Synthesis and antitumor evaluation of fluoroquinolone C3 fused heterocycles (II): From triazolothiadiazines to pyrazolotriazoles

Article abstract of DOI:10.1016/j.cclet.2011.01.018

To further expand an effective modified route for the shift from an antibacterial fluoroquinolone (FQ) to an antitumor FQ, two series of title compounds based on an isostere of the FQ C3 carboxylic group with two fused heterocyclic rings, [1,2,4]triazolo[

Full text of DOI:10.1016/j.cclet.2011.01.018

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 804–806
www.elsevier.com/locate/cclet
Synthesis and antitumor evaluation of fluoroquinolone C3 fused
heterocycles (II): From triazolothiadiazines to pyrazolotriazoles
a
a
a
a
Guo Qiang Hu a, , Li Li Hou , Yong Yang , Lei Yi , Song Qiang Xie ,
*
Guo Qiang Wang a, Nan Nan Duan a, Tie Yao Chao a, Xiao Yi Wen a, Wen Long Huang b
a Institute of Chemistry & Biology, Henan University, Kaifeng 475001, China
b China Pharmaceutical University, Nanjing 210009, China
Received 14 October 2010
Available online 17 April 2011
Abstract
To further expand an effective modified route for the shift from an antibacterial fluoroquinolone (FQ) to an antitumor FQ, two
series of title compounds based on an isostere of the FQ C3 carboxylic group with two fused heterocyclic rings, [1,2,4]triazolo[3,4-
b][1,3,4]thiadiazine and pyrazolo[5,1-c][1,2,4]triazole, respectively, were designed and synthesized starting from the current
antibacterial FQs, and their in vitro antitumor activity against L1210, CHO cell lines were evaluated via their respective IC50 values.
# 2011 Guo Qiang Hu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Fluoroquinolone; Triazolothiadiazine; Pyrazolotriazole; Antitumor evaluation
Recently, an attempt on the shift from an antibacterial fluoroquinolone (ABFQ) to an antitumor fluoroquinolone
(ATFQ) has been also paid an attractive attention based on the mechanistic similarities and sequence homologies
exhibited for targeting topoisomerases as the eukaryotic topoisomerases [1]. However, many ATFQs were mainly
derived from the structural modifications of clinical ABFQs related to the nitrogen-ring, such as piperazine, bearing
the 7-position and the 2-position of FQ scaffold [2,3], whereas few of modifications for the carboxylic group at the 3-
position were reported [3,4]. Indeed, it does not seem necessary for an ATFQ to remain the carboxylic group,
moreover, a (fused) heterocyclic ring as an isostere of the carboxylic group perfectly showed an anticancer activity as
well as an excellent water solubility [5]. Nevertheless, it is less known that heterocylces might be used as efficient
isosteres for carboxlate acid. Thus, the lasted attempt on discovery of ATFQs as potential new lead compounds derived
from ABFQ C3 fused s-triazolothiadiazines 3a–3e and pyrazolo s-triazoles 5a–5e (Scheme 1) was reported.
Five starting materials 4-amino-5-mercapto-3-FQ-3-yl-1,2,4-triazole 1a–1e derived from clinical ABFQs
corresponding to norfloxacin, ciprofloxacin, enrofloxacin, ofloxacin and levofloxacin, respectively, were prepared
according to the known procedure [5]. A condensation of 1 with 4-(chloroacetyl)catechol in sodium hydroxide-
ethanol–water solvents at room temperature formed the opening products 2a–2e, respectively. Then, these opening
products were directly subjected to an acid catalyzed intramolecular cyclocondensation to yield the corresponding
closed-ring products, 3-(6-catechol-4-yl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl)-quinolon-4(1H)-ones 3a–
* Corresponding author.
E-mail addresses: hgqxy@sina.com.cn, hgq@henu.edu.cn (G.Q. Hu).
1001-8417/$ – see front matter # 2011 Guo Qiang Hu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.01.018

[()TD$FIG]
G.Q. Hu et al. / Chinese Chemical Letters 22 (2011) 804–806
805
OH
OH
OH
N N
OH
EtOH-H2O, NaOH
N N
FQ
SH
FQ
+
N
NH2
S
N
rt
NH2
O
Cl
2a~2e
1a~1e
O
Ac
N N
Ac
1'
OH
OH
S
FQ'
Ac2O
reflux
S
HCl
N
N
N
N
N
OAc
reflux
N
3'
.
HCl
FQ
4a~4e
OAc
3a~3e
O
N
O
H
5
5
N N
F
F
HOAc-HCl
reflux
OH
FQ
7'
3'
2
N
N
2
N
1
N
N
R
1
OH
7
N
O
N
.
5a~5e
R'
HCl
FQ (a~c)
FQ (d, e)
Scheme 1. R/R0 for FQ: C2H5/H (3a, 5a); cyclopropyl/H (3b, 5b); cyclopropyl/C2H5 (3c, 5c); (ꢀ)-S/R (3d, 5d); (ꢁ)-S (3e, 5e).
3e, as their respective hydrochloride. But, it is unsuccessful at preparing this known fused heterocyclic system
according to a general procedure [6] due to a slight solubility in refluxing ethanol. Occasionally, while heating the
fused heterocycles 3a–3e in acetic acid readily resulted in a ring-contraction of fused six-membered thiadiazine by a
sulfur extrusion reaction leading to formation of fused five-membered pyrazole corresponding to new fused
heterocycles, 3-(1-acetyl-6-diacetylcatechol-4-yl-7-acetylsulfanyl-1H-pyrazolo[5,1-c][1,2,4]triazol-3-yl)-(N-acetyl)-
quinolon-4-(1H)-ones 4a–4e, followed by one-pot conversion of 4a–4e by an acetic acid and a hydrochloric acid
catalyzed hydrolysis occurring desulfurization and deacetylation reactions to give the title compounds, 6-catechol- 4-
yl-3-FQ-3-yl-1H-pyrazolo [5,1-c][1,2,4]triazole 5a–5e as the respective hydrochloride.
The in vitro antitumor activity for compounds 3a–3e and 5a–5e against L1210 (murine leukemia) and CHO
(Chinese hamster ovary) cell lines was evaluated via their respective IC50 values by the standard MTT assay [7]. The
results demonstrated that five parent fluoroquinolones had a poor inhibitory activity against the above tested cancer
line cells (IC50 > 150 mmol/L), but the ten isolated fused heterocycles 3a–3e and 5a–5e had a potential activity with
an IC50 values within 10.0 mmol concentration, especially compounds 3b, 3e, 5b and 5e displayed a better potent
against L1210 with an IC50 value of 1.4, 1.8, 0.14 and 1.2 mmol/L than against CHO with an IC50 value of 3.6, 5.7, 2.2
and 3.5 mmol/L, respectively. Conclusion, the construction of the FQ flavanoids by three structural units
corresponding to FQ scaffold, fused heterocyclic core and catechol moiety for a promising development of new
antitumor lead compounds are value for further study.
The structures of the title compounds 5a–5e were confirmed by elemental and spectral data [8].
Acknowledgments
This project was supported by National Natural Science Foundation of China (Nos. 20872028, 21072045).
References
[1] G.Q. Hu, Y. Yang, L. Yi, et al. Acta Pharm. Sin. 45 (2010) 1012 (in Chinese).

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G.Q. Hu et al. / Chinese Chemical Letters 22 (2011) 804–806
[2] A. Foroumadi, S. Emami, S.F S. Rajabalian, et al. Biomed. Pharmacother. 63 (2009) 216.
[3] Y.H. Chang, M.H. Hsu, S.H. Wang, et al. J. Med. Chem. 52 (2009) 4883.
[4] Q.D. You, Z.Y. Li, C.H. Huang, et al. J. Med. Chem. 52 (2009) 5649.
[5] G.Q. Hu, Z.Q. Zhang, H.Y. Wang, et al. Acta Chim. Sin. 67 (2009) 2592 (in Chinese).
[6] Y.A. Ibrahim, N.A. Al-Awadi, E. John, Tetrahedron 64 (2008) 10365.
[7] S.Q. Xie, Z.Q. Zhang, G.Q. Hu, et al. Toxicology 254 (2008) 68.
[8] (a) A general procedure for synthesis of 3-(6-catechol-4-yl-3-FQ-3-yl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines 3a–3e:To a mixture of each
of the starting materials 1a–1e (10 mmol) and 4-(chloroacetyl)catechol (2.0 g, 10 mmol) in ethanol (50 mL) was added 30% sodium hydroxide
(1.5 g, 11 mmol), and stirred at room temperature for 12 h. Then, a concentrated hydrochloric acid (5 mL) was added to the above reaction
solution, the resultant mixture was refluxed for 6 h. The resultant solid was collected, and recrystallized from ethanol to give the title compounds
3a–3e as respective hydrochloride. (b) A general procedure for synthesis of 6-catechol-4-yl-3-FQ-3-yl-1H-pyrazolo[5,1-c][1,2,4]triazole 5a–5e:
Each of compounds 3a–3e hydrochloride (5 mmol) in refluxing acetic anhydride (10 mL) was stirred for 1 h, a concentrated hydrochloric acid
(5 mL) was then added to the above reaction solution. Refluxing was continued for 3 h. After removal of the solvents on a rotary evaporator, the
residue was recrystallized from ethanol to give the title compounds 5a–5e as respective hydrochloride. 3-(6-Catechol-4-yl-1H-pyrazolo[5,1-
c][1,2,4]triazol-3-yl)-1-ethyl-6-fluoro-7-piperazin-1-yl-quinolin-4(1H)-one HCl 5a: yield 52%, mp >260 8C. IR (KBr, y): 3458, 3158, 1626,
1574, 1457, 1248 cmꢁ1; 1H NMR (DMSO-d6) d: 13.16 (s, 1H, NH), 11.45 (brs, 1H, HCl), 9.66, 9.53 (2 s, 2H, 2 ꢂ OH), 9.07 (s, 1H, H-2), 7.84 (d,
1H, J = 5.4 Hz, H-8), 7.75 (s, 1H, Ph–H), 7.62 (d, 1H, J = 13.2 Hz, H-5), 7.52 (dd, J = 7.2 Hz, Ph-H), 7.44 (dd, J = 7.2 Hz, Ph-H), 6.76 (s, 1H, 70-
H), 3.48–3.22 (m, 8H, piperazine-H), 2.67 (q, 2H, J = 7.2 Hz, N–CH2), 1.38(t, J = 7.2 Hz, 3H, CH3); MS m/z: Found 490 (M+ + H), Calcd.
489.51 (M+) for C25H24FN7O3. Anal. Calcd. for C25H24FN7O3 HCl: C 57.09, H 4.79, N 18.64; Found C 57.32, H 4.61, N 18.83. 3-(6-Catechol-4-
yl-1H-pyrazolo[5,1-c][1,2, 4]triazol-3-yl)-1-cyclopropyl-6-fluoro-7-piperazin-1-yl-quinolin-4-(1H)-oneꢃHCl 5b: yield 52%, mp >260 8C. IR
(KBr, y): 3528, 3356, 2894, 1632, 1568, 1455, 1268 cmꢁ1; 1H NMR (DMSO-d6) d: 12.67 (s, 1H, NH), 11.36 (br s, 1H, HCl), 9.58, 9.50 (2 s, 2H,
2 ꢂ OH), 8.97 (s, 1H, H-2), 8.04 (d, 1H, J = 5.5 Hz, H-8), 7.86 (d, 1H, J = 13.2 Hz, H-5), 7.68–7.47 (m, 3H, Ph–H), 6.54 (s, 1H, 70-H), 3.74–3.68
(m, 1H, CH-cyclopropyl), 3.36–2.58 (m, 8H, piperazine-H), 1.36–1.21 (m, 4H, CH2CH2-cyclopropyl); MS m/z: Found 524 (M+ + Na), Calcd.
501.52 (M+) for C26H24FN7O3S. Anal. Calcd. for C26H24FN7O3 HCl: C 58.05, H 4.68, N 18.22; Found C 58.29, H 4.47, N 18.40. 3-(6-Catechol-
4-yl-1H-pyrazolo[5,1-c][1,2,4]triazol-3-yl)-1-cyclopropyl-6-fluoro-7-(4-ethyl-piperazin-1-yl)-quinolin-4-(1H)-one HCl 5c: yield 46%, mp
255–257 8C. IR (KBr, y): 3368, 3057, 2854, 1627, 1562, 1457, 1264 cmꢁ1 1H NMR (DMSO-d6) d: 13.17 (s, 1H, NH), 11.26 (brs, 1H,
;
HCl), 9.66, 9.53 (2 s, 2H, 2 ꢂ OH), 8.96 (s, 1H, H-2), 8.24 (d, 1H, J = 5.7 Hz, H-8), 7.79 (d, 1H, J = 13.2 Hz, H-5), 7.68–7.52 (m, 3H, Ph–H),
6.68 (s, 1H, 70-H), 3.72–3.38 (m, 1H, CH-cyclopropyl), 3.36–3.17 (m, 8H, piperazine-H), 2.58 (q, J = 7.2 Hz, 2H, N-CH2), 1.45–1.17 (m, 7H,
NCH2CH3 and CH2CH2-cyclopropyl); MS m/z: Found 530 (M+ + H), Calcd. 529.58 (M+) for C28H28FN7O3. Anal. Calcd. for C28H28FN7O3
HCl: C 59.41, H 5.16, N 17.32; Found C 59.66, H 5.32, N 17.48. (ꢀ)-3-(6-Catechol-4-yl-1H-pyrazolo[5,1-c][1,2,4]triazol-3-yl)-1,8-(2,1-
propoxy)-6-fluoro-7-(4-methyl-piperazin-1-yl)-quinol- in-4-(1H)-one HCl 5d: yield 47%, mp >260 8C. IR (KBr, y): 3426, 3057, 1636, 1574,
1458, 1266 cmꢁ1; 1H NMR (DMSO-d6) d: 13.28 (s, 1H, NH), 11.36 (brs, 1H, HCl), 9.57, 9.52 (2 s, 2H, 2 ꢂ OH), 9.12 (s, 1H, H-2), 8.26 (d, 1H,
J = 13.3 Hz, H-5), 7.80–7.52 (m, 3H, Ph-H), 6.64 (s, 1H, 70-H), 4.57–4.53 (m, 3H, OCH2CH), 3.50–3.28 (m, 8H, piperazine-H), 2 .56 (s, 3H, N-
CH3), 1.46–1.35 (m, 3H, CH3); MS m/z: Found 554 (M+ + Na), Calcd. 531.55 (M+) for C27H26FN7O4. Anal. Calcd. for C27H26FN7O4 HCl: C
57.09, H 4.79, N 17.26; Found C 57.33, H 4.60, N 17.45. (S)-3-(6-Catechol-4-yl-1H-pyrazolo[5,1-c][1,2,4]triazol-3-yl)-1,8-(2,1-propoxy)-6-
fluoro-7-(4-methyl-piperazin-1-yl)-quinol- in-4-(1H)-one HCl 5e: yield 42%, mp 253–255 8C. IR (KBr, y): 3415, 3054, 1625, 1557, 1455,
1
1266 cmꢁ1; H NMR (DMSO-d6) d: 13.15 (s, 1H, NH), 11.30 (brs, 1H, HCl), 9.64, 9.58 (2 s, 2H, 2 ꢂ OH), 9.07 (s, 1H, H-2), 8.17 (d, 1H,
J = 13.3 Hz, H-5), 7.68–7.47 (m, 3H, Ph-H), 6.68 (s, 1H, 70-H) 4.62–4.56 (m, 3H, OCH2CH), 3.55–3.36 (m, 8H, piperazine-H), 2.62 (s, 3H, N-
CH3), 1.44–1.32 (m, 3H, CH3); MS m/z: Found 532 (M+ + H), Calcd. 531.55 (M+) for C27H26FN7O4. Anal. Calcd. for C27H26FN7O4 HCl: C
57.09, H 4.79, N 17.26; Found C 57.28, H 4.84, N 17.48.