bluuebunny/crossref_metadata_2025 huggingface dataset:
9‐(2′‐Deoxy‐β‐D‐xylofuranosyl)adenine Building Blocks for Solid‐Phase Synthesis and Properties of Oligo(2′‐deoxy‐xylonucleotides)
Authors: Roscmeycr Helmut , Krečmerova Marcela , Seela Frank
Published: December 2004

The 9‐(2′‐deoxy‐à‐D‐threo‐pentofuranosyl)adenine (=9‐(2′‐deoxy‐à‐D‐xylofuranosyl)adeninc, xAd; 2) was protected at its 6‐NH2 group with cither a benzoyl (5a) or a (dimethyfamino)methylidcnc (6a) residue and with a dimethoxytntyl group at 5′‐OH (5b, 6b). Compounds 5b and 6b were then converted into the 3′‐phosphonates 5c and 6c; moreover, the 2‐cyanoethyl phosphoramidite 6d was synthesized starting from fib. The DNA building blocks were used for solid‐phase synthesis of d[(xA)122‐A] (8). The latter was hybridized with d[(xT)12‐T] (Tm = 35°); in contrast, with d(T12), complex formation was not observed. Moreover, xAd and xTd were introduced into the self‐complementary dodccamcr d(G‐T‐A‐G‐A‐A‐T‐T‐C‐T‐A‐C) (12) at different positions lo give the oligomcrs 13–16. All oligonucleotides were characterised by temperature‐dependent CD and UV spectroscopy, and in addition, 14 by T‐jump experiments. From concentration‐dependent Tm measurements, the thermodynamic paraneters of the melting as well as the tendency of hairpin formation of the oligonucleotides were deduced. Oligemer 14 was hydrolyzed by snake‐venom phosphodiesterase in a discontinuous way implying a fast hydrolysis of unmodified 3′‐ and 5′‐flanks followed by a slow hydrolysis of the remaining modified tetramer. In contrast to this, oligonucleotide 16 was hydrolyzed in a continuous reaction. In both cases, calf‐spleen phosphodiesterase hydrolyzed the oligomer only marginally.
Synthese von Makrocyclen durch Ringerweiterung von 14gliedrigen cyclischen Imiden
Authors: Koch Thomas , Ognyanov Vassil I. , Hesse Manfred
Published: December 2004

Synthesis of Macrocyles by Ring Enlargement of 14‐Membered Cyclic Imides

In the presence of a base, cyclododecanone derivative 2, activated in α‐position by an allyloxycarbonyl group, underwent ring enlargement with isocyanates to give 14‐membered imides (Schemes 1–3). Cleavage of the activating group gave new 14‐membered imides which could be transformed by further ring‐enlargement reactions into new macrocyclic compounds.
Endohedral fullerene‐noble gas clusters formed with high‐energy bimolecular reactions of C (x = 60, 70; n = 1, 2, 3)
Authors: Weiske Thomas , Hrušák Jan , Bohme Diethard K. , Schwarz Helmut
Published: December 2004

Results are reported for high‐energy beam experiments which establish the formation of endohedral carbon cluster‐noble gas compounds by bimolecular reactions of C (x = 60, 70; n = 1, 2, 3) with He and C with Ne. The ions were accelerated up to 8 ke V in a four‐sector mass spectrometer and allowed to collide with the noble gas in a collision chamber at room temperatur. Product ions were monitored with a B/E = constant linked scan. Within the sensivity of the experiments, no carbon cluster‐gas compounds were observed in the reactions of C with H2, D2, O2, Ar, and SF6, or of C with O2. The observed fall in the cross‐section for carbon cluster‐noble gas compounds with increasing size of the noble gas, the observation of unimolecular loss of C2 from mass‐selected CxHe+ ions, and the elimination of carbon fragments instead of He observed in the formation of the collision‐induced CxHen+ product ions are taken as evidence for endohedral compound formation. Results of ab initio molecular‐orbital calculations for the perpendicular penetration of the plane of ionized benzene with He, Ne, and Ar indicate that sufficient kinetic energy should be available in the collisions with C to penetrate the C cage at the collision energies of the experiments.
Radical Cations and Radical Anions of Three Bridgehead Azopolycycloalkanes: A fluid‐solution ESR study
Authors: Gescheidt Georg , Lamprecht Axel , Rüchardt Christoph , Schmittel Michael
Published: December 2004

The radical mono‐ions of three azoalkanes in which the azo group is connected to the polycyclic alkane moieties at the bridgehead C‐atoms, i.e. 1,1′‐azonorbornane (1), 1,1′‐azotwistane (2), and 1,1′‐azobicyclo[3.2.1]octane (3), were studied in fluid solution by ESR spectroscopy. According to the ESR parameters and MO models, the radical cations of 1–3 should be considered as σ radicals, whereas the corresponding radical anions are π radicals. INDO calculations point to a a remarkable dependence of the 14N‐coupling constants on the geometry at the N‐atoms in the radical cations of aliphatic azo compounds.
α,α,α′,α′‐Tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols (TADDOLs) for Resolutions of Alcohols and as Chiral Solvating Agents in NMR Spectroscopy
Authors: Von Dem Bussche‐Hünnefeld Christoph , Beck Albert K. , Lengweiler Urs , Seebach Dieter
Published: December 2004

The use of α,α,α′,α′ ‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols ( = TADDOLs;1) as chiral NMR shift reagents (1H, 13C, 19F) is described. In many cases, the ratio of enantiomeric alcohols and amines can be determined under standard conditions of measurement (CDCl3 as solvent, room temperature). The preparation and use of a new type of TADDOL, the tetrakis(dimethylamino) derivative 1d, is described. Menthol, octan‐2‐ol, and oct‐1‐yn‐3‐ol are partially resolved by crystallization of clathrates with 1c and 1d.
Synthese und Reaktionsverhalten 2′‐substituierter Isoflavone
Authors: Süsse Manfred , Johne Siegfried , Hesse Manfred
Published: December 2004

Synthesis and Behaviour of Isoflavones Substituted in 2′‐Position

The protected chalcones 6–8 prepared from acetophenone and benzaldehydes rearranged to the dimethoxypropanone derivatives 9–11 in the presence of trimethyl orthoformate by Tl(NO3)3. 3 H2O. These compounds could be cyclized to the isoflavones 12–14 in high yields (Scheme 2). The conversion of these isoflavones to the corresponding isoflavanes (model compounds of the phytoalexin glabridin; see Scheme 1) was the main goal of this work. Hydrogenation of 13 and 14 gave the isoflavanes 15 and 16, respectively and their deprotection the racemic natural product 4′‐O‐demethylvestitol (17). Reduction of 13 and 14 yielded different compounds depending on the reducing agent (Scheme 3). The saturated alcohols 20–23 could be obtained with NaBH4 or LiBH4. They were transferred into the racemic 9‐O‐demethylmedicarpin (24) and haginin D (25) under acidic conditions. The ketones 26–28 (Scheme 4) were obtained in high yields by reduction of 12–14 with DIBAH. Deprotection of 26 yielded the racemic 2,3‐dihydrodaidzein (29). Compounds 13 and 27 as well as 20 and 22 showed different behaviour under reduction conditions with Li in liquid ammonia. An efficient method for the introduction of the MeOCH2O and the MeOCH2CH2OCH2 protecting groups into hydroxylated benzaldehydes and acetophenones (Scheme 5) is described. The appropriate experimental conditions depend on the regioselectivity and on the number of the protected groups. The protected aldehydes, especially those with a protected ortho OH group, show an extraordinary ionization behaviour in chemical‐ionization mass spectrometry (isobutane; Scheme 6).
The Isotopomeric (Z)‐ and (E)‐2,3‐Dimethyl(1,1,1,4,4,4‐2H6)but‐2‐enes: Mechanistic Probes for Stereospecific Epoxidation
Authors: Müller Paul , Pfyffer Jean
Published: December 2004

By unambiguous methods, (Z)‐ and (E)‐2, 3‐dimethyl(1, 1, 1, 4, 4, 4‐2H6)but‐2‐enes (3) were synthesized and transformed to the epoxides 4 with 3‐chloroperbenzoic acids. Both the isotopomeric olefins and the epoxides are detected separately by 1H‐NMR at 400 MHz. Epoxidation of (Z)‐3 with [RhICl(PPh3)3]/cumene hydroperoxide resulted in a 1: 1 mixture of (Z)‐ and (E)‐4, while reaction of (Z)‐3 with [FeIII(tpp)]Cl/PhIO gave only (Z)‐4 (tpp = tetraphenylporphyrin).
Absolute Configuration and Synthesis of (+)‐Caudoxirene, the Gamete‐Releasing and Gamete‐Attracting Pheromone of the Brown Alga Perithalia caudata (Phaeophyceae)
Authors: Wirth Dieter , Boland Wilhelm , Müller Dieter G.
Published: December 2004

The absolute configuration of the gamete‐releasing and ‐attracting pheromone 2‐vinyl‐3‐(5′‐vinylcyclopent‐2′‐enyl)oxirane ( =(+)‐caudoxirene; (+)‐1) of the marine brown alga Perithalia caudata is established as (2R,3R,1′S,5′S). Highly diastereoselective syntheses and the biological activities of three diastereoisomers of 1 are described. Compound (+)‐(2R,3R,1′S,5′S)‐1 is the first fully characterized epoxypheromone from marine brown algae (Phaeophyceae).
Fluoro‐Analoga von Cycloheptadien‐Pheromonen mariner Braunalgen: ungewöhnlich leicht verlaufende [3,3]‐sigmatrope Umlagerung eines trans‐di(alkenyl)‐substituierten geminalen Difluorocyclopropans
Authors: Erbes Petra , Boland Wilhelm
Published: December 2004

Fluoro Analoga of Cycloheptadiene Pheromones of Marine Brown Algae: Exceptionally Facile [3,3]‐Sigmatropic Rearrangement of a trans‐Di(alkenyl)‐Substituted Geminal Difluorocyclopropane

The 3,3,‐difluorocyclopropane‐1,2‐dicarbonyl compounds 9a and 9b are obtained by addition of difluorocarbene to methyl cinnamate or trans‐stilbene followed by oxidative degradation of the phenyl rings(s) (Scheme 2). Compound 9b is a versatile building block for the synthesis of the di(alkenyl)‐substituted geminal difluorocyclopropane 5 or the chrysanthemum ester 10b. Cyclopropane 5 is unstable at room temperature and rearranges to the 3,3,‐difluorocyclohepta‐1,4‐diene 4, an analog of the algal pheromone dictyotene (1; Scheme 3). The kinetic parameters of the [3,3]‐sigmatropic rearrangement are determined. The data support the view that a geminal difluoro group within a cyclopropane weakens the distal bond.
Synthesis and N‐Methyl‐D‐aspartate (NMDA) Antagonist Properties of the Enantiomers of α‐Amino‐5‐(phosphonomethyl)[1,1′‐biphenyl]‐3‐propanoic Acid. Use of a New Chiral Glycine Derivative
Authors: Müller Werner , Lowe David A. , Neijt Hans , Urwyler Stephan , Herrling Paul L. , Blaser Denis , Seebach Dieter
Published: December 2004

The enantiomers of the title compound, 7a and ent‐7a, and of substituted analogues are synthesized. The absolute configuration of 7a is deduced from that of (tert‐butyl 2‐tert‐butyl)‐3‐methyl‐4‐oxoimidazolidin‐1‐carboxylate (15) and from the trans‐configuration of the intermediate 17a which in turn is assigned on the basis of 1H‐NMR nuclear Overhauser effect (NOE) measurements. Instead of 15, the 2‐isopropyl‐substituted analogue 21 can also be employed. Its preparation from glycine, methylamine, isobutyraldehyde, and (Boc)2O, and the resolution through the bis‐O,O′‐(4‐toluyl)tartrate salt 20 are described. In two functional tests (rat neocortical slice and frog hemisected spinal cord preparation) the (S)‐enantiomer 7a (SDZ EAB 515) is shown to be a very potent, selective competitive NMDA antagonist.
An Efficient Synthesis of Racemic 4‐Hydroxy‐2‐oxo‐1‐pyrrolidineacetamide (Oxiracetam) Using Tetramic‐Acid Intermediates
Authors: Laffan David D. P. , Bänziger Markus , Duc Lauren , Evans Andrew R. , McGarrity John F. , Meul Thomas
Published: December 2004

The title compund, 1a, has been synthesised in racemic form from ethyl (E)‐4‐chloro‐3‐ethoxybut‐2‐enoate in 43% overall yield in five steps. Several routes to the final product are described, but the most efficient involves hydrogenation of a C(5)‐unsubstituted tetramic acid 5b. The instability of this class of compounds required the use of a catalyst which could operate under very acidic aqueous conditions, a role that was successfully filled by a 5% Ru/C catalyst.
Electron‐Transfer‐Catalyzed cis → trans Isomerization of 1,1′‐Azonorborane. Prototype of a reversible two‐stage storage system
Authors: Gescheidt Georg , Lamprecht Axel , Heinze Jürgen , Schuler Barbara , Schmittel Michael , Kiau Susanne , Rüchardt Christoph
Published: December 2004

ESR and cyclic voltammetry investigations show that isomerization of the radical cation of cis‐1,1′‐azonorbornane (cis‐1) to the trans‐radical ion proceeds too fast in solution for direct investigation of the cis‐radical ion even at −78°. The facile isomerization of the radical cation is in agreement with PM3 calculations proposing an activation barrier of only 17 kJ/mol. As a consequence, quantitative cis → trans isomerization of 1,1′‐azonorbornane can effectively be accomplished by addition of catalytic amounts of one‐electron oxidants. This is the first evidence for a radical‐cation‐catalyzed cis → trans isomerization of azo compounds.
Carbocyclic analogs of nucleosides. Part 2.. Synthesis of 2′,3′‐dideoxy‐5′‐homonucleoside analogs
Authors: Jenny Thomas F. , Horlacher Jennifer , Previsani Nicoletta , Benner Steven A.
Published: December 2004

A set of derivatives of cyclopentaneacetic acid cis‐substituted at position 3 by nucleoside bases (both purines and pyrimidines) were prepared and characterized (see 11, 14, and 23a, b; Schemes 2–4). These molecules are carbocyclic analogs of 2′,3′‐dideoxy‐5′‐homonucleosides. In this synthesis, the skeleton was constructed from norbornanone and a novel method based on Mitsunobu chemistry used for the introduction of nucleoside‐base substituents. The scope of this method was further explored via the preparation of a cyclobutyl analog of dideoxyguanosine (see 17, Scheme 3).
Conformational Studies of Marine Polyhalogenated α‐Chamigrenes Using Temperature‐Dependent NMR Spectra. Cyclohexene‐ring flipping and rigid‐chair cyclohexane ring in the presence of equatorial halogen atoms at C(8) and C(9)
Authors: Guella Graziano , Chiasera Giuseppe , Pietra Francesco
Published: December 2004

Temperature‐dependent NMR spectra indicate that the α‐chamigren‐3‐ones (−)‐11, (+)‐12, (+)‐14 (−)‐15, (+)‐16, 18, and 19 bearing equatorial halogen atoms at C(8) and C(9) undergo slow conformational flipping of the envelope‐shaped enone ring, while the cyclohexane ring is maintained in the chair conformation. The α‐chamigren‐3‐ols (+)‐20 and (+)‐21, obtained by hydride reduction of (+)‐12, behave similarly, with slow half‐chair inversion of the cyclohexenol ring. In each case, both conformers are about equally populated and detectable by NMR, except in the case of (+)‐15, where repulsive interactions between BrC(2) and Heq−C(7) make the population of the conformer 15b with Me—C(5) faced to Hax−C(10) so low that it escapes direct 1H‐NMR detection. The energy barriers to these conformational motions are viewed to arise mainly from repulsive interactions between Me—C(5) and the axial H‐atoms at C(8) and C(10), while, contrary to previous beliefs, no twist‐boat conformations of the cyclohexane ring intervene. Similar conclusions hold for the 4,5‐epoxides of both (−)‐6 and (+)‐7. Clean Jones oxidatio of (−)‐2 to 17, where the CH2C(5) bond is maintained, and acid dehydration‐isomerization of the α‐chamigrene (+)‐21 to the β‐chamigrene (+)‐24, reflect the special stability of β‐chamigrenes, providing a reason for their frequent occurrence in nature.
Investigations of Steric and Electronic Factors Influencing the Cyclopalladation of meta‐Toluidine Analogues
Authors: Mossi Waldo , Klaus Alfred J. , Rys Paul
Published: December 2004

The cyclopalladation of two different types of aniline derivatives is described: the acetylated anilines N‐(3‐methylphenyl)acetamide (2a), 3‐(acetylamino)‐4‐chlorobenzoic acid (2c), and N‐(2‐chlorophenyl)acetamide (2d) are cyclometalated easily with palladium(II) acetate and trifluoroacetic acid to yield the corresponding complexes 4a, 4c, and 4d, respectively, whereas the acetylated meta‐toluidine N‐(2‐chloro‐5‐methylphenyl)acetamide (2b) cannot be metalated at the only accessible site between the acetylamino and the methyl group. This aromatic CH bond can be activated, however, with the second type of meta‐toluidine derivatives: the 2‐chloro‐5, N‐dimethyl‐N‐nitrosoaniline (3b) readily undergoes cyclopalladation to yield the corresponding PdII complex di‐μ‐trifluoro‐acetato‐bis[3‐chloro‐6‐methyl‐2‐(N‐methyl‐N‐ nitrosoamino)phenyl‐C,NO]dipalladium(II) (5b) containing a five‐membered palladacycle with coordination of PdII at the nitroso N‐atom, which is established by 15N‐NMR spectroscopy.
Synthesen der Phosphono‐ bzw. Phosphino‐Analoga des Pantothensäure‐ethylesters und des Phosphono‐Analogons des Pantetheins
Authors: Neidlein Richard , Greulich Peter
Published: December 2004

Syntheses of Phosphonic‐ and Phosphinic Analogues of Pantothenic Acid Ethyl Ester and of the Phosphonic Analogue of Pantetheine

The replacement of amino acids in peptides by phosphono‐analogous (aminoalkyl)phosphonic acids 1, (2‐aminoethyl)phosphonic acid (2) and substituted derivatives has been an important aspect of peptides research in the last years. In pantothenic acid (3), there is a peptide linkage between (2R)‐2,4‐dihydroxy‐3,3‐dimethylbutyric acid and the amino group of β‐alanine, and in pantetheine (4), there is a second peptide linkage between the β‐alanine and cysteamine. The synthesis of phosphono and phosphino analogues of pantothenic acid ethyl ester, where the β‐alanine is replaced by the diethyl ester of (2‐aminoethyl)phosphonic acid and the ethyl ester of (2‐aminoethyl)methylphosphonic acid, respectively, and the syntheses of the phosphono analogue of pantetheine, where the β‐alanine is replaced by (2‐aminoethyl)phosphonic acid, are described.
(o ‐Hydroxyphenyl)methylphosphonic Acids: Spectrophotometric determination of their pKa values and of the deprotonation sequence
Authors: Chafaa Salah , Meullemeestre Jean , Schwing Marie‐José , Vierling François , Böhmer Volker , Vogt Walter
Published: December 2004

UV/VIS Absorption spectra of nitrosubsituted (o‐hydroxyphenyl)methylphosphonic acids (o‐(phosphonomethyl)phenols) were measured as a function of pH at 25° in 0.1M NaClo4 solutions. Computational treatment of the whole set of optical density data between 200 and 500 nm resulted in the determination of the dissociation constants of these polyacids and also of the individual electronic spectra of all the species involved in the deprotonation sequence. The spectral behavior gives information on the structure of the anions formed and consequently the order of the subsequent deprotonation steps could be deduced. For the (2‐hydroxy‐3‐nitro(or 5‐nitro)phenyl)methylphosphonic acid and the 2‐hydroxy‐5‐nitro‐1,3‐phenylenebis(methylphosphonic acid), the phenolic proton dissociates in the last step, while, in the case of (2‐hydroxy‐3,5‐dinitrophenyl)methylphosphonic acid, the last dissociating proton comes from a POH group. An intermediate situation is found for (3‐chloro‐2‐hydroxy‐5‐nitrophenyl)methylphosphonic acid. Generally, the deprotonation sequence is governed by intramolecular H‐bonds involving the phenolic OH group.
Definitive Proof for the Operation of Isotopically Sensitive Branching (‘Metabolic Switching’) in FeI‐Mediated CH Bond Activation in the Gas Phase Short Communication
Authors: Seemeyer Katrin , Prüsse Tilmann , Schwarz Helmut
Published: December 2004

Rigorous regio‐ and stereospecific labeling experiments are performed to demonstrate the operation of the previously suggested operation of ‘isotopically sensitive branching’ in FeI‐mediated CH bond activation. For the hexane‐1,6‐diol/Fe+‐complex, it is shown that dehydrogenation involves specifically the central C(3)/C(4) position, and the study of the stereospecifically labeled D,L‐ and meso‐[3,4‐D2]‐isotompomers 1e and 1f demonstrates that dehydrogenation proceedes via two competing pathways (i.e. ‘anti’‐ vs. ‘syn’‐route). The contribution of these routes to the product formation is – due to a kinetic isotope effect – controlled by the relative configuration at the labeled positions C(3)/C(4). For the D,L‐form 1e, we estimate a ratio of 49:1 in favor of the ‘anti’‐route; due to an isotope effect, this ratio drops to 4.3:1 for the meso‐form 1f.
Synthesis and Solvent Effects on the Conformation of Hymenistatin 1
Authors: Konat Robert K. , Mierke Dale F. , Kessler Horst , Kutscher Bernhard , Bernd Michael , Voegeli Rainer
Published: December 2004

The cyclic octapeptide cyclo(‐Pro‐Pro‐Tyr‐Val‐ProLeu‐Ile‐Ile‐) (1), isolated from the Hymeniacidon sponge, was synthesized and examined conformationally using NMR and molecular‐dynamics simulations. Most structural parameters of synthetic 1 are in accord with those reported for the isolated material. Our study indicates some small but significant differences in the assignment of the 1H‐ and 13C‐NMR resonances from those of the natural material. The Conformation was determind in both CHCl3 and DMSO using 1H‐NMR and molecular‐dynamics simulations. Both NOE's and coupling constants were used as experimental restraints during the simulations which utilized explicitly the same solvent as in the NMR study. The differences in the interaction of the solvent with 1 were examined, providing insight into the observed differenced in conformation. The dominant conformation contains a ßVIa turn about Ile8‐Tyr3 including a Pro1‐Pro2 cis‐peptide bond and a ßI or ßII turn about Val4‐Ile7 in CHCl3 and DMSO, respectively.
Approaches to the Synthesis of Cytochalasans. Part 11. Further transformations and cyclization attempts directed towards proxiphomin
Authors: Boutellier Markus , Wallach Daniel , Tamm Christoph
Published: December 2004

Starting from iodoalcohol 9, the monoprotected dialdehyde 5 was synthesized (Scheme 2) and converted to 17 by reaction with oxo‐phosphonate 15 (Scheme 3). The latter was prepared from 13. Cyclisation of 17 to the target compound 18 failed. Also the attachment of thiol 22 to lactone 19 was unsatisfactory (Scheme 4). Therefore, the building blocks 28 and 29 were synthesized using diene 33 and diester 30 as starting material for 28 and 9 for 29 (Scheme 5 and 6). Hydroxy acid 28 was converted into formyl‐ester 46 (Scheme 7). However, the condensation of its derivatives 48 and 49 with ‘Umpolung’ of the carbonyl reactivity was unsuccessful, probably due to steric hindrance.
The Terpenoids of Maytenus boaria MOL. (Celastraceae)
Authors: Muñoz Orlando , Ruiz Roberto , Gonzáles Antonio , Nüñez Mercedes P. , Jiménez Ignacio , Ravelo Angel
Published: December 2004

The known triterpenoids β‐amyrin (= olean‐12‐en‐3β‐ol; 22), lupeol (= lup‐20(29)‐en‐3β‐ol; 17), betulin (= lup‐20(29)‐ene‐3β,28‐diol; 18), lup‐20(29)‐ene‐3β,30‐diol (20), oleanolic acid (= 3β‐hydroxyolean‐12‐en‐28‐oic acid; 21), and betulonic acid (= 3‐oxolup‐20(29)‐en‐28‐oic acid; 19), together with epicatechol (= cis‐2‐(3,4‐dihydroxyphenyl)‐3,4‐dihydro‐2H‐1‐benzopyran‐3,5,7‐triol; 23), 5′‐O‐methylgallocatechol (= trans‐2‐(3,4‐dihydroxy‐5‐methoxyphenyl)‐3,4‐dihydro‐2H‐1‐benzopyran‐3,5,7‐triol; 24), and 4‐hydroxybenzaldehyde were isolated from the aerial parts of Maytenus boaria (MOL.). Additonally, the eight 4,C4‐dihydro‐β‐agarofuran sesquiterpenoids 1–8, one of them a diol with a (4R)‐configuration, and compound 9 were present in the extract. The structures of these compounds were established by spectroscopic and chemical means.
3‐(Acylamino)‐3‐amino‐2‐nitroacrylonitriles from N‐Acyl‐S‐methyl‐3,3‐diamino‐2‐nitroacrylthioimidates
Authors: Trimiño María I. García , Linden Anthony , Heimgartner Heinz , Cabrera Arturo Macías
Published: December 2004

Reaction of N‐acyl‐3,3‐diamino‐2‐nitroacrylthioamides 1 with MeI at room temperature leads to N‐acyl‐S‐methyl‐3,3‐diamino‐2‐nitroacrylthioimidates 2 in moderate yields. The latter react with Hg(OAc)2 in DMF yielding 3‐(acylamino)‐3‐amino‐2‐nitroacrylonitriles 8. The structures of 2a and 8a were established by X‐ray crystallography.
Nucleotides Part XL. Synthesis and Characterization of Modified 2′–5′ Adenylate Trimers–Potential Antiviral Agents
Authors: Schirmeister Helga , Pfleiderer Wolfgang
Published: December 2004

2′–5′ Adenylate trimers 41–44 carrying the (tert‐butyl)dimethylsilyl (tbds) group at the 3′‐OH position of various sugar moieties were synthesized via the phosphoramidite method. The use of the (tert‐butyloxy)carbonyl (boc) and 2‐(4‐nitrophenyl)ethylsulfonyl (npes) groups for 2′‐OH protection in neighbourhood to the 3′‐O‐tbds residue was compared during the synthesis of the target trimers. For other functional positions, the use of the 2‐(4‐nitrophenyl)ethyl (npe) and 2‐(4‐nitrophenyl)ethoxycarbonyl (npeoc) blocking groups were favoured.
Nitrostyrene Derivatives of Adenosine 5′‐Glutarates Modified with an Alkyl Spacer and their inhibitory activity on epidermal growth factor receptor protein tyrosine kinase
Authors: Peterli Stefan , Hubmann Dieter , Séquin Urs , Mett Helmut , Traxler Peter
Published: December 2004

β‐Nitrostyrene derivatives of adenosine 5′‐glutarates are potent and selective bisubstrate‐type inhibitors of the epidermal growth factor receptor protein tyrosine kinase (EGF‐R PTK). In an attempt to improve the inhibitory activity, this type of compounds was modified with alkyl spacers of varying length between the nitrostyrene and the glutaryl units. The spacers consisted of 1, 3, 4, and 5 atoms to give compounds of the benzyl, oxyethyl, oxypropyl, and oxybutyl series, respectively (Schemes 1 and 2). Adenosine 5′‐esters were prepared in the benzyl and oxypropyl series only. Compared to the compounds in the parent series without spacer (IC50 = 0.7–12 μM), most of the modified compounds inhibited the EGF‐R PTK only marginally or were inactive (IC50 ≥ 100 μM). The only exceptions were the free acids 19 and 20 with IC50 values of ca. 5 μM. It is noteworthy that esterification of these two hydrogen glutarates with either MeOH or adenosine yielded inactive compounds, which is in contrast to the corresponding substances without spacers.
Crystal Structure of (−)‐Corycavinium (+)‐10‐Camphorsulfonate, a biosynthetic intermediate to hexahydrobenzo[c]phenanthridine alkaloids
Authors: Kamigauchi Miyoko , Noda Yuko , Iwasa Kinuko , Nishijo Zjujiro , Ishida Toshimasa , In Yasuko , Wiegrebe Wolfgang
Published: December 2004

The crystal structure of (−)‐corycavinium (+)‐10‐camphorsulfonate has been investigated by X‐ray analysis. The structure of (−)‐corycavinium ion (  (−)‐(7S,13S,14R)‐5,6,13,13a‐tetrahydro‐13a‐hydroxy‐7‐methyl‐2,3;9,10‐bis(methylenedioxy)‐8H‐dibenzo[a,g]quinolizinium), has been determined. The conformation with B/C‐cis‐conjunction, a twisted half‐chair of ring B, and a half‐chair of ring C, as well as α‐oriented substituted groups N…Me, C…Me, and C…OH is revealed. Feeding experiments with cell suspension cultures of Corydalis incisa (Papaveraceae) defined the intermediacy of (−)‐corycavinium in the route from protoberberine‐type to hexahydrobenzo[c]phenanthridine‐type of alkaloids. On the basis of the present crystal conformation, the stereospecificity of the relating enzyme is biogenetically considered.
Synthesis and NMR Spectroscopic Investigation of a Macrocyclic Diphosphine Ligand and its nickel(II) and palladium(II) complexes
Authors: Widhalm Michael , Kalchhauser Hermann , Kählig Hanspeter
Published: December 2004

The preparation of a macrocyclic diphosphine ligand 5 incorporating a binaphthyl unit and its NiII and PdII complexes, 6 and 7, is described. A complete assignment of 1H,‐ 13C‐, and 31P‐NMR data on the basis of 2D NMR spectroscopy (1H, 1H‐, 13C, 1H‐, 31P, 1H‐, 31P, 13C‐COSY) was possible for 5, and also – in part – for 6 and 7.
Umsetzung von Di(tert‐butyl)‐ und Diphenyldiazomethan mit 1,3‐Thiazol‐5(4H)‐thionen: Isolierung und Kristallstruktur des primären Cycloadduktes
Authors: Mlostoń Grzegorz , Petit Mireille , Linden Anthony , Heimgartner Heinz
Published: December 2004

Reaction of Di(tert‐butyl)‐ and Diphenyldiazomethane and 1,3‐Thiazole‐5(4H)‐thiones: Isolation and Crystal Structure of the Primary Cycloadduct

Reactions of diazo compounds with CS bonds proceed via the formation of thiocarbonyl ylides, which, under the reaction conditions, undergo either 1,3‐dipolar cycloadditions or electrocyclic ring closer to thiiranes (Scheme 1). With the sterically hindered di(tert‐butyl)diazomethane (2c), 1,3‐thiazole‐5(4H)‐thiones 1 react to give spirocyclic 2,5‐dihydro‐1,3,4‐thiadiazoles 3 (Scheme 2). These adducts are stable in solution at −20°, and they could be isolated in crystalline form. The structure of 3c was established by X‐ray crystallography. In CDCl3 solution at room temperature, a cycloreversion occurs, and the adducts of type 3 are in an equilibrium with 1 and 2c. In contrast, the reaction of 1 with diphenyldiazomethane (2d) gave spirocyclic thiiranes 4 as the only product in high yield (Scheme 3). The crystal structure of 4b was also determined by X‐ray analysis. The desulfurization of compounds 4 to 4,5‐dihydro‐5‐(diphenylmethylidene)‐1,3‐thiazoles 5 was achieved by treating 4 with triphenylphosphine in boiling THF. The crystal structure of 5f is shown.
Syntheses of Bile Pigments. Part 17. Synthesis of a non‐racemizable urobilin derivative
Authors: Floch Lubomir , Nydegger Fredy , Gossauer Albert , Kratky Christoph
Published: December 2004

The optically active urobilin model compound 7 was synthesized, in which Me groups instead of H‐atoms are bound to the asymmetric centers, thus preventing loss of chirality by tautomerization. The key intermediate of the eleven‐step synthesis of 7 is the 1,4,5,10‐tetrahydro‐10‐hydroxy‐1‐oxo‐11H‐dipyrrin‐9‐carboxylate rac‐2, which could be resolved into enantiomers by fractional crystallization of the corresponding methyl N‐[1‐(naphth‐1‐yl)ethyl]carbamates 3 and 4. The absolute configuration of enantiomerically pure (−)‐2 was determined by X‐ray diffraction analysis of its camphor‐10‐sulfonate 5. As the CD spectrum of the urobilin analogue 7 obtained from (−)‐(R)‐2 displays a positive Cotton effect, the present results prove, in connection with previous work, that substitution of Me groups for the H‐atoms bound to the asymmetric centers of a chiral urobilin chromophore do not influence the relationship between absolute configuration of the latter and its helicity.
4,4‐Disubstituierte Imidazol‐Derivate aus der Umsetzung von 3‐Amino‐2H‐azirinen mit Salicylamid
Authors: Magirius Florian , Linden Anthony , Heimgartner Heinz
Published: December 2004

4,4‐Disubstituted Imidazole Derivatives from the Reaction of 3‐Amino‐2H‐azirines with Salicylamide

Reaction of 3‐amino‐2H‐azirines 1a–c with salicylamide (7) in MeCN leads to imidazoles 10 and 11 in different rates, depending on the conditions. In the case of 1a and 1b, 11a and 11b, respectively, have been obtained as the main product at 50°; in reactions at 80°, 10a and 10b are the favored products (Tables 1 and 2). 2,2‐Dimethyl‐3‐(N‐methyl‐N‐phenylamino)‐2H‐azirine (1c) reacts with 7 in MeCN mainly to 2‐(2‐hydroxyphenyl)‐5,5‐dimethyl‐3,5‐dihydroimidazol‐4‐one (10a); in boiling toluene, 11c is formed with low preference (Table 3). The structure of the products has been established by spectroscopic means, and in the case of 10b and 11c, by X‐ray crystallography. Two different reaction mechanisms for the formation of the products are discussed (Scheme 2).
Novel Juvenoids of the 2‐(4‐hydroxybenzyl)cyclohexan‐1‐one Series
Authors: Wimmer Zdenêk , S̆aman David , Francke Wittko
Published: December 2004

A series of insect juvenile hormone analogs (juvenoids) was synthesized and studied. The basic skeleton of these juvenoids contains three rings and a short aliphatic subunit and bears two or three chiral centers (depending on the appropriate structure; see 6–9). The chiral center located in the 1,2‐diphenoxypropane subunit has the configuration (RS), (R) (a series), or (S) (b series). The juvenoids were subjected to a biological screening, the preliminary results of which are briefly described.
Facile Synthesis of 2′‐Deoxyisoguanosine and Related 2′,3′‐Dideoxyribonucleosides
Authors: Seela Frank , Gabler Bert
Published: December 2004

The 2′‐deoxyisoguanosine (1) was synthesized by a two‐step procedure from 2′‐deoxyguanosine (5). Amination of silylated 2′‐deoxyguanosine yielded 2‐amino‐2′‐deoxyadenosine (6) which was subjected to selective deamination of the 2‐NH2 group resulting in compound 1. Also 2′,3′‐dideoxyisoguanosine (2) was prepared employing the photo‐substitution of the 2‐substituent of 2‐chloro‐2′,3′‐dideoxyadenosine (4). The latter was synthesized by Barton deoxygenation from 2‐chloro‐2′‐deoxyadenosine (3) or via glycosylation of 2,6‐dichloropurine (12) with the lactol 13. Compound 1 was less stable at the N‐glycosylic bond than 2′‐deoxyguanosine (5). The dideoxynucleoside 2 was deaminated by adenosine deaminase affording 2′,3′‐dideoxyxanthosine (17).
Oligosaccharides Related to Tumor‐Associate Antigens. Part 2. Conformational analysis of the trisaccharide α‐L‐Fucp‐(1→2)‐β‐D‐Galp‐(1→3)‐β‐D‐GalpNAc, epitope structure recognized by the MBr1 antibody
Authors: Toma Lucio , Ciuffreda Pierangela , Colombo Diego , Ronchetti Fiamma , Lay Luigi , Panza Luigi
Published: December 2004

The conformational space of the trisaccharide α‐L‐Fuc‐(1→2)‐β‐ D‐Gal‐(1→3)‐β ‐D‐GalNAc‐1‐OPr (2) and of its component disaccharide moieties α ‐L‐Fuc‐(1→2)‐β ‐D‐Gal‐1‐OMe (3) and β ‐D‐Gal‐(1→3)‐β‐ D‐GalNAc‐1‐OPr (4) was investigated with the aid of molecular‐mechanics energy minimizations and molecular‐dynamics simulations. These calculations suggested the occurrence of two conformations for each compound characterized by different ϕ and Ψ glycosidic angles. However, 1H‐NMR investigation of D2O solutions of 2–4 indicated a sure preference for one of the two conformers with a contribution of the other one ranging from negligible to low.
Large Water‐Soluble Cyclophanes with Convergent Intracavity Functionality
Authors: Diederich François , Carcanague Daniel R.
Published: December 2004

New tricyclic spacers, readily available through fourfold Mannich reaction of substituted dibenzyl ketones, were introduced into a series of ten H2O‐soluble cyclophanes with spacious preorganized cavity binding sites. These spacers provide H2O‐solubility with amine or crown‐ether functionality remote from the cyclophane cavity while directing functional groups such as keto or OH groups in a precise geometrical array inside the cavity. The cyclophanes were designed to include organic substrates via a combination of apolar and specific polar functional group interactions. The X‐ray crystal‐structure analysis of the tritopic receptor 18 with one potential neutral‐molecule and two cation‐binding sites showed a large rectangular open cavity with dimensions of roughly 9 × 14 Å and a spacing of 9.7 Å between the O‐atoms of two convergent CO groups. Despite the binding‐site preorganization, cyclophanes incorporating two of the new spacers did not show any substrate binding in aqueous solutions. The failure of these systems to function as receptors is mainly due to steric hindrance to important cyclophane aromatic ring‐guest interactions. Also, the favorable solvation of the intracavity functionality may prevent the formation of complexes. Hybrid receptors constructed from the novel spacers and diphenylmethane units were found to bind flat aromatic substrates as well as bulky [4.2]paracyclophanes. The observed large differences in stability (ΔΔG°> 2 kcal mol−1) of the complexes formed by three structurally closely related hybrid receptors with convergent CO, OH or CH2 groups and 6‐hydroxynaphthalene‐2‐carbonitrile as guest can be explained by a strong solvation effect of the convergent functional groups on apolar inclusion complexation.
Radical Anions of Polyalkylazulenes: An ESR and ENDOR Study
Authors: Bachmann Rainer , Burda Clemens , Gerson Fabian , Scholz Markus , Hansen Hans‐Jürgen
Published: December 2004

Proton‐hyperfine data are reported for the radical anions generated from azulene (1) and its alkyl derivatives 2–11 in 1,2‐dimethoxyethane both ‘chemically’ with K and electrolytically. The alkyl derivatives are 1,3‐dimethyl‐ (2), 5,7‐dimethyl‐ (3), 1,3,5,7‐tetramethyl‐ (4), 2‐methyl‐ (5), 4,6,8‐trimethyl‐ (6), 2,4,6,8‐tetramethyl‐(7), 1,3,4,6,8‐pentamethyl‐ (8), 1,3,4,8‐tetramethyl‐6‐propyl‐ (9), 6‐(tert‐butyl)‐1,3,4,8‐tetramethyl‐ (10), and 1,2,3,4,6,8‐hexamethylazulene (11). Alkyl substituents at the odd‐numbered centers μ = 1, 3, 5, and 7 partly shift the π‐spin population from the seven‐ to the five‐membered ring, whereas those at the even‐numbered centers μ = 4, 6, and 8 exert an opposite effect on the π‐spin distribution.
An Efficient Total Synthesis of Carbocyclic 2′‐Deoxyribonucleosides
Authors: Lang Hanspeter , Moser Heinz E.
Published: December 2004

The present work describes a new and efficient method for the preparation of either racemic or enantiomerically pure carbocyclic 2′‐deoxyribonucleosides 1. Key steps are the efficient assembly of the racemic carbocyclic 2′‐deoxyribose core (±)‐12, its enzymatic resolution, and a new approach to covalently link the purine and pyrimidine bases with the cyclopentane moiety via the cyclic sulfate (+)‐19. This total synthesis of enantiomerically pure and racemic carbocyclic 2′‐deoxyribonucleosides 1 represents one of the most efficient approaches reported to date. Starting from cyclopentadiene, the four carbocycles corresponding to the naturally occurring 2′‐deoxyribonucleosides could be prepared in 12 steps and 9–12% overall yield. For the corresponding racemic compounds, 10 steps were used with overall yields between 22 and 30%.
Preparation and Structural Analysis of Several New α,α,α′,α′‐Tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols (TADDOL's) and TADDOL analogs, their evaluation as titanium ligands in the enantioselective addition of methyltitanium and diethylzinc reagents to benzaldehyde, and refinement of the mechanistic hypothesis
Authors: Ito Yoshio N. , Ariza Xavier , Beck Albert K. , Boháč Andrej , Ganter Camille , Gawley Robert E. , Kühnle Florian N. M. , Tuleja Juraj , Wang Yan Ming , Seebach Dieter
Published: December 2004

Preparation and screening of twenty new ligands, all analogs of α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol (TADDOL), for the Ti‐catalyzed asymmetric addition of methyltri(isopropoxy)titanium and diethylzinc to benzaldehyde are described. These ligands have the dioxolane ring of the TADDOL's replaced by cyclobutane, cyclopentane, cyclohexene, cyclohexane, bicyclo[2.2.1]heptene and ‐heptane and bicyclo[2.2.2]octene and ‐octane moieties; several have H‐atoms or alkyl groups in place of the aryl groups, and nine of them have C2 symmetry. X‐Ray crystallography and molecular mechanics are used to analyze the structure of the ligands, and two structural features appear to correlate with selectivity: (i) the torsion angle for the chelating O‐atom and the ortho‐C‐atom of the axial Ph group (a small, ca. 19°, angle is optimum, Fig.8) and (ii) the “degree of perpendicularity” of the axial Ph group (Fig. 9). Competition experiments indicate that TADDOL 1a catalyzes both the methyltitanium and diethylzinc additions ≥ 50 times faster than the related dioxolane analogs 12a, 12c, and 12e (Scheme 7), indicating that both axial and equatorial aryl groups (see Footnote 6) are necessary for ligand‐accelerated catalysis of these reactions. A refined mechanistic hypothesis is presented (Fig. 10) to explain the selectivities observed for these new ligands. Our analysis suggests that a combination of structural features appear necessary for good catalytic efficiency and high selectivity. These features, especially the rather subtle conformational effects, appear to be optimized (among the ligands tested) in the TADDOL's.
Duplex Stabilization of DNA: Oligonucleotides containing 7‐substituted 7‐deazaadenines
Authors: Seela Frank , Thomas Horst
Published: December 2004

The oligonucleotide building blocks 4b–d derived from 7‐bromo‐, 7‐chloro‐, and 7‐methyl‐substituted 7‐deaza‐2′‐deoxyadenosines 3b–d were prepared. They were employed in the solid‐phase synthesis of the oligonucleotides 7–25. The dA residues of the homomer d(A12), the alternating d[(A‐T)6], and the palindromic d(G‐T‐A‐G‐A‐A‐T‐T‐C‐T‐A‐C) were replaced by 3b–d as well as by the parent 7‐deaza‐2′‐deoxyadenosine (3a). The melting profiles and CD spectra of oligonucleotide duplexes, showing this major groove modification, were measured, and the Tm values as well as the thermodynamic data were determined. It was found that small substituents such as Br, Cl, or Me introduced in the 7‐position of a 7‐deazaadenine residue increase the duplex stability compared to oligonucleotides containing adenine.
Synthesis of (+)‐Multifidene
Authors: Hemamalini Sundarababu , Scheffold Rolf
Published: December 2004

(+)‐Multifidence ((+)‐1) has been synthesized starting from (R)‐(cyclopent‐2‐enyl)methanol ((+)‐2) via its chloroformate 4, Co‐mediated radical cyclization reaction to the lactone (+)‐6, and introduction of the olefinic side chains.
3‐(Prop‐2‐enylidene)azetidin‐2‐one Derivatives: Synthesis, structure, and formation of 3‐spiro‐β‐lactams via Diels–Alder reactions
Authors: Ruf Sabine , Otto Hans‐Hartwig
Published: December 2004

Reactions of 3‐silylated β‐lactams (1) with α,β‐unsaturated ketones give the propylidene‐β‐lactams 3 and the cycloalkenylidene derivatives 5. Structure and configuration are elucidated by spectroscopic methods, and the reactivity is discussed. While compounds 5 do not react with dienophiles, the (Z)‐isomers of 3 are the favored substrates for Diels‐Alder reactions yielding the spiro compounds 6 and 7.
Metal Complexes with Macrocyclic Ligands. Part XXXIX. Mono‐ and binuclear copper(II) complexes of a bridging bis[1, 4, 7‐triazacyclononane]
Authors: Behle Lutz , Neuburger Markus , Zehnder Margaretha , Kaden Thomas A.
Published: December 2004

The new bis‐macrocycle 1, 1′‐[(1H‐pyrazol‐3], 5‐diyl)bis(methylene)bis[1, 4, 7‐triazacyclononane] (1) was synthesized and its complexation with Cu2+ studied. Potentiometric and spectrophotometric titrations indicate that, in addition to the mononuclear species [Cu(LH2)]4+, [Cu(LH)]3+, [CuL]2+, and [Cu(LH−1)]+, binuclear complexes such as [Cu2L]4+, [Cu2(LH−1)]3+, and [Cu2(LH‐2)]2+ are also formed in solution. The stability constants and spectral properties of these are reported. The binuclear species [Cu2(LH−1)]3+ specifically reacts with an azide ion to give a ternary complex [Cu2(LH−1)(N3)]2+, the stability and structure of which were determined spectrophotometrically and by X‐ray diffraction, respectively. The two Cu2+ ions are in a square‐pyramidal coordination geometry. The axial ligand is one of the N‐atoms of the 1, 4, 7‐triazacyclononane ring, whereas at the base of the square pyramid, one finds the other two N‐atoms of the macrocycle, one N‐atom of the pyrazolide and one of the azide, both of which are bridging the two metal centres. In [Cu2(LH−1)(N3)]2+, a strong antiferromagnetic coupling is present, thus resulting in a species with a low magnetic moment of 1.36 B.M. at room temperature.
Thermal Reaction of Azulenes with Dimethyl Acetylenedicarboxylate in Supercritical Carbon Dioxide
Authors: Hunziker Richard , Sperandio David , Hansen Hans‐Jürgen
Published: December 2004

1,3,4,6,8‐Pentamethylazulene (9), when heated at 100° in supercritical CO2 at 150 bar in the presence of 4 equiv. of dimethyl acetylenedicarboxylate (ADM), led to the formation of 16% of a 1:1 mixture of dimethyl 3,5,6,8,10‐pentamethylheptalene‐1,2‐dicarboxylate 12a) and its double‐bond‐shifted isomer 12b as well as 4% of the corresponding azulene‐1,2‐dicarboxylate 13 (Scheme 4). The formation of the [1 + 2] adduct 11 (cf. Scheme 2) was not observed. Similarly, benz[a]azulene (25) yielded in supercritical CO2 (150°/170 bar) in the presence of 4 equiv. of ADM dimethyl benzo[d]heptalene‐6,7‐dicarboxylate (29; 30%) and dimethyl benzo[a]cyclopent[cd]azulene‐1,2‐dicarboxylate (28; 22%; Scheme 5). The reaction of 5,9‐diphenylbenz[a]azulene (26) and ADM in supercritical CO2 (100°/150 bar) gave the corresponding benzo[d]heptalene‐6,7‐dicarboxylate 31 (22%) and dimethyl 5,9‐diphenyl‐4b,10‐etheno‐10H‐benz[a]azulene‐11,12‐dicarboxylate(30; 25%; Scheme 5).
Substituent Reactivity and Tautomerism of Isoguanosine and Related Nucleosides
Authors: Seela Frank , Wei Changfu , Kazimierczuk Zygmunt
Published: December 2004

The substituent reactivity and tautomerism of isoguanine nucleosides is studied. Benzoylation or tosylation of isoguanine nucleosides (pyridine, room temperature) yields the 2‐benzoyl derivatives 7c, 11, and 12 or the 2‐tosyl compounds 13 and 14. The isobutyrylation of the 6‐amino group which did not occur under these conditions was induced in the presence of Me3SiCl. In the absence of Me3SiCl, the reactivity of isoguanine substituents decreases in the order from 2‐oxo → 5′‐OH → 3′‐OH → 6‐NH2. From isoguanine nucleosides, the N1‐(2b), N3‐(17), N6‐(15a,b), and 2‐O‐alkylated (3b) derivatives were prepared. Their pKa values were determined and the UV and 13C‐NMR spectra compared with regard to the alkylation position. Also the tautomeric forms of isoguanine nucleosides were determined UV‐spectrophotometrically in aqueous and nonaqueous solution. Isoguanosine (1a), its 2′‐deoxy analogue 1b as well as the N6‐methyl‐ and 8‐substituted derivatives form lactam tautomers in aqueous solution, whereas the lactim form is present in dioxane.
Synthesis, Characterization, and Structural Properties of Luminescent Lanthanide Complexes
Authors: Paul‐Roth Christine O. , Lehn Jean‐Marie , Guilhem Jean , Pascard Claudine
Published: December 2004

The crystal structure of the macrobicyclic europium(III) complex [Eu3+ ⊂1]3Cl− incorporating a N,N′ ‐ dioxide unit has been determined. It confirms the cryptate nature of this species, the included cation being bound to six N‐ and two O‐sites. The efficient shielding of the bound Eu3+ ion may be related to the efficient luminescence of this cryptate and points to the role played by the N‐oxide sites. To further explore the effect of such binding groups, the two macrocyclic ligands 4 and 5 bearing two bipyridine N,N′ ‐dioxide lateral arms have been synthesized and their EuIII and TbIII complexes prepared.
Reactions of Diazo Compounds with Imines. Preliminary communication
Authors: Moran Mary , Bernardinelli Gérald , Müller Paul
Published: December 2004

The [Rh2(OAc)4]‐catalyzed addition of methyl diazoacetate to N‐benzylideneaniline (1a) afforded the imine cis‐2 in 35% yield. Under catalysis by chiral RhII catalysts, however, only racemic 1a was produced, and the yield was low. In the presence of dimethyl maleate, aziridine formation was suppressed, and an intermediate ylide 6 was trapped as cycloadduct 7. No aziridines were obtained, however, from 1b, 1c, and 3. The iminium salt 8 reacted with (trimethylsilyl)diazomethane in the absence of [Rh2(OAc)4] via dipolar cycloaddition followed by extrusion of N2 to 10.
10‐Alkyl‐10‐demethylcolchicines
Authors: Kouroupis Pavlos , Kessler Jacqueline , Hansen Hans‐Jürgen
Published: December 2004

It is shown that colchicine (4) can regiospecifically be transetherified at C(10) by heating in ROH in the presence of (RO)4M (M = Ti, Zr; cf. Scheme 2). (PrO)4Zr in PrOH gives better yields than (PrO)4Ti in PrOH, and also in the catalytic variant of the conversion is (PrO)4Zr more effective than (PrO)4Ti.
Theoretical Calculations of β‐Lactam Antibiotics. Part VII. Influence of the solvent on the basic hydrolysis of the β‐lactam ring
Authors: Frau Juan , Donoso Josefa , Muñoz Francisco , Gracia‐Blanco Francisco
Published: December 2004

We used semi‐empirical and ab initio calculations to investigate the nucleophilic attack of the OH− ion on the β‐lactam carbonyl group. Both allowed us to detect reaction intermediates pertaining to proton‐transfer reactions rather than the studied reaction. We also used the PM3 semi‐empirical method to investigate the influence of the solvent on the process. The AMSOL method predicts the occurrence of a potential barrier of 20.7 kcal/mol due to the desolvation of the OH− ion in approaching the β‐lactam carbonyl group. Using the supermolecular approach and a H2O solvation sphere of 20 molecules around the solute, the potential barrier is lowered to 17.5 kcal/mol, which is very close to the experimental value (16.7 kcal/mol).
New Addition Reactions of Organometal Compounds with 4,4‐Dimethyl‐1,3‐thiazole‐5(4H)‐thiones
Authors: Shi Junxing , Heimgartner Heinz
Published: December 2004

Addition reactions of organometallic reagents with 4,4‐disubstituted 1,3‐thiazole‐5(4H)‐thiones were studied. Whereas the reactions with alkyllithium and alkyl Grignard reagents occurred in the thiophilic manner, the carbophilic addition was observed with allyllithium and allyl Grignard reagents. A radical reaction mechanism is proposed for rationalizing these observations (Scheme 5). A radical cyclization of the prepared 5‐allyl‐4,5‐dihydro‐1,3‐thiazole‐5‐thiol derivatives yielded 1,6‐dithia‐3‐azaspiro[4.4]non‐2‐enes (Table 4).