André De Bruyn

Modifications in lignin and accumulation of phenolic glucosides in poplar xylem upon down-regulation of caffeoyl-coenzyme A O-methyltransferase, an enzyme involved in lignin biosynthesis.

Caffeoyl-coenzyme AO-methyltransferase (CCoAOMT) methylates, in vitro, caffeoyl-CoA and 5-hydroxyferuloyl-CoA, two possible precursors in monolignol biosynthesis in vivo. To clarify the in vivo role of CCoAOMT in lignin biosynthesis, transgenic poplars with 10% residual CCoAOMT protein levels in the stem xylem were generated. Upon analysis of the xylem, the affected transgenic lines had a 12% reduced Klason lignin content, an 11% increased syringyl/guaiacyl ratio in the noncondensed lignin fraction, and an increase in lignin-attached p-hydroxybenzoate but otherwise a lignin composition similar to that of wild type. Stem xylem of the CCoAOMT-down-regulated lines had a pink-red coloration, which coincided with an enhanced fluorescence of mature vessel cell walls. The reduced production of CCoAOMT caused an accumulation ofO 3-β-d-glucopyranosyl-caffeic acid,O 4-β-d-glucopyranosyl-vanillic acid, andO 4-β-d-glucopyranosyl-sinapic acid (GSA), as authenticated by 1H NMR. Feeding experiments showed thatO 3-β-d-glucopyranosyl-caffeic acid and GSA are storage or detoxification products of caffeic and sinapic acid, respectively. The observation that down-regulation of CCoAOMT decreases lignin amount whereas GSA accumulates to 10% of soluble phenolics indicates that endogenously produced sinapic acid is not a major precursor in syringyl lignin biosynthesis. Our in vivo results support the recently obtained in vitroenzymatic data that suggest that the route from caffeic acid to sinapic acid is not used for lignin biosynthesis.

In vivo synthesis of complex N-glycans by expression of human N-acetylglucosaminyltransferase I in the filamentous fungus Trichoderma reesei

The human N‐acetylglucosaminyltransferase I gene was introduced in the genome of Trichoderma reesei strain VTT‐D‐80133. Expression was studied after induction from the cellobiohydrolase I promoter. Successful in vivo transfer of GlcNAc was demonstrated by analyzing the neutral N‐glycans which were synthesized on cellobiohydrolase I. Final proof of the formation of GlcNAcMan5GlcNAc2 was obtained by NMR analysis.

Patterns of phenolic compounds in leafy galls of tobacco

The chemical composition of ethanolic and aqueous extracts from leafy galls produced after infection of Nicotiana tabacum L. plants with Rhodococcus fascians was drastically changed compared to uninfected controls. Chlorogenic acid was abundant both in uninfected and infected plants, but caffeic acid and another cinnamoyl analogue were new in leafy galls. The most pronounced product induced in leafy galls was identified as 7-O-methyl-6-O-β-D-glucopyranosyl coumarin (7-methyl esculin). This is the first report of the presence of this coumarin derivative in tobacco. Interestingly, 7-methyl esculin did not accumulate in the presence of avirulent R. fascians strains nor was it found in leafy galls on other plant species. However, it did appear in crown galls induced by Agrobacterium tumefaciens on tobacco plants. Intriguingly, none of the phenolics known to accumulate in Solanaceae under pathogen attack were found in leafy galls. 7-Methyl esculin barely affected growth of R. fascians nor was it catabolized. Microscopical analysis showed that autofluorescent compounds were located mainly in the abundant meristematic regions of the leafy galls. We postulate that 7-methyl esculin might locally influence plant cell division.

An efficient synthesis and physico-chemical properties of 2'-O-D-ribofuranosylnucleosides, minor tRNA components

ABSTRACT A high yield preparation of 9-(2-O-β-D-ribofuranosyl-β-D-ribofuranosyl)adenine, guanine- and the pyrimidine analogs (cytosine, thymine and uracil base moiety) has been achieved, and the conformational properties of the ring systems were investigated using NMR spectroscopy and X-ray.

Influence of amylovoran production on virulence of Erwinia amylovora and a different amylovoran structure in E. amylovora isolates from Rubus

The amylovoran structures of five Erwinia amylovora isolates from Malaceae sp. and four isolates from Rubus sp. host plants were fully established, mainly by NMR. The structural data on one E. amylovora isolate from a Malaceae sp. host, which had been previously suggested by mass and NMR (Nimtz et al., 1996), were completed. E. amylovora strains infective on Malaceae sp. host plants had an amylovoran composed of pentasaccharide and 30–40% hexasaccharide repeating-substructures, whereas amylovoran from E. amylovora isolates from Rubus sp. host plants had only the pentasaccharide substructures. On the other hand, the exopolysaccharide (EPS) production differed in wild-type E. amylovora strains. Data on in vitro amylovoran production per cell could account for the differences in aggressiveness found in E. amylovora strains, as deduced from a pilot test with highly, moderately, and weakly aggressive strains. This correlation was confirmed with several other wild-type E. amylovora strains from different origin.

Selective Removal of the Isopropylidene Group in 4-O-Protected 1,6-Anhydro-2,3-O-Isopropylidene-β-D-Mannopyranose and the Conformational Impact of it

Abstract Pyridinium p-toluenesulfonate (PPTS) is a reagent of choice for the selective removal of an O-isopropylidene group in a 1,6-anhydro-β-d-aldohexopyranose, where the remaining OH-group is protected.

Synthesis and apoptogenic activity of fluorinated ceramide and dihydroceramide analogues

Short-chain 3-fluoro-(dihydro)ceramide analogues are synthesized from L-serine using diethylaminosulfur trifluoride (DAST) as fluorinating agent. The apoptogenic activity of these compounds was measured in three different cell lines and compared with their hydroxylated counterparts.

3′-Deoxy-3′-hydroxymethyl-aldopentopyranosyl nucleoside synthesis. Part I

A straightforward synthesis of 3′-deoxy-3′-hydroxymethyl-aldopentopyranosyl nucleosides is described starting from β-d-xylopyranosyl nucleosides. β-d-xylopyranosyl thymine 17a,b,c and uracil 17d are converted into the 4′-benzoylated derivatives 18a,b and further into the 2′,3′-enepyranosyl compounds 19b,c. A 3′-hydroxymethyl appendix has been introduced using a free-radical methodology to furnish 20a,b. Inversion of configuration of the 4′-position yielded the target nucleosides 22a,b. X-ray and 1H NMR conformation analysis prove the equatorial orientation of the base moiety in the target compounds.

NMR EVIDENCE FOR A NOVEL ASPARAGINE-LINKED OLIGOSACCHARIDE ON CELLOBIOHYDROLASE I FROM TRICHODERMA REESEI RUTC 30

© 1997 Federation of European Biochemical Societies.

1H NMR Study of Methyl O-Acetyl-α-and-β-D-Xylopyranosides Conformational Studies and Non Additivity of 1H-Shift Increments

Abstract 1H NMR spectra of the complete series of fully and partially acetylated methyl α-and β-D-xylopyranosides have been studied. The α-anomers occur exclusively in 4C1 chairs but the 1C4 chair becomes increasingly populated in the β-forms especially when the OH-3 is not acetylated. Increments used for the prediction of the chemical shifts of ring protons are discussed and compared with the literature data. The predictability for changes in shifts upon acetylation is poor.