Pharmacological and structure-activity relationship evaluation of 4-aryl-1-Diphenylacetyl(thio)semicarbazides

Article abstract of DOI:10.3390/molecules19044745

This article describes the synthesis of six 4-aryl-(thio)semicarbazides (series a and b) linked with diphenylacetyl moiety along with their pharmacological evaluation on the central nervous system in mice and computational studies, including conformational analysis and electrostatic properties. All thiosemicarbazides (series b) were found to exhibit strong antinociceptive activity in the behavioural model. Among them, compound 1-diphenylacetyl-4-(4-methylphenyl)thiosemicarbazide 1b was found to be the most potent analgesic agent, whose activity is connected with the opioid system. For compounds from series a significant anti-serotonergic effect, especially for compound 1-diphenylacetyl-4- (4-methoxyphenyl)semicarbazide 2b was observed. The computational studies strongly support the obtained results.

Full text of DOI:10.3390/molecules19044745

Molecules 2014, 19, 4745-4759; doi:10.3390/molecules19044745
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Pharmacological and Structure-Activity Relationship
Evaluation of 4-aryl-1-Diphenylacetyl(thio)semicarbazides
Monika Wujec 1,*, Ewa Kędzierska 2, Edyta Kuśmierz 1, Tomasz Plech 1, Andrzej Wróbel 3,
Agata Paneth 1,4, Jolanta Orzelska 2, Sylwia Fidecka 2 and Piotr Paneth 4
1
Department of Organic Chemistry, Medical University, Chodźki 4a, 20-093 Lublin, Poland;
E-Mails: monika.wujec@umlub.pl (M.W.); edyta.kusmierz@umlub.pl (E.K.);
tomasz.plech@umlub.pl (T.P.); agata.siwek@umlub.pl (A.P.)
2
Department of Pharmacology and Pharmacodynamics, Medical University, Chodźki 4a,
20-093 Lublin, Poland; E-Mails: ewa.kedzierska@umlub.pl (E.K.);
jolanta.orzelska@umlub.pl (J.O.); sylwia.fidecka@umlub.pl (S.F.)
3
History of Medical Sciences Department, Medical University, Szkolna 18, 20-124 Lublin, Poland;
E-Mail: wand@bg.umlub.pl
4
Institute of Applied Radiation Chemistry, Technical University of Lodz, Zeromskiego 116,
90-924 Lodz, Poland; E-Mail: piotr.paneth@p.lodz.pl
* Author to whom correspondence should be addressed; E-Mail: monika.wujec@umlub.pl;
Tel./Fax: +48-081-535-7351.
Received: 7 February 2014; in revised form: 27 March 2014 / Accepted: 3 April 2014 /
Published: 16 April 2014
Abstract: This article describes the synthesis of six 4-aryl-(thio)semicarbazides (series a
and b) linked with diphenylacetyl moiety along with their pharmacological evaluation on
the central nervous system in mice and computational studies, including conformational
analysis and electrostatic properties. All thiosemicarbazides (series b) were found to
exhibit strong antinociceptive activity in the behavioural model. Among them, compound
1-diphenylacetyl-4-(4-methylphenyl)thiosemicarbazide 1b was found to be the most potent
analgesic agent, whose activity is connected with the opioid system. For compounds from
series a significant anti-serotonergic effect, especially for compound 1-diphenylacetyl-4-
(4-methoxyphenyl)semicarbazide 2b was observed. The computational studies strongly
support the obtained results.
Keywords: (thio)semicarbazides; conformational analysis; electrostatic properties; CNS
activity; analgesic activity; serotonergic activity

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1. Introduction
It is well known that many diseases are accompanied by inflammation and pain. Therefore, the
search for new compounds with a large spectrum of biological activities is an important focus of
attention for chemists as well as for pharmacologists. Semicarbazides and thiosemicarbazides appear to
be ideal candidates for pharmacologically significant scaffolds. It follows from the literature that
thiosemicarbazide derivatives possess a wide range of pharmacological activities such as
antituberculosis [1,2], antiviral [3,4], anti-inflammatory [5], anticonvulsant [6–8], analgesic [5],
antibacterial [9–11], antifungal [12,13], and anticancer properties [14].
Semicarbazides are also an important class of molecules with a large spectrum of biological
properties. These compounds have been studied as anticonvulsant [15], antitubercular [16] and
antinociceptive [17–19] agents. Additionally semicarbazides with aryl substitution are reported to
display excellent anticonvulsant activity in mice and rats compared to that of phenytoin [20]. It is
important to note that some of tested compounds showed lesser CNS depression and behavioural
despair side effects than the conventional antiepileptic drugs [7], and were defined as lead molecules in
the design of potent anticonvulsant drugs [8]. Based on these facts, many (thio)semicarbazides and
their cyclic analogues have been synthesized in our laboratory and their antimicrobial and CNS system
bioactivity was studied [10,21,22]. This work is continuation of our efforts to find bioactive
(thio)semicarbazides with central nervous system pharmacological activity in mice.
2. Results and Discussion
2.1. Chemistry
The synthetic route employed for the preparation of the title 4-aryl-1-diphenylacetyl(thio)semicarbazides
(series a and b) is shown in Scheme 1. As can be seen, a simple synthesis was carried out, starting
from the commercially available diphenylacetic acid hydrazide and the appropriate iso(thio)cyanates.
At the end of the reaction, the isolated (thio)semicarbazide derivatives were obtained as white coloured
solids. This procedure was adapted from an procedures previously reported by Kusmierz et al. [23] and
Wujec et al. [24] and gave us satisfactory yields.
Scheme 1. Synthetic route for 4-aryl-1-diphenylacetylsemicarbazides (series a) and
4-aryl-1-diphenylacetylthiosemicarbazides (series b).
NC
R
X
R
X
= O, S
X
series : = O, = 4-CH3Ph, = 4-OCH3Ph, = 4-OC2H5Ph
a X
1
2
3
series
:
= S, = 4-CH3Ph, = 4-OCH3Ph, = 4-OC2H5Ph
b X 1 2 3

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2.2. Pharmacological Activity
The results of the pharmacological investigation showed that both groups of tested compounds—
semicarbazides (series a) and thiosemicarbazides (series b)—exerted significant influence on the
central nervous system (CNS) of laboratory animals. All substances exhibited very low toxicity: over
2,000 mg/kg (i.p.), therefore an ED50 = 2,000 mg/kg was accepted, and regressive doses of 200 and
100 mg/kg (i.p.; 0.1 and 0.05 ED50 respectively) were used for further studies.
Semicarbazide derivatives (series a) seem to affect serotonergic neurotransmission, since all
compounds inhibited significantly L-5-HTP-induced head-twitches (Figure 1). The drug-elicited
head-twitch response (HTR) [25,26] is a selective behavioural model for 5-HT2 agonist activity in
rodents, and several previous studies have established that direct and indirect 5-HT agonists induce this
effect [27–32]. Furthermore, 5-HT2 receptor antagonists selectively block HTR [30,33,34], and their
potency is highly correlated with the antagonist’s affinity for 5-HT2 receptors [25,35].
Figure 1. The influence of 1a, 2a and 3a on “head-twitch” responses (HTR) evoked by
L-5-HTP (200 mg/kg). One-way ANOVA showed significant changes in the number of
HTR [F(3.40) = 16.49; p < 0.0001]. Post hoc Dunnett’s test confirmed a significant reduction
in HTR of mice after the administration of the compound 1a, 2a and 3a in the dose of
0.1 ED50 (p < 0.001).
8
control
0.1 ED50
6
*** p < 0.01
vs control
4
***
2
***
***
0
1a
3a
2a
In addition, compounds 2a and 3a substantially decreased the body temperature of normothermic
mice (Figure 2), which also may confirm the involvement of serotonergic system. Serotonin has been
reported to play an important role in central regulation of body temperature [36]. The MAO
(monoamine oxidase) type A inhibitors appear to be crucially involved in hypothermia [37].
Hypothermia in rodents has been reported for MAO (monoamine oxidase) type A enzyme inhibitors
such as clorgyline [38] and harman (1-methyl-β-carboline) [39]. As a result of MAO-inhibition, 5-HT
levels in the body are increased and may precipitate a serotonin syndrome.

Molecules 2014, 19
Figure 2. The influence of compound 2a and 3a (used in a dose of 0.1 ED50) on the body
4748
temperature of the mice. Two-way ANOVA revealed significant effects for both
compounds [F(2.142) = 22.14; p < 0.0001] and time [(F(5.142) = 6.22; p < 0.0001], but not
interaction [F(10.142) = 1.57; p = 0.122]. Post hoc Bonferroni test confirmed a significant
decrease in the body temperature of the mice after the administration of compound 2a in
the dose of 0.1 ED50 in 60 and 90 min (p < 0.001), and compound 3a in the dose of
0.1 ED50 in 30 min (p < 0.001), 60 and 90 min (p < 0.05).
control
0.1 ED50 2a
0.1 ED50 3a
Δ°C
1.0
0.5
0.0
*
-0.5
-1.0
-1.5
*
**
**
**
180 [min]
0
30
60
90
120
150
All series a compounds decreased the locomotor activity of the mice (Figure 3), which seem to
suggest their depressive effects on the CNS [40], while none of them changed the hyperactivity caused
by administration of amphetamine. Tested series a compounds did not show antinociceptive activity in
a “writhing” test.
Figure 3. The influence of 1a, 2a and 3a on the spontaneous locomotor activity of mice.
One-way ANOVA showed significant changes in locomotor activity of mice [F(6.49) = 6.857;
p < 0.0001]. The post hoc Dunnett’s test confirmed a significant reduction in motility of
mice after the administration of the compound 1a in the dose of 0.1 ED50 (p < 0.001) and
compounds 2a, 3a in the dose of 0.1 ED50 (p < 0.01).
400
300
200
100
0
control
0.1 ED50
0.05 ED50
** p < 0.01
*** p < 0.001
vs control
**
**
***
1a
2a
3a

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Thiosemicarbazide derivatives (series b) exerted antinociceptive activity on mice in the “writhing”
test, with compound 1b (in the dose of 0.1 ED50) causing the strongest reaction (Figure 4). Naloxone
completely reversed this effect which seems to suggest the endogenous opioid system’s contribution
(Figure 5) [41]. In other performed tests, these substances were not active.
Figure 4. The antinociceptive effects of 1b, 2b and 3b assessed in the ‘writhing’ test in
mice. One-way ANOVA showed significant changes in the number of writhing episodes of
mice after the administration of compounds 1b, 2b and 3b (F6.58 = 4.725, p < 0.001). Post
hoc Dunnett’s test confirmed a significant reduction in the writhing episodes of mice after
the administration of the compound 1b in the dose of 0.1 ED50 (p < 0.01) and compounds
2b and 3b in the dose of 0.1 ED50 (p < 0.05).
20
15
10
5
control
0.1 ED50
0.05 ED50
* p < 0.05;
** p < 0.01
vs control
*
*
**
0
1b
2b
3b
Figure 5. The influence of naloxone, 5 mg/kg, s.c. on antinociceptive activity of 1b, 2b
and 3b evaluated in the “writhing” test. One-way ANOVA showed significant changes in
the number of writhing episodes of mice after the administration of compounds 1b, 2b and
3b (F6.67 = 6.589, p < 0.0001). Post hoc Dunnett’s test confirmed a significant reduction in
the writhing episodes of mice after the administration of the compound 1b in the dose of
0.1 ED50 (p < 0.001), 2b in a dose of 0.1 ED50 (p < 0.01) and 3b in a dose of 0.1 ED50
(p < 0.05). Naloxone inhibited antinociceptive action of 1b (p < 0.001 vs. compound 1b;
post hoc Dunnett’s test).
control
25
20
15
10
5
0.1 ED50
0.1 ED50 + naloxone 5 mg/kg
^^^
*
p < 0.05
** p < 0.01
*** p<0.001
vs control
^^^ p < 0.001 vs compound
**
*
***
0
1b
2b
3b

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4750
Both investigated series of compounds a and b did not cause any coordination impairments as
measured in the rota-rod and chimney tests. These results show the lack of neurotoxicity, and muscle
relaxant potency of the substances, this is important because it can change the results of other tests
(e.g., motility test) and affecting reliability of the tests results [38]. Moreover, pentetrazole-induced
seizures were not affected by the compounds of either series.
2.3. Computational Part
It is not surprising that high protein(s) specificity results in significantly different biological activity
of closely related compounds. Nonetheless frequently computational modeling allows to rationalize
observed bioactivities and provides background for rational design of molecules with expected
bioactivity. In particular, electrostatic properties have been recently correlated with the binding affinity
of low molecular weight heterocycles to various receptors and enzymes involved in CNS. In the light
of these facts, we have compared the electrostatic and geometrical properties of studied compounds in
hope of gaining some insight into their bioactivity.
The structures of molecules from series a and b were optimized at the molecular mechanics level
with the OPLS force field which has been shown to correctly described both the geometries and the
energetic of these classes of compounds [42]. As illustrated in Figure 6, OPLS-optimized structures of
semicarbazides a and thiosemicarbazides b exhibit some differences: both oxygen atoms of the
C(=O)–NH–NH–C–(=O) core in a are located on opposite sides of molecule (a “trans”conformation)
while the oxygen and sulphur atoms of the C(=O)–NH–NH–C–(=S) core in b are on the same sides
(“cis” conformation). Another observation that comes from the analysis of the presented structures is
that the benzoyl ring at N4 position of semicarbazide a is almost in the same plane with the
C(=O)–NH–NH–C–(=O) core, while in b it is nearly perpendicular to C(=O)–NH–NH–C–(=S)
(Figure 1). These results together might imply that differentiation of the biological activity of tested
semicarbazides a and thiosemicarbazides b originates in the molecular shape. Following this finding,
we analyzed the geometry of a and b in details. As shown in Figure 7, the geometries of 1a and 3a
(Figure 7, top) are practically identical, but they differ significantly from the most active
anticonvulsant agent 2a, mainly in the orientation of phenyl rings (Figure 7, bottom). Thus, the
geometry of molecule might be important for the antiserotonergic activity of semicarbazide derivatives
a. Unfortunately, comparison of the molecular shape of thiosemicarbazides b did not show any
recognizable relationship with their antinociceptive activity (data not shown).
The assumption of the existence of the relationship between bioactivity of studied
(thio)semicarbazides a and b and their molecular structure can be further inferred from the
corresponding dipole moments of the molecules. As seen in Figure 6, dipole moments for series a are
1.58, 0.92, 0.97 D, while for series b are 7.04, 6.34, 6.42 D, respectively. These values show that
electrostatic distribution in the series a differs significantly from that in the series b. This can be
explained mainly by the geometry of series a that, as it was mentioned above, differs significantly
from that in the series b.

Molecules 2014, 19
Figure 6. Molecular shapes of semicarbazides a (left) and thiosemicarbazides b (right)
4751
optimized at the molecular mechanics level with OPLS force field.
1a (1.58 D)
1b (7.04 D)
2a (0.92 D)
2b (6.34 D)
3a (0.97 D)
3b (6.42 D)
Within series a the best antiserotonergic activity was noted for derivative with the lowest dipole
moment value (compound 2a). This suggest that the dipole moment might be a good descriptor for the
(Q)SAR studies relating antiserotonergic activity to the structure. Unfortunately, no close correlation
could be deducted from the generated electrostatic potential surfaces (Figure 8). When the
antinociceptive activity of thiosemicarbazides b is considered, it seems that the observed bioactivity
correlates with charge density around the oxygen atom of the methoxy (compound 2b) and ethoxy
group (compound 3b). Its lack in 1b may be responsible for its higher activity (Figure 8).

Molecules 2014, 19
Figure 7. Overlay of structures of 1a (balls and sticks) and 3a (sticks) (top) and 1a (sticks)
4752
and 2a (balls and sticks) (bottom).
Figure 8. The electrostatic potential surfaces of semicarbazides a and thiosemicarbazides b.
1a
1b

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Figure 8. Cont.
2a
2b
3a
3b
3. Experimental
3.1. General Information
The reagents were purchased from Sigma-Aldrich (St. Louis, MS, USA) or Lancaster (Ward Hill,
NY, USA) and were used without further purification. The melting points were determined on a
Fisher-Johns block and are uncorrected. Elemental analyses (within ±0.4% of theoretical values) were
determined by a AMZ-CHX elemental analyzer (PG, Gdańsk, Poland). IR spectra was recorded in KBr
using a Specord IR-75 spectrophotometer (Carl Zeiss, Jena, Germany). ¹H-NMR spectrum was
recorded on a Bruker Avance (300 MHz) spectrometer (Bruker BioSpin GmbH, Rheinstetten,
Germany). Analytical thin layer chromatography was performed with Merck 60F254 silica gel plates
(Merck Co., Darmstadt, Germany) visualized by UV irradiation (254 nm).

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3.2. Chemistry
3.2.1. General Procedure for the Synthesis of 4-aryl-1-Diphenylacetylsemicarbazides 1a and 2a
A reaction mixture of diphenylacetic acid hydrazide (0.01 mol) and related isocyanate (0.01 mol) in
diethyl ether (10 mL) was kept in room temperature for 24 h, then the compound formed was filtered
off and crystallized from ethanol.
1
1-Diphenylacetyl-4-(4-methylphenyl)semicarbazide (1a). Yield: 93%. Mp. 205–207 °C. H-NMR
(DMSO-d6)  (ppm): 2.49 (s, 3H, CH3); 5.00 (s, 1H, CH); 6.95–7.36 (m, 14H, CHarom); 8.10 (s, 1H,
NH); 8.63 (s, 1H, NH); 10.15 (s, 1H, NH). IR (KBr, ν, cm−1): 3350, 2800, 1675, 1540, 1478, 1355.
Anal. Calc. for C22H21N3O2 (359.42): C 73.52, H 5.89, N 11.69. Found: C 73.48, H 5.77, N 11.70.
1
1-Diphenylacetyl-4-(4-methoxyphenyl)semicarbazide (2a). Yield: 89%. Mp. 194–196 °C. H-NMR
(DMSO-d6)  (ppm): 3.32 (s, 3H, OCH3); 5.00 (s, 1H, CH); 6.82–7.35 (m, 14H, CHarom); 8.04 (s, 1H,
NH); 8.53 (s, 1H, NH); 10.12 (s, 1H, NH). IR (KBr, ν, cm−1): 3356, 2800, 1680, 1540, 1488, 1360.
Anal. Calc. for C22H21N3O3 (375.42): C 70.38, H 5.64, N 11.19. Found: C 70.45, H 5.67, N 11.25.
3.2.2. Procedure for the Synthesis of 4-(4-Ethoxyphenyl)-1-(diphenylacetyl)semicarbazide 3a and
4-Aryl-1-(diphenylacetyl)thiosemicarbazides 1b–3b
A reaction mixture of diphenylacetic acid hydrazide (0.01 mol) and 4-ethoxyphenylisocyanate or
related isothiocyanate (0.01 mol) was heated in an oil bath at 70–80 °C and progress of reaction was
monitored by thin layer chromatography. After 10–12 h, the reaction was completed and the crude
reaction mixture was washed with diethyl ether and crystallized from ethanol. Physicochemical data
for compounds 1b, 2b, and 3b were presented in our previous papers [21].
1
4-(4-Ethoxyphenyl)-1-diphenylacetylsemicarbazide (3a). Yield: 93%. Mp. 205–207 °C. H-NMR
(DMSO-d6)  (ppm): 1.27, 1.29, 1.31 (t, 3H, CH3, J = 6.9 Hz); 3.92, 3.94, 3.96, 4.01 (q, 2H, CH2,
J = 6.9 Hz); 5.00 (s, 1H, CH); 6.81–7.34 (m, 14H, CHarom); 8.05 (s, 1H, NH); 8.53 (s, 1H, NH); 10.14
(s, 1H, NH). IR (KBr, ν, cm−1): 3365, 2805, 1680, 1530, 1460, 1340. Anal. Calc. for C23H23N3O3
(389.45): C 70.93, H 5.95, N 10.79. Found: C 70.98, H 5.90, N 10.70.
3.3. Pharmacology
The experiments were performed on male Albino Swiss mice (16–30 g). 8–10 animals were kept in
a cage, at room temperature of 22 ± 1 °C, on a natural dark-light cycle with free access to food (LSM,
Motycz, Poland) and water. All experiments were performed in accordance with the opinion of The
Local Ethics Committee for Animal Experimentation.
All substances were administered intraperitoneally (i.p.), as suspensions in aqueous solution of
0.5% methylcellulose (tylose) and were injected 60 min before tests. In the “writhing” procedure,
the investigated compounds were injected subcutaneously (s.c.) because the acetic acid (0.6%) was
administered i.p. All substances were given in a volume of 0.1 mL per 10 g of body weight.
The control animals received an equivalent volume of the solvent at the respective time before the test.

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All tests performed, suggested by [38], are generally accepted as basic in investigation of the central
activity by behavioural methods. The acute toxicity of the compounds were assessed acc. to Litchfield
and Wilcoxon method [43], as the ED50 calculated as “the loss of righting reflex” within 48 h. The
compounds were injected in doses equivalent to 0.1 ED50 (200 mg/kg) and 0.05 ED50 (100 mg/kg). In
addition, the activity of the compounds was assessed in the following tests:
Locomotor activity was measured in photocell apparatus (round Plexiglas cage, 32 cm, Multiserv,
Lublin, Poland) for a single mouse for 30 min as:
(a) spontaneous activity
(b) amphetamine-induced hyperactivity: mice received s.c. 5 mg/kg of amphetamine 30 min
before the test;
Nociceptive reactions were studied in the acetic acid (0.6%)—Induced “writhing” test [44]—
The number of writhing episodes was measured for 10 min, starting 5 min after i.p. administration of
acid solution;
Motor coordination was evaluated in the rota-rod [45]—motor impairments, defined as the inability
to remain on the rotating rod for 1 min were measured and the mean time spent on the rota-rod was
counted for each mouse, and in the chimney test [46]—motor impairments were indicated by the
inability to perform the test within 1 min;
Body temperatue in normothermic mice was measured in the rectum of animals with a thermistor
thermometer and was recorded 30, 60, 90, 120, 150 and 180 min after the injection of investigated
compounds in the doses of 0.1 and 0.05 ED50 i.p.;
Pentylenetetrazole-induced convulsions (PTZ, 110 mg/kg, s.c.) were evaluated as the number of
mice with clonic seizures, tonic convulsions and dead animals;
Head twitch responses (HTR) after 5-hydroxy-L-tryptophan (L-5-HTP) administration, were
estimated acc. to Corne et al. [23]. Mice received L-5-HTP (200 mg/kg, i.p.) and the number of HTR
was recorded in 6 two-minutes intervals (4–6, 14–16, 24–26, 34–36, 44–46, 54–56 min) during 1 h;
Influence of naloxone on the antinociceptive effect (5 mg/kg, s.c.) of the compounds was assessed in
the “writhing” test.
3.4. Statistics
Obtained data were calculated by Fisher exact test (PTZ-induced seizures), two-way analysis of
variance (ANOVA) followed by Bonferroni post hoc test (body temperature) and one-way ANOVA
followed by Dunnett’s post hoc test (other tests). All results are presented as means ± SEM. p < 0.05
was considered as statistically significant.
3.5. Computational Part
Computational procedure described previously [9] has been followed; extensive conformational
searches were carried out using the molecular mechanics level with OPLS [47] force field as
implemented in HyperChem8.0.3 [48]. The most stable structures obtained were subsequently

Molecules 2014, 19
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optimized to the closest local minimum at the semiempirical level using RM1 parametrization.
Convergence criteria were set to 0.1 and 0.01 kcal/mol/Å for OPLS and RM1 calculations,
respectively. Electrostatic potentials were calculated and visualized using Gaussian 09 and GaussView
5 [49], respectively at the HF/6-31G level [50].
4. Conclusions
In this contribution, a pharmacological evaluation of the activity of six (thio)semicarbazide
derivatives on the central nervous system in mice was performed. The results suggest a possible
involvement of the serotonin system in the effects of compounds series a, whereas the opioid system
apppears to be involved in the effects of compound 1b. The precise mechanism, however, remains
elusive and future studies are needed. Computational analysis suggest that the dipole moment and
geometry of molecule might be a good descriptors for the (Q)SAR studies of novel (thio)semicarbazides
as potent antiserotonergic and antinociceptive agents.
Author Contributions
M.W., A.P. designed research; M.W., A.P., E.K., E.K.1, J.O., P.P. performed research and wrote
the paper; M.W., A.P., E.K., E.K.1, J.O., T.P., A.W., S.F., P.P. analyzed the data. All authors read and
approved the final manuscript.
Conflicts of Interest
The authors declare no conflict of interest.
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