C. Hervé du Penhoat

AN EFFICIENT PROCEDURE FOR STUDYING PECTIN STRUCTURE WHICH COMBINES LIMITED DEPOLYMERIZATION AND 13C NMR

Abstract A protocol for partial thermally-induced depolymerization of differently methoxylated pectin samples is described. The resulting macromolecules have been fully characterized with various complementary techniques, such as size exclusion chromatography (SEC), potentiometry, viscometry and 13C NMR. Optimum conditions afford samples at 50–80% yield with weight-average molecular weights in the 4 to 20 kDa range. The major fraction of these polysaccharides adopts the random-coil conformation and such samples are suitable for 13C NMR structural studies at room temperature. The methoxyl distributions of two apple pectin samples with a degree of esterification (DE) between 54 and 74% and a citrus pectin (DE, 72%) were shown to be random in nature, whereas that of a lightly methoxylated apple pectin (DE 39%) was partially blockwise. The carbon relaxation parameters of the depolymerized pectins attain asymptotic values for MW > 4 kDa. The MW values estimated from intrinsic viscosity data with the Mark-Houwink relationship reported for native pectins are in good agreement with those obtained by either end-group analysis (NMR) or SEC. Thus, all the physicochemical data indicate that the secondary structure of the isolated chains of depolymerized pectin is closely related to that of the parent polymers. Finally, pectinmethylesterase activity towards the depolymerized pectins was similar to that of the untreated samples.

Preparation, structural analysis and anticonvulsant activity of 3- and 5-aminopyrazole N-benzoyl derivatives

Summary Some unsymmetrical N -exocyclic and N -endocyclic derivatives from benzoylation of 3- and 5-aminopyrazole were prepared with the aim of comparing their anticonvulsant activity towards the MES and scMET tests. Unambiguous proof of their structure was obtained from heteronuclear long-range correlation spectroscopy and NOE difference spectra. Only the N - exo -pyrazole benzamides showed good protection with respect to these tests.

Syntheses with sulfones XLIX : stereo- and enantioselective synthesis of (s)-(-)-3,9-dimethyl 6-(1-methylethyl) (e)-5,8-decadien 1-ol acetate, sexual pheromone of yellow scale.

Abstract The stereo- and enantioselective synthesis of the yellow scale pheromone, (S)-(-)-3,9-dimethyl 6-(1-methylethyl) (E)-5,8-decadien 1-ol acetate, from 3-(R) ( +)-valerolactone 5 and [(4-methyl 3-pentenyl) sulfonyl] benzene 8 is described. The key step is the introduction of the isopropyl group by the stereoselective cross-coupling reaction of the dienesulfone 12 with isopropylmagnesium chloride in the presence of FeCl3.

Synthesis with sulfones XLIV Stereoselective preparation of EE 1,3-dienes by elimination of benzenesulfinic acid from E homoallylic sulfones.

Abstract The preparation of pure E and Z homoallylic 1,1-disulfones followed by the stereoselective reduction of one sulfonyl moiety afforded pure E and Z homoallylic sulfones respectively Basis elimination with tBuOK in THF gave the corresponding 1,3-dienes in good yield. This reaction, highly stereoselective in the case of E homoallylic sulfones, has been used in the synthesis of (8E,10E) 8,10-dodecadienol, 10 and (9E)9,11-dodecadienol, 15 , insect pheromone components.

Syntheses with sulfones. XLVI: Stereoselective preparation of 2-benzenesulfonyl-1,3-dienes and 2-benzenesulfonyl-1,4-dienes

Abstract The stereoselective syntheses of EE 2-benzenesulfonyl-1,3-dienes and 2-benzenesulfonyl-1,4-dienes are described. Diels-Alder cycloaddition of the EE 2-benzenesulfonyl-1,3-dienes 3b with methylvinyketone is reported.

Syntheses with sulfones XLVII : stereoselective access to 1,3- and 1,4-dienes through hydrogenolysis of benzenesulfonyldienes. Application to pheromone synthesis

Abstract The stereospecific reduction of EE 2-benzenesulfonyl-1,3-dienes to ZE 1,3-dienes with Grignard reagents under transition metal catalysis ie described, Hydrogenolysis of the sulfonyl moiety of 2-benzenesulfonyl-1,4-dienes to ZE 1,4-dienes with sodium dithionite ie reported. These techniques have been applied to the stereoselective synthesis of (7E, 9Z) dodecadienyl acetate 3d , (9Z, 11E)tetradecadienyl acetate 3e and (9Z, 12E) tetradeoadienyl acetate, 6b .

Syntheses with sulfones XLVIII : stereoselective synthesis of 2-isopropyl 1,4-dienes through the iron-catalysed cross-coupling reaction of 2-benzenesulfonyl 1,4-dienes and isopropylmagnesium chloride

Abstract The stereoselective synthesis of 2-isopropyl 1,4-dienes through the cross-coupling reaction of 2-benseneaulfonyl 1,4-diene e and isopropylmagnesium chloride under transition-metal catalysis is described. Iron salts, which were better catalysis than palladium or nickel ones, led to substitution, of the sulfonyl group with > 97% stereospecifcity and without isomerisation of the isopropyl Grignard moiety to the n-propyl derivative. Notable amounts of the compound resulting from reduction of the sulfonyl group were also formed.

Synthesis with sulfones (noXXXI) : The stereospecific reduction of 2-benzenesulfonyl-1,3 dienes to conjugated Z,E-dienes. Synthesis of (9Z,11E)-9,11-tetradecadienyl acetate.

The stereospecific reduction of 2-phenylsulfonyl-1,3-dienes li to conjugated EZ dienes 2 catalysed by transition metal complexes in the presence of n-butyl magnesium chloride is described. This method is illustrated by the synthesis of the pheromone of Spodoptera littoralis : 9Z,11E-tetradecadien-1 yl acetate 8,R=Ac.

Internal motion in carbohydrates as probed by n.m.r. spectroscopy

In the present study a combination of proton and carbon relaxation rates have been measured for several oligosaccharides at different temperatures. Correlation times, which have been calculated from both sets of data, have been compared in an attempt to establish the relative rate of internal motion. All the data suggest that these motions are not slow with respect to the overall tumbling.

Synthesis with sulfones (noXXX) : Stereoselective synthesis of arenesulfonyl-1,3-dienes.

Abstract Basic treatment of allylic 1,1-disulfones gives 1-arenesulfonyl 1,3-dienes, Condensation of aldehydes with lithiated allylic sulfones and in situ acetylation of the alkoride thus formed followed by basic elimination of acetic acid leads to EE 2-arenesulfonyl 1,3-dienes. Good to very good stereoselectivity can be achieved.