Synthesis and cytotoxicity studies of novel 2-hydrazonylpyrido[2,3-b] pyrazin-3(4H)-ones

Article abstract of DOI:10.1002/ardp.201100103

In an attempt to develop potent antitumor agents, a series of novel 2-hydrazonylpyrido[2,3-b]pyrazin-3(4H)-one derivatives were designed and synthesized. All the prepared compounds were screened for their cytotoxic activities against A549, MDA-MB-231 and HT-29 cell lines in vitro. Pharmacological data indicated that five of the target compounds showed cytotoxicity against A549 cell line below a concentration of 1 μM. Compound 15g was the most potent one with IC₅₀ values of 0.19, 2.11 and 2.15 μM against A549, MDA-MB-231 and HT29 cell lines, respectively. A series of 2-hydrazonylpyrido[2,3-b]pyrazin-3(4H)-one derivatives was designed and synthesized. Preliminary structure-activity relationships suggested that compounds with 4-methoxyphenyl or 4-(trifluoromethoxy)phenyl groups on the N-4 position were generally more potent than those with an unsubstituted phenyl group. Copyright

Full text of DOI:10.1002/ardp.201100103

Arch. Pharm. Chem. Life Sci. 2012, 345, 49–56
49
Full Paper
Synthesis and Cytotoxicity Studies of Novel 2-
Hydrazonylpyrido[2,3-b]pyrazin-3(4H)-ones
Guogang Zhang, Yajing Liu, Shuobing Wang, Chuan Zhou, Qingchang Huang, and Ping Gong
Key Laboratory of Original New Drugs Design and Discovery of Ministry of Education,
School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shenyang, P. R. China
In an attempt to develop potent antitumor agents, a series of novel 2-hydrazonylpyrido[2,3-b]pyrazin-
3(4H)-one derivatives were designed and synthesized. All the prepared compounds were screened for
their cytotoxic activities against A549, MDA-MB-231 and HT-29 cell lines in vitro. Pharmacological data
indicated that five of the target compounds showed cytotoxicity against A549 cell line below a
concentration of 1 mM. Compound 15g was the most potent one with IC50 values of 0.19, 2.11 and
2.15 mM against A549, MDA-MB-231 and HT29 cell lines, respectively.
Keywords: Anticancer activity / Apoptosis / 2-Hydrazonylpyrido[2,3-b]pyrazin-3(4H)-ones
Received: March 24, 2011; Revised: May 17, 2011; Accepted: May 18, 2011
DOI 10.1002/ardp.201100103
Introduction
0.12 mM (m-calpain) and 0.17 mM (m-calpain), respectively
[13].
Apoptosis plays a vital role in the control of cell numbers and
defective apoptosis represents a major causative factor in the
development and progression of cancer [1]. The ability of
tumor cells to evade apoptosis led to their resistance to
conventional therapeutic regimens [2]. Therefore, develop-
ment of apoptosis inducers as new anticancer agents is a
promising approach and has been a focus of research recently
[3–6].
Caspase-3 is an important effector protease in the caspase
family, which can catalyze the hydrolysis of a multitude of
protein substrates within the cells and induce apoptosis in
cancer cells selectively [14]. Putt et al. reported that PAC-1
(Fig. 1) induced death in cancer cells through direct acti-
vation of procaspase-3 via the sequestration of inhibitory
zinc ions. The phenolic hydroxyl group is the essential
PAC-1 functional group responsible for zinc chelation [15].
Inspired by SJA-7029 and PAC-1, we designed and synthes-
ized a series of 2-hydrazonylpyrido[2,3-b]pyrazin-3(4H)-one
derivatives. Various substituted ortho-hydroxyl hydrazones
were incorporated into the C-2 position to investigate the
influence of substituted position and spatial effects of aryli-
dene motif. Furthermore, phenyl, 4-methoxyphenyl and 4-
(trifluoromethoxy)phenyl groups were introduced into the
N-4 position of skeleton, in order to develop novel analogues
and to investigate the cytotoxic activities against human
cancer cell lines in vitro.
Calpains and caspases are families of cysteine proteases
and there is a level of collaboration between them in the
induction of apoptosis [7–9]. Calpains are ubiquitously
expressed in many tissues and implicated in numerous
calcium-regulated cellular processes, such as signal trans-
duction, cell proliferation, differentiation and apoptosis
[9–11]. Inhibitors of two major isoforms of calpain (m-calpain
and m-calpain) were selectively cytotoxic to various human
tumor cells in a dose-dependent manner, and were not cyto-
toxic to normal cells and tissues [12]. SJA7029 (Fig. 1),
a 3,4-dihydroquinoxalin-2(1H)-one derivative, was identified
as a new potent inhibitor of calpains with IC50 values of
Results and discussion
Chemistry
The synthetic route of the target compounds 5a–5h, 10a–10h
and 15a–15h is illustrated in Scheme 1. The commercially
available 2-chloro-3-nitropyridine and aniline were treated
with N,N-diisopropylethylamine in isopropanol to give the
compound 1, which was reduced and cyclized with oxalic
Correspondence: Ping Gong, Key Laboratory of Original New Drugs
Design and Discovery of Ministry of Education, School of Pharmaceutical
Engineering, Shenyang Pharmaceutical University, 103 Wenhua Road,
Shenhe District, 110016 Shenyang, Liaoning, P. R. China.
E-mail: gongpinggp@126.com
Fax: þ86 24 2398-6429
ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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G. Zhang et al.
Arch. Pharm. Chem. Life Sci. 2012, 345, 49–56
Figure 1. Structures of SJA7029, PAC-1 and
2-hydrazonylpyrido[2,3-b]pyrazin-3(4H)-ones.
Scheme 1. Synthesis of target compounds.
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Arch. Pharm. Chem. Life Sci. 2012, 345, 49–56
2-Hydrazonylpyrido[2,3-b]pyrazin-3(4H)-ones
51
acid to afford compound 2. Subsequent treatment of 2 with
phosphorus oxychloride afforded chloro-derivative 3.
Compound 3 was reacted with an excess of 80% hydrazine
hydrate in ethanol to furnish the key intermediate 4. Another
two important intermediates 9 and 14 were obtained accord-
ing to the same method as described for compound 4 when
aniline was replaced by 4-methoxyaniline and 4-(trifluorome-
thoxy)aniline, respectively. Finally, the target compounds
5a–5h, 10a–10h and 15a–15h were successfully obtained
via the reaction of intermediate 4, 9 and 14 with different
aromatic aldehydes in the refluxing ethanol, respectively.
The products were purified by column chromatography on
200–300 mesh silica gel.
The preliminary structure–activity relationships (SARs)
suggested that compounds with 4-methoxyphenyl or 4-(tri-
fluoromethoxy)phenyl groups on the N-4 position were
generally more potent than with unsubstituted phenyl
group. The pharmacological data indicated that 4-methoxy-
phenyl analogue 10d showed a dramatic 7-fold improvement
in cytotoxicity against A549 cell lines (IC50 ¼ 0.95 mM) com-
pared with phenyl analogue 5c (IC50 ¼ 6.94 mM). It could be
observed that 4-methoxyphenyl group was generally pre-
ferred and that 4-(trifluoromethoxy)phenyl group was also
well tolerated. Further data indicated that 4-(trifluorome-
thoxy)phenyl analogue 15b was nearly 5-fold more active
than phenyl analogue 5b against A549 cell line.
The pharmacological results indicated that the substitu-
ents on 40-postion of the 20-hydroxybenzylidene were benefit
to activity. It was obvious that introducing a hydroxyl group
to the 40-postion of 20-hydroxybenzylidene of compound (15g)
improved its potency against all three cell lines, other sub-
stitution such as chloro (15d) and benzyloxy (15h) group at
the same position were well tolerated but not significantly
better than hydroxyl group.
Biological evaluation
The newly synthesized twenty-four compounds (5a–5h, 10a–
10h and 15a–15h) were performed by MTT assay using three
human cancer cell lines, A549, MDA-MB-231 and HT29, with
PAC-1 as a positive control. The results of the assay are
summarized in Table 1. Among them, compounds 10d,
15a, 15b, 15d and 15g showed cytotoxicity against A549 cell
line below a concentration of 1 mM. Compound 15g was the
most active compound on A549, MDA-MB-231 and HT-29 with
IC50 value of 0.19, 2.11 and 2.15 mM, respectively.
Interestingly, the volume of groups on 30-position and
50-position of the 20-hydroxybenzylidene would influence
antitumor activity. Generally, introducing the bulky groups,
Table 1. The substituents. Cytotoxicity of the tested compounds against A549, MDA-MB-231 and HT-29 cell lines.
Compd.
X
R
IC50 (mM)
A549
MDA-MB-221
HT-29
5a
5b
5c
5d
5e
5f
5g
H
H
H
H
H
H
H
H
2,3,4-trihydroxy
3-allyl-2-hydroxy
13.35 ꢀ 1.58
4.75 ꢀ 0.67
6.94 ꢀ 0.78
9.04 ꢀ 0.83
13.54 ꢀ 1.47
NAa
16.82 ꢀ 1.84
3.63 ꢀ 0.48
12.42 ꢀ 1.53
15.87 ꢀ 1.68
48.66 ꢀ 3.66
18.54 ꢀ 1.23
NAa
6.04 ꢀ 0.14
28.16 ꢀ 2.34
8.54 ꢀ 0.94
11.83 ꢀ 0.88
11.63 ꢀ 1.19
13.83 ꢀ 1.76
19.63 ꢀ 2.49
10.86 ꢀ1.67
8.57 ꢀ 0.68
28.57 ꢀ 3.31
4.47 ꢀ 0.36
12.85 ꢀ 1.87
3.85 ꢀ 0.23
6.91 ꢀ 0.85
NAa
4.23 ꢀ 0.45
4.67 ꢀ 0.43
5.26 ꢀ 0.49
13.61 ꢀ 1.12
52.98 ꢀ 4.84
2.78 ꢀ 0.46
NAa
12.03 ꢀ 1.08
12.24 ꢀ 0.48
6.23 ꢀ 0.48
2.58 ꢀ 0.37
2.43 ꢀ 0.33
26.25 ꢀ 2.41
12.61 ꢀ 1.17
10.94 ꢀ 1.98
2.38 ꢀ 0.39
48.38 ꢀ 3.69
1.61 ꢀ 0.27
2.41 ꢀ 0.38
4.61 ꢀ 0.68
1.67 ꢀ 0.36
NAa
3-allyl-2-hydroxy-5-methyl
3-allyl-2-hydroxy-5-isopropyl
3-allyl-5-tert-butyl-2-hydroxy
2-hydroxy-3-(2-methylallyl)
3,5-di-tert-butyl-2-hydroxy
4-(4-chlorobenzyloxy)-2-hydroxy
2-hydroxy
4-chloro-2-hydroxy
3-allyl-2-hydroxy
3-allyl-2-hydroxy-5-methyl
3-allyl-5-tert-butyl-2-hydroxy
2-hydroxy-3-(2-methylallyl)
2,4-dihydroxy
2,3,4-trihydroxy
3-allyl-5-tert-butyl-2-hydroxy
3-allyl-2-hydroxy
2-hydroxy-3-(2-methylallyl)
4-chloro-2-hydroxy
3-allyl-2-hydroxy-5-methyl
3,5-di-tert-butyl-2-hydroxy
2,4-dihydroxy
NAa
5h
2.82 ꢀ 0.09
6.53 ꢀ 0.22
4.82 ꢀ 0.59
1.24 ꢀ 0.15
0.95 ꢀ 0.15
11.8 ꢀ 0.18
NAa
3.84 ꢀ 0.29
3.83 ꢀ 0.43
0.83 ꢀ 0.13
0.94 ꢀ 0.13
NAa
0.81 ꢀ 0.07
1.49 ꢀ 0.25
NAa
0.19 ꢀ 0.05
1.09 ꢀ 0.06
0.66 ꢀ 0.08
10a
10b
10c
10d
10e
10f
10g
10h
15a
15b
15c
15d
15e
15f
15g
15h
PAC-1
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCF3
–OCF3
–OCF3
–OCF3
–OCF3
–OCF3
–OCF3
–OCF3
2.11 ꢀ 0.25
3.47 ꢀ 0.53
6.67 ꢀ 0.58
2.15 ꢀ 0.39
5.72 ꢀ 0.47
1.62 ꢀ 0.13
4-(benzyloxy)-2-hydroxy
a
NA means no activity.
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52
G. Zhang et al.
Arch. Pharm. Chem. Life Sci. 2012, 345, 49–56
such as tert-butyl, isopropyl and 2-methylallyl resulted in
dramatic decrease or abolishment in antitumor potency. A
case in point was incorporation of allyl group at 30-position
appeared to be beneficial, with compounds 5b, 10c and 15b
displaying potent activities. However, incorporation of 2-
methylallyl group at the same position exhibited a reduction
of potency against MDA-MB-231 cell line and no cytotoxicity
against A549 cell line. In addition, substitution to the 50-
position of the 30-allyl-20-hydroxybenzylidene with a more
bulky aliphatic group resulted in declined antitumor activity
(methyl 5c > isopropyl 5d > tert-butyl 5e). Significantly,
introduction of 3,5-di-tert-butyl group into the 20-hydroxyben-
zylidene (5g and 15f) led to no antitumor activity against all
three cell lines.
a mixture of water and EtOH to afford a black solid (42.3 g,
33%). M.p.: >3008C. ESI-MS m/z: 239.1 (MþH)þ. C13H9N3O2
(239.07).
2-Chloro-4-phenylpyrido[2,3-b]pyrazin-3(4H)-one (3)
To a stirred solution of POCl3 (210 mL) and CH3CN (420 mL)
42.3 g 2 (0.17 mol) were added at room temperature, and
then 3 drops of DMF were added to the mixture. The reaction
mixture was heated to 808C for 3 h. The mixture was con-
centrated under reduced pressure. The residue was poured
into ice water (1000 mL), separated by filtration to give off a
grey solid (34.2 g, 71.6%). M.p.: 180–1818C. ESI-MS m/z: 257.1,
259.1 (MþH)þ. C13H8ClN3O (257.68).
2-Hydrazinyl-4-phenylpyrido[2,3-b]pyrazin-3(4H)-one (4)
A solution of 80% hydrazine hydrate (NH2NH2 ꢁ H2O) 170 mL
(4.9 mol) and 34.2 g 3 (0.13 mol) was stirred at 608C for 1 h.
The mixture was cooled, separated by filtration and washed
with EtOH to give off a light yellow crystal (34.9 g, 75%). M.p.:
210–2118C. ESI-MS m/z: 254.1 (MþH)þ. C13H11N5O (253.26).
Experimental protocols
Chemistry
All melting points were obtained on a Bu¨chi Melting Point B-
540 apparatus (Bu¨chi Labortechnik, Flawil, Switzerland) and
were uncorrected. Mass spectra (MS) were taken in ESI mode
on Agilent 1100 LC-MS (Agilent, Palo Alto, CA, USA). Proton
nuclear magnetic resonance spectroscopy (1H-NMR) was per-
formed using Bruker ARX-400, 400-MHz spectrometers
(Bruker Bioscience, Billerica, MA, USA) with TMS as an
internal standard. Elemental analyses were performed with
a Carlo-Erba 1106 analyzer. Unless otherwise noted, all the
materials were obtained from commercially available sour-
ces and were used without further purification.
General procedure for preparation of 4-phenyl-
(2-arylmethylenehydrazinyl)pyrido[2,3-b]-
pyrazin-3(4H)-one (5a–5h)
To a stirred solution of aromatic aldehydes (1.8 mmol) in
anhydrous ethanol 0.3 g (1.2 mmol) was added 4 at room
temperature. The mixture was heated to 608C for 5 h. The
mixture was cooled, separated by filtration and washed with
EtOH to give off a light yellow crystal and purified by chroma-
tography on silica gel using MeOH/CH2Cl2 to obtain 5a–5h as
light yellow crystals.
2-Anilino-3-nitropyridine (1)
To a stirred solution of aniline 111.6 g (1.2 mol) and triethyl-
amine 187.6 mL (1.3 mol) in isopropanol (1500 mL) 2-chloro-
3-nitropyridine 124.0 g (1.0 mol) was added slowly at 258C,
and then the reaction mixture was stirred at room tempera-
ture for 1 h and heated to reflux for 8 h. The mixture was
cooled, separated by filtration and washed with EtOH and
water to give off an orange crystal (114.0 g, 53%). M.p.: 72–
738C. ESI-MS m/z: 216.1 (MþH)þ. C11H9N3O2 (215.07).
4-Phenyl-2-(2-(2,3,4-trihydroxybenzylidene)hydrazinyl)-
pyrido[2,3-b]pyrazin-3(4H)-one (5a)
Yield: 56%. M.p.: 207–2088C. ESI-MS m/z: 390.1 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 13.13 (s, 1H), 11.85 (s, 1H),
9.75 (s, 1H), 8.15 (m, 2H), 7.95 (m, 3H), 7.56 (d, J ¼ 7.7 Hz,
2H), 7.41–7.36 (m, 3H), 7.36–7.32 (m, 2H), 7.26 (m, 2H); anal.
calcd. for C20H15N5O4 (%): C 61.69, H 3.88, N 17.99, O 16.44;
found C 62.02, H 4.63, O 16.38. C20H15N5O4 (389.36).
1,4-Dihydro-4-phenylpyrido[2,3-b]pyrazine-2,3-dione (2)
To a stirred solution of 1 114 g (0.53 mol) in 95% EtOH
(1000 mL) a solution of zinc powder 175 g (2.7 mol) and
NH4Cl 14.4 g (0.27 mol) was portionwise added, then the
reaction mixture was stirred at room temperature for 1 h
and heated to reflux. After 5 h later, the mixture was separ-
ated by filtration at hot and washed with hot EtOH. The filter
liquor was concentrated under reduced pressure and the
residue was cooled to room temperature. Oxalate 47.7 g
(0.53 mol) and 4 N HCl (900 mL) were added after which
the mixture was refluxed for additional 15 h. At last the
mixture was cooled, separated by filtration and washed with
2-(2-(3-Allyl-2-hydroxybenzylidene)hydrazinyl)-4-
phenylpyrido[2,3-b]pyrazin-3(4H)-one (5b)
Yield: 53%. M.p.:169–1708C. ESI-MS m/z: 398.2 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 12.14 (s, 1H), 11.86 (s, 1H),
8.78 (s, 1H), 8.12 (d, J ¼ 4.2 Hz, 1H), 7.95 (d, J ¼ 7.7 Hz,
1H), 7.59 (t, J ¼ 7.7 Hz, 2H), 7.47 (t, J ¼ 7.3 Hz, 1H), 7.41
(d, J ¼ 7.1 Hz, 2H), 7.31 (dd, J ¼ 7.7, 4.7 Hz, 1H), 7.25 (d,
J ¼ 7.5 Hz, 1H), 7.20 (d, J ¼ 7.2 Hz, 1H), 6.90 (t, J ¼ 7.5 Hz,
1H), 6.04 (m, 1H), 5.08 (t, J ¼ 13.6 Hz, 2H), 3.44 (d, J ¼ 6.4 Hz,
2H); anal. calcd. for C23H19N5O2 (%): C 69.51, H 4.82, N 17.62,
O 8.05; found C 69.32, H 4.62, O 17.73. C23H19N5O2 (397.43).
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Arch. Pharm. Chem. Life Sci. 2012, 345, 49–56
2-Hydrazonylpyrido[2,3-b]pyrazin-3(4H)-ones
53
2-(2-(3-Allyl-2-hydroxy-5-methylbenzylidene)hydrazinyl)-
4-phenylpyrido[2,3-b]pyrazin-3(4H)-one (5c)
8.70 (s, 1H), 8.05 (dd, J ¼ 4.6, 1.2 Hz, 1H), 7.90 (dd, J ¼ 7.8,
1.2 Hz, 1H), 7.51 (t, J ¼ 7.5 Hz, 2H), 7.44 (t, J ¼ 7.3 Hz, 1H),
7.35 (d, J ¼ 7.4 Hz, 2H), 7.24 (m, 2H), 7.08 (d, J ¼ 2.0 Hz, 1H),
1.39 (s, 9H), 1.20 (s, 9H); anal. calcd. for C28H31N5O2 (%): C
71.62, H 6.65, N 14.91, O 6.81; found C 72.45, H 7.36, O 7.29.
Yield: 46%. M.p.: 185–1868C. ESI-MS m/z: 442.2 (MþH)þ; 1H-
NMR (400 MHz, DMSO) d: 11.99 (s, 1H), 11.94 (s, 1H), 8.73 (s,
1H), 8.12 (s, 1H), 7.95 (d, J ¼ 7.9 Hz, 1H), 7.57 (t, J ¼ 7.7 Hz,
2H), 7.47 (t, J ¼ 7.3 Hz, 1H), 7.41 (d, J ¼ 7.1 Hz, 2H), 7.33 (dd,
J ¼ 7.9, 4.6 Hz, 1H), 7.05 (s, 1H), 7.02 (s, 1H), 6.03 (m, J ¼ 17.0,
10.2 Hz, 1H), 5.08 (t, J ¼ 12.3 Hz, 2H), 3.41 (d, J ¼ 6.6 Hz, 2H),
2.25 (s, 3H); anal. calcd. for C24H21N5O2 (%): C 70.06, H 5.14, N
17.02, O 7.78; found C 69.98, H 5.23, O 7.89. C24H21N5O2
(411.46).
C
28H31N5O2 (469.58).
2-(2-(4-(4-Chlorobenzyloxy)-2-hydroxybenzylidene)-
hydrazinyl)-4-phenylpyrido[2,3-b]pyrazin-3(4H)-one (5h)
Yield: 53%. M.p.: 158–1598C. ESI-MS m/z: 498.1, 500.1 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 11.51 (s, 1H), 8.96 (s, 1H), 8.06 (d,
J ¼ 3.3 Hz, 1H), 7.93 (m, 2H), 7.63–7.45 (m, 10H), 7.39 (d,
J ¼ 7.1 Hz, 2H), 7.27 (m, J ¼ 7.8, 4.7 Hz, 1H), 6.87 (d,
J ¼ 1.9 Hz, 1H), 6.78 (d, J ¼ 8.7 Hz, 1H); anal. calcd.
for C27H20ClN5O3 (%): C 65.13, H 4.05, Cl 7.12, N 14.06,
O 9.64; found C 65.08, H 4.09, O 9.58. C27H20ClN5O3 (497.93).
2-(2-(3-Allyl-2-hydroxy-5-isopropylbenzylidene)-
hydrazinyl)-4-phenylpyrido[2,3-b]pyrazin-3(4H)-one (5d)
Yield: 54%. M.p.: 192–1938C. ESI-MS m/z: 440.2 (MþH)þ; 1H-
NMR (400 MHz, DMSO) d: 11.99 (s, 1H), 11.90 (s, 1H), 8.68 (s,
1H), 8.05 (dd, J ¼ 4.6, 1.5 Hz, 1H), 7.89 (dd, J ¼ 7.9, 1.4 Hz,
1H), 7.51 (t, J ¼ 7.4 Hz, 2H), 7.44 (t, J ¼ 7.3 Hz, 1H), 7.35 (d,
J ¼ 7.2 Hz, 2H), 7.24 (dd, J ¼ 7.9, 4.7 Hz, 1H), 7.01 (s, 2H), 5.98
(m, 1H), 5.03 (m, 2H), 3.36 (d, J ¼ 6.5 Hz, 2H), 2.79 (m, 1H),
1.14 (s, 3H), 1.12 (s, 3H); anal. calcd. for C26H25N5O2 (%):
C 71.05, H 5.73, N 15.93, O 7.28; found C 71.23, H 5.90,
O 7.33. C26H25N5O2 (439.51).
2-(4-Methoxyphenyl)-3-nitropyridine (6)
It was prepared in a similar procedure as described for 1,
from 2-chloro-3-nitropyridine 79 g (0.5 mol) and 4-methoxy-
aniline 92.2 g (0.75 mol) to give off a dark brown solid (78 g,
64.3%). M.p.: 147–1488C. ESI-MS m/z: 216.0 (MþH)þ. C15H10O2
(215.21).
2-(2-(3-Allyl-5-tert-butyl-2-hydroxybenzylidene)-
1,4-Dihydro-4-(4-methoxyphenyl)pyrido[2,3-b]-
pyrazine-2,3-dione (7)
hydrazinyl)-4-phenylpyrido[2,3-b]pyrazin-3(4H)-one (5e)
Yield: 44%. M.p.: 189–1908C. ESI-MS m/z: 454.2 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 12.02 (s, 1H), 11.89 (s, 1H),
8.69 (s, 1H), 8.05 (dd, J ¼ 4.6, 1.5 Hz, 1H), 7.89 (dd, J ¼ 7.9,
1.5 Hz, 1H), 7.51 (t, J ¼ 7.4 Hz, 2H), 7.44 (t, J ¼ 7.3 Hz, 1H),
7.35 (d, J ¼ 7.2 Hz, 2H), 7.24 (dd, J ¼ 7.9, 4.7 Hz, 1H), 7.18 (d,
J ¼ 2.1 Hz, 1H), 7.11 (d, J ¼ 2.3 Hz, 1H), 5.98 (m, J ¼ 16.7, 10.0,
6.6 Hz, 1H), 5.02 (m, 2H), 3.37 (d, J ¼ 6.5 Hz, 2H), 1.22 (s, 9H);
anal. calcd. for C27H27N5O2 (%): C 71.50, H 6.00, N 15.44, O 7.06;
found C 71.56, H 6.10, O 7.03. C27H27N5O2 (453.54).
It was prepared in a similar procedure as described for 2,
from 78 g 6 (0.32 mol) to give off a black crystal (30.2 g, 35%).
M.p.: >3008C. ESI-MS m/z: 270.1 (MþH)þ. C14H11N3O3 (269.26).
2-Chloro-4-(4-methoxyphenyl)pyrido[2,3-b]-
pyrazin-3(4H)-one (8)
It was prepared in a similar procedure as described for 4, from
30 g 7 (0.11 mol) to give off a gray solid (24.0 g, 76%). M.p.: 145–
1468C. ESI-MS m/z: 288.0, 290.0 (MþH)þ. C14H11N3O3 (287.71).
2-(2-(2-Hydroxy-3-(2-methylallyl)benzylidene)hydrazinyl)-
4-phenylpyrido[2,3-b]pyrazin-3(4H)-one (5f)
2-Hydrazinyl-4-(4-methoxyphenyl)pyrido[2,3-b]-
pyrazin-3(4H)-one (9)
Yield: 46%. M.p.: 185–1868C. ESI-MS m/z: 412.2 (MþH)þ; 1H-
NMR (400 MHz, DMSO) d: 12.12 (s, 1H), 11.88 (s, 1H), 8.72 (s,
1H), 8.05 (dd, J ¼ 4.6, 1.6 Hz, 1H), 7.89 (dd, J ¼ 7.9, 1.6 Hz,
1H), 7.51 (t, J ¼ 7.4 Hz, 2H), 7.44 (t, J ¼ 7.3 Hz, 1H), 7.35 (d,
J ¼ 7.2 Hz, 2H), 7.24 (dd, J ¼ 7.9, 4.7 Hz, 1H), 7.19 (dd, J ¼ 7.7,
1.4 Hz, 1H), 7.11 (d, J ¼ 7.4 Hz, 1H), 6.85 (t, J ¼ 7.5 Hz, 1H),
4.74 (s, 1H), 4.59 (s, 1H), 3.32 (s, 2H), 1.67 (s, 3H); anal. calcd.
for C24H21N5O2 (%): C 70.06, H 5.14, N 17.02, O 7.78; found C
70.15, H 5.14, O 7.67. C24H21N5O2 (411.46).
It was prepared in a similar procedure as described for 5,
from 24.0 g 8 (83.6 mmol) to give off a light yellow solid
(14.4 g, 61%). M.p.: 177–1788C. ESI-MS m/z: 284.1 (MþH)þ.
C
14H13N5O2 (283.29).
General procedure for preparation of compound (10a–10h)
They were prepared in a similar procedure as described for
5a–5h.
2-(2-(3,5-Di-tert-butyl-2-hydroxybenzylidene)hydrazinyl)-
4-phenylpyrido[2,3-b]pyrazin-3(4H)-one (5g)
2-(2-(2-Hydroxybenzylidene)hydrazinyl)-4-
(4-methoxyphenyl)pyrido[2,3-b]pyrazin-3(4H)-one (10a)
Yield: 64%. M.p.: 173–1758C. ESI-MS m/z: 388.1 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 11.93 (s, 1H), 11.58 (s, 1H),
Yield: 57%. M.p.: 174–1758C. ESI-MS m/z: 470.23 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 12.32 (s, 1H), 11.82 (s, 1H),
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8.72 (s, 1H), 8.12 (s, 1H), 7.93 (d, J ¼ 8.0 Hz, 1H), 7.35 (t,
J ¼ 6.8 Hz, 1H), 7.25–7.29 (m, 4H), 7.09 (d, J ¼ 8.9 Hz, 2H),
7.07 (d, J ¼ 8.0 Hz, 1H), 6.95 (d, J ¼ 6.8 Hz, 1H), 3.85 (s, 3H);
anal. calcd. for C21H17N5O3 (%): C 65.11, H 4.42, N 18.08,
O 12.39; found C 65.06, H 4.46, O 12.47. C21H17N5O3 (387.39).
2-(2-(2-Hydroxy-3-(2-methylallyl)benzylidene)hydrazinyl)-
4-(4-methoxyphenyl)pyrido[2,3-b]pyrazin-3(4H)-one (10f)
Yield: 62%. M.p.: 80–818C. ESI-MS m/z: 442.2 (MþH)þ; 1H-NMR
(400 MHz, DMSO) d: 12.13 (s, 1H), 11.92 (s, 1H), 8.76 (s, 1H),
8.07 (dd, J ¼ 4.6, 1.5 Hz, 1H), 7.96 (dd, J ¼ 7.9, 1.5 Hz, 1H),
7.34–7.28 (m, 3H), 7.27 (d, J ¼ 7.9 Hz, 1H), 7.19 (d, J ¼ 7.5 Hz,
1H), 7.10 (d, J ¼ 8.9 Hz, 2H), 6.88 (t, J ¼ 7.5 Hz, 1H), 4.76 (s,
1H), 4.63 (s, 1H), 3.83 (s, 3H), 3.37 (s, 2H), 1.70 (s, 3H); anal.
calcd. for C25H23N5O3 (%): C 68.01, H 5.25, N 15.86, O 10.87;
found C 68.06, H 5.28, O 10.84. C25H23N5O3 (441.48).
2-(2-(4-Chloro-2-hydroxybenzylidene)hydrazinyl)-4-
(4-methoxyphenyl)pyrido[2,3-b]pyrazin-3(4H)-one (10b)
Yield: 61%. M.p.: 177–1798C. ESI-MS m/z: 422.1, 424.1 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 11.98 (s, 1H), 11.92 (s, 1H), 8.75 (s,
1H), 8.11 (d, J ¼ 4.6 Hz, 1H), 7.93 (d, J ¼ 7.3 Hz, 1H), 7.56 (d,
J ¼ 8.2 Hz, 1H), 7.32–7.29 (m, 3H), 7.10 (d, J ¼ 8.8 Hz, 2H),
7.05 (s, 1H), 6.99 (d, J ¼ 8.0 Hz, 1H), 3.84 (s, 3H); anal. calcd.
for C21H16ClN5O3 (%): C 59.79, H 3.82, Cl 8.40, N 16.60,
O 11.38; found C 59.83, H 3.89, O 11.37. C21H16ClN5O3
(421.84).
2-(2-(2,4-Dihydroxybenzylidene)hydrazinyl)-4-
(4-methoxyphenyl)pyrido[2,3-b]pyrazin-3(4H)-one (10g)
Yield: 52%. M.p.: 177–1788C. ESI-MS m/z: 404.1 (MþH)þ; 1H-
NMR (400 MHz, DMSO) d: 11.90 (s, 1H), 11.76 (s, 1H), 10.12 (s,
1H), 8.71(s, 1H), 8.12 (s, 1H), 7.91 (d, J ¼ 7.2 Hz, 1H), 7.31 (m,
3H), 7.23 (d, J ¼ 8.3 Hz, 1H), 7.10 (d, J ¼ 8.9 Hz, 2H), 6.34 (m,
2H), 3.83 (s, 3H); anal. calcd. for C21H17N5O4 (%): C 62.53, H
4.25, N 17.36, O 15.86; found C 62.52, H 4.30, O 15.79.
2-(2-(3-Allyl-2-hydroxybenzylidene)hydrazinyl)-4-
(4-methoxyphenyl)pyrido[2,3-b]pyrazin-3(4H)-one (10c)
Yield: 53%. M.p.: 177–1798C. ESI-MS m/z: 428.2 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 12.10 (s, 1H), 11.79 (s, 1H),
8.81 (s, 1H), 8.14 (dd, J ¼ 4.2, 1.4 Hz, 1H), 7.96 (dd, J ¼ 7.7,
1.4 Hz, 1H), 7.32 (dd, J ¼ 7.7, 4.7 Hz, 1H), 7.28 (m, 3H), 7.22 (d,
J ¼ 7.2 Hz, 1H), 7.11 (d, J ¼ 9.0 Hz, 2H), 6.92 (t, J ¼ 7.7 Hz,
1H), 6.06 (m, 1H), 5.09 (t, J ¼ 13.6 Hz, 2H), 3.83 (s, 3H), 3.38 (d,
J ¼ 6.9 Hz, 2H); anal. calcd. for C24H21N5O3 (%): C 67.44, H
4.95, N 16.38, O 11.23; found C 67.40, H 4.99, O 11.29.
C
21H17N5O4 (403.39).
4-(4-Methoxyphenyl)-2-(2-(2,3,4-trihydroxybenzylidene)-
hydrazinyl)pyrido[2,3-b]pyrazin-3(4H)-one (10h)
Yield: 51%. M.p.: 176–1788C. ESI-MS m/z: 420.1 (MþH)þ; 1H-
NMR (400 MHz, DMSO) d: 8.62 (s, 1H), 8.14 (s, 1H), 8.10 (d,
J ¼ 8.0 Hz, 1H), 7.46 (d, J ¼ 1.6 Hz, 1H), 7.34 (dd, J ¼ 7.9,
4.7 Hz, 1H), 7.28 (d, J ¼ 8.8 Hz, 2H), 7.22 (d, J ¼ 7.2 Hz,
1H), 7.11 (d, J ¼ 9.0 Hz, 1H), 7.04 (d, J ¼ 8.4 Hz, 1H), 3.84
(s, 3H); anal. calcd. for C21H17N5O5 (%): C 60.14, H 4.09, N
16.70, O 19.07; found C 60.24, H 4.04, O 18.96. C21H17N5O5
(419.39).
C
24H21N5O3 (427.46).
2-(2-(3-Allyl-2-hydroxy-5-methylbenzylidene)hydrazinyl)-
4-(4-methoxyphenyl)pyrido[2,3-b]pyrazin-3(4H)-one (10d)
Yield: 53%. M.p.: 191–1928C. ESI-MS m/z: 442.2 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 12.15 (s, 1H), 11.83 (s, 1H),
8.72 (s, 1H), 8.12 (d, J ¼ 4.7 Hz, 1H), 7.93 (d, J ¼ 8.0 Hz,
1H), 7.34 (dd, J ¼ 7.9, 4.7 Hz, 1H), 7.30 (d, J ¼ 8.8 Hz, 2H),
7.09 (d, J ¼ 8.9 Hz, 2H), 7.04 (s, 1H), 7.01 (s, 1H), 6.02 (m, 1H),
5.10 (t, J ¼ 12.4 Hz, 2H), 3.83 (s, 3H), 3.39 (d, J ¼ 6.7 Hz, 2H),
2.24 (s, 3H); anal. calcd. for C25H23N5O3 (%): C 68.01, H 5.25, N
15.86, O 10.87; found C 67.94, H 5.26, O 10.92. C25H23N5O3
(441.48).
3-Nitro-N-(4-(trifluoromethoxy)phenyl)pyridin-2-amine (11)
It was prepared in a similar procedure as described for 1,
from 2-chloro-3-nitropyridine, 79 g (0.50 mol), and 4-(trifluor-
omethoxy)aniline, 133 g (0.75 mol), to give off an orange
solid (65.4 g, 43.6%). M.p.: 157–1598C. ESI-MS m/z: 300.3
(MþH)þ. C12H8F3N3O3 (299.21).
1,4-Dihydro-4-(4-(trifluoromethoxy)phenyl)pyrido-
[2,3-b]pyrazine-2,3-dione (12)
2-(2-(3-Allyl-5-tert-butyl-2-hydroxybenzylidene)-
hydrazinyl)-4-(4-methoxyphenyl)pyrido[2,3-b]
It was prepared in a similar procedure as described for 2,
from 65 g 11 (0.22 mol) to give off a black crystal (28.4 g,
40%). M.p.: >3008C. ESI-MS m/z: 270.3 (MþH)þ. C15H9F3N2O3
(322.24).
pyrazin-3(4H)-one (10e)
Yield: 44%. M.p.: 168–1698C. ESI-MS m/z: 484.2 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 11.90 (s, 1H), 11.66 (s, 1H), 8.77
(s, 1H), 8.12 (d, J ¼ 4.6 Hz, 1H), 7.90 (dd, J ¼ 7.9, 1.5 Hz, 1H),
7.31 (m, J ¼ 8.7 Hz, 3H), 7.10 (d, J ¼ 8.9 Hz, 2H), 6.92 (s, 1H),
6.90 (s, 1H), 6.05 (dd, J ¼ 17.0, 10.1 Hz, 1H), 5.07 (t, J ¼ 12.4 Hz,
2H), 3.82 (s, 3H), 3.45 (d, J ¼ 6.7 Hz, 2H), 1.29 (s, 9H); anal. calcd.
for C28H29N5O3 (%): C 69.55, H 6.04, N 14.48, O 9.93; found
C 69.42, H 6.11, O 10.02. C28H29N5O3 (483.56).
2-Chloro-4-(4-(trifluoromethoxy)phenyl)pyrido-
[2,3-b]pyrazin-3(4H)-one (13)
It was prepared in a similar procedure as described for 4,
from 28.4 g 12 (88 mmol) to give off a gray solid (22.4 g,
74.7%). M.p.: 157–1588C. ESI-MS m/z: 340.8, 342.8 (MþH)þ.
C
15H8ClF3N2O2 (340.68).
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2-Hydrazonylpyrido[2,3-b]pyrazin-3(4H)-ones
55
2-Hydrazinyl-4-(4-(trifluoromethoxy)phenyl)pyrido-
[2,3-b]pyrazin-3(4H)-one (14)
2-(2-(4-Chloro-2-hydroxybenzylidene)hydrazinyl)-4-
(4-(trifluoromethoxy)phenyl)pyrido[2,3-b]-
pyrazin-3(4H)-one (15d)
Yield: 57%. M.p.: 167–1698C. ESI-MS m/z: 476.1, 478.1 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 11.94 (br, 2H), 8.79 (s, 1H), 8.11 (s,
1H), 7.93 (d, J ¼ 7.3 Hz, 1H), 7.57–7.52 (m, 5H), 7.31 (s, 1H),
7.05 (s, 1H), 6.99 (d, J ¼ 8.0 Hz, 1H); anal. calcd.
for C21H13ClF3N5O3 (%): C 53.01, H 2.75, Cl 7.45, F 11.98, N
It was prepared in a similar procedure as described for 5,
from 22.4 g 13 (66 mmol) to give off a light yellow solid
(13.2 g, 59%). M.p.: 185–1868C. ESI-MS m/z: 337.3
(MþH)þ. C15H11F3N4O2 (336.27).
General procedure for preparation of compound
(15a–15h)
They were prepared in a similar procedure as described for
14.72, O, 10.09; found
C21H13ClF3N5O3 (475.81).
C 52.83, H 2.84, O 10.26.
5a–5h.
2-(2-(3-Allyl-2-hydroxy-5-methylbenzylidene)hydrazinyl)-
4-(4-(trifluoromethoxy)phenyl)pyrido[2,3-b]-
2-(2-(3-Allyl-5-tert-butyl-2-hydroxybenzylidene)-
hydrazinyl)-4-(4-(trifluoromethoxy)phenyl)-
pyrazin-3(4H)-one (15e)
pyrido[2,3-b]pyrazin-3 (4H)-one (15a)
Yield: 64%. M.p.: 167–1698C. ESI-MS m/z: 496.2 (MþH)þ; 1H-
NMR (400 MHz, DMSO) d: 11.88 (s, 1H), 11.72 (s, 1H), 8.75 (s,
1H), 8.14 (d, J ¼ 4.6 Hz, 1H), 7.97 (d, J ¼ 8.0 Hz, 1H), 7.59 (s,
4H), 7.36 (d, J ¼ 8.0 Hz, 1H), 7.06 (s, 1H), 7.03 (s, 1H), 6.04 (m,
1H), 5.12 (t, J ¼ 12.6 Hz, 2H), 3.85 (s, 3H), 3.41 (d, J ¼ 6.8 Hz,
2H), 2.26 (s, 3H); anal. calcd. for C25H20F3N5O3 (%): C 60.60, H
4.07, F 11.50, N 14.14, O 9.97; found C 62.32, H 4.40, O 10.59.
Yield: 64%. M.p.: 180–1818C. ESI-MS m/z: 538.2 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 11.96 (s, 1H), 11.29 (s, 1H),
8.79 (s, 1H), 8.14 (dd, J ¼ 4.6, 1.5 Hz, 1H), 7.95
(d, J ¼ 7.6 Hz, 1H), 7.57 (s, 4H), 7.36 (d, J ¼ 8.0 Hz, 1H),
6.92 (s, 1H), 6.90 (s, 1H), 6.05 (m, 1H), 5.07 (t, J ¼ 12.4 Hz,
2H), 3.45 (d, J ¼ 6.7 Hz, 2H), 1.29 (s, 9H); anal. calcd.
for C28H26F3N5O3 (%): C 62.56, H 4.88, F 10.60, N 13.03,
O 8.93; found C 62.60, H 4.82, O 9.04. C28H26F3N5O3
(537.53).
C
25H20F3N5O3 (495.45).
2-(2-(3,5-Di-tert-butyl-2-hydroxybenzylidene)hydrazinyl)-
4-(4-(trifluoromethoxy)phenyl)pyrido[2,3-b]-
2-(2-(3-Allyl-2-hydroxybenzylidene)hydrazinyl)-4-
(4-(trifluoromethoxy)phenyl)pyrido[2,3-b]-
pyrazin-3(4H)-one (15f)
Yield: 60%. M.p.: 144–1458C. ESI-MS m/z: 534.2 (MþH)þ; 1H-
NMR (400 MHz, DMSO) d: 12.42 (s, 1H), 11.93 (s, 1H), 8.73 (s,
1H), 8.08 (dd, J ¼ 4.6, 1.2 Hz, 1H), 7.93 (dd, J ¼ 7.9, 1.2 Hz,
1H), 7.58 (s, 4H), 7.46 (t, J ¼ 7.3 Hz, 1H), 7.26 (s, 1H), 7.13 (s,
1H), 1.40 (s, 9H), 1.22 (s, 9H); anal. calcd. for C29H30F3N5O3 (%):
C 62.92, H 5.46, F 10.30, N 12.65, O 8.67; found C 62.85, H 5.42,
O 8.74. C29H30F3N5O3 (553.58).
pyrazin-3(4H)-one (15b)
Yield: 61%. M.p.: 192–1938C. ESI-MS m/z: 482.1 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 11.96 (s, 1H), 11.83 (s, 1H),
8.80 (s, 1H), 8.15 (dd, J ¼ 4.2, 1.3 Hz, 1H), 7.97 (dd, J ¼ 7.7,
1.2 Hz, 1H), 7.61 (s, 4H), 7.33 (dd, J ¼ 7.8, 4.7 Hz, 1H),
7.27 (d, J ¼ 7.5 Hz, 1H), 7.22 (d, J ¼ 7.2 Hz, 1H), 6.92
(t, J ¼ 7.5 Hz, 1H), 6.06 (m, J ¼ 16.9, 6.6, 3.4 Hz, 1H),
5.10 (t, J ¼ 13.6 Hz, 2H), 3.46 (d, J ¼ 6.4 Hz, 2H); anal. calcd.
for C24H18F3N5O3 (%): C 59.88, H 3.77, F 11.84, N 14.55,
O 9.97; found C 60.09, H 3.84, O 9.96. C24H18F3N5O3
(481.43).
2-(2-(2,4-Dihydroxybenzylidene)hydrazinyl)-4-
(4-(trifluoromethoxy)phenyl)pyrido[2,3-b]-
pyrazin-3(4H)-one (15g)
Yield: 63%. M.p.: 158–1608C. ESI-MS m/z: 458.1 (MþH)þ; 1H-
NMR (400 MHz, DMSO) d: 11.88 (s, 1H), 11.72 (s, 1H), 9.99 (s,
1H), 8.66 (s, 1H), 8.08 (s, 1H), 7.88 (d, J ¼ 7.2 Hz, 1H), 7.57 (s,
4H), 7.29 (s, 1H), 7.24 (d, J ¼ 8.3 Hz, 1H), 6.47–6.16 (m, 2H);
anal. calcd. for C21H14F3N5O4 (%): C 55.15, H 3.09, F 12.46, N
15.31, O 13.99; found C 55.20, H 3.40, O 14.03. C21H14F3N5O4
(457.36).
2-(2-(2-Hydroxy-3-(2-methylallyl)benzylidene)hydrazinyl)-
4-(4-(trifluoromethoxy)phenyl)pyrido[2,3-b]pyrazin-3(4H)-
one (15c)
Yield: 55%. M.p.: 170–1718C. ESI-MS m/z: 496.2 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 12.14 (s, 1H), 11.97 (s, 1H),
8.79 (s, 1H), 8.12 (dd, J ¼ 7.9, 1.5 Hz, 1H), 7.96 (dd, J ¼ 7.9,
1.5 Hz, 1H), 7.59 (s, 4H), 7.31 (dd, J ¼ 7.9, 4.7 Hz, 1H), 7.27
(d, J ¼ 7.9 Hz, 1H), 7.19 (d, J ¼ 7.5 Hz, 1H), 6.92 (t, J ¼ 7.5 Hz,
1H), 4.80 (s, 1H), 4.66 (s, 1H), 3.39 (s, 2H), 1.73 (s, 3H);
anal. calcd. for C25H20F3N5O3 (%): C 60.60, H 4.07, F 11.50,
N 14.14, O 9.97; found C 60.71, H 4.12, O 9.84. C25H20F3N5O3
(495.45).
2-(2-(4-(Benzyloxy)-2-hydroxybenzylidene)hydrazinyl)-4-
(4-(trifluoromethoxy)phenyl)pyrido[2,3-b]-
pyrazin-3(4H)-one (15h)
Yield: 64%. M.p.: 180–1818C. ESI-MS m/z: 548.2 (MþH)þ;
1H-NMR (400 MHz, DMSO) d: 11.92 (s, 1H), 11.19 (s, 1H),
8.75 (s, 1H), 8.12 (d, J ¼ 4.7 Hz, 1H), 7.93 (d, J ¼ 7.9 Hz,
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Arch. Pharm. Chem. Life Sci. 2012, 345, 49–56
1H), 7.58 (s, 4H), 7.46 (d, J ¼ 7.1 Hz, 2H), 7.40 (t, J ¼ 7.4 Hz,
2H), 7.35–7.30 (m, 2H), 7.15 (d, J ¼ 3.0 Hz, 1H), 7.01
(d, J ¼ 8.9 Hz, 1H), 6.89 (d, J ¼ 8.9 Hz, 1H), 5.08 (s, 2H); anal.
calcd. for C28H20F3N5O4 (%): C 61.43, H 3.68, F 10.41, N 12.79,
O 11.69; found C 62.05, H 3.46, O 11.53. C28H20F3N5O4
(547.48).
potency than unsubstituted phenyl group. Furthermore, sub-
stituents, especially hydroxyl, on the 40-position of 20-hydrox-
ybenzylidene led to the greatly enhanced activity.
Significantly, bulky groups on 3’-position or 5’-position
resulted in a decrease in cytotoxicity, dramatically even
vanished.
This work was supported by a grant from the National S & T Major Project
(No.2009ZX09301-012).
Cytotoxicity assay in vitro
The cytotoxic activities of compounds 5a–5h, 10a–10h and
15a–15h were evaluated with A549 (human lung adenocar-
cinoma epithelial cell line), MDA-MB-231 (human breast can-
cer cell line) and HT-29 (human colon adenocarcinoma cell
line) by the standard MTT assay in vitro [16], with PAC-1 as the
positive control. The cancer cell lines were cultured in mini-
mum essential medium (MEM) supplement with 10% fetal
bovine serum (FBS).
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Conclusion
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CO 1999.
In summary, we have designed and synthesized twenty-four
2-hydrazonylpyrido[2,3-b]pyrazin-3(4H)-one derivatives, and
evaluated their cytotoxic activities against three cancer cell
lines (A549, MDA-MB-231 and HT-29). Some compounds dis-
played potential inhibition in the low micromolar or sub-
micromolar range. The preliminary SARs showed that intro-
duction of 4-methoxylphenyl or 4-(trifluoromethoxy)phenyl
group into the N-4 position resulted in more antitumor
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