Synthesis of Fmoc-Thr Unit Carrying Core 1 O-Linked Sugar With Acid-Sensitive O-Protecting Group and Its Application to the Synthesis of Glycosylated Peptide Thioester

We newly designed and synthesized a 9-fluorenylmethoxycarbonyl (Fmoc)-threonine unit carrying the core 1 O-glycan, which is protected by the 4-methylbenzyl (MBn) group. This protection tactic enabled not only efficient assembly of glycoamino acid derivatives but also one-step deprotection by trifluoroacetic acid (TFA) after the Fmoc-solid-phase peptide synthesis (SPPS). The usefulness of this unit was demonstrated by the Fmoc-SPPS of peptide thioester using the N-alkylcysteine (NAC)-assisted thioesterification method. The human interleukin-2 (1-27) sequence was assembled on the NAC resin and the obtained resin was treated with TFA containing cation scavengers to achieve one-step deprotection. The crude peptide was then thioesterified by reacting with an arylthiol to successfully obtain the desired peptide thioester carrying the core 1 O-glycan.