SYNTHESES OF TRIGLYCOSYL TETRAPEPTIDES AND A HEXAGLYCOSYL TETRAPEPTIDE

A stereo-controlled synthesis of the model compound for the phytoalexe n elicitor-active glycoprotein is described. Glycosylation of the tris accharide, 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl-(1 --> 6)-2,3, 4-tri-O-acetyl-alpha-D-mannopyranosyl-(1 --> 6)-2,3,4-tri-O-acetyl-alp ha-D-mannopyranosyl trichloroacetimidate (12), with N-(9-fluorenylmeth oxycarbonyl)-L-seryl-L-proline benzyl ester (3) or N-(carbobenzoxy)-L- seryl-L-proline methyl ester (4) by use of BF3 . OEt(2) gave the trigl ycosyl-seryl-proline derivatives. The N- as well as C-terminus of thes e triglycosyl dipeptides could be deblocked selectively to give compou nds 14 and 16, which are versatile intermediates for the completion of model compound synthesis of glycopeptide. Triglycosyl tetrapeptides ( 18, 21) and hexaglycosyl tetrapeptide (23) have been prepared by the c onvergent block synthesis.