bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational Approach to the Receptor‐Bound Conformation of Cyclosporin A
Authors: Köck Matthias , Müller Gerhard , Kessler Horst
Published: December 2004

The conversion of the conformation of cyclosporin A (CsA) observed in CHCl3 to the receptor‐bound state is investigated by two molecular‐mechanics methods, template forcing and dynamic forcing. The conformations of CsA in CHCl3 and complexed with LiCl in THF as determined by NMR are used as starting structures. The transition starting from the CsA/CHCl3‐derived conformation is hindered by steric interactions of two side chains (MeBmt1 and Val5). While starting with the CsA/LiCl‐derived conformation, the conversion is facile. It is illustrated that these calculations, which are of artificial character, using only the starting and final structures of the observed conformational transition during the receptor‐binding event, allow an insight into the interactions between the substrates and receptor in terms of an induced fit.
NMR of Terminal Oxygen. Part 13. 17O‐NMR spectra of C‐nitroso compounds, thionitrites and NO+ Ion: Resonance effects in ON—X compounds and correlation with CD spectra
Authors: Dahn Hans , Péchy Peter , Flögel Rainer
Published: December 2004

The 17O‐NMR signals of four true C‐nitroso compounds 1–4 appear at particularly low field (1550–1265 ppm), whereas the dimers (azodioxy type) resonate at ca. 400 ppm and the ‘isonitroso compounds’ (  quinone‐oximes; 5 and 6) at ca. 250 ppm. S‐Nitroso compounds (  thionitrites; 8 and 9) show shift values of ca. 1300 ppm, not far from C—NO; the NO+ ion is much stronger shielded (474 ppm). The results, together with those for higher‐shielded nitroso compounds X—NO (X  RO, R2N, Cl, O−) are discussed in terms of (a) resonance stabilization through n‐donation from X(π‐bond order, approximated by the known barriers of rotation around the X—N bond) and of (b) electronic excitation energies ΔE. The latter are approximated by long‐wave (symmetry‐forbidden) UV/VIS absorptions and confirmed, where available, by the maxima of the curves of circular dichroism (CD); the CD curve of thionitrite 9 has been measured. It is found that the δ(17O) values of X—NO depend both on bond order and on ΔE, which could not be separated. The higher shielding of NO+ compared with X—NO is explained on the basis of anisotropy effects, which differ between sp and sp2 systems.
Stereoselektive Synthesen von (Z)‐(10‐Methoxy‐4H‐benzo[4,5]cyclohepta[1,2‐b]thiophen‐4‐yliden)essigsäure
Authors: Waldvogel Erwin
Published: December 2004

Stereoselective Syntheses of (Z)‐(10‐Methoxy‐4H‐benzo[4,5]cyclohepta[1,2‐b]thiophen‐4‐ylidene)acetic Acid

Two stereoselective syntheses for the antiinflammatory compound 1 ((Z)‐isomer) are described. In the first approach (Strategy A, Scheme 1) the stereoselective synthesis of 1 was realized via the bicyclic compound 11 under thermodynamic conditions, followed by a thiophene annelation with retention of the double‐bond geometry (Schemes 2–4). Optimized conditions were necessary to avoid (E/Z)‐isomerization during annelation. In the second approach (Strategy B, Scheme 1), diastereoisomer 17b was obtained selectively from a mixture of the diastereoisomers 17b and 18b by combining thermodynamic epimerization and solubility differences (Scheme 5). Diastereoisomer 17b was converted into the tricyclic compound 23 using a novel thiophene annelation method which we described recently (Scheme 6). In a final step, a stereospecific ‘syn’‐elimination transformed the sulfoxide 24 into the target compound 1 (Scheme 7). To avoid (E/Z)‐isomerization, it was necessary to trap the sulfenic acid liberated during the reaction. The key reactions of both approaches are highly stereoselective (> 97:3).
Construction de complexes tétranucléaires de ruthénium à ossature planaire par condensation de deux unités diruthénium à l'aide de ligands pontants: Synthèse et structure moléculaire de [Ru4(CO)8{μ2‐P(Cy)2}4] et de [Ru4(CO)8{μ4‐P(Cy)}2{μ2‐P(Cy)2}2] (Cy = cyclohexyl)
Authors: Béguin Alain , Rheinwald Gerd , Stoeckli‐Evans Helen , Süss‐Fink Georg
Published: December 2004

Assembly of Tetranuclear Ruthenium Complexes with Planar Metal Core by Condensation of Two Diruthenium Units Using Bridging Ligands: Synthesis and Molecular Structure of [Ru4(CO)8{μ2‐P(Cy)2}4] and [Ru4(CO)8{μ4‐P(Cy)}2{μ2}2](Cy = Cyclohexyl)

The dinuclear complexes [Ru2(CO)6{μ‐P(Cy)2}2] (1) or [Ru2(CO)4{μ‐(HCO2)}2{P(Cy)2H}2] (2) react in THF solution at 160° to give the tetranuclear complexes [Ru4(CO)8{μ2‐P(Cy)2}4] (3) and [Ru4(CO)8{μ4‐P(Cy)}2{μ2‐P(Cy)2}2] (4), as well as the trinuclear complex [Ru3(CO)7(μ2‐H){μ2‐P(Cy)2}3] (5). If the reaction is performed at 200°, the bicapped tetranuclear species 4 is obtained in a higher yield, whereas 3 and 5 are formed in trace amounts only. The phenyl derivatives [Ru2(CO)6{μ‐P(Ph)2}2] (6) or [Ru2(CO)4{μ‐(EtCO2)}2{P(Ph)2H}2] (7) react in a similar manner to give only the complex [Ru4(CO)8{μ4‐P(Ph)}2{μ2‐P(Ph)2}2] (8), analogous to 4. The molecular structure of 3 consists of a planar framework of four Ru‐atoms, each Ru—Ru bond being bridged by a μ2‐dicyclohexylphosphino ligand. The complex 4 represents a planar rectangular Ru core, both faces being capped by μ4‐cyclohexylphosphinidene ligands and two opposite edges being bridged by μ2‐dicyclohexylphosphino ligands.
An Easy and Fast Conversion of N2‐[(tert‐Butoxy)carbonyl]‐L‐amino Acids to Corresponding Amino‐aldehydes
Authors: Zlatoidsky Pavol
Published: December 2004

A new method for the preparation of N2‐[(tert‐butoxy)carbonyl]‐L‐amino‐aldehydes from N2‐[(tert‐butoxy)carbonyl]‐L‐amino acids based on reduction of mixed anhydrides with LiAl(t‐BuO)3H is described.
1:1 Metal Complexes of Bivalent Cobalt, Nickel, Copper, Zink, and Cadmium with the Tripodal Ligand tris[2‐(dimethylamino)ethyl]amine: Their stabilities and the X‐ray crystal structure of its copper(II) complex sulfate
Authors: Anderegg Giorgio , Gramlich Volker
Published: December 2004

The complex formation by Co2+, Ni2+, Cu2+, Zn2+, and Cd2+ with tris[2‐(dimethylamino)ethyl]amine (N(CH2CH2NMe2)3, Me6tren) was investigated at 25° and at an ionic strength of 1, using VIS spectroscopy and potentiometric measurements. The stability constants of these complexes are compared with those of tris(2‐aminoethyl)amine (N(CH2CH2NH2)3, tren), obtained under the same conditions. The values of the constants for Me6tren are much lower than those for tren, due to the bulky Me substituents. The values of the constants can be correlated with the ability of the individual metal ions to adopt coordination number 5. This appears to be easier for Cu2+ and Co2+ than for Cd2+ and Zn2+ and is very difficult for Ni2+. The 1:1 complexes [ML(H2O)]2+ are monoprotonic acids whose pKs values are similar or lower than those of the corresponding aquametal ions. The X‐ray crystal structure of the copper(II) complex [Cu(SO4)(Me6tren)] · 8H2O reveals pentacoordination at the central ion. The UV/VIS spectra of the aqueous solutions of the Co2+, Ni2+, and Cu2+ 1:1 complexes confirm that the same coordination number is present also in these complexes.
Studies Directed toward the Synthesis of Phomenoic Acid. Part 1. Enantioselective synthesis of the C(1)‐to‐C(6) segment
Authors: Hassan Hammed H. A. M. , Tamm Christoph
Published: December 2004

Based on a retrosynthetic analysis, a concept for the synthesis of all stereoisomers of the C(1)‐to‐C(6) segment of phomenoic acid has been developed. Both enantiomers of the chiral synthon 9 were prepared starting from rac‐epoxy‐diester 10. They were converted to both enantiomers of the epoxyalcohol, 16 and 21, respectively, using Sharpless epoxydation. They served as building blocks for the synthesis of the tetrol derivatives 20 and 22, respectively. All four stereoisomers were obtained in optically pure form. They contain the correct assembly of protected functional groups, allowing selective deprotection in view of further transformations.
Asymmetric Catalysis by Vitamin B12: The isomerization of achiral cyclopropanes to optically active olefins
Authors: Troxler Thomas , Scheffold Rolf
Published: December 2004

Achiral spiroactivated cyclopropanes are isomerized to optically active (R)‐(cycloalk‐2‐enyl)‐Meldrum's acids ( = (R)‐5‐(cycloalk‐2‐enyl)‐2,2‐dimethyl‐1,3‐dioxane‐4,6‐diones) in high yield and ee's up to 86% by catalytic amounts of cob(I)alamin in polar protic solvents.
Synthesis of Enantiomerically Pure D‐ and L‐(Heteroaryl)alanines by asymmetric hydrogenation of (Z)‐α‐amino‐αβ‐didehydro esters
Authors: Masquelin Thierry , Broger Emil , Müller Klaus , Schmid Rudolf , Obrecht Daniel
Published: December 2004

Homogeneous asymmetric hydrogenation of a wide range of methyl and tert‐butyl (Z)‐2‐(acylamino)‐3‐(heteroaryl)acrylates (see 1a–f and 2a–d, f, g, resp.) catalyzed by diphosphinerhodium catalysts was studied for the synthesis of enantiomerically pure 3‐furyl‐, 3‐thienyl‐, and 3‐pyrrolylalanines (see 3a–f, and 4a–d, g; Scheme 1). The precursors, the (Z)‐α‐amino‐α,β‐didehydro esters 1a–f and 2a–d, f, g were prepared in high yields using the phosphorylglycine‐ester method (Scheme 1). Isomerically pure (Z)‐α‐amino‐α,β‐didehydro esters were required to obtain the highest enantiomeric excesses (ee's) in the asymmetric hydrogenation, and the tert‐butyl‐ester strategy was beneficial in terms of both getting pure (Z)‐α‐amino‐α,β‐didehydro esters and obtaining high ee's in the hydrogenation. Finally, in contrast to the methyl‐ester series, deprotection of the tert‐butyl esters 4a–d, g was easily performed using CF3CO2H without any racemization.
A Reinvestigation of the α‐Alkylation of 4‐Monosubstituted 2‐phenyloxazol‐5(4H)‐ones (‘azlactones’): A general entry into highly functionalized α,α‐disubstituted α‐amino acids
Authors: Obrecht Daniel , Bohdal Udo , Ruffieux Ruth , Müller Klaus
Published: December 2004

Novel, more reliable and general reaction conditions for the α‐alkylation of 4‐monosubstituted 2‐phenyloxazol‐5(4H)‐ones ( = 4‐monosubstituted 2‐phenyl‐azlactones) rac‐2 to 4,4‐disubstituted 2‐phenyloxazol‐5(4H)‐ones rac‐1 were found (Scheme 2). Thus, a whole range of highly functionalized rac‐1 were prepared in medium‐to‐good overall yields (40‐90%, see Table). Azlactones rac‐1 are ideal precursors for the synthesis of optically pure α,α ‐disubstituted (R)‐ and (S)‐α‐amino acids.
Synthetic Routes to the Cyclo[n]carbons
Authors: Diederich François , Rubin Yves , Chapman Orville L. , Goroff Nancy S.
Published: December 2004

Cyclo[n]carbons (cyclo‐Cn) are n‐membered monocyclic rings of sp‐hybridized C‐atoms with unique electronic structures resulting from two perpendicular systems of conjugated π‐orbitals, one in‐plane and one out‐of‐plane. Several synthetic approaches to generate cyclo‐C18 from stable precursors were investigated. In a six‐step sequence from anthracene, tris(anthraceno)hexadehydro[18]annulene 5 was prepared and shown by laser‐desorption time‐of‐flight mass spectrometry to generate C18 in three successive retro‐Diels‐Alder reactions, together with anthracene as the by‐product. The attempted preparation of C18 by flash‐vacuum pyrolysis of 5 using solvent‐assisted sublimation only afforded anthracene next to polymers. The reaction of 1,6‐bis(triisopropylsilyl)hexa‐1,3,5‐triyne with [Co2(CO)8] followed by exchange of two CO groups for a bridging bis(diphenylphosphino)methane (dppm) ligand gave Co complex 22 which, after removal of the silyl groups, was oxidatively cyclized to afford the very stable trimeric and tetrameric macrocycles 6 and 7, complexes with cyclo‐C18 and cyclo‐C24, respectively. An X‐ray crystal structure established the identity of 6 and showed that the butadiyne units within the C18 core are considerably bent. Attempts to free cyclo‐C18 from the coordinating metal atoms in 6 did not succeed, presumably due to the steric shielding of the Co‐atoms by the dppm ligands. Low‐temperature matrix isolation studies using IR and UV/VIS spectroscopy showed that irradiation of carbon oxide 2 (C24O6) leads to ketene intermediates and, by subsequent loss of six CO molecules, presumably to cyclo‐C18.
Theoretical Calculations of β‐Lactam Antibiotics. Part VI. AM1 calculations of alkaline hydrolysis of clavulanic acid
Authors: Frau Juan , Donoso Josefa , Muñoz Francisco , Blanco Francisco García
Published: December 2004

The gas‐phase basic hydrolysis of clavulanic acid (a) was studied by using the AM1 semi‐empirical method. The results obtained show that the hydroxyethylidene side chain at C(2) is pivotal to the stability of the different reaction products involved. The products with an open oxazolidine ring are more stable than those with a closed ring fused to the β‐lactam ring. This behaviour differs from that of penicillins and cephalosporins where the most stable degradation products are those with an intact thiazolidine or dihydrothiazine ring, respectively, fused to the β‐lactam ring. The different chemical reactivity of clavulanic acid relative to penicillins and cephalosporins could explain the disparate behaviour of the latter two types of compound towards β‐lactamases. Once the acyl‐enzyme intermediate of clavulanic acid has been formed, it can evolve with cleavage of the oxazolidine ring to form a difficult to deacylate compound.
Stereoselective Formation of Ternary Copper(II) Complexes of (S)‐amino‐acid amides and (R)‐ or (S)‐amino acids in aqueous solution
Authors: Dallavalle Francesco , Folesani Giuseppina , Marchelli Rosangela , Galaverna Gianni
Published: December 2004

Formation constants of ternary complexes of CuII with (S)‐amino‐acid amides (phenylalaninamide, prolinamide, and tryptophanamide) and (R)‐ or (S)‐amino acids (valine, phenylalanine, proline, and tryptophan) were determined potentiometrically at 25° and I = 0.1M (KC1). Significant stereoselectivity was found for the systems (S)‐tryptophanamide/proline, (S)‐prolinamide/tryptophan, and (S)‐phenylalaninamide/proline, the diastereoisomeric complexes with ‘homochiral’ (SS) being more stable than with ‘heterochiral’ (SR) ligands. The stereoselectivity observed may be explained on the basis of repulsive interactions between the ligand side‐chain residues. The present data on the stability of mixed complexes in solution allow to draw some conclusions on the mechanism of chiral discrimination of amino acids in HPLC (reversed‐phase) using CuII complexes of (S)‐amino‐acid amides as selectors for ligand‐exchange chromatography (LEC).
Chemistry of the Higher Fullerenes: Preparative isolation of C76 by HPLC and synthesis, separation, and characterization of Diels‐Alder monoadducts of C70 and C76
Authors: Herrmann Andreas , Diederich François , Thilgen Carlo , Meer Hans‐Ulrich Ter , Müller Wolfgang H.
Published: December 2004

HPLC Separation of higher fullerenes was compared on two different stationary phases, and the preparative isolation of pure C76 is described. Higher‐fullerene derivatives 1 and 2 were prepared by Diels‐Alder reaction of C70 and C76 with an ortho‐quinodimethane intermediate generated in situ. Three out of four possible isomeric C70 monoadducts, i.e. 1a–c, and, for the first time, one isomeric C76 monoadduct, i.e. 2c, could be isolated in pure form and characterized by 1H‐NMR, 13C‐NMR, UV/VIS, and mass spectrometry. Five other C76 isomers i.e., 2a,b,d–f were obtained in partially separated product fractions. Coalescence temperatures and energy barriers were determined for the cyclohexene‐ring inversion in two of the isomeric C70 derivatives. The structure of the C70 adducts could be deduced unambiguously from symmetry considerations based on high‐ and low‐temperature 1H‐NMR spectroscopy. A simple model for the qualitative evaluation of the local curvature of fullerene surfaces is presented and used for the prediction of addition sites in higher fullerenes. These predictions are compared to the experimental results mentioned above as well as to predictions resulting from π‐bond‐order considerations and from calculated pyramidalization angles.
The Reaction Mechanism of Chromanol‐Ring Formation Catalyzed by tocopherol cyclase from Anabaena variabilis KÜTZING (Cyanobacteria)
Authors: Stocker Achim , Derungs Giusep , Woggon Wolf‐Dietrich , Netscher Thomas , Rüttimann August , Müller Robert K. , Schneider Heinz , Todaro Louis J.
Published: December 2004

Incubation of the synthetic 18O‐labelled phytyl‐hydroquinone (O4‐18O)‐2 with the tocopherol cyclase from Anabaena variabilis KÜTZING (Cyanobacteria) in D2O furnished the doubly labelled γ‐tocopherol, (2R,3S,4′R,8′R)‐(1‐18O,3‐2H)‐1. The chirality at C(3) was determined by two independent routes providing interlocking evidence that the enzyme‐catalyzed ring closure proceeds by si‐protonation of the double bond of 2 and concomitant re‐attack of the phenolic O‐atom.
Conformational Preferences and Absolute Configuration of Agelastatin A, a Cytotoxic Alkaloid of the Axinellid Sponge Agelas dendromorpha from the Coral Sea, via combined molecular modelling, NMR, and exciton splitting for diamide and hydroxyamide derivatives
Authors: Guerriero Antonio , D'Ambrosio Michele , Chiasera Giuseppe , Pietra Francesco
Published: December 2004

The absolute configuration of agelastatin A (1), the major, strongly cytotoxic alkaloid of the axinellid sponge Agelas dendromorpha from the Coral Sea, is proposed here to be (5aS,5bS,8aS,9aR), as deduced from combined molecular‐mechanics calculations and a novel application of exciton splitting to the bis[4‐(dimethylamino)benzoyl] compounds (–)‐9 and (–)‐13, derivatives of a diamide and a hydroxyamide, respectively. The position of the conformational equilibrium of A 1 could be finely tuned by slight molecular changes. The minor analogue, agelastatin B (3), was isolated as the trimethyl derivative (–)‐4.
Almazole C, a New Indole Alkaloid Bearing an Unusually 2,5‐Disubstituted Oxazole Moiety, and its putative biogenetic peptidic precursors, from a senegalese delesseriacean seaweed
Authors: Guella Graziano , Mancini Ines , Pietra Francesco
Published: December 2004

From product isolation and biomimetic synthesis – which also establishes absolute configurations – the known oxazole alkaloids almazoles A ((+)‐1) and B ((+)‐2) seem to arise in a Senegalese delesseriacean seaweed from, in seuence, the new modified peptide prealmazole C ((+)‐4) and the oxazole alkaloid almazole C ((+)‐3a). N,N‐Dimethyl‐L‐phenylalaninamide ((+)‐7) and the new peptides (+)‐5 and (+)‐6, as well as a series of known small units, are also involved. In all cases, the oxazole ring is peculiarly 2,5‐inserted.
Monocarboxylates of 3‐Methylidene‐β‐lactams: Synthesis and unusual oxidative rearrangement into a spiro[azetidine‐3,3′‐pyrrolidine] derivative
Authors: Johner Michael , Rihs Grety , Gürtler Susanne , Otto Hans‐Hartwig
Published: December 2004

Reaction of the 3‐silylated β‐lactams 1 with glycoxalates gives bis‐lactam 3, but the same reaction in the presence of 1 equiv. of Me3SiCl leads to the formation of the disilylated adducts 5. The latter is desilylated by (Bu4N)F yielding the monocarboxylates 7 of 3‐methylidene‐β‐lactams, which, with oxidizing agents, give the spiro compound 8. The structure of 8 is established by spectroscopic data and a crystal‐structure analysis.
In vivo Investigation of Plant‐Cell Metabolism by means of natural‐abundance 13C‐NMR spectroscopy
Authors: Lutterbach Ralf , Stöckigt Joachim
Published: December 2004

Based on the natural abundance of 13C, in vivo 13C‐NMR was used for the first time to monitor the metabolism of sucrose and hydroquinone (1) in cell suspensions of the plant Rauwolfia serpentina (L.) BENTH. ex KURZ. Cells converted sucrose extracellularly into α‐D‐ and β ‐D‐glucose as well as into β ‐D‐fructofuranose and β ‐D‐fructopyranose, respectively. The sugar mixture was completely taken up by the cells after 4 days. Hydroquinone fed at that time resulted in optimum conversion into its β ‐D‐glucoside arbutin (2) within 10 h. A further metabolite, the primeveroside (3) of hydroquinone, appeared as a trace compound after 10 h. The formation of this diglycoside can be increased by further addition of sucrose.
Temporary Protection and Activation in the Regioselective Synthesis of Saccharide Sulfates
Authors: Langston Steven , Bernet Bruno , Vasella Andrea
Published: December 2004

Regioselective sulfation with Et3N · SO3 of partially protected or unprotected glycosides via stannanediyl acetals or stannyl ethers, combined with persistent or temporary protecting groups is described. Stannylation of phenylboronates, followed by sulfation and aqueous workup, is an efficient way for the synthesis of monosulfated monosaccharides. The stannanediyl acetal 2 led in high yields to 3a, while sulfation of the diol 1 proceeded more slowly and led in lower yield to a mixture 1/3a/4a/5a (Scheme 1). The trehalose disulfate 8a was obtained in high yields from 7; reducing the amount of sulfating agent led to a mixture 6/8a/9a. Stannylation and sulfation of the galactoside 11 afforded 13a, while direct sulfation of 11 gave a mixture of the 2‐and 3‐sulfates 13a/14a besides some disulfate 15a. Sulfation of the lactose derivative 16 and the stannanediyl acetal 17 gave the 3‐sulfate 18a, with some disulfate 19a being formed from 16. The mannopyranoside 21 was selectively sulfated at OH–C(2), leading to 22a, while the corresponding diol 20 yielded mostly the isomer 23a and some disulfate 24a. Sulfation of the stannyl ethers derived from the gluco‐and galactopyranosides 25 and 28 and (Bu3Sn)2O afforded high yields of the 2,6‐disulfate 26a and the 3,6‐disulfate 29a, respectively. Stannylation of 25 and 28 with Bu2SnO and sulfation proceeded less satisfactorily. Stannylation of the phenylboronate 32 (Bu2SnO) and sulfation gave good yields of the 2‐sulfate 27a; stannylation and benzoylation yielded the 2‐benzoate 34 (Scheme 2). Similarly, the galactose‐derived 37 provided high yields of the 3‐sulfate 30a and of the 3‐benzoate 39. Direct sulfation of the phenylboronates 32 and 37 proceeded in lower yields and gave mixtures.
Interaction of Double‐Helical Polynuclear Copper(I) complexes with double‐stranded DNA
Authors: Schoentjes Bruno , Lehn Jean‐Marie
Published: December 2004

Double‐helical metal complexes, the helicates H2–H5, were found to bind to double‐helical DNA by spectroscopic, DNA‐melting, and electrophoretic‐mobility measurements. The helicates also inhibited the cleavage of DNA by two restriction enzymes, Sspl and EcoRV, a property which agrees with the binding occurring in the major groove of the double helix. Visible‐light irradiation of solutions containing a helicate and the pBR322 plasmid led to single‐strand cleavage, indicating that these complexes could be of interest as potential probes for nucleic‐acid structure.
Chelate‐Controlled Asymmetric Synthesis of 2‐Substituted 2,3‐Dihydropyridin‐4(1H)‐ones: Synthesis of D‐ and L‐aminodeoxyaltrose derivatives
Authors: Streith Jacques , Boiron Arnaud , Paillaud Jean‐Louis , Rodriguez‐Perez Elsa‐Maria , Strehler Christiane , Tschamber Théophile , Zehnder Margareta
Published: December 2004

Asymmetric methylation and phenylation of the chiral pyridinium salt 7, as well as methylation of chiral pyridinium salt 18, with Grignard reagents occurred in good yield and with good‐to‐excellent diastereoselectivities (Schemes 2 and 3, resp.). These results are best explained by assuming chelate control to govern the asymmetric alkylation/arylation process. The minimum‐energy conformations of the out‐of‐plane twisted pyridinium salts 7 and 18, as determined by the ‘Molecular Simulations Cerius‐Dreiding II’ program, are in good agreement with the postulated asymmetric chelate‐control mechanism.
Neuartige Alkaloide aus dem Giftdrüsensekret sozialparasitischer Ameisen (Myrmicinae: Leptothoracini)
Authors: Reder Elke , Veith Hans Jürgen , Buschinger Alfred
Published: December 2004

Novel Alkaloids from the Poison Glands of Ants Leptothoracini

Novel pyrrolidine alkaloids were isolated from the poison glands of ants Leptothoracini(Myrmicinae) and identified as a mixture of N‐alkylated 3‐methylpyrrolidines. The females of these species produce male‐attracting pheromones in their poison glands. The basic compounds in the secretions were found to be active. The major alkaloid, 3‐methyl‐1‐(3‐methylbutyl)pyrrolidine (5), is present in only ng quantities per gland.
Angular Alkylation of cis‐Decalin Epoxides with C‐nucleophiles: Mechanism, scope, and limitations of a novel bridgehead functionalisation
Authors: Huber Udo , Boland Wilhelm
Published: December 2004

The angular alkylation of cis‐decalin epoxides like 5 or 7 can be achieved at C(8a)

For convenience, the arbitrary numbering given for 5 (Scheme I) is used throughout the General Part; for systematic names, see Exper. Part.

in good yield by using CuI and a large excess of Grignard reagents without an sp3 centre at C(2). The reaction proceeds via a carbenium‐ion intermediate which is stabilised by homoconjugative interaction with the adjacent double bond. Due to 1,3‐diaxial strain in the alkoxides resulting from alkylation or reduction at C(4a) of the epoxides 5 or 7, the nucleophile is delivered selectively to C(8a). Grignard reagents possessing H‐atoms at C(β), transfer a hydride to the epoxide yielding the trans‐decalol 11 (Grignard reduction). The angular alkylation of 5 with allylic and benzylic Grignard reagents proceeds with good yield.
Complete π‐Facial Stereoselectivity in the TiCl4‐Mediated [4 + 2] Cycloaddition of Cyclopentadiene to N,N′‐fumaroyldi[(2R)‐bornane‐10,2‐sultam]
Authors: Chapius Christian , Rzepecki Piotr , Bauer Tomasz , Jurczak Janusz
Published: December 2004

Under the co‐operative influence of two prosthetic groups, and independent of the TiCl4 concentration, complete and constant diastereofacial π‐selection was achieved during the [4 + 2] cycloaddition of cyclopentadiene to N,N′‐fumaroyl‐di[(2R)‐bornane‐10,2‐sultam] ((−)‐1c); reactive conformations are discussed.
NMR‐Spectroscopic Investigations of Potentially Planarized Nonafulvenes
Authors: Chai Shengyong , Bönzli Peter , Neuenschwander Markus
Published: December 2004

1H‐ and 13C‐NMR spectra of nonafulvene 1e and nonafulvenes 2 and 3 have been assigned, high‐resolution 1H‐NMR spectra of 2 (600 MHz, Fig. 3) and of 3 (400 MHz, Fig. 2) have been analyzed, and the data are compared with those of other nonafulvenes (Tables 1–6). Generally speaking, according to their spectroscopic behavior, four classes of nonafulvenes (A–D) may be distinguished (Fig. 1). The investigation shows that compounds 1e and 3 belong to class A, being characterized by 1H‐chemical shifts around 6 ppm, strongly alternating 3J(H,H) and 13C chemical shifts in the range of 123 to 130 ppm, thus existing in the olefinic form with a non‐planar nine‐membered ring. On the other hand, 2 is the first nonafulvene of class D, being characterized by 1H chemical shifts in the aromatic range, large 3J(H,H) values of the same size, and 13C chemical shifts around 110 ppm. Since NMR parameters are virtually not influenced by temperature (−50° to 50°) or solvents, it is concluded that 2 exclusively exists in the dipolar structure 2± with a planarized nine‐membered ring. According to Fig. 4, these classes (and their spectroscopic data) are linked by 10,10‐bis(dimethylamino)nonafulvene (1c; and its temperature‐dependent NMR parameters): for 1c, a temperature‐dependent equilibrium 1c⇌1c± had earlier been established.
Synthesis of 4,6,8‐Trisubstituted Methyl Azulene‐2‐carboxylates
Authors: Rippert Andreas Johannes , Hansen Hans‐Jürgen
Published: December 2004

It is shown that sodium (methoxycarbonyl)cyclopentadienide (1), which is easily accessible from sodium cyclopentadienide and dimethyl carbonate in THF, reacts with 2,4,6‐trisubstituted pyrylium tetrafluoroborates 2a–d in boiling MeOH to afford the corresponding methyl azulene‐2‐carboxylates 4a–d in good yields. The corresponding 1‐carboxylates 3 were not found (cf. Schemes 1 and 2).
Biosynthetic Production of [N2,1,3,7,9‐15N]Guanosine and [1,3,7,9‐15N]inosine and conversion into [N6,1,3,7,9‐15N]adenosine for structure elucidation of RNA by heteronuclear NMR
Authors: Niemann Annette C. , Meyer Mónica , Engeloch Thomas , Botta Oliver , Hädener Alfons , Strazewski Peter
Published: December 2004

A procedure was developed for the biosynthetic preparation of 15N‐labelled guanosine and inosine through the action of a mutant Bacillus subtilis strain. Crude [N2,1,3,7,9‐15N]guanosine and [1,3,7,9‐15N]inosine were isolated from the culture filtrate by precipitation and anion‐exchange chromatography (Scheme 1). No cell lysis and no enzymatic degradation was necessary. The per‐isobutyrylated derivatives 1 and 2 were isolated from a complex mixture, purified by virtue of their different lipophilicity, and separated in three steps involving normal‐and reversed‐phase silica‐gel chromatography. One litre of complex nutrient medium yielded 8.44 mmol of guanosine derivative and 2.84 mmol of inosine derivative with high average 15N enrichment (83.5 and 91.9 atom‐%, resp.). [N6,1,3,7,9‐15N]Adenosine (4) was obtained from 2′,3′,5′‐tri‐O‐isobutyryl[1,3,7,9‐15N]inosine (1) through the ammonolysis of its 1,2,4‐triazolyl derivative with aqueous 15NH3 (Scheme 2).
Lipophilic Functionalized Cobyrinic‐Acid Derivatives. Part 1. Cobester α‐monoacids (α,α,α,β,β,β‐hexamethyl α‐hydrogen Coα, Coβ‐dicyanocobyrinates)
Authors: Kräutler Bernhard , Caderas Christian , Konrat Robert , Puchberger Michael , Kratky Christoph
Published: December 2004

The four α,α,α, β,β,β,‐hexamethyl α‐hydrogen Coα, Coβ‐dicyanocobyrinates 2b, d–f, with a free b‐, d‐, e‐, and f‐propionic‐acid function, respectively, were prepared by partial hydrolysis of heptamethyl Coα, Coβ‐dicyanocobyrinate (cobester; 1) in aqueous sulfuric acid. The cobester monoacids 2b, d–f were obtained as a ca. 1:1:1:1 mixture which was separated. The monoacids were purified by chromatography and isolated in crystalline form. The position of the free propionic‐acid function was determined by an extensive analysis of 2b, d–f using 2D‐NMR techniques; an analysis of the C,H‐coupling network topology resulted in an alternative assignment strategy for cobyrinic‐acid derivatives, based on pattern recognition. Additional information on the structure of the most polar of the four hexamethyl cobyrinates, of the b‐isomer 2b, was also obtained in the solid state from a single‐crystal X‐ray analysis. Earlier structural assignments based on 1D‐NMR spectra of the corresponding regioisomeric monoamides 3b, d–f (obtained from crystalline samples of the monoacids 2b, d–f) were confirmed by the present investigations.
Synthesis, Characterization, and Electrochemical and Photophysical Properties of Rhenium(I) and ruthenium(II) complexes of 2,2′‐bipyridine ligand functionalized β‐cyclodextrins
Authors: Deschenaux Robert , Ruch Thomas , Deschenaux Pierre‐François , Juris Alberto , Ziessel Raymond
Published: December 2004

The synthesis, characterization, and electrochemical and photophysical properties of the ReI and RuII complexes of permethylated β‐cyclodextrins, functionalized on the primary face by a 2,2′‐bipyridine ligand, are reported. For comparison, model compounds, in which the cyclodextrin was replaced by a Me group, were also prepared and their properties investigated.
Determination of the Absolute Configuration of a Series of Halogenated Furanones from the marine alga delisea pulchra
Authors: König Gabriele M. , Wright Anthony D. , Bernardinelli Gérald
Published: December 2004

The absolute configuration of a series of naturally occurring and semi‐synthetic halogenated furanones is proposed on the basis of chemical interconversions and X‐ray and CD analyses. The CD analyses clearly reveal that the presence of the allylic O‐atom has a strong influence in determining the sign and intensity of the low energy π→π* transition.
An Efficient Straightforward Synthesis of Benz[a]azulene
Authors: Sperandio David , Hansen Hans‐Jürgen
Published: December 2004

Benz[a]azulene (1) is synthesized in five steps (cf. Scheme 2) starting from commercially available 2‐iodobenzyl alcohol (4) and tropylium tetrafluoroborate in an overall yield of 44%. The key step (cf. also Scheme 1) is the intramolecular Heck reaction of the 8‐phenylsulfonyl‐substituted heptafulvene 7, which leads in nearly quantitative yield directly to 10‐(phenylsulfonyl)benz[a]azulene (8). The desulfonylation of 8 can be accomplished by Julia's method with Na2S2O4/NaHCO3 in DMF/H2O at 85–90°, thus leading to pure 1 in 78% yield. The phenylation of 8 with PhLi or PhCul at −78° in THF occurs regioselectively at C(9). Dehydrogenation of the formed dihydroazulenes with o‐chloroanil in toluene at room temperature gives 9‐phenyl‐10‐(phenylsulfonyl)‐benz[a]azulene (9) in 70% yield (cf. Scheme 3), which, again, can be desulfonylated with Na2S2O4/NaHCO3 in DMF/H2O in good yields. The addition of PhLi to 1 in THF occurs at temperatures ⩾ −25°. Ionic dehydrogenation (1. Ph3C+BF/MeCN; 2. Et3N) of the dihydro forms leads to 3, as the main product, and its positional isomers.
Synthesis of Spiro[cyclohexane‐1,2′‐[2H]indene] derivatives as inhibitors of steroid 5α‐reductase
Authors: Lin Shu‐Kun , Rasetti Vittorio
Published: December 2004

The spiro[cyclohexane‐1,2′‐[2H]indene] derivatives 15a,b with molecular dimensions and nucleophilic functional groups similar to known steroid 5α‐reductase inhibitors (e.g. 2) were synthesized. The spiro[cyclohexane‐1,2′‐[2H]indene]‐1′(3′H),4‐dione (5) was synthesized from 5‐methoxyindan‐l‐one ( = 2,3‐dihydro‐5‐methoxy‐1H‐inden‐1‐one). A Grignard reaction and a dehydration step led to the cyclohexene (±)‐7 which, upon a stereoselective hydrogenation catalyzed by Raney‐Ni under mild conditions, gave 8a as a pure epimer. Further hydrogenation and hydrogenolysis of 8a over Pd/C at room temperature reduced the keto group to give pure 9a. Finally, the 5′‐substituted derivatives 12a, 14a, and 15a were generated by deprotection and Heck‐type reaction.
Functionalized Nitroalkanes in Organic Synthesis. The first concise preparation of 4‐hydroxyheptadecan‐7‐one and 14‐hydroxyoctadecan‐8‐one, two new hydroxy ketones isolated from Chiococca alba
Authors: Ballini Roberto , Bosica Giovanna , Rafaiani Gianni
Published: December 2004

The 4‐hydroxyheptadecan‐7‐one (1) and 14‐hydroxyoctadecan‐8‐one (2), two new hydroxyketones isolated from leaves of Chiococca alba, were synthesized, for the first time, by hydroxy‐functionalized nitroalkanes 4 and 9, respectively, via two chemoselective key steps: i) nitroaldol condensation with basic alumina, and ii) direct Nef conversion of nitroalkenes to carbonyl derivatives with sodium hypophosphite, in order to preserve the OH group.
Enantioselective Alternating Olefin‐Carbon Monoxide Copolymerization: A new concept for activity and stereoselectivity
Authors: Bronco Simona , Consiglio Giambattista , Di Benedetto Silvia , Fehr Matthias , Spindler Felix , Togni Antonio
Published: December 2004

Cationic Pd‐complexes modified by dicyclohexyl{(R)‐1‐[(S)‐2‐(diphenylphosphino)ferrocenyl]ethyl}phosphine (1a) give very active catalytic systems for the regioregular isotactic specific copolymerization of propene with CO. Other alk‐1‐enes also give stereoregular and regioregular copolymers, even if with lower productivity. The copolymers are isolated as poly(4‐alkyl‐tetrahydrofuran‐2,2,5,5‐tetrayl‐2‐oxy‐2‐methylenes) B in the solid state and give the isomeric poly(2‐alkyl‐1‐oxopropane‐1,3‐diyls) A by dissolution in (CF3)2CHOH. Solid polymer A (R = Et) is formed back at least partially when the dissolved material is reprecipitated from MeOH. The use of the related (ferrocenyl)diphosphine ligands 1b−e and 2 as the catalyst modifier shows that the presence of both elements of chirality and of large substituents on the P‐atoms of the ligand is necessary to achieve good stereocontrol, and that the large difference in basicity between the two P‐atoms is probably the reason for the good catalytic activity.
High‐Yield Syntheses of Sodium, Potassium, and Thallium Hydrotris[3,5‐bis(trifluoromethyl)pyrazolyl]borates and the X‐ray crystal structure of {hydrotris[3,5‐bis(trifluoromethyl)pyrazolyl]borato} thallium(I)
Authors: Renn Oliver , Venanzi Luigi M. , Marteletti Arianna , Gramlich Volker
Published: December 2004

An improved synthesis of 3,5‐bis(trifluoromethyl)pyrazole (1) is described. This compound was used for the high‐yield syntheses of the tris(pyrazoly1)borates Nd[HB(3,5‐(CF3),‐pz)3] (2a) and the corresponding potassium salt, 2b, starting from 1 and NaBH4 and KBH4, respectively. A convenient route to the corresponding thallium(I) salt, 2c, using thallium(I) acetate and either 2a or 2b in CHCI3, is also described. The sodium (3a), potassium (3b), and thallium (3c) salts of bis(pyrazolyl)borate [H2B(3,5‐(CF3)2‐pz)2]− were also prepared. The above pyrazolylborates were characterized by 1H‐, 13C‐, 19F‐, and 11B‐NMR spectroscopy. The X‐ray crystal structure of the thallium derivative 2c was determined. The compound crystallizes in the monoclinic space group P21/m with a = 8.248(9) Å, b = 15.034(12) Å c = 9.243(8) Å, β = 100.10(7)°, Z = 2. The Tl‐atom adopts a pyramidal geometry with respect to the three N‐atoms. However, two TI–N distances (2.725(7) Å) are longer than the third (2.675(10) Å).
Diastereoselective Radical Reactions Starting from Cyclic Iodohydrin Derivatives
Authors: Moufid Nadira , Renaud Philippe
Published: December 2004

The stereoselectivity of radical reactions using cyclic iodohydrins and 2‐alkoxy iodides was investigated on a simple model system obtained from indene (see 1a−d). The low level of stereoselectivity inherent to this type of systems could neither be overcome by using large protective group on the O‐atom of 1c nor by complexation with Lewis acids. However, starting from the free alcohol 1c, it was possible to obtain very high selectivities (trans/cis > 100:1) by forming an aluminium alkoxide derivative upon treatment with methylaluminium bis[2,6‐di(tert‐butyl)‐4‐methylphenoxide] (MAD) before running the radical reaction. Despite the high steric demand of these complexes, the reactions gave satisfactory yields even for the formation of CC bonds.
Glycosylidene Carbenes. Part 21. Synthesis of N‐tosylglycono‐1,4‐lactone hydrazones as precursors of glycofuranosylidene carbenes
Authors: Mangholz Sissi E. , Vasella Andrea
Published: December 2004

The N′‐(glycofuranosylidene)toluene‐4‐sulfonohydrazides 5 and 10 (Scheme 1) were prepared in good yields by oxidation (1,3‐dibromo‐5,5‐dimethylhydantoin/Et3N) of the N′‐glycosyltoluene‐4‐sulfonohydrazides 4 and 9, which were obtained from 2,3,5‐tri‐O‐benzyl‐D‐ribose (3) and 2,3,5‐tri‐O‐benzyl‐D‐arabinose (8), respectively, and toluene‐4‐sulfonohydrazide. The analogous naphthalene‐2‐sulfonohydrazides 7 and 12 were similarly prepared from 3 and 8 via 6 and 11. Photolysis in the presence of phenol of the sodium salt 15 (Scheme 2), best generated in situ, yielded the anomeric glycosides 16, some 5, and traces of the glycosides (1R)/(1S)‐17. Photolysis of 15 in THF gave the sulfones α‐D/β‐D‐18. Photolysis of 15 (quartz filter) and dimethyl fumarate led to a single cyclopropane 19, the sulfones α‐D/β‐D‐18, and the N‐(ribofuranosyl)‐N′‐(ribofuranosylidene)toluene‐4‐sulfonohydrazide 20. Similarly, N‐phenylmaleimide afforded the cyclopropanes 21 and 22. Photolysis of the sodium salt of 10 and phenol afforded the anomeric glycosides α‐D/β‐D‐23, the C‐glycoside 24, and the sulfone 25. Photolytic glycosidation of 15 with N6‐benzyladenine gave the two nucleosides 26 and 27 (Scheme 3).
(±)‐4‐Amino‐4,5‐dideoxyribose, (±)‐4‐amino‐4‐deoxyerythrose, and (±)‐dihydroxyproline derivatives from N‐dienyl‐γ‐lactams
Authors: Behr Jean‐Bernard , Defoin Albert , Mahmood Naheed , Streith Jacques
Published: December 2004

Hetero‐Diels‐Alder cycloaddition of acylnitroso dienophile 4 with the N‐(butadienyl)pyrrolidinone derivatives 2a, b led with complete regioselectivity to the oxazine adducts 5a, b (Scheme 1). Sequential osmylation, protection of the ensuing glycol, and reduction of the NO bond gave the expected hemiaminals 11a, b which were characterized by their crystalline sulfite adducts 12a, b (Schemes 1 and 2). Deprotection and saponification of the latter led to aminodeoxyerythrose and to aminodeoxyribose derivatives as an equilibrium of pyrrolidinose equivalents, i.e., hemiaminals 14a, b, imines 14′a, b, and dimers 14″a,b, respectively (Scheme 3). Hydrocyanic acid addition to 11a, b led ultimately to the proline derivatives 16a, b (Scheme 2). Compound 11b proved to be an inhibitor of syncytium formation in AIDS‐infected cells.
Total Synthesis with a Chirogenic Opening Move Demonstrated on Steroids with Estrane or 18a‐Homoestrane Skeleton
Authors: Quinkert Gerhard , Del Grosso Michael , Döring Astrid , Döring Wolfgang , Schenkel Ralf I. , Bauch Markus , Dambacher Gernot T. , Bats Jan W. , Zimmermann Gottfried , Dürner Gerd
Published: December 2004

A concept of first choice for the synthesis of the title compounds had been proposed by Dane in the late 1930s. It was soon turned down, because the opening move–a chirogenic Diels‐Alder reaction – did not work. With Lewis acids as mediators, however, a successful start has been achieved now. With Ti complexes of chelating ligands (Seebach's TADDOLs (= α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols)), enantioselective formation of the desired adducts does occur. Efficient total syntheses of 2 and 3a have been accomplished.
Bis‐allylic Reactivity of the Funicolides, 5,8(17)‐diunsaturated briarane diterpenes of the sea pen Funiculina quadrangularis from the tuscan archipelago, leading to 16‐nortaxane derivatives
Authors: Guerriero Antonio , D'Ambrosio Michele , Pietra Francesco
Published: December 2004

Funicolides A–C (1–3), D (5), and E (7) and 7‐epifunicolide A (4), new 5,8(17)‐diunsaturated briarane diterpenes, as well as the known analogue brianthein W (6), were isolated from the pennatulacean coral Funiculina quadrangularis (PALLAS, 1766) collected in the Tuscan archipelago. Easy degradation under oxidative and/or basic conditions served to assign the ester groups at C(2) or C(14), while revealing bis‐allylic reactivity at C(7) with formation of 16‐nortaxane derivatives.
Caulerpenyne‐Amine Reacting System as a Model for in vivo Interactions of Ecotoxicologically Relevant Sesquiterpenoids of the mediterranean‐adapted tropical green seaweed caulerpa taxifolia
Authors: Guerriero Antonio , Depentori Daniela , D'Ambrosio Michele , Pietra Francesco
Published: December 2004

Caulerpenyne (1), the most abundant of the ecotoxicologically relevant sesquiterpenoids of the Mediterranean‐adapted tropical green seaweed Caulerpa taxifolia, was found to react with Et3N or pyridine in MeOH by initial deprotection of C(1)HO to give oxytoxin 1 (2a), previously isolated from the sacoglossan mollusc Oxynoe olivacea. With BuNH2, without any precaution to exclude light, 1 gave the series of racemic 3 and 4, and achiral (4E,6E)‐5, (4E,6Z)‐5, (4Z,6E)‐5, and (4Z,6Z)‐5 pyrrole compounds, corresponding to formal C(4) substitution, 4,5‐β‐elimination, and (E/Z)‐isomerization at the C(4)C(5) and C(6)C(7) bonds. Changing to CDCl3 as solvent in the dark, 1 gave cleanly, via 2a as an intermediate, 3 and (4E,6E)‐5. The latter proved to be prone to (E/Z)‐photoisomerization. Under standard acetylation conditions, 3 gave (4E,6E)‐5 via acetamide 7 as an intermediate. Particular notice is warranted by selective deprotection of 1 at C(1), mimicking enzyme reactions, and unprecedented formation of pyrrole compounds from freely‐rotating, protected 1,4‐dialdehyde systems.
Nucleotides. Part XLV. Synthesis of new (2′–5′)adenylate trimers, containing 5′‐amino‐5′‐deoxyadenosine residues at the 5′‐end of the oligoadenylate chain, and of its analogues, carrying a 9‐[(2‐hydroxyethoxy)methyl]adenine residue at the 2′‐terminus
Authors: Kvasyuk Evgeny I. , Kulak Tamara I. , Mikhailopulo Igor A. , Charubala Ramamurthy , Pfleiderer Wolfgang
Published: December 2004

The 5′‐amino‐5′‐deoxy‐2′,3′‐O‐isopropylideneadenosine (4) was obtained in pure form from 2′,3′‐O‐isopropylideneadenosine (1), without isolation of intermediates 2 and 3. The 2‐(4‐nitrophenyl)ethoxycarbonyl group was used for protection of the NH2 functions of 4 (→7). The selective introduction of the palmitoyl (= hexadecanoyl) group into the 5′‐N‐position of 4 was achieved by its treatment with palmitoyl chloride in MeCN in the presence of Et3N (→5). The 3′‐O‐silyl derivatives 11 and 14 were isolated by column chromatography after treatment of the 2′,3′‐O‐deprotected compounds 8 and 9, respectively, with (tert‐butyl)dimethylsilyl chloride and 1H‐imidazole in pyridine. The corresponding phosphoramidites 16 and 17 were synthesized from nucleosides 11 and 14, respectively, and (cyanoethoxy)bis(diisopropylamino)phosphane in CH2Cl2. The trimeric (2′–5′)‐linked adenylates 25 and 26 having the 5′‐amino‐5′‐deoxyadenosine and 5′‐deoxy‐5′‐(palmitoylamino)adenosine residue, respectively, at the 5′‐end were prepared by the phosphoramidite method. Similarly, the corresponding 5′‐amino derivatives 27 and 28 carrying the 9‐[(2‐hydroxyethoxy)methyl]adenine residue at the 2′‐terminus, were obtained. The newly synthesized compounds were characterized by physical means. The synthesized trimers 25–28 were 3‐, 15‐, 25‐, and 34‐fold, respectively, more stable towards phosphodiesterase from Crotalus durissus than the trimer (2′–5′)ApApA.
Syntheses and Reactions of 1′,2′‐Unsaturated 2′,3′‐Seconucleoside Analogues
Authors: Vrček Valerije , Čaplar Vesna
Published: December 2004

The 1′,2′‐unsaturated 2′,3′‐secoadenosine and 2′,3′‐secouridine analogues were synthesized by the regioselective elimination of the corresponding 2′,3′‐ditosylates, 2 and 18, respectively, under basic conditions. The observed regioselectivity may be explained by the higher acidity and, hence, preferential elimination of the anomeric H–C(1′) in comparison to HC(4′). The retained (tol‐4‐yl)sulfonyloxy group at C(3′) of 3 allowed the preparation of the 3′‐azido, 3′‐chloro, and 3′‐hydroxy derivatives 5–7 by nucleophilic substitution. ZnBr2 in dry CH2Cl2 was found to be successful in the removal (85%) of the trityl group without any cleavage of the acid‐sensitive, ketene‐derived N,O‐ketal function. In the uridine series, base‐promoted regioselective elimination (→19), nucleophilic displacement of the tosyl group by azide (→20), and debenzylation of the protected N(3)‐imide function gave 1′,2′‐unsaturated 5′‐O‐trityl‐3′‐azido‐secouridine derivative 21. The same compound was also obtained by the elimination performed on 2,2′‐anhydro‐3′‐azido‐3′‐azido‐3′‐deoxy‐5′‐O‐2′,3′‐secouridine (22) that reacted with KO(t‐Bu) under opening of the oxazole ring and double‐bond formation at C(1′).
Synthesen, chemische Reaktionen und NMR‐spektroskopische Untersuchungen substituierter Phosphonopyruvate
Authors: Feistauer Helmut , Neidlein Richard
Published: December 2004

Phosphonopyruvates: Syntheses, NMR Investigations, and Reactions

The new 3‐(diethoxyphosphoryl)‐2‐oxopropanoates 5–24 and ‐propanamides 25–38 with various substituents at C(3) were prepared in moderate‐to‐good yields (Schemes 2 and 3, Tables 1 and 2). It was shown that they adopt a preferred conformation in which the diethoxyphosphoryl group and the substituent at C(4) are antiperiplanar to each other (see B). The keto‐enol tautomerization of phosphonopyruvates with PhC(3) (see 20) and MeSC(3) (see 24 and 33) was examined. In CHCl3, two tautomeric species exist, whereas in dimetylsulfoxide (DMSO), three tautomeric forms are observed. Oxime ethers, an oxime, and a phenylhydrazone of unsubstituted phosphonopyruvates were prepared (see 40–44), and quinoxalin‐2(1H)‐ones could be obtained from the reaction of pyruvates with 4,5‐dimethylbenzene‐1,2‐diamine (see 45–47).
On the Way to Glycoprocessing Inhibitors. Synthesis of an imidazo‐L‐xylo‐piperidinose derivative
Authors: Frankowski Andrzej , Deredas Dariusz , Nouen Didier Le , Tschamber Théophile , Streith Jacques
Published: December 2004

An eight‐step synthetic sequence led from the known D‐xylo‐pentodialdose 8 to imidazo‐L‐xylo‐piperidinose 15, the key steps being the build‐up of imidazole compound 12 by a van Leusen methodology and the intramolecular SN2 ring closure of the O‐triflated benzylidene derivative 13. xylo‐Piperidinose 15 appears in a half‐chair conformation like the oxocarbonium ions which are the postulated intermediates in the glycoprocessing of the pyranose polysaccharides. This bicyclic azasugar should be a glycosidase inhibitor.