Radiosynthesis of N-[4-(4-fluorobenzyl) piperidin-1-yl]-N'-(2-[ 11C]oxo-1,3-dihydrobenzimidazol-5-yl)oxamide, a NR2B-selective NMDA receptor antagonist

Article abstract of DOI:10.1002/jlcr.1702

In order to perform in vivo imaging of the NR2B NMDA receptor system by positron emission tomography, a NR2B selective NMDA receptor antagonist has been labelled with carbon-11 (half-life: 20 min). N-[4-(4-fluorobenzyl)piperidin-1- yl]-N'-(2-oxo-1,3-dihydrobenzimidazol-5-yl)oxamide has been described demonstrating high affinity and selectivity for the NR2B receptors (IC ₅₀ of 5 nM in [³H]Ro-25,6981 binding assay). The labelling precursor and the reference compound were synthesized by coupling the 4-(4-fluorobenzyl)piperidine with the corresponding oxalamic acid. The reaction of [¹¹C]phosgene with phenylenediamine precursor led the formation of the [¹¹C]benzimidazolone ring present on the ligand. The labelling occurred in THF or acetonitrile and the decay corrected radiochemical yield was 30-40% from the produced [¹¹C]methane. HPLC purification and formulation led to 2.6-3.7 GBq (70-100 mCi) of radioligand within 30-35 min. The specific radioactivity was 72-127 GBq/μmol (2-3.4 Ci/μmol) at the end of synthesis. Copyright

Full text of DOI:10.1002/jlcr.1702

Research Article
Received 18 June 2009,
Revised 22 October 2009,
Accepted 23 October 2009
Published online 8 December 2009 in Wiley Interscience
(www.interscience.wiley.com) DOI: 10.1002/jlcr.1702
Radiosynthesis of N-[4-(4-fluorobenzyl)
piperidin-1-yl]-N0-(2-[11C]oxo-1,3-
dihydrobenzimidazol-5-yl)oxamide,
a NR2B-selective NMDA receptor antagonist
Ã
c
Romain Labas,a,b Franck Sobrio,a,b Yann Bramoulle,
´
Anne-Sophie Herard, Martine Guillermier, Philippe Hantraye,
c
c
c
´
Frederic Dolle, and Louisa Barre
c
a,by
´ ´
´
´
In order to perform in vivo imaging of the NR2B NMDA receptor system by positron emission tomography, a NR2B selective
NMDA receptor antagonist has been labelled with carbon-11 (half-life: 20 min). N-[4-(4-fluorobenzyl)piperidin-1-yl]-N0-
(2-oxo-1,3-dihydrobenzimidazol-5-yl)oxamide has been described demonstrating high affinity and selectivity for the NR2B
receptors (IC50 of 5 nM in [3H]Ro-25,6981 binding assay). The labelling precursor and the reference compound were
synthesized by coupling the 4-(4-fluorobenzyl)piperidine with the corresponding oxalamic acid. The reaction of
[
11C]phosgene with phenylenediamine precursor led the formation of the [11C]benzimidazolone ring present on the
ligand. The labelling occurred in THF or acetonitrile and the decay corrected radiochemical yield was 30–40% from the
produced [11C]methane. HPLC purification and formulation led to 2.6–3.7 GBq (70–100 mCi) of radioligand within
30–35 min. The specific radioactivity was 72–127 GBq/lmol (2–3.4 Ci/lmol) at the end of synthesis.
Keywords: carbon-11; PET; NR2B; NMDA; radiolabelling
metabolic properties than the phenolic groups usually present
in NR2B antagonists (Figure 1). These oxamides presented high
Introduction
N-methyl-D-aspartate (NMDA) receptors play a specific role
among the excitatory ionotropic glutamate receptors by its
pharmacological and functional properties. Its high permeability
to calcium ions confers to the NMDA receptors a specific
importance in synaptic plasticity and neuronal death. NMDA
receptors are an assembly of four subunits consisting of two NR1
and NR2 subunits.1 Four different NR2 subunits exist (A, B, C and
D) and particularly, the NR2B subtype is involved in synaptic
plasticity, schizophrenia, neurodegenerative diseases, pain percep-
tion and ischemia.2 The NR2B subunit containing receptor is still
the sole subtype of NMDA receptors having highly selective
antagonists such as CP-101,606, Cl-1041 or Ro-25,6981, derived
from ifenprodil, the first selective antagonist known (Figure 1).3,4
The visualization and quantification of the NR2B receptors by a
non-invasive imaging technique like positron emission tomography
(PET) could facilitate the understanding of pathologies and offer a
diagnostic tool. For a few years, NR2B selective antagonists from
the different series were labelled with carbon-115–9 or fluorine-1810
(Figure 2). However, in spite of promising in vitro pharmacological
data, these compounds demonstrated a lack of specificity or
insufficient brain penetration to qualify as good radiotracers.
Recently a new series of NR2B antagonist was described11
consisting of a benzylpiperidine moiety related to the ifenprodil
structure as well as an oxamide function and a condensed
heterobicycle. The bicycle containing an NH group offers better
NR2B affinities and activities and a good selectivity towards
NR2A. Compound (N-[4-(4-fluorobenzyl)piperidin-1-yl]-N’-
1
(2-oxo-1,3-dihydrobenzimidazol-5-yl)oxamide, Figure 3) showed
the best affinity in this series with an IC50 of 5 nM in [3H]Ro-
25,6981 binding assay and 2 nM in functional assays of NMDA-
evoked changes of intracellular Ca21 flux measured by
fluorescence. These data were of the same order as for
Cl-1041 (IC50 = 8 nM) but better than Ro-25,6981 (IC50 = 57 nM)
for the NMDA-evoked Ca21 flux functional assay. Compound 1
also demonstrated a very low NR2A inhibition of 2% at 15 mM
measured using the same NMDA-evoked Ca21 assay. This
selectivity was better than for compound E (50% at 35 mM
aCEA, I2BM, CINAPS, GDM-TEP, Caen, France
b
´
Universite de Caen Basse Normandie, UMR 6232 CI-NAPS, Centre Cyceron,
Caen, France
cCEA, I2BM, SHFJ, LIME, Orsay, France
*Correspondence to: Franck Sobrio, UMR 6232 CI-NAPS, Centre Cyceron,
BP 5229, F-14074 CAEN, France.
E-mail: sobrio@cyceron.fr
y
´
Correspondence to: Louisa Barre, UMB 6232 CI-NAPS, Centre Cyceron, BP 5229,
F-14074 CAEN, France.
E-mail: barre@cyceron.fr
J. Label Compd. Radiopharm 2010, 53 63–67
Copyright r 2009 John Wiley & Sons, Ltd.

R. Labas et al.
OH
OH
Me
Me
N
N
OH
OH
HO
Ifenprodil
CP-101,606
O
S
OH
F
O
N
N
O
Me
N
H
OH
CI-1041
Ro-25,6981
Figure 1. NR2B NMDA receptor antagonists.
11CH3
Me
OH
11CH3
N
OH
NH
O
N
H
N
N
O
11CH3
Me
HO
A
B
C
NH
H
N
11C
N
Cl
18F
N
H
O
D
O
N
H
D
E
D
Cl
Figure 2. Radiolabelled selective NR2B antagonists : [11C]Ro-647312 (A), N-(2-[11C]methoxyphenyl)cinnamidine (B), [11C]methoxy-CP-101,606 (C), N-(3,5-dichlorobenzyl)-4-
([18F]fluoromethoxy)phenylcarboximidamine-d2 (D), 5-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]-1,3-dihydrobenzimidazol-2-[11C]one (E).
O
1-yl]oxalamic acid.11 The ethyl chlorooxoacetate was added to the
5-amino-2-benzimidazolinone affording the ethyl ester 2. After
hydrolysis, the coupling reaction of the corresponding oxalamic
acid 3 with 4-(4-fluorobenzyl)piperidine14 in presence of HBTU led
to the compound 1 with an overall yield of 39%.
H
N
H
N
F
N
O
O
N
H
1
The labelling precursor 7 was obtained analogously (Scheme 2)
from 2-nitro-1,4-phenylenediamine. After the addition of the ethyl
chlorooxoacetate and hydrolysis, the resulting acid 5 has reacted
with 4-(4-fluorobenzyl)piperidine in the presence of HBTU. The
reduction of the nitro group was not optimized since the amount
of product obtained was sufficient for this study. The precursor 7
was obtained in 15% overall yield in 5 steps.
The ligand 1 was labelled (Scheme 3) by reaction of precursor
7 with [11C]phosgene obtained as described previously.15 The
cyclization reaction occurred instantaneously during the bub-
bling of [11C]phosgene in a reactor containing precursor 7
(3 mmol) in solution either in acetonitrile or in THF containing
TEA. The decay-corrected radiochemical yield was 30–40% from
the [11C]methane in both conditions. After HPLC purification
using a C18 column, the collected fraction was diluted and
passed through a C18 SPE cartridge to retain [11C]-1 that was
then eluted with ethanol. A dilution with saline followed by
sterilization by filtration (0.22 mm) resulted in a 10% ethanol
physiological solution with a pH of 5–7. Typically, 2.6–3.7 GBq
(70–100 mCi) of [11C]-1 was produced within 30–35 min includ-
ing the purification and formulation with chemical and radio-
chemical purities measured by HPLC greater than 98%. The
specific radioactivities were 72–127 GBq/mmol (2–3.4 Ci/mmol) at
the end of the synthesis.
Figure 3. Compound 1.
towards NR2A subunit) and 1 presented no adrenergic activity3
when E showed an IC50 of 500 nM for a1 adrenergic receptors.12
Due to its planarity, the series of alkynyl compounds demon-
strated a poor solubility13 that would be better with the
oxamides. Moreover, the fluorinated compound 1 offers the
possibility of a labelling with fluorine-18 in case of promising
in vivo properties.
The intention of this study was to develop the labelling of
compound 1 with carbon-11 to evaluate in vivo its potency as a
PET radiotracer for imaging NR2B containing NMDA receptors.
Results and discussion
The presence of a benzimidazolinone moiety on 1 (Figure 3)
permits the labelling by cyclization reaction with [11C]phosgene
of the corresponding ring-open precursor phenylenediamine.
The reference compound 1 and the labelling precursor 7 were
prepared following the same strategy (Schemes 1 and 2). The
synthesis of compound 1 was slightly different than the previously
described pathway using a coupling reaction between the
5-amino-2-benzimidazolinone and N-[4-(4-fluorobenzyl)piperidin-
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Copyright r 2009 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2010, 53 63–67

R. Labas et al.
EtOCOCOCl
TEA, CHCl3
85%
O
H
N
H
N
H
N
H2N
KOH, EtOH
99%
EtO
O
O
N
H
O
N
H
2
O
O
4-(4-fluorobenzyl)piperidine
HBTU, TEA, DMF
H
N
H
N
H
N
H
N
F
HO
N
O
O
O
O
46%
N
H
N
H
3
1
Scheme 1.
O
H
N
EtOCOCOCl
TEA, CHCl3
O
KOH
EtOH
H2N
NO2
NH2
H
N
NO2
NH2
HO
NO2
NH2
EtO
O
67%
80%
O
4
5
O
O
H
H
N
HBTU, TEA, DMF
4-(4-fluorobenzyl)piperidine
NO2
NH2
NH2
NH2
N
N
Fe, HCl
36%
N
O
O
79%
7
6
F
F
Scheme 2.
11CH4
O
O
H
H
N
H
N
F
NH2
NH2
F
N
N
11COCl2
N
11 C
N
H
O
O
O
[
11C]-1
7
Scheme 3.
occurred on a target filled with nitrogen containing 5%
hydrogen (Air Liquide, N60 quality).
Conclusion
All melting points were determined on a Barnstead Electro-
thermal IA 9100 melting point apparatus and are uncorrected.
1H, 13C and 19F NMR spectra were measured on a Brucker DRX
400, at 400 MHz (1H), 100.6 MHz (13C) and 376.4 MHz (19F) or on a
Brucker DPX 250, at 250 MHz (1H), 62.5 MHz (13C) and 235 MHz
(19F). Chemical shifts are reported as parts per million (d) by
reference to the proton resonance resulting from the incom-
plete deuteration of the NMR solvent. Coupling constants are
given in Hz and coupling patterns are abbreviated as: s (singlet),
d (doublet), t (triplet), q (quadruplet), m (mutiplet), bs (broad
singlet) and dd (doublet of doublet). High-resolution mass
spectra (HRMS) were obtained on a Waters Q-TOF micro
spectrometer by electrospray ionisation (ESI). Elemental analyses
were performed on a ThermoQuest analyser CHNS and were
within 70.4% of the calculated values.
We have labelled compound 1,
a NR2B-selective NMDA
antagonist, by a cyclization reaction from the phenylenediamine
precursor 7 with [11C]phosgene. The radiochemical yield was
30–40%. The mPET scans on rodents are under progress to
evaluate the potential of [11C]-1 as a PET radiotracer for imaging
the cerebral NR2B NMDA receptors.
Experimental
All reagents were purchased from Fluka or Sigma-Aldrich (Saint-
Quentin Fallavier, France) and were used without further
purification. Anhydrous THF, DMF and acetonitrile were
obtained from a Mbraun SPS-800 solvents delivery system.
HPLC quality solvent was purchased from Merck (France) or SDS
(Peypin, France). No-carrier-added [11C]methane was produced
using a Cyclone 18/9 (IBA) cyclotron using the14N(p,a)11C
nuclear reaction with a 20 MeV proton beam. Irradiation
Thin-layer chromatographies (TLC) were run on pre-coated
aluminium plates of silica gel 60F254 (Merck) and Rf were
J. Label Compd. Radiopharm 2010, 53 63–67
Copyright r 2009 John Wiley & Sons, Ltd.
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R. Labas et al.
established using an UV-lamp at 254 nm or by ninhydrin or room temperature then 10% aqueous NaHCO3 (80 mL) and
phosphomolybdic acid hydrate spray reagents. Liquid chroma- dichloromethane (50 mL) were added. The layers were separated
tographies were performed on 40–63 mesh silica gel 60 (Merck) and the aqueous layer was extracted with dichloromethane
columns. Radioactive TLC was measured using an Instant (3 ꢀ 50 mL). The combined organic layers were dried over
Imagers Packard apparatus. Radioactivity quantities were MgSO4, filtered, concentrated and purified by chromatography
determined with a dose calibrator (Capintec R15C). Semi- on silica gel (96/4/0.1 to 94/6/0.1, dichloromethane/methanol/
preparative HPLC was performed using a Waters 501 pump, a NH4OH) to afford 1 as a white solid (156 mg, 46%). M.p.:
spectrophotometer (l = 254 nm) coupled with a Geiger-Mu¨ller 295–3001C. 1H NMR (DMSO-d6): 10.64–10.53 (m, 3H), 7.45
probe (SDS, Paris, France) using a Symmetry C18 column (d, J= 1.6 Hz, 1H), 7.25–7.17 (m, 2H), 7.14–7.04 (m, 3H), 6.85
(300 ꢀ 7.8 mm, 7 mm, Waters) with an eluent made of water/ (d, J= 8.4 Hz, 1H), 4.33–4.23 (m, 1H), 3.77–3.67 (m, 1H), 3.09–2.98
acetonitrile/trifluoroacetic acid (63/37/0.1) at 7 mL/min (tR (1) = (m, 1H), 2.72–2.61 (m, 1H), 2.53 (m, 2H), 1.85–1.73 (m, 1H), 1.66–1.55
5.5–6.0 min). Radiochemical purity analysis were performed (m, 2H), 1.21–1.04 (m, 2H). 13C NMR (DMSO-d6): 162.7, 162.0, 160.7
on a Merck HPLC system coupled with a NaI radioactive (d, J=240.9Hz), 155.5, 136.0 (d, J= 3.1 Hz), 131.4, 130.7 (d, J=7.6Hz),
detector (Novelec, France) using a Macherey Nagel Nucleosil 129.7, 126.3, 114.8 (d, J= 20.8 Hz), 112.4, 108.3, 101.0, 45.8, 41.0, 40.7,
100–5 Protect 1 column (4.6 ꢀ 250 mm, 5 mm) at a flow rate 37.2, 31.8, 30.8. 19F NMR (DMSO-d6): ꢁ117.42. HRMS: m/z found for
of 1 mL/min with methanol/0.01 M phosphoric acid solution [M1H]1 C21H22FN3O4: 397.1662 (calcd.: 397.1676). Anal. found for
(64/36) as eluent.
C21H21FN4O3 ꢂ 0.3 H2O: C = 62.59%, H = 5.77%, N = 13.79% (calcd.:
C = 62.41%, H = 5.45%, N = 13.86%).
Ethyl 2-acetamido-N-(2-oxo-2,3-dihydrobenzimidazol-5-yl)
acetate 2
Ethyl 2-acetamido-N-(4-amino-3-nitrophenyl)acetate 4
A solution of ethyl chlorooxoacetate (2.92 mL, 26 mmol) in DMF
(20 mL) was added dropwise at 01C to a solution of 2-nitro-1,4-
phenylenediamine (2.0 g, 13 mmol) and triethylamine (3.66 mL,
26 mmol) in chloroform (100 mL). The reaction was stirred at
room temperature for 1 h and decomposed with a 10% NaHCO3
solution (100 mL). The layers were separated and the aqueous
layer was extracted with dichloromethane (3 ꢀ 100 mL). The
combined organic layers were dried over MgSO4, filtered,
concentrated and purified by column chromatography (70/30
to 50/50, heptane/ethyl acetate) to give 4 as an orange solid (2.21 g,
67%). M.p.: 1761C. 1H NMR (CDCl3): 8.19 (d, J= 2.4 Hz, 1H), 7.46 (dd,
J=9.2Hz, J= 2.4 Hz, 1H), 6.68 (d, J=9.2Hz, 1H), 4.28 (bs, 3H), 4.14
(q, J= 7.2 Hz, 2H), 1.16 (t, J= 7.2 Hz, 3H). 13C NMR (CDCl3): 160.9,
155.7, 144.2, 130.9, 129.9, 126.3, 119.8, 117.8, 63.8, 14.1. HRMS: m/z
found for [M1H]1 C10H12N3O5 : 254.0767 (calcd.: 254.0777). Anal.
found for C10H11N3O5: C = 47.42%, H = 4.53%, N = 16.61% (calcd.:
C = 47.43%, H = 4.38%, N = 16.59%).
Ethyl chlorooxoacetate (900 mL, 8.05 mmol) was added dropwise
to a solution of 5-amino-1,3-dihydrobenzoimidazol-2-one (1.0 g,
6.70 mmol) and sodium acetate (660 mg, 8.05 mmol) in acetic
acid (35 mL). The reaction mixture was stirred at 351C for 1 h and
further 45 min at 90 C. Then, water was added (70 mL) and the
resulting precipitate was filtered, washed with water (2 ꢀ 30 mL)
and dried overnight under vacuum affording 2 (1.41 g, 85%) as a
1
white solid. M.p.: dec. 3301C. H NMR (DMSO-d6): 10.66 (s, 1H),
10.65 (s, 1H), 10.61 (s, 1H), 7.52 (d, J = 1.5 Hz, 1H), 7.26 (dd,
J = 8.4 Hz, J = 1.5 Hz, 1H), 6.88 (d, J = 8.4 Hz, 1H), 4.30 (q, J = 7.1 Hz,
2H), 1.31 (t, J = 7.1 Hz, 3H). 13C NMR (DMSO-d6): 160.9, 155.5,
155.1, 131.0, 129.6, 126.8, 113.2, 108.2, 101.6, 62.3, 13.9. HRMS: m/z
found for [M1H]1 C11H12N3O4: 250.0840 (calcd.: 250.0828). Anal.
found for C11H11N3O4: C = 53.11%, H = 4.83%, N = 16.50% (calcd.:
C = 53.01%, H = 4.45%, N = 16.86%).
2-Acetamido-N-(2-oxo-2,3-dihydrobenzimidazol-5-yl)acetic
acid 3
2-Acetamido-N-(4-amino-3-nitrophenyl)acetic acid 5
A solution of potassium hydroxide (810 mg, 14.4 mmol) in water
(3 mL) was added to a suspension of compound 2 (1.2 g,
4.8 mmol) in ethanol (25 mL). Once the reaction mixture was
stirred at room temperature for 2 h, water (15 mL) was added
and the solution was acidified using concentrated hydrochloric
acid. The resulting precipitate was filtered off and dried
overnight under vacuum to afford the hydrochloride salt
(1.22 g, 99%) as a white solid. M.p.: dec. 3601C. 1H NMR
(DMSO-d6): 10.64 (s, 1H), 10.60 (s, 1H), 10.58 (s, 1H), 7.54 (d, J =
2.0 Hz, 1H), 7.28 (dd, J = 2.0 Hz, J = 8.4 Hz, 1H), 6.87 (d, J = 8.4 Hz,
1H). 13C NMR (DMSO-d6): 163.2, 157.3, 156.3, 132.1, 130.4, 127.5,
114.0, 109.1, 102.3. HRMS: m/z found for [MꢁH]ꢁ C9H6N3O4:
220.0357 (calcd.: 220.0358 ). Anal. found for C9H7N3O4 ꢂ HCl ꢂ 0.2
H2O : C = 41.48%, H = 3.53%, N = 16.05% (calcd.: C = 41.38%,
H = 3.24%, N = 16.09%).
Potassium hydroxide (10 N, 2.1 mL, 21.3 mmol) was added under
vigorous stirring to a suspension of 4 (1.8 g, 7.1 mmol) in ethanol
(60 mL). The reaction mixture was stirred for 1 h at room
temperature and was acidified with concentrated hydrochloric
acid. The precipitate was filtered off and dried overnight under
vacuum affording 5 as a red solid (1.27 g, 80%). M.p.: 2311C. H
NMR (DMSO-d6): 10.74 (s, 1H), 8.56 (d, J = 2.4 Hz, 1H), 7.72 (dd,
J = 9.2 Hz, J = 2.4 Hz, 1H), 7.43 (bs, 2H), 7.00 (d, J = 9.2 Hz, 1H). 13
NMR (DMSO-d6): 162.0, 156.5, 143.7, 129.7, 129.1, 126.3, 119.4,
115.8. HRMS: m/z found for [MꢁH]ꢁ C8H6N3O5: 224.0310 (calcd.:
224.0307). Anal. found for C8H7N3O5: C = 42.52%, H = 3.30%,
N = 18.26% (calcd.: C = 42.67%, H = 3.13%, N = 18.66%).
1
C
N-[4-(4-Fluorobenzyl)piperidin-1-yl]-N0-(4-amino-3-nitrophenyl)
oxamide 6
N-[4-(4-Fluorobenzyl)piperidin-1-yl]-N0-(2-oxo-1,3-dihydro-
benzimidazol-5-yl)oxamide 1
Triethylamine (548 mL, 3.90mmol), 4-(4-fluoro-benzyl)piperidine
(276mg, 1.43mmol) and HBTU (542mg, 1.43mmol) were added
Under a nitrogen atmosphere, triethylamine (242 mL, 1.72 mmol), to 5 (340mg, 1.52mmol) in solution in DMF (20 mL). The solution
4-(4-fluorobenzyl)piperidine (221 mg, 0.86 mmol) and HBTU was stirred for 24h at room temperature then sodium
(391 mg, 1.03 mmol) were added to a solution of 3 (266 mg, bicarbonate aqueous solution (10%, 40mL) was added. The
1.03 mmol) in DMF (20 mL). The solution was stirred for 24 h at aqueous phase was extracted with dichloromethane (4 ꢀ 50mL).
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R. Labas et al.
The combined organic layers were dried over MgSO4, filtered, [11C]COCl2 was passed on-line through an antimony-guard in
concentrated and purified by chromatography on silica gel (99/1/ order to remove the excess of chlorine.
0.1, dichloromethane/methanol/NH4OH) to afford 6 as an orange
solid (452mg, 79%). M.p.: 1911C. 1H NMR (DMSO-d6): 10.68 (s, 1H), Radiosynthesis and purification of [11C]-1
8.45 (d, J = 2.4 Hz, 1H), 7.55 (dd, J = 9.2 Hz, J = 2.4 Hz, 1H), 7.38 (s,
2H), 7.23–7.16 (m, 2H), 7.11–7.03 (m, 2H), 7.01 (d, J = 9.2 Hz, 1H),
The synthesized [11C]COCl2 was bubbled at room temperature in
a conic reaction vial containing the labelling precursor 7
4.34–4.25 (m, 1H), 3.84–3.75 (m, 1H), 3.09–2.98 (m, 1H), 2.72–2.62
(m, 1H), 2.53 (m, 2H), 1.86–1.71 (m, 1H), 1.70–1.55 (m, 2H),
(1–1.6 mg) dissolved in 300 mL of THF or 500 mL of acetonitrile.
When the transfer of [11C]COCl2 was completed, the reaction
solution was diluted with 0.5 mL of the HPLC mobile phase and
1.25–1.05 (m, 2H). 13C NMR (DMSO-d6): 162.3, 162.0, 160.7 (d,
J = 241.5 Hz), 143.5, 138.4, 136.1, 136.0, 130.7 (d, J = 7.5 Hz), 129.1
injected onto the column. The pure fraction of [11C]-1 was
collected and diluted with water (30 mL). The solution was
passed through a Chromabond C18ec Shorty cartridge (20 mg,
(d, J = 11.3 Hz), 126.4, 119.6, 114.8 (d, J = 27.0Hz), 45.8, 41.0, 40.8,
37.3, 31.8, 30.9. 19F NMR (DMSO-d6): ꢁ117.42. HRMS: m/z found
for [M1H]1 C20H22FN4O4: 401.1613 (calcd.: 401.1625). Anal. for
Macherey Nagel). The cartridge was washed twice with water
C20H21FN4O4.0.2H2O: C = 59.34%, H = 5.72%, N = 13.92% (calcd.:
(5 mL) and the radiotracer was eluted with ethanol (500 mL).
Physiological saline (5 mL) was added and the resulting solution
C = 59.33%, H = 5.35%, N = 13.84%).
was filtered on a sterile 0.22 mm GV-Millipore filter.
N-(3,4-Diaminophenyl)-N0-[4-(4-fluorobenzyl)piperidin-1-yl]
oxamide 7
Acknowledgements
A suspension of 6 (400 mg, 0.99 mmol) and powdered iron
(392 mg, 6.99 mmol) in water (2 mL) was refluxed during 30 min
under vigorous stirring. Then concentrated hydrochloric acid
(83 mL, 0.49 mmol) was carefully added and the reaction mixture
was heated for further 3 h. After cooling to room temperature,
the iron was filtered off and washed with methanol (5 ꢀ 10 mL).
The combined filtrates were concentrated under vacuum and
purified on silica gel column (98/2/0.1 to 95/5/0.1 dichloro-
methane/methanol/NH4OH) to give 7 as a white solid (131 mg,
The authors thank Mr Tirel for performing the cyclotron
11
irradiation and Mr Ibazizene for his help on [ C]phosgene
`
preparation at Cyceron Centre. This work was supported by the
´
CEA and the Conseil Regional de Basse-Normandie.
References
1
36%). M.p.: 1851C. H NMR (DMSO-d6): 10.09 (s, 1H), 7.25–7.05
(m, 4H), 6.87 (d, J = 2.2 Hz, 1H), 6.59 (dd, J = 8.2 Hz, J = 2.2 Hz, 1H),
6.42 (d, J= 8.2 Hz, 1H), 4.54 (bs, 2H), 4.37–4.22 (m, 3H), 3.75–3.65
(m, 1H), 3.10–2.90 (m, 1H), 2.75–2.60 (m, 1H), 2.53 (m, 2H),
1.88–1.48 (m, 3H), 1.25–0.98 (m, 2H). 13C NMR (DMSO-d6): 163.1,
161.5, 160.7 (d, J = 240.8 Hz), 136.3 (d, J = 3.1Hz), 135.1, 131.8, 130.7
(d, J = 7.5 Hz), 128.3, 114.8 (d, J= 20.7Hz), 114.1, 109.3, 106.9, 45.7,
40.6, 41.0, 37.3, 31.7, 30.8. 19F NMR (DMSO-d6): ꢁ117.44. HRMS: m/
z found for [M1H]1 C20H24FN4O2: 371.1883 (calcd.: 371.1883).
Anal. for C20H23FN4O2 ꢂ 0.5 H2O: C = 63.48%, H = 6.54%, N = 14.77%
(calcd.: C =63.31%, H = 6.38%, N =14.77%).
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Preparation of [11C]COCl2
´
Briefly, the [11C]CH4 produced by the cyclotron was passed
through two guards containing soda lime or P2O5. The [11C]CH4
was separated from the target gas and concentrated by
trapping in two successive U-tube filled with Porapak-Q
(80–100 mesh, Waters) dipped in liquid argon. [11C]CH4 was
then released and gently swept in a minimum volume of helium
into a 20 mL mixing chamber containing chlorine (99.99%, Air
Liquide). Using N2/O2 (98/2) gas, the [11C]CH4/chlorine mixture
was passed successively through an empty horizontal quartz
tube (300 mm length, 4 mm internal diameter) heated at 5601C
and then through a Pyrex tube (300 mm length, 4 mm internal
diameter) containing 2 g of iron chips (Aldrich 99.98%) heated at
3201C. Finally, the gaseous reaction mixture containing the
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