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Université de Neuchâtel

Bafoudiosbulbins A, and B, two anti-salmonellal clerodane diterpenoids from Dioscorea bulbifera L. var sativa

Teponno, Rémy Bertrand ; Tapondjou, Azefack Léon ; Gatsing, Donatien ; Djoukeng, Jules Désiré ; Abou-Mansour, Eliane ; Tabacchi, Raphael ; Tane, Pierre ; Stoeckli-Evans, Helen ; Lontsi, David

In: Phytochemistry, 2006, vol. 67, no. 17, p. 1957-1963

Two clerodane diterpenoids, Bafoudiosbulbins A 1, and B 2, together with five known compounds: tetracosanoic acid, 1-(tetracosanoyl)-glycerol, trans-tetracosanylferulate, β-sitosterol and 3-O-β-d-glucopyranosyl-β-sitosterol were isolated from the tubers of Dioscorea bulbifera L. var sativa. Their structures were established by spectroscopic methods (1D and 2D-NMR,...

Université de Neuchâtel

The gas-solid interface The Interaction of Argon, Xenon and Sulfur Hexafluoride with Rhombic Sulfur

Stoeckli, Fritz ; Stoeckli-Evans, Helen

In: Helvetica Chimica Acta, 1975, vol. 58, no. 8, p. 2291 - 2294

Further theoretical calculations have been carried out for the adsorption potentials of Ar on the (011) face of rhombic sulfur, and for Xe and SF6 on the (011) and (111) faces. By using the same sites for the three molecules and pair-potentials of the Lennard-Jones type, specific scaling factors were found. These are constant within 5-10%, for each adsorbate, and therefore the...

Université de Neuchâtel

The Interaction of Argon with Sulfur Surfaces. Experimental and calculated variations of the adsorption potential with surface coverage

Stoeckli-Evans, Helen ; Stoeckli, Fritz

In: Helvetica Chimica Acta, 1975, vol. 58, no. 1, p. 194-198

The adsorption potentials of argon on the (111), (001) and (110) planes of rhombic sulfur have been calculated for a total of 818 sites, using an intermolecular potential of the Lennard-Jones (6:12) type with the Kirkwood-Müller expression. Direct summation over the nearest 100-150 atoms of the solid was used. There is a good agreement between the experimental and the calculated...

Université de Neuchâtel

Diastereoselective synthesis of (1S,2S,3R,6S) 3-Chloro-3-methyl-6-isopropenyl-1,2-cyclohexanediol via Prins reaction induced by zinc and trimethylsilyl chloride

Marty, Maurus ; Stoeckli-Evans, Helen ; Neier, Reinhard

In: Tetrahedron, 1996, vol. 52, no. 13, p. 4645-4658

While attempting to synthesize a potential inhibitor of the biosynthetic step of formation of PBG, a novel catalytic system inducing the Prins reaction was discovered. Treatment of epoxy geranial with Zn and trimethylsilyl chloride gave (1S,2S,3R,6S) 3-Chloro-3-methyl-6-isopropenyl-1,2-cyclohexanediol in high diastereoselectivity.

Université de Neuchâtel

The Synthesis of a Pyrazol Analogon of Porphobilinogen with the Help of the Mukaiyama Aldol Reaction

Chaperon, André ; Bertschy, Hugo ; Franz-Schrumpf, Anne-Laurence ; Hugelet, Bertrand ; Neels, Antonia ; Stoeckli-Evans, Helen ; Neier, Reinhard

In: Chimia, 2003, vol. 57, p. 601-606

The synthesis of a pyrazol analogon of porphobilinogen is described. The Mukaiyama crossed aldol reaction is the key step of our approach. The retrosynthetic analysis follows the mechanism for the biosynthesis of porphobilinogen initially proposed by Shemin.

Université de Neuchâtel

An Unexpected Tandem Reaction between N-Butadienyl-N-alkylketeneN,0-Trimethylsilylacetals of Propionamide and Activated Dienophiles like N-Phenylmaleimide or Acryloyl Chloride

Baak, Marcel ; Rubin, Yves ; Franz, Andreas ; Stoeckli-Evans, Helen ; Bigler, Laurant ; Nachbauer, Jürgen ; Neier, Reinhard

In: Chimia, 1993, vol. 47, p. 233-240

Starting from the N-butadienyl-N-alkylpropionamides 1a-1c the corresponding N,0-trimethylsilylacetals could be obtained using the mixture ofLDA and trimethylsilyl chloride in THF. The unexpected reaction sequence Diels-Alder reaction/acylation between the N-butadienyl-N-alkylketene N,0-trimethylsilylacetal ofpropionamide (2a-2b) and...

Université de Neuchâtel

Dinuclear ruthenium sawhorse-type complexes containing bridging ligands with ferrocenyl substituents in endo/endo, endo/exo and exo/exo orientations

Auzias, Mathieu ; Therrien, Bruno ; Labat, Gaël ; Stoeckli-Evans, Helen ; Süss-Fink, Georg

In: Inorganica Chimica Acta, 2006, vol. 359, p. 1012-1017

The dinuclear ruthenium complexes Ru2(CO)4(OOCC5H4FeC5H5)2L2 (L = NC5H5: 1, L = PPh3: 2) have been synthesized from Ru3(CO)12, ferrocene carboxylic acid and pyridine or triphenylphosphine, respectively. The single-crystal X-ray structure analysis reveals...

Université de Fribourg

Novel HEXOL-type cyclometallated iridium(III) complexes: stereoselective synthesis and structure elucidation

Yang, Liangru ; Zelewsky, Alexander von ; Stoeckli-Evans, Helen

In: Chemical Communications, 2005, vol. (33), p. 4155

Two diastereoisomers of tetranuclear cyclometallated iridium complexes, either having an inner core of HEXOL-type [Ir(IrCl₂)₃]⁶⁺ unit and a surface of six chiral, didentate, cyclometallated ligands, are stereoselectively synthesized from an enantiopure pinenopyridine derivative.

Université de Fribourg

Diastereoselective synthesis of coordination compounds: a chiral tripodal ligand based on bipyridine units and its ruthenium(II) and iron(II) complexes

Hamann, Christine ; Zelewsky, Alexander von ; Neels, Antonia ; Stoeckli-Evans, Helen

In: Dalton Transactions, 2004, vol. 3, p. 402-406

The enantiomerically pure chiral tris-chelating ligand (+)-(7S,10R)-L(L) comprising three 4,5-pinenobipyridine subunits connected through a mesityl spacer has been synthesized. Complexes of L with RuII and FeII have been prepared and characterised. NMR spectroscopy indicates that...