Synthesis and Antiviral Bioassay of New Diphenyl Ether-based Compounds

Article abstract of DOI:10.1111/cbdd.12775

A set of diphenyl ether derivatives bearing different heterocycles were synthesized from 4-phenoxybenzohydrazide 1 in good yield. Synthesized compounds were screened against a broad panel of viruses in different cell cultures and some of the synthesized compounds showed promising antiviral properties.

Full text of DOI:10.1111/cbdd.12775

Chem Biol Drug Des 2016
Research Article
Synthesis and Antiviral Bioassay of New Diphenyl
Ether-based Compounds
Tarek S. Ibrahim1, Amany M. M. AL-Mahmoudy1,
Various antiviral agents are available in the market, but
most of them are suffering from some limitations such
as limited efficacy, development of resistance, and
adverse effects. At present, many researches are going
Mohamed Elagawany2, Mohamed A. Ibrahim3,4
and Siva S. Panda5,*
1Department of Pharmaceutical Organic Chemistry,
on to search new lead compounds that either target
Faculty of Pharmacy, Zagazig University, Zagazig 44519,
Egypt
distinct stages of the viral replication cycle in a virus-
specific way or have a broader spectrum of activity
with minimum adverse effect or without any adverse
effect. (4,5) In this context, we have synthesized a set
of diphenyl ether attached to various heterocyclic
moieties and screened them against a broad panel of
viruses.
2Department of Pharmaceutical Chemistry, Faculty of
Pharmacy, Damanhour University, Damanhour 22516, Egypt
3Department of Pharmaceutical Chemistry, College of
Pharmacy, Almaarefa Colleges for Science and
Technology, Riyadh 11597,Saudi Arabia
4Department of Organic Chemistry, College of Pharmacy,
Misr University for Science and Technology, 6th of
October, P.O. Box: 77, Giza, Egypt
Biaryl ether derivatives are routinely found as very impor-
tant structural elements for organic synthesis, (6–8) natural
products (9,10), and other biologically active compounds.
(11) Etravirine and Rilpivirine are biaryl ether antiviral drugs
(Figure 1) that used in the treatment of HIV (12–14) and
MK-4965 is under clinical trial for antiviral properties. (15)
But these drugs are still having major issue with their
side-effects.
5Department of Chemistry & Physics, Augusta University,
Augusta, GA 30912, USA
*Corresponding author: Siva S. Panda,
sspanda12@gmail.com
A set of diphenyl ether derivatives bearing different
heterocycles were synthesized from 4-phenoxybenzo-
hydrazide 1 in good yield. Synthesized compounds
were screened against a broad panel of viruses in
different cell cultures and some of the synthesized
compounds showed promising antiviral properties.
Azaheterocycle derivatives are known for their versatile
biological properties. The nitrogen atom in the heterocy-
cles may modify the electron distribution inside the scaf-
fold which may lead to a modification of the chemical and
physical properties of the compounds (solubility, polar sur-
face area, etc.).
Key words: antiviral, chemical biology, diphenyl ethers, drug
discovery, heterocycles
Received 24 December 2015, revised 10 March 2016 and
accepted for publication 29 March 2016
Herein, we designed and synthesized some modified ana-
logs of biaryl ether antiviral agents using 4-phenoxybenzo-
hydrazide
1 as building block. All the synthesized
Viral infections is a devastating and one of the common
infectious health problems. Acquired immunodeficiency
syndrome (AIDS) caused by the human immunodeficiency
virus (HIV) remains a health threat of global significance.
Beside HIV, there are several other virus causing various
diseases like herpesvirus family that contains eight known
human viruses, including herpes simplex virus 1 (HSV-1)
and herpes simplex virus 2 (HSV-2). HSV-1 causes stomati-
tis, encephalitis, and ocular infections, while herpes simplex
virus 2 (HSV-2) causes genital lesions. (1) Vesicular stomati-
tis virus (VSV) causes an economically important disease in
cattle, horses, and swine. (2) Varicella-zoster virus (VZV) is
the causative agent of chickenpox and shingles. (3) Influ-
enza is another serious public health problem that causes
severe illness and death in high-risk populations.a
compounds screened for in vitro antiviral properties
against various viruses.
Experimental Section
All chemicals were purchased from Sigma-Aldrich and
Cornell Lab (Cairo, Egypt). 1H and 13C NMR spectra were
recorded at 500 and 125 MHz, respectively, on a Varian
Inova 500 MHz spectrometer at School of Chemistry,
University of Wollongong, Wollongong 2522, Australia.
Melting points were determined using a Gallenkamp (Grif-
fin) melting point apparatus. Elemental analyses were car-
ried out at the Micro Analytical Center, Faculty of Science,
Cairo University, Cairo, Egypt.
ª 2016 John Wiley & Sons A/S. doi: 10.1111/cbdd.12775
1

Ibrahim et al.
Figure 1: Biaryl ether-derived antiviral
agents.
General procedure for preparation of pyrazole/
pyrazoline derivatives (2, 3, 4a, b)
155.8, 165.2, 169.4. Found, %: C, 73.61; H, 5.48; N
9.87. C18H16N2O2. Calculated, %: C, 73.95; H, 5.52; N,
9.58.
To a solution of the acid hydrazide 1 (10 mmol) in 30 mL
EtOH containing 2 mL glacial acetic acid, an equimolar
amount of 1,3-diketo compounds (acetylacetone, benzoy-
lacetone, or ethyl acetoacetate or ethyl cyanoacetate) was
added. The reaction mixture was heated under reflux con-
dition for 12 h. The mixture was cooled, concentrated to a
small volume, and added to ice-cold water. The product
was filtered, washed with H2O, and recrystallized from
ethanol.
(3-Methyl-5-phenyl-1H-pyrazol-1-yl)(4-
phenoxyphenyl)methanone (4b)
Yield 84%; mp 191–193 °C; 1H NMR (DMSO-d6) d 2.36
(s, 3H), 6.37 (s, 1H), 7.08 (d, J = 7.0 Hz, 2H), 7.12–7.24
(m, 2H), 7.32 (t, J = 8.0 Hz, 3H), 7.42 (t, J = 7.5 Hz, 3H),
7.95 (d, J = 8.5 Hz, 2H), 8.04 (d, J = 8.5 Hz, 2H);13C
NMR (DMSO-d6) d 15.2, 107.4, 117.8, 118.4, 121.6,
122.0, 125.9, 126.4, 127.9, 128.3, 128.9, 129.4, 142.3,
144.5, 152.0, 155.8, 164.5, 165.6. Found, %: C, 77.67;
H, 5.43; N 7.97. C23H18N2O2. Calculated, %: C, 77.95; H,
5.12; N, 7.90.
5-Methyl-2-(4-phenoxybenzoyl)-2,4-dihydro-3H-
pyrazol-3-one (2)
Yield 80%; mp 155–157 °C; 1H NMR (DMSO-d6) d 1.98
(s, 3H), 4.17 (s, 2H), 7.08 (d, J = 7.5 Hz, 2H), 7.32 (t,
J = 8.0 Hz, 3H), 7.97 (d, J = 8.0 Hz, 2H), 8.02 (d,
J = 8.5 Hz, 2H);13C NMR (DMSO-d6) d 15.5, 46.2, 117.4,
117.8, 118.4, 121.8, 122.0, 126.9, 127.4, 128.3, 128.9,
152.0, 155.8, 157.3, 164.5, 170.2. Found, %: C, 69.04;
H, 4.85; N 9.76. C17H14N2O3. Calculated, %: C, 69.38; H,
4.79; N, 9.52.
2-(4-Phenoxybenzoyl)-N-phenylhydrazine-1-
carbothioamide (5)
A mixture of phenyl isothiocyanates (1.5 mmol) and acid
hydrazide 1 (1 mmol) in anhydrous ethanol was refluxed
on a water bath for 3 h. The solid obtained on cooling
was filtered, washed with water, and recrystallized from
ethanol. Yield 92%; mp 205–207 °C; 1H NMR (DMSO-d6)
d 7.08 (t, J = 8.5 Hz, 3H), 7.15 (t, J = 7.5 Hz, 2H), 7.22
(t, J = 7.5 Hz, 2H), 7.32 (d, J = 8.0 Hz, 2H), 7.45 (t,
J = 7.5 Hz, 3H), 7.98 (d, J = 8.5 Hz, 2H), 9.68 (s, 1H),
9.79 (s, 1H), 10.48 (s, 1H); 13C NMR (DMSO-d6) d 117.8,
120.0, 124.9, 125.5, 126.5, 127.7, 128.4, 130.6, 130.8,
139.7, 156.1, 160.4, 165.7. Found, %: C, 66.25; H, 4.34;
N 11.76. C20H17N3O2S. Calculated, %: C, 66.10; H, 4.72;
N, 11.56.
5-Amino-2-(4-phenoxybenzoyl)-2,4-dihydro-3H-
pyrazol-3-one (3)
Yield 81%; mp 211–213 °C; 1H NMR (DMSO-d6) d 3.67
(s, 2H), 6.32 (s, 2H), 7.06 (d, J = 7.5 Hz, 2H), 7.22 (t,
J = 8.0 Hz, 3H), 7.45 (d, J = 8.0 Hz, 2H), 7.92 (d,
J = 8.5 Hz, 2H);13C NMR (DMSO-d6)
d 70.2, 116.8,
117.5, 117.9, 118.4, 121.8, 122.0, 152.0, 155.8, 157.3,
160.3, 164.5, 170.0. Found, %: C, 64.94; H, 4.23; N
14.66. C16H13N3O3. Calculated, %: C, 65.08; H, 4.44; N,
14.23.
5-(4-Phenoxyphenyl)-4-phenyl-4H-1,2,4-triazole-3-
thiol (6) (16)
(3,5-Dimethyl-1H-pyrazol-1-yl)(4-phenoxyphenyl)
methanone (4a)
Yield 84%; mp 169–171 °C; 1H NMR (DMSO-d6) d 7.02
(d, J = 8.0 Hz, 2H), 7.11 (d, J = 8.0 Hz, 3H), 7.24 (t,
Yield 85%; mp 175–177 °C; 1H NMR (DMSO-d6) d 2.17
(s, 3H), 2.49 (s, 3H), 6.27 (s, 1H), 7.02–7.09 (m, 4H), 7.32
(t, J = 8.0 Hz, 1H), 7.45 (t, J = 7.5 Hz, 2H), 7.95 (d,
J = 8.5 Hz, 2H); 13C NMR (DMSO-d6) d 14.3, 14.6, 111.6,
116.9, 118.4, 121.6, 122.0, 128.3, 129.4, 144.5, 152.0,
J = 6.5 Hz, 2 H), 7.36 (t, J = 8.0 Hz, 2H), 7.46 (t,
J = 7.0 Hz, 3H), 7.94 (d, J = 8.5 Hz, 2H), 12.74 (s, 1H);
13C NMR (DMSO-d6) d 117.7, 118.3, 120.4, 125.2, 125.7,
127.6, 128.0, 128.4, 128.6, 130.8, 132.1, 133.6, 143.1,
155.6, 161.5, 167.2, 172.3.
2
Chem Biol Drug Des 2016

Diphenyl Ether Derivatives as Antivirals
General procedure for synthesis of compounds
(7a–c)
7.06 (m, 4H), 7.11–7.20 (m, 4H), 7.25 (t, J = 10.5 Hz, 2H),
7.47 (d, J = 12.0 Hz, 2H), 7.95 (d, J = 15.0 Hz, 2H),
10.41 (s, 1H); 13C NMR (DMSO-d6) d 117.9, 118.6, 121.4,
121.9, 124.3, 125.5, 126.1, 128.4, 130.0, 139.6, 153.1,
155.8, 169.4. Found, %: C, 69.60; H, 4.32; N 12.11.
A mixture of compound 5 (0.01 mol), phenacyl bromide
derivatives (0.01 mol), and sodium acetate (0.2 mol) in etha-
nol (60 mL) was heated under reflux condition for 8–10 h.
The mixture was cooled and diluted with water. The precipi-
tate obtained was filtered, dried, and recrystallized using
aqueous ethanol.
C
20H15N3OS. Calculated, %: C, 69.54; H, 4.38; N, 12.17.
Synthesis of potassium 2-(4-phenoxybenzoyl)
hydrazine-1-carbodithioate (9)
(E)-N’-(3,4-Diphenylthiazol-2(3H)-ylidene)-4-
Acid hydrazide 3 was treated with carbon disulfide in ethano-
lic potassium hydroxide by following the method of Reid and
Heindel (17) to afford potassium salt of N’-phenoxybenzoyl-
hydrazine carbodithioic acid. Potassium salt was washed
with ether and used in next step without purification.
phenoxybenzohydrazide (7a)
1
Yield 83%; mp = 169–170 °C; H NMR (DMSO-d6) d 6.69
(s, 1H), 7.0 (t, J = 7.5 Hz, 2H), 7.12–7.18 (m, 3H), 7.23 (t,
J = 7.0 Hz, 2H), 7.36 (t, J = 8.0 Hz, 2H), 7.45 (t, J =
8.5 Hz, 2H), 7.52 (t, J = 7.5 Hz, 2H), 7.62 (d, J = 8.0 Hz,
2H), 7.89 (d, J = 9.0 Hz, 2 H), 7.96 (t, J = 7.5 Hz, 2H),
10.63 (s, 1H); 13C NMR (DMSO-d6) d 100.3, 116.9, 118.3,
119.7, 121.7, 121.9, 124.5, 127.6, 128.0, 128.4, 128.6,
129.8, 130.2, 133.4, 133.6, 139.8, 146.3, 155.3, 159.7,
166.4. Found, %: C, 72.41; H, 4.32; N 9.40. C28H21N3O2S.
Calculated, %: C, 72.55; H, 4.57; N, 9.06.
Synthesis of 4-amino-5-(4-phenoxyphenyl)-4H-
1,2,4-triazole-3-thiol (10)
A suspension of potassium dithiocarbazinate 9 (0.1 mole)
in water (5 mL) and hydrazine hydrate (15 mL, 0.3 mole)
was refluxed for 30 min with occasional shaking. The color
of the reaction mixture changed to green with the evolu-
tion of hydrogen sulfide gas (lead acetate paper and odor).
A homogeneous reaction mixture was obtained during the
reaction process. The reaction mixture was cooled to
room temperature and diluted with water (100 mL). On
acidification with AcOH, the desired triazole was precipi-
tated out. The precipitate was filtered, washed with cold
water, and recrystallized from ethanol. Yield 80%; mp
160–162 °C; 1H NMR (CDCl3) d 4.83 (s, 2H), 7.07–7.11
(m, 4H), 7.20 (t, J = 7.5 Hz, 1H), 7.40 (t, J = 8.0 Hz, 2H),
8.08 (d, J = 8.5 Hz, 2H), 10.59 (s, 1H); 13C NMR (CDCl3)
d 117.6, 118.7, 122.3, 127.3, 127.5, 131.4, 147.6, 158.1,
160.4, 182.5. EI-MS (m/z, 100%): 284 [M+] (100). Found,
%: C, 58.95; H, 4.55; N 20.05. C14H12N4OS. Calculated,
%: C, 59.14; H, 4.25; N, 19.70.
(E)-N’-(4-(4-Chlorophenyl)-3-phenylthiazol-2(3H)-
ylidene)-4-phenoxybenzohydrazide (7b)
Yield 85%; mp 169–170 °C; 1H NMR (DMSO-d6) d 6.99–
7.02 (m, 3H), 7.06–7.14 (m, 6H), 7.24 (t, J = 7.0 Hz, 2H),
7.36 (t, J = 7.5 Hz, 2H), 7.45 (t, J = 8.5 Hz, 2H), 7.61 (d,
J = 8.0 Hz, 2H), 7.89 (d, J = 9.0 Hz, 2 H), 10.66 (s, 1H);
13C NMR (DMSO-d6) d 104.7, 117.7, 118.4, 119.1, 119.3,
120.5, 122.5, 125.3, 127.6, 128.4, 129.8, 131.0, 139.4,
144.3, 146.2, 156.0, 158.1, 160.4, 160.4, 163.2. Found,
%: C, 67.65; H, 4.12; N 8.81. C28H20ClN3O2S. Calculated,
%: C, 67.53; H, 4.05; N, 8.44.
(E)-N’-(4-(4-Methoxyphenyl)-3-phenylthiazol-2(3H)-
ylidene)-4-phenoxybenzohydrazide (7c)
Yield 86%; mp 179–181 °C; 1H NMR (DMSO-d6) d 3.93
(s, 3H), 6.94 (d, J = 8.5 Hz, 2H), 6.99–7.12 (m, 3H), 7.19
(t, J = 7.5 Hz, 2H), 7.26 (t, J = 7.5 Hz, 2H), 7.35–7.44 (m,
6H), 7.53 (d, J = 8.0 Hz, 2H), 7.92 (d, J = 9.0 Hz, 2 H),
10.67 (s, 1H); 13C NMR (DMSO-d6) d 56.4, 106.3, 117.7,
118.4, 119.1, 119.3, 120.5, 122.5, 125.2, 126.6, 128.4,
129.7, 130.9, 139.3, 145.1, 146.3, 155.9, 158.1, 160.4,
160.4, 164.1. Found, %: C, 70.49; H, 4.63; N 8.35.
C29H23N3O3S. Calculated, %: C, 70.57; H, 4.70; N, 8.51.
General procedure for compound (11a-b)
Method A: To 0.10 mmol KOH in 150 mL of methanol
solution were added 0.10 mmol of 10 and then 20 mL of
CS2. After the mixture was heated to reflux for 24 h, the
solvent was removed under reduced pressure, the residue
was poured into 200 mL of water, and the latter was acid-
ified with conc. HCl to yield a white solid of 11a. Method
B: A mixture of 10 (10 mmol) and thiourea or urea
(12 mmol) was fused at 180–190 °C for 3 h and then
allowed to cool and washed with water. The solid was fil-
tered and recrystallized from ethanol to give white plates
of 11a or 11b.
Synthesis of 5-(4-phenoxyphenyl)-N-phenyl-1,3,4-
thiadiazol-2-amine (8)
Concentrated sulfuric acid (1 mL) was added dropwise to
compound 7 (0.001 mol) and stirred at room temperature
for 30 min. The reaction mixture was poured into ice water
and the precipitate was washed with sodium carbonate
solution followed by water and recrystallized from ethanol.
Yield 92%; mp 201–203 °C; 1H NMR (DMSO-d6) d 7.02–
3-(4-Phenoxyphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]
thiadiazole-6-thiol (11a)
Yield 75%; mp 176–178 °C; H NMR (DMSO-d6) d 7.13 (d,
1
J = 7.5 Hz, 2H), 7.22 (t, J = 8.0 Hz, 3H), 7.46 (d,
J = 7.5 Hz, 2H), 8.22 (d, J = 8.5 Hz, 2H), 10.44 (s, 1H); 13C
Chem Biol Drug Des 2016
3

Ibrahim et al.
NMR (DMSO-d6) d 117.4, 117.8, 118.3, 119.4, 119.7,
with water, dried, and finally recrystallized from ethanol to
124.6, 128.9, 130.0, 130.3, 141.2, 154.4, 155.2, 163.8,
furnish the desired compound. Yield 90%; mp 223–
225 °C; H NMR (DMSO-d6) d 7.01–7.21 (m, 3H), 7.24 (d,
1
181.5. Found, %: C, 55.30; H, 3.13;
N
17.45.
C
15H10N4OS2. Calculated, %: C, 55.20; H, 3.09; N, 17.17.
J = 8.5 Hz, 2H), 7.44 (t, J = 8.0 Hz, 2H), 7.85 (d,
J = 8.0 Hz, 1H), 7.92 (d, J = 9.0 Hz, 1H), 11.89 (s, 1H);
13C NMR (DMSO-d6) d 117.7, 118.4, 122.1, 123.3, 123.5,
130.0, 133.4, 135.6, 158.1, 160.4, 165.1, 182.5. Found,
%: C, 58.52; H, 3.33; N 9.67. C14H10N2OS2. Calculated,
%: C, 58.72; H, 3.52; N, 9.78.
3-(4-Phenoxyphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]
thiadiazol-6-ol (11b)
Yield 73%; mp 213- 215 °C; 1H NMR (DMSO-d6) d 7.02
(d, J = 7.5 Hz, 2H), 7.07–7.23 (m, 2H), 7.25 (t,
J = 7.5 Hz, 3H), 8.13 (d, J = 8.5 Hz, 2H), 10.42 (s, 1H);
13C NMR (DMSO-d6) d 117.9, 118.4, 119.9, 123.4, 128.9,
129.4, 130.4, 149.9, 155.1, 157.8, 163.8. EI-MS (m/z,
100%): 310 [M+] (100). Found, %: C, 58.01; H, 3.21; N
18.26. C15H10N4O2S. Calculated, %: C, 58.06; H, 3.25;
N, 18.05.
Synthesis of 2-(4-phenoxyphenyl)-1,3,4-oxadiazole
(14)
Hydrazide 1 (1 mmol) and triethyl orthoformate (2 mL)
were refluxed for 3 h. The excess ester was evaporated;
the residue was cooled and triturated with hexane. The
solid was filtered off and recrystallized from 1:1 ethanol–
water. White solid, yield 73%; mp 140–144 °C; 1H NMR
(DMSO-d6) d 7.19–7.23 (m, 4H), 7.25 (t, J = 7.5 Hz, 1H),
7.45 (t, J = 7.5 Hz, 2H), 7.08 (d, J = 8.2 Hz, 2 H), 9.01 (s,
1H);13C NMR (DMSO-d6) d 117.8, 118.3, 119.9, 124.7,
128.9, 130.3, 154.2, 155.1, 160.2, 163.3. Found, %: C,
70.50; H, 4.48; N 11.37. C14H10N2O2. Calculated, %: C,
70.58; H, 4.23; N, 11.76.
General procedure for compound (12a-b)
A mixture of 10 (0.005 mol) and a cyano compound
RCH2CN (0.005 mol) in glacial AcOH (25 mL) and a cat-
alytic amount of conc. H2SO4 was refluxed for 3 h and
then, after cooling, was diluted with H2O (20 mL) and neu-
tralized with NH3 solution. The crude product thus
obtained was collected by filtration, washed with H2O, and
crystallized (EtOH) to give 12a,b as colorless crystals in
62–80% yield.
General procedure for preparation of Hydrazones
(15a–c)
A solution of hydrazide 3 (10 mmol) in ethanol (40 ml) was
refluxed with various aldehydes (10 mmol) for 3–6 h. The
excess of solvent was removed under reduced pressure.
After cooling to room temperature, a white solid appeared.
This crude product was filtered, washed with diethyl ether,
dried, and recrystallized from ethanol.
6-Methyl-3-(4-phenoxyphenyl)-[1,2,4]triazolo[3,4-
b][1,3,4]thiadiazole (12a)
Yield 80%; mp 180–182 °C; 1H NMR (DMSO-d6) d 2.98
(s, 3H), 7.02 (d, J = 7.5 Hz, 2H), 7.09–7.24 (m, 2H), 7.25
(t, J = 7.5 Hz, 3H), 8.33 (d, J = 8.5 Hz, 2H); 13C NMR
(DMSO-d6) d 21.3, 118.2, 118.6, 120.4, 123.4, 128.7,
129.6, 131.4, 149.9, 155.3, 157.8, 166.8. Found, %: C,
61.99; H, 3.54; N 18.25. C16H12N4OS. Calculated, %: C,
62.32; H, 3.92; N, 18.17.
(E)-N’-(Furan-2-ylmethylene)-4-
phenoxybenzohydrazide (15a)
White solid, yield 89%; mp 192–194 °C; 1H NMR (DMSO-
d6): d 6.63 (t, J = 5.4 Hz, 1H), 6.92 (d, J = 7.5 Hz, 2H),
7.11 (t, J = 8.0 Hz, 4H), 7.22 (t, J = 7.5 Hz, 1H), 7.45 (t,
J = 7.0 Hz, 2H), 7.94 (d, J = 8.0 Hz, 2H), 8.35 (s, 1H),
11.76 (s, 1H);13C NMR (DMSO-d6) d 112.3, 117.5, 119.6,
124.4, 127.9, 129.8, 130.3, 137.3, 145.1, 149.5, 155.5,
159.9, 162.3. Found, %: C, 70.37; H, 4.32; N 9.50.
2-{3-(4-Phenoxyphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]
thiadiazol-6-yl}acetamide (12b)
Yield 62%; mp 210–212 °C; H NMR (DMSO-d6) d 3.96 (s,
2H), 6.94 (d, J = 7.5 Hz, 2H), 7.09–7.24 (m, 2H), 7.25 (t,
J = 7.5 Hz, 3H), 7.91 (s, 2H), 8.04 (d, J = 8.5 Hz, 2H); 13C
NMR (DMSO-d6) d 37.2, 117.8, 118.3, 121.4, 123.5, 128.7,
129.7, 131.6, 149.9, 155.3, 157.8, 166.8, 167.3, 169.9.
Found, %: C, 58.37; H, 3.62; N 20.08. C17H13N5O2S. Cal-
culated, %: C, 58.11; H, 3.73; N, 19.93.
1
C
18H14N2O3. Calculated, %: C, 70.58; H, 4.61; N, 9.15.
(E)-4-Phenoxy-N’-(thiophen-2-ylmethylene)
benzohydrazide (15b)
White solid, yield 92%; mp 182–183 °C; 1H NMR (DMSO-
d6): d 7.08–7.14 (m, 5H), 7.22 (t, J = 7.0 Hz, 1H), 7.44 (d,
J = 7.5 Hz, 3H), 7.65 (d, J = 7.0 Hz, 1H), 7.94 (d,
J = 8.5 Hz, 2H), 8.68 (s, 1H), 11.78 (s, 1H); 13C NMR
(DMSO-d6) d: 117.5, 119.6, 124.4, 127.8, 127.9, 128.8,
129.8, 130.2, 130.3, 133.8, 139.2, 142.7, 159.9, 162.3.
Found, %: C, 67.36; H, 3.39; N 9.04. C18H14N2O2S. Cal-
culated, %: C, 67.06; H, 4.38; N, 8.69.
Synthesis of 5-(4-phenoxyphenyl)-1,3,4-
thiadiazole-2-thiol (13)
Potassium salt 11 (0.05 mol) was added portion-wise to
98% H2SO4 (15 mL) and the resulting clear solution was
stirred at room temperature for 4 h. The mixture was cau-
tiously added to crushed ice, stirred for 20 h, and refriger-
ated for 2 h, and the precipitates were filtered, washed
4
Chem Biol Drug Des 2016

Diphenyl Ether Derivatives as Antivirals
(E)-4-Phenoxy-N’-(pyridin-4-ylmethylene)
benzohydrazide (15c)
2-(4-Phenoxyphenyl)-5-(thiophen-2-yl)-1,3,4-
oxadiazole (16c)
White solid, yield 90%; mp 149–151 °C; 1H NMR (DMSO-d6)
d 7.08 (d, J = 7.4 Hz, 2H), 7.17–7.21 (m, 3H), 7.44 (t,
J = 9.0 Hz, 2H), 7.80 (d, J = 11 Hz, 2H), 7.98 (d, J = 14 Hz,
2H), 8.65 (s, 1H), 8.64 (d, J = 10.3 Hz, 2H), 11.84 (s, 1H);
13C NMR (DMSO-d6) d 117.6, 118.3, 118.3, 120.5, 121.6,
125.7, 126.8, 127.5, 142.5, 145.6, 148.8, 157.4, 160.92,
164.62. Found, %: C, 71.46; H, 4.54; N 13.55. C19H15N3O2.
Calculated, %: C, 71.91; H, 4.76; N, 13.24.
White solid, yield 75%; mp 139–141 °C; 1H NMR (DMSO-
d6) d 6.94 (d, J = 8 Hz, 2 H), 7.11 (d, J = 7.0 Hz, 2H),
7.21–7.24 (m, 4H), 7.40 (t, J = 8.2 Hz, 2H), 7.70 (d,
J = 6.0 Hz, 1H), 7.95 (d, J = 8.0 Hz, 1H); 3C NMR
(DMSO-d6) d 114.4, 115.1, 118.3, 120.5, 127.3, 127.8,
128.2, 129.4, 132.3, 133.2, 156.8, 157.4, 162.92, 165.62.
Found, %: C, 67.35; H, 3.36; N 9.02. C18H12N2O2S. Cal-
culated, %: C, 67.48; H, 3.78; N, 8.74.
Synthesis of 1,3,4-oxadiazole derivatives (16a–d)
An equimolar mixture of hydrazide 1 (0.0054 mol) with var-
ious carboxylic acids (0.0054 mol) was refluxed with phos-
phorus oxychloride (5 mL) for 2–3 h on water bath.
Reaction mixture was cooled to room temperature and
poured into ice water. The precipitate obtained was filtered
off, washed with water, and further purified by recrystal-
lization with ethanol to give 1,3,4-oxadiazoles 16a-d.
2-(4-Phenoxyphenyl)-5-(pyridin-4-yl)-1,3,4-
oxadiazole (16d)
White solid, yield 70%; mp 143–144 °C; 1H NMR (DMSO-
d6) d 7.03 (d, J = 7.5 Hz, 2H), 7.06 (d, J = 8.2 Hz, 2H),
7.19–7.22 (m, 3H), 7.39 (t, J = 9.0 Hz, 2H), 7.98 (d,
J = 7.5 Hz, 2H), 8.83 (d, J = 8.0 Hz, 2H); 13C NMR
(DMSO-d6) d 114.9, 115.1, 118.3, 120.5, 121.6, 123.5,
127.3, 129.4, 131.2, 132.45, 151.07, 162.92, 165.62.
Found, %: C, 72.66; H, 4.39; N 13.65. C19H13N3O2. Cal-
culated, %: C, 72.37; H, 4.16; N, 13.33.
2-(Furan-2-yl)-5-(4-phenoxyphenyl)-1,3,4-
oxadiazole (16a)
White solid, yield 77%; mp 129–132 °C; 1H NMR (DMSO-
d6) d 6.63 (t, J = 5.4 Hz, 1 H), 7.09 (d, J = 7.5 Hz, 2H), 7.18
(d, J = 7.5 Hz, 1H), 7.23–7.25 (m, 3H), 7.39 (t, J = 8.2 Hz,
2H), 7.98 (d, J = 8.0 Hz, 1H), 8.83 (d, J = 8.0 Hz, 2H); 13C
NMR (DMSO-d6) d 112.3, 114.4, 115.1, 118.3, 120.5,
127.3, 129.4, 139.2, 145.9, 156.8, 157.4, 162.92, 165.62.
Found, %: C, 71.36; H, 4.39; N 9.55. C18H12N2O3. Calcu-
lated, %: C, 71.05; H, 4.67; N, 9.21.
Results and Discussion
Compound 1, which was synthesized by following the
reported method (16), was used as key intermediate
because it is a building block for various biological active
compound and is the basic moiety of some antiviral agents.
(19–22) Compound 3 screened against various viruses and
it showed antiviral activity at micromolar concentration.
Cyclocondensation of compound 1 with an appropriate b-
dicarbonyl compounds in ethanol using catalytic amount
of acetic acid gives the corresponding pyrazole derivatives
2 and 4a,b, respectively, while cyclocondensation of com-
pound 1 with ethyl cyanoacetate yields compound 3
(Scheme 1).
2,5-Bis(4-phenoxyphenyl)-1,3,4-oxadiazole (16b)
White solid, yield 82%; mp 161–163 °C; 1H NMR (DMSO-
d6) d 7.12 (d, J = 8.7 Hz, 4H), 7.25–7.28 (m, 6H), 7.32 (t,
J = 9.0 Hz, 4H), 8.23 (d, J = 8.0 Hz, 4H); 13C NMR
(DMSO-d6) d 113.6, 117.5, 120.5, 125.6, 128.6, 152.07,
154.0, 164.62 (18).
Scheme 1: Synthesis of compounds 2, 3, and 4a,b.
Chem Biol Drug Des 2016
5

Ibrahim et al.
Scheme 2: Synthesis of compounds 7a-c, 8, 10, 11a,b, 12a,b, and 13.
Thiosemicarbazide 5 was afforded by refluxing acid hydra-
zide 1 with phenyl isothiocyanate in ethanol. Cyclization of
thiosemicarbazide 5 using 2N NaOH in ethanol yields the
triazole derivative 6. On the other hand, heating thiosemi-
carbazide 5 with different phenacyl bromide derivatives
and sodium acetate in ethanol yields the corresponding
thiazole derivatives 7a-c, while stirring compound 5 with
sulfuric acid gives thiadiazole ring 8 (Scheme 2).
Furthermore, compound 1 stirred in ethanolic potassium
hydroxide followed by the addition of carbon disulfide gave
potassium salt of N0-phenoxybenzoyl-hydrazine carbodithioic
acid 9 which was cyclized to 4-amino-5-(4-phenoxyphenyl)-
4H-1,2,4-triazole-3-thiol 10 by refluxing with hydrazine
hydrate. Fused heterocyclic derivatives 11a,b and 12a,b
were prepared by reacting compound 10 with thiourea, urea,
acetonitrile, or cyanoacetamide, respectively (Scheme 3). 5-
(4-Phenoxyphenyl)-1,3,4-thiadiazole-2-thiol 13 was prepared
by stirring 9 with ice-cooled sulfuric acid (Scheme 2).
Scheme 3: Synthesis of compounds 14, 15a-c, and 16a-d.
Cyclization of compound
gives 2-(4-Phenoxyphenyl)-1,3,4-oxadiazole 14. In addi-
tion, condensation of compound with different
1 with triethyl orthoformate
Finally, we synthesized diphenyl ether bearing oxadiazole,
thiophene, furan, and pyridine heterocyclic derivatives.
1
6
Chem Biol Drug Des 2016

Diphenyl Ether Derivatives as Antivirals
Table 1: Antiviral activities of the synthesized compounds
a
EC50 (lM)
Herpes simplex
Influenza
Cytomegalovirus Varicella-zoster virus
AD-169 Davis
Vesicular Feline
Vaccinia stomatitis Herpes
virus 1
virus
2 (G)
A
A
Compounds (KOS)
virus
virus
Virus
H1N1
H3N2
B
strain
strain
TK+ OKA TKꢀ 07-1
1
9
>20
>100
>20
73
>20
>20
>20
9
9
>20
>100
>20
100
>20
>20
>20
10
9
>100
>20
>100
>20
>100
>20
>20
>20
9
>20
45
>250
>100
–
13.6
>20
>20
>100
5.8
>20
0.8
>20
>20
0.8
>20
>100
–
>20
>20
>100
>20
>20
0.8
>20
>20
0.8
>20
>100
–
>20
8.94
>20
63.1
>20
>20
10.94
>20
100
>20
>20
10.7
3.35
53.1
>20
62.7
>20
>20
12.3
>20
45.8
>20
>20
>20
>20
>20
>20
0.8
>20
–
–
–
3
4a
>20
>100
>20
>100
>20
>20
>20
9
>100
>100
>100
>100
>100
>100
>20
>20
>100
>20
8
10
>20
11a
11b
0.8 >20
>20 20
>20 8.94
0.8 >20
>20
>100
>20
>20
12b
13
8.18 >20
>20 >20
0.8
>20
15b
16b
>20
>100
2
>20
>100
>20
>100
17
>100
>100
–
13.7
–
–
>20
>20
0.22
1.52
–
–
>20
>20
>20
–
–
–
1.34
Cidofovir
Ganciclovir
Zanamivir
Acyclovir
1.2
–
–
3.2
0.16
1.20
–
–
0.032
–
–
0.032 >100
–
–
–
0.7
–
–
10.4
–
–
–
–
–
29.3
aRequired to reduce virus-induced cytopathogenicity by 50%.
aromatic aldehydes in ethanol yields new hydrazone
derivatives 15a-c, while refluxing of compound 1 with
substituted aromatic acids in phosphorous oxychloride
leads to the substituted 1,3,4-oxadiazole derivatives 16a-
d (Scheme 3).
concentration (MCC) that causes a microscopically detect-
able alteration of normal cell morphology (Table S1).
Conclusion
A series of novel diphenyl ether substituted with different
heterocyclic rings were synthesized in good yield. The
effects of various heterocyclic moieties were studied for
antiviral properties. Among all the synthesized compounds
11a, 13, and 15b were more significantly active. The
observed bioassay and cytotoxicity data will serve as effi-
cient guide for the future design of potential antiviral agents.
Antiviral Bioassay
Screening of this focus library over 17 viruses [herpes
simplex virus type 1 (KOS), herpes simplex virus type 2
(G), vaccinia virus, vesicular stomatitis virus, thymidine
kinase-deficient herpes simplex virus type 1 (TK- KOS
ACVr), para-influenza 3 virus, reovirus-1, Sindbis virus,
Coxsackie virus B4, Punta Toro virus, feline corona virus
(FIPV), feline herpesvirus, influenza
A H1N1 subtype,
influenza A H3N2 subtype, influenza B, cytomegalovirus
(AD-169 strain and Davis strain), and varicella-zoster virus
[TK+ VZV strain and TKꢀ VZV strain] leads to demon-
strate the effect of various heterocyclic moieties on inhibi-
tion of virus-induced cytopathogenicity (19–22) (Table 1,
Tables S2–S7).
Acknowledgments
The authors would like to thank Professors Jan Balzarini,
Robert Snoeck, and Graciela Andrei at Rega Institute for
Medical Research, Faculty of Medicine, K.U. Leuven, Leu-
ven, Belgium, for the antiviral bioassay. Also, thanks to Dr.
Adel A. Rashad School of Chemistry, University of Wollon-
gong, Wollongong 2522, Australia, for his help and
support.
Compound 11a showed selectively significant activity
against A H1N1, A H3N2, and B influenza viruses. How-
ever, compound 13 showed promising broad-spectrum
activity against various viruses (herpes simplex, vaccinia
virus, vesicular stomatitis virus, and influenza virus). Com-
pound 15b was selectively active against varicella-zoster
virus. Compounds 3 and 8 were found moderate activity
against TK+ and A H1N1, respectively. Rest of the other
compounds were possessed mild to negligible antiviral
activity. The cytotoxicity of the compounds was evaluated
in parallel with their antiviral activity in uninfected cell
cultures and is expressed as the minimum cytotoxic
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