Gérard Dauphin

Reduction of 1,1-dideuterio-2-methyl-2-penten-1-ol by beauveria sulfurescens. Mechanism of the microbiological reduction of α,β-unsaturated ald

Abstract Reduction of 1,1-dideuterio-2-methyl-2-penten-1-ol by Beauveria sulfurescens leads to the corresponding saturated mono-deuterated alcohol. This result allows the understanding of the mechanism of the microbiological reduction of α,β-unsaturated alcohols by B. sulfurescens. Thus, the stereochemical rule previously established for the reduction of α,β-unsaturated ketones can be carried out to the reduction of unsaturated aldehydes by B. sulfurescens.

Carbon-nitrogen bond formation in cyclisations by deoxygenation, thermolysis, or photolysis of phenylimidazo[1,2-a]pyridine systems: access to pyrido[1′,2′ : 1,2]imidazo[4,5-b]indoles

Reductive cyclisation of 2-(2-nitrophenyl)imidazo[1,2-a]pyridine with triethyl phosphite gives the indolic structures (5) and (6). The latter are of interest because of preferential C insertion rather than reaction of the nitrene at N-1 of the imidazole ring. 2D N.m.r. confirms structure (5). Both thermolysis or photolysis of the representative 2-(2-azidophenyl)imidazo[1,2-a]pyridines (7) and (8) are also reported and shown to produce novel indole, cinnoline, and benzofuran structures in an extremely facile fashion.

Conditions modulating the ionic selectivity of transport by monensin examined on Enterococcus hirae (Streptococcus faecalis) by23Na-NMR and K+ atomic absorption

Factors likely to modulate the ionic selectivity of monensin were examined on Enterococcus hirae (Streptococcus faecalis) in two states previously characterized: the resting (de-energized) cell and the active (energized) cell. Internal and external Na+ were followed by corresponding 23Na-NMR resonances K+ concentrations were measured by atomic absorption. For a given cellular population of de-energized cells, the apparent transport rates and the final cationic concentrations reached at the steady state were decreasing with the ionophore dose. Monensin was selective for sodium only at low concentrations, in the range 1 mM-10(-4) mM the transport was depending on the effective cationic gradients. Comparison of the activity curves for two cell populations (7.10(9) and 7.10(10) cells/ml) showed the importance of the ratios of monensin/mg phospholipid and also of the ratios of external/internal volumes. On energized cells, except for low monensin concentrations, the main effect was a K(+)-induced efflux and not a Na+ influx. Two factors were modulating the resulting selectivity of this ionophore: the response of the intrinsic bacterial carriers and the generation of the gradients (mainly the external pH) which were favourable to a K+/Na+ transport. Once again the results obtained for two cell populations could be compared, the determining factors were the ratio external/internal volume and the generation of the pH gradient.

Microbiological synthesis and circular dichroism of optically active 2-deuterio-cycloalkanones

Abstract Optically active 2-deuterio-cyclopentanone and 2-deuterio-cyclohexanone have been prepared by microbiological reduction of 2-deuterio α,β-unsaturated cyclic ketones by Beauveria sulfurescens .

Interactions between metal cations and the ionophore lasalocid. Part 14. Structure of lasalocid–alkali metal cation complex salts in methanol from NMR spectroscopy and computational experiments

13 C and 1H NMR spectra were obtained and totally assigned for all the alkali metal cation complex salts of lasalocid in methanol. Most of the corresponding 1H–1H coupling constants were also accessed. Computational experiments in the solvent methanol involving either Monte-Carlo statistical mechanics simulations or quantum semiempirical calculations in a continuum were also carried out. These data provided insight into the structure and solvation of these species in methanol.

Interactions between metal cations and the ionophore lasalocid. Part 12: alkaline-earth–lasalocid 1–2 complex salts in chloroform. Formation and structure

Extraction of alkaline-earth cations M2+ in water by lasalocid HA in chloroform results in formation of neutral complex salts MA2. Corresponding reaction constants are obtained. An increase in the selectivity of lasalocid as a function of cation size is observed. A systematic investigation of the structure in chloroform of the species formed with all the alkaline-earth cations is carried out using 1H and 13C NMR spectroscopy. The two anion ligands consistently play a strongly dissymmetric role but significant structure variations are observed according to the cation involved, coordination sites, respective location of the two ligands, and rate of exchange between them. Data on lasalocid–divalent cation interaction processes in water-membranes, either natural or model, are tentatively related to these findings.

Interactions between metal cations and the ionophore lasalocid. Part 13. Structure of 1:1 and 2:1 lasalocid anion–divalent cation complexes in methanol

The successive formation of complexes MA+ and MA2 of alkaline-earth cations M2+ with lasalocid HA is observable in methanol. Knowing the corresponding formation constants, it was possible to access NMR parameters specific to these two types of species for the four alkaline-earth cations. 13C and 1H chemical shifts are reported for MA+ and MA2; 1H–1H coupling constants for MA+ only. Experiments at low temperature and experiments using the paramagnetic cation Mn2+ determined the coordination sites. All these data show an appreciable variability of coordination in the series of alkaline-earth cations. Computations using the semi-empirical quantum methods AM1 and PM3 and Monte-Carlo simulations in methanol according to BOSS, mainly on MgA+ and BaA+ fully confirmed these findings.

Structure and conformation of bioconversion products of a carboxylic ionophorous antibiotic, grisorixin, by means of two-dimensional nuclear magnetic resonance

The structures of two bioconversion products of a carboxylic ionophorous antibiotic, grisorixin, have been determined by means of two-dimensional n.m.r. The potassium salt conformations of grisorixin and its bioconversion products are very similar. Grisorixin metabolites still complex the cations, but no longer transport them, and have no antibiotic activity.

Microbial conversion of grisorixin: conformational properties of a bioconversion product

Abstract On the basis of 1H and 13C NMR spectra, the conformation of a bioconversion product of grisorixin is elucidate.

SYNTHESIS AND REACTIVITY OF 6,7,8,9-TETRAHYDROPYRIDO[1,2-a ] BENZIMIDAZOL-9-ONE

Synthesis of a tricyclic imidazo[l,2-a]pyridine system (1), and reactivity of the cyclohexyl moiety are described. Tetrahydrocarbazoles are of great interest for the construction of many complex alkaloids belonging to the Murrayaquinones families (1) . As a part of our program on azaindolic structures, we have recently described the photochemistry of azineenaminones with a view to construct azacarbazole skeleton (2) . In continuation of our studies, we now develop a program concerning the synthesis and antitumoral potentiality of modified murrayaquinone ring system 2. In this context, the synthesis of the tricyclic bridgehead heterocyclic system 1, and our preliminary investigations on the reactivity of the cyclohexyl moiety are reported (scheme 1) . Scheme 1 Ο