Design, synthesis and SAR study of hydroxychalcone inhibitors of human β-secretase (BACE1)

Article abstract of DOI:10.3109/14756366.2010.543420

According to the structural characteristics of isoliquiritigenin from Glycyrrhiza uralensis, a series of hydroxychalcones has been designed, synthesized and evaluated for their in vitro inhibitory activities of β-secretase (BACE1). Structure-activity relationship study suggested that inhibitory activity against BACE1 was governed to a greater extent by the hydroxyl substituent on A-and B-ring of the chalcone, and the most active compound was substituted with four hydroxyl group (17, IC₅₀=0.27 μM).

Full text of DOI:10.3109/14756366.2010.543420

Journal of Enzyme Inhibition and Medicinal Chemistry, 2011; 26(5): 643–648
© 2011 Informa UK, Ltd.
ISSN 1475-6366 print/ISSN 1475-6374 online
DOI: 10.3109/14756366.2010.543420
ORIGINAL ARTICLE
Design, synthesis and SAR study of hydroxychalcone
inhibitors of human β-secretase (BACE1)
Lei Ma1,2, Zhengyi Yang1, Chenjing Li1, Zhiyuan Zhu1, Xu Shen1, and Lihong Hu1,2
1Shanghai Research Center for Modernization of Traditional Chinese Medicine, Shanghai Institute of Materia Medica,
Chinese Academy of Sciences, Shanghai, P. R. China, and 2School of Pharmacy, East China University of Science and
Technology, Shanghai, P. R. China
Abstract
According to the structural characteristics of isoliquiritigenin from Glycyrrhiza uralensis, a series of hydroxychalcones
has been designed, synthesized and evaluated for their in vitro inhibitory activities of β-secretase (BACE1). Structure-
activity relationship study suggested that inhibitory activity against BACE1 was governed to a greater extent by the
hydroxyl substituent on A- and B-ring of the chalcone, and the most active compound was substituted with four
hydroxyl group (17, IC50 =0.27 μM).
Keywords: Alzheimer’s disease, BACE1, chalcone, SAR, Glycyrrhiza uralensis
Introduction
inhibitors against BACE1 which would be more likely to
Alzheimer’s disease (AD) is a devastating neurodegen-
erative disorder characterized by loss of memory and
cognition. e accumulation of the β-amyloid peptide
(Aβ) in the brain has been thought to be a key factor in
the pathogenesis of the disease1. Aβ peptides are derived
from a sequential proteolytic cleavage of amyloid-
precursor protein (APP) by β-secretase (BACE1) and
g-secretase2. e limiting step in this process is cleavage
of membrane-bound APP by BACE11 to form soluble
APP3–6. So BACE1 is becoming a molecular target for
therapeutic intervention in AD4,7–10. And then numer-
ous BACE1 inhibitors have been synthesized and tested,
but most of reported inhibitors have focused on peptide-
derived structures, which act as transition state analogs
based on the amino acid sequences at the cleavage site of
APP by BACE111. ese species showed good activity in
italics, but their viability as drug candidates in this case is
minimal because the enzyme inhibitors with therapeu-
tic potential are preferably smaller than 700Da, so large
peptide-based inhibitors are not viable drug candidates.
us, we tried to find the plant-derived non-peptidic
be able to reach the target.
With the goal of obtaining new natural inhibitors, we
decided to investigate BACE1 inhibitors from the roots of
Glycyrrhiza uralensis F., a traditional medicinal herb and
an important perennial legume. is herb has long been
valued as a demulcent, to relieve respiratory ailments,
stomach burn including heart burn, gastritis, inflamma-
torydisorders,skindiseases,andliverproblems.Recently,
it was reported that G. uralensis water extract markedly
improved the cognitive deficits induced in mice by Aβ25–35
administration12. To look for the biologically active
compounds conferring this activity, extract compounds
were purified by conventional chromatography and the
individual components were assess for BACE1 activity
using a BACE1 enzyme-based bioassay. Fortunately,
we found isoliquiritigenin (2′, 4′, 4-trihydroxychalcone,
1) showed moderate BACE1 inhibit activity (IC50 = 33.0
μM), and we also found 1 was structurally similar to the
natural products catechins13 and hispidin14 which have
also been reported to have BACE1 activity. In this paper,
we describe the development of low molecular weight
Address for Correspondence: Lihong Hu, Shanghai Research Center for Modernization of Traditional Chinese Medicine, Shanghai
Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, P. R. China. Tel: 86 21 50272221. Fax: 86 21 50272221. E-mail:
simmhulh@mail.shcnc.ac.cn.
(Received 29 March 2010; revised 27 June 2010; accepted 18 November 2010)
643

644 L. Ma et al.
BACE1 inhibitors containing a chalcone skeleton through
enzymatic assays.
and number of hydroxyl groups at A-ring, nine com-
pounds with the general structure shown in Table 3 were
designed. e activity results for these compounds are
listed in Table 3. It seems that BACE1 is also sensitive to
the substituted positions and numbers of the hydroxyls
on the A-ring. e tendency is obvious: the compounds
with two hydroxyls (3, 12–16) showed higher inhibitory
activity, and the compounds without or with only one
hydroxyl (8–11) in ring A show unsatisfactory reduction
of the activity of BACE1, so we choose 3, the best activity
compound as the beginning compound of the next struc-
ture modification.
To investigate the SAR of B-ring, six 2-hydroxyl-
substituted compounds (Table 4) were designed. As
can be seen from Table 1 and 4, the compounds with
two hydroxyls (17–22) at B-ring showed better inhibi-
tory activity than those with only one hydroxyl (1–3).
Compound 17 with two hydroxyls substituted at the
position 2 and 3 showed the best inhibitory activity
(IC50 = 0.27 μM).
Chemistry
e synthesis of targeted hydroxychalcone analogues
(2–22) were achieved using commercially available
hydroxyacetophenone and hydroxybenzaldehyde as
starting materials, following route as shown in Scheme 1.
Hydroxyacetophenone and hydroxybenzaldehyde was
benzyl protected under basic conditions, and subse-
quently reacted in 40% aqueous solution of KOH to form
the benzyl protected hydroxychalcone. en deprotec-
tion of the benzyl ether was achieved by treatment with
boron trichloride to produce the targeted hydroxychal-
cone analogues.
Results and discussion
Isoliquiritigenin was prepared to confirm the scaffold
compound, and a series of derivatives were synthesized
to evaluate their potential in terms of modification of the
initial compound, to clarify their structure-activity rela-
tionships (SARs).
To determine the best substitution position of a
hydroxyl group at B-ring, three compounds with the gen-
eral structure shown in Table 1 were designed. e activity
results for these compounds are listed in Table 1. It seems
that BACE1 is sensitive to the position of the substituted
group on the B-ring. e result for a hydroxyl substituted
at position 2 was superior to those for the hydroxyl substi-
tuted at position 3 or position 4. ese results indicate the
B-ring of isoliquiritigenin (1) for modification to improve
the activity of the inhibitor.
In summary, according to the SARs of all the 22
hydroxychalcones, we found that inhibitory activity
against BACE1 was governed to a greater extent by the
hydroxyl substituent on A- and B-ring of the chalcone,
and the hydroxyl at the position 2, 2′ and 4′ of the chal-
cone maybe play a critical role in the activity.
Table 1. Importance of the position of a hydroxyl substituent at
B-ring.
OH
O
2
3
B
A
OH
4
HO
To further improve the inhibitory potency and deter-
mine the effect of the substituted group at position 2, four
compounds (3–6) with different substituents at position
2 of B-ring were synthesized. e inhibitory activities
of these compounds toward BACE1 are summarized in
Table 2. To the position 2, the introduction of electron-
donating substituents showed better activity than of
electron-withdrawing substituents, and the compound 3
with the hydroxyl substituent had the best activity.
We next turned our attention to modify the A-ring of
compound 3. To determine the best substitution position
Compound
Position of OH
Position 4
IC50a (μM) to BACE1
33.00 3.75
1
2
3
Position 3
8.03 0.92
Position 2
2.45 0.39
HEAb
0.049 0.011
aIn all tables, IC50s reported are means of the values of three
different experiments. Each IC50 is within threefold of the mean
value.
bHydroxyethylamine, the positive control in the assay
demonstrated an IC50 value of 0.049 0.011 μM, see ref. 16 for
details.
O
O
BnO
HO
a
O
O
OBn
BnO
OH
HO
b
c
O
O
BnO
HO
a
H
H
Reagents and conditions :
a, BnBr, K2CO3, DMSO, r.t., overnight.
b, 40% KOH, EtOH, r.t. overnight
c, BCl3, DCM, 0°C, 0.5h
Scheme 1. Preparation of hydroxychalcones.
Journal of Enzyme Inhibition and Medicinal Chemistry

Design, synthesis and SAR study of BACE1 645
Table 2. Diverse compounds at the position 2 of B-ring.
Table 3. Importance of the positions of hydroxyl substituents at
A-ring.
OH
O
R
O
OH
2'
A
B
1'
3'
HO
R
6'
4'
Compound
R
IC50 (μM) to BACE1
2.45 0.39
2.63 0.28
>60
5'
3
4
5
6
7
OH
Compound
Position of OH
IC50 (μM) to BACE1
2.45 0.39
>60
OMe
3
Positions 2′ and 4′
OCH2CH=CH2
8
9
Cl
11.40 1.36
>60
>60
Position 2′
NO2
10
11
12
13
14
15
16
30.4 4.25
58.1 4.92
21.8 2.31
41.8 5.52
15.6 1.83
11.8 1.35
19.4 2.33
Position 3′
Position 4′
Experimental section
Positions 2′ and 3′
Positions 2′ and 5′
Positions 2′ and 6′
Positions 3′ and 4′
Positions 3′ and 5′
General experimental procedures
Unless otherwise mentioned, all chemicals and mate-
rials were used as received from commercial suppliers
without further purification. Dichloromethane was
distilled from calcium hydride. in-layer chromatog-
raphy (TLC) plates (silica gel 60 GF, with glass support)
from Yantai jiangyou company were used for monitor-
ing progress of a reaction and visualized with 254 nm
UV light. Nuclear magnetic resonance (NMR) spectra
were recorded on a Bruker AM-400 spectrometer.
EI-MS was obtained on a SHIMADZU GCMS-QP5050A
spectrometer.
Table 4. Importance of the positions of hydroxyl substituents at
B-ring.
OH
O
2
1
3
R
4
6
HO
5
Compound
Position of OH
IC50 (μM) to BACE1
2.45 0.39
Extraction and isolation
3
Position 2
e air-dried and powdered roots of G. uralensis (2 kg)
were percolated with 70% EtOH to afford 130 g of
brown extract. en the extract was suspended in water
(500 mL) and further extracted with EtOAc to afford a
brown semisolid (33 g after evaporation). e organic
layer was subjected to CC (RP-18; MeOH/H2O 60:40) to
afford isoliquiritigenin (1) (320 mg).
17
18
19
20
21
22
Positions 2 and 3
Positions 2 and 4
Positions 2 and 5
Positions 2 and 6
Positions 3 and 4
Positions 3 and 5
0.27 0.05
0.62 0.08
1.94 0.20
1.71 0.21
2.37 0.34
2.08 0.38
General procedure for the preparation of compounds
(2–22)
for 30 min under ice-bath, then stirred at room tem-
perature overnight. After completion of the reaction
as indicated by TLC, the mixture was concentrated
in a vacuum and the residue was diluted with water
and extracted with ethyl acetate (3 × 15 mL). e com-
bined organic layer was washed with brine, dried over
Na2SO4, and concentrated in a vacuum, the residue was
chromatographed on silica gel to afford benzyloxy-
chalcone.
To a stirred solution of benzyloxy-chalcone in anhy-
drous dichloromethane (15 mL) was added drop-wise
with 5 mL of BCl3 (1 M in dichloromethane) under ice-
bath and the mixture was stirred for 30 min under the
same condition. en ice water (15 mL) was added to
the mixture and stirred at room temperature for another
2.5 h. After completion of the reaction as indicated by
TLC, the mixture was concentrated in a vacuum and the
residue was extracted with ethyl acetate (3 × 15 mL). e
combined organic layer was washed with brine, dried
over Na2SO4, and concentrated in a vacuum, and the
residue was chromatographed on silica gel to afford
hydroxylchalcone (2–22).
To a stirred solution of hydroxyacetophenone (1 mmol)
or hydroxybenzaldehyde (0.1mL, 1 mmol) in dimethyl
sulfoxide (DMSO) (10mL), was added K2CO3 552mg or
276mg, respectively. en, BnBr 0.2mL (2 mmol) was
added to the mixture, and the mixture was stirred at room
temperature overnight. After completion of the reaction
as indicated by TLC, the mixture was diluted with water
and extracted with ethyl acetate (3×10mL). e com-
bined organic layer was washed with brine and dried over
Na2SO4. en, the organic layer was concentrated in a
vacuum to afford the corresponding compound of ben-
zyloxyacetophenone or benzyloxybenzaldehyde, which
could be used directly for the next step without further
purification.
A 40% aqueous solution of potassium hydroxide
(5 mL) was added drop-wise to the stirred solution of
benzyloxyacetophenone (prepared by the first step)
in ethanol (15 mL) under ice-bath. en, a solution of
benzyloxybenzaldehyde in ethanol (10 mL) was added
drop-wise to the above mixture, and continued to stir
© 2011 Informa UK, Ltd.

646 L. Ma et al.
(E)-1-(2,4-dihydroxyphenyl)-3-(3-hydroxyphenyl)-2-
propen-1-one (2)
(E)-1-phenyl-3-(2-hydroxyphenyl)-2-propen-1-one (8)
Yield 81%, yellow solid. 1H NMR (CDCl3, 400MHz): δ: 8.16
(1 H, d, J=15.6, H-α), 8.04 (2 H, d, J=6.9), 7.70 (1 H, d,
J=15.6, H-β), 7.60 (1 H, d, J=7.2), 7.58 (1 H, d, J=6.6), 7.52
(1 H, d, J=7.5), 7.49 (1 H, d, J=6.9), 7.28 (1 H, t, J=7.5), 6.96
(1 H, t, J=7.5), 6.91 (1 H, d, J=8.1), 6.56 (1 H, br s, OH-2′);
Yield 82%, yellow solid. Proton-NMR (1H NMR) (DMSO-
d6, 400 MHz): δ: 13.4 (1 H, br s), 10.8 (1 H, br s), 9.64 (1 H,
br s), 8.19 (1 H, d, J= 8.7), 7.89 (1 H, d, J= 15.6), 7.70 (1 H,
d, J= 15.6), 7.23–7.34 (3 H, m), 6.87 (1 H, d, J= 7.5), 6.42
(1 H, d, J= 8.7), 6.30 (1 H, d, J= 2.1); HR-EI-MS: 256.0730
HR-EI-MS: 224.0833 (M+, C15H12O2 ; calc. 224.0837).
+
(M+, C15H12O4 ; calc. 256.0736).
+
(E)-1-(2-hydroxyphenyl)-3-(2-hydroxyphenyl)-2-
propen-1-one (9)
(E)-1-(2,4-dihydroxyphenyl)-3-(2-hydroxyphenyl)-2-
propen-1-one (3)
Yield 73%, yellow solid. 1H NMR (CDCl3, 400 MHz): δ: 8.20
(1 H, d, J= 15.6, H-α), 7.94 (1 H, d, J= 7.8), 7.85 (1 H, d,
J= 15.6, H-β), 7.61 (1 H, d, J= 7.5), 7.50 (1 H, t, J= 7.2), 7.30
(1 H, d, J= 7.2), 7.03 (1 H, d, J= 7.2), 6.98 (1 H, d, J= 8.1),
6.93 (1 H, d, J= 8.1), 6.85 (1 H, d, J= 8.4), 5.73 (1 H, br s);
1H NMR (DMSO-d6, 400 MHz): δ: 13.52 (1 H, s, OH-2),
10.72 (1 H, br s, OH-4), 10.31 (1 H, br s, OH-2′), 8.07 (1
H, d, J= 15.6, H-α), 7.74 (1 H, d, J= 15.6, H-β), 7.78 (1 H,
d, J= 8.7, H-6′), 7.51 (1 H, dd, J= 8.7, 2.1, H-6), 7.19 (1 H,
td, J= 8.7, 2.7, H-5), 6.85 (1 H, td, J= 8.7, 2.4, H-4), 6.83 (1
H, td, J= 8.7, 2.7, H-3), 6.39 (1 H, dd, J= 8.7, 2.4, H-5′), 6.32
HR-EI-MS: 240.0791 (M+, C15H12O3 ; calc. 240.0786).
+
(E)-1-(3-hydroxyphenyl)-3-(2-hydroxyphenyl)-2-
propen-1-one (10)
(1 H, d, J= 2.4, H-3′); HR-EI-MS: 256.0731 (M+, C15H12O4 ;
calc. 256.0736).
+
1
Yield 75%, yellow solid. H NMR (DMSO-d6, 400 MHz):
δ: 10.3 (1 H, br s), 9.79 (1 H, br s), 8.00 (1 H, d, J= 15.6,
H-α), 7.83 (1 H, dd, J= 5.2, 1.2), 7.77 (1 H, d, J= 15.6, H-β),
7.25 (1 H, dt, J= 5.2, 0.9), 7.40 (1 H, m), 7.36 (1 H, t, J= 7.8),
7.27 (1 H, td, J= 7.5, 1.5), 7.04 (1 H, ddd, J= 7.9, 2.4, 0.9),
6.93 (1 H, dd, J= 7.9, 0.9), 6.87 (1 H, t, J= 7.2); HR-EI-MS:
(E)-1-(2,4-dihydroxyphenyl)-3-(2-methoxyphenyl)-2-
propen-1-one (4)
Yield 83%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
13.5 (1 H, br s), 8.19 (1 H, d, J= 15.6, H-α), 7.84 (1 H, d,
J= 9.6), 7.69 (1 H, d, J= 15.6, H-β), 7.63 (1 H, d, J= 7.5), 6.40
(1 H, t, J= 7.5), 7.00 (1 H, d, J= 7.8), 6.96 (1 H, d, J= 8.7),
6.41–6.45 (2 H, m), 3.94 (3 H, s); HR-EI-MS: 270.0899 (M+,
240.0790 (M+, C15H12O3 ; calc. 240.0786).
+
(E)-1-(4-hydroxyphenyl)-3-(2-hydroxyphenyl)-2-
propen-1-one (11)
+
C16H14O4 ; calc. 270.0892).
Yield 71%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
10.4 (1 H, br s), 10.2 (1 H, br s), 8.01 (2 H, d, J= 8.4), 7.98
(1 H, d, J= 15.6, H-α), 7.84 (1 H, d, J= 5.4), 7.82 (1 H, d,
J= 15.6, H-β), 7.25 (1 H, td, J= 7.8, 1.2), 6.84–6.94 (4 H, m);
(E)-1-(2,4-dihydroxyphenyl)-3-(2-allyloxyphenyl)-2-
propen-1-one (5)
Yield 23%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
13.5 (1 H, br s), 10.7 (1 H, br s), 9.28 (1 H, br s), 8.24 (1 H,
d, J= 15.0, H-α), 8.16 (1 H, d, J= 8.4), 7.87 (1 H, d, J= 15.6,
H-β), 7.83 (1 H, d, J= 7.2), 7.17 (1 H, d, J= 7.2), 6.90 (1 H, t,
J= 7.8), 6.41 (1 H, d, J= 9.3), 6.29 (1 H, d, J= 2.4), 5.89–6.00
(1 H, m), 5.06 (1 H, dd, J= 3.3, 1.5), 5.02 (1 H, d, J= 1.2),
HR-EI-MS: 240.0793 (M+, C15H12O3 ; calc. 240.0786).
+
(E)-1-(2,3-dihydroxyphenyl)-3-(2-hydroxyphenyl)-2-
propen-1-one (12)
Yield 61%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
12.7 (1 H, br s), 10.3 (1 H, br s), 9.37 (1 H, br s), 8.16 (1 H,
d, J= 15.6, H-α), 7.89 (1 H, d, J= 9.9), 7.93 (1 H, d, J= 15.6,
H-β), 7.63 (1 H, d, J= 8.1), 7.30 (1 H, t, J= 6.9), 7.07 (1 H,
d, J= 7.8), 6.95 (1 H, d, J= 8.1), 6.89 (1 H, t, J= 7.8), 6.82
3.39 (2 H, d, J= 5.7); HR-EI-MS: 296.1046 (M+, C18H16O4 ;
calc. 296.1049).
+
(E)-1-(2,4-dihydroxyphenyl)-3-(2-chlorophenyl)-2-
propen-1-one (6)
(1 H, t, J= 7.8); HR-EI-MS: 256.0733 (M+, C15H12O4 ; calc.
+
Yield 85%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
13.2 (1 H, br s), 10.8 (1 H, br s), 8.19–8.25 (2 H, m), 8.10
(1 H, d, J= 15.6, H-α), 8.03 (1 H, d, J= 15.6, H-β), 7.56–7.60
(1 H, m), 7.45–7.51 (2 H, m), 6.43 (1 H, dd, J= 8.7, 2.1),
256.0736).
(E)-1-(2,5-dihydroxyphenyl)-3-(2-hydroxyphenyl)-2-
propen-1-one (13)
Yield 68%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
11.9 (1 H, br s), 10.4 (1 H, br s), 9.20 (1 H, br s), 8.08 (1 H,
d, J= 15.6, H-α), 7.82 (1 H, d, J= 8.7), 7.86 (1 H, d, J= 15.6,
H-β), 7.42 (1 H, d, J= 2.7), 7.29 (1 H, t, J= 7.8), 7.02 (1 H,
dd, J= 9.0, 2.7), 6.82–6.96 (3 H, m); HR-EI-MS: 256.0732
6.31 (1 H, d, J= 2.7); HR-EI-MS: 274.0391 (M+, C15H11ClO3 ;
+
calc. 274.0397).
(E)-1-(2,4-dihydroxyphenyl)-3-(2-nitrophenyl)-2-
propen-1-one (7)
(M+, C15H12O4 ; calc. 256.0736).
+
Yield 77%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
13.1 (1 H, br s), 10.9 (1 H, br s), 8.20 (2 H, t, J= 6.6), 8.10 (1
H, dd, J= 4.8, 1.5), 8.00 (1 H, d, J= 4.2), 7.83 (1 H, td, J= 5.1,
1.2), 7.70 (1 H, td, J= 5.7, 1.5), 6.45 (1 H, d, J= 5.7), 6.34 (1
(E)-1-(2,6-dihydroxyphenyl)-3-(2-hydroxyphenyl)-2-
propen-1-one (14)
Yield 63%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
11.2 (2 H, br s), 10.2 (1 H, br s), 7.89 (1 H, d, J= 15.6, H-α),
H, d, J= 1.2); HR-EI-MS: 285.0642 (M+, C15H11NO5 ; calc.
+
285.0637).
Journal of Enzyme Inhibition and Medicinal Chemistry

Design, synthesis and SAR study of BACE1 647
7.58 (1 H, d, J= 7.8), 7.79 (1 H, d, J= 15.6, H-β), 7.26 (1 H,
t, J= 7.2), 7.20 (1 H, t, J= 8.1), 6.92 (1 H, d, J= 8.1), 6.86 (1
H, t, J= 7.8), 6.38 (2 H, d, J= 8.1); HR-EI-MS: 256.0729 (M+,
(E)-1-(2,4-dihydroxyphenyl)-3-(3,4-dihydroxyphenyl)-
2-propen-1-one (21)
Yield 49%, yellow solid. H NMR (DMSO-d6, 400 MHz):
1
+
C15H12O4 ; calc. 256.0736).
δ: 7.73 (1 H, d, J= 8.4), 7.65 (1 H, d, J= 15.3), 7.32 (1 H,
d, J= 15.3), 7.08 (1 H, s), 7.00 (1 H, d, J= 8.4), 6.76 (1 H,
d, J= 8.4), 6.33 (1 H, dd, J= 8.4, 1.8), 6.28 (1 H, d, J= 1.8);
(E)-1-(3,4-dihydroxyphenyl)-3-(2-hydroxyphenyl)-2-
propen-1-one (15)
HR-EI-MS: 272.0688 (M+, C15H12O5 ; calc. 272.0685).
+
1
Yield 59%, yellow solid. H NMR (DMSO-d6, 400 MHz):
(E)-1-(2,4-dihydroxyphenyl)-3-(3,5-dihydroxyphenyl)-
2-propen-1-one (22)
Yield 55%, yellow solid. H NMR (DMSO-d6, 400 MHz):
δ: 10.2 (2 H, br s), 9.91 (1 H, br s), 9.39 (1 H, br s), 7.94
(1 H, d, J= 15.6, H-α), 7.81 (1 H, d, J= 6.3), 7.78 (1 H, d,
J= 15.6, H-β), 7.56 (1 H, d, J= 8.4), 7.48 (1 H, br s), 7.25 (1
H, d, J= 7.2), 6.92 (1 H, t, J= 8.1), 6.87 (1 H, d, J= 5.7), 6.85
1
δ: 13.4 (1 H, br s), 10.7 (1 H, br s), 9.49 (2 H, br s), 7.78
(1 H, d, J= 15.6, H-α), 8.17 (1 H, d, J= 9.0), 7.58 (1 H, d,
J= 15.6, H-β), 6.70 (2 H, s), 6.28–6.42 (3 H, m); HR-EI-MS:
(1 H, d, J= 8.1); HR-EI-MS: 256.0733 (M+, C15H12O4 ; calc.
+
256.0736).
272.0687 (M+, C15H12O5 ; calc. 272.0685).
+
(E)-1-(3,5-dihydroxyphenyl)-3-(2-hydroxyphenyl)-2-
propen-1-one (16)
Biochemical assay
Yield 65%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
10.2 (1 H, br s), 9.60 (2 H, br s), 7.93 (1 H, d, J= 15.6, H-α),
7.77 (1 H, d, J= 7.8), 7.66 (1 H, d, J= 15.6, H-β), 7.26 (1 H,
t, J= 6.9), 6.84–6.98 (4 H, m), 6.47 (1 H, br s); HR-EI-MS:
e biochemical assay was employed to determine the
IC50 of compounds. e assay based on fluorescence-
resonance energy transfer was carried out with BACE1
enzyme at pH 4.5 with a substrate, H-Lys(DABSYL)-
SEVNLDAEFR-Gin-(LY) (Merck) according to Ermolieff’s
approach15. Briefly, the assay was carried out by incu-
bation of the substrate peptide (5 µM), BACE1 enzyme
(550 ng/mL) that was expressed and purified from insect
expression system and varied concentrations of com-
pounds at pH 4.5. After 1 h incubation at 37°C, stop buf-
fer (3 M sodium acetate) was introduced into the reaction
mixture to stop the reaction. Finally, the fluorescence
intensity was measured on a TECAN GENios reader
(Tecan) at room temperature with excitation at 420 nm
and emission at 530 nm.
256.0738 (M+, C15H12O4 ; calc. 256.0736).
+
(E)-1-(2,4-dihydroxyphenyl)-3-(2,3-dihydroxyphenyl)-
2-propen-1-one (17)
Yield 54%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
13.5 (1 H, br s), 8.15 (1 H, d, J= 15.6, H-α), 8.09 (1 H, d,
J= 9.0), 7.83 (1 H, d, J= 15.6, H-β), 7.35 (1 H, d, J= 7.8), 6.87
(1 H, d, J= 7.8), 6.71 (1 H, t, J= 7.8), 6.41 (1 H, dd, J= 9.0,
1.5), 6.29 (1 H, d, J= 1.2); EI-MS: 272 [M]+.
(E)-1-(2,4-dihydroxyphenyl)-3-(2,4-dihydroxyphenyl)-
2-propen-1-one (18)
1
Yield 51%, yellow solid. H NMR (DMSO-d6, 400 MHz):
Declaration of interest
δ: 13.8 (1 H, br s), 8.07 (1 H, d, J= 15.6, H-α), 8.05 (1 H,
d, J= 9.0), 7.68 (1 H, d, J= 15.6, H-β), 7.73 (1 H, d, J= 8.4),
6.37–6.41 (2 H, m), 6.32 (1 H, dd, J= 7.2, 2.4), 6.26 (1
is work was supported by the Chinese National Science
& Technology Major Project “Key New Drug Creation
and Manufacturing Program” (grants 2009ZX09301-001,
2009ZX09102-022), the Chinese National High-Tech
R&D Program (grants 2007AA02Z147), the National
Natural Science Foundation of China (grants 90713046,
30772638, 30925040), CAS Foundation (grant KSCX2-
YW-R-179) and China 111 Project (B07023).
H, d, J= 2.1); HR-EI-MS: 272.0681 (M+, C15H12O5 ; calc.
+
272.0685).
(E)-1-(2,4-dihydroxyphenyl)-3-(2,5-dihydroxyphenyl)-
2-propen-1-one (19)
Yield 47%, yellow solid. 1H NMR (DMSO-d6, 400 MHz): δ:
13.5 (1 H, br s), 10.7 (1 H, br s), 9.61 (1 H, br s), 8.91 (1 H,
br s), 8.05 (1 H, d, J= 15.6, H-α), 8.09 (1 H, d, J= 8.4), 7.77
(1 H, d, J= 15.6, H-β), 7.22 (1 H, br s), 6.75 (1 H, d, J= 0.9),
6.41 (1 H, dd, J= 9.0, 2.4), 6.28 (1 H, d, J= 2.7); HR-EI-MS:
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