Design, synthesis and evaluation of oxime-functionalized nitrofuranylamides as novel antitubercular agents

Article abstract of DOI:10.1016/j.bmcl.2018.07.046

A series of oxime-functionalized nitrofuranylamides were designed, synthesized and evaluated for their in vitro anti-mycobacterial activities against MTB H37Rv and drug-resistant clinical isolates. Among them, two compounds 7a and 7b exhibited excellent activity against the three tested strains. Both of them were comparable to the first-line anti-TB agents INH and RIF against MTB H37Rv, and were far more potent than INH and RIF against MDR-TB 16833 and 16995 strains. Thus, both of them could act as leads for further optimization.

Full text of DOI:10.1016/j.bmcl.2018.07.046

Accepted Manuscript
Design, synthesis and evaluation of oxime-functionalized nitrofuranylamides as
novel antitubercular agents
Yi-Lei Fan, Jian-Bing Wu, Xing Ke, Zhong-Ping Huang
PII:
S0960-894X(18)30641-3
https://doi.org/10.1016/j.bmcl.2018.07.046
BMCL 25977
DOI:
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
5 June 2018
30 July 2018
31 July 2018
Please cite this article as: Fan, Y-L., Wu, J-B., Ke, X., Huang, Z-P., Design, synthesis and evaluation of oxime-
functionalized nitrofuranylamides as novel antitubercular agents, Bioorganic & Medicinal Chemistry Letters (2018),
doi: https://doi.org/10.1016/j.bmcl.2018.07.046
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Design, synthesis and evaluation of oxime-functionalized
nitrofuranylamides as novel antitubercular agents
Yi-Lei Fan*,a, Jian-Bing Wua, Xing Kea, Zhong-Ping Huangb
aKey Laboratory of Drug Prevention and Control Technology of Zhejiang Province, Zhejiang
Police College, Hangzhou, P R China;
bCollege of Chemical Engineering, Zhejiang University of Technology, Hangzhou, P R China
Abstract: A series of oxime-functionalized nitrofuranylamides were designed, synthesized and
evaluated for their in vitro anti-mycobacterial activities against MTB H37Rv and drug-resistant
clinical isolates. Among them, two compounds 7a and 7b exhibited excellent activity against the
three tested strains. Both of them were comparable to the first-line anti-TB agents INH and RIF
against MTB H37Rv, and were far more potent than INH and RIF against MDR-TB 16833 and
16995 strains. Thus, both of them could act as leads for further optimization.
Keywords: nitrofuran; nitrofuranylamides; oxime; anti-mycobacterial; anti-tubercular; multi-drug
resistant; structure-activity relationship
Tuberculosis (TB), which is caused mainly by Mycobacterium tuberculosis (MTB), is
one of the oldest infectious diseases known to man. TB is still a public health issue,
and continues to reign as one of the world's most lethal infectious diseases [1,2].
Although the overall mortality rate has declined by around 50% since 1990, the
number of deaths - especially of people infected with the hard-to-treat strains such as
drug-resistant TB (DR-TB), multidrug-resistant TB (MDR-TB) and extremely
drug-resistant TB (XDR-TB) still remains too large [3-8]. The World Health
Organization (WHO) estimated that around 10.4 million people fell ill with TB and
1.67 million died in 2016 [9]. Among them, 600,000 new cases were resistant to
rifampicin (RIF), of which 490,000 were MDR-TB [9]. Therefore, development of
*Corresponding author: fanyieli@zjjcxy.cn
1

new anti-TB agents active against various virulent forms of MTB has become
increasingly urgent.
Nitrofuran derivatives are found to possess various biological and pharmacological
properties such as anti-bacterial [10], anti-viral [11], anti-tumor [12], anti-leishmanial
[13], anti-Trypanosoma cruzi [14] and anti-TB [15-21] activities. Among nitrofuran
derivatives, the nitrofuranylamides exhibited excellent in vitro anti-TB activity
against both drug-sensitive and drug-resistant MTB strains, but poor in vivo efficacy,
which attributed to their low oral bioavailability and aqueous solubility [22-24].
Oxime is the common functional group in cephalosporins, and the incorporation of
oxime into fluoroquinolones could increase the anti-bacterial activity and improve the
pharmacokinetic profiles, which emphasize the importance of the oxime group with
respect to biological activity [25,26]. Besides, some oxime-functionalized compounds
demonstrated promising anti-TB activities [27-30], so the introduction of oximes into
nitrofuranylamides may provide more effective anti-TB candidates.
Figure 1 Illustration of design strategy
As a part of an ongoing program to discover novel nitrofuran scaffolds against MTB,
we recently synthesized a series of nitrofuran derivatives, and some of them showed
excellent in vitro activity against MTB H37Rv and MDR-TB strains [31]. In this
paper, a set of novel oxime-functionalized nitrofuranylamides were synthesized and
evaluated for their in vitro anti-mycobacterial activities against MTB H37Rv and two
2

MDR-TB strains. The illustration of the design strategy is depicted in Figure 1.
Detailed synthetic route for oxime-functionalized nitrofuranylamides 7a-j and
nitrofuranylamide 7k was depicted in Scheme 1. The intermediates 2a-e (yield:
73.2-94.8%) were obtained by alkylation of N-hydroxyphthalimide (NOP) with
substituted benzyl bromide in presence of potassium carbonate according to
well-established procedures [32,33]. Treatment of 2a-e with hydrazine hydrate in
methanol and then hydrochloride in ethanol generated substituted
O-benzylhydroxylamine hydrochlorides 3a-e (yield: 91.7-98.9%). Condensations of
pyrrolidin-3-one
4a
or
piperidin-4-one
3a-e
4b
with
the
substituted
O-benzylhydroxylamine
hydrochlorides
or
O-alkylhydroxylamine
hydrochlorides in the presence of potassium carbonate produced the key intermediates
5a-j (yield: 46.3-59.6%). Finally, condensation of 5-nitrofuran-2-carboxylic acid 6
with
intermediates
5a-j
or
4c
in
hydrochloride
triethylamine (TEA)
7a-j (yield: 44.5-60.4%)
presence
of
(EDCI),
provided
N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide
1-hydroxybenzotriazole
oxime-functionalized
(HOBT)
and
nitrofuranylamides
and
nitrofuranylamide 7k (yield: 48.2%).
3

Scheme 1 Synthesis of oxime-functionalized nitrofuranylamides 7a-j and
nitrofuranylamide 7k
All oxime-functionalized nitrofuranylamides 7a-j and nitrofuranylamide 7k together
with the first-line anti-TB agents, isoniazid (INH) and RIF, were initially screened
for in vitro activity against MTB H37Rv ATCC 27294 strain using the Microplate
Alamar Blue Assay (MABA) [34,35]. The minimum inhibitory concentration (MIC)
is defined as the lowest concentration effecting a reduction in fluorescence of >90%
relative to the mean of replicate bacterium-only controls.
4

As shown in Table 1, six oxime-functionalized nitrofuranylamides displayed activity
against MTB H37Rv strain (MIC: 0.158-14.145 μg/mL), and the most active 7a and
7b (MIC: 0.291 and 0.158 μg/mL) were comparable to INH and RIF (MIC: 0.035
and 0.059 μg/mL). Moreover, the nitrofuranylamide 7k without oxime group also
showed activity against MTB H37Rv strain, and MIC was 0.482 μg/mL. Encouraged
by their strong potency against the drug sensitive MTB H37Rv strain, four
oxime-functionalized nitrofuranylamides 7a, 7b, 7g and 7i along with
nitrofuranylamide 7k were further evaluated against two clinically isolated 16833 and
16995 MDR-TB strains resistant to both of INH and RIF. As shown in Table 2, two
oxime-functionalized nitrofuranylamides 7a and 7b exhibited potential activity (MIC:
0.207-0.482 μg/mL), which were far more potent than the references INH (MIC: >40
μg/mL) and RIF (MIC: >40 μg/mL) against MDR-TB 16833 and 16995 strains.
While, the nitrofuranylamide 7k (MIC: >4 μg/mL) was inactive against the two
MDR-TB strains, suggested that the introduction of oxime group favored the activity
against MDR-TB. It is worth to notice that the resistance index (RI) for the four
oxime-functionalized nitrofuranylamides was around 1, suggesting they may bear a
novel action mechanism.
Table 1 Structures and anti-mycobacterial activities of oxime-functionalized nitrofuranylamides
7a-j and nitrofuranylamide 7k
MIC (μg/mL)
Compds
n
1
R
MTB H37Rv MDR-TB 16833
MDR-TB 16995
0.380
Bn
0.291
0.207
7a
5

2
2
2
2
2
1
1
2
2
-
Bn
0.158
5.884
>32
0.482
0.426
7b
7c
4-FBn
-
-
4-CF3Bn
-
-
7d
7e
4-NO2Bn
>32
-
-
-
-
4-OCF3Bn
>32
7f
Me
Et
Me
Et
-
1.829
>32
1.928
-
1.908
-
7g
7h
7i
1.932
14.145
0.482
0.035
0.059
1.914
-
1.935
-
7j
>4
>4
7k
INH
RIF
>40
>40
>40
>40
-
-
-
-
The SAR indicated that 1) oxime-functionalized nitrofuranylamides bearing
piperidinyl were slightly more potent than the corresponding analogs with
pyrrolidinyl against all tested strains; 2) the installation of oxime group favored the
activity against MDR-TB as evidenced by nitrofuranylamide 7k was inactive against
the tested two MDR-TB strains; 3) the oxime functional groups influenced the
anti-TB activity significantly, and the derivatives with benzoxime group were more
active than the alkyloxime analogs, but introduction of substituents such as -F (7c),
-CF3 (7d), -NO2 (7e) and -OCF3 (7f) were detrimental to the activity; 4) for
6

alkyloxime derivatives, the shorter -NOMe was much better than -NOEt, such as 7g
vs 7h and 7i vs 7j.
In conclusion, a series of oxime-functionalized nitrofuranylamides were designed,
synthesized and evaluated for their anti-mycobacterial activities against drug-sensitive
and multi-drug resistant MTB strains. Among them, two compounds 7a and 7b
exhibited excellent activity against the three tested strains, which were no inferior to
first-line anti-TB agents INH and RIF, and both of them could act as starting points
for further optimization.
This work was supported by the National Key Research and Development Program of
China (No. 2017YFC0803606).
References and Notes
[1] Fan YL, Wu JB, Cheng XW, et al. Fluoroquinolone derivatives and their anti-tubercular
activities. Eur. J. Med. Chem. 2018;146:554-563
[2] Bruhn D, Madhura DB, Maddox M, et al. Antitubercular nitrofuran isoxazolines with
improved pharmacokinetic properities. Bioorg. Med. Chem. 2012;15:6063-6072
[3] Fan YL, Jin XH, Huang ZP, et al. Recent advances of imidazole-containing derivatives as
anti-tubercular agents. Eur. J. Med. Chem. 2018;150:347-365
[4] Xu Z, Gao C, Ren QC, et al. Recent advances of pyrazole-containing derivatives as
anti-tubercular agents. Eur. J. Med. Chem. 2017;139:429-440
[5] Hu YQ, Zhang S, Zhao F, et al. Isoniazid Derivatives and Their Anti-Tubercular Activity. Eur.
J. Med. Chem. 2017;133:255-267
[6] Hu YQ, Xu Z, Zhang S, et al. Recent Developments of Coumarin-containing Derivatives and
Their Anti-tubercular Activity. Eur. J. Med. Chem. 2017;136:122-130
[7] Xu Z, Zhang S, Gao C, et al. Feng. Isatin hybrids and their anti-tuberculosis activity. Chin.
Chem. Lett. 2017;28:159-167
[8] Zhang S, Xu Z, Gao C, et al. Triazole Derivatives and Their Anti-tubercular Activity. Eur. J.
Med. Chem. 2017;138:501-513
[9] World Health Organization, Global Tuberculosis Report 2017.
7

[10] Verbitskiy EV, Baskakova SA, Gerasimova NA, et al. Synthesis and biological evaluation of
novel 5-aryl-4-(5-nitrofuran-2-yl)-pyrimidines as potential anti-bacterial agents. Bioorg. Med.
Chem. Lett. 2017;27:3003-3006
[11]
Barbosa-Lima
G,
Pinto
LSS,
Kaiser
CR,
et
al.
N-(2-(arylmethylimino)ethyl)-7-chloroquinolin-4-amine derivatives, synthesized by thermal
and ultrasonic means, are endowed with anti-Zika virus activity. Eur. J. Med. Chem.
2017;127:434-441
[12] Duan HL, Li Y, Lim HY, et al. Identification of 5-nitrofuran-2-amide derivatives that induce
apoptosis in triple negative breast cancer cells by activating C/EBP-homologous protein
expression. Bioorg. Med. Chem. 2015;23:4514-4521
[13] Tahghighi A, Razmi S, Mahdavi M, Foroumadi PS, et al. Synthesis and anti-leishmanial
activity
of
5-(5-nitrofuran-2-yl)-1,3,4-thiadiazol-2-amines
containing
N-[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl] moieties. Eur. J. Med. Chem. 2012;50:124-128
[14] Palace-Berl F, Pasqualoto KFM, Zingales B, et al. Investigating the structure-activity
relationships
of N’-[(5-nitrofuran-2-yl)
methylene]
substituted
hydrazides
against Trypanosoma cruzi to design novel active compounds. Eur. J. Med. Chem.
2018;144:29-40
[15] Ran K, Gao C, Deng HX, et al. Identification of novel 2-aminothiazole conjugated nitrofuran
as antitubercular and antibacterial agents. Bioorg. Med. Chem. Lett. 2016;26:3669-3674
[16] Krasavin M, Parchinsky V, Kantin G, et al. New nitrofurans amenable by isocyanide
multicomponent
chemistry
are
active
against
multidrug-resistant
and
poly-resistant Mycobacterium tuberculosis. Bioorg. Med. Chem. 2017;25:1867-1874
[17] Kamal A, Hussaini SMA, Faazil S, et al. Anri-tubercular agents. Part 8: Synthesis,
antibacterial and antitubercular activity of 5-nitrofuran based 1,2,3-triazoles. Bioorg. Med.
Chem. Lett. 2013;23:6842-6846
[18] Goncalves RSB, Kaiser CR, Lourenco MCS, et al. Mefloquine-oxazolidine derivatives,
derived from mefloquine and arenecarbaldehydes: In vitro activity including against the
multidrug-resistant tuberculosis strain T113. Bioorg. Med. Chem. 2012;20:243-248
[19] Gong YL, Karakaya SS, Guo XY, et al. Benzimidazole-based compounds kill
Mycobacterium tuberculosis. Eur. J. Med. Chem. 2014;75:336-353
[20] Sriram D, Yogeeswari P, Dhakla P, et al. 5-Nitrofuran-2-yl derivatives: Synthesis and
inhibitory activities against growing and dormant mycobacterium species. Bioorg. Med.
Chem. Lett. 2009;19:1152-1154
8

[21] Yempalla KR, Munagala G, Singh S, et al. Nitrofuranyl Methyl Piperazines as New Anti-TB
Agents: Identification, Validation, Medicinal Chemistry, and PK Studies. ACS Med. Chem.
Lett. 2015;6:1041-1046.
[22] Tangallapally RP, Raghunandan Y, Lee REB, et al. Synthesis and Evaluation of Cyclic
Secondary Amine Substituted Phenyl and Benzyl Nitrofuranyl Amides as Novel
Antituberculosis Agents. J. Med. Chem. 2005;48:8261-8269.
[23] Budha NR, Mehrotra N, Tangallapally R, et al. Pharmacokinetically Guided lead
optimization of nitrofuranylamide anti-tuberculosis agents. AAPS Journal 2008;10:157-165.
[24] Tangallapally RP, Raghunandan Y, Lee REB, et al. Synthesis and Evaluation of Cyclic
Secondary Amine Substituted Phenyl and Benzyl Nitrofuranyl Amides as Novel
Antituberculosis Agents. J. Med. Chem. 2004;47:5276-5283.
[25] Hu YQ, Zhang S, Xu Z, et al. 4-Quinolone Hybrids and Their Antibacterial Activities. Eur. J.
Med. Chem. 2017;141:335-345.
[26] Zhang GF, Zhang S, Pan BF, et al. 4-Quinolone Derivatives and Their Activities against
Gram Positive Pathogens. Eur. J. Med. Chem. 2018;144:710-723.
[27] Xu Z, Song XF, Hu YQ, et al. Azide-alkyne cycloaddition towards 1H-1,2,3-triazole-tethered
gatifloxacin and isatin conjugates: design, synthesis and in vitro anti-mycobacterial
evaluation. Eur. J. Med. Chem. 2017;138:66-71.
[28] Xu Z, Zhang S, Song XF, et al. Design, synthesis and in vitro anti-mycobacterial evaluation
of
gatifloxacin-1H-1,2,3-triazole-isatin
hybrids.
Bioorg.
Med.
Chem.
Lett.
2017;27:3643-3646
[29] Feng LS, Liu ML, Zhang S, et al. Synthesis and in vitro antimycobacterial activity of 8-OCH3
ciprofloxacin methylene and ethylene isatin derivatives. Eur. J. Med. Chem.
2011;46:341-348.
[30] Feng LS, Liu ML, Wang B, et al. Synthesis and in vitro antimycobacterial activity of
balofloxacin ethylene isatin derivatives. Eur. J. Med. Chem. 2010;45:3407-3412.
[31] Wang AP, Yang Y, Jun YS, et al. Synthesis, evaluation and CoMFA/CoMSIA study of
nitrofuranyl methyl N-heterocycles as novel antitubercular agents. Bioorg. Med. Chem.
2018;26:2073-2084
[32] Zhang TT, Shen, WY, Liu ML, et al. Synthesis, antimycobacterial and antibacterial activity of
fluoroquinolone
derivatives
containing
an
3-alkoxyimino-4-(cyclopropylanimo)methylpyrrolidine moiety. Eur. J. Med. Chem.
2015;104:73-85.
9

[33] Feng LS, Lv K, Liu ML, et al. Synthesis and in vitro antibacterial activity of gemifloxacin
derivatives containing
2012;55:125-136.
a substituted benzyloxime moiety. Eur. J. Med. Chem.
[34] Colins L, Franzblau SG. Microplatealamar blue assay versus BACTEC 460 system for
high-throughput screening of compounds against Mycobacterium tuberculosis and
mycobacterium avium. Antimicrob. Agents Chemother. 1997;41:1004-1009.
[35] Lu Y, Zheng M, Wang B, et al. Clofazimine analogs with efficacy against experimental
tuberculosis and reduced potential for accumulation. Antimicrob. Agents Chemother.
2011;55:5185-5193.
[36] (4-((benzyloxy)imino)piperidin-1-yl)(5-nitrofuran-2-yl)methanone (7b): Yield: 49.3%,
off-white solid. 1H NMR (500 MHz, CDCl3) δ 7.77 (d, J = 2.0 Hz, 1H, Ar-H), 7.30-7.35 (m,
6H, Ar-H), 5.04 (s, 2H, CH2), 3.69-3.81 (m, 4H, piperidinyl-4H), 2.66 (s, 2H, piperidinyl-2H),
2.43 (s, 2H, piperidinyl-2H). 13C NMR (101 MHz, CDCl3) δ 156.47, 156.19, 137.95, 128.37,
128.01, 127.75, 112.43, 111.86, 54.44, 53.51, 52.26, 29.73, 25.41. ESI-MS m/z: 344 [M+H]+.
10

All oxime-functionalized nitrofuranylamides showed considerable activity against the tested MTB
strains;
Targets 7a and 7b were far more potent than INH and RIF against drug-resistant clinical isolates;
The SAR was enriched.
11

Graphical Abstract
Design, synthesis and evaluation of oxime-functionalized
nitrofuranylamides as novel antitubercular agents
Yi-Lei Fan*,a, Jian-Bing Wua, Xing Kea, Zhong-Ping Huangb
aKey Laboratory of Drug Prevention and Control Technology of Zhejiang Province, Zhejiang
Police College, Hangzhou, P R China;
bCollege of Chemical Engineering, Zhejiang University of Technology, Hangzhou, P R China
A series of novel oxime-functionalized nitrofuranylamides were designed, synthesized and
evaluated for their in vitro anti-mycobacterial activities against MTB H37Rv and
drug-resistant clinical isolates. Among them, two compounds 7a and 7b which were
comparable to the first-line anti-TB agents INH and RIF against MTB H37Rv, also
demonstrated great potency against drug-resistant clinical isolates, suggesting they may serve
as new and promising candidates for further anti-TB drug discovery.
12