Imidazo[2,1-b]thiazoles, imidazo[2,1-b]imidazoles and pyrrolo[1,2-c]imidazoles. Synthesis, structure and evaluation of benzodiazepine receptor binding

Article abstract of DOI:10.1002/jhet.5570390201

As a continuation of our studies on bicyclic heterocycles with benzodiazepine receptor affinity, derivatives with a 5:5 bicyclic skeleton, namely imidazo[2,1-b]thiazoles, imidazo[2,1-b]imidazoles and pyrrolo[1,2-c]imidazoles were prepared. The compounds p

Full text of DOI:10.1002/jhet.5570390201

Mar-Apr 2002
Imidazo[2,1-b]thiazoles, Imidazo[2,1-b]imidazoles
and Pyrrolo[1,2-c]imidazoles. Synthesis, Structure
and Evaluation of Benzodiazepine Receptor Binding
243
K. Kiec´-Kononowicz* [a], C.E. Müller [b], E. Pe¸kala [a],
•
⁄
J. Karolak-Wojciechowska [c], J. Handzlik [a] and D. Lazewska [a]
[a] Jagiellonian University, Medical College, Department of Chemical Technology of Drugs,
Medyczna 9, Pl 30-688 Kraków, Poland
[b] Pharmaceutical Institute Poppelsdorf, University of Bonn, Kreuzbergweg 26, D-53115 Bonn, Germany
•
⁄
[c] Institute of General and Ecological Chemistry, Technical University, Zwirki 36, Pl 90-924Lódz´, Poland
Received August 21, 2000
As a continuation of our studies on bicyclic heterocycles with benzodiazepine receptor affinity, deriva-
tives with a 5:5 bicyclic skeleton, namely imidazo[2,1-b]thiazoles, imidazo[2,1-b]imidazoles and
pyrrolo[1,2-c]imidazoles were prepared. The compounds possessed an aromatic substituent with different
spatial arrangement and distance to the bicyclic skeleton. X-ray structure analysis was performed for Z-2-(4-
chlorobenzylidene)-5,5-diphenyl-2,3,5,6-tetrahydroimidazo[2,1-b]imidazoline-3,6-dione (6a) and 5-amino-
6-cyano-7-phenyl-1-oxo-3-thioxo-2,3-dihydro-1H-pyrrolo[1,2-c]imidazole (20a). In contrast to the
previously described arylideneimidazo[2,1-b]thiazepinones the smaller heterocyclic ring systems
investigated in this study were devoid of meaningful benzodiazepine receptor affinity as well as anti-
convulsant activity.
J. Heterocyclic Chem., 39, 243 (2002).
Introduction.
condensed nitrogen-containing heterocyclic compounds. The
importance of rotatable aromatic rings in BZR ligands for the
recognition and activation of BZR has been underlined [11].
As part of our wider program on SAR studies evaluating
the BZR binding of bicyclic heterocycles, we have
previously synthesized and biologically examined
diphenyl and arylidene imidazo[2,1-b]thiazines,
imidazo[2,1-b]thiazepines [1] (Scheme 1a), imidazo-
[2,1-b]pyrimidines, and imidazo[2,1-b]diazepines [3].
In the present work, the synthesis and BZR binding of a
new series of imidazo[2,1-b]thiazoles, imidazo[2,1-b]-
imidazoles and pyrrolo[1,2-c]imidazoles possessing
aromatic groups, with different lipophilic, steric and
electronic features are reported.
Various hetero-bicyclic structures with two five-
membered rings (abbreviated as 5+5 bicyclic skeleton)
were obtained. All of them contain at least two nitrogen
atoms (Scheme 1b) and an –N=C– structure. For reasons
of clarity in the future discussion, four quadrants in the
5+5 bicyclic skeleton were assigned as shown in Scheme
1b. According to this convention, the nitrogen that forms
the double bond with a neighboring carbon atom is located
In our studies on bicyclic heterocycles with potential
central nervous system activity containing an imidazole
moiety, we focused on central benzodiazepine receptor
(BZR) ligands [1–3]. Benzodiazepines [4], which mediate
their actions at the BZR as full agonists, exhibit a wide
variety of pharmacological actions, such as anxiolytic,
sedative/hypnotic and anticonvulsant activities. They are
the most widely studied and most commonly used drugs in
the treatment of generalized anxiety disorders.
Benzodiazepines are very potent, rapid-onset anxiolytics,
however non-curative. In severe cases of anxiety, patients
may need life-long therapy. Benzodiazepines exhibit
numerous side effects such as physical dependence,
amnesia, oversedation, muscle relaxation, or ethanol
potentiation. For therapeutic purposes, it would be useful
to find BZR partial agonists devoid of the above-
mentioned side effects.
Ligands at BZR do not only belong to the structural class of
benzodiazepines [5], but a large number of ligands from
different chemical families including imidazopyridines [6],
β-carbolines [7], imidazoquinoxalines [8], triazinobenz-
imidazolones [9] and pyrazoloquinolines [10] have been
shown to bind with high affinity to BZR. All of them are

244
K. Kiec´-Kononowicz, C.E. Müller, E. Pe¸kala,
Vol. 39
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J. Karolak-Wojciechowska, J. Handzlik and D. Lazewska

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Imidazo[2,1-b]thiazoles, Imidazo[2,1-b]imidazoles and Pyrrolo[1,2-c]imidazoles
245
on the axis separating quadrants C and D. Consequently,
two possible positions for the second imidazole nitrogen
atoms lead to two series of derivatives as shown in
Scheme 1b: series aa with the second nitrogen atom in
quadrant A (e.g., imidazothiazoles 3, 4 – Scheme 2, 18, 19
– Scheme 3b and imidazoimidazolones 5, 6 – Scheme 2,
11, 12 – Scheme 3a) and series bb with a nitrogen atom on
the line between quadrants A and C (Scheme 1b)
(pyrroloimidazoles 20 – Scheme 4). It should be noted that
the derivatives from the series aa contain an additional
heteroatom in the quadrant B marked as X (sulfur or
nitrogen). Moreover, some examples of that series can
differ significantly in substitution pattern and hybridiza-
tion of the four border carbon atoms. This results in
different chemical and biological properties and causes a
variety of geometrical phenomena. In the present paper,
the chemical aspects of the 5+5 bicyclic compounds will
be discussed. The description of structural variations will
be the subject of a subsequent paper [12].
substituent (or substituents) should be placed in different
spatial arrangements and different distances. So, diphenyl
derivatives 3 and 4 (Scheme 2) as well as phenyl deriva-
tives 20a and 20b (Scheme 4) were designed. In addition,
the synthesis of compounds 6 (Scheme 2), 11a–11c
(Scheme 3a), 18 and 19 (Scheme 3b), possessing more
than one aromatic substituent were projected. Among
them, compounds 6, 11a–11c and 18 were aimed at
probing the areas of quadrants B and D of the molecules
with respect to aromatic substituents.
The second aim of this study was to examine the
influence of the differently organized hetero-bicyclic
skeletons (Scheme 1b) on BZR affinity of the compounds.
The designed imidazothiazole derivatives 3, 4, 18, and 19
were intended for comparison with the imidazoimidazole
derivatives 6, 11a–11c, 12a–12b, both from series aa, and
with the pyrroloimidazoles 20a, 20b (Scheme 2–4)
representing series bb.
Chemistry.
One important goal was to synthesize and investigate
bicyclic compounds bearing aromatic substituents in
different spatial positions. Up to now, the compounds that
we had examined possessed phenyl substituents mainly in
quadrants A and C [1–3]. In the present study, new
compounds were to be synthesized in which the phenyl
5+5 Bicyclic Derivatives from Series aa.
The synthesis of the diphenyl derivatives 3a, 3b, 4a, 4b
with X=S and 5a, 5b with X=N (Scheme 1 and 2) was
described previously [13–15]. Condensation of 5a or 5b

246
K. Kiec´-Kononowicz, C.E. Müller, E. Pe¸kala,
Vol. 39
•
⁄
J. Karolak-Wojciechowska, J. Handzlik and D. Lazewska
with 4-chlorobenzaldehyde, led to 6a (X=N). Acetyl
derivative 5b was deacetylated during the reaction. The
6b
1
13
spectral ( H, C nmr, ms) and elemental analyses allowed
to confirm structure 6a. Such a compound may exist in E
or Z form. Our experience with the condensation of
benzaldehydes with compounds containing active
methylene groups suggested that the Z-isomer would be
preferred [2,15,16–20]. Moreover, 6a may exist in the two
tautomeric forms presented in Scheme 2. In order to
confirm the structure, configuration and topological
properties of 6a, X-ray structure analysis was performed.
The ORTEP drawing of structure 6a with atom numbering
is shown in Figure 1. All X-ray details, non-hydrogen
atoms fractional coordinates and selected geometrical data
are collected in Tables 1, 2 and 3.
X-ray structure analysis (Figure 1) confirms the
Z-configuration of 6a. However, the unambiguous
assignment to either tautomer 6a-I or 6a-II (Scheme 2) is not
possible. This is due to the fact that in the independent unit
cell two units of 6a were found, marked as molecules a and b
(Table 2). These molecules are not identical (Table 3);
differences are found particularly in the bond lengths of C2-N
(3 and/or 6). Molecule a, with double bond N3a-C2a =
1.293(4) Å corresponds to the tautomer 6a-I, while the
molecule b with shorter N6b-C2b = 1.266(4) Å suggests the
existence of a 6a-II tautomer. Unfortunately, the obtained
difference electron density map did not allow for the
assignment of the two hydrogen atoms attached to the hetero-
cyclic nitrogen atoms (N3a or N6a in molecule a and N3b or
N6b in molecule b) (Figure 2). Due to the monocrystal
properties (crashing), low temperature diffraction measure-
ment was impossible. The only rational interpretation of the
6a
Figure 1. ORTEP view of two independent molecules of 6a. Possibly H-
bonds directions were marked by dotted lines.
molecules of 6a-I or 6a-II. Having this conclusion in mind,
only H-bonds were marked in Figure 1 by dashed lines, but
unquestionably both tautomers are present in the crystal. In
addition, based on crystallographic data, it was established
that elements of the bicyclic structure (5+5) are practically
planar and incline to each other at 2.4(2)° and 3.9(2)° respec-
tively in molecules a and b.
From theoretical calculations (MOPAC.6 in AM1 approx-
imation [25]), tautomer 6a-II is thermodynamically more
stable by 11 kcal/mol. However, in solution (DMSO), we
1
suppose that form 6a-I dominates on the basis of H nmr
….
H-bond pattern [with distances N3a (or b) N6b (or a)
equaling 2.995(3) Å] would be that in the crystal the dimeric
associates shown in Figure 1 are statistically formed by two
analysis, which is well in accordance with the structure of
5a. An earlier performed X-ray analysis confirmed structure
5a as presented in Scheme 2 [15]. The signal of the N–H

Mar-Apr 2002
Imidazo[2,1-b]thiazoles, Imidazo[2,1-b]imidazoles and Pyrrolo[1,2-c]imidazoles
247
Table 1
X-ray Structure Analysis of 6a and 20a
A. Crystals Parameters
Data for 6a
Data for 20a
H N O S, C H N O
formula
C
H
Cl N O
C
13
24 16
3
2
8
4
3
7
molecular weight
crystallization medium
colour
crystal size, mm
cell dimensions
413.86
ethanol
colourless
341.39
DMF
intensive yellow
0.1 x 0.1 x 0.5 mm
a = 3.9220(10) Å
b = 39.026(8) Å
c = 10.621(2) Å
β = 99.11(3) °
0.1 x 0.15 x 0.3 mm
a = 9.232(2) Å
b = 14.366(3) Å
c = 29.996(6) Å
β = 96.98(3) °
space group
P2 /n
P2 /c
1
1
molecules/unit cell
density calcd.
linear absorption factor, mm
8
1.392 Mg•m
19.3
4
–3
–3
1.413 Mg•m
1.966
–1
B. Refinement Parameters.
number of reflections
nonzero reflection [I>4σ(I)]
R-index
4608
1709
0.0699
0.73
3361
1319
0.0482
0.677
GOF
secondary extinction factor C, χ
NONE
0.00000(17)
proton was observed at 10.30 ppm. The N–H signal of struc-
ture 6a was found at 13.20 ppm. The significant downfield
shift was presumably caused by the influence of the neigh-
boring arylidene substituent. Such a deshielding effect was
also observed when the signals of the unsubstituted
5,5-diphenyl hydantoin protons (N –H, N –H) observed at
9 and 11 ppm were compared with those of the 5-arylidene
ones occurring both at ~12 ppm (e.g., 17).
Arylidene imidazo[2,1-b]imidazole-3,5-dione deriva-
tives 11a–11c and 12a–12b were obtained by a method
which had been developed in our group for the preparation
of compound 12b [15]. So, the appropriate 5-arylidene-2-
thiohydantoin derivatives 7 were methylated using methyl
iodide to yield the 2-methylthio-derivatives 8, which were
treated with glycine or glycine derivatives 9. The resulting
glycine-amidine derivatives were refluxed with acetic acid
anhydride to yield the imidazo[2,1-b]imidazole-3,5-diones
11a–11c and 12a–12b (Scheme 3a). For the synthesis of
compounds 18 and 19, the starting benzaldehyde (15) was
obtained by alkylation of 3-hydroxybenzaldehyde with
2,4-dichlorobenzyl chloride (Scheme 3b). Compound 15
was condensed with 2-thiohydantoin (16) to yield 5-aryli-
dene-2-thiohydantoin derivative 17. Cyclization of 17 with
1
3
Figure 2. Different electron density map for 6a. Projection in the plane
Figure 3. ORTEP view of 20a, 20a crystallized with dimethyl formamide
passes by the atoms N3a, N6b and N6b.
molecule. Intramolecular H-bonds are marked by dotted lines.

248
K. Kiec´-Kononowicz, C.E. Müller, E. Pe¸kala,
Vol. 39
•
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J. Karolak-Wojciechowska, J. Handzlik and D. Lazewska
Table 2
Table 2 (continued)
4
x
Atomic Coordinates ( 10 )) and Equivalent
2
x
Isotropic Displacement Parameters (Å 10 )
Compound 20a
x
y
z
U(eq)
Compound 6a
x
y
z
U(eq)
S
C1
C2
C9
N10
C3
N3
N4
C5
N6
C7
O7
C8
C11
C12
C13
C14
C15
C16
O1'
C2'
N3'
C4'
C5'
2214(2)
-2094(5)
-2282(5)
-3660(6)
-4826(5)
-1135(5)
-772(4)
-234(4)
1121(5)
1185(4)
34(5)
3659(1)
4137(1)
4395(1)
4729(1)
4998(1)
4262(1)
4399(1)
3927(1)
3652(1)
3395(1)
3483(1)
3289(1)
3845(1)
4176(1)
3892(1)
3938(1)
4258(1)
4537(1)
4497(1)
2748(1)
2629(1)
2312(1)
2188(1)
2079(1)
3834(1)
7616(2)
6638(2)
6654(2)
6587(2)
5553(2)
4449(2)
5854(2)
5234(2)
6093(2)
7250(2)
8134(1)
7061(2)
8877(2)
9569(2)
10760(2)
11307(2)
10658(2)
9454(2)
5728(2)
6694(3)
6864(2)
8019(3)
5777(3)
69(1)
56(1)
54(1)
59(1)
82(1)
53(1)
66(1)
53(1)
53(1)
62(1)
59(1)
77(1)
54(1)
55(1)
68(1)
78(1)
79(1)
75(1)
71(1)
89(1)
81(1)
83(1)
136(1)
138(1)
Molecule a
Cl1
O4a
O8a
N1a
N3a
N6a
C2a
C4a
C5a
C7a
C8a
C9a
C41a
C42a
C43a
C44a
C45a
C46a
C51a
C52a
C53a
C54a
C55a
C56a
C91a
C92a
C93a
C94a
C95a
C96a
8154(1)
-2610(3)
2825(3)
0859(3)
-0717(3)
1761(3)
0561(4)
-1457(4)
-0453(4)
2820(4)
2238(5)
4235(4)
0832(4)
1200(7)
0767(6)
-0083(9)
-0477(6)
-0048(4)
-1162(4)
-0676(4)
-1458(5)
-2696(5)
-3215(4)
-2469(4)
5084(4)
4675(4)
5592(4)
7013(4)
7431(4)
6514(4)
6865(1)
9438(2)
8159(2)
8560(2)
8915(2)
8324(2)
8625(2)
9178(2)
8964(3)
8064(3)
8265(3)
7721(3)
9781(3)
10533(4)
11388(3)
11467(3)
10655(3)
9822(3)
8202(3)
7299(3)
6675(3)
6919(3)
7831(3)
8480(3)
7497(2)
7652(2)
7450(3)
7104(2)
6960(3)
7097(3)
1908(1)
3292(1)
4074(1)
3570(1)
2938(1)
2929(1)
3105(1)
3314(1)
3756(1)
3268(1)
3703(1)
3285(1)
4426(1)
4679(2)
4530(2)
4139(2)
3889(2)
4038(1)
4027(1)
4067(1)
4297(1)
4464(1)
4434(1)
4200(1)
2930(1)
2481(1)
2170(1)
2303(1)
2752(1)
3051(1)
79(5)
68(1)
66(1)
50(1)
52(1)
48(1)
54(2)
49(2)
50(2)
55(2)
63(2)
62(2)
109(2)
143(3)
107(3)
178(4)
120(3)
60(2)
52(2)
65(2)
82(9)
75(9)
70(2)
60(2)
53(2)
55(2)
62(1)
51(2)
75(2)
58(2)
-79(4)
-895(5)
-3008(5)
-3926(6)
-4795(6)
-4698(6)
-3706(6)
-2890(5)
3398(4)
4941(7)
6195(5)
7974(8)
5587(9)
dibromoethane yielded a mixture of imidazo[2,1-b]thiazole
derivatives 18 and 19. In accordance with previously
described results [19], compound 19, the product of the
2,3-cyclization of 2-thiohydantoin 17, was obtained as the
major product and 18, 19 are in Z-configuration.
Molecule b
Cl2
O4b
O8b
N1b
N3b
N6b
C2b
C4b
C5b
C7b
C8b
C9b
C41b
C42b
C43b
C44b
C45b
C46b
C51b
C52b
C53b
C54b
C55b
C56b
C91b
C92b
C93b
C94b
C95b
C96b
163(1)
2818(3)
-2728(3)
-0664(3)
0873(3)
-1554(3)
-0488(4)
1563(4)
0521(4)
-2727(4)
-2157(4)
-4082(4)
0128(4)
-0733(5)
-1071(4)
-0801(6)
0116(6)
0460(4)
1284(4)
0859(4)
1590(5)
2756(4)
3305(5)
2430(4)
-4969(4)
-4531(4)
-5403(4)
-6746(4)
-7275(4)
-6339(4)
10683(1)
8103(2)
9295(2)
8931(2)
8604(2)
9229(2)
8933(2)
8379(3)
8552(2)
9408(2)
9198(3)
9734(3)
7634(3)
7717(3)
6888(3)
6053(3)
5975(3)
6782(3)
9251(3)
10232(3)
10853(3)
10578(3)
9667(3)
9029(3)
9958(2)
9825(3)
10054(3)
10436(3)
10642(3)
10382(3)
3011(1)
1596(1)
0823(1)
1327(1)
1944(1)
1971(1)
1783(1)
1574(1)
1134(1)
1618(1)
1196(1)
1622(1)
0878(1)
0456(1)
0236(1)
0408(1)
0817(1)
1053(1)
864(1)
79(5)
65(1)
85(1)
51(1)
45(1)
50(1)
49(2)
57(2)
48(1)
46(1)
54(2)
55(2)
57(2)
88(9)
82(2)
100(9)
99(9)
68(2)
57(2)
70(2)
89(2)
89(2)
90(9)
68(2)
46(1)
54(2)
58(2)
62(2)
66(2)
66(2)
5+5 Bicyclic Derivatives from Series bb.
The synthesis of the monophenyl derivatives 20a and 20b
from series bb of the 5+5 bicyclic derivatives under discus-
sion is presented in Scheme 4. The compounds were obtained
according to a method described in the literature [21] with the
addition of malononitrile to the 5-arylidene-2-thiohydantoin.
However, in contrast to the described product (21) and the
claimed yields, we were only able to isolate starting material 7
in addition to small amounts of pyrrolo[1,2-c]imidazoles 20a
and 20b as products. The structures of the obtained
compounds 20 were confirmed by elemental and spectral
analyses. In the mass spectra, the molecular ions of the
1
compounds were observed. In the H nmr spectra, the
absence of signals characteristic of alkane protons eliminated
structure 21. Due to unclear structural identification, the struc-
ture of 20a was determined by means of X-ray structure
analysis. The ORTEP drawing of structure 20a with atom
numbering is shown in Figure 3. All X-ray details, non-
hydrogen atoms fractional coordinates and selected geo-
metrical data are collected in Tables 1, 2 and 3, respectively.
The structure of 20a (Figure 3) was unambiguously
confirmed by the values of the bond lengths observed in
the 5+5 skeleton (Table 3). All bonds in the
847(1)
605(1)
407(1)
423(1)
656(1)
1969(1)
2420(1)
2739(1)
2601(1)
2156(1)
1842(1)

Mar-Apr 2002
Imidazo[2,1-b]thiazoles, Imidazo[2,1-b]imidazoles and Pyrrolo[1,2-c]imidazoles
249
Table 3
Selected Geometrical Details in the Structures of 6a and 20a
Compound 6a: Selected bond distances (Å)
Molecule A
Molecule B
N1b
N3b
N3b
N6b
N6b
C4b
C7b
N1a
N3a
N3a
N6a
N6a
C4a
C7a
-C2a
-C2a
-C4a
-C2a
-C7a
-C5a
-C8a
1.393(3)
1.293(4)
1.437(4)
1.354(4)
1.374(4)
1.554(4)
1.498(5)
-C2b
-C2b
-C4b
-C2b
-C7b
-C5b
-C8b
1.356(4)
1.374(4)
1.385(4)
1.266(4)
1.442(4)
1.555(5)
1.461(5)
N3b……..N6a
2.995(3)
N6a……..N3b
2.995(3)
Compound 20a
a. Selected bond distances (Å)
S-C5
1.611(2)
C3-N4
N4-C8
N4-C5
C5-N6
N6-C7
C7-O7
C7-C8
1.379(2)
1.386(2)
1.407(2)
1.355(2)
1.418(2)
1.213(2)
1.463(2)
C1-C8
C1-C2
C2-C3
C2-C9
C9-C10
C3-N3
1.399(2)
1.442(2)
1.402(2)
1.412(2)
1.144(2)
1.316(2)
b. H-bonds geometry in the crystal of 20a
D-H….a
d(D-H)
0.9000
0.8985
0.8989
d(H….a)
2.5340
2.2095
1.8182
d(D….a)
3.2241(18)
3.019(3)
<(DHa)[°]
133.91
149.65
symm. cod.
N3 --H3a…S
N3 --H3b…N10
N6 --H6a…O1'
-1-x, 1-y, 1-z
2.716(2)
175.94
five-membered ring defined by the atoms C1, C2, C3, N4
and C8 are conjugated bonds. Therefore, all carbon atoms
are in sp hybridization including C1 holding the aromatic
evaluated by the Antiepileptic Drug Development (ADD)
Program with Phase I testing procedures [22,23]. Phase I
of the evaluation involved three tests: maximal
electroshock (MES), subcutaneous pentylenetetrazole
(scMet), and neurologic toxicity.
2
substituent. Moreover, the C1–C8 bond of 1.399(2) Å
showed double bond character with the shortest C-C bond
in the 5+5 skeleton. The second C-C double bond
corresponding to C2–C3 shows a distance of 1.402(2) Å.
In the structure of 20a, both five-membered rings from
5+5 moiety are planar and only slightly inclined against
each other at 1.9(1)°. The planarity of the skeleton is also
Results and Discussion.
The physicochemical properties of the obtained
compounds were preliminarily evaluated by calculation
(PALLAS program [24]) of their log P and log D values. For
6a, log P and log D values were calculated for both tautomers
I and II. Calculated physicochemical properties of the
obtained compounds (Table 4) have shown that only
compounds 20a and 20b are very sensitive to the pH of the
milieu showing very different values of log P and log D at pH
7 equal to pH 7.4, respectively, the remaining compounds
showed equal values. Calculated values of log P and log D for
both tautomers (I and II) of 6a were slightly different.
Although the log P/log D values of 18 and 19 are very high,
higher than those of 11a – 11c, contrary to 11a – 11c (which
were insoluble at test concentration of 25 µM) it was possible
to examine the in vitro 18 and 19 biological properties.
…
stabilized by an intramolecular N3–H S bond (Table 3
and Figure 3). In the crystal, two additional intermolecular
H-bonds are stabilizing the structure (Table 3).
Biological Evaluation of Selected Compounds.
Biological evaluation was performed for selected
compounds, namely 3a, 3b, 4a, 4b, 6a, 12a, 12b, 18, 19,
20a, and 20b (Table 4). These compounds were
investigated in radioligand binding assays at rat brain
cortical membranes [1]. All compounds were screened for
3
their potency to displace [ H]diazepam from its binding
site in a single concentration (25 µM). Compounds
11a–11c were excluded from the biological evaluation
since they were insoluble in the test concentration of
25 µM. In addition, compounds 6a, 12a and 12b were
The results of the biological in vitro evaluation obtained
for the 5+5 bicyclic diphenyl, arylidene and phenyl deriva-
tives are presented in Table 4. The 5+5 bicyclic derivatives

250
K. Kiec´-Kononowicz, C.E. Müller, E. Pe¸kala,
Vol. 39
•
⁄
J. Karolak-Wojciechowska, J. Handzlik and D. Lazewska
Table 4
3
Inhibition of [ H]Diazepam Binding to Rat Brain Cortical Membranes by Bicyclic Diphenyl
(3a, 3b, 4a, 4b, 6a), Arylidene (12a, 12b, 11a-11c, 18, 19), and Phenyl Derivatives (20a, 20b)
Compound
%
[a]
Ref.
Log P
[b]
log D
[b]
pH=7.0
pH=7.4
3a
4a
3b
4b
6a
3 ± 10
8 ± 6
0 ± 11
0 ± 22
8 ± 2
[13]
[13]
[14]
[14]
2.06
2.23
2.64
2.06
2.23
2.64
2.06
2.23
2.64
2.81
2.81
2.81
3.49 [c]
3.79 [c]
2.60
3.33
2.15
0.39
0.39
4.54
4.79
3.49 [c]
3.79 [c]
2.60
3.33
2.15
0.39
0.39
4.54
4.79
3.49 [c]
3.79 [d]
2.60
3.33
2.15
0.39
0.39
4.54
4.79
11a
11b
11c
12a
12b
18
[e]
[e]
[e]
38 ± 1
10 ± 11
28 ± 3
1
[15]
19
20a
20b
0 ± 10
14 ± 5
0.33
0.97
-2.50
-2.06
-2.50
-2.06
3
[a] Percent specific inhibition of [ H]diazepam binding to rat brain cortical membranes at a drug concentration of 25 µM; results from at least 3 separate
experiments each in triplicate; [b] Log P, log D values calculated by means of the program PALLAS [24]; [c], [d] log P, log D values calculated for 6a
tautomer I [c] and tautomer II [d]; [e] Insoluble at the test concentration of 25 µM.
impact mass spectra were recorded on a Finningan MAT CH 7A
(70eV, 170 °C) spectrometer with direct inlet. Infrared spectra
were measured with an FT IR 410 spectrometer (Jasco). The H
were generally less potent as compared to the previously
described imidazothiazinones and imidazothiazepinones
[1] with bicyclic 5+6 and 5+7 skeletons. For the 5+5
bicyclic derivatives, the character of the nature of the
annelated ring (imidazothiazoles and imidazoimidazoles
from series aa or pyrroloimidazoles belonging to series
bb) as well as the nature of the attached aromatic ring(s)
(diphenyl, monophenyl, and arylidene) as well as their
distance or localization in the quadrants were without
influence on the activity. Similarly, neither the spatial
localization of the aromatic rings nor the physicochemical
properties of the compounds had any influence on the BZR
affinity. It seems that the small size and the coplanarity of
the 5+5 bicyclic skeleton are the factors that eliminate
BZR binding in this group of compounds. In the in vivo
tests, compounds 6a, 12a and 12b were devoid of
anticonvulsant activity (in doses up to 300 mg/kg), they
did not show neurological toxicity (in doses up to
300 mg/kg). Thus, pharmacological in vitro and in vivo test
results were in accordance.
1
nmr spectra were performed on a Bruker DPX 400, DPX 250
AVANCE, or a Bruker AC-200F in [d ]dimethylsulfoxide using
6
tetramethylsilane as internal standard; D O exchangable signals
2
were marked (*), splitting patterns are designated as s, singlet; d,
13
doublet; t, triplet; m, multiplet; br, broad; def, deformed. The
C
nmr spectra were measured with a Varian-Mercury 300 MHz
spectrometer. The uv spectra were obtained for solutions of
–5
5•10 mol/L concentration with a uv-vis-spectrometer (UV-VIS
V-530 Jasco). The elemental analyses were performed at the
Department of Pharmaceutical Chemistry of the Jagiellonian
University, Medical College.
The starting 2-thiohydantoins (7 and 17) were obtained as
previously described or in analogy to the described procedure
[26]. The new derivative was prepared described below.
3-(2,4-Dichlorobenzyloxy)-benzaldehyde (15).
a: A suspension of 3-hydroxybenzaldehyde (14) (6.1 g,
0.05 mole), 2,4-dichlorobenzyl chloride (9.8 g, 0.05 mole) and
K CO (3.45 g, 0.025 mole) in 50 ml of ethanol was refluxed for
2
3
4.5 hours. After cooling the solid was filtered off and washed
several times with water to give 15 (13.5 g), mp. 78–80 °C, tlc R
(A) – 0.61.
EXPERIMENTAL
f
Z-5-[3-(2,4-Dichlorobenzyloxy)benzylidene]-2-thiohydantoin (17).
Chemistry.
b: A mixture of 3-(2,4-dichlorobenzyloxy)benzaldehyde (15)
(15.46 g, 0.055 mole), anhydrous sodium acetate (16.5 g,
0.20 mole) and 2-thiohydantoin (5.8 g, 0.05 mole) in 65 ml of
glacial acetic acid was refluxed for 0.5 hour. The obtained
solution became dark. After cooling the precipitate that formed
was isolated by filtration, washed with water and recrystallized
Melting points were measured on a Mel-Temp II apparatus
(LD Inc, USA) and were not corrected. The tlc was performed on
Merck Silica gel GF
precoated tlc Al sheets; the solvent
254
systems used were: A, methylene chloride; B, chloroform:ethyl
acetate (1:1); C, toluene:acetone (20:1.5); D, chloroform:
isopropanol:ammonia aq 25% (9:11:2). Column chromatography
was performed on Merck silica gel 60 (70–230 mesh). Electron
from acetic acid to give 17 (15.6 g; 82%), mp 209–210 °C; tlc, R
f

Mar-Apr 2002
Imidazo[2,1-b]thiazoles, Imidazo[2,1-b]imidazoles and Pyrrolo[1,2-c]imidazoles
251
1
3'-H, 5'-H), 7.53–7.58 (m, 1H, 4'-H), 8.56–8.61 (m, 1H, 6'-H); ir
(KBr): ν 3085, 3066, 3027, (C–H), 1808 (CH CO), 1722 (C =O,
(A) –0.85; H nmr (250 MHz): δ 5.22 (s, 2H, CH O), 6.46 (s, 1H,
2
ArCH=), 7.03–7.07 (m, 1H, 5'-H), 7.34–7.39 (m, 3H, 3"-H, 5"-H,
6"-H), 7.47–7.51 (m, 1H, 4'-H), 7.63–7.70 (m, 2H, 2'-H, 6'-H),
12.20 (s, 1H, N –H), 12.39 (s, 1H, N –H); ir (KBr): ν 3172, 3052
(NH), 1727 (C=O), 1654 (ArCH=), 1484, 1369, 1241, 1031, 788,
689, 676.
Anal. Calcd. for C H N O SCl (379.27): C, 53.83; H, 3.19;
N, 7.39. Found: C, 53.64; H, 3.13; N, 7.04.
Compounds 3a, 4a [13], 3b, 4b [14], 5a, 5b [27], 8, [28], 12b
[15] were prepared as previously described.
3
2
C =O), 1664 (ArCH=), 1600 (C=N), 1419, 1257, 894, 773, 715.
4
Anal. Calcd. for C H N O Cl (393.82): C, 64.04; H, 4.09;
21 16 3 3
1
3
N, 10.67; Found: C, 64.29; H, 3.85; N, 10.46.
N-[Z-5-(2-Chlorobenzylidene)-4-oxo-2-imidazolidinyl]-(4-
chlorophenyl)alanine (10b).
17 12
2
2
2
Compound 10b was obtained by reaction of 8 and
4-chlorophenylalanine according to the method described for the
preparation of 10a; yield 62%, mp 248–250 °C (from
Z-2-(4-Chlorobenzylidene)-5,5-diphenyl-2,3,5,6-tetrahydro-
imidazo[2,1-b]imidazoline-3,6-dione (6a).
1
DMF/H O); tlc, R (D) 0.39; H nmr (400 MHz): δ 3.09 (br s,
2
f
1H, CH Ph), 3.23 (br s, 1H, CH Ph), 4.70 (br s, 1H, CHCH ),
2
2
2
6.64 (br s, 1H, ArCH=), 7.33 (m, 7H, 3'-H, 4'-H, 5'-H, 2"-H,
3"-H, 5"-H, 6"-H), 7.94 (br s, 1H, NHCH)*, 8.71 (br s, 1H, 6'-H),
10.66 (br s, 1H, NH)*, 13.13 (br s, 1H, COOH)*; ir (KBr): ν
3400 (COOH), 3164 (NH), 3083 (C–H), 1704 (C=O), 1650
(ArCH=), 1616 (C=N), 1536, 1357, 1292, 1186, 1035, 767.
Anal. Calcd. for C H N O Cl (404.24): C, 56.45; H, 3.74;
a: A mixture of 5a (2.91 g, 0.01 mole), anhydrous sodium
acetate (5.0 g, 0.06 mole) and 4-chlorobenzaldehyde (1.54 g,
0.011 mole) in 100 ml of acetic acid was refluxed for 4 hours.
After cooling, the formed precipitate was isolated by filtration
and recrystallized from ethanol to give 6 (1.9 g; 46%), mp
1
19 15
3
3
2
266–268 °C; tlc, R (B) – 0.72; H nmr (300 MHz): δ 6.92 (s, 1H,
f
N, 10.39; Found: C, 56.22; H, 3.65; N, 10.01.
ArCH=), 7.35–7.41 (m, 10H, ArH), 7.53 (d, J = 8.0 Hz, 2H, 3'-H,
5'-H), 8.08 (d, J = 8.0 Hz, 2H, 2'-H, 6'-H), 13.20 (br s, 1H, N -H);
1-Acetyl-2-(4-chlorobenzyl)-Z-6-(2-chlorobenzylidene)-2,3,5,6-
tetrahydroimidazo[2,1-b]imidazole-3,5-dione (11b).
7
13
C nmr: δ 73.50 (Ph C), 127.39, 128.73, 128.87 (aromatic
2
carbons), 128.73 (ArCH=), 132.48 (3'-C, 5'-C), 134.08 (2'-C,
6'-C), 136.21 (2'-C); ir (KBr): ν 3438, 3058 (NH), 1760, 1743
(C=O), 1673 (ArCH=), 1608 (C=N), 1488, 1120, 943, 790, 692;
Compound 11b was obtained as described for 11a; yield 25%,
1
mp 199–201 °C (from acetic acid); tlc, R (D) 0.77; H nmr
f
(200 MHz): δ 2.69 (s, 3H, CH CO), 3.33–3.39 (m, 2H, CH Ph),
3
2
uv (MeOH) λ
339 nm (log ε 4.55), λ
262 nm (log ε 3.96),
max
max
+•
5.21–5.26 (m, 1H, CHCH ), 7.14 (s, 1H, ArCH=), 7.15 (d, J = 8.3
2
λ
214 nm (log ε 4.22); ms: m/z 413 (M , 79), 385 (14), 357
max
Hz, 2H, 3"-H, 5"-H), 7.37 (d, J = 8.3 Hz, 2H, 2"-H, 6"-H),
7.42–7.46 (m, 2H, 3'-H, 5'-H), 7.52–7.58 (m, 1H, 4'-H),
8.58–8.63 (m, 1H, 6'-H); ir (KBr): ν 3085, 3060, 3019, 2931
(53), 308 (9), 274 (14), 246 (14), 208 (19), 205 (25), 194 (12),
180 (13), 165 (100), 150 (65), 129(20), 104 (57), 89(13).
Anal. Calcd. for C H N O Cl (413.87): C, 69.65; H, 3.90;
24 16
3 2
(C–H), 1803 (CH CO), 1737 (C =O), 1725 (C =O), 1664
3
2
4
N, 10.15; Found: C, 69.53; H, 3.92; N, 9.84.
b: Compound 6a was obtained with 64% yield under similar
conditions as described above, starting from 5b.
(ArCH=), 1600 (C=N), 1492, 1411, 1369, 1290, 1276, 1257,
1238, 1120, 894, 763.
Anal. Calcd. for C H N O Cl (428.26): C, 58.89; H, 3.53;
21 15
3
3
2
N, 9.81; Found: C, 58.65; H, 3.37; N, 9.59.
N-[Z-5-(2-Chlorobenzylidene)-4-oxo-2-imidazolidinyl]phenyl-
alanine (10a).
N-[Z-5-(2-Chlorobenzylidene)-4-oxo-2-imidazolidinyl]-phenyl-
glycine (10c).
A mixture of Z-5-(2-chlorobenzylidene)-2-methylthioimidazo-
line-4-one (8) (2.53 g, 0.01 mole) and phenylalanine (1.7 g,
0.011 mole) in 50 ml of acetic acid was refluxed for 6 hours.
After cooling the obtained precipitate was recrystallized from
Compound 10c was obtained as described for 10a; yield 35%,
1
mp 268–270 °C (from DMF/H O); tlc, R (D) 0.36; H nmr
2
f
(400 MHz): δ 3.82 (s, 1H, CHPh), 6.63 (s, 1H, ArCH=),
7.35–7.68 (m, 8H, 3'-H, 4'-H, 5'-H, 2"-H, 3"-H, 4"-H, 5''-H,
6"-H), 8.46 (br s, 1H, NHCH)*, 8.79 (s, 1H, 6'-H), 10.41 (br s,
1H, NH)*, 13.22 (br s, 1H, COOH)*; ir (KBr): ν 3261 (NH,
COOH), 3060 (C–H), 1700 (C=O), 1650 (ArCH=), 1614 (C=N),
1531, 1369, 1288, 1024, 750, 705.
DMF/H O to give 10a (2.5 g; 68%), mp 224–226 °C; tlc, R (D)
2
f
1
0.32; H nmr (400 MHz): δ 3.09 (def t, 1H, CH Ph), 3.24 (def t,
2
1H, CH Ph), 4.71 (br s, 1H, CHCH ), 6.64 (s, 1H, ArCH=),
2
2
7.29–7.37 (m, 8H, 3'-H, 4'-H, 5'-H, 2"-H, 3"-H, 4"-H, 5"-H,
6"-H), 7.92 (br s, 1H, NHCH)*, 8.72 (br s, 1H, 6'-H), 10.63 (br s,
1H, NH)*, 12.83 (br s, 1H, COOH)*; ir (KBr): ν 3421
(NH, COOH), 3064, 3031, (C–H), 1700 (C=O), 1602 (C=N),
1357, 1290, 1033, 761, 700.
Anal. Calcd. for C H N O Cl (355.77): C, 60.76; H, 3.97;
18 14
3 3
N, 11.81; Found: C, 60.48; H, 3.91; N, 11.58.
1-Acetyl-2-phenyl-Z-6-(2-chlorobenzylidene)-2,3,5,6-terahydro-
imidazo[2,1-b]imidazole-3,5-dione (11c).
Anal. Calcd. for C H N O Cl (369.80): C, 61.71; H, 4.36;
19 16
3 3
N, 11.36; Found: C, 61.46; H, 4.31; N, 11.22.
Compound 11c was obtained as described for 11a; yield
1-Acetyl-2-benzyl-Z-6-(2-chlorobenzylidene)-2,3,5,6-
tetrahydroimidazo[2,1-b]imidazole-3,5-dione (11a).
1
35%, mp 175–176 °C (from acetic acid); tlc, R (D) 0.69; H
f
nmr (200 MHz): δ 2.61 (s, 3H, CH CO), 5.93 (s, 1H, CHPh),
3
A suspension of 10a (1 g) in 10 ml of acetic acid anhydride
was refluxed for 4 hours. The obtained precipitate was
recrystallized from acetic acid (yield 35%), mp 218–220 °C; tlc,
7.26 (s, 1H, ArCH=), 7.37–7.61 (m, 8H, 3'-H, 4'-H, 5'-H,
2"-H, 3"-H, 4"-H, 5"-H, 6"-H), 8.24–8.28 (m, 1H, 6'-H); ir
(KBr): ν 3099, 3062, 3033, 2948 (C–H), 1805 (CH CO), 1766
3
1
R (D) 0.77; H nmr (200 MHz): δ 2.68 (s, 3H, CH CO),
(C =O), 1735 (C =O), 1660 (ArCH=), 1598 (C=N), 1432,
f
3
2
4
3.31–3.41 (m, 2H, CH Ph), 5.24–5.29 (m, 1H, CHCH ), 7.11
(dd, J = 7.6 Hz, J = 1.5 Hz, 2H, 2"-H, 6"-H), 7.12 (s, 1H,
ArCH=), 7.23–7.31 (m, 3H, 3"-H, 4"-H, 5"-H), 7.41-7.46 (m, 2H,
1236, 1122, 906, 763.
Anal. Calcd. for C H N O Cl (379.79): C, 63.25; H, 3.71;
N, 11.06; Found: C, 63.01; H, 3.58; N, 10.80.
2
2
20 14
3 3

252
K. Kiec´-Kononowicz, C.E. Müller, E. Pe¸kala,
Vol. 39
•
⁄
J. Karolak-Wojciechowska, J. Handzlik and D. Lazewska
1-Acetyl-Z-6-(2-chlorbenzylidene)-2,3,5,6-tetrahydroimi-
dazo[2,1-b]imidazole-3,5-dione (12a).
13
(s, 1H, NH); C nmr: δ 75.57 (7a-C), 110.76 (6-C), 115.18 (CN),
127.95 (3'-C, 5'-C), 128.81 (2'-C, 6'-C), 128.84 (4'-C), 130.39
(1'-C), 130.70 (7-C), 149.09 (5-C), 157.29 (1-C), 172.00 (3-C); ir
Compound 12a was prepared analogous to 12b [3]; yield 49%,
(KBr): ν 3380, 3289, 3221, 3163 (NH, NH ), 2359, 2213 (CN)
1705 (C=O), 1631 (CN), 1555, 1447, 1347, 1170, 1017, 828,
742; ms: (electron impact) m/z 268(M , 94), 209 (100), 181
(46), 153 (31), 133 (15), 127 (20), 100 (4), 77 (9), 60 (3).
Anal. Calcd. for C H N OS (268.29): C, 58.19; H, 3.00; N,
20.88; Found: C, 58.02; H, 3.09; N, 21.03.
1
2
mp 271–273 °C (from acetic acid); tlc R (D) 0.20; H nmr
f
(400 MHz): δ 2.66 (s, 3H, CH CO), 4.63 (s, 2H, CH CO), 7.21
3
2
+•
(s, 1H, ArCH=), 7.42–7.51 (m, 2H, 3'-H, 5'-H), 7.59–7.61
(m, 1H, 4'-H), 8.70 (dd, J = 7.7 Hz, J = 1.8 Hz, 1H, 6'-H); ir
13
8 4
(KBr): ν 3093, 2973, 2942 (C–H), 1805 (CH CO), 1741 (C =O),
3
2
1716 (C =O), 1671 (ArCH=), 1600 (C=N), 1446, 1405, 1270,
4
1240, 904, 781.
5-Amino-6-cyano-7-(4-chlorophenyl)-1-oxo-3-thioxo-2,3-
dihydro-1H-pyrrolo[1,2-c]imidazole (20b).
Anal. Calcd. for C H N O Cl (303.70): C, 55.36; H, 3.32;
N, 13.84; Found: C, 55.28; H, 3.17; N, 13.68.
14 10
3 3
Compound 20b was obtained according to the procedure
Z-5-[3-(2,4-Dichlorobenzyloxy)benzylidene]-2,3-dihydro-
imidazo[2,1-b]thiazol-6(5H)-one (18); Z-6-[3-(2,4-dichloro-
benzyloxy)benzylidene]-2,3-dihydroimidazo[2,1-b]thiazol-5(6H)-
one (19).
described for 20a as dark yellow crystals (7.2%), mp 302–304 °C
1
(from dimethylformamide); tlc, R (B) 0.76, R (C) 0.35; H nmr
f
f
(300 MHz): δ 7.65 (d, J = 8.7 Hz, 2H, 3'-H, 5'-H); 8.07 (d, J = 8.7
13
Hz, 2H, 2'-H, 6'-H), 8.57* (s, 2H, NH ), 13.01* (s, 1H, NH);
C
2
nmr: δ 75.40 (7a-C), 111.00 (6-C), 115.06 (CN), 127.75 (1'-C),
128.99 (3'-C, 5'-C), 129.05 (7-C), 129.59 (2'-C, 6'-C), 134.96
(4'-C), 149.04 (5-C), 157.38 (1-C), 172.04 (3-C); ir (KBr): ν
To a stirred suspension of thiohydantoin derivative 17 (1.9 g, 5
mmole), potassium carbonate (2.0 g), and benzyltriethyl-
ammonium chloride (0.15 g, 0.5 mmole) in 20 ml of acetone, a
solution of 1,2-dibromoethane (1.03 g, 5.5 mmole) in 5 ml of
acetone was added dropwise. The mixture was stirred at room
temperature for two days. Then, the solvent was removed in
vacuo. The residue was washed with water and subsequently with
1% aqueous sodium hydroxide and 1% aqueous hydrochloric
acid solutions, and separated by means of column chroma-
tography using methylene chloride:ethyl acetate (1:1) as the
3320, 3164, (NH , NH), 2360, 2200 (CN), 1728, 1712 (C=O),
2
1666, 1620 (CN), 1564, 1492, 1440, 1164, 744, 668; ms: (elec-
+•
tron impact) m/z 302 (M , 4), 301 (25), 242 (38), 208 (8), 180
(100), 161 (30), 153 (16), 112 (17), 85 (16), 73 (8).
Anal. Calcd for C H N OSCl•C H NO (302.75•73.09 =
13
7
4
3 7
375.84): C, 51.13; H, 3.75; N, 18.64; Found: C, 50.74; H, 3.59;
N, 18.35.
eluent. Product 19 was eluted first: yellow crystals 1.30 g (64%).
Benzodiazepine Binding Assays.
1
19: mp 142–145 °C (from dioxane); tlc, R (B) 0.66; H nmr
f
®
Frozen rat brains were obtained from Pel-Freez , Rogers,
(250 MHz): δ 3.87 (s, 4H, CH CH ), 5.16 (s, 2H, CH O), 6.73
2
2
2
Arkansas, USA. The cortex was dissected and inhibition of
(s, 1H, ArCH=), 7.05 (d, J = 8.0 Hz, 1H, 5"-H), 7.33 (t, J = 7.8
Hz, 1H, 5'-H), 7.45 (d, J = 6.3 Hz, 1H, 4'-H), 7.48–7.68 (m, 3H,
3"-H, 6"-H, 6'-H), 7.87 (s, 1H, 2'-H); ir (KBr): ν 1720 (C=O),
1637 (ArCH=), 1571, 1508 (C=N), 1251, 1116, 1045, 817, 690.
3
binding of [ H]diazepam to rat brain cortical membranes was
determined as previously described [1]. The compounds were
dissolved in dimethyl sulfoxide and further diluted with
tris(hydroxymethyl)-aminomethane hydrochloride buffer
(50 mM, pH 7.4); the final dimethyl sulfoxide concentration was
1%. In a final volume of 1 mL, each test tube contained 790 µL of
compound solution, 100 µL of rat cerebral cortical membrane
preparation with a protein concentration of ca. 100 µg per tube,
Anal. Calcd. for C H N O SCl (405.32): C, 56.30; H, 3.48;
19 14
2
2
2
N, 6.91; Found: C, 56.53; H, 3.31; N, 6.76.
As a second fraction, 18 was obtained as yellow crystals,
120 mg (6%). 18: mp 187–190 °C (from methylene
1
chloride:ethyl acetate, 1:1); tlc, R (B) 0.26; H nmr (250 MHz):
3
f
and 100 µL of [ H]diazepam solution, to give a final concentra-
δ 3.68 (def t, 2H, SCH ), 3.81 (def t, 2H, NCH ), 5.17 (s, 2H,
2
2
tion of 1 nM. Dimethyl sulfoxide was necessary since the
compounds possessed low water solubility.
CH O), 6.84 (s, 1H, ArCH=), 7.07 (t, J = 8.5 Hz, 2H, 5"-H,
2
6"-H), 7.17 (s, 1H, 3"-H), 7.37 (def t, 1H, 5'-H), 7.47 (d, J = 8.2
Hz, 4'-H), 7.61–7.69 (m, 1H, 6'-H), 7.69 (d, J = 2.0 Hz, 2'-H); ir
(KBr): ν 1706 (C=O), 1650 (ArCH=), 1596 (C=N), 1471, 1353,
1236, 1041, 794, 698.
Incubations were performed at 2 °C for 1 hour and were
terminated by rapid filtration through glass fiber filters
(Schleicher & Schüll GF 51) using a Brandel cell harvester M-24
(Brandel, Gaithersburg, Maryland, USA). Three 5 mL washes
with ice-cold tris(hydroxymethyl)aminomethane hydrochloride
buffer were performed. Unlabelled diazepam (5 µM) was used to
define non-specific binding. All compounds were tested in a
single concentration of 25 µM in at least three independent
experiments each in triplicate.
Anal. Calcd. for C H N O SCl (405.32): C, 56.30; H, 3.48;
19 14
2
2
2
N, 6.91; Found: C, 56.21; H, 3.35; N, 6.78.
5-Amino-6-cyano-7-phenyl-1-oxo-3-thioxo-2,3-dihydro-1H-
pyrrolo[1,2-c]imidazole (20a).
A suspension of Z-5-benzylidene-2-thiohydantoin (4.08 g,
0.02 mole), triethylamine (2 ml) and malononitrile (1.32 g,
0.02 mole) in 40 ml of absolute ethanol was refluxed for 6 hours
and then allowed to cool. The solid isolated by filtration (2.0 g)
was identified as starting 2-thiohydantoin (7). The filtrate was
evaporated in vacuo, washed with water and crystallized from
dimethylformamide to give lemon yellow crystals of 20a
Anticonvulsant Assays.
Evaluation for anticonvulsant activity of 6a, 12a and 12b was
done by the Epilepsy Branch, National Institute of Neurological
Disorders and Stroke, National Institutes of Health, Bethesda, MD,
USA. These tests were performed in male Carworth Farms No. 1
(CF 1) mice. Phase I of the evaluation was a qualitative assay,
which used small groups of animals (1-8) and included three tests:
maximal electroshock (MES), subcutaneous pentylenetetrazole
(scMet), and rotorod test for neurological toxicity (Tox).
(500 mg; 9%), mp 288–290 °C (from dimethylformamide); tlc,
1
R (B) 0.77; R (C) 0.10; H nmr (400 MHz): δ 7.79 (s, 3H, 3'-H,
f
f
4'-H, 5'H), 8.11 (s, 2H, 2'-H, 6'-H), 8.60* (s, 2H, NH ), 13.01*
2

Mar-Apr 2002
Imidazo[2,1-b]thiazoles, Imidazo[2,1-b]imidazoles and Pyrrolo[1,2-c]imidazoles
253
[3] K. Kiec´-Kononowicz J. Karolak-Wojciechowska, C. E.
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(2001).
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(2000).
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G. R. Wenger, R. McKernan and J. M. Cook, J. Med. Chem., 43, 71
(2000).
Compounds were suspended in 30% polyethylene glycol 400 and
were administered by intraperitoneal injection at three dosage lev-
els (30, 100 and 300 mg/kg) with anticonvulsant activity and neu-
rotoxicity noted 30 minutes and 4 hours after administration.
Details of these procedures have been published [22,23].
Crystal Structure Determination.
The crystals of 6a were obtained by slow evaporation of an
ethanol solution, while crystals of 20a were selected from
dimethylformamide solution. All crystallographic data are
gathered in Table 1. Preliminary crystallographic data were
obtained from a KM4 four-cycle diffractometer; the accurate cell
dimensions were determined by the least-squares refinement from
the angular settings of 25 reflections located within 10<Θ<40° for
both compounds; crystal of 0.1 x 0.15 x 0.3 mm for 6a, and 0.1 x
0.1 x 0.5 mm for 20a were applied to collect diffraction data on a
KM4 diffractometer by the ω/2Θ scan technique and using
graphite monochromated CuKα radiation at room temperature for
Θ<60° [h:-9/9, k: 0/16, l: 0/33 ] for 6a, and Θ<80° [h:-4/4, k: 0/49,
l: 0/13 ] for 20a; an absorption correction was not applied; the
intensity of three standard reflections monitored every 100 reflec-
tions showed no significant fluctuations for both compounds; 4608
reflections for 6a and 3361 reflections for 20a were measured,
1709 for 6a and 1319 for 20a reflections were considered observed
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and R. I. Fryer, J. Med. Chem., 38, 950 (1995).
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Des. Discov., 12, 193 (1995).
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J. Mol. Str. in preparation.
⁄
[13] J. Karolak-Wojciechowska, M. Mikolajczyk, A. Zatorski,
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K. Kiec´-Kononowicz, Acta Cryst., C45, 1467 (1989).
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K. Kiec´-Kononowicz, Acta Cryst., C47, 1256 (1991).
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Cryst., C47, 2371 (1991).
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Phosphorus, Sulfur and Silicon, 73, 235 (1992).
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[22] R. L. Krall, J. K. Penry, B. G. White, H. J. Kupferberg, E. A.
Swinyard, Epilepsia, 19, 400 (1978).
using the criterion F >4σ(F ). The structures were solved by a
0
0
direct method (SHELXTL-PC) [29]. E-map provided positions for
all non-H-atoms; full-matrix least-squares refinement was carried
out on F's using anisotropic temperature factors for all non-H-
atoms; the positions of all H-atoms were from ∆ρ-maps except two
amide hydrogens in 6a; such atoms were localised geometrically at
four nitrogens and subsequently refined with occupation factor of
0.5; isotropic thermal parameters of all H-atoms were taken as
1.5 times of the temperature factors for their parent-atoms than the
positions of H-atoms were refined in the riding model, being
2
2
finished at R1 = 0.0699, wR2 = 0.0794 (with w=1/[ρ (Fo )]) for 6a
2
2
and R1 = 0.0482, wR2 = 0.0526 (with w=1/[ρ (Fo ) 0.1128
2
2
2
P) +0.2078 P] where P=( Fo + 2Fc )/3) for 20a; S = 0.73(543
parameters) for 6a and S=0.66(218 parameters) for 20a; final
-3
-3
changes ∆ / ρ < 0.01; ∆ρ = -0.33 e Å , ∆ρ
6a and ∆ρ
= 0.35 e Å for
-3
min
max
-3
= -0.213 e Å , ∆ρ
= 0.251 e Å for 20a. The
min
max
atomic scattering factors were taken from SHELXL-93 [30]. The
X-ray structure analysis results are presented in the form of non-
H-atoms coordinates in Table 2 as well as in Figures 1 and 3 [31].
[23] R. J. Porter, J. J. Cereghino, G. D. Gladding, B. J. Hessie, H.
J. Kupferberg, B. Scoville, B. G. White, Cleveland Clin. Q., 51, 293
(1984).
Acknowledgements.
[24] PALLAS for Windows 1.2, CompuDrug Chemistry Ltd.,
1995.
[25] MOPAC 6.0, QCPE No. 455; Department of Chemistry,
Indiana University, Bloomington, IN 47405, 1990.
[26] A. F. A. Shalaby, H. A. Daboun and S. S. M. Z. Boghdadi,
Z. Naturforsch., 29B, 99 (1974).
The authors wish to thank Professor James Stables for providing
pharmacological data through the Antiepileptic Drug Development
Program National Institutes of Health in Bethesda. We thank
Mrs. Maria Kaleta for excellent technical assistance. The financial
support for the synthetic, crystallographic and computational parts of
this research carried out under the Polish State Committee for
Scientific Research, grant No 4 P05F 007 13 is gratefully
acknowledged.
[27] K. Kiec´-Kononowicz, J. Karolak-Wojciechowska, A. Mrozek
⁄
and M. Posel, Arch. Pharm. (Weinheim), 328, 517 (1995).
[28] K. Kiec´ -Kononowicz, J. Karolak-Wojciechowska and
J. Handzlik, Acta Polon.-Drug Res., 55, 381 (1998).
REFERENCES AND NOTES
[29] G. M. Sheldrick, Acta Cryst., A 46, 467 (1990).
[30] G. M. Sheldrick, SHELXL-93. Program for the Refinement of
the Crystal Structures. University of Göttingen, Germany (1993).
[31] Further details of the crystal structure 6a and 20a including
structure factors, anisotropic displacement parameters and H-atom
coordinatea are available on request from one of the authors
[J. K.-W.].
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•
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