Anti-leishmanial activity of novel homo- and heteroleptic bismuth(iii) thiocarboxylates

Article abstract of DOI:10.1071/CH13374

Two new thiocarboxylic acids, p-bromothiobenzoic BTA and thionaphthoic acid TNA, and five new homo- and heteroleptic bismuth(iii) compounds derived from thiocarboxylic acids: [Bi{S(C≤O)C6H4Br}3] 1, [PhBi{S(C≤O)C6H4Br}2] 2, [Bi{S(C≤O)C10H7}3] 3, [PhBi{S(C≤O)C10H7}2] 4, and [Ph2Bi{S(C≤O)C10H7}] 5 were synthesised and fully characterised. The solid-state structure of complex [PhBi{S(C≤O)C6H4Br}2] 2 was confirmed by X-ray crystallography. In complex 2, the two thiocarboxylate ligands are coordinated to the bismuth(iii) centre in a didentate fashion, forming a distorted octahedral geometry in which the phenyl group and the lone pair are oriented axial to the plane formed by the two thiocarboxylate ligands. Long-range Bi-S interactions (3.54A) link these monomeric units to form a one-dimensional polymer. These compounds, in addition to six previously synthesised complexes: [Bi{SC(≤O)C6H5}3] 6, [PhBi{SC(≤O)C6H5}2] 7, [Ph2Bi{SC(≤O)C6H5}] 8, [Bi{SC(≤O)C6H4NO2}3] 9, [PhBi{SC(≤O)C6H4NO2}2] 10, and [PhBi{SC(≤O)C6H4SO3}] 11, and the thiocarboxylic acids themselves, were assessed for their in vitro activity against Leishmania major promastigotes, and for general toxicity against human fibroblast cells. The thiocarboxylic acids, with the exception of thiobenzoic acid and sulfothiobenzoic acid, were toxic to both L. major parasites and the mammalian cells at high concentrations of 50-100M. The bismuth(iii) thiocarboxylate derivatives proved to be more active than the corresponding acids. Among these, the heteroleptic phenyl-substituted bismuth(iii) complexes 2, 4, 5, and 7 were highly active, showing IC50 (half maximal inhibitory concentration) values ranging from 0.39 to 4.69M, and a clear ligand dependence on activity.

Full text of DOI:10.1071/CH13374

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2013, 66, 1297–1305
Full Paper
http://dx.doi.org/10.1071/CH13374
Anti-Leishmanial Activity of Novel Homo- and Heteroleptic
Bismuth(III) Thiocarboxylates
A E
,
B
C D
,
Philip C. Andrews, Peter C. Junk, Lukasz Kedzierski,
A
and Roshani M. Peiris
A
School of Chemistry, Monash University, PO Box 23, Melbourne, Vic. 3800, Australia.
School of Pharmacy and Molecular Sciences, James Cook University,
Townsville, Qld 4811, Australia.
B
C
Walter and Eliza Hall Institute of Medical Research,
Parkville, Melbourne, Vic. 3052, Australia.
D
Department of Medical Biology, The University of Melbourne,
Parkville, Melbourne, Vic. 3010, Australia.
E
Corresponding author. Email: phil.andrews@monash.edu
Two new thiocarboxylic acids, p-bromothiobenzoic BTA and thionaphthoic acid TNA, and five new homo- and
heteroleptic bismuth(III) compounds derived from thiocarboxylic acids: [Bi{S(C¼O)C6H4Br}3] 1, [PhBi{S(C¼O)
C6H4Br}2] 2, [Bi{S(C¼O)C10H7}3] 3, [PhBi{S(C¼O)C10H7}2] 4, and [Ph2Bi{S(C¼O)C10H7}] 5 were synthesised and
fully characterised. The solid-state structure of complex [PhBi{S(C¼O)C6H4Br}2] 2 was confirmed by X-ray crystallog-
raphy. In complex 2, the two thiocarboxylate ligands are coordinated to the bismuth(III) centre in a didentate fashion,
forming a distorted octahedral geometry in which the phenyl group and the lone pair are oriented axial to the plane formed
˚
by the two thiocarboxylate ligands. Long-range Bi–S interactions (3.54 A) link these monomeric units to form a one-
dimensional polymer. These compounds, in addition to six previously synthesised complexes: [Bi{SC(¼O)C6H5}3] 6,
[PhBi{SC(¼O)C6H5}2] 7, [Ph2Bi{SC(¼O)C6H5}] 8, [Bi{SC(¼O)C6H4NO2}3] 9, [PhBi{SC(¼O)C6H4NO2}2] 10, and
[PhBi{SC(¼O)C6H4SO3}] 11, and the thiocarboxylic acids themselves, were assessed for their in vitro activity against
Leishmania major promastigotes, and for general toxicity against human fibroblast cells. The thiocarboxylic acids, with
the exception of thiobenzoic acid and sulfothiobenzoic acid, were toxic to both L. major parasites and the mammalian cells
at high concentrations of 50–100 mM. The bismuth(III) thiocarboxylate derivatives proved to be more active than the
corresponding acids. Among these, the heteroleptic phenyl-substituted bismuth(III) complexes 2, 4, 5, and 7 were highly
active, showing IC50 (half maximal inhibitory concentration) values ranging from 0.39 to 4.69 mM, and a clear ligand
dependence on activity.
Manuscript received: 18 July 2013.
Manuscript accepted: 12 August 2013.
Published online: 10 September 2013.
Introduction
library of bismuth(III) thiocarboxylates and turned to another
organism against which bismuth compounds could have great
potential: the Leishmania parasite.
One unique feature of bismuth compared with other heavy
metals is its apparent low toxicity. It has been used in medicine
for more than 250 years,[1] and currently a broad spectrum of
bismuth(III) compounds are present as active ingredients in
many drugs used to treat medical conditions such as gastroin-
testinal disorders, syphilis, colitis, hypertension, veterinary skin
diseases, eye infections, and malaria.[2–6] The most important
current medical application of bismuth compounds (bismuth
subsalicylate, colloidal bismuth citrate) is in treating and erad-
icating Helicobacter pylori, the bacterium responsible for gas-
tritis, peptic and duodenal ulcers, and gastric cancers.[7–13] We
recently reported on the bactericidal activity of a series of novel
homo- and heteroleptic bismuth(III) thiocarboxylates against
H. pylori, demonstrating that the compounds displayed better
activity at 6.25 mg mLꢀ1 than commercial bismuth drugs, and
that the thiocarboxylate ligand is very good at rapidly increasing
the antibacterial properties of organometallic bismuth(III)
complexes.[14] In light of these results, we have extended the
Leishmaniasis is a cluster of diseases caused by protozoan
parasites that belong to the genus Leishmania and are spread to
humans by the bite of an infected female sand fly.[15] It is
widespread in developing countries and affects ,12 million
people in 88 countries, with 1.5–2 million new cases every
year.[16,17] Of the three main forms of leishmaniasis that afflict
humans, cutaneous leishmaniasis (CL) and mucocutaneous
leishmaniasis (MCL) result in small papules and large ulcers
that can be found in the skin of exposed parts of the body.[18] In
contrast, visceral leishmaniasis (VL) affects the liver, spleen,
bone marrow, and other viscera, and is fatal if left untreated.[19]
For over 70 years, the treatment of leishmaniasis has relied
on the pentavalent antimonial drugs sodium stibogluconate
(Pentosam) and meglumine antimonite (Glucantime). They
are cheap to produce and effective.[17,20] However, there are
also significant drawbacks: the compounds, particularly when
Journal compilation Ó CSIRO 2013
www.publish.csiro.au/journals/ajc

1298
P. C. Andrews et al.
reduced to the SbIII form, are highly toxic; intravenous injection
over the necessary period of 28 days leads to low compliance
rates; the drugs are not orally active; and areas of resistance,
particularly in India, have developed.[18]
[Ph2Bi{SC(¼O)C6H5}] 8, [Bi{SC(¼O)C6H4NO2}3] 9, [PhBi
{SC(¼O)C6H4NO2}2] 10, and [PhBi{SC(¼O)C6H4SO3}]
11.[14] For the present study, two new thiobenzoic acids were
synthesised: p-bromothiobenzoic acid, p-BrC6H4C(¼O)SH,
BTA, and b-thionaphthoic acid, C10H7C(¼O)SH, TNA, and
these were included alongside thiobenzoic acid, C6H5C(¼O)
SH, TBA, m-nitrothiobenzoic acid, m-NO2-C6H4C(¼O)SH,
NTA, and m-sulfothiobenzoic acid, m-SO3H-C6H4C(¼O)SH,
STA, in the bioactivity studies.[22] All the novel compounds
1–5, BTA, and NTA were characterised using NMR, Fourier-
transform (FT)-IR, electrospray ionisation mass spectrometry
(ESI-MS) and elemental analysis. The solid-state structure of
[PhBi{S(C¼O)C6H4Br}2] 2 was determined by single-crystal
X-ray diffraction.
The periodic relationship between bismuth and antimony and
its apparent lower systemic toxicity in humans means that
compounds of bismuth offer the potential of anti-Leishmanial
drugs with lower toxicity and side effects. Our knowledge of
the behaviour of bismuth compounds in the stomach and
gastrointestinal tract could assist in the development of orally
active drugs. However, there are very few reports of bismuth(III)
compounds being investigated as anti-Leishmanial drugs. We
published the results into our investigations on a wide variety
of bismuth carboxylates, showing their good activity against
Leishmania promastigotes,[21] while Demiceli and coworkers
recently described comparative activities of SbIII and BiIII
complexes of dipyridophenazine (dppz) with the ligand itself.[22]
Biological targets for bismuth are peptides and proteins rich
in cysteine and methionine.[23,24] The S-rich peptides of trypa-
nothione, which is parasite-specific, and glutathione are impli-
cated in the intracellular reduction chemistry of the antimonial
drugs.[25,26] As such, bismuth(III) compounds with thermody-
namically stable and non-labile Bi–S bonds provide interesting
targets in the search for new metallodrugs active against
Leishmania.
In this paper, we investigate the synthesis, characterisation,
anti-Leishmanial activity, and cell toxicity of a novel series
of homo- and heteroleptic bismuth(III) thiocarboxylates: [Bi{S
(C¼O)C6H4Br}3] 1, [PhBi{S(C¼O)C6H4Br}2] 2, [Bi{S(C¼O)
C10H7}3] 3, [PhBi{S(C¼O)C10H7}2] 4, and [Ph2Bi{S(C¼O)
C10H7}] 5. Also included are complexes we have previously
reported on in relation to their activity against Helicobacter
pylori: [Bi{SC(¼O)C6H5}3] 6, [PhBi{SC(¼O)C6H5}2] 7,
Results and Discussion
Synthesis of Thiocarboxylic Acids
Fig. 1 shows the thiocarboxylic acids used in the synthesis of
bismuth(III) complexes 1–11. Thiobenzoic acid TBA is com-
mercially available whereas the other four, m-nitrothiobenzoic
acid NTA, m-sulfothiobenzoic acid STA, p-bromothiobenzoic
acid BTA, and b-thionaphthoic acid TNA, were synthesised
before use.
NTA and STA were synthesised through an electrophilic
substitution reaction with TBA, as we reported previously
(Scheme 1).[14]
BTA and TNA were synthesised through modification of
a method used to prepare thiobenzoic acid TBA. The synthesis
of TBA involves the reaction of benzoyl chloride with hydrogen
sulfide (H2S) gas, followed by neutralisation of the produced
sodium thiobenzoate with hydrochloric acid (HCl). In light of
the toxicity of H2S, it was replaced with sodium hydrogen
sulfide (NaHS) as the thionating agent (Scheme 2). This resulted
in yields of BTA and TNA of between 60 and 65 %. In
comparison with the electrophilic substitution method used to
synthesise NTA and STA,[14] the types of thiocarboxylic acids
that can be accessed through this method are not limited to only
meta-substituted acids, but can include ortho-, para- or even
multiply substituted acids.
O
O
O
SH
SH
SH
NO2
SO3H
Thiobenzoic acid
m-Sulfothiobenzoic acid
m-Nitrothiobenzoic acid
TBA
STA
O
NTA
O
O
O
(i) NaHS
(ii) HCl
SH
SH
R
SH
R
Cl
Br
R ꢀ p-BrC6H4
R ꢀ C10H7
BTA
TNA
p-Bromothiobenzoic acid
BTA
Thionaphthoic acid
TNA
Scheme 2. Reaction of acid chlorides with NaHS and HCl to give p-
bromothiobenzoic, BTA, and b-thionaphthoic acid, TNA.
Fig. 1. Thiocarboxylic acids used in the synthesis of bismuth complexes.
O
O
O
(i) Fuming
H2SO4
Conc. HNO3/
Conc. H2SO4
SH
SH
SH
(ii) BaCO3
NTA
STA
SO3N
NO2
Scheme 1. Synthesis of m-nitrothiobenzoic acid, NTA, and m-sulfothiobenzoic acid, STA, by electrophilic
substitution method.[14]

Activity of Bismuth Thiocarboxylates Against Leishmania
1299
Synthesis of Bismuth(III) Thiocarboxylates
solution at room temperature or under reflux produced only the
bis-substituted product [PhBi{S(C¼O)C10H7}2] 4, regardless of
the reaction stoichiometry or the time. Predictably, the best yield
of 4 (60 %) achieved under SM conditions was from the 2 : 1
reaction (TNA: BiPh3) carried out in ethanol under reflux for
a period of 4 h. The same reaction carried out under SF condi-
tions produced 4 in 79 % yield after heating at 708C for 10 min.
Obtaining [Ph2Bi{S(C¼O)C10H7}] 5 from the 1 : 1 reaction
of TNA and BiPh3 was unsuccessful. However, it was obtained
using salt metathesis in 58 % yield reacting Ph2BiCl and the
sodium salt of TNA at 08C for 20 min (Scheme 5).
Following the synthetic methods developed for our previously
reported bismuth(III) thiocarboxylate complexes 6–11,[14] the
bismuth(III) complexes of BTA and TNA were also obtained by
reacting the thiocarboxylic acid with triphenylbismuth (BiPh3)
under both solvent-free (SF) and solvent-mediated (SM) con-
ditions (Scheme 3). The compounds obtained and their physical
properties are summarised in Table 1.
Before commencing the SF reaction, the thermochemical
profile of the reactions was studied using differential scanning
calorimetry (DSC). The DSC plot for the reaction between
three equivalents of BTA and one BiPh3 is shown in Fig. 2.
The trace shows an endotherm at 558C corresponding to the
melting of the acid, and then a large exothermic peak in the
range 60–808C, indicating protolysis of BiPh3 and subsequent
loss of benzene. Using this information, the SF reaction was
conducted in the temperature range of 70–808C.
Characterisation of Thiocarboxylic Acids
and their Bismuth(III) Derivatives
Infrared Spectroscopy
In the IR spectrum of thiobenzoic acid TBA, the stretching
vibration of the C¼O, C–Ph, and C–S bonds can be found at
The tris-substituted product, [Bi{S(C¼O)C6H4Br}3] 1, was
obtained in a 72 % yield when the 1 : 3 reaction of BiPh3 and
BTA was carried out under SF conditions at 708C for 10 min.
However, when the same components were heated under
reflux in ethanol for 1 h, only the bis-substituted product
[PhBi{S(C¼O)C6H4Br}2] 2 was obtained, in 37 % yield.
Increasing the reaction time to 4 h resulted in a mixture of
1 and 2 in 9 and 91 % yield respectively. This was not improved
on by longer reactions times. Product 2 was also obtained in
56 % yield from the 1 : 2 stoichiometric reaction of BiPh3
and BTA when heated in ethanol under reflux for 4 h. In
contrast, the SF method always produced a mixture of 1 and 2
in a 1 : 9 ratio. The 1 : 1 reaction of BiPh3 with BTA under SF or
SM conditions failed to give the desired mono-substituted
product, [Ph2Bi{S(C¼O)C6H4Br}], as was previously observed
with related systems.[14] Therefore, a simple metathesis route
was attempted, treating Ph2BiCl with one equivalent of the
sodium salt of BTA at 08C using dry methanol as the solvent.
Unfortunately, obtaining an isolated sample of [Ph2Bi{S(C¼O)
C6H4Br}] proved unsuccessful owing to its highly facile
rearrangement into the more stable 2 and BiPh3, as shown below
in Scheme 4.
6
54.73ꢃC
4
2
369.0 Jgꢂ1
0
ꢂ2
ꢂ4
51.72ꢃC
102.0 Jgꢂ1
63.41ꢃC
20
40
60
80
100
120
140
160
180
Temperature [ꢃC]
Fig. 2. Differential scanning calorimetry (DSC) plot for the reaction
between 3 equivalents of p-bromothiobenzoic, BTA, with BiPh3.
PhBi{SC(ꢀO)C6H4Br}2
2 Ph2Bi{SC(ꢀO)C6H4Br}
ꢁ
BiPh3
The 3 : 1 reaction of TNA with BiPh3 under SF conditions
resulted in the formation of the expected tris-substituted
product, [Bi{S(C¼O)C10H7}3] 3, in 73 % yield after 10 min of
heating at 708C. However, the SM reaction carried out in ethanol
2
Scheme 4. Rearrangement of [Ph2Bi{SC(¼O)C6H4Br}] into 2 and BiPh3.
Methanol/N2
SF/SM
C10H7C(ꢀO)SNa
Ph BiCl
2
Ph2Bi {SC(ꢀO)C10H7} ꢁ NaCl
ꢁ
n RC(ꢀO)SH ꢁ BiPh3
Ph3ꢂnBi{SC(ꢀO)R}n ꢁ n PhH
0ꢃC
5
Scheme 3. Reaction of thiocarboxylic acids (R ¼ p-BrC6H4 and C10H7)
and BiPh3 under solvent-free (SF) and solvent-mediated (SM) conditions
(n ¼ 1–3).
Scheme 5. Reaction of sodium salt of b-thionaphthoic acid, TNA, and
Ph2BiCl under Schlenk conditions to obtain 5.
Table 1. Bismuth(III) complexes of thiocarboxylates produced under solvent-free (SF) and solvent-mediated
(SM) methods
BTA, p-bromothiobenzoic; TNA, thionaphthoic acid
Thiocarboxylic acid
Bismuth precursor
Isolated yield [%]
Compound
Mp [8C]
SF
SM
BTA
BTA
TNA
TNA
TNA
BiPh3
BiPh3
BiPh3
BiPh3
Ph2BiCl
72
–
–
[Bi{S(C¼O)C6H4Br}3] 1
[PhBi{S(C¼O)C6H4Br}2] 2
[Bi{S(C¼O)C10H7}3] 3
[PhBi{S(C¼O)C10H7}2] 4
[Ph2Bi{S(C¼O)C10H7}] 5
dec. .176
dec. .200
dec. .220
dec. .220
129–130
56
–
73
79
–
60
58

1300
P. C. Andrews et al.
Table 2. Summary of IR bands and assignments of thiocarboxylic acids and their bismuth(III)
derivatives (cm21
BTA, p-bromothiobenzoic; TNA, thionaphthoic acid
)
BTA
1
2
TNA
3
4
5
n(C¼O)
n(CS)
n(C–Ph)
d(CH)
1654 s
968 m
1210 m
–
1566 s
919 m
1208 m
–
1576 s
1686 s
957 m
1274 m
–
1564 s
912 s
1216 s
–
1556 m
930 w
1564 m
932 w
931 s
1215 s
1211 w
1210 w
726 m 694 m
722 m 692 m
725 m 694 m
O
O
Table 3. Comparison of the 1H NMR shifts (ppm) of bismuth(III)
thiocarboxylates with their free acids and bismuth precursors
BTA, p-bromothiobenzoic; TNA, thionaphthoic acid
d
a
a
e
e
b
SH
SH
b
a
CHa
–
CHb
–
CHc
–
CHd
–
o-Ph
m-Ph
p-Ph
Br
c
c
d
BiPh3
7.76
8.29
–
7.38
7.61
–
7.31
7.33
–
BTA
TNA
Ph2BiCl
Fig. 3. Labelling system used to assign the protons in the 1H NMR spectra
BTA
8.02
7.92
7.91
8.92
8.71
8.70
8.68
7.88
7.72
7.70
8.30
8.15
8.14
8.11
7.68
7.72
7.70
8.11
8.07
8.06
8.02
–
1
–
–
–
–
of the thiocarboxylic acids.
2
–
8.80
–
7.70
–
7.36
–
TNA
8.11
8.01
8.00
7.96
of the bismuth(III) thiocarboxylates showed the expected number
of resonances, confirming the formation of the desired products.
Full details are provided in the Experimental section.
3
4
5
–
–
–
8.87
8.27
7.74
7.55
7.37
7.32
X-Ray Crystallography
1687, 1212, and 950 cmꢀ1 respectively. When compared with
TBA, the C¼O absorptions in p-bromothiobenzoic acid BTA
were found to shift to lower wave numbers (Dn ¼ 33 cmꢀ1),
whereas C–S appeared at higher wave numbers (Dn ¼ 18 cmꢀ1).
However, thionaphthoic acid TNA does not show much
difference in its C¼O and C–S vibrations relative to TBA.
The C¼O and the C–S stretching vibrations of all the bismuth
(III) complexes 1–5 show bathochromic shifts relative to their
corresponding free acids, indicating the ligand binds to bismuth
(III) through the deprotonated S atom and the carbonyl O atom.
The magnitude of shift of the C–Ph frequency can determine the
strength of the metal–sulfur (M–S) bond formed. A weaker M–S
bond results in a larger increment of the C–Ph frequency due
to the electron drift increasing the bond order of C–Ph. However,
when the coordination through sulfur is strong, the back-
bonding from the filled metal orbitals to the vacant orbitals of
sulfur can hinder this electron drift from the Ph–C bond.[27]
None of the bismuth(III) complexes show any significant incre-
ment of C–Ph frequency indicating a stronger Bi–S bond, which
was also confirmed by crystallography studies. Presence of the
phenyl ligands in the heteroleptic bismuth(III) complexes can
be confirmed by the appearance of bands in the range of
694–726 cmꢀ1, which can be assigned to the C–H bending
frequencies. Table 2 summarises the main IR absorption
bands observed for the new thiocarboxylic acids and their
bismuth(III) complexes.
Pink needle-shaped crystals of [PhBi{SC(¼O)C6H4Br}2] 2
were isolated from a solution of DMSO after 2 weeks. The
complex crystallises in a monoclinic crystal system with space
group P21/n. The asymmetric unit is shown in Fig. 4, along with
selected bond lengths and angles. The two thiocarboxylate
ligands are attached to the bismuth(III) centre primarily through
their anionic S atom, with Bi–S bond distances of Bi(1)–S(1)
˚
2.64(9), and Bi(1)–S(2) 2.61(9) A. This is typical of such bond
distances observed in bismuth(III) thiolates.[27–30] The structure
is further stabilised by relatively short Bi–O(¼C) interactions of
˚
˚
Bi(1)–O(1) 2.67(2) A, and Bi(1)–O(2) 2.62(2) A. The bismuth
(III) centre is five-coordinate when considering the two didentate
ligands and the phenyl group. The stereochemically active lone
pair can be assumed to take the void opposite the phenyl group.
The structure shows a distorted octahedral geometry, in which
the two ligands forming the plane and the phenyl group and the
lone pair are orientated axial to the plane. These monomeric
units of [PhBi{SC(¼O)C6H4Br}2] are linked by secondary Bi–S
˚
interactions of 3.54 A to form one-dimensional polymer chains.
Interaction of these polymers chains through weak Bi–S inter-
˚
actions of 3.65 A results in an increase in the coordination
number of the bismuth(III) centre to seven (Fig. 5).
Similarly, the bismuth(III) complexes derived from thioben-
zoic acid, [Bi{SC(¼O)C6H5}3] and [PhBi{SC(¼O)C6H5}2]2,
also show didentate binding modes through their S and O
atoms, with the reported Bi–S and Bi–(O¼C) bond lengths
˚
ranging from 2.61(7) to 2.62(15) and 2.71(4) to 2.78(2) A
respectively.[14] In contrast, the As and Sb derivates of thioben-
zoic acid, [As{SC(¼O)C6H5}3] and [Sb{SC(¼O)C6H5}3], only
show monodentate behaviour via the thiolate S atom.[31]
NMR Spectroscopy
1
The H NMR spectrum of each of the bismuth(III) thiocarbox-
ylates,takenin[D6]DMSO,showedlow-frequency shiftsfortheir
thiocarboxylate resonances compared with the respective free
acids, indicating deprotonation and subsequent binding to bis-
muth(III) (Table 3, Fig. 3). The ortho-, meta-, and para-Ph signals
of the heteroleptic bismuth thiocarboxylates showed increasing
high-frequency shifts as the number of Ph groups bound to the
BiIII centre decreased from three through to one. The 13C NMR
Biological Testing
Solubility and Stability
Stability is an important feature of the quality, safety, and
efficiency of a drug product. To assess the bismuth(III) thio-
carboxylate complexes for stability to atmospheric conditions,

Activity of Bismuth Thiocarboxylates Against Leishmania
1301
L. major
140
120
100
80
C(15)
O(1)
O(2)
TBA
NTA
BTA
TNA
STA
C(1)
C(8)
S(2)
Br(2)
Bi(1)
60
S(1)
Br(1)
40
Fig. 4. Molecular structure of [PhBi{SC(¼O)C6H4Br}2] 2. Thermal
20
ellipsoids are shown at 50 % probability. H atoms are omitted for clarity.
˚
Selected bond lengths [A] and angles [8]: Bi(1)–S(1) 2.6374(9), Bi(1)–S(2)
0
2.6131(9), Bi(1)–O(1) 2.670(2), Bi(1)–O(2) 2.624(2), Bi(1)–C(15) 2.225(4),
S(1)–C(1) 1.758(4), S(2)–C(8) 1.760(3), C(1)–O(1) 1.234(4), O(2)–C(8)
1.231(4); S(2)–Bi(1)–O(2) 59.62(5), S(2)–Bi(1)–S(1), 86.99(3), O(2)–Bi
(1)–S(1), 145.95(5), S(2)–Bi(1)–O(1), 145.04(5), O(2)–Bi(1)–O(1) 151.96
(7), C(15)–Bi(1)–O(1) 81.47(10), C(15)–Bi(1)–S(2), 93.65(9), C(15)–Bi
(1)–O(2), 84.10(11), C(15)–Bi(1)–S(1), 92.21(9).
0.048 0.97 0.19 0.39 0.78 1.56 3.125 6.25 12.5 25 50 100
Concentration [µM]
Fig. 6. Effect of thiocarboxylic acids on Leishmania major promastigotes.
Definition of acronyms provided in Fig. 1.
Fibroblasts
120
100
80
TBA
60
NTA
BTA
40
TNA
STA
20
0
0.048 0.97 0.19 0.39 0.78 1.56 3.125 6.25 12.5 25 50 100
Concentration [µM]
Fig. 7. Effect of thiocarboxylic acids on human primary fibroblast cells.
Sulfothiobenzoic acid, STA, showed a similar behaviour to
TBA against both the promastigotes and fibroblasts. However,
the other substituted thiobenzoic acids: m-nitrothiobenzoic acid,
NTA, p-bromothiobenzoic acid, BTA, and the thionaphthoic
acid, TNA, showed some activity against the promastigotes at
higher concentrations. p-Bromothiobenzoic acid, BTA, was the
most active acid of the series, killing ,80 % of the promasti-
gotes at a concentration of 50 mM (10.9 mg mLꢀ1). Interestingly,
the compound was not toxic to the fibroblasts cells, even at a
higher concentration of 100 mM (21.7 mg mLꢀ1). However,
when compared with Amphotericin B, which kills ,80 % of the
parasites at a concentration of 4.33 mM (4.00 mg mLꢀ1),[32] the
activity of BTA is too low to be considered useful as a drug. Acid
NTA was shown to kill ,70 % of promastigotes at a concen-
tration of 100 mM (18.3 mg mLꢀ1) whereas TNA killed 50 % of
the population at 50 mM (9.4 mg mLꢀ1). The toxicity of NTA
against fibroblasts was nearly the same as observed against
promastigotes. TNA, though, was shown to be less toxic to the
fibroblasts cells, requiring a concentration of 100 mM to kill
50 % (18.8 mg mLꢀ1) of the population (Figs 6 and 7). When
compared with the activity of substituted thiocarboxylic acids
NTA, BTA, and TNA, the inactivity of STA could be due to the
presence of the sulfonic acid group. The primary difference with
the thiocarboxylates is that an arene sulfonic acid has a typical
pKa of 1–2, and in the buffered cell medium, this will be ionised
to the arene sulfonate anion. The cell membrane will be
impermeable to the anion and will be, in the absence of specific
ion transporters, effectively non-toxic.
Fig. 5. Polymeric structure of [PhBi{SC(¼O)C6H4Br}2]N 2 showing
weak intermolecular Bi–S interactions.
NMR spectral data were recorded on samples of the compounds
that had been stored under air and at ambient temperatures on
a regular basis over a period of 6 months. During this time, there
was no change in the observed NMR spectra. The chemical
shifts did not change from the initial spectrum, providing good
evidence that these compounds are stable to hydrolysis by
atmospheric moisture and oxygen.
Thiocarboxylic Acids and their Bismuth(III)
Derivatives as Potential Anti-Leishmanial Drugs
The bismuth(III) thiocarboxylates 1–11, the corresponding free
acids, and BiPh3 were assessed for their in vitro activity against
Leishmania major promastigotes, and on human fibroblast cells
to establish overall toxicity towards mammalian cells. DMSO
was used as the solvent to make the required concentrations
of the bismuth(III) compounds and free acids, as it shows no
toxicity against either the L. major promastigotes or the fibro-
blast cells at concentrations #100 mM. Amphotericin B (IC50
(half maximal inhibitory concentration) 2.17 mM for L. major
promastigotes),[32] one of the well-known anti-Leishmanial
drugs, was used as the reference drug.
Thiobenzoic Acids
Thiobenzoic acid, TBA, did not show any activity against the
Leishmania major promastigotes, or the human fibroblasts cells.

1302
P. C. Andrews et al.
Thiobenzoic acid, TBA, is a yellow liquid, which is usually
Table 4. Half maximal inhibitory concentration (IC50) values of the
bismuth(III) complexes 1 7 and 9 11, and Amphotericin B against
]
Leishmania major promastigotes
]
stored at 4–58C. When exposed to air at room temperature, it
converts rapidly into the disulfide [Ph–C(¼O)S–S–C(¼O)–Ph],
which is a white solid. The substituted thiocarboxylic acids are
stable in their acid form, as evidenced by NMR studies. This is a
possible explanation for the contradictory results observed for
the thiobenzoic acid TBA and the other substituted thiobenzoic
acids; TBA in its disulfide form is non-toxic whereas the others,
which are in the acid form, are toxic.
Compound
IC50
[mg mLꢀ1
IC50
cLogPA
]
[mM]
Amphotericin B
2.01
.1.38
4.57
2.17
.100
25.0
.100
20.0
42.9
.100
1.49
TBA [C6H5C(¼O)SH]
2.08
1.94
ꢀ0.71
2.99
3.25
9.46
8.10
10.39
8.72
7.05
6.87
6.37
5.87
6.10
5.86
2.75
NTA [m-NO2C6H4C(¼O)SH]
STA [m-SO3HC6H4C(¼O)SH]
BTA [p-BrC6H4C(¼O)SH]
TNA [C10H7C(¼O)SH]
.21.8
4.34
Tris-Thiocarboxylato Bismuth(III) Complexes
8.06
Though TBA was not toxic to the Leishmania major parasites
and fibroblasts, its tris-substituted bismuth complex [Bi{SC
(¼O)C6H5}] 6 was, killing ,70 % of the population of both
promastigotes and fibroblasts at a concentration of 25 mM
(15.5 mg mLꢀ1). This indicates the effect of bismuth on
improving activity, but also that the toxic effect may be general.
The tris-substituted bismuth complex of NTA, 9, was less active
against promastigotes than fibroblasts cells, killing 60 % of
promastigotes at a concentration of 100 mM (75.5 mg mLꢀ1),
while complex 9 killed 70 % of the fibroblasts at the same
concentration. In contrast, complex 3, the tris-substituted com-
plex derived from TNA, showed approximately similar activity
against both the promastigotes and fibroblast cells, killing
,80 % at a concentration of 100 mM (77.0 mg mLꢀ1). Com-
pound 1 was the least active tris-substituted bismuth(III) thio-
carboxylate, killing ,20 % of promastigotes at 100 mM
(85.8 mg mLꢀ1), while being much less toxic to the fibroblasts.
1
[Bi{SC(¼O)C6H4Br}3]
[PhBi{SC(¼O)C6H4Br}2]
[Bi{SC(¼O)C10H7}3]
.85.7
1.07
2
3
insoluble insoluble
4
[PhBi{SC(¼O)C10H7}2]
[Ph2Bi{SC(¼O)C10H7}]
[Bi{SC(¼O)C6H5}3]
3.01
0.32
4.69
0.59
5
6
insoluble insoluble
7
[PhBi{SC(¼O)C6H5}2]
[Ph2Bi{SC(¼O)C6H5}]
[Bi{SC(¼O)C6H4-m-NO2}3]
[PhBi{SC(¼O)C6H4-m-NO2}2]
[PhBi{SC(¼O)C6H4-m-SO3}]
0.22
–
0.39
8
–
9
75.5
.100
0.78
0.39
10
11
0.50
0.19
ACalculated partition coefficient.
Fibroblasts
1
2
3
4
120
100
80
60
40
20
0
Mono- and Bis-Thiocarboxylato Bismuth(III) Complexes
The phenyl-substituted bismuth(III) complexes of thiocarbox-
ylates [PhBi{SC(¼O)C6H4Br}2] 2, [PhBi{SC(¼O)C10H7}2] 4,
[Ph2Bi{SC(¼O)C10H7}] 5, [PhBi{SC(¼O)C6H5}2] 7, [PhBi
{SC(¼O)C6H4NO2}2] 10, and [PhBi{SC(¼O)C6H4SO3}] 11 all
showed similar or higher inhibitory activity against Leishmania
major when compared with Amphotericin B. The half-maximal
inhibitory concentration (IC50) values of these complexes
are shown in Table 4. However, these also showed consistent
though variable toxicity towards the human fibroblasts, as
illustrated in Figs 8–10. The comparative trends shown in Fig. 10
indicate that the difference in toxicity towards the parasites and
the fibroblasts is marginal.
5
6
7
9
10
11
BiPh3
0.048 0.97 0.19 0.39 0.78 1.56 3.125 6.25 12.5 25 50 100
Concentration [µM]
Fig. 8. Effect of bismuth(III) thiocarboxylates and BiPh3 on Leishmania
major promastigotes.
We recently also studied the toxicity of Bi(NO)3 and BiCl3
against human fibroblasts and showed that they are non-toxic
even at a higher concentration of 500 mg mLꢀ1 [21]
BiPh3
.
showed a moderate activity against Leishmania major promas-
tigotes whereas it was non-toxic to fibroblasts.
1
L. major
160
140
120
100
80
2
The presence of the Ph group in the complexes increases the
activity of the compounds against the parasite significantly.
Comparisons of the IC50 values for two sets of complexes
illustrate this well: [Bi{SC(¼O)C6H4Br}3] (.100 mM) versus
[PhBi{SC(¼O)C6H4Br}2] (1.49 mM), and [Bi{SC(¼O)C6H4-
m-NO2}3] (100 mM) versus [PhBi{SC(¼O)C6H4-m-NO2}2]
(0.78 mM).
3
4
5
6
60
7
When considering the activity of bismuth(III) salts Bi(NO)3
and BiCl3, which provide labile Bi3þ ions, and of BiPh3, which
contains phenyl groups attached to bismuth, it could be con-
cluded that the presence of Bi3þ ions or phenyl groups alone is
not responsible for the higher activity of the heteroleptic
bismuth(III) complexes 2, 4, 5, 7, 10, and 11, but also the
thiocarboxylato ligands and the degree of substitution play an
important role.
40
9
20
10
11
BiPh3
0
0.0480.97 0.19 0.39 0.78 1.563.1256.25 12.5 25 50 100
ꢂ20
Concentration [µM]
Fig. 9. Effect of bismuth(III) thiocarboxylates and BiPh3 on human
primary fibroblast cells.

Activity of Bismuth Thiocarboxylates Against Leishmania
1303
Compound 2
Compound 4
Compound 5
Compound 7
Compound 10
Compound 11
120
100
140
120
100
80
120
100
80
60
40
20
0
120
100
80
60
40
20
0
120
100
80
60
40
20
0
120
100
80
60
40
20
0
Promastigotes
Fibroblasts
80
60
40
20
0
60
40
20
0
0
0
0
0
0
0
0.39 1.56 6.25 25.0
0.39 1.56 6.25 25.0
0.39 1.56 6.25 25.0
0.39 1.56 6.25 25.0
0.39 1.56 6.25 25.0
0.39 1.56 6.25 25.0
0.097
100.0
0.097
100.0
0.097
100.0
0.097
100.0
0.097
100.0
0.097 100.0
Concentration [µM]
Fig. 10. Comparison of the toxicity of the bis-thiocarboxylato BiIII complexes 2, 4, 5, 7, and 10 on human primary fibroblast cells.
Conclusions
ether at 08C, and subsequently recrystallised from ethanol.
Ph2BiCl was synthesised by mixing BiPh3 and BiCl3 in a 2 : 1
ratio in dried diethyl ether.
In order to assess the activity of range of bismuth(III) thio-
carboxylates against Leishmania, two new thiocarboxylic acids,
p-bromothiobenzoic acid BTA and b-thionaphthoic acid TNA,
and five new mono-, bis-, and tris-substituted bismuth(III)
thiocarboxylates, [Bi{S(C¼O)C6H4Br}3] 1, [PhBi{S(C¼O)
C6H4Br}2] 2, [Bi{S(C¼O)C10H7}3] 3, [PhBi{S(C¼O)C10H7}2]
4, and [Ph2Bi{S(C¼O)C10H7}] 5, were synthesised and fully
characterised. The solid-state structure of complex 2 was deter-
mined by X-ray crystallography and revealed that the thio-
carboxylato ligands bind to the bismuth(III) centre in a didentate
manner through both O and S atoms, resulting in a formally five-
coordinate complex. The coordination number of BiIII is raised to
NMR spectra were recorded on a Bruker DRX 400 spec-
trometer. All spectra were internally referenced using the
deuterated solvent signal. ESI mass spectra were generated on
a Micromass Platform II QMS spectrometer. Infrared spectra,
as Nujol mulls, were recorded on a Perkin–Elmer 1600 FT-IR
spectrometer. Elemental microanalyses were performed by
the Campbell Microanalytical Laboratory, Department of
Chemistry, University of Otago, Dunedin, New Zealand. Melt-
ing points were measured on a Stuart Scientific melting point
apparatus SMP3.
˚
seven through longer, weaker Bi–S bonds (3.54 A), resulting in
the formation of an extended polymeric structure.
Cell Viability Assay
The Celltiter Blue cell viability assay (Promega, Madison, WI)
was used for screening for anti-Leishmanial activity and toxic-
ity. Compounds were dissolved in DMSO at 10 mmol Lꢀ1
working stock and diluted out in appropriate culture media. The
assay was set up in duplicates in 96-well plates according to the
manufacturer’s instructions. Concentrations of 106 promasti-
gotes per mL and 105 per mL primary human fibroblasts were
used. Cell viability was assessed by measuring fluorescence at
550 nm excitation and 590 nm emission as per manufacturer’s
instructions.[33] The Celltiter Blue dye was added to samples
at the time of setting up the assay and the negative control
(no cells) value was subtracted from all subsequent readings as a
background value. All readings were compared with the no-drug
control and the percentage growth inhibition was calculated.
DMSO controls were included. All plates were assessed
microscopically.[34] The graphs shown in the present paper give
the average of duplicate values plotted for each concentration,
expressed as a percentage of non-treated, positive control.
The anti-Leishmanial activity of the five novel bismuth(III)
thiocarboxylates and of six previously described – [Bi{SC(¼O)
C6H5}3] 6, [PhBi{SC(¼O)C6H5}2] 7, [Ph2Bi{SC(¼O)C6H5}]
8, [Bi{SC(¼O)C6H4NO2}3] 9, [PhBi{SC(¼O)C6H4NO2}2] 10,
[PhBi{SC(¼O)C6H4SO3}]11– was assessedagainst Leishmania
major promastigotes, alongside the respective free acids. The
toxicity of all the compounds towards human fibroblasts was
also assessed. All of the free thiocarboxylic acids except thio-
benzoic acid TBA and sulfothiobenzoic acid STA were highly
toxic to the L. major promastigotes at high concentrations of
50–100mM. Among these, p-bromothiobenzoic acid BTA was
non-toxic to the human fibroblasts, displaying some potential as
an anti-Leishmanial agent. The remaining compounds also
proved toxic to the mammalian cells at relatively high concentra-
tions (.25 mM). TBA, which exists in its disulfide form, did not
show any activity against either L. major parasites or mammalian
cells, demonstrating the importance of the S–H group on the
displayed activity.
The bismuth complexes of all the thiocarboxylato complexes
showed an increase in activity over the free acids. Among these,
the heteroleptic phenyl-substituted bismuth(III) complexes [PhBi
{SC(¼O)C6H4Br}2] 2, [PhBi{SC(¼O)C10H7}2] 4, [Ph2Bi{SC
(¼O)C10H7}] 5, [PhBi{SC(¼O)C6H5}2] 7, [PhBi{SC(¼O)
C6H4NO2}2] 10, and [PhBi{SC(¼O)C6H4SO3}] 11 were all
highly active, with IC50 values ranging from 0.39 to 4.69mM,
and are comparable with the commercial drug Amphotericin B.
Compounds 7 and 11 were the most active. The importance of the
presence of the Ph group is illustrated in comparing the IC50
valuesofthe tris-substituted complexes [Bi{S(C¼O)C6H4Br}3] 1
and [Bi{SC(¼O)C6H4NO2}3] 9, which were an order of magni-
tude less active than their bis-substituted PhBiL2 analogues.
Cell Culture
Leishmania major was maintained at 268C in M199 medium
(Invitrogen) supplemented with 10 % heat-inactivated fetal
bovine serum (HI-FBS) (TraceBiosciences). The human pri-
mary fibroblast were cultured in Dulbecco’s Modified Eagle’s
Medium (DMEM) (Life Technologies) supplemented with 10 %
HI-FBS at 378C in 5 % CO2.
Synthesis
Chart 1 shows the labelling system used to assign carbon atoms
in the 13C NMR spectra of thiocarboxylic acids.
p-BrC6H4C(¼O)SH, BTA
Experimental
All manipulations were carried out under standard Schlenk
conditions. p-Bromobenzoyl chloride (4.39 g, 20.00 mmol) was
added to a solution of NaHS (2.35 g, 42.00 mmol) in 50 mL of
BiPh3 was synthesised through a standard Grignard metathesis
reaction by the treatment of BiCl3 with PhMgBr in dried diethyl

1304
P. C. Andrews et al.
O
g
O
k
PhBi{SC(¼O)C6H4Br}2, 2
f
b
b
d
e
Solvent-mediated synthesis. BiPh3 (0.44 g, 1.00 mmol) and
BTA (0.43 g, 2.00 mmol) were stirred together in refluxing
ethanol for a period of 4 h. The resultant precipitate was
collected by filtration and washed with a small amount of
ethanol and toluene to remove any unreacted acid and BiPh3.
The remaining white solid was identified as [PhBi{SC(¼O)
C6H4Br}2] 2.
a
a
g
c
SH
SH
d
f
c
h
Br
e
i
j
BTA
TNA
Chart 1.
Yield: 0.40g, 55.7 %, mp dec. .2008C. Found: C 33.47,
H 1.89. Anal. calc. for C20H13BiO2S2Br: C 33.42, H 1.81%. nmax
(Nujol)/cmꢀ1 1576s, 1215m, 1162m, 931m, 726m, 694m. dH
(400.1 MHz, [D6]DMSO) 8.80 (d, 3J 9.0, 2H, o-HPh), 7.91 (d, 3J
9.0, 4H, Hb,f), 7.70 (m, 6H, Hc,e þ m-HPh), 7.36 (t, 3J 9.0, 2H,
p-HPh). dC (100.0 MHz, [D6]DMSO) 140.1 (Ca), 138.1 (Cb,f),
132.3 (C–Bi), 131.6 (Cc,e þ o, p-Cph), 130.1 (C–Br þ p-CPh).
m/z (ESIþ) 501.1 {40 %, [PhBiL]þ (79Br isotope)}, 503.1 {40 %,
[PhBiL]þ (81Br isotope)}. m/z (ESI–) 214.9 {99 %, [L]– (79Br
isotope)}, 216.9 {100 %, [L]– (81Br isotope)}, 762.9 (20 %,
[PhBiL2 þ EtO]–), 842.9 {90 %, [PhBiL2 þ DMSO þ EtO]–
(81Br isotope}, 933.0 {52 %, [PhBiL2 þ DMSO þ (H2O)5 þ
EtO]– (81Br isotope)}. {LH ¼ p-BrC6H4C(¼O)SH}.
absolute ethanol at 08C and stirred for 1 h. The resultant
precipitate of NaCl was separated from the reaction mixture
by filtering through a Buchner funnel and solvent was evapo-
rated from the yellow filtrate under vacuum to obtain the sodium
salt of BTA as a yellow solid. This was dissolved in distilled
water and any undissolved solid was removed by filtration. 1 M
HCl was added to the filtrate until no more precipitation
occurred and the yellow-green precipitate of BTA was removed
by filtration and washed with copious amount of water until
the filtrate did not show any acidic reaction to pH paper.
Yield: 2.60 g, 60.2 %, mp 79.5–80.58C. Found: C 38.90,
H 2.28. Anal. calc. for C7H5OSBr: C 38.71, H 2.30 %. nmax
(Nujol)/cmꢀ1 1654s, 1210m, 1171m, 1065m, 968m, 870m. dH
(400.1 MHz, [D6]DMSO) 8.02 (d, J3 7.5, 2H, Hb,f), 7.88 (d, J3
8.4, 1H, Hc), 7.68 (d, J3 6.0, 1H, He). dC (100.0 MHz, [D6]
DMSO) 189.3 (Cg), 135.5 (Ca), 132.2 (Cc,e), 129.4 (Cb,f), 129.2
(Cd). m/z (ESI–) 215.0 {98 %, [L–] (79Br isotope)}, 217.0
{100 %, [L–] (81Br isotope)}, 366.9 (5 %, [LH þ CHCl3 þ
MeO]–). {LH ¼ BrC6H4C(¼O)SH}.
Bi{SC(¼O)C10H7}3, 3
Solvent-free synthesis. BiPh3 (0.44 g, 1.00 mmol) and TNA
(0.56 g, 3.00 mmol) were mixed together, and transferred to a
glass tube that was open at one end. The mixture was heated to
708C in a Kugelrohr oven for 10 min. The residual white product
was washed with a small amount of ethanol and toluene.
Analysis of the white compound was consistent with [Bi{SC
(¼O)C10H7}3] 3.
C
10H7C(¼O)SH, TNA
Yield: 0.56 g, 72.7 %, mp dec. .2208C. Found: C 51.92,
H 2.76. Anal. calc. for C33H21BiO3S3: C 51.42, H 2.72 %. nmax
(Nujol)/cmꢀ1 1564s, 1216m, 1172m, 1121m, 912m, 817m. dH
(400.1 MHz, [D6]DMSO) 8.71 (s, 1H, Hb), 8.15 (d, 3J 8.0, 2H,
Hc), 8.07–7.98 (m, 3H, Hf,I,j), 7.68 (t, 3J 8.0, 1H, Hg), 7.60 (t, 3J
8.0, 1H, Hh). dC (100.0 MHz, [D6]DMSO) 136.7 (Ca), 135.3
(Cd), 131.9 (Ce), 129.8 (Cf), 129.7 (Cb), 128.7 (Ch), 128.2 (Cj),
127.7 (Ci), 127.1 (Cg), 123.8 (Cc). m/z (ESIþ) 189.2 (45 %, [LH
þ H]þ), 583.3 (8 %, [BiL2]þ), 793.2 (10 %, [BiL3 þ Na]þ). m/z
(ESI–) 187.1 (100 %, [L]–). {LH ¼ C10H7C(¼O)SH}.
This was synthesised by reacting b-naphthoyl chloride
(4.48 g, 23.50 mmol) and NaHS (2.80 g, 50.00 mmol) in a
similar way to that described for the synthesis of BTA.
Yield: 2.87 g, 64.9 %, mp 54.0–55.08C. Found: C 70.31,
H 4.17. Anal. calc. for C11H8OS: C 70.18, H 4.28 %. nmax
(Nujol)/cmꢀ1 1686s, 1274m, 1167m, 1021m, 957m, 898m. dH
(400.1 MHz, [D6]DMSO) 8.92 (s, 1H, Hb), 8.30 (d, J3 8.0, 1H,
Hc), 8.11 (m, 3H, Hj,f,i), 7.79 (t, J3 8.0, 1H, Hg), 7.67 (t, J3 8.0,
1H, Hh). dC (100.0 MHz, [D6]DMSO) 185.3 (Ck), 135.8 (Cd),
134.8 (Ca), 132.8 (Ce), 132.1 (Cf), 131.6 (Ch,b,j), 130.4 (Ci,g),
129.8 (Cc). m/z (ESIþ) 189.3 (100 %, [LH þ H]þ), 229.3 (8 %,
[LH þ Naþ þ H2O]þ), 367.3 {25 %, [LH þ (DMSO)2 þ Naþ]þ}.
m/z (ESI–) 187.2 (100 %, [L–]). {LH ¼ C10H7C(¼O)SH}.
PhBi{SC(¼O)C10H7}2, 4
Solvent-mediated synthesis. BiPh3 (0.44 g, 1.00 mmol) and
TNA (0.38 g, 2.00 mmol) were stirred together in refluxing
ethanol for a period of 4 h. The resultant precipitate was
collected by filtration and washed with a small amount of
ethanol and toluene to remove any unreacted acid and BiPh3.
The remaining white solid was identified as [PhBi{SC(¼O)
C10H7}2] 4.
Bi{SC(¼O)C6H4Br}3, 1
Solvent-free synthesis. BiPh3 (0.44 g, 1.00 mmol) and BTA
(0.65 g, 3.00 mmol) were mixed together, and transferred to a
glass tube that was open at one end. The mixture was heated to
708C in a Kugelrohr oven for 10 min. The residual white product
was washed with a small amount of ethanol and toluene.
Analysis of the white compound was consistent with [Bi{SC
(¼O)C6H4Br}3] 1.
Yield: 0.40 g, 60.6 %, mp dec. .2208C. Found: C 50.95,
H 2.78. Anal. calc. for C28H19BiO2S2: C 50.90, H 2.87 %. nmax
(Nujol)/cmꢀ1 1556s, 1211m, 1163m, 1121m, 930m, 862m,
722m, 692m. dH (400.1 MHz, [D6]DMSO) 8.87 (d, J3 8.0, 2H,
o-HPh), 8.70 (s, 2H, Hb) 8.14 (d, J3 8.0, 2H, Hc), 8.06 (d, J3 8.0,
2H, Hj), 8.00 (m, 4H, Hf,i), 7.74 (t, J3 8.0, 2H, m-HPh), 7.63
(m, 4H, Hg,h), 7.37 (t, J3 8.0, 1H, p-HPh). dC (100.0 MHz, [D6]
DMSO) 139.9 (Ca), 138.1 (Cd), 136.4 (Ce), 135.0 (C–Bi), 132.1
(o-CPh), 132.0 (m-CPh), 131.0 (p-CPh), 129.7 (Cf), 129.6 (Cb),
128.1 (Ch), 127.6 (Cj), 127.4 (Ci), 126.9 (Cg), 124.0 (Cc).
m/z (ESIþ) 473.2 (20 %, [PhBiL]þ), 583.1 (10 %, [BiL2]þ),
683.2 (10 %, [PhBiL2 þ Na]þ). m/z (ESI–) 187.1 (100 %,
[L]–). {LH ¼ C10H7C(¼O)SH}.
Yield: 0.62 g, 72.1%, mp dec. .1768C. Found: C 30.20,
H 1.47. Anal. calc. for C21H12BiO3S3Br: C 29.40, H 1.40 %. nmax
(Nujol)/cmꢀ1 1566s, 1208m, 1168m, 1067m, 919m, 832m. dH
(400.1MHz, [D6]DMSO) 7.92 (d, J3 6.0, 2H, Hb,f), 7.72 (d, J3
6.0, 2H, Hc,e). dC (100.0 MHz, [D6]DMSO) 138.3 (Ca), 131.7
(Cb,f), 130.0 (Cc,e), 128.3 (Cd). m/z (ESIþ) 640.9 (100%,
[BiL2]þ)). m/z (ESI–) 215.0 {39 %, [L]– (79Br isotope)}, 217.0
{40 %, [L]– (81Br isotope)}, 892.8 (35 %, [BiL3 þ Cl]–), 982.8
{40 %, [BiL3 þ (H2O)5 þ Cl]–}. {LH ¼ p-BrC6H4C(¼O)SH}.

Activity of Bismuth Thiocarboxylates Against Leishmania
1305
Solvent-free synthesis. BiPh3 (0.44 g, 1.00 mmol) and TNA
(0.38 g, 2.00 mmol) were mixed together, and transferred to a
glass tube that was open at one end. The mixture was heated to
708C in a Kugelrohr oven for 10 min. The residual white product
was washed with a small amount of ethanol and toluene to give 4
in 78.8 % (0.52 g) yield.
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13, 547. doi:10.1097/00042737-200105000-00014
[9] J. Houghton, J. G. Fox, T. C. Wong, J. Gastroenterol. Hepatol. 2002,
Ph2Bi{SC(¼O)C10H7}, 5
17, 495. doi:10.1046/J.1440-1746.2002.02770.X
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J.GASTRO.2007.07.008
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Aust. J. Chem. 2012, 65, 883. doi:10.1071/CH12042
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S. Kipngetich, C. Davies, Clin. Infect. Dis. 2004, 38, 612. doi:10.1086/
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J. G. MacLellan, J. Inorg. Biochem. 2011, 105, 454. doi:10.1016/
J.JINORGBIO.2010.08.007
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doi:10.1021/IC50086A011
All manipulations were carried out under a nitrogen atmo-
sphere. NaOH pellets (0.04 g, 1.00 mmol) were dissolved in dry
methanol (10 mL), followed by addition of TNA (0.19 mL,
1.00 mmol). The resultant yellow-brown solution was cooled
to 08C before diphenylbismuth chloride (0.40 g, 1.00 mmol) was
added directly as a solid. The reaction mixture was maintained at
08C for 20 min and then the resultant precipitate was collected
by filtration and washed with methanol and ethanol. The solid
was analysed as [Ph2Bi{SC(¼O)C10H7}] 5.
Yield: 0.32 g, 58.2 %, mp 129–1308C. Found: C 50.34,
H 2.79. Anal. calc. for C23H17BiOS: C 50.18, H 3.09 %. nmax
(Nujol)/cmꢀ1 1564s, 1210w, 1159m, 1120m, 932w, 862m,
725m, 694m. dH (400.1 MHz, [D6]DMSO) 8.68 (s, 1H, Hb),
8.27 (d, J3 8.0, 4H, o-HPh), 8.11 (d, J3 7.2, 1H, Hc), 8.02 (d, J3
7.2, 1H, Hj), 7.96 (t, J3 4.8, 2H, Hf,i), 7.63 (m, 2H, Hg,h), 7.55
(t, J3 8.0, 4H, m-HPh), 7.32 (t, J3 8.0, 2H, p-HPh). dC (100.0 MHz,
[D6]DMSO) 140.0 (Ca), 138.1 (Cd), 136.5 (Ce), 134.7 (C–Bi),
132.0 (o-CPh), 131.0 (m-CPh), 129.6 (p-CPh), 129.5 (Cf), 128.3
(Cb), 127.9 (Ch), 127.6 (Cj), 126.9 (Ci), 126.5 (Cg), 124.2 (Cc).
m/z (ESIþ) 209 (40 %, [Bi]þ), 417.1 {10 %, [Ph2Bi þ
(H2O)3]þ}, 440.9 (5 %, [Ph2Bi þ DMSO]þ), 473.8 (5 %,
[PhBLi]þ), 491.1 (7 %, [PhBLi þ H2O]þ) . m/z (ESI–) 187.1
(100 %, [L]–). {LH ¼ C10H7C(¼O)SH}.
Crystallography
Crystal data were collected on Oxford Gemini Ultra
CCD diffractometer with monochromated MoKa radiation
˚
(l ¼0.71073 A). Crystalline samples were mounted on a glass
fibre in highly viscous oil and then flash-cooled to 123 K. X-ray
data were processed using the ChrysalisPRO software package.[35]
[PhBi(SC(¼O)C6H4Br)2] 2: C20H13BiO2S2Br2, M ¼ 718.22;
˚
monoclinic, space group P 21/n. a ¼ 12.2785 (7) A, b ¼ 5.9045
3
˚
˚
˚
(3) A, c ¼ 28.1921 (18) A, b ¼ 90.6488 (3); V ¼ 2043.8 (2) A ,
Z ¼ 4, Dc ¼ 2.334 g cmꢀ3
,
m ¼ 12.754 mmꢀ1
,
F000 ¼ 1336,
[28] L. Agocs, G. G. Briand, N. Burford, T. S. Cameron, W. Kwiatkowski,
K. N. Robertson, Inorg. Chem. 1997, 36, 2855. doi:10.1021/
IC961262Y
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B. W. Skelton, A. H. White, J. Chem. Soc., Dalton Trans. 2002, 4634.
doi:10.1039/B209347B
[30] G. G. Briand, N. Burford, T. S. Cameron, W. Kwiatkowski, J. Am.
Chem. Soc. 1998, 120, 11374. doi:10.1021/JA981575N
[31] P. Singh, S. Singh, V. D. Gupta, H. Noth, Z. Naturforsch. B: Chem. Sci.
1998, 53, 1475.
[32] R. M. Peiris, Bismuth(III) compounds as antibiotics against Helico-
bacter pylori and anti-Leishmanial drugs 2013 (thesis submitted to
Monash University, Melbourne, for review).
T ¼122.99 (13) K, 2ymax ¼ 61.028, 11728 reflections collected,
5478 unique (Rint ¼ 0.0318). R1 ¼ 0.0283, wR2 ¼ 0.0430 for
data with I . 2s(I); R1 ¼ 0.0392, wR2 ¼ 0.0458 for all data.
GoF ¼ 1.058.
Acknowledgements
We thank the Australian Research Council and Monash University for
financial support.
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