Synthesis and actin-depolymerizing activity of mycalolide analogs

Article abstract of DOI:10.1016/j.tetlet.2004.05.078

Mycalolide analog 4, consisting only of the side chain of mycalolide B (2), was stereoselectively synthesized and was found to have strong actin-depolymerizing activity.

Full text of DOI:10.1016/j.tetlet.2004.05.078

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 5383–5386
Synthesis and actin-depolymerizing activity of mycalolide analogs
Kiyotake Suenaga, Saori Miya, Takeshi Kuroda, Tomohisa Handa, Kengo Kanematsu,
Akira Sakakura and Hideo Kigoshi*
Department of Chemistry, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan
Received 26 April 2004; revised 12 May 2004; accepted 17 May 2004
Abstract—Mycalolide analog 4, consisting only of the side chain of mycalolide B (2), was stereoselectively synthesized and was
found to have strong actin-depolymerizing activity.
ꢀ 2004Elsevier Ltd. All rights reserved.
Actin-disrupting marine natural products are of interest
to natural products chemists and pharmacologists.1
These natural products consist of macrolides, cyclic
peptides, and cyclodepsipeptides. Aplyronine A (1), an
anti-tumor macrolide isolated from Aplysia kurodai2
interacts with actin, the major protein in cytoskeleton.
Aplyronine A (1) not only inhibits polymerization of
actin by sequestering G-actin and forming a 1:1 com-
plex, but also depolymerizes F-actin to G-actin by
severing.3 We achieved the total synthesis of 1 and
investigated the structure–activity relationships of ap-
lyronine A (1) using natural and synthetic analogs: the
O
O
OMe
NMe2
*
O
O
OH
O
1
Me
N
OH OH OH
21
OAc
NMe2
O
CHO
O
34
O
Me
N
OMe
OH
OAc
NMe2
21
3 (* S/R = 9/1)
MeO
CHO
34
1
OMe O
OMe O
O
OH OH OMe
OAc
Me
N
OMe
28
22
O
O
CHO
N
N
35
29
4
HO
OMe O
1
O
O
O
N
OMe
OMe
OAc
Me
N
OMe
TBS TBS
OMe
35
22
O
CHO
OBn O
O
O
OMe SO2Ph
35
+
22
28
2
OHC
29
5
6
* Corresponding author. Tel./fax: +81-29-853-4313; e-mail: kigoshi@chem.tsukuba.ac.jp
0040-4039/$ - see front matter ꢀ 2004Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.05.078

5384
K. Suenaga et al. / Tetrahedron Letters 45 (2004) 5383–5386
side chain in 1 is essential for actin-depolymerizing
activity, and analog 3, which consists only of the side
chain moiety of 1, exhibits strong activity.4
the chiral auxiliary of 8 and reduction with LiAlH4
followed by silylation gave silyl ether 10. Cleavage of the
benzyl protecting group in 10 and Dess–Martin oxida-
tion12 of the resultant alcohol afforded aldehyde 11.
Evans aldol reaction between aldehyde 11 and imide
1210 gave hydroxy imide 13, which was converted into
diol 14. The primary hydroxy group of diol 14 was
transformed into a phenylsulfonyl group by reaction
with (PhS)2–Bu3P13 and subsequent oxidation of the
resultant sulfide group, and the secondary hydroxy
group was methylated to afford C22–C28 segment 5
(33% from 7).
Mycalolide B (2) is a cytotoxic and anti-fungal macro-
lide isolated from a sponge of the genus Mycale sp.5
Mycalolide B (2) inhibits actomyosin Mg2þ-ATPase6
and also interacts with actin in the same manner as 1.7
Recently, the total synthesis of mycalolide A was re-
ported.8 Since mycalolide B (2) possesses a similar side
chain to that of 1, analog 4 is expected to show actin-
depolymerizing activity. We describe herein the stereo-
controlled synthesis of mycalolide analog 4 and its
activity against actin.
The synthesis of C29–C35 segment 6 is shown in Scheme
2. While compound 6, with four contiguous syn–anti–
anti-stereocenters, was previously prepared by using the
Evans aldol reaction and Sharpless epoxidation as the
key steps,4a;b the improved synthesis of 6 was developed
by using the Paterson aldol reaction14 as the key step.
Thus, the Paterson aldol reaction between ethyl ketone
15 and crotonaldehyde gave the hydroxy ketone 16.15
Stereoselective reduction of 16 with tetramethylammo-
nium triacetoxyborohydride16 afforded an anti-1,3-diol,
which was transformed into acetonide 17. Conversion of
The synthesis of mycalolide analog 4 has been carried
out according to a convergent synthetic methodology
connecting C22–C28 and C29–C35 segments, 5 and 6.
The synthesis of C22–C28 segment 5 started with an
anti-selective aldol reaction (Scheme 1).9 An aldol
reaction between imide 710 and 3-benzyloxypropanal
under Heathcock conditions afforded hydroxy imide 8
(64%) along with the syn-isomer 9 (20%).11 Removal of
O
TBS TBS
TBS TBS
O
OBn
O
O
X Y
O
O
OBn
O
O
O
b–d
e, f
a
24
O
N
O
N
23
H
11
10
8: X = OH, Y = H
9: X = H, Y = OH
7
O
O
N
Bn
O
TBS TBS
TBS TBS
O
O
O
OH
O
O
O
OH OH
h
j–l
12
N
O
5
g
14
13
Bn
Scheme 1. Reagents and conditions: (a) Bu2BOTf (2 equiv for 7), 3-benzyloxypropanal, i-Pr2EtN, )78 ꢁC (8) 64%, (9) 20%; (b) H2O2, LiOH, THF,
H2O, 0 ꢁC; (c) LiAlH4, THF, rt; (d) TBSCl, imidazole, DMF, rt, 77% (three steps); (e) H2, 5% Pd–C, NaHCO3, EtOAc, 50 ꢁC, 85%; (f) Dess–Martin
periodinane, pyridine, CH2Cl2, rt, 96%; (g) 12, Bu2BOTf, Et3N, CH2Cl2, )78 ꢁC fi 0 ꢁC, 100%; (h) LiBH4, EtOH, Et2O, )10 ꢁC, 100%; (j) (PhS)2,
Bu3P, DMF, rt, 96%; (k) m-CPBA, NaHCO3, CH2Cl2, rt, 93%; (l) MeI, NaH, THF, rt, 92%.
O
OBn
OH
O
OBn
O
O
OBn
d–g
b, c
a
CHO
+
15
16
17
OMe
35
MeO OMe
O
OH
O
O
O
CHO
i, j
h
O
6
29
19a
19b
18
19c
Scheme 2. Reagents and conditions: (a) Sn(OTf)2, Et3N, CH2Cl2, )78 ꢁC fi )60 ꢁC, 85%; (b) Me4NBH(OAc)3, AcOH, MeCN, )25 ꢁC; (c)
(MeO)2CMe2, PPTS, acetone, rt, 84% (two steps); (d) Ca, liq. NH3, i-PrOH, THF, )78 ꢁC, 98%; (e) p-TsCl, pyridine, 0 ꢁC, 100%; (f) NaCN, DMSO,
50 ꢁC, 98%; (g) DIBAL, CH2Cl2, hexane, )78 ꢁC, 93%; (h) PPTS, MeOH, rt, 82%; (i) BnBr, NaH, DMF, rt, 93%; (j) OsO4, NMO, H2O, acetone, rt;
then NaIO4, rt, 99%.

K. Suenaga et al. / Tetrahedron Letters 45 (2004) 5383–5386
5385
Table 1. Actin-depolymerizing activity of aplyronine A (1) and com-
pounds 3, 4, and 26
17 into the aldehyde 18 was effected by a four-step
sequence of reactions. Aldehyde 18 was treated with
PPTS in methanol to provide a separable mixture of
diastereomeric acetals, 19a and 19b, and the dimethyl
acetal 19c.17 After chromatographic separation, two
minor products, 19b and 19c, were subjected to
equilibration (PPTS in methanol) to afford a mixture of
19a, 19b, and 19c, from which the major acetal 19a was
again obtained. By repeating this procedure, 19b and
19c could be transformed into 19a. Protection of the
hydroxy group in 19a followed by oxidative cleavage of
the double bond provided the C29–C35 segment 6 (48%
from 15).
Compound
Actin-depolymerizing activitya
IC50 (lM)b Relative potencyc
Aplyronine A (1)
3
1.6
7.9
2.7
4.4
100
20
4
26
59
36
a Activity was monitored by measuring the fluorescent intensity of
pyrenyl actin. For the conditions of assay, see Ref. 20.
b IC50 indicates the concentration required to depolymerize F-actin
(3.7 lM) to 50% of its control amplitude.
c The relative potencies were calculated from the IC50 values of the
compound (aplyronine A ¼ 100).
The Julia coupling reaction between 5 and 6 gave a
hydroxy sulfone, which was converted into the olefin 20
by reduction (Scheme 3). Manipulation of the protecting
group in 20 and catalytic hydrogenation of the double
bond afforded compound 21. The acidic hydrolysis of 21
gave a hemiacetal, which was reduced to afford the diol
22. The secondary hydroxy group in 22 was acetylated
to give alcohol 23 by a three-step sequence of reactions.
Oxidation of 23 and subsequent condensation with N-
methylformamide provided the enamide 24. Deprotec-
tion of the 3,4-dimethoxybenzyloxymethyl group of 24
gave an alcohol, which was esterified with 2,3-di-O-
Table 1. The mycalolide analog 4 exhibited strong
activity comparable to that of aplyronine A (1). This
result revealed that the side chain portion in mycalolide
B (2) was responsible for the potent activity of 2, as was
also the case with aplyronine A (1). Comparison of the
activities of 3, 4, and 26 revealed that the structure and
stereochemistry of the acyl group both influenced
activity.
In conclusion, the stereocontrolled synthesis of mycal-
olide analog 4, consisting only of the side chain of
mycalolide B (2), was carried out. In addition, the
mycalolide analog 4 was found to exhibit strong actin-
depolymerizing activity.
methyl-
afford a mixture of diastereomeric esters 25, which re-
sulted from the racemization of 2,3-di-O-methyl- -gly-
D-glyceric acid under Yamaguchi conditions to
D
ceric acid. After removal of the silyl groups in 25, HPLC
separation of the diastereomers provided analogs 418
and 26.19
Acknowledgements
The actin-depolymerizing activity of mycalolide analogs
4 and 26, aplyronine A (1), and its analog 3 is shown in
We are grateful to Professors Hiroshi Ozaki and
Masatoshi Hori (The University of Tokyo) for their
TBS TBS
TBDPS
O
TBDPS
OMe
DMBOM
OMe
OMe
c–g
a, b
O
O
OMe
OBn O
O
O
O
5 +
6
20
21
OR1 OR1 OMe
OR2 OAc
Me
N
TBDPS
O
TBDPS
OMe
DMBOM
m, n
h, i
O
O
OR
22
CHO
OH
35
24: R1 = TBDPS, R2 = DMBOM
o, p
q
22: R = H
OMe
25: R1 = TBDPS, R2 =
MeO
j–l
23: R = Ac
O
OMe
OMe
OMe
MeO
4: R1 = H, R2 =
O
DMBOM =
O
OMe
MeO
26: R1 = H, R2 =
O
Scheme 3. Reagents and conditions: (a) BuLi, THF, )78 ꢁC; (b) 5% Na–Hg, NaH2PO4, MeOH, 0 ꢁC, 72% (two steps); (c) Ca, liq. NH3, i-PrOH,
THF, )78 ꢁC, 90%; (d) H2, 5% Pd–C, NaHCO3, EtOH, 55 ꢁC, 86%; (e) 3,4-dimethoxybenzyloxymethyl chloride, i-Pr2NEt, CH2Cl2, rt, 84%; (f)
Bu4NF, THF, rt, 99%; (g) TBDPSCl, imidazole, DMF, rt, 75%; (h) 1 M HCl, DME, rt; (i) NaBH4, EtOH, rt, 70% (two steps); (j) TrCl, pyridine,
50 ꢁC, 95%; (k) Ac2O, pyridine, DMAP, rt, 100%; (l) HCO2H, Et2O, rt, 77%; (m) Dess–Martin periodinane, pyridine, CH2Cl2, rt, 91%; (n)
MeNHCHO, PPTS, hydroquinone, MS 3 A, benzene, reflux, 55%; (o) DDQ, 1 M phosphate buffer (pH 6), t-BuOH, CH2Cl2, rt, 90%; (p) 2,3-di-O-
methyl-
D
-glyceric acid, 2,4,6-trichlorobenzoyl chloride, Et3N, DMAP, CH2Cl2, rt, 74%; (q) HFÆpyridine, pyridine, THF, rt; separation by HPLC (4)
55%, (26) 34%.

5386
K. Suenaga et al. / Tetrahedron Letters 45 (2004) 5383–5386
anti. On the other hand, the oxidation of 27 and 8 afforded
diastereomeric ketones 28 and 29, respectively, establish-
ing that the absolute configuration of C23 in 8 was S.
From these results, the stereochemistry of 8 was deter-
mined to be 23S and 24S (anti), as expected from the
results9 of Heathcook and co-workers.
donation of actin and their helpful advice and discus-
sions. This study was supported in part by the 21st
Century COE program and Grants-in-Aid for Scientific
Research from Ministry of Education, Culture, Sports,
Science, and Technology, Suntory Institute for Bioor-
ganic Research, Yamada Science Foundation, the Fu-
jisawa Foundation, the Naito Foundation, University of
Tsukuba Research Projects, and Wako Pure Chemical
Industries, Ltd.
O
O
O
OH OBn
O
O
OBn
23R
24S
23R
O
N
O
N
27
OH OBn
28
References and notes
O
O
O
O
OBn
O
23S
1. (a) Fenteany, G.; Shoutian, Z. Curr. Top. Med. Chem.
2003, 3, 593–616; (b) Yeung, K.-S.; Paterson, I. Angew.
Chem., Int. Ed. 2002, 41, 4632–4653.
O
N
O
N
2. (a) Yamada, K.; Ojika, M.; Ishigaki, T.; Yoshida, Y.;
Ekimoto, H.; Arakawa, M. J. Am. Chem. Soc. 1993, 115,
11020–11021; (b) Ojika, M.; Kigoshi, H.; Ishigaki, T.;
Yamada, K. Tetrahedron Lett. 1993, 34, 8501–8504; (c)
Ojika, M.; Kigoshi, H.; Ishigaki, T.; Nisiwaki, M.;
Tsukada, I.; Mizuta, K.; Yamada, K. Tetrahedron Lett.
1993, 34, 8505–8508; (d) Ojika, M.; Kigoshi, H.; Ishigaki,
T.; Tsukada, I.; Tsuboi, T.; Ogawa, T.; Yamada, K.
J. Am. Chem. Soc. 1994, 116, 7441–7442.
8
29
12. Dess, D. B.; Martin, J. J. Org. Chem. 1983, 48, 4155–
4156.
13. Nakagawa, I.; Hata, T. Tetrahedron Lett. 1975, 16, 1409–
1412.
14. (a) Paterson, I.; Tiller, R. D. Tetrahedron Lett. 1991, 32,
1749–1752; (b) Paterson, I.; Lister, M. A.; Ryan, G. R.
Tetrahedron Lett. 1992, 33, 4233–4236.
3. Saito, S.; Watabe, S.; Ozaki, H.; Kigoshi, H.; Yamada, K.;
Fusetani, N.; Karaki, H. J. Biochem. 1996, 120, 552–555.
4. (a) Kigoshi, H.; Ojika, M.; Ishigaki, T.; Suenaga, K.;
Mutou, T.; Sakakura, A.; Ogawa, T.; Yamada, K. J. Am.
Chem. Soc. 1994, 116, 7443–7444; (b) Kigoshi, H.;
Suenaga, K.; Mutou, T.; Ishigaki, T.; Atsumi, T.; Ishiw-
ata, H.; Sakakura, A.; Ogawa, T.; Ojika, M.; Yamada, K.
J. Org. Chem. 1996, 61, 5326–5351; (c) Suenaga, K.;
Kamei, N.; Okugawa, Y.; Takagi, M.; Akao, A.; Kigoshi,
K.; Yamada, K. Bioorg. Med. Chem. Lett. 1997, 7, 269–
274; (d) Kigoshi, H.; Suenaga, K.; Takagi, M.; Akao, A.;
Kanematsu, K.; Kamei, N.; Okugawa, Y.; Yamada, K.
Tetrahedron 2002, 58, 1075–1102.
5. (a) Fusetani, N.; Yasumuro, K.; Matsunaga, S.; Hashi-
moto, K. Tetrahedron Lett. 1989, 30, 2809–2812; (b)
Matsunaga, S.; Liu, P.; Celatka, C. A.; Panek, J. S.;
Fusetani, N. J. Am. Chem. Soc. 1999, 121, 5605–5606.
6. Hori, M.; Saito, S.; Shin, Y.; Ozaki, H.; Fusetani, N.;
Karaki, H. FEBS Lett. 1993, 322, 151–154.
15. A diastereomer of 16 was obtained as a minor product
(6%), the stereochemistry of which was not determined.
16. Evans, D. A.; Chapman, K. T.; Carreira, E. M. J. Am.
Chem. Soc. 1988, 110, 3560–3578.
17. The stereochemistry at C35 of acetals 19a and 19b was not
determined.
28
D
18. ½aꢀ +88.5 (c 0.067, CHCl3); IR (CHCl3) 3675, 1575, 1488,
1237, 1202, 1043 cmꢁ1
;
1H NMR (400 MHz, CDCl3): d
8.30 [8.08] (s, 1H), 6.49 [7.17] (d, J ¼ 14:0 Hz, 1H), 5.11
(m, 1H), 4.97 [4.99] (dd, J ¼ 9:6 Hz, 14.0 Hz, 1H), 4.80
(dd, J ¼ 2:8 Hz, 10.0 Hz, 1H), 3.93 (m, 1H), 3.79–3.29 (m,
5 H), 3.50 (s, 3H), 3.40 (s, 3H), 3.37 (s, 3H), 3.20 (m, 1H),
3.03 [3.07] (s, 3H), 2.51 (m, 1H), 2.09 [2.08] (s, 3H), 1.90–
1.72 (m, 2H), 1.76 (m, 1H), 1.69–1.36 (m, 6H), 1.02 [1.01]
(d, J ¼ 6:8 Hz, 3H), 0.98 (d, J ¼ 6:8 Hz, 3H), 0.89 (d,
J ¼ 6:8 Hz, 3H), 0.82 (d, J ¼ 6:8 Hz, 3H). The minor
counterparts of doubled signals in the ratio of 3:2 are in
brackets; HRMS (ESI) calcd for C28H51NNaO10
[(M+Na)þ] 584.3398, found 584.3411.
7. Saito, S.; Watabe, S.; Ozaki, H.; Fusetani, N.; Karaki, H.
J. Biol. Chem. 1994, 269, 29710–29714.
8. (a) Liu, P.; Panek, J. S. J. Am. Chem. Soc. 2000, 122,
1235–1236; (b) Panek, J. S.; Liu, P. J. Am. Chem. Soc.
2000, 122, 11090–11097.
9. (a) Walker, M. A.; Heathcock, C. H. J. Org. Chem. 1991,
56, 5747–5750; (b) Raimundo, B. C.; Heathcock, C. H.
Synlett 1995, 1213–1214.
10. Evans, D. A.; Bartroli, J.; Shih, T. L. J. Am. Chem. Soc.
1981, 103, 2127–2129.
11. The stereochemistry of 8 was determined as follows. The
coupling constant between C23 and C24of 8 was 7.3 Hz,
whereas that of its syn-diastereomer 27, prepared by Evans
aldol reaction, was 3.6 Hz. This finding indicated that the
relative stereochemistry between C23 and C24in 8 was
19. The stereochemistry of 4 and 26 concerning the 2,3-di-O-
methylglyceroyl group was determined by degradation
and chiral HPLC analyses in the same manner as that used
for mycalolide B.5b
20. Actin was purified from rabbit skeletal muscle21 using G-
buffer containing 0.2 mM CaCl2, 0.2 mM ATP, 0.5 mM b-
mercaptoethanol, and 2 mM Tris–HCl (pH 8.0) and the
actin was polymerized to F-actin with 1 mM MgCl2 at
25 ꢁC for 1 h. The test compounds were dissolved in
DMSO and added to the F-actin solution (3.7 lM).
The incubated actin solutions were monitored with
a fluorometer (excitation at 365 nm and emission at
407 nm).
21. Spudich, J. A.; Watt, S. J. Biol. Chem. 1971, 246, 4866–
4871.