2-phenylindole and arylsulphonamide: Novel scaffolds bactericidal against mycobacterium tuberculosis

Article abstract of DOI:10.1021/ml5001933

A cellular activity-based screen on Mycobacterium tuberculosis (Mtb) H37Rv using a focused library from the AstraZeneca corporate collection led to the identification of 2-phenylindoles and arylsulphonamides, novel antimycobacterial scaffolds. Both the series were bactericidal in vitro and in an intracellular macrophage infection model, active against drug sensitive and drug resistant Mtb clinical isolates, and specific to mycobacteria. The scaffolds showed promising structure-activity relationships; compounds with submicromolar cellular potency were identified during the hit to lead exploration. Furthermore, compounds from both scaffolds were tested for inhibition of known target enzymes or pathways of antimycobacterial drugs including InhA, RNA polymerase, DprE1, topoisomerases, protein synthesis, and oxidative-phosphorylation. Compounds did not inhibit any of the targets suggesting the potential of a possible novel mode of action(s). Hence, both scaffolds provide the opportunity to be developed further as leads and tool compounds to uncover novel mechanisms for tuberculosis drug discovery.

Full text of DOI:10.1021/ml5001933

Letter
pubs.acs.org/acsmedchemlett
2‑Phenylindole and Arylsulphonamide: Novel Scaffolds Bactericidal
against Mycobacterium tuberculosis
Maruti Naik,† Sandeep Ghorpade,† Lalit Kumar Jena,† Gopinath Gorai,† Ashwini Narayan,‡
Supreeth Guptha,‡ Sreevalli Sharma,‡ Neela Dinesh,‡ Parvinder Kaur,‡ Radha Nandishaiah,‡ Jyothi Bhat,‡
Gayathri Balakrishnan,‡ Vaishali Humnabadkar,‡ Vasanthi Ramachandran,‡ Lava Kumar Naviri,†
Pallavi Khadtare,† Manoranjan Panda,† Pravin S. Iyer,*,† and Monalisa Chatterji*,‡
‡
†Department of Medicinal Chemistry and Department of Biosciences, IMED Infection, AstraZeneca, Bellary Road, Hebbal,
Bangalore 560024, India
S
* Supporting Information
ABSTRACT: A cellular activity-based screen on Mycobacterium tuberculosis
(Mtb) H37Rv using a focused library from the AstraZeneca corporate collection
led to the identification of 2-phenylindoles and arylsulphonamides, novel
antimycobacterial scaffolds. Both the series were bactericidal in vitro and in an
intracellular macrophage infection model, active against drug sensitive and drug
resistant Mtb clinical isolates, and specific to mycobacteria. The scaffolds
showed promising structure−activity relationships; compounds with submicro-
molar cellular potency were identified during the hit to lead exploration.
Furthermore, compounds from both scaffolds were tested for inhibition of
known target enzymes or pathways of antimycobacterial drugs including InhA,
RNA polymerase, DprE1, topoisomerases, protein synthesis, and oxidative-
phosphorylation. Compounds did not inhibit any of the targets suggesting the potential of a possible novel mode of action(s).
Hence, both scaffolds provide the opportunity to be developed further as leads and tool compounds to uncover novel
mechanisms for tuberculosis drug discovery.
KEYWORDS: Tuberculosis, Mycobacterium tuberculosis, 2-phenylindoles, arylsulphonamides
rates. The present first line therapy for drug sensitive TB
consists of four drugs, i.e., isoniazid (INH), rifampicin (RIF),
ethambutol (ETM), and pyrazinamide (PZA).5,6 While INH
and ETM inhibit cell wall biosynthesis, RIF acts by inhibiting
transcription. PZA is a prodrug that is active on nonreplicating
Mtb and is believed to act via multiple mechanisms, i.e.,
accumulation of pyrazinoic acid disrupting membrane potential
and energy production, inhibition of fatty acid synthesis, and
inhibition of trans−translation. Among second line drugs,
compounds act by inhibiting cell wall biosynthesis including
peptidoglycan synthesis, DNA gyrase, and protein synthesis.5,6
Interestingly, identification of a novel drug like bedaquiline was
instrumental in uncovering the critical nature of oxidative
phosphorylation and the ATP synthesis pathway under varied
physiological states.7 Similarly bactericidal compounds, SQ109,
led to the identification of MmpL38 and benzothiazinones
(BTZ043) to DprE1.9 Therefore, prioritizing whole cell actives
that are inactive on known targets/mechanisms could
potentially uncover hitherto unknown mechanisms that can
be exploited for TB drug discovery.
ne of the major factors for tuberculosis (TB) developing
Ointo global health emergency is the rise of multi and
extensively drug resistant (MDR and XDR) Mycobacterium
tuberculosis (Mtb) strains. Although a large number of
antibiotics are available for TB therapy, both as first and
second line treatment, TB continues to have a high mortality
rate. WHO reported 1.3 million deaths in the year 2012.1 TB
therapy is a multidrug therapy for a duration of up to 6−24
months for drug sensitive and resistant TB, respectively. The
recent emergence of strains that are resistant to nearly all
antimycobacterials has left very limited options for TB
patients.2 Moreover, most TB drugs were discovered decades
ago and exhibit suboptimal safety profiles in relation to modern
anti-infective therapy. Therefore, there is a critical need for
antimycobacterials that work via novel mechanisms and have
better tolerability. For the first time since the 1960s, novel TB
drugs are emerging.3 Approvals of bedaquiline and delamanid
provide hope for MDR-TB patients and for TB research,
despite the associated toxicities with these novel agents. The
challenge, therefore, is to find new classes of antibiotics that are
safe and more efficacious on both MDR and XDR TB.
Mtb exists in multiple physiological phases, e.g., replicating
and nonreplicating phase in human lung.4 It was long realized
that multidrug combination is crucial to target all Mtb
populations in order to cure patients and reduce relapse
Received: May 13, 2014
Accepted: July 11, 2014
© XXXX American Chemical Society
A
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A representative collection of 320,000 compounds from
AstraZeneca’s corporate library was initially evaluated at 20 μM
against Mtb for their growth inhibitory activities. About 1600
compounds exhibited ≥80% inhibition of growth as compared
to the culture control in the primary single point screen. These
compounds were prioritized for minimum inhibitory concen-
tration (MIC) determination. Compounds with potent MIC
were tested for minimum bactericidal concentration (MBC).
Hit evaluation and prioritization of chemical scaffolds were
carried out based on MIC, MBC, and lead-like properties.
Solids of the prioritized scaffolds and their near neighbors were
procured from AstraZeneca corporate collection for confirma-
tion and to derive a preliminary structure−activity relationship
(SAR). To rule out preliminary safety issues, cytotoxicity was
evaluated by measuring the CC50 against mammalian cells.
Finally, representative compounds were tested for inhibition of
known antitubercular mechanisms. Chemical scaffold with
potent cellular activity, attractive physicochemical properties,
and potentially novel mode(s) of inhibition were prioritized.
Here, we report two such novel scaffolds: the 2-phenylindoles
(compound 1) and arylsulphonamides (compound 21) that
possess potent antimycobacterial properties (Figure 1).
substituents on ring A revealed that electron donating
substitutions like methyl, methoxy, and isopropyl were
tolerated at the C-7 position (compounds 8 and 15); however,
a disubstitution on the indole ring (compounds 12 and 16)
resulted in increased MICs. Saturating the phenyl ring (ring A,
compound 20) compromised potency to a certain extent. The
2-phenyl group (ring B) was essential for the activity as removal
of it (compound 13) made the molecule inactive, suggesting
the role of large aromatic group and/or hydrophobic
interactions for activity. The benzyl group attached to the
indole NH (compound 11) failed to occupy this hydrophobic
space as in the case of 2-phenyl, hence the compound was
weakly active. Both electron withdrawing and electron donating
groups were tolerated on the ring B; however, the best results
were obtained when there was an unsubstituted phenyl ring at
2-position (compound 1). A pyridine ring was not tolerated at
C-2 position of the indole ring (compound 14). The
substitution on the pyrolidine ring at the C-3 position of the
indole has limited effect on the cellular potency; MIC was
retained even when the side chain was completely removed on
pyrrolidine (compound 6) or one of the side chains was
maintained (compounds 2 and 5). This provided a greater
opportunity for structural modifications and also to improve
physicochemical properties. The stereochemistry at C-3
position of pyrolidine had no role in defining potency as
both the enantiomers (compounds 18 and 19) and the
racemate (compound 2) had similar MICs.
2-Phenylindole Synthesis. Compounds involving ring A
and ring B modifications were synthesized starting from their
corresponding anilines and bromoacetyl derivatives using the
general indole synthesis protocol11 outlined below (Scheme 1).
Figure 1. Lead molecules: 2-phenylindole (compound 1) and
arylsulphonamide (compound 21).
a
Scheme 1. Synthesis of Phenylindoles
A robust SAR was developed for the 2-phenylindole scaffold,
which resulted in lead like structures with good physicochem-
ical properties. Herein, we report the chemical optimization of
2-phenylindoles. The SAR of these modifications is summarized
in Supporting Table 1.
The strategy was to identify a key pharmacophore required
for cellular activity, by checking the essentiality of different
groups in the molecule and building an understanding of a MIC
based SAR. Toward this end, the scaffold was broadly divided
into ring A, ring B, and ring C as shown in Figure 2. It was
observed that methylating the NH of indole (compound 3)
retained cellular potency hence, confirming that the indole NH
is not essential for activity. Further, the effects of various
a
Reagents and conditions: (a) phenacyl bromide derivative, N,N-
dimethylaniline, MW, 140 °C, 20 min; (b) amine, ZnCl2, ethanol, RT,
3 h; (c) phenacyl bromide, xylene, DMA, 150 °C, overnight.
Optimum results for the indole synthesis were obtained
when the reactions were performed under microwave
conditions using the corresponding anilines (I) and acetyl
bromide derivatives in minimum amount of dimethylaniline. An
alternate procedure was also tried for few compounds
(condition c) as shown in Scheme 1.12 The corresponding
acetyl bromides were made by bromination of acetyl derivatives
using general protocols available in the literature.13 The
Mannich reaction on this indole derivative (II) at 3-position
with the corresponding amines using ZnCl2 and formaldehyde
solution in ethanol provided the final compounds (Supporting
Table 1) in very good yield. The intermediate amine was made
according to the procedures mentioned in the Supporting
Information.
Arylsulphonamide, a low molecular weight scaffold with
potent Mtb activity was another promising scaffold that
emerged out of this screening.
Figure 2. SAR for 2-phenylindoles.
B
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ACS Medicinal Chemistry Letters
Letter
a
Similar to 2-phenylindoles, the initial strategy here was also
to discern the key pharmacophoric features required for cellular
activity. The requirement of different functionalities on the
molecule was checked by making targeted analogues. The
molecule was broadly divided into four parts as shown in Figure
3. The initial exploration concluded that the pyrazole on the
Scheme 2. Synthesis of Arylsulphonamide
a
Reagents and conditions: (a) 4-pyridinemethyl chloride, potassium
carbonate, DMF, RT, 5 h; (b) HCl in dioxane, RT; (c) potassium
carbonate, phenyl sulphonyl chloride, RT, 3 h; (d) (1R,2R)-(−)-1,2-
diaminocyclohexane, copper iodide, pyrazole, 1,4-dioxane, MW, 30
min.
Figure 3. SAR for arylsulphonamides.
phenyl ring is not essential as replacing pyrazole with oxazole
(compound 24) and phenyl group (compound 29) retained the
potency. This provided opportunities for structural modifica-
tions on ring A. The phenyl ring tolerated substitution ortho to
the sulphonamide (compound 22). Methyl substitution on the
phenyl ring ortho to the sulphonamide linkage improves the
activity (MIC = 0.55 μM), and the corresponding 2-pyridine
derivative retained MIC (compound 23). The pyridine
derivative reduced the logD of the molecule (1.7) and
improved the solubility to 1000 μM. The sulphonamide was
essential for activity, as the corresponding amide derivative
(compound 32) was inactive; however, alkylation of NH of the
sulphonamide (compound 25) was moderately active (12.5
μM). A methoxy substitution on the linker piperidine (ring C,
compound 26) made the compound much weaker compared to
the original compound. Replacing the aminopiperidine with
piperazine (compound 31) gave a moderate MIC of 12.5 μM.
The potency was lost (MIC > 200 μM) when 4-pyridine (Ring
D) was replaced with 3-methoxyphenyl (compound 33)
indicating that phenyl group may not be tolerated at this
position. The methylene linker between the piperidine and
pyridine rings was converted to carbonyl (compound 30); the
compound showed MIC of 6.25 μM, which opened up an
opportunity for modifications at this portion of the molecule.
The SAR of these modifications is summarized in Supporting
Table 2.
Table 1. In Vitro Evaluation of logD (Experimentally
Determined) and Solubility for Representative Compounds
a
PI
logD
solubility (μM)
AS
logD
solubility (μM)
1
3
5.4
21
22
23
2.6
2.3
1.7
149
66
8
2.8
1.8
103
752
17
1000
a
PI: 2-phenylindoles. AS: arylsulphonamides.
retaining MIC. The solubility for the compounds were poor in
general (as seen for compound 1); however, replacing methyl
with methoxy at C-7 position of indole (compound 8)
improved the solubility significantly (100 μM). The changes
in ring C are expected to have maximum impact on solubility
without impacting the potency (compound 17, solubility 752
μM). The logDs for arylsulfonamides were in the range of 1.7
to 2.3 with good solubility (Table 1).
The antibacterial properties were assessed in detail for
representative compounds from both the scaffolds (Table 2 and
Figure 4). 2-Phenylindoles (compounds 1 and 2) were active
and bactericidal against H37Rv with MBC to MIC ratio of ∼5−
10, while arylsulphonamides (compounds 21 and 22) showed
MBC to MIC ratio of ∼1−2. Compounds 1 and 21 both were
Arylsulphonamide Synthesis. The general synthesis
involved is shown in Scheme 2. The corresponding BOC
protected 4-aminopiperidine (I) was treated with pyridine-
methyl halides using potassium carbonate in DMF. After
removal of the BOC protecting group, compound III was
treated with corresponding sulphonyl chloride in DMF using
potassium carbonate as base. The final conversion to
compound V was done using (1R,2R)-(−)-1,2-diaminocyclo-
hexane and copper iodide in dioxane using microwave
conditions.
In a few cases the corresponding 4-(1H-pyrazol-1-yl)-
benzenesulphonyl chloride derivatives were commercially
available, so these were converted into the corresponding
sulphonamides using the condition mentioned in Scheme 2.
Representative compounds from both the scaffolds were
profiled for logD (experimental) and aqueous solubility
(Table 1). For 2-phenylindoles, the logDs were in the range
of 3 to 3.5, with multiple SAR handles to reduce logD, while
Table 2. In Vitro Microbiology Profile
1
2
21
22
1.6
a
MIC (μM)
0.8−1.6
3.8−12.5
3.1−12.5
0.8−6.3
3.3−6.2
50
0.8−3.1
1.6−3.1
>200
MBC (μM)
1.6
b
HBC (μM)
25
>200
1.6−6.3
Clinical isolates
3.3−12.5
0.8−3.1
MIC (μM)
INHR, RIFR, EMBR
0.8−6.3
>200
∼1.5
3.3−12.5
>200
ND
0.8−3.1
>200
∼1.5
32
1.6−6.3
>200
ND
MIC (μM)
G−ve and G+ve
MIC (μM)
THP1 log10 CFU
reduction
THP1 cytotoxicity
(CC50) (μM)
>64
>64
32
a
b
Four-fold variations are acceptable. Compound concentration,
which shows ≥2 log10CFU/mL reduction under hypoxic conditions.
C
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ACS Medicinal Chemistry Letters
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Table 5. Macromolecular Biosynthesis in μg/mL
compd
MIC adenine (IC50) uracil (IC50) leucine (IC50)
1
5
NI*
NI
NI
NI
7.3
2.9
NI
NI
NI
11.4
2
21
4.25
0.25
0.03
16
sparfloxacin
rifampicin
16.7
NI
chloramphenicol
NI
5.6
*
NI: no inhibition observed.
wild-type H37Rv. On similar lines, compounds were tested for
activity in DprE1 biochemical assay and MIC modulation for
DprE1 overexpression strain compared to wild-type Mtb. They
were inactive in both assays, whereas reference compounds
BTZ043,9 a covalent inhibitor, and 1,4-azaindoles, a non-
covalent inhibitor of DprE1,10 behaved as expected. Inhibition
of DNA topoisomerases, i.e., DNA gyrase and DNA
topoisomerase I (TopoI), were assessed using gel-based
supercoiling and relaxation assays, respectively. Both com-
pounds did not inhibit topoisomerase catalyzed reactions even
at 100 μM, ruling them out as targets. Moxifloxacin and
novobiocin, known DNA gyrase inhibitors, both inhibited the
supercoiling reaction. A potent and specific bacterial TopoI
inhibitor has not been identified yet. Therefore, we used
camptothecin, an inhibitor of eukaryotic TopoI and poor
inhibitor of mycobacterial enzyme, as the tool compound in the
DNA relaxation assay. The test compounds also failed to show
significant inhibition of mycobacterial oxidative phosphoryla-
tion (Oxphos) assay, whereas bedaquiline (TMC207) in the
same assay had an IC50 of 1 nM. Although, compound 1 did
show an IC50 of 15 μM in this assay, the potent MIC observed
for the molecule did not correlate with the IC50s, hence
minimizing the possibility of oxidative phosphorylation as a
potential target mechanism. Compounbds 1 and 21 were found
to be inactive in in vitro transcription assay catalyzed by
Mycobacterium smegmatis RNA polymerase. Additionally, they
did not inhibit incorporation of radioactively labeled [3H]uracil
in Mycobacterium bovis-BCG (Mbo-BCG), a surrogate readout
for transcription ongoing in the cell. Rifampicin, an inhibitor of
RNA polymerase (RNAP), shows an IC50 of 30 nM under the
assay conditions and also inhibited incorporation of labeled
[3H]uracil and [3H]leucine (marker for protein synthesis) in
the cells. Finally, compounds also did not show inhibition of
protein synthesis, while chloramphenicol, a protein synthesis
inhibitor, specifically inhibited incorporation of radioactive
[3H]leucine in Mbo-BCG. Taken together, we conclude that
both chemical series do not act by primary antitubercular
mechanisms known and hence are expected to have novel
mechanisms of action. Experiments are underway to identify
the mode of action for the chemical scaffolds.
Figure 4. Activity in THP1 infection model.
active in intracellular THP1 model and showed ∼1.5 Log10CFU
reduction, respectively, at MIC post 7 days treatment (Figure
4). Interestingly, 2-phenylindoles as a series (represented by
compounds 1 and 2) were bactericidal under hypoxic
conditions (HBC, Table 2), a nonreplicating in vitro Mtb
model,14 whereas arylsulphonamides did not show bacterici-
dality under these conditions (Table 2). Both series did not
show activity against a panel of Gram-positive and Gram-
negative bacteria, namely, Escherichia coli, Haemophilus
influenzae, Pseudomonas aeruginosa, Klebsiella pneumoniae,
Staphylococcus aureus, and Streptococcus pneumoniae; and
thereby appear to be specific for Mtb. Moreover, the observed
activity against H37Rv was retained on drug sensitive Mtb
clinical isolates and on isoniazid, rifampicin, and ethambutol
single resistant strains. Compounds were tested for cytotoxicity
against mammalian cell line THP1 (human monocytic cell
line); compounds 1 and 2 were not cytotoxic at concentrations
tested, whereas compounds 21 and 22 (arylsulphonamides)
showed cytotoxicity beyond 32 μM.
Compounds 1 and 21 were also used as representative
compounds for understanding the mechanism of action of 2-
phenylindoles and arylsulphonamides, respectively. These were
screened for known antitubercular mechanisms using varied
phenotypic and biochemical assays (Tables 3−5). InhA, target
Table 3. Assessing Inhibition of Various Mtb Strains
H37Rv MIC
InhA OE MIC
DprE1 OE MIC
compd
(μM)
(μM)
(μM)
1
0.8−1.6
0.8−3.1
0.5
0.8−1.6
1.6−3.1
>7.5
1.6
21
1.6
isoniazid
rifampicin
BTZ043
0.5
0.01
0.01
0.01
12.5−50
0.003−0.006
0.003−0.006
Table 4. Inhibition of Known Target Biochemical Assays
IC50 (μM)
1
21
control (IC50)
In summary, we have identified two novel scaffolds that have
potent antimycobacterial activity against extracellular and
intracellular bacterium. We also present SAR understandings
for the two series with respect to potency. Finally, we have
tested the compound against available assays for understanding
the mode of action. The compounds do not act by primary
known mechanisms and therefore are expected to have a novel
mode of action. Moreover, both series retain activity on single
drug resistant Mtb strains. Taking all the information together,
we believe 2-phenylindoles and arylsulphonamides have the
potential to be progressed further and are also valuable as tool
compounds for the identification of novel targets for TB drug
discovery.
InhA
>100
>10
>100
>10
triclosan 0.63 μM isoniazid (prodrug)
BTZ043 10 nM
DprE1
Gyrase
TopoI
Oxphos
RNAP
>100
>100
15.6
>00
>100
>100
>70
moxifloxacin 10 μM; novobiocin 15 nM
camptothecin 500 μM
bedaquiline 1 nM
>100
rifampicin 30 nM
for isoniazid, was ruled out as a target, as compounds did not
inhibit InhA biochemical assay and also did not show an upshift
of MIC on target overexpression compared to wild-type.
Isoniazid in the phenotypic assay showed an 8- to 16-fold
increase in MIC for InhA overexpressing strain compared to
D
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ACS Medicinal Chemistry Letters
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Kordulakova, J.; Sala, C.; Fullam, E.; Schneider, P.; McKinney, J. D.;
Brodin, P.; Christophe, T.; Waddell, S.; Butcher, P.; Albrethsen, J.;
Rosenkrands, I.; Brosch, R.; Nandi, V.; Bharath, S.; Gaonkar, S.;
Shandil, R. K.; Balasubramanian, V.; Balganesh, T.; Tyagi, S.; Grosset,
J.; Riccardi, G.; Cole, S. T. Benzothiazinones kill Mycobacterium
tuberculosis by blocking arabinan synthesis. Science 2009, 324, 801−
804.
ASSOCIATED CONTENT
* Supporting Information
Tables describing the SAR, details of biological assays, and
chemical synthesis. This material is available free of charge via
the Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Authors
*(P.S.I.) E-mail: pravin.iyer@astrazeneca.com.
*(M.C.) E-mail: monalisa.chatterji@gmail.com.
Author Contributions
M.N., S.G., M.P., and P.I. were responsible for medicinal
chemistry design and analyses. M.N., L.K.G., G.G., and L.K.N.
performed the synthesis of the compounds. A.N., S.G., S.S.,
N.D., P.K., and V.R. performed whole cell screen and
microbiology experiments. R.N., J.B., G.B. and V.H. performed
biochemical assays. P.K. was responsible for compound
management. M.C. has steered the evaluation of the screen
hits based on bactericidality and novel mechanism and driving
the overall biology. M.N. and M.C. wrote the manuscript.
(10) Shirude, P. S.; Shandil, R.; Sadler, C.; Naik, M.; Hosagrahara, V.;
Hameed, S.; Shinde, V.; Bathula, C.; Humnabadkar, V.; Kumar, N.;
Reddy, J.; Panduga, V.; Sharma, S.; Ambady, A.; Hegde, N.; Whiteaker,
J.; McLaughlin, B.; Gardner, H.; Madhavapeddi, P.; Ramachandran, V.;
Kaur, P.; Narayan, A.; Guptha, S.; Awasthy, D.; Narayan, C.;
Mahadevaswamy, J.; Vishwas, K. G.; Ahuja, V.; Srivastava, A.;
Prabhakar, K. R.; Bharath, S.; Kale, R.; Ramaiah, M.; Roy
Choudhury, N.; Sambandamurthy, V.; Solapure, S.; Iyer, P.;
Narayanan, S.; Chatterji, M. Azaindoles: Noncovalent DprE1
inhibitors from scaffold morphing efforts, kill Mycobacterium tuber-
culosis and are efficacious in vivo. J. Med. Chem. 2013, 56, 9701−9708.
■
́ ́
(11) Yosu, V.; Eneko, A.; Ana, A.; Jose, L. P.; Marıa, I. A.; Fernando,
P. C. Regiochemistry of the microwave-assisted reaction between
1
aromatic amines and a-bromoketones to yield substituted H-indolesi.
Org. Biomol. Chem. 2008, 6, 1763−1772.
(12) Siavosh, M.; Emerich, E.; Matthias, W.; Andreas, S.; Ute, M.
Antibacterial activity of a novel series of 3-bromo-4-(1H-3-indolyl)-
2,5-dihydro-1H-2,5-pyrroledione derivatives: An extended structure-
activity relationship study. Eur. J. Med. Chem. 2008, 43, 633−656.
(13) Amblard, F.; Zhang, H.; Zhou, L.; Shi, J.; Bobeck, D. R.; Nettles,
J. H.; Chavre, S.; McBrayer, T. R.; Tharnish, P.; Whitaker, T.; Coats, S.
J. Synthesis and evaluation of non-dimeric HCV NS5A inhibitors.
Bioorg. Med. Chem. Lett. 2013, 23, 2031−2034.
Funding
The research leading to these results has received funding from
the European Community’s Seventh Framework Programme
([FP7/2007−2013]) under grant agreement no. 260872″ and
AstraZeneca India Pvt. Ltd.
Notes
(14) Wayne, L. G.; Hayes, L. G. An in vitro model for sequential
study of shiftdown of Mycobacterium tuberculosis through two stages of
nonreplicating persistence. Infect. Immun. 1996, 64, 2062−2069.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Shahul Hameed, Pravin S. Shirude, Anand K
Raichurkar, Sreekanth Ramachandran, Tantry J. Subramanyam,
and Vasan Sambandamurthy for hit evaluation discussions. We
also thank Maria Rosalia Pasca and Giovanna Riccardi for
further efforts on identification of the mechanism of the
compounds.
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