Lead detoxification activities and ADMET hepatotoxicities of a class of novel 5-(1-carbonyl-l-amino-acid)-2,2-dimethyl-[1,3]dithiolane-4-carboxylic acids

Article abstract of DOI:10.1016/j.bmcl.2011.01.070

By linking the mercapto groups with isopropyl and introducing l-amino acid into the 5-carboxyl of DMSA a class of novel 5-(1-carbonyl-l-amino-acid)-2,2- dimethyl-[1,3]dithiolane-4-carboxylic acids were prepared. Their in vivo activities were evaluated on

Full text of DOI:10.1016/j.bmcl.2011.01.070

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1754–1757
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
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Lead detoxification activities and ADMET hepatotoxicities of a class of novel
5-(1-carbonyl-L-amino-acid)-2,2-dimethyl-[1,3]dithiolane-4-carboxylic acids
Yanxia Xu a, Yuji Wang b, Ming Zhao b, , Baoguang Hou b, Li Peng b, Meiqing Zheng b, Jianhui Wu b,
⇑
Shiqi Peng a,b,
⇑
a College of Pharmaceutical Sciences, Peking University, Beijing 100083, PR China
b College of Pharmaceutical Sciences, Capital Medical University, Beijing 100069, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
By linking the mercapto groups with isopropyl and introducing L-amino acid into the 5-carboxyl of DMSA
Received 18 November 2010
Revised 14 January 2011
Accepted 18 January 2011
Available online 22 January 2011
a class of novel 5-(1-carbonyl-L-amino-acid)-2,2- dimethyl-[1,3]dithiolane-4-carboxylic acids were pre-
pared. Their in vivo activities were evaluated on lead loaded mice at the dose of 0.4 mmol/kg. The results
showed that the lead levels of the livers, kidneys, femurs and brains in particular could be efficiently
decreased by 0.4 mmol/kg of 5-(1-carbonyl-
L-amino-acid)-2,2-dimethyl-[1,3]dithiolane-4-carboxylic
acids. The benefit of 5-(1-carbonyl- -amino-acid)-2,2-dimethyl-[1,3]dithiolane-4-carboxylic acids to
the detoxification of the brain lead was attributed to their transmembrane ability. Compared with the
lead detoxification efficacy, they did not affect the essential metals such as Fe, Cu, Zn, and Ca of the trea-
L
Keywords:
DMSA
Structural modification
Brain lead
Detoxification
ted mice. Silico molecular modeling predicted that 5-(1-carbonyl-
[1,3]dithiolane-4-carboxylic acids had no hepatotoxicity.
L-amino-acid)-2,2-dimethyl-
Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
Owing to rapid industrialization and agriculture modernization
in both developed and developing countries, during the past two
decades the levels of lead (Pb) in air, water, and soils have
increased.1–5 In terms of a widespread toxic metal, lead has a
half-life time of 6–10 years.4,6,7 In addition to hypertension, hyper-
thyroidism, oste-oporosis and skeletal disorders,3–5,8 Pb accrued
from environmental exposure has been associated with the devel-
opmental, neuropsychological and behavioral deficits.9 Lead expo-
sure will continue to be a major public health issue around the
world for the fore-seeable future and there is an urgent need to
find novel therapy for the treatment of lead poisoning.10–13 It has
been well documented that the chelation therapy is one of the
most common methods in the treatment of Pb intoxication, and
meso-2,3-dimer-captosuccinic acid (DMSA) has been known to
be the most acceptable antidote in lowering the Pb levels of bone
and brain without causing major redistributions of Pb to other or-
gans, especially to the brain.9,11,14–18, To increase the efficacy of
DMSA in lowering the Pb levels of the organs, especially in lower-
ing the Pb level of the brain in this Letter DMSA was modified and a
the thioketal-acid (1) and the amidation of the thioketal-anhydride
(2) and amino acids, which were mentioned in Scheme 1 and 5-(1-
carbonyl-L-amino-acid)-2,2-dimethyl-[1,3]dithiolane-4-carboxylic
acids (3a–l) were prepared. The yields of 1, 2 and 3a–l were 78%,
91% and 22–56%, respectively. The synthetic and chemical physical
data of all compounds are given in the file of Supplementary data.
The data imply that using this three-step-reaction procedure 3a–l
can be smoothly obtained.
In the lead detoxification assay, the lead-loaded mice were trea-
ted with normal saline (NS, negative control), DL-penicillamine
(positive control), sodium meso-2,3-dimercaptosuccinate (NaDMS,
positive control), 2,2-dimethyl-[1,3]dithiolane-4,5-dicarboxylic
acid (1) and 5-(1-carbonyl-L-amino-acid)-2,2-dimethyl-[1,3]-
dithio-lane-4-carboxylic acids (3a–l), the lead levels of the livers,
the kidneys, the brains and the femurs of the mice were measured
and the data are shown in Table 1. The results illustrate that the
lead levels of the livers, the kidneys, the left femurs and the brains
of the mice receiving 0.4 mmol/kg of DL-penicillamine, NaDMS, 1
and 3a–l are significantly lower than that of the corresponding or-
gans of the mice receiving NS. This suggests that DL-penicillamine,
NaDMS, 1 and 3a–l are effective in lowering the organs’ lead level
of the mice. On the other hand, however, the lead level of the
brains of the mice receiving 0.4 mmol/kg of 1 is significantly lower
than that of the brains of the mice receiving 0.4 mmol/kg of NaD-
MS. This suggests that the modification of the mercapto groups of
meso-2,3-dimercaptosuccinate benefits lowering the lead level of
the brains. While the lead level of the brains of the mice receiving
class
of
novel
5-(1-carbonyl-L-amino-acid)-2,2-dimethyl-
[1,3]dithiolane-4-carboxylic acids were investigated.
In appropriate conditions via three-step-reaction procedure,
namely the addition of DMSA and acetone, the dehydration of
⇑
Corresponding authors. Tel./fax: +86 10 8391 1528 (S.P.); tel./fax: +86 10 8391
1535 (M.Z.).
E-mail addresses: mingzhao@bjmu.edu.cn (M. Zhao), sqpeng@bjmu.edu.cn (S.
Peng).
0960-894X/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.01.070

Y. Xu et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1754–1757
1755
H
O
O
S
*
S
S
S
S
S
HS
SH
S
S
ii
CO2H
iii
i
*
*
H
R
N
*
HO2C
CO2H HO2C
HO2C
COAA
C
C
O
O
O
O
O
2
H
OH
3a-l
1
Scheme 1. Synthetic route of 5-(1-carbonyl-
room temperature; (ii) acetyl chloride, 2.5 h, reflex; (iii) amino acid, 48 h, room temperature. In 3a AA = Gly, 3b AA =
L
-amino-acid)-2,2-dimethyl-[1,3]dithiolane-4-carboxylic acids. Reagents and conditions: (i) hydrogen chloride and acetone, 9 h,
-Ser, 3c AA = -Val, 3d AA = -Leu, 3e AA = -Ile, 3f AA =
-Trp. ⁄Represents possible binding sites of Pb.
L
L
L
L
L-
Asn, 3g AA =
L
-Asp, 3h AA =
L-Gln, 3i AA =
L-Glu, 3j AA =
L
-Met, 3k AA =
L-Phe, 3l AA = L
Table 1
Lead in organs of the treated micea
Compd
lead in following organs
Brain
Lead in feces/urine
Feces
Femurs
Kidney
Liver
Urine
NS
DL-PA
1
NaDMS
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
23.70 3.08
14.99 2.45b
15.47 2.06b
14.31 2.07b
20.82 2.90c
14.70 2.93b
14.93 2.58b
16.33 4.70b
14.32 3.14b
16.62 4.33b
11.10 1.30d
14.59 2.62b
13.69 1.34b
13.71 1.50b
16.75 2.92b
17.66 2.15b
2.04 0.40
1.61 0.42b
1.42 0.32f
1.72 0.34b
1.39 0.28e
1.05 0.51c
1.49 0.47b
1.44 0.55b
1.42 0.61b
0.58 0.42c
1.22 0.46e
1.02 0.50c
1.22 0.48e
0.91 0.40c
1.11 0.27c
1.21 0.80b
8.92 1.46
7.24 2.08b
7.12 2.05b
6.23 1.89b
6.68 2.53b
6.43 2.54b
6.16 1.35b
7.32 2.02b
6.49 1.16b
7.06 1.77b
7.09 1.36b
6.86 1.75b
7.21 2.64b
6.36 1.89b
6.61 1.02b
7.50 1.58b
7.22 1.64
3.52 0.86b
4.02 1.26b
4.75 1.35b
3.29 1.56b
3.21 0.69b
3.19 0.74b
3.64 1.74b
5.00 1.41b
3.99 1.02b
3.82 1.36b
3.07 1.03b
5.64 1.32c
3.51 1.79b
4.60 1.95b
5.59 1.50c
1.27 1.15
3.26 1.40b
4.57 0.89c
4.59 0.84c
4.53 0.56c
4.41 0.74c
4.76 0.84c
3.99 1.71b
4.10 1.84b
4.71 0.35c
4.80 1.04c
4.50 1.41b
4.49 1.61b
4.35 1.12c
4.85 1.38c
4.14 1.05b
0.93 0.11
1.94 0.67b
1.93 0.81b
1.79 1.46b
2.07 0.47b
2.83 1.41b
2.65 1.08b
3.44 1.16c
2.42 0.93b
2.12 0.81b
2.83 0.48c
2.89 0.23c
2.65 0.85c
2.26 1.40b
1.72 0.26b
2.84 1.40b
For femurs lead: (b) compared to NS p <0.01; (c) compared to NS p <0.05; (d) compared to NS, DL-PA, 1 and NaDMS p <0.01. For brain lead: (b) compared to NS p <0.01;
(c) compared to NS, DL-PA, NaDMS and 1 p <0.01; (d) compared to NS and NaDMS p <0.01, to DL-PA p <0.05; (e) compared to NS p <0.01, to DL-PA and NaDMS p <0.05;
(f) compared to NS p <0.01, to NaDMS p <0.05. For kidney lead: (b) compared to NS p <0.05. For liver lead: (b) compared to NS p <0.01; (c) compared to NS p <0.05. For fecal lead:
(b) compared to NS p <0.01; (c) compared to NS and p <0.01, to DL-PA p <0.05. For urinary lead: (b) compared to NS p <0.01; (c) compared to NS p <0.01, to NaDMS, DL-PA and 1
p <0.05.
a
Date is represented with mean SD
lg of Pb/g of organ or excrement, NS = normal saline = vehicle, NaDMS = sodium meso-2,3-dimercaptosuccinate, DL-PA = DL-
penicillamine, dose of DL-PA, 1, NaDMS and 3a–l = 0.4 mmol/kg, n = 12.
0.4 mmol/kg of 3b,f,h,j,k is significantly lower than that of the
brains of the mice receiving 0.4 mmol/kg of 1. This suggests that
and 3a–l are at the same level as that of the mice receiving NS. This
suggests that the treatment of 0.4 mmol/kg of 1 and 3a–l does not
lower the essential metal level of the treated mice.
the coupling of 5-carboxyl and
L-Ser, L-Asn, L-Gln, L-Met and
L
-Phe may lead to the increase of lead detoxification activity.
To evaluate the effect of the treatment on the growth of the
treated mice the body weights of the mice receiving NS,
0.4 mmol/kg of 1 and 3a–l were measured and the data are given
in the file of Supplementary data (Table 4). The data indicate that
the body weights of the mice receiving 0.4 mmol/kg of 1 and
3a–l are at the same level as that of the mice receiving NS. This
suggests that the treatment of 0.4 mmol/kg of 1 and 3a–l does
not affect on the growth of the treated mice.
To examine the dose-dependent response of the mice to the
treatment, 3g was selected as a representative of 3a–l and three
doses, that is, 0.2, 0.4 and 0.6 mmol/kg, were used. The lead levels
of the livers, kidneys, left femurs and brains of the treated mice
were measured and the data are listed in Table 2. The data indicate
that the lead levels are progressively decreased with the increase
of the dose. Therefore, 3g dose-dependently moves the lead accu-
mulated in the tissues.
The relationship of the membrane permeability and the lead
detoxification activity of 1 and 3a–l were examined with the
Caco-2 cell monolayer experiment. To correlate the membrane
permeability with the lead detoxification 3e,f,j were selected as
the representatives of 3a–l, the membrane permeability’s of DL-
PA, NaDMS, 1 and 3e,f,j were measured with the experiments of
Caco-2 cell monolayer, and the data are listed in Table 3.
Besides, no any obvious adverse behavioral reaction in mice fol-
lowing injection of 3a–l was observed.
To evaluate the effect of 1 and 3a–l on the lead excretion, the
lead levels of the feces and the urine of the mice receiving NS (neg-
ative control), DL-penicillamine (positive control), NaDMS (posi-
tive control), 1 and 3a–l were measured and the results are also
shown in Table 1. The data demonstrate that the lead level of the
feces of the mice receiving 0.4 mmol/kg of 3d,e,h,i,l is significantly
higher than that of the feces of the mice receiving NS, while the
lead level of the feces of the mice receiving 0.4 mmol/kg of NaDMS,
1 and 3a,b,c,f,g,j,k is significantly higher than that of the feces of
the mice receiving NS and DL-penicillamine. These suggest that
NaDMS, 1 and 3a–l are able to effectively increase the lead excre-
tion via the feces. The data also demonstrate that the lead level of
the urine of the mice receiving 0.4 mmol/kg of DL-penicillamine,
NaDMS, 1 and 3a–l is significantly higher than that of the urine
of the mice receiving NS. This suggests that DL-penicillamine,
NaDMS, 1 and 3a–l are able to effectively increase the lead
excretion via the urine.
To explore the effect of the treatment on the essential metals,
the Fe, Cu, Zn, Mn and Ca in the kidneys, livers, and brains of the
mice receiving NS, and 0.4 mmol/kg of 1 as well as 3a–l were mea-
sured and the data are given in the file of Supplementary data
(Tables 1–3). The data indicate that these essential metals of the
livers, kidneys and brains of the mice receiving 0.4 mmol/kg of 1
The experiments gave DL-PA, NaDMS,
1 and 3e,f,j the
11.01 Â 10À6 cm/s to 16.65 Â 10À6 cm/s of Papp values from the
apical side to the basolateral side and the 4.68 Â 10À6 cm/s to

1756
Y. Xu et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1754–1757
Table 2
Lead in organs of three doses of 3 g treated micea
Compd
Dose (mmol/kg)
Lead in following organs
Femurs
Brain
Kidney
Liver
NS
3g
0.2 ml
0.6
0.4
23.70 3.08
9.64 1.02b
11.10 1.30c
17.21 2.11d
2.04 0.40
0.84 0.36b
1.22 0.46c
1.69 0.38d
8.92 1.46
5.90 1.30b
7.09 1.36c
7.68 1.40c
7.22 1.64
2.77 1.03b
3.82 1.36c
5.81 1.52d
0.2
For femurs lead: (b) compared to NS and 0.2 mmol/kg of 3g p <0.01, to 0.4 mmol/kg of 3g p <0.05; (c) compared to NS and 0.2 mmol/kg of 3g p <0.01; (d) compared to NS
p <0.01. For brain lead: (b) compared to NS and 0.2 mmol/kg of 3g p <0.01, to 0.4 mmol/kg of 3g p <0.05; (c) compared to NS p <0.01, to 0.2 mmol/kg of 3g p <0.05; (d)
compared to NS p <0.05. For kidney lead: (b) compared to NS and 0.2 mmol/kg of 3g p <0.01, to 0.4 mmol/kg of 3g p <0.05; (c) compared to NS p <0.01, to 0.2 mmol/kg of 3g
p <0.05; (d) compared to NS p <0.01. For liver lead: (b) compared to NS and 0.2 mmol/kg of 3g p <0.01, to 0.4 mmol/kg of 3g p <0.05; (c) compared to NS p <0.01, to 0.2 mmol/
kg of 3g p <0.05; (d) compared to NS p <0.01.
a
Date is represented with mean SD lg of Pb/g of organ, NS = normal saline = vehicle, n = 12.
Table 3
The apparent permeability coefficients of 1 and 3e,f,j
10% of the human population. To predict hepatotoxicity two scores
(0 represents non-hepatotoxin and 1 represents hepatotoxin) are
defined. The predicted scores (0.019–0.317) of NaDMS, 1 and
3a–l are listed in Table 4. The data are much less than 1. This sug-
gests that NaDMS, 1 and 3a–l possess no hepatotoxicity.
Compd
Papp  10À6 (cm/s)
A?B
B?A
A?B/B?A
DL-PA
NaDMS
1
3e
3f
3j
13.12
11.01
13.68
14.25
16.65
15.70
11.50
10.00
4.68
4.91
5.15
5.05
1.14
1.10
2.91
2.90
3.23
3.11
In conclusion, linking the mercapto groups with isopropyl and
introducing L-amino acid into the 5-carboxyl is a desirable struc-
tural modification of DMSA. This modification significantly in-
creases the brain-lead detoxification activity without increasing
the lead levels of other organs. This modification significantly in-
creases the membrane permeability and possibly increases the
capacity of blood–brain barrier permeability. These properties with
the non-hepatotoxin prediction together provide a promising de-
sign for brain-lead detoxification agents.
The standard deviations were generally less than 10% (n = 4); A?B, From apical side
to basolateral side; B?A, From basolateral side to apical side.
Table 4
ADMET hepatotoxicity probability of 3a–l
Acknowledgements
Compd
ADMET score
Compd
ADMET score
This work was finished in the Beijing area major laboratory of
peptide and small molecular drugs, supported by PHR (IHLB,
KZ200810025010, KM200910025009 and KM200710025010), the
National Natural Scientific Foundation of China (30801426), and
Special Project (2008ZX09401-002) of China.
NaDMS
1
3a
3b
3c
0.033
0.019
0.079
0.086
0.072
0.099
0.086
3f
3g
3h
3i
3j
3k
3l
0.092
0.059
0.112
0.099
0.105
0.317
0.264
3d
3e
Supplementary data
Supplementary data (experimental procedures, biological eval-
uation methods, synthetic data, analytical data, physical chemical
constants and spectral data) associated with this article can be
found, in the online version, at doi:10.1016/j.bmcl.2011.01.070.
11.50 Â 10À6 cm/s of Papp values from the basolateral side to the
apical side, and defined the Papp values from the apical side to
the basolateral side to be 1.10-fold to 3.23-fold higher than the Papp
value from the basolateral side to the apical side. It is generally ac-
cepted that an actively absorbed compound shows much faster
transport from the apical to the basolateral direction and its Papp
value from the apical side to the basolateral side should be more
than 10 Â 10À6 cm/s.19 According to the Papp values from the apical
side to the basolateral side, DL-PA, NaDMS, 1 and 3e,f,j are trans-
ported actively across the Caco-2 cell monolayer. For 1 and 3e,f,j,
the Papp values from the apical side to the basolateral side are
2.90-fold to 3.23-fold higher than the Papp values from the basolat-
eral side to the apical side, while for NaDMS the Papp values from
the apical side to the basolateral side is only 1.10-fold higher than
the Papp values from the basolateral side to the apical side. The
comparison suggests that the present modification significantly
improves the membrane permeability and should be responsible
for the higher brain-lead detoxification activities of 1 and 3e,f,j.
The hepatotoxicities of 1 and 3e,f,j were calculated by using the
absorption, distribution, metabolism, elimination and toxicity
(ADMET) program,20,21 which was developed from available litera-
ture data of 382 compounds known to exhibit liver toxicity or trig-
ger dose-related elevated aminotransferase levels in more than
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