X.-J. Zheng, et al.
Bioorganic&MedicinalChemistryLetters30(2020)127237
Table 1
presence of different substituents (R1) on the phenyl ring of the 1,3,4-
oxadiazole group was found to exert an appreciable influence on the
observed effect on antioxidant activity, but no clear pattern could be
Results of ABTS+% antioxidant assay.
Compound
R1
R2
ABTS+%
IC50(mmol/L)
found for the SAR. The derivatives 8b (IC50 = 0.51
0.24 mmol/L)
and 10b (IC50 = 17.72
not exhibit better antioxidant activity than derivatives with a single Cl
atom. The 2-chlorinated derivative 10a (IC50 = 0.30 0.16 mmol/L)
0.15 mmol/L), containing two Cl atoms, did
8a
2-Cl
H
0.45
0.51
4.13
0.23
0.29
2.29
0.11
0.05
0.88
0.75
3.53
0.07
0.19
1.28
0.42
0.30
17.72
1.71
0.39
0.27
1.42
0.14
0.24
0.16
0.08
0.17
0.25
0.05
0.02
0.20
0.22
0.14
0.03
0.07
0.21
0.25
0.16
8b
2,4-di-Cl
2-Br
H
8c
H
was more potent than the 2,4-dichlorated compound 10b. The impact
of the substituent position on the benzene ring on the efficacy was not
predictable. For the derivatives bearing electron-donating substituents
of the phenyl ring, it seems that the methyl group displays much more
impact on the antioxidant activity than the methoxy group with an 4–8
fold increase in potency. The introduction of vanillin ring, which con-
taining electron-withdrawing groups substituents (R1) on the phenyl
ring of the 1,3,4-oxadiazole group, improved the activity, as ex-
emplified by a comparison of results for the compounds 8l–n and 8a–c.
Furthermore, the position of the substituents (R1) on the benzene ring
of compounds 8g–i had a pronounced effect on their activity, which
varied according to the following orders: 3-CH3 > 2-CH3 > 4-CH3 for
the methyl-substituted compounds. This concept is also supported by
our docking simulations described below. From these results, we fo-
cused on compound 8h in subsequent studies. Further investigations
are currently underway in our laboratory to modify and better under-
stand these types of structure.
8d
3-Br
H
8e
3-F
H
8f
4-F
H
8g
2-CH3
3-CH3
4-CH3
2-OCH3
4-OCH3
2-Cl
H
8h
H
8i
H
8j
H
8k
H
8l
OCH3
8m
2,4-di-Cl
2-Br
OCH3
8n
OCH3
8o
3-CH3
2-Cl
OCH3
10a
–
–
–
–
–
10b
2,4-di-Cl
3-Br
0.13
10c
0.16
0.24
0.17
0.12
10d
3-F
10e
4-CH3
a
b
SD is the standard deviation.
Resveratrol as a positive control.
Oxidative stress has been demonstrated to be involved with the
pathogenesis of Alzheimer’s disease (AD).23 Resveratrol, a native stil-
bene derivative with multiple activities has been advanced into phase II
clinical trial for the treatment of AD due to its radical scavenging ac-
tivity.24 To further study the interaction mode and analyze the SAR
profile of these derivatives for the amyloid precursor protein (PDB ID:
5BUO),25 a molecular docking study was performed using the LibDock
program in Discovery Studio 3.1. Enzyme structures were checked for
missing atoms, bonds and contacts. Hydrogen atoms were added to the
enzyme structure. Water molecules and bound ligands were manually
deleted. The automated molecular docking program of MOE 2008.10
was used to dock compounds 8g, 8h, 8i and 10e on the active site of the
amyloid precursor protein. The docking results for resveratrol are in-
cluded as a reference. The result are shown in Fig. 3 and Table 3.
(4.85 Å) and His436 (4.12 Å), respectively. Compound 8h is bound into
the active site, in which the benzothiazole ring formed a hydrogen bond
with Gln454 (4.69 Å). The m-CH3 atom of 8h formed alkyl bond with
Ala372 (4.39 Å) and the benzene ring of 8h showed interaction with the
backbone of Met383 (4.02 Å). Compound 8h is bound into the active
site, in which the 1,3,4-oxadiazole moiety formed a hydrogen bond
with Lys447 (6.11 Å). Compound 8i showed interaction with Met383
(4.00 Å) and Lys447 (5.76 Å), respectively. Moreover, Compound 10e
also had interactions with Lys447 (6.21 Å), His436 (5.58 Å) and His447
(6.21 Å), respectively. Especially, compound 8h strongly bind to the
target with a highest LibDock score of 106.12 among the examined
compounds. These results therefore provide further evidence that the
compound 8h showed the greatest activity of these compounds, which
are consistent with the results observed in the ABTS+% assay.
Table 2
%
%
Results of DPPH and OH antioxidant assay.
%
%
Compound
R1
R2
DPPH
OH
IC50 (mmol/L)
SD
IC50 (mmol/L)
8h
3-CH3
2-Cl
H
0.03
0.05
0.99
0.01
0.03
0.15
292.55
340.12
370.12
0.24
8l
OCH3
0.17
0.21
a
b
SD is the standard deviation.
Resveratrol as a positive control.
inhibition of the superoxide production and the antioxidant activity
were calculated from the percentage decrease in the absorbance. As
indicated in Table 1, most of the synthesized compounds presented
product for affecting a wide range of intracellular mediators. Among
these compounds, 8h and 8l seem to have high radical scavenging ef-
ficacy, IC50 values in ABTS+% bioassay of 0.05
0.02 and
0.07
0.03 mmol/L, respectively. Table 2 shows that compounds 8h
and 8l were also evaluated for their in vitro radical scavenging activity
%
using the DPPH (1,1-diphenyl-2-picrylhydrazyl) radical as a reagent
%
sveratrol was taken as a standard drug.22 Compounds 8h and 8l ex-
hibited potent antioxidant activity with respective IC50 values of
%
0.03
0.01 mmol/L and 0.05
0.03 mmol/L in the DPPH assay,
showing more potent antioxidant activity than the positive controls
resveratrol (IC50 = 0.99
0.15 mmol/L). The radical anion was then
The in vivo anti-inflammatory activities of the synthesized com-
pound 8h was evaluated using the in vivo para-xylene-induced mice ear-
swelling model. Dimethyl sulfoxide was used as the vehicle for the
primary screening and the compound 8h was administered at a dose of
100 mg/kg. Indomethacin (100 mg/kg) was used as reference drugs. As
shown in Table 4, compound 8h exhibited good anti-inflammatory
activity at 100 mg/kg, measured as 57.35%, higher than the values for
the reference drug indomethacin (43.62%). Furthermore, considering
its promising anti-inflammatory activity, compound 8h was chosen for
further evaluation. A dose of 100 mg/kg was orally administered at
chemically or enzymatically converted into H2O2, which is then trans-
%
formed into a highly reactive hydroxyl radical (OH ) in the presence of
reduced transition metals. Compounds 8h and 8l also exhibited good
antioxidant activity with the IC50 values of 292.55
0.24 mmol/L and
%
340.12
0.17 mmol/L in the OH assay, respectively. Those values
conformed with the high performance observed in the ABTS+% and
%
DPPH assay.
Detailed structure-activity relationships (SAR) analysis on the ben-
zothiazole and 1,3,4-oxadiazole moieties revealed several structural
features that are crucial to maintaining the antioxidant activity. The
3