hamiltonii.11 Aurones, are secondary metabolite belong to the
flavonoids family and are structural isomers of flavones.12
Several synthesized aurone derivatives are possessed a wide
range of biological activities including anticancer,13,14 tubulin
agent,15 CDK inhibitor,16 anti-malarial,17 and acetylcholinesterase
inhibitors.18 Besides, the main reason for the anticancer activity
of aurone derivatives was due to the position and the number of
hydroxyl groups present on phenyl ring attached to carbon
skeleton. In general, aurone derivatives containing the hydroxyl
group in para position are more potent than that of ortho and
meta positions.
compounds (9a-g). The compounds 7a and 7b were taken
separately and treated with different substituted aromatic
aldehydes (8a-d) in ethanol and 3 drops of piperidine was added
then the mixture was refluxed for 2 hours to afford pure
compounds (9a-g). The intermediates 9a-g was reacted with
ethyl bromoacetate (10) in presence of K2CO3 in anhydrous
acetone and reaction mixture was stirred at reflux for 12 hours to
obtain compounds (11a-g). Further, these compounds (11a-g)
were hydrolyzed under basic condition to afford pure compounds
(12a-g). Finally, these acid intermediates were subjected to
coupling reaction with 4-aminopodophyllotoxin (13) in
presence of EDCI, HOBt as coupling reagents and stirred at room
temperature for 3 hours in anhydrous DCM as a solvent to afford
pure corresponding products 14a-g as shown in Scheme 2.
In view of the above impressive biological properties of both
podophyllotoxin and aurone scaffolds, we are interested to know
the combined effect of both these moieties in a single molecular
framework. Hence we would like to synthesize these hybrid
molecules to evaluate their anticancer effect.
The synthesized (Z)-2-benzylidenebenzofuran-3(2H)-one acid
linker derivatives (12a-g) and 4β-Acetamidobenzofuranone-
1
podophyllotoxin hybrids (14a-g) were characterized by H/13C
In furtherance of our research work in the fields of (i) natural
product based hybrid molecules,19-21 NHCs,22-25 and anti-cancer
hybrid molecules,26-28 herein we report for the first time in this
manuscript a facile and new series of aurone-podophyllotoxin
hybrids. In the present work, we have synthesized a series of 4β-
Acetamidobenzofuranone-podophyllotoxin hybrids (14a-g) from
4-aminopodophyllotoxin (13) and 7-substituted (Z)-2-
benzylidenebenzofuran-3(2H)-one acid linkers (12a-g) (Scheme
2). The main chemical differences are the different substituted
aurones and substituted aromatic aldehydes with constant two
carbons chain acid linker. Further, anti-cancer activity of these
derivatives (14a-g) were examined towards four human cancer
cell lines i.e., human breast (MCF-7, MDA MB-231), lung
(A549), and prostrate (DU-145).
NMR and mass spectral analysis (ESI). The absence of 1H-NMR
signals of acid functional group, and emerging of a new signal
corresponds to N-H proton of amide provides a good support for
the amide coupling to form aurone-podophyllotoxin hybrids. The
same features were reflected in 13C-NMR spectra, where the
signal belongs to acid carbon was disappeared and a new signal
belongs to amide carbon, was appeared after amide coupling.
R1
O
NH2
O
O
HN
O
O
O
DCM, EDCI
O
R2
O
O
O
O
HOBt, rt, 3 h
R1
O
O
R
O
R
R3
R, R1 = OCH3, R2 = -OCH2CO2H, R3 = H (
12c
R2
MeO
OMe
MeO
OMe
12a
)
OMe
OMe
R,R1,R3 = OCH3, R2 = -OCH2CO2H (
)
13
12d
12e
R = OCH3, R1,R3 = H, R2 = -OCH2CO2H (
R,R3 = H, R1 = OCH3, R2 = -OCH2CO2H (
)
)
O
R, R1 = methoxy, R2 = H (14a)
14b
R,R1,R2 = methoxy (
R = methoxy, R1,R2 = H (
R,R2 = H, R1 = methoxy (
)
O
R1
12g
R,R1,R3 = H, R2 = -OCH2CO2H (
)
14c
14d
)
)
EtOH, piperidine,
Reflux, 2h
DCM, EDCI
O
OHC
R2
14e
R,R1,R2 = H (
)
HOBt, rt, 3 h
O
O
R1
R
R3
R
7a-b
R3
R2
8a-d
9a-g
O
12b
R,R2 = OCH3, R1 = -OCH2CO2H, R3 = H (
)
R1
O
R
12f
( )
R,R3 = H, R1 = -OCH2CO2H, R2 = OCH3
10
BrCH2CO2Et ( ),
Acetone, K2CO3,
Reflux, 12 h
O
R3
R2
O
O
O
O
HN
LiOH/H2O/THF
RT, 3 h
O
R
R1
O
O
O
R2
O
R1
R1
R
R
O
R3
7b
R2
R3
R2
14f
R,R1 = OCH3, R2 = H (
14g
R,R2 = H, R1 = OCH3, ( )
)
;
12a-g
11a-g
MeO
OMe
OMe
7a
R = H ( ), OCH3, (
11a
R, R1 = OCH3, R2 = -OCH2CO2Et, R3 = H (
)
)
8a
R1 = OCH3, R2 = OH, R3 = H (
11b
)
R,R2 = OCH3, R1 = -OCH2CO2Et, R3 = H (
11c
)
Scheme 2. Synthesis of 4β-Acetamidobenzofuranone-podophyllotoxin
hybrids (14a-g).
8b
R1 = OH, R2 = OCH3, R3 = H (
)
R,R1,R3 = OCH3, R2 = -OCH2CO2Et (
)
8c
11d
R1,R3 = OCH3, R2 = OH (
)
R = OCH3, R1,R3 = H, R2 = -OCH2CO2Et (
R,R3 = H, R1 = OCH3, R2 = -OCH2CO2Et (
)
)
8d
11e
11f
R1,R3 = H, R2 = OH (
)
9a
R, R1 = OCH3, R2 = OH, R3 = H (
)
)
R,R3 = H, R1 = -OCH2CO2Et, R2 = OCH3 (
11g
)
In vitro cytotoxic activity: All the compounds prepared herein
(14a-g) were screened for their anti-cancer activity towards four
human cancer cell lines including MCF-7 (human breast), A549
(human lung), DU-145 (human prostrate) and MDA MB-231
(human breast) by using MTT assay method and the results
acquired were incorporated in Table 1. Etoposide used as
standard reference drug and most of tested compound were
displayed good to moderate activity with respect to all cell lines.
The IC50 values of synthesized compounds range from
0.10±0.072 to 8.23±3.61 µM and standard drug showed from
1.91 ± 0.84 to 3.08 ± 0.135 µM. Among them, two compounds,
14b and 14e were exhibited excellent activity than etoposide. The
other compounds 14c and 14f were showed anticancer activity
equivalent to etoposide. Further, structure-activity relationship
9b
R,R2 = OCH3, R1 = OH, R3 = H (
9c
R,R1,R3 = H, R2 = -OCH2CO2Et (
)
12a
)
R,R1,R3 = OCH3, R2 = OH (
)
R, R1 = OCH3, R2 = -OCH2CO2H, R3 = H (
9d
12b
R = OCH3, R1,R3 = H, R2 = OH (
R,R3 = H, R1 = OCH3, R2 = OH (
)
)
R,R2 = OCH3, R1 = -OCH2CO2H, R3 = H (
12c
)
9e
9f
R,R1,R3 = OCH3, R2 = -OCH2CO2H (
)
12d
R,R3 = H, R1 = OH, R2 = OCH3
9g
(
)
R = OCH3, R1,R3 = H, R2 = -OCH2CO2H (
R,R3 = H, R1 = OCH3, R2 = -OCH2CO2H (
)
)
)
12e
12f
R,R1,R3 = H, R2 = OH (
)
R,R3 = H, R1 = -OCH2CO2H, R2 = OCH3 (
12g
R,R1,R3 = H, R2 = -OCH2CO2H (
)
Scheme 1. Synthesis of (Z)-2-benzylidenebenzofuran-3(2H)-one acid (12a-
g).
The synthesis of the (Z)-2-benzylidenebenzofuran-3(2H)-one
acid linker derivatives (12a-g) is outlined in Scheme 1.
Benzofuran-3(2H)-one (7a) and 7-methoxybenzofuran-3(2H)-one
(7b) are key intermediates for the preparation of the desired