One-step radiosynthesis of 4-nitrophenyl 2-[18F]fluoropropionate ([18F]NFP); Improved preparation of radiolabeled peptides for PET imaging

Article abstract of DOI:10.1002/jlcr.3111

The versatile ¹⁸F-labeled prosthetic group, 4-nitrophenyl 2-[¹⁸F]fluoropropionate ([¹⁸F]NFP), was synthesized in a single step in 45 min from 4-nitrophenyl 2-bromopropionate, with a decay corrected radiochemical yield of 26.2% ± 2.2%. Employing this improved synthesis of [¹⁸F]NFP, [¹⁸F]GalactoRGD - the current 'gold standard' tracer for imaging the expression of α_Vβ ₃ integrin - was prepared with high specific activity in 90 min and 20% decay corrected radiochemical yield from [¹⁸F]fluoride. 4-Nitrophenyl 2-[18F]fluoropropionate ([18F]NFP), was synthesized in a single radiochemical step in 45 minutes and 26% d.c. radiochemical yield from 4-nitrophenyl 2-bromopropionate. Employing this improved synthesis of [18F]NFP, [18F]GalactoRGD was prepared with high specific activity in 90 minutes and 20% d.c. radiochemical yield from [18F]fluoride. Copyright

Full text of DOI:10.1002/jlcr.3111

Research Article
Received 30 June 2013,
Revised 6 August 2013,
Accepted 12 August 2013
Published online 16 September 2013 in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.3111
One-step radiosynthesis of 4-nitrophenyl 2-
1
[
8
18
F]fluoropropionate ([ F]NFP); improved
preparation of radiolabeled peptides
for PET imaging
a,b,c
c
c
b
c
Mohammad B. Haskali,
Peter D. Roselt, John A. Karas, Wayne Noonan,
d
c
Christian W. Wichmann, Andrew Katsifis, Rodney J. Hicks,
a,b
and Craig A. Hutton *
1
8
18
18
The versatile F-labeled prosthetic group, 4-nitrophenyl 2-[ F]fluoropropionate ([ F]NFP), was synthesized in a single
step in 45 min from 4-nitrophenyl 2-bromopropionate, with a decay corrected radiochemical yield of 26.2% ± 2.2%.
1
8
18
Employing this improved synthesis of [ F]NFP, [ F]GalactoRGD — the current ‘gold standard’ tracer for imaging the
expression of α integrin — was prepared with high specific activity in 90 min and 20% decay corrected radiochemical
yield from [ F]fluoride.
V 3
β
1
8
18
Keywords: radiofluorination; PET imaging; fluoropropionate; RGD peptide; [ F]fluoride
1
8
18
Introduction
2-[ F]fluoroproprionate ([ F]NFP), respectively. Both of these
agents have been used in the radiolabeling of numerous peptides
Positron emission tomography (PET) is a powerful molecular
imaging technique, which enables the real-time imaging of
in vivo biochemistry, provides valuable insight into the staging
of disease, and uniquely allows one to observe and monitor
the affects of intervention on a timescale not readily available
to more conventional structural imaging techniques. The
successful application of this technique relies largely upon the
development of radiolabeled agents, which probe molecular
targets specific to the disease being interrogated.
v 3
for PET imaging, including the α β integrin-targeting RGD
13–17
10
18
peptides,
and somatostatin analogs.
cysteine-knot peptides, bombesin derivatives,
19,20
18
12
2-[ F]Fluoropropionate offers
considerable advantages due to its relatively small size, minimal
effect on the hydrophobicity of the peptide, and its metabolic
16
stability.
One of the most widely studied and clinically applied PET
18
4,12,15
v 3
tracers targeting α β integrin is [ F]GalactoRGD 1 (Figure 1).
The imaging of integrin expression is an important strategy for
The use of radiolabeled peptides and proteins in PET has the
potential to provide an inexhaustible number of agents with
monitoring the neovasculature of tumors, as α β integrin plays
v
3
6–11,21–25
an important role in tumor angiogenesis
and
1
–4
which to probe disease.
This has in part been borne out in
26,27 18
metastasis.
[ F]GalactoRGD 1 incorporates an aminomethyl
the molecular imaging of cancer with agents such as
radiolabeled analogs of the somatostatin receptor-selective
18
galacturonic acid linker between the cyclic peptide and the [ F]
fluoropropionyl group to improve biodistribution. Despite the
5
,6
agent octreotate –1a1nd radiolabeled ‘RGD’ peptides that target
7
the α β integrin.
v
3
1
8
a
The radionuclide F is ideally suited to PET imaging due to its
School of Chemistry, The University of Melbourne, Vic., 3010, Australia
optimal half life (110 min), high positron emission efficiency
b
Bio21 Molecular Science and Biotechnology Institute, The University of
(97%), low positron energy (0.64 MeV), and its amenity to chemical
Melbourne, Vic., 3010, Australia
incorporation into molecules of biological interest. Therefore, the
c
development of radiofluorinated peptides remains of important
The Centre for Molecular Imaging and Translational Research Laboratory, The
18
Peter MacCallum Cancer Centre, Melbourne, Vic., Australia
clinical interest. Most commonly, F is incorporated into a peptide
through the attachment of a radiolabeled prosthetic group.
There exists a range of prosthetic groups for this purpose, the
most common being 4-fluorobenzoate and 2-fluoropropionate,
each imparting its own pharmacokinetic characteristics upon the
d
ANSTO LifeSciences, Sydney, NSW, Australia
*
Correspondence to: Craig A. Hutton, School of Chemistry, The University of
Melbourne, Vic., 3010, Australia.
E-mail: chutton@unimelb.edu.au
1
2
resultant adduct.
The most versatile of the reagents available for fluorobenzoylation
and fluoropropionylation are the corresponding activated esters;
N-succinimidyl 4-[ F]fluorobenzoate ([ F]SFB) and 4-nitrophenyl thin layer chromatography.
Abbreviations: DMSO, dimethyl sulfoxide; NFP, 4-nitrophenyl 2-fluoropropionate;
K222, Kryptofix®222; n.d.c., non decay corrected; TBA, tetrabutylammonium; TLC,
18
18
J. Label Compd. Radiopharm 2013, 56 726–730
Copyright © 2013 John Wiley & Sons, Ltd.

M. B. Haskali et al.
purifications, which are both time-consuming and has to date
presented considerable challenges to the automation of this process.
Recently, Chen and co-workers reported the preparation
1
8
13,15,28,29
of [ F]FPP(RGD) 2 (Figure 1),
a promising new tracer
2
14,30
currently undergoing clinical trials.
In their preparation of
18
31,32
[
F]NFP 7, Chen and co-workers adapted Stöcklin’s synthesis
1
8
18
of [ F]2-fluoropropionic acid ([ F]FPA, 6b) in order to improve
18
the overall synthesis of [ F]NFP 7 (Scheme 2). Although this
improved method can be conducted in one pot and therefore
a
single radiosynthesis module, it still requires multiple
radiochemical steps, separated by an azeotropic drying of the
18
10,30
2
-[ F] fluoropropionate 6b.
18
Improvements in the radiochemical synthesis of [ F]NFP 7
18
would greatly assist the clinical preparation of F-labeled
peptides, such as 1 and 2, for PET imaging. Incorporation of
18
the F radionuclide in the final step of the synthesis of 7 would
clearly be optimal as this would minimize the number of
processes and thereby simplify automation and reduce the time
from end-of-beam to the final, ready-to-inject tracer.
18
Herein, we report an improved synthesis of [ F]NFP 7 in a
single radiochemical step and the use of this process in the
preparation of the clinically relevant tracers for PET imaging of
18
18
v 3 2
α β -related tumors, [ F]GalactoRGD 1 and [ F]FPP(RGD) 2.
Materials and methods
1
8
All reagents were purchased from commercially available
Figure 1.
expression.
v 3
[ F]-Fluoropropionylated peptides for PET imaging of α β integrin
18
sources and were used as received. No-carrier-added [ F]
fluoride ion was obtained from a PETtrace 16.5 MeV cyclotron
incorporating a high pressure niobium target (GE Healthcare,
18
18
desirable properties of 1 as a PET imaging agent, its lengthy, USA and Cyclotek, Vic., Australia) via the O(p,n) F nuclear
18
multistep synthesis presents a considerable limitation, and there reaction. F-Separation cartridges (Waters Accell Plus QMA
remains a need to improve its preparation in order for it to be Sep-Pak Light, MA, USA) were pre-conditioned with the base
widely available for clinical use. The syntheses of both the employed in the radiofluorination step (K
2
CO
). Reversed phase SPE cartridges (Phenomenex,
lengthy and complicated. The standard method for the synthesis Strata X 33 μ polymeric reversed phase (30 mg/mL), CA, USA)
3 3
, TBA–HCO ,
18
galacturonic acid moiety and the activated ester [ F]NFP 7 are
2 2 4 3
K C O , or KHCO
18
of [ F]NFP 7 is a multistep, labor intensive and time consuming were pre-conditioned with ethanol and water before use.
9,16
exercise (Scheme 1).
Because of the volatile nature of simple Radio-HPLC analyses were performed using a Shimadzu HPLC
fluoropropionate esters, a bulky 9-anthrylmethyl ester is (SCL-10AVP system controller, SIL-10ADVP auto injector,
employed for ease of handling during the radiolabeling LC-10ATVP solvent delivery unit, CV-10AL control valve,
procedure. Treatment of 2-bromopropionyl bromide 3 with DGU-14A degasser, and SPD-10AVPV detector, Kyoto, Japan)
9
-anthrylmethanol generates ester 4, which is then treated coupled to a scintillation detector (Ortec 276 Photomultiplier
1
8
with [ F]KF/K
under typical nucleophilic radiofluorination Base with Preamplifier, Ortec 925-SCINT ACE mate Preamplifier,
2
22
conditions to incorporate the radionuclide. The fluorinated ester Amplifier, BIAS supply and SCA, and a Bicron 1 M 11/2
18
5
is purified and then hydrolyzed to give [ F]2-fluoropropionate Photomultiplier Tube). Manual radio-HPLC purifications were
6
a, and subsequent treatment with p-nitrophenyl carbonate achieved using a similar system fitted with a manual injector.
18
generates the active ester [ F]NFP 7. The overall process Semi-preparative HPLC purification of non-radioactive materials
incorporates three radiochemical steps and two radio-HPLC was performed using an Agilent 1200 series HPLC system.
Analytical HPLC was performed on an Agilent 1100 series HPLC
system. The following columns, solvents and flow rates were
used for the purification of both radioactive and non-radioactive
material: NFP and its precursor; Synergi 10 μ Hydro-RP 80 Å,
2
8
1
50 × 15 mm, (0.1% TFA in 20–100% CH
mL/min. [ F]NFP 7; Macherey–Nagel EP250/16 nucleosil
00-7 C18 column, (0.1% TFA in 60:40 CH CN–H O), 6 mL/min.
3 2
3
CN–H
2
O over 80 min),
18
1
8
18
Scheme 2. Chen’s synthesis of [ F]NFP 7.
Scheme 1. Synthesis of [ F]NFP 7 via anthrylmethyl ester.
J. Label Compd. Radiopharm 2013, 56 726–730
Copyright © 2013 John Wiley & Sons, Ltd.
www.jlcr.org

M. B. Haskali et al.
GalactoRGD; Protecol C18 HQ305, 250 × 4.6 mm, 5 μ, 300 Å, (0.1% for 2 min, and then a portion (620 MBq) of the mixture was
18
3 2
TFA in 0–80% CH CN–H O over 40 min), 8 mL/min. [ F] diluted with water (1.5 mL) and purified by HPLC. To remove
18
18
GalactoRGD 1 and [ F]FPP(RGD)
2
2; Luna 5 μ C18(2) 100 Å, mobile phase and concentrate [ F]GalactoRGD 1, the HPLC
2
4
[
50 × 10.00 mm, 5 μ, (0.1% TFA in 10–80% CH CN–H O over fraction containing 1 was diluted with water (20 mL) and passed
3
2
0 min) 4 mL/min. QC and specific activity determination of through a pre-conditioned reversed phase SPE cartridge.
18
18
F]NFP 7; Luna 5 μ C18(2), 150 × 4.60 mm, (0.1% TFA in 60:40 Cartridge retained [ F]GalactoRGD 1 was then washed with
H O–CH CN), 1 mL/min. QC and specific activity determination phosphate buffered saline (PBS) (5 mL, pH 7.4) and finally eluted
2
3
1
8
of [ F]peptides: Phenomenex Jupiter 5u Proteo 90 Å, using ethanol (0.6 mL). The eluent was diluted with PBS (7 mL,
1
8
2
1
50 × 4.6 mm, (0.1% TFA in 2–80% CH CN–H O over 40 min), pH 7.4) and filtered to obtain [ F]GalactoRGD 1 (350 MBq, 69%
3 2
1
13
19
mL/min. H NMR, C NMR, and F NMR spectra were obtained decay corrected radiochemical yield). Specific activity was
À1
on a Varian Unity INOVA-500 MHz spectrometer or a Bruker 122 GBq μmol
.
AVANCE III-600 MHz spectrometer. MS data was obtained using
1
8
[
2
F]FPP(RGD) 2
Agilent 6510 Q-TOF LC/MS mass spectrometer (CA, USA)
18
1
8
equipped with an Agilent 1100 LC system. [ F]NFP 7 was
[
F]NFP 7 (5.0 GBq) isolated on a pre-conditioned reversed
Cl (2 mL) into a vial,
via an anhydrous sodium sulfate drying cartridge. The CH Cl
was evaporated at room temperature for 3 min and at 70 °C for
synthesized using a GE TRACERlab FXFN radiosynthesis module.
phase SPE cartridge was eluted with CH
2
2
2
2
4
-Nitrophenyl 2-bromopropionate 15
To a solution of (±)-2-bromopropionylbromide (0.50 g, 2.32 mmol) a further 2 min. MiniPEG-E(RGD)2 (1 mg, 0.6 μmol) and TEA
in CH Cl (10 mL), triethylamine (0.32 mL, 2.32 mmol) and (15 μL, 0.11 μmol) in DMSO (0.35 mL) were added. The reaction
2
2
p-nitrophenol (0.33 g, 2.32 mmol) were added at 0 °C. The was heated at 70 °C for 5 min. Water containing 0.1% TFA
mixture was stirred for 1 h, then the precipitate formed was (3 mL) was added to the reaction mixture. The reaction was left
removed by filtration and washed with CH Cl . The filtrate was at 70 °C for 5 min and then diluted with additional water (3 mL)
2
2
evaporated under vacuum, and the residue was purified by and purified by HPLC. The HPLC fraction containing 2 was
crystallization from ethyl acetate to yield the title compound diluted with water (40 mL) and isolated on a pre-conditioned
1
(
(
(
(
0.61 g, quant.) as white crystals, m.p. 37–39 °C. H NMR reversed phase SPE cartridge. The cartridge was washed with
500 MHz, CDCl
q, 1H, CH), 1.95 (d, 3H, CH
C=O), 155.0 (Ar–O), 145.6 (Ar–NO
3
) δ 8.30 (d, 2H, ArH), 7.31 (d, 2H, ArH), 4.60 PBS (5 mL, pH 7.4) and eluted with ethanol (0.6 mL). The eluent
13
18
3
3
). C NMR (125 MHz, CDCl ) δ 167.8 was diluted with PBS (7 mL, pH 7.4) and filtered to obtain [ F]
2
), 126.3 (Ar–C), 122.0 (Ar–C), FPP(RGD) 2 (1.1 GBq, 30% decay corrected radiochemical yield).
2
À1
3
9.0 (C–Br), 21.2 (CH
3
).
Specific activity was 255 GBq μmol
.
18
18
4
-Nitrophenyl 2-[ F]fluoropropionate ([ F]NFP 7)
Results and discussion
18
18
[
F]Fluoride in [ O]water was transferred to the TRACERlab FXFN
radiosynthesis module and passed through a pre-conditioned A simple, one-step synthesis of a small and versatile radiolabeled
18
QMA cartridge. Trapped [ F]fluoride (12.3–29.7 GBq) was prosthetic group has long been considered a valuable addition
18
eluted to the reactor with a solution containing KHCO
.03–0.07 mmol) and Kryptofix 222 (12–14 mg, 0.03–0.04 mmol) such an agent, except for its problematic preparation. Until now,
(3–7 mg, to a radiochemist’s armamentarium. Indeed, [ F]NFP 7 represents
3
0
18
in CH
5°C under helium flow and vacuum for 13 min, followed by substitution reactions of the propionate group, including
3 2
CN–H
O (60:40, 1.0 mL). The solution was evaporated at the synthesis of [ F]NFP 7 has necessarily incorporated multiple
6
18
heating at 120 °C under helium then vacuum for a further 7 min. substitution of the 2-bromo substituent with [ F]fluoride and
18
To the anhydrous [ F]KF/K222/KHCO3 residue, 4-nitrophenyl conversion of the acid to the ‘activated’ ester (Schemes 1 and 2).
-bromopropionate 15 (20 mg, 0.05 mmol) in tBuOH–CH CN In order to minimize the number of radiochemical steps,
2
3
18
(
4:1, 2 mL) was added. After 5 min at 100 °C, the solvent was substitution of the bromide with [ F]fluoride should be performed
18
evaporated to half volume, and the residue was diluted with as late as possible. Ideally, the substitution reaction with [ F]
mobile phase (0.1% TFA in 60:40 CH CN–H O, 1.5mL). The mixture fluoride would be performed as the final step, but this would
3
2
was transferred to the loop injection vial. The reaction vial was involve selective substitution of a secondary alkyl bromide in the
washed with mobile phase (1.5mL) and transferred to the loop presence of an activated ester, with the obvious potential side
1
8
injection vial. [ F] NFP 7 was then purified by preparative HPLC reactions of fluoride substitution at the acyl position and hydrolysis
31
to afford the title compound (3.2–7.7 GBq, 29% highest decay of the activated ester. Indeed, Block et al. attempted the aliphatic
18
corrected radiochemical yield), with the highest specific activity substitution of activated esters of 2-bromoacetate with [ F]
À1
achieved being 474 GBq μmol . The total reaction time was 45 min. fluoride in acetonitrile, without success. Other substitution
1
8
When [ F]NFP 7 was subsequently used for peptide labeling reactions in the presence of activated esters have also met with
33
34
experiments, the collected HPLC fraction was diluted in water limited success. However, Kim et al. recently reported that the
60 mL) and passed through a Strata X reversed phase SPE use of the tertiary alcoholic solvents generates a tert-alcohol-
(
1
8
cartridge. [ F]NFP 7 was retained on the cartridge. The cartridge solvated fluoride ion that reacts as a strong nucleophile yet
was rinsed with water (10 mL) and then removed from the moderate base, with minimal base-catalyzed side reactions.
35
radiosynthesis module to perform further labeling experiments. Olberg et al. employed t-butanol solvent mixtures in the
radiofluorination of a nicotinic acid tetrafluorophenyl ester. We
1
8
[
F]GalactoRGD 1
therefore envisaged that there may be a window of reactivity of
F]NFP 7 (3.7 GBq) isolated on a Strata X cartridge was eluted an activated 2-bromopropionate ester in which the activated ester
18
[
with DMSO (300 μL) into a vial charged with Galacto-RGD was relatively stable to hydrolysis during the radiofluorination
1.0 mg, 1.2 μmol). DMSO–TEA (20:1, 10 μL) was then added to stage, yet would still be reactive enough to acylate peptides
the same vial. The reaction mixture was left at room temperature rapidly and in good yield.
(
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Copyright © 2013 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2013, 56 726–730

M. B. Haskali et al.
18
Accordingly, the preparation of a variety of activated esters
This redesigned route to [ F]NFP 7 has enabled the synthesis
(
see Figure 2) of 2-bromopropionate (10–15) was attempted, of this valuable radiolabeled prosthetic group in a single
18
through treatment of 2-bromopropionylbromide 3 with the radiochemical step. Furthermore, the synthesis of [ F]NFP 7
respective hydroxy compounds N-hydroxysuccinimide (NHS), was fully automated on a TRACERlab FXFN system, with the
N-hydroxybenzotriazole (HOBt), N-hydroxy-7-azabenzotriazole overall preparation time reduced to an amenable 45 min.
(
4
HOAt), 2,3,5,6-tetrafluorophenol, 2,4-dinitrophenol, and
-nitrophenol. Most reactions proceeded to generate the [ F]NFP 7 by incorporating this method into the preparation
corresponding active esters 10–15 in good conversion, according of both the current gold standard ‘RGD’ peptide for clinical PET
We sought to exemplify the utility of this improved route to
18
18
to TLC analysis. However, the NHS, HOBt, and HOAt esters 10–12 imaging, [ F]GalactoRGD 1, and the recently reported dimeric
were unstable and hydrolyzed to the corresponding acid during ‘RGD’ peptide tracer, [ F]FPP(RGD) 2.
chromatography. Reaction of 2,4-dinitrophenol gave a mixture
of the desired dinitrophenyl ester 14 together with the method of Haubner et al. in our laboratory resulted in sluggish
hydrolysis product, presumably because of the dinitrophenol reaction and consequently low yields of [ F]GalactoRGD 1. We
containing water as an additive to minimize its explosive nature.
18
2
18
Treatment of GalactoRGD with [ F]NFP 7 according to the
16
18
This active ester was not pursued further. The tetrafluorophenyl
ester 13 was stable but due to its volatility was lost upon
removal of the solvent under reduced pressure. Uniquely, the
4
-nitrophenyl ester 15 was prepared in excellent yield and
afforded a white, non-volatile, crystalline solid that was stable to
HPLC, column chromatography, and crystallization conditions.
Radiofluorination of 15 was therefore investigated.
1
8
Scheme 3. One-step radiosynthesis of [ F]NFP 7.
18
Treatment of 15 under typical radiofluorination conditions ([ F]
KF/K222/K CO , CH CN, 80–100 °C, see Scheme 3 and Table 1) gave
2
3
3
18
*
only trace amounts of the desired product 7, with mainly
unreacted starting material 15 returned (Table 1, entry 1).
Nevertheless, it was promising that the p-nitrophenylester 15
was not hydrolyzed significantly under these conditions.
Table 1. Optimisation of [ F]NFP 7 synthesis
Temp.
(°C)
Yield %
(d.c.)
Entry
Solvent
CN
Time (min)
Use of tertiary alcoholic solvents according to the method of
†
1
CH
3
5
5
5
10
15
5
5
5
5
5
100
100
100
100
100
80
120
100
100
100
4
3
4
Kim et al. was next investigated. Use of t-amyl alcohol resulted
2
3
4
5
6
7
t-Amyl alcohol
14
in an increase in decay corrected yield to 14%, whereas use of
¶
CH
3
CN–tBuOH
CN–tBuOH
CN–tBuOH
CN–tBuOH
CN–tBuOH
CN–tBuOH
CN–tBuOH
CN–tBuOH
29
35
acetonitrile/t-butanol (1:4) resulted in a further increase to
9% decay corrected yield (Table 1, entries 2-3). Optimization
CH
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
3
19
11
20
21
17
18
9
2
of temperature, time, base, and concentration of starting
material were investigated. A temperature of 100 °C was found
to be optimal, with slightly lower yields at 80 °C and 120 °C (Table
†
8
9
1
, entries 6-7). Increasing the reaction time resulted in
‡
significantly reduced yields, presumably because of partial
degradation of the product at 100 °C over time (Table 1, entries 4-5).
Potassium hydrogen carbonate was the optimal base, with potassium
carbonate, potassium oxalate, and tetrabutylammonium hydrogen
carbonate all giving reduced yields (Table 1, entries 8-10). Decreasing
the concentration of the bromopropionate starting material 15
resulted in lower yields. The optimum conditions were found to be
§
10
Bold signifies the optimum conditions for the preparation of
compound 7.
*
18
Standard reaction conditions; [ F]KF/K222, KHCO
min, CH CN–tBuOH (1:4).
used in place of KHCO3.
NHCO used in place of KHCO3.
used in place of KHCO3.
Over three runs; 26.2% ± 2.2%.
3
, 100 °C,
5
3
†
K
2
CO
3
1
8
the use of acetonitrile/t-butanol solvent with [ F]KF/K /KHCO at
1
‡
§
¶
222
3
Bu
4
3
18
00 °C for 5 min, which provided [ F]NFP 7 in 26.2% ± 2.2%
2 2 4
K C O
(
3
maximum 29%) decay corrected radiochemical yield (Table 1, entry
18
). The [ F]NFP 7 was prepared in >99% radiochemical purity
À1
(Figure 3), with a specific activity of 474 GBq μmol
.
1
8
Figure 3. Co-injection of [ F]NFP 7 with cold standard (red, radio-HPLC trace;
Figure 2. Activated esters of 2-bromopropionate.
J. Label Compd. Radiopharm 2013, 56 726–730
blue, UV trace (254 nm)).
Copyright © 2013 John Wiley & Sons, Ltd.
www.jlcr.org

M. B. Haskali et al.
1
8
found that the ligation of [ F]NFP 7 to GalactoRGD was enhanced
when triethylamine was added, resulting in quantitative labeling
as judged by HPLC analysis of the reaction mixture (see SI). The
[7] A. J. Beer, H. Kessler, H.-J. Wester, M. Schwaiger, Theranostics 2011, 1, 48–57.
[
8] S. Liu, Bioconj. Chem. 2009, 20, 2199–2213.
[
9] R. Haubner, A. J. Beer, H. Wang, X. Chen, Eur. J. Inorg. Chem. 2010,
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purified tracer
1
was 1isolated in 69% decay corrected
[
10] S. Liu, H. Liu, G. Ren, R. H. Kimura, J. R. Cochran, Z. Cheng,
8
radiochemical yield from [ F]NFP 7. Employing our new method
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for the preparation of [ F]NFP 7 in combination with a modified [11] M. Schottelius, B. Laufer, H. Kessler, H.-J. Wester, Acc. Chem. Res.
method for conjugation to GalactoRGD resulted in the production
of [ F]GalactoRGD 1 in overall 20% decay corrected yield. The
specific activity was 122 GBq μmol at end of synthesis, and
the total synthesis time was 90 min.
Conjugation of [ F]NFP 7 to miniPEG-E(RGD) was performed [14] E. S. Mittra, M. L. Goris, A. H. Iagaru, A. Kardan, L. Burton, R. Berganos,
according to the method of Chin et al, to provide [ F]FPP(RGD) 2
in overall 7% decay corrected yield. The specific activity was 255 GBq
2
009, 42, 969–980.
18
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[
X. Chen, Bioconj. Chem. 2011, 22, 2415–2422.
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2
2
À1
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μmol at end of synthesis, and the total reaction time was 100 min.
In summary, a one-step radiochemical synthesis has been
developed for the preparation of [ F]NFP 7. The p-nitrophenyl
[
18
M. Schwaiger, Bioconj. Chem. 2004, 15, 61–69.
ester moiety appears uniquely stable under nucleophilic [17] R. Haubner, H.-J. R. Wester, W. A. Weber, C. Mang, S. I. Ziegler,
S. L. Goodman, R. Senekowitsch-Schmidtke, H. Kessler, M. Schwaiger,
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19] M. Fani, H. R. Maecke, S. M. Okarvi, Theranostics 2012, 2, 481–501.
radiofluorination conditions, yet is reactive enough to couple
with peptides in 5 min. This route to the synthesis of [ F]NFP 7
18
[
was automated on a TRACERlab FXFN system and enables the
18
preparation of PET imaging agents, such as [ F]GalactoRGD 1
[
1
8
2
and [ F]FPP(RGD) 2, with greatly reduced reaction times and [20] H.-J. Wester, M. Schottelius, T. Poethko, K. Bruus-Jensen, M. Schwaiger,
potentially higher specific activities.
Cancer Biother. Radiopharm. 2004, 19, 231–244.
[
[
21] J. S. Desgrosellier, D. A. Cheresh, Nat. Rev. Cancer 2010, 10, 9–22.
22] R. Haubner, H. J. Wester, U. Reuning, R. Senekowitsch-Schmidtke, B.
Diefenbach, H. Kessler, G. Stöcklin, M. Schwaiger, J. Nucl. Med.
Supporting Information
1
999, 40, 1061–1071.
Experimental procedures for the preparation of precursors and
non-radiolabeled standards; 4-nitrophenyl 2-fluoropropionate,
[
23] M. L. Janssen, W. J. Oyen, I. Dijkgraaf, L. F. Massuger, C. Frielink,
D. S. Edwards, M. Rajopadhye, H. Boonstra, F. H. Corstens, O. C. Boerman,
Cancer Res. 2002, 62, 6146–6151.
[24] A. J. Beer, A. L. Grosu, J. Carlsen, A. Kolk, M. Sarbia, I. Stangier,
P. Watzlowik, H. J. Wester, R. Haubner, M. Schwaiger, Clin. Cancer
Res. 2007, 13, 6610–6616.
GalactoRGD, FP-GalactoRGD, E(RGD) , miniPEG-E(RGD) , FP-P
2
2
18
(
RGD) . HPLC traces of crude and purified [ F]GalactoRGD 1
2
1
8
and [ F]FPP(RGD) 2.
2
[
25] A. J. Beer, R. Haubner, M. Goebel, S. Luderschmidt, M. E. Spilker,
Acknowledgements
H.-J. Wester, W. A. Weber, M. Schwaiger, J. Nucl. Med. 2005, 46,
1
333–1341.
This work was supported by the Australian Research Council
Cooperative Research Centre for Biomedical Imaging Development
[
26] B. Felding-Habermann, T. E. O’Toole, J. W. Smith, E. Fransvea,
Z. M. Ruggeri, M. H. Ginsberg, P. E. Hughes, N. Pampori, S. J. Shattil,
A. Saven, B. M. Mueller, Proc. Natl. Acad. Sci. U. S. A. 2001, 98,
1853–1858.
[27] M. Lorger, J. S. Krueger, M. O’Neal, K. Staflin, B. Felding-Habermann,
Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 10666–10671.
(
CRC-BID), including a postgraduate scholarship to MH. The
authors would also like to thank Cyclotek (Aust) Pty Ltd for the
1
8
generous supply of [ F]fluoride.
[
[
[
[
[
[
28] X. Zhang, Z. Xiong, Y. Wu, W. Cai, J. R. Tseng, S. S. Gambhir, X. Chen,
Conflict of Interest
J. Nucl. Med. 2006, 47, 113–121.
29] S. Liu, Z. Liu, K. Chen, Y. Yan, P. Watzlowik, H.-J. Wester, F. T. Chin,
X. Chen, Mol. Imaging Biol. 2009, 12, 530–538.
30] F. T. Chin, B. Shen, S. Liu, R. A. Berganos, E. Chang, E. Mittra, X. Chen,
S. S. Gambhir, Mol. Imaging Biol. 2011, 14, 88–95.
31] D. Block, H. H. Coenen, G. Stocklin, J. Label. Compd. Radiopharm.
The authors did not report any conflict of interest.
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