G. Dauphin

The anodic tetramerization of the N-benzylaziridine : A chain process

Abstract Benzylaziridine is oxidized anodically in organic solvents. The tetramer (tetra-aza-cyclododecane) is obtained in good yield and the electrical consumption is very low. Authors propose a chain process mechanism in comparison with the chemical method.

Study by NMR of the mode of action of monensin on Streptococcus faecalis de-energized and energized cells

Streptococcus faecalis was used as a bacterial model for studying the mode of action of monensin by NMR investigations. Experiments were carried out in two states, characterized by several complementary methods: (i) the resting (de-energized) cell which was considered as an inert biological membrane, on which cationic transport induced by the ionophore alone can be investigated; (ii) the active (energized) cell where the ionophore-sensitive response of the living organism, particularly the cation pumps and the glycolysis, is probed. Studies of resting cells were performed, with changing external ionic concentrations, in the presence of monensin, which is preferentially a sodium carrier. Internal and external Na+ and H+ were followed by corresponding 23Na and 31P (inorganic phosphate) NMR resonances, K+ fluxes were measured by atomic absorption. It was shown that the induced cationic movements were linked to the existing ionic gradients for K+ and Na+. 31P and 13C NMR spectra for the intermediary metabolites detected in active cells showed that glycolysis is dramatically modified in the presence of monensin.

SEMI-SYNTHESIS OF A23187 (CALCIMYCIN) ANALOGS

Semisynthesis of two demethylamino A23187 with a methyl group in the 4- or 5-position on the benzene ring were carried out via the cleavage of A23187 oxazole ring and rebuilding of modified benzoxazoles. These compounds were shown to release Ca++ and MG++ from mitochondria and to keep part the antibacterial activity of the natural metabolite.

2- And 8-functionalized 1,4,7,10-tetraoxaspiro[5.5]undecanes. II: Synthesis of (+)-E,E and (±)-Z,E structures from chiral isopropylideneglycerols

Abstract Using a short synthetic protocol, the enantiomerically pure ( + )-E,E title compound was made from (S,S)-diisopropylidenetriglycerol 4 in order to obtain a reference for correlations in this unexplored series. Analogously (S,R)-diisopropylidenetriglycerol 11 would afford the (±)-Z,E isomer which was also prepared. Conformations were deduced from 1 H NMR data.

Photochemical behaviour of 2-biphenylol in acidic aqueous solution

Abstract When 2-biphenylol (o·phenylphenol) was irradiated in acidic aqueous solution, five photoproducts were isolated. Three of them were previously identified to phenylhydroquinone, phenylbenzoquinone and 2-hydroxydibenzofuran. Two other photoproducts are now identified by 300 MHz 1D and 2D NMR, as two isomeric acids from the scission of the phenolic ring. A photochemical equilibrium between these two photoproducts was observed: A mechanism involving phenylphenoxyl and superoxide radicals is suggested.

Synthesis of a biomimetic model of calcimycin (A 23187) with a demethylated skeleton

Abstract A demethylated model ( 15 ) of Calcimycin ( 1 ) has been synthesized from the known 2,8-dibromo-1,7 dioxaspiro (5.5) undecane ( 6 ) ; biphasic extraction experiments indicated a net decrease of affinity towards Mg++ and Ca++ for ( 15 ) versus ( 1 ).

Oxidative photocyclisation of 2-biphenylol in dilute aqueous solution

Formation of 2-hydroxydibenzofuran (2-HODBF) was observed when an air-saturated solution of 2-biphenylol (OPP - o.phenylphenol) was irradiated at 296, 313 or 334 nm (2<pH<11). The isolated product was identified by 300 MHz 1H NMR and MS spectra. The quantum yield of OPP conversion was higher with the anionic form (Φ=0.06±0.01 at pH=10.5) than with the molecular form (Φ=0.015±0.005 for 5.5≤pH≤7). On the contrary, chemical yield for 2-HODBF was higher in neutral solution (about 0.15 for conversion extent equal to 0.2–0.7) than in basic solution (0.1 at pH=10.5 at 20% conversion). The intermediate formation of phenylbenzoquinone (PBQ) was pointed out by HPLC analysis. OPP is commonly used for fruit preservation and the biological properties of 2-HODBF should be controlled. Among the phenolic compounds currently investigated in our Research Group for many years, 2-biphenylol, more commonly named o.phenylphenol (OPP), has interesting fundamental properties like a dual fluorescence emission and prompts ecotoxicological concern.

2- and 8- functionalized 1,4,7,10-tetraoxaspiro[5.5]undecanes. I. Synthesis of (±)-E,E and (±)-Z,E structures.

Abstract The synthesis of (±)-E,E and (±)-Z,E 2,8-dihydroxymethyl-1,4,7,10-tetraoxaspiro[5.5]undecane is described. The selective modification of one sidechain is examined for the (±)-E,E isomer, and a tetraoxygenated analogue of a commonly encountered insect pheromone is prepared.

Na+ and K+ transport by 4-chlorophenylurethane-monensin in Enterococcus hirae de-energized and energized cells studied by 23Na-NMR and K+ atomic absorption

Na+ and K+ movements induced by 4-chlorophenylurethane-monensin, which presents an inverted ion selectivity (K+ > Na+) in model systems compared with monensin, were followed on Enterococcus hirae cells by 23Na-NMR and K+ atomic absorption. For de-energized cells, the urethane derivative is much more selective for K+ than monensin, but only at low concentrations (10(-3)-10(-4) mM). For higher concentrations, as previously shown for monensin, the sodium and potassium movements are driven by the ion gradients present. On energized cells, both K+ and Na+ gradients were highly perturbed, and this can be related to the higher toxicity in mice and bacteria for this derivative.

Enzyme-catalysed hydrolysis of the dibutylester of (±) E,E-2,8-bishydroxymethyl-1,7-dioxaspiro[5,5]undecane

Abstract The title compound was converted into the corresponding (2S,6S,8S) monoester with 94 % e.e. by porcine pancreatic lipase (PPL) in water/DMF (9/1).