Synthesis of new quinoxaline, pyrimidine, and pyrazole furochromone derivatives as cytotoxic agents

Article abstract of DOI:10.1007/s00706-017-1960-6

Abstract: A series of novel quinoxaline, pyrimidine, and pyrazole furochromone derivatives were synthesized for the first time. These derivatives were prepared under mild conditions using a stepwise efficient methodology. The developed protocol led to the synthesis of furochromone derivatives in moderate to good yields (60–75%). The structures of the prepared derivatives were identified using several spectroscopic techniques including IR, NMR, and mass spectrometry. The cytotoxic activity of the synthesized derivatives was evaluated using in vitro Ehrlich ascites assay. Pyrazolobenzofurans exhibited the most potent effect suggesting the importance of pyrazole nucleus for the cytotoxic activity. Graphical abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s00706-017-1960-6

Monatsh Chem
DOI 10.1007/s00706-017-1960-6
ORIGINAL PAPER
Synthesis of new quinoxaline, pyrimidine, and pyrazole
furochromone derivatives as cytotoxic agents
Ameen A. Abu-Hashem1,2 Mohamed El-Shazly3
•
Received: 14 December 2016 / Accepted: 19 March 2017
Ó Springer-Verlag Wien 2017
Abstract A series of novel quinoxaline, pyrimidine, and
pyrazole furochromone derivatives were synthesized for
the first time. These derivatives were prepared under mild
conditions using a stepwise efficient methodology. The
developed protocol led to the synthesis of furochromone
derivatives in moderate to good yields (60–75%). The
structures of the prepared derivatives were identified using
several spectroscopic techniques including IR, NMR, and
mass spectrometry. The cytotoxic activity of the synthe-
sized derivatives was evaluated using in vitro Ehrlich
ascites assay. Pyrazolobenzofurans exhibited the most
potent effect suggesting the importance of pyrazole nucleus
for the cytotoxic activity.
Graphical abstract
Keywords Furochromones Á Visnagenone Á Khellinone Á
Quinoxalines Á Pyrimidines Á Pyrazolobenzofurans Á
Cytotoxic activity
Introduction
Furochromones such as khellin and visnagin represents one
of the oldest classes of secondary metabolites isolated from
a well-known medicinal plant, Ammi visnaga L. (Apiaceae)
(Fig. 1). Their structures were elucidated during the first
half of the last century [1, 2]. The medicinal uses of A.
visnaga were documented in ancient scrolls and papyri [3].
It was prescribed for the treatment of urinary infection and
renal colics. Following the isolation of A. visnaga active
constituents, furochromones, the therapeutic applications
of the herb and its components entered a new era. Fur-
ochromones were not only isolated from A. visnaga but
also from other plants [4]. The activities of furochromones
against different ailments were evaluated. It was found that
these components possess potent phototoxic properties
which led to their application in the treatment of vitiligo [5]
and certain microbial infections [6]. Also furochromones
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-017-1960-6) contains supplementary
material, which is available to authorized users.
& Ameen A. Abu-Hashem
aminaliabuhashem@yahoo.com
1
Photochemistry Department (Heterocyclic Unit), National
Research Center, Dokki, Giza 12622, Egypt
2
Chemistry Department, Faculty of Science, Jazan University,
Jezan 2097, Saudi Arabia
3
Department of Pharmacognosy and Natural Products
Chemistry, Faculty of Pharmacy, Ain Shams University,
Cairo 11566, Egypt
123

A. A. Abu-Hashem, M. El-Shazly
of three methoxy groups and the mass spectra of 3a and 3b
showed molecular ion peaks at m/z = 220 (M?, 12%) and
250 (M?, 15%), respectively. Similar derivatives were
prepared by Hafez et al. using acetone as the solvent which
led to lower yields [20].
Bromination [21] of 3a or 3b in acetic acid furnished the
corresponding 2-bromo-1-(7-bromo-4,6-dimethoxy- or
1
4,6,7-trimethoxybenzofuran-5-yl)ethan-1-one (4a, 4b). H
NMR spectrum of 4a or 4b showed one singlet signal at
4.65 or 4.62 ppm indicative of two methylene (CH2)
groups and the molecular ion peaks at m/z = 378 (M?,
100%) and 329 (M?, 86%), respectively.
Fig. 1 Chemical structures of visnagin, khellin and visnagenone,
khellinone
were found to exhibit potent anti-atherosclerotic and lipid-
altering activity [7]. The interesting biological activities of
this class of compounds promoted the synthesis of different
derivatives which showed a plethora of important biolog-
ical activities. Furochromones with pyrimidine moiety
exhibited anti-inflammatory and analgesic activities [8].
Visnaginone derivatives were prepared using different
protocols and demonstrated potent antibacterial activity
[9–11]. Benzofuran derivatives showed potent vasodilata-
tory, hypotensive, antibacterial, antifungal, and
antiparasitic activities [11–14]. Pyrazoline derivatives were
synthesized and exhibited bacteriostatic, fungicidal and
anticancer activity [15–17].
Moreover, the treatment of 4a or 4b with o-phenylene-
diamine [22] in boiling absolute methanol resulted in the
formation of 2-(7-bromo-4,6-dimethoxy- or 4,6,7-
trimethoxybenzofuran-5-yl)-1,4-dihydroquinoxaline (5a,
5b). IR spectra of compounds 5a and 5b revealed the
presence of a broad band absorption at 3420–3400 cm-1
1
indicative of two (NH) groups. Additionally, the H NMR
spectra of 5a showed a singlet broad signal at 8.30 and
9.20 ppm corresponding to the two protons of the two
(NH) groups, which were D2O exchangeable. Closely
related derivatives were reported by Mohamed et al. with
similar yields [23].
Alkylation of 5a or 5b with methyl iodide yielded 2-(7-
bromo-4,6-dimethoxy- or 4,6,7-trimethoxybenzofuran-5-
yl)-1,4-dimethyl-1,4-dihydroquinoxaline (6a, 6b). The
mass spectra of 5a, 5b, 6a, and 6b showed molecular ion
peaks at m/z = 387 (M?, 90%), 338 (M?, 92%), 415 (M?,
88%), and 366 (M?, 82%), respectively (Scheme 1).
Condensation of visnagenone (2a) or khellinone (2b)
with thiourea in acetic acid afforded 1-[1-(6-hydroxy-4-
The synthesis of molecules with highly strained rings
represents one of the most challenging tasks in synthetic
organic chemistry. Certain rings such as the six and five
membered rings are kinetically favorable and can be pre-
pared easily in high yields.
In a continuation of our work on the synthesis of new
heterocyclic compounds derived from the naturally occur-
ring furochromones (visnagin and khellin) [2, 8, 18, 19],
we prepared and characterized a series of derivatives
containing a benzodifuran nucleus (visnaginone, khelli-
none) combined with quinoxaline, pyrimidine, or pyrazole
moiety. The cytotoxic activity of the prepared compounds
was evaluated.
methoxy-
or
4,7-dimethoxybenzofuran-5-yl)ethyli-
dene]thiourea (7a, 7b). IR spectra of 7a and 7b showed
absorption of a broad band at 3400–3200 cm-1 corre-
sponding to NH2 and OH groups. Also, peaks at
1618 cm-1 for (C=N) and 1355 cm-1 for (CS) were
detected in the IR spectrum. 1H NMR spectrum of 7a
showed one singlet at 6.68 ppm corresponding to the two
protons of NH2 group and one a broad singlet at 12.46 ppm
for OH proton (D2O exchangeable).
Results and discussion
Chemistry
Similar derivatives were reported by Ragab et al. but the
products were formed after 72 h in lower yields [24].
Mohamed et al. also synthesized similar compounds
through condensation of thiourea with ethoxycoumarin
derivatives forming the corresponding thiomaide deriva-
tives in good yields using DMF as the refluxing solvent
[23].
In the current research, visnagin (1a) or khellin (1b) was
hydrolyzed with aqueous KOH yielding visnagenone (2a)
or khellinone (2b) [18]. Treatment of 2a, 2b with absolute
methanol containing 2–3 drops of concentrated H2SO4 or
refluxing of 2a, 2b in ethanolic potassium hydroxide
solution with methyl iodide provided 1-(4,6-di- or 4,6,7-
trimethoxybenzofuran-5-yl)ethan-1-one (3a, 3b), respec-
Refluxing of 7a and 7b in dimethylformamide yielded
5-methoxy- or 5,9-dimethoxy-4-methylfuro[2,3-b]benzo[50,60-
e]pyrimidine-2(1H)-thione (8a, 8b). The reaction of 7a or 7b
with secondary aliphatic amines [25], namely piperazine in
glacial acetic acid yielded 1-[1-[4-methoxy- or 4,7-dimethoxy-
1
tively. The H NMR spectrum of compound 3b showed
three singlet signal at d = 3.84, 3.85, 3.91 ppm indicative
123

Synthesis of new quinoxaline, pyrimidine, and pyrazole furochromone derivatives as cytotoxic…
Scheme 1
6-(piperazin-1-yl]benzofuran-5-yl]ethylidene]thiourea
(9a,
ethoxide (NaOEt) yielded the corresponding sodium salt,
which upon treatment with acetic anhydride (Ac2O) pro-
vided the acetylated derivatives (13a or 13b) and the
treatment with methyl iodide (MeI) yielded the methylated
derivatives (14a or 14b) (Scheme 3). In all of the prepared
pyrazole derivatives the characteristic 13C imine signal
(130.1–145.9 ppm) was consistent with the reported data
for similar derivatives [27, 29]. Assignment of the new
synthesized compounds was based on elemental analyses,
9b). Furthermore, 9a or 9b reacted with malononitrile in
boiling ethanol solution and triethylamine producing 2-[amino-
[[1-[4-methoxy- or 4,7-dimethoxy-6-(piperazin-1-yl)benzofu-
ran-5-yl]ethylidene]amino]methylene]malononitrile
(10a,
10b). The IR spectrum of 10a and 10b revealed the presence of
a wide band at 3355–3220 cm-1 for NH and NH2 groups as
well as two bands (2210 and 2205 cm-1) corresponding to two
cyano groups. Mass spectra of 7a, 7b, 8a, 8b, 9a, 9b, 10a, and
10b displayed molecular ion peaks at m/z = 264 (M?, 100%),
294 (M?, 100%), 246 (M?, 100%), 276 (M?, 42%), 332 (M?,
73%), 362 (M?, 95%), 364 (M?, 82%), 394 (M?, 12%),
respectively (Scheme 2).
1
IR, H, 13C NMR, and mass spectral data (c.f. Exp. Part,
Scheme 3).
Evaluation of cytotoxic activity using in vitro
Ehrlich ascites assay
Compounds with pyrazole moiety showed potent bio-
logical activity and were successfully synthesized using
different protocols [26]. o-Halogenated alkanoylphenones,
benzophenones, and arylcarboxylic acids were successfully
converted to pyrazole derivatives via copper-catalyzed
amination [27]. Metal free protocols were also developed
converting o-aminobenzoximes to pyrazole derivatives
using methanesulfonyl chloride and triethylamine [28], or
triphenylphosphine, I2, and imidazole [26]. To prepare
pyrazole derivatives of furochromones, 2a or 2b was
treated with phenyl hydrazine in the presence of absolute
ethanol (EtOH) providing 4-methoxy-3-methyl-1-phenyl-
1H-furo[3,2-f]indazole (11a), or 4,8-dimethoxy-3-methyl-
1-phenyl-1H-furo[3,2-f]indazole (11b), respectively, as a
yellowish white powder. Moreover, the reaction of 2a or
2b with hydrazine hydrate afforded 4-methoxy-3-methyl-
1H-furo[3,2-f]indazole (12a) or 4,8-dimethoxy-3-methyl-
1H-furo[3,2-f]indazole (12b), respectively, as a yellowish
brown powder. The reaction of 12a or 12b with sodium
The newly synthesized compounds were screened for their
cytotoxic activity using in vitro Ehrlich ascites assay
(Table 1). 5-Fluorouracil was used as the positive control
causing 99.5% mortality. The viability of the cells used in
the control experiments exceeded 95%. The use of com-
pounds 13b and 13a resulted in 94.44 and 92.90%
mortality, respectively. Other compounds also resulted in
high percentage of mortality including 11b, 11a, 14b, 14a,
12b, and 12a (76.90–90.84%). Mediocre percentages of
mortality were observed after the treatment with 8a, 8b,
10a, 10b, 9a, 9b, 6a, 6b, 5a, and 5b (52.25–74.50%). Other
compounds showed weaker activity.
Structural activity relationship (SAR)
The cytotoxic results indicated that the pyrazole moiety is
important for the activity. Compounds 13b and 13a with
123

A. A. Abu-Hashem, M. El-Shazly
Scheme 2
Scheme 3
123

Synthesis of new quinoxaline, pyrimidine, and pyrazole furochromone derivatives as cytotoxic…
Table 1 Cytotoxic evaluation
Compounds no.a
Mortality/%
SEM
–
of the prepared compound using
Ehrlich in vitro assay
Control (no drugs)
5-Fluorouracilb
0
99.50
20.75
22.64
24.92
27.80
35.45
38.50
42.40
44.20
52.25
55.60
58.15
60.55
48.24
50.10
70.15
74.50
62.33
64.40
66.35
69.10
88.52
90.84
76.90
80.30
92.90
94.44
82.10
85.45
0.005
1a
0.048
0.044
0.041
0.039
0.024
0.027
0.022
0.042
0.052
0.045
0.032
0.026
0.035
0.020
0.024
0.022
0.040
0.028
0.030
0.020
0.014
0.013
0.018
0.017
0.009
0.007
0.016
0.015
1b
2a
2b
3a
3b
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
9a
9b
10a
10b
11a
11b
12a
12b
13a
13b
14a
14b
a
1 mg cm-3 in DMSO/RPMI-1640 (1:10)
b
25 mg cm-3 in DMSO/RPMI-1640 (1:10). All the values are mean SEM of three samples
this nucleus showed the highest activity. Also, compounds
14a and 14b exhibited potent activity albeit lower than the
acetylated derivatives (13b and 13a) highlighting the
importance of the acetyl group for the cytotoxic activity.
The importance of the pyrazole moiety was also supported
by the high activity demonstrated by 11a and 11b. One the
other hand, pyrazole derivatives without substitution on the
nitrogen atom showed lower activity (12a and 12b).
Compounds carrying pyrazole moiety showed potent tox-
icity in previous studies [30]. Furobenzopyrimidinethione
(8a, 8b); piperazinbenzofuran, malononitrile thiourea (10a,
10b and 9a, 9b) and benzofuranquinoxaline (6a, 6b and 5a,
5b) derivatives resulted in mediocre mortality
(52.25–74.50%). The natural furochromone derivatives (1a
and 1b) as well as their hydrolyzed products (2a and 2b)
exhibited weak cytotoxic activity suggesting the future
potential of the synthesized derivatives as cytotoxic agents.
Conclusion
Furochromones (visnagin and khellin) were converted into
polyfunctionalized heterocycles with promising cytotoxic
activity. Different derivatives were prepared including
benzofuranquinoxalines,
furobenzopyrimidinethione,
piperazinbenzofurans, and pyrazolo[4,5-f]benzofuran
derivatives. Compounds with pyrazole moiety and substi-
tuted nitrogen atom showed potent cytotoxic activity. The
simplicity of the synthetic procedures and the potent
activity of the prepared compounds render these
123

A. A. Abu-Hashem, M. El-Shazly
1
(CH-aryl), 2950 (CH-aliph), 1695 (CO- acetyl) cm-1; H
derivatives interesting targets for future development as
cytotoxic agents.
NMR (DMSO-d6): d = 2.39 (s, 3H, CH3), 3.85 (s, 3H,
OCH3), 3.95 (s, 3H, OCH3), 6.27 (s, 1H, H-7), 7.04 (d, 1H,
J = 2.30 Hz, furan), 7.24 (d, 1H, J = 2.33 Hz, furan)
ppm; 13C NMR (DMSO-d6): d = 33.1, 56.9, 61.8, 92.7,
106.5, 109.5, 115.9, 146.2, 155.9, 156.9, 163.1, 179.8 ppm;
MS (70 eV): m/z = 221 ([M?1]?, 18%), 220 (M?, 12%).
Experimental
All melting points were taken on an Electrothermal IA
9100 series digital melting point apparatus (Shimadzu,
Japan). Elemental analyses were performed on Vario EL
(Elementar, Germany). Microanalytical data were pro-
cessed in the microanalytical center, Faculty of Science,
Cairo University and National Research Center. The IR
spectra (KBr disc) were recorded using a Perkin-Elmer
1650 spectrometer (USA). NMR spectra were determined
using JEOL 270 MHz and JEOL JMS-AX 500 MHz
(JEOL, Japan) spectrometers with Me4Si as an internal
standard. Mass spectra were recorded on an EI Ms-QP
1000 EX instrument (Shimadzu, Japan) at 70 eV. Phar-
macological evaluation was done by the Pharmacology
Unit, Department of Pharmacognosy, Faculty of Pharmacy,
Mansoura University, Egypt. All starting materials and
solvents were purchased from Sigma Aldrich (Saint Lewis,
USA).
1-(4,6,7-Trimethoxybenzofuran-5-yl)ethan-1-one
(3b, C13H14O5)
The compound was obtained from the reaction of 2.36 g
khellinone (2b, 0.01 mol) and methanol/conc. H2SO4 or
methyl iodide, as a pale yellow powder, crystallized from
methanol (80%). M.p.: 125–127 °C; IR (KBr): vꢀ = 3038
(CH-aryl), 2948 (CH-aliph), 1692 (CO-acetyl) cm-1; H
1
NMR (DMSO-d6): d = 2.38 (s, 3H, CH3), 3.84 (s, 3H,
OCH3), 3.85 (s, 3H, OCH3), 3.91 (s, 3H, OCH3), 7.06 (d,
1H, J = 2.32 Hz, furan), 7.25 (d, 1H, J = 2.34 Hz, furan)
ppm; 13C NMR (DMSO-d6): d = 33.5, 56.5, 61.2, 61.7,
106.8, 110.3, 118.2, 135.1, 144.3, 146.4, 149.4, 150.5,
178.9 ppm; MS (70 eV): m/z = 250 (M?, 15%).
2-Bromo-1-(7-bromo-4,6-dimethoxy- or 4,6,7-trimethoxy-
benzofuran-5-yl)ethan-1-one (4a, 4b)
A solution of 2.20 g 3a (10 mmol) or 2.50 g 3b (10 mmol)
in 10 cm3 acetic acid was stirred with 1 cm3 (20 mmol) or
0.50 cm3 (10 mmol) bromine for 2–4 h in direct sun-light.
The solid formed was collected by filtration, washed with
acetic acid, then ethanol, and dried. The product was
recrystallized from the proper solvent to give 4a and 4b,
respectively.
1-(4,6-Di- or 4,6,7-trimethoxybenzofuran-5-yl)ethan-1-one
(3a, 3b)
Method A: compounds 1a or 1b were prepared according
to the reported procedures [31]. Previous studies reported
the synthesis of quinoxaline derivatives which were
followed with slight modification [31]. A mixture of
2.06 g visnaginone (2a, 0.01 mol) or 2.36 g khellinone
(2b, 0.01 mol) in 30 cm3 absolute methanol containing a
few drops of concentrated sulfuric acid was refluxed for
3 h. The solid formed was filtered off, dried, and crystal-
lized from the proper solvent to give 3a and 3b,
respectively.
2-Bromo-1-(7-bromo-4,6-dimethoxybenzofuran-5-yl)ethan-
1-one (4a, C12H10Br2O4)
The compound was obtained from the reaction of 2.20 g 3a
(10 mmol) and 1 cm3 bromine (20 mmol), as a yellow
powder, crystallized from dioxane (75%). M.p.: 266–
268 °C; IR (KBr): vꢀ = 3035 (CH-aryl), 2946 (CH-aliph),
Method B: to a warmed ethanolic potassium hydroxide
solution (prepared by dissolving 0.56 g of potassium
hydroxide (10 mmol) in 50 cm3 ethanol) was added
2.06 g visnaginone (2a, 0.01 mol) or 2.36 g khellinone
(2b, 0.01 mol) and heating was continued for 40 min. The
mixture was allowed to cool to room temperature, and
2 cm3 methyl iodide was added. The mixture was stirred
under reflux for 6 h and then allowed to cool to room
temperature and finally poured into 100 cm3 cold water.
The solid product precipitated was filtered off and washed
with 100 cm3 water and crystallized.
1
1700 (CO-acetyl) cm-1; H NMR (DMSO-d6): d = 3.81
(s, 3H, OCH3), 3.86 (s, 3H, OCH3), 4.65 (s, 2H, CH2), 7.09
(d, 1H, J = 2.30 Hz, furan), 7.22 (d, 1H, J = 2.31 Hz,
furan) ppm; 13C NMR (DMSO-d6): d = 32.4, 61.4, 61.9,
85.6, 105.7, 110.8, 111.5, 146.1, 155.8, 160.6, 169.3,
180.5 ppm; MS (70 eV): m/z = 378 (M?, 100%).
2-Bromo-1-(4,6,7-trimethoxybenzofuran-5-yl)ethan-1-one
(4b, C13H13BrO5)
The compound was obtained from the reaction of 2.50 g 3b
(10 mmol) and 0.50 cm3 bromine (10 mmol), as a yellow-
ish powder, crystallized from benzene (70%). M.p.: 242–
244 °C; IR (KBr): vꢀ = 3037 (CH-aryl), 2945 (CH-aliph),
1-(4,6-Dimethoxybenzofuran-5-yl)ethan-1-one
(3a, C12H12O4)
1
1705 (CO-acetyl) cm-1; H NMR (DMSO-d6): d = 3.81
The compound was obtained from the reaction of 2.06 g
visnaginone (2a, 0.01 mol) and methanol/conc. H2SO4 or
methyl iodide, as a yellowish powder, crystallized from
ethanol (85%). M.p.: 133–135 °C; IR (KBr): vꢀ = 3040
(s, 3H, OCH3), 3.88 (s, 3H, OCH3), 3.91 (s, 3H, OCH3),
4.62 (s, 2H, CH2), 7.04 (d, 1H, J = 2.36 Hz, furan), 7.33
(d, 1H, J = 2.37 Hz, furan) ppm; 13C NMR (DMSO-d6):
123

Synthesis of new quinoxaline, pyrimidine, and pyrazole furochromone derivatives as cytotoxic…
d = 32.8, 61.5, 61.7, 97.2, 108.3, 108.6, 123.9, 135.3,
146.6, 152.7, 155.03, 168.1 ppm; MS (70 eV): m/z = 329
(M?, 86%).
to cool to room temperature and finally poured into
100 cm3 cold water. The solid product precipitated was
filtered off and washed with 100 cm3 water. The products
were recrystallized from the proper solvent to give 6a and
6b.
2-(7-Bromo-4,6-dimethoxy- or 4,6,7-trimethoxybenzofu-
ran-5-yl)-1,4-dihydroquinoxaline (5a, 5b)
A solution of 3.78 g 4a (10 mmol) or 3.29 g 4b (10 mmol)
and 1.08 g o-phenylenediamine (10 mmol) in 40 cm3
absolute methanol was refluxed for 4–6 h. The solid
obtained was filtered, washed with ethanol, and dried
under vacuum. The crude product was recrystallized from
the proper solvent to give 5a or 5b.
2-(7-Bromo-4,6-dimethoxybenzofuran-5-yl)-1,4-dimethyl-
1,4-dihydroquinoxaline (6a, C20H19BrN2O3)
The compound was obtained from the reaction of 3.87 g 5a
(0.01 mol) and methyl iodide (20 mmol), as a pale yellow
crystals, crystallized from dioxane (66%). M.p.: [350 °C;
1
IR (KBr): vꢀ = 3052 (CH-aryl), 2954 (CH-aliph) cm-1; H
NMR (DMSO-d6): d = 3.25 (s, 3H, CH3), 3.30 (s, 3H,
CH3), 3.82 (s, 3H, OCH3), 3.85 (s, 3H, OCH3), 5.58 (d, 1H,
CH, pyrazine), 7.05 (d, 1H, J = 2.38 Hz, furan), 7.30 (d,
1H, J = 2.37 Hz, furan), 7.50–7.62 (m, 4H, phenyl) ppm;
13C NMR (DMSO-d6): d = 35.2, 45.8, 62.1, 62.5, 84.4,
99.1, 103.2, 106.1, 111.9, 117.6, 117.8, 118.5, 118.6,
122.1, 129.6, 129.7, 146.2, 150.8, 160.1, 160.3 ppm; MS
(70 eV): m/z = 415 (M?, 88%).
2-(7-Bromo-4,6-dimethoxybenzofuran-5-yl)-1,4-dihydro-
quinoxaline (5a, C18H15BrN2O3)
The compound was obtained from the reaction of 3.78 g 4a
(10 mmol) and 1.08 g o-phenylenediamine (10 mmol), as a
brownish crystals, crystallized from toluene (72%). M.p.:
[350 °C; IR (KBr): vꢀ = 3415 broad (2NH), 3055 (CH-
aryl), 2960 (CH-aliph) cm-1
;
1H NMR (DMSO-d6):
d = 3.86 (s, 3H, OCH3), 3.88 (s, 3H, OCH3), 5.81 (d,
1H, CH, pyrazine), 7.03 (d, 1H, J = 2.35 Hz, furan), 7.16
(d, 1H, J = 2.34 Hz, furan), 7.55–7.76 (m, 4H, phenyl),
8.35 (br, NH, D2O exchangeable), 9.25 (br, NH, D2O
exchangeable) ppm; 13C NMR (DMSO-d6): d = 61.6,
62.4, 85.1, 99.3, 103.4, 106.2, 111.5, 117.3, 119.5, 119.8,
120.2, 122.5, 131.1, 131.4, 146.1, 150.6, 157.2, 160.1 ppm;
MS (70 eV): m/z = 387 (M?, 90%).
1,4-Dimethyl-2-(4,6,7-trimethoxybenzofuran-5-yl)-1,4-di-
hydroquinoxaline (6b, C21H22N2O4)
The compound was obtained from the reaction of 3.38 g 5b
(0.01 mol) and methyl iodide (20 mmol), as a yellowish
crystals, crystallized from hexane (64%). M.p.: [350 °C;
1
IR (KBr): vꢀ = 3050 (CH-aryl), 2952 (CH-aliph) cm-1; H
NMR (DMSO-d6): d = 3.31 (s, 3H, CH3), 3.35 (s, 3H,
CH3), 3.80 (s, 3H, OCH3), 3.84 (s, 3H, OCH3), 3.91 (s, 3H,
OCH3), 5.61 (d, 1H, CH, pyrazine), 7.02 (d, 1H,
J = 2.35 Hz, furan), 7.26 (d, 1H, J = 2.34 Hz, furan),
7.45–7.58 (m, 4H, phenyl) ppm; 13C NMR (DMSO-d6):
d = 35.1, 46.2, 61.6, 61.8, 62.1, 98.6, 102.2, 106.3, 111.7,
117.5, 117.7, 118.6, 118.8, 122.4, 129.5, 129.6, 134.6,
142.2, 143.8, 144.3, 146.3 ppm; MS (70 eV): m/z = 366
(M?, 82%).
2-(4,6,7-Trimethoxybenzofuran-5-yl)-1,4-dihydroquinoxa-
line (5b, C19H18N2O4)
The compound was obtained from the reaction of 3.29 g 4b
(10 mmol) and 1.08 g o-phenylenediamine (10 mmol), as a
brown crystals, crystallized from benzene (67%). M.p.:
[350 °C; IR (KBr): vꢀ = 3418 broad (2NH), 3058 (CH-
aryl), 2965 (CH-aliph) cm-1
;
1H NMR (DMSO-d6):
d = 3.89 (s, 3H, OCH3), 3.91 (s, 3H, OCH3), 3.95 (s,
3H, OCH3), 5.83 (d, 1H, CH, pyrazine), 7.01 (d, 1H,
J = 2.31 Hz, furan), 7.12 (d, 1H, J = 2.32 Hz, furan),
7.63–7.80 (m, 4H, phenyl), 8.23 (br, NH, D2O exchange-
able), 9.16 (br, NH, D2O exchangeable) ppm; 13C NMR
(DMSO-d6): d = 61.8, 61.9, 97.3, 100.5, 115.5, 115.6,
115.8, 116.7, 123.9, 126.4, 129.9, 131.9, 132.5, 132.9,
135.3, 141.9, 148.8, 155.1 ppm; MS (70 eV): m/z = 338
(M?, 92%).
1-[1-(6-Hydroxy-4-methoxy- or 4,7-dimethoxybenzofuran-
5-yl)ethylidene]thiourea (7a, 7b)
Following reported procedures with slight modification
[24]. A solution of visnaginone 2.06 g (2a, 0.01 mol) or
2.36 g khellinone (2b, 0.01 mol) and 0.76 g thiourea
(10 mmol) in 40 cm3 glacial acetic acid the mixture was
refluxed for 3–5 h After cooling the solid mass was
collected by filtration, washed with water, dried, and
recrystallized from appropriate solvent to give compounds
7a and 7b, respectively.
2-(7-Bromo-4,6-dimethoxy- or 4,6,7-trimethoxybenzofu-
ran-5-yl)-1,4-dimethyl-1,4-dihydroquinoxaline (6a, 6b)
To a warmed ethanolic potassium hydroxide solution
(prepared by dissolving 0.56 g of potassium hydroxide
(10 mmol) in 45 cm3 ethanol), 3.87 g 5a (0.01 mol) or
3.38 g 5b (0.01 mol) was added and heating was continued
for 30 min. The mixture was allowed to cool to room
temperature, and methyl iodide (20 mmol) was added. The
mixture was stirred under reflux for 5–7 h and then allowed
1-[1-(6-Hydroxy-4-methoxybenzofuran-5-yl)ethyli-
dene]thiourea (7a, C12H12N2O3S)
The compound was obtained from the reaction of 2.06 g
visnaginone (2a, 10 mmol) and 0.76 g thiourea (10 mmol),
as a yellow crystals, crystallized from methanol (75%).
M.p.: 186–188 °C; IR (KBr): vꢀ = 3400–3200 (br. NH2,
OH), 3045 (CH-aryl), 2955 (CH-aliph), 1618 (C = N),
123

A. A. Abu-Hashem, M. El-Shazly
1
1355 (C = S) cm-1; H NMR (DMSO-d6): d = 1.68 (s,
1622 (C=N), 1357 (C=S) cm-1 1H NMR (DMSO-d6):
;
3H, CH3), 3.83 (s, 3H, OCH3), 6.34 (s, 1H, H-7), 6.68 (s,
2H, NH2), 7.04 (d, 1H, J = 2.32 Hz, furan), 7.33 (d, 1H,
J = 2.31 Hz, furan), 12.46 (brs, OH D2O exchangeable)
ppm; 13C NMR (DMSO-d6): d = 18.2 (1C, CH3), 61.6
(1C, OCH3), 95.4 (1C, C7), 99.1, 106.2, 109.8, 146.1,
151.3, 155.2, 160.4 (Ar–C), 164.5 (1C, C=N), 191.6 (1C,
C=S) ppm; MS (70 eV): m/z = 264 (M?, 100%).
d = 1.90 (s, 3H, CH3), 3.83 (s, 3H, OCH3), 3.84 (s, 3H,
OCH3), 7.11 (d, 1H, J = 2.36 Hz, furan), 7.36 (d, 1H,
J = 2.37 Hz, furan), 10.88 (brs, NH D2O exchangeable)
ppm; 13C NMR (DMSO-d6): d = 23.2 (1C, CH3), 56.5
(1C, OCH3), 61.6 (1C, OCH3), 106.3, 109.7, 115.9, 122.8,
134.6, 146.1, 146.4, 150.2 (Ar–C), 164.5 (1C, C=N), 180.3
(1C, C=S) ppm; MS (70 eV): m/z = 276 (M?, 42%).
1-[1-(6-Hydroxy-4,7-dimethoxybenzofuran-5-yl)ethyli-
dene]thiourea (7b, C13H14N2O4S)
1-[1-[4-Methoxy- or 4,7-dimethoxy-6-(piperazin-1-yl)ben-
zofuran-5-yl]ethylidene]thiourea (9a, 9b)
The compound was obtained from the reaction of 2.36 g,
khellinone (2b, 0.01 mol) and 0.76 g thiourea (10 mmol),
as a yellowish crystals, crystallized from ethanol (70%).
M.p.: 200–202 °C; IR (KBr): vꢀ = 3405–3210 (br. NH2,
OH), 3048 (CH-aryl), 2956 (CH-aliph), 1615 (C=N), 1354
(C=S) cm-1; 1H NMR (DMSO-d6): d = 1.92 (s, 3H, CH3),
3.80 (s, 3H, OCH3), 3.84 (s, 3H, OCH3), 6.74 (s, 2H, NH2),
7.05 (d, 1H, J = 2.37 Hz, furan), 7.32 (d, 1H,
J = 2.38 Hz, furan), 12.55 (brs, OH D2O exchangeable)
ppm; 13C NMR (DMSO-d6): d = 18.4 (1C, CH3), 61.7
(1C, OCH3), 61.8 (1C, OCH3), 99.8, 106.3, 112.4, 129.5,
146.2, 147.5, 152.3, 154.1 (Ar–C), 164.7 (1C, C=N), 191.8
(1C, C=S) ppm; MS (70 eV): m/z = 294 (M?, 100%).
Freshly distilled piperazine (0.9 cm3, 10 mmol) was added
to a warm solution of 2.64 g 7a (10 mmol) or 2.94 g 7b
(10 mmol) in 45 cm3 glacial acetic acid. The reaction
mixture was stirred under reflux for 4 h, then allowed to
cool to 0 °C for 5 h, and the solid obtained was filtered,
washed with 100 cm3 water, dried, and recrystallized from
appropriate solvent to produce 9a, 9b.
1-[1-[4-Methoxy-6-(piperazin-1-yl)benzofuran-5-yl]ethyl-
ene]thiourea (9a, C16H20N4O2S)
Compound 9a was obtained from the reaction of 2.64 g 7a
(10 mmol) and 0.9 cm3 piperazine (10 mmol), as a yellow
crystals, crystallized from n-hexane (62%). M.p.: 212–
214 °C; IR (KBr): vꢀ = 3360–3200 (br. NH, NH2), 3050
(CH-aryl), 2960 (CH-aliph), 1617 (C=N), 1352 (C=S)
5-Methoxy-
or
5,9-dimethoxy-4-methylfuro[2,3-
b]benzo[50,60-e]pyrimidine-2(1H)-thione (8a, 8b)
A solution of 2.64 g 7a (0.01 mol) or 2.94 g 7b (0.01 mol)
in 40 cm3 DMF was refluxed for 10–12 h. The product
formed was filtered off, washed with ethanol, dried, and
recrystallized from appropriate solvent to give compounds
8a or 8b.
cm-1 1H NMR (DMSO-d6): d = 1.82 (s, 3H, CH3),
;
2.79–2.87 (m, 8H, piperazine), 3.85 (s, 3H, OCH3), 6.80 (s,
2H, NH2), 7.08 (d, 1H, J = 2.34 Hz, furan), 7.35 (d, 1H,
J = 2.32 Hz, furan), 8.01 (s, 1H, CHphenyl), 9.55 (brs, NH
D2O exchangeable) ppm; 13C NMR (DMSO-d6): d = 21.2
(1C, CH3), 46.5 (2C, 2CH2, piperazine), 51.7 (2C, 2CH2,
piperazine), 61.5 (1C, OCH3), 88.2 (1C, CH phenyl), 96.4,
107.2, 107.6, 137.4, 140.5, 148.5, 152.8 (Ar–C),160.5 (1C,
C=N), 190.8 (1C, C=S) ppm; MS (70 eV): m/z = 334
([M?2]?, 76%), 333 ([M?1]?, 25%), 332 (M?, 73%).
5-Methoxy-4-methylfuro[2,3-b]benzo[50,60-e]pyrimidine-
2(1H)-thione (8a, C12H10N2O2S)
The compound was obtained from the reaction of 2.64 g 7a
(0.01 mol) and 40 cm3 DMF, as a pale yellow crystals,
crystallized from benzene (70%). M.p.: 288–290 °C; IR
(KBr): vꢀ = 3250 (NH), 3040 (CH-aryl), 2951 (CH-aliph),
1-[1-[4,7-Dimethoxy-6-(piperazin-1-yl)benzofuran-5-
yl]ethylidene]thiourea (9b, C17H22N4O3S)
1620 (C=N), 1360 (C=S) cm-1
;
1H NMR (DMSO-d6):
Compound 9b was obtained from the reaction of 2.94 g 7b
(10 mmol) and 0.9 cm3 piperazine (10 mmol), as a
yellowish crystals, crystallized from toluene (64%). M.p.:
232–234 °C; IR (KBr): vꢀ = 3365–3205 (br. NH, NH2),
3052 (CH-aryl), 2961 (CH-aliph), 1616 (C=N), 1351 (C=S)
d = 1.92 (s, 3H, CH3), 3.82 (s, 3H, OCH3), 7.10 (d, 1H,
J = 2.39 Hz, furan), 7.35 (d, 1H, J = 2.38 Hz, furan), 8.05
(s, 1H, CHphenyl), 10.85 (brs, NH D2O exchangeable) ppm;
13C NMR (DMSO-d6): d = 23.5 (1C, CH3), 61.7 (1C,
OCH3), 99.9 (1C, CHphenyl), 106.1, 108.5, 113.5, 137.2,
146.2, 154.1, 160.3, (Ar–C),164.7 (1C, C=N), 180.5 (1C,
C=S) ppm; MS (70 eV): m/z = 246 (M?, 100%).
cm-1 1H NMR (DMSO-d6): d = 1.84 (s, 3H, CH3),
;
2.80–2.88 (m, 8H, piperazine), 3.80 (s, 3H, OCH3), 3.82 (s,
3H, OCH3), 6.84 (s, 2H, NH2), 7.12 (d, 1H, J = 2.30 Hz,
furan), 7.44 (d, 1H, J = 2.31 Hz, furan), 9.60 (brs, NH
D2O exchangeable) ppm; 13C NMR (DMSO-d6): d = 21.3
(1C, CH3), 46.9 (2C, 2CH2, piperazine), 51.9 (2C, 2CH2,
piperazine), 54.4 (1C, OCH3), 61.8 (1C, OCH3), 100.5,
108.4, 108.9, 125.8, 129.8, 144.5, 146.6,146.9 (Ar–C),
154.5 (1C, C=N), 192.3 (1C, C=S) ppm; MS (70 eV): m/
z = 362 (M?, 95%).
5,9-Dimethoxy-4-methylfuro[2,3-b]benzo[50,60-e]pyrim-
idine-2(1H)-thione (8b, C13H12N2O3S)
The compound was obtained from the reaction of 2.94 g 7b
(0.01 mol) and 40 cm3 DMF, as a yellowish crystals,
crystallized from methanol (72%). M.p.: 328–330 °C; IR
(KBr): vꢀ = 3255 (NH), 3042 (CH-aryl), 2954 (CH-aliph),
123

Synthesis of new quinoxaline, pyrimidine, and pyrazole furochromone derivatives as cytotoxic…
2-[Amino-[[1-[4-methoxy- or 4,7-dimethoxy-6-(piperazin-
1-yl)benzofuran-5-yl]ethylidene]amino]methylene]-
malononitrile (10a, 10b)
absolute ethanol was refluxed for 4 h and then left to cool.
The precipitate formed was filtered off, dried, and crystal-
lized from the proper solvent to give 11a or 11b [27, 29].
A solution of 3.32 g 9a (10 mmol) or 3.62 g 9b (10 mmol)
in 35 cm3 ethanol was treated with 0.66 g malononitrite
(10 mmol) and 1 cm3 triethylamine was added. The
reaction mixture was refluxed for 4 h and then evaporated
in vacuo. The solid product was collected by filtration and
crystallized from appropriate solvent to produce 10a, 10b.
4-Methoxy-3-methyl-1-phenyl-1H-furo[3,2-f]indazole
(11a, C17H14N2O2)
Compound 11a was obtained from the reaction of 2.06 g
visnaginone (2a, 10 mmol) and 1.08 cm3 phenylhydrazine
(10 mmol) as a yellowish powder, crystallized from
dioxane (75%). M.p.: 220–222 °C; IR (KBr): vꢀ = 3032
1
2-[Amino-[[1-[4-methoxy-6-(piperazin-1-yl)benzofuran-5-
yl]ethylidene]amino]methylene]malononitrile
(CH-aryl), 2948 (CH-aliph) cm-1; H NMR (DMSO-d6):
d = 2.81 (s, 3H, CH3), 3.82 (s, 3H, OCH3), 7.11 (d, 1H,
J = 2.30 Hz, furan), 7.15 (d, 1H, J = 2.30 Hz, furan),
7.46–7.97 (m, 5H, phenyl), 8.12 (s, 1H, H-8) ppm; 13C
NMR (DMSO-d6): d = 15.5, 61.7, 100.1, 108.3, 108.9,
118.2, 124.5, 125.6, 126.3, 129.2, 139.5, 145.7, 146.1,
155.3, 157.8 ppm; MS (70 eV): m/z = 278 (M?, 95%).
(10a, C19H20N6O2)
Compound 10a was obtained from the reaction of 3.32 g
9a (10 mmol) and 0.66 g malononitrite (10 mmol), as a
brownish crystals, crystallized from methanol (60%). M.p.:
165–167 °C; IR (KBr): vꢀ = 3355–3220 (br. NH, NH2),
3056 (CH-aryl), 2958 (CH-aliph), 2210, 2205 (2CN), 1619
(C=N) cm-1; 1H NMR (DMSO-d6): d = 1.86 (s, 3H, CH3),
2.83–2.97 (m, 8H, piperazine), 4.09 (s, 3H, OCH3), 6.28 (s,
2H, NH2), 7.28 (d, 1H, J = 2.35 Hz, furan), 7.39 (d, 1H,
J = 2.36 Hz, furan), 8.01 (s, 1H, CHphenyl), 9.32 (brs, NH
D2O exchangeable) ppm; 13C NMR (DMSO-d6): d = 18.6
(1C, CH3), 45.7 (2C, 2CH2, piperazine), 51.4 (2C, 2CH2,
piperazine), 52.1 (1C, C(CN)2), 61.8 (1C, OCH3), 88.4
(1C, CHphenyl), 96.2, 106.1, 107.2, 113.5, 142.3, 146.2,
154.7, 160.9 (Ar–C),164.8 (1C, C=N), 186.5 (1C, C–NH2)
ppm; MS (70 eV): m/z = 364 (M?, 82%).
4,8-Dimethoxy-3-methyl-1-phenyl-1H-furo[3,2-f]indazole
(11b, C18H16N2 O3)
The compound was obtained from the reaction of 2.36 g
khellinone (2b, 10 mmol) and 1.08 cm3 phenylhydrazine
(10 mmol) as a white powder, crystallized from n-hexane
(76%). M.p.: 255–257 °C; IR (KBr): vꢀ = 3035 (CH-aryl),
2944 (CH-aliph) cm-1; 1H NMR (DMSO-d6): d = 2.88 (s,
3H, CH3), 3.83 (s, 3H, OCH3), 4.09 (s, 3H, OCH3), 7.12 (d,
1H, J = 2.30 Hz, furan), 7.25 (d, 1H, J = 2.30 Hz, furan),
7.55–7.98 (m, 5H, phenyl) ppm; 13C NMR (DMSO-d6):
d = 15.9, 61.5, 108.4, 108.9, 112.5, 118.8, 124.6, 126.5,
129.7, 137.8, 139.9, 145.8, 146.3, 147.2, 147.8 ppm; MS
(70 eV): m/z = 309 ([M?1]?, 16%), 308 (M?, 13%), 307
([M-1]?, 38%).
2-[Amino-[[1-[4,7-dimethoxy-6-(piperazin-1-yl)benzofu-
ran-5-yl]ethylidene]amino]methylene]malononitrile
(10b, C20H22N6O3)
Compound 10b was obtained from the reaction of 3.62 g
9b (10 mmol) and 0.66 g malononitrite (10 mmol), as a
brown crystals, crystallized from dioxane (61%). M.p.:
176–178 °C; IR (KBr): vꢀ = 3352–3222 (br. NH, NH2),
3054 (CH-aryl), 2956 (CH-aliph), 2212, 2208 (2CN), 1617
(C=N) cm-1; 1H NMR (DMSO-d6): d = 1.82 (s, 3H, CH3),
2.82–2.95 (m, 8H, piperazine), 3.84 (s, 3H, OCH3), 3.85 (s,
3H, OCH3), 6.42 (s, 2H, NH2), 7.18 (d, 1H, J = 2.34 Hz,
furan), 7.44 (d, 1H, J = 2.33 Hz, furan), 9.55 (brs, NH
D2O exchangeable) ppm; 13C NMR (DMSO-d6): d = 18.5
(1C, CH3), 45.5 (2C, 2CH2, piperazine), 51.6 (2C, 2CH2,
piperazine), 52.2 (1C, C(CN)2), 56.4 (1C, OCH3), 61.7
(1C, OCH3), 97.5, 106.3, 109.5, 113.8,122.5, 127.9, 146.1,
146.9, 150.5 (Ar–C), 164.7 (1C, C=N), 186.8 (1C, C–NH2)
ppm; MS (70 eV): m/z = 395 ([M?1]?, 10%), 394 (M?,
12%).
4-Methoxy-3-methyl-1H-furo[3,2-f]indazole (12a) or 4,8-
dimethoxy-3-methyl-1H-furo[3,2-f]indazole (12b)
A mixture of 2.06 g 2a (10 mmol) or 2.36 g 2b (10 mmol)
and 0.5 cm3 hydrazine monohydrate (NH2NH2.H2O,
0.01 mol) in 40 cm3 absolute ethanol was heated at reflux
for 4 h and then left to cool. The precipitate formed was
filtered off, dried, and crystallized from the proper solvent
to give 12a or 12b.
4-Methoxy-3-methyl-1H-furo[3,2-f]indazole
(12a, C11H10N2O2)
The compound was obtained from the reaction of 2.06 g
visnaginone (2a, (10 mmol) and 0.5 cm3 NH2NH2.H2O
(0.01 mol) as a yellow powder, crystallized from methanol
(78%). M.p.: 278–280 °C; IR (KBr): vꢀ = 3320 (NH),
1
3032(CH-aryl), 2942 (CH-aliph) cm-1; H NMR (DMSO-
d6): d = 2.11 (s, 3H, CH3), 3.73 (s, 3H, OCH3), 7.10 (d,
1H, J = 2.30 Hz, furan), 7.24 (d, 1H, J = 2.30 Hz, furan),
8.15 (s, 1H, H-8), 9.04 (br, 1H, NH, D2O exchangeable)
ppm; 13C NMR (DMSO-d6): d = 15.6, 61.8, 101.2, 108.4,
108.8, 117.3, 125.7, 138.5, 146.4, 155.2, 157.6 ppm; MS
(70 eV): m/z = 202 (M?, 92%).
4-Methoxy-3-methyl-1-phenyl-1H-furo[3,2-f]indazole
(11a) or 4,8-dimethoxy-3-methyl-1-phenyl-1H-furo[3,2-
f]indazole (11b)
A mixture of 2.06 g 2a (0.01 mol) or 2.36 g 2b (0.01 mol)
and 1.08 cm3 phenylhydrazine (10 mmol) in 40 cm3
123

A. A. Abu-Hashem, M. El-Shazly
4,8-Dimethoxy-3-methyl-1H-furo[3,2-f]indazole
(12b, C12H12N2O3)
1780 (C=O) cm-1; 1H NMR (DMSO-d6): d = 2.28 (s, 3H,
COH3), 2.33 (s, 3H, CH3), 3.84 (s, 3H, OCH3), 3.98 (s, 3H,
OCH3), 7.13 (d, 1H, J = 2.30 Hz, furan), 7.38 (d, 1H,
J = 2.30 Hz, furan) ppm; 13C NMR (DMSO-d6):
d = 19.7, 23.3, 55.6, 58.4, 108.4, 108.9, 117.7, 120.02,
132.9, 135.4, 141.9, 148.9, 155.03, 167.6 ppm; MS
(70 eV): m/z = 275 ([M?1]?, 10%), 274 (M?, 74%),
273 ([M-1]?, 100%).
The compound was obtained from the reaction of 2.36 g
khellinone (2b, (10 mmol) and 0.5 cm3 hydrazine mono-
hydrate (0.01 mol) as a brown powder, crystallized from
acetone (75%). M.p.: 298–300 °C; IR (KBr): vꢀ = 3335
(NH), 3030 (CH-aryl), 2936 (CH-aliph) cm-1; H NMR
1
(DMSO-d6): d = 2.14 (s, 3H, CH3), 3.80 (s, 3H, OCH3),
4.08 (s, 3H, OCH3), 7.09 (d, 1H, J = 2.30 Hz, furan), 7.27
(d, 1H, J = 2.30 Hz, furan), 9.08 (br, 1H, NH, D2O
exchangeable) ppm; 13C NMR (DMSO-d6): d = 15.8,
61.6, 108.2, 108.7, 111.4, 118.2, 137.8, 138.5, 146.5,
147.1, 147.8 ppm; MS (70 eV): m/z = 232 (M?, 96%).
4-Methoxy-1,3-dimethyl-1H-furo[3,2-f]indazole
(14a, C12H12N2O2)
The compound was obtained from the reaction of 2.02 g
12a (10 mmol) and 0.7 cm3 methyl iodide (0.01 mol) as a
yellow powder, crystallized from n-hexane (78%). M.p.:
338–340 °C; IR (KBr): vꢀ = 3046 (CH-aryl), 2942 (CH-
aliph) cm-1; 1H NMR (DMSO-d6): d = 2.17 (s, 3H, CH3),
3.82 (s, 3H, OCH3), 4.02 (s, 3H, CH3), 7.04 (d, 1H,
J = 2.30 Hz, furan), 7.33 (d, 1H, J = 2.30 Hz, furan), 8.02
(s, 1H, H-8) ppm; 13C NMR (DMSO-d6): d = 15.5, 42.1,
61.7, 100.2, 108.1, 108.5, 116.6, 125.4, 143.4, 146.3,
155.1, 157.4 ppm; MS (70 eV): m/z = 216 (M?, 88%).
1-(4-Methoxy-3-methyl-1H-furo[3,2-f]indazol-1-yl)ethan-
1-one (13a), 1-(4,8-dimethoxy-3-methyl-1H-furo[3,2-f]in-
dazol-1-yl)ethan-1-one (13b), 4-methoxy-1,3-dimethyl-1H-
furo[3,2-f]indazole (14a), or 4,8-dimethoxy-1,3-dimethyl-
1H-furo[3,2-f]indazole (14b)
To a warm (50–70 °C) solution of sodium ethoxide
(prepared by dissolving 0.23 g of sodium metal in
30 cm3 ethanol), 2.02 g 12a (10 mmol) or 2.32 g 12b
(10 mmol) was added and heating (50–70 °C) was contin-
ued for 30 min. The mixture was allowed to cool to room
temperature and acetic anhydride or methyl iodide
(10 mmol) was added. The mixture was stirred under
reflux for 6–8 h, allowed to cool to room temperature and
finally poured into 100 cm3 cold water. The solid product
precipitated was filtered off and washed with 100 cm3
water. The solid obtained was filtered off, dried, and
crystallized from the proper solvent to give 13a, 13b, 14a,
and 14b.
4, 8-Dimethoxy-1,3-dimethyl-1H-furo[3,2-f]indazole
(14b, C13H14N2O3)
The compound was obtained from the reaction of 2.32 g
12b (10 mmol) and 0.7 cm3 methyl iodide (0.01 mol) as a
yellowish powder, crystallized from ethanol (76%). M.p.:
348–350 °C; IR (KBr): vꢀ = 3044 (CH-aryl), 2928 (CH-
aliph) cm-1; 1H NMR (DMSO-d6): d = 2.18 (s, 3H, CH3),
3.85 (s, 3H, OCH3), 4.04 (s, 3H, CH3), 4.15 (s, 3H, OCH3),
7.03 (d, 1H, J = 2.30 Hz, furan), 7.35 (d, 1H,
J = 2.30 Hz, furan) ppm; 13C NMR (DMSO-d6):
d = 15.8, 43.60, 61.6, 108.2, 108.6, 111.4, 118.1, 137.5,
143.2, 146.4, 147.2, 147.8 ppm; MS (70 eV): m/z = 246
(M?, 79%).
1-(4-Methoxy-3-methyl-1H-furo[3,2-f]indazol-1-yl)ethan-
1-one (13a, C13H12N2O3)
The compound was obtained from the reaction of 2.02 g
12a (10 mmol) and 1 cm3 acetic anhydride (0.01 mol), as a
white powder, crystallized from dioxane (82%). M.p.: 308–
310 °C; IR (KBr): vꢀ = 3030 (CH-aryl), 2938 (CH-aliph),
1785 (C=O) cm-1; 1H NMR (DMSO-d6): d = 2.29 (s, 3H,
COH3), 2.32 (s, 3H, CH3), 3.82 (s, 3H, OCH3), 7.09 (d, 1H,
J = 2.30 Hz, furan), 7.39 (d, 1H, J = 2.30 Hz, furan), 8.17
(s, 1H, H-8) ppm; 13C NMR (DMSO-d6): d = 15.9, 22.4,
61.5, 100.8, 108.1, 108.6, 117.4, 126.1, 138.3, 146.2,
155.2, 157.4, 170.9 ppm; MS (70 eV): m/z = 245
([M?1]?, 4%), 244 (M?, 8%), 243 ([M-1]?, 35%), 242
([M-2]?, 100%).
Ehrlich cells
Ehrlich cells (Ehrlich ascites carcinoma, EAC) were derived
from ascetic fluid from diseased mice (the cells were pur-
chased from the National Cancer institute, Cairo, Egypt).
Cytotoxic activity using Ehrlich ascites in vitro assay
Different concentrations of the tested compounds were
prepared (100, 50 and 25 g/cm3 DMSO). Ascites fluid from
the peritoneal cavity of the donor animal (contains Ehrlich
cells) was aseptically aspirated. The cells were grown
partly floating and partly attached in a suspension culture in
RPMI 1640 medium, supplemented with 10% fetal bovine
serum. They were maintained at 37 °C in a humidified
atmosphere with 5% CO2 for 2 h. The viability of the cells
was determined by the microscopical examination using a
1-(4,8-Dimethoxy-3-methyl-1H-furo[3,2-f]indazol-1-yl)e-
than-1-one (13b, C14H14N2O4)
The compound was obtained from the reaction of 2.32 g
12b (10 mmol) and 1 cm3 acetic anhydride (0.01 mol) as a
white powder, crystallized from dioxane (82%). M.p.: 318–
320 °C; IR (KBr): vꢀ = 3035 (CH-aryl), 2936 (CH-aliph),
123

Synthesis of new quinoxaline, pyrimidine, and pyrazole furochromone derivatives as cytotoxic…
15. Kumar S, Bawa S, Drabu S, Kumar R, Gupta H (2009) Recent Pat
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16. Karthikeyan MS, Holla BS, Kumari NS (2007) Eur J Med Chem
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hemocytometer and using trypan blue stain (stains only the
dead cells) [32].
Acknowledgement The authors would like to thank Prof. Dr. Farid
Abd-Elraheem Badria (Department of Pharmacognosy, Faculty of
Pharmacy and Mansoura University 35516, Egypt) for carrying out
the biological activity tests. The presented work was supported by the
Department of Photochemistry (Heterocyclic unit); Chemical Indus-
tries Research Division, National Research Centre in Cairo, Egypt.
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