The compound A~GlcNACgl-NH-Fmoc (3) was eynthesixed and transformed into the &gluwsyl amine (1) which was subsequently acylated with Fmoc-Asp(CI)-Gpfp (5) prepared from the readily available Fmoc-Asp@-tBu)-G-pfp (4). The resulting Fmoc-Asn(A~GlcNAcfil-N-)-O-Pfp (6) was used as a buildiug block in the solid phase synthesis of an 11 residue glycopeptide fragment of the enxyme glucuam YR= WvW.
Transport of proteins and a variety of important recognition phenomena in the eukariotic ceUular compartment and on the cell membrane are controlled by signals mediated e. g. via oligosaccluuides N-linked to asparagine sidecimins of glycoproteins. In contrast to other proteins, the glywsylated proteins are not easily available by geneteohnology since they arc posttranslational products resulting from the activity of trimming glywsyl hydrolascs and tmnsferases. Therefore, organic synthesis provide a valuable alternative.
The core structure of the N-glywsylated glywproteins is a trisaccharide. Man&-4GicNA~$1-4GlcNAc~, the terminal N-acetylglucosamine residue is w~ected to the amide of an asparagine residue of the glywprotein. Access to partial structures of glycqeptides consisting of longer peptides with e. g. GlcNAc or its diier chitobiose attached will make it possible to study the structur+function relationship e. g. the conformational preference (the interaction bctwcw the sugar and the peptide) and the application of glywsyl transfemses for the elongation to more complex glycopeptides.
The N-glycosylated asparagine molecule with more or less permanent protection of the o-amino and the cu-carboxyl group has been reported previously. I-' The permanent character of these protection groups has, however, prevented the application of these derivatives for the solid phase synthesis of larger N-glywsylated peptides. Recently KUIU reported strategies using Boc-or Alec-protection of the a-amino group and allyl-or t-butyl ester for the wcarboxyl group for the solution synthesis of small N-lied glycosylated peptides.8*9 Recently we have reported the application of the pentafluorophenyl (pfp) group for the temporary protection of the (Ycarboxyl group in the G-glywsylation of serine and threonine. lo In the present communication we demonstrate that the pfp ester also can be used as a general temporary protection group in the solid phase synthesis of N-glycopsptides. During degradation studies on the glywhydrolsse, gluwamylase, in this laboratoryl' a glywsylated undeca-peptide (residue 388-398) H-Thr-His-Ala-Ala-Ser-Asn(glywside)-Gly-Ser-Met-Ser-Glu-OH was isolated and subjected to further characterization. We have therefore selected this glywpeptide as a synthetic target for the demonstration of the new methodology. As a glywsyl model 2-awtamido-2-deoxy-3,4,6-tri-G-acetyl-~-~g-pglucopyranosylamine (3) was pmpared by a new approach from N-acetylgluwsamine.'* Thus reaction of N-acetylgluwsamine with ammonium carbonate and lyophili&ion to wnstant weight afforded a mixture which according to 'H-NMK was 85% of the &glywsyl amine (1) and 15% starting material. This mixture was dissolved in pyridine and treated with Fmoc-GSu for 3 h followed by addition of pyridii and acetic anhydride