Deubiquitinating Enzyme Inhibitors
[M+H]+; Anal. calcd (%): C 58.6, H 1.1, N 21.0, found: C 58.2, H 1.0,
N 21.0.
d=186.84, 165.35, 163.62, 139.32, 136.75, 135.24, 133.50, 132.93,
123.51, 121.99, 119.01, 117.77, 117.57 ppm; ESIMS (+) calcd for
C13H5N5O: 247.05, found: 248.1 [M+H]+.
2,5-dioxo-2,5-dihydro-1H-indeno[1,2-b]pyridine-3-carbonitrile
(9). A suspension of 1 (5.66 g, 24.3 mmol) in aqueous NaOH (2%
w/v, 81 mL) was stirred at room temperature for 16 h. The mixture
was acidified with 3n HCl to pH 1, the precipitate was collected by
filtration, washed with H2O, and dried under vacuum to afford 9
9-(1’,3’-Dioxolan-2’-yl)-9H-indeno[1,2-b]pyrazine-2,3-dicarboni-
trile (20). Ethylene glycol (2.4 mL, 43.8 mmol) and PTSA (6.25 g,
32.8 mmol) were added to a suspension of 1 (5.09 g, 21.9 mmol) in
toluene (146 mL). The mixture was held at reflux in a Dean–Stark
apparatus for 28 h, and then the solvent was evaporated. The
crude was purified by flash chromatography on silica (CH2Cl2) to
afford 20 (3.87 g, 64%) as a light-yellow solid. 1H NMR (300 MHz,
[D6]DMSO): d=8.03 (m, 1H), 7.83–7.70 (m, 3H), 4.47 ppm (s, 4H);
13C NMR (75 MHz, [D6]DMSO): d=162.05, 155.41, 144.27, 135.19,
134.90, 134.40, 133.14, 131.44, 126.10, 123.60, 115.06, 114.80,
106.26, 67.00 ppm; ESIMS (+) calcd for C15H8N4O2: 276.06, found:
277.2 [M+H]+; Anal. calcd (%): C 65.2, H 2.9, N 20.3, found: C 65.0,
H 2.6, N 20.5.
1
(4.88 g, 90%) as a light-brown solid. H NMR (300 MHz, [D6]DMSO):
d=7.89 (d, 1H), 7.79–7.62 ppm (m, 3H); 13C NMR (75 MHz,
[D6]DMSO): d=185.78, 158.15, 157.35, 135.52, 135.37, 134.62,
134.42, 129.30, 125.57, 124.10, 123.84, 116.44 ppm; ESIMS (+) calcd
for C12H5N3O2: 223.04, found: 224.0 [M+H]+.
3-Methoxy-9-oxo-9H-indeno[1,2-b]pyrazine-2-carbonitrile
Sodium (110 mg) was added to suspension of
(10).
(1.10 g,
a
1
4.7 mmol) in MeOH (47 mL), and the mixture was stirred at room
temperature for 16 h. The precipitate was filtered, washed with
EtOH, and dried under vacuum to yield 10 (1.03 g, 93%) as a
General procedure B: synthesis of alkyloxyimines 22a–h.
NH2OH·HCl (134 mg, 1.94 mmol) was added to a suspension of 1
(150 mg, 0.646 mmol) in pyridine (10 mL) at 08C. Molecular sieves
(MS) were added, and the mixture was stirred at room temperature
for 16 h or at 608C for 1.5 h. The insoluble residue was filtered, the
solvent was evaporated, and the crude was purified by flash chro-
matography.
1
yellow–green solid. H NMR (300 MHz, [D6]DMSO): d=7.92 (d, 1H),
7.83 (m, 2H), 7.71 (dd, 1H), 4.25 ppm (s, 3H); ESIMS (+) calcd for
C13H7N3O2: 237.05, found: 238.0 [M+H]+.
3-Ethoxy-9-oxo-9H-indeno[1,2-b]pyrazine-2-carbonitrile (11). Pre-
pared according to the procedure described for compound 10 in
1
89% yield as a pale-yellow solid. H NMR (300 MHz, [D6]DMSO): d=
9-Allyloxyimino-9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile
(22c). Prepared according to general procedure B (column eluent:
petroleum ether/EtOAc 9:1) in 15% yield as a yellow solid in dia-
7.95 (d, 1H), 7.84 (m, 2H), 7.70 (dd, 1H), 4.53 (q, 2H), 1.34 ppm (t,
3H); ESIMS (+) calcd for C14H9N3O2: 251.07, found: 252.0 [M+H]+.
1
3-Amino-9-oxo-9H-indeno[1,2-b]pyrazine-2-carbonitrile (13).
A
stereomeric ratio 1:1. H NMR (300 MHz, [D6]DMSO; mixture of syn/
mixture of 1 (201 mg, 0.86 mmol), NH4CO2CH3 (331 mg, 4.3 mmol),
and Na2SO4 (200 mg) in THF (2.9 mL) was stirred at 708C in a
sealed tube for 18 h. The solvent was evaporated, H2O (5 mL) was
added, and the precipitate was filtered, washed with H2O, and
dried under vacuum to afford 13 (171 mg, 90%) as a green solid.
1H NMR (300 MHz, [D6]DMSO): d=8.43 (brs, 2H), 7.83–7.71 (m, 3H),
7.71–7.59 ppm (m, 1H); 13C NMR (75 MHz, [D6]DMSO): d=187.31,
163.58, 158.71, 138.83, 136.51, 136.44, 136.07, 133.66, 124.04,
122.47, 116.41, 110.55 ppm; ESIMS (+) calcd for C12H6N4O: 222.05,
found: 223.1 [M+H]+.
anti diastereomers): d=8.43 (m, 1H), 8.22 (m, 1H), 7.90–7.80 (m,
2H), 6.20 (m, 1H), 5.47 (m, 1H), 5.35 (m, 1H), 5.13 (ddd, 2H), and
d=8.12 (m, 1H), 7.96 (m, 1H), 7.80–7.69 (m, 2H), 6.14 (m, 1H), 5.53
(m, 1H), 5.38 (m, 1H), 5.08 ppm (ddd, 2H); 13C NMR (75 MHz,
[D6]DMSO; mixture of syn/anti diastereomers): d=155.54, 151.70,
146.45, 134.94, 134.55, 133.73, 133.60, 132.82, 132.42, 131.40,
129.27, 123.95, 123.88, 122.23, 119.88, 119.44, 115.14, 115.03,
114.90, 78.62, 78.38 ppm; ESIMS (+) calcd for C16H9N5O: 287.08,
found: 288.2 [M+H]+; Anal. calcd (%): C 66.9, H 3.2, N 24.4, found:
C 67.2, H 2.9, N 24.5.
3-(4,4-Difluoropiperidin-1-yl)-9-oxo-9H-indeno[1,2-b]pyrazine-2-
carbonitrile (15). 4,4-Difluoropiperidine·HCl (249 mg, 1.58 mmol)
was dissolved in 1n NaOH (5 mL) and extracted with CH2Cl2 (2ꢂ
5 mL). The organic phase was dried over Na2SO4, filtered, and
evaporated. The residue was dissolved in THF (2 mL), and this solu-
tion was added to a solution of 1 (185 mg, 0.79 mmol) in THF
(2 mL); the mixture was stirred at room temperature for 48 h. The
solvent was evaporated, the crude solid washed with EtOH and
dried under vacuum to afford 15 (245 mg, 95%) as a yellow–
brown solid. 1H NMR (300 MHz, [D6]DMSO): d=7.89 (d, 1H), 7.79
(dd, 1H), 7.78 (d, 1H), 7.69 (dd, 1H), 4.13 (m, 4H), 2.22 ppm (m,
4H); 13C NMR (75 MHz, [D6]DMSO): d=187.07, 161.33, 156.91,
138.57, 137.40, 136.56, 136.30, 133.93, 124.27, 122.76, 122.69,
118.03, 111.93, 44.69, 33.86 ppm; ESIMS (+) calcd for C17H12F2N4O:
326.10, found: 327.1 [M+H]+.
9-Benzyloxyimino-9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile
(22d). Prepared according to general procedure B (column eluent:
petroleum ether/EtOAc 9:1) in 32% yield as a yellow solid in dia-
1
stereomeric ratio 2:1. H NMR (300 MHz, [D6]DMSO; mixture of syn/
anti diastereomers): d=8.42 (m, 1H), 8.21 (m, 1H), 7.88–7.78 (m,
2H), 7.56–7.49 (m, 2H), 7.47–7.33 (m, 3H), 5.67 (s, 2H), and d=8.11
(m, 1H), 7.97 (m, 1H), 7.79–7.69 (m, 2H), 7.56–7.49 (m, 2H), 7.47–
7.33 (m, 3H), 5.63 ppm (s, 2H); 13C NMR (75 MHz, [D6]DMSO; mix-
ture of syn/anti diastereomers): d=156.22, 155.57, 151.71, 146.60,
137.15, 134.55, 134.26, 133.25, 132.70, 132.44, 132.15, 131.40,
129.15, 128.98, 128.84, 123.88, 122.25, 115.15, 115.02, 114.89, 79.69,
79.44 ppm; ESIMS (+) calcd for C20H11N5O: 337.10, found: 338.2
[M+H]+; Anal. calcd (%): C 71.2, H 3.3, N 20.8, found: C 71.0, H 3.0,
N 23.0.
7-Chloro-9-methoxyimino-9H-indeno[1,2-b]pyrazine-2,3-dicarbo-
nitrile (22g). Prepared according to general procedure B (column
eluent: petroleum ether/CH2Cl2 1:1) in 65% yield as a light-brown
2-Cyano-9-oxo-9H-indeno[1,2-b]pyrazin-3-yl-cyanamide
(16).
Under N2 atmosphere, CN2H2 (44 mg, 1.037 mmol) was dissolved in
dry DMF (1 mL), and NaH (21 mg, 0.519 mmol) was added in one
portion. After 20 min, a solution of 1 (96 mg, 0.415 mmol) in dry
DMF (2 mL) was added dropwise. After 1 h the solvent was evapo-
rated, and the crude was purified by flash chromatography
(CH2Cl2/MeOH 8:2) to afford 16 (84 mg, 82%) as an orange solid.
1H NMR (300 MHz, [D6]DMSO): d=7.85 (ddd, 1H), 7.77 (ddd, 1H),
7.76 (m, 1H), 7.67 ppm (ddd, 1H); 13C NMR (75 MHz, [D6]DMSO):
1
solid in diastereomeric ratio 2:1. H NMR (300 MHz, [D6]DMSO; mix-
ture of syn/anti diastereomers): major product: d=8.39 (d, 1H),
8.22 (d, 1H), 7.88 (dd, 1H), 4.42 ppm (s, 3H); minor product: d=
8.12 (d, 1H), 7.95 (d, 1H), 7.77 (dd, 1H), 4.37 ppm (s, 3H); 13C NMR
(75 MHz, [D6]DMSO; mixture of syn/anti diastereomers): major
product: d=154.59, 151.33, 145.32, 145.28, 139.25, 133.43, 133.14,
132.85, 131.26, 128.68, 125.46, 114.95, 114.92, 66.20 ppm; minor
ChemMedChem 2010, 5, 552 – 558
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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