Syntheses of triglycosyl tetrapeptides and a hexaglycosyl tetrapeptide.

Abstract A stereo-controlled synthesis of the model compound for the phytoalexin elicitor-active glycoprotein is described. Glycosylation of the trisaccharide, 2,3,4,6-tetra- O -acetyl- β -d-glucopyranosyl-(1 → 6)-2,3,4-tri- O -acetyl- α -d-mannopyranosyl- (1 → 6)-2,3,4-tri- O -acetyl- α -d-mannopyranosyl trichloroacetimidate ( 12 ), with N -(9-fluorenylmethoxycarbonyl)-l-seryl-l-proline benzyl ester ( 3 ) or N -(carbobenzoxy)-l-seryl-l-proline methyl ester ( 4 ) by use of BF 3 · OEt 2 gave the triglycosyl-seryl-proline derivatives. The N - as well as C -terminus of these triglycosyl dipeptides could be deblocked selectively to give compounds 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 convergent block synthesis.