Synthesis of the Highly Glycosylated Hydrophilic Motif of Extensins

Extensin, the structural motif of plant extracellular matrix proteins, possesses a unique highly glycosylated, hydrophilic, and repeating Ser₁Hyp₄ pentapeptide unit, and has been proposed to include post‐translational hydroxylation at proline residue and subsequent oligo‐L ‐arabinosylations at all of the resultant hydroxyprolines as well as galactosylation at serine residue. Reported herein is the stereoselective synthesis of one of the highly glycosylated motifs, Ser(Galp₁)‐Hyp(Araf₄)‐Hyp(Araf₄)‐Hyp(Araf₃)‐Hyp(Araf₁). The synthesis has been completed by the application of 2‐(naphthyl)methylether‐mediated intramolecular aglycon delivery to the stereoselective construction of the Ser(Galp₁) and Hyp(Araf_n) fragments as the key step, as well as Fmoc solid‐phase peptide synthesis for the backbone pentapeptide.