An efficacious synthesis of N-1–, C-3–substituted indole derivatives and their antimicrobial studies

Article abstract of DOI:10.1002/jhet.3799

A novel series of 11 C-3– and N-1–substituted oxoacetamide indole derivatives were synthesized by reacting with various aromatic amines and alkyl halides. These compounds were characterized by using various spectral techniques, ie, ¹HNMR, ¹HNMR-D₂O, ¹³CNMR, UV, elemental analysis, IR, and mass spectrometery. In vitro, antimicrobial studies of resultant compounds were carried out against two bacterial strains, Pseudomonas aeruginosa and Pseudomonas oryzihabitans using disc plate method. All the tested compounds showed vital efficiency as antimicrobial agents against both the bacterial strains. The results revealed that synthesized indole derivative 2-(1-(3-bromopropyl)-1H-indol-3-yl)-N-(2-nitrophenyl)-2-oxoacetamide displayed the best antimicrobial activity as compared with all other synthesized compounds.

Full text of DOI:10.1002/jhet.3799

Received: 11 September 2019
DOI: 10.1002/jhet.3799
Revised: 7 October 2019
Accepted: 8 October 2019
A R T I C L E
An efficacious synthesis of N‐1–, C‐3–substituted indole
derivatives and their antimicrobial studies
Palak Jain1 | Divya Utreja1
| Poonam Sharma2
1 Department of Chemistry, Punjab
Abstract
Agricultural University, Ludhiana, India
A novel series of 11 C‐3– and N‐1–substituted oxoacetamide indole derivatives
were synthesized by reacting with various aromatic amines and alkyl halides.
These compounds were characterized by using various spectral techniques,
ie, HNMR, 1HNMR‐D2O, 13CNMR, UV, elemental analysis, IR, and mass
2 Department of Plant Breeding and
Genetics, Punjab Agricultural University,
Ludhiana, India
1
Correspondence
Divya Utreja, Department of Chemistry,
Punjab Agricultural University, Ludhiana,
Punjab, India.
spectrometery. In vitro, antimicrobial studies of resultant compounds were
carried out against two bacterial strains, Pseudomonas aeruginosa and Pseudo-
monas oryzihabitans using disc plate method. All the tested compounds
showed vital efficiency as antimicrobial agents against both the bacterial
strains. The results revealed that synthesized indole derivative 2‐(1‐(3‐
bromopropyl)‐1H‐indol‐3‐yl)‐N‐(2‐nitrophenyl)‐2‐oxoacetamide displayed the
best antimicrobial activity as compared with all other synthesized compounds.
Email: utrejadivya@yahoo.com
1 | INTRODUCTION
(FDA)‐approved indole‐based pharmacores include
Dragmacidin, a marine bisindole natural alkaloid that act
Heterocyclic compounds are pivotal tools in the invention
of new bioactive drugs of pharmaceutical interest and
importance.[1] Because of their great structural diversity,
unique ability of binding reversibly to enzymes, and mim-
icking the structure of peptides,[2] it forms a basis for the
synthesis of a library of biologically active compounds.[3]
It is not surprising that a five‐membered nitrogen‐
containing ring is an important structural motif in most
pharmacores.[4,5] Indole, a privileged scaffold, is widely
known for its significance not only in the area of syn-
thetic chemistry but also in biological, pharmaceutical,
and material science.[6–8] Indole derivatives have shown
a wide range of biological activities such as plant growth
regulation[9] and antifungal,[10] antibacterial,[11] antitu-
bercular,[12] anticancer,[13] antiulcer,[14] antiviral,[15] anti-
oxidant,[16] antidepressant,[17] anti‐inflammatory,[18]
antidiabetic,[19] antimalarial,[20] anti‐HIV,[21] insecticidal,
and analgesic activities.[22]
as anticancer agent.[25,26] Sumatriptan belongs to the class
of triptan drugs called serotonin (5‐HT) receptor, which is
used for the treatment of migraine attacks and neuro-
genic plasma extravasations.[27] The nonsteroidal anti‐
inflammatory drug Etodolac is a COX‐inhibitor used in
the prevention of rheumatoid arthritis and inflammatory
disorders.[28] Arbisol, also known as Umifenovir, act as
antiviral drug against influenza A and B viruses by
targeting the glycoproteins to prevent the fusion of viral
and endosomal membranes.[29] Ondansteron, called
5‐hydroxytryptamine receptor, is used in the treatment of
nausea and vomiting caused by emetogenic chemotherapy
and act as antiemetic agent[30] (Figure 1).
Infectious diseases caused by pathogenic bacteria
such as Pseudomonas aeruginosa, Escherichia coli, and
Staphylococcus aureus are preeminent causes of early
deaths in humans and plants.[31,32] The genus Pseudo-
monas is responsible for infecting roots of sweet basil
and Arabidopsis.[33] A recent estimate showed that
nosocomial infections caused by P. aeruginosa affect 2
million people every year.[34] In the recent decades,
there is a need for the development of a new generation
It has been reported that, out of 10 000 discovered bio-
logically active indole derivatives, 200 indole derivatives
are approved as marketed drugs and are undergoing med-
ical trials.[23,24] Some of the Food and Drug Administration
J Heterocyclic Chem. 2019;1–8.
wileyonlinelibrary.com/journal/jhet
© 2019 Wiley Periodicals, Inc.
1

2
JAIN ET AL.
FIGURE 1 Biologically active indole‐
based drugs
of antimicrobial agents that exhibits improved drug
resistance profile because of rapid development in drug
resistance, tolerance, and side effects.
In the view of active participation of indole derivatives
in various biological activities, we have planned to syn-
thesize C‐3– and N‐1–substituted indole derivatives and
explored their antimicrobial activity against P. aeruginosa
and Pseudomonas oryzihabitans.
procedure, is cost effective, increases the yield of product
(85%), and decreases the reaction time. Therefore, N‐1–
substituted indole derivatives were synthesized by reaction
of C‐3–substituted indole derivatives with different alkyl
halides in the presence of base NaH and solvent DMF as
shown in Scheme 2. Considerable variation in carbon
chains (R) was introduced so as to understand the scope
and limitation of the reaction. Long‐chain alkyl halides
react slowly as compared with short‐chain alkyl halides.
2 | RESULTS AND DISCUSSION
3 | ANTIMICROBIAL ACTIVITY
The 3‐substituted indole derivatives were synthesized by
the reaction of indole (1) with oxalyl chloride (2) to obtain
an intermediate (3), which was further reacted with vari-
ous aromatic amines to afford the corresponding
oxoacetamide derivatives of indole (4a‐c) (Scheme 1).[35]
Considerable variation in the nature of substituent (R)
was introduced so as to understand the scope and limita-
tion of the reaction. The indole derivatives (4a‐c) were syn-
thesized in good to excellent yield, and the compounds
were characterized with various spectral techniques.
In vitro, antimicrobial screening of indole and its deriva-
tives (4a‐c) and (5a‐h) were carried out against two
Gram‐negative bacterial strains P. aeruginosa and P.
Furthermore,
a
convenient approach used for
N‐alkylation of indole derivatives is mediated by use of
base sodium hydride and solvent dimethylformamide
(DMF). The use of sodium hydride as base for N‐1 alkyl-
ation of indole derivative is superior to many other
reagents as it is safer, less toxic, and easy to handle. Also,
N‐alkylation by using NaH involves a simple reaction
SCHEME 2 Synthesis of N‐1–substituted indole derivative 5a‐h
SCHEME 1 Synthesis of oxoacetamide
derivatives of indole 4a‐c

JAIN ET AL.
3
TABLE 2 Effect of different concentrations of indole (1) and its
derivatives (4a‐c) and (5a‐h) on the growth of Pseudomonas
oryzihabitans
oryzihabitans using disc plate method at five different con-
centrations (2000, 1500, 1000, 500, and 250 μg/mL).[36] The
zone of inhibition for different compounds was measured
and expressed in millimeters. Furthermore, minimum
inhibitory concentration (MIC) of different tested com-
pounds was also determined in micrograms per milliliter.
The data revealed that all the compounds exhibited
considerable inhibitory effect against both the strains.
Among oxoacetamide derivatives, 4b, bearing three
chlorine atoms on benzene ring, showed onefold better
activity as compared with 4a and 4c against P. aeruginosa
(Table 1). The mentioned results also revealed that com-
pound 5e, bearing chloro alkyl chain at N‐1 position
and oxoacetamide moiety at C‐3 position to the basic
indole ring, was found to be most effective as compared
with all other analogs with zone of inhibition 14.0 mm
at 2000 μg/mL against P. aeruginosa.
Meanwhile, Table 2 depicts that compounds 4b, 5e, 5f,
and 5g showed excellent inhibitory effect against the
growth of P. oryzihabitans with inhibition zone of 15.3,
15.6, 14.0, and 14.0 mm as compared with standard Cipro-
floxacin (37.3 mm) at 2000 μg/mL. It was found that there
was a steady decrease in the zone of inhibition of com-
pound with decrease in concentration from 2000 to 250
μg/mL. Alternatively, compounds 5a, 5b, 5c, and 5d, bear-
ing different alkyl groups at N‐1 position, significantly
attenuated the inhibition zone with increasing alkyl chain
length. However, none of the tested compounds were
found to be as effective as the standard drug Ciprofloxacin.
Average Diameter of Growth Inhibition Zone
(mm) at Different Concentrations (μg/mL)
Compounds 2000
1500
1000
500
250
1
10.0
12.6
15.3
13.0
13.0
12.0
10.6
11.0
15.6
14.0
14.0
12.6
9.0
12.0
13.0
12.3
12.0
11.0
9.6
8.3
10.0
11.6
11.0
10.3
10.0
9.0
7.3
9.3
6.0
8.3
9.3
9.3
7.6
7.3
7.3
6.3
10.3
9.0
8.3
7.0
26.0
4a
4b
4c
5a
5b
5c
5d
5e
5f
10.0
10.0
9.3
8.3
8.0
10.0
12.6
13.0
12.0
11.0
35.0
1.63
8.0
7.3
11.6
11.3
11.3
11.0
31.3
1.74
11.0
10.0
9.0
5g
5h
8.3
Ciprofloxacin 37.3
28.0
CD (P = .05) 1.54
1.67
1.91
Note. CD: critical difference at P = 5%.
MIC of indole 1 and its derivatives 4a‐c and 5a‐h against
bacterial strains P. aeruginosa and P. oryzihabitans is
presented in Table 3. Biological screening experiment
demonstrated that compounds substituted with electron‐
withdrawing groups showed better activity as compared
with compounds bearing long alkyl chains at N‐1 position.
TABLE 1 Effect of different concentrations of indole (1) and its
derivatives (4a‐c) and (5a‐h) on growth of Pseudomonas aeruginosa
TABLE 3 Minimum inhibitory concentration of indole 1 and its
derivatives 4a‐c and 5a‐h against Pseudomonas aeruginosa and
Pseudomonas oryzihabitans
Average Diameter of Growth Inhibition Zone
(mm) at Different Concentrations (μg/mL)
Compounds 2000
1500
1000
500
250
Minimum Inhibitory Concentration, μg/mL
1
10.0
11.0
13.0
11.6
13.6
13.3
11.6
11.0
14.0
13.3
12.0
12.0
9.0
10.3
12.0
11.0
11.6
11.0
10.0
9.6
8.0
9.6
7.0
9.0
6.0
8.0
9.0
9.0
7.0
7.3
0.0
0.0
9.6
8.0
9.0
8.0
21.0
Compounds P. aeruginosa
P. oryzihabitans
4a
4b
4c
5a
5b
5c
5d
5e
5f
1
210
190
120
160
180
170
310
330
100
130
150
180
1
220
160
110
120
150
160
180
190
90
10.6
10.3
9.0
9.3
4a
9.6
4b
8.0
4c
9.6
9.0
5a
9.6
8.0
5b
8.0
7.6
5c
13.0
11.6
11.0
11.0
32.0
1.49
11.6
10.6
10.3
9.3
10.0
10.0
10.0
9.0
5d
5e
5g
5h
5f
110
130
170
2
5g
Ciprofloxacin 35.0
26.6
1.25
25.3
5h
CD (P = .05) 1.51
1.49
1.44
Ciprofloxacin
Note. CD: critical difference at P = 5%.

4
JAIN ET AL.
Among all synthesized derivatives, 5e exhibited the lowest
MIC of 100 and 90 μg/mL against both tested strains,
respectively. Compounds 5g and 5h, having the same butyl
chain at N‐1 position but different positions of electron‐
withdrawing nitro group on benzene ring at ortho and para
positions, resulted in significant changes in inhibitory
effect with MIC value of 150 and 180 μg/mL against
P. aeruginosa and MIC of 130 and 170 μg/mL against
P. oryzihabitans.
addition, dependency of indole 1 and its derivatives 4a‐c
and 5a‐h with respect to each other and calculation of
average diameter of zone of inhibition against bacterial
strains P. aeruginosa and P. oryzihabitans were analyzed
for each compound using Tukey's B test (Table 4).
4 | CONCLUSIONS
Statistical analysis of indole and its derivatives was
carried out using Factorial CRD test, and critical differ-
ence was recorded for all tested compounds. All the com-
pounds vary significantly at different concentrations. In
N‐alkylation of indole derivatives by using base sodium
hydride and solvent DMF involves single‐step reactions
with easy analysis of reaction products. Contrary to the
other reactions of N‐1 alkylation, which require use of
hazardous bases, exorbitant catalyst, coupling reagents,
and multistep reaction procedures, this procedure is quite
simple and cost effective as it does not purify by using col-
umn chromatography and product can be recovered by
simple filtration and recrystallization methods. From the
antimicrobial assay, it was concluded that compounds
substituted with short alkyl chains and halogens are more
effective against both the Gram‐negative strains. Thus,
the compound 5e, ie. 2‐(1‐(3‐bromopropyl)‐1H‐indol‐3‐
yl)‐N‐(2‐nitrophenyl)‐2‐oxoacetamide was found to be
most effective antimicrobial agent against tested strains.
While among oxoacetamide derivatives, 4b 2‐(1H‐indol‐
TABLE 4 Comparative effects of indole 1 and its derivatives 4a‐c
and 5a‐h against bacterial strain Pseudomonas aeruginosa and
Pseudomonas oryzihabitans
Diameter of Zone of Inhibition, mm
Compounds
P. aeruginosa
P. oryzihabitans
1
8.00d
9.60c
8.13f
4a
4b
4c
5a
5b
5c
5d
5e
5f
10.46cd
11.86ab
11.13bc
10.46cd
9.73de
8.93ef
10.80b
10.33bc
9.86bc
10.06bc
7.86d
3‐yl)‐N‐(2,3,5‐trichlorophenyl)‐2‐oxoacetamide
was
proved to be most effective drug.
The results of antimicrobial potential of the synthe-
sized derivatives revealed that the antimicrobial potential
is greatly affected by the nature of substituents present in
the compounds. N‐substituted indole derivatives with
halogen substituents at the end of alkyl chain and in
oxoacetamide moiety account for their better activity
because of the electron‐withdrawing nature of chloro
and bromo groups, which are responsible for the decrease
in electron density in the indolyl ring. Literature also
witnessed that the presence of electron‐withdrawing
groups leads to increase in acidic character in the synthe-
sized derivatives, which in turn strongly inhibits the bac-
terial growth.[37,38]
7.26d
8.53f
11.66a
10.73b
10.46bc
9.86bc
12.26a
11.46abc
10.86bc
9.60de
5g
5h
Note. Values followed with different superscripts are significantly different,
and compounds with similar alphabets are nonsignificant to each other.
5 | EXPERIMENTAL SECTION
Melting points of various indole derivatives were recorded
with the help of digital melting point apparatus in open
1
capillaries. HNMR and 13CNMR spectral studies of syn-
thesized compounds were carried out using solvents
DMSO‐d6 and CDCl3 on a BRUKER AVANCE II and
JEOL‐JNM‐ECS 400 MHz and 100 MHz NMR spectrome-
ters. IR spectral studies of the indole derivatives were car-
ried out on a Perkin Elmer Spectrum Two‐IR Fourier‐
Transform spectrophotometer using KBr pellets, ranging
FIGURE 2 UV‐visible spectra of indole derivatives [Color figure
can be viewed at wileyonlinelibrary.com]

JAIN ET AL.
5
1
from 400 to 4000 cm−1. The mass spectrum data were col-
lected using Calimero instrument operating in ESI mode.
(N─H str), and 3354 (N─H str) cm−1. HNMR (DMSO‐
d6, 400 MHz) δ: 7.29‐7.33 (m, 2H, Ar─H), 7.55‐7.59 (m,
1H, Ar─H), 8.03 (s, 1H, Ar─H), 8.24‐8.28 (m, 1H, Ar─H),
8.35 (s, 1H, Ar─H), 8.89 (s, 1H, Ar─H), 10.36 (bs, 1H,
D2O exchangeable ─NH), and 12.44 ppm (bs, 1H, D2O
exchangeable ─NH). 13CNMR (DMSO‐d6, 100 MHz) δ:
112.12, 112.71, 122.60, 122.68, 123.54, 125.50, 126.15,
126.26, 128.13, 128.25, 132.59, 133.88, 136.52, 138.69,
163.96, and 182.79 ppm. Anal. Calcd. for C16H9Cl3N2O2
(%): C, 52.28; H, 2.47; N, 7.62. Found: C, 51.80; H, 2.55;
N, 7.14. MS (ESI): m/z 368.9 (M + 1).
5.1 | General procedure for synthesis of
oxoacetamide derivatives of indole (4a‐c)
A dropwise addition of oxalyl chloride (2) (8.5 mmol) was
made with the help of a syringe to the stirring solution of
indole (1) (8.5 mmol) dissolved in dry diethyl ether (15
mL), taken in a round‐bottom flask (RBF) at 0°C. The
yellow colored product (3) so formed was immediately fil-
tered, press dried, and dissolved in dry ACN (10 mL) taken
in another RBF (100 mL). A slow addition of base K2CO3
(6.2 mmol) was made with continuous stirring at 0°C. Fur-
ther, aromatic amines (6.2 mmol) dissolved in dry ACN (10
mL) was added dropwise, and the mixture was stirred con-
tinuously till the completion of the reaction (TLC, 3 to 6
hours). After completion of the reaction, the reaction was
quenched with brine and extracted from ethyl acetate (3
× 60 mL). The collected ethyl acetate extract was dried over
anhydrous sodium sulfate and mixture was evaporated
under reduced pressure, and recrystallization from dichlo-
romethane offered the pure products (4a‐c).
5.1.3 | 2‐(1H‐Indol‐3‐yl)‐N‐(4‐nitrophenyl)‐
2‐oxo acetamide (4c)
Brown crystalline solid, Rf: 0.75 (benzene/ethylacetate),
Yield: 85%, dichloromethane, m.p. 225°C to 227°C. IR
(KBr) υmax: 1241 (C─N str), 1327 (N─O str), 1488 (C═C
str), 1533 (N═O str), 1630 (C═O str), 1684 (C═O str),
3342 (N─H str), and 3374 (N─H str) cm−1 1HNMR
.
(DMSO‐d6, 400 MHz) δ: 6.46 (s, 2H, Ar─H), 6.59‐6.62
(m, 2H, Ar─H), 7.27‐8.80 (m, 5H, Ar─H), 11.15 (bs, 1H,
D2O exchangeable –NH), and 12.27 ppm (bs, 1H, D2O
exchangeable –NH). 13CNMR (DMSO‐d6, 100 MHz) δ:
112.25, 113.23, 120.67, 121.67, 123.36, 124.22, 125.28,
126.57, 136.92, 139.28, 143.48, 144.74, 163.42, and 181.46
ppm. Anal. Calcd. for C16H11N3O4 (%): C, 62.17; H, 3.72;
N, 13.45. Found: C, 61.84; H, 3.56; N, 13.64. MS (ESI):
m/z 310.1 (M + 1).
5.1.1 | 2‐(1H‐Indol‐3‐yl)‐N‐(2‐nitrophenyl)‐
2‐oxoacetamide (4a)
Yellow crystalline solid, Rf: 0.6 (benzene/ethylacetate),
Yield: 92%, methanol, m.p. 270°C to 272°C. IR (KBr) υmax
:
1238 (C─N str), 1335 (N─O str), 1488 (C═C str), 1575
(N═O str), 1605 (C═O str), 1704 (C═O str), 3064 (═C─H
5.2 | General procedure for N‐1 alkylation
of indole derivatives (5a‐h)
1
str), 3313 (N─H str), and 3384 (N─H str) cm−1. HNMR
(DMSO‐d6, 400 MHz) δ: 7.29‐7.32 (m, 2H, Ar─H), 7.41
(t, J = 7.64 Hz, 1H, Ar─H), 7.56‐7.58 (m, 1H, Ar─H),
7.82 (t, J = 7.80 Hz, 1H, Ar─H), 8.17‐8.19 (d, J = 8.24
Hz, 1H, Ar─H), 8.29‐8.32 (m, 1H, Ar─H), 8.41‐8.43 (m,
1H, Ar─H), 8.91 (s, 1H, Ar─H), 11.66 (bs, 1H, D2O
exchangeable –NH), and 12.39 ppm (bs, 1H, D2O
exchangeable ─NH). 13CNMR (DMSO‐d6, 100 MHz) δ:
111.58, 112.75, 121.35, 122.96, 123.47, 123.78, 125.19,
125.59, 126.28, 131.75, 135.06, 136.26, 139.16, 139.84,
161.19, and 179.30 ppm. Anal. Calcd. for C16H11N3O4
(%): C, 62.14; H, 3.58; N, 13.59. Found: C, 62.98; H,
3.75; N, 13.69. MS (ESI): m/z 310.1 (M + 1).
To the solution of 3‐substituted indole (4a‐c) (1.01 mmol)
in dry DMF, slow addition of activated sodium hydride
(15 mmol) was made and allowed to stir for 5 minutes
at room temperature. Sodium hydride was activated by
giving the washing of hexane to remove the paraffin oil
from it. Further, alkyl halide (1.01 mmol) was added
slowly, and completion of reaction was monitored with
the help of TLC (10 to 15 minutes). After completion of
reaction, the reaction mixture was poured on the satu-
rated ice cold solution, and precipitates so formed were
filtered and washed with water, and recrystallization
from dichloromethane offered the pure products (5a‐h).
5.1.2 | 2‐(1H‐Indol‐3‐yl)‐N‐(2,3,5‐
trichlorophenyl)‐2‐oxoacetamide (4b)
5.2.1 | 2‐(1‐Butyl‐1H‐indol‐3‐yl)‐N‐(2‐nitro-
phenyl)‐2‐oxoacetamide (5a)
Pale yellow crystalline solid, Rf: 0.7 (benzene/
ethylacetate), Yield: 80%, dichloromethane, m.p. 268°C
to 270°C. IR (KBr) υmax: 677 (C─Cl str), 1240 (C─N str),
1490 (C═C str), 1621 (C═O str), 1686 (C═O str), 3317
Yellow crystalline solid, Rf: 0.72 (ethylacetate/hexane),
Yield: 75%, dichloromethane, m.p. 95°C to 97°C. IR
(KBr) υmax: 1235 (C─N str), 1343 (N─O str), 1484 (C═C

6
JAIN ET AL.
str), 1570 (N═O str), 1629 (C═O str), 1705 (C═O str),
2868 (─C─H str), 2961 (═C─H str), and 3284 (N─H str)
8.94 (s, 1H, Ar─H), and 12.13 ppm (bs, 1H, D2O
exchangeable –CONH). 13CNMR (DMSO‐d6, 100 MHz)
δ: 14.08, 22.61, 26.86, 29.10, 29.70, 31.74, 47.60, 110.26,
111.51, 121.78, 122.95, 123.01, 123.98, 124.04, 127.86,
133.67, 135.59, 135.63, 137.29, 140.90, 140.95, 161.33,
and 178.05 ppm. Anal. Calcd. for C24H27N3O4 (%): C,
68.39; H, 6.46; N, 9.97. Found: C, 67.52; H, 6.93; N, 9.18.
MS (ESI): m/z 421.9 (M + 1).
1
cm−1. HNMR (DMSO‐d6, 400 MHz) δ: 0.97 (t, J = 7.4
Hz, 3H, Me), 1.38‐1.43 (m, 2H, CH2), 1.88‐1.95 (m, 2H,
CH2) and 4.21 (t, J = 7.2 Hz, 2H, N─CH2), 7.26‐7.28 (m,
1H, Ar─H), 7.35‐7.42 (m, 3H, Ar─H), 7.69‐7.73 (m, 1H,
Ar─H), 8.27‐8.30 (dd, J = 8.44 Hz, 1H, Ar─H), 8.51‐8.53
(m, 1H, Ar─H), 8.89‐8.91 (dd, J = 8.48 Hz, 1H, Ar─H),
8.97 (s, 1H, Ar─H), 12.16 ppm (bs, 1H, D2O exchangeable
–CONH). 13CNMR (DMSO‐d6, 100 MHz) δ: 13.63, 20.11,
31.74, 47.34, 110.26, 111.56, 121.83, 123.02, 123.72,
124.04, 126.13, 127.88, 133.66, 135.61, 136.40, 137.38,
140.94, 161.39, and 178.12 ppm. Anal. Calcd. for
C20H19N3O4 (%): C, 65.74; H, 5.24; N, 11.50. Found: C,
64.72; H, 5.69; N, 11.98. MS (ESI): m/z 366.1 (M + 1).
5.2.4 | 2‐(1‐Decyl‐1H‐indol‐3‐yl)‐N‐(2‐nitro-
phenyl)‐2‐oxoacetamide (5d)
Pale‐yellow crystalline solid, Rf: 0.72 (ethylacetate/hex-
ane), Yield: 80%, dichloromethane, m.p. 72°C to 75°C.
IR (KBr) υmax: 1270 (C─N str), 1334 (N─O str), 1499
(C═C str), 1572 (N═O str), 1606 (C═O str), 1697 (C═O
str), 2851 (─C─H str), 2916 (═C─H str) and 3274 (N─H
5.2.2 | 2‐(1‐Hexyl‐1H‐indol‐3‐yl)‐N‐(2‐
nitrophenyl)‐2‐oxoacetamide (5b)
1
str) cm−1. HNMR (DMSO‐d6, 400 MHz) δ: 0.86 (t, J =
7.08 Hz, 3H, Me), 1.24‐1.37 (m, 14H, 7 × CH2), 1.89‐1.93
(m, 2H, CH2), 4.17 (t, J = 7.28 Hz, 2H, CH2), 7.24‐7.26
(m, 1H, Ar─H), 7.33‐7.40 (m, 3H, Ar─H), 7.67‐7.71 (m,
1H, Ar─H), 8.25‐8.28 (dd, J = 8.4 Hz, 1H, Ar─H), 8.48‐
8.51 (m, 1H, Ar─H), 8.87‐8.90 (dd, J = 8.44 Hz,1H,
Ar─H), 8.95 (s, 1H, Ar─H), 12.14 ppm (bs, 1H, D2O
exchangeable –CONH). 13CNMR (DMSO‐d6, 100 MHz)
δ: 14.12, 22.67, 26.85, 29.14, 29.26, 29.43, 29.49, 29.70,
31.85, 47.60, 110.26, 111.52, 121.78, 123.01, 123.68,
123.98, 124.05, 126.08, 127.87, 133.67, 135.61, 136.38,
137.31, 140.94, 161.34, and 178.06 ppm. Anal. Calcd. for
C26H31N3O4 (%): C, 69.47; H, 6.95; N, 9.35. Found: C,
68.75; H, 6.39; N, 9.68. MS (ESI): m/z 450.2 (M + 1).
Yellow crystalline solid, Rf: 0.69 (ethylacetate/hexane),
Yield: 85%, chloroform, m.p. 90°C to 92°C. IR (KBr) υmax
:
1271 (C─N str), 1331 (N─O str), 1496 (C═C str), 1571
(N═O str), 1602 (C═O str), 1695 (C═O str), 2865 (─C─H
str), 2926 (═C─H str), and 3286 (N─H str) cm−1.1HNMR
(DMSO‐d6, 400 MHz) δ: 0.89 (t, J = 6.92 Hz, 3H, Me),
1.27‐1.38 (m, 6H, 3 × CH2), 1.87‐1.94 (m, 2H, CH2), 4.16
(t, J = 7.28 Hz, 2H, N─CH2), 7.21‐7.25 (m, 1H, Ar─H),
7.30‐7.39 (m, 3H, Ar─H), 7.66‐7.70 (m, 1H, Ar─H),
8.24‐8.26 (dd, J = 8.44 Hz, 1H, Ar─H), 8.47‐8.50 (m, 1H,
Ar─H), 8.86‐8.88 (dd, J = 8.44 Hz, 1H, Ar─H), 8.94 (s,
1H, Ar─H), and 12.13 ppm (bs, 1H, D2O exchangeable –
CONH). 13CNMR (DMSO‐d6, 100 MHz) δ: 14.06, 22.55,
26.60, 29.76, 31.37, 47.69, 110.33, 111.62, 121.88, 123.09,
123.77, 124.10, 124.15, 126.18, 133.74, 135.68, 140.98,
161.45, and 178.17 ppm. Anal. Calcd. for C22H23N3O4
(%): C, 67.16; H, 5.89; N, 10.68. Found: C, 66.89; H,
6.02; N, 10.65. MS (ESI): m/z 394.2 (M + 1).
5.2.5 | 2‐(1‐(3‐Bromopropyl)‐1H‐indol‐3‐
yl)‐N‐(2‐nitrophenyl)‐2‐oxoacetamide (5e)
Yellow crystalline solid, Rf: 0.72 (ethylacetate/hexane),
Yield: 82%, dichloromethane, m.p. 120°C to 122°C. IR
(KBr) υmax: 562 (C─Br str), 1261 (C─N str), 1332 (N─O
str), 1499 (C═C str), 1572 (N═O str), 1625 (C═O str),
5.2.3 | 2‐(1‐Octyl‐1H‐indol‐3‐yl)‐N‐(2‐nitro-
phenyl)‐2‐oxoacetamide (5c)
1704 (C═O str), and 3287 (N─H str) cm−1 1HNMR
.
(DMSO‐d6, 400 MHz) δ: 2.35‐2.38 (m, 2H, CH2), 3.51 (t,
J = 6.52 Hz, 2H, CH2─Br), 4.48 (t, J = 6.92 Hz, 2H,
N─CH2), 7.36‐7.45 (m, 3H, Ar─H), 7.70‐7.72 (m, 1H,
Ar─H), 7.81‐7.85 (m, 1H, Ar─H), 8.17‐8.19 (dd, J = 8.36
Hz, 1H, Ar─H), 8.32‐8.37 (m, 2H, Ar─H), 8.97 (s, 1H,
Ar─H), and 11.61 ppm (bs, 1H, D2O exchangeable –
CONH). 13CNMR (DMSO‐d6, 100 MHz) δ: 31.14, 32.31,
45.07, 110.81, 111.22, 121.72, 123.35, 123.43, 123.97,
125.19, 125.61, 126.93, 131.79, 135.10, 136.12, 139.71,
141.56, 160.94, and 178.86 ppm. Anal. Calcd. for
C19H16BrN3O4 (%): C, 53.04; H, 3.75; N, 9.77. Found: C,
52.97; H, 3.36; N, 9.56. MS (ESI): m/z 432 (M + 1).
Yellow crystalline solid, Rf: 0.68 (ethylacetate/hexane),
Yield: 86%, chloroform, m.p. 82°C to 85°C. IR (KBr) υmax
:
1268 (C─N str), 1330 (N─O str), 1495 (C═C str), 1570
(N═O str), 1628 (C═O str), 1701 (C═O str), 2851 (─C─H
str), 2925 (═C─H str), and 3309 (N─H str) cm−1. 1HNMR
(DMSO‐d6, 400 MHz) δ: 0.86 (t, J = 7.04 Hz, 3H, Me),
1.25‐1.37 (m, 10H, 5 × CH2), 1.87‐1.95 (m, 2H, CH2),
4.17 (t, J = 7.32 Hz, 2H, N─CH2), 7.22‐7.26 (m, 1H,
Ar─H), 7.31‐7.39 (m, 3H, Ar─H), 7.67‐7.71 (m, 1H,
Ar─H), 8.24‐8.27 (dd, J = 8.44 Hz, 1H, Ar─H), 8.48‐8.50
(m, 1H, Ar─H), 8.87‐8.89 (dd, J = 8.44 Hz, 1H, Ar─H),

JAIN ET AL.
7
2876 (─C─H str), 2933 (═C─H str), and 3316 (N─H str)
5.2.6 | 2‐(1‐(6‐Bromohexyl)‐1H‐indol‐3‐yl)‐
N‐(2‐nitrophenyl)‐2‐oxoacetamide (5f)
1
cm−1. HNMR (DMSO‐d6, 400 MHz) δ: 0.98 (t, J = 7.40
Hz, 3H, Me), 1.38‐1.44 (m, 2H, CH2), 1.89‐1.96 (m, 2H,
CH2), 4.23 (t, J = 7.20 Hz, 2H, N─CH2), 7.37‐7.45 (m,
3H, Ar─H), 7.89‐7.92 (m, 2H, Ar─H), 8.26‐8.29 (m, 2H,
Ar─H), 8.43‐8.46 (m, 1H, Ar─H), 9.03 (s, 1H, Ar─H),
and 9.77 ppm (bs, 1H, D2O exchangeable –NH).
13CNMR (DMSO‐d6, 100 MHz) δ: 13.62, 20.10, 31.73,
47.43, 110.46, 111.40, 119.41, 122.79, 123.88, 124.26,
125.21, 127.80, 136.47, 141.51, 142.70, 144.03, 160.54,
and 178.16 ppm. Anal. Calcd. for C20H19N3O4 (%): C,
65.74; H, 5.24; N, 11.50. Found: C, 64.98; H, 5.79; N,
10.98. MS (ESI): m/z 366.1 (M + 1).
Yellow solid, Rf: 0.72 (ethylacetate/hexane), Yield: 85%,
dichloromethane, m.p. 112°C to 115°C. IR (KBr) υmax
:
564 (C─Br str), 1270 (C─N str), 1332 (N─O str), 1496
(C═C str), 1572 (N═O str), 1629 (C═O str), 1701 (C═O
str), 2880 (─C─H str), 2930 (═C─H str), and 3309
1
(N─H str) cm−1. HNMR (DMSO‐d6, 400 MHz) δ: 1.28‐
1.34 (m, 2H, CH2), 1.37‐1.43 (m, 2H, CH2), 1.73‐1.83 (m,
4H, 2 × CH2), 3.48 (t, J = 6.68 Hz, 2H, CH2─Br), 4.35
(t, J = 7.08 Hz, 2H, N─CH2), 7.33‐7.38 (m, 2H, Ar─H),
7.41‐7.45 (m, 1H, Ar─H), 7.68‐7.70 (m, 1H, Ar─H),
7.81‐7.85 (m, 1H, Ar─H), 8.17‐8.19 (dd, J = 8.32 Hz, 1H,
Ar─H), 8.31‐8.37 (m, 2H, Ar─H), 8.95 (s, 1H, Ar─H),
and 11.60 ppm (bs, 1H, D2O exchangeable –CONH).
13CNMR (DMSO‐d6, 100 MHz) δ: 25.12, 26.98, 29.13,
31.99, 34.96, 46.45, 110.55, 111.39, 121.65, 123.33,
123.37, 123.84, 125.18, 125.61, 126.94, 131.79, 135.07,
136.22, 139.75, 141.49, 161.07, and 178.78 ppm. Anal.
Calcd. for C22H22BrN3O4 (%): C, 55.94; H, 4.69; N, 8.90.
Found: C, 55.19; H, 4.87; N, 8.26. MS (ESI): m/z
472.1 (M + 1).
5.3 | UV‐visible spectral studies
The absorption spectra of synthesized C‐3– and N‐1–
substituted derivatives were recorded in DMSO (4a‐c)
and DCM (5a‐h) as shown in Figure 2. The compound
4a shows an intense broad peak centered at 330 nm and
a weak twin band at 271 and 266 nm. Its para derivative
4c depicts a similar band at almost the same wavelength,
but the trichloro derivative 4b shows a bathochromic
shift in the low energy band by 20 nm (350 nm) probably
due to increased number of electron‐withdrawing groups
being attached. The N‐butyl–substituted derivative 5a of
compound 4a shows a bathochromically shifted band
centered at 350 nm, which is expected because of increase
in the donating ability of the heterocyclic moiety. Similar
bathochromic shift but to a much lower extent is
observed in the compounds 5b‐5f as the chain on nitro-
gen is increased. However, the para nitro–substituted
derivative 5h of 5a depicts a similar band at 350 nm,
whereas its trichloro 5g derivative depicts a bathochromic
shift of 5 nm again because of increased electron‐
accepting tendency of the moiety.
5.2.7 | 2‐(1‐Butyl‐1H‐indol‐3‐yl)‐N‐(2,3,5‐
trichlorophenyl)‐2‐oxoacetamide (5g)
Off‐white crystalline solid, Rf: 0.72 (ethylacetate/hexane),
Yield: 90%, dichloromethane, m.p. 125°C to 127°C. IR
(KBr) υmax: 677 (C─Cl str), 1203 (C─N str), 1497 (C═C
str), 1626 (C═O str), 1695 (C═O str), 2884 (─C─H str),
1
2921 (═C─H str), and 3329 (N─H str) cm−1. HNMR
(DMSO‐d6, 400 MHz) δ: 0.97 (t, J = 7.40 Hz, 3H, Me),
1.36‐1.43 (m, 2H, CH2), 1.88‐1.95 (m, 2H, CH2), 4.21 (t,
J = 7.24 Hz, 2H, N─CH2), 7.34‐7.38 (m, 2H, Ar─H),
7.40‐7.43 (m, 1H, Ar─H), 7.53 (s, 1H, Ar─H), 8.44‐8.46
(m, 1H, Ar─H), 8.77 (s, 1H, Ar─H), 9.01 (s, 1H, Ar─H),
and 10.06 ppm (bs, 1H, D2O exchangeable –CONH).
13CNMR (DMSO‐d6, 100 MHz) δ: 13.71, 20.18, 31.81,
47.47, 110.44, 111.48, 121.71, 122.47, 122.89, 123.89,
124.24, 130.25, 133.43, 136.49, 141.42, 160.25, and 178.06
ppm. Anal. Calcd. for C20H17Cl3N2O2 (%): C, 56.69; H,
4.04; N, 6.61. Found: C, 55.24; H, 4.56; N, 6.23. MS
(ESI): m/z 424 (M + 1).
6 | ANTIMICROBIAL SCREENING
EXPERIMENT
In vitro, antimicrobial evaluation of indole (1) and its syn-
thesized derivatives (4a‐c) and (5a‐h) were carried out
against P. aeruginosa and P. oryzihabitans by using disc
plate method as compared with the standard Ciprofloxa-
cin. The sterilized plates were prepared by pouring 15 to
20 mL of sterilized nutrient agar medium in sterilized petri
plates, and plates were allowed to solidify for 2 to 3 hours.
Afterwards, suspension of 24‐hour old broth containing
test organisms was spread on the medium plates. All tested
compounds were serially diluted by dissolving them in
DMSO. HiMedia sterile discs were dipped in solution of test
compounds and placed on the medium under aseptic con-
ditions. Sterilized discs moistened with DMSO served as
5.2.8 | 2‐(1‐Butyl‐1H‐indol‐3‐yl)‐N‐(2‐nitro-
phenyl)‐2‐oxoacetamide (5h)
White crystalline solid, Rf: 0.72 (ethylacetate/hexane),
Yield: 90%, dichloromethane, m.p. 120°C to 123°C. IR
(KBr) υmax: 1204 (C─N str), 1343 (N─O str), 1494 (C═C
str), 1597 (N═O str), 1624 (C═O str), 1685 (C═O str),

8
JAIN ET AL.
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control. All the samples were done in triplicates. Further,
the prepared plates were kept in incubator at 28 2°C.
The zone of inhibition (mm) and MIC was recorded after
24 to 48 hours. The inhibition of pathogenic bacteria strain
on medium containing the test compound was also com-
pared with the inhibition on the plates containing no tested
compound as standard.
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ACKNOWLEDGMENTS
We gratefully acknowledge Punjab Govenment (section
P‐5B‐1972) and Sophisticated Analytical Instrumentation
Facility, Panjab University, Chandigarh for analysis of
compounds reported in this article.
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Divya Utreja https://orcid.org/0000-0003-2286-9375
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