X. Cheng et al. / Bioorg. Med. Chem. xxx (2013) xxx–xxx
7
(21 mL) and stirred for 2 h at 0 °C and for 24 h at room tempera-
ture. The mixture was poured into 35 mL of aqueous sodium sulfite
(10%). The layers were separated and the aqueous layer was ex-
tracted two times with 30 mL of dichloromethane each. The com-
bined organic layers were dried over magnesium sulfate,
concentrated and stored at ꢁ20 °C. The colourless crystalline
product was collected, washed with cold ethyl acetate and dried
in vacuo. Yield: 82.7 mg (0.5 mmol, 17%). 1H NMR (400.13 MHz,
4.1.14. 2-Amino-3-pyridylacetic acid (7)
The residue 6 was dissolved in 6 N HCl and refluxed overnight.
Adjustment with 6 N NaOH to pH 5 produced a precipitate, that
was collected by filtration to afford 7 as a white solid (2 g,
12.0 mmol, 38%). 1H NMR (400 MHz, DMSO-d6, d = 2.49 ppm):
7.83 (dd, 1H, 3JH,H = 4.8 Hz, 4JH,H = 1.4 Hz), 7.26 (dd, 1H, 3JH,H = 7.2 Hz,
3
4
4JH,H = 1.4 Hz,), 6.50 (dd, 1H, JH,H = 7.2 Hz, JH,H = 5.1 Hz), 5.70, (s,
3H) 3.42 (s, 2H).
3
DMSO-d6, d = 2.49 ppm): 8.66 (s, 1H), 8.49 (dd, 1H, JH,H = 4.8 Hz,
3
4
4JH,H = 1.5 Hz,), 8.08 (s, 1H), 8.05 (dd, 1H, JH,H = 7.9 Hz, JH,H = 1.7 -
4.1.15. 7-Azaoxindole (8)
3
3
Hz), 7.39 (dd, 1H, JH5,H4 = 7.7 Hz, JH5,H6 = 4.8 Hz), 2.98 (s, 3H).
The mother liquor of the synthesis of 7 was extracted three
times with an equal volume of ethyl acetate and the combined or-
ganic phases were dried over sodium sulfate. Removal of the sol-
vent afforded the product 8 as a white solid. A suspension of 7
(2.0 g, 12.0 mmol) in amyl alcohol was refluxed with a catalytic
amount of p-toluenesulfonic acid for 48 h. After removal of the sol-
vent from the clear solution, the residue was purified by column
chromatography on silica gel using ethyl acetate/hexane (3:1) as
eluent to provide 8 as a white solid (0.5 g, 3.7 mmol, 31%). The total
yield was 40%. 1H NMR (400 MHz, DMSO-d6, d = 2.49 ppm): 10.96
4.1.11. 7-Aza-3-indoxyl acetate (4)
Under argon atmosphere at room temperature, a solution of
thallium(III) acetate (3.82 g, 10.0 mmol) in acetic acid (51 mL)
and water (2.5 mL) was added dropwise to a solution of 1
(1.075 g, 9.1 mmol) in glacial acetic acid (7.5 mL). The mixture
was refluxed for 1 h, poured onto crushed ice (200 g) and neutral-
ized with sodium carbonate at 0 °C. The precipitate was collected,
dissolved in hot ethyl acetate and cooled to 0 °C. The residue was
discarded and the solvent was removed in vacuo to yield 7-azain-
doxyl-3-acetate (507 mg, 2.9 mmol, 32%) as a reddish solid. 1H
NMR (400 MHz, DMSO-d6, d = 2.49 ppm): 11.58 (s, 1H), 8.24 (dd,
3
3
(s, 1H), 8.02 (d, 1H, JH,H = 5.3 Hz), 7.52 (d, 1H, JH,H = 7.0 Hz),
3
4
6.91 (dd, 1H, JH,H = 7.0 Hz, JH,H = 5.3 Hz), 3.53 (s, 2H). 13C–{1H}
NMR (150 MHz, DMSO-d6, d = 39.5 ppm): 176.6, 150.8, 146.1,
131.8, 120.4, 117.3, 35.2. C7H6N2O. Found: C 62.75, H 4.65, N
20.97; requires: C 62.68, H 4.51, N 20.88.
3
4
3
1H, JH,H = 4.4 Hz, JH,H = 1.3 Hz), 7.83 (dd, 1H, JH,H = 8.3 Hz,
4JH,H = 1.8 Hz), 7.42 (s, 1H), 7.07 (dd, 1H, JH,H = 4.4 Hz, JH,H = 7.9 -
Hz), 2.31 (s, 3H). 13C–{1H} NMR (150 MHz, DMSO-d6,
d = 39.5 ppm): 168.7, 144.9, 143.3, 127.2, 125.7, 115.4, 115.0,
112.3, 20.4. C9H8N2O2. Found: C 60.90, H 4.29, N 16.42; requires:
C 61.36, H 4.58, N 15.90.
3
3
4.1.16. 7-Azaisatin (9)
Dried DMSO (6 mL) was heated to 120 °C and a solution of 8
(500 mg, 3.7 mmol) and N-bromosuccinimide (690.6 mg,
3.9 mmol) in dry DMSO (2 mL) was added dropwise. The mixture
was stirred at 120 °C for 30 min, adjusted to pH 5–6 with aqueous
NaHCO3 (5%) and extracted with ethyl acetate. The solvent was re-
moved and the residue was purified by column chromatography
using ethyl acetate: hexane (3:1) as eluent to afford 9 as a yellow
solid (259.2 mg, 1.76 mmol, 65%). 1H NMR (400 MHz, DMSO-d6,
d = 2.49 ppm): 11.6 (s, 1H), 8.38 (dd, 1H, 3JH,H = 3.3 Hz, 4JH,H = 0.9 Hz),
7.87 (dd, 1H, 3JH,H = 5.0 Hz, 4JH,H = 1.1 Hz), 7.01 (dd, 1H, 3JH,H = 4.8 -
Hz, 4JH,H = 3.5 Hz). 13C–{1H} NMR (150 MHz, DMSO-d6,
d = 39.5 ppm): 183.0, 164.0, 160.0, 155.2, 132.6, 119.0, 112.9.
C7H6N2O2. Found: C 56.66, H 2.83, N 18.72; requires: C 56.76, H
2.72, N 18.91.
4.1.12. 2-(Trimethylacetylamino)-3-methylpyridine (5)
Trimethylacetyl chloride (13.26 g, 0.11 mol) in methylene chlo-
ride (20 mL) was slowly added to a solution of 2-amino-3-methyl-
pyridine (10.81 g, 0.1 mol) and triethylamine (12.63 g, 0.12 mol) in
150 ml of methylene chloride at 0 °C. The mixture was stirred in an
ice bath for 1 h and further at room temperature for 2 h. Subse-
quently, the mixture was washed three times with an equal vol-
ume of aqueous sodium hydrogen carbonate (5%). The organic
layer was dried with magnesium sulfate and concentrated to yield
a colourless solid (14.52 g, 0.076 mol, 76%).
1H NMR (400 MHz, DMSO-d6, d = 2.49 ppm): 9.55 (s, 1H), 8.25
4.1.17. 7,70-Diazaindigo (10)
3
3
(d, 1H, JH,H = 4.7 Hz), 7.64 (d, 1H, JH,H = 7.4 Hz), 7.19 (dd, 1H,
3JH,H = 7.4 Hz, JH,H = 4.7 Hz), 2.10 (s, 3H),1.22 (s, 9H). 13C–{1H}
4
Under normal atmosphere condition, a suspension of 7-aza-3-
indoxyl acetate (200 mg, 1.1 mmol) was stirred in 25% aq ammo-
nium hydroxide (10 mL). After 24 h water (50 mL) was added.
The precipitate was filtered and dried to give 10 as dark blue solid
(68 mg, 23.4%).
NMR (150 MHz, DMSO-d6, d = 39.5 ppm): 176.5, 150.6, 145.7,
139.0, 129.9, 121.9, 38.7, 27.3, 17.4.
4.1.13. 3-(2-Trimetylacetylamino)pyridyl acetic acid (6)
50 mL of n-butyllithium in hexane (1.6 M, 80 mmol) were
slowly added within 1 h to a solution of 5 (6.15 g, 32 mmol) in
dry THF (90 mL) at ꢁ78 °C in a period of 1 h. The mixture was stir-
red for 1 h at ꢁ78 °C and for 3 h at ꢁ20 °C. Powdered dry ice was
added to this suspension at ꢁ78 °C. The mixture was allowed to
warm up to room temperature, diluted with water and adjusted
to pH 5 with 4 N HCl. It was extracted three times with an equal
volume of ethyl acetate. The combined organic layers were dried
over magnesium sulfate and the solvent was removed to yield 6
as a whitish solid.
1H NMR (600 MHz, 2 N DCl: DMSO-d6 (1:3), d = 2.49 ppm): 8.63
3
3
(d, 1H, JH,H = 5.0 Hz), 8.22 (d, 1H, JH,H = 3.8 Hz), 7.38 (t, 1H,
3JH,H = 4.4 Hz). C14H8N4O2ꢂ0.2 H2O. Found: C 63.04, H 2.90, N
20.74; requires: C 62.78, H 3.16, N 20.92.
4.1.18. 7,70-Diazaisoindigo (11)
Under argon atmosphere, 7-azaisatin (67.1 mg, 0.45 mmol) and
7-azaindole (97.3 mg, 0.45 mmol) were suspended in acetic acid
(4 mL) and conc. HCl (340
lL). The mixture was stirred at room
temperature for 12 h and diluted with water (30 mL). The precipi-
1H NMR (400 MHz, DMSO-d6, d = 2.49 ppm): 12.31 (s, 1H,
tate was filtered and dried to yield
0.43 mmol, 95.8%).
a red solid (113.8 mg,
3
4
COOH), 9.61 (s, 1H), 8.32 (dd, 1H, JH,H = 4.8 Hz, JH,H = 1.7 Hz),
7.71 (dd, 1H, 3JH,H = 7.4 Hz, 4JH,H = 1.7 Hz), 7.25 (dd, 1H, 3JH,H = 7.5 Hz,
4JH,H = 4.8 Hz), 3.50 (s, 2H), 1.2 (s, 9H). 13C–{1H} NMR (150 MHz,
DMSO-d6, d = 39.5 ppm): 176.8, 172.0, 150.6, 146.7, 139.9, 127.7,
121.8, 38.7, 36.8, 27.1.
1H NMR (400 MHz, DMSO-d6, d = 2.49 ppm): 11.6 (s, 1H), 9.30
3
3
4
(d, 1H, JH,H = 5.4 Hz), 8.20 (dd, 1H, JH,H = 3.4 Hz, JH,H = 1 Hz),
3
3
7.07 (dd, 1H, JH,H = 5.1 Hz, JH,H = 3.2 Hz). C14H8N4O2ꢂ0.25 H2O.
Found: C 62.67, H 2.97, N 20.95; requires: C 62.57, H 3.19, N 20.85.