Broad spectrum anti-infective properties of benzisothiazolones and the parallels in their anti-bacterial and anti-fungal effects

Article abstract of DOI:10.1016/j.bmcl.2017.01.027

Various mono- and bis-benzisothiazolone derivatives were synthesized and screened against different strains of bacteria and fungi in order to understand the effect of multiple electrophilic sulfur atoms and substitution pattern in the immediate vicinity of reactive sulfur. Staphyllococcus aureus-ATCC 7000699, MRSA and S. aureus-ATCC 29213 (Quality Control strain) were more susceptible to this class of compounds, and the most potent derivative 1.15 had MIC₅₀ of 0.4?μg/mL (cf. Gentamicin?=?0.78?μg/mL). CLogP value, optimally in the range of 2.5–3.5, appeared to contribute more to the activity than the steric and electronic effects of groups attached at nitrogen. By and large, their anti-fungal activities also followed a similar trend with respect to the structure and CLogP values. The best potency of IC₅₀?=?0.1?μg/mL was shown by N-benzyl derivative (1.7) against Aspergillus fumigatus; it was also potent against Candida albicans, Cryptococcus neoformans, Sporothrix schenckii, and Candida parapsilosis with IC₅₀ values ranging from 0.4 to 1.3?μg/mL. Preliminary studies also showed that this class of compounds have the ability to target malaria parasite with IC₅₀ values in low micromolar range, and improvement of selectivity is possible through structure optimization.

Full text of DOI:10.1016/j.bmcl.2017.01.027

Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Broad spectrum anti-infective properties of benzisothiazolones and the
parallels in their anti-bacterial and anti-fungal effects
P. Gopinath a, R.K. Yadav b, P.K. Shukla b, K. Srivastava c, S.K. Puri c, K.M. Muraleedharan a,
⇑
a Department of Chemistry, Indian Institute of Technology-Madras, Chennai 600036, India
b Division of Microbiology, CSIR-Central Drug Research Institute, Lucknow 226031, India
c Division of Parasitology, CSIR-Central Drug Research Institute, Lucknow 226031, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Various mono- and bis-benzisothiazolone derivatives were synthesized and screened against different
strains of bacteria and fungi in order to understand the effect of multiple electrophilic sulfur atoms
and substitution pattern in the immediate vicinity of reactive sulfur. Staphyllococcus aureus-ATCC
7000699, MRSA and S. aureus-ATCC 29213 (Quality Control strain) were more susceptible to this class
Received 30 October 2016
Revised 6 January 2017
Accepted 11 January 2017
Available online xxxx
of compounds, and the most potent derivative 1.15 had MIC50 of 0.4 lg/mL (cf. Gentamicin = 0.78 lg/
mL). CLogP value, optimally in the range of 2.5–3.5, appeared to contribute more to the activity than
the steric and electronic effects of groups attached at nitrogen. By and large, their anti-fungal activities
also followed a similar trend with respect to the structure and CLogP values. The best potency of
Keywords:
Benzisothiazolones
Antibacterial
Antifungal
Antimalarial
IC50 = 0.1
against Candida albicans, Cryptococcus neoformans, Sporothrix schenckii, and Candida parapsilosis with IC50
values ranging from 0.4 to 1.3 g/mL. Preliminary studies also showed that this class of compounds have
lg/mL was shown by N-benzyl derivative (1.7) against Aspergillus fumigatus; it was also potent
l
Anti-infective agents
the ability to target malaria parasite with IC50 values in low micromolar range, and improvement of selec-
tivity is possible through structure optimization.
Ó 2017 Elsevier Ltd. All rights reserved.
Introduction
A literature search revealed that most of the isothiazolones and
benzisothiazolones (BITs) investigated thus far are ‘monomeric’ in
Combating infectious diseases is a major challenge of the pre-
sent century due to increasing resistance against common thera-
peutic agents. Among various classes of heterocyclic compounds
with anti-infective properties, benzisothiazolones (BITs) are spe-
cial because of the presence of electrophilic sulfur as part of the
bicyclic skeleton.1,2 Its ability to form disulfide bonds with sulfur
nucleophiles in the target cells, or to chelate biologically relevant
metals such as zinc from the functional domains of proteins have
been correlated with the biological effects.3–6 Recently we have
conducted a series of studies to understand the effect of benzisoth-
iazolones on cancer cells and found that they are capable of induc-
ing apoptosis through intrinsic pathway, and can arrest the cell
cycle of HeLa cells at G2/M phase.7 Although the IC50 values were
in micromolar range, their ability to induce DNA fragmentation,
perturb mitochondrial membrane potential and more importantly,
the ability of externally added sulfur nucleophiles like N-acetyl
cysteine (NAC) to reverse the inhibitory effects of BITs were indica-
tive of the direct role of sulfur in the biochemical responses.
the sense that they contain only one electrophilic sulfur atom.
These reports showed their effect on whole cell/infectious agent
(anti-proliferative effects, inhibition of blood platelet aggregation,
antiviral, antibacterial & anti-fungal activities),7–13 as well as
against specific targets like human leukocyte elastase (BIT as 1,1-
dioxide),14–16 RNA polymerase,5 HIV-NCp-7,6 macrophage migra-
tion inhibitory factor,17 histone acetyltransferases,3,18 telomerase19
and phosphomannose isomerase.20 Introduction of additional elec-
trophilic sulfur in the molecule could in principle augment the bio-
logical response but comparative assessment of their properties
remains to be carried out in a systematic manner. The present
work primarily aims to compare the activities of monomeric and
dimeric BITs (Fig. 1) against different strains of bacteria, fungi
and malaria parasite to understand the structural features/molec-
ular properties that are decisive. They were synthesized by reac-
tion of either bromosulfenyl benzoyl chloride or dithiodibenzoyl
chloride with appropriate amines in presence of a base such as tri-
ethylamine.7 Experimental procedures and spectral data of these
compounds are presented in the supporting material. They differ
in the nature of N-substitution and present varying degrees of
steric and electronic influences in the vicinity of electrophilic
sulfur.
⇑
Corresponding author.
E-mail address: mkm@iitm.ac.in (K.M. Muraleedharan).
http://dx.doi.org/10.1016/j.bmcl.2017.01.027
0960-894X/Ó 2017 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Gopinath P., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.01.027

2
P. Gopinath et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
(ATCC 29213) (Table 1) in general were more susceptible com-
pared to wild type. Although a clear structure-activity relationship
in accordance with variation in N-substitution was not obvious, the
fact that simple N-aryl benzisothazolones are as active as dimeric
systems shows that increase in the number of electrophilic sulfur
atoms does not lead to a proportionate increase in activities. Com-
pounds 1.1–1.4, 1.7 and 1.10 had IC50 values <2
aureus, 1.2 being the most potent (0.6 g/mL). In the case of methi-
cillin resistant S. aureus, compounds 1.7 and 1.15 were superior
with IC50 of 0.4 g/mL each. Other compounds with IC50 value
<2 g/mL against this strain are 1.8, 1.9, 1.11, 1.14, and 1.16–
1.19. The compound 1.15 was found to be the most potent
(IC50 = 0.3 g/mL) against the Quality Control S. aureus (ATCC
29213), and compounds 1.1–1.4, 1.7 and 1.9 had the IC50 value
within 2 g/mL. Simple aryl groups or amino acid units as part of
lg/mL against S.
l
l
l
l
l
N-substitution gave sub-micro IC50 values while introduction of
more than one amino acid residue doesn’t give any advantage
which becomes clear if we compare the activities of 1.17&1.18
vs. 1.21&1.22. The fact that a number of these compounds are more
active than the standard drugs Gentamycin and Norfloxacin in
assays against resistant strains is particularly noteworthy (see
Table 2).
Fig. 1. Benzisothiazolone derivatives used in the present study.
After understanding the antibacterial activities of these com-
pounds we continued our studies by evaluating their effect on var-
ious fungal strains namely: 1. Candida albicans, 2. Cryptococcus
neoformans, 3. Sporothrix schenckii, 4. Trichophyton mentagrophytes,
5. Aspergillus fumigatus and 6. Candida parapsilosis (ATCC-22019).
The MICs of compounds were determined by broth microdilution
technique as per the guidelines of the National Committee for Clin-
ical Laboratory Standards using RPMI-1640 media buffered with
MOPS [3-(N-morpholino)propanesulfonic acid]. Starting inoculums
of test culture was 1–5 Â 103 CFU mLÀ1. Micro titer plates were
incubated at 35 °C. The MIC values were recorded after 48 h of
incubation.22,23 Interestingly, there were some parallels in the anti-
fungal and antibacterial assay results. While, most of them were
active with low IC50 values (1.7 being one of the most potent with
IC50 = 0.1 lg/mL against Aspergillus fumigatus), the compounds 1.6,
1.10, 1.13, 1.14, 1.21 and 1.22, which were less potent in antibac-
terial assays, remained so against fungal strains as well. Among the
active ones, IC50 value of <1 lg/mL was shown by simple N-aryl
(1.1–1.4), N-alkyl (1.11–1.12) and N-arylalkyl (1.7–1.9)
derivatives.
Similar trend in their antibacterial and antifungal activity
prompted us to look for physicochemical properties that are likely
decisive. Of various descriptors, partition coefficients (LogP) which
reflects organic/aqueous solubility, seemed important as it affects
Results and discussion
Antibacterial and antifungal assay results: Compounds 1.1–1.22
(Fig. 1) were screened against various bacteria and fungi as per lit-
erature protocols. The bacteria were tested by NCCLS method in
Mueller Hinton Broth.21 Gentamicin and Norfloxacin were used
as standard drugs to compare antibacterial activity whereas Flu-
conazole and Amphotericin B were used for antifungal studies as
controls. The bacterial strains used were: (1) Escherichia coli (ATCC
9637) (2) Pseudomonas aeruginosa (ATCC BAA-427) (3) Klebsiella
pneumoniae (ATCC 27736) (4) Staphylococcus aureus (ATCC
25923) (5) S. aureus (ATCC 700699, MRSA), and (6) S. aureus (ATCC
29213, Quality Control strain).
Compounds 1.1–1.22 can be broadly categorized into four
groups: (i) N-aryl and N-alkylaryl substituted benzisothiazolone
(1.1–1.10), (ii) those derived from aliphatic or alicyclic amines
(1.11–1.12), (iii) those based on amino acid esters or peptides
(1.17–1.22), and (iv) benzisothiazolone dimers (1.13–1.16); the
alanine-based 1.17 has previously been studied by Dou et al.10
Among the six bacterial strains tested, S. aureus was more sensitive
to these compounds (column 4–6, Table 1); for others (strains 1–3,
SI), IC50 values were >50 lg/mL and are presented in SI. Among S.
aureus strains, MRSA (ATCC 700699) and the Quality Control strain
Table 1
Antibacterial activities of benzisothiazolones 1.1–1.22.
No
4*
5*
6*
No
4*
5*
6*
MIC
IC50
MIC
IC50
MIC
IC50
MIC
IC50
MIC
IC50
MIC
IC50
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.6
1.07
1.6
1.1
0.6
1.5
1.0
>50
>50
1.5
6.8
2.2
1.1
6.8
10.6
0.77
0.75
0.73
1.07
>50
>50
0.8
1.9
1.0
4.2
2.5
ND
ND
ND
ND
>50
>50
0.4
1.0
0.6
2.6
1.0
4.7
2.1
1.0
1.9
2.4
>50
>50
2.3
8.5
2.5
18.7
7.1
9.8
1.6
0.6
1.2
1.6
>50
>50
1.7
4.6
1.9
13.5
4.6
6.3
1.13
1.14
1.15
1.16
1.17
1.18
1.19
1.20
1.21
1.22
Std17
Std28
18.0
3.4
16.7
12.4
3.0
2.9
4.2
3.5
7.5
10.0
3.2
4.1
6.1
2.0
2.4
2.0
2.1
3.6
>50
–
10.2
2.3
0.9
4.7
1.4
0.4
1.5
0.84
0.82
0.43
2.1
3.6
>50
–
6.5
3.7
0.4
4.1
8.4
4.6
4.3
6.9
5.6
>50
0.78
0.78
6.3
2.5
0.3
2.0
6.4
2.6
2.1
2.7
3.5
>50
–
2.0
2.6
>50
>50
1.6
10.2
2.6
1.5
9.8
15.4
0.87
0.97
0.89
3.5
1.9
7.5
1.10
1.11
1.12
>50
6.25
0.39
>50
>50
>50
5.2
–
–
–
*
MIC and IC50 values in lg/mL, MIC-Minimum inhibitory concentration; (1) E. coli (ATCC 9637), (2) Pseudomonas aeruginosa (ATCC BAA-427), (3) Klebsiella pneumoniae
(ATCC 27736); results from assays involving these strains are given in SI; (4) Staphylococcus aureus (ATCC 25923), (5) Staphylococcus aureus (ATCC 700699, MRSA), (6)
Staphylococcus aureus (ATCC 29213 Quality control strain for susceptibility testing), (7) Gentamicin and (8) Norfloxacin.
Please cite this article in press as: Gopinath P., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.01.027

P. Gopinath et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
3
Table 2
Antifungal activities of benzisothiazolones.
No
1
2
3
4
5
6
MIC
IC50
MIC
IC50
MIC
IC50
MIC
IC50
MIC
IC50
MIC
IC50
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
3.02
2.4
3.5
7.2
4.3
>50
1.5
1.0
0.7
>50
0.5
0.6
25
>50
1.54
3.1
2.7
2.3
2.5
1.9
>50
>50
1
2.9
1.3
2.4
2.9
2.6
>50
1.3
0.5
0.56
>50
ND
ND
14.2
>50
1.51
2.2
1.9
1.2
1.6
1.5
>50
>50
–
1.21
1.5
1.1
3.8
2.3
>50
0.9
2.9
0.8
>50
1.3
0.9
1.2
0.9
0.9
1.9
>50
0.7
1.0
0.8
>50
1.0
ND
13.7
>50
1.4
1.61
1.4
2.5
7.3
8.6
>50
>50
–
1.7
1.0
0.8
4.0
11.7
>50
0.5
1.6
0.5
>50
0.6
1.4
>50
>50
3.5
0.6
0.9
0.4
0.6
5.7
>50
0.4
0.4
0.3
>50
0.4
ND
>50
>50
2.3
3.7
2.9
2.5
4.7
2.9
>50
>50
–
0.8
1.7
>50
2.6
3.3
>50
>50
0.4
1.5
>50
1.0
>50
13.6
>50
2.9
4.3
12.0
2.4
>50
11.4
>50
>50
>32
0.25
0.7
ND
>50
0.7
ND
>50
>50
0.7
ND
>50
0.7
>50
12.5
>50
ND
ND
11.4
1.7
>50
6.2
>50
>50
–
6.4
6.1
4.1
6.9
>50
ND
>50
0.1
0.4
1.5
>50
0.4
1.3
>50
>50
ND
ND
ND
ND
ND
ND
>50
>50
–
0.8
0.6
0.7
3.2
>50
>50
0.78
2.1
>50
>50
0.9
0.7
0.4
0.6
0.7
>50
>50
0.76
0.7
ND
>50
0.7
1.0
15.2
>50
>50
>50
ND
1.6
3.1
2.4
>50
>50
–
13.3
11.0
>50
12.5
>50
1.0
6.5
1.7
>50
3.7
2.6
>50
>50
12.5
12.5
25
12.5
12.5
>50
>50
>50
>32
0.5
1.9
1.10
1.11
1.12
1.13
1.14
1.15
1.16
1.17
1.18
1.19
1.20
1.21
1.22
Std17
Std28
0.4
1.1
14.4
>50
2.2
1.67
2.0
4.5
8.3
10.5
>50
>50
2
17.1
>50
>50
>50
12.5
3.1
4.5
4.9
>50
>50
2
6.6
12.2
11.9
18.2
20.4
>50
>50
2
0.016
–
0.125
–
0.25
–
–
–
0.016
–
* MIC and IC50 values in
phytes, 5. Aspergillus fumigatus, 6. Candida parapsilosis (ATCC-22019), 7. Fluconazole and 8. Amphotericin-B.
lg/mL, MIC-Minimum inhibitory concentration. 1. Candida albicans, 2. Cryptococcus neoformans, 3. Sporothrix schenckii, 4. Trichophyton mentagro-
membrane permeation. To make comparison, ClogP values of com-
pounds studied here were first calculated (SI). Among N-aryl & N-
alkylaryl substituted benzisothiazolones (1.1–1.10), compounds
1.5 and 1.6 had ClogP values of 2.13 and 2.37 respectively while
that of others were higher, in the range of 2.74–3.85 (SI). Since
1.5 and 1.6 were the least potent in antibacterial assays, their
lower partition coefficients appeared as one of the contributory
factors. Among dimers, 1.13 with ClogP of 4.56 was least potent
while the others (1.14–1.16) with this value in the range of 3.1–
4.1 were relatively more active against S. aureus strains. This sug-
gested that there is a threshold value beyond which ClogP value
could adversely affect the potency. In the case of benzisothia-
zolones having simple hydrophobic groups (1.11–1.12), aminoa-
cids (1.17–1.20), and peptides (1.21–1.22), the alanine-based
systems 1.17 and 1.21 had lower ClogP values (1.76 and 1.50
respectively). For others, it was in the range of 2.7–3.6. In the case
of 1.17–1.19 there is a likelyhood of amino acid transporters also
getting involved in cellular uptake. It is important to mention that
transporters of amino acids, especially hydrophobic ones are
highly functional in S. aureus. The transporter BrnQ1, for example
is involved in the uptake of Val & Leu where as BrnQ2 is linked
with Ileu trasport.24 In general, a larger fraction of active com-
pounds have partition coefficients in the range of 2.5–3.5 A plot
of Log(1/IC50) vs. ClogP in the case of S. aureus (ATCC 700699,
MRSA) is given in Fig. 2a.
With regard to antifungal assay results, the compounds 1.6,
1.10, 1.13, 1.14, 1.21 and 1.22 remained less potent compared to
others. As in the case of antibacterial assay results, CLogP values
in the range of 2.5–3.5 seem to favour antifungal activities which
is more pronounced in the case of Candida albicans, Cryptococcus
neoformans and Trichophyton mentagrophytes as shown in
Figs. 2b–d. Relatively lower activities of dipeptide derivatives
1.21–1.22 compared to their lower homologues 1.17–1.18, lower
potencies of dimers 1.13 and 1.14 (ClogP > 4) compared to 1.15 &
1.16 (ClogP 2.78–3.1) were also consistent. Since antibacterial
and antifungal activities of the simple N-phenyl derivative 1.1
was comparable to that of other potent ones listed in Fig. 1, we pre-
pared a subset of compounds (1.23–1.31, Fig. 3) with halogen or
CF3 groups on the aromatic ring to see whether any structure-
activity relationship would emerge. Since the N-aryl derivatives
listed in Fig. 1 all carry electron-donating substituents, these new
compounds were expected to reveal the effect of electron with-
drawing groups and the influence of steric effects. They were syn-
thesized and screened against bacteria and fungi as per the
protocol described earlier. To our surprise, these compounds were
less potent in antibacterial and antifungal assays. Their MIC values
were >50 lg/mL against E. coli (ATCC 9637), Pseudomonas aerugi-
nosa (ATCC BAA-427) and Klebsiella pneumoniae (ATCC 27736),
whereas that against S. aureus strains were between 3.12 and
25 lg/mL. Their MIC values against fungal strains were also low
Fig. 2. Log 1/IC50 vs. CLogP plot for antibacterials and antifungal activities of various compounds showing the importance of optimal partition coefficient for better activity.
Please cite this article in press as: Gopinath P., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.01.027

4
P. Gopinath et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
Table 3
Antimalarial activities of benzisothiazolones against Plasmodium falciparum (Strain
3D7; CQ sensitive).
No.
IC50
l
M
CC50
lM
SI
1.1
1.2
1.3
1.4
1.5–1.28
1.29
1.30
1.31
0.74
1.66
>2.0
>2.0
>2.0
0.97
0.92
2.64
19.43
19.95
32.59
24.49
ND
85.4
71.7
90.8
–
26.256
12.018
na
na
na
84.43
70.78
34.39
125.85
Chloroquine diphosphate
0.0054 0.0001
Fig. 3. A subset of benzisothiazolones derivatives synthesized to understand the
effect of halogen substitution around the aromatic ring.
IC50 values of other compounds (1.5–1.28 and 1.31) were above
2.0 M (SI). This includes benzisothiazolone dimers as well and
l
shows that the presence of multiple electrophilic sulfur atoms
need not give an advantage in this case. Interestingly, compounds
1.29 and 1.30 with fluorine or chlorine at the para position exhibit
comparable activity as that of 1.1 with ꢀ3-fold increase in the
selectivity index which is remarkable.
These observations have lot of significance because of the
increasing need to identify new anti-plasmodial agents from new
structural classes. Apart from making a comparative assessment
of antibacterial and antifungal activities of benzisothiazolones,
our studies show that the bioactivities of benzisothiazolones can
be modulated by fine-tuning the substitution pattern around the
core. This can be used favourably to improve the selectivity profile
as in the case of halo-substituted derivatives mentioned above.
and ranged between 12.5 and 50 lg/mL (SI). Importance of correct
lipophilicity/hydrophilicity balance for better activity was evident
in these cases also. Compounds 1.23, 1.26 and 1.30 contain addi-
tional chlorine atom compared to compound 1.1, which led to
increase in ClogP from 3.353 to 4.066 (increase of 0.713). Similarly
compounds 1.25, 1.28, and 1.31 had ClogP values of 4.476, 4.236
and 4.527 respectively, which is outside the favorable limit as
per the previous observations. The fluorine analogues 1.24, 1.27
and 1.29 were the exceptions, which, despite having ClogP value
of 3.5, were not superior in their potencies (3.12–25 lg/mL). Influ-
ence of factors other than partition coefficient in the potencies of
these compounds need to be investigated in detail and will be
the subject of our future investigations.
Previously, Lu and coworkers have reported the inhibition of
trypanothione reductase by benzisothiazolones. In this study, they
also demonstrated their anti-trypanosomial activity through effect
on ROS detoxification.25 Malaria is another parasitic disease posing
threat due to decreasing clinical efficacy of existing drugs, and
there is lot of interest to identify new drug candidates against
the plasmodium parasites.26 Since parasite survival in the host
relies on the action of cysteine-containing proteins like falcipain
(in P. falciparum), we envisioned that benzisothiazolone derivatives
will be interesting candidates to look at, and in vitro anti-malarial
assays involving the monomeric and dimeric BITs in our hand were
performed following literature protocol (SI). During the course of
publication of these results, a very relevant publication has come
from the group of Odom John and coworkers which highlight abil-
ity of this class of compounds to interfere with methylerythritol
pathway (MEP) in malaria parasites by targeting IspD (2-C-
methyl-D-erythritol-4-phosphate cytidyltransferase) which cat-
alyzes the condensation of methylerythritol phosphate (MEP) with
cytidine triphosphate (CTP).27 Although the initial leads were iden-
tified through high throughput screening, detailed structure activ-
ity relationship studies were performed and a clear understanding
on their affinity towards this target was confirmed through molec-
ular modeling, site-directed mutagenesis and crystallographic
studies. These results also point towards an initial non-covalent
recognition of BITs in the active site of IspD followed by disulfide
formation with its Cys202. More focused experiments to under-
stand the specificity towards MEP pathway by supplementing the
isoprenoid precursor IPP however showed that off-target effects
could also contribute to their anti-parasitic effects. These observa-
tions make comparative assessment of the activities of monomeric
and dimeric BITs more relevant and the results we have obtained
are discussed below.
Conclusion
In this study, we have compared the antibacterial and antifungal
activities of a selected group of benzisothiazolones in both mono-
meric and dimeric forms. A number of derivatives with sub-micro-
molar IC50 values against these infectious agents were identified.
Drug resistant S. aureus (ATCC 700699) and the Quality Control S.
aureus (ATCC 29213) were more susceptible to these compounds,
and the most active compounds 1.7 and 1.15 had IC50 values of
0.4
lg/mL each against S. aureus (ATCC 700699, MRSA; cf. Gentam-
icin = 0.78
l
g/mL). Interestingly, CLogP value, optimally in the
range of 2.5–3.5, was found to exert more influence on the activity
than steric and electronic effects from groups attached to nitrogen.
Dimeric benzisothiazolones, despite having two electrophilic súlfur
atoms, did not exhibit a proportionate increase in potency. Prelim-
inary antimalarial evaluation led to the identification of a few sim-
ple N-aryl derivatives with sub-micromolar IC50 values. Significant
improvement in selectivity index on introducing halo-substituents
on this aromatic ring is noteworthy since such structure optimiza-
tion would enable us to identify candidates with acceptable safety
profile for further development.
Acknowledgement
We sincerely acknowledge the support of this work by IIT
Madras (exploratory research grant: CHY/14-15/831/RFER/
KMMU), Department of Science and Technology (DST), India
(SR/NM/NS-1051/2012(G)) and DST-FIST (New Delhi) for infras-
tructure facility. We also thank CDRI Lucknow for support with
biological assays.
Among the compounds tested against Plasmodium falciparum
(Strain 3D7), the simple N-phenyl derivative (1.1) was the most
A. Supplementary material
potent with an IC50 value of 0.74
for the tolyl derivative 1.2 was 1.66
of these two compounds against Verona cells were 19.43 and
19.95 M with the selectivity indices of 26 and 12 M respectively.
l
M while the corresponding value
lM (Table 3). The CC50 values
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2017.01.
027.
l
l
Please cite this article in press as: Gopinath P., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.01.027

P. Gopinath et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
5
17. Jorgensen WL, Trofimov A, Du X, Hare AA, Leng L, Bucala R. Bioorg Med Chem
Lett. 2011;21:4545.
References
18. Furdas SD, Hoffmann I, Robaa D, et al. MedChemComm. 2014;5:1856.
19. Hayakawa N, Nozawa K, Ogawa A, et al. Biochemistry. 1999;38:11501.
20. Dahl R, Bravo Y, Sharma V, et al. J Med Chem. 2011;54:3661.
21. National Committee for Clinical Laboratory Standards. Methods for Dilution
AntimicrobialSusceptibility Tests for Bacteria that Grow Aerobically. 5th
ed. Villanova, PA: Approved Standard, NCCLS; 2000, pp. M7–A5.
22. National Committee for Clinical Laboratory Standard. Reference Method for
Broth Dilution Antifungal Susceptibility Testing of Yeast, Approved Standard,
Document M27-A. Wayne, PA, USA: National Committee for Clinical Laboratory
Standards; 1997.
23. National Committee for Clinical Laboratory Standard. Reference Method for
Broth Dilution Antifungal Susceptibility Testing of Conidium Forming Filamentous
Fungi: Proposed Standard, Document M38-P. Wayne, PA, USA: National
Committee for Clinical Laboratory Standard; 1998.
24. Kaiser JC, Omer S, Sheldon JR, Welch I, Heinrichs DE. Infect. Immun..
2015;83:1019.
1. Siegemund A, Taubert K, Schulze B. Sulfur Rep. 2002;23:279.
2. Taubert K, Kraus S, Schulze B. Sulfur Rep. 2002;23:79.
3. Stimson L, Rowlands Martin G, Newbatt Yvette M, et al. Mol Cancer Ther.
2005;4:1521.
4. Loo JA, Holler TP, Sanchez J, Gogliotti R, Maloney L, Reily MD. J Med Chem.
1996;39:4313.
5. Ranganathan S, Muraleedharan KM, Bharadwaj P, Chatterji D, Karle I.
Tetrahedron. 2002;58:2861.
6. Miller Jenkins LM, Hara T, Durell SR, et al. J Am Chem Soc. 2007;129:11067.
7. Gopinath P, Ramalingam K, Muraleedharan KM, Karunagaran D.
MedChemComm. 2013;4:749.
8. Tiew K-C, Dou D, Teramoto T, et al. Bioorg Med Chem. 2012;20:1213.
9. Baggaley KH, English PD, Jennings LJA, Morgan B, Nunn B, Tyrrell AWR. J Med
Chem. 1985;28:1661.
10. Dou D, Alex D, Du B, et al. Bioorg Med Chem. 2011;19:5782.
11. Alex D, Gay-Andrieu F, May J, et al. Antimicrob Agents Chemother. 2012;56:4630.
12. Vicini P, Zani F, Cozzini P, Doytchinova I. Eur J Med Chem. 2002;37:553.
13. Zani F, Vicini P, Incerti M. Eur J Med Chem. 2004;39:135.
14. Desai RC, Dunlap RP, Farrell RP, et al. Bioorg Med Chem Lett. 1995;5:105.
15. Desai RC, Court JC, Ferguson E, et al. J Med Chem. 1995;38:1571.
16. Leung D, Abbenante G, Fairlie DP. J Med Chem. 2000;43:305.
25. Lu J, Vodnala SK, Gustavsson A-L, et al. J Biol Chem. 2013;288:27456.
26. Teixeira C, Vale N, Perez B, Gomes A, Gomes JRB, Gomes P. Chem Rev.
2014;114:11164.
27. Price KE, Armstrong CM, Imlay LS, et al. Sci Rep. 2016;6:36777.
Please cite this article in press as: Gopinath P., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.01.027