1-vinyl-3- and 1-vinyl-5-pyrazolecarboxylic acids. synthesis and anti-burn activity of their chitosan salts

Article abstract of DOI:10.1134/S1070363214100156

The synthesis of 1-vinyl-3- and 1-vinyl-5-pyrazolcarboxylic acids is developed and the anti burn activity of the chitosan salts of 1-vinyl-3(5)-carboxylic acids is studied.

Full text of DOI:10.1134/S1070363214100156

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 10, pp. 1945–1949. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © V.I. Rstakyan, A.E. Akopyan, А.А. Saakyan, О.S. Attaryan, G.V. Asratyan, 2014, published in Zhurnal Obshchei Khimii, 2014,
Vol. 84, No. 10, pp. 1667–1671.
1
-Vinyl-3- and 1-Vinyl-5-pyrazolecarboxylic Acids.
Synthesis and Anti-Burn Activity of Their Chitosan Salts
V. I. Rstakyan, A. E. Akopyan, А. А. Saakyan, О. S. Attaryan, and G. V. Asratyan
Institute of Organic Chemistry, Scientific and Technological Center of Organic and Pharmaceutical Chemistry,
National Academy of Sciences of Armenia, 26 Azatutyan ave., Yerevan, 0014 Armenia
e-mail: vrstakyan@gmail.com
Received June 30, 2014
Abstract—The synthesis of 1-vinyl-3- and 1-vinyl-5-pyrazolcarboxylic acids is developed and the anti burn
activity of the chitosan salts of 1-vinyl-3(5)-carboxylic acids is studied.
Keywords: chitosan, vinylpyrazolecarboxylic acids, anti burn activity
DOI: 10.1134/S1070363214100156
Pyrazolecarboxylic acids occupy an important place
among functionally substituted pyrazoles. Some
derivatives of pyrazolecarboxylic acids, like their
amides, possess an expressed pharmacological activity
For chemoselective vinylation of the nitrogen atom,
the carbonyl group remaining intact in the molecule of
3(5)-pyrazole carboxylic acid (I), the method of introduc-
tion of protecting groups was suggested, which are
stable in various reactions and can be easily removed [7].
[
1]. 1-Carboxyethylpyrazoles were used as new curing
and modifying agents for hot curing of epoxide resins
Even the first experiments have shown that the
alkyl group meets the mentioned conditions. The alkyla-
tion of potassium salt of 3(5)-pyrazole carboxylic acid
[
2]. Chitosan (natural polymer) salts with 1-vinyl-
pyrazole-4-carboxylic acids were studied [3] and
shown to possess very weak antimicrobial activity.
(
Iа) with ethyl bromide in dimethylformamide (DMF)
The search for anti burn coatings, which are
biologically compatible with the organism, capable of
resorption in the process of healing wounds, do not
leave pathological traces and do not cause intoxication
with metabolites, is one of most important problems of
regenerative medicine. Taking into account that one of
promising natural polymers used in the preparation of
such biotransplants is chitosan and its modified
derivatives [4], a synthesis of new modifications of
chitosan and investigation of their biological activity is
a very actual problem.
gave ester II in 60% yield. No products of N-alkylation
are formed under these conditions.
OK
O
Et
O
O
C H Br
2
5
N
N
N
DMF/KOH
N
H
H
Iа
II
The aim of the present work was the development
of methods of synthesis of 1-vinyl-3- and 1-vinyl-5-
pyrazolecarboxylic acids V, VI, their use as modifiers
of chitosan, and investigation of anti burn activity of
the chitosan salts of 1-vinyl-3(5)-carboxylic acids.
Oxidation of technically available 3(5)-methyl-
pyrazole [5] with potassium permanganate in aqueous
medium is known to result in the formation of 3(5)-
pyrazolecarboxylic acid (I) [5], which opens wide pos-
sibilities for preparation of new pyrazole derivatives.
Dioxane, benzene, or water cannot be used for alkyla-
tion of compound I. The use of phase transfer catalysts
did not give any advantage, either.
Transvinylation of the esters of 3(5)-pyrazole car-
boxylic acid (II) with vinyl acetate in the presence of
catalytic amounts of mercury(II) sulfate gave a mixture
of isomeric esters of 1-vinyl-3- and 1-vinyl-5-pyrazole
carboxylic acids III, IV in total yield of 80% and the
ratio of isomers 3 : 2, respectively [8]. The isomers
were separated by conventional distillation. In most
1
945

1
946
RSTAKYAN et al.
Scheme 1.
O
O
Et
Et
O
O
O
O
Me
O
Et
N
N
+
N
Hg+2
N
N
H
N
O
II
III
IV
Scheme 2.
O
O
H
Et
O
N
O
N
N
N
N
(
1) KOH/H O
2
(
2) HCl/H O
2
III
V
O
O
Et
N
H
N
N
O
O
IV
VI
cases the substituted pyrazoles formed by alkylation at
nitrogen form difficultly separable mixtures [9]
The reaction proceeds smoothly at refluxing
chitosan VIIа, VIIb and the corresponding pyra-
zolecarboxylic acid V, VI in water in the course of 1–
(
Scheme 1).
3
min; after filtration and removal of insoluble residues
The ease of separation of the isomers in the case of
the solution was dried by pouring to form thin films
whose elasticity increases with the growing amount of
chitosan.
esters of 1-vinylpyrazole carboxylic acid III, IV is due
to the existence of the intramolecular hydrogen bond
between the α-proton of the vinyl group and the
carbonyl oxygen atom (CH···O=C) in ester IV lacking
In the IR spectra of the chitosan salts of 1-vinyl-3-
1
in its isomer III. In the H NMR spectrum the signal of
and 1-vinyl-5-pyrazolecarboxylic acids Vа, Vb, VIа,
–
1
the α-proton in IV is shifted downfield and appears at
VIb the absorption of the pyrazol ring at 1510 cm
–1
8
.03 ppm [10]. In compound III, the α-proton is not
and the vinyl group (C=C) at 1640 cm is observed, as
well as the stretching vibrations of the C–H groups of
deshielded by the hydrogen bond and resonates
upfield, at 7.01 ppm.
–
1
chitosan at 2878 cm and OH groups at 3450–
–
1
3
050 cm . Unlike the pattern of IR spectra of the
The hydrolysis of esters of 1-vinyl-3- and 1-vinyl-
-pyrazolecarboxylic acids with aqueous potassium
starting 1-vinyl-3- and 1-vinyl-5-pyrazole carboxylic
5
acids V, VI, the intensity of the vinyl group is several
hydroxide affords the corresponding salts and, after
acidification, 1-vinyl-3- and 1-vinyl-5-pyrazolecarboxylic
acids V, VI (Scheme 2).
times reduced. The same is true of the absorption of
+
the pyrazole ring but not of the N H , OH, CH
3
vibrations of the chitosan motif. Interestingly, the
bending vibrations of the primary amino group are
practically lacking, which is indicative of the
formation of the chitosan salts with 1-vinylpyrazole
Salts Vа, Vb, VIа, VIb of 1-vinyl-3- and 1-vinyl-5-
pyrazole carboxylic acids with chitosans VIIа, VIIb
were obtained by the earlier described general
procedure [11] (Scheme 3).
1
carboxylic acids V, VI. In the H NMR spectra of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 10 2014

1
-VINYL-3- AND 1-VINYL-5-PYRAZOLECARBOXYLIC ACIDS
1947
Scheme 3.
OH
O
O
OH
+
NH
OOC
COOH
3
n
_
OH
N
N
N
N
O
Vа, Vb
V
OH
+
O
OH
NH2
VIIа, VIIb
n
N
HOOC
O
N
O
OH
+
VI
NH
OOC
3
n
_
N
N
VIа, VIb
compounds Vа, Vb, VIа, VIb the signals of protons of
chitosan with 1-vinyl-3- and 1-vinyl-5-pyrazole car-
boxylic acids Vа, Vb, VIа, VIb were investigated. The
dynamics of the regeneration process was evaluated on
the basis of objective data: macrofotographic and
planimetric methods of measuring variation of the
wound surface as well as morphological analysis of
histological and cytological skin cuts of the control and
experimental animals.
the vinyl group at 4.94, 5.71 ppm and 4.90, 5.79 ppm
(
=CH ) and 7.2, 8.05 ppm (=CH) are retained, as well
2
as the signals of the pyrazole ring protons at 6.73,
6
3
.85 ppm and 7.52, 7.94 ppm. In a stronger field, at
1 2
.5–4.0 ppm, the resonance of the CH groups (H , H ,
3
4
5
6
6'
H , H , H , H and H ) of chitosan is observed.
It was noted that practically all functional
properties of chitosan depend on its molecular param-
eters, mainly on the mass (degree of polymerization)
These studies have shown that 1-vinyl-3- and
1-vinyl-5-pyrazolecarboxylic acids V, VI do not show
anti burn activity compared to chitosan VIIа, VIIb or
to the control group. However, salts Vb, VIb of high-
molecular chitosan with 1-vinyl-3- and 1-vinyl-5-
pyrazolecarboxylic acids V, VI show notable anti burn
activity against experimental thermal 2nd degree burns
as compared with both the control group and 1-vinyl-
3- and 1-vinyl-5-pyrazolecarboxylic acids V, VI or
high-molecular chitosan VIIb.
[
12, 13]. From this point of view, introduction of 1-
vinylpyrazole carboxylic acids in the molecule of
chitosan is not a simple substitution because poly-
merization of the vinyl groups can change the mole-
cular mass of chitosan and thus control its functional
properties. However, polymerization of salts Vа, Vb,
VIа, VIb under the used conditions (H O, T = 20–50°C,
2
Na S O ) failed, apparently, because of hindering the
2
2
7
polymerization process by macromolecules of
chitosan.
Note, that high-molecular chitosan VIIb as com-
pared to low-molecular chitosan VIIa possesses a
more emphasized anti burn activity. The same is true
for the salts of chitosan with 1-vinyl-3- and 1-vinyl-5-
pyrazolecarboxylic acids Vb, VIb. The anti burn
Anti burn activity of 1-vinyl-3- and 1-vinyl-5-pyra-
zolecarboxylic acids V, VI, low-molecular (VIIа) and
high-molecular (VIIb) chitosan, as well as the salts of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 10 2014

1
948
RSTAKYAN et al.
2
0
–1
activity of compounds Vb, VIb are practically the
d
1.1427. IR spectrum, ν, cm : 1530 (ring), 1640
4
1
same.
(C=C), 1720 (C=O). H NMR (DMSO-d
6
), δ, ppm:
1
.40 t (3H, –CH –CH , J 7.2 Hz), 4.24 q (2H, –CH –
2
3
2
EXPERIMENTAL
СH , J 7.2 Hz), 4.95 d.d (1H, CH=СH , J 15.6 and
3
2
1
.3 Hz), 5.95 d.d (1H, CH=СH , J 8.7 and 1.3 Hz),
2
IR spectra were obtained on a Nexus Thermo
1
6.78 d (1H, 4-H, J 2.2 Hz), 7.50 d (1H, 5-H, J 2.2 Hz),
Nicolet Corporation spectrometer. Н NMR spectra
7
.01 d.d (1H, CH=СH , J 15.6 and 8.7 Hz). Found, %:
2
were registered on a Varian Mercury instrument
C 57.34; H 5.81; N 16.39. C H N O . Calculated, %:
8
10
2
2
(
300 MHz) in DMSO-d –CCl or D O–CF COOH.
6
4
2
3
C 57.82; H 6.07; N 16.86.
Commercial chitosan (Sigma Aldrich) with medium-
or low-viscosity molecular mass was used.
1-Vinyl-3-pyrazolecarboxylic acid (V). The mix-
ture of 8.3 g (0.05 mol) of compound III, 4 g (0.1 mol)
NaOH, and 20 mL of water was stirred for 2 h at room
temperature, washed with ether, water layer was
neutralized with HCl, the formed crystals were filtered
and dried to obtain 3.1 g (45%) of compound V, mp
Ethyl 3(5)-pyrazolecarboxylate (II). To a mixture
of 11.2 g (0.1 mol) of 3(5)-pyrazolecarboxylic acid (I)
and 5.6 g (0.1 mol) of potassium hydroxide in 100 mL
of DMF 16.4 g (0.15 mol) of ethyl bromide was added
dropwise at 40°С. After completion of the addition, the
reaction mixture was stirred at this temperature for 12 h,
cooled, filtered, the solvent was removed at a reduced
pressure, to the residue the solution of sodium
carbonate was added, and the crystals formed were
filtered to obtain 8.6 g (60%) of compound II, mp 162-
–
1
8
1
9°С (benzene). IR spectrum, ν, cm : 1530 (ring),
1
645 (C=C), 1720 (C=O). Н NMR (DMSO-d ), δ,
6
ppm: 4.94 d.d (1Н, CH=CH , J 8.8 and 1.2 Hz), 5.71
2
d.d (1H, CH=CH , J 15.7 and 1.2 Hz), 6.73 d (1H,
2
4
-H, J 2.4 Hz), 7.20 d.d (1H, CH=CH , J 15.7 and
2
–
1
8.9 Hz), 7.94 d (1H, 5-H, J 2.4 Hz), 12.20 br.s (1H,
COOH). Found, %: С 52.49; Н 4.14; N 20.44.
С Н N О . Calculated, %: С 52.17; Н 4.34; N 20.28.
1
3
–
6
63°С, IR spectrum, ν, cm : 1530 (ring), 1720 (C=O),
1
260 (NH). H NMR (DMSO-d ), δ, ppm: 1.42 t (3H,
6
6
6
2
2
CH –CH , J 7.2 Hz), 4.20 q (2H, –CH –CH , J 7.2 Hz),
2
3
2
3
.78 d (1H, 4-Н, J 1.9 Hz), 7.50 d [1H, 3(5)-H,
1
-Vinyl-5-pyrazole carboxylic acid (VI). Prepared
J 1.9 Hz], 12.0 br.s (1H, NH). Found, %: C 51.05; H
as above from 8.3 g (0.05 mol) of ethyl ester of
5
5
.94; N 20.14. C H N O . Calculated, %: C 51.43; H
6
8
2
2
1-vinyl-5-pyrazole carboxylic acid (IV). Yield 3.3 g
–
1
.71; N 20.00.
Ethyl 1-vinyl-3- and 1-vinyl-5-pyrazolecar-
(
(
48%), mp 85°С (benzene). IR spectrum, ν, cm : 1520
1
ring), 1645 (C=C), 1720 (C=O). Н NMR (DMSO-
d ), δ, ppm: 4.90 d.d (1Н, CH=CH , J 8.8 and 1.2 Hz),
6
2
boxylates (III, IV). To 50 mL of vinyl acetate 1.0 g of
mercury(II) sulfate and 14 g (0.1 mol) of ethyl 3(5)-
pyrazolecarboxylate (II) was added, heated at reflux
for 1 h, cooled, filtered, vinyl acetate was removed at a
reduced pressure, the residue was washed with 2 N
solution of sodium carbonate, extracted with chloro-
5
(
.79 d.d (1H, CH=CH , J 15.4 and 1.2 Hz), 6.85 d
2
1H, 4-H, J 1.9 Hz), 7.52 d (1H, 3-H, J 1.9 Hz), 8.05
d.d (1H, CH=CH , J 15.4 and 8.8 Hz), 12.70 br.s (1H,
2
COOH). Found, %: С 52.39; Н 4.14; N 20.44.
С Н N О . Calculated, %: С 52.17; Н 4.34; N 20.28.
6
6
2
2
form, dried over MgSO , chloroform was removed, the
4
Salts of chitosan with 1-vinyl-3-pyrazolecarboxy-
residue was distilled in a vacuum.
lic acid and 1-vinyl-5-pyrazolecarboxylic acid (Vа, Vb,
VIa, VIb). 1.38 g (0.01 mol) of 1-vinyl-3- or 1-vinyl-
-pyrazolecarboxylic acid V, VI and 0.0125 mol of
chitosan VIIa, VIIb (degree of deacetylation 75–85%)
was refluxed in 50 mL of distilled water for 1–3 min to
complete dissolution of chitosan with subsequent
filtration of the obtained solution.
Ethyl 1-vinyl-5-pyrazolecarboxylate (IV). Yield
2
0
20
4
5
3
1
1
–
7
5
4
.95 g (23.5%), bp 75°C (1 mmHg), n 1.5112, d
D
–1
.0620. IR spectrum, ν, cm : 1540 (ring), 1640 (C=C),
1
720 (C=O). H NMR (DMSO-d ), δ, ppm: 1.40 t (3H,
6
CH –CH , J 7.2 Hz), 4.22 q (2H, –CH –СH , J
2
3
2
3
.2 Hz), 4.95 d.d (1H, CH=СH , J 15.6 and 1.3 Hz),
2
.85 d.d (1H, CH=СH , J 8.7 and 1.3 Hz), 6.80 d (1H,
2
Polymer films were prepared from the solutions of
the corresponding salts Vа, Vb, VIa, VIb by pouring
in polyethylene dishes of 5–10 cm diameter and drying
at room temperature. All samples were used as 5%
aqueous solutions of 50 mL volume. For this, 5%
aqueous solutions of compounds V, VI, Vа, Vb, VIa,
VIb were prepared. For dissolution of chitosan VIIa,
-H, J 1.9 Hz), 7.95 d (1H, 3-H, J 1.9 Hz), 8.03 d.d
(
1H, CH=СH , J 15.6 and 8.7). Found, %: C 58.08; H
2
6
6
.49; N 16.30. C H N O . Calculated, %: C 57.82; H
8
10
2
2
.07; N 16.86.
Ethyl 1-vinyl-3-pyrazolecarboxylate (III). Yield
2
0
9
.3 g (56%), bp 106°C (1 mmHg), n
1.5220,
D
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 10 2014

1
-VINYL-3- AND 1-VINYL-5-PYRAZOLECARBOXYLIC ACIDS
1949
VIIb and 1-vinylpyrazolecarboxylic acid V, VI 1%
6. Knorr, L. and Macdonald, J., Lieb. Ann., 1894, vol. 279,
p. 217. DOI: 10.1002/jlac.18942790113.
HCl was used.
7
8
9
. McOmie, J.F.W., Protective Groups Inorganic
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