Design, synthesis, and bioevaluation of a novel class of (E)-4-oxo-crotonamide derivatives as potent antituberculosis agents

Article abstract of DOI:10.1016/j.bmcl.2019.01.001

A series of novel (E)-4-oxo-2-crotonamide derivatives were designed and synthesized to find potent antituberculosis agents. All the target compounds were evaluated for their in vitro activity against Mycobacterium tuberculosis H₃₇Rv(MTB). Results reveal that 4-phenyl moiety at part A and short methyl group at part C were found to be favorable. Most of the derivatives displayed promising activity against MTB with MIC ranging from 0.125 to 4 μg/mL. Especially, compound IIIa16 was found to have the best activity with MIC of 0.125 μg/mL against MTB and with MIC in the range of 0.05–0.48 μg/mL against drug-resistant clinical MTB isolates.

Full text of DOI:10.1016/j.bmcl.2019.01.001

Accepted Manuscript
Design, synthesis, and bioevaluation of a novel class of (E)-4-oxo-crotonamide
derivatives as potent antituberculosis agents
Jinfeng Ren, Jian Xu, Guoning Zhang, Changliang Xu, LiLi Zhao, XueFu You,
Yucheng Wang, Yu Lu, Liyan Yu, Juxian Wang
PII:
S0960-894X(19)30001-0
https://doi.org/10.1016/j.bmcl.2019.01.001
BMCL 26238
DOI:
Reference:
Bioorganic & Medicinal Chemistry Letters
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Accepted Date:
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4 December 2018
2 January 2019
Please cite this article as: Ren, J., Xu, J., Zhang, G., Xu, C., Zhao, L., You, X., Wang, Y., Lu, Y., Yu, L., Wang, J.,
Design, synthesis, and bioevaluation of a novel class of (E)-4-oxo-crotonamide derivatives as potent antituberculosis
agents, Bioorganic & Medicinal Chemistry Letters (2019), doi: https://doi.org/10.1016/j.bmcl.2019.01.001
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Design, synthesis, and bioevaluation of a novel class of (E)-4-oxo-
crotonamide derivatives as potent antituberculosis agents
Jinfeng Rena,#, Jian Xua,b,#, Guoning Zhanga, Changliang Xua,c, LiLi Zhaoa, XueFu
Youa, Yucheng Wanga, Yu Lub, Liyan Yua,* and Juxian Wanga,*
a Institute of Medicinal Biotechnology, Chinese Academy of Medical Science and Peking Union
Medical College, Beijing 100050, China
b Beijing Key Laboratory of Drug Resistance Tuberculosis Research, Beijing Tuberculosis and
Thoracic Tumor Research Institute, and Beijing Chest Hospital, Capital Medical University,
Beijing, China
c Jiangsu Protein Drug Engineering Laboratory, Food & Drug Analysis and Testing Center,
Jiangsu Food & Pharmaceutical Science College, Huai'an 223003, Jiangsu, China.
Abstract: A series of novel (E)-4-oxo-2-crotonamide derivatives were designed and
synthesized to find potent antituberculosis agents. All the target compounds were
evaluated for their in vitro activity against Mycobacterium tuberculosis H37Rv(MTB).
Results reveal that 4-phenyl moiety at part A and short methyl group at part C were
found to be favorable. Most of the derivatives displayed promising activity against
MTB with MIC ranging from 0.125 - 4 µg/mL. Especially, compound IIIa16 was
found to have the best activity with MIC of 0.125 μg/mL against MTB and with MIC
in the range of 0.05 - 0.48 µg/mL against drug-resistant clinical MTB isolates.
Keywords: Mycobacterium tuberculosis; antituberculosis agents; (E)-4-oxo-2-
crotonic acid derivatives; drug-resistant-TB.
*Corresponding author. Tel./fax:+86 10 63187118, yly@cpcc.ac.cn (L. Yu); Tel./fax:+86 10 63165263, E-mail
addresses: imbjxwang@163.com (J. Wang).
#These authors contributed equally to this work.
Tuberculosis (TB) is an airborne, highly contagious, infectious disease caused by
the Mycobacterium tuberculosis (MTB), which kills about 1.3 million people

worldwide in 2016.1 The recent upsurge in the incidence of multidrug-resistant TB
(MDR-TB) and extensively drug-resistant TB (XDR-TB) has reaffirmed TB as a
serious public health problem worldwide.2-4 Besides, MTB-HIV coinfection further
emphasizes the desperate need for new anti-TB agents.5-7 However, the fact is that
few new TB drugs have been introduced to the repertoire of anti-TB therapies over
the past 50 years.8-10 Although the discovery of bedaquiline and delamanid has
renewed hope for the treatment of TB and especially MDR-TB, it is strictly
recommended for the treatment of MDR-TB owing to side effects such as QT
prolongation and liver function abnormalities.11-15 Therefore, it is urgently and highly
valuable to discover and develop antimycobacterial molecules with novel scaffolds as
effective anti-TB drug candidates.
In our previous research, leading compound IMB-YH-8 (3a, Fig. 1), was
identified as a protein kinase B (PknB) inhibitor from a high throughput screen (HTS),
which is one of the most important serine/threonine protein kinases (STPKs) for MTB
and plays a critical role in the growth of mycobacteria.16-20 It exhibited good anti-
tuberculosis activity (MIC: H37Rv 0.25 μg/mL, MDR-TB 0.25-1 μg/mL) and low
toxicity ( LD50 568 mg/kg, BALB/c mice, p.o.), which encouraged us to explore its
structure-activity relationship (SAR) against MTB as a new scaffold.21-22 In the
preceding work,23 we reported the biological activity and SAR of series (E)-4-oxo-
crotonester derivatives of IMB-YH-8 as potential PknB inhibitors. The results
indicated that α,β-unsaturated ketone scaffold and “trans-” configuration are essential
for the activity against PknB (Fig. 1).
Based on the above research results, considering the amide analogs had stable
metabolism, it was decided to replace the ester group with the amide group at part C,
and meanwhile introduce various substituents to the benzene ring at part A in this
study (Fig. 1). Thus, a series of novel (E)-4-oxo-crotonamide derivatives were
designed, synthesized, the targeted compounds and the esters were evaluated in vitro
anti-tuberculosis activities. Our primary objective was to optimize the potency of

these compounds against MTB including MDR-TB. A preliminary SAR study was
also explored to facilitate the further development of the (E)-4-oxo-2-crotonyl
scaffold.
Pharmacophore
C
O
O
A
O
CH3
O
Confirm
CH3
O
H3CO
O
B
H3CO
IMB-YH-8 (3a)
H Rv:MIC = 0.25 g/mL
"trans-" 4-oxo-crotonyl scaffold

37
O
R3
N
O
R1
R2
O
R1
R2
O
O
R1
R2
R3
= aryl
R1
R2
= aryl, alkyl, cycloalkyl
= H, CH3, CH2CH3,
= CH3, CH2CH3, CH2CH2CH3
= CH3, CH2CH3, CH2CH2CH3
CH(CH3)2, CH2CH2NHBoc
Fig. 1 Illustration of Compounds Design Strategy
The ester analogs were easily prepared based on the (E)-4-oxo-2-crotonyl
scaffold of IMB-YH-8 for SAR investigations in the preceding work23 (Scheme 1).
2
3a-u :
R = Me
O
O
O
ii
i
2
4a-u :
5a-u :
OH
O
R = Et
R1
1a-u
R1 = aryl, alkyl, cycloalkyl.
R1
R1
R2
2
R = i-Pro
O
O
2a-u
2
6a-u :
R =CH2CH2NHBoc
2a-q
2s-u
; glyoxylic
Reagents and conditions: (i) glyoxylic acid, sulfuric acid (Cat.), AcOH, reflux, 8h, for
and
2r
acid, morpholine hydrochloride (Cat.), reflux, overnight, for ; (ii) ROH, sulfuric acid (Cat.), reflux, overnight,
3a-u 4a-u 5a-u 6a-u
for
,
,
; IBCF, TEA, anh. DCM, -15 °C, then N-Boc-ethanolamine, rt, 6 h, for
.
Scheme 1. Synthesis of (E)-4-oxo-crotonester derivatives

Synthetic pathways to novel (E)-4-oxo-crotonamide derivatives IIIa1-20, IIIb1-
19 and IIIc1-19 (58 compounds in total) are depicted in Scheme 2. A series of
substituted 4-phenyl-4-oxo-crotonic acids (II-1~20) were directly prepared from
corresponding substituted acetophenone I-1~I-20 and glyoxylic acid in 85%-93%
yields. Amidation of acids II-1~20 with different amines through an
EDCI/HOBT/DIEA mediated coupling afforded the amides IIIa1-20, IIIb1-19 and
IIIc1-19 in around 50% yield.
R2
O
O
2 = Me, R3 = Me
IIIa1-20 :
R
O
2 = Me, R3 = Et
N
i
OH
IIIb1-19 :
IIIc1-19 :
R
ii
R3
CH3
R1
R1
R1
2 = n-Pr, R3 =n-Pr
O
R
O
II-1~II-20

I-1~I-20


R1=

O
-OCH3,-OCH2CH3,-NO2,-F,-Cl,-Br,-OCF3
N
O
Reagents and conditions: (i) glyoxylic acid,conc. H2SO4 (Cat.),AcOH, reflux, 6 h; (ii) R2R3NH, EDCI,HOBt, DBU, dry DMF,
r.t., 24 h.
Scheme 2. Synthesis of (E)-4-oxo-crotonamide derivatives
All target compounds were preliminarily screened for in vitro activity against
MTB H37Rv ATCC27294 strain using the Microplate Alamar Blue Assay (MABA)24-
25, including the esters synthesized in preceding work.23 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. The
MIC values of them along with the lead compound IMB-YH-8 (3a), and isoniazid
(INH) for comparison were presented in μg/mL in Table 1and Table 2.
The data for esters in Table 1 reveal that the carboxylic acids and N-Boc ethyl
esters are inactive against this strain (MIC: >4 μg/mL), while most of the esters show
only moderate activity (MIC: <1μg/mL), weaker than IMB-YH-8 (MIC: 0.25 μg/mL).
Only compounds 3k, 4k and 5k with 4-phenyl have a little better activities (MIC: 0.2-
0.24 μg/mL), suggesting the presence of the 4-phenyl moiety at part A is found to be
favorable.

For the esters groups at part C, methyl (3) makes more contribution to anti-
tuberculosis activity than ethyl (4), while isopropyl (5) is the lowest with few
exceptions and N-Boc ethyl (6) eliminates the activity in vitro. Mostly, compounds
containing an aryl group at part A show higher potency than that substituded with
alkyl analogs (3r-t, 4r-t and 5r-t). Compounds bearing a substituent on the para-
position of the phenyl (R1) generally show higher activities than the corresponding
meta- and ortho-substituent analogs (3a,4a vs 3e-3f, 4e-4f), whereas benzodiazepyl
moiety possesses antitubercular activity among the double substituted derivatives (3g-
3j, 4g-4j and 5g-5j). There are small differences in activity between the electron-
donating groups and the electron-withdrawing groups. The contribution of the
electron-donating groups is generally as follows: phenyl > methoxyl > methyl >
ethyoxyl > naphthyl > H > benzyloxyl > phenoxyl . On the other hand, the activity of
the electron-withdrawing groups is in the order: Br > NO2 > 2,4-dichloro. Overall, the
potency of the derivatives is related to the substituents on benzene ring at part A and
the size of alkyl groups at part C.

Table 1 Structures of ester analogs and their ain vitro activity against MTB H37Rv
2
2a-u
3a-u
: R = H
O
2
: R = Me
O
2
R1
R2
4a-u
5a-u
6a-u
: R = Et
2
: R = i-Pr
O
2
: R = BocNH(CH2)2
R1
Compd.
2a
MIC(μg/mL)
Compd.
3a
MIC(μg/mL)
Compd.
4a
MIC(μg/mL)
Compd.
5a
MIC(μg/mL)
Compd.
6a
MIC(μg/mL)
>4
0.25
0.46
1.64
>4
O
2b
2c
2d
2e
2f
>4
>4
>4
>4
>4
3b
3c
3d
3e
3f
0.86
0.37
0.41
0.99
0.39
4b
4c
4d
4e
4f
0.82
>4
5b
5c
5d
5e
5f
0.78
0.77
0.47
1.91
0.92
6b
6c
6d
6e
6f
>4
>4
0.54
1.82
0.82
1.45
>4
O
O
O
>4
O
2g
2h
>4
>4
3g
3h
0.88
0.44
4g
4h
1.05
0.82
5g
5h
1.48
1.94
6g
6h
>4
>4
O
O
O

O
O
2i
2j
2k
2l
>4
>4
>4
>4
3i
3j
3k
3l
0.38
0.84
0.20
0.87
4i
4j
4k
4l
0.49
0.94
0.23
1.52
5i
5j
5k
5l
0.87
1.02
0.24
1.69
6i
6j
6k
6l
>4
>4
O
Ph
1.23
>4
PhO
2m
2n
2o
>4
>4
>4
3m
3n
3o
0.45
1.85
0.54
4m
4n
4o
0.61
1.09
0.48
5m
5n
5o
0.69
1.01
0.50
6m
6n
6o
>4
>4
>4
Cl
Cl
O2N
2p
2q
2r
2s
>4
>4
>4
>4
3p
3q
3r
3s
0.49
0.52
0.86
1.20
4p
4q
4r
4s
0.52
1.09
3.51
>4
5p
5q
5r
5s
0.41
0.65
2.50
>4
6p
6q
6r
6s
>4
>4
>4
>4
Br
O
Me
2t
>4
>4
3t
>4
4t
>4
5t
0.68
1.14
6t
1.45
1.91
2u
3u
0.67
4u
0.96
5u
6u
BnO
Positive control: Isoniazid: MIC=0.025 µg/ml; IMB-YH-8(3a): MIC=0.25 µg/ml.

A further strategy to increase activity and improve pharmacokinetic properties
was to replace ester group by N-substituted amide groups at part C containing an aryl
group at part A. Thus, we synthesized a series of N-substituted amide analogs and
evaluated their anti-tuberculosis activities against MTB H37Rv (Table 2). Though
most of the analogs had considerable activity against this strain, they all were much
less than IMB-YH-8 except IIIa16 (MIC: 0.125 μg/mL). Only considering the para-
substitued groups, compounds IIIa1-20 with simple and short methyl group on the N
atom exhibits higher activity than the amides IIIb1-19 and IIIc1-19 with long alkyl
substituents (ethyl and propyl), except for fluoro substitution compounds. Therefore,
it indicates that introduction of a longer alkyl substituents would be detrimental to the
activity. In addition introduction of the substituents at the meta-position of the
benzene ring also leads to decreased activity (e.g. IIIa1-IIIa3, IIIa5-IIIa7). In the
N,N-diethyl series of compounds (IIIb1-19), quite surprisingly, compounds with
electron-withdrawing groups (F, Cl, NO2) show good activity (MIC: 0.24 μg/mL),
which is more active than that with electron-donating groups (methoxyl, ethyoxyl,
phenyl, benzodiazepyl), and comparable to IMB-YH-8 (3a). However, it is difficult to
distinguish whether an electron-donating group contributes more to the activity or an
electron-withdrawing group in the N,N- dimethyl series of compounds (IIIa1-20), and
the activity of the para-substitued groups is in the order: phenyl > bromo > methoxyl
≈ cloro > fluoro ≈ ethyoxyl > nitro.

Table 2 Structures of N-substituded amides and their in vitro activity against MTB H37Rv
IIIa1-20: R2 = R3 = Me
IIIb1-19: R2 = Me, R3 = Et
IIIc1-19: R2 = R3 = n-Pr
R3
O
N
R1
R2
O
R1
Compd. MIC (μg/mL) Compd. MIC (μg/mL) Compd. MIC (μg/mL)
IIIa1
IIIa2
IIIa3
IIIa4
IIIa5
IIIa6
IIIa7
IIIa8
IIIa9
IIIa10
IIIa11
IIIa12
0.92
1.62
0.38
0.96
0.84
0.89
0.38
0.48
0.95
1.84
0.47
1.95
IIIb1
IIIb2
IIIb3
IIIb4
IIIb5
IIIb6
IIIb7
IIIb8
IIIb9
IIIb10
IIIb11
IIIb12
0.95
1.88
0.93
1.52
0.65
0.97
0.24
0.48
0.24
0.48
0.25
>2
IIIc1
IIIc2
IIIc3
IIIc4
IIIc5
IIIc6
IIIc7
IIIc8
IIIc9
IIIc10
IIIc11
IIIc12
>2
>2
O
O
1.89
>2
O
Br
>2
Cl
1.91
1.67
1.91
0.94
0.96
0.95
>2
Cl
Cl
O
F
F
F
CF3

IIIa13
IIIa14
IIIa15
IIIa16
IIIa17
IIIa18
IIIa19
IIIa20
1.51
>2
IIIb13
IIIb14
IIIb15
IIIb16
IIIb17
IIIb18
IIIb19
-
0.24
>2
IIIc13
IIIc14
IIIc15
IIIc16
IIIc17
IIIc18
IIIc19
-
1.24
>2
NO2
NO2
0.93
0.125
0.41
0.84
0.79
0.25
1.70
0.49
>2
1.89
1.4
>2
O2N
Ph
Cl
Cl
0.24
>2
0.88
>2
Cl
Cl
O
O
-
-
Br
-
-
Compound was not synthesized.
Positive control: Isoniazid: MIC=0.025 µg/ml; IMB-YH-8(3a): MIC=0.25 µg/ml.
As shown in Table 1 and 2, converting the acids into esters and N-substituded
carboxamides enhanced the anti-tuberculosis activity. Generally, the activity of the
derivatives against Mycobacterium tuberculosis as follows: methyl ester > ethyl ester >
isopropyl ester > amide > Boc aminoethyl ester. The date reveal that 4-phenyl moiety
at part A and short methyl group at part C are found to be favorable and introduction
of the substituents at the para-position of the benzene ring at part A is acceptable.
While most of esters and N-substituded amides retained activity against H37Rv
(MIC: 0.125 - 4 μg/mL), the most active compounds IIIa16 (MIC: 0.125 μg/mL)
were found more potent than that of IMB-YH-8 (MIC: 0.25 μg/mL). Then we
selected compounds IIIa16 for further in vitro anti-tuberculosis activity against some
drug-resistant TB strains. MIC values indicated that IIIa16 also showed good activity

(MIC: 0.05 - 0.48 µg/mL) against drug-resistant clinical isolates (Table 3).
Table 3 In vitro activity of IIIa16 against drug-resistant clinical isolates of M. tuberculosis
Clinical isolates
IIIa16
INH
RFP
SM EMB MXF
Amoxicillin/
Clavulanic acid
(MIC: μg/mL)
19809
19852
19874
19769
19675
19863
19805
19806
19810
11168
0.48
0.19
0.23
0.43
0.45
0.23
0.25
0.23
0.12
0.05
S
S
R
R
S
S
S
S
R
R
S
S
R
R
S
S
S
S
R
R
S
S
S
S
S
S
S
S
R
S
S
S
S
S
S
S
S
S
R
R
R
S
R
R
R
R
R
R
R
R
R
S
R
R
S
S
R
R
R
S
S: Susceptible; R: Resistant; INH: Isoniazid; RFP: Rifampicin; SM: Sterptomycin; EMB: Ethambutol; MXF:
Moxifloxacin.
In summary, a series of novel (E)-4-oxo-crotonamide derivatives were designed
and synthesized as new anti-TB agents, including esters synthesized in preceding
work. In part A, the aryl group had been replaced with an alkyl group, reducing their
antituberculosis activities, and the diphenyl group may be a preferred structure. In part
C, the ester and N-substituted amide analogs had generally considerable activity
against MTB H37Rv (MIC: 0.125 - 4 μg/mL). Among all tested compounds,
compound IIIa16 displayed the best activity of MIC 0.125 μg/mL against MTB
H37Rv and also exhibited potent anti-tuberculosis activity against drug-resistant
clinical MTB isolates (MIC: 0.05-0.48 µg/mL) and it may serve as a new and
promising lead compound for further antitubercular drug discovery.

Acknowledgments
This work was supported by the major New Drug Innovation
(2014ZX09201001-011, 2015ZX09102007-016-001), the National Natural Science
Foundation of China (Nos. 81473099, 81373452, 81473098 and 81621064),
Microbial Resources (No.NIMR-2018-3), and CAMS Innovation Fund for Medical
Sciences (2016-I2M-2-002, 2016-I2M-3-014).
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protein kinase B (PknB) inhibitors: synthesis and SAR study. RSC Adv., 2017, 7, 4763-4775.
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High-Throughput Screening of Compounds against Mycobacterium tuberculosis and
Mycobacterium avium. Antimicrob Agents and Chemother., 1997, 41 (5), 1004 - 1009.
25. Xu J, Wang B, Hu MH, et al. Primary Clofazimine and Bedaquiline Resistance among
Isolates from Patients with Multidrug-Resistant Tuberculosis. Antimicrob Agents and
Chemother., 2017, 61(6), e00239 - 17.
Design, synthesis, and bioevaluation of a novel class of (E)-4-oxo-
crotonamide derivatives as potent antituberculosis agents
Jinfeng Ren1,#, Jian Xu1,2,#, Guoning Zhang1, Changliang Xu1,3, LiLi Zhao1, XueFu
You1, Yucheng Wang1, Yu Lu2, Liyan Yu1,* and Juxian Wang1,*
A series of novel (E)-4-oxo-2-crotonamide derivatives were designed and synthesized
to find potent antituberculosis agents and evaluated for their biological activity. Our
results reveal that compound IIIa16 was found to have the best activity with MIC of
0.125 μg/mL against MTB and with MIC in the range of 0.05 - 0.48 µg/mL against

drug-resistant clinical MTB isolates. Results reveal that 4-phenyl moiety at part A and
short methyl group at part C were found to be favorable.
Pharmacophore
C
O
O
A
O
CH3
O
Confirm
CH3
O
H3CO
O
B
H3CO
IMB-YH-8 (3a)
H Rv:MIC = 0.25 g/mL
"trans-" 4-oxo-crotonyl scaffold

37
O
R3
N
O
R1
R2
O
R1
R2
O
O
R1
R2
R3
= aryl
R1
R2
= aryl, alkyl, cycloalkyl
= H, CH3, CH2CH3,
= CH3, CH2CH3, CH2CH2CH3
= CH3, CH2CH3, CH2CH2CH3
CH(CH3)2, CH2CH2NHBoc
*Corresponding author. Tel./Fax: +86-010-6318-7118, yly@cpcc.ac.cn (L. Yu); Tel./fax:+86 10 63165263, E-mail
addresses: imbjxwang@163.com (J. Wang).
#These authors contributed equally to this work.
26.

Pharmacophore
O
C
O
A
O
CH3
O
Confirm
CH3
O
H3CO
O
B
H3CO
IMB-YH-8 (3a)
H Rv:MIC = 0.25 g/mL
"trans-" 4-oxo-crotonyl scaffold

37
O
R3
N
O
R1
R2
O
R1
R2
O
O
R1
R2
R3
= aryl
R1
R2
= aryl, alkyl, cycloalkyl
= H, CH3, CH2CH3,
= CH3, CH2CH3, CH2CH2CH3
= CH3, CH2CH3, CH2CH2CH3
CH(CH3)2, CH2CH2NHBoc
Figure.1 Illustration of Compounds Design Strategy
27.
2
3a-u :
R = Me
O
O
O
ii
i
2
4a-u :
5a-u :
OH
O
R = Et
R1
1a-u
R1 = aryl, alkyl, cycloalkyl.
R1
R1
R2
2
R = i-Pro
O
O
2a-u
2
6a-u :
R =CH2CH2NHBoc
2a-q
2s-u
; glyoxylic
Reagents and conditions: (i) glyoxylic acid, sulfuric acid (Cat.), AcOH, reflux, 8h, for
and
2r
acid, morpholine hydrochloride (Cat.), reflux, overnight, for ; (ii) ROH, sulfuric acid (Cat.), reflux, overnight,
3a-u 4a-u 5a-u 6a-u
for
,
,
; IBCF, TEA, anh. DCM, -15 °C, then N-Boc-ethanolamine, rt, 6 h, for
.
Scheme 1. Synthesis of (E)-4-oxo-crotonester derivatives

R2
O
O
R
2 = Me, R3 = Me
2 = Me, R3 = Et
2 = n-Pr, R3 =n-Pr
O
IIIa1-20 :
IIIb1-19 :
N
i
OH
R
ii
R3
CH3
R1
R1
R1
O
IIIc1-19 :
R
O
II-1~II-20

I-1~I-20


R1=

O
-OCH3,-OCH2CH3,-NO2,-F,-Cl,-Br,-OCF3
N
O
Reagents and conditions: (i) glyoxylic acid,conc. H2SO4 (Cat.),AcOH, reflux, 6 h; (ii) R2R3NH, EDCI,HOBt, DBU, dry DMF,
r.t., 24 h.
Scheme 2. Synthesis of (E)-4-oxo-crotonamide derivatives
28.
1. Novel (E)-4-oxo-crotonamide derivatives containing different substituents were
designed and synthesized.
2. The SAR were summarized for further antitubercular drug discovery.
3. Compound IIIa16 exhibit potent MIC values against MTB H37Rv and some
MDR-MTB strains.
29.