Total synthesis of the natural isoprenylcysteine carboxyl methyltransferase inhibitor spermatinamine

Article abstract of DOI:10.1016/j.tetlet.2009.06.087

The first total synthesis of spermatinamine, an inhibitor of isoprenylcysteine carboxyl methyltransferase (Icmt) with a bromotyrosine-spermine-bromotyrosine dimeric structure is described.

Full text of DOI:10.1016/j.tetlet.2009.06.087

Tetrahedron Letters 50 (2009) 5028–5030
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Tetrahedron Letters
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Total synthesis of the natural isoprenylcysteine carboxyl methyltransferase
inhibitor spermatinamine
*
José García, Raquel Pereira, Angel R. de Lera
Departamento de Química Orgánica, Facultade de Química. Universidade de Vigo, 36310 Vigo, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The first total synthesis of spermatinamine, an inhibitor of isoprenylcysteine carboxyl methyltransferase
(Icmt) with a bromotyrosine–spermine–bromotyrosine dimeric structure is described.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 27 May 2009
Accepted 17 June 2009
Available online 21 June 2009
Post-translational modifications of eukaryotic proteins are
important for their cellular localization and function.1 The covalent
attachment of isoprenoid groups to proteins that contain CAAX
motifs (C, cysteine; A, aliphatic amino acid; X, any amino acid)
has gained considerable attention recently because it is the initial
step of cell signaling pathways that control diverse biological pro-
cesses.2,3 C15-farnesyl or C20-geranylgeranyl groups are the most
common isoprenoids enzymatically attached to the cysteine at or
near the carboxy terminus of the CAAX-containing protein4
through a mechanism that depends upon the sequence of amino
Fig. 1)17 have shown promising antitumour properties in tissue
cultures and animal models.18–20
Aplysamine 6 221 and spermatinamine 3 (Fig. 1),22 isolated from
extracts of the Verongida sponge Pseudoceratina sp., were the first
natural products shown to inhibit Icmt. More recently, bioassay-
guided purification of Hovea parvicalyx extracts23 led to isolation
and identification of new b-hydroxychalcone derivatives (4 and
5, Fig. 1) with Icmt inhibitory activity.
Spermatinamine 3 (IC50 = 1.9 lM for Icmt) is representative of a
group of antitumour natural products extracted from Verongidas
that biosynthetically derive from the condensation of bromotyro-
sine and spermine.22 Due to its potential as a lead to discover more
potent Icmt inhibitors with better bioavailability, we undertook
the total synthesis of spermatinamine 3 and analogues. The first
synthesis of aplysamine 6 2 reported recently24 prompted us to
disclose our approach to spermatinamine 3.
acids of the X residue,5 and in general involves Zn2+ 6
ent prenyltransferases,7 namely farnesyltransferase (FT), geranyl-
geranyltransferase (GGT1) and geranylgeranyltransferase
. Three differ-
1
2
(GGT2) mediate transfer of isoprenoids in humans, although these
enzymes have also been found in other eukaryotes including verte-
brates, insects, plants, protozoa and fungi.4
One of the best-studied CAAX motif-containing proteins is the
Ras GTPase superfamily (39 members)8–10 which can be prenylated
at the cysteine side chain with either C15 (X small aminoacid: Ala,
Ser) or C20 (X = Leu) prenyl chains. S-prenylation of CAAX proteins
is followed by additional post-translational modifications in se-
quence involving S-palmitoylation of neighbouring cysteine
groups, specific endo proteolytic cleavage of the AAX residue (by
Ras-converting enzyme Rce1, a farnesyl-S-Ras endoprotease),11–13
and methylation of the carboxyl cysteine residue (by isoprenylcys-
teine carboxyl methyltransferase, Icmt).11,14,15
Hyperactivation of Ras is thought to contribute to carcinogene-
sis and tumour progression.3,16 Inhibition of (some of the) steps
that covalently modify the Ras oncogene with a prenyl group prior
to its recruitment to the plasma membrane are attractive targets
for drug development.10 Given the limited success of farnesyltrans-
ferase inhibitors (TFIs), attention has been turned to other proteins
on the Ras processing pathway as new anticancer drug targets.10 In
fact, drugs that inhibit Icmt (methotrexate and cysmethynil 1,
The synthesis of spermatinamine 3 utilizes commercially avail-
able O-methyl-L-tyrosine 10 and spermine 6 as suitable precursors
b
BocHN
N
Me
RHN
N
H
2
2
8
6 R = H
a
7 R = Boc
c
HCl·H2N
N
Me
2
9
Scheme 1. Reagents and conditions: (a) BOC-ON, THF, 0 °C, 2 min, 80%; (b) 37%
HCHO, NaBH3CN, CH3COOH, EtOH, 25 °C, 12 h, 96%; (c) 4 M HCl, 1,4-dioxane, 25 °C,
4 h, 87%.
* Corresponding author. Tel.: +34 986812316; fax: +34 986811940.
E-mail address: qolera@uvigo.es (A. R. de Lera).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.06.087

J. García et al. / Tetrahedron Letters 50 (2009) 5028–5030
5029
Me
Br
OMe
H
N
Br
O
H2N
H2N
O
N
Br
O
Cysmethynil, 1
Aplysamine 6, 2
O
O
O
N
Br
HO
OMe
OH
N
Me
R
H
N
MeO
HO
Br
2
Spermatinamine, 3
4, R = H
5, R =
Figure 1. Chemical structure of Icmt inhibitors.
to build the bis-bromotyrosine–spermine skeleton. After the initial
attempts to protect the primary amino groups of spermine 6 using
Boc2O failed, protected amine 7 could be obtained by treatment of
6 with BOC-ON25 in THF. Subsequently methylation of 7 by reduc-
tive amination gave 8 in good yield (Scheme 1). Final deprotection
of the terminal amino group with 4 M HCl afforded hydrochloride
9 in excellent yield (Scheme 1).
oxime ester 13 using sodium tungstate and 30% aqueous hydrogen
peroxide.27 Only freshly opened bottles of hydrogen peroxide
afforded good to excellent yields in the oxidation of amino ester
12. E-Oxime ester 13 was obtained as the only geometric isomer
and its configuration was confirmed by comparison with that of
spermatinamine 3.22 After saponification, oxime acid 14 was con-
densed with methylated spermine 9 following the procedure de-
scribed by Hoshino28 which uses N-hydroxyphthalimide and
dicyclohexylcarbodiimide (DCC) as activating agents to couple
oxime acids with amines, to give spermatinamine 3 in 50% overall
yield (Scheme 2).29 The spectroscopic data of synthetic 3 matched
those of the natural specimen.22 Other coupling agents (HOBt,
As shown in Scheme 2, the synthesis of 3,5-dibromo-O-methyl-
L-tyrosine 11 was carried out by direct bromination of commercial
O-methyl-L-tyrosine 10 with bromine in a water/37% hydrochloric
acid mixture at 0 °C.26 Treatment of acid 11 with thionyl chloride
in MeOH afforded amino ester 12 which was then converted to
O
O
O
Br
MeO
Br
a
c
OR
NH2·HCl
OMe
OH
N
NH2
MeO
HO
MeO
Br
Br
10
11 R = H
13
b
12 R = Me
d
O
Br
N
H
N
Me
N
N
O
MeO
HO
Me
Br
Br
e
OH
N
HN
O
MeO
HO
Br
N
3
14
OH
Br
Br
OMe
Scheme 2. Reagents and conditions: (a) Br2, 37% HCl, H2O, 0 °C, 15 min, 56%; (b) SOCl2, MeOH, 80 °C, 4 h, 85%; (c) Na2WO4ꢀ2H2O, EtOH, H2O2, H2O, 25 °C, 4 h, 68%; (d) LiOH,
(1:1) THF/H2O, 25 °C, 14 h, 95%; (e) 9, N-hydroxyphthalimide, DCC, 1,4-dioxane, 25 °C, 8 h, 50%.

5030
J. García et al. / Tetrahedron Letters 50 (2009) 5028–5030
16. Doll, R. J.; Kirschmeier, P.; Bishop, W. R. Curr. Opin. Drug Discov. 2004, 7, 478–
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M.; Bergo, M. O.; Young, S. G.; Toone, E. J.; Casey, P. J. Proc. Natl. Acad. Sci. U.S.A.
2005, 102, 4336–4341.
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Young, S. G. J. Clin. Invest. 2004, 113, 539–550.
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20. Clarke, S.; Tamanoi, F. J. Clin. Invest. 2004, 113, 513–515.
21. Buchanan, M. S.; Carroll, A. R.; Fechner, G. A.; Boyle, A.; Simpson, M.; Addepalli,
R.; Avery, V. M.; Hooper, J. N. A.; Cheung, T.; Chen, H.; Quinn, R. J. J. Nat. Prod.
2008, 71, 1066–1067.
22. Buchanan, M. S.; Carroll, A. R.; Fechner, G. A.; Boyle, A.; Simpson, M.; Addepalli,
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Med. Chem. Lett. 2007, 17, 6860–6863.
N-hydroxysuccinimide, EDC) failed to afford amide 3 with the
unprotected oxime group, thus lengthening the sequence to reach
the target.30,31
Although as indicated22 spermatinamine 3 does not exhibit the
required drug-like pharmacokinetic properties, the synthetic ap-
proach described herein should pave the way for the preparation
and biological evaluation of novel analogs that might expand the
number of marine natural product-inspired anticancer drugs32 in
particular as inhibitors of relatively unexplored targets, such as
Icmt.17
Acknowledgements
23. Buchanan, M. S.; Carroll, A. R.; Fechner, G. A.; Boyle, A.; Simpson, M.; Addepalli,
R.; Avery, V. M.; Forster, P. I.; Guymer, G. P.; Cheung, T.; Chen, H.; Quinn, R. J.
Phytochemistry 2008, 69, 1886–1889.
24. Ullah, N.; Arafeh, K. M. Tetrahedron Lett. 2009, 50, 158–160.
25. Wang, L.; Price, H. L.; Juusola, J.; Kline, M.; Phanstiel, O., IV J. Med. Chem. 2001,
44, 3682–3691.
This work was supported by the European Union LSHC-CT-
2005-518417 ‘Epitron’, MEC-Spain (SAF2007-63880-FEDER) and
Xunta de Galicia (Grant 08CSA052383PR from DXI+D+i; Consolida-
ción 2006/15 from DXPCTSUG).
26. Stewart, J.; Katsuyama, I.; Fahmy, H.; Fronczek, F. R.; Zjawiony, J. K. Synth.
Commun. 2004, 34, 547–555.
Supplementary data
27. Boehlow, T. R.; Harburn, J. J.; Spilling, C. D. J. Org. Chem. 2001, 66, 3111–3118.
28. Hoshino, O.; Murakata, M.; Yamada, K. Bioorg. Med. Chem. Lett. 1992, 2, 1561–
1562.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2009.06.087.
29. N-Hydroxyphthalimide (0.07 g, 0.41 mmol) and DCC (0.08 g, 0.41 mmol) were
added to a solution of acid 14 (0.15 g, 0.41 mmol) in dioxane (1 mL). After the
mixture had been stirred for 8 h at room temperature, a solution of amine 9
(0.06 g, 0.20 mmol), Et3N (0.11 mL, 0.82 mmol) and MeOH (1 mL) was added.
The reaction mixture was stirred for 12 h, the solvent was removed in vacuo
and the residue was purified by column chromatography (SiO2, 95:5 CH3OH/
NH4OH) to afford 0.09 g (50%) of 3 as a white solid, mp: 172–173 dec. (MeOH/
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m 3500–3100 (br, NH and OH), 2944 (m, C–H), 2864
(w, C–H), 1662 (s, C@O and C@N), 1524 (s), 1470 (s), 1421 (m), 1259 (m), 1000
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[
929 ([M + 1]+ 81Br2] [79Br2], 54), 927 ([M+1]+
[ [
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