HBED-NN: A Bifunctional Chelator for Constructing Radiopharmaceuticals

Article abstract of DOI:10.1021/acs.joc.9b00832

Radiometal-based radiopharmaceuticals bearing bifunctional HBED chelators are powerful radiotracers for cancer diagnosis and therapy. Bifunctional HBED chelators make strong complexes with trivalent gallium and are able to bind to bioactive molecules thro

Full text of DOI:10.1021/acs.joc.9b00832

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HBED-NN: A Bifunctional Chelator for Constructing Radiopharmaceuticals
Ata Makarem, Karel D. Klika, German Litau, Yvonne Remde, and Klaus Kopka
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00832 • Publication Date (Web): 08 May 2019
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The Journal of Organic Chemistry
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HBED-NN: A Bifunctional Chelator for Constructing
Radiopharmaceuticals
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,†
‡
†
†
†,§
Ata Makarem,* Karel D. Klika, German Litau, Yvonne Remde, and Klaus Kopka
†German Cancer Research Center (DKFZ), Division of Radiopharmaceutical Chemistry, INF 223, D-69120 Heidelberg,
Germany
‡
German Cancer Research Center (DKFZ), Molecular Structure Analysis, INF 280, D-69120 Heidelberg, Germany
§
German Cancer Consortium (DKTK), Heidelberg, Germany
ABSTRACT: Radiometal-based radiopharmaceuticals bearing bifunctional HBED chelators are powerful radiotracers for cancer
diagnosis and therapy. Bifunctional HBED chelators make strong complexes with trivalent gallium and are able to bind to bioactive
molecules through covalent bonds. However, thus far no bifunctional HBED chelator capable of direct conjugation via click chemistry
has been reported. We hereby introduce HBED-NN as a structurally new bifunctional HBED chelator for direct click coupling. We
also investigated the complex chemistry of [Ga-(HBED-NN)] for potential use in gallium-based radiopharmaceuticals.
chemoselective
transformation.28,29
Furthermore,
the
Radiopharmaceuticals are important drugs for tumor diagnosis
corresponding aromatic 1,2,3-triazole is much stronger than
ordinary covalent linkages such as amide, ester, thioether, etc.
In recent years, new and useful bioactive molecules bearing
alkyne groups with various structures and different targeting
properties have been introduced,
be used in combination with HBED chelator types for the
development of radiopharmaceuticals. This is especially
attractive for the synthesis of precursors for radiolabeling
conjugated with macromolecules such as proteins. However,
to the best of our knowledge, there are no reported examples of
bifunctional HBED chelators which accomplish direct “click”
1
–3
and cancer treatment.
Among the various types of
radiopharmaceuticals introduced to date, radiometal-based
radiopharmaceuticals bearing the bifunctional complexing
4
agent HBED have been drawing the attention of different
30–32
and potentially they could
5
–15
research groups during the past years.
The most important
6
8
example in this category is [ Ga]Ga-PSMA-11 for use in non-
invasive prostate cancer diagnosis.7 Bifunctional HBED
chelators build strong complexes with trivalent gallium through
33
2 4
N O coordinating sites and are conjugated to bioactive
16,17
molecules (e.g., antibodies).
ester-protected variants of HBED are employed as chelator
precursors for the synthesis of metal-based
(radio)pharmaceuticals with the HBED framework
As a typical synthetic strategy,
34
coupling. Herein we present HBED-NN as a protected diazide
variant of the bifunctional HBED chelator. The two terminal
azide groups available on this structure successfully undergo
CuAAC reactions. The presence of two functional groups also
1
8–22
(Scheme 1).
1
5,19,22
provides the possibility for unsymmetrical conjugation.
Scheme 1. Typical Synthetic Pathway for HBED-Based
Radiopharmaceuticals
The current work describes the synthesis, CuAAC reaction
and complex chemistry of the HBED-NN chelator type for
application in radiopharmaceutical chemistry. For this purpose,
we have simulated the general synthetic route of HBED-based
radiopharmaceuticals for the preparation of a hexadentate [Ga-
t-BuO2C
2
HO C
CO2t-Bu
1) bioconjugation
2
CO H
N
N
N
2) t-Bu deprotection
N
OH
OH
(
HBED-NN)] complex (Scheme 2). The HBED-NN chelator
R
G
HO
HO
R
G
entered into defined CuAAC reactions as well as complexation
reactions under various conditions. The synthesis of ester-
protected HBED-NN (1) was accomplished in 5 steps
(Scheme 3). However, It is essential to understand the behavior
of any structurally new chelator in both conjugation and
coordination reactions before planning (radio)pharmaceutical
syntheses with bioactive molecules.
HBED chelator (ester protected)
G = modified bioactive molecule
free HBED chelator
O
O
3
) radiolabeling
O
O
N
N
G
G
O
O
HBED-based radiopharmaceutical
The CuAAC23 (“click”) reaction is an important tool for the
24–
conjugation of targeting molecules to bifunctional chelators.
27
24
In contrast to other commonly used methods (e.g., amide
coupling), the CuAAC reaction is an irreversible and
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Scheme 2. Preparation of Hexadentate [Ga-(HBED-NN)]
Complex Using a HBED-NN Chelator Conjugated to
Phenyl Acetylene as Vector Model
resting states and rate-determining steps.35–37 The CuAAC
reaction for chelator 1 was optimized on phenyl acetylene and
copper(II) acetate/sodium ascorbate in CH CN/H O was
3 2
selected as the catalytic system. The reaction between phenyl
acetylene and compound 1 was conducted both at room
temperature as well as at an elevated temperature. At 80 °C in
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1) phenyl acetylene
Cu(OAC)2/Na+ ascorbate
N3 H2O/CH3CN
80 oC, 1 h
HO2C
t-BuO2C
CO2H
CO2t-Bu
N
Ar
N
N
N
2
the presence of 0.05 equiv Cu(OAc) and 0.10 equiv sodium
OH
OH
ascorbate, the reaction was relatively fast and after 15 min it
was complete with an isolated yield of 59%. By contrast, at
room temperature the reaction progress was very slow. To
explore the chelator behavior in the presence of an excess
amount of copper catalyst, the CuAAC reaction of phenyl
acetylene with compound 1 was tested with 0.5 equiv of
2) r.t., 5 h
TFA/CHCl3
Ar
HO
HO
N3
isolated yield: 58%
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HBED-NN chelator (protected)
Ar =
free chelator
N
Ph
N
N
O
2
Cu(OAc) and 1.0 equiv of sodium ascorbate at room
temperature, though using excess amounts of copper source in
CuAAC reactions usually results in copper-containing
natGaCl3
NaOAc
O
3
8,39
G
N
N
byproducts.
The reaction of 1 with a 10-fold excess of the
DMF/H2O
[Ga-(HBED-NN)]Na
(racemic mixture)
Ga
O
G
catalytic mixture was finished after 15 min and, as expected, the
amount of byproducts had increased whereby the isolated yield
was only 47%. The CuAAC reaction between compound 1 and
phenyl acetylene with acetic acid added was also checked since
in some reported cases, catalytic amounts of acetic acid
increased the reaction rate by affecting the catalytic cycle and
pH 4
O
O
O
9
0 oC, 4 min
isolated yield: 81%
3
G = (CH2)2 Ar
proven geometry for one of the two enantiomers with
the complexing oxygens of the carboxylate groups trans
to each other and the phenolic oxygens cis (isomer II)
36,40,41
without causing side reactions.
However, no change in the
Thus, we next investigated the click chemistry of the HBED-
NN chelator (1) using three small terminal alkynes, viz. phenyl
acetylene, ethyl propiolate and propargyl alcohol, in a standard
CuAAC reaction with compound 1 (Scheme 3). These alkynes
were selected because they show different kinetics in CuAAC
reactions due to their different acidities which influence catalyst
reaction rate for compound 1 and phenyl acetylene was
observed. CuAAC reactions of 1 with ethyl propiolate and
propargyl alcohol were conducted at 80 °C with 0.05 equiv
Cu(OAc) and 0.10 equiv sodium ascorbate and isolated yields
2
were determined as 43% and 50%, respectively [Table S1 in the
Supporting Information (SI)].
Scheme 3. Synthesis and CuAAC Reactions of Ester-Protected HBED-NN
OH
OH
OH
NaBH4
MgCl2 , Et3N
NH2
OH
N3
NaN3
paraformaldehyde
CHO
H2N
CF3CH2OH
0 oC to r.t.
overnight
inert gas
N
DMF
N
toluene
r.t., 30 min
5 oC, 1.5 h
CH3CN
reflux, overnight
4
N3
HO
inert gas
Br
N3
N3
quantitative yield
isolated yield: 96%
isolated yield: 95%
isolated yield: 93%
1b
1a
1c
1d
t-BuO2C
N
CO2t-Bu
N
N
t-BuO2C
CO2t-Bu
R
N
OH
N3
N
N3
N
BrCH2CO2t-Bu
N
H
N
N
H
R
OH
OH
Na2CO3
CH3CN
reflux, 5 h
N
N
HO
N
R
Cu(OAc)2/
N3
HO
N3
HO
Na+ ascorbate
isolated yield: 77%
overall yield: 65%
H2O/CH3CN
yield: 43-59%
aa : R = Ph, 1ab: R = CO2Et, 1ac: R = CH2OH
1e
HBED-NN (protected)
1
1
For investigating the complex chemistry of HBED-NN, it
2
in DMF–H O media (pH ~4) at both room temperature as well
was necessary to use a representative vector model with a
as at an elevated temperature. At 90 °C, chelation went very fast
and was complete in 4 min, while at room temperature the
reaction was comparatively slow. However, only the first 10
min of the reaction was perused because complexation of
HBED derivatives with longer reaction times have limited use
1
simple structure and uncomplicated spectral pattern in the H
NMR spectrum, especially in the upfield region where protons
from the chelate cage appear. Phenyl acetylene met these
requirements and therefore its click product phenyl 1,2,3-
triazole 2 was used as the complexing agent. Compound 2 was
synthesized in two steps: firstly the CuAAC reaction was
performed on structure 1 followed by the removal of the t-butyl
protecting groups using trifluoroacetic acid (Scheme 2).
6
8
½
in [ Ga]Ga-radiolabeling (t = 68 min). The room temperature
reaction was quenched after 10 min and the mixture analyzed
1
by H NMR.
nat
3+
Compound 2 (1 equiv) was then reacted with Ga (1.5 equiv)
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The Journal of Organic Chemistry
Previous reports of Ga-(HBED)-type complexes have simply
are present for these protons. The methylenes in the –
NCH CH N– bridge are diastereotopic and, as well, the
1
2
3
4
5
6
7
8
9
assumed
structure,
a
structure or perpetuated
though some reports
a
prior assumed
2
2
1
6,42,44
17,42–44
have recognized the
chemically equivalent protons from each methylene pair are
also magnetically inequivalent, thus a complex higher-order
sub-spectrum results. Likewise, the protons of the equivalent
phenyl substituents at the terminus of the scaffold also provide
a complex higher-order sub-spectrum while the two isolated
triazole protons are present as one singlet. The protons of the
equivalent phenolic groups provide the expected pattern for a
1,2,4-substituted phenyl while the methylene protons adjacent
to the triazole moiety appear higher-order due to the chiral-at-
metal stereocenter.
possibility of three NMR distinguishable geometric isomers for
a hexadentate Ga-(HBED)-type complex (Figure 1), viz.
octahedral complexes witheither carboxylate group oxygens cis
to each other and the phenolic oxygens trans to each other
(
isomer I), the carboxylate group oxygens trans to each other
and the phenolic oxygens cis to each other (isomer II), or a
cis,cis arrangement (isomer III). All three isomers are chiral-at-
metal constructs and thus any structure formed under symmetric
conditions will be a racemic mixture of the Δ and Ʌ
1
1
1
1
1
1
1
1
1
1
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6,17,42
enantiomers, as has been shown.
The formation of these
From models of isomer II (see SI), only one proton of the
methylenes adjacent to the carboxylate group should have
geometric isomers is temperature and pH dependent, and at 90
°C the reaction results in the formation of a predominant
sizeable NOE’s with the protons of the –NCH
while both benzylic protons should have sizeable NOE’s with
the protons of the –NCH CH N– bridge. For isomer I, the
converse applies whereby only one of the benzylic protons
should have sizeable NOE’s with the –NCH CH N– bridge
2 2
CH N– bridge
4
2–44
isomer, ostensibly the thermodynamically favored one.
It is
worth noting that reports of multiple species resulting from a
reaction may not only be mixtures of isomers, they may also
include incompletely formed HBED complexes, e.g., with other
ligands also in attendance such as water replacing one phenolic
2
2
2
2
protons while both protons of the carboxylate group methylenes
should have sizeable NOE’s with these protons. From the
NOESY spectrum, the observed NOE’s for these protons
unequivocally implied isomer II. Depictions of these stereo
relationships and the NOESY spectrum are presented in the SI.
Additionally, the couplings between the protons on the 
carbons to the coordinating nitrogen atom and the other two 
carbons also provide an indication of the structural isomer
adopted since the dihedral angles were either highly optimal
(i.e., either very large or very small) – and therefore conducive
to providing a correlation in the HMBC spectrum optimized for
a long-range coupling of 8 Hz – or were otherwise not due to
4
3
binding. The three geometric isomers may exhibit different
pharmaceutical profiles, though oddly while the enantiomers
42
have been shown to be distinct in this respect, a mixture of
species actually appeared to be indifferent to the composition
4
4
of the sample.
(
PhO)
(OAc)
O
(OAc)
O
O
N
N
N
N
N
N
Ga
Ga
Ga
(OAc)O
O(OAc)
(PhO)O
O(PhO)
(OAc)O
O(PhO)
O(PhO)
O(OAc)
O(PhO)
isomer I
isomer II
isomer III
-
-
-
3
PhO ligands trans
PhO ligands cis
PhO ligands cis
dihedral angles of intermediate size. Thus, these JH,C’s can be
-
-
-
OAc ligands cis
OAc ligands trans
OAc ligands cis
assigned as either expected to be observable or not observable
in the HMBC spectrum acquired here. For example, for isomer
II, while both methylene protons adjacent to the carboxylate
group are suitably disposed in terms of dihedral angles to
Figure 1. Possible geometrical isomers of Ga-HBED
complexes.
3
possess sizeable JH,C’s to the respective nearest carbon of the –
The geometry of the predominant isomer is invariably an
open question, but considering the X-ray-determined crystal
2 2
NCH CH N– bridge, neither of the benzylic protons are so
4
3,45,46
3+
4+
disposed. For isomer I, the converse applies whereby both
benzylic protons are suitably disposed in terms of dihedral
structures of analogous HBED complexes
with Ga , Ti
3
+
and Fe , the product obtained here is expected to attain
3
angles to possess sizeable JH,C’s to the respective nearest
isomer II (Scheme 2). Applying free HBED-NN chelator 2, the
nat
3+
2 2
carbon of the –NCH CH N– bridge, while neither of the
carboxylate group methylene protons are so disposed. In the
HMBC spectrum, only the two methylene protons adjacent to
complexation of Ga at 90 °C resulted in only one geometric
isomer. Product purity was proven by HPLC and NMR and the
isolated yield was 81%. The room temperature-conducted
1
the carboxylate group provided correlations to the
–
reaction retained reasonable selectivity whereby H NMR
NCH CH N– bridge carbons, thereby providing further support
2
2
analysis of the crude reaction mixture revealed 49% of the
favored isomer with only 6% of another complex – presumably
another isomer or a mixed ligand complex – together with 45%
for isomer II as the structure of the product. (See the SI for
presentation of this example portion of the HMBC spectrum.)
Overall, of the 12 considered relationships present in the
molecule, 6 should yield correlations while 6 should not, and
indeed the HMBC spectrum revealed observations fully in
accordance with these expectations for isomer II. For isomer I,
the converse applies, thus distinctly eliminating isomer I as the
structure of the product. The experimental observations for the
of unreacted chelator 2. As a comparison, the synthesis of
nat
[
~
Ga-PSMA-HBED-CC] complex at room temperature and pH
4 provided 50% of the favored isomer and 50% of another
4
4
species.
Full NMR characterization of the synthesized [Ga-(HBED-
NN)] complex (3) provided spectra that were fully consistent
with the postulated geometry (Scheme 2). Accordingly, there
are only three distinct methylene environments in the chelate
cage, thereby isomer III is eliminated as all methylene groups
are distinct in this structure. Two equivalent pairs of
diastereotopic protons are each present for the methylene
groups adjacent to the carboxylate group and the benzylic
methylenes, thus two spin systems consisting of two doublets
each with a relative integration of two protons for each signal
1
2 possible correlations are presented in Table S2 in the SI.
An interesting point raised by a referee was the possible
4
7
occurrence of the self-disproportion of enantiomers (SDE),
i.e., the spontaneous fractionation of nonracemic material into
enantioenriched and -depleted fractions when any
4
8
physicochemical process is applied to a nonracemic sample.
Since only racemates were prepared herein, this is of no concern
presently but would be of considerable interest if in future work
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enantioselective preparation of the chelator was undertaken,
either during sample preparation or after pharmacological
3
(5 g, 24.86 mmol, 1 equiv) and NaN (8.08 g, 124.35 mmol, 5 equiv)
in dry DMF (80 mL) was stirred at 45 °C under an inert gas atmosphere
for 1.5 h. The reaction mixture was diluted with water (500 mL) and
extracted with CH Cl . The organic layer was dried over Na SO ,
2 2 2 4
filtered and the solvent removed under reduced pressure. The residue
was dissolved in diethyl ether (100 mL) and washed with HCl solution
(2.5% × 1) and brine (× 3). The organic layer was dried over Na SO ,
2 4
filtered and evaporated to give azide 1b (3.88 g, 23.78 mmol, 95.6%)
as a yellow oil. Spectroscopic data is identical to previously reported
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
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3
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3
3
3
3
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4
4
4
4
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4
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5
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5
5
5
5
5
5
5
6
4
2,49
administration.
Pertinently, there is also the possibility of
analogous SDE-type processes occurring between other
stereochemically related species due to intermolecular
4
8
association, e.g. between diastereomers or between geometric
isomers, but such occurrences have never been enunciated.
3
+
Although additional Ga complexes have been observed here
4
2–44
52 1
3
and elsewhere,
whether they represent geometric isomers or
results. H NMR (400 MHz, CDCl , 25 °C):  = 7.09 (d, J = 8.6
3
H–H
4
3
3
incompletely formed HBED complexes is uncertain as their
characterization was lacking. For readers unfamiliar with the
SDE in all its manifestations, they are referred to the literature
Hz, 2H, m-CH), 6.78 (d, JH–H = 8.6 Hz, 2H, ortho-CH), 4.69 (s, 1H,
3
3
OH), 3.46 (t, JH–H = 7.2 Hz, 2H, CH
2
N
3
), 2.82 (t, JH–H = 7.2 Hz, 2H,
C) ppm. C{ H} NMR (100 MHz, CDCl , 25 °C):  = 154.5
(COH), 130.4 (CCH ), 130.1 (meta-CH), 115.6 (ortho-CH), 52.8
CH ), 34.6 (CH C) ppm.
1
3
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
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9
0
1
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0
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2
3
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9
0
1
2
3
4
5
6
7
8
9
0
CH
2
3
4
8
2
for detailed descriptions of the phenomenon.
(
2
N
3
2
In conclusion, we have introduced HBED-NN as a diazide
variant of the bifunctional HBED chelator, which coordinates
trivalent gallium successfully and results in a hexadentate [Ga-
(HBED-NN)] complex as a single geometric isomer. NMR
experiments unequivocally confirmed the geometry of this
complex. This study shows that the HBED-NN chelator-type is
potentially an excellent candidate for the development of new
precursors for radiolabeling with the positron emitter
gallium-68.
Synthesis of 5-(2-azidoethyl)-2-hydroxybenzaldehyde (1c):
This new compound was synthesized using standard ortho-
5
3
formylation. To a mixture of compound 1b (3.88 g, 23.78 mmol,
1equiv), paraformaldehyde (5.71 g, 190.14 mmol, 8 equiv) and
anhydrous MgCl
2
(4.53 g, 47.58 mmol, 2 equiv) in absolute acetonitrile
(100 mL), was added dry triethylamine (13.26 mL, 95.12 mmol, 4
equiv). The reaction mixture was stirred overnight under reflux
conditions and then cooled to room temperature. The mixture was
diluted with water (500 mL) and HCl (5%, 100 mL) and then the
product was extracted with toluene. The organic layer was washed
EXPERIMENTAL SECTION
several times with brine, dried over Na
was removed under reduced pressure to give compound 1c (4.25 g,
2.21 mmol, 93.4%) as a yellow oil on high purity. For structural
2 4
SO and filtered. The solvent
General Experimental Methods
2
Chemicals and solvents used in this work were supplied by the division
of Radiopharmaceutical Chemistry at the German Cancer Research
Center or bought commercially. Reactions involving air-sensitive
reagents were carried out under an atmosphere of nitrogen or argon
using standard Schlenk techniques. The progress of chemical reactions
was monitored by using HPLC and TLC techniques. For column
chromatography, silica gel with grain size between 0.063 and 0.200
mm was employed as stationary phase. For thin layer chromatography
commercially, available ready-to-use plates supplied by Macherey &
Nagel (POLYGRAM© SIL G/UV254) were used as stationary phase.
The following RP-HPLC system was used for analysis: Agilent (1100
series) reverse phase system, equipped with a multi-wavelength
detector (MWD) and a Chromolith RP-18e analytical column. The
following RP-HPLC system was used for purification: LaPrep P314
characterization, this product was further purified by preparative
HPLC. IR (reflection):  = 3308 (w, br), 2858 (m), 2090 (s), 1652 (s)
−
1 1
cm . H NMR (400 MHz, CDCl , 25 °C):  = 10.92 (s, 1H, OH), 9.89
3
3
(s, 1H, CHO), 7.40 (m, 2H, CHCCH), 6.97 (d, J
CHCOH), 3.52 (t, J = 7.0 Hz, 2H, CH N ), 2.88 (t, J = 7.0 Hz,
H, CH
H–H
3
= 8 Hz, 1H,
3
H–H
2
3
H–H
13
1
2
2
C) ppm. C{ H} NMR (100 MHz, CDCl
3
, 25 °C):  = 196.5
(
(
(
CHO), 160.7 (COH), 137.6 (CHCHCOH), 133.7 (CCHC), 129.7
CHCCH), 120.7 (CCHO), 118.2 (CHCOH), 52.5 (CH
2
N
3
), 34.4
: 191.1;
: 135.0; Found:
35.0 (100%). Elemental Analysis (analysis no. 42014): Anal. Calcd
for C C, 56.54; H, 4.75; N, 21.98. Found: C, 56.75; H, 4.61; N,
22.38.
2+
2 18 6 4
CH C) ppm. MS (EI+): m/z [2M] Calcd for C18H N O
+
2 3 8 7 2
Found: 191.1 (11%), [M−(CH N )] Calcd for C H O
1
9
9 3 2
H N O
Synthesis of 2,2'-{[ethane-1,2-diylbis(azaneylylidene)]bis
(methaneylylidene)}bis[4-(2-azidoethyl)phenol] (1d):
(VWR International, Radnor, USA) equipped with a DAD and a
Nucleodur Sphinx RP 5 μm preparative column. IR spectra were
recorded with a Bruker Lumos, Germanium ATR-crystal, and the
following abbreviations were used to describe both the intensity and
profile of the signals: w (weak), m (medium), s (strong), br (broad).
NMR spectra were recorded with a Bruker Avance III (400 MHz) NMR
spectrometer. Chemical shifts (δ) are reported in ppm relative to TMS
Ethylene diamine (0.37 mL, 0.33 g, 5.50 mmol, 1 equiv) was added to
a solution of compound 1c (2.00 g, 10.46 mmol, 1.9 equiv) in toluene
(10 mL). The reaction mixture was stirred at room temperature for 30
min and then n-hexane (~40 mL) was added to the mixture. The
precipitate was filtered and washed with n-hexane to yield imine 1d
50
and the spectra calibrated with respect to the solvent peaks. The
(2.01 g, 4.95 mmol, 94.6%) as an orange solid. Considerable impurities
assignment of signals in the NMR spectra was achieved by
interpretation of two-dimensional NMR spectra (COSY, HMBC,
HSQC and NOSEY). For processing, analysis and interpretation of
NMR spectra, the program TopSpin 3.5 pl7 was used. Mass spectra
were recorded by the Mass Spectrometry Service Facility of the
Department of Chemistry at Ruprecht-Karls-Universität-Heidelberg
and the Division of Radiopharmaceutical Chemistry at the German
Cancer Research Center. The following instruments were employed:
Bruker ApexQe hybrid 9.4 T FT-ICR (HR-ESI), Bruker MALDI-MS
Daltonics Microflex and JEOL JMS-700 magnetic sector (EI).
Elemental analyses were carried out by the Laboratory of
Microanalysis of the Department of Chemistry at the Ruprecht-Karls-
Universität-Heidelberg on vario EL and vario MICRO cube
instruments by Elementar Analysensysteme GmbH. The determination
of melting points was done in Büchi (B-540) melting point apparatus.
were not detected by NMR spectra and thus the compound was used in
the next step without further purification. However, for spectroscopic
characterization, the product was washed with a dilute solution of
sodium hydrogen sulfite and water, while for elemental analysis it was
purified by preparative HPLC. MP 114-116 °C. IR (ATR):  = 2926
−
1 1
(
°
w), 2124 (s), 1638 (s), 1279 (m) cm . H NMR (400 MHz, CDCl
3
, 25
3
4
C MHz):  = 8.33 (s, 2H, CHN), 7.15 (dd, JH–H = 8.5 Hz, JH–H = 2.3
Hz, 2H, CHCHCOH), 7.07 (d, JH–H = 2.3, 2H, CCHC), 6.90 (d, JH–H
= 8.5 Hz, 2H, CHCHCOH), 3.94 (s, 4H, CH Nimine), 3.45 (t, JH–H = 7.1
2
), 2.81 (t, JH–H = 7.1 Hz, 4H, CH
, 25 °C):  = 166.4 (CHN), 160.0 (COH), 132.9
CHCHCOH), 131.7 (CCHC), 128.2 (CHCCH), 118.7 (CCHN), 117.4
imine), 52.7 (CH
ppm. MS (MALDI): m/z [M+H] Calcd for C20
4
4
3
3
13
1
Hz, 4H, CH
NMR (100 MHz, CDCl
2
N
3
2 2 3
CH N ) ppm. C{ H}
3
(
(
CHCHCOH), 59.9 (CH
2
N
2
N
H
3
), 34.49 (CH
2 2 3
CH N )
+
23
N
8
O
2
: 407.2; Found:
4
07.2 (100%). Elemental Analysis (analysis no. 42993): Anal. Calcd
Synthesis of 4-(2-azidoethyl)phenol (1b):
for C20H N O : C, 59.10; H, 5.46; N, 27.57. Found: C, 59.14; H, 5.59;
22 8 2
N, 27.66.
The compound was synthesized according to a literature procedure
5
1
with some modification. A mixture of 4-(2-bromoethyl)phenol (1a)
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The Journal of Organic Chemistry
Synthesis of 2,2'-{[ethane-1,2-
diylbis(azanediyl)]bis(methylene)}bis[4-(2-azidoethyl)phenol]
1e):
1aa in the presence of 0.5 equiv of Cu(OAc)
ascorbate at room temperature gave 47% ( 0.06 g, 0.07mmol) as
isolated yield. In this case, Cu(OAC) and sodium ascorbate were
added directly and the reaction mixture stirred for 30 min.
Characterization data for di-tert-Butyl 2,2'-[ethane-1,2-diylbis({2-
hydroxy-5-[2-(4-phenyl-1H-1,2,3-triazol-1-
2
and 1.0 equiv of sodium
1
2
3
4
5
6
7
8
9
(
2
Compound 1d (1.91 g, 4.69 mmol, 1 equiv) was dissolved in warm
,2,2-trifluoroethanol (40 mL, ~50 °C) and then cooled in an ice-bath.
To this solution was added NaBH (0.71 g, 18.78 mmol, 4 equiv) in
2
4
yl)ethyl]benzyl}azanediyl)]diacetate (1aa): IR(ATR): 2929 (w), 1726
portions and then the reaction mixture was allowed to warm up to room
temperature. After being stirred overnight under an inert gas
atmosphere, the reaction was quenched with water (100 mL), dried over
1
(
(
m), 1152 (s), 765 (m). H NMR (400 MHz, CDCl
3
, 25 °C):  = 9.57
3
4
s, br, 2H, COH), 7.76 (dd, 4H, JH–H = 7.8 Hz, JH–H = 1.4 Hz, Ph-
3
substituent, ortho-H), 7.52 (s, 2H, CHN), 7.38 (t, 4H, JH–H = 7.6 Hz,
Ph-substituent, meta-H), 7.30 (m, 2H, Ph-substituent, para-H), 6.97
2 4
Na SO , filtered and evaporated to provide product 1e as a colorless to
pale yellow solid in quantitative yield. NMR showed no considerable
impurities and thus this compound was used in the next step without
further purification. However, for structural characterization product 1e
was further purified by preparative HPLC. MP 99-102 °C. IR (ATR):
3
4
3
(
dd, 2H, JH–H = 8.2 Hz, JH–H = 2.2 Hz, CHCHCOH), 6.76 (d, 2H, JH–H
4
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
= 8.1 Hz, CHCHCOH), 6.52 (d, 2H, JH–H = 2.2 Hz, CCHC), 4.56 (t,
3
N), 3.53 (s, 4H, BnCH
CO ), 2.45 (s, 4H, N-C
) ppm. C{ H} NMR (100 MHz, CDCl , 25 °C):
2
), 156.6 (COH), 147.5 (NCCH), 130.8 (Ph-substituent,
3
4
H
H, JH–H = 7.2 Hz, CCH
2
CH
2
2
), 3.12 (t, 4H, JH–
= 7.2 Hz, CCH CH N), 3.08 (s, 4H, CH
2
2
2
2
2 4
H -
−
1 1
 = 3287 (m), 2833 (w), 1614 (m), 1458 (s) cm . H NMR (400 MHz,
13
1
N), 1.46 (s, 18H, CH
= 170.4 (CO
ipso-C), 129.9 ( CH
Ph-substituent, meta-C), 127.6 (Ph-substituent, para-C), 125.8 (Ph-
substituent, ortho-C), 122.1 (CCH CH N), 120.25 (CHN), 116.9
3
3
3
4
CDCl , 25 °C):  = 7.02 (dd, JH–H = 8.3 Hz, JH–H = 2.1 Hz, 2H,
3

4
3
CHCHCOH), 6.83 (d, JH–H = 2.1 Hz, 2H, CCHC), 6.78 (d, JH–H = 8.3
Bn
2
C), 129.5 (CCHC), 129.0 (CHCHCO), 128.2
Bn
3
Hz, 2H, CHCHCOH), 3.98 (s, 4H, CH
2
), 3,44 (t, JH–H = 7.2 Hz, 4H,
(
3
CH
2
N
3
), 2.84 (s, 4H, CH
2
NH), 2.78 (t, JH–H = 7.2 Hz, 4H, CH
2
CH
, 25 °C):  = 156.9 (COH),
129.3 (CHCHCOH), 129.0 (CCHC), 128.7 (CHCCH), 122.35
2 3
N )
2
2
13
1
ppm. C{ H} NMR (100 MHz, CDCl
3
Bn
(
(
CHCHCO), 82.3 (CCH
CCH CH N), 49.8 (N-C
HRMS (ESI+): m/z [M+H] Calcd for C48H N O
59 8 6
3
), 57.8 ( C), 55.7 (CH
-N), 36.1 (CCH CH N), 28.2 (CH
: 843.4552; Found:
2
CO
2
), 52.2
2
2
2
H
4
2
2
3
) ppm.
Bn
Bn
(
(
CH
CH NH), 34.70 (CH
: 407.2; Found: 407.2 (100 %). HRMS (ESI+): m/z
2
C), 116.8 (C(OH)CHCH), 52.9 (CH
2
N
3
), 52.7 ( CH
2
+
), 48.0
+
2
2
CH ) ppm. MS (MALDI): m/z [M+H] Calcd
2 3
N
843.4556 (100%).
27 8 2
for C20H N O
Characterization data for diethyl 1,1'-{[({2,2,13,13-tetramethyl-4,11-
dioxo-3,12-dioxa-6,9-diazatetradecane-6,9-diyl}bis(methylene))bis(4-
hydroxy-3,1-phenylene)]bis(ethane-2,1-diyl)}bis(1H-1,2,3-triazole-4-
+
[MH+(H
2 2 4 2 2 4 3 53 16 4
N-C H -NH )+2(PhOH-C H -N )] Calcd for C38H N O :
797.4430; Found: 797.4417 (99%).
carboxylate) (1ab): IR(ATR): 2980 (w), 1722 (s), 1153 (s), 775 (m).
Synthesis of di-tert-butyl 2,2'-(ethane-1,2-diylbis{[5-(2-azidoethyl)-
-hydroxybenzyl]azanediyl}) diacetate [HBED-NN-di(t-Bu ester)]
1)
1
H NMR (400 MHz, CDCl , 25 °C):  = 9.63 (s, br, 2H, COH), 7.83 (s,
3
2
(
3
4
2H, CHN), 6.92 (dd, 4H, JH–H = 8.3 Hz, JH–H = 2.2 Hz, CHCHCOH),
6
CCHC), 4.58 (t, 4H, JH–H = 7.2 Hz, CCH
3
4
.76 (d, JH–H = 8.3 Hz, 2H, CHCHCOH), 6.55 (d, JH–H = 2.2 Hz, 2H,
A mixture of compound 1f (0.56 g, 1.36 mmol, 1 equiv), anhydrous
Na CO (0.58 g, 5.46 mmol, 4 equiv) and tert-butyl 2-bromoacetate
(0.56 g, 2.86 mmol, 2.1 equiv) was suspended in anhydrous acetonitrile
25 mL) and stirred under reflux conditions for 5 h, and then the
3
N), 4.39 (q, 4H, 3JH–H
), 3.16 (s, 4H, CH
2
CH
2
=
), 3.62 (s, 4H, BnCH
2
3
7
4
.2 Hz, CH CH
H, JH–H = 7.0 Hz, CCH
2 2
CO ), 3.11 (t,
3
2
2
3
2
CH
), 1.39 (t, 6H, JH–H = 7.2 Hz, CH
MHz, CDCl , 25 °C):  = 170.4 (CO
COH), 140.1 (NCCH), 129.8 (CCHC), 129.3 (CHCHCO), 127.9
2
N), 2.60 (s, 4H, N-C -N), 1.46 (s, 18H,
2 4
H
(
3
13
1
CCH
3
3
CH
2
) ppm. C{ H} NMR (100
reaction mixture was cooled to room temperature and filtered. The
solvent was removed under reduced pressure and the residue was
3
2
t-Bu), 160.9 (CO
2
Et), 156.7
(
(
(
(
purified by flash column chromatography (R
f
= 0.4, hexane–EtOAc,
Bn
2
CHN), 127.0 (CHCCH), 122.2 ( CH C), 117.1 (CHCHCO), 82.4
2:1). The obtained product was recovered in ethanol to give HBED-
NN-di(t-Bu ester) (1) as a colorless solid (0.76 g, 1.05 mmol, 77%).
MP 93-95 °C. IR (ATR): 2975 (w), 2091 (s), 1733 (s), 1500 (m), 1152
Bn
CCH
CCH
3
), 61.4 (CH
CH N), 50.0 (N-C
) ppm. HRMS (ESI+): m/z [M+H] Calcd for C42
35.4349; Found: 835.4356 (100%). Elemental Analysis (analysis no.
2221): Anal. Calcd for C42 10: C, 60.42; H, 7.00; N, 13.42.
2
CH
3
), 57.9 ( C), 55.7 (CH
2
CO
2
), 52.4
2
2
2
H
4
-N), 35.9 (CCH CH N), 28.2 (CCH
2
2
3
), 14.5
+
(CH
8
4
2
CH
3
59 8 10
H N O :
−
1 1
(
7
s) cm . H NMR (400 MHz, CDCl
3
, 25 °C):  = 9.62 (s, 2H, COH),
3
4
3
.02 (dd, JH–H = 8.2 Hz, JH–H = 2.2 Hz, 2H, CHCHCOH), 6.79 (d, JH–
= 8.2 Hz, 2H, CHCHCOH), 6.76 (d, JH–H = 2.2 Hz, 2H, CCHC), 3.71
(s, 4H, CH
CH CO
N), 1.46 (s, 18H, CH
58 8
H N O
4
H
Found: C, 60.20; H, 6.85; N, 13.03.
Characterization data for di-tert-Butyl 2,2'-{ethane-1,2-diylbis[(2-
hydroxy-5-{2-[4-(hydroxymethyl)-1H-1,2,3-triazol-1-
Bn
3
2
), 3.42 (t, JH–H = 7.3 Hz, 4H, CH
2
N
3
), 3.16 (s, 4H,
3
2
2
), 2.77 (t, JH–H = 7.3 Hz, 4H, CH
2
CH
) ppm. C{ H} NMR (100 MHz, CDCl
), 156.4 (COH), 129.7 (CCHC), 129.6 (CHCHCOH),
2
N
3
), 2.68 (s, 4H, N-C
2 4
H -
1
3
1
3
3
, 25 °C):
yl]ethyl}benzyl)azanediyl]}diacetate (1ac): IR(ATR): 3323 (w), 2931

1
5
(CH
C
C
= 170.1 (CO
28.6 (CHCCH), 121.8 ( CH
2
1
(
(
3
w), 1725 (m), 1154 (s). H NMR (400 MHz, CDCl , 25 °C):  = 7.33
4
Bn
2
C), 116.8 (CHCHCOH), 82.2 (CCH
), 52.9 (CH ), 50.4 (N-C -N), 34.7
) ppm. HRMS (ESI+): m/z [M+H] Calcd for
3
),
s, 2H, CHN), 6.95 (dd, 4H,
CHCHCOH), 6.76 (d, JH–H = 8.2 Hz, 2H, CHCHCOH), 6.49 (d, JH–H
3
JH–H = 8.2 Hz, JH–H = 2.2 Hz,
Bn
8.10 ( CH
CH ), 28.2 (CH
: 639.3613; Found: 639.3634 (18%), [M+Na] , Calcd for
NaO 661.3433; Found: 661.3451 (36%). Elemental
: C, 60.17;
2
), 55.6 (CH
2
CO
2
2
N
3
2
H
4
3
4
+
N
3
3
3
2
2
=
2.1 Hz, 2H, CCHC), 4.72 (s, 4H, CH
OH), 4.50 (t, 4H, JH–H = 7.3
), 3.18 (s, 4H, CH CO ), 3.10 (t,
N), 2.60 (s, 4H, N-C -N), 1.46 (s, 18H,
) ppm. 13C{ H} NMR (100 MHz, CDCl
, 25 °C):  = 170.51
2
t-Bu), 156.5 (COH), 147.6 (NCCH), 129.9 (CCHC), 129.4
2
+
H
H
47
N
N
8
O
6
Bn
32
Hz, CCH
4
CCH
(
CH
N), 3.58 (s, 4H, CH
CH
2
2
2
2
2
:
3
32
46
8
6
H, JH–H = 7.3 Hz, CCH
2 4
H
2
2
Analysis (analysis no. 41992): Anal. Calcd for C32
H
46
N
8
O
6
1
3
3
H, 7.26; N, 17.54. Found: C, 60.17; H, 7.29; N, 17.28.
CO
CHCHCO), 127.6 (CHCCH), 122.2 (CHN or CH
Bn
(
2
C), 122.1 (CHN
Syntheses and characterization of substrates 1aa, 1ab and 1ac:
Bn
Bn
or CH
(CH OH), 56.0 (CH
(CCH CH N), 28.2 (CCH
55 8 8
for C38H N O : 751.4137; Found: 751.4142 (100%).
2
C), 117.0 (CHCHCO), 82.5 (CCH
CO ), 52.1 (CCH CH N), 50.2 (N-C
) ppm. HRMS (ESI+): m/z [M+H] Calcd
3
), 57.8 ( C), 56.7
These compounds were synthesized according to the standard CuAAC
2
2
2
2
2
2 4
H
-N), 36.1
5
4
+
reaction. To a mixture of HBED-NN (0.1 g, 0.16 mmol, 1 equiv) and
a terminal alkyne (0.39 mmol, 2.5 equiv) in CH CN/H O (0.5 mL: 0.3
mL) were added 78 µL of an aqueous Cu(OAc) solution (0.1 M; 7.8
2
2
3
3
2
2
Synthesis of 2,2'-[ethane-1,2-diylbis({2-hydroxy-5-[2-(4-phenyl-
H-1,2,3-triazol-1-yl)ethyl]benzyl}azanediyl)]diacetic acid (2):
µmol, 0.05 equiv) and 156 µL of an aqueous sodium ascorbate solution
(0.1 M; 15.6 µmol, 0.1 equiv). The reaction mixture stirred at 80 °C
and reaction progress was followed by HPLC and TLC. After being
stirred for 1 h, the reaction mixture was cooled to room temperature
and the product isolated by preparative HPLC. Note: Product 1aa was
additionally filtered through a short column packed with silica gel
(eluent: CHCl ). Isolated yields for 1aa, 1ab and 1ac were 59% (0.08
3
g, 0.09 mmol), 43% (0.06 g, 0.07 mmol) and 50% (0.06 g, 0.08 mmol),
respectively. Each product is a colorless solid. Synthesis of compound
1
Compound 1 (0.60 g, 0.94 mmol, 1 equiv) and phenyl acetylene (0.24
g, 2.35 mmol, 2.5 equiv) were dissolved in CH CN (2 mL). To this
mixture were added 470 µL of an aqueous Cu(OAc) solution (0.1 M;
7 µmol, 0.05 equiv) and 940 µL of an aqueous sodium ascorbate
3
2
4
solution (0.1 M; 94 µmol, 0.1 equiv). After being stirred at 80 °C for 1
h, the reaction mixture was cooled to room temperature and filtered
through a thick layer of silica gel (eluent: CHCl ). The solvent was
3
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 9
evaporated under reduced pressure and the residue was dissolved in
CHCl /trifluoroacetic acid (1 mL: 4 mL). This mixture stirred for 5 h
AUTHOR INFORMATION
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
at room temperature. Then, the volatiles were removed under reduced
pressure and the crude product purified by preparative HPLC to give
compound 2 as a colorless solid (0.40 g, 0.54 mmol, 58%). Note:
Compound 2 could also be synthesized directly from product 1aa. IR
Corresponding Author
E-mail: a.makarem@dkfz.de
*
Notes
New address for German Litau: Faculty of Biology, Heidelberg
University, INF 234, 69120 Heidelberg, Germany. The authors
declare no competing financial interest.
1
(ATR): 3036 (w), 1613 (m), 1195 (s), 765 (s). H NMR (400 MHz,
3
MeOD, 25 °C):  = 8.13 (s, 2H, CHN), 7.74 (d, 4H, JH–H = 7.8 Hz, Ph-
3
substituent, ortho-H), 7.40 (t, 4H, JH–H = 7.8 Hz, Ph-substituent, meta-
3
H), 7.32 (t, 2H, JH–H = 7.8 Hz, Ph-substituent, para-H), 7.03 (dd, 2H,
3
4
ACKNOWLEDGMENTS
J
H–H = 8.3 Hz, JH–H = 1.44 Hz, CHCHCO), 6.97 (s, br, 2H, CCHC),
3
3
6
.78 (d, 2H, JH–H = 8.3 Hz, CHCHCO), 4.63 (t, 4H, JH–H = 6.7 Hz
CCH CH ), 3.57 (s, 4H, CH CO ), 3.15 (t, 4H,
N), 3.99 (s, 4H, BnCH
H–H = 6.7 Hz, CCH CH N), 3.05 (s, 4H, N-C -N) ppm. C{ H}
NMR (100 MHz, MeOD, 25 °C):  = 171.8 (CO ), 158.6 (COH), 148.6
NCCH), 133.8 (CCHC), 132.3 (CHCHCO), 131.6 (Ph-substituent,
ipso-C), 130.0 (Ph-substituent, meta-C), 129.4 (Ph-substituent, para-
C), 126.6 (Ph-substituent, ortho-C), 122.4 (CHN), 120.2 (CCH CH
), 52.9
N) ppm. HRMS
: 729.3155; Found:
The authors gratefully acknowledge the assistance of Mrs. Jana
Schmidt (technical assistant) from the German Cancer Research
Center and Mrs. Petra Krämer from the IR spectroscopy service of
the Organic Chemistry Institute, Heidelberg University. This work
was partly funded by a grant of German Cancer Aid (Deutsche
Krebshilfe); project number: 70112043.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
2
2
2
3
13
1
J
2
2
2 4
H
2
(
2
2
N
Bn
Bn
and CH
2
C), 116.9 (CHCHCO), 54.2 ( C), 54.0 (CH
N), 50.9 (N-C -N), 36.5 (CCH CH
ESI−): m/z [M−H] Calcd for C40
29.3152 (100%).
Synthesis of sodium gallium(III){2,2'-[ethane-1,2-diylbis({2-oxido-
-[2-(4-phenyl-1H-1,2,3-triazol-1-
2 2
CO
REFERENCES
(
(
7
CCH
2
CH
2
2
H
4
2
2
−
(1) Velikyan, I. Molecular Imaging and Radiotherapy: Theranostics for
Personalized Patient Management. Theranostics 2012, 2 (5), 424–426.
https://doi.org/10.7150/thno.4428.
(2) Ambrosini, V.; Fani, M.; Fanti, S.; Forrer, F.; Maecke, H. R.
Radiopeptide Imaging and Therapy in Europe. J. Nucl. Med. 2011, 52,
41 8 6
H N O
5
yl)ethyl]benzyl}azanediyl)]diacetate} (3):
4
(
2S–55S. https://doi.org/10.2967/jnumed.110.085753.
3) Chen, K.; Conti, P. S. Target-Specific Delivery of Peptide-Based
Probes for PET Imaging. Adv. Drug Deliv. Rev. 2010, 62 (11), 1005–
022. https://doi.org/10.1016/j.addr.2010.09.004.
3
Stock solution S1: In a 1 mL flask, 100 µL of an aqueous GaCl solution
(1 M) was mixed with 550 µL of an aqueous solution of NaOAc (1 M).
The pH of the Stock solution was ~4.
1
To a solution of compound 2 (20 mg, 27 µmol, 1.0 equiv) in DMF (2
mL) was added 275 µL of fresh S1 (containing 1.6 equiv Ga3+ and 8.6
(4) HBED full name: N,N’-bis(2-hydroxybenzyl)ethylenediamine-
N,N’-diacetic acid.
(5) Eder, M.; Knackmuss, S.; Le Gall, F.; Reusch, U.; Rybin, V.; Little,
equiv NaOAc) at room temperature. The reaction mixture was stirred
at 90 °C for 15 min (full conversion reached in 4 min as determined by
TLC). After the elapsed time, the reaction mixture was cooled to ~50
6
8
M.; Haberkorn, U.; Mier, W.; Eisenhut, M.
Ga-Labelled
°
C and the solvent removed under reduced pressure. The residue was
washed with water and then with THF, or alternatively, a dilute
NaHCO solution, and dried in vacuo to give complex 3 (isomer II) as
Recombinant Antibody Variants for Immuno-PET Imaging of Solid
Tumours. Eur. J. Nucl. Med. Mol. Imaging 2010, 37 (7), 1397–1407.
https://doi.org/10.1007/s00259-010-1392-6.
3
a colorless solid (18 mg, 22 µmol, 81%). The room temperature gallium
complexation was run under the same reaction conditions, with half-
scale in quantities. The reaction was quenched after 10 min by diluting
with water (~50 mL). Then, the aqueous mixture was immediately
(6) Eder, M.; Schäfer, M.; Bauder-Wüst, U.; Hull, W. E.; Wängler, C.;
68
Mier, W.; Haberkorn, U.; Eisenhut, M. Ga-Complex Lipophilicity
and the Targeting Property of a Urea-Based PSMA Inhibitor for PET
Imaging.
https://doi.org/10.1021/bc200279b.
7) Afshar-Oromieh, A.; Zechmann, C. M.; Malcher, A.; Eder, M.;
Bioconjug.
Chem.
2012,
23
(4),
688–697.
1
centrifuged and the residue was washed several times with water. H
NMR analysis of the crude reaction mixture revealed 49% of isomer II,
and 45% of the unreacted chelator (2) together with 6% of another
complex species. IR (ATR): 2919 (w), 1652 (s), 1498 (m), 1367 (m),
(
Eisenhut, M.; Linhart, H. G.; Holland-Letz, T.; Hadaschik, B. A.;
Giesel, F. L.; Debus, J. J.; et al. Comparison of PET Imaging with a
−
1 1
7
69 (m) cm . H NMR (400 MHz, d
6
-DMSO, 25 °C):  = 8.43 (s, 2H,
6
8
18
3
Ga-Labelled PSMA Ligand and F-Choline-Based PET/CT for the
CHN), 7.80 (d, 4H, JH–H = 7.5 Hz, Ph-substituent, ortho-H), 7.44 (t,
H, JH–H = 7.5 Hz, Ph-substituent, meta-H), 7.32 (t, 2H, JH–H = 7.5
Hz, Ph-substituent, para-H), 6.86 (dd, 2H, JH–H = 8.3 Hz, JH–H = 2.0
Hz, CHCHCO), 6.66 (d, JH–H = 2.0 Hz, 2H, CCHC), 6.46 (dd, JH–H
3
3
Diagnosis of Recurrent Prostate Cancer. Eur. J. Nucl. Med. Mol.
Imaging 2014, 41 (1), 11–20. https://doi.org/10.1007/s00259-013-
2525-5.
4
3
4
4
3
=
2
8.3 Hz, 2H, CHCHCO), 4.53 (m, 4H, CCH
2
CH
2
N), 4.18 (d, 2H, JH–H
(8) Verburg, F. A.; Krohn, T.; Heinzel, A.; Mottaghy, F. M.; Behrendt,
F. F. First Evidence of PSMA Expression in Differentiated Thyroid
Bn
2
Bn
=
(
CCH
N-C
12.9 Hz, C[H
,H
a b
]), 3.52 (d, 2H, JH–H = 12.9 Hz, C[H
a
,H
), 3.00 (t, 4H, JH–H = 7.3 Hz
N), 2.93 (d, 2H, JH–H = 17.2 Hz, C[H ,H ]CO ), 2.81 (m, 4H,
-N) ppm. C{ H} NMR (100 MHz, d -DMSO, 25 °C):  =
171.2 (CO
), 162.4 (PhOC), 146.0 (NCCH), 130.9 (Ph-substituent, ipso-
C), 130.4 (CCHC), 129.3 (CHCHCO), 128.9 (Ph-substituent, meta-C),
27.7 (Ph-substituent, para-C), 125.1 (Ph-substituent, ortho-C), 122.6
b
]), 3.20
2
3
d, 2H, JH–H = 17.2 Hz, C[H
,H
a b
]CO
2
68
Cancer Using [ Ga] PSMA-HBED-CC PET/CT. Eur. J. Nucl. Med.
2
2
CH
2
a
b
2
Mol.
https://doi.org/10.1007/s00259-015-3065-y.
9) Rauscher, I.; Maurer, T.; Beer, A. J.; Graner, F.-P.; Haller, B.;
Imaging
2015,
42
(10),
1622–1623.
13
1
2
H
4
6
2
(
Weirich, G.; Doherty, A.; Gschwend, J. E.; Schwaiger, M.; Eiber, M.
1
68
Value of Ga-PSMA HBED-CC PET for the Assessment of Lymph
Bn
(
(
(
CCH
2
CH
C), 55.9 (CH
8 6
CCH CH N) ppm. HRMS (ESI−): m/z [M] Calcd for C40H38GaN O :
2
N), 121.3 (CHN), 120.3 ( CH
2
C), 120.1 (CHCHCO), 60.9
Bn
Node Metastases in Prostate Cancer Patients with Biochemical
Recurrence: Comparison with Histopathology After Salvage
Lymphadenectomy. J. Nucl. Med. 2016, 57 (11), 1713–1719.
https://doi.org/10.2967/jnumed.116.173492.
(10) Haberkorn, U.; Eder, M.; Kopka, K.; Babich, J. W.; Eisenhut, M.
New Strategies in Prostate Cancer: Prostate-Specific Membrane
Antigen (PSMA) Ligands for Diagnosis and Therapy. Clin. Cancer
Res. 2016, 22 (1), 9–15. https://doi.org/10.1158/1078-0432.CCR-15-
0820.
2
CO ), 55.3 (N-C -N), 51.3 (CCH
2
2
H
4
2
CH N), 35.2
2
−
2
2
795.2176; Found: 795.2181 (100%).
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.organo-met.####
Spectra and more details about the complex geometry are available
in the SI.
(11) Pyka, T.; Weirich, G.; Einspieler, I.; Maurer, T.; Theisen, J.;
Hatzichristodoulou, G.; Schwamborn, K.; Schwaiger, M.; Eiber, M.
ACS Paragon Plus Environment

Page 7 of 9
The Journal of Organic Chemistry
68Ga-PSMA-HBED-CC PET for Differential Diagnosis of Suggestive
Lung Lesions in Patients with Prostate Cancer. J. Nucl. Med. 2016, 57
Endoradiotherapy by Means of Click Chemistry. Front. Chem. 2018,
6, 107. https://doi.org/10.3389/fchem.2018.00107.
(26) Zeng, D.; Zeglis, B. M.; Lewis, J. S.; Anderson, C. J. The Growing
Impact of Bioorthogonal Click Chemistry on the Development of
Radiopharmaceuticals. J. Nucl. Med. 2013, 54 (6), 829–832.
https://doi.org/10.2967/jnumed.112.115550.
(27) Baranyai, Z.; Reich, D.; Vágner, A.; Weineisen, M.; Tóth, I.;
Wester, H.-J.; Notni, J. A Shortcut to High-Affinity Ga-68 and Cu-64
Radiopharmaceuticals: One-Pot Click Chemistry Trimerisation on the
TRAP Platform. Dalton Trans. 2015, 44 (24), 11137–11146.
https://doi.org/10.1039/C5DT00576K.
(28) Tornøe, C. W.; Christensen, C.; Meldal, M. Peptidotriazoles on
Solid Phase: [1,2,3]-Triazoles by Regiospecific Copper(I)-Catalyzed
1,3-Dipolar Cycloadditions of Terminal Alkynes to Azides. J. Org.
1
2
3
4
5
6
7
8
9
(3), 367–371. https://doi.org/10.2967/jnumed.115.164442.
(12) Hope, T. A.; Truillet, C.; Ehman, E. C.; Afshar-Oromieh, A.;
Aggarwal, R.; Ryan, C. J.; Carroll, P. R.; Small, E. J.; Evans, M. J.
6
8
Ga-PSMA-11 PET Imaging of Response to Androgen Receptor
Inhibition: First Human Experience. J. Nucl. Med. 2017, 58 (1), 81–84.
https://doi.org/10.2967/jnumed.116.181800.
(13) Hope, T. A.; Aggarwal, R.; Chee, B.; Tao, D.; Greene, K. L.;
Cooperberg, M. R.; Feng, F.; Chang, A.; Ryan, C. J.; Small, E. J.; et al.
6
8
Impact of Ga-PSMA-11 PET on Management in Patients with
Biochemically Recurrent Prostate Cancer. J. Nucl. Med. 2017, 58 (12),
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
956–1961. https://doi.org/10.2967/jnumed.117.192476.
(
14) Fendler, W. P.; Eiber, M.; Beheshti, M.; Bomanji, J.; Ceci, F.; Cho,
6
8
S.; Giesel, F.; Haberkorn, U.; Hope, T. A.; Kopka, K.; et al. Ga-
PSMA PET/CT: Joint EANM and SNMMI Procedure Guideline for
Prostate Cancer Imaging: Version 1.0. Eur. J. Nucl. Med. Mol. Imaging
2017, 44 (6), 1014–1024. https://doi.org/10.1007/s00259-017-3670-z.
(15) Baranski, A.-C.; Schäfer, M.; Bauder-Wüst, U.; Wacker, A.;
Schmidt, J.; Liolios, C.; Mier, W.; Haberkorn, U.; Eisenhut, M.; Kopka,
K.; et al. Improving the Imaging Contrast of Ga-PSMA-11 by
Targeted Linker Design: Charged Spacer Moieties Enhance the
Pharmacokinetic Properties. Bioconjug. Chem. 2017, 28 (9), 2485–
Chem.
2002,
67
(9),
3057–3064.
https://doi.org/10.1103/PhysRevE.70.051307.
(29) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. A
Stepwise Huisgen Cycloaddition Process: Copper(I)-Catalyzed
Regioselective “Ligation” of Azides and Terminal Alkynes. Angew.
Chem.,
Int.
Ed.
2002,
41
(14),
2596–2599.
6
8
https://doi.org/10.1002/1521-3773(20020715)41:14<2596::AID-
ANIE2596>3.0.CO;2-4.
(30) Das, S. K.; Trono, M. C.; Roy, R. Transition Metal-Catalyzed
Cross-Coupling Reactions toward the Synthesis of α-D-
Mannopyranoside Clusters. Methods Enzymol. 2003, 362, 3–17.
https://doi.org/10.1016/S0076-6879(03)01001-2.
(31) Niu, S.-L.; Ulrich, G.; Retailleau, P.; Harrowfield, J.; Ziessel, R.
New Insights into the Solubilization of Bodipy Dyes. Tetrahedron Lett.
2009, 50 (27), 3840–3844. https://doi.org/10.1016/j.tetlet.2009.04.017.
(32) (a) Scates, B. A.; Lashbrook, B. L.; Chastain, B. C.; Tominaga,
K.; Elliott, B. T.; Theising, N. J.; Baker, T. A.; Fitch, R. W.
Polyethylene Glycol-Based Homologated Ligands for Nicotinic
Acetylcholine Receptors. Bioorg. Med. Chem. 2008, 16 (24), 10295–
10300. https://doi.org/10.1016/j.bmc.2008.10.045. (b) Schultz, M. K.;
Parameswarappa, S. G.; Pigge, F. C. Synthesis of a DOTA−Biotin
Conjugate for Radionuclide Chelation via Cu-Free Click Chemistry.
2
(
492. https://doi.org/10.1021/acs.bioconjchem.7b00458.
16) Zöller, M.; Schuhmacher, J.; Reed, J.; Maier-Borst, W.; Matzku,
S. Establishment and Characterization of Monoclonal Antibodies
against an Octahedral Gallium Chelate Suitable for
Immunoscintigraphy with PET. J. Nucl. Med. 1992, 33 (7), 1366–1372.
17) Schuhmacher, J.; Klivenyi, G.; Hull, W. E.; Matys, R.; Hauser, H.;
Kalthoff, H.; Schmiegel, W. H.; Maier-Borst, W.; Matzku, S. A
(
6
7
Bifunctional HBED-Derivative for Labeling of Antibodies with Ga,
1
11
In and Fe. Comparative Biodistribution with In-DPTA and 131I-
59
111
Labeled Antibodies in Mice Bearing Antibody Internalizing and Non-
Internalizing Tumors. Nucl. Med. Biol. 1992, 19 (8), 809–824.
https://doi.org/10.1016/0883-2897(92)90167-W.
(18) Trencsényi, G.; Dénes, N.; Nagy, G.; Kis, A.; Vida, A.; Farkas, F.;
Szabó, J. P.; Kovács, T.; Berényi, E.; Garai, I.; et al. Comparative
Org.
Lett.
2010,
12
(10),
2398–2401.
6
8
68
Preclinical Evaluation of
Ga-NODAGA and
Ga-HBED-CC
https://doi.org/10.1021/ol100774p.
Conjugated Procainamide in Melanoma Imaging. J. Pharm. Biomed.
Anal. 2017, 139, 54–64. https://doi.org/10.1016/j.jpba.2017.02.049.
(33) (a) Yoshida, S.; Kuribara, T.; Ito, H.; Meguro, T.; Nishiyama, Y.;
Karaki, F.; Hatakeyama, Y.; Koike, Y.; Kii, I.; Hosoya, T. A Facile
Preparation of Functional Cycloalkynes via an Azide-to-Cycloalkyne
Switching Approach. Chem. Commun. 2019, 55 (24), 3556–3559.
https://doi.org/10.1039/C9CC01113G. (b) Hofmann, S.; Maschauer,
S.; Kuwert, T.; Beck-Sickinger, A. G.; Prante, O. Synthesis and in Vitro
and in Vivo Evaluation of an 18 F-Labeled Neuropeptide Y Analogue
for Imaging of Breast Cancer by PET. Mol. Pharm. 2015, 12 (4), 1121–
1130. https://doi.org/10.1021/mp500601z.
(34) HBED-NN (ester-protected) full name: di-tert-butyl 2,2’-(ethane-
1,2-diylbis{[5-(2-azidoethyl)-2-hydroxybenzyl]azanediyl})diacetate.
(35) Berg, R. Highly Active Dinuclear Copper Catalysts for
Homogeneous Azide-Alkyne Cycloadditions, PhD Thesis, Ruprecht-
Karls-Universität-Heidelberg, 2013.
(36) Makarem, A.; Berg, R.; Rominger, F.; Straub, B. F. A Fluxional
Copper Acetylide Cluster in CuAAC Catalysis. Angew. Chem., Int. Ed.
2015, 54 (25), 7431–7435. https://doi.org/10.1002/anie.201502368.
(37) Makarem, A. Complex Chemistry of Dicopper Click Catalysts,
PhD Thesis, Ruprecht-Karls-Universität-Heidelberg, 2015.
(38) Reich, D.; Wurzer, A.; Wirtz, M.; Stiegler, V.; Spatz, P.;
Pollmann, J.; Wester, H.-J.; Notni, J. Dendritic Poly-Chelator
Frameworks for Multimeric Bioconjugation. Chem. Commun. 2017, 53
(17), 2586–2589. https://doi.org/10.1039/c6cc10169k.
(
19) Zha, Z.; Song, J.; Choi, S. R.; Wu, Z.; Ploessl, K.; Smith, M.;
68
Kung, H. Ga-Bivalent Polypegylated Styrylpyridine Conjugates for
Imaging Aβ Plaques in Cerebral Amyloid Angiopathy. Bioconjug.
Chem.
https://doi.org/10.1021/acs.bioconjchem.6b00127.
20) (a) Grimmond, B. J.; Rishel, M. J.; Luttrell, M. T. Intermediates
2016,
27
(5),
1314–1323.
(
for Hydroxylated Iron(III) Chelate Contrast Enhancement Agents. U.S.
Pat. Appl, US 20110077396, 2011. (b) Grimmond, B. J.; Rishel, M. J.
Preparation of Bifunctional Chelating Agents and Their Metal
Complexes as MRI Contrast Agent. U.S. Pat. Appl. US 20140088314,
2014.
(21) Makarem, A.; Konrad, M.; Liolios, C.; Kopka, K. A Convenient
Synthesis for HBED-CC-tris(tert- butyl ester). Synlett 2018, 29 (9),
1
239–1243. https://doi.org/10.1055/s-0036-1591950.
(22) Kung, H. F.; Wu, Z.; Choi, S. R.; Ploessl, K.; Zha, Z. Preparation
of Gallium Complex with HBED-Bisphosphonates Conjugates as
Theranostic Agents. PCT Int. Appl, WO 2017007790, 2017.
(23) CuAAC: copper(I)-catalyzed azide–alkyne cycloaddition.
(24) Price, E. W.; Orvig, C. Matching Chelators to Radiometals for
Radiopharmaceuticals. Chem. Soc. Rev. 2014, 43 (1), 260–290.
https://doi.org/10.1039/c3cs60304k.https://doi.org/10.1039/c3cs60304
k.
(39) Notni, J.; Wester, H. J. A Practical Guide on the Synthesis of Metal
Chelates for Molecular Imaging and Therapy by Means of Click
Chemistry. Chem.–Eur. J. 2016, 22 (33), 11500–11508.
https://doi.org/10.1002/chem.201600928.
(25) Wurzer, A.; Vagner, A.; Horvath, D.; Fellegi, F.; Wester, H.-J.;
Kalman, F. K.; Notni, J. Synthesis of Symmetrical Tetrameric
Conjugates of the Radiolanthanide Chelator DOTPI for Application in
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 9
(
40) Shao, C.; Wang, X.; Xu, J.; Zhao, J.; Zhang, Q.; Hu, Y. Carboxylic
Acid-Promoted Copper(I)-Catalyzed Azide−Alkyne Cycloaddition. J.
Org. Chem. 2010, 75 (20), 7002–7005.
https://doi.org/10.1021/jo101495k.
41) Nolte, C.; Mayer, P.; Straub, B. F. Isolation of a Copper(I)
Triazolide: A “Click” Intermediate. Angew. Chem., Int. Ed. 2007, 46
https://doi.org/10.1039/C6CS00703A. (c) Han, J.; Wzorek, A.;
Kwiatkowska, M.; Soloshonok, V. A.; Klika, K. D. The self-
disproportionation of enantiomers (SDE) of amino acids and their
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
derivatives.
Amino
Acids
2019,
in
press.
(d)
(
https://link.springer.com/article/10.1007/s00726-019-02729-y.
Han, J.; Wzorek, A.; Soloshonok, V. A.; Klika, K. D. The self-
disproportionation of enantiomers (SDE): The effect of scaling down,
potential problems versus prospective applications, possible new
occurrences, and unrealized opportunities? Electrophoresis 2019, in
press. https://doi.org/10.1002/elps.201800414.
(49) Tokunaga, E.; Yamamoto, T.; Ito, E.; Shibata, N. Understanding
the Thalidomide Chirality in Biological Processes by the Self-
disproportionation of Enantiomers. Sci. Rep. 2018, 8 (1), Art. no.
17131. https://doi.org/10.1038/s41598-018-35457-6.
(50) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.;
Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. NMR
Chemical Shifts of Trace Impurities: Common Laboratory Solvents,
Organics, and Gases in Deuterated Solvents Relevant to the
Organometallic Chemist. Organometallics 2010, 29 (9), 2176–2179.
https://doi.org/10.1021/om100106e.
(51) Mondal, M.; Unver, M. Y.; Pal, A.; Bakker, M.; Berrier, S. P.;
Hirsch, A. K. H. Fragment-Based Drug Design Facilitated by Protein-
Templated Click Chemistry: Fragment Linking and Optimization of
Inhibitors of the Aspartic Protease Endothiapepsin. Chem. –Eur. J.
(12), 2101–2103. https://doi.org/10.1002/anie.200604444.
(42) Schuhmacher, J.; Klivényi, G.; Matys, R.; Stadler, M.; Regiert, T.;
Hauser, H.; Doll, J.; Maier-Borst, W.; Zöller, M. Multistep Tumor
Targeting in Nude Mice Using Bispecific Antibodies and a Gallium
Chelate Suitable for Immunoscintigraphy with Positron Emission
Tomography. Cancer Res. 1995, 55 (1), 115–123.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(43) Tsionou, M. I.; Knapp, C. E.; Foley, C. A.; Munteanu, C. R.;
Cakebread, A.; Imberti, C.; Eykyn, T. R.; Young, J. D.; Paterson, B.
M.; Blower, P. J.; et al. Comparison of Macrocyclic and Acyclic
Chelators for Gallium-68 Radiolabelling. RSC Adv. 2017, 7 (78),
4
9586–49599. https://doi.org/10.1039/c7ra09076e.
(44) Eder, M.; Neels, O.; Müller, M.; Bauder-Wüst, U.; Remde, Y.;
Schäfer, M.; Hennrich, U.; Eisenhut, M.; Afshar-Oromieh, A.;
Haberkorn, U.; et al. Novel Preclinical and Radiopharmaceutical
Aspects of [ Ga]Ga-PSMA-HBED-CC: A New PET Tracer for
Imaging of Prostate Cancer. Pharmaceuticals 2014, 7 (7), 779–796.
https://doi.org/10.3390/ph7070779.
6
8
(45) Larsen, S. K.; Jenkins, B. G.; Memon, N. G.; Lauffer, R. B.
Structure-Affinity Relationships in the Binding of Unsubstituted Iron
Phenolate Complexes to Human Serum Albumin. Molecular Structure
2016,
22
(42),
14826–14830.
https://doi.org/10.1002/chem.201603001.
of
Diacetate.
https://doi.org/10.1021/ic00331a008.
46) Tinoco, A. D.; Incarvito, C. D.; Valentine, A. M. Calorimetric,
Iron(III)
N,N’-Bis(2-Hydroxybenzyl)Ethylenediamine-N,N’-
(52) Yang, Y.-Y.; Ascano, J. M.; Hang, H. C. Bioorthogonal Chemical
Reporters for Monitoring Protein Acetylation. J. Am. Chem. Soc. 2010,
132 (11), 3640–3641. https://doi.org/10.1021/ja908871t.
(53) Hofslokken, N. U.; Skattebol, L. Convenient Method for the
Orffto-Formylation of Phenols. Acta Chem. Scand. 1999, 53 (4), 258–
262. https://doi.org/10.3891/acta.chem.scand.53-0258.
(54) (a) Tornøe, C. W.; Christensen, C.; Meldal, M. Peptidotriazoles on
Solid Phase: [1,2,3]-Triazoles by Regiospecific Copper(i)-Catalyzed
1,3-Dipolar Cycloadditions of Terminal Alkynes to Azides. J. Org.
Inorg.
Chem. 1990, 29 (6), 1147–1152.
(
Spectroscopic, and Model Studies Provide Insight into the Transport of
Ti(IV) by Human Serum Transferrin. J. Am. Chem. Soc. 2007, 129 (11),
3
444–3454. https://doi.org/10.1021/ja068149j.
(47) (a) Klika, K. D.; Soloshonok, V. A. Terminology Related to the
Phenomenon ‘Self‐Disproportionation of Enantiomers’ (SDE). Helv.
Chim.
Acta
2014,
97
(11),
1583–1589.
Chem.
2002,
67
(9),
3057–3064.
https://doi.org/10.1002/hlca.201400122. (b) Soloshonok, V. A.
Remarkable Amplification of the Self‐Disproportionation of
Enantiomers on Achiral‐Phase Chromatography Columns. Angew.
https://doi.org/10.1103/PhysRevE.70.051307. (b) Rostovtsev, V. V.;
Green, L. G.; Fokin, V. V.; Sharpless, K. B. A Stepwise Huisgen
Cycloaddition Process: Copper(I)-Catalyzed Regioselective “Ligation”
of Azides and Terminal Alkynes. Angew. Chem., Int. Ed. 2002, 41 (14),
Chem.,
https://doi.org/10.1002/anie.200503373.
48) (a) Han, J.; Kitagawa, O.; Wzorek, A.; Klika, K. D.; Soloshonok,
V. A. The self-disproportionation of enantiomers (SDE): a menace or
an opportunity? Chem. Sci. 2018, (7), 1718–1739.
Int.
Ed.
2006,
45
(5),
766–769.
2596–2599.
https://doi.org/10.1002/1521-
(
3773(20020715)41:14<2596::AID-ANIE2596>3.0.CO;2-4.
9
https://doi.org/10.1039/C7SC05138G. (b) Han, J.; Soloshonok, V. A.;
Klika, K. D.; Drabowicz, J.; Wzorek, A. Chiral sulfoxides: advances in
asymmetric synthesis and problems with the accurate determination of
the stereochemical outcome. Chem. Soc. Rev. 2018, 47 (4), 1307–1350.
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