Design of potential bisubstrate inhibitors against Mycobacterium tuberculosis (Mtb) 1-deoxy-d-xylulose 5-phosphate reductoisomerase (Dxr)-evidence of a novel binding mode

Article abstract of DOI:10.1039/c3md00085k

In most bacteria, the nonmevalonate pathway is used to synthesize isoprene units. Dxr, the second step in the pathway, catalyzes the NADPH-dependent reductive isomerization of 1-deoxy-d-xylulose-5-phosphate (DXP) to 2-C-methyl-d-erythritol-4-phosphate (MEP). Dxr is inhibited by natural products fosmidomycin and FR900098, which bind in the DXP binding site. These compounds, while potent inhibitors of Dxr, lack whole cell activity against Mycobacterium tuberculosis (Mtb) due to their polarity. Our goal was to use the Mtb Dxr-fosmidomycin co-crystal structure to design bisubstrate ligands to bind to both the DXP and NADPH sites. Such compounds would be expected to demonstrate improved whole cell activity due to increased lipophilicity. Two series of compounds were designed and synthesized. Compounds from both series inhibited Mtb Dxr. The most potent compound (8) has an IC₅₀ of 17.8 μM. Analysis shows 8 binds to Mtb Dxr via a novel, non-bisubstrate mechanism. Further, the diethyl ester of 8 inhibits Mtb growth making this class of compounds interesting lead molecules in the search for new antitubercular agents.

Full text of DOI:10.1039/c3md00085k

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Design of potential bisubstrate inhibitors against
Mycobacterium tuberculosis (Mtb) 1-deoxy-D-xylulose
5-phosphate reductoisomerase (Dxr)—evidence of a
novel binding mode†
Cite this: Med. Chem. Commun., 2013,
4, 1099
a
a
a
bc
´
Geraldine San Jose, Emily R. Jackson, Eugene Uh, Chinchu Johny,
Amanda Haymond,bc Lindsay Lundberg,c Chelsea Pinkham,c Kylene Kehn-Hall,c
Helena I. Boshoff,d Robin D. Couchbc and Cynthia S. Dowd
a
*
In most bacteria, the nonmevalonate pathway is used to synthesize isoprene units. Dxr, the second step in
the pathway, catalyzes the NADPH-dependent reductive isomerization of 1-deoxy-D-xylulose-5-phosphate
(DXP) to 2-C-methyl-D-erythritol-4-phosphate (MEP). Dxr is inhibited by natural products fosmidomycin and
FR900098, which bind in the DXP binding site. These compounds, while potent inhibitors of Dxr, lack whole
cell activity against Mycobacterium tuberculosis (Mtb) due to their polarity. Our goal was to use the Mtb
Dxr-fosmidomycin co-crystal structure to design bisubstrate ligands to bind to both the DXP and NADPH
sites. Such compounds would be expected to demonstrate improved whole cell activity due to increased
lipophilicity. Two series of compounds were designed and synthesized. Compounds from both series
inhibited Mtb Dxr. The most potent compound (8) has an IC50 of 17.8 mM. Analysis shows 8 binds to
Mtb Dxr via a novel, non-bisubstrate mechanism. Further, the diethyl ester of 8 inhibits Mtb growth
making this class of compounds interesting lead molecules in the search for new antitubercular agents.
Received 14th March 2013
Accepted 28th May 2013
DOI: 10.1039/c3md00085k
www.rsc.org/medchemcomm
Tuberculosis (TB) remains a signicant threat to global public
As in most bacteria, Mtb synthesizes ve-carbon isoprenoids
health.1 TB is caused by the bacillus Mycobacterium tuberculosis via the nonmevalonate pathway (NMP). These metabolites are
(Mtb). According to the World Health Organization (WHO),2 needed for bacterial cell wall biosynthesis and other essential
one-third of the world's population is currently infected with processes. Humans use the alternate (mevalonate) pathway to
Mtb, which is responsible for nearly 2 million deaths each year. biosynthesize the same isoprenoid units. Thus, there are no
Current treatment of uncomplicated TB requires a combination human homologs for the enzymes of the NMP. Targeting the
of four drugs (isoniazid, rifampin, pyrazinamide, ethambutol) bacterial enzymes for antibiotic development should not
over a 6–9 months period.3 Emergence of drug-resistant Mtb interfere with human isoprene biosynthesis,7 making the NMP
strains is a serious threat to TB control and treatment.4–6 an attractive pathway in the search for novel drugs.
Further, co-infection of TB and HIV has fueled the epidemic.
Therefore, there remains an urgent need for the discovery and 1-deoxy-D-xylulose
The second step of the NMP is mediated by the enzyme
5-phosphate reductoisomerase (Dxr,
development of novel antitubercular agents.
Fig. 1).1,8 Dxr is essential for Mtb survival9 and catalyzes the
isomerization and reduction of 1-deoxy-D-xylulose-5-phosphate
(DXP) to 2-C-methyl-D-erythritol-4-phosphate (MEP). In the
aDepartment of Chemistry, George Washington University, Washington, DC 20052, reaction, NADPH is a hydride donor and a metal cation (Mg2+ or
USA. E-mail: cdowd@gwu.edu; Fax: +1 202 994 5873; Tel: +1 202 994 8405
bDepartment of Chemistry and Biochemistry, George Mason University, Manassas, VA
Mn2+) is a required enzyme cofactor. Current anti-TB drugs do
not target the NMP, thus, Dxr inhibition would be a new
20110, USA. E-mail: rcouch@gmu.edu; Fax: +1 703 993 8430; Tel: +1 703 993 4770
cNational Center for Biodefense and Infectious Diseases, George Mason University,
Manassas, VA 20110, USA. E-mail: kkhall@gmu.edu; Fax: +1 703 993 4280; Tel: +1
703 993 8869
dTuberculosis Research Section, Laboratory of Clinical Infectious Diseases, National
Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD 20892, USA. E-mail:
hboshoff@niaid.nih.gov; Fax: +1 301 480 5705; Tel: +1 301 451 9438
† Electronic supplementary information (ESI) available: Full experimental details
and spectral information for intermediates N-(benzyloxy)acetamide, 10–13a-d,
17–18a,b, and ligand 9, as well as biochemical and Mtb assay methods and full
results. See DOI: 10.1039/c3md00085k
Fig. 1 Dxr catalyzes the reduction and isomerization of DXP to form MEP.
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nicotinamide ring of NADPH binds approximately 3.5 A from
the formyl carbon atom of fosmidomycin (Fig. 3A). Hence, our
approach toward Dxr inhibitor development was based on the
design of fosmidomycin/FR900098 analogs that target the two
major binding sites in Dxr: the fosmidomycin/DXP site and the
NADPH site. Our goal was to bridge these adjacent binding sites
to yield a high affinity, bisubstrate ligand, while considering the
need for increased lipophilicity compared with fosmidomycin/
FR900098. We report here the design, synthesis, and evaluation
of two series of compounds with either amide- or O-linked
substituents appended to the retrohydroxamate moiety of
FR900098 (Fig. 2) and evidence of a novel, non-bisubstrate
mode of binding.
Fig. 2 Structures of fosmidomycin (1), FR900098 (2) and amide- or O-linked
analogs (3–9).
mechanism of action, and Dxr inhibitors would be expected to
be effective against drug-resistant strains of Mtb.
Fosmidomycin (1) and its acetyl derivative FR900098 (2) are
natural products isolated from Streptomyces lavendulae
(Fig. 2).10 These secondary metabolites are both known inhibi-
tors of Dxr,11 and fosmidomycin is currently under clinical
investigation due to its activity against a variety of Gram-nega-
tive and Gram-positive bacteria, as well as malaria parasites.12–14
In these pathogens, fosmidomycin is actively transported into
cells via a glycerol-3-phosphate transporter, GlpT.15 Mtb,
however, does not have GlpT. This, combined with both the
hydrophilic nature of fosmidomycin and the highly hydro-
phobic Mtb cell wall, renders fosmidomycin inactive against
Mtb.9,16 However, we have shown that lipophilic prodrugs of
FR900098 demonstrate effective antitubercular activity17 and act
in a GlpT-independent manner.18 Additionally, a range of
synthetic fosmidomycin and FR900098 analogs have been
described, designed to compete with DXP at the substrate-
binding site.19–27 While demonstrating potent inhibition of the
puried enzyme, none of these analogs, to our knowledge, is
active against intact mycobacteria. Our goal was to expand on
this work designing Dxr inhibitors with a novel binding mech-
anism and sufficient lipophilicity to gain whole cell anti-
mycobacterial activity.
Several crystal structures of Dxr have been reported, facili-
tating the rational design of novel inhibitors.28,29 The structure
of Mtb Dxr in complex with the competitive inhibitor fosmi-
domycin has led to the identication of binding sites in the
enzyme and is an excellent template for protein-ligand dock-
ing.28 In particular, the crystal structure has revealed chelation
between the retrohydroxamate moiety of fosmidomycin and a
metal cation, the phosphonate binding site, and the close
binding proximity of fosmidomycin and NADPH. The
Results
Modeling of amide- and O-linked ligands
Several studies describe the in silico evaluation of inhibitors
against Dxr.20,30–35 These reports highlight the challenges of
modeling a protein that undergoes signicant conformational
change upon cofactor binding. We sought to use docking to
discern whether bisubstrate inhibition of Mtb Dxr with amide
or O-linked compounds was feasible.
200 Compounds with the general structures shown in Fig. 2
were docked into the Mtb Dxr structure.28 NADPH and fosmi-
domycin were removed from the active site, while Mn2+ was kept
in place. The analogs retained the phosphonate and backbone
of the parent compounds, designed to ensure affinity to the DXP
binding site in the enzyme. The analogs were appended with
(un)substituted aromatic, alkylaryl, or (cyclo)alkyl substituents
to the N-hydroxy oxygen atom or the amide carbonyl group of
the retrohydroxamate. These structural features were designed
to increase affinity to the NADPH binding site. Specically, we
were interested in testing aromatic substituents as mimics of
the nicotinamide ring of NADPH, aiming to increase affinity to
that pocket. Cycloalkyl groups were used to examine the
importance of an aryl substituent.
The docking results predicted that our ligands would adopt a
bisubstrate binding mode and bridge the two adjacent binding
sites. Representative docking images are shown in Fig. 3B and
C. In general, the amide-linked compounds were expected to
bind with greater affinity compared with the O-linked
Fig. 3 Mtb Dxr active site and docking results. (A) Active site of Mtb Dxr with fosmidomycin (left ligand) and NADPH (right ligand) bound (pdb 2JCZ).18 Ligands are
separated by ꢀ3.5 A. (B) Docked O-linked ligand 4. (C) Docked amide ligand 8. Protein chain A is shown as cartoon (blue), Mn2+ as a sphere (pink), ligands are shown as
˚
sticks colored by atom type, protein residues as lines colored by atom type. Hydrogen atoms have been hidden for clarity.
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Scheme 1 Synthesis of O-linked compounds 3–6. Conditions: (a) BnONHAc, NaH, NaI, THF, 70 ꢁC, 75%; (b) H2, Pd/C, MeOH, 76%; (c) R(CH2)nBr, NaH, THF, 70 ꢁC,
27–81%; (d) (i): TMSBr, CH2Cl2, (ii): H2O, (iii): NaOHaq., 61%-quant.
Scheme 2 Synthesis of amide ligands 7 and 8. Conditions: (a) 2N HCl, 84%; (b) BnONH2, MeOH, 40 ꢁC, then NaBH3CN, HCl, MeOH, 79%; (c) R(CH2)nCOCl, Et3N, CH2Cl2,
50–75%; (d) H2, Pd/C, MeOH, 56–59%; (e) (i): TMSBr, CH2Cl2, (ii): H2O, (iii): NaOHaq., quant.
compounds. This was anticipated due to differences between bromotrimethylsilane, hydrolysis of the resulting silylester with
the two series in binding the divalent cation. Prior work has water, and treatment with 1 equivalent of sodium hydroxide.
shown that the unsubstituted hydroxyl oxygen of the retro-
Amide ligands 7 and 8 were prepared using the synthetic
hydroxamate is required for tight coordination of the metal.36 route shown in Scheme 2. Aldehyde 15 was synthesized from
The aryl groups from each series docked in the NADPH binding commercially available acetal 14 in acidic conditions.
site (Fig. 3B and C). Collectively, the docking results indicated Compound 15 was combined with O-benzylhydroxylamine.
that the two series might work well as bisubstrate inhibitors of Reduction with sodium cyanoborohydride and hydrochloric
Mtb Dxr and, as such, bind in a manner distinct from fosmi- acid gave diethyl ester 16.38 Alkylation of 16 using triethylamine
domycin and FR900098.
and the corresponding acyl chloride gave amide intermediates
17. Monosodium salts 7 and 8 were afforded aer deprotection
of both the retrohydroxamate and the phosphonate ester.
Amide 9 was prepared using a similar path shown in the ESI.†
As has been seen with related compounds, most of the mono-
sodium salts were isolated and evaluated as a mixture of two
Synthesis
The preparation of these compounds is shown in Schemes 1
and 2 and in ESI.† A new synthetic route was developed for the
synthesis of the O-linked compounds 3–6, using straightforward
reactions allowing fast access to small, structurally modied
molecules in good yield (Scheme 1).
3-Bromopropylphosphonate 10 was prepared from triethyl
phosphite and 1,3-dibromopropane, using the Arbuzov reaction
under microwave irradiation.37 Compound 10 and N-(benzyloxy)
acetamide were then combined under basic conditions to give
11, which yielded hydroxylamine 12 aer hydrogenation.
conformers.39 Indeed, Zingle et al. showed that N-substituted or N-
´
and O-substituted hydroxamic acids were usually present as a
mixture of Z and E conformers because of the restricted rotation
around the C–N bond.39 Moreover, the ratio was dependent on the
substituent and the nature of the solvent.
Biochemical and antitubercular evaluation
O-linked compounds 13a–d were obtained by alkylation of To evaluate the inhibitory activity of compounds 3–9, enzyme
intermediate 12 using sodium hydride and the corresponding assays were performed with puried Mtb Dxr using a reported
aryl or alkyl bromide. The four desired monosodium salts 3–6 spectrophotometric assay monitoring NADPH consump-
were obtained aer removal of the diethyl ester using tion.28,40,41 The half maximal inhibitory activity (IC50) of the
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Table 1 Mtb Dxr IC50 values of amide and O-linked ligands
compd
R1
R2
IC50 (mM)
1
2
3
4
5
6
7
8
9
H
H
H
CH3
CH3
CH3
CH3
CH3
CH2Ph
(CH2)3Ph
Cyclohexyl
0.3116
2.39
(CH2)2Ph
(CH2)3Ph
4-Ipr-benzyl
CH2cyclohexyl
H
H
H
(81.5)a
(77.5)a
48.4
(83.5)a
26.9
17.8
(80.0)a
a
Values in parentheses are percent remaining enzyme activity at
100 mM.
Fig. 4 Mode of inhibition by ligand 8. The Lineweaver–Burk plots indicate that 8 is
competitive with respect to DXP (A), but noncompetitive with respect to NADPH (B).
compounds is shown in Table 1 (see also ESI,† Fig. 1). Among
the O-linked ligands (compounds 3–6), compound 5 demon-
strated the greatest inhibition, with an IC50 of 48.4 mM. The
activity of the O-linked ligands is surprising and challenges the
notion that chelation of the metal cation by the retro-
hydroxamate is required for binding to the enzyme. For the
O-linked compounds, binding of the aryl substituent could
compensate for diminished coordination of the cation.
Table 1 shows that amide ligands 7 and 8 are more potent
inhibitors of the enzyme with values of 26.9 and 17.8 mM,
respectively. This result may arise from more efficient coordi-
nation of the metal cation by the amide versus O-linked analogs.
In the amide series, a slightly longer chain length between the
retrohydroxamate and the aryl group may be preferable, as
compound 8 gave slightly better inhibition than compound 7.
Weaker inhibition by compounds 6 and 9, both with a nonar-
omatic ring, highlight the importance of having an aromatic
group in the inhibitor.
Since we designed our inhibitors to occupy both the DXP and
NADPH binding sites, compound 8 was further examined to
discern its mechanism of inhibition. Catalysis by Mtb Dxr
undergoes an ordered bi bi reaction mechanism, wherein
NADPH must bind to the enzyme before DXP can bind.42 This
process is reective of a protein conformational change that
occurs upon NADPH binding, resulting in the formation of the
DXP binding site. Fosmidomycin and FR900098 are competitive
inhibitors with respect to DXP and uncompetitive relative to
NADPH42 (see also ESI Fig. 1†). Hence, NADPH must bind to Dxr
before either of these inhibitors can occupy the Dxr binding
site. With this mechanism in mind, we used classical compe-
tition experiments to assess the mode of binding of ligand 8.
As illustrated in Fig. 4, the double reciprocal plots indicate that
ligand 8 is competitive with respect to DXP, but noncompetitive
relative to NADPH. Thus, in stark contrast to fosmidomycin and
FR900098, the binding mechanism of compound 8 does not
require the initial binding of NADPH. Since inhibitor 8 does not
directly compete with the binding of NADPH, the phenylpropyl
Table 2 Antitubercular activity of ligands and their diethyl esters
H37Rv Mtb MIC
Compd
(mg mLÀ1
)
Fosmidomycin (1)
FR900098 (2)
Diethyl-1
>500
>500
250
8
>200
200
Diethyl-8 (18b)
substituent of 8 is likely binding in an alternate location. Inter-
estingly, this site is likely distinct from the NADPH site, but may
promote the same structural change that gives rise to DXP
binding. Studies are underway to further elucidate the nature and
kinetics of this novel mode of inhibitor binding to Dxr.
To complement the characterization of compound 8 against
puried Mtb Dxr, we assayed the efficacy of 8 and its lipophilic
diethyl phosphonate ester (diethyl-8, 18b) against whole cell
Mtb (H37Rv, Table 2). While the hydrophilic fosmidomycin,
FR900098, and compound 8 do not inhibit Mtb, the diethyl
phosphonate ester of fosmidomycin17 and 18b display
measurable antitubercular activity (Table 2). Collectively, the
enzyme and growth inhibition assays highlight the novel anti-
tubercular activity of the amide-linked series of Dxr inhibitors,
identifying compound 8 as a prototypical lead molecule for the
further development of a new class of novel antimycobacterial
agents.
Conclusions
There is an urgent need for the development of new, highly
active, and less toxic anti-TB drugs. Dxr is an attractive target
since humans do not have the enzyme or a homolog. Dxr
inhibitors should be effective against drug-resistant Mtb
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strains, and, due to NMP's importance in early points of
bacterial metabolism, may be effective against both active and
latent Mtb. Aided by an available co-crystal structure, our
docking studies suggested that analogs of FR900098 with
7 C. A. Testa and M. J. Brown, Curr. Pharm. Biotechnol., 2003, 4,
248–259.
8 P. J. Proteau, Bioorg. Chem., 2004, 32, 483–493.
9 A. C. Brown and T. Parish, BMC Microbiol., 2008, 8, 78.
amide- or O-linked aryl substituents on the retrohydroxamate 10 M. Okuhara, Y. Kuroda, T. Goto, M. Okamoto, H. Terano,
could be novel and potent inhibitors of Mtb Dxr. The inhibition
data from our initial set of ligands (3–9), while not more active
M. Kohsaka, H. Aoki and H. Imanaka, J. Antibiot., 1980, 33,
13–17.
than the parent compounds, show promising results, with our 11 T. Kuzuyama, T. Shimizu, S. Takahashi and H. Seto,
best compound (8) having an IC50 of 17.8 mM. Indeed, our Tetrahedron Lett., 1998, 39, 7913–7916.
inhibition results align with prior reports of similar N-acyl 12 H. Jomaa, J. Wiesner, S. Sanderbrand, B. Altincicek,
analogs against E. coli and P. falciparum Dxr.26,33,35
Compound 8 displays a new mode of binding to Mtb Dxr not
previously seen with parent compounds fosmidomycin and
C. Weidemeyer, M. Hintz, I. Turbachova, M. Eberl,
J. Zeidler, H. K. Lichtenthaler, D. Soldati and E. Beck,
Science, 1999, 285, 1573–1576.
FR900098 or other known Dxr inhibitors. Prior modeling 13 N. Singh, G. Cheve, M. A. Avery and C. R. McCurdy, Curr.
studies on similar N-acyl analogs indicated possible binding in Pharm. Des., 2007, 13, 1161–1177.
a non-NADPH site.26 Ligand 8 could be using this alternate 14 Y. Nolan, D. Martin, V. A. Campbell and M. A. Lynch, J.
binding site and current studies are aimed at elucidating this. Neuroimmunol., 2004, 151, 12–23.
While this binding mode was not part of our original bisub- 15 Y. Sakamoto, S. Furukawa, H. Ogihara and M. Yamasaki,
strate design per se, demonstration of a novel binding mode is
both interesting and signicant.
Biosci., Biotechnol., Biochem., 2003, 67, 2030–2033.
16 R. K. Dhiman, M. L. Schaeffer, A. M. Bailey, C. A. Testa,
H. Scherman and D. C. Crick, J. Bacteriol., 2005, 187, 8395–8402.
The MIC of the simple diethyl ester of 8 is comparable to the
corresponding fosmidomycin ester and represents a new class of 17 E. Uh, E. R. Jackson, G. San Jose, M. Maddox, R. E. Lee,
antitubercular compounds. As the MIC reects both the lip-
ophilicity and enzyme inhibition of 8, we expect it to improve as
R. E. Lee, H. I. Boshoff and C. S. Dowd, Bioorg. Med. Chem.
Lett., 2011, 21, 6973–6976.
inhibitors with optimized potencies against Dxr are developed. 18 E. S. McKenney, M. Sargent, H. Khan, E. Uh, E. R. Jackson,
Work is currently underway to explore an expanded set of
analogs, reveal a comprehensive SAR, prove an on-target mech-
G. San Jose, R. D. Couch, C. S. Dowd and M. L. van Hoek,
PLoS One, 2012, 7, e38167.
anism, and discern details of this new binding mode. Taken 19 M. Andaloussi, L. M. Henriksson, A. Wieckowska, M. Lindh,
together, our data suggests new possibilities in the design and
development of novel, antimycobacterial Dxr inhibitors.
C. Bjorkelid, A. M. Larsson, S. Suresh, H. Iyer, B. R. Srinivasa,
T. Bergfors, T. Unge, S. L. Mowbray, M. Larhed, T. A. Jones
and A. Karlen, J. Med. Chem., 2011, 54, 4964–4976.
20 L. Deng, J. Diao, P. Chen, V. Pujari, Y. Yao, G. Cheng,
D. C. Crick, B. V. Prasad and Y. Song, J. Med. Chem., 2011,
54, 4721–4734.
21 V. Devreux, J. Wiesner, H. Jomaa, J. Rozenski, J. Van der
Eycken and S. Van Calenbergh, J. Org. Chem., 2007, 72,
3783–3789.
Acknowledgements
This work was supported by the Intramural Research Program
of NIAID/NIH, the George Washington University Department
of Chemistry, the GWU University Facilitating Fund, and NIH
(AI086453 to CSD). RDC was supported by George Mason Uni-
versity's Department of Chemistry and Biochemistry and the
U.S. Army Medical Research and Materiel Command
W23RYX1291N601.
22 V. Devreux, J. Wiesner, H. Jomaa, J. Van der Eycken and
S. Van Calenbergh, Bioorg. Med. Chem. Lett., 2007, 17,
4920–4923.
23 T. Haemers, J. Wiesner, S. Van Poecke, J. Goeman,
D. Henschker, E. Beck, H. Jomaa and S. Van Calenbergh,
Bioorg. Med. Chem. Lett., 2006, 16, 1888–1891.
24 T. Kurz, C. Behrendt, M. Pein, U. Kaula, B. Bergmann and
R. D. Walter, Arch. Pharm., 2007, 340, 661–666.
25 T. Kurz, K. Schluter, M. Pein, C. Behrendt, B. Bergmann and
R. D. Walter, Arch. Pharm., 2007, 340, 339–344.
26 R. Ortmann, J. Wiesner, K. Silber, G. Klebe, H. Jomaa and
M. Schlitzer, Arch. Pharm., 2007, 340, 483–490.
27 T. Verbrugghen, P. Cos, L. Maes and S. Van Calenbergh, J.
Med. Chem., 2010, 53, 5342–5346.
28 L. M. Henriksson, T. Unge, J. Carlsson, J. Aqvist,
S. L. Mowbray and T. A. Jones, J. Biol. Chem., 2007, 282,
19905–19916.
29 A. Mac Sweeney, R. Lange, R. P. Fernandes, H. Schulz,
G. E. Dale, A. Douangamath, P. J. Proteau and C. Oefner, J.
Mol. Biol., 2005, 345, 115–127.
Notes and references
1 C. Dye, P. Glaziou, K. Floyd and M. Raviglione, Annu. Rev.
Public Health, 2013, 34, 271–286.
2 Global Tuberculosis Control 2009: Epidemiology, Strategy,
Financing, WHO Press, Geneva, Switzerland, 2009.
3 WHO, Treatment of Tuberculosis: Guideline for National
Programmes, Geneva, Switzerland, 2003.
4 A. Wright, MMWR Morb. Mortal. Wkly. Rep., 2006, 55, 301–
305.
5 Emergency Update, 2008: Guidelines for the programmatic
management of drug-resistant tuberculosis, WHO Press,
Geneva, Switzerland, 2008.
6 Z. F. Udwadia, R. A. Amale, K. K. Ajbani and C. Rodrigues,
Clin. Infect. Dis., 2012, 54, 579–581.
This journal is ª The Royal Society of Chemistry 2013
Med. Chem. Commun., 2013, 4, 1099–1104 | 1103

View Article Online
MedChemComm
Concise Article
30 M. Andaloussi, M. Lindh, C. Bjorkelid, S. Suresh, 36 C. J. Marmion, D. Griffith and K. B. Nolan, Eur. J. Inorg.
A. Wieckowska, H. Iyer, A. Karlen and M. Larhed, Bioorg.
Med. Chem. Lett., 2011, 21, 5403–5407.
31 T. Bodill, A. C. Conibear, G. L. Blatch, K. A. Lobb and
Chem., 2004, 15, 3003–3016.
37 D. Villemin, F. Simeon, H. Decreus and P.-A. Jaffres,
Phosphorus, Sulfur Silicon Relat. Elem., 1998, 133, 209–213.
P. T. Kaye, Bioorg. Med. Chem. Lett., 2011, 19, 1321– 38 P. D. M. Puyau and J. J. Perie, Phosphorus, Sulfur Silicon Relat.
1327. Elem., 1996, 112, 71–90.
32 L. Deng, S. Sundriyal, V. Rubio, Z. Z. Shi and Y. Song, J. Med. 39 C. Zingle, L. Kuntz, D. Tritsch, C. Grosdemange-Billiard and
Chem., 2009, 52, 6539–6542. M. Rohmer, J. Org. Chem., 2010, 75, 3203–3207.
33 D. Giessmann, P. Heidler, T. Haemers, S. Van Calenbergh, 40 S. Jawaid, H. Seidle, W. Zhou, H. Abdirahman, M. Abadeer,
A. Reichenberg, H. Jomaa, C. Weidemeyer, S. Sanderbrand,
J. Wiesner and A. Link, Chem. Biodiversity, 2008, 5, 643–
656.
J. H. Hix, M. L. van Hoek and R. D. Couch, PLoS One, 2009,
4, e8288.
41 A. Tsang, H. Seidle, S. Jawaid, W. Zhou, C. Smith and
R. D. Couch, PLoS One, 2011, 6, e20884.
34 A. K. Patel, Int. J. Pharma Bio Sci., 2012, 3, 72–91.
35 K. Silber, P. Heidler, T. Kurz and G. Klebe, J. Med. Chem., 42 A. T. Koppisch, D. T. Fox, B. S. Blagg and C. D. Poulter,
2005, 48, 3547–3563.
Biochemistry, 2002, 41, 236–243.
1104 | Med. Chem. Commun., 2013, 4, 1099–1104
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