Synthesis and anxiolytic activity of 4-amino-2,6-dimethylnicotinic acid esters and amides

Full text of DOI:10.1023/A:1015185525121

Pharmaceutical Chemistry Journal
Vol. 35, No. 11, 2001
SYNTHESIS AND ANXIOLYTIC ACTIVITY OF 4-AMINO-2,6-
DIMETHYLNICOTINIC ACID ESTERS AND AMIDES
O. M. Glozman,1 L. A. Zhmurenko,1 V. P. Lezina,1 G. M. Molodavkin,1
and T. A. Voronina1
Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 35, No. 11, pp. 8 – 10, November, 2001.
Original article submitted June 5, 2001.
The class of 2- and 4-aminopyridinecarboxylic acid de-
rivatives contains compounds possessing anxiolytic, anticon-
vulsant, and antiamnesic activity [1 – 3]. This study was de-
voted to the search for new effective anxiolytics among
4-amino-2,6-dimethylnicotinic acid esters and amides.
In the first step, 4-chloro-2,6-dimethylnicotinic acid
ethylate (I) [4] reacted with the corresponding amines to
yield 4-amino-2,6-dimethylnicotinic acid ethyl esters (IIa –
IIf, III) in the form of bases or salts. Subsequent
saponification of ethylate I led to acid IV, which was con-
verted into 2,6-dimethylnicotinic acid amide (V) under the
action of thionyl chloride and ammonia. Heating compound
V with amines led to amides VI.
of acid I [4] and 6.48 g (0.04 mole) of 4-phenylpiperazine in
20 ml of anhydrous xylene was boiled for 12 h, evaporated in
vacuum, and filtered. The residue was washed with ether and
treated with anhydrous oxalic acid (1.39 g) to obtain 5.75 g
of hemioxalate IIa.
NR2
Cl
COOC2H5
· nHX
COOC2H5
+ HNR2
H3C
N
CH3
H3C
N
I
CH3
IIa –IIf
2
;
(COOH)
;
, n = 0,5,
IIa:
HX =
NR =
N
N
2
1
The IR and H NMR spectra of the synthesized com-
2
pounds (Table 1) agree with the proposed structures. The IR
spectra if compounds IIa – IIc contain intense absorption
bands due to carboethoxy groups at 1716 – 1695 cm – 1. In
addition, the spectrum of compound IIc displays the stretch-
2 , n = 2,HX = HCl
IIb:
IIc:
NHCH CH N(CH )
NR =
2
2
3
;
, n = 1 ,
HX = HCl
NR2 NH
ing vibrations of free amino groups at 3341 and 3202 cm – 1
.
H2N
1
The H NMR spectra of compounds IIa – IIf, III, and
VIb show the signals from 5-H protons of the pyridine cycle,
2- and 6-methyl groups, and substituents in position 4. The
proposed structures were also confirmed by the results of el-
emental analyses. The synthesized compounds were charac-
terized with respect to anxiolytic activity in the conflict situ-
ation test.
;
2
, n = 1 ,
O
HX =(COOH)2
N
IId:
NR =
;
2
Ñl, n = 1 ,HX = HCl
IIe:
IIf:
NH
NR =
NR2 =NH
, n = 1 ,HX = HCl
ÑOOC2H5
NHCH2
EXPERIMENTAL CHEMICAL PART
I + H2NCH2CH2NH2
· 2HCl
H3C
N
CH3
The IR spectra were recorded on a Perkin-Elmer Model
457 spectrophotometer. The 1H NMR spectra were measured
on a Bruker AC-250 spectrometer using TMS as the internal
standard.
4-(N¢-Phenylpiperazino)-2,6-dimethylnicotinic acid
ethylate hemioxalate (IIa). A mixture of 4.26 g (0.02 mole)
2
III
4-(4-Carboethoxyanilino)-2,6-dimethylnicotinic acid
ethylate hydrochloride (IIf). mixture of 2.55 g
(0.012 mole) of acid I and 1.65 g (0.01 mole) of anesthesine
in 20 ml of anhydrous toluene was boiled for 15 h in the
presence of 2.21 g (0.022 mole) triethylamine. Then 20 ml of
anhydrous DMF was added and the homogeneous reaction
A
1
Institute of Pharmacology, Russian Academy of Medical Sciences,
Moscow, Russia.
591
0091-150X/01/3511-0591$25.00 © 2001 Plenum Publishing Corporation

592
O. M. Glozman et al.
TABLE 1. Yields and Physicochemical Characteristics of the Synthesized Compounds
Com- Yield,
pound
M.p.,
°C (solvent)
Empirical
formula
IR spectrum:
1H NMR spectrum
in DMSO-d6: d, ppm
%
nmax, cm – 1
IIa
66.9 187 – 188 anhydr. etha-
nol
1716(C=O)
1.32 (t, 3H, CH3), 2.44 (s, 3H, CH3), 2.45 (s, 3H, CH3),
C20H25N3O2 × 0.5(COOH)2
1654(C=O) 1613 4.37 (q, 2H, CH2), 5.2 (ms, 1H, COOH), 6.8 – 7.5 (m, 5H,
C6H5)
IIb
IIc
50.0 238 – 239 anhydr. etha-
nol
1702(C=O)
1665(C=O)
1.30 (t, 3H, CH3), 2.42 [2s, 6H, 2, 6-(CH3)2], 2.68 [s, H,
N(CH3)2], 2.92 – 3.50 (m, 4H, CH2CH2), 4.35 (q, 2H,
CH2), 7.05 (s, 1H, 5-H)
C14H23N3O2 × 2HCl
97.0 171 – 172
acetone
3341 (NH2)
3202
1695(C=O)
1652(N–H)
1637(N–H)
1.42 (t, 3H, CH3), 2.45 (s, 3H, 6-CH3), 2.78 (s, 3H,
2-CH3), 4.42 (q, 2H, CH2), 6.35 (s, 1H, 5-H pyridine),
6.45 – 7.2 (m, 4H, C6H4), 9.5 (bs, 1H, NH)
C16H19N3O2 × HCl
IId
34.7 173 – 174
ethanol
…
1.32 (t, 3H, CH3), 2.44, 2.45 [2s, 6H, 2, 6-(CH3)2], 3.37,
3.69 (2m, 8H, morpholine), 4.32 (q, 2H, CH2), 5.06 (bs,
1H, COOH), 7.06 (s, 1H, 5-H pyridine)
C14H20N2O3 × (COOH)2
IIe
IIf
94.0 200 – 201
2-propanol
…
…
C16H17ClN2O2 × HCl
C19H22N2O4 × HCl
94.0 194 – 195
2-propanol
1.25, 1.38 (2t, 6H, 2 × CH3), 2.51 (s, 3H, 6-CH3), 2.65 (s,
3H, 2-CH3), 4.32 (q, 4H, 2 × CH2), 7.05 (s, 1H,
5-H pyridine), 7.45, 8.05 (m, 4H, C6H4), 10.3 (s, 1H, NH)
III
36.0 > 290 anhydr.
ethanol
…
C22H30N4O4 × 2HCl
[in CCl4]: 1.37 (t, 6H, 2 × CH3), 2.37 (s, 6H, 2 × CH3), 2.58
(2s, 6H, 2 × CH3), 3.44 (m, 4H, CH2CH2), 4.35 (q, 4H,
2 × CH2-ethyl), 6.24 (s, 2H, 2 × 5-H pyridine); 7.92 (bs,
2H, 2 × NH)
V
59.4 192 – 193 acetone
C8H9ClN2O
C12H17N3O2
…
…
…
…
VIa
62.7 170 – 171
ethyl acetate
VIb
VIc
56.0 279 – 280 (decomp.)
(ethanol – acetone)
3428(NH2)
3363 (NH2)
1676(C–O)
1643
2.55 [s, 6H, 2, 6-(CH3)2], 3.52, 4.00 (2m, 8H,
2 × CH2CH2), 5.60 (bs, 1H, COOH), 7.25 – 7.40 (m, 5H,
C6H5), 7.25 (s, 1H, 5-H pyridine), 8.10 (s, 1H, NH), 8.45
(s, 1H, NH)
C18H22N4O × 2HCl
50.0 191 – 192 anhydr.
ethanol–acetone
…
…
C15H17N3O × HCl
mass was boiled for 35 h, cooled, and diluted with water. The
precipitated oil was extracted with benzene, and the extract
was dried over MgSO4 and filtered. Finally, the filtrate was
treated with HCl-saturated ether to obtain 1.75 g of com-
pound IIf.
4-(2-Dimethylamionoethylamino)-2,6-dimethylnicoti
nic acid ethylate dihydrochloride (IIb). A mixture of
2.13 g (0.01 mole) of acid I and 0.88 g (0.01 mole) of
N,N-dimethylethylenediamine in 10 ml of butanol was
boiled for 17 h. The precipitate was washed with ether and
converted into dihydrochloride to obtain 1.7 g of compound IIb.
sized using a procedure analogous to that described above
for compound IIb.
1,2-Bis-(2,6-dimethyl-3-carboethoxypyridinyl-4-amin
o)ethane dihydrochloride (III). A mixture of 2.13 g
(0.01 mole) of acid I and 0.6 g (0.01 mole) of ethyl-
enediamine in 15 ml of butanol was boiled for 15 h, cooled,
diluted with ether, and treated with HCl-saturated ether to
obtain 1.75 g of compound III.
4-Chloro-2,6-dimethylnicotinic acid amide (V). A
mixture of 10 g (0.054 mole) of 4-chloro-2,6-dimethylnicoti-
nic acid and 70 ml of SOCl2 was boiled for 1 h and evapo-
rated in vacuum. The residue was diluted with 50 ml of an-
hydrous benzene and distilled in vacuum. The residue was
dissolved in 250 ml of anhydrous benzene and the solution
was bubbled with gaseous NH3 for 2 h. To this solution was
added 43 ml of concentrated NH4OH solution and the mix-
ture was allowed to stand overnight. The precipitate was sep-
arated by filtration to obtain 0.4 g of compound V; 5.9 g of
compound V was isolated from benzene solution.
4-(2-Amionoanilino)-2,6-dimethylnicotinic
acid
ethylate hydrochloride (IIc). Compound IIc was synthe-
sized using a procedure analogous to that described above
for compound IIb.
4-Morpholino-2,6-dimethylnicotinic acid ethylate ox-
alate (IId). Compound IId was synthesized using a proce-
dure analogous to that described above for compound IIa.
4-(4-Chloroanilino)-2,6-dimethylnicotinic
acid
ethylate hydrochloride (IIe). Compound IIe was synthe-

Synthesis and Anxiolytic Activity of 4-Amino-2,6-dimethylnicotinic Acid Esters
593
TABLE 2. Anxiolytic Activity of 4-Amino-2,6-dimethylnicotinic
Acid Esters and Amides
4-Morpholino-2,6-dimethylnicotinic
acid
amide
(VIa). A mixture of 1.0 g (0.0054 mole) of amide V and 2 g
of morpholine was heated to ~ 100°C for 9 – 10 h, cooled,
and diluted with 100 ml of ether, The precipitate was sepa-
rated by filtration and dissolved in water. The solution was
saturated with solid NaCl. Then the product was extracted
with chloroform, the extract was dried over MgSO4 and fil-
tered, and the filtrate was evaporated in vacuum to obtain
0.8 g of compound VIa.
4-(N¢-phenylpiperazino)-2,6-dimethylnicotinic acid
dihydrochloride (VIb). A mixture of 1.85 g (0.01 mole) of
amide V and 3.24 g (0.02 mole) N-phenylpiperazine in
10 ml of anhydrous DMF was heated to 100°C for 17 h, di-
luted with ~150 ml of water, and filtered. The filtrate was
washed with 50 ml of ether and the precipitated base was
converted into dihydrochloride VIb.
Dose,
mg/kg
Number of punished
water takes, M ± m
Compound
Control
–
15.96 ± 5.28
15.75 ± 6.4
17.15 ± 9.53
21.86 ± 18.18
11.43 ± 5.53
33.58 ± 14.59*
27.67 ± 21.62
–
IIa
5
10
20
40
20
40
–
IIb
IIc
IId
IIe
III
–
–
40
10
20
–
60.25 ± 38.42*
18.00 ± 12.10
17.5 ± 11.45
–
4-Benzylamino-2,6-dimethylnicotinic acid amide hy-
drochloride (VIc). Compound VIc was synthesized pro-
ceeding from amide V and benzylamine using a procedure
analogous to that described above for compound VIa.
VIa
VIb
10
20
40
–
22.00 ± 15.68
29.4 ± 16.43
22.5 ± 20.25
–
Cl
Cl
VIc
CONH2
CH3
COOH
CH3
–
1 . SOCl
OH
2
Medazepam
10
I
39.42 ± 9.19*
2. NH3
Phenazepam
1
H3C
N
V
114.72 ± 28.45**
H3C
N
Notes. Difference from control reliable for * P < 0.05, ** P < 0.01.
IV
NR2
CONH2
V + HNR2
· n · HX
trained animals were placed into the experimental chamber
again, but an increased voltage corresponding to a dc current
of 1 mA was applied between feeder and floor 10 sec after
the first water take, so that each next water take was pun-
ished. The anxiolytic effect was evaluated by a reliable in-
crease in the punished water takes in the test group relative to
the untreated control. The reference drug was tranquilizers
medazepam and phenazepam.
The experimental results (Table 2) showed that most of
the studied substances produced anxiolytic action compara-
ble to that of medazepam but inferior to the effect of
phenazepam.
H3C
N
CH3
VIà –VIc
VIa:
NR2 =N
O, n = 0
;
VIb:
N
N
, n = 2, HX = HCl
, n = 1 ,HX = HCl
NR2 =
VIc:
NR2 =NHCH2
EXPERIMENTAL BIOLOGICAL PART
The anxiolytic activity was studied using a model con-
flict between drinking motivation and electric-pain irritation
[5 – 7]. The experiments were performed during three days
on white mongrel male rats weighing 200 – 250 g. On the
first day, the test animals were deprived of water. On the next
day, the reflex of taking water from a feeder was elaborated
by placing each test animal into experimental boxes
(27.5 ´ 87.5 ´ 40 cm) with stainless steel feeder fountains
and metal electrode floor connected to a stabilized current
source. The animals investigated the chamber for some time,
found the feeder, and began to drink. At this instant, a weak
current (~50 mA, which is below the sensitivity threshold)
was passed through the feeder – floor circuit. Thus, taking
water was not punished and the number of takes was deter-
mined by the drinking motivation. On the third day, the
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