Synthesis and cytotoxicity of (-)-renieramycin G analogs

Article abstract of DOI:10.1016/j.bmcl.2011.01.025

(-)-Renieramycin G and fifteen C-22 analogs were prepared employing l-tyrosine as the chiral starting material. These analogs, along with (-)-renieramycin G itself, were evaluated in vitro for cytotoxicity against HCT-8, BEL-7402, A2780, MCF-7, A549, BGC-823, Ketr3, KB, Hela cells. The IC ₅₀ values of most of these analogs were at the level of μM. Among these analogs, 2-thiophenecarboxylate ester derivative 17 exhibited potent cytotoxic activity against KB cell line with the IC₅₀ of 20 nM. From this study, it could be concluded that the C-22 side chain played an important role in the cytotoxic potency and specificity of this class of (-)-renieramycin G derivatives.

Full text of DOI:10.1016/j.bmcl.2011.01.025

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1419–1421
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and cytotoxicity of (ꢀ)-renieramycin G analogs
Wei Liu, Wenfang Dong, Xiangwei Liao, Zheng Yan, Baohe Guan, Nan Wang, Zhanzhu Liu
⇑
Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine (Ministry of Education), Institute of Materia Medica,
Peking Union Medical College & Chinese Academy of Medical Sciences, No. 1, Xiannongtan Street, Beijing 100050, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
(ꢀ)-Renieramycin G and fifteen C-22 analogs were prepared employing
L
-tyrosine as the chiral starting
Received 16 November 2010
Revised 4 January 2011
Accepted 6 January 2011
Available online 11 January 2011
material. These analogs, along with (ꢀ)-renieramycin G itself, were evaluated in vitro for cytotoxicity
against HCT-8, BEL-7402, A2780, MCF-7, A549, BGC-823, Ketr3, KB, Hela cells. The IC50 values of most
of these analogs were at the level of lM. Among these analogs, 2-thiophenecarboxylate ester derivative
17 exhibited potent cytotoxic activity against KB cell line with the IC50 of 20 nM. From this study, it could
be concluded that the C-22 side chain played an important role in the cytotoxic potency and specificity of
this class of (ꢀ)-renieramycin G derivatives.
Keywords:
Renieramycin
Cytotoxicity
Ó 2011 Elsevier Ltd. All rights reserved.
Structure–activity relationship
Synthesis
The tetrahydroisoquinoline family1 of alkaloids includes a num-
ber of natural compounds that display a range of biological proper-
ties such as antitumor and antimicrobial activities. Ecteinascidin
743 (Et 743) is the most potent one of this family. The structure–
activity relationship of Et 7432 and saframycin3–5 had been
studied. So far, the research in this field has resulted in the discov-
ery of a few promising antitumor analogs,6 such as phthalascidin
(Pt 650)2,7 and ZalypsisÒ8–10 (Fig. 1).
OCH
3
O
H
CH
3
OCH3
NH
O
O
H
N
O
HO
H
CH3
H C
3
O
N
CH
3
O
H
AcO
21
O
S
H
H CO
3
H
O
H3C
O
N
CH3
22
CH
3
N
O
H
(ꢀ)-Renieramycin G was isolated from the marine sponge Xesto-
spongia caycedoi by Davidson in 1992.11 Despite having an amide
carbonyl residue at C-21, which was unique in this family, it was re-
ported to retain cytotoxicity against KB and LoVo cell lines with MIC
O
CH
3
H
OH
(-)-Renieramycin G
Et 743
OCH3
OCH3
values of 0.5 and 1.0 l
g/mL,12 respectively. This result is surprising
O
O
HO
CH3
HO
CH3
because virtually all other members of the tetrahydroisoquinoline
alkaloids with cytotoxic activity possess a carbinolamine or cyano
function at C-21, which permits the formation of a potent, electro-
philic iminium ion species involving in the formation of covalent
bonds to DNA and possibly, other biomacromolecules at this
position.
H3C
H3C
H3C
O
O
H
O
H
H
N
H
N
H3C
N
CH3
H
N
CH3
O
H
O
O
O
CN
OH
N
NH
There have been several reports on the total synthesis of (ꢀ)-
renieramycin G.13–15 A few studies on the structure–activity rela-
tionship of the related tetrahydoisoquinoline alkaloids have also
been reported.16–20 However, the structure–activity relationship
of (ꢀ)-renieramycin G has not been studied so far. In this paper,
we reported the total synthesis and the cytotoxic activities of
(ꢀ)-renieramycin G and its C-22 derivatives.
CF3
O
O
Pt 650
Zalypsis®
Figure 1. Structures of tetrahydroisoquinoline compounds.
Our synthesis of (ꢀ)-renieramycin G via a new method employ-
route for the synthesis of (ꢀ)-renieramycin G and its C-22 analogs,
which avoided the use of the Br protection group on the left
benzene ring (Scheme 1).
ing L-tyrosine as the chiral starting material has been reported
previously.15 In this report, we tried a more efficient total synthetic
The synthesis of amino acid 1 and the key 1,2,3,4-tetrahydroiso-
quinoline precursor 2 basically followed our published proce-
dures.15,21 The difference was that the use of the bromine
⇑
Corresponding author.
E-mail address: liuzhanzhu@imm.ac.cn (Z. Liu).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.01.025

1420
W. Liu et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1419–1421
OCH
HO
3
H
HO
Br
CH
H
H
3
H C
3
H C
3
H C
3
COOH
OH
a
BocHN
+
NH
Br
N
NHBoc
H CO
3
H CO
3
H CO
3
OH
H
H
OH
OBn
OH
O
OBn
3
1
2
HO
OCH
3
OCH
TBSO
3
HO
CH
3
OH
H
H
H C
3
CH
3
d, e
H C
3
NBoc
H
b
c
Br
NHBoc
H
N
Br
N
H CO
3
H CO
3
H
HO
O
H
TBSO
O
OBn
OBn
4
5
OCH
3
OCH
3
CH
Br
HO
H
3
HO
CH
3
3
H
H
H
f
g
h
H C
3
H C
3
N
N
CH
3
CH
N
H
N
H CO
3
H CO
3
H
H
OH
OH
O
O
OH
OH
6
7
OCH
3
OCH
3
O
CH
3
H
O
O
O
CH
H
N
3
H
H
N
O
O
H C
3
O
3
N
H C
3
j
i
O
3
CH
N
CH
H CO
3
H
H CO
3
O
H
O
R
O
OH
O
8
CH
3
H C
CH
3
3
H
CH
O
O
3
R=
H C
3
H C
3
O
CH
H C
3
3
12
13
11
10
9
(-)-renieramycin G
S
N
H
N
17
16
18
14
15
CH
3
O
H C
3
O
N
O
O
F
H C
3
H C
3
19
24
22
21
20
23
Scheme 1. Reagents and conditions: (a) BOPCl, Et3N, CH2Cl2, 88%; (b) TBSCl, Et3N, DMAP, CH2Cl2, rt, 88%; (c) HCOOH, THF, H2O, 92%; (d) Dess–Martin periodinane, CH2Cl2,
94%; (e) TBAF, THF, 2 h, 90% (f) CF3SO3H, 82%; (g) HCHO, NaBH3CN, HOAc, CH3OH, 83%; (h) H2 (50 psi), Pd(OH)2, CH3OH, 12 h, 87%; (i) air, salcomine, CH3CN, 86%; (j) DMAP,
EDC, CH2Cl2, 74%. Salcomine = N,N0-bis(salicylidene) ethylenediaminocobalt (II) hydrate.
protecting groups on the benzene ring for the synthesis of precur-
sor 2 was obviated. 1,2,3,4-tetrahydroisoquinoline 2 was first cou-
periodinane provided hemiaminal as a mixture of diastereomers.
Cleavage of the aryl TBS ether using TBAF provided compound 5.
Treatment of 5 with CF3SO3H at room temperature provided pen-
tacyclic compound in a satisfactory yield with the Boc- and O-ben-
zyl groups being removed simultaneously. Without purification,
the crude pentacyclic product was reductively methylated with
HCHO provided product 6, which was further converted into
pled with
1 through the action of bis(2-oxo-3-oxazolidinyl)
phosphinic chloride (BOPCl) to afford amide 3. Next, complete sily-
lation of compound 3 with tert-butyldimethylsilyl chloride (TBSCl),
and the subsequent cleavage of the TBS group of the primary
alcohol provided compound 4. Oxidation of 4 with Dess–Martin

W. Liu et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1419–1421
1421
Table 1
Cytotoxicity against nine cell lines of (ꢀ)-renieramycin G and its analogs
Compounds
Cytotoxicity IC50
A549
(lM)
HCT-8
BEL-7402
A2780
MCF-7
BGC-823
Ketr3
KB
Hela
9
8.81
5.68
24.66
3.47
2.73
7.85
19.43
6.06
1.48
27.97
8.85
9.15
5.00
9.07
3.96
23.90
2.13
2.26
4.59
6.47
3.78
1.60
10.92
7.28
14.18
2.30
2.30
14.03
9.81
4.17
3.26
25.29
2.44
2.16
3.80
12.20
3.07
1.44
14.97
4.16
15.75
5.00
3.78
4.92
23.78
2.54
2.04
3.88
17.45
4.94
1.86
14.08
3.74
9.67
3.55
2.23
10.62
3.94
5.00
4.49
7.42
3.20
2.23
4.07
5.94
3.88
0.71
12.46
8.34
8.32
5.00
2.05
10.58
5.00
3.37
4.27
10.68
3.50
1.18
2.60
3.38
8.35
0.52
17.51
3.84
7.43
3.31
1.26
9.34
11.65
3.42
4.58
17.24
3.86
2.16
4.42
4.62
8.82
1.67
13.77
3.12
10.44
7.83
1.43
9.29
7.89
3.30
2.25
5.28
2.03
1.79
3.36
3.16
2.83
0.02
5.41
3.73
3.95
2.96
0.39
8.22
8.67
2.88
2.68
12.72
2.43
1.28
2.70
3.39
3.10
0.47
7.58
2.81
9.99
4.39
1.18
5.10
7.42
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
2.05
12.44
9.31
2.24
16.76
9.09
HTC-8: human colon cancer; BEL-7402: human hepatic carcinoma; A2780: human ovarian cancer; MCF-7: human breast cancer; A549: human lung cancer; BGC-823:
human gastric adenocarcinoma; Ketr3: human renal cell carcinoma; KB: human oral epidermoid carcinoma; Hela: human cervical cancer.
compound 7 by removal of the bromine atoms through catalytic
hydrogenation. Oxidation of 7 with air in the presence of salcomine
gave bisquinone 8.
gram of Higher Education (No. 20060023025), and the National
S&T Major Special Project on Major New Drug Innovation (Item
Number: 2009ZX09301-003-9-1) for financial support.
With compound 8 in hand, 15 analogs with a variety of side
chains at C-22 were prepared besides (ꢀ)-renieramycin G (9) in
70–85% yields. All the compounds were characterized by HRMS,
1H and 13C NMR measurements.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2011.01.025.
All of these analogs including (ꢀ)-renieramycin
G were
screened in vitro for cytotoxic activities against HCT-8, BEL-7402,
A2780, MCF-7, A549, BGC-823, Ketr3, KB, and Hela cells using
the standard MTT method (Table 1). It can be seen from the screen-
ing result that the IC50 values of the (ꢀ)-renieramycin G analogs
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is interesting that both compound 10 with the simple acetyl group,
which is the case in another bistetrahydroisoquinoline natural
product (ꢀ)-jorumycin, and compound 12, which had an elongated
conjugate system, exhibited similar potency to (ꢀ)-renieramycin
G. Among the six aromatic carboxylic acid ester derivatives (com-
pounds 13–18), compound 18 with a bulky 1-naphthyl group was
the least potent with the IC50 values of 5–30 lM. Noticeably, com-
pound 17 with a 2-thiophenyl group was the most potent among
all of the 16 compounds. It exhibited a very potent inhibitory activ-
ity against KB cell line with the IC50 value of 20 nM. Among the six
aromatic acrylic acid analogs (compounds 19–24), compound 23,
which had three electron-donating methoxy groups on the ben-
zene ring, showed a decrease in the cytotoxic potency in compar-
ison with (ꢀ)-renieramycin G. From these results, it could be
concluded that the C-22 side chain played an important part in
the cytotoxic potency and specificity of this class of (ꢀ)-renieramy-
cin G derivatives.
In conclusion, 15 analogs of (ꢀ)-renieramycin G along with it-
self were prepared through an improved synthetic route consisted
of 19-steps with L-tyrosine as the starting material. Most of the
analogs exhibited similar cytotoxic potency to (ꢀ)-renieramycin
G. Among these analogs, 2-thiophene carboxylic ester derivative
17 exhibited potent cytotoxic activity against KB cell line with
the IC50 value of 20 nM.
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Acknowledgments
We thank the National Natural Science Foundation of China
(No. 30672518), Specialized Research Fund for the Doctoral Pro-