New 7-arylpiperazinylalkyl-8-morpholin-4-yl-purine-2,6-dione derivatives with anxiolytic activity - Synthesis, crystal structure and structure-activity study

Article abstract of DOI:10.1016/j.molstruc.2014.03.018

On the basis of our earlier studies with serotonin (5-HT) receptor ligands in the group of long-chain arylpiperazines (LCAPs), a new series of 7-arylpiperazinylalkyl-8-morpholin-4-yl-purine-2,6-dione derivatives (5-12) has been designed, synthesised and studied in vitro for their affinity for 5-HT _1A, 5-HT_2A, 5-HT₆ and 5-HT₇ receptors. The introduction of o-OCH₃ and m-Cl into the phenylpiperazinyl moiety as well as the elongation of the linker between purine-2,6-dione core and arylpiperazine fragment modified the affinity for the tested 5-HT receptors. The structures of compounds 9-11 (hydrochloride salts) were confirmed by an X-ray diffraction method. All molecules adopted a different conformation in the crystal. The strongest observed type of interaction is a charge assisted hydrogen bond N⁺-H?Cl^-. Additionally, the π-π interactions between 1,3-dimethyl-3,7-dihydropurine- 2,6-dione cores of the neighbouring molecules were also observed. As it is observed in the presented crystal structures, the morpholine ring (a potential donor and acceptor of the hydrogen bonds) seems to be an attractive substituent, that may support binding to the non-specific sites of 5-HT receptors. Another interesting feature is the mutual orientation of rings in the arylpiperazine fragment, with plausible influence on ligand-receptor recognition. For compound 10, with strong 5-HT_1A binding affinity, the mutual orientation of rings is determined by the intramolecular weak C-H?O hydrogen bond. This observation may contribute to a better understanding of the more selective binding of o-OCH₃ arylpiperazine derivatives to the 5-HT_1A receptor.

Full text of DOI:10.1016/j.molstruc.2014.03.018

Journal of Molecular Structure 1067 (2014) 243–251
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
New 7-arylpiperazinylalkyl-8-morpholin-4-yl-purine-2,6-dione
derivatives with anxiolytic activity – Synthesis, crystal structure
and structure–activity study
a
a
a
b
c
_
_
´
Grazyna Chłon-Rzepa , Paweł Zmudzki , Maciej Pawłowski , Anna Wesołowska , Grzegorz Satała ,
c
d
d,
⇑
´
´
Andrzej J. Bojarski , Mateusz Jabłonski , Justyna Kalinowska-Tłuscik
a Department of Medicinal Chemistry, Jagiellonian University, Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
b Department of Clinical Pharmacy, Jagiellonian University, Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
c Department of Medicinal Chemistry, Institute of Pharmacology, Polish Academy of Science, 12 Sme˛tna Street, 31-343 Kraków, Poland
d Department of Crystal Chemistry and Crystal Physics, Faculty of Chemistry, Jagiellonian University, 3 Ingardena Street, 30-060 Kraków, Poland
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
Synthesis and biological activity of
new ligands of the 5-HT receptors are
reported.
ꢀ
Conformation and interactions were
studied with results of X-ray single
crystal experiment.
9
10
ꢀ
ꢀ
Hydrogen bond motives observed,
differ for presented crystal structures.
Mutual rings orientation in
arylpiperazine moiety determine the
selective binding to 5-HT.
11ns
11s
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 January 2014
Received in revised form 11 March 2014
Accepted 12 March 2014
Available online 19 March 2014
On the basis of our earlier studies with serotonin (5-HT) receptor ligands in the group of long-chain
arylpiperazines (LCAPs), a new series of 7-arylpiperazinylalkyl-8-morpholin-4-yl-purine-2,6-dione deriv-
atives (5–12) has been designed, synthesised and studied in vitro for their affinity for 5-HT1A, 5-HT2A, 5-
HT6 and 5-HT7 receptors. The introduction of o-OCH3 and m-Cl into the phenylpiperazinyl moiety as well
as the elongation of the linker between purine-2,6-dione core and arylpiperazine fragment modified the
affinity for the tested 5-HT receptors. The structures of compounds 9–11 (hydrochloride salts) were con-
firmed by an X-ray diffraction method. All molecules adopted a different conformation in the crystal. The
strongest observed type of interaction is a charge assisted hydrogen bond N+–HÁ Á ÁClÀ. Additionally, the
Keywords:
Long-chain arylpiperazines
Purine-2,6-dione derivatives
5-HT receptor ligands
X-ray structure analysis
p–p interactions between 1,3-dimethyl-3,7-dihydropurine-2,6-dione cores of the neighbouring
molecules were also observed. As it is observed in the presented crystal structures, the morpholine ring
(a potential donor and acceptor of the hydrogen bonds) seems to be an attractive substituent, that may
support binding to the non-specific sites of 5-HT receptors. Another interesting feature is the mutual ori-
entation of rings in the arylpiperazine fragment, with plausible influence on ligand-receptor recognition.
For compound 10, with strong 5-HT1A binding affinity, the mutual orientation of rings is determined by
the intramolecular weak C–HÁ Á ÁO hydrogen bond. This observation may contribute to a better under-
standing of the more selective binding of o-OCH3 arylpiperazine derivatives to the 5-HT1A receptor.
Ó 2014 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel.: +48 12 663 22 68; fax: +48 12 634 05 15.
E-mail address: kalinows@chemia.uj.edu.pl (J. Kalinowska-Tłus´cik).
http://dx.doi.org/10.1016/j.molstruc.2014.03.018
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

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244
[12]. 1,3-Dimethyl-8-morpholin-4-yl-3,7-dihydropurine-2,6-dione
Introduction
(2) was obtained from 1 according to the previously described
method [13] 7-(3-chloropropyl)-1,3-dimethyl-8-morpholin-4-yl-
3,7-dihydropurine-2,6-dione (3) and new 7-(4-chlorobutyl)-1,3-di-
Arylpiperazine is a core fragment of many bioactive com-
pounds, exhibiting a wide variety of psychotropic activity (antipsy-
chotic, anxiolytic, antidepressant, procognitive) including
compounds being investigated under clinical trials [1]. The most
thoroughly studied group of arylpiperazine derivatives are the
one called long-chain arylpiperazines (LCAPs) which have been
recognised as 5-HT receptor ligands, particularly 5-HT1A, 5-HT2
and 5-HT7 ones [2–5]. Their general chemical structure contains
an alkyl chain (two to four methylene units) attached to the N4
atom of the piperazine moiety and a terminal amide or an imide
fragment. For several years we have been interested in developing
LCPAs containing 1,3-dimethyl-3,7-dihydropurine-2,6-dione as a
terminal fragment. This has enabled the selection of potent 5-
HT1A, 5-HT2A and 5-HT7 receptor ligands displaying potential
anxiolytic and/or antidepressant activity [6–11]. Recently, we have
reported on a series of new 7-arylpiperazinylalkyl derivatives of 8-
alkoxy-purine-2,6-dione as potent 5-HT receptors’ ligands with 5-
HT1A agonist properties [9]. To continue our research, we have
designed a new series of 7-arylpiperazinyl-1,3-dimethyl-3,7-pur-
ine-2,6-dione with a morpholine moiety in the 8-position. In com-
parison to the previous work [9], present modification introduced a
more electron rich cyclic amine (morpholine) system having less
hydrophobic nature.
Herein we report on a synthesis of the designed new series of
differently substituted arylpiperazines (R = H, o-OCH3, m-Cl), con-
nected by three or four methylene linker to the purine-2,6-dione
with morpholine in 8 position, their in vitro evaluation for 5-
HT1A, 5-HT2A, 5HT6 and 5-HT7 receptors and the X-ray structure
analysis of selected, the most pharmacologically interesting com-
pounds. We also wished to determine a potential impact of the
morpholine moiety on molecular properties and conformation,
by analysis of the intermolecular interactions, mostly C–HÁ Á ÁO
hydrogen bond patterns. We also focused on arylpiperazine frag-
ment responsible for pharmacological activity of LCAPs. Hence
the main aim was to establish the influence of a kind of substituent
in the arylpiperazine moiety on the mutual orientation of both
rings which seems to be very interesting in searching for new
selective 5-HT1A and/or 5-HT2A receptor ligands.
methyl-8-morpholin-4-yl-3,7-dihydropurine-2,6-dione
4
were
prepared in a reaction of 2 with 1-bromo-3-chloropropane or 1-
bromo-4-chlorobutane according to the previously described
method [14]. The designed purine-2,6-dione derivatives were syn-
thesised by nucleophilic substitution of 3 or 4 with the appropriate
phenylpiperazines in the presence of K2CO3, yielding final com-
pounds 5–12, which were directly isolated from the reaction mix-
tures as hydrochloride salts.
7-(4-chlorobutyl)-1,3-dimethyl-8-morpholin-4-yl-3,7-dihydropurine-
2,6-dione (4)
Yield 88%, m.p. 111–113 °C, Rf 0.69 (A), 1H NMR d: 1.73–1.80 (m,
2H, –CH2–CH2–Cl); 2.01–2.04 (m, 2H, N7–CH2–CH2–CH2–),
3.21–3.24 ((m, 4H, N(CH2–CH2)2O); 3.18 (s, 3H, N1–CH3);
3
3.53 (s, 3H, N3–CH3); 3.57 (t, J = 6.5 Hz, 2H, CH2–CH2–Cl); 3.83–3.86
(m, 4H, N(CH2–CH2)2O); 4.14 (t, 3J = 7.3 Hz, 2H, N7–CH2). Anal.
(C15H22ClN5O3) C, H, N. LC/MS: m/z calcd. for C15H22ClN5O3
[M + H]+: 356.14, found: 356.28.
A general procedure for preparing 7-phenylpiperazin-1-yl-alkyl-1,3-
dimethyl-8-morpholin-4-yl-3,7-dihydropurine-2,6-diones
hydrochlorides (5–12)
Equimolar amounts (50 mmol) of the appropriate 7-chloroal-
kyl-8-morpholin-4-yl-purine-2,6-dione derivatives (3 and 4) and
the respective phenylpiperazine derivatives (1-phenylpiperazine,
1-(2-methoxyphenyl)-piperazine, 1-(3-chlorophenyl)-piperazine
or 1-(4-fluorophenyl)-piperazine), and 100 mmol anhydrous
K2CO3 were refluxed in propan-1-ol (10 ml) for 30 h. The mixtures
was filtered off and the solvent was evaporated under reduced
pressure, yielding free bases which were then converted into the
hydrochloride salts by treatment with an excess of conc. HCl in
an acetone solution. Hydrochloride salts were purified by crystalli-
sation from anhydrous ethanol.
1,3-Dimethyl-8-(morpholin-4-yl)-7-[3-(4-phenylpiperazin-1-yl)
propyl]-3,7-dihydropurine-2,6-dione hydrochloride (5)
Yield 62%; m.p. 226–227 °C; Rf = 0.18 (A); 1H NMR d: 2.20–2.51
(m, 2H, CH2CH2CH2), 2.95–3.21 (m, 10H, CH2N(CH2CH2)2NPh,
N(CH2CH2)2O), 3.18 (s, 3H, N1CH3), 3.38 (s, 3H, N3CH3), 3.43–3.61
(m, 4H, N(CH2CH2)2NPh), 3.73–3.81 (m, 4H, N(CH2CH2)2O), 4.18
(t, 3J = 7.1 Hz, 2H, N7CH2), 6.83 (t, 3J = 7.3 Hz, 1H, 4-Ph), 6.95 (d,
3J = 8.0 Hz, 2H, 2,6-Ph), 7.23 (t, 3J = 8.0 Hz, 2H, 3,5-Ph), 10.44 (s,
1H, H+); Anal. (C24H33N7O3ÁHCl) C, H, N. LC/MS: m/z calcd. for
Experimental
Methods
Melting points (m.p.) were determined in open glass capillaries
with Büchi-540 melting point apparatus and are uncorrected. 1H
NMR spectra were taken with a Varian Mercury-VX (300 MHz)
spectrophotometer in DMSO solution. Chemical shifts are ex-
pressed in d (ppm), and the coupling constants, J, are given in Hertz
(Hz). LC/MS analyses were obtained with the Waters Acquita TQD
apparatus. The purity of the compound were routinely checked by
thin layer chromatography (TLC) using Kieselgel 60 F254 sheets
using the following eluents: A: methylene chloride/metha-
nol = 95:5, v/v, B: methylene chloride/methanol = 90:10, v/v. Spots
were detected under UV light. Elemental analyses were deter-
mined with an Elementar Vario EL III apparatus and were within
0.4% of the theoretical values.
C
24H33N7O3 [M + H]+: 468.27, found: 468.36.
7-{3-[4-(2-Methoxyphenyl)piperazin-1-yl]propyl}-1,3-dimethyl-
(8-morpholin-4-yl)-3,7-dihydropurine-2,6-dione hydrochloride (6)
Yield 64%; m.p. 266–267 °C; Rf = 0.16 (A); 1H NMR d: 2.23–2.25
(m, 2H, CH2CH2CH2), 2.97–3.19 (m, 10H,, CH2N(CH2CH2)2NPh,
N(CH2CH2)2O), 3.20 (s, 3H, N1CH3), 3.38 (s, 3H, N3CH3), 3.40–3.61
(m, 4H, N(CH2CH2)2NPh), 3.73–3.76 (m, 4H, N(CH2CH2)2O), 3.76
(s, 3H, OCH3), 4.18 (t, 3J = 7.1 Hz, 2H, N7CH2), 6.87–7.02 (m, 4H,
Ph), 10.78 (s, 1H, H+); Anal. (C25H35N7O4ÁHCl) C, H, N. LC/MS: m/z
calcd for C25H35N7O4 [M + H]+: 498.28, found: 498.32.
Chemical synthesis and characterisation
7-{3-[4-(3-Chlorophenyl)piperazin-1-yl]propyl}-1,3-dimethyl-8-
(morpholin-4-yl)-3,7-dihydropurine-2,6-dione hydrochloride (7)
Yield 68%; m.p. 248–249 °C; Rf = 0.21 (A); 1H NMR d: 2.23–2.25
(m, 2H, CH2CH2CH2); 3.10–3.21 (m, 13H, N1CH3, CH2N(CH2CH2)2NPh,
N(CH2CH2)2O), 3.33–3.38 (s, 3H, N3CH3), 3.50–3.53 (m, 2H,
N(CH2CH2)2NPh), 3.74–3.76 (m, 4H, N(CH2CH2)2O), 3.85–3.89 (m,
The investigated compounds (5–12) were obtained by multi-
step procedure according to Scheme 1.
The starting 8-bromo-1,3-dimethyl-3,7-dihydro-purine-2,6-
dione (1) was synthesised by a procedure published elsewhere

´
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O
O
O
(CH2)n Cl
N
H
N
H
N
H3C
O
H3C
O
H3C
O
N
N
3 n = 3
4 n = 4
N
N
N
N
a
b
Br
1
O
N
O
N
N
N
N
N
CH3
2
CH3
CH3
R
9 R = H
n = 4
5 R = H
n = 3
N
O
N
(CH2)n
N
10 R = o-OCH3 n = 4
6 R = o-OCH3 n = 3
H3C
O
N
N
11 R = m-Cl
12 R = p-F
n = 4
n = 4
x HCl
7 R = m-Cl
n = 3
n = 3
c, d
N
O
8 R = p-F
CH3
Scheme 1. Reagents and conditions: (a) morpholine, n-BuOH, reflux; (b) 1-bromo-3-chloropropane or 1-bromo-4-chlorobutane, K2CO3, TEBA, (CH3)2CO, reflux;
(c) 1-arylpiperazine, n-PrOH, K2CO3, reflux and (d) conc. HCl, (CH3)2CO.
2H, N(CH2CH2)2NPh), 4.16–4.21 (m, 2H, N7CH2), 6.83–6.86 (m, 1H,
4-Ph), 6.92–6.95 (m, 1H, 6-Ph), 6.96–7.03 (s, 1H, 2-Ph), 7.21–7.27
(m, 1H, 5-Ph), 10.79 (s, 1H, H+); Anal. (C24H32ClN7O3ÁHCl) C, H, N.
LC/MS: m/z calcd for C24H32ClN7O3 [M + H]+: 502.23, found: 502.33.
7-{4-[4-(4-Fluorophenyl)piperazin-1-yl]butyl}-1,3-dimethyl-8-
(morpholin-4-yl)-3,7-dihydropurine-2,6-dione hydrochloride (12)
Yield 61%; m.p. 217–218 °C; Rf = 0.82 (B); 1H NMR d: 1.67–1.82
(m, 4H, CH2CH2CH2CH2), 3.05–3.20 (m, 13H, N1CH3,
CH2N(CH2CH2)2NPh, N(CH2CH2)2O), 3.38 (s, 3H, N3CH3), 3.47–3.68
(m, 4H, N(CH2CH2)2O), 3.72–3.76 (m, 4H, N(CH2CH2)2NPh),
4.09–4.14 (m, 2H, N7CH2), 6.99–7.11 (m, 4H, Ph), 10.61 (s, 1H,
H+); Anal. (C25H34FN7O3ÁHCl) C, H, N. LC/MS: m/z calcd for
C25H34FN7O3 [M + H]+: 500.27, found: 500.12.
7-{3-[4-(4-Fluorophenyl)piperazin-1-yl]propyl}-1,3-dimethyl-8-
(morpholin-4-yl)-3,7-dihydropurine-2,6-dione hydrochloride (8)
Yield 69%; m.p. 251–252 °C; Rf = 0.32 (A); 1H NMR d: 2.25–2.29
(m, 2H, CH2CH2CH2), 3.02–3.11 (m, 6H, CH2N(CH2CH2)2NPh), 3.16–
3.19 (m, 4H, N(CH2CH2)2O), 3.20 (s, 3H, N1CH3), 3.38 (s, 3H, N3CH3),
3.38–3.48 (m, 4H, N(CH2CH2)2O), 3.51–3.78 (m, 4H, N(CH2CH2)2-
NPh), 4.18 (t, 3J = 6.8 Hz, 2H, N7CH2), 6.96–7.10 (m, 4H, Ph);
10.56 (s, 1H, H+); Anal. (C24H32FN7O3ÁHCl) C, H, N. LC/MS: m/z calcd
for C24H32FN7O3 [M + H]+: 486.26, found: 486.38.
The elemental C, H, N analyses of compounds 4–12 are
presented in Supplementary Materials (Table 1A).
X-ray structure determination and refinement
Crystals of 9–11 were obtained by slow evaporation of the solvent
under ambient conditions from propan-2-ol: water mixture in ratio
of 4:1. Two crystal forms of compound 11 were obtained. Crystals of
11ns were unstable, clarity being lost over time upon exposure to air.
Several re-crystallisations of 11 under the same conditions resulted
in obtaining more stable crystals marked in this paper as 11s. Both
alternative structures of 11 have been presented in this paper, due
to the observed difference in the molecular conformation. X-ray dif-
fraction data for all but 11ns crystals were collected using Nonius
1,3-Dimethyl-(8-morpholin-4-yl)-7-[4-(4-phenylpiperazin-1-yl)
butyl]-3,7-dihydropurine-2,6-dione hydrochloride (9)
Yield 70%; m.p. 229–231 °C; Rf = 0.23 (A); 1H NMR d: 1.68–1.79
(m, 4H, CH2CH2CH2CH2), 3.04–3.20 (m, 13H, N1CH3,
CH2N(CH2CH2)2NPh, N(CH2CH2)2O), 3.37 (s, 3H, N3CH3), 3.46–3.50
(m, 2H, N(CH2CH2)2NPh), 3.72–3.79 (m, 4H, N(CH2CH2)2O),
4.07–4.13 (m, 4H, N7CH2, N(CH2CH2)2NPh), 6.82–6.87 (m, 1H,
4-Ph), 6.96–6.99 (m, 2H, 2,6-Ph), 7.22–7.27 (m, 2H, 3,5-Ph), 10.94
(s, 1H, H+); Anal. (C25H35N7O3ÁHCl) C, H, N. LC/MS: m/z calcd for
Brucker KappaCCD diffractometer with Mo
Ka
radiation
(k = 0.71073 Å), with the software COLLECT [15]. Data were pro-
cessed with HKL SCALEPACK [16] and HKL DENZO [16]. For the crys-
tal of 11ns intensities were collected using SuperNova
C
25H35N7O3 [M + H]+: 482.28, found: 482.30.
diffractometer with Mo Ka radiation (k = 0.71073 Å). Data were pro-
cessed with CrysAlis PRO [17]. Experiments were performed at
293(2) K for all but 9. For the last mentioned compound the temper-
ature was 130(2) K. The phase problem was solved by direct meth-
ods with SHELXS-97 [18]. The model parameters were refined by
full-matrix least-squares on F2 using SHELXL-97 [18]. All non hydro-
gen atoms were refined anisotropically. H atoms attached to basic
nitrogen N15 were located on the difference Fourier map and refined
without restraints for 9 and 11ns and with isotropic displacement
parameter Uiso[H] = 1.2 Ueq[N15] in case of structures 10 and 11s.
The hydrogen atoms of water molecules in structures 10 and 11s
were located on the difference Fourier map and refined with Uiso[-
H] = 1.5 Ueq of the parent atom. For 10 and 11ns the water hydrogen
treatment was different due to the observed disorder of the solvent
molecule. The hydrogen positions for mentioned molecules were
determined with CALC-OH [19] program by combined geometric
and force-field calculations on the basis of hydrogen-bonding inter-
actions. Displacement parameters for these hydrogen atoms were
refined with Uiso[H] equal 1.2 Ueq or 1.5 Ueq for 10 and 11ns, respec-
tively. For all presented structures, DFIX and DANG restrains were
applied on bond lengths and angles to approximate water geometry.
Positions of hydrogens attached to C atoms were calculated
with C–H = 0.93 Å for aromatic, C–H = 0.97 Å for methylene,
7-{4-[4-(2-Methoxyphenyl)piperazin-1-yl]butyl}-1,3-dimethyl-8-
(morpholin-4-yl)-3,7-dihydropurine-2,6-dione hydrochloride (10)
Yield 67%; m.p. 196–198 °C; Rf = 0.27 (A); 1H NMR d: 1.64–1.88
(m, 4H, CH2CH2CH2CH2), 2.98–3.18 (m, 10H, CH2N(CH2CH2)2NPh,
N(CH2CH2)2O), 3.20 (s, 3H, N1CH3), 3.37 (s, 3H, N3CH3), 3.44–3.54
(m, 4H, N(CH2CH2)2NPh), 3.72–3.75 (m, 4H, N(CH2CH2)2O), 3.76
(s, 3H, OCH3), 4.11 (t, 3J = 6.2 Hz, 2H, N7CH2), 6.85–7.00 (m, 4H,
Ph), 10,38 (s, 1H, H+); Anal. (C26H37N7O4ÁHCl) C, H, N. LC/MS: m/z
calcd for C26H37N7O4 [M + H]+: 512.29, found: 512.10.
7-{4-[4-(3-Chlorophenyl)piperazin-1-yl]butyl}-1,3-dimethyl-8-
(morpholin-4-yl)-3,7-dihydropurine-2,6-dione hydrochloride (11)
Yield 64%; m.p. 224–225 °C; Rf = 0.86 (B); 1H NMR d: 1.65–1.78
(m, 4H, CH2CH2CH2CH2), 3.10–3.17 (m, 10H, CH2N(CH2CH2)2NPh,
N(CH2CH2)2O), 3.19 (s, 3H, N1CH3), 3.37 (s, 3H, N3CH3), 3.44–3.48
(m, 4H, N(CH2CH2)2NPh), 3.72–3.76 (m, 4H, N(CH2CH2)2O), 4.10
(t, 3J = 7.1 Hz, 2H, N7CH2), 6.85 (d, 3J = 7.7 Hz, 1H, 6-Ph), 6.92 (d,
3J = 7.6 Hz, 1H, 4-Ph), 7.02 (s, 1H, 2-Ph); 7.24 (t, 3J = 8.1 Hz, 1H,
5-Ph); Anal. (C25H34ClN7O3ÁHCl) C, H, N. LC/MS: m/z calcd for
C
25H34ClN7O3 [M + H]+: 516.24, found: 516.36.

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246
C–H = 0.96 Å for methyl groups and were refined using the riding
model with the isotropic displacement parameter Uiso = 1.2 Ueq
and Uiso = 1.5 Ueq (methyl groups only) of the parent atom.
The methyl groups in the 1,3-dimethyl-3,7-dihydropurine-2,6-
dione fragment of structures 10 and 11s were modelled as rotating,
with site occupancy set as 0.5 for both alternative positions. In
structures 10 and 11ns an additional disorder is observed for water
molecule and, in the case of the unstable structure, also for chlo-
ride anion. For 10 the site occupancy of a solvent molecule was re-
fined with 0.2:0.8. For 11ns the disorder is most probably related
to low stability of the crystal. The site occupancies for disordered
water molecule and chloride anion were refined separately but
achieved the same ratio equal 0.4:0.6.
affinity for the 5-HT1A and 5-HT7 receptors as compared with the
unsubstituted compounds 5 and 9. The elongation of the linker
between purine-2,6-dione core and arylpiperazine fragment from
three to four carbon generally increase the affinity for tested 5-
HT receptors.
On the basis of radioligands binding studies 9–11 derivatives
were selected for behavioral evaluations in order to established
their potential as antidepressant and anxiolytic compounds
in the forced swim (FST) and the four-plate (FPT) tests in
mice, respectively [10]. Among them 7-{4-[4-(3-chlorophenyl)
piperazin-1-yl]butyl}-1,3-dimethyl-8-(morpholin-4-yl)-3,7-dihydro-
purine-2,6-dione hydrochloride (11), a mixed 5-HT1A/5-HT2A
ligand with moderate 5-HT7 and 5-HT6 affinity revealed specific
anxiolytic, but not antidepressant, activity in mice. This com-
pound, administered at a dose of 5 mg/kg, significantly and
comparable to diazepam used as a reference drug, increased
the number of punished crossing in FPT [10].
All crystallographic data for presented structures are shown in
Table 1.
WinGX [20] software was used to prepare materials for publica-
tion. The figures showing asymmetric units and unit cell packing
of presented structures were made with ORTEP-3 for Windows
[21]. The figure presenting structural motives were made with
Mercury [22] and the superposition of molecules was prepared
with PyMOL [23]. For calculation of the weighted least-squares
planes through selected atoms program PARST [24,25] was used.
The crystallographic study of the investigated 7-aryl-
piperazinylalkyl-8-morpholin-4-yl-purine-2,6-diones has been
presented for the very first time, allowing search for structural
features which could help to explain the observed differences
within the chosen 5-HT receptors affinities. This in turn will sup-
port the future designing of more selective 5-HT receptor ligands.
In vitro radioligand binding assays
Comparative structural analysis
Radioligand binding assays were employed for determining the
affinity and selectivity profile of the synthesized compounds 5–12
for native 5-HT1A and 5-HT2A, receptors, as well as for cloned hu-
man 5-HT6 and 5-HT7 ones according to the previously published
procedures [5,9,26].
The crystal structures of four LCAPs derivatives in the
hydrochloride form with terminal 8-morpholin-4-yl-1,3-di-
methyl-3,7-dihydropurine-2,6-dione fragment (9, 10 and 11) were
solved and refined. The last mentioned compound occurs in two
alternative crystal forms (11ns, 11s). The diversity in molecular
geometry was investigated in order to find explanation for differ-
ent affinity of tested compounds to selected receptors. A molecular
structure in crystals of 9–11 presenting the atom labelling scheme
is shown in Fig. 1.
Results and discussion
In vitro radioligand binding assay results
The radioligand binding assay results presented in Table 2 have
conclusively proven that the introduction of o-OCH3 and m-Cl into
the phenylpiperazine moiety (6, 7, 10 and 11) leads to higher
Despite apparent similarities within compared molecules, they
adopt different conformations in the crystal (Fig. 2). The most pe-
culiar conformation is observed for compound 10 (yellow in Fig. 2),
Table 1
Crystal data and structure refinement.
Identification code
9
10
11ns
11s
Molecular formula
Formula weight
Crystal system
[C25H36N7O3]+ClÀ, 2H2O
554.09
Monoclinic
C2/c
[C26H38N7O4]+ClÀ, H2O
566.10
Monoclinic
[C25H35ClN7O3]+ClÀ, 2H2O
588.53
Monoclinic
[C25H35ClN7O3]+ClÀ, H2O
570.52
Monoclinic
Space group
P21/a
C2/c
P21/a
Unit cell dimensions
a = 37.5559(7) Å
b = 7.7608(2) Å
c = 18.9313(5) Å
b = 92.189(1)°
5513.8(2)
a = 14.5313(3) Å
b = 10.8374(2) Å
c = 19.5677(4) Å
b = 109.984(1)°
2896.0(1)
a = 36.255(4) Å
b = 9.7224(8) Å
c = 18.4333(19) Å
b = 112.432(12)°
6005.8(10)
a = 14.3021(4) Å
b = 10.8224(2) Å
c = 20.4734(6) Å
b = 113.335(2)°
2909.73(13)
4
1.302
0.266
1208
Volume [Å3]
Z
8
4
8
Dcalc [g/cm3]
Absorption coefficient [mmÀ1
F(000)
1.335
0.187
2368
0.20 Â 0.20 Â 0.10
2.88–27.47
À48 6 h 6 48,
À9 6 k 6 10,
À24 6 l 6 24
21,539
1.298
0.180
1208
1.302
0.262
2496
]
Crystal size [mm3]
h range [°]
0.50 Â 0.20 Â 0.20
0.20 Â 0.20 Â 0.10
0.30 Â 0.30 Â 0.20
2.80–26.34
3.29–28.49
2.41–26.75
Index ranges
À18 6 h 6 17,
À13 6 k 6 13,
À24 6 l 6 24
34,558
À48 6 h 6 47,
À13 6 k 6 12,
À24 6 l 6 20
16,911
À17 6 h 6 18,
À13 6 k 6 13,
À25 6 l 6 25
34,770
Reflections collected
Independent reflections
6302
5884
6838
6168
[R(int) = 0.0473]
99.9%
0.9815 and 0.9635
6302/11/362
1.040
R1 = 0.0488, wR2 = 0.1341
R1 = 0.0726, wR2 = 0.1484
0.305/À0.649
[R(int) = 0.1016]
99.6%
0.9649 and 0.9155
5884/14/372
1.013
R1 = 0.0502, wR2 = 0.1292
R1 = 0.0697, wR2 = 0.1409
0.411/À0.344
[R(int) = 0.1480]
98.7%
1.0000 and 0.4270
6838/10/394
0.961
R1 = 0.0709, wR2 = 0.2054
R1 = 0.1391, wR2 = 0.2414
0.558/À0.345
[R(int) = 0.1448]
99.8%
0.9488 and 0.9245
6168/4/352
1.074
R1 = 0.0706, wR2 = 0.1699
R1 = 0.1057, wR2 = 0.1911
0.703/À0.376
Completeness to h = 27.47°
Tmax. and Tmin.
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
Dq max/Dq ]
max [e ÅÀ3

´
247
G. Chłon-Rzepa et al. / Journal of Molecular Structure 1067 (2014) 243–251
Table 2
Binding affinity of the investigated 7-arylpiperazinylalkyl-8-morpholin-4-yl-purine-
2,6-dione derivatives 5–12 for 5-HT receptors.
Compound
Ki (nM)
5-HT1A
5-HT2A
5-HT6
5-HT7
5
6
7
8
9
10
11
12
233
32
28
140
1750
137
68
22,400
21,240
19,430
12,250
3958
6104
207
1782
5730
596
736
1168
1277a
335a
112a
1940
1171
138a
7a
77a
205a
22a
500
21a
127
a
Data taken from Ref. [10].
Fig. 2. Superposition of molecules 9 (blue), 10 (yellow), 11ns (magenta) and 11s
(orange) with respect to piperazine atoms, presenting conformations in the crystal
structures. (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
which among all the presented derivatives is the most potent, but
also most selective ligand of 5-HT1A receptor. It is interesting that
compound 11, with anxiolytic, but not antidepressant activity
evaluated in behavioural models in mice [10], is three times less
active for 5-HT1A receptor than 10. At the same time, this m-Cl
derivative demonstrates the highest binding affinity of all other
5-HT receptors tested (especially nearly equal affinities for 5-
HT1A and 5-HT2A). This may suggest a more flexible nature of the
m-Cl phenylpiperazine fragment, which allows easier adaptation
to the receptor’s binding site and, in consequence, the multi-recep-
tor activity. In case of compound 10, the o-OCH3 substituted phe-
nylpiperazine moiety exhibits conformational preferences,
resulting in more specific binding to 5-HT1A receptor. It may be re-
lated to the chemical and steric nature of the substituent. A weak
hydrogen bond C–HÁ Á ÁO formed between one of the methylene
group of the piperazine and oxygen within a methoxy group may
stabilise mutual orientation of the arylpiperazine rings.
For presented crystal structures, the spacer linking terminal 8-
morpholin-4-yl-1,3-dimethyl-3,7-dihydropurine-2,6-dione
and
arylpiperazine fragments consists of four methylene groups. The
linker adopts elongated form with torsion angles which are found
to vary near the values 170° among the individual molecules (see
Table 3 for the exact values). Analysis of similar structures found in
the Cambridge Crystallographic Database (CSD) [27] shows that
extended conformation of the tetramethylene chain is favourable.
Sixteen structures were selected, for which the linker between
arylpiperazine and the opposite cyclic moiety (aromatic or
9
10
11ns
11s
Fig. 1. Molecular geometry of crystal structures, showing the atom labelling scheme. Dashed lines represent a charge-assisted hydrogen bond N+–HÁ Á ÁClÀ. In 10, the weak
intramolecular hydrogen bond C–HÁ Á ÁO is additionally distinguished. Displacement ellipsoids of non-hydrogen atoms are drawn at the 30% probability level. H atoms are
presented as small spheres with an arbitrary radius. Water molecules and disordered methyl groups were deleted for the figure clarity.

´
G. Chłon-Rzepa et al. / Journal of Molecular Structure 1067 (2014) 243–251
248
aliphatic) consists of tetramethylene aliphatic chain only (for Ref-
codes see Table 2A in Supplementary Materials). All but 3 selected
CSD structures (CCDC ID: OFAZIE, OFAZOK [28] and BAMGED [29])
are in the extended conformation. The detailed study on the influ-
ence of conformation and length of the aliphatic linker on bioactiv-
ity was already widely discussed in the literature [30–34]. It was
postulated that the tetramethylene chain in extended geometry
is observed in structures of the most potent LCAPs’ derivatives
and thus this conformation is considered as the bioactive one.
Considering high flexibility and molecular similarity, the
presented LCAP derivatives could adopt nearly identical conforma-
tions within receptor molecule, leading to corresponding binding
affinities. However, the observed differences (Table 2) suggest
various conformational preferences. The change in the binding
affinities for compound 9, 10 and 11 is most probably related to
the diverse electronic properties of the substituted (10 and 11)
and unsubstituted (9) aromatic ring of the arylpiperazine moiety,
influencing the mutual orientation of both rings. The electron
withdrawing effect of the chloro substituent is evident in the
shortening of N18–C21 bond length and increasing C17–N18–
C19 angle, whereas the electron donating effect of the methoxyl
group is reflected in elongation of this bond and decreasing C17–
N18–C19 angle, in comparison to unsubstituted arylpiperazine
derivative (Table 3).
The inter-correlated position of piperazine and aromatic rings
of the LCAPs may play a crucial role in ligand-receptor recognition.
It is especially evident for o-OCH3 derivative (10), with strong 5-
HT1A binding affinity (Table 2), where the mutual orientation of
both mentioned rings is very well conserved among all o-OCH3
substituted structures found in the CSD (see Table 3A in Supple-
mentary Materials). This conservative conformation is related to
the intramolecular weak hydrogen bond formation between aryl-
piperazine methylene group as a donor (equatorial hydrogen
atom) and oxygen atom of the methoxy group as an acceptor
(Fig. 1, Table 4). Such interaction causes additional distortion
among piperazine moiety, reflected in N18–C19 bond elongation
in comparison to the other presented structures. This preferred ori-
entation is an interesting molecular feature which may allow
selective ligand–receptor recognition.
Among all studied m-Cl substituted arylpiperazines in the CSD
(for Refcodes see Table 4A in Supplementary Materials), the mutual
orientation of considered rings is less conserved. This higher rota-
tional freedom with strong electron withdrawing properties of the
substituent, allows less selective and multireceptor profile of the
ligand. Due to its wider spectrum of binding to CNS receptors,
among all presented structures only compound 11 is a promising
drug, the most potent 5-HT1A and 5-HT2A ligand.
The strongest type of interaction observed in presented
structures is the charge assisted hydrogen bond N+–HÁ Á ÁClÀ
(Fig. 1; Table 4). In the neutral pH of the tissue, the basic atom
N15 of the piperazine ring is protonated. The acquired positive
charge is crucial for tight salt bridge formation between this nitro-
gen and carboxyl group of the well conserved Asp residue in the
third transmembrane helix of the monoaminergic receptors [35].
The protonation of the nitrogen atom in presented crystal struc-
tures changes the properties of carbon atoms in the ring, allowing
weak hydrogen bond formation of C–HÁ Á ÁO, C–HÁ Á ÁN and C–HÁ Á ÁCl
type (Table 4).
Different type of interactions which governs the crystal packing
of the presented structures (see Figs. 1A–4A in Supplementary
Materials for unit cells packing in the structures 9–11) are strong
hydrogen bonds, in which water molecules are involved (Table 4).
The observed hydrogen bond motives differ for all presented
structures (Fig. 3). The solvent molecule creates interesting
patterns in the crystal lattice. In all structures water molecules
form the strong hydrogen bond O–HÁ Á ÁClÀ. For structures 11ns
and 11s water-induced dimers are observed, formed by molecules
related via inversion centre (Fig. 3). The additional water molecule
in the crystal structure of 11ns is a hydrogen bond donor with the
carbonyl oxygen atom of the terminal aromatic fragment acting as
Table 3
Selected geometrical values for structures 9, 10, 11ns and 11s [Å and °].
Compound
Compound
9
N(7)–C(8)
N(7)–C(5)
N(7)–C(10)
N(18)–C(21)
N(18)–C(19)
N(18)–C(17)
C8–N81–C86
C8–N81–C82
1.362(3)
1.397(2)
1.471(2)
1.423(3)
1.462(3)
1.465(3)
117.0(2)
120.4(2)
110.8(2)
115.9(2)
116.2 (2)
109.4(2)
164.4(2)
171.5(2)
175.6(2)
11ns
N(7)–C(8)
N(7)–C(5)
N(7)–C(10)
N(18)–C(21)
N(18)–C(17)
N(18)–C(19)
C8–N81–C86
C8–N81–C82
1.358(3)
1.400(3)
1.456(3)
1.422(3)
1.449(4)
1.463(3)
118.2(2)
115.6(2)
111.1(3)
118.0(2)
117.4(2)
111.5(2)
179.2(2)
171.2(2)
À175.2(2)
C86–N81–C82
C86–N81–C82
C(21)–N(18)–C(19)
C(21)–N(18)–C(17)
C(19)–N(18)–C(17)
N(7)–C(10)–C(11)–C(12)
C(10)–C(11)–C(12)–C(13)
C(11)–C(12)–C(13)–N(15)
C(21)–N(18)–C(17)
C(21)–N(18)–C(19)
C(17)–N(18)–C(19)
N(7)–C(10)–C(11)–C(12)
C(10)–C(11)–C(12)–C(13)
C(11)–C(12)–C(13)–N(15)
10
N(7)–C(8)
N(7)–C(5)
N(7)–C(10)
N(18)–C(21)
N(18)–C(17)
N(18)–C(19)
C(8)–N(81)–C(82)
C(8)–N(81)–C(86)
C(82)–N(81)–C(86)
C(21)–N(18)–C(17)
C(21)–N(18)–C(19)
C(17)–N(18)–C(19)
N(7)–C(10)–C(11)–C(12)
C(10)–C(11)–C(12)–C(13)
C(11)–C(12)–C(13)–N(15)
1.354(2)
1.393(2)
1.467(2)
1.434(2)
1.461(2)
1.472(2)
114.1(2)
114.8(2)
110.5(2)
114.9(1)
113.5(1)
109.1(2)
166.5(2)
À172.7(2)
167.5(2)
11s
N(7)–C(8)
N(7)–C(5)
N(7)–C(10)
N(18)–C(21)
N(18)–C(17)
N(18)–C(19)
C(8)–N(81)–C(85)
C(8)–N(81)–C(82)
C(85)–N(81)–C(82)
C(21)–N(18)–C(17)
C(21)–N(18)–C(19)
C(17)–N(18)–C(19)
N(7)–C(10)–C(11)–C(12)
C(10)–C(11)–C(12)–C(13)
C(11)–C(12)–C(13)–N(15)
1.356(3)
1.394(3)
1.463(3)
1.410(3)
1.462(4)
1.462(3)
114.7(2)
114.3(2)
110.1(2)
116.0(2)
118.1(2)
110.2(2)
À166.1(2)
173.0(2)
À164.2(2)

´
249
G. Chłon-Rzepa et al. / Journal of Molecular Structure 1067 (2014) 243–251
Table 4
Strong and weak hydrogen bonds geometry for structures 9, 10, 11ns and 11s [Å and °].
Compound
D–HÁ Á ÁA
d(D–H)
d(HÁ Á ÁA)
d(DÁ Á ÁA)
<(DHA)
9
N(15)–H(15)Á Á ÁCl(1)
0.87(3)
0.84(2)
0.84(2)
0.94(2)
0.97(2)
0.97
2.24(3)
2.37(2)
2.39 (2)
1.86(2)
1.94(2)
2.59
3.105(2)
3.199(2)
3.225(2)
2.703(3)
2.889(3)
3.525(3)
3.681(2)
3.538(2)
171(2)
168(3)
172(3)
147(3)
167(5)
163
O(1W)–H(1WB)Á Á ÁCl(1)
O(1W)–H(1WA)Á Á ÁCl(1)_1
O(2W)–H(2WA)Á Á ÁO(1W)
O(2W)–H(2WB)Á Á ÁO(1)_2
C(17)–H(17A)Á Á ÁO(1W)_3
C(19)–H(19B)Á Á ÁCl(1)_4
C(20)–H(20B)Á Á ÁN(18)_5
0.97
0.97
2.87
2.61
142
161
10
N(15)–H(15)Á Á ÁCl(1)
0.96(2)
0.853(9)
0.852(9)
0.895(9)
0.893(9)
0.97
2.10(2)
2.43(1)
2.32 (2)
2.42(4)
2.46(2)
2.87
3.057 (2)
3.276(4)
3.139(4)
2.99(1)
3.28(1)
3.31(2)
2.94(2)
175(2)
172(6)
160(5)
122(4)
154(3)
108
O(1WB)–H(1WB)Á Á ÁCl(1)_6
O(1WB)–H(2WB)Á Á ÁCl(1)_7
O(1WA)–H(2WA)Á Á ÁCl(1)_6
O(1WA)–H(1WA)Á Á ÁO(3)_8
C(16)–H(16B)Á Á ÁCl(1)_7
C(19)–H(19A)Á Á ÁO3(1)a
0.97
2.32
121
11ns
N(15)–H(15)Á Á ÁCl(2A)
0.89(3)
0.89(3)
0.82(1)
0.82(1)
0.82(1)
0.82(1)
0.82(1)
0.82(1)
0.82(1)
0.97
2.22(3)
2.20(3)
2.53(8)
2.53(8)
2.07(5)
2.58(1)
2.20(7)
2.20(5)
2.89(11)
2.645
3.08(1)
3.088(5)
3.21(1)
3.21(1)
2.86(1)
2.89(1)
2.961(9)
2.990(7)
3.51(2)
3.57(1)
162(3)
175(3)
N(15)–H(15)Á Á ÁCl(2B)
O(1W)–H(1W)Á Á ÁCl(2A)
O(1W)–H(1W)Á Á ÁCl(2A)
O(2WA)–H(1WA)Á Á ÁO(1W)
O(1W)–H(2W)Á Á ÁO(1W)_9
O(2WA)–H(2WA)Á Á ÁO(2)_9
O(2WB)–H(2WB)Á Á ÁO(2)_9
O(2WB)–H(1WB)Á Á ÁCl(2B)_9
C(17)–H(17A)Á Á ÁO(2WA)_10
142(12)
142(12)
161(14)
104.6(7)
155(15)
163(16)
134(12)
159
11s
N(15)–H(15)Á Á ÁCl(2)
0.874(10)
0.834(10)
0.832(10)
0.97
2.17(2)
2.26(3)
2.54(2)
2.54
3.043(2)
3.082(7)
3.361(7)
3.28(1)
173(8)
168(13)
168(10)
133
O(1W)–H(2W)Á Á ÁCl(2)
O(1W)–H(1W)Á Á ÁCl(2)_11
C(16)–H(16B)Á Á ÁO(1W)_12
a
Intramolecular C–HÁ Á ÁO hydrogen bond; Symmetry transformations used to generate equivalent atoms: _1: Àx + 1/2, Ày + 3/2, Àz; _2: x + 1/2, y + 1/2, z; _3: x, yÀ1, z; _4:
Àx + 1/2, yÀ1/2, Àz + 1/2; _5: Àx + 1/2, y + 1/2, Àz + 1/2; _6: xÀ1/2, Ày + 1/2, z; _7: Àx + 1/2, y + 1/2, Àz _8: Àx, Ày + 1, Àz; _9: Àx + 1/2, Ày + 1/2, Àz; _10: x, Ày, z + 1/2; _11:
Àx + 1, Ày + 1, Àz + 2; _12: Àx + 1/2, y + 1/2, Àz + 2.
9
10
11ns
11s
Fig. 3. Hydrogen bond motives in crystal structures of presented derivatives. Hydrogen atoms not involved in the hydrogen bond patterns were removed for figure clarity.

´
G. Chłon-Rzepa et al. / Journal of Molecular Structure 1067 (2014) 243–251
250
an acceptor. Dimers are observed in the crystal structure of 9, in
which the second water molecule forms a hydrogen bond with
the 1,3-dimethyl-3,7-dihydropurine-2,6-dione moiety, addition-
arylpiperazine fragment is related to the intramolecular weak C–
HÁ Á ÁO hydrogen bond formation. This preferential orientation of
rings in o-OCH3 substituted arylpiperazine may be the key to
understanding the more selective binding of compound 10 to the
5-HT1A receptor. Similar conformation of arylpiperazine moiety is
allowed, but not observed, in the crystal structure of the m-Cl
derivative 11. Flexibility within the arylpiperazine’s mutual orien-
tation of rings in this compound results in less selective binding
mode to 5-HT receptors, but at the same time allowing multi-
receptor profile.
ally stabilising the molecules involved in
p–p interaction (Fig. 3).
In the crystal of 10, a water molecule interacts with an oxygen
atom of the methoxy group of the neighbouring molecule related
via 21 parallel to [010].
Another observed type of interaction occurs between
p systems
of terminal purine ends with the shortest interatomic distances be-
tween parallel rings 3.4–3.6 Å. It is interesting, that the aromatic
ring of the arylpiperazine moiety does not form this type of inter-
action in all structures, but only observed in structure 11ns. In this
last mentioned structure, the 3-chlorophenyl fragment interacts
strongly with six-member ring of the purine-2,6-dione, with the
shortest interatomic distance 3.35 Å. Overlapping of aromatic rings
is shown in the crystal packing projections presented in Figs. 1A,
2A and 4A and the parallel orientation of rings in Fig. 3A (Supple-
mentary Materials).
The properties of morpholine ring attached to C8 may play an
important role in molecule stabilisation within the binding site
of the receptor. It is observed in the crystal structure, that a strong
hydrogen bond formed by carbonyl oxygen of the purine-2,6-dione
moiety (9 and 11ns) influence the bond length C8–N81, which is
shorter, being 1.372(3) Å and 1.377(3) Å for 9 and 11ns, respec-
tively, whereas for structures 10 and 11s it is 1.397(2) Å and
1.396(3) Å, respectively. The bond angles on N81 are changed (Ta-
ble 3) with a tendency to more planar geometry for structures 9
and 11ns. However, this causes distortions, leading to stronger
deviation of N81 from least-squares planes of the purine-2,6-dione
atoms. All these observations suggest that the withdrawal of elec-
trons, occurring during above mentioned hydrogen bond forma-
tion, is compensated by the morpholine nitrogen lone pair shift
in the aromatic system direction. It is noteworthy, that the mor-
pholine ring is involved in weak hydrogen bonds C–HÁ Á ÁO, both
as donor and acceptor. The electron withdrawing effect in struc-
tures 9 and 11ns makes the morpholine fragment more attractive
and it plays role of a donor in additional weak hydrogen bond for-
Acknowledgment
Financial support for this study was provided by the NCN
funded grant no. UMO-2011/01/B/NZ4/00695.
The research was carried out with the equipment purchased
thanks to the financial support of the European Regional Develop-
ment Fund in the framework of the Polish Innovation Economy
Operational Program (contract no. POIG.02.01.00-12-023/08).
Appendix A. Supplementary material
Crystallographic data for the structures in this paper have been
deposited with the Cambridge Crystallographic Data Centre as sup-
plementary publication nos. CCDC 928727 (9), CCDC 928728 (10),
CCDC 928729 (11ns) and CCDC 928730 (11s). Copies of the data
can be obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK, (fax: +44 (0)1223 336033 or e-mail:
deposit@ccdc.cam.ac.uk). Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.molstruc.2014.03.018.
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