- Synthesis of Functionalised Phenylalanines Using Rhodium Catalysis in Water
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The efficient synthesis of substituted phenylalanine-type amino acids using a rhodium-catalysed, conjugate addition of arylboronic acids is described. The reactions are run in water and use a low loading (0.5 mol %) of rhodium catalyst.
- Chapman, Christopher J.,Frost, Christopher G.
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p. 353 - 355
(2007/10/03)
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- 2,2',5,5'-tetramethyl-4,4'-bis(diphenylphoshino)-3,3'-bithiophene: A new, very efficient, easily accessible, chiral biheteroaromatic ligand for homogeneous stereoselective catalysis
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The four-step straightforward synthesis of enantiopure (+)- and (-)- 2,2',5,5'-tetramethyl-4,4'-bis(diphenylphoshino)-3,3'-bithiophene (tetraMe- BITIOP), anew C2-symmetry chelating ligand for transition metals, is described, starting from 2,5-dimethylthiophene. The complexes of this electron-rich diphosphine with Ru(II) and Rh(I) were used as catalysts in some homogeneous hydrogenation reactions of prostereogenic carbonyl functions of α- and β-ketoesters, of prostereogenic carbon-carbon double bonds of substituted acrylic acids, and of N-acetylenamino acids. The enantiomeric excesses were found to be excellent in all the experiments and comparable with the best results reported in the literature for the same reactions, carried out under similar experimental conditions, with the metal complexes of the most popular chiral diphosphine ligands as catalysts.
- Benincori, Tiziana,Cesarotti, Edoardo,Piccolo, Oreste,Sannicolo, Franco
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p. 2043 - 2047
(2007/10/03)
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- TRICYCLIC AMIDES
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The invention relates to a compound selected from these of formula (I) : STR1 in which R 7, R 8, Y, n and A are as defined in the description, and medicinal product containing the same useful for treating a disorder of the melatoninergic system.
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- Solveni and temperature effects on the intramolecular fluorescence quenching in dipeptide model compounds [1]
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The mechanism of fluorescence quenching through intramolecular electron transfer (ET) was investigated in the dipeptide model compounds DL-N-[4-(diethylaraino)alkyl]-2-acetylamino-3-(1-naphthyl)propionamides (1) by stationary and time-resolved fluorescence spectroscopy in non-polar and polar solvents. An analysis of the observed singlet-exciplex fluorescence and the biexponential decay of monomer fluorescence established that emission quenching in non-polar solvents proceeds through the singlet-exciplex intermediate with a strong charge-transfer character, and that the quenching rate constant increases with a decrease in free-energy change for ET (ΔGet) but it is not very sensitive to the variation of methylene chain length in 1. The observations of biexponential emission decay and very weak exciplex emission in polar solvents suggest that a singlet exciplex and/or a solvent-separated radical ion pair become a key intermediate in the quenching process. The finding that the magnitude of ΔGet, being regarded as a measure of the stability of an intermediate formed, linearly correlates with the logarithm of solvent viscosity is explained in terms of a short-lived singlet excipiex that serves as a precursor of tne radical ion pair intermediate. Thus, solvent viscosity effects on the biexponential emission decay processes of 1 with small |ΔGet in proitic polar solvents provide a good criterion for the exclusive operation of a singlet-exciplex mechanism in the case that a short-lived exciplex and a long-lived radical ion pair are produced. It was also found that any of activation parameters for ET fluorescence quenching process in acetonisrile is comparable to the corresponding parameter obtained in methylcyclohexane. This finding may present kinetic evidence for the participation of a singlet-exciplex mechanism in the aprotic polar solvent, acetonitrile. VCH Verlagsgesellschaft mbH, 1996.
- Sakurai, Tadamitsu,Miyoshi, Kenichiro,Obitsu, Mitsuhiro,Inoue, Hiroyasu
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- Synthesis of 2-amido-2,3-dihydro-1H-phenalene derivatives as new conformationally restricted ligands for melatonin receptors
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Tetrahydroanthracene, tetrahydrophenanthrene, and tetrahydrophenalene moieties were used to design novel constrained melatoninergic agents. Compounds 1 and 2 were synthesized from the cyclization of the aryl succinic acids 6a,b followed by catalytic reduction, Curtius degradation to the amino derivatives, and acetylation. The phenalene derivatives 3 were prepared by cyclization of the aza lactones of the corresponding α-N-acetyl amino acids. The ketone derivatives were reduced directly by catalytic hydrogenation to produce the compounds 3. The different compounds were evaluated in vitro in binding assays using 2-[125I]iodomelatonin and chicken brain membranes. Melatonin and 2-acetamido-8-methoxytetralin were used as the reference compounds. The results showed the superiority of the dihydrophenalene framework 3 over those of tetrahydroanthracene and tetrahydrophenanthrene. 3a had relatively good affinity for melatonin receptors (K(i) = 28.7 nM). Introduction of an additional methoxy group gave a derivative (3c) with nanomolar affinity (K(i) = 0.7 nM), confirming the existence of a secondary binding site in the receptor which has been described previously. An increase in the affinity was also observed with the propionamido derivative 3e (K(i) = 6.0 nM). The potential agonist properties of the compound 3e were evaluated on the dermal melanocytes of Xenopus laevis tadpoles. At the concentration of 2.3 nM (5 x K(i)), melatonin gave a melanophore index value of 1. Similarly to melatonin, 3e was shown to be a potent agonist of the melanosome aggregation.
- Mathé-Allainmat, Monique,Gaudy, Florence,Sicsic, Sames,Dangy-Caye, Anne-Laure,Shen, Shuren,Brémont, Béatrice,Benatalah, Zohra,Langlois, Michel,Renard, Pierre,Delagrange, Philippe
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p. 3089 - 3095
(2007/10/03)
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- Synthesis and biological activities of cholecystokinin analogues substituted in position 30 by 3-(1-naphthyl)-L-alanine [Nal(1)] or 3-(2-naphthyl)-L-alanine [Nal(2)]
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Acetyl derivatives of ethyl esters of 3-(1-naphthyl)-D,L-alanine and 3-(2-naphthyl)-D,L-alanine were synthesized through a malonic condensation. Resolution of these derivatives by subtilisin Carlsberg followed by acid hydrolysis afforded the 2 optical isomers of 3-(1-naphthyl)-alanine [Nal(1)] and 3-(2-naphthyl)-alanine [Nal(2)]. The L enantiomers of these amino acids were incorporated into the sequence of cholecystokinin in place of the tryptophan in position 30. The cholecystokinin analogues thus obtained behaved as full agonists, with reduced potencies on rat pancreatic acini and on guinea pig brain membranes, by about one order of magnitude for the Nal(1) derivative, as compared to the potent parent compound Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-Phe-NH2.
- Rodriguez,Bernad,Galas,Lignon,Laur,Aumelas,Martinez
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p. 245 - 253
(2007/10/02)
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