Topological control of supramolecular crystal structures of phenylene bis-monothiooxamate derivatives and in?vitro anticancer activity

Article abstract of DOI:10.1016/j.molstruc.2017.08.051

This paper describes the synthesis, physical characterization, X-ray crystal structures and antitumoral activity against human carcionogenic cells of three new diethyl ester acid derivatives of phenylene bis-monothiooxamate compounds, namely Et₂

Full text of DOI:10.1016/j.molstruc.2017.08.051

Accepted Manuscript
Topological control of supramolecular crystal structures of phenylene bis-
monothiooxamate derivatives and in vitro anticancer activity
Tamyris T. da Cunha, Willian X.C. Oliveira, Ivana M. Marzano, Carlos B. Pinheiro,
Elene Cristina Pereira-Maia, Cynthia L.M. Pereira
PII:
S0022-2860(17)31118-3
10.1016/j.molstruc.2017.08.051
MOLSTR 24189
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 5 June 2017
Revised Date: 14 August 2017
Accepted Date: 15 August 2017
Please cite this article as: T.T. da Cunha, W.X.C. Oliveira, I.M. Marzano, C.B. Pinheiro, E.C. Pereira-
Maia, C.L.M. Pereira, Topological control of supramolecular crystal structures of phenylene bis-
monothiooxamate derivatives and in vitro anticancer activity, Journal of Molecular Structure (2017), doi:
10.1016/j.molstruc.2017.08.051.
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ACCEPTED MANUSCRIPT
Graphical abstract
Topological control of supramolecular crystal structures of
phenylene bis-monothiooxamate derivatives and in vitro
anticancer activity
Tamyris T. da Cunhaa, Willian X. C. Oliveiraa, Ivana M. Marzanoa,b, Carlos B.
Pinheiroc, Elene Cristina Pereira-Maiaa, Cynthia L. M. Pereiraa,*
a
Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de
Minas Gerais. Av. Antônio Carlos 6627, Pampulha, Belo Horizonte, Minas Gerais,
31270-901 Brazil. E-mail: cynthialopes@ufmg.br
b Instituto Federal de Educação, Ciência e Tecnologia de Roraima
Av. Glaycon de Paiva 2496 - Pricumã, Boa Vista, Roraima, 69303-340 Brazil.
c
Departamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas
Gerais. Av. Antônio Carlos 6627, Pampulha, Belo Horizonte, Minas Gerais, 31270-901
Brazil.

ACCEPTED MANUSCRIPT
The ortho-, meta- and para- isomers of phenylenebis(2-thiooxamate) are obtained in
mild conditions using Lawesson´s reagent. Crystal structures indicate supramolecular
one-dimensional architectures. Preliminary in vitro anticancer studies against leukemia
cell line showed a topological (positional isomerism) dependence with the molecular
architecture along this series.

ACCEPTED MANUSCRIPT
Topological control of supramolecular crystal structures of
phenylene bis-monothiooxamate derivatives and in vitro
anticancer activity
Tamyris T. da Cunhaa, Willian X. C. Oliveiraa, Ivana M. Marzanoa,b, Carlos B.
Pinheiroc, Elene Cristina Pereira-Maiaa, Cynthia L. M. Pereiraa,*
a
Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de
Minas Gerais. Av. Antônio Carlos 6627, Pampulha, Belo Horizonte, Minas Gerais,
31270-901 Brazil. E-mail: cynthialopes@ufmg.br
b Instituto Federal de Educação, Ciência e Tecnologia de Roraima
Av. Glaycon de Paiva 2496 - Pricumã, Boa Vista, Roraima, 69303-340 Brazil.
c
Departamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas
Gerais. Av. Antônio Carlos 6627, Pampulha, Belo Horizonte, Minas Gerais, 31270-901
Brazil.
1

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ABSTRACT
This paper describes the synthesis, physical characterization, X-ray crystal structures
and antitumoral activity against human carcionogenic cells of three new diethyl ester
acid derivatives of phenylene bis-monothiooxamate compounds, namely Et2H2opbta
(1), Et2H2mpbta (2) and Et2H2ppbta (3) [opbta = N,N’-1,2-phenylenebis(2-thiooxamate),
mbpta = N,N’-1,3-phenylenebis(2-thiooxamate) and ppbta = N,N’-1,4-phenylenebis(2-
thiooxamate)]. Compounds 1–3 were obtained under mild conditions by reaction of the
corresponding N,N’-phenylenebis(oxamate) analogues and Lawesson´s reagent resulting
in the formation of C=S bonds at the carbonyl amide functions. Crystal structures of 1–3
consist of 1D supramolecular assemblies of centrosymmetric H2Et2ppbta (3) or
noncentrosymmetric chiral H2Et2opbta (1) and H2Et2mpbta (2) molecules with opposite
helical chirality (M and P enantiomers) resulting from intermolecular
N―HꢀꢀꢀO (1 and
3) or N―HꢀꢀꢀS (2) hydrogen bonds between the amide hydrogen atoms and the
carbonyl ester oxygen or thionyl amide sulfur atoms from the thiooxamate moieties
respectively, together with weak SꢀꢀꢀS bonds between the thionyl amide sulfur atoms
(1). The cytotoxicity of H2Et2xpbta [x = o (1), m (2) and p (3)] against chronic
myelogenous leukemia cells was evaluated and the bioactivity follows the order 1 >> 2
> 3, compound 1 being six and ten times more active than 2 and 3, respectively.
KEYWORDS: thiooxamate; synthesis; Lawesson´s reagent; supramolecular chemistry;
X-ray crystallography
2

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1. Introduction
The development of new and more efficient pharmaceutical agents is a
major challenge which requires of an intimate knowledge of the molecular
structures and binding affinities of the target compounds [1,2]. Organosulfur
compounds have received widespread attention of many researchers due to their
potential as anticancerigens, fungicides, or bactericides [3,4], and their role in
molecular recognition processes [5,6]. Several strategies for the synthesis of
organosulfur compounds have been investigated over the past years and, more
recently, the obtention of C−S bonds via C−H functionalization and
decarboxylation under mild conditions has been reported, opening a new avenue
for the synthesis of such compounds [7,8].
Molecules containing the oxamate group (C2O3N2−) have been synthetized
during the past three decades due to their role as chelate ligands in coordination
chemistry [8–10]. Structural and magnetic properties [9–14] were the main
purpose of studies involving transition metal oxamato complexes, but recent
studies of biological activity, specifically anticancer one [15], have created a new
perspective for them. Besides coordination compounds, organic molecules with
oxamate groups exhibit remarkable activity as antiallergic [16,17], antimalarial
[18] and also anticancer agents [19]. In this paper, we report the first thionation
reaction of oxamate ligands to give monothiooxamate derivatives which are
tested for the first time as anticancer agents.
The conversion of a carbonyl group to thiocarbonyl one is a commonly
used procedure for the preparation of organosulfur compounds [20]. Thionation
can be achieved using several reagents such as phosphorus pentasulfide [21],
hydrogen sulfide in the presence of acid [22], and bis(trimethylsilyl)sulfide with
cobalt chloride [23] leading to only moderate yields. Moreover, this reaction must
be carried out under inert atmosphere with anhydrous aromatic hydrocarbon
solvents and excess of thionation agents. Nowadays, 2,4-bis(4-methoxyphenyl)-
2,4-dithioxo-1,3,2,4-dithiadiphosphetane, known as Lawesson’s reagent [24], is
the thionation agent with more advantages since the thionation reaction proved to
be effective, clean, of easy purification, and can be done under mild conditions
with good yields [25]. In tetrahydrofurane (THF), Lawesson’s reagent lies in
equilibrium with a more reactive dithiophosphine ylide and the reaction is
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normally faster toward ketones, amides, lactams and lactones when compared to
ester derivatives [26]. Depending on the reaction conditions, esters are unreactive
which allow selective transformations [27].
Herein, we report the synthesis of the series of diethyl ester acid derivatives of
N,N’-1,2-phenylenebis(2-thiooxamate) (1), N,N’-1,3-phenylenebis(2-thiooxamate) (2)
and N,N’-1,4-phenylenebis(2-thiooxamate) (3) through the thionation reaction of the
parent oxamate ligands [28] by Lawesson’s reagent (Scheme 1). Compounds 1–3 were
1
characterized by elemental analysis, FT-IR, H-NMR and 13C-NMR spectroscopy, as
well as single crystal X-ray diffraction. A preliminary in vitro evaluation of cytotoxic
effects against one leukemia cell line is also described.
Scheme 1. Chemical structures of 1–3 (X = S) and their corresponding oxamate
precursors (X = O).
We are particularly interested on the study of the influence of the topological
effects in the hydrogen bond-directed self-assembly in the solid state of this new class
of N,N’-1,n-phenylenebis(2-thiooxamic acid ethyl ester) derivatives of formula
H2Et2opbta (n = 2), H2Et2mpbta (n = 3) and H2Et2ppbta (n = 4). In order to ascertain the
role of the thionation reaction in the solid-state supramolecular self-assembly process, a
comparison is made with the situation found by Cano and Muñoz for the N,N’-1,n-
phenylenebis(oxamic acid ethyl ester) analogues of formula H2Et2opba (n = 2),
H2Et2mpba (n = 3) and H2Et2ppba (n = 4) [28].
2. Experimental Section
2.1. Materials and Instrumentation
Lawesson’s reagent (LR) and solvents were purchased from Sigma-Aldrich and used as
received, without any further purification. The starting materials, derivatives of diethyl
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phenylenebis(oxamate), were synthetized by a known method [9–11]. Chromatographic
separations were performed by using standard column methods with silica gel (230–400
mesh). Melting points were determined by the digital device MQAPF-302 12038DV.
All NMR spectra were obtained with a Bruker DPX-200 Advance (200 MHz)
spectrometer. Chemical shifts (δ) are reported in ppm with respect to tetramethylsilane
in CDCl3 (1H NMR), or CDCl3 or dmso-d6 (13C NMR, DEPT-135) as internal standards.
IR spectra were obtained with a Perkin Elmer 882 spectrometer in KBr pellets.
Elemental analyses (C, H, N and S) were performed using a Perkin-Elmer 2400
analyser.
2.2. X-ray analysis
Single crystal X-ray diffraction data were collected on an Oxford-Diffraction GEMINI-
Ultra diffractometer at 150 K using Cu Kα radiation (λ = 1.5418 Å) for 1 and 2 and Mo
Kα radiation (λ = 0.71073 Å) for 3. Reduction data and analytical absorption corrections
were performed using CRYSALIS suite [30]. Space group identification was done with
XPREP [31] and structure solution was carried out by direct methods using SIR-92
[32]. Structures were solved by direct methods and refined by full-matrix least-squares
against F2 by using the program SHELX [33]. Hydrogen atoms were assigned riding
isotropic displacement parameters and constrained to idealized geometries. Absorption
correction was carried out in CrysAllis suit of programs by means of analytical
numeric absorption correction using a multifaceted crystal model [34]. Molecular
graphics were produced with the ORTEP [35] and CrystalMaker®[36] programs.
CCDC 1528836 (1), 1528837 (2), 1528838 (3) contain the supplementary
crystallographic data for this paper. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre.
2.3. Cell line and culture
The K562 cell line, purchased from the Rio de Janeiro Cell Bank (number CR083 of the
RJCB collection), was established from pleural effusion of a 53-year-old female with
chronic myelogenous leukemia in terminal blast crisis. Cells were cultured in RPMI
1640 (Sigma Co.) supplemented with 10% of fetal calf serum (CulLab, São Paulo,
Brazil) at 37°C in humidified 5% CO2 atmosphere. Cultures initiated at 105 cells mL–1
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and grew exponentially to about 8 × 105 cells mL–1 in 3 days. Cell viability was
checked by Trypan Blue exclusion with an optical microscope and the cell number was
determined by Coulter counter analysis.
2.4. Drug sensitivity assay
Cells at the density of 105 cells mL–1 were incubated with different concentrations of
tested drug for 3 days. Afterward, cells were counted and the concentration of drug
necessary to inhibit 50% of cellular growth, the IC50 value, was determined. Compound
concentration varied from 0 to 150 µmol L–1 in the case of 1 and from 0 to 400 µmol L–
1 in the case of 2 and 3.
2.5. Preparation of N,N’-1,2-phenylenebis(2-thiooxamic acid ethyl ester) (1).
N,N’-1,2-phenylenebis(oxamic acid ethyl ester) (0.308 g, 1.0 mmol) and LR (0.809 g,
2.0 mmol) were dissolved in THF and the reaction mixture was heated under reflux for
20h resulting in an orange solution. Purification of 1 was carried out by column
chromatography (silica gel; CH2Cl2), yield 70%; m.p. 99-100 °C. 1H NMR (CDCl3, 200
MHz, 25 °C): δ = 1.3 (t, J = 7.1, 6H); 4.3 (q, J = 7.1, 4H); 7.4 (dd, J = 6.0; 3.5, 2H); 7.7
13
(dd, J = 5.8; 3.6, 2H); 10.37 (s, 2H). C NMR (dmso-d6, 50 MHz, 25°C): δ = 185.9;
160.8; 132.5; 128.0; 126.8; 62.7; 13.8 ppm. IR (KBr, cm–1): 3198, 1731, 1496, 1244,
1065. C14H16N2O4S2 (340.41 g mol–1) calcd. C 49.40, H 4.74, N 8.23, S 18.84; found C
49.29, N 4.88, H 7.91, S 18.29 %.
2.6. Preparation of N,N’-1,3-phenylenebis(2-thiooxamic acid ethyl ester) (2).
N,N’-1,3-phenylenebis(oxamic acid ethyl ester) (0.308 g, 1.0 mmol) and LR (0.809 g,
2.0 mmol) were dissolved in THF and the reaction mixture was heated under reflux for
20h resulting in an orange solution. Purification of 2 was carried out by column
1
chromatography (silica gel; CH2Cl2), yield 63%; m.p. 97-98 °C. H NMR (CDCl3, 200
MHz, 25 °C): δ = 1.4 (t, J = 6.8, 6H); 4.4 (q, J = 6.3, 4H); 7.4 (t, J = 7.8, 1H); 7.8 (d, J =
7.5, 2H); 8.9 (s, 1H); 10.6 (s, 2H). 13C NMR (CDCl3, 50 MHz, 25°C): δ = 179.9, 159.6,
138.4, 129.8, 120.7, 115.0, 64.7, 14.1 ppm. IR (KBr, cm–1): 3286, 3210, 1714, 1701,
1527, 1289, 790, 728. C14H16N2O4S2 (340.41 g mol–1) calcd. C 49.40, H 4.74, N 8.23, S
18.84; found C 49.61, N 4.85, H 8.35, S 18.84 %.
2.7. Preparation of N,N’-1,4-phenylenebis(2-thiooxamic acid ethyl ester) (3).
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N,N’-1,4-phenylenebis(oxamic acid ethyl ester) (0.308 g, 1.0 mmol) and LR (0.809 g,
2.0 mmol) were dissolved in THF and the reaction mixture was heated under reflux for
20h resulting in an orange solution. Purification of 3 was carried out by column
1
chromatography (silica gel; CH2Cl2/ n-hexane, 95:5), yield 59%; m.p. 184-185 °C. H
NMR (CDCl3/dmso 1:1, 200 MHz, 25 °C): δ = 1.3 (t, J = 7.0, 6H); 4.3 (q, J = 7.0, 4H);
8.0 (s, 4H); 11.6 (s, 2H). 13C NMR (CDCl3/dmso 1:1, 50 MHz, 25°C): δ = 182.1; 160.8;
136.4; 122.9; 63.5; 13.9 ppm. IR (KBr, cm–1): 3271, 1699, 1557, 1285, 847, 735.
C14H16N2O4S2 (340.41 g mol–1) calcd. C 49.40, H 4.74, N 8.23, S 18.84; found C 49.21,
N 4.78, H 8.31, S 18.72 %.
3. Results and discussion
All reactions of this work were carried out using Lawesson’s reagent as
thionation complexing agent, dry THF as the reaction solvent and the corresponding
phenylenebis(oxamic acid ethyl ester) compounds as precursors. As expected, only the
carbonyl amide groups were converted to thioamides [7,37], meanwhile the ester groups
are maintained even with excess of LR, leading to the bis-monothiooxamate derivatives.
A 1:2 phenylenebis(oxamic acid ethyl ester):LR stoichiometry was used to ensure the
complete reaction of both carbonyl amide groups from the starting oxamate precursors.
The overall yields of the synthetic route were satisfactory, ranging between 59 and 70%.
For single crystal X-ray diffraction experiments, suitable orange single crystals of 1–3
were obtained by slow evaporation of the CH2Cl2 solutions at room temperature.
A summary of crystallographic data of 1–3 is listed in Table 1 and additional
crystal structural information is shown in Supporting Information (Tables S3, S4 and
S5). Selected structural and conformational data of 1–3 are given in Table 2 (see
Scheme 2).
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Scheme 2. General scheme for the conformation of the thiooxamic acid ethyl ester
moieties of 1–3 showing the notation used for the torsion angles (R1= C6H4 and R2 =
C2H5 with X = S).
1
crystallizes in the monoclinic P21/c space group with two
crystallographically independent N’-1,2-phenylenebis(2-thiooxamic acid ethyl
ester) molecules (1A and 1B, Figure 1) in the asymmetric unit (Z' = 2). chiral
N,
A
nonplanar (helical) conformation has been found for both 1A and 1B, where the two
monothiooxamate moieties adopt a cis configuration around the central C–C bond
[
ψ = 17.8(5)/20.1(5) (1A) and 19.7(5)/17.4(5)˚ (1B); Table 2] with an exo
disposition of the C=S groups, as observed before for similar oxamate molecules
containing C=O groups [38]. However, this situation contrasts with that earlier
reported for the parent ortho-phenylenebis(oxamic acid ethyl ester), where the two
oxamate moieties adopt different cis and trans configurations with exo and endo
carbonyl amide groups, respectively [28]. The average C=S bond length of c.a.
1.65(5) Ǻ in 1A and 1B is longer than the C=O bond of 1.21(4) Ǻ in the parent
ortho-phenylenebis(oxamic acid ethyl ester) precursor [28], further supporting the
occurrence of the thionation reaction.
These two distinct 1A and 1B molecules with a pseudo two-fold (C2) molecular
symmetry are characterized by small differences in the torsion angles capable to
rotation (see Table 2), which forces the two monothiooxamate moieties to be
rather tilted up and down with respect to the ortho-substituted phenylene ring [
φ
= 51.8(5)/52.2(6) (1A) and 53.4(6)/52.2(5)˚ (1B); Table 2], mainly as a result of
steric hindrance between the adjacent ethyl substituents. The thionyl amide and
the carboxy ethyl ester functions from the monothiooxamate groups of 1A and 1B
slightly deviate from planarity
[
ω
= 7.0(6)/9.3(5) (1A) and 5.9(5)/10.3(6)˚ (1B);
κ
=
5.8(5)/4.0(5) (1A) and 55.2(5)/5.5(5)˚ (1B); Table 2].
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Figure 1. Isolated fragments of asymmetric unit of 1A (a) and 1B (b), with
atom labels. Thermal ellipsoids are drawn at 50% probability level and hydrogen
atoms were omitted for the sake of clarity.
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Table 1. Summary of Crystallographic Data for 1-3.
Compound
Formula
Fw /g mol–1
T /K
1
C14H16N2O4S2
340.41
2
C14H16N2O4S2
340.41
3
C14H16N2O4S2
340.41
150(2)
150(2)
293(2)
λ /Å
1.5418
Monoclinic
P 21/c
1.5418
Monoclinic
C2/c
0.71073
Triclinic
Crystal System
Space group
a / Å
ꢀ
P1
11.6653 (5)
28.1338(12)
9.9424 (4)
90
101.987(4)
90
24.837(2)
7.8010(15)
8.2815(15)
90
91.996(12)
90
4.5006(4)
7.4006(6)
12.0727(9)
95.917(6)
90.225(7)
102.136 (8)
390.89(6)
2/2
b / Å
c / Å
α / o
β / o
γ / o
V / Å3
3191.8 (11)
4/8
1603.6(3)
4/4
Z / Z’
ρ / mg m–3
ꢀ /mm–1
F(000)
1.417
3.201
1424
1.417
3.186
712
2.89
0.72
356
Crystal size/ mm3 0.12 x 0.16 x 0.79
0.35 x 0.03 x 0.02
7226 (0.066)
0.83 x 0.07 x 0.04
4775 (0.046)
Reflections
collected (Rint)
Goodness-of-fit on
F2
Ra, wRb (all data)
Larg. diff. peak and
hole / e Å–3)
21152 (0.073)
1.02
1.05
0.98
0.0968,0.1644
0.449, –0.429
0.0620, 0.1193
0.341, – 0.445
0.0661, 0.1311
0.700, -0.488
aR = Σ ||Fo| – |Fc|| / Σ|Fo|. bwR [Σ (|Fo|2 – |Fc|2)2 / Σ|Fo|2]1/2.
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Table 2. Selected bond distances (Å) and angles (o) for 1-3
.
1A
1B
2
3
C=S (thiooxamide) 1.652(4)/1.6528 (3)
1.653(3)/ 1.658(3)
1.205(5)/ 1.208(4)
1.337(4)/ 1.324(3)
1.342(4)/ 1.331(4)
1.518(5)/ 1.526(5)
1.418(5)/ 1.425(5)
0.880
1.651(3)
1.197(3)
1.320(3)
1.336(3)
1.540(3)
1.414(3)
0.860
1.643(2)
1.211(3)
1.318(3)
1.346(3)
1.535(3)
1.409(3)
0.860
C=O (ester)
1.206(5)/ 1.205(4)
1.328(4)/ 1.333(3)
1.345(5)/ 1.336(5)
1.524(5)/ 1.519(5)
1.415(5)/ 1.414(5)
0.880
C
C
C
−
−
−
O (ester)
N (thiooxamide)
C(thiooxalamide)
N−C (benzene)
N−H (thiooxamide)
φa
ωb
ψc
κd
τe
51.8(5)/ 52.2(6)
7.0(6)/9.3(5)
53.4(6)/ 52.2(5)
5.9(5)/ 10.3(6)
19.7(5)/ 17.4(5)
5.2(5)/ 5.5(5)
32.2(4)
1.4(4)
7.3(3)
3.0(3)
17.8(5)/20.1(5)
5.8(5)/4.0(5)
176.0(4)
2.5(5)
173.3(3)
2.3(3)
4.8(2)
65.9(2)1/64.1(2)
66.2(1)/63.5(1)
32.1(1)
a
b
Torsion angle around the N
−
C single bond of the aromatic ring. Torsion angle around the N
−C
single bond around thiooxalamide function. c Torsion angle around the central C
−C single bond of
d
the thiooxalamide group. Torsion angle around the C
−O
single bond of the carboxy ester
e
function.
Dihedral angle between best-fit plane of thioxalamide groups (plane formed by
C2O2SN) and the mean plane of the phenylene ring.
Figure 2 highlights the significant twisting of the monothiooxamate groups
with respect to the phenylene ring from both 1A and 1B molecules [
65.9(2)1/64.1(2) (1A) and 66.2(1)/63.5(1)˚ (1B); Table 2].
τ
=
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Figure 2. Side views of the molecular structure of (a) 1A and (b) 1B, showing the
twist of the thiooxamate groups. Thermal ellipsoids are drawn at 50% probability
level and hydrogen atoms were omitted for the sake of clarity.
Crystal packing of
1 relies on both intermolecular N―HꢀꢀꢀO and SꢀꢀꢀS
bonds between the closest thiooxamate groups from identical 1A and 1B
molecules (Figures 3a and 3b) through amide hydrogen and carbonyl ester
oxygen atoms on the one hand (Table S1, see SI) and thionyl amide sulfur atoms
on the other hand [S1ꢀꢀꢀS2ii = 3.383(2) Å for 1A and S1ꢀꢀꢀS2i = 3.386(2) for 1B
; i
= x, y, 1+z and ii = x, y, –1+z]. These weak non-covalent intermolecular
interactions result in a close packing of alternating ribbon-like supramolecular 1D
chains built upon 1A and 1B molecules growing along the crystallographic
c axis
(Figures 3c and 3d). Intramolecular N H O hydrogen bonds also occur in 1A
−
and 1B involving the amide hydrogen and carboxy ester oxygen atoms from each
cis-monothiooxamate moiety (N1–H1ꢀꢀꢀO2 = 2.212 Å and N2–H2ꢀꢀꢀO4 = 2.218 Å
for 1A, N3–H3ꢀꢀꢀO6 = 2.243 Å and N4–H4ꢀꢀꢀO8 = 2.205 Å for 1B). Interestingly,
each segregated chain contains a racemic mixture of adjacent 1A or 1B molecules
of opposite helical chirality (M and P enantiomers) related by a crystallographic
inversion center, so that they are both achiral [28].
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Figure 3. Projection view of the supramolecular 1D chains of 1A (a) and 1B (b)
molecules along crystallographic
b axis, showing the intra- and intermolecular
hydrogen bonds of the type N―HꢀꢀꢀO (dashed lines) and the intermolecular SꢀꢀꢀS
interactions (dotted lines). Stick (c) and space filling model representation (d) of
the crystal packing of
1
showing the parallel array of supramolecular 1D chains
axis.
built upon 1A (blue) and 1B (red) molecules along crystallographic
c
Hydrogen atoms from the ethyl ester substituents have been omitted for the sake
of clarity.
2 crystallizes in the monoclinic C2/c space group with with half molecule of
N,N’-1,3-phenylenebis(2-thiooxamic acid ethyl ester) in the asymmetric unit (Figure 4).
The molecular structure of
2 has a nonplanar (helical) conformation similar to 1,
where the two monothiooxamate moieties are somewhat tilted up and down with respect
to the meta-substituted phenylene ring [φ = 32.2(4)˚; Table 2]. The overall molecule
has a crystallographically imposed two-fold (C2) molecular symmetry generated
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by the proper rotation along C1 to C4 axis. Like , the steric hindrance results in
non-coplanarity of the thiooxamate moieties and the phenylene ring [ =32.1(1)º].
1
τ
However, the conformation around the central carbon-carbon single bond of the two
monothiooxamate moieties is trans [ψ = 176.0(4)˚; Table 2], with the C=S groups
pointing toward the inner cavity site in an endo disposition.
Figure 4. Front (a) and side (b) views of the molecular structure of 2 with atom labels,
showing the twist of the thiooxamate moieties. Thermal ellipsoids are drawn at 50%
probability level and hydrogen atoms were omitted for the sake of clarity. Symmetry
code: i = 1–x, y, 1/2–z.
Unlike 1, crystal packing of 2 is mainly driven by the non-classical N–HꢀꢀꢀS
hydrogen bonds (N1–H1···S1ii = 2.850 Å; ii: x, –y, 1/2+z) (see SI, Table S2)
between amide hydrogen and thionyl amide sulfur atoms of the closest
thiooxamate groups from adjacent molecules of opposite M and P chiralities
related by a crystallographic inversion center, together with weak π-π stacking
interactions of parallel-displaced type between their phenylene rings (C1 C2 =
3.586(4) Å) (Figure 5a). In this type of interaction the sulfur atom is considered a
weak acceptor, due to its low electronegativity in comparison with classical
hydrogen bond heteroatoms (F, O, N and Cl) [39]. In addition, there are
intramolecular N
−H O hydrogen bonds involving the amide hydrogen and
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carbonyl ester oxygen atoms from each trans-monothiooxamate moiety (N1–
H1ꢀꢀꢀO1 = 2.177 Å), as well as non-classical C
−H S hydrogen bonds involving
the phenylene hydrogen and thionyl amide sulfur atoms from each trans
-
monothiooxamate moiety (C4–H4ꢀꢀꢀS1 = 2.680 Å). These weak non-covalent
intermolecular interactions result in a parallel packing of supramolecular ribbon-
like 1D chains growing along the crystallographic c axis (Figure 5b).
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Figure 5. (a) Projection view of the supramolecular 1D chain of
2 along
crystallographic
b axis, showing the intramolecular N―HꢀꢀꢀO and non-classical
intra- and intermolecular C―HꢀꢀꢀS and N―HꢀꢀꢀS hydrogen bonds (dashed lines)
and the weak intermolecular π-π stacking interactions (solid lines). (b) Crystal
packing view of
2 along crystallographic c axis showing the parallel array of
supramolecular 1D chains. Hydrogen atoms from the ethyl ester substituents have
been omitted for the sake of clarity.
The crystal packing of thionated compound
2 is analogous to that of the related
polymorph of N’-1,3-phenylenebis(oxamic acid ethyl ester) reported by
N,
Padilla-Martínez et al. [40], regarding both space group, crystal lattice dimension,
and crystal packing features, where the intermolecular non-classical N–
HꢀꢀꢀSthioamide hydrogen bond is replaced by classical N–HꢀꢀꢀOamide one resulting in
a very similar supramolecular ribbon-like 1D chains. In contrast, the other
polymorph of N,N’-1,3-phenylenebis(oxamic acid ethyl ester) reported by Muñoz
et al. consists of supramolecular meso-helical 1D chains built upon
intermolecular double N–HꢀꢀꢀOester hydrogen bonds [10],
ꢂ
crystallizes in the triclinic centrosymmetric ꢁ1 with the assymetric unit
3
composed of half centrosymmetric molecule of N,N’-1,4-phenylenebis(2-thiooxamic
acid ethyl ester), with the geometric center of aromatic ring placed over an
inversion center (Figure 6). Unlike
phenylene ring can avoid the steric hindrance between the monothiooxamate
moieties leading to an almost coplanar molecular conformation [ = 4.8(2)º],
1 and 2, the substitution at 1,4 positions of the
τ
where each monothiooxamate moiety adopts a trans conformation [ψ = 173.3(4)˚;
Table 2] like in the crystal structure of the related N,N’-1,4-phenylenebis(oxamic
acid ethyl ester) [28,41].
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Figure 6. Front (a) and side (b) views of the molecular structure of 3 with atom
labels. Thermal ellipsoids are drawn at 50% probability level and hydrogen atoms
were omitted for the sake of clarity. Symmetric code: i = 2–x, –y, 1–z.
Crystal packing of
3
relies on double N–HꢀꢀꢀO [N1–H1ꢀꢀꢀO1ii = 2.472 Å, ii
= 1–x, 1–y, 1–z] between amide hydrogen and carbonyl ester oxygen atoms of
the closest thiooxamate groups from adjacent molecules in trans configuration,
which is a very common hydrogen-bonded supramolecular synthon in oxamate
crystal engineering [10,26,42]. This situation leads to supramolecular zigzag 1D
chains growing along the crystallographic
b
axis (Figure 7a), which are closely
packed within the ab plane (Figure 7b).
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Figure 7. (a) Projection view of the supramolecular 1D chain of
3 along
crystallographic
a
axis, showing the intramolecular double N―HꢀꢀꢀO hydrogen
along crystallographic axis
bonds (dashed lines). (b) Crystal packing view of
3
c
showing the parallel array of supramolecular 1D chains. Hydrogen atoms from
the ethyl ester substituents have been omitted for the sake of clarity.
1–3 in polycrystalline form were used to the fully characterization and also
in the cytotoxic tests. Elemental analyses are in agreement with proposed
formula.
IR spectra of
absorption bands in 3286, 3210 cm–1 (
vibrations (Figure S1, see SI). The strong absorption bands at 1731 cm–1 (
1714, 1701 cm–1 ( ) and 1699 cm–1 (
) were related to C=O of ethyl ester group.
1
–
3
exhibit a strong absorption in 3198 cm–1(
) and 3271 cm–1 (
) assigned to
1) and mean
2
3
ν N−H
1
),
2
3
ν
When compared to the related oxamate analogues, it was noticed the shifting of
these C=O stretching vibrations to lower frequencies and the appearance of new
bands at 1244 cm–1
(
1
), 1289 cm–1
(
2
) and 1285 cm–1
(3) related to νC=S
1
stretching vibrations. The spectra of H-NMR and 13C-NMR are also in
agreement with the expected molecular structures determined by single-crystal X-
ray diffraction in the solid state (Figures S2-S7, see SI), suggesting that the
molecules are stable in solution.
All thionated compounds
1–3 were able to inhibit cellular growth of
myelogenous leukemia cells in a concentration dependent manner with the IC50
values shown in Table 3. It is not possible to establish consistent structure-
activity relationships from the results obtained with this limited series of
compounds. Nevertheless, the spatial arrangement of the monothiooxamate
moieties in the molecule seems to influence the cytotoxic effect. So compound
which possesses an ortho substitution pattern, is approximately 6 and 10 times
more potent than the corresponding meta and para derivatives and
respectively. In addition, exhibits greater activity (approximately 12 times more
1,
2
3,
1
cytotoxic) compared to the starting material N,N’-1,2-phenylenebis(oxamic acid
ethyl ester) [15]. These results corroborate the previous studies for which the
replacement of oxygen by sulfur atoms in well-known antitumor compounds
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leads to a higher antitumor activity against various solid tumor xenografts in mice
[43].
Table 3. Selected cytotoxic data of 1
–3 and cisplatin
against myelogenous leukemia cells
IC50a (µmol L–1 ± s.d.)
36.0 ± 3.0
Compound
1
203 ± 10
367 ± 19
1.1 ± 0.2
2
3
cisplatin
a
IC50 is the concentration required to inhibit 50% of
cellular growth. The values are the mean of triplicate
determinations.
4. Conclusions and perspectives
In summary, we describe here the synthesis, physical and structural
characterization and the evaluation of anticancer activity in leukemic cells of
three positional isomers derived from thiooxamate ethyl ester-based organosulfur
molecules. The effective thionation in
1
-
3
is proved by their crystal structure
1
determination through X-ray diffraction along with the H and 13C NMR, IR
spectra and elemental analysis. Compound
cytotoxic than the analogue N’-1,2-phenylenebis(oxamate) described earlier
[15]. Although exhibits a cytotoxicity of about 6 times and 10 times higher than
and , respectively, it still showed a small activity when compared to cisplatin.
Yet
can be used as a potential ligand toward PtII and PdII ions, as earlier
1 is approximately 12 times more
N,
1
2
3
1
reported for the parent oxamate ligand [15]. Further studies to obtain the
corresponding platinum(II) and palladium(II) coordination compounds will be
carried soon, being an inspiration in the design of new anticancer drugs.
Acknowledgements
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Financial support for this work was provided by Conselho Nacional de
Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo à
Pesquisa do Estado de Minas Gerais (FAPEMIG) and Coordenação de
Aperfeiçoamento de Pessoal de Nível Superior (CAPES).
Supporting Information
1
IR spectra for 1–3, H and 13C NMR spectra for 1–3, classical and non-classical
hydrogen bonds parameters for 1 and 2, respectively (Tables S1 and S2) and main bond
lengths for 1–3 (Tables S3-S5). This material can be found at DOI:
dx.doi.org/10.1016/jmolstruc.XXXX
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Topological control of supramolecular crystal structures of
phenylene bis-monothiooxamate derivatives and in vitro
anticancer activity
Tamyris T. da Cunhaa, Willian X. C. Oliveiraa, Ivana M. Marzanoa,b, Carlos B.
Pinheiroc, Elene Cristina Pereira-Maiaa, Cynthia L. M. Pereiraa,*
Highlights
⦁ The ortho-, meta- and para- isomers of phenylenebis(2-thiooxamate) are synthesized.
⦁ Lawesson´s reagent is used on the thionation reaction.
⦁ X-ray single crystal structures indicate supramolecular one-dimensional structures.
⦁ Preliminary in vitro anticancer studies against leukemia cell line is evaluated.
⦁ Dependence of anticancer activity with the molecular architectures.