Simplified captopril analogues as NDM-1 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2013.10.068

Captopril is a New Delhi metallo-β-lactamase-1 (NDM-1) inhibitor with an IC₅₀ value of 7.9 μM. It is composed of two units: a 3-mercapto-2-methylpropanoyl fragment and a proline residue. In this study, we synthesized simple amide derivatives of 3-mercapto-2-methylpropanoic acid, and then tested them as NDM-1 inhibitors in order to identify the pharmacophore for NDM-1 inhibition. We found that the lead compound 22 had an IC₅₀ value of 1.0 μM. Further structure simplification provided compounds 31 and 32, which had IC₅₀ values of 15 and 10 μM, respectively. As compound 32 is a clinically used antidote for metal poisoning, it has great potential to be repurposed to treat bacterial infections.

Full text of DOI:10.1016/j.bmcl.2013.10.068

Bioorganic & Medicinal Chemistry Letters 24 (2014) 386–389
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Simplified captopril analogues as NDM-1 inhibitors
Ningning Li a,b, , Yintong Xu a,b, , Qiang Xia a,b, , Cuigai Bai b, Taiyi Wang a,b, Lei Wang a,b, Dingdi He a,b
Nannan Xie a,b, Lixin Li b, Jing Wang b, Hong-Gang Zhou a,b, Feng Xu a,b, Cheng Yang a,b, Quan Zhang a,
,
a,
a,b,
Zheng Yin a,b, , Yu Guo , Yue Chen
⇑
⇑
⇑
a College of Pharmacy and the State Key Laboratory of Elemento-Organic Chemistry, Synergetic Innovation Center of Chemical Science and Engineering (Tianjin), and Tianjin
Key Laboratory of Molecular Drug Research, Nankai University, Tianjin 300071, PR China
b High-throughput Molecular Drug Discovery Center, Tianjin International Joint Academy of Biotechnology & Medicine, Tianjin 300457, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 July 2013
Revised 10 October 2013
Accepted 29 October 2013
Available online 6 November 2013
Captopril is a New Delhi metallo-b-lactamase-1 (NDM-1) inhibitor with an IC50 value of 7.9 lM. It is com-
posed of two units: a 3-mercapto-2-methylpropanoyl fragment and a proline residue. In this study, we
synthesized simple amide derivatives of 3-mercapto-2-methylpropanoic acid, and then tested them as
NDM-1 inhibitors in order to identify the pharmacophore for NDM-1 inhibition. We found that the lead
compound 22 had an IC50 value of 1.0
32, which had IC50 values of 15 and 10
l
l
M. Further structure simplification provided compounds 31 and
M, respectively. As compound 32 is a clinically used antidote for
Keywords:
Captopril
NDM-1 inhibitor
Metalantidote
metal poisoning, it has great potential to be repurposed to treat bacterial infections.
Ó 2013 Elsevier Ltd. All rights reserved.
3-Mercapto-2-methylpropanoic acid
New Delhi metallo-b-lactamase-1 (NDM-1) is a newly discov-
ered carbapenemase that causes bacterial resistance to a broad
range of b-lactam antibiotics.1 NDM-1 belongs to the Class B metal-
lo-b-lactamase superfamily, which contains enzymes that hydro-
lyze b-lactams.2,3 The bacteria that produce carbapenemases are
often referred to as ‘superbugs’ because infections with them are
difficult to treat. Bacteria containing NDM-1 were first identified
in a patient who visited India in 2008, and the strain spread rapidly
worldwide. In less than one month after it was first detected, many
cases of infection had been reported in several countries.4–7
Although many compounds have been reported to inhibit metal-
lo-b-lactamase,9–41 few compounds have been found to be effec-
tive inhibitors of NDM-1 because NDM-1 can break down the
drugs that target b-lactamase.8
HOBT/NMM or CDI/DBU afforded amides III. The hydrolysis reac-
tion using aqueous NaHCO3 or Na2CO3 provided the target thiols
IV (5–30, Table 1).
The initial screening of NDM-1 inhibitory activities was carried
out on the analogs at a concentration of 1 mM (1–30, Table 1), and
the compounds with greater than 50% inhibition at 1 mM were fur-
ther tested to obtain their IC50 values against NDM-1.
Racemic 3-mercapto-2-methylpropanoic acid (1) and its opti-
cally pure enantiomers (2 and 3) all showed comparable inhibition
of NDM-1, indicating that the absolute configuration has little
impact on the inhibitory activity. The ester form of 3-mercapto-
2-methylpropanoic acid (4) as well as the acetyl form of mercapto-
propanoic acid were inactive, showing no inhibitory activity at a
concentration of 1 mM. These results suggest that the thiol group
and the carboxylic acid group may be important for binding to
the active site of NDM-1 protein. In addition, dimethyl hydroxyla-
mides 5 and 6 demonstrated relatively high inhibition activities
Captopril is one of the few compounds that effectively inhibits
NDM-1 with an IC50 value of 7.9 lM. It is composed of two units:
a 3-mercapto-2-methylpropanoyl fragment and a proline resi-
due.42 Herein, we report the stepwise simplification of captopril
in order to identify the pharmacophore for NDM-1 inhibition.
First, the proline residue was replaced with a simpler unit such
as a primary or secondary amine using the general synthetic
sequence shown in Scheme 1.43 The coupling reaction between
acetyl sulfhydryl isobutyric acid I and amines II using EDCI/
(IC50 = 20 and 48 lM, respectively) compared to the corresponding
monosubstituted hydroxylamides 7 and 8; phenyl amide 10;
substituted phenyl amides 11, 12, and 13; imidazole 14; and thioz-
ole amide 15; which were inactive at 200
thiozole amide 16 and methyl oxazole amide 17 were relatively
potent inhibitors with IC50 values of 52 and 21 M, respectively.
When the linear aliphatic amides were studied, it was found that
butyl amide 18 had an IC50 value of 20 M and methyl sulfyl ethyl
amide (19) had an IC50 of 13 M, while the corresponding methyl
sulfonyl ethyl amide (20) was less active (IC50 = 120 M).
lM. Furthermore, bromo
l
l
⇑
Corresponding authors. Tel./fax: +86 22 23508090.
E-mail addresses: zheng_yin@nankai.edu.cn (Z. Yin), guoyu@nankai.edu.cn
(Y. Guo), yuechen@nankai.edu.cn (Y. Chen).
l
l
These authors contributed equally to this work.
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.10.068

N. Li et al. / Bioorg. Med. Chem. Lett. 24 (2014) 386–389
387
O
O
Table 1 (continued)
O
O
R1
H
N
a
Compounds
Structure
IC50
S
N
+
S
b
OH
HS
R1
O
R2
R3 R2
III
HN
II
I
O
13
14
N/Aa
HS
HS
N
H
R1
N
R3 R2
O
HN
>200
IV
N
N
H
Scheme 1. Reagents and conditions: (a) EDCI/HOBT/NMM or CDI/DBU, 0 °C to rt,
30–85%. (b) NaHCO3 or Na2CO3, H2O, MeOH, rt, 33–91%.
O
N
N
15
16
17
>200
S
N
HS
HS
HS
H
O
O
Table 1
Br
52 12
3-Mercapto-2-methylpropanoic acid derivatives and inhibition ratio
S
N
H
Compounds
Structure
IC50
O
HO
N
21
20
13
2
1
1
O
N
O
N
H
7.9 0.1
D-Captopril
HS
O
18
19
20
O
HS
HS
N
H
1
56 10
81 10
HS
OH
O
S
N
O
H
2
O
O
HS
HS
OH
S
120 21
HS
HS
N
O
O
H
3
53
9
O
O
OH
21
22
23
5
0.4
N
O
H
4
N/Aa
20
HS
HS
HS
HS
O
N
1.5 0.2
O
O
O
HS
HS
HS
N
H
O
O
O
5
1
2
4
9
O
O
OH
5
0.8
N
H
6
48
N
N
H
24
25
26
>200
>200
>200
7
55
N
H
OH
O
O
O
O
8
92
HS
HS
N
H
N
H
HS
HS
OMe
O
9
>200
O
N
H
N
H
O
F
10
135 24
O
HS
N
H
27
28
29
>200
>200
HS
N
H
O
O
11
12
>200
>200
O
O
N
H
F
HS
HS
HS
HS
N
H
F
O
N
>200
H
S
N
H
(continued on next page)

388
N. Li et al. / Bioorg. Med. Chem. Lett. 24 (2014) 386–389
had a minimal effect on the activity, although
captopril demonstrated slightly different inhibition activities
(IC50 = 7.9 and 39.0
M, respectively).7,44 Various 3-mercapto-2-
methylpropanoic amides were synthesized and tested as NMD-1
inhibitors. The benzyl amide of (R)-3-mercapto-2-methylpropa-
noic acid (22) was identified to be the most potent NDM-1 inhibi-
D-captopril and L-
Table 1 (continued)
Compounds
Structure
IC50
l
O
30
N/Aa
HS
N
O
tor with an IC50 value of 1 lM. Finally, captopril was further
a
Not available, but showing no inhibitory activity at a concentration of 1 mM.
simplified to compounds 31 and 32. Clinically used antidote 32
was determined to be a relatively potent NDM-1 inhibitor; thus,
it is a promising candidate to treat bacterial infections. Currently,
the NDM-1 inhibitory effects of the compounds identified in this
study are being tested in cells, and the co-crystallization of inhib-
itors with NDM-1 protein are being carried out. The results will be
reported in due course.
Interestingly, benzyl amide 21 demonstrated high potency
(IC50 = 5
lM). An additional study showed that its enantiomer 22
was an even better NDM-1 inhibitor (IC50 = 1
l
M), which is
approximately seven times more potent than captopril. Prelimin-
ary studies that analyzed different phenyl substituents showed
that meta-hydroxyl benzyl amide 23 had a similar potency as ben-
zyl amide 21, while ortho-hydroxyl benzyl amide 24, meta-methyl
benzyl amide 25, and ortho-fluoro benzyl amide 26 were inactive
Acknowledgments
This work was supported by the National Natural Science Foun-
dation of China (NSFC) (No. 21072106 and No. 21372129 to Y.C.,
No. 81102374 to H.-G.Z.), the National Biomedical Special Project
of International Innovation Park (11ZCKFSY06800), Fok Ying Tong
Education Foundation (No. 122037) to Y.C., Program for New Cen-
tury Excellent Talents in University, the Scientific Research Starting
Foundation of Returned Overseas Chinese Scholars, Ministry of
Education of China and the ‘111’ Project of the Ministry of Educa-
tion of China (Project No. B06005) to Z.Y., and National Program on
Key Basic Research Project (No. 2013CB967200).
at the highest test concentration (IC50 > 200 lM). In addition, other
types of modified compounds such as 27, 28, 29, and 30 showed no
activity at the highest test concentration. These results indicated
that the benzyl amine moiety is not well tolerated towards modi-
fication. Thus, the sulfur atom and the carbonyl oxygen of the
amide (especially the benzyl amide) may chelate with the zinc
ion in the active site of NDM-1.
Further simplification of the captopril structure was carried out
on 3-(acetylthio)-2-methylpropanoic acid I as the starting mate-
rial. Treatment of I with thionyl chloride, followed by the addition
of MeOH supplied ester V. Ester V was reduced with LiAlH4 to ob-
tain compound 31 (Scheme 2).
Supplementary data
Table 2 summarizes the biological activities of captopril, com-
pound 31, and commercially available compound 32 (purchased
from TCI). Interestingly, the IC50 values of compounds 31 and 32
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.bmcl.2013.10.068.
were 15 and 10
of captopril (IC50 = 7.9
l
M, respectively, which were comparable to that
l
M).42 Structurally, compounds 31 and 32
References and notes
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opportunities for further optimization. Of note, compound 32 is a
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potential to be repurposed to treat bacterial infections by targeting
NDM-1.
In summary, the captopril subunit 3-mercapto-2-methylpropa-
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