Organic Letters
Letter
AUTHOR INFORMATION
Corresponding Authors
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ORCID
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This work was supported by the Japan Society for the
Promotion of Science (JSPS) Grant-in-Aid for Scientific
Research (A) 18H03931 and Grant-in-Aid for Scientific
Research (C) 18K05313. We thank Dr. Minami Matsui
(RIKEN Center for Sustainable Resource Science) to kindly
allow us to use an automated peptide synthesizer and thank Dr.
Emiko Kurihara and Ms. Tomoko Kuriyama (RIKEN Center
for Sustainable Resource Science) for help in our peptide
synthesis.
Figure 3. HPLC profiles of chemical synthesis of H3 bearing K9me3.
HPLC peaks were monitored at 220 nm in the linear gradient with
water/acetonitrile containing 0.1% TFA. (A) One-pot three-segment
peptide ligation. 13′ = alloc-protected peptide 13. Gradient: 10−70%
for 30 min. (a) NCL between peptides 11 and 12 after 3 min and (b)
2 h. (c) Alloc deprotection with Pd/TPPTS. (d) NCL between
peptides 10′′ and 13. * = peptide 10 bearing an amide at its C-
terminus and # = mixture of peptide 10′′ and hydrolyzed 10′′. (B)
(a) Removal of Acm groups of peptide 15 before reaction and (b)
after 40 min. Gradient: 38−58% for 20 min. (C) HPLC profile
(gradient: 38−63% for 25 min) and MALDI-TOF mass spectrum of
purified peptide 16 with the observed mass 15318.4 Da (calcd
15316.0 Da).
REFERENCES
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(Figure S12). Subsequent desulfurization, which converted two
mutated residues and Pen into the original Ala residues and a
Val residue, respectively, afforded peptide 15 in 65% isolated
yield (Figure S13). Finally, we removed Acm groups with
Na2PdCl4. The deprotection reached completion within 1 h
(Figure 3B), and an excess amount of dithiothreitol (DTT)
was added to the peptide solution to detach Pd complexes
from the peptide before HPLC purification.6d,h The desired
peptide 16, full-length H3, was obtained in 82% isolated yield
(Figure 3C). The total yield of histone H3 bearing K9me3 was
21%. These results demonstrated the applicability of the
chemoselective deprotection of Alloc and Acm groups for
chemical protein synthesis of Cys-containing proteins.
In summary, we have described selective deprotection of
Alloc groups for N-terminal Cys and Acm groups for internal
Cys employing different Pd complexes. The valence of Pd and
steric hindrance of ligands greatly affected the reactivity of Pd
complexes toward Alloc and Acm groups. Utilizing this
chemoselectivity, total chemical synthesis of histone H3
bearing K9me3 was accomplished. We believe that a wide
variety of proteins bearing various modifications will be created
through the Pd-mediated orthogonal removal of protecting
groups for N-terminus and internal Cys residues.
ASSOCIATED CONTENT
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* Supporting Information
The Supporting Information is available free of charge on the
(7) Kamo, N.; Hayashi, G.; Okamoto, A. Angew. Chem., Int. Ed.
2018, 57, 16533−16537.
(8) Johnson, E. C. B.; Kent, S. B. H. J. Am. Chem. Soc. 2006, 128,
6640−6646.
Experimental details (PDF)
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