Total Synthesis and Biological Evaluation of Sericetin for Protection against Cisplatin-Induced Acute Kidney Injury

Article abstract of DOI:10.1021/acs.jnatprod.8b00434

A concise synthesis of sericetin (1) was performed in four steps from readily available 3-O-benzylgalangin (4), featuring electrocyclization to produce the tricyclic core and a sequential aromatic Claisen/Cope rearrangement to incorporate the 8-prenyl group of 1. In addition, the therapeutic potential of sericetin (1), isosericetin (2), and three prenylated tetracyclic synthetic intermediates (11, 12, and 14) against cisplatin-induced nephrotoxicity using renal tubular cells were evaluated. Compound 14 showed therapeutic potential against cisplatin-induced kidney damage.

Full text of DOI:10.1021/acs.jnatprod.8b00434

Article
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Cite This: J. Nat. Prod. XXXX, XXX, XXX−XXX
Total Synthesis and Biological Evaluation of Sericetin for Protection
against Cisplatin-Induced Acute Kidney Injury
Eun-Sun Kim,†,§ Hongjun Jang,‡,§ Sun-Young Chang,‡ Seung-Hoon Baek,‡ Ok-Nam Bae,*,†
and Hyoungsu Kim*,‡
†College of Pharmacy and Institute of Pharmaceutical Science and Technology, Hanyang University, Ansan 15588, Republic of
Korea
‡College of Pharmacy and Research Institute of Pharmaceutical Science and Technology (RIPST), Ajou University, Suwon 16499,
Republic of Korea
S
* Supporting Information
ABSTRACT: A concise synthesis of sericetin (1) was
performed in four steps from readily available 3-O-
benzylgalangin (4), featuring electrocyclization to produce
the tricyclic core and a sequential aromatic Claisen/Cope
rearrangement to incorporate the 8-prenyl group of 1. In
addition, the therapeutic potential of sericetin (1), isosericetin
(2), and three prenylated tetracyclic synthetic intermediates
(11, 12, and 14) against cisplatin-induced nephrotoxicity
using renal tubular cells were evaluated. Compound 14 showed therapeutic potential against cisplatin-induced kidney damage.
renylated flavonoids are a subclass of flavonoids that
As part of continuing efforts in the synthesis and biological
evaluation of flavonoids,6 we have been interested in the
synthesis of the tetracyclic flavonoid sericetin (1) and its effect
on cisplatin-induced acute kidney injury (AKI). Reported
herein are a concise synthesis of 1 exploiting an aromatic [3,3]-
sigmatropic rearrangement and the evaluation of the effect of
synthesized sericetin, isosericetin, and prenylated tetracyclic
synthesized intermediates against cisplatin-induced nephrotox-
icity.
P
possess a wide range of biological properties, such as
antioxidant, anticancer, antifungal, and estrogenic activities.1
The addition of a lipophilic prenyl group to these flavonoids
could increase their lipophilicity, thereby increasing their
permeabilities and bioavailabilities in vivo.2
Sericetin (1), a prenylated flavonoid, was first isolated from
the root-bark of Mundulea sericea in 1960 (Figure 1). This
RESULTS AND DISCUSSION
■
Chemistry. The retrosynthetic plan for sericetin (1) is
outlined in Scheme 1. Sericetin (1) could be synthesized from
phenol 3 via a prenylation/aromatic [3,3]-sigmatropic
rearrangement. In turn, the tetracyclic phenol 3 could be
obtained through electrocyclization of prenal with 5,7-
dihydroxyflavonol (4), which could be readily prepared from
the commercially available phloroglucinol (5) through conven-
tional Friedel−Crafts/pyrone annulation.
Figure 1. Structures of sericetin and isosericetin.
natural flavonoid has two isoprene units, i.e., an 8-prenyl group
and as part of the (2H)-pyran ring.3 The structure of sericetin
was proposed to be 1 or 2, based on the results of
spectroscopic data analyses. The first synthesis of 1 was
achieved by Jain and Zutshi and utilized 6- and 8-
bisprenylation/DDQ-mediated oxidative cyclization of galan-
gin to afford sericetin (1) as a minor product at less than 1%
yield, thereby defining its structure as 1.4
The biological properties of this unique prenylated flavonol
natural product had not been reported until Mahidol and
Ruchirawat isolated it in 2011 from the whole plant of
Dunbaria longeracemosa and showed that it possesses antitumor
activities in various cancer cell lines.5
Initial attempts to synthesize sericetin (1) are shown in
Scheme 2. The synthesis commenced with the preparation of
8-prenylflavonol 9. Selective THP (tetrahydropyran) protection
of the 7-hydroxy group in the flavonol 4,6h prepared from the
commercially available phloroglucinol (5), followed by
prenylation of the 5-hydroxy group in the known compound
6,6g afforded the aryl prenyl ether 7 in 77% yield over the two
steps. Compound 7 was subjected to sequential aromatic
Claisen/Cope rearrangement conditions to afford 8-prenyl-
Received: May 30, 2018
© XXXX American Chemical Society and
American Society of Pharmacognosy
A
DOI: 10.1021/acs.jnatprod.8b00434
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the natural product (1H and 13C NMR and HRMS),4,5 thereby
confirming the structure of 11 (Scheme 3). The structure of
isomer 12 was also confirmed through synthesis from known
136f,g via (i) propargylation, (ii) hydrogenation, and (iii)
Claisen rearrangement (13 → 12).
Scheme 1. Retrosynthetic Plan
Scheme 3. Determination of the Structures 11 and 12
Scheme 2. Initial Attempts at the Synthesis of Sericetin (1)
The rationale for the observed skeletal rearrangement is
shown in Figure 2. The 6,7-pyran 11 was formed from aryl
flavonol 9 in 75% yield over two steps after deprotection of the
THP group in 8 under acidic conditions.
Having installed the 8-prenyl group, the construction of the
D-ring in the natural product was next attempted. Thus, the
aryl propargyl ether 10 was prepared through selective
propargylation of the 7-hydroxy group in 9 under Claisen
rearrangement/cyclization conditions. However, the Claisen
rearrangement/cyclization of 10 yielded a roughly 1:1 mixture
of 11 and 12 in an 88% combined yield. Analysis of the
spectroscopic data revealed that the 1:1 mixture contained the
target 8-prenylated 6,7-pyran adduct 11 and the 6-prenylated
7,8-pyran adduct 12.
Figure 2. Rationale for the observed isomerization.
To investigate the mechanism of the unexpected isomer-
ization, 11 and 12 were separately subjected to the reaction
conditions of Claisen rearrangement/cyclization. No inter-
conversion was obtained, suggesting that the isomerization
must have occurred prior to closing of the D-ring.
Compound 11 was debenzylated to afford sericetin (1),
whose spectroscopic data were identical to those reported for
propargyl ether 10 through a [3,3]-sigmatropic rearrangement,
followed by keto−enol tautomerization, a [1,5]-sigmatropic
rearrangement, and an oxa-Diels−Alder reaction. In contrast,
the route to the formation of 12 appears to be more
complicated. Initially, the 7-propargyloxy group migrated to
C-8 through Claisen rearrangement to form intermediate A.
B
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The 8-prenyl group in intermediate A sequentially underwent
Cope rearrangements to furnish intermediate B, which further
participated in a Cope rearrangement to afford C, followed by
sequential aromatization, [1,5]-sigmatropic rearrangement, and
an oxa-Diels−Alder cyclization to form 12. Consequently, the
prenyl group in 10 was transferred from C-8 to C-6 through
sequential Claisen/double Cope rearrangements to afford 12
with the prenyl unit at C-6.
On the basis of the initial results, the construction of the D-
ring in sericetin (1) must occur prior to the installation of the
prenyl group at C-8 in order to obtain only the target 11 and
avoid the previously observed skeletal rearrangement. Thus,
the 8-prenyl tetracyclic 11 should be obtainable through the
transfer of a prenyl group across the A/D or A/C aromatic ring
system in 14 from the C-5 hydroxy group to C-8 through
sequential Claisen/Cope rearrangements, as described in
Scheme 4. The synthesis of 3, which had been previously
isomer in excellent yield (88%) without any skeletal rearrange-
ment. The optimized synthesis route afforded the penultimate
intermediate to sericetin (1) in three steps from 3-O-
benzylgalangin (4) with the introduction of two C5-isoprene
units to the A ring in of 4. Deprotection of the benzyl group
with BCl3 in CH2Cl2 (83%) completed the synthesis of
sericetin (1).
Biological Assay. Upon completion of the concise total
synthesis of sericetin (1), biological activities of sericetin (1),
isosericetin (2), and the three prenylated tetracyclic synthetic
intermediates (11, 12, and 14) were evaluated. After testing all
five compounds via the 3-(4,5-dimethylthiazol-2-yl)-2,5-
diphenyltetrazolium bromide) (MTT) assay, their therapeutic
potential against cisplatin-induced AKI was assessed.
AKI is a representative renal injury induced by drugs or
chemicals. It is associated with high mortality and contributes
to the development of chronic renal failure.8 There have been
intensive efforts to develop therapeutic candidates for treating
drug-induced AKI.9,10 Cisplatin is commonly used as an
anticancer chemotherapeutic,11 but despite its clinical efficacy,
its use is limited due to its adverse effects, including
nephrotoxicity.12 The accumulation of high concentrations of
cisplatin in the kidneys leads to nephrotoxicity,13 and patients
treated with cisplatin may show impaired renal function.14
Cisplatin-induced nephrotoxicity is known to be mediated by
oxidative stress, mitochondrial dysfunction, inflammatory
tissue damage, and apoptosis.11,13 Cisplatin-induced AKI is a
well-established representative model to investigate the
therapeutic potential and mechanisms of drug candidates to
treat or prevent AKI. Since renal damage is mediated by
complicated modes of action, natural products such as
flavonoids that have shown multiple biological properties are
considered to be good therapeutic candidates against drug-
induced nephrotoxicity. In fact, several natural products have
been suggested as potential therapeutic interventions and/or
adjuvants to prevent drug-induced kidney injury.9,15
Scheme 4. Successful Route to Concise and Efficient
Synthesis of Sericetin (1)
Based on the cytotoxicity results obtained using the MTT
assay, 14 showed the most potent protective activity against
cisplatin-induced cytotoxicity in renal tubular cells (Figure 3).
Figure 3. Protective effect of compounds (CPDs) 1, 2, 11, 12, and 14
against cisplatin-induced cytotoxicity in rat renal tubular cells. NRK-
52E cells (rat tubular epithelial cells) were treated with compounds 1,
2, 11, 12, and 14 (20 μM) with or without cisplatin (CP; 30 μM) for
24 h. Cell viability was measured via the MTT assay. DMSO (final
concentration 0.2%) was used as a vehicle control. Values are mean
SEM. **p < 0.01 vs control; ##p < 0.01 vs cisplatin-treated cells. N =
3.
prepared in four steps from 4 in the synthesis of macakurzin C
was optimized first.6f,g Recently, electrocyclization was
successfully used in the one-step pyran annulation of resorcinol
derivatives from α,β-unsaturated aldehydes,7 which prompted
application of this method to the synthesis of the D-ring in the
natural product. Electrocyclization of the resorcinol derivative
4 with 3,3-dimethylacrylaldehyde smoothly provided the target
pyran 3 in 54% yield. Prenylation (95%) of the 5-hydroxy
group in 3 and subjecting the resulting arylprenyl ether 14 to
the conditions of aromatic Claisen rearrangement afforded the
8-prenyl tetracyclic 11 via intermediates D or E as a single
In order to further evaluate the protective activity of 14,
NRK-52E cells were treated with various concentrations of 14.
As shown in Figures 4A and B, 14 showed protective effects
against cisplatin-induced cytotoxicity in a dose-dependent
manner, and the compound was not cytotoxic in the dose
range tested (Figure 4C).
C
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Reactive oxygen species (ROS) generation and mitochon-
drial dysfunction have been suggested as the main mechanisms
for apoptotic cell death in cisplatin-induced nephrotoxici-
ty.14a,16 In this study, cisplatin increased ROS generation, as
quantified by the 5-(and-6)-chloromethyl-2′,7′-dichlorodihy-
drofluorescein diacetate (CM-H2DCFDA) assay, in renal
tubular cells, whereas treatment with 14 significantly reduced
the ROS generation (Figure 5A). Since impaired redox balance
induced by cisplatin could result in mitochondrial damages in
tubular cells, mitochondrial membrane potentials using
5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolo carbo-
cyanine iodide (JC-1) fluorescence was measured. The result
showed that green fluorescence significantly increased in
tubular cells exposed to cisplatin, which suggests that cisplatin
affected the mitochondrial membrane potentials. The increase
in green fluorescence was reversed in cells cotreated with 14
and cisplatin, showing that normal membrane potentials were
restored (Figure 5B). Cisplatin-induced ROS generation and
altered mitochondrial membrane potentials can result in
apoptotic cell death in renal tubular cells. As observed with
the levels of cleaved caspase-3 (active form), cisplatin activated
the apoptotic caspase cascade in tubular cells, whereas 14
significantly reduced the level of cleaved caspase-3 (Figure
5C).
Figure 4. Inhibition of cisplatin-induced cytotoxicity by 14 in renal
tubular cells. NRK-52E cells were treated with 14 (0, 1, 10, and 50
μM) for 24 h in the absence or presence of cisplatin (CP; 30 μM).
(A) Morphologic changes were observed via microscopy. Scale bar:
100 μm. (B, C) Cell viability was measured via MTT assay. Values are
mean SEM. ** p < 0.01 vs control. ##p < 0.01 vs cisplatin-treated
cells. N = 3.
The in vivo relevancy of the nephroprotective effects of 14
was demonstrated in a rat model of cisplatin-induced AKI.
Consistent with the caspase-3 activation seen in tubular cells
Figure 5. Protective mechanisms of 14 against cisplatin-induced cellular damage in renal tubular cells. NRK-52E cells were treated with cisplatin
(CP; 30 μM) with or without 14 (10 μM) for 24 h. (A) Changes in reactive oxygen species generation were measured via dichlorofluorescein
(DCF) staining (left panel). The percentage of ROS generation was calculated with DCF fluorescence signal using an ROI program (right panel).
(B) Mitochondria membrane potentials were analyzed using JC-1 dye and fluorescence microscopy (left panel). The fluorescence signals were
calculated using an ROI statistics program (right panel). Red fluorescence represents JC-1 aggregates with normal membrane potentials, while
green fluorescence indicates JC-1 monomers at disrupted potentials. (C) Expressions of cleaved caspase-3 were determined in Western blot
analysis. The densities were calculated by the ImageJ program. Values are mean SEM. * p < 0.05, ** p < 0.01 vs control; # p < 0.05, ## p < 0.01 vs
cisplatin-treated cells. N = 3.
D
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(Figure 5C), cleaved caspase-3 levels significantly increased in
kidney tissues isolated from cisplatin-exposed rats, while the
increase of caspase-3 activation was not observed in kidneys of
rats treated with 14 and cisplatin (Figure 6A). The level of
cisplatin were evaluated. The data demonstrated that 5-O-
prenyl tetracyclic 14 has beneficial effects against cisplatin-
mediated cytotoxicity through antioxidant, mitochondria
preserving, and antiapoptotic properties in renal tubular cells.
Notably, the nephro-protective efficacy and the mechanisms
of 14 were confirmed in a cisplatin-exposed rat model, with
histopathologic and functional improvement. 14 is expected to
have therapeutic potential against drug-induced kidney
damage.
EXPERIMENTAL SECTION
■
General Experimental Procedures. Melting points were
determined with an IA9100 melting point apparatus. 1H and 13C
NMR spectra were obtained on a Varian Mercury 400 and JEOL
ECZ600R. Chemical shifts are reported in ppm units with Me4Si or
CHCl3 as the internal standard. HREIMS data were acquired using a
JEOL JMS-700. Unless otherwise noted, materials and all solvents
were obtained from commercial suppliers and were used without
purification. Toluene, CH2Cl2, and tetrahydrofuran (THF) were dried
with 4 Å molecular sieve. Cisplatin (cis-diamminedichloroplatinum II)
was purchased from Sigma-Aldrich (St. Louis, MO, USA). Cisplatin
was freshly prepared as a stock solution dissolved in phosphate-
buffered saline (PBS) for the in vitro and in vivo experiments. CM-
H2-DCFDA and JC-1 were purchased from Invitrogen (Waltham,
MA, USA). Primary antibody targeting caspase-3 was obtained from
Cell Signaling Technology (Danvers, MA, USA). All other chemicals
were purchased from Sigma-Aldrich.
Sigmatropic Rearrangement of Aryl Propargyl Ether 10.
Aryl propargyl ether 10 (40.1 mg, 0.081 mmol) was dissolved in
diethylaniline (10 mL), and the mixture was stirred at 270 °C for 12
h. The mixture was cooled to room temperature, concentrated in
vacuo, and filtered through a pad of silica gel (hexanes/EtOAc, 5:1) to
afford the 1:1 mixture of 11 and 12. The mixture was separated by
column chromatography (silica gel; hexanes/EtOAc, 50:1 to 30:1) to
afford 11 (18.1 mg, 45%) and 12 (17.3 mg, 43%). For 11: light yellow
1
solid (mp 140−141 °C): H NMR (600 MHz, CDCl3) δ 12.88 (s,
Figure 6. In vivo nephroprotection by 14 against cisplatin-induced
kidney impairment in rats. Cisplatin (CP; 6 mg/kg) and/or 14 (1
mg/kg) were administered to rats. (A) The level of caspase-3
activation in the kidneys was analyzed via Western blotting. (B)
Histological changes in renal tissues were observed via hematoxylin
and eosin (H&E) staining. Scale bar: 100 μm. *, Exfoliation and
shallowing; #, cell death and tubular damages; arrowhead, cast
formation. (C and D) Functional changes in kidney were determined
by the levels of blood urea nitrogen (BUN) and serum creatinine.
Values are mean SEM. * p < 0.05, ** p < 0.01 vs rats in control
1H), 8.01−7.97 (m, 2H), 7.48−7.40 (m, 3H), 7.33−7.29 (m, 2H),
7.28−7.23 (m, 2H), 6.75 (d, J = 10.0 Hz, 1H), 5.62 (d, J = 10.0 Hz,
1H), 5.19 (tqq, J = 6.8, 1.6, 1.6 Hz, 1H), 5.06 (s, 2H), 3.45 (d, J = 6.8
Hz, 2H), 1.77 (s, 3H), 1.68 (s, 3H), 1.46 (s, 6H); 13C NMR (100
MHz, CDCl3) δ 179.0, 156.6, 156.0, 154.1, 153.5, 137.6, 136.2, 131.5,
130.7, 130.5, 128.58, 128.51, 128.19, 128.09, 128.00, 127.85, 122.1,
115.7, 107.3, 105.7, 105.0, 77.8, 74.4, 28.3, 25.9, 21.6, 18.1; HREIMS
m/z found 494.2095 (calcd for C32H30O5 [M]+ 494.2093). For 12:
light yellow solid (mp 114−115 °C): 1H NMR (600 MHz, CDCl3) δ
12.9 (s, 1H), 7.96−7.94 (m, 2H), 7.48−7.41 (m, 3H), 7.30−7.28 (m,
2H), 7.25−7.22 (m, 3H), 6.73 (d, J = 9.9 Hz, 1H), 5.57 (d, J = 10.0
Hz, 1H), 5.26 (tqq, J = 7.3, 1.2, 1.2 Hz, 1H), 5.07 (s, 2H), 3.36 (d, J =
7.4 Hz, 2H), 1.82 (s, 3H), 1.69 (s, 3H), 1.47 (s, 6H); 13C NMR (150
MHz, CDCl3) δ 179.0, 158.7 157.2, 155.9, 149.5, 137.8, 136.3, 131.5,
130.8, 130.6, 128.81, 128.60, 128.33, 128.19, 128.13, 127.0, 122.0,
115.1, 112.5, 105.5, 100.7, 77.9, 74.4, 28.1, 25.8, 21.3, 17.9; HREIMS
m/z found 494.2092 (calcd for C32H30O5 [M]+ 494.2093).
#
group; p < 0.05 vs rats treated with cisplatin. N = 6 rats/group.
cleaved caspase-3 was similar between the rats in control group
and rats treated with 14 and cisplatin. The protective effects of
14 were revealed through both histopathological analyses of
kidney tissues (Figure 6B) and analysis of renal functional
parameters. BUN and serum creatinine levels, which are
representative clinical markers for renal function, were severely
affected in the cisplatin-treated rats, and 14 treatment
significantly restored impaired renal function (Figure 6C and
6D). There were no histological or functional changes in rats
treated with 14 alone (data not shown).
In summary, the concise synthesis of sericetin (1) was
accomplished in four steps (39.7% overall yield) from readily
available 3-O-benzylgalangin (5), using electrocyclization to
obtain the tricyclic core and a sequential aromatic Claisen/
Cope rearrangement to incorporate the prenyl group at C(8).
In addition, the therapeutic potential of sericetin (1),
isosericetin (2), and three prenylated tetracyclic synthetic
intermediates (11, 12, and 14) against in vitro AKI induced by
Synthesis of Sericetin (1). The 8-prenyl-6,7-pyran adduct 11
(120.1 mg, 0.242 mmol) was dissolved in CH2Cl2 (10 mL), and the
mixture was cooled to −78 °C. To this solution was added BCl3
(0.484 mL, 1.0 M solution in toluene, 0.484 mmol), and the reaction
mixture was stirred for 2 h at the same temperature. The reaction was
quenched with H2O (10 mL) and diluted with EtOAc (30 mL). The
layers were separated, and the aqueous layer was extracted with
EtOAc. The combined organic layers were washed with brine, dried
over anhydrous Na2SO4, and concentrated in vacuo. The residue was
purified by column chromatography (silica gel; hexanes/EtOAc, 4:1
to 2:1) to afford sericentin (1) (86.1 mg, 88%) as a yellow solid (mp
1
151−152 °C): H NMR (600 MHz, CDCl3) δ 11.9 (s, 1H), 8.22−
8.19 (m, 2H), 7.54−7.51 (m, 2H), 7.48−7.45 (m, 1H), 6.75 (d, J =
10.0 Hz, 1H), 6.67 (s, 1H), 5.65 (d, J = 10.0 Hz, 1H), 5.23 (tqq, J =
7.1, 1.3, 1.3 Hz, 1H), 3.53 (d, J = 7.1 Hz, 2H), 1.83 (s, 3H), 1.69 (s,
E
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3H), 1.48 (s, 6H); 13C NMR (150 MHz, CDCl3) δ 175.7, 157.2,
153.8, 153.0, 144.8, 136.4, 131.8, 131.2, 130.1, 128.6, 128.2, 127.6,
122.1, 115.7, 107.8, 104.9, 103.6, 77.9, 28.3, 25.8, 21.5, 18.1;
HREIMS m/z found 404.1625 (calcd for C25H24O5 [M]+ 404.1624).
Synthesis of Flavonol 3 by Electrocyclization. To a solution
of 4 (248.7 mg, 0.69 mmol) in MeOH (5 mL) were added 3,3-
dimethylacrylaldehyde (0.67 mL, 6.90 mmol) and Ca(OH)2 (204.4
mg, 2.76 mmol) at room temperature. After being stirred for 58 h at
the same temperature, the mixture was concentrated in vacuo, diluted
with EtOAc/H2O, and acidified with 5 N HCl. The layers were
separated, washed with H2O and brine, dried over anhydrous Na2SO4,
and concentrated in vacuo. The residue was purified by column
chromatography (silica gel; hexanes/EtOAc, 20:1) to afford known
36f,g (159.2 mg, 54%).
kidney tissues were homogenized and used in Western blot. Details
on each experimental procedure were described in the Supporting
Information.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jnat-
prod.8b00434.
Experimental procedures and characterization data of
compounds 1, 2, 7, 9−12, and 14; copies of 1H and 13
C
NMR spectra of compounds 1, 2, 7, 9−12, and 14
(PDF)
Synthesis of Aryl Prenyl Ether 14. Phenol 3 (498.5 mg, 1.169
mmol) was dissolved in DMF (20 mL) at room temperature. To this
solution were added sequentially K2CO3 (807.8 mg, 5.845 mmol) and
prenyl chloride (0.395 mL, 3.507 mmol), and the resulting mixture
was stirred for 14 h at 40 °C. The reaction was quenched with
saturated aqueous NH4Cl and diluted with EtOAc. The layers were
separated, and the aqueous layer was extracted with EtOAc. The
combined organic layers were washed with brine, dried over
anhydrous Na2SO4, and concentrated in vacuo. The residue was
purified by column chromatography (silica gel; hexanes/EtOAc, 2:1)
to afford aryl prenyl ether 14 (547.9 mg, 95%): 1H NMR (400 MHz,
CDCl3) δ 7.96−7.92 (m, 2H), 7.43−7.37 (m, 3H), 7.32−7.28 (m,
2H), 7.24−7.19 (m, 3H), 6.76 (d, J = 9.6 Hz, 1H), 6.64 (s, 1H), 5.68
(d, J = 10.0 Hz, 1H), 5.67 (dd, J = 7.6, 7.6 Hz, 1H), 5.07(s, 2H), 3.45
(d, J = 7.2 Hz, 2H), 1.78 (s, 3H), 1.71 (s, 3H), 1.46 (s, 6H); 13C
NMR (100 MHz, CDCl3) δ 173.4, 157.66, 157.44, 153.84, 153.66,
139.5, 138.3, 136.5, 130.7, 129.99, 129.97, 128.7, 128.3, 127.96,
127.87, 120.1, 113.4, 112.9, 100.3, 77.5, 74.0, 72.2, 28.3, 25.9, 18.2;
HREIMS m/z found 494.2094 (calcd for C32H30O5 [M]+ 494.2093).
Synthesis of 11 by Sigmatropic Rearrangement of Aryl
Prenyl Ether 14. A solution of aryl prenyl ether 14 (547.9 mg, 1.108
mmol) in diethylaniline (100 mL) was stirred at 270 °C for 4 h. The
reaction mixture was concentrated in vacuo and purified by column
chromatography (silica gel; hexanes/EtOAc, 20:1 to 10:1) to afford 11
(481.3 mg, 88%)
AUTHOR INFORMATION
Corresponding Authors
*Tel: 82-31-400-5805. Fax: 82-31-400-5958. E-mail: onbae@
hanyang.ac.kr (O.-N. Bae).
*Tel: 82-31-219-3448. Fax: 82-31-219-3435. E-mail:
hkimajou@ajou.ac.kr (H. Kim).
ORCID
■
Hyoungsu Kim: 0000-0002-2774-8727
Author Contributions
§E.-S. Kim and H. Jang contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Professor S. Ruchirawat (Chulabhorn Graduate
Institute) for providing the spectra of sericetin. This work was
supported by the National Research Foundation of Korea
(NRF) grant funded by the Korea government (NRF-
2017R1A2B4004155 and NRF-2017R1C1B3002626).
In Vitro Study in Renal Tubular Cells. In vitro protective
activity and the underlying mechanisms were studied in NRK-52E, rat
renal tubular epithelial cell line, purchased from ATCC (American
Type Culture Collection, Manassas, VA, USA). After cells were
treated with cisplatin and/or analyte such as 14 for 24 h, biochemical
assays were conducted to determine the cisplatin-induced cellular
changes. Cell viability was determined using the MTT assay.9
Changes in ROS level or mitochondrial membrane potential were
determined by fluorescent dyes of DCF and JC-1, respectively.17,18
Activation of caspase-3 was determined by Western blotting analysis
of cleaved active caspase-3.9 Details on each experimental procedures
are described in the Supporting Information.
In Vivo Acute Kidney Injury Models in Rats. Protocols for
animal experiments were approved by the Hanyang University
Institutional Animal Care and Use Committee (IACUC 2016-
0155A). To induce acute kidney injury, cisplatin (6 mg/kg) was
administered to Sprague−Dawley rats (male, body weight 200 10
g) by intraperitoneal injection. Compound 14 was dissolved in 5%
DMSO in 0.9% normal saline and injected once at 24 h before
cisplatin administration and once a day for five consecutive days after
cisplatin treatment. The rats were divided into four groups and treated
as follows: vehicle control group treated with 1% DMSO in saline,
cisplatin alone with single administration of cisplatin (6 mg/kg) in
saline, 14 + cisplatin group treated with cisplatin (6 mg/kg) and 1
mg/kg 14, and 14 alone treated with 1 mg/kg 14. Rats were sacrificed
at day 7 after cisplatin treatment. To analyze renal function and/or
tissue damage, blood and kidney tissue samples were collected from
each rat. The levels of BUN and serum creatinine in serum samples
were determined by clinical chemistry analysis in Neodin VetLab
(Seoul, Korea). Histologic observations were performed with isolated
kidney samples. To detect caspase-3 activation in vivo, isolated rat
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