S. Ren et al.
at RT overnight, the reaction was diluted with CH2Cl2 (500 mL), washed
with 1-N NaOH (2ꢀ 100 mL) and brine (100 mL), dried over Na2SO4,
filtered, and concentrated. The resulting white solid was dried under
vacuum overnight to give crude 8 (2.93 g and 100%). The crude product
was used directly in the next step without further purification. 1H NMR
(400 MHz, CDCl3): d7.38 (s, 1H), 7.28 (d, J = 8.787, 2H), 6.88 (d, J = 8.787,
2H), 5.37 (s, 2H), 4.04 (q, J = 6.80, 2H), 3.79 (s, 3H), 1.29 (t, J = 7.60, 3H).
LC–MS m/z: 330 [M+H]+.
System 5: Agilent Zorbax Extend C18, 150ꢀ 3.0 mmꢀ 254 nm,
and 0.05-M pH 4 triethylammonium acetate : CH3CN
(77: 23) isocratic for 11 min, followed by a step
gradient to CH3CN, at 0.5 mL/min.
System 6: Agilent Zorbax SB C18, 250ꢀ 9.4 mmꢀ 254 nm, and
0.05-M pH 4 triethylammonium acetate : CH3CN
(77:23) isocratic, at 4.0 mL/min.
Mass spectra were acquired on the JEOL MStation magnetic sector
mass spectrometer operating in the ESI+ or fast-atom bombardment
(FAB) ionization mode.
7,8-[2H4]-2-chloro-3-(3-chloro-4-methoxybenzyl)-5-ethyl-7,8-dihydro-3H-
imidazo[2,1-b]purin-4(5H)-one (9)
To a suspension of 8 (2.93 g and 8.89 mmol) in CH3CN (30 mL), HCl
solution was added (1.06 mL and 6.8 M). The resulting clear solution
was cooled to 5ꢁC, and NCS (2.85 g, 21.4 mmol, and 2.4 eq, in 30 mL of
CH3CN) was added dropwise during 1 h. The reaction was stirred at 5ꢁC
under N2 and monitored by HPLC System 1 (the retention time of
compound 9 is 10.1 min, whereas that of monochloro 11 is 8.8 min). After
2 h, the reaction was complete, quenched with 10% sodium sulfite
(10 mL) at 5ꢁC, warmed to RT, and stirred for an additional 45 min. The
solvent was removed under reduced pressure until about 10 mL of
solution was left. The residue was diluted with CH3OH (20 mL) and water
(12 mL) and then slowly neutralized with saturated K2CO3 (7.0 mL) to
keep the temperature below 30ꢁC. After stirring at RT for 1 h, the solid
was filtered, washed with water (3ꢀ 5 mL), and dried. The crude product
was purified by column chromatography (CH2Cl2, 0.5% Et3N, 1–3%
CH3OH, gradient) to give 2.50 g (71% yield) of 9. 1H NMR (400 MHz,
CDCl3): d7.42 (s, 1H), 7.28 (d, J = 8.055, 1H), 6.88 (d, J = 8.878,1H), 5.40
(s, 2H), 4.01 (q, J = 6.590, 2H), 3.88 (s, 3H), 1.28 (t, J = 7.323, 3H). LC–MS
m/z: 398 [M+H]+.
Synthesis of [3H]SCH 444877
Tert-butyl (2,3-[3H]tetrahydro-2H-pyran-4-yl)carbamate (2)
A suspension of olefin 1 (1.2mg) and 10% Pd/C (2.8mg) in EtOAc (0.4mL)
in a reaction vial was degassed three times at the stainless steel vacuum
manifold and stirred under an atmosphere of tritium gas (796 mCi) for
6h. The reaction was diluted with EtOAc (20mL), filtered to remove the
catalyst, and washed with water (5mL). The solvent was removed under
reduced pressure to give 152-mCi crude product with an RCP of 57% by
TLC (EtOAc : hexanes, 1:3). The crude product was purified by silica gel
chromatography (1g), eluting with EtOAc : hexane (1:4) to give the
compound 2, which was directly used in the next step.
2,3-[3H]tetrahydro-2H-pyran-4-amine hydrochloride (3)
Compound 2 was dissolved in 4-M HCl in dioxane (0.50 mL) and stirred at
room temperature (RT) for 2 h. The solvent was removed under N2 to give
crude product 3, which was directly used in the next step.
3-(3-Chloro-4-methoxybenzyl)-2-((2,3-[3H]tetrahydro-2H-pyran-4-
yl)amino)-5-ethyl-7,8-dihydro-3H-imidazo[2,1-b]purin-4(5H)-one
[3H]SCH 444877 (5)
7,8-[2H4]-3-(3-chloro-4-methoxybenzyl)-2-((tetrahydro-2H-pyran-4-yl)
amino)-5-ethyl-7,8-dihydro-3H-imidazo[2,1-b]purin-4(5H)-one
[2H4]SCH 444877 (10)
To the crude [3H] compound 3, 4 (32 mg), unlabeled 3 (10 mg), DIPEA
(0.20 mL), and NMP (0.20 mL) were added. The reaction was stirred at
160ꢁC overnight. The reaction was cooled to RT, diluted with water
(2 mL), and extracted with CH2Cl2 (3ꢀ 2 mL). The combined organic
phase was concentrated to dryness to give the crude product, which
was initially purified by silica gel chromatography (1 g, eluting with
10 mL of CH2Cl2 and then 60 mL of 0.5% 7-N NH3 in CH2Cl2), followed
by HPLC purification (System 6) to give 8.2 mCi of [3H]SCH 444877 (5)
with 99.6% RCP by HPLC System 5. The specific activity is 693 mCi/mmol.
To a suspension of 9 (1.45 g and 3.63 mmol) and tetrahydro-pyran-4-
ylamine (1.47 g and 14.5 mmol) in NMP (6 mL), DIPEA (6.0 mL) was added
and stirred at 150ꢁC under N2 overnight. The reaction was cooled to RT,
diluted with water (250 mL), and extracted with EtOAc (3ꢀ 200 mL). The
combined organic phase was washed with brine (150 mL), dried over
Na2SO4, filtered, and concentrated in vacuo. The crude product was
initially purified by silica gel column (CH2Cl2, 1–3% CH3OH, gradient)
and then recrystallized from EtOAc (10 mL)/methyl-t-butyl ether (20 mL)
at 50ꢁC to yield 1.21 g of [2H4]SCH 444877 (72% yield) with a 98.4% purity
by HPLC System 2. 1H NMR (400 MHz, CDCl3): d7.26 (s, 1H), 7.23 (d,
J = 2.19, 1H), 7.14 (dd, J = 8.787, J = 2.197, 1H), 6.90 (d, J = 8.787,1H, NH),
5.22 (s, 2H), 4.03–3.79 (m, 8H), 3.38 (dd, J = 11.716, 1.465, 2H), 1.96 (d,
J = 12.449, 2H), 1.39–1.25 (m, 5H). 13C NMR (DMSO-d6, d): 153.79, 152.93,
152.90, 152.72, 148.7, 130.3, 129.0, 127.3, 120.7, 112.8, 98.3, 65.9, 56.0,
48.8, 43.9, 36.1, 32.8, 12.6. FAB-MS/MS m/z: 463 [M+H]+. Fragmentations
of the labeled compound are consistent with the unlabeled standard.
Synthesis of [2H4]SCH 444877
2-((1,2-[2H4]-2-hydroxyethyl)amino)-1-ethyl-7-(4-methoxybenzyl)-1H-
purin-6(7H)-one (7)
Compound 6 (3.58 g and 11.2 mmol) and [2H4]ethanolamine (2.26 g and
34.8 mmol) were suspended in 1-methyl-2-pyrrolidinone (NMP, 18 mL)
and were stirred under N2 at 130ꢁC for 4 h. Most of the solvent was
removed by distillation under vacuum at 120ꢁC. The residue was
dissolved in CH2Cl2 (500 mL), washed with saturated NaHCO3
(2ꢀ 100 mL) and brine (500 mL), then dried over Na2SO4, and filtered.
The solvent was removed under reduced pressure until ~100 mL of
the solvent was left. The precipitated solid was filtered and washed with
isopropyl alcohol (2ꢀ 5 mL). The solid was dried under vacuum
overnight to give compound 7 (3.09 g and 79%). 1H NMR (400 MHz,
CDCl3): d7.63 (s, 1H), 7.28 (d, J = 8.787, 2H), 6.86 (d, J = 8.787, 2H), 5.42
(s, 2H), 5.07 (s, 1H), 4.09 (q, J = 7.323, 2H), 3.79 (s, 3H), 2.05 (br, 1H),
1.33 (t, J = 7.323, 3H). LCMS m/z: 370 [M+Na+], 348 [M+H]+.
Synthesis of [14C]SCH 444877
[14C]cyanamide
Barium
[
14C]cyanamide (105.2 mCi, 319.5 mg, 59 mCi/mmol, and
1.783 mmol) was suspended in water (1.9 mL) and stirred at 0ꢁC for 1 h
and 30 min. To the suspension, sulfuric acid (0.89 mL and 2.0-M solution)
was added dropwise at 0ꢁC and stirred for 3 h at 0ꢁC. The precipitate was
removed by centrifuging and washed with H2O (4ꢀ 2.5 mL). The
combined aqueous solution was concentrated under vacuum and then
taken up in ether (4ꢀ 5 mL). The ether solution was dried over anhydrous
sodium sulfate, filtered, and concentrated to give 76.8 mCi (73% yield) of
7,8-[2H4]-5-ethyl-3-(4-methoxybenzyl)-7,8-dihydro-3H-imidazo[2,1-b]
purin-4(5H)-one (8)
[
14C]cyanamide as a white solid after drying under vacuum for 1 h and
To a suspension of 7 (3.09 g and 8.89 mmol) in anhydrous CH2Cl2 (70 mL), 30 min. The product was directly used in the next step without further
SOCl2 (0.79 mL and 10.67 mmol) was added dropwise. After being stirred purification.
J. Label Compd. Radiopharm 2013, 56 480–484
Copyright © 2013 John Wiley & Sons, Ltd.