Synthesis and antiarrhythmic effect of 4-aryl-5-nitro-6-phenyl-3,4-dihydro-(1H)-pyrimidin-2-ones

Full text of DOI:10.1023/A:1020864220253

Pharmaceutical Chemistry Journal
Vol. 36, No. 6, 2002
SEARCH FOR NEW DRUGS
SYNTHESIS AND ANTIARRHYTHMIC EFFECT
OF 4-ARYL-5-NITRO-6-PHENYL-3,4-DIHYDRO-(1H)-PYRIMIDIN-2-ONES
V. F. Sedova,1 T. V. Voevoda,1 T. G. Tolstikova,1 and O. P. Shkurko1
Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 36, No. 6, pp. 4 – 7, June, 2002.
Original article submitted January 9, 2001.
+
As is known [1, 2], 1,4-dihydropyridine derivatives act
RC6H4CHO
+
RC6H4CHNHCONH2
C6H5COCH NO2
+
as calcium channel blockers. Some compounds of this group
(nifedipine, nicardipine, amlodipine, etc.) are used as
antihypertensive and antianginal agents [2, 3]. In addition,
these compound possess antiarrhythmic activity, which has
drawn the interest of clinical chemotherapists [4, 5].
3,4-Dihydro-(1H)-pyrimidin-2-ones, which are close
analogs of 1,4-dihydropyridines, possess the same spectrum
of pharmacological activity [3]. The hypotensive and
spasmolytic properties of dihydropyrimidin-2-ones were
originally demonstrated for 5-alkoxycarbonyl-4-phenyl de-
rivatives [6]. Most of the aforementioned dihydropyridine
and dihydropyrimidinone derivatives contain ester groups in
position 5 of the heterocycle [7, 8]. It was demonstrated that
substitution of NO2 for COOR in the dihydropyridine mole-
cule changes the character of biological action and leads to
compounds exhibiting higher toxicity [9, 10].
In the search for new effective cardiovascular drugs
among dihydropyrimidines, we have synthesized a series of
4-aryl-5- nitro-6-phenyl-3,4-dihydro-(1H)-pyrimidin-2-ones
(I – VII) and studied their pharmacological properties. The
interest in these derivatives is due to the generally lower tox-
icity of pyrimidines as compared to that of pyridines [11, 12].
Below we present data on the antiarrhythmic activity of the
synthesized compounds.
The new compounds (II – VII) were obtained via interac-
tion of a-nitroacetophenone, aromatic aldehydes, and urea,
by analogy with the synthesis of well-known compound I
[13].
The reaction includes the following sequential transfor-
mations: (i) acid-catalyzed condensation of aldehyde and
urea with the formation of active N-acylimmonium cations,
(ii) reaction of these N-acylimmonium cations with
nitroacetophenone with the formation of ureido derivatives,
and (iii) cyclization of these derivatives into dihydropyrimi-
dinones.
H
C6H5COCH2NO2
CHC6H4R
H2NCONH
+
RC6H4CH NHCONH2
NH2CONH2
H
C6H4R
NO2
H
C6H4R
NO2
HN
HN
H
OH
O
N
H
C6H5
O
N
H
C6H5
I – VII
R = H (I), p-HO (II), p-CH3O (III), m-F (IV), m-Cl (V), m-NO2 (VI), and
o-NO2 (VII).
The
proposed
structures
of
the
new
nitrodihydropyrimidinones (II – VII) were confirmed by the
1
data of IR, UV, and H NMR spectroscopy and mass spec-
trometry (Table 1). The UV absorption spectra exhibit two
intense bands in the regions of 230 – 250 and 344 – 347 nm.
The IR spectra display the characteristic absorption bands of
C=O group (1685 – 1712 cm – 1) and NO2 groups featuring
antisymmetric
(1495 – 1510 cm – 1
)
and
symmetric
(1323 – 1335 cm – 1) vibrations. The 1H NMR spectra of
compounds I – VII contain doublet signals from 4-H protons
at 6.11 – 6.31 ppm (J ~ 3 Hz) and broad doublets from two
NH groups in the regions of 7.95 – 7.97 and 8.86 ppm (Ta-
ble 2).
The mass spectra of nitrodihydropyrimidinones (I – VII)
are characterized by low intensity of the peaks of molecular
ions (3 – 10 %). There are two possible pathways of
dissociative ionization of these compounds: via detachment
of NO2 and OH groups. The main pathway is [M]+ ® F1
(Irel, 74 – 100 %) ® F3 (Irel, 32 – 43 %) ® F4 (Irel, 64 –
100 %).
Another characteristic feature is the detachment of an
aryl substituent occurring in position 4 of the pyrimidine
1
Vorozhtsov Institute of Organic Chemistry, Siberian Division, Russian
284
Academy of Sciences, Novosibirsk, Russia.
0091-150X/02/3606-0284$27.00 © 2002 Plenum Publishing Corporation

Synthesis and Antiarrhythmic Effect of 4-Aryl-5-nitro-6-phenyl-3,4-dihydro-(1H)-pyrimidin-2-ones
285
ring, with the formation of the F5 ion with m/z = 218 (Irel,
22 – 100 %). The only exception is presented by the mass
spectrum of compound VII containing 4-(o-O2NC6H4)
group, in which maximum intensity is observed for the ion
[M–OH–NO–OH]+ with m/z = 276; this is probably ex-
plained by spatial proximity of the C6H5, NO2, and
o-C6H4NO2 in the heterocycle.
4-(m-Fluorophenyl)-5-nitro-6-phenyl-3,4-dihydro-(1H)-
pyrimidin-2-one (IV). To a solution of 12.0 g (0.2 mole) urea
in a mixture of 75 ml isopropanol and 6 ml of concentrated
HCl was added 7.4 g (0.06 mole) of m-fluorobenzaldehyde
and the reaction mixture was stirred for 1 h and allowed to
stand overnight. Then 6.6 g (0.04 mole) of a-nitroacetophe-
none was added and the mixture was heated to boiling for
12 h. The precipitate was separated, washed sequentially
with ethanol, saturated sodium bicarbonate solution, and eth-
anol again, and crystallized from ethanol to obtain 7.2 g
(57%) of compound IV.
Aroyl derivatives I – III and V – VII were obtained using
analogous procedures. The products were recrystallized from
ethanol (compounds I – III, VI), 60% aqueous ethanol solu-
tion (compound V), and an ethanol – dioxane (2 : 1) mixture
(compound VII).
–H
–H
Ô4
Ô2
Ô3
[C6H5]+
–NO2
–OH
–NO
m/z 77
–CO
[M]+
Ô1
Ô7 –C6H4R
–C6H4R
–NO2, –H
Ô5
Ô6
[C6H5CH=N]+
m/z 171
m/z 104
EXPERIMENTAL PHARMACOLOGICAL PART
EXPERIMENTAL PART
The antiarrhythmic activity of compounds I, II, and IV
were studied in a group of mature male rats weighing
170 – 220 g narcotized with thiopental sodium (25 mg/kg,
i.p.). The reference drugs were lidocaine and quinidine.
The doses effective in 50% of the test animals (ED50) for
the three compounds and reference drugs were determined
by probit analysis [14] upon single intraperitoneal adminis-
tration in rats with model arrhythmias induced by calcium
chloride (CaCl2) and epinephrine hydrochloride (EH). Pre-
liminary experiments were used to determine the
arrhythmogen doses inducing medium-level heart rhythm vi-
olation without lethal ventricular fibrillation. The ED50 val-
ues were calculated using the experimental data for five
doses of each compound (ranging from 3 to 10 mg/kg) and
reference drugs (3 to 12 mg/kg). A criterion of the positive
action was complete absence of arrhythmia signs.
The IR absorption spectra were measured on a Bruker
Vector 22 spectrophotometer (Germany) using samples pel-
letized with KBr. The UV spectra of ethanol solution were
recorded with a Specord M-40 spectrophotometer (Ger-
many). The mass spectra were obtained with a Finnigan
MAT 8200 instrument using direct injection of samples into
1
the ion source. The H NMR spectra were measured on a
Bruker AC 200 spectrometer using CF3COOH as a solvent
and CH2Cl2 as an internal standard. The parameters of IR,
UV, 1H NMR, and mass spectra are given in Tables 1 and 2.
The course of reactions was monitored and the purity of
the reaction products was checked by TLC on Silufol
UV-254 plates eluted with CHCl3. The data of elemental
analyses of compounds II – VII for C, H, Cl, F, and N agree
with the results of analytical calculations.
TABLE 1. Yields and Physicochemical Characteristics of the Synthesized Compounds II – VII
[M]+, m/z
found
IR spectrum: n, cm – 1
UV spectrum
Empirical
Compound
M.p., °C
Yield, %
lmax, nm
(log e)
formula
C16H13N3O4
C17H15N3O4
C16H12FN3O3
C16H12ClN3O3
C16H12N4O5
C16H12N4O5
NO2(as)
1496
NO2(s)
1324
C=O
1688
NH
calcd.
311.0876
311.0906
325.1046
325.1062
313.0867
313.0863
329.0537
329.0567
340.0807
340.0808
*
II
218 – 221
247 – 249
203 – 205
190 – 192
221 – 223
263 – 265
3206, 3408
231 (4.12),
347 (3.81)
57
58
57
65
62
64
III
IV
V
1696
1686
1688
1686
1711
1510
1502
1335
1326
1323
1326
1326
3207, 3420
3208, 3428
3204, 3438
3201, 3360
230 (4.32),
346 (3.92)
242 (3.95),
345 (3.91)
1500
242 (3.97),
345 (3.87)
VI
VII
1497, 1530
1495, 1534
250 (4.19),
345 (3.92)
3199, 3386,
3444
245 (3.77),
345 (3.74)
* [M]+ peak is absent; for [C16H12N4O5–OH]+ fragment, m/z = 323.0734; C16H11N4O4; calcd., 323.0780.

286
V. F. Sedova et al.
TABLE 2. Parameters of the 1H NMR Spectra of Compounds
I – VII
ous needle electrodes in II standard lead. The first record was
made immediately after calming of each rat and the dynam-
ics was monitored by EEGs measured 1, 5, 10, and 15 min
after drug administration (when possible, up to 45 min).
Each test group contained 10 rats. The experimental data
were statistically processed using the Student t-criterion [14].
It was established that compounds I, II, and IV belong to
the class of low-toxicity substances; none of these com-
pounds produced significant effect on the heart rhythm and
frequency in control rats observed for up to 45 min.
Chemical shift: d, ppm (J, Hz)
Com-
pound
4-H
Ar
N–H
CH3O
4.07 s
I
6.14 d (3) 7.51 – 7.71 m
7.89 bd,
8.83 s
II
6.11 d (3) 7.15 d (8), 7.56 – 7.77 m 7.85 bd,
8.79 s
III
IV
6.09 d (3) 7.20 d (8), 7.50 – 7.72 m *, 8.62 s
6.12 d (3) 7.20 – 7.65 m
7.75 bd,
8.68 s
V
6.12 d (3) 7.51 – 7.70 m
7.74 bd,
8.77 s
RESULTS AND DISCUSSION
VI
6.31 d (3) 7.60 – 7.68 m, 7.82 t (8), 7.98 bd,
Administration of the compounds studied in an effective
dose (ED50) before induction of the CaCl2 arrhythmia model
significantly reduced the loss of test animals (Table 3). The
maximum protection was offered by compounds II and IV.
An analysis of the heart rhythm showed that compound IV in
all cases prevented the development of dangerous rhythm vi-
olations characteristic of this model.
8.11 d (8), 8.45 d (8),
8.60 s
8.86 s
8.78 s
VII
6.67 s
7.62 – 7.85 m, 7.91 m,
8.22 d (8)
* Signal in the region of aromatic protons.
Against the background of compound I, no arrhythmia
was developed in 50% of test rats, while the other half of the
test animals exhibited cardiac fibrillation at a ventricular rate
of about 55 cpm, followed by restoration of the sinus rhythm
within 30 – 35 min. Compound II prevented arrhythmia de-
velopment in 60% of cases and relieved the arrhythmia at-
tack within 2 – 10 min.
The therapeutic activity of the compounds studied was
characterized by the antiarrhythmic index determined as the
ratio of the acute toxicity LD50 to ED50. The acute toxicity
was studied by single intraperitoneal injections in white
mongrel mice and evaluated by the Litchfield – Wilcoxon
method [14].
The results of tests on the CaCl2 arrhythmia model
showed that the average antiarrhythmic activity of com-
pounds I, II, and IV is greater than that of lidocaine and
quinidine by a factor of 31 and 15, respectively (Table 4).
The administration of compounds I, II, and IV in effec-
tive doses before induction of the epinephrine model showed
that the maximum protection of animals from loss was en-
sured by compound II (Table 3). The average antiarrhythmic
activity of compounds I, II, and IV on this model is greater
than that of lidocaine and quinidine by a factor of 21 and 8,
respectively (Table 4).
A special series of experiments was devoted to determin-
ing the effect of compounds I, II, and IV on the survival of
rats with CaCl2 and EH arrhythmia models. These experi-
ments were performed with rats divided into eight groups:
group 1, intraperitoneal injection of compounds I, II, and IV
(ED50); group 2, CaCl2 control (250 mg/kg, i.v.); group 3,
compounds I, II, and IV injected (ED50, i.p.) 10 min before
CaCl2 model induction; group 4, EH control (0.3 mg/kg,
i.v.); group 5, compounds I, II, and IV injected (ED50, i.p.) 10
min before EH model induction; group 6, intact control
(narcotized animals).
The EEGs were recorded at a velocity of 50 mm/sec on
an EKIT-03M electrocardiograph (Russia) using subcutane-
TABLE 4. Comparative Efficacy of Compounds I, II, and IV and
Reference Antiarrhythmic Drugs in the Tests with Calcium Chloride
(CaCl2) and Epinephrine Hydrochloride (EH) Induced Arrhythmia
Models
TABLE 3. Effect of Compounds I, II, and IV on the Survival of Ex-
perimental Animals in the Tests with Calcium Chloride (CaCl2) and
Epinephrine Hydrochloride (EH) Induced Arrhythmia Models
Experiment
Dose, mg/kg
Survival, %
Antiarrhythmic index
ED50, mg/kg
(LD50/ED50)
LD50,
CaCl2 (control)
I + CaCl2
250
40
70
90
100
10
40
90
70
Compound
mg/kg
CaCl2
model
EH
CaCl2
model
EH
model
3.85 + 250
3.75 + 250
3.60 + 250
0.3
model
II + CaCl2
IV + CaCl2
EH (control)
I + EH
I
3.85
3.75
3.60
9.80
8.30
3.90
3.75
3.75
6.90
4.60
> 1500
> 1500
> 1500
128
390
400
385
400
II
IV
417
400
3.90 + 0.3
3.75 + 0.3
3.75 + 0.3
Lidocaine
Quinidine
13.06
26.50
18.55
47.83
II + EH
220
IV + EH

Synthesis and Antiarrhythmic Effect of 4-Aryl-5-nitro-6-phenyl-3,4-dihydro-(1H)-pyrimidin-2-ones
287
An analysis of the heart rhythm showed that the injection
of epinephrine against the background of compound I was
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