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Expression of Agrobacterium tumefaciens virulence genes and transformation of dicots by this organism are dependent upon host plant phenolic compounds. Several alkylsyringamides have recently been shown to be powerful inducers of these vir-genes. These synthetic amides, and especially ethylsyringamide, are much stronger inducers than syringic acid. In this work, four alkylamides derived from ferulic or sinapic acids were synthesized by a dicyclohexylcarbodiimide method and tested for their potential to induce vir-gene expression on A. tumefaciens strains harbouring virB::lacZ or virE::lacZ fusion plasmids. Their effectiveness was compared to that of ethylsyringamide and tyraminylferulamide, a naturally occurring amide in plants. Whatever the amine moiety of the amide (ethylamine, propylamine, tyramine or beta-alanine ethyl ester) conjugation of the acid functional group clearly diminished the toxicity to the bacteria of the respective acid at high concentration and thereby increased the vir-inducing potential. However, none of the inducers tested exhibited higher activity than acetosyringone, the reference compound for vir-gene induction, with the exception of ethylsyringamide at concentrations above 1mM. When tested on Agrobacterium tumefaciens strain A348(pSM243cd), ethylferulamide and ethylsinapamide were more efficient than the corresponding phenolic acids but only above 100 microM.

International audience; Lectins are present on the surface of many cells. Many lectins actively recycle from membrane to endosomes and efficiently take up glycoconjugates in a sugar-dependent manner. On this basis, glycoconjugates, specially those obtained by chemical means, are good candidates as carriers of drugs, oligonucleotides or genes. In this paper, we present a panel of methods suitable to transform unprotected reducing oligosaccharides into glycosynthons designed to be easily linked to therapeutic agents. All the glycosynthons presented here are glycosylamines or derivatives, mainly glyco-amino acids or glycopeptides. Glycosylamines are easy to obtain, but they are very labile in slightly acidic or neutral medium; they must be stabilized, by acylation for instance. The coupling efficiency of a reducing sugar with ammonia as well as an alkylamine or an arylamine is higher at high temperature, however, because of the Amadori rearrangement, special conditions have to be selected to prepare the expected glycosylamine derivative with a high yield. Glycosylamines are easily acylated by N-protected amino acids, or by halogeno acids which can then be transformed into amino acids. Alternatively, unprotected reducing oligosaccharides may very efficiently be transformed into N-glycosyl-amino acids and then protected by N-acylation. With a glutamyl derivative having both the alpha-amino and the gamma-carboxylic groups free, the coupling and the acylation, which is intramolecular, are roughly quantitative. N-oligosaccharyl-amino acid derivatives are interesting glycosynthons, because their sugar moiety bears the specificity towards membrane lectins while the amino acid part has the capacity to easily substitute a therapeutic agent.

The virulence genes of Agrobacterium tumefaciens are specifically activated by plant phenolic compounds and allow this organism to genetically transform plant cells. New types of phenolic compounds, three phenol amides derived from syringic acid, were synthesized. Introduction of an amide group in syringic acid strongly enhances its vir gene inducing activity.

Coniferyl alcohol β-glycosides were synthesized by coupling coniferyl alcohol sodium salt in aqueous acetone with peracetylated glycosyl halides of d -glucopyranose, d -galactopyranose and l -fucopyranose. After O -deacetylation by sodium methoxide, the glycosides were tested for their potential vir gene-inducing activities in Agrobacterium tumefaciens A348/pSM358 and A348/pSM243cd harbouring, respectively, virE::lacZ and virB::lacZ fusion plasmids. In the large range of concentrations tested, these synthetic derivatives had vir -inducing activity on strain A348/pSM358: d -Gal > d -Glc. The dose-response curves of these glycosylated compounds were completely different from those of free coniferyl alcohol; the β-galactopyranoside at 500,μM exhibited interestingly a greater activity than the free aglycone after a 12 hr incubation period. The coniferyl alcohol β-glucopyranoside was a better inducer than the related β-galactopyranoside on strain A348/pSM243cd. The β- l -fucopyranoside was inactive with both A. tumefaciens strains. The activities of these glycosylated inducers were correlated with the presence of intracellular glycosylhydrolases from the various A. tumefaciens strains studied. It is noteworthy that the vir -gene induction activity of the coniferyl alcohol β-galactopyranoside on strain A348/pSM358 was due to a high basal level of expression of the virE::lacZ fusion gene.

Aryl β-glycopyranosides have been synthesized by coupling syringaldehyde (3-methoxyvanillin) with l -fucose, d -galactose, and maltose; acetosyringone (4-hydroxy-3,5-dimethoxyacetophenone) with l -fucose and maltose; acetovanillone (4-hydroxy-3-methoxyacetophenone) with l -fucose; and syringic acid (4-hydroxy-3,5-dimethoxybenzoic acid) with d -galactose. The procedure using peracetylated glycosyl halides and sodium phenolates in aqueous acetone afforded the acetylated β-glycosides, which were deacetylated.