Nicole Platzer

Easy alkylation of purine bases by solid-liquid phase transfer catalysis without solvent. : structural analysis by 2D heteronuclear 1H 13C correlated nmr spectroscopy.

Abstract Solid-liquid PTC without added organic solvent promotes alkylation of purine derivatives leading in particular to an efficient synthesis of the antiviral DHPA. The location of the substituent on the ring was determined by analysis of coupling interactions through 2D δ-δ heteronuclear 1H 13C correlated NMR spectroscopy.

Chimie organometallique: XXX. Etude par resonance magnetique nucleaire du proton et par radiocristallographie du N-methylindolechrome-tricarbonyle

Abstract The structure of N -methylindolechromium tricarbonyl ( 4 ) in the solid state has been determined by X-ray crystallography. The projection of the chromium atom on the N -methylindole plane does not coincide with the center of symmetry of the benzene ring; the tripod is distorted and the overall conformation of the complex is gauche rather than eclipsed. Study of the 1 H NMR spectrum of complex 4 in solution at +20°C and −38°C leads to similar conclusions. The results explain the nucleophilic attack at carbon atoms 4 and 7 of complex 4 .

Complexes olefiniques du ruthenium ☆: III. Structure cristalline de [RuCl2(nbd)(pipéridine)2] et de [RuCl2(cod)(hexylamine)2], etude spectrale des complexes [RuCl2(diène)(amine)2]

Abstract The reactivity of about twenty amines towards [RuCl 2 (diene)] n has been studied. These polymeric compounds undergo chlorobridge splitting to give the mononuclear species [RuCl 2 (diene)(amine) 2 ]. Two forms of these complexes can sometimes be isolated according to the temperature. The structures of two different isomers have been determined crystallographically to elucidate the stereochemical arrangement of the ligands about the ruthenium atom. [RuCl 2 (C 7 H 8 )(C 5 H 11 N) 2 ] crystallizes in space group P 1 with a = 14.864(4); b = 9.888(3); c = 6.695(1)A: α = 80.24(3)°; β = 102.31(2)°; ψ = 104.50(9)° and Z = 2. The structure was refined by least squares techniques to R = 0.035 and R p = 0.042 for 6835 reflections. The coordination geometry about the ruthenium atom is distorted octahedral with trans chloro ligands, cis amine ligands and the norbornadiene moiety bound through the two double bonds. The CC distances of the olefinic bonds are lengthened (1.388(3) and 1.389(3)A) compared with 1.35. A in the free ligand. The olefin exerts a slight trans influence on the Ru—N bonds (2.237(2) and 2.248(2) A). The Ru—Cl distances ( trans to Cl) are close to the expected values. [RuCl 2 (C 8 H 12 )(C 6 H 15 N) 2 ] is monoclinic C 2/ c with a = 24.804(5); b = 7.760(2); c = 12.318(3) A; β = 99.71(2)° and Z = 4. The structure was refined by least squares procedure to R = 0.047 and R p = 0.055 for 2802 reflections. The complex has the same pseudo-octahedral geometry but a different arrangement of the ligands about the ruthenium atom. The complex possesses crystallographically imposed C2 symmetry with the amine ligands trans to each other. Principal bond lengths are: Ru—Cl 2.458(1) A (demonstrating a slight trans influence of the olefinic double bonds), Ru—N 2.174(3) A. The observed C=C distance of 1.389(6) A in the coordinated cyclooctadiene is due to the participation of π electrons in the bonding to the metal. The NMR spectra of all the complexes prepared are discussed. The structures of the two isomers being known, we show that a definite conclusion about the configuration of each compound could be drawn, using 13 C NMR spectroscopy. The characteristics of the infrared spectra are reported.

Structural analysis of five lactose-containing oligosaccharides by improved, high-resolution, two-dimensional 1H-n.m.r. spectroscopy

Abstract The 1H-n.m.r. spectra of five oligosaccharides, lactose, 6′- and 3′-sialyl-lactose, lacto-N-tetraose, lacto-N-fucopentaose I, and A-pentasaccharide in deuterium oxide have been obtained, at 500 MHz and 25°. COSY, COSY LR, RECSY, and COSY LR-R determinations, the latter two involving multistep transfer of magnetization revealed the J connectivities, including very small interactions which do not result in resolved multiplicity. Complete sets of unambiguous resonance assignments were obtained, including resonances in the poorly resolved region between δ 3.4 and 4.1. In the 2D patterns, each group of signals aligned with the “head group” (generally one of the reporter groups) constitutes a finger-print characteristic of the type of residue and of its position in the carbohydrate chain. Numerous coupling constants were measured from resolution-enhanced 1D spectra. Small long-range glycosidation shifts are most likely representative of slight changes in conformation and/or conformational equilibria. The large, reciprocal, long-range glycosidation shifts shown by the resonances of the two l -fucosyl groups of A-pentasaccharide indicated through-space interactions between these residues.

The role of proline in the asymmetric step of the Woodward synthesis of erythromycin

Abstract Proline induces the enantioselectivity of the title reaction in an aldol reaction and not in a conjugate addition. This was demonstrated by the two following sets of experiments. (i) Recovered keto sulfides 4 and 5 did not show any optical activity when the racemic substrates were treated with (S)-proline; moreover (S)-proline was unable to induce chirality during the conjugate addition of thiophenol on cyclohexenone. (ii) Kinetic resolution of racemic keto aldehyde 6 occured when this compound was submitted to a (S)-proline-catalyzed aldol reaction.

Sur la transformation du β-nitrostyrène sous l'action du chlorure d'acétyle en présence d'un chlorure métallique

Abstract While β-nitrostyrene yields only hydroxymic or hydroxamic acid derivatives by treatment with acetyl chloride in the presence of zinc, tin, titanium or aluminium chloride, it also gives 3-chloro 2-indolinone and a 5-acetyl derivative of the latter, when the reaction is carried out with ferric chloride. The procedures of this reaction are examined, and a mechanism is suggested.

Etude en resonance magnetique nucleaire du carbone-13 de complexes η-1,5-cyclooctadiene β-dicetonato iridium(I)

Abstract The 13 C NMR spectra of iridium complexes of 1,5-cyclooctadiene are reported and discussed. For compounds containing β-diketonato ligands, a correlation is found between the ethylenic carbon chemical shifts and the Swain and Lupton and values of the substituents of the β-diketonato ligand. The relationship is satisfactorily explained by considering the Dewar, Chatt and Duncanson model of bonding. Tentative interpretation of the observed chemical shifts of the other carbons is presented.

Structural analysis of the carbohydrate chain of glycopeptides isolated from Robinia pseudoacacia seed lectins.

Robinia pseudoacacia seeds contain lectins which are closely related. Pronase digestion of the dimeric and tetrameric lectins, RPA1 and RPA3, gave glycopeptides. The structure of the oligosaccharide was determined by 1H NMR spectroscopy and carbohydrate determination as alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)]-[alpha-D-Manp+ ++-(1-->6)]-beta- D-Manp-(1-->4)-beta-D-GlcpNAc-(1-->4)-[alpha-L-Fucp-(1-->3)] -beta-D-GlcpNAc - (1-->4)-Asn. It appears that the 34-kDa constitutive polypeptide of RPA1 contains 4-5 carbohydrate chains whereas the 30.5-kDa and 29-kDa subunits of RPA3 contain two and one oligosaccharide chains, respectively.

Interactions des alcynes avec les complexes carbéniques du tungstène portant une double liaison carbone— carbone: Accès aux dérivés bicyclo[4,1,0] heptaniques par insertion-cyclopropanation

Resume The carbene complex (CO) 4 W = C(OCH 3 )CH 2 CH 2 CH = CH 2 , in which the carbon—carbon double bond is coordinated to the metal center, reacts with alkynes to give, after an insertion-rearrangement reaction, followed by an intramolecular cyclopropanation reaction, bicyclo[4.1.0] heptane derivatives.

Complexes olefiniques du ruthenium: V. Structure cristalline et etude RMN de [RuClH(cod)(pyridine)2]

Abstract The complexes [RuClH(cod)(amine) 2 ] undergo amine exchange reactions with pyridine, γ-picoline or 4-(dimethylamino)pyridine. The crystalstructure of [RuClH(cod)(py) 2 ] has been determined from three-dimensional X-ray data. It crystallizes in space group P 2 1 / n of the monoclinic system; a 11.278(5); b 10.619(9); c 14.231(4) A; β 90.34(3)°; Z = 4. The structure was solved by standard heavy atom methods and has been refined by least squares to a conventional R factor of 0.038 based on 5535 reflections. The coordination geometry around the ruthenium atom is octahedrally distorded with cis -aminepyridine ligands, the chloro and hydrido ligands being trans to each other and the cyclooctadiene moiety bound through the two double bonds. Principal bond lengths are: Ru-H 1.60(3); Ru-Cl 2.584(1), Ru-N 2.167(2) and 2.153(2) A. 1 H and 13 C NMR data are presented for the three complexes. The 13 C NMR shifts of the olefin group indicate a large degree of π-back-bonding.