Synthesis and antitumor activity of simplified ecteinascidin-saframycin analogs

Article abstract of DOI:10.1016/j.bmcl.2005.11.069

Two series of simplified analogs of the ecteinascidin-saframycin type alkaloids were prepared from l-DOPA. Their in vitro antitumor activity was tested against three human cancer cell lines (HCT-8 colon carcinoma, Bel-7402 liver carcinoma, and BGC-823 gas

Full text of DOI:10.1016/j.bmcl.2005.11.069

Bioorganic & Medicinal Chemistry Letters 16 (2006) 1282–1285
Synthesis and antitumor activity of simplified
ecteinascidin–saframycin analogs
Zhan-Zhu Liu,* Ye Wang, Ye-Feng Tang, Shi-Zhi Chen,
Xiao-Guang Chen and Hong-Yan Li
Institute of Materia Medica, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing 100050, PR China
Received 24 October 2005; revised 16 November 2005; accepted 18 November 2005
Available online 9 December 2005
Abstract—Two series of simplified analogs of the ecteinascidin–saframycin type alkaloids were prepared from L-DOPA. Their in vi-
tro antitumor activity was tested against three human cancer cell lines (HCT-8 colon carcinoma, Bel-7402 liver carcinoma, and
BGC-823 gastric carcinoma). Among these compounds, the ester analogs have stronger activities than those of amide analogs in
general. Among them, 1-naphthalene carboxylate ester analog 31 has the strongest activity against BGC-823 cells.
Ó 2005 Elsevier Ltd. All rights reserved.
Ecteinascidin 743 (Et 743, 1), a highly promising,
exceedingly potent antitumor agent, isolated from ex-
tracts of the marine tunicate Ecteinascidin turbinate,1 is
currently in phase II/III clinical trials.2 The novel struc-
ture of Et 743 combined with its remarkable biological
activities and the lack of availability from natural sourc-
es has made it an attractive synthetic target. The first to-
tal synthesis of Et 743 was accomplished by Corey et al.3
In 2000, a semisynthesis of Et 743 from cyanosafracin B
was described.4 And in 2002, another total synthesis of
Et 743 was accomplished by Fukuyama and co-
workers.5
While Et 743 shows a potent antitumor activity, it has a
complex architecture and the available synthetic proce-
dures are not practical enough to provide large amounts
of the compound. Therefore, we felt that attempts to-
ward designing a more practical synthetic route and syn-
thesizing the simpler analogs of Et 743 are of
considerable significance. As a result of a project aimed
to synthesize Et 743 and its analogs, we have recently
OCH3
HO
H
CH3
HO
AcO
E
OCH3
H
N
NH
HO
CH3
D
CH3
CH3
N
CH3
O
C
A
O
B
AcO
H
In addition to the natural product, several structurally
simplified Et 743 analogs6 were synthesized for the pre-
liminary structure–activity relationship (SAR) study.
One of them, phthalascidin (Pt 650, 2), was found to
exhibit comparable antitumor activity to that of Et
743 and may be a more practical therapeutic agent.6
In view of the structural feature, the cores of both 1
and 2 are characterized by a bis(tetrahydroisoquinoline)
pentacyclic system (ABCDE), which is believed to be the
primary pharmacophore through the preliminary struc-
ture–activity study of Et 743 and its analogs (Fig. 1).6
E
S
H
N
H
O
O
CH3
D
O
N
CH3
CN
B
C
A
O
N
H
O
O
H
OH
Et 743 1
Pt 650 2
OCH3
E
OCH3
OCH3
OCH3
H
H
H
E
H
4
4
B
1
11
CH3O
CH3O
D
N
D
N
11
C
21
CH3
CH3
3
3
C
B
A
A
14
N
14
N
21
1
H
H
13
13
CH3O
CH3O
CN
CN
R
Keywords: Et 743; Antitumor; Alkaloid; L-DOPA; Synthesis;
Tetrahydroisoquinoline.
a: R=OBn
3
4
b: R=NHCbz
*
Corresponding author. Tel.: +86 10 63165253; fax: +86 10
63017757; e-mail: liuzhanzhu@imm.ac.cn
Figure 1.
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.11.069

Z.-Z. Liu et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1282–1285
1283
established a novel synthetic process for constructing the
pentacyclic system of Et 743 37 and two functionalized
pentacylic intermediates 4. Herein, we reported the syn-
thesis and the in vitro cytotoxic evaluation of two series
of the simplified analogs of Et 743.
mitted to Pictet–Spengler reaction using the
corresponding aldehydes in NaOAc/HOAc to afford
cis-1-substituted
tetrahydroisoquinoline-3-carboxylic
acid esters 6 due to the 1,3-induction effect.9 Then, pro-
tection of the nitrogen of 6 by the formyl group afforded
7, which was transformed into the methylated product 8
upon treatment with Me2SO4/K2CO3 in acetone at re-
flux. Cleavage of the formyl group in HCl/CH3OH pro-
vided 9. Reduction of the ester group of 9 with LiAlH4
The synthesis of these analogs started from the readily
available L-DOPA, which is thought to be the biosyn-
thetic origin of Et 743.8 L-DOPA methyl ester 5 was sub-
HO
HO
CO2CH3
HO
HO
CO2CH3
NH2.HCl
HO
HO
CO2CH3
CHO
CH3O
CH3O
CO2CH3
CHO
a
c
d
b
NH
N
N
R
R
R
a: R=OBn
b: R=NHCbz
8
7
5
6
CH3O
CH3O
CO2CH3
CH3O
CH2OH
CH3O
CH3O
COOH
NHBoc
CH3O
CH3O
CH2OH
NHBoc
OCH3
e
f
NH.HCl
+
NH
N
CH O
3
OCH3
O
R
R
R
10
9
11
12
OCH3
OCH3
CH3O
CHO
NHBoc
OCH3
OCH3
OCH3
OCH3
N
CH3O
H
H
H
H
CH3O
CH3O
CH3O
O
g
N
N
R
h
i
H
CH3
OH
N
N
CH3O
H
H
CH3O
CH3O
OCH3
OCH3
NBoc
O
O
R
R
N
15
14
O
R
13
Scheme 1. Reagents and conditions: (a) aldehyde, NaOAc/HOAc, rt, 20 h; (b) Ac2O/HCO2H, 4 h; then H2O/CH3OH, 87%; (c) Me2SO4, K2CO3,
CH3COCH3, reflux, 90%; (d) HCl/CH3OH, reflux, 4 h, 85%; (e) LiAlH4, THF, 0 °C, 0.5 h, then rt 1.5 h, 83%; (f) BOP-Cl, Et3N, CH2Cl2, 4 h, 80%;
(g) (COCl)2/DMSO, CH2Cl2, 30 min, then Et3N, 5 min, ꢀ70 °C, 85%; (h) HCO2H, 70 °C, 1 h, 67%; (i) HCHO/HCO2H, 70 °C, 2 h, 95%.
OCH3
OCH3
OCH3
OCH3
H
H
H
H
CH3O
CH3O
CH3O
CH3O
N
N
b
a
CH3
CH3
N
N
H
H
H
H
O
O
OH
OBn
16
15a
OCH3
OCH3
OCH3
OCH3
H
H
H
N
H
CH3O
CH3O
N
N
c
CH3
CH3
N
H
CH3O
H
CH3O
H
H
CN
CN
O
OH
R
O
18-35
17
Scheme 2. Reagents and conditions: (a) 10% Pd–C, CH3CH2OH, 70 °C, 50 psi; (b) LiAlH4, THF, ꢀ17 °C, 0.5 h, then 0 °C, 1 h; KCN, phosphate
buffer (pH 7), 2 h; (c) EDC, DMAP, acid, CH2Cl2, 5 h.

1284
Z.-Z. Liu et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1282–1285
OCH3
OCH3
OCH3
OCH3
H
H
H
H
CH3O
CH3O
CH3O
CH3O
N
a
N
CH3
CH3
N
N
H
H
H
H
O
O
NH2
NHCbz
36
15 b
OCH3
OCH3
OCH3
OCH3
H
H
H
H
CH3O
CH3O
CH3O
N
N
b
c
CH3
CH3
N
N
H
CH3O
H
H
H
CN
O
NH
NH
R
R
47-56
37-46
O
O
Scheme 3. Reagents and conditions: (a): HBr/HOAc, 1 h; (b) EDC, DMAP, acid, CH2Cl2, 5 h; (c) LiAlH4, THF, ꢀ17 °C, 0.5 h, then 0 °C, 1 h; KCN,
phosphate buffer (pH 7), 2 h.
in THF at 0 °C afforded the primary alcohol 10, which
was subsequently coupled with 11 through the action
of bis(2-oxo-3-oxazolidinyl) phosphinic chloride (BOP-
Cl) to afford the amide 12. Compound 12 was oxidized
to 13 via Swern oxidation.10 Compound 13 was the
key intermediate of our synthesis and existed as a mix-
ture of amino aldehyde and hemiaminal, and when it
was submitted to intramolecular Pictet–Spengler cycli-
zation using CF3CO2H at room temperature, the expect-
ed pentacyclic intermediate 14 was obtained in a
moderate yield with the Boc-group being removed
simultaneously. It should be noted that a similar cycliza-
tion strategy had been used by two other research
groups.11 Reductive methylation of 12 with HCHO/
HCO2H at 70 °C for 2 h provided 15 (Scheme 1).
concentration which results in a 50% decrease in cell
growth after six days of incubation. The given values
are mean values of three experiments.
The pharmacological results are summarized in Table 1
for anti-HCT-8, anti-Bel-7402, and anti-BGC-823 cell
Table 1. Structure and in vitro cytotoxicity of the simplified analogs of
Et 743 against the HCT-8, Bel-7402, and BGC-823 cell lines
Compound
R
IC50 (lM)
HCT-8 Bel-7402 BGC-823
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
47
48
49
50
51
52
53
54
55
56
Phenyl
0.44
3.48
0.69
5.15
2.14
0.62
3.28
0.037
1.42
3.56
0.1
0.59
3.50
0.75
2.02
0.76
0.85
2.10
0.68
1.69
3.01
1.12
1.49
0.82
0.71
0.34
0.20
0.12
0.11
1.35
2.08
0.95
1.22
1.45
0.79
1.20
1.87
1.87
0.18
0.015
1.69
0.58
1.44
0.46
0.01
1.02
0.058
0.36
1.14
0.029
0.45
0.21
0.006
0.15
0.20
0.75
0.15
1.40
1.86
1.01
1.37
1.31
1.16
1.32
2.00
1.91
0.42
Pyrazin-2-yl
Furan-2-yl
Pyridin-2-yl
Vinyl
The O-benzyl group of compound 15a was removed by
catalytic hydrogenation. Then the lactam ring of 16
could be easily reduced through treatment with an ex-
cess of LiAlH4 in THF at ꢀ17 °C and then 0 °C for
l h to the corresponding cyclic hemiaminal, which upon
exposure to KCN in phosphate buffer (pH 7) afforded
the pentacyclic amino nitrile 17 as an enantiomerically
pure product. Finally, the primary alcohol compound
17 was esterified with different acid to afford the corre-
sponding ester analogs 18–35 (Scheme 2).
Indol-2-yl
Pyridin-3-yl
Styryl
A
4-Methoxyl-benzyl
3-Chloro-phenyl
5-Bromo-piridin-3-yl 1.17
Thiophen-2-yl
1-Naphthyl
Methyl
1.60
0.34
0.31
0.24
0.83
0.30
1.35
1.72
1.54
1.23
1.78
1.28
1.38
2.71
1.85
0.50
4-Fluoro-benzyl
3-Phenyl-propyl
Ethyl
Removal of the N-Cbz group of 15b with HBr/HOAc
was followed by acylation of the amine 36 with different
acid to afford the corresponding amides 37–46. Finally,
partial reduction of the lactam ring to the corresponding
cyclic hemiaminal was followed by treatment with KCN
to form the corresponding amide analogs 47–56
(Scheme 3). All the structures of the analogs were deter-
Phenyl
1-Naphthyl
3-Chloro-phenyl
4-Nitro-phenyl
Styrenyl
Thiophen-2-yl
Furan-2-yl
Acryl
1
13
mined by H, C NMR, and FAB-MS.13
All the analogs were tested for their in vitro anticancer
activities against HCT-8, Bel-7402, and BGC-823 cell
lines by the MTT-based assay. The assays were
performed in 96-well plates essentially as described by
Mosmann.12 The IC50 concentration represents the
2-Chloro-phenyl
Phthalimide
CH3O
A=
N
CH3O
Bn

Z.-Z. Liu et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1282–1285
1285
J.; Guzman, C.; Jimeno, J.; Demetri, G. D. J. Clin. Oncol.
2004, 22, 1480; (d) Laverdiere, C.; Kolb, E. A.; Supko, J.
G.; Gorlick, R.; Meyers, P. A.; Maki, R. G.; Wexler, L.;
Demetri, G. D.; Healey, J. H.; Huvos, A. G.; Goorin, A.
M.; Bagatell, R.; Ruiz-Casado, A.; Guzman, C.; Jimeno,
J.; Harmon, D. Cancer 2003, 98, 832; (e) Aune, G. J.;
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lines, respectively. As shown in Table 1, most of the
compounds showed considerable cytotoxicities to these
three cell lines, while the ester analogs (18–35) showed
stronger cytotoxicity than that of amide analogs (47–
56) in general. Although a general structure–activity
relationship of the simplified analogs of Et 743 to anti-
cancer effect could not be summarized from these data,
the following points were noteworthy: compound 25
had better inhibitory activity to HCT-8 cells, com-
pounds 18, 23, 25, 28, and 31 had stronger activities
against BGC-823 cells, compound 31 showed the most
significant activity.
3. Corey, E. J.; Gin, D. Y.; Kania, R. S. J. Am. Chem. Soc.
1996, 118, 9202.
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4. Cuevas, C.; Perez, M.; Martın, M. J.; Chicharro, J. L.;
Fernadez-Rivas, C.; Flores, M.; Francesch, A.; Gallego,
´
´
In conclusion, we have synthesized a class of simplified
analogs of Et 743. The preliminary structure–activity
relationship study indicated that the ester analogs had
stronger activity than that of the amide analogs, and
1-naphthalene carboxylate ester analog 31 showed the
most significant activity against BGC-823 tumor cells.
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Acknowledgments
9. Wang, Y.; Liu, Z. Z.; Chen, S. Z.; Liang, X. T. Chin.
Chem. Lett. 2004, 15, 505.
10. Mancuso, A. J.; Swern, D. Synthesis 1981, 165.
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We thank the National Natural Sciences Foundation of
China (No. 30472077) and Beijing Municipal Natural
Sciences Foundation (No. 7042041) for financial
support.
12. Mosman, T. J. Immunol. Methods 1983, 65, 55.
20
References and notes
13. Compound 30: mp: 111–113 °C, ½aꢁD +64.4 (c 0.59,
CHCl3); 1H NMR (300 MHz, d ppm, CDCl3): 7.53 (d,
1H, J = 4.2 Hz, C@CH), 7.52 (d, 1H, J = 4.8 Hz,
C@CH), 7.06 (t, 1H, J = 4.2, 4.8 Hz, C@CH), 6.61 (s,
2H, Ar-H), 6.44 (s, 1H, Ar-H), 6.43 (s, 1H, Ar-H), 4.28
(dd, 1H, J = 4.2, 10.8 Hz, 22-H), 4.17 (s, 1H, 21-H), 4.03
(t, 1H, J = 3.6 Hz, 1-H), 3.96 (dd, 1H, J = 4.8, 10.8 Hz,
22-H), 3.86 (s, 3H, CH3O), 3.85 (s, 3H, CH3O), 3.80 (s,
3H, CH3O), 3.77 (s, 3H, CH3O), 3.54 (s, 1H, 11-H), 3.38
(d, 1H, J = 7.8 Hz, 13-H), 3.32 (d, 1H, J = 11.7 Hz, 3-H),
3.04 (dd, 1H, J = 7.8, 17.7 Hz, 14-H), 2.55 (d, 2H, 4-
H + 14-H), 2.42 (d, 1H, J = 11.7 Hz, 4-H), 2.33 (s, 3H, –
NCH3). 13C NMR d (300 MHz, CDCl3, ppm): 161.54
(C@O), 148.00, 147.97, 147.61, 146.23, 133.40 (–CH–),
132.85, 132.34 (–CH–), 127.72 (–CH–), 127.47, 126.52,
124.46, 123.03, 118.17 (–CN), 112.14 (–CH–), 110.56
(–CH–), 110.28 (–CH–), 110.08 (–CH–), 68.50 (–CH2–),
62.90 (–CH–), 60.83 (–CH–), 60.78 (–CH–), 56.59 (–CH–),
56.03 (–CH3), 55.88 (–CH3), 55.87 (–CH3), 55.64
(–CH–), 55.56 (–CH3), 41.69 (–CH3), 32.83 (–CH2–),
25.73 (–CH2–). FABMS (m/z): 576 (M+1), 549 (MꢀCN),
434, 244, 204 (100%), 190, 111.
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