ENGEN ET AL.
mass spectra (HRMS) were recorded on a Micromass Q-Tof2
mass spectrometer that was equipped with an electrospray ion
isomers), 7.47–7.18 (m, 4H+4H, 2 isomers), 6.98 (dd, J = 2.2,
1.1 Hz, 1H, 1 isomer), 6.95 (dd, J = 2.2, 1.1 Hz, 1H, 1 isomer),
6.94–6.86 (m, 1H+1H, 2 isomers), 6.45 (t, J = 8.9 Hz, 1H, 1
isomer), 6.37 (t, J = 7.2 Hz, 1H, 1 isomer), 4.35–4.21 (m,
1H+1H, 2 isomers), 3.75 (d, J = 2.3 Hz, 3H+3H, 2 isomers), 3.34
(m, 3H+3H, 2 isomers), 2.19–1.96 (m, 1H+1H, 2 isomers),
1.90–1.68 (m, 3H+3H, 2 isomers), and 1.47–1.16 (m, 9H+9H, 2
isomers); and 13C NMR (101 MHz, DMSO-d6) d Isomer 1:
171.51 (major rotamer), 171.1 (minor rotamer), 160.6, 156.3,
153.8, 148.8, 136.64, 129.7, 128.4, 128.2, 122.13, 121.8
(major rotamer), 121.6 (minor rotamer), 120.2, 111.0, 78.8
(minor rotamer), 78.42 (major rotamer), 59.6 (major rotamer),
59.4 (minor rotamer), 55.43, 51.9, 46.7, 31.0, 28.1, and 23.9.
Isomer 2: 171.46 (major rotamer), 171.0 (minor rotamer), 160.2,
156.3, 153.4, 148.8, 136.55, 129.5, 128.3, 127.5, 122.08, 121.42
(minor rotamer), 121.25 (major rotamer), 120.2, 111.0, 78.7
(minor rotamer), 121.36 (major rotamer), 120.2, 110.94, 78.71
(minor rotamer), 78.36 (major rotamer), 59.5 (major rotamer),
59.3 (minor rotamer), 55.40, 51.7, 46.5, 29.5, 27.8, and 23.1.
1
source. H and 13C NMR spectra were recorded at 25ꢁC on a
Varian 400-MR spectrometer at 400 and 100 MHz, respec-
tively. For rotamers, NMR experiments were performed both
at room temperature and at elevated temperature; see Sup-
plementary Data (Supplementary Data are available online at
ppm, with the solvent residual peak as the internal standard
(CDCl3 dH 7.26, dC 77.16; CD3OD dH 3.31, dC 49.00; DMSO-d6
dH 2.50, dC 39.52). The synthesis and characterization of
compounds 235 and 736 have been previously reported.
(2-Methoxyphenyl)(pyridine-2-yl)methanamine (24). A solution
of 2-cyanopyridine (0.5 mL, 5.2 mmol) in dry toluene (25 mL)
under inert atmosphere was cooled to 0ꢁC on an ice bath.
Then, 2-Methoxymagnesiumbromide in THF (1 M, 6.2 mL, 6.2
mmol) was added dropwise. The reaction mixture was stirred
for 40 min at 0ꢁC. Isobutanol was added dropwise to a clear
brown solution. NaBH4 (393 mg, 10.4 mmol) was added, and
the mixture was stirred at ambient temperature for 14 h. The
reaction was quenched with a 1:1 mixture of MeOH and H2O,
and the organic solvents were removed under reduced pres-
sure. The remaining aqueous mixture was extracted with
DCM (·3) and the combined organic phases were washed with
brine, dried over MgSO4, filtered, and concentrated. The crude
product was purified by flash column chromatography by
using 5% MeOH in CHCl3 as eluent to afford 24 as a yellow oil
(1.06 g, 95%):1H NMR (400 MHz, CD3OD) d 8.48 (ddd, J = 1.0,
1.9, 5.0 Hz, 1H), 7.72 (td, J = 1.8, 7.7 Hz, 1H), 7.35 (dt, J = 1.0,
7.6 Hz, 1H), 7.27–7.21 (m, 3H), 6.98–6.90 (m, 2H), 5.45 (s, 1H),
4.85 (s, 2H), and 3.78 (s, 3H); 13C NMR (101 MHz, CDCl3) d
163.4, 156.8, 149.1, 136.3, 133.3, 128.2, 127.8, 121.8, 121.7,
120.9, 110.7, 55.4, and 55.0.
(S)-tert-Butyl-2-(1-(2-methoxyphenyl)imidazo[1,5-a]pyridine-3-
yl)pyrrolidine-1-carboxylate (26). A solution of 25 (300 mg, 0.73
mmol) and pyridine (0.35 mL, 4.37 mmol) in dry DCM (5 mL)
under inert atmosphere was cooled to 0ꢁC on an ice bath, and
POCl3 (0.12 mL, 1.3 mmol) was added dropwise. The reaction
mixture was stirred at room temperature for 14 h. The reaction
mixture was washed with NaOH (1%, aq), dried over MgSO4,
filtered, and concentrated under reduced pressure. The crude
product was purified by flash column chromatography by
using 30% EtOAc in pentane as eluent to afford 26 as a brown
oil (240 mg, 84%): 1H NMR (400 MHz, DMSO-d6, 100ꢁC) d 8.26
(d, J = 7.2 Hz, 1H), 7.60 (dd, J = 7.6, 1.8 Hz, 1H), 7.47 (dt, J = 9.2,
1.3 Hz, 1H), 7.29 (ddd, J = 8.3, 7.3, 1.8 Hz, 1H), 7.10 (dd, J = 8.2,
1.1 Hz, 1H), 7.02 (td, J = 7.4, 1.1 Hz, 1H), 6.73 (ddd, J = 9.2, 6.3,
1.0 Hz, 1H), 6.64 (ddd, J = 7.4, 6.3, 1.3 Hz, 1H), 5.35 (dd, J = 7.4,
4.6 Hz, 1H), 3.80 (s, 3H), 3.62–3.49 (m, 2H), 2.38–2.21 (m, 2H),
2.19–2.11 (m, 1H), and 2.01–1.90 (m, 1H), 1.18 (s, 9H); 13C
NMR (101 MHz, DMSO-d6, 100ꢁC) d 156.7, 154.1, 140.0,
131.4, 131.2, 127.4, 127.2, 125.0, 122.4, 120.4, 120.1, 118.2,
112.3, 78.9, 56.1, 55.9, 53.1, 46.9, 28.5, 28.3, and 24.1.
(2S)-tert-Butyl-2-(((2-methoxyphenyl)(pyridine-2-yl)methyl)-
carbamoyl)pyrrolidine-1-carboxylate (25). To a solution of 24
(300 mg, 1.4 mmol), N-Boc-L-Proline (362 mg, 1.7 mmol),
HOBt (257 mg, 1.7 mmol), and TEA (0.4 mL, 2.9 mmol) in dry
DCM (14 mL) were added to EDC*HCl (322 mg, 1.7 mmol). The
reaction mixture was stirred at room temperature for 3 h,
washed with H2O and brine, dried over MgSO4, filtered, and
concentrated under reduced pressure. The crude product was
purified by flash column chromatography by using 3% MeOH
in CHCl3 as eluent to afford 25 as a white semi-solid, mixture
of diastereomers (1:1) and rotamers (542 mg, 94%): [a]D22-68ꢁ
(S)-1-(2-Methoxyphenyl)-3-(pyrrolidine-2-yl)imidazo[1,5-a]pyridine
hydrochloride (27). To a solution of 26 (230 mg, 0.59 mmol) in
dioxane, HCl in dioxane (4M, 1.5 mL, 5.9 mmol) was added
and the reaction mixture was stirred overnight. The obtained
beige salt 27 was filtered and used in the next step without
further purification (170 mg, 99%, >99% pure according
1
(c = 1.12, CHCl3); H NMR (400 MHz, DMSO-d6) d 8.59 (d,
to LCMS): [a]D23-7.1ꢁ (c = 1.10, MeOH); H NMR (400 MHz,
1
J = 8.3 Hz, 1H, 1 isomer) 8.52 (d, J = 8.3 Hz, 1H, 1 isomer),
8.49–8.44 (m, 1H+1H, 2 isomers), 7.77–7.68 (m, 1H+1H, 2
CD3OD) d 8.19 (dt, J = 7.2, 1.1 Hz, 1H), 7.53 (ddd, J = 7.5, 1.8,
184 ASSAY and Drug Development Technologies APRIL 2016
ª MARY ANN LIEBERT, INC.