Discovery of novel and ligand-efficient inhibitors of plasmodium falciparum and plasmodium vivax N-myristoyltransferase

Article abstract of DOI:10.1021/jm301474t

N-Myristoyltransferase (NMT) is an attractive antiprotozoan drug target. A lead-hopping approach was utilized in the design and synthesis of novel benzo[b]thiophene-containing inhibitors of Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) NMT. These inhibitors are selective against Homo sapiens NMT1 (HsNMT), have excellent ligand efficiency (LE), and display antiparasitic activity in vitro. The binding mode of this series was determined by crystallography and shows a novel binding mode for the benzothiophene ring.

Full text of DOI:10.1021/jm301474t

Brief Article
pubs.acs.org/jmc
Discovery of Novel and Ligand-Efficient Inhibitors of Plasmodium
falciparum and Plasmodium vivax N‑Myristoyltransferase
Mark D. Rackham,† James A. Brannigan,‡ David K. Moss,§ Zhiyong Yu,† Anthony J. Wilkinson,‡
Anthony A. Holder,§ Edward W. Tate,† and Robin J. Leatherbarrow*,†
†Department of Chemistry, Imperial College London, South Kensington Campus, London, SW7 2AZ, U.K.
‡York Structural Biology Laboratory, Department of Chemistry, University of York, York, YO10 5DD, U.K.
§Division of Parasitology, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, U.K.
S
* Supporting Information
ABSTRACT: N-Myristoyltransferase (NMT) is an attractive antiprotozoan drug target. A lead-hopping approach was utilized in
the design and synthesis of novel benzo[b]thiophene-containing inhibitors of Plasmodium falciparum (Pf) and Plasmodium vivax
(Pv) NMT. These inhibitors are selective against Homo sapiens NMT1 (HsNMT), have excellent ligand efficiency (LE), and
display antiparasitic activity in vitro. The binding mode of this series was determined by crystallography and shows a novel
binding mode for the benzothiophene ring.
attrition. We therefore sought to develop this series with the
aim of producing more ligand efficient, selective, and novel hit
series for PfNMT and PvNMT.
INTRODUCTION
■
Diseases resulting from parasitic infections are a global health
crisis, responsible for over 700 000 annual deaths and
predominantly affecting developing countries.1 The most
serious is malaria, caused by parasites of the genus Plasmodium.
The vast majority of malaria infections stem from the species
Plasmodium falciparum (Pf) and Plasmodium vivax (Pv).
Emerging resistance to current therapies highlights the urgent
requirement for new antimalarial medications in the near
future.2
On the basis of the available crystallographic information,12 it
was hypothesized that lead hopping by moving the amine
substituent from the 4-position on the benzo[b]furan scaffold
to the 3-position would be tolerated by the enzyme. This
modification would allow the exploration of novel chemical
space, facilitating the discovery of novel parasitic NMT
inhibitors.
Synthesis of the template was achieved by a Williamson ether
synthesis followed by Dieckmann condensation, affording 3 in
high yield. A Mitsunobu reaction and deprotection resulted in
5, designed as an analogue of 1 (Scheme 1). Pleasingly, this
shift in substitution pattern resulted in a 10-fold affinity
improvement against PvNMT, a 3-fold improvement against
PfNMT, and no measurable activity against HsNMT up to 100
μM. Coupled with the loss of one heavy atom, this improved
the LE to 0.38 for PvNMT and 0.35 for PfNMT (Table 1).
A range of amines was synthesized to investigate the linker
length, basicity, and lipophilicity requirements (see Supporting
Information). All changes resulted in complete loss of affinity
against all three enzymes, reinforcing previous results from a
related series that the piperidine substituent is strongly
preferred for affinity.10 For each of these syntheses, the
Mitsunobu reaction proceeded with a disappointingly poor
yield, typically less than 50%. It was hypothesized that despite
the potential for an intramolecular hydrogen bond, the weakly
aromatic furan ring13 resulted in significant tautomerism
between 3 and the undesired ketone tautomer 6 (Figure 1).
Mitsunobu reactions utilizing the disfavored enol tautomer
have been previously reported with reactive electrophiles;14
however, it is also known that the presence of carbonyls15 and
N-Myristoyltransferase (NMT) is an enzyme found
exclusively in eukaryotes and is responsible for the co- and
post-translational attachment of the C14 fatty acid myristic acid
to the N-terminal glycine of substrate proteins.3 In malaria,
essential proteins such as calcium dependent protein kinase 14
and glideosome associated protein 455 have been shown to
require myristoylation to carry out their biological functions.
Furthermore, genetic experiments have shown NMT to be
essential in Plasmodium berghei in vivo.6 This evidence strongly
suggests that NMT is a highly promising antiparasitic drug
target.
RESULTS AND DISCUSSION
■
Our previous work has led to the identification of parasite
NMT inhibitors via high throughput screening.7,8 As an
alternative strategy for hit discovery, NMT has been highlighted
as a target for the piggy-back approach.9 We have used this
methodology successfully to produce a series of moderate
affinity and selective PfNMT inhibitors adapted from antifungal
NMT inhibitors developed initially by Roche (1, Table 1).10
Although 1 displays selectivity over the human NMT
orthologues (HsNMT) and moderate enzyme affinity, its
relatively large size means that the ligand efficiency (LE) is
significantly lower than 0.35, the average LE of high-throughput
screening hits.11 A poor LE limits the potential of a series in hit
to lead development, increasing the chances of later stage
Received: October 15, 2012
Published: November 22, 2012
© 2012 American Chemical Society
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Table 1. Enzyme Affinity, Parasitic LE, and in Vitro Activity for Compounds 1, 5, 9, 12a,b, 14a,b
a
Ki values are quoted in place of IC50 values as a means of expressing the inhibitor affinity while correcting for differing Michaelis constants between
enzymes. Enzyme Ki values are calculated from the IC50 values using the Cheng−Prusoff equation (see Supporting Information). IC50 values are the
b
c
mean of two or more determinations. Standard deviation is within 20% of the IC50. LE = [−log(Ki)](1.374)/(no. of heavy atoms). The HsNMT
affinities reported in this work refer to HsNMT1; no significant difference in inhibition has been observed between HsNMT1 and HsNMT2
d
isoforms. EC50 values for P. falciparum cultured in vitro. 3D7 is a chloroquine-sensitive strain of P. falciparum.
a
It is known that the aromatic stabilization energy of
benzo[b]thiophenes is far greater than that of benzo[b]furans13
and that this results in a higher population of the enol
tautomer.17 It was therefore proposed that the bioisosteric
replacement of the benzo[b]furan core with benzo[b]thiophene
may improve the synthetic efficiency. Furthermore, the
benzo[b]furan scaffold is known to form π-interactions with
Tyr334 and Ty211 in PvNMT;10 therefore, the increased
aromatic character of the benzo[b]thiophene scaffold may
result in improved interactions between the scaffold and these
residues.
Scheme 1. Synthesis of Benzo[b]furan 1
Replacement of oxygen with sulfur enabled modification of
the Williamson ether synthesis/Dieckmann condensation into a
one-pot cascade procedure and dramatically improved the yield
of the Mitsunobu ether synthesis from 26% to 97% (Scheme
2).
a
Reagents and conditions: (a) ethyl bromoacetate, K2CO3, acetone,
reflux, 3 h, 96%; (b) t-BuOK, THF, rt, 15 min, 94%; (c) 1-Boc-4-
piperidinol, diisopropyl azodicarboxylate, PPh3, THF, rt, 18 h, 26%;
(d) 10% TFA in DCM (v/v), rt, 2 h, 97%.
a
Scheme 2. Synthesis of Benzo[b]thiophene 9
Figure 1. Tautomeric forms of benzo[b]furan 3.
highly acidic α-carbonyl protons16 can produce side reactions.
Furthermore, the unstable heterocycle may lead to problems
with stability and toxicity due to the presence of an (albeit
hindered) α,β-unsaturated carbonyl in 5 not stabilized by
aromaticity.
a
Reagents and conditions: (a) ethyl bromoacetate, t-BuOK, THF, rt,
15 min, 88%; (b) 1-Boc-4-piperidinol, diisopropyl azodicarboxylate,
PPh3, THF, rt, 1.5 h, 97%; (c) 10% TFA in DCM (v/v), rt, 2 h, 82%.
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9 had 3-fold higher PfNMT affinity than 5, retained HsNMT
selectivity, increased structural diversity in the series, and
displayed favorable ligand efficiency (Table 1). In addition, 9
displayed significantly improved antiparasitic activity in vitro
compared to 5 (Table 1) and exhibited equal binding affinity to
PvNMT and PfNMT. 9 was therefore a highly promising
plasmodial NMT inhibitor and was selected for further hit to
lead development.
Although incorporation of 3-methoxyphenyl (12b, Table 1)
produced only a modest improvement in PfNMT enzyme
affinity (9 vs 12b, Table 1), the improvement in PvNMT is far
more pronounced. In addition, 12b is the most potent
antiplasmodial compound of this series with an EC50 of 2.0 μM.
The results in Table 1 indicate that the targeted interactions
from the additional aromatic group are not being formed; the
benzyl ester 12a is less potent than 9, implying suboptimal
interactions for this substituent. Nonetheless, 12b displays
excellent PvNMT enzyme affinity and is 10-fold selective over
PfNMT. This is in contrast to previous results with a related
series, indicating the potential for a novel binding mode of this
series compared to the 2,3,4-benzofuran analogues (exemplified
by 1).10
Previous work indicated that replacement of the ethyl ester
with a m-methoxybenzyl may provide additional affinity (>100-
fold in a related series) via hydrophobic interactions and
introduction of a methoxy substituent capable of forming a
polar interaction with a serine residue in the active site.10
A
small selection of benzyl esters and amides was synthesized to
probe this possibility within this series of inhibitors (Scheme 3).
The strong enzyme affinity of 12b for PvNMT facilitated
determination of the structure of 12b bound to the active site
of PvNMT (Figure 2, PDB accession code 4BBH). As implied
by the structure−activity relationship in Table 1, 12b adopts an
overlapping but distinct binding mode to the 2,3,4-benzofuran
series (Figure 2C, PDB accession code 4B14). The interaction
between the basic amine moiety and the α-carboxylate of the C-
terminal leucine of the protein appears to dominate (Figure
2A), with both inhibitors aligning to form this interaction
(Figure 2C). The chemically similar benzofuran and
benzothiophene rings occupy distinct locations within the
enzyme pocket (Figure 2C). The altered substitution pattern
results in the benzothiophene scaffold being buried deeper
within a hydrophobic pocket (Figure 2B), providing a
rationalization for the high PvNMT enzyme affinity of 12b.
As a result of the displacement of the scaffold, the
methoxyphenyl group of 12b is unable to reach the pocket
occupied by this substituent in the 2,3,4-benzofuran inhibitor
(Figure 2C). This results in suboptimal binding of this portion
of the molecule, with multiple alternative binding positions
visible in the three protein chains present in the asymmetric
unit (Figure 2B,C). There is clearly scope for optimizing this
substituent, perhaps by extending the linker between the
methoxyphenyl group and the scaffold to reach the targeted
pocket.
a
Scheme 3. Synthesis of Benzyl Esters and Amides
a
Reagents and conditions (a) LiOH·H2O, MeOH, rt, 3 h, 58%; (b) 1-
ethyl-3-(3-dimethylaminopropyl)carbodiimide, hydroxybenzotriazole,
N,N-diisopropylethylamine, MeCN, rt, 18 h, 55−66%; (c) benzo-
triazo-1-yloxytripyrrolidinophosphonium hexafluorophosphate, N,N-
diisopropylethylamine, DCM, rt, 18 h, 66−74%; (d) 10% TFA in
DCM (v/v), rt, 2 h, 18−81%.
The fluctuating selectivity of inhibitors in this series for
NMT orthologues is difficult to rationalize based on the
crystallographic information; the only residue difference within
5 Å of the active site is the substitution of Tyr334 in PvNMT
Throughout this series, amides displayed consistently lower
affinity than esters, and the benzyl substituent resulted in the
loss of a great deal of selectivity compared to ethyl ester 9.
Figure 2. X-ray structure of inhibitors bound to PvNMT.18 (A) A crucial interaction between the enzyme and inhibitor involves the amine of the
piperidine moiety of 12b (purple) and a hydrophilic pocket incorporating the enzyme C-terminal carboxylate (Leu410). (B) In this binding mode
the benzo[b]thiophene scaffold is deeply buried within the binding pocket. Although this portion of the inhibitor is well-defined, the electron density
identifies multiple alternative binding positions for the benzyl ester moiety, as shown by thin bonds (see Supporting Information). This substituent is
clearly suboptimal, suggesting an area of future development for this series. (C) The contrasting binding modes are clearly shown by overlay of the
PvNMT complex formed by 12b (purple) with that formed by a previously discovered 2,3,4-benzofuran inhibitor (green).10 The novel binding
mode explains the difference in SAR between the two series.
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of 10 (50 mg, 0.13 mmol) in MeCN (2 mL) were added
hydroxybenzotriazole (27 mg, 0.20 mmol), N,N-diisopropylethylamine
(26 μL, 0.16 mmol), and 1-ethyl-3-(3-dimethylaminopropyl)-
carbodiimide hydrochloride (30 mg, 0.16 mmol). The mixture was
stirred at rt for 15 min. (3-Methoxyphenyl)methanol (20 μL, 0.16
mmol) was added and the mixture stirred at rt for 18 h. The mixture
was concentrated under reduced pressure and dissolved in 10 mL of
saturated NH4Cl solution. 11b was extracted with 3 × 10 mL EtOAc.
Combined organic layers were washed with 10 mL of brine, dried over
MgSO4, and concentrated under reduced pressure. The crude product
was purified by flash chromatography, yielding 11b as a colorless oil
by Phe334 in PfNMT, with HsNMT and PvNMT displaying a
completely homologous active site. The reasons for selectivity
are likely to be more subtle, perhaps because of long-range
factors modulating stereoelectronic interactions or protein
dynamics in the binding site.
The current series contains a potentially biologically labile
ester group, and as yet we have no information about the
metabolic stability. Further development will focus on
compound stability with potency and selectivity to produce a
robust lead series for further development.
1
(37 mg, 60%). H NMR (CDCl3, δ, ppm) 7.86 (1H, d, J = 8.0), 7.75
(1H, d, J = 8.2), 7.51−7.46 (1H, m), 7.43−7.37 (1H, m), 7.32 (1H,
apparent t, J = 7.9), 7.04 (1H, d, J = 7.8), 7.02−7.00 (1H, m), 6.90
(1H, dd, J = 8.2, 2.3), 5.35 (2H, s), 4.74−4.66 (1H, m), 3.94−3.86
(2H, m), 3.84 (3H, s), 3.07−2.98 (2H, m), 1.98−1.88 (2H, m), 1.85−
1.73 (2H, m), 1.48 (9H, s).
CONCLUSION
■
Analysis of structural information indicated the potential for
chemical diversity of a Pf/PvNMT inhibitor via a lead-hopping
approach. Altering the positions of scaffold substitution and
scaffold-hopping based on aromatic stabilization yielded highly
selective and ligand efficient 9 that is built around a
benzo[b]thiophene core. Attempts to translate structure−
activity relationships developed in a related series yielded
12b. Compound 12b is a structurally novel, high affinity
PvNMT inhibitor that displays excellent LE and antiplasmodial
activity in vitro. The crystal structure of 12b bound to PvNMT
highlighted a novel binding mode for this scaffold.
3-Methoxybenzyl-3-(piperidin-4-yloxy)benzo[b]thiophene-
2-carboxylate 12b. To a solution of 11b (34 mg, 0.07 mmol) in
DCM (1.00 mL) was added TFA (100 μL). The solution was stirred at
rt for 2 h. The mixture was concentrated under reduced pressure and
purified by HPLC, yielding 12b as a colorless oil (5 mg, 18%). tR =
12.3 min; 1H NMR (CDCl3, δ, ppm) 7.82 (1H, d, J = 8.0), 7.76 (1H,
d, J = 8.1), 7.56−7.48 (1H, m), 7.47−7.40 (1H, m), 7.33 (1H,
apparent t, J = 7.9), 7.04 (1H, d, J = 7.4), 7.01−6.98 (1H, m), 6.91
(1H, dd, J = 8.2, 2.4), 5.34 (2H, s), 4.88−4.81 (1H, m), 3.84 (3H, s),
3.54−3.44 (2H, m), 3.11−3.01 (2H, m), 2.22−2.11 (4H, m). 13C
NMR (CDCl3, δ, ppm) 161.48, 159.84, 153.90, 138.23, 136.98,
134.06, 129.82, 128.39, 125.07, 123.14, 122.61, 120.34, 115.87, 113.81,
113.79, 76.10, 66.82, 55.29, 41.01, 28.07. ESI HRMS, found 398.1425
(C22H24NO4S, [M + H]+, requires 398.1426).
EXPERIMENTAL SECTION
Purity of tested compounds was ≥95% unless otherwise specified, as
confirmed by LC−MS.
■
Ethyl 3-Hydroxybenzo[b]thiophene-2-carboxylate 7. To a
solution of methyl 2-mercaptobenzoate (1.63 mL, 11.9 mmol) and
ethyl bromoacetate (1.32 mL, 11.9 mmol) in dry THF (130 mL) at 0
°C was added potassium tert-butoxide (5.14 g, 71.3 mmol) gradually
over 2 min. The mixture was stirred and allowed to warm to rt over 15
min, quenched with 2 M HCl solution to pH 2, and diluted with 75
mL of water. 7 was extracted with 3 × 75 mL portions of EtOAc. The
organic layers were combined, washed with 75 mL of brine, dried over
MgSO4, and concentrated under reduced pressure to give product 7 as
a yellow solid (2.32 g, 88%). 1H NMR (CDCl3, δ, ppm) 10.21 (1H, s),
7.94 (1H, d, J = 8.0), 7.74 (1H, d, J = 8.0), 7.50 (1H, ddd, J = 8.0, 7.5,
1.4), 7.44−7.37 (1H, m), 4.43 (2H, q, J = 7.1), 1.43 (3H, t, J = 7.1).
tert-Butyl 4-((2-(Ethoxycarbonyl)benzo[b]thiophen-3-yl)-
oxy)piperidine-1-carboxylate 8. To a solution of 7 (2.70 g, 12.2
mmol) in THF (30 mL) were added tert-butyl 4-hydroxypiperidine-1-
carboxylate (4.89 g, 24.3 mmol) and triphenylphosphine (6.38 g, 24.3
mmol). The mixture was stirred under nitrogen for 20 min and cooled
to 0 °C. Diisopropyl azodicarboxylate (4.79 mL, 24.3 mmol) in THF
(10 mL) was added dropwise over 5 min. The mixture was warmed to
rt and stirred for 1.5 h, then concentrated under reduced pressure and
purified by flash chromatography, yielding 8 as a pink oil (4.77 g,
97%). 1H NMR (CDCl3, δ, ppm) 7.86 (1H, d, J = 7.9), 7.74 (1H, d, J
= 8.0), 7.47 (1H, ddd, J = 8.0, 7.8, 0.8), 7.39 (1H, dd, J = 7.9, 7.8),
4.79−4.69 (1H, m), 4.38 (2H, q, J = 7.2), 4.01−3.86 (2H, m), 3.20−
3.07 (2H, m), 2.05−1.95 (2H, m), 1.91−1.79 (2H, m), 1.48 (9H, s),
1.41 (3H, t, J = 7.2).
ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental procedure, characterization of intermediates and
target compounds, description of biological assays, determi-
nation of Ki values, biological data of supplementary
compounds, and crystallographic information. This material is
available free of charge via the Internet at http://pubs.acs.org.
Accession Codes
The coordinates and structure factor files have been deposited
in the Protein Data Bank under the accession code 4BBH.
AUTHOR INFORMATION
■
Corresponding Author
*Phone: +44 (0) 20 7594 5752. E-mail: r.leatherbarrow@
imperial.ac.uk.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are grateful to Andrew Bell, Victor Goncalves,
Jennie Hickin, and William Heal for valuable discussions. We
thank Munira Grainger for providing the parasites used in the
in vitro assay. We acknowledge the European Synchrotron
Radiation Facility, Grenoble, France, for the provision of data
collection facilities and Marek Brzozowski for expert crystal
handling. This work was supported by the Engineering and
Physical Sciences Research Council (DTA Award), Medical
Research Council (Grants 0900278 and U117532067).
3-((1-(tert-Butoxycarbonyl)piperidin-4-yl)oxy)benzo[b]-
thiophene-2-carboxylic Acid 10. To a solution of 8 (2.50 g, 6.17
mmol) in MeOH (30 mL) was added LiOH·H2O (3.35 g, 79.8
mmol). The mixture was stirred at rt for 3 h. The mixture was
concentrated under reduced pressure, dissolved in 100 mL water, and
acidifed to pH 2 with 2 M HCl solution (30 mL). Precipitate was
removed by filtration and washed with 5 × 10 mL of water, then dried
in a vacuum desiccator, yielding 10 as an off-white solid (1.36 g, 58%).
1H NMR (CDCl3, δ, ppm) 7.87 (1H, d, J = 8.0), 7.81 (1H, d, J = 8.2),
7.53 (1H, ddd, J = 8.0, 7.0, 0.9), 7.44 (1H, dd, J = 8.2, 7.0), 4.82−4.73
(1H, m), 4.06−3.93 (2H, m), 3.15−3.03 (2H, m), 2.11−2.00 (2H, m),
1.94−1.80 (2H, m), 1.49 (9H, s).
tert-Butyl 4-((2-(((3-Methoxybenzyl)oxy)carbonyl)benzo[b]-
thiophen-3-yl)oxy)piperidine-1-carboxylate 11b. To a solution
ABBREVIATIONS USED
■
nd, not determined; Pf, Plasmodium falciparum; Pv, Plasmodium
vivax; NMT, N-myristoyltransferase; Hs, Homo sapiens
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REFERENCES
■
(1) TDR Biennial Report 2010/11; TDR: For Research on Diseases of
Poverty; World Health Organization: Geneva, Switzerland, 2012.
(2) Dondorp, A. M.; Nosten, F.; Yi, P.; Das, D.; Phyo, A. P.; Tarning,
J.; Lwin, K. M.; Ariey, F.; Hanpithakpong, W.; Lee, S. J.; Ringwald, P.;
Silamut, K.; Imwong, M.; Chotivanich, K.; Lim, P.; Herdman, T.; An,
S. S.; Yeung, S.; Singhasivanon, P.; Day, N. P. J.; Lindegardh, N.;
Socheat, D.; White, N. J. Artemisinin Resistance in Plasmodium
falciparum Malaria. N. Engl. J. Med. 2009, 361, 455−467.
(3) Johnson, D.; Bhatnagar, R.; Knoll, L.; Gordon, J. Genetic and
Biochemical-Studies of Protein N-Myristoylation. Annu. Rev. Biochem.
1994, 63, 869−914.
(4) Moskes, C.; Burghaus, P. A.; Wernli, B.; Sauder, U.;
̈
Durrenberger, M.; Kappes, B. Export of Plasmodium falciparum
̈
calcium-dependent protein kinase 1 to the parasitophorous vacuole
is dependent on three N-terminal membrane anchor motifs. Mol.
Microbiol. 2004, 54, 676−691.
(5) Rees-Channer, R. R.; Martin, S. R.; Green, J. L.; Bowyer, P. W.;
Grainger, M.; Molloy, J. E.; Holder, A. A. Dual acylation of the 45 kDa
gliding-associated protein (GAP45) in Plasmodium falciparum
merozoites. Mol. Biochem. Parasitol. 2006, 149, 113−116.
(6) Pino, P.; Soldati-Favre, D. Personal communication.
(7) Goncalves, V.; Brannigan, J. A.; Whalley, D.; Ansell, K. H.; Saxty,
B.; Holder, A. A.; Wilkinson, A. J.; Tate, E. W.; Leatherbarrow, R. J.
Discovery of Plasmodium vivax N-Myristoyltransferase Inhibitors:
Screening, Synthesis, and Structural Characterization of Their Binding
Mode. J. Med. Chem. 2012, 55, 3578.
(8) Bell, A. S.; Mills, J. E.; Williams, G. P.; Brannigan, J. A.;
Wilkinson, A. J.; Parkinson, T.; Leatherbarrow, R. J.; Tate, E. W.;
Holder, A. A.; Smith, D. F. Selective Inhibitors of Protozoan Protein
N-Myristoyltransferases as Starting Points for Tropical Disease
Medicinal Chemistry Programs. PLoS Neglected Trop. Dis. 2012, 6,
e1625.
(9) Bowyer, P. W.; Tate, E. W.; Leatherbarrow, R. J.; Holder, A. A.;
Smith, D. F.; Brown, K. A. N-Myristoyltransferase: A Prospective Drug
Target for Protozoan Parasites. ChemMedChem 2008, 3, 1−8.
(10) Yu, Z.; Brannigan, J. A.; Moss, D. K.; Brzozowski, A. M.;
Wilkinson, A. J.; Holder, A. A.; Tate, E. W.; Leatherbarrow, R. J.
Design and Synthesis of Inhibitors of Plasmodium falciparum N-
Myristoyltransferase, a Promising Target for Anti-Malarial Drug
Discovery. J. Med. Chem. 2012, 55, 8879−8890.
(11) Keseru, G. M.; Makara, G. M. The Influence of Lead Discovery
Strategies on the Properties of Drug Candidates. Nat. Rev. Drug
Discovery 2009, 8, 203−212.
(12) Kawasaki, K.; Masubuchi, M.; Morikami, K.; Sogabe, S.;
Aoyama, T.; Ebiike, H.; Niizuma, S.; Hayase, M.; Fujii, T.; Sakata, K.;
Shindoh, H.; Shiratori, Y.; Aoki, Y.; Ohtsuka, T.; Shimma, N. Design
and Synthesis of Novel Benzofurans as a New Class of Antifungal
Agents Targeting Fungal N-Myristoyltransferase. Part 3. Bioorg. Med.
Chem. Lett. 2003, 13, 87−91.
(13) Katritzky, A.; Karelson, M.; Malhotra, N. Heterocyclic
Aromaticity. Heterocycles 1991, 32, 127.
(14) Redman, A. M.; Dumas, J.; Scott, W. J. Preparation of 5-
Substituted 3-Aminofuran-2-carboxylate Esters. Org. Lett. 2000, 2,
2061−2063.
(15) Liu, Y.-x.; Xu, C.-f.; Liu, L.-z. The Preparation of Vinyl-
hydrazinedicarboxylates from Ketones via Mitsunobu Reaction.
Synthesis 2003, 9, 1335−1338.
(16) Coppola, G. M. Cyclization of 4-Hydroxy-3-hydroxyalkylcar-
bostyrils Under Mitsunobu Conditions. Synth. Commun. 2004, 34,
3381−3387.
(17) Friedrichsen, W.; Traulsen, T.; Elguero, J.; Katritzky, A. R.
Tautomerism of Heterocycles: Five-Membered Ring with One
Heteroatom. Adv. Heterocycl. Chem. 2000, 76, 85−156.
(18) This figure was produced using the program PyMol (www.
pymol.org). The protein surfaces are color-coded according to the
electrostatic surface potentials: red is negatively charged; blue is
positively charged.
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