Synthesis of macrosphelides with a thiazole side chain: New antitumor candidates having apoptosis-inducing property

Article abstract of DOI:10.1021/ol061922v

Hybrid compounds of macrosphelides and epothilones, both of which are natural macrolides having a 16-membered skeleton, were designed and synthesized using a ring-closing metathesis (RCM) strategy. Some of these hybrids were found to exhibit notable apopt

Full text of DOI:10.1021/ol061922v

ORGANIC
LETTERS
2006
Vol. 8, No. 20
4609-4612
Synthesis of Macrosphelides with a
Thiazole Side Chain: New Antitumor
Candidates Having Apoptosis-Inducing
Property
Yuji Matsuya,† Takanori Kawaguchi,† Kentaro Ishihara,† Kanwal Ahmed,‡
Qing-Li Zhao,‡ Takashi Kondo,‡ and Hideo Nemoto*,†
Faculty of Pharmaceutical Sciences, and Department of Radiological Sciences,
Faculty of Medicine, UniVersity of Toyama, 2630 Sugitani, Toyama 930-0194, Japan
nemotoh@pha.u-toyama.ac.jp
Received August 3, 2006
ABSTRACT
Hybrid compounds of macrosphelides and epothilones, both of which are natural macrolides having a 16-membered skeleton, were designed
and synthesized using a ring-closing metathesis (RCM) strategy. Some of these hybrids were found to exhibit notable apoptosis-inducing
activity against human lymphoma cells with higher potency than parent natural macrosphelides, and to be a promising lead compound for
development of a new antitumor agent.
Hybridization of two or more biologically active natural
products has been one of the most promising approaches for
the development of new lead compounds and drug discovery
in the field of medicinal chemistry.1 In particular, artificial
hybrid molecules of partial structures of natural compounds
have been, in some cases, demonstrated to exhibit more
potent activity than the parent compounds.1 The concept
based on the combination of fragments of natural bioactive
compounds seems to have advantages because numerous
numbers of such hybrid structures can be designed and
accessible in the light of recent advances of molecular
biology and synthetic organic chemistry.
During our research project on the synthesis and biological
properties of macrosphelides,2 16-membered natural mac-
rolide compounds,3 we have recently noticed that some of
natural macrosphelides and analogues (1-5, Scheme 1) can
activate apoptotic program in human lymphoma U937 cells,
albeit with rather weak potency. This preliminary result is
the first observation on the apoptosis inducing potential of
† Faculty of Pharmaceutical Sciences.
(2) (a) Matsuya, Y.; Kawaguchi, T.; Nemoto, H. Org. Lett. 2003, 5,
2939-2941. (b) Kawaguchi, T.; Funamori, N.; Matsuya, Y.; Nemoto, H.
J. Org. Chem. 2004, 69, 505-509. (c) Ishihara, K.; Kawaguchi, T.; Matsuya,
Y.; Sakurai, H.; Saiki, I.; Nemoto, H. Eur. J. Org. Chem. 2004, 3973-
3978. (d) Matsuya, Y.; Kawaguchi, T.; Nemoto, H.; Nozaki, H.; Hamada,
H. Heterocycles 2003, 59, 481-484. (e) Matsuya, Y.; Kawaguchi, T.;
Nemoto, H. Heterocycles 2003, 61, 39-43. (f) Matsuya, Y.; Ishihara, K.;
Funamori, N.; Kawaguchi, T.; Nemoto, H. Heterocycles 2003, 61, 59-63.
For a review, see: (g) Matsuya, Y.; Nemoto, H. Heterocycles 2005, 65,
1741-1749.
‡ Faculty of Medicine.
(1) (a) Terasaka, T.; Kinoshita, T.; Kuno, M.; Nakanishi, I. J. Am. Chem.
Soc. 2004, 126, 34-35. (b) Ojima, I.; Chakravarty, S.; Inoue, T.; Lin, S.;
He, L.; Horwitz, S. B.; Kuduk, S. D.; Danishefsky, S. J. Proc. Natl. Acad.
Sci. U.S.A. 1999, 96, 4256-4261. (c) Merrifield, R. B.; Juvvadi, P.; Andreu,
D.; Ubach, J.; Boman, A.; Boman, H. G. Proc. Natl. Acad. Sci. U.S.A.
1995, 92, 3449-3453. For recent reviews, see: (d) Tietze, L. F.; Bell, H.
P.; Chandrasekhar, S. Angew. Chem., Int. Ed. 2003, 42, 3996-4028. (e)
Mehta, G.; Singh, V. Chem. Soc. ReV. 2002, 31, 324-334.
10.1021/ol061922v CCC: $33.50
© 2006 American Chemical Society
Published on Web 09/01/2006

is the side-chain containing a thiazole ring, which is supposed
to play an important role for their bioactivity.7 Thus, we
designed novel hybrid compounds (8-13, Scheme 1) com-
posed of the 16-membered trilactone core structure of
macrosphelides and the thiazole-containing side chain of
epothilones, aiming at improved potential of macrosphelides
as a new efficient apoptosis inducing agent. Herein, we wish
to report synthesis of the hybrid compounds based on a ring-
closing metathesis (RCM) strategy and their potent apoptosis
inducing ability.
Scheme 1. Hybridization of Natural Macrosphelides and
Epothilones
We have already developed an efficient synthetic strategy
of natural macrosphelides A, B, and E using RCM as a key
macrocyclization reaction.8 It is expected that broad ap-
plicability and high functional group compatibility of RCM
may bring a favorable opportunity for the synthesis of the
hybrids containing the thiazole function. For the synthesis
of the hybrids 8-11, three chiral blocks 14,9 15,2b and 182b
were prepared according to established methods, and they
were combined to RCM substrates having full components
(side chains, triester backbone, and requisite chiral centers)
of the target compounds. Practically, as shown in Scheme
2, thiazole-containing chiral alcohol 14 was subjected to
Scheme 2. Synthesis of Hybrid Compounds 8 and 9
macrosphelides.4 In conjunction with that, we have noted
the same 16-membered natural polyketides, epothilones
(Scheme 1),5 which have been reported to exhibit extraor-
dinarily potent cytotoxicity in a broad range of human cancer
cell lines through a paclitaxel (Taxol)-like mechanism of
action.5 In addition, epothilones are known to induce mitotic
arrest at the G2/M transition as a result of aberrant spindle
formation, leading to apoptotic cell death,6 which is suggested
to have close correlation with the tumor cell growth
inhibitory effects. One of the structural features of epothilones
(3) For isolation, structure elucidation, and biological activities, see: (a)
Hayashi, M.; Kim, Y.-P.; Hiraoka, H.; Natori, M.; Takamatsu, S.;
Kawakubo, T.; Masuma, R.; Komiyama, K.; Omura, S. J. Antibiot. 1995,
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Natori, M.; Komiyama, K.; Omura, S. J. Antibiot. 1996, 49, 95-98. (c)
Takamatsu, S.; Hiraoka, H.; Kim, Y.-P.; Hayashi, M.; Natori, M.;
Komiyama, K.; Omura, S. J. Antibiot. 1997, 50, 878-880. (d) Fukami, A.;
Taniguchi, Y.; Nakamura, T.; Rho, M.-C.; Kawaguchi, K.; Hayashi, M.;
Komiyama, K.; Omura, S. J. Antibiot. 1999, 52, 501-504. (e) Numata, A.;
Iritani, M.; Yamada, T.; Minoura, K.; Matsumura, E.; Yamori, T.; Tsuruo,
T. Tetrahedron Lett. 1997, 38, 8215-8218. (f) Yamada, T.; Iritani, M.;
Doi, M.; Minoura, K.; Ito, T.; Numata, A. J. Chem. Soc., Perkin Trans. 1
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Kobayashi, Y.; Wang, Y.-G. J. Antibiot. 2002, 55, 147-154.
(4) Unpublished results; manuscript has been submitted for publication.
(5) (a) Bollag, D. M.; McQueney, P. A.; Zhu, J.; Hensens, O.; Koupal,
L.; Liesch, J.; Goetz, M.; Lazarides, E.; Woods, C. M. Cancer Res. 1995,
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K. H.; Zaharevitz, D.; Bollbuck, B.; Poy, G.; Sackett, D.; Nicolaou, K. C.;
Fojo, T. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 2904-2909. For a review,
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H. Curr. Pharm. Design 2005, 11, 1595-1613.
esterification with TBS-masked hydroxy acid 15, and then
successive desilylation-esterification sequence with 18 and
acryloyl chloride provided the compound 21 with high
efficiency. RCM of 21 proceeded smoothly in the presence
of the second Grubbs’ ruthenium catalyst10 to afford the 16-
membered macrocycle with an exclusive stereoselectivity.
Subsequent removal of the MEM group and further oxidation
of the hydroxyl group gave the hybrids 8 and 9, respectively.
Similarly, the hybrids 10 and 11 were synthesized by simply
changing the coupling order of the chiral parts 14, 15, and
18 (Scheme 3).
(6) (a) Wolff, A.; Technau, A.; Brandner, G. Int. J. Oncol. 1997, 11,
123-126. (b) Blagosklonny, M. V.; Schulte, T.; Nguyen, P.; Trepel, J.;
Neckers, L. M. Cancer Res. 1996, 56, 1851-1854. (c) Blagosklonny, M.
V.; Giannakakou, P.; El-Deiry, W. S.; Kingston, D. G. I.; Higgs, P. I.;
Neckers, L.; Fojo, T. Cancer Res. 1997, 57, 130-135. For a minireview,
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Acta 2000, 1470, M79-M91.
(7) Nicolaou, K. C.; Scarpelli, R.; Bollbuck, B.; Werschkun, B.; Pereira,
M. M. A.; Wartmann, M.; Altmann, K.-H.; Zaharevitz, D.; Gussio, R.;
Giannakakou, P. Chem. Biol. 2000, 7, 593-599. See also ref 5b.
4610
Org. Lett., Vol. 8, No. 20, 2006

removed by DDQ prior to RCM, considering our previous
finding that a steric congestion considerably affected the
efficiency of RCM.2b Cyclization of 33 by RCM provided
the hybrid 12, which was further transformed to 13 by PDC
oxidation.
Scheme 3. Synthesis of Hybrid Compounds 10 and 11
Examination of the apoptosis-inducing activity of the
hybrid compounds synthesized in this study gave results of
great interest: that introduction of the thiazole substituent
significantly enhanced the activity as compared with the
parent natural macrosphelides and analogous compounds (1-
5). The assay was performed using a human lymphoma cell
line (U937), and assessment of early apoptosis and secondary
necrosis was carried out by flow cytometry of annexin
V/FITC and propidium iodide (PI) staining cells.14 As shown
in Figure 1, the hybrid 9 exhibited the most potent activity
The hybrids 12 and 13, which have a thiazole side chain
at the 3-position, were synthesized according to Scheme 4.
Scheme 4. Synthesis of Hybrid Compounds 12 and 13
Figure 1. Apoptosis-inducing activities of the hybrid compounds
8-13. U937 cells were treated with 1 µM concentration of each
compound and incubated for 6 h. Early apoptosis and secondary
necrosis were measured by flow cytometry using annexin V-FITC
and PI staining. C represents a control experiment without drug
treatment. Under the same conditions, fractions of cells (%) treated
with the parent compounds 1-5 were almost identical with the
control. Among them, the most potent derivative 5, which exhibited
the activity at 10 µM concentration, is shown as a positive control
for comparison.
with negligible secondary necrosis at 1 µM concentration
after 6 h incubation, and the hybrids 13 and 11 also induced
apoptosis slightly. It is an important note that the parent
macrosphelides 1-5 did not display any apoptosis-inducing
ability at the same concentration even after 12 h incubation.
Although detailed mechanism of action remains unclear at
present, these results indicate that the thiazole-containing
substituent installed at a suitable position can give rise to
significant interactions with a living substance controlling
an apoptotic program.
A carboxylic acid 2611 was coupled with an alcohol 272b by
dehydration using 2-methyl-6-nitrobenzoic anhydride (MNBA)
as a reagent,12 and the resulting ester 28 was subjected to
sequential desilylation-esterification with 30,13 analogous
to Scheme 2. After acryloylation of 32, the PMB group was
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Hayashi, M.; Komiyama, K.; Omura, S.; Sprengeler, P. A.; Smith, A. B.,
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B. G.; Kurachi, T. Tetrahedron Lett. 2000, 41, 1559-1563. (c) Kobayashi,
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T. J. Org. Chem. 2001, 66, 2011-2018. (d) Kobayashi, Y.; Acharya, H. P.
Tetrahedron Lett. 2001, 42, 2817-2820. (e) Ono, M.; Nakamura, H.; Konno,
F.; Akita, H. Tetrahedron: Asymmetry 2000, 11, 2753-2764. (f) Kusaka,
S.-I.; Dohi, S.; Doi, T.; Takahashi, T. Tetrahedron Lett. 2003, 44, 8857-
8859. (g) Nakamura, H.; Ono, M.; Shida, Y.; Akita, H. Tetrahedron:
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(11) This compound was prepared by a slight modification of the reported
method; see ref 2c.
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Org. Lett., Vol. 8, No. 20, 2006
4611

In this paper, we designed and synthesized novel mac-
rosphelide-epothilone hybrids based on the RCM strategy
and revealed their high potential as a new artificial antitumor
agent having an apoptosis inducing ability. Elucidation of
functions of the thiazole side chain is currently underway in
our laboratory and will be reported in due course.
Supporting Information Available: Experimental pro-
cedures, compound characterization data, and assay protocol.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OL061922V
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