Michel Giraud

Soluble proteins of the nacre of the giant oyster Pinctada maxima and of the abalone Haliotis tuberculata:: extraction and partial analysis of nacre proteins

Several proteins from nacre of the oyster Pinctada maxima and the abalone Haliotis tuberculata were extracted and partly characterized. Proteins dispersed in aragonite were solubilized during demineralization with acetic acid whereas proteins adsorbed on conchiolin were extracted with sodium dodecyl sulfate and beta-mercaptoethanol. The matrix of Pinctada maxima nacre is composed of one main protein with an apparent molecular weight of 20 kDa (p20). This protein was found in the acetic acid soluble fraction of nacre, as well as in the Laemmli-solubilized extract of conchiolin. In addition, the p20 solubilized with acetic acid can form oligomers made of 6 monomers linked together by disulfide bridges. The first N-terminal 21 amino acids of p20 were determined and no homology with known proteins was found. In Haliotis tuberculata nacre, 5 main proteins were solubilized during demineralization and 3 glycoproteins were detected. Stains-all and Alcian blue staining revealed polyanionic proteins in the extracts isolated from Pinctada maxima and Haliotis tuberculata nacre.

Characterization and quantification of chitosan extracted from nacre of the abalone Haliotis tuberculata and the oyster Pinctada maxima.

Abstract: This study was performed to characterize and quantify chitosan by simple physicochemical methods (infrared spectroscopy and potentiometric measurements). These procedures were validated with well-characterized chitosan before being used to investigate chitosan in nacre of the abalone Haliotis tuberculata and of the giant oyster Pinctada maxima. Potentiometric study revealed a chitosan extract from the nacre of H. tuberculata with a degree of deacetylation of around 88% and an intrinsic pK of 6.5. According to infrared and potentiometric data, a low yield (η) of extraction was calculated (η= 0.064%). For experiments performed on the nacre of P. maxima, and in spite of more stringent deacetylation conditions, results suggested that a chitin-protein complex (η= 0.053%) was isolated rather than chitosan.

Synthèses Stéréosélectives des Acides 13 E et 13 Z Rétinoı̈ques via un Nouvel Intermédiaire β-Méthylènealdéhyde en C-15

Resume The methylene-de-oxo-bisubstitution reaction between dimethyl isopropylidene malonate and the C-15 β-methylenealdehyde 1 which could serve as substitute for E β-ionylideneacetaldehyde 2, produces stereoselectively the E,E olefin. Hence, new stereoselective syntheses of 13 E and 13 Z retinoic acids were described.

New preparation of an important synthon for vitamin A synthesis

Abstract The “C-18 ketone” 1, key intermediate for vitamin A synthesis, is prepared in a few steps from β-ionone 3 via β-ionylidene acetonitrile 2 (32% overall yield).

KYNURENIC ACID — I. SPECTROSCOPIC PROPERTIES

Abstract— The presence of different ground state species in ionic and/or keto s enol equilibrium has been demonstrated by studying NMR, IR and UV spectroscopic properties of kynurenic acid and related quinoline derivatives. The optical and emission properties of kynurenic acid and related compounds are thus very sensitive to pH conditions. Fluorescence and intersystem crossing (ISC) quantum yields have been measured in various solvents. The first excited singlet state is probably very short‐lived in neutral aqueous solution. The triplet state is long‐lived (10 μs) as shown by 353 nm laser flash spectroscopy. A high ISC quantum yield and a large molar extinction coefficient make it easy to detect the T1→ Tn transient (Δmax≃ 570 nm).

KYNURENIC ACID — II. PHOTOSENSITIZING PROPERTIES

Abstract— The photosensitizing properties of kynurenic acid have been studied by 353 nm laser flash spectroscopy and steady state irradiations. Laser flash spectroscopy indicates that the kynurenic acid triplet is reduced by amino acids and nucleic acid bases. Photoreactions implying singlet oxygen formation are shown to occur. The photosensitized destruction of tryptophan which does not involve singlet oxygen is very efficient and shows specific features. Chemical and biological implications of this photo‐reactivity are discussed.

First synthesis of 9-demethyl-14-carboxyretinoic acid

Abstract A short synthesis of 9-demethyl-14-carboxyretinoic acid from β-ionone via 9-demethyl-β-ionylideneacetaldehyde is reported (48% overall yield).

Stereoselective synthesis of 13Z retinoic acids via β-methylenealdehydes as synthons

Abstract A stereoselective synthesis of 13Z retinoic acids via β-methylenealdehydes is described. In methylene-de-oxo-bisubstitution reactions (Knoevenagel, Stobbe, etc.), these new synthons produce stereoselectively E olefins. Hence, a synthesis of 13Z retinoic acids is described, via a stereospecific monodecarboxylation of carboxy-14-retinoic acids.

Amino acid-pyrrole N-conjugates; a new class of antioxidants II. Effectiveness of singlet oxygen quenching by luminescence measurements

Abstract The pyrrole-amino acid and peptide N -conjugates synthesized from tyrosine, histidine and glutathione very effectively quench the 1270 nm singlet oxygen luminescence, at rates ranging from 10 8 to 10 9 M −1 s −1 . Nuclear magnetic resonance spectroscopy suggests that the electron-donating properties of the methyl groups after 2,5-dimethyl substitution on the pyrrole ring are probably an important determinant of the reactivity of singlet oxygen with the N -conjugate of glutathione. However, intramolecular interactions between the pyrrole ring and the side chain may also modulate the reactivity of the antioxidant as suggested by absorption and fluorescence spectroscopies carried out on tyrosine derivatives. Efficient fluorescence quenching of the phenol ring by the pyrrole ring occurs in the tyrosine derivatives. The reactivities of these antioxidants with 1 O 2 are comparable in methanol, ethanol and D 2 O.

N-conjugates of 2,5-disubstituted pyrrole and glutathione evaluation of their potency as antioxidants against photosensitization of NCTC 2544 keratinocytes by excess endogenous protoporphyrin IX

A novel glutathione compound in which the amino group has been derivatized by a 2,5-dimethyl pyrrole is shown to be very effective against cell photosensitization in vitro. Protoporphyrin IX either added to the medium or produced endogenously by incubation of NCTC 2544 keratinocytes with 5-aminolevulinic acid has been chosen as the photosensitizer. The antioxidant effectiveness of glutathione-pyrrole derivatives against protoporphyrin photosensitization depends critically on the type of 2,5 substitution on the pyrrole ring. This structure-function relationship may be attributed to the difference in compartmentation and/or uptake of the various glutathione-pyrrole derivatives under study. The 2,5-dimethyl pyrrole derivative is much more effective than glutathione as a protective agent against phototoxic reactions induced by protoporphyrin IX.