Synthesis of glycopeptides with phytoalexin elicitor activity — III. Syntheses of hexaglycosyl hexapeptides and a nonaglycosyl hexapeptide Original Research Article

A block synthesis of the model compound for the phytoalexin elicitor-active glycoprotein is described. Combination of the C-terminus free compounds, N-(9-fluorenylmethoxycarbonyl)-O-(tert-butyl)-l-seryl-l-proline (1) or N-(9-fluorenylmethoxycar bonyl)-(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)-l-seryl-l-proline (2) with the N-terminus free compounds, 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)-l-seryl-l- prolyl-l-seryl-l-proline methyl ester (4), O-(tert-butyl)-l-seryl-l-prolyl-(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)-l-seryl-l-proline methyl ester (6) or 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)-l-seryl-l-prolyl-(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)-l-seryl-l-proline methyl ester (8), by use of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) gave three hexaglycosyl hexapeptides and a nonaglycosyl hexapeptide derivatives (9, 11, 14, and 17). These N-terminus free compounds were derived from triglycosyl tetrapeptides (3, and 5) or a hexaglycosyl tetrapeptide (7) on selective deblock reaction by morpholine. The hexaglycosyl hexapeptides (10, 13, and 16) and the nonaglycosyl hexapeptide (18) have been prepared by the convergent block synthesis.