9632
L. A. Smyth et al. / Tetrahedron 63 (2007) 9627–9634
3a precipitated (143 mg, 0.72 mmol, 29%); mp 205–208 ꢀC;
1H NMR (500 MHz, DMSO-d6) dH 3.47 (3H, s, CH3), 3.57
(2H, s, CH2), 6.08 (2H, s, amine NH2), 6.78 (2H, s, amide
NH2), 12.78 (1H, br s, OH); 13C NMR (126 MHz, DMSO-
d6) dC 33.7, 34.8, 96.3, 142.0, 149.9, 166.6, 172.1; MS
(ESI) m/z 199 (M+H)+; HRMS (M+H)+ calcd for
C7H11N4O3 199.0831, found 199.0829; HPLC tR¼1.76 min;
purity >99%. Anal. Calcd for C7H10N4O3: C, 42.42; H, 5.09;
N, 28.27%. Found: C, 42.45; H, 5.10; N, 28.07%.
The resulting red-brown solution was cooled and the solvent
was removed in vacuo. The brown solid was taken up in 10%
NaOH aq (14 mL) and water (70 mL) and heated at reflux for
15 min. Glacial AcOH was added to the hot orange solution
until it became turbid. On cooling, 4 precipitated as a bright
orange solid (620 mg, 2.98 mmol, 30%).
4.1.5.2. Method B. A solution of 3-amino-2-methyl-
2H-pyrazolo[4,3-c]pyridine-4,6(5H,7H)-dione (7) (30 mg,
0.17 mmol) in AcOCHO14 (0.49 mL) and (MeO)3CH
(0.33 mL) was heated at reflux for 3 h. The resulting brown
solution was cooled and the solvent was removed in vacuo.
The brown solid was suspended in THF (2 mL) and 5%
HCl (2 mL) was added. The suspension was heated at reflux
for 10 min and then cooled. The resulting pale orange solid
(4) was collected by filtration (13 mg, 0.063 mmol, 38%);
mp >350 ꢀC (DMSO); IR (Nujol mull, cmꢁ1) 1668
(C]O), 1611 (C]O); UV (0.1 M NaOH, lmax) 227, 237–
Alternative purification (2.00 g scale):10 the cream suspen-
sion formed following basic hydrolysis was cooled, neu-
tralised with 10% HCl and collected by filtration to give
3a, which was used without further purification (mixture
of free acid and Na salt) (1.70 g, 8.57 mmol, 69%); mp
202–204 ꢀC; Rf¼0.68 (50:50, MeOH–CH2Cl2); IR (Nujol
mull, cmꢁ1) 3397 (NH2), 3200–3300 (br, NH), 1583
1
(C]N); H NMR (500 MHz, DMSO-d6) dH 3.13 (2H, s,
1
CH2), 3.41 (3H, s, CH3), 5.96 (2H, s, amine NH2), 6.17
(1H, br s, amide NH2), 10.36 (1H, br s, amide NH2); 13C
NMR (126 MHz, DMSO-d6) dC 33.4 (CH3), 39.3 (CH2),
96.7, 145.1, 150.2, 167.8, 174.3; MS (ESI) m/z 199
(M+H)+; HRMS (M+H)+ calcd for C7H11N4O3 199.0831,
found 199.0830; HPLC tR¼1.76 min; purity >99%. Anal.
Calcd for 0.9(C7H9N4O3Na)$0.1(C7H10N4O3)$1.2(H2O):
C, 35.09; H, 4.84; N, 23.38%. Found: C, 34.83; H, 4.60;
N, 23.41%.
246 (shoulder), 284, 332; H NMR (500 MHz, DMSO-d6)
dH 3.56 (3H, s, CH3), 7.12 (2H, s, NH2), 9.26 (1H, s,
CHO), 9.89 (1H, br s, NH); 13C NMR (126 MHz, DMSO-
d6) dC 33.0 (CH3), 89.0, 93.9, 147.3, 148.7, 160.8, 166.2,
178.4 (CH); MS (ESI) m/z 209 (M+H)+; HRMS (M+H)+
calcd for C8H9N4O3 209.0675, found 209.0679; HPLC
tR¼2.37 min; purity >99%. Anal. Calcd for C8H8N4O3$0.1
(AcOH): C, 45.99; H, 3.95; N, 26.16%. Found: C, 45.60; H,
3.73; N, 26.45%.
On recrystallisation of this white solid by dissolving in hot
AcOH, clear crystals of 3a were formed. 1H NMR
(500 MHz, DMSO-d6) dH 3.47 (3H, s, CH3), 3.57 (2H, s,
CH2), 6.08 (2H, s, amine NH2), 6.78 (2H, s, amide NH2),
12.78 (1H, br s, OH); 13C NMR (126 MHz, DMSO-d6) dC
33.7, 34.8, 96.3, 142.0, 149.9, 166.6, 172.1.
4.1.6. (Z)-3-Amino-7-(1-hydroxyethylidene)-2-methyl-
2H-pyrazolo[4,3-c]pyridine-4,6(5H,7H)-dione (5).
4.1.6.1. Method A. A solution of 2-(5-amino-4-carb-
amoyl-1-methyl-1H-pyrazol-3-yl)acetic acid (3a) (1.00 g,
5.05 mmol) in Ac2O (13.0 mL) and (MeO)3CMe (10.0 mL)
was heated at reflux for 3 h. The resulting brown solution
was cooled and the solvent was removed in vacuo. The
brown solid was taken up in 10% NaOH aq (6 mL) and water
(30 mL) and heated at reflux for 15 min. Glacial AcOH was
added to the hot orange solution until it was turbid. On cool-
ing, a pink solid precipitated. The solid was collected by fil-
tration, taken up in 5% HCl (18 mL) and THF (18 mL) and
the suspension heated at reflux for 15 min. On cooling, the
pink precipitate of 5 was isolated by filtration (487 mg,
2.19 mmol, 43%).
4.1.4. 2-(5-Amino-4-carbamoyl-1-phenyl-1H-pyrazol-3-
yl)acetic acid (3b).6,10 A solution of 5-amino-3-cyano-
methyl-1-phenyl-pyrazolidine-4-carbonitrile (2b) (2.00 g,
8.97 mmol) in 10% NaOH aq (6.46 mL, 16.1 mmol) was
heated at reflux for 50 min. The resulting brown solution
was cooled and acidified to pH 3 with 10% HCl. N-Phenyl
pyrazole acetic acid 3b precipitated as a pale brown solid,
which was collected by filtration and was used without fur-
ther purification (1.81 g, 6.95 mmol, 77%); mp 186–187 ꢀC;
Rf¼0.74 (50:50, MeOH–CH2Cl2); IR (Nujol mull, cmꢁ1
)
4.1.6.2. Method B. A solution of 3-amino-2-methyl-
2H-pyrazolo[4,3-c]pyridine-4,6(5H,7H)-dione (7) (30 mg,
0.17 mmol) in Ac2O (0.43 mL) and (MeO)3CMe (0.33 mL)
was heated at reflux for 3 h. The resulting brown solution
was cooled and the solvent was removed in vacuo. The
brown solid was suspended in THF (2 mL) and 5% HCl
(2 mL) and heated at reflux for 10 min. After cooling, the re-
sulting orange solid (5) was collected by filtration (11 mg,
0.05 mmol, 30%); mp 299–301 ꢀC (DMSO); IR (Nujol
mull, cmꢁ1) 3135 (NH), 1662 (C]N), 1616 (C]O), 1599
3313 (NH2), 3185 (amide), 1709 (C]O), 1640 (C]C),
1608 (C]O); 1H NMR (500 MHz, DMSO-d6) dH 3.72
(2H, s, CH2), 6.30 (2H, s, amine NH2), 6.93 (2H, s, amide
NH2), 7.38 (1H, tt, J¼7.0, 1.5 Hz, ArH), 7.50–7.55 (4H,
m, ArH), 12.71 (1H, br s, OH); 13C NMR (126 MHz,
DMSO-d6) dC 34.7, 97.1, 123.3, 127.1, 129.3, 137.9,
144.2, 149.9, 166.6, 172.0; MS (ESI) m/z 161 (M+H)+;
HRMS (M+H)+ calcd for C12H13N4O3 261.0988, found
261.0984; HPLC tR¼3.88 min; purity 95%. Anal. Calcd
for C12H12N4O3: C, 55.38; H, 4.65; N, 21.53%. Found: C,
55.03; H, 4.59; N, 21.14%.
1
(C]O); H NMR (500 MHz, DMSO-d6) dH 2.56 (3H, s,
C–CH3), 3.58 (3H, s, N–CH3), 6.42 (2H, s, NH2), 10.95
(1H, br s, NH); 13C NMR (126 MHz, DMSO-d6) dC 22.6
(CH3), 34.1 (CH3), 91.8, 94.4, 145.3, 147.8, 159.6, 172.1,
182.3; MS (ESI) m/z 223 (M+H)+; HRMS (M+H)+ calcd
for C9H11N4O3 223.0831, found 223.0829; HPLC
tR¼3.89 min; purity >99%. Anal. Calcd for C9H10N4O3$0.1
(AcOH): C, 48.42; H, 4.59; N, 24.55%. Found: C, 48.05; H,
4.31; N, 24.45%.
4.1.5. 3-Amino-2-methyl-4,6-dioxo-2,4,5,6-tetrahydro-
1H-pyrazolo[4,3-c]pyridine-7-carbaldehyde (4).
4.1.5.1. Method A. A solution of 2-(5-amino-4-carb-
amoyl-1-methyl-1H-pyrazol-3-yl)acetic acid (3a) (2.00 g,
10.1 mmol) in AcOCHO (29.88 mL), prepared in situ,14
and (MeO)3CH (19.86 mL) was heated at reflux for 3 h.