S. R. Pollack and D. J. Schenk
acid solution. The mixture was then concentrated in vacuo. This crude sodium hydroxide solution (200 μl, 0.2 mmol). After stirring at ambient
material was diluted with water and the salts removed by adsorption
temperature for 2 h, HPLC-MS analysis of the reaction showed > 95%
conversion to the desired sulfide. HPLC of the crude showed product at
90% radiochemical purity (Curosil PFP, 5 μm, 4.6 × 250 mm, 1 ml/min
40% acetonitrile/water + 20 mM NH4OAc, Rt = 13.6 min).The reaction
was concentrated in vacuo and purified by semi-preparative reversed
phase HPLC (Curosil PFP, 5u, 10 × 250 mm, 5 ml/min 40%
acetonitrile/water + 20 mM NH4OAc) to give (after solvent switch of
product containing fractions to an ethanol solution using C18 Sep-Pak®
SPE cartridges) 210 mCi (72.6%) of [3H]-5-methoxy-2-(((4-methoxy-3,5-
dimethylpyridin-2-yl)methyl)thio)-1H-benzo[d]imidazole (28) (specific
activity = 5.2 Ci/mmol, 15.7 mCi/mg; radiochemical purity > 98%.) The
labeled material had the same Rt as the unlabeled as seen by both HPLC
and HPLC-MS analyses (individually and co-injection).
of compound onto two stacked Waters C18 Sep-Pak® Plus long
cartridges (820-mg sorbent each) [conditioned with 10-ml ethanol and
then 10-ml water]. The SPE cartridges were then washed with water
(20 ml), and the flask used for concentrating the reaction was rinsed with
ethanol (10 ml) and flushed through cartridges followed by an additional
20-ml ethanol. Negligible radioactivity was observed in the water wash.
The ethanol wash contained 321 mCi (89% accounting for radiochemical
purity) of [3H]-5-methoxy-1H-benzo[d]imidazole-2-thiol (23) (91.4%
radiochemical purity; specific activity = 5.23 Ci/mmol, 29.0 mCi/mg.) The
labeled material has the same Rt as the unlabeled standard as seen by
both HPLC and HPLC-MS analyses (individually and co-injection). The
material required no further purification and was used directly in the next
step (synthesis of compound 28).
Preparation of [3H]5-methoxy-2-(((4-methoxy-3,5-dimethylpyridin-
2-yl)methyl)sulfinyl)-1H-benzo[d]imidazole (omeprazole) (29)
Preparation of N-(5-methoxy-2-nitrophenyl)acetamide (25)
To a solution of [3H]-5-methoxy-2-(((4-methoxy-3,5-dimethylpyridin-2-yl)
methyl)thio)-1H-benzo[d]imidazole (28) (210 mCi, 13.4 mg, 0.040 mmol)
in 2.5-ml DCM, at ~ À40°C to À45°C (acetonitrile/CO2 bath), was added
3-chloroperoxybenzoic acid (9 mg, 0.04 mmol; 77% purity) as a solid in
one portion. The reaction was stirred at À40°C for 1 h, then an additional
equivalent of 3-chloroperoxybenzoic acid (9 mg, 0.04 mmol; 77% purity)
was added and stirring was continued for 1 h at À40°C. HPLC-MS analysis
showed a mixture 2:1 of desired sulfoxide and sulfone (30) from over-
oxidation. The reaction was quenched by the addition of 1 ml of
concentrated ammonium hydroxide, warmed to ambient temperature
and then diluted with dichloromethane (20 ml) and saturated aqueous
sodium bicarbonate (5 ml). The dichloromethane layer was separated
and concentrated in vacuo. The crude material was purified by reversed
phase HPLC (Develosil RP Aqueous C30, 5 μm, 10 × 250 mm, 30%
acetonitrile/water + 20 mM NH4OAc, PDA detector, Rt = 14.6 min)
to give (after solvent switch of product containing fractions to an ethanol
solution using C18 Sep-Pak® SPE cartridges) 95.3 mCi (45.4%) of
[3H]-5-methoxy-2-(((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)sulfinyl)-
1H-benzo[d]imidazole (omeprazole) (29) with acceptable specific activity
(5.4 Ci/mmol, 15.63 mCi/mg) and radiochemical purity (>99%). The
labeled material had the same Rt as the unlabeled as seen by both HPLC
and HPLC-MS analyses (individually and co-injection). No loss in specific
activity was observed throughout the course of the synthesis.
To a 20-ml vial with stir bar was added 2-nitro-5-methoxyaniline (24) (3
g, 17.8 mmol) and acetic anhydride (5.40 ml, 57.1 mmol). The vial was
capped and heated at 120°C in an aluminum heating block (heating
block temp) overnight. The reaction was cooled and a solid precipitated.
The suspension was poured into 150-ml water then filtered followed by
washing with water (50 ml) and then 100-ml chloroform that was
collected separately. The chloroform fraction was washed with saturated
aqueous sodium chloride solution (100 ml), water (50 ml), dried over
Na2SO4, filtered and concentrated in vacuo to give 3.56 g of a yellow
solid. The crude product was purified by silica gel chromatography
(Biotage SNAP 100-g cartridge, column conditioned with hexanes,
sample loaded in dichloromethane, elute three column volumes (CV) of
hexanes then gradient from hexanes to 30% ethyl acetate/hexanes over
6 CV, hold at 30% ethyl acetate/hexanes for 6 CV) to give N-(5-methoxy-
2-nitrophenyl)acetamide (27) (1.39 g, 6.62 mmol, 37.1% yield) as a yellow
solid. 1H NMR is consistent with reported values.15
Preparation of [3H]-N-(5-methoxy-2-nitrophenyl)acetamide (26)
To a tritiation reaction bulb with a flea stir bar was added Crabtree’s
catalyst (5 mg, 0.0062 mmol) and
a solution of N-(5-methoxy-2-
nitrophenyl)acetamide (25) (4.5 mg, 0.021 mmol) in 1.1-ml
dichloromethane. The vessel was cooled in an ethanol/CO2 bath,
degassed under high vacuum and filled with T2 (160 Torr, ~0.84 Ci). The
solution was then stirred at ambient temperature for 18 h. The reaction
was cooled in an ethanol/CO2 bath, and excess tritium was transferred
onto one of the tritiation manifold’s uranium beds. The reaction was
Acknowledgements
warmed to ambient temperature, transferred with the aid of The authors thank Dr. Jeffrey Kuethe, Dr. Rebecca Ruck and Mr.
dichloromethane from the reaction bulb and concentrated in vacuo on Nelo Rivera for assistance in proof-reading the manuscript.
a rotary evaporator. Ethanol (10 ml) was added and the evaporation
repeated two times to ensure removal of volatile radioactive material.
The crude material was purified by semi-preparative reversed phase
Conflict of interest
HPLC
(Luna
C18(2),
5u,
10 × 250 mm,
5 ml/min,
35%
acetonitrile/water + 20 mM NH4OAc, PDA detector, Rt on corresponding The authors did not report any conflict of interest.
analytical column [5 μm, 4.6 × 250 mm, 1 ml/min, 40%
acetonitrile/water + 20 mM NH4OAc] = 10.9 min) to give (after solvent
switch of product containing fractions to an ethanol solution using C18
Sep-Pak® SPE cartridges) 46.8 mCi (5.6% radiochemical yield) of [3H]-N-
(5-methoxy-2-nitrophenyl)acetamide (26) (specific activity = 3.76 Ci/
mmol, 17.8 mCi/mg.) The labeled material had the same Rt as the
unlabeled standard as seen by both HPLC and HPLC-MS analyses
(individually and co-injection).
References
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To a 4-ml vial with stir bar was added 2-(chloromethyl)-4-methoxy-3,5-
dimethylpyridine hydrochloride (6) (16.0 mg, 0.072 mmol), a solution of
[3H]-5-methoxy-1H-benzo[d]imidazole-2-thiol (23) (10.1 mg, 0.056 mmol,
321mCi, 91.4% radiochemical purity) in 2-ml ethanol and 1 M aqueous
Copyright © 2015 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2015, 58 433–441