Design, synthesis of symmetrical bivalent mimetics of annonaceous acetogenins and their cytotoxicities

Article abstract of DOI:10.1016/j.bmcl.2011.04.095

A new series of linear dimeric compounds mimicking naturally occurring annonaceous acetogenins have been synthesized by bivalent analogue design, and their cytotoxicities have been evaluated against the growth of cancer cells by MTT method. Most of these compounds show selective action favored to human cancer cell lines over normal cell lines, and compound 9 with bis-terminal benzoquinone functionality exhibits an IC₅₀ = 0.40 μM against MCF7 cell lines. This work mentions that appropriate conformational constraints might be a useful optimizing tool for this unique class of anticancer compounds.

Full text of DOI:10.1016/j.bmcl.2011.04.095

Bioorganic & Medicinal Chemistry Letters 21 (2011) 3613–3615
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, synthesis of symmetrical bivalent mimetics of annonaceous
acetogenins and their cytotoxicities
Qicai Xiao a,b, Yongqiang Liu c, Yatao Qiu a, Zhiyi Yao b, Guangbiao Zhou c, Zhu-Jun Yao d, , Sheng Jiang a,
⇑
⇑
a Laboratory of Regenerative Biology, Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou 510530, China
b Shanghai Institute of Technology, Shanghai 210032, China
c Division of Molecular Carcinogenesis and Targeted Therapy for Cancer, State Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology,
Chinese Academy of Sciences, Beijing 100101, China
d State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Nanjing University,
22 Hankou Road, Nanjing 210093, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of linear dimeric compounds mimicking naturally occurring annonaceous acetogenins have
been synthesized by bivalent analogue design, and their cytotoxicities have been evaluated against the
growth of cancer cells by MTT method. Most of these compounds show selective action favored to human
cancer cell lines over normal cell lines, and compound 9 with bis-terminal benzoquinone functionality
Received 19 February 2011
Revised 18 April 2011
Accepted 22 April 2011
Available online 28 April 2011
exhibits an IC50 = 0.40
constraints might be a useful optimizing tool for this unique class of anticancer compounds.
Ó 2011 Elsevier Ltd. All rights reserved.
lM against MCF7 cell lines. This work mentions that appropriate conformational
Keywords:
Annonaceous acetogenins
Mimicry
Bivalent analogue
Cytotoxicity
Selectivity
More than 400 annonaceous acetogenins have been isolated
from the various plants of annonaceae family growing in tropical
and subtropical regions.1–3 These acetogenins exhibit a broad spec-
trum of biological activities, among which the most impressive is
their anticancer activity (cytotoxicity). They were considered to
be the most powerful inhibitors of complex I (NADH: ubiquinone
oxidoreductase) in mitochondria,4,5 and there is evidence that
some members of the family induce apoptosis in cancer cells.6
Due to their attractive biological activities and unique structures,
annonaceous acetogenins have been attracting worldwide atten-
tion for several decades.1,2,7 We have been engaged in modifying
natural acetogenins into the corresponding mimetics with simpler
structures for several years.7–16 In our previous studies, we suc-
cessfully invented AA005, a mimic of naturally occurring acetoge-
nins, by replacement of the THF rings of natural bullatacin with an
ethylene glycol ether unit. This compound exhibited very potent
antitumor activity against a variety of human cancer cell lines in
low to medium nanomolar range (Fig. 1).9–11 Recently, we also
developed a new mimic by replacement of the hydrophobic tail
of AA005 with a biphenyl moiety, which was identified to show
more potent inhibitory activity and higher selectivity against
cancer cells over normal cells (in comparison with AA005).17 These
results mention that the introduction of appropriate groups into
the linear AA005 skeleton could be a further optimizing tool for
this unique class of anticancer agents.
Recently, bivalent ligand approach has attracted worldwide
attention in the design of chemotherapeutic agents. It is adopted
as a strategy to improve interactions of some designed small-mol-
ecule ligands with their corresponding receptors.18 To explore the
potential of dimeric symmetrical ligands in the development of
potent mimicry of acetogenins, in this study, we assumed that
a,b-unsaturated c-methylbutyrolactone and quinone moieties
were the essential structural requirement for the cytotoxicity of
such acetogenin mimetics. Embedment of benzoquinone function-
ality into this series of acetogenin mimetics is due to some qui-
none-containing compounds serving as potent inhibitors of
NADH: ubiquinone oxidoreductase in mitochondria.7 Accordingly,
these two subunits were applied in the construction of dimeric
mimicking compounds, respectively. Additional consideration on
the linker (bridge) property includes good physicochemical charac-
ters, little nonspecific binding affinity and low toxicity. Therefore,
some diamine-fragments frequently appeared in the synthetic
drugs were considered to employ as the bridge unit in this work.
In this Letter, we want to report our recent results in the design,
chemical synthesis of new bivalent compounds 2–9 and their bio-
logical evaluation (Fig. 1).
⇑
Corresponding authors.
E-mail addresses: yaoz@nju.edu.cn (Z.-J. Yao), jiang_sheng@gibh.ac.cn (S. Jiang).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.04.095

3614
Q. Xiao et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3613–3615
O
P
P
Bivalent
design
O
N
H
N
H
R1
R1
O
O
OH
OH
bridge units
1 (AA005)
analogues 2-9
functional unit P
OMe
Me
H2N
NH2
N
H
N
H2N
NH2
MeO
b =
OMe
OMe
H
3 : R1 = OH; P = a
2: R1= OH; P = a
4: R1= OH; P = a
O
a =
O
NH
HN
H2N
6 : R1 = OH; P = a
NH2
N
H
N
H
OMe
O
OMe
7: R1 = OH; P = a
8: R1 = H; P = b
9: R1 = H; P = c
5 : R1 = OH; P = a
c =
O
Me
Figure 1. Design of new dimeric AA005-like molecules with conformational constraints.
To synthesize the bivalent AA005 analogues 2–7, a parallel syn-
OCH3
OCH3
H3CO
H3CO
thetic approach from the common precursor 12 was designed as
shown in Scheme 1. Following our previous work,11,14,19,20 buteno-
lide 11 was obtained in a three-step sequence: (1) aldol condensa-
tion of ester 10 with freshly prepared (S)-O- tetrahydropyranyl
lactal; (2) acid-catalyzed deprotection of the O-THP group and
in situ lactonization, and (3) elimination of the b-hydroxy group
with (CF3CO)2O and Et3N. Regioselective epoxidation of 11 was
achieved by treatment with m-CPBA to give 12 in 83% yield. Subse-
quently, regioselective opening of epoxide 12 (2 equiv) with vari-
ous diamines 13–18 in the presence of ZnCl2 provided the final
products 2–7 in 52–62% yield.
Br
OH
a
Br
O
b
Br
5
19
5
H
5
21
20
OH
22
OCH3
OCH3
OCH3
H3CO
H3CO
H3CO
O
c
d
Br
Br
O
5
5
24
23
e
e
The other two bivalent quinone compounds 8 and 9 were syn-
thesized using the procedure described in Scheme 2. The commer-
cially available 9-bromononan-1-ol 19 was firstly transformed into
the aldehyde 20 by Swern oxidation. ortho-Lithiation of 2,3,4,5-tet-
ramethoxytoluene 21 followed by reaction with aldehyde 20 gave
the alcohol 22. The newly born hydroxyl group of alcohol 22 was
then removed by reduction with Et3SiH/BF3ÁEt2O. The resulting
intermediate 23 was further oxidized with ceric ammonium ni-
trate (CAN) to yield the quinone 24. Subsequently, parallel assem-
bly of intermediate 23 and 24 (2 equivalents) with piperazine was
carried out in MeCN under refluxing conditions, affording target
compounds 8 and 9 in 65% and 66% yield, respectively.
OCH3
OCH3
O
O
OCH3
H3CO
OCH3
O
OCH3
5
5
N
N
N
N
O
OCH3
OCH3
5
5
OCH3
OCH3
H3CO
9
OCH3
8
Scheme 2. Reagents and conditions: (a) (COCl)2, DMSO, NEt3, DCM, À78 °C, 86%;
(b) 2,3,4,5-tetramethoxytoluene 21, n-BuLi, TMEDA, THF, 0 °C, 52%; (c) Et3SiH,
BF3ÁEt2O, DCM, À78 °C to rt, 82%; (d) CAN, CH3CN/H2O, RT, 83%. (e) CH3CN, TBAI,
reflux, 65–66%.
OEt
O
a
O
O
b
Cytotoxicity of compounds 1–9 was evaluated with MTT assays
by inhibition of cell growth against several human solid tumor cell
lines, such as SGC7901, MCF7, HCT-116, and HT-29, and human
normal cell lines, such as HLF and Beas-2B. The results are summa-
rized in Table 1. Some of these compounds were found to show
good to excellent selectivity between human cancer cell lines
(SGC7901, MCF7, HCT-116, and HT-29) and normal cell lines
(HLF and Beas-2B). For instance, compound 2 (1,2-ethanediamine
as the linkage) shows significant action preference to human can-
cer cell lines HCT-116 and HT-29 and no cytotoxicities were ob-
served against HLF and Beas-2B cell lines, though it is 40–50
times less potent than AA005 in inhibition of cell growth (HCT-
116 and HT-29).
5
10
5
11
5
12
O
O
O
O
O
N
O
H
O
O
O
c
O
R1
R2 R3
diamines
N
(S)-O-tetrahydropyranyl lactal
(13-18)
OH
OH
2: R1 = -2CH2-, R2 = R3 = H; 4: R1 = -2CH2-, R2 = R3= CH3
3: R1 = -3CH2-, R2 = R3 = H; 5: R1 = -3CH2-, R2= R2= CH3
6: R1 = -Ph-, R2 = R3 = H; 7: R1 = -2CH2-, R2 =R3= -CH2-
Compared with 2, compound 4 with an N-methylated 1,2-eth-
anediamine linker shows opposite selectivity among the four hu-
man cancer cell lines (SGC7901 and MCF7, HCT-116 and HT-29),
and it is inactive against HCT-116 and HT-29 cell lines. Compound
Scheme 1. Reagents and conditions: (a) (i) LDA, THF–HMPA, (S)-O-tetrahydropyr-
anyl lactal, À78 °C; (ii) 10% H2SO4, THF, rt; (iii) (CF3CO)2O, Et3N, CH2Cl2, 67%.
(b) m-CPBA, CH2Cl2, 0 °C, 83%. (c) ZnCl2, i-PrOH, 52–62%.

Q. Xiao et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3613–3615
3615
Table 1
based on the MTT assay. Furthermore, application of the bivalent
analogue strategy in the mimicry of annonaceous acetogenins
makes the AA005-based anticancer agents much simpler and more
flexible for future further development.
Inhibitory activity of AA005 and analogues 2–9 against cell growtha
Compounds
GI50 (l
M)b,c,d,e
SGC7901
MCF7
HCT116
HT29
HLF
Beas-2B
1 (AA005)
0.06
>10
NA
6.22
4.12
4.40
1.67
NA
0.26
>10
NA
3.16
2.38
7.37
2.19
NA
0.11
5.48
NA
0.35
14.3
NA
NA
1.5
0.87
>10
NA
>10
NA
NA
>10
4.42
NA
>10
NA
>10
NA
NA
>10
10.6
NA
NA
NA
>10
Acknowledgments
2
3
4
5
6
7
8
9
NA
We thank the National Major Scientific and Technological
Program for Drug Discovery (2009ZX09103-101, 2009ZX09501),
NSFC (Grant No. 20802078, 20972160, 20921091), Shanghai Uni-
versity Distinguished Professor (Eastern scholars) Program
(DF2009-02), Pujiang Talent Plan Project (09PJ1409200) and MOST
(Grant No. 2009CB940900, 2010CB529201, 2010CB833200).
>10
2.49
3.72
NA
0.49
0.40
0.50
>10
>10
a
AA005 was used as a positive control, and compounds 2–7 were measured in
distereomeric mixtures.
b
SGC7901: human gastric cancer cell line; MCF7: human breast cancer cell line;
Supplementary data
HCT116: colorectal carcinoma cell line; HT29: human colon cancer cell line; HLF:
human lung fibroblasts; Beas-2B: human bronchial epithelial cell.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2011.04.095.
c
Inhibition of cell growth by the listed compounds was determined by using
MTT assay.
d
NA, not active.
Standard error of the GI50 was generally less than 10%.
e
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