Synthesis, X-ray structure analysis and computational studies of novel bis(thiocarbamoyl) disulfides with non-covalent S?N and S?S interactions

Article abstract of DOI:10.1016/j.cplett.2006.02.022

In this Letter, we describe the synthesis of several bis(thiocarbamoyl) disulfides that present interesting intramolecular S?N and S?S interactions. In one case, crystals suitable for X-ray characterization have been obtained. The non-covalent interaction

Full text of DOI:10.1016/j.cplett.2006.02.022

Chemical Physics Letters 422 (2006) 234–239
www.elsevier.com/locate/cplett
Synthesis, X-ray structure analysis and computational studies
of novel bis(thiocarbamoyl) disulfides with non-covalent Sꢀ ꢀ ꢀN
and Sꢀ ꢀ ꢀS interactions
a,
b,
c
a
*
*
Jarosław S a˛ czewski , Antonio Frontera , Maria Gdaniec , Zdzisław Brzozowski ,
a
a
b
b
Franciszek S a˛ czewski , Piotr Tabin , David Qui n˜ onero , Pere M. Dey a`
a
Department of Chemical Technology of Drugs, Medical University of Gda n´ sk, 80-416 Gda n´ sk, Poland
b
Department of Chemistry, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain
c
Faculty of Chemistry, A. Mickiewicz University, 60-780 Pozna n´ , Poland
Received 17 January 2006; in final form 7 February 2006
Available online 23 February 2006
Abstract
In this Letter, we describe the synthesis of several bis(thiocarbamoyl) disulfides that present interesting intramolecular Sꢀ ꢀ ꢀN and
Sꢀ ꢀ ꢀS interactions. In one case, crystals suitable for X-ray characterization have been obtained. The non-covalent interactions have been
studied analyzing the crystal structure and by means of high level density functional theory (DFT) calculations (RI-PB86/TZVP) using
both ‘atoms-in-molecules’ (AIM) and natural bond orbital (NBO) analyses.
ꢀ
2006 Elsevier B.V. All rights reserved.
1
. Introduction
quantum chemical calculations. The non-covalent interac-
tions have been studied using the Bader’s theory of
‘atoms-in-molecules’ [10], which has been used successfully
to understand a great variety of non-covalent interactions.
Additionally, the interactions have been rationalized using
the natural bond orbital (NBO) method [11], taking advan-
tage of the perturbative analysis of NBO donor–acceptor
interactions.
It is well known that bis(thiocarbamoyl) disulfides such
as antabus (tetraethylthiuram disulfide) act as antioxidants
and inhibitors of aldehyde dehydrogenase [1]. In addition,
compounds of this type are found to possess antiviral activ-
ity [2] and they are potential drug formulations for the pre-
vention and treatment of cataracts [3]. On the other hand,
the non-bonding Sꢀ ꢀ ꢀN, Sꢀ ꢀ ꢀS and Sꢀ ꢀ ꢀO interactions play
an important role in mechanism of action of anticancer
2. Experimental and theoretical methods
[
4,5] and antibacterial [6] agents as well as antagonists of
angiotensine II (AT ) receptors [7–9].
2.1. Synthesis
1
In this Letter, we describe a convenient synthetic
methodology for the preparation of a novel class of bis(thi-
ocarbamoyl) disulfides which exhibit both the Sꢀ ꢀ ꢀN and
Sꢀ ꢀ ꢀS short contacts. Nature of these interactions was
investigated by means of X-ray structure analysis and
Melting points were measured on a Boetuis apparatus
and are not corrected. IR spectra were taken in KBr pellets
on a Perkin–Elmer FTIR 1600 spectrometer. NMR spectra
were recorded on a Varian Unity 500 apparatus using TMS
as the internal standard. Elemental analyses of C, H, N were
within ± 0.4ꢀ of the theoretical values. Starting N-{1-[(3-
thioxo-5,6-dihydroimidazo[2,1-c][1,2,4]thiadiazol-7-lythio)-
thiocarbonyl]2-imidazolidene}-arylsulfonamides (1–5) were
prepared according to the described procedure [12].
*
Corresponding authors. Fax: +48 583 493251 (J. S a˛ czewski), +34 971
173426 (A. Frontera).
E-mail addresses: js@amg.gda.pl (J. S a˛ czewski), toni.frontera@uib.es
(A. Frontera).
0
009-2614/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.cplett.2006.02.022

J. S a˛ czewski et al. / Chemical Physics Letters 422 (2006) 234–239
235
2
.1.1. Preparation of bis{[2-(arylsulfonylimino)imidazoli-
din-1-yl]thiocarbonyl}disulfides (6–10)
.1.1.1. General procedure. N-{1-[(3-thioxo-5,6-dihydro-
CH , J = 8.3 Hz), 4.19 (t, 4H, CH , J = 8.3 Hz), 7.64 (d,
2 2
4H, CH, J = 8.8 Hz), 7.91 (d, 4H, CH, J = 8.8 Hz), 9.15
2
(s 2H, NH); IR: 3396, 1629, 1473, 1417, 1330, 1297,
ꢁ
1
imidazo[2,1-c][1,2,4]thiadiazol-7-lythio)-thiocarbonyl]2-imi-
dazolidene}arylsulfonamide 1–5 (0.4 mmol) was dissolved
in wet DMF (15 mL) and the reaction mixture was heated
under reflux for 10 min. The product that precipitated was
isolated according to the procedure described below and
purified by crystallization from suitable solvent.
1147 cm .
Crystallization of the amorphous compound 9 from
DMF in the presence of equimolar amount of CuCl2
yielded crystals of 9 · 2 DMF suitable for X-ray structure
analysis.
2.1.6. Bis{[2-((4-trifluoromethylphenyl)sulfonylimino)
imidazolidin-1-yl] thiocarbonyl} disulfide (10)
2.1.2. Bis{[2-(phenylsulfonylimino)imidazolidin-1-
yl]thiocarbonyl}disulfide (6)
The reaction mixture was evaporated to dryness under
reduced pressure. The solid residue was treated with hot
methanol (20 mL). After 12 h product 10 that precipitated
was collected by filtration and washed with methanol.
The reaction mixture was concentrated to a volume of
5
mL under reduced pressure. Then chloroform (10 mL)
was added. After 12 h the product 6 that precipitated was
1
filtered off and washed with chloroform. Yield: 0.060 g
Yield: 0.095 g (64ꢀ); m.p. 227–229 ꢁC (DMF); H NMR
1
(
(
50ꢀ); m.p., 212–213 ꢁC (DMSO/methanol); H NMR
(DMSO-d ) d 3.58–3.66 (m, 4H, CH ), 4.16–4.24 (m, 4H,
6
2
DMSO-d ): d 3.63 (t, 4H, CH , J = 7.9 Hz), 4.23 (m,
CH ), 7.96 (d, 4H, CH, J = 8.4 Hz), 8.14 (d, 4H, CH,
6
2
2
4
H, CH , J = 7.9 Hz), 7.55–7.67 (m, 6H, CH), 7.94–7.98
J = 8.4 Hz), 9.24 (s 2H, NH); IR: 3404, 1662, 1477, 1420,
2
1
3
ꢁ1
(
m, 4 H, CH), 9.12 (s 2H, NH); C NMR (DMSO-d ) d
1328, 1300, 1155 cm
.
6
4
3
0.9, 51.8, 126.4, 129.3, 132.8, 142.2, 151.2, 193.5; IR:
ꢁ
1
392, 1636, 1410, 1382, 1341, 1307, 1283 cm
.
2.2. X-ray structure analysis
The filtrate obtained after isolation of compound 6 was
concentrated under reduced pressure to a volume of 2 mL.
After 6 h the compound 11 that deposited was separated by
suction and washed with methanol. Yield 30ꢀ; m.p., 190–
The diffraction data were collected at 130 K with a
KumaCCD diffractometer using graphite monochromated
Mo Ka radiation. The intensity data were collected and
processed using Oxford Diffraction CrysAlis Software
1
92 ꢁC (Ref. [13]: 190–192 ꢁC).
[
14]. The structure was solved by direct methods with the
2
1
.1.3. Bis{[2-((4-methylphenyl)sulfonylimino)imidazolidin-
-yl]thiocarbonyl}disulfide (7)
program SHELXS-97 [15] and refined by full-matrix least-
squares method on F with SHELXL-97 [16].
2
Chloroform (10 mL) was added to the reaction mixture.
After 12 h compound 7 thus obtained was filtered off and
Crystal data for 9: C H Cl N O S Æ 2(C H NO),
2
0
18
2
6
4
6
3
7
˚
monoclinic, space group P2 /n, a = 7.2427(4) A, b =
1
˚
˚
washed with chloroform. Yield: 0.055 g (40ꢀ); m.p., 218–
11.5538(5) A, c = 20.7267(9) A, b = 93.078(4)ꢁ, V =
1
3
ꢁ3
˚
2
(
19 ꢁC (DMF/chloroform); H NMR (DMSO-d ) d 2.36
1731.92(14) A , Z = 2, d = 1.564 g cm , T = 130 K.
6
x
s, 3H, CH ), 3.59 (t, 4H, CH , J = 8.2 Hz), 4.19 (t, 4H,
Final R indices for 2486 reflections with I > 2r(I) and 257
refined parameters are: R = 0.0329, wR = 0.0822
3
2
CH , J = 8.2 Hz), 7.36 (d, 4H, CH, J = 8.1 Hz), 7.81 (d,
2
1
2
1
3
4
H, CH, J = 8.1 Hz), 9.02 (s 2H, NH); C NMR (DMSO-
(R = 0.0430, wR = 0.0863 for all 3042 data). The solvent
1 2
d ) d 21.2, 41.5, 51.8, 126.1, 130.0, 139.9, 143.7, 151.4,
molecule is disordered over two overlapping positions with
the occupation ratio of 2:1.
6
ꢁ
1
1
93.5; IR: 3400, 1632, 1415, 1331, 1297, 1146, 1082 cm .
Crystallographic data for compound 9 have been depos-
ited with Cambridge Crystallographic Data Centre (CCDC
Deposition Number CCDC 294718). Copies of the data
can be obtained upon request from CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK, quoting the deposition
numbers.
2
.1.4. Bis{[2-((4-methoxyphenyl)sulfonylimino)
imidazolidin-1-yl]thiocarbonyl}disulfide (8)
The reaction mixture was concentrated under reduced
pressure to a volume of 5 mL. Then chloroform (10 mL)
was added. After 12 h the product 8 was filtered off and
washed with chloroform. Yield: 0.028 g (21ꢀ); m.p., 203–
1
2
3
04 ꢁC (DMF/chloroform); H NMR (DMSO-d ) d 3.57–
2.3. Computational methods
6
.64 (m, 4H, CH ), 4.16–4.24 (m, 4H, CH ), 7.08 (d, 4H,
2
2
CH, J = 8.9 Hz), 7.86 (d, 4H, CH, J = 8.9 Hz), 9.02 (s 2H,
The geometry of compound 9 was fully optimized using
the density functional BP86 method with the resolution of
the identity (RI) approximation and the TZVP (triple-f
with polarization) basis set. The RI method [17,18] uses
an auxiliary fitting basis to avoid treating the complete
set of two-electron repulsion integrals. The calculations at
the RI-BP86/TZVP level of theory were performed using
the program TURBOMOLE version 5.7 [19]. The AIM analy-
sis was performed by means of the AIMPAC program [20]
ꢁ
1
NH); IR: 3408, 1631, 1592, 1497, 1412, 1332, 1266 cm
.
2
1
.1.5. Bis{[2-((4-chlorophenyl)sulfonylimino)imidazolidin-
-yl]thiocarbonyl}disulfide (9)
Chloroform (10 mL) was added to the reaction mixture.
After 12 h compound 9 was filtered off and washed with
chloroform. Yield: 0.073 g (40ꢀ); m.p., 224–225 ꢁC
1
(
DMF/chloroform); H NMR (DMSO-d ) d 3.60 (t, 4 H,
6

236
J. S a˛ czewski et al. / Chemical Physics Letters 422 (2006) 234–239
using the BP86/TZVP//RI-BP86/TZVP wavefunction. The
NBO analysis was performed using the NBO 3.0 program
implemented in the GAUSSIAN-03 package [21] at the
BP86/TZVP//RI-BP86/TZVP level of theory.
scopic data for 11 were identical with those described
previously for authentic sample [13].
It should be pointed out that the above reaction did not
proceed in dry DMF, which suggests that an alternative
mechanism involving the hydrolytic cleavage of S–N bond
might be operative. If it is the case, the sulfenic acid-type
species with unstable R–S–OH moiety should be formed.
One reagent that has been reported to be useful for trap-
ping the unstable sulfenic acid is methyl acetylenecarboxy-
late [24]. However, upon heating of 1–5 in the presence of
methyl acetylenecarboxylate, adducts with alkenyl struc-
ture were not detected (NMR evidence).
3
. Results and discussion
3
.1. Synthesis
The target bis{[2-(arylsulfonylimino)imidazolidin-1-
yl]thiocarbonyl}disulfides 6–10 were obtained by refluxing
a solution of corresponding N-{1-[(3-thioxo-5,6-dihydro-
imidazo[2,1-c][1,2,4]thiadiazol-7-lythio)-thiocarbonyl]2-imi-
dazolidene}arylsulfon-amide 1–5 in wet dimethylformamide
3.2. X-ray structure analysis
(
DMF) for 10 min. A proposed mechanism of this reaction
is presented in Scheme 1.
Molecular structure adopted by 9 in the solid state is
shown in Fig. 1. This molecule is centrosymmetric with
the inversion center located in the middle of the S–S bond
that leads to the trans conformation at the disulfide S–S
bond. This is a seldom case for the disulfide bridges and
our survey of the Cambridge Structural Database (CSD)
[25] shows that among 401 molecules containing the acyclic
C–S–S–C fragment as much as 384 have the C–S–S–C tor-
sion angle in the range 60–120ꢁ and only in 8 cases the tor-
sion angle around the S–S bond points to the trans
conformation. Interestingly, the change in the conforma-
First step of the reaction sequence is the homolytic
cleavage of the sulfonamide S–N bond at elevated temper-
ature leading to the radicals A and B. Such a thermal
decomposition of sulfenamides is well documented in the
chemical literature [22,23]. Then, recombination of sulfur
radicals A gives rise to the formation of disulfides 6–10.
Simultaneously, the radical B reacts with water molecule
to give 6,7-dihydro-5H-imidazo[2,1-c][1,2,4]thiadiazol-3-
thione (11) and hydroxyl radical which subsequently rec-
ombinates to hydrogen peroxide. Analytical and spectro-
Ar
H
N
SO2
N
S
Ar
H
N
N
SO2
N
°
DMF/ 150 C
N
N
N
S
N
S
S
N
N
S
S
N
S
A
B
1
-5
S
recombination
of radicals
2 H O
2
H
N
S
N
Ar
HN
N
S
SO2
2HO
N
S
N
N
S
O2S
Ar
S
N
NH
S
1
1
6
7
8
9
10
H O
2
2
Ar
CH
3
OCH
3
Cl
CF
3
Scheme 1. Proposed mechanism for the formation of disulfides 6–10.

J. S a˛ czewski et al. / Chemical Physics Letters 422 (2006) 234–239
237
3.3. Computational studies
Starting from the X-ray structure of 9, we have opti-
mized its geometry at the RI-BP86/TZVP level of theory.
In Fig. 2, we compare the experimental and theoretical
geometries in order to verify the reliability of the theoreti-
cal level. It is worth mentioning that the distances and
angles of the atoms involved in the Sꢀ ꢀ ꢀS and Sꢀ ꢀ ꢀN non-
covalent interactions are very similar. The main difference
is located on the conformation of the aromatic ring, where
the theoretical and experimental N6–S7–C10–C11 (see
labeling of Fig. 1) dihedral angles are 68.0 and 99.4, respec-
tively. This difference is probably due to packing forces
that act in the solid state, however it does not affect the
non-covalent interactions focus of this study.
Once verified the reliability of the level of theory, we
have used the AIM theory to study the Nꢀ ꢀ ꢀS and Sꢀ ꢀ ꢀS
non-covalent interactions analyzing the topology of the
charge density q(r) distribution and properties of critical
points (CP), which provides an unambiguous definition
of chemical bonding [31]. The exploration of the CPs (see
Fig. 1. Ortep drawing of 9 showing atom labelling and short intramo-
lecular Sꢀ ꢀ ꢀS and Sꢀ ꢀ ꢀN contacts in A˚ .
tion is accompanied by a significant change in the S–S
bond length: for the 384 skewed fragments and for the
eight fragments in the trans conformation calculated mean
˚
˚
values of the S–S bond lengths are 2.04(2) A and 2.12(3) A,
˚
respectively. The S–S bond length of 2.124(1) A in 9 is close
to the mean value for the trans conformation. Tetraisopro-
pylthiuram disulfide (12) [26] is among the eight trans disul-
fides found in the CSD and it is the only one among 14
bis(thiocarbamoyl) disulfides found in the database which
adopts the trans conformation. Molecular structure of 9,
which can also be considered a thiuram disulfide analogue,
closely resembles that of 12. There are two short intramo-
˚
lecular Sꢀ ꢀ ꢀS contacts in both structures (2.979 A and
˚
2
.989 A in 9 and 12, respectively) and by adopting the trans
conformation the C–Sꢀ ꢀ ꢀS fragments of the molecule
become nearly linear, i.e. allow for the involvement of
the nucleophilic S2 atom in the interaction with the C–S1
*
r orbital. Whereas Sꢀ ꢀ ꢀS contacts shorter than the sum
of van der Waals radii are also observed in compounds
with the nearly perpendicular thiocarbamoyl moieties,
there the C–Sꢀ ꢀ ꢀS angles are close to 90ꢁ and the Sꢀ ꢀ ꢀS con-
tacts are significantly longer with the mean value of
˚
3
.25(3) A. Another geometrical parameter influenced by
the conformational change and the Sꢀ ꢀ ꢀS interaction in
the thiuram disulfide moiety is the C–S–S angle, which is
much smaller for trans conformers (95.0ꢁ in 9 and 97.8ꢁ
in 2) than for the skewed forms [mean value of 104.2(9)ꢁ].
In compound 9, the disulfide S atom is additionally
involved in the interaction with another nucleophilic atom
as evidenced by short S1ꢀ ꢀ ꢀN6 contact to the imide nitro-
˚
gen atom [N6ꢀ ꢀ ꢀS1 2.624 A, <S7–N6ꢀ ꢀ ꢀS1 165.4ꢁ]. There
are four structures [27–30] in the CSD where the disulfide
S atom is involved in the Sꢀ ꢀ ꢀN interaction closing a five-
membered ring, however, in all cases the Nꢀ ꢀ ꢀS contacts
˚
are much longer and fall within the range 2.724–2.815 A.
The above might be indicative of a cooperative effect of
the Sꢀ ꢀ ꢀS and Sꢀ ꢀ ꢀN interactions in 9.
Fig. 2. Theoretical RI-PB86/TZVP optimized structure (top) and exper-
imental X-ray structure (bottom). Distances in A and angles in (ꢁ).
˚

2
38
J. S a˛ czewski et al. / Chemical Physics Letters 422 (2006) 234–239
Table 1
Fig. 3) revealed the presence of one (3,ꢁ1) and (3,+1) CPs
for each non-bonded interaction. The bond CPs (repre-
sented by white circles) connect the S1 and S1A atoms with
the N6/S2A and NA6/S2 pair of atoms, respectively. The
presence of the ring CPs (black circles) indicate the forma-
tion of a four- and a five-membered rings as a consequence
of the interactions. The Laplacian of the charge density at
the (3,ꢁ1) CPs is positive which indicates a depletion of the
2
The electron density q(r) and its Laplacian $ q(r) in atomics units at the
critical points originated from the non-covalent interactions of compound
9
computed at the BP86/TZVP//RI-BP86/TZVP level of theory
2
2 2
10 $ q(r)
Non-covalent interaction
CP
10 q(r)
Nꢀ ꢀ ꢀS–S
Nꢀ ꢀ ꢀS–S
Sꢀ ꢀ ꢀS–C
Sꢀ ꢀ ꢀS–C
Oꢀ ꢀ ꢀH–N
Oꢀ ꢀ ꢀH–N
(3,+1)
(3,ꢁ1)
(3,+1)
(3,ꢁ1)
(3,+1)
(3,ꢁ1)
2.889
1.671
1.966
1.785
2.707
1.427
7.806
8.922
5.492
7.211
9.865
8.115
electron density, as is common in closed-shell interactions
2
[
10]. The values of q(r) and $ q(r) at the CPs are summa-
rized in Table 1. The value of the charge density at the
ꢁ
2
bond CP of the Nꢀ ꢀ ꢀS interaction (q(r) = 2.889 · 10 a.u.)
is higher than the value obtained for the Sꢀ ꢀ ꢀS interaction
participate in the non-covalent interactions present in
compound 9 indicate that there is an interaction between
the electron lone pair of nitrogen atoms N6 and N6A
ꢁ2
(
q(r) = 1.966 · 10 a.u.) indicating that the Nꢀ ꢀ ꢀS interac-
tion is stronger. For comparison purposes we have also
included in Fig. 3 and Table 1 the AIM analysis and prop-
erties of CPs of the intramolecular hydrogen bond that is
formed between the oxygen atom labeled O8 and the H–
N3 bond (see Fig. 1). The value of q(r) at the bond CP is
ꢂ
and the S1–S1A sigma antibond orbital ðr Þ. The sec-
(2)
SꢁS
(
2)
ond-order energy (DE ) lowering computed for each
ꢂ
LP
N
! r
interaction is DE = 6.87 kcal/mol. The
SꢁS
NBO analysis also indicates an interaction between a
lone pair of sulfur atoms S1 and S1A and the C16A–
S2A and C16–S2 sigma antibond orbitals, respectively.
ꢁ
2
2
.707 · 10 a.u., which is comparable to the value
obtained for the Nꢀ ꢀ ꢀS bond CP indicating that the
strength of the Nꢀ ꢀ ꢀS non-covalent interaction is compara-
ble to the N–Hꢀ ꢀ ꢀO hydrogen bond. This result stresses the
importance of these interactions which have a significant
effect on the final geometry of the compound.
(2)
! rꢂ inter-
The DE lowering computed for each LP
S
CꢁS
(2)
action is DE = 5.32 kcal/mol. These results of energy
lowering are in agreement with the values of charge den-
sity computed at the bond CPs obtained from the AIM
analysis which indicate that in 9 the strength of the
Nꢀ ꢀ ꢀS interactions is higher than the strength of the
Sꢀ ꢀ ꢀS interactions.
We have also analyzed the non-covalent interaction
from another point of view. We have used the natural
bond orbital (NBO) method to understand which orbitals
are involved in the interaction and the energetic contribu-
tion to the stabilization of the molecule in terms of
donor–acceptor interactions. The results obtained from
the second order perturbation theory analysis of NBO
donor–acceptor interactions that involve the atoms that
4. Conclusion
In summary, we have synthesized six new bis(thiocar-
bamoyl) disulfides derivatives. In one case, crystals suit-
able for X-ray spectroscopy analysis have been
obtained. Several non-covalent Nꢀ ꢀ ꢀS and Sꢀ ꢀ ꢀS interac-
tions have been observed in the solid state and the phys-
ical nature of these interactions has been analyzed using
DFT calculations and AIM and NBO analyses. The
AIM analysis confirms the formation of these interactions
through the presence of bond and ring CPs. The com-
puted values of charge density at the bond CPs give
emphasis to the importance and strength of such interac-
tions. From the NBO analysis, we learn that the interac-
tion can be explained by means of electron donation from
lone pairs of N and S atoms to sigma antibond S–S and
S–C orbitals, respectively.
Acknowledgement
Authors (J.S. and Z.B.) thank the Polish State Commit-
tee for Scientific Research for financial support of this
work (Grant No. 2 P05F 01026). We thank the DGICYT
of Spain (Project CTQ2005-08989-01) for financial
support. We thank the Centre de Supercomputaci o´ de
Catalunya (CESCA) for computational facilities. A.F.
and D.Q. thank the MEC for ‘Ram o´ n y Cajal’ and ‘Juan
de la Cierva’ contracts, respectively.
Fig. 3. Representation of the location of the (3,ꢁ1) CPs (white circles)
and (3,+1) CPs (black circles) originated from the Nꢀ ꢀ ꢀS and Sꢀ ꢀ ꢀS
interactions.

J. S a˛ czewski et al. / Chemical Physics Letters 422 (2006) 234–239
239
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