Synthesis of 7-aminopyrazolo[3,4-c]pyridine as a probe for the preparation of compounds of pharmacological interest

Article abstract of DOI:10.3987/com-02-9621

A synthetic route towards the preparation of 7-aminopyrazolo[3,4-c]pyridine is developed, starting from the readily accessible 2-amino-4-methyl-3-nitropyridine. The unexpected formation of 7-methylimidazolo[4,5-b]pyridin-2-one during the reaction sequence is also described.

Full text of DOI:10.3987/com-02-9621

HEREROCYCLES, Vol. 57, No. 12, 2002, pp. 2335 - 2343, Received, 6th September, 2002
SYNTHESIS OF 7-AMINOPYRAZOLO[3,4-c]PYRIDINE AS A PROBE
FOR THE PREPARATION OF COMPOUNDS OF PHARMACOLOGICAL
INTEREST
Vassilios Ν. Κourafalos,a Panagiotis Marakos,a Nicole Pouli, a* Aris Terzis,b and
Leroy B. Townsend c*
a
University of Athens, Department of Pharmacy, Division of Pharmaceutical
b
Chemistry Panepistimiopolis-Zografou, Athens 15771, Greece
Institute of
c
Material Science, NCSR Demokritos, Aghia Paraskevi, 15310, Athens, Greece
Department of Medicinal Chemistry, College of Pharmacy and Department of
Chemistry, College of Literature, Science and The Arts, The University of
Michigan, Ann Arbor, Michigan 48109, USA
Abstract - A synthetic route towards the preparation of 7-aminopyrazolo[3,4-
c]pyridine is developed, starting from the readily accessible 2-amino-4-methyl-3-
nitropyridine. The unexpected formation of 7-methylimidazolo[4,5-b]pyridin-2-
one during the reaction sequence is also described.
In view of the interesting biological and pharmacological properties of the deazapurine nucleosides, such
as 3-deazaadenosine,1 7-deazaadenosine2 and the formycins3 (Scheme 1) and in conjunction with our
ongoing interest towards the preparation of novel nucleoside analogues,4 we have recently focused on the
synthesis of derivatives of pyrazolo[3,4-c]pyridine.5
Scheme 1
NH2
O
NH2
NH2
O
N
H
N
H
N
N
N
N
N
N
HN
N
N
N
N
O
N
O
HO
HO
HO
HO
O
HO
OH
HO
OH
HO
OH
HO
OH
3-Deazaadenosine
7-Deazaadenosine
Formycin A
Formycin B

In this context, we have also decided to develop a synthetic approach for the preparation of 7-
aminopyrazolo[3,4-c]pyridine. This heterocyclic system can be used as a substrate for the synthesis of
derivatives with potential pharmacological interest, since they could be viewed as singly modified (4-
deaza analogues) of the formycins.
There are only a few convenient methods for the preparation of pyrazolo[3,4-c]pyridines. During our
initial attempts towards the synthesis of the target heterocycle, we used 7-chloropyrazolo[3,4-c]pyridine,
as starting material. The preparation of this compound has already been published in a 39 % yield starting
from 3-acetamido-2-methoxy-4-methylpyridine in four steps.6 Using the methodology that we have
previously developed for the preparation of substituted pyrazolo[3,4-c]pyridines,5 we have prepared 7-
chloropyrazolo[3,4-c]pyridine (3) in two steps (Scheme 2) starting from the readily accessible 3-
acetamido-2-chloro-4-methylpyridine (1)7 in very good yield (79%). Unfortunately, heating of 3 with
liquid ammonia or anhydrous hydrazine in a sealed bomb failed to give the corresponding 7-amino
derivative and unchanged starting material was only recovered.
Scheme 2
Cl
Cl
Cl
H
N
NHAc
CH3
Ac
N
N
N
N
b
a
N
N
1
2
3
a: AcOK, Ac2O, isoamyl nitrite, C6H6, reflux, b: NH3/CH3OH.
Consequently, since the reactivity of the halogen atom towards nucleophilic displacement is reduced
compared to 3-deazapurines,1a we were obliged to figure out an alternative route for the preparation of the
target heterocycle. Thus, we used 2-amino-4-methyl-3-nitropyridine (4a) as starting material, which was
first converted to the Boc-protected derivative (4b) (Scheme 3). The presence of the nitro group renders
the amino group less reactive, consequently the anion of 4a with sodium hydride must be formed prior to
the addition of di-tert-butyl dicarbonate. The amount of the base is critical, since at least two equivalents
should be used in order to obtain a high yield of the desired derivative (4b). On the other hand, the use of
one equivalent of sodium hydride results in the formation of the di-Boc-protected picoline (5), while
unreacted starting material is also recovered. The formation of 5 under these conditions is probably due to
the increased acidity of the carbamate NH of 4b versus the 2-NH2 of 4a, and so the initial formation of 4b
is followed by its conversion to 5, as it is obvious from TLC monitoring of the reaction as well. Catalytic
hydrogenation of the nitro group of 4b over Pd/C catalyst provided the aminopicoline (6a), which was

converted to the corresponding acetamide (6b). Treatment of 6b with isoamyl nitrite in the presence of
potassium acetate and acetic anhydride in refluxing benzene followed by treatment of the resulting
derivative with methanolic ammonia did not provide the expected Boc-protected 7-aminopyrazolo[3,4-
1
c]pyridine, as it was obvious from the H-NMR spectrum of the product. In this spectrum, the signal of
the Boc group was not present, but we observed a singlet at 2.24 ppm ascribable to a methyl group
together with two doublets at 6.78 and 7.73 ppm (J= 5.37 Hz) corresponding to neighboring aromatic
protons and two broad singlets corresponding to acidic protons (D2O exchangeable). This compound
furnished crystals from ethanol suitable for an X-Ray analysis study, which provided the unambiguous
assignment of its structure as the imidazolopyridinone (7) (Figure 1).
Scheme 3
H
N
N
O
NHR
BocNH
N
N
d,e
(Boc)2N
N
NO2
CH3
NHR
CH3
H
N
CH3
b
NO2
CH3
7
NR2
f
NHAc
CH3
4a : R=H
4b : R=Bo c
6a :R=H
6b :R=Ac
N
a
c
5
h
i
from4a
8a : NR2=NH2
g
8b : NR =N-phthaloyl
2
c
O
O
O
O
O
N
O
N
N
NH2
H
N
NO2
NH2
N
Ac
N
N
N
N
N
e
j
N
CH3
CH3
10
9
11
12
a: 1) NaH (2.5 eq.), THF, rt, 2) Boc2O, THF, b: H2, 10% Pd/C, EtOH, 50 psi, c: Ac2O, toluene, rt, d:
AcOK, Ac2O, C6H6, reflux, e: NH3/CH3OH, f: CF3CO2H, CH2Cl2, rt, g: phthalic anhydride, toluene, 50
oC, h: AcOK, Ac2O, isoamyl nitrite, C6H6, reflux, i: AcOH, phthalic anhydride, reflux, j: AcOH, Fe,
acetone, H2O, reflux.
The crystallographic analysis reveals that there exist two hydrogen bonds [N2-H---N3 = 163 (2)0, N1-H---
O = 176 (2)0], which through centers of symmetry generate chains of H-bonded molecules. There is also
an extensive overlap between the chains and the distance between overlapped molecules is 3.4 Ǻ. This

derivative was probably obtained by the intermolecular nucleophilic attack of the acetamide nitrogen of
6b on the carbamate carbonyl followed by ring closure and elimination of tert-butanol. Cyclizations in
related systems have also been reported previously, but their formation required the presence of strong
bases or extreme reaction conditions.8 According to the abovementioned mechanism, prior nitrosation of
6b is not required. So we have repeated the ring-closure reaction in the absence of isoamyl nitrite, and we
have isolated compound (7), after treatment with methanolic ammonia. Consequently, we removed the
Boc-protective group of 6b by treatment with trifluoracetic acid, and the resulting aminopicoline (8a) was
converted to the corresponding phthaloyl derivative (8b). Treatment of 8b with isoamyl nitrite in the
presence of potassium acetate and acetic anhydride in refluxing benzene provided a mixture of the
regioisomers (9), which were not isolated, but were treated with methanolic ammonia to result in 7-
aminopyrazolo[3,4-c]pyridine (10).
Since our initial goal was to discover an efficient
procedure for the preparation of the abovementioned
heterocycle, we have finally altered the synthetic
approach and have prepared the target compound in a
reasonable overall yield starting from the commercially
available picoline (4a), which was converted to the
phthaloyl derivative (11). Due to the presence of the
deactivating 3-nitro group, this derivative was prepared
by treatment with phthalic anhydride in the presence of
acetic acid.9 The nitro group was then reduced with iron
and acetic acid in aqueous acetone,10 and the resulting 3-
aminopicoline (12) was acetylated to give the
corresponding acetamide (8b). This acetamide was ring
closed according to the already mentioned procedure5 to
provide compound (10) in a 49 % overall yield.
Figure 1. X-Ray crystal structure of 7
In conclusion, we have developed and optimized a facile procedure for the preparation of 7-
aminopyrazolo[3,4-c]pyridine. In addition, we have clarified the structure of 7-methylimidazolo[4,5-
b]pyridin-2-one, which was unexpectedly formed during the reaction sequence.
EXPERIMENTAL
All chemicals were purchased from Aldrich Chemical Co. Melting points were determined on a Büchi
1
apparatus and are uncorrected. H-NMR spectra and 2-D spectra were recorded on a Bruker Avance 400

instrument at 400 MHz, whereas 13C-NMR spectra were recorded on a Bruker AC 200 spectrometer at 50
MHz in deuterated solvents and were referenced to TMS (δ scale). The signals of 1H and 13C spectra were
1
unambiguously assigned by using 2D NMR techniques: H-1H COSY, HMBC and HMQC. Flash
chromatography was performed on Merck silica gel 60 (0.040-0.063 mm). Analytical TLC was carried out
on precoated (0.25 mm) Merck silica gel F-254 plates. Elemental analyses were performed at the
Microanalytical Sections of the National Hellenic Research Foundation on a Perkin-Elmer PE 240C
elemental analyzer (Norwalk, CT).
7-Chloropyrazolo[3,4-c]pyridine (3)
Potassium acetate (130 mg, 1.32 mmol) and acetic anhydride (0.25 mL, 2.64 mmol) were added to a
solution of 3-acetamido-2-chloro-4-methylpyridine (1) (162 mg, 0.88 mmol)7 in dry benzene (40 mL)
under Ar. The reaction mixture was heated at 80 οC, isoamyl nitrite (0.12 mL, 0.88 mmol) was added and
the resulting mixture was refluxed for 8 h. The insoluble material was then filtered off, the solvent was
vacuum-evaporated and the residue was purified by column chromatography (silica gel) with
cyclohexane/ethyl acetate (60/40, v/v) as the eluent, to give 3 (106 mg, 79 %), mp 163 oC (toluene), (lit.,6
13
161-163 oC); (1H-NMR spectral data are identical to those reported in the literature6); C-NMR (CDCl3)
δ: 114.6 (C-4), 128.8 (C-3a), 134.6 (C-7a), 135.1 (C-7), 135.3 (C-3), 138.8 (C-5).
tert-Butyl-N-(4-methyl-3-nitropyridin-2-yl) carbamate (4b)
To a solution of 2-amino-4-methyl-3-nitropyridine (4a) (5 g, 32.68 mmol) in dry THF (180 mL) sodium
hydride (3.27 g, 82 mmol, 60% suspension in paraffin oil) was added under argon at 0 οC and the resulting
mixture was stirred at rt for 90 min. It was then cooled at 0 οC, a solution of di-tert-butyl dicarbonate (7.5
mL, 32.68 mmol) in dry THF (20 mL) was added dropwise and the mixture was stirred at rt for an
additional 18 h. The solvent was vacuum-evaporated, a solution of HCl (0.5 N, 60 mL) was added to the
residue and the product was extracted with ethyl acetate. The organic extracts were dried (Na2SO4) and
o
1
concentrated to dryness to give pure 4b (8 g, 97%), mp 154-155 C (Et2O/n-pentane); H-NMR (CDCl3)
δ: 1.52 (s, 9H, (CH3)3C), 2.50 (s, 3H, CH3), 7.08 (d, 1H, H-5, J5,6=5.13 Hz), 8.43 (d, 1H, H-6, J6,5=5.13
13
Hz), 9.55 (br s, 1H, -NHBoc, D2O exchangeable); C-NMR (CDCl3) δ: 19.4 (4-CH3), 28.1 [(CH3)3C],
82.3 [(CH3)3C], 122.2 (C-5), 143.9 (C-4), 144.5 (C-3), 147.2 (C-2), 149.9 (C-6), 151.4 (C=O). Anal.
Calcd for C11H15N3O4: C, 52.17; H, 5.97; N, 16.59. Found: C, 51.93; H, 5.79; N, 16.27.
2-Bis(tert-butoxycarbonyl)amino-4-methyl-3-nitropyridine (5)
This compound was prepared by an analogous procedure to 4b with the use of one equivalent of sodium
o
1
hydride and one equivalent of di-tert-butyl dicarbonate. Yield: 43 %, mp 93 C (Et2O/n-pentane); H-

NMR (CDCl3) δ: 1.44 (s, 18H, 2 x (CH3)3C), 2.46 (s, 3H, CH3), 7.29 (d, 1H, H-5, J5,6=5.12 Hz), 8.50 (d,
1H, H-6, J6,5=5.12 Hz); 13C-NMR (CDCl3) δ: 17.8 (4-CH3), 27.7 [2 x (CH3)3C], 84.1 [2 x (CH3)3C],
126.5 (C-5), 142.2 (C-4), 144.0 (C-3), 149.6 (C-2), 149.8 (C-6), 150.2 (2 x C=O). Anal. Calcd for
C16H23N3O6: C, 54.38; H, 6.56; N, 11.89. Found: C, 54.47; H, 6.45; N, 11.67.
tert-Butyl-N-(3-amino-4-methylpyridin-2-yl) carbamate (6a)
A solution of 4b (8 g, 31.6 mmol) in dry ethanol (150 mL) was hydrogenated in the presence of 10% Pd/C
(500 mg) under a pressure of 45 psi at rt for 3 h. The solution was filtered through a celite pad to remove
the catalyst and the filtrate was evaporated to dryness to give pure 6a (7 g, 99%), mp >250 oC (EtOH); 1H-
NMR (CDCl3) δ: 1.49 [s, 9H, (CH3)3C], 2.20 (s, 3H, CH3), 4.24 (br s, 2H, -NH2, D2O exchangeable), 6.88
(d, 1H, H-5, J5,6=4.76 Hz), 7.74 (d, 1H, H-6, J6,5=4.76 Hz), 8.37 (br s, 1H, -NHBoc, D2O exchangeable);
13C-NMR (CDCl3) δ: 17.4 (4-CH3), 28.4 [(CH3)3C], 81.0 [(CH3)3C], 123.2 (C-5), 133.6 (C-3), 135.0 (C-
4), 137.2 (C-6) 138.6 (C-2), 154.3 (C=O). Anal. Calcd for C11H17N3O2: C, 59.17; H, 7.67; N, 18.82.
Found: C, 59.03; H, 7.71; N, 18.63.
tert-Butyl-N-(3-acetamido-4-methylpyridin-2-yl) carbamate (6b)
To a solution of 6a (7 g, 31.4 mmol) in dry toluene (120 mL) acetic anhydride (6 mL, 65 mmol) was
added and the resulting solution was stirred at rt for 1 h. The solvent was vacuum-evaporated and the
residue was purified by column chromatography (silica gel) with cyclohexane/ethyl acetate (60/40, v/v) as
the eluent to give pure 6b (8.15 g, 98 %), mp 148 oC (Et2O/n-pentane); 1H-NMR (CDCl3) δ: 1.53 (s, 9H,
(CH3)3C), 2.13 (s, 3H, CH3), 2.29 (s, 3H, COCH3), 7.04 (d, 1H, H-5, J5,6=4.73 Hz), 7.65 (br s, 1H, -
NHBoc, D2O exchangeable), 8.15 (d, 1H, H-6, J6,5=4.73 Hz), 8.72 (br s, 1H, -NHAc, D2O exchangeable);
13C-NMR (CDCl3) δ: 18.7 (4-CH3), 23.5 (CH3-CO), 28.3 [(CH3)3C], 81.9 [(CH3)3C], 123.1 (C-5), 124.9
(C-3), 145.5 (C-6), 146.6 (C-4), 148.5 (C-2), 154.8 (t-BuOCO), 168.3 (NHCOCH3). Anal. Calcd for
C13H19N3O3: C, 58.85; H, 7.22; N, 15.84. Found: C, 59.06; H, 7.17; N, 15.59.
7-Methylimidazolo[4,5-b]pyridin-2-one (7)
Potassium acetate (56 mg, 0.57 mmol) and acetic anhydride (0.11mL, 1.14 mmol) were added under
argon to a solution of 6b (100 mg, 0.38 mmol) in dry benzene (30 mL) and the reaction mixture was
refluxed for 6 h. The precipitate was filtered off, the filtrate was concentrated to dryness and the residue
was treated with methanolic ammonia at 0οC for 15 min. The solvent was then vacuum-evaporated and
the solid residue was purified by flash chromatography on silica gel (dichloromethane/methanol: 90/10,
v/v, as eluent) to afford 7 (47 mg, 83%), mp >250 oC (EtOH/H2O); 1H-NMR (DMSO-d6) δ: 2.24 (s, 3H,
CH3), 6.78 (d, 1H, H-6, J6,5=5.37 Hz), 7.73 (d, 1H, H-5, J5,6=5.37 Hz), 10.92 (br s, 1H, NH, D2O

exchangeable), 11.20 (br s, 1H, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ: 15.7 (CH3), 118.5 (C-
6), 122.9 (C-7a), 125.6 (C-7), 139.8 (C-5), 144.4 (C-3a), 154.7 (C-2). Anal. Calcd for C7H7N3O: C, 56.37;
H, 4.73; N, 28.17. Found: C, 56.02; H, 4.69; N, 28.27.
X-Ray crystal data of 7
Compound (7) crystallizes from ethanol. C7H7N3O, M= 149.157. α=7.110(3), b= 7.516 (3), c= 13.112 (6),
3
β= 98.10 (1)o, V= 693.8 (4) Ǻ , space group P21/ n, Z=4, T= 298 K. Reflections measured/independent
1385/1222. Dc= 1.428 mg.m-3, µ(M0Kα)= 1.02 cm-1, F(000)= 312, crystal size= 005 x 0.25 x 0.5 mm.
Crystal Logic diffractometer. R1 0.044, wR2 0.114, 142 parameters.
N-(2-Amino-4-methylpyridin-3-yl)acetamide (8a)
Trifluoroacetic acid (0.07 mL, 0.9 mmol) was added at 0οC to a solution of 6b (200 mg, 0.75 mmol) in
dry dichloromethane and the mixture was stirred at rt for 12 h. The solvent was vacuum-evaporated and
the residue was treated with a saturated NaHCO3 solution and ethyl acetate. The organic layer was dried
(Na2SO4) and concentrated to dryness. The residue was purified by flash chromatography (silica gel) with
1
dichloromethane/methanol (90/10, v/v) as the eluent to give 8a (0.12 mg, 97%) as an oil. H-NMR
(CDCl3) δ: 2.19 (s, 3H, CH3), 2.24 (s, 3H, COCH3), 4.32 (br s, 2H, -NH2, D2O exchangeable), 6.58 (d, 1H,
H-5, J5,6=5.10 Hz), 6.82 (br s, 1H, -NHAc, D2O exchangeable), 7.88 (d, 1H, H-6, J6,5=5.10 Hz); 13C-NMR
(CDCl3) δ: 18.0 (CH3), 23.5 (CH3CO), 117.2 (C-5), 119.6 (C-3), 145.3 (C-4), 146.6 (C-6), 155.5 (C-2),
169.4 (C=O). Anal. Calcd for C8H11N3O: C, 58.17; H, 6.71; N, 25.44. Found: C, 58.30; H, 6.62; N, 25.19.
N-(4-Methyl-2-phthalimidopyridin-3-yl)acetamide (8b)
A mixture of the aminopyridine (8a) (220 mg, 1.33 mmol) and phthalic anhydride (197 mg, 1.33 mmol)
in dry toluene (60 mL) was heated at 50 oC under argon for 12 h. The precipitate was filtered off, the
filtrate was vacuum-evaporated and the solid residue was recrystallized to give pure 8b as a white solid
o
1
(350 mg, 89%), mp >250 C (EtOH); H-NMR (DMSO-d6) δ: 1.84 (s, 3H, CH3), 2.27 (s, 3H, COCH3),
7.48 (d, 1H, H-5, J5,6=4.76 Hz), 7.91 (m, 2H, H-4’, H-5’), 7.98 (m, 2H, H-3’, H-6’), 8.38 (d, 1H, H-6,
13
J6,5=4.76 Hz), 9.67 (br s, 1H, -NHAc, D2O exchangeable); C-NMR (DMSO-d6) δ: 18.1 (4-CH3), 22.5
(CH3CO), 123.6 (C-3’, C-6’), 126.5 (C-5), 130.2 (C-2a’, C-6a’), 131.5 (C-3), 134.9 (C-4’, C-5’), 142.7
(C-2), 146.0 (C-6), 147.1 (C-4), 166.0 [C=O(Phth)], 167.8 (COCH3). Anal. Calcd for C16H13N3O3: C,
65.08; H, 4.44; N, 14.23. Found: C, 64.82; H, 4.51; N, 13.96.

7-Aminopyrazolo[3,4-c]pyridine (10)
This compound was prepared by an analogous procedure to 3 and the product was purified by flash
chromatography (silica gel) with dichloromethane/methanol (90/10, v/v) as the eluent to afford 10 (82%),
1
mp 165-167 oC (MeOH); H-NMR (DMSO-d6) δ: 6.38 (br s, 2H, NH2, D2O exchangeable), 6.85 (d, 1H,
H-4, J4.5=5.85 Hz), 7.48 (d, 1H, H-5, J5.4=5.85 Hz), 7.97 (s, 1H, H-3), 13.2 (br s, 1H, NH, D2O
13
exchangeable); C-NMR (DMSO-d6) δ: 103.7 (C-4), 125.9 (C-3a), 127.5 (C-7a), 132.5 (C-3), 137.1 (C-
5), 146,4 (C-7). Anal. Calcd for C6H6N4: C, 53.73; H, 4.50; N, 41.77. Found: C, 53.91; H, 4.57; N, 41.52.
N-(4-Methyl-3-nitropyridin-2-yl)phthalimide (11)
A mixture of 4a (1.3 g, 8.5 mmol) and phthalic anhydride (1.25 g, 8.5 mmol) in acetic acid (4 mL) was
heated at reflux for 24 h. Dichloromethane (50 mL) was then added and the solution was washed with
water and a saturated Na2CO3 solution. The organic phase was dried (Na2SO4) and concentrated to
dryness to provide 11 as a white solid (1.88 g, 78 %), mp 228 oC (MeOH); 1H-NMR (CDCl3) δ: 2.56 (s,
3H, CH3), 7.46 (d, 1H, H-5, J5,6=4.88 Hz), 7.83 (m, 2H, H-4’, H-5’), 7.98 (m, 2H, H-3’, H-6’), 8.68 (d,
1H, H-6, J6,5=4.88 Hz); 13C-NMR (CDCl3) δ: 18.6 (4-CH3), 124.4 (C-3’, C-6’), 127.4 (C-5), 131.7 (C-2a’,
C-6a’), 134.9 (C-4’, C-5’), 139.2 (C-2), 142.3 (C-4), 143.7 (C-3), 150.7 (C-6), 165.7 (C=O). Anal. Calcd
for C14H9N3O4: C, 59.37; H, 3.20; N, 14.84. Found: C, 59.08; H, 3.12; N, 15.12.
N-(3-Amino-4-methylpyridin-2-yl)phthalimide (12)
The protected pyridine (11) (300 mg, 1.06 mmol) was dissolved in hot acetone (30 mL) and acetic acid (3
mL) and water (3 mL) were added. The resulting solution was refluxed and finely powdered iron (712 mg,
12.7 mmol) was added in portions. The reaction was stirred and refluxed for an additional 90 min. The
solids were then filtered through a celite pad and washed with acetone, and acetone was vacuum-
evaporated. A saturated solution of sodium bicarbonate was added to the residue, and the precipitate was
o
filtered, washed with water and air-dried to give pure 12 as a white solid (268 mg, 78%), mp 214 C
1
(EtOH); H-NMR (CDCl3) δ: 2.28 (s, 3H, CH3), 3.79 (br s, 2H, -NH2, D2O exchangeable), 7.08 (d, 1H,
13
H-5, J5,6=4.39 Hz), 7.78 (m, 2H, H-4’, H-5’), 7.98 (m, 3H, H-6, H-3’, H-6’); C-NMR (CDCl3) δ: 17.3
(4-CH3), 124.0 (C-3’, C-6’), 126.6 (C-5), 132.0 (C-3), 132.2 (C-2a’, C-6a’), 134.0 (C-4), 134.6 (C-4’, C-
5’), 138.5 (C-2), 139.1 (C-6), 167.2 (C=O). Anal. Calcd for C14H11N3O2: C, 66.40; H, 4.38; N, 16.59.
Found: C, 66.61; H, 4.53; N, 16.32.
ACKNOWLEDGEMENTS
The present study was supported by a grant from the National Scholarship Foundation of Greece.

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