Erythropoietin (EPO) is one of the best-studied
glycoproteins because of its high medical importance. For stability and in vivo
activity the carbohydrate moiety is essential. EPO with tetraantennary
N-glycans shows higher activity compared to non-glycosylated EPO.[1]
Due to the microheterogeneity it is difficult to isolate homogeneous glycoforms
and to investigate detailed structure-activity-relationships. Homogenous EPO glycoforms
can be obtained by sequential native chemical ligation.[2][3] The
glycosylated thioester A[4]
and the glycopeptides B and C bearing C‑terminal hydrazides[5]
were obtained by convergent solid phase peptide synthesis. The sugar moiety was
introduced by Lansbury aspartylation[6] assisted by pseudoprolines
placed in the Asp-X-Ser/Thr consensus sequence.[4] Thereby aspartimide
formation was greatly reduced. Incorporation of multiantennary N-glycans into
fragments A-C was investigated.
[1] Takeuchi, M;
Inoue, N.; Strickland, T.W.; Kubota, M.; Wada, M.; Shimizu, R.; Hoshi, S.;
Kozutsumi, H.; Takasaki, S.; Kobata, A. Proc.
Natl. Acad. Sci. USA 1989, 86, 7819. [2] Murakami, M.; Okamoto, R.;
Izumi, M; Kajihara, Y Angew. Chem. Int.
Ed. 2012, 51, 3567. [3] Wang, Q.; Dong, S.; Brailsford, J.A.; Iyer, K.;
Zhang, Q.; Hendrickson, R.C.; Shieh, J.; Moore, M.A.S.; Danishefsky, S.J. Angew. Chem.
Int. Ed.
2012, 51, 11576. [4] Ullmann, V.; Rädisch, M.; Boos, I.; Freund, J.;
Pöhner, C.; Schwarzinger, S.; Unverzagt, C. Angew.
Chem. Int. Ed. 2012, 51, 11566. [5] Fang, G.-M.; Li, Y.-M.;
Shen, F.; Huang, Y.-C.; Li, J.-B.; Lin, Y.; Cui, H.-K.; Liu, L. Angew. Chem. Int. Ed. 2011, 50, 7645. [6] Cohen-Anisfeld, S.T.; Lansbury, P.T. J. Am. Chem. Soc. 1993, 115, 10531.
