Synthesis, sciatic nerve block activity evaluation and molecular docking of fluoro-substituted lidocaine analogs as local anesthetic agents

Article abstract of DOI:10.1007/s00044-019-02415-4

Thirty fluoro-substituted lidocaine analogs (10a–e, 11a–e, 14a–e, 15a–e, 18a–e and 19a–e) were synthesized, and their sciatic nerve block activity were evaluated as local anesthesia. Most of the compounds displayed significant potency, and compound 10a in particular was much more potent than the parent lidocaine. Fifteen analogs including 10a demonstrated pKa values of 7.5–7.8 suitable for local anesthesia. Compound 10a, 14e, and lidocaine were docked into three target receptors of local anesthetics by molecular docking studies to delineate structure-activity relationships and explain the differences in activities. Hydrophobic interactions and hydrogen bonds were identified key to molecular binding, suggesting that optimization of these interactions and/or trifluoro-substitution at the benzene ring of lidocaine could enhance the properties of lidocine analogs for local anesthesia.

Full text of DOI:10.1007/s00044-019-02415-4

MEDICINAL
CHEMISTRY
RESEARCH
Medicinal Chemistry Research
https://doi.org/10.1007/s00044-019-02415-4
ORIGINAL ARTICLE
Synthesis, sciatic nerve block activity evaluation and molecular
docking of fluoro-substituted lidocaine analogs as local
anesthetic agents
Wen Li1,2,3 Ying Yan1 Yingjie Chang1 Lina Ding1,3 Hongmin Liu1,3 Qidong You2
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Received: 1 January 2019 / Accepted: 26 July 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Thirty fluoro-substituted lidocaine analogs (10a–e, 11a–e, 14a–e, 15a–e, 18a–e and 19a–e) were synthesized, and their
sciatic nerve block activity were evaluated as local anesthesia. Most of the compounds displayed significant potency, and
compound 10a in particular was much more potent than the parent lidocaine. Fifteen analogs including 10a demonstrated
pKa values of 7.5–7.8 suitable for local anesthesia. Compound 10a, 14e, and lidocaine were docked into three target
receptors of local anesthetics by molecular docking studies to delineate structure-activity relationships and explain the
differences in activities. Hydrophobic interactions and hydrogen bonds were identified key to molecular binding, suggesting
that optimization of these interactions and/or trifluoro-substitution at the benzene ring of lidocaine could enhance the
properties of lidocine analogs for local anesthesia.
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Keywords Lidocaine Synthesis Local anesthetic activity Molecular docking
Introduction
has been discovered, such as reduced risk of tumor metas-
tasis and recurrence (D’Agostino et al. 2018; Le Gac et al.
2017; Tavare et al. 2012; Wang et al. 2016), antimicrobial
effect (Adler et al. 2017; Epstein 1998; Estebe 2017;
Neuwersch et al. 2017; Tulgar et al. 2018), anti-
inflammatory effect (Kan et al. 2018; Wang et al. 2018),
anti-acute lung injury effect (Bonniaud, Camus 2015; Van
Ness et al. 2013), and reduced the cognitive impairment
(Lin et al. 2012; Yang et al. 2017). These imply that we still
have much to learn about the structure and activity rela-
tionships (SAR) of lidocaine and its analogous.
Lidocaine (Fig. 1), also named as lignocaine and xylocaine,
is a well-known local anesthetic (Li et al. 2018; E Silva
et al. 2018) and a broad-spectrum antiarrhythmia (Hebbes
and Thompson 2018; McLeod et al. 2017), has been used in
clinical practice for more than 60 years. Recently, lidocaine
become in the spotlight again for its new diversity activities
The voltage-gated sodium channel (VGSC) has been
found to be the target for local anesthetics (Boukhabza et al.
2016; Wang et al. 2015), gamma aminobutyric acid receptor
(GABAA-R) (Nakahata et al. 2010; Sugimoto et al. 2000;
Ye et al. 1999) and N-methyl-D-aspartate acid receptor
(NMDA-R) (Chen et al. 2011; Gronwald et al. 2012; Zhang
et al. 2014) are also targets for some local anesthetics.
Therefore, lidocaine may be a multi-target agent and com-
prehensive research into the relationships between ligands
and multiple targets may be useful for the rational design of
local anesthetic agents.
* Wen Li
liwen@zzu.edu.cn
* Qidong You
youqd@gmail.com
1
School of Pharmaceutical Sciences, Zhengzhou University,
450002 Zhengzhou, PR China
2
Jiangsu Key Laboratory of Drug Design and Optimization and
Department of Medicinal Chemistry, China Pharmaceutical
University, 210009 Nanjing, PR China
3
Collaborative Innovation Center of New Drug Research and Safety
Evaluation, Henan Province & Key Laboratory of Technology of
Drug Preparation (Zhengzhou University), Ministry of Education
& Key Laboratory of Henan Province for Drug Quality and
Evaluation, 450002 Zhengzhou, PR China
Structural modifications of lidocaine have been pre-
viously explored on replacing the CH3 group on the phenyl
ring or the CH2CH3 group on the amine with different alkyl

Medicinal Chemistry Research
Biology
All of the synthesized compounds were tested in vitro for
their sciatic nerve block activities in toads, using lidocaine
hydrochloride as a positive control. The ED50 (mg/mL) and
the latent period time (min) were determined according to
previously described methods (Li et al. 2017). The biolo-
gical activities are summarized in Table 1.
Fig. 1 Structure of lidocaine
groups (Strother et al. 1977). Meanwhile, our group has
reported sodium channel blockers containing benzene rings
substituted with fluorine or trifluorine in the o-, m- and p-
positions, such as substituted imipramine compounds (Li
et al. 2010; Li and You 2007) and fluoro-ropivacaine ana-
logs (Li et al. 2017). Some of these compounds exhibited
greater potency than the parent compounds when tested for
infiltration anesthesia, surface anesthesia and analgesic
actions. In addition, when the phenyl ring was substituted
with fluorine at position-1, imipramine exhibited sub-
stantially increased antidepressant activity and significantly
decreased anticholinergic toxicity (Kyburz and Spiegelberg
1975). In fact, fluoro-substituted drugs account for a con-
siderable proportion of clinical treatment drugs, and the
total number has exceeded 180 (Wang and Liu 2011). The
fluorine substitution strategy in drug design is also one of
the important research strategies for drug structural trans-
formation (Ojima 2004). These exciting findings inspired us
to further research fluoro-substituted sodium channel
blockers.
The ED50 of all compounds were in the range of
0.010–0.140 mg/mL except compound 19e which demon-
strated no sciatic nerve block activity. Under the same
conditions, the ED50 of the reference compound lidocaine
was 0.019 mg/mL. Six compounds, namely 10a, 11a, 11d,
15a, 15c, and 19a, were much potent with ED50 in the range
of 0.010–0.019 mg/mL. Compound 10a in particular dis-
played the highest block activity, which was almost twice
that of lidocaine. Although compounds 11c, 14c, 14d, 15d,
18b, and 18c were slightly weaker than lidocaine, they also
exhibited significant potency of 0.020–0.023 mg/mL.
Compounds 10b, 10c, 10d, 11b, 14a, 14b, 15b, 18a, 18d,
19b, 19c, and 19d showed moderate potency of
0.028–0.054 mg/mL, while the least potent compounds 10e,
11e, 14e, 15e, 18e, and 19e gave ED50 greater than
0.086 mg/mL. Structurally, the morpholinyl group was
obviously not favorable for nerve block activity.
The latent periods of the analogs were 18.0–50.7 min
while that of lidocaine was 37.2 min. Among of these
compounds, only 11a, 18b, 18c, 18d, and 19a showed
longer latent periods than lidocaine. Structurally, the propyl
on the amino and the methyl on the phenyl group may be
the reason why the latent periods of the compounds have
been extended.
Herein we presented the syntheses of new fluoro-
substituted lidocaine analogs, the evaluation of their scia-
tic nerve block activities, and the potential mechanism of
action based on molecular docking, as well as their dis-
sociation constants (pKa).
Dissociation constant
Results and discussion
pKa (dissociation constant) is an important physicochemical
parameter for local anesthetics. Most local anesthetics have
pKa values between 7.0 and 7.7. When a drug has pKa
below 7.0, it is not sufficiently ionized at physiological pH
to produce any anesthetic effect, even though it can pene-
trate the cell membrane. In contrast, when a drug has pKa
above 9.5, it is almost fully ionized at physiological pH and
has difficulty penetrating the axon, thus limiting its effec-
tiveness. The pKa values of the lidocaine analogs in this
study were determined using the potentiometric titration
method (Li et al. 2017). The volume of hydrochloric acid
added was plotted against the pH of the solution.
Dissociation constants were obtained as the pH value at
the half-equivalence point of the titration curve. The pKa
values of the lidocaine analogs are summarized in Table 1.
Among all the compounds, 10a, 10b, 10c, 11a, 11b, 11c,
14a, 14b, 14c, 15a, 15b, 15c, 18a, 18c, and 19c showed
Synthesis
The synthesis route of the lidocaine analogs followed the
general pathway outlined in Scheme 1. Firstly, 2-
Trifluoromethyl aniline (1) was converted to sulfilimine
(2), and then treated with succinimide to form 2-tri-
fluoromethyl-6-[(methylthio)methyl]aniline (3). Treatment
of compound
3
with NaIO4 produced 2-tri-
fluoromethylphenyl-6-(methylsulfoxidemethyl)aniline (4),
which was subsequently treated with dry hydrogen chloride
gas to afford compound (5). Catalytic hydrogenation of 5
using 10% Pd–C gave a 3:1 mixture of 2-trifluoromethyl-6-
methylaniline (6) and 2-trifluoromethyl-6-(methoxymethyl)
aniline (7). After chloroacylation and N-alkylation reactions
on intermediates 3, 6, and 7, 30 lidocaine analogs were
obtained.

Medicinal Chemistry Research
CF3
CF3
CF3
Scheme 1 Synthesis procedure
for compounds 10a–e, 11a–e,
14a–e, 15a–e, 18a–e, and 19a–e.
Reagents and conditions: (i) (1)
P2O5, DMSO, r. t., 8 h; (ii)
Succinimide, CH2ClCH2Cl,
reflux, 4 h; (iii) NaIO4, CH3OH, r.
t., 4 h; (iv) HCl, CH2ClCH2Cl,
50 °C., 1 h; (v) 10% Pd–C,
HCOONH4, CH3OH, r. t., 0.5 h;
(vi) ClCH2COCl or ClCH(CH3)
COCl, CH3COOH–CH3COONa,
r. t., 0.5 h; (vii) (1) HX, K2CO3,
80 °C, 10 h; (2) HCl
CF3
NH2
N
NH2
S(CH3)2
NH2
i
iii
ii
CH2SCH3
O
CH2SCH3
4
3
2
1
CF3
CF3
CF3
NH2
.HCl
NH2
NH2
CH3
iv
v
+
CH2Cl
CH2OCH3
6
(
7
= 3mol : 1mol)
:
7
6
5
CF3
CF3
NH COCHCl
NH COCH
X
.HCl
vii
vi
R
R
3
CH2SCH3
CH2SCH3
8
9
R=H
R=CH3
10a 10e
R=H
R=CH3
-
11a 11e
-
CF3
CF3
NH COCHCl
a
X=NHC3H7-n
NH COCH
X
.HCl
vii
vii
vi
R
R
6
CH3
CH3
b
X=N(CH2CH3)2
12
13
R=H
R=CH3
14a-14e
15a-15e
R=H
R=CH3
c X=
N
CF3
CF3
d
e
X=
X=
N
NH COCHCl
NH COCH
X
.HCl
vi
7
R
R
N
O
CH2OCH3
CH2OCH3
16
17
R=H
R=CH3
18a-18e
19a-19e
R=H
R=CH3
pKa values of 7.5–7.8 appropriate for local anesthetics. The
others displayed pKa values below 7.5, suggesting that they
would remain in the uncharged form at the pH of body
fluids.
(Boukhabza et al. 2016; Lipkind, Fozzard 2010). The first
crystal structure of human VGSC Nav1.4 has been revealed
by the Yan Ning’s research group. The structure is complex
with its specific regulatory subunit β1 and has a resolution of
3.2 Å (PDB code: 6AGF) (Pan et al. 2018). This could
provide a reliable template for further understanding of the
potential mechanism of local anesthesia. We therefore
selected 6AGF as the receptor for our docking studies.
The GABAA-R is an another potential target of local
anesthetics (Amin and Subbarayan 2017; Sugimoto et al.
2000). Chen et al. have established two crystal structures of
human GABAA-R (PDB code: 6D1S and 6CDU) and
revealed the possible binding sites for endogenous neuro-
transmitter GABA and anesthetics (Chen et al. 2018). In
this study, 6D1S was selected as the docking receptor
because it offered a higher resolution (3.2 Å) than 6CDU
(3.45 Å).
Docking studies
Molecular docking studies
To investigate the potential mechanism of local anes-
thetics, three representative compounds of different levels
activity, namely compound 10a (strongest activity,
0.010 mg/mL), 14e (lowest activity, 0.14 mg/mL), and
lidocaine (0.019 mg/mL), were selected as subjects for
molecular docking studies, and researched their binding
models with three different potential targets of local
anesthetics (VGSC, GABAA-R, and NMDA-R).
One molecular target of local anesthetics is the human
VGSC and previous studies have identified that the active
site is the cavity consisting of the I-S6 to IV-S6 segments
The NMDA-R is important for controlling synaptic
plasticity and memory function, and could be another
potential target of local anesthetics (Zhang et al. 2014). In

Medicinal Chemistry Research
Table 1 The infiltration
anesthesia activities of
compounds 4b, 4c, 4j, and 4l
Compound The regress equation of AP ED50
The regress equation of
Latent period (min) and
compounds concentration
Latent
period (min)
pKa
decreasing extent(%) and
compounds concentration
(mg/
mL)
10a
10b
10c
10d
10e
11a
11b
11c
11d
11e
14a
14b
14c
14d
14e
15a
15b
15c
15d
15e
18a
18b
18c
18d
18e
19a
19b
19c
19d
19e
y = 72.75logx + 195.5
y = 96.61logx + 186.12
y = 110.43logx + 216.60
y = 105.33logx + 202.06
y = 109.57logx + 150.89
y = 89.49logx + 218.70
y = 102.71logx + 192.48
y = 93.21logx + 206.39
y = 98.32logx + 219.23
y = 142.27logx + 199.47
y = 92.43logx + 168.68
y = 93.16logx + 188.02
y = 78.71logx + 178.95
y = 75.85logx + 175.73
y = 124.57logx + 156.37
y = 63.12logx + 165.13
y = 102.36logx + 183.17
y = 125.95logx + 269.75
y = 115.22logx + 234.59
y = 116.76logx + 175.00
y = 97.13logx + 187.95
y = 110.37logx + 232.95
y = 92.45logx + 205.11
y = 104.09logx + 183.65
y = 116.31logx + 171.63
y = 63.21logx + 160.28
y = 102.93logx + 208.27
y = 129.74logx + 243.94
y = 117.13logx + 217.71
No activity
0.010
0.039
0.031
0.036
0.120
0.013
0.041
0.021
0.019
0.089
0.052
0.033
0.023
0.022
0.140
0.015
0.050
0.018
0.025
0.085
0.038
0.022
0.021
0.052
0.090
0.018
0.029
0.032
0.037
–
y = −26.97logx − 24.34
y = −27.45logx − 9.28
y = −25.81logx − 14.74
y = −25.93logx − 13.64
y = −36.67logx − 7.57
y = −26.85logx − 8.43
y = −20.25logx − 4.19
y = −19.13logx − 2.80
y = −39.65logx − 36.45
y = −31.38logx − 4.57
y = −33.08logx − 9.97
y = −9.20logx + 4.37
y = −16.66logx − 3.49
y = −16.02logx − 1.75
y = −29.21logx + 7.86
y = −17.32logx − 5.29
y = −32.81logx − 16.99
y = −34.00logx − 28.82
y = −32.11logx − 21.54
y = −35.14logx − 8.32
y = −27.32logx − 3.40
y = −14.93logx + 14.25
y = −29.44logx − 11.69
y = −41.33logx − 10.07
y = −28.82logx −5.14
y = −41.89logx − 22.39
y = −23.97logx − 11.96
y = −32.66logx − 19.52
y = −18.89logx − 5.85
–
29.6
29.4
24.2
23.8
26.2
42.2
23.9
29.3
31.8
28.4
32.5
18.0
23.8
24.8
32.8
26.3
25.7
30.5
29.9
29.3
35.4
39.0
37.7
43.0
25.0
50.7
24.9
29.3
21.2
–
7.6
7.5
7.7
6.8
5.5
7.7
7.6
7.5
7.3
6.1
7.5
7.5
7.6
7.1
6.0
7.7
7.5
7.8
7.3
6.2
7.5
7.4
7.5
7.3
6.0
7.3
7.3
7.5
7.1
6.0
7.9
lidocaine y = 111.39logx + 241.73
0.019
y = −27.64logx − 10.38
37.2
the RCSB protein database bank, there are 20 X-ray crystal
structures of the human NMDA-R, among which 5I2N
(Volgraf et al. 2016) gives a relatively high resolution and
its ligand is similar in structure to our compounds. There-
fore, 5I2N was selected as the docking receptor in our
studies.
cavity surrounded by residues Phe-436, Phe-1601, Leu-443,
Tyr-450, Phe-797, forming π-π stacking interactions with
the residue Phe-1601 (Fig. 2). The differences in potency of
these compounds could be explained by that the tri-
fluoromethyl and dimethylsulfide groups of 10a had stron-
ger hydrophobic interactions with the surrounding residues
Tyr-1593, Phe-1586, Phe-1290, and Phe-797 than the sub-
stituted groups of lidocaine (Fig. 2a, c). Therefore, Com-
pound 10a bound tighter to the active site than lidocaine
and was more potent. Conversely, the hydrophilic mor-
pholine group of compound 14e showed weaker affinity to
the surrounding hydrophobic residues Phe-1586, Phe-1290,
Tyr-1593, and Phe-797 (Fig. 2b); hence lower potency than
10a and lidocaine. We herein propose that the ligand
activity may be enhanced by increasing the hydrophobicity
of the substituents appropriately.
VGSC docking
Compounds 10a, 14e, and lidocaine were docked into the
predicted binding site of VGSC and the results showed that
compound 10a had the best score (−6.2737), followed by
lidocaine (−5.9143) and 14e (−5.7564). When compound
10a, 14e, and lidocaine were placed in the center of the
channel lumen, the substituted benzenes of compounds 10a,
14e, and lidocaine were found to occupy the hydrophobic

Medicinal Chemistry Research
Fig. 3 Binding models of compound 10a (a), 14e (b), and lidocaine c
in anesthetics binding site of GABAA-R. Ligands were shown in
green sticks, and key residues of GABAA-R were shown in white stick
models. The nitrogen, oxygen, sulfur, and fluorine atoms were shown
in blue, red, yellow and cyan, respectively (Color figure online)
Fig. 2 Binding models of compound 10a (a), 14e (b) and lidocaine c
in the active site of VGSC. Ligands were shown in green stick modes,
and key residues of VGSC were shown in white stick models. The
nitrogen, oxygen, fluorine and sulfur atoms were shown in blue, red,
cyan and yellow, respectively. I-S6 to IV-S6 segments of VGSC were
shown in cyan, yellow, orange and green cartoon ribbons, respectively
(Color figure online)
−5.7675, respectively. The benzene groups of 10a, 14e, and
lidocaine formed hydrophobic interactions with surrounding
residues Ile-302, Phe-298, Ile-239, Gln-242, Pro-401, and
Trp-246. Apart from these hydrophobic interactions, the
trifluoromethyl and dimethylsulfide groups of 10a had
stronger hydrophobic interactions with the surrounding
residues than those of the methyl groups of lidocaine, and
GABAA-R docking
Compounds 10a, 14e, and lidocaine were docked into the
binding site of GABAA-R (Fig. 3), revealing the docking
score of 10a, 14e, and lidocaine as −5.8481, −5.4714,

Medicinal Chemistry Research
substituted morpholine of 14e afforded weak hydrophobic
interactions with surrounding residues Ile-302, Phe-310,
Tyr-309, and Trp-246, hence the lowest potency among the
three compounds (Fig. 3b). These results again indicate that
hydrophobic interactions are crucial to activity.
NMDA-R docking
Compounds 10a, 14e, and lidocaine were docked well into
the binding site of NMDA-R and a similar docking pattern
was obtained with docking score of −6.8702, −6.0990, and
−6.7101, respectively (Fig. 4). The benzene groups of
compounds 10a, 14e, and lidocaine formed hydrophobic
interactions with surrounding residues Val-A128, Pro-
A129, Ile-B128, Pro-B141, and Tyr-B144. The amide
groups of 10a and lidocaine formed hydrogen bonds with
Pro-A129 at distances of 2.1 Å (N–H…O = Pro-A129) and
2.0 Å (N–H…O = Pro-A129), respectively. Meanwhile,
both the propylamino group of 10a and the diethylamino
group of lidocaine formed hydrophobic interactions with
residues Val-A266, Met-A271, and Val-A131. Despite all
these interactions, the higher potency of 10a was likely
explained by the stronger hydrophobic interactions formed
by the trifluoromethyl and dimethylsulfide groups on the
benzene ring of 10a, with the surrounding residues Val-
A128, Pro-A129, Ile-B128, Pro-B141 and Tyr-B144, than
those by the methyl groups on benzene ring of lidocaine
(Fig. 4a, c). Moreover, the substituted benzene of 10a also
formed π–π staking interactions with Tyr-B144. In contrast,
no hydrogen bond formation was observed between 14e and
NMDA-R, and the hydrophobicity of the substituted mor-
pholine in 14e was poor (Fig. 4b), resulting in loose binding
and hence low potency. Therefore, it was speculated that
hydrogen bonds and hydrophobic interactions could
enhance the binding of the compounds to NMDA-R.
Experimental
(2-Trifluoromethyl)-6-[(methylthio)methyl]aniline
(3)
Fig. 4 Binding models of compound 10a (a), 14e (b), and lidocaine c
in the active site of NMDA-R. Ligands were shown in cyan stick
models, and key residues of NMDA-R were shown in white stick
models. The nitrogen, oxygen, hydrogen, fluorine and sulfur atoms
were shown in blue, red, gray, green and yellow, respectively. And the
corresponding distances were given in Å (Color figure online)
2-TriFluoromethyl aniline 1 (100 mL, 0.8 mol) and phos-
phorus pentoxide (340 g, 2.4 mol) were suspended in
1600 mL CH2Cl2 and stirred at room temperature while
DMSO (400 mL, 5.6 mol) and triethylamine (78 mL,
0.56 mol) were added slowly during 30 min, the reaction
mixture was heated to 30 °C for 8 h. Then, the reaction
mixture was poured to 200 mL 10% ice NaOH solution. N-
(2-trifluoromethylphenyl)-S, S-dimethyl sulfilimine (2,
104.0 g) was obtained by separated CH2Cl2 layer, dried
with anhydrous sodium sulfate and removed solvent by
rotaryevaporation. Compound 2 (104 g, 0.47 mol) and
the substituted benzene of compound 10a could also form
π–π stacking interactions with the residue Phe-298 (Fig. 3a,
c). Thus, compound 10a demonstrated a stronger local
anesthetic effect than lidocaine because of the tighter
binding. Compared with the propylamino group of com-
pound 10a and the diethylamino group of lidocaine, the

Medicinal Chemistry Research
succinimide (2.3 g, 0.023 mol) were then added to 600 mL
1, 2-dichloroethane, the mixture was heated to reflux for
4 h. The reaction mixture was poured to 200 mL 10% ice
NaOH solution. 2-Trifluoromethyl-6-[(methylthio)methyl]
aniline (3, 80 g) was obtained by separated 1,2-dichlor-
oethane layer, dried with anhydrous sodium sulfate and
removed solvent by rotaryevaporation. Yield 77%.
N-(2-trifluoromethylphenyl)-6-[(methylthiomethyl)
phenyl]-2-chloroacetylamide (8)
Compound 3 (7.0 g, 0.03 mol) and chloroacetic chloride
(7.2 mL, 0.09 mol) were dissolved in 50 mL acetonitrile.
The reaction mixture was stirred and heated at 50 °C for 3 h
and then was removed the acetonitrile. The residue was
dissolved in 50 mL dichloromethane, washed with the 10%
NaOH solution, dried with anhydrous sodium sulfate and
removed solvent by rotaryevaporation. Compound 8 was
obtained as a white solid. Yield 72%. Compounds 9, 12, 13,
16, and 17 were synthesized by the similar procedure in the
yields of 68–97%.
(2-Trifluoromethylphenyl)-6-[(methylthio) methyl]
aniline (4)
At 0 °C, NaIO4 (4.8 g, 0.023 mol) was dissolved in
CH3OH–H2O (50 mL: 50 mL) mixture, compound 3 (50 g,
0.23 mol) added by dripping in 1 h. The mixture was then
stirred for 4 h and extracted by chloroform. (2-Tri-
fluoromethylphenyl)-6-[(methylthio) methyl]aniline (4,
45 g) was obtained by dried chloroform layer with anhy-
drous sodium sulfate and removed solvent by rotar-
yevaporation. Yield 84%.
General procedure for preparation of the objective
compounds
Compound 8 (1.0 g, 0.003 mol), n-propylamine (5.5 mL,
0.067 mol), and K2CO3 (0.6 g, 0.004 mol) were added to
10 mL DMF. The mixture was stirred and heated at 40 °C
for 10 h and then allowed to cool to room temperature. The
excessive n-propylamine was removed by rotaryevaporation
and the residue was poured to 100 mL H2O. The mixture
was extracted by CH3COOEt and the extract was dried with
anhydrous sodium sulfate and removed solvent by rotar-
yevaporation. The residue was dissolved in 50 mL anhy-
drous ether and dried gas of hydrogen chloride was added at
r.t. for 10 min, N-[(2-trifluoromethylphenyl)-6-(methylthio-
(2-Trifluoromethylphenyl)-6-(chloromethyl)
anilinium chloride (5)
Compound 4 was dissolved in 1,2-dichloroethane and dried
gas of hydrogen chloride was added at 50 °C for 50 min.
Then, white solid of (2-Trifluoromethylphenyl)-6-(chlor-
omethyl) anilinium chloride (5, 42.3 g) was got after the
reaction mixture cooled to room temperature. Yield 92%.
methyl)phenyl]-2-(1-propylamine)acetylamide
hydro-
(2-Trifluoromethylphenyl)-6-(methyl)aniline (6) and
(2-trifluoromethylphenyl)-6-(methoxymethyl)aniline
(7)
chloride (10a) was got as a white solid. The other objective
compounds were prepared by following the same
procedure.
Compound 5 (42 g, 0.17 mol) were dissolved in 350 mL
CH3OH at room temperature and stirred while 10% Pd–C
(14 g), HCOONH4 (322 g, 5.1 mol) were added slowly during
30 min, the reaction mixture was stirred at room temperature
overnight before it was filtered through a sintered filter funnel
which covered by diatomite. The filtrate was removed
CH3OH by rotaryevaporation and the residue was dissolved
in 350 mL H2O. The pH of the solution was adjusted to 8–9
with 10% NaOH solution. And then the solution was
extracted by CH3COOEt in three times and the ethyl acetate
extracts were combined. Compounds 6 and 7 were obtained
by dried with anhydrous sodium sulfate, removed solvent by
rotaryevaporation and vacuum distillation. Compound 6 was
got at the condition of 60–75 °C/20 mm Hg, the yield is 70%
and compound 7 was got at the condition of 120–130 °C/
20 mm Hg, the yield is 20%, respectively.
N-[(2-trifluoromethyl-6-methylthiomethyl)phenyl]-2-(1-
propylamine) acetylamide hydrochloride (10a)
Yield 79%; mp 99–102 °C; 1H-NMR (500 MHz, CD3OD) δ
1.03 (3H, t, J = 7.5 Hz, 3′-CH3), 1.77 (2H, m, 2′-CH2), 2.01
(3H, s, –SCH3), 3.07 (2H, t, J = 8.0 Hz, 1′-NCH2), 3.72
(2H, m, Ar–CH2S–), 4.09 (2H, m, 2-COCH2), 7.53 (1H, m,
ArH), 7.69 (1H, m, ArH), 7.76 (1H, m, ArH); 13C-NMR
(100 MHz, (CD3)2SO) δ 13.49 (3′-CH3), 14.66 (–SCH3),
27.23 (2′-CH2), 32.70 (Ar–CH2S–), 46.46 (1′-NCH2), 47.48
(2-COCH2), 121.93 (C-CF3), 124.45(Ar), 124.76-127.60 (q,
J = 284, Ar-CF3), 128.80 (Ar), 132.62 (Ar), 134.4 (Ar),
139.58 (Ar), 165.14 (NHCO). IRνmax (KBr, cm−1) 3142,
2968, 1696, 1536, 1469, 1324; ES-MS (m/z) [M + H]+:
321; anal. calcd for C14H19F3N2OS.HCl: C, 47.12; H, 5.65;
N, 7.85. Found C, 46.94; H, 5.87; N, 7.74.

Medicinal Chemistry Research
N-[(2-trifluoromethyl-6-methylthiomethyl)phenyl]-2-(N,N-
N-[(2-trifluoromethyl-6-methylthiomethyl)phenyl]-2-(1-
diethylamine) acetylamide hydrochloride (10b)
propylamine) propionamide hydrochloride (11a)
1
1
Yield 83%; mp 163–167 °C; H-NMR (500 MHz, CD3OD)
Yield 93%; mp 134–138 °C; H-NMR (500 MHz, CD3OD)
δ 1.36 (6H, t, J = 7.5 Hz, 2′-CH3), 1.99 (3H, s, –SCH3),
3.30 (4H, m, 1′-NCH2), 3.69 (2H, m, Ar–CH2S-), 4.20 (2H,
m, 2-COCH2), 7.54 (1H, m, ArH), 7.70 (1H, m, ArH), 7.74
(1H, m, ArH); IRνmax (KBr, cm−1) 3116, 2982, 1696, 1546,
1469, 1389; ES-MS (m/z) [M + H] +: 335; anal. calcd for
C15H21F3N2OS.HCl: C, 48.58; H, 5.98; N, 7.55. Found C,
48.28; H, 5.82; N, 7.59.
δ 1.03 (3H, t, J = 7.5 Hz, 3′-CH3), 1.70 (3H, m, 3-CH3),
1.79 (2H, m, 2′-CH2), 2.01 (3H, s, –SCH3), 3.01 (2H, t, J =
8.0 Hz, 1′-NCH2), 3.66 (2H, m, Ar–CH2S-), 4.18 (1H, m, 2-
COCH), 7.54 (1H, m, ArH), 7.72 (2H, m, ArH); IRνmax
(KBr, cm−1) 3121, 2971, 1697, 1538, 1323, 1163; ES-MS
(m/z) [M + H]+: 335; anal. calcd for C15H21F3N2OS.HCl:
C, 48.50; H, 5.98; N, 7.55. Found C, 48.45; H, 5.99;
N, 7.40.
N-[(2-trifluoromethyl -6-methylthiomethyl)phenyl]-2-
pyrrolidino acetylamide hydrochloride (10c)
N-[(2-trifluoromethyl-6-methylthiomethyl)phenyl]-2-(N,N-
diethylamine) propionamide hydrochloride (11b)
1
Yield 75%; mp 183-185 °C; H-NMR (500 MHz, CD3OD)
1
δ 2.13 (3H, s, –SCH3), 2.22 (4H, m, 2′-CH2, 3′-CH2), 3.30
(2H, m, 1′-NCH, 4′-NCH), 3.82 (2H, m, Ar–CH2S-), 3.86
(2H, m, 1′-NCH, 4′-NCH), 4.45 (2H, m, 2-COCH2), 7.66
(1H, m, ArH), 7.81 (1H, m, ArH), 7.88 (1H, m, ArH);
IRνmax (KBr, cm-1) 3490, 2971, 1692, 1535, 1322, 1162;
ES-MS (m/z) [M + H]+: 333; anal. calcd for
C15H19F3N2OS.HCl: C, 46.57; H, 5.73; N, 7.24. Found C,
46.43; H, 6.00; N, 7.26.
Yield 81%; mp 145-148 °C; H-NMR (500 MHz, CD3OD)
δ 1.50 (6H, t, J = 7.5 Hz, 2′-CH3), 1.74 (3H, m, 3-CH3),
2.02 (3H, s, –SCH3), 3.40 (4H, m, 1′-NCH2), 3.66 (2H, m,
Ar–CH2S-), 4.28 (2H, m, 2-COCH2), 7.54 (1H, m, ArH),
7.73 (2H, m, ArH); IRνmax (KBr, cm−1) 3146, 2983, 1697,
1529, 1468, 1323; ES-MS (m/z) [M + H]+: 349; anal. calcd
for C16H23F3N2OS.HCl: C, 52.10; H, 6.56; N, 7.60. Found
C, 52.19; H, 6.56; N, 7.43.
N-[(2-trifluoromethyl-6-methylthiomethyl)phenyl]-2-
N-[(2-trifluoromethyl-6-methylthiomethyl)phenyl]-2-
piperidino acetylamide hydrochloride (10d)
pyrrolidino propionamide hydrochloride (11c)
1
1
Yield 97%; mp 92–95 °C; H-NMR (500 MHz, CD3OD) δ
Yield 88%; mp 23–25 °C; H-NMR (500 MHz, CD3OD) δ
1.60 (2H, m, 2′-CH2), 1.88 (4H, m, 3′-CH2, 4′-CH2), 2.01
(3H, s, –SCH3), 3.15 (2H, m, 1′-NCH, 5‘-NCH), 3.63 (2H,
m, 1′-NCH, 5′-NCH), 3.71 (2H, m, Ar–CH2S-), 4.21 (2H,
m, 2-COCH2), 7.53 (1H, m, ArH), 7.69 (1H, m, ArH), 7.76
(1H, m, ArH); IRνmax (KBr, cm−1) 3490, 2971, 1692, 1535,
1322, 1162; ES-MS (m/z) [M + H] +: 347; anal. calcd for
C16H21F3N2OS.HCl: C, 47.94; H, 6.03; N, 6.99. Found C,
48.24; H, 6.32; N, 7.10.
1.77 (3H, m, 3-CH3), 2.05 (3H, s, –SCH3), 2.20 (4H, m, 2′-
CH2, 3′-CH2), 3.28 (2H, m, 1′-NCH, 4′-NCH), 3.66 (2H,
m, Ar–CH2S–), 3.67 (2H, m, 1′-NCH, 4′-NCH), 4.24 (2H,
m, 2-COCH2), 7.51 (1H, m, ArH), 7.72 (2H, m, ArH);
IRνmax (KBr, cm-1) 3416, 2963, 1693, 1536, 1322, 1163;
ES-MS (m/z) [M + H]+: 347; anal. calcd for
C16H21F3N2OS.HCl: C, 50.19; H, 5.79; N, 7.32. Found C,
50.45; H, 6.05; N, 7.34.
N-[(2-trifluoromethyl-6-methylthiomethyl)phenyl]-2-
N-[(2-trifluoromethyl-6-methylthiomethyl)phenyl]-2-
piperidino acetylamide hydrochloride (10e)
piperidino propionamide hydrochloride (11d)
1
Yield 85%; mp 98–101 °C; 1H-NMR (500 MHz, CD3OD) δ
2.01 (3H, s, –SCH3), 3.37 (2H, m, 1′-NCH), 3.60 (2H, m,
5′-NCH2), 3.72 (2H, m, Ar–CH2S–), 3.85 (2H, m, 2′-
OCH2), 4.05 (2H, m, 4′-OCH2), 4.32(2H, m, 2-COCH2),
7.54 (1H, m, ArH), 7.70 (1H, m, ArH), 7.76 (1H, m, ArH);
Yield 79%; mp 185-187 °C; H-NMR (500 MHz, CD3OD)
δ 1.60 (2H, m, 2′-CH2), 1.70 (3H, m, 3-CH3), 1.88 (4H, m,
3′-CH2, 4′-CH2), 2.02 (3H, s, –SCH3), 3.08 (2H, m, 1′-
NCH, 5‘-NCH), 3.63 (2H, m, 1′-NCH, 5‘-NCH), 3.70 (2H,
m, Ar–CH2S–), 4.20 (2H, m, 2-COCH2), 7.55 (1H, m,
ArH), 7.73 (2H, m, ArH); IRνmax (KBr, cm-1) 3111, 2980,
1692, 2543, 1702, 1532; ES-MS (m/z) [M + H]+: 362; anal.
calcd for C17H23F3N2OS.HCl: C, 49.94; H, 6.28; N, 7.28.
Found C, 49.67; H, 6.58; N, 7.06.
IRνmax (KBr, cm−1) 3434, 2974, 1693, 1537, 1323, 1164;
+
ES-MS (m/z) [M + H]
:
349; anal. calcd for
C15H19F3N2O2S.HCl: C, 45.74; H, 5.37; N, 7.11. Found C,
45.75; H, 5.66; N, 7.16.

Medicinal Chemistry Research
N-[(2-trifluoromethyl-6-methylthiomethyl)phenyl]-2-
piperidino propionamide hydrochloride (11e)
(3H, s, –ArCH3), 3.26 (2H, m, 1′-NCH, 5′-NCH), 3.73 (2H,
m, 1′-NCH, 5′-NCH), 4.30 (2H, m, 2-COCH2), 7.59 (1H,
m, ArH), 7.73 (2H, m, ArH); IRνmax (KBr, cm−1) 3382,
1
Yield 85%; mp 92-95 °C; H-NMR (500 MHz, CD3OD) δ 1690, 1575, 1544, 1472, 1323; ES-MS (m/z) [M + H]+:
1.77 (3H, m, 3-CH3), 2.02 (3H, s, –SCH3), 3.30 (2H, m, 301; anal. calcd for C15H19F3N2O.HCl: C, 50.78; H, 6.25;
Ar–CH2S-), 3.45(2H, m, 1′-NCH2), 3.49 (2H, m, 5′-NCH2), N, 7.90. Found C, 50.67; H, 6.27; N, 7.84.
3.96 (2H, m, 2′-OCH2), 4.06 (2H, m, 4′-OCH2), 4.26(2H,
m, 2-COCH2), 7.54 (1H, m, ArH), 7.73 (2H, m, ArH);
N-[(2-trifluoromethyl-6-methyl)phenyl]-2-piperidino
IRνmax (KBr, cm−1) 3147, 2971, 1693, 1533, 1322, 1162; acetylamide hydrochloride (14e)
+
ES-MS (m/z) [M + H]
:
363; anal. calcd for
1
C16H21F3N2O2S.HCl: C, 46.10; H, 5.80; N, 6.72. Found C, Yield 74%; mp 115–118 °C; H-NMR (500 MHz, CD3OD) δ
46.36; H, 6.07; N, 6.71.
2.30 (3H, s, –ArCH3), 3.33 (2H, m, 1′-NCH), 3.47 (2H, m, 5′-
NCH2), 3.87 (2H, m, 2′-OCH2), 4.04 (2H, m, 4′-OCH2), 4.29
(2H, m, 2-COCH2), 7.75 (1H, m, ArH), 7.60 (2H, m, ArH);
IRνmax (KBr, cm−1) 3438, 2977, 1692, 1536, 1323, 1164; ES-
MS (m/z) [M + H] +: 303; anal. calcd for C14H17F3N2O2.HCl:
N-[(2-trifluoromethyl-6-methyl)phenyl]-2-(1-propylamine)
acetylamide hydrochloride (14a)
1
Yield 81%; mp 225-228 °C; H-NMR (500 MHz, CD3OD) C, 47.13; H, 5.65; N, 7.85. Found C, 47.43; H, 5.93; N, 7.89.
δ 1.03 (3H, t, J = 7.5 Hz, 3′-CH3), 1.76 (2H, m, 2′-
CH2),2.35(3H, s, ArCH3), 3.05 (2H, m, 1′-NCH2), 4.08 N-[(2-trifluoromethyl-6-methyl)phenyl]-2-(1-propylamine)
(2H, m, 2-COCH2), 7.40 (1H, m, ArH), 7.59 (2H, m, ArH);
propionamide hydrochloride (15a)
IRνmax (KBr, cm−1) 3262, 2954, 2772, 1682, 1537, 1324,
1161; ES-MS (m/z) [M + H] +: 275; anal. calcd for Yield 92%; mp 115–118 °C; H-NMR (500 MHz, CD3OD)
1
C13H17F3N2O.HCl: C, 50.25; H, 5.84; N, 9.01. Found C, δ 1.03 (3H, t, J = 7.2 Hz, 3′-CH3), 1.70 (3H, m, 3-CH3),
50.31; H, 5.99; N, 9.01.
1.79 (2H, m, 2′-CH2), 2.29 (3H, m, Ar–CH3), 2.97 (2H, m,
1′-NCH2), 4.18 (1H, m, 2-COCH), 7.44 (1H, m, ArH), 7.61
(2H, m, ArH); IRνmax (KBr, cm−1) 3533, 3194, 2978, 1697,
1557, 1550, 1323, 1165; ES-MS (m/z) [M + H] +: 289;
anal. calcd for C14H19F3N2O.HCl: C, 51.78; H, 6.21; N,
N-[(2-trifluoromethyl-6-methyl)phenyl]-2-(N,N-
diethylamine) acetylamide hydrochloride (14b)
1
Yield 77%; mp 170–172 °C; H-NMR (500 MHz, CD3OD) 8.63. Found C, 51.67; H, 6.34; N, 8.49.
δ 1.37 (6H, t, J = 7.2 Hz, 2′-CH3), 2.29 (3H, s, –CH3), 3.35
(4H, m, 1′-NCH2), 4.25 (2H, m, 2-COCH2), 7.45 (1H, m, N-[(2-trifluoromethyl-6-methyl)phenyl]-2-(N,N-
ArH), 7.60 (2H, m, ArH); IRνmax (KBr, cm−1) 3459, 3123, diethylamine) propionamide hydrochloride (15b)
2983, 1691, 1537, 1472, 1323; ES-MS (m/z) [M + H]+:
1
289; anal. calcd for C14H19F3N2O.HCl: C, 50.38; H, 6.34; Yield 80%; mp 205-207 °C; H-NMR (500 MHz, CD3OD)
N, 8.39. Found C, 50.34; H, 6.60; N, 8.51.
δ 1.50 (6H, m, 2′-CH3), 1.86 (3H, m, 3-CH3), 2.42 (3H, s,
Ar–CH3), 3.45(4H, m, 1′-NCH2), 4.45 (1H, m, 2-COCH),
N-[(2-trifluoromethyl-6-methyl)phenyl]-2-pyrrolidino
acetylamide hydrochloride (14c)
7.59 (1H, m, ArH), 7.74 (2H, m, ArH); IRνmax (KBr, cm−1
)
+
3170, 2985, 1695, 1527, 1325; ES-MS (m/z) [M + H]
:
303; anal. calcd for C15H21F3N2O.HCl: C, 53.18; H, 6.55;
Yield 75%; mp 183–185 °C; H-NMR (500 MHz, CD3OD) N, 8.27. Found C, 52.96; H, 6.64; N, 8.00.
δ 2.03 (2H, m, 2′-CH2), 2.20 (2H, m, 3′-CH2), 2.29(3H, s,
1
ArCH3), 3.18(2H, m, 1′-NCH, 4′-NCH), 3.75 (2H, m, 1′- N-[(2-trifluoromethyl-6-methyl)phenyl]-2-pyrrolidino
NCH, 4′-NCH), 4.35 (2H, m, 2-COCH2), 7.45 (1H, m, propionamide hydrochloride (15c)
ArH), 7.59 (2H, m, ArH); IRνmax (KBr, cm−1) 3419, 2948,
1
1692, 1599, 1471, 1323; ES-MS (m/z) [M + H]+: 287; anal.
Yield 75%; mp 220-221 °C; H-NMR (500 MHz, CD3OD)
calcd for C14H17F3N2O.HCl: C, 50.38; H, 5.73; N, 8.39. δ 1.73 (3H, d, J = 17.5 Hz, 3-CH3), 2.18 (4H, m, 2′-CH2,
Found C, 50.34; H, 5.72; N, 8.49.
3′-CH2), 2.29 (3H, d, J = 16 Hz, Ar–CH3), 3.29 (2H, 1′-
NCH, 4′-NCH), 3.67 (2H, m, 1′-NCH, 4′-NCH), 4.25 (1H,
m, 2-COCH), 7.46 (1H, m, ArH), 7.60 (2H, m, ArH);
IRνmax (KBr, cm−1) 3458, 2963, 1690, 1686, 1543, 1323,
1165; ES-MS (m/z) [M + H]+: 301; anal. calcd for
N-[(2-trifluoromethyl-6-methyl)phenyl]-2-piperidino
acetylamide hydrochloride (14d)
1
Yield 74%; mp 173–175 °C; H-NMR (500 MHz, CD3OD) C15H19F3N2O.HCl.1/2H2O: C, 52.10; H, 6.12; N, 8.10.
δ 1.60 (2H, m, 2′-CH2), 2.28 (4H, m, 3‘-CH2, 4′-CH2), 2.42 Found C, 51.98; H, 6.36; N, 8.01.

Medicinal Chemistry Research
N-[(2-trifluoromethyl-6-methyl)phenyl]-2-piperidino
N-[(2-trifluoromethyl-6-methylxymethyl)phenyl]-2-
propionamide hydrochloride (15d)
pyrrolidino acetylamide hydrochloride (18c)
1
Yield 78%; mp 98–101 °C; 1H-NMR (500 MHz, CD3OD) δ
1.50 (2H, m, 2′-CH2), 1.60 (3H, m, 3-CH3), 1.80 (4H, m,
3′-CH2, 4′-CH2), 2.29 (3H, d, J = 11 Hz, Ar–CH3), 3.12
(2H, m, 1′-NCH, 5′-NCH), 3.63 (2H, m, 1′-NCH, 5′-NCH),
4.25 (1H, m, 2-COCH), 7.46 (1H, m, ArH), 7.60 (2H, m,
ArH); IRνmax (KBr, cm−1) 3438, 2953, 1692, 1536, 1471,
1322; ES-MS (m/z) [M + H]+: 315; anal. calcd for
C16H21F3N2O.HCl.H2O: C, 52.10; H, 6.56; N, 7.60. Found
C, 51.92; H, 6.61; N, 7.53.
Yield 72%; mp 205–208 °C; H-NMR (500 MHz, CD3OD)
δ 2.10 (4H, m, 2′-CH2, 3‘-CH2), 3.18 (2H, m, 1′-NCH, 4′-
NCH), 3.38 (3H, s, –OCH3), 3.77 (2H, m, 1′-NCH, 4‘-
NCH), 4.34 (2H, m, 2-COCH2), 4.47 (2H, s, Ar–CH2O),
7.57 (1H, m, ArH), 7.74 (1H, m, ArH), 7.79 (1H, m, ArH);
IRνmax (KBr, cm−1) 3471, 2977, 1692, 1536, 1323; ES-MS
(m/z) [M + H] +: 317; anal. calcd for C15H19F3N2O2.HCl:
C, 51.07; H, 5.71; N, 7.94. Found C, 51.57; H, 5.87;
N, 7.98.
N-[(2-trifluoromethyl-6-methyl)phenyl]-2-piperidino
N-[(2-trifluoromethyl-6-methylxymethyl)phenyl]-2-
propionamide hydrochloride (15e)
piperidino acetylamide hydrochloride (18d)
1
1
Yield 85%; mp 126–128 °C; H-NMR (500 MHz, CD3OD)
Yield 77%; mp 157–159 °C; H-NMR (500 MHz, CD3OD)
δ 1.46 (3H, d, J = 6.9 Hz, 3-CH3), 2.30 (3H, m, Ar–CH3),
3.46 (2H, m, 2′-NCH2), 3.52 (2H, m, 5′-NCH2), 4.06 (2H,
m, 3′-OCH2), 4.11 (1H, m, 4′-OCH2), 4.21(1H, m, 2-
COCH), 7.48 (1H, m, ArH), 7.62 (2H, m, ArH); IRνmax
(KBr, cm−1) 3444, 2972, 1692, 1536, 1323, 1165; ES-MS
(m/z) [M + H]+: 317; anal. calcd for C15H19F3N2O2.HCl.
H2O: C, 48.59; H, 5.98; N, 7.55. Found C, 48.79; H, 6.29;
N, 7.56.
δ 1.60 (2H, m, 2′-CH2), 1.88 (4H, m, 3′-CH2, 4′-CH2), 3.15
(2H, m, 1′-NCH, 5′-NCH), 3.37 (3H, s, –OCH3), 3.61(2H,
m, 1′-NCH, 5′-NCH), 4.20 (2H, m, 2-COCH2), 4.47 (2H,
m, Ar–CH2O–), 7.58 (1H, m, ArH), 7.73 (1H, m, ArH),
7.79 (1H, m, ArH); IRνmax (KBr, cm−1) 3119, 2950, 1686,
1539, 1469, 1322, 1163; ES-MS (m/z) [M + H]+: 331; anal.
calcd for C16H21F3N2O2.HCl: C, 52.39; H, 6.05; N, 7.64.
Found C, 52.46; H, 5.99; N, 7.68.
N-[(2-trifluoromethyl-6-methylxymethyl)phenyl]-2-(1-
N-[(2-trifluoromethyl-6-methylxymethyl)phenyl]-2-
propylamine) acetylamide hydrochloride (18a)
piperidino acetylamide hydrochloride (18e)
1
1
Yield 82%; mp 167–170 °C; H-NMR (500 MHz, CD3OD)
Yield 81%; mp 101–103 °C; H-NMR (500 MHz, CD3OD)
δ 1.03 (3H, t, J = 7.5 Hz, 3′-CH3), 1.76 (2H, m, 2′-CH2),
3.05 (2H, t, J = 8.0 Hz, 1′-NCH2), 3.30 (3H, s, –OCH3),
4.06 (2H, m, 2-COCH2), 4.46 (2H, s, Ar–CH2O–), 7.56
(1H, m, ArH), 7.72 (1H, m, ArH), 7.78 (1H, m, ArH);
δ 3.30 (3H, s, –OCH3), 3.33 (2H, m, 1′-NCH), 3.57 (2H, m,
5′-NCH2), 3.89 (2H, m, 2′-OCH2), 4.05 (2H, m, Ar–CH2O-
), 4.30 (2H, m, 2-OCH2), 4.47(2H, m, 4′-CH2O), 7.57 (1H,
m, ArH), 7.71 (1H, m, ArH), 7.78 (1H, m, ArH); IRνmax
(KBr, cm−1) 3414, 1685, 1325, 1166, 1125; ES-MS (m/z)
[M + H]+: 333; anal. calcd for C15H19F3N2O3.HCl.H2O: C,
46.58; H, 5.73; N, 7.24. Found C, 46.83; H, 5.99; N, 7.37.
IRνmax (KBr, cm−1) 3269, 2943, 2886, 1681, 1542, 1325;
+
ES-MS (m/z) [M + H]
:
305; anal. calcd for
C14H19F3N2O2.HCl: C, 46.87; H, 6.17; N, 7.81. Found C,
47.13; H, 6.17; N, 7.89.
N-[(2-trifluoromethyl-6-methylxymethyl)phenyl]-2-(1-
N-[(2-trifluoromethyl-6-methylxymethyl)phenyl]-2- (N,N-
propylamine) propionamide hydrochloride (19a)
diethylamine) acetylamide hydrochloride (18b)
1
Yield 96%; mp 96–98 °C; H-NMR (500 MHz, CD3OD) δ
1
Yield 80%; mp 165–168 °C; H-NMR (500 MHz, CD3OD)
1.03 (3H, t, J = 7.5 Hz, 3′-CH3), 1.70 (3H, d, J = 6.6 Hz, 3-
CH3), 1.80 (2H, m, 2′-CH2), 3.00 (2H, D, J = 6.6 Hz, 1′-
NCH2), 3.30 (3H, s, –OCH3), 4.17 (1H, m, 2-COCH), 4.45
(2H, s, Ar–CH2O-), 7.58 (1H, m, ArH), 7.77 (2H, m, ArH);
IRνmax (KBr, cm−1) 3152, 2975, 1702, 1536, 1465, 1326,
1163; ES-MS (m/z) [M + H]+: 319; anal. calcd for
C15H21F3N2O2.HCl: C, 50.78; H, 6.25; N, 7.90. Found C,
50.68; H, 6.40; N, 7.76.
δ 1.37 (6H, t, J = 7.2 Hz, 2′-CH3), 3.30 (3H, s, –OCH3),
3.36 (4H, m, 1′-NCH2), 4.20 (2H, m, Ar–CH2O-), 4.47 (2H,
s, 2-COCH2), 7.59 (1H, m, ArH), 7.77 (2H, m, ArH);
IRνmax (KBr, cm−1) 3519, 2947, 1688, 1538, 1467, 1391;
+
ES-MS (m/z) [M + H]
:
319; anal. calcd for
C15H21F3N2O2.HCl: C, 50.78; H, 6.25; N, 7.90. Found C,
50.75; H, 6.40; N, 7.70.

Medicinal Chemistry Research
N-[(2-trifluoromethyl-6-methylxymethyl)phenyl]-2-(N,N-
Biological evaluation
diethylamine) propionamide hydrochloride (19b)
The sciatic nerve block activities in toads of the objective
compounds were determined as previously described (Li
et al. 2017). Electrophysiological experimental data were
obtained on Doctor-95 Super Lab (Jiangsu Medicine tech-
nological institute). All the experiments were tested with the
isolated sciatic nerves of wild adult toads. Lidocaine was
got from Shanghai Xidi Biotech. Co., Ltd and was tested
after dissolving in Ringer’s solutions. Record the experi-
mental data. The regress equation of AP decreasing extent
(%) and compounds concentration was y = blogx + a (y: AP
decreasing extent (%); x: drug concentration; a, b: regress
coefficient). The regress equation of latent period and
compounds concentration was y = blogx + a (y: latent per-
iod; x: drug concentration; a, b: regress coefficient). The
ED50 and latent time were calculated by those equations.
1
Yield 84%; mp 121–123 °C; H-NMR (500 MHz, CD3OD)
δ 1.36 (6H, d, J = 7.5 Hz, 2′-CH3), 1.72 (3H, m, 3-CH3),
3.30 (3H, s, –OCH3), 3.33 (4H, m, 1′-NCH2), 4.27 (1H, m,
2-COCH), 4.47(2H, s, Ar–CH2O–), 7.59 (1H, m, ArH),
7.77 (2H, m, ArH); IRνmax (KBr, cm−1) 3147, 2983, 1693,
1527, 1324, 1162; ES-MS (m/z) [M + H] +: 333; anal. calcd
for C16H23F3N2O2.HCl: C, 50.78; H, 6.25; N, 7.90. Found
C, 50.88; H, 6.25; N, 7.69.
N-[(2-trifluoromethyl-6-methylxymethyl)phenyl]-2-
pyrrolidino propionamide hydrochloride (19c)
1
Yield 81%; mp 218–220 °C; H-NMR (500 MHz, CD3OD)
δ 1.73 (3H, m, 3-CH3), 2.20 (4H, m, 2′-CH2, 3′-CH2), 3.29
(2H, m, 1′-NCH, 4′-NCH), 3.34 (3H, s, –OCH3), 3.67 (2H,
m, 1′-NCH, 4′-NCH), 4.34 (1H, m, 2-COCH), 4.47 (2H, d,
J = 11.5 Hz, Ar–CH2O-), 7.57 (1H, m, ArH), 7.76 (2H, m,
ArH); IRνmax (KBr, cm-1) 3110, 2951, 1685, 1535, 1321,
1163; ES-MS (m/z) [M + H] +: 331; anal. calcd for
C16H21F3N2O2.HCl: C, 52.39; H, 6.05; N, 7.64. Found C,
52.10; H, 6.32; N, 7.65.
Molecular docking studies
In this research, the crystal structures of VGSC (PDB code:
6AGF), GABAA-R (PDB code: 6D1S), and NMDA-R
(PDB code: 5I2N) were obtained from RSCB Protein Data
Bank, and the docking studies were performed on the
software program MOE 2015.10. The preparation of the
docking study has two parts, the pretreatment of receptor
proteins and ligands. Firstly, under Amber 10: EHT force
field, these protein structures are processed using the default
parameters of the Quickprep module: adding hydrogen
atoms, removing water, and repairing missing residues.
After pretreatment, the protonation state of the residues was
determined under the condition of pH = 7. Next, the three-
dimensional structures of compounds 10a, 14e, and lido-
caine were constructed under Amber 10: EHT force field
and the conformational database of structures were provided
for further docking study by energy minimization and
conformation search. Finally, all conformations were
docked into the binding sites of three different receptor
proteins using the Induced Fit protocol under default para-
meters, and the amino acid residues within 6 Å of the
ligand, and ligands were set to be flexible. The docking
poses were obtained by the Triangle Matcher method and
scored by GBVI/WSA dG. And the docking results held 20
docking postures per ligand with default parameters for
further visual analysis.
N-[(2-trifluoromethyl-6-methylxymethyl)phenyl]-2-
piperidino propionamide hydrochloride (19d)
1
Yield 74%; mp 180–183 °C; H-NMR (500 MHz, CD3OD)
δ 1.60 (2H, m, 2′-CH2), 1.70 (3H, m, 3-CH3), 1.88 (4H, m,
3′-CH2, 4′-CH2), 3.09 (2H, m, 1′-NCH, 5′-NCH), 3.30 (3H,
s, –OCH3), 3.64 (2H, m, 1′-NCH, 5′-NCH), 4.18 (1H, m, 2-
COCH), 4.48(2H, m, Ar–CH2O-), 7.58 (1H, m, ArH), 7.77
(2H, m, ArH); IRνmax (KBr, cm−1) 3092, 2939, 1690, 1532,
1466, 1386, 1319, 1161; ES-MS (m/z) [M + H]+: 345; anal.
calcd for C17H23F3N2O2.HCl: C, 53.61; H, 6.35; N, 7.36.
Found C, 53.57; H, 6.57; N, 7.45.
N-[(2-trifluoromethyl-6-methylxymethyl)phenyl]-2-
piperidino propionamide hydrochloride (19e)
1
Yield 79%; mp 235–238 °C; H-NMR (500 MHz, CD3OD)
δ 1.76 (3H, d, J = 6.6 Hz, 3-CH3), 3.36 (3H, s, –OCH3),
3.39 (2H, m, 1′-NCH2), 3.41 (2H, m, 5′-NCH2), 3.82 (2H,
m, 2′-OCH2), 4.08(2H, M, Ar–CH2O-), 4.27(1H, m, 2-
COCH), 4.53 (2H, m, 4′-OCH2), 7.60 (1H, m, ArH), 7.77
(2H, m, ArH); IRνmax (KBr, cm−1) 3100, 2943, 1688, 1532,
1320, 1165; ES-MS (m/z) [M + H]+: 347; anal. calcd for
C16H21F3N2O3.HCl: C, 50.20; H, 5.79; N, 7.32. Found C,
50.20; H, 6.04; N, 7.31.
Conclusion
In this paper, we presented the synthesis, sciatic nerve block
activities, dissociation constants and molecular docking

Medicinal Chemistry Research
results of fluoro-substituted lidocaine analogs. Twelve of
compounds displayed significant potency higher than or
similar to that of the reference compound lidocaine.
Twenty-five of these compounds had shorter latent periods
than that of lidocaine. Fifteen of them showed pKa values
of 7.5–7.8 suitable for local anesthesia. Among these, 10a
was the most favorable analog proving the highest potency,
relatively short latent periods and suitable pKa. The mole-
cular docking results identified the hydrophobic interactions
and hydrogen bonding formed by compounds 10a and
lidocaine and receptor proteins VGSC, GABAA-R and
NMDA-R, which may be crucial in optimization and pre-
diction of the sciatic nerve block activities of the lidocaine
analogs in local anesthesia. Most importantly, this work
verified our initial proposition that substitution with a tri-
fluoromethyl group at the benzene ring of lidocaine could
induce higher local anesthetic activity and shorter latent
periods.
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Acknowledgements This work was supported by a grant from Jiangsu
Hengrui Pharmaceutical Com. Ltd and a foundation on the integration
of industry, education, and research of He’nan science and technology
commission (No. 152107000041). The authors are grateful to Dr J.H.
Fu (Pharmaceutical School, China Pharmaceutical University) for the
determination of biological activity. We thank Amy Tong from Liwen
Bianji, Edanz Editing China (www.liwenbianji.cn/ac), for editing the
English draft of this paper.
Compliance with ethical standards
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Conflict of interest The authors declare that they have no conflict of
interest.
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Publisher’s note: Springer Nature remains neutral with regard to
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