Ionic liquid-promoted one-pot synthesis of thiazole-imidazo[2,1-b][1,3,4]thiadiazole hybrids and their antitubercular activity

Article abstract of DOI:10.1039/c5md00346f

In this paper, we report the facile and efficient one-pot three-component synthesis of 1-((6-phenylimidazo[2,1-b][1,3,4]thiadiazol-5-yl)methylene)-2-(4-phenylthiazol-2-yl)hydrazine derivatives (5a-w) using an ionic liquid, namely 1-butyl-3-methylimidazolium bromide ([Bmim]Br). The compounds were screened for their in vitro antimycobacterial activity against Mycobacterium tuberculosis. Compound 5s showed the highest inhibitory activity with an MIC of 6.03 μM which is slightly lower than the MIC values of standard drugs ethambutol (15.3 μM) and ciprofloxacin (9.4 μM). Four other compounds of the series viz.5e, 5i, 5t and 5w also showed significant inhibitory activity with MIC values in the range of 11.7-13.9 μM. The structure-activity relationship revealed that the trifluoromethyl substitution at position-2 and p-chlorophenyl substitution at position-6 of the imidazo[2,1-b][1,3,4]thiadiazole ring enhanced the inhibitory activity. Also, the methyl, methoxy, fluoro or nitro substituents on the thiazole ring enhanced the activity of the compounds. None of the active compounds were toxic to a normal cell line (NIH 3T3), which signifies the lack of general cellular toxicity of the molecules. In silico molecular docking studies revealed the favourable interaction of the potent compounds with the target enzymes InhA and CYP121.

Full text of DOI:10.1039/c5md00346f

View Article Online
View Journal
MedChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: R. Jurupula, N.
Nayak, U. Dalimba, P. Yogeeswari and S. Dharmarajan, Med. Chem. Commun., 2015, DOI:
10.1039/C5MD00346F.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/medchemcomm

Page 1 of 16
MedChemComm
View Article Online
DOI: 10.1039/C5MD00346F
Ionic liquid promoted one-pot synthesis of thiazole-imidazo[2,1-b]
[1,3,4]thiadiazole hybrids and their antitubercular activity†
Jurupula Ramprasada, Nagabhushana Nayaka, Udayakumar Dalimbaa,*, Perumal Yogeeswarib
and Dharmarajan Sriramb
aOrganic Chemistry Laboratory, Department of Chemistry, National Institute of Technology
Karnataka, Surathkal, Srinivasanagar, Mangaloreꢀ575025, India.
bMedicinal Chemistry and Drug Discovery Research Laboratory, Pharmacy Group, Birla
Institute of Technology and ScienceꢀPilani, Hyderabad Campus, Jawahar Nagar, Telangana
Stateꢀ500078, India.
† The authors declare no competing interest.
*Corresponding author email: udayaravi80@gmail.com, udayakumar@nitk.ac.in Phone:
+91ꢀ824ꢀ2473207. Fax: +91ꢀ824ꢀ2474033
Abstract
In this paper, we report the facile and efficient oneꢀpot three component synthesis of
1ꢀ((6ꢀphenylimidazo[2,1ꢀb][1,3,4]thiadiazolꢀ5ꢀyl)methylene)ꢀ2ꢀ(4ꢀphenylthiazolꢀ2ꢀyl)
hydrazine derivatives (5aꢀw) using an ionic liquid, 1ꢀbutylꢀ3ꢀmethyl imidazolium bromide
([Bmim]Br). The compounds were screened for their in vitro antimycobacterial activity
against Mycobacterium tuberculosis. Compound 5s showed the highest inhibitory activity
with a MIC of 6.03 µM which is slightly lower than the MIC values of standard drugs
ethambutol (15.3 µM) and ciprofloxacin (9.4 µM). Four other compounds of the series viz.
5e, 5i, 5t and 5w also showed significant inhibitory activity with MIC values in the range
11.7 ꢀ 13.9 µM. The structureꢀactivity relationship revealed that a trifluoromethyl substitution
at positionꢀ2 and a pꢀchlorophenyl substitution at positionꢀ6 of the imidazo[2,1ꢀ
b][1,3,4]thiadiazole ring enhance the inhibition activity. Also, methyl, methoxy, fluoro or
nitro substituents on the thiazole ring enhanced the activity of the compounds. None of the
active compounds were toxic to a normal cell line (NIH 3T3) which signifies the lack of
general cellular toxicity of the molecules. In silico molecular docking studies revealed the
favourable interaction of the potent compounds with target enzymes, InhA and CP121.
Keywords: Imidazo[2,1ꢀb][1,3,4]thiadiazole; 1,3ꢀthiazole; ionic liquids; oneꢀpot synthesis;
Mycobacterium tuberculosis; Cytotoxicity; Molecular docking.

MedChemComm
Page 2 of 16
View Article Online
DOI: 10.1039/C5MD00346F
1. Introduction
Tuberculosis (TB) is caused by the Mycobacterium tuberculosis (Mtb) and it mainly
affects the lungs of human respiratory system. According to the report released from world
health organization (WHO) in 2014,1 around 9 million people fell sick and 1.5 million people
died from the disease, 360 000 of them were HIVꢀpositive. The current treatment with routine
drugs for the treatment of multi drugꢀresistant TB (MDRꢀTB) and extensively drugꢀresistant
TB (XDRꢀTB) is prolonged and challenging with limited efficacy. Generally, the MDRꢀTB
patients require treatment for 20 months and the drugs used for the treatment are more toxic
and less effective than those used to treat drugꢀsusceptible TB. Therefore, there is an
emergence requirement for the development of novel pharmacophores to treat MDRꢀTB and
XDRꢀTB effectively in a shorter duration and with fewer side effects.
In view of this, the imidazo[2,1ꢀb][1,3,4]thiadiazole (ITD) scaffold2ꢀ5 is a promising
heterocyclic moiety to develop efficient antitubercular leads.6,7 The derivatives with a
pharmacophoric substitution at positionꢀ5 of the ring exhibited significant inhibition activity
against Mtb H37Rv strain.8,9 For instance, Alegaon et al. reported the synthesis and
antitubercular evaluation of a series of 5ꢀsubstituted ITD derivatives and the compound
which contains a rhodanine acetic acid group (I, Figure 1) showed excellent antitubercular
activity with a MIC of 3.12 µM.10 In our earlier studies,11,12 we incorporated a benzimidazole
and 1,2,3ꢀtriazole moieties at positionꢀ5 of the ITD ring and evaluated the antitubercular
activity of the hybrid molecules. Interestingly, most of the compounds (II, III) exhibited
significant activity against Mtb H37Rv strain. These results motivated us to incorporate other
pharmacophores at positionꢀ5 of the ITD ring and to investigate the effect of the structural
modification on the antitubercular activity of the molecules. Further, the molecular design
strategy which involves the hybridization of two active pharmacophores into a single
molecular framework has become one of most promising approaches to develop potent
antiTB agents. In this direction, we envisaged the integration of substituted thiazoles with the
core ITD ring considering the fact that thiazole derivatives are being considered as important
pharmacophores in the development of new antitubercular leads against Mtb H37Rv strain.13,14
In addition, the thiazole based molecules15,16 exhibit low toxic level which is evident also
from the safety profile of some of the marketed drugs like nitazoxanide, tizoxanide,
aztreonam, meloxicam and relutex. Further, some thiazolylhydrazone derivatives (IVꢀVI)
exhibited remarkable growth inhibitory activity against Mycobacterium tuberculosis.17,18 For
instance, Ozadali et al (2014) synthesized a series of thiazolyl hydrazone derivatives, among
which compound V exhibited excellent activity with MICMABA of 1.03 µM.19 So we have

Page 3 of 16
MedChemComm
View Article Online
DOI: 10.1039/C5MD00346F
introduced the thiazole ring at positionꢀ5 of the ITD core through an amineꢀimine linkage.
The target compounds, 1ꢀ((6ꢀphenylimidazo[2,1ꢀb][1,3,4]thiadiazolꢀ5ꢀyl)methylene)ꢀ2ꢀ(4ꢀ
phenylthiazol ꢀ2ꢀyl)hydrazines (5a-w) were synthesized by a oneꢀpot threeꢀcomponent
synthesis in an ionic liquid medium. Ionic liquids (ILs) unlike conventional organic solvents
are nonꢀvolatile, green, nonꢀhazardous, easy to handle and thermally durable.20,21 Ionic
liquids, particularly based on Nꢀalkylꢀ3ꢀmethylimidazolium cation have exhibited great
importance in modern heterocyclic chemistry and these are considered as substitution for
conventional organic solvents.22ꢀ24 So, 1ꢀbutylꢀ3ꢀmethylimidazolium bromide ([Bmim]Br),
which is one of the widely used ILs, was employed in the present study. The oneꢀpot reaction
was carried out between threeꢀcomponents viz 2,6ꢀdisubstituted imidazo[2,1ꢀ
b][1,3,4]thiadiazoleꢀ5ꢀcarbaldehyde, thiosemicarbazide and pꢀsubstituted phenacyl bromide.
This method is highly atom efficient and there is no formation of byꢀproducts. Hence, the
pure product was isolated straightaway (without column purification procedure) from the
reaction system.
(Figure 1 here)
2. Results and discussion
2.1. Chemistry
One of the key intermediates, 5ꢀmethylꢀ1,3,4ꢀthiadiazolꢀ2ꢀamine (2a) was synthesized
by treating acetyl chloride with thiosemicarbazide whereas the other intermediate, 5ꢀtriflouro
methylꢀ1,3,4ꢀthiadiazoleꢀ2ꢀamine (2b) was synthesized according to the reported procedure.25
Compounds 3a–e were synthesized by the reaction between 2a-b and the corresponding
°
substituted αꢀhaloarylketone at 80ꢀ85 C for 24 h. In the next step, these compounds (3a–
e) were subjected to the Vilsmeier–Haack formylation reaction to afford 2ꢀsubstitutedꢀ6ꢀ
arylimidazo[2,1ꢀb][1,3,4]thiadiazoleꢀ5ꢀcarbaldehydes (4a-e).10,11 For the synthesis of target
molecules, a one pot synthetic protocol (scheme 1) was employed instead of conventional
two step procedure19 which generally takes a longer duration for the isolation of the final
products. The solvent system, temperature and reaction time for the oneꢀpot threeꢀcomponent
protocol was optimized so as to get a good yield of the product. For this, the oneꢀpot reaction
of 2ꢀmethylꢀ6ꢀ(4ꢀmethylphenyl)imidazo[2,1ꢀb][1,3,4]thiadiazoleꢀ5ꢀcarbaldehyde (4a) with
thiosemicarbazide and 4ꢀflouro phenacyl bromide (scheme 2) was investigated under
different reaction conditions as presented in ESI (Table S1). Among these, the reaction in a
mixture of [bmim]Br and ethanol at 80° C resulted in a better product (5e) yield. Also, the
reaction under this condition was complete in a shorter duration of 30 minutes. The optimized
reaction condition was applied for the reaction of all five aldehydes (4a-e) with

MedChemComm
Page 4 of 16
View Article Online
DOI: 10.1039/C5MD00346F
thiosemicarbazide and different phenacyl bromides. The corresponding derivatives (5a-w)
were isolated in good yields. The structural features, reaction time and yield of the target
compounds (5a-w) are given in ESI (Table S2). The plausible reaction mechanism for the
formation of final derivatives (5a-w) is shown in the scheme 3.
(Scheme 1 here)
(Scheme 2 here)
(Scheme 3 here)
The target molecules were analysed using spectroscopic techniques to confirm their
1
structure. For instance, the H NMR spectrum of compound 5e showed a singlet with one
proton at δ 12.14 ppm due to the ꢀNH proton. Another singlet at δ 8.41 ppm is due to the ꢀCH
proton of the imine (CH=Nꢀ) linkage. The singlets at δ 2.80 and 2.38 ppm represent the
methyl protons on the 1,3,4ꢀthiadiazole and phenyl rings respectively. The spectrum
displayed a multiplet in the region δ 7.93 – 7.81 ppm and two triplets at δ 7.31 and 7.24 ppm
due to the aromatic protons. Also, its mass spectrum showed a molecular ion peak at m/z
1
449.0, which corresponds to M+1 peak of the molecule. The H and 13C NMR spectral data
along with the elemental data of all the target molecules and some representative spectra are
given in the ESI.
2.2. In vitro antimycobacterial activity
The target compounds (5a-w) were screened against Mtb H37Rv (ATCC27294) using
the agar dilution method to evaluate their antimycobacterial activity in terms of minimum
inhibitory concentration (MIC) values. The MIC is defined as the minimum concentration of
a compound required to completely inhibit the bacterial growth. The MIC values of 5a-w
along with those of standard drugs for comparison are presented in Table 1 and Figure 2.
Compound, 1ꢀ((6ꢀ(4ꢀchlorophenyl)ꢀ2ꢀ(trifluoromethyl)imidazo[2,1ꢀb] [1,3,4] thiadiazolꢀ5ꢀyl)
methylene)ꢀ2ꢀ(4ꢀpꢀtolyl thiazolꢀ2 yl)hydrazine (5s) is the most active derivative of the series
and its MIC (6.03 ꢁM) is lower than those of standard drugs, ethambutol and ciprofloxacin.
Additionally, compounds 5e, 5i, 5t and 5w with MIC values 13.94, 12.72, 11.70 and 11.97
ꢁM respectively are more active than ethambutol. The structural activity relationship reveals
that the various substituents (R1/R2) on the imidazo[2,1ꢀb][1,3,4]thiadiazole ring affect
significantly the antitubercular activity of the compounds. The trifluoromethyl substitution at
positionꢀ2 (R1) was found to enhance the activity of the molecules. All the trifluoromethyl
substituted derivatives except 5q, showed lower MIC values than their methyl analogues.
That is to say, compounds 5o, 5p, 5r, 5s, 5t, 5u and 5w are more active than compounds 5f,
5g, 5j, 5k, 5l, 5m and 5n respectively. Among trifluoromethyl substituted derivatives, the pꢀ

Page 5 of 16
MedChemComm
View Article Online
DOI: 10.1039/C5MD00346F
chlorophenyl substituted (i.e R2 = Cl) compounds (5s, 5t, 5u and 5w) showed better activity
than the respective pꢀmethoxyphenyl (i.e R2 = OCH3) analogues (5o, 5p, 5q and 5r). A
similar structureꢀactivity relationship was observed with most of the methyl (R1) substituted
derivatives (5f ꢀ 5n) as well. Though the substituents (R3) on the thiazole ring affect
remarkably the activity of the compounds, we did not observe a uniform trend in the
structureꢀactivity relationship. However, compounds with methyl, methoxy, fluoro or nitro
substituents on the thiazole ring showed significant activity. Hence, the imidazo[2,1ꢀ
b][1,3,4]thiadiazole ring with a trifluoromethyl group at positionꢀ2 and a pꢀchlorophenyl
substituent at positionꢀ6 could be an active core for further structural modification,
particularly by introducing different pharmacophoric units at positionꢀ5 of the core structure,
in order to develop promising antiTB agents.
(Figure 2 here)
2.3. Antibacterial activity
The in vitro antibacterial activity of compounds 5a-w was tested using serial plate
dilution method.26 All the compounds were screened against three bacterial strains viz. S.
aureus, P. aeruginosa and E. coli. The MIC values were evaluated at concentration range of
3.125 ꢀ 50 µg/mL and ciprofloxacin was taken as the standard drug. Compound 5w
demonstrated significant inhibition activity against all three tested bacterial strains. The
antibacterial screening results are displayed in Table 1. It can be seen that the molecules
show a better inhibition activity against Mtb H37Rv when compared to their activity against
the other tested bacterial strains. So it may be concluded that these molecules are somewhat
selective in their inhibition action against Mtb H37Rv strain.
(Table 1 here)
2.4.
In vitro cytotoxicity studies
The in vitro cytotoxicity of the active compounds (MIC ≤ 30 µM against M.
tuberculosis) was evaluated against NIH 3T3 mouse embryonic fibroblasts cell line using
MTT assay.27 The cell growth inhibition of potent compounds at a concentration of 50 ꢁg/mL
is shown in Figure 3. It can be seen that none of the active compounds are toxic to the
normal cells thus proving the lack of general cellular toxicity.
(Figure 3 here)

MedChemComm
Page 6 of 16
View Article Online
DOI: 10.1039/C5MD00346F
2.5.
Molecular docking studies
In order to gain an insight about the mechanism of action of the new thiazoleꢀITD
hybrids, the active molecules were subjected to molecular docking studies against two
enzymes, enoylꢀacyl carrier protein reductase (InhA) and cytochrome P450 monooxygenase
(CYP121) of M. tuberculosis, which have been validated as effective antiꢀTB targets.19
Further, Isoniazid (the first line antiTB drug) acts by inhibiting enoyl acyl carrier protein
reductase (InhA). Recent studies on thiazolylhydrazone and 1,3,4ꢀthiadiazole derivatives with
InhA revealed good binding interaction of these molecules with amino acid residue of the
enzyme.28,29 InhA is one of the key enzymes involved in the type II fatty acid biosynthesis
pathway. Tyr 158 is an important amino acid residue which interacts with the long chain fatty
acyl substrates required for the synthesis of mycolic acids in the mycobacteria.30,31 On the
other hand, cytochrome P450 monooxygenase (CYP121) was selected based on the earlier
reports on active inhibition of the target by some triazole derivatives.28 The molecules
synthesized in the present study also belong to the azole group of compounds. The molecules
were docked with in the active sites of InhA (PDB code: 1P44) and CYP121 (PDB code:
4KTF) using Glide 6.6 (Schrodinger, 2015ꢀ1). The ligands from the crystal structure of the
enzymeꢀligand complexes were rebuilt and redocked to validate the docking procedure. The
RMSD values of the docking pose from the original orientation of the ligands were found to
be 0.6106 and 1.1467 Å respectively for 1P44 and 4KTF. The docking poses of molecules
5d, 5s and 5w are shown in figure 4. Compound 5d showed the highest docking score of ꢀ
8.89 with 1P44 and exhibited Hꢀbond interactions with residues Ala 157, Gly 104 (back
bone) and Gln 100 (side chain) as well as πꢀπ stacking interaction with residues Phe 149 and
Tyr 158. The most potent antiꢀTB compound 5s with a docking score of ꢀ7.23 showed πꢀπ
stacking interaction with residues Phe 149 and Tyr 158. It is interesting to note that most of
the active compounds have shown interaction with amino acid residue Tyr 158. Similarly, the
active compounds showed favourable interactions with enzyme 4KTF as well. Compound 5w
has the highest docking score of ꢀ9.75 whereas compound 5s with a docking score of ꢀ8.27
showed an Hꢀbond interaction with Ala 167 and πꢀπ stacking interactions with Phe 168 and
Trp 182. The docking score of all the active molecules and details of interacting amino acid
residues are given in ESI (Table S3).
(Figure 4 here)

Page 7 of 16
MedChemComm
View Article Online
DOI: 10.1039/C5MD00346F
3.
Conclusions
We synthesized
a
series of 1ꢀ((6ꢀphenylimidazo[2,1ꢀb][1,3,4]thiadiazolꢀ5ꢀyl)
methylene)ꢀ2ꢀ(4ꢀphenylthiazolꢀ2ꢀyl)hydrazine derivatives via oneꢀpot threeꢀcomponent
approach using an ionic liquid ([Bmim]Br), with excellent product yields. The antitubercular
screening of the molecules revealed that derivative 5s, which contain a trifluoromethyl and a
pꢀchlorophenyl substituents at positionsꢀ2 and 6 respectively of the ITD ring, is the most
active molecule with an MIC of 6.03 µM. The inhibition activity of this molecule is higher
than that of the standard drugs Ethambutol and Ciprofloxacin. Other four derivatives, 5e, 5i,
5t and 5w showed better inhibitory activity than ethambutol. The trifluoromethyl substituted
derivatives exhibited superior activity when compared to the activity of methyl substituted
analogues. Also, it was observed that a pꢀcholorophenyl substitution (at positionꢀ6 of the ITD
ring) contributes better than a pꢀmethoxyphenyl group towards the antitubercular activity.
The structureꢀactivity relationship revealed that the imidazo[2,1ꢀb][1,3,4]thiadiazole ring
with a trifluoromethyl group at position ꢀ2 and a pꢀchlorophenyl substituent at position ꢀ6
could be an active core for further structural modification in order to develop potent antiTB
agents. Further, none of the active molecules are toxic to a normal cell line which signifies
the lack of general cellular toxicity. Also, these molecules are somewhat selective in their
inhibition action against Mtb H37Rv strain. The molecular docking studies revealed the
strong interaction of the active molecules with the target enzymes, InhA and CP121. Active
compounds 5d, 5e, 5h, 5i and 5s showed interaction with amino acid Tyr 158 which is an
important residue to interact with the long chain fatty acyl substrates required for the
synthesis of mycolic acids in the mycobacteria. Hence, these compounds with significant
inhibition activity could serve as promising lead molecules for further development as antiꢀ
TB agents.
Acknowledgements
Authors are thankful to NITK, Surathkal for providing the research facilities. Also,
we thank Dr.Reddy’s institute of life sciences, Hyderabad Central University for providing
NMR and mass spectral analysis. We are obliged to Dr. K. G. Bhat, Maratha Mandal’s Dental
College, Hospital and Research Centre, Belgaum, India, for providing the facilities for
biological screening.

MedChemComm
Page 8 of 16
View Article Online
DOI: 10.1039/C5MD00346F
References
1.
Global tuberculosis report 2014ꢀworld health organization (http://www.who.int/tb/
publications/global_ report/en/).
2.
3.
4.
5.
I. A. M. Khazi, A. K. Gadad, R. S. Lamani and B. A. Bhongade, Tetrahedron, 2011,
67, 3289ꢀ3316.
Y. Hu, C.ꢀY. Li, X.ꢀM. Wang, Y.ꢀH. Yang and H.ꢀL. Zhu, Chem. Rev., 2014, 114,
5572ꢀ5610.
M. Narasimhaá Rao and V. Lakshmaá Nayak, Med. Chem. Commun., 2014, 5, 1644ꢀ
1650.
A. Kamal, V. S. Reddy, K. Santosh, G. Bharath Kumar, A. B. Shaik, R. Mahesh, S. S.
Chourasiya, I. B. Sayeed and S. Kotamraju, Med. Chem. Commun., 2014, 5, 1718ꢀ
1723.
6.
7.
8.
A. K. Gadad, M. N. Noolvi and R. V. Karpoormath, Bioorg. Med. Chem., 2004, 12,
5651ꢀ5659.
M. B. Palkar, M. N. Noolvi, V. S. Maddi, M. Ghatole and L. G. Nargund, Med. Chem.
Res., 2012, 21, 1313ꢀ1321.
V. S. Hegde, G. D. Kolavi, R. S. Lamani and I. A. M. Khazi, J. Sulfur Chem., 2006,
27, 553ꢀ569.
9.
G. Kolavi, V. Hegde and P. Gadad, Bioorg. Med. Chem., 2006, 14, 3069ꢀ3080.
10.
S. G. Alegaon, K. R. Alagawadi, P. V. Sonkusare, S. M. Chaudhary, D. H. Dadwe and
A. S. Shah, Bioorg. Med. Chem. Lett., 2012, 22, 1917ꢀ1921.
11.
12.
J. Ramprasad, N. Nayak, U. Dalimba, P. Yogeeswari, D. Sriram, S. K. Peethambar, R.
Achur and H. S. S. Kumar, Eur. J. Med. Chem., 2015, 95, 49ꢀ63.
J. Ramprasad, N. Nayak, U. Dalimba, P. Yogeeswari and D. Sriram, Bioorg. Med.
Chem. Lett., 2015, 25, 4169ꢀ4173.
13.
14.
P. Makam and T. Kannan, Eur. J. Med. Chem., 2014, 87, 643ꢀ656.
A. Meissner, H. I. Boshoff, M. Vasan, B. P. Duckworth, C. E. Barry Iii and C. C.
Aldrich, Bioorg. Med. Chem., 2013, 21, 6385ꢀ6397.
15.
E. Pitta, E. Tsolaki, A. Geronikaki, J. Petrovic, J. Glamoclija, M. Sokovic, E. Crespan,
G. Maga, S. S. Bhunia and A. K. Saxena, Med. Chem. Commun., 2015, 6, 319ꢀ326.

Page 9 of 16
MedChemComm
View Article Online
DOI: 10.1039/C5MD00346F
16.
17.
18.
D. Garella, E. Borretto, A. Di Stilo, K. Martina, G. Cravotto and P. Cintas, Med.
Chem. Commun., 2013, 4, 1323ꢀ1343.
P. Makam, R. Kankanala, A. Prakash and T. Kannan, Eur. J. Med. Chem., 2013, 69,
564ꢀ576.
M. S. Shaikh, M. B. Palkar, H. M. Patel, R. A. Rane, W. S. Alwan, M. M. Shaikh, I.
M. Shaikh, G. A. Hampannavar and R. Karpoormath, RSC. Adv., 2014, 4, 62308ꢀ
62320.
19.
K. Ozadali, O. Unsal Tan, P. Yogeeswari, S. Dharmarajan and A. Balkan, Bioorg.
Med. Chem. Lett., 2014, 24, 1695ꢀ1697.
20.
21.
22.
23.
24.
25.
26.
J. Dupont, R. F. de Souza and P. A. Suarez, Chem. Rev., 2002, 102, 3667ꢀ3692.
J. H. Davis, James, Chem. Lett., 2004, 33, 1072ꢀ1077.
S. V. Dzyuba and R. A. Bartsch, Angew. Chem. Int. Ed., 2003, 42, 148ꢀ150.
A. K. Yadav, P. Dhakad and G. R. Sharma, Tetrahedron Lett., 2013, 54, 6061ꢀ6063.
J. Noei and A. R. Khosropour, Tetrahedron Lett., 2013, 54, 9ꢀ11.
K. Li and W. Chen, Heteroat. Chem., 2008, 19, 621ꢀ629.
B. Garudachari, A. M. Isloor, M. Satyanaraya, K. Ananda and H.ꢀK. Fun, RSC. Adv.,
2014, 4, 30864ꢀ30875.
27.
28.
29.
30.
31.
L.ꢀL. Gundersen, J. NissenꢀMeyer and B. Spilsberg, J. Med. Chem., 2002, 45, 1383ꢀ
1386.
K. J. McLean, K. R. Marshall, A. Richmond, I. S. Hunter, K. Fowler, T. Kieser, S. S.
Gurcha, G. S. Besra and A. W. Munro, Microbiology, 2002, 148, 2937ꢀ2949.
S. D. Joshi, U. A. More, D. Koli, M. S. Kulkarni, M. N. Nadagouda and T. M.
Aminabhavi, Bioorg. Chem., 2015, 59, 151ꢀ167.
L. Jena, P. Waghmare, S. Kashikar, S. Kumar and B. C. Harinath, Int. J.
Mycobacteriol., 2014, 3, 276ꢀ282.
T. Matviiuk, F. Rodriguez, N. Saffon, S. MalletꢀLadeira, M. Gorichko, A. L. d. J. L.
Ribeiro, M. R. Pasca, C. Lherbet, Z. Voitenko and M. Baltas, Eur. J. Med. Chem.,
2013, 70, 37ꢀ48.

MedChemComm
Page 10 of 16
View Article Online
DOI: 10.1039/C5MD00346F
Contents
List of tables
Table 1. In vitro inhibition activity of title compounds (5a-w) against Mycobacterium
tuberculosis, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli.
List of Figures
Figure 1. Imidazo[2,1ꢀb][1,3,4]thiadiazole and thiazolylhydrazone based active
antitubercular agents I – V. The corresponding reference number is given in
parenthesis.
Figure 2. Antitubercular activity in terms of MIC (µM) of the target compounds (5a-w)
against M. tuberculosis H37Rv strain. Isoniazid (INH), Ethambutol (EMB) and
Ciprofloxacin (INN) were used as standard drugs.
Figure 3. Growth inhibition activity of active compounds (at a concentration of 50 µg/mL)
against NIH 3T3 cell line.
Figure 4. The docking poses of some active compounds with target enzymes, InhA and
CP121 (a) 5d with InhA; (b) 5s with InhA; (c) 5w with CP121; (d) 5s with CP121
List of schemes
Scheme 1. Synthesis of 1ꢀ((6ꢀphenylimidazo[2,1ꢀb][1,3,4]thiadiazolꢀ5ꢀyl)methylene)ꢀ2ꢀ(4ꢀ
phenylthiazolꢀ2ꢀyl)hydrazine derivatives. Reaction conditions: (i) Acetyl
°
chloride, 0 C ꢀ RT, 3 h, 76%; (ii) Polyphosphoric acid, 110 °C, 8h, 65%; (iii)
°
Substituted phenacyl bromide, ethanol, 80ꢀ85 C, 24 h, 70ꢀ82%; (iv) DMF,
POCl3, 60° C, 6h, 60ꢀ85%; (v) Thiosemicarbazide, substituted phenacyl bromide,
[bmim]Br and ethanol, 80 °C, 30ꢀ45 mins, 82ꢀ96%.
Scheme 2. Three component oneꢀpot synthesis of 5e. This reaction was taken as a model to
optimize the reaction conditions for the oneꢀpot synthesis of target molecules
5aꢀw.
Scheme 3. Plausible reaction mechanism for the formation of final derivatives (5a-w).

Page 11 of 16
MedChemComm
View Article Online
DOI: 10.1039/C5MD00346F
Table 1. In vitro inhibition activity of title compounds (5a-w) against Mycobacterium
tuberculosis, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli.
Compound
M. tuberculosis
E. coli
S. aureus
P. aeruginosa
MIC (µg/mL) MIC (µM) MIC (µg/mL) MIC (µg/mL)
MIC (µg/mL)
25
50
56.29
108.66
53.87
26.31
13.94
108.66
105.01
26.03
12.72
107.73
107.74
52.07
103.1
53.87
24.13
94.32
93.63
24.12
6.03
50
50
50
50
25
25
50
12.5
50
50
50
12.5
25
50
50
50
25
50
25
25
50
25
25
25
50
25
6.25
6.25
ꢀ
5a
5b
25
50
50
5c
12.5
6.25
50
6.25
50
12.5
50
5d
5e
50
50
5f
50
12.5
6.25
25
50
5g
12.5
6.25
50
12.5
25
5h
5i
50
50
5j
50
50
50
5k
25
25
50
5l
50
25
25
5m
25
25
25
5n
12.5
50
25
50
5o
12.5
50
25
5p
50
50
5q
6.25
3.125
6.25
50
50
50
5r
25
25
5s
11.70
92.94
91.07
11.97
9.44
12.5
12.5
12.5
6.25
6.25
ꢀ
25
5t
5u
12.5
12.5
12.5
6.25
ꢀ
50
5v
6.25
3.125
0.1
5w
Ciprofloxacin
Isoniazid
Ethambutol
0.729
15.32
3.125
ꢀ
ꢀ
ꢀ

MedChemComm
Page 12 of 16
View Article Online
DOI: 10.1039/C5MD00346F
II: MIC= 6.56ꢀ 9.05 ꢁ M (11)
III: MIC= 7.0ꢀ 15.6 ꢁ M (12)
I: MIC= 3.12 ꢁ M (10)
VI: MIC= 1.03 ꢁ M (19)
IV: MIC= 12.5 ꢁ M (17)
V: MIC= 21.0 ꢁ M (18)
Figure 1.
Figure 2

Page 13 of 16
MedChemComm
View Article Online
DOI: 10.1039/C5MD00346F
Figure 3
Figure 4

MedChemComm
Page 14 of 16
View Article Online
DOI: 10.1039/C5MD00346F
Scheme 1
Scheme 2

Page 15 of 16
MedChemComm
View Article Online
DOI: 10.1039/C5MD00346F
Scheme 3.

MedChemComm
Page 16 of 16
View Article Online
DOI: 10.1039/C5MD00346F
Graphical abstract
Ionic liquid promoted one-pot synthesis of thiazole-imidazo[2,1-b]
[1,3,4]thiadiazole hybrids and their antitubercular activity
Jurupula Ramprasada, Nagabhushana Nayaka, Udayakumar Dalimbaa,*, Perumal Yogeeswarib
and Dharmarajan Sriramb
The antiTB activity of new thiazole-imidazo[2,1-b][1,3,4]thiadiazoles, which are
synthesized via one-pot synthesis, is comparable with that of the standard drugs.