Jean-Paul Lellouche

Mediated electrochemical detection of catechol by tyrosinase-based poly(dicarbazole) electrodes

A new dicarbazole derivative functionalised by an N-hydroxysuccinimide group has been synthesised and electrochemically characterised. Upon oxidative electropolymerisation of this monomer in organic electrolytes, electroactive poly(dicarbazole) films were formed on platinum electrodes. The subsequent chemical grafting of tyrosinase on the poly(dicarbazole) film was easily performed by immersion in an enzymatic aqueous solution. The amperometric response of the resulting biosensors to catechol has been studied at -0.2 V vs. saturated calomel electrode (SCE). Since the reduction of quinone generates radicals which may induce electrode fouling, thionine, a phenothiazine dye, was covalently bound to the poly(dicarbazole) backbone as it mediates the reduction of quinoid products and therefore induces an enhancement of the performance of the tyrosinase-based biosensor.

Novel electro-oxidizable chiral N-substituted dicarbazoles and resulting electroactive films for covalent attachment of proteins

Novel chiral electro-oxidizable dicarbazoles functionalized by N-succinimidyl/phthalimidyl or pentafluorophenyl carboxylates 6a–c were synthesized from l-lysine methyl ester 1 and characterized electrochemically. The corresponding chiral polycarbazole films 8a–c constitute polymers suitable for covalent grafting of proteins, as demonstrated for bovine serum albumin as a model compound.

Face selectivity during the cycloaddition reaction of nitrile oxides with iron complexed trienes

Abstract Various nitrile oxides were reacted with iron complexed trienes of type 1. The reaction proceeded with good yield and diastereoselectivity (c.a. 90 10 ) to give Δ2-isoxazolines which structures were determined by X-Ray and 1H-NMR spectroscopy.

FIXED CARBON PARTITIONING IN THE RED MICROALGA PORPHYRIDIUM SP. (RHODOPHYTA)

The main products of carbon fixation in the red algae are sulfated cell‐wall polysaccharides, floridean starch, and low molecular weight (LMW) carbohydrates, mainly floridoside. In the red microalga Porphyridium sp., sulfated polysaccharide—cell bound and soluble—comprises up to 70% of the algal biomass. The purpose of this study was to elucidate the partitioning of fixed carbon in Porphyridium sp. toward the different products of carbon fixation. Using pulse‐chase technique with [14C]bicarbonate, we followed 14C flow into the major compounds, namely, cell‐wall polysaccharide, floridoside, starch, and protein, under various environmental conditions (i.e. carbon dioxide enrichment and nitrate starvation). 13C‐NMR and gas chromatography analysis showed the main LMW product in Porphyridium sp. to be floridoside. After the short [14C]bicarbonate pulse (20 min), 42%–53% of total 14C uptake was initially found in floridoside. The appearance of 14C in the soluble polysaccharide was evident immediately at the end of the 20‐min [14C]bicarbonate pulse. The specific radioactivity in the floridoside fraction declined by 80% after the 48‐h chase, this decline being accompanied by increased labeling of starch and the soluble polysaccharide. In cells exposed to high CO2 concentration, larger amounts of 14C (about twice as much) were channeled into starch and soluble polysaccharide than in cells under low CO2 concentration. The most significant increase (1500%) in labeling during chase was found in the soluble polysaccharide of the nitrate‐deprived cultures. It therefore seems likely that the large amounts of carbon incorporated by Porphyridium sp. cells into floridoside were subsequently used for the synthesis of macromolecular components. The data thus support the premise that floridoside serves as a dynamic carbon pool, which channels the fixed carbon toward polysaccharides and other end products according to the ambient conditions.

An organo-iron mediated chiral synthesis of (+)-(S)-[6]-gingerol

Abstract A short and efficient synthesis of (+)-(S)-[6]-Gingerol is described. The key step is a highly stereoselective cycloaddition of a nitrile oxide with a chiral iron complexed triene.

TOTAL SYNTHESIS OF (11R, 12S)-DIHETE

Abstract The first total synthesis of (11R, 12S) diHETE is reported. The key step is the highly chemio- and stereoselective osmylation of a double bond in a trienyne system selectively complexed by an Fe(CO) 3 group.

Conversion of 5,6-dihydroxyeicosatetraenoic acids A novel pathway for lipoxin formation by human platelets

Leukotriene A4 may be metabolized to 5(S),6(R)‐ and 5(S),6(S)‐dihydroxy‐7,9‐trans‐11,14‐cis‐eicosatetraenoic acids by enzymatic or non‐enzymatic hydrolysis. Incubation of human platelet suspensions with these dihydroxy acids led to the formation of lipoxin A4 and 6(S)‐lipoxin A4 via lipoxygenation at C‐15. Furthermore, human platelets converted the two 5(R),6(S)‐ and 5(R),6(R)‐dihydroxy‐7,9‐trans‐11,14‐cis‐eicosatetraenoic acids to tetraene‐containing trihydroxyeicosatetraenoic acids. In contrast, leukotrienes C4, D4 and E4 were not transformed to cysteinyl‐lipoxins, Time‐course studies of leukotriene A4 metabolism in human platelet suspensions indicated lipoxin formation via two pathways: (i) direct conversion of leukotriene A4, leading to formation of the lipoxin intermediate 15‐hydroxy‐leukotriene A4; and (ii) 15‐lipoxygenation of the 5(S),6(R)‐ and 5(S),6(S)‐dihydroxyeicosatetraenoic acids. The results demonstrate that lipoxygenation at C‐15 of 5,6‐dihydroxy‐7,9,11,14‐eicosatetraenoic acids may be an alternative novel pathway for platelet‐dependent lipoxin formation.

Electrogenerated Poly(Chiral Dicarbazole) Films for the Reagentless Grafting of Enzymes

New chiral dicarbazole derivatives functionalized by N-hydroxysuccinimide and pentafluorophenoxy groups have been synthesized and electrochemically characterized. Upon oxidative electropolymerization of these monomers in organic electrolytes electroactive poly(dicarbazole) films were formed on platinum electrodes. The subsequent chemical grafting of glucose oxidase on the poly(dicarbazole) films was easily performed by immersion in an enzymatic aqueous solution. The amperometric response of the resulting biosensors to glucose has been studied at 0.6 V vs. aqueous saturated calomel electrode.

Preparation of formate esters from O-TBDMS/O-TES protected alcohols. A one-step conversion using the Vilsmeier-Haack complex POCl3DMF

Abstract O-tert-Butyldimethylsilylated (O-TBDMS) or O-triethylsilylated (O-TES) alcohols were converted in one step to their corresponding formates under Vilsmeier-Haack conditions ( POCl 3 DMF ). The scope and limitations of this novel reaction for interconverting alcohol protecting groups are described.

Synthesis and reactivity of chiral organometallic phosphonium salts

Abstract A short and efficient synthesis of the two enantiomeric iron-complexed phosphonium salts (+)- 1 and (−)- 2 is described. Upon reaction with the chiral formyloxirane 3 , the corresponding chiral ylides exhibit quite different reactivities.