Design, synthesis and structure-activity relationship studies of novel partial FXR agonists for the treatment of fatty liver

Article abstract of DOI:10.1016/j.bioorg.2020.104262

Nonalcoholic fatty liver disease (NAFLD) is now the most common chronic liver disease, while there is still no medicine available. Farnesoid X receptor (FXR) is considered as a potential target for the treatment of NAFLD, and there are several FXR agonists reached in clinical trials. Based on better safety, industry and academia are pursuing development of the partial FXR agonists. To extend the chemical space of existing partial FXR agonists, we performed a structure-activity relationship study based on previously reported partial agonist 1 by using bioisosteric strategy. All of these efforts resulted in the identification of novel partial FXR agonist 13, which revealed the best agonistic activity in this series. Notably, compound 13 significantly alleviated the hepatic steatosis and hepatic function index in methionine-choline deficient (MCD) induced db/db mice, a classical nonalcoholic steatohepatitis (NASH) model widely used in preclinical evaluation. These results suggested that partial FXR agonist 13 might be a promising lead compound worthy further researches.

Full text of DOI:10.1016/j.bioorg.2020.104262

BioorganicChemistry104(2020)104262
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Design, synthesis and structure-activity relationship studies of novel partial
FXR agonists for the treatment of fatty liver
Qianqian Qiu⁎,1, Wenling Wang1, Xiaojuan Zhao, Yanli Chen, Shiyuan Zhao, Jilan Zhu,
Xiaojuan Xu⁎, Rongqing Geng⁎
School of Pharmacy, Yancheng Teachers’ University, Yancheng, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Bioisosteres
Fatty liver
FXR
Nonalcoholic fatty liver disease (NAFLD) is now the most common chronic liver disease, while there is still no
medicine available. Farnesoid X receptor (FXR) is considered as a potential target for the treatment of NAFLD,
and there are several FXR agonists reached in clinical trials. Based on better safety, industry and academia are
pursuing development of the partial FXR agonists. To extend the chemical space of existing partial FXR agonists,
we performed a structure-activity relationship study based on previously reported partial agonist 1 by using
bioisosteric strategy. All of these efforts resulted in the identification of novel partial FXR agonist 13, which
revealed the best agonistic activity in this series. Notably, compound 13 significantly alleviated the hepatic
steatosis and hepatic function index in methionine-choline deficient (MCD) induced db/db mice, a classical
nonalcoholic steatohepatitis (NASH) model widely used in preclinical evaluation. These results suggested that
partial FXR agonist 13 might be a promising lead compound worthy further researches.
NASH
Partial agonist
1. Introduction
inflammation and fibrosis in the kidney, indicating the capacity of FXR
agonists for the treatment of diabetic nephropathy and renal fibrosis
Nonalcoholic fatty liver disease (NAFLD) includes a broad category
ranging from simple liver steatosis to nonalcoholic steatohepatitis
(NASH) and even cirrhosis [1,2]. NAFLD is closely related to other
metabolic syndrome including obesity, diabetes and dyslipidemia
[3–5]. NAFLD is now the most common chronic liver disease [6]. Al-
though the morbidity of NAFLD is fast-growing, there is still no medi-
cine available [7]. Therefore, it is urgent demand to develop effective
drugs for the treatment of NAFLD. Currently, a lot of researches come
from institutes and companies have focused on this field, including
farnesoid X receptor (FXR) agonist and peroxisome proliferators-acti-
vated receptors agonist [8–12]. FXR, a sensor of chenodeoxycholic acid,
regulates the synthesis and transport of bile acid [13,14]. FXR is highly
expressed in the liver, intestine, and adipose tissue, and bile acids are
the endogenous ligands of FXR [15]. The activation of FXR is related to
glycometabolism, inflammation, and hepatoprotective effect [16,17].
Activation of FXR lowers the levels of triglycerides by modulating the
expression of hepatic sterol regulatory element binding protein-1c and
glucose-dependent lipogenic genes [18]. In addition, FXR improves
glucolipid metabolism through regulation of peripheral insulin sensi-
tivity and gluconeogenesis [19,20]. Moreover, FXR agonists reduced
[21]. Therefore, FXR is considered as a potential target for the treat-
ment of metabolic syndrome [22,23].
There are several FXR agonists such as obeticholic acid, Cilofexor
and LJN452 are studied in clinical trials for the treatment of NAFLD
[23]. However, full FXR agonists may cause side effects by inhibiting
cholesterol 7-hydroxylase, resulting in the interference of cholesterol
metabolism [24]. The defect could be improved by partial activation of
FXR to avoid total loss of cholesterol conversion [25,26]. There are a
series of partial FXR agonist have been reported, exemplified by com-
pound 1, a candidate derived from pranlukast high potency on FXR
(Fig. 1) [25]. Herein, we explore the further structure-activity re-
lationship based on compound 1 by bioisosteric strategy to extend the
chemical space of existing partial FXR agonists (Fig. 2).
2. Results and discussion
2.1. Chemistry
The compounds 2–13 were synthesized as shown in Scheme 1.
Treatment of raw material 1a with carboxylic acid 2a under the
⁎ Corresponding author at: School of Pharmacy, Teachers’ University, Yancheng 224007, PR China.
E-mail addresses: qiuqianqian1117@163.com (Q. Qiu), xuxj@yctu.edu.cn (X. Xu), rqgeng@163.com (R. Geng).
1 Qianqian Qiu and Wenling Wang contributed equally as first authors.
https://doi.org/10.1016/j.bioorg.2020.104262
Received 21 July 2020; Received in revised form 27 August 2020; Accepted 31 August 2020
Availableonline02September2020
0045-2068/©2020ElsevierInc.Allrightsreserved.

Q. Qiu, et al.
BioorganicChemistry104(2020)104262
bioisosteres of amide scaffold [27]. As shown in Table 1, replacing
amide of lead compound 1 with oxadiazole ring provided compound 2
with reduced potency on FXR, while maintaining the efficiency of
maximal activation. To identify a better hydrophobic segment, we ex-
plored the ether substituents (compounds 3–7) for the replacement of
tertiary butyl based on previous report on amide series [25]. SAR stu-
dies have shown that large substituent (compounds 5–7) is better than
that of small substituent (compounds 3–4), indicating that the hydro-
phobic interaction in this site is crucial to the agonistic activity on FXR.
Among them, compound 5 revealed the best agonistic activity on FXR
and keep partial agonistic efficiency. Inspired by previous research
[28], we also explored the non-carboxylic acid derivatives 8 and 9, but
none of them exert potency on FXR. These results suggested that the
previous SAR cannot be converted to our oxadiazole series. Notably, the
thiadiazole series revealed better potencies on FXR than oxadiazole
derivatives (10 vs 2, 11 vs 3, 12 vs 4, and 13 vs 5). This difference might
be attributed to the larger hydrophobic effect of thiadiazole than that of
oxadiazole, which match better with hydrophobic pocket of FXR. Si-
milar to oxadiazole series, the isobutoxy derivative 13 (EC50 = 142 nM,
28% max. efficiency) revealed the strongest activity on FXR.
Fig. 1. Structure of representative FXR agonists.
2.3. Effects on NASH
Fig. 2. Our design strategy and structure-activity relationship study to extend
the chemical space of existing partial FXR agonists.
The effects of compound 13 on fatty liver were evaluated in db/db
mice fed by MCD, a classical NASH model [29]. As shown in Fig. 3, the
model group revealed significant liver steatosis, which was remarkably
improved in compound 1 and 13 treated groups. The liver to brain
weight ratio was significantly decreased in compound 13 treated group
compared model control, which indicated that compound 13 alleviates
fatty liver. Moreover, serum levels of alanine aminotransferase (ALT)
and aspartate aminotransferase (AST) were obviously decreased in
treated groups (Fig. 3). These results suggested that partial FXR agonist
13 provides significant improvement on NASH.
condition of condensating agent EDCI provided intermediate 3a, which
was converted into oxadiazoles ring under the dehydrating agent, fol-
lowed by hydrolysis provided the target compounds 2–7. A similar
procedure provided compounds 8 and 9 with high yield. Cyclization of
intermediate 3a with Lawesson’s reagent provided thiadiazoles ring,
followed by hydrolysis afforded compounds 10–13.
2.2. Structure-activity relationship study
The oxadiazole and thiadiazole rings are usually reported as the
Scheme 1. Synthesis of target compounds 2–13. Reagents and conditions: (a) EDCI, Et3N, dichloromethane; (b) POCl3, acetonitrile, reflux, 4 h; (c) LiOH·H2O, THF/
MeOH/H2O, r.t., 4 h; (d) Lawesson’s reagent, THF, reflux, 4 h.
2

Q. Qiu, et al.
BioorganicChemistry104(2020)104262
Table 1
In vitro activities of target compounds on FXR.
Compd.
R
X
EC50 (nM)a
max. activation
GW4064
246
75
100%
15%
23%
1
2
O
362
3
4
5
MeO
EtO
O
O
O
4560
2175
205
31%
19%
26%
6
7
O
O
328
285
17%
21%
8
> 10 μM
> 10 μM
227
9
10
S
14%
11
12
13
MeO
EtO
S
S
S
2058
941
25%
22%
28%
142
a
EC50 value represents the mean of three determinations.
Fig. 3. Effect of compound 13 on NASH model. Representative photomicrographs of liver stained with Hematoxylin-Eosin at 400× magnification. Liver/brain-
weight ratio, the plasma levels of AST and ALT. All the values are expressed as mean
way ANOVA with Tukey’s multiple-comparison post hoc test.
SD (n = 6). *p ≤ 0.05 compared to model control were analyzed using a one-
3. Conclusion
extend the new skeleton of existing partial FXR agonist, and the optimal
compound 13 was considered as a potential lead structure worth in-
depth study.
In order to extend the chemical space of existing partial FXR ago-
nists, we performed a SAR study based on previously reported partial
agonist 1 by using bioisosteric strategy. The further exploration of
amide bioisosteres, oxadiazole and thiadiazole, resulted in the identi-
fication of novel partial FXR agonist 13 (EC50 = 142 nM, 28% max.
efficiency), which revealed the best agonistic activity in this series. To
evaluate the potential of compound 13 on fatty liver, a NASH model
was developed by fed db/db mice with MCD. Notably, the hepatic
steatosis, hepatic function index, and liver to brain weight ratio were
significantly alleviated in compound 13 treated group. In brief, we
4. Experimental section
4.1. General chemistry
All starting materials were obtained from commercial sources.
Purifications of chromatography were performed by silica gel and de-
tected by thin layer chromatography using UV light at 254 and 365 nm.
NMR spectra were recorded on a Bruker ACF-300Q instrument
3

Q. Qiu, et al.
BioorganicChemistry104(2020)104262
(300 MHz for 1H NMR and 75 MHz for 13C NMR spectra) and AVANCE
29%; 1H NMR (400 MHz, DMSO‑d6) δ 8.56–8.52 (m, 1H), 8.29 (d,
J = 7.9 Hz, 1H), 8.14 (d, J = 7.9 Hz, 1H), 8.02–7.99 (m, 2H),
7.77–7.71 (m, 1H), 7.12–7.08 (m, 2H), 3.80 (d, J = 6.6 Hz, 2H),
2.05–1.97 (m, 1H), 0.97 (d, J = 6.8 Hz, 6H). 13C NMR (75 MHz,
DMSO‑d6) δ 166.76, 164.62, 163.31, 162.14, 132.68, 132.40, 130.94,
130.35, 129.03, 127.41, 124.33, 115.70, 74.45, 28.10, 19.39. HRMS Anal.
NEO 400MHZ instrument (400 MHz for 1H NMR and 100 MHz for 13
C
NMR spectra). Chemical shifts (δ) are reported in ppm relative to tet-
ramethylsilane (TMS) as reference; multiplicity: s, singlet; d, doublet;
dd, double doublet; t, triplet; m, multiplet; approximate coupling con-
stants (J) are shown in hertz (Hz). High resolution mass spectrometry
(HRMS) was performed on AB SCIEX X500R system.
Calcd. for C19H18N2O4: m/z
z = 337.1264 [M−H]−.
=
337.1267, [M−H]−, found: m/
4.1.1. General synthetic procedure for intermediates 3a, 6a and 9a
The substituted benzoic acid (1 equiv) and EDCI (1.2 equiv) were
dissolved in dichloromethane, and stirred for 30 min. To a stirred above
solution added substituted benzoyl hydrazine (1 equiv) and Et3N (2
equiv). The mixture was stirred at room temperature for 12 h. The
organic layers were washed with brine (25 mL), dried over anhydrous
sodium sulfate and filtered. The filtrate was concentrated to give in-
termediates 3a, 6a and 9a, which was used for the next reaction
without further purification.
4.1.2.5. 3-(5-(4-butoxyphenyl)-1,3,4-oxadiazol-2-yl)benzoic acid (6). Yield
25%; 1H NMR (400 MHz, DMSO‑d6) δ 8.57–8.51 (m, 1H), 8.32 (d,
J = 7.8 Hz, 1H), 8.16 (d, J = 7.8 Hz, 1H), 8.03 (d, J = 8.6 Hz, 2H),
7.77–7.71 (m, 1H), 7.13 (d, J = 8.6 Hz, 2H), 4.05 (t, J = 6.4 Hz, 2H),
1.76–1.71 (m, 2H), 1.46–1.42 (m, 2H), 0.93 (t, J = 7.2 Hz, 3H). 13C NMR
(101 MHz, DMSO‑d6) δ 166.85, 164.66, 162.09, 132.75, 132.41, 131.02,
130.42, 129.09, 127.45, 124.40, 115.71, 68.06, 31.06, 19.15, 14.16. HRMS
Anal. Calcd. for C19H18N2O4: m/z = 337.1267, [M−H]−, found: m/
z = 337.1269 [M−H]−.
4.1.2. General synthetic procedure for target compounds 2–7
To a solution of intermediates 3a (1 equiv) in 15 mL acetonitrile was
added POCl3 (2 equiv) at ambient temperature. After addition was
complete, the solution was heated to reflux for 4 h. The reaction mix-
ture was concentrated in vacuo, then diluted with ethyl acetate
(20 mL), and washed with water (2 × 20 mL), NaHCO3 (2 × 25 mL)
and brine (2 × 25 mL). The organic layer was dried over anhydrous
sodium sulfate, filtered and evaporated under reduced pressure. The
filtrate was evaporated and the residue was purified by silica gel
column chromatography (petroleum ether/ethyl acetate, 10:1, v/v). To
a solution of the obtained solid (1 equiv) in 2:3:1 THF/MeOH/H2O
(18 mL) was added LiOH·H2O (3 equiv). After stirring at room tem-
perature for 4 h, the volatiles were removed under reduced pressure.
The residue was acidified with 1 N hydrochloric acid solution and then
filtered and the filter cake was washed with 5 mL of cool water, dried in
vacuum to afford a white powder. The white powder was purified by
column chromatography using a mixture of petroleum ether/ethyl
acetate (2:1–1:2, v/v) as eluent to afford the target compounds as white
solid.
4.1.2.6. 3-(5-(4-(isopentyloxy)phenyl)-1,3,4-oxadiazol-2-yl)benzoic acid
(7). Yield 28%; 1H NMR (400 MHz, DMSO‑d6) δ 8.57–8.51 (m, 1H),
8.35–8.31 (m, 1H), 8.18–8.15 (m, 1H), 8.05 (d, J = 8.7 Hz, 2H),
7.78–7.72 (m, 1H), 7.15 (d, J = 8.7 Hz, 2H), 4.08 (t, J = 6.6 Hz, 2H),
1.82–1.74 (m, 1H), 1.64 (q, J = 6.7 Hz, 2H), 0.94 (d, J = 6.6 Hz, 6H).
13C NMR (75 MHz, DMSO‑d6) δ 166.87, 164.70, 163.38, 132.37,
132.37, 130.46, 129.12, 127.46, 124.41, 115.77, 66.82, 37.72, 25.03,
22.89. HRMS Anal. Calcd. for C20H20N2O4: m/z = 351.1423, [M−H]−,
found: m/z = 351.1426 [M−H]−.
4.1.2.7. 2-(4-chlorophenyl)-5-(o-tolyl)-1,3,4-oxadiazole (8). Yield 57%;
1H NMR (400 MHz, DMSO‑d6) δ 8.14 (d, J = 7.8 Hz, 2H), 8.03 (d,
J = 8.0 Hz, 2H), 7.71 (d, J = 8.0 Hz, 2H), 7.45 (d, J = 7.8 Hz, 2H),
2.42 (s, 3H). 13C NMR (75 MHz, DMSO‑d6) δ 165.00, 136.95, 133.26,
132.45, 131.46, 129.48, 129.31, 128.93, 120.95, 20.99. HRMS Anal.
Calcd. for C15H11ClN2O: m/z = 269.0560, [M−H]−, found: m/
z = 269.0563 [M−H]−.
4.1.2.8. 2-(4-phenoxyphenyl)-5-(o-tolyl)-1, 3, 4-oxadiazole (9). Yield
1
4.1.2.1. 3-(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl)benzoic acid
(2). Yield 42%; 1H NMR (400 MHz, DMSO‑d6) δ 8.65 – 8.57 (m,
1H), 8.33 (d, J = 7.6 Hz, 1H), 8.17 (d, J = 7.4 Hz, 1H), 8.09–7.99 (m,
2H), 7.82–7.72 (m, 1H), 7.70–7.58 (m, 2H), 1.32 (s, 9H). 13C NMR
(75 MHz, DMSO‑d6) δ 166.83, 164.73, 163.71, 155.56, 132.84,
132.64, 131.01, 130.40, 127.54, 127.09, 126.68, 124.28, 120.97,
35.29, 31.26. HRMS Anal. Calcd. for C19H18N2O3: m/z = 321.1317,
[M−H]−, found: m/z = 321.1315 [M−H]−.
41%; H NMR (400 MHz, DMSO‑d6) δ 8.13 (d, J = 8.7 Hz, 2H), 8.06
(d, J = 7.5 Hz, 1H), 7.54–7.49 (m, 5H), 7.27 (d, J = 7.3 Hz, 1H), 7.21
(d, J = 3.1 Hz, 1H), 7.20–7.17 (m, 2H), 7.15 (d, J = 1.8 Hz, 1H), 2.70
(s, 3H). 13C NMR (101 MHz, DMSO‑d6) δ 164.49, 163.70, 160.61,
155.61, 138.11, 132.25, 131.93, 130.84, 129.41, 129.32, 126.97,
125.17, 122.99, 120.31, 118.83, 118.44, 22.04. HRMS Anal. Calcd.
for C21H16N2O2: m/z = 327.1212, [M−H]−, found: m/z = 327.1215
[M−H]−.
4.1.2.2. 3-(5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl)benzoic acid (3). Yield
35%; 1H NMR (400 MHz, DMSO‑d6) δ 8.64–8.58 (m, 1H), 8.31 (d,
J = 8.1 Hz, 1H), 8.15 (d, J = 8.2 Hz, 1H), 8.05 (d, J = 8.7 Hz, 2H),
7.82–7.74 (m, 1H), 7.14 (d, J = 8.7 Hz, 2H), 3.85 (s, 3H). 13C NMR
(75 MHz, DMSO‑d6) δ 166.82, 164.62, 163.37, 162.59, 132.72, 132.44,
130.95, 130.38, 129.07, 127.42, 124.30, 115.92, 115.29, 55.98. HRMS
Anal. Calcd. for C16H12N2O4: m/z = 295.0797, [M−H]−, found: m/
z = 295.0794 [M−H]−.
4.1.3. General synthetic procedure for target compounds 10–13
To a solution of 3a (1 equiv) in 20 mL THF was added Lawesson’s
reagent (2 equiv), and the mixture was heated to reflux for 4 h. The
reaction mixture was concentrated in vacuo, then diluted with ethyl
acetate (25 mL), and washed with 1 N NaHCO3 (3 × 15 mL) and brine
(2 × 15 mL). The organic layer was dried over anhydrous sodium
sulfate, filtered and evaporated under reduced pressure. The residue
was purified by silica gel column chromatography (petroleum ether/
ethyl acetate, 20:1, v/v). To a solution of the obtained solid (1 equiv) in
2:3:1 THF/MeOH/H2O (18 mL) was added LiOH·H2O (3 equiv). After
stirring at room temperature for 4 h, the volatiles were removed under
reduced pressure. The residue was acidified with 1 N hydrochloric acid
solution and then filtered and the filter cake was washed with 5 mL of
cool water, dried in vacuum to afford a white powder. The white
powder was purified by column chromatography using a mixture of
petroleum ether/ethyl acetate (2:1–1:2, v/v) as eluent to afford the
target compounds as white solid.
4.1.2.3. 3-(5-(4-ethoxyphenyl)-1,3,4-oxadiazol-2-yl)benzoic acid (4). Yield
38%; 1H NMR (400 MHz, DMSO‑d6) δ 8.54–8.51 (m, 1H), 8.27 (d,
J = 7.9 Hz, 1H), 8.13 (d, J = 7.8 Hz, 1H), 8.02–7.96 (m, 2H),
7.76–7.70 (m, 1H), 7.10–7.06 (m, 2H), 4.07 (d, J = 7.0 Hz, 2H), 1.33 (t,
J = 7.0 Hz, 3H). 13C NMR (101 MHz, DMSO‑d6) δ 166.86, 164.61, 163.34,
161.88, 132.64, 131.09, 130.85, 130.36, 129.05, 127.40, 124.25, 115.64,
64.01, 14.94. HRMS Anal. Calcd. for C17H14N2O4: m/z = 309.0954,
[M−H]−, found: m/z = 309.0956 [M−H]−.
4.1.2.4. 3-(5-(4-ethoxyphenyl)-1, 3, 4-oxadiazol-2-yl)benzoic acid (5). Yield
4.1.3.1. 3-(5-(4-(tert-butyl)phenyl)-1,3,4-thiadiazol-2-yl)benzoic
acid
4

Q. Qiu, et al.
BioorganicChemistry104(2020)104262
(10). Yield 45%; 1H NMR (300 MHz, DMSO‑d6) δ 8.55–8.51 (m, 1H),
8.23 (d, J = 8.0 Hz, 1H), 8.13 (d, J = 7.8 Hz, 1H), 7.94 (d, J = 8.1 Hz,
2H), 7.76–7.71 (m, 1H), 7.59 (d, J = 8.1 Hz, 2H), 1.32 (s, 9H). 13C
NMR (101 MHz, DMSO‑d6) δ 168.46, 167.12, 167.08, 154.97, 133.19,
132.29, 131.84, 130.38, 130.23, 128.46, 127.99, 127.14, 126.78,
35.21, 31.27. HRMS Anal. Calcd. for C19H18N2O2S: m/z = 337.1089,
[M−H]−, found: m/z = 337.1086 [M−H]−.
National Institutes of Health (NIH Publication NO. 85-23, revised
2011).
4.4. Effects of compound 13 on NASH
db/db mice were randomly divided into groups (n = 6 per group),
and fed the MCD in parallel with daily oral gavage with vehicle, com-
pound 1 (30 mg/kg) or compound 13 (30 mg/kg). After treatment for
40 days, mice were fasted overnight and sacrificed under deep an-
esthesia. Liver and serum samples were collected and processed for
histological and serological analysis. Serum levels of ALT and AST were
measured by automatic biochemical analyzer (Beckman Coulter,
AU5811, Tokyo, Japan). Liver tissue was fixed in 10% formalin, em-
bedded in paraffin, sectioned, and stained with hematoxylin and eosin
(H&E) staining according to a standard procedure.
4.1.3.2. 3-(5-(4-methoxyphenyl)-1,3,4-thiadiazol-2-yl)benzoic
acid
(11). Yield 45%; 1H NMR (300 MHz, DMSO‑d6) δ 8.53–8.47 (m, 1H),
8.20 (d, J = 7.8 Hz, 1H), 8.12 (d, J = 7.8 Hz, 1H), 7.99–7.90 (m, 2H),
7.76–7.71 (m, 1H), 7.17–7.05 (m, 2H), 3.84 (s, 3H). 13C NMR (75 MHz,
DMSO‑d6) δ 168.31, 166.91, 162.22, 132.37, 132.05, 130.45, 130.36,
129.82, 128.29, 122.28, 115.31, 55.94. HRMS Anal. Calcd. for
C
16H12N2O3S: m/z = 311.0569, [M−H]−, found: m/z = 311.0566
[M−H]−.
Declaration of Competing Interest
4.1.3.3. 3-(5-(4-ethoxyphenyl)-1,3,4-thiadiazol-2-yl)benzoic acid (12). Yield
40%; 1H NMR (300 MHz, DMSO‑d6) δ 8.53–8.47 (m, 1H), 8.19 (d,
J = 7.7 Hz, 1H), 8.11 (d, J = 7.6 Hz, 1H), 7.91 (d, J = 8.4 Hz, 2H),
7.76–7.70 (m, 1H), 7.06 (d, J = 8.4 Hz, 2H), 4.08 (q, J = 6.9 Hz, 2H), 1.35
(t, J = 7.0 Hz, 3H). 13C NMR (75 MHz, DMSO‑d6) δ 168.30, 166.93,
161.51, 132.39, 132.13, 132.03, 130.40, 129.79, 128.31, 122.13, 115.66,
63.95, 14.95. HRMS Anal. Calcd. for C17H14N2O3S: m/z = 325.0725,
[M−H]−, found: m/z = 325.0722 [M−H]−.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgments
This study was supported by National Natural Science Foundation of
China (No.81803353), Natural Science Foundation of Jiangsu Province
(No. BK20191482), and Jiangsu Qing Lan Project.
4.1.3.4. 3-(5-(4-isobutoxyphenyl)-1,3,4-thiadiazol-2-yl)benzoic
acid
(13). Yield 36%; 1H NMR (300 MHz, DMSO‑d6) δ 8.54–8.46 (m,
1H), 8.20 (d, J = 7.7 Hz, 1H), 8.12 (d, J = 7.7 Hz, 1H), 7.93 (d,
J = 8.3 Hz, 2H), 7.76–7.70 (m, 1H), 7.08 (d, J = 8.3 Hz, 2H), 3.81 (d,
J = 6.5 Hz, 2H), 2.11–1.96 (m, 1H), 0.99 (d, J = 6.6 Hz, 6H). 13C
NMR (101 MHz, DMSO‑d6) δ 168.32, 166.91, 166.38, 161.78, 132.40,
132.13, 132.06, 130.43, 129.81, 128.32, 122.17, 115.77, 74.44,
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