Anti-Mycobacterium tuberculosis activity of platinum(II)/N,N-disubstituted-N′-acyl thiourea complexes

Article abstract of DOI:10.1016/j.inoche.2015.11.020

Synthesis, characterization and anti-Mycobacterium tuberculosis assays of new platinum(II)/dppf/N,N-disubstituted-N′-acyl thiourea complexes with general formulae [Pt(dppf)(L)]PF₆, [dppf = 1,1′-bis(diphenylphosphino)ferrocene; L = N,N-disubstit

Full text of DOI:10.1016/j.inoche.2015.11.020

Inorganic Chemistry Communications 63 (2016) 74–80
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Anti-Mycobacterium tuberculosis activity of platinum(II)/
N,N-disubstituted-N′-acyl thiourea complexes
a
a
a
b
c
Ana M. Plutín a, , Anislay Alvarez , Raúl Mocelo , Raúl Ramos , Eduardo E. Castellano , Monize M. da Silva ,
⁎
Legna Colina-Vegas c, Fernando R. Pavan d, Alzir A. Batista c,
Facultad de Química, Universidad de La Habana, La Habana, Cuba
Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, SP, Brazil
Departamento de Química, Universidade Federal de São Carlos, São Carlos, SP, Brazil
⁎
a
b
c
d
Faculdade de Ciências Farmacêuticas, UNESP, Araraquara, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 July 2015
Accepted 29 November 2015
Available online 4 December 2015
Synthesis, characterization and anti-Mycobacterium tuberculosis assays of new platinum(II)/dppf/N,N-
disubstituted-N′-acyl thiourea complexes with general formulae [Pt(dppf)(L)]PF6, [dppf =1,1′-bis
(diphenylphosphino)ferrocene; L = N,N-disubstituted-N′-acyl thioureas] is reported. The complexes
were characterized by elemental analysis, molar conductivity, IR, NMR (1H, 13C and 31P{1H}) spectroscopy. The
spectroscopic data are consistent with the complexes containing one dppf and one O, S chelated ligand. The
crystal structures of complexes with N,N-diphenyl-N′-benzoylthiourea (L4), N,N-diethyl-N′-furoylthiourea
(L5) and N,N-diphenyl-N′-(thiophene-2-carbonyl)thiourea (L8) were determined by X-ray crystallography,
confirming the coordination of the ligands with the metal through sulfur and oxygen atoms, forming distorted
square-planar structures. The complexes were screened with respect to their anti-M. tuberculosis activity
(H37Rv ATCC 27294).
Keywords:
Platinum(II) complexes
1,1′-Bis(diphenylphosphino)ferrocene
N,N-Disubstituted-N′-acyl thioureas
Anti-Mycobacterium tuberculosis assays
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
reported [9], following the Scheme 1 below, by reacting methanolic
solutions of acylthioureas with the precursor, dichloro[1,1′-bis
Thiourea and its derivatives act as chelating agents [1] and have
found extensive applications in the fields of medicine, agriculture
and analytical chemistry. These compounds exhibit a wide variety of
biological activities, such as antiviral, antibacterial, antifungal [2],
antitubercular, herbicidal, and insecticidal [3]. They are also involved
in catalysis [4], and in anion recognition [5]. Coordination compounds
of thiourea have been studied for various biological systems with re-
spect to antibacterial, antifungal and anticancer activities [6]. Moreover,
luminescence properties of a series of Pt(II) complexes bearing N-
benzoylthiourea derivatives have been investigated, which find applica-
tions in optoelectronic devices, luminescent probes for biomolecules
and chemical sensors [7]. More recently, there have been efforts to
design non-classical platinum-acylthiourea complexes in order to
investigate their antifungal activity and inhibitory activities against
viruses [8].
(diphenylphosphino)ferroceno]platinum(II). The coordination be-
tween acylthiourea derivatives and the precursor proceeded by an
exchange reaction, which involved deprotonation of the acyl thioureido
group of the ligands during the complexes formation [10].
2. Experimental
2.1. Material and measurements
The dichloro[1,1′-bis(diphenylphosphino)ferrocene]platinum(II)
was obtained from Strem. All reagents were purchased with reagent
grade and used without further purification. Solvents were dried and
used freshly distilled, unless otherwise specifically indicated. Thin
layer chromatography (TLC) was performed on 0.25 mm silica gel pre-
coated plastic sheets (40/80 mm) (Polygram_SIL G/UV254, Macherey
& Nagel, Düren, Germany) using benzene/methanol (9/1) as eluent.
The IR spectra were recorded on a FTIR Bomem-Michelson 102 spec-
trometer in the 4000–200 cm−1 region using CsI pellets. Conductivity
values were obtained using 1.0 mM solutions of complexes in CH2Cl2,
using a Meter Lab CDM2300 instrument. 1H, 31P{1H} and 13C NMR spec-
tra, were recorded in CDCl3, on a Bruker DRX 400 MHz. The 1H chemical
shifts are referenced to TMS. The 31P{1H} shifts are reported in relation
Here we report the synthesis, characterization and anti-Mycobacterium
tuberculosis activity of new platinum(II) complexes containing 1,1′-
bis-(diphenylphosphino)ferrocene and N,N-disubstituted-N′-acyl
thioureas as ligands. The N,N-disubstituted-N′-acyl thioureas used
as ligands in this work were synthesized by the procedure previously
⁎
Corresponding authors.
http://dx.doi.org/10.1016/j.inoche.2015.11.020
1387-7003/© 2015 Elsevier B.V. All rights reserved.

A.M. Plutín et al. / Inorganic Chemistry Communications 63 (2016) 74–80
75
Scheme 1. Pathway for the synthesis of Pt(II)/N,N-disubstituted-N′-acyl thiourea complexes.
to H3PO4, 85%. Elemental analyses were carried out in an FISONS instru-
ment, CHNS EA-1108.
down, and left in the refrigerator overnight. The obtained yellow solids
were filtered off and washed, successively, with hot water and diethyl
ether (3 × 20 mL). The obtained compounds are stable in the air.
The 1H and 13C NMR data, the elemental analyses, melting point
temperature and molar conductivity (Λm, 1.0 × 10−3 mol/L, in CH2Cl2)
for the complexes are listed below and the other data used for the
characterization of the complexes are in the text:
2.2. Synthesis of N,N-disubstituted-N′-acyl thioureas
The N,N-disubstituted-N′-acyl thioureas L(1–8) used in this work
were synthesized as crystalline solids, in good yields, by the procedure
previously reported in the literature [9]. A solution of an appropriately
acyl chloride (30 mmol) in acetone (50 mL) was added, drop wise, to
a suspension of KSCN (0.01 mol) in acetone (30 mL). The mixture was
stirred until a precipitate appeared (ammonium chloride), indicating
the formation of the respective organic isothiocyanate. The correspond-
ing amine (40 mmol), dissolved in acetone (20 mL) was slowly added to
the reaction flask, with constant stirring. The solution was cooled in an
ice-water bath and the stirring was continued, at room temperature,
during 2–9 h longer, until the reaction was completed (the reaction
progress was monitored by TLC). The reaction mixture was then poured
into cold water (20 mL). Solids of N,N-disubstituted-N′-acyl thioureas
were collected by filtration and finally purified by recrystallization
from methanol. The identity of the products was confirmed by compar-
ing their 1H and 13C NMR data with those reported in the literature [9].
Scheme 2 shows the pathway for the synthesis of the thioureas and the
structures of the ligands are shown in Fig. 1.
(1) [Pt(dppf)(N,N-dimethyl-N′-benzoylthioureato-k2O,S)]PF6
Anal. calcd for C45H42F6FeN2OP3PtS2, (%): exp. (cal) C, 47.86 (47.97);
H, 3.65 (3.57); N, 2.43 (2.54); S, 2.94 (2.91).
1H NMR ppm: 7.86–7.81 (m; 5 H; Ph); 7.64–7.51 (m; 5 H); 7.37–7.17
(m; 10 H); 3.48 (3 H; s; CH3) and 3.18 (3 H; s; CH3). NMR 13C ppm:
169.69 (CS); 161.84 (CO); 134.49, 134.42, 134.37, 134.23, 134.11,
132.75–127.73 (C-Ph); 29.70 (CH3); 15.27 (CH3); 31P{1H}}: 21.10
(d) and 9. 86 (d); 2JP-P = 23.48 Hz. IR: ν(CO) 1437; ν(CS) 748; ν(CN)
1505; Anal. (%): Found (Calc): C, 60.38 (60.35); H, 4.30 (4.25); N, 2.35
(2.37); S, 2.70 (2.82). MP: 262–264 °C. ΛM = 49.6 Ω−1 cm2 mol−1
(2) [Pt(dppf)(N,N-diethyl-N′-benzoylthioureato-k2O,S)]PF6
.
Anal. calcd C47H46F6FeN2OP3PtS2, (%): exp. (cal) C, 48.76 (48.90); H,
3.85 (3.84); N, 2.43 (2.48); S, 2.74 (2.84).
1H NMR ppm: 7.87–7.82 (m; 1 H); 7.61–7.48 (m; 5 H); 7.36–7.31
(m; 5 H); 7.15–6.99 (m; 10 H); 3.81 (d; J = 7.07 Hz; 2 H; CH2); 3.58
(d; J = 7.07 Hz; 2 H; CH2); 1.28 (t; J = 7.02 Hz; 3 H; CH3), 1.31
(t; J = 7.02 Hz; 3 H; CH3); NMR 13C ppm: 168.20 (CS); 166.22 (CO);
135.65, 135.59, 134.60, 134.49, 134.23–127.50 (C-Ph); 47.46 (CH2);
46.53 (CH2); 13.15 (CH3); 12.01 (CH3); 31 P{1H}: 20.85 (d) and 10.19
(d); 2JP-P = 24.29 Hz. IR: ν(CO) 1436; ν(CS) 750; ν(C = N) 1503. MP:
2.3. Synthesis of the complexes
The complexes were prepared by a similar method used for
[Pd(PPh3)2Cl2] [11] from direct reactions of the precursor [Pt(dppf)Cl2],
with the N,N-disubstituted-N′-acyl thioureas, in methanol solutions.
The complexes were separated from the reaction mixtures as white
crystalline solids. Filtration and further washing with hot water and
diethyl ether were enough to afford pure and stable compounds, with
yields at about 80%. Thus, the general procedure for the synthesis of
the complexes is described: a solution of [Pt(dppf)Cl2] (164 mg;
0.2 mmol) in 5 mL of methanol, was added dropwise to a solution of
the corresponding N,N-dialkyl-N′-acyl thiourea ligand (0.2 mmol), dis-
solved in 30 mL of the same solvent. To this solution KPF6 (368 mg,
2 mmol) was added. The reaction mixture was heated under magnetic
stirring at 80 °C, for 2 h. After this time the reaction mixture was cooled
272–274 °C. ΛM = 45.6 Ω−1 cm2 mol−1
.
(3) [Pt(dppf)(N,N-dibuthyl-N′-benzoylthioureato-k2O,S)]PF6
Anal. calcd for C51H54F6FeN2OP3PtS2, (%): exp. (cal) C, 50.46 (50.64);
H, 4.45 (4.33); N, 2.43 (2.36); S, 2.64 (2.70).
1H NMR ppm: 8.04–7.99 (m; 1 H); 7.80–7.08 (m; 34 H); 4.88 (d; J =
7.08 Hz; 2 H, CH2); 3.68 (4 H; q; CH2); 2.07–1.70 (2 H; m; CH2); 0.93
(t; 3H,\\CH3; J = 7.01 Hz). NMR 13C ppm: 168.90 (CS); 167.91 (CO);
135.55, 135.32, 135.21, 133.56–128.82 (C-Ph); 53.58 (CH2); 52.38
(CH2); 20.86 (CH2); 14.20 (CH3); 31P{1H}: 20.97 (d) and 10. 14 (d);
2JP-P = 22.67 Hz. IR: ν(CO) 1436; ν(CS) 747; ν(CN) 1500. MP: 232–
234 °C. ΛM = 49.6 Ω−1 cm2 mol−1
.
(4) Pt(dppf)(N,N-diphenyl-N′-benzoylthioureato-k2O,S)]PF6
Anal. calcd for C54H43F6FeN2OP3PtS], (%): exp. (cal) C, 52.96 (52.91);
H, 3.74 (3.54); N, 2.33 (2.29); S, 2.64 (2.62).
Scheme 2. Pathway for the synthesis of the N,N-disubstituted-N′-acyl thioureas.

76
A.M. Plutín et al. / Inorganic Chemistry Communications 63 (2016) 74–80
Fig. 1. Structures of the N,N-disubstituted-N′-acyl thioureas ligands used in this work.
1H NMR ppm: 7.86–7.82 (m; 1 H); 7.14 (s; 1 H); 6.73 (d; J = 1.60 Hz;
1H NMR ppm: 8.32 (1H; dd; J1 = 7.2 Hz; J2 = 8.1 Hz; Thiophene
CH); 8.10 (1 H; dd; J1 = 7.5 Hz; J2 = 8.2 Hz; thiophene CH);
7.23 (1 H; dd; J1 = 6.7 Hz; J2 = 8.3 Hz; thiophene CH); 7.63–7.27
(m; 10 H; arom-H). NMR 13C ppm: 167.04 (CS); 164.19 (CO); 134.60,
134.49, 134.17, 134.06, 132.71, 132.49, 132.24, 132.10, 129.42, 129.30,
128.53–127.83 (C-Ph); 25.28 (2CH3). 31P{1H}: 20.66 (d) and 9. 99 (d);
2JP-P = 22.67 Hz. IR: ν(CO) 1480; ν(CS) 747; ν(CN) 1590. MP: 255–
1 H), 6.86–6.83 (m; 1 H). NMR 13C ppm: 170.81. (CS); 168.48 (CO);
144.03, 143.08, 134.37, 134.26, 134.22, 134.10–127. 27 (C\Ph). 31P
{1H}: 20.77 (d) and 9.77 (d); 2JP-P = 22.67 Hz. IR: ν(CO) 1428; ν(CS)
750; ν(CN) 1485. MP: 272–276 °C. ΛM = 50.6 Ω−1 cm2 mol−1
.
(5) [Pt(dppf(N,N-diethyl-N′-furoylthioureato-k2O,S)]PF6
257 °C. ΛM = 50.6 Ω−1 cm2 mol−1
.
Anal. calcd for C44H41F6FeN2O2P3PtS, (%): exp. (cal) C, 47.26 (47.20);
H, 3.65 (3.69); N, 2.43 (2.50); S, 2.84 (2.86).
2.4. Crystal structure determination
1H NMR ppm: 7.85–7.80 (m; 1H), 7.60–6.18 (3H; m; furoyl), 3.74
(2H; c; CH2), 3.34 (2H; c; CH2); 1.22 (3H; t; CH3); 0.95 (3H; t; CH3).
NMR 13C ppm: 165.67 (CS); 159.79 (CO); 145.90, 134.58, 134.47,
134.12–129.38 (C-Ph); 128.80–112.04 (C-Ph and furan ring); 47.17
(CH2); 46.48 (CH2); 13.11 (CH3) 11.90 (CH3).31 P{1H}: 20.44 (d) and
10.34 (d); 2JP-P = 20.34 Hz. IR: ν(CO) 1423; ν(CS) 758; ν(CN) 1483.
Single crystals suitable for X-ray diffraction were obtained by slow
evaporation of CHCl3:n-hexane (3:1) solutions of the complexes (4),
(5) and (8). Diffraction data were collected on an Enraf-Nonius Kappa-
CCD diffractometer with graphite-monochromated Mo Ka radiation
(λ = 0.71073 Å). The final unit cell parameters were based on all reflec-
tions. Data collections were performed using the COLLECT program
[12]; integration and scaling of the reflections were performed with
the HKL Denzo-Scalepack system of programs [13]. Absorption correc-
tions were carried out using the Gaussian method [14]. The structures
were solved by direct methods with SHELXS-97 [15]. The models were
refined by full-matrix least-squares on F2 by means of SHELXL-97 [16].
The projection views of the structures were prepared using ORTEP-3
for Windows [17]. Hydrogen atoms were stereochemically positioned
and refined with the riding model. Data collections and experimental
details are summarized in Table 1. Relevant interatomic bond lengths
and angles are listed in Table 2.
MP: 246–248 °C. ΛM = 49.6 Ω−1 cm2 mol−1
.
(6) [Pt(dppf)(N,N-dibenzyl-N′-furoylthioureato-k2O,S)]PF6
Anal. calcd for C53H44F6FeN2OP3PtS2, (%): exp. (cal) C, 52.26 (52.14);
H, 3.68 (3.65); N, 2.33 (2.25); S, 2.54 (2.58).
1H NMR ppm: 7.91–7.80 (m; 1H); 7.63–7.43 (m; 1H); 7.20–6.99 (m;
1H), 6.53–6.16 (m; 1H); 4.98 (s; 2H; CH2); 4.77 (s; 2H; CH2) PPM. NMR
13C ppm: 167.74 (CS); 161.98 (CO); 149.50, 146.75, 146.14, 145.72,
145.23–112.28 (C-Ph); 53.47 (CH2); 52.78 (CH2). 31P{1H}: 20.35
(d) and 9.80 (d); 2JP-P = 22.67 Hz. IR: ν(CO) 1528; ν(CS) 752; ν(CN)
1578. MP: 266–268 °C. ΛM = 52.6 Ω−1 cm2 mol−1
.
(7) [Pt(dppf)(N,N-dimethyl-N′-thiophenylthioureato-k2O,S)]PF6
2.5. Anti-M. tuberculosis activity assay
Anal. calcd for C43H40F6FeN2OP2PtS2, (%): exp. (cal) C, 45.26 (45.54);
H, 3.45 (3.37); N, 2.43 (2.53); S, 5.84 (5.79).
The anti-MTB activity of the compounds was determined by
the REMA (Resazurin Microtiter Assay) method [18]. Stock solutions
of the tested compounds were prepared in DMSO and diluted in
Middlebrook 7H9 broth (Difco) supplemented with oleic acid, albumin,
dextrose and catalase (OADC), performed by Precision XS (Biotek®) to
obtain the final drug concentration range of 0.09–25 μg mL−1. Isoniazid
was dissolved in distilled water and rifampicin in DMSO, and both were
used as standard drugs. A suspension of MTB H37Rv ATCC 27294 was
cultured in Middlebrook 7H9 broth supplemented with OADC and
0.05% Tween 80. The cultures were frozen at −80 °C in aliquots. After
two days the CFU per mL (colony formation unit per mL) of an aliquot
was determined. The concentrations were adjusted by 5 × 105 CFU
per mL and 100 μL of the inoculum were added to each well of a 96-
well microplate together with 100 μL of the compounds. Samples
1H NMR ppm: 7.87 (1 H; dd; J1 = 7.2 Hz; J2 = 8.1 Hz, Thiophene
CH); 7.82 (1 H; dd, J1 = 7.59 Hz; J2 = 8.2 Hz, thiophene CH); 6.69
(1 H; dd; J1 = 6.7 Hz; 2 = 8.6 Hz, thiophene CH), 7.59–7.57 (C-Ph);
0.97 (6H; t; −CH3; J = 7.1 Hz), NMR 13C ppm: 166.73 (CS); 164.10
(CO); 141.19, 134.57, 134.50, 134.47, 134.40, 132.3 8, 132.27, 132.18,
131.74, 128.90–125.62 (C-Ph); 21.80 (2CH3). 31P{1H}: 20.90 (d) and
10.22 (d); 2JP-P = 22.67 Hz. IR: ν(CO) 1437; ν(CS) 748; ν(CN) 1494.
MP: 246–248 °C. ΛM = 49.6 Ω−1 cm2 mol−1
.
(8) [Pt(dppf)(N,N-diphenyl-N′-thiophenylthioureato-k2O,S)]PF6
Anal. calcd for C52H41F6FeN2OP3PtS2, (%): exp. (cal) C, 50.85 (50.70);
H, 3.45 (3.35); N, 2.23 (2.27); S, 2.84 (2.90).

A.M. Plutín et al. / Inorganic Chemistry Communications 63 (2016) 74–80
77
Table 1
Crystal data and refinement parameters of complexes 4, 5 and 8.
Compound
(4)
(5)
(8)
Empirical formula
Formula weight
C54H43F6N2OP3PtS
1225.81
C44H41F6FeN2O2P3Pt S
1119.70
C52H41F6FeN2OP3PtS2
1231.84
Crystal system
Space group
Triclinic
P − 1
Monoclinic
P21/a
Triclinic
P − 1
a (Å)
b (Å)
c (Å)
α (°)
12.2463(3)
13.5534(3)
15.8064(4)
80.542(2)
77.027(2)
85.821(2)
2520.05(11)
2
10.8472(2)
28.8535(8)
14.0972(3)
90
92.4280(10)
90
4408.18(17)
4
1.687
12.5714(3)
13.7954(2)
15.0969(4)
96.074(2)
107.5660(10)
91.973(2)
2476.03(10)
2
β (°)
γ (°)
V (Å3)
Z
D. calc (mg/m3)
1.615
3.260
1216
1.652
3.359
1220
Absorption coefficient (mm−1
F(000)
)
3.720
2216
θ range for data collection (°)
Index ranges
2.847 to 26.000
−15 ≤ h ≤ 15
−16 ≤ k ≤ 16
19 ≤ l ≤ 19
28,024
2.56 to 26.00
−13 ≤ h ≤ 12
−35 ≤ k ≤ 33
−13 ≤ l ≤ 17
28,060
2.837 to 25.998
−15 ≤ h ≤ 15
−17 ≤ k ≤ 17
−18 ≤ l ≤ 18
31,475
Reflections collected
Independent reflections (Rint)
Goodness-of-fit on F2
Final R indices
9795 [R(int) = 0.0867]
1.076
R1 = 0.0712
wR2 = 0.1815
2.683 and −2.685
8616 [R(int) = 0.0764]
0.988
R1 = 0.0514
wR2 = 0.1225
2.778 and −1.317
9664 [R(int) = 0.0469]
1.033
R1 = 0.0384
wR2 = 0.0978
1.104 and −1.376
[I N 2σ (I)]
Largest diff. peak and hole (eÅ)_3
were set up in triplicate. The plates were incubated for 7 days at 37 °C.
Resazurin (solubilized in water) was added (30 μL of 0.01%). The fluo-
rescence of the wells was read after 24 h with a Cytation 3 (Biotek®).
The MIC was defined as the lowest concentration resulting in 90% inhi-
bition of growth of MTB.
in the complexes at 1483–1590 cm−1, is absent in the free ligands,
suggesting that when coordinated to the metal the nitrogen changes
from sp3 to sp2 hybridization, as shown in Scheme 1. In agreement
with the literature the coordination between the metal and carbonyl
group, present in the thioureas, decreases of ca. 180 cm−1 the C\\O
stretching vibration frequency, when compared with the free ligand
[19]. Thus, considering that the free ligands have their νCO bands at
about 1680 cm−1, it is reasonable to assign the bands in the range of
1428–1528 cm−1 to the coordinated CO group. The absorptions at
815–878 cm−1 in the spectra of free bases, N,N-disubstituted-N′-
acylthioureas, attributed to the ν(C\\S) stretching vibrations, shift to
the 747–758 cm−1 range in the spectra of the complexes. This substan-
tial change suggests deprotonation of the ligands, indicating coordina-
tion through the sulfur atom with a formally C\\S single bond [20–23].
The absorptions at about 471 cm−1 in the IR spectra of the complexes
can be assigned to the Metal-O vibration mode [24,25] and the assign-
ment of the Pt\\S stretching vibration bands at about 360 cm−1 are in
accordance with the reported by Bayazeed H. Abdullah and others for
platinum(II) complexes with s-donor ligands [26,27]. Thus, from the IR
data it is possible to suggest that the N,N-disubstituted-N′-acyl thioureas
are attached to the metal through the oxygen and sulfur, by a chelating
system. The molar conductivity of the complexes, in CH2Cl2, show they
are ionic species in the range of 1:1 electrolytes [28].
3. Results and discussion
All the synthesized platinum(II) complexes are of yellow color, and
their most useful infrared spectral bands for determining the ligands
mode of coordination are given in Section 2, as well as the elemental
analyses data, melting point temperatures, and molar conductivities.
These data suggest the formation of complexes with the general formu-
lae [Pt(dppf)2(L)]PF6, in which L represents the anionic ligand formed
upon deprotonation, when the N,N-disubstituted-N′-acyl thioureas
coordinate to the metal center.
The IR spectra of the ligands reveal broad and strong absorption
bands in the range of 3053–3267 cm−1, due to NH stretching vibrations.
As expected, these bands, present in the free ligands, are absent in the IR
spectra of the complexes. On the other hand, the ν(C\\N) band, present
Table 2
Selected bond lengths (Å) and angles (°) for the complexes (4), (5) and (8).
The molecular structures of the complexes were also investigated by
NMR (1H, 13C and 31P{1H}) spectroscopy and a comparative analysis on
the basis of the spectroscopic data corresponding to both, free and coor-
dinated ligands with the metallic ion, was carried out. The 1H NMR data
for the complexes are given in the experimental section. The 1H NMR
spectra of the free ligands show basically three sets of well separated
signals corresponding to their R1, R2 substituents and to the NH proton.
The signals of the NH protons appear as broad singlets in the region be-
tween 8.35 and 8.80 ppm [9]. The absence of the N\\H proton after the
coordination of the ligands to the metal is associated with an increase in
electron density at the CN bond upon complexation [29,30]. A slight
downfield shift was also observed in the aromatic protons and in the
protons of the nitrogen substituents in the coordinated ligands, when
compared to the chemical shift of the free ligands. The aromatic protons
appear as a complex pattern in the region δ 8.32–6.16 ppm. In the 13C
NMR spectra the chemical shifts of the C\\S carbon atoms of the ligands
moved up field after their coordination to the metal for all complexes
(4)
(5)
(8)
Bond lengths (Å)
Pt–O
Pt–P(2)
Pt–S
Pt–P(1)
S–C(1)
O–C(2)
N(1)–C(2)
N(1)–C(1)
N(2)–C1
2.072(5)
2.034(4)
2.067(3)
2.3227(19)
2.304(2)
2.244(2)
1.725(8)
1.272(9)
1.311(10)
1.372(10)
1.331(11)
2.3228(16)
2.3075(16)
2.2410(17)
1.736(7)
1.281(8)
1.306(9)
2.3232(10)
2.3034(10)
2.2444(11)
1.661(5
1.273(5)
1.311(5)
1.361(5)
1.332(6)
1.350(9)
1.348(8)
Angles (°)
O–Pt–S
91.06(15)
178.77(17)
84.22(15)
174.32(7)
88.73(8)
90.95(13)
176.39(15)
83.09(13)
173.75(6)
90.82(6)
91.97(8)
178.76(10)
82.87(8)
173.64(4)
88.16(4)
97.08(4)
O–Pt–P(1)
O–Pt–P(2)
P(2)–Pt–S
S–Pt–P(1)
P(2)–Pt–P(1)
96.05(7)
95.24(6)

78
A.M. Plutín et al. / Inorganic Chemistry Communications 63 (2016) 74–80
studied, but in the case of the C\\O group, this tendency was not
observed for all complexes. The explanation for this is the fact that
with the deprotonation of the secondary amide and with the formation
of a “NC–S–Pt” species, the sulfur atoms, and consequently their neigh-
bor carbon atoms, became more shielded in all complexes, something
that does not happen with the carbon from the carbonyl group, to the
same extent. The 31P{1H} NMR spectrum of the precursor [Pt(dppf)Cl2],
in CH2Cl2 solution, shows a singlet peak for phosphorous atoms at
13.06 ppm. For all complexes, in dimethyl sulfoxide solutions, two dou-
blets arise, at about 20.53 and 9.83 ppm, indicating the presence of two
magnetically different phosphorus atoms coordinated to the
platinum(II) ion, all signals were flanked by satellite peaks of the re-
spective multiplicity generated for the coupling of the phosphorus
atoms with the isotope 195Pt.
Also in the region of −138–158 ppm a multiple signal of the PF6−
functioning as outer-sphere anions for the complexes obtained is ob-
served, in accordance with the molar conductivity measurements for
these complexes (see experimental section). These data are consistent
with those obtained for some palladium(II) thiosemicarbazones and
N,N-disubstituted-N′-acyl thioureas complexes [10,21]. The 1H NMR
Fig. 2. ORTEP view of (4), (5) and (8) complexes showing 50% probability ellipsoids. Hydrogen atoms, the PF−6 anion and some labels of the ligands are omitted for clarity.

A.M. Plutín et al. / Inorganic Chemistry Communications 63 (2016) 74–80
79
integrations and signal multiplicities are consistent with [Pt(dppf)2(L)]
PF6 structures for the complexes. All complexes are stable in dimethyl
sulfoxide solutions, for at least 48 h, according to their NMR spectra in
this solvent.
10-fold and 20-fold higher activities, than the respective free N,N-
disubstituted-N′-acyl thiourea.
The in vitro activity found for the complexes (1), (2), (5) and (7) is
comparable to those of some commonly used anti-M. tuberculosis
agents, like cycloserine (MIC = 122.4–489.7 μM), gentamicin (MIC =
4.19–8.38 μM), tobramycin (MIC = 8.56–17.11 μM), clarithromycin
(MIC = 10.70–21.40 μM) and ethambutol (MIC = 5.62 μM), which is
the clinically used as a first-line drug in several schemes of conventional
tuberculosis treatment [32].
The structural changes in the ligands and in the complexes probably
affect the interaction of the complexes with bacterial membrane. In our
previous work with some ruthenium complexes it was suggested that
the mechanism of their action against M. tuberculosis occurs in the cell
wall biosynthesis [33]. This could be also a suggestion for the mecha-
nism of the biological activity of the platinum complexes here studied,
where the interaction of them with the mycobacterium membrane is
modulated by the nature of the ligands present in the compounds.
The structures of complexes (4), (5) and (8) were determined by
X-ray diffraction analysis, and their ORTEP views are in Fig. 2 and select-
ed bond lengths (Å) and angles (°) for the complexes are listed in
Table 2. The thione C\\S bond in the coordinated anionic ligands
becomes formally a single bond making it longer (average = 1.707 Å)
than the C\\S bond of the neutral moieties [10], and the N(2)\C bond
(average 1.337 Å), which some double bond in the anionic moieties, is
typical for C\\N distances [31]. The N(1)\\C distance, 1.361 Ả (average),
is anionic and in the amine form. Thus the metal is coordinated to the
negatively charged organic molecules, which act as bidentate ligands,
through oxygen (average distance Pt–O = 2.058 Å) and through sulfur
(average distance Pt\\S = 2.304 Å) atoms. The Pt–S average distance
is close to the ones found for other copper(II)/thiosemicarbazones
complexes [23]. The remaining binding sites are occupied by dppf
diphosphane ligand (average distance Pt–P1 = 2.243 Å and Pt–
P(2) = 2.3229 Å). The distances for the C\S, C\N and C\O bonds in the
chelate rings, listed in Table 2, are the characteristic of single and double
bond lengths, respectively [31]. The CO bond distances are slightly sen-
sitive to the coordination of the ligand to the metal. In the case of the
bis-triphenylphosphine-N,N-diethyl-N′-furoilthioureato-k2O,S the CO
distance for the free ligand is 1.226(3) Å (average for two independent
molecules per asymmetric unit), and 1.271(9) and 1.281(8) Å respec-
tively, after its coordination to the metal [10].
4. Conclusions
A novel series of Pt(II) complexes with N,N-disubstituted-N′-acyl
thioureas as bidentate ligands was synthesized and thoroughly charac-
terized by several spectroscopic techniques and X-ray crystallography.
The X-ray crystallographic characterization shows that these ligands
coordinate with the metal through the oxygen and sulfur atoms. The
anti-M. tuberculosis activity assays of the new complexes provided
evidence that they show activity against M. tuberculosis H37Rv, in the
same order than the ethambutol, a first-line drug in several schemes
of conventional tuberculosis treatment. Thus, as can been seen from
Table 3, the MIC values are in order [Pt(dppf)(L5)]PF6 b [Pt(dppf)(L1)]
3.1. Anti-M. tuberculosis activity
PF6
[Pt(dppf)(L7)]PF6
[Pt(dppf)(L2)]PF6
[Pt(dppf)(L3)]PF6
b
b
b
b
The compounds (L1–L8) and complexes (1–8) were investigated for
their in vitro antimycobacterial activity against M. tuberculosis H37Rv
strains, by the REMA. The minimum inhibitory concentrations (MICs)
found for the platinum complexes, free ligands and ethambutol are
shown in Table 3.
As can be seen from Table 3 results some compounds exhibited anti-
M. tuberculosis activity, with reasonable low MIC values. Comparing the
MIC values of the free N,N-disubstituted-N′-acyl thiourea with the
values obtained for the complexes, it can be seen that the activity
of the complexes is much higher than those of the uncoordinated N,N-
disubstituted-N′-acyl thiourea, emphasizing the importance of the
presence of the metal for anti-M. tuberculosis activity presented by the
new complexes. Complexes (1), (2), (5) and (7) present approximately
[Pt(dppf)(L4)]PF6 ≈ [Pt(dppf)(L6)]PF6 ≈ [Pt(dppf)(L8)]PF6, showing
that the most active complexes are those containing small R2 groups,
like methyl or ethyl groups. Also, considering that the difference be-
tween complexes (1) and (7) is the R1 group and that their MIC values
are practically the same, it is possible to suggest that this group does not
influence substantially the activity of the complexes. The similar MIC
values of complexes (2) and (5) give support to this suggestion. Shortly,
the size of the R2 group influences the anti-M. tuberculosis activity of the
[Pt(dppf)(Ln)]PF6 complexes, which does not happen with the type of
R1 group, at least in the same extend. Taken altogether, the influence
of the R1 and R2 groups in the activity of the complexes can be due the
steric hindrance or polarity in their interaction with the Mycobacterium
membrane, affecting their cell wall biosynthesis. Thus, in this process the
size of the R2 group plays a crucial role. The low antimycobacterial activ-
ity of the free ligands probably is due to their no interactions with the
mycobacterium membrane.
Table 3
MIC values of antimycobacterial activity of Pt(II) complexes, free ligands and reference
drug.
Acknowledgments
Compounds
μg/mL
μmol/L
L1
L2
L3
L4
L5
L6
L7
L8
N25
N25
N25
N25
N25
N25
N25
N25
5.49 0.27
6.51 0.64
23.66 0.48
N25
4.62 0.06
N25
5.76 0.27
N25
N25
˃119.61
˃107.30
˃85.62
This work was supported by CAPES (Project Oficio/CSS/CGCI/
23038009487/2011-25/DRI/CAPES, AUX CAPES-MES-Cuba, 339/2011),
CNPq and FAPESP (Process 2013/14957-5 and 2014/13691-4) of Brazil.
˃75.30
˃110.62
˃75.30
˃116.82
˃73.96
Appendix A. Supplementary data
(1) [Pt(dppf)(L1)]PF6
(2) [Pt(dppf)(L2)]PF6
(3) [Pt(dppf)(L3)]PF6
(4) [Pt(dppf)(L4)]PF6
(5) [Pt(dppf)(L5)]PF6
(6) [Pt(dppf)(L6)]PF6
(7) [Pt(dppf)(L7)]PF6
(8) [Pt(dppf)(L8)]PF6
[Pt(dppf)Cl2]
Ethambutol
5.73 0.28
6.63 0.65
22.74 0.46
˃23.14
CCDC 1405958, 1405957 and 1405956 contain the supplementary
crystallographic data for Pt(dppf)(N,N-diphenyl-N′-benzoylthioureato-
k2O,S)]PF6 (4), Pt(dppf(N,N-diethyl-N′-furoylthioureato-k2O,S)]PF6 (5)
and Pt(dppf)(N,N-diphenyl-N′-thiophenylthioureato-k2O,S)]PF6 (8),
respectively. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223–336 033; or e-mail: deposit@ccdc.cam.ac.uk.
4.74 0.06
˃23.14
5.99 0.28
˃23.01
˃30.47
5.00
5.62

80
A.M. Plutín et al. / Inorganic Chemistry Communications 63 (2016) 74–80
[18] J.C. Palomino, A. Martin, M. Camacho, H. Guerra, J. Swings, F. Portaels, Antimicrob.
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