Pierre Angibeaud

Immunocytochemical localisation of para-coumaric acid and feruloyl-arabinose in the cell walls of maize stem

Two phenolic compounds, p-coumaric acid and feruloyl-arabinose, were localised by immunocytochemistry in the cell walls of the apical internode of two lines of maize (Co125 and W401) of different digestibility. The compounds were detected at two stages of cell maturity in the lignified tissues (sclerenchyma, fibres and xylem) and in the medullary parenchyma, which, in the samples studied, was not lignified. p-Coumaric acid is a phenolic acid associated with lignins, which confer resistance on plant cell walls to microbial degradation in the rumen. Feruloyl-arabinose is a compound associated with xylans, the principal hemicelluloses in Gramineae, which are potentially degradable. Labelling of p-coumaric acid decreased in both maize lines with cell age and as the cell walls became lignified. The mass of lignin deposited in the cell walls masked p-coumaric acid, thereby making it less accessible to the antibodies. There was an inverse relationship in the labelling of p-coumaric acid and feruloyl-arabinose. Feruloyl-arabinose was more heavily labelled as the plant cell walls matured in all the lignified tissues of both maize lines and in the parenchyma of the less digestible line. All tissues except the parenchyma were more heavily labelled with both sera in Co125, the more digestible line.

Specific reactivity of the O-(β-d-glucopyranosyl-(1→6)-d-glucopyranose) linkage with acetic anhydride in the presence of trimethylsilyl trifluoromethanesulfonate

On obtient un compose O-[acetoxy-«1» penta-O acetyl-2,3,4,5,6 glucityl]-6 tetra-O-acetyl-1,2,3,4 glucopyranose qui reagit ensuite avec le methanolate de sodium et donne le D-glucose penta-O-acetyle

Stereoselective reaction of methyl α- and β-D-glycopyranosides with acetic anhydride in the presence of trimethylsilyl trifluoromethanesulphonate

Treatment of methyl β-D-glycopyranosides with TMSOtf–Ac2O gives acyclic products by selective cleavage of the ring carbon–oxygen bond, whereas methyl α-D-isomers undergo replacement of the anomeric methoxy by an acetoxy group with retention of configuration.

Immunogold labelling of feruloyl-arabinose of maize stem after rumen microbial degradation

Immunogold labelling of feruloyl-arabinose was performed on the base and the top of the apical internode of the stem of Co125 and W401 maize, harvested at anthesis +5 days, after incubation in the rumen in nylon bags for 4, 8 and 24h. The description of labelling evolution during rumen degradation was permitted by the quantification of the intensity of labelling in four tissues: sclerenchyma, fibres, xylem and parenchyma. The results are discussed in relation to maize digestibility.

Nitrous acid deamination of acyclic, polyfunctional systems. Part 3. Vicinal participation in the nitrous acid deamination of chiral 1-thio-2-aminoalkanepolyols: the deamination of 2-amino-2-deoxy-D-glucose ethylene and propan-1,3-diyl dithioacetals, and the crystal and molecular structure of 1,2-SS′-ethylene-5,6-O-isopropylidene-1,2-dithio-α-D-mannofuranoside

Deamination of 2-amino-2-deoxy-D-glucose ethylene dithioacetal (1) at pH 5.6, followed by acetylation of the product, gave an 8 : 40 : 3 mixture of 3,5,6-tri-O-acetyl-1,2-SS′-ethylene-1,2-dithio-α-D-mannofuranoside (5b), 3,4,6-tri-O-acetyl-1,2-SS′-ethylene-l,2-dithio-α-D-mannopyranoside (4b), and 3,5,6-tri-O-acetyl-2-deoxy-D-arabino-hexono-1,4-lactone (2b). Deamination of (1) at pH <1 by use of dinitrogen trioxide followed by acetylation gave the lactone (2b) essentially exclusively. Similar treatment of the propan-1,3-diyl analogue (3) of (1) at pH <1 also gave the lactone (2b) : at pH 5.6 the main product was 3,5,6-tri-O-acetyl-1,2-SS′-(propan-1,3-diyl)-1,2-dithio-α-D-mannofuranoside (7b). Structural assignments were based on formation of the 5,6-isopropylidene acetals [(8) and (10)] from the non-acetylated precursors of (5b) and (7b), by 1H n.m.r. spectroscopy at 250 MHz for compounds (2b), (4b), (5b), (7b), (8), and (10), and by electron-impact mass spectrometry. An X-ray crystal structure-determination conducted on 1,2-SS′-ethylene-5,6-O-isopropylidene-1,2-dithio-α-D-mannofuranoside (8) permitted unambiguous assignment of the ring size, relative stereochemistry, and favoured conformation of this strained molecule. The reaction course and product distribution in the deamination were monitored and quantitated by g.l.c.–mass spectrometry of the corresponding per-trimethylsilylated derivatives and are discussed from preparative and mechanistic standpoints.

Accès à des sulfures d'alkyle et de furannyle à partir de dithio-acétals de pentoses

Abstract Sodium iodide—zinc in N,N -dimethylformamide at 150° converted 2,5-anhydro-3,4-di- O - p -tolylsulfonyl- D -xylose diisobutyl dithioacetal into a mixture of three substituted furans, namely 2-[(isobutylthio)methyl]furan ( 2 ), and its 3-isobutylthio- ( 3 ), and 4-isobutylthio- ( 5 ) derivatives. The relative proportions of 2, 3 , and 5 , determined by g.l.c.—mass spectrometry, varied according to the relative proportions of reactants employed. A similar type of transposition—elimination is also encountered in the absence of sodium iodide. Compound 3 is also produced from D -xylose disobutyl dithioacetal by extended treatment with 2-methylpropanethiol—hydrochloric acid. The furan derivatives 3 and 5 were characterized mainly by n.m.r.—spectral studies on their Diels—Alder adducts with maleic anhydride, and the mechanism of their formation is discussed. 2,5-Anhydro-3,4-di- O - p -tolylsulfonyl- D -xylose ethylene dithioacetal ( 13 ), its ribo epimer ( 15 ), and its L - arabino diisobutyl dithioacetal analog ( 20 ) all reacted with sodium iodide—zinc in N,N -dimethylformamide exclusively by an E2 type of elimination with formation of the anticipated 3-alkenes, namely 2,5-anhydro-3,4-dideoxy- D - glycero -pent-3-enose ethylene dithioacetal ( 14 ) and its diisobutyl dithioacetal analog.