Structure-property relationship of 3-(4-substituted benzyl)-1,3-diazaspiro[4.4]nonane-2,4-diones as new potentional anticonvulsant agents. An experimental and theoretical study

Article abstract of DOI:10.1016/j.molstruc.2016.07.069

The structure-property relationship of newly synthesized 3-(4-substituted benzyl)-1,3-diazaspiro [4.4]nonane-2,4-diones was studied by experimental and calculated methods. The prepared compounds were characterized by UV-Vis, FT-IR, ¹H NMR and ¹³C NMR spectroscopy and elemental analysis. The crystal structure was elucidated by single-crystal X-ray diffraction. The 3-benzyl-1,3-diazaspiro[4.4]nonane-2,4-dione crystallizes in triclinic P?1 space group, with two crystallographically independent molecules in the asymmetric unit. Cyclopentane ring adopts an envelope conformation. A three-dimensional crystal packing is governed by hydrogen N?H?O bonds, numerous C?H?O/N and C–H … π interactions between neighboring molecules. Density functional theory (DFT) calculations with B3LYP and M06-2X methods using 6–311++G(d,p) basis set were performed to provide structural and spectroscopic information. Comparisons between experimental and calculated UV-Vis spectral properties suggest that the monomeric form of the investigated spirohydantoins is dominant in all used solvents. The effects of substituents on the absorption spectra of spirohydantoins are interpreted by correlation of absorption frequencies with Hammett equation. The lipophilicities of the investigated molecules were estimated by calculation of their log P values. Some of the spirohydantoins synthesized in this work, exhibit the lipophilicities comparable to the standard medicine anticonvulsant drug Phenytoin. The results obtained in this investigation afford guidelines for the preparation of new derivatives of spirohydantoin as potential anticonvulsant agents and for better understanding the structure-activity relationship.

Full text of DOI:10.1016/j.molstruc.2016.07.069

Journal of Molecular Structure 1127 (2017) 88e98
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Structure-property relationship of 3-(4-substituted benzyl)-1,3-
diazaspiro[4.4]nonane-2,4-diones as new potentional anticonvulsant
agents. An experimental and theoretical study
a
a
b
b
c
ꢁ
Anita M. Lazi ꢀc , Bojan Ð. Bo ꢁz i ꢀc , Vesna D. Vitnik , Zeljko J. Vitnik , Jelena R. Rogan ,
d
a
a, *
Lidija D. Radovanovi ꢀc , Nata ꢁs a V. Valenti ꢀc , Gordana S. U ꢁs ꢀc umli ꢀc
Department of Organic Chemistry, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia
Department of Chemistry, Institute of Chemistry, Technology and Metallurgy, University of Belgrade, Studentski trg 12-16, 11001 Belgrade, Serbia
Department of General and Inorganic Chemistry, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia
Innovation Centre, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia
a
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 April 2016
Received in revised form
The structure-property relationship of newly synthesized 3-(4-substituted benzyl)-1,3-diazaspiro [4.4]
nonane-2,4-diones was studied by experimental and calculated methods. The prepared compounds were
characterized by UV-Vis, FT-IR, 1H NMR and C NMR spectroscopy and elemental analysis. The crystal
structure was elucidated by single-crystal X-ray diffraction. The 3-benzyl-1,3-diazaspiro[4.4]nonane-2,4-
dione crystallizes in triclinic Pꢀ1 space group, with two crystallographically independent molecules in
the asymmetric unit. Cyclopentane ring adopts an envelope conformation. A three-dimensional crystal
13
15 July 2016
Accepted 15 July 2016
Available online 25 July 2016
packing is governed by hydrogen NꢀH/O bonds, numerous CꢀH/O/N and CeH …
p interactions be-
Keywords:
tween neighboring molecules. Density functional theory (DFT) calculations with B3LYP and M06-2X
methods using 6e311þþG(d,p) basis set were performed to provide structural and spectroscopic in-
formation. Comparisons between experimental and calculated UV-Vis spectral properties suggest that
the monomeric form of the investigated spirohydantoins is dominant in all used solvents. The effects of
substituents on the absorption spectra of spirohydantoins are interpreted by correlation of absorption
frequencies with Hammett equation. The lipophilicities of the investigated molecules were estimated by
calculation of their log P values. Some of the spirohydantoins synthesized in this work, exhibit the lip-
ophilicities comparable to the standard medicine anticonvulsant drug Phenytoin. The results obtained in
this investigation afford guidelines for the preparation of new derivatives of spirohydantoin as potential
anticonvulsant agents and for better understanding the structure-activity relationship.
Spirohydantoin
Absorption spectra
Crystal structure
Substituent effect
Quantum chemical calculation
Lipophilicity
©
2016 Published by Elsevier B.V.
1
. Introduction
diphenylhydantoin) [4]. Experimental evidence indicates that spi-
rohydantoin derivatives can be used in treating disorders of central
nervous system, such as epilepsy [5,6] and psychiatric disorders,
like depression [7,8]. Depending on the nature of the substitution
on the hydantoin ring, a wide range of other pharmacological
properties, e.g., antiarrhythmic [9], anti-inflammatory [10], anti-
HIV [11], hypolipidermic [12] and antihypertensive activities [13]
have been identified. Numerous compounds with hydantoin ring
exhibit physiological activity such as serotonin and fibrinogen
antagonist [14], inhibitors of the glycine binding site of the NMDA
receptor [15] also, antagonist of leukocyte cell adhesion, acting as
allosteric inhibitors of the protein-protein interactions [16]. Some
hydantoin derivatives have been identified as antitumor agents
Spirohydantoins and their derivatives represent a pharmaco-
logically important class of heterocycles. Many of them are
important anticonvulsant drugs [1e3]. A substantial structure
fragment of anticonvulsive drugs is defined by a nitrogen hetero-
aromatic system, usually a cyclic imide, at least one carbonyl group
and lipophilic phenyl or alkyl/cycloalkyl substituents attached to
heterocyclic system. This common template is present in the
structure of well known antiepileptic drug, such as Phenytoin (5,5-
*
Corresponding author.
[17,18]. Lipophilic derivatives of hydantoin bearing cycloalkyl,
E-mail address: goca@tmf.bg.ac.rs (G.S. U ꢁs ꢀc umli ꢀc ).
http://dx.doi.org/10.1016/j.molstruc.2016.07.069
022-2860/© 2016 Published by Elsevier B.V.
0

A.M. Lazi ꢀc et al. / Journal of Molecular Structure 1127 (2017) 88e98
89
phenyl or benzhydril substituents show inhibitory activities against
several cancer cell lines [19]. Spiromustine (SHM), which due to its
lipophilicity readily crosses the bloodꢀbrain barrier, is well known
anticancer compound [20]. Its activity is established on the pres-
ence of N,N-bis(2-chloroethyl)amino group which is transported to
the target by a cycloalkanespiro hydantoin ring.
understanding the mechanism of biological activities of investi-
gated compounds as well as their chemical properties.
2. Experimental
2.1. Synthesis of spirohydantoins
The structure-property relationship of spirohydantoins are
interesting in view of the development of novel drugs and for better
understanding their biological activity. As part of our previous
research on the structural characterization and biological activity of
The compounds 1e7 were obtained following the synthetic
protocol shown in Scheme 1. 1,3-Diazaspiro[4.4]nonane-2,4-dione
was synthesized according to the modified procedure of Bucherer
and Lieb [25]. 3-(4-Substituted benzyl)-1,3-diazaspiro[4.4]nonane-
2,4-diones (1e7) were prepared by modification of the method
described previously [26]. Optimal molar proportion of the re-
agents was found to be 1.54 g (0.01 mol) of 1,3-diazaspiro[4.4]
nonane-2,4-dione and 6 g (0.09 mol) of potassium carbonate dis-
solved in 60 ml of dimethylformamide. After half an hour 0.011 mol
of alkyl halide was added in the solution. The reaction mixture was
3
,5-disubstituted-5-phenylhydantoins, a series of four such com-
pounds were synthesized and their anticonvulsant and anti-
proliferative activity described [21e23].
In this work, new series of 3-(4-substituted benzyl)-1,3-
diazaspiro[4.4]nonane-2,4-diones (Fig. 1) was synthesized. The
chemical structure and the purity of the synthesized compounds
1
13
were confirmed by melting point, H and C NMR, FT-IR and UV-
Vis spectra and elemental analysis. The crystal structure of 3-(4-
substituted benzyl)-1,3-diazaspiro[4.4]nonane-2,4-diones was
resolved by single-crystal X-ray diffraction. Crystal packing is
mainly governed by hydrogen NꢀH/O bonds building centro-
ꢁ
heated at 80 C for three days. Obtained product was poured into
three times the volume of water and extracted with 60 ml of ethyl
acetate. The organic layer was washed with 20 ml of 5% sodium
hydroxide and 20 ml of water and dried with the addition of small
amounts of anhydrous magnesium sulphate. Residual solvent is
removed by distillation and the crude product is purified by
recrystallization from ethyl acetate. The data obtained during
characterization are given below.
symmetric R2
(8) dimmers that stabilize the crystal lattice. The ef-
2
fects of substituents on the absorption spectra of spirohydantoins
are interpreted by correlation of absorption frequencies with
Hammett equation [24]. Density functional theory (DFT) calcula-
tions, with B3LYP and M06-2X methods using 6e311þþG(d,p)
basis set, have been performed to support our spectroscopic and
structural properties of investigated spirohydantoins. The elec-
tronic absorption spectra were calculated and compared with the
experimental results. The UV-Vis spectroscopic studies along with
frontier molecular orbital (FMO) analysis have been used to eluci-
date information regarding charge transfer within the molecule.
The stability of the investigated spirohydantoins arising from
hyperconjugative interactions has been studied by using the Nat-
ural Bond Orbital (NBO) analysis. To estimate chemical and bio-
logical activity of the molecule log P values were calculated for the
optimized geometries of the investigated spirohydantoins. Under-
standing the relationship between the activity, structure and
physicochemical properties of various compounds provides the
opportunity to identify features that are important for the activity
and to identity potential bioactive compounds. Thus, structural and
electronic information, presented in this study, is relevant to
2.1.1. 3-Benzyl-1,3-diazaspiro[4.4]nonane-2,4-dione (1)
ꢁ
White crystalline solid; Yield 66%; m.p.: 87e90 С; IR (KBr,
n
/
ꢀ1
1
cm ): 3238 (NH), 1768 (C]O), 1711 (C]O); H NMR (200 MHz,
DMSO-d /ppm): 8.59 (s, 1H, N(1)H), 7.37e7.20 (m, 5H, C ), 4.53
(s, 2Н, eCH ); C NMR (50 MHz, DMSO-
/ppm): 177.7 (C4), 155.8 (C2), 137.2 (C11), 128.8 (C13,C15), 127.6
(C14), 127.4 (C12,C16), 67.5 (С5), 41.6 (С10), 37.4 (С6,С9), 24.9
(С7,С8). Anal. calcd. for C14 (244.30): C, 68.83; H, 6.60; N,
6
,
d
6 5
H
13
2
5 8
e), 1.99e1.68 (m, 8H, C H
6
d , d
16 2 2
H N O
11.47. Found (%): C, 68.80; H, 6.62; N, 11.43.
2.1.2. 3-(4-Methylbenzyl)-1,3-diazaspiro[4.4]nonane-2,4-dione (2)
ꢁ
White crystalline solid; Yield: 57%; m.p.: 141e143 C; IR (KBr,
n
/
ꢀ1
1
cm ): 3216 (NH), 1772 (C]O), 1706 (C]O); H NMR (200 MHz,
DMSO-d /ppm): 8.56 (s, 1H, N(1)H), 7.13 (s, 4H, C ), 4.48 (s, 2H,
eCH e), 2.12 (s, 3H, eCH ), 1.91e1.67 (m, 8H, C
(50 MHz, DMSO-d /ppm): 177.6 (C4), 155.8 (C2), 136.8 (C14),
34.2 (C11), 129.3 (C13,C15), 127.5 (C12,C16), 67.5 (C5), 41.00 (C10),
7.4 (C6,C9), 24.9 (C7,C8), 20.9 (C17). Anal. calcd. for C15
258.32): C, 69.74; H, 7.02; N, 10.84. Found (%): C, 69.80; H, 7.03; N,
6
,
d
6 4
H
13
2
3
5 8
H ); C NMR
6
, d
1
3
(
18 2 2
H N O
10.89.
2.1.3. 3-(4-Methoxybenzyl)-1,3-diazaspiro[4.4]nonane-2,4-dione
(
3)
ꢁ
.1.4White crystalline solid; Yield: 56%; m.p.: 96e98 C; IR (KBr,
2
ꢀ
1
1
n
/cm ): 3216 (NH), 1771 (C]O), 1706 (C]O); H NMR (200 MHz,
DMSO-d ),
e), 3.72 (s, 3H,
); C NMR (50 MHz, DMSO-d
6
,
d
/ppm): 8.55 (s, 1H, N(1)H), 7.17 (d, 2H, J ¼ 8 Hz, C
6 4
H
6
.89 (d, 2H, J ¼ 10 Hz, C
H
6 4
), 4.45 (s, 2H, eCH
2
1
3
eOCH
3
), 1.94e1.65 (m, 8H, C
5
H
8
6
, d/
ppm): 177.7 (C4), 158.8 (C14), 155.9 (C2), 129.2 (C11), 129.0
(
(
C12,C16), 114.2 (C13,C15), 67.5 (C5), 55.3 (C17), 40.7 (C10), 37.4
C6,C9), 24.9 (C7,C8). Anal. calcd. for C15 (274.32): C, 65.68;
18 2 3
H N O
H, 6.61; N, 10.21. Found (%): C, 65.78; H, 6.65; N, 10.15.
2
.1.4. 3-(4-Chlorobenzyl)-1,3-diazaspiro[4.4]nonane-2,4-dione (4)
ꢁ
White crystalline solid; Yield: 62%; m.p.: 128e131 C; IR (KBr,
n
/
ꢀ1
1
cm ): 3211 (NH), 1771 (C]O), 1711 (C]O); H NMR (200 MHz,
DMSO-d ),
e), 1.92e1.74 (m, 8H,
/ppm): 177.7 (C4), 155.6 (C2),
6
,
d
/ppm): 8.61 (s, 1H, N(1)H), 7.40 (d, 2H, J ¼ 10 Hz, C
), 4.53 (s, 2H, eCH
); C NMR (50 MHz, DMSO-d
6 4
H
Fig. 1. Chemical structures of the investigated 3-(4-substituted benzyl)-1,3-diazaspiro
7
C
.24 (d, 2H, J ¼ 10 Hz, C
6
H
4
2
[
(
4.4]nonane-2,4-diones where X is: H (1); CH
7).
3 3 2
(2); OCH (3); Cl (4); Br (5); CN (6); NO
1
3
5
H
8
6
, d

90
A.M. Lazi ꢀc et al. / Journal of Molecular Structure 1127 (2017) 88e98
Scheme 1. Synthesis of 3-(4-substituted benzyl)-1,3-diazaspiro[4.4]nonane-2,4-diones.
136.1 (C11), 132.3 (C14), 129.4 (C12,C16), 128.8 (C13,C15), 67.6 (C5),
2.3. X-ray structure determination
4
2 2
0.6 (C10), 37.4 (C6,C9), 24.8 (C7,C8). Anal. calcd. for C14H15ClN O
(
1
278.74): C, 60.33; H, 5.42; N, 10.05. Found (%): C, 60.40; H, 5.45; N,
0.00.
Single colorless crystals of compound 1 suitable for X-ray
diffraction measurement were grown from ethyl acetate by slow
evaporation in ambient conditions for 24 h. Single crystal X-ray
diffraction data were collected at room temperature (293 K) on an
Oxford Gemini S diffractometer equipped with CCD detector using
2
.1.5. 3-(4-Bromobenzyl)-cyclopentanespiro-5-hydantoin (5)
ꢁ
White crystalline solid; Yield: 68% m.p.: 162e165 C; IR (KBr, n/
cm ): 3216 (NH), 1768 (C]O), 1709 (C]O); 1H NMR (200 MHz,
DMSO-d ),
e), 1.92e1.75 (m, 8H,
/ppm): 177.6 (C4), 155.6 (C2),
ꢀ1
monochromatized Mo K
were corrected for absorption using the multi-scan method. The
a
radiation (
l
¼ 0.71073 Å). Intensities
6
,
d
/ppm): 8.61 (s, 1H, N(1)H), 7.54 (d, 2H, J ¼ 8 Hz, C
), 4.51 (s, 2H, eCH
); C NMR (50 MHz, DMSO-d
6
H
4
7
C
.20 (d, 2H, J ¼ 8 Hz, C
6
H
4
2
structure was solved by direct methods (SIR92) [27] and refined on
1
3
2
H
5 8
6
, d
F by full-matrix least-squares using the programs SHELXL-97 [28]
1
4
(
36.6 (C11), 131.7 (C13,C15), 129.8 (C12,C16), 120.7 (C14), 67.6 (C5),
0.7 (C10), 37.4 (C6,C9), 24.8 (C7,C8). Anal. calcd. for C14 15BrN
323.19): C, 52.03; H, 4.68; N, 8.67. Found (%): C, 52.10; H, 4.70; N,
and WinGX [29]. All non-hydrogen atoms were refined anisotrop-
ically. Positions of H atoms connected to the C atoms were calcu-
lated on geometric criteria and refined using the riding model with
H
2 2
O
8
.70.
U
iso ¼ 1.2Ueq(C). Hydrogen atoms bonded to N1A and N1B in 1 were
found in F maps and added to the structural model before the final
D
2
.1.6. 3-(4-Cyanobenzyl)-1,3-diazaspiro[4.4]nonane-2,4-dione (6)
cycle of refinement with fixed positional and atomic displacement
parameters. Selected crystal data and refinement results for 1 are
listed in Table 1. The figures were produced with Mercury [30].
Crystallographic data for 1 are deposited at the Cambridge Crys-
tallographic Data Centre with CCDC reference number 1404431.
ꢁ
White crystalline solid; Yield: 52%; m.p.: 154e157 C; IR (KBr, n/
cm ): 3310 (NH), 2232 (CN), 1758 (C]O), 1708 (C]O); 1H NMR
200 MHz, DMSO-d /ppm): 8.65 (s, 1H, N(1)H), 7.81 (d, 2H,
J ¼ 8 Hz, C ), 7.40 (d, 2H, J ¼ 8 Hz, C ), 4.62 (s, 2H, eCH e),
.97e1.74 (m, 8H, C ); C NMR (50 MHz, DMSO-d /ppm):
77.7 (C4), 155.5 (C2), 142.7 (C11), 132.8 (C13,C15), 128.2 (C12,C16),
18.9 (C17), 110.5 (C14), 67.7 (C5), 40.9 (C10), 37.4 (C6,C9), 24.8
C7,C8). Anal. calcd. for C15 (269.31): C, 66.90; H, 5.61; N,
ꢀ1
(
6
, d
H
6 4
6
H
4
2
13
1
1
1
(
H
5 8
6
, d
2.4. Computational details
15 3 2
H N O
All the density functional theory (DFT) calculations were per-
15.60. Found (%): C, 67.00; H, 5.65; N, 15.57.
formed using Gaussian 09 program package [31] at the B3LYP [32]
and M06-2X [33] level with 6e311þþG(d,p) basis set. The geom-
etries of the investigated spirohydantoins were fully optimized
with the DFT B3LYP/6e311þþG(d,p) method. The validity of the
2
.1.7. 3-(4-Nitrobenzyl)-1,3-diazaspiro[4.4]nonane-2,4-dione (7)
ꢁ
Yellow crystalline solid; Yield: 72%; m.p.: 139e142 C; IR (KBr,
n
/
ꢀ
1
1
cm ): 3111 (NH), 1768 (C]O), 1709 (C]O); H NMR (200 MHz,
DMSO-d ),
e), 1.99e1.65 (m, 8H,
/ppm): 177.7 (C4), 155.5 (C2),
6
,
d
/ppm): 8.67 (s, 1H, N(1)H), 8.21 (d, 2H, J ¼ 10 Hz, C
), 4.67 (s, 2H, eCH
); C NMR (50 MHz, DMSO-d
6 4
H
7
C
.49 (d, 2H, J ¼ 8 Hz, C
6
H
4
2
Table 1
1
3
H
5 8
6
,
d
Crystal data and structure refinements for 1.
1
4
(
1
47.1 (C14), 144.7 (C11), 128.6 (C12,C16), 124.1 (C13,C15), 67.7 (C5),
0.8 (C10), 37.4 (C6,C9), 24.8 (C7,C8). Anal. calcd. for C14
289.29): C, 58.13; H, 5.23; N, 14.53. Found (%): C, 58.05; H, 5.20; N,
4.57.
Compound
1
15 3 4
H N O
Formula
C
14 16 2 2
H N O
Formula weight (g molꢀ1)
Crystal system
Space group
a (Å)
244.29
Triclinic
Pe1
5.976 (1)
12.801 (3)
17.604 (4)
106.51(3)
91.33 (3)
92.01 (3)
1289.6 (4)
4
2.2. Spectral measurements
b (Å)
c (Å)
The chemical structure of the synthesized compounds (1e7)
ꢁ
a
b
g
( )
1
13
was confirmed by instrumental methods. H and C nuclear
magnetic resonance (NMR) spectra were recorded on a Varian
Gemini 200 spectrometer on 200 MHz and 50 MHz respectively.
The spectra were recorded at room temperature in DMSO-d . The
6
chemical shifts are expressed in ppm values in reference to TMS.
Fourier-transform infrared spectra (FT-IR) were recorded on a
Bomem MB 100 spectrophotometer (
form of KBr pellets. The absorption spectra were measured with a
Shimadzu 1700 spectrophotometer. The UV-Vis spectra were taken
in spectroquality solvents (Fluka) at
1
ꢁ
( )
ꢁ
( )
3
V (Å )
Z
m
(mm 1
ꢀ
)
0.085
520
1.258
F (000)
ꢀ3
r
c
(g cm
)
ꢀ
1
n
max are given in cm ) in the
Range of h, k, l
Reflections collected/unique
Data/restraints/parameters
ꢀ6 / 7; ꢀ15 / 15; ꢀ21 / 12
8309/5073
2252/0/333
0.0376
R
R
int
a
concentration of
(I)]a
R indices [I > 2
R indices (all data)
s
1
¼ 0.0569; wR ¼ 0.1234
2
ꢀ5
ꢀ3
$10 mol dm and showed no dependence on the concentration.
R1 ¼ 0.1357; wR2 ¼ 0.1609
The elemental analyses of the investigated compounds were car-
ried out by standard analytical micromethods using an Elemental
Vario EL III microanalyzer.
GOOF
Drmax
0.922
Drmin (e Å 3
ꢀ
)
0.174, 0.208
,
a
2
2
2
2
2
w ¼ 1/[s (F
o
) þ (0.0520P) ] where P ¼ (F
o
þ 2F
c
)/3.

A.M. Lazi ꢀc et al. / Journal of Molecular Structure 1127 (2017) 88e98
91
optimized geometry was confirmed by frequency calculations,
which gave real values for all the obtained frequencies, and used for
the further investigations.
The UV-Vis absorption energies of the investigated compounds
were calculated by TD-DFT B3LYP and M06-2X methods in ethanol
as solvent. The effect of solvent on the theoretical electronic pa-
rameters of the investigated spirohydantoins was included using
conductor polarisable continuum model (CPCM) [34]. The frontier
molecular orbital energies and HOMO-LUMO energy gaps were
calculated with the same methods.
The Natural Bonding Orbital (NBO) calculations were performed
using NBO 3.1 program [35] as implemented in the Gaussian 09
package. The optimized geometries from DFT calculation were
further used for the estimation of physicochemical descriptors by
applying Vega 22 version 2.4 [36].
The effects of substituent on the absorption spectra of the
investigated spirohydantoins were interpreted by correlation of
absorption frequencies (
(Tables 2 and S1) with Hammett
plot max versus constants gives correlation which shows devi-
ation from the Hammett equation. Different slopes for electron
donor substituents (eOCH , eCH , including H) and electron
n
¼ 1/
l
) for the higher energy band
p
s substituent constants [24]. The
n
s
p
3
3
acceptor substituents (eCl, eBr, eCN, eNO2, including H) were
obtained in all investigated solvents (Fig. 3). Results of correlations
are given in Supplementary Tables S2 and S3. Electron donor sub-
stituents increase the electron density at nitrogen atom in position
ꢀ
þ
3 of hydantoin ring and favours the OꢀC]N resonance structure.
The correlation results were presented by Eq. (1) obtained in all
used solvents:
n
max ¼ 48:71ð±0:200Þ þ 14:06ð±1:083Þ
s
p
(
1)
R ¼ 0:9331; s ¼ 0:627; F ¼ 168; n ¼ 27
3
. Results and discussion
Effect of electron acceptor substituent is opposite to the effect of
local polarization in the amide group of hydantoin, and stabilizes
O]CꢀNꢀ structure. The correlation results were presented by
corresponding Eq. (2):
3.1. Solvent and substituent effects on the experimental UV-Vis
spectral parameters
The ultraviolet absorption spectra of the investigated spi-
rohydantoins (1e7) were recorded in nine solvents in the range
from 200 to 400 nm. The values of the wavelengths corresponding
to the most intense absorption maxima (higher energy band) are
collected in Table 2 (corresponding frequencies are given in
Table S1) and the characteristic spectra in ethanol as solvent is
shown in Fig. 2. Evidently, the absorption spectra show similar
n
max ¼ 48:38 ð±0:272Þ ꢀ 12:17ð±0:568Þ
s
p
(
2)
R ¼ 0:9562; s ¼ 1:115; F ¼ 459; n ¼ 45
These results are in accordance with previous investigations of
the reversal of substituent effects on electronic absorption spectra
of amide-type of molecules [40,41].
experimental features, i.e., there are two peaks corresponding to
3.2. Crystal structure analysis of 1
*
p/p
transitions in the phenyl nucleus and the hydantoin ring. It
-delocalization originates mainly from the
-electron density shift from the substituted benzyl unit, influ-
can be concluded that
p
p
The crystal structure of 1 is presented in Fig. 4. Two chemically
identical, but crystallographically different A and B molecules exist
in the asymmetric unit of 1 (Fig. 4). In both molecules, the cyclo-
pentane rings adopt the envelope conformation with atoms C7A
and C7B displaced by 0.153(5) and 0.163(5) Å, respectively, from the
corresponding planes of the cyclopentane rings. The bond distances
and angles (Table 4) are as expected for compounds containing
hydantoin rings [21] and there are mutually very similar in A and B
molecules, and in a good accordance with the calculated values. The
values of selected torsion angles of 1 are shown in Table 4. These
values are similar with corresponding torsion angles found in ex-
amples of some hydantoin derivatives [21,23]. In the crystal packing
of 1, intermolecular hydrogen NeH/O bonds (Table 3) exist be-
enced by the substituent, to the C]O group of the amide moiety in
the hydantoin ring.
The data from Table 2 confirm that the positions of the UV-Vis
absorption maxima significantly depends on the nature of the
substituent on the phenyl ring and is of lower dependence with
respect to solvent properties. This is characteristic of molecules
with low dipolarity in the ground state, as electronic transitions in
these molecules are associated with intramolecular electron ex-
change [37]. Such compounds include hydantoins [21,23] and
succinimides [38,39], where electron delocalization is possible
between atoms of nitrogen and oxygen, i.e., overlap occurs between
the
p
-electrons of carbonyl groups and a lone pair of an amide
tween neighboring A molecules, as well as between B molecules,
2
nitrogen. The introduction of substituent into the phenyl ring
produced bathochromic shift of absorption maxima, as compared
to the unsubstituted 3-benzyl-1,3-diazaspiro[4.4]nonane-2,4-
dione (1), in all solvents. The spectra of the investigated spi-
rohydantoins were not significantly changed in phosphate buffer.
and make R
2
(8) centrosymmetric dimmers along a-axis (Fig. 5). The
interactions (H
molecules A and B are connected by weak CeH …
p
… Cg distance is 2.960 Å) between H9A1 atom from the cyclo-
pentane ring belonging to the molecule A and phenyl ring from the
molecule B (Fig. 5) and stacking
p … p edge-to-face (T-shaped)
interaction of phenyl rings from molecule A and B (Cg(A) … Cg(B)
ꢁ
distance are 4.717 Å and 4.971 Å; angle between planes is 54.38 ).
Table 2
Furthermore, a three-dimensional framework is achieved through
the numerous CeH/O/N contacts (Table 3) that stabilize the
crystal lattice.
The absorption maxima of the investigated spirohydantoins 1e7 in selected
solvents.
Solvent/Comp. No.
lmax (nm)
1
2
3
4
5
6
7
3.3. Theoretical calculation of optimal geometries and UV-Vis
Methanol
Ethanol
208
207
209
207
206
205
206
206
204
212
212
214
212
212
212
212
212
212
225
225
226
225
226
225
226
226
221
220
221
221
221
221
220
221
221
218
221
219
221
220
220
220
222
221
221
237
237
236
237
237
237
237
237
239
267
266
265
265
266
270
259
269
274
spectral data
1
2
1
-Propanol
-Propanol
-Butanol
The optimized geometrical parameters of investigated com-
pounds (1e7) calculated by B3LYP level with 6e311þþG(d,p) basis
set are listed in Tables 4 and 5. The selected structural parameters of
the experimentally determined geometries (A and B molecules)
and calculated structure of the compound 1, as a representative
example of the synthesized spirohydantoin derivatives, are listed in
Acetonitrile
Hexane
Cyclohexane
Phosphate buffer

92
A.M. Lazi ꢀc et al. / Journal of Molecular Structure 1127 (2017) 88e98
Fig. 2. The absorption spectra of 3-(4-substituted benzyl)-1,3-diazaspiro[4.4]nonane-2,4-diones in ethanol.
experimental conformation 1 (in both molecules) than in opti-
mized conformation 1 (Fig. 6) or in other compounds 2e7 (Table 5).
The main difference between the experimental structures and
structures calculated by the DFT method results from the different
spatial orientation of the benzyl group relative to the spi-
rohydantoin moiety. The deviations can fairly be attributed to the
fact that theoretical calculations were performed on isolated mol-
ecules. The solid-state structure can easily be affected by packing
effects, which modify the geometry of the molecule [42].
The energy difference between most stable geometry of mole-
cule 1 and x-ray geometry of molecule A and B are 1.31 and
1.64 kcal/mol, respectively (the x-ray geometries are fully opti-
mized except torsion angle N3ꢀC10ꢀC11ꢀC12 which is kept frozen
ꢁ
ꢁ
on ꢀ145.9 for A and 171.6 for B molecule). In the x-ray geometry
the phenyl ring of molecule B is identified as acceptor of CeH …
interaction from cyclopentane ring from molecule A, stacking
p
p
Fig. 3. Relationship between nmax and s for the spirohydantoins in all investigated
p
…
solvents.
p
edge-to-face interaction from phenyl ring of molecule A (1-x,-y,-
z) and CeH … interaction from benzyl group of molecule A (1-x,-
y,-z). Energy contribution from a single CH/ bond (0.5e2 kcal/mol)
43] or stacking edge-to-face interaction (~3 kcal/mol) [44] is
p
p
Table 4. These parameters are in accordance with the atom
numbering scheme given in Fig. 6. The optimized geometry of the
compound 1 (Table 4; and Fig. 6) was found to be consistent with
the X-ray crystal structure results. The data given in Tables 4 and 5
have shown that there are no significant differences between bond
lengths, angles and torsion angles. The only difference has been
observed for bigger N3ꢀC10ꢀC11ꢀC12 torsion angle found in
[
p … p
small but the enthalpy of the total interaction may become
appreciable as a result of the interplay of many interactions. Total
energy of these interactions in crystal packing for molecule B can
easily overcome the distortion energy for torsion angle
N3ꢀC10ꢀC11ꢀC12.
The phenyl ring of molecule A is identified as acceptor of

A.M. Lazi ꢀc et al. / Journal of Molecular Structure 1127 (2017) 88e98
93
Table 4
ꢁ
The experimental and calculated values of selected bond lengths (Ǻ), bond angles ( )
and torsion angles ( ) for compound 1.
ꢁ
Parameters
Molecule A (X-ray)
Molecule B (X-ray)
1 (calc.)
Bond lengths
N1ꢀC2
1.334 (4)
1.450 (4)
1.221 (3)
1.398 (4)
1.368 (4)
1.200 (4)
1.518 (5)
1.545 (4)
1.537 (5)
1.463 (6)
1.469 (7)
1.455 (7)
1.460 (4)
1.503 (4)
1.375 (5)
1.381 (4)
1.374 (5)
1.378 (5)
1.364 (5)
1.377 (5)
1.335 (5)
1.451 (5)
1.208 (5)
1.396 (4)
1.348 (5)
1.215 (4)
1.518 (5)
1.533 (5)
1.543 (5)
1.493 (7)
1.439 (9)
1.395 (8)
1.445 (4)
1.505 (5)
1.375 (4)
1.386 (4)
1.376 (5)
1.369 (5)
1.374 (5)
1.370 (5)
1.366
1.462
1.212
1.414
1.375
1.212
1.537
1.568
1.554
1.542
1.536
1.535
1.466
1.516
1.399
1.398
1.394
1.394
1.394
1.394
N1ꢀC5
C2ꢀO2
C2ꢀN3
N3ꢀC4
C4ꢀO1
C4ꢀC5
C5ꢀC6
C5ꢀC9
C6ꢀC7
C7ꢀC8
C8ꢀC9
N3ꢀC10
C10ꢀC11
C11ꢀC12
C11ꢀC16
C12ꢀC13
C13ꢀC14
C14ꢀC15
C15ꢀC16
Bond angles
N1ꢀC5ꢀC4
N1ꢀC5ꢀC9
C4ꢀC5ꢀC9
N1ꢀC5ꢀC6
C4ꢀC5ꢀC6
C6ꢀC5ꢀC9
Torsion angles
C4ꢀN3ꢀC10ꢀC11
N3ꢀC10ꢀC11ꢀC12
N1ꢀC5ꢀC6ꢀC7
C4ꢀC5ꢀC6ꢀC7
N3ꢀC4ꢀC5ꢀC9
C11ꢀC10ꢀN3ꢀC2
101.1 (2)
114.5 (2)
111.6 (3)
113.4 (2)
112.3 (2)
104.3 (2)
99.1 (3)
100.6
113.9
112.0
113.4
112.2
104.9
115.1 (3)
111.4 (3)
115.0 (3)
112.6 (3)
104.0 (3)
ꢀ96.3 (4)
ꢀ145.9 (3)
ꢀ130.8 (3)
115.4 (3)
ꢀ121.3 (3)
82.3 (3)
ꢀ84.4 (4)
171.6 (3)
ꢀ145.9 (3)
101.5 (4)
ꢀ119.2 (3)
90.9 (4)
ꢀ90.2
89.6
ꢀ127.1
119.6
ꢀ124.0
90.3
Fig. 4. ORTEP-like representation of asymmetric unit of 1 with atomic numbering
scheme. The thermal ellipsoids are plotted at the 30% probability level and the H atoms
are shown as small spheres of arbitrary radii.
upon changing the substituent X.
The N1ꢀC2 and N3ꢀC4 bond lengths of around 1.36 and 1.37 Å,
respectively, exhibit doubleꢀbond character and indicate strong
stabilizing conjugation of the N1 and N3 atoms with the carbonyl
group. The N3ꢀC10 bond becomes slightly longer (from 1.462 to
Table 3
Geometry of possible hydrogen bonds for 1.
1.467 Å) with increasing electron-donating ability of the benzyl
ꢁ
DeH···A
d(DeH), Å
d(D···A), Å
d(H···A), Å
DeH···A,
substituent X, while the opposite is observed for the C10ꢀC11 bond
(from 1.517 to 1.514 Å). As expected, the bond lengths in the ben-
zene ring depend on the nature of the substituents on the benzyl
group. An electron donor substituent supports an electron density
shift from the benzyl group to the hydantoin moiety and leads to an
increase in bond lengths. The results are quite the opposite for the
electron acceptor substituted compounds.
Mechanism of electronic excitations and changes in the overall
charge distribution in both ground and excited state of the inves-
tigated spirohydantoin derivatives were studied by calculations of
the energy gaps between the HOMO (highest occupied molecular
orbital) and LUMO (lowest unoccupied molecular orbital) orbitals
for the unsubstituted derivative 1 and derivatives having a strong
electron donor 3 and a strong electron acceptor substituent 7 in the
benzyl group. The results are presented in Fig. 7 and Table 6. The
HOMO-LUMO energies were calculated by time-dependent DFT
N1AeH17A$$$O2Ai
0.902
0.780
0.970
0.970
0.970
0.930
0.930
0.930
0.930
0.970
0.970
0.930
0.930
2.869 (4)
2.913 (4)
3.809 (4)
3.758(4)
3.077 (5)
3.453 (5)
3.465 (5)
3.602 (4)
3.263 (4)
3.609 (5)
3.322 (4)
3.250 (4)
2.873 (5)
1.970
2.168
2.881
2.936
2.709
2.578
2.948
2.941
2.539
2.862
2.413
2.512
2.537
174
160
160
143
103
157
117
129
135
135
156
136
102
ii
N1BeH17B/O2B
iii
C6AeH6A1$$$O2A
C6AeH6A1$$$N1A
C9AeH9A1$$$O1A
iii
iv
C13AeH13A$$$O1Bv
iii
C15AeH15A$$$O2A
C16AeH16A$$$O1A
C16AeH16A$$$O2A
iv
iii
vi
C6BeH6B2/O2B
iii
C9BeH9B2/O1B
vii
C13BeH13B/O1A
C16BeH16B/N3B
iv
Symmetry codes. (i): exþ1, eye1, ez; (ii): ex, ey, ezþ1; (iii): xe1, y, z; (iv): x, y, z;
v): exþ1, ey, ez; (vi): exþ1, ey, ezþ1; (vii): xþ1, y, z.
(
stacking
weak CeH …
-x,-y,-z). The lower total enthalpy of these interactions causes the
p
…
p
edge-to-face interaction from phenyl ring and very
(TD-DFT) approach [45].
p
interaction from cyclopentane ring of molecule B
Compound 1 has largest energy gap with 6.26 eV, while some-
(
what smaller energy gaps for compound 3 and 7 with 5.60 and
.82 eV, respectively, were observed (Fig. 7). This is consistent with
lower deviation of torsion angle N3ꢀC10ꢀC11ꢀC12 for molecule A
4
relative to calculated geometry of compound 1.
red shift of their absorption maxima relative to those of 1. Ac-
cording to the calculations, the electron density of the HOMO for
unsubstituted spirohydantoin 1 is shifted toward the central
It can be seen from Tables 4 and 5, that the geometric features of
the substituted derivatives are very similar to those of the unsub-
stituted one. The bonds in the hydantoin ring change very slightly

94
A.M. Lazi ꢀc et al. / Journal of Molecular Structure 1127 (2017) 88e98
Fig. 5. Crystal packing of 1 in bc-plane showing centrosymmetric dimmers. Hydrogen bonds and CeH …
p interactions are represented by dash and dash-dot lines, respectively.
Table 5
ꢁ
The calculated values of selected bond lengths (Å), bond angles ( ) and torsion an-
ꢁ
gles ( ) for compounds 2e7.
Parameters
2
3
4
5
6
7
Bond lengths
N1ꢀC2
1.366
1.461
1.212
1.413
1.375
1.212
1.537
1.567
1.557
1.539
1.535
1.536
1.467
1.515
1.397
1.398
1.393
1.399
1.399
1.392
1.366
1.461
1.212
1.413
1.375
1.212
1.537
1.568
1.555
1.541
1.535
1.535
1.468
1.514
1.402
1.394
1.387
1.400
1.397
1.396
1.364
1.462
1.212
1.415
1.376
1.212
1.536
1.567
1.552
1.545
1.536
1.534
1.465
1.515
1.398
1.398
1.393
1.391
1.391
1.393
1.364
1.462
1.212
1.415
1.376
1.212
1.536
1.566
1.549
1.549
1.538
1.534
1.465
1.515
1.398
1.398
1.394
1.391
1.391
1.393
1.362
1.462
1.212
1.416
1.377
1.212
1.536
1.567
1.552
1.545
1.536
1.534
1.463
1.516
1.399
1.399
1.390
1.402
1.402
1.389
1.362
1.462
1.212
1.416
1.377
1.212
1.536
1.566
1.556
1.542
1.536
1.535
1.462
1.517
1.399
1.400
1.391
1.391
1.391
1.390
N1ꢀC5
C2ꢀO2
C2ꢀN3
N3ꢀC4
C4ꢀO1
C4ꢀC5
C5ꢀC6
C5ꢀC9
C6ꢀC7
C7ꢀC8
C8-C9
N3ꢀC10
C10ꢀC11
C11ꢀC12
C11ꢀC16
C12ꢀC13
C13ꢀC14
C14ꢀC15
C15ꢀC16
Bond angles
N1ꢀC5ꢀC4
N1ꢀC5ꢀC9
C4ꢀC5ꢀC9
N1ꢀC5ꢀC6
C4ꢀC5ꢀC6
C6ꢀC5ꢀC9
Torsion angles
C4ꢀN3ꢀC10ꢀC11
100.6
114.3
111.7
113.5
112.1
104.9
100.6
114.0
111.8
113.5
112.3
104.9
100.6
113.6
112.1
113.5
112.6
104.7
100.7
113.3
112.3
113.5
112.9
104.5
100.6
113.6
112.0
113.4
112.7
104.7
100.6
114.0
111.6
113.3
112.8
104.9
Fig. 6. Optimized conformation of 3-benzyl-1,3-diazaspiro[4.4]nonane-2,4-dione (1).
the LUMO is to a large extent delocalized over the hydantoin and
cyclopentane rings. By contrast, when X is a strongly electron-
accepting substituent (e.g. NO ), the HOMO is uniformly placed
2
over the whole molecule, while the LUMO is mostly localized on the
benzyl acceptor moiety. The energy differences between the HOMO
and LUMO (Table 6) were obtained as 6.29, 5.63 and 4.39 eV in
ethanol and 6.26, 5.60 and 4.82 eV in the gas phase calculations
ꢀ90.4
ꢀ91.0
ꢀ91.1
ꢀ90.0
ꢀ91.0
ꢀ89.6
N3ꢀC10ꢀC11ꢀC12 92.0
89.8
92.1
91.6
92.3
93.9
N1ꢀC5ꢀC6ꢀC7
C4ꢀC5ꢀC6ꢀC7
N3ꢀC4ꢀC5ꢀC9
C11ꢀC10ꢀN3ꢀC2
ꢀ131.7 ꢀ128.8 ꢀ121.6 ꢀ115.8 ꢀ121.6 ꢀ126.4
115.2 117.9 124.9 130.4 124.8 120.1
ꢀ124.2 ꢀ123.9 ꢀ122.5 ꢀ122.0 ꢀ121.9 ꢀ119.4
89.7 88.2 88.7 89.6 89.1 90.3
(compounds 1, 3, and 7, respectively). With these large energy gaps,
it can be concluded that the investigated molecules have high ki-
netic stability and low chemical reactivity.
The UV-Vis absorption energies of all of the investigated spi-
rohydantoins were calculated with B3LYP and M06-2X methods
hydantoin and benzene rings, while the LUMO is spread over the
whole molecule. When substituent X is an electron-donating group
(
3
e.g. OCH ), the HOMO is mostly localized on the benzyl moiety and

A.M. Lazi ꢀc et al. / Journal of Molecular Structure 1127 (2017) 88e98
95
Fig. 7. The molecular orbitals and energy gaps between HOMO and LUMO of compounds 1, 3 and 7 in the gas phase calculations.
Table 6
The computed results show that the HOMO to LUMOþ8 transition
corresponds to the max absorption band in the UV-Vis spectrum.
Calculated energies of the HOMO and LUMO orbitals and energy gap for compound
l
1
e7 in gas phase and ethanol.
The solvent effect was calculated by using TD-DFT method.
Electronic absorption wavelengths calculated by the B3LYP and
M06-2X methods and the experimental values, excitation energy
and oscillator strength of the most significant excited state are
listed in Tables S4 and S5.
No. Gas phase
Ethanol
HOMO (eV)
E
HOMO (eV)
E
LUMO (eV)
E
gap (eV)
E
E
LUMO (eV)
Egap (eV)
1
2
3
4
5
6
7
ꢀ6.98
ꢀ6.67
ꢀ6.19
ꢀ6.90
ꢀ6.83
ꢀ7.45
ꢀ7.68
ꢀ0.69
ꢀ0.63
ꢀ0.59
ꢀ0.91
ꢀ0.95
ꢀ1.84
ꢀ2.86
6.26
6.04
5.60
5.99
5.88
5.61
4.82
ꢀ7.13
ꢀ6.81
ꢀ6.37
ꢀ7.03
ꢀ6.95
ꢀ7.41
ꢀ7.49
ꢀ0.84
ꢀ0.74
ꢀ0.74
ꢀ0.99
ꢀ1.02
ꢀ1.83
ꢀ3.10
6.29
6.07
5.63
6.04
5.93
5.58
4.39
In order to explain these results, the values of experimentally
recorded positions of the UV-Vis absorption maxima of investi-
gated spirohydantoins were correlated with computationally
determined absorption wavelengths (Tables S4 and S5). The better
correlation results were observed between the experimental and
calculated UV-Vis maxima obtained from TD-DFTcalculations using
M06-2X/6e311þþG(d,p) level of theory (Fig. S1, R ¼ 0.9834) than
from the TD-DFT calculations using B3LYP/6e311þþG(d,p) level of
theory (Fig. S2, R ¼ 0.9679). Comparisons between experimental
and calculated UV-Vis spectral properties, suggest that the mono-
meric form of the investigated spirohydantoins is dominant in all
used solvents. The M06-2X method is better than B3LYP method for
prediction UV-Vis spectra of the spirohydantoins and this is in
accordance with the published literature data for the similar
compounds [46,47].
with 6e311þþG(d,p) basis set. The lowꢀlying excited states of the
investigated compounds were obtained based on the fully opti-
mized groundꢀstate structures. The electronic absorption spec-
trum of the compound 3 in ethanol as solvent was recorded within
the 200e400 nm range, and the representative spectrum of
computed transitions plot on the experimental is shown in Fig. 8.
3.4. Natural bond orbitals (NBO) analysis
NBO analysis has been performed on spirohydantoin derivatives
using NBO 3.1 program as implemented in the Gaussian 09 package
at the B3LYP/6e311þþG(d,p) level in order to elucidate intra-
molecular charge transfer and delocalization of electron density
within the molecule. Delocalization of electron density between
occupied Lewis-type (bonding or lone pair) NBO orbitals and
formally unoccupied (antibonding or Rydberg) non-Lewis NBO
orbitals corresponds to a stabilizing donor-acceptor interaction.
The larger the energy of hyperconjugative interactions E (2), the
more intensive is the interaction between the electron donors and
electron acceptors. The important interactions between ‘filled’
Lewis type NBO's-donor (i) and ‘empty’ non Lewis NBO'sꢀacceptor
(j) of spirohydantoin 1 are given in Table 7.
In 3-(4-substituted benzyl)-1,3-diazaspiro[4.4]nonane-2,4-
Fig. 8. Experimental (dashed line) and simulated (full line) UV-Vis absorption spectra
of 3-(4-methoxy benzyl)-1,3-diazaspiro[4.4]nonane-2,4-dione in ethanol.
diones the intramolecular interactions are formed by the orbital

96
A.M. Lazi ꢀc et al. / Journal of Molecular Structure 1127 (2017) 88e98
Table 7
Second order perturbation theory analysis of Fock matrix in NBO basis for spirohydantoin 1.
Donor NBO (i)
Type
ED (i) (e)
Acceptor NBO (j)
Type
ED (j) (e)a
E (2)b kcal/mol
E(j)-E(i)c a.u.
F (i,j)d a.u.
N3ꢀC4
N3ꢀC4
N3ꢀC4
N3ꢀC4
N3ꢀC10
N3ꢀC10
C4ꢀC5
C4ꢀC5
C11ꢀC12
C11ꢀC12
C11ꢀC12
N3
s
s
s
s
s
s
s
s
1.985
N3ꢀC2
N3ꢀC10
C5ꢀC6
s
s
s
s
s
s
s
s
s
p
p
p
p
p
*
*
*
*
*
*
*
*
*
*
*
*
*
*
0.099
0.038
0.033
0.032
0.085
0.099
0.038
0.011
0.038
0.323
0.332
0.264
0.353
0.353
0.099
0.073
0.72
1.44
0.50
0.55
1.41
0.80
5.13
1.06
1.21
1.15
1.16
1.18
1.19
1.13
0.96
1.01
0.57
0.28
0.28
0.28
0.28
0.28
0.64
0.70
0.027
0.037
0.022
0.023
0.037
0.027
0.063
0.029
0.054
0.068
0.067
0.117
0.105
0.117
0.121
0.120
C5ꢀC9
1.982
1.962
1.654
N3ꢀC4
N3ꢀC2
N3ꢀC10
C8ꢀC9
p
p
p
LP (1)
LP (1)
LP (1)
LP (2)
LP (2)
N3ꢀC10
C15ꢀC16
C13ꢀC14
C4ꢀO1
C2ꢀO2
C2ꢀO2
N3ꢀC2
N1ꢀC2
5.47
20.63
20.24
58.73
49.07
58.40
27.98
24.52
1.624
N3
N1
O2
O2
1.742
1.837
s
s
*
*
a
ED electron density.
E (2) means energy of hyperconjugative interactions.
Energy difference between donor and acceptor i and j NBO orbitals.
F (i,j) is the Fock matrix element between i and j NBO orbitals.
b
c
d
overlap between bonding CꢀC, CꢀN and C]O antibonding orbital,
which result in intramolecular charge transfer (ICT) causing stabi-
lization of the molecules. These interactions are observed due to an
increase in the electron density in CꢀC, CꢀN and C]O antibonding
orbitals that weakens the respective bonds. The strong intra-
benzyl group, electron-donating substituents cause an increase in
electron density on the oxygen atoms of the hydantoin ring
(Table S6), whereby the O1 is less electron-rich than that of O2
owing to the vicinity of the electron-donating ability of nitrogen
atom in position 1. This shift of electron density towards the oxygen
atoms produces a polarization of the molecules and the oxygen
atoms become preferred sites for the hydrogen bond donor attack.
The effect of electron-accepting substituents on the nitrogen atom
in position 3 is reversed (Table S6). When X is an electron-accepting
substituent, the polarization of the molecule occurs as a result of
the electron-accepting competition between the benzyl group and
N3 and O1 atoms of the hydantoin moiety.
molecular hyperconjugative interaction of the
s and p electrons of
CeC to the anti CeC bond of the hydantoin and phenyl rings leads
to stabilization of molecule 1 as shown in Table 7. Also, these in-
teractions are spread toward cyclopentane ring and cause the sta-
bilization of the whole molecule. Thus, the intramolecular
hyperconjugative interaction of s(N3eC4) distribute to s*(N3eC2),
N3eC10, C5eC6 and C5eC9, leading to stabilization of 0.5e1.4 kcal/
mol. It can be noticed from Table 7 that the same kind of interaction
is calculated in the
from *(C4eC5) to
the range of 0.8e5.13 kcal/mol. These results suggest that the most
electron delocalization is around (CeC) and CeN bonds of
hydantoin ring.
The NBO analysis of spirohydantoin 1 (Table 7) also indicates
intramolecular interactions due to the orbital overlap of (CeC)
and *(CeC) in phenyl ring of benzyl group with high electron
density (approx. 0.323e0.3332 e) of anti-bonding orbitals (CeC).
The orbital overlap in phenyl ring between (CeC) and *(CeC)
results in intramolecular charge transfer causing stabilization of the
whole molecule. The delocalization of electron (C11eC12) to
*(C15eC16) and *(C13eC14) are with stabilization energy of
0.63 and 20.24 kcal/mol while the delocalization toward hydan-
toin ring from phenyl group (C11eC12)/ *(N3eC10) is with
stabilization energy of 5.47 kcal/mol.
The interaction energy, related to the resonance in the molecule,
is electron withdrawing to the ring through *(N3eC2 and N1eC2)
s
(N3eC10) to
s*(N3eC4) and N3eC2 as well as
s
s
*(N3eC10) and C8eC9 bond, with E(2) value in
3.5. ADMET factor profiling
s
s
Oral bioavailability is a significant factor in design of biologically
therapeutic species. In order to determine which of the investigated
spirohydantoins possess pharmacokinetic activity, they have been
tested by the empirical ‘rule of five’ established by Lipinski [48].
According to this rule, a compound exhibits good in vivo perme-
ability if the molecule satisfies following four structural features:
(1) molecular weight lower than 500; (2) maximum 5 atoms that
are proton-donors of the hydrogen bonds (eOH and eNH); (3)
maximum 10 atoms (N and O) that are hydrogen bond acceptors
and (4) calculated value of the logarithm of the octanolewater
partition coefficient (log P) lower than 5 [49]. Another empirical
rule that should be considered for prediction of good bioavailability
includes reduced molecular flexibility, i.e. number of rotatable
p
p
p
p
p
p
p
2
p
p
s
2
bonds should be lower than 8, low polar surface area (<140 Å ) and
molar refractivity in the range from 40 to 130 Å [49e51].
3
s
bond from the lone pair LP(2)O2 with moderate stabilization en-
ergy of 24e28 kcal/mol. The most important interaction energies of
Since log P is associated with solubility and permeability of the
molecule, this physicochemical parameter is important in estima-
tion of the molecule capability of transfer through the cell mem-
branes. If the compound is too hydrophilic, expressed through
negative log P, passing through membranes would not be possible
due to hydrophobic character of the lipid bilayer. On the other hand,
hydrophobic compounds (high log P) are not appropriate due to the
insolubility and possibility to be retained in the lipid membrane.
The investigated spirohydantoin derivatives are moderately lipo-
philic compounds with lipophilicity between 2.09 and 3.20
(Table 8), whereby all substituents, excluding strong electron-
donating methoxy group, induce increase of hydrophobic
LP(1)N3
/ p*(C4eO1) and p*(C2eO2) as well as LP(1)
N1 / *(C2eO2) are 58.73, 49.07 and 58.04 kcal/mol, respectively.
p
In conclusion, the NBO analysis of spirohydantoin 1 confirms ICT
throughout the whole molecule which is in accordance with FMO
analysis.
The calculated natural atomic charges obtained in NBO analysis
are listed in Table S6. This calculation depicts the charges of the
nitrogen, oxygen and some carbon atoms in the molecules of spi-
rohydantoins 1e7. As a result of the resonant interaction with the

A.M. Lazi ꢀc et al. / Journal of Molecular Structure 1127 (2017) 88e98
97
Table 8
Evaluation of drug candidates.
Compounds
Molecular weight
log P
Hydrogen bonds
Rotatable bonds
Polar surface area/Å2
Molar refractivity/Å3
Donorsa
Acceptorsb
1
2
3
4
5
6
7
244.29
258.32
274.32
278.73
323.19
269.30
289.29
252.27
<500
2.37
2.65
2.09
2.93
3.20
2.51
2.41
2.18
<5
1
1
1
1
1
1
1
2
4
4
5
4
4
5
7
4
2
2
3
2
2
2
3
2
79.60
79.00
96.60
77.90
78.40
134.60
171.00
58.20
<140
64.81
70.72
71.27
68.93
72.34
72.60
72.31
70.28
Phenytoinc
Ideal compound
d
<5
<10
<8
40e130
a
A donor indicates any OeH or NeH group.
An acceptor indicates any O or N including those in donor groups.
Partitiion coefficient values calculated by Molinspiration interactive log P calculator.
Data obtained from reference [54].
b
c
d
character compared to unsubstituted molecule (1). Classification of
newly synthesized spirohydantoins according to the lipophilicity as
well as polarity of the substituent X may be of importance for the
activity since the literature point out that presence of electron-
donating groups like methoxy in the 4-position of the phenyl ring
and log P values in a range from 2.4 to 3.3 are favorable for the
activity [8]. Furthermore, the investigated derivatives contain a low
number of the rotatable bonds (Table 8), and thus moderate
conformational changes due to binding to a receptor are possible.
Moreover, drug molecules passing through the cell membrane
in order to achieve corresponding biological activity, need to pri-
marily break hydrogen bonds with its aqueous environment.
Compounds which can easily form hydrogen-bonds or electrostatic
interactions with lipid bilayer commonly posses great difficulties in
penetration and absorption. Additionally, it was observed that polar
surface area (PSA) is a very important descriptor for drug transport
properties such as human intestinal permeation and blood-brain
barrier penetration [52,53]. From Table 8, it is obvious that all
investigated spirohydantoins (excluding 7) meet these empirical
criteria and potentially qualify for the pharmacodynamic phase of
the drug development, whereby compound 3 stands out as
physico-chemicaly most similar molecule relative to Phenytoin,
commercially available anticonvulsive drug.
spectroscopic, electronic and reactivity aspects of 3(4-substituted
benzyl)-1,3-diazaspiro[4.4]nonane-2,4-diones were compared
with the experimental. The main difference between the experi-
mental structures and structures calculated by the DFT method
results from the different spatial orientation of the benzyl group
relative to the spirohydantoin moiety. The solid state structure can
easily be affected by packing effect, which modify the geometry of
the molecule.
A detailed analysis of the effect of substituents on both hydan-
toin and benzyl moieties on the frontier molecular orbitals was
performed. The experimental and theoretical UV-Vis spectral
analysis has provided insight into the excitation energy and oscil-
lator strength and predicted mainly the
p/p* type electronic
transitions which are attributed as intramolecular charge transfer.
Molecular electrostatic potential surface map indicates that the
most suitable atomic sites for electrophylic attack are O1 and O2
atom of the carbonyl groups, while the most probable site which
can be involved in nucleophylic process is N1 atom of the hydantoin
ring. The evaluation of empirical criteria of drug candidates applied
in this study indicate that all investigated spirohydantoins
(excluding 7) meet these criteria and potentially qualify for the
pharmacodynamic phase of the drug development. Compound 3
represents starting point for the development of new anticonvul-
sive spirohydantoins.
4
. Conclusion
Acknowledgment
In this study, new series of 3-(4-substituted benzyl)-1,3-
diazaspiro[4.4]nonane-2,4-diones was synthesized and character-
This work has been financially supported by Ministry of Edu-
cation, Science and Technological Development, of the Republic of
Serbia, under Grant Nos. 172013, 172035 and III 45007.
ized using spectroscopic methods and crystal structure determi-
nation. The 1H and 13C NMR chemical shifts of the atoms under
investigation in the series of 3-(4-substituted benzyl)-1,3-
diazaspiro[4.4]nonane-2,4-diones show that the electron-donor
substituent influences increase in electron density at all observed
atoms, while electron-acceptor substituent cause a decrease in
electron density at these atoms. These results are in complete
accordance with the structure of 3-(4-substituted benzyl)-1,3-
diazaspiro[4.4]nonane-2,4-diones as well as with the presented
mechanism of transmission of the substituent electronic effects
through the molecule. The crystal structure of compound 1 was
resolved by X-ray diffraction. The 3-benzyl-1,3-diazaspiro[4.4]
nonane-2,4-dione crystallizes in triclinic P-1 space group, with two
crystallographically independent molecules in the asymmetric
unit. In the crystal packing of 1, intermolecular hydrogen NeH/O
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2016.07.069.
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