Microwave-assisted synthesis of some novel fluorinated pyrazolo[3,4-d] pyrimidine derivatives containing 1,3,4-thiadiazole as potential antitumor agents

Article abstract of DOI:10.1016/j.cclet.2011.05.012

A facile microwave-assisted procedure for synthesis of novel fluorinated pyrazolo[3,4-d]pyrimidine derivatives containing 1,3,4-thiadiazole is described. This protocol presented such advantages as short reaction time, high yields, simple purification and

Full text of DOI:10.1016/j.cclet.2011.05.012

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 1036–1038
www.elsevier.com/locate/cclet
Microwave-assisted synthesis of some novel fluorinated
pyrazolo[3,4-d]pyrimidine derivatives containing
1,3,4-thiadiazole as potential antitumor agents
a
b
Xin Jian Song a, , Yu Shao , Xing Gao Dong
*
a Key Laboratory of Biological Resources Protection and Utilization of Hubei Province,
Hubei University for Nationalities, Enshi 445000, China
b Medical School, Hubei University for Nationalities, Enshi 445000, China
Received 30 December 2010
Available online 25 June 2011
Abstract
A facile microwave-assisted procedure for synthesis of novel fluorinated pyrazolo[3,4-d]pyrimidine derivatives containing
1,3,4-thiadiazole is described. This protocol presented such advantages as short reaction time, high yields, simple purification and
environmentally benign procedures. Their antitumor activities were evaluated against HL-60 by an MTT assay. The preliminary
results indicated that some title compounds exhibit more potent antitumor inhibitory activity than doxorubicin (DOX).
# 2011 Xin Jian Song. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Pyrazolo[3,4-d]pyrimidine; 1,3,4-Thiadiazole; Microwave-assisted synthesis; Antitumor activity
Pyrazolo[3,4-d]pyrimidines have drawn considerable attention on the account of their structural similarity with
purines and pharmacological importance. They are known to exhibit significant pharmacological activities, such as
antimicrobial [1,2], antitumor [3–5], antiviral [6,7], and anti-inflammatory activities [8]. 1,3,4-Thiadiazole derivatives
have attracted continuing interest over the last few decades due to their broad-spectrum biological activities [9–14],
especially anticancer properties [15,16]. Moreover, in recent years, fluorinated compounds are one of the research
hotspots in modern medicinal and agrochemistry chemistry [17]. In general, incorporation of a fluoro or
trifluoromethyl group provides compounds with increased biological activity because of enhanced pharmacokinetic
and physicochemical properties as compared to their non-fluorinated analogues [18,19].
It is well known that microwave (MW) irradiation technique possesses such advantages as short reaction time,
environmentally benignity, easy work-up and high yield compared with the traditional heating methods [20]. MW
irradiation is widely used in the field of medicinal chemistry and total syntheses of natural products.
Keeping these in mind, it was aimed in this paper to synthesize a series of novel fluorinated compounds containing
both pyrazolo[3,4-d]pyrimidine and 1,3,4-thiadiazole nuclei under MW irradiation for evaluating their antitumor
activity.
* Corresponding author.
E-mail address: whxjsong@yahoo.com.cn (X.J. Song).
1001-8417/$ – see front matter # 2011 Xin Jian Song. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.05.012

[(Scheme_1)TD$FIG]
X.J. Song et al. / Chinese Chemical Letters 22 (2011) 1036–1038
1037
N
N
NH
CN
CN
N
N
RF
3 a-e
AcOH, MW
NH2
S
RF
N
DMFDMA
S
N
N
N
NH2
N
N
CH3CN, reflux, 2-3 h
N
N
N
R
N
R
R
2a-b
4 a-j
1a-b
R = H (1a, 2a, 4 a-e); C 6H5 (1b, 2b, 4 f-j)
Scheme 1. Synthetic route of the title compounds 4a–j.
The title compounds 4a–j were prepared using the synthetic strategy described in Scheme 1. The synthesis began by
reacting commercially available 2-(ethoxymethylene)malononitrile with phenylhydrazine or hydrazine hydrate to
deliver 1-phenyl or 1H-5-amino-4-cyanopyrazoles 1a and b according to the literature methods [21,22]. The
aminopyrazoles 1 were then refluxed with N,N-dimethylformamide dimethlyacetal (DMFDMA) in acetonitrile to
afford the corresponding amidines 2a and b which underwent a cyclo-condensation with the appropriate 2-amino-5-
subsitituted-1,3,4-thiadiazoles 3a–e [23] or their hydrochloride in acetic acid under MW irradiation to give the desired
products 4a–j with mp >300 8C, in good to excellent isolated yields (81–93%), as shown in Table 1. It only took 18–
22 min to finish the reaction under microwave irradiation compared to the reaction time of about 6 h under the
conventional heating.
The structures of the newly synthesized compounds 4a–j [24] were confirmed by IR, 1H NMR, mass spectroscopy
and elemental analysis. The IR spectra contained the vibration absorption bands revealing the existence of the N–H
and C N groups, while no cyano group peak was observed. The NMR spectra of 4 showed all the expected signals for
two CH protons (d 8.88–8.53), phenyl protons and NH singlets (d 14.12–13.06). The EI mass spectra gave the
anticipated molecular ion peaks and main fragmentation peaks, which were in accordance with the title structures.
The in vitro antitumor activities of the synthesized pyrazolo[3,4-d]pyrimidine derivatives containing 1,3,4-
thiadiazole against HL-60 (human leukaemia cancer cell) were evaluated by the standard MTT assay [25]. As
described in Table 1, compounds 4a, 4f, 4g, 4i and 4j exhibit good anticancer activity against HL-60, especially 4f and
4j exhibit even higher activity than doxorubicin (DOX). As can be seen from the results, these compounds (4f–j) show
better anticancer activity when H atom in position 1 of the pyrazole ring is substituted with a phenyl group. Further,
incorporation of CF3 group in the molecules enhanced biological activity significantly.
In summary, we described the facile microwave-assisted synthesis of novel fluorinated pyrazolo[3,4-d]pyrimidine
derivatives containing 1,3,4-thiadiazole. This protocol presented many advantages, such as good to excellent yields,
shorter reaction time (18–22 min), readily available starting material, simple purification and environmentally benign
Table 1
Data of synthesis, characterization, in vitro antitumor activity against HL-60 for the title compounds 4a–j.
Compd.
RF
Formula
Mode of activation
Time
Temp.
Yield
(%)
EI-MS
(m/z, M+)
IC50
(8C)
(mmol/L)
4a
4b
4c
4d
4e
4f
CF3
C8H4F3N7S
C13H8FN7S
C13H8FN7S
C13H8FN7S
C14H8F3N7S
C14H8F3N7S
C19H12FN7S
C19H12FN7S
C19H12FN7S
C20H12F3N7S
MW
18 min
18 min
18 min
18 min
18 min
22 min
22 min
22 min
22 min
22 min
6 h
140
140
140
140
140
150
150
150
150
150
118
88
87
89
93
91
83
81
82
87
86
85
287
313
313
313
363
363
389
389
389
439
1.05
3.16
10.16
4.47
2.56
0.08
0.90
2.75
1.01
0.21
2-FC6H4
3-FC6H4
4-FC6H4
4-CF3C6H4
CF3
MW
MW
MW
MW
MW
4g
4h
4i
2-FC6H4
3-FC6H4
4-FC6H4
4-CF3C6H4
CF3
MW
MW
MW
4j
4a
MW
Traditional heating
DOX
0.55

1038
X.J. Song et al. / Chinese Chemical Letters 22 (2011) 1036–1038
procedures. The results of antitumor inhibitory activity test indicated that this class of pyrazolo[3,4-d]-pyrimidine
derivatives can be developed as novel antitumor candidate drugs. Further pharmacological evaluation, optimization
and structure–activity relationships of the title compounds are underway.
Acknowledgments
We are thankful for the National Nature Science Foundation of Hubei Province (No. 2008CDB016) and the
Scientific Research Fund of Hubei Provincial Education Department (No. D20111904).
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[24] General procedure for the synthesis of 5-(5-substituted-1,3,4-thiadiazol-2-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-imine (4a–e): the solution
of 1H-4-cyano-5-[(N,N-dimethylaminomethylene)amino]pyrazole 2a (0.33 g, 2 mmol) and the appropriate aminothiadiazoles 3 (2 mmol) in
6 mL glacial acetic acid was irradiated at 140 8C for 18 min by microwave. The reaction mixture was then cooled to room temperature, and
stirred with ice-water. The resulting suspension was filtered, washed with ethanol/water (2:1), and dried in vacuum to give the desired products
4a–e as pale yellow or white solids. While, the corresponding aminothiadiazole hydrochloride needed to be used for the preparation of
compounds 4f–j by employing this method. The spectral data of selected compounds: 4a: 1H NMR (400 MHz, DMSO-d6): d 14.12 (s, 1H, NH),
13.63 (s, 1H, NH), 8.71 (s, 1H, N CH), 8.53 (s, 1H, N CH); IR (KBr) (nmax, cmÀ1): 3436 (N–H), 1629, 1585 (C N), 1327, 1162 (CF3); Anal.
Calcd. for C8H4F3N7S: C 33.45, H 1.40, N 34.14; found: C 33.62, H 1.18, N 34.37. 4e: 1H NMR (400 MHz, DMSO-d6): d 14.02 (s, 1H, NH),
13.18 (s, 1H, NH), 8.69 (s, 1H, N CH), 8.55 (s, 1H, N CH), 8.23–7.90 (m, 4H, Ar–H); IR (KBr, n cmÀ1): 3435 (N–H), 1625, 1595 (C N),
1328, 1163 (CF3); Anal. Calcd. for C14H8F3N7S: C 46.28, H 2.22, N 26.99; found: C 46.49, H 2.45, N 27.24. 4f: 1H NMR (400 MHz, DMSO-
d6): d 13.86 (s, 1H, NH), 8.88 (s, 1H, N CH), 8.80 (s, 1H, N CH), 8.20À7.41 (m, 5H, Ar–H); IR (KBr) (nmax, cmÀ1): 3438 (N–H), 1617, 1590
(C N), 1323, 1148 (CF3); Anal. Calcd. for C14H8F3N7S: C 46.28, H 2.22, N 26.99; found: C 46.03, H 2.06, N 26.75. 4j: 1H NMR (400 MHz,
DMSO-d6): d 13.42 (s, 1H, NH), 8.84 (s, 2H, N CH), 8.80 (s, 1H, N CH), 8.24À7.40 (m, 9H, Ar-H); IR (KBr) (nmax, cmÀ1): 3432 (N–H),
1622, 1596 (C N), 1327, 1163 (CF3); Anal. Calcd. for C20H12F3N7S: C 54.67, H 2.75, N 22.31; found: C 54.85, H 2.94, N 22.52.
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