Thiocster method [1] is one of the ligation methods useful for (glyco)protein synthesis. This method has the advantage that there is no limitation on selecting the ligation site, whereas the coupling by the native chemical ligation [2] is almost exclusively carried at Xaa-Cys site. Instead, the side chain amino and thiol groups have to be protected to achieve the chemosclective ligation in the thioester method. To realize this, the Boc groups have to be reintroduced to the side chain amino groups, which are made free during the deprotection step after SPPS. In this paper, we examined the direct preparation of the side chain-N-protected peptide segments by introducing azido- and pyruvoyl (Pyr)-protected Fmoc-lysine (Figure 1) during SPPS to overcome the inconvenience for segment preparation. Using pigment dispersing hormone (PDH)-I and glycopeptide toxin, Contulakin-G as models, the usefulness of these protecting groups were examined.
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