The competitive N1-, N2-, O- and C-methylation of 3-trifluoromethyl-1H-pyrazol-5-ol for synthesis of analgesic compounds

Article abstract of DOI:10.1016/j.jfluchem.2018.11.009

We have found selective conditions for methylation of 3-trifluoromethyl-1H-pyrazol-5-ol that allowed us to obtain mono-Me-substituted N¹- and O-isomers as well N¹,N²-, N¹,O- and N²,O-disubstituted isomers. A tautomeric structure of the parent pyrazole and its Me-substituted derivatives was investigated using quantum-chemical calculations, X-ray diffraction analysis, IR and NMR spectroscopy. Besides, the quantum-chemical calculations were used to explain the methylation direction. An analgesic activity and acute toxicity of some synthesized compounds were evaluated in vivo experiments.

Full text of DOI:10.1016/j.jfluchem.2018.11.009

Accepted Manuscript
Title: The competitive N1-, N2-, O- and C-methylation of
3-trifluoromethyl-1H-pyrazol-5-ol for synthesis of analgesic
compounds
Authors: Ya.V. Burgart, N.A. Agafonova, E.V. Shchegol’kov,
S.S. Borisevich, S.L. Khursan, V.V. Maslova, G.A.
Triandafilova, S.Yu. Solodnikov, O.P. Krasnykh, V.I. Saloutin
PII:
S0022-1139(18)30463-9
DOI:
Reference:
https://doi.org/10.1016/j.jfluchem.2018.11.009
FLUOR 9252
To appear in:
FLUOR
Received date:
Accepted date:
13 November 2018
14 November 2018
Please cite this article as: Burgart YV, Agafonova NA, Shchegol’kov EV, Borisevich SS,
Khursan SL, Maslova VV, Triandafilova GA, Solodnikov SYu, Krasnykh OP, Saloutin
VI, The competitive N1-, N2-, O- and C-methylation of 3-trifluoromethyl-1H-pyrazol-
5-ol for synthesis of analgesic compounds, Journal of Fluorine Chemistry (2018),
https://doi.org/10.1016/j.jfluchem.2018.11.009
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

The competitive N1-, N2-, O- and C-methylation of 3-trifluoromethyl-1H-
pyrazol-5-ol for synthesis of analgesic compounds
Ya.V. Burgart1, N.A. Agafonova1, E.V. Shchegol’kov*1, S.S. Borisevich2, S.L. Khursan2, V.V.
Maslova3, G.A. Triandafilova3, S.Yu. Solodnikov3, O.P. Krasnykh3, V.I. Saloutin1
1Postovsky Institute of Organic Synthesis of Ural Branch of Russian Academy of Science, S. Kovalevskoy Str., 22,
Ekaterinburg 620990, Russia;
2Ufa Institute of Chemistry of Russian Academy of Science, Octyabrya Av., 71, Ufa 450078, Russia
3Perm National Research Polytechnic University, Komsomolsky Av., 29, Perm 614990, Russia
Email: schegolkov@ios.uran.ru
*Corresponding author
Graphical abstract

HIGHLIGHTS
 The approach for selective methylation of 3-trifluoromethyl-1H-pyrazol-5-ol was
developed to obtain mono-Me-substituted N1 and O-isomers as well N1,N2-, N1,O- and
N2,O-disubstituted isomers.
 The quantum-chemical calculations were used to explain methylation direction.

The isomeric and tautomeric structure of the initial pyrazole and its methylated
derivatives was studied.
 An analgesic activity of the obtained pyrazoles was investigated.
Abstract
We have found selective conditions for methylation of 3-trifluoromethyl-1H-pyrazol-5-ol that allowed us to obtain
mono-Me-substituted N1- and O-isomers as well N1,N2-, N1,O- and N2,O-disubstituted isomers. A tautomeric
structure of the parent pyrazole and its Me-substituted derivatives was investigated using quantum-chemical
calculations, X-ray diffraction analysis, IR and NMR spectroscopy. Besides, the quantum-chemical calculations
were used to explain the methylation direction. An analgesic activity and acute toxicity of some synthesized
compounds were evaluated in vivo experiments.
Keywords
Trifluoromethyl-1H-pyrazol-5-ol, Methylation, Chemoselectivity, Quantum-chemical calculations, Analgesic
activity
1. Introduction
The pyrazoles are a privileged structure with a broad-ranging pharmacological potential because
their derivatives have the various biological properties, including antitumor, anti-inflammatory
and antibacterial, antifungal, analgesic, antipyretic, antidepressant, antihypercholesterolemic,
anticonvulsant, hypoglycemic, anticancer, cannabinoid and antioxidant activities [1–8].
Moreover, the pyrazoles have found successful application as drugs. The most known of them
and long-living on the pharmaceutical market are antipyretic analgesics: non-steroidal anti-
inflammatory drugs (NSAIDs) of antipyrine series having N-disubstituted pyrazol-5-ones
structure (e.g., aminophenazone, metamizole etc.). Besides, (trifluoromethyl)pyrazole derivatives
such as a selective COX-2 inhibitor celecoxib [9] and veterinary anti-arthritic mavacoxib [10]
take a worthy place among modern NSAIDs. In this regard, the search for analgesic and anti-
inflammatory properties in the trifluoromethyrazolone series is very promising. An introduction

of fluorinated substituents in organic compounds including the pyrazoles is the known strategy in
the medicinal chemistry to improve both pharmacokinetic parameters and the target
pharmacological effect in vivo [11].
To regulate bioavailability and metabolism of organic molecules, the introduction of
methyl group is often used, since the stereoelectronic changes promoted by methyl groups are
directly involved in many biological processes that is widely used for structural modification in
the rational design of bioactive compounds and drugs [12]. Recently, we have shown the
perspective of
a
search for new effective analgesics among methylated
polyfluoroalkylpyrazolone derivatives. For this, we have developed approaches to regioselective
methylation of polyfluoroalkyl-containing pyrazoles with different nucleophilic centers. It was
found that methylation of 3(5)-polyfluoroalkyl-5(3)-alkyl(aryl)pyrazoles having two non-
equivalent N1 and N2 reaction centers, under basic conditions led to the preferred formation of 3-
RF-pyrazoles, whereas the use of dimethyl sulfate in the absence of a base resulted in the
predominant formation of 5-RF-pyrazoles [13]. The conditions for chemoselective methylation of
3-polyfluoroalkyl-1-phenylpyrazol-5-ols were developed also. The N-methylpyrazolones were
obtained using 5-fold excess of Me2SO4, while refluxing with 1 equiv of Me2SO4 and K2CO3 in
acetonitrile promoted O-methylpyrazoles synthesis [14]. Besides, we established that the
presence of polyfluoroalkyl substituent in pyrazoles influences their structure and reactivity in
methylation process compared to non-fluorinated analogs. The developed methods allowed us to
obtain polyfluoroalkyl-containing antipyrine derivatives. Primary biological testing revealed a
significant analgesic activity of CF3-antipyrine.
Herein, we have investigated methylation of 3-CF3-1H-pyrazol-5-ol 1 having three
alternative reaction N1, N2 and O-centers, that makes it possible to obtain three mono-Me-
substituted N1-, N2-, O-isomers (2-4) and three disubstituted N1, N2-, N1, O-,N2, O-isomers (5-7)
(Scheme 1). A tautomeric structure of the parent pyrazole and its methyl-substituted derivatives
was investigated by the quantum-chemical calculations (QCC), X-ray analysis, IR and NMR
spectroscopies. An analgesic activity and acute toxicity of some synthesized compounds were
evaluated in vivo.

Scheme 1. The possible products of pyrazole 1 methylation
2. Results and Discussion
First of all, we studied a structure of the starting unsubstituted pyrazole 1 because it did
not succeed to obtain the reliable data on in the literature. Amide-imide and imine-enamine
tautomerism are typical for heterocycle 1, therefore, it can exist in the form of five tautomers 1,I
– 1,V (Scheme 2).
Scheme 2
According to X-Ray analysis pyrazole 1 in crystals exists as N1H,OH-tautomer I (Fig.
1a), which is stabilized via intermolecular H-bonds. Thus, two molecules of pyrazoles 1 are
bound in dimer due to two H-bonds between oxygen O1 of hydroxyl group and a proton H1 of
NH group with distance 1.965 Å (Fig. 1b). Moreover, each from these molecules binds else two
pyrazole molecules through H-bonds between proton H1A of hydroxyl group and nitrogen N2 of
pyrazole moiety with distance 1.570 Å.

а
b
Fig. 1. The ORTEP view of pyrazole 1 (a). Molecular packing of 1 (b)
The IR spectra of pyrazole 1 in MeCN and the solid state do not contain an absorption
1
19
band of carbonyl group. Its H, F NMR spectra (DMSO-d6, CD3CN) are characterized by one
set of signals, at that the signals of CF3 group are observed at equal values. There are the signal
of methine proton at δ 5.66 ppm and two low-field signals of OH and NH protons at δ 11.23 and
12.82 ppm in the 1H NMR spectrum (DMSO-d6). All this indicates the existence of pyrazole 1 in
DMSO and MeCN in the same form as in solid form. Pyrazole 1 have poor solubility in the
chloroform, therefore studying its IR spectrum is difficult for it in this solvent. However, the 1H,
19F NMR spectra (CDCl3) contain signals of two tautomers in a ratio of 1 : 0.6, and the 1H NMR
spectrum has the signals of methine (δ 8.06 ppm) and methylene (δ 4.68 ppm) protons of
presumably tautomers I and II, correspondingly (see Experimental section).
In contrast to fluorinated analog 1, 3-methylpyrazol-5-one exists as N1H,N2H-tautomer
analogous to V (Scheme 2) in crystals according to the X-Ray analysis [15,16] and in solutions
[17,18].
According to QCC in an ideal gas approximation and with considering of non-specific
solvation model, a tautomer II is the most thermodynamically stable form of pyrazole 1. Howev
er, it does not agree with experiments data. In this case, a method of polarized continuum for
modeling of solvation effects (implicit) of investigated pyrazoles seems to lead to incorrect
results during evaluation of the Gibbs free energy of tautomers I and II (Scheme 2). The used
approach does not take into account the specific interactions between tautomers and solvents that
influences on their thermodynamic stability. Earlier [14], we have shown that the similar 3-
polyfluoroalkyl-1-phenylpyrazol-5-ones form the solvation complexes with solvent due to
1
intramolecular hydrogen bonds. The low-field chemical shifts of OH and NH protons in the H
NMR spectra (DMSO-d6 and CD3CN) of pyrazole 1 prove the existence of such interactions.
This fact forces us to use the approach of specific solvation (explicit) in the calculations under

experimental conditions with consideration of the structure of solvate complexes. The most
advantageous mono- and dicomplexes of tautomers I and II with MeCN and DMSO are
presented in Fig. 2. All proposed solvate complexes see in Supplementary. The calculated data
show that the solvate complexes of tautomer I are more stable comparing to analogous
complexes of tautomer II, thus pyrazole 1 exists in form I in the polar solvents. Besides,
tautomer I (μ 6.5 D) is more polar than form II (μ 0.4 D), and the polar molecules are known to
be more stable in polar solvents.
Fig. 2. The thermodynamically preferable complexes of pyrazole 1 with a solvent.
The calculation of Fukui double descriptors (Δf) of tatutomer I (pyrazole 1)reaction
centers showed that the most nucleophilic center is atom N2, and then atoms O and C4, while
center N1 is slightly electrophilic (Scheme 1).
A variation of conditions for methylation of pyrazole 1 allowed us to find the selective
methods for synthesis of mono-substituted MeO-pyrazole 2 [K2CO3 (1.5 equiv), MeI (1.5 equiv),
MeCN (Table 1, Entry 2)], MeN2-pyrazole 4 [Me2SO4 (1 equiv), toluene (Entry 11)] and Me2-
N,N-pyrazole 5 [Me2SO4 (5 equiv) (Entry 1)]. It should be noted that MeN2-pyrazole (5-CF3-
pyrazole) 4 was isolated previously as by-product in yield 9% during refluxing of ethyl
trifluoroacetoacetate with aqueous methyl hydrazine [19]. Thus, methylation can be used for
selective synthesis of such isomer.
We did not find the optimal conditions for the selective synthesis of MeN1- (or 3-RF)-
substituted pyrazole 3 although its formation as by-product was revealed by the GC-MS-
spectrometry and NMR spectroscopy when pyrazole 1 was methylated with Me2SO4 in
methanol, acetonitrile and dioxane (Table 1, Entries 6, 11-13). The main product in these cases
was pyrazole 4. When using of MeI, a small formation of isomer 3 was noted with a slight
conversion of the starting pyrazole 1 even after prolonged heating (Entry 14). More effective
method for MeN1-pyrazole 3 synthesis was condensation of ethyl trifluoroacetoacetate with
methylhydrazine in refluxing ethanol which was earlier suggested by our research group [20].

Besides, compound 3 can be obtained from trifluoromethylacetylenic ester [21] and 4,4-
diethoxy-1,1,1-trifluorobut-3-en-2-one [22].
It is interesting that formation of N,O-disubstituted pyrazoles 6 and 7 did not occur under
methylation of pyrazole 1.
We did not observe formation of C-methylated product but using of DMF-DMA as
methylating agent led to 4-dimethylaminomethylidenepyrazolone 8 (Scheme 3).
Scheme 3
Table 1. The conditions for pyrazole 1a methylation and the ratio of products 2-7a
En
try
Reaction conditions
Compounds
1
-
2
-
3
-
4
-
5
100
7
1
2
Me2SO4 (5 eq.)
K2CO3 (1 eq.), Me2SO4 (1 eq.), MeOH
MeI (1.5 eq.), K2CO3 (1.5 eq,), MeCN
Me2SO4 (1 eq.), K2CO3 (1.5 eq,), MeCN
Me2SO4 (1 eq,), K2CO3 (1.5 eq,), MeCN, r.t.
Me2SO4 (1 eq.), MeCN
-
89
95
91
57
-
-
4
3
-
-
-
5
4
-
-
7
2
5
43
89
-
6
-
11
-
-
-
7
Me2CO3 (1 eq.), K2CO3 (1.5 eq.), MeCN
Me2SO4 (1 eq.), K2CO3 (3 eq.), MeCN
Me2SO4 (1 eq,), NaOH (1.5 eq.), MeCN
Me2SO4 (2 eq.), MeCN
100
-
8
-
-
-
90
70
-
-
7
3
9
-
30
65
-
10
-
35

11
12
13
14
Me2SO4 (1 eq.), MeOH
Me2SO4 (1 eq.), toluene
Me2SO4 (1 eq.), dioxane
MeI (1 eq.), MeCN
28
-
-
-
-
26
2
46
97
51
-
1
-
3
46
91
9
aThe ratio of products was determined by the 19F NMR spectra (DMSO-d6) after the heating of initial
pyrazoles 1 for 6-7 h in corresponding conditions
Comparing the behavior of trifluoromethylpyrazolol 1 and methyl analogs under
methylation, it should be noted that we did not find data on the reaction of non-fluorinated
pyrazol-5-ones with methylating agent at the O-center. Thus, 4-ethoxycarbonyl-3-
methylpyrarolin-5-one reacts with dimethyl sulfate to give N1- and N2-monomethyl, N1,N2-
dimethyl-substituted derivatives depending on the conditions [17]. To obtain 3-methoxy-5-
methylpyrazole, first an acylation is carried out for protection of N2-center followed by
methylation with MeI under basic conditions [23]. A difference on reactivity of 3-
trifluoromethylpyrazol-5-ol and 3-methylpyrazol-5-ones can be explained by their existence in
the various tautomeric forms. A stability of hydroxyl tautomer in the case of trifluoromethyl
pyrazole causes by higher acidity of hydroxyl proton. More acidic nature of the fluorinated
alcohols is well-known [24].
Using QCC, earlier we have proposed a mechanism of selective methylation of
polyfluoroalkyl-1H-pyrazoles having two competitive nitrogen reaction centers [13]. It was
shown that under basic conditions the reaction occurred via intermediate anionic salts to lead to
the preferred formation of 3-RF-pyrazoles, whereas without base – through cationic
intermediates, which were generated, upon addition of the methyl group to pyridine-like type
nitrogen to form predominantly 5-RF-pyrazoles. When mechanism of chemoselective
methylation of 1-aryl-3-polyfluoroalkylpyrazol-5-ols bearing competitive O- and N-centers was
theoretically investigated, the same “cationic” mechanism in the reactions without the base was
supposed. It allowed us to obtain methyl-N-substituted derivatives [14]. Under basic conditions,
another mechanism take places, during which a metal cation blocks the pyridine-like nitrogen of
pyrazole with the formation of cationic salt. As a result, the subsequent attack of the methylating
agent occurs on the free oxygen atom to lead to O-methylated isomer.
According to theoretical modeling both in a gas phase approximation and with
considering of non-specific solvation of the solvents (toluene and DMSO), cation N2 formation
via addition of the methylating agent to pyridine-like nitrogen is more thermodynamically
preferable when pyrazole 1 was methylated without a base. The subsequent deprotonation of salt
N2 leads to product 4 (Scheme 4), that is observed during the experiment (Entries 5, 9, 11, Table
1).

Scheme 4
The methylation under basic conditions might proceed via the formation of three types of
salts KO, KN1 and KN2 (Scheme 5) with potassium ion localization at various centers.
According to values of Fukui double descriptors (Fig. 2), pyridine-like nitrogen N2 is the most
reaction center for electrophilic attack by potassium cation. It influences on thermodynamic
stability of forming intermediate KN2 which is more stable on 11 kJ/mol than KO. Less stability
of salt KO leads to formation of product 4 as by-product under these conditions (Table 1, Entry
2-5, 8, 9). Attempts to localize potassium cation next to protonated nitrogen (cation KN1) seems
to be unsuccessful. Obviously, pyrrole-like nitrogen N1 is the center for nucleophilic attack so it
cannot participate in coordination with the potassium ion.
The methylation of salt KN2 followed by deprotonation can proceed on oxygen via cation
KN2O formation or on nitrogen N1 via intermediate KN2N1. Their decomposition must lead to
products 2 and 3. According to calculated data, KN2N1 is more thermodynamically stable in
contrast to cation KN2O. However, we did not observe the compound 3 formation in experiment.
It can assumed that an attack of cation Me did not occur on pyrrole-like nitrogen N1 of salt KN2
owing to repulsion of the positive methyl and potassium cations. Moreover, in accordance with
the value of the Fukui double descriptors on the atoms of KN2 salt (marked with red color on
Scheme 6), the oxygen atom is the most negative, which makes it the most preferable for Me
cation attack.

Scheme 5
Methyl-substituted pyrazoles 2, 3 can undergo imine-enamine tautomerism, and N-Me
isomers 3, 4 can get amide-imide one. Therefore, each type of heterocylces can have two (for 4)
or three (for 2, 3) tautomeric forms (Scheme 6).
Scheme 6

1
The structure of all products was investigated using the IR and H, 13C, 19F NMR
spectroscopy. The X-Ray experiments were performed for pyrazoles 3 and 4 (Fig. 3, 4), and
crystal structure of isomer 3 have been investigated by J. Xu et al. [22].
A crystalline structure of pyrazole 2 is characterized by the presence of two tautomeric
form I and II (Fig. 3), because its X-Ray analysis contains not only main H1 proton of 3-CF3-
isomer I, but also disordered H2 proton of 5-CF3-isomer II. It can be explained by similar values
of the Gibbs free energies of tautomer I and II (Scheme 6), which are evaluated both in an ideal
gas approximation and with considering of specific and non-specific solvation of the solvents.
There are the intramolecular hydrogen bonds between NH···N= groups (2.081 Å) in the crystals
of this heterocycle. As a result, four molecules of pyrazole 2 generate cluster with pairwise
antidirectionally molecules and their eight nitrogen atoms form a saddle-like cavity.
According to the NMR spectroscopy data, the compound 2 also exists in DMSO-d6 as a
mixture of two tautomers I:II in a ratio of 81:19. Earlier, we have found that the chemical shift
19
of CF3 group in the F NMR spectra is a convenient criterion for tautomer assignment [25].
Thus, fluorine atoms of 3-CF3-tautomer I resonates as a singlet at δ -61.7 ppm whereas 5-CF3-
tautomer II has analogous signals at δ -59.8 ppm.
Hence, pyrazole 2 exists both in the crystals and in the polar solvents as two tautomers I
and II in contrast to other pyrazoles. Note, the detection of two NH-tautomers by the NMR
spectroscopy and X-Ray diffraction analysis under usual conditions is a rare case.
Fig 3. The X-Ray diffraction analysis of pyrazole 2.
The regioisomeric structure of methyl-N-substituted pyrazole 3 and 4 was determined
13
based on their C NMR spectra by L.F. Lee et al. [19]. However, tautomeric structure of these
heterocycles did not investigate. In accordance with our [20] and literature data [19,21]
compounds 3 and 4 exist in the solutions of polar solvents (DMSO-d6, acetone-d6, CD3CN) as a
hydroxyl tautomer I. The NMR spectra in less polar CDCl3 did not measured owing to their poor

solubility. The X-Ray experiments show that these heterocycles in the crystals are also hydroxyl
tautomers I, which are stabilized via intramolecular hydrogen bonds O—H···N2 between two
molecules. Thus, the methyl group position in pyrazoles 3 and 4 does not influence on their
tautomeric structure. However, 5-CF3-pyrazoles 4 form dimers due to double intramolecular H-
binding (1.872 Å) (Fig. 4), while 3-CF3-pyrazoles 4 generate sequential polymeric chain [22].
Fig. 4. The ORTEP view of compound 4
According to QCC, tautomer I is more thermodynamically preferable for 5-CF3-pyrazole
4, whereas tautomer III – for 3-CF3-pyrazole 3 (see Supplementary data). A discrepancy
between the calculated and experimental data in the case of pyrazole 3 can be due to non-specific
solvation of this heterocycle with solvent molecules similarly the initial pyrazole 1 (Scheme 2).
An energy evaluation of solvate complexes of various tautomeric structures of isomer 3 (see
Supplementary) allows us to draw conclusion about stability of tautomer I that is agreed with
experimental data.
4-Aminomethylidene-substituted pyrazole 8 can reveal not only amide-imide
tautomerism but also Z,E-isomerism (Scheme 6). However, its crystalline structure is
characterized by the presence of Z-isomeric amide tautomer I (Fig. 5). The molecules of
pyrazole 8 have plane structure, and they are connected in dimers due to double intramolecular
hydrogen bonds N—H···O (1.926 Å). The IR spectra in the solid state and in MeOH contain the
absorption bands of carbonyl group at 1676 to 1681 cm-1 which correspond to Z-amide form too.
The NMR spectra (DMSO-d6) of compound 8 have one set of signals. A chemical shift of
carbonyl carbon in the 13C NMR spectrum at δ 163 ppm can be used to prove for the existence of
product 8 in amide form. Thus, it can be to conclude that pyrazole 8 exists both in the crystals
and in the solutions as (4Z)-4-[(dimethylamino)methylidene]-5-(trifluoromethyl)-2,4-dihydro-
3H-pyrazol-3-one 8,ZI. According to the calculated data, this structure is thermodynamically
stable (see Supplementary data).

Fig. 5. The ORTEP view of compound 8.
Then, we tried to find the conditions for dimethyl-substituted pyrazoles 6 and 7 synthesis
via methylation of mono-methylated pyrazoles 2–4. The methylation of pyrazole 4 with Me2SO4
without and with a base led to N,N-dimethylated pyrazole 5 (Scheme 7), which had been
obtained by methylation of pyrazole 1 in an excess of methylating agent (Scheme 3). In addition,
the presence of a base resulted in pyrazole 6 as by-product. The methylation with 1.5 eq. of MeI
in the presence of 1.5 eq. of K2CO3 in acetonitrile yielded to mainly pyrazole 5 and isomers 6, 7
in small quantities without full conversion of the initial pyrazole 1. The regioisomeric structure
of pyrazole 5 was confirmed by the presence of an absorption band of carbonyl group in its IR
spectrum (ν 1660 cm-1) as well as the signals of carbonyl carbon at δ 161.36 ppm and two N-
methyl group’s carbons at δ 27.75 and 34.43 ppm in its 13C NMR spectrum. Moreover, N-methyl
group’s carbon next to CF3 substituent was observed as quartet (J 1.2 Hz).
Scheme 7
The methylation of pyrazole 3 with Me2SO4 resulted in dimethyl-N1,O-pyrazole 6
(Scheme 8), and the reaction direction did not depend on the presence of base comparing to
chemoselective transformations of 1-aryl-3-trifluoromethylpyrazol-5-ols [14]. Although the
basic conditions are more effective because the full conversion of the initial pyrazole 3 did not
occur without a base. Structure of N1,O-isomer 6 was determined by the absence of an
absorption band of carbonyl group in IR spectrum and the presence of carbons singlet signals of
NMe (δ 34.08 ppm) and OMe (δ 59.35 ppm) groups in the 13C NMR spectrum.

Scheme 8
We could not selectively obtain pyrazole 7 and isolate it in an individual form. Its
formation proceeded in reactions of pyrazole 2 as the by-product in a mixture with disubstituted
pyrazole 6 (Scheme 9). The spectrum of the isomer 7 was differed by quartet signal of N-Me
protons at 3.79 ppm because of the spin-spin interaction with the neighboring CF3 group, which
19
resonated as an unsolved quartet at -59.8 ppm in the F NMR spectrum. The ratio of isomeric
products 6 and 7 was determined from the integrated intensity of their signals in the NMR
spectra.
Scheme 9
An analgesic activity of pyrazoles 1-4, 6, 8 was evaluated in “hot plate” test in rats at the
dose of 15 mg/kg (Table 2). Diclofenac, the known nonsteroidal anti-inflammatory drug and an
analgesic reducing pain in certain conditions was used as a reference drug [26]. The obtained
experimental data support the search for analgesics among the fluorinated derivatives of
methylated pyrazoles: except MeO-pyrazole 2, all the tested compounds manifested anti-
nociceptive properties to a certain extent. In addition, the compounds were more active at 120
minutes after the administration of the substances than at the 60 minutes. This tendency may be
related to the pharmacokinetic aspects and metabolism peculiarities. Non-substituted pyrazole 1
revealed the strongest analgesic activity at 120 min after administration. However, this
compound was more toxic than its methylated derivatives. It was found that N- and / or O-
methylation (compounds 2-5) as well as the introduction of substituent in the position 4
(compound 8) led to significant reducing of acute toxicity.

Table 2. Analgesic activity and approximate acute toxicity of pyrazoles 1-4, 6, 8
Compound
Structure
Analgesic activity: latent period
prolongation, %
Approximate acute
toxicityа
(at the dose of 15 mg/kg)
60 min
120 min
17,7*
82,6**
150 (0)
300 (3)
1
2
3
4
6
8
н/а
н/а
67,0****
46,2*
77,4*
n/a
300 (0)
300 (0)
300 (0)
300 (0)
300 (0)
29,0§
41,1*
52,6**
37,3**
Diclofenacb
-
58,88,5d
84,819,9d
LD50 74, mice, ip[27]
n/a – not active;
a
represented as a dose, mg/kg (in parenthesis - number of mice which are not survived from the three taken in the
experiment); b at the dose of 10 mg/kg; d median for five different independent experiments  standard deviation;
§ trend is observed: p=0.05; * p<0.05; ** p<0.01; ***p<0.001; ****p<0.0001.
3. Conclusion
In summary, we found differences of structure and reactivity of 3-trifluoromethyl- and 3-
methylpyrazoles. It is typical for trifluoromethylpyrazole 1 to exist as hydroxyl tautomer in
contrast to the ketone form of the methyl analog. The presence of such tautomeric form in the
crystals and polar solvents becomes possible due to an increase of acidity of hydroxyl substituent
in CF3-pyrazole via an influence of electron-withdrawing trifluoromethyl group. This leads to
stabilization of OH-tautomer through the formation of intermolecular H-bonds. This causes a
difference of reactivity of trifluoromethyl- and methylpyrazoles during methylation process
because it is possible for trifluoromethylpyrazole 1 to undergo chemoselective O- and N-
methylation while the methyl analog reacts only by the N-center. We succeeded in founding the
conditions for selective methylation of 3-trifluoromethylpyrazol-5-ol 1 that allowed us to obtain
mono-Me-substituted N1- and O-isomers as well di-Me-substituted N1,N2-, N1,O- and N2,O-

isomers. In addition, we showed a possibility to modification of pyrazole 1 at its C-center in the
aminomethylation. The biological investigation of some synthesized compounds in vivo
experiments revealed their good analgesic activity in conjunction with moderate acute toxicity.
4. Experimental section
4.1. Chemical part
Melting points were measured in open capillaries on “Stuart SMP30” melting point
apparatus and uncorrected. The IR spectra were recorded on “Perkin Elmer Spectrum One FT-
1
IR” by diffuse reflection accessory (DRA). The H (13C) NMR spectra were registered on
“Bruker Avance DRX-500” spectrometer, 500 MHz (125 MHz) relative to SiMe4. The 19F NMR
spectra were obtained on “Bruker Avance DRX-500” spectrometer (470 MHz) using C6F6 as an
internal standard. The chemical shifts were converted from C6F6 to CCl3F. The microanalyses
(C, H, N) were carried out on “Perkin Elmer PE 2400” series II elemental analyzer.
A single crystal of compound 1 was obtained by crystallization from the mixture of
EtOAc:CHCl3:hexane – 1:2:1. The X-ray studies were performed on “Xcalibur Eos”
diffractometer with graphite monochromator,  scanning, λMoK 0.71073Å radiation, T 295 K.
The registration of absorption was carried out analytically by the model of multi-facet crystal
using a program “CrysAlis RED 1.171.36.28”.
Main crystallographic data for 1: 2C4H3F3N2O, M = 304.17, space group P21/c,
monoclinic, a = 9.1039(6), b = 6.8948(4), c = 10.3679(7) Å, β = 113.779(8)°, V = 595.54(7) Å3,
Z = 2, Dcalc = 1.696 g∙cm-3, (Mo-K) = 0.184 mm-1, 131 refinement parameters, 1611 reflections
measured, 1183 unique reflections which were used in all calculations. The final R is 0.052.
CCDC 1861658 contains the supplementary crystallographic data for this compound.
A single crystal of compound 2 was obtained by crystallization from hexane. The X-ray
studies were performed on “Xcalibur 3 CCD” diffractometer with graphite monochromator, φ/
scanning, λMoK 0.71073Å radiation, T 295 K. The registration of absorption was carried out
analytically by the model of multi-facet crystal using a program “CrysAlis RED 1.171.29.9”.
Main crystallographic data for 2: C5H5F3N2O, M = 166.11, space group I41/a, tetragonal,
a, b = 16.3767(11), c = 11.0283(12)Å, V = 2957.7(4) Å3, Z = 16, Dcalc = 1.492 g∙cm-3, (Mo-K)
= 0.155 mm-1, 140 refinement parameters, 2462 reflections measured, 711 unique reflections
which were used in all calculations. The final R is 0.040. CCDC 1861659 contains the
supplementary crystallographic data for this compound.
A single crystal of compound 4 was obtained by crystallization from the mixture of
EtOAc:CH2Cl2 – 3:1. The X-ray studies were performed on “Xcalibur 3 CCD” diffractometer
with graphite monochromator, φ/ scanning, λMoK 0.71073Å radiation, T 295 K. The

registration of absorption was carried out analytically by the model of multi-facet crystal using a
program “CrysAlis RED 1.171.29.9”.
Main crystallographic data for 4: C5H5F3N2O, M = 166.11, space group P-1, triclinic, a =
4.7687(8), b = 6.7756(10), c = 10.9615(19) Å, α = 72.854(15), β = 82.210(14), γ = 83.472(14)°,
V = 334.29(9) Å3, Z = 2, Dcalc = 1.650 g∙cm-3, (Mo-K) = 0.172 mm-1, 109 refinement
parameters, 1331 reflections measured, 753 unique reflections which were used in all
calculations. The final R is 0.047. CCDC 1861660 contains the supplementary crystallographic
data for this compound.
A single crystal of compound 8 was obtained by crystallization from methanol. The X-
ray studies were performed on “Xcalibur 3 CCD” diffractometer with graphite monochromator,
φ/ scanning, λMoK 0.71073Å radiation, T 295 K. The registration of absorption was carried
out analytically by the model of multi-facet crystal using a program “CrysAlis RED 1.171.29.9”.
Main crystallographic data for 8: C7H8F3N3O, M = 207.16, space group P21/c,
monoclinic, a = 12.8560(13), b = 9.0504(10), c = 7.3652(8) Å, β = 93.545(9)°, V = 855.32(16)
Å3, Z = 4, Dcalc = 1.609 g∙cm-3, (Mo-K) = 0.155 mm-1, 137 refinement parameters, 2962
reflections measured, 1206 unique reflections which were used in all calculations. The final R is
0.045. CCDC 1861661 contains the supplementary crystallographic data for this compound.
The all crystal structures were solved by direct methods followed by Fourier synthesis
with SHELXS-97 [28] and refined with full-matrix least-squares methods for all non-hydrogen
atoms with SHELXL-97 software packages [28].
4.1.1. 3-(Trifluoromethyl)-1H-pyrazol-5-ol (1) was synthesized by the method [29].
Yield: 1.16 g (75%), colorless crystals, mp 216 °С. IR (DRA): ν 1594, 1538, 1501 (С=С, C=N),
1252-1137 (С—F) cm-1. 1Н NMR (DMSO-d6):  5.66 (s, 1H, CH), 11.23 (s, 1H, OH), 12.83 (s,
19
1
1H, NH). F NMR (DMSO-d6):  -61.6 (s, CF3). Н NMR (CDCl3): mixture of tautomers I:II
(61:39);  I, 8.09 (1H, CH), II, 4.68 (2H, CH2). 19F NMR (CDCl3):  I, -64.2 (s, CF3); II, -65.3
19
(s, CF3). 1Н NMR (CD3CN):  5.82 (s, 1H, CH), 8.94 (br. s, 1H, OH), 10.47 (br. s, 1H, NH). F
NMR (CD3CN):  -61.9 (s, CF3).
4.1.2. 5(3)-Methoxy-3(5)-(trifluoromethyl)-1H-pyrazole (2). A mixture of 1.06 g (7
mmol) of pyrazole 1, 1.38 g (10 mmol) of K2CO3 and 1.42 g (10 mmol) of MeI in 10 mL of
acetonitrile was refluxed for 6-7 h. After cooling, the reaction mass was diluted with 10 of mL
water and extracted with ether (210 mL). Organic lays were combined, dried over MgSO4 and
the solvent was removed. The residue was recrystallized twice from hexane. Yield: 1.16 g
(70%), colorless crystals, mp 110-111 °С. IR (DRA): ν 1598, 1596, 1466 (С=С, C=N), 1251-

1
1130 (С—F) cm-1. Н NMR (DMSO-d6): mixture of tautomers I:II (81:19);  I, 3.87 (s, 3Н,
Me), 6.11 (br. s, 1H, CH), 13.27 (br. s, 1H, NH); II, 3.81 (s, 3Н, Me), 6.31 (br. s, 1H, CH), 13.35
(br. s, 1H, NH). 13C NMR (DMSO-d6):  I, 58.83 (Me), 83.12 (CH), 121.44 (q, CF3, J 268.1 Hz),
140.42 (q, C—CF3, J 37.1 Hz), 157.56 (C—OMe); II, 56.32 (Me), 90.09 (CH), 119.32 (unsolv.
19
q, CF3), 131.66 (unsolv. q, C—CF3), 163.46 (C—OMe). F NMR (DMSO-d6):  I, -61.7 (s,
CF3); II, -59.8 (s, CF3). Anal. Calcd. for C5H5F3N2O. C, 36.16; H, 3.03; N, 16.87. Found: С,
36.02; Н, 3.15; N, 16.81.
4.1.3. 1-Methyl-3-(trifluoromethyl)-1H-pyrazol-5-ol (3). A mixture of 2.02 g (11 mmol)
of ethyl trifluoroacetylacetate, 1.58 g (11 mmol) of methylhydrazine hydrosulfate and 1.52 g (11
mmol) of K2CO3 in 10 mL of ethanol was refluxed for 4 h. After cooling, the solvent was
removed in vacuo, added water. The residue was recrystallized twice from methylene chloride.
Yield: 1.82 g (72%), off-white crystals, mp 175-176 °С. (lit. [19], mp 172-175 °С).
4.1.4. 1-Methyl-5-(trifluoromethyl)-1H-pyrazol-3-ol (4). A mixture of 1.06 g (7 mmol) of
pyrazole 1 and 0.88g (7 mmol) of dimethyl sulfate in 8 mL of toluene was refluxed for 6-7 h.
The solvent was removed under vacuo. The residue was extracted with ether (215 mL). The
organic lays were combined and dried over MgSO4. The ether was evaporated and precipitate
was recrystallized from methylene chloride. Yield: 1.13 g (68%), colorless crystals, mp 128-129
°С. (lit. [19], mp 129.5-131.5 °С).
4.1.5. 1,2-Dimethyl-5-(trifluoromethyl)-1,2-dihydro-3H-pyrazol-3-one monohydrate (5).
A mixture of 1.06 g (7 mmol) of pyrazole 1 and 4.41g (35 mmol) of dimethyl sulfate was stirring
at 80 °C for 6-7 h. After cooling, a reaction mass was quenched with sodium hydrocarbonate and
diluted with 20 mL of ether. The organic lay was dried over MgSO4 and the solvent was
evaporated to give compound 5. Yield: 1.38 g (71%), light-yellow powder, mp 43-44 °С. IR
1
(DRA): ν 1660 (C=O), 1565, 1519, 1459, 1429 (С=С, C=N), 1260-1115 (С—F) cm-1. Н NMR
13
(DMSO-d6):  3.34 (s, 3Н, N1-Me), 3.48 (s, 3Н, N2-Me), 5.94 (s, 1H, CH). C NMR (DMSO-
d6):  27.75 (N1-Me), 34.43 (q, N2-Me, J 1.2 Hz), 97.06 (q, CH, J 2.4 Hz), 119.13 (q, CF3, J
19
270.3 Hz), 138.28 (q, C—CF3, J 38.8 Hz), 161.36 (C=O). F NMR (DMSO-d6):  -62.0 (s,
CF3). Anal. calcd. for C6H9F3N2O2. C, 36.37; H, 4.58; N, 14.14. Found: С, 36.42; Н, 4.78; N,
13.37.
4.1.6. 5-Methoxy-1-methyl-3-(trifluoromethyl)-1H-pyrazole (6). A mixture of 1.00 g (6
mmol) of pyrazole 3, 0.83 g (9 mmol) of K2CO3 and 0.76 g (6 mmol) of dimethyl sulfate in 10
mL of acetonitrile was refluxed for 6-7 h. After cooling, a reaction mass was diluted with water
and extracted with ether (215 mL). The organic lay was dried over MgSO4 and the solvent was
evaporated to give compound 6. Yield: 1.08 g (55%), red crystals, mp 33-35 °С. IR (DRA): ν

1
1569, 1495, 1434 (С=С, C=N), 1292-1093 (С—F) cm-1. Н NMR (DMSO-d6):  3.63 (s, 3Н,
NMe), 3.93 (s, 3Н, OMe), 6.20 (s, 1H, CH). 13C NMR (DMSO-d6):  34.08 (NMe), 59.35
(OMe), 83.75 (q, CH, J 2.1 Hz), 121.31 (q, CF3, J 268.0 Hz), 138.28 (q, C—CF3, J 37.4 Hz),
19
155.50 (C—OMe). F NMR (DMSO-d6):  -61.7 (s, CF3). Anal. calcd. for C6H9F3N2O2. C,
40.01; H, 3.92; N, 15.55. Found: С, 39.45; Н, 3.99; N, 15.25.
4.1.7. 3-Methoxy-1-methyl-5-(trifluoromethyl)-1H-pyrazole (7). A mixture of 1.00 g (6
mmol) of pyrazole 2, 0.83g (9 mmol) of K2CO3 and 0.76 g (6 mmol) of dimethyl sulfate in 10
mL of acetonitrile was refluxed for 6-7 h. After cooling, a reaction mass was diluted with water
and extracted with ether (215 mL). The organic lay was dried over MgSO4 and the solvent was
evaporated to give a mixture of compound 6 and 7 with 80:20 ratio. 1Н NMR (DMSO-d6):  3.79
19
(q, 3Н, N-Me, J 0.8 Hz), 3.80 (s, 3Н, O-Me), 6.35 (s, 1H, CH). F NMR (DMSO-d6):  -59.8
(unsolv. q, CF3).
4.1.8. (4Z)-4-[(dimethylamino)methylidene]-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-
3-one (8). A mixture of 1.06 g (7 mmol) of pyrazole 1 and 1.54g (13 mmol) of DMF-DMA in 10
mL of acetonitrile was refluxed for 6-7 h. After cooling, precipitate was filtered off and washed
with acetonitrile. Yield: 1.19 g (82%), light-yellow powder, mp 243-245 °С. IR (DRA): ν 1681
(C=O), 1590, 1538, 1459, 1434 (С=С, C=N), 1250-1140 (С–F) cm-1. IR (MeOH): ν 1678 (C=O)
1
cm-1. Н NMR (DMSO-d6):  3.40 and 3.73 (both s, 6Н, 2Me), 7.54 (s, 1H, CH), 11.47 (s, 1H,
NH). 13C NMR (DMSO-d6):  43.22 (Me), 47.79 (Me), 92.55 (CH), 120.79 (q, CF3, J 269.8 Hz),
139.22 (q, C—CF3, J 35.1 Hz), 153.00 (s, C=CH), 163.63 (C=O). 19F NMR (DMSO-d6):  -61.5
(s, CF3). Anal. calcd. for C7H8F3N3O. C, 40.59; H, 3.89; N, 20.28. Found: С, 40.55; Н, 3.82; N,
20.15.
4.2. Computational details
Theoretical calculations were performed using the GAUSSIAN 09 program [30]. The
TPSSTPSS [31] density functional with the 6–311+G(d,p) basic sets [32,33] was used
throughout the work for geometry optimization, frequency calculation and electron population
analysis [34,35]. The type of stationary points of the potential energy surface (PES) was
characterized by the Hessian matrix. If the Hessian matrix was positive definite at the total
energy, then the stationary point attained a local minimum of the PES (reagent or product of
reaction). Thermodynamic parameters were calculated by simulating the solvent effect of
acetonitrile and DMSO (IEF polarized continuum model [36]). Solvation model includes specific
solute-solvent interactions in a form of 1 : 1 or 1 : 2 complex. The basis set superposition error
(BSSE, in milliHartree) was shown to be rather small ( 2 for CH3CN,  2 for DMSO

complexes) at the level of theory used. The Gibbs free energies of complexes were BSSE
corrected.
Definition of Fukui function [37] for an atom A (in our case – atoms C, O, N in the figures 2 and
scheme 5), can be shown as:
fA+=qAN-qNA+1 for nucleophilic attack,
f-A=qA -qAN for electrophilic attack,
N-1
when qAN is the atomic charge.
Summarily, dual descriptors of Fukui function can be written as:
∆fA=f+-f-A=(qA-qAN-1)-(qAN-1-qNA)=2qNA-qNA+1-qNA-1
A
N
4.3. Biological part
Laboratory animals (Sprague Dawley rats and CD-mice) were obtained from the Animal
Unit ‘Pushino’ at the M.M. Shemyakin and Yu.A. Ovchinnikov from Institute of Bioorganic
Chemistry RAS (Russia). The animals were housed at natural light cycle and otherwise in a
controlled environment, in propylene cages (Bioskape), on standard bedding (Rehofix MK 2000,
J. Rettenmaier&Söhne, Germany), supplied with feed for conventional laboratory rodents
(Chara,”Assortiment-Agro”, Russia and ProKorm, “BioPro”, Russia) and water ad libitum.
Animal care and all the procedures were performed by professional staff according to the Federal
Law №61-FZ [38] and guidelines for pre-clinical study of medicinal products [39].
4.3.1. The Hot plate test
The hot plate test was conducted according to established guidelines [39,40] on Hot plate
60200 series (TSE-systems, Germany). Rats were administered with substances suspension 15
mg/kg in 1% starch mucilage, ip. Base line controls were animals that received vehicle only.
Diclofenac (“Hemofarm”, Serbia, 10 mg/kg in 1% starch mucilage solution) was used as a
reference drug. Rats were placed on an electrically heated plate at 50 ºC in a Plexiglas cylindrical
restrainer (19 cm diameter  30 cm). The nociceptive response time was measured by observing
movements consisting of jumping, licking, or shaking their hind paws. Maximal cutoff time was
30 s regardless of response. Data are expressed as a percentage change in withdrawal response
time from baseline.
4.3.2. Acute toxicity evaluation

The toxicity evaluation was performed on CD-1 mice. The procedure was based on
OECD Recommendations [41] and guidelines for pre-clinical study of medicinal products [39].
For general estimating of the toxicity range of synthesized compounds three mice per one dose
were applied. The tested compounds in 1% starch mucilage solution were injected
intraperitoneally. Animals were observed during 14 days, the number of deaths was counted.
4.3.3. Statistical analysis
The data were analyzed by a statistical software package GraphPad Prism 6 using the
«Multiplet tests» approach. The values were considered significantly different at p <0.05.
Acknowledgments
This work was supported by the Russian Scientific Foundation (Grant No. 16-13-10255).
Analytical studies were carried out using equipment of the Center for Joint Use “Spectroscopy
and Analysis of Organic Compounds” at the Postovsky Institute of Organic Synthesis of the
Russian Academy of Sciences (Ural Branch). All calculations were carried out on a cluster in the
regional center for shared computer equipment at the Ufa Institute of Chemistry RAS.
References
[1] A. Ansari, A. Ali, M. Asif, S. Shamsuzzaman, Review: biologically active pyrazole
derivatives, New J. Chem. 41 (2017) 16–41. doi:10.1039/C6NJ03181A.
[2] J.-J. Liu, M. Zhao, X. Zhang, X. Zhao, H.-L. Zhu, Pyrazole Derivatives as Antitumor,
Anti-Inflammatory and Antibacterial Agents, Mini-Reviews Med. Chem. 13 (2013) 1957–
1966. doi:10.2174/13895575113139990078.
[3] Ş.G. Küçükgüzel, S. Şenkardeş, Recent advances in bioactive pyrazoles, Eur. J. Med.
Chem. 97 (2015) 786–815. doi:10.1016/j.ejmech.2014.11.059.
[4] J.V. Faria, P.F. Vegi, A.G.C. Miguita, M.S. dos Santos, N. Boechat, A.M.R. Bernardino,
Recently reported biological activities of pyrazole compounds, Bioorg. Med. Chem. 25
(2017) 5891–5903. doi:10.1016/j.bmc.2017.09.035.
[5] R. Perez-Fernandez, P. Goya, J. Elguero, A review of recent progress (2002-2012) on the
biological activities of pyrazoles, Arkivoc 2014 (2013) 233.

doi:10.3998/ark.5550190.p008.131.
[6] A. Marella, M. Rahmat Ali, M. Tauquir Alam, R. Saha, O. Tanwar, M. Akhter, M.
Shaquiquzzaman, M. Mumtaz Alam, Pyrazolines: A Biological Review, Mini-Reviews
Med. Chem. 13 (2013) 921–931. doi:10.2174/1389557511313060012.
[7] V.L.M. Silva, A.M.S. Silva, D.C.G.A. Pinto, P. Rodríguez, M. Gómez, N. Jagerovic, L.F.
Callado, J.A.S. Cavaleiro, J. Elguero, J. Fernández-Ruiz, Synthesis and pharmacological
evaluation of new (E)- and (Z)-3-aryl-4-styryl-1H-pyrazoles as potential cannabinoid
ligands, Arkivoc. 2010 (2010) 226. doi:10.3998/ark.5550190.0011.a19.
[8] V.L.M. Silva, J. Elguero, A.M.S. Silva, Current progress on antioxidants incorporating the
pyrazole core, Eur. J. Med. Chem. 156 (2018) 394–429.
doi:10.1016/j.ejmech.2018.07.007.
[9] T.D. Penning, J.J. Talley, S.R. Bertenshaw, J.S. Carter, P.W. Collins, S. Docter, M.J.
Graneto, L.F. Lee, J.W. Malecha, J.M. Miyashiro, R.S. Rogers, D.J. Rogier, S.S. Yu, G.D.
Anderson, E.G. Burton, J.N. Cogburn, S.A. Gregory, C.M. Koboldt, W.E. Perkins, K.
Seibert, A.W. Veenhuizen, Y.Y. Zhang, P.C. Isakson, Synthesis and Biological
Evaluation of the 1,5-Diarylpyrazole Class of Cyclooxygenase-2 Inhibitors: Identification
of 4-[5-(4-Methylphenyl)-3- (trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide (SC-
58635, Celecoxib), J. Med. Chem. 40 (1997) 1347–1365. doi:10.1021/jm960803q.
[10] S.R. Cox, S.P. Lesman, J.F. Boucher, M.J. Krautmann, B.D. Hummel, M. Savides, S.
Marsh, A. Fielder, M.R. Stegemann, The pharmacokinetics of mavacoxib, a long-acting
COX-2 inhibitor, in young adult laboratory dogs, J. Vet. Pharmacol. Ther. 33 (2010) 461–
470. doi:10.1111/j.1365-2885.2010.01165.x.
[11] K. Kaur, V. Kumar, G.K. Gupta, Trifluoromethylpyrazoles as anti-inflammatory and
antibacterial agents: A review, J. Fluorine Chem. 178 (2015) 306–326.
doi:10.1016/j.jfluchem.2015.08.015.
[12] E.J. Barreiro, A.E. Kümmerle, C.A.M. Fraga, The Methylation Effect in Medicinal
Chemistry, Chem. Rev. 111 (2011) 5215–5246. doi:10.1021/cr200060g.
[13] A.E. Ivanova, Y. V. Burgart, V.I. Saloutin, P.A. Slepukhin, S.S. Borisevich, S.L. Khursan,
Ambident polyfluoroalkyl-substituted pyrazoles in the methylation reactions, J. Fluorine
Chem. 195 (2017) 47–56. doi:10.1016/j.jfluchem.2017.01.009.
[14] N.A. Nemytova, E.V. Shchegol’kov, Y.V. Burgart, P.A. Slepukhin, S.S. Borisevich, S.L.

Khursan, V.I. Saloutin, Regiocontrolled N-, O- and C-methylation of 1-phenyl-3-
polyfluoroalkyl-1H-pyrazol-5-ols, J. Fluorine Chem. 206 (2018) 72–81.
doi:10.1016/j.jfluchem.2017.12.011.
[15] W.H. De Camp, J.M. Stewart, The crystal and molecular structure of 3-methyl-3-
pyrazolin-5-one, Acta Crystallogr. Sect. B Struct. Crystallogr. Cryst. Chem. 27 (1971)
1227–1232. doi:10.1107/S0567740871003789.
[16] Z. Zhang, S. Jin, S. Wang, B. Liu, J. Guo, 3-Methyl-3-pyrazolin-5-one, Acta Crystallogr.
Sect. E Struct. Reports Online. 60 (2004) o315–o316. doi:10.1107/S160053680302974X.
[17] B. Juršić, N. Bregant, The Selective Methylation of 4-Ethoxycarbonyl-3-Methylpyrazolin-
5-one with Dimethyl Sulfate, Synth. Commun. 19 (1989) 2087–2093.
doi:10.1080/00397918908052602.
[18] M.A. Metwally, S.A. Bondock, S.I. El-Desouky, M.M. Abdou, Pyrazol-5-ones:
Tautomerism, Synthesis and Reactions, Int. J. Mod. Org. Chem. 1 (2012) 19–54.
http://modernscientificpress.com/Journals/ViewArticle.aspx?pd2T1QECjbDHPPMZhNX
772uNDAFVeK71lr9s5O3YnibAuV/4EbQza9kKtolAOWrz.
[19] L.F. Lee, F.M. Schleppnik, R.W. Schneider, D.H. Campbell, Synthesis and 13 C NMR of
(trifluoromethyl)hydroxypyrazoles, J. Heterocycl. Chem. 27 (1990) 243–245.
doi:10.1002/jhet.5570270224.
[20] V.I. Saloutin, M.I. Kodess, A.N. Fomin, S.I. Selivanov, B.A. Ershov, K.I. Pashkevich,
Study of the reaction of fluoroalkylꢀ?-ketoesters with methylhydrazine by1H and19F
NMR spectroscopy, Bull. Acad. Sci. USSR Div. Chem. Sci. 37 (1988) 318–321.
doi:10.1007/BF00957434.
[21] B.C. Hamper, Regioselective synthesis of 1-methyl-3-hydroxy-5-perfluoroalkylpyrazoles
by the addition of methylhydrazine to perfluoroalkylacetylenic esters, J. Fluorine Chem.
48 (1990) 123–131. doi:10.1016/S0022-1139(00)82607-X.
[22] J. Xu, W. Cheng, J. Yan, G. Quan, 1-Methyl-3-trifluoromethyl-1 H -pyrazol-5-ol, Acta
Crystallogr. Sect. E Struct. Reports Online 65 (2009) o2377–o2377.
doi:10.1107/S1600536809035624.
[23] E. Diamanti, G. Bottegoni, L. Goldoni, N. Realini, C. Pagliuca, F. Bertozzi, D. Piomelli,
D. Pizzirani, Pyrazole-Based Acid Ceramidase Inhibitors: Design, Synthesis, and
Structure–Activity Relationships, Synthesis 48 (2016) 2739–2756. doi:10.1055/s-0035-

1561456.
[24] I. Shuklov, N. Dubrovina, A. Börner, Fluorinated Alcohols as Solvents, Cosolvents and
Additives in Homogeneous Catalysis, Synthesis 2007 (2007) 2925–2943. doi:10.1055/s-
2007-983902.
[25] O.G. Khudina, E.V. Shchegol’kov, Y.V. Burgart, M.I. Kodess, O.N. Kazheva, A.N.
Chekhlov, G.V. Shilov, O.A. Dyachenko, V.I. Saloutin, O.N. Chupakhin, Synthesis and
the reactions of trifluoromethylated 1,2,3-triketones 2-(het)arylhydrazones and 4,7-
dihydroazolo[5,1-c]triazines, J. Fluorine Chem. 126 (2005) 1230–1238.
doi:10.1016/j.jfluchem.2005.06.001.
[26] R. Altman, B. Bosch, K. Brune, P. Patrignani, C. Young, Advances in NSAID
Development: Evolution of Diclofenac Products Using Pharmaceutical Technology,
Drugs. 75 (2015) 859–877. doi:10.1007/s40265-015-0392-z.
[27] Diclofenac, Sodium Salt. Safety Data Sheet. Revision 09.30.2014. Cayman, (n.d.).
[28] G.M. Sheldrick, Programs for crystal structure solution and refinement, (1997).
[29] V.I. Saloutin, A.N. Fomin, K.I. Pashkevich, Reaction of fluorine-containing b-ketoesters
with bifunctional N-nucleophiles, Bull. Acad. Sci. USSR Div. Chem. Sci. 34 (1985) 135–
141. doi:10.1007/BF01157341.
[30] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G.
Scalmani, V. Barone, G.A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. Marenich, J.
Bloino, B.G. Janesko, R. Gomperts, B. Mennucci, H.P. Hratchian, J. V. Ortiz, A.F.
Izmaylov, J.L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F. Egidi, J.
Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V.G. Zakrzewski, J. Gao, N.
Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M.
Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J.A.
Montgomery, Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N.
Kudin, V.N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A.
Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, J.M. Millam, M. Klene, C.
Adamo, R. Cammi, J.W. Ochterski, R.L. Martin, K. Morokuma, O. Farkas, J.B.
Foresman, D.J. Fox, Gaussian 09, Revision C.01, (2010).
[31] J. Tao, J.P. Perdew, V.N. Staroverov, G.E. Scuseria, Climbing the Density Functional
Ladder: Nonempirical Meta–Generalized Gradient Approximation Designed for

Molecules and Solids, Phys. Rev. Lett. 91 (2003) 146401.
doi:10.1103/PhysRevLett.91.146401.
[32] A.D. McLean, G.S. Chandler, Contracted Gaussian basis sets for molecular calculations. I.
Second row atoms, Z =11–18, J. Chem. Phys. 72 (1980) 5639–5648.
doi:10.1063/1.438980.
[33] R. Krishnan, J.S. Binkley, R. Seeger, J.A. Pople, Self-consistent molecular orbital
methods. XX. A basis set for correlated wave functions, J. Chem. Phys. 72 (1980) 650–
654. doi:10.1063/1.438955.
[34] J.P. Foster, F. Weinhold, Natural hybrid orbitals, J. Am. Chem. Soc. 102 (1980) 7211–
7218. doi:10.1021/ja00544a007.
[35] F. Weinhold, J.E. Carpenter, The Natural Bond Orbital Lewis Structure Concept for
Molecules, Radicals, and Radical Ions, in: Struct. Small Mol. Ions, Springer US, Boston,
MA, 1988: pp. 227–236. doi:10.1007/978-1-4684-7424-4_24.
[36] J. Tomasi, B. Mennucci, R. Cammi, Quantum Mechanical Continuum Solvation Models,
Chem. Rev. 105 (2005) 2999–3094. doi:10.1021/cr9904009.
[37] J. Oláh, C. Van Alsenoy, A.B. Sannigrahi, Condensed Fukui Functions Derived from
Stockholder Charges: Assessment of Their Performance as Local Reactivity Descriptors,
J. Phys. Chem. A. 106 (2002) 3885–3890. doi:10.1021/jp014039h.
[38] On Circulation of Medicines. Federal Law of 12.04.2010.№61-FZ RF, n.d.
[39] A.N. Mironov, Guidelines for Pre-Clinical Study of Medicinal Products. Part One (in
Russian), Grif&Ko, Moscow, 2012.
[40] H.G. Vogel, Drug Discovery and Evaluation: Pharmacological Assays, Springer-Verlag,
Berlin-Heidelberg-New York, 2008.
[41] OECD Guideline 423: Acute oral toxicity. Paris: OECD 1996, n.d.