Synthesis of new bioisosteric hemiasterlin analogues with extremely high cytotoxicity

Article abstract of DOI:10.1016/j.bmcl.2014.09.065

In this Letter, the synthesis and the evaluation of the cytotoxicity of new hemiasterlin analogues were reported. The indole moiety was replaced respectively by benzofurane, naphthalene and 4-bromobenzene groups. Most of these derivatives possess strong c

Full text of DOI:10.1016/j.bmcl.2014.09.065

Bioorganic & Medicinal Chemistry Letters 24 (2014) 5216–5218
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis of new bioisosteric hemiasterlin analogues with extremely
high cytotoxicity
Tuyet Anh Dang Thi a, Chinh Pham The a, Quoc Anh Ngo a, Thu Ha Vu Thi a, Tien Dung Nguyen a,
Duy Tien Doan a, Cham Ba Thi a, M. Jean b, P. van de Weghe b, , Tuyen Nguyen Van a,
⇑
⇑
a Institute of Chemistry—Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Viet Nam
b Equipe Produits Naturels, Synthèses et Chimie Médicinale (PNSCM), UMR CNRS 6226—Institut des Sciences Chimiques de Rennes, Université de Rennes 1, UFR
Sciences Pharmaceutiques et Biologiques, 2, Avenue du Prof L. Bernard, F-35043 Rennes Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
In this Letter, the synthesis and the evaluation of the cytotoxicity of new hemiasterlin analogues were
reported. The indole moiety was replaced respectively by benzofurane, naphthalene and 4-bromoben-
zene groups. Most of these derivatives possess strong cytotoxic activity on two human tumour cell lines
(KB and Hep-G2), and some analogues showed comparable cytotoxic activity to that observed for paclit-
axel and ellipticine, against KB and Hep-G2 cancer cell lines.
Received 3 September 2014
Revised 22 September 2014
Accepted 24 September 2014
Available online 2 October 2014
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Tripeptides
Hemiasterlin
Unnatural hemiasterlin
Cytotoxicity
Approximately 3.2 million new cases of cancer and 1.7 million
deaths from cancer occurred in Europe in 2008 and the medical
costs associated with cancer in 2010 were projected to reach
$124.6 billion in the US. The increasing costs of cancer care illus-
trate the crucial need to advance our scientific knowledge to
improve cancer treatments and reduce costs.1 In the 1950s, scien-
tists discovered two plant-derived antileukemic agents, vinblastine
and vincristine, and isolated podophyllotoxin. These discoveries
prompted the National Cancer Institute (NCI) and the US Depart-
ment of Agriculture to start the systematic collection and screening
of plants for antitumor activity. Finally, the list of natural product
used as cancer therapeutics is impressive (Vinca alkaloids, anthra-
cycline antitumor antibiotics, camptothecins, epothilones, podo-
phyllotoxins, rapamycin mTOR inhibitors, taxanes, etc.).
Hemiasterlin (1), a natural tripeptide isolated from marine
sponges, is a potent antimitotic agent acting by inhibition of micro-
tubule depolymerization. The observed antimitotic activity was
found to be due to the binding of 1 to the vinca-peptide site in
tubulin.2,3 The synthetic related analogue HTI-286 (2) displayed
especially potent cytotoxicity against paclitaxel (Taxol™) resistant
cancer cell lines in vitro and in vivo and is currently in clinical trials
(Fig. 1).3b
There are several reports on the preparation of new hemiaster-
lin derivatives in which the indole aromatic ring moiety A was
replaced by other aromatic systems.4,5 Nevertheless, and in spite
of the substantial efforts accomplished during the last decade, only
few hemiasterlin analogues as 3a and 3b were reported with
promising cytotoxicity activities.6–8 Recently, we synthesized
new hemiasterlin analogues in which the
group and amino NHMe moiety were replaced respectively by a
,b-unsaturated aryl and an amide NHAc group leading to the sup-
a,a-dimethylbenzylic
a
pression of one chiral center. Among our prepared compounds, the
two analogues 4a and 4b showed a comparable cytotoxicity activ-
ity to paclitaxel and ellipticine against KB cancer cell lines (Fig. 1).9
As a part of our ongoing work, we will continue to focus on the
new biological active hemiasterlin analogues. For this purpose, we
investigated the synthesis and the cytotoxicity of new hemiasterlin
derivatives in which the indole moiety was replaced by various
aryl groups as bioisosteric moieties.10 These new compounds will
be prepared by classical peptide coupling approach between the
racemic carboxylic acid fragments A 8a–c (Scheme 1) and enantio-
pure dipeptide 10 (Scheme 2).9
The preparation of the carboxylic acids 8a–c is depicted in
Scheme 1. Azalactones 5a–c, prepared as previously reported from
common aldehydes,9,11 were first hydrolyzed under classical reac-
tion conditions to lead to 6a–c and then converted into
a,a-dim-
⇑
Corresponding authors. Tel.: +33 2 23 23 38 03 (P.v.d.W.), +84 9 17 68 39 79
(T.N.V.).
ethylketocarboxylic acids 7a–c. The last step of this preparation,
aiming to obtain 8a–c, consists then to convert the ketone into
methylamine via a reductive amination reaction. The reduction
E-mail addresses: pierre.van-de-weghe@univ-rennes1.fr (P. van de Weghe),
ngvtuyen@hotmail.com (T. Nguyen Van).
http://dx.doi.org/10.1016/j.bmcl.2014.09.065
0960-894X/Ó 2014 Elsevier Ltd. All rights reserved.

T. Anh Dang Thi et al. / Bioorg. Med. Chem. Lett. 24 (2014) 5216–5218
5217
O
O
N
CO2H
N
CO2H
N
H
N
H
NH
O
NH
O
N
A
B
C
Hemiasterlin (1)
HTI-286 (2)
O
O
N
CO2H
CO2Et
N
CO2H
CO2H
N
H
N
H
O
NH
O
NH
3a (IC50 = 7.9 nM (KB))
3b (IC50 = 17.0 nM (KB))
O
O
N
N
N
N
H
H
O
NHAc
O
NHAc
O
H3CO
4a (IC50 = 3.5 nM (KB))
4b (IC50 = 3.7 nM (KB))
Figure 1. Structures of hemiasterlin derivatives and HTI analogues.
O
CO2H
OH
CO2H
CO2H
NHMe
i
ii
iii
Ar
Ar
Ar
Ar
O
N
O
5a-c
6a (85%)
6b (95%)
6c (89%)
7a (93%)
7b (90%)
7c (95%)
8a (61%)
8b (35%)
8c (28%)
Ar =
O
Br
a
b
c
Scheme 1. Reagents and conditions (i) (1) 1.6 equiv NaOH (1 N), 85 °C, 1 h, (2) HCl (5 N) then HCl (12 N), 4 h, 120 °C. (ii) 3 equiv NaOH, 3.0 equiv MeI, THF, rt, 48 h (iii)
3.5 equiv MeNH2, THF, rt, 1 h then 1.5 equiv BH3 pyridine, 50 °C, 4 h.
O
N
CO2Et
Ar
N
H
NH
O
11a (24%), 11b (21%), 11c (26%)
N
O
CO2Et
i
H3N
CF3CO2
O
O
N
CO2Et
10
Ar
N
H
NH
O
11a' (32%), 11b' (22%), 11c' (23%)
N
CO2H
Ar
Ar
N
H
a
Ar =
NH
O
Br
12a (69%), 12b (64%), 12c (72%)
ii
b
O
O
N
CO2H
N
H
c
NH
O
12a' (68%), 12b' (63%), 12c' (80%)
Scheme 2. Reagents and conditions (i) 1.1 equiv 8a–c, 1.2 equiv PyBOP, 2.5 equiv DIEA, DMF, rt, 18 h. (ii) 10.0 equiv LiOH, MeOH/H2O (3:1), rt, 10 h.
of the imines formed in situ by condensation of 7a–c with methyl-
amine was only possible by treatment with the borane-pyridine
complex.4b The expected products were isolated with moderate
yields (Scheme 1).
The first analogues of hemiasterlin (12 and 120) were obtained
in two steps after peptide coupling of 8a–c with 10, separation of
the diastereoisomers and saponification of the ethyl ester function
(Scheme 2). The peptide coupling reaction was accomplished with

5218
T. Anh Dang Thi et al. / Bioorg. Med. Chem. Lett. 24 (2014) 5216–5218
Table 1
Acknowledgments
Cytotoxicity evaluationa
Entry
Compound
IC50
Hep-G2
(
l
M)
LU
This work was financially supported in part by scientific
research and technological development project (code: ÐT.NCCB-
ÐHUD.2011-G/07).
KB
MCF7
1
2
3
4
5
6
7
8
11a
11a0
11b
11b0
11c
11c0
12a
12a0
12b
12b0
12c
12c0
Ellipticine
Paclitaxel
0.012
0.172
0.013
0.76
0.013
0.181
0.0017
0.011
0.0017
0.043
0.0019
0.014
1.26
0.006
0.010
0.011
0.73
0.013
0.144
0.0018
0.013
0.0019
0.037
0.0019
0.034
1.26
32.5
66.9
54.9
148.7
>269.0
>269.0
>269.0
>269.0
133.2
>269.0
>269.0
>269.0
>269.0
>269.0
>269.0
2.1
Supplementary data
>269.0
132.2
25.5
>269.0
>269
193.4
42.3
>269.0
205.0
1.8
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2014.09.
065.
9
10
11
12
13b
14b
References and notes
1. Mariotto, A. B.; Yabroff, K. R.; Shao, Y.; Feuer, E. J.; Brown, M. L. J. Natl. Cancer
Inst. 2011, 103, 117.
2. Isolation and first biological evaluation: (a) Talpir, R.; Benayahu, Y.; Kashman,
Y.; Pannell, L.; Schleyer, M. Tetrahedron Lett. 1994, 35, 4453; Isolation: (b)
Coleman, J. E.; de Silva, E. D.; Kong, F.; Andersen, R. J.; Allen, T. M. Tetrahedron
1995, 51, 10653.
3.9
0.19
—
—
a
MTT cellular assay, 3 d exposure (more details in Supplement material).
IC50 in nM.
b
3. (a) Anderson, H. J.; Coleman, J. E.; Andersen, R. J.; Roberge, M. Cancer Chemother.
Pharmacol. 1997, 39, 223; (b) Loganzo, F.; Discafani, C. M.; Annable, T.; Beyer,
C.; Musto, S.; Hari, M.; Tan, X.; Hardy, C.; Hernandez, R.; Baxter, M.;
Singanallore, T.; Khafizova, G.; Poruchynsky, M. S.; Fojo, T.; Nieman, J. A.;
Ayral-Kaloustian, S.; Zask, A.; Andersen, R. J.; Greenberger, L. M. Cancer Res.
2003, 63, 1838.
4. (a) Andersen, R.; Piers, E.; Nieman, J.; Coleman, J.; Roberge M., WO 9932509.;
(b) Yamashita, A.; Norton, E. B.; Kaplan, J. A.; Niu, C.; Loganzo, F.; Hernand, R.;
Beyer, C. F.; Annable, T.; Musto, S.; Discafani, C.; Zask, A.; Ayral-Kaloustian, S.
Bioorg. Med. Chem. Lett. 2004, 14, 5317; (c) Greenberger, L. M.; Loganzo, F. Jr.;
Discafani-Marro, C.; Zask, A.; Ayral-Kaloustian, S. WO 2004026293.
5. Niew, J. A.; Coleman, J. E.; Wallace, D. J.; Piers, E.; Lim, L. Y.; Roberge, M.;
Andersen, R. J. J. Nat. Prod. 2003, 6, 183.
6. (a) Simoni, D.; Lee, R. M.; Durrant, D.; Chi, N. W.; Baruchello, R.; Rondanin, R.;
Rullo, C.; Marchetti, P. Bioorg. Med. Chem. Lett. 2010, 20, 3431; (b) Niu, C.; Ho, D.
M.; Zask, A.; Ayral-Kaloustian, S. Bioorg. Med. Chem. Lett. 2010, 20, 1535; (d)
Murray, W. V.; Sun, S.; Turchi, I. J.; Brown, F. K.; Gauthier, A. D. J. Org. Chem.
1999, 64, 5930; (e) Grison, C.; Geneve, S.; Halbin, E.; Coutrot, P. Tetrahedron
2001, 57, 4903.
7. Zask, A.; Birnberg, G.; Cheung, K.; Kaplan, J.; Niu, C.; Norton, E.; Suayan, R.;
Yamashita, A.; Cole, D.; Tang, Z.; Krishnamurthy, G.; Williamson, R.; Khafizova,
G.; Musto, S.; Hernandez, R.; Annable, T.; Yang, X.; Discafani, C.; Beyer, C.;
Greenberger, L. M.; Loganzo, F.; Ayral-Kaloustian, S. J. Med. Chem. 2004, 47,
4774.
8. Milton, M. J.; Williamson, T. R.; Koehn, F. E. Bioorg. Med. Chem. Lett. 2006, 16,
4279.
9. Pham The, Chinh; Anh Dang Thi, Tuyet; Phuong Hoang, Thi; Anh Ngo, Quoc; Tien
Doan, Duy; Ha Nguyen Thi, Thu; Pham Thi, Tham; Ha Vu Thi, Thu; Jean, M.; van de
Weghe, P.; Van, Tuyen Nguyen Bioorg. Med. Chem. Lett. 2014, 24, 2244.
10. Meanwell, N. A. J. Med. Chem. 2011, 54, 2529.
11. (a) Herbst, R. M.; Shemin, D. Org. Synth. 1939, 19, 1; (b) Thomas, C.; Jodie, B.;
Flavio, C. Tetrahedron Lett. 2010, 51, 625; (c) Mesaik, M. A.; Rahat, S.; Khan, K.
M.; Zia-Ullah; Choudhary, M. I.; Murad, S.; Ismail, Z.; Atta-ur-Rahman; Ahmad,
A. Bioorg. Med. Chem. 2004, 12, 2049; (d) RajanBabu, T. V.; Ayers, T. A.; Halliday,
G. A.; You, K. K.; Calabrese, J. C. J. Org. Chem. 1997, 62, 6012; (e) Cutolo, M.;
Fiandanese, V.; Naso, F.; Sciacovelli, O. Tetrahedron Lett. 1983, 24, 4603; (f)
Baell, J. B.; Garrett, T. P. J.; Hogarth, P. M.; Mattews, B. R.; McCarthy, T. D.;
Pietersz, G. A. WO 2,000,015,214.; (g) Sawant, S. D.; Barvrkar, A. A.;
Chabukswar, A. R.; Sarak, S. D. J. Appl. Chem. 2013, 2, 372; (h) Blanco-Lomas,
M.; FunesArdoiz, I.; Campos, P. J.; Sampedro, D. Eur. J. Org. Chem. 2013, 6611; (i)
FunesArdoiz, I.; Blanco-Lomas, M.; Campos, P. J.; Sampedro, D. Tetrahedron
2013, 69, 9766.
PyBOP in the presence of an excess of base to lead to the stereo-
chemically pure 11 and 110 after separation by column chromatog-
raphy on silica gel of both diastereoisomers. The saponification of
esters was then carried out using lithium hydroxide solution to
give 12a–c and 12a0–c0 in moderate to good yields (Scheme 2).
According to the literature7,12 we assigned the stereochemistry
of the diastereoisomers as S,S,S for compounds 11a–c and R,S,S for
11a0-c0.
All final compounds were evaluated in vitro for their cytotoxic
activity against four human cell lines (KB, Hep-G2, LU and MCF7)
and the results were summarized in Table 1 (the most significative
results are indicated in bold). Most of analogues of hemiasterlin
prepared during this work possess a potent cytotoxicity against
KB and Hep-G2 and some of them showed comparable activities
to ellipticine and paclitaxel. As noticed in the literature7 the abso-
lute configuration of the chiral center C14 plays an essential role in
the cytotoxicity. Indeed, the R,S,S-diastereoisomers 11a0–c0 and
12a0–c0 presented an IC50 ten to fifteen time weaker than the
S,S,S-diastereoisomers 11a–c and 12a–c.
In conclusion, preparation of new modified hemiasterlin deriv-
atives was achieved in which the indol moiety were replaced by a
naphthalene, benzofurane and 4-bromobenzene groups. This
approach served to produce mixture of two separable diastereoiso-
mers in which the carbon atom C14 can be either R or S. Most of
these new analogues of hemiasterlin possess strong cytotoxic
activities comparable to ellipticine and paclitaxel on two human
tumor cell lines (KB and Hep-G2). As it has been previously demon-
strated that the hemiasterlin analogues act as tubulin polymeriza-
tion inhibitors6a we are henceforth engaged in more detailed
biological studies for compounds 12a–c and the results will be
reported in due course.
12. Falk, M.; Spierenburg, P. F.; Walter, J. A. J. Comput. Chem. 1996, 17, 409.