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SHCH 3Ocyclication/pH 7.5OON(AA)nONSONHS-N acyl shift1OOHSNODmmb removalNO2O(AA)nNCH 33O(AA)nNCH 3Scheme 2. End-to-end cyclization.After 2 days at rt, the cyclic peptide 2 was observed by analytical UPLC and no byproductswere observed. The yield of the cyclization after purification of the peptide was 50%. TheDmmb group was then removed with 1M TFMSA and 1M thioanisol in TFA to give thetarget peptide 3 [12] and LC-MS confirmed the expected mass.In conclusion, the auxiliary group Dmmb has been applied to form an end-to-endcyclic peptide at an Ala-Gly site and no polymerization was observed. The linear peptideprecursor which contains both N -(Dmmb(Trt)-Gly and C -thioester was generated bystandard Fmoc-chemistry.References1. Davies, J.S. J. Pept. Sci. 9, 471-501 (2003).2. Dawson, P.E., Muir, T.W., Clark-Lewis, I., Kent, S.B. Science 266, 776-779 (1994).3. Kawakami, T., Akaji, K., Aimoto, S. Org. Lett. 3, 1403-1405 (2001).4. Spetzler, J.C., Hoeg-Jensen, T. Bioorg. Med. Chem. 15, 4700-4704 (2007).5. Vizzavona, J., Dick, F., Vorherr, T. Bioorg. Med. Chem. Lett. 12, 1963-1965 (2002).6. Botti, P., Carrasco, M.R., Kent., S.B.H. Tetrahedron Lett. 42, 1831-1833 (2001).7. Marinzi, C., Offer, J., Longhi, R., Dawson, P.E. Bioorg. Med. Chem. 12, 2749-2757 (2004).8. Tchertchian, S., Hartley, O., Botti, P. J. Org. Chem. 69, 9208-9214 (2004).9. Shao, Y., Lu, W., Kent, S.B.H. Tetrahedron Lett. 39, 3911-3914 (1998).10. Zhang, L., Tam, J.P. J. Am. Chem. Soc. 119, 2363-2370 (1997).11. Von Eggelkraut-Gottanka, R., Klose, A., Beck-Sickinger, A., Beyermann M. Tetrahedron Lett. 44,3551-3554 (2003).12. Mohri, H., Ohkubo,T. Peptides 14, 861-865 (1993).141