A novel series of napabucasin derivatives as orally active inhibitors of signal transducer and activator of transcription 3 (STAT3)

Article abstract of DOI:10.1016/j.ejmech.2018.10.067

The transcription factor STAT3 is an attractive target for a variety of cancers therapy. Napabucasin, applied in phase III clinical trials for the treatment of a variety of cancers, was regarded as one of the most promising anticancer drug by targeting ST

Full text of DOI:10.1016/j.ejmech.2018.10.067

Accepted Manuscript
A novel series of napabucasin derivatives as orally active inhibitors of signal
transducer and activator of transcription 3 (STAT3)
Chungen Li, Caili Chen, Qi An, Tao Yang, Zitai Sang, Yang Yang, Yuan Ju, Aiping
Tong, Youfu Luo
PII:
S0223-5234(18)30944-9
DOI:
https://doi.org/10.1016/j.ejmech.2018.10.067
EJMECH 10853
Reference:
To appear in: European Journal of Medicinal Chemistry
Received Date: 30 July 2018
Revised Date: 29 October 2018
Accepted Date: 30 October 2018
Please cite this article as: C. Li, C. Chen, Q. An, T. Yang, Z. Sang, Y. Yang, Y. Ju, A. Tong, Y. Luo, A
novel series of napabucasin derivatives as orally active inhibitors of signal transducer and activator of
transcription 3 (STAT3), European Journal of Medicinal Chemistry (2018), doi: https://doi.org/10.1016/
j.ejmech.2018.10.067.
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A Novel Series of Napabucasin Derivatives as Orally Active Inhibitors of Signal
Transducer and Activator of Transcription 3 (STAT3)
Chungen Li1, Caili Chen1, Qi An1, Tao Yang, Zitai Sang, Yang Yang, Yuan Ju,
Aiping Tong*, Youfu Luo*
State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, West
China Medical School, Sichuan University, and Collaborative Innovation Center for
Biotherapy, Chengdu, 610041, China
1 These authors contributed equally to this work.
* Corresponding authors.
E-mail addresses: luo_youfu@scu.edu.cn, aipingtong@scu.edu.cn
Highlights
1. In vitro, compound 8q was over 10-fold more potent than napabucasin on U251,
HepG2, HT29 and CT26 cells.
2. In mouse model of colorectal cancer, 8q significantly reduced tumor growth. The
TGI of 8q at 50 mg/kg was 63 %.
3. Compound 8q has a KD of 110.2 nM for full-length STAT3 recombinant protein
by surface plasmon resonance analysis.
4. The aqueous solubility of 8q was over 4.5-fold higher than that of napabucasin.
5. Compound 8q exhibited good safety profile in BALB/c mice model.
Abstract
The transcription factor STAT3 is an attractive target for a variety of cancers
therapy. Napabucasin, applied in phase III clinical trials for the treatment of a variety
of cancers, was regarded as one of the most promising anticancer drug by targeting
STAT3. Herein, a novel series of napabucasin derivatives were designed and
synthesized, which presented a potent inhibitory activity on a variety of cancers cells.
Among the derivatives compound 8q exhibited potent inhibitory activity on U251,
HepG2, HT29 and CT26 cells with the IC50 values of 0.22, 0.49, 0.07 and 0.14 µM,
respectively, which was over 10-fold more potent than napabucasin. Treatment with
compound 8q decreased protein expression level of total STAT3 and p-STAT3Y705 in
vitro. The binding of compound 8q with STAT3 were further validated by

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electrophoretic mobility shift assay and surface plasmon resonance analysis.
Compound 8q has a KD of 110.2 nM for full-length STAT3 recombinant protein.
Moreover, the aqueous solubility of 8q was over 4.5-fold than that of napabucasin. In
addition, compound 8q in vivo significantly reduced tumor growth compared to
untreated mice, and exhibited good safety profile, indicating its great potential as an
efficacious drug candidate for oncotherapy.
Key words: antitumor activity, STAT3 inhibitors, napabucasin derivatives.
1. Introduction
Signal transducer and activator of transcription 3 (STAT3), a STAT protein
family member [1], is an oncogene being frequently activated in numerous cancers,
such as glioma, lung, liver and other cancers [2]. It plays a critical role in some
cellular processes such as cell growth and apoptosis by mediating the expression of
target genes [3]. Furthermore, evidences from recent studies have indicated that
STAT3 was related with the regulation of tumor microenvironment and tumor stem
cell, suggesting an important role for STAT3 inhibitors in the self-renewal and
differentiation of tumor stem cell and immunotherapy [4]. Thus, inhibiting the
activation of STAT3 is an effective strategy in the cancer therapies, and the STAT3
may be used widely as one of the most promising anticancer target.
Over the past few years, there were significant advances in the discovery of
STAT3 inhibitors [5, 6]. Several potent compounds have been discovered and
promoted to early phase of drug development pipelines, such as niclosamide,
HJC0152, stattic, STX-0119, STA-21, LLL12, LY-5, napabucasin [7-14] (Figure
1).

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Figure 1. Representative small-molecule STAT3 inhibitors
Napabucasin, an excellent STAT3 small molecule inhibitor by targeting and
blocking cancer stem cell pathway activity, which was applied in phase III clinical
trials for the treatment of a variety of cancers such as metastatic colorectal carcinoma,
pancreatic cancer, gastric cancer and non-small cell lung cancer [15-17]. Napabucasin
was regarded as one promising lead compound to generate novel STAT3 inhibitors
[18]. Several new anticancer derivatives of napabucasin were developed through
chemical structural modifications toward napabucasin in recent years [19-21] (Figure
2).
Figure 2. Representative napabucasin derivatives
To seek napabucasin derivatives with enhanced physicochemical properties, it is
necessary to identify the position suitable to modify in the scaffold. Napabucasin was
docked into STAT3 protein (PDB code: 1BG1). The acetyl group at 2-position of
furan ring protrudes towards the receptor surface, indicating that it is a good site to
conduct structural modification and the binding affinity will not decreases. In our first
series of compounds, α, β-Unsaturated ketone was selected as a linker for its extensive
application in antitumor drugs, for example curcumin (Figure 3). The second series
of napabucasin derivatives was introduced with hydrophilic groups, such as piperidyl,

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pyrazinyl, and substituted amino groups by an amidation reaction.
Figure 3. The design concept of the target compounds
2. Results and discussion
2.1. Chemistry
The synthesis of 2a-d was carried out following the procedures shown in
Scheme 1. The compounds 2a-d were prepared by aldol condensation reaction
between commercially available 2-acetylnaphtho[2,3-b]furan-4,9-dione (1) and
substituted aromatic aldehydes under the condition of piperidine in ethanol. As
illustrated in Scheme 2, compounds 8a-u were prepared starting from reaction of
2-hydroxy-1,4-naphthoquinone (3) with iodobenzene diacetate to give intermediate
3-phenyliodonio-1,2,4-trioxo-1,2,3,4-tetrahydronaphthalenide (4). Then cyclization
reaction
2-hydroxymethyl-naphtho[2,3-b]furan-4,9-dione (5). The subsequent oxidation
reaction of with pyridinium chlorochromate (PCC) yielded
between
4
with
propargyl
alcohol
afforded
5
2-formyl-4,9-dihydronaphtho[2,3-b]-furan-4,9-dione (6), which was further oxidized
to the 4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-carboxylic acid (7) by H2O2 and
glacial acetic acid. Finally, amidation reaction of intermediate compound 7 with
different substituted alkyl amines or N-heterocycles to give target compounds 8a-u.

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Scheme 1. Synthesis of 2a-d. Reagents and conditions: (a) piperidine, EtOH, reflux, 6-12h.
Scheme 2. Synthesis of 8a-u. Reagents and conditions: (a) PhI(OAc)2, CHCl3, 5 h. (b) Propargyl
alcohol, Cu2O, 80°C, 2 h. (c) PCC, CH2Cl2, r.t., overnight. (d) H2O2 30%, AcOH, 75 °C, 4h. (e)
HATU, Et3N, r.t., 2h.
2.2. In vitro cell growth inhibitory activity
To evaluate the anticancer activities of the synthetic compounds, three STAT3
over- activated human cancer cell lines (U251, HepG2 and HT29 cells) and mice
CT-26 cells were examined (Table 1). The inhibitory activity of compounds 2a and
2d were significantly decreased compared with that of napabucasin. 2b and 2c, which
were substituted with heterocyclic groups, maintained the inhibitory activities in
U251 and HT29 cells with the IC50 values of 0.87-2.20 µM. But the activities of 2b
and 2c had not been improved compared with that of napabucasin, indicating that
aromatic substitution was adverse to improve activity, and substitution of heterocyclic
groups was favorable for the inhibitory activity.
Replaced with heterocyclic alkyl group at R2 position (8a-g) was tolerated. The
inhibitory activity of compound 8f, substituted with the 4-ethylpiperazin-1-yl at R2
position, was increased for U251, HT29 and CT26 cells with the IC50 values of 0.87,
0.21, and 0.59 µM, respectively. However, the compounds 8h-l, substituted with big
size on the cyclic amine, exhibited declined inhibitory activity. It demonstrated that
the substitutions with small size on the cyclic amine were beneficial to improve

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inhibitory activity.
Compound 8q, with 2-(piperidin-1-yl)ethylamino- group substituted at the R2
position, inhibited the growth of U251, HepG2, HT29 and CT26 cells with the IC50
values of 0.22, 0.49, 0.07 and 0.14 µM, respectively. The values were lowered over
10-fold compare with napabucasin. When the corresponding position transformed to
aromatic alkyl amine (8s-u), the inhibitory activity declined obviously, suggesting
that the aromatic alkyl substitution at R2 position was not versatile to improve activity.
Moreover, to evaluate the selectivity, the effects of the derivatives on STAT3-negative
prostate cancer PC-3 cell line were examined. As a result, the IC50 values of 16
derivatives were over 10 µM and the remaining 10 derivatives and napabucasin were
over 2 µM.
Table 1 Activity of compounds in vitro
IC50 ±SD a (µM)
Cpd.
R1/ R2
U251
>10
HepG2
>10
HT29
>10
CT26
>10
PC-3
>10
2a
2b
2c
1.50±0.25
2.20±0.06
>10
>10
0.87±0.01
1.52±0.01
2.48±0.07
>10
>10
>10
2d
>10
>10
>10
>10
>10
8a
8b
8c
2.18±0.11
2.16±0.11
>10
>10
1.08±0.03
1.57±0.01
0.86±0.11
0.58±0.05 9.65±1.24
0.95±0.14 >10
2.19±0.09 7.30±0.06
3.10±0.04 9.63±0.15
0.57±0.04 6.84±0.71
1.35±0.24 5.83±0.74
8d
1.65±0.13

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8e
8f
1.37±0.02 5.27±0.13
0.39±0.09
0.26±0.05 4.58±0.62
0.59±0.06 2.06±0.30
0.87±0.03
>10
0.21±0.01
1.13±0.02
>10
8g
8h
8i
0.58±0.02 2.50±0.05
5.92±0.43 9.66±0.31
0.61±0.03
>10
>10
-
-
-
-
-
>10
>10
>10
>10
>10
>10
>10
>10
>10
>10
8j
>10
>10
8k
8l
>10
9.64±1.13
>10
>10
8m
8n
8o
8p
8q
8r
2.65±0.43 11.25±0.36
>10
>10
-
-
-
>10
>10
>10
>10
>10
>10
HN
3.02±0.09
>10
0.90±0.08 1.75±0.22
0.30±0.38
0.20±0.27 4.45±0.69
0.22±0.03 0.49±0.04 0.07±0.001 0.14±0.01 4.13±0.46
1.63±0.33
>10
>10
>10
0.37±0.01 0.05±0.009 7.19±0.82
8s
8t
>10
>10
-
>10
3.36±0.57
6.32±0.62
>10
>10
-
-
>10
>10
8u
>10
Napabucasin
-
2.60±0.38 6.60±0.36
1.60±0.11
2.50±0.09 5.25±0.57

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a Values were the average of at least three separate determinations (Mean ± SD). Dash (-) indicates
not determined.
2.3. Molecular docking
To explore the possible interaction modes of compounds with STAT3, molecular
docking studies were performed in Discovery Studio (DS) 3.1. As shown in Figure 4,
napabucasin could bind to the STAT3 (PDB code: 1BG1) SH2 domain by hydrogen
bonds with Arg609 and Arg595 residues. Furthermore, napabucasin was formed
cation-π interactions with Ser636 and Lys591 residues. The representative compound
8q not only formed hydrogen bonds with Arg609 and Arg595 residues, but also new
hydrogen bonds with Lys591 and Arg595 residues, and it also formed cation-π
interactions with the Ser636 and Lys591 residues. The result of the docking study
indicated that compound 8q matched perfectly with the configuration of the SH2
domain of STAT3, providing a rationale explaining the excellent activity of compound
8q.
Figure 4. The binding mode of napabucasin, 8q and STAT3 SH2 domain. (A) Napabucasin in 3D
representation. (B) Napabucasin in 2D representation. (C) 8q in 3D representation (D) 8q in 2D
representation. Hydrogen bond is shown in green and blue dash lines in 3D and 2D representation,
respectively.
2.4. The physicochemical properties of several final compounds
The aqueous solubility was tested by HPLC method, and the Clog P was
calculated by ChemBioDraw Ultra 14.0. The aqueous and lipid solubility of most
compounds were improved (Table 2). For example, the solubility of compound 8q

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and 8e was improved to 70.7 and 109.4 µg/mL, respectively. Compounds 8q and 8e,
with introduction of basic amino groups to R2 position, were beneficial to increase the
water-solubility.
Table 2 Aqueous solubility of compounds 8c-g, 8q and 8r
Aqueous solubility ±SD b
(µg/mL)
Aqueous solubility ±SD
(µM)
Cpd.
Structure
Clog P a
1.38
8c
50.4±0.95
<25.0
162.1±3.05
<76.5
8d
2.11
1.94
2.47
1.32
3.28
2.07
1.66
8e
109.4±3.76
81.5±0.98
38.1±2.38
70.7±0.50
<25.0
337.4±11.60
240.9±2.89
117.7±7.36
200.9±1.42
<70.6
8f
8g
8q
8r
Napabucasin
<15.0
<62.5
a Octanol-water partition coefficient (log P) was calculated by ChemBioDraw Ultra 14.0.
b Values were the average of at least three separate determinations (Mean ± SD).
2.5. In Vivo Antitumor Activity Evaluation
The amino acid sequence of STAT3 is conserved between human and mice. And
the antitumor effects of STAT3 inhibitor is partly depend on its regulation of the
immune systems [22]. Thus, to evaluate the effects of STAT3 inhibitors,
immunocompetent mice are always used as animal model. Consistently, our data also
show that STAT3 inhibitor exhibit efficacy both in human colorectal cancer cell line
HT29 and in mouse colorectal cancer cell line CT26 (Table 1). To further investigate

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the antitumor potential in vivo, we evaluated the effects of compound 8q in CT26
mouse tumor model. As shown in Figure 5, compound 8q exhibited potent oral
antitumor activity compared with the control. The tumor growth delay induced by 8q
was visualized by the final tumor tissue size in Figure 5A and the tumor growth curve
in Figure 5B. The TGI (tumor growth inhibition) and T/C (relative increment ratio)
with 8q at 50 mg/kg were 63% and 28%, respectively.
Figure 5. (A) Anatomical mice’s tumor tissues treated with 8q and vehicle. (B) Growth curves of
mice’s tumor volume (Mean ± SD, n = 5; *, p < 0.05, **, p < 0.01).
2.6. Preliminary safety profile of compound 8q
Compound 8q was well tolerated and no significant difference of body weights
was observed between control and 8q treated mice (Figure S1). All mice survived
without apparent behavioral alterations or other side effects.
Furthermore, the pathological change in major organs was examined by H&E
staining. As shown in Figure 6, the histology of the heart, liver, spleen, lung and
kidney indicated that the cells of organ tissues from the 8q treated group kept a
complete morphology, without obvious cellular inflammatory, edema or necrosis,
implying no noticeable toxicity to the five major organs.
Figure 6. Histological section of anatomical heart, liver, spleen, lung and kidney stained with

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H&E from colorectal cancer model mice treated with compound 8q.
2.7. Compound 8q decrease protein expression of total STAT3 and p-STAT3Y705
To gain insight into the mechanism of compound 8q, we conducted western blot,
immunofluorescence and sandwich enzyme-linked immunosorbent assays to examine
the protein expression level of total and p-STAT3Y705 in U251 and HepG2 after
treatment. As shown in Figure 7A, decrease of both total STAT3 and p-STAT3Y705
was observed at 200 nM concentrations after 24 hours of treatment in U251 and
HepG2 cells. Through immunofluorescence staining, the expression of total STAT3
decreased obviously in HepG2 cells treated with 8q (400 nM) for 24 h (Figure 7B).
Furthermore, we evaluated the total and p-STAT3Y705 levels in U251 and HepG2 cells
by sandwich enzyme-linked immunosorbent assay. As shown, both total STAT3 and
p-STAT3Y705 decreased significantly after treatment with 8q (200 nM for U251 and
400 nM for HepG2 cells) for 24 h or 48 h (Figure 7C, D).
Figure 7. 8q treatment decrease protein expression level of total STAT3 and p-STAT3Y705 in vitro.
(A) Western blot analysis of STAT3 and p-STAT3Y705 in U251 and HepG2 cells treated with 8q
(200 nM for U251 and 400 nM for HepG2 cells) for 24 and 48 h. (B) Immunofluorescence
analysis of total STAT3 in HepG2 cells treated with 8q (400 nM) for 24 h. Images were taken on a
Zeiss inverted microscope with 20× objective lens. BF, Bright-Field. Scale bar: 50µm. (C, D)

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Sandwich enzyme-linked immunosorbent assay of total and p-STAT3Y705 in U251 and HepG2
cells treated with 8q (200 nM for U251 and 400 nM for HepG2 cells) for 24 and 48 h. Error bars
represent standard deviations. Paired t-test was used for statistical analyses of treatment groups
compared with control group. *, p< 0.05; **, p< 0.01.
2.8. Binding of Compound 8q with STAT3
Furthermore, we validate the binding of compound 8q with STAT3 using EMSA
and SPR analysis. As shown in Figure 8A, compound 8q incubation at 100 nM and
200 nM concentration dramatically decreased the binding of STAT3 with
biotin-labeled DNA probe. SPR analyses with Biacore X100 also show that
compound 8q has a KD of 110.2 nM for full-length STAT3 recombinant protein
(Figure 8B).
Figure 8. Electrophoretic mobility shift assay (EMSA) and surface plasmon resonance (SPR)
analysis. (A) The effects of compound 8q on the DNA binding activity of STAT3 was determined
by EMSA with biotin-labeled DNA probe and Flag-tagged STAT3 pull-downed from HEK293T
cells transiently transfected with full-length STAT3 cDNA. Ab, antibody; Pro, protein. (B) STAT3
and compound 8q binding analyses with Biacore X100. The concentrations of 8q are varied from
18.75 nM to 600 nM. The equilibrium dissociation constant (KD) was obtained by using the GE
BIA evaluation 2.0 software.
3. Conclusion
In summary, a novel series of napabucasin derivatives were designed,
synthesized and biologically evaluated. Most of the designed compounds exerted
promising inhibitory activity on U251, HepG2, HT29 and CT26 cells, and exhibited

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improved solubility compared with napabucasin. The most potent compound 8q
exhibited remarkable inhibitory activity on U251, HepG2, HT29 and CT26 cells with
the IC50 values of 0.22, 0.49, 0.07 and 0.14 µM, respectively. In mouse model of
colorectal cancer, 8q significantly inhibited tumor growth. Treatment with compound
8q decreased protein expression level of total STAT3 and p-STAT3Y705 in vitro. The
binding of compound 8q with STAT3 were validated by EMSA and SPR analysis.
Compound 8q has a KD of 110.2 nM for full-length STAT3 recombinant protein.
Molecular docking suggested that compound 8q bound to the SH2 domain of STAT3.
Together, compound 8q is worth of further investigations toward the discovery of
STAT3 inhibitor as a drug candidate for oncotherapy.
4. Experimental section
4.1. Chemistry
All common reagents and solvents were obtained from commercial suppliers and
used without further purification. Reaction progress was monitored using analytical
thin layer chromatography (TLC) on precoated silica gel 60 F254 plates (0.25 mm,
Qingdao Haiyang Inc.) and components were visualized by ultraviolet light (254 nm).
All the NMR spectra were recorded on Bruker Avance (Varian Unity Inova)
spectrometer in CDCl3 or DMSO-d6 with TMS as internal standard. 1H NMR and 13C
NMR spectra were recorded respectively at 400 MHz and 100 MHz, analyzed by
using MestReNova Software. Chemical shifts were reported in ppm. Splitting patterns
were expressed as s, singlet; d, doublet; t, triplet; q, quartet; dd, doublet of doublets; m,
multiplet; brs, broad singlet. High resolution mass spectrometry (HRMS) was
performed on an Agilent LC/MSD TOF system G3250AA. Silicycle silica gel
300−400 (particle size 40−63 µm) mesh was used for all flash column
chromatography experiments.
4.1.1. General procedures for the preparation of 2a-d
To a solution of 2-acetylnaphtho[2,3-b]furan-4,9-dione (1) (0.42 mmol) in EtOH
(5 mL), piperidine (1.25 mmol) and aromatic aldehydes (0.62 mmol) were added. The
reaction mixture was heated to reflux and stirred for 7 hours, then cooled to room
temperature. The mixture was filtered and the filter cake was washed with 10mL of

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EtOH for three times, and dried under vacuum to give compounds 2a-d.
(E)-2-cinnamoylnaphtho[2,3-b]furan-4,9-dione(2a)
1H NMR (400 MHz, DMSO) δ 8.53 (s, 1H), 8.19 – 8.13 (m, 2H), 7.99 – 7.90 (m,
5H), 7.87 (d, J = 15.6 Hz, 1H), 7.52 – 7.48 (m, 3H).13C NMR (100 MHz, Pyr) δ 179.8,
178.0, 174.0, 156.3, 153.5, 145.6, 134.6, 134.3, 134.2, 133.4, 133.0, 131.3, 130.9,
129.2 (2C), 129.2 (2C), 127.0, 126.9, 121.0, 113.7. HRMS (Q-TOF): calculated for
C21H12O4 329.0736 [M + H]+, found 329.0815. Purity ≥ 95.0%.
(E)-2-(3-(1-methyl-1H-pyrrol-2-yl)acryloyl)naphtho[2,3-b]furan-4,9-dione(2b)
1H NMR (400 MHz, DMSO) δ 8.30 (s, 1H), 8.19 – 8.13 (m, 2H), 7.95 – 7.90 (m,
2H), 7.80 (d, J = 15.2 Hz, 1H), 7.52 (d, J = 15.2 Hz, 1H), 7.17 (d, J = 3.2 Hz, 2H),
6.25 – 6.23 (m, 1H), 3.80 (s, 3H).13C NMR (100 MHz, DMSO) δ 180.4, 177.1, 174.1,
156.5, 153.7, 134.9 (2C), 133.4, 133.3, 133.0, 130.8, 130.6, 130.1, 127.1, 127.0, 115.4,
115.4, 114.0, 110.5, 34.5. HRMS (Q-TOF): calculated for C21H13NO4 332.0845 [M +
H]+, found 332.0905. Purity ≥ 95.0%.
(E)-2-(3-(thiophen-2-yl)acryloyl)naphtho[2,3-b]furan-4,9-dione(2c)
1H NMR (400 MHz, DMSO) δ 8.44 (s, 1H), 8.20 – 8.13 (m, 2H), 8.05 (d, J =
15.4 Hz, 1H), 7.96 – 7.91 (m, 2H), 7.88 (d, J = 5.0 Hz, 1H), 7.79 (d, J = 3.4 Hz, 1H),
7.61 (d, J = 15.4 Hz, 1H), 7.24 (m, 1H).13C NMR (100 MHz, DMSO) δ 180.2, 177.6,
174.1, 155.8, 153.9, 139.8, 138.1, 135.0, 134.9, 134.3, 133.4, 133.0, 132.2, 130.8,
129.4, 127.2, 127.0, 120.1, 115.0. HRMS (Q-TOF): calculated for C19H14O4S
335.0300 [M + H]+, found 335.0385. Purity ≥ 95.0%.
(E)-2-(3-([1,1'-biphenyl]-4-yl)acryloyl)naphtho[2,3-b]furan-4,9-dione(2d)
1H NMR (400 MHz, DMSO) δ 8.55 (s, 1H), 8.19 – 8.14 (m, 2H), 8.04 (m, 2H),
7.97 (d, J = 14.0 Hz, 1H), 7.94 (m, 2H), 7.90 (d, J = 10.2 Hz, 1H), 7.79 (m, 4H), 7.51
(t, J = 7.6 Hz, 2H), 7.42 (t, J = 7.4 Hz, 1H). 13C NMR (100 MHz, DMSO) δ 180.3,
177.9, 174.2, 155.9, 154.1, 144.9, 143.2, 139.6, 135.0, 134.9, 133.8, 133.5, 133.1,
130.8, 130.4, 129.5, 128.6, 127.6, 127.3, 127.2, 127.1, 121.9, 115.5. HRMS (Q-TOF):
calculated for C27H16O4 406.1082 [M + H]+, found 406.2045. Purity ≥ 95.0%.
4.1.2. Synthesis of 3-phenyliodonio-1, 2, 4-trioxo-1,2,3,4-tetrahydronaphthalenide
(4)

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The synthesis of compound 4 was carried out according to the previously
reported procedure [23].To a solution of 2-hydroxy-1,4-naphthoquinone (3) (5 g,
28.7mmol) in CHCl3 (60 mL), iodobenzene diacetate (15 g, 46.6mmol) was added at
room temperature. After the reaction mixture stirred at this temperature for 6 h, the
mixture was filtered to give an orange precipitate, washed with CHCl3 for three times
and dried to afford compound 4 as orange solid (9.8 g, 91.0%).
4.1.3. Synthesis of 2-hydroxymethyl-naphtho[2,3-b]furan-4,9-dione (5)
To a stirred solution of 4 (5.0 g, 13.3 mmol) in pyridine (60 mL), cuprous oxide
(5.0 g) was added at room temperature. Then the reaction mixture was heated to 80 °C.
The mixture solution was added propargyl alcohol (10 mL) slowly, and stirred at this
temperature for 2.5 h. The solution was cooled to room temperature, filtered and
diluted with 400 mL of 10% aqueous HCl. The acidic solution was extracted three
times with 50 mL of EtOAc. The organic layer was washed with saturated copper
sulfate solution and dried over anhydrous Na2SO4, filtered and concentrated under
reduced pressure. The residue was purified by chromatography on Si gel column with
DCM- MeOH to obtain compound 5 as an orange solid (540 mg, 17.8%).1H NMR
(400 MHz, DMSO) δ 8.14 – 8.04 (m, 2H), 7.94 – 7.81 (m, 2H), 6.94 (s, 1H), 5.72 (t, J
= 4.8 Hz, 1H), 4.61 (d, J = 4.8 Hz, 2H).
4.1.4. Synthesis of 2-formyl-4,9-dihydronaphtho[2,3-b]-furan-4,9-dione (6)
To a solution of 5 (500 mg, 2.19 mmol) in DCM (5 mL), pyridinium
chlorochromate (1.5 g) was added. The mixture was stirred at room temperature for
overnight. Then the solution was diluted with H2O and extracted with DCM for three
times. The combined organic phase was washed with brine and dried over anhydrous
Na2SO4, filtered and concentrated under reduced pressure. The residue was purified
by chromatography on Si gel column with DCM to give compound 6 as a yellow solid
(398 mg, 80.4%).1H NMR (400 MHz, DMSO) δ 9.91 (s, 1H), 8.23 – 8.09 (m, 2H),
8.04 (s, 1H), 7.98 – 7.86 (m, 2H).
4.1.5. Synthesis of 4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-carboxylic acid (7)
The synthesis of intermediate compound 7 was carried out according to the
previously reported procedure [19].To a solution of 6 (300 mg, 1.33 mmol) in glacial

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HOAc (20 mL), H2O2 (30%, 10 mL) was added at 75 °C, and the mixture was stirred
at this temperature for 4 h. Then it was concentrated under reduced pressure, and the
residue was filtered and washed with H2O for three times, and dried in a vacuum
dryer to afford compound 7 as a yellow solid (289 mg, 90.0%).1H NMR (400 MHz,
DMSO) δ 14.17 (brs, 1H), 8.40 – 8.05 (m, 2H), 8.02 – 7.84 (m, 2H), 7.68 (s, 1H).
4.1.6. General procedures for the preparation of 8a-u
The solution of intermediate compound 7 (0.20 mmol) in DCM (3 mL) was
stirred with HATU (0.31 mmol) at room temperature for 10 minutes and then
triethylamine (0.31 mmol), substituted alkyl amines or N-heterocycles (0.36 mmol)
was added. After the reaction mixture stirred at room temperature for 2h, the mixture
was evaporated under vacuum, purified by chromatography on Si gel column with
DCM to afford compounds 8a-u.
2-(pyrrolidine-1-carbonyl)naphtho[2,3-b]furan-4,9-dione(8a)
1H NMR (400 MHz, CDCl3) δ 8.16 – 8.10 (m, 2H), 7.95 – 7.88 (m, 2H), 7.55 (s,
1H), 3.81 (t, J = 6.8 Hz, 2H), 3.52 (t, J = 6.8 Hz, 2H), 1.95 (m, 2H), 1.91 – 1.83 (m,
2H).13C NMR (100 MHz, DMSO) δ 180.4, 173.8, 156.4, 152.6, 152.5, 134.9, 134.9,
133.3, 132.8, 130.4, 127.1, 127.0, 111.7, 48.2, 47.5, 26.4, 23.8. HRMS (Q-TOF):
calculated for C17H13NO4 318.0845 [M + Na]+, found 318.0705. Purity ≥ 95.0%.
2-(piperidine-1-carbonyl)naphtho[2,3-b]furan-4,9-dione (8b)
1H NMR (400 MHz, DMSO) δ 8.17 – 8.09 (m, 2H), 7.95 – 7.88 (m, 2H), 7.44 (s,
1H), 3.71 – 3.54 (m, 4H), 1.61 (m, 6H).13C NMR (100 MHz, DMSO) δ 180.4, 173.7,
157.7, 152.3, 152.2, 134.9, 134.8, 133.3, 132.8, 130.2, 127.1, 126.9, 110.7, 47.9, 43.5,
26.7, 25.7, 24.3. HRMS (Q-TOF): calculated for C18H15NO4 310.1001 [M + H]+,
found 310.1030. Purity ≥ 95.0%.
2-(morpholine-4-carbonyl)naphtho[2,3-b]furan-4,9-dione (8c)
1H NMR (400 MHz, DMSO) δ 8.17 – 8.08 (m, 2H), 7.92 – 7.87 (m, 2H), 7.53 (s,
13
1H), 3.68 (s, 8H). C NMR (100 MHz, DMSO) δ 180.3, 173.7, 157.9, 152.5, 151.4,
134.9, 134.9, 133.3, 132.7, 130.2, 127.1, 126.9, 111.6, 66.6, 66.5, 66.5, 66.5. HRMS
(Q-TOF): calculated for C17H13NO5 334.0794 [M + Na]+, found 334.0603. HPLC
purity 100.0%.

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2-(thiomorpholine-4-carbonyl)naphtho[2,3-b]furan-4,9-dione (8d)
1H NMR (400 MHz, DMSO) δ 8.19 – 8.05 (m, 2H), 8.01 – 7.85 (m, 2H), 7.48 (s,
1H), 3.90 (m, 4H), 2.82 – 2.68 (m, 4H).13C NMR (100 MHz, DMSO) δ 180.3, 173.7,
158.2, 152.4, 151.6, 134.9, 134.9, 133.3, 132.7, 130.2, 127.1, 126.9, 111.2, 27.7, 27.5,
27.3, 27.2. HRMS (Q-TOF): calculated for C17H13NO4S 350.0564 [M + Na]+, found
350.0402. HPLC purity ≥ 99.3%.
2-(4-methylpiperazine-1-carbonyl)naphtho[2,3-b]furan-4,9-dione (8e)
1H NMR (400 MHz, DMSO) δ 8.15 – 8.09 (m, 2H), 7.94 – 7.87 (m, 2H), 7.48 (s,
1H), 3.67 (s, 4H), 2.41 – 2.37 (m, 4H), 2.22 (s, 3H).13C NMR (100 MHz, DMSO) δ
180.3, 173.7, 157.7, 152.4, 151.7, 134.9, 134.8, 133.2, 132.7, 130.2, 127.1, 126.9,
111.3, 55.3, 54.6, 46.8, 46.0, 42.6. HRMS (Q-TOF): calculated for C18H16N2O4
347.1110 [M+ Na]+, found 347.0997. HPLC purity ≥ 99.5%
2-(4-ethylpiperazine-1-carbonyl)naphtho[2,3-b]furan-4,9-dione (8f)
1H NMR (400 MHz, DMSO) δ 8.16 – 8.09 (m, 2H), 7.96 – 7.87 (m, 2H), 7.49 (s,
1H), 3.67 (s, 4H), 2.46 – 2.42 (m, 4H), 2.38 (q, J = 7.2 Hz, 2H), 1.02 (t, J = 7.2 Hz,
3H).13C NMR (100 MHz, DMSO) δ 180.3, 173.7, 157.7, 152.4, 151.7, 134.9, 134.8,
133.2, 132.7, 130.2, 127.1, 126.9, 111.3, 53.1, 52.3, 51.8, 47.0, 42.7, 12.3. HRMS
(Q-TOF): calculated for C19H18N2O4 339.1267 [M + H]+, found: 339.1235. HPLC
purity ≥ 99.8%
2-(4-oxopiperidine-1-carbonyl)naphtho[2,3-b]furan-4,9-dione (8g)
1H NMR (400 MHz, DMSO) δ 8.17 – 8.10 (m, 2H), 7.94 – 7.87 (m, 2H), 7.57 (s,
1H), 3.96 (brs, 4H), 2.55 (t, J = 6.4 Hz,4H).13C NMR (100 MHz, DMSO) δ 207.3,
180.4, 173.7, 158.3, 152.5, 151.6, 134.9, 134.9, 133.3, 132.8, 130.2, 127.1, 126.9,
111.6, 44.6, 41.4, 40.8, 39.5. HRMS (Q-TOF): calculated for C18H13NO5 324.0794 [M
+ H]+, found 324.0898. HPLC purity ≥ 99.4%
Methyl-2-(1-(4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-carbonyl)piperidin-4-yl)ac
etate (8h)
1H NMR (400 MHz, DMSO) δ 8.16 – 8.10 (m, 2H), 7.91 (m, 2H), 7.44 (s, 1H),
4.39 (m, 1H), 4.09 – 4.00 (m, 1H), 3.60 (s, 3H), 3.25 (m, 1H), 2.94 – 2.83 (m, 1H),
2.32 (d, J = 7.0 Hz, 2H), 2.08 – 1.98 (m, 1H), 1.82 – 1.72 (m, 2H), 1.31 – 1.15 (m,

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2H).13C NMR (100 MHz, DMSO) δ 180.4, 173.7, 172.7, 157.7, 152.3, 152.1, 134.9,
134.8, 133.3, 132.8, 130.2, 127.1, 126.9, 110.9, 51.7, 46.9, 42.6, 40.2, 32.8, 32.3, 31.4.
HRMS (Q-TOF): calculated for C21H19NO6 382.1212 [M + H]+, found: 382.1282.
Purity ≥ 95.0%.
2-(4-(3-chlorophenyl)piperidine-1-carbonyl)naphtho[2,3-b]furan-4,9-dione (8i)
1H NMR (400 MHz, CDCl3) δ 8.28 – 8.19 (m, 2H), 7.84 – 7.76 (m, 2H), 7.45 (s,
1H), 7.26 (s, 1H), 7.23 – 7.20 (m, 2H), 7.13 – 7.10 (m, 1H), 4.83 (brs, 1H), 4.44 (brs,
1H), 3.35 (brs, 1H), 2.93 (brs, 1H), 2.85 (m, 1H), 2.01 (m, 2H), 1.78 (m, 2H).13C
NMR (100 MHz, DMSO) δ 180.4, 173.7, 157.8, 152.4, 152.0, 148.4, 134.9, 134.8,
133.6, 133.3, 132.8, 130.8, 130.3, 127.3, 127.1, 126.9, 126.8, 126.1, 110.9, 47.2, 44.4,
43.1, 41.8 , 32.8. HRMS (Q-TOF): calculated for C24H18ClNO4 442.0924 [M + Na]+,
found 442.0811. Purity ≥ 95.0%.
2-(4-(4-fluorophenyl)piperidine-1-carbonyl)naphtho[2,3-b]furan-4,9-dione (8j)
1H NMR (400 MHz, DMSO) δ 8.17 – 8.10 (m, 2H), 7.95 – 7.88 (m, 2H), 7.51 (s,
1H), 7.36 – 7.31 (m, 2H), 7.16 – 7.09 (m, 2H), 4.58 (brs, 1H), 4.20 (brs, 1H), 3.49
(brs, 1H), 2.92 (m, 2H), 1.85 (brs, 2H), 1.69 (brs, 2H).13C NMR (100 MHz, DMSO) δ
180.4, 173.7, 162.5, 160.1, 157.8, 152.4, 152.0, 142.0, 134.9, 133.3, 132.8, 130.2,
129.1, 129.0, 127.1, 126.9, 115.6, 115.4, 110.9, 47.6, 43.2, 41.3, 33.7, 33.2. HRMS
(Q-TOF): calculated for C24H18FNO4 426.1220 [M + Na]+, found: 426.1106. Purity ≥
95.0%.
2-(4-(4-methoxyphenyl)piperidine-1-carbonyl)naphtho[2,3-b]furan-4,9-dione(8k)
1H NMR (400 MHz, DMSO) δ 8.15 – 8.10 (m, 2H), 7.93 – 7.87 (m, 2H), 7.50 (s,
1H), 7.20 (d, J = 8.6 Hz, 2H), 6.87 (d, J = 8.6 Hz, 2H), 4.57 (brs, 1H), 4.19 (brs, 1H),
3.72 (s, 3H), 3.36 (brs, 1H), 2.94 (brs, 1H), 2.88 – 2.78 (m, 1H), 1.84 (m, 2H), 1.66
(m, 2H).13C NMR (100 MHz, DMSO) δ 180.4, 173.7, 158.2, 157.8, 152.3, 152.1,
137.8, 134.9, 134.8, 133.3, 132.8, 130.2, 128.1 (2C), 127.1, 126.9, 114.3 (2C), 110.9,
55.5, 47.6, 43.3, 41.2, 33.6, 33.4. HRMS (Q-TOF): calculated for C25H21NO5
438.1420 [M + Na]+, found: 438.1308. Purity ≥ 95.0%.
2-(4-(3-(trifluoromethyl)phenyl)piperazine-1-carbonyl)naphtho[2,3-b]furan-4,9-dione
(8l)

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1H NMR (400 MHz, DMSO) δ 8.17 – 8.10 (m, 2H), 7.94 – 7.88 (m, 2H), 7.56 (s,
1H), 7.46 (t, J = 7.6 Hz, 1H), 7.27 (d, J = 7.6 Hz, 1H), 7.23 (s, 1H), 7.11 (d, J = 7.6
Hz, 1H), 3.86 (s, 4H), 3.41 – 3.36 (m, 4H). 13C NMR (100 MHz, DMSO) δ 180.4,
173.7, 157.8, 152.5, 151.5, 151.2, 134.9, 134.9, 133.3, 132.8, 130.6, 130.3, 130.2,
127.1, 126.9, 119.6, 115.5, 111.8, 111.7, 48.2, 46.6, 42.4, 40.6. HRMS (Q-TOF):
calculated for C24H17F3N2O4 455.1140 [M + H]+, found: 455.1151. Purity ≥ 95.0%.
N-(4,4-dimethylcyclohexyl)-4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-carboxamid
e (8m)
1H NMR (400 MHz, DMSO) δ 8.72 (d, J = 8.0 Hz, 1H), 8.17 – 8.09 (m, 2H),
7.94 – 7.88 (m, 2H), 7.67 (s, 1H), 3.74 (m, 1H), 1.67 – 1.52 (m, 4H), 1.41 (m, 2H),
1.32 – 1.21 (m, 2H), 0.93 (d, J = 9.4 Hz, 6H).13C NMR (100 MHz, DMSO) δ 180.4,
173.8, 156.1, 152.7, 152.6, 134.9, 134.8, 133.3, 132.9, 130.8, 127.0, 127.0, 110.2,
48.8, 38.0 (2C), 32.6, 29.8, 28.2 (2C), 24.6. HRMS (Q-TOF): calculated for
C21H21NO4 374.1471 [M + Na]+, found: 374.1358. Purity ≥ 95.0%.
N-(adamantan-1-yl)-4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-carboxamide (8n)
1H NMR (400 MHz, DMSO) δ 8.19 – 8.07 (m, 2H), 8.02 (s, 1H), 7.91 (m, 2H),
7.75 (s, 1H), 2.08 (s, 9H), 1.67 (s, 6H).13C NMR (100 MHz, DMSO) δ 180.5, 173.7,
156.3, 152.9, 152.5, 134.9, 134.8, 133.3 (s), 132.9, 130.7, 127.0, 127.0, 110.1, 52.8,
41.1 (3C), 36.4 (2C), 29.3 (4C). HRMS (Q-TOF): calculated for C23H21NO4 376.1471
[M + H]+, found 376.1539. Purity ≥ 95.0%.
N-cyclohexyl-4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-carboxamide (8o)
1H NMR (400 MHz, DMSO) δ 8.70 (d, J = 8.0 Hz, 1H), 8.17 – 8.08 (m, 2H),
7.94 – 7.88 (m, 2H), 7.68 (s, 1H), 3.77 (m, 1H), 1.82 (m, 1H), 1.77 – 1.71 (m, 2H),
1.61 (m, 2H), 1.37 – 1.31 (m, 3H), 1.23 (m, 2H).13C NMR (100 MHz, DMSO) δ
180.4, 173.8, 156.1, 152.7, 152.6, 134.9, 134.8, 133.3, 132.9, 130.7, 127.0, 127.0,
110.2, 48.9, 32.6 (2C), 25.3 (2C). HRMS (Q-TOF): calculated for C19H17NO4
324.1158 [M + H]+, found: 324.1235. Purity ≥ 95.0%.
4,9-dioxo-N-(2-(pyrrolidin-1-yl)ethyl)-4,9-dihydronaphtho[2,3-b]furan-2-carboxamid
e(8p)
1H NMR (400 MHz, DMSO) δ 8.88 (t, J = 5.8 Hz, 1H), 8.18 – 8.08 (m, 2H),

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7.96 – 7.86 (m, 2H), 7.63 (s, 1H), 3.40 (q, J = 6.6 Hz, 2H), 2.59 (t, J = 6.6 Hz, 2H),
2.49 (m, 4H), 1.76 – 1.60 (m, 4H).13C NMR (100 MHz, DMSO) δ 180.4, 173.8, 156.9,
152.7, 152.5, 134.9, 134.8, 133.3, 132.9, 130.7, 127.1, 127.0, 110.3, 55.1 (2C), 54.1,
38.8 (2C), 23.6. HRMS (Q-TOF): calculated for C19H18N2O4 339.1267 [M + H]+,
found 339.1348. Purity ≥ 95.0%.
4,9-dioxo-N-(2-(piperidin-1-yl)ethyl)-4,9-dihydronaphtho[2,3-b]furan-2-carboxamide
(8q)
1H NMR (400 MHz, DMSO) δ 8.83 (t, J = 5.8 Hz, 1H), 8.18 – 8.08 (m, 2H),
7.94 – 7.86 (m, 2H), 7.62 (s, 1H), 3.39 (q, J = 6.6 Hz, 2H), 2.44 (t, J = 6.6 Hz, 2H),
2.38 (m, 4H), 1.49 (m, 4H), 1.41 – 1.34 (m, 2H).13C NMR (100 MHz, DMSO) δ
180.4, 173.8, 156.9, 152.7, 152.5, 134.9, 134.8, 133.3, 132.9, 130.7, 127.1, 127.0,
110.2, 57.9, 54.5 (2C), 37.1, 26.0 (2C), 24.5. HRMS (Q-TOF): calculated for
C20H20N2O4 353.1423 [M + H]+, found 353.1504. HPLC purity ≥ 98.8%
N-(2-morpholinoethyl)-4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-carboxamide
(8r)
1H NMR (400 MHz, DMSO) δ 8.87 (t, J = 5.6 Hz, 1H), 8.19 – 8.09 (m, 2H),
7.96 – 7.87 (m, 2H), 7.63 (s, 1H), 3.61 – 3.54 (m, 4H), 3.41 (q, J = 6.6 Hz, 2H), 2.47
(t, J = 6.6 Hz, 2H), 2.42 (m, 4H).13C NMR (100 MHz, DMSO) δ 180.4, 173.8, 156.9,
152.7, 152.5, 134.9, 134.8, 133.3, 132.9, 130.7, 127.1, 127.0, 110.3, 66.7 (2C), 57.6,
53.7 (2C), 36.7. HRMS (Q-TOF): calculated for C19H18N2O5 355.1216 [M + H]+,
found: 355.1290. HPLC purity ≥ 98.8%
4,9-dioxo-N-phenethyl-4,9-dihydronaphtho[2,3-b]furan-2-carboxamide (8s)
1H NMR (400 MHz, DMSO) δ 9.03 (t, J = 5.6 Hz, 1H), 8.16 – 8.08 (m, 2H),
7.95 – 7.86 (m, 2H), 7.60 (s, 1H), 7.26 (m, 5H), 3.57 – 3.48 (q, J = 7.4 Hz, 2H), 2.87
(t, J = 7.4 Hz, 2H).13C NMR (100 MHz, DMSO) δ 180.3, 173.8, 156.9, 152.7, 152.5,
139.6, 134.9, 134.8, 133.3, 132.8, 130.7, 129.1 (2C), 128.9 (2C), 127.0, 127.0, 126.7,
110.2, 41.0, 35.3. HRMS (Q-TOF): calculated for C21H15NO4 368.1001 [M + Na]+,
found: 368.0698. Purity ≥ 95.0%.
N-(4-chlorophenethyl)-4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-carboxamide (8t)
1H NMR (400 MHz, DMSO) δ 9.01 (t, J = 5.6 Hz, 1H), 8.17 – 8.08 (m, 2H),

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7.94 – 7.87 (m, 2H), 7.61 (s, 1H), 7.38 – 7.33 (m, 2H), 7.30 – 7.26 (m, 2H), 3.52 (q,
7.2 Hz, 2H), 2.86 (t, J = 7.2 Hz, 2H).13C NMR (100 MHz, DMSO) δ 180.4, 173.8,
156.9, 152.7, 152.4, 138.7, 134.9, 134.8, 133.3, 132.9, 131.3, 131.1 (2C), 130.7, 128.7
(2C), 127.1, 127.0, 110.3, 40.7, 34.5. HRMS (Q-TOF): calculated for C21H14ClNO4
380.0611 [M + H]+, found: 380.0690. Purity ≥ 95.0%.
N-(4-methoxyphenethyl)-4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-carboxamide(8
u)
1H NMR (400 MHz, DMSO) δ 8.99 (t, J = 5.6 Hz, 1H), 8.17 – 8.07 (m, 2H),
7.96 – 7.86 (m, 2H), 7.61 (s, 1H), 7.16 (d, J = 8.4 Hz, 2H), 6.86 (d, J = 8.4 Hz, 2H),
3.72 (s, 3H), 3.48 (q, J = 7.4 Hz, 2H), 2.80 (t, J = 7.4 Hz, 2H).13C NMR (100 MHz,
DMSO) δ 180.4, 173.8, 158.2, 156.9, 152.7, 152.5, 134.9, 134.8, 133.3, 132.9, 131.5,
130.7, 130.1 (2C), 127.0, 127.0, 114.3 (2C), 110.2, 55.5, 41.2, 34.5. HRMS (Q-TOF):
calculated for C22H17NO5 398.1107 [M + Na]+, found: 398.1009. Purity ≥ 95.0%.
4.2. In vitro inhibitory activity
U251, HepG2, HT29, CT26 and PC-3 cells were seeded in 96-well plates at a
density of 5×103 cells/well and cultured for 24 h. Following the addition of different
concentrations of compounds, the cells were further cultured for 72 h, with 0.5%
DMSO as the solvent control group. Then cells were incubated for 4 h with 5mg/ml of
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) solution, and
the formazan crystals were dissolved with 150ul of DMSO. After gentle shaking for
10min, the optical density (OD) was measured at 570nm using a Spectra MAX M5
microplate spectrophotometer. Each treatment was performed in triplicate. Results
were analyzed with GraphPad Prism 6 and data were shown as Mean ± SD.
4.3. Molecular docking
Molecular docking studies were carried out using the Discovery Studio (DS) 3.1
software. The protein was constructed based on the X-ray structure of STAT3, which
was available through the RCSB Protein Data Bank (PDB code: 1BG1). Both the
compounds and the structure of STAT3 were prepared and optimized using Discovery
Studio 3.1. The protein was prepared with adding hydrogens, deleting water
molecules. The low energy clusters were identified and binding energies were

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evaluated.
4.4. The determination of aqueous solubility
The aqueous solubility of the compounds 8c-g, 8q and 8r were determined by
HPLC method. The calibration standards were prepared with concentrations for 15,
25, 50, 75, 100, 125 µg/mL and used to assess calibration curves. The compounds (2
mg) were added into 1.5 mL EP tubes respectively. The pure water (1 mL) was added
into each EP tube. Then the EP tubes were vortexed for 30s and swung at room
temperature for 24 h to obtain saturated solution, which were disposed by HPLC
system.
4.5. In Vivo Antitumor Activity Evaluation
CT-26 cells (1 × 106) were subcutaneously implanted in the right flanks of
6-week-old male BALB/c mice, which were purchased from DaShuo experimental
animal Co. Ltd. (Chengdu, Sichuan, China). After the solid tumors volume were
reached about 70 mm3, mice were randomized to two groups with five mice per group
and were orally administrated with 8q 50mg/kg and vehicle per day. Compound 8q
was dissolved at 5% 1-methyl-2-pyrrolidinone in polyethylene glycol 400, and the
blank control group received oral administration of equal volume of 5% NMP, 95%
PEG. The tumors were measured every 3 days with a caliper. Tumor volume (V) was
estimated using the equation V = ab2/2, where a and b stand for the longest and
shortest diameter, respectively. After treatment, mice were sacrificed and dissected to
weigh the tumor tissues and to examine the internal organ injury by macroscopic
analysis. TGI and T/C were calculated according to the following formula:
TGI = (the mean tumor weight of control group - the mean tumor weight of treated
group)/ (the mean tumor weight of control group).
T /C=mean RTV of treated group/mean RTV of control group
RTV, namely, relative tumor volume, is Vt/ V0 (Vt is the tumor volume measured at
the end of treatment; V0 is the tumor volume measured at the beginning of treatment).
4.6. Western blot and immunofluorescence analysis
Total cellular proteins were extracted in RIPA buffer (Beyotime Biotechnology)
supplemented with protease inhibitor cocktail (Sigma-Aldrich). Protein concentrations

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were determined with BCA protein assay kit (Thermo Fisher Scientific). Equal
amounts of protein were run out on 10% SDS-PAGE gel and subsequently transferred
onto PVDF membranes (Millipore). Membranes were blocked in 5% skimmed milk
and incubated with the following primary antibodies at 4 overnight: mouse
monoclonal antibody to total STAT3 (Cell Signaling, 1:1000, #9139), rabbit
monoclonal antibody to p-STAT3 (Tyr705) (Cell Signaling, 1:1,000, #9145) and
rabbit polyclonal antibody to GADPH (BOSTER, 1:500, BA2913). Second antibodies
were from Beyotime Biotech and used at a dilution of 1:2,000. Enhanced
chemiluminescence (ECL) and digital imaging (Clinx Science Instruments,
Chemiscope 5300) were used for detection of target proteins. For
immunofluorescence analysis, the primary antibody of total STAT3 was the same as
used in western blot. Cell nucleus was stained with DAPI (Roche). Images were taken
on a Zeiss microscope (Axio Observer).
4.7. Total STAT3 and p-STAT3Y705 sandwich enzyme-linked immunosorbent
assay
Whole-cell lysates were prepared using cell lysis buffer (Beyotime
Biotechnology) containing protease inhibitor cocktail (Sigma-Aldrich). Protein
concentrations were quantified with BCA protein assay kit (Thermo Fisher Scientific).
Levels of total and p-STAT3Y705 were measuring by using PathScan Total Stat3 and
Phospho-Stat3 (Tyr705) Sandwich ELISA Kit (Cell Signaling, 7305 & 7300)
according to the manufacturer’s instructions. The measurements were repeated three
times. For statistical analyses, treatment groups were compared with control group by
paired t-test and data are represented as means ± S.D.
4.8. Electrophoretic Mobility Shift Assay (EMSA)
HEK293T cells were transiently transfected with N-terminal FLAG-tagged
STAT3 expression construct (10 µg/10 cm dish). Forty-eight hours post transfection,
cells were harvested and dissolved in lysis buffer (500 µL/10 cm dish). After
sonification and centrifugation, STAT3 were purified by Anti-FLAG M2 Magnetic
Beads from Sigma (M8823) according to the instructions. Protein was eluted from
beads with 200 µL flag peptide (200 µg/mL). EMSA was performed by using

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Chemiluminescent EMSA Kit (GS009, Beyotime) according to the instructions.
Biotin labeled STAT3 probe, cold probe and nylon membranes were also purchased
from Beyotime (GS083B, FFN10 ). 5 µL eluted protein and 1 µL probe were loaded
with each lane. Anti-total STAT3 antibody is the same as used in western blot.
Enhanced chemiluminescence (ECL) and digital imaging (Clinx Science Instruments,
Chemiscope 5300) were used for detection of target proteins. Compond 8q was added
as indicated.
4.9. Purification of STAT3 and Surface Plasmon Resonance (SPR) analysis
Full-length STAT3 with N-terminal His-tag was expressed by baculovirus in Sf9
insect cells. Briefly, STAT3 vector was co-transfected with Bac-N-Blue DNA into Sf9
cells. Recombinant virus was amplified in Sf9 cells and expressed in High Five cells.
2–3 d post-infection, cells were spun down and the medium was collected for
purification. After filter, concentration and dialysis, protein was purified by Ni-NTA
Agarose and gel-filtration columns. Protein purity (>90%) and concentration were
determined by SDS-PAGE with Coomassie staining and UV spectrometry.
STAT3 and compound 8q binding analyses was performed by using Biacore
X100 (GE Healthcare, UK) according to standard methods. Protein was covalently
immobilized to the surface of a CM5 sensor chip using a amine coupling kit (GE
Healthcare). Compound 8q was diluted with 5% DMSO in PBS buffer. The
concentrations were set at 600, 300, 150, 75, 37.5 and 18.75 nM. The equilibrium
dissociation constant (KD) was obtained by using the BIAevaluation 2.0 software.
Conflicts of interest
The authors declare no other conflicts of interest.
Acknowledgments
This work was supported by the National Natural Science Foundation of China
(No.81473253), the National Mega-projects of China for Innovative Drugs
(2018ZX09721001-001-001).

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Highlights
1. In vitro, compound 8q was over 10-fold more potent than napabucasin on U251,
HepG2, HT29 and CT26 cells.
2. In mouse model of colorectal cancer, 8q significantly reduced tumor growth. The
TGI of 8q at 50 mg/kg was 63 %.
3. Compound 8q has a KD of 110.2 nM for full-length STAT3 recombinant protein
by surface plasmon resonance analysis.
4. The aqueous solubility of 8q was over 4.5-fold higher than that of napabucasin.
5. Compound 8q exhibited good safety profile in BALB/c mice model.