Design, synthesis and SAR exploration of hybrid 4-chlorophenylthiazolyl-s- triazine as potential antimicrobial agents

Article abstract of DOI:10.3109/14756366.2011.587418

Two novel series of hybrid class 4-chlorophenylthiazole-s-triazine were synthesized via nucleophilic substitution of 2,4,6-trichloro-1,3,5-triazine with distinguished alkenyl/alkyl/aryl/hetero alkylaryl amino and mercapto nucleophiles under nitrogen atmosphere. We identified that the spectrums of antibacterial activity of all tested compounds reveal promising and significant inhibition of gram-positive and gram-negative micro-organisms and the most active compounds, 31d and 32d, were found to be non-toxic in preliminary cytotoxicity assay. We also report that the Molinspiration and Osiris Property Explorer calculations have found a new lead 32d, which binds preferentially to the nuclear receptor to exhibit antibacterial potency.

Full text of DOI:10.3109/14756366.2011.587418

Journal of Enzyme Inhibition and Medicinal Chemistry, 2012; 27(2): 281–293
© 2012 Informa UK, Ltd.
ISSN 1475-6366 print/ISSN 1475-6374 online
DOI: 10.3109/14756366.2011.587418
RESEARCH ARTICLE
Design, synthesis and SAR exploration of hybrid
4-chlorophenylthiazolyl-s-triazine as potential
antimicrobial agents
Prashant Gahtori and Surajit K. Ghosh
Department of Pharmaceutical Sciences, Dibrugarh University, Dibrugarh, Assam, India
Abstract
Two novel series of hybrid class 4-chlorophenylthiazole-s-triazine were synthesized via nucleophilic substitution of
2,4,6-trichloro-1,3,5-triazine with distinguished alkenyl/alkyl/aryl/hetero alkyl–aryl amino and mercapto nucleophiles
under nitrogen atmosphere. We identified that the spectrums of antibacterial activity of all tested compounds reveal
promising and significant inhibition of gram-positive and gram-negative micro-organisms and the most active
compounds, 31d and 32d, were found to be non-toxic in preliminary cytotoxicity assay. We also report that the
Molinspiration and Osiris Property Explorer calculations have found a new lead 32d, which binds preferentially to the
nuclear receptor to exhibit antibacterial potency.
Keywords: s-Triazine, synthesis, MIC, substituent effect, Molinspiration, Osiris
Introduction
compounds possess potent antimicrobial activities as
Subsequent development of antibiotics, or agents derived
from them, has produced impressive reduction in the
burden of disease imposed by bacterial infections. In
the United States alone, the expenditure for bacterial
and fungal diseases is more than $20 billion annually1,2.
A summary report from Italian Ministry of research sug-
gests that no single technology will represent the magic
bullet for antibiotic discovery, but only the painstaking
integration of a multidisciplinary team with profound
knowledge of microbiology, chemistry and bioinformatics
will ultimately lead to new antibacterial agents of medi-
cal relevance and commercial success3. Indeed, World
Health Organization and many experts also recommend
that this area of research benefits tremendously through
enhancing the efforts in the lead generation and optimi-
zation to develop new, cost-effective and innovative enti-
ties (http://www.idsociety.org/Content.aspx?id=5558)4.
1,3,5-Triazine scaffold provides the basis for the design
of biologically relevant molecules with widespread
application in therapeutics. For example, these versatile
antimalarial5,6, antiprotozoal7, anticancer8,9, antiviral10,
antibacterial agent11,12 etc. In continuation of our endea-
vour programme in the area of s-triazines, particularly
hybrid phenylthiazolyl-s-triazine derivatives (Figure 1),
two series A (1a–9a) and B (10b–18b) of s-triazines as
novel antibacterial agents, and compounds with phenyl
group showing potent antibacterial activity has been
already reported13–15
.
Bearing in mind the most popular hypotheses in the
field of medicinal chemistry, the appropriate attachment
of bulk groups (bulky flanking groups) to new bioactive
chemical entities, such as halogen atoms, could lead to
volumetric and conformational changes. More conspicu-
ously, the possibility to establish halogen bonds or polar
interactions may increase protein–ligand stability and
subsequently, contribute to the binding affinity that will
enable more selective drug candidates to be discovered16.
Encouraged by these observations and in order to explore
the scope of antibacterial potential of hybrid phenylthi-
azolyl-s-triazines in detail, here we incorporate 4-chloro
is article supersedes the one previously published online (10th june 2011), due to an author error in figure 1, which has now been
corrected in this version.
Address for Correspondence: Prashant Gahtori, Department of Pharmaceutical Sciences, Dibrugarh University, 786004 Dibrugarh, Assam,
India. Tel.: +91 373 2370254; Fax: +91 373 2370323. E-mail: praniori@gmail.com
(Received 31 March 2011; revised 08 May 2011; accepted 09 May 2011)
281

282 P. Gahtori and S. K. Ghosh
and 3,4-dichloro to design a new class of diethylamino-
chloro (series C) and diethylamino-dichloro (series D)
phenylthiazolyl-s-triazine derivatives (Figure 2).
with water and purified by flash column chromatogra-
phy (silica gel mesh size 100–200) using methanol/ethyl
acetate (1:20 v/v) as eluent to yield pure diethylamino-
chlorophenylthiazolyl-s-triazine derivatives (20c–27c)
and diethyl amino dichlorophenylthiazolyl-s-triazine
derivatives (29d–36d).
Methods
All the chemicals used in the synthesis were of analyti-
cal grade and used without further purification. Melting
points (m.p.) were determined on a Veego, model no.
MPI open capillary melting point apparatus and boiling
points (b.p.) were measured by 10–12-mm diameter test
tube–inverted capillary tube and both were uncorrected.
e completion of reaction was checked by thin layer
chromatography using silica gel-GF254 (0.5-mm thickness,
benzene, ethyl acetate and 0.1M alcoholic KOH solvent
system) and spots were visualized under ultraviolet radia-
tion.ecompoundsreportedinthisstudyhavebeenthor-
oughly characterized by their spectral data and elemental
analysis (Tables 1 and 2). Fourier transform infrared read-
ings (in KBr) were recorded on Perkin Elmer-Spectrum
Antimicrobial assay
Finally, the purified products were tested for their mini-
mum inhibitory concentration (MIC) against three rep-
resentatives each from gram-positive viz. Lactobacillus
casei (NCIM-2651), Bacillus cereus (NCIM-2458),
Staphylococcus aureus (NCIM-2120) and gram-negative
viz. Salmonella typhimurium (NCIM-2501), Escherichia
coli (NCIM-2065), Klebsiella aerogenes (NCIM-2098)
organisms by broth dilution method18. Penicillin G and
streptomycin were used as reference antibacterial agents
(Table 3). Solution of the test compounds and reference
drugsweredissolvedinDMSO.Nutrientbroth(M002)was
procured from Hi-Media Laboratories (Mumbai, India).
e test compounds were dissolved in DMSO (200 μg/
ml) and were serially diluted from 1 to 7 to obtain gradual
dilution starting from 100, 50, 25, 12.5, 6.25 and 3.125 μg/
ml. e inocula of test bacteria was adjusted to a volume
of 0.5–2.5 × 105 colony-forming units/ml by matching
with the turbidity of 0.5 McFarland reagent. A volume of
1 ml of the standardized broth culture was added to 1 ml
of each serially diluted test tube. e capped tubes with
cotton plugs were incubated at 35 2°C for 20 h and com-
pared with standardized 0.5 McFarland reagent.
1
RX-I spectrophotometer. H NMR spectra were recorded
on Bruker Avance II 400 NMR spectrometer in dimethyl
sulfoxide (DMSO)-d6 using trimethylsilane as an internal
standard (chemical shift in δ, ppm). Elemental analysis
was carried out on a Vario EL III elemental analyzer.
General procedure for synthesis of hybrid
diethylamino chlorophenylthiazolyl-s-triazine
derivatives, series C (19c–27c) and D (28d–36d)
As outlined in Scheme 1, 2-diethylamino-4,6-dichloro-
1,3,5-triazine (α) was prepared as per published pro-
cedure using cyanuric chloride and diethyl amine17.
e equimolar quantities of α (1 mol) and synthesized
(4′-chlorophenyl)thiazolyl-2-amine (1 mol) mixture was
heated to 40–45°C under aqueous NaHCO3–dioxane for
10 min with constant stirring, filtered immediately under
vacuum to furnish (4′-chlorophenyl)thiazolyl-s-triazine
(19c). Whereas (3′,4′-dichlorophenyl)thiazolyl-s-triazine
(28d) was prepared under similar conditions using (3′,4′-
dichlorophenyl)thiazolyl-2-amine (1 mol). ese precur-
sors (19c and 28d) were further intended for preparation
of final compounds− 0.1 mmol each of them was added
to various alkenyl/alkyl/aryl/hetero alkyl–aryl amines
(0.1 mmol) and similar thiols (0.1 mmol) under nitrogen
atmosphere in basic NaHCO3 (0.1 mmol) and 100 ml diox-
ane at 120°C for 6 h. e products were filtered, washed
Cytotoxicity test
To increase the chances for clinical success, assess-
ment of toxicological studies on chemically diverse
series is a necessary step in the drug discovery pathway.
Nevertheless, the low therapeutic index of compounds,
due to their general toxicity, may once more prevent
their development as a drug. Consequently, it remains
attractive to develop new derivatives possessing high
efficacy and potency and higher therapeutic indices. We
have reviewed our attention on the results of antibacte-
rial screening as well as lead analogues 31d and 32d
executed against brine shrimp assay that eventually led
to preliminary assessment of their toxicity. Cytotoxicity
test was carried out using brine shrimp assay19 for the
most active compounds 31d and 32d (Table 4). Samples
Figure 1. Hybrid phenylthiazolyl-s-triazine derivatives.
Journal of Enzyme Inhibition and Medicinal Chemistry

Hybrid 4-chlorophenylthiazolyl-s-triazine as antimicrobial agent 283
Figure 2. Hybrid diethylamino-chloro (series C) and diethylamino-dichloro (series D) phenylthiazolyl-s-triazine derivatives.
were prepared by dissolving in DMSO to obtain a
stock concentration of 1000 μg/ml, which was serially
diluted six times to obtain a concentration of 15.63 μg/
ml. Each concentration was tested for cytotoxicity in
triplicates, using DMSO as control. Brine shrimp eggs
(Artemia salina) were hatched in a hatching chamber
filled with fresh sea water. Ten larvae of brine shrimps
were transferred to each sample test tube using dispos-
able pipettes. Survivors were counted after 24 h and the
mortality at each concentration was determined.
group contributions. ese have been obtained by fitting
the sum of O- and N-centred polar fragment contribu-
tions to real three-dimensional (3D) volume for a train-
ing set of about 12,000, mostly drug-like molecules. e
3D molecular geometries for a training set were fully
optimized by the semi-empirical AM1 method. In our
studies, molecular properties of a total of 18 compounds
from series C and D were valued, and the results were
compared with the values obtained for standard drugs
penicillin G (Table 5).
Molecular properties’ calculations
Osiris calculations
A viable drug candidate should have bioavailability,
metabolic stability, toxicity and transport properties
comparable to known drugs. ese “drug-like” properties
depend on the compound’s size, molecular flexibility,
hydrophobicity and electronic bond distributions. e
advanced computational design has sped up research by
identifying new molecules with possible medical appli-
cations prior to laborious experiments and expensive
preclinical studies20,21. e intuitive and user-friendly
open-access Molinspiration and Osiris Property Explorer
programmes were used in this study to yield a matrix for
each property.
Inhibition of one of the very important class of enzymes
like Cytochrome P450 or production of unwanted
metabolites might induce a variety of adverse drug
reactions. The second stage of the process with online
Osiris programme invokes the prediction of ADME-Tox
liabilities as well as score of any entities with increas-
ing success by using a combined electronic/structure
docking procedure. According to the recent work on
the drug design using Osiris-based calculation, it is
now possible to predict activity and/or inhibition with
increasing success in drug targets. The important fea-
tures like solubility, toxicity and drug likeness can be
predicted through these studies (http://www.organic-
chemistry.org/prog/peo/). The outcome from these
studies is successfully drawn in comparison to penicil-
lin G (Table 6).
Molinspiration calculations
Molinspiration methodology offers calculation of impor-
tant molecular properties like logP (milogP), topological
polar surface area (TPSA), number of hydrogen bond
acceptors and donors, bioactivity score and possible
molecular toxicity toolkit written in Java-based system.
e statistical parameters rank milogP as one of the best
methods available for logP prediction, whereas TPSA is
also calculated based on the methodology as a sum of
fragment contributions (http://www.molinspiration.
com/cgi-bin)22,23. Method for the calculation of molecu-
lar volume developed at Molinspiration is based on
Results
Our present study was undertaken to synthesize some
novel phenylthiazolyl-s-triazine derivatives by nucleo-
philic substitution of cyanuric chloride (2,4,6-trichlo-
ro-1,3,5-triazine) with various amino and mercapto
nucleophiles in basic dioxane medium under neat nitro-
gen atmosphere with simple standard work up procedures
© 2012 Informa UK, Ltd.

284 P. Gahtori and S. K. Ghosh
Journal of Enzyme Inhibition and Medicinal Chemistry

Hybrid 4-chlorophenylthiazolyl-s-triazine as antimicrobial agent 285
© 2012 Informa UK, Ltd.

286 P. Gahtori and S. K. Ghosh
Journal of Enzyme Inhibition and Medicinal Chemistry

Hybrid 4-chlorophenylthiazolyl-s-triazine as antimicrobial agent 287
© 2012 Informa UK, Ltd.

288 P. Gahtori and S. K. Ghosh
Scheme 1. Reagents and condition: (a) Na2CO3 0 -5°C; (b) 4-chloro-phenylthiazole-2-amine and 3,4-dichlorophenylthiazolyl-2-amine,
NaHCO3, aqueous dioxane 45–50°C; (c) Alkenyl/alkyl/aryl/hetro alkyl–aryl amines or thiols in NaHCO3, dioxane 90–100°C under nitrogen
atmosphere.
in good yields (Scheme 1). e first substitution is exother-
mic and, therefore, the temperature of the reaction mix-
ture has to be maintained at 0°C. e substitution of the
second chloride can be performed at room temperature.
Finally, the third position is functionalized under reflux of
the solvent. As a result, a careful control of the temperature
during the substitution reactions will allow the synthesis
of 2,4,6-trisubstituted-triazines by sequential and very
selective addition of amines or thiols. e first substitu-
tion of chlorine in cyanuric chloride was carried out with
diethyl amine at 0°C in aqueous dioxane medium followed
by simple re-crystallization to facilitate isolation of pure
product 1, in 81% yield17. e second substitution in 1 was
carried out by 4-(4′-chloro)phenylthiazolyl-2-amine and
4-(3′,4′-dichloro)phenylthiazolyl-2-amine, respectively,
at room temperature to afford 19c and 28d in good yields.
esecompoundswerefurtherreactedwithvariousamino
and mercapto nucleophiles by refluxing at 120°C under
basic nitrogen dioxane environment to furnish targeted
series C and D. e FTIR spectra of all C=N group vibra-
tions were in the range of 1644–1682cm−1. Absorption of
−NH was confirmed in a broad range of 3287–3320cm−1.
e nuclear magnetic resonance spectra of the signals cor-
responding to−CH3 group appeared at 0.83–1.36ppm. All
compounds gave correct elemental analysis within 0.4%
of their respective theoretical values.
e synthesized phenylthiazolyl-s-triazine derivatives
have been found to have significantly comparable anti-
bacterial activity with that of standard antibiotic used.
e heterocyclic entity 32d exhibited equipotent activity
towards gram-positive (L. casei and S. aureus) organisms
and 31d has marked equipotent activity against B. cereus
when compared with standard drug penicillin G. e title
compounds 23c, 26c, 30d and 34d have also shown equi-
potent activity against S. typhimurium when compared
with penicillin whereas 22c, 29d, 31d and 32d showed
more potent activity than penicillin. Moreover, in case
of L. casei, compounds 22c, 23c and 31d were found to
be more potent, on comparing with the standard drug
streptomycin. e compound 32d was found to be more
potent against B. cereus with the same reference standard
streptomycin, as well as both 31d and 32d were found to
Journal of Enzyme Inhibition and Medicinal Chemistry

Hybrid 4-chlorophenylthiazolyl-s-triazine as antimicrobial agent 289
Table 3. MIC values of series C and D against gram-positive/negative bacteria.
MIC (µg/ml)
Gram positive
Gram negative
Salmonella
Lactobacillus casei
Bacillus cereus
Staphylococcus
typhimurium
Escherichia coli Klebsiella aerogenes
Compound
Series C
19c
20c
21c
22c
23c
24c
25c
(NCIM-2651)
(NCIM-2458)
aureus (NCIM-2120)
(NCIM-2501)
(NCIM-2065)
(NCIM-2098)
100
50
100
25
50
25
100
50
100
100
50
100
100
100
50
25
25
25
50
6.25
6.25
25
12.5
6.25
12.5
12.5
12.5
25
12.5
6.25
6.25
50
6.25
12.5
25
25
25
50
50
50
25
25
100
25
50
26c
27c
12.5
25
12.5
25
12.5
50
50
25
50
Series D
28d
29d
30d
31d
32d
33d
34d
35d
100
12.5
12.5
3.125
1.562
50
50
12.5
6.25
1.562
3.125
25
50
6.25
6.25
1.562
3.125
25
100
6.25
12.5
6.25
3.125
25
100
12.5
6.25
6.25
6.25
25
100
50
50
50
50
100
25
25
25
12.5
12.5
25
12.5
25
6.25
25
25
25
50
36d
Penicillin G
Streptomycin
50
25
50
50
100
12.5
1.562
1.562
12.5
1.562
6.25
3.125
6.25
12.5
1.562
12.5
3.125
e supreme biological activity appears when the sub-
stituent is a phenyl-substituted amino or thiol derivative.
Substitution of phenyl-amino group in 22c at fifth posi-
tion on phenylthiazolyl-s-triazine enhanced the activity
as compared to other s-triazines. In continuation, substi-
tution with furfuryl-amino group in 23c also enhanced
activity against B. cereus and S. aureus, respectively,
whereas no prominent effect was observed against E. coli
and K. aerogenes. Introduction of thioallyl group in 24c
gives equipotent compound like streptomycin against S.
aureus. ere was further decrease in antibacterial activ-
ity if furfuryl-amino group was replaced by thiobutyl in
25c, thiophenyl in 26c and thiofurfuryl in 27c groups. By
inserting allyl-amino group in 29d, which was equipotent
with streptomycin against S. aureus, the effect of muzzling
amino phenyl group would seem to predominate, except
in the case of 35d. e free phenyl and furfuryl groups
enhance the activity whereas free allyl and butyl groups
interfere with the biological activity in the phenylthiaz-
olyl-s-triazine. Perhaps the most intriguing starting point
for a molecule upon which to build selectivity is the allyl
type side chain as in case of 31d and 32d; the most intui-
tive efficacy was observed in compounds with this com-
mon substituted side chain. However, interestingly in allyl
substitution all alone no remarkable evidence is reported
and overall 3,4-dichlorophenylthiazolyl-s-triazine deriva-
tives (series D) were found to be more active than their
4-chlorosubstituted (series C). As different alkenyl/alkyl/
aryl/hetero alkyl–aryl substitution patterns with delocal-
ized electronic structure were introduced in the s-triazine
Table 4. Brine shrimp cytotoxicity assay for compounds 31d and
32d.
Mortalitya
Concentration (μg/ml)
31d
32d
1000.00
Control
LD50
4
4
1
1
>1000μg/ml
>1000μg/ml
Toxicity
Non-toxic
Non-toxic
aTen larvae (Artemia salina) for each test concentration.
be more potent than streptomycin in case of gram-positive
S. aureus. e distinguished equipotent activities are also
reported against different gram-positive bacteria by 23c,
24c, 26c, 28d, 29d and 30d when compared with the
same antibiotic streptomycin. Clearly, in order to reach
pocket, the title compounds 31d and 32d displayed the
most interesting antibacterial activities against all gram-
positive/negative bacteria used. However, it is particularly
noteworthy that even though its significance is not clear,
the novel class of these compounds have displayed no
marked activity in case of K. aerogenes. Rest of compounds
exhibited very weak to moderate antibacterial activities.
Discussion
Structure–activity relationships
e structure–activity relationship (SAR) study of
the lead compound clearly indicates the presence of
furfuryl-amino substitution in 23c and 32d as a core
bioactive group against gram-positive micro-organisms.
© 2012 Informa UK, Ltd.

290 P. Gahtori and S. K. Ghosh
Table 5. Molinspiration calculations of compounds.
Molinspiration calculations (series C & D)
Compound
31d
32d
milogP
7.65
TPSA
78.86
92.00
natoms
32
MW
nON
nOHNH
nViolations
nrotb
Volume
403.74
402.11
486.43
490.42
7
8
2
2
1
1
8
9
6.59
32
aFor average MIC.
MIC, minimum inhibitory concentration; MW, molecular weight; nOHNH, number of hydrogen bond donors; nON, number of hydrogen
bond acceptors; TPSA, topological polar surface area.
Table 6. Osiris calculations of compounds.
Toxicity level
Tumorigenic
Osiris calculations
DL
Compound
19c
20c
21c
22c
23c
24c
25c
26c
Mutagenic
Irritant
RE
DS
0.09
0.22
0.20
0.17
0.21
0.19
0.17
0.17
0.18
0.07
0.21
0.21
0.19
0.22
0.19
019
+
−
−
−
−
−
−
−
−
+
−
−
−
−
−
−
−
2.11
1.59
2.50
2.49
4.13
1.48
1.72
2.36
4.12
1.47
0.99
1.92
1.86
3.53
0.88
1.13
1.76
3.52
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
27c
28d
29d
30d
31d
32d
33d
34d
35d
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
0.19
0.20
0.91
36d
Penicillin G
−
−
−
−
−
−
−
−
11.28
DL, drug likeness; DS, drug score; RE, reproductive effect; S, solubility; +, high toxic effects; −, drug-conform behaviour; , undesired
effect.
ring and hereby, a great variance in biological efficacy is
predominant as evidenced in Table 3. For instance, in its
infancy rest of the compounds demonstrated moderate-
to-weak antibacterial efficacy against all gram positive/
negative bacteria.
drugs to be able to penetrate through bio-membranes
according to Lipinski’s rules. However, the lowest degree
of lipophilicity among all the compounds was exhibited
by compounds 19c, 20c and 23c, which is an indica-
tion for good water solubility (see supplemental file for
details). e polar surface area (PSA) is calculated from
the surface areas that are occupied by oxygen and nitro-
gen atoms and by hydrogen atoms attached to them.
Molecules with PSA values of 140 or more are expected
to exhibit poor intestinal absorption. e results state
that all the compounds are having optimal TPSA values
among which the highest degree of TPSA was achieved in
the case of 23c and 32d. ese identified entities can be
characterized as permissible candidates for active drug
absorption. All the compounds, excluding 35d and 36d
have only one violation of the rule 5.
For the development of novel agent from hybrid chlo-
rophenylthiazolyl-1,3,5-triazine, the identification of the
presence of active structures is important, which can
be drawn by sound knowledge of their physicochemi-
cal properties. Correlation results showed no single
physicochemical parameter that triggers the biological
activity of these phenylthiazolyl-s-triazines. For instance,
the relationship between the average MIC (y) and most
Cytotoxicity brine shrimp assay
In continuation of this study to explore preliminary
therapeutic potential, the lead compounds 31d and 32d
were further analyzed for toxicity results in terms of LC50
values, which were obtained from the best-fit line by plot-
ting concentration verses percentage lethality. From the
data in Table 4, it should be easy to see that brine shrimp
assay for the most active compounds 31d and 32d pos-
tulated the non-toxicity of these compounds. Although
in its infancy, molecular similarity matrices seem to have
a lot to offer in the optimization of molecular structures
for antibacterial effect and currently there is a great deal
of research on these compounds for use as a medicinal
agent in near future.
Molinspiration description
Molinspiration clearly depicts the calculated values
of logP greater than 5, which is the lowest limit for the
Journal of Enzyme Inhibition and Medicinal Chemistry

Hybrid 4-chlorophenylthiazolyl-s-triazine as antimicrobial agent 291
influencing physicochemical property − volume (x) − a
simple regression was performed and a weak linear cor-
relation was established as expressed by straight line
Equation 1 (Figure 3).
and score to model the possible therapeutic efficacy
of compounds (Table 6). The present results also sup-
port the previous observations remarkably with well-
behaved drug-likeness data to quantify the role played
by various organic groups in promoting or interfer-
ing with the way a drug can associate to mimic the
antibacterial efficacy. Activity of all test compounds
and standard drug, penicillin G, were rigorously ana-
lyzed under four criteria of toxicological activities in
areas of mutagenicity, tumorigenicity, irritation and
reproductive action.
y = −0.775x +333.178 (r2 = 0.649)
(1)
From this hallmark of MIC and volume, as well as bearing
the potential of 3,4-dichlorosubstitution over 4-chloro-
substitution from earlier studies, it can be assumed that
only optimized volume of chlorophenylthiazolyl-1,3,5-
triazine is a general amplicon for biological activity. In this
sequence, slight low correlation of natoms (r2 =0.610) and
comparatively weak for molecular weight (r2 =0.389) was
also observed. However, no correlation yet exists for logP
(r2 =0.208) in our studies, as this parameter has never been
noteworthy for the most antimicrobial activities. For a stan-
dard drug penicillin G, the predicted set of simple molecu-
lar descriptors viz. logP (1.725), molecular weight (320.37),
number of hydrogen bond acceptors (6), and number of
hydrogen bond donors (2) were also found in agreement
with the Lipinski rule of 5. e obtained set of molecular
descriptors excluding logP, for novel compounds 31d and
32d by the same Molinspiration methodology, also sup-
port the Lipinski rule from such studies (Table 5).
e putative mechanism of this observed antibacterial
action is brought about by predicted bioactivity for the
most active compounds 31d and 32d. An understand-
ing of the concepts discussed, preferred mechanism to
underpin all this work is the availability of nuclear recep-
tors. A major aspect of the utilization of this information
will be the provision of these small molecules, which will
recognize selected sequences, perhaps with the goal of
switching off particular nuclear receptor as in bacterial
chemotherapy. For some time, these identified entities
have been known to bind preferentially to nuclear recep-
tor to produce possible antibacterial action through the
molecular mechanisms in terms of binding score of
active compounds 31d (0.93) and 32d (1.47).
As seen in Table 6, it is also a hallmark in our stud-
ies that substitution of chlorine directly from triazine
with distinguished alkenyl/alkyl/aryl/hetero alkyl–aryl
amines or mercaptans and on other hand, clubbing
of chlorine direct to phenylthiazole tends to drug-
conform behaviour. In fact, chlorine is a moderate hal-
ogen-bond acceptor, the forming C–Cl bond is enough
stable and has good binding affinity. Replacement
of hydrogen with chlorine can provide a substantial
alteration on the volumetric and shape issues. It was
also described that subunits bearing chlorine can be
accommodated in tight and deep cavities, as well as in
hydrophobic pockets of the biological targets24. In the
light of these features, 3,4-dichlorophenylthiazole may
be best accommodated on the active site of targets to
produce desired antibacterial action and justify their
predominance over 4-chlorophenylthiazole. However,
direct attachment of chlorine to triazine renders drug-
likeness behaviour possibly through comparatively low
logP value and supposed to be impermeable to bio-
logical membranes to exert pharmacological action.
erefore, successful attempt can be accomplished by
replacement of third chloro group from 19c and 28d
with these amines or thiols to generate series C and D.
e efficacy of the given set of molecules in terms of
threshold drug-likeness behaviour was predicted for
23c (4.13), 27c (4.12) and 32d (3.53), in contrast to the
relative activity score of the standard drug penicillin
(11.28). By analyzing, we can see that except in case
of 29d (0.22), dichloro substitution to phenylthiazole
conforms high drug behaviour over mono substitution.
As predicted by this modelling, the best drug-conform
behaviour in terms of drug score and drug likeness was
also profound for the same 32d (0.22), in comparison
to penicillin.
Osiris description
As a consequence of this analogue system, the com-
pounds have been subjected to toxicity, drug likeness
In order to reach clinical settings, drug has to cross
various trials, where the odds of success are ever lower.
For instance, plenty of new and novel candidates are
being discovered each and every year; however, only
six new antibiotics have been approved since 2003 by
the US Food and Drug Administration (http://www.
fda.gov/cder/approval/index.htm)25. More advanced
targeted drug delivery systems are nowadays available.
In the light of this, lead identification is an essential
exercise in the field of medicinal chemistry (http://
www.nanomed.gazi.edu.tr)26,27. Nevertheless, the out-
come of our wet-lab studies is in closer fitting with
Figure 3. Straight-line correlation between average MIC and
volume. MIC, minimum inhibitory concentration.
© 2012 Informa UK, Ltd.

292 P. Gahtori and S. K. Ghosh
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Molinspiration and Osiris property calculations. From
all the studies performed, the compound 32d shows
good inhibition against gram positive/negative bac-
teria and possess good characteristic as novel agent.
Further, systematic modification studies around this
lead can produce antibiotics with increased potency
and spectrum in near future.
Conclusion
In summary, the preliminary in vitro antibacterial
screening reported here indicates the antimicrobial
potency of these novel synthesized compounds 19c–
27c and 28d–36d against reference standard (penicillin
G and streptomycin). e SAR observation has shown
the insertion of furfuryl-amino or phenyl-amino group
in mono-chloro-3,4-dichlorophenylthiazolyl-s-triazine
(28d) to have more antibacterial potency than their
allyl-amino, butyl-amino or any mercapto 3,4-dichlo-
rophenylthiazolyl-s-triazine counterpart. e most
effective compounds 31d and 32d were also found to
be non-toxic in the brine shrimp lethality assay. e
present studies also enable the execution of important
physicochemical parameters like natoms, molecular
weight and volume to reassemble compounds enriched
in antibacterial activity. e above-mentioned anti-
bacterial screening and the facts drawn allow us to
find the new lead 32d, which may bind preferentially
to nuclear receptor to produce possible antibacterial
action. To elucidate the robustness, lead optimization
work in chemotherapy is ongoing and will be reported
subsequently.
Acknowledgements
The authors acknowledged the valuable contribu-
tions made to their work by Lonza, Switzerland for
arranging a gift sample of cyanuric chloride for the
work included in this paper and critical reading and
supports from Archana Uppal, SGRRITS, Dehradun
for structuring the manuscript. The authors are also
thankful to an anonymous reviewer for carefully read-
ing the manuscript and for his critical comments and
valuable suggestions.
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Infectious Diseases (ESCMID). EUCAST Definitive Document
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Declaration of interest
e authors declared no conflict of interest.
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