Synthesis, molecular docking and α-glucosidase inhibition of 5-aryl-2-(6′-nitrobenzofuran-2′-yl)-1,3,4-oxadiazoles

Article abstract of DOI:10.1016/j.bioorg.2016.04.006

Twenty derivatives of 5-aryl-2-(6′-nitrobenzofuran-2′-yl)-1,3,4-oxadiazoles (1–20) were synthesized and evaluated for their α-glucosidase inhibitory activities. Compounds containing hydroxyl and halogens (1–6, and 8–18) were found to be five to seventy folds more active with IC₅₀ values in the range of 12.75?±?0.10–162.05?±?1.65?μM, in comparison with the standard drug, acarbose (IC₅₀?=?856.45?±?5.60?μM). Current study explores the α-glucosidase inhibition of a hybrid class of compounds of oxadiazole and benzofurans. These findings may invite researchers to work in the area of treatment of hyperglycemia. Docking studies showed that most compounds are interacting with important amino acids Glu 276, Asp 214 and Phe 177 through hydrogen bonds and arene-arene interaction.

Full text of DOI:10.1016/j.bioorg.2016.04.006

Bioorganic Chemistry 66 (2016) 117–123
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Synthesis, molecular docking and
a
-glucosidase inhibition of 5-aryl-2-
(60-nitrobenzofuran-20-yl)-1,3,4-oxadiazoles
Muhammad Taha a,b, , Nor Hadiani Ismail a,b, Syahrul Imran a,b, Abdul Wadood c, Fazal Rahim d,
⇑
Syed Muhammad Saad e, Khalid Mohammed Khan e, Abdul Nasir c
a Atta-ur-Rahman Institute for Natural Product Discovery, Universiti Teknologi MARA (UiTM), Puncak Alam Campus, 42300 Bandar Puncak Alam, Selangor, Malaysia
b Faculty of Applied Science, Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia
c Computational Medicinal Chemistry Laboratory, Department of Biochemistry, Abdul Wali Khan University, Mardan, Mardan 23200, Pakistan
d Department of Chemistry, Hazara University, Mansehra, 21300, Pakistan
e H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi 75270, Pakistan
a r t i c l e i n f o
a b s t r a c t
Twenty derivatives of 5-aryl-2-(60-nitrobenzofuran-20-yl)-1,3,4-oxadiazoles (1–20) were synthesized
Article history:
Received 24 February 2016
Revised 18 April 2016
Accepted 26 April 2016
Available online 26 April 2016
and evaluated for their
halogens (1–6, and 8–18) were found to be five to seventy folds more active with IC50 values in the range
of 12.75 0.10–162.05 1.65 M, in comparison with the standard drug, acarbose (IC50 = 856.45
5.60 M). Current study explores the -glucosidase inhibition of a hybrid class of compounds of
a-glucosidase inhibitory activities. Compounds containing hydroxyl and
l
l
a
oxadiazole and benzofurans. These findings may invite researchers to work in the area of treatment of
hyperglycemia. Docking studies showed that most compounds are interacting with important amino
acids Glu 276, Asp 214 and Phe 177 through hydrogen bonds and arene-arene interaction.
Ó 2016 Elsevier Inc. All rights reserved.
Keywords:
1,3,4-Oxadiazole
a
-Glucosidase inhibition
Structure-activity relationship
Molecular docking
1. Introduction
in their structures. The first one is a launched drug acting as an
anti-HIV, while latter two are at the late phase clinical trials.
Oxadiazole is a five membered heterocyclic compound with one
oxygen and two nitrogen atoms in a ring. Based on varied pattern
of substitution of these heteroatoms inside the nucleus, oxadia-
zoles may have four possible isomers (Fig. 1).
a-Glucosidase is a hydrolase enzyme with EC number 3.2.1.20.
It exists in the human intestinal cells at the brush border surfaces.
Since human intestine can only absorb monosaccharides, the car-
bohydrate hydrolysis into glucose monomers by a-glucosidase is
The wide application in research made 1,3,4-oxadiazole
most widely studied off these four isomers [1]. A variety of
pharmaceutical significance has been linked with this simple but
important motif such as antibacterial [2], anticonvulsant [3],
anti-inflammatory [4], anti-HIV [5], anticancer [6], analgesic [7],
fungicidal [8], and herbicidal activities [9].
The ligancy potential of oxadiazole as a pharmacophore for the
exploration of lead molecules has been studied during several drug
discovery programs [10]. The bioisosterism of oxadiazoles have
been reported for a variety of carbonyl containing compounds such
as esters, hydroxamic esters, amides, and carbamates [11–13].
RaltegravirÒ [14], Ataluren [15] and Zibotentan [16] (Fig. 2), are
some of the drugs that contain oxadiazole ring as a key skeleton
essential [17]. It plays a vital role in digestion of carbohydrates
and processing of glycoprotiens. For the same reason, inhibitors
of a-glucosidase may be regarded as a convincing therapeutic tar-
get in the development of drugs against diseases such as obesity,
diabetes, HIV, and cancer [18–20]. In this connection, few synthetic
a
-glucosidase inhibitors (AGI’s), such as acarbose, miglitol and
voglibose are in use since last two decades [21,22]. Off the six drug
classes for the management of diabetes mellitus (DM),
a
-
glucosidase inhibitors are one of them [23]. These inhibitors are
quite target specific as they act in the intestine locally, in contrast
to other oral antihyperglycemic drugs which, in addition, alter cer-
tain biochemical processes in human body [24,25]. However, these
inhibitors are associated with few side effects, as diarrhea, abdom-
inal discomfort, and flatulence [26,27].
Recently we have reported the a-glucosidase inhibitory poten-
⇑
Corresponding author at: Atta-ur-Rahman Institute for Natural Product Dis-
covery, Universiti Teknologi MARA (UiTM), Puncak Alam Campus, 42300 Bandar
Puncak Alam, Selangor, Malaysia.
tial of oxadiazole benzohydrazones [28]. In continuation of this
exploration, we extended our research by incorporating benzofu-
ran moiety in oxadiazole. The hybrid effect of oxadiazole with
E-mail addresses: taha_hej@yahoo.com, muhamm9000@puncakalam.uitm.edu.
my (M. Taha).
http://dx.doi.org/10.1016/j.bioorg.2016.04.006
0045-2068/Ó 2016 Elsevier Inc. All rights reserved.

118
M. Taha et al. / Bioorganic Chemistry 66 (2016) 117–123
Fig. 1. Four possible oxadiazole isomers.
Fig. 2. Oxadiazole containing drugs.
benzofuran was subjected to
Encouraging results were found, which we are disclosing here for
the first time.
a
-glucosidase inhibitory assessment.
Compound 10 (IC50 = 12.75 0.10 lM) with two adjacent
hydroxyl groups at C-200 and C-300 was found to be the most active
compound in a series of twenty analogs of 5-aryl-2-(60-nitrobenzo
furan-20-yl)-1,3,4-oxadiazoles 1–20. The adjacent hydroxyl groups
at C-200 and C-300 must have been engaged in hydrogen bonding
2. Results and discussion
with the active site of the amino acid present in
make it around seventy folds more active than the standard drug,
acarbose (IC50 = 856.45 5.60 M). One methine separation of the
two hydroxyl groups, as in compound 11 (IC50 = 18.06 0.10 M),
a-glucosidase to
2.1. Chemistry
l
l
The 5-aryl-2-(60-nitrobenzofuran-20-yl)-1,3,4-oxadiazoles ana-
logs synthesis begins with the synthesis of methyl 6-nitrobenzo
furan-2-carbohydrazide then 6-nitrobenzofuran-2-carbohydrazide
was treated with different benzoic acid derivatives in the presence
of POCl3 to produce 5-aryl-2-(60-nitrobenzofuran-20-yl)-1,3,4-oxa
diazoles 1–20 Scheme 1. All the synthesized compounds 1–20
were characterized by various spectroscopy methods 1H NMR, EI
MS and elemental analysis Table 1.
slightly lowered the activity. A further decline in activity was
observed upon further separation of these two hydroxyl groups,
as shown by compound 12 (IC50 = 23.50 0.40
13 (IC50 = 22.60 0.39
M) with two hydroxyl groups at C-300 and
C-400 showed almost similar activity as of compound 12. However,
compound 14 (IC50 = 45.30 0.52 M) with two hydroxyl groups
at C-300 and C-500, halved the activity.
Among the monohydroxylated analogs, hydroxyl group at ortho
position (C-200) as in compound 15 (IC50 = 29.10 0.54
M),
lM). Compound
l
l
l
showed the highest inhibitory potential. It was found to be thirty
folds more active than the standard. When the hydroxyl group
moved to para position (C-400), decrement in activity was observed,
2.2. Enzyme inhibitory studies
In continuation of our search on new enzyme inhibitor [29], we
as in compound 9 (IC50 = 42.70 0.64 lM). Switching of hydroxyl
have evaluated 20 derivatives (1–20) of oxadiazole for their
group to meta position (C-300) resulted in further decline in activity.
The activity order (ortho > para > meta) of the regio-isomeric
monohydroxylated analogs was faithfully reproduced for the fluo-
rinated and chlorinated versions as well.
a-glucosidase inhibition potential. Structure-activity relationship
(SAR) studies propose that -glucosidase inhibitory potential of 5
a
-aryl-2-benzofuran-1,3,4-oxadiazoles mainly rely upon the
different substitutions at the phenyl part present at C-5.
Scheme 1. Synthesis of 5-aryl-2-(60-nitrobenzofuran-20-yl)-1,3,4-oxadiazoles 1–20.

M. Taha et al. / Bioorganic Chemistry 66 (2016) 117–123
119
Table 1
-Glucosidase inhibitory activity of 5-aryl-2-(60-nitrobenzofuran-20-yl)-1,3,4-oxadiazoles (1–20).
a
Comp.
Ar
IC50 SEMa
(lM)
Comp.
Ar
IC50 SEMa
(lM)
1
23.60 0.40
11
12
18.06 0.10
2
92.70 1.24
23.50 0.40
3
4
72.70 0.80
13.40 0.10
13
14
22.60 0.39
45.30 0.52
5
6
63.10 1.10
52.70 0.60
15
16
29.10 0.54
132.50 1.60
7
8
232.70 2.60
52.70 0.70
17
18
162.05 1.65
160.12 1.63
9
42.70 0.64
12.75 0. 10
19
20
N.A.b
N.A.b
10
Acarbose (standard drug)
856.45 5.60
a
SEM is the Standard Error of the Mean.
N.A. means Not Active.
b
Fluorine at C-200 (ortho), as in compound 4, displayed the
inhibitory potential with IC50 value of 13.40 0.10
M. Para (C-400)
substitution of fluorine lowered activity to 52.70 0.60
(compound 6). Fluorine at meta (C-300) position, as in compound
5, exhibited the IC50 value of 63.10 1.10 M.
Chlorine substituted analogs, overall showed the same
activity pattern (o > p > m) but with respect to fluorine, the
activity was found to be slightly lowered. Ortho (C-200) substi-
Methoxylation, alone, did not show any activity (compound 19)
until unless it has hydroxyl groups in addition to it (compounds
16–18). The ortho and para linkages of hydroxyl and methoxy
groups, as in compounds 18 and 17, had the matching IC50 values
l
lM
l
of 160.12 1.63 and 162.05 1.65
meta linkage (compound 16) raised the activity to
IC50 = 132.50 1.60 M. Substitution of methyl group at
4-position (compounds 20) did not display any activity. The entry
of furan (compound 7; IC50 = 232.70 2.60 M) displayed some
lM, respectively. However, the
l
tuted chlorine as in compound
IC50 = 23.60 0.40 M, which is almost half with respect to its
fluorine derivative (compound 4). Para (C-400) isomer of chlorine
had an activity of IC50 = 72.70 0.80 M (as in compound 3),
1
showed the activity at
l
l
activity which is the least active among the library of active
analogs.
l
which was again lesser to the corresponding fluorine analog
2.3. Molecular docking
(compound 6). Same is the case for the meta (C-300) substitution
Molecular docking of 5-aryl-2-(60-nitrobenzofuran-20-yl)-1,3,4-
of chlorine (compound 2; IC50 = 92.70 1.24
compared with compound 5.
lM) when
oxadiazoles analogs to the enzyme
a-glucosidase was performed

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M. Taha et al. / Bioorganic Chemistry 66 (2016) 117–123
to investigate their binding modes. From the docking simulation, it
was observed that most of the compounds are fitted well into the
3. Conclusion
binding cavity of
a-glucosidase enzyme making interactions with
Twenty oxadiazole derivatives of 6-nitrobenzofuran had been
the active site residues. Ten different conformations of protein
ligand interactions for each compound were generated and exam-
ined visually.
synthesized and evaluated for their a-glucosidase inhibitory activ-
ities. Based on results obtained through in vitro activity, hydroxyl
and halogens played a significant role in this activity as they were
found to be five to seventy folds more active as compared to acar-
bose. Docking results of the most active compound suggest that
compound 10 is interacting with important amino acids Glu 276,
Asp 214 and Phe 177 through hydrogen bonds and arene-arene
interaction. Based on these interactions, it can be further con-
cluded that the good inhibitory activity of the compound may be
due to the existence of the electron donating group (OH), creating
an electron flow in the whole compound and causes polarizability.
The top-ranked docking conformation of the most active com-
pound (Compound 10) demonstrated three hydrogen bonds and
one arene-arene interaction with the active site residues Glu 276,
Asp 214 and Phe 177 (Fig. 3a). The two adjacent hydroxyl groups
attached to the phenyl ring of the compound formed hydrogen
bonds with Glu 276 and Asp 214. Furthermore, one arene-arene
interactions between the compound and the active site residues
(Phe 177) were also observed. The docking analysis demonstrated
valuable in silico inhibition by compound 10 and the good inhibi-
tory activity of the compound may be due to the existence of the
electron donating group (OH) which create an electron flow in
the whole compound and cause polarizability.
In case of second most active compound (compound 4) in the
series four interactions with the active site residues were observed
(Fig. 3b). Phe 157 formed two arene-arene interaction with the
benzofuran ring while His 279 form two arene-cation interaction
with the oxadiazole and furan ring of the compound respectively.
In our analysis the fluorobenzene group of compound 4 and
dihydroxy benzene group of compound 10 demonstrated almost
similar interaction mode.
4. Experimental
4.1. Chemistry
Melting points were determined using Sinosource SGW X-4
melting point apparatus with microscope (Guangzhou, China). IR
spectra obtained using PerkinElmer Spectrum 100 FTIR Spectrom-
eter (Waltham, MA, USA) equipped with a diamond crystal Atten-
uated Total Reflectance (ATR) accessory by PIKE Technologies
(Madison, WI, USA). NMR spectroscopy was obtained using Bruker
Ultra Shield FT NMR 500 MHz and Avance III 600 Ascend spectrom-
eter (Wissembourg, France). EI-MS spectroscopic analysis had
been obtained using Finnigan-MAT-311-A instrument (Bremen,
Germany). Thin layer chromatography (TLC) was performed using
precoated silica gel plates (Merck, Kieselgel 60 F-254, 0.20 mm).
In case of compound 11, four interactions were observed
with His 279, Phe 157, Glu 304 and His 239 as shown in
Fig. 4a. Phe 157 and His 239 demonstrated an arene-arene bond
with the
p electronic cloud of the furan and resorcinol moiety
of the compound. His 279 made an arene-cation interaction
with the oxidazole moiety of the compound. Glu 304 was
observed making hydrogen bonds with the AOH moiety of
the compound. The potency of this compound might be due
to the presence of the electron donating group, i.e. OH at one
side while electron withdrawing group on the other side which
facilitate polarizability in the compound. Compound 12 and 13
showed almost similar behavior regarding interactions. In case
of compound 12 His 279 and Phe 157 of the protein are linked
to the compound while in compound 13 only Phe 157 showed
two interactions.
4.2. General procedure for the synthesis of compounds 1–20
A mixture of 6-nitrobenzofuran-2-carbohydrazide (0.5 mmol)
and various aromatic acid (0.5 mmol) in POCl3 (5 ml) was refluxed
for 6–10 h. The mixture was cooled and poured onto crushed ice. It
was neutralized with NaHCO3 solution and the resulting solid mass
precipitated out was filtered, dried, and crystallized.
4.2.1. 2-(2-Chlorophenyl)-5-(6-nitrobenzofuran-2-yl)-1,3,4-
oxadiazole (1)
Compounds having methoxy, methyl or no substitution group
on the benzene ring among the series of the compounds with
Yield: 75%; 1H NMR (500 MHz, DMSO-d6): d 8.84 (d, 2H,
J = 2.0 Hz), 8.37 (dd, 1H, J = 2.0, 9.0 Hz), 8.03 (d, 1H, J = 7.0 Hz),
7.95 (d, 1H, J = 9.0 Hz), 7.75 (s, 1H), 7.52 (d, 1H, J = 7.0 Hz), 7.50–
7.44 (m, 1H); 13C NMR (125 MHz, DMSO-d6) d 164.7, 155.2,
low or no inhibitory activity against
a-glucosidase enzyme were
observed having mild interaction with the active residue of the tar-
get (Fig. 4b).
Fig. 3. Docking pose of the compound 10, and 4 in the active site.

M. Taha et al. / Bioorganic Chemistry 66 (2016) 117–123
121
Fig. 4. Docking pose of the compound 11 and 19 in the active site.
154.1, 145.3, 143.5, 135.9, 134.4, 133.3, 132.1, 127.8, 126.1, 125.3,
122.9, 121.0, 118.8, 111.4, Anal. Calcd for C16H9ClN2O2, C = 64.77,
H = 3.06, N = 9.44, Found C = 64.76; H = 3.08; N = 9.47; HR MS for
N, 10.00; Found C, 68.59; H, 3.25; N, 9.98; HR MS for C16H9FN2O2
calculated 280.0648 and found 280.0652.
C
16H9ClN2O2, calculated 296.0353 and found 296.0359.
4.2.6. 2-(4-Fluorophenyl)-5-(6-nitrobenzofuran-2-yl)-1,3,4-oxadia-
zole (6)
4.2.2. 2-(3-Chlorophenyl)-5-(6-nitrobenzofuran-2-yl)-1,3,4-oxadia-
zole (2)
Yield: 73%; 1H NMR (500 MHz, DMSO-d6): d 8.83 (d, 1H,
J = 1.5 Hz), 8.37 (dd, 1H, J = 2.0, 8.0), 7.97 (d, 1H, J = 9.0 Hz), 7.96
(s, 1H), 7.81–7.78 (m, 2H), 7.33–7.30 (m, 2H); 13C NMR
(125 MHz, DMSO-d6) d 165.8, 164.1 (d, J = 261.3 Hz), 161.7, 161.7,
156.3, 142.3, 140.5, 129.5, 129.5, 123.4, 121.8, 120.1, 119.5,
117.2, 115.0, 110.6, Anal. Calcd for C16H9FN2O2, C, 68.57; H, 3.24;
N, 10.00; Found C, 68.55; H, 3.23; N, 10.01; HR MS for C16H9FN2O2
calculated 280.0648 and found 280.0642.
Yield: 77%; 1H NMR (500 MHz, DMSO-d6): d 8.87 (s, 1H), 8.34
(dd, 1H, J = 2.0, 8.0 Hz), 7.96 (d, 1H, J = 8.0 Hz), 7.92 (s, 1H), 7.80
(s, 1H), 7.71 (d, 1H, J = 7.0 Hz), 7.54–7.51 (m, 2H); 13C NMR
(125 MHz, DMSO-d6) d 166.3, 163.8, 156.3, 145.3, 142.5, 137.9,
134.4, 132.2, 130.4, 128.3, 127.6, 126.3, 122.9, 122.1, 119.5,
110.6, Anal. Calcd for C16H9ClN2O2, C = 64.77, H = 3.06, N = 9.44,
Found C = 64.77, H = 3.06, N = 9.44, HR MS for C16H9ClN2O2, calcu-
lated 296.0353 and found 296.0356.
4.2.7. 2-(Benzofuran-2-yl)-5-(furan-2-yl)-1,3,4-oxadiazole (7)
Yield: 72%; 1H NMR (500 MHz, DMSO-d6): d 8.83 (d, 1H,
J = 1.8 Hz), 8.35 (dd, 1H, J = 2.0, 8.0 Hz), 7.96 (d, 1H, J = 8.0 Hz),
7.90 (d, 2H, J = 8.0 Hz), 7.02 (d, 1H, J = 4.0 Hz), 6.64 (t, 1H,
J = 5.0 Hz); 13C NMR (125 MHz, DMSO-d6) d 165.7, 163.6, 154.2,
148.7, 143.0, 141.3, 129.4, 125.2, 123.1, 122.6, 120.1, 117.2,
113.6, 111.5, Anal. Calcd for C14H8N2O3, C, 66.67; H, 3.20; N,
11.11; Found C, 66.66; H, 3.18; N, 11.13; HR MS for C14H8N2O3 cal-
culated 252.0535and found 252.0529.
4.2.3. 2-(4-Chlorophenyl)-5-(6-nitrobenzofuran-2-yl)-1,3,4-oxadia-
zole (3)
Yield: 71%; 1H NMR (500 MHz, DMSO-d6): d 8.83 (d, 1H,
J = 2.0 Hz), 8.32 (dd, 1H, J = 2.0, 8.0), 7.95 (d, 1H, J = 8.0 Hz), 7.92
(s, 1H), 7.82 (d, 2H, J = 8.0 Hz), 7.52 (d, 2H, J = 8.0 Hz); 13C NMR
(125 MHz, DMSO-d6) d 164.8, 162.7, 156.8, 143.7, 141.4, 137.1,
134.9, 129.2, 129.2, 127.3, 127.0, 127.0, 122.9, 120.1, 119.5,
110.6, Anal. Calcd for C16H9ClN2O2, C = 64.77, H = 3.06, N = 9.44,
Found C = 64.78, H = 3.08, N = 9.43, HR MS for C16H9ClN2O2, calcu-
lated 296.0353 and found 296.0347.
4.2.8. 2-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)phenol (8)
Yield: 79%; 1H NMR (500 MHz, DMSO-d6): d 9.60 (s, 1H, OH),
8.82 (d, 1H, J = 2.0 Hz), 8.36 (dd, 1H, J = 2.0, 8.0 Hz), 7.97 (d, 1H,
J = 8.0 Hz), 7.91 (s, 1H), 7.32 (t, 1H, J = 8.0 Hz), 7.21 (s, 1H), 7.12
(d, 1H, J = 8.0), 6.85 (d, 1H, J = 8.0 Hz); 13C NMR (125 MHz,
DMSO-d6) d 167.7, 159.4, 156.3, 154.6, 140.5, 132.7, 131.2, 128.7,
125.8, 123.6, 122.2, 120.1, 119.6, 118.9, 113.3, 111.5, Anal. Calcd
for C16H10N2O3, C, 69.06; H, 3.62; N, 10.07; Found C, 69.07; H,
3.61; N, 10.08; HR MS for C16H10N2O3 calculated 278.0691 and
found 278.0699.
4.2.4. 2-(2-Fluorophenyl)-5-(6-nitrobenzofuran-2-yl)-1,3,4-oxadia-
zole (4)
Yield: 83%; 1H NMR (500 MHz, DMSO-d6): d 8.84 (d, 1H, J = 2.0),
8.36 (dd, 1H, J = 2.0, 8.0), 7.84–7.99 (m, 2H), 7.92 (s, 1H), 7.51 (d,
1H, J = 7.0 Hz), 7.38–7.35 (m, 2H); 13C NMR (125 MHz, DMSO-d6)
d 164.7, 161.6 (d, J = 261.3 Hz), 157.3, 154.2, 142.3, 140.5, 136.8,
131.5, 128.5, 125.6, 122.6, 121.2, 119.5, 118.7, 116.5, 112.6, Anal.
Calcd for C16H9FN2O2, C, 68.57; H, 3.24; N, 10.00; Found C, 68.55;
H, 3.26; N, 10.03, HR MS for C16H9FN2O2 calculated 280.0648 and
found 280.0653.
4.2.9. 3-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)phenol (9)
4.2.5. 2-(3-Fluorophenyl)-5-(6-nitrobenzofuran-2-yl)-1,3,4-oxadia-
zole (5)
Yield: 74%; 1H NMR (500 MHz, DMSO-d6): d 9.70 (s, 1H, OH),
8.85 (d, 1H, J = 2.0 Hz), 8.36 (dd, 1H, J = 2.0, 8.0 Hz), 7.95 (d, 1H,
J = 8.0 Hz), 7.91 (s, 1H), 7.62 (d, 2H, J = 8.0 Hz), 6.84 (d, 2H,
J = 8.0 Hz); 13C NMR (125 MHz, DMSO-d6) d 163.2, 161.7, 159.1,
154.9, 141.6, 131.9, 129.5, 127.1, 127.1, 125.2, 120.1, 119.0,
118.6, 114.3, 114.3, 113.1, Anal. Calcd for C16H10N2O3, C, 69.06;
H, 3.62; N, 10.07; Found C, 69.05; H, 3.64; N, 10.04; HR MS for
Yield: 76%; 1H NMR (600 MHz, DMSO-d6): d 8.85 (d, 1H,
J = 2.0 Hz), 8.36 (dd, 1H, J = 2.0, 8.0), 7.96 (d, 1H, J = 8.0 Hz), 7.92
(s, 1H), 7.64–7.61 (m, 3H), 7.31–7.28 (t, 1H, 8H); 13C NMR
(125 MHz, DMSO-d6) d 167.2, 164.7, 162.3 (d, J = 261.3 Hz), 156.5,
142.3, 140.5, 137.9, 130.9, 128.1, 126.2, 124.8, 121.6, 120.1,
119.5, 117.4, 111.7, Anal. Calcd for C16H9FN2O2, C, 68.57; H, 3.24;
C16H10N2O3 calculated 278.0691 and found 278.0686.

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M. Taha et al. / Bioorganic Chemistry 66 (2016) 117–123
4.2.10. 3-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)benzene-1,2-diol
(10)
69.06; H, 3.62; N, 10.07; Found C, 69.07; H, 3.63; N, 10.05; HR
MS for C16H10N2O3 calculated 278.0691 and found 278.0689.
Yield: 80%; 1H NMR (500 MHz, DMSO-d6): d 10.05 (s, 1H, OH),
9.60 (s, 1H, OH), 8.82 (d, 1H, J = 2.0 Hz), 8.34 (dd, 1H, J = 2.0,
8.0 Hz), 7.95 (d, 1H, J = 8.5 Hz), 7.90 (s, 1H), 7.02 (d, 1H,
J = 8.0 Hz), 6.84 (dd, 1H, J = 2.0, 8.0 Hz), 6.74 (t, 1H, J = 8.0 Hz);
13C NMR (125 MHz, DMSO-d6) d 163.3, 157.5, 156.6, 145.7, 143.5,
141.4, 128.2, 125.7, 124.5, 122.2, 121.5, 120.1, 120.4, 119.1,
117.2, 113.5, Anal. Calcd for C16H10N2O4, C, 65.31; H, 3.43; N,
9.52; Found C, 65.29; H, 3.45; N, 9.53; HR MS for C16H10N2O4 cal-
culated 294.0641 and found 294.0638.
4.2.16. 2-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)-5-methoxy-
phenol (16)
Yield: 83%; 1H NMR (500 MHz, DMSO-d6): d 11.40 (s, 1H, OH),
8.83 (d, 1H, J = 2.0 Hz), 8.34 (dd, 1H, J = 2.0, 8.0 Hz), 7.95 (d, 1H,
J = 8.0 Hz), 7.90 (s, 1H), 7.49 (d, 1H, J = 8.0 Hz), 6.50 (dd, 1H,
J = 2.0, 8.0 Hz), 6.50 (d, 1H, J = 2.0 Hz), 3.77 (s, 3H, OCH3); 13C
NMR (125 MHz, DMSO-d6) d 163.8, 160.7, 159.9, 156.3, 155.7,
141.2, 133.3, 127.5, 126.3, 122.5, 122.2, 120.1, 113.5, 110.9,
106.5, 103.1, 57.0, Anal. Calcd for C17H12N2O4, C, 66.23; H, 3.92;
N, 9.09; Found C, 66.25; H, 3.93; N, 9.08; HR MS for C17H12N2O4 cal-
culated 308.0797and found 308.0796.
4.2.11. 4-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)benzene-1,3-diol
(11)
Yield: 75%; 1H NMR (500 MHz, DMSO-d6): d 10.20 (s, 1H, OH),
9.90 (s, 1H, OH), 8.94 (s, 1H), 8.80 (d, 1H, J = 2.0), 8.33 (dd, 1H,
J = 2.0, 8.0 Hz), 7.93 (d, 1H, J = 8.0 Hz), 7.92 (s, 1H), 7.02 (d, 1H,
J = 2.0 Hz), 6.76–6.72 (m, 2H); 13C NMR (125 MHz, DMSO-d6) d
163.5, 159.8, 159.1, 157.4, 156.6, 142.5, 127.7, 127.2, 124.3,
123.3, 122.2, 120.1, 114.2, 110.0, 106.1, 103.0, Anal. Calcd for
4.2.17. 2-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)-4-methoxy-
phenol (17)
Yield: 76%; 1H NMR (500 MHz, DMSO-d6): d 10.52 (s, 1H, OH),
8.84 (d, 1H, J = 2.0 Hz), 8.34 (dd, 1H, J = 2.0, 8.0 Hz), 7.96 (d, 1H,
J = 8.0 Hz), 7.92 (s, 1H), 7.15 (d, 1H, J = 2.0 Hz), 6.91 (dd, 1H,
J = 2.0, 8.0 Hz), 6.88 (d, 1H, J = 8.0 Hz), 3.76 (s, 3H, OCH3); 13C
NMR (125 MHz, DMSO-d6) d 164.7, 157.6, 153.9, 152.3, 151.7,
139.5, 126.5, 124.3, 122.5, 122.2, 120.1, 117.0, 115.6, 113.8,
112.2, 109.6, 57.1, Anal. Calcd for C17H12N2O4, C, 66.23; H, 3.92;
N, 9.09; Found C, 66.24; H, 3.93; N, 9.08; HR MS for C17H12N2O4 cal-
culated 308.0797and found 308.0802.
C16H10N2O4, C, 65.31; H, 3.43; N, 9.52; Found C, 65.33; H, 3.45;
N, 9.54; HR MS for C16H10N2O4 calculated 294.0641 and found
294.0646.
4.2.12. 2-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)benzene-1,4-diol
(12)
Yield: 82%; 1H NMR (500 MHz, DMSO-d6): d 11.10 (s, 1H, OH),
9.69 (s, 1H, OH), 8.83 (d, 1H, J = 2.0 Hz), 8.32 (dd, 1H, J = 2.0,
8.0 Hz), 7.96 (d, 1H, J = 8.0 Hz), 7.87 (s, 1H), 7.37 (d, 1H,
J = 8.0 Hz), 6.34 (dd, 1H, J = 2.0, 8.0 Hz), 6.32 (d, 1H, J = 2.0); 13C
NMR (125 MHz, DMSO-d6) d 164.7, 156.6, 153.9, 152.1, 150.2,
140.5, 128.8, 125.5, 122.5, 123.7, 121.8, 120.0, 119.0, 114.6,
112.2, 110.1, Anal. Calcd for C16H10N2O4, C, 65.31; H, 3.43; N,
9.52; Found C, 65.33; H, 3.41; N, 9.51; HR MS for C16H10N2O4 cal-
culated 294.0641 and found 294.0635.
4.2.18. 5-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)-2-methoxyphenol
(18)
Yield: 85%; Yield: 81%; 1H NMR (500 MHz, DMSO-d6): d 9.42 (s,
1H, OH), 8.81 (d, 1H, J = 2.0 Hz), 8.32 (dd, 2H, J = 2.0, 8.0), 7.94 (d,
1H, J = 8.0 Hz), 7.92 (s, 1H), 7.33 (d, 1H, J = 2.0 Hz), 7.07 (d, 1H,
J = 2.0 Hz), 7.03 (d, 1H, J = 8.0 Hz), 3.83 (s, 3H, OCH3); 13C NMR
(125 MHz, DMSO-d6) d 168.2, 164.7, 153.6, 150.8, 148.1, 141.3,
128.7, 125.2, 123.6, 122.2, 120.6, 120.1, 119.1, 118.4, 113.8,
107.2, 54.7, Anal. Calcd for C17H12N2O4, C, 66.23; H, 3.92; N, 9.09;
Found C, 66.24; H, 3.94; N, 9.07; HR MS for C17H12N2O4 calculated
308.0797and found 308.0791.
4.2.13. 4-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)benzene-1,2-diol
(13)
Yield: 76%; 1H NMR (600 MHz, DMSO-d6): d 10.78 (s, 1H, OH),
9.57 (s, 1H, OH), 8.83 (d, 1H, J = 2.0 Hz), 8.35 (dd, 1H, J = 2.0,
8.0 Hz), 8.32 (s, 1H), 7.98 (d, 1H, J = 8.0 Hz), 7.92 (s, 1H), 7.25 (d,
1H, J = 2.0 Hz), 6.95 (dd, 1H, J = 2.0, 8.0 Hz), 6.80 (d, 1H, J = 8.0);
13C NMR (125 MHz, DMSO-d6) d 165.2, 164.7, 153.6, 149.2, 147.2,
142.5, 129.5, 126.3, 122.5, 121.2, 120.4, 119.5, 118.0, 116.5,
114.2, 111.3, Anal. Calcd for C16H10N2O4, C, 65.31; H, 3.43; N,
9.52; Found C, 65.30; H, 3.44; N, 9.50; HR MS for C16H10N2O4 cal-
culated 294.0641 and found 294.0645.
4.2.19. 2-(Benzofuran-2-yl)-5-(4-methoxyphenyl)-1,3,4-oxadiazole
(19)
Yield: 77%; 1H NMR (500 MHz, DMSO-d6): d 8.85 (d, 1H,
J = 2.0 Hz), 8.35 (dd, 1H, J = 2.0, 8.0), 7.96 (d, 1H, J = 8.0 Hz), 7.90
(s, 1H), 7.70 (d, 2H, J = 8.0 Hz), 7.03 (d, 2H, J = 8.0 Hz), 3.82 (s, 3H,
OCH3); 13C NMR (125 MHz, DMSO-d6) d 165.9, 163.6, 161.1,
154.6, 138.3, 128.3, 126.0, 126.0, 124.3, 122.5, 122.1, 120.5,
120.1, 114.8, 112.2, 112.2, 57.0, Anal. Calcd for C17H12N2O3, C,
69.86; H, 4.14; N, 9.58; Found C, 69.88; H, 4.15; N, 9.59; HR MS
for C17H12N2O3 calculated 292.0848 and found 292.0856.
4.2.14. 5-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)benzene-1,3-diol
(14)
Yield: 74%; 1H NMR (500 MHz, DMSO-d6): d 10.60 (s, 2H, OH),
8.97 (s, 1H), 8.84 (d, 1H, J = 2.0 Hz), 8.33 (dd, 1H, J = 2.0, 8.0 Hz),
7.96 (d, 1H, J = 8.0 Hz), 7.90 (s, 1H), 7.01 (d, 1H, J = 2.0 Hz); 6.89–
6.86 (m, 1H); 13C NMR (125 MHz, DMSO-d6) d 163.8, 162.7,
162.7, 160.6, 156.6, 140.5, 129.5, 127.4, 124.3, 122.5, 122.2,
120.1, 113.3, 109.8, 109.8, 103.9, Anal. Calcd for C16H10N2O4, C,
65.31; H, 3.43; N, 9.52; Found C, 65.32; H, 3.46; N, 9.51; HR MS
for C16H10N2O4 calculated 294.0641 and found 294.0632.
4.2.20. 2-(Benzofuran-2-yl)-5-(p-tolyl)-1,3,4-oxadiazole (20)
Yield: 84%; 1H NMR (500 MHz, DMSO-d6): d 8.83 (d, 1H,
J = 2.0 Hz), 8.32 (dd, 1H, J = 2.0, 8.0), 7.95 (d, 1H, J = 9.5 Hz), 7.90
(s, 1H), 7.85 (d, 1H, J = 7.5 Hz), 7.80 (t, 1H, J = 6.5 Hz), 7.26 (t, 2H,
J = 9.0 Hz), 2.46 (s, 3H, CH3); 13C NMR (125 MHz, DMSO-d6) d
163.8, 162.7, 151.6, 143.5, 142.6, 131.0, 131.0, 127.5, 125.9,
125.9, 124.4, 124.3, 122.5, 122.2, 120.1, 112.2, 20.1, Anal. Calcd
for C17H12N2O2, C, 73.90; H, 4.38; N, 10.14; Found C, 73.92; H,
4.37; N, 10.13; HR MS for C17H12N2O2 calculated 276.0899 and
found 276.0895.
4.2.15. 2-(5-(Benzofuran-2-yl)-1,3,4-oxadiazol-2-yl)phenol (15)
Yield: 80%; 1H NMR (500 MHz, DMSO-d6): d 10.10 (s, 2H, OH),
9.50 (s, 1H, OH), 8.82 (d, 1H, J = 2.0 Hz), 8.34 (dd, 1H, J = 2.0,
8.0 Hz), 8.30 (s, 1H), 7.95 (d, 1H, J = 8.0 Hz), 7.90 (s, 1H), 6.60 (d,
2H, J = 2.0 Hz); 13C NMR (125 MHz, DMSO-d6) d 163.9, 158.7,
156.6, 155.3, 139.5, 132.7, 129.1, 127.5, 124.3, 122.5, 122.1,
120.1, 118.8, 117.8, 114.2, 111.7, Anal. Calcd for C16H10N2O3, C,
4.3. Assay for a-glucosidase inhibitory activity
The
baker’s yeast a-glucosidase (EC 3.2.1.20) and p-nitrophenyl-
-Dglucopyranoside. The samples (5 mg/mL) were prepared by
a-glucosidase inhibition assay had been carried out using
a

M. Taha et al. / Bioorganic Chemistry 66 (2016) 117–123
123
dissolving the compounds 1–20 in DMSO. Test samples (10 mL)
which had been prepared were reconstituted in 100 mL of phos-
phate buffer (100 mM) at pH 6.8 in 96-well micro-plate and incu-
bated with 50 mL of baker’s yeast a-glucosidase for 5 min before
LESTARI (54/2015) and Atta-ur-Rahman Institute for Natural pro-
duct Discovery (RiND) to provide excellent designed lab and facil-
ity for the research and all technical and non-technical staff for a
lot of support for this work.
50 mL of p-nitrophenyl-a-Dglucopyranoside (5 mM) was added.
After incubating for 5 min, the absorbance was measured at
405 nm using SpectraMax plus384 (Molecular Devices Corpora-
tion, Sunnyvale, CA, USA). Blank in which the substrate was chan-
ged with 50 mL of buffer were analyzed to accurately determine
the background absorbance. Control sample was prepared to con-
tain 10 mL
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4.3.1. Molecular docking
Protein–Ligand docking study on 5-aryl-2-(60-nitrobenzofuran-
20-yl)-1,3,4-oxadiazoles analogs were carried out against
a
-glucosidase enzyme to understand the ligand–enzyme interac-
tions with the following communications; IntelÒ xenonÒ CPU
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a
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selected as a template [33]. The 3D structure of
a-glucosidase for
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up to 0.05 gradients.
Before docking, ligands and protein were prepared using MOE
v2010.11. The 3D structures of these newly synthesized com-
pounds were built using MOE-Builder Module program imple-
mented in MOE and save as a (.mdb) file for molecular docking.
Subsequently, the energy of all compounds was minimized up to
0.05 Gradient using MMFF 94x force field. Energy minimization
of all compounds was followed by the preparation of protein for
docking purposes. Most macromolecular crystal structures contain
little or no hydrogen coordinate data due to limited resolution and
thus protonation was done prior to docking using Protonate 3D
tools. Protonation was followed by energy minimization up to
0.05 Gradient using Amber 99 force field. All the synthesized com-
pounds was docked into the active site of protein using the Trian-
gular Matching docking method and 30 conformations of all the
compounds and protein complex were generated with docking
score, The complex was analyzed for interactions and their 3D
images were taken by using visualizing tool PyMol.
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Acknowledgments
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Arshad, Z. Hussain, K.M. Khan, Bioorg. Med. Chem. 22 (2014) 3441.
Authors would like to acknowledge Universiti Teknologi MARA,
Malaysia for the financial support under 600-RMI/DANA5/3