SYNTHETIC STUDIES ON GLYCOPEPTIDES CONCERNED WITH DEFENSE RESPONSE OFPLANTS .1. SYNTHESES OF SUPPRESCIN-A AND SUPPRESCIN-B

Two glycopeptides, supprescins A and B, that suppress the production o f pisatin, a phytoalexin of pea, were synthesized. In the synthesis of supprescin A, condensation of -O-acetyl-2-azido-2-deoxy-alpha-D-galac topyranosyl trichloroacetimidate or its glycosidic beta isomer with N- (carbobenzoxy)-L-seryl-O-benzyl-L-seryl-glycine methyl ester was carri ed out in the presence of trimethylsilyl trifluoromethanesulfonate (TM SOTf) to give the monoglycosyl tripeptide derivatives, For the synthes is of supprescin B, glycosylation of 2,3,4,6-tetra-O-acetyl-alpha-D-ga lactopyranosyl bromide and 1,2,3,6-tetra-0-benzoyl-alpha-D-galactopyra n was promoted by silver trifluoromethanesulfonate (AgOTf) to provide a disaccharide derivative. The coupling of diglycosyl imidate, 2,3,4,6 -tetra-O-acetyl-beta-D-gaIactopyranosyl-(1 --> ,6-di-O-beazoyl-2-azido -2-deoxy-D-galactopyranosyl trichloroacetimidate, and -aspartyl-5-benz yl-L-glutamyl-O-benzyl-L-threonine methyl ester in the presence of TMS OTf afforded the diglycosyl hexapeptide derivatives, Reduction, follow ed by N-acetylation, and then removal of the remaining protecting grou ps afforded the desired supprescin B.