1,1'-carbonyldiimidazole (cdi) mediated facile synthesis, structural characterization, antimicrobial activity, and in-silico studies of coumarin- 3-carboxamide derivatives

86

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Medicinal Chemistry, 2018, 14, 86-101

RESEARCH ARTICLE

ISSN: 1573-4064

eISSN: 1875-6638

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1,1'-Carbonyldiimidazole (CDI) Mediated Facile Synthesis, Structural

Characterization, Antimicrobial Activity, and in-silico Studies of Couma-

rin-3-carboxamide Derivatives

Uzma Salar¹, Khalid M. Khan^1,*, Muhammad I. Fakhri¹, Shafqat Hussain^1,2, Saima Tauseef³,

Shagufta Ameer³, Abdul Wadood⁴, Huma Khan⁴and Shahnaz Perveen⁵

¹H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Kara-

chi, Karachi-75270, Pakistan; ²Deparment of Chemistry, Karakoram International University Gilgit, Pakistan;

³Department of Microbiology, Federal Urdu University of Arts, Sciences and Technology, Gulshan-e-Iqbal Campus,

Karachi-75370, Pakistan; ⁴Department of Biochemistry, Computational Medicinal Chemistry Laboratory, UCSS, Abdul

5

Wali Khan University Mardan, Mardan, Pakistan; PCSIR Laboratories Complex, Karachi, Shahrah-e-Dr. Salimuz-

zaman Siddiqui, Karachi-75280, Pakistan

Abstract: Background: Despite the availability of a variety of antibacterial agents, re-emergence of

pathogenic bacteria is still a serious medical concern. So, identification of new, safer, and selective an-

tibacterial agents is the key interest in the medicinal chemistry research.

Method: To explore the antimicrobial activity of coumarin-3-carboxamides for a range of bacterial and

fungal strains, twenty eight derivatives were synthesized by the reaction of coumarin-3-carboxylic acid

with a variety of aniline derivatives in the presence of 1,1'-carbonyldiimidazole (CDI). All compounds

were structurally characterized by different spectroscopic techniques EI-MS, HREI-MS, ¹H-NMR,

¹³C-NMR, and evaluated for antimicrobial activities (antibacterial and antifungal).

A R T I C L E H I S T O R Y

Results: A number of compounds showed good to weak antibacterial activity against various strains of

Gram-positive and Gram-negative bacteria. Amongst them, compound 28 displayed noticeable inhibi-

Received: February 13, 2017

Revised: June 02, 2017

tion against five strains of Gram-positive (Bacillus subtilis, Corynebacterium xerosis, Staphylococcus

Accepted: June 02, 2017

aureus, Streptococcus faecalis, and MRSA) and four strains of Gram-negative bacteria (Klebsiella

DOI:

pneumoniae, Pseudomonas aeruginosa, Enterobacter aerogene, and Shigella dysenteria). However,

10.2174/1573406413666170623083116

none of the compounds showed antifungal activity against tested fungi. MIC values were determined

for most of the active compounds 2, 15, and 28 against particular bacterial cultures. In silico studies

were performed on the most active compound 28 in order to specify and verify the target for antibacte-

rial activity of synthetic coumarin-3-carboxamide derivatives. The cytotoxicity of these compounds on

mammalian cells is unknown yet but we are planning to carry out research on the cytotoxic aspect of

these compounds in future.

Conclusion: The newly identified compounds may serve as lead molecules for the future research re-

garding the identification of new antibacterial agents.

Keywords: Antibacterial, antifungal, coumarin-3-carboxamide, 1,1'-carbonyldiimidazole (CDI), in silico studies, synthesis.

1. INTRODUCTION

Identification of novel and safer medication of various infec-

tious diseases is a challenging task due to the chemical di-

versity and diverse mechanisms of actions of drugs [3]. So,

finding new antibacterial agents is an important area of re-

search in order to overcome this serious medical concern [4].

The exploration for novel, selective, and nontoxic anti-

bacterial agents is the key interest in the medicinal chemistry

[1, 2]. A number of antibacterial agents are available in the

market, but re-emergence of pathogenic bacteria is still raising.

Coumarin-3-carboxamide derivatives were reported to

have diverse spectrum of biological activities such as anti-

cancer [5, 6], antioxidant [7, 8], and antiinflammatory activi-

ties [9]. This class also possess the inhibitory effect of cho-

linesterase [10], acetylcholinesterase [11], ꢀ-secretase (BACE1)

*Address correspondence to this author at the H.E.J. Research Institute of

Chemistry, International Center for Chemical and Biological Sciences,

University of Karachi, Karachi-75270, Pakistan; Tel: 00922134824910;

Fax: 00922134819018; E-mails: khalid.khan@iccs.edu;

drkhalidhej@gmail.com

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1,1'-Carbonyldiimidazole (CDI) Mediated Facile Synthesis

Medicinal Chemistry, 2018, Vol. 14, No. 1 87

[12], monoamine oxidase [13], FXIIa [14], and mycobacte-

rium tuberculosis DNA [15]. Our group has been working on

the synthesis and biological evaluation of coumarin scaffolds

since one and a half decade [16-23], and had reported the

antimicrobial activity of coumarin and isocoumarin scaffolds

(Fig. 1) [20, 21]. Antimicrobial activity of coumarin-3-

carboxamides has been reported by Chimenti et al. [24],

however, the reported derivatives are different except

compound 8. Similarly, they used few strains of Gram-

positive, Gram-negative bacteria, and fungi. Whilst, in the

current study, we used a variety of microbial strains to fur-

ther explore antimicrobial activity of this class.

electron impact (EI) on MAT 312 and MAT 113D mass

spectrometer. The ¹H- and ¹³C-NMR were recorded on

Avance Bruker AM spectrometer, operating at 300, 400, and

500 MHz instrument. The chemical shift values are present-

ed in ppm (ꢀ), relative to tetramethylsilane (TMS) as an in-

ternal standard and the coupling constant (J) are in Hz. Mul-

tiplicities are reported as singlet (s), doublet (d), triplet (t),

doublet of doublets (dd), doublet of triplets (dt), quartet (q)

or multiplet (m). Melting points of the compounds were de-

termined on Stuart^®SMP10 melting point apparatus.

3. RESULTS AND DISCUSSION

3.1. Chemistry

Me

Me Me

Coumarin-3-carboxamide derivatives 1-28 were synthe-

sized from coumarin-3-carboxylic acid by following one-step

transformation. Coumarin-3-carboxylic acid was coupled with

different derivatives of aniline in the presence of CDI as a

coupling agent (Scheme 1). The carboxylic functional group

was readily reacted with 1,1'-carbonyldiimidazole to form 3-

imidazolyl coumarin intermediate which reacted with aniline

derivatives to afford a variety of coumarin-3-carboxamide

derivatives 1-28 (Scheme 1, Table 1). Synthetic derivatives

were structurally characterized by different spectroscopic

RO

O

RO

Cl

O

Cl

O

Fig. (1). Coumarin and isocoumarin based antibacterial and anti-

fungal leads [18, 19].

1

techniques, such as EI-MS, HREI-MS, H-NMR, and ¹³C-

NMR.

Generally, Knoevenagel condensation of active meth-

ylene containing compounds, such as N-substituted cyano-

acetamides and salicylaldehyde in basic conditions, was used

to synthesize N-substituted coumarin-3-carboxamides [9]. A

circuitous method also employed by condensation of malo-

nic esters with salicylaldehydes, followed by hydrolysis,

thionyl chloride mediated halogenation, and then substitution

with amines [12-14]. In the current study, we avoided the

two-step synthesis of coumarin-3-carboxamide, via halogen-

ation with thionyl chloride followed by substitution, and

preferred to adopt the direct one-step transformation of cou-

marin-3-carboxylic acid into amide by using 1,1'-carbonyl

diimidazole (CDI) as coupling agent. Thus, this report por-

trayed the CDI-mediated one-pot synthesis of coumarin-3-

carboxamide derivatives (1-28) (Fig. 2), their structure char-

acterization, and evaluation of their antibacterial and anti-

fungal activities in vitro.

O

CDI , Et₃N

CH₃CN

R

OH

NH

+

H₂N

R

1-28

O

Scheme 1. Synthesis of coumarin-3-carboxamide derivatives 1-28.

3.2. Characteristic Spectral Features of Representative

Compound 8

Deuterated DMSO-d₆was used as a solvent for recording

the H- and ¹³C-NMR spectra of N-(4-methylphenyl)-2-oxo-

1

2H-chromene-3-carboxamide 8. In ¹H-NMR spectrum, amid-

ic NH was resonated at ꢀ 10.59 as the most downfield sin-

H

glet. H-4 of coumarin ring was resonated at ꢀ 8.91 and ap-

peared as downfield singlet due to the electro^Hn withdrawing

effect of carbonyl moiety. H-5, H-6, H-7, and H-8 were re-

3'

sonated in the usual aromatic region ꢀ 7.49-8.02 Hz. H-

4'

2'

H

O

R

2'/H-6' and H-3'/H-5' of aryl ring, were resonated at ꢀ 7.62

5

4

H

10

9

5'

1'

(d, J_2',3'/6',5'= 8.4 Hz) and 7.20 (d, J_3',2'/5',6'= 8.1 Hz), repecti-

6

7

N

H

3

6'

vely, and appeared as doublets. Methyl protons was appeared

2

as singlet at ꢀ 2.28 (Fig. 3).

O

H

8

1

Fig. (2). General structure of synthetic derivatives 1-28 with num-

7.56 (d, J_8,7= 8.4 Hz)

bering.

H

7.79 (t, J_7,6= J_7,8= 7.2 Hz)

1

8

H

O

7.62 (d, J_2',3'/6',5'= 8.4 Hz)

2

7

6

10.59 (s, 1H)

H

2. MATERIALS AND METHODS

H

3

2'

^{= 7.5 H}H^z)

7.49 (t, J_6,5= J_6,7

N

H

1'

Analytical grade reagents and solvents were purchased

from Sigma-Aldrich, USA and used as received. Thin layer

chromatography (TLC) was performed on pre-coated silica

gel aluminum plates (Kieselgel 60, 254, E. Merck, Germa-

ny). TLC chromatograms were visualized under ultraviolet

light at 254 and 366 nm. Mass spectra were recorded under

7.20 (d, J_{3',5'/ 2',6'}= 8.1 Hz)

4

3'

4'

5

6'

H

O

8.02 (d, J_5,6= 6.9 Hz)

H

Me

8.91 (s, 1H)

5'

2.28 (s, 3H)

7.20 (d, J_{3',5'/ 2',6'}= 8.1 Hz)

7.62 (d, J_{2',6'/ 3',5'}= 8.4 Hz)

H

Fig. (3). ¹H-NMR chemical shifts of compound 8.

88 Medicinal Chemistry, 2018, Vol. 14, No. 1

Salar et al.

Table 1. Substitution “R” on Coumarin-3-carboxamide derivatives 1-28.

Compound

R

Compound

R

Compound

21

R

1

11

Br

F

OMe

2

3

12

13

22

23

MeO

F

OMe

Me

Cl

F

Me

Bu

Cl

OMe

4

5

14

15

24

25

F

Br

Et

OMe

Me

6

7

16

17

18

19

20

26

27

28

-

Cl

OMe

OBu

NO₂

Me

I

Me

8

NO₂

F

Me

OMe

9

-

F₃C

Me

10

-

Me

SMe

1,1'-Carbonyldiimidazole (CDI) Mediated Facile Synthesis

Medicinal Chemistry, 2018, Vol. 14, No. 1 89

118.8

CO₂to yield cations at m/z 145 and m/z 101, respectively

(Fig. 5).

154.5

O

161.8

117.2

134.5

125.4

H

N

129.6

120.5

134.2

116.9

159.1

135.1

3.3. Antimicrobial Activity In Vitro

129.9

148.7

O

Me ^20.9

129.6

3.3.1. Antibacterial Activity

120.5

All synthetic compounds 1-28 were screened for their

antimicrobial activity against Gram-positive and Gram-

negative bacterial strains by using standard disc diffusion

method [25] keeping DMSO as a control. Results are shown

in Tables 2, and 3 as inhibition zone diameter (mm). Bacillus

subtilis, Corynebacterium xerosis, Staphylococcus aureus,

Streptococcus faecalis, multidrug resistant Staphylococcus

aureus (MRSA), Corynebacterium diphtheria, and Bacillus

ceresus were used as Gram-positive bacterial strains.

Fig. (4). ¹³C-NMR chemical shifts of compound 8.

Total fifteen carbon signals were appeared in the ¹³C-

NMR broad-band decoupled spectrum including seven quar-

ternary carbons, nine methine carbons (C2'/6' and C3'/5' were

appeared as two signals), and one methyl carbon. Lactone

and amidic quaternary carbonyl carbons were resonated at ꢀ

161.8 and ꢀ 159.1, respectively, as the most downfield sig^C-

C

nals. Another quaternary carbon was also appeared as down-

field signal at ꢀ 154.5, due to the adjacent electronegative

C

Results depicted in Table 2 showed that compounds with

substitution at 4'-position showed a varying degree of inhibi-

tion as compared to the standard gentamicin. Such as com-

pound 2 with 4'-methoxy substitution, showed 20 mm inhi-

bition against Bacillus subtilis and 18 mm inhibition against

Bacillus ceresus. Similarly, compounds 15 (18 mm inhibi-

tion) and 20 (16 mm inhibition) having 4'-ethyl and 4'-

thiomethyl substitution, respectively, demonstrated good

inhibition, selectively against multidrug resistant Staphylo-

coccus aureus (MRSA). Another compound 26 displayed 17

mm inhibition against Bacillus subtilis and 15 mm inhibition

against Corynebacterium. xerosis. Other 4'-substituted com-

pounds such as 8 and 13 having 4'-methyl and 4'-n-butyl

substitutions, respectively, didn’t show activities against all

the tested strains (Fig. 6).

oxygen. The methine C-4 present at ꢀ position of carbonyl

appeared at ꢀ 148.7. Quaternary C-1^ꢀ, directly attached to

C

nitrogen, resonated at ꢀ 135.1. C-4' which is ipso to the me-

C

thyl group, appeared at ꢀ 134.2. Signals of the remaining

C

carbons of coumarin nucleus appeared in the range of ꢀ

C

116.9-134.5 (Fig. 4).

Compound 8 was subjected to low resolution EI-MS for

the identification of molecular ion peak corresponding to the

formation of the desired compound. EI-MS spectrum of

compound 8 showed the molecular ion peak [M]⁺at m/z 279.

The compound was then also subjected to HREI-MS which

gave the exact mass of the compound with the possible mo-

lecular compositions. Thus, HREI-MS showed the [M]⁺at

279.0906 corresponding to the formula C₁₇H₁₃NO₃calcd

(279.0895). However, the fragmentation pattern observed in

the EI-MS spectrum further confirmed the structure of the

desired compound.

Dimethylated derivatives showed relatively weak activi-

ties against some strains. Amongst them, compound 3 with

3',4'-dimethyl substitutions, showed 7 mm inhibition against

two strains (Bacillus subtilis and MRSA) and 8 mm inhibi-

tion against Streptococcus faecalis. Its structurally similar

analogs compound 9 with 3',4'-dimethyl and 10 with 2',5'-

dimethyl substitutions, displayed 9 mm inhibition against

Corynebacterium diptheriae and Bacillus ceresus, respec-

tively. Similarly, 2',3'-dimethyl substituted derivative 18

showed 6 mm inhibition against MRSA (Fig. 7).

The favourable losses of neutral molecules of carbon

monooxide CO and carbon dioxide CO₂lead to the forma-

tion of radical cations, appeared at m/z 251 and m/z 234, res-

pectively. Molecular ion was further fragmented by the loss

of 4-methyl aniline and yielded a cation at m/z 173 which is

also the base peak. Now this most abundant ion was further

fragmented by the two successive neutral losses of CO and

Me

O

H

N

O

-CO₂

-CO

N

H

HN

Me

O

Me

m/z = 251

m/z = 279

m/z = 234

O

-CO₂

H₂N

-CO

+

Me

O

m/z = 101

m/z = 145

m/z = 173

Fig. (5). Key EI-MS fragmentation of compound 8.

90 Medicinal Chemistry, 2018, Vol. 14, No. 1

Salar et al.

Table 2. Antibacterial activity in vitro against Gram-positive bacteria.

Gram-positive Bacteria

Corynebacte-

rium. xerosis

Staphylococcus

aureus

Staphylococcus

feacalis

Corynebacte-

rium diptheriae

Bacillus

ceresus

Bacillus subtilis

MRSA

Compounds

Inhibition Zone Diameter (mm) of Compounds

1

-

20

7

9

7

-

6

18

-

2

3

-

8

7

8

-

7

8

6

-

4

-

5

-

5

-

7

-

6

-

9

-

9

-

10

-

9

-

12

-

7

6

18

7

6

16

6

-

14

-

15

-

16

-

18

-

19

-

20

-

22

8

6

7

17

10

17

22

-

23

-

6

5

-

24

-

6

7

-

25

-

10

-

7

-

26

15

-

27

28

10

20

25

8

19

25

-

6

-

16

22

19

20

-

Gentamicin

25

22

Keys: - = No zone of inhibition, 8-10 mm = weakly active, 12-14 mm = moderately active, >15 = good activity.

OBu

Et

OMe

O

N

H

N

H

N

H

O

26

15

2

20 mm (Bacillus subtilis)

18 mm (Bacillus ceresus)

17 mm (Bacillus subtilis)

15 mm (Corynebacterium. xerosis)

18 mm (MRSA)

nBu

Me

SMe

O

N

H

N

H

N

H

O

13

No Inhibition

8

20

16 mm (MRSA)

No Inhibition

Fig. (6). Structure activity relationship of compounds 2, 8, 13, 15, 20, and 26.

1,1'-Carbonyldiimidazole (CDI) Mediated Facile Synthesis

Medicinal Chemistry, 2018, Vol. 14, No. 1 91

Me

O

N

H

N

H

Me

O

3

9

10

7 mm (Bacillus subtilis)

8 mm (Staphylococcus feacalis)

7 mm (MRSA)

9 mm (Bacillus ceresus)

9 mm (Corynebacterium diptheriae)

O

N

H

Me

O

18

6 mm (MRSA)

Fig. (7). Structure activity relationship of compound 3, 9, 10, and 18.

OMe

O

N

H

N

H

N

H

OMe

O

4

2

12

9 mm (Bacillus subtilis)

7 mm (Staphylococcus feacalis)

8 mm (MRSA)

20 mm (Bacillus subtilis)

7 mm (MRSA)

18 mm (Bacillus ceresus)

Cl

OMe

O

N

H

OMe

O

16

7 mm (MRSA)

Fig. (8). Structure activity relationship of compounds 2, 4, 12, and 16.

O

N

H

Br

Cl

N

H

Cl

O

5

O

N

H

7 mm (Bacillus subtilis)

7 mm (Staphylococcus feacalis)

6 mm (MRSA)

5 mm (Corynebacterium diptheriae)

7 mm (Bacillus ceresus)

23

O

6 mm (Bacillus subtilis)

6 mm (Staphylococcus feacalis)

6 mm (MRSA)

14

6 mm (MRSA)

Fig. (9). Structure activity relationship of compounds 5, 14, and 23.

Amongst the methoxy containing derivatives, compound

2 with 4'-methoxy substitution, showed 20 mm inhibition

against Bacillus subtilis and 18 mm inhibition against Bacil-

lus ceresus. Switching methoxy group from 4'-position to 2'

as in case of compound 4, displayed 9 mm, 7 mm, and 8 mm

inhibition against Bacillus ceresus, Streptococcus faecalis,

and MRSA, respectively. Compounds 12 and 16 showed 7

mm inhibition selectively against MRSA (Fig. 8).

Halogens substituted derivatives also displayed antimi-

crobial activity against different strains of Gram-positive

bacteria. Amongst them, compound 5 with 3'-bromo substi-

tution showed weak inhibition against many strains such as

Bacillus subtilis, Streptococcus faecalis, multidrug resistant

Staphylococcus aureus (MRSA), Corynebacterium diphtheria,

and Bacillus ceresus. Compound 14 having 4'-chloro substi-

tution showed 6 mm inhibition against MRSA and com-

92 Medicinal Chemistry, 2018, Vol. 14, No. 1

Salar et al.

nella typhi, Klebsiella pneumoniae, Pseudomonas aerugino-

sa, Salmonella paratyphi B, Enterobacter aerogene, and

Shigella dysenteriae. Table 3 demonstrated that a number of

derivatives demonstrated antibacterial activities against

Gram-negative bacteria.

pound 23 showed 6 mm inhibition against Bacillus subtilis,

Streptococcus faecalis, and MRSA, respectively (Fig. 9).

Similarly, fluoro containing compounds such as 16, 22,

24, and 28 showed interesting inhibition potential against

various Gram-positive strains. Amongst them, compound 24

having 3',4'-difluoro substitutions displayed 6 mm inhibition

against Bacillus subtilis, Streptococcus faecalis, and Bacillus

ceresus. Its activity can be compared with its structurally

similar analog 28 having nitro group instead of flouro at po-

sition-3', showed noticeable inhibition against five strains

Bacillus subtilis (17 mm), Corynebacterium xerosis (16

mm), Staphylococcus aureus (20 mm), Streptococcus faecal-

is (19 mm), and MRSA (19 mm). It shows that nitro group is

playing an important role in the inhibition along with other

structural features. Activity of compound 28 can also be

compared with 3',4'-dimethyl substituted compound 3 which

has dimethyl instead of 4'-fluoro-3'-nitro substitutions,

showed much weaker inhibition against few Gram-positive

bacteria. It confirms the participation of flouro and nitro

groups in the activity. Other compounds 16 and 22 showed

relatively weak inhibition in comparison to compound 28

(Fig. 10).

Compound 2 with 4'-methoxy substitution was found to

be active against Shigella dysenteriae and Klebsiella pneu-

moniae showed 20 mm and 17 mm inhibition, respectively.

Other 4'-substituted derivatives such as 8, 13, 15, and 20

were found to be inactive, however, compound 26 with 4'-

butoxy substitution showed 15 mm inhibition against Salmo-

nella typhi (Fig. 11).

Another compound 10 having 2',5'-dimethyl substitution,

showed 10 mm inhibition against two strains such as Salmo-

nella paratyphi B and Shigella dysenteriae, and 9 mm inhibi-

tion against Escherichia coli. Its positional isomer 9 which has

2',4'-dimethyl substitution, selectively showed 7 mm inhibition

against Shigella dysenteriae. Other positional isomers 3 and

18 didn’t show inhibition against any strain (Fig. 12).

Amongst the fluoro substituted derivatives, compound 28

having 4'-fluoro-3'-nitro substitution showed comparable to

good potential against various strains Klebsiella pneumoniae

(16 mm), Pseudomonas aeruginosa (20 mm), Enterobacter

aerogene (20 mm), and Shigella dysenteria (18 mm). Never-

theless, its structurally similar analog 24 with 3',4'-difluoro

It was found that most of the derivatives showed inhibi-

tion against MRSA followed by Bacillus subtilis, and Strep-

tococcus faecalis.

All compounds 1-28 were also evaluated against Gram-

negative bacterial strains including Escherichia coli, Salmo-

Table 3. Antibacterial activity in vitro against gram-negative bacteria.

Gram-negative bacteria

Escherichia

coli

Salmonella

typhi

Klebsiella

pneumoniae

Pseudomonas

aeruginosa

Salmonella

paratyphi B

Enterobacter

aerogene

Shigella dysen-

teriae

Compounds

Inhibition Zone Diameter (mm) of Compounds

1

-

17

7

-

8

-

20

-

2

5

-

9

-

7

10

-

10

9

-

10

-

11

-

6

-

12

7

-

17

-

21

7

-

5

-

7

-

22

-

9

8

7

-

23

-

24

-

5

-

25

7

-

26

15

-

27

28

-

7

20

22

7

18

23

-

16

22

20

22

-

Gentamicin

29

25

Keys: - = No zone of inhibition, 8-10 mm = weakly active, 12-14 mm = moderately active, >15 = good activity.

1,1'-Carbonyldiimidazole (CDI) Mediated Facile Synthesis

Medicinal Chemistry, 2018, Vol. 14, No. 1 93

F

O

N

H

O

F

24

O

6 mm (Bacillus subtilis)

6 mm (Staphylococcus feacalis)

6 mm (Bacillus ceresus)

N

H

NO₂

N

H

F

O

28

22

CF₃

17 mm (Bacillus subtilis)

16 mm (Corynebacterium. xerosis)

20 mm (Staphylococcus aureus)

19 mm (Staphylococcus feacalis)

19 mm (MRSA)

8 mm (Bacillus subtilis)

O

6 mm (MRSA)

N

H

OMe

O

16

7 mm (MRSA)

Fig. (10). Structure activity relationship of compounds 16, 22, 24, and 28.

OMe

nBu

OBu

O

N

H

N

H

N

H

O

2

13

26

20 mm (Shigella dysenteriae)

15 mm (Salmonella typhi)

No Inhibition

17 mm (Klebsiella pneumoniae)

Me

SMe

O

Et

O

N

H

N

H

N

H

O

8

20

No Inhibition

15

No Inhibition

Fig. (11). Structure activity relationship of compounds 2, 8, 13, 15, 20, and 26.

O

N

H

Me

O

18

N

H

N

H

Me

No Inhibition

O

9

10

Me

O

10 mm (Salmonella paratyphi B)

10 mm (Shigella dysenteriae)

9 mm (Escherichia coli)

7 mm (Shigella dysenteriae)

N

H

O

3

No Inhibition

Fig. (12). Structure activity relationship of compound 3, 9, 10, and 18.

94 Medicinal Chemistry, 2018, Vol. 14, No. 1

Salar et al.

F

O

F

O

N

H

NO₂

N

H

F

N

H

O

28

24

22

16 mm (Klebsiella pneumoniae)

20 mm (Pseudomonas aeruginosa)

20 mm (Enterobacter aerogene)

18 mm (Shigella dysenteriae)

5 mm (Klebsiella pneumoniae)

7 mm (Enterobacter aerogene)

9 mm (Enterobacter aerogene)

Fig. (13). Inhibition zone diameter of compound 28.

Table 4. MIC of the most active synthetic compounds (ꢀg/disc).

Corynebac-

terium.

xerosis

Bacillus

subtilis

Staphylococcus Staphylococcus

Bacillus Klebsiella Pseudomonas Enterobacter Shigella

Compounds

MRSA

aureus

feacalis

ceresus pneumoniae aeruginosa

aerogene

dysenteriae

2

0.6

-

0.8

0.7

-

1.0

-

15

28

1.5

0.7

-

0.7

0.8

0.9

0.8

0.5

0.6

0.9

Gentamicin

MIC = ꢀg/disc

0.2

0.1

0.2

0.8

0.2

0.4

0.8

substitutions showed 5 mm inhibition against Klebsiella

pneumoniae and 7 mm against Enterobacter aerogene.

Comparison of activities of compounds 24 and 28 revealed

that nitro group is playing an important role in the inhibition

potential. Another fluorinated compound 22 showed 9 mm

inhibition against Enterobacter aerogene (Fig. 13).

The linear growth of all fungi i.e. Aspergillus niger, As-

pergillus terrus, Fusarium, Candida tropicalis, Candida

sacromyces, Cryptococcus neoformen, Candida albicans,

Rhizopus, Microsporum canis, and Absidia were acquired by

measuring the diameter of the fungal colony after one week.

Results were denoted as zone diameter of growth inhibition

(mm) and ketoconazole was used as standard. All com-

pounds were found to be inactive against all fungal cultures.

It was found that most of the derivatives showed activity

against Klebsiella pneumoniae followed by Enterobacter

aerogene and Shigella dysenteriae.

The cytotoxicity of these compounds on mammalian cells

is not yet explored, however, we are planning to carry out

detailed cytotoxic studies on these compounds in future.

Minimum inhibitory concentrations for the most active

compounds, such as 2, 15, and 28 were calculated against

particular bacterial cultures (Table 4).

3.4. Molecular Docking Analysis

Compound 1 with 4'-methoxy substitution showed MIC

values 0.6, 0.8, 0.7, and 1.0 ꢀg/mL against Bacillus subtilis,

Bacillus ceresus, Klebsiella pneumoniae, and Shigella dysen-

teriae, respectively. Similarly, compound 15 having 4'-ethyl

substitution showed MIC value of 1.5 ꢀg/mL against MRSA.

However, the most active compound 28 with 4'-fluoro-3'-

nitro groups showed activity against Bacillus subtilis,

Corynebacterium xerosis, Staphylococcus aureus, Staphylo-

coccus feacalis, MRSA, Klebsiella pneumoniae, Pseudomo-

nas aeruginosa, Enterobacter aerogene, and Shigella dysen-

teriae with MIC value of 0.7, 0.7, 0.8, 0.9, 0.7, 0.8, 0.5, 0.6,

and 0.9 ꢀg/mL, respectively. MIC data in Table 4 displayed

that compounds 2, 15, and 28 have comparable activity as

compared to the standard gentamicin.

Molecular docking is used to validate the binding relia-

bility and interaction poses of small molecules in the binding

site of protein targets [27]. To specify and verify the target

for antibacterial activity of synthetic coumarin-3-

carboxamide derivatives, sixteen different target proteins i.e.,

sortase A (PDB ID 1T2W), thymidylate kinase (PDB ID

2CCJ) and penicillin-binding protein 2a (PDB ID 4DKI)

from MRSA, dihydrofolate reductase (PDB ID 3FYV), sort-

ase A (PDB ID 2MLM), tyrosyl-tRNA synthetase (PDB

ID1JIJ), DNA gyrase B (PDB ID 3G75) from Staphylococ-

cus aureus and glycerophosphoryl diester phosphodiesterase

(PDB ID 5T91) and nitric oxide synthase (PDB ID 5G66)

from Bacillus subtilis were selected as Gram-positive bacte-

rial targets. While for Gram-negative bacterial targets; ꢁ-

lactamase (PDB ID 4WMC), ꢁ-lactamase shv-1 (PDB ID

2ZD8) and pantothenate kinase (PDB ID 4F7W) from

Klebsiella pneumonia, fosfomycin resistance protein (PDB

ID 1NKI), penicillin-binding protein 3 (PDB ID 5DF9)

and UDP-3-O-[3-hydroxymyristoyl] N-acetylglucosamine

3.3.2. Antifungal Activity

Inhibitory potential of all compounds 1-28 were evaluat-

ed for their antifungal potential against various fungal cul-

tures by using agar plate technique [26].

1,1'-Carbonyldiimidazole (CDI) Mediated Facile Synthesis

Medicinal Chemistry, 2018, Vol. 14, No. 1 95

deacetylase (PDB ID 3UHM) from Pseudomonas aerugino-

sa, glycerophosphodiesterase (PDB ID 2ZOA) from Entero-

bacter aerogene, were taken from protein data bank (PDB)

[28].

nia showed three hydrogen bonds with active site residues

(Tyr1244, Arg1243 and Asn1282) (Fig. 15). Additionally,

hydrophobic interactions with Val1097, Phe1244, Phe1259,

and Leu1277 were also observed.

Two target proteins from these sixteen retrieved proteins,

i.e., pantothenate kinase (PDB ID 4F7W) from Klebsiella

pneumonia (Gram-negative bacteria) and penicillin-binding

protein (PDB ID 4DKI) from MRSA (Gram-positive bacte-

ria) were preferred, as good docking score was observed for

the most active compound 28 against these proteins as com-

pared to other proteins (Table 5), in docking study by MOE-

2016 [29].

It is determined from docking study that coumarin-3-

carboxamide 28 showed noticeable hydrogen bonding and

hydrophobic interactions with vital residues of pantothenate

kinase (PDB ID 4F7W) from Klebsiella pneumonia and pen-

icillin-binding protein (4DKI) from MRSA and is the most

active antibacterial inhibitor.

Prior to running docking, the 3D structure of the most ac-

tive synthetic compound 28 was built using MOE. Whereas,

all sixteen target proteins were protonated, charged, prepared,

and energy minimized by MOE-2016. Default docking pa-

rameters of MOE were used for docking; 10 conformations

of the compound were allowed to generate for each target

protein. Results were finally reviewed to find the most suita-

ble antibacterial target protein by visualizing different inter-

actions of ligand in the binding site and calculating their

docking score. As shown in the experimental results, the

docking analysis of compound 28 also revealed its potency

as antibacterial inhibitor. Compound 28 contains 4 -fluoro-

3 -nitro substitution, showed visible hydrogen bonding

along with some hydrophobic interactions with the active

site residues of selected proteins, pantothenate kinase, and

penicillin-binding protein, due to the existence of electro-

negative functionalities.

Fig. (15). Molecular docking interaction model for the most potent

antibacterial compound 28 with pantothenate kinase (PDB ID

4F7W) from Klebsiella pneumonia, showing hydrogen bonding and

hydrophobic interactions.

Furthermore, the docking results of compound 28 against

penicillin-binding protein (PDB ID 4DKI) from MRSA

showed five hydrogen bonds with active site residues

Ser403, Asn464, Ser598, Thr600, and Ala601, respectively

(Fig. 14). This compound also showed several hydrophobic

interactions with active site residues (Met605 and Tyr446

etc.). In case of docking results of compound 28 against pan-

tothenate kinase (PDB ID 4F7W) from Klebsiella pneumo-

4. EXPERIMENTAL

4.1. General Procedure for the Syntheses of Coumarin-3-

carboxamide derivatives (1-28)

Coumarin-3-carboxylic acid was activated by using CDI

(1,1'-carbonyldiimidazole) as a coupling agent. For that pur-

pose, coumarin-3-carboxylic acid (1 mmol) was taken in

acetonitrile (10 mL) into a 100 mL round-bottomed flask.

Then, CDI (1.2 mmol) and triethylamine (1 mmol) were

added and stirred for half an hour at room temperature. For-

mation of acid imidazole (intermediate) was checked by the

thin layer chromatography (TLC). Afterward, different ani-

line derivatives (1 mmol) were added into it and further

stirred for 16 h to afford coumarin-3-carboxamides. Comple-

tion of reaction was monitored by the TLC analysis. In most

cases, precipitates were formed which were collected via

filtration. In some cases precipitates were not formed, for

those reactions, mixture was poured onto chilled distilled

water to afford the products in the form of precipitates which

were filtered and dried under air. Purity of all compounds

was checked by TLC.

4.1.1. 2-Oxo-N-phenyl-2H-chromene-3-carboxamide (1)

Fig. (14). Molecular docking interaction model for the most potent

antibacterial compound 28 with penicillin-binding protein (4DKI)

from Gram-positive MRSA, showing hydrogen bonding and hydro-

phobic interactions.

Yield: 79%; M.p.: 253-255 C; ¹H-NMR (300 MHz,

º

DMSO-d₆): ꢀ 10.65 (s, 1H, NH), 8.92 (s, 1H, H-4), 8.02

(bd.d, J_5,6= 7.2 Hz, 1H, H-5), 7.80 (m, 3H, H-7, H-2’, H-6’),

96 Medicinal Chemistry, 2018, Vol. 14, No. 1

Salar et al.

Table 5. List of retrieved proteins of Gram-positive and Gram-negative bacteria from protein data bank and their binding ener-

gies after docking with compound 28.

S. No.

Target Protein

PDB ID’s

Docking Score

1

2

Pantothenate Kinase

Penicillin-Binding Protein 2a

Nitric Oxide Synthase

4F7W

4DKI

5G66

5DF9

1JIJ

-12.319

-12.301

-11.524

-11.516

-10.873

-10.618

-10.274

-9.9999

-9.9668

-9.8235

-9.259

3

4

Transferase (Penicillin-Binding Protein)

Tyrosyl-Trna Synthetase

5

6

Transferase (Fosfomycin Resistance Protein)

Glycerophospho Diesterase

DNA Gyrase B

3UHM

2ZOA

3G75

5T91

7

8

9

Glycerophosphoryl diester phosphodiesterase

Thymidylate Kinase

10

11

12

13

14

15

16

2CCJ

4WMC

2ZD8

1NKI

2MLM

3FYV

1T2W

Beta-Lactamase

Beta-Lactamase shv-1

-8.765

Udp-3-O-[3-Hydroxymyristoyl] N-Acetylglucosamine Deacetylase

Sortase A

-8.583

-6.9258

-6.315

Dihydrofolate Reductase

Sortase A

-5.3525

7.56 (d, J_8,7= 8.4 Hz, 1H, H-8), 7.49 (t, J_6,5= J_6,7= 7.5 Hz,

1H, H-6), 7.41 (t, J_3’,2’= J_3’,4’= J_5’,4’= J_5’,6’= 7.5 Hz, 2H, H-

3’, H-5’), 7.17 (t, J_4’,3’= J_4’,5’= 7.5 Hz, 1H, H-4); ¹³C-NMR

(100 MHz, CDCl₃-d₁): ꢀ 161.8, 159.3, 154.5, 148.9, 137.7,

134.3, 129.9, 129.1, 125.5, 124.8, 120.6, 118.7, 116.7; EI

MS m/z (% rel. abund.): 265 (M⁺, 97), 212 (11), 173 (100),

101 (29), 93 (72), 77 (10); HREI-MS Calcd for C₁₆H₁₁NO₃:

m/z = 265.0739, found 265.0730.

129.9, 128.2, 127.1, 125.9, 125.4, 120.8, 118.9, 118.7, 116.7,

20.7, 13.8; EI MS m/z (% rel. abund.): 293 (M⁺, 52), 275

(25), 265 (13), 173 (100), 120 (64), 101 (19); HREI-MS

Calcd for C₁₈H₁₅NO₃: m/z = 293.1052, found 293.1062.

4.1.4. N-(2-Methoxyphenyl)-2-oxo-2H-chromene-3-

carboxamide (4)

Yield: 72%; M.p.: 244-246°C; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 11.18 (s, 1H, NH), 9.05 (s, 1H, H-4), 8.47 (d,

4.1.2. N-(4-Methoxyphenyl)-2-oxo-2H-chromene-3-

carboxamide (2)

J

_5,6= 7.8 Hz, 1H, H-5), 8.06 (d, J_6’,5’= 6.9 Hz, 1H, H-6’), 7.81

(t, J_7,6= J_7,8= 8.4 Hz, 1H, H-7), 7.56 (d, J_8,7= 8.4 Hz, 1H, H-8),

7.50 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-6), 7.12 (d, J_{3’,4’/4’,3’}= 7.2 Hz,

2H, H-3’, H-4’), 7.01(m, 1H, H-5’), 3.91 (s, 3H, OCH₃); ¹³C-

NMR (100 MHz, DMSO-d₆): ꢀ 161.1, 159.0, 154.0, 148.4,

134.5, 130.5, 127.3, 125.3, 124.4, 120.6, 119.6, 118.6, 116.2,

111.0, 56.1; EI MS m/z (% rel. abund.): 295 (M⁺, 100), 264

(25), 173 (100), 146 (35), 123 (50), 68 (73); HREI-MS Calcd

for C₁₇H₁₃NO₄: m/z = 295.0845, found 295.0833.

º

Yield: 76%; M.p.: 268-270 C; ¹H-NMR (500 MHz,

DMSO-d₆): ꢀ 10.55 (s, 1H, NH), 8.93 (s, 1H, H-4), 8.01 (dd,

J_5,7= 1.5 Hz, J_5,6= 6.0 Hz, 1H, H-5), 7.78 (m, 1H, H-7),

7.66(m, 2H, H-2’, H-6’), 7.55(d, J_8,7= 8.0 Hz, 1H, H-8), 7.48

(m, 1H, H-6), 6.96(m, 2H, H-3’, H-5’), 3.75 (s, 3H, OCH₃);

¹³C-NMR (75 MHz, DMSO-d₆): ꢀ 160.5, 159.4, 155.9,

153.8, 147.2, 134.2, 131.1, 130.3, 125.3, 121.4, 119.9, 118.5,

116.2, 114.1, 55.2; EI MS m/z (% rel. abund.): 295 (M⁺, 100),

272 (17), 173 (100), 123 (41), 108 (34), 89 (16); HREI-MS

Calcd for C₁₇H₁₃NO₄: m/z = 295.0845, found 295.0846.

4.1.5. N-(3-Bromophenyl)-2-oxo-2H-chromene-3-

carboxamide (5)

Yield: 75%; M.p.: 259-261°C; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.73 (s, 1H, NH), 8.89 (s, 1H, H-4), 8.10

(bd.s, 1H, H-2’), 8.02 (bd.d, J_5,6= 7.5 Hz, 1H, H-5), 7.81

(bd.t, J_7,6= J_7,8= 7.5 Hz, 1H, H-7), 7.62 (m, 1H, H-5’), 7.56

(d, J_8,7= 8.1 Hz, 1H, H-8), 7.49 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-

6), 7.38 (m, 2H, H-4’, H-6’); ¹³C-NMR (100 MHz, CDCl₃-

d₁): ꢀ 159.4, 154.6, 149.3, 138.9, 134.6, 130.3, 130.0, 127.8,

125.6, 123.5, 122.7, 119.0, 118.7, 118.3, 116.8; EI MS m/z

(% rel. abund.): 343 (M⁺, 5), 345 (M⁺+ 2, 5), 197 (30), 173

4.1.3. N-(3,4-dimethylphenyl)-2-oxo-2H-chromene-3-

carboxamide (3)

Yield: 75%; M.p.: 240-242°C; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.59 (s, 1H, NH), 9.05 (s, 1H, H-4), 8.06 (m,

2H, H-5, H-6’), 7.80 (t, J_7,6= J_7,8= 8.2 Hz, 1H, H-7), 7.58 (d,

J

_8,7= 8.2 Hz, 1H, H-8), 7.51 (t, J_6,5= J_6,7= 7.4 Hz, 1H, H-6),

7.07 (bd.s, 1H, H-3’), 7.05 (d, J_5’,6’= 8.3 Hz, 1H, H-5’), 2.28

(s, 3H, CH_3a), 2.25 (s, 3H, CH_3b); ¹³CNMR (300 MHz,

CDCl₃-d₁): ꢀ 162.0, 159.4, 154.5, 148.9, 137.3, 135.7, 134.2,

1,1'-Carbonyldiimidazole (CDI) Mediated Facile Synthesis

Medicinal Chemistry, 2018, Vol. 14, No. 1 97

(100), 146 (27), 118 (28), 92 (33), 68 (97); HREI-MS Calcd

abund.): 293 (M⁺, 59), 275 (22), 265 (14), 173 (100), 120

(59), 101 (16); HREI-MS Calcd for C₁₈H₁₅NO₃: m/z =

293.1052, found 293.1041.

for C₁₆H₁₀BrNO₃: m/z = 342.9844, found 342.9792.

4.1.6. N-(2-Methylphenyl)-2-oxo-2H-chromene-3-

carboxamide (6)

4.1.10. N-(2,5-Dimethylphenyl)-2-oxo-2H-chromene-3-

carboxamide (10)

Yield: 79%; M.p.: 245-247^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.61 (s, 1H, NH), 9.02 (s, 1H, H-4), 8.07 (d,

Yield: 70%; M.p.: 225-227 ^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.66 (s, 1H, NH), 9.05 (s, 1H, H-4), 8.18 (d,

J

_5,6= 8.1 Hz, 1H, H-5), 8.07 (d, J_6’,5’= 7.5 Hz, 1H, H-6’),

7.83 (t, J_7,6= J_7,8= 8.4 Hz, 1H, H-7), 7.58 (d, J_8,7= 8.1 Hz,

1H, H-8), 7.51 (t, J_6,5= J_6,7= 7.8 Hz, 1H, H-6), 7.29 (m, 2H,

H-3’, H-5’), 7.11(t, J_4’,3’= J_4’,5’= 7.8 Hz, 1H, H-4’), 2.34 (s,

3H, CH₃); ¹³C-NMR (100 MHz, CDCl₃-d₁): ꢀ 162.0, 159.3,

154.5, 149.0, 136.1, 134.3, 130.5, 129.9, 128.7, 126.7, 125.5,

125.0, 122.0, 198.0, 118.8, 116.7, 18.1; EI MS m/z (% rel.

abund.): 279 (M⁺, 47), 261 (17), 251 (13), 173 (100), 146

(12), 106 (51), 101 (19); HREI-MS Calcd for C₁₇H₁₃NO₃:

m/z = 279.0895, found 279.0897.

J

_5,6= 6.9 Hz, 1H, H-5), 7.99 (s, 1H, H-6’), 7.82 (t, J_7,6= J_7,8=

7.2 Hz, 1H, H-7), 7.58 (d, J_8,7= 7.8 Hz, 1H, H-8), 7.51 (t, J_6,5

= J_6,7= 7.8 Hz, 1H, H-6), 7.16 (d, J_3’,4’= 7.8 Hz, 1H, H-3’),

6.92 (d, J_4’,3’= 7.2 Hz, 1H, H-4’), 2.29 (s, 6H, 2CH₃);

¹³CNMR (300 MHz, DMSO-d₆): ꢀ 161.3, 159.2, 153.9,

148.1, 136.0, 134.4, 130.4, 130.2, 129.9, 125.3, 125.2, 125.0,

121.9, 119.1, 118.6, 116.2, 20.9, 17.1; EI MS m/z (% rel.

abund.): 293 (M⁺, 59), 275 (20), 265 (20), 248 (6), 173

(100), 120 (94), 101 (20); HREI-MS Calcd for C₁₈H₁₅NO₃:

m/z = 293.1052, found 293.1066.

4.1.7. N-(3-Methylphenyl)-2-oxo-2H-chromene-3-

carboxamide (7)

4.1.11. N-(4-Bromophenyl)-2-oxo-2H-chromene-3-

carboxamide (11)

Yield: 78%; M.p.: 201-203^oC; ¹H-NMR (300 MHz,

Yield: 75%; M.p.: 269-271^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.62 (s, 1H, NH), 8.91 (s, 1H, H-4), 8.02 (d,

J

_5,6= 6.9 Hz, 1H, H-5), 7.80 (t, J_7,6= J_7,8= 6.9 Hz, 1H, H-7),

DMSO-d₆): ꢀ 10.72 (s, 1H, NH), 8.90 (s, 1H, H-4), 8.02 (d,

7.56 (d, J_{8,7/6’,5’}= 8.4 Hz, 2H, H-8, H-6’), 7.52 (s, 1H, H-2’),

7.49 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-6), 7.28 (t, J_5’,4’= J_5’,6’= 7.8

Hz, 1H, H-5’), 6.98 (d, J_4’,5’= 7.8 Hz, 1H, H-4’), 2.32 (s, 3H,

CH₃); ¹³C-NMR (100 MHz, CDCl₃-d₁): ꢀ 161.8, 159.2,

154.5, 148.8, 139.0, 137.6, 134.3, 129.9, 128.9, 125.7, 125.4,

121.2, 118.7, 117.7, 116.7, 21.5; EI MS m/z (% rel. abund.):

279 (M⁺, 14), 173 (36), 146 (100), 118 (78), 106 (19), 90 (27);

HREI-MS Calcd for C₁₇H₁₃NO₃: m/z = 279.0895, found

279.0885.

J

_5,6= 6.9 Hz, 1H, H-5), 7.80 (t, J_7,6= J_7,8= 7.2 Hz, 1H, H-7),

7.73 (d, J_{3’,2’/5’,6’}= 8.7 Hz, 2H, H-3’, H-5’), 7.58 (m, 3H, H-8,

H-2’, H-6’), 7.49 (t, J_6,5= J_6,7= 7.8 Hz, 1H, H-6); ¹³C-NMR

(75 MHz, CDCl₃-d₁): ꢀ 161.8, 159.4, 154.5, 149.2, 136.7,

134.6, 132.1, 130.0, 125.6, 122.1, 117.5, 116.8; EI MS m/z

(% rel. abund.): 343 (M⁺, 60), 345 (M⁺+ 2, 63), 173 (100),

145 (5), 118 (3), 101 (19), 89 (15); HREI-MS Calcd for

C₁₆H₁₀BrNO₃: m/z = 342.9844, found 342.9796.

4.1.12. N-(2,5-Dimethoxyphenyl)-2-oxo-2H-chromene-3-

carboxamide (12)

Yield: 74%; M.p.: 225-227^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 11.20 (s, 1H, NH), 9.06 (s, 1H, H-4), 8.12 (d,

4.1.8. N-(4-Methylphenyl)-2-oxo-2H-chromene-3-

carboxamide (8)

Yield: 78%; M.p.: 229-231^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.59 (s, 1H, NH), 8.91 (s, 1H, H-4), 8.02 (d,

J

_6’,4’= 3.0 Hz, 1H, H-6’), 8.06 (d, J_5,6= 6.6 Hz, 1H, H-5),

J

_5,6= 6.9 Hz, 1H, H-5), 7.79 (t, J_7,6= J_7,8= 7.2 Hz, 1H, H-7),

7.81 (t, J_7,6= J_7,8= 7.2 Hz, 1H, H-7), 7.57 (d, J_8,7= 8.4 Hz,

1H, H-8), 7.50 (t, J_6,5= J_6,7= 7.8 Hz, 1H, H-6), 7.05 (d, J_3’,4’

= 9.0 Hz, 1H, H-3’), 6.69 (m, 1H, H-4’), 3.86 (s, 3H,

OCH_3b), 3.72 (s, 3H, OCH_3a); ¹³C-NMR (75 MHz, CDCl₃-

d₁): ꢀ 161.4, 159.2, 154.5, 153.8, 148.6, 143.5, 134.2, 129.9,

128.4, 125.3, 119.1, 118.7, 116.7, 111.2, 109.5, 106.8, 56.7,

55.8; EI MS m/z (% rel. abund.): 325 (M⁺, 67), 310 (29), 294

(11), 173 (100), 101 (11); HREI-MS Calcd for C₁₈H₁₅NO₅:

m/z = 325.0950, found 325.0943.

7.62 (d, J_{2’,3’/6’,5’}= 8.4 Hz, 2H, H-2’, H-6’), 7.56 (d, J_8,7= 8.4

Hz, 1H, H-8), 7.49 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-6), 7.20 (d,

J

_{3’,2’/5’,6’}= 8.1 Hz, 2H, H-3’, H-5’), 2.28 (s, 3H, CH₃); ¹³C-

NMR (75 MHz, CDCl₃-d₁): ꢀ 161.8, 159.1, 154.5, 148.7,

135.1, 134.5, 134,2, 129.9, 129.6, 125.4, 120.5, 118.8, 117.2,

116.9, 20.9; EI MS m/z (% rel. abund.): 279 (M⁺, 56), 251

(3), 173 (100), 145 (4), 101 (15); HREI-MS Calcd for

C₁₇H₁₃NO₃: m/z = 279.0895, found 279.0906.

4.1.9. N-(2,4-Dimethylphenyl)-2-oxo-2H-chromene-3-

carboxamide (9)

4.1.13. N-(4-Butylphenyl)-2-oxo-2H-chromene-3-

carboxamide (13)

Yield: 70%; M.p.: 285-287^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.59 (s, 1H, NH), 8.91 (s, 1H, H-4), 8.02 (d,

Yield: 70%; M.p.: 243-245^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.58 (s, 1H, NH), 9.03 (s, 1H, H-4), 8.07 (d,

J

_5,6= 9.6 Hz, J_6’,5’= 8.7 Hz, 2H, H-5, H-6’), 7.82 (t, J_7,6= J_7,8

J

_5,6= 6.6 Hz, 1H, H-5), 7.79 (t, J_7,6= J_7,8= 7.2 Hz, 1H, H-7),

= 8.4 Hz, 1H, H-7), 7.59 (d, J_8,7= 8.4 Hz, 1H, H-8), 7.50 (t,

_6,5= J_6,7= 7.5 Hz, 1H, H-6), 7.09 (s, 1H, H-3’), 7.06 (d, J_5’,6’

7.63 (d, J_{3’,2’/5’,6’}= 8.1 Hz, 2H, H-3’, H-5’), 7.56 (d, J_8,7= 8.4

Hz, 1H, H-8), 7.49 (t, J_6,5= J_6,7= 7.8 Hz, 1H, H-6), 7.21 (d,

J_{2’,3’/6’,5’}= 8.4 Hz, 2H, H-2’, H-6’), 2.58 (t, 2H, CH₂-1’’),

1.59 (m, 2H, CH₂-2’’), 1.36 (m, 2H, CH₂-3’’), 0.91 (t, 3H,

CH₃-4’’); ¹³C-NMR (75 MHz, CDCl₃-d₁): ꢀ 161.8, 159.1,

154.5, 148.8, 139.6, 135.3, 134.3, 129.9, 128.9, 125.4, 120.5,

J

= 8.4 Hz, 1H, H-5’), 2.29 (s, 3H, CH_3a), 2.26 (s, 3H, CH_3b);

¹³C-NMR (100 MHz, CDCl₃-d₁): ꢀ 162.0, 159.2, 154.5,

148.8, 134.7, 134.2, 133.5, 131.2, 129.9, 128.7, 127.2, 125.4,

122.1, 119.0, 118.8, 116.7, 20.9, 18.0; EI MS m/z (% rel.

98 Medicinal Chemistry, 2018, Vol. 14, No. 1

Salar et al.

118.7, 116.7, 35.1, 33.6, 22.3, 13.9; EI MS m/z (% rel.

abund.): 321 (M⁺, 79), 278 (100), 173 (100), 145 (7), 101

(17), 83 (14); HREI-MS Calcd for C₂₀H₁₉NO₃: m/z =

321.1365, found 321.1366.

(13); HREI-MS Calcd for C₁₆H₁₀N₂O₅: m/z = 310.0590,

found 310.0587.

4.1.18. N-(2,3-Dimethylphenyl)-2-oxo-2H-chromene-3-

carboxamide (18)

Yield: 76%; M.p.: 227-229^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.58 (s, 1H, NH), 9.02 (s, 1H, H-4), 8.06 (d,

4.1.14. N-(4-Chlorophenyl)-2-oxo-2H-chromene-3-

carboxamide (14)

Yield: 79%; M.p.: 249-251^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.72 (s, 1H, NH), 8.90 (s, 1H, H-4), 8.02 (d,

J_5,6= 6.9 Hz, 1H, H-5), 7.80 (m, 3H, H-7, H-3’, H-5’),

7.56(d, J_8,7= 8.4 Hz, 1H, H-8), 7.49 (m, 3H, H-6, H-2’, H-

6’); ¹³CNMR (400 MHz, CDCl₃-d₁): ꢀ 161.9, 159.4, 149.1,

136.3, 134.5, 130.0, 129.8, 129.1, 125.6, 121.8, 118.7, 116.8;

EI MS m/z (% rel. abund.): 299 (M⁺, 67), 301 (M⁺+ 2, 23),

173 (100), 145 (13), 101 (61), 89 (38), 75 (9); HREI-MS

Calcd for C₁₆H₁₀ClNO₃: m/z = 299.0349, found 299.0352.

J

_5,6= 6.9 Hz, 1H, H-5), 7.87 (d, J_6’,5’= 7.8 Hz, 1H, H-6’),

7.81 (t, J_7,6= J_7,8= 7.2 Hz, 1H, H-7), 7.58 (d, J_8,7= 8.4 Hz,

1H, H-8), 7.50 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-6), 7.15 (t, J_5’,4’

=

J

_5’,6’= 7.8 Hz, 1H, H-5’), 7.03 (d, J_4’,5’= 7.5 Hz, 1H, H-4’),

2.29 (s, 3H, CH_3b), 2.22 (s, 3H, CH_3a); ¹³C-NMR (75 MHz,

CDCl₃-d₁): ꢀ 162.0, 159.4, 154.5, 148.9, 137.3, 135.7, 134.3,

129.9, 128.2, 127.1, 125.9, 125.4, 120.8, 118.9, 118.7, 116.7,

20.7, 13.8; EI MS m/z (% rel. abund.): 293 (M⁺, 86), 275

(82), 173 (100), 120 (100), 101 (26), 89 (16); HREI-MS

Calcd for C₁₈H₁₅NO₃: m/z = 293.1052, found 293.1043.

4.1.15. N-(4-Ethylphenyl)-2-oxo-2H-chromene-3-

carboxamide (15)

Yield: 75%; M.p.: 176-178^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.59 (s, 1H, NH), 8.91 (s, 1H, H-4), 8.02 (d,

4.1.19. N-[2-(Methyloxy)-5-(trifluoromethyl)phenyl]-2-oxo-

2H-chromene-3-carboxamide (19)

Yield: 75%; M.p.: 254-256^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 11.36 (s, 1H, NH), 9.07 (s, 1H, H-4), 8.84

(bd.s, 1H, H-6’), 8.08 (d, J_5,6= 6.9 Hz, 1H, H-5), 7.81 (m,

1H, H-7), 7.58 (m, 3H, H-6, H-3’, H-4’), 7.33 (d, J_8,7= 8.4

Hz, 1H, H-8), 4.01 (s, 3H, OCH₃); ¹³C-NMR (75 MHz,

DMSO-d₆): ꢀ 159.7, 154.0, 151.1, 148.8, 134.7, 130.6,

127.7, 125.4, 121.6, 118.5, 116.2, 115.7, 111.3, 56.7; EI MS

m/z (% rel. abund.): 363 (M⁺, 40), 344 (4), 332 (6), 173

(100), 145 (3), 101 (14); HREI-MS Calcd for C₁₈H₁₂F₃NO₄:

m/z = 363.0718, found 363.0718.

J

_5,6= 7.2 Hz, 1H, H-5), 7.79 (t, J_7,6= J_7,8= 7.2 Hz, 1H, H-7),

7.64 (d, J_{2’,3’/6’,5’}= 8.1 Hz, 2H, H-2’, H-6’), 7.56 (d, J_8,7= 8.4

Hz, 1H, H-8), 7.49 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-6), 7.23 (d,

J

_{3’,2’/5’,6’}= 8.4 Hz, 2H, H-3’, H-5’), 2.59 (q, 2H, CH₂), 1.19 (t,

3H, CH₃); ¹³C-NMR (100 MHz, DMSO-d₆): ꢀ 160.5, 159.6,

153.9, 147.3, 139.8, 135.6, 134.2, 130.3, 128.2, 125.2, 119.9,

118.5, 116.2, 27.6, 15.6; EI MS m/z (% rel. abund.): 293

(M⁺, 53), 278 (24), 173 (100), 150 (3), 120 (5), 101 (12), 89

(9); HREI-MS Calcd for C₁₈H₁₅NO₃: m/z = 293.1052, found

293.1036.

4.1.20. N-[4-(Methylsulfanyl)phenyl]-2-oxo-2H-chromene-

3-carboxamide (20)

4.1.16. N-[5-Chloro-2,4-bis(methyloxy)phenyl]-2-oxo-2H-

chromene-3-carboxamide (16)

Yield: 73%; M.p.: 275-277^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 11.08 (s, 1H, NH), 9.03 (s, 1H, H-4), 8.50 (s,

1H, H-3’), 8.07 (d, J_5,6= 7.2 Hz, 1H, H-5), 7.82 (d, J_7,6= J_7,8

= 8.1 Hz, 1H, H-7), 7.56 (d, J_8,7= 8.4 Hz, 1H, H-8), 7.50 (t,

Yield: 78%; M.p.: 205-207^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.64 (s, 1H, NH), 8.91 (s, 1H, H-4), 8.02 (d,

J

_5,6= 7.5 Hz, 1H, H-5), 7.80 (t, J_7,6= J_7,8= 8.4 Hz, 1H, H-7),

7.70 (d, J_8,7= 8.7 Hz, 1H, H-8), 7.56 (d, J_{2’,3’/6’,5’}= 8.4 Hz,

2H, H-2’, H-6’), 7.49 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-6), 7.30

(d, J_{3’,2’/5’,6’}= 8.7 Hz, 2H, H-3’, H-5’), 2.47 (s, 3H, SCH₃);

¹³C-NMR (100 MHz, CDCl₃-d₁): ꢀ 161.8, 159.2, 154.5,

148.9, 135.3, 134.4, 134.3, 129.9, 127.9, 125.5, 121.1, 118.7,

116.7, 16.6; EI MS m/z (% rel. abund.): 311 (M⁺, 92), 173

(100), 165 (18), 150 (11), 139 (12), 124 (15), 101 (10);

HREI-MS Calcd for C₁₇H₁₃NO₃S: m/z = 311.0616, found

311.0625.

J

_6,5= J_6,7= 7.5 Hz, 1H, H-6), 6.94 (s, 1H, H-6’), 3.97 (s, 3H,

OCH_3b), 3.89 (s, 3H, OCH_3a); ¹³C-NMR (100 MHz, DMSO-

d₆): ꢀ 161.1, 158.8, 153.9, 151.3, 148.6, 148.3, 134.5, 130.5,

125.3, 120.8, 120.4, 118.6, 118.4, 116.2, 111.3, 97.9, 56.7,

56.5; EI MS m/z (% rel. abund.): 359 (M⁺, 69), 361 (M⁺+ 2,

25), 186 (12), 173 (100), 145(5), 123 (11), 101 (12); HREI-

MS Calcd for C₁₈H₁₄ClNO₅: m/z = 359.0561, found 359.0556.

4.1.21. N-(4-Fluorophenyl)-2-oxo-2H-chromene-3-

carboxamide (21)

Yield: 72%; M.p.: 260-262^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.66 (s, 1H, NH), 8.90 (s, 1H, H-4), 8.02 (d,

4.1.17. N-(3-Nitrophenyl)-2-oxo-2H-chromene-3-

carboxamide (17)

Yield: 75%; M.p.: 270-272^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.98 (s, 1H, NH), 8.92 (s, 1H, H-4), 8.81 (s,

J

_5,6= 6.9 Hz, 1H, H-5), 7.80 (m, 3H, H-6, H-7, H-2’), 7.56(d,

1H, H-2’), 8.04 (m, 3H, H-5, H-6, H-4’), 7.82(t, J_7,6= J_7,8

=

_8,7= 8.1 Hz, 1H, H-8), 7.49 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-6),

7.25 (t, J_3’,2’= J_5’,6’= 9.0 Hz, 2H, H-3’, H-5’); ¹³C-NMR (75

MHz, DMSO-d₆): ꢀ 161.2, 159.9, 153.9, 147.3, 134.3, 130.3,

125.3, 121.9, 121.8, 120.0, 118.4, 116.2, 115.7, 115.4; EI

MS m/z (% rel. abund.): 283 (M⁺, 28), 173 (100), 145 (6),

101 (34), 89 (47), 63 (33); HREI-MS Calcd for C₁₆H₁₀FNO₃:

m/z = 283.0645, found 283.0641.

8.7 Hz, 1H, H-7), 7.70 (t, J_5’,4’= J_5’,6’= 8.1 Hz, 1H, H-5’),

7.58 (d, J_8,7= 8.4 Hz, 1H, H-8), 7.51 (t, J_6,5= J_6,7= 7.8 Hz,

1H, H-6); ¹³C-NMR (75 MHz, DMSO-d₆): ꢀ 161.9, 159.9,

153.9, 147.4, 139.2, 134.3, 130.3, 130.1, 125.3, 121.9, 121.8,

120.0, 118.4, 116.3, 115.7, 115.4; EI MS m/z (% rel.

abund.): 310 (M⁺, 12), 173 (100), 145 (6), 123 (10), 101

1,1'-Carbonyldiimidazole (CDI) Mediated Facile Synthesis

Medicinal Chemistry, 2018, Vol. 14, No. 1 99

4.1.22. N-(3-Fluorophenyl)-2-oxo-2H-chromene-3-

carboxamide (22)

J

_5,6= 6.9 Hz, 1H, H-5), 7.77 (t, J_7,6= J_7,8= 8.1 Hz, 1H, H-7),

7.61 (d, J_{2’,3’/6’,5’}= 9.0 Hz, 2H, H-2’, H-6’), 7.53 (d, J_8,7= 8.4

Hz, 1H, H-8), 7.46 (t, J_6,7= J_6,8= 7.5 Hz, 1H, H-6), 6.92 (d,

J_{3’,2’/5’,6’}= 8.7 Hz, 2H, H-3’, H-5’), 3.94 (t, 2H, CH₂-1’’),

1.70(m, 2H, CH₂-2’’), 1.44 (m, 2H, CH₂-3’’), 0.92 (t, 3H,

CH₃-4’’); ¹³C-NMR (100 MHz, DMSO-d₆): ꢀ 160.5, 159.3,

155.4, 153.8, 147.2, 134.2, 130.9, 130.2, 125.2, 121.4, 119.9,

118.5, 116.2, 114.6, 67.3, 30.7, 18.7, 13.7; EI MS m/z (% rel.

abund.): 337 (M⁺, 88), 281 (88), 173 (100), 145 (3), 108 (6),

101 (12), 89 (8); HREI-MS Calcd for C₂₀H₁₉NO₄: m/z =

337.1314, found 337.1310.

Yield: 79%; M.p.: 242-244^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.78 (s, 1H, NH), 8.91 (s, 1H, H-4), 8.02 (d,

J

_5,6= 6.9 Hz, 1H, H-5), 7.81 (m, 2H, H-7, H-2’), 7.56 (d, J_8,7

= 8.4 Hz, 1H, H-8), 7.49 ((m, 3H, H-6, H-5’, H-6’), 7.00 (m,

1H, H-4’); ¹³CNMR (400 MHz, CDCl₃-d₁): ꢀ 161.8, 159.5,

154.6, 149.3, 139.2, 134.6, 130.1, 130.0, 125.6, 118.7, 116.8,

115.9, 111.6, 111.4, 108.2, 107.9; EI MS m/z (% rel.

abund.): 283 (M⁺, 45), 255 (5), 173 (100), 145 (16), 101

(75), 89 (80), 63 (50); HREI-MS Calcd for C₁₆H₁₀FNO₃: m/z

= 283.0645, found 283.0626.

4.1.27. N-(4-Iodophenyl)-2-oxo-2H-chromene-3-

carboxamide (27)

4.1.23. N-(3-Chlorophenyl)-2-oxo-2H-chromene-3-

carboxamide (23)

Yield: 70%; M.p.: 240-244^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.75 (s, 1H, NH), 8.90 (s, 1H, H-4), 8.02 (d,

Yield: 75%; M.p.: 234-236^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.69 (s, 1H, NH), 8.89 (s, 1H, H-4), 8.02

(bd.d, J_5,6= 7.5 Hz, 1H, H-5), 7.80 (m, 1H, H-7), 7.73 (d,

J

_{2’,3’/6’,5’}= 8.7 Hz, 2H, H-2’, H-6’), 7.58 (m, 3H, H-8, H-3’,

J

_5,6= 7.8 Hz, 1H, H-5), 7.97 (bd.s, 1H, H-2’), 7.81 (t, J_7,6=

H-5’), 7.49 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-6); ¹³C-NMR (100

MHz, CDCl₃-d₁): ꢀ 161.8, 159.4, 149.2, 138.0, 137.5, 134.6,

130.0, 125.6, 122.4, 116.8, 88.2; EI MS m/z (% rel. abund.):

391 (M⁺, 77), 265 (17), 173 (100), 145 (4), 101 (12), 89 (10);

HREI-MS Calcd for C₁₆H₁₀INO₃: m/z = 390.9075, found

390.9071.

_7,8= 8.4 Hz, 1H, H-7), 7.59 (t, J_6,5= J_6,7= J_5’,4’= J_5’,6’= 8.4

Hz, 2H, H-6, H-5’), 7.49 (m, 2H, H-8, H-6’), 7.22 (bd.d, J_4’,5’

= 8.1 Hz, 1H, H-4’); ¹³C-NMR (100 MHz, CDCl₃-d₁): ꢀ

161.8, 159.4, 154.6, 149.3, 138.8, 134.7, 134.6, 130.0, 125.6,

124.8, 120.7, 118.7, 118.5, 116.8; EI MS m/z (% rel.

abund.): 301 (M⁺, 76), 303 (M⁺+ 2, 20), 173 (100), 145 (4),

101 (24), 89 (13), 75 (4); HREI-MS Calcd for C₁₆H₁₀ClNO₃:

m/z = 299.0349, found 299.0357.

4.1.28. N-(4-Fluoro-3-nitrophenyl)-2-oxo-2H-chromene-3-

carboxamide (28)

Yield: 75%; M.p.: 270-272^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.91 (s, 1H, NH), 8.91 (s, 1H, H-4), 8.71 (bd.d,

1H, H-2’), 8.02 (m, 2H, H-5, H-5’), 7.81 (t, J_7,6= J_7,8= 8.1 Hz,

1H, H-7), 7.65 (d, J_8,7= 10.5 Hz, 1H, H-8), 7.57 (d, J_6’,5’= 8.4

Hz, 1H, H-6’), 7.49 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-6); ¹³CNMR

(300 MHz, DMSO-d₆): ꢀ 161.9, 159.9, 153.9, 147.4, 139.3,

134.3, 130.3, 130.1, 125.3, 121.9, 121.8, 120.0, 118.5, 116.3,

115.8, 115.5; EI MS m/z (% rel. abund.): 328 (M⁺, 17), 173

(100), 145 (6), 105 (5), 89 (40), 63 (18); HREI-MS Calcd for

C₁₆H₉FN₂O₅: m/z = 328.0495, found 328.0487.

4.1.24. N-(3,4-Difluorophenyl)-2-oxo-2H-chromene-3-

carboxamide (24)

Yield: 73%; M.p.: 270-272^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.75 (s, 1H, NH), 8.91 (s, 1H, H-4), 8.02 (m,

2H, H-5, H-5’), 7.81 (t, J_7,6= J_7,8= 8.4 Hz, 1H, H-7), 7.57 (d,

J_8,7= 8.1 Hz, 1H, H-8), 7.49 (m, 3H, H-6, H-2’, H-6’);

¹³CNMR (300 MHz, DMSO-d₆): ꢀ 161.9, 159.9, 153.9, 147.4,

139.2, 134.3, 130.3, 130.0, 125.3, 121.9, 121.8, 120.0, 118.4,

116.2, 115.7, 115.4; EI MS m/z (% rel. abund.): 301 (M⁺, 90),

173 (100), 145 (7), 101 (29), 89 (15), 75 (4); HREI-MS Calcd

for C₁₆H₉F₂NO₃: m/z = 301.0550, found 301.0546.

4.2. Bioassay

4.1.25. N-[2-(1-Methylethyl)phenyl]-2-oxo-2H-chromene-

3-carboxamide (25)

4.2.1. Antibacterial Assay

The disc diffusion method [24] was adopted to check the

antibacterial potential of compounds 1-28. Stock solutions of

compounds 1-28 (10 mg/mL) were prepared by dissolving in

DMSO. Bacterial cultures were mixed with pre-sterile

physiological (0.85%) saline solution and subjected for 24 h

incubation. Turbidity of all samples was agreed with the

standard inoculum of 0.5 MacFarland scale [~10⁶CFU/mL].

The Mueller Hinton agar (Oxoid) plates were seeded with all

bacterial cultures grown in Mueller Hinton broth (Oxoid).

All prepared discs containing test compounds (10 ꢂL) were

positioned on to the surfaces and plates were incubated for

24 h at 37°C. Results were obtained by measuring the zone

of inhibitions in mm. DMSO and gentamicin were used as

negative and positive control, respectively.

Yield: 74%; M.p.: 190-192^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.67 (s, 1H, NH), 9.04 (s, 1H, H-4), 8.07 (d,

J_5,6= 7.5 Hz, 1H, H-5), 8.02 (d, J_6’,5’= 8.1 Hz, 1H, H-

6’),7.82 (t, J_7,6= J_7,8= 7.5 Hz, 1H, H-7), 7.57 (d, J_8,7= 8.4

Hz, 1H, H-8), 7.51 (t, J_6,5= J_6,7= 7.5 Hz, 1H, H-6), 7.38 (d,

J

_3’,4’= 7.5 Hz, 1H, H-3’), 7.27 (m, 2H, H-4’, H-5’), 3.21 (m,

1H, CH), 1.25(d, 6H, 2CH₃); ¹³C-NMR (75 MHz, CDCl₃-d₁):

ꢀ 161.8, 159.1, 154.4, 148.7, 139.6, 135.2, 134.2, 129.9,

128.9, 127.1, 125.4, 125.2, 121.1, 120.5, 118.7, 116.7, 33.6,

13.8; EI MS m/z (% rel. abund.): 307 (M⁺, 59), 292 (6), 173

(100), 145 (6), 101 (24), 89 (15), 75 (5); HREI-MS Calcd for

C₁₉H₁₇NO₃: m/z = 307.1208, found 307.1203.

4.1.26. N-[4-(Butyloxy)phenyl]-2-oxo-2H-chromene-3-

carboxamide (26)

4.2.2. Antifungal Assay

Yield: 78%; M.p.: 192-194^oC; ¹H-NMR (300 MHz,

DMSO-d₆): ꢀ 10.50 (s, 1H, NH), 8.88 (s, 1H, H-4), 7.99 (d,

Antifungal activity of synthetic compounds 1-28 was also

checked by using disc diffusion method [25]. Concisely, a

100 Medicinal Chemistry, 2018, Vol. 14, No. 1

Salar et al.

small fraction of fungal culture was shifted to normal saline

2-3 mL in a screw capped tube with few glass beads (diame-

ter = 1 mm) and vortexes for about 10 min to formulate a

homogeneous suspension of fungal cultures. Sabouraud dex-

trose agar (SDA) plates were seeded with these fungal sus-

pensions. Sterile filter discs containing stock solutions 10 ꢃL

were positioned on to the surfaces. Plates were incubated for

one week at room temperature. Results were obtained by

measuring the zone of inhibitions in mm. Ketoconazole was

used as positive control for antifungal activity.

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Butler, M.M.; Williams, J.D.; Peet, N.P.; Moir, D.T.; Panchal,

R.G.; Bavari, S.; Bowlin, T.L. Comparative in vitro activity pro-

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4.2.3. Determination of Minimum Inhibitory Concentration

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The compounds showing zone of inhibition of 15 mm or

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Coumarin-3-carboxamides 1-28 were synthesized by

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Not applicable.

HUMAN AND ANIMAL RIGHTS

No Animals/Humans were used for studies that are base

of this research.

CONSENT FOR PUBLICATION

Not applicable.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or

otherwise.

[16]

ACKNOWLEDGEMENTS

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The authors thankful to the Higher Education Commis-

sion (HEC), Pakistan, for the financial support to this re-

search work under the National Research Program for Uni-

versities (Project No. 20-1910).

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DISCLAIMER: The above article has been published in Epub (ahead of print) on the basis of the materials provided by the author. The Edito-

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1,1'-carbonyldiimidazole (cdi) mediated facile synthesis, structural characterization, antimicrobial activity, and in-silico studies of coumarin- 3-carboxamide derivatives

DOI: 10.2174/1573406413666170623083116

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