Studies on synthesis of 2-carboxylic acid phenyl heptaglucoside and its phytoalexin-elicitor activity

The elicitor-active heptaglucose (2) acts as, a regulatory molecule in plants, which can stimulate biosynthesis of phytoalexins in quantities sufficient to inhibit growth of microbial pathogens. Salicylic acid can also stimulate plants to produce phytoalexin as a defense response to the pathogen. In order to investigate the synergic effect of the heptaglucose (2) and salicylic acid, 2-carboxylic acid phenyl gluco-heptasaccharide (1) was synthesized by condensation of the hexasaccharide donor (7) and 2-methylearboxylate phenyl glucoside acceptor (6), which was obtained by 6-O-deacetylation of 2-methylcarboxylate phenyl 6-O-acetyl-2,3,4-tri-O-benzoyl-alpha-D-glucopyranoside (5). Compound 5 was synthesized by coupling of 6-O-acetyl-2,3,4-tri-O-benzoyl-alpha-D-glucopyranosyl trichloroacetimidate (3) with methyl salicylate (4). The structures of all compounds synthesized were determined by NMR and elemental analysis. The ability of elicitor to stimulate phytoalexin accumulation in soybean tissue has been used as the basis for biological assays of its activity. Bioassay indicates that the heptaglucose derivative synthesized here has slightly more phytoalexin-elicitor activity than its corresponding heptaglucose, heptaglucose 2 and salicylic acid have a synergic effect.