Novel S-substituted aminoalkylamino ethanethiols as potential antidotes against sulfur mustard toxicity

Article abstract of DOI:10.1021/jm030099v

Sulfur mustard (SM) is a highly toxic chemical warfare agent. A satisfactory treatment regimen is not yet available for this toxicant. In a search for an effective antidote against SM, a series of novel S-2(ω-aminoalkylamino)ethyl alkyl/aryl thioethers [H₂N(CH ₂)_nNHCH₂CH₂SR], where R = alky, alicyclic, aryl, and heterocyclic substituents, have been designed and synthesized as candidate antidotes against SM toxicity. These compounds were screened for their protective efficacy through the oral route against dermally applied sulfur mustard in female mice measured on the basis of percent survival following percutaneous administration of SM. A number of compounds demonstrated significant protection.

Full text of DOI:10.1021/jm030099v

J . Med. Chem. 2004, 47, 3817-3822
3817
Novel S-Su bstitu ted Am in oa lk yla m in o Eth a n eth iols a s P oten tia l An tid otes
a ga in st Su lfu r Mu sta r d Toxicity
Uma Pathak, Syed K. Raza,* A. S. Kulkarni, Rajagopalan Vijayaraghvan, Pravin Kumar, and
Devendra K. J aiswal
Defence Research & Development Establishment, J hansi Road, Gwalior-474 002, India
Received February 26, 2003
Sulfur mustard (SM) is a highly toxic chemical warfare agent. A satisfactory treatment regimen
is not yet available for this toxicant. In a search for an effective antidote against SM, a series
of novel S-2(ω-aminoalkylamino)ethyl alkyl/aryl thioethers [H2N(CH2)nNHCH2CH2SR], where
R ) alky, alicyclic, aryl, and heterocyclic substituents, have been designed and synthesized as
candidate antidotes against SM toxicity. These compounds were screened for their protective
efficacy through the oral route against dermally applied sulfur mustard in female mice measured
on the basis of percent survival following percutaneous administration of SM. A number of
compounds demonstrated significant protection.
Sch em e 1. General Scheme for the Synthesis of
Thioethers
In tr od u ction
Bis(2-chloroethyl)sulfide, commonly known as sulfur
mustard (SM) or mustard gas, is an alkylating agent
that causes serious blisters upon contact with human
skin. SM is a frequently used chemical warfare agent,
and several reports are available of its recent use.1-4
SM forms the sulfonium ion in the body and alkylates
DNA, leading to DNA strand breaks and cell death.5
Eyes, skin, and the respiratory tract are the principal
target organs of SM toxicity.5-7 Several compounds have
been evaluated for reducing the systemic toxicity of SM
but with limited protection.8-20 So far, no accepted
antidote is available for SM and the treatment is
symptomatic.
The fact that symptoms of SM exposure are similar
to those caused by radiation21-23 led us to investigate
the protection offered by radioprotectors against SM.
Amifostine or WR-2721 [S-2(3-(aminopropyl)amino)-
ethylphosphorothioate] (Scheme 1), is a potent radio-
protector. This compound has also been found useful in
cancer treatment where it protects the normal cells
against the chemotherapeutic agent including nitrogen
mustard.24-30 We reasoned, therefore, that amifostine
might be a promising antidote against SM also. Ami-
fostine and two of its homologues, which are essentially
the S-substituted derivative ofaminoalkylaminoethaneth-
iol, were synthesized and evaluated against SM toxicity.
Initial screening of these compounds showed that ami-
fostine is impressively active by ip and oral routes,31,32
though the protection was marginally less by the oral
route. These observations encouraged us to synthesize
a series of S-substituted aminoalkylamino ethanethiols
as potential antidotes against sulfur mustard toxicity
and to undertake their evaluation.
potential antidotes against SM. A survey of the litera-
ture revealed that most of the studies on these com-
pounds are with reference to radioprotection. A number
of compounds structurally related to aminoalkylamino
ethanethiol have been synthesized but limited by varia-
tion at S substitution. The types that have received
main attention and accounted for much method devel-
opment are phosphorothioates, thiosulfates, and oc-
It is well-known that the presence of a phosphoric
group reduces lipophilicity and therefore limits bioavail-
ability of a compound. In view of this fact, we explored
the possibility of other types of S-substituted amino-
alkylamino ethanethiols than phosphorothioates as
* To whom correspondence should be addressed. Phone: (0091) 751-
2233488. Fax: (0091) 751-2341148. E-mail: skraza2k@hotmail.com.
10.1021/jm030099v CCC: $27.50 © 2004 American Chemical Society
Published on Web 06/19/2004

3818 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 15
Pathak et al.
casionally isothiourium derivatives and disulfides.33-37
For effective modification of the compound, we envis-
aged thioethers as a target structure having an ami-
noalkylamino ethane backbone and focused our atten-
tion on varying the substitution at sulfur with a wide
range of functional groups. The rationale behind the
synthesis of these compounds was to develop new
compounds with enhanced lipophilicity, sharing some
properties of aminoalkyamino ethanethiols.
The toxicity of SM has been attributed to the reactiv-
ity of the intermediate sulfonium ion with various cell
constituents.5 SM is reported to have the potential to
react with a number of compounds that are present in
cells and tissues, such as thiols, carboxylic groups of
proteins, aromatic nitrogen atoms (e.g., pyridine and
imidazol), amino groups of amino acids, peptides, pu-
rines, pyrimidines, and sulfide sulfur (e.g., methionine).
Any reagent having an affinity for the sulfonium ion
can be expected to help prevent sulfur mustard injury.
The various groups introduced at the thiol moiety of
aminoalkylamino ethanethiol were guided by these
observations and selected on the basis of reported SM
chemistry. Mainly, two types of groups were selected:
one that will simply influence the lipophilicity and the
other that will have potential to contribute toward the
desired activity by reacting with SM in addition to the
modification in lipophilicity.
It has been observed that an increase in alkyl chain
length increased the lipophilicity of the molecule, and
hence, compounds with a gradual increase in carbon
chain length at the sulfur atom were synthesized. For
bioisosteric replacement of the phosphoric moiety, cy-
clohexyl, phenyl, and substituted phenyl groups were
selected.38 Furthermore, since SM has affinity for a ring
nitrogen, S-heterocyclic substituted compounds with
pyridine and nicotinamide moieties were also synth-
sised. In this paper we report the synthesis of a series
of aminoalkylamino ethane thioethers and their evalu-
ation against SM.
treatment with 48% aqueous HBr afforded the respec-
tive bromides in the form of the dihydrobromide salt as
illustrated in Scheme 1.
Arylthioethers 4a -6c were prepared by reacting
bromides 3a -c with aryl mercaptans using triethyl-
amine as a base. This reaction afforded clean products
in quantitative yields, and the compounds resulting
from this reaction were conveniently purified further
by crystallization. Compound 7 was obtained by reacting
aminoethyl bromide with thiophenol using triethyl-
amine as base.
This synthetic pathway, however, was applicable only
to aromatic thioethers. Alkyl and cyclohexyl thioethers
could not be obtained by this method. Compounds 8a -
13b were prepared by reacting the bromide salt with
the corresponding thiols in the presence of sodium
methoxide as base. Sodium methoxide was generated
in situ by adding methanol to the reaction mixture
containing sodium metal. During this reaction, a small
amount of oxy ether was also formed as a byproduct,
which was separated from the thioether by column
chromatography. To increase the lipophilicity, we
changed the groups from methyl to cyclohexyl.
The synthesis of 4-pyridyl thioethers 14a ,b was
achieved by the reaction of the corresponding bromide
with mercaptopyridine in the presence of NaOH as a
base. Nicotinamide derivatives (15a ,b) were prepared
by heating bromides (3a -c) with thionicotinamide in
ethylene glycol.
Biology
All the compounds synthesized as potential antidotes
to SM toxicity were screened for their protective efficacy
by oral route. To select the appropriate dose for protec-
tion, the LD50 values through the oral route for all the
compounds were determined (Table 1).
To establish the preferred time of administration of
drug, the compounds were administered as pretreat-
ment (30 min), simultaneous treatment (0 min), and
posttreatment (30 min). After the preliminary experi-
ments, it was observed that 0.2 LD50 of the compound
4a given 30 min prior to SM application yielded the
maximum protection. The other compounds were given
orally at a molar equivalent dose of 4a . The results of
the protective efficacies of the compounds at 30 min
pretreatment are summarized in Table 1.
Ch em istr y
Thioethers and sulfides can be synthesized by a halide
mercaptan reaction. Various methods have been re-
ported in the literature.39-43 These methods center on
a common scheme in which a halide and mercaptan are
allowed to react in the presence of a suitable base in
different reaction media at varying temperatures. First,
we took aminoalkylamino ethanethiol as a substrate
and treated it with the halide of the required moiety.
But this approach was abandoned because formation of
disulfide and polymerization thwarted the preparation
of the desired thioether. Then we investigated the
alternative approach, i.e., reacting aminoalkylamino
ethyl halide with the thiol of the required moiety, and
finally compounds were synthesized by this method
(Scheme 1).
We selected aminoalkylamino ethyl bromides (3a -
c) as the key intermediates to synthesize all the target
compounds because bromides were reported to be the
most effective for the synthesis of thioethers and
sulfides. These bromides were obtained by the method
reported by Piper et al.33 In the first step, diamino-
alkanes (1a -c) were reacted with ethylene oxide to give
the corresponding alcohols (2a -c). These alcohols on
Resu lts a n d Discu ssion
The results of evaluation of the compounds through
the oral route in vivo are summarized in Table 1. It is
evident from the table that most of the compounds have
given protection against SM. Bioisosteric replacement
of the phosphoric moiety of amifostine by phenyl and
cyclohexyl groups proved to be quite useful; these
compounds gave better protection than amifostine. The
introduction of substitution at the para position of the
phenyl ring gave interesting results. An increase in
activity was observed for the tolyl derivatives (4a , 4b
f 5a , 5b). In the case of chlorophenyl derivatives,
however, the activity remained the same for the ami-
noethylamino analogue (4a f 6a ) but changed drasti-
cally for the (aminopropyl)amino analogue (4b f 6b).
To find out the importance of the aminoalkylamino
ethane backbone, we prepared aminoethylphenyl sulfide

Aminoalkylamino Ethanethiols
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 15 3819
Ta ble 1. Protective Efficacy of S-Substituted Aminoalkylamino Ethane Thiols through Oral Route against SM (38.7 mg/kg
Percutaneously)
LD50
(mg/kg)
% survival
% survival
compd
analogue
(oral route)
after 7 days
after 14 days
S-2-(3-(aminopropylamino)ethyl phosphorothioate (amifostine)
S-2(2-aminoethylamino)ethyl phenyl sulfide dihydrochloride
S-2(3-(aminopropylamino)ethyl phenyl sulfide dihydrochloride
S-2(4-aminobutylamino)ethyl phenyl sulfide dihydrochloride
S-2(2-aminoethylamino)ethyl tolyl sulfide dihydrochloride
S-2(3-(aminopropylamino)ethyl tolyl sulfide dihydrochloride
S-2(2-aminethylamino)ethyl chlorophenyl sulfide dihydrochloride
S-2(3-aminpropylamino)ethyl chlorophenyl sulfide dihydrochloride
aminoethylphenyl sulfide hydrochloride
S-2(2-aminoethylamino)ethylmethyl sulfide dihydrochloride
S-2(3-(aminopropylamino)ethyl methyl sulfide dihydrochloride
S-2(2-aminoethylamino)ethyl ethyl sulfide dihydrochloride
S-2(3-(aminopropylamino)ethyl ethyl sulfide dihydrochloride
S-2(2-aminoethylamino)ethyl propyl sulfide dihydrochloride
S-2(3-aminopropylamino)ethyl propyl sulfide dihydrochloride
S-2(2-aminoethylamino)ethyl isopropyl sulfide dihydrochloride
S-2(3-(aminopropylamino)ethyl isopropyl sulfide dihydrochloride
S-2(2-aminoethylamino)ethyl butyl sulfide dihydrochloride
S-2(3-(aminopropylamino)ethyl butyl sulfide dihydrochloride
S-2(2-aminoethylamino)ethyl cyclohexyl sulfide dihydrochloride
S-2(3-(aminopropylamino)ethyl cyclohexyl sulfide dihydrochloride
S-2(2-aminoethylamino)ethyl 4-pyridyl sulfide dihydrochloride
S-2(3-(aminopropylamino)ethyl 4-pyridyl sulfide dihydrochloride
S-2(2-aminoethylamino)ethyl isothionicotinamide dihydrobromide
S-2(3-(aminopropylamino)ethyl isothionicotinamide dihydrobromide
SM only
1049
1247
1345
952
75
100
75
25
75
0
4a
4b
4c
5a
5b
6a
6b
7
8a
8b
9a
9b
10a
10b
11a
11b
12a
12b
13a
13b
14a
14b
15a
15b
100
100
100
100
100
100
100
50
100
100
100
75
0
1902
1131
1131
1588
2262
4525
3200
3200
4525
4525
2263
4525
2263
4525
100
75
75
75
25
0
0
50
25
75
0
50
25
75
100
100
100
1131
1131
4525
100
100
100
100
75
50
4525
4525
100
50
50
0
0
0
(7) by removing the aminoalkylamino part of the phenyl
analogue. The resultant compound 7 lost its activity,
indicating that this backbone was essential but not
sufficient for activity. Initially, three homologues (n )
2, 3, 4) were prepared for each type of derivative. The
screening of these compounds, however, showed a
general trend where ethyl homologues (n ) 2) were the
most effective and the least toxic followed by propyl and
butyl homologues. Hence, for subsequent compounds n
was restricted to 2 and 3 only.
Attempts were also made to see the effects of in-
creased lipophilicity of the compounds, by gradually
increasing the chain length of the alkyl groups at sulfur,
on the protective efficacy. Except for the methyl and
ethyl analogues, all the alkyl analogues were effective.
The lack of efficacy of methyl and ethyl analogues may
be due to the poor pharmacokinetic profile originating
from the lower lipophilicity of methyl and ethyl groups.
Among the propyl and isopropyl analogues, propyl was
more effective. Installation of the heterocyclic moiety
was not useful because heterocyclic analogues were
significantly less effective.
It is well-known that SM causes toxicity by reacting
with important biomolecules that are present in cells
and tissues.5 Critical reactions of SM are complete
within minutes of absorption through the formation of
an intermediate sulfonium ion. The adduct formed with
SM is quite stable under physiological conditions, and
hence, reversal of reaction is very difficult (i.e., regen-
eration of biomolecules causing the reversal of injury
is difficult).
A compound that prevents SM toxicity by preferen-
tially binding with it and thus removing SM from the
site of action is called a scavenger. This suggests that
for a scavenger to prevent SM toxicity, it should be
present in the critical target organs before SM. This
condition can be achieved by two means: one is the
administration of the scavenger before SM so that it has
sufficient time to reach cells and tissue; the other
requires that the rate of distribution of the compound
be fast enough to reach the critical target organs before
SM. The second requirement is difficult to achieve even
if the drug is given simultaneously. Most probably, the
compounds tested in these studies are acting as scav-
engers because they are able to reduce the SM toxicity
only when given prior to SM application. The simulta-
neous administration is not providing any protective
effect because it is not able to reach the target organs
before SM, and once SM has caused injury, the com-
pound is not of much use even if it is present in high
concentrations.
Con clu sion
Novel S-substituted aminoalkylamino ethane thiols
have been made and evaluated. These studies clearly
demonstrate that most of the compounds exhibited good
to excellent in vivo efficacy against SM. In particular,
compounds 4a , 5a , 5b, 6a , 6b, 10a , 12a , 13a , and 13b
are the most effective. These compounds are being
pursued further for detailed investigations. In depth
pharmacological studies of the most effective compound
and antidotal efficacy of other compounds will be
reported in due course.
Exp er im en ta l Section
Gen er a l Ch em istr y Meth od s. All reactions described
below were performed using laboratory grade materials and
solvents under a dry atmosphere. All solvents were distilled
prior to use or stored over molecular sieves. Melting points
were determined in an open capillary and are uncorrected. The
IR spectra were recorded on a Perkin-Elmer 1700 FTIR
spectrophotometer in KBr. The NMR spectra were recorded
on
a Bruker Avance 400 MHz NMR spectrophotometer.
Chemical shifts are expressed as δ values (ppm) relative to
1
TMS as the internal standard for H NMR. The mass spectral

3820 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 15
Pathak et al.
analysis was performed on a TSQ 7000 mass spectrometer.
In most of the cases, the compounds were identified by
recording their pseudomolecular ion (M + H)+ under electro-
spray ionization (ESI) because, being salts, most compounds
could not be analyzed by the conventional electron impact (EI)
mass spectrometry. Electrospray MS analysis was performed
using methanol-water (50:50) with 1% acetic acid. Nitrogen
was used as a sheath gas, and the ESI needle was held at 4.5
eV.
S-2(4-Am in obu tyla m in o)eth yl 4-Ch lor op h en yl Su lfid e
Dih yd r och lor id e (6c). Yield 70%, mp 274-275 °C. IR: 1476,
1
1094, 1013,871 cm-1. H NMR (CD3OD): δ 1.86 (4H, t), 2.95
(2H, t), 2.99-3.33 (6H, m), 7.26 (2H, d), 7.38 (2H, d). MS (ESI
m/z): 259/261 (M + H)+•. Anal. (C12H19ClN2S‚2HCl‚H2O) C,
H, N.
Syn th esis of Am in oeth ylp h en yl Su lfid e Hyd r och lo-
r id e (7). Compound 7 was prepared by the same procedure
as described for 4a using aminoethyl bromide in place of 3a .
Yield 73%, mp 100-102 °C. IR: 1471, 1094, 754, 696 cm-1
.
S-2(ω-Am in oa lk yla m in o)eth a n ol (2a -c). These com-
1H NMR (CD3OD): δ 3.12 (2H, t), 3.23 (2H, t), 3.30 (3H, m),
7.29 (1H, t), 7.38 (2H, t), 7.49 (2H, d). MS (ESI m/z): 154 (M
+ H)+•. Anal. (C8H11NS.HCl‚H2O) C, H, N.
pounds were prepared according to the literature procedure.33
S-2(ω-Am in oa lk yla m in o)eth yl Br om id e Dih yd r obr o-
m id e (3a -c). These compounds were prepared according to
the literature procedure.33
Syn th esis of S-2(ω-Am in oa lk yla m in o)eth yl Alk yl Su l-
fid e Dih yd r och lor id e. Gen er a l P r oced u r e. Aminoalkyl-
aminoethyl bromide hydrobromide (0.025 mol) and alkane
thiols (0.027 mol) was taken in benzene (50 mL) in a two-
necked round-bottom flask equipped with a magnetic stirring
bar, calcium chloride guard tube, and an ice-filled cooling bath.
For methyl analogues, sodium methanethiolate was used.
Sodium metal (2 g) was added to the flask followed by the
addition of anhydrous methanol (10 mL) dropwise through a
pressure-equalizing dropping funnel. The mixture was stirred
continuously at 0-5 °C. The progress of the reaction was
monitored by TLC. After the completion of the reaction, ether
(50 mL) was added to it. The white precipitate, which was
mostly inorganic salt, was removed by filtration under reduced
pressure, and the solid was further washed with an ether-
chloroform mixture (80:20). The combined filtrate was evapo-
rated to dryness on a water bath. The residue was treated with
methanolic HCl, and acetone was added to it until the
precipitation was complete. The white salt thus obtained was
filtered and dried. The salt was then dissolved in 10 mL of
water, and sodium hydroxide (3 g) was added to it for
converting the hydrochloride salt into the free amine. The
amine was then extracted with ether and again converted into
the HCl salt as described above. This process was repeated
until it gave a single spot from TLC.
Syn th esis of S-2(ω-Am in oa lk yla m in o)eth yl Ar yl Su l-
fid e Dih yd r och lor id e. Gen er a l P r oced u r e. Thiophenol
(0.028 mol) and triethylamine (12 mL) were taken in chloro-
form at 0 °C, and aminoalkylamino ethyl bromide dihydro-
bromide (0.025 mol) was added to it in portions. The reaction
mixture was stirred at 0-5 °C for 3 h and then refrigerated
overnight. The compound was washed with water and ex-
tracted with chloroform. The solvent was removed under
reduced pressure, and the contents were washed with chilled
petroleum ether (40-60 °C) (50 mL) followed by chilled ether
(20 mL). The compound thus obtained was dissolved in ethanol
and treated with HCl to get a white crystalline hydrochloride
salt of the compound. The resulting crystals were collected by
filtration. The compound was purified by recrystallization from
ethanolic solution by the addition of acetone.
S-2(2-Am in oeth yla m in o)eth yl P h en yl Su lfid e Dih y-
d r och lor id e (4a ). Yield 72%, mp 192-194 °C. IR: 1438, 1025,
807, 736.7, 689 cm-1. 1H NMR (CD3OD): δ 3.33 (8H, m), 7.24-
7.56 (5H, m). MS (ESI m/z): 197 (M + H)+•. Anal. (C10H16N2S‚
2HCl‚H2O) C, H, N.
S-2(3-(Am in op r op yla m in o)eth yl P h en yl Su lfid e Dih y-
d r och lor id e (4b). Yield 75%, mp 248-250 °C. IR: 1438, 1039,
1
1025, 899, 737, 689 cm-1. H NMR (CD3OD): δ 2.22 (2H, m),
3.08 (2H, t) 3.19-3.34 (6H, m), 7.24-7.51 (5H, m). MS (ESI
S-2(2-Am in oeth yla m in o)eth yl Meth yl Su lfid e Dih y-
d r och lor id e (8a ). Yield 50%, mp 196 °C. IR: 1458, 1025, 816
cm-1. 1H NMR (CD3OD): δ 2.19 (3H, s), 2.80 (2H, t), 3.42 (9H,
m). MS (CI m/z): 135 (M + H)+•. Anal. (C5H14N2S‚2HCl‚H2O)
C, H, N.
m/z): 211 (M + H)+•. Anal. (C11H18N2S‚2HCl‚H2O) C, H, N.
S-2(4-Am in obu tyla m in o)eth yl P h en yl Su lfid e Dih y-
d r och lor id e (4c). Yield 75%, mp 243-245 °C. IR: 1481, 1438,
1
1026, 738, 689 cm-1. H NMR (CD3OD): δ 1.76 (4H, m), 2.59
(2H, t), 3.30-3.42 (6H, m), 7.22-7.49 (5H, m). MS (ESI m/z):
S-2(3-(Am in op r op yla m in o)eth yl Meth yl Su lfid e Dih y-
d r och lor id e (8b). Yield 45%, mp 252 °C. IR: 1449, 1174,
225 (M + H)+•. Anal. (C12H20N2S‚2HCl‚H2O) C, H, N.
1
1050, 990, 902, 784 cm-1. H NMR (CD3OD): δ 2.11 (2H, m),
S-2(2-Am in oeth yla m in o)eth yl 4-Tolyl Su lfid e Dih y-
d r och lor id e (5a ). Yield 70%, mp 200-204 °C. IR: 1494, 1088,
1027, 806 cm-1. 1H NMR (CD3OD): δ 2.20 (3H, s), 3.20 (2H, t,
J ) 7 Hz), 3.39 (6H, m), 7.13 (2H, d), 7.32 (2H, d). MS (ESI
m/z): 211 (M + H)+•. Anal. (C11H18N2S‚2HCl‚H2O) C, H, N.
2.84 (2H, t), 3.30 (3H,m) 3.06 (2H, t), 3.16 (2H, t), 3.27 (2H, t).
MS (CI m/z): 149 (M + H)+•. Anal. (C6H16N2S‚2HCl‚H2O) C,
H, N.
S-2(2-Am in oeth yla m in o)eth yl Eth yl Su lfid e Dih yd r o-
ch lor id e (9a ). Yield 52%, mp 194-196 °C. IR: 1460, 1022,
S-2(3-(Am in op r op yla m in o)eth yl 4-Tolyl Su lfid e Dih y-
d r och lor id e (5b). Yield 72%, mp 236-38 °C. IR: 1496, 1166,
980, 814 cm-1 1H NMR (CD3OD): δ 1.10 (3H, t), 2.65 (2H,
.
1
1087, 985, 817, 784 cm-1. H NMR (CD3OD): δ 1.91 (2H, m),
m), 2.90 (2H, t), 3.35 (9H, m). MS (CI m/z): 149 (M + H)+•
Anal. (C6H16N2S‚2HCl‚H2O) C, H, N.
.
2.23 (3H, s), 2.89 (2H, t, J ) 7 Hz), 2.96-3.33 (6H, m), 7.12-
(2H, d), 7.32 (2H, d). MS (ESI m/z): 225 (M + H)+•. Anal.
(C12H20N2S‚2HCl‚H2O) C, H, N.
S-2(3-(Am in op r op yla m in o)eth yl Eth yl Su lfid e Dih y-
d r och lor id e (9b). Yield 50%, mp 256-258 °C. IR: 1461, 1173,
991, 908, 785 cm-1 1H NMR (CD3OD): δ 1.28 (3H, t), 2.22
.
S-2(4-Am in obu tyla m in o)eth yl 4-Tolyl Su lfid e Dih y-
d r och lor id e (5c). Yield 74%, mp 246-47 °C IR: 1493, 1459,
1052, 1034, 804 cm-1. 1H NMR (CD3OD): δ 1.70 (4H, m), 2.22
(3H, s), 2.89 (2H, t), 2.94-3.29 (6H, m), 7.14 (2H, d), 7.24 (2H,
d). MS (ESI m/z): 239 (M + H)+•. Anal. (C13H22N2S‚2HCl‚H2O)
C, H, N.
(2H, m), 2.60 (2H, m), 2.88 (2H, t), 3.08 (2H, t), 3.12 (2H, t),
3.23 (2H,t), 3.34 (3H, m). MS (CI m/z): 163 (M + H)+•. Anal.
(C7H18N2S‚2HCl‚H2O) C, H, N.
S-2(2-Am in oeth yla m in o)eth yl P r op yl Su lfid e Dih y-
d r och lor id e (10a ). Yield 60%, mp 196-198 °C. IR: 1459,
1377, 1924, 1026, 811 cm-1. 1H NMR (CD3OD): δ 1.10 (3H, t),
1.67 (2H, m), 2.60 (2H, t), 2.88 (2H, t), 3.29-3.42 (9H, m). MS
(CI m/z): 163 (M + H)+•. Anal. (C7H18N2S‚2HCl‚H2O) C, H,
N.
S-2(2-Am in oeth yla m in o)eth yl 4-Ch lor op h en yl Su lfid e
Dih yd r och lor id e (6a ). Yield 70%, mp 238-39 °C. IR: 1478,
1
1092, 1006, 815 cm-1. H NMR (CD3OD): δ 3.1 (2H, t, J ) 7
Hz), 3.20-3.26 (6H, m), 7.28 (2H, d), 7.39 (2H, d). MS (ESI
m/z) 231/233 (M + H)+•. Anal. (C10H15ClN2S‚2HCl‚H2O) C, H,
S-2(3-(Am in op r op yla m in o)eth yl P r op yl Su lfid e Dih y-
d r och lor id e (10b). Yield 60%, mp >160 °C (dec). IR: 1455,
N.
1
1400, 11293, 1050, 992, 109, 779 cm-1. H NMR (CD3OD): δ
S-2(3-(Am in op r op yla m in o)eth yl 4-Ch lor op h en yl Su l-
fid e Dih yd r och lor id e (6b). Yield 70%, mp 261-62 °C. IR:
1.03 (3H, t), 1.62 (2H, m), 2.12 (2H, m), 2.56 (2H, t), 2.89 (2H,
t), 3.18 (2H, t), 3.20 (2H, t), 3.25 (2H, t), 3.34 (3H, m). MS (CI
m/z): 177 (M + H)+•. Anal. (C8H20N2S‚2HCl‚H2O) C, H, N.
S-2(2-Am in oeth yla m in o)eth yl Isop r op yl Su lfid e Dih y-
d r och lor id e (11a ). Yield 52%, mp 192-194 °C. IR: 1461,
1477, 1096, 1012, 808 cm-1 1H NMR (CD3OD): δ 2.21 (2H,
.
m), 2.89 (2H,t), 3.12-3.26 (6H, m), 7.27 (2H, d)-7.40 (2H, d).
MS (ESI m/z): 245/247 (M + H)+•. Anal. (C11H17ClN2S‚2HCl‚
H2O) C, H, N.

Aminoalkylamino Ethanethiols
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 15 3821
1
1082, 1026, 810 cm-1. H NMR (CD3OD): δ 1.21 (6H, d), 2.94
S-2(3-(Am in opr opylam in o)eth yl Isoth ion icotin iu m Su l-
fid e Tr ih yd r obr om id e (15b). Yield 60%, mp 221-222 °C.
IR: 1474, 1208, 824, 673 cm-1. 1H NMR (CD3OD): δ 2.20 (2H,
m), 3.12 (2H, t), 3.44 (2H, t), 3.93 (2H, t), 5.19 (2H, t), 8.21
(1H, t), 8.90 (1H, d), 9.31 (1H, d), 9.72 (1H, s). MS (ESI m/z):
239 (M + H)+•. Anal. (C11H18N4S‚3HBr) C, H, N.
(2H, t), 3.10 (1H, m), 3.31-3.46 (9H, m). MS (ESI m/z): 163
(M + H)+•. Anal. (C7H18N2S‚2HCl‚H2O) C, H, N.
S-2(3-(Am in op r op yla m in o)eth yl Isop r op yl Su lfid e Di-
h yd r och lor id e (11b). Yield 39%, mp 259-262 °C (dec). IR:
1457, 1398, 1154, 1050, 992 cm-1. H NMR (CD3OD): δ 1.21
1
(6H, d), 2.22 (2H, m), 2.88 (2H, t), 3.08 (1H, m), 3.17 (2H, t),
3.23 (2H, t), 3.29 (2H, t), 3.32 (3H, m). MS (ESI m/z): 177 (M
+ H)+•. Anal. (C8H20N2S‚2HCl‚H2O) C, H, N.
Gen er a l Biology Meth od s. Randomly bred adult female
Swiss mice obtained from the animal house of Defence
Research & Development Establishment, weighing between
25 and 28 g body weight, were used in the present study. The
Institute’s Ethical Committee approval was obtained for these
studies. The animals were housed in polypropylene cages (five
per cage) with dust-free husk as bedding material and were
provided with food (Lipton India Ltd.) and water ad libitum.
Freshly prepared solutions of the compounds were adminis-
tered orally for the estimation of LD50. The compound was
administered as a single oral dose, and the animals were
observed for mortality for a period of 14 days. The LD50 was
estimated by the moving average method of Gad and Weil
using three to four log doses, consisting of four animals per
dose.44
S-2(2-Am in oeth yla m in o)eth yl Bu tyl Su lfid e Dih yd r o-
ch lor id e (12a ). Yield 48%, mp 194-195 °C. IR: 1463, 1029,
812, 744 cm-1 1H NMR (CD3OD): δ 0.84 (3H, t), 1.38 (2H,
.
m), 1.53 (2H, m), 2.53 (2H, t), 2.82 (2H, t), 3.22 (6H, m), 3.35
(3H, m). MS (CI m/z): 177 (M + H)+•. Anal. (C8H20N2S‚2HCl‚
H2O) C, H, N.
S-2(3-(Am in op r op yla m in o)eth yl Bu tyl Su lfid e Dih y-
d r och lor id e (12b). Yield 52%, mp >262 °C (dec). IR: 1466,
1
1029, 813, 746 cm-1. H NMR (CD3OD): δ 0.82 (3H, t), 1.22-
1.34 (2H, t), 1.52 (2H, m), 2.03 (2H, m), 2.55 (2H, t), 2.76 (2H,
t), 3.06 (2H, t), 3.12 (2H, t), 3.16 (2H, t), 3.28 (3H, m). MS (CI
m/z): 191 (M + H)+•. Anal. (C9H22N2S‚2HCl‚H2O) C, H, N.
After the preliminary experiments, it was observed that 0.2
LD50 of compound 4a given 30 min prior to SM application
yielded the maximum protection. The other compounds were
given orally as a molar dose of 4a .
S-2(2-Am in oeth yla m in o)eth yl Cycloh exyl Su lfid e Di-
h yd r och lor id e (13a ). Yield 41%, mp 193-195 °C. IR: 1452,
1344, 1032, 956, 762 cm-1 1H NMR (CD3OD): δ 1.32-1.47
.
(2H, m), 1.32-1.47 (2H, m), 2.08 (4H, m), 2.62 (1H, m), 2.93
(2H, t), 3.39 (6H, m), 3.42 (3H, m). MS (CI m/z) 203 (M + H)+•
Anal. (C10H22N2S‚2HCl‚H2O) C, H, N.
.
For the protection studies, 38.7 mg/kg SM (LD50 of SM is
8.1 mg/kg by percutaneous route)32 dissolved in 3 N poly-
(ethylene glycol) was applied topically on the back of the mice
(n ) 4 for each test compound) after closely clipping the hair.
The dose of 38.7 mg/kg was selected (which is more than 4-fold
LD50) such that the unprotected animals died in 8-10 days
after percutaneous administration of SM. A freshly prepared
solution of the test compounds in distilled water was admin-
istered orally 30 min before SM application (using an autopi-
pet), and the animals were observed for 14 days for mortality.
In the mouse model, the animals died before 14 days after SM
administration and no death occurred as a result of SM beyond
this. Hence, the percent mortality was calculated at 7 and 14
days after SM administration.
S-2(3-(Am in op r op yla m in o)eth yl Cycloh exyl Su lfid e
Dih yd r och lor id e (13b). Yield 40%, mp >255 °C (dec). IR:
1455, 1000, 763 cm-1. 1H NMR (CD3OD): δ 1.33 (2H, m), 1.52-
1.73 (4H, m), 2.06 (4H, m), 2.16 (2H, m), 2.82 (1H, m), 2.91
(2H, t), 3.06 (2H, t), 3.17 (2H, t), 3.28 (2H, t), 3.31 (3H, m).
MS (CI m/z): 217 (M + H)+•. Anal. (C11H24N2S‚2HCl‚H2O) C,
H, N.
Syn th esis of S-2-(ω-Am in oa lk yla m in o)eth yl 4-P yr id yl
Su lfid e Tr ih yd r och lor id e. Gen er a l P r oced u r e. 4-Mercap-
topyridine (25 mmol) and aminoalkylaminoethyl bromide
dihydrobromide (25 mmol) were mixed together in a flask. A
solution of NaOH (75 mmol) dissolved in 10 mL of water was
added. The reaction starts immediately. The reaction mixture
was heated at 90-95 °C for 10 min. The compound was
extracted with chloroform. After solvent removal, the residue
was dissolved in ethanol and treated with concentrated HCl.
The hydrochloride salt formed was further purified by recrys-
tallization from ethanol-acetone.
Ack n ow led gm en t . The authors thank Mr. K.
Sekhar, Director, DRDE, for providing the necessary
facilities. The technical assistance offered by Mr. Basant
lal, Mrs. Mamta Sharma, Dr. R. P. Semwal, Mr. Vijay
Pal, and Mr. Ram Singh is gratefully acknowledged.
S-2(2-Am in oeth yla m in o)eth yl 4-P yr id yl Su lfid e Tr i-
h yd r och lor id e (14a ). Yield 42%, mp 205-206 °C. IR: 1479,
1218, 1106, 828, 780 cm-1. 1H NMR (CD3OD): δ 3.29 (2H, m),
3.35 (2H, m), 3.42 (2H, m), 3.57 (2H, m), 7.73 (2H, m), 8.38
(2H, m). MS (ESI m/z): 198 (M + H)+•. Anal. (C9H15N3S‚3HCl‚
H2O) C, H, N.
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IR: 1451, 1399, 1190, 980, 946, 678 cm-1. H NMR (CD3OD):
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