Structure and activity studies of glycine receptor ligands. Part 8. Arylidene-imidazoline-4-one aminoacids

Article abstract of DOI:10.1016/S0022-2860(02)00568-9

Based on chemical and preliminary biological experiments (inhibition to glycine receptor), structure and activity relationship of arylidene-imidazoline-4-one amino acids has been studied. In the course of our work, the simulation of the hydrogen bonds formation between ligand molecule and hypothetical receptor has been designed. Computed interactions are going to simulate possible ligand-receptor interaction with selected amino acids (in this investigation - with basic lysine and acidic aspartic acid). Obtained model estimates roughly the binding energy of the amino acids with ligand molecules. The proposed amino acids binding energies approximately agree with activity of the isomeric benzylidene-imidazoline-4-one glycines and α-alanines which decreases in the order of m-Cl > p-Cl > o-Cl substituents in benzylidene moiety. Additionally, the lowering of activity is caused by lipophilic pocket volume.

Full text of DOI:10.1016/S0022-2860(02)00568-9

Journal of Molecular Structure 649 (2003) 25–36
www.elsevier.com/locate/molstruc
Structure and activity studies of glycine receptor ligands. Part 8.
Arylidene-imidazoline-4-one aminoacids
a,
Janina Karolak-Wojciechowska , Agnieszka Mrozek , Katarzyna Kiec-Kononowicz ,
a
b
*
´
Jadwiga Handzlikb
a
˙
Institute of General and Ecological Chemistry, Technical University of L⁄ odz, ul Zwirki 36, 90-924 L⁄ odz, Poland
´ ´
´ ´
b
´
Department of Chemical Technology of Drugs, Collegium Medicum of Jagiellonian University, Medyczna 9, 30-688 Krakow, Poland
Received 24 June 2002; revised 14 October 2002; accepted 21 October 2002
Abstract
Based on chemical and preliminary biological experiments (inhibition to glycine receptor), structure and activity relationship
of arylidene-imidazoline-4-one amino acids has been studied. In the course of our work, the simulation of the hydrogen bonds
formation between ligand molecule and hypothetical receptor has been designed. Computed interactions are going to simulate
possible ligand–receptor interaction with selected amino acids (in this investigation—with basic lysine and acidic aspartic acid).
Obtained model estimates roughly the binding energy of the amino acids with ligand molecules. The proposed amino acids
binding energies approximately agree with activity of the isomeric benzylidene-imidazoline-4-one glycines and a-alanines
which decreases in the order of m-Cl . p-Cl . o-Cl substituents in benzylidene moiety. Additionally, the lowering of activity is
caused by lipophilic pocket volume.
q 2002 Elsevier Science B.V. All rights reserved.
Keywords: Glycine receptor ligands; Anticonvulsant activity; Molecular modelling; Model of the ligand–receptor interaction
1. Introduction
postulated. Additionally, it was clear from our study
[6] that the substitutions in carboxyl group (proceed-
ing to amides and esters) have been deceptive and the
unsubstituted COO2 group was found to be essential
for observable activity [8,9]. The model of ligand–
receptor interaction for studied derivatives was also
proposed (Fig. 1) [6].
The objective of our latest research was to find new
ligands for the glycine–NMDA binding site (iGluRs).
In order to achieve this goal, the glycine derivatives of
arylidene-imidazoline-4-ones were investigated
[1–6]. It was found that some glycines have shown
the noticeable affinity to iGluRs receptor [1]. To
improve the affinity of those compounds, the increase
of log P values [7] by chemical modification has been
Recently, based on our current results, only several
5-substituted-imidazoline-4-one amino acids have
been selected, namely three series of the derivatives
marked as A–C on Scheme 1. Based on chemical and
preliminary biological investigation (Table 1), struc-
ture and activity studies on imidazoline-4-one amino
acids were conducted.
*
Corresponding author. Tel.: þ48-42-631-3122; fax: þ48-42-
631-3103.
E-mail address: jkarolak@ck-sg.p.lodz.pl (J. Karolak-
Wojciechowska).
0022-2860/03/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(02)00568-9

26
J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
obtained as the result of the well-known Knoevenagel
condensation of 2-thiohydantoin with suitable alde-
hydes carried out in acetic acid in the presence of
sodium acetate [10]. 5-Benzylo-2-thiohydantoin was
synthesised through 1-acetyl intermediate in the
reaction of phenylalanine with ammonium thiocya-
nate in the presence of acetic acid and acetic
anhydride, which was followed by hydrolysis with
10% hydrochloric acid, as it was previously described
[11]. 2-Thiohydantoin derivatives reacted, according
to the method worked up by us earlier [1,12], with
methyl iodide to give the methylthio derivatives
which were condensed into the target compounds
upon the reaction with (un)substituted glycine or
alanine derivatives.
Fig. 1. The model of the iGluRs binding site for arylidene-
imidazoline-4-one glycines.
Presented below discussion is based on molecular
modelling using quantum chemistry calculations and
includes simulation model of hydrogen bonds for-
mation between basic molecule and hypothetical
receptor. We hope that this ligand-receptor interaction
with selected amino acids will also provide some
information on the iGluRs.
2.1.2. Experimental
Melting points (uncorrected) were determined on
1
Mel.-Temp. II (LD Inc., USA) apparatus. H-NMR
spectra were recorded on a Gemini 200, Bruker 250,
VARIAN MERCURY 300 MHz or Bruker DPX 400
Avance spectrometer, chemical shifts are reported in
d[ppm] values relative to internal reference of TMS.
13C-NMR spectra were recorded on a Gemini 200
spectrometer. IR spectra were measured in KBr
pellets with FT IR 410 spectrometer (Jasco). MS for
compounds 13 and 17 were recorded on Finnigan
MAT CH-7A spectrometer (ionisation) energy—
70 eV). Elemental analyses were performed for C,
H, N and the results differed no more than ^0.4%
from the theoretical values. TLC was conducted on Al
2. Materials and methods
2.1. Chemical part
2.1.1. General procedure
As starting materials for the designed compounds,
the 5-substituted derivatives of 2-thiohydantoins were
used (Scheme 2). 5-(Z)-arylidene derivatives were
Scheme 1.

J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
27
Table 1
Chemical and pharmacological details of 5-substituted-imidazolidyno-4-one amino acids (atoms numbering as in Scheme 1)
Imidazolidyno-4-one substituents
Pharmacological data
log P
log D (at pH ¼ 7.4)
Ref
At C5
Amino acid
Inhibition (%)
ASP
A
1
2
p-Cl–Ph–CHy
p-NO2–Ph–CHy
p-OCH3–Ph–CHy
Ph–CHy
Glycine
Glycine
Glycine
Glycine
Glycine
a-Alanine
Glycine
Glycine
a-Alanine
Glycine
51
2
3
2
1
2
3
1
3
3
3
1.00
20.53
21.31
21.24
21.21
20.37
20.65
20.48
21.25
20.60
20.55
[1]
[1]
[1]
[1]
[1]
18
0.19
0.23
0.27
1.16
0.85
1.05
0.25
0.93
0.98
3
32
4
59
5
p-Br–Ph–CHy
p-Cl–Ph–CHy
m-Cl–Ph–CHy
m-NO2–Ph–CHy
m-C–Ph–CHy
o-Cl–Ph–CHy
0.4
28.6
90
6
7
[1]
[1]
8
30
9
10
90.3
18
[1]
B
C
11
12
13
14
15
16
p-Cl–Ph–CHy
p-Cl–Ph–CHy
p-Cl–Ph–CHy
p-Cl–Ph–CHy
p-Cl–Ph–CHy
p-Cl–Ph–CHy
p-Cl-Ph-a-alanine
o-Cl-Ph-a-alanine
p-F-Ph-a-alanine
Ph-a-alanine
23
1
2
3
3
2
1
3.20
3.17
2.62
2.47
2.69
2.02
20.15
20.17
20.61
20.58
20.33
20.53
17
34.9
27.7
Indoilo-a-alanine
Ph-glycine
17
18
19
20
21
22
23
Pyridine–CHy
Glycine
Glycine
Glycine
Glycine
Glycine
Glycine
Glycine
16.5
24
3
4
2
3
3
3
3
20.94
1.49
1.49
0.92
1.40
0.97
0.03
22.29
20.05
20.05
20.58
20.13
20.46
21.30
a-Naphthalene–CHy
b-Naphthalene–CHy
Ph–CHyCH2–CHy
Ph–CHyCH(CH3)–CHy
Ph–, Ph–
-1.1
[1,3,5]
Ph–CH2–, H–
10.5
Sheets, 0.2 mm layer of silica gel (60F254 Merck). The
developing solvent system used was CHCl3: i-PrOH:
NH3 aq (9:11:2).
(s, 1H, CH ¼ ); 7.39 (d, J ¼ 8.56 Hz, 2H, H-30, H-
50); 8.02 (br. d, J ¼ 7.27 Hz, 2H, H-20, H-60); 10.61
(br.s, 1H, 3-NH); IR (KBr) g: 3336 (OH), 3128
(NH), 2924 (CH), 1752, 1748, 1696 (CyO), 1680,
1670, 1648 (ArCHy), 1594 (CyN), 1552, 1452,
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]alanine (6): C13H12N3O3Cl (293.72); mp
250–251 8C (DMF þ H2O); Yield 44%; Rf ¼ 0.11;
1H-NMR (200 MHz) s ¼ 1.43 (d, J ¼ 7.23 Hz, 3H,
CH3); 4.48 (br.d, J ¼ 7.40 Hz, 1H, CHCH3); 6.31
1088, 1012, 824, 668, 630 cm21
.
N-[5-(Z)-(3-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]alanine (9): C13H12N3O3Cl (293.72); cream
Scheme 2.

28
J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
amorphous powder; mp 232–234 8C (DMF þ H2O);
Yield 58%; Rf ¼ 0.14; 1H-NMR (200 MHz) s ¼ 1.45
(d, J ¼ 7.23 Hz, 3H, CH3); 4.46 (d, J ¼ 5.46 Hz, 1H,
CHCH3); 6.30 (s, 1H, CH ¼ ); 7.23–7.39 (m, 2H, H-
40, H-50); 7.86 (br.s, 1H, H-60); 8.20 (br.s, 1H, H-20);
10.74 (br. s, 1H, 3-NH); IR (KBr) ?: 2981 (CH), 1765,
1730 (CyO), 1671 (ArCHy), 1603, 1566, 1456, 1386,
612 cm21; MS (m/z): 387 (3), 268 (16), 344 (14), 342
(63), 218 (76), 162 (23), 125 (68), 108 (97), 97 (100).
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]-phenylalanine (14): C19H16N3O3Cl (369.80);
cream coloured amorphous powder, mp 245–247 8C
(from DMF þ H2O); Yield 24%; Rf ¼ 0.19; 1H-NMR
(250 MHz) s ¼ 2.96–3.16 (m, 1H, HCH–CH); 3.26
(dd, J ¼ 13.87 Hz, 4.90 Hz, 1H, HCH–CH); 4.70
(br.s, 1H, HCH–CH ); 6.31 (s, 1H, ArCHy); 7.18–
7.34 (m, 5H, Ph–H); 7.40 (d, J ¼ 8.51 Hz, 2H, H-30,
H-50); 7.81 (br. s, 1H, NHCH2); 8.04 (br. d, 2H, H-20,
H-60); 10.56 (br. s, 1H, 3-NH); IR (KBr) g: 3424
(OH), 3118, 3028 (NH),1741, 1702 (CyO), 1655
(ArCHy), 1587 (CyN), 1379, 1311, 1090, 699,
1363, 1305, 1083, 1059, 904, 857, 779 cm21
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]-(4-chlorophenyl)alanine (11):
.
C19H15N3O3Cl2 (404.26); vivid yellow amorphous
powder, mp 238–239 8C (from DMF); Yield 73%;
1
Rf ¼ 0.13; H-NMR (250 MHz) s ¼ 3.03–3.16 (m,
1H, HCH–CH), 3.25 (dd, J ¼ 13.90 Hz, 5.04 Hz, 1H,
HCH–CH); 4.67 (br.s, 1H, CH–HCH)); 6.30 (s, 1H,
CH ¼ ); 7.27–7.42(m, 6H, H-30, H-50, H-200, H-300,
H-500, H-600), 7.82 (br. s, 1H, HNCH); 8.03 (br. d;
J ¼ 7.60 Hz, H-20, H-60); 10.62 (br. s, 1H, 3-NH); IR
(KBr) g: 3422 (OH), 2921 (CH), 1700 (CyO), 1614
(ArCHy), 1490, 1376, 1089, 1016, 808, 710,
660 cm21
.
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]-tryptophan (15): C21H17N4O3Cl (408.85);
vivid yellow amorphous powder, mp 253–254 8C
(from DMF þ H2O); Yield 63%; Rf ¼ 0.17; 1H-NMR
(200 MHz) s ¼ 3.21–3.37 (m, 2H, CH–CH2); 4.78
(br.s, 1H, CHCH2); 6.31 (s, 1H, CHy); 6.95–7.11 (m,
2H, H-500, H-600); 7.17 (d, J ¼ 2.23 Hz, 1H, H-200); 7.35
(d, J ¼ 7.76 Hz, 1H, H-700); 7.39 (d, J ¼ 8.60 Hz, 2H,
H-30, H-50); 7.56 (d, J ¼ 7.51 Hz, 1H, H-400); 8.05 (d,
J ¼ 7.55 Hz, 2H, H-20, H-60); 8.21 (d, J ¼ 8.62 Hz,
1H, NHCH2); 10.49 (br.s, 1H, 3-NH); 10.90 (br.s, 1H,
NHindol); IR (KBr) g: 3384 (OH, NH), 1768, 1758,
1712, 1700 (CyO), 1648 (CHy), 1552, 1358, 1090,
667 cm21
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]-(2-chlorophenyl)alanine (12):
.
C19H15N3O3Cl2 (404.26); cream yellow amorphous
powder, mp 242–244 8C (from DMF þ H2O); Yield
50%; Rf ¼ 0.30; 1H-NMR (300 MHz) s ¼ 3.09–3.17
(m, 2H, CHCH2); 4.83 (br.s, 1H, CHCH2); 6.22 (s,
1H, ArCHy); 7.21 (d, J ¼ 3.58 Hz, H-300, H-500); 7.36
(d, J ¼ 7.98 Hz, 4H, H-30, H-50, H-400, H-600); 7.98 (d,
J ¼ 7.98 Hz, 2H, H-20, H-60); 10.65 (br. s, 1H, 3-NH);
IR (KBr) g: 3389 (OH), 3054 (NH), 2929 (CH); 1756,
1698 (CyO), 1664 (ArCHy), 1600, 1377, 1092, 1050,
816, 748, 674 cm21
.
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]phenylglycine (16): C18H14N3O3Cl (355.78);
cream yellow amorphous powder, mp 240–2428C
(from DMF þ H2O); Yield 50%; Rf ¼ 0.21; 1H-NMR
(200 MHz) s ¼ 5.56 (s, 1H, NHCH ); 6.35 (s, 1H,
ArCHy); 7.30–7.53 (m, 7H, H-30, H-50, 5 £ Ph–H);
8.07 (br.s, 2H, H-20, H-60); 8.34 (br.s, 1H, NHCH);
10.36 (br.s, 1H, 3-NH); IR (KBr) g: 3169, 3066 (OH,
NH), 2812 (CH), 1759, 1708 (CyO), 1666 (ArCHy),
823, 764, 660 cm21
.
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]-4-fluorophenylalanine (13): C19H15N3O3-
ClF(387.80); lemon yellow amorphous powder, mp
236–237 8C (from DMF þ H2O); Yield 28%;
Rf ¼ 0.22; 1H-NMR (400 MHz) s ¼ 3.24 (d,
J ¼ 4.19 Hz, 1H, HCH–CH); 3.26 (d, J ¼ 4.44 Hz,
1H, HCH–CH); 4.68 (br.s, 1H, HCH–CH ); 6.30 (s,
1H, ArCHy); 7.12 (t, J ¼ 8.21 Hz, 2H, H-200, H-600);
7.30 (t, J ¼ 5.57 Hz, 2H, H-300, H-500); 7.40 (d,
J ¼ 7.58 Hz, 2H, H-30, H-50); 7.52 (br. s, 1H,
NHCH2); 8.03 (br. s, 2H, H-20, H-60); 10.52 (br. s,
1H, 3-NH); 13.03 (br. s, 1H, COOH); IR (KBr) g:
3440 (OH, NH), 1768, 1728, 1712, 1696 (CyO), 1648
(ArCHy), 1564 (CyN), 1528, 1504, 1220, 668, 648,
1590, 1378, 1181, 1090, 1023, 1011, 697 cm21
.
N-[5-(pyridyl-3)-methylene-4-oxo-2-imidazolidi-
nyl]glycine (17): C11H10N4O3 (246.23); bright yellow
amorphous powder; mp 265–266 8C; Yield 41%;
Rf ¼ 0.05; 1H-NMR (300 MHz) s ¼ 4.04 (s, 1H,
NHCH2) 6.69 (s, 1H, CHy); 7.04–7.15 (m, 3H, H-20,
H-30, H-60); 7.39 (d, J ¼ 7.69 Hz, 1H, H-50); 7.86 (d,
J ¼ 7.42 Hz, 1H, H-40); 8.10 (br.s, 1H, NHCH2);
11.51 (s, 1H, 3-NH); 13H-NMR (75 MHz) s ¼ 42.64
(C H2COOH); 122.88 (C-5); 123.38 (ArCHy); 131.79

J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
29
(C-50); 135.96 (C-60); 136.12 (C-20); 147.46 (C-4);
147.89 (C-3); 150.49 (COOH); 150.74 (CyO); 170.88
(CyN); IR (KBr) g: 3340 (OH), 3078 (NH), 1731
(CyO), 1682 (CyO), 1621 (ArCHy), 1600 (CyN),
1524, 1371, 1265, 1119,874, 805, 761, 684 cm21; MS
(m/z): 246 (Mþz,4), 230 (12), 228 (21), 200 (24), 188
(10), 145 (7), 118 (40), 93 (46), 77 (3), 44 (100).
N-[5-(naphthyl-1)-methylene-4-oxo-2-imidazolidi-
nyl]glycine (18): C16H13N3O3 (295.28);light yellow
amorphous powder, mp 281–282 8C; yield 59%;
Rf ¼ 0.11; 1H-NMR (200 MHz) s ¼ 4.11 (s, 2H,
NHCH2); 7.09 (s, 1H, CHy); 7.51–7.63 (m, 3H, H-30,
H-60, H-70); 7.85 (d, J ¼ 7.99 Hz, 1H, H-50); 7.94 (dd,
J ¼ 7.90 Hz, 1.77 Hz, 1H, H-40); 8.21 (br. s, 1H, H-
2,); 8.83 (br. s, 1H, H-80); IR (KBr) g: 3424 (OH);
3180 (NH), 2944 (CH), 2720, 1754 (CyO), 1728,
1704 (CyO), 1658, 1648 (CHy), 1392, 1296, 1244,
(CH), 1756 (CyO), 1702 (CyO), 1648 (CHy), 1620
(CyN), 1528, 1388, 1264, 1192, 1040, 840,
750 cm21
.
N-(5-benzyl-4-oxo-2-imidazolidinyl)glycine (23):
C12H13N3O3 (247.25); cream yellow amorphous
powder; mp 233–234 8C (CH3COOH); Yield 30%;
Rf ¼ 0.09;
1H-NMR
(200 MHz)
s ¼ 1.91
(s,0.66 £ 3H, CH3COOH); 2.61–2.72 (m, 1H, CH);
3.03 (dd, J ¼ 14.02 Hz, J ¼ 4.10 Hz, 1H, CH); 3.86
(s, 2H, NHCH2); 4.08 (br.s, 1H, CH), 7.16–7.27 (m,
5H, Ph–H); IR (KBr) g: 3408 (OH), 3284, 3076 (NH),
2976, 2912 (CH), 1768, 1712, 1708, 1696 (CyO),
1680, 1612, 1552, 1294, 1262, 1030, 702, 618 cm21
.
2.2. Pharmacological part
2.2.1. Receptor binding determinations
1224, 1040, 978, 884, 780, 652 cm21
.
Radioligand binding studies were performed
according to the method described by Grimwood
et al. [13]. Affinities of tested compounds used at
concentrations of 100 mM, for the glycine site of the
NMDA receptor were determined by displacement of
the glycine site antagonist [3H]-L-689,560 binding to
rat cortex (hippocampus membranes). The percent of
inhibition of the ligand was estimated; the results are
presented in Table 1.
N-[5-(naphthyl-2)-methylene-4-oxo-2-imidazolidi-
nyl]glycine (19): C16H13N3O3 (295.28); cream yellow
amorphous powder, mp 279–281 8C (from
DMF þ H2O); yield 68%; Rf ¼ 0.12; 1H-NMR
(250 MHz) s ¼ 4.13 (s, 2H, NHCH2); 6.51 (s, 1H,
CHy); 7.46–7.53 (m, 2H, H-60, H-70); 7.84–7.89 (m,
3H, H-40, H-50, H-80); 8.28 (br.s, 2H, NHCH2, H-10);
8.46 (br.s, 1H, H-30); 10.90 (br.s, 3-NH); IR (KBr) g:
3336 (OH); 3212 (NH), 2932 (CH), 1756, 1742, 1712
(CyO), 1648 (CHy), 1606, 1512, 1396, 1340, 1292,
1112, 1028, 874, 826, 772 cm.21
2.2.2. Anticonvulsant assays
All animal anticonvulsant and neurotoxicity assays
were conduced by the Antiepileptic Drug Develop-
ment (ADD) Program, Epilepsy Branch, Neurological
Disorders Program, National Institutes of Neurologi-
cal and Communicative Disorders and Stroke
(NINCDS) according to testing procedures which
have been described earlier [14,15]. Phase I, and the
threshold tonic extension (TTE) testing procedures.
Phase I of the evaluation consisted of three tests:
maximal electroshock (MES), subcutaneous pentyle-
netetrazol (ScMet), and rotorod test for neurological
toxicity (Tox). Alls compounds apart were injected
intraperitoneally into mice as suspensions in 0.5%
methylcellulose. Small groups of animals were used
(l–8) at dose levels of 30, 100 and 300 mg/kg. These
data are presented in Table 2. The classifications were
as follows (Table 2): (1) anticonvulsant activity at
100 mg/kg or less; (2) anticonvulsant activity at doses
greater than 100 mg/kg; (3) compound inactive at
300 mg/kg.
N-(5-cinnamylidene-4-oxo-2-imidazolidinyl)gly-
cine (20): C14H13N3O3 (271.28); yellow amorphous
powder; mp 287–288 8C; yield 85%; Rf¼0.10; H-
1
NMR (200 MHz) s ¼ 1.91 (s, 0.33 £ 3H, CH3-
COOH); 4.04 (s, 2H, NHCH2); 6.21 (d,
J ¼ 11.54 Hz, 1H, ArCHy); 6.88 (d, J ¼ 15.66 Hz,
1H, CHy); 7.26 (d, J ¼ 11.70 Hz, 1H, CHy); 7.27–
7.48 (m, 3H, H-30,H-40,H-50); 7.52 (d, J ¼ 1.43 Hz,
2H, H-20,H-60); IR (KBr) g: 3436 (OH,NH), 2916
(CH), 1732, 1712, 1696 (CyO), 1680, 1648, 1552,
1512, 1500, 1452, 1356, 1298, 978, 668 cm21
.
N-[5-(2-methyl)-cinnamylidene-4-oxo-2-imidazo-
lidinyl]glycine (21): C15H15N3O3 (285.31); cream
yellow amorphous powder; mp 238–239 8C; Yield
1
58%; Rf ¼ 0.11; H-NMR (200 MHz) s ¼ 2.27 (s,
3H, CH3); 4.02 (s, 2H, NHCH2); 6.12 (s, 1H, ArCHy);
6.93 (s, 1H, CHy) 7.24–7.28 (m, 1H, H-40); 7.37 (d,
J ¼ 4.29 Hz, 4H, H-20, H-30, H-50 H-60); 10.63 (br.s,
1H, 3-NH); IR (KBr) g: 3432 (OH), 3068 (NH), 2916

30
J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
Table 2
Anticonvulsant activity in the MES, ScMet test and acute neurological toxicity in the rotorod test after intraperitoneal administration to mice.
The data are expressed as animals protected/animals tested
Dose (mg/kg)
MES
0.5 h
ScMet
0.5 h
Rotorod
0.5 h
Dose (mg/kg)
MES
0.5 h
ScMet
0.5 h
Rotorod
0.5 h
4 h
4 h
4 h
4 h
4 h
4 h
6
30
100
300
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/4
1/8
0/4
0/2
0/4
0/2
16
17
18
19
20
21
23
30
100
300
0/1
0/3
0/1
0/1
0/3
0/1
1/5
1/5
0/1
0/1
0/1
0/1
0/4
0/8
0/4
0/2
0/4
0/2
9
30
100
300
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/4
0/8
0/4
0/2
0/4
0/2
30
100
300
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/4
0/8
0/4
0/2
0/4
0/2
11
12
13
14
15
30
100
300
0/1
0/3
0/1
0/1
1/3
1/1
0/1
0/1
0/1
0/1
0/1
0/1
0/4
0/8
0/4
0/2
0/4
1/2
30
100
300
0/1
0/3
0/1
0/1
1/3
1/1
2/5
0/1
1/1
2/5
0/1
1/1
0/4
0/8
2/4
0/2
0/4
2/2
30
100
300
0/1
0/3a
1/1
0/1
0/3
1/1
0/1
0/1
0/1
0/1
0/1
0/1
1/4
2/8b
4/4
0/2
0/4
2/2
30
100
300
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/1
1/5
0/1
0/1
2/5
0/4
0/8
0/4
0/2
0/4
0/2
30
100
300
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/4
0/8
0/4
0/2
0/4
0/2
30
100
300
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/4
0/8
0/4
0/2
0/4
0/2
30
100
300
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/4
0/8
0/4
0/2
0/4
0/2
30
100
300
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/1
1/5
0/1
0/1
0/1
0/4
0/8
3/4
0/2
1/4
1/2
30
100
300
0/1
0/3c
0/1
0/1
0/3
1/1
0/1
0/1
0/1
0/1
0/1
0/1
0/4
0/8d
0/4
0/2
0/4
0/2
30
100
300
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/4
0/8
0/4
0/2
0/4
0/2
a
b
c
d
At 15 min 0/3; 1 h 0/3; 2 h 0/3; 6 h 0/3.
At 15 min 0/3; 1 h 1/3; 2 h 0/3; 6 h 0/3.
At 2 h 1/3; 6 h 0/3.
At 2 h 0/3; 6 h 0/3.
2.3. Computational procedure
3. Results and discussion
3.1. Reviewing the chemical materials
All molecules were built on the basis of the
crystallographic structure of p-Cl-phenyl-imidazo-
line-4-one ethyl glycinate [5] and roughly optimised
using PCMODEL.6 program [16]. MO calculations
were carried out by AM1 method using MOPAC
program (version 6.0) [17] in water environment
(dielectric constant 78.4). The structures of complexes
with small molecules (water and ammonia) and/or
with amino acids were obtained by DOC procedure
from PCMODEL.6 and were subsequently optimised
by AM1. The values of log P and log D were
calculated by means of PALLAS (version 1.2)
program [18].
The discussion in this paper relates to 23 amino
acidic derivatives of imidazoline-4-ones glycines
and/or a-alanines, for which chemical details and
chosen properties are collected in Table 1. In general,
all objects under consideration can be divided into two
groups: simple amino acids (set A-compounds 1–10
and set C-compounds 17–23 in Table 1) and modified
ones (set B-compounds 11–16 in Table 1). The amino
acid modification was employed for lipophilicity
increase (Table 1). In fact, the values of log P for
all simple amino acids were approximately equal to 1,

J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
31
diphenyl-imidazolone-4-one glycine [1,5]) and 23,
form a group of species having C5 atom in sp3
hybridisation.
3.2. Pharmacological properties
Selected compounds, whose chemical details are
described in Table 1, were evaluated in vitro for
their affinity to the glycine-binding site of NMDA
receptor (iGluRs). The in vivo preliminary phar-
macological testing results of all newly synthesised
compounds are presented in Tables 2 and 3. The
MES assay has predictive value for agents of
potential therapeutic value in the treatment of grand
mal epilepsy, whereas the ScMet test is for those
likely to be effective against petit mal. The TTE
test is a clinically non-selective electroconvulsive
seizure model, which detects compounds that raise
seizure threshold as well as those, which prevent
seizure spread. In addition, this test can identify
certain compounds that are inactive in both the
MES and the ScMet tests.
Fig. 2. Scattegram of log P vs. log D (at pH ¼ 7.4).
while those for the modified ones—ranged from 2 to
3. It is well illustrated by Fig. 2, which presents
the dependence of log P vs. log D (at pH ¼ 7.4) for
two sets of derivatives. Therefore, our search for
imidazoline-4-ones with log P , 3 has been well
designed (set B). Unfortunately, so far we have not
been able to improve compound affinity.
To support our discussion, simple amino acids
from Table 1 have been divided into two sets—A and
C. The natures of C5 atom, its substitution and/or
hybridisation were the reason for distinguishing
between both sets. Consequently, the set A gathers
previously studied [1] differently substituted benzyli-
dene-imidazoline-4-one glycines (1–5, 7, 8, 10 in
Table 1) and two new a-alanine analogues (6 and 9).
The 5-substituted-[4-oxo-2-imidazolidinyl]-glycines
from set C were studied in order to estimate the
lipophilic pocket size. Subsequently, in all derivatives
17–23, various aromatic groups and various linking
spacers have been located at C5. As follows, this set
collects compounds 17–19 accompanied with stan-
dard [–CHy] spacer (as in A and B sets) and various
aromatic cycles. In order to explore the lipophilic
pocket length, compounds with longer [–CHyCR3–
CHy] linking spacer joining phenyl and imidazole
rings (20 and 21) were investigated (see Scheme 1). In
the end, the change in hybridisation from sp2 to sp3 at
C5 atom in species 4 produced a new derivative 23.
That last compound has been designed as perceptive
analogue of the derivatives from set A. Derivative 23
differs from 4 only in hybridisation of C5 and,
consequently, possesses [–CH2 –] group as the
linking spacer. Thus, two derivatives, 22 (5,5-
The results from anticonvulsant assays for the
newly obtained compounds 6, 9, 11–21, and 23 are
summarised in Tables 2 and 3. Compounds 11, 12, 15,
and 18 have shown protective activity in the MES test
for mice, compounds 16, 18, 19, and 21 were active in
the ScMet test, compounds 6, 13, 14, 17, 19, 20, 21
and 23 were active in the TTE test, neurotoxicity has
been shown by compounds 6, 11, 12, 18, and 21.
Table 3
Anticonvulsant activity in the TTE test. The data are expressed as
animals protected/animals tested
Compound Dose
(mg/kg)
Time
0.25 h 0.5 h 1.0 h 2.0 h 4.0 h 6.0 h
6
100
1/4
1/4
1/4
0/4
0/4
0/4
0/4
0/4
1/4
0/4
0/4
0/4
0/4
1/4
0/4
0/4
0/4
1/4
1/4
0/4
0/4
0/4
0/4
0/4
1/4
0/4
1/4
0/4
0/4
0/4
0/4
0/4
1/4
3/4
1/4
0/4
3/4
0/4
0/4
0/4
0/4
0/4
2/4
1/4
0/4
–
13
14
16
17
19
20
21
23
100
100
100
100
100
100
100
100
0/4
–
–
–
–
–
–
0/4

32
J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
Fig. 3. The complex based on H-bonds interactions for [(Z)-5-(m-chlorol-benzylidene)-4-oxo-2-imidazolidinyl]-glycine 7. (a) With water and
ammonia ion; (b) with water and ammonia; (c) MEP distribution in the plane of imidazole; dotted lines with negative potential.
3.3. Structure–activity studies of benzylidene-
imidazolidyno-4-one amino acids
minimised by semiempirical methods (AM1). The
final complex of the most active derivative [(Z)-5-(m-
Cl-benzylidene)-4-oxo-2-imidazolidinyl]-glycine 7 is
presented in Fig. 3(a). Water molecule, corresponding
to H-bond acceptor from Fig. 1(b), binds both N–H
groups. Ammonia ion NHþ4 forms two H-bonds with
both potential acceptors (Fig. 3(a)) from the ligand
molecule. It should be noticed that ammonia mol-
ecule—also H-bond donor—is linked only to one of
two possible acceptors (Fig. 3(b)). It is understandable
from the distribution of molecular electrostatic
potential round the ligand molecule (MEP-calculated
after AM1 optimisation) depicted in Fig. 3(c). We can
find two MEP minima designed as potential H-bond
acceptors: one near the endocyclic nitrogen and the
other one at the carboxyl oxygen. However, only
As it was postulated in the introduction, we
adapted receptor binding model with iGluRs (Fig. 1)
to benzylidene-imidazolidyno-4-one glycines [6].
Analysing this model, it seems possible and useful
to simulate the complex formation of a selected
molecule with at least H-bond donor and acceptor (the
proposed strategy can be classified as 4D QSAR [19]
methodology). To achieve this objective, in first stage
we were trying to simulate interactions between only
two small particles: water (H-bond acceptor) and
ammonia ion (H-bond donor). After the docking
procedure (employing molecular mechanics formal-
ism), the energy of the joined molecules was

J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
33
Fig. 4. (a) The complex of [(Z)-5-(m-chlorol-benzylidene)-4-oxo-2-imidazolidinyl]-glycine 7 with basic lysine and acidic aspartic acid; (b)
MEP distribution in the plane of imidazole.
the deeper one at nitrogen was useful in the formation
of the complex with ammonia.
Fig. 4(b). If this model is realistic, the energy of
the complex formation (or binding energy of the
amino acids with ligand molecules) should more or
less correlate with the inhibition to the receptor
[21]. Three isomers 1, 7, and 10 with p-, m-, o-Cl
substituents in benzylidene and different inhibition
(Table 1) are convenient examples to confirm
model implicitly. The thermodynamic stability
data (in the form of Hf—heat of formation) of all
three ligands Hf (1) and corresponding complexes
Hf (2) are gathered in Table 4. These values
indicate that the complex of the most active
Promising results, presented in Fig. 3, have
stimulated us to construct a complex of the [(Z)-5-
(m-Cl-benzylidene)-4-oxo-2-imidazolidinyl]-glycine
7 with selected amino acids. It is clear that the
chosen amino acids should be present in the
corresponding receptor [9,20]. In this example,
basic lysine and acidic aspartic acid were desig-
nated as the species for complex formation. Finally,
the complex given in Fig. 4(a) was obtained and
the corresponding MEP distribution is presented in
Table 4
Thermodynamic parameters for selected [(Z)-5-(chlorol-benzylidene)-4-oxo-2-imidazoli-dinyl]-glycines and a-alanines and their correspond-
ing complexes with basic lysine and acidic aspartic acid
Compound
Inhibition
(%)
Heat of formation [kcal/mol]
Hf(1)
Hf
DHf ¼ Hf (1) 2 Hf (2)
(2)
1
51
274.76
273.95
273.33
278.07
275.39
2370.70
2370.39
2369.30
2374.55
2372.37
2296.01
2296.44
2295.97
2296.48
2296.98
7
90
10
6
18
28.6
90.3
9

34
J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
derivative 7 (90% of inhibition) is also the most
stable thermodynamically. Thus, we are able to
assume that the following difference:
only two such groups of derivatives can be found,
both described above.
3.4. Structures and properties of non-benzylidene-
imidazolidyno-4-one glycines
DHf ¼ Hfð2Þ 2 Hf
ð1Þ
The compounds from set C (all glycines) have
been designed to focus our attention to substitu-
ent(s) at C5 atom. In all 17–23 glycines from this
set, benzylidene rings are unsubstituted. For this
reason compound 4 was selected as a reference
molecule for the subsequent structure–activity
analysis.
corresponds to the binding energy of the amino acids
with ligand molecules. It was found that the
inhibition and DHf for three chlorine isomeric
derivatives (1, 7, and 10) exhibit logical dependence
visible in Fig. 5.
During the investigation, the docking procedure
was applied for simple as well as for isomeric
a-alanines 9 and 6. Numerical results of those
calculations are included into Table 4. After
supplementation of the data for three isomeric
glycines with those for two isomeric a-alanines (9
and 6), analogous logical dependence between
inhibition and DHf was obtained (Fig. 5). These
two examples have confirmed that the substitution
pattern in benzylidene is very important. The
binding energy of the amino acids with ligand
molecules in the form of DHf (Table 4) approxi-
mately agrees with activity of the isomeric
molecules. The activity of these compounds is
affected by the substituent position and decreases in
the order m-Cl . p-Cl . o-Cl.
Despite the differences in C5 atom hybridisation
and/or the number of atoms in the spacer between
aromatic and imidazole rings, the volume of whole
substituent(s) at C5 is presumed to be important for
binding. To validate such assumption, the volumes of
molecules from set C and of respective substituents at
C5 have been calculated (Table 5). One can see that
only volumes of 17 and 23 agree with the volume of
the reference molecule 4. Thus, presumably the
activity lowering for 18–22 was a direct result of
the volume limitation in lipophilic pocket. Never-
theless, based on contemporary knowledge, the
deeper discussion on this subject is impossible at
this moment.
The molecules 17 and 23 are especially interesting.
Despite comparable molecule volume, these deriva-
tives are significantly less active than the reference
one 4 (Table 1). To explain this observation,
conformational analyses of both molecules were
performed firstly. It was established that there are
It should be emphasised that the procedure
described above is based on comparison of the heat
of formations for group of isomeric species. In Table 1
Table 5
The volume of the substituent(s) at C5 for derivatives from sets C.
The compound 4 was added as reference molecule
3
Volume (A ) of
˚
Compound Substituent at C5
Molecule Substituent
4
Phenyl–CHy
278
273
340
339
318
116
111
178
177
156
177
194
126
17
18
19
20
21
22
23
Pyridine–CHy
a-Naphtalene–CHy
b-naphtalene–CHy
Ph–CHyCH2–CHy
Fig. 5. Relationship between inhibition to iGluRs and binding
energy in complex with basic lysine and acidic aspartic acid for
isomeric [Z-(Cl-substituted-benzylidene)-4-oxo-2-imidazolidinyl]-
glycines and a-alanines.
Ph–CHyCH(CH3)–CHy 339
Ph, Ph
356
288
Ph–CH2–, H

J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
35
Fig. 6. Two possible (I and II) complexes of 17 with water and ammonia.
three possible conformations for molecule 23 of
almost equal energy. However, all of them are far
from planarity and none of them is superimposed with
the reference molecule 4. Therefore, molecule 23
cannot fulfil binding model environs. Now, it becomes
clear why the benzyl analogue is less active than the
benzylidene reference molecule. After conformation-
al calculations for 17 it was established that the
pyridil-3 substituent was able to adopt, with similar
probability, two opposing orientations in the molecule
(Fig. 6). Hence, the complexes simulation with water
and ammonia ion should be performed for both
conformers of 17. As one can see, in complex with
first form (I), the pyridine nitrogen participates as
dominating H-bond acceptor. This complex does not
agree with the model accepted previously for
benzylidene reference derivatives (see Fig. 3). One
can anticipate that two potential and different ways of
H-bond formation unquestionably reflect-on the
inhibition lowering with respect to the reference
molecule 4.
all, these small molecules are able to easily
distinguish some pharmacophoric points in the
molecule of the ligand. Subsequently, it can be
utilised to simulate potential ligand–receptor inter-
action with chosen amino acids. In some cases (for
example: isomeric molecule) heat of formations,
being corresponding to binding energy of the amino
acids with ligands, can provide a rational interpret-
ation of discrepancy in biological properties of the
studied isomeric derivatives. On the other hand, the
model of the complex with small particles may be
used as advantageous tool for preliminary selection
of the studied molecules.
5. Elemental analyses
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]alanine (6): C13H12N3O3Cl. Calcd:
C
53.15; H 4.12; N 14.31. Found: C 52.93, H 4.18,
N 14.03.
N-[5-(Z)-(3-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]alanine (9): C13H12N3O3Cl. Calcd: C 53.15; H
4.12; N 14.31. Found: C 53.34, H 4.00, N 14.18.
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
4. Conclusion
Model of the hydrogen bonds formation between
ligand molecule and small chemical particles (water
and ammonia), proposed in this paper, might be
very useful in structure–activity studies. First of
lidinyl]-(4-chlorophenyl)alanine
(11):
C19H15N3O3Cl2. Calcd: C 56.45; H 3.74; N 10.39.
Found: C 56.61, H 3.59, N 10.06.

36
J. Karolak-Wojciechowska et al. / Journal of Molecular Structure 649 (2003) 25–36
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]-(2-chlorophenyl)alanine (12):
C19H15N3O3Cl2. Calcd: C 56.45; H 3.74; N 10.39.
Found: C 56.27, H 3.67, N 10.21.
Professor P. Leeson and Dr S. Grimwood (Merck,
Sharp and Dohme Research Laboratories, Harlow,
UK) for the financial support and for providing the
tests of inhibition of [3H]-L-689 560 binding to rat
brain membranes. We are also grateful to Professor
J.P. Stables for providing pharmacological data
through the Antiepileptic Drug Development Pro-
gram, National Institutes of Health.
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]-4-fluorophenylalanine (13): C19H15N3O3ClF.
Calcd: C 58.84; H 3.90; N 10.84. Found: C 58.61, H
4.07, N 10.90.
N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]-phenylalanine (14): C19H16N3O3Cl. Calcd: C
61.71; H 4.36; N 11.36. Found: C 61.42, H 4.51, N
11.05.
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[1] K. Kiec-Kononowicz, J. Karolak-Wojciechowska, J. Hand-
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N-[5-(Z)-(4-chlorobenzylidene)-4-oxo-2-imidazo-
lidinyl]-tryptophan (15): C21H17N4O3Cl. Calcd: C
61.69; H 4.19; N 13.71. Found: C 62.01, H 4.02, N
13.81.
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[3] A. Drabczyn˜ska, J. Karolak-Wojciechowska, K. Kiec-Kono-
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lidinyl]phenylglycine (16): C18H14N3O3Cl. Calcd: C
60.77; H 3.97; N 11.81. Found: C 60.44, H 3.77, N
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N-[5-(pyridyl-3)-methylene-4-oxo-2-imidazolidi-
nyl]glycine (17): C11H10N4O3. Calcd: C 53.66; H
4.09; N 22.76. Found: C 53.97, H 4.20, N 22.97.
N-[5-(naphthyl-1)-methylene-4-oxo-2-imidazolidi-
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C
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N 14.30.
N-[5-(naphthyl-2)-methylene-4-oxo-2-imidazolidi-
nyl]glycine (19): C16H13N3O3. Calcd: C 65.08; H
4.44; N 14.23. Found: C 65.39, H 4.57, N 13.92.
N-(5-cinnamylidene-4-oxo-2-imidazolidinyl)gly-
cine (20): C14H13N3O3 £ 0.33 CH3COOH. Calcd: C
60.49; H 4.96; N 14.44. Found: C 60.26, H 5.19, N
14.10.
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lidinyl]glycine (21): C15H15N3O3. Calcd: C 63.15; H
5.30; N 14.73. Found: C 63.41, H 5.24, N 14.97.
N-(5-benzyl-4-oxo-2-imidazolidinyl)glycine (23):
C12H13N3O3 £ 0.66 CH3COOH. Calcd: C 55.76; H
5.49; N 14.65. Found: C 55.57, H 5.69, N 14.53.
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Acknowledgements
The financial support for the synthetic and
computational parts of this research—carried out
under the Polish State Committee for Scientific
Research, grant No 4 P05F 007 17—is gratefully
acknowledged. The authors wish to acknowledge
[21] C.G. Wermuth, The practice of Medicinal Chemistry,
Academic Press, New York, 2001, pp. 167–180, fourth
printing.