Research in the field of imidazo[1,2-a]benzimidazole derivatives. XXX. Synthesis and properties of (imidazo[1,2-a]benzimidazolyl-2)acetic acids

Article abstract of DOI:10.1134/S1068162011060033

Ethyl esters of (9-subtituted-imidazo[1,2-a]benzimidazolyl-2)acetic acids have been synthesized. The chemical properties of these esters have been studied: hydrolysis, decarboxylation, hydrazinolysis, and hydrazone formation. Some of these compounds demonstrate biological activity (fungicidal, antimicrobial, antiarrhythmic) and effects on brain rhythmogenesis. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S1068162011060033

ISSN 1068ꢀ1620, Russian Journal of Bioorganic Chemistry, 2011, Vol. 37, No. 6, pp. 758–764. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.A. Anisimova, I.E. Tolpygin, A.A. Spasov, T.S. Serdyuk, A.G. Sukhov, 2011, published in Bioorganicheskaya Khimiya, 2011, Vol. 37, No. 6, pp. 836–843.
Research in the Field of Imidazo[1,2ꢀ
a]benzimidazole Derivatives.
XXX. Synthesis and Properties
of (Imidazo[1,2ꢀ
a
]benzimidazolylꢀ2)acetic Acids1
V. A. Anisimovaa, 2, I. E. Tolpygina, A. A. Spasovb, T. S. Serdyukc, and A. G. Sukhovc
aInstitute of Physical and Organic Chemistry, Southern Federal University, pr. Stachki 194/2, RostovꢀonꢀDon, 344090 Russia
bVolgograd State Medical University, Volgograd, Russia
cKogan Research Institute of Neurocybernetics, Southern Federal University, RostovꢀonꢀDon, Russia
Received May 25, 2011; in final form, June 16, 2011
Abstract—Ethyl esters of (9ꢀsubtitutedꢀimidazo[1,2ꢀa]benzimidazolylꢀ2)acetic acids have been synthesized.
The chemical properties of these esters have been studied: hydrolysis, decarboxylation, hydrazinolysis, and
hydrazone formation. Some of these compounds demonstrate biological activity (fungicidal, antimicrobial,
antiarrhythmic) and effects on brain rhythmogenesis.
Keywords: imidazo[1,2ꢀa]benzimidazoles; acids; synthesis; biological activity
DOI: 10.1134/S1068162011060033
2 1
INTRODUCTION
a]benzimidazole derivatives, which
The reaction of benzimidazoles (Ia–c) with esters
ꢀhalogenoacetoacetic acids (Scheme 1) was carꢀ
ried out in acetone, methyl ethyl ketone (at room temꢀ
perature for the ꢀbrominated ester and with boiling
for the ꢀchlorinated one), or by brief fusion of the
reagents. When conducted in alcohols (ethanol or
2ꢀpropanol), the reaction was accompanied by the
formation of numerous byꢀproducts and tars. Thereꢀ
fore, the yields of target products (IIa–c) were poor.
of
γ
Imidazo[1,2ꢀ
contain a guanidine group, demonstrate a wide range
of pharmacological activities, often modulated by the
presence of known pharmacophore groups in their
structures [2–6]. Residues of acetic acid and its derivꢀ
atives belong to pharmacophores, and their presence
in various heterocyclic systems endows them with varꢀ
ious activities. For example, acetic acid residues are
γ
γ
responsible for the antiꢀinflammatory and analgesic The IR spectra of the resulting salts had bands at
1780–1770 and 1750–1735 cm–1, corresponding to
acetyl and ester groups, respectively, and two bands at
3260 and 3090–3070 cm–1 corresponding to amino
group, which confirmed the structures of 2ꢀamiꢀ
nobenzimidazolium salts. The structures were also
proven by 1H NMR signals from N+CH2CO (singlet at
~3.90 ppm) and NH2 (singlet at 9.28–9.54 ppm).
activities of many aromatic and heterocyclic acetic
acids [7–10]. Antitumor activity has been found in
various derivatives of indolyzineꢀ3ꢀacetic acid [11]. In
this work, derivatives of (imidazo[1,2ꢀa]benzimidaꢀ
zolylꢀ2)acetic acids were synthesized by interaction of
1ꢀsubstituted 2ꢀaminobenzimidazoles with esters of
γ
ꢀhalogenoacetoacetic acids and chemical and biologꢀ
ical properties of the compounds synthesized were
studied [12].
The resulting halogenides (IIa–c) were unstable,
and their melting ranges changed notably after recrysꢀ
tallization from ethanol or after storage. Their IR
spectra lost bands characteristic of carbonyl and carꢀ
RESULTS AND DISCUSSION
Many esters of hetarylacetic acids can be obtained boxy group vibrations and acquired a band at
1745 cm–1, which can be attributed to vibrations of the
C=O group in intermediate hydrohalogenides of ethyl
esters of 9ꢀsubstituted (2ꢀhydroxyꢀ2,3ꢀdihydroxyimiꢀ
in one step. An example is the interaction of 2ꢀamiꢀ
nopyridines [13], 2ꢀaminoisoquinolines [14], 2ꢀamiꢀ
nothiazoles, and 2ꢀaminobenzothiazoles [15] with
ethyl ꢀbromoacetate. However, 1ꢀalkylꢀ2ꢀaminobenꢀ
zimidazoles (Ia–c) interacted with this ester to proꢀ
duce corresponding quaternary salts (IIa–c).
γ
dazo[1,2ꢀа]benzimidazolylꢀ2)acetic acids (III). The
1H NMR spectra of the cyclic products had additional
signals in the weaker field range: OH protons (8.70–
9.10 ppm) and N+H (12.80–13.20 ppm) groups, and
signals from protons of substituents at position 9 were
doubled.
1
For communication XXIX, see [1].
2
Corresponding
author:
phone:
+7(863)243ꢀ47ꢀ00,
fax:+7(863)243ꢀ46ꢀ67, eꢀmail: anis@ipoc.sfedu.ru.
758

RESEARCH IN THE FIELD OF IMIDAZO[1,2ꢀ
a
]BENZIMIDAZOLE DERIVATIVES
759
CH2COCH2CO2Et
EtOH,
+
N
N
N
XCH COCH CO Et
2
Δ
OH ⋅ HCl(HBr)
2
2
–
N
R
NH2
N
R
NH2Cl–(Br )
N
R
N
CH2CO2Et
(Iа–c
)
(
IIа–c
)
(III)
Na CO ,
3
Δ
2
EtOH,
Δ
–H O
2
1. 20% solꢀn NaOH,
HCl, pH 3–4
Δ
5
2.
NH NH ,
2
Δ
N
N
conc.
N
2
6
4
3
7
R=Bzl
2
1
8
9
N
N
CH2CONHNH2
N
N
CH2CO2H
N
R
N
(
CH2CO2Et
R
ArCHO,
Bzl
(
VIIIа, c
)
IVа–c
)
(
(
V
)
HCl,
Δ
conc.
EtOH,
R=Me
Δ
R=Me
N
N
N
HCl,
Δ
conc.
+
N
N
CH2CO–2
N
N
CH2CONHN=CHAr
IX), (
N
N
Me
VIIа, c)
Bzl
H
Me
R
VI)
(
X
)
(
(
I
)–(IV), (VII), (VIII
)
а
R=Me,
b
R=nꢀBu, c R=Bzl; (IX) Ar=C6H4NO2ꢀ4, (X) Ar=5ꢀnitrofuryl
Scheme 1. Synthesis of (9ꢀsubstituted imidazo[1,2ꢀa]benzimidazolylꢀ2)acetic acids.
Dehydration reactions of hydroxy derivatives (III
)
showed the absorption band of the carbonyl group and
yielding esters (IVa–c) were carried out by treatment deformation vibrations of the NH group at 1680 and
with aqueous ammonia or NaHCO3 at room temperaꢀ 1630 cm–1, respectively. The stretch vibrations of the
ture or in boiling ethanol. In the latter case, the proꢀ NH2 group were indicated by two bands within 3500–
cess was accompanied by side reactions, and the yields 3050 cm–1. Hydrazide (VIIIa) was readily condensed
of target products (IVa
–
c
) were lower. For example, to aromatic and heterocyclic aldehydes to form hydraꢀ
).
boiling of salt (IIc) in ethanol brought about a mixꢀ zones (IX) and (
X
ture of ester
(Vc ) and 9ꢀbenzylꢀ2ꢀmethylimiꢀ
Hydrolysis of ester (IVc) with 20% NaOH proꢀ
duced the sodium salt of the acid. It proved to be
hygroscopic. It emerged in the form of an oil, crystalꢀ
lizing after long desiccation over phosphorus pentoxꢀ
ide. Acidification of an aqueous solution of this salt to
dazo[1,2ꢀ ]benzimidazole (VIIc). The formation of
a
the latter product can be explained by hydrolysis of the
ester group followed by decarboxylation, catalyzed by
the HX present in the original mixture.
Refluxing of salts (IIa
bicarbonate caused their easy cyclization to esters amount of the decarboxylation product (VIIc). The
IVa ) with 65–75% yields. The IR spectra of tricyꢀ latter could be removed by washing with petroleum
clic compounds (IVa ) in conꢀ
) showed bands at 1750 cm–1 ether or benzene. Hydrolysis of esters (IVa
(C=O) and 1150 cm–1 (C–O). The H NMR spectra centrated hydrochloric acid yielded 2,9ꢀdisubstituted
had signals characteristic of ethyl protons and protons imidazo[1,2ꢀ ]benzimidazoles (VIIa ).
of the CH2CO group at 3.70–3.80 ppm in the form of
–c) in ethanol with sodium pH 3–4 yielded free acid (V) mixed with a small
(
–c
–
c
, c
1
a
, c
Acid (
V
) readily decomposes during storage. Its
a narrow doublet with ~ 1 Hz. This shape of the signal
appears to be related to the retarded rotation of these
protons.
J
IR spectrum showed vibrations of the C=O group at
1670 cm–1, and the stretch vibrations of the N+H
group formed a broad band at 2700–2500 cm–1. The
shift of the carbonyl absorption to lower frequencies
Cautious acidification of solutions of esters (IVa–c)
to pH 3–4 with hydrochloric acid yielded waterꢀsoluꢀ pointed to the existence of acid (
ble hydrochlorides (IVa HCl). Esters (IVa ) were [16]. The hydrolysis was accompanied by a shift of
V) as betaine (VI)
–c
⋅
–c
inert to ammonia in the cold or with heating. No protons of the СН2СО group about 0.6 ppm upfield
amides were obtained even by long heating of the and a shift of aromatic H5 proton about 0.2 ppm
esters with piperidine or morpholine. However, the downfield. The readiness of decarboxylation of this
reaction of (IVa
readily to produce hydrazides (VIIIa
yields within 5–10 min. The IR spectra of (VIIIa
,
c
) with hydrazine hydrate occurred acid may be related to its betaine structure, because
) with high there is evidence that decarboxylation of many heteroꢀ
cyclic carboxylic acids is mediated by zwitterions [17].
,
c
, c)
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 37
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2011

760
ANISIMOVA et al.
(а)
(b)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1.0
0.9
0.8
0.5 mV
1 с
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.5 mV
1 с
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Hz
(c)
Hz
(d)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.5 mV
1 с
0.5 mV
1 с
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Hz
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Hz
The activity patterns of a cortical column of rat somatic cortex before and after microapplication of compound (IVa ⋅ HCl)
(50 nl, 0.75 mM) in isotonic NaCl solution. Power spectra and the focal baseline bioelectric activity of a cortical column (inset)
are shown: (a) before microapplication; (b–d) after microapplication: (b) 5 min; (c) 10 min; (d) 30 min.
Investigation of biological properties of the comꢀ reduced heart rate by 33% and insignificantly, by 9%,
pounds synthesized revealed a fungicidal activity in elongated ventricular conduction at 45 mg/kg.
bromides (IIa X=Br). These salts reduced the Procainamide had a similar effect at 20 mg/kg.
–c,
damage to wheat by rust and cucumber plants by powꢀ
dery mildew by 48–50 and 54–56%, respectively, at a
concentration of 0.02%. The compounds showed no
activity against late blight of tomatoes. The reference
compound Benomyl at 0.02% reduced the degree of
wheat damage by rust by 97% and tomato damage by
late blight, by 24% (by 43% at 0.1%), whereas the
damage to cucumbers by a Benomylꢀresistant powdery
mildew was reduced by only 6%.
Thus, the activity of (IVa ⋅ HCl) in the cardiac musꢀ
cle excitation reduction test exceeded that of procainꢀ
amide by a factor of 5.1, but had a lesser effect on venꢀ
tricular conduction.
As the heart rateꢀreducing effect of many pharmaꢀ
ceuticals, such as ꢀadrenergic blocking or antiarꢀ
β
rhythmic agents, is often related to the action on the
pacemaking activity of sinoatrial node cells [18], it is
reasonable to suppose a similar effect of compounds of
Large concentrations (300–1000
zones (IX) and ( ) exerted bacteriostatic action on ticular, the effect on the excitation of pacemaking
cocci. At 1 g/ml, they were active against salꢀ neurons characteristic of cholinesterase inhibitors and
10–3
μ
g/ml) of hydraꢀ similar types on rhythmogenesis in the brain, in parꢀ
X
μ
×
monellas and causative agents of dysentery and the development of epileptiform activity [19, 20].
typhoid fever.
Microapplication of (IVa ⋅ HCl) solution to cortical
columns of the somatic cortex of rats induced a regular
change in the focal baseline activity of the recorded
cortical columns, which points to a significant rise of
their excitability (figure).
Experiments with isolated rat atria showed that
esters (IVa HCl) reduced heart rate at concentraꢀ
tions: (IVa HCl), 7.2 HCl),
10–4 M, and (IVc
10–4 M. Procainamide had a similar effect at
10–3 M, and quinidine, at 3.4 10–4 M. Thus, the
, c ⋅
⋅
×
⋅
9.5
3.7
×
×
×
Largeꢀamplitude negative potentials appeared on
compounds under study overpower procainamide by the baseline 5 min after the microapplication, pointing
factors of 5.1 and 3.9, respectively, but rank below quiꢀ to an increase in cortex excitability in the microappliꢀ
nidine. The most active compound (IVa
⋅ HCl), cation site (figure, b). Later, largeꢀamplitude potenꢀ
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RESEARCH IN THE FIELD OF IMIDAZO[1,2ꢀ
a
]BENZIMIDAZOLE DERIVATIVES
761
tials became more frequent, and they grouped into ture darkened. After cooling, the matter was filtered
rhythmic discharges of highꢀamplitude activity and thoroughly washed with acetone. Yield: 2.5 g
(figure, c). The increase in amplitudes of baseline (79%). Melting range: 161–162 (decomp., MeCN).
activity after (IVa HCl) microapplication was specꢀ IR: 3280, 3050 (NH2), 1770, 1740 (C=O), 1670
θ
°С
⋅
trometrically confirmed by a significant, fiveꢀ to tenꢀ (C=N), 1600, 1530, 1500 (C=C). Anal. Found:
fold, increase in the power of recorded focal activity at C, 54.02; H, 5.74; Cl, 11.28; N, 13.55%; Calcd. for
the frequencies 1–2 Hz and 5–7 Hz, that is, in the C14H18ClN3O3: C, 53.94; H, 5.82; Cl, 11.37;
1
ranges of
δ
and
θ
activities (figure, b and c).
N, 13.48%. H NMR: 9.30 (2 H, s, NH2), 7.13–7.62
(4 H, m, HAr), 5.52 (2 H, s, CH2), 4.13 (2 H, q,
CH2), 3.90 (2 H, s, CH2), 3.63 (3 H, s, CH3), 1.21
(3 H, t, 7.2, CH3).
B. A finely pound mixture of 1.5 g (10 mmol) of
amine (Ia) and 2.7 ml (20 mmol) of ethyl ꢀchloroacꢀ
etoacetate was melted at 70–80 for 15 min. The
melt was cooled and treated with acetone. The sediꢀ
ment was filtered and thoroughly washed with aceꢀ
tone. Yield: 2.1 g (68%). The salt was identical to that
obtained by protocol A.
J 7.2,
The effect of butylated derivative (IVb
⋅
HCl) on the
baseline activity of cortical columns showed basically the
J
same pattern, but the activation of focal rhythmic activꢀ
ity was more pronounced. The action of (IVb
manifested itself as an initial increase in the ampliꢀ
tudes of slow waves at the frequency 2–3 Hz, which
⋅ HCl)
γ
°С
δ
turned to typical epileptiform activity 10 min after the
microapplication.
The activating effect of (IVa, b ⋅ HCl) at the experꢀ
imental concentrations lasted usually for no more than
30 min. The increase in the amplitude of negative
Ethylꢀ4ꢀ(1ꢀmethylꢀ2ꢀaminobenzimidazoliumꢀ3)aceꢀ
toacetate bromide (IIa, X=Br). Ethyl ꢀbromoaceꢀ
γ
potentials after microapplication of (IVa, b ⋅ HCl) was
toacetate (3.6 g, 15 mmol) was added to a solution of
amine (Ia) (2.2 g, 15 mmol) in 50 ml of acetone. The
mixture was thoroughly mixed and left at room temꢀ
perature overnight. The quaternary salt sediment
formed on the next day was filtered and washed with
acetone, benzene, and diethyl ether. Yield: 4.6 g
similar to the variation of the focal activity of cortical
columns under the effect of acetylcholine agonists,
such as carbachol or neostigmine. This fact is indicaꢀ
tive of the involvement of choline receptors in cortex
activation. The effect on cholinergic synapses was
confirmed by investigation of antiarrhythmic activity.
A decrease in rat atrial contraction rate was observed,
which is typical of cholinergic reagents.
(87%). Melting range: 199–200 С (decomp., MeCN).
°
IR: 3260, 3070 (NH2), 1780, 1735 (C=O), 1685
(C=N), 1600, 1530, 1505 (C=C). Anal. Found:
C, 47.15; H, 5.16; Br, 22.35; N, 11.88%; Calcd. for
C14H18ВгN3O3: C, 47.21; H, 5.09; Br, 22.43;
N, 11.80%.
To sum up, experiments with microapplication of
IVa, b ⋅ HCl) solutions revealed the activating effect of
(
these compounds, which manifested itself in an
increase in the excitability of cortical columns mediꢀ
ated by choline receptors of cortical neurons. Esters of
(9ꢀalkylimidazo[1,2ꢀa]benzimidazolylꢀ2)acetic acids
can be utilized as reversible acetylcholine esterase
inhibitors.
Ethylꢀ4ꢀ(1ꢀbutylꢀ2ꢀaminobenzimidazoliumꢀ3)aceꢀ
toacetate chloride (IIb, X=Cl) was synthesized similar
to (IIa, X=Cl). Yield: 89%. Melting range: 163–164 С
°
(decomp., MeCN). IR: 3200, 3080 (NH2), 1760, 1725
(C=O), 1675 (C=N), 1605, 1530, 1505 (C=C). Anal.
Found: C, 57.75; H, 6.78; Cl, 10.11; N, 11.80%;
Calcd for C17H24ClN3O3: C, 57.70; H, 6.84; Cl, 10.02;
N, 11.88%. 1H NMR: 9.28 (2 H, s, NH2), 7.20–7.68
EXPERIMENTAL
1H NMR spectra (
, ppm; J, Hz) were recorded
δ
(4 H, m, HAr), 5.50 (2 H, s, CH2), 4.24 (2 H, t,
CH2), 4.12 (2 H, q, 7.2, CH2), 3.90 (2 H, s, CH2),
1.57–1.75 (2 H, m, CH2), 1.26–1.42 (2 H, m, CH2),
1.20 (3 H, t, 7.4, CH3), 0.89 (3 H, t, 7.4, CH3).
J 7.4,
on a Unityꢀ300 spectrometer (Varian, United States,
300 MHz) in DMSОꢀd6, unless otherwise indicated.
Signals from residual protons of the solvents were used
J
as an internal reference. Infrared spectra (
, cm–1)
ν
J
J
were recorded in Nujol on a Specordꢀ75ꢀIR (Gerꢀ
many). Melting ranges were measured in glass capilꢀ
lary tubes on a PTP (M) device (Russia). The reaction
monitoring and determination of the identity of synꢀ
thesized compounds were done by TLC on plates with
aluminum oxide. Chloroform was used as the mobile
phase. Spots were visualized with iodine vapor in a
humid chamber.
Ethylꢀ4ꢀ(1ꢀbenzylꢀ2ꢀaminobenzimidazoliumꢀ3)aceꢀ
toacetate chloride (IIc, X=Cl) was synthesized simiꢀ
larly to (IIa, X=Cl). Yield: 46%. Melting range: 157–
158 (decomp., MeCN). IR: 3230, 3050 (NH2), 1770,
1730 (C=O), 1680 (C=N), 1600, 1540, 1500 (C=C).
Anal. Found: C, 61.85; H, 5.80; Cl, 9.07; N, 10.90%;
Calcd. for C20H22ClN3O3: C, 61.93; H, 5.72; Cl, 9.14;
N, 10.83%. 1H NMR: 9.54 (2 H, s, NH2), 7.10–7.60
(9 H, m, HAr), 5.53 (2 H, s, CH2), 5.47 (2 H, s, CH2),
Ethylꢀ4ꢀ(1ꢀmethylꢀ2ꢀaminobenzimidazoliumꢀ3)aceꢀ
4.13 (2 H, q,
(3 H, t, 7.1, CH3).
Ethylꢀ4ꢀ(1ꢀbenzylꢀ2ꢀaminobenzimidazoliumꢀ3)aceꢀ
J 7.2, CH2), 3.91 (2 H, s, CH2), 1.20
toacetate chloride (IIa, X=Cl). A. Ethyl ꢀchloroaceꢀ
γ
J
toacetate (2 ml, ~15 mmol) was added to a stirred
solution of amine (Ia) (1.5 g, 10 mmol) in 50 ml of
acetone. The mixture was refluxed for 3 h. Fibrous toacetate bromide (IIc, X=Br). A mixture of amine
matter began to precipitate after 15–20 min. The mixꢀ
(
Ic) (2.2 g, 10 mmol), ethyl γꢀbromoacetoacetic acid
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 37
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ANISIMOVA et al.
(2.5 ml, 10 mmol), and 5 ml of acetone was thoroughly Melting point: 110 С (petroleum ether). IR: 1750
°
mixed and, after the completion of the spontaneous (C=O), 1630, 1600, 1500 (C=C, C=N), 1450 (СН2),
exothermic reaction, heated in a water bath at 60– 1150 (C–O). Anal. Found: C, 72.14; H, 5.65;
70
orless sediment was filtered and washed on the filter N, 12.60%. H NMR (CDCl3): 7.46 (1 H, d,
with acetone and diethyl ether. Yield: 2.3 g (53%). H5), 7.20ꢀ7.35 (9 H, m, HAr), 5.36 (2 H, s, NCH2),
Melting range: 184–185 (decomp., MeCN). IR: 4.20 (2 H, q, OCH2), 3.77 (2 H, d, 1.0, CH2), 1.27
°
С for 15 min. The mixture was cooled, and the colꢀ N, 12.68%; Calcd. for C20H19N3O2: C, 72.05; H, 5.74;
1
J
8.1,
°С
J
3260, 3090 (NH2), 1760, 1730 (C=O), 1665 (C=N), (3 H, t, J 7.2, CH3).
1605, 1535, 1500 (C=C). Anal. Found: C, 55.52; H,
Ethylꢀ(9ꢀbenzylimidazo[1,2ꢀ
tate hydrochloride (IVc HCl) was obtained similarly to
IVa HCl). Yield: 95%. Melting point: 204°C
a]benzimidazolylꢀ2) (decomp., EtOH–Et2O). Anal. Found: C, 65.02; H,
a]benzimidazolylꢀ2)aceꢀ
5.04; Br, 18.55; N, 9.80%; Calcd. for C20H22ВгN3O3
:
⋅
C, 55.57; H, 5.13; Br, 18.48; N 9.72%.
(
⋅
Ethylꢀ(9ꢀmethylimidazo[1,2ꢀ
acetate (IVa). Bromide (IIa) (2.1 g, 6 mmol) and 5.40; Cl, 9.50; N, 11.44; Calcd. for C20H19N3O2 HCl:
NaHCO3 (0.5 g, 6 mmol) were suspended in 10 ml of C, 64.95; H, 5.45; Cl, 9.59; N, 11.36%.
ethanol and refluxed for 2 h. The ethanol was evapoꢀ
(9ꢀBenzylimidazo[1,2ꢀa]benzimidazolylꢀ2)acetic acid
rated, and the residue was dissolved in a small volume
of chloroform. The insoluble inorganic salts were filꢀ
tered out, and the filtrate was run through a column
with aluminum oxide. Chloroform was used as the
mobile phase. Chloroform was evaporated from the
eluate, and the residue was dried over phosphorus penꢀ
toxide. Yield: 1.1 g (73%). Melting range: 68–69°C
(MeCN). IR: 1750 (C=O), 1630, 1605, 1500 (C=C,
C=N), 1450 (CH2), 1150 (C–O). Anal. Found: C,
(V). A suspension of ester (IVc) (2.0 g, 6 mmol) in
20 ml of 20% NaOH was refluxed for 2 h. The mixture
was cooled, and the sodium salt precipitated in the
form of an oil was separated. It crystallized after a proꢀ
longed standing in air. The salt was dissolved in 30 ml
of water and carefully acidified to pH 3–4 with conꢀ
centrated hydrochloric acid. The mixture was evapoꢀ
rated to a small volume and cooled. The sediment was
filtered and washed with cold water. After drying at
room temperature, the product was suspended in
30 ml of benzene, thoroughly mixed, and the undisꢀ
solved acid (VI) was filtered and washed with petroꢀ
leum ether. Yield: 1.2 g (65%). Melting range: 228–
65.42; H, 5.96; N, 16.25%. Calcd. for C14H15N3O2: C,
1
65.36; H, 5.88; N, 16.33%. H NMR (CDCl ): 7.45
3
(1 H, d,
(2 H, q,
J
J
7.9, H5), 7.10–7.32 (4 H, m, H ), 4.19
7.4, OCH2), 3.71–3.78 (5 H, m, NCH3,
Ar
CH ), 1.27 t (3 H,
J
7.2, CH3).
Ethylꢀ(9ꢀmethylimidazo[1,2ꢀ
acetate hydrochloride (IVa HCl) was obtained by C, 70.74; H, 5.02; N, 13.69%; Calcd. for C18H15N3O2
careful acidification of a solution of (IVa) in acetone to C, 70.81; H, 4.95; N, 13.76%. 1H NMR: 7.68 (1 H, d,
pH 2–3 with hydrochloric acid. Yield: 90%. The salt 7.5, H5), 7.05–7.50 (9 H, m, HAr), 5.37 (2 H, s,
С
(decomp.) IR: 2700ꢀ2500 (N+H), 1670 (C=O),
2
229°
a
]benzimidazolylꢀ2) 1620, 1600, 1510 (C=C, C=N). Anal. Found:
⋅
:
J
was purified either by recrystallization from a small NCH2), 3.21 (2 H, s, CH2).
volume of ethanol or precipitation from ethanol soluꢀ
tion with diethyl ether. Melting point: 197 С
(decomp.) Anal. Found: C, 57.18; H, 5.55; Cl, 12.13;
N, 14.23%; Calcd. for C14H15N3O2 HCl: C, 57.24;
H, 5.49; Cl, 12.07; N, 14.30%.
2,9ꢀDimethylimidazo[1,2ꢀa]benzimidazole (VIIc).
°
A mixture of ester (IVa) (0.77 g, 3 mmol) and 10 ml of
concentrated hydrochloric acid was refluxed for 2 h.
The solution was cooled and alkalized to pH 9–10
with 22% NH4OH. Base (VIIa) was extracted with
Ethylꢀ(9ꢀbutylimidazo[1,2ꢀ
a
]benzimidazolylꢀ2) chloroform (3
×
10 ml). The extract was dried over
acetate hydrochloride (IVb HCl). Base (IVb) was sodium sulfate, evaporated to a small volume, and run
⋅
obtained similarly to (IVa) in the form of an oil by through aluminum oxide with chloroform as the
cyclization of salt (IIb). Acidification of a solution of base mobile phase. The solvent was evaporated from the
(
IVb) in acetone to pH 2–3 with concentrated hydroꢀ extract, and the residue was recrystallized from ethaꢀ
chloric acid produced hydrochloride (IVb HCl). Yield: nol. Yield: 0.53 g (95%). Melting point: 94
72%. Melting range: 133–134 (decomp., MeCN). (decomp., EtOH). IR: 1635 (C=N), 1610, 1500,
⋅
°С
°С
IR: 1760 (C=O), 1630, 1600, 1505 (C=C, C=N), 1470, 1460 (C=C). Anal. Found: C, 78.17; H, 5.84; N,
1455 (СН2), 1150 (C–O). Anal. Found: C, 60.72; H, 15.99%; Calcd. for C11H11N3: C, 71.33; H, 5.99; N,
6.54; Cl, 10.65; N, 12.58%. Calcd. for C17H21N3O2 22.69%. 1H NMR: 7.44 (1 H, d,
J 8.0, H5), 7.14–7.37
HCl. C, 60.80; H, 6.60; Cl, 10.56; N, 12.51%. (4 H, m, HAr), 3.78 (2 H, s, NCH2), 2.40 (3 H, s,
1H NMR: 12.80 (1 H, wid. s, N+H), 7.30–8.20 (5 H, CH3).
m, HAr), 4.52 (2 H, t,
CH2), 3.86 (2 H, s, CH2), 1.80–2.00 (2 H, m, CH2),
1.38–1.56 (2 H, m, CH2), 1.33 (3 H, t, 7.4, CH3),
0.97 (3 H, t, 7.2, CH3).
J 6.9, CH2), 4.20 (2 H, q, J 7.2,
9ꢀBenzylꢀ2ꢀmethylimidazo[1,2ꢀ
(VIIc) was obtained similarly to tricyclic compound
VIIa) by decarboxylation of acid (Vc) with concenꢀ
trated hydrochloric acid. Yield: 76%. Melting point:
]benzimidazolylꢀ2) 111 (decomp., EtOH). IR: 1640 (C=N), 1600,
a]benzimidazole
J
(
J
Ethylꢀ(9ꢀbenzylimidazo[1,2ꢀ
a
°С
acetate (IVc) was obtained similarly to (IVb) by 1500, 1470, 1460 (C=C). Anal. Found: C, 78.17;
cyclization of the corresponding salt (IIc). Yield: 83%. H, 5.84; N, 15.99%; Calcd. for C17H15N3: C, 78.13;
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 37
No. 6
2011

RESEARCH IN THE FIELD OF IMIDAZO[1,2ꢀ
a
]BENZIMIDAZOLE DERIVATIVES
763
1
H, 5.79; N, 16.08%. H NMR: 7.43 (1 H, d,
J 7.8, with Phytophthora zoospores. Their efficacy was
H5), 7.04–7.35 (9 H, m, HAr), 5.35 (2 H, s, NCH2), assessed on day 7 after the infection from the decrease
2.38 (3 H, s, CH3).
in the degree of leaf injury with reference to control
plants infected without sprinkling.
(9ꢀMethylimidazo[1,2ꢀa]benzimidazolylꢀ2)acetoꢀ
In tests of activity against wheat leaf rust, wheat
plants of age 10–12 days were sprinkled with suspenꢀ
sions of compounds to be tested and three days later
inoculated with Puccinia uredospores. Their efficacy
was assessed on day 10 after the infection from the
decrease in the degree of leaf injury with reference to
unsprinkled control plants.
In experiments with powdery mildew of cucumꢀ
bers, seed leaves of cucumber plants were inoculated
with the fungus 24 h after sprinkling with aqueous susꢀ
pensions of compounds to be tested. The degree of leaf
injury was assessed from the area covered by the powꢀ
dery coating on day 9 or 10 after the infection.
hydrazide (VIIIa). Ester (IVa) (0.26 g, 1 mmol) and
hydrazine hydrate (2 ml) were refluxed for 5 min. At
first, a solution formed, and it immediately gave rise to
white needles. The sediment was filtered and washed
with cold ethanol and diethyl ether. Yield: 0.22 g
(92%). Melting range: 189–190 С (decomp., EtOH).
°
IR: 3500ꢀ3030 (NH2, two bands), 1680 (C=O), 1630
(NH). Anal. Found: C, 59.19; H, 5.48; N, 28.72%;
Calcd. for C12H13N5O: C, 59.25; H, 5.39; N, 28.79%.
1H NMR: 9.09 (1 H, s, NH), 7.72 (1 H, d,
J
7.8, H5),
7.5, HAr), 7.15
7.5, HAr), 4.23 (2 H, s, NH2), 3.67 (3 H, s,
NCH3), 3.38 (2 H, s, CH2).
(9ꢀBenzylimidazo[1,2ꢀ
7.42ꢀ7.53 (2 H, m, HAr), 7.28 (1 H, t,
(1 H, t,
J
J
a
]benzimidazolylꢀ2)acetoꢀ
The results were compared with the fungicide
Benomyl (methyl [1ꢀ(butylcarbamoyl)benzimidaꢀ
zolylꢀ2]carbamate).
hydrazide (VIIIc) was obtained from ester (IVc) simiꢀ
larly to (VIIIa). Yield: 91%. Melting point: 165°C
(decomp., EtOH). IR: 3500–3030 (NH2, two bands),
1675 (C=O), 1628 (NH). Anal. Found: C, 67.62;
H, 5.45; N, 22.00%; Calcd. for C18H17N5O: C, 67.70;
H, 5.37; N, 21.93%. 1H NMR: 9.11 (1 H, s, NH), 7.75
Antimicrobial activity was evaluated by the agar difꢀ
fusion test in vitro from the measurement of the zone
of microbial growth inhibition around samples. A well
was cut in an agar layer with a target microbial strain
with a sterile 8ꢀmm cork borer down to the plate botꢀ
tom. To each of the wells, 0.1 ml of test solution was
added. The plates were incubated in a temperatureꢀ
controlled cabinet at 37°C for 16–18 h. Then the
growth inhibition zones forming around the wells were
measured.
(1 H, d,
J 7.8, H5), 7.45–7.56 (2 H, m, HAr), 7.10–
7.40 (7 H, m, HAr), 5.37 (2 H, s, NCH2), 4.24 (2 H, s,
NH2), 3.39 (2 H, s, CH2).
N
'ꢀ(4ꢀNitrobenzylidene)ꢀ(9ꢀmethylimidazo[1,2ꢀ
benzimidazolylꢀ2)acetohydrazide (IX). Hydrazide
VIIIa) (0.2 g, 0.8 mmol) and 4ꢀnitrobenzaldehyde
a]
(
(0.12 g, 0.8 mmol) were refluxed in 4 ml of ethanol for
2 h. The mixture was cooled and the resulting sediꢀ
ment was filtered. Yield: 0.3 g (98%). Melting range:
The target microorganisms were Gram negative
(typhoid fever agent, salmonella, pathogenic Escheriꢀ
chia coli) and Gram positive (various staphylococci
213–214 С (decomp., H2O–DMF). IR: 3455, 3100
°
species). The microbial load was 3
×
106 bacteria in
(NH, two bands), 1685 (C=O), 1605 (NH). Anal.
Found: C, 60.55; H, 4.34; N, 22.26%; Calcd. for
C19H16N6O3: C, 60.63; H, 4.28; N, 22.33%. 1H NMR:
11.82 and 11.72 (1 H, 2 s, NH), 9.09 and 8.87 (1 H,
2 s, CH), 7.07–8.42 (9 H, m, HAr), 4.04 (2 H, s, CH2),
3.67 (3 H, s, NCH3).
1 ml of washing from an 18ꢀh agar culture. The assessꢀ
ment was done with reference to Furadonin, a pharꢀ
maceutical active at 100 g/ml (except for pathogenic
μ
Escherichia coli).
Antiarrhythmic action. The antiarrhythmic properꢀ
ties of the compounds under study were assessed from
their action on cardiac muscle excitability [21].
Experiments were carried out with isolated rat atria
superfused with Krebs–Ringer solution (composition,
mM: NaCl, 124; KCl, 3; MgSO4 – 2, CaCl2 – 2,
NaHCO3 – 26, KH2PO4, 1.24; glucose, 10; pH 7.4) at
N
'ꢀ(4ꢀNitrofurfurylidene)ꢀ(9ꢀmethylimidazo[1,2ꢀ
benzimidazolylꢀ2)acetohydrazide (X) was obtained
similarly to hydrazone (IX) from hydrazide (VIIIa
and 5ꢀnitrofuranꢀ2ꢀcarbaldehyde. Yield: 97%. Meltꢀ
ing point: 143 (decomp., EtOH). IR: 3470, 3125
a]
)
°С
(NH, two bands), 1690 (C=O), 1600 (NH). Anal.
Found: C, 55.80; H, 3.92; N, 22.85%; Calcd. for
C17H14N6O4: C, 55.74; H, 3.85; N, 22.94%. 1H NMR:
11.86 and 11.75 (1 H, 2 s, NH), 8.25 and 7.91 (1 H,
2 s, CH), 7.00–7.70 (7 H, m, HAr), 3.95 (2 H, s, CH2),
3.72 (3 H, s, NCH3).
Fungicidal activity. The fungicidal activities of the
compounds under study against late blight of tomato,
brown leaf rust of wheat, and powdery mildew of
cucumbers, were tested in a greenhouse.
a flow rate of 2.4 ml/min, temperature 32 С, with oxyꢀ
°
genation (95% oxygen and 5% carbon dioxide). The
activity of compounds was judged from the minimum
effective concentration (MEC) of substances preventꢀ
ing paced rhythm (3 Hz, pulse duration 0.5 ms, and
voltage twice as high as the threshold value; pacemaker
ESLꢀ3) within 15 s, which was indicative of an
increase in the refraction time of the cardiac muscle.
The activities were compared with the action of
procainamide and quinidine [22].
The effects on late blight of tomato were tested on
Activation of the excitability of cortical columns.
tomato plants with 5 to 7 leaves. Plants were sprinkled The tests were carried out by acute experiments with
with suspensions of the compounds and inoculated unanesthetized immobilized genetically heterogeꢀ
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 37
No. 6
2011

764
ANISIMOVA et al.
6. Anisimova, V.A.,. I.E. Tolpygin, Minkin, V.I., Spasov, A.A.,
Stepanov, A.V., Ar’kova, N.V., Naumenko, L.V., and
Petrov, V.I., RF Patent No. 2290404, Byull. Izobret.
2006, vol. 36.
neous white rats, males and females, weighing 200–
250 g [23]. The protocol met the international regulaꢀ
tions for experiments with animals [24]. It had been
approved by the Biomedical Ethics Committee of the
Russian Academy of Sciences [protocol 98 of March 11,
2002]. Burr holes 3 mm in diameter were drilled for
recording bioelectrical activity and stimulating brain
regions: 2 mm caudal to bregma and 5.5 mm lateral to
the sagittal suture above the vibrissa cortical representaꢀ
tion. Deflection of focal activity from particular colꢀ
umns was done with glass microelectrodes filled with
,
7. Middlemiss, D., Ashton, M.R., Boyd, E.A., and
Brookfield, F.A., GB Patent No. 2407318, 2005.
8. Mamolo, M.G., Falagiani, V., Zampieri, D., Vio, L.,
and Banfi, E., Il Farmaco, 2001, vol. 56, pp. 587–592.
9. Stapper, C., Gretzke, D., Glombik, H., Falk, E., Goerꢀ
litzer, J., Keil, S., Schaefer, H.ꢀL., and Wendler, W.,
WO Patent No. 04076427, 2004.
2.5 M NaCl, resistance 2–5 M
Ω
, tip diameter 2–3
μ
m.
10. Falco, J.L., Palomer, A., and Guglietta, A., EP Patent
No. 1973907, 2009.
Microapplication of solutions of compounds
(
IVa HCl) (volume 50 nl, concentration 0.75 mM
, b ⋅
11. Casagrande, C., Invernizzi, A., Ferrini, R., and
Miragoli, G., Farmaco Ed. Sci., 1971, vol. 26,
pp. 1059–1073.
in isotonic NaCl solution) was done by local injection
with pressure using noncapillary glass microelectrodes
with tip diameters 5–10 m. The volume of the soluꢀ
tion injected was determined by recording the position
of the top of the meniscus in the thick portion of the
electrode with an MBSꢀ2 microscope (Russia)
equipped with an eyepiece micrometer.
μ
12. Anisimova, V.A., Tolpygin, I.E., Spasov, A.A., Serꢀ
dyuk, T.S., and Sukhov, A.G., Meditsina v Kuzbasse
2009, no. 7 (special issue), pp. 35–36.
,
13. Abignente, E., Arena, F., De Caprariis, P., and Parente, L.,
Farmaco Ed. Sci., 1976, vol. 31, pp. 209–217.
Analysis of the baseline activity and construction of
averaged power spectra (range 1–30 Hz, step 1 Hz,
baseline time 30–60 s, averaging epoch 1 s) were done
by time series analysis using the Fourier transform
(DataView software, Yu.I. Gusach, Kogan Research
Institute of Neurocybernetics).
14. Kuz’menko, T.A., Kuz’menko, V.V., Simonov, A.M.,
and Simkin, B.Ya., Khim. Geterotsikl. Soed., 1980,
pp. 1656–1661.
15. Abignente, E., Arena, F., De Caprariis, P., and Parente, L.,
Farmaco Ed. Sci., 1976, vol. 31, pp. 880–887.
16. Takahashi, S. and Kano, H., J. Org. Chem., 1965,
vol. 30, no. 4, pp. 1118–1122.
ACKNOWLEDGMENTS
17. Haake, P., Bausher, L.P., and McNeal, J.P., J. Am.
Chem. Soc., 1971, vol. 93, pp. 7045–7049.
This work was supported by the Ministry of Educaꢀ
tion and Science of the Russian Federation, grant
AVTsP RNP VSh No. 2.2.1.1/11794.
18. Mironova, T.F., Mironov, V.A., and Tyurin, A.Yu.,
Vestn. Aritmol., 2005, no. 39, pp. 53–65.
19. Sukhov, A.G., Lysenko, L.V., and Logvinov, A.K.,
Valeologiya, 2009, no. 4, pp. 54–59.
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RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 37
No. 6
2011