Toward Homogeneous Erythropoietin: Chemical Synthesis of the Ala1 —Gly28 Glycopeptide Domain by "Alanine" Ligation.

The Ala1—Gly28 glycopeptide fragment (28) of EPO was prepared by chemical synthesis as a single glycoform. Key steps in the synthesis include attachment of a complex dodecasaccharide (7) to a seven amino acid peptide via Lansbury aspartylation, native chemical ligation to join peptide 19 with the glycopeptide domain 18, and a selective desulfurization at the ligation site to reveal the natural Ala19. This glycopeptide fragment (28) contains both the requisite N-linked dodecasaccharide and a C-terminal αthioester handle, the latter feature permitting direct coupling with a glycopeptide fragment bearing N-terminal Cys29 without further functionalization. [ABSTRACT FROM AUTHOR]