Synthesis and antibacterial activity of a novel series of DNA gyrase inhibitors: 5-[(E)-2-arylvinyl]pyrazoles

Article abstract of DOI:10.1016/j.bmcl.2005.06.103

The 2-arylvinyl moiety in 1-(3-chlorophenyl)-3-(4-piperidyl)-5-[(E)-2-(5- chloro-1H-indol-3-yl)vinyl]pyrazole 2, which has previously shown improved DNA gyrase inhibition and target-related antibacterial activity, was transformed to other groups and the i

Full text of DOI:10.1016/j.bmcl.2005.06.103

Bioorganic & Medicinal Chemistry Letters 15 (2005) 4299–4303
Synthesis and antibacterial activity of a novel series of DNA
gyrase inhibitors: 5-[(E)-2-arylvinyl]pyrazoles
Akihiko Tanitame,a,* Yoshihiro Oyamada,b Keiko Ofuji,a Hideo Terauchi,a,d
Motoji Kawasaki,a Masaaki Wachic and Jun-ichi Yamagishib,d
aChemistry Research Laboratories, Dainippon Pharmaceutical Co., Ltd, 33-94, Enoki, Suita, Osaka 564-0053, Japan
bPharmacology and Microbiology Research Laboratories, Dainippon Pharmaceutical Co., Ltd, 33-94,
Enoki, Suita, Osaka 564-0053, Japan
cDepartment of Bioengineering, Tokyo Institute of Technology, 4259, Nagatsuda, Midori-ku, Yokohama 226-8501, Japan
dPharmaceutical Research and Technology Center, Dainippon Pharmaceutical Co., Ltd, 1-5-51,
Ebie, Fukushima, Osaka 553-0001, Japan
Received 16 May 2005; revised 15 June 2005; accepted 17 June 2005
Abstract—The 2-arylvinyl moiety in 1-(3-chlorophenyl)-3-(4-piperidyl)-5-[(E)-2-(5-chloro-1H-indol-3-yl)vinyl]pyrazole 2, which has
previously shown improved DNA gyrase inhibition and target-related antibacterial activity, was transformed to other groups and
the in vitro antibacterial activity of the synthesized compounds was evaluated. Many of the 5-[(E)-2-arylvinyl]pyrazoles synthesized
in this study exhibited potent antibacterial activity against quinolone-resistant clinical isolates of Gram-positive bacteria with min-
imal inhibitory concentration values equivalent to those against susceptible strains.
Ó 2005 Elsevier Ltd. All rights reserved.
Antibacterial resistance to hospital-acquired Gram-posi-
tive bacterial pathogens, including methicillin-resistant
Staphylococcus aureus (MRSA), penicillin-resistant
Streptococcus pneumoniae (PRSP), and vancomycin-re-
sistant enterococci (VRE), has been increasing at an
alarming rate. Furthermore, these drug-resistant bacte-
ria commonly infect healthy people in large communi-
ties, thus creating a serious health problem around the
globe. Consequently, the discovery of novel and potent
bactericides is the best way to overcome bacterial resis-
tance and develop effective therapies.
bacterial agents that can overcome bacterial resistance,
promising new lead structures of DNA gyrase inhibitors
have not been found.4–9
Using a new screening system for specific inhibitors of
chromosome partitioning in Escherichia (E.) coli,10,11
we have previously reported compounds 1, 2 and 3
(Fig. 1) as moderate inhibitors of DNA gyrase and topo-
isomerase IV with potent antibacterial activity against
multidrug resistant strains as well as susceptible
NH2
NH2
O
N
Bacterial DNA gyrase is a proven target for antibacteri-
al chemotherapy.1 Quinolones, such as sparfloxacin2
(SPFX, Fig. 1), inhibit bacterial DNA gyrase and topo-
isomerase IV and cause bacterial cell death. Besides the
quinolones, other naturally occurring bacterial DNA
gyrase inhibitors, such as novobiocin (NB, Fig. 1), have
also been known as antibacterial agents.3 Although
many efforts have been dedicated to finding potent anti-
OH
F
COOH
O
O
O
OH
O
H
N
O
OH
N
O
HN
F
O
O
NB
SPFX
Cl
Cl
N
NH
N
N
N
N
Cl
Cl
Cl
Cl
HN
HN
HN
1
3
Keywords: DNA gyrase inhibitor; 5-[(E)-2-Arylvinyl]pyrazoles; Multi-
drug resistant strains.
2
NH
Cl
*
Corresponding author. Tel.: +81 6 6337 5900; fax: +81 6 6337
6010; e-mail: akihiko-tanitame@dainippon-pharm.co.jp
Figure 1.
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.06.103

4300
A. Tanitame et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4299–4303
strains.12 In addition, we have published the synthesis
and structure–activity relationships (SARs) of 3-substi-
tuted pyrazole derivatives.13 In this study, we derived
the 2-arylvinyl moieties of 1, 2 and 3 to other 2-arylvinyl
and 2-arylethyl substituents to find novel potent DNA
gyrase inhibitors with antibacterial activity against
MRSA, PRSP and VRE. Here, we report the synthesis
and SARs of a series of 5-[(E)-2-arylvinyl]pyrazoles
and 5-(2-arylethyl)pyrazoles.
The (E)-2-[4-(3,4-dichlorobenzyloxy)phenyl]vinyl deriv-
ative 7a and the (E)-2-(3,4-dichlorophenyl)vinyl deriva-
tive 7b showed almost the same antibacterial activity
against the four strains of bacteria compared to 1. The
(E)-2-(5-chloro-1-methylindol-3-yl)vinyl derivative 7c
and the (E)-2-(5-chloro-1H-indol-2-yl)vinyl derivative
7d showed 2-fold less potent antibacterial activity
against Staphylococcus (S.) aureus than 2. Compound
7c, which was the N-methyl derivative of 2, did not show
antibacterial activity against E. coli NIHJ JC-2. This re-
sult suggests that the 5-chloro-1H-indol-3-yl groups in 2
and 7d are important for antibacterial activity against
Gram-negative bacteria. The 2-(2,6-dichlorophenyl)eth-
yl derivative 10a and the 2-(5-chloro-1H-indol-3-yl)ethyl
derivative 10b exhibited 4- to 16-fold less potent antibac-
terial activity than the corresponding 5-[(E)-2-arylvi-
nyl]pyrazoles 1 and 2, respectively. This result suggests
that the vinyl moieties in the R groups appended on
the pyrazoles are essential for antibacterial activity.
The novel 5-[(E)-2-arylvinyl]pyrazoles 7a–d, 8a,b were
prepared as shown in Scheme 1. Condensation of alde-
hydes 4 with acetone using aqueous NaOH gave the var-
ious 2-acetylvinyl derivatives 5. The requisite
intermediate 1,3-diketones 6 were synthesized by cou-
pling reaction of the N-[tert-butoxycarbonyl (Boc)]-
piperidine-4-carboxylic acid with 5 in THF using 1,10-
carbonyldi-1H-imidazole (CDI) and lithium hexamethyl-
disilazide (LHMDS).14 Condensation of 6 with 3-chloro-
phenylhydrazine hydrochloride, followed by cleavage of
the Boc group under acidic conditions and separation
using CHP-20P (reverse phase) column chromatography
and/or recrystallization gave one of the isomers, the
1-(3-chlorophenyl)-5-[(E)-2-arylvinyl]pyrazoles 7a–d as
acid salts. The position of 3-chlorophenyl groups in
7a–d was determined on the basis of nuclear Overhauser
effects (NOE) experiments. For example, in compound
7b, a correlation of NOE was observed between the
protons of the vinyl moiety and the ortho protons of the
3-chlorophenyl moiety.
The 1H-pyrazoles 3 and 8a showed almost the same
antibacterial activity against two Gram-positive bacteria
compared to 1-(3-chlorophenyl)pyrazoles 7a and 7b,
respectively. Remarkably, compound 8a showed 8-fold
more potent antibacterial activity against E. coli NIHJ
JC-2 than the corresponding 1-(3-chlorophenyl)pyrazole
7a. Also, the 5-(2-arylethyl)pyrazole 11 showed almost
the same antibacterial activity against two Gram-posi-
tive bacteria compared to the corresponding 1-(3-chloro-
phenyl)pyrazole 10a. Compound 8b resulted in less potent
antibacterial activity compared to the 1-(3-chloro-
phenyl)pyrazole 1. Thus, the substituents on the pyrazole
ring of the isomers of the 5-[(E)-2-dichlorophenylvi-
nyl]pyrazole derivatives show different effects on the
antibacterial activity from each other.
The 1H-pyrazoles 8a,b were synthesized by condensa-
tion of 6 with hydrazine hydrate and aqueous NaOH
in a similar manner to that described above. 5-(2-Aryl-
ethyl)pyrazoles 10a,b and 11 having 2-arylethyl groups
at the 5-position on the pyrazole ring instead of the 2-
arylvinyl of 1, 2 and 8b were prepared from the corre-
sponding 1,3-diketones 9 (Scheme 1), which were pre-
pared by hydrogenation of 6, in a similar manner to
that described above.
Since the 1H-pyrazoles 3 and 8a showed nearly the same
antibacterial activity against E. coli NIHJ JC-2 and
W3110 DacrA, it is presumed that these derivatives are
not affected by bacterial outer membrane pump. The
pyrazole derivatives synthesized in this study showed al-
most same antibacterial activity against susceptible and
resistant S. aureus.
To investigate the effects of R groups on the pyrazole
ring on the antibacterial activity, the vinyl moieties in
1, 2 and 3 were transformed to other groups and the
minimal inhibitory concentration (MIC) of compounds
obtained was evaluated against two Gram-positive mic-
rodilution method (Table 1).
To examine whether the novel 5-[(E)-2-arylvinyl]pyraz-
oles are effective against multidrug resistant Gram-posi-
tive bacteria, MIC values of selected compounds against
Cl
O
O
O
N
N
O
a
c
b
H3C
tBuOOC
e
H
Ar
N
HN
Ar
Ar
Ar
7a-d
4
5
6
d
Cl
O
O
N
NH
N
N
N NH
c
d
tBuOOC
HN
N
HN
HN
9
Ar
10a,b
11
8a,b
Ar
Ar
Ar
Scheme 1. General synthesis of the pyrazole derivatives. Reagents: (a) acetone, aqueous NaOH, EtOH; (b) (i) LHMDS, THF (ii) N-Boc-piperidine-
4-carboxylic acid, CDI, THF; (c) (i) 3-chlorophenylhydrazineÆHCl, aqueous NaOH, EtOH; (ii) TFA, CH2Cl2; (d) (i) NH2NH2ÆH2O, EtOH; (ii) TFA,
CH2Cl2, (e) H2, 5% Pd–C, EtOH.

A. Tanitame et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4299–4303
Table 1. Antibacterial activity of the pyrazole derivatives
4301
Cl
N
N
N
NH
R
R
HN
HN
3, 8a,b, 11
1, 2, 7a-d, 10a,b
No
R
MIC (lg/mL)
NIHJ JC-2a
S. aureus
FDA 209Pa
E. coli
KMP9b
W3110 DacrAc
Cl
Cl
7a
7b
2
4
32
16
4
4
O
Cl
Cl
8
2
4
2
Cl
7c
>128
4
N
CH3
H
N
7d
2
2
4
2
16
4
4
2
Cl
Cl
Cl
8a
O
Cl
Cl
8b
128
32
>128
32
>128
>128
>128
16
Cl
Cl
10a
Cl
10b
11
16
32
16
64
64
16
64
N
H
Cl
128
Cl
Cl
Cl
1
2
4
1
4
1
64
8
4
4
Cl
N
H
Cl
Cl
3
4
4
8
4
SPFX
NB
—
—
0.125
0.25
128
0.032
64
0.004
0.5
0.25
a Susceptible strain.
b Multidrug resistant S. aureus.
c A multidrug efflux pump mutant.
quinolone-resistant clinical isolates of Gram-positive
bacteria were determined and compared with those of
1, 2 and sparfloxacin (Table 2). Although the ratio of
MIC values of sparfloxacin against susceptible and resis-
tant strains was more than 32, that of 7c, 8a and 10b
ranged between 1 and 2. Thus, the 5-[(E)-2-arylvi-
nyl]pyrazoles were effective against quinolone-resistant
Gram-positive bacteria. In particular, compounds 7c
and 8a demonstrated the most potent antibacterial
activity against susceptible and resistant Gram-positive
bacteria with across-the-board MIC values of 1–2 lg/
mL.

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A. Tanitame et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4299–4303
Table 2. Antibacterial activity of the selected 5-[(E)-2-arylvinyl]pyrazoles against susceptible and resistant Gram-positive bacteria
Organisma
MIC (lg/mL)
7c
8a
10b
1
2
SPFX
0.125
128
0.125
b
S. aureus FDA 209P (MSSA)
c
S. aureus KMP9 (MRSA)
2
2
1
1
2
1
2
2
2
1
2
1
16
16
16
8
4
4
4
4
8
8
1
1
2
2
2
2
b
S. pneumoniae ATCC49619 (PSSP)
S. pneumoniae KT2524 (PRSP)c
E. faecium ATCC19434 (VSE)b
E. faecium KU1778 (VRE)d
4
0.25
16
16
64
a SPFX: sparfloxacin, CAM: clarithromycin, ABPC: ampicillin, VCM: vancomycin.
b Susceptible strain.
c SPFX-, CAM-, ABPC-resistant strain.
d SPFX-, CAM-, ABPC-, VCM-resistant strain.
To elucidate the mechanism by which the novel 5-[(E)-
2-arylvinyl]pyrazoles induce their antibacterial activity,
Acknowledgments
the inhibitory activity of selected compounds 7c and
8a against DNA gyrase and topoisomerase IV isolated
from E. coli was examined (Table 3).15,16 Compounds
7c and 8a showed moderate inhibition against the two
enzymes (IC50 = 13.9–27.8 lg/mL). There was a good
correlation between the MICs and the IC50s of 2, 7c
and 8a (Tables 1 and 3), suggesting that inhibition
of the DNA gyrase and topoisomerase IV by the 5-
[(E)-2-arylvinyl]pyrazoles suppresses bacterial cell
growth. While ratio of inhibition of DNA gyrase
and topoisomerase IV of sparfloxacin was more than
20, that of 7c and 8a ranged between 1.2 and 2.0.
Thus, 7c and 8a showed almost the same inhibitory
activity against both enzymes as the dual inhibitors.
These results suggest that resistance against the 5-
[(E)-2-arylvinyl]pyrazoles would not be easily devel-
oped by bacteria.
We thank Dr. S. Matsuyama for supplying the E. coli
W3110 DacrA.
References and notes
1. (a) Ferrero, L.; Cameron, B.; Manse, B.; Lagneaux, D.;
Crouzet, J.; Famechon, A.; Blanche, F. Mol. Microbiol.
1994, 13, 641; (b) Kim, O. K.; Ohemeng, K. A. Exp. Opin.
Ther. Patents 1998, 8, 959.
2. Miyamoto, T.; Matsumoto, J.; Chiba, K.; Egawa, H.;
Shibamori, K.; Minamida, A.; Nishimura, Y.; Okada, H.;
Kataoka, M.; Fujita, M.; Hirose, T.; Nakano, J. J. Med.
Chem. 1990, 33, 1645.
3. Maxwell, A. Mol. Microbiol. 1993, 9, 681.
4. (a) Nakada, N.; Gmuender, H.; Hirata, T.; Arisawa, M.
Antimicrob. Agents Chemother. 1994, 38, 1966; (b) Nak-
ada, N.; Gmunder, H.; Hirata, T.; Arisawa, M. J. Biol.
Chem. 1995, 270, 14286.
5. Rudolph, J.; Theis, H.; Hanke, R.; Endermann, R.;
Johannsen, L.; Geschke, F. J. Med. Chem. 2001, 44, 619.
6. Angehrn, P.; Buchmann, S.; Funk, C.; Goetschi, E.;
Gmuender, H.; Hebeisen, P.; Kostrewa, D.; Link, H.;
Luebbers, T.; Masciadri, R.; Nielsen, J.; Reindl, P.;
Ricklin, F.; Schmitt-Hoffmann, A.; Theil, F. J. Med.
Chem. 2004, 47, 1487.
7. Boehm, H.; Boehringer, M.; Bur, D.; Gmuender, H.;
Hunber, W.; Klaus, W.; Kostrewa, D.; Kuehne, H.;
Luebbers, T.; Meunier-Keller, N.; Mueller, F. J. Med.
Chem. 2000, 43, 2664.
8. Lubbers, T.; Angehrn, P.; Gmunder, H.; Herzig, S.;
Kulhanek, J. Bioorg. Med. Chem. Lett. 2000, 10, 821.
9. Galm, U.; Heller, S.; Shapiro, S.; Page, M.; Li, S.; Heide,
L. Antimicrob. Agents Chemother. 2004, 48, 1307.
10. Wachi, M.; Iwai, N.; Kunihisa, A.; Nagai, K. Biochimie
1999, 81, 909.
In this study, we have described the synthesis and
SARs of the novel pyrazole derivatives. Among the
1-(3-chlorophenyl)pyrazole
derivatives,
7c
had
comparatively strong antibacterial activity, whereas
among the 1H-pyrazole derivatives, 8a showed com-
paratively strong antibacterial activity. Compounds
7c and 8a exhibited potent antibacterial activity
against not only susceptible strains but also multidrug
resistant strains. We are pursuing further modifica-
tions of the 5-[(E)-2-arylvinyl]pyrazole scaffold to ob-
tain more potent inhibitors of both DNA gyrase and
topoisomerase IV.
11. Hiraga, S.; Niki, H.; Ogura, T.; Ichinose, C.; Mori, H.;
Ezaki, B.; Jaffe, A. J. Bacteriol. 1989, 171, 1496.
12. Tanitame, A.; Oyamada, Y.; Ofuji, K.; Fujimoto, M.;
Iwai, N.; Hiyama, Y.; Suzuki, K.; Ito, H.; Terauchi, H.;
Kawasaki, M.; Nagai, K.; Wachi, M.; Yamagishi, J. J.
Med. Chem. 2004, 47, 3693.
13. Tanitame, A.; Oyamada, Y.; Ofuji, K.; Fujimoto, M.;
Suzuki, K.; Ueda, T.; Terauchi, H.; Kawasaki, M.; Nagai,
K.; Wachi, M.; Yamagishi, J. Bioorg. Med. Chem. 2004,
12, 5515.
Table 3. Inhibitory effects of the selected 5-[(E)-2-arylvinyl]pyrazoles
against DNA gyrase and topoisomerase IV
Compound
IC50(lg/mL)a
Gyraseb
Topo IVc
7c
8a
13.9
13.9
8.0
16
27.8
13.9
6.9
2
SPFX
0.25
a Isolated from E. coli.
14. (a) Rowley, M.; Broughton, H. B.; Collins, I.; Baker, R.;
Emms, F.; Marwood, R.; Patel, S.; Patel, S.; Ragan, C. I.;
Freedman, S. B.; Leeson, P. D. J. Med. Chem. 1996, 39,
b DNA gyrase supercoiling activity.
c Topoisomerase IV decatenation activity.

A. Tanitame et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4299–4303
4303
1943; (b) Rowley, M.; Collins, I.; Broughton, H. B.;
Davey, W. B.; Baker, R.; Emms, F.; Marwood, R.; Patel,
S.; Patel, S.; Ragan, C. I.; Freedman, S. B.; Ball, R.;
Leeson, P. D. J. Med. Chem. 1997, 40, 2374.
15. Sato, K.; Inoue, Y.; Fujii, T.; Aoyama, H.; Inoue, M.;
Mitsuhashi, S. Antimicrob. Agents Chemother. 1986, 30,
777.
16. Peng, H.; Marians, K. J. J. Biol. Chem. 1993, 268, 24481.