Z. Han et al.
Bioorganic Chemistry 105 (2020) 104428
Fig. 3. Docking of the inhibitor 8b into the active site of AKR1B1. (a) The protein structure is shown as a cartoon diagram with selected residues labeled and shown
in line representation, ligand and NADP are shown as stick models. The docked pose of 8b is shown in cyan (C), red (O) and blue (N). Hydrogen bonds are shown as
yellow dashed lines. (b) Protein residues are in surface representation. (For interpretation of the references to colour in this figure legend, the reader is referred to the
web version of this article.)
detoxification. The results are expressed as IC50
Table 1.
(
μ
M) summarized in
significantly. The number and position of phenolic hydroxyl also had
effect on activity, and the phenolic 3,5-dihydroxyl substituent was the
most effective on activity enhancement when comparing all the phenolic
hydroxyl derivatives. Moreover, comparison of compounds 7b-d with
7a revealed that the halogen substituent had little impact on the radical
scavenging activity.
As shown in Table 1, most of the 3,4-dihydroquinolin-2(1H)-one
derivatives showed significant AKR1B1 inhibition and selectivity. Of all
the
droquinolin-1(2H)-yl)acetic acid 8a was the most active with an IC50
value of 0.035 M, and it was more potent than the positive control
compounds,
2-(6-(4-hydroxybenzamido)-2-oxo-3,4-dihy-
μ
epalrestat. In compounds 7a-g, it was found that the introduction of
halogen atom or methoxyl to the C6-aryl side chain of 7a could enhance
the inhibitory activity, and halogen atom showed better enhancement.
Compounds 7e, 7f and 7 g having one or two methoxyl on the C6-aryl
side chain displayed relatively low AKR1B1 inhibition with IC50
2.4. Molecular docking
To better understand the mechanistic details and the above-
described SARs, compound 8b with excellent activities both in the
AKR1B1 inhibition and anti-ROS activity was docked with the confor-
+
values ranging from 7.047 to 10.421
μ
M, compared with compounds 7b,
mation of the human AKR1B1/NADP /lidorestat complex (PDB code:
7
c and 7d having halogen atom on the corresponding position of aryl
1Z3N). As shown in Fig. 3, compound 8b was tightly bound into the
active site of AKR1B1. The carboxylate group was inserted deeply in the
anion binding site by forming tight hydrogen-bonding interaction with
the side chain of His110 (2.95 Å). Besides, the 3-hydroxyl oxygen atom
of the phenolic hydroxyl on C6-aryl side chain formed an additional
hydrogen bond with the side chain of Thr113 (3.01 Å), confirming the
importance of phenolic hydroxyl on the activity enhancement of
AKR1B1 inhibition. Moreover, the 3,5-dihydroxyphenyl ring of the C6
side chain was well placed into the specificity pocket and paralleled to
the indole ring of Trp111 forming a stable stacking interaction. Mean-
while, the 3,4-dihydroquinolin-2(1H)-one core structure matched very
well the hydrophobic pocket and a tight hydrogen-bonding interaction
with Trp20 (2.69 Å) was formed, which indicates that the 3,4-dihy-
droquinolin-2(1H)-one is a potent core structure for developing AKR1B1
inhibitor. All these interactions anchor the inhibitor 8b tightly within
the active site of AKR1B1.
side chain. Moreover, the effect of halogen substituent on AKR1B1in-
hibition was in the rank order of 4-F > 4-Cl > 4-Br and the corre-
sponding IC50 values were 0.107
μ
M, 0.231
μM and 0.358
μM,
respectively. Besides, it was encouraging to find that the inhibitory ac-
tivity of AKR1B1 was enhanced when the methoxy was replaced to
hydroxyl group, which was concluded by comparing the inhibitory ac-
tivity of compounds 7e-g and 8a-c. Particularly, compound 8b having
two phenolic hydroxyl groups on C6-aryl side chain were endowed with
significant AKR1B1 inhibitory activity with an IC50 value of 0.042 M.
μ
Meanwhile, all target compounds were also evaluated for their inhibi-
tion ability against AKR1A1, and showed low activity with IC50 values
more than 15.214
inhibition.
μM, demonstrating good selectivity for the AKR1B1
2
.3. The antioxidant activity
The anti-ROS properties of the synthesized compounds were also
3. Conclusion
investigated in the present work by using the model reaction with the
stable free radical of 2,2-diphenyl-1-picrylhydrazyl (DPPH) according to
the modified method [21], and 6-hydroxy-2,5,7,8-chroman-2-carbox-
ylic acid (Trolox) was employed as a positive control. As shown in
Table 1, all derivatives showed DPPH radical scavenging activity
In conclusion, a series of inhibitor candidates based on a novel core
structure 3,4-dihydroquinolin-2(1H)-one were synthesized and biologi-
cally evaluated for AKR1B1 inhibition and anti-ROS properties. The
biological results showed that all compounds exhibited excellent
AKR1B1 inhibitory activity with IC50 values ranging from 0.035 to
ranging from 19.7 to 94.1% at the concentration of 100 M. Of all tested
μ
compounds, 8b with phenolic 3,5-dihydroxyl on the C6-aryl ring
12.187
μ
M,
and
2-(6-(4-hydroxybenzamido)-2-oxo-3,4-dihy-
showed the best scavenging activity, that is, 94.1%, 81.4%, and 69.6% at
droquinolin-1(2H)-yl)acetic acid 8a was the most active. Compounds
8a, 8b and 8c containing phenolic hydroxyl on the C6-aryl side chain
were not only sufficient to inhibit AKR1B1 but also effective for DPPH
radical scavenging, which indicated success in the development of dual
inhibitor targeting for AKR1B1 and ROS. Therein, compound 8b with
phenolic 3,5-dihydroxyl on the C6-aryl ring showed the best DPPH
concentrations of 100
μ
M, 50
μ
M and 10 M respectively, which had an
μ
commensurate activity compared with Trolox at high concentrations.
Structure-activity relationship (SAR) study of compounds (7e vs 8a, 7f
vs 8b and 7 g vs 8c) indicated that demethylation of the methoxyl on C6-
aryl side chain could improve the radical scavenging activity
4