Suzanne Toppet

Inulin hydrogels as carriers for colonic drug targeting: I. Synthesis and characterization of methacrylated inulin and hydrogel formation

AbstractPurpose. Vinyl groups were introduced in inulin chains in order to form hydrogels of this sugar polymer by free radical polymerization. Methods. Inulin was reacted with glycidyl methacrylate in N,N-dimethylformamide in the presence of 4-dimethylaminopyridine as catalyst. 1H and 13C NMR spectroscopy were used for the characterization of the obtained reaction product. Solid state 13C NMR spectroscopy revealed the conversion of the incorporated vinyl groups into covalent cross-links upon free radical polymerization of aqueous solutions of the derivatized inulin. Results. During reaction of inulin with glycidyl methacrylate, transesterification occurred, leading to the direct attachment of the methacryloyl group to inulin. Consequently, the obtained reaction product is methacrylated inulin. The extent of chemical modification of inulin could be tuned by varying the molar ratio of glycidyl methacrylate to inulin in the reaction mixture. Aqueous solutions of methacrylated inulin were converted into cross-linked hydrogels by free radical polymerization using ammonium persulphate and N,N,N′,N′-tetramethylethylenediamine as initiating system. Conclusions. Inulin hydrogels can be formed by free radical polymerization of aqueous solutions of methacrylated inulin.

Nucleophilic Intramolecular Cyclization Reactions of Alkynechalcogenolates

Abstract 2-( ortho -Hydroxyphenyl)-alkynethiolates and -selenolates, obtained through base catalyzed ring cleavage of 4-( ortho -hydroxyphenyl)-1,2,3-thiadiazoles and -1,2,3-selenadiazoles, smoothly transform into 2-benzofuranthiolates and -selenolates. These reactive intermediates can be alkylated in high yield. This reaction sequence could be applied to the synthesis of electron rich thiacrown ethers. The 2-( ortho -aminophenyl)-alkynethiolate analogously forms 2-methylsulfanylindole.

Synthesis, extraction ability and application in asymmetric synthesis of azacrown ethers derived from D-glucose

New chiral monoaza-15-crown-5 ethers have been synthesised from 1,2:5,6-di-O-isopropylidene-D-mannitol. The substituent at the nitrogen atom has a major influence on the cation extraction ability of the azacrown. These sugar-based crown ethers show asymmetric induction as chiral phase transfer catalysts in the Michael addition of 2-nitropropane to chalcone (67% ee).

Molecular rearrangements of 5-azido substituted 1,2,3-triazoles

Abstract 5-Azido-4-methoxycarbonyl-1-phenyl-1,2,3-triazole ( 8a ) and its phenyl substituted derivatives 8b , c rearrange at 60–80°C to give tetrazolyldiazoacetates 9 , which have been isolated. When the reactions are allowed to go to completion, products derived from the diazo compounds are obtained; i.e. norcaradienes ( 10 ) from benzene solutions and imidazotetrazoles ( 12 ) from nitrite solutions. The latter decompose photochemically into diazacyclopentadienonimines ( 13 ). A kinetic study of the rearrangement 8 → 9 has been carried out and the mechanism (Scheme VI) is discussed in comparison with the Dimroth rearrangement.

Synthesis of a conformationally restricted dipeptide analogue and its evaluation as a β-turn mimic

Abstract Dichloropyrazinone 3 was converted into a conformationally restricted dipeptide analogue 8 by means of a Diels–Alder strategy. The β-turn characteristics of molecule 8 were examined by molecular modeling and NMR spectroscopy.

Intramolecular Diels-Alder reactions of 2(1H)-pyrazinones: Synthesis of new Furo/Pyrano-pyridinones and -pyridines

Abstract 2(1 H )-Pyrazinones 2–5 with in 3-position either a 3- or 4-alkynyloxy side chain and 2(1 H )-pyrazinones 9–10 carrying the corresponding 2- or 3-alkynyloxy(m)ethyl substituent are shown to undergo intramolecular Diels-Alder reaction. The formation of either fused pyridinones 13 , 16 , 20 , 22 or 24 and/or pyridines 14 , 17 , 19 or 25 depends on the substitution pattern of the anchored pyrazinone and runs via the loss of either nitrile or isocyanate from the intermediate cycloadduct. The influence of the position of the oxygen atom and the length of the side chain on the reaction conditions is also discussed.

Nuclear magnetic resonance studies on sequence distributions in vinyl alcohol-vinyl acetate copolymers

Abstract The microstructure of vinyl alcohol-vinyl acetate copolymers was studied using both 13C n.m.r. and 1H n.m.r. techniques. The sequence lengths of vinyl acetate units calculated respectively from the compositional dyads, from the methylene absorptions and feom the triple carbonyl absorptions in the 13C n.m.r. spectrum were not identical, and moreover the dyad-triad relationship showed a large discrepancy. 1H and 13C n.m.r. spectra of a 5 mol% re-acetylated random sample, containing mainly isolated acetate units, indicate that configurational splitting complicates the assignment of the triple carbonyl absorption, which originally was interpreted as a compositional triad. After correcting for tacticities the results could be brought in line and the C=O resonances proved to be useful in obtaining information on the percentage of isolated vinyl acetate units and the sequence length nA2+ (the average length of vinyl acetate units ≥2).

Cannabiorci- and 8-chlorocannabiorcichromenic acid as fungal antagonists from Cylindrocarpon olidum

Cannabiorcichromenic acid and 8-chlorocannabiorcichromenic acid [8-chloro-5-hydroxy-2,7-dimethyl-2-(4-methyl-3-pentenyl)-2H-1-benzopyran -6- carboxylic acid] were identified as active components in cultures of Cylindrocarpon olidum which antagonized various other fungi. Experiments performed with the purified acids confirmed the antifungal activity; in addition, they revealed that the acids had antibiotic properties towards gram-positive bacteria and were toxic to nematodes.

Diels-Alder reactions of the heterodiene system in 2(1H)-pyrazinones

Abstract Variously substituted 2(1H-pyrazinones react with acetylenic derivatives to give specifically substituted pyridones or pyridines. The observed selectivity can be explained in terms of HO-LU interactions for the reagents and two competitive retro Diels-Alder reactions of the primary bicycloadducts. With cyanotosylate as dienophile no pyrimidone derivative but a new 2(1H)-pyrazinone is obtained.

Diels-alder reactions of pyrano[3,4-b]indol-3-ones with olefinic compounds: synthesis of (1,2-dihydro)carbazoles

Abstract The Diels-Alder reaction of substituted pyrano [3, 4-b]indol-3-ones 1 with olefinic dienophiles is described. The role of the substitution pattern on the stability of the obtained 1, 2-dihydrocarbazoles is interpreted in terms of electronic and steric effects on the aromatization to the corresponding carbazoles.