Synthesis and anticancer activity of some New Pyrazolo[3,4-d]pyrimidin-4- one derivatives

Article abstract of DOI:10.3390/molecules19033297

3,6-Dimethyl-1-phenyl-1H-pyrazolo[3,4-d][1,3]oxazin-4-one (3) was prepared by hydrolysis of ethyl 5-amino-3-methyl-1-phenyl-1H-pyrazole-4-carboxylate (1) to afford the corresponding carboxylic acid 2, which was reacted with acetic anhydride to give 3. The pyrazolo[3,4-d][1,3]oxazin-4-one 3 was reacted with hydroxylamine hydrochloride, urea, thiourea, thiosemicarbazide, phenylhydrazine and aromatic amines to afford the corresponding pyrazolo[3,4-d]pyrimidin-4-ones 4, 5a,b, 6, 7, 8a-e, respectively. Condensation of pyrazoloxazine derivative 3 with 99% hydrazine hydrate afforded the 5-aminopyrazolo[3,4-d] pyrimidine derivative 9. Coupling of 9 with aromatic aldehydes yielded a series of 3,6-dimethyl-5-(4-substitutedbenzylideneamino)-1-phenyl-1,5-dihydropyrazolo[3, 4-d]pyrimidin- 4-ones 10a-e. The new compounds were tested for their antitumor activity on the MCF-7 human breast adenocarcinoma cell line. Almost all the tested compounds revealed antitumor activity, especially 3,6-dimethyl-5-(4- nitrobenzylideneamino)-1-phenyl-1,5- dihydropyrazolo[3,4-d]pyrimidin-4-one (10e) which displayed the most potent inhibitory activity with a half maximal inhibitory concentration (IC50) of 11 μM.

Full text of DOI:10.3390/molecules19033297

Molecules 2014, 19, 3297-3309; doi:10.3390/molecules19033297
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis and Anticancer Activity of Some New
Pyrazolo[3,4-d]pyrimidin-4-one Derivatives
Khaled R. A. Abdellatif 1, Eman K. A. Abdelall 1, Mohamed A. Abdelgawad 1, Rasha R. Ahmed 2
and Rania B. Bakr 1,*
1
Pharmaceutical Organic Chemistry Department, Faculty of Pharmacy, Beni-Suef University,
Beni-Suef 62514, Egypt; E-Mails: khaled.ahmed@bsu.edu.eg (K.R.A.A.);
Emansherif94@yahoo.com (E.K.A.A.); mhmdgwd@yahoo.com (M.A.A.)
2
Cell Biology and Histology Division, Zoology Department, Faculty of Science,
Beni-Suef University, Beni-Suef 62514, Egypt; E-Mail: shorouk2002os@yahoo.com
* Author to whom correspondence should be addressed; E-Mail: raniabakr@ymail.com or
rania.mohamed@pharm.bsu.edu.eg; Fax: +2-082-231-7958.
Received: 31 December 2013; in revised form: 27 February 2014 / Accepted: 5 March 2014 /
Published: 18 March 2014
Abstract: 3,6-Dimethyl-1-phenyl-1H-pyrazolo[3,4-d][1,3]oxazin-4-one (3) was prepared
by hydrolysis of ethyl 5-amino-3-methyl-1-phenyl-1H-pyrazole-4-carboxylate (1) to afford
the corresponding carboxylic acid 2, which was reacted with acetic anhydride to give 3.
The pyrazolo[3,4-d][1,3]oxazin-4-one 3 was reacted with hydroxylamine hydrochloride, urea,
thiourea, thiosemicarbazide, phenylhydrazine and aromatic amines to afford the corresponding
pyrazolo[3,4-d]pyrimidin-4-ones 4, 5a,b, 6, 7, 8a–e, respectively. Condensation of
pyrazoloxazine derivative 3 with 99% hydrazine hydrate afforded the 5-aminopyrazolo[3,4-d]
pyrimidine derivative 9. Coupling of 9 with aromatic aldehydes yielded a series of
3,6-dimethyl-5-(4-substitutedbenzylideneamino)-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-
4-ones 10a–e. The new compounds were tested for their antitumor activity on the MCF-7
human breast adenocarcinoma cell line. Almost all the tested compounds revealed
antitumor activity, especially 3,6-dimethyl-5-(4-nitrobenzylideneamino)-1-phenyl-1,5-
dihydropyrazolo[3,4-d]pyrimidin-4-one (10e) which displayed the most potent inhibitory
activity with a half maximal inhibitory concentration (IC50) of 11 µM.
Keywords: pyrazolo[3,4-d]pyrimidin-4-one; anticancer activity; MCF7

Molecules 2014, 19
3298
1. Introduction
Cancer remains one of the most life-threatening diseases, taking nearly 7 million lives each year
worldwide. It is realized that neither surgery nor radiation nor the two in combination can adequately
control metastatic cancer [1], therefore, efforts to cure cancer have been focusing on conventional
chemotherapy. However, this type of treatment usually does not discriminate between dividing normal
cells and tumor cells, leading to severe side effects [2]. In the last decade, the use of molecular targeted
therapies (a new generation of selective cancer drugs which interfere with specific receptors and
signaling pathways that promote tumor cell growth) has made treatments more tumor-specific [3].
The chemistry of pyrazolo[3,4-d]pyrimidine derivatives has received great attention due to their
structural similarity with purines and hence several pyrazolo[3,4-d]pyrimidine derivatives exhibit
promising anticancer activity [4–9]. Different mechanisms account for the cytotoxic effect of this class
of compounds, where they had been reported to act as glycogen synthase kinase (GSK) inhibitors [10],
cyclin dependent kinase (CDK) inhibitors [11], dual src/Ab1 kinase inhibitors [12] and epidermal
growth factor receptor (EGFR) inhibitors [13]. Moreover, many 5-substituted-1-phenyl-1H-
pyrazolo[3,4-d]pyrimidin-4-ones were reported to possess antiproliferative activity against breast
carcinoma, MCF7 [14,15].
Examples of anticancer drugs currently used in anticancer therapy can be represented by erlotinib
(TarcevaTM) [16] and gefitinib (IressaTM) [17] which have been approved for the chemotherapeutic
treatment of patients with advanced non-small lung cancer. Also, lapatinib (TykerbTM) [18] was
approved for the treatment of breast cancer.
In the view of the previous rationale and in continuation of an ongoing program on the synthesis
of antitumor compounds [19], in the present study a new series of pyrazolo[3,4-d]pyrimidin-4-ones
has been synthesized and screened in vitro for antitumor activity. The series comprises the derived
5,6-disubstituted pyrazolo[3,4-d]pyrimidin-4-one pharmacophore that is structurally related to
erlotinib and lapatinib (Figure 1). In the present study, the substitution pattern at the 5,6-disubstituted
pyrazolo[3,4-d]pyrimidin-4-one pharmacophore was manipulated so as to create different electronic
environments that might affect the lipophilicity and hence the activity of target molecules.
The rationale for the design of target compounds was based upon some structural modifications on
the general features of anilinoquinazoline-containing compounds (Figure 1). These modifications
comprise a replacement of the benzene moiety in the quinazoline skeleton by a pyrazolo moiety as the
pyrazolo moiety is naturally found in the body’s purine bases and this is expected to enhance
cytotoxic activity. Prompted by these claims, we present a new series of compounds containing
5,6-disubstituted pyrazolo[3,4-d]pyrimidin-4-ones core as anticancer agents. Our strategy is directed
toward designing a variety of compounds with diverse chemical properties hypothesizing that the
potency of these compounds might be increased by adding alternative binding groups such as a methyl
group at position 6, and aroylhydrazone, phenylamino, amide, thioamide, thiosemicarbazide and
substituted aryl at position 5 of the pyrazolo[3,4-d]pyrimidine ring.

Molecules 2014, 19
3299
Figure 1. Planned design of new pyrazolo[3,4-d]pyrimidine derivatives for cytotoxic activity.
O
Large Fragment
F
Large Fragment
Cl
NH
NH
O
O
O
N
N
O
O
N
O
N
S
O
lipophilic group insertion
lipophilic group insertion
Lapatinib
Erlotinib
(Tarceva)
Large Fragment
F
F
F
Large Fragment
Cl
NH
O
NH
O
N
O
O
N
N
N
O
N
N
lipophilic group insertion
lipophilic group insertion
Gefitinib
(Iressa)
Vandetanib
Fragment replacemnt
O
R
X
N
Isosteric replacement
N
N
H3
C
N
lipophilic group insertion
2. Results and Discussion
2.1. Chemical Synthesis
The synthesis of the target compounds is outlined in Schemes 1 and 2. Accordingly, basic
hydrolysis of ethyl 5-amino-3-methyl-1-phenyl-1H-pyrazole-4-carboxylate (1) [20] gave 5-amino-3-
methyl-1-phenyl-1H-pyrazole-4-carboxylic acid (2) (Scheme 1). The formation of compound 2 was
1
confirmed by H-NMR that showed two D2O exchangeable singlet signals at δ 6.30, 12.08 ppm

Molecules 2014, 19
3300
corresponding to NH2 and COOH, respectively. Heating compound 2 with acetic anhydride gave a
cyclized product, 3,6-dimethyl-1-phenyl-1H-pyrazolo[3,4-d][1,3]oxazin-4-one (3). The 1H-NMR
spectrum of compound 3 revealed the appearance of a singlet signal at δ 2.49 ppm corresponding to
the pyrimidine CH3 protons. The mass spectrum of compound 3 showed a molecular ion peak at m/z
241 which appeared as the base peak. Reaction of compound 3 with hydroxylamine hydrochloride in
dry pyridine afforded 5-hydroxy-3,6-dimethyl-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one
(4). The presence of a singlet OH band at 3,426 cm−1 and C=O at 1,680 cm−1 confirmed the formation
1
of 4. Its H-NMR spectrum showed the appearance of a D2O exchangeable singlet signal at δ 11.52
ppm corresponding to the OH proton. The target compounds 5a,b and 6 were synthesized by fusion at
200 °C of pyrazoloxazine derivative 3 with urea, thiourea and thiosemicarbazide, respectively. The
1
formation of compounds 5a,b and 6 was confirmed by their H-NMR spectra that indicated the
appearance of exchangeable singlet signals at δ 11.15–12.45 ppm corresponding to NH and NH2.
In addition, the mass spectra agreed with the calculated molecular weights of the expected products.
On the other hand, reaction of pyrazoloxazine derivative 3 with phenylhydrazine afforded
1
3,6-dimethyl-1-phenyl-5-phenylamino-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one (7). The H-NMR of
this compound revealed in addition to the corresponding integration for aromatic protons, the presence
of NH at δ 9.09 ppm. The mass spectrum also showed a molecular ion peak at m/z 331 as the base peak.
Scheme 1. Synthetic pathway for target compounds 4, 5a,b, 6, 7.
O
O
O
OH
NH2
N
N
i
N
N
NH2
1
2
ii
O
N
H
O
N
N
O
N
vi
OH
N
N
iii
O
N
N
N
N
N
N
7
4
3
iv
v
S
O
N
X
O
N
N
NHNH2
N
NH2
N
N
N
N
5a X= O
5b X=S
5a,5b
6
Reagents and conditions: (i) NaOH, CH3OH, reflux 5 h; (ii) (CH3CO)2O, reflux 5 h; (iii) NH2OH·HCl, dry
pyridine, reflux 8h; (iv) NH2CXNH2, fusion at 200 °C 1 h; (v) NH2CSNHNH2, fusion at 200 °C 1 h;
(vi) RC6H4NH2, dry pyridine, reflux 6 h.

Molecules 2014, 19
Scheme 2. Synthetic pathway for target compounds 8a–e and 10a–e.
3301
O
N
O
NH2
R
N
O
N
O
N
N
ii
i
N
N
N
N
N
N
9
3
iii
8a-8e
8a R= CH3
R 1
8b R=OH
8c R=COCH3
8d R=COOH
8e R=COOC2H5
O
N
N
N
N
N
10a R1= H
10b R1=F
10c R1=OCH3
10a-10e
10d R1=Cl
10e R1=NO2
Reagents and conditions: (i) RC6H4NH2, dry pyridine, reflux 6 h; (ii) NH2NH2·H2O, n-butanol, reflux 6 h;
(iii) RC6H4CHO, acetic acid, reflux 20 h.
Moreover, reaction of compound 3 with appropriate aromatic amines furnished 3,6-dimethyl-1-
phenyl-5-(4-substitutedphenyl)-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-ones 8a–e (Scheme 2). The
structure of these compounds was established on the basis of their elemental analyses and spectral data.
The 1H-NMR spectra revealed signals at δ 6.89-8.15 ppm for aromatic protons. Also, the mass spectra
were in agreement with the calculated molecular weights of the synthesized compounds. Condensation
of pyrazoloxazine derivative 3 with hydrazine hydrate afforded the 5-amino-pyrazolo[3,4-d]pyrimidin-
4-one derivative 9. Finally, coupling of 9 with appropriate aromatic aldehydes yielded the corresponding
5-(substituted benzylideneamino)-pyrazolo[3,4-d]pyrimidine derivatives 10a‒e. The structures of 10a–e
1
were established on the basis of their elemental analysis and spectral data. The H-NMR spectra of
10a–e showed singlet downfield CH=N signals at δ 8.32–10.94 ppm. It is worth mentioning that the
1
lack of NH2 bands in the IR spectra and D2O exchangeable NH2 signals in the H-NMR spectra
confirmed the production of the pyrazolo[3,4-d]pyrimidine derivatives 10a–e.
2.2. In Vitro Anticancer Screening
The newly synthesized compounds were evaluated for their in vitro cytotoxic activity against
human breast cell line (MCF7) using doxorubicin as the reference drug according to the method
described as reported by Vichai and Kirtikara [21]. The cytotoxicity was assessed at concentrations of
0, 0.01, 0.1, 10 and 100 µg/mL. The relation between surviving fraction and drug concentration was
plotted to obtain the survival curve of MCF7 tumor cell line after addition of the specified compound.
The parameter used here is IC50, which corresponds to the concentration required for 50% inhibition of
cell viability. The IC50 values of the synthesized compounds compared to the reference drug are shown
in Table 1.

Molecules 2014, 19
3302
Table 1. Results of in vitro cytotoxic activity of the synthesized compounds on human
breast cancer cell line (MCF7).
Compound No.
IC50 in µM
Doxorubicin
5
4
5a
5b
6
49
52
38
52
14
33
25
26
25
27
84
17
12
18
12
11
7
8a
8b
8c
8d
8e
9
10a
10b
10c
10d
10e
The obtained data revealed that most of the newly synthesized compounds showed potent antitumor
activity. Among the tested compounds, the most potent cytotoxic effect against MCF-7 cell line was
obtained with the compound 5-(4-nitrobenzylideneamino)pyrazolo[3,4-d]pyrimidin-4-one (10e) with
an IC50 value of 11 µM, followed by 10d which showed an IC50 value of 12 µM. Compound 9
exhibited the least cytotoxic activity.
From the antitumor screening results the against the MCF-7 cell line, some structure activity
relationships can be suggested. Aromatic substitution on N5 position favors the activity; this is obvious
upon comparing 5-(4-hydroxyphenylpyrazolo[3,4-d]pyrimidin-4-one derivative 8b (IC50 = 25) and
5-hydroxy-3,6-dimethyl-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one (4) (IC50 = 49). Also, the
introduction of a 5-amino function on the pyrazolo[3,4-d]pyrimidine core produced inactive compound
9 (IC50 = 84), while the introduction of an anilino function favors the anticancer activity as shown by
compound 7 (IC50 = 14). Conversion of inactive compound 9 into a 5-substituted benzylidene amino
function yielded compounds 10a–e, the most active members of this study. The influence of
substituents on the benzylideneamino group on the antitumor activity was in the order NO2 > F > Cl >
OCH3 > H. Moreover, 5-(4-substituted benzylideneamino) derivatives 10a–e with azomethine spacer
groups were more potent than the 5-(4-substituted phenyl) derivatives 8a–e.
3. Experimental
3.1. General
Melting points were determined on a Griffin apparatus and are uncorrected. IR spectra were
determined on Shimadzu IR 435 spectrophotometer and values are presented in cm−1. 1H-NMR spectra

Molecules 2014, 19
3303
were recorded on Varian Gemini 300 MHz spectrometer, using TMS as internal standard and chemical
shifts are reported in ppm on the δ scale. The electron impact (EI) mass spectra were recorded on a
Shimadzu QP-2010 plus instrument. Analytical thin layer chromatography (TLC) on silica gel plates
containing UV indicator was routinely employed to follow the course of reactions and to check the
purity of products. All reagents and solvents were purified and dried by standard techniques. Elemental
microanalyses were carried out at the Microanalytical Center, Cairo University.
5-Amino-3-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid (2). A mixture of ethyl 5-amino-3-methyl-
1-phenyl-1H-pyrazole-4-carboxylate (1, 12.25 g, 50 mmol) and sodium hydroxide (4.20 g, 10 mmol)
in methanol (60 mL) was heated under reflux for 5 h. After cooling, the reaction mixture was poured
into ice-cold water, then adjusting pH of the mixture to 4 using concentrated hydrochloric acid. The
solid obtained was filtered, dried and crystallized from ethanol/water. Mp 156–157 °C; yield: 56%; IR
(cm−1): 3389–3204 (OH & NH2); 3009 (CH aromatic); 2927 (CH aliphatic); 1651 (C=O); 1613 (C=N);
1H-NMR (DMSO-d6) δ ppm: 2.25 (s, 3H); 6.30 (s, 2H); 7.36–7.54 (m, 5H); 12.08 (s, 1H); MS m/z:
217 (M+, 27.65);. Anal. Calcd for C11H11N3O2 (217.23): C, 60.82; H, 5.10; N, 19.34. Found: C, 60.69;
H, 5.20; N, 19.67.
3,6-Dimethyl-1-phenyl-1H-pyrazolo[3,4-d][1,3]oxazin-4-one (3). A mixture of 5-amino-3-methyl-1-
phenyl-1H-pyrazole-4-carboxylic acid (2, 2.17 g, 10 mmol) and acetic anhydride (5 mL) was heated
under reflux for 5 h. After cooling, the formed solid was filtered, dried and crystallized from methanol.
Mp 129–130 °C; yield: 49%; IR (cm−1): 3078 (CH aromatic); 2923 (CH aliphatic); 1764 (C=O); 1599
(C=N); 1H-NMR (DMSO-d6) δ ppm: 2.46 (s, 3H); 2.49 (s, 3H); 7.43 (t, J = 9 Hz, 1H); 7.57 (t, J = 9 Hz,
2H); 7.90 (d, J = 9 Hz, 2H); MS m/z: 241 (M+, 100). Anal. Calcd for C13H11N3O2 (241.25): C, 64.72; H,
4.60; N, 17.42. Found: C, 65.01; H, 4.73; N, 17.19.
3,6-Dimethyl-5-hydroxy-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one (4). A mixture of
compound 3 (2.41 g, 10 mmol) and hydroxylamine hydrochloride (0.69 g, 10 mmol) in dry pyridine
(30 mL) was heated under reflux for 8 h. The reaction mixture was concentrated to its half volume and
the separated solid was filtered, washed with water, dried and crystallized from dioxane. Mp 180–181 °C;
yield: 74%; IR (cm−1): 3426 (OH); 2926 (CH aliphatic); 1680 (C=O); 1568 (C=N); 1H-NMR (DMSO-d6)
δ ppm: 2.48 (s, 3H); 2.54 (s, 3H); 7.35 (t, J = 8.4 Hz, 1H); 7.53 (t, J = 8.4 Hz, 2H); 8.03 (d, J = 9 Hz,
2H); 11.52 (s, 1H); 13C-NMR (DMSO-d6) δ ppm: 13.71, 21.38, 105.07, 121.58, 126.92, 129.59,
138.75, 145.98, 149.94, 155.24, 157.86. MS m/z: 256 (M+, 89.42); Anal. Calcd for C13H12N4O2
(256.27): C, 60.93; H, 4.72; N, 21.86. Found: C, 60.81; H, 5.00; N, 21.66.
3.1.1. General Procedure for the Synthesis of 3,6-Dimethyl-1-phenyl-5-substituted-1,5-dihydro-
pyrazolo[3,4-d]pyrimidin-4-ones 5a,b
A mixture of 3,6-dimethyl-1-phenyl-1H-pyrazolo[3,4-d][1,3]oxazin-4-one (3, 2.41 g, 10 mmol) and
urea or thiourea (10 mmol) was fused at 200 °C for 1 h. The mixture was cooled and methanol was
added to the reaction mixture. The separated solid was filtered, washed with methanol, dried and
crystallized from ethanol.

Molecules 2014, 19
3304
3,6-Dimethyl-4-oxo-1-phenyl-1,4-dihydropyrazolo[3,4-d]pyrimidine-5-carboxamide (5a). Mp > 300 °C;
yield: 65%; IR (cm−1): 3432–3344 (NH2); 3073 (CH aromatic); 2926 (CH aliphatic); 1671 (broad band
1
of 2C=O); 1592 (C=N); H-NMR (DMSO-d6) δ ppm: 2.35 (s, 3H); 2.46 (s, 3H); 7.34 (t, J = 7.5 Hz,
1H); 7.51 (t, J = 7.5 Hz, 2H); 8.02 (d, J = 9 Hz, 2H); 12.20 (s, 2H); MS m/z: 283 (M+, 12.81); Anal.
Calcd for C14H13N5O2 (283.29): C, 59.36; H, 4.63; N, 24.72. Found: C, 59.55; H, 4.52; N, 24.94.
3,6-Dimethyl-4-oxo-1-phenyl-1,4-dihydropyrazolo[3,4-d]pyrimidine-5-carbothioamide (5b). Mp > 300 °C;
yield: 45%; IR (cm−1): 3425 (NH2); 2923 (CH aliphatic); 1675 (C=O); 1596 (C=N); 1118 (C=S);
1H-NMR (DMSO-d6) δ ppm: 2.38 (s, 3H); 2.48 (s, 3H); 7.35 (t, J = 7.2 Hz, 1H); 7.51 (t, J = 7.2 Hz,
2H); 8.02 (d, J = 9 Hz, 2H); 12.45 (s, 2H); Anal. Calcd for C14H13N5OS (299.36): C, 56.17; H, 4.38;
N, 23.39. Found: C, 56.22; H, 4.21; N, 23.64.
3,6-Dimethyl-4-oxo-1-phenyl-1,4-dihydropyrazolo[3,4-d]pyrimidine-5-carbothioic acid hydrazide (6).
A mixture of 3,6-dimethyl-1-phenyl-1H-pyrazolo[3,4-d][1,3]oxazin-4-one (3, 2.41 gm, 10 mmol) and
thiosemicarbazide (0.91 g, 10 mmol) was fused at 200 °C for 1 h. The reaction mixture was cooled and
methanol was added to the reaction mixture. The separated solid was filtered, washed with methanol,
dried and crystallized from acetone. Mp > 250–251 °C; yield: 63%; IR (cm−1): 3321 (broad band of
NH &NH2); 3064 (CH aromatic); 2920 (CH aliphatic); 1694 (C=O); 1590 (C=N); 1105 (C=S);
1H-NMR (DMSO-d6) δ ppm: 2.37 (s, 3H); 2.49 (s, 3H); 7.35 (t, J = 6 Hz,1H); 7. 51 (t, J = 7.2 Hz, 2H);
8.01 (d, J = 9 Hz, 2H); 11.15 (s, 1H); 12.19 (s, 2H); MS m/z: 314 (M+, 6.92); Anal. Calcd for
C14H14N6OS (314.37): C, 53.49; H, 4.49; N, 26.73. Found: C, 53.28; H, 4.47; N, 26.89.
3,6-Dimethyl-1-phenyl-5-phenylamino-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one (7). A mixture of
3,6-dimethyl-1-phenyl-1H-pyrazolo[3,4-d][1,3]oxazin-4-one (3, 2.41 g, 10 mmol) and phenylhydrazine
(1.08 gm, 10 mmol) in ethanol (20 mL) was heated under reflux for 6 h. The separated solid was
filtered while hot, dried and crystallized from butanol. Mp 265–266 °C; yield: 54%; IR (cm−1): 3250
(NH); 3115–3011 (CH aromatic); 2930 (CH aliphatic); 1685 (C=O); 1H-NMR (DMSO-d6) δ ppm: 2.49
(s, 3H); 2.53 (s, 3H); 6.69 (d, J = 7.2 Hz, 2H); 6.86 (t, J = 7.5 Hz, 1H); 7.21 (t, J = 7.5 Hz, 2H); 7.39 (t,
J = 7.8 Hz, 1H); 7.56 (t, J = 7.8 Hz, 2H); 8.05 (d, J = 9 Hz, 2H); 9.09 (s, 1H); MS m/z: 331 (M+, 100);
Anal. Calcd for C19H17N5O (331.38): C, 68.87; H, 5.17; N, 21.13. Found: C68.68; H, 5.09; N, 21.05.
3.1.2. General Procedure for the Synthesis of 3,6-Dimethyl-1-phenyl-5-(4-substitutedphenyl)-1,5-
dihydropyrazolo[3,4-d]pyrimidin-4-ones 8a–e
A mixture of 3,6-dimethyl-1-phenyl-1H-pyrazolo[3,4-d][1,3]oxazin-4-one (3, 2.41 g, 10 mmol) and
the appropriate aromatic amine (10 mmol) in dry pyridine (30 mL) was heated under reflux for 6 h.
The reaction mixture was poured into ice-cold water and the mixture was neutralized with
hydrochloric acid (10%). The separated product was filtered, washed with water, dried and crystallized
from the appropriate solvent.
3,6-Dimethyl-1-phenyl-5-p-tolyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one (8a). Mp 170–171 °C
(crystallized from methanol); yield: 50%; IR (cm−1): 2923 (CH aliphatic); 1693 (C=O); 1568 (C=N);
1H-NMR (DMSO-d6) δ ppm: 2.16 (s, 3H); 2.51 (s, 3H); 2.66 (s, 3H); 7.38–7.41 (m, 1H); 7.56–7.62

Molecules 2014, 19
3305
(m, 4H); 8.07–8.15 (m, 4H); MS m/z: 330 (M+, 100); Anal. Calcd for C20H18N4O (330.39): C, 72.71;
H, 5.49; N, 16.96. Found: C, 72.77; H, 5.20; N, 16.64.
3,6-Dimethyl-5-(4-hydroxyphenyl)-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one (8b). Mp
250–252 °C (crystallized from acetone); yield: 76%; IR (cm−1): 3439 (OH); 2930 (CH aliphatic); 1694
1
(C=O); 1566 (C=N); H-NMR (DMSO-d6) δ ppm: 2.17 (s, 3H); 2.51 (s, 3H); 6.89 (d, J = 9 Hz, 2H);
7.17 (d, J = 9 Hz, 2H); 7.38 (t, J = 7.5 Hz, 1H); 7.53 (t, J = 7.5 Hz, 1H); 8.07 (d, J = 9 Hz, 2H); 9.80
(s, IH); MS m/z: 332 (M+, 100); Anal. Calcd for C19H16N4O2 (332.36): C, 68.66; H, 4.85; N, 16.86.
Found: C, 68.30; H, 4.50; N, 16.98.
5-(4-Acetylphenyl)-3,6-dimethyl-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one (8c). Mp 186–187 °C
(crystallized from ethanol); yield: 66%; IR (cm−1): 2924 (CH aliphatic); 1699 (broad band of 2C=O);
1
1591 (C=N); H-NMR (DMSO-d6) δ ppm: 2.17 (s, 3H); 2.44 (s, 3H); 2.50 (s, 3H); 7.23 (d, J = 9 Hz,
2H); 7.26 (d, J = 9 Hz, 2H); 7.52–7.64 (m, 3H); 8.08 (d, J = 9 Hz, 2H); MS m/z: 358 (M+, 100); Anal.
Calcd for C21H18N4O2 (358.40): C, 70.38; H, 5.06; N, 15.63. Found: C, 69.97; H, 4.98; N, 15.94.
4-(3,6-Dimethyl-4-oxo-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-5-yl)benzoic acid (8d). Mp
200–201 °C (crystallized from acetic acid); yield: 59%; IR (cm−1): 3450 (OH); 3068 (CH aromatic);
1
2929 (CH aliphatic); 1713, 1678 (2C = O); 1558 (C = N); H NMR (DMSO-d6) δ ppm: 2.16 (s, 3H);
2.51 (s, 3H); 7.38 (t, J = 7.2 Hz, 1H); 7.54-7.65 (m, 4H); 8.07-8.13 (m, 4H); 13.15 (s, IH); MS m/z:
360 (M+, 79.41); Anal. Calcd for C20H16N4O3 (360.38): C, 66.66; H, 4.48; N, 15.55. Found: C, 66.90;
H, 4.71; N, 15.78.
Ethyl 4-(3,6-dimethyl-4-oxo-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-5-yl)benzoate (8e). Mp
190–191 °C (crystallized from ethanol); yield: 85%; IR (cm−1): 2925 (CH aliphatic); 1709 (broad band
1
of 2C=O); 1555 (C=N); H NMR (DMSO-d6) δ ppm: 1.36 (t, J = 7.2 Hz, 3H); 2.15 (s, 3H);
2.51 (s, 3H); 4.37 (q, J = 7.2 Hz, 2H); 7.39 (t, J = 7.2 Hz, 1H); 7.53–7.62 (m, 4H); 8.07–8.15 (m, 4H);
MS m/z: 388 (M+, 93.03); Anal. Calcd for C22H20N4O3 (388.43): C, 68.03; H, 5.19; N, 14.42. Found: C
68.21; H, 5.51; N, 14.66.
5-Amino-3,6-dimethyl-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one (9).
A
mixture of
compound 3 (2.41 g, 10 mmol) and hydrazine hydrate (0.5 mL, 10 mmol) in butanol (20 mL) was
heated under reflux for 6 h. After cooling, the separated solid was filtered, dried and crystallized from
ethanol. Mp 129–130 °C; yield: 47%; IR (cm−1): 3322–3262 (forked, NH2); 3065 (CH aromatic); 2924
(CH aliphatic); 1692 (C=O); 1H-NMR (DMSO-d6) δ ppm: 2.50 (s, 3H); 2.59 (s, 3H); 5.71 (s, 2H); 7.34
(t, J = 7.5 Hz, 1H); 7.52 (t, J = 7.5 Hz, 2H); 8.05 (d, J = 9 Hz, 2H); MS m/z: 255 (M+, 100). Anal.
Calcd for C13H13N5O (255.28): C, 61.17; H, 5.13; N, 27.43. Found: C, 61.53; H, 5.03; N, 27.23.
3.1.3. General Procedure for the Synthesis of (E)-3,6-Dimethyl-5-(4-substitutedbenzylideneamino)-1-
phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-ones 10a–e
A mixture of compound 9 (2.55 gm, 10 mmol) and the appropriate aromatic aldehyde (12 mmol) in
acetic acid (15 mL) was heated under reflux for 20 h. The reaction mixture was concentrated under

Molecules 2014, 19
3306
vacuum then cooled. The obtained solid was filtered, washed with water, dried and crystallized from
the appropriate solvent. The spectral data for compounds 10a–e are listed below.
(E)-5-(Benzylideneamino)-3,6-dimethyl-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one (10a).
Mp 250–251 °C (crystallized from ethanol); yield: 70%; IR (cm−1): 3055 (CH aromatic); 2925 (CH
1
aliphatic); 1702 (C=O); 1555 (C=N); H-NMR (DMSO-d6) δ ppm: 2.50 (s, 3H); 2.55 (s, 3H); 7.39
(t, J = 9 Hz, 1H); 7.53-7.65 (m, 5H); 7.98 (d, J = 9Hz, 2H); 8.08 (d, J = 9 Hz, 2H); 8.89 (s, 1H); MS
m/z: 343 (M+, 4.62); Anal. Calcd for C20H17N5O (343.39): C, 69.96; H, 4.99; N, 20.39. Found: C,
69.77; H, 5.20; N, 20.54.
(E)-3,6-Dimethyl-5-(4-fluorobenzylideneamino)-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one
(10b). Mp 160–161 °C (crystallized from methanol); yield: 79%; IR (cm−1): 3067 (CH aromatic); 2928
1
(CH aliphatic); 1709 (C=O); 1596 (C=N); H NMR (DMSO-d6) δ ppm: 2.10 (s, 3H); 2.41 (s, 3H);
7.38–7.40 (m, 1H); 7.52–7.57 (m, 4H); 7.99-8.01 (m, 4H); 10.94 (s, 1H); Anal. Calcd for C20H16FN5O
(361.38): C, 66.47; H, 4.46; N, 19.38. Found: C, 66.38; H, 4.02; N, 19.61.
(E)-3,6-Dimethyl-5-(4-methoxybenzylideneamino)-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-
one (10c). Mp 255–256 °C (crystallized from toluene); yield: 55%; IR (cm−1): 3027 (CH aromatic);
1
1671 (C=O); 1594 (C=N); H-NMR (DMSO-d6) δ ppm: 2.49 (s, 3H); 2.51 (s, 3H); 3.84 (s, 3H); 7.22
(t, J = 6 Hz, 1H); 7.37–7.57 (m, 6H); 8.07 (d, J = 9Hz, 2H); 8.85 (s, 1H); MS m/z: 373
(M+, 10.42); Anal. Calcd for C21H19N5O2 (373.42): C, 67.55; H, 5.13; N, 18.75. Found: C, 67.10; H,
5.01; N, 18.47.
(E)-5-(4-Chlorobenzylideneamino)-3,6-dimethyl-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one
(10d). Mp > 300 °C (crystallized from ethanol); yield: 60%; IR (cm−1): 3064 (CH aromatic); 2925 (CH
1
aliphatic); 1698 (C=O); 1596 (C=N); H-NMR (DMSO-d6) δ ppm: 2.09 (s, 3H); 2.54 (s, 3H); 7.37
(t, J = 8.1 Hz); 7.56 (t, J = 8.1 Hz, 2H); 7.66 (d, J = 8.4 Hz, 2H); 7.99 (d, J = 8.4 Hz, 2H); 8.32
(d, J = 8.7 Hz, 2H); 8.32 (s, 1H); 13C-NMR (DMSO-d6) δ ppm: 13.72, 23.32, 104.40, 121.72, 127.13,
129.68, 129.83, 130.93, 131.63, 137.96, 138.66, 146.86, 150.30, 154.86, 157.74, 168.91. MS m/z: 377
(M+, 11.12), Anal. Calcd for C20H16ClN5O (377.85): C, 63.58; H, 4.27; N, 18.51. Found: C, 63.28; H,
4.04; N, 18.13.
(E)-3,6-Dimethyl-5-(4-nitrobenzylideneamino)-1-phenyl-1,5-dihydropyrazolo[3,4-d]pyrimidin-4-one
(10e). (Crystallized from acetic acid); mp > 300 °C; yield: 95%; IR (cm−1): 3057 (CH aromatic); 2925
1
(CH aliphatic); 1690 (C=O); 1597 (C=N); H-NMR (DMSO-d6) δ ppm: 2.60 (s, 3H); 2.61 (s, 3H);
7.39 (t, J = 7.8 Hz, 1H); 7.57 (t, J = 7.8 Hz, 2H); 8.07 (d, J = 8.7 Hz, 2H); 8.25 (d, J = 9 Hz, 2H); 8.42
(d, J = 9 Hz, 2H); 9.16 (s, 1H); MS m/z: 388 (M+, 18.10). Anal. Calcd for C20H16N6O3 (388.39): C,
61.85; H, 4.15; N, 21.64. Found: C, 62.15; H, 4.44; N, 21.40.

Molecules 2014, 19
3307
3.2. Biological Testing
3.2.1. Materials and Methods
Human breast cancer cell line, MCF was grown as monolayer culture in RPM 11640 medium
supplemented with 10% fetal bovine serum (FBS) and 1% penicillin/streptomycin. The cell line was
incubated at 37 °C 5% CO2 95% air and high humidity atmosphere in the water jacketed incubator
(Revco, GS Laboratory Equipment, RCO 3000 TVBB, Asheville, NC, USA). The cell line was
regularly subcultured to be maintained in the exponential growth phase. The sterile conditions were
strictly attained by working under the equipped laminar flow (Microflow laminar flow cabinet, Hamsphire
SP 105aa, Andover, UK).
3.2.2. Measutement of Potential Cytotoxicity
The cytotoxicity was carried out using the sulphorhodamine-B (SRB) assay. Cells were seeded in
96 well microtiter plates at a concentration of 1,000–2,000 cells/well, 100 µL/well, After 24 h, cells
will be incubated for 72 h with various concentrations of drugs (0, 0.01, 0.1, 1, 10 and 100 µg/mL).
For each derivative concentration and doxorubicin, 3 wells were used. The plates were incubated for
72 h. The medium is discarded. The cells were fixed with 150 μL cold trichloroacetic acid 10% final
concentration for 1 h at 4 °C.
The plates were washed with distilled water using a Tecan automatic washer (Crailsheim, Germany)
and stained with 50 μL 0.4% SRB dissolved in 1% acetic acid for 30 min at room temperature in dark.
The plates were washed with 1% acetic acid to remove unbound dye and air-dried (24 h).
The dye was solubilized with 150 µL/well of 10 mMtris base (PH 7.4) for 5 min on a shaker at
1,600 rpm. The optical density (OD) of each well will be measured spectrophotometrically at 490 nm
with an ELISA microplate reader. The mean background absorbance was automatically subtracted and
mean values of each derivative and doxorubicin concentration was calculated. The experiment was
repeated 3 times. The percentage of cell survival was calculated as follows:
Surviving fraction = O.D. (treated cells)/O.D. (control cells)
4. Conclusions
In conclusion, series of new 5-substituted pyrazolo[3,4-d]pyrimidin-4-ones 4, 5a,b, 6, 7, 8a–e, 10a–e
were synthesized. The cytotoxic activity of the newly synthesized compounds against the human breast
adenocarcinoma cell line MCF-7 was investigated. Almost all the tested compounds revealed some
antitumor activity, in particular 3,6-dimethyl-5-(4-nitrobenzylideneamino)-1-phenyl-1,5-dihydropyrazolo
[3,4-d]pyrimidin-4-one (10e) which exhibited the highest activity among the tested compounds with an
IC50 equal to 11 µM. The antitumor screening revealed that aromatic substitution on the N5 position
favors the activity. Moreover, 5-(4-substituted benzylideneamino) derivatives 10a–e with azomethine
spacer groups were more potent than the 5-(4-substituted phenyl) derivatives 8a–e.

Molecules 2014, 19
3308
Acknowledgments
We are grateful to Samia Shouman, of Pharmacology, and all members of the Department of Cancer
Biology, National Cancer Institute, Cairo, Egypt, for their kind help on carrying out the cytotoxicity testing.
Author Contributions
K.R.A.A. proposed the subject, designed the study and offered necessary guidance to R.B.B to
carry out the synthesis, purification and characterization of the compounds. E.K.A.A. and M.A.A.
conceived the study and participated in its design, results and discussion, and coordination. R.R.A.
carried out the biological assay.
Conflicts of Interest
The authors declare no conflict of interest.
References
1. Wu, H.; Chang, D.; Huang, C. Targeted therapy for cancer. J. Cancer Mol. 2006, 2, 57–66.
2. Sierra, J.R.; Cepero, V.; Giordano, S. Molecular mechanisms of acquired resistance to tyrosine
kinase targeted therapy. Mol. Cancer 2010, 9, 75–88.
3. Riley, L.B.; Desai, D.C. The molecular basis of cancer and the development of targeted therapy.
Surg. Clin. N. Am. 2009, 89, 1–15.
4. Cheng, C.C.; Robins, R.K. Potential Purine Antagonists. VI. Synthesis of 1-alkyl- and 1-aryl-4-
substituted pyrazolo[3,4-d]pyrimidines. J. Org. Chem. 1956, 21, 1240–1256.
5. Ismail, Z.H.; Abdel-Gawad, S.M.; Abdel-Aziem, A.; Ghorab, M.M. Synthesis of some new
biologically active sulfur compounds containing pyrazolo[3,4-d]pyrimidine moiety. Phosphor.
Sulfur Silicon 2003, 178, 1795–1805.
6. Carraro, F.; Naldini, A.; Pucci, A.; Locatelli, G.A.; Maga, G.; Schenone, S.; Bruno, O.; Ranise, A.;
Bondavalli, F.; Brullo, C.; et al. Pyrazolo[3,4-d]pyrimidines as potent antiproliferative and
proapoptotic agents toward A431 and 8701-BC cells in culture via inhibition of c-Src
phosphorylation. J. Med. Chem. 2006, 49, 1549–1561.
7. El-Enany, M.M.; Kamel, M.M.; Khalil, O.M.; El-Nassan, H.B. Synthesis and antitumor activity
of novel 6-aryl and 6-alkylpyrazolo[3,4-d]pyrimidin-4-one derivatives. Eur. J. Med. Chem. 2010,
45, 5286–5291.
8. Abd El Hamid, M.K.; Mihovilovic, M.D.; El-Nassan, H.B. Synthesis of novel pyrazolo[3,4-
d]pyrimidine derivatives as potential anti-breast cancer agents. Eur. J. Med. Chem. 2012, 57, 323–328.
9. Kandeel, M.M.; Mohamed, L.W.; Abd El Hamid, M.K.; Negmeldin, A.T. Design, synthesis, and
antitumor evaluation of novel pyrazolo[3,4-d]pyrimidine derivatives. Sci. Pharm. 2012, 80, 531–545.
10. Peat, A.J.; Garrido, D.; Boucheron, J.A.; Schweiker, S.L.; Dickerson, S.H.; Wilson, J.R.; Wang, T.Y.;
Thomson, S.A. Novel GSK-3 inhibitors with improved cellular activity. Bioorg. Med. Chem. Lett.
2004, 14, 2127–2130.

Molecules 2014, 19
3309
11. Kim, D.C.; Lee, Y.R.; Yang, B.S.; Shin, K.J.; Kim, D.J.; Chung, B.Y.; Yoo, K.H. Synthesis
and biological evaluations of pyrazolo[3,4-d]pyrimidines as cyclin-dependent kinase 2 inhibitors.
Eur. J. Med. Chem. 2003, 38, 525–532.
12. Schenone, S.; Brullo, C.; Bruno, O.; Bondavalli, F.; Mosti, L.; Maga, G.; Crespan, E.; Carraro, F.;
Manetti, F.; Tintori, C.; et al. Synthesis, biological evaluation and docking studies of 4-amino
substituted 1H-pyrazolo[3,4-d]pyrimidines. Eur. J. Med. Chem. 2008, 43, 2665–2676.
13. Schenone, S.; Bruno, O.; Bondavalli, F.; Ranise, A.; Mosti, L.; Menozzi, G.; Fossa, P.; Manetti, F.;
Morbidelli, L.; Trincavelli, L.; et al. 1-(2-Chloro-2-phenylethyl)6-methylthio-1H-pyrazolo[3,4-
d]pyrimidines-4-amino substituted and their biological evaluation. Eur. J. Med. Chem. 2004, 39,
153–160.
14. Ghorab, M.M.; Ragab, F.A.; Alqasoumi, S.I.; Alafeefy, A.M.; Aboulmagd, S.A. Synthesis of
some new pyrazolo[3,4-d]pyrimidine derivatives of expected anticancer and radioprotective activity.
Eur. J. Med. Chem. 2010, 45, 171–178.
15. Hassan, G.S.; Kadry, H.H.; Abou-Seri, S.M.; Ali, M.M.; Mahmoud, A.E. Synthesis and in vitro
cytotoxic activity of novel pyrazolo[3,4-d]pyrimidines and related pyrazole hydrazones toward
breast adenocarcinoma MCF-7 cell line. Bioorg. Med. Chem. 2011, 19, 6808–6817.
16. Reck, M.; Mok, T.; Wolf, J.; Heigener, D.; Wu, Y.L. Reviewing the safety of erlotinib in non
small cell lung cancer. Expert Opin. Drug Saf. 2011, 10, 147–157.
17. Omar, H.A.; Sargeant, A.M.; Weng, J.-R.; Wang, D.; Kulp, S.K.; Patel, T.; Chen, C.-S. Pulmonary
endothelial impairment during gefitinib therapy: A preliminary assessment with iodine-123-
metaiodobenzylguanidine (1231-MIBG) scintigraphy. Open Lung Cancer J. 2011, 4, 957–968.
18. Fang, L.; Barekati, Z.; Zhang, B.; Liu, Z.; Zhong, X. Targeted therapy in breast cancer: What’s new?
Eur. J. Med. Sci. 2011, 141, 1–9.
19. Bakr, R.B.; Abdelall, E.K.A.; Abdel-Hamid, M.K.; Kandeel, M.M. Design and synthesis of new
EGFR-tyrosine kinase inhibitors containing pyrazolo[3,4-d]pyrimidine cores as anticancer agents.
Bull. Pharm. Sci. Assiut Univ. 2012, 35, 1–16.
20. Heravi, M.M.; Nami, N.; Seifi, N.; Oskooie, H.A.; Hekmatshoar, R. Microwave-assisted synthesis
of substituted pyrazoles and pyrazolo[3,4-d]thiopyrimidines. Phosphor. Sulfur Silicon 2006, 181,
591–599.
21. Vichai, V.; Kirtikara, K. Sulforhodamine B colorimetric assay for cytotoxicity screening.
Nat. Protoc. 2006, 1, 1112–1116.
Sample Availability: Samples of the compounds 1–10 are available from the authors.
© 2014 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).