Structure-activity relationship of s-triazoles and thiadiazoles as analgesics

Article abstract of DOI:10.1002/hc.20605

The influence of s-triazoles (6-9)and thiadiazoles (10-11) on the central nervous system of mice in some behavioral tests was investigated. It was found that compounds (10)and (11) are the possible candidates for further development as analgesic agents. The correlation between the molecular descriptors and analgesic potential has been studied by using the pattern recognition methods: principal component analysis (PCA) and hierarchical cluster analysis (HCA). Our results, however, showed that the relationship between molecular descriptors and analgesic activity of s-triazoles and thiadiazoles cannot be easily explained on the basis of PCA and HCA.

Full text of DOI:10.1002/hc.20605

Heteroatom Chemistry
Volume 21, Number 4, 2010
Structure–Activity Relationship of s-Triazoles
and Thiadiazoles as Analgesics
Agata Siwek,1 Monika Wujec,1 Tomasz Plech,1 Edyta Kus´mierz,1
Ewa Jagiełło-Wo´jtowicz,2 and Anna Chodkowska2
1Department of Organic Chemistry, Faculty of Pharmacy, Medical University, Staszica 6, 20-081
Lublin, Poland
2Department of Toxicology, Faculty of Pharmacy, Medical University, Chodzki 8, 20-093
Lublin, Poland
Received 11 October 2009; revised 31 March 2010
tigated [1–3]. Previous studies [2,3] have shown
ABSTRACT: The influence of s-triazoles (6–9) and
a strong analgesic activity of s-triazoles, having
thiadiazoles (10–11) on the central nervous system
furane or thiophene moiety. Furthermore, some of
of mice in some behavioral tests was investigated. It
tested compounds possessed anticonvulsant, antide-
was found that compounds (10) and (11) are the
pressive, and antiserotoninergic properties. In addi-
possible candidates for further development as anal-
tion, the promising results for azole-like compounds
gesic agents. The correlation between the molecular
as potent anti-inflammatory and analgesic agents
descriptors and analgesic potential has been studied
were described and discussed in several publications
by using the pattern recognition methods: principal
[4–9]. Promoted by these observations, we herein
component analysis (PCA) and hierarchical cluster
present preliminary evaluation of pharmacological
analysis (HCA). Our results, however, showed that
properties of four s-triazoles with pyrazine moiety
the relationship between molecular descriptors and
and, for comparison, two pyrazine-thiadiazoles. Al-
analgesic activity of s-triazoles and thiadiazoles can-
though most of the titled compounds are known,
not be easily explained on the basis of PCA and
their activities on central nervous system (CNS) have
ꢀ
C
HCA.
2010 Wiley Periodicals, Inc. Heteroatom Chem
not yet been reported.
21:256–264, 2010; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20605
Nowadays, structure–activity relationship (SAR)
studies have been proven to be helpful in the un-
derstanding of the influence of molecular properties
on the biological activity presented by several kinds
of compounds [10]. To this end, a large number of
various molecular descriptors have been proposed
for establishing the SAR and a number of program
packages have been developed for the calculations of
these descriptors [11]. However, the practice showed
that the number of molecular descriptors accessible
for the calculation can be significantly greater than
the number of compounds in the teaching set. Such a
relation between the number of descriptors and that
of compounds in the teaching set makes highly prob-
able the appearance of accidental correlations and
classification rules, which describe well the learn-
ing set as such but are incapable of predicting the
INTRODUCTION
Many compounds bearing an azole ring in their
structure have an extensive spectrum of pharma-
cological activities. Therefore, s-triazoles and thia-
diazoles have been synthesized in our laboratory
for a long time and their anticonvulsant, antide-
pressant, and analgesic potentials have been inves-
Correspondence to: Agata Siwek; e-mail: agata.siwek@am.lublin
.pl.
c
ꢀ
2010 Wiley Periodicals, Inc.
256

Structure–Activity Relationship of s-Triazole and Thiadiazole as Analgesics 257
O
activity of new compound. In addition, molecular
descriptors used in the search for SARs—especially
descriptors belonging to the same type (such as topo-
logical indices of molecular connectivity of various
orders)—were frequently rather strongly correlated,
which led to additional difficulties. One possible ap-
proach to eliminating the aforesaid problems con-
sists of using so-called principal components (PCs)
[12]. Principal component analysis (PCA) is one of
the most popular chemometric method used to study
interdependencies between molecular descriptors,
to eliminate the correlation between the variables,
and to reduce dimensionality of the data [13].
N
N
NH2
NH
RNCS
O
N
N
NH
NH
NH
R
S
(1-5)
R = 2-FC6H4 (1), C6H11 (2), C4H9 (3), CH2CHCH2 (4), COOEt (5)
Thus, with the aim to correlate some molecu-
lar descriptors of s-triazoles and thiadiazoles and
their biological analgesic activity, PCA has been em-
ployed. To test the results obtained on the basis of
PCA method, another statistical analysis has been
performed. Because, in such cases, it is good practice
to apply a method leaning on a completely different
algorithm, the hierarchical cluster analysis (HCA)
has been used. This technique consists of grouping
samples into respective clusters according to their
similarities and differences. The results of a cluster-
ing method are generally reported in a plot (so-called
dendrogram), where the ordinate is the similarity be-
tween groups and the abscissa has no specific mean-
ing, but is used only to separate the clusters [14].
H2SO4 (for (10))
CH3COOH (for (11))
NaOH
N
NH
N
N
N
N
S
NH
R
N
S
R
N
N
(6-9)
(10-11)
R = 2-FC6H4 (6), C6H11 (7), C4H9 (8), CH2CHCH2 (9), C6H11 (10), COOEt (11)
SCHEME 1 Synthesis of 1-(pyrazin-2-ylcarbonyl)-4-sub-
stituted thiosemicarbazides (1–5), 4-substituted-5-(pyrazin-
2-yl)-s-triazole-3-thiones (6–9), and 2-aminosubstituted-5-
(pyrazin-2-yl)-1,3,4-thiadiazoles (10) and (11).
Pharmacological Evaluation
RESULTS AND DISCUSSION
Chemistry
Preliminary behavioral study showed that none of
the tested compounds (6–11) was found to show
neurotoxic activity because in the dose of 0.1 LD50
they did not affect the motor coordination of mice in
the “chimney test.” Interestingly, of the six examined
compounds, the most active compounds were thia-
diazoles (10) and (11). Compounds (10) and (11)
in the doses 0.025, 0.05, and 0.1 of LD50 showed
strong analgesic activity in the “writhing syndrome”
test. Among tested s-triazoles, only (6) and (7) in the
doses 0.05 and 0.1 of LD50 displayed the analgesic
effect. In addition, compound (7) in the doses 0.05
and 0.1 of LD50 showed antiserotoninergic activity in
the “head twitches” test as well as antiepileptic ac-
tion in the “pentetrazole-induced convulsions” test.
In the remaining tests, the title compounds did not
produce any significant activity on the CNS of mice.
Compounds (6) and (9) showed depressive activity
in mice; they significantly prolonged the thiopental
sleeping time in the “thiopental-induced sleep” test.
Compound (11) increased the tonic pentetrazole-
induced seizures as well as mortality of mice in the
The synthesis of the titled compounds (6–11) based
on a common procedure in this structural class
[15–18] is depicted in Scheme 1. In short, pyrazine-
2-carboxylic acid hydrazide was reacted with isoth-
iocyanates. Cyclization of the formed thiosemicar-
bazides (1–5) to the s-triazoles (6–9) occurred in the
presence of aqueous sodium hydroxide solution. The
thiadiazoles (10) and (11) were prepared by treat-
ment of (2) and (5) with sulfuric acid or glacial acetic
acid, respectively.
The structures of known compounds (2–4) and
(6–10) were confirmed by the results of elemen-
tal analysis, melting points, and spectroscopic data
compared to literature values [19–23]. The charac-
terization and spectral data of original compounds
1
(1), (5), and (11) are presented later. The H NMR
spectra of (6–9) show a sharp singlet at 14.21–14.58
ppm typical for the proton linked to N1, indicating
the presence the thione tautomer [24].
Heteroatom Chemistry DOI 10.1002/hc

258 Siwek et al.
“pentetrazole-induced convulsions” test. Compound
(8) was pharmacologically inactive.
point representing the compound (11), which has
the highest negative score on PC2, does not group
with either cluster. It is proper to note that this com-
pound is characterized by the highest value of the
PA parameter.
PCA and HCA of Variables
With the aim to correlate some structural param-
eters of s-triazoles and thiadiazoles and their anal-
gesic potential, we employed the chemometric meth-
ods PCA and HCA. For this evaluation, we included
title compounds (6–11) as well as compounds (12–
28) reported in the literature as having different de-
grees of analgesic activities [1–3,25–27] (Fig. 1).
Among 16 variables tested, the most impor-
tant descriptors found in our PCA analysis were
Vol, R, MW, ꢀELUMO-HOMO, ET, A (grid), ELUMO, PA,
and μ. The calculated values of these nine vari-
ables are presented in Table 1. It has been assumed
that the power must exceed the value of 0.900 (see
Table 2). The selected parameters were subjected to
the proper classification analysis.
The PCA results presented in Table 3 reveal that
the first four PCs explain 97.24% of the variance. Be-
cause the first two PCs explain a great percentage
of the variance (79.23%), further presentation of the
results will be shown on the basis of the aforesaid
two dimensions. In two generated dimensions (PC1
vs. PC2), two clusters of compounds comprising ac-
tive, moderately active, and inactive s-triazoles and
thiadiazoles have observed (see Fig. 2 and Table 4).
The loading values for the nine selected structural
descriptors have been described as well (see Fig. 3
and Table 5). According to the values displayed in
Table 5, PC1 and PC2 are expressed through the fol-
lowing equations:
To save time, money, and research animals, it
is crucial to develop efficient means of predicting
biological effects of untested compounds. One way
to accomplish the estimation of the pharmacologi-
cal profile of novel molecules is to construct mathe-
matical models, the so-called quantitative structure–
activity relationship (QSAR) models. The useful
tools in deriving multivariate QSARs are chemo-
metric methods such as PCA and HCA. Successful
applications of the use of PCA and HCA for the recog-
nition of lipophilicity, steric, and electronic proper-
ties as major determinants of analgesic activity of
cannabinoid compounds were described by Arroio
et al. [10] With this aim in mind, we employed the
same procedure to obtain the relationship between
the molecular descriptors and the analgesic activ-
ity of s-triazoles and thiadiazoles. Our results, how-
ever, revealed that the pattern recognition methods
PCA and HCA are far from being universally appli-
cable for screening new s-trazioles and thiadiazoles
as analgesic agents.
In conclusion, although we have found that com-
pounds (10) and (11) are a possible candidates for
further development as analgesic agents, our results
cannot be easily explain on the basis of PCA and HCA
methods.
EXPERIMENTAL
Chemistry
PC1 = −0.968 [Mw] − 0.717 [ELUMO
]
Melting points were determined on a Fischer–Johns
block and are uncorrected. Elemental analyses were
determined by an AMZ-CHX elemental analyzer
− 0.688 [ꢀELUMO-HOMO] − 0.977 [Vol]
+ 0.957 [ET] + 0.330 [μ] − 0.958 [Agrid
− 0.984 [R] + 0.301 [PA]
]
1
and are within 0.4% of the theoretical values. H
NMR spectra were recorded on a Bruker Avance
(300 MHz) spectrometer. The chemical shifts are ex-
pressed in parts per million (δ value) downfield from
tetramethylsilane as an internal standard. Analyti-
cal thin layer chromatography (TLC) was performed
with Merck 60F254 silica gel plates and visualized by
UV irradiation (254 nm). All of the chemicals used
in the syntheses were purchased from Sigma-Aldrich
and Lancaster and were used as such.
PC2 = −0.102 [Mw] + 0.565 [ELUMO
]
+ 0.030 [ꢀELUMO-HOMO] − 0.100 [Vol]
+ 0.187 [ET] + 0.470 [μ] − 0.151 [Agrid
+ 0.012 [R] − 0.794 [PA]
]
Based on the above-mentioned analysis, it may be in-
ferred that the first cluster of compounds (on the left-
hand side of the Fig. 2) shows higher values of such
structural descriptors as: ELUMO, R, Mw, ꢀELUMO-HOMO
,
Vol, and A (grid). The other cluster (on the right-
hand side of the Fig. 2) shows higher values for ET
and μ. Distinguished two clusters, however, include
both active and inactive molecules. The HCA results
were similar to the PCA ones as shown in Fig. 4. The
Synthesis of 1-(Pyrazin-2-ylcarbonyl)-4-
Substituted Thiosemicarbazides (1–5)
The mixture of pyrazin-2-carboxylic acid hydrazide
(0.01 mol) and isothiocyanate (0.01 mol) was heated
Heteroatom Chemistry DOI 10.1002/hc

Structure–Activity Relationship of s-Triazole and Thiadiazole as Analgesics 259
N
NH
N
NH
N
NH
S
S
S
S
S
S
N
N
N
O
CH3
12
13
14
Moderately active
Moderately active
Moderately active
CH3
CH3
CH3
N
NH
N
NH
N
NH
O
O
O
S
S
S
N
N
N
O
CH3
15
Moderately active
16
17
Moderately active
Moderately active
N
NH
N
NH
N
O
S
N
NH
N
S
S
Cl
N
N
N
S
N
NH
Cl
18
Moderately active
19
Active
20
Moderately active
F
N
NH
N
N
Cl
N
N
Cl
Cl
S
NH
N
S
NH
NH
NH
S
NH
O
Cl
Cl
Cl
21
Moderately active
22
Moderately active
23
Moderately active
N
N
N
NH
O
N
N
S
NH
Cl
N
F
S
NH
N
S
NH
O
O
O
Cl
24
Moderately active
25
Moderately active
26
Active
N
N
N
N
O
O
NH
NH
S
S
27
Inactive
28
Inactive
FIGURE 1 Chemical structures of s-triazoles and thiadiazoles studied.
Heteroatom Chemistry DOI 10.1002/hc

260 Siwek et al.
TABLE 1 Calculated Values for the Nine More Important Descriptors used in PCA and HCA Analyses
Compound
Vol
R
Mw
ꢀELUMO-HOMO
ET
A (grid)
ELUMO
PA
μ
6
7
8
9
729.77
749.71
698.89
634.13
759.02
702.68
687.67
748.16
728.90
714.32
722.89
752.17
825.02
999.15
1125.78
1133.89
1115.55
1099.55
1169.59
768.99
1020.81
1037.91
1081.96
72.56
72.75
65.61
60.90
71.02
61.05
78.56
85.02
78.97
76.63
76.84
77.04
86.90
109.51
136.82
138.91
131.12
119.99
137.37
76.44
120.45
107.77
123.06
273.29
261.35
235.31
219.26
261.34
251.26
259.34
289.37
265.39
257.31
275.30
263.36
304.39
339.46
441.38
457.38
445.34
407.36
457.38
276.31
377.44
339.46
373.47
7.76
7.58
7.39
7.46
7.76
7.84
7.54
7.29
7.72
8.16
7.80
7.60
7.81
8.29
8.20
8.20
7.90
7.82
7.94
8.16
8.33
8.00
7.82
−77407.51
−68485.75
−61938.86
−57684.12
−68512.61
−72505.53
−61469.89
−72426.91
−63427.50
−69907.78
−67939.70
−78789.12
−76721.80
−88895.44
−111398.80
−118776.00
−118699.00
−103172.20
−118806.57
−77533.14
−104362.94
−88916.70
−97109.77
449.36
454.97
428.01
400.24
468.44
454.05
422.45
450.14
441.09
434.23
439.49
448.55
499.64
582.16
629.29
626.60
646.85
634.92
661.59
477.01
596.59
625.51
642.34
−1.07
−1.03
−1.20
−1.17
−1.14
−1.46
−0.96
−0.84
−0.70
−0.20
−0.68
−0.76
−0.72
−0.29
−0.33
−0.32
−0.83
−0.40
−0.59
−0.83
−0.52
−0.62
−0.82
59.40
59.40
59.40
59.40
63.60
89.90
33.62
42.85
33.62
46.76
55.99
46.76
64.34
42.85
45.64
54.88
49.84
49.84
59.07
72.96
42.85
47.04
47.04
4.66
4.58
4.42
4.45
4.97
2.56
4.27
3.21
4.78
4.54
4.15
5.12
8.99
4.25
3.89
2.83
3.68
3.20
4.33
3.76
3.77
3.54
2.62
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
in an oil bath at 80◦C and progress of reaction was
monitored by TLC. After 12 h, the reaction was com-
pleted and crude reaction mixture was washed with
diethyl ether and crystallized from ethanol.
1690, 1671, 1627, 1600, 1489, 1460, 1244, 755; anal.
Calcd C12H10FN5OS: C 49.48, H 3.46, N 24.04, found:
C 49.52, H 3.20, N 24.44.
4-Ethoxycarbonyl-(pyrazin-2-ylcarbonyl)-thiose-
micarbazide (5). Yield 81%; mp 239–241◦C; 1H
NMR (DMSO-d6): δ 1.24–1.29 (t, 3H, CH3), 4.19–4.26
(q, 2H, CH2), 8.80–8.81 (dd, 1H, ArH), 8.94–8.95
(d, 1H, ArH), 9.21–9.22 (d, 1H, ArH), 11.20, 11.35,
11.68 (3s, 3H, 3NH, D2O exchangeable); IR (KBr)
cm−1: 3295, 2966, 2915, 1725, 1683, 1575, 1458,
1395, 1285; anal. Calcd. for C9H11N5O3S: C 40.14, H
4.12, N 26.01, found: C 39.75, H 3.69, N 25.72.
4-(2-Fluorophenyl)-1-(pyrazin-2-yl-carbonyl)-
thiosemicarbazide (1). Yield 94%; mp 193–195◦C;
1H NMR (DMSO-d6): δ 7.15–7.32 (m, 4H, ArH), 8.77–
8.78 (dd, 1H, ArH), 8.90–8.91 (d, 1H, ArH), 9.21–9.22
(d, 1H, ArH), 9.55, 9.97, 10.99 (3s, 3H, 3NH, D2O ex-
changeable); IR (KBr) cm−1: 3316, 3249, 3063, 3007,
TABLE 2 Variable Importance
Variable
Power
Importance
Synthesis of 5-(Pyrazin-2-yl)-4-Substituted-s-
triazole-3-thiones (6–9)
Vol
R
Mw
0.974
0.972
0.971
0.958
0.955
0.945
0.925
0.911
0.906
0.871
0.822
0.822
0.744
0.742
0.722
0.560
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A solution of (1–4) (0.01 mol) in 2% sodium hydrox-
ide solution (30 mL) was heated under reflux for
ꢀELUMO-HOMO
ET
A (grid)
ELUMO
PA
μ
Non
EHOMO
A
HE
TABLE 3 Ratio of Variance Explained by the PC’s
Principal
Component
Variance
Explained (%)
Total Variance
Explained (%)
PC1
PC2
PC3
PC4
65.34
13.89
10.37
7.64
65.34
79.23
89.60
97.24
Nrotb
NOHNH
log P
Heteroatom Chemistry DOI 10.1002/hc

Structure–Activity Relationship of s-Triazole and Thiadiazole as Analgesics 261
4
3
15 [m]
18 [m]
14 [m]
2
12 [m]
19 [a]
26 [a]
1
17 [m]
20 [m]
13 [m]
27 [i]
16 [m]
6 [m] 7 [m]
23 [m]
28 [i]
0
9 [i]
8 [i]
21 [m]
10 [a]
25 [m]
–1
–2
–3
–4
–5
24 [m] 22 [m]
11 [a]
–7
–6
–5
–4
–3
–2
–1
0
1
2
3
4
5
6
PC1: 65.34%
FIGURE 2 PC1 vs. PC2 score plot. Activity signature: [a]-active, [m]-moderately active, [i]-inactive.
2 h. After cooling, the mixture was neutralized with
11% hydrochloric acid solution. The resulting pre-
cipitates were collected by filtration and crystallized
from ethanol.
Synthesis of 2-Arylamino-5-(pyrazin-2-yl)-
1,3,4-thiadiazoles (10) and (11)
Procedure for (10): The thiosemicarbazide (2)
(0.01 mol) was dissolved in concentrated H2SO4
(10 mL). The solution was kept at room temperature
for 2 h and then poured into crushed ice to precip-
itate a crude solid. The product was then filtered,
dried, and crystallized from ethanol.
TABLE 4 Score Values for PC1 and PC2
Procedure for (11): The thiosemicarbazide (5)
(0.01 mol) was dissolved in glacial acetic acid
(10 mL), and the reaction mixture was refluxed for
9 h. Then it was kept at room temperature to com-
plete precipitation of the product, which was filtered,
dried, and crystallized from ethanol.
Compound
PC1
PC2
6
7
8
9
1.748
2.047
2.964
3.369
2.000
2.517
2.071
1.469
1.471
0.704
1.439
1.463
1.113
−1.955
−3.697
−3.993
−3.066
−2.671
−3.499
0.898
−2.612
−1.653
−2.129
−0.406
−0.317
−0.502
−0.315
−0.602
−3.342
1.277
0.374
1.791
1.751
0.316
0.911
1.145
1.153
0.380
−0.555
−0.810
−0.121
−0.803
−1.125
0.444
0.066
−0.710
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
2-Ethoxycarbonylamino-5-(pyrazin-2-yl)-1,3,4-
thiadiazole (11). Yield 52%; mp 266–268◦C; 1H
NMR (DMSO-d6): δ 1.28–1.32 (t, 3H, CH3), 4.25–
4.32 (q, 2H, CH2), 8.75–8.78 (m, 2H, ArH), 9.37–9.38
(m, 1H, ArH), 12.48 (s, 1H, NH, D2O exchangeable);
IR (KBr) cm−1: 3428, 2991, 2896, 1447, 1723, 1563;
anal. Calcd. for C9H9N5O2S: C 43.02, H 3.61, N 27.87,
found: C 42.64, H 3.95, N 28.10.
Pharmacology
The experiments were carried out on male Albino
Swiss mice (20–25 g). The animals were housed
in colony cages with free access to tap water and
food (standard laboratory pellets, Bacutil, Motycz,
Heteroatom Chemistry DOI 10.1002/hc

262 Siwek et al.
1.0
0.5
ELUMO
μ
ET
R
ELUMO-HOMO
0.0
Mas s
Vol
A(grid)
–0.5
–1.0
PA
–1.0
–0.5
0.0
0.5
1.0
PC1 : 65.34%
FIGURE 3 Loading vectors for the nine selected descriptors (details are given in the text).
Poland) and maintained in the 12/12 h light–dark
cycle (light on from 7 a.m. to 7 p.m.). Experimental
and control groups consisting of 10 animals. The
experiments were performed between 8 a.m. and
3 p.m. The investigated compounds were adminis-
trated intraperitoneally (ip) in doses of 25, 50, and
100 mg/kg (equivalent to 0.025, 0.05, and 0.1 of their
LD50) as suspensions in a 1% Tween 80 in the con-
trast volume 10 mL/kg. Control animals received the
equivalent volume of solvent. The rectal body tem-
perature was measured with a thermometer (Ellab,
Copenhagen, Denmark) before the administration of
compounds in the dose of 0.1 of their LD50 and 15,
30, 45, 60, 90, and 120 min afterwards. The screen-
ing of CNS activity in mice was performed in a series
of tests described below. Mean values were obtained
with uncertainties evaluated using the Student’s t-
test or the exact Fischer test.
Motor impairment was quantified with the
“chimney test” [28]; 30 min after the administration
of the investigated compounds, mice had to climb up
backwards in a plastic tube (3-cm inner diameter,
25-cm length). Mice unable to perform the task
within 60 s were considered to display motor impair-
ment. Motor impairment was quantified as the per-
centage of animals that failed to complete the test.
Anxiolytic activity was assessed by the “four
plate” test in mice according to Aron et al. [29];
30 min after the injection. The number of punished
crossings was counted for 1 min.
TABLE 5 Loading Values for the Selected Descriptors
Variable
PC1
PC2
Mw
ELUMO
−0.968
−0.717
−0.688
−0.977
0.957
−0.102
0.565
0.030
ꢀELUMO-HOMO
Vol
ET
−0.100
Antidepressive properties were assessed by the
“forced swimming” test according to Porsolt et al.
[30]; 30 min after the administration of the tested
compound mice were individually placed and forced
to swim in a glass cylinder (27 × 16 cm) containing
0.187
μ
0.330
0.470
A (grid)
R
PA
−0.958
−0.984
0.301
−0.151
0.012
−0.794
Heteroatom Chemistry DOI 10.1002/hc

Structure–Activity Relationship of s-Triazole and Thiadiazole as Analgesics 263
12000
10000
8000
6000
4000
2000
0
22 24 21 28 26 23 20 27 19
9
14 12
8 13 11 15 16 10 7 17 18 25 6
Compounds
FIGURE 4 Dendrogram obtained for the investigated s-triazoles and thiadiazoles.
15 mL of water (25◦C). A mouse was considered im-
mobile when it floated in the water, in an upright
position, and made only small movements to keep
its head above water. The total immobility time of
mice was measured during the last 4 min of the
6-min test.
L -5-Hydroxytryptophan-induced head-twitches.
Head-twitches responses were measured according
to Corne et al. [33]; L-5-hydroxytryptophan, L-5HTP,
(190 mg/kg ip) was administered 30 min after the
investigated compound. The number of head twitch
episodes was observed during 60 min after the L-
5HTP administration.
Thiopentanal-induced sleep. Thiopental (60 mg/
kg ip) was given 30 min after the administration
of compounds in doses varying from 0.025 to 0.1
of their LD50. The sleeping time of mice (from dis-
appearance to return of the righting reflex) was
measured.
Pain reactivity was measured by the “writhing
syndrome” test [31]. The test was performed by the
ip injection of a 0.6% solution of acetic acid 30 min
after the administration of compounds in doses vary-
ing from 0.0031 to 0.1 of their LD50. The number of
writhing episodes was counted for 30 min after the
injection of acetic acid.
Computational Methods
The following molecular descriptors: mass (Mw),
logarithm of the partition coefficient (log P), en-
ergy of the highest occupied molecular orbital
(EHOMO), energy of the lowest unoccupied molec-
ular orbital (ELUMO), energy of the gap HOMO–
LUMO (ꢀELUMO-HOMO), hydration energy (HE), vol-
ume (Vol), hydrogen bond donor/acceptor (nOHNH/
nON), total energy (ET), dipole moment (μ), polariz-
ability (α), rotatable bonds (nrotb), surface area (A),
refractivity (R), and polar surface area (PA) were cal-
culated using AM1 as implemented in HyperChem
[34] or were obtained with the Interactive Polar Sur-
face Area Calculator [35].
Pentetrazole-induced seizures [32]. Pentetrazol
(115 mg/kg sc) was administered 30 min after the
injection of investigated compounds in the doses of
0.05 or 0.1 of their LD50. The mice were placed singly
in plexiglass cages (25 × 15 × 10 cm) and were ob-
served for 30 min. The clonic and tonic seizures, as
well as mortality, were recorded in this period.
In a first step, the molecular geometries of s-
triazoles and thiadiazoles were fully optimized in
the gas phase to gradients of 0.01 kcal/(mol A)
and afterwards the molecular descriptors were per-
formed. Next, to select the most characteristic
˚
Heteroatom Chemistry DOI 10.1002/hc

264 Siwek et al.
[15] Ezabadi, I. R.; Camoutsis, C.; Zoumpoulakis, P.;
structural parameters for a set of s-triazoles and thia-
diazoles, PCA and HCA methodologies have been
performed. Investigated compounds were divided
into three groups (active, inactive, and moderately
active) according to their pain inhibition percentage
(% PIP). All statistical analyses were done by using
Statistica 8.0 package for Windows [36].
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