Synthesis, antimicrobial evaluation, and molecular docking studies of novel chromone based 1,2,3-triazoles

Article abstract of DOI:10.1007/s11164-016-2602-z

Abstract: In Search of novel antimicrobial agents with improved potency, we designed and synthesized a series of 3-((1-benzyl-1H-1,2,3-triazol-4-yl)methoxy)-2-(4-fluorophenyl)-4H-chromen-4-ones 5a–f using click chemistry. The structures of synthesized com

Full text of DOI:10.1007/s11164-016-2602-z

Res Chem Intermed
DOI 10.1007/s11164-016-2602-z
Synthesis, antimicrobial evaluation, and molecular
docking studies of novel chromone based 1,2,3-triazoles
Vidya S. Dofe1 Aniket P. Sarkate2 Deepak K. Lokwani2
•
•
•
Santosh H. Kathwate3 Charansingh H. Gill1
•
Received: 20 May 2016 / Accepted: 31 May 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract In Search of novel antimicrobial agents with improved potency, we designed
and synthesized a series of 3-((1-benzyl-1H-1,2,3-triazol-4-yl)methoxy)-2-(4-fluo-
rophenyl)-4H-chromen-4-ones 5a–f using click chemistry. The structures of synthesized
1
compounds were found using IR, H NMR, 13C NMR, and MS. All the synthesized
compounds were assayed for their in vitro antibacterial activity against Staphylococcus
aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa and antifungal
activity against Candida albicans, Candida glabrata, and Candida tropicalis by micro
broth dilution method. The antimicrobial data suggested that from the series, compounds
3e, 4e, 5e, and 5f shows pronounced antimicrobial activity against the tested strain with
low MIC value. Molecular docking study was used to rationalize binding interaction at
the active site and the results showed good binding interaction.
Electronic supplementary material The online version of this article (doi:10.1007/s11164-016-2602-z)
contains supplementary material, which is available to authorized users.
&
Charansingh H. Gill
chgill16@gmail.com
1
2
3
Department of Chemistry, Dr. Babasaheb Ambedkar Marathwada University,
Aurangabad 431 004, India
Department of Chemical Technology, Dr. Babasaheb Ambedkar Marathwada University,
Aurangabad 431 004, India
Department of Biotechnology, Rajarshi Shahu College, Latur 413 512, India
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V. S. Dofe et al.
Graphical Abstract
Keywords 1,2,3-Triazoles Á Chromones Á Antimicrobial activity Á Molecular
docking
Introduction
The increasing prevalence of infections caused by microorganisms is a major threat
across the world, so the development of a diversified series of biologically active
scaffolds is of great interest in drug designing [1]. This includes several popular
pharmaceutical drugs such as fluorocytosine, fludarabine, panomifene, and diflu-
nisal contain fluorine. The introduction of fluorine into a molecule may lead to
significant influences on the biological and physical properties of compounds such
as metabolic stability, bioavailability, solubility, and lipophilicity [2]. Furthermore,
the substitution of fluorine into a potential drug molecule can improve its
therapeutic efficacy due to hydrogen bonding interactions at the active sites of
enzyme [3].
Interest in chromones continues unabated because of their usefulness as
biologically active agents. Some biological activities attributed to chromone
derivatives are antitumor [4], antimicrobial [5], antioxidant [6], antiallergic [7],
anti-inflammatory [8], antiplaque [9], and neuroprotection [10]. Chalcones are the
precursors of chromones, and are significant pharmacophores exhibiting a variety of
biological activities, such as antimalarial [11], antimicrobial [12], antifilarial [13],
antioxidant [14], anti-inflammatory [15], and antiproliferation [16].
1,2,3-Triazoles emerged as an attractive and desirable scaffold in the develop-
ment of potential drug molecules due to their easy synthesis by click chemistry.
Click chemistry refers to facile efficient, selective, and versatile chemical
transformation of a reactant to single regioisomer [17]. The concept of click
chemistry was first introduced by Huisgen, involving 1,3-dipolar cycloaddition
between an alkyne and azide [18] to afford the mixture of 1,4- and 1,5-disubstituted
isomers. Recently, regioselectivity of the reaction was improved by Sharpless and
Meldal by introducing Cu(I) catalyzed alkyne-azide 1,3-dipolar cycloaddition
(CuAAC) to afford 1,4-disubstituted 1,2,3-triazole [19, 20]. The triazole nucleus is
an important pharmacophore appearing extensively in various types of pharmaceu-
tical agents and bioactive molecules, such as anti-HIV [21], antitubercular [22],
anti-inflammatory, anticancer [23], antimicrobial [24], anticonvulsant [25],
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Synthesis, antimicrobial evaluation, and molecular…
antimalarial [26], analgesic [27], antiviral [28], antidiabetic [29], antimycobacterial
[30], and anticholinesterase [31]. The biological activity of these compounds is
enhanced probably due to their high aromatic stabilisation, high dipole moment, and
high bonding capacity. Along with the biological applications they are also used as
photo stabilisers, photographic elements, and organochemicals [32].
Therefore, in continuation of our earlier work on the synthesis of chromone
derivatives [33], and owing to the significant features of nitrogen containing
heterocycles to modulate the physiochemical properties, herein, we designed and
synthesized 1,2,3-triazole tethered chromone derivatives in a single molecular
framework to investigate the influence on biological activity and evaluated for their
antimicrobial activity with molecular docking study.
Experimental
Materials and methods
All regents used for chemical synthesis were purchased from commercial suppliers
and required no further purification. Analytical thin-layer chromatography (TLC)
was carried out using Merck silica gel 60 F254 plates and visualized using UV light
and iodine vapours as visualizing reagent. Melting points were determined in open
capillaries and are uncorrected. IR spectra were recorded on Carry 600 Series FTIR
spectrometer. 1H NMR and 13C NMR spectra were recorded on Bruker AVANCE II
400 NMR spectrometer in CDCl3 and/or DMSO-d6 solution using tetramethylsilane
as an internal standard. Chemical shift values are given in ppm relative to TMS as
internal reference and coupling constant (J) in Hertz. The splitting pattern
abbreviations are assigned as singlet (s), broad singlet (brs), doublet (d), double
doublet (dd), doublet of double doublet (ddd), triplet (t), and multiplet (m). Mass
were recorded on a WATERS, Q-TOF micro-mass equipped with an Electron Spin
Impact (ESI) Source.
General procedure for the synthesis of compounds 2a–f
2-Hydoxyacetophenones 1a–f (0.01 mol) and 4-fluorobenzaldehyde (0.01 mol)
were added to a solution of KOH (0.03 mol) in ethanol (15 mL) at 0–5 °C. The
reaction mixture was stirred 2–3 h at room temperature. Then the reaction mixture
was poured over crushed ice and neutralized carefully with 2 N HCl, and the
obtained precipitate was filtered, washed with water, and dried. The crude product
was crystallized with chloroform-ethanol to afford desired compound.
(E)-3-(4-fluorophenyl)-1-(2-hydroxyphenyl)prop-2-en-1-one (2a)
Yellow solid, m.p. 96–98 °C, yield: 68 %. IR (KBr, cm-1): 3218 (OH), 2915 (CH),
1
1604 (C=O), 1562 (C=C). H NMR (400 MHz, CDCl3, dH ppm): 6.95 (ddd, 1H,
J = 1.1, 7.2, 8.2 Hz, ArH), 7.03 (dd, 1H, J = 0.7, 8.4 Hz, ArH), 7.13 (t, 2H,
J = 8.6 Hz, ArH), 7.51 (ddd, 1H, J = 1.8, 7.5, 7.7 Hz, ArH), 7.58 (d, 1H,
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V. S. Dofe et al.
J = 15.4 Hz, olefinic proton), 7.66 (dd, 2H, J = 5.3, 8.6 Hz, ArH), 7.89 (d, 1H,
J = 15.4 Hz, olefinic proton), 7.92 (d, 1H, J = 1.8 Hz, ArH), 12.81 (s, 1H, OH).
13C NMR (100 MHz, CDCl3, dC ppm): 116.1(CH), 116.3(CH), 118.6(CH),
118.8(CH), 119.7(C), 119.9(CH), 129.6(CH), 130.5(CH), 130.6(C), 130.8(CH),
136.4(CH), 144.1(CH), 163.6(C), 165.5(C), 193.5(C). LCMS Anal. Calcd. For
C15H11FO2 (M ? H)?: 243.1. Found: 243.1.
General procedure for the synthesis of compounds 3a–f
A mixture of (E)-3-(4-fluorophenyl)-1-(2-hydroxyphenyl)prop-2-en-1-one 2a–
f (1 mmol), ethanol (15 mL), NaOH (10 %, 5 ml), and hydrogen peroxide (30 %,
1.5 mL) was stirred vigorously for 30 min and kept for 2–3 h in ice cold conditions.
The progress of reaction was observed by TLC using ethyl acetate: hexane as a
solvent system. After completion of reaction indicated by TLC, the reaction mixture
was poured into ice cold water and acidified with 1 M HCl, and the precipitate was
collected by filtration, washed with water, and recrystallized from chloroform-
ethanol to afford pure product.
2-(4-Fluorophenyl)-3-hydroxy-4H-chromen-4-one (3a)
Yellow solid, m. p. 152–154 °C, yield: 74 %. IR (KBr, cm-1): 3297 (OH), 2925
1
(CH), 1618 (C=O), 1572 (C=C). H NMR (400 MHz, CDCl3, dH ppm): 7.11 (brs,
1H, OH), 7.22 (t, 2H, J = 8.6 Hz, ArH), 7.42 (ddd, 1H, J = 1.1, 7.5, 7.6 Hz, ArH),
7.58 (d, 1H, J = 8.4 Hz, ArH), 7.71 (ddd, 1H, J = 1.7, 7.1, 8.5 Hz, ArH), 8.24 (d,
1H, J = 1.8 Hz, ArH), 8.27–8.30 (m, 2H, ArH). 13C NMR (100 MHz, CDCl3, dC
ppm): 115.7(CH), 115.9(CH), 118.2(CH), 120.7(CH), 124.6(C), 125.5(C),
127.3(CH), 129.9(CH), 133.7(CH), 138.2(CH), 144.1(C), 155.3(C), 162.3(C),
164.8(C), 173.4(C). LCMS Anal. Calcd. For C15H9FO3 (M ? H)?: 257.1. Found:
257.0.
General procedure for the synthesis of compounds 4a–f
Potassium carbonate (2 mmol) and propargyl bromide (1 mmol) were added to the
stirred solution of substituted 2-(4-fluorophenyl)-3-hydroxy-4H-chromen-4-one 3a–
f (1 mmol) in DMF at room temperature for about 3–4 h, and on completion, as
evident by TLC, the reaction mixture was quenched with crushed ice and the
precipitated solid was collected by filtration and recrystallized from ethanol.
2-(4-Fluorophenyl)-3-(prop-2-ynyloxy)-4H-chromen-4-one (4a)
Yellow solid, m. p. 106–108 °C, yield: 74 %. IR (KBr, cm-1): 3238(C:CH), 3069
1
(=CH), 2952 (–CH), 2108 (C:C), 1628 (C=O), 1600 (C=C). H NMR (300 MHz,
CDCl3, dH ppm): 2.32 (t, 1H, J = 2.4 Hz, alkyne proton), 5.00 (d, 2H, J = 2.4 Hz,
OCH2), 7.16–7.26 (m, 2H, ArH), 7.42 (ddd, 1H, J = 1.2, 7.5, 7.6 Hz, ArH), 7.54
(dd, 1H, J = 1.2, 8.6 Hz, ArH), 7.70 (ddd, 1H, J = 1.8, 7.8, 7.8 Hz, ArH), 8.18 (dd,
2H, J = 5.4, 9.3 Hz, ArH), 8.26 (dd, 1H, J = 1.2, 8.0 Hz, ArH). 13C NMR
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Synthesis, antimicrobial evaluation, and molecular…
(100 MHz, CDCl3, dC ppm): 59.2(CH2), 76.3(CH), 78.5(C), 115.5(CH), 115.7(CH),
118(CH), 124(CH), 124.9(C), 125.8(C), 127.1(CH), 131.3(CH), 133.7(CH),
138.4(CH), 155.2(C), 155.8(C), 162.8(C), 165.3(C), 174.8(C). HRMS Anal. Calcd.
For C18H11FO3 (M ? H)?: 295.077. Found: 295.0073. For C18H11FO3 (M ? Na)?:
317.059. Found: 316.9881.
6-Chloro-2-(4-fluorophenyl)-3-(prop-2-ynyloxy)-4H-chromen-4-one (4b)
Yellow solid, m. p. 136–138 °C, yield: 76 %. IR (KBr, cm-1): 3245 (C:CH), 3064
(=CH), 2916 (–CH), 2116 (C:C), 1625 (C=O), 1601 (C=C).1H NMR (400 MHz,
CDCl3, dH ppm): 2.33 (t, 1H, J = 2.4 Hz, alkyne proton), 4.99 (d, 2H, J = 2.6 Hz,
OCH2), 7.20 (t, 2H, J = 8.6 Hz, ArH), 7.51 (d, 1H, J = 9.2 Hz, ArH), 7.63 (dd, 1H,
J = 2.8, 9.0 Hz, ArH), 8.15 (dd, 2H, J = 5.3, 9.0 Hz, ArH), 8.20 (d, 1H,
J = 2.6 Hz, ArH). 13C NMR (100 MHz, CDCl3, dC ppm): 59.2(CH2), 76.4(CH),
78.3(C), 115.5(CH), 115.8(CH), 119.7(CH), 125.1(C), 126.8(C), 130.9(CH),
131.2(C), 131.3(CH), 133.9(CH), 138.4(CH), 153.5(C), 156.1(C), 162.9(C),
165.4(C), 173.7(C). HRMS Anal. Calcd. For C18H10ClFO3 (M ? H)?: 329.0381.
Found: 328.9676. For C18H10ClFO3 (M ? Na)?: 351.02. Found: 350.9520.
6,8-Dichloro-2-(4-fluorophenyl)-3-(prop-2-ynyloxy)-4H-chromen-4-one (4e)
1
Yellow solid, m. p. 187–189 °C, yield: 73 %. H NMR (400 MHz, DMSO, dH
ppm): 3.35 (t, 1H, J = 2.2 Hz, alkyne proton), 5.16 (d, 2H, J = 2.2 Hz, OCH2),
7.53 (t, 2H, J = 8.8 Hz, ArH), 8.18 (s, 1H, ArH), 8.30 (s, 1H, ArH), 8.43 (dd, 2H,
J = 5.5, 8.8 Hz, ArH). 13C NMR (100 MHz, DMSO, dC ppm): 58.8(CH2),
72.6(CH), 74.3(C), 115.5(CH), 115.7(CH), 123.1(C), 124.5(C), 125.1(C),
125.4(CH), 131(CH), 131.1(CH), 133.4(C), 142.3(C), 147.4(CH), 157.6(C),
164.3(C), 168.5(C), 170.5(C). HRMS Anal. Calcd. For C18H9Cl2FO3 (M ? H)?:
362.9991. Found: 362.9759.
6-Chloro-2-(4-fluorophenyl)-7-methyl-3-(prop-2-ynyloxy)-4H-chromen-4-one (4f)
Yellow solid, m. p. 144–146 °C, yield: 80 %. 1H NMR (400 MHz, CDCl3, dH ppm):
2.25 (t, 1H, J = 2.1 Hz, alkyne proton), 2.42 (s, 3H, CH3), 4.89 (d, 2H, J = 2.2 Hz,
OCH2), 7.10 (t, 2H, J = 8.4 Hz, ArH), 7.34 (brs, 1H, ArH), 8.01–8.08 (m, 3H,
ArH). 13C NMR (100 MHz, CDCl3, dC ppm): 20.9(CH3), 59.2(CH2), 76.4(CH),
78.4(C), 115.5(CH), 115.7(CH), 119.8(CH), 123(C), 125.3(C), 126.9(CH),
131.2(CH), 131.7(C), 138.2(CH), 143(C), 153.4(C), 155.7(C), 162.8(C), 165.3(C),
173.6(C). HRMS Anal. Calcd. For C19H12ClFO3 (M ? H)?: 343.0537. Found:
342.9975. For C19H12ClFO3 (M ? Na)?: 365.0357. Found: 364.9731.
General procedure for the synthesis of compounds (5a–f)
A catalytic amount of copper acetate Cu(OAc)2 (20 mol%) and sodium ascorbate
(10 mol%) in t-BuOH:H2O (3:1) were added to the stirred solution of substituted
2-(4-fluorophenyl)-3-(prop-2-ynyloxy)-4H-chromen-4-one (4a–f) (1 mmol) and
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V. S. Dofe et al.
benzyl azide (1 mmol) at room temperature for 18–20 h. The reaction progress was
observed by TLC using pet ether: ethyl acetate as a solvent system. After
completion of the reaction, the mixture was poured onto crushed ice and extracted
with ethyl acetate. The organic extract was dried over anhydrous sodium sulphate
and concentrated under reduced pressure to afford the corresponding crude product,
which was crystallized using ethanol.
3-((1-Benzyl-1H-1,2,3-triazol-4-yl)methoxy)-2-(4-fluorophenyl)-4H-chromen-4-one
(5a)
Yellow solid, m. p. 156–158 °C, yield: 86 %. IR (KBr, cm-1): 3134 (triazole ring
CH), 3011 (=CH), 2916 (–CH), 1627 (C=O), 1616 (C=C). H NMR (400 MHz,
1
CDCl3, dH ppm): 5.29 (s, 2H, NCH2), 5.45 (s, 2H, OCH2), 7.12 (t, 2H, J = 8.8 Hz,
ArH), 7.20 (dd, 2H, J = 3.1, 6.8 Hz, ArH), 7.34–7.35 (m, 3H, ArH), 7.41 (t, 1H,
J = 7.5 Hz, ArH), 7.52 (d, 1H, J = 8.4 Hz, ArH), 7.55 (s, 1H, triazole-H), 7.69
(ddd, 1H, J = 1.6, 7.7, 7.8 Hz, ArH), 8.05 (dd, 2H, J = 5.5, 8.8 Hz, ArH), 8.24 (dd,
1H, J = 1.8, 8.1 Hz, ArH). 13C NMR (100 MHz, CDCl3, dC ppm): 54.1(CH2),
65(CH2), 115.4(CH), 115.7(CH), 118(CH), 123.8(CH), 124(CH), 124.9(C),
125.7(C), 126.7(CH), 126.8(CH), 128.1(CH), 128.8(CH), 129.1(CH), 131(CH),
131.1(CH), 133.6(CH), 134.4(CH), 139.3(C), 144.1(C), 155.2(C), 155.3(C),
162.6(C), 165.2(C), 175(C). LCMS Anal. Calcd. For C25H18FN3O3 (M ? H)?:
428.1. Found: 428.1. For C25H18FN3O3 (M ? Na)?: 450.1. Found: 450.0.
3-((1-Benzyl-1H-1,2,3-triazol-4-yl)methoxy)-6-chloro-2-(4-fluorophenyl)-4H-
chromen-4-one (5b)
Yellow solid, m. p. 177–179 °C, yield: 90 %. IR (KBr, cm-1): 3136 (triazole ring
CH), 3064 (=CH), 2916 (–CH), 1636 (C=O), 1603 (C=C). H NMR (400 MHz,
1
DMSO, dH ppm): 5.25 (s, 2H, NCH2), 5.47 (s, 2H, OCH2), 7.14–7.17 (m, 2H, ArH),
7.18 (s, 1H, ArH), 7.20 (s, 1H, ArH), 7.28–7.30 (m, 3H, ArH), 7.70 (d, 1H,
J = 9.2 Hz, ArH), 7.77 (dd, 1H, J = 2.6, 9.2 Hz, ArH), 7.95 (s, 1H, triazole-H),
7.99 (dd, 2H, J = 5.5, 8.8 Hz, ArH), 8.03 (d, 1H, J = 2.2 Hz, ArH). 13C NMR
(100 MHz, DMSO, dC ppm): 54.1(CH2), 65(CH2), 115.5(CH), 115.7(CH),
119.7(CH), 123.8(CH), 125(CH), 125.1(C), 126.5(C), 126.6(CH), 128.1(CH),
128.8(CH), 129.1(CH), 130.9(CH), 131(C), 131.1(CH), 133.8(CH), 134.3(CH),
139.3(C), 143.8(C), 153.5(C), 155.6(C), 162.8(C), 165.3(C), 173.9(C). LCMS Anal.
Calcd. For C25H17ClFN3O3 (M ? H)?: 462.1. Found: 462.0. For C25H17ClFN3O3
(M ? Na)?: 484.1. Found: 484.0.
3-((1-Benzyl-1H-1,2,3-triazol-4-yl)methoxy)-2-(4-fluorophenyl)-8-methyl-4H-
chromen-4-one (5c)
Yellow solid, m. p. 187–189 °C, yield: 85 %. IR (KBr, cm-1): 3126 (triazole ring
CH), 3067 (=CH), 2918 (–CH), 1634 (C=O), 1615 (C=C). H NMR (400 MHz,
1
CDCl3, dH ppm): 2.51 (s, 3H, CH3), 5.25 (s, 2H, NCH2), 5.47 (s, 2H, OCH2),
7.14–7.20 (m, 4H, ArH), 7.26–7.29 (m, 3H, ArH), 7.33 (t, 1H, J = 7.7 Hz, ArH),
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Synthesis, antimicrobial evaluation, and molecular…
7.59 (d, 1H, J = 7.0 Hz, ArH), 7.94 (s, 1H, triazole-H), 8.02 (dd, 2H, J = 5.3,
9.0 Hz, ArH), 8.11 (s, 1H, ArH); 13C NMR (100 MHz, CDCl3, dC ppm): 15.3(CH3),
52.8(CH2), 64(CH2), 115.1(CH), 115.4(CH), 122.6(CH), 123.3(CH), 124.4(C),
124.6(CH), 126.9(CH), 127.2(C), 127.6(C), 127.9(CH), 128.5(CH), 130.6(CH),
130.7(CH), 134.3(CH), 135.4(CH), 138.3(CH), 142.1(C), 142.5(C), 153.1(C),
154.1(C), 161.9(C), 163.7(C), 174.2(C). HRMS Anal. Calcd. For C26H20FN3O3
(M ? H)?: 442.1567. Found: 442.0818. For C26H20FN3O3 (M ? Na)?: 464.1386.
Found: 464.0328.
3-((1-Benzyl-1H-1,2,3-triazol-4-yl)methoxy)-2-(4-fluorophenyl)-6-methyl-4H-
chromen-4-one (5d)
Yellow solid, m. p. 182–183 °C, yield: 87 %. IR (KBr, cm-1): 3106 (triazole ring
CH), 3012 (=CH), 2942 (–CH), 1637 (C=O), 1605 (C=C). H NMR (400 MHz,
1
CDCl3, dH ppm): 2.47 (s, 3H, CH3), 5.25 (s, 2H, NCH2), 5.49 (s, 2H, OCH2),
7.16–7.24 (m, 4H, ArH), 7.30–7.32 (m, 3H, ArH), 7.56–7.63 (m, 2H, ArH), 7.91 (s,
1H, triazole-H), 7.98–8.01 (m, 3H, ArH). 13C NMR (100 MHz, CDCl3, dC ppm):
20.5(CH3), 52.7(CH2), 64(CH2), 115.1(CH), 115.3(CH), 118(CH), 123.1(CH),
124.1(C), 124.8(CH), 126.7(C), 127.6(CH), 127.9(CH), 128.5(CH), 130.8(CH),
130.8(CH), 134.4(CH), 135(CH), 135.7(C), 138.3(CH), 142.4(C), 142.5(C), 153(C),
154.5(C), 162.6(C), 165.8(C), 173.9(C). HRMS Anal. Calcd. For C26H20FN3O3
(M ? H)?: 442.1567. Found: 442.1130. For C26H20FN3O3 (M ? Na)?: 464.1386.
Found: 464.0844.
3-((1-Benzyl-1H-1,2,3-triazol-4-yl)methoxy)-6,8-dichloro-2-(4-fluorophenyl)-4H-
chromen-4-one (5e)
Yellow solid, m. p. 197–199 °C, yield: 89 %. IR (KBr, cm-1): 3194 (triazole ring
CH), 3073 (=CH), 2939 (–CH), 1655 (C=O), 1601 (C=C). H NMR (400 MHz,
1
CDCl3, dH ppm): 5.24 (s, 2H, NCH2), 5.44 (s, 2H, OCH2), 7.11–7.15 (brs, 2H, ArH),
7.21–7.27 (m, 5H, ArH), 7.96 (s, 1H, triazole-H), 8.00–8.05 (m, 3H, ArH), 8.18
(brs, 1H, ArH). 13C NMR (100 MHz, CDCl3, dC ppm): 58.3(CH2), 69.4(CH2),
115.5(CH), 115.7(CH), 122.2(CH), 123.1(CH), 127.6(C), 128(C), 128.50(C),
130.9(CH), 131(CH), 131.3(CH), 133.6(CH), 137.4(CH), 138.2(CH), 140.3(CH),
140.8(C), 142.1(C), 142.5(C), 152.1(CH), 154.8(C), 158.7(C), 162(C), 167.7(C),
173.4(C). LCMS Anal. Calcd. For C25H16Cl2FN3O3 (M ? H)?: 496.1. Found:
496.2. For C25H16Cl2FN3O3 (M ? Na)?: 518. Found: 518.2.
3-((1-Benzyl-1H-1,2,3-triazol-4-yl)methoxy)-6-chloro-2-(4-fluorophenyl)-7-methyl-
4H-chromen-4-one (5f)
Yellow solid, m. p. 180–182 °C, yield: 93 %. IR (KBr, cm-1): 3180 (triazole ring
CH), 3035 (=CH), 2992 (–CH), 1622 (C=O), 1605 (C=C). H NMR (400 MHz,
1
DMSO, dH ppm): 2.48 (s, 3H, CH3), 5.23 (s, 2H, NCH2), 5.45 (s, 2H, OCH2),
7.13–7.17 (m, 4H, ArH), 7.27–7.29 (m, 3H, ArH), 7.62 (s, 1H, ArH), 7.90 (s, 1H,
triazole-H), 7.94–7.98 (dd, 2H, J = 5.5, 8.8 Hz, ArH), 8.01 (s, 1H, ArH). 13C NMR
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V. S. Dofe et al.
(100 MHz, DMSO, dC ppm): 20.3(CH3), 52.8(CH2), 64(CH2), 115.1(CH),
115.3(CH), 120.2(CH), 122.6(CH), 124.2(C), 124.6(CH), 126.4(C), 127.6(CH),
127.9(CH), 128.4(CH), 130.7(CH), 130.8(C), 135.4(CH), 138.3(CH), 139.7(CH),
142.4(C), 143.3(C), 147.3(C), 153(C), 154.7(C), 162.1(C), 165.4(C), 172.8(C).
HRMS Anal. Calcd. For C26H19ClFN3O3 (M ? H)?: 476.1177. Found: 476.0362.
For C26H19ClFN3O3 (M ? Na)?: 498.0997. Found: 498.0004.
Biological methods
Antimicrobial activity
The compounds were diluted in dimethylsulfoxide (DMSO) with 1 lg/mL
concentrations for bioassay. In vitro minimum inhibitory concentrations (MIC) of
the compounds were determined by the micro-broth dilution method in 96-well
microtitre plates according to the methods defined by the National Committee for
Clinical Laboratory Standards (NCCLS) against a panel of human pathogens. Test
compounds are serially double-diluted in growth medium. Plates were incubated at
30 °C for fungi and 37 °C for bacteria for 24 h.
Molecular docking
Molecular docking studies were performed using Glide v6.2 (Schrodinger, LLC).
For our studies, X-ray crystal structure of E. coli KAS III and S. aureus KAS III
were taken from PDB entry 1MZS and 1ZOW, respectively [34], and prepared for
docking using a protein preparation wizard. Water molecules in the structure were
removed and termini were capped by adding ACE and NMA residue. The bond
orders and formal charges were added for hetero groups, and hydrogen was added
to all atoms in the structure. Side chains that were not close to the binding cavity
and do not participate in salt bridges were neutralized. After preparation, the
structures were refined to optimize the hydrogen bond network using OPLS_2005
force field. This helps in reorientation of the side chain hydroxyl group. The
minimization was terminated when the energy converged or the RMSD reached a
maximum cut off of 0.30 A. Grids were then defined around refined structure by
centering on ligand using default box size. The extra precision (XP) docking mode
for compounds, optimized by Ligprep, was performed on the generated grid of
protein structure.
Results and discussion
Chemistry
The reaction sequence for title compounds 5a–f is as outlined in Scheme 2. The
synthesis of novel 3-((1-benzyl-1H-1,2,3-triazol-4-yl)methoxy)-2-(4-fluorophenyl)-
4H-chromen-4-one derivatives 5a–f furnished from 2-(4-fluorophenyl)-3-hydroxy-
123

Synthesis, antimicrobial evaluation, and molecular…
4H-chromen-4-ones 3a–f resulted in good yield according to the literature
procedure [35, 36] (Scheme 1). Claisen-Schmidt condensation of substituted
2-hydoxyacetophenone 1a–f and 4-fluorobenzaldehyde in ethanolic solution of
potassium hydroxide at room temperature gives derivatives of (E)-3-(4-fluo-
rophenyl)-1-(2-hydroxyphenyl)prop-2-en-1-ones 2a–f, which were converted into
corresponding 2-(4-fluorophenyl)-3-hydroxy-4H-chromen-4-ones 3a–f on oxidative
cyclization using hydrogen peroxide in ethanol (Scheme 1), which were alkylated
with propargyl bromide in the presence of K2CO3 in N,N0-dimethyl formamide
(DMF) afforded the substituted 2-(4-fluorophenyl)-3-(prop-2-ynyloxy)-4H-chro-
men-4-ones 4a–f in 70–80 % yield, which on further reaction with benzyl azide in
the presence of copper acetate and sodium ascorbate as catalyst in tert-butanol and
water (3:1) at room temperature for 18–20 h furnished the desired product 5a–f in
85–95 % yield (Scheme 2).
1
The synthesized compound 5a was confirmed by IR, MS, H NMR, and 13C
NMR spectral analysis. In the mass spectrum of 5a, the [M ? H]? was observed at
428.1 and [M ? Na]? was observed at 450.0. In the 1H NMR spectrum of
compound 5a, the two methylene groups attached to nitrogen & oxygen showed
singlets at d 5.29 and 5.45 ppm, respectively. In addition to this, the proton of
triazole ring observed at d 7.55 ppm. In the 13C NMR spectrum of compound 5a,
Scheme 1 Synthesis of 3-hydroxychromone derivatives 3a–f
F
F
N3
R1
R1
R2
R3
O
O
Br
R2
R3
O
Cu(OAc)2, Na-ascorbate
tBuOH:H2O (3:1), RT
K2CO3, DMF, RT
O
OH
O
4a-f
3a-f
F
R1
R2
R3
O
O
a R1=H
b R1=H
R2=H
R2=H
R3=H
R3=Cl
R3=H
O
N
N
c R1=CH3 R2=H
N
d R1=H
e R1=Cl
R2=H
R2=H
R2=CH3 R3=Cl
R3=CH3
R3=Cl
5a-f
f
R1=H
Scheme 2 Synthesis of 1,2,3-triazole derivatives 5a–f
123

V. S. Dofe et al.
the signal at 54.07 and 65.04 ppm indicate the presence of methylene carbon
attached to the nitrogen of the triazole ring and oxygen to the phenyl ring,
respectively. Similarly, all other derivatives 5b–f was satisfactory in good
conformity with the spectroscopic properties.
Antimicrobial activity
All the synthesized compounds were evaluated for their in vitro antibacterial
activity against Gram-positive bacteria viz. Staphylococcus aureus (NCIM 2178),
Bacillus subtilis (NCIM 2250), and Gram-negative bacteria Escherichia coli (NCIM
2137) and Pseudomonas aeruginosa (NCIM 2036). The compounds were also
screened for antifungal activity against Candida albicans (MTCC 277), Candida
Table 1 Antimicrobial
screening data of the compounds
2a–f, 3a–f, 4a–f, and 5a–f
Entry
Antimicrobial activitya (lg/mL)
Antibacterial activity Antifungal activity
Sa
Bs
Ec
Pa
Ca
Cg
Ct
2a
100
200
50
100
200
100
50
200
200
100
400
200
100
50
200
200
100
200
200
100
50
100
50
100
100
25
100
50
2b
2c
25
50
2d
50
25
50
50
2e
100
100
200
400
200
200
100
400
100
100
50
200
200
200
200
100
200
100
200
100
100
50
50
50
25
2f
25
25
25
3a
25
25
25
3b
100
50
50
50
50
50
3c
50
50
50
25
3d
50
50
50
25
25
3e
25
25
100
50
50
50
3f
200
400
400
100
400
200
100
400
100
50
100
200
200
100
200
200
100
400
100
100
100
200
50
100
100
100
50
100
50
4a
25
4b
50
200
100
50
4c
50
4d
50
100
50
25
25
4e
25
25
25
25
4f
200
200
100
100
200
50
200
400
200
100
100
25
50
50
50
5a
25
50
25
Sa, Staphylococcus aureus; Bs,
Bacillus subtilis; Ec,
Escherichia coli; Pa,
5b
100
25
50
100
50
5c
25
Pseudomonas aeruginosa; Ca,
Candida albicans; Cg, Candida
glabrata; Ct, Candida tropicalis
5d
200
100
50
50
50
25
5e
12.5
12.5
–
25
12.5
25
a
5f
25
25
12.5
–
Minimum inhibitory
concentration (lg/mL) against
the pathological strains based on
micro-broth dilution method
Streptomycin
Miconazole
12.5
–
400
–
400
–
200
–
–
12.5
400
800
123

Synthesis, antimicrobial evaluation, and molecular…
glabrata (NCIM 3236), and Candida tropicalis (NCIM 3110) (Table 1). The
minimum inhibitory concentration (MIC) values were determined by micro-broth
dilution method. The results of antimicrobial screening were compared with the
standard antibacterial drug streptomycin and antifungal drug miconazole.
Among the newly synthesised compounds, compound 5a showed similar activity
against B. subtilis, and compounds 2d, 4a, 4b, 4d, 5a showed similar activity
against E. coli and P. aeruginosa as compared to standard streptomycin. Compound
2d has a methyl group in chalcone, 4a, and 5a have no substituent on a chromone
ring, 4b contains a chloro group and 4d contains a methyl group on a chromone ring,
which accounts for the enhanced activity. Compound 4e with dichloro and
compound 5f with chloro, methyl substituent on a chromone ring showed good
activity with a MIC of 25 lg/mL against S. aureus. Compound 5e with dichloro and
compound 5f with chloro, methyl substituent on a chromone ring showed potent
activity with a MIC of 25 lg/mL against B. subtilis and compound 3e with dichloro
substituent on a chromone ring also showed potent activity with a MIC of 25 lg/mL
against E. coli and P. aeruginosa.
Remarkably and interestingly, 1,2,3-triazole-based chromones are more
susceptible to C. tropicalis and C. glabrata fungal strains. Compounds 5e and
5f showed similar activity against C. albicans as compared with the standard drug
miconazole. Compounds 5e and 5f with a MIC of 12.5 lg/mL are highly potent
antifungal agents against C. tropicalis and C. glabrata, respectively, while
compounds 2c, 2f, 3a, 3d, 4d, 4e, 5c, and 5e with a MIC of 25 lg/mL also
showed excellent activity against C. glabrata, and compounds 2e, 2f, 3a, 3c, 3d,
4e, 4a, 5d, and 5f with a MIC of 25 lg/mL also showed excellent activity against
C. tropicalis as compared with the standard drug miconazole. Compound 5e with
dichloro substituent and compound 5f with chloro, methyl substituent indicated
that the compounds with more electron donating groups are responsible for the
enhanced activity of the compounds.
Among the four series, 5a–f which contains chromone based 1,2,3-triazole
moieties showed potent antimicrobial activity and highlight the importance of 1,2,3-
triazole moiety. The results suggest compounds 3e, 4e, 5e, and 5f would be the most
promising for further development as antimicrobial agents.
Molecular docking
In order to understand the binding of the synthesized compounds with the receptor,
docking study was performed. All the compounds were docked in the crystal
structure of Escherichia coli KAS III (PDB ID 1MZS) and Staphylococcus aureus
KAS III (PDB ID 1ZOW). b-Ketoacyl carrier protein synthase KAS III is a
condensing enzyme that initiates fatty acid bio synthesis in most bacteria and is a
key target enzyme to overcome the antibiotic resistance problem. Streptomycin was
used as a standard for docking at both the receptors. The docking pose of
compounds showing higher scores from each series compounds 2b, 5d, 3a, 4d for
Escherichia coli KAS III and compounds 2d, 3d, 4a, 5a for Staphylococcus aureus
KAS III were compared with the standard (Table 2). Molecular basis of interactions
between target enzymes and synthesized compounds can be understood with the
123

V. S. Dofe et al.
Table 2 Docking Score of the compounds 2a–f, 3a–f, 4a–f, and 5a–f
Entry
G-score with
E. coli
KAS III
G-score with S.
aureus
KAS III
Entry
G-score with
E. coli
KAS III
G-score with
S. aureus
KAS III
Streptomycin
-11.162
-11.4328
-7.7021
4a
4b
4c
4d
4e
4f
-5.25426
-5.08994
-5.38016
-5.86049
-4.61324
-4.81936
-4.66795
-5.06158
-3.64827
-6.2981
-6.1598
2a
2b
2c
2d
2e
2f
-7.18584
-7.55733
-5.61404
-7.34917
-6.74524
-6.19819
-6.74347
-6.18159
-5.39618
-5.9225
-6.12157
-5.68088
-5.17253
-4.37662
-5.81738
-6.09342
-5.30517
-4.47729
-4.77076
-4.86242
-5.82797
-7.81756
-7.00403
-8.17479
-7.84359
-7.45888
-6.23065
-6.54076
-5.16771
-6.47826
-6.0011
5a
5b
5c
5d
5e
5f
3a
3b
3c
3d
3e
3f
-4.99221
-4.73574
-6.22402
-6.22402
-6.6416
Fig. 1 Binding pose of compound 5d within the Escherichia coli KAS III (1MZS) active site
help of docking pose. Docking pose of streptomycin with Escherichia coli KAS III
indicates that it forms hydrogen bonding with ARG 36, ARG 249, and ASP 150. For
the crystal structure of Escherichia coli KAS III, similar poses have been observed
for the compound 5d (Fig. 1).
123

Synthesis, antimicrobial evaluation, and molecular…
Fig. 2 Binding pose of Compound 5a within the Staphylococcus aureus KAS III (1ZOW) active site
Docking pose of compound 5a with the crystal structure of Staphylococcus
aureus KAS III has been observed as depicted in Fig. 2.
Conclusions
In conclusion, we have efficiently synthesized series of chromone derivatives and
evaluated for antimicrobial activities. Biological testing showed that the synthesized
derivatives played an altered pattern of biological activity compared to the standard
drugs streptomycin and miconazole. Compounds 5a–f, which contain chromone-
based 1,2,3-triazoles showed potent antimicrobial activity as compared with 3a–f
and 4a–f series. The compounds 3e, 4e, 5e, and 5f were identified as potent
antimicrobial agents. It can be concluded that incorporation of a 1,2,3-triazole ring
into chromone moiety has enhanced the biological effect with the scope of
developing chromone-based 1,2,3-triazole derivatives as promising antibacterial
and antifungal derivatives. Binding of the most active compounds against bacteria
Escherichia coli and Staphylococcus aureus into the crystal structure of Escherichia
coli KAS III and Staphylococcus aureus KAS III was studied using molecular
docking studies.
Acknowledgments Author V.S.D. is very grateful to the Council of Scientific and Industrial Research
(CSIR), New Delhi, India, for providing Senior Research Fellowship and Sophisticated Analytical
Instrumentation Facility (SAIF), Panjab University, Chandigarh for providing spectral data. We are
thankful to Head, Department of Chemistry, Dr. Babasaheb Ambedkar Marathwada University,
Aurangabad, Maharashtra, for providing laboratory facility. We are also thankful to the Rajarshi Shahu
College, Latur, for providing biological activities.
123

V. S. Dofe et al.
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