Scandium(III) triflate-promoted serine/threonine-selective peptide bond cleavage

Article abstract of DOI:10.1039/c6cc10300f

The site-selective cleavage of peptide bonds is an important chemical modification that is useful not only for the structural determination of peptides, but also as an artificial modulator of peptide/protein function and properties. Here we report site-selective hydrolysis of peptide bonds at the Ser and Thr positions with a high conversion yield. This chemical cleavage relies on Sc(iii)-promoted N,O-acyl rearrangement and subsequent hydrolysis. The method is applicable to a broad scope of polypeptides with various functional groups, including a post-translationally modified peptide that is unsuitable for enzymatic hydrolysis. The system was further extended to site-selective cleavage of a native protein, Aβ1-42, which is closely related to the onset of Alzheimer's disease.

Full text of DOI:10.1039/c6cc10300f

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. Ni, Y. Sohma
and M. Kanai, Chem. Commun., 2017, DOI: 10.1039/C6CC10300F.
This is an Accepted Manuscript, which has been through the
Volume 52 Number
1 4 January 2016 Pages 1–216
Royal Society of Chemistry peer review process and has been
accepted for publication.
ChemComm
Accepted Manuscripts are published online shortly after
Chemical Communications
www.rsc.org/chemcomm
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1359-7345
COMMUNICATION
Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc3N@C2n (2n 68 and 80). Synthesis of the
first methanofullerene derivatives of Sc N@D5h-C80
=
3
rsc.li/chemcomm

Please do not adjust margins
ChemComm
Page 1 of 5
View Article Online
DOI: 10.1039/C6CC10300F
Chemical Communications
COMMUNICATION
Scandium(III) triflate‐promoted serine/threonine‐selective
peptide bond cleavage
Jizhi Ni,ab Youhei Sohma,*ab and Motomu Kanai*ab
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Site‐selective cleavage of peptide bonds is an important chemical chemoselective reaction at a specific functional group in a side
modification that is useful not only for the structural chain. Significant progress toward site‐selective peptide bond
determination of peptides, but also as an artificial modulator of cleavage using this type of mechanism has been reported in recent
peptide/protein function and properties. Here we report site‐ years.7 For example, diacetoxyiodobenzene‐mediated8 and metal‐
9
10
selective hydrolysis of peptide bonds at the Ser and Thr positions catalysed [Ru(III)/NaIO4 and Cu(I)/ketoABNO/O2
] side‐chain
with a high conversion yield. This chemical cleavage relies on oxidations initiated peptide bond cleavage at Asn and Ser or Thr
Sc(III)‐promoted N,O‐acyl rearrangement and subsequent residues, respectively. Selective activation of side‐chain
hydrolysis. The method is applicable to a broad scope of functionalities at Ser and Glu residues using condensation reagents
polypeptides with various functional groups, including a post‐ (e.g., N,N′‐disuccinimidyl carbonate or PyBOP), followed by
translationally modified peptide that is unsuitable for enzymatic cyclisation of the main chain amide nitrogen atom and hydrolytic
hydrolysis. The system was further extended to site‐selective cleavage were also reported.11 The functional group tolerance of
cleavage of a native protein, Aβ1‐42, which is closely related to these methods, however, remains challenging. Undesired oxidation
the onset of Alzheimer's disease.
of sensitive amino acid residues (e.g., His, Tyr, Trp, and Met) and
non‐selective activation of carboxylic acid functionalities of Asp side
chains and the C‐terminal are unavoidable. These side reactions
often complicate interpretation of the data.
Methods for site‐selective peptide bond cleavage are valuable tools
for the structural determination of proteins and peptides, chemical
biology, and therapeutics.1,2 Although several proteases (e.g.,
trypsin, chymotrypsin, and pepsin) promote the hydrolysis of
peptide bonds at specific sites with high fidelity,3,4 the scope of the
scissile bonds is still narrow, and the substrates are limited, in
principle, to genetically encoded amino acid sequences. Substrates
comprising unnatural amino acids and/or amino acids with post‐
translational modifications are generally out of the scope of
enzymatic reactions. In addition, proteases used for digestion
contaminate the protein fragments, which could interfere with
peptide mapping. Moreover, these proteases often require strict pH
and temperature control.
Hydrolysis of peptide bonds without modifying side‐chain
structures is more straightforward.12 Although intensive studies
have been devoted to metal‐catalysed, site‐selective peptide bond
cleavage, its practical use for the structural determination of
proteins remains undeveloped. For example, through selective
interactions between soft metals and soft heteroatoms (S and N
atoms) of side chains, Pd(II)13 and Pt(II)14 catalysts promote site‐
selective hydrolytic cleavage of peptide bonds proximate to the
coordinating residues, His, Cys, and Met. Another approach
providing selectivity utilises the reactivity of a side‐chain hydroxy
group at a Ser (or Thr) residue via N,O‐acyl rearrangement (Fig. 1).15
Lewis acid metal ions could promote this rearrangement and the
successive hydrolysis of the thus‐formed ester by polarising the
carbonyl group.16 Although the Zn(II) ion assists cleavage of a Xaa‐
Ser bond in dipeptides,16,17 a His residue next to the Ser residue is
required for the cleavage of longer peptides.18 In Cu(II)‐19 and Ni(II)‐
promoted20 hydrolysis, a neighbouring His is also involved in the
cleavage of Xaa‐Ser or ‐Thr
As chemical methods for site‐selective peptide/protein
cleavage, cyanogen bromide in 70% formic acid (scissile bond: Met–
Xaa), 2‐nitro‐5‐thio‐cyanobenzoic acid (scissile bond: Cys–Xaa),5 and
2‐iodosylbenzoic acid (scissile bonds: Trp–Xaa and Tyr–Xaa)6 were
used more than 30 years ago. The cleavage was triggered by a
a. Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7‐3‐1
Bunkyo‐ku, Tokyo 113‐0033 (Japan), E‐mail: ysohma@mol.f.u‐tokyo.ac.jp;
kanai@mol.f.u‐tokyo.ac.jp
b. Japan Science Technology Agency (JST), ERATO Kanai Life Science Catalysis
Project, 7‐3‐1 Bunkyo‐ku, Tokyo 113‐0033 (Japan).
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
Fig. 1 N,O‐Acyl rearrangement
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 1
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 5
COMMUNICATION
Journal Name
bonds. Other metal ions often suffer from a limited substrate scope
We then applied the optimised conditions to longer peptides
View Article Online
or lack of reliable site‐specificity [e.g., Zr(IV)21 and Mo(VI)22]. To (Table 2). Except 1b where the N‐terminal DisOpI:r1o0t.e10c3te9d/Cw6CitCh10a3C00bFz
enable artificial protease‐like catalysis, a reliable and practical group (entry 1), 100% water was used as a solvent because most of
method with high generality for site‐selective peptide/protein the peptides/proteins were dissolved in water. Pentapeptide 1c was
hydrolysis is highly demanded. We report herein Sc(III)‐mediated cleanly cleaved at the Ser site in high yield without affecting the
Ser‐ or Thr‐selective peptide cleavage, including a native protein, oxidatively sensitive Tyr side chain (97%, Table 2, entry 2 and Fig.
via N,O‐acyl rearrangement and subsequent hydrolysis. This 2a). We observed no side products derived from peptide bond
chemical and site‐selective peptide bond cleavage exhibited a wide cleavage at alternative sites. A biorelevant nonapeptide, bradykinin
substrate scope, including a chemically modified (N‐acetylated at a (1d), was also hydrolytically cleaved at the Ser site in high yield
Lys side‐chain) peptide that was not cleavable by a protease.
(85%, entry 3). HPLC analysis of the reaction profile revealed that
We aimed to develop a novel catalyst for site‐selective the reaction was clean and well‐defined (Fig. 2b); two fragments of
cleavage of peptides at Ser or Thr residues that does not require the both the N‐ and C‐terminal sides were observed after the cleavage.
assistance of neighbouring coordination residues (e.g., His and Met). An intermediate ester after N,O‐acyl rearrangement was not
Hard metals could be attractive candidate promoters of peptide observable, indicating that acyl rearrangement was the rate‐
hydrolysis, because they preferentially interact with hard bases (e.g., determining step for the overall peptide cleavage reaction. When
a carbonyl oxygen atom). We therefore screened several metal the Ser residue in 1d was replaced with a Thr residue (1e), the bond
promoters (50 mol%) in a model reaction for the cleavage of a cleavage was slower, giving both the N‐ and C‐terminal fragments in
dipeptide substrate, Cbz‐Gly‐Ser‐OMe (Table 1). The reaction was 40% yield with the same reaction time (entry 3 vs. entry 4). The
conducted in aqueous medium with 50% ethanol to solubilize the higher steric hindrance of a Thr side chain than a Ser side chain
substrate. Zn(OTf)2 promoted the reaction in low yield (4%, entry 2). probably slowed down both the N,O‐acyl rearrangement and the
This is in stark contrast to the previously reported effective cleavage following ester hydrolysis processes.25
of unprotected dipeptides, H‐Xaa‐Ser‐OH, in which
a
five‐
To further investigate the substrate scope of this method, six
membered chelate was formed by coordination of the amino group more derivatives of bradykinin were synthesised (Table 2, entries 5‐
at the N‐terminal and the carbonyl oxygen atom at the cleavage site 10). In these peptides, the Phe residue adjacent to the Ser residue
with a zinc ion.17a Poor yield was observed in the case of Cu(OTf)2 in the wild‐type bradykinin was replaced by various amino acids, i.e.,
(entry 3), while NiCl2 was inactive for cleavage (entry 4). Further Asn (1f), Met (1g), His (1h), Tyr (1i), Trp (1j), and Lys (1k). Under the
screening (entries 5‐19) revealed that a Sc(III) ion afforded the
Table 2. Sc(OTf)3 promoted Ser/Thr‐selective peptide cleavage.a
highest yield for peptide cleavage (78%‐86%, entries 17‐19). The
loading of Sc(OTf)3 could be decreased to 10 mol%, affording 80%
yield after a prolonged reaction time (entry 20). To the best of our
knowledge, this is the first example of Lewis acidic Sc(III) ion‐
catalysed peptide bond hydrolysis (catalyst turnover number = 8.0).
Entry Substrate
Yield (%)b
1c
2e
3
Cbz‐Phe‐Gly‐Ser‐OMe (1b)
90d
97
Table 1. Catalyst screening for peptide bond cleavage reactiona
H‐Tyr‐Ile‐Gly‐Ser‐Arg‐NH2 (1c)
H‐Arg‐Pro‐Pro‐Gly‐Phe‐Ser‐Pro‐Phe‐Arg‐OH (1d,
bradykinin)
85
4
5f
H‐Arg‐Pro‐Pro‐Gly‐Phe‐Thr‐Pro‐Phe‐Arg‐OH (1e)
40
95
H‐Arg‐Pro‐Pro‐Gly‐Asn‐Ser‐Pro‐Phe‐Arg‐OH (1f)
Entry MXn
Yield (%)b Entry MXn
Yield (%)b
6
H‐Arg‐Pro‐Pro‐Gly‐Met‐Ser‐Pro‐Phe‐Arg‐OH (1g)
H‐Arg‐Pro‐Pro‐Gly‐His‐Ser‐Pro‐Phe‐Arg‐OH (1h)
H‐Arg‐Pro‐Pro‐Gly‐Tyr‐Ser‐Pro‐Phe‐Arg‐OH (1i)
H‐Arg‐Pro‐Pro‐Gly‐Trp‐Ser‐Pro‐Phe‐Arg‐OH (1j)
H‐Arg‐Pro‐Pro‐Gly‐Lys‐Ser‐Pro‐Phe‐Arg‐OH (1k)
H‐Arg‐Pro‐Pro‐Gly‐Lys(Ac)‐Ser‐Pro‐Phe‐Arg‐OH (1l)
96
91
88
80
97
90
1
2
3
4
5
6
7
8
9
10
none
trace
4
11
12
13
14
15
16
17
18
19
20c
Sm(OTf)3
Eu(OTf)3
Er(OTf)3
YbCl3
19
17
16
21
17
12
78
81
86
80
7
Zn(OTf)2
Cu(OTf)2
NiCl2
8
22
9
trace
trace
trace
10
11
MgCl2
CaCl2
Lu(OTf)3
YCl3
a
Standard conditions: substrate (2 mM) and Sc(OTf)3 (200 mM) in
H2O were stirred at 80 oC for 40 h unless otherwise noted.24 b Yields
were determined based on the UV absorption intensity of the
reverse‐phase HPLC peak(s) corresponding to N‐terminal fragment
(entries 1 and 2), or N‐ and C‐terminal fragments (entries 3‐11),
detected at 254 nm (entry 1) or 230 nm (entries 2−11). c Substrate
(150 mM) and Sc(OTf)3 (75 mM) in EtOH/H2O (1:1) were stirred at
100 oC for 40 h. d Combined yield of Cbz‐Phe‐Gly‐OH (2b), Cbz‐Phe‐
Gly‐OEt (2b’), and Cbz‐Phe‐Gly‐OMe (2b’’) e A mixture of substrates
Pd(OAc)2 trace
ScCl3•H2O
Sc(O3SOC12H25
Sc(OTf)3
Sc(OTf)3
AgOTf
11
13
11
)
3
La(OTf)3
Ce(OTf)3
a
Standard reaction conditions: a solution of substrate (150 mM)
and MXn (75 mM) was stirred at 100 oC for 18 h. b Combined yields
of N‐terminal fragments (Cbz‐Gly‐OH (2a) and Cbz‐Gly‐OEt (2a’))
calculated from the absorbance at 254 nm using reverse‐phase
HPLC. c Substrate (150 mM), MXn (15 mM), t = 48 h. Sc(O3SOC12H25)3
= scandium tris(dodecyl sulfate).23
o
(0.5 mM) and Sc(OTf)3 (50 mM) was stirred in H2O at 60 C for 52
h.24 f Asn was hydrolysed to Asp during the reaction.
2 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 5
ChemComm
Please do not adjust margins
Journal Name
COMMUNICATION
although Trp (indole) underwent oxidation to some extent (entry 9,
Fig. S8).
View Article Online
DOI: 10.1039/C6CC10300F
2c
2c 352.3
[M+H]+
(a)
We next studied whether the present method is applicable to
a substrate that is resistant to enzymatic digestion. N‐Acetylation of
Lys side‐chain amino group is
a typical post‐translational
1c
modification.26 Therefore, a method for site‐selective peptide bond
cleavage applicable to substrates comprising N‐acetylated Lys will
be useful for the structural determination of post‐translationally
modified peptides and proteins. Enzymatic digestion of peptide 1l
comprising N‐acetylated Lys did not proceed efficiently using
endoproteinase Lys‐C (Fig. S11), while digestion of unacetylated 1k
proceeded smoothly using the same enzyme (Fig. S10). In contrast,
when 1l was treated with an aqueous solution of Sc(OTf)3, LC/MS
spectroscopy of the reaction mixture at t = 40 h (Fig. 2c) revealed
two products, H‐Ser‐Pro‐Phe‐Arg‐OH (3d, retention time = 13.1
min) with an m/z of 506.3 Da (calcd. [M+H]+ = 506.3) and H‐Arg‐Pro‐
Pro‐Gly‐Lys(Ac)‐OH (2l, retention time = 11.5 min) with an m/z of
596.4 Da (calcd. [M+H]+ = 596.4) (90%, Table 2, entry 11). This result
demonstrates the advantage of the developed chemical method
over enzymatic digestion in site‐selective peptide bond cleavage of
structurally modified peptides.
506.3
2d
573.3
3d
3d
(b)
[M+H]+
[M+H]+
2d
1d
3d
2l
3d
506.3
596.4
(c)
[M+H]+
[M+H]+
2l
1l
retation time (min)
Finally, to demonstrate the substrate scope of the present
method, we applied the method to cleavage of an Alzheimer's
disease‐related protein, A1‐42 (molecular weight = 4514.1 Da; Fig.
3a),27 which comprises 42 amino acid residues, including two Ser
(Ser8, Ser26). The starting material, A1‐42, was completely
consumed after 20 h [A1‐42 (0.25 mM) and Sc(OTf)3 (100 mM) in
Fig. 2 HPLC charts of the reaction mixture of 1c, 1d, and 1l
under the conditions described in Table 2.
Sc(III)‐mediated hydrolysis conditions, the Xaa‐Ser peptide bond
was cleanly and selectively cleaved in 80% to 97% yield. These
results indicate that the side‐chain functionalities of the amino acid
neighbouring the Ser residue at the N‐terminal side does not greatly
participate in the cleavage reaction. No fragment peaks were
derived from the cleavage proximate to the Met and His residues, in
contrast to the previously reported soft metal Pd(II)‐catalysed
peptide cleavage (entries 6 and 7) 13 In contrast to the previously
reported oxidative conditions,8‐10 oxidant‐sensitive functionalities in
Met (sulphide), His (imidazole), and Tyr (phenol) residues remained
intact under the present Sc(III)‐promoted conditions (entries 6‐8),
o
H2O at 80 C]. Analysis of the crude reaction mixture using MALDI‐
TOF‐MS indicated that the major cleavage products were three
fragments, A1‐7 (observed m/z = 889.7 Da), A8‐25 (observed m/z
= 2064.0 Da), and A1‐25 (observed m/z = 2935.6 Da; Fig. 3b).
Although the A26‐42 fragment was not observed by MALDI‐TOF‐
MS due to its poor ionizability, its ESI mass signal was detected by
LC‐MS (observed m/z = 1599.0 Da). Four minor fragments, Aβ1‐6
(observed m/z = 774.8 Da), A8‐23 (observed m/z = 1906.8 Da),
Fig. 3 (a) Site‐selective hydrolysis of Aβ1‐42. (b) MALDI‐MS analysis of the reaction mixture at t = 0 and 20 h.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 5
View Article Online
DOI: 10.1039/C6CC10300F
Chemical Communications
COMMUNICATION
2002, 124, 4759; (c) N. M. Milovic and N. M. Kostić, J. Am.
Chem. Soc., 2003, 125, 781.
14 (a) N. M. Milović, L. M. Dutcă and N. M. Kostić, Inorg. Chem.,
2003, 42, 4036–4045; (b) L.‐M. Dutcă, K.‐S. Ko, N. L. Pohl and
N. M. Kostić, Inorg. Chem., 2005, 44, 5141.
15 (a) J. A. Moore, J. R. Dice, E. D. Nicolaides, R. D. Westland
and E. L. Wittle, J. Am. Chem. Soc., 1954, 76, 2884; (b) H.
Hoermann, W. Grassman, E. Wuensch and H. Preller, Ber.,
1956, 89, 933; (c) S. Sakakibara, K. H. Shin and G. P. Hess, J.
Am. Chem. Soc., 1962, 84, 4921; (d) M.‐Q. Xu, M. W.
Southworth, F. B. Mersha, L. J. Hornstra and F. B. Perler, Cell,
1993, 75, 1371.
A1‐23 (observed m/z = 2779.1 Da), and A1‐22 (observed m/z =
2663.8 Da), were also identified to be derived from cleavage at the
Asp7 and Asp23 residues. This suggests that a hard carboxylate
functional group also directs the hard metal ion Sc(III) for cleavage
of the peptide bonds at Asp residues. Again, no hydrolysis was
detected at the His and Met sites. The predominant production of
the three expected fragments (A1‐7, A8‐25, and A26‐42) clearly
demonstrated that the Ser‐selectivity of the present method is
reliable when using complex peptide/protein substrates.
In conclusion, we developed the first Sc(III)‐promoted site‐
selective hydrolysis of peptide/protein chains at the Ser and Thr
positions. Side‐chain functionalities were little affected during the
hydrolysis. Penta‐ to nona‐peptide substrates, including post‐
translationally modified peptides (e.g., N‐acetylated at a Lys residue
side‐chain), were site‐selectively cleaved in high yields. The reaction
conditions were also successfully applied to site‐selective cleavage
of a native protein, A1‐42, which is related to Alzheimer's disease.
Due to its broad substrate scope, this method will be a useful
complement to enzymatic degradation of peptides.
16 M. Yashiro, A. Yamamura, T. Takarada and M. Komiyama, J.
Inorg. Biochem. 1997, 67, 225.
17 (a) M. Yashiro, Y. Sonobe, A. Yamamura, T. Takarada, M.
Komiyama and Y. Fuji, Org. Biomol. Chem., 2003, 1, 629; (b) Y.
Kita, Y. Nishii, T. Higuchi and K. Mashima, Angew. Chem. Int.
Ed., 2012, 51, 5723.
18 B. Lyons, A. H. Kwan and R. J. W. Truscott, Aging Cell, 2016,
15, 237.
19 (a) G. Allen and R. O. Campbell, Int. J. Peptide. Protein. Res.,
1996, 48, 265; (b) M. Mylonas, J. C. Plakatouras and N.
Hadjiliadis, Dalton Trans., 2004, 4152; (c) M. Mylonas, A.
Krężel, J. C. Plakatouras, N. Hadjiliadis and W. Bal, J. Mol. Liq.,
2005, 118, 119.
This work is supported by JST‐ERATO KANAI Life Science
Catalysis Project.
20 (a) W. Bal, H. Kozlowski and K. S. Kasprzak, J. Inorg. Biochem.,
2000, 79, 213; (b) W. Bal, J. Lukszo, K. Bialkowski and K. S.
Kasprzak, Chem. Res. Toxicol., 1998, 11, 1014; (c) W. Bal, R.
Liang, J. Lukszo, S.‐H. Lee, M. Dizdaroglu and K. S. Kasprzak,
Chem. Res. Toxicol., 2000, 13, 616; (d) A. Kreężel, E. Kopera,
A. M. Protas, J. Poznański, A. Wysłouch‐Cieszyńska and W.
Bal, J. Am. Chem. Soc., 2010, 132, 3355.
21 (a) M. Kassai, R. G. Ravi, S. J. Shealy and K. B. Grant, Inorg.
Chem., 2004, 43, 6130; (b) M. Kassai and K. B. Grant, Inorg.
Chem. Commun., 2008, 11, 521; (c) S. S. Cepeda and K. B.
Grant, New J. Chem., 2008, 32, 388.
Notes and references
1
J. Thorner, S. D. Emr and J. Abelson, Eds. Applications of
chimeric genes and hybrid proteins, Part A: Gene expression
and protein purification. Methods Engymol. 2000, 326
.
2
a) J. J. Thomas, R. Bakhtiar and G. Siuzdak, Acc. Chem. Res.,
2000, 33, 179; b) T. Durek and C. F. W. Becker, Biomol. Eng.,
2005, 22, 153; c) T. W. Muir, Annu. Rev. Biochem., 2003. 72
,
249.
22 (a) A, Erxleben, Inorg. Chem., 2005, 44, 1082; (b) S. Yenjai, P.
Malaikaew, T. Liwporncharoenvong and A. Buranaprapuk,
Biochem. Biophys. Res. Commun., 2012, 419, 126; (c) B.
Jityuti, A. Buranaprapuk and T. Liwporncharoenvong, Inorg.
Chem. Commun., 2015, 55, 129.
23 K. Manabe, Y. Mori, T. Wakabayashi, S. Nagayama and S.
Kobayashi, J. Am. Chem. Soc., 2000, 122, 7202.
24 Preparing the solution of 1c‐1l at the concentration higher
3
4
5
6
J. Arnau, C. Lauritzen, G. E. Petersen and J. Pedersen, Protein
Expr. Purif., 2006, 48, 1.
W.S. Hancock (ed), New Methods in Peptide Mapping for the
Characterization of Proteins. CRC Press, Boca Raton, FL, 1996.
(a) E. Gross and B. Witkop, J. Biol. Chem., 1962, 237, 1856;
(b) R. Kaiser and L. Metzka, Anal. Biochem., 1999, 266, 1.
W. C. Mahoney, P. K. Smith and M. A. Hermodson,
Biochemistry, 1981, 20, 443.
than 0.5‐2 mM was difficult due to the solubility limits (vs. 1a
and 1b). The concentration of Sc(III) ion (> 50 mM) was
important for complete substrate consumption within the
indicated time periods. Accordingly, the concentration of
Sc(III) ion exceeded that of the substrate.
7
8
J. Ni and M, Kanai, Top. Curr. Chem., 2016, 372, 103.
K. Tanabe, A. Taniguchi, T. Matsumoto, K. Oisaki, Y. Sohma
and M. Kanai, Chem. Sci., 2014, 5, 2747.
9
(a) D. Ranganathan and S. Saini, J. Am. Chem. Soc., 1991, 113
1042; (b) D. Ranganathan, N. K. Vaish and K. Shah, J. Am.
Chem. Soc., 1994, 116, 6545.
,
25 A peak (11% yield) giving the same mass value as 1e was
observed at earlier retention time in HPLC analysis. Possibly
it was the ester intermediate after N,O‐acyl rearrangement.
See Fig. S3 for detail.
10 Y. Seki, K. Tanabe, D. Sasaki, Y. Sohma, K. Oisaki and M. Kanai,
Angew. Chem. Int. Ed., 2014, 53, 6501.
11 (a) J. M. Nalbone, N. Lahankar, L. Buissereth and M. Raj. Org.
Lett., 2016, 18, 1186; (b) H. E. Elashal and M. Raj, Chem.
Commun., 2016, 52, 6304.
12 T. Zhang, M. Ozbil, A. Barman, T. J. Paul, R. P. Bora and R.
Prabhakar, Acc. Chem. Res., 2015, 48, 192.
13 (a) N. M. Milovic and N. M. Kostić, Inorg. Chem., 2002, 41
26 E. Verdin and M. Ott. Nat. Rev. Mol. Cell Biol., 2015, 16, 258.
27 D. M. Holtzman, J. C. Morris, A. M. Goate, Sci. Transl. Med.
2011, 3, 77sr1.
,
7053; (b) N. M. Milovic and N. M. Kostić, J. Am. Chem. Soc.,
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 4
Please do not adjust margins

Page 5 of 5
ChemComm
Please do not adjust margins
Journal Name
Table of Contents
COMMUNICATION
View Article Online
DOI: 10.1039/C6CC10300F
O
H
HO
R'
O
O
Peptide A
N
H
H
OH
Sc(OTf)3
H2O
Peptide A
N
N
Peptide B
N
O
R
H
O
R
+
HO
R'
O
13 examples
H
N
High side-chain FG tolerance
Post-translationally modified substrate
Native protein (A1-42
Peptide B
H2N
)
(R' = H/Me)
Site‐selective hydrolysis of peptide bonds at Ser and Thr
positions was promoted by Scandium(III) triflate with a high
conversion yield.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 5
Please do not adjust margins