Highly Efficient and Stable Strain-Release Radioiodination for Thiol Chemoselective Bioconjugation

Article abstract of DOI:10.1021/acs.bioconjchem.7b00790

We report a novel thiol selective radioiodination method based on strain-release reaction. A new heterobifunctional radioiodination agent which has very good thiol selectivity and excellent stability with high radiolabeling yield was synthesized, characterized, and applied successfully for thiol-contained peptide labeling.

Full text of DOI:10.1021/acs.bioconjchem.7b00790

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Article
Highly efficient and stable strain-release
radioiodination for thiol chemoselective bioconjugation
Pu Zhang, Rongqiang Zhuang, Xiangyu Wang, Huanhuan Liu,
Jindian Li, Xinhui Su, Xiaoyuan Chen, and Xianzhong Zhang
Bioconjugate Chem., Just Accepted Manuscript • DOI: 10.1021/acs.bioconjchem.7b00790 • Publication Date (Web): 27 Jan 2018
Downloaded from http://pubs.acs.org on January 29, 2018
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Bioconjugate Chemistry
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Highly Efficient and Stable Strain-Release Radioiodination for Thiol
Chemoselective Bioconjugation
Pu Zhang,† Rongqiang Zhuang,† Xiangyu Wang,† Huanhuan Liu,† Jindian Li,† Xinhui Su,‡ Xiaoyuan
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Chen,§ and Xianzhong Zhang*†
†Center for Molecular Imaging and Translational Medicine, State Key Laboratory of Molecular Vaccinology and Molecular
Diagnostics, School of Public Health, Xiamen University, Xiamen 361102, China
‡Zhongshan Hospital Affiliated of Xiamen University, Xiamen 361004, China
§Laboratory of Molecular Imaging and Nanomedicine (LOMIN), National Institute of Biomedical Imaging and Bioengineerꢀ
ing (NIBIB), National Institutes of Health (USA), Bethesda, Maryland 20892, United States
ABSTRACT: We report a novel thiol selective radioiodination method based on strainꢀrelease reaction. A new heterobifunctional
radioiodination agent which has very good thiol selectivity and excellent stability with high radiolabeling yield was synthesized,
characterized and applied successfully for thiolꢀcontained peptide labeling.
INTRODUCTION
tide, protein and antibody, while it is a special challenge for
traditional radioiodination because of the abundant functional
groups in these biomolecules.
Radioactive iodine isotopes (123I, 124I, 125I and 131I) labeled
radiopharmaceuticals are widely used in nuclear medicine for
disease diagnosis and therapy.1ꢀ4 Among these radiopharmaꢀ
ceuticals, radiolabeled peptides have always played an imꢀ
portant role in both research and clinical application.5 Methods
used for those radiopharmaceuticals direct radioiodination are
usually based on electrophilic substitution reaction with amino
acids containing aromatic substituents like tyrosine, histidine
and tryptophane or just phenol structure.6 Due to the electronꢀ
donating substituent hydroxyl, tyrosine becomes the main
peptide and protein radioiodination site, which can be radioioꢀ
dinated by ChloramineꢀT,7 iodogen,8 iodobead9 methods. Altꢀ
hough these methods are most widely used in radioiodination
procedure up to now for their efficiency and ease of handling,
the using of oxidation agents as well as the reducing agents to
stop the labeling process may cause undesirable side reactions
of the biomolecules.10 To avoid the oxidizing conditions, twoꢀ
step labeling procedure using preꢀradioiodinated heterobifuncꢀ
tional agents such as Bolton and Hunter agent11 and SIB12 via
amidation reaction with lysine residue is used, however the
hydrolysis of the succinimidyl ester group especially at the
optimum labeling condition which is often alkaline is also one
disadvantage that may decrease the radiochemical yield and
purity. Besides these problems, no matter the direct radioioꢀ
dination methods or using the Bolton and Hunter agent, volaꢀ
tile molecule iodine will be generated during the labeling proꢀ
cess which limits the operation to avoid the airborne release.
Except for SIB, the in vivo deiodination of radioiodinated
phenol structure which may result in low targetꢀtoꢀbackground
ratio of the images and increase the radiation dose to nonꢀ
target tissues is another inherent drawback of these traditional
radioiodination labeling methods.13ꢀ14 Moreover, the chemoseꢀ
lective radiolabeling is also very important especially for pepꢀ
Thiol alkylation is also a powerful method for peptide, protein
and nanoꢀbiomaterials modification.15ꢀ18 As the most widely
used alkylating agents which based on Michael addition, maꢀ
leimides have always played an important role in both reꢀ
search and clinical analysis, of which radioiodinated maleiꢀ
mide derivatives were also studied for antibody labeling.19ꢀ22
Although useful, limitations of these agents such as the disrupꢀ
tive cleavage because of undergoing thiol exchange reaction
with free cysteine and glutathione residues and the ring openꢀ
ing of the succinimide linkage decrease the stability in vivo.23
Considering these reasons, the development of one new mild,
efficient, chemoselective and stable in vitro and in vivo radioꢀ
iodination method is a subject of much current interest.
Small strained ring systems such as bicyclo[1.1.1]pentanes,
azetidines or cyclobutanes are increasingly valued for their
chemical application.24 Recently, Phil Baran and coꢀworkers
reported one new mild and simple operation synthesis method
for strainꢀrelease amination,25ꢀ27 besides these, the remarkable
chemoselectivity of thiol and the excellent stability exhibited
by strainꢀrelease agents motivated us to develop a new kind
heterobifunctional radioiodination agent for thiolꢀcontained
peptide labeling.
To overcome the limitations of conventional radioiodination
methods, we recently developed a highly efficient copperꢀ
mediated radioiodination approach using aryl boronic acids
which is technically simple, mild and no volatile molecular
iodine generated.28 For these reasons, herein we report a novel
stable and thiol chemoselective radioiodination method using
a new developed heterobifunctional agent based on strainꢀ
release reaction.
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Scheme 1. Thiol selectively heterobifunctional radioiodination agents: maleimideꢀbased radioiodination agents (A) and bicyꢀ
clo[1.1.0]butane
based
strainꢀrelease
radioiodination
agent
(B).
bling argon through the solution to exclude oxygen. At 25 °C,
this approach gave high radiochemistry yield (91%) taking 3 h
and at 60 °C it just took 30 min to obtain the excellent yield
(95%) which are both acceptable for radioiodine labeling. The
only one new radioactive product testified by high perforꢀ
mance liquid chromatography (radioꢀHPLC) indicated the
highly chemoselective of thiol (Figure 1b). The excellent staꢀ
bility of 131IꢀS8 in vitro was confirmed by radioꢀHPLC analyꢀ
sis after incubation in the mixed solvents for 24 h at room
temperature (Figure 1c).
RESULTS AND DISCUSSION
Synthesis of the heterobifunctional agent 131I-S8. 1ꢀ((4ꢀ
bromophenyl)sulfonyl)bicyclo[1.1.0]butane (S6) was syntheꢀ
sized from 4ꢀbromobenzeneꢀ1ꢀsulfonyl chloride according to
the synthesis route reported by Phil Baran and coꢀworkers.25
Then
the
product
(4ꢀ(bicyclo[1.1.0]butanꢀ1ꢀ
ylsulfonyl)phenyl)ꢀboronic acid (S7) which contains phenylꢀ
boronic acid structure for radioiodine labeling was obtained by
photoꢀinduced reaction under ultraviolet irradiation.29 Based
on the previous results from our group,28 the radioiodination
conditions of S7 were as follows: substrate S7 (2 ꢁmol), Cu2O
(0.4 ꢁmol), and 1,10ꢀphenanthroline (0.8 ꢁmol) dissolved in
acetonitrile (50 ꢁL), [131I]NaI (about 37 MBq, 5ꢀ10 ꢁL in waꢀ
ter), reacted for 1 h at 25 °C to give the desired new heterobiꢀ
functional agent 131IꢀS8.
O
S
O
S
B2(OH)4
O
O
HO
UV, 254 nm
Br
B
S6
S7
OH
O
S
Na131
Cu2O/1,10-phenanthroline
I
O
131I
131I-S8
Figure 1. a HPLC analysis of 131I-S8 and non-radioactive
reference with radiometric and UV detection; b HPLC
analysis of 131I-CAQK; c Stability analysis of 131I-S8 after
incubation in the mixture solvent of DMF (40 µL), K2CO3
in water (0.2 M, 20 µL) and phosphate buffer (0.2 M, pH
8.0, 90 µl) for 24 h; d HPLC analysis of 131I-c(RGDyC).
Scheme 2. Synthesis route of 131I-S8.
Chemoselective radiolabeling of peptide. At the start invesꢀ
tigation of thiol radioiodine labeling, the short peptide (seꢀ
quence CAQK) which can target the proteoglycan complex
upregulated in acute brain injuries30 was selected as the model
substrate to verify the feasibility and the chemoselectivity of
this approach for the reason that it has both thiol and amino
group. Considering the water solubility of peptide and the
lipophilicity of 131IꢀS8, mixed solvents N, Nꢀ
dimethylformamide (DMF) and phosphate buffer were chosen
as solvents to develop this labeling method. Strainꢀrelease
reaction with thiol do not proceed under acidic condition has
been testified according to the published report. To make sure
the pH of the reaction mixture was alkaline, phosphate buffer
(pH 8.0) and K2CO3 were employed allowing the deprotonaꢀ
tion of the cysteine thiol of CAQK. To keep the thiol in reꢀ
duced form, the solvents were degassed prior to use by bubꢀ
Finally, the optimized labeling conditions of peptide are: 2
ꢁmol substrate in 90 ꢁL phosphate buffer (0.2 M, pH 8.0), 20
ꢁL K2CO3 in water (0.2 M), and 40 ꢁL 131IꢀS8 in DMF were
mixed together and reacted for 30 min at 60 °C.
Substrate scope and further thiol chemoselectivity study.
To further investigate the substrate scope and the thiol selecꢀ
tivity of this method, several amino acids with or without thiol
served as substrates and the labeling results were shown in
Table 1, when mixed glycine and NꢀAcetylꢀcysteine together
with the molar ratio 1:1, there was still no reaction with glyꢀ
2
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Bioconjugate Chemistry
cine which confirmed the excellent chemoselectivity of thiol
again.
this novel heterobifunctional agent may make this method be a
universal procedure for peptide, protein antibody and nanoꢀ
biomaterials radioiodine labeling.
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Table 1. Reactions of thiol-contained substrates with 131I-
EXPERIMENTAL PROCEDURES
S8. [a
]
Materials and general methods. Commercially available
chemicals were obtained from commercial suppliers (Energy
Chemical and Alfa Aesar) and used as received without furꢀ
ther purification. Silica gel GF254 aluminum plates used for
thin layer chromatography (TLC) analysis were purchased
from Energy Chemical and preparation silica gel plates used
for product purification were purchased from Sinopharm
Chemical Reagent Beijing Co., Ltd. TLC plates were visualꢀ
ized by exposure to short wave ultraviolet light (254 nm,
365nm) and/or iodine. RadioꢀTLC analysis was performed on
BioScan MiniꢀScan radioꢀTLC Strip Scanner. HPLC analysis
was performed on Thermo Fisher Dionex UltiMate 3000 using
the Nucleosil C18 (250 × 4 mm, 10 ꢁm, 100 Å) column and
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Entry
Substrate
RCY[b]
100
88
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L-Cysteine
L-Cysteine methyl ester hydrochloride
N-Acetyl-cysteine
CAQK
100
95
1
chromatograms were collected at 254 nm wavelength. H and
13C NMR spectra were recorded on Bruker AVANCE III 600
MHz and Bruker AVANCE II 400 MHz spectrometer. Mass
spectra were recorded on Waters Xevo G2ꢀXS QTof mass
spectrometer. SPECT/CT imaging was performed using naꢀ
noScan SC (Mediso Medical Imaging System) equipped with
pinhole collimator under standard animal scan procedure. All
animal experimental protocols were carried out in accordance
with the relevant guidelines of Xiamen University.
c(RGDyC)
99
N-Acetyl-cysteine, glycine
100
[a] All reactions were performed using substrate 2 µmol. [b] RCY determined
by radio-HPLC.
Procedure
for
the
preparation
of
S7.
4ꢀ
Bromobenzenesulfonyl chloride (10.0 g, 39.0 mmol) was addꢀ
ed to a solution of Na2SO3 (9.8 g, 2.0 equiv) and NaHCO3 (6.5
g, 2.0 equiv) in H2O (50 mL) portionwise at room temperature
and then reacted at 80 °C for 6 h. After cooled to room temꢀ
perature, the mixture was extracted with EtOH (3 × 50 mL)
and the combined solution was evaporated, then dissolved in
DMF (50 mL). Added 4ꢀbromoꢀ1ꢀbutene (6.3 g, 1.2 equiv)
and reacted at 50 °C for 2 h. The reaction mixture was cooled
to room temperature, diluted with EtOAc (50 mL), washed
with brine (3 × 25 mL), dried with Na2SO4, concentrated unꢀ
der reduced pressure, and purified by silica gel flash chromaꢀ
tography with petroleum ether/ethyl acetate (8:1) to give S2
Figure 2. SPECT imaging of U87MG tumor bearing mice
with 125I-c(RGDyC) obtained from 125I-S8.
Stability study and SPECT imaging. To demonstrate the
stability and the targeting ability of the peptide labeled with
radioiodine using this method, cyclic peptide c(RGDyC)
served as substrate and was labeled with 131I and 125I respecꢀ
tively using this strainꢀrelease radioiodination approach. The
specific activity of the radioiodinated c(RGDyC) was calculatꢀ
ed as 1.13×1012 Bq/g based on the standard curve (Figure S8).
Good stability in vitro was verified by HPLC analysis after
incubated in fetal bovine serum (FBS) for 96 h (Figure S6). Ex
vivo biodistribution study in normal mice was performed and
compared with the conventional Iodogen method (Table S2),
the uptakes of thyroid and stomach indicated that the radioioꢀ
dinated peptide c(RGDyC) prepared by using this strainꢀ
release method had obviously less deiodination in vivo than
that of conventional Iodogen method. Single photon emission
computed tomography (SPECT) imaging of tumorꢀbearing
mice with 125Iꢀc(RGDyC) showed moderate tumor uptake
(Figure 2) and very low thyroid accumulation at 4 h after inꢀ
jection (Figure S9), which confirmed the targeting ability and
excellent in vivo stability of this tracer.
1
(3.9 g, 36%). H NMR (600 MHz, CDCl3): δ 7.80 ꢀ 7.78 (m,
2H), 7.74 ꢀ 7.72 (m, 2H), 5.73 (ddt, J = 16.8 Hz, 10.2 Hz, 6.6
Hz, 1H), 5.09 ꢀ 5.06 (m, 2H), 3.18 ꢀ 3.16 (m, 2H), 2.49 ꢀ 2.45
(m, 2H); 13C NMR (600 MHz, CDCl3): δ 138.00, 133.50,
132.68 (2C), 129.72 (2C), 129.17, 117.39, 55.41, 26.83; m/z
(ESI): 296.99 and 298.99 ([M+Na]+, C10H11BrNaO2S+, reꢀ
quires 296.96 and 298.95).
S2 (3.8 g, 13.8 mmol) was dissolved in CH2Cl2 (40 mL) and
mCPBA (5.6 g, 85%) was added into the solution in portions
at 0 °C. The mixture was stirred at room temperature until
TLC analysis indicated complete consumption of S2. At the
end of the reaction, the mixture was filtered using funnel, and
the organic phase was first washed with aqueous Na2SO3 (1M,
2 × 30 mL), then washed with NaHCO3 (sat., aq., 2 × 30 mL)
and finally washed with brine (2 × 20 mL), dried with Na2SO4,
filtered, and concentrated under reduced pressure, purified by
silica gel flash chromatography with petroleum ether/ethyl
1
acetate (2:1) to give S3 (3.5 g, 87%). H NMR (600 MHz,
In conclusion, we have developed a new mild and efficient
thiol selective radioiodination method using strainꢀrelease
reaction. The excellent stability and thiol chemoselectivity of
CDCl3): δ 7.79 ꢀ 7.77 (m, 2H), 7.74 ꢀ 7.72 (m, 2H), 3.22 (m,
2H), 3.01 (dtd, J = 10.8 Hz, 3.0 Hz, 1.2 Hz, 1H), 2.78 (dd, J =
4.2 Hz, 4.2 Hz, 1H), 2.50 (dd, J = 4.5 Hz, 3.0 Hz, 1H), 2.21 ꢀ
3
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2.15 (m, 1H), 1.83 ꢀ 1.77 (m, 1H); 13C NMR (600 MHz,
CDCl3): δ 137.83, 132.76 (2C), 129.62 (2C), 129.32, 52.77,
49.97, 47.09, 25.83; m/z (ESI): 312.99 and 314.99 ([M+Na]+,
C10H11BrNaO3S+, requires 312.95 and 314.95).
Page 4 of 7
7.82 (m, 4H), 2.65 ꢀ 2.60 (m, 1H), 2.46 ꢀ 2.43 (m, 2H), 1.43 ꢀ
1.40 (m, 2H); 13C NMR (600 MHz, CD3OD): δ 145.01, 136.55
(2C), 128.00 (2C), 39.46, 24.69 (2C), 14.24; m/z (ESI): 238.17
and 239.17 ([M+H]+, C10H12BO4S+, requires 238.06 and
239.05).
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Epoxide S3 (1.2 g, 4.0 mmol) was dissolved in THF (20
mL) and nꢀBuLi (2.5 M in hexane, 1.7 mL, 1.06 equiv) was
added dropwise at 0 °C. After the addition was complete, the
mixture was stirred a further 5 min before being quenched
with sat. aq. NH4Cl. The organic layer was separated and the
aqueous layer was extracted with EtOAc twice. The combined
organic layers were dried with Na2SO4, concentrated under
reduced pressure, and purified by silica gel flash chromatogꢀ
raphy with petroleum ether/ethyl acetate (2:1) to give S4 (0.9
Synthesis of stable reference compound (127I-S8). NaI (1.3
mg, 8.4 ꢁmol) was added to a solution of S7 (1.0 mg, 4.2
ꢁmol), Cu2O (0.6 mg, 4.2 ꢁmol), 1,10ꢀphenanthroline (1.7 mg,
8.4 ꢁmol) in 50 ꢁL acetonitrile, the mixture was stirred for 3 h,
and then the crude product was purified using HPLC. m/z
(ESI): 342.98 ([M+Na]+, C10H9INaO2S+, requires 342.93).
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Radioiodination of S7 to synthesize 131I-S8 or 125I-S8. Addꢀ
ed precursor S7 (2 ꢁmol) into one 1.5 mL reaction vial, 50 ꢁL
solution of Cu2O/1,10ꢀphenanthroline in acetonitrile which
contained Cu2O (0.4 ꢁmol) and 1,10ꢀphenanthroline (0.8
1
g, 75%). H NMR (600 MHz, CDCl3): δ 7.77 ꢀ 7.76 (m, 2H),
7.71 ꢀ 7.69 (m, 2H), 3.74 (dd, J = 11.4 Hz, 4.8 Hz, 1H), 3.51
(dd, J = 11.4 Hz, 6.0 Hz, 1H), 2.46 (dt, J = 8.4 Hz, 4.8 Hz,
1H), 2.07 ꢀ 2.02 (m, 1H), 1.74 (s, 1H), 1.47 (dt, J = 9.6 Hz, 4.8
Hz, 1H), 1.12 ꢀ 1.09 (m, 1H); 13C NMR (600 MHz, CDCl3): δ
139.50, 132.60 (2C), 129.10 (2C), 128.72, 61.81, 36.80, 21.65,
10.07; m/z (ESI): 313.00 and 315.00 ([M+Na]+,
C10H11BrNaO3S+, requires 312.95 and 314.95).
ꢁmol) was then added into the vial, after that, Na131I or Na125
I
(about 37 MBq) in 5 ꢀ 10 ꢁL water was added into the mixture
and reacted for one hour at 25 °C. To separate the 131IꢀS8 or
125IꢀS8 from the precursor S7, preparation silica gel plate was
used with petroleum ether/ethyl acetate (4:1), 127IꢀS8 was used
as standard substance. The radioiodination product 131IꢀS8 or
125IꢀS8 was eluted from the silica gel using petroleum
ether/ethyl acetate (1:1), and then was blown to dryness under
a stream of argon.
S4 (5.1 g, 17.6 mmol) was dissolved in anhydrous CH2Cl2
(15 mL), anhydrous Et3N (2.8 mL, 1.1 equiv) and methanesulꢀ
fonyl chloride (2.8 mL, 1.1 equiv) was added successively at
room temperature. After stirring for 2 h, the reaction mixture
was washed with brine twice, dried with Na2SO4, concentrated
under reduced pressure, and purified by silica gel flash chroꢀ
matography with petroleum ether/ethyl acetate (1:1) to give S5
Radioiodination of peptide and amino acids. Peptide or
amino acid (2 ꢁmol) was dissolved in phosphate buffer (90
ꢁL, 0.2 M, pH 8.0) which was degassed prior to use by bubꢀ
bling argon through the solution to exclude oxygen, K2CO3 in
water (20 ꢁL, 0.2 M) was added into the peptide solution, then
added the mixture into the 131IꢀS8 or 125IꢀS8 in DMF (40 ꢁL)
which was degassed prior to use by bubbling argon through
the solution to exclude oxygen and reacted at 60 °C for 30
min, the radioiodination products were analyzed and purified
by radioꢀHPLC.
1
(4.5 g, 69%). H NMR (600 MHz, CDCl3): δ 7.79 ꢀ 7.77 (m,
2H), 7.75 ꢀ 7.73 (m, 2H), 4.33 (dd, J = 11.4 Hz, 5.4 Hz, 1H),
3.99 (dd, J = 11.4 Hz, 7.2 Hz, 1H), 2.98 (s, 3H), 2.60 (dt, J =
8.4 Hz, 4.8 Hz, 1H), 2.21 ꢀ 2.15 (m, 1H), 1.72 (s, 1H), 1.66
(dt, J = 9.6 Hz, 5.4 Hz, 1H), 1.22 ꢀ 1.19 (m, 1H); 13C NMR
(600 MHz, CDCl3): δ 138.92, 132.72 (2C), 129.28 (2C),
129.08, 68.72, 38.07, 37.82, 18.71, 10.90; m/z (ESI): 390.86
+
and 392.86 ([M+Na]+, C11H13BrNaO5S2 , requires 390.93 and
Biodistribution study. Biodistribution of radioiodinated
c(RGDyC) were performed in normal ICR mice. The tracers
were obtained by using this strainꢀrelease method and Iodogen
method (see Supporting Information) respectively and purified
by HPLC. About 0.185 MBq 131Iꢀc(RGDyC) (in 100 ꢁL saline
solution) was injected through tail vein. At 30 min, 90 min,
and 240 min after injection, mice (n=5 at each time point)
were sacrificed, the tissues and organs of interest were collectꢀ
ed, wetꢀweighted and counted in a γꢀcounter. The percentage
injected dose (%ID/g and %ID) were calculated accordingly
and expressed as mean ± standard deviation (n=5).
SPECT imaging. 125Iꢀc(RGDyC) was dissolved in phosphate
buffer (0.05 M, pH 7.4) and passed through 0.22ꢀꢁm Millipore
filter. SPECT/CT imaging of male BALB/c nude mice bearing
U87MG tumor were performed at 30 min, 1 h and 2 h after
intravenously injected about 18.5 MBq 125Iꢀc(RGDyC). The
SPECT imaging parameter was 250 sec/frame. All images
were performed in the same manner and reconstructed, proꢀ
cessed and analyzed with Nucline software (Mediso Medical
Imaging System).
392.93).
S5 (1.0 g, 2.7 mmol) was dissolved in THF (20 mL) and nꢀ
BuLi (2.5 M in hexane, 1.0 mL, 0.95 equiv) was added dropꢀ
wise at 0 °C. After the addition was complete, the mixture was
stirred a further 5 min before being quenched with sat. aq.
NH4Cl. The organic layer was separated and the aqueous layer
was extracted with EtOAc twice. The combined organic layers
were dried with Na2SO4, concentrated under reduced pressure,
and purified by silica gel flash chromatography with petroleꢀ
1
um ether/ethyl acetate (8:1) to give S6 (0.3 g, 40%). H NMR
(600 MHz, CDCl3): δ 7.81 ꢀ 7.80 (m, 2H), 7.71 ꢀ 7.69 (m, 2H),
2.62 ꢀ 2.60 (m, 1H), 2.53 ꢀ 2.51 (m, 1H), 1.41 ꢀ 1.39 (m, 1H);
13C NMR (600 MHz, CDCl3): δ 141.01, 132.45 (2C), 128.70
(2C), 128.12, 38.40, 22.87 (2C), 13.04; m/z (ESI): 294.95 and
296.95 ([M+Na]+, C10H9BrNaO2S+, requires 294.94 and
296.94).
S6 (54.6 mg, 0.2 mmol) and B2(OH)4 (89.6 mg, 1.0 mmol)
were dissolved in anhydrous CH3OH (2.0 mL), then the mixꢀ
ture was irradiated under UV light for 2 h in a waterꢀcooled
quartz reactor. The crude product was purified using HPLC to
give S7 (10 mg, 21%). 1H NMR (600 MHz, CD3OD): δ 7.98 ꢀ
ASSOCIATED CONTENT
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Bioconjugate Chemistry
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Supporting Information. This material is available free of
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optimization condition, cell culture and animal model, HPLC
analysis method, NMR and mass spectra.
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AUTHOR INFORMATION
Corresponding Author
* Eꢀmail: zhangxzh@xmu.edu.cn
ORCID
Xianzhong Zhang: 0000ꢀ0002ꢀ1001ꢀ1884
Xiaoyuan Chen: 0000ꢀ0002ꢀ9622ꢀ0870
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ACKNOWLEDGMENT
This research was supported by the National Key Basic Research
Program of China (2014CB744503), the National Natural Science
Foundation of China (81471707, 21271030), and the Scientific
Research Foundation of State Key Laboratory of Molecular Vacꢀ
cinology and Molecular Diagnostics (2016ZY002).
NOTES
The authors declare no competing financial interest.
ABBREVIATION
SIB, succinimidyl pꢀiodobenzoate; HPLC, high performance liqꢀ
uid chromatography; CAQK, cysteineꢀalanineꢀglutamineꢀlysine;
RGDyC, arginineꢀglycineꢀ(aspartic acid)ꢀ(Dꢀtyrosine)ꢀcysteine;
DMF, N,Nꢀdimethylformamide; SPECT, single photon emission
computed tomography; RCY, radiochemical yield; FBS, fetal
bovine serum; TLC, thin layer chromatography; NMR, nuclear
magnetic resonance; ESI, electrospray ionization; mCPBA, mꢀ
chloroperoxybenzoic acid; THF, tetrahydrofuran; %ID, percentꢀ
age injected dose per organ; %ID/g, percentage injected dose per
gram
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tions of nanomaterials for sensing, imaging, drug delivery and theraꢀ
py. Chem Soc Rev 43, 744ꢀ764.
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Highly Efficient and Stable Strain-
Release Radioiodination for Thiol
Chemoselective Bioconjugation
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A novel heterobifunctional agent for thiol selective radioiodination based on strainꢀrelease
reaction was developed and demonstrated in thiolꢀcontained amino acid and peptide radioꢀ
iodine labelling successfully.
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