SYNTHESIS OF A METHYL HEPTAGLUCOSIDE - ANALOG OF THE PHYTOALEXIN ELICITOR FROM PHYTOPHTORA-MEGASPERMA

The ethylthio-laminaribioside 29, prepared by regiospecific glycosylat ion of ethyl 4,6-O-benzylidene-1-thio-beta-D-glucopyranoside (9) with 2,3,4,6-tetra-O-benzoyl-D-glucopyranosyl imidate 17 and subsequent ben zoylation, could be elongated in a step-wise fashion by consecutive io donium ion promoted condensations with methyl 2,3,4-tri-O-benzoyl-alph a-D-glucopyranoside (5), ethyl t-butyldimethylsilyl-1-thio-beta-D-gluc opyranoside (7), the laminaribioside 29 and ethyl ,4,6-tetra-O-benzoyl -1-thio-beta-D-glucopyranoside (8), and intermittent protective group manipulations, to yield the partially acylated heptasaccharide 36. Fin ally, one-step deacylation of branched heptamer 36 afforded the target compound alpha-methyl 3(2),3(4)-di-beta-D-glucopyranosylgentiopentaos ide (2).