Synthesis, electrochemistry, and molluscicidal activity of nitroaromatic compounds: Effects of substituents and the role of redox potential

Article abstract of DOI:10.1016/S0968-0896(00)00283-2

Molluscicidal bioassays and electrochemical studies (measurement of first wave reduction potential, Epc1) were performed on several synthetic nitroaromatics, in relation to possible correlation between biological activity, redox potential and structural effects. Five of them presented a significant molluscicidal activity on Biomphalaria glabrata (LD₅₀<20ppm). The Epc1 values ranged from -0.532 to -0.857V versus Ag/AgCl (0.1M) (-0.260 to -0.585V versus NHE), all of them, in the favorable range for reduction in vivo. Data comparison between Epc1 and molluscicidal activity indicates that the presence of the electroactive nitro group is important for the biological activity. Correlation with redox potential, however, was not evident. Structural effects seem to be the most important parameter. Higher activity is noticeable for phenols, including the para-nitro azo or hydrazo-containing compounds. No activity was observed for compounds having the benzylic substituent in meta position to the nitro group. These results suggest that activity undoubtedly involves more than reduction characteristics and that the possible formation of electrophilic species, after nitro reduction, can play an important role in molluscicidal activity against B. glabrata. Copyright

Full text of DOI:10.1016/S0968-0896(00)00283-2

Bioorganic & Medicinal Chemistry 9 (2001) 659±664
Synthesis, Electrochemistry, and Molluscicidal Activity of
Nitroaromatic Compounds: E€ects of Substituents
and the Role of Redox Potential
Fabiane C. de Abreu,a,b Francine S. de Paula,a Aldenir F. dos Santos,a Antonio Euzebio
G. Sant'Ana,a,* Mauro V. de Almeida,c Eloi T. Cesar,d Marcio N. Trindadec
a,
and Marõlia O. F. Goulart, *
a
Â
Departamento de Quõmica, Universidade Federal de Alagoas, 57.092-970, Maceio, AL, Brazil
Â
Departamento de Quõmica Fundamental, Universidade Federal de Pernambuco, 50.670.901, Recife, PE, Brazil
b
Â
c
Â
NuÂcleo de Pesquisas Quõmicas, ICE, Universidade Federal de Juiz de Fora, 36038-330, Juiz de Fora, MG, Brazil
d
Â
Departamento de Quõmica, ICEX, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
Received 19 April 2000; accepted 17 October 2000
AbstractÐMolluscicidal bioassays and electrochemical studies (measurement of ®rst wave reduction potential, Epc1) were per-
formed on several synthetic nitroaromatics, in relation to possible correlation between biological activity, redox potential and
structural e€ects. Five of them presented a signi®cant molluscicidal activity on Biomphalaria glabrata (LD50<20 ppm). The Epc1
values ranged from À0.532 to À0.857 V versus Ag/AgCl (0.1 M) (À0.260 to À0.585 V versus NHE), all of them, in the favorable
range for reduction in vivo. Data comparison between Epc1 and molluscicidal activity indicates that the presence of the electro-
active nitro group is important for the biological activity. Correlation with redox potential, however, was not evident. Structural
e€ects seem to be the most important parameter. Higher activity is noticeable for phenols, including the para-nitro azo or hydrazo-
containing compounds. No activity was observed for compounds having the benzylic substituent in meta position to the nitro
group. These results suggest that activity undoubtedly involves more than reduction characteristics and that the possible formation
of electrophilic species, after nitro reduction, can play an important role in molluscicidal activity against B. glabrata. # 2001
Elsevier Science Ltd. All rights reserved.
Introduction
The molluscicides currently in use are either synthetical
or from natural origin. Several of them possess the nitro
group functionality. Since the 1960s, the only com-
pound that has been widely and e€ectively used as a
molluscicide in the control of schistosomiasis is the
synthetic compound niclosamide (23).2 Niclosamide can
kill B. glabrata adults at concentrations as low as
1.5 ppm after 2 h exposure. The mode of action of
niclosamide against snails and cestodes has received
relatively little attention3 and is still uncertain.4 From
the available data, it is clear that it exerts most of its
e€ects on respiration and carbohydrate metabolism.4
The main drawback of the use of niclosamide appears
to be that formulations cause high ®sh mortality at
concentrations used to control snails.4 The high cost of
these products, together with their toxic e€ects to non-
target organisms and the risk of potential development
of heritable resistance has strongly stimulated the search
for new molluscicides.2
Schistosomiasis is an endemic parasitic disease, a€ecting
the tropical and subtropical regions of the world, and is
second only to malaria in the havoc it causes to the
social and economic development of countries located
in these areas.1 It is caused by the presence of the worm
Schistosoma mansoni in the liver of the a€ected person,
the fresh-water mollusk Biomphalaria glabrata acting as
intermediate host. This disease is in a growing stage due
to poverty and lack of basic sanitation. The reduction of
its transmission is crucial. The use of molluscicides in
the prophylactic treatment promotes the rupture of the
evolutionary cycle of the worm with the destruction of
its intermediate host, the snail B. glabrata.1
*Corresponding author. Tel.: +55-82-214-1389; fax: +55-82-214-
1389; e-mail: mofg@qui.ufal.br
0968-0896/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(00)00283-2

660
F.C. de Abreu et al. / Bioorg. Med. Chem. 9 (2001) 659±664
Reduction potentials provide information on the feasi-
bility of electron transfer (ET) in vivo. Established rela-
tionship between the ease of reduction, represented by
Epc, E12 or Eredox, and biological activities, shows the
relevance of electrochemical studies as tools for the
comprehension of drug mechanism of action against
various diseases, for prediction of biological activities
and for the design of potentially active compounds.
Absolute correlation is not expected, since other factors
as solubility, metabolism, di€usion, adsorption, site
binding, cell permeability and stereochemistry undoubt-
edly play critical roles.5 Signi®cantly large number of
physiologically active substances possess E12 values greater
than about À0.5 V versus normal hydrogen electrode
(NHE), in the physiological active range, which can per-
mit electron acceptance from biological donors6 or they
can su€er metabolic changes, furnishing easily reduced
derivatives.7 In the case of antihelmintic compounds,
electrochemical data was acquired.8,9 To our knowledge,
no previous work has been hitherto done in relation to
molluscicidal activity.
The redox potentials were obtained in aqueous medium
(phosphate bu€er, pH 7), by use of cyclic voltammetry,
using mercury as the working electrode. Biological and
electrochemical data were compared. The question of
toxicity is not addressed at the present time.
In the area of molluscicides, to our knowledge there is
only one report of electrochemical studies and it refers
to the electrochemical determination of niclosamide
(23), with postulation of a possible reduction mechan-
ism involving the transfer of four electrons.15
Results and Discussion
The 22 compounds investigated were divided into four
groups, I to IV, to facilitate the discussion (Table 1,
columns 1 and 2). Group I (1±5) is represented by
nitrocompounds para-substituted with methyl (5), or
methyl-substituted groups. One of them has one addi-
tional substituent (4). Group II (6±16) comprises com-
pounds where electron donating groups (-OH, -NH2,
-NHNH2, -OCH3, -NHCOR) are directly coupled to
the ortho- or para-nitro-substituted aromatic ring. 15
and 16 are similar in structure to yurumin (24), an active
molluscicide.16 They were included in group II, since the
azo substituent in those structures can be considered
electron donating, due to the in¯uence of the ortho-
phenolic-OH and to the presence of the highly electron-
withdrawing para-nitro substituent. Group III (17±19)
is constituted by meta-nitro substituted aromatics.
Group IV (20±22) has no nitro functionality.
The nitroaromatic compounds are exceptional for their
range of activity, the relative lack of resistance, and their
interesting chemistry.10 The main chemical parameter
that determines the e€ectiveness of nitro drugs is the
reduction potential of the nitro group.11 There is good
evidence that some electrochemical properties of nitro
compounds can be correlated with the pharmacological
e€ects of these compounds.12 This indicates that part of
their activity may derive from the nitro-catalyzed pro-
duction of superoxide (futile cycle) or is due to the action
of their reduced metabolites (bioreductive alkylation).
The most biologically relevant measure of nitro group
reduction potential is the thermodynamically reversible
addition of the ®rst electron, Epc1 (or E 12). Although the
values determined in aqueous solutions by cyclic voltam-
metry (CV) or polarography are not reversible reactions,
and for nitroaromatic compounds may involve the addi-
tion of up to four electrons, the ®rst is usually the most
dicult.13 The reductive metabolism, in vivo, is carried out
by widely distributed constitutive ¯avo-enzymes that are
able to use nitroaromatics as alternative electron acceptors
(¯avine dependent reductases, cytochrome P450).14
The aim of the present study was to conduct laboratory
evaluation of molluscicidal activity of synthetic nitro-
aromatics on the adult snail of B. glabrata and compare
the results with measured Epc1. Nineteen nitroaro-
matics and three other compounds, several of them
described for the ®rst time, were tested. The compounds
were selected from a series of para- and meta-substituted
nitrocompounds, preliminarily synthesized as possible
ligands in a program for preparation of new platinum
complexes, similar to cis-platin, and others with mixed
functionalities. Compounds 5 and 6 could be considered
standards. Compounds 15 and 16 were commercially
available and similar to yurumin (24). A wide structural
range of compounds was chosen, due to the present
interest of establishing a possible correlation between elec-
trochemical parameters and molluscicidal activity in a
hitherto unexplored area.
N-Benzylalkyldiamine or N-benzylaminoethanethiol
derivatives were easily synthesized, in 60±70% yield, by
reacting the respective nitrobenzyl halogenide with the
requisite diamine or aminothiol, following a published
procedure.17 The others were obtained from commercial
sources.
The biological assay was slightly modi®ed18 including an
inert solvent to allow the complete dissolution of the
compounds. This alternative of dissolving the test sample
in DMSO with a maximum ®nal solvent concentration of
0.5% v/v19,20 was tested before, without problems.

F.C. de Abreu et al. / Bioorg. Med. Chem. 9 (2001) 659±664
Table 1. Analysed substances and their respective groups
661
Basic structure
Group I
Compounds with respective substituents
1 X=NH(CH2)6NH2; R1=H; R2=NO2
2 X=NH(CH2)4NHCH2C6H4-4-NO2;
R1=H; R2=NO2
3 X=NH(CH2)2SH; R1=H; R2=NO2
4 X=H; R1=Cl; R2=NO2
5 X=H; R1=R2=NO2
Group II
6 X=OH; R1=R3=H; R2=NO2
7 X=NH2; R1=R3=H; R=2 NO2
8 X=NHNH2; R1=R3=H; R2=NO2
9 X=NHCOCH3; R1=R3=H; R2=NO2
10 X=OCH3; R1=NH2; R2=NO2; R3=H
11 X=NH2; R1=NO2; R2=OCH3, R3=H
12 X=NH2; R1=CF3; R2=NO2; R3=H
13 X=NH2; R1=H; R2=NO2; R3=CF3
14 X=NHNH2; R1=H; R2=R3=NO2
15
16
Group III
17 X=CH2NH(CH2)2NH2; R1=NO2; R2=H
18 X=CH2NH(CH2)2SH; R1=NO2; R2=H
19 X=COOH; R1=R2=NO2
Figure 1. Typical cyclic voltammograms of nitroaromatics, aqueous
bu€ered medium, pH 7.0, Hg electrode, versus Ag/AgCl (0.1 M),
0.035 V sÀ1: (A) compound 1 (1 mM); (B) compound 6 (1 mM).
Group IV
20 R1=CF3, R2=R3=H
21 R1=CF3, R2=R3=NH2
22 R1=CH2NH(CH2)4CH2C6H5, R2=R3=H
Table 2. Biological and electrochemical data of the substances
Substance
LD50
(ppm)
Epc1 versus
Ag/AgCl
Epc1 versus
NHE
The potentials of the ®rst waves were obtained, using
Ag/AgCl as a reference electrode and calculated in
relation to NHE electrode.21À23 Figure 1 is representa-
tive of cyclic voltammograms and the Epc1 value is
obtained directly from the curve. Epc1 of compound 16
was measured at pH 9, to help dissolution and 15 was
not analyzed by cyclic voltammetry due to its lack of
solubility, even at higher pH.
1
2
3
4
5
6
7
8
72.4
40.2
116.5
1.8
100.7
8.2
56.1
0.7
I
À0.532
À0.260
À0.541
À0.533
À0.606
À0.556
À0.857
À0.840
À0.833
À0.773
À0.762
À0.730
À0.840
À0.816
À0.743
ND
À0.269
À0.261
À0.334
À0.284
À0.585
À0.568
À0.561
À0.501
À0.490
À0.458
À0.568
À0.544
À0.471
ND
9
10
11
12
13
14
15
16
17
18
19
20
21
22
I
Table 2 lists the values of LD50 against B. glabrata (column
2), together with the potentials of the ®rst wave for the
electrochemically active compounds (columns 3 and 4).
86.8
55.6
52.9
32.1
7.6
6.4
I
I
I
I
I
In the biological assays, some compounds presented a
signi®cant molluscicidal activity on B. glabrata with
LD50<20 ppm, speci®cally 0.7, 1.8, 6.4, 7.6, and 8.2, for
8, 4, 16, 15, and 6, respectively. Some of them were
superior to various synthetic or plant molluscicides such
as muzigadial, LD50=5 to 10ppm; warburganal, LD50=
2 ppm and mukaadial, LD50=20 ppm,24 but, still less
active than pentachlorophenol, LD50=0.06 ppm (LD90=
À0.699a
À0.636
À0.597
À0.558
Ð
À0.427
À0.364
À0.325
À0.286
Ð
Ð
Ð
Ð
Ð
I
apH 9.

662
F.C. de Abreu et al. / Bioorg. Med. Chem. 9 (2001) 659±664
0.15 ppm)25 and niclosamide, LD50=0.06 ppm (LD90=
0.10 ppm).25
The others are reasonably active, with LD50<60 ppm
(2, 7, 12, 13, and 14). The compounds were recognized
as inactive (9, 10, 17, 18, 19, 20, 21, and 22), or poorly
active, when, in preliminary tests, they killed less than
40% of the initial number of snails or, after, at the
accurate tests, their LD50 were greater than 60 ppm (1,
3, 5, and 11).
The Epc1 values ranged from À0.532 to À0.857 V versus
Ag/AgCl (0.1 M) (À0.260 V to À0.585 V versus NHE),
all of them, in the favorable range6,7 (versus NHE), to be
reduced in vivo. The order of nitro reduction facility,
related to their electron anity, represented as Epc1 is
1>3>2>5>19>18>4>17>16>11>14>10>9>
13>8>12=7>6. The compounds 20, 21 and 22 were
electroinactive. The range of redox potential for active
compounds is very broad and no correlation with mol-
luscicidal activity is evidenced. Data comparison between
Epc1 and molluscicidal activity (Table 2, column 2 versus
columns 3 or 4), in spite of the relatively small number of
some derivatives, suggests that the presence of the nitro
group is important for the biological activity, as well as
its appropriate location in ortho- or para- to electron
donating groups. No activity was evidenced for com-
pounds of groups III or IV (17±22). Higher activity is
noticeable for phenol derivatives (6, 15 and 16), for
mononitrohydrazo derivative (8) and for chlorine sub-
stituted nitrotoluene (4).
Figure 2. Reductive fragmentation of substituted amino or hydroxy-
amino aromatic compounds, generating electrophilic intermediates.
ticipate, as they are, usually, more electrophilic than the
parent compounds. It should be also remembered that
azonitrocompounds undergo reductive cleavage to
amino derivatives.28 The biological activity in a live host
is always a complex outcome not usually dominated by
one parameter.
A more detailed analysis of the relationship between
electroactivity and structural parameters will be reported
elsewhere.
Although nitro-aromatic compounds are probably not
the ®rst choice for a drug development, because of their
often undesirable side e€ects, several proved to be suit-
able for the treatment of tropical diseases.29
These results suggest that the reductive activation may
contribute to the molluscicidal activity, but undoubt-
edly involves more than reduction characteristics. This
fact may indicate that the armory of reductases present
in the mollusk are able to reduce the nitro group in dif-
ferent environments. As shown in the schistosome area,
correlation with redox potential was also not evident.26
These results justify the synthesis of derivatives in the
most active series and the performance of toxicity tests.
Further investigations on the importance of nitro group
or azo versus hydrazo groups are under way.
Experimental
The possible formation of electrophilic species, after
nitro reduction, may play an important role in mollus-
cicidal activity against B. glabrata (Fig. 2, pathways A
and B). Reduction of the electron-withdrawing nitro
group gives the strong electron donating amino or
hydroxyamino substituent, which can stabilize an inci-
pient benzyl cation in the transition state of a reaction.
Therefore, ortho- or para-aminobenzyl compounds pos-
sessing a good leaving group are very reactive and the
benzylic substitution generally occurs by an elimina-
tion±addition mechanism involving a very electrophilic
quinonimine methide intermediate (Fig. 2A).27 Addi-
tionally, electron-donating groups can originate elec-
Melting points were determined on a MQAPF appara-
tus and were uncorrected. Infra-red spectra were
obtained in KBr on a Bonem FT IR MB-102 spectro-
meter. NMR spectra were recorded on a Bruker Avance
DRX 200 and DRX 400 spectrometers.
Electrochemical measurements
Cyclic voltammetry (CV) was performed using a PAR
model 273 A/PAR EG & G potentiostat/galvanostat
equipped with an HP 7090A measuring plotter system.
A 386 SX/Microtec compatible PC controlled the whole
system. A SMDE 303 A/EG & G PARC hanging mercury
electrode (area 0.009664cm2) was used as the working
electrode, together with a platinum counter-electrode and
a home-built Ag/AgCl/NaCl (0.1M) Luggin reference
electrode, isolated from the solution by a Vycor1 rod. The
trophilic
electrogenerated hydroxyamino derivative (Fig. 2B).
species,
by
interaction
with
the
The activity may be related to the above mentioned
facts or other features not yet identi®ed, for example,
the nitroso derivatives (2 eÀ reduction) could also par-
scan rate was in the range 0.020±35V sÀ1
.

F.C. de Abreu et al. / Bioorg. Med. Chem. 9 (2001) 659±664
663
Epc1 values, in volts (V), were obtained, in Hg electrode,
in phosphate bu€ered aqueous medium, pH 7, versus Ag/
AgCl, ClÀ (0.1 M) and calculated versus NHE,21 except in
the case of 16, where pH 9 was used. The scan rate used
was 0.035 V sÀ1. Compounds 1, 2, 3, 17, 18, and 22 were
analyzed as their respective chloridrates.
diamines or aminoethanethiol, with benzyl halogenide
derivatives, as described (methods A and B). All the
compounds were analyzed as their respective chlori-
drates. The free base, used for mass spectrometry, was
obtained by reaction with methanolic NaOH (pH 11),
evaporation of the solvent, followed by ¯ash chromato-
graphy of the residue in silica gel.
Bioassays
Method A: synthesis of 1, 2, 17, and 22. The corre-
sponding benzyl chloride (20 mmol) was slowly added
during 6 h to ethylenediamine (100 mmol), 1,4-butane-
diamine (40 mmol) or 1,6-hexanediamine (40 mmol) in
ethanol (30 mL). The reaction mixture was stirred for
24 h at room temperature. The solvent was removed and
the residue was puri®ed on silica gel, using as eluent di-
chloromethane/methanol (9/1).
The method was slightly modi®ed18 by inclusion of an
inert solvent to help in the dissolution of samples. The
compounds (as chloridrates) were dissolved ®rst in a
small amount of DMSO and added to dechlorinated
water, in order to have a solution 0.1% in DMSO. The
bioassay involved basically the immersion of the snail B.
glabrata adult in the mixed aqueous solution of the
compound under investigation at appropriate con-
centrations and followed a described procedure.18 In
order to verify the snails susceptibility, two control sets
were usedÐone with cupric carbonate at 50 ppm (posi-
tive control, killed all the snails) and one with dechlori-
nated water, 0.1% in DMSO (negative control).30
[N-(4-nitrobenzyl)]-1,6-hexanediamine 1. Analyzed as its
ꢀ
1
chloridrate. Melting point 234±237 C. H N MR (DO)
2
d 1.32, 1.59 (2m, 8H, CH2), 3.02 (m, 4H, CH2N), 4.27
(s, 2H, CH2Ph), 7.63 (d, 2H, H2, H3 J2À3=J5À6
=
8.5 Hz), 8.20 (d, 2H, J5À6=8.5 Hz, H5, H6); 13C N MR
(CDCl3) d 25.5, 25.6, 26.9 (CH2), 39.7 (CH2NH2), 47.7
(CH2NH), 50.4 (PhCH2), 124.6; 131.2; 138.4; 148.6
(Ph). IR (KBr) 3339, 3053, 2944, 1562, 1447, 1063, 819,
710 cmÀ1. HRMS (C13H21N3O2)=251.31.
The 100 ppm stock solutions of the test compounds
were prepared by adding 2.5 mg of the dry compound to
250 mL of dechlorinated water±DMSO for the pre-
liminary test with adult snails. For the accurate one, the
same procedure was used and the desired concentrations
were obtained by dilution with dechlorinated water at
0.1% DMSO.
Di-[N,N0-(4-nitrobenzyl)]-1,4-butanediaminꢀe 2. Analyzed
1
as its chloridrate. Melting point 235±237 C. H N MR
(D2O) d 1.76 (m, 4H, CH2), 3.08 (m, 4H, CH2N), 4.32 (s,
4H, CH2Ph), 7.65 (d, 4H, H2, H3, J2À3=J5À6=8.7 Hz),
8.24 (d, 4H, J5À6=8.7 Hz, H5, H6); 13C NMR (D2O) d
22.7 (CH2), 46.7 (CH2NH), 50.1 (PhCH2), 124.2, 130.8,
137.8, 148.2 (Ph). IR (KBr) 3419, 3087, 2981, 1525,
1447, 1049, 870, 748 cmÀ1. HRMS (C19H25N4O4)=
373.41.
Reagents
All chemicals, reagent grade, were used without further
puri®cation. The compounds 4, 6, 7, 8, 10, 11, 12, 13,
14, 15, 16, 19, 20, and 21 were from commercial sources:
2-chloro-4-nitro-toluene (4) 97% from Aldrich; 4-nitro-
phenol (6) 95% from Merck, 4-nitroaniline (7) 98% from
Merck, 4-nitro-phenylhydrazine (8) 98% from Riedel De
Haen AG, 2-methoxy-5-nitroaniline (10) and 4-methoxy-
2-nitroaniline (11) 98% from Aldrich, 2-amino-5-nitro-
benzotri¯uoride (12), 5-amino-2-nitro-benzotri¯uoride
(13) from Aldrich, 4,4-dinitro-phenylhydrazine (14)
98% from Quõmica Fina LTDA, 4-nitro-benzene-azo-
alpha-naphthol (15) 98% from Carlo Erba, 4-(4-nitro-
phenylazo)resorcinol (16) from BHD Chemicals Ltd, 3,5-
dinitrobenzoic acid (19) 99% from Riedel De Haen AG,
benzotri¯uoride (20) from Aldrich, 3,4-diamino-benzotri-
¯uoride (21) from Fluorochem Ltd. The compounds 2,4-
dinitrotoluene (5) and 4-nitro-acetanilide (9) were obtained
by nitration of toluene and N-acetylation of 7, respectively.
The reagents used for synthesis were 1,4-butanediamine
98% (Fluka), benzyl chloride 99% (Riedel De Haen AG),
1,6-hexanediamine 98% (Aldrich), 2-amino-ethanethiol
hydrochloride 98% (Aldrich), 4-nitro-benzyl alcohol
99% (Aldrich) and 3-nitro-benzyl bromide 99%
(Aldrich).
[N-(3-Nitrobenzyl)]-ethylenediamine 17. Analysed as a
free base. Melting point 146±147 ꢀC. 1H NMR (DMSO-
d6) d 2.67 (t, 2H, J=6.1 Hz, CH2NH2), 2.86 (t, 2H,
J=6.1 Hz, CH2NH), 3.80 (m, 5H, CH2Ph, NH, NH2),
7.60 (t, 1H, J5À4=J5À6=8 Hz, H5), 7.80 (dl, 1H, H6),
8.10 (dd, 1H, H4), 8.23 (sl, 1H, H2); 13C NMR (DMSO-
d6) d 38.5 (CH2NH2), 45.4 (CH2NH), 51.3 (CH2Ph),
121.7, 122.5, 129.6, 134.60, 134.8, 143.0, 147.8 (Ph). IR
(KBr) 3245, 3062, 1625, 1531, 1343, 1123, 988,
799 cmÀ1
.
Di-(N,N0-benzyl)-1,4-butanediamine 22. Melting point
241±244 ꢀC. H NMR (D2O) d 1.71 (m, 4H, (CH2)2),
1
3.02 (m, 4H, 2CH2NH), 4.17 (s, 4H, CH2Ph), 7.43 (sl,
10H, Ph); 13C NMR (D2O) d 23.1 (CH2CH2), 46.5
(CH2NH), 51.3 (CH2Ph), 129.5, 129.6, 130.0, 130.1,
130.9 (Ph). IR (KBr) cmÀ1 3050, 2995, 2937, 2796, 1591,
1443, 1110, 872, 751, 702.
Method B: Synthesis of 3 and 18. 4-Nitro-benzyl chlor-
ide (20 mmol) or 3-nitro-benzyl bromide were slowly
added during 4 h to 2-aminoethanethiol hydrochloride
(40 mmol) and NaHCO3 (40 mmol) in ethanol (30 mL).
The reaction mixture was stirred for 7 days at room tem-
perature, after which, NaOH aqueous solution was added
until pH=10. The solvent was evaporated under reduced
Synthesis
The compounds 1, 2, 3, 18, and 22, reported here for
the ®rst time, and 17 described using di€erent prepara-
tion procedures,31 were synthesized by N-alkylation of

664
F.C. de Abreu et al. / Bioorg. Med. Chem. 9 (2001) 659±664
pressure. The obtained residue was puri®ed on silica gel,
using as eluent dichloromethane/methanol (9/1).
5. Kunz, K. R.; Iyengar, B. S.; Dorr, R. T.; Alberts, D. S.;
Remers, W. A. J. Med. Chem. 1991, 34, 2281.
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1981, 44, 741.
1
[N-(4-Nitrobenzyl)]-2-aminoethanethiol 3. Oil. H N MR
(C5D5N) d 3.05 (t, J=6.7 Hz, 2H, CH2SH), 3.57 (t, 2H,
J=6.7 Hz, CH2NH), 3.96 (s, 2H, CH2Ph), 7.60 (d, 2H,
J2À3=8.5 Hz, H2, H3), 8.15 (d, 2H, J5À6=8.5 Hz, H5,
H6); 13C NMR (C5D5N) d 29.2 (CH2SH), 34.9 (CH2
NH), 39.2 (CH2Ph), 129.8, 130.3, 135.0, 147.5 (Ph). IR
(KBr) 2897, 2683, 2582, 1600, 1510, 1351, 1245, 1109,
853, 799, 709 cmÀ1. Anal. calcd for C9H12N2O2S.2 HCl:
C, 37.90, H, 4.95; N, 9.82. Found: C, 38.20; H, 5.17; N,
9.53.
12. Wilson, R.; Anderson, R. F.; Denny, W. J. Med. Chem.
1989, 32, 23.
13. Palmer, B. D.; Wilson, W. R.; Cli€e, S.; Denny, W. A. J.
Med. Chem. 1992, 35, 3214.
14. Clarke, E. D.; Goulding, K. H.; Wardman, P. Biochem.
Pharmacol. 1982, 31, 3237.
15. Sridevi, C.; Reddy, S. J. J. Ind. Chem. Soc. 1991, 68, 263.
16. Webbe, G.; In Plant Molluscicides; Mott, K. E., Ed.; John
Wiley and Sons Ltd: Chichester, 1987.
17. de Almeida, M. V.; Cesar, E. T.; Felicio, E. C. A.; Fontes,
A. P.; Robert-Gero, M. J. Braz. Chem. Soc. 2000, 11, 154.
18. dos Santos, A. F.; Sant'Ana, A. E. G. Phytother. Res.
1999, 13, 660.
19. Thiilborg, S. T.; Christensen, S. B.; Cornett, C.; Olsen, C.
E.; Lemmich, E. Phytochem. 1994, 36, 753.
20. Adewunmi, C. O.; Monache, F. D. Fitoterapia 1989, 1, 79.
21. The values of Epc1 versus NHE were obtained by adding
0.272V to the acquired values, in Ag/AgCl. Literature data22
showed that observed potentials, using saturated calomel elec-
trode (SCE) as a reference can be converted to the NHE by
adding 0.24 V to the SCE values. In relation to Ag/AgCl, SCE is
generally quite similar, with values ꢁ 0.04 V more positive often
being found with SCE.23 So, using those conventions, a full set of
Epc1 using di€erent reference electrodes can be compared.
22. Kovacic, P.; Kiser, P. F.; Feinberg, B. A. Pharm. Res.
1990, 7, 283.
1
[N-(3-Nitrobenzyl)]-2-aminoethanethiol 18. Oil. H N MR
(D2O) d 2.77 (t, 2H, J=6.7 Hz, CH2SH), 3.01 (t, 2H,
J=6.7Hz, CH2NH), 3.89 (s, 2H, CH2Ph), 7.65 (t, 1H, H5,
J5À4=J5À6=8Hz), 7.75 (d, 1H, J5À6=8 Hz, H6), 8.04 (d,
1H, H4), 8.12 (s, 1H, H2); 13C NMR (CDCl3) d 28.1
(CH2SH), 34.4 (CH2NH), 38.6 (CH2Ph), 112.9, 124.1,
130.3, 136.1, 140.4, 148.4 (Ph). IR (KBr) 3065, 3033,
2924, 2872, 2573, 1531, 1450, 1348, 1127, 930, 811,
709 cmÀ1. Anal. calcd for C9H12N2O2S.2 HCl.H2O: C,
35.65; H, 5.32; N, 9.24. Found: C, 35.45; H, 5.07; N,
9.13.
Acknowledgements
This work was supported by CNPq, CAPES, FAPE-
MIG, FAPEAL (Fundacao de Apoio a Pesquisa do
Estado de Alagoas) and WHO through the concession
of scholarships and ®nancial support. The authors wish
to thank Professor Dr. Ricardo Jose Alves (Faculdade
de Farmacia da UFMG, Minas Gerais, Brazil) for
fruitful discussions and to the referees for improvements
on the present paper.
23. Mann, S. Arch. Mikrobiol. 1970, 71, 304.
24. Marston, A.; Hostettmann, K. Phytochem. 1985, 24, 639.
25. de Souza, C. P.; Jannotti-Passos, L. K.; Pereira, J. P. Rev.
Inst. Med. Trop. 1992, 11, 345.
26. Lin, Y.; Hulbert, P. B.; Bueding, E.; Robinson, C. H. J.
Med. Chem. 1974, 17, 835.
27. Wakselman, M. Nouv. J. Chim. 1983, 7, 439.
28. Barek, J.; Drevinkova, D.; Mejstrik, V.; Zima, J. Collect.
Czech. Chem. Commun. 1993, 58, 295.
References and Notes
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trol. Cupric carbonate is recommended by WHO.18
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Â
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