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Heterogeneous asymmetric direct aldol reactions between aldehydes (2-nitrobenzaldehyde, 2-methylpropanal) and acetone catalyzed by polystyrene resin (PS) supported di- and tripeptides H-Pro-Pro-, H-Pro-Pro-Pro-, H-Pro-Glu(OH)-, H-Pro-Pro-Glu(OH)-, H-Pro-Asp(OH)-, H-Pro-Pro-Asp(OH)-, H-Ser-Glu(OH)-, H-Ser-Ser-Glu(OH)-, H-Val-Glu(OH)-, H-Val-Val-Glu(OH)-MBHA-PS, were studied under identical experimental conditions at room temperature in a continuous-flow fixed-bed reactor (CFBR) system. In the asymmetric aldol reactions reversal of enantioselectivity was observed on H-Pro-Pro-Glu(OH)- and H-Pro-Pro-Asp(OH)-MBHA-PS-supported catalysts (ee 42–67% S) as compared to the H-Pro-Glu(OH)- and H-Pro-Asp(OH)-MBHA-PS-supported catalyst (ee 28–82% R). In the case of H-Pro-Pro- and H-Pro-Pro-Pro-MBHA-PS-supported catalysts reversed enantioselectivity was observed by using the benzoic acid additive (12% S) as compared to the H-Pro-MBHA-PS catalyst (25% R). The stability of the catalysts in the flow system was consistent with the heterogeneous character of the reaction, as was the linear behavior obtained using mixtures of L- and D-enantiomers of the supported H-Pro-MBHA-PS catalyst. The enamine character of the reaction intermediates was supported by ESI-MS measurements. Based on these and the computed structure of the peptides, the conformation of the intermediate adducts is held responsible for chiral induction, therefore for the enantioselectivity inversion observed in these reactions.

Synthese d'alcoxy-4 chloro-5 tetrahydro-1,2,3,4 [oxo-3 thiadiazole-1,2,4ine-4yl-5]-1 pyrimidones-2 a partir de chloro-5 thiadiazole-1,2,4ine-4ones-3 et de chloro-5 pyrimidinolate dans des solvants alcanols-1

The endogenous production of taurine and gamma-aminobutyric acid (GABA) in rat ocular tissues was investigated. The activities of taurine-producing enzyme, cysteine sulfinic acid decarboxylase (CSAD), and GABA-synthesizing enzyme, glutamic acid decarboxylase (GAD), were observed in the retina, lens, iris-ciliary body and cornea. The highest specific activity of CSAD was in the cornea and that of GAD in the retina. The discrepancy between CSAD activity and taurine content within the ocular tissues indicates that intra- or extraocular transport processes may regulate the concentration of taurine in the rat eye. The GAD activity and the content of GABA were distributed in parallel within the rat ocular tissues. The quantitative results suggest that the GAD/GABA system has functional significance only in the retina of the rat eye.

Treize systemes chromatographiques en couche mince sont utilises pour caracteriser seize monosaccharides (aldoses et aminoglycosides). Utilisation de l'analyse a composantes principales

Calcul des energies de conjugaison 3p-3pΠ dans le sulfure de methyle vinyle et des energies de conjugaison 2p-2pΠ dans l'ether de methylvinyle ethyle

Syntheses des composes du titre via la reaction de tributylstannyl-5 pyrimidines avec le bromo ethylene

Synthese des composes du titre a partir de bis-hydroxymethyl malonate de diethyle et de [disodiothio-3,3 cyano-2] acrylamide; potentiels d'ionisation des composes synthetises

C 15 H 15 NSO 6 cristallise dans P2 1/n avec affinement jusqu'a 0,053. Le noyau benzenique du cation et de l'anion sont quasiment plans. Anions et cations forment des chaines dans la direction b grâce a des liaisons hydrogenes

Preparation de cyanines en Y avec trois groupes dimethylamino au bout des 3 chaines par reaction de Vielsmeier de cyanines lineaires avec la dimethylamino-3 acroleine

Les (dibromo-2'2' cyclopropyl-4) dioxolannes-1,3 reagissent avec le methyllithium pour donner des allenyl-4 dioxolannes-1,3 et des (bromo-2' cyclopropyl-4) dioxolannes-1,3

Le bromo-6 oxo-2 bornane sulfonate-8 d'ammonium cristallise dans le systeme orthorhombique avec le groupe d'espace P2 1 2 1 2 1 et sa structure est affinee jusqu'a 0,033

Cinetique des reactions a pH ∼ 7. Pour certaines reactions, le radical intermediaire forme dans la 1ere etape serait piege par la N-t-butyl-α-phenylnitrone

Synthese de methyl-3 α-aryl thiatriazole-1,2,3,5io-3amidures-4 par reaction du chlorure de thionyle et d'amino-1 aryl-3 methyl-1 guanidines dans la pyridine suivie d'un traitement basique

Cinetique des reactions de substitution entre divers nucleophiles conjugues (enolates, dianions et nucleophiles neutres) et des halogenoalcanes et halogenures benzyliques

Application des concepts empruntes a la geometrie differentielle, des surfaces minimales et de la transformation de Bonnet a la reorganisation moleculaire. Interpretation de la racemisation et de l'isomerisation E/Z des doubles liaisons en termes de transformation de surface

Synthese a partir d'ethylthiomethanol et de chloro t-butyl dimethyl silane; application a la synthese de chloro-5 phenacyl-1 phenyl-4 1H-pyrimidone-2 a partir de chloro-5 1H-pyrimidone-2 et a la synthese de benzyloxymethyl-3 thymine a partir de bis-trimethylsiloxy-2,4 methyl-5 pyrimidine

Dedoublement optique de la benzylamino-2 methoxy-8 tetraline, intermediaire synthetique de l'hydroxy-8 dipropylamino-2 tetraline. Les enantiomeres de ce dernier sont analyses par chromatographie paire ion et on en etudie la configuration absolue par diffraction RX

Le TCNE, la dichloro-2,3 dicyano-5,6 benzoquinone et le dicyano fumarate de diethyle reagissent avec les composes du titre pour donner des derives de l'acide cyclopropanedicarboxylique-1,1 et de l'acide norcarene-3 dicarboxylique-7,7

Etude de l'oxydation electrochimique de l'isopropyl-4 anisole dans l'acide trifluoroacetique

Synthese de bis-bromomethyl-2,6 bromo-4 pyridine (A) a partir d'acetyl-3 dihydro-3,4 methyl-6 pyrannedione-2,4 ou d'acide hydroxy-4 pyridinedicarboxylique-2,6; A reagit avec l'imino-2,2' bis-acetate de di-t-butyle puis avec l'ethynylbenzene pour donner le compose du titre

Rose Bengal mediated photooxidation of mitochondrial F1-ATPase and its beta-subunit resulted in inactivation and loss of about 50 and 60% of their histidine residues, respectively. The beta-subunit was not cleaved upon photooxidation. Photooxidation of histidine probably results in changes in the conformational stability of F1-ATPase leading to its inactivation. The participation of singlet molecular oxygen during the photooxidation process is suggested by the selective loss of histidine residues, while other amino acids, also sensitive to singlet oxygen attack, were not affected. Photochemical damage of F1-ATPase was prevented by various phenanthroline compounds, the order of efficiency being bathophenanthroline-Fe chelate greater than bathophenanthroline greater than orthophenanthroline-Fe chelate greater than bathophenanthroline-sulfonate-Fe chelate. The prevention by bathophenanthroline-Fe chelate of photochemical damage is interpreted on the basis of its interaction with the photosensitizer, Rose Bengal, probably implying a chemical reaction which decreases the actual concentration of the sensitizer and, thereby, the extent of photoinactivation.

Preparation d'enaldehydes par reaction d'aldehydes ou de cetones avec le (cyclohexylimino-4 butene-2yl O,O-diethyl) phosphonate qui est prepare a partir de l'acetate de diethoxyphosphoryl-4 butene-«2»yle

Synthese du compose du titre par reaction de l'ethynyl aniline avec le phenyl-3 dimethyl-2,2 propyne-2ol-1

Les derives marques des O-methyl-1 isomaltoside, O-methyl-1 maltoside, et du di-O-α-D-glucopyranosyl-4,6 O-methyl-1 glucopyranoside sont synthetises a partir des composes marques anhydro-1,6 correspondants. Leur spectre RMN a 500 MHZ est effectue