Solid-phase synthesis of a glycosylated hexapeptide of human sialophorin, using the trichloroacetimidate method

Article abstract of DOI:10.1016/0008-6215(94)00364-L

A hexapeptide containing a β-D-Gal p-(1<*>3)-α-D-Gal pNAc-(1<*>O)-L-threonine unit was synthesized using glycosylated pentafluorophenyl esters in an Fmoc-based strategy.In all of the glycosylation reactions, trichloroacetimidates were successfully employed.The disaccharide moiety was prepared from tetra-O-acetyl-α-D-galactopyranosyl trichloroacetimidate and tert-butyldimethylsilyl 2-azido-6-O-benzoyl-2-deoxy-β-E-galactopyranoside with boron trifluoride etherate as a catalyst.The glycosylated active esters were obtained in the reaction of α and β 2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl-(1<*>3)-4-O-acetyl-2-azido-6-O-benzoyl-2-deoxy-D-galactopyranosyl trichloroacetimidates with Fmoc-protected pentafluorophenyl esters of L-serine and L-threonine in the presence of trimethylsilyl trifluoromethanesulfonate as Lewis acid.The glycosylated pentafluorophenyl ester of L-threonine was transformed into glycopeptides via a solid-phase synthesis.Azide reduction and N-acetylation were performed on the solid phase with a thioacetic acid-pyridine mixture.The glycopeptide was then cleaved from the resin with strong acid, also removing the acid-labile protecting groups of the peptide chain.Finally, the acyl groups used for sugar protection were cleaved with sodium methoxide, affording the completely deprotected N-acetyl-L-leucyl-L-glutamyl-O-<β-D-galactopyranosyl-(1<*>3)-2-acetamido-2-deoxy-α-D-galactopyranosyl>-L-threonyl-L-seryl-L-threonyl-glycinamide (1) in high purity. Keywords: O-Glycopeptides; Glycosyl trichloroacetimidates; Peptide synthesis, solid phase; N-Fmoc protection; Pentafluorophenyl esters