Synthesis of Oligosaccharins, Phytoalexin Elicitor-Active Fragments of Cell Wall Glycans.

In this article are described the synthetic studies on two types of “oligosaccharins”, oligosaccharides from both fungal and plant origins, that elicit phytoalexin accumulation in soybean.Two research groups have synthesized oligosaccharides related to β-glucan elicitor derived from pathogenic fungal cell wall.Biological examination of the chemically synthesized oligo-β-glucosides revealed that minimum structure required for the elicitor activity is β-D-glucohexaoside, and that the branched trisaccharide at nonreducing end of the oligoglucosides is essential for maximum elicitor activity.α- (1→4) -Linked oligogalacturonic acids (d.p. 10-13) derived from plant cell wall pectic polysaccharides are the “endogeneous elicitors” of phytoalexin accumulation in soybean.Total synthesis of dodecagalacturonic acid was achieved by way of highly stereoselective glycosylation that involved glycosyl fluorides as the donors and oxidation of the twelve primary hydroxy groups in the α- (1→4) -linked galactododecaoside derivative. The synthetic dodecagalacturonic acid was active as an elicitor of soybean phytoalexin and was synergistic with the hepta-β-glucoside elicitor.