Journal of Medicinal Chemistry
Article
biological data are presented have >95% purity as determined by
HPLC. Mass spectrometric analysis was performed according to the
following liquid chromatography/mass spectrometry (LC/MS)
method: Waters ACQUITY UPLC system equipped with a ZQ
2000 MS system; column, Kinetex by Phenomenex, 2.6 μm, 2.1 × 50
mm; column temperature 50 °C; gradient 2−88% (or 0−45% or 65−
95%) solvent B over a 1.29 min period; flow rate 1.2 mL/min.
Compounds were detected by a Waters photodiode array detector. All
masses were reported as those of the protonated parent ions,
molecular weight range 150−850, cone voltage 20 V. 1H and 13C
NMR spectra of all compounds were recorded at 300 and 75 MHz,
(R)-Ethyl 3-(2-Bromo-4-fluorophenyl)-3-(3-oxobutanamido)-
propanoate (6). To a stirred solution of 5 (20 g, 61.5 mmol) in
DCM (400 mL) were added triethylamine (25.7 mL, 184.6 mmol) and
diketene (5 mL, 64.6 mmol). The reaction was stirred for 18 h at rt.
The mixture was partitioned between DCM and aq NaHCO3 and
extracted with DCM. The organic layer was washed with water and
brine, dried (Na2SO4), filtered, and evaporated to give a crude oil
which was purified on silica gel (hexane/EtOAc) to provide 6 as an oil
(18.5 g, 80%): LC/MS m/z 373.8 (MH+), tR = 2.22 min.
(6R)-3-Acetyl-6-(2-bromo-4-fluorophenyl)-piperidine-2,4-
dione (7). To a glass pressure vessel containing 6 (7.1 g, 19 mmol)
was added NaOMe in MeOH (0.3 M, 150 mL). The vessel was sealed
and the reaction heated in an oil bath at 100 °C for 18 h behind a blast
shield. After being cooled to room temperature, the reaction mixture
was diluted with aq NH4Cl and extracted with DCM. The organic
layer was washed with water and brine, dried (Na2SO4), filtered, and
evaporated to give crude 7 (5.7 g, 91%) which was used directly in the
next step: LC/MS m/z 329.9 (MH+), tR = 2.48 min.
(R)-2-Amino-7-(2-bromo-4-fluorophenyl)-4-methyl-7,8-
dihydropyrido[4,3-d]pyrimidin-5(6H)-one (8). To the mixture of
7 (5.7 g, 17.4 mmol) and acetylguanidine (2.6 g, 26 mmol) in ethanol
(170 mL) was added pyrrolidine (1.6 mL, 19.1 mmol). The reaction
mixture was heated in an oil bath at 110 °C for 18 h. After being
cooled to room temperature, the reaction mixture was further cooled
to 0 °C for 1 h. A crystalline material was collected, washed with cold
ethanol, and air-dried to afford 8 (2.6 g, 29%): LC/MS m/z 374.0
(MH+ + Na+), tR = 2.27 min; 1H NMR (400 MHz, d6-DMSO) δ 7.97
(d, J = 3.13 Hz, 1 H) 7.61 (dd, J = 8.44, 2.57 Hz, 1 H) 7.30−7.37 (m,
1 H) 7.21−7.30 (m, 1 H) 7.11 (br s, 2 H), 4.91−5.00 (m, 1 H) 3.22
(dd, J = 16.31, 6.09 Hz, 1 H) 2.83 (dd, J = 16.29, 5.97 Hz, 1 H) 2.61
(s, 3 H); 13C NMR (101 MHz, d6-DMSO) δ 168.94, 166.97, 164.95,
162.24, 159.77, 136.49, 136.46, 129.28, 129.19, 121.74, 120.10, 119.85,
115.17, 114.96, 109.91, 50.99, 36.87, 24.15.
1
400 and 101 MHz, or 500 and 125 MHz, respectively. H shifts are
referenced to the residual protonated solvent signal (e.g., δ 2.50 for d6-
DMSO), and 13C shifts are referenced to the deuterated solvent signal
(δ 39.5 for d6-DMSO).
(S,E)-N-(2-Bromo-4-fluorobenzylidene)-2-methylpropane-2-
sulfinamide (3). A round-bottom flask was charged with dry THF
(50 mL), titanium ethoxide (41 mL), (S)-(−)-tert-butanesulfinamide
(12.0 g, 99.1 mmol), and 2-bromo-4-fluorobenzaldehyde (2) (18.2 g,
90.1 mmol). The resulting reaction mixture was stirred under N2 at rt
for 4 h. The reaction mixture was diluted with EtOAc, and a mixture of
brine with Celite was added with vigorous stirring. The resulting
emulsion was filtered through a pad of Celite and washed with EtOAc.
The filtrate was transferred to a separatory funnel and the aqueous
layer removed. The organics were washed with brine, dried (Na2SO4),
and concentrated to afford 3 as a yellow oil that solidified upon
1
standing (26.5 g, 86.3 mmol, 96%): H NMR (300 MHz, CDCl3) δ
8.86 (s, 1H), 8.03 (m, 1H), 7.35 (m, 1H), 7.11 (m, 1H), 1.11 (s, 9H);
LC/MS m/z 307.9 (MH+), tR = 3.22 min.
(R)-Ethyl 3-(2-Bromo-4-fluorophenyl)-3-((S)-(1,1-
dimethylethyl)sulfinamido)propanoate (4). An oven-dried
three-necked round-bottom flask, reflux condensor, and addition
funnel were assembled under positive N2 pressure and cooled to room
temperature. The flask was charged with Zn dust (21.3 g, 326.0
mmol), CuCl (32.6 g, 32.6.mmol), and dry THF (60 mL). The
reaction mixture was heated to reflux temperature and stirred
vigorously with an overhead stirrer for 30 min. The reaction was
removed from the oil bath, and the addition funnel was charged with
ethyl bromoacetate (3.6 mL, 32.6 mmol) and dry THF (30 mL). The
ethyl bromoacetate solution was added slowly so that a gentle refluxing
of the reaction mixture was maintained. Once addition was complete,
the reaction mixture was stirred for 20 min and then heated to 50 °C
for 30 min. The reaction mixture was then cooled to 0 °C and the
addition funnel charged with 3 (6.60 g, 21.5 mmol) in dry THF (20
mL). This solution was then added dropwise and the reaction mixture
stirred for an additional 4 h at 0 °C. The reaction mixture was filtered
through a pad of Celite, and the filter pad was washed twice with Et2O.
The filtrate was washed with 0.25 M citric acid, satd NaHCO3(aq),
dried (Na2SO4), and concentrated to afford 4 (7.30 g, 18.4 mmol,
86%) as a clear oil: 1H NMR (300 MHz, CDCl3) δ 7.39 (m, 1H), 7.28
(m, 1H), 7.01 (m, 1H), 5.14 (m, 1H), 4.92 (d, J = 5.4, 2H), 4.1 (m,
2H), 2.90 (m, 2H), 1.22 (m, 12H); LC/MS m/z 396.0 (MH+), tR =
2.96 min; HPLC tR = 4.11 min (major diastereomer), tR = 3.88 min
(minor diastereomer); de = 96%.
(R)-2-Amino-7-(4-fluoro-2-(6-methoxypyridin-2-yl)phenyl)-
4-methyl-7,8-dihydropyrido[4,3-d]pyrimidin-5(6H)-one (9). To
a small glass pressure vessel containing a mixture of 8 (226 mg, 0.65
mmol) and 2-methoxy-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
pyridine (395 mg, 2.58 mmol) in DME (4 mL) were added
Pd(dppf)Cl2/CH2Cl2 (53 mg, 0.064 mmol) and 2 M Na2CO3(aq)
(2 mL, 4 mmol). The reaction mixture was degassed with argon and
sealed. The mixture was then heated to 100 °C in an aluminum block
for 2 h. Additional 2-methoxy-6-(4,4,5,5-tetramethyl-1,3,2-dioxabor-
olan-2-yl)pyridine (198 mg, 1.29 mmol) and Pd(dppf)Cl2/CH2Cl2
(53 mg, 0.064 mmol) were added. The reaction mixture was again
heated to 100 °C for 17 h. After being cooled to room temperature,
the mixture was diluted with EtOAc, washed with 2 M Na2CO3(aq)
and brine, dried (Na2SO4), filtered, and evaporated to give the crude
product, which was purified by reversed-phase preparative HPLC and
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freebased to give 9 (112 mg, 46%): H NMR (400 MHz, CDCl3) δ
7.65 (dd, J = 8.4, 7.2 Hz, 1 H), 7.60 (dd, J = 8.6, 5.5 Hz, 1 H), 7.09−
7.18 (m, 2 H), 6.96 (dd, J = 7.4, 0.8 Hz, 1 H), 6.76 (dd, J = 8.2, 0.8 Hz,
1 H), 6.14 (s, 1 H), 5.48 (s, 2 H), 5.11 (ddd, J = 10.8, 4.7, 1.0 Hz, 1
H), 3.93 (s, 3 H), 3.19−3.26 (m, 1 H), 3.02−3.10 (m, 1 H), 2.72 (s, 3
H); 13C NMR (125 MHz, CDCl3) δ 171.13, 168.89, 165.44, 163.22,
162.76, 162.30, 160.78, 155.12, 141.81, 139.28, 134.38, 128.46, 117.16
(d, J = 21 Hz), 116.98, 116.82 (d, J = 21 Hz), 111.30, 53.71, 49.52,
39.40, 24.47; LC/MS m/z 380.1 (MH+), tR = 0.67 min; HRMS found
m/z 380.1525, C20H19FN5O2 requires m/z 380.1523.
(R)-Ethyl 3-Amino-3-(2-bromo-4-fluorophenyl)propanoate
Hydrochloride (5). Compound 4 (7.30 g, 18.4 mmol) was stirred
with Et2O (37 mL), EtOH (1.2 mL), and 4 M HCl in Et2O (37 mL)
for 30 min. The resulting suspension was filtered, and the solids were
triturated with Et2O and hexanes. The solid was dried under vacuum
(R)-2-Amino-7-(4-fluoro-2-(6-methoxypyrazin-2-yl)phenyl)-
1
4-methyl-7,8-dihydropyrido[4,3-d]pyrimidin-5(6H)-one (17).
to afford 5 as a white solid (5.23 g, 15.2 mmol, 83%): H NMR (300
1
17 was synthesized by the same method as 9: H NMR (400 MHz,
MHz, CD3OD) δ 7.61 (m, 2H), 7.33 (m, 1H), 5.18 (m, 1H), 4.85 (br
s, 3H), 4.13 (q, J = 7.2, 2H), 3.15 (ddd, 2H), 1.22 (t, J = 7.5, 3H); LC/
MS m/z 292.0 (MH+), tR = 1.97 min. To analyze the ee, a portion of
the material was freebased by dissolving it in EtOAc and washing the
organic layer three times with 10% Na2CO3(aq). The organic layer was
dried over Na2SO4 and concentrated to afford the freebase. A racemic
mixture of 5 was also prepared and analyzed by chiral HPLC to
confirm separation of the enantiomers (Chiralpak AD column, 1 mL/
CDCl3) δ 8.27 (d, J = 6.3 Hz, 1 H), 7.69 (dd, J = 8.6, 5.5 Hz, 1 H),
7.21−7.26 (m, 1 H), 7.18 (dd, J = 9.0, 2.7 Hz, 1 H), 5.87 (s, 1 H), 5.29
(s, 2 H), 5.04 (dd, J = 11.2, 4.9 Hz, 1 H), 3.99 (s, 3 H), 3.24−3.30 (m,
1 H), 3.10−3.20 (m, 1 H), 2.75 (s, 3 H); 13C NMR (125 MHz,
CDCl3) δ 170.75, 168.30, 165.49, 164.78, 162.37, 159.34, 149.43,
138.36, 136.10, 135.22, 129.11, 117.58 (d, J = 22.5 Hz), 117.24 (d, J =
22.5 Hz), 111.58, 54.28, 49.92, 39.93, 24.73; LC/MS m/z 381.0
(MH+), tR = 0.59 min; HRMS found m/z 381.1475, C19H18FN6O2
requires m/z 381.1475
min, MeOH): (S)-enantiomer, tR = 5.84 min; (R)-enantiomer, tR
=
7.47 min; >95% ee.
E
dx.doi.org/10.1021/jm501107q | J. Med. Chem. XXXX, XXX, XXX−XXX