Benzo[d]thiazol-2-yl(piperazin-1-yl)methanones as new anti-mycobacterial chemotypes: Design, synthesis, biological evaluation and 3D-QSAR studies

Article abstract of DOI:10.1016/j.ejmech.2016.03.060

The benzo[d]thiazol-2-yl(piperazin-1-yl)methanones scaffold has been identified as new anti-mycobacterial chemotypes. Thirty-six structurally diverse benzo[d]thiazole-2-carboxamides have been prepared and subjected to assessment of their potential anti-tu

Full text of DOI:10.1016/j.ejmech.2016.03.060

Accepted Manuscript
Benzo[d]thiazol-2-yl(piperazin-1-yl)methanones as New Anti-mycobacterial
Chemotypes: Design, Synthesis, Biological Evaluation and 3D-QSAR Studies
Sahaj Pancholia, Tejas M. Dhameliya, Parth Shah, Pradeep S. Jadhavar,
Jonnalagadda Padma Sridevi, Perumal Yogeshwari, Dharmarajan Sriram, Asit K.
Chakraborti
PII:
S0223-5234(16)30243-4
10.1016/j.ejmech.2016.03.060
EJMECH 8485
DOI:
Reference:
To appear in: European Journal of Medicinal Chemistry
Received Date: 30 January 2016
Revised Date: 10 March 2016
Accepted Date: 21 March 2016
Please cite this article as: S. Pancholia, T.M. Dhameliya, P. Shah, P.S. Jadhavar, J.P. Sridevi, P.
Yogeshwari, D. Sriram, A.K. Chakraborti, Benzo[d]thiazol-2-yl(piperazin-1-yl)methanones as New Anti-
mycobacterial Chemotypes: Design, Synthesis, Biological Evaluation and 3D-QSAR Studies, European
Journal of Medicinal Chemistry (2016), doi: 10.1016/j.ejmech.2016.03.060.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Graphical Abstract
Benzo[d]thiazol-2-yl(piperazin-1-yl)methanones as New
Anti-mycobacterial Chemotypes: Design, Synthesis,
Biological Evaluation and 3D-QSAR Studies
Sahaj Pancholia,† Tejas M. Dhameliya,† Parth Shah,† Pradeep S. Jadhavar,† Jonnalagadda
Padma Sridevi,‡ Perumal Yogeshwari,‡ Dharmarajan Sriram‡ and Asit K. Chakraborti*†
†
Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and
Research (NIPER), Sector 67, S. A. S. Nagar 160 062, Punjab, India.
‡
Department of Pharmacy, Birla Institute of Technology & Science – Pilani, Hyderabad
Campus, Jawahar Nagar, Hyderabad 500 078, India.
* Corresponding author. E-mail: akchakraborti@niper.ac.in; akchakraborti@rediffmail.com
O
N
S
N
R
4/5/6a-l
Z
36 compounds
Biological Evaluation
Six Positive Hits (MIC: 2.35ꢀ7.94 ꢁM)
R = CF3: Leat cytotoxic
3D QSAR
r2
= 0.718; r2
= 0.995
ncv
pred
The benzo[d]thiazol-2-yl(piperazin-1-yl)methanones scaffold has been identified as new
anti-mycobacterial chemotypes. The quantitative structure activity relationship has been
2
established adopting a statistically reliable CoMFA model showing high prediction (r
pred
2
ncv
= 0.718, r
= 0.995).

ACCEPTED MANUSCRIPT
Benzo[d]thiazol-2-yl(piperazin-1-yl)methanones as New
Anti-mycobacterial Chemotypes: Design, Synthesis,
Biological Evaluation and 3D-QSAR Studies
Sahaj Pancholia,a Tejas M. Dhameliya,a Parth Shah,a Pradeep S. Jadhavar,a Jonnalagadda
Padma Sridevi,b Perumal Yogeshwari,b Dharmarajan Sriramb and Asit K. Chakrabortia*
aDepartment of Medicinal Chemistry, National Institute of Pharmaceutical Education and
Research (NIPER), Sector 67, S. A. S. Nagar 160 062, Punjab, India.
*Corresponding author. E-mail: akchakraborti@niper.ac.in; akchakraborti@rediffmail.com
bDepartment of Pharmacy, Birla Institute of Technology & Science – Pilani, Hyderabad
Campus, Jawahar Nagar, Hyderabad 500 078, India.
Abstract: The benzo[d]thiazol-2-yl(piperazin-1-yl)methanones scaffold has been identified
as new anti-mycobacterial chemotypes. Thirty-six structurally diverse benzo[d]thiazole-2-
carboxamides have been prepared and subjected to assessment of their potential anti-
tubercular agents through in vitro testing against M. tuberculosis H37Rv strain and
evaluation of cytotoxicity against RAW 264.7 cell lines. Seventeen compounds showed
anti-mycobacterial potential having MICs in the low (1-10) µM range. The 5-
trifluoromethyl benzo[d]thiazol-2-yl(piperazin-1-yl)methanones emerged to be the most
promising resulting in six positive hits (2.35-7.94 µM) and showed low-cytotoxicity (<50%
inhibition at 50 µg/mL). The therapeutic index of these hits is 8–64. The quantitative
structure activity relationship has been established adopting a statistically reliable CoMFA
2
pred
2
ncv
model showing high prediction (r
= 0.718, r
= 0.995).
Keywords: Tuberculosis, benzo[d]thiazole-2-carboxamides, new antibacterial chemotypes,
Anti-mycobacterial activity, COMFA, and 3D-QSAR.
Page 1 of 36

ACCEPTED MANUSCRIPT
1. Introduction
Tuberculosis (TB), caused by the infectious mycobacteria Mycobacterium tuberculosis
(Mtb),[1] is responsible for the highest death globally. The disease affected about 9.0
million people and caused 1.5 million deaths [includes 360,000 patients co-infected with
HIV (Human Immunodeficiency Virus] in 2013. Being next to Acquired Immuno
Deficiency Syndrome (AIDS), TB is the second cause of death amongst the infectious
diseases in the global scenario.[2]
The growth of TB is a threat to public health majorly due to the development of multi
(MDR-TB; tolerant to isoniazid and rifampicin), extensively (XDR-TB; tolerant to all the
first and a few second line drugs),[3] and the lately covered totally drug resistant Mtb
(TDR-TB)[4] strains. The spread of MDR-TB could increase the cost of the available
treatment between 100 and 1400 times apart from the threat to make TB incurable. At
present, 5.3% of TB incidences are due to MDR-TB. The World Health Organization
(WHO) reports yearly 490,000 new MDR-TB infections causing > 110,000 deaths and has
announced TB a worldwide health crisis.[3] Most of first line TB drugs had been
discovered in 1950s and 1960s. For nearly half a century, TB treatment lacked the
availability of new drug until bedaquiline was launched at the end of 2012 to treat MDR-
TB.[5] All the above facts necessitate the re-engineering and repositioning of synthetic
bioactive for the development of new anti-TB drugs. The present work relates to the
findings of benzo[d]thiazol-2-yl(piperazin-1-yl)methanones as new chemotypes with anti-
TB activity.
Insert Figure 1 here.
1.1. Design
Encouraged by our recent findings on the anti-TB activity of benzo[d]thiazole-2-
carboxamides,[6] we planned to search for more effective anti-TB new molecular entities
and adopted scaffold hopping strategy[7] to construct new anti-bacterial chemotypes. In
search for different antibacterial scaffolds we noticed that diverse new chemical entities
bearing functionalized piperazine motif exhibited anti-TB potential (motifs A-H, Figure
1)[8-15].
Page 2 of 36

ACCEPTED MANUSCRIPT
In the present study, we designed the benzo[d]thiazol-2-yl(piperazin-1-yl)methanone
scaffold (I) as new anti-TB chemotype through hybridization by covalent attachment of the
piperazine moiety with the benzo[d]thiazole-2-carboxamide framework (Figure 2). The
current pharmaceutical applications of benzothiazoles for treatment of AIDS[16] suggest
anti-TB potency of the benzo[d]thiazol-2-yl(piperazin-1-yl)methanones through synergistic
intervention of the TB-AIDS co-infection and provide support to the design of scaffold I.
Insert Figure 2 here.
2. Results and Discussion
2.1. Chemistry
The target benzo[d]thiazol-2-carboxamides can be prepared through two step reactions:
aquatic cyclocondensation of aldehydes with 2-aminothiophenol 1a at 110 ˚C[17] or at
room temperature under the catalytic presence of SDOSS (sodium dioctyl sulfosuccinate)
[18] followed by NH4Cl catalyzed amide coupling[6] with diverse alicyclic amines 3a-l
(Scheme 1). The SDOSS-catalysed reaction (5 h) of 1a with ethyl glyoxalate in water
formed 2a (83%). Following similar procedures two more derivatives ethyl 5-chloro
benzo[d]thiazole-2-carboxylate 2b and ethyl 5-trifluoromethyl benzo[d]thiazole-2-
carboxylate 2c were synthesized from the corresponding 4-chloro (1b) and 4-
trifluoromethyl (1c) substituted 2-aminothiophenols.
Insert Scheme 1 here.
The desired amides 4/5/6a-l were formed from ethyl benzo[d]thiazole-2-carboxylate
derivatives 2a/2b/2c and diverse piperazine derivatives 3a-l under neat condition using
NH4Cl as catalyst (20 mol%) at 100 °C in moderate to good yields (Table 1). Dilution of
the reaction mixture with cold water, filtration of the precipitated solid afforded the desired
products (total thirty-six compounds) without any further requirement of purification.
Insert Table 1 here.
2.2. Biological Evaluation
The anti-tuberculosis activity of the synthesized thirty-six benzo[d]thiazole-2-
carboxamide conjugates were evaluated against M. tuberculosis H37Rv (ATCC27294)
strain.[19] The minimum inhibitory concentration (MIC; ꢀg/mL) values of all the
Page 3 of 36

ACCEPTED MANUSCRIPT
synthesized compound along with the standard drugs Isoniazid (INH), Rifampin (R),
Ethambutol (E), Pyrazinamide (Z) and Ciprofloxacin (Cfx) were determined thrice at pH
7.4 (Table 1). All the synthesized compounds exhibited MICs in the micromolar
range, varying from 0.78-25 µg/mL. Out of thirty six compounds, eighteen compounds (4a,
4d, 4e, 4f, 4g, 4i, 4j, 4l, 5g, 5h, 5i, 5l, 6a, 6b, 6e, 6h, 6j and 6k) exhibited MICs values of
0.78 - 3.125 µg/mL. In comparison with standard drugs E (1.56 ꢀg/mL), Cfx (1.56 ꢀg/mL),
and Z (6.25 ꢀg/mL) the synthesized compounds 4l, 5l, 6a and 6b (MIC of 0.78 ꢀg/mL)
were found to be more potent.
2.3. Cytotoxicity Evaluation
The cytotoxicity (determined at 50 ꢀg/mL) of the compounds with anti-mycobacterial
potency ≤ 6.25 µg/mL was evaluated against RAW 264.7 (mouse leukemic monocyte
macrophage) cell lines by adopting (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium
bromide) MTT assay (Table 1). The graphical representation of the anti-TB activity (Figure
3) and cytotoxicity of the synthesized compounds (activity ≤ 6.25 µg/mL; Figure 4)
indicate that all CF3 derivatives are less-cytotoxic compared to H and Cl derivatives. Out of
the most active compounds (4l, 5l, 6a and 6b), the compound 6a and 6b found to be more
potent (MIC of 2.47 and 2.35 µM) and less cytotoxic (24.56% and 18.12% inhibition) and
therapeutic index >60.
Insert Figure 3 here.
Insert Figure 4 here.
2.4. Evaluation of drug-like properties of the active compounds
The intermediate 2a was thirty-two fold less active than 4l. By attaching the 1-
(diphenylmethyl)piperazine group, the lipophilicity of 2a (cLogP, calculated using
ChemDraw Ultra version 12.0.) increased from 2.3 to 4.72. The lipophilicity is an
important attribute for the permeation of the compounds across the high lipid containing
mycobacterium cell wall.[20] The most promising compound 5l (MIC of 1.74 µM) has
been found with higher cLogP value (5.44) and comparison of the cLogP data of
compounds with those of the standard drugs reveal that the synthetic analogues are
more lipophilic in nature compared to the first line drugs i.e., INH (-0.668), E (0.118),
and Z (-0.676). The compounds with MIC ≤ 6.25 µg/mL were further subjected to analysis
Page 4 of 36

ACCEPTED MANUSCRIPT
for drug likeness such as the “Lipinski rule of 5”.[21] The Lipinski properties (molecular
weight, no. of hydrogen bond donors, no. of hydrogen bond acceptors and no. of rotational
bonds) were computed using Accelrys Discovery Studio 2.5 and all the twenty-five hits
qualify drug likeness property (Table 2).
Insert Table 2 here.
A complete structure activity relationship (SAR) can be drawn by correlating the anti-
mycobacterial activity (µM) of the tested compounds (Table 1). Among the initially tested
compounds 4a-c, 5a-c and 6a-c by exploring combination of morpholine, thiamorpholine
and piperidine ring with their corresponding 5-H, 5-Cl and 5-CF3 derivatives,
trifluoromethyl group gave superior activity among their other counterpart (Figure 5). Due
to the limitation of further diversity generation in the scaffold with morpholine,
thiamorpholine and piperidine fragment, piperazine derivatives were explored. Among
twenty-seven piperazine derivatives synthesized, biological activity of fourteen compounds
(4e, 4f, 4g, 4i, 4j, 4l, 5g, 5h, 5i, 5l, 6e, 6h, 6j and 6k) were found to be between 1-10 µM.
Insert Figure 5 here.
To establish quantitative correlation among various piperazine derivatives the 3D-QSAR
technique comparative molecular filed analysis (CoMFA)[7a,22] was applied.
2.5. 3D-QSAR
Using SYBYL 7.1 (Tripos Inc., USA) molecular modeling package,[23] CoMFA model
was developed to recognize the morphological characteristics requisite for the anti-TB
potential. Alignment of compounds in their lowest energy state was considered using
benzothiazole as common fragment (Figure 6). The statistically competent CoMFA model
was developed and corroborated by the partial least squares (PLS) method. The regression
analysis of CoMFA field energies has been performed using PLS algorithm with the leave-
one-out (LOO) method acquired for cross validation. The statistical parameters of the
model derived from the benzo[d]thiazole-2-carboxamides series are summarized in Table 2.
The CoMFA gave the prediction of the activity of the test set compounds within
statistically permissible range. Plot of experimental pMIC versus the predicted pMIC value
of the test set and training set (Figure 8) demonstrated the reliability of the CoMFA model
Page 5 of 36

ACCEPTED MANUSCRIPT
to serve as useful tool for prediction of the anti-mycobacterial potential of newly designed
benzo[d]thiazole-2-carboxamides (Table 3).
Insert Figure 6 here.
Insert Table 3 here.
2.5.1. Data Set and Biological Data
For 3D-QSAR analyses, 23 compounds with defined MIC values were employed. Total
compounds were divided into a training set of 18 compounds, and a test set of 5
compounds. The most important step in the QSAR is the selection of a suitable training set
with wide activity range, responsible for determining the quality of the generated QSAR
model. The calculated MIC values (pMIC = -log MIC) of dataset spanned across a small
range from 4.99 to 7.91. These activity values were rescaled to the range of four log units to
develop statistically reliable model. To rescale the activity data following formula was
employed. The test compounds were selected manually considering the structural diversity
and wide range of activity in the data set.
Rescaling data set:
Existing series = a-b, Rescale series = x-y, Rescale value = x + (n-a)*[(y-x)/(b-a)]
=3.92+(n-4.04)*[4/1.84]
Where n is query. In our study, x= 3.92, y=7.92, a= 3.92, b= 5.76
2.5.2. Molecular modeling
All the molecular modeling calculations were performed using SYBYL 7.1 (Tripos Inc.,
USA) molecular modeling package installed on a Silicon Graphics Fuel Workstation
running IRIX 6.5. Structures of all monophosphonate derivatives were generated using
sketch molecule module. Compound 5l being the most potent was selected as a template
molecule (Figure 6). Geometry-optimized was carried out by applying Tripos molecular
mechanics force field with conjugate gradient method. No constraints were applied on the
internal geometries of the molecules. The minimization was terminated when the energy
gradient convergence criterion of 0.001 kcal/mol was reached or when the 10,000 steps
Page 6 of 36

ACCEPTED MANUSCRIPT
minimization cycle was exceeded. Gasteiger-Hückel charges were applied to all the
molecules of dataset, used for 3D-QSAR studies.
Insert Figure 7 here.
Molecular alignment is considered one of the most sensitive parameter in CoMFA analysis.
Each molecule was aligned to the lowest energy conformation of the most active compound
5l, (Figure 7) by performing an rms fitting of each conformer to those of the template using
the alignment function of the Sybyl 7.1. The aligned molecules obtained through pairwise
super positioning using the maximum common subgroup method, placed all molecules in
the same reference frame as the reference compound shown in Figure 6.
2.5.3. Calculation of CoMFA descriptors
For generating CoMFA contour maps, a 3D cubic lattice with grid spacing of 2.0 Å was
created around aligned molecule. For CoMFA, the steric (The Lennard-Jones potential) and
electrostatic (Coulombic potential) field at each lattice point was calculated using the
default probe, a sp3 carbon atom with a charge of +1 and a van der Waals radius of 1.52 Å.
The steric and electrostatic fields at these lattice points were calculated using Tripos force
field. Energy values for these fields were truncated at 30 kcal/mol. The minimum column
filtering was set to 2.0 kcal/mol to improve the signal-to noise ratio by retaining best fit
model while omitting those lattice points whose energy variation was below this threshold.
2.5.4. Calculation of CoMFA descriptors
The optimal number of components in the final model was determined by using leave-one-
out (LOO), a cross-validation method. The non-cross-validated conventional analysis was
produced with the optimal number of components equal to that yielding the highest rc2v
,
Final model was evaluated based on the standard error of estimation values (SEE), non-
cross validated rn2cv value and also by the F test value.
2.5.5. Predictive correlation coefficient
The predictive abilities were determined from a test set of 5 compounds. MIC values for
test molecules were predicted by using developed CoMFA. The predictive correlation
2
coefficient (rpred ), based on the molecules of test set, was calculated according to the
equation shown below;
Page 7 of 36

ACCEPTED MANUSCRIPT
Where SD is the sum of squared deviations between the inhibitory activities of the test set
and mean activities of the training molecules and PRESS is the sum of squared deviations
between predicted and actual activity values for each molecule in the test set.
All test set compounds were predicted within statistically acceptable range using the
CoMFA model. The scattered plots of experimental pMIC against the predicted
pMIC value of the training set and test set is shown in Figure 8. These results suggest
that the model is reliable and it could serve as a useful tool for predicting the MIC
values of newly designed benzo[
d]thiazole-2-carboxamides (Table 4).
Insert Figure 8 here.
Insert Table 4 here.
2.5.6. CoMFA Contour Maps and Discussion
Insert Figure 9 here.
The steric and electrostatic contributions in the contour maps for the statistically reliable
CoMFA model were observed to be 47.6% and 52.4%, respectively. Green and yellow
contours represent the steric interactions whilst red and blue contours represent the
electrostatic interactions as shown in Figure 9. Green contours represent the place where
bulkier groups are expected to favour the anti-TB activity while the yellow contours coded
for less favored bulky groups for biological activity. In a similar way, the red contours
display the region bearing electronegative group that is anticipated to enhance the anti-
mycobacterial potential and the blue plots predict the region having positive charge that is
anticipated to contribute to increase the anti-TB activity.
Figure 9a shows the distribution of steric fields generated around the compound 4i. A large
green contour present at the center of the phenyl ring shows favorable activity for the
presence of a bulky group such as aromatic substituent's 4f and 5f compared to their
aliphatic counterpart 4d and 5d respectively. However, in the case of CF3 substituent 6f
there is reverse trend. For CF3 substituents, hydrophobic group are unfavorable (6f and 6l)
whereas aliphatic (3d, 3e) and heterocyclic rings (6a, 6b, 6j, 6k) show positive correlation
Page 8 of 36

ACCEPTED MANUSCRIPT
with their biological activity. This is the reason why in case of CF3 derivative, hydrophobic
substituent (6f-l) gave unexpected low activity compared to their H (4f-l) and Cl (5f-l)
counterparts. Similar reverse trend is observed in case of small green contour present at
ortho methoxy substituent, where H and Cl derivative (4g, 5g) shows favorable activity, on
the other hand, CF3 derivative 6g show lower activity. Moreover, presence of yellow
contour at the para position suggests avoiding the hydrophobic groups in future design.
In Figure 9b, two red contours were sighted in close proximity to the ortho and para
position of the phenyl ring. The red contour indicates that electronegative group at the ortho
and para position augments the anti-tuberculosis activity. As seen in SAR, the presence of
acetyl or methoxy group at the para position of the phenyl ring gave positive impact in all
three derivatives 4i, 5h, 5i, 6h, 6i (except 4h) compared to unsubstituted phenyl ring 4f, 5f
and 6f respectively. Presence of small blue contour at the meta position of the phenyl ring
suggests to incorporate electropositive group in future design of the molecules.
Apart from this, in case of morpholine, thiamorpholine and piperidine derivatives, future
direction include, there is either scope to incorporate more variation in the benzenoid
nucleus of the benzo[d]thiazole ring or keeping CF3 position constant or even bioisosteric
replacement of benzo[d]thiazole ring with benzoxazole and benzimidazole ring might
enhance anti-TB activity. Overall SAR of this series suggests that introduction of various
aryl substituent in H and Cl derivative improves the anti-TB activity whereas heteroaryl
and alicyclic amine will enhance the anti-TB activity of the CF3 derivatives. As per the 3D-
QSAR's steric and electrostatic contour there is scope to incorporate more variation by
incorporating electron donating and withdrawing functional group in the diphenyl
substituent of the 4l and 5l.
3. Conclusions
In conclusion, in this work a new series of benzo[d]thiazol-2-yl(piperazin-1-yl)methanones
have been designed through molecular hybridization of N-benzyl benzo[d]thiazole-2-
carboxamides and alicyclic piperazines. Thirty-six new analogues were prepared by amide
coupling of ethyl benzo[d]thiazole-2-carboxyalte with various cyclic amines 3a-l using
ammonium chloride as catalyst under solvent free condition in moderate to good yields.
Adopting the MABA assay, all these thirty six derivatives have been evaluated in vitro for
Page 9 of 36

ACCEPTED MANUSCRIPT
anti-TB activity against M. tuberculosis H37Rv (Mtb) strain. Out of thirty six compounds
synthesized, twenty-seven compounds have shown biological activity comparable to
clinically used standard drug pyrazinamide (6.25 µg/mL) and nineteen compounds
displayed anti-TB activity ranging from 0.78 to 3.125 µg/mL. The cytotoxicity of all the
potent compounds was performed against RAW 264.7 cell lines and found among three
series, CF3 derivatives (6a-l) are specifically having low cytotoxicity. CF3 derivative stood
different from H and Cl derivative by being potent and non-cytotoxic, providing future
direction for design. The results described here demonstrate the potential utility of
benzo[d]thiazol-2-yl(piperazin-1-yl)methanones as anti-tubercular agents. The favourable
drug like properties in conformity with the Lipinski rule and devoid of cytotoxicity of the
most active compounds would provide further impetus to derive new chemical entities with
optimized structure as potent anti-mycobacterial drug candidate.
4. Experimental Section
Chemicals and all solvents were commercially available (Aldrich Chemical, Merck AG,
Fluka, Alfa Aesar and S-D Fine Chemicals) and used without further purification. 1H NMR
13
and C NMR spectra were recorded on Bruker Advance DX spectrometer at 400 and 100
MHz, respectively, with TMS as an internal standard and using CDCl3/MeOD/DMSO as
solvent. Coupling constants were reported in hertz (Hz). 13C NMR spectra were fully
decoupled. For analysis of the results of NMR, Topspin software was used. The
abbreviations used to characterize the signals are as follows: s = singlet, m = multiplet, d =
doublet, dd = doublet of doublet, dt = doublet of triplet, t = triplet, q = quartet, br s = broad
singlet. Mass spectra were measured in the APCI mode at an ionization potential of 70 eV
with LCMS MSD (Hewlett Packard) and on a GCMS-QP 5000 (Shimadzu) (for EI) mass
spectrometers; Infra-red spectra were recorded on Perkin Elmer FT-IR spectrometer in the
range of 4000-600 cm-1 either as neat samples or using KBr for preparing pellets for solid
samples or in solvent. Compounds were routinely checked for their purity on the silica gel
GF-254 and visualized under UV at wavelength 254 nm. Melting points were measured
with Gupta Scientific melting point apparatus. Evaporation of solvent was performed at
reduced pressure, using a Buchi rotary evaporator. HPLC (model SCL-10AVP, Shimadzu,
Japan) of all the target compounds has been performed using Qualisil Gold C18 column
(4.6 × 250 mm, 5 micron, LCGC Chromatography Solution Pvt. Ltd) and acetonitrile :
Page 10 of 36

ACCEPTED MANUSCRIPT
water (80:20) as the mobile phase at 30 ºC utilizing 20 µL of the sample with flow rate of 1
mL min-1 using binary pump. Photo diode array detector (model no. SPD-M20A) was used
for variable wavelength ranging from 200-800 nM. For interpretation of the results of
HPLC, Class VP software was used. Elemental analyses were performed on organic
element analyzer (Thermo SCIENTIFIC FLASH 2000) and, indicated by the symbols of
the elements or functions were within ± 0.4 % of the theoretical values. For interpretation
of the results of elemental analysis, Eager Xperience software was used.
The following compounds [4a-d, 4i, 4l, 5d, 5f and 4f] are commercially available and
intermediates (2a-c)6 are thus reported.
4.1 Experimental procedure for the synthesis
Synthesis of ethyl 5-substituted benzo[d]thiazole-2-carboxlate (2a/2b/2c)
To a magnetically stirred miceller solution of SDOSS (44 mg, 10 mol %) in demineralised
water (2 mL), was added 2-aminothiophenol 1a (0.12 mL, 1 mmol, 1 equiv) and ethyl
glyoxalate (0.118 mL, 1 mmol, 1.2 equiv) and the mixture was stirred at room temperature.
After completion of the reaction (5 h, TLC), the reaction mixture was extracted with EtOAc
(4 × 15 mL). The combined EtOAc extracts were washed with saturated brine (15 mL),
dried (anhydrous Na2SO4), filtered and concentrated under vacuum rotary evaporation. The
crude product was purified by passing through a column of silica gel (60-120 mesh) and
eluted with hexane-EtOAc to afford the pure 2a. Following this general procedure 2b and
2c were prepared by the cyclocondensation of ethyl glyoxalate with 2-amino-4-
chlorothiophenol 1b and 2-amino-4-(trifluoromethyl)thiophenol 1c, respectively.
4.1.1 Ethyl benzo[d]thiazole-2-carboxylate (2a): Yield: 172 mg, 83% (yellow solid), mp
68-72°C. IR (KBr) ν: 1750 cm-1. 1H NMR (CDCl3, 400 MHz)
1H), 7.97 (d, J = 7.92 Hz, 1H), 7.60-7.52 (m, 2H), 4.56 (q, J = 7.12 Hz, 2H), 1.49 (t, J =
7.12, 3H). 13C NMR (100 MHz, CDCl3)
(ppm): 160.68, 158.57, 153.22, 136.78, 127.54,
δ (ppm): 8.25 (d, J = 8.16 Hz,
δ
127.09, 125.52, 122.08, 63.13, 14.29. MS (APCI) m/z 208.21 (M + H)+.
4.1.2 Ethyl 5-chlorobenzo[d]thiazole-2-carboxylate (2b): Yield: 176 mg, 73% (yellowish
1
solid), mp 91-93°C. IR (KBr) ν: 1743 cm-1. H NMR (400 MHz, CDCl3) δ (ppm): 8.24 (d,
J = 1.88 Hz, 1H), 7.91 (d, J = 8.68 Hz, 1H), 7.53 (dd, J = 8.64, 1.96 Hz), 4.57 (q, J = 7.16
Page 11 of 36

ACCEPTED MANUSCRIPT
Hz, 2H), 1.50 (t, J = 7.12 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ (ppm): 160.35, 160.31,
153.95, 134.98, 133.28, 128.26, 125.05, 122.89, 63.37, 14.27. MS (ESI) (m/z) 242.23 (M)+.
4.1.3 Ethyl 5-(trifluoromethyl)benzo[d]thiazole-2-carboxylate (2c): Yield: 193 mg, 70%
°
1
(white solid), mp 73-75 C. IR (KBr) ν: 1736 cm-1. H NMR (400 MHz, CDCl3) δ (ppm):
8.53 (s, 1H), 8.13 (d, J = 8.52 Hz, 1H), 7.79 (dd, J = 8.52, 1.32 Hz, 1H), 4.60 (q, J = 7.12
13
Hz, 2H), 1.52 (t, J = 7.12 Hz, 3H). C NMR (100 MHz, CDCl3) δ (ppm): 160.80, 160.01,
152.87, 139.93, 130.22, 129.89, 123.62, 123.59, 122.77, 122.49, 63.22, 14.05. MS (APCI)
(m/z) 275.97 (M+H)+.
General procedure for the synthesis of library of compounds
Method: The 5-substituted benzo[d]thiazole-2-carboxylate 2a/2b/2c (1 mmol) was taken in
a round bottom flask (10 mL). To it the amine (1 equiv) was added along with catalytic
amount (20 mol%) of NH4Cl and reaction mixture was heated at 100 ºC for 1-2 h under
magnetic stirring. After completion of reaction (TLC), ice-cold water (2 mL) was added to
the reaction mixture and the mixture was allowed to stir for 10 min. The solid precipitate
was filtered and air dried to furnish the final product that did not require any further
purification.
4.1.4 Benzo[d]thiazol-2-yl(morpholino)methanone (4a): Yield: 219 mg, 88% (white
1
solid), IR (CHCl3) ν: 1621 cm-1. H NMR (400 MHz, CDCl3) δ (ppm): 8.01 (d, J = 6.56
Hz, 1H), 7.99 (d, J = =7.6 Hz, 1H), 7.59-7.49 (m, 2H), 4.54 (t, J = 4.64 Hz, 2H), 3.88-3.83
13
(m, 6H). C NMR (100 MHz, CDCl3) δ (ppm): 164.50, 159.72, 153.07, 136.19, 126.79,
126.62, 124.64, 121.87, 67.24, 66.90, 47.18, 43.91. MS (EI) (m/z) 249.10 (M+H)+. HPLC
analysis: retention time = 4.384 min; peak area, 100%.
4.1.5 Benzo[d]thiazol-2-yl(thiomorpholino)methanone (4b): Yield: 233 mg, 88%
1
(yellowish solid), mp 112-115 ºC. IR (CHCl3) ν: 1618, 1498 cm-1. H NMR (400 MHz,
CDCl3) δ (ppm): 8.11 (d, J = 7.92 Hz, 1H), 7.98 (d, J = 8.04 Hz, 1H), 7.59-7.49 (m, 2H),
13
4.66 (t, J = 4.56 Hz, 2H), 4.12 (t, J = 4.76 Hz, 2H), 4.82 (q, J = 5.96 Hz, 4H). C NMR
(100 MHz, CDCl3) δ (ppm): 164.35, 160.08, 152.99, 136.15, 126.78, 126.61, 124.66,
121.86, 49.44, 46.35, 28.53, 27.55. MS (APCI) (m/z) 265.06 (M+H)+. HPLC analysis:
retention time = 4.405 min; peak area, 100%.
Page 12 of 36

ACCEPTED MANUSCRIPT
4.1.6 Benzo[d]thiazol-2-yl(piperidin-1-yl)methanone (4c): Yield: 165 mg, 67%
1
(brownish yellow solid), mp 80-83 ºC. IR (KBr) ν: 1615, 1505 cm-1. H NMR (400 MHz,
CDCl3) δ (ppm): 8.10 (d, J = 8.2 Hz, 1H), 7.97 (d, J = 7.68 Hz, 1H), 7.56-7.46 (m, 2H),
4.26 (t, J = 9.96 Hz, 2H), 3.79 (t, J = 5.4 Hz, 2H), 1.74 (s, 6H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 164.91 (C=O), 159.90, 153.04, 136.08, 126.47, 126.42, 124.51, 121.79,
47.69, 44.74, 26.75, 25.80, 24.57. MS (APCI) (m/z) 247.13 (M+H)+. HPLC analysis:
retention time = 4.821 min; peak area, 98.79%.
4.1.7 Benzo[d]thiazol-2-yl(4-methylpiperazin-1-yl)methanone (4d): Yield: 97 mg, 37%
1
(white solid). IR (CHCl3) ν: 3432, 1630 cm-1. H NMR (400 MHz, [D4]MeOD) δ (ppm):
8.12-8.07 (m, 2H), 7.63-7.54 (m, 2H), 4.42 (t, J = 4.72 Hz, 2H), 3.86 (t, J = 4.2 Hz, 2H),
2.60 (t, J = 4.52 Hz, 4H), 2.37 (s, 3H, -OCH3). 13C NMR (100 MHz, [D4]MeOD) δ (ppm):
163.82 (C=O), 159.99, 152.79, 135.77, 126.77, 126.82, 126.66, 124.11, 121.73, 54.79,
54.14, 45.95, 44.54, 42.82 (-OCH3). MS (APCI) (m/z) 262.11 (M)+. HPLC analysis:
retention time = 4.363 min; peak area, 95.65%.
4.1.8 1-(4-(benzo[d]thiazole-2-carbonyl)piperazin-1-yl)ethanone (4e): Yield: 159 mg,
1
55% (yellowish solid), mp 79-91 ºC. H NMR (400 MHz, CDCl3) δ (ppm): 8.14-8.08 (m,
1H), 7.99 (d, J = 7.8 Hz, 1H), 7.59-7.50 (m, 2H), 4.58-4.48 (m, 2H), 3.90-3.85 (m, 2H),
3.81-3.78 (m, 2H), 3.67-3.63 (m, 2H), 2.19 (s, 3H). 13C NMR (100 MHz, CDCl3) δ (ppm):
169.29 (C=O), 164.03, 160.10, 153.03, 136.19, 126.93, 126.72, 124.80, 124.62, 121.93,
121.87, 46.68, 46.35, 45.94, 43.59, 43.46, 41.87, 41.13, 21.42. MS (APCI) (m/z) 290.93
(M)+. Anal. Calcd for C14H15N3O2S: C, 58.11; H, 5.23; N, 14.52; S, 11.08. Found: C, 58.40;
H, 5.49; N, 14.47; S, 11.35. HPLC analysis: retention time = 4.413 min; peak area, 98.99%.
4.1.9 Benzo[d]thiazol-2-yl(4-phenylpiperazin-1 -yl)methanone (4f): Yield: 246 mg, 76%
1
(pale yellow solid), mp 95-98 ºC. IR (neat) ν: 1622, 1597 cm-1. H NMR (400 MHz,
[D6]DMSO) δ (ppm): 8.22 (d, J = 7.6 Hz, 1H), 8.17 (d, J = 7.91 Hz, 1H), 7.62 (quin, J =
6.92 Hz, 2H), 7.25 (t, J = 7.8 Hz, 2H), 7.00 (d, J = 8.12 Hz, 2H), 6.84 (t, J = 7.2 Hz, 1H),
4.47 (s, 2H), 3.87 (s, 2H), 3.29 (s, 4H).13C NMR (100 MHz, [D6]DMSO) δ (ppm): 164.65
(C=O), 158.83, 152.47, 150.59, 135.34, 128.99, 126.97, 124.29, 122.47, 119.38, 115.85,
48.77, 48.25, 45.74, 42.90. Anal. Calcd for C18H17N3OS: C, 66.85; H, 5.30; N, 12.99; S,
9.91. Found: C, 66.54; H, 5.26; N, 13.24; S, 9.99. HPLC analysis: retention time = 5.397
min; peak area, 98.04%.
Page 13 of 36

ACCEPTED MANUSCRIPT
4.1.10 1-(Benzo[d]thiazol-2-yl)-2-(4-(2-methoxyphenyl)piperazin-1-yl)ethanone (4g):
1
Yield: 194 mg, 55% (white solid). IR (CHCl3) ν: 3410, 1626 cm-1. H NMR (400 MHz,
CDCl3) δ (ppm): 8.10 (d, J = 8 Hz, 1H), 7.96 (d, J = 7.72 Hz, 1H), 7.56-7.47 (m, 2H), 7.07-
13
7.03 (m, 1H), 6.95-6.89 (m, 3H), 4.65 (s, 2H), 4.05 (s, 2H), 3.90 (s, 3H), 3.2 (s, 4H). C
NMR (100 MHz, CDCl3) δ (ppm): 164.82 (C=O), 159.74, 153.12, 152.30, 140.62, 136.22,
126.68, 126.55, 124.62, 123.61, 121.86, 121.10, 118.52, 111.33, 55.46 (-OCH3), 51.34,
50.72, 46.84, 43.87. MS (APCI) (m/z) 354.24 (M+H)+. Anal. Calcd for C19H19N3O2S: C,
64.57; H, 5.42; N, 11.89; S, 9.07. Found: C, 64.27; H, 5.24; N, 11.81; S, 8.99. HPLC
analysis: retention time = 3.445 min; peak area, 98.56%.
4.1.11 1-(Benzo[d]thiazol-2-yl)-2-(4-(4-methoxyphenyl)piperazin-1-yl)ethanone (4h):
1
Yield: 187 mg, 53% (yellowish solid). IR (CHCl3) ν: 1623 cm-1. H NMR (400 MHz,
CDCl3) δ (ppm): 8.13 (d, J = 7.88 Hz, 1H), 8.00 (d, J = 7.64 Hz, 1H), 7.59-7.50 (m, 2H),
6.98-6.88 (m, 4H), 4.65 (s, 2H), 4.04 (s, 2H), 3.81 (s, 3H, -OCH3), 3.23 (s, 4H). 13C NMR
(100 MHz, CDCl3) δ (ppm): 164.68 (C=O), 159.73, 154.44, 153.10, 145.23, 136.22,
126.74, 126.59, 124.65, 118.95, 114.57, 55.57 (-OCH3), 51.59, 51.05, 46.60, 43.71. MS
(EI) (m/z) 353 (M)+. Anal. Calcd for C19H19N3O2S: C, 64.57; H, 5.42; N, 11.89; S, 9.07.
Found: C, 64.25; H, 5.21; N, 11.80; S, 8.95. HPLC analysis: retention time = 4.928 min;
peak area, 95.66%.
4.1.12 1-(4-(4-(Benzo[d]thiazole-2-carbonyl)piperazin-1-yl)phenyl)ethanone (4i): Yield:
183 mg, 50% (dark yellow solid), mp 150-154 ºC. IR (neat) ν: 1712 (w; v(O=CMe)), 1670
(s; v(O=C-N)) cm-1. 1H NMR (400 MHz, [D6]DMSO) δ (ppm): 8.25-8.16 (m, 2H), 7.85 (d,
J = 8.72 Hz, 2H), 7.66-7.58 (m, 2H), 7.02 (d, J = 8.72 Hz, 2H), 4.49 (s, 2H), 3.87 (s, 2H),
3.54 (s, 4H), 2.47 (s, 3H). 13C NMR (100 MHz, [D6]DMSO) δ (ppm): 196.16 (-C=OMe),
165.15 (C=O), 159.42, 153.82, 152.99, 135.86, 130.59, 127.49, 127.38, 124.79, 122.99,
113.70, 47.35, 46.64, 45.83, 43.16, 26.60 (-CH3). MS (EI) (m/z) 364.99 (M)+. HPLC
analysis: retention time = 4.256 min; peak area, 95.62%.
4.1.13 Benzo[d]thiazol-2-yl(4-(pyridin-4-yl)piperazin-1-yl)methanone (4j): Yield: 175
1
mg, 54% (white solid), mp 149-153 ºC. IR (neat) ν: 1622 cm-1. H NMR (400 MHz,
[D4]MeOD) δ (ppm): 8.18-8.08 (m, 4H), 7.64-7.55 (m, 2H), 7.25 (d, J = 6.32 Hz, 2H), 4.59
13
(d, J = 4.44 Hz, 2H), 3.97 (t, J = 4.48 Hz, 2H), 3.63-3.59 (m, 4H). C NMR (100 MHz,
[D4]MeOD) δ (ppm): 163.91 (C=O), 160.05, 155.21, 152.89, 148.74, 135.87, 126.87,
Page 14 of 36

ACCEPTED MANUSCRIPT
126.67, 124.17, 121.75, 108.23, 45.73, 45.57, 44.87, 42.79. Anal. Calcd for C17H16N4OS:
C, 62.94; H, 4.97; N, 17.27; S, 9.88. Found: C, 62.72; H, 4.96; N, 17.13; S, 9.96. MS
(APCI) (m/z) 324.96 (M+H)+. HPLC analysis: retention time = 3.307 min; peak area,
100%.
4.1.14 Benzo[d]thiazol-2-yl(4-(pyrazin-2-yl)piperazin-1-yl)methanone (4k): Yield: 120
1
mg, 37% (yellow solid), mp 80-83 ºC. IR (KBr) ν: 1620, 1574 cm-1. H NMR (400 MHz,
CDCl3) δ (ppm): 8.13-8.08 (m, 34), 7.64-7.55 (m, 2H), 6.09 (t, J = 4.44 Hz, 2H), 3.97 (t, J
13
= 4.48, 2H), 3.62-3.59 (m, 4H), 6.90 (J = 6.32 Hz, 2H). C NMR (100 MHz, CDCl3) δ
(ppm): 163.91 (C=O), 160.05, 155.21, 152.89, 148.74, 135.87, 132.11, 126.87, 126.67,
124.17, 121.75, 108.23, 45.73, 45.57, 44.87, 42.79. MS (APCI) (m/z) 325.13 (M+H)+.
HPLC analysis: retention time = 4.085 min; peak area, 95.25%.
4.1.15 (4-Benzhydrylpiperazin-1-yl)(benzo[d]thiazol-2-yl)methanone (4l): Yield: 261
1
mg, 63% (pale yellow solid), mp 133-136 ºC. IR (CHCl3) ν: 3434, 1622 cm-1. H NMR
(400 MHz, [D6]DMSO) δ (ppm): 8.19 (d, J = 7.32 Hz, 1H), 8.08 (d, J = 7.6 Hz, 1H), 7.61-
7.54 (m, 2H), 7.46 (d, J = 7.48 Hz, 4H), 7.32 (t, J = 7.44 Hz, 4H), 7.21 (t, J = 7.24 Hz, 2H),
13
4.40 (s, 1H), 4.31 (s, 2H), 3.75 (s, 2H), 2.44 (s, 4H). C NMR (100 MHz, [D6]DMSO) δ
(ppm): 164.47 (C=O), 158.70, 152.39, 142.30, 135.23, 128.58, 127.60, 126.98, 126.90,
124.23, 122.47,74.51, 51.84, 51.19, 46.00, 43.05. Anal. Calcd for C25H23N3OS: C, 72.61;
H, 5.61; N, 10.16; S, 7.75. Found: C, 72.41; H, 5.67; N, 9.82; S, 7.54. MS (EI) (m/z) 414.05
(M+H)+. HPLC analysis: retention time = 9.109 min; peak area, 100%.
4.1.16 (5-Chlorobenzo[d]thiazol-2-yl)(morpholino)methanone (5a): Yield: 217 mg, 77%
1
(white solid), IR (KBr) ν: 1618 cm-1. H NMR (400 MHz, CDCl3) δ (ppm): 8.11 (s, 1H),
7.91 (d, J = 8.6 Hz, 1H), 7.50 (d, J = 8 Hz, 1H), 4.52 (t, J = 4.68, 2H), 3.87-3.83 (m, 6H).
13C NMR (100 MHz, CDCl3) δ (ppm): 166.50, 159.25, 153.85, 134.48, 132.70, 127.44,
124.32, 122.66, 67.20, 66.88, 47.15, 44.00. MS (APCI) (m/z) 283 (M+H)+. Anal. Calcd for
C12H11ClN2O2S: C, 50.97; H, 3.92; N, 9.91; S, 11.34. Found: C, 50.91; H, 3.89; N, 9.55; S,
11.22. HPLC analysis: retention time = 4.395 min; peak area, 97.73%.
4.1.17 (5-Chlorobenzo[d]thiazol-2-yl)(thiomorpholino)methanone (5b): Yield: 200 mg,
1
67% (brown solid), mp 109-111 ºC. IR (DMSO) ν: 3432, 1651 cm-1. H NMR (400 MHz,
1H NMR [D6]DMSO) δ (ppm): 8.23 (s, 2H), 7.64 (s, 1H), 4.43 (s, 2H), 3.96 (s, 2H), 2.77 (s,
Page 15 of 36

ACCEPTED MANUSCRIPT
4H). 13C NMR (100 MHz, [D6]DMSO) δ (ppm): 166.56 (C=O), 158.88, 153.08, 133.99,
131.58, 127.03, 124.00, 123.49, 48.75, 45.62, 27.44, 26.57. HRMS (ESI): m/z for
C12H11ClN2NaOS2 [M + Na+] calc.: 320.9899; observed: 320.9899. HPLC analysis:
retention time = 5.376 min; peak area, 97.73%.
4.1.18 (5-Chlorobenzo[d]thiazol-2-yl)(piperidin-1-yl)methanone (5c): Yield: 216 mg,
1
77% (pale yellow solid), mp 50-52 ºC. IR (DMSO) ν: 3432, 1652 cm-1. H NMR (400
MHz, [D6]DMSO) δ (ppm): 8.28 – 8.22 (m, 2H), 7.64-7.62 (m, 1H), 4.12 (t, J = 5.2 Hz,
2H), 3.68 (t, J = 5.24 Hz, 2H), 1.68-1.62 (m, 6H). 13C NMR (100 MHz, [D6]DMSO) δ
(ppm): 166.92 (C=O), 158.49, 153.16, 133.92, 131.52, 126.90, 123.95, 123.43, 46.85,
43.91, 26.22, 25.34, 23.78. HRMS (ESI): m/z for C13H13ClN2NaOS [M + Na]+, calc.:
303.0335; observed: 303.0335. HPLC analysis: retention time = 6.251 min; peak area,
91.06%.
4.1.19 (5-Chlorobenzo[d]thiazol-2-yl)(4-methylpiperazin-1-yl)methanone (5d): Yield:
172 mg, 58% (white solid), 1H NMR (400 MHz, [D6]DMSO) δ (ppm): 8.09 (d, J = 1.88 Hz,
1H), 7.88 (d, J = 8.44 Hz, 1H), 7.47 (dd, J = 9, 2.04 Hz, 1H), 4.44 (t, J = 4.28 Hz, 2H), 3.87
(t, J = 4.4 Hz, 2H), 2.54 (q, J = 4.64 Hz, 4H), 2.36 (s, 3H). 13C NMR (100 MHz, CDCl3) δ
(ppm): 166.51 (C=O), 159.30, 153.58, 134.66, 132.26, 129.08, 127.84, 124.14, 52.84,
52.40, 43.55, 42.72. HPLC analysis: retention time = 3.147 min; peak area, 94.28%.
4.1.20 1-(4-(5-Chlorobenzo[d]thiazole-2-carbonyl)piperazin-1-yl)ethanone (5e): Yield:
266 mg, 82% (white solid), mp 103-106 ºC. IR (MeOH) ν: 3409, 1621 cm-1. 1H NMR (400
MHz, [D4]MeOD) δ (ppm): 8.14-8.06 (m, 2H), 7.56 (dd, J = 8.64, 1.68 Hz, 1H), 4.50-4.40
13
(m, 2H), 3.91-3.82 (m, 2H), 3.77-3.72 (m, 4H), 2.19 (d, J = 4.2 Hz, 3H, -CH3). C NMR
(100 MHz, CDCl3) δ (ppm): 170.78 (-COMe), 166.07 (C=O), 159.71, 153.59, 134.38,
132.57, 127.24, 123.56, 122.99, 45.92, 43.31, 43.02, 19.85 (-CH3). Anal. Calcd for
C14H14ClN3O2S: C, 51.93; H, 4.36; N, 12.98; S, 9.90. Found: C, 51.55; H, 4.35; N, 12.89;
S, 9.57. MS (ESI) (m/z) 323.87 (M)+. HPLC analysis: retention time = 3.765 min; peak
area, 94.02%.
4.1.21 (5-Chlorobenzo[d]thiazol-2-yl)(4-phenylpiperazin-1-yl)methanone (5f): Yield:
1
279 mg, 78% (buff white solid), mp 108-111 ºC. IR (neat) ν: 3454, 1622, 1598 cm-1. H
NMR (400 MHz, [D6]DMSO) δ (ppm): 8.25 (s, 2H), 7.64 (d, J = 8.12 Hz, 1H), 7.25 (t, J =
Page 16 of 36

ACCEPTED MANUSCRIPT
7.08 Hz, 2H), 7.00 (d, J = 7.32 Hz, 2H), 6.83 (t, J = 6.4 Hz, 1H), 4.43 (s, 2H), 3.87 (s, 2H),
3.28 (s, 4H). 13C NMR (100 MHz, [D6]DMSO) δ (ppm): 167.38 (C=O), 159.07, 153.79,
151.07, 134.63, 132.17, 129.50, 127.65, 124.61, 124.10, 119.90, 116.37, 49.26, 48.72,
46.26, 43.43. MS (EI) (m/z) 358.06 (M+H)+. HPLC analysis: retention time = 11.040 min;
peak area, 96.77%.
4.1.22
1-(5-Chlorobenzo[d]thiazol-2-yl)-2-(4-(2-methoxyphenyl)piperazin-1-
yl)ethanone (5g): Yield: 221 mg, 57% (brick red solid), mp 116-118 ºC. IR (KBr) ν: 3453,
1
1637, 1589 cm-1. H NMR (400 MHz, [D6]DMSO) δ (ppm): 8.28-8.25 (m, 2H), 7.66-7.63
(m, 1H), 7.02-6.89 (m, 4H), 4.41 (t, J = 4.24 Hz, 2H), 3.86 (t, J = 4.28 Hz, 2H), 3.81 (s,
3H), 3.08 (q, J = 4.76 Hz, 4H). 13C NMR (100 MHz, [D6]DMSO) δ (ppm): 167.36 (C=O),
159.05, 153.76, 152.48, 140.95, 134.59, 132.13, 127.61, 125.09, 124.57, 124.09, 123.49,
121.28, 112.30, 55.81, 50.99, 50.52, 46.78, 43.76. HRMS (ESI): m/z for C19H19ClN3O2S
[M + H]+, calc.: 388.0887; observed: 388.0886. HPLC analysis: retention time = 3.179 min;
peak area, 95.54%.
4.1.23
1-(5-Chlorobenzo[d]thiazol-2-yl)-2-(4-(4-methoxyphenyl)piperazin-1-
yl)ethanone (5h): Yield: 209 mg, 54% (brick red solid), mp 125-127 ºC. IR (KBr) ν: 3456,
1615, 1506 cm-1. 1H NMR (400 MHz, [D6]DMSO) δ (ppm): 8.28-8.25 (m, 2H), 7.65 (dd, J
= 8.64, 2 Hz, 1H), 6.96 (d, J = 9.04 Hz, 2H), 6.85 (d, J = 9.04 Hz, 2H), 4.40 (t, J = 4.48 Hz,
2H), 3.86 (t, J = 4.32 Hz, 2H), 3.69 (s, 3H), 3.14 (q, J = 5.84 Hz, 4H). 13C NMR (100 MHz,
[D6]DMSO) δ (ppm): 167.35 (C=O), 159.03, 153.85, 153.75, 145.38, 134.60, 132.15,
127.62, 127.52, 125.08, 124.57, 124.08, 123.69, 118.56, 114.76, 55.63 (-OCH3), 50.76,
50.29, 46.44, 43.54. Anal. Calcd for C19H18ClN3O2S C, 58.83; H, 4.68; N, 10.83; S, 8.27.
Found: C, 58.43; H, 4.51; N, 10.82; S, 8.57. HRMS (ESI): m/z for C19H19ClN3O2S [M +
H]+, calc.: 388.0887; observed: 388.0869. HPLC analysis: retention time = 6.304 min; peak
area, 96.75%.
4.1.24 1-(4-(4-(5-Chlorobenzo[d]thiazole-2-carbonyl)piperazin-1-yl)phenyl)ethanone
1
(5i): Yield: 216 mg, 54% (orange solid), mp 150-153 ºC. IR (KBr) ν: 1660, 1598 cm-1. H
NMR (400 MHz, [D6]DMSO) δ (ppm): 8.26-8.25 (m, 1H), 7.84 (d, J = 8.8 Hz, 2H), 7.65
(dd, J = 8.6, 1.92 Hz, 1H), 7.02 (d, J = 8.92 Hz, 3H), 4.44 (t, J = 5.08 Hz, 2H), 3.86 (t, J =
13
4.6 Hz, 2H), 3.56-3.52 (m, 4H), 2.47 (s, 3H). C NMR (100 MHz, [D6]DMSO) δ (ppm):
195.54 (-COMe), 166.80 (C=O), 158.60, 153.22, 134.08, 131.60, 130.01, 127.10, 126.83,
Page 17 of 36

ACCEPTED MANUSCRIPT
124.04, 123.93, 123.52, 113.14, 46.74, 46.04, 45.27, 42.61, 26.04. Anal. Calcd for
C20H18ClN3O2S: C, 60.67; H, 4.54; N, 10.51; S, 8.02. Found: C, 61.05; H, 4.90; N, 10.61;
S, 7.99. HPLC analysis: retention time = 5.163 min; peak area, 96.27%.
4.1.25 (5-Chlorobenzo[d]thiazol-2-yl)(4-(pyridin-4-yl)piperazin-1-yl)methanone (5j):
Yield: 209 mg, 58% (pale yellow solid), mp 143-147 ºC. IR (MeOH) ν: 1626, 1595 cm-1.
1H NMR (400 MHz, [D6]DMSO) δ (ppm): 8.28-8.20 (m, 4H), 7.65 (d, J = 8.28 Hz, 1H),
6.88 (d, J = 5.2 Hz, 2H), 4.43 (s, 2H), 3.84 (s, 2H), 3.55 (s, 4H). 13C NMR (100 MHz,
[D6]DMSO) δ (ppm): 166.79 (C=O), 158.64, 154.11, 153.21, 149.20, 134.07, 131.67,
127.12, 124.06, 123.52, 108.23, 45.45, 45.08, 44.71, 42.46. HRMS (ESI): m/z for
C17H16ClN4OS [M + H]+, calc.: 359.0733; observed: 359.0748. HPLC analysis: retention
time = 3.595 min; peak area, 96.86%.
4.1.26 (5-Chlorobenzo[d]thiazol-2-yl)(4-(pyrazin-2-yl)piperazin-1-yl)methanone (5k):
Yield: 169 mg, 47% (white solid), mp 90-95 ºC. 1H NMR (400 MHz, [D6]DMSO) δ (ppm):
8. 22 (s, 1H), 8.13 (s, 2H), 7.95 (s, 1H), 7.92 (d, J = 8.56 Hz, 1H), 7.51 (dd, J = 8.52, 1.32
Hz, 1H), 4.64 (t, J = 4.84 Hz, 2H), 4.02 (t, J = 4.88 Hz, 2H), 3.82-3.79 (m, 4H). 13C NMR
(100 MHz, [D6]DMSO) δ (ppm): 165.41 (C=O), 158.43, 153.62, 152.85, 140.82, 133.50,
132.80, 131.74, 130.02, 126.49, 123.36, 121.67, 44.89, 44.01, 43.22, 42.26. HRMS (ESI):
m/z for C16H15ClN5NaOS [M + Na]+, calc.: 360.0686; observed: 360.0689. HPLC analysis:
retention time = 4.843 min; peak area, 99.84%.
4.1.27 (4-Benzhydrylpiperazin-1-yl)(5-chlorobenzo[d]thiazol-2-yl)methanone (5l):
Yield: 345 mg, 77% (pale yellow solid), mp 149-153 ºC. IR (CHCl3) ν: 3398, 1634 cm-1.
1H NMR (400 MHz, [D6]DMSO) δ (ppm): 8.18 (t, J = 8.56 Hz, 1H), 8.12 (br s, 1H), 7.44
(d, J = 7.28 Hz, 4H), 7.30 (t, J = 7.2 Hz, 4H), 7.21 (t, J = 7.04 Hz, 2H), 4.43 (s, 1H), 4.22
(s, 2H), 3.75 (s, 2H). 13C NMR (100 MHz, CDCl3) δ (ppm): 166.89 (C=O), 159.09, 153.86,
142.09, 134.45, 132.53, 128.68, 128.47, 127.89, 127.24, 124.21, 122.60, 75.99, 52.41,
51.70, 46.67, 43.88. Anal. Calcd for C25H22ClN3OS: C, 67.03; H, 4.95; N, 9.38; S, 7.16.
Found: C, 67.66; H, 4.89; N, 9.27; S, 7.04. HPLC analysis: retention time = 13.195 min;
peak area, 100%.
4.1.28 Morpholino(5-(trifluoromethyl)benzo[d]thiazol-2-yl)methanone (6a): Yield: 278
1
mg, 88% (yellow solid), mp 119-121 ºC. IR (CHCl3) ν: 1627 cm-1. H NMR (400 MHz,
Page 18 of 36

ACCEPTED MANUSCRIPT
CDCl3) δ (ppm): 8.38 (s, 1H), 8.09 (d, J = 8.48 Hz, 1H), 7.73 (dd, J = 1.36, 8.44 Hz, 1H),
13
4.53 (t, J = 4.72, 2H), 3.88-3.82 (m, 6H). C NMR (100 MHz, CDCl3) δ (ppm): 166.95,
159.02, 152.60, 139.50, 129.54, 129.21, 123.05, 122.67, 122.03, 67.18, 66.86, 47.13, 44.0.
HRMS (ESI): m/z for C13H12F3N2O2S [M + H+] calc.: 317.0572; observed: 317.0572.
HPLC analysis: retention time = 4.384 min; peak area, 98.02%.
4.1.29 Thiomorpholino(5-(trifluoromethyl)benzo[d]thiazol-2-yl)methanone (6b): Yield:
306 mg, 92% (yellow solid), mp 82-85 ºC. IR (CHCl3) ν: 1626 cm-1. 1H NMR (400 MHz,
CDCl3) δ (ppm): 8.23 (s, 1H), 7.64 (d, J = 8.44 Hz, 1H), 7.73 (dd, J = 1.28, 8.52 Hz, 2H),
4.65 (t, J = 4.92 Hz, 2H), 4.11 (t, J = 5.04 Hz, 2H), 2.84-2.79 (m, 4H). 13C NMR (100
MHz, CDCl3) δ (ppm): 166.83 (C=O), 159.33, 152.52, 139.46, 129.53, 125.34, 123.05,
122.66, 122.02, 49.41, 46.53, 28.54, 27.58. HRMS (ESI): m/z for C13H11F3N2NaOS2 [M +
Na+] calc.: 355.0163; observed: 355.0160. HPLC analysis: retention time = 5.280 min;
peak area, 100%.
4.1.30 Piperidin-1-yl(5-(trifluoromethyl)benzo[d]thiazol-2-yl)methanone (6c): Yield:
233 mg, 74% (orange yellow solid), mp 85-87 ºC. IR (CHCl3) ν: 1625 cm-1. 1H NMR (400
MHz, CDCl3) δ (ppm): 8.38 (s, 1H), 8.07 (d, J = 8.4 Hz, 1H), 7.71 (dd, J = 1.4, 8.48 Hz),
4.28 (t, J = 5.8 Hz, 2H), 3.79 (t, J = 5.48 Hz, 2H), 1.74 (s, 6H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 167.42 (C=O), 159.11, 152.61, 139.48, 129.31, 125.41, 122.74, 122.57,
121.91, 47.64, 44.96, 26.75, 25.82, 24.51. HRMS (ESI): m/z for C14H13F3N2NaOS [M +
Na]+, calc.: 337.0598; observed: 337.0594. HPLC analysis: retention time = 6.144 min;
peak area, 98.78%.
4.1.31
(4-Methylpiperazin-1-yl)(5-(trifluoromethyl)benzo[d]thiazol-2-yl)methanone
(6d): Yield: 254 mg, 77% (yellowish brown solid), mp 44-46 ºC. IR (CHCl3) ν: 1627 cm-
1.1H NMR (400 MHz, CDCl3) δ (ppm): 8.38 (s, 1H), 8.08 (d, J = 8.48 Hz, 1H), 7.72 (d, J =
8.48 Hz, 1H), 4.48 (t, J = 4.64 Hz, 2H), 3.89 (t, J = 4.92 Hz, 2H), 2.56 (q, J = 4.96 Hz, 4H),
2.36 (s, 3H). 13C NMR (100 MHz, CDCl3) δ (ppm): 167.14 (C=O), 159.01, 152.60, 139.51,
129.44, 129.11, 122.93, 122.64, 121.95, 55.40, 54.68, 46.32, 45.91, 43.61 (-OCH3). HRMS
(ESI): m/z for C14H15F3N3OS [M + H]+, calc.: 330.0888; observed: 330.0888. HPLC
analysis: retention time = 6.709 min; peak area, 100%.
Page 19 of 36

ACCEPTED MANUSCRIPT
4.1.32 1-(4-(5-(Trifluoromethyl)benzo[d]thiazole-2-carbonyl)piperazin-1-yl)ethanone
(6e): Yield: 314 mg, 88% (pale yellow solid), mp 167-169 ºC. IR (CHCl3) ν: 1630 cm-1. 1H
NMR (400 MHz, CDCl3) δ (ppm): 8.41 (d, J = 16.84 Hz, 1H), 8.12 (d, J = 8.36 Hz, 1H),
7.76 (dd, J = 1.12, 8.48 Hz, 1H), 4.59-4.49 (m, 2H), 3.92-3.80 (m, 4H), 3.69-3.65 (m, 4H),
2.19 (s, 3H, -CH3). 13C NMR (100 MHz, CDCl3) δ (ppm): 169.25 (-COMe), 164.20 (C=O),
159.07, 152.57, 141.32, 125.30, 123.18, 122.77, 122.68, 122.16, 46.61, 46.31, 41.80, 41.09,
21.41 (-CH3). HRMS (ESI): m/z for C14H15F3N3OS [M + H]+, calc.: 330.0837; observed:
330.0835. HPLC analysis: retention time = 3.733 min; peak area, 98.79%.
4.1.33
(4-Phenylpiperazin-1-yl)(5-(trifluoromethyl)benzo[d]thiazol-2-yl)methanone
(6f): Yield: 282 mg, 72% (yellowish white solid), mp 108-111 ºC. IR (CHCl3) ν: 1627 cm-
1. 1H NMR (400 MHz, CDCl3) δ (ppm): 8.43 (s, 1H), 8.12 (d, J = 8.48 Hz, 1H), 7.76 (dd, J
= 1.24, 8.48 Hz, 1H), 7.36-7.32 (m, 2H), 7.01-6.94 (m, 3H), 4.68 (t, J = 5 Hz, 2H), 4.05 (t,
J = 4.96 Hz, 2H), 3.38-3.35 (m, 4H). 13C NMR (100 MHz, CDCl3) δ (ppm): 167.11 (C=O),
159.02, 152.64, 150.82, 139.55, 129.51, 129.33, 122.01, 120.70, 116.92, 116.70, 50.08,
49.52, 46.37, 43.74. HRMS (ESI): m/z for C19H17F3N3OS [M + H]+, calc.: 392.1044;
observed: 392.1046. HPLC analysis: retention time = 6.891 min; peak area, 96.42%.
4.1.34
(4-(2-Methoxyphenyl)piperazin-1-yl)(5-(trifluoromethyl)benzo[d]thiazol-2-
yl)methanone (6g): Yield: 325 mg, 77% (pale yellow solid), mp 124-126 ºC. IR (CHCl3)
ν: 1627 cm-1. 1H NMR (400 MHz, CDCl3) δ (ppm): 8.40 (s, 1H), 8.09 (d, J = 8.48 Hz, 1H),
7.73 (d, J = 8.48 Hz, 1H), 7.08-7.04 (m, 1H), 6.96-6.90 (m, 3H), 4.66 (t, J = 4.64 Hz, 2H),
4.06 (t, J = 4.76 Hz, 2H), 3.91 (s, 3H), 3.21 (t, J = 5 Hz, 4H). 13C NMR (100 MHz, CDCl3)
δ (ppm): 167.27 (C=O), 160.92, 159.01, 152.65, 152.29, 140.48, 139.55, 129.12, 123.69,
122.94, 122.65, 121.97, 121.10, 118.51, 111.34, 55.46, 51.29, 50.69, 46.80, 44.03. HRMS
(ESI): m/z for C20H19F3N3O2S [M + H]+, calc.: 422.1150; observed: 422.1151. HPLC
analysis: retention time =6.688 min; peak area, 98.32%.
4.1.35 2-(4-(4-Methoxyphenyl)piperazin-1-yl)-1-(5-(trifluoromethyl)benzo[d]thiazol-2-
yl)ethanone (6h): Yield: 371 mg, 88% (brick red solid), mp 167-170 ºC. IR (CHCl3) ν:
1
1628 cm-1. H NMR (400 MHz, CDCl3) δ (ppm): 8.40 (s, 1H), 8.09 (d, J = 8.52 Hz, 1H),
7.73 (d, J = 8.44 Hz, 1H), 6.96-6.92 (m, 2H), 6.90-6.83 (m, 2H), 4.63 (t, J = 4.84 Hz, 2H),
13
4.02 (t, J = 4.84 Hz, 2H), 3.78 (s, 3H), 3.22-3.20 (m, 4H). C NMR (100 MHz, CDCl3) δ
(ppm): 167.14 (C=O), 159.01, 154.51, 152.63, 145.12, 139.54, 129.34, 124.71, 123.03,
Page 20 of 36

ACCEPTED MANUSCRIPT
122.67, 121.99, 118.99, 118.68, 114.59, 114.49, 55.57 (-OCH3), 51.57, 51.06, 46.56, 43.88.
HRMS (ESI): m/z for C20H19F3N3O2S [M + H]+, calc.: 422.1150; observed: 422.1151.
HPLC analysis: retention time = 6.197 min; peak area, 96.75%.
4.1.36
1-(4-(4-(5-(Trifluoromethyl)benzo[d]thiazole-2-carbonyl)piperazin-1-
yl)phenyl)ethanone (6i): Yield: 334 mg, 77% (orange solid), mp 104-107 ºC. IR (CHCl3)
1
ν: 1667, 1627, 1598 cm-1. H NMR (400 MHz, CDCl3) δ (ppm): 8.40 (s, 1H), 8.11 (d, J =
8.4 Hz, 2H), 7.92 (d, J = 8.92 Hz, 2H), 7.75 (d, J = 8.48 Hz, 1H), 6.92 (d, J = 8.06 Hz, 2H),
13
4.69 (t, J = 4.96 Hz, 2H), 4.03 (t, J = 4.92 Hz, 2H), 3.55-3.53 (m, 4H), 2.55 (s, 3H). C
NMR (100 MHz, [D6]DMSO) δ (ppm): 196.90 (-COMe), 166.87 (C=O), 159.11, 153.61,
152.62, 139.55, 130.47, 129.59, 129.26, 128.48, 125.33, 123.14, 122.74, 122.64, 122.03,
113.87, 48.02, 47.31, 45.89, 43.37, 26.20. HRMS (ESI): m/z for C21H19F3N3O2S [M + H]+,
calc.: 434.1150; observed: 434.1139. HPLC analysis: retention time = 6.165 min; peak
area, 98.39%.
4.1.37
(4-(Pyridin-4-yl)piperazin-1-yl)(5-(trifluoromethyl)benzo[d]thiazol-2-
yl)methanone (6j): Yield: 290 mg, 74% (pale yellow solid), mp 130-132 ºC. IR (CHCl3) ν:
1
1627 cm-1. H NMR (400 MHz, CDCl3) δ (ppm): 8.40 (s, 1H), 8.35 (d, J = 5.96 Hz, 2H),
8.11 (d, J = 8.48 Hz, 1H), 7.75 (d, J = 8.48 Hz, 1H), 6.73 (d, J = 6.44 Hz, 2H), 4.69 (t, J =
5.08 Hz, 2H), 4.02 (t, J = 5.08 Hz, 2H), 3.55 (t, J = 5.4 Hz, 4H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 166.77 (C=O), 159.14, 154.65, 152.61, 150.03, 139.54, 129.62, 129.29,
125.31, 123.22, 122.22, 122.60, 122.04, 108.51, 46.44, 45.68, 45.62, 43.14. HRMS (ESI):
m/z for C18H16F3N4OS [M + H]+, calc.: 393.0997; observed: 393.0992. HPLC analysis:
retention time = 1.685 min; peak area, 99.85%.
4.1.38
(4-(Pyrazin-2-yl)piperazin-1-yl)(5-(trifluoromethyl)benzo[d]thiazol-2-
yl)methanone (6k): Yield: 295 mg, 75% (pale yellow solid), mp 97-100 ºC. IR (CHCl3) ν:
1627 cm-1.1H NMR (400 MHz, CDCl3) δ (ppm): 8.41 (s, 1H), 8.21 (s, 1H), 8.12-8.09 (m,
2H) 7.94 (d, J = 2.48 Hz, 1H), 7.75 (d, J = 8.48 Hz, 1H), 4.65 (t, J = 4.92 Hz, 2H), 4.01 (t, J
= 4.76 Hz, 2H), 3.81-3.78 (m, 4H). 13C NMR (100 MHz, [D6]DMSO) δ (ppm): 166.88
(C=O), 159.23, 154.62, 152.62, 141.85, 139.55, 133.88, 131.04, 129.52, 129.27, 123.16,
122.72, 122.10, 45.91, 45.03, 44.25, 43.34. HRMS (ESI): m/z for C17H15F3N5OS [M +
Na]+, calc.: 394.0949; observed: 394.0949. HPLC analysis: retention time = 4.821 min;
peak area, 98.41%.
Page 21 of 36

ACCEPTED MANUSCRIPT
4.1.39
(4-Benzhydrylpiperazin-1-yl)(5-(trifluoromethyl)benzo[d]thiazol-2-
yl)methanone (6l): Yield: 356 mg, 74% (pale yellow solid), mp 136-139 ºC. IR (CHCl3) ν:
1
1629 cm-1. H NMR (400 MHz, CDCl3) δ (ppm): 8.30 (s, 1H), 8.05 (d, J = 8.44 Hz, 1H),
7.69 (d, J = 8.48 Hz, 1H), 7.45-7.38 (m, 5H), 7.31-7.18 (m, 5H), 4.47 (t, J = 4.64 Hz, 2H),
4.30 (s, 1H), 3.86 (t, J = 4.8 Hz, 2H), 2.55 (q, J = 5.12, 4H). 13C NMR (100 MHz, CHCl3) δ
(ppm): 167.30 (C=O), 158.87, 152.60, 142.04, 139.49, 129.39, 128.67, 127.89, 127.81,
127.25, 122.90, 122.61, 121.90, 75.97, 52.39, 51.70, 46.68, 43.96. HRMS (ESI): m/z for
C26H23F3N3OS [M + H]+, calc.: 482.1514; observed: 482.1507. HPLC analysis: retention
time = 27.659 min; peak area, 96.94%.
4.2. Biological Evaluation
4.2.1 Determination of the minimal inhibitory concentration (MIC) of 2 and 4, 5, 6
benzo[d]thiazole-2-carboxamides:
The drug susceptibility of Mycobacterium tuberculosis strain H37Rv was determined using
the method recommended by the National Committee for Clinical Laboratory Standards for
the determination of MIC in triplicate. Two-fold serial dilutions (50.0, 25.0, 12.5, 6.25,
3.13, 1.56, 0.78 and 0.4 µg/mL) of each test compounds and drugs were prepared and
incorporated into Middlebrook 7H11 agar medium with OADC Growth Supplement.
Inoculum of M. tuberculosis H37Rv ATCC 27294 was prepared from fresh Middlebrook
7H11 agar slants with OADC (oleic acid, albumin, dextrose and catalase; Difco) Growth
Supplement adjusted to 1 mg/mL (wet weight) in Tween 80 (0.05%) saline diluted to 10−2
to give a concentration of ~ 107 cfu/mL. A 5 ꢀL amount of bacterial suspension was spotted
into 7H11 agar tubes containing 10-fold serial dilutions of drugs per mL. The tubes were
incubated at 37 ºC, and final readings were recorded after 28 days.7 Isoniazid (INH),
Rifampin (R), Ethambutol (E) and Pyrazinamide (Z) were purchased from Lupin
Pharmaceuticals, Inc. and Ciprofloxacin (Cfx) was procured from Matrix laboratories
Limited.
Page 22 of 36

ACCEPTED MANUSCRIPT
4.2.2 Cytotoxicity Evaluation
Anti-TB active compounds with MIC ≤ 12.5ꢀg/mL were further examined for toxicity
evaluated against RAW 264.7 (mouse leukemic monocyte macrophage) cell lines by using
(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) MTT assay at the
concentration of 50 µg/mL. After 72 h of exposure, viability was assessed on the basis of
cellular conversion of MTT into a formazan product using the Promega Cell Titer 96 non-
radioactive cell proliferation assay.
5. References
1.
Zumla, A.; Nahid, P.; Cole, S. T. Advances in the Development of New Tuberculosis
Drugs and Treatment Regimens. Nat. Rev. Drug Dis. 2013, 12, 388-404.
Global Tuberculosis Report 2014, World Health Organization, Geneva, 2014.
http://apps.who.int/iris/bitstream/10665/137094/1/9789241564809_eng.pdf?ua=1
(Accessed on Apr 30, 2015)
2.
3.
4.
http://www.who.int/tb/challenges/mdr/en/index.html.
(a) Migliori G.B.; De Iaco G.; Besozzi G.; Centis R.; Cirillo D. M. First tuberculosis
cases in Italy resistant to all tested drugs. Euro Surveill. 2007, 12, E070517.1. (b)
Velayati A. A.; Masjedi M. R.; Farnia P.; Tabarsi P., Ghanavi J.; ZiaZarifi A. H.;
Hoffner S. E. Emergence of new forms of totally drug resistant tuberculosis bacilli:
super extensively drug-resistant tuberculosis or totally drug-resistant strains in Iran.
Chest 2009, 136, 420–425. (c) Udwadia, Z. F., Amale, R. A.; Ajbani, K. K.;
Rodrigues, C. Totally drug-resistant tuberculosis in India. Clin. Infect. Dis. 2012,
54, 579–581.
5.
6.
FDA
news
release.
http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm333695.html
(accessed Dec 12, 2014).
Shah, P.; Dhameliya, T. M.; Bansal, R.; Nautiyal, M.; Kommi, D. N.; Jadhavar, P.
S.; Sridevi, J. P.; Yogeeswari, P.; Sriram D.; Chakraborti, A. K. N-
Arylalkylbenzo[d]thiazole-2-carboxamides as Anti-mycobacterial Agents: Design,
New Methods of Synthesis and Biological Evaluation. Med. Chem. Commun. 2014,
5, 1489-1495.
Page 23 of 36

ACCEPTED MANUSCRIPT
7.
(a) Bhagat, S.; Shah, P.; Garg, S. K.; Mishra, S.; Kaur, P. K.; Singh S.; Chakraborti,
A. K. α-Aminophosphonates as Novel Anti-leishmanial Chemotypes: Synthesis,
Biological Evaluation, and CoMFA Studies. Med. Chem. Commun. 2014, 5, 665-
670. (b) Seth, K.; Garg, S. K.; Kumar, R.; Purohit, P.; Meena, V. S.; Goyal, R.;
Banerjee U. C.; Chakraborti, A. K. 2-(2-Arylphenyl)benzoxazole As a Novel Anti-
Inflammatory Scaffold: Synthesis and Biological Evaluation. ACS Med Chem. Lett.
2014, 5, 512-516. For review (c) Sun, H.; Tawa G.; Wallqvist, A. Classification of
scaffold-hopping approaches. Drug Discov. Today 2012, 17, 310-324.
Bogatcheva, E.; Hanrahan, C.; Nikonenko, B.; Samala, R.; Chen, P.; Gearhart, J.;
Barbosa, F.; Einck, L.; Nacy C. A.; Protopopova, M. Identification of New Diamine
Scaffolds with Activity against Mycobacterium tuberculosis. J. Med. Chem. 2006,
49, 3045-3048.
8.
9.
Deidda, D.; Lampis, G.; Fioravanti, R.; Biava, M.; Porretta, G. C.; Zanetti S.;
Pompei, R. Bactericidal Activities of the Pyrrole Derivative BM212 against
Multidrug-Resistant and Intramacrophagic Mycobacterium tuberculosis Strains.
Antimicrob. Agents Chemother. 1998, 42, 3035-3037.
10.
11.
Dover L. G.; Coxon, D. J. Current status and research strategies in tuberculosis drug
development. J. Med. Chem. 2011, 54, 6157-6165.
Mao, J.; Wang, Y.; Wan, B.; Kozikowski, A. P.; Franzblau, S. G. Design, Synthesis,
and Pharmacological Evaluation of Mefloquine-based Ligands as Novel Anti-
tuberculosis Agents. ChemMedChem 2007, 2, 1624-1630.
12.
Nagesh, H. N.; Suresh, N.; Naidu, K. M.; Arun, B.; Sridevi, J. P.; Sriram, D.;
Yogeeswari, P.; Chandra Sekhar, K. V. G. Synthesis and Evaluation of Anti-
tubercular Activity of 6-(4-Substitutedpiperazin-1-yl)phenanthridine Analogues.
Eur. J. Med. Chem. 2014, 74, 333-339.
13.
14.
Srivastav, M. K.; Shantakumar, S. M. Design and Synthesis of Novel 2-
Trichloromethyl-4-substituted Quinazoline Derivatives as Anti-tubercular Agents.
Chem. Sci. Trans. 2013, 2, 1056-1062.
Chollet, A.; Mori, G.; Menendez, C.; Rodriguez, F.; Fabing, I.; Pasca, M. R.;
Madacki, J.; Korduláková J.; Constant, P.; Quémard, A.; Génisson, V. B.; Lherbet,
C.; Baltas M. Design, Synthesis and Evaluation of New GEQ Derivatives as
Page 24 of 36

ACCEPTED MANUSCRIPT
Inhibitors of InhA Enzyme and Mycobacterium tuberculosis Growth. Eur. J. Med.
Chem. 2015, 101, 218-235.
15.
Suresh, N.; Nagesh, H. N.; Renuka, J.; Rajput, V.; Sharma, R.; Khan I. A.; Chandra
Sekhar, K. V. G. Synthesis and Evaluation of 1-Cyclopropyl-6-fluoro-1,4-dihydro-4-
oxo-7-(4-(2-(4-substitutedpiperazin-1-yl)acetyl)piperazin-1-yl)quinoline-3-
carboxylic Acid Derivatives as Anti-tubercular and Antibacterial Agents. Eur. J.
Med. Chem. 2014, 71, 324-332.
16.
17.
Mitchell, M. L.; Roethle, P. A.; Xu, L.; Yang, H.; McFadden, R.; Babaoglu, K.
Benzothiazole Compounds and their Pharmaceutical Use. WO Patent 2012/145728
A1, 2012.
Chakraborti, A. K.; Rudrawar, S.; Jadhav, K. B.; Kaur G.; Chankeshwara, S. V. ‘‘On
water’’ Organic Synthesis: A Highly Efficient and Clean Synthesis of 2-
Aryl/heteroaryl/styryl benzothiazoles and 2-Alkyl/aryl alkyl Benzothiazolines.
Green Chem. 2007, 9, 1335-1340.
18.
19.
Parikh, N.; Kumar, D.; Roy S. R.; Chakraborti, A. K. Surfactant Mediated Oxygen
Reuptake in Water for Green Aerobic Oxidation: Mass-spectrometric Determination
of Discrete Intermediates to Correlate Oxygen Uptake with Oxidation Efficiency.
Chem. Comm. 2011, 47, 1797-1799.
National Committee for Clinical Laboratory Standards. Antimycobacterial
Susceptibility Testing for Mycobacterium tuberculosis, Tentative Standard M24-T.
Wayne, PA: NCCLS, 1995.
20.
21.
Hett E. C.; Rubin, E. J. Bacterial Growth and Cell Division: A Mycobacterial
Perspective. J. Microbiol. Mol. Biol. Rev. 2008, 72, 126-156.
Lipinski, C. A.; F. Lombardo; B. W. Dominy; P. J. Feeney. Experimental and
Computational Approaches to Estimate Solubility and Permeability in Drug
Discovery and Development Settings. Adv. Drug Delivery Rev. 2001, 46, 3-26.
(a) Chakraborti, A. K.; Thilagavathi, R. Computer-aided Design of Non Sulphonyl
COX-2 Inhibitors: An Improved Comparative Molecular Field Analysis
Incorporating Additional Descriptors and Comparative Molecular Similarity Indices
Analysis of 1,3-Diarylisoindole Derivatives. Bioorg. Med. Chem. 2003, 11, 3989-
3996. (b) Chakraborti, A. K.; Gopalakrishnan, B.; Sobhia M. E.; Malde, A.
Comparative Molecular Field Analysis (CoMFA) of Phthalazine Derivatives as
22.
Page 25 of 36

ACCEPTED MANUSCRIPT
Phosphodiesterase IV Inhibitors. Bioorg. Med. Chem. Lett. 2003, 13, 2473-2479. (c)
Chakraborti, A. K.; Gopalakrishnan, B.; Sobhia M. E.; Malde, A. 3D-QSAR Studies
on Thieno[3,2-d]pyrimidines as Phosphodiesterase IV Inhibitors. Bioorg. Med.
Chem. Lett. 2003, 13, 1403-1408. (e) For review please see Zhang, L.; Tsai, K. C.;
Du, L.; Fang. H.; Li, M.; Xu, W. How to Generate Reliable and Predictive CoMFA
Models. Curr. Med. Chem. 2011, 18, 923-930.
23.
SYBYL7.1, Tripos Associate Inc.; 1699, S. Hanley Rd., St. Louis, MO 631444,
USA.
Page 26 of 36

ACCEPTED MANUSCRIPT
FIGURE CAPTIONS
Figure 1. Reported bioactive compounds with piperazine scaffold having anti-TB
activity.[8-15]
Figure 2. Design of benzo[d]thiazol-2-yl(piperazin-1-yl)methanone I as new anti-TB
scaffold.
Figure 3. Graphical representation of the anti-TB activity of the synthesized compounds
with MIC ≤ 1.56 µg/mL in comparison with standard drugs.
Figure 4. Graphical representation of the in-vitro cell viability profile of the synthesized
compounds with MIC ≤ 6.25 µg/mL.
Figure 5. Structure activity correlation chart of the compounds 4/5/6a-c.
Figure 6. Confirmation of the template molecule compound 5l.
Figure 7. Alignment of all molecules used for CoMFA molecular field generation.
Figure 8. Correlation plot of the predicted pMIC with the experimental pMIC values
generated through CoMFA.
Figure 9. CoMFA contours for benzo[d]thiazole-2-carboxamides: (a) steric, and (b)
electrostatic interaction regions of 4i.
Page 27 of 36

ACCEPTED MANUSCRIPT
Table 1. Yields of the 5-substituted benzo[d]thiazole-2-carboxylates (2a/b/c) and
carboxamides (4/5/6a-l) and their biological activitiesa
MICc
(µg/mL)
25
MIC
(µM)
120.63
12.93
22.71
6.28
Cytotoxicityd
Yieldb
(%)
Entry
R
Z
R1
Compd no.
(% Inhibition)
-
1
-
-
-
83
73
70
88
83
67
56
55
76
55
53
51
54
77
63
77
67
77
60
82
78
57
54
2a
2b
2c
4a
4b
4c
4d
4e
4f
2
-
-
-
3.125
6.25
1.56
25
37.40
29.12
36.16
-
3
-
-
-
4
H
H
H
H
H
H
H
H
H
H
H
H
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
O
-
5
S
-
-
94.56
101.49
11.96
5.39
6
CH2
NR1
NR1
NR1
NR1
NR1
25
-
7
Me
3.125
1.56
1.56
3.125
12.5
1.56
3.125
6.25
0.78
6.25
6.25
12.5
25
52.10
48.82
67.23
53.36
-
8
COMe
C6H5
9
4.82
10
11
12
13
14
15
16
17
18
19
20
21
22
23
2-OMe-C6H4
4-OMe-C6H4
8.84
4g
4h
4i
35.37
4.27
NR1 4-COMe-C6H4
62.34
61.95
65.34
60.66
26.12
62.54
-
NR1
NR1
NR1
O
4-Pyridyl
9.63
4j
2-Pyrazinyl
19.21
1.89
4k
4l
CH(C6H5)2
-
22.10
20.92
44.52
84.52
38.60
17.46
8.06
5a
5b
5c
5d
5e
5f
S
-
-
CH2
NR1
NR1
NR1
NR1
NR1
Me
-
COMe
C6H5
12.5
6.25
3.125
3.125
-
41.21
63.36
42.81
2-OMe-C6H4
4-OMe-C6H4
5g
5h
8.06
Page 28 of 36