New peptide deformylase inhibitors design, synthesis and pharmacokinetic assessment

Article abstract of DOI:10.1016/j.bmcl.2016.05.077

The docking approach for the screening of designed small molecule ligands, led to the identification of a critical arginine residue in peptide deformylase for spiro cyclopropyl PDF inhibitor's extra hydrophobic binding, providing us a useful tool for searching more efficient PDF inhibitors to fight for horrifying antibiotics resistance. Further synthetic modification was undertaken to optimize the potency of amide compounds. To lower metabolic susceptibility and in turn reduce unwanted metabolic toxicity that was observed clinically, while retaining desired antibacterial activity, the use of azoles as amide bioisosteres had also been investigated. After the completion of chemical synthesis, all the compounds were evaluated through in vitro antibacterial activity assay, some of which were further subject to in vivo rat pharmacokinetic assessment. Those findings in this letter showed that spiro cyclopropyl proline N-formyl hydroxylamines, and especially the bioisosteric azoles, can represent a promising class of PDF inhibitors.

Full text of DOI:10.1016/j.bmcl.2016.05.077

Bioorganic & Medicinal Chemistry Letters xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
New peptide deformylase inhibitors design, synthesis and
pharmacokinetic assessment
a,
Fengping Lv a, Chen Chen a, Yang Tang a, Jianhai Wei a, Tong Zhu b, , Wenhao Hu
⇑
⇑
a Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, School of Chemistry and Molecular Engineering, East China Normal University,
North Zhongshan Road 3663, Shanghai, China
b Department of Physics and State Key Laboratory of Precision Spectroscopy, East China Normal University, North Zhongshan Road 3663, Shanghai 200062, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The docking approach for the screening of designed small molecule ligands, led to the identification of a
critical arginine residue in peptide deformylase for spiro cyclopropyl PDF inhibitor’s extra hydrophobic
binding, providing us a useful tool for searching more efficient PDF inhibitors to fight for horrifying
antibiotics resistance. Further synthetic modification was undertaken to optimize the potency of amide
compounds. To lower metabolic susceptibility and in turn reduce unwanted metabolic toxicity that was
observed clinically, while retaining desired antibacterial activity, the use of azoles as amide bioisosteres
had also been investigated. After the completion of chemical synthesis, all the compounds were evaluated
through in vitro antibacterial activity assay, some of which were further subject to in vivo rat pharma-
cokinetic assessment. Those findings in this letter showed that spiro cyclopropyl proline N-formyl
hydroxylamines, and especially the bioisosteric azoles, can represent a promising class of PDF inhibitors.
Ó 2016 Elsevier Ltd. All rights reserved.
Received 14 March 2016
Revised 12 May 2016
Accepted 27 May 2016
Available online xxxx
Keywords:
PDF inhibitor
Antibacterial drug
Antibiotics resistance
MRSA
Docking study
Amide bioisosteres
The excessive and inappropriate use of antibiotics accelerates
the occurrence of their resistance and nowadays makes the resis-
tance to an appalling situation.1–3 The escalated resistance towards
existing antibiotics, alongside with shortage of new drugs with
novel mechanism of action poses great fear that we are risking fail-
ure in the army race between antibiotics discovery and resistance
evolvement, and stepping into a predicament of post-antibiotics
era where common infections are deadly.4–6
Because of grave concern over the weak pipeline of antibiotics
to fight against the ever-growing bacterial drug resistance, there
is an urgent need for the development of new antibiotics with
novel mechanism of action against multi-drug resistance.7,8
Peptide deformylase (PDF)9,10 has become a promising and
attractive bacterial target to explore for the discovery of new
antibacterial agents, because of difference between bacterial and
mammalian protein synthesis.11,12
Gram-positive and Gram-negative bacteria, due to poor structural
stability and tendency of quick clearance.17 LBM41518–20, the first
candidate recruited to run phase I clinical trial, had potency and
broad spectrum of activity, but was found to have structure-related
safety issue, methemoglobinemia.21 GSK132232222, showed broad
spectrum antibacterial activity against pathogens involved in
respiratory tract infections as well as methicillin-resistant Staphy-
lococcus aureus (MRSA), while potential reactive metabolites led to
a recent termination of its phase II clinical trial.23
Given that the dose-related in vivo toxicity of developed PDF
inhibitors are attributable to metabolic instability and harmful
implication of reactive metabolites, two chemistry strategies could
be undertaken: the synthesis of more peptidyl analogs, with higher
potency over bacterial PDF, and the bioisosteric replacement of
scissile amide bond, using heterocyclic azoles as non-peptide scaf-
folds. In continuation of our efforts to search more PDF inhibi-
tors,24–26 we, on the basis of virtual design and molecular
docking analysis, disclosed spiro cyclopropane-containing N-for-
myl hydroxylamines as a kind of novel and more efficient PDF inhi-
bitors. Besides extensive study on structural modification by
integrating various aromatic amines, especially heterocyclic
aromatic amines into proline’s carboxylic motif, preliminary inves-
tigation on isosteres was also made using different heterocycles as
amide mimics, hoping to mitigate the expected metabolic liability-
induced toxicity to the body. After synthetic completion of all
Numerous kinds of bacterial PDF inhibitors have been invented,
and several of them have even been developed into human clinical
trials (Fig. 1);13,14 however, to date, no effective PDF inhibitors
have been marketed. Actinonin15
, the first discovered PDF
inhibitor,16 could not secure acceptable in vivo antibacterial
activity, though exhibited moderate activity against several
⇑
Corresponding authors. Tel.: +86 18801626247 (T.Z.), +86 13636307166 (W.H.).
E-mail addresses: tongzhu@chem.ecnu.edu.cn (T. Zhu), whu@chem.ecnu.edu.cn
(W. Hu).
http://dx.doi.org/10.1016/j.bmcl.2016.05.077
0960-894X/Ó 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Lv, F.; et al. Bioorg. Med. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.bmcl.2016.05.077

2
F. Lv et al. / Bioorg. Med. Chem. Lett. xxx (2016) xxx–xxx
H
O
O
H
HO
N
N
F
H
N
O
O
N
N
H
N
N
HO
HO
N
H
N
O
HO
N
H
N+
O-
O
N
H
O
F
N
O
O
Actinonin
LBM415
GSK1322322
Figure 1. Representative PDF inhibitors in developmental pipeline.
designed compounds, not only in vitro antibacterial activities, but
also in vivo pharmacokinetic profiles were evaluated.
Through structure-based design, molecular docking and scor-
ing, spiro cyclopropane-containing N-formyl hydroxylamine B
was chosen from series of established virtual compounds A to F,
with competitive score given by Sybyl X2 (Table 1).
Finally, p-methoxybenzyl (PMB) groups were removed in presence
of triisopropylsilane, trifluoroacetic acid and dichloromethane
(TIPS/TFA/DCM) to successfully secure the desired products 1a–1i.
There is one held notion that side-effect to body for aromatic
amides is associated with the easy-to-hydrolyze tendency, as their
metabolized aromatic amines are often oxidized to generate reac-
tive nitroso species.28,29 For reducing the possible structure-related
toxicity, we also prepared several azole compounds as amide iso-
steres. Condensing acid 5 with variety of spiro proline-derived
azoles 4j–4m (synthetic procedures in Supplementary Informa-
tion), followed by PMB removal, allowed for the efficient access
to amide-isosteric azoles 1j–1m (Scheme 2).
The relatively high score and possibly high activity against bac-
teria strains could be demonstrated via X-ray crystallographic
structure of complex with ligand bound in the S. aureus PDF
(PDB: 1Q1Y). Figure 2 illustrated the binding mode between inhi-
bitor (LBM415 or compound B) and PDF. Compared to the crystal-
lographic binding mode of LBM415, compound B have additional
stabilized hydrophobic force between cyclopropyl group in com-
pound B and protein residue ARG56 (4.0 Å), other than highly-con-
served interaction in the metal binding region, side aliphatic
chain’s hydrophobic forces to LEU105, ILE150 and HIS158, and
two hydrogen bondings: N–H of VAL 59 to carbonyl of ligand, N–
H of LEU112 to oxygen atom in reverse hydroxamic moiety.
According to the result of molecular modeling study, N-formyl
hydroxylamine bearing spiro cyclopropane unit (compound B)
was considered as a starting point for chemical modification. In
order to afford additional binding, higher activity and favorable
pharmacokinetic, we synthesized a number of amide N-formyl
hydroxylamines (1a–1i).
Synthetic route for preparation of diverse aromatic amide PDF
inhibitors was illustrated in Scheme 1. Accordingly, by treatment
of methanesulfonyl chloride, amidation between judiciously
selected aromatic amines a–i and commercially available N-Boc
spiro proline derivative 2 gave the coupled compounds 3, which
were then subjected to deprotection under the condition of
ethanolic HCl/ether to precipitate the amides 4a–4i. HATU conden-
sation of amines 4 with acid 5 yielded amides 6, and the acid 5
itself could be obtained through the reported route by Liu et al.27
After structure confirmation by LC–MS, 1H NMR, 13C NMR and
HRMS, all the newly synthesized compounds were evaluated for
in vitro antibacterial activity. Minimum inhibitory concentration
(MIC) against bacteria was calculated for each compound and the
results were summarized in Table 2 (for detail information, see
Table S1), where three to four strains for each bacterial species,
such as methicillin-resistant S. aureus, methicillin-susceptible S.
aureus, methicillin-resistant Staphylococcus epidermidis, methi-
cillin-susceptible S. epidermidis, Enterococcus faecalis, Escherichia
coli were screened. All the tested compounds had preferable anti-
Gram-positive bacterial activity over Gram-negative bacteria. Most
of the compounds, except compound 1a, showed higher or compa-
rable activity comparing to their reference compounds LBM415,
GSK1322322, ceftizoxime sodium, levofloxacin and rifampicin,
whose amide had small size aromatic ring. We were pleased to find
that compounds 1c, 1d and 1f exhibited excellent activity (MIC:
low to <0.008 lg/mL, activity: 60 times higher than that of
LBM415). The more attractive antibacterial activities of those com-
pounds were probably due to favorable lipophilicity. Satisfyingly,
when the amide tail of the compound was replaced by heterocyclic
azole, those derivatives still kept acceptable antibacterial potency,
Table 1
Molecular docking study
Compounds
LBM415
A
B
O
O
H
H
O
H
F
Structure
F
F
N
N
N
N
N
N
HO
HO
HO
N+
O-
O
O
N+
O-
N+
O-
N
H
O
O
N
H
N
H
O
O
Scorea
8.7015
8.8965
7.9033
C
D
E
F
O
H
O
H
O
H
H
F
F
O
F
N
N
N
O
N
N
N
HO
F
HO
HO
N
N
N+
O-
O
N+
N+
O-
N
O
N
N
HO
O
O
H
N+
O-
H
O
H
-O
O
N
H
O
8.4583
8.7949
7.9274
8.8397
a
Scores given by Sybyl X2.
Please cite this article in press as: Lv, F.; et al. Bioorg. Med. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.bmcl.2016.05.077

F. Lv et al. / Bioorg. Med. Chem. Lett. xxx (2016) xxx–xxx
3
Figure 2. Binding site interaction was predicted through docking study in Sybyl X2. (a) 3D interaction of LBM415 and S. aureus PDF; (b) additional 3D interaction of
compound B and PDF; (c) 2D relation diagram of compound B and key amino acid residues in PDF. Metal binding interaction was shown in grey color, hydrophobic forces
were in blue and hydrogen-bonding interactions were drawn in green dashed arrow to denote the direction of the hydrogen bond.
a
NHAr
OH
ArNH2
N
N
Boc
Boc
O
b
O
3
2
O
H
O
H
O
H
c
d
NHAr
N
N
N
N
HO
N
OH
N
H
PMBO
PMBO
O
O
NHAr
O
6
HCl
NHAr
O
1a-1i
O
O
4a-4i
5
N
N
F
O
N
NH
Aromatic amine
N
H2N
N
H2N
H2N
H2N
N
N
H
a
b
c
d
N
N
N
N
N
N
H2N
H2N
F
H2N
N
H
N
H2N
S
N
H2N
e
f
g
h
i
Scheme 1. Synthesis of amide PDF inhibitors. Reagents and conditions: (a) MsCl, NMM, DMF, rt, overnight; (b) HCl/MeOH/ether, rt, overnight; (c) HATU, DIPEA, DMF, rt, 3 h;
(d) TIPS/TFA/DCM (volume ratio: 0.1/1/2), rt, 1 h. MsCl: methanesulfonyl chloride; NMM: N-methylimidazole; DMF: N,N-dimethylformamide; HATU: 1-[bis(dimethylamino)
methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate; DIPEA: N,N-diisopropylethylamine.
O
H
O
H
H
O
a
b
N
N
N
N
PMBO
HO
N
OH
Het
N
H
PMBO
O
O
O
Het
Het
4j-4m
5
1j-1m
H
N
N
O
N
N
Heterocyclic Azoles
N
N
N
O
N
N
N
N
j
k
l
m
Scheme 2. Synthesis of heterocyclic azole PDF inhibitors. Reagents and conditions: (a) HATU, DIPEA, DMF, rt, 3 h; (b) TIPS/TFA/DCM (volume ratio: 0.1/1/2), rt.
suggesting that the tail amide bond was not indispensable to activ-
ity, and that bioisosteric replacement of amides with azoles was
effective for PDF inhibitor optimization.
Of the compounds in those two kinds of synthesized deriva-
tives, we selected high-activity representatives with various aro-
matic amines or azoles for further rat pharmacokinetic study
Please cite this article in press as: Lv, F.; et al. Bioorg. Med. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.bmcl.2016.05.077

4
F. Lv et al. / Bioorg. Med. Chem. Lett. xxx (2016) xxx–xxx
Table 2
In vitro minimum inhibitory concentration (MIC) in a range of 0.008–128 lg/mL for compounds against various clinical separated strains
Compound
Structure
MRSA (4)
MSSA (4)
MRSE (4)
MSSE (3)
EFA (4)
ECO (4)
NH
N
1a
8–32
16
4–8
4–>16
64–>128
16–>128
N
O
O
H
F
1b
1c
0.125–0.25
0.125
0.03–0.125
0.015–0.03
0.03–0.125
64–>128
0.5–>128
1–128
1–64
N
O
O
N
H
N
<0.008–0.06
0.06–0.125
0.015–0.125
N
H
O
N
N
1d
<0.008–0.015
0.015
<0.008
<0.008–0.015
0.015–>128
4–>128
N
H
N
H
N
O
N
1e
1f
0.25–0.5
<0.008
0.5
0.125–0.5
<0.008
0.125–>0.25
<0.008
2
2–>64
N
H
O
F
N
<0.008
0.125–0.5
0.125–32
N
H
S
O
N
1g
0.125
0.125
0.06–0.125
0.06–0.125
0.25–0.5
0.5–32
N
H
O
N
1h
1i
1
1
0.25–1
0.125–0.25
0.125–>0.5
4–8
2–128
2–>64
N
N
N
O
H
H
N
N
0.25–2
0.25–0.5
0.125–0.25
0.5–1
N
H
O
N
H
N
1j
0.5–2
0.5
2
0.5–1
0.5–>2
0.125–0.5
0.5–1
64–>128
16–>128
1–64
N
N
1k
1l
0.5
2–4
0.125–0.5
0.5–4
2
O
N
N
O
N
N
2–4
4–8
0.5–128
N
N
N
1m
1
1
0.25–1
0.25–0.5
0.06–0.5
4–8
2–128
1–64
N
O
H
F
N
N
LBM415
0.5–1
0.5
0.06–0.125
2–128
HO
N+
O-
O
N
H
O
O
H
N
N
H
GSK1322322
0.25–2
1
0.015–0.25
32–>128
0.06–0.25
32–>128
8–>64
>128
1–>64
1–32
N
N
HO
N
H
N
S
O
O
F
N
OMe
N
H
H
N
N
N
H2N
Ceftizoxime Sodium
64–128
2–4
O
O
S
COONa
O
O
F
OH
Levofloxacin
Rifampicin
128–>128
>128
0.5–32
16
0.5
2–4
1–4
0.5–64
2
N
N
N
O
—
<0.008–0.008
<0.008–0.008
<0.008–0.008
Abbreviation for screened strains: MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-susceptible Staphylococcus aureus; MRSE: methicillin-resistant Sta-
phylococcus epidermidis; MSSE: methicillin-susceptible Staphylococcus epidermidis; EFA: Enterococcus faecalis; ECO: Escherichia coli.
(shown in Table 3). All the compounds were rapidly absorbed with
very short time of maximum observed concentration (Tmax < 1 h).
The pharmacokinetic (PK) profiles of compound 1j were similar
to 1b, with lower clearance (p.o. CL = 70.9 mL h/kg) and higher oral
Please cite this article in press as: Lv, F.; et al. Bioorg. Med. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.bmcl.2016.05.077

F. Lv et al. / Bioorg. Med. Chem. Lett. xxx (2016) xxx–xxx
5
Table 3
In vivo rat PK profiles evaluation
Compound
Route
Cmax (ng/mL)
Tmax (h)
AUC0-t (ngꢀh/mL)
AUC0-1 (ngꢀh/mL)
t1/2 (h)
MRT0-t (h)
CL (mLꢀh/kg)
Vdss (L/kg)
F (%)
1b
i.v.
p.o.
1783
1849
0.14
0.25
1265
1958
1282
1990
3.63
4.94
1.65
2.04
26.2
91.3
2.6
39.4
31
1c
1d
1f
i.v.
p.o.
930
860
0.08
0.58
1136
1951
1143
1979
1.23
4.52
1.50
3.43
29.6
90.6
2.7
36.2
35
3
i.v.
p.o.
1084
100
0.08
0.25
881
126
892
134
3.60
2.24
1.15
3.32
37.7
334.0
2.6
1772.0
i.v.
p.o.
1090
630
0.08
0.58
653
2084
653
2129
1.14
5.00
1.74
4.42
23.5
82.3
3.6
36.5
30
37
40
1j
i.v.
p.o.
1739
1675
0.08
0.25
1257
2341
1268
2377
5.23
4.46
1.91
4.13
26.4
70.9
3.0
27.4
1k
i.v.
p.o.
929
893
0.08
0.25
654
1283
657
1303
1.11
1.28
0.61
1.68
51.2
136.0
1.9
15.1
Sprague Dawley rat, male, 2 mg/kg i.v. (5% DMSO + 10% solutol + 10% EtOH + 75% saline), 10 mg/kg p.o. (5% DMSO + 95% (0.5% MC)).
bioavailability (F = 37%); the PK for 1f was similar to that of 1c
except that the maximum plasma concentration and bioavailabil-
ity for 1f were much lower than those of 1c (Cmax: 630 ng/mL vs
860 ng/mL, F: 30% vs 35%). Amongst tested compounds, 1k dis-
played highest bioavailability (F = 40%), but showed relatively
short half-life (t1/2 = 1.28 h). Unexpectedly, 1d gave very low
References and notes
1. World Health Organization (WHO) Antimicrobial Resistance: Global Report on
Surveillance, 2014.
2. Center for Disease Dynamics, Economics and Policy (CDDEP) The State of the
World’s Antibiotics, 2015.
3. Fair, R. J.; Tor, Y. Perspect. Med. Chem. 2014, 6, 25.
4. Alanis, A. J. Arch. Med. Res. 2005, 36, 697.
5. Laxminarayan, R.; Matsoso, P.; Pant, S.; Brower, C.; Rottingen, J. A.; Klugman, K.;
Davies, S. Lancet 2016, 387, 168.
6. Brown, E. D.; Wright, G. D. Nature 2016, 529, 336.
7. Gould, I. M.; Bal, A. M. Virulence 2013, 4, 185.
8. Brooks, B. D.; Brooks, A. E. Adv. Drug Deliv. Rev. 2014, 78, 14.
9. Adams, J. M. J. Mol. Biol. 1968, 33, 571.
10. Nguyen, K. T.; Hu, X.; Colton, C.; Chakrabarti, R.; Zhu, M. X.; Pei, D. Biochemistry
2003, 42, 9952.
11. Chen, D.; Yuan, Z. Expert Opin. Invest. Drugs 2005, 14, 1107.
12. Jain, R.; Chen, D.; White, R. J.; Patel, D. V.; Yuan, Z. Curr. Med. Chem. 2005, 12,
1607.
bioavailability (F = 3%), likely due to both its poor absorption (Cmax
:
100 ng/mL vs 1849 ng/mL for 1b, because of high lipophilicity or
poor water-solubility) and high oral clearance (CL: 334.0 mL/h/kg
vs 91.3 mL/h/kg for 1b). It should be noted that azole scaffolds
appeared to have better bioavailability than any other compounds.
Taken together, those data indicated that structural modification
through change of different amides and replacement of amides
by azoles to optimizing the PK properties was promising.
In conclusion, under the guide of in silico molecular modeling,
two novel series of spiro cyclopropane-contained reverse hydrox-
amic acids: amide derivatives and isosteric azoles have been
obtained. Our designed new PDF inhibitors showed excellent and
wide range of antibacterial activities, especially for those drug-
resistant strains, such as methicillin-resistant Staphylococcus aur-
eus, which are severely resistant to penicillin, ceftizoxime sodium,
levofloxacin, and recently even to rifampicin. In vivo pharmacoki-
netic profiles for selected compounds with excellent inhibitory
activity were subsequently assessed. Critical to achieving higher
activity was the introduction of the spiro cyclopropyl group to
LBM415’s backbone. The use of benzoimidazole, 1,2,4-oxadiazole,
1,3,4-oxadiazole and triazole as amide bioisosteres was helpful to
improve metabolic stability, and potentially good to the reduction
of metabolic toxicity.
13. East, S. P. In New and Old Molecules in the Fight Against Multi-resistant Bacteria;
Marinelli, F., Genilloud, O., Eds.; Springer, 2006; Vol. 44, pp 287–305.
14. Sangshetti, J. N.; Kalam Khan, F. A.; Shinde, D. Curr. Med. Chem. 2015, 22, 214.
15. Gordon, J. J.; Kelly, B. K.; Miller, G. A. Nature 1962, 195, 701.
16. Chen, D. Z.; Patel, D. V.; Hackbarth, C. J.; Wang, W.; Dreyer, G.; Young, D. C.;
Margolis, P. S.; Wu, C.; Ni, Z. J.; Trias, J.; White, R. J.; Yuan, Z. Biochemistry 2000,
39, 1256.
17. Broughton, B. J.; Chaplen, P.; Freeman, W. A.; Warren, P. J.; Wooldridge, K. R. H.;
Wright, D. E. J. Chem. Soc., Perkin Trans. 1 1975, 857.
18. Jones, R. N.; Fritsche, T. R.; Sader, H. S. Diagn. Microbiol. Infect. Dis. 2004, 49, 63.
19. Jones, R. N.; Fritsche, T. R.; Sader, H. S. In Antimicrobial Spectrum and Activity of
LBM415, A Novel Peptide Deformylase Inhibitor, Tested Against 1,837 Recent
Gram-Positive Clinical Isolates, 14th Congress of Clinical Microbiology and
Infectious Diseases (ECCMID), 2004. Poster, P914.
20. Fritsche, T. R.; Sader, H. S.; Cleeland, R.; Jones, R. N. Antimicrob. Agents
Chemother. 2005, 49, 1468.
21. Rolan, P.; Sun, H.; MacLeod, C.; Bracken, K.; Evans, T. G. Clin. Pharmacol. Ther.
2011, 90, 256.
22. Singley, C.; Hoover, J.; DeMarsh, P.; Elefante, P.; Zalacain, M. In Efficacy of PDF
Inhibitor GSK1322322 Against Abscess Infections Caused by MRSA Using
a
Acknowledgments
Computer-Controlled Infusion System to Recreate Human PK Profiles in Rats,
50th Interscience Conference on Antimicrobial Agents and Chemotherapy
Conference (ICAAC), 2010. Poster, F1–2114.
We would like to thank doctor Dong Xing and associate-profes-
sor Shunying Liu for kind assistances in this program. This work
was financially supported by the National Natural Science Founda-
tion of China (NSFC: 21125209 and 21332003).
23. This study has been registered at ClinicalTrials.gov under registration No.
NCT01818011.
24. Shi, W.; Duan, Y. J.; Qian, Y.; Li, M.; Yang, L.; Hu, W. H. Biorg. Med. Chem. Lett.
2010, 20, 3592.
25. Shi, W.; Ma, H. K.; Duan, Y. J.; Aubart, K.; Fang, Y.; Zonis, R.; Yang, L.; Hu, W. H.
Bioorg. Med. Chem. Lett. 2011, 21, 1060.
26. Yang, S. N.; Shi, W.; Xing, D.; Zhao, Z.; Lv, F. P.; Yang, L.; Yang, Y.; Hu, W. H. Eur.
J. Med. Chem. 2014, 86, 133.
Supplementary data
ˇ
27. Liu, Y.; Prashad, M.; Ciszewski, L.; Vargas, K.; Repic, O.; Blacklock, T. J. Org.
Process Res. Dev. 2008, 12, 183.
28. Kies, M. Pharmacol. Rev. 1966, 18, 1091.
29. McLean, S.; Starmer, G. A.; Thomas, J. J. Pharm. Pharmacol. 1969, 21, 441.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2016.05.
077.
Please cite this article in press as: Lv, F.; et al. Bioorg. Med. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.bmcl.2016.05.077