Chemoselective Glycosylation Strategy for the Convergent Assembly of Phytoalexin-Elicitor Active Oligosaccharides and Their Photoreactive Derivatives

A highly convergent route for the synthesis of branched glucosides having phytoalexin-elicitor activity has been developed. The readily available building blocks 2, 3, and 6 were used for the assembly of a core trisaccharide in two chemo- and regioselective glycosylations. Compound 7 was converted into the artificial spacer-containing glycosyl acceptor 9. Regioselective condensation of fragment 7 with 9 led to the formation of fully protected hexasaccharide 14. Deprotection of hexasaccharide 14 followed by the reaction with 4-azidosalicylate gave compound 1b. It was established that compound 1b is a photoreactive compound. Reaction time and conditions were established for photolysis of compound 1b and labeling with radioactive iodine. A soybean root binding site for an elicitor-active hepta-β-glucoside bound compound 1b with the same affinity as the underivatized hepta-β-glucoside.