Synthesis and structure of 3-arylidene and 3-hetarylidene-1,2-dihydro-3H-1, 4-benzodiazepin-2-ones and their affinity toward CNS benzodiazepine receptors

Article abstract of DOI:10.1007/s10593-007-0161-3

The condensation of 5-aryl-7-bromo-1,2-dihydro-3H-1,4-benzodiazepin-2-ones with aromatic aldehydes gives 5-aryl-3-arylidene-and 5-aryl-7-bromo-3- hetarylidene-1,2-dihydro-3H-1,4-benzodiazepin-2-ones. X-ray diffraction structural analysis yielded the molecular and crystal structures of 7-bromo-3-(4′-methoxybenzylidene)-5-phenyl-1,2-dihydro-3H-1, 4-diazepin-2-one and showed that this compound has cis configuration. Radioligand analysis was used to study the affinity of these products toward central nervous system and peripheral benzodiazepine receptors.

Full text of DOI:10.1007/s10593-007-0161-3

Chemistry of Heterocyclic Compounds, Vol. 43, No. 8, 2007
SYNTHESIS AND STRUCTURE OF 3-ARYLIDENE
AND 3-HETARYLIDENE-1,2-DIHYDRO-3H-1,4-BENZO-
DIAZEPIN-2-ONES AND THEIR AFFINITY TOWARD
CNS BENZODIAZEPINE RECEPTORS
V. I. Pavlovsky1, S. Yu. Bachinskii1, N. A. Tkachuk1, S. Yu. Makan1,
S. A. Andronati1, Yu. A. Simonov2, I. G. Filippova2, and M. Gdaniec3
The condensation of 5-aryl-7-bromo-1,2-dihydro-3H-1,4-benzodiazepin-2-ones with aromatic aldehydes
gives 5-aryl-3-arylidene- and 5-aryl-7-bromo-3-hetarylidene-1,2-dihydro–3H-1,4–benzodiazepin–2–ones.
X-ray diffraction structural analysis yielded the molecular and crystal structures of 7-bromo-3-(4'-
methoxybenzylidene)-5-phenyl-1,2-dihydro-3H-1,4-diazepin-2-one and showed that this compound has
cis configuration. Radioligand analysis was used to study the affinity of these products toward central
nervous system and peripheral benzodiazepine receptors.
Keywords: 3-arylidene- and 3-hetarylidene-1,2-dihydro-3H-1,4-benzodiazepin-2-ones, affinity, central
and peripheral benzodiazepine receptors.
1,4-Benzodiazepin-2-one derivatives bind to two types of benzodiazepine receptors: central (CBDR) and
peripheral (PBDR). The CBDR are found exclusively in the central nervous system (CNS). Ligands of these
receptors are commonly used in medicine as anticonvulsants, anxiolytics, hypnotics, myorelaxants, and sedatives
[1, 2].
PBDR are found predominantly in tissues such as kidney, adrenal gland, placenta, and heart but are also
observed in the CNS (glial cells) [3].
These relatively small proteins with molecular mass 18 kDa hold interest due to their biological effects such
as cell proliferation regulation, immunomodulation (chemotaxis, apoptosis), cholesterol and porphyrin transport, the
biosynthesis of heme, steroids, and neurosteroids, and mitochondrial oxidative phosphorylation [4, 5].
Recent studies to determine the density of PBDR in neurodegenerative and oncological diseases stress
the importance of developing new strategies for the diagnosis and therapy of these diseases using PBDR ligands.
In a search for potentially selective ligands for central and peripheral benzodiazepine receptors of the
CNS, we synthesized a series of new 3-arylidene- and 3-hetarylidene-1,2-dihydro-3H-1,4-benzodiazepin-2-one
derivatives and studied the capacity of these products to competitively replace [3H]PK 11195 and
[3H]flunitrazepam radioligands from the sites of their specific binding to PBDR and CBDR, respectively.
__________________________________________________________________________________________
1A. V. Bogatsky Physico-Chemical Institute, National Academy of Sciences of Ukraine, Division of
2
Medicinal Chemistry, Odessa 65090, Ukraine; e-mail: phychem@paco.net. Institute of Applied Physics,
3
Academy of Sciences of Moldova, Chisinau 2028, Moldova. Chemical Faculty, A. Mickiewicz University,
60-780 Poznan, Poland. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1213-1225,
August, 2007. Original article submitted April 17, 2007.
0009-3122/07/4308-1029©2007 Springer Science+Business Media, Inc.
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In previous work [6-9], we described the preparation of 3-arylidene- and 3-hetarylidene-1,2-dihydro-
3H-1,4-benzodiazepin-2-ones under conditions of the Perkin reaction using acetic anhydride and sodium acetate.
Methods have been described for the formation of a C=C bond in the reaction of 1,4-benzodiazepin-2-ones with
aldehydes in the presence of sodium butylate in tetrahydrofuran [10] or in the presence of potassium hydroxide
in ethanol [11].
In the present work, we synthesized 3-arylidene- and 3-hetarylidene-1,2-dihydro-3H-1,4-benzodiazepin-
2-ones 1-17 (Table 1) by the condensation of dihydrobenzodiazepines I with aromatic aldehydes upon heating in
benzene at reflux in the presence of potassium hydroxide.
O
H
O
H
N
O
R2
C6H6, KOH, ∆
N
R2
N
N
Br
Br
R1
R1
I
1–17
1
The structure of 1-17 was supported by IR, UV, and H NMR spectroscopy, mass spectrometry
(Table 2), and X-ray diffraction structural analysis for 2.
The IR spectra of 1-17 contain narrow bands corresponding to vibrations of nonassociated
(3370-3340 cm-1) and associated N-H groups (3190-3160 cm-1), strong carbonyl group bands at 1670-1640 cm-1,
and bands at 1600-1580 cm-1 corresponding to the azomethine group and benzene ring C=C bonds.
The UV spectra for 1-17 show bands characteristic for 1,2-dihydro-3H-1,4-benzodiazepin-2-ones,
corresponding to π→π* transitions of the benzene ring electrons and π→π* and n→π* transitions of the
azomethine bond conjugated with aromatic substituents and the hetarylidene fragment [12].
The 1H NMR spectra of 1-17 (Table 2) show signals for all the proton types: a singlet for the NH group
proton at 8.01-11.07 ppm, aromatic proton multiplet at 7.02-7.94 ppm, and a singlet for the C-H proton at the
C=C bond at 6.58-6.99 ppm.
The mass spectra of 1-17 (with the exception of 3 and 7) have a molecular ion peak with 100% intensity.
The molecular ion peak intensity for 3 and 7, containing an o-bromophenyl substituent, is only ~8%, while the
major peak is found for the [M-Br]+ cation. The subsequent fragmentation is similar to the fragmentation
characteristic for 1,2-dihydro-3H-1,4-benzodiazepin-2-ones [12].
The molecular and crystal structure of 2 was studied by X-ray diffraction analysis (Figs. 1 and 2,
Tables 3 and 4).
The molecules of 2 in the crystal are arranged in dimers due to the N(1)-H···O(2) hydrogen bonds
(N(1)···O(2), 2.824 Å; H···O(2), 2.044 Å; N(1)-H···O(2), 178.17º). This bond is similar in its parameters to the
hydrogen bond characteristic for benzodiazepines unsubstituted at N(1) [13-15].
The major lengths in the seven-membered heterocycle are similar to those found for other
benzodiazepines. The heterocycle has pseudoboat conformation with dihedral angles between the C(2)C(3)N(4)
plane and the N(1)C(2)N(4)C(5) and C(10)N(1)C(5)C(11) planes equal to 135.6º and 98.2º, respectively.
Substituent R2 is in the cis position relative to the C=C bond.
The bromophenyl group forms an angle of 56.6º with the methoxyphenyl substituent.
We should note that there are deviations from the standard bond lengths in the C(5)–N(4)–C(3)–C(31)–C(32)
chain (Table 3), indicating strain in this molecular fragment.
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Fig. 1. General view of 2 in the crystal with numbering of the independent atoms.
Formation of the dimer is shown.
Fig. 2. Crystal packing of 2 (the intermolecular N(1)-H···O(2)
hydrogen bonds are shown by dashed lines).
Figure 2 shows a fragment of the crystal packing for 2. In addition to the N(1)-H···O(2) hydrogen bond
in the crystal, there is also a weak C-H···Br interaction (C···Br, 3.777 Å; H···Br, 2.996 Å) and a dipole-dipole
interaction between the O(38)-C(39) fragments (O···C, 3.216 Å). The other contacts conform to van der Waals
forces.
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TABLE 3. Some Bond Lengths (d) and Bond Angles (ω) in 2
Bond
d, Å
Angle
ω, deg
N(1)–C(2)
C(2)–C(3)
C(2)–O(2)
C(3)–N(4)
N(4)–C(5)
C(5)–C(11)
1.360(2)
1.496(2)
1.235(2)
1.407(2)
1.286(2)
1.488(2)
1.398(2)
1.409(2)
1.344(3)
1.469(2)
N(1)–C(2)–C(3)
C(2)–N(1)–C(10)
O(2)–C(2)–N(1)
O(2)–C(2)–C(3)
N(4)–C(3)–C(2)
N(4)–C(3)–C(31)
С(31)–C(3)–C(2)
C(3)–N(4)–C(5)
N(4)–C(5)–C(11)
N(4)–C(5)–C(51)
C(10)–C(11)–C(5)
C(11)–C(10)–N(1)
117.6(2)
125.8(2)
120.8(2)
121.6(2)
117.4(2)
124.5(2)
117.6(2)
122.7(2)
124.1(2)
117.5(2)
121.3(2)
122.4(2)
C(10)–C(11)
N(1)–C(10)
C(3)–С(31)
C(31)–С(32)
TABLE 4. Some Torsion Angles (τ) in 2
Angle
N(1)C(2)C(3)N(4)
τ, deg
Angle
τ, deg
46.0
25.8
-48.5
-6.0
N(4)C(5)C(11)C(10)
C(3)N(4)C(5)C(11)
C(2)C(3)N(4)C(5)
44.4
-0.7
C(10)N(1)C(2)C(3)
C(11)N(1)C(10)C(2)
C(5)C(11)C(10)N(1)
-62.0
The radioligand data given in Table 1 indicate that these compounds are competitive with commercial
radioligands for sites with specific binding both with rat brain CBDR and PBDR but display different affinities.
3-Benzylidene-7-bromo-5-phenyl-1,2-dihydro-3H-1,4-benzodiazepin-2-one (1) shows low affinity to
both types of receptors. This compound in concentration 1 µM inhibits the specific binding of radioligands
[3H]PK 11195 and [3H]flunitrazepam with PBDR and CBDR by 37.2 and 61.9%, respectively (Table 1).
Variation of the position of the bromine atom in the 3-benzylidene fragment in
3-(bromo)benzylidene-7-bromo-5-(2'-chloro)phenyl-1,2-dihydro-3H-1,4-benzodiazepin-2-ones
yielded
the
following trend for the affinity of these compounds toward CNS BDR. The compounds with a
p-bromobenzylidene substituent at C(3) in the benzodiazepine system bind more actively to CNS PBDR than the
o- and m-bromobenzylidene derivatives.
Different behavior is observed in the case of CBDR: higher affinity is found for compounds containing
an o-bromobenzylidene substituent at C(3) in the 7-bromo-5-(2'-chloro)phenyl-1,2-dihydro-3H-1,4-benzo-
diazepin-2-one molecule.
Thus, we should note the following trend for the influence of the position of the bromine atom in the
benzylidene moiety on the affinity toward BRD found in the series of 7-bromo-5-phenyl- and
7-bromo-5-(2'-chloro)phenyl-1,2-dihydro-3H-1,4-benzodiazepin-2-ones:
p-Br > > o-Br > m-Br (affinity toward PBDR)
p-Br > > o-Br ≥ p-Br (affinity toward CBDR)
The greatest capacity to form the ligand-PBDR molecular complex is found for 12, 17, and 6. These
compounds in concentration 1 µM inhibit the specific binding of [3H]flunitrazepam with PBDR by 96.4, 86.9,
and 79.9%, respectively.
Linearization of the curves for inhibition of specific binding of [3H]flunitrazepam with CNS PBDR by
12 and 6 (Fig. 3) gave IC50 values of 45.7 and 575.4 nM, respectively.
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I , %
100
-7.5
7
-6.5
-6
-5.5
-5
-4.5
36.8
69.2
9
85
27.4
94.3
70
100
87
100
95
100
99
2.9
80
a
60
40
20
0
b
-9.5 -9 -8.5 -8 -7.5
7
-6.5 -6 -5.5 -5 -4.5
log C
Fig. 3. Dependence of the inhibition (I, %) of the specific binding of the [3H]flunitrazepam radioligand
with CBDR of the synaptic fraction of rat brain cortex membranes on the concentrations of 12 (a) and 6 (b),
respectively. log C – logarithm of the concentration of 12 (a) and 6 (b), I, % – inhibition of specific
binding of the [3H]flunitrazepam radioligand with CNS CBDR.
O
H
N
O
H
N
N
Br
N
Br
Cl
Cl
Br
Cl
10
9
Fig. 4. Inhibition of specific binding of [3H]flunitrazepam with CBDR (1)
and of [3H]PK 11195 with rat brain cortex PBDR (2) by compounds 9 and 10 (C = 1 µM).
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Selective PBDR ligands were found in the series of 7-bromo-5-(2'-chloro)phenyl-1,2-dihydro-
3H-1,4-benzodiazepin-2-one derivatives containing different substituents in the para position in the
3-benzylidene fragment. The affinity of these ligands (9 and 10) is two orders of magnitude greater toward
PBDR than toward CBDR (Fig. 4).
In the series of compounds studied, 12 and 17 bind predominantly with CBDR, 9, 5, and 10 bind
predominantly with PBDR, while 3 and 6 show equal affinity toward the two types of receptors.
EXPERIMENTAL
The course of the reactions and purity of the products were monitored by thin-layer chromatography on
Silufol UV-254 plates using 1:10 methanol-chloroform as the eluent and detection with UV light (λ = 254 nm).
The IR spectra were taken on a Specord IR-75 spectrometer for solutions in CHCl3. The UV spectra were taken
1
on an SF-56 spectrometer for solutions in ethanol. The H NMR spectra were taken for ~2% solutions of the
compounds in CDCl3 on a Bruker spectrometer at 300 MHz using TMS as the internal standard. The mass
spectra were taken on an MKh-1321 mass spectrometer. The ionizing voltage was 70 eV and the temperature of
the ionization chamber was 220°C.
X-Ray Diffraction Structural Analysis. A monocrystal of 7-bromo-3-(4'-methoxybenzyidene)-
5-phenyl-1,2-dihydro-3H-1,4-benzodiazepin-2-one (2) was obtained by crystallization from ethanol. The unit
cell parameters of the monoclinic crystal were as follows: a = 11.0595(5), b = 9.4768(8), c = 19.2114(9) Å,
γ = 105.33(1)°, space group P21/n, V = 1941.8(4) Å3, M = 433.3, Z = 4, dcalc = 1.482 g/cm3.
The X-ray diffraction study was carried out on a monocrystal (0.4×0.3×0.1 mm) on a KUMA-4CCD
diffractometer using MoKα radiation with ω-scanning at 123 K. A total of 11,214 reflections were measured, of
which 3938 were symmetrically independent (Rint = 0.0211). No correction for absorption was introduced
(µ = 1.666 mm-1). The structure was solved by the direct method using the SHELX-97 program [16] and refined
by the method of least squares in the full-matrix anisotropic approximation for the non-hydrogen atoms. All the
hydrogen atoms were found from the electron density difference map and refined isotropically. The final
R factor for reflections with I > 2σ(I) was 0.0264 and for all reflections was 0.349. The residual electron density
from the Fourier difference map was in the range from +0.435 to -0.302 eÅ3. The atomic coordinates were
deposited at the Cambridge Crystal Data Center, CCDC 643684.
cis-7-Bromo-3-(4'-methoxybenzylidene)-5-phenyl-1,2-dihydro-3H-1,4-benzodiazepin-2-one (2). A
mixture of 7-bromo-5-phenyl-1,2-dihydro-3H-1,4-benzodiazepin-2-one (2 g, 6.4 mmol), p-methoxybenz-
aldehyde (1.3 ml, 10.7 mmol), and potassium hydroxide (0.2 g, 3.6 mmol) in benzene (15 ml) was heated at
reflux for 24 h with monitoring of the reaction course by thin-layer chromatography. The hot reaction mixture
was filtered and evaporated in vacuum to dryness. The solid residue was crystallized from ethanol.
Recrystallization from ethanol gave 1.92 g (70%) 2, Rf = 0.43.
Products 1-17 were obtained analogously. Tar formation was noted in the preparation of 1 and 6.
Affinity to Central and Peripheral Benzodiazepine CNS Receptors was determined by the in vitro
radioligand method. Amersham flunitrazepam (2960 TBq/mol) was used for CBDR and Du Pont NEN
[3H]PK 11195 (2775 TBq/mol) was used for PBDR.
All the experiments were carried out on white nonpedigreed male rats with mass 180-220 g maintained
in a vivarium under standard conditions with free access to food and water. The anesthetized animals were
decapitated and the brain cortex, characterized by high BDR content, was rapidly removed in the cold. The
analysis of the interaction of 1-17 with CBDR and PBDR was carried out according to previous procedures [17,
18]. The affinity was found relative to the compounds at 1 µM to remove radioligands from sites of their specific
binding with receptors. IC50 values (concentrations at which the tested compound gives 50% inhibition of
specific binding of the radioligand with the receptor) were determined for the most active compounds.
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A total of eight concentrations in the range from 10-9 to 10-5 M were used to determine the IC50 values.
Each experimental point was obtained in sextets. The data are given at M ± m, where M is the mean value of
three independent experiments and m is the standard mean error.
REFERENCES
1.
2.
S. A. Andronati and S. Yu. Makan, Ukr. Khim. Zh., 65, No. 9-10, 5 (1999).
E. A. Barnard, P. Skolnick, R. W. Olsen, H. Mohler, W. Sieghart, G. Biggio, C. Braestrup,
A. N. Bateson, and S. Z. Langer, Pharmacol. Rev., 50, 291 (1998).
3.
M. Gavish, I. Bachman, R. Shoukrun, Y. Katz, L. Veenman, G. Weisinger, and A. Weizman,
Pharmacol. Rev., 51, 629 (1999).
4.
5.
6.
P. Casellas, S. Galiegue, and A. S. Basile, Neurochem. Int., 40, 475 (2002).
V. Papadopoulos, L. Lecanu, R. C. Brown, Z. Han, and Z. X. Yao, Neuroscience, 138, 749 (2006).
A. V. Bogatsky, S. A. Andronati, Z. I. Zhilina, O. V. Kobzareva, P. A. Sharbatyan, and R. Yu. Ivanova,
Zh. Obshch. Khim., 45, 396 (1975).
7.
8.
9.
Z. I. Zhilina, A. V. Bogatsky, E. D. Sych, T. K. Chumachenko, and S. A. Andronati, Khim. Geterotsikl.
Soedin., 992 (1971) [Chem. Heterocycl. Comp., 7 (1971)].
A. V. Bogatsky, S. A. Andronati, T. A. Klygul, Z. I. Zhilina, Yu. N. Vikhlyaev, and R. Yu. Ivanova,
Khim.-farm. Zh., 11, No. 2, 37 (1977).
A. V. Bogatsky, Z. I. Zhilina, S. A. Andronati, S. D. Isaev, A. G. Yurchenko, Yu. I. Vikhlyaev,
T. A. Klygul, N. Ya. Golovenko, and S. S. Isaeva, in: Physiologically Active Compounds [in Russian],
issue 11, Naukova Dumka, Kiev (1979), p. 52.
10.
B. E. Evans, K. E. Rittle, M. G. Bock, R. M. DiPardo, R. M. Freidinger, W. L. Whitter, N. P. Gould,
G. F. Lundell, C. F. Homnick, and D. F. Veber, J. Med. Chem., 30, 1229 (1987).
M. A. Berghot, Arch. Pharm. (Weinheim), 325, 285 (1992).
A. V. Bogatsky, S. A. Andronati, and N. Ya. Golovenko, Tranquilizers. 1,4-Benzdiazepines and Related
Structures [in Russia], Naukova Dumka, Kiev (1980).
11.
12.
13.
14.
G. Gilli, V. Bertolasi, M. Sacerdoti, and P. A. Borea, Acta Crystallogr., 33, 2664 (1977).
J. Rambaud, J. L. Delarbre, B. Pauvert, L. Maury, A. Dubourg, and J.-P. Declercq, Acta Crystallogr., 43,
2195 (1987).
15.
16
A. A. Karapetyan, V. G. Andrianov, Yu. T. Struchkov, A. V. Bogatsky, S. A. Andronati, and
T. I. Korotenko, Bioorg. Khim., 5, 1684 (1979).
G. M. Sheldrick, SHELX-97. Program for the Refinement of Crystal Structure, Univ. Göttingen,
Göttingen, Germany (1997).
17.
18.
N. A. Tkachuk, S. Yu. Makan, S. V. Vlasyuk, V. I. Pavlovsky, and S. A. Andronati, Vesn. ONU, 10, 97
(2005).
G. Trapani, M. Franco, A. Latrofa, L. Ricciardi, A. Caroni, M. Serra, E. Sanna, G. Biggio, and G. Liso,
J. Med. Chem., 42, 3934 (1999).
1037