Synthesis, antimicrobial evaluation and QSAR analysis of novel nalidixic acid based 1,2,4-triazole derivatives

Article abstract of DOI:10.1016/j.ejmech.2011.06.009

Novel nalidixic acid based 1,2,4-triazole derivatives were synthesized and characterized using spectral techniques like ¹H NMR, ¹³C NMR, IR and mass spectrometry. All these compounds were screened for antimicrobial activity against f

Full text of DOI:10.1016/j.ejmech.2011.06.009

European Journal of Medicinal Chemistry 46 (2011) 4089e4099
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis, antimicrobial evaluation and QSAR analysis of novel nalidixic acid
based 1,2,4-triazole derivatives
,
,
a
b,
Nisha Aggarwal a b, Rajesh Kumar a , Prem Dureja , J.M. Khurana
*
**
a Division of Agricultural Chemicals, IARI, Pusa Campus, New Delhi 110 012, India
b Department of Chemistry, University of Delhi, Delhi 110 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel nalidixic acid based 1,2,4-triazole derivatives were synthesized and characterized using spectral
techniques like 1H NMR, 13C NMR, IR and mass spectrometry. All these compounds were screened for
antimicrobial activity against five bacteria and two pathogenic fungi. Most of these compounds showed
better antimicrobial activity than the parent compound, 4-amino-5-mercapto-1,2,4-triazole. Among all
the screened compounds, 3-{6-(2-chlorophenyl)-1,2,4-triazolo [3,4-b] [1,3,4]thiadiazol-3-yl}-1-ethyl-7-
Received 21 April 2011
Received in revised form
4 June 2011
Accepted 10 June 2011
Available online 23 June 2011
methyl-1,8-naphthyridin-4(1H)-one (23) was emerged as promising antimicrobial agent (MIC ¼ 16
mg/
mL). Quantitative structure activity relationship (QSAR) analysis was carried out using various distance-
based topological indices, steric and hydrophobic parameters. Based on the QSAR analysis it is indicative
that lipophilic and steric parameters are the pre-requisites for these molecules to act as potent anti-
microbial agents.
Keywords:
Nalidixic acid
1,2,4-Triazole
Antimicrobial activity
QSAR
Ó 2011 Elsevier Masson SAS. All rights reserved.
1. Introduction
possessing 1,2,4-triazole nucleus are well known as drugs, for
example, fluconazole, itraconazole, terconazole [42,43], ribavirin
Nalidixic acid (1,8-naphthyridine derivative) was the first
synthetic quinolone derivative introduced for the treatment of
urinary tract infections in 1963 [1]. It inhibits DNA synthesis by
promoting cleavage of bacterial DNA in the DNAeenzyme
complexes of DNA gyrase, resulting in rapid bacterial death [2]. It is
particularly effective against gram-negative bacteria particularly
Escherichia coli and resistant to most of the pseudomonas species [3].
The development of hybrid molecules through the combination of
different pharmacophores in one frame may lead to compounds
with interesting biological profiles [3]. The considerable biological
importance of triazoles has stimulated a lot of interest in its
derivatives. 1,2,4-triazoles, being an important pharmacophores
have a wide range of therapeutic properties like antibacterial [4e7],
antifungal [8e13], antimycobacterial [14e19], antiviral [20], anti-
inflammatory [21e24], anticonvulsant [25,26], antidepressant
[27], antitubercular [19], antitumoral [28,29], antihypertensive
[30], analgesic [31], enzyme inhibitor [32], hypoglycemic [33],
sedative, hypnotic [34], antiparasitic, herbicidal [35], insecticidal
[36,37] and plant growth activities [38e41]. Several compounds
[44] and triazolam [45]. 1,2,4-triazoles, by virtue of their ambident
nucleophilic centers, are good starting materials for the synthesis of
several interesting N and S-bridged heterocycles. The triazoles can
be converted to thiazolotriazoles, triazolothiadiazoles, tri-
azolothiazines, triazolothiazepines and triazolothiadiazines. In the
quest for biologically more potent antimicrobial agents and to
increase the molecular diversity and analyze the structureeactivity
relationships, we envisioned to design and synthesize the nalidixic
acid based 1,2,4-triazole derivatives.
2. Results and discussion
2.1. Chemistry
Nalidixic acid based 4-amino-5-mercapto-1,2,4-triazole (1), was
prepared by the reaction of nalidixic acid hydrazide with carbon
disulfide in ethanolic potassium hydroxide, a potassium dithio-
carbazinate intermediate was found which on condensation with
excess hydrazine hydrate produced the 3-(4-amino-5-mercapto-
4H-1,2,4-triazol-3-yl)-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one
(1) as a white solid in good yield (Scheme 1).
Compound 1 was condensed with different aldehydes in dioxane
in the presence of catalytic amounts of concentrated sulfuric acid to
give the corresponding Schiff’s bases (2e21, Scheme 2). Cyclization of
* Corresponding author. Tel.: þ91 11 25841390; fax: þ91 11 25843272.
** Corresponding author. Tel.: þ91 11 27667725; fax: þ91 11 27667501.
E-mail addresses: rkb1973@gmail.com (R. Kumar), jmkhurana1@yahoo.co.in
(J.M. Khurana).
0223-5234/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2011.06.009

4090
N. Aggarwal et al. / European Journal of Medicinal Chemistry 46 (2011) 4089e4099
O
O
O
N
O
O
N
O
NH2
O
OH
NH2NH2. H2O
DMS
K2CO3
N
H
N
N
N
N
1.KOH
2. CS2
N
O
N
O
N
O
H
SH
N
SK
N
NH2NH2. H2O
Reflux
N
H
NH2
S
N
N
N
1
Scheme 1. Synthesis of nalidixic acid based 4-amino-1,2,4-triazole.
1 with aromatic acids in presence of polyphosphoric acid resulted in
the formation of 4-(3-substituted-1,2,4-triazolo [3,4-b] [1,3,4]thia-
diazol-6-yl) derivatives of nalidixic acid(22e27, Scheme 3). The effect
of alteration at the C-6 position of triazolothiadiazoles was examined
by preparing 3-substituted [1,2,4]-triazolo-[3,4-b] [1,3,4]thiadiazole-
6-thiol (28) by the reaction of 4-amino-5-substituted-1,2,4-triazole-
3-thiol (1) with carbon disulphide in refluxing pyridine (Scheme 4).
3-Substituted-4-amino-5-mercapto-1,2,4-triazole (1) on treat-
ment with an equivalent amount of acetic anhydride underwent
selective acylation of the amino group to form the monoacetyl
derivative (29), whereas the treatment of compound 1 with
benzoyl chloride in refluxing acetone using pyridine as a base
afforded benzoyl amino derivative (30, Scheme 4). 1,2,4-Triazolo-
[3,4-b] [1,3,4]-thiadiazine derivative (31) was readily prepared by
reaction of compound 1 with phenacyl bromide in refluxing
acetonitrile using potassium carbonate as a mild base. Furthermore,
treatment of the 4-amino triazole (1) with oxalyl chloride in dry
benzene resulted in the formation of corresponding tri-
azolothiadiazine-6,7-dione (32, Scheme 4).
3-Substituted-4H-5-mercapto-1,2,4-triazoles (33) was synthe-
sized by the cyclization of the nalidixic acid thiosemicarbazide with
potassium hydroxide under reflux. The thiosemicarbazide, in turn,
was obtained by the reaction of nalidixic acid hydrazide with
potassium thiocyanate in the presence of dilute hydrochloride acid
(Scheme 5).
All the synthesized compounds were characterized by
elemental analysis, IR, 1H NMR, 13C NMR and mass spectrometry.
The IR spectra (KBr) of compounds (1e33) showed the
characteristic bands corresponding to the thiol, imine group,
carbonyl and amide moieties etc. The CeH stretching vibration
bands appeared at 2853e3059 cmꢀ1 confirmed the presence of the
CH2 groups. The characteristic stretching vibrations of the C]N are
at 1514e1652 cmꢀ1. The presence of thiol group was confirmed by
SeH stretching vibration band in the range of 2329e2541 cmꢀ1. In
the 1H NMR spectra of the Schiff’s bases (2e21), additional reso-
nances assigned to the ꢀHC]N-group at
d 8.89e9.12 were
observed, which confirmed the condensation between the amino
group and the carbonyl group. A downfield signal appearing at
d
12.93e13.61 was attributed to the eN¼CeSH#eNHeC¼S
tautomer moiety. This signal was absent in the 1H NMR spectra of
triazolothiadiazoles (22e27) and triazolothiadiazines (31e32). The
amide group of triazoles was confirmed by the signal appeared at
d
9.05 and 10.10.
2.2. In vitro antibacterial activity
All the synthesized compounds along with the 3-mercapto-
1,2,4-triazole were subjected to the antibacterial screening using
broth dilution technique. Streptomycin drug was used as the
standard. The minimum inhibitory concentration (MIC) was noted
by observing the lowest concentration of the drug at which there
was more than 90% inhibition of bacteria. The compounds were
screened against gram positive bacteria namely, Staphylococcus
aureus ATCC 2937 and Bacillus subtilis ATCC 12711,and gram-
negative bacteria namely, E. coli ATCC 8739, Klebesilla pneumoniae
ATCC 31488 and Pseudomonas aeruginosa ATCC 9027 in nutrient
broth medium. The results are listed in Table 1.
N
O
N
The investigation of antibacterial screening data revealed that
all the tested compounds 1e33 showed moderate to good bacterial
inhibition as compared to the standard drug streptomycin
SH
R
N
RCHO
1
N
Dioxane, H2SO4
N
N
N
O
N
N
N
O
S
CS2, pyridine
Triethylamine
RCOOH
PPA
N
S
N
1
N
2-21
N
R
N
N
SH
N
N
2. R= -C6H5
9. R= 4-NCC6H4
16. R= 4-(CH3)2HCC6H4
17. R= 4-(CH3)3CC6H4
18. R= 4-(CH3)2NC6H4
19. R= 4-CH3SC6H4
20. R= 2,4-Cl2C6H3
22-27
3. R= 4-FC6H4
4. R= 4-ClC6H4
5. R= 3-BrC6H4
6. R= 4-BrC6H4
7. R= 3-O2NC6H4
8. R= 4-O2NC6H4
10. R= 4-F3CC6H4
28
11. R= 4-HOC6H4
22. R= -C6H5
12. R= 4-CH3OC6H4
13. R= 4-CH3CH2OC6H4
14.R= 4-CH3C6H4
15. R= 4-CH3H2CC6H4
23. R= 2-ClC6H4
24. R=3-ClC6H4
25. R= 4-ClC6H4
21. R= 2,6-Cl2C6H3
26. R= 3-O2NC6H4
27. R= 2,3-Cl2C6H3
Scheme 2. Synthesis of nalidixic acid based 4-arylidene amino-4H-1,2,4-triazole-3-
thiols (2e21).
Scheme 3. Synthesis of nalidixic acid based 1,2,4-triazolo [3,4-b] [1,3,4]thiadiazole
derivatives (22e28).

N. Aggarwal et al. / European Journal of Medicinal Chemistry 46 (2011) 4089e4099
4091
N
O
N
N
N
SH
N
O
N
SH
N
HN
PhCOCl,
CH3COOH
(CH3CO)2O
Ph
HN
N
N
1
N
C5H5N
O
O
29
PhCOCH2Br
K2CO3
ClCOCOCl
Dioxane
30
Reflux
N
O
N
N
S
N
O
N
N
N
O
S
HN
N
N
O
N
N
32
31
Scheme 4. Synthesis of nalidixic acid based acylamino-1,2,4-triazoles (29e30) and triazolothiadiazines (31e32).
(Tables 1e3). Most of the compounds exhibited significant anti-
bacterial activity against Pseudomonas aeruginosa (MIC ¼ 16e125
nitro group showed decreased antibacterial activity as compared to
unsubstituted phenyl moiety. The benzamide derivative
(compound 30) showed effective bacterial activity against all
bacteria (Table 1). This excellent inhibition by compound 30 could
be attributed to the participation of the amide group. Conversion of
triazole (1) to triazolothiadiazines i.e. the moieties linked through
methylene spacers resulted in loss of activity against all tested
bacterial species (Table 1).
m
g/mL). They showed moderate activity against E. coli and showed
lower potency against S. aureus. The difference in the activity was
observed due to molecular diversity. Conversion of free NH2 group
(compound 1, MIC ¼ 63e125
m
g/mL) to phenylmethyleneamino
moiety (compound 2, MIC ¼ 16
mg/mL) greatly increased the
antibacterial activity against gram-negative bacteria but showed
3e4 fold decrease against gram-positive bacteria (Table 1). Among
the azomethine derivatives of 1,2,4-triazole, compound 5 was the
most potent against S. aureus, B. subtilis, E. coli, K. pneumoniae and
Table 1
In vitro antimicrobial activity of nalidixic acid based 1,2,4-Triazole derivatives.
P. aeruginosa with the MIC range of 125, 16, 31, 31 and 16 mg/mL
Compd
Minimum Inhibitory Concentration (MIC, mg/mL)
Most of the compounds with electron-releasing substitutents
showed better activity against all the tested microorganisms than
the compound with unsubstituted phenyl ring. 3-Bromo
Saa
Bsa
Eca
Kpa
Paa
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
63
63
250
63
16
16
250
125
125
63
63
125
16
63
125
63
16
31
125
16
63
16
250
250
31
250
250
63
63
16
16
16
16
62
63
63
63
63
63
16
63
63
63
16
63
16
63
63
63
63
16
63
125
63
63
31
250
63
125
125
125
4
250
125
125
125
125
125
125
63
250
125
125
125
63
substituted compound
5 showed highest activity. Replacing
250
250
125
250
125
125
125
250
125
250
125
125
250
250
63
hydroxyl group with methoxy or ethoxy group (compounds 11, 12
and 13), resulted in marked enhancement in the antibacterial
activity against B. subtilis, K. pneumoniae and P. aeruginosa. Some of
the tested compounds, 3, 6, 10, 19 and 20 showed very weak anti-
bacterial activity. Triazolothiadiazoles depicted moderate to strong
activity against all bacterial strains (Table 1). Compound 23 having
chloro substitutent at 2-position on aromatic ring showed
maximum antimicrobial potency against all tested microorganisms
63
125
125
31
63
63
63
125
63
63
63
(MIC ¼ 16
mycin drug (MIC ¼ 2e8
and mesomeric effect. Compound 26 having electron withdrawing
m
g/mL) which was comparable to the standard strepto-
mg/mL). This could be due to the inductive
63
63
125
125
250
125
125
63
16
63
O
O
O
N
O
125
125
31
125
16
250
250
16
63
16
NH2
H
N
250
125
125
16
NH2
N
KCNS/HCl
H2O
N
H
H
S
N
N
N
16
24
25
26
27
28
29
30
31
63
63
125
125
250
63
63
63
250
63
15
31
63
125
63
125
63
63
63
125
31
63
63
63
125
125
63
63
125
125
63
63
31
63
63
63
63
10% KOH
reflux
N
N
O
SH
63
N
125
125
31
5
12.5
H
32
33
N
N
Streptomycin
Ciprofloxcin
13
12.5
2
2.5
10
1.25
33
Scheme 5. Synthesis of nalidixic acid based 3-mercapto-4H-1,2,4-traizole (33).
a
Sa
¼
Staphylococcus aureus, Bs
¼
Bacillus subtillis, Ec
¼
Escherichia coli,
Kp ¼ Klebsiella pneumoniae, Pa ¼ Pseudomonas aeruginosa; MIC ¼ 90% inhibition.

4092
N. Aggarwal et al. / European Journal of Medicinal Chemistry 46 (2011) 4089e4099
Table 2
steric parameters) which are used as independent variables in
QSAR modeling [46]. The DRAGON 5.4 software [47] and Marvin
Sketch [48] were used to generate the descriptors for model
development. In Tables 3 and 4, the calculated values for topolog-
ical indices and steric parameters along with the LogP have
been reported. The following QSAR model, based on antibacterial
activity and various physicochemical parameters for hydrophobic
and steric properties, were developed using stepwise linear
regression analysis technique [49e51]. The predictive ability of the
model is discussed on the basis of predictive correlation coefficient
(Table 5).
Antifungal activity of nalidixic acid based 1,2,4-triazole derivatives.
Compound
Fusarium oxysporum
Aspergillus niger
ED50
Chi square
ED50
Chi square
1
2
3
4
5
6
7
8
382.18
78.18
163.31
79.5
0.70
5.40
2.11
3.40
4.51
5.69
3.84
2.86
0.10
7.69
1.40
3.25
5.05
0.44
0.47
3.84
2.87
1.66
5.35
5.27
2.86
3.35
5.51
1.87
2.54
3.33
3.76
0.92
3.90
5.72
1.60
1.99
4.98
567.35
77.74
0.42
2.54
2.41
5.03
4.03
2.54
5.03
2.13
1.95
3.12
5.23
2.96
5.51
3.55
4.75
4.45
2.37
2.48
1.87
0.09
0.34
3.02
4.56
5.06
1.99
5.09
0.68
5.68
3.41
5.61
2.07
5.57
3.71
133.77
120.00
111.43
143.73
160.74
148.72
156.2
298.84
548.65
104.74
86.57
76.64
228.93
113.3
133.64
101.00
250.68
502.17
101.47
79.57
74.08
106.74
138.18
100.23
177.15
100.68
203.16
152.31
89.31
205.06
190.89
106.42
116.79
103.8
104.46
102.8
112.49
102.82
86.57
102.88
121.44
148.165
96.89
266.89
165.74
109.91
144.48
164.2
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
MICE:Coli ¼ ꢀ21:641 logPðꢁ5:911Þ þ 144:245ðꢁ23:022Þ
n ¼ 33; r ¼ 0:549; r2 ¼ 0:302; F ¼ 13:405; SE ¼ 39:43
(1)
In equation (1), n stands for number of compounds, r is the
correlation coefficient, SE the standard error of estimate, F the ratio
of correlation respectively. In QSAR equation, the log P value is
negatively correlated, indicating that the compounds having high
log P values will have less MIC value. Substitutions favoring the
lipophilic phase will be leading to increase in activity. The negative
contribution of log P values may be due to fact that compounds
require to penetrate the bacterial cell wall to interact with the
actual target inside the cell.
75.45
144.49
513.79
70.99
109.34
92.67
110.9
88.45
148.45
347.56
76.03
Initial regression analysis for the antifungal activity indicated
that out of 16 descriptors used molecular weight in combination of
other physiochemical descriptor plays
a dominating role in
imparting the activity to the molecule. The intercorelatedness
among molecular descriptors with the activity showed that except
hydrogen bond acceptor all other physicochemical parameters are
mutually well correlated (Table 6). The successive regression
analysis indicates that a tri-parametric model including MW, log P
and MV yielded still better results (Table 7).
111.16
*ED50 values (
mg/mL), calculated from mean percentage inhibition which is an
average of four replicates and its standard deviation (ꢁ) ranged from ꢁ0.09
to ꢁ 5.87; Chi Square for Heterogeneity (tabular value at 0.05 level) ¼ 5.99 (degrees
of freedom ¼ 3).
EC50 for FO ¼ ꢀ1:344*MW þ 705:423
(2)
(3)
2.3. Antifungal activity
EC50for FO ¼ ꢀ2:047*MW þ 27:289*logP þ 897:246
Antifungal activity was screened against two fungal species
Aspergillus niger and Fusarium oxysporum. Hexaconazole was used
EC50forFO ¼ ꢀ2:154*MWþ45:051*logPþðꢀ0:592Þ*MV
þ1042:814
(4)
as
a standard antifungal agent. All the compounds showed
moderate to weak activity against both fungi (Table 2). The results
showed that aryldiaminotriazoles 2e21 possessed better activity
against F. oxysporum than A. niger. In general, compounds with e-
releasing substitutent showed better activity than e-withdrawing
substitutent against both the tested fungi except compound 11
The mol wt and molar volume have negative correlation with
the EC50 value i.e. increase in molecular weight resulted in decrease
in EC50 value. The log P has positive correlation with the EC50 value
i.e. increase in log P value resulted in increase in EC50 value. Thus
steric parameters of the molecules strongly influenced the
antifungal activity than hydrophobic and other topological
parameters.
(R
¼
4eOHC6H4). Among the triazolothiadiazoles derivatives
compound 23 performed better against both fungi as compared to
their corresponding para and meta substitutent. On comparing the
triazoles derivatives, five membered cylised products showed good
fungicidal activity than the six membered thiadiazines compound.
The amide derivatives (29 and 30) also showed promising inhibi-
tory effect against both fungi as compared to the parent compound
(1). The parent compound with free NH2 group in the 4 position
showed the lowest inhibitory effect against both fungi compared to
its all the substituted derivatives.
3. Conclusions
A series of nalidixic acid based triazole derivatives like tri-
azolothiadiazoles, triazolothiadiazines, arylideneamino triazoles,
triazolothiadiazine-6,7-dione were synthesized in good yield and
evaluated for in vitro antimicrobial activity. The study revealed that
all tested compounds showed moderate to good antibacterial
activity against pathogenic strains. Among the synthesized
compounds, 5 and 23 possessed the most prominent and consistent
activity. Most of the compounds showed lower fungicidal activity
than the bactericidal activity. Therefore, such compounds would
represent a fruitful matrix for the development of a new class of
antibacterial agents and with the suitable molecular modification
potency of these compounds may be further increased.
Consequent to the observation of high unit activity against
Pseudomonas aeurogenosa and F. oxysporum QSAR analysis was
carried out utilizing the activity data with respect to above two
pathogens.
2.3.1. QSAR analysis
The 2D QSAR study requires the calculation of a variety of
molecular descriptors (e.g., topological indices, hydrophobic and

N. Aggarwal et al. / European Journal of Medicinal Chemistry 46 (2011) 4089e4099
4093
Table 3
Physiochemical parameters used in the study.
Compd no.
MW
MR
87.23
h
MV
ST
D
Pr
Polar 2D SA
Polar 3D SA
Hb D
1
2
3
4
5
6
7
8
302
1.79
1.71
1.71
1.73
1.74
1.74
1.75
1.75
1.73
1.66
1.74
1.7
1.69
1.71
1.68
1.69
1.68
1.67
1.72
1.73
1.73
1.78
1.79
1.79
1.79
1.82
1.8
193.1
285
63.9
54.4
52.3
55.4
57
1.56
1.36
1.41
1.44
1.57
1.57
1.5
546
774
774
89.93
76.27
76.27
76.27
76.27
76.27
122.09
122.09
100.06
76.27
96.5
380.34
502.29
509.24
518.34
522.53
522.7
542.88
542.87
519.44
552.06
513.55
550.44
581.5
538.21
564.97
594.48
629.67
558.19
533.82
532.51
589.07
490.93
506.52
507.21
507.28
531.77
522.14
400.08
442.71
513.83
513.83
417.88
357.53
2
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
390.46
408.45
424.91
469.36
469.36
435.46
435.46
415.47
458.46
406.46
420.49
434.514
404.49
418.52
432.54
446.18
433.55
436.55
459.35
459.35
388.11
422.89
422.89
422.89
433.44
457.33
344.42
344.39
406.46
402.47
356.36
287.34
115.84
116.06
120.65
123.47
123.47
123.17
123.17
121.57
121.82
117.82
122.31
127.06
120.88
125.49
130.03
134.31
130.27
128.6
125.45
125.45
141.55
146.35
146.35
146.35
148.87
151.16
113.93
95.61
287.8
294.2
297.5
207.5
290.2
290.2
297.8
315
802.9
817.9
817.6
819.5
819.5
819.8
828.1
779.7
824.3
862.9
805.1
843.8
874.8
920.8
870.4
854.6
831.7
831.7
740
768.8
768.8
768.8
785.4
797.7
591.9
633.9
779.7
613
57
63.5
63.5
57.4
47.7
58.2
52.2
51.1
51.7
50.6
48.4
46.8
50.7
54.4
56.3
56.3
63.3
64.2
64.2
64.2
74.2
65
1.5
9
1.39
1.45
1.44
1.37
1.34
1.34
1.32
1.3
1.26
1.32
1.38
1.51
1.51
1.48
1.55
1.55
1.55
1.61
1.62
1.69
1.49
1.44
1.73
1.44
1.41
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
282.2
306.6
322.7
300.1
316.7
331.4
351.9
326.1
314.6
303.5
303.5
262.5
271.5
271.5
271.5
267.5
280.8
203.1
229.6
282.2
205
85.5
85.5
115.07
76.27
76.27
76.27
79.51
101.57
76.27
76.27
104.52
104.52
104.52
104.52
150.34
104.52
104.52
93.01
90.21
101.57
135.38
71.87
1.87
1.74
1.74
1.85
1.76
1.68
72.1
58.1
58.2
79.9
61.2
74.8
116.28
118
94.33
278.3
203.7
778.6
599.6
81.33
MW ¼ Molecular weight, MR ¼ Molar Refractivity,
h
¼ Index of Refraction, MV ¼ Molar Volume, ST ¼ Surface Tension, D ¼ Density, Pc ¼ Parachor, Polar 2D SA ¼ polar 2D
surface area, Polar 3D SA ¼ polar 3D surface area, Hb D ¼ Hydrogen bond donor.
Table 4
Calculated values of distance-based topological indices used in the present study.
Compd no.
J
W
Sz
1
c
log P
POL
1
2
3
4
5
6
7
8
1.54
1.38
1.32
1.32
1.33
1.32
1.24
1.21
1.26
1.37
1.32
1.26
1.37
1.32
1.26
1.21
1.37
1.21
1.26
1.29
1.31
1.21
1.18
1.17
1.16
1.08
1.14
1.47
1.64
1.37
1.18
1.36
1.58
848
1461
3177
3539
3539
3495
3539
4191
4323
3930
4718
3539
3930
4351
3539
3930
4323
4718
4323
3930
3819
3731
3414
3719
3763
3807
4521
4072
1889
1993
3391
3838
2504
1320
10.02
13.58
13.97
13.97
13.97
14.88
13.97
14.88
14.51
15.18
13.97
14.51
15.01
13.97
14.51
14.88
15.18
14.88
14.51
14.38
14.4
13.65
14.06
14.05
14.05
14.96
14.47
11.08
11.42
13.99
14.15
11.99
9.6
1.49
3.93
4.07
4.53
4.73
4.07
3.87
3.87
3.79
4.81
3.63
3.77
4.13
4.44
4.89
5.18
5.48
4.04
4.56
5.14
5.14
3.21
3.72
3.72
3.72
3.16
4.24
1.71
1.2
30.52
41.74
41.41
43.68
44.49
44.49
43.64
43.64
43.57
42.8
2024
2266
2266
2266
2244
2744
2810
2537
3085
2266
2537
2838
2266
2537
2810
3085
2810
2537
2468
2424
1988
2181
2203
2225
2693
2399
1093
1245
2184
2161
1388
752
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
42.36
44.27
46.11
43.2
45.34
47.18
49.03
46.56
46.62
45.65
45.66
40.48
42.45
42.44
42.43
42.41
44.44
33.6
34.52
41.95
42.56
33.68
29.32
3.06
2.64
0.96
1.79
J ¼ Balaban index, W ¼ Wiener index, Sz ¼ Szeged index, 1
¼ Connectivity index, log P ¼ octanol/water partition coefficient, POL ¼ polarzibility.
c

4094
N. Aggarwal et al. / European Journal of Medicinal Chemistry 46 (2011) 4089e4099
Table 5
Correlation matrix for antibacterial activity against P. aeurogenosa independent variables.
PA
MW
log P
2D SA
3D SA
MR
POL
Hb D
J
W
Sz
1
c
MV
Pr
h
ST
D
PA
1
MW
log P
2D SA
ꢀ0.409
1
ꢀ0.549
0.838
1
0.227 ꢀ0.097 ꢀ0.399
1
0.869 ꢀ0.177
0.595 0.214
0.896 ꢀ0.182
3D SA ꢀ0.375
0.856
0.727
0.912
1
MR
POL
Hb D
W
ꢀ0.371
ꢀ0.449
0.637
0.959
1
0.713
1
0.302 ꢀ0.553 ꢀ0.581
0.084 ꢀ0.487 ꢀ0.557 ꢀ0.566
1
0.469
0.389 ꢀ0.649 ꢀ0.473 ꢀ0.388 ꢀ0.553 ꢀ0.844 ꢀ0.644
1
J
Sz
ꢀ0.412
ꢀ0.382
ꢀ0.41
0.877
0.876
0.922
0.639
0.819
0.827 ꢀ0.044
0.945
0.918
0.925
0.807
0.866
0.672
0.755
0.75
0.441
0.555
0.928 ꢀ0.528 ꢀ0.646
0.913 ꢀ0.543 ꢀ0.746
0.948 ꢀ0.565 ꢀ0.726
1
0.781 0.054
0.984
0.959
0.8
1
1
c
0.807 ꢀ0.024
0.762 ꢀ0.167
0.967
0.744
0.828
1
MV
Pr
h
ꢀ0.407
ꢀ0.431
0.767 ꢀ0.35
0.87
ꢀ0.373
0.712
0.848
1
0.904
0.82
ꢀ0.126
ꢀ0.461 ꢀ0.501
0.872
1
0.154 ꢀ0.198 ꢀ0.486
0.324 ꢀ0.427 ꢀ0.623
0.195 ꢀ0.057 ꢀ0.39
0.593 ꢀ0.418
0.521 ꢀ0.598 ꢀ0.075 ꢀ0.541
0.375 ꢀ0.405 0.106 ꢀ0.322
0.187 ꢀ0.336
0.103 ꢀ0.235 ꢀ0.386 ꢀ0.262 ꢀ0.263 ꢀ0.63
ꢀ0.568
1
ST
D
0.036 ꢀ0.086 ꢀ0.521 ꢀ0.408 ꢀ0.465 ꢀ0.759 ꢀ0.709 0.802
1
0.054 ꢀ0.146 ꢀ0.346 ꢀ0.243 ꢀ0.235 ꢀ0.692 ꢀ0.571 0.875 0.784
1
4. Experimental
43.05 mmol) was added and stirred for 1 h. After 1 h dimethyl
sulphate (1.63 mL, 12.92 mmol) was added to it and refluxed at
70 ꢂC. After refluxing, the solvent was removed under reduced
pressure on a rotary evaporator and the product was extracted with
chloroform. The chloroform layer was dried over anhydrous
sodium sulphate and concentrated under reduced pressure to give
methyl nalidixate (1.95 g, 95%).
4.1. Materials and methods
All the chemicals used were purchased from SigmaeAldrich and
were used without further purification. Reactions were monitored
by thin layer chromatography (TLC) on pre-coated Merck silica gel
60F254 and the spots were visualized either under UV or by iodine
vapour. Melting points were determined on the Digital Image
Processing Tech model EZ-120 automated melting point apparatus
and are uncorrected. Infra-red (IR) spectra were recorded on Per-
kineElmer model 2000 FT-IR spectrophotometer as KBr pellet and
values are expressed as nmax cmꢀ1. Mass spectra were recorded on
a Joel (Japan) JMS-DX303 and micro mass LCT, Mass Spectrometer/
Data system. The 1H NMR and 13C NMR spectra were recorded on
Bruker Spectrospin spectrometer (400 MHz), using tetramethylsi-
lane as an internal standard. The chemical shift values were
4.2.2. Synthesis of nalidixic acid hydrazide
The methyl nalidixate (2 g, 8.17 mmol) was dissolved in tetra-
hydrofuran (10 mL) and hydrazine hydrate (0.5 mL, 12.25 mmol)
was added to it. The contents were refluxed for 3 h. To the resultant
reaction mixture, cold water (50 mL) was added and stirred for
10 min. A solid separated out which was filtered at pump and dried
to give nalidixic acid hydrazide (1.7g, 85%).
4.2.3. Synthesis of nalidixic acid based 4-amino-3-mercapto-1,2,4-
triazole (1)
recorded on
d scale and the coupling constants (J) are in Hz.
Elemental analysis was performed on a Carlo Erba Model EA-1108
elemental analyzer and data of C, H and N were within ꢁ0.4% of
calculated values.
To a solution of potassium hydroxide (10.0 mmol) in absolute
ethanol (50 mL), nalidixic acid hydrazide (5.0 mmol) and carbon
disulphide (11.0 mmol) was added to it. The mixture was stirred for
4e6 h at room temperature followed by addition of dry acetone.
The precipitated potassium dithiocarbazinate was filtered, washed
with acetone and dried under vacuum. The potassium salt was
obtained in quantitative yield and was used in the next step
without further purification. A suspension of the potassium salt
(10 mmol) and hydrazine hydrate (15 mmol) was heated under
4.2. Synthesis
4.2.1. Synthesis of nalidixic acid methyl ester
To the solution of nalidixic acid (2 g, 8.611 mmol) in tetrahy-
drofuran (50 mL) anhydrous potassium carbonate (5.96 g,
Table 6
Correlation matrix for antifungal activity against F. oxysporum.
FO
MW
log P
2D SA
3D SA
MR
POL
Hb AcP
J
W
Sz
1
c
MV
Pr
h
ST
D
FO
1
MW
log P
2D SA
3D SA
MR
ꢀ0.823
1
ꢀ0.562
0.852
1
0.126 ꢀ0.263 ꢀ0.481
1
0.878 ꢀ0.341
0.591 0.099
0.907 ꢀ0.337
ꢀ0.643
ꢀ0.629
ꢀ0.716
0.809
0.695
0.885
1
0.57
0.947
1
0.67
0.352 ꢀ0.256
POL
1
Hb AcP ꢀ0.004 ꢀ0.125 ꢀ0.338
0.618 ꢀ0.289
1
W
J
Sz
0.51
ꢀ0.588 ꢀ0.439 ꢀ0.316 ꢀ0.466 ꢀ0.806 ꢀ0.583 ꢀ0.354
1
ꢀ0.675
ꢀ0.706
ꢀ0.757
ꢀ0.52
0.839
0.839
0.897
0.576
0.79
0.828 ꢀ0.177
0.78
0.815 ꢀ0.178
0.734 ꢀ0.248
0.803 ꢀ0.221
0.929
0.894
0.903
0.782
0.844
0.621
0.91
ꢀ0.116 ꢀ0.585
1
ꢀ0.075
0.713
0.697
0.377
0.891 ꢀ0.004 ꢀ0.7
0.981
0.953
0.775
0.852
1
1
c
0.933 ꢀ0.066 ꢀ0.674
0.962
0.712
0.802
1
MV
Pr
h
0.73
ꢀ0.232 ꢀ0.298
0.671
0.83
1
0.89
ꢀ0.676
0.504
0.849 ꢀ0.224 ꢀ0.436
1
0.279 ꢀ0.379 ꢀ0.584
0.211 ꢀ0.313 ꢀ0.574
0.111 ꢀ0.145 ꢀ0.438
0.563 ꢀ0.618
0.638 ꢀ0.53
0.343 ꢀ0.536
0.063 ꢀ0.523
0.067 ꢀ0.451
0.052 ꢀ0.436
0.576 ꢀ0.137 ꢀ0.571 ꢀ0.442 ꢀ0.473 ꢀ0.766 ꢀ0.719
0.577 ꢀ0.24
0.433 ꢀ0.096 ꢀ0.466 ꢀ0.356 ꢀ0.355 ꢀ0.783 ꢀ0.669 0.884 0.877
1
ST
D
ꢀ0.442 ꢀ0.307 ꢀ0.358 ꢀ0.725 ꢀ0.668 0.957
1
1

N. Aggarwal et al. / European Journal of Medicinal Chemistry 46 (2011) 4089e4099
4095
Table 7
nmax: 2914, 2378, 1607, 1558, 1432, 1252, 791; MS calculated for
C20H17ClN6OS: 424.0873, Observed ESI-MS (m/z): 424.22[Mþ],426.36.
Regression parameters and quality of correlation of the proposed models.
Model
Parameters
n
SE
R
R2
F
4.2.4.4. 3-{4-(3-bromobenzylideneamino)-5-mercapto-4H-1,2,4-
1
2
3
MW
MW, log P
MW, log P, MV,
29
29
29
37.22
33.563
29.611
0.823
0.865
0.90
0.667
0.768
0.811
56.716
38.486
35.527
triazol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one (5). Yellow
solid; M.p.: 188.3 ꢂC; Yield: 72%; 1H NMR (
d): 1.53 (t, 3H, N-CH2CH3),
2.70 (s, 3H, 7eCH3), 4.54 (q, 2H, N-CH2), 7.25 (d, J ¼ 8.0 Hz, 1H, H-6-
naphthyridine), 7.30e7.33 (m, 1H, Ar-H), 7.45 (dd, J ¼ 7.2 Hz, 1H, Ar-
H), 7.99e8.19 (m, 1H, Ar-H), 8.30 (s, 1H, Ar-H), 8.50 (d, J ¼ 8.0 Hz, 1H,
H-5-naphthyridine), 8.64 (s, 1H, H-2-naphthyridine), 8.94 (s, 1H, N]
reflux for 5 h. Hydrogen sulphide gas was evolved and a homoge-
nous solution was obtained which was diluted with 50 mL of water
and acidified with dilute hydrochloric acid to give a white precip-
itate which was filtered at pump, washed repeatedly with water
(3 ꢃ 10 mL) and dried to yield 3-(4-amino-5-mercapto-4H-1,2,4-
triazol-3-yl)-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one (1).
CH), 13.28 (s, 1H, SH); 13C NMR (
d
): 15.09, 25.11, 47.35, 119.43, 121.19,
123.06, 125.24, 127.45, 128.40, 130.22, 132.79, 133.99, 135.77, 137.78,
146.25, 148.32, 148.73, 160.67, 163.33, 178.52; IR (KBr, cmꢀ1
nmax
)
:
2888, 2385, 1624, 1607, 1566, 1441, 1254, 791; MS calculated for
C20H17BrN6OS: 468.0368, Observed ESI-MS (m/z): 469.85 [Mþ þ 1],
471.58.
4.2.3.1. 3-(4-Amino-5-mercapto-4H-1,2,4-triazol-3-yl)-1-ethyl-7-
methyl-1,8-naphthyridin-4(1H)-one (1). Pale Yellow solid; M.p.:
>300 ꢂC; Yield: 88%; 1H NMR (
d): 1.49 (t, 3H, N-CH2CH3), 2.71 (s, 3H,
7eCH3), 4.58 (q, 2H, N-CH2), 5.70 (s, 2H, NH2), 7.45 (d, J ¼ 8.0 Hz, 1H,
4.2.4.5. 3-{4-(4-Bromobenzylideneamino)-5-mercapto-4H-1,2,4-
H-6-naphthyridine), 8.50 (d, J ¼ 8.0 Hz,1H, H-5-naphthyridine), 8.67
triazol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one
(6)
(s, 1H, H-2-naphthyridine), 13.87 (s, 1H, SH); 13C NMR (
d): 15.42,
[52]. Yellow solid; M.p.: 217.5 ꢂC; Yield: 75%; 1H NMR (
d
): 1.49 (t,
25.38, 46.03, 108.57, 119.36, 121.77, 136.00, 146.28, 147.28, 148.30,
3H, N-CH2CH3), 2.70 (s, 3H, 7eCH3), 4.52 (q, 2H, N-CH2), 7.31 (d,
J ¼ 8.0 Hz, 1H, H-6-naphthyridine), 7.55 (d, J ¼ 8.4 Hz, 2H, Ar-H),
7.72 (d, J ¼ 7.6 Hz, 2H, Ar-H), 8.35 (d, J ¼ 8.0 Hz, 1H, H-5-
naphthyridine), 8.82 (s, 1H, H-2-naphthyridine), 9.06 (s, 1H, N]
163.63, 164.48, 174.78; IR (KBr, cmꢀ1
)
nmax: 3287, 3053, 2358, 1635,
1609, 1537, 1439, 1292, 802; HRMS calculated for C13H14N6OS:
302.0950, Observed 302.1870 [Mþ].
CH), 13.28 (s, 1H, SH); IR (KBr, cmꢀ1
) nmax: 2954, 2382, 1626, 1585,
4.2.4. GeneralsynthesisofnalidixicacidbasedSchiffbasesof4-amino-
3-mercapto-1,2,4-triazole (2e21)
1497, 1256, 794; MS calculated for C20H17BrN6OS: 468.0368,
Observed ESI-MS (m/z): 468.22 [Mþ], 470.44.
A suspension of substituted benzaldehyde (5 mmol) in dioxane
(10 mL) along with triazole (1, 5 mmol) was heated until a clear
solution was obtained. A few drops of conc. sulfuric acid were
added as a catalyst and the solution was refluxed for 3 h on a water
bath. After the completion, the reaction was quenched with water
and cooled. The precipitated solid was filtered, thoroughly washed
with water and dried.
4.2.4.6. 1-Ethyl-3-{5-mercapto-4-(3-nitrobenzylideneamino)-4H-
1,2,4-triazol-3-yl}-7-methyl-1,8-naphthyridin-4(1H)-one (7). Yellow
solid; M.p.: 258.6 ꢂC; Yield: 73%; 1H NMR (
d): 1.57 (t, 3H,
NeCH2CH3), 2.73 (s, 3H, 7eCH3), 4.62 (q, 2H, N-CH2), 7.33 (d,
J ¼ 8.0 Hz, 1H, H-6-naphthyridine), 7.78e7.80 (m, 1H, Ar-H),
8.18e8.24 (m, 1H, Ar-H), 8.35 (d,
J
¼
8.0 Hz, 1H, H-5-
naphthyridine), 8.52e8.55 (m, 1H, Ar-H), 8.73 (s, 1H, Ar-H), 8.74
(s, 1H, H-2-naphthyridine), 9.12 (s, 1H, N]CH), 13.14 (s, 1H, SH); 13
NMR ( ): 15.34, 25.27, 47.24, 111.73, 120.14, 121.76, 123.26, 125.80,
128.25, 129.62, 130.28, 132.95, 134.17, 136.33, 145.54, 148.70, 148.16,
160.55, 163.87, 176.76; IR (KBr, cmꢀ1
nmax: 2926, 2402, 1628, 1614,
4.2.4.1. 3-{4-(Benzylideneamino)-5-mercapto-4H-1,2,4-triazol-3-yl)-
C
1-ethyl-7-methyl-1,8-naphthyridin-4(1H}-one (2) [52]. Yellow solid;
d
M.p.: 298 ꢂC; Yield: 80%; 1H NMR (
d): 1.52 (t, 3H, N-CH2CH3), 2.71 (s,
3H, 7eCH3), 4.60 (q, 2H, N-CH2), 7.35 (d, J ¼ 8.0 Hz, 1H, H-6-
naphthyridine), 7.45e7.82 (m, 5H, Ar-H), 8.25 (d, J ¼ 7.6 Hz, 1H,
H-5-naphthyridine), 8.92 (s, 1H, H-2-naphthyridine), 9.07 (s, 1H, N]
)
1530, 1440, 1255, 805; MS calculated for C20H17N7O3S: 435.1114,
Observed ESI-MS (m/z): 436.42 [Mþ þ 1].
CH), 13.25 (s, 1H, SH); IR (KBr, cmꢀ1
) nmax: 2932, 2348, 1670, 1603,
1525, 1479, 1250, 790; MS calculated for C20H18N6OS: 390.1263,
4.2.4.7. 1-Ethyl-3-{5-mercapto-4-(4-nitrobenzylideneamino)-4H-1,2,4-
Observed ESI-MS (m/z): 390.52 [Mþ].
triazol-3-yl}-7-methyl-1,8-naphthyridin-4(1H)-one (8). Yellow solid;
M.p.: 189.7 ꢂC; Yield: 77%; 1H NMR (
d): 1.52 (t, 3H, N-CH2CH3), 2.71 (s,
4.2.4.2. 1-Ethyl-3-{4-(4-fluorobenzylideneamino)-5-mercapto-4H-
1,2,4-triazol-3-yl}-7-methyl-1,8-naphthyridin-4(1H)-one (3). White
3H, 7eCH3), 4.61 (q, 2H, N-CH2), 7.37 (d, J ¼ 8.0 Hz, 1H, H-6-
naphthyridine), 7.98 (d, J ¼ 8.8 Hz, 2H, Ar-H), 8.34 (d, J ¼ 8.8 Hz,
2H, Ar-H), 8.68 (d, J ¼ 8.0 Hz,1H, H-5-naphthyridine), 8.72 (s,1H, H-2-
naphthyridine), 9.05 (s, 1H, N]CH), 13.40 (s, 1H, SH); IR (KBr, cmꢀ1)
nmax: 2939, 2343, 1613, 1520, 1443, 1256, 795; MS calculated for
C20H17N7O3S: 435.1114, Observed ESI-MS (m/z): 436.1 [Mþ þ 1].
solid; M.p.: 192 ꢂC; Yield: 78%; 1H NMR (
d): 1.54 (t, 3H, N-CH2CH3),
2.72 (s, 3H, 7eCH3), 4.60 (q, 2H, N-CH2), 7.35 (d, J ¼ 8.4 Hz, 1H, H-6-
naphthyridine), 7.14 (d, J ¼ 8.8 Hz, 2H, Ar-H), 7.81 (d, J ¼ 8.8 Hz, 2H,
Ar-H), 8.22 (d, J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 8.68 (s, 1H, H-2-
naphthyridine), 9.04 (s, 1H, N]CH), 13.26 (s, 1H, SH); 13C NMR (
d):
15.34, 25.25, 47.14, 115.88, 115.92 (2C), 116.14, 120.16, 121.60, 129.64,
129.72, 130.28 (2C), 136.30, 147.17, 147.97, 160.86, 161.62, 163.70,
4.2.4.8. 4-{(3-(1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridin-
3-yl)-5-mercapto-4H-1,2,4-triazol-4-ylimino)methyl}benzonitrile
176.75; IR (KBr, cmꢀ1
)
nmax: 2954, 2541, 1680, 1603, 1533, 1506,
(9). Yellow solid; M.p.: 236.7 ꢂC; Yield: 77%; 1H NMR (
d): 1.47 (t, 3H,
1443, 1229, 829; MS calculated for C20H17FN6OS: 408.1169,
N-CH2CH3), 2.68 (s, 3H, 7eCH3), 4.55 (q, 2H, N-CH2), 7.34 (d,
J ¼ 8.0 Hz,1H, H-6-naphthyridine), 7.52 (d, J ¼ 8.8 Hz, 2H, Ar-H), 7.81
(d, J ¼ 8.0 Hz, 2H, Ar-H), 8.44 (s, 1H, H-2-naphthyridine), 8.55 (d,
J ¼ 8.4 Hz, 1H, H-5-naphthyridine), 9.06 (s, 1H, N]CH), 13.30 (s, 1H,
Observed ESI-MS (m/z): 408.42 [Mþ].
4.2.4.3. 3-{4-(4-Chlorobenzylideneamino)-5-mercapto-4H-1,2,4-
triazol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one (4) [52]. Yel
SH); IR (KBr, cmꢀ1
) nmax: 3242, 2343, 1623, 1568, 1440, 1256, 790; MS
low solid; M.p.: 180.5 ꢂC; Yield: 75%; 1H NMR (
d): 1.55 (t, 3H, N-
calculated for C21H17N7OS: 415.1215, Observed ESI-MS (m/z): 416.2
CH2CH3), 2.69 (s, 3H, 7eCH3), 4.59(q, 2H, N-CH2), 7.35 (d, J¼ 8.0Hz,1H,
H-6-naphthyridine), 7.38(d, J¼ 8.8 Hz, 2H, Ar-H), 7.76 (d, J¼ 8.4 Hz, 2H,
Ar-H), 8.21 (s, 1H, H-2-naphthyridine), 8.68 (d, J ¼ 8.0 Hz, 1H, H-5-
[Mþ þ 1].
4.2.4.9. 1-Ethyl-3-{5-mercapto-4-(4-(trifluoromethyl)benzylidenea-
mino)-4H-1,2,4-triazol-3-yl}-7-methyl-1,8-naphthyridin-4(1H)-one
naphthyridine), 9.05 (s, 1H, N]CH), 13.19 (s, 1H, SH); IR (KBr, cmꢀ1
)

4096
N. Aggarwal et al. / European Journal of Medicinal Chemistry 46 (2011) 4089e4099
(10). Pale yellow solid; M.p.: 226.4 ꢂC; Yield: 70%; 1H NMR (
d): 1.49
cmꢀ1
) nmax: 2985, 2357, 1633, 1608, 1585, 1441, 1253, 794; MS
(t, 3H, N-CH2CH3), 2.71 (s, 3H, 7eCH3), 4.62 (q, 2H, N-CH2), 7.35 (d,
J ¼ 8.0 Hz, 1H, H-6-naphthyridine), 7.65 (d, J ¼ 8.4 Hz, 2H, Ar-H),
7.92 (d, J ¼ 8.0 Hz, 2H, Ar-H), 8.27 (s, 1H, H-2-naphthyridine),
8.68 (d, J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 9.05 (s, 1H, N]CH), 13.30
calculated for C22H22N6OS: 418.1576, Observed ESI-MS (m/z): 419.3
[Mþ þ 1].
4.2.4.15. 1-Ethyl-3-{4-(4-isopropylbenzylideneamino)-5-mercapto-
4H-1,2,4-triazol-3-yl}-7-methyl-1,8-naphthyridin-4(1H)-one
(s, 1H, SH); IR (KBr, cmꢀ1
) nmax: 2949, 2342, 1682, 1612, 1532, 1444,
1256, 797; MS calculated for C21H17F3N6OS: 458.1137, Observed ESI-
(16). Yellow solid; M.p.: 174.4 ꢂC; Yield: 82%; 1H NMR (
d): 1.24
MS (m/z): 458.4 [Mþ].
(d, 6H, 2CH3), 1.51 (t, 3H, N-CH2CH3), 2.71 (s, 3H, 7eCH3), 2.90
(heptet, 1H, CH), 4.58 (q, 2H, N-CH2), 7.24 (d, J ¼ 8.0 Hz, 2H, Ar-
4.2.4.10. 1-Ethyl-3-{4-(4-hydroxybenzylideneamino)-5-mercapto-
H), 7.31 (d,
J
¼
8.0 Hz, 1H, H-6-naphthyridine), 7.72 (d,
4H-1,2,4-triazol-3-yl}-7-methyl
ꢀ1,8-naphthyridin-4(1H)-one
J ¼ 8.4 Hz, 2H, Ar-H), 8.18 (s, 1H, H-2-naphthyridine), 8.64 (d,
(11). Yellow solid; M.p.: >300 ꢂC; Yield: 68%; 1H NMR (
d
): 1.51 (t,
J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 9.01 (s, 1H, N]CH), 13.06 (s,
3H, N-CH2CH3), 2.70 (s, 3H, 7eCH3), 4.57 (q, 2H, N-CH2), 6.96 (d,
J ¼ 8.4 Hz, 2H, Ar-H), 7.30 (d, J ¼ 8.4 Hz, 1H, H-6-naphthyridine),
7.65 (d, J ¼ 8.4 Hz, 2H, Ar-H), 8.13 (s, 1H, H-2-naphthyridine), 8.68
(d, J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 8.99 (s, 1H, OH), 9.01 (s, 1H,
1H, SH), 13C NMR (
d): 15.31, 23.79 (2C), 25.25, 34.13, 47.08,
112.20, 120.14, 121.53, 126.91 (2C), 127.94 (2C), 128.62, 131.61,
136.29, 147.91, 148.49, 151.49, 152.45, 161.45, 163.60, 176.73; IR
(KBr, cmꢀ1
) nmax: 2956, 2353, 1675, 1606, 1531, 1442, 1255, 796;
N]CH), 13.07 (s, 1H, SH); 13C NMR (
d): 15.34, 25.3, 46.8, 113.3, 116.02
MS calculated for C23H24N6OS: 432.1732, Observed ESI-MS (m/
(2C), 119.01, 120.6, 122.0, 125.47, 129.70 (2C), 136.7, 145.9, 147.65,
z): 432.1 [Mþ].
148.95, 156.5, 160.33, 163.0, 176.22; IR (KBr, cmꢀ1
)
nmax: 3324, 2935,
2363, 1660, 1607, 1515, 1444, 1253, 796; MS calculated for
4.2.4.16. 3-{4-(4-tert-Butylbenzylideneamino)-5-mercapto-4H-
1,2,4-triazol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one
C20H18N6O2S: 406.1212, Observed ESI-MS (m/z): 407.3 [Mþ þ 1].
(17). Yellow solid; M.p.: 158.2 ꢂC; Yield: 80%; 1H NMR (
d): 1.35 (s,
4.2.4.11. 1-Ethyl-3-{5-mercapto-4-(4-methoxybenzylideneamino)-
9H, 3CH3), 1.39 (t, 3H, N-CH2CH3), 2.68 (s, 3H, 7eCH3), 4.59 (q, 2H,
N-CH2), 7.44 (d, J ¼ 8.4 Hz, 1H, H-6-naphthyridine), 7.49 (d,
J ¼ 8.0 Hz, 2H, Ar-H), 7.67 (d, J ¼ 8.4 Hz, 2H, Ar-H), 8.34 (s, 1H, H-2-
naphthyridine), 8.66 (d, J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 9.06 (s,
4H-1,2,4-triazol-3-yl}-7-methyl ꢀ1,8-naphthyridin-4(1H)-one (12)
[52]. Yellow solid; M.p.: 163.1 ꢂC; Yield: 85%; 1H NMR (
d): 1.52 (t,
3H, N-CH2CH3), 2.72 (s, 3H, 7eCH3), 3.81 (s, 3H, OCH3), 4.58 (q, 2H,
N-CH2), 6.86 (d, J ¼ 8.0 Hz, 2H, Ar-H), 7.39 (d, J ¼ 8.0 Hz, 1H, H-6-
naphthyridine), 7.82 (d, J ¼ 8.0 Hz, 2H, Ar-H), 8.24 (s, 1H, H-2-
naphthyridine), 8.64 (d, J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 8.95
1H, N]CH), 13.01 (s, 1H, SH); 13C NMR (
d): 15.87, 25.62, 31.14 (3C),
34.33, 47.55, 111.74, 118.78, 121.75, 126.03 (2C), 127.55 (2C),
129.94 132.01, 136.17, 146.19, 148.51, 148.93, 156.17, 160.94, 163.95,
(s, 1H, N]CH), 13.07 (s, 1H, SH); IR (KBr, cmꢀ1
)
nmax: 3043, 2366,
176.14; IR (KBr, cmꢀ1
) nmax: 2948, 2329, 1690, 1613, 1533, 1440,
1672, 1612, 1528, 1424, 1256, 795; MS calculated for C21H20N6O2S:
1250, 793; MS calculated for C24H26N6OS: 446.1889; Observed ESI-
420.1368, Observed ESI-MS (m/z): 420.5 [Mþ].
MS (m/z): 446.5 [Mþ].
4.2.4.12. 3-{4-(4-ethoxybenzylideneamino)-5-mercapto-4H-1,2,4-
4.2.4.17. 3-{4-(4-(Dimethylamino)benzylideneamino)-5-mercapto-
4H-1,2,4-triazol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one
triazol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one (13). Yellow
solid; M.p.: 207.7 ꢂC; Yield: 73%; 1H NMR (
d): 1.35 (t, 3H, O-CH2CH3),
(18). Red-orange solid; M.p.: 252.8 ꢂC; Yield: 88%; 1H NMR (
d): 1.51
1.40 (t, 3H, N-CH2CH3), 2.67 (s, 3H, 7eCH3), 4.07 (q, 2H, O-CH2), 4.52
(q, 2H, N-CH2), 6.99 (d, J ¼ 8.8 Hz, 2H, Ar-H), 7.52 (d, J ¼ 8.0 Hz, 1H, H-
6-naphthyridine), 7.68 (d, J ¼ 8.8 Hz, 2H, Ar-H), 8.33 (s, 1H, H-2-
naphthyridine), 8.59 (d, J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 9.08 (s,
(t, 3H, N-CH2CH3), 2.70 (s, 3H, 7eCH3), 3.68 (s, 6H, 2CH3), 4.53 (q,
2H, N-CH2), 6.68 (d, J ¼ 8.0 Hz, 2H, Ar-H), 7.32 (d, J ¼ 8.0 Hz,1H, H-6-
naphthyridine), 7.42 (d, J ¼ 8.4 Hz, 2H, Ar-H), 8.29 (s, 1H, H-2-
naphthyridine), 8.60 (d, J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 8.94
1H, N]CH), 12.97 (s, 1H, SH); 13C NMR (
d): 15.04, 15.50, 25.37, 47.10,
(s, 1H, N]CH), 13.61 (s, 1H, SH); 13C NMR (
d): 15.12, 25.28, 46.51,
63.72, 112.0, 115.17 (2C), 118.40, 122.32, 127.24, 129.34 (2C), 130.57,
135.41, 136.43, 148.54, 148.96, 151.35, 160.82, 164.00, 173.46; IR (KBr,
66.90 (2C), 108.74, 109.43 (2C), 119.54, 121.21 (2C), 122.30, 125.63,
129.51, 135.88, 136.01, 144.33, 146.18, 148.29, 148.59, 163.38, 175.24;
cmꢀ1
)
nmax: 2980, 2359, 1607, 1514, 1439, 1250, 834; MS calculated for
IR (KBr, cmꢀ1
) nmax: 2930, 2385, 1621, 1567, 1479, 1255, 791; MS
C22H22N6O2S: 434.1525, Observed ESI-MS (m/z): 434.1 [Mþ].
calculated for C22H23N7OS: 433.1685; Observed ESI-MS (m/z): 433.2
[Mþ], 434.4 [Mþ þ 1].
4.2.4.13. 1-Ethyl-3-{5-mercapto-4-(4-methylbenzylideneamino)-
4H-1,2,4-triazol-3-yl}-7-methyl-1,8-naphthyridin-4(1H)-one
(14)
d): 1.54 (t,
4.2.4.18. 1-Ethyl-3-{5-mercapto-4-(4-(methylthio)benzylidenea-
mino)-4H-1,2,4-triazol-3-yl}-7-methyl-1,8-naphthyridin-4(1H)-one
[52]. Yellow solid; M.p.: 174.0 ꢂC; Yield: 71%; 1H NMR (
3H, N-CH2CH3), 2.41 (s, 3H, CH3), 2.72 (s, 3H, 7eCH3), 4.61 (q, 2H, N-
CH2), 6.99 (d, J ¼ 7.6 Hz, 2H, Ar-H), 7.33 (d, J ¼ 7.6 Hz, 1H, H-6-
naphthyridine), 7.53 (d, J ¼ 7.6 Hz, 2H, Ar-H), 8.14 (s, 1H, H-2-
naphthyridine), 8.69 (d, J ¼ 8.4 Hz, 1H, H-5-naphthyridine), 8.89
(19). Yellow solid; M.p.: 214.9 ꢂC; Yield: 82%; 1H NMR (
d): 1.51 (t,
3H, N-CH2CH3), 2.70 (s, 3H, 7eCH3), 2.53 (s, 3H, S-CH3), 4.60 (q, 2H,
N-CH2), 7.24 (d, J ¼ 8.4 Hz, 2H, Ar-H), 7.34 (d, J ¼ 8.4 Hz, 1H, H-6-
naphthyridine), 7.72 (d, J ¼ 8.4 Hz, 2H, Ar-H), 8.18 (s, 1H, H-2-
naphthyridine), 8.66 (d, J ¼ 8.4 Hz, 1H, H-5-naphthyridine), 9.03
(s, 1H, N]CH), 12.93 (s, 1H, SH); IR (KBr, cmꢀ1
) nmax: 2957, 2345,
1623, 1583, 1440, 1254, 795; MS calculated for C21H20N6OS:
(s, 1H, N]CH), 13.12 (s, 1H, SH); IR (KBr, cmꢀ1
) nmax: 2902, 2376,
4045.1419, Observed ESI-MS (m/z): 404.8 [Mþ].
1688, 1610, 1530, 1441, 1254, 796; MS calculated for C21H20N6OS2:
436.1140; Observed ESI-MS (m/z): 436.2 [Mþ].
4.2.4.14. 1-Ethyl-3-{4-(4-ethylbenzylideneamino)-5-mercapto-4H-
1,2,4-triazol-3-yl}-7-methyl-1,8-naphthyridin-4(1H)-one
4.2.4.19. 3-{4-(2,4-dichlorobenzylideneamino)-5-mercapto-4H-
1,2,4-triazol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one
(15). Yellow solid; M.p.: 192.5 ꢂC; Yield: 80%; 1H NMR (
d): 1.27 (t,
3H, CH3), 1.52 (t, 3H, N-CH2CH3), 2.65 (q, 2H, CH2), 2.70 (s, 3H,
7eCH3), 4.60 (q, 2H, N-CH2), 7.24 (d, J ¼ 8.0 Hz, 2H, Ar-H), 7.33 (d,
J ¼ 8.0 Hz, 1H, H-6-naphthyridine), 7.73 (d, J ¼ 8.4 Hz, 2H, Ar-H),
8.20 (s, 1H, H-2-naphthyridine), 8.66 (d, J ¼ 8.0 Hz, 1H, H-5-
naphthyridine), 9.03 (s, 1H, N]CH), 13.09 (s, 1H, SH); IR (KBr,
(20). Yellow solid; M.p.: 275.0 ꢂC; Yield: 82%; 1H NMR (
d): 1.49 (t,
3H, N-CH2CH3), 2.69 (s, 3H, 7eCH3), 4.60 (q, 2H, N-CH2), 7.27 (d,
J ¼ 7.2 Hz, 1H, Ar-H), 7.35 (d, J ¼ 8.0 Hz, 1H, H-6-naphthyridine),
7.82 (s, 1H, Ar-H), 8.16 (d, J ¼ 7.2 Hz, 1H, Ar-H), 8.21 (s, 1H, H-2-
naphthyridine), 8.57 (d, J ¼ 8.4 Hz, 1H, H-5-naphthyridine), 9.03

N. Aggarwal et al. / European Journal of Medicinal Chemistry 46 (2011) 4089e4099
4097
(s, 1H, N]CH), 13.15 (s, 1H, SH); IR (KBr, cmꢀ1
)
nmax: 2892, 2386,
solid; M.p.: 200.5 ꢂC; Yield: 70%; 1H NMR (
d
): 1.54 (t, 3H, N-
1632, 1609, 1585, 1494, 1253, 794; MS calculated for
C20H16Cl2N6OS: 458.0482; Observed ESI-MS (m/z): 458.4 [Mþ],
460.2, 462.7.
CH2CH3), 2.69 (s, 3H, 7eCH3), 4.59 (q, 2H, N-CH2), 7.30 (d, J ¼ 8.4 Hz,
1H, H-6-naphthyridine), 7.55 (dd, J ¼ 8.0 Hz, 2H, Ar-H) 8.10 (d, 2H,
Ar-H), 8.58 (d, J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 8.70 (s, 1H, H-2-
naphthyridine); IR (KBr, cmꢀ1
) nmax: 2977, 1608, 1541, 1433, 1250,
4.2.4.20. 3-{4-(2,6-Dichlorobenzylideneamino)-5-mercapto-4H-1,2,4-
789; MS calculated for C20H15ClN6OS: 422.0717; Observed ESI-MS
triazol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one (21). Yellow
(m/z): 422.1 [Mþ], 424.2.
solid; M.p.: 135.6 ꢂC; Yield: 68%; 1H NMR (
d): 1.48 (t, 3H, N-CH2CH3),
2.69 (s, 3H, 7eCH3), 4.58 (q, 2H, N-CH2), 7.35 (d, J ¼ 8.0 Hz, 1H, H-6-
naphthyridine), 7.53e7.75 (m, 3H, Ar-H), 8.16 (s, 1H, H-2-
naphthyridine), 8.62 (d, J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 9.01 (s,
4.2.5.5. 1-Ethyl-7-methyl-3-{6-(3-nitrophenyl)-1,2,4-triazolo [3,4-b]
[1,3,4]thiadiazol-3-yl}-1, 8-naphthyridin-4(1H)-one (26). Yellow-
brown solid; M.p.: 150.0 ꢂC; Yield: 81%; 1H NMR (
d): 1.54 (t, 3H, N-
1H, N]CH), 13.10 (s, 1H, SH); IR (KBr, cmꢀ1
)
nmax: 2986, 2369, 1611,
CH2CH3), 2.71 (s, 3H, 7eCH3), 4.60 (q, 2H, N-CH2), 7.28 (d, J ¼ 8.4 Hz,
1H, H-6-naphthyridine), 7.60e7.64 (m, 1H, Ar-H), 8.13 (dd,
J ¼ 1.2 Hz,1H, Ar-H), 8.16 (dd, J ¼ 1.2 Hz,1H, Ar-H), 8.48 (s,1H, Ar-H),
8.65 (d, J ¼ 8.4 Hz, 1H, H-5-naphthyridine), 8.85 (s, 1H, H-2-
1525, 1435, 1254, 793; MS calculated for C20H16Cl2N6OS: 458.0482;
Observed ESI-MS (m/z): 458.2 [Mþ], 460.4, 462.1.
4.2.5. General synthesis of nalidixic acid based 1,2,4-triazolo [3,4-b]
[1,3,4]thiadiazol-6-yl (22e27)
naphthyridine); 13C NMR (
d): 15.21, 25.23, 47.04, 111.02, 119.43,
121.57, 125.14, 127.53, 128.88, 129.47, 130.20, 132.55, 133.75, 134.54,
A mixture of 4-amino-5-substituted-1,2,4-triazole-3-thiol (1,
5 mmol) and polyphosphoric acid (20 mL) was heated to 50e60 ꢂC
with stirring. Substituted benzoic acid (6 mmol) was added portion
wise. The mixture was then heated at 180e200 ꢂC for 3 h with
stirring. After completion of the reaction, the reaction mixture was
poured into ice and neutralized with concentrated aqueous
ammonia solution. The crude product filtered, washed with water
and recrystallized from hexane/ethyl acetate to give 4-(3-
substituted-1,2,4-triazolo [3,4-b] [1,3,4]thiadiazole) derivatives.
136.84, 143.10, 147.33, 162.39, 166.90, 172.15; IR (KBr, cmꢀ1
)
nmax:
2977, 1682, 1598, 1452, 1281, 777; MS calculated for C20H15N7O3S:
433.0957; Observed ESI-MS (m/z): 433.1 [Mþ].
4.2.5.6. 3-{6-(2,3-Dichlorophenyl)-1,2,4-triazolo [3,4-b] [1,3,4]thiadia-
zol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one (27). Yellow-
brown solid; M.p.: 119.2 ꢂC; Yield: 71%; 1H NMR (
d): 1.53 (t, 3H,
N-CH2CH3), 2.70 (s, 3H, 7eCH3), 4.58 (q, 2H, N-CH2), 7.32 (d,
J ¼ 7.2 Hz, 1H, H-6-naphthyridine), 7.39e7.44 (m, 1H, Ar-H),
7.55e7.67 (m, 1H, Ar-H), 7.91e7.99 (m, 1H, Ar-H), 8.64 (d,
J ¼ 7.6 Hz, 1H, H-5-naphthyridine), 8.81 (s, 1H, H-2-naphthyridine);
4.2.5.1. 1-Ethyl-7-methyl-3-(6-phenyl-1,2,4-triazolo [3,4-b] [1,3,4]
thiadiazol-3-yl)-1,8-naphthyridin-4(1H)-one (22). Brown solid;
13C NMR (
d): 15.14, 25.06, 46.29, 108.54, 120.82, 121.38, 124.77,
M.p.: 122.3 ꢂC; Yield: 78%; 1H NMR (
d): 1.51 (t, 3H, N-CH2CH3), 2.70
125.34, 127.80, 129.54, 130.05, 132.86, 134.44, 136.26, 144.94, 148.71,
(s, 3H, 7eCH3), 4.60 (q, 2H, N-CH2), 7.25 (d, J ¼ 8.4 Hz, 1H, H-6-
naphthyridine), 7.28 (dd, J ¼ 5.6 Hz, 1H, Ar-H) 7.30e7.35 (m, 2H,
H-3, Ar-H), 8.24e8.27 (m, 2H, Ar-H), 8.65 (d, J ¼ 8.4 Hz, 1H, H-5-
162.01, 163.18, 173.47, 174.34; IR (KBr, cmꢀ1
)
nmax: 2875, 1632, 1556,
1439, 1255, 790; MS calculated for C20H14Cl2N6OS: 456.0327;
Observed ESI-MS (m/z): 456.2 [Mþ], 458.1, 460.1.
naphthyridine), 9.01 (s, 1H, H-2-naphthyridine); 13C NMR (
d):
15.02, 25.23, 47.34, 111.31, 119.52, 121.66, 122.00, 128.50, 129.32,
130.20, 131.67, 133.81, 136.28, 148.59, 151.36, 163.78, 164.82, 168.25,
4.2.6. Synthesis of 3-substituted-1,2,4-triazolo [3,4-b] [1,3,4]
thiadiazole-6-thioles (28)
172.14, 176.26; IR (KBr, cmꢀ1
)
nmax: 2962, 1693, 1652, 1574, 1452,
A solution of 4-amino-5-substituted-1,2,4-triazole-3-thiol (1,
5 mmol) in pyridine (20 mL) was taken and carbon disulfide
(8 mmol) with few drops of triethylamine were added to the
reaction mixture. The reaction mixture was refluxed at 100 ꢂC with
stirring for 6 h. Then the reaction mixture was cooled, poured into
ice-cold water and acidified with dil. HCl till the solution was
slightly acidic. The solid product was obtained which was filtered,
washed with water and dried to yield the 1-ethyl-3-(6-mercapto-
1272, 801; MS calculated for C20H16N6OS: 388.1106; Observed ESI-
MS (m/z): 388.4 [Mþ].
4.2.5.2. 3-{6-(2-Chlorophenyl)-1,2,4-triazolo [3,4-b] [1,3,4]thiadia-
zol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one (23). Brown
solid; M.p.: 195.6 ꢂC; Yield: 70%; 1H NMR (
d): 1.58 (t, 3H, N-
CH2CH3), 2.65 (s, 3H, 7eCH3), 4.60 (q, 2H, N-CH2), 7.40 (d, J ¼ 8.4 Hz,
1H, H-6-naphthyridine), 7.63e7.67 (m, 2H, Ar-H) 7.68e7.70 (m, 1H,
Ar-H), 8.10 (dd, J ¼ 8.8 Hz, 1H, Ar-H), 8.45 (d, J ¼ 8.4 Hz, 1H, H-5-
1,2,4-triazolo
[3,4-b]
[1,3,4]thiadiazol-3-yl)-7-methyl-1,8-
naphthyridin-4(1H)-one.
naphthyridine), 8.71 (s, 1H, H-2-naphthyridine); 13C NMR (
d):
15.34, 25.55, 47.76, 111.38, 119.59, 121.17, 122.96, 128.71, 129.02,
129.51, 130.07, 131.42, 136.65, 145.35, 148.05, 160.70, 163.12, 168.49,
4.2.6.1. 1-Ethyl-3-(6-mercapto-1,2,4-triazolo [3,4-b] [1,3,4]thiadia-
zol-3-yl)-7-methyl-1,8-naphthyridin-4 (1H)-one (28). Yellow solid;
174.45, 176.20; IR (KBr, cmꢀ1
)
nmax: 2874, 1612, 1549, 1481, 1445,
M.p.: 273.0 ꢂC; Yield: 72%; 1H NMR (
d): 1.25 (t, 3H, N-CH2CH3), 2.69
1340, 792; MS calculated for C20H15ClN6OS: 422.0717; Observed
(s, 3H, 7eCH3), 4.57 (q, 2H, N-CH2), 7.56 (d, J ¼ 8.4 Hz, 1H, H-6-
ESI-MS (m/z): 423.2 [Mþ þ 1], 425.7.
naphthyridine), 8.60 (d, J ¼ 7.6 Hz, 1H, H-5-naphthyridine), 8.69
(s, 1H, H-2-naphthyridine), 13.06 (s, 1H, SH); 13C NMR (
d): 15.40,
4.2.5.3. 3-{6-(3-Chlorophenyl)-1,2,4-triazolo [3,4-b] [1,3,4]thiadiazol-
25.38, 46.64, 113.4, 120.9, 129.59, 130.7, 136.7, 145.6, 160.2, 163.34,
3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one
(24). Yellow-
): 1.55 (t, 3H,
166.76, 174.17, 184.6; IR (KBr, cmꢀ1
)
nmax: 2863, 2531, 1644, 1611,
brown solid; M.p.: 110.3 ꢂC; Yield: 71%; 1H NMR (
d
1442, 1255, 796; MS calculated for C14H12N6OS2: 344.0514;
N-CH2CH3), 2.70 (s, 3H, 7eCH3), 4.58(q, 2H, N-CH2), 7.28 (d, J ¼ 8.4 Hz,
1H, H-6-naphthyridine), 7.40e7.44 (m, 1H, Ar-H), 7.53e7.55 (m, 1H,
Ar-H), 8.13 (dd, J ¼ 1.6 Hz, 1H, Ar-H), 8.40 (s, 1H, Ar-H), 8.71 (d,
J ¼ 8.4 Hz,1H, H-5-naphthyridine), 8.80(s,1H, H-2-naphthyridine);IR
Observed ESI-MS (m/z): 345.4 [Mþ þ 1].
4.2.7. Synthesis of N-{3-(1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-
naphthyridin-3-yl)-5-mercapto-4H-1,2,4-triazol-4-yl}acetamide
(29)
To a solution of 4-amino-4H-1,2,4-triazole-3-thiol (5 mmol) in
glacial acetic acid (3 mL), acetic anhydride (10 mmol) was added to
it and refluxed for 2 h. After refluxing the reaction mixture was
cooled and poured into ice-cold water. The solid product formed
(KBr, cmꢀ1
) nmax: 2853,1614,1547,1435,1253, 789; MS calculated for
C20H15ClN6OS: 422.0717; Observed ESI-MS (m/z): 422.1 [Mþ], 424.3.
4.2.5.4. 3-{6-(4-Chlorophenyl)-1,2,4-triazolo [3,4-b] [1,3,4]thiadia-
zol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one (25). Brown

4098
N. Aggarwal et al. / European Journal of Medicinal Chemistry 46 (2011) 4089e4099
was filtered, washed with water and oven dried to give the title
refluxed for 3 h. After cooling, the resulting nalidixic acid thio-
semicarbazide was filtered, washed with water and dried. It was
recrystallized from ethanol. A mixture of nalidixic acid thio-
semicarbazide (5 mmol) and 10% KOH (50 mL) was then refluxed
for 3 h. The mixture was then cooled to room temperature and
filtered to remove the unwanted impurities. The filtrate was
neutralized by the gradual addition of glacial acetic acid. The
resulting solid 5-mercapto-4H-1,2,4-triazole (33) was filtered,
washed with water, dried and recrystallized from ethanol.
compound.
White solid; M.p.: 198.4 ꢂC; Yield: 66%; 1H NMR (
d): 1.53 (t, 3H,
N-CH2CH3), 2.18 (s, 3H, CH3), 2.70 (s, 3H, 7eCH3), 4.58 (q, 2H, N-
CH2), 7.33 (d, J ¼ 8.0 Hz, 1H, H-6-naphthyridine), 8.67 (d, J ¼ 8.0 Hz,
1H, H-5-naphthyridine), 8.83 (s, 1H, H-2-naphthyridine), 9.05 (s,
1H, NH), 12.78 (s, 1H, SH); IR (KBr, cmꢀ1
) nmax: 3441, 2362, 1687,
1603, 1531, 1445, 1254, 796; MS calculated for C14H16N6O2S:
344.1055; Observed ESI-MS (m/z): 345.2 [Mþ þ 1].
Pale Yellow solid; M.p.: >300 ꢂC; Yield: 82%; 1H NMR (
d): 1.37 (t,
4.2.8. Synthesis of N-{3-(1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-
naphthyridin-3-yl)-5-mercapto-4H-1,2,4-triazol-4-yl}benzamide (30)
To a solution of 1,2,4-triazole (1, 5 mmol) in acetone and pyri-
dine, benzoyl chloride (6 mmol) was slowly added to it and refluxed
for 6e8 h. The reaction was quenched by adding water to it. A solid
separated out which was treated with aqueous sodium bicarbonate
solution for the removal of excess of benzoic acid. The crude
product was filtered, washed with water and oven dried to get the
desired product.
3H, N-CH2CH3), 2.68 (s, 3H, 7eCH3), 4.48 (q, 2H, N-CH2), 7.42 (d,
J ¼ 8.4 Hz, 1H, H-6-naphthyridine), 8.49 (d, J ¼ 8.0 Hz, 1H, H-5-
naphthyridine), 8.77 (s, 1H, H-2-naphthyridine), 12.81 (s, 1H, NH),
13.59 (s, 1H, SH); 13C NMR (
d
): 15.40, 25.49, 46.13, 107.75, 119.48,
121.69, 136.15, 144.49, 147.59, 148.59, 163.43, 166.00, 174.19; IR (KBr,
cmꢀ1
) nmax: 3360, 3039, 1629, 1605, 1561, 1441, 1255, 792; MS
calculated for C13H13N5OS: 287.0841, Observed 288.4 [Mþ þ 1].
4.3. In vitro antibacterial activity
White solid; M.p.: 192.5 ꢂC; Yield: 66%; 1H NMR (
d): 1.33 (t, 3H,
N-CH2CH3), 2.61 (s, 3H, 7eCH3), 4.40 (q, 2H, N-CH2), 7.13 (d,
J ¼ 8.0 Hz, 1H, H-6-naphthyridine), 7.16e7.20 (m, 2H, Ar-H)
7.33e7.38 (m, 1H, Ar-H), 8.07e8.12 (m, 2H, Ar-H), 8.42 (d,
J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 8.68 (s, 1H, H-2-naphthyridine),
Agar dilution method: Antibacterial susceptibility testing was
carried out using National Committee for Clinical Laboratory
Standards (NCCLS) micro dilution broth assay against five patho-
genic strains S. aureus ATCC 2937, B. subtilis ATCC 12711, E. coli ATCC
8739, Pseudomonas aeruginosa ATCC 9027 and K. pneumoniae ATCC
31488. Initially bacteria were grown at 37 ꢂC in Nutrient Broth
(HIMEDIA) until exponential growth. This culture was used to
inoculate 100 mL of Nutrient Broth so that an initial number of
2 ꢃ 106 CFU/mL could be achieved. Test compound was dissolved in
DMSO/Water and was added to 20 mL inoculated media to get
10.10 (s, 1H, NH), 13.53 (s, 1H, SH); IR (KBr, cmꢀ1
) nmax: 3417, 3059,
2324, 1625, 1606, 1573, 1253, 795; MS calculated for C20H18N6O2S:
406.1212; Observed ESI-MS (m/z): 406.1 [Mþ].
4.2.9. Synthesis of 1-ethyl-7-methyl-3-(6-phenyl-7H-1,2,4-triazolo
[3,4-b] [1,3,4] thiadiazin-3-yl)-1,8-naphthyridin-4(1H)-one (31)
A mixture of triazole (5 mmol), anhydrous potassium carbonate
(11.5 mmol) and phenacyl bromide (5 mmol) in dry acetonitrile
(25 mL) was refluxed for 6e7 h. The reaction mixture was poured
into crushed ice. Solid product obtained was filtered, washed with
water and oven dried.
a final concentration of 250
compound was achieved by transferring 10 mL of this 250
test compound containing media to another 10 mL inoculated
media to get a final concentration 125 g/mL of the test compound.
All other dilutions of the test compound were prepared in a similar
fashion to get the minimal dilution to 15.68 g/mL. Each 10 mL
mg/mL. Two-fold dilution of this
mg/mL
m
White solid; M.p.: >300.0 ꢂC; Yield: 75%; 1H NMR (
d): 1.35 (t, 3H,
m
N-CH2CH3), 2.68 (s, 3H, 7eCH3), 4.55 (q, 2H, N-CH2), 4.65 (s, 2H,
CH2), 7.35 (d, J ¼ 8.0 Hz, 1H, H-6-naphthyridine), 7.41e7.71 (m, 5H,
Ar-H), 8.66 (d, J ¼ 8.0 Hz, 1H, H-5-naphthyridine), 8.78 (s, 1H, H-2-
inoculated media along with the test compound was dispensed
equally into 3 screw capped 10 mL glass culture tubes. Controls
without the test compound, only media and in the presence of
streptomycin were set up simultaneously. All culture tubes were
incubated at 37 ꢂC for 24 h. After incubation, the growth of bacteria
was determined by measuring optical density at 600 nm using UV-
Specord 200/1 (Analytik JENA InstrumentsÒ). The lowest concen-
tration at which there was more than 90% inhibition of bacteria as
compared to the culture without test compound was taken up as
minimal inhibitory concentration (MIC).
naphthyridine); IR (KBr, cmꢀ1
) nmax: 2928, 1673, 1609, 1442, 1255,
797; MS calculated for C21H18N6OS: 402.1263; Observed ESI-MS (m/
z): 402.1 [Mþ].
4.2.10. Synthesis of 3-(1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-
naphthyridin-3-yl)-5H-[1,2,4]-triazolo [3,4-b] [1,3,4]-thiadiazine-
6,7-dione (32)
A mixture of 1 (1 mmol) and oxalyl chloride (1.2 mmol) in dry
benzene (10 mL) was heated under reflux for 6 h. The reaction
mixture was cooled to room temperature. The solvent was removed
under reduced pressure, the solid product obtained was filtered
and recrystallized from ethanol to afford the final product.
4.4. Invitro antifungal activity
The antifungal activity of the compounds was evaluated in vitro
using food poison technique [53].
White solid; M.p.: 180.3 ꢂC; Yield: 70%; 1H NMR (
d): 1.50 (t, 3H,
N-CH2CH3), 2.70 (s, 3H, 7eCH3), 4.58 (q, 2H, N-CH2), 7.35 (d,
J ¼ 8.0 Hz, 1H, H-6-naphthyridine), 8.57 (d, J ¼ 7.6 Hz, 1H, H-5-
naphthyridine), 8.29 (s, 1H, H-2-naphthyridine), 8.98 (s, 1H, NH);
4.5. QSAR
All the topological indices used were calculated using all
hydrogen suppressed graph. These molecular graphs were obtained
by deleting all the carbon hydrogen as well as heteroatomic
hydrogen bonds from the structure of the triazole derivatives. The
calculations of these indices are well documented in the literature
and therefore are not given here.
13C NMR (
d
): 15.17, 25.21, 46.32, 109.44, 119.99, 120.76, 128.93,
131.56, 133.91, 136.42, 148.41, 149.02, 162.81, 174.57, 184.24; IR (KBr,
cmꢀ1
nmax: 3248, 3056, 1678, 1609, 1580, 1442, 1255, 790; MS
)
calculated for C15H12N6O3S: 356.0692; Observed ESI-MS (m/z):
356.1 [Mþ].
4.2.11. Synthesis of 1-ethyl-3-(5-mercapto-4H-1,2,4-triazol-3-yl)-
7-methyl-1,8-naphthyridin-4(1H)-one (33)
A mixture of nalidixic acid hydrazide (5 mmol), potassium
thiocyanate (10 mmol), conc. HCl (10 mL) and water (20 mL) was
4.5.1. Physicochemical parameters
Various physicochemical parameters (descriptors) viz, MW
(molecular weight), MR (molar refraction), MV (molar volume), Pc
(parachor), h(refractive index), Surface tension (ST), density (d), Pol

N. Aggarwal et al. / European Journal of Medicinal Chemistry 46 (2011) 4089e4099
4099
[20] M. Kritsanida, A. Mouroutsou, P. Marakos, N. Pouli, S. Papakonstantinou-
Garoufalias, C. Pannecouque, M. Witvouw, E. De Clercq, Il Farmaco 57 (2002)
253e257.
[21] V. Mathew, J. Keshavayya, V.P. Vaidya, D. Giles, Eur. J. Med. Chem. 42 (2007)
823e840.
[22] B. Tozkoparan, N. Gokhan, G. Aktay, E. Yesilada, M. Ertan, Eur. J. Med. Chem. 35
(2000) 743e750.
[23] B. Tozkoparan, E. Kupeli, E. Yesilada, M. Ertan, Bioorg. Med. Chem. 15 (2007)
1808e1814.
(polarizability), LogP (logarithm of octanol/water partition coeffi-
cient), H Bnd Acp (hydrogen bond acceptor), 2D SA (Polar 2D
surface area), and 3D SA (Polar 3D surface area), were calculated
using DRAGON evaluation version software [47] and Marvin sketch
[48]. The expressions for the calculation of these parameters are
available in the literature.
[24] M. Amir, S. Kumar, Acta Pharm. 57 (2007) 31e45.
[25] M.S. Langley, S.P. Clissold, Drugs 35 (1988) 104e122 Adis International.
[26] J.L. Kelley, C.S. Koble, R.G. Davis, E.W. McLean, F.E. Soroko, B.R. Cooper, J. Med.
Chem. 38 (1995) 4131e4134.
[27] E. Przegalinski, A. Lewandowska, J. Neural Transm. 46 (1979) 303e312.
[28] N. Demirbas, R. Ugurluoglu, A. Demirbas, Bioorg. Med. Chem. 10 (2002)
3717e3723.
4.5.2. Statistical analysis
The regression analysis is made using maximum R2 method and
stepwise regression analysis [49e51] for obtaining statistically
significant models.
[29] A. Howell, J. Cuzick, M. Baum, A. Buzdar, M. Dowsett, J.F. Forbes, G. Hoctin-
Boes, J. Houghton, G.Y. Locker, J.S. Tobias, Lancet 365 (2005) 60e62.
[30] A. Czarnocka-Janowicz, H. Foks, A. Nasal, J. Petrusewicz, B. Damasiewicz,
A. Radwanska, R. Kaliszan, Pharmazie 46 (1991) 109e112.
[31] G. Turan-Zitouni, Z.A. Kaplancikli, K. Erol, F.S. Killic, Il Farmaco 54 (1999)
218e223.
Acknowledgement
Author (NA) is thankful to Council of Scientific and Industrial
Research, New Delhi, Indiaforgrantingthesenior researchfellowship.
[32] M. Ghannoum, L.B. Rice, Clin. Microbiol. Rev. 12 (1999) 501e517.
[33] M.Y. Mhasalkar, M.H. Shah, S.T. Nikam, K.G. Ananthanarayana, C.V. Deliwala,
J. Med. Chem. 13 (1970) 672e674.
References
[34] J.N. Delgado, W.A. Remers, Text Book of Organic, Medicinal Pharmaceutical
Chemistry, tenth ed.. J.B., Lippincott Company, Philadelphia, 1998, p. 189.
[35] M. Moreno-Manas, Y. Arredondo, R. Pleixats, M. Teixido, M.M. Haga, C. Palacin,
J.M. Castello, J.A. Oritizz, J. Heterocycl. Chem. 29 (1992) 1557e1560.
[36] L. Czollner, G. Sxilagli, J. Janaky, Arch. Pharm. 323 (1990) 225e229.
[37] C.H. Chu, X.W. Sun, L. Sun, Z.Y. Zhang, Z.C. Li, R.A. Liao, J. Chin. Chem. Soc. 46
(1999) 229e235.
[1] G.Y. Leisher, E.J. Froelich, M.D. Gruett, J.H. Bailey, P.R. Brundage, J. Med. Pharm.
Chem. 5 (1962) 1063e1065.
[2] A.M. Pedrini, D. Geroldi, A. Siccardi, A. Balaschi, Eur. J. Biochem. 25 (1972)
359e365.
[3] (a) G.C. Crumplin, J.T. Smith, Antimicrob. Agents Chemother. 8 (3) (1975)
251e261;
[38] A. Er-Rhaimini, R. Mornet, Indian J. Heterocycl. Chem. 29 (1992) 1561.
[39] H.L. EIbe, K.H. Buechel, W. Brandes, S. Dutzmann, K. Luerssen, Ger. Offen 4
(1996) 803883.
[40] B. Wolfgan, R. Wolfgan, P. Arbold, S. Bartel, Ger. Offen DE. 4,425,660, Chem.
Abstr. 124 (1996) 261076.
[41] Y. Liu, A. Gangguly, F. Bennet, Chem. Abstr. 129 (1998) 260464.
[42] M. Sztanke, T. Tuzimski, J. Rzymowska, K. Pasternak, M.K. Szerszen, Eur. J.
Med. Chem. 43 (2008) 404e419.
(b) N. Aggarwal, R. Kumar, C. Srivastava, P. Dureja, J.M. Khurana, J. Agric. Food
Chem. 58 (2010) 3056e3061.
[4] D.J. Prasad, M. Ashok, P. Karegoudar, B. Poojary, B.S. Holla, N.S. Kumari, Eur. J.
Med. Chem. 44 (2009) 551e557.
[5] A. Foroumadi, S. Mansouri, Z. Kiani, A. Rahamani, Eur. J. Med. Chem. 38 (2003)
851e854.
[6] V.J. Ram, L. Mishra, N.H. Pandey, D.S. Kushwaha, L.A.C. Pieters, A.J. Vlietinck,
J. Heterocycl. Chem. 27 (1990) 351e355.
[43] J. Haber, Cas. Lek. Cesk 140 (2001) 596e604.
[44] R.W. Sidwell, L.B. Allen, J.H. Hoffman, J.T. Witkowsti, L.N. Simon, Proc. Soc. Exp.
Biol. Med. 148 (1975) 854e858.
[45] W.J. Adams, P.A. Bombardt, R.A. Code, J. Pharma. Sci. 72 (10) (1983)
1185e1189.
[7] N. Ergenc, E. Ilhan, G. Otuk, Pharmazie 47 (1992) 59e60.
[8] V.J. Ram, H.N. Pandey, Chem. Pharm. Bull. 22 (1974) 2778e2783.
[9] K.R. Reddy, K. Mogilaiah, B. Swamy, Acta Chim. Hung 127 (1990) 45e50.
[10] S.P. Hiremath, V.N. Sonar, K.R. Sekhar, M.G. Purohit, Indian J. Chem. 28B (1989)
626e630.
[46] R. Todeschini, V. Consonni, Handbook of Molecular Descriptors. Wiley VCH,
Weinheim, 2000.
[11] B.K. Bhattacharya, V.D. Dirk, G. Hoornaert, S. Sawant, Chem. Abstr. 102 (1985)
24441.
[47] Dragon 5.0 evaluation version.http://www.disat.unimib.it/chm.
[48] Marvinsketch 5.4 evaluation version.www.chemaxon.com/products/marvin/
marvinsketch.
[49] S. Chaterjee, A.S. Hadi, B. Price, Regression Analysis by Examples, third ed..
Wiley VCH, New York, 2000.
[50] H. Waterbeemd Vande, in: , Methods and Principles in Medicinal Chemistry,
vol 2, VCH, Weinleium (Ger), 1995.
[51] J. Devillers, W. Karcher (Eds.), Chemical and Environmental Sciences, Klawer
Academic Pub., Dorderch (Netherland), 1991.
[52] G.S. Abdelmoty, H.F. Heta, Bull. Pharm. Sci. 32 (1) (2009) 125e140 Assiut
University.
[53] N. Aggarwal, R. Kumar, P. Dureja, D.S. Rawat, J. Agric. Food Chem. 57 (2009)
8520e8525.
[12] N. Kalyoncuoglu, S. Rollas, D. Sur-Altiner, Y. Yegenoglu, A. Ong, Pharmazie 47
(1992) 796e797.
[13] S. Rollas, N. Kalyoncuoglu, D. Sur-Altiner, Y. Yegenoglu, Pharmazie 48 (1973)
308e309.
[14] S.C. Bennur, V.B. Jigajinni, V.V. Badiger, Rev. Roum. Chim. 21 (1976) 757e762.
[15] C.S. Andotra, S.K. Sharma, Indian J. Pharm. Sci. 51 (1989) 107.
[16] Z. Zhang, X. Feng, L. Chen, Q. Meng, D. Gao, Gaodeng Xuexiao Huaxue Xuebao
10 (1989) 471.
[17] W. Rudnicka, H. Foks, M. Janowiec, Z. Zwolska-Kwiek, Acta Pol. Pharm. 43
(1986) 523e528.
[18] W. Rudnicka, J. Sawlewicz, Acta Pol. Pharm. 35 (1978) 135e142.
[19] I. Kuçukguzel, S.G. Kuçukguzel, S. Rollas, M. Kiraz, Bioorg. Med. Chem. Lett. 11
(2001) 1703e1707.