Jean-Claude Poulin

Reduction asymetrique catalysee par des complexes de metaux de transition : III. Diphosphines chirales derivees de l'isopropylidene dihydroxy-2,3 bis(diphenylphosphino)-1,4 butane (diop)

Abstract Various chiral diphosphines related to diop, isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane, have been prepared. Substitution of a methyl group at the meta position of each aromatic ring increases optical yields, which can reach 90% (asymmetric synthesis of a 3-(3,4-dihydroxyphenyl)alanine derivative). Excellent results from asymmetric catalysis have also been obtained using structural analogues of diop in which the acetonide ring is placed by a carbon ring.

Non reciprocal writing and chirality in femtosecond laser irradiated silica

We ascertain by measuring the surface topography of a cleaved sample in which damage lines have been written in volume by scanning with a femtosecond laser, that matter shearing occur along the laser track with alternating sign (scissor or chiral effect). We note that the shearing in the head of the laser tracks change its sign with the change in scanning direction (pen effect or non reciprocal writing). We also show that nanostructures in the head are nano-shearing, with all the same sign whatever the direction of writing may be. We suggest that symmetries revealed by the shearing mimic the laser induced electron plasma density structures and inform on their unusual symmetries induced by the laser beam structures.

Partial resolution through chiral synthesis using a racemic mixture

Abstract A racemic mixture of a compound bearing a reactive prochiral center can partially react with a chiral reagent ; diastereomeric products are formed and the starting material is kinetically resolved. The relationships between the relative amounts and the enantiomeric excesses of reaction products and recovered starting material are discussed. Applications are given for asymmetric hydrogenation of racemic AcΔPheAlaOMe catalyzed by a rhodiumdiop complex.

Hydrogenation catalytique homogene a l'aide de complexes rhodium—diphosphines

Abstract The catalytic activity of Wilkinsons rhodium complexes with a diphosphine is studied in the hydrogenation of styrene and α-acetamido cinnamic acid. There is a large effect of the chain linking the two diphenylphosphino groups, which can change the selectivity of the obtained catalyst.

Diastereoselective hydrogenation of monodehydro enkephalins controlled by chiral rhodium catalysts

Abstract Protected (Z)dehydrophenylalanyl-Leu-enkephalin, (Z)dehydrotyrosyl-Leuenkephalin and (Z)dehydrotyrosyl-(R)Ala 2 -Leu-enkephalin. have been synthesized. These compounds have been hydrogenated to give protected Leu-enkephalins in the presence of various chiral rhodium complexes. Deprotection of the product gave Leu-enkephalins or epimers, ytterbium in liquid ammonia allows smooth deprotection of NHCBz or OTs groups on small amounts of peptides. Strong stereocontrol could be achieved by suitable choice of the chiral catalyst. This method has good potential for stereospecific labelling of enkephalins and other small peptides.

Asymmetric tritiation of N-acetyl dehydrophenylalanyl-(S) phenylalanine (methylester) catalyzed with a rhodium (+) diop complex

Abstract Rhodium-(+)diop complex catalyzes the stereoselective addition of two tritium atoms in Ac-ΔPhe-( S ) PheOMe (diop stands for isopropylidene - 2,3 - dihydroxy - 2,3- bis - diphenylphosphino - 1,4 - butane). Tritiated Ac( S ) Phe-( S ) PheOMe and Ac-( R ) Phe-( S ) PheOMe were obtained with a theoretical specific radioactivity. Each diastereoisomer was isolated in a pure state, their 3 H-nmr spectra indicated the ratio and the sites (C α -C β ) of 3 H labelling. 3 H- 3 H and 1 H- 1 H coupling constants used together allowed the unequivocal assignment of the three staggered rotamers around C α -C β in the N-terminal phenylalanine moiety. The scope of the reaction for selective preparation of tritiated dipeptides is discussed.

Asymmetric homogeneous reduction of dehydropeptides

Abstract Monodehydropeptides with the dehydroaminoacid fragment in C-terminal or N-terminal position were synthetized as well as a family with the general formula Ac-ΔPhe-(Gly) n -Leu-OR (n = 0–2, R  H or Me). Asymmetric reduction of these compounds catalyzed by chiral rhodium complexes was investigated. The results were discussed in terms of double asymmetric induction. A method was developped to avoid the use of both enantiomers of the substrate or of the catalyst, it consists in the total reduction of a racemic dehydropeptide. The products distribution gives access to the two desired facial selectivities.

Synthesis of a protected monodehydro Leu-enkephalin and its hydrogenation catalyzed by chiral rhodium complexes

Abstract (S,S)-Z-(0)Ts-Tyr-Gly 2 -ΔPhe-Leu-OMe was synthesized. Some chiral rhodium complexes catalyze the reduction of the CC bond. The stereochemistry of reduction of the ΔPhe moiety was investigated, 93 % de could be achieved with dipamp as ligand in the catalyst.

Scanning tunneling microscopy observation of giant palladium-561 clusters

Abstract STM observation showed giant palladium-561 clusters which are larger in size than observed earlier by TEM and HREM studies. The difference is presumably due to the ligand shell of the clusters, which is invisible to electron microscopy.

Charge-transfer complexes interactions evidenced by chemical force microscopy

Charge-transfer complexes have been detected by chemical force microscopy (CFM) between a tip and a substrate respectively functionalized with trinitrofluorenone and 9-anthracenemethanol siloxane derivatives.