The total chemical synthesis of peptides/proteins by native chemical ligation (NCL) has contributed much to the biological and medicinal fields. However, peptides having low water-solubility do not match with general NCL using aqueous buffers. Thus, solubilizing tag-aided NCLs have drawn much attention. Important requirements for solubilizing tags are as follows: i) easy attachment, ii) efficient solubilizing property, and iii) easy detachment. In this context, we developed solubilizing tag methods (Trt-K and Trt-R method) using trityl chemistry. In our system, the solubilizing tag can be attached to the Cys side chain thiol by simply mixing the tag introducing reagent (trityl alcohol derivative) under acidic conditions. The tagged peptides/proteins exhibited high water-solubility thanks to the introduction of redundant oligo-Lys/Arg in the structure of the tag. Additionally, in the final reaction, the tag can be quickly and cleanly detached by a standard deprotection reaction using trifluoroacetic acid and cation scavenger. After the method was successfully applied to the synthesis of hepatitis B virus capsid protein [1], our method was further confirmed to be compatible with desulfurization [2,3]. In this presentation, we will present development and application of these methods [4].
[1] S. Tsuda et al. Angew. Chem. Int. Ed. 2018, 57, 2105. [2] S. Tsuda et al. Org. Biomol. Chem. 2019, 17, 1202. [3] T. Yoshiya et al. ChemBioChem in press (DOI: 10.1002/cbic.201900105). [4] S. Tsuda et al. ChemBioChem in press (DOI: 10.1002/cbic.201900193).