K. Kumata et al.
and desiccated through a small column filled with 250 mg of mixture and the mixture was heated at 1201C for 3 min in a hot
CaO (3 mm f  30 mm, kept at 1501C), and introduced into a vial cell. After the reaction, the mixture was diluted with 500 mL of an
(Pyrex, 5.0 mL) containing various anhydrous organic solvents HPLC mobile phase, and transferred onto a column (10 mm
(1 mL) cooled at À151C. The production time of [13N]NH3 was f  250 mm). Elution with CH3CN/H2O (4/6) (254 nm) at a flow
about 4 min from the end of bombardment. The specific activity rate of 4 mL/min gave a radioactive fraction corresponding to
of [13N]NH3 was assumed from that of [13N]1a determined by pure [13N]4. The fraction was collected in a rotary evaporator
HPLC analysis. The analytical condition of [13N]1a was as flask and evaporated to dryness at about 901C in a vacuum. The
follows: J’sphore ODS H80 (4 mm f  150 mm), CH3CN/H2O residue was dissolved in 10 mL of ethanol and 3 mL of sterile
(4/6), 1 mL/min and 254 nm (3.6 min). The effluent was isotonic saline, and passed through a 0.22-mm Millipore filter.
monitored by a UV detector at 254 nm and a radioactivity Total synthesis time was about 17 min from the EOB. At the end
detector and quantified using a calibration curve obtained with of the syntheses (EOS), 23 MBq of [13N]4 was obtained as an i.v.
0.5–10.0 mg/mL solutions of the authentic 1a.
injectable solution. The radiochemical purity of [13N]4 was
determined by analytical HPLC (J’sphore ODS H80 (4 mm
General analysis procedure for identification and radiochemical f  150 mm), CH3CN/H2O (4/6), 1 mL/min and 254 nm). The
identity of [13N]4 was confirmed by co-injection with the non-
yield
radioactive sample. The specific activity of [13N]4 was calculated
After the addition of CH3CN/H2O (1/1, 200 mL) terminated the
by comparing the assayed radioactivity with the carrier at the
reaction, the radiochemical yield (decay-corrected) of [13N]am-
UV peak of 254 nm.
monolysis for [13N]1, [13N]2 or [13N]3 was determined by analytic
HPLC based on [13N]NH3. The analytical condition was as
Conclusions
follows: J’sphore ODS H80 (4 mm f  150 mm), CH3CN/H2O
We determined a practical method for preparing [13N]urea and
(4/6–1/1), 1–2 mL/min and 254 nm. The confirmation of identity
[13N]carbamate analogues using nca [13N]NH3 with high specific
for each product was achieved by co-injection with the non-
radioactive standard.
activity. This method provides
a labeling technique for
synthesizing 13N-labeled radiopharmaceuticals with abundant
pharmacological profiles and biological activities. We are using
this method to synthesize other [13N]ligands for PET study on
animal and human.
[13N]ammonolysis of isocyanate 5a, carbamoyl chloride 6a and
chloroformate 7a using nca [13N]NH3
In a hot cell, a solution of [13N]NH3 (37–185 MBq) in 100 mL of
DCE was added to a reaction vial (Pyrex, 5.0 mL) containing 5a,
6a or 7a (10 mmol), 200 mL of anhydrous THF, CH3CN, DMF or
DCE and various bases (K2CO3, pyridine, Et3N, DMAP, i-Pr2NEt or
lutidine: 30 mmol). The reaction mixture was sealed and heated
at 751C for 3 min in a hot oil bath. After the reaction, the
reaction vial was cooled rapidly to determine the radiochemical
yield of [13N]ammonolysis based on [13N]NH3.
Acknowledgement
We thank the staff of the Cyclotron Operation Section and
Radiochemistry Section, Department of Molecular Probes,
National Institute of Radiological Sciences (NIRS) for their
support in the operation of the cyclotron and production of
radioisotopes. This study was partially supported by a consign-
ment grant for Molecular Imaging Program on Research Base for
PET Diagnosis from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japanese Government.
One-pot synthesis
(1) Removing excess COCl2: A solution of triphosgene (20 mmol) in
100 mL of DCE was added to a reaction vial containing a mixture
of 8a, 9a or 10a (10 mmol) and i-Pr2NEt (50 mmol) in 100 mL of
DCE, respectively. The mixture was heated at 751C under N2 for
30 min. The excess COCl2 was removed by flowing N2 into the
mixture. Then, an anhydrous [13N]NH3 solution (37–185 MBq) in
100–400 mL of DCE was added into the reaction mixture. The
mixture was heated for further 3 min at 751C.
(2) Controlling the amount of triphosgene: A solution of
triphosgene (2.5 mmol) in 100 mL of DCE was added to a reaction
vial containing a mixture of 8, 9 or 10 (10 mmol) and i-Pr2NEt
(50 mmol) in 100 mL of DCE, respectively. The mixture was heated
at 751C under N2 for 30 min. Then, an anhydrous [13N]NH3
solution (37–185 MBq) in 100–400 mL of DCE was added into the
reaction vial. The reaction mixture was continuously heated for
3 min at 751C.
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