Journal of Medicinal Chemistry
Drug Annotation
was degassed with argon for 15 min. To this solution, 1-bromo-3,5-
difluorobenzene (63) (63 mL, 549 mmol, 1.1 equiv), NaOt-Bu (67 g,
699 mmol, 1.4 eq.; portion-wise over a period of 10 min), and BINAP
(15.5 g, 25 mmol, 0.05 equiv) were added. The mixture was degassed
with argon for 5 min before Pd2(dba)3 (6.9 g, 7.5 mmol, 0.015 equiv)
was added. The flask was equipped with a condenser, and the reaction
mixture was stirred at 80 °C for 2.5 h and at reflux for 1 h. The
mixture was diluted with water (650 mL) and EtOAc (600 mL). The
aqueous layer was extracted with EtOAc (400 mL). Combined
organic layers were washed with water (450 mL) and brine (450 mL),
dried over Na2SO4, filtered, and concentrated in vacuo. The crude
product was purified by filtration through a cake of SiO2 (elution
heptane/EtOAc: 100/0, 95/5, 80/20) to afford tert-butyl (S)-4-(3,5-
difluorophenyl)-3-methylpiperazine-1-carboxylate (145 g, 93%). 1H
NMR (400 MHz, DMSO-d6): δ 6.62−6.50 (m, 2H), 6.45 (tt, J = 9.2,
2.2 Hz, 1H), 4.07 (br. s, 1H), 3.94 (br. s, 1H), 3.83−3.73 (m, 1H),
3.45−3.36 (m, 1H), 3.15 (br. s, 2H), 3.04−2.81 (m, 1H), 1.43 (s,
9H), 0.95 (d, J = 6.5 Hz, 3H). LC-MS: m/z = 313.4 [M + H].
(S)-1-(3,5-Difluorophenyl)-2-methylpiperazine ([S]-65). To a
solution of tert-butyl (S)-4-(3,5-difluorophenyl)-3-methylpiperazine-
1-carboxylate (S-64) (145 g, 466 mmol, 1 equiv) in acetonitrile (580
mL), cooled in an ice bath, a 4 N HCl solution in dioxane (580 mL,
2320 mmol, 5 equiv) was added in five portions over a 20 min period.
The reaction mixture was stirred at 0 °C for 20 min and then at rt for
3 h. The suspension was filtered, washed with acetonitrile (3 × 250
mL) and diethyl ether (2 × 300 mL), and dried under vacuum to
afford (S)-1-(3,5-difluorophenyl)-2-methylpiperazine as dihydrochlor-
ide salt (117 g, 88%). 1H NMR (400 MHz, DMSO-d6): δ 9.74 (br. s,
1H), 9.24 (br. s, 1H), 7.08 (br. s, 1H), 6.71−6.59 (m, 2H), 6.54 (tt, J
= 9.2, 2.2 Hz, 1H), 4.38−4.12 (m, 1H), 3.62 (d, J = 13.7 Hz, 1H),
3.30−3.20 (m, 2H), 3.20−3.09 (m, 2H), 3.05−2.92 (m, 1H), 1.17 (d,
J = 6.9 Hz, 3H). LC-MS: m/z = 213.4 [M + H].
stirred at reflux for 1 h, and allowed to cool down to rt under stirring.
The resulting solid was separated by filtration, washed twice with
acetonitrile (2 × 30 mL), and finally dried under vacuum at 45 °C to
afford 3-(4-cyclopropyl-2,5-dioxo-imidazolidin-4-yl)propanoic acid
1
(120 g, 76%) as a white solid. H NMR (400 MHz, DMSO-d6): δ
12.19 (br s, 1H), 10.61 (s, 1H), 7.70 (s, 1H), 2.33−2.22 (m, 1H),
2.18−2.09 (m, 1H), 1.99−1.87 (m, 2H), 1.10−1.04 (m, 1H), 0.47−
0.41 (m, 1H), 0.39−0.28 (m, 2H), 0.13−0.06 (m, 1H). LC-MS: m/z
= 213.2 [M + H].
(S)-3-(4-Cyclopropyl-2,5-dioxoimidazolidin-4-yl)propanoic Acid
([S]-61). The racemic 3-(4-cyclopropyl-2,5-dioxoimidazolidin-4-yl)-
propanoic acid (61) (600.0 g) was separated by chiral SFC to afford
253.33 g (42%) of the faster-eluting isomer and 258.92 g (43%) of the
slower-eluting isomer. The slower-eluting isomer, (S)-3-(4-cyclo-
propyl-2,5-dioxoimidazolidin-4-yl)propanoic acid, was the isomer of
1
interest. H NMR (400 MHz, DMSO-d6): δ 12.20 (s, 1H), 10.62 (s,
1H), 7.70 (s, 1H), 2.33−2.20 (m, 1H), 2.18−2.07 (m, 1H), 2.00−
1.86 (m, 2H), 1.11−1.02 (m, 1H), 0.48−0.40 (m, 1H), 0.39−0.25
(m, 2H), 0.14−0.03 (m, 1H). LC-MS: m/z = 213.1 [M + H]. ee:
99.1% [ChiralPak AD-3 μm, 250 × 4.6 mm, CO2 and ethanol (0.05%
DEA) (gradient ethanol 5−40%), 35 °C, wavelength 210 nm].
The purification was done in two stages.
Conditions of the first separation were as follows: preparative SFC;
column, ChiralPak AD-10 μm, 300 × 50 mm ID; mobile phase, CO2/
EtOH (55/45) in isocratic mode; flow rate, 200 mL/min; column
temperature, 38 °C; wavelength, 220 nm; cycle time, approximately
10.0 min; sample preparation, compound dissolved in MeOH to
approximately 120 mg/mL; workup: fractions dried off via rotary
evaporator to obtain the desired isomer, which was further upgraded
by preparative HPLC to remove traces of ethyl ester formed.
Conditions of the second separation were as follows: preparative
HPLC; column, C18, 250 × 50 mm ID; mobile phase, H2O and
acetonitrile (5−20%) in 15 min linearly; flow rate, 80 mL/min;
wavelength, 220 nm; sample preparation, compound dissolved in
MeOH at approximately 100 mg/mL. Evaporation and lyophilization
afforded the desired enantiomer.
(S)-5-Cyclopropyl-5-(3-((S)-4-(3,5-difluorophenyl)-3-methylpiper-
azin-1-yl)-3-oxopropyl)imidazolidine-2,4-dione (GLPG1972). The
reaction was performed four times, starting with 50 g of (S)-3-(4-
cyclopropyl-2,5-dioxoimidazolidin-4-yl)propanoic acid ([S]-61). The
crude materials obtained were gathered before the purification step.
(S)-3-(4-Cyclopropyl-2,5-dioxoimidazolidin-4-yl)propanoic acid
([S]-61) (50 g, 0.24 mol, 1.1 equiv) was dissolved in DMF (360
mL). (S)-1-(3,5-Difluorophenyl)-2-methylpiperazine (S-65) (61 g,
0.21 mol, 1 equiv) as a dihydrochloride salt, DIPEA (148 mL, 0.84
mol, 4 equiv; added through glass funnel over 2 min), EDC HCl (45
g, 0.24 mol, 1.1 equiv), and HOBt (4.95 g, 0.032 mol, 0.15 equiv)
were added, and the reaction mixture was stirred at rt for 18 h. The
reaction mixture was poured into cold, stirring water (1.8 L) and
stirred for 45 min. A small precipitate was formed and filtered off.
Filtrate was extracted with EtOAc (2 × 650 and 300 mL). Combined
organic layers were washed with saturated aqueous NaHCO3 (2 ×
800 and 500 mL) and brine (2 × 500 mL), dried over Na2SO4, and
concentrated in vacuo. Four separate batches of 50 g gave 321.8 g of
crude material, which was purified by flash chromatography on silica
gel (elution DCM/MeOH/NH3: 100/0/0 to 90/5/0.5) to afford (S)-
5-cyclopropyl-5-(3-((S)-4-(3,5-difluorophenyl)-3-methylpiperazin-1-
yl)-3-oxopropyl)imidazolidine-2,4-dione (285 g, 82%). 1H NMR (400
MHz, DMSO-d6; mixture of rotamers was observed): δ 10.62 (s, 1H),
7.73 (d, J = 17.1 Hz, 1H), 6.66−6.50 (m, 2H), 6.46 (td, J = 9.2, 2.0
Hz, 1H), 4.41−4.26 (m, 0.5H), 4.26−4.00 (m, 1.5H), 3.81 (d, J =
13.1 Hz, 0.5H), 3.66 (d, J = 13.5 Hz, 0.5H), 3.52−3.36 (m, 1.5H),
3.32−3.15 (m, 0.5H), 3.16−2.72 (m, 2H), 2.49−2.12 (m, 2H), 2.09−
1.77 (m, 2H), 1.36−1.01 (m, 1H), 0.95 (dd, J = 26.4, 6.5 Hz, 3H),
0.62−0.23 (m, 3H), 0.22 to −0.00 (m, 1H). 13C NMR (300 MHz,
DMSO-d6; mixture of rotamers was observed): δ −1.1, −1.0, 0.5, 0.6,
12.0, 12.4, 15.8, 16.0, 26.6, 26.9, 32.0, 32.1, 40.7, 41.2, 44.3, 45.1,
49.1, 49.38, 49.42, 63.8, 63.9, 92.4, 96.9, 97.3, 151.7, 156.9, 161.9,
162.1, 170.2, 170.3, 177.5, 177.6. LC-MS: m/z = 407.5 [M + H].
HRMS [M + H]+ calcd for C20H25F2N4O3, 407.1895; found,
tert-Butyl 4-Cyclopropyl-4-oxo-butanoate (59). A solution of
LDA 2 M (3.0 L, 5.98 mol, 1.17 equiv) in THF (2.5 L) was cooled to
−78 °C. A solution of 1-cyclopropylethanone (57) (460 g, 5.47 mol,
1.07 equiv) in THF (0.5 L) was added dropwise, then warmed to −20
°C, and stirred for 30 min. The reaction mixture was cooled to −78
°C, and tert-butyl bromoacetate (58) (997 g, 5.11 mol, 1 equiv) in
THF (0.5 L) was added slowly. The reaction was: stirred at 0 °C
overnight; quenched with saturated aqueous NH4Cl (3.3 L);
extracted with EtOAc (3 × 0.5 L); washed with water (2 × 0.5 L),
saturated aqueous NH4Cl (1 L), and brine (1 L); and dried over
Na2SO4. Purification by distillation under reduced pressure (5 mbar,
95 °C) afforded tert-butyl 4-cyclopropyl-4-oxo-butanoate (350 g,
1
35%) as an oil. H NMR (400 MHz, chloroform-d): δ 2.82 (td, J =
6.7, 1.7 Hz, 2H), 2.50 (td, J = 6.8, 1.7 Hz, 2H), 1.97−1.90 (m, 1H),
1.43 (m, 9H), 1.05−1.00 (m, 2H), 0.91−0.84 (m, 2H).
tert-Butyl 3-(4-Cyclopropyl-2,5-dioxo-imidazolidin-4-yl)-
propanoate (60). A mixture of tert-butyl 4-cyclopropyl-4-oxo-
butanoate (59) (120 g, 605 mmol, 1 equiv), (NH4)2CO3 (494 g,
5.15 mol, 8.5 equiv), NaCN (CAUTION! Sodium cyanide is highly
toxic, 60 g, 1.45 mol, 2.4 equiv), water (600 mL), and EtOH (600
mL) was heated at 60 °C for 18 h in a sealed reactor. The reaction
mixture was poured into a mixture of EtOAc (900 mL) and water
(900 mL), and the aqueous layer was additionally extracted with
EtOAc (3 × 600 mL). The organic layer was concentrated until there
was only about 100 mL of EtOAc left, and petroleum ether (500 mL)
was added dropwise to afford, after filtration, the expected tert-butyl 3-
(4-cyclopropyl-2,5-dioxo-imidazolidin-4-yl)propanoate (110 g, 68%)
1
as a white solid. H NMR (400 MHz, DMSO-d6): δ 10.62 (s, 1H),
7.66 (s, 1H), 2.30−2.20 (m, 1H), 2.17−2.09 (m, 1H), 1.96−1.88 (m,
2H), 1.39 (s, 9H), 1.10−1.03 (m, 1H), 0.48−0.40 (m, 1H), 0.39−
0.27 (m, 2H), 0.14−0.05 (m, 1H). LC-MS: m/z = 269.3 [M + H].
3-(4-Cyclopropyl-2,5-dioxo-imidazolidin-4-yl)propanoic Acid
(61). A flask was charged with a solution of tert-butyl 3-(4-
cyclopropyl-2,5-dioxo-imidazolidin-4-yl)propanoate (60) (200 g,
746 mmol, 1 equiv) in dioxane (100 mL) and was cooled in an ice
bath; a 4 N HCl solution in dioxane (1 L) was added slowly. The
reaction mixture was stirred at rt for 4 h and concentrated in vacuo.
The resulting solid was suspended in 240 mL of acetonitrile, then
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J. Med. Chem. 2021, 64, 2937−2952