2‐methoxyethoxy)purin‐2‐arnine (3i) gave mainly the N9‐nucleoside (2:1). Oligonucleotides containing compound 1 were prepared by solid‐phase synthesis and hybridized with complementary strands having the four conventional nucleosides located opposite to N7Gd. According to Tm values and enthalpy data of duplex formation, a base pair between N7Gd and dG is suggested. From the possible N7Gd dG base pair motives, Hoogsteen pairing can be excluded as 7‐deaza‐2′‐deoxyguanosine forms the same stable base pair with N7Gd as dG.
Synthesis and Properties of 2′‐Deoxy‐1′,2′‐seco‐D‐ribosyl (5′ → 3′)oligonucleotides (= 1′,2′‐seco‐DNA) containing adenine and thymine
Authors: Peng Ling , Roth Hans‐Jorg
Published: December 2004

Some 2′‐deoxy‐1′,2′‐seco‐D‐ribosyl (5′→3′)oligonucleotides (= 1′,2′‐seco‐DNA), differing from natural DNA only by a bond scission between the centers C(1′) and C(2′), were synthesized and studied in order to compare their structure properties and pairing behavior with those of corresponding natural DNA and homo‐DNA oligonucleotides (2′,3′‐dideoxy‐β‐D‐glucopyranosyl oligonucleotides). Starting from (−)‐D‐tartaric acid, 2′‐deoxy‐1′,2′‐secoadenosine derivative 9a and 1′,2′‐secothymidine (9b) were obtained in pure crystalline form. Using the phosphoramidite variant of the phosphite‐triester method, a dinucleotide monophosphate 1′,2′‐seco‐d(T2) was synthesized in solution, while oligonucleotides 1′,2′‐seco‐d[(AT)6], 1′,2′‐seco‐d(A10) and 1′,2′‐seco‐d(T10) were prepared on solid phase with either automated or manual techniques. Results of UV‐ and CD‐spectroscopic as well as gel‐electrophoretic studies indicated that neither adenine‐thymine base pairing (as observed in natural DNA and homo‐DNA), nor the adenine‐adenine base pairing (as observed in homo‐DNA) was effective in 1′,2′‐seco‐DNA, Furthermore, hybrid pairing was observed neither between 1′.2′‐seco‐DNA and natural DNA nor between 1′,2′‐seco‐DNA and homo‐DNA.
Catalytic Cyclophanes. Part XI. A flavo‐thiazolio‐cyclophane as a biomimetic catalyst for the preparative‐scale electro‐oxidation of aromatic aldehydes to methyl esters
Authors: Mattei Patrizio , Diederich François
Published: December 2004

Flavo‐thiazolio‐cyclophane 6 was prepared on a gram scale by an 18‐step synthesis (Schemes 3 and 4). This pathway involved the very efficient preparation of bromo‐cyclophane 32 (37% yield over 13‐steps), which can be readily modified to create various multiply functionalized receptors. This bromide 32 was subsequently converted into the corresponding boronic acid and connected to the 7‐bromoflavin 10 (Scheme 2) via Suzuki coupling to give flavo‐cyclophane 36. The thiazolium unit was then introduced after quaternization of the tertiary amino groups of 36. Flavo‐thiazolio‐cyclophane 6, with both prosthetic groups attached in proximity to the well‐defined cyclophane binding site, is a functional model for the enzyme pyruvate oxidase. In basic methanolic solution, 6 catalyzes the oxidation of aromatic aldehydes to their corresponding methyl esters. Cyclophane 6 shows saturation kinetics, and the turnover number calculated for the oxidation of naphthalene‐2‐carbaldehyde to methyl naphthalene‐2‐carboxylate (kcat = 0.22 s−1) is one of the highest reported for an artificial enzyme. Control experiments showed that the catalytic advantages of 6 result from the macrocyclic binding and reaction site as well as from the covalent attachment of both cofactors to this site. The catalytic cycle is completed by electrochemical re‐oxidation of the reduced flavin moiety at a low working electrode potential (‐ 0.3 V vs. Ag/AgCl), and up to ca. 100 catalytic cycles can be performed on a preparative scale, The intramolecular nature of the electron transfer from the active aldehyde intermediate to the flavin is particularly conducive to the oxidation of unreactive aldehydes.
Synthesis and Odor of Chiral Partial Structures of Khusimone. Part 2
Authors: Spreitzer Helmut , Pichler Andrea , Holzer Wolfgang , Shahabi Manocher
Published: December 2004

Khusimone (1), one of the main odor‐donating compounds of vetiver oil, is subject of the following study on structure/odor relationship. Ring opening of the carbonyl‐functionalized bridge of the tricyclic khusimone leads to the bicyclic structures 2a/b. The enantioselective approach to these degraded structures is described, and the olfactory consequences are studied. Starting point of the synthesis is an enantiomerically pure enone ester which is easily obtainable from camphorsulfonic acid.
Enantioselective Synthesis of Planar Chiral [Cr(η6‐Arene)(CO)3] complexes via nucleophilic addition/hydride abstraction. Preliminary communication
Authors: Fretzen Angelika , Kündig E. Peter
Published: December 2004

Non‐racemic, planar chiral 1, 2‐disubstituted [Cr(η6‐arene)(CO)3] complexes were obtained via external chiral ligand‐controlled nucleophilic addition of alkyl‐, vinyl‐, and aryllithium reagents to monosubstituted complexes followed by an endo‐hydride abstraction with trityl cation. The reactions with [Cr(CO)3(η6‐phenyloxazoline)], [Cr(CO)3(η6‐phenylmethaneimine)], and [Cr(CO)3 (η6‐phenylmethanenydrazone)] took place with complete ortho‐selectivity and a high degree of enantioselectivity (up to 98% ee).
TADDOLs under closer scrutiny – why bulky substituents make it all different
Authors: Beck Albert K. , Dobler Max , Plattner Dietmar A.
Published: December 2004

A systematic investigation of the rotational behavior of aryl substituents in α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols (TADDOLs) is presented. In the use as chiral ligands for enantioselective metal‐catalyzed reactions, a change from phenyl to bulkier substituents, e.g., 1‐naphthyl, gives rise to an astounding alteration of the selectivity, The possible existence of preferred rotamers of TADDOLs has so far not been given due attention, which encouraged us to look at the validity of the Knowles model, originally formulated for diaryl substituted bisphosphines. 1H‐NMR Investigations at various temperatures as well as X‐ray powder diffraction were employed to study the rotation in the case of tetra(1‐naphthyl) TADDOL 1. To support the interpretation of the experimental results, molecular mechanics, semiempirical, and ab initio calculations were performed. For comparison, the energy surface of tetraphenyl TADDOL 2 was calculated as well. Our results lead to the conclusion that for 1, only one major conformation is present in both solution and solid state, which determines the stereochemical outcome of the catalyzed reactions.
Properties and reactivity in groups of the periodic system: Ion‐molecule reactions CH3X + CH3X+· (X = F through At)
Authors: Zahradník Rudolf , Šroubková Libuše
Published: December 2004

The reactions indicated in the title have been studied in terms of direct processes and complex formation. Quantum‐chemical methods have been applied to the passage of an acid (H+, CH, X+) from CH3X+· to CH3X, and the abstraction of a radical (H· CH, X·) from CH3X by CH3X+·. It has been shown that a complex represented by a dimer of a methyl‐halide radical cation, (CH3X), with a two‐center three‐electron bond XX, has fairly high stability. These investigations were based on non‐empirical quantum‐chemical calculations, the results being systematically compared with experimental determinations. Some calculations included all electrons (X=F, Cl, Br), others were based on relativistic pseudopotentials (X=F through At). The two sets of calculations agree qualitatively with each other and with experimental observations.
Comparative study of the cope rearrangement of hexa‐1,5‐diene and barbaralane
Authors: Baumann Harold , Voellinger‐Borel Aline
Published: December 2004

The classical rules for Cope rearrangements predict a transition state with chair form to be favored over the boat form. On the other hand, bridged homotropylidenes, which allow only a boat‐form transition state by steric reasons, have extremely low barriers. A controversy about the correct pathway and the different possible intermediates and transition states of the reaction has gone on for years. In this work, the hypersurfaces of barbaralane, in comparison with the boat‐ and chair‐form of hexa‐1,5‐diene, are computed by the ab inito CASSCF (6,6)/6‐31G** method starting with UMP2/6‐31G** natural orbitals (NO's). All three hypersurfaces show characteristic features, and, moreover differ from each other. A hitherto undiscussed intermediate, bicyclo[2.2.0]hexane, was localized on the boat‐hexa‐1,5‐diene pathway. So it is noteworthy that our transition state for the boat‐hexa‐1,5‐diene does not correspond to the transition states found by other authors for this conformation. The computed enthalpies of activation of boat‐ and chair‐hexa‐1,5‐diene, and barbaralane are in good agreement with the experimental data.
Nucleic Acid Analogs with Constraint Conformational Flexibility in the Sugar‐Phosphate Backbone “Tricyclo‐DNA”. Part 1. Preparation of [(5′R,6′R)‐2′‐deoxy‐3′,5′‐ethano‐5′,6′‐methano‐β‐D‐ribofuranosyl]thymine and ‐adenine, and the corresponding phosphoramidites for oligonucleotide synthesis
Authors: Steffans Ralph , Leumann Christian
Published: December 2004

The synthesis of the tricyclo‐deoxynucleoside analogs 1 and 2 and of the corresponding cyanoethyl phosphoramidite building blocks 16 and 21 for oligonucleotide synthesis is described. These tricyclic deoxynucleoside analogs differ from the recently introduced bicyclo‐deoxynucleosides by an additional cyclopropane unit joined to the centers C(5′) and C(6′) of the latter (se Fig. 1), and thus represent a further member of the class of nucleoside analogs with constraint conformational flexibility. The synthesis of the tricyclo‐deoxynucleoside was achieved by a diastereoselective carbene addition to the enantiomerically pure silyl enol either 8/9 and a Vorbrüggen condensation of the tricyclic carbohydrate unit 10/11 with in situ persilylated thymine and N6‐benzoyladenine. Selective tritylation of the tertiary OHC(5′) and phosphinylation of OHC(3′) of 1 and 2 afforded the corresponding phosphoramidites 16 and 21. The ‘exo’‐configuration of the newly introduced cyclopropane ring was confirmed by 1H‐NMR‐NOE spectroscoy. The α‐D‐ and β‐D‐configuration at C(1′) of the nucleoside analogs 1 and 14 (2 and 19, resp.) was assigned by 1H‐NMR‐NOE spectroscopy and NOESY. Modeling studies of the β‐D‐anomeric nucleoside analog 1 indicate a preference for the 2′‐endo‐conformation of the furanose ring and a partial correction of the torsion angle γ to the anti‐clinal range compared to bicyclo‐deoxynucleosides.
Four Novel Glycosides from the Aphid Pseudoregma bambmicola T
Authors: Zhang Guo‐lin , He Mei‐yu , Xing Qi‐yi
Published: December 2004

Four novel glycosides, bambusicolasides III–VI (1–4), were isolated from the aphid Pseudoregma bambusicola T. The structures of 1–4 were elucidated by spectral evidence including FAB‐MS and C.H‐COSY, HMBC, and NOE difference experiments, and by hydrolysis. In vitro tests with these compounds showed little cytotoxic activity against human KB cells (< 10%).
TADDOLs with Unprecedented Helical Twisting Power in Liquid Crystals. Preliminary communication
Authors: Kuball Hans‐Georg , Weiß Bernhard , Beck Albert K. , Seebach Dieter
Published: December 2004

A large number of TADDOL (α,α,α′, α′‐tetraaryl‐1,3‐dioxolan‐4,5‐dimethanol) derivatives has been tested as chiral dopants for inducing conversion of nematic to cholesteric phases. With the Merck liquid‐crystal materials ZLI‐1695 and K15, it was demonstrated that some TADDOLs have unprecedentedly high helical twisting powers (HTP). Thus, the TADDOL with four 9‐phenanthryl α‐substituents has a HTP in the achiral mesophase 4‐(4‐pentylphenyl)benzonitrile of 405 μm−1 between 24 and 34°. The temperature‐dependent HTP measurements have been performed by analyzing Grandjean textures microscopically (Cano method). The structure‐dependent HTP of various types of TADDOL dopants is discussed. There are similarities between size and sign of HTP on the one hand, and between degree and relative topicity of enantioselectivity in reactions, on the other hand, as caused by TADDOLs and by 1,1′‐binaphthols.
[2+3] Cycloadditions of ‘Thiocarbonyl Ylides’ (= (Alkylidenesulfonio)methanides) and diazoalkanes with N,N′‐(thiocarbonyl)diimidazole (= 1,1′‐(carbonothioyl)bis[1H‐imidazole])
Authors: Mlostoń Grzegorz , Gendek Tomasz , Linden Anthony , Heimgartner Heinz
Published: December 2004

Heating of a mixture of N,N′‐(thiocarbonyl)diimidazole (= 1,1′‐(carbonothioyl)bis[1H‐imidazole]; 1) and 2,5‐dihydro‐1,3,4‐thiadiazole 2a or 2b gave the 1,3‐dithiolanes 4a and 4b, respectively, via a regiospecific 1,3‐dipolar cycloaddition of the corresponding ‘thiocarbonyl methanides’ 3a,b onto the CS group of 1 (Schemes 1 and 2). The adamantane derivative 4b was not stable in the presence of 1H‐imidazole and during chromatographic workup. The isolated 1,3‐dithiole 5 is the product of a base‐catalyzed elimination of 1H‐imidazole from the initial cycloadduct 4b. The formation of the S,N‐acetal 6 can be rationalized by a protonation of the ‘thiocarbonyl ylide’ 3b followed by a nucleophilic addition of 1H‐imidazole. With the diazo compounds 8a–e (Scheme 3) 1 underwent a regiospecific 1,3‐dipolar cycloaddition to give the corresponding 2,5‐dihydro‐1,3,4‐thiadiazole derivatives 9, which spontaneously eliminated 1H‐imidazole to yield (1H‐imidazol‐1‐yl)‐1,3,4‐thiadiazoles 10. The structures of 10a and 10d were established by X‐ray crystallography. In the case of diazodiphenylmethane (8f), the initial cycloadduct 9f decomposed via a ‘twofold extrusion’ of N2 and S to give 1,1′‐(2,2‐diphenylethenylidene)bis[1H‐imidazole] (11; Scheme 3).
A Study of the Metabolic Degradation of an insect juvenile hormone analog using different radiolabeling
Authors: Tykva Richard , Wimmer Zdenêk , Bennettová Blanka , Vlasáková Vêra
Published: December 2004

The fate of an insect juvenile hormone analog applied to the insect body of the flesh fly (Sarcophaga bullata) or the tsetse fly (Glossina palpalis), respectively, was studied using three different radiolabeled positions in the parent biologically active compound 1. Several metabolites were found and analyzed. A mechanism of degradation of the applied molecule was designed using a combination of several radioanalytical methods. A unique monitoring of the applied compound and its metabolites was provided, based on the different radiolabeling of the structure (cf. 1a–1c), and established their fate in an insect body during a 10‐day experiment. A 14C and 3H radiolabeling, respectively, was employed to synthesize three different radiolabeled forms 1a–1c derived from the parent non‐labeled 1. A combination of three different ways of radiolabeling resulted in an advantage in tracing the metabolic pathway of degradation of the employed compound 1 in its radiolabeled forms 1a–1c.
Structure and Properties of Transition‐Metal Complexes with Chiral C2‐symmetric binucleating ligands
Authors: Fahrni Christoph J. , Pfaltz Andreas , Neuburger Markus , Zehnder Margareta
Published: December 2004

The coordination behavior of chiral binucleating ligands of type 1–4 with various transition metals has been investigated. 1H‐NMR Titration experiments with zinc(II) salts gave detailed structural information about the structure of the resulting zinc complexes. Ligand 1 forms an unusual C3‐symmetric dinuclear zinc complex [Zn2CIL3] (8a) which was characterized by X‐ray crystallography. Treatment of complex 8a with various carboxylic acids resulted in ligand‐exchange reactions. With ligand 2, a hydroxo‐bridged dinuclear copper complex 15 was synthesized and its structure elucidated by X‐ray analysis. Solution studies UV and 1H‐NMR spectroscopy of the reaction of ligand 3 with ZnII and NII salts revealed the formation of dimeric species of the type [M2X4L2]. Ligand 4 formed well‐defined dinuclear complexes with NiII and CuII salts of which the corresponding NiII complex [Ni2(AcO)2(ClO4)2L] (22a) was characterized by crystal‐structure analysis.
Synthesis and Biological Evaluation of 14‐Alkoxymorphinans. Part 15. Novel δ opiod receptor antagonists with high affinity and selectivity in the 14‐alkoxy‐substituted indolomorphinan series
Authors: Schmidhammer Helmut , Krassnig Roland , Greiner Elisabeth , Schütz Johannes , White Angela , Berzetei‐Gurske Ilona P.
Published: December 2004

The indolomorphinans 4–7 were prepared from their corresponding morphinan‐6‐one derivatives 8–11 via Fischer indole synthesis. Compounds 4 and 5 exhibited higher antagonist potency at δ opioid receptors in the mouse vas deferens preparation than the reference drug HS 378 (2), while compounds 6 and 7 were less potent.
Tetraepoxy[22]annulen(2.2.2.0): Ein neuartiges Tetraepoxy‐verbrücktes, neutrales, aromatisches [22]Annulen
Authors: Märkl Gottfried , Sauer Heinrich , Stiegler Jürgen , Kreitmeier Peter , Burgemeister Thomas
Published: December 2004

Tetraepoxy[22]annulene(2.2.2.0): a Tetraepoxy‐Bridged Neutral Aromatic [22]Annulene of a New Type

We describe the synthesis of tetraepoxy[22]annulene(2.2.2.0) 4, the first aromatic annulene of type B by a cyclizing twofold Wittig reaction of 2,2′‐bifuran‐5,5′‐dicarbaldehyde (5) and the bis[phosphonium] salt 8. The configuration of 4, mainly determined by NMR spectroscopy is (Z,E,Z). According to the UV/VIS spectrum and the 1H‐NMR data, the electronic situation in 4 is quite different from that of tetraepoxy[22]annulene(3.0.3.0) 2 and tetraepoxy[22]annulene(2.1.2.1) 3. According to variable‐temperature 1H‐NMR spectroscopy, 4 is a highly dynamic system, where the (E)‐double bond rotates around the adjacent σ‐bonds. At ca. −130°, this dynamic process is frozen, and 4 appears as a diatropic aromatic system; the free activation energy of the rotation ΔG≠ is ca. 8.75 kcal/mol.
Aminocyclopentitols from N‐Alkylpyridinium Salts: A photochemical approach
Authors: Acar Ersin A. , Glarner Fabrice , Burger Ulrich
Published: December 2004

The photolysis of N‐alkylpyridinium halides 9a–e in alkaline H2O gave 6‐azabicyclo[3.1.0]hexenol derivatives 10a–e. N–Substituents bearing ether, acetal, and alcohol functions were found to do not adversely influence the photochemical reaction course. The free OH groups of the N–(3‐hydroxypropyl) derivative 10d were protected by benzoylation. The ensuing dibenzoate 14 underwent stereocontrolled opening of the aziridine ring on reaction with MeSH/BF3 to give a thioether 15. With benzoic acid in CHCI3, 10d gave the 4‐hydroxy‐5‐aminocyclopent‐2‐enyl benzoate 11. The meso‐2‐aminocyclopent‐4‐ene‐1,3‐diol 12 was obtained by hydrolysis of 11. On reaction with Boc2O and NaI, the aziridine ring of 14 was converted to a bicyclic compound 17. Hydrolysis of 17 provided the trans‐1,3‐diol 18, the epimer of 12. Face‐selective dihydroxylation of Boc‐protected 12 gave a meso‐aminocyclopentanetetrol 23 which was characterized upon peracetylation. Dihydroxylation of 15 provided a racemic analogue of epi‐mannostatin A (26).
Asymmetric syn‐Dihydroxylation of β‐Substituted (2R)‐N‐(α,β‐Enoyl)bornane‐10,2‐sultams
Authors: Raczko Jerzy , Achmatowicz Michael , Jezewski Artur , Chapuis Christian , Urbañczyk‐Lipkowska Zofia , Jurczak Janusz
Published: December 2004

Variously β‐substituted (2R)‐N‐[(E)‐α,β‐enoyl]bornane‐10,2‐sultams were oxidized with OsO4/4‐methylmorpholine 4‐oxide in a highly stereoselective manner. In all cases, the attack occurred on the C(α)‐re face. The absolute configurations of all products were determined by chemical correlation. Mechanistic considerations about the reactive conformation as well as fully refined X‐ray crystal structures of the dihydroxylated products are discussed. New neutral conditions for sultam acylation, applicable to the preparation of the taxol and Taxotere® C(13) side chain as well as of Cardizem® and chloramphenicol precursors, are also presented.
Nucleotides. Part LVI. Synthesis and biological activity of modified (2′–5′)triadenylates containing 2′‐terminal 2′,3′‐dideoxy‐3′‐fluoroadenosine derivatives
Authors: Kvasyuk Evgeny I. , Kulak Tamara I. , Tkachenko Olga V. , Sentyureva Svetlana L. , Mikhailopulo Igor A. , Suhadolnik Robert J. , Henderson Earl E. , Horvath Susan E. , Guan Ming‐Xu , Pfleiderer Wolfgang
Published: December 2004

Some new (2′–5′)triadenylates 13–16, containing at the 2′‐terminal end 3′‐fluoro‐2′,3′‐dideoxyadenosine derivatives, have been synthesized by the phosphotriester method. The selectively blocked nucleosides 2, 4, 5, and 7, were synthesized from the corresponding unprotected nucleosides 1, 3, and 6. The synthesized trimers 13, and 14 were 4‐ and 8‐fold, respectively, more stable towards phosphodiesterase from Crotalus durissus than the natural trimer 17. In comparison to trimer 17 the new compounds 13–15 inhibit HIV‐1 reverse transcriptase (RT) activity, and 15 and 16 the HIV‐1 induced syncytia formation 2–3 fold whereas none of 13–16 can improve R Nase L activity.
Synthesis of the Spermidine Alkaloid (−)‐(4R)‐Dihydroisomyricoidine
Authors: Horni Albert , Linden Anthony , Hesse Manfred
Published: December 2004

An asymmetric synthesis of (−)‐(4R)‐dihydroisomyricoidine (28), a 13‐membered amino lactam of type A, was performed by a diastereoselective Michael addition between the spermidine derivative 3 and the commercially available optically active ethyl carboxylate 4, and the cyclization of the resulting ω‐amino acid 7 using diethyl phosphorocyanidate ((EtO)2POCN), followed by a Wittig reaction to introduce the (Z)‐side chain. Some side reactions are also discussed.
3‐Hydroxy‐2‐cyanoalk‐2‐enamides, and 2‐Cyano‐2‐(tetrahydrofuran‐2‐ylidene)‐ and 2‐Cyano‐2‐(tetrahydropyran‐2‐ylidene)acetamides: Synthesis, structure, and solvent‐dependent (Z)/(E)‐isomerism
Authors: Papageorgiou Christos , Akyel Kayhan , Borer Xaver , Oberer Lukas , Rihs Grety
Published: December 2004

3‐Hydroxy‐2‐cyanoalk‐2‐enamides, and 2‐cyano‐2‐(tetrahydrofuran‐2‐ylidene)‐ and 2‐cyano‐2‐(tetrahydropyran‐2‐ylidene)acetamides with N‐alkyl and N‐aryl substituents have been synthesized in three steps from cyanoacetic acid. Their conformations were investigated by X‐ray crystallography and 1H‐NMR ROESY spectroscopy at room temperature. The enolic compounds 1–3 adopt an extended conformation stabilized by a strong intramolecular OH …︁ OC bond both in the solid state and in (D6)DMSO solution. In contrast, the structure of the cyclic derivatives 5a,b–8a,b is solvent‐dependent. In the solid state and in CDCl3 solution, the compounds adopt an extended conformation of type I or III, while, in (D6)DMSO solution, their structures undergo time‐dependent (Z)/(E)‐isomerization structures (of type II or IV). This observation is compatible with a dipolar transition state of rotation. The kinetics of the isomerization are controlled by the N‐substituent, the N‐(t‐Bu) derivatives 7a and 7b having the highest barrier of rotation around the CC bond. The whole body of experimental evidence together with the results of molecular‐mechanics calculations with I–IV, indicate that, in DMSO, two (E)/(Z)‐isomers with two conformations are present, and that they undergo interconversion at room temperature with four different constants. The very fast exchange rates kI,II and kIII,IV in the NMR time‐scale might be responsible for the detection of only two isomers.
1,2‐Carbonyl Transposition of a Protected Rubanone: Stereoselective synthesis of bicyclic and tricyclic lactams derived from quinidine
Authors: Frackenpohl Jens , Langer Peter , Hoffmann H. Martin R.
Published: December 2004

α‐Bromination of 9‐acetoxy rubanone 2 and subsequent reaction with secondary amines gave bicyclic α‐amino ketones as a kinetic product and a 4‐oxa‐1‐azatwistan‐2‐one 6 under thermodynamic conditions. This two‐step procedure represents a concise 1,2‐carbonyl transposition and provides a short route to lactam alkaloids.
Nucleotides. Part LVII.. Synthesis of phosphoramidite building blocks of 2′‐amino‐2′‐deoxyribonucleosides: New compounds for oligonucleotide synthesis
Authors: Greiner Beate , Pfleiderer Wolfgang
Published: December 2004

The chemical synthesis of 2′‐amino‐2′‐deoxyribonucleosides of uracil, cytosine, adenine, and guanine, and their conversion into suitably protected 3′‐phosphoramidite building blocks 35–40 for oligonucleotide synthesis are described. The aglycone and the 2′‐amino functions were protected using the 2‐(4‐nitrophenyl)ethoxycarbonyl (npeoc) group. The synthesis of the 3′‐O‐succinyl (3′‐O‐(3‐carboxypropanoyl))‐substituted starting nucleoside 41 is described and its behavior examined in solution and on solid phase with regard to an anticipated migration during 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) deprotection. Oligonucleotides were prepared using the new building blocks, and their hybridization properties were studied by UV‐melting techniques.
New prospects for a prolonged functional life‐span of artificial hip joints by using the material combination polyethylene/aluminium oxide ceramic/metal
Authors: Semlitsch M. , Lehmann M. , Weber H. , Doerre E. , Willert H. G.
Published: December 2004

Investigations over the years have shown that the mirror‐finished Al2O3 ceramic is a much more suitable frictional counterpart to ultrahigh molecular weight (UHMW) polyethylene than metal. Despite the extremely great hardness difference between polyethylene and Al2O3 ceramic, a considerable lower wear rate is obtained for the polyethylene socket with this new low‐friction material combination. The unexpectedly favorable tribological behavior of this ceramic material in contact with polyethylene may be attributed to the following factors: better values for corrosion resistance characteristics, wettability with liquids, surface gloss, hardness, and scratch resistance of the ceramic material in comparison with those of the hitherto used metallic implant materials (AISI‐316L steel or cast CoCrMo alloy). It appears that, by using this new combination of materials for the socket and the ball, it will be possible to prolong the service life of artificial hip joints considerably without having to effect any fundamental changes in the present design and implantation principle retaining the hitherto used anchorage shaft made of wrought CoNiCrMoTi alloy Protasul‐10 of extremely high corrosion fatigue strength.
Cellulosic ion‐exchange membranes for hemodialysis
Authors: Mollison A. N. , Graydon W. F.
Published: December 2004

The application of cellulosic ion‐exchange membranes to hemodialysis was studied in vitro. The membranes were prepared by radiation‐grafting methacrylic acid and vinylpyridine to films of DuPont cellophane PD‐215 to produce cation‐exchange and anion‐exchange membranes, respectively.

Solutions of urea, creatinine, glucose, and uric acid were studied for their interactions with and diffusion through the membranes. Ultrafiltration rates were also determined. Cuprophane and PD‐215 cellophane were studied as controls.

Dialysis plots for the membranes revealed a mechanism of “assisted transport”. Initially, the solutes were removed from solution by a sorption/adsorption mechanism followed by a steady‐state diffusion process. The calculated diffusivities for these later steady‐state regions increased linearly with capacity for urea, creatinine, and uric acid, while for glucose the reverse was true.

The combined processes involved provided considerably greater mass transport per unit thickness than either DuPont PD‐215 cellophane or Cupropane.