Synthesis and antiproliferative activity of some dihydro-1 H-furo[2,3-c]pyrazole-Flavone hybrids

Article abstract of DOI:10.14233/ajchem.2017.20550

A new series of dihydro-1 H-furo[2,3-c]pyrazole-flavone hybrids were synthesized from one-pot four-component reaction of β-keto ester (1), hydrazine (2),7-hydroxy 8-formyl flavones (3), pyridiniumylide (4) in presence of NEt₃ as catalyst under ethanol reflux conditions and their antiproliferative properties were evaluated against human cancer cell lines, namely, laryngeal carcinoma (Hep2), lung adenocarcinoma (A549) and cervical cancer (HeLa). The best among them, furo[2,3-c]pyrazole-flavone with C4′-methoxy substitution was selected for further structure activity relationship (SAR) studies. Among the derivatives, (4S,5S)-ethyl 4-(7-hydroxy-5-methoxy-4-oxo-2-(2,4,6-trimethoxyphenyl)-4H-chromen-8-yl)-3-methyl-4,5-dihydro-1 H-furo[2,3-c]pyrazole-5-carboxylate (8r) showed most potent cytotoxic activity against all three cancer cell lines. Toxicity studies revealed that the dihydro-1H-furo[2,3-c]pyrazole-flavones are specifically target the cancer cell lines.

Full text of DOI:10.14233/ajchem.2017.20550

Asian Journal of Chemistry; Vol. 29, No. 7 (2017), 1525-1532
ASIAN JOURNAL OF CHEMISTRY
https://doi.org/10.14233/ajchem.2017.20550
Synthesis and Antiproliferative Activity of Some Dihydro-1H-furo[2,3-c]pyrazole-Flavone Hybrids
3
1
4
VENKATA SWAMY TANGETI1,2,*, D. VASUNDHARA , K.V.V.V. SATYANARAYANA and KAJA SRINIVAS PAVAN KUMAR
1Department of Chemistry, Raghu Engineering College, Visakhapatnam-531 162, India
2Vector Control Research Center (ICMR), Puducherry-605 006, India
3Department of Chemistry, Raghu Institute of Technology, Visakhapatnam-531 162, India
4GVK Biosciences Pvt. Ltd., Nacharam, Hyderabad-500 076, India
*Corresponding author: E-mail: swamychempcu@gmail.com
Received: 29 January 2017;
Accepted: 21 March 2017;
Published online: 13 May 2017;
AJC-18387
A new series of dihydro-1H-furo[2,3-c]pyrazole-flavone hybrids were synthesized from one-pot four-component reaction of β-keto ester
(1), hydrazine (2),7-hydroxy 8-formyl flavones (3), pyridiniumylide (4) in presence of NEt3 as catalyst under ethanol reflux conditions
and their antiproliferative properties were evaluated against human cancer cell lines, namely, laryngeal carcinoma (Hep2), lung
adenocarcinoma (A549) and cervical cancer (HeLa). The best among them, furo[2,3-c]pyrazole-flavone with C4'-methoxy substitution
was selected for further structure activity relationship (SAR) studies. Among the derivatives, (4S,5S)-ethyl 4-(7-hydroxy-5-methoxy-4-
oxo-2-(2,4,6-trimethoxyphenyl)-4H-chromen-8-yl)-3-methyl-4,5-dihydro-1H-furo[2,3-c]pyrazole-5-carboxylate (8r) showed most potent
cytotoxic activity against all three cancer cell lines. Toxicity studies revealed that the dihydro-1H-furo[2,3-c]pyrazole-flavones are specifically
target the cancer cell lines.
Keywords: Furo[2,3-c]pyrazole-flavone hybrids, Pyridiniumylide, 7-Hydroxy 8-formyl flavone, Antiproliferative.
ylide utilizing microwave irradiation under solvent-free
conditions. Schlager et al. [34] reported that spiro cyclicfuro-
pyrazoles acts as σ-receptor ligands. Chavan et al. [35] reported
anti-inflammatory activity of pyrazole amalgamated flavones.
Now we are contemplated to synthesize furopyrazole-flavone
hybrids by in incorporating furopyrazole on 7-hydroxy flavone
by employing our newly developed methodology and in order
to study their biological activity. Such hybrid molecules represent
both 3-furopyrazoles and flavones characteristics. Moreover,
furopyrazole-flavone hybrids, target molecules of present study
are not known.
INTRODUCTION
Flavones are widely distributed heterocyclic natural
products with varied biological activities [1]. In technological
and medicinal fields, flavones, find extensive uses [2]. Flavones,
particularly those with several phenolic hydroxyl groups are
used as antioxidants. Flavopyridol, demifin, flavone-c-glycoside,
cannflavin, mitoflaxone, flavoxate are some of the commer-
cially available flavone drugs [3-10]. Several reports are avail-
able for antiprolifirative activity of natural and synthetic flavones
[11-26]. The ability to manipulate flavone activity through
structural variation motivates research on the synthesis of flava-
none derivatives and evaluation of their bioactivity. Beutler et
al. [27] reported results of a comparative cytotoxicity screening
and subsequent tubulin polymerization studies carried out with
a series of 79 natural and synthetic flavones. Maximum potencies
for cytotoxicity and tubulin interaction were found only with
compounds bearing an OMe group at C-5 on the A-ring, 3'-
hydroxy-4'-methoxy groups on the B-ring and an OCH3 at
C-3 on the C-ring [28]. In the continuous efforts towards the
synthesis of different biologically active heterocyclic mole-
cules [29-32] in our laboratory recently we have developed a
new methodology for synthesis of biologically active dihydro-
1H-furo[2,3-c]-pyrazole flavones from four-component reaction
of β-keto ester, hydrazine, aromatic aldehydes, pyridinium
EXPERIMENTAL
The progression of all the reactions were monitored by
TLC using hexanes (60-80 °C boiling mixture)/ethyl acetate
mixture as eluent. Column chromatography was carried on
silica gel (100-200 mesh, SRL chemicals) using increasing
percentage of ethyl acetate in hexanes. 1H NMR spectra (400
MHz) and 13C NMR (100 MHz) and DEPT-135 spectra were
recorded for CDCl3 solutions on a Bruker-400 spectrometer
with tetramethylsilane (TMS) as internal standard; J-values
are in Hz. Number of hydrogens attached to each carbon was
determined from DEPT spectra and are given next to the
corresponding 13C NMR spectral data. IR spectra were recorded
as KBr pellets on a Nicolet-6700 spectrometer. Melting points

1526 Tangeti et al.
Asian J. Chem.
were recorded using open-ended capillary tubes on VEEGO
VMP-DS instrument. High resolution mass spectra were
recorded on a Waters Micromass Q-TOF micro mass spectro-
meter using electron spray ionization mode. Organic solvents
were distilled and dried before use.
c]pyrazole-5-carboxylate (8c): Light yellow colour solid,
m.p.: 141.4 °C, IR (KBr, νmax, cm–1): 3315, 3205, 3075, 2987,
1746, 1681, 1649, 1490, 1422, 1350, 1335, 1203, 1123, 1102,
1089, 1043, 996, 885, 842, 765; 1H NMR (400 MHz, CDCl3)
δ 12.16 (s, 1H), 8.27 (d, J = 8.4 Hz, 1H), 7.61 (d, J = 7.8 Hz,
2H), 7.44 (d, J = 8.8 Hz, 1H), 7.05 (d, J = 7.8 Hz, 2H), 6.79
(s, 1H), 6.09 (br s, 1H), 5.29 (d, J = 4.6 Hz, 1H), 5.16 (d, J =
4.6 Hz, 1H), 4.16 (q, J = 6.6 Hz, 2H), 1.91 (s, 3H), 0.95 (t, J
= 7.4 Hz, 3H) ppm; 13C NMR (100 MHz, CDCl3) δ191.0,
175.3, 166.8, 163.3, 161.4, 157.6, 139.2, 133.7, 129.4, 126.7,
124.6,123.3, 121.7, 118.6, 117.3, 112.3, 105.1, 88.0, 62.7,
26.7, 14.2, 12.3 ppm; HRMS (ESI, m/z) 533.0319 calcd. for
C24H19N2O6Br (M+Na) found 533.0317; Anal. calcd. for
C24H19N2O6Br; C, 56.37; H, 3.75; Br, 15.63; N, 5.48; Found;
C, 56.36; H, 3.74; N, 5.46.
General procedure for synthesis of dihydro-1H-furo[2,3-
c]pyrazole-flavone hybrids (8a-r)
(4R,5R)-Ethyl 4-(7-hydroxy-4-oxo-2-phenyl-4H-
chromen-8-yl)-3-methyl-4,5-dihydro-1H-furo[2,3-
c]pyrazole-5-carboxylate (8a): Mixture of ethyl acetoacetate
(1, 211 mg, 0.153 mmol), hydrazine (2, 81 mg, 0.153), 7-hydroxy-
4-oxo-2-phenyl-4H-chromene-8-carbaldehyde (4a, 406 mg,
0.153 mmol), 1-(2-ethoxy-2-oxoethyl)pyridinium ylide (4, 272
mg, 0.153 mmol), 0.1 equivalents of trimethylamine (16 mg,
0.015 mmol) in15 mL EtOH were refluxed in a pre-heated oil
bath (80 °C) under the blanket of nitrogen for 30 min till the
completion of reaction (TLC, 20 % dicholromethane in hexanes;
Rf = 0.3). The reaction mixture was diluted with dichloro-
methane (10 mL) and the organic solution was washed with
water (20 mL) and brine (20 mL) and dried over anhydrous
Na2SO4. Column chromatographic purification on silica gel
with increasing amount of dichlormethane in hexanes provided
8a as a free flowing solid in about 88 % yield. Analytical
samples were obtained through from the recrystallization in
EtOH. Light yellow colour solid. Yield 581 mg (88 %); m.p.:
136.5 °C, IR (KBr, νmax, cm–1): 3310, 3206, 3035, 2998, 2680,
2622, 1746, 1670, 1642, 1490, 1421, 1374, 1343, 1213, 1182,
(4R,5R)-Ethyl 4-(7-hydroxy-4-oxo-2-p-tolyl-4H-
chromen-8-yl)-3-methyl-4,5-dihydro-1H-furo[2,3-
c]pyrazole-5-carboxylate (8d): Light yellow colour solid,
m.p.: 130.7 °C, IR (KBr, νmax, cm–1): 3313, 3202, 3032, 2987,
1746, 1672, 1644, 1483, 1411, 1365, 1338, 1210, 1184, 1123,
1075, 1034, 987, 893; 1H NMR (400 MHz, CDCl3) δ 12.04 (s,
1H), 8.25 (d, J = 8.4 Hz, 1H), 7.79 (d, J = 7.8 Hz, 2H), 7.43
(d, J = 8.8 Hz, 1H), 7.05 (d, J = 7.7 Hz, 2H), 6.81 (s, 1H),
6.11 (br s, 1H), 5.29 (d, J = 4.6 Hz, 1H), 5.16 (d, J = 4.6 Hz,
1H), 4.16 (q, J = 6.6 Hz, 2H), 1.91 (s, 3H), 0.95 (t, J = 7.4 Hz,
3H) ppm; 13C NMR (100 MHz, CDCl3) δ191.1, 176.7, 166.3,
163.3, 161.3, 157.4, 141.7, 139.2, 129.4, 126.3, 124.6, 124.6,
123.3, 121.7, 118.6, 117.7, 112.3, 105.1, 88.0, 62.8, 28.6, 21.7,
14.1, 12.1 ppm; HRMS (ESI, m/z) 469.1370 calcd. for
C25H22N2O6 (M+Na) found 469.1367; Anal. calcd. for
C25H22N2O6; C, C, 67.26; H, 4.97; N, 6.27; Found; C 67.25; H,
4.96; N, 6.25.
1
1114, 1076, 1022, 982, 880, 822, 775; H NMR (400 MHz,
CDCl3): δ 12.26 (s, 1H), 8.25 (d, J = 8.8 Hz, 1H), 7.79 (d, J =
8.7 Hz, 2H), 7.44-7.42 (m, 3H), 7.14 (d, J = 7.9 Hz, 1H), 6.80
(s, 1H), 6.09 (br s, 1H), 5.29 (d, J = 4.6 Hz, 1H), 5.16 (d, J =
4.6 Hz, 1H), 4.16 (q, J = 6.6 Hz, 2H), 1.91 (s, 3H), 0.95 (t, J
= 7.4 Hz, 3H) ppm; 13C NMR (100 MHz, CDCl3) δ191.7,
176.8, 165.6, 163.3, 161.5, 157.8, 139.6, 132.1, 129.9, 126.7,
124.9, 122.3, 121.7, 118.6, 117.3, 112.6, 105.2, 88.0, 62.7,
26.7, 14.2, 12.3 ppm; HRMS (ESI, m/z) 455.1214 calcd. for
C24H20N2O6 (M+Na) found 455.1212; Anal. calcd. for
C24H20N2O6; C, 66.66; H, 4.66; N, 6.48; Found; C, 66.65;
H, 4.65; N, 6.46.
(4R,5R)-Ethyl 4-(7-hydroxy-2-(4-hydroxyphenyl)-4-
oxo-4H-chromen-8-yl)-3-methyl-4,5-dihydro-1H-furo[2,3-
c]pyrazole-5-carboxylate (8e): Light yellow colour solid,
m.p.: 138.2 °C, IR (KBr, νmax, cm–1): 3341, 3231, 3023, 2987,
1746, 1672, 1644, 1496, 1398, 1330, 1218, 1198, 1145, 1081,
1023, 995, 878; 1H NMR (400 MHz, CDCl3) δ 12.29 (s, 1H),
9.09 (s, 1H), 8.30 (d, J = 8.8 Hz, 1H), 7.63 (d, J = 7.1 Hz,
2H), 7.34 (d, J = 8.8 Hz, 1H), 7.15 (d, J = 7.9 Hz, 2H), 6.79
(s, 1H), 6.13 (br s, 1H), 5.28 (d, J = 4.6 Hz, 1H), 5.16 (d, J =
4.6 Hz, 1H), 4.17 (q, J = 6.8 Hz, 2H), 1.92 (s, 3H), 0.95 (t, J
= 7.4 Hz, 3H) ppm; 13C NMR (100 MHz, CDCl3) δ191.2,
178.7, 168.3, 164.3, 161.0, 159.7, 158.5, 138.4, 129.6, 127.7,
125.6, 123.7, 121.7, 119.5, 118.3, 113.3, 105.7, 88.3, 62.6,
26.6, 14.4, 12.2 ppm; HRMS (ESI, m/z) 471.1163 calcd. for
C24H20N2O7 (M+Na) found 471.1161; Anal. calcd. for
C24H20N2O7; C, 64.28; H, 4.50; N, 6.25; Found; C, 64.27; H,
4.49; N, 6.23.
(4R,5R)-Ethyl 4-[2-(4-chlorophenyl)-7-hydroxy-4-oxo-
4H-chromen-8-yl]-3-methyl-4,5-dihydro-1H-furo[2,3-
c]pyrazole-5-carboxylate (8b): Light yellow colour solid,
m.p.: 138.1 °C, IR (KBr, νmax, cm–1): 3312, 3212, 3075, 2987,
2686, 2630, 1743, 1672, 1644, 1496, 1406, 1377, 1330, 1215,
1
1179, 1115, 1081, 1023, 995, 963, 881, 848, 769; H NMR
(400 MHz, CDCl3) δ 12.28 (s, 1H), 8.25 (d, J = 8.8 Hz, 1H),
7.79 (d, J = 7.1 Hz, 2H), 7.44 (d, J = 8.8 Hz, 1H), 7.05 (d, J =
7.9 Hz, 2H), 6.80 (s, 1H), 6.06 (br s, 1H), 5.29 (d, J = 4.6 Hz,
1H), 5.16 (d, J = 4.6 Hz, 1H), 4.16 (q, J = 6.6 Hz, 2H), 1.91
(s, 3H), 0.95 (t, J = 7.4 Hz, 3H) ppm; 13C NMR (100 MHz,
CDCl3) δ191.3, 176.6, 166.9, 163.3, 161.3, 157.6, 139.2, 133.3,
129.4, 126.7, 124.6,123.3, 121.7, 118.6, 117.3, 112.3, 105.1,
88.0, 62.7, 26.7, 14.2, 12.3 ppm; HRMS (ESI, m/z) 489.0824
calcd. for C24H19N2O6Cl (M+Na) found 489.0821;Anal. calcd.
for C24H19N2O6Cl; C, 61.74; H, 4.10; N, 6.00; Found; C, 61.72;
H, 4.10; N, 5.98.
(4R,5R)-Ethyl 4-[7-hydroxy-2-(4-methoxyphenyl)-4-
oxo-4H-chromen-8-yl]-3-methyl-4,5-dihydro-1H-furo[2,3-
c]pyrazole-5-carboxylate (8f): Light yellow colour solid,
m.p.: 135.7 °C, IR (KBr, νmax, cm–1): 3327, 3212, 3137, 3075,
2987, 1746, 1687, 1644, 1498, 1407, 1379, 1336, 1207, 1179,
1129, 1081, 1023, 992, 875, 778; 1H NMR (400 MHz, CDCl3)
δ 12.26 (s, 1H), 8.30 (d, J = 8.2 Hz, 1H), 7.83 (d, J = 7.8 Hz,
2H), 7.45 (d, J = 8.8 Hz, 1H), 7.05 (d, J = 7.8 Hz, 2H), 6.79
(s, 1H), 6.09 (br s, 1H), 5.29 (d, J = 4.6 Hz, 1H), 5.16 (d, J =
(4R,5R)-Ethyl 4-[2-(4-bromophenyl)-7-hydroxy-4-oxo-
4H-chromen-8-yl]-3-methyl-4,5-dihydro-1H-furo[2,3-

Vol. 29, No. 7 (2017)
Synthesis and Antiproliferative Activity of Some Dihydro-1H-furo[2,3-c]pyrazole-Flavone Hybrids 1527
4.6 Hz, 1H), 4.16 (q, J = 6.6 Hz, 2H), 1.91 (s, 3H), 0.95 (t, J
= 7.4 Hz, 3H) ppm; 13C NMR (100 MHz, CDCl3) δ191.2,
177.7, 167.3, 163.3, 161.4, 159.4, 157.7, 139.4, 128.6, 126.7,
124.6, 123.7, 121.7, 118.5, 117.3, 112.3, 105.1, 88.3, 62.6,
59.4, 26.6, 14.1, 12.1 ppm; C25H22N2O7, C, 64.93; H, 4.80; N,
6.06; O, 24.22, (M + Na) 485.1319. HRMS (ESI, m/z)
485.1319 calcd. for C25H22N2O7 (M+Na) found 485.1316;Anal.
calcd. for C25H22N2O7; C, 64.93; H, 4.80; N, 6.06; O, 24.22.
Found; C, 64.91; H, 4.78; N, 6.05.
(4R,5R)-Ethyl 4-(7-hydroxy-2-mesityl-4-oxo-4H-
chromen-8-yl)-3-methyl-4,5-dihydro-1H-furo[2,3-c]-
pyrazole-5-carboxylate (8j): Light yellow colour solid, m.p.
144.2 °C, IR (KBr, νmax, cm–1): 3354, 3212, 3075, 2987, 1746,
1672, 1644, 1496, 1404, 1379, 1337, 1212, 1184, 1127, 1094,
1017, 989, 958, 887, 851, 769; 1H NMR (400 MHz, CDCl3) δ
12.19 (s, 1H), 8.27 (d, J = 8.8 Hz, 1H), 7.79 (s, 2H), 7.43 (d,
J = 8.8 Hz, 1H), 6.79 (s, H), 6.16 (br s, 1H), 5.29 (d, J = 4.6
Hz, 1H), 5.15 (d, J = 4.6 Hz, 1H), 4.16 (q, J = 6.6 Hz, 2H),
2.29 (s, 3H), 2.22 (s, 6H), 1.91 (s, 3H), 0.97 (t, J = 7.4 Hz,
3H) ppm. 13C NMR (100 MHz, CDCl3) δ 191.0, 175.3, 166.8,
163.3, 161.3, 157.7, 139.3, 136.2, 133.7, 127.4, 125.8, 124.6,
121.7, 118.6, 117.3, 112.3, 105.1, 88.0, 62.6, 26.7, 21.7, 21.1,
14.3, 12.3 ppm; HRMS (ESI, m/z) 497.1683 calcd. for
C27H26N2O6 (M+Na) found 497.1680; Anal. calcd. for
C27H26N2O6; C, 68.34; H, 5.52; N, 5.90. Found; C, 68.32; H,
5.50; N, 5.89.
(4R,5R)-Ethyl 4-[2-{4-(dimethylamino)phenyl}-7-
hydroxy-4-oxo-4H-chromen-8-yl]-3-methyl-4,5-dihydro-
1H-furo[2,3-c]pyrazole-5-carboxylate (8g): Light yellow
colour solid, m.p. 143.1 °C, IR (KBr, νmax, cm–1): 3304, 3212,
3075, 2987, 2686, 2630, 1746, 1672, 1644, 1496, 1406, 1377,
1330, 1215, 1179, 1115, 1081, 1023, 995, 963, 881, 848, 769;
1H NMR (400 MHz, CDCl3) δ 12.27 (s, 1H), 8.30 (d, J = 8.8
Hz, 1H), 7.53 (d, J = 7.1 Hz, 2H), 7.34 (d, J = 8.8 Hz, 1H),
7.05 (d, J = 7.9 Hz, 2H), 6.79 (s, 1H), 6.12 (br s, 1H), 5.28 (d,
J = 4.6 Hz, 1H), 5.15 (d, J = 4.6 Hz, 1H), 4.16 (q, J = 6.6 Hz,
2H), 3.16 (s, 6H), 1.91 (s, 3H), 0.95 (t, J = 7.4 Hz, 3H) ppm;
13C NMR (100 MHz, CDCl3) δ 190.2, 177.4, 166.3, 163.7,
161.3, 156.5, 150.3, 140.4, 127.6, 126.5, 124.6, 123.7, 121.7,
118.5, 117.7, 112.3, 105.2, 88.3, 62.6, 41.1, 26.6, 14.1, 12.1
ppm; HRMS (ESI, m/z) 498.1636 calcd. for C26H25N3O6
(M+Na) found 498.1634; Anal. calcd. for C26H25N3O6; C,
65.67; H, 5.30; N, 8.84. Found; C, 65.66; H, 5.28; N, 8.82.
(4R,5R)-Ethyl 4-(7-hydroxy-2-(4-nitrophenyl)-4-oxo-
4H-chromen-8-yl)-3-methyl-4,5-dihydro-1H-furo[2,3-
(4R,5R)-Ethyl 4-(2-(2,4-dichlorophenyl)-7-hydroxy-4-
oxo-4H-chromen-8-yl)-3-methyl-4,5-dihydro-1H-furo[2,3-
c]pyrazole-5-carboxylate (8k): Light yellow colour solid,
m.p.: 135.4 °C, IR (KBr, νmax, cm–1): 3310, 3205, 3085, 2981,
2690, 2639, 1746, 1670, 1644, 1491, 1404, 1370, 1338, 1215,
1179, 1119, 1086, 1026, 998, 965, 883, 842, 769, 742, 692;
1H NMR (400 MHz, CDCl3) δ 12.14 (s, 1H), 8.27 (d, J = 8.8
Hz, 1H), 7.81 (d, J = 7.1 Hz, 1H), 7.59 (s, 1H), 7.44 (d, J =
8.8 Hz, 1H), 7.05 (d, J = 7.9 Hz, 1H), 6.79 (s, 1H), 6.09 (br s,
1H), 5.29 (d, J = 4.6 Hz, 1H), 5.16 (d, J = 4.6 Hz, 1H), 4.16
(q, J = 6.6 Hz, 2H), 1.91 (s, 3H), 0.95 (t, J = 7.4 Hz, 3H) ppm;
13C NMR (100 MHz, CDCl3) δ 191.0, 175.3, 166.8, 163.3,
161.3, 157.7, 143.3, 139.2, 133.7, 129.4, 127.8, 125.7, 124.6,
123.3, 121.7, 118.6, 117.3, 112.3, 105.1, 88.0, 69.6, 26.7, 14.3,
12.3 ppm; HRMS (ESI, m/z) 523.0434 calcd. for C24H18N2O6Cl2
(M+Na) found 523.0431. Analysis calcd. for C24H18N2O6Cl2:
C, 57.50; H, 3.62; N, 5.59; Found C, 57.49; H, 3.60; N, 5.57.
(4S,5S)-Ethyl 4-[7-hydroxy-4-oxo-2-(2,4,6-trichloro-
phenyl)-4H-chromen-8-yl]-3-methyl-4,5-dihydro-1H-
furo[2,3-c]pyrazole-5-carboxylate (8l): Light yellow colour
solid, m.p.: 138.1 °C, IR (KBr, νmax, cm–1): 3320, 3221, 3072,
2970, 2692, 2641, 1746, 1672, 1643, 1490, 1408, 1375, 1333,
1212, 1177, 1119, 1085, 1027, 994, 964, 886, 842, 764, 744,
698; 1H NMR (400 MHz, CDCl3) δ 12.12 (s, 1H), 8.28 (d, J =
8.8 Hz, 1H), 7.79 (d, J = 7.1 Hz, 1H), 7.44 (d, J = 8.8 Hz,
1H), 7.05 (d, J = 7.9 Hz, 1H), 6.79 (s, 1H), 6.09 (br s, 1H),
5.29 (d, J = 4.6 Hz, 1H), 5.16 (d, J = 4.6 Hz, 1H), 4.16 (q, J =
c]pyrazole-5-carboxylate (8h): m.p. 139.3 °C, IR (KBr, νmax
,
cm–1): 3340, 3210, 3021, 2994, 1745, 1672, 1644, 1496, 1406,
1377, 1330, 1215, 1179, 1115, 1081, 1023, 995, 963, 881; 1H
NMR (400 MHz, CDCl3) δ 12.26 (s, 1H), 8.20 (d, J = 8.8 Hz,
1H), 7.54 (d, J = 7.2 Hz, 1H), 7.36 (d, J = 8.4 Hz, 2H), 7.07
(d, J = 8.1 Hz, 2H), 6.86 (s, H), 6.11 (br s, 1H), 5.41 (d, J =
4.6 Hz, 1H), 5.16 (d, J = 4.6 Hz, 1H), 4.19 (q, J = 6.6 Hz,
2H),1.91 (s, 3H), 0.97 (t, J = 7.4 Hz, 3H). 13C NMR (100
MHz, CDCl3) δ191.0, 175.3, 166.8, 163.3, 161.3, 157.7, 147.3,
139.2, 136.7, 126.7, 124.6, 123.3, 121.7, 118.6, 117.3, 112.3,
105.1, 88.0, 62.6, 26.7, 14.3, 12.3 ppm; HRMS (ESI, m/z)
500.1064 calcd. for C24H19N3O8 (M+Na) found 500.1064;Anal.
calcd. for C24H19N3O8; C, 60.38; H, 4.01; N, 8.80; Found; C,
60.36; H, 4.00; N, 8.79.
(4R,5R)-Ethyl 4-(2-(2,4-dimethylphenyl)-7-hydroxy-4-
oxo-4H-chromen-8-yl)-3-methyl-4,5-dihydro-1H-furo[2,3-
c]pyrazole-5-carboxylate (8i): Light yellow colour solid,
m.p.: 141.6 °C, IR (KBr, νmax, cm–1): 3337, 3212, 3075, 2987,
1746, 1672, 1644, 1487, 1404, 1383, 1330, 1210, 1183, 1126,
1085, 1018, 969, 881, 848, 769; 1H NMR (400 MHz, CDCl3)
δ 12.14 (s, 1H), 8.27 (d, J = 8.8 Hz, 1H), 7.58 (s, 1H), 7.43 (d,
J = 8.8 Hz, 2H), 7.07 (d, J = 8.2 Hz, 2H), 6.77 (s, H), 5.29 (d,
J = 4.6 Hz, 1H), 6.14 (br s, 1H), 5.15 (d, J = 4.6 Hz, 1H), 4.16
(q, J = 6.6 Hz, 2H), 2.38 (s, 3H), 2.26 (s, 3H), 1.91 (s, 3H),
0.97 (t, J = 7.4 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 191.3,
175.3, 166.8, 163.3, 161.3, 157.7, 142.2, 139.7, 133.4, 129.8,
127.7, 125.6, 124.3, 123.7, 122.6, 118.7, 117.3, 112.3, 105.1,
88.1, 62.8, 26.7, 21.84, 21.82, 14.3, 12.3 ppm; HRMS (ESI,
m/z) 483.1524 calcd. for C26H24N2O6 (M+Na) found 483.1527;
Anal. calcd. for C26H24N2O6; C, 67.82; H, 5.25; N, 6.08; Found;
C, 67.80; H, 5.24; N, 6.06.
6.6 Hz, 2H), 1.92 (s, 3H), 0.95 (t, J = 7.4 Hz, 3H) ppm; 13
C
NMR (100 MHz, CDCl3) δ191.3, 176.2, 167.2, 163.5, 161.3,
157.9, 139.1, 136.3, 133.2, 127.2, 125.8, 124.6, 121.7, 118.6,
117.3, 112.4, 105.2, 88.2, 62.7, 26.8, 14.3, 12.3 ppm; HRMS
(ESI, m/z) 557.0044 calcd. for C24H17N2O6Cl3 (M+Na) found
557.0042.Analysis calcd. for C24H17N2O6Cl3: C, 53.80; H, 3.20;
N, 5.23; Found C, 53.78; H, 3.19; N, 5.22.
(4R,5R)-Ethyl 4-[7-hydroxy-4-oxo-2-(pyridin-3-yl)-
4H-chromen-8-yl]-3-methyl-4,5-dihydro-1H-furo[2,3-
c]pyrazole-5-carboxylate (8m): Light yellow colour solid,
m.p.: 140.5 °C, IR (KBr, νmax, cm–1): 3324, 3234, 3046, 2970,
1746, 1672, 1648, 1490, 1405, 1378, 1331, 1225, 1164, 1119,
1
1081, 1034, 994, 964, 886, 842, 764; H NMR (400 MHz,
CDCl3) δ 12.28 (s, 1H), 8.42 (s, 1H), 8.25 (d, J = 8.8 Hz, 1H),
7.79 (d, J = 8.7 Hz, 1H), 7.45-7.42(m, 2H), 7.13 (d, J = 7.9

1528 Tangeti et al.
Asian J. Chem.
Hz, 1H), 6.80 (s, 1H), 6.11 (br s, 1H), 5.29 (d, J = 4.6 Hz,
1H), 5.16 (d, J = 4.6 Hz, 1H), 4.16 (q, J = 6.6 Hz, 2H), 1.92
(s, 3H), 0.95 (t, J = 7.4 Hz, 3H) ppm; 13C NMR (100 MHz,
CDCl3) δ191.0, 175.6, 168.8, 165.3, 164.3, 160.7, 157.4, 151.8,
139.3, 135.72, 135.71, 125.8, 124.3, 118.67, 118.64, 117.3,
112.3, 105.1, 88.0, 62.6, 26.7, 14.3, 12.3 ppm; HRMS (ESI,
m/z) 456.1166 calcd. for C23H19N3O6 (M+Na) found 456.1162;
Anal. calcd. for C23H19N3O6; C, 63.74; H, 4.42; N, 9.70; Found;
C, 63.72; H, 4.41; N, 9.68.
515.1425 calcd. for C26H24N2O8 (M+Na) found 515.1423;Anal.
calcd. for C26H24N2O8; C, 63.41; H, 4.91; N, 5.69; Found; C,
63.40; H, 4.90; N, 5.67.
(4S, 5S)-Ethyl 4-(7-hydroxy-4-oxo-2-(2,4,6-trime-
thoxyphenyl)-4H-chromen-8-yl)-3-methyl-4,5-dihydro-1H-
furo[2,3-c]pyrazole-5-carboxylate (8q): Light yellow colour
solid, m.p.: 141.7 °C, IR (KBr, νmax, cm–1): 3210, 3072, 2989,
2676, 2621, 1746, 1672, 1644, 1491, 1402, 1379, 1333, 1217,
1
1177, 1115, 1086, 1023, 997, 963, 871, 845, 765; H NMR
(4R,5R)-Ethyl 4-(2-(furan-2-yl)-7-hydroxy-4-oxo-4H-
chromen-8-yl)-3-methyl-4,5-dihydro-1H-furo[2,3-
c]pyrazole-5-carboxylate (8n): Light yellow colour solid,
m.p.: 138.9 °C, IR (KBr, νmax, cm–1): 3342, 3214, 3058, 2970,
1748, 1671, 1643, 1490, 1403, 1375, 1333, 1212, 1177, 1104,
(400 MHz, CDCl3) δ 12.09 (s, 1H), 8.30 (d, J = 8.8 Hz, 1H),
7.72 (s, 2H), 7.42 (d, J = 8.8 Hz, 2H), 6.79 (s, 1H), 6.19 (br s,
1H), 5.32 (d, J = 4.7 Hz, 1H), 5.19 (d, J = 4.7 Hz, 1H), 4.19
(q, J = 6.6 Hz, 2H), 3.727 (s, 6H), 3.726 (s, 3H), 1.92 (s, 3H),
0.97 (t, J = 7.4 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 191.0,
175.6, 168.8, 165.3, 164.3, 160.7, 157.4, 155.8, 139.3, 125.8,
118.67, 118.64, 117.3, 112.3, 105.1, 88.0, 62.6, 61.89, 61.87,
26.74, 14.3 ppm; HRMS (ESI, m/z) 545.1531 calcd. for
C27H26N2O9 (M+Na) found 545.1528; Anal. calcd. for
C27H26N2O9; C, 62.06; H, 5.02; N, 5.36;. Found; C, 62.04; H,
5.01; N, 5.35.
1
1085, 1027, 994, 921, 854, 876, 744; H NMR (400 MHz,
CDCl3) δ 12.26 (s, 1H), 8.25 (d, J = 8.8 Hz, 1H), 7.60 (d, J =
8.7 Hz, 1H), 7.45 (d, J = 8.8 Hz, 1H), 7.16-7.12 (m,2H), 6.80
(s, 1H), 6.16 (br s, 1H), 5.29 (d, J = 4.6 Hz, 1H), 5.16 (d, J =
4.6 Hz, 1H), 4.16 (q, J = 6.6 Hz, 2H), 1.92 (s, 3H), 0.95 (t, J
= 7.4 Hz, 3H) ppm; 13C NMR (100 MHz, CDCl3) δ191.0,
175.6, 168.8, 164.3, 162.6, 160.7, 157.4, 147.1, 143.8, 139.3,
125.8, 118.67, 118.64, 117.3, 115.3, 110.6, 105.1, 88.0, 62.6,
26.7, 14.3, 12.3 ppm. HRMS (ESI, m/z) 445.1012 calcd. for
C22H18N2O7 (M+Na) found 445.1010; Anal. calcd. for
C22H18N2O7; C, 62.56; H, 4.30; N, 6.63; Found; C, 62.54; H,
4.28; N, 6.62.
(4S,5S)-Ethyl 4-(7-hydroxy-5-methoxy-4-oxo-2-(2,4,6-
trimethoxyphenyl)-4H-chromen-8-yl)-3-methyl-4,5-
dihydro-1H-furo[2,3-c]pyrazole-5-carboxylate (8r): Light
yellow colour solid, m.p.: 148.5 °C, IR (KBr, νmax, cm–1): 3327,
3212, 3075, 2987, 1746, 1672, 1644, 1490, 1403, 1370, 1326,
1
1217, 1183, 1124, 1081, 1020, 995, 961, 881, 842, 769; H
(4R,5R)-Ethyl 4-(7-hydroxy-4-oxo-2-(thiophen-2-yl)-
4H-chromen-8-yl)-3-methyl-4,5-dihydro-1H-furo[2,3-
c]pyrazole-5-carboxylate (8o): Light yellow colour solid,
m.p.: 140.8 °C, IR (KBr, νmax, cm–1): 3318, 3243, 3042, 2970,
1746, 1681, 1644, 1490, 1408, 1373, 1321, 1212, 1178, 1120,
NMR (400 MHz, CDCl3) δ12.11 (br s, 1H), 7.04 (s, 1H), 6.79
(s, 1H), 6.02 (br s, 1H),5.32 (d, J = 4.7 Hz, 1H), 5.19 (d, J =
4.7 Hz, 1H), 4.19 (q, J = 6.6 Hz, 2H), 3.727 (s, 3H), 3.726 (s,
6H), 3.723 (S, 3H), 1.92 (s, 3H), 0.97 (t, J = 7.4 Hz, 3H); 13C
NMR (100 MHz, CDCl3) δ191.0, 175.6, 168.8, 165.3, 164.3,
160.7, 157.4, 155.8, 154.8, 139.3, 119.7, 118.67, 118.64,
117.3, 105.1, 97.1, 95.8, 88.0, 62.8, 61.89, 61.87, 60.7, 26.7,
14.3, 12.3 ppm; HRMS (ESI, m/z) 575.1636 calcd. for
C28H28N2O10 (M+Na) found 575.1633; Anal. calcd. for
C28H28N2O10; C, 60.87; H, 5.11; N, 5.07;. Found; C, 60.85; H,
5.10; N, 5.06.
1
1085, 1025, 994, 963, 887, 843, 764; H NMR (400 MHz,
CDCl3) δ 12.20 (s, 1H), 8.26-8.20 (m, 2H), 7.45 (d, J = 8.8
Hz, 1H), 7.16-7.12 (m, 2H), 6.80 (s, 1H), 6.12 (br s, 1H), 5.29
(d, J = 4.6 Hz, 1H), 5.16 (d, J = 4.6 Hz, 1H), 4.16 (q, J = 6.6
Hz, 2H), 1.92 (s, 3H), 0.95 (t, J = 7.4 Hz, 3H) ppm; 13C NMR
(100 MHz, CDCl3) δ 191.2, 175.7, 168.6, 164.5, 162.6, 160.7,
157.1, 147.3, 143.8, 139.3, 125.6, 118.34, 118.32, 117.4,
115.3, 110.6, 105.1, 88.0, 62.6, 26.7, 14.3, 12.3 ppm. HRMS
(ESI, m/z) 461.0778 calcd. for C22H18N2O6S (M+Na) found
461.0773; Anal. calcd. for C22H18N2O6S; C, 60.27; H, 4.14; N,
6.39; S, 7.31; Found; C, 60.26; H, 4.14; N, 6.37; S, 7.30.
(4R,5R)-Ethyl 4-[2-(2,4-dimethoxyphenyl)-7-hydroxy-
4-oxo-4H-chromen-8-yl]-3-methyl-4,5-dihydro-1H-
furo[2,3-c]pyrazole-5-carboxylate (8p): Light yellow colour
solid, m.p.: 137.2 °C, IR (KBr, νmax, cm–1): 3327, 3212, 3075,
2987, 1746, 1672, 1644, 1490, 1403, 1370, 1326, 1217, 1183,
RESULTS AND DISCUSSION
Synthesis commenced with reaction of resacetophenone
(1) with benzoyl chloride in acetone, K2CO3 medium by
modified Baker-Venkataraman reaction conditions provided
acylated flavones. These products were treated with 5 %
methanolic KOH followed by acidification with dil. HCl to
give 7-hydroxy flavones (3a-r). 7-Hydroxy 8-formyl flavones
(4a-r) was synthesized by the Duff reaction. A mixture of
7-hydroxy flavones (3a-r) and hexamethelenetetramine were
refluxed in glacial acetic acid medium for 12 h. The resulting
imminium complex was hydrolyzed by the addition of 0.1 N
aq. HCl to furnish 8-formyl-7-hydroxy flavones (4a-r) (Scheme-
I) [36].
1
1124, 1081, 1020, 995, 961, 881, 842, 769; H NMR (400
MHz, CDCl3) δ 12.19 (s, 1H), 8.27 (d, J = 8.8 Hz, 1H), 7.71
(d, J = 7.1 Hz, 1H), 7.61 (s, 1H), 7.43 (d, J = 6.9 Hz, 1H),
7.04 (d, J = 7.9 Hz, 1H), 6.81 (s, H), 6.18 (br s, 1H), 5.28 (d,
J = 4.6 Hz, 1H), 5.17 (d, J = 4.6 Hz, 1H), 4.16 (q, J = 6.6 Hz,
2H), 3.79 (s, 3H), 3.78 (s, 3H), 1.91 (s, 3H), 0.95 (t, J = 7.4
Hz, 3H) ppm. 13C NMR (100 MHz, CDCl3) δ 191.3, 175.4,
168.3, 165.3, 164.3, 160.7, 160.0, 157.4, 139.0, 130.0, 125.8,
119.0, 118.1, 117.3, 112.3, 110.0, 105.1, 101.4, 88.0, 62.6,
61.84, 61.82, 26.7, 14.3, 12.3 ppm; C26H24N2O8, C, 63.41; H,
4.91; N, 5.69; O, 25.99, (M + Na) 515.1425.HRMS (ESI, m/z)
In the next step of the reaction protocol, when equimolar
amounts of 7-hydroxy 8-formylflavones (4), β-keto ester (5),
hydrazine (6), ethyl ester pyridinium bromides (7) were reacted
in the presence of 0.1 equivalents of Et3N in a sealed vial under
microwave-irradiation at 90 °C for 5 min afforded after work-
up, dihydrofuro[1,2-b]pyrazole flavone derivative (8a) as a

Vol. 29, No. 7 (2017)
Synthesis and Antiproliferative Activity of Some Dihydro-1H-furo[2,3-c]pyrazole-Flavone Hybrids 1529
(a) Acetone,
K2CO3, reflux,
8h, N2, 80-95 %
CHO
HO
O
O
Ar
HO
O
O
Ar
HO
OH
Hexamine
ArCOCl
AcOH, 2-3 h
45 - 65 %
(b) dil HCl,
78 -93 %
COCH3
2a-r
1
3a-r
4a-r
18 Examples
Scheme-I: Formylation of 7-hydroxy, 8-formyl flavones
racemic trans stereo isomer in very good yield. A series of
substituted 7-hydroxy 8-formyl flavone derivatives were
reacted with ethylacetoacetate, hydrazine, pyridinium ylides
to prepare a series of dihydro-1H-furo[2,3-c]pyrazole flavone
hybrid (8a-o) with different substituents on their B-ring
(Scheme-II).
(human cervical cancer). Out of which, the compound 8f
emerged as the most promising lead compound open for further
structure activity relationship (SAR) studies (Table-1). Two
domains in compound 8f namely, the aromatic ring (ring A &
B, Fig. 1) of flavone were agreeable for alteration with different
substituents while keeping rest of the molecule intact. Then,
the substrate scope of the reaction was explored by using
various 7-hydroxy, 8-formyl flavones in the model reaction.
In all cases the substitution reaction provided the product
dihydro-1H-furo[2,3-c]pyrazole flavone hybrid (8a-r) without
any difficulty (Scheme-III). Based on the biological activity
of compound 8f and substitution pattern of natural flavonoids
[37], we changed different substituents on ring A (Fig. 2) to
alter steric and electronic effects. Electronic effects were also
observed in the reaction process. The electron-donating group
(EDG) at 2,5 positions of ortho-hydroxy benzaldehyde
required less reaction time to give comparatively high yields
of the product while stronger EWG-substituted ones gave
evidently poor yields. The electronic properties of the substi-
The structure of the compounds was fully characterized
by 1H NMR and 13C NMR, MS and IR spectra and elemental
analysis. In the 1H NMR spectra, two protons at 2,3-position
of dihydrofuran ring display two doublets at 5.29 and 5.15
ppm with the vicinal coupling constant J = 4.6 Hz and 4.6
Hz, respectively. It has been documented that in cis-2,3-
dihydrofuran the vicinal coupling constant of the two methine
protons J = 7-10 Hz, while in trans-2,3-dihydrofuran vicinal
coupling constant J = 4-7 Hz. Appearance of two singlet
1
signals at about δ 8.2 and 6.8 ppm in the H NMR spectra
assignable to two olefinic CH groups confirmed formation of
the product. As anticipated all the 22 signals are appeared in
13C NMR. Moreover, the 13C NMR spectra displayed ester
carbonyl at about δ 191 ppm and α,β-unsaturated carbonyl
carbon at 163 ppm. So we concluded that thermodynamically
stable trans isomer of 2,3-dihydrofuropyrazole unit
incorporated on flavone moity. Further, it was confirmed from
the analysis of the NOESY spectrum of the compound. The
mass spectrum shows, a sharp distinguishable peak of
compound 8a at 455.1212 [M+Na]+.
H
N
O
N
5'
B
2'
6'
EtOOC
HO
4'
3'
CH3
8
O
1'
Similarly, all the synthesized compounds 8b-r was charac-
terized. Newly prepared dihydro-1H-furo[2,3-c]pyrazole
flavone derivatives (8a-r) was subjected to in vitro screening
against three cancer cell lines namely Hep2 (human laryngeal
carcinoma), A549 (human lung adenocarcinoma) and HeLa
A
6
5
O
Fig. 1. Structure of 1H-furo[2,3-c]pyrazole flavone
H
N
O
N
O
O
N
Br
EtOOC
HO
NH2-NH2
O
CH3
OEt
NEt3, 90 oC
H3C
O
Ar
OEt
EtOH, 30 - 1h
78 - 91 %
5
7
6
O
CHO
8a-o
O
HO
Ar
`15 Examples
O
4a-o
Scheme-II: Synthesis of dihydro-1H-furo[2,3-c]pyrazole flavones

1530 Tangeti et al.
Asian J. Chem.
H
H
H
H
H
N
N
N
N
N
O
O
O
O
O
N
N
N
N
N
COOEt
COOEt
O
COOEt
O
COOEt
O
COOEt
O
Cl
Br
Me
OH
H3C
H3C
H3C
H3C
H3C
O
HO
HO
HO
HO
HO
O
O
O
O
O
8a, 30 min, 88 %
8b, 40 min , 78%
8c, 35 min, 80%
8d, 45 min, 89%
8e, 1h, 88%
H
N
H
N
H
N
H
N
H
N
O
O
O
O
O
N
N
N
N
N
COOEt
H3C
COOEt
COOEt
COOEt
COOEt
OMe
NMe2
NO2
CH3
CH3
H3C
HO
H3C
HO
H3C
HO
H3C
HO
H3C
O
O
O
O
O
HO
CH3
CH3
O
O
O
O
O
8f, 55 min, 91%
8g, 45 min, 89%
8h, 1.5 h, 73%
8i, 1.2 h, 85 %
8j, 2 h, 81%
H
N
H
N
H
N
H
N
H
N
N
O
O
O
O
O
CH3
Cl
N
N
N
N
COOEt
COOEt
COOEt
COOEt
Cl
Cl
EtOOC
HO
H3C
HO
H3C
HO
H3C
HO
H3C
HO
O
O
O
O
N
O
O
O
S
Cl
Cl
O
O
O
O
8k, 1.5 h, 78%
8l, 2 h, 79%
8m, 45 min, 85%
8n, 40 min, 82%
8o, 1h, 84%
H
N
H
N
H
N
N
N
O
O
O
CH3
CH3
N
COOEt
OMe
MeO
OMe
MeO
OMe
EtOOC
HO
EtOOC
HO
H3C
HO
O
O
O
OMe
OMe
OMe
O
O
OMe O
8p, 1.2 h 81%
8q, 1.5 h, 78%
8r, 2.5 h 72%
Fig. 2. Synthesis of SAR directed a combinatorial library of dihydro-1H-furo[2,3-c]pyrazole-flavones (8a-r)
TABLE-1
in vitro ANTIPROLIFERATIVE ACTIVITY OF DIHYDRO-
1H-FURO[2,3-c]PYRAZOLE-FLAVONE DERIVATIVES (8a-r)
AGAINST Hep2, A549, HeLa HUMAN CANCER CELLS BY
MMT ASSAY EXPRESSED IN IC50 (µM)a
tuents of aromatic aldehydes significantly affect the reactivity.
The electron-donating group (NMe2) at the para position of
the aldehyde to give comparatively high yield of the product
while stronger EWG-substituted one (NO2) gave evidently poor
yield. Spectral (IR, 1H NMR, 13C NMR and DEPT) and analy-
tical (ESI-MS HRMS) data of the all the derivatives 8b-r agreed
well with the assigned structures. We gathered structures of
all dihydro-1H-furo[2,3-c]pyrazole flavone hybrids (8a-r)
along with the time taken for the substitution reaction and
yield of the product in Fig. 2 to provide overall picture of the
substitution pattern and to discern SAR results. List of synthetic
compounds used for in vitro studies were given in Fig. 2.
Antiproliferative activity: In the first phase, antiproli-
ferative activity of eighteen furo[2,3-c]pyrazole-flavone (8a-r,
Fig. 2) was evaluated in vitro against a panel of three human
cancer cell lines, namely human laryngeal carcinoma (Hep2),
human lung adenocarcinoma (A549) and human cervical
cancer (HeLa) cells and the results for inhibitory concentration
(IC50) values are gathered in Table-1. The studies reveal that
methoxy group substituted derivative 8f showed significant
cytotoxic activity in comparison with other derivatives in all
the three cancer cell lines (entry 5, Table-1).
Entry Compounds
Hep2b
A549c
HeLad
1
2
50 0.91
50 1.85
45 1.32
25 2.5
>100
>100
>100
8a
>100
8b
3
30 1.78
20 1.72
>100
50 1.12
35 4.78
>100
8c
4
8d
5
40 0.80
2.5 0.20
50 3.63
50 4.78
24 1.65
30 1.65
100 9.83
35 2.8
8e
6
24 1.85
24 1.85
10 0.95
35 2.5
35 2.5
25 1.37
60 5.7
35 1.25
20 0.84
23 1.25
18 1.31
35 2.8
>100
8f
7
8g
8
8h
9
15 0.96
35 0.96
>100
8i
10
11
12
13
14
15
16
17
18
19
20
8j
8k
12 1.0
35 1.90
35 0.96
11 1.90
14 0.82
12 0.78
10 1.31
1.54 0.08
8l
30 1.45
20 0.52
21 1.45
8m
8n
8o
8p
6
4
0.24
0.85
8
7
6
0.52
0.28
0.85
8q
For the next batch of three furo[2,3-c]pyrazole-flavones
(8p-r) methoxy group substitutions were made in ring A & B.
Antiproliferative evaluation of 8p-r revealed that furo[2,3-
c]pyrazole-flavone derivative 6r (entry 18, Table-1) which
has total four methoxy groups at aromatic ring A and B
displays better activity compared to others. In summary in vitro
2.5 0.20
10 0.8
8r
Doxorubicin
Paclitaxel
0.65 0.04
1.8 0.12
0.175 0.01
0.26 0.01
b
aResults are the average of three independent experiments; Hep2-
Human laryngeal carcinoma; cA549-Human lung adenocarcinoma;
dHeLa-Human cervical cancer.

Vol. 29, No. 7 (2017)
Synthesis and Antiproliferative Activity of Some Dihydro-1H-furo[2,3-c]pyrazole-Flavone Hybrids 1531
H
N
N
O
O
O
N
R3
R2
Br
NH2-NH2
O
EtOOC
HO
OEt
o
H3C
NEt3, 90 C
O
OEt
EtOH, 0.5 - 1h
72 - 81 %
R1
7
5
6
R4
O
R3
R2
CHO
8p-r
3 Examples
HO
O
O
R1
R4
4p-r
8p
8r = R1 = OMe; R2 = OMe; R3 = OMe, R4 = OMe;
8q
= R1 = OMe; R2 = OMe; R3 = OMe, R4 = H;
= R1 = OMe; R2 = OMe; R3 = H, R4 = H;
Scheme-III: SAR oriented synthesis of furo[2,3-c]pyrazole-flavone hybrids (8p-r)
evaluation revealed that furo[2,3-c]pyrazole-flavone (8r) is the
most potent molecule within the batch of 8a-r. In order to
determine the cytotoxic effects, all the eighteen compounds
were subjected to in vitro cytotoxicity assay using 3-[4,5-
dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide
(MTT) reduction test with the panel of three cancer cell lines
for 48 h. All the compounds exhibited minimal cytotoxicity
on ‘human peripheral blood mononuclear cell (hPBMC),
which indicates that furo[2,3-c]pyrazole-flavone (8a-r) are
selectively toxic towards cancer cell lines.
compound 8r is found to be the most potential anticancer
molecule.
ACKNOWLEDGEMENTS
One of the authors, VST thanks to Indian Institute of
Chemical Technology, Hyderabad, India and IIT Chennai for
recording NMR, HRMS data and Mr. Sri kalidindi Raghu,
Chairman, Raghu Engineering College,Visakhapatnam, India
for his valuable support.
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