Syntheses and studies of hydantoin derivatives as potential anti-tuberculosis inhibitors

Article abstract of DOI:10.1016/j.cclet.2011.11.017

A short and efficient synthesis of (Z)-2-substituted-5-(4-((2-substitued-5- oxoimidazolidin-4-ylidene)methyl)benzamido)benzoic acid derivatives (8a-g) as potential type of FabH inhibitors is described. Their structures were confirmed by MS, NOE and ¹H NMR.

Full text of DOI:10.1016/j.cclet.2011.11.017

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 133–136
www.elsevier.com/locate/cclet
Syntheses and studies of hydantoin derivatives as potential
anti-tuberculosis inhibitors
b
Yan Liu a,b, Wu Zhong b, , Song Li
*
a School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shenyang 110016, China
b Laboratory of Computer-Aided Drug Design & Discovery, Beijing Institute of Pharmacology and Toxicology, Beijing 100850, China
Received 28 June 2011
Available online 22 December 2011
Abstract
A short and efficient synthesis of (Z)-2-substituted-5-(4-((2-substitued-5-oxoimidazolidin-4-ylidene)methyl)benzamido)ben-
zoic acid derivatives (8a–g) as potential type of FabH inhibitors is described. Their structures were confirmed by MS, NOE and 1H
NMR.
# 2011 Wu Zhong. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Tuberculosis; Mycobacterium tuberculosis FabH; Enzyme inhibitor; Synthesis; NOE
According to the data of the World Health Organization, tuberculosis (TB) caused by Mycobacterium tuberculosis,
is considered to be a major cause of death from a single infectious agent in the world especially in countries lacking the
necessary health care organization to provide the long and costly treatment adapted to patients [1]. As resistant strains
of Mycobacterium tuberculosis and increasing HIV-positive TB cases have emerged, treatment failure is too often a
fact [2,3]. An urgent requirement exists for the development of new anti-mycobacterial agents with a unique
mechanism of action.
Fatty acid synthase (FAS) is a single multifunctional polypeptide that catalyzes all the reactions in the elongation
pathway [4,5]. Mycobacteria contain both type I (FAS I) and type II (FAS II) pathways. M. tuberculosis b-ketoacyl–
acyl carrier protein synthase III (mtFabH) is a key condensing enzyme responsible for initiation of FAS II fatty acid
biosynthetic pathway, and has emerged as an attractive new target for novel anti-mycobacterial agents in recent years.
We studied all available information concerning mtFabH inhibitors [6,7], substrates, and the active site topology from
available mtFabH crystal structures. According to the known anti-mycobacterial 5-arylidene derivatives of hydration
[8], we designed a serials scaffold of hydantoin derivatives. We chose mtFabH (PDB ID: 1HZP) [9] as the docking
target, and used an automated molecular docking and database screening program DOCK 4.0 (http://
www.cmpharm.ucsf.edu/kuntz/, University of California at San Francisco) [10]. The top 500 hydantoin derivatives
from computer screening were carefully investigated. After taking drug-like property and synthetic accessibility into
account, a subset of 7 candidate compounds were firstly chosen to be synthesized. The synthesis of a serious of
potential mtFabH inhibitors are reported in this paper.
* Corresponding author.
E-mail address: zhongwu@nic.bmi.ac.cn (W. Zhong).
1001-8417/$ – see front matter # 2011 Wu Zhong. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.11.017

134
Y. Liu et al. / Chinese Chemical Letters 23 (2012) 133–136
COOCH3
COOCH3
COOCH3
ii
HO
RO
RO
i
NO2
NH2
NO2
3
1
2
iv
H
O
O
CHO
iii
NH
NH
HN
HN
HOOC
RO
HOOC
RO
S(O)
S(O)
6
4
5
COOCH3
COOH
O
H
v
O
O
H
O
NH
NH
NH
NH
S(O)
HN
HN
S(O)
7
8
Scheme 1. Reagents and conditions: (i) RBr, K2CO3, DMF; (ii) SnCl2ꢀH2O, C2H5OH; (iii) CH3COOH, CH3COONa; (iv) EDC HOBT, DIEA, DMF;
(v) LiOH, CH3OH, THF, H2O.
The synthesis of the target compounds is shown in Scheme 1. Methyl 2-hydroxy-5-nitrobenzoate 1 was alkylated by
the halogenated aliphatic hydrocarbons with n-Bu4NI and anhydrous K2CO3 to get compound 2 [11]. The reduction of
nitro with stannous chloride in refluxing ethanol afforded compound 3 [12]. On the other hand, compounds 6 were
prepared as a result of condensation of 2-thioxoimidazolidin-4-one or imidazolidine-2,4-dione with 4-formylbenzoic
acid refluxed in acetic acid with anhydrous sodium acetate [13]. The compound 3 and compound 6 converted into
amide which was catalyzed by EDC hydrochloride with DIEA and HOBT [14].
Table 1
Analytical data of the compound 8a-g.
Compd.
R
S or O
O
FAB MS (m/z)
1H NMR (400 MHz, DMSO-d6)
8a
Hexyl
450.6
12.17 (s, 1H), 11.35 (s, 1H), 10.73 (s, 1H), 10.27 (d, 1H, J = 12 Hz), 8.07 (d, 1H,
J = 2.8 Hz), 7.98 (d, 2H, J = 8.4 Hz), 7.89 (m, 1H), 7.75 (d, 2H, J = 8.4 Hz), 7.11 (m,
1H), 6.47 (s, 1H), 4.00 (m, 2H), 1.45 (m, 2H), 1.44 (m, 2H), 1.30 (m, 4H), 0.88 (t, 3H,
J = 6.8 Hz).
8b
8c
8d
8e
8f
Pentyl
Propyl
Ethyl
O
O
S
436.6
408.6
410.5
424.4
466.5
452.6
12.58 (s, 1H), 11.36 (s, 1H), 10.74 (s, 1H), 10.32 (m, 1H), 8.07 (d, 1H, J = 2.8 Hz), 8.01
(d, 2H, J = 8.4 Hz), 7.90 (m, 1H), 7.76 (d, 2H, J = 8.8 Hz), 7.11 (d, 1H, J = 9.2 Hz), 6.47
(s, 1H), 4.00 (m, 2H), 1.68 (m, 2H), 1.30 (m, 4H), 0.88 (t, 3H, J = 14.8 Hz).
12.59 (s, 1H), 11.34 (s, 1H), 10.73 (s, 1H), 10.27 (m, 1H), 8.07 (d, 1H, J = 2.8 Hz), 7.98
(d, 2H, J = 8.4 Hz), 7.90 (m, 1H), 7.76 (d, 2H, J = 8.4 Hz), 7.10 (d, 1H, J = 9.2 Hz), 6.47
(s, 1H), 3.97 (t, 2H, J = 12.4 Hz), 1.70 (q, 2H, J = 14 Hz), 0.98 (t, 3H, J = 17.2 Hz).
12.67 (s, 1H), 12.53 (s, 1H), 12.34 (s, 1H), 10.51 (s, 1H), 8.12 (d, 1H, J = 2.4 Hz), 8.05
(d, 2H, J = 8.4 Hz), 7.94 (m, 1H), 7.88 (d, 2H, J = 8.4 Hz), 7.11 (d, 1H, J = 9.6 Hz), 6.54
(s, 1H), 4.06 (q, 2H, J = 21.2 Hz), 1.32 (t, 3H, J = 14 Hz).
Propyl
Hexyl
Pentyl
S
12.70 (s, 1H), 12.52 (s, 1H), 12.33 (s, 1H), 10.47 (s, 1H), 8.11 (d, 1H, J = 2.4 Hz), 8.04
(d, 2H, J = 8.4 Hz), 7.93 (m, 1H), 7.89 (d, 2H, J = 8.8 Hz), 7.11 (d, 1H, J = 8.8 Hz), 6.54
(s, 1H), 3.97 (t, 2H, J = 12.8 Hz), 1.71 (m, 2H), 0.98 (t, 3H, J = 14.8 Hz).
12.51 (s, 1H), 12.32 (s, 1H), 10.33 (s, 1H), 8.08 (d, 1H, J = 2.8 Hz),8.02 (d, 2H,
J = 8.4 Hz), 7.89 (m, 3H), 7.11 (d, 1H, J = 9.2), 6.55 (s, 1H), 4.00 (t, 2H, J = 12.8 Hz),
1.69 (m, 2H), 1.29 (m, 6H), 0.86 (t, 3H, J = 14 Hz).
S
8g
S
12.65 (s, 1H), 12.52 (s, 1H), 12.33 (s, 1H), 10.46 (s, 1H), 8.11 (d, 1H, J = 2.8 Hz), 8.04
(d, 2H, J = 8.4 Hz) 7.89 (m, 3H), 7.11 (d, 1H, J = 8.8 Hz), 6.54 (s, 1H), 4.00 (t, 2H,
J = 12.8 Hz), 1.70 (m, 2H), 1.33 (m, 4H), 0.88 (t, 3H, J = 14 Hz).

Y. Liu et al. / Chinese Chemical Letters 23 (2012) 133–136
135
Fig. 1. The NOE analysis of compound 8c.
The compound 7 underwent saponification by lithium hydroxide then were acidified by hydrochloride to yield the
target compound 8 [15]. The target compounds were listed in Table 1.
As the steric position of benzylidene substituent was restricted by C/C bond, the target compounds could occur in
either E-or Z-configuration. The steric position of the (Z)-5-(4-((2,5-dioxoimidazolidin-4-ylidene)methyl)benz-
amido)-2-propoxybenzoic acid 8c was established by the H-a 1H NMR(400 MHz, DMSO-d6): d 6.47 (s, 1H), coupled
1
H-bb0 H NMR(400 MHz, DMSO-d6): d 7.75 ꢁ 7.77 (d, 2 H, J = 8 Hz), coupled H-cc0 1H NMR(400 MHz, DMSO-
d6): d 7.98 ꢁ 8.00 (d, 2H, J = 8 Hz) and 1-NH 1H NMR(400 MHz, DMSO-d6): d 10.724 (brs, 1H), as shown in Fig. 1.
In the NOE difference experiment for compound 8c in DMSO-d6 (Fig. 1), the 2nd part shows enhancement of the H-a,
H-cc0 and 1-NH on irradiation of the H-bb0, and the 3th part shows enhancement of the H-bb0 on irradiation of the H-a.
The result indicated that the formation of compound 8c is Z-configuration. Spectrum associated with the NOE
difference experiment can be found in the supporting information.
The antimycobacterial activities in vitro of the target compounds were studied. At a concentration of 12.5 mg/mL,
all compounds exhibited inhibition on the growth of M. tuberculosis strain H37Rv at 2 weeks, the resistant strains of
Mycobacterium tuberculosis activity evaluation is still in progress.
Acknowledgment
This work was financially supported by the National High Technology Research and Development Program of
China (No. 2006AA020601).

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Y. Liu et al. / Chinese Chemical Letters 23 (2012) 133–136
References
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[11] Methyl 2-substituted-5-nitrobenzoate 2. General procedure: To a solution of ethyl 2-hydroxy-5-nitrobenzoate 1 (2.0 g, 10 mmol) and n-
Bu4NBr (6.4 g, 20 mmol) in DMF (20 mL) were added anhydrous K2CO3 (2.8 g, 20 mmol) and halogenated aliphatic hydrocarbons
(15 mmol). After stirring for 4 h at room temperature, to the reaction mixture 1 mol/L HCl (30 mL) was added. The organic portion was
extracted with EtOAc (3 mL ꢂ 40 mL). The combined organic phase was dried for a while and then Na2SO4 was filtered out, the filtrate was
removed in vacuo. The residue was purified by column chromatography (silica gel, gradient elution with hexane: EtOAc (v/v) = 1:10–1:5) to
give the corresponding product.
[12] Methyl 5-amino-2-substituted benzoate 3. General procedure: To a solution of compound 2 (8 mmol) in ethanol (60 mL) was added stannous
chloride dehydrate (0.99 g, 48 mmol). The mixture was stirred at 70 8C for 7 h, and half of the solvent was removed in vacuo. The residue was
added ethyl acetate (3 mL ꢂ 40 mL). The organic layer was washed with aqueous solution of sodium hydroxide, dried with anhydrous sodium
sulfate, and evaporated in vacuo. Chromatography the residue on silica gel gave the title compounds.
[13] (Z)-4-((5-substitued-2-thioxoimidazolidin-4-ylidene)methyl)benzoic acid 6. General procedure: 4-Formylbenzoic acid 4 (10.0 g, 67 mmol)
with anhydrous sodium acetate (22.0 g, 268 mmol) were successively added to a stirred solution of 2-substitued-imidazolidin-4-one 5
(70 mmol) in acetic acid (300 mL). The mixture was stirred at 120 8C for 0.5 h and then poured into water. The resulting mixture was stood
overnight to form the precipitation. The crude solid was collected through filtration and air dried. The crude solid was crystallized twice with
EtOAc to give pure compound.
[14] (Z)-Methyl-2-substituted-5-(4-((2-substitued-5-oxoimidazolidin-4-ylidene)methyl)benzamido)benzoate 7. General procedure: To a stirred
solution of compoud 6 (4 mmol) and compound 3 (4 mmol) in anhydrous DMF (50 mL), were successively added EDC hydrochloride with
DIEA and HOBT. The mixture was stirred at 40 8C for 24ꢁ48 h and then poured into water. The resulting mixture was stood overnight to form
the precipitation. The solid was collected through filtration and air crystallized twice with MeOH to give the title compound.
[15] (Z)-2-Substituted-5-(4-((2-substitued-5-oxoimidazolidin-4-ylidene)methyl)benzamido)benzoic acid 8. General procedure: To a stirred solu-
tion of compound 7 in MeOH (50 mL) was added 1 mol/L LiOH (10 mL) at 25 8C. The mixture was stirred at the same temperature for 30 min.
The aqueous layer was separated and was acidified with 1 mol/L HCl to pH-4. The aqueous layer was extracted with EtOAc (3 mL ꢂ 50 mL).
The combined organic layer was dried (Na2SO4), filtered, and crystallized twice with EtOAc to give pure 8a–g.