3704
M. Wang et al. / Bioorg. Med. Chem. Lett. 24 (2014) 3700–3705
(l) 3-Amino-N-methoxy-4-methylbenzamide hydrochloride (9a): To
solid. 1H NMR (CDCl3): d 8.43 (br s, 1H), 7.38–7.37 (m, 1H), 6.54–6.53 (m, 1H),
a
stirred
3.80 (s, 3H), 2.29 (d, J = 1.0 Hz, 2H).
suspension of compound 8a (5.0 g, 18.9 mmol) in dioxane (25 mL) was added a
4 N solution of HCl in dioxane (30 mL). The reaction mixture was stirred
overnight at rt. The solid was collected by filtration and wash with dioxane to
afford 9b (3.02 g, 74%) as a white solid. 1H NMR (DMSO-d6): d 11.83 (s, 1H),
7.71 (s, 1H), 7.53 (d, J = 8.0 Hz, 1H), 7.36 (d, J = 8.0 Hz, 1H), 3.70 (s, 3H), 2.36 (s,
3H).
(m) 3-Amino-N-ethoxy-4-methylbenzamide hydrochloride (9b): Compound 9b
was prepared according to the procedure described in 9a from compound 8b as
a white solid (2.96 g, 79%). 1H NMR (DMSO-d6): d 11.73 (s, 1H), 7.75 (d,
J = 1.0 Hz, 1H), 7.58 (d, J = 1.0, 8.0 Hz, 1H), 7.37 (d, J = 8.0 Hz, 1H), 3.92 (q,
J = 7.0 Hz, 2H), 2.38 (s, 3H), 1.20 (t, J = 7.0 Hz, 3H).
(c) Methyl 4-methyl-5-(2,2,2-trichloroacetyl)-1H-pyrrole-3-carboxylate (2): To a
suspension of aluminum chloride (51.16 g, 384 mmol) in DCE (200 mL) was
added trichloroacetyl chloride (43 mL, 384 mmol) dropwise at À40 °C under
nitrogen atmosphere, followed by
a solution of compound 1 (10.6 g,
76.7 mmol) in DCE (50 mL). The reaction mixture was gradually warmed to
rt and stirred for 2 days. The mixture was poured into ice-water carefully and
extracted with CH2Cl2. The combined organic layer was washed with 3 N HCl,
brine, dried over anhydrous Na2SO4, and filtered. The solvent was evaporated
in vacuo to afford 2 (20.3 g, 94%) as a dark oil which was used for next step
without further purification.
(d) Dimethyl 3-methyl-1H-pyrrole-2,4-dicarboxylate (3): To a cooled and stirred
solution of compound 2 (20.0 g, 70.7 mmol) in MeOH (80 mL) was added a
solution of sodium methoxide in MeOH (25% wt, 70 mL, 306 mmol) at 0 °C
under nitrogen atmosphere. After finishing the addition, the reaction mixture
was allowed to warm to rt and stirred for 1 h. The mixture was concentrated in
vacuo, diluted with ice-water and then adjusted pH to 6 with 2 N HCl. The
mixture was extracted with CH2Cl2. The combined organic layer was washed
with brine, dried over anhydrous Na2SO4, and filtered. The solvent was
evaporated in vacuo, and the crude product was purified by column
(n)
Methyl
4-(2-methyl-5-(methoxycarbamoyl)phenylamino)-5-
methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylate (10a): To a stirred suspension
of compound 6 (300 mg, 1.33 mmol) in DMF (5 mL) was added compound 9a
(347 mg, 1.60 mmol). After the reaction mixture was stirred overnight at rt, it
was poured into ice-water and neutralized with saturated NaHCO3. The
precipitate was collected by filtration and washed with water. The crude
product was purified by semi-preparative HPLC to afford 10a (212 mg, 43%) as
a white solid. 1H NMR (DMSO-d6, rotameric): d 11.78 (s, 1H), 10.22, 8.86 (s+s,
1H), 8.09–7.20 (m, 5H), 3.80 (s, 3H), 3.70 (s, 3H), 2.83 (s, 3H), 2.23 (s, 3H). LC–
MS (ESI, m/z): Calcd for C18H19N5O4 ([M+H]+) 370.1, found: 370.0.
(o) Methyl 4-(2-methyl-5-(ethoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-
f][1,2,4]triazine-6-carboxylate (10b): Compound 10b was prepared according to
the procedure described in 10a from methyl compound 6 (300 mg, 1.33 mmol)
and compound 9b (369 mg, 1.60 mmol) as a white solid (243 mg, 48%). 1H
NMR (DMSO-d6, rotameric): d 11.59 (s, 1H), 10.18, 8.86 (s+s, 1H), 8.02-7.37 (m,
5H), 3.92 (q, J = 7.0 Hz, 2H), 3.41 (s, 3H), 2.80 (s, 3H), 2.20 (s, 3H), 1.20 (t,
J = 7.0 Hz, 3H).
chromatography (7:3 hexanes/EtOAc) to afford
3 (12.6 g, 91%) as a pale
yellow solid. 1H NMR (CDCl3): d 9.33 (br s, 1H), 7.48 (d, J = 3.5 Hz, 1H), 3.88 (s,
3H), 3.82 (s, 3H), 2.60 (s, 3H).
(e) Preparation of anhydrous ethereal monochloroamine (NH2Cl): To a cooled and
stirred suspension of NH4Cl (12.0 g, 224 mmol) in Et2O (440 mL) was added
concentrated ammonium hydroxide (18.8 mL) at À5 °C, followed by
commercial bleach (Clorox, 288 mL) slowly. After stirring at same
temperature for 15 min, the organic layer was separated and washed with
brine. The organic layer was dried over powered CaCl2 in a freezer for 1 h and
stored at À40 °C.
(p)
4-(2-Methyl-5-(methoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-
f][1,2,4]triazine-6-carboxylic acid (11a): To a stirred suspension of compound
10a (150 mg, 0.41 mmol) in THF (2 mL) and MeOH (2 mL) was added 1 N NaOH
(1.5 mL, 1.5 mmol). The reaction mixture was heated and stirred at 60 °C
overnight. The solvent was evaporated in vacuo, the residual was diluted with
ice-water and 1 N HCl was added to adjust pH to 5–6. The precipitate was
collected by filtration and washed with water, Et2O/EtOAc (1:1), and dried in
(f) Dimethyl 1-amino-3-methyl-1H-pyrrole-2,4-dicarboxylate (4): To a stirred
solution of compound 3 (8.73 g, 44.3 mmol) in DMF (60 mL) was added NaH
(60% dispersion in mineral oil, 2.30 g, 57.5 mmol). After stirring for 1 h,
anhydrous ethereal monochloroamine (340 mL) was added under nitrogen
atmosphere. The reaction mixture was stirred for 10 min and then quenched
with aqueous Na2S2O3 (100 g/L, 200 mL). The mixture was diluted with water.
The organic layer was separated and washed with brine, dried over anhydrous
Na2SO4, and filtered. The solvent was evaporated in vacuo, and the crude
product was purified by column chromatography (3.5:1 hexanes/EtOAc) to
afford 4 (7.55 g, 80%) as a white solid. 1H NMR (CDCl3): d 7.48 (s, 1H), 5.22 (br s,
2H), 3.88 (s, 3H), 3.79 (s, 3H), 2.56 (s, 3H).
vacuo to afford 11a (100 mg, 69%) as
a
white solid. 1H NMR (DMSO-d6,
rotameric): d 12.42 (br s, 1H), 11.71 (s, 1H), 10.12, 8.77 (s+s, 1H), 8.03-7.19 (m,
5H), 3.69 (s, 3H), 2.82 (s, 3H), 2.23 (s, 3H). LC–MS (ESI, m/z): Calcd for
C
17H17N5O4 ([M+H]+) 356.1, found: 356.1.
(q) 4-(2-Methyl-5-(ethoxycarbamoyl)phenylamino)-5-methylpyrrolo[2,1-f][1,2,4]
triazine-6-carboxylic acid (11b): Compound 11b was prepared according to the
procedure described in 11a from compound 10b (150 mg, 0.39 mmol) as a
white solid (115 mg, 80%). 1H NMR (DMSO-d6, rotameric): d 12.43 (br s, 1H),
11.60 (s, 1H), 10.11, 8.78 (s+s, 1H), 8.03-7.19 (m, 5H), 3.90 (q, J = 6.5 Hz, 2H),
2.83 (s, 3H), 2.23 (s, 3H), 1.19 (t, J = 6.5 Hz, 3H). LC–MS (ESI, m/z): Calcd for
(g) Methyl 4-oxo-5-methyl-1,4-dihydropyrrolo[2,1-f][1,2,4]triazine-6-carboxylate
(5): A suspension of compound 4 (6.0 g, 28.3 mmol) in formamide (60 mL) was
heated and stirred at 160 °C overnight. The resulting mixture was cooled. The
solid was collected by filtration and washed with water, cold Et2O to afford 5
(4.78, 82%) as a white solid. 1H NMR (DMSO-d6): d 11.64 (s, 1H), 7.93 (s, 1H),
7.84 (s, 1H), 3.76 (s, 3H), 2.61 (s, 3H).
C
18H19N5O4 ([M+H]+) 370.1, found: 370.1.
(r) General procedure for the preparation of the target tracers
[
11C]10a–b:
(h) Methyl 4-chloro-5-methylpyrrolo[2,1-f][1,2,4]triazine-6-carboxylate (6):
A
[ a)
11C]CO2 was produced by the 14N(p, 11C nuclear reaction in the small volume
suspension of compound 5 (4.1 g, 19.8 mmol) in POCl3 (45 mL) was heated
and stirred at 115 °C overnight. The resulting mixture was cooled, then diluted
with CH2Cl2 and poured into ice cold mixture of saturated NaHCO3 (150 mL)
and CH2Cl2 (50 mL) with rapidly stirring to ensure quenching of the excess
POCl3. The organic layer was separated and washed with brine, dried over
anhydrous Na2SO4, filtered, and concentrated in vacuo to afford 6 (3.91 g, 88%)
as a tan solid which was used without further purification.
(9.5 cm3) aluminum gas target provided with the Siemens RDS-111 Eclipse
cyclotron. The target gas consisted of 1% oxygen in nitrogen purchased as a
specialty gas from Praxair, Indianapolis, IN. Typical irradiations used for the
development were 50
run produced approximately 25.9 GBq of [11C]CO2 at EOB. The acid precursor
11a or 11b (0.1–0.3 mg) was dissolved in CH3CN (300 L). To this solution was
added 2 N NaOH (2 L). The mixture was transferred to a small reaction vial.
No-carrier-added (high specific activity)
11C]CH3OTf (13.9 GBq) that was
lA beam current and 15 min on target. The production
l
l
(i) 3-(tert-Butoxycarbonylamino)-4-methylbenzoic acid (7): A suspension of 3-
[
amino-4-methylbenzoic
acid
(20.0 g,
132 mmol)
and
N-(tert-
produced by the gas-phase production method25 within 11 min from [11C]CO2
(25.9 GBq) through [11C]CH4 (21.8 GBq) and [11C]CH3Br (13.9 GBq) with silver
triflate (AgOTf) column was passed into the reaction vial at rt until
radioactivity reached a maximum (2 min), and then the reaction vial was
isolated and heated at 80 °C for 3 min. The contents of the reaction vial were
diluted with NaHCO3 (0.1 M, 1 mL). Method A: The reaction vial was connected
to a C-18 Plus Sep-Pak cartridge. The labeled product mixture solution was
passed onto the cartridge for SPE purification by gas pressure. The cartridge
was washed with H2O (2 Â 3 mL), and the aqueous washing was discarded. The
product was eluted from the cartridge with EtOH (2 Â 2 mL), and then passed
onto a rotatory evaporator. The solvent was removed by evaporation (3 min)
under vacuum. The final volume of ethanol after evaporation was ꢀ1 mL. The
labeled product was reformulated with saline (10 mL), sterile-filtered through
butoxycarbonyl)anhydride (30.0 g, 219 mmol) in THF (200 mL) was heated
and stirred at 50 °C overnight. The resulting mixture was cooled to rt. The
solvent was evaporated in vacuo, and the crude product was recrystallized
from EtOAc to afford 7 (29.1 g, 88%) as a pink solid. 1H NMR (DMSO-d6): d 12.8
(s, 1H), 8.66 (s, 1H), 7.97 (s, 1H), 7.59 (dd, J = 2.0, 8.0 Hz, 1H), 7.28 (d, J = 8.0 Hz,
1H), 3.25 (s, 3H), 1.47 (s, 9H).
(j) tert-Butyl 2-methyl-5-(methylcarbamoyl)phenylcarbamate (8a): To a stirred
solution of compound 7 (5.0 g, 19.9 mmol) in DMF (30 mL) was added EDC
(3.9 mL, 21.9 mmol), HOBt (3.35 g, 21.9 mmol). After stirring at rt for 30 min,
methoxyamine hydrochloride (1.83 g, 21.9 mmol) was added. The resulting
mixture was stirred for another 10 min, and cooled to 0 °C. DIPEA (8.09 mL,
46.4 mmol) was added slowly to maintain the internal reaction temperature
below 25 °C. After finishing the addition, the reaction mixture was allowed to
warm to rt and stirred at rt overnight. The resulting mixture was poured into
water and extracted with EtOAc. The combined organic layer was washed with
cold 0.5 N HCl and water. The organic layer was then extracted with cold 0.5 N
NaOH, and the combined basic aqueous extract was adjusted pH to 8 by a slow
addition of cold 0.5 N HCl. The resulting precipitate was collected by filtration,
and washed with cold water. The crude product was recrystallized in EtOH to
afford 8a (5.17 g, 98%) as a white solid. 1H NMR (DMSO-d6): d 11.65 (s, 1H),
8.65 (s, 1H), 7.75 (s, 1H), 7.40 (dd, J = 1.5, 8.0 Hz, 1H), 7.25 (d, J = 8.0 Hz, 1H),
3.69 (s, 3H), 2.23 (s, 3H), 1.47 (s, 9H).
a sterile vented Millex-GS 0.22 lm cellulose acetate membrane and collected
into a sterile vial. Total radioactivity (4.7–7.1 GBq) was assayed and the total
volume (10–11 mL) was noted for tracer dose dispensing. The overall synthesis
time including SPE purification and reformulation was 23 min. The
radiochemical yields decay corrected to EOB, from [11C]CO2, were 50–60%.
Method B: The reaction vial was connected to a 3-mL HPLC injection loop. The
labeled product mixture solution was injected onto the semi-preparative HPLC
column for purification. The product fraction was collected in a recovery vial
containing 30 mL water. The diluted tracer solution was then passed through a
C-18 Sep-Pak Plus cartridge, and washed with water (5 mL Â 4). The cartridge
was eluted with EtOH (1 mL Â 2) to release the labeled product, followed by
saline (10 mL). The eluted product was then sterile-filtered through a Millex-
(k) tert-Butyl 5-(ethylcarbamoyl)-2-methylphenylcarbamate (8b): Compound 8b
was prepared according to the procedure described in 8a from O-
ethylhydroxylamine hydrochloride as a white solid (5.07 g, 92%). 1H NMR
(DMSO-d6): d 11.53(s, 1H), 8.65 (s, 1H), 7.75 (d, J = 1.0 Hz, 1H), 7.40 (dd, J = 1.5,
8.0 Hz, 1H), 7.24 (d, J = 8.0 Hz, 1H), 3.91 (q, J = 7.0 Hz, 2H), 2.22 (s, 3H), 1.47 (s,
9H), 1.19 (t, J = 7.0 Hz, 3H).
FG 0.2 lm membrane into a sterile vial. Total radioactivity (3.8–5.9 GBq) was
assayed and total volume (10–11 mL) was noted for tracer dose dispensing.
The overall synthesis time including HPLC–SPE purification and reformulation
was 40–45 min. The same procedure was used to prepare the target tracers
Wang, Min
