Total synthesis and cytotoxicity of haterumalides NA and B and their artificial analogues

Article abstract of DOI:10.1021/jo802806z

The total synthesis of haterumalides NA and B, potent cytotoxic marine macrolides, was achieved by using B-alkyl Suzuki-Miyaura coupling and Nozaki-Hiyama-Kishi coupling as key steps. Compared to our first-generation approach for enf-haterumalide NA methy

Full text of DOI:10.1021/jo802806z

Total Synthesis and Cytotoxicity of Haterumalides NA and B and
Their Artificial Analogues
Mitsuru Ueda, Masashi Yamaura, Yoichi Ikeda, Yuta Suzuki, Kensaku Yoshizato,
Ichiro Hayakawa, and Hideo Kigoshi*
Department of Chemistry, Graduate School of Pure and Applied Sciences, and Center for Tsukuba
AdVanced Research Alliance, UniVersity of Tsukuba, Ibaraki 305-8571, Japan
kigoshi@chem.tsukuba.ac.jp
ReceiVed December 25, 2008
The total synthesis of haterumalides NA and B, potent cytotoxic marine macrolides, was achieved by
using B-alkyl Suzuki-Miyaura coupling and Nozaki-Hiyama-Kishi coupling as key steps. Compared
to our first-generation approach for ent-haterumalide NA methyl ester, this second-generation synthesis
yielded much more of the key intermediate. This synthesis established the relative stereochemistry of
haterumalide B. Furthermore, the structure-cytotoxicity relationships of haterumalides were investigated.
The combination of macrolide and side chain parts proved to be important to the cytotoxicity.
Introduction
structure as haterumalide NA (2). In 2004, we isolated biselides
A (8) and B (9) from the Okinawan ascidian Didemnidae sp.
and determined their structures to be oxygenated analogues of
haterumalides (Figure 1).4a The next year, we reported the
isolation of three analogues, biselides C (10)-E (12), and
compared the cytotoxicity of haterumalide NA (2), haterumalide
NA methyl ester (7), and biselides A (8), B (9), and C (10).4b
Among the tested cell lines, haterumalide NA (2), haterumalide
NA methyl ester (7), and biselides A (8) and B (9) showed
stronger cytotoxicity than did anticancer drug cisplatin against
human breast cancer MDA-MB-231 and human nonsmall cell
lung cancer NCI-H460.4b Interestingly, haterumalide NA (2)
showed strong toxicity against brine shrimp, with an LD50 of
0.6 µg/mL, while biselides A (8) and C (10) and haterumalide
NA methyl ester (7) exhibited no toxicity against this animal,
even at 50 µg/mL. In 2005, researchers at Fujisawa Pharma-
ceutical Company isolated an antimicrobial component FR177391,
the enantiomer of haterumalide NA (2), from the soil bacterium
Serratia liquefaciens.5a In addition, they identified its molecular
target as protein phosphatase 2A (PP2A).5b-d
In 1999, haterumalide B (1) was isolated from the Okinawan
ascidian Lissoclinum sp. by Ueda and Hu.1 At the same time,
haterumalides NA (2)-NE (6) were isolated from the Okinawan
sponge Iricinia sp. by Uemura and co-workers.2 Haterumalide
NA (2) exhibited cytotoxicity against P388 cells with an IC50
of 0.32 µg/mL, and moderate acute toxicity against mice with
an LD99 of 0.24 g/kg. Also, haterumalide B (1) completely
inhibited the first cleavage of fertilized sea urchin eggs at a
concentration of 0.01 µg/mL.1 Oocydin A3a and haterumalide
A3b were also isolated from the South American epiphyte
Serratia marcescens and the soil bacterium Serratia plymuthica,
respectively, and they were found to have the same gross
* To whom correspondence should be addressed. Fax: +81-29-853-4313.
(1) Ueda, K.; Hu, Y. Tetrahedron Lett. 1999, 40, 6305.
(2) Takada, N.; Sato, H.; Suenaga, K.; Arimoto, H.; Yamada, K.; Ueda, K.;
Uemura, D. Tetrahedron Lett. 1999, 40, 6309.
(3) (a) Strobel, G.; Li, J.-Y.; Sugawara, F.; Koshino, H.; Harper, J.; Hess,
W. M. Microbiology 1999, 145, 3557. (b) Thaning, C.; Welch, C. J.; Borowiez,
J. J.; Hedman, R.; Gerhardson, B. Soil Biol. Biochem. 2001, 33, 1817.
(4) (a) Teruya, T.; Shimogawa, H.; Suenaga, K.; Kigoshi, H. Chem. Lett.
2004, 33, 1184. (b) Teruya, T.; Suenaga, K.; Maruyama, S.; Kurotaki, M.;
Kigoshi, H. Tetrahedron 2005, 61, 6561.
(5) (a) Sato, B.; Nakajima, H.; Fujita, T.; Takase, S.; Yoshimura, S.;
Kinoshita, T.; Terano, H. J. Antibiot. 2005, 58, 634. (b) Inai, M.; Kawamura, I.;
Tsujimoto, S.; Yasuno, T.; Lacey, E.; Hirosumi, J.; Takakura, S.; Nishigaki, F.;
Naoe, Y.; Manda, T.; Mutoh, S. J. Antibiot. 2005, 58, 640. (c) Kobayashi, M.;
Sato, K.; Yoshimura, S.; Yamaoka, M.; Takase, S.; Ohkubo, M.; Fujii, T.;
Nakajima, H. J. Antibiot. 2005, 58, 648. (d) Yamaoka, M.; Sato, K.; Kobayashi,
M.; Nishio, N.; Ohkubo, M.; Fujii, T.; Nakajima, H. J. Antibiot. 2005, 58, 654.
The unique structures of haterumalides and biselides, in
conjunction with their potent biological activities, have made
them attractive synthetic targets.6 Several groups have reported
approaches to synthesize the haterumalide NA (2). In 2003,
Snider and Gu synthesized ent-haterumalide NA methyl ester
(7).7a Their strategy involved a key fragment coupling at
3370 J. Org. Chem. 2009, 74, 3370–3377
10.1021/jo802806z CCC: $40.75 2009 American Chemical Society
Published on Web 04/03/2009

Total Synthesis of Haterumalides NA and B
SCHEME 1. Retrosynthetic Analyses of Haterumalides B
(1) and NA (2)
SCHEME 2. Synthesis of r,ꢀ-Unsaturated Ester 24
FIGURE 1. Structures of haterumalides and biselides.
C-5-C-6 using a Stille reaction. Hoye and Wang achieved the
first total synthesis of haterumalide NA (2) itself.7b Their
synthetic route involved a key intramolecular cyclization at
C-6-C-7, based on the Kaneda reaction. Recently, Schomaker
and Borhan synthesized haterumalides NA (2) and NC (4) by
using chromium-mediated macrocyclization.7c Prior to those
reports, we reported the first synthesis of ent-haterumalide NA
methyl ester (7).8 This synthesis revised the stereochemistry of
haterumalide NA (2) and determined its absolute configuration.
However, because our previous synthetic route included low-
yield steps, we planned to develop an efficient second-generation
method for synthesizing haterumalides, biselides, and their
derivatives, which will provide a practical supply for further
biological studies. The second-generation synthesis of hateru-
malide NA was preliminarily reported.9
Results and Discussion
Our retrosynthetic analyses of haterumalides NA (2) and B
(1) are shown in Scheme 1. Our strategy involved a key
fragment coupling between macrolactone 13 and the ap-
propriately protected side chain unit 14 or 15 using Nozaki-
Hiyama-Kishi coupling. We expected that macrolactonization
of seco acid 16 provided macrolactone 13. Seco acid 16 might
be obtained from a common intermediate 17 for haterumalides
and biselides. The synthetic route to a common intermediate
17 for haterumalides and biselides involved the B-alkyl
Suzuki-Miyaura coupling10 between the alkenylsilane segment
1911 and alkylborane 20, with subsequent stereoselective
construction of a chloroolefin part from alkenylsilane 18.
We describe in detail the synthesis of haterumalides NA (2)
and B (1) by using a convergent synthetic methodology with a
B-alkyl Suzuki-Miyaura coupling.10 Very recently, Roulland
reported the total synthesis of haterumalide NA (2) using a
similar cross-coupling strategy.7d
(6) Kigoshi, H.; Hayakawa, I. Chem. Rec. 2007, 7, 254.
(7) (a) Gu, Y.; Snider, B. B. Org. Lett. 2003, 5, 4385. (b) Hoye, T. R.; Wang,
J. J. Am. Chem. Soc. 2005, 127, 6950. (c) Schomaker, J. M.; Borhan, B. J. Am.
Chem. Soc. 2008, 130, 12228. (d) Roulland, E. Angew. Chem., Int. Ed. 2008,
47, 3762.
(8) Kigoshi, H.; Kita, M.; Ogawa, S.; Itoh, M.; Uemura, D. Org. Lett. 2003,
5, 957.
The starting point for this work was the construction of the
common intermediate 17 (Scheme 2). The known glycal 21 was
(9) Hayakawa, I.; Ueda, M.; Yamaura, M.; Ikeda, Y.; Suzuki, Y.; Yoshizato,
K.; Kigoshi, H. Org. Lett. 2008, 10, 1859.
(10) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457.
(11) Miura, K.; Hondo, T.; Okajima, S.; Nakagawa, T.; Takahashi, T.;
Hosomi, A. J. Org. Chem. 2002, 67, 6082.
J. Org. Chem. Vol. 74, No. 9, 2009 3371

Ueda et al.
SCHEME 4. Synthesis of the Precursors of B-Alkyl
TABLE 1. Study of Intramolecular Oxy-Michael Cyclization of
r,ꢀ-Unsaturated Ester 24
Suzuki-Miyaura Coupling
entry
conditions
yielda (%)
1
2
NaOMe, MeOH, 0 °C f rt, 30 min 80% (trans:cis ) 9:1)
Triton B, MeOH, 0 °C f rt, 15 min 87% (single diastereomer)
a Isolated yields calculated from dihydrofuran 22 (in 3 steps).
SCHEME 3. Intramolecular Oxy-Michael Cyclization in the
Previous Work8
TABLE 2. Study of B-Alkyl Suzuki-Miyaura Coupling
synthesized from commercially available D-mannose.12 The
hydroxy group of glycal 21 was protected to give the 3,4-
dimethoxybenzyl (DMPM) ether 22. The DMPM ether 22 was
transformed into the hemiacetal 23 by the oxymercuration-
reduction sequence.13 The hemiacetal 23 was converted into
R,ꢀ-unsaturated ester 24 by the Wittig reaction.
Table 1 summarizes our attempts toward the intramolecular
oxy-Michael cyclization of R,ꢀ-unsaturated ester 24. In our
previous report,8 similar intramolecular oxy-Michael cyclization
was carried out by using NaOMe in MeOH, but the yield and
stereoselectivity were not so high (56%, trans/cis ) 5.3:1)
(Scheme 3).
Treatment of R,ꢀ-unsaturated ester 24 under the same
conditions gave the desired tetrahydrofuran 25 (80% in 3 steps,
trans/cis ) 9:1) (entry 1). Next, oxy-Michael cyclization was
performed with Triton B in MeOH (entry 2).14 This cyclization
improved the stereoselectivity and enhanced the reaction rate.
The success of oxy-Michael cyclization of the R,ꢀ-unsaturated
ester 24 might be due to two factors: (1) steric hindrance of the
acetonide group in 24 directed the addition and (2) Triton B
was more effective in promoting oxy-Michael cyclization and
the reaction was completed at lower temperature.
The LiAlH4 reduction of 25 gave alcohol 26 (Scheme 4).
Alcohol 26 was converted to iodide 27, a precursor of the
requisite boranate. On the other hand, the primary alcohol of
26 was converted to the corresponding selenoether. Upon
treatment with H2O2 and pyridine, the selenoether was oxidized
and then eliminated to form the terminal olefin 28.15
entry
precursor
reagent
yield (%)
1
2
3
27
28
28
t-BuLi, 9-BBN-OMe
9-BBN-H/THF
9-BBN-H dimer
32
0
quant
THF, followed by the addition of PdCl2(dppf) and alkenylsilane
19, did not give the coupling compound 18 (entry 2). In this
reaction, the hydroboration step was slow, and the intermediate
borane decomposed gradually. The use of 9-BBN-H dimer
instead of 9-BBN-H/THF gave the best result, maybe because
of the concentrated conditions (entry 3).
We next tried to construct a chloroolefin part stereoselectively
from the alkenylsilane 18. In our previous report,8 a chloroolefin
part was stereoselectively constructed from an alkenylsilane 18
by a modification of Tamao’s procedure.17 We reported that
the addition of a small amount of water was important for the
reaction to be reproducible. In this study, we attempted the same
conditions with the alkenylsilane 18 but obtained a low and
irreproducible yield. Thus, preparation of the chloroolefin 31
required optimization (Table 3). Chlorination of the alkenylsilane
18 without water gave the desired chloroolefin 31 and recovery
of the alkenylsilane 18, but the yield was low (35%) (entry 1).
We expected that a small amount of base would be neutralized
in this reaction system. So we attempted the chlorination of the
alkenylsilane 18 by NCS with a base. The reaction with CaCO3
did not give chloroolefin 31 (entry 2). An attempt at chlorination
with KF afforded the desired chloroolefin 31 in 25% yield (entry
3). However, the reaction at higher temperature did not afford
the desired chloroolefin 31 (entry 4). Treatment of alkenylsilane
18 with NCS-K2CO3 (1.0 equiv) did not further the reaction
(entry 5). However, the chlorination was most efficiently
effected by NCS (2.0 equiv) in DMF at 50 °C in the presence
of K2CO3 (0.5 equiv) as a base (entry 6). This modification
increased the yield of the desired chloroolefin to 58%,
reproducibly.
With iodide 27 and terminal olefin 28 in hand, we attempted
B-alkyl Suzuki-Miyaura coupling, as depicted in Table 2. The
alkylboranate 29 generated in situ from iodide 2716 participated
in the cross-coupling reaction with alkenylsilane 1911 to provide
the desired coupling compound 18 in 32% yield (entry 1). We
next tried B-alkyl Suzuki-Miyaura coupling with terminal olefin
28. Hydroboration of the terminal olefin 28 with 9-BBN-H/
(12) Ireland, R.; Thaisrivongs, S.; Vanier, N.; Wilcox, C. J. Org. Chem. 1979,
45, 48.
(13) Oishi, T.; Ando, K.; Inomiya, K.; Sato, H.; Iida, M.; Chida, N. Bull.
Chem. Soc. Jpn. 2002, 75, 1927.
(14) (a) Ko, S.; Klein, L.; Pfaff, K.; Kishi, Y. Tetrahedron Lett. 1982, 23,
4415. (b) The stereochemistry was determined by NOESY correlations.
(15) Grieco, P. A.; Gilman, S.; Nishizawa, M. J. Org. Chem. 1976, 41, 1485.
(16) Marshall, J. A.; Johns, B. A. J. Org. Chem. 1998, 63, 7885.
(17) Tamao, K.; Akita, M.; Maeda, K.; Kumada, M. J. Org. Chem. 1987,
52, 1100.
3372 J. Org. Chem. Vol. 74, No. 9, 2009

Total Synthesis of Haterumalides NA and B
TABLE 3. Study of Stereoselective Construction of Chloroolefin
SCHEME 6. Synthesis of Lactone 38
entry
additive
temp, °C yield, % recovery of 18, %
1
2
3
4
5
6
none
CaCO3 (2.0 equiv)
KF (1.0 equiv)
KF (1.0 equiv)
K2CO3 (1.0 equiv)
K2CO3 (0.5 equiv)
50
50
50
100
50
50
35
<40
complex mixture
<42
complex mixture
no reaction
<29a
25
58
a This compound contained byproduct such as 32, which could not be
isolated.
SCHEME 5. Synthesis of Common Intermediate 17 for
Haterumalides and Biselides
SCHEME 7. Macrolactonization of a Seco Acid by Snider
and Gu
Treatment of chloroolefin 31 with PPTS provided a triol, the
1,2-diol group of which was reprotected as an acetonide group
to afford the common intermediate 17 for haterumalides and
biselides (Scheme 5). The overall sequence proceeded in 13
steps from D-mannose and in 32% overall yield, and thus the
common intermediate 17 could be synthesized in multigram
quantities.
SCHEME 8. Synthesis of Seco Acid 40
Total Synthesis of Haterumalide NA. Next, we tried to
synthesize haterumalide NA (2) from the common intermediate
17 (Scheme 6). The primary alcohol of the common intermediate
17 was oxidized to afford an aldehyde, which was converted
into the Z-conjugated ester 34 by using Ando’s modified
Horner-Wadsworth-Emmons reaction.18 Reduction of 34 with
DIBALH gave an alcohol, which was converted to aldehyde
35, a precursor of the aldol reaction. The aldol reaction between
aldehyde 35 and isopropyl acetate by LHMDS provided a
ꢀ-hydroxy ester as a diastereomeric mixture at C-3. The
secondary hydroxy group of the ꢀ-hydroxy ester was protected
as the TBS ether to give 36. Removal of the DMPM group in
36 by using DDQ in CH2Cl2-t-BuOH-phosphate buffer (pH
6.6) and subsequent hydrolysis of the isopropyl ester group
afforded seco acid 37, a precursor of macrolactonization. The
macrolactonization of seco acid 37 under Yamaguchi condi-
tions19 afforded the corresponding lactone 38, but the yield was
low (17%). An attempt at macrolactonization under Shiina
conditions20 did not afford the desired lactone 38. On the other
hand, Snider and Gu achieved satisfactory macrolactonization
of a similar seco acid under Yamaguchi conditions (Scheme
7).7a This suggested that steric hindrance of the acetonide group
in our seco acid 37 interfered with macrolactonization. There-
fore, we next tried to synthesize a seco acid without an acetonide
group.
Removal of the acetonide group in 36 gave the diol, which
was converted into a primary alcohol by NaIO4 oxidation and
reduction with NaBH4 (Scheme 8). The primary hydroxy group
was protected as a trityl group to afford compound 39. Removal
of the DMPM group in compound 39 gave an alcohol, and
hydrolysis of the isopropyl ester afforded seco acid 40.
Next, we attempted the macrolactonization of 40, as depicted
in Table 4. The macrolactonization of 40 under Yamaguchi
conditions afforded the desired lactone 41 (61%) and the dimer
(6%) (entry 1). We next tried the macrolactonization under
Shiina conditions. However, the reaction gave only undesired
C-3 hydroxy isomer in 12% yield (entry 2).
The TBS group in lactone 41 was removed by TBAF, and
the C-3 isomers 42a and 42b were separated by silica gel
chromatography (Scheme 9). The undesired C-3 isomer 42a was
able to be converted to the desired C-3 isomer 42b via
(18) Ando, K. J. Org. Chem. 1998, 63, 8411.
(19) Inanaga, J.; Hirata, K.; Saeki, H.; Katsuki, T.; Yamaguchi, M. Bull.
Chem. Soc. Jpn. 1979, 52, 1989.
(20) Shiina, I.; Kubota, M.; Ibuka, R. Tetrahedron Lett. 2002, 43, 7535.
J. Org. Chem. Vol. 74, No. 9, 2009 3373

Ueda et al.
TABLE 4. Study of Macrolactonization of Seco Acid 40
SCHEME 10. Synthetic Study of Ester 50
SCHEME 11. Synthesis of Iodide 15
entry
1
conditions
results
2,4,6-Cl3C6H2COCl, Et3N, THF,
rt then DMAP, toluene, rt
41: 61%
dimer: 6%
2
2-methyl-6-nitrobenzoic anhydride, 41: 12% (only undesired
Et3N, DMAP, toluene, rt
C-3 hydroxy isomer)
dimer: 11%
recovered 40: 14%
SCHEME 9. Total Synthesis of Haterumalide NA (2)
iodide 457b and aldehyde 13, derived from 43 by Dess-Martin
periodinane,21 afforded the coupling product 47. However, we
could not remove the 4-methoxybenzyl (MPM) ester in 47 under
reported conditions (TFA, Et3SiH).25 Therefore, we next tried
Nozaki-Hiyama-Kishi coupling with 2,4-dimethoxybenzyl
ester46insteadoftheMPMester45.TheNozaki-Hiyama-Kishi
coupling with iodide 46, prepared from 44,8 afforded hateru-
malide NA 2,4-dimethoxybenzyl ester 48.26 Removal of the 2,4-
dimethoxybenzyl group with TFA and anisole gave haterumalide
NA (2).27 Synthetic haterumalide NA (2) gave spectral data (1H
NMR, 13C NMR, HRMS, and CD28) in full agreement with
those of the natural one,2 completing the total synthesis.
Total Synthesis of Haterumalide B. We next tried the
synthesis of haterumalide B (1) from aldehyde 13. To the best
of our knowledge, there are few natural products with the
2-methylene-3-oxobutyl ester group and no total synthesis has
been reported about these types of natural products. First we
tried to synthesize the side chain unit of haterumalide B (1) for
Nozaki-Hiyama-Kishi coupling. We attempted to prepare
iodide 50 from carboxylic acid 44 and alcohol 4929 by DCC-
DMAP, Yamaguchi conditions, Shiina conditions, and (COCl)2
(Scheme 10). However, the desired iodide 50 could not be
obtained because it is unstable. Therefore, we next tried to
synthesize iodide with a masked enone group.
The secondary hydroxy group in (()-5130 was protected as
an MPM ether, and methyl ester was reduced by DIBALH to
give allylic alcohol (()-52 (Scheme 11). Esterification between
iodide 44 and allylic alcohol (()-52 by DCC-DMAP afforded
the desired iodide (()-15.
The Nozaki-Hiyama-Kishi coupling reaction of aldehyde
13 and iodide (()-15 afforded the coupling product 53 (48%,
5.5:1 ratio of 53:15-epi-53) (Scheme 12). The newly generated
C-15 stereochemistry of 53 has been determined by modified
Mosher’s method.31 Removal of the MPM group and subsequent
selective oxidation of C-22 allylic alcohol with MnO2 afforded
Dess-Martin oxidation21 followed by Luche reduction.22 To
convert 42b to 43, we followed the reported procedure by Snider
and Gu.7a Thus, acetylation of the hydroxy group at C-3 in 42b
and removal of the trityl group gave the primary alcohol 43,
which is the natural enantiomer of the key intermediate of our
previous total synthesis of ent-haterumalide NA methyl ester
(7).8,23 The stereochemistry at C-3 was determined by com-
1
parison of the H NMR spectra with those of our authentic
sample.8 To convert 43 into haterumalide NA (2), we followed
our first-generation synthesis with modification by Hoye and
Wang.7b The Nozaki-Hiyama-Kishi coupling reaction24 of
(25) Hoye et al.7b and Roulland7d successfully cleaved under this condition.
(26) Due to the small reaction scale of Nozaki-Hiyama-Kishi coupling,
we could not isolate the minor isomer at C-15.
(27) Kobayashi et al. have reported removal of the 2,4-dimethoxybenzyl group
in similar esters.5c
(21) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155.
(22) Gemal, A. L.; Luche, J.-L. J. Am. Chem. Soc. 1981, 103, 5454.
(23) The alcohol 43 gave spectral data (1H NMR, 13C NMR, and HRMS) in
full agreement with the authentic sample. The optical rotation of our sample 43
{[R]24D-11.7 (c 0.18, CHCl3)} corresponded to the reported values (+10.7 for
ent-437a and-16.0 for 437b).
(24) (a) Takai, K.; Kimura, K.; Kuroda, T.; Hiyama, T.; Nozaki, H.
Tetrahedron Lett. 1983, 24, 5281. (b) Jin, H.; Uenishi, J.; Christ, W. J.; Kishi,
Y. J. Am. Chem. Soc. 1986, 108, 5644.
(28) Comparison of the CD spectra of synthetic and natural samples identified
absolute configuration. The CD spectral data of the synthetic sample, CD (MeOH)
λext 220 nm, ∆ε +0.12, was the same sign as the natural sample [CD (MeOH)
λext 220 nm, ∆ε +0.10].
(29) Is¸eri, R.; Ku¨sefog˘lu, S. H. J. Appl. Polym. Sci. 2000, 77, 509.
(30) Maguire, R. J.; Mulzer, J.; Bats, J. W. Tetrahedron Lett. 1996, 37, 5487.
(31) (a) Ohtani, I.; Kusumi, T.; Kashman, Y.; Kakisawa, H. J. Am. Chem.
Soc. 1991, 113, 4092. (b) The detailed experimental procedures of MTPA esters
of 53 are given in the Supporting Information.
3374 J. Org. Chem. Vol. 74, No. 9, 2009

Total Synthesis of Haterumalides NA and B
SCHEME 12. Total Synthesis of Haterumalide B (1)
SCHEME 13. Synthesis of Artificial Analogues of
Haterumalides
haterumalide B (1), which is identical in all respects to the
natural product.1 Therefore, this synthesis established the relative
stereochemistry of haterumalide B (1).32
Synthesis of Artificial Analogues of Haterumalides. To
investigate the structure-cytotoxicity relationships of hateru-
malides, three analogues 55, 56, and 57 were synthesized (Figure
2).
TABLE 5. Cytotoxicity Against HeLa S3 Cells of Haterumalides
and the Artificial Analogues
IC50 values,
µg/mL
haterumalide NA (2) (natural)
haterumalide NA (2) (synthetic)
0.019
0.024
0.023
0.021
haterumalide NA methyl ester (7)
haterumalide B (1)a
lactone part of haterumalides (43)
artificial analogue of haterumalide NA (55)
artificial analogue of haterumalide NA methyl ester (56)
artificial analogue of haterumalide B (57)
93.2
81.6
405
2.87
a A diastereomeric mixture {4:1 ratio of haterumalide B (1):15-epi-
haterumalide B (1)} was used for the cytotoxicity assay.
C-22 allylic alcohol with MnO2 afforded artificial analogue 57
of haterumalide B.
FIGURE 2. Artificial analogues of haterumalides.
Structure-Cytotoxicity Relationships of Haterumalides.
Table 5 summarizes the cytotoxicity of haterumalides NA (2),
NA methyl ester (7), B (1), lactone part (synthetic intermediate)
43 of haterumalides, and artificial analogues 55, 56, and 57 of
haterumalides against HeLa S3 cells. The cytotoxic activity of
synthetic haterumalide NA (2) against HeLa S3 cells had the
same IC50 value as that of natural haterumalide NA (2).
Haterumalide NA methyl ester (7) and haterumalide B (1)
showed cytotoxicity with IC50 of 0.023 and 0.021 µg/mL,
respectively. From these results, the carboxylic acid group at
the side chain of haterumalide NA (2) was shown to be
unimportant for the strong cytotoxicity of haterumalide NA (2).
The lactone part 43 of haterumalides showed a very weak
cytotoxicity, indicating the importance of the side chain part to
cytotoxicity. However, side chain analogues 55, 56, and 57 of
haterumalides were much less cytotoxic than the corresponding
haterumalides. These results showed that the combination of
lactone and side chain parts is essential for the strong cytotox-
icity of haterumalides. It is of worth noting that analogue 57 of
haterumalide B was more cytotoxic than analogues 55 and 56
of haterumalide NA. These results indicated that the conjugated
ketone moiety was somewhat responsible for the cytotoxicity.
These artificial analogues were prepared from synthetic
intermediate 28 by a strategy similar to that used for hateru-
malides NA (2), NA methyl ester (7),8 and B (1), respectively
(Scheme 13). The DMPM group in 28 was removed by using
DDQ to give a secondary alcohol, which was converted into
acetate 58. Acidic hydrolysis of 58 gave a diol. Oxidative
cleavage of the diol group by NaIO4 afforded aldehyde 59. The
Nozaki-Hiyama-Kishi coupling of aldehyde 59 and 2,4-
dimethoxybenzyl ester 46 afforded the coupling product 61. The
2,4-dimethoxybenzyl group in 61 was removed by using TFA
and anisole to give the artificial analogue 55 of haterumalide
NA. The artificial analogue 56 of haterumalide NA methyl ester
was prepared from aldehyde 59 and iodide 608 by Nozaki-
Hiyama-Kishi coupling. We next tried to synthesize the
artificialanalogue57ofhaterumalideB.TheNozaki-Hiyama-Kishi
coupling reaction of aldehyde 59 and iodide 15 afforded the
coupling product 62. The MPM group in 62 was removed by
using DDQ to give an allylic alcohol 63. Selective oxidation of
(32) The optical rotation of natural haterumalide B (1) was reported. However,
the value of the optical rotation was too small {[R]23D-0.002 (c 0.08, CHCl3)}1
to determine the absolute stereochemistry. We measured the CD spectrum of
synthetic 1; however, the spectrum of the natural one was not reported.
J. Org. Chem. Vol. 74, No. 9, 2009 3375

Ueda et al.
1H), 4.01 (q, J ) 6.8 Hz, 1H), 3.80 (s, 3H), 3.23 (d, J ) 1.1 Hz,
2H), 1.93 (d, J ) 1.4 Hz, 3H), 1.32 (d, J ) 6.8 Hz, 3H); 13C NMR
(67.8 MHz, CDCl3) δ 169.4, 159.0, 144.4, 140.1, 130.4, 129.2 (2C),
114.3, 113.7 (2C), 79.8, 76.0, 69.9, 63.9, 55.3, 44.2, 24.1, 20.6;
HRMS (ESI) m/z 453.0543, calcd for C18H23INaO4 [M + Na]+
453.0539.
Conclusion
In conclusion, we have achieved the total synthesis of
haterumalides NA (2) (1.3% overall yield in 33 steps) and B
(1) (1.5% overall yield in 34 steps). From this synthetic work,
we determined the relative stereochemistry of haterumalide B
(1). Furthermore, we have investigated the structure-cytotoxicity
relationships and revealed that the combination of lactone and
side chain parts is important to the strong cytotoxicity of
haterumalides. This strategy is being applied to the synthesis
of biselides and probe molecules for searching target biomol-
ecules. Further investigation into the structure-activity relation-
ship and synthetic studies of biselides by using intermediate 17
are in progress.
MPM Ether 53. DMSO was degassed by freeze-thawing. To
a stirred solution of aldehyde 13 (7.1 mg, 19.1 µmol) and iodide
(()-15 (60.8 mg, 141 µmol) in DMSO (1.9 mL) was added CrCl2
doped with 1% NiCl2 (49.5 mg, CrCl2: 399 µmol, NiCl2: 3.82 µmol)
at room temperature in a glovebox. The mixture was stirred at room
temperature for 28 h, diluted with Et2O (10 mL) and H2O (3 mL),
and extracted with Et2O (7 × 6 mL). The combined extracts were
dried (MgSO4) and concentrated. The residual oil was purified by
column chromatography on silica gel (1.6 g, hexane-EtOAc 2:1
f 1:1 f 1:2) to give MPM ether 53 (6.2 mg, 48%) as a colorless
oil: IR (film) 3456, 2931, 1738, 1652, 1371, 1246, 1149, 1065,
1020, 821, 755 cm-1; 1H NMR (500 MHz, CDCl3) δ 7.25 (d, J )
8.6 Hz, 2H), 6.87 (d, J ) 8.6 Hz, 2H), 5.77 (dd, J ) 11.0, 5.0 Hz,
1H), 5.67 (dd, J ) 10.0, 7.5 Hz, 1H), 5.44 (m, 1H), 5.33 (ddd, J
) 6.4, 3.3, 3.3 Hz, 1H), 5.21 (s, 2H), 5.21 (m, 1H), 4.66 (s, 2H),
4.63 (m, 1H), 4.46 (d, J ) 11.4 Hz, 1H), 4.27 (d, J ) 11.4 Hz,
1H), 4.04-3.90 (m, 3H), 3.80 (s, 3H), 3.54 (ddd, J ) 17.8, 10.1,
7.7 Hz, 1H), 3.11 (br s, 2H), 2.80 (dd, J ) 11.4, 11.4 Hz, 1H),
2.76 (dd, J ) 11.6, 4.7 Hz, 1H), 2.56-2.48 (m, 2H), 2.39 (m, 1H),
2.17 (dd, J ) 13.0, 5.5 Hz, 1H), 2.13 (m, 1H), 2.04 (s, 3H), 1.89
(s, 3H), 1.87 (s, 3H), 1.50-1.37 (m, 2H), 1.32 (d, J ) 2.5 Hz,
1.5H), 1.31 (d, J ) 2.5 Hz, 1.5H), a signal due to one proton (OH)
was not observed; 13C NMR (125 MHz, CDCl3) δ 171.0, 169.5,
168.0, 159.1, 144.6 (0.5C), 144.5 (0.5C), 134.4, 133.2, 132.0, 130.5,
129.9, 129.5, 129.3 (0.5C), 129.3 (0.5C), 125.5, 114.3 (0.5C), 114.1
(0.5C), 113.8 (2C), 82.7, 76.1, 76.0, 75.8, 69.9 (0.5C), 69.8 (0.5C),
67.4, 66.4 (0.5C), 66.4 (0.5C), 63.6 (0.5C), 63.6 (0.5C), 55.3, 45.0,
38.0, 37.8, 34.8, 27.9, 26.7, 21.1, 20.5, 18.3, 17.6; HRMS (ESI)
m/z 697.2759, calcd for C36H4735ClNaO10 [M + Na]+ 697.2755.
Allylic Alcohol 54. To a stirred solution of MPM ether 53 (4.8
mg, 7.1 µmol) in CH2Cl2 (1.9 mL), t-BuOH (0.11 mL), and pH
6.6 phosphate buffer (0.11 mL) was added DDQ (2.3 mg, 10.1
µmol) at 0 °C. The mixture was stirred at 0 °C for 2 h, and pH 6.6
phosphate buffer (0.11 mL) and DDQ (2.7 mg, 11.9 µmol) were
added. The mixture was stirred at 0 °C for 2 h, and pH 6.6
phosphate buffer (0.11 mL) and DDQ (2.3 mg, 10.1 µmol) were
added. The mixture was stirred at 0 °C for 2 h, and pH 6.6
phosphate buffer (0.11 mL) and DDQ (2.3 mg, 10.1 µmol) were
added. The mixture was stirred at 0 °C for 15 h, diluted with
saturated aqueous NaHCO3 (2 mL), and extracted with EtOAc (3
× 4 mL). The combined extracts were washed with brine, dried
(Na2SO4), and concentrated. The residual oil was purified by column
chromatography on silica gel (0.6 g, hexane-EtOAc 1:3 f 1:4)
to give allylic alcohol 54 (3.9 mg, quant) as a colorless oil: IR
Experimental Section
Allylic Alcohol (()-52. To a stirred solution of alcohol (()-51
(578 mg, 4.44 mmol) in CH2Cl2 (10 mL) were added a solution of
MPM 2,2,2-trichloroacetimidate (2.13 g, 7.57 mmol) in CH2Cl2 (8
mL) and PPTS (53 mg, 5 mol %) at 0 °C. The mixture was stirred
at room temperature for 19 h, diluted with saturated aqueous
NaHCO3 (6 mL), and extracted with EtOAc. The combined extracts
were washed with brine, dried (Na2SO4), and concentrated. The
residue oil was purified by column chromatography on silica gel
(50 g, hexane-EtOAc 20:1) to give an MPM ether (721 mg, 65%)
as a colorless oil: IR (film) 2976, 2952, 1716, 1612, 1514, 1290,
1248, 1097 cm-1; 1H NMR (270 MHz, CDCl3) δ 7.26 (d, J ) 8.6
Hz, 2H), 6.87 (d, J ) 8.6 Hz, 2H), 6.31 (d, J ) 1.4 Hz, 1H), 5.96
(dd, J ) 1.4, 1.4 Hz, 1H), 4.47 (d, J ) 11.3 Hz, 1H), 4.33 (d, J )
11.3 Hz, 1H), 4.42 (q, J ) 6.5 Hz, 1H), 3.80 (s, 3H), 3.77 (s, 3H),
1.34 (d, J ) 6.5 Hz, 3H); 13C NMR (67.8 MHz, CDCl3) δ 166.6,
159.0, 142.3, 130.4, 129.1 (2C), 124.3, 113.7 (2C), 72.9, 70.5, 55.3,
51.8, 22.0; HRMS (ESI) m/z 273.1111, calcd for C14H18NaO4 [M
+ Na]+ 273.1103.
To a stirred solution of the MPM ether (353 mg, 1.41 mmol)
in CH2Cl2 (20 mL) was added DIBALH (0.94 M solution in
hexane, 3.8 mL, 3.57 mmol) at -78 °C. The mixture was stirred
at the same temperature for 3 h, diluted with saturated aqueous
Na/K tartrate (7.5 mL) at 0 °C, and filtrated through a pad of
Celite. The aqueous mixture was extracted with EtOAc. The
combined extracts were dried over Na2SO4 and concentrated.
The residual oil was purified by column chromatography on silica
gel (5 g, hexane-EtOAc 5:1) to give allylic alcohol (()-52 (269
mg, 85%) as a colorless oil: IR (film) 3390, 2976, 2866, 1612,
1514, 1302, 1248, 1092, 1034, 912, 822 cm-1; 1H NMR (270 MHz,
CDCl3) δ 7.25 (d, J ) 8.6 Hz, 2H), 6.87 (d, J ) 8.6 Hz, 2H), 5.21
(dd, J ) 3.0, 1.4 Hz, 1H), 5.11 (s, 1H), 4.47 (d, J ) 11.3 Hz, 1H),
4.34 (d, J ) 11.3 Hz, 1H), 4.28 (dd, J ) 13.8, 4.9 Hz, 1H), 4.16
(dd, J ) 13.8, 6.5 Hz, 1H), 4.09 (q, J ) 6.5 Hz, 1H), 3.80 (s, 3H),
2.17 (t, J ) 5.7 Hz, 1H), 1.35 (d, J ) 6.5 Hz, 3H); 13C NMR (67.8
MHz, CDCl3) δ 159.0, 148.6, 130.2, 129.2 (2C), 113.8 (2C), 112.5,
77.0, 69.9, 63.1, 55.3, 20.3; HRMS (ESI) m/z 245.1155, calcd for
C13H18NaO3 [M + Na]+ 245.1154.
(film) 3436, 2929, 1734, 1370, 1231, 1149, 1069, 1019, 757 cm-1
;
1H NMR (500 MHz, CDCl3) δ 5.77 (dd, J ) 10.8, 5.1 Hz, 1H),
5.67 (dd, J ) 10.1, 7.1 Hz, 1H), 5.45 (dd, J ) 8.2, 1.1 Hz, 1H),
5.33 (dd, J ) 3.4, 3.4 Hz, 1H), 5.24 (s, 1H), 5.21 (d, J ) 6.8 Hz,
1H), 5.15 (s, 1H), 4.73 (dd, J ) 12.2, 12.2 Hz, 1H), 4.67-4.58
(m, 2H), 4.36 (dddd, J ) 6.0, 6.0, 6.0, 6.0 Hz, 1H), 3.98-3.91 (m,
2H), 3.54 (ddd, J ) 18.0, 10.0, 8.0 Hz, 1H), 3.09 (s, 2H), 2.82-2.75
(m, 2H), 2.56-2.49 (m, 2H), 2.37 (m, 1H), 2.19-2.11 (m, 2H),
2.05 (s, 3H), 1.89 (s, 3H), 1.86 (s, 3H), 1.51-1.39 (m, 2H), 1.33
(d, J ) 6.5 Hz, 3H), signals due to two protons (OH) were not
observed; 13C NMR (125 MHz, CDCl3) δ 170.9, 169.6, 168.0, 147.1
(0.5C), 147.0 (0.5C), 134.4 (0.5C), 134.4 (0.5C), 133.1, 132.0,
129.8, 129.5 (0.5C), 129.5 (0.5C), 125.6, 113.9 (0.5C), 113.7 (0.5C),
82.7 (0.5C), 82.7 (0.5C), 75.7 (0.5C), 75.7 (0.5C), 68.8, 68.7, 67.4,
66.3 (0.5C), 66.2 (0.5C), 64.8 (0.5C), 64.8 (0.5C), 45.1, 38.0, 37.8,
34.8, 27.9, 26.7, 21.9, 21.1, 18.3, 17.6; HRMS (ESI) m/z 577.2177,
calcd for C28H3935ClNaO9 [M + Na]+ 577.2180.
Iodo Ester (()-15. To a stirred solution of carboxylic acid 44
(120 mg, 530 µmol) and alcohol (()-52 (354 mg, 1.59 mmol) in
CH2Cl2 (3.1 mL) were added DMAP (19.5 mg, 159 µmol) and DCC
(220 mg, 1.06 mmol) at 0 °C. The mixture was stirred at room
temperature for 21 h, diluted with saturated aqueous NH4Cl (6 mL),
and extracted with EtOAc (3 × 6 mL). The combined extracts were
washed with brine, dried (Na2SO4), and concentrated. The residual
oil was purified by column chromatography on silica gel (18.8 g,
hexane-EtOAc 20:1 f 10:1 f 5:1) to give iodo ester (()-15 (206
mg, 90%) as a colorless oil: IR (film) 2976, 2866, 1738, 1612,
1514, 1302, 1248, 1173, 1144, 1034, 918, 822 cm-1; 1H NMR (270
MHz, CDCl3) δ 7.25 (d, J ) 8.6 Hz, 2H), 6.87 (d, J ) 8.9 Hz,
2H), 6.16 (q, J ) 1.1 Hz, 1H), 5.23 (s, 1H), 5.20 (d, J ) 1.4 Hz,
1H), 4.67 (s, 2H), 4.45 (d, J ) 11.3 Hz, 1H), 4.28 (d, J ) 11.3,
Haterumalide B (1). To a stirred solution of allylic alcohol 54
(3.0 mg, 5.4 µmol) in CH2Cl2 (0.55 mL) was added MnO2 (20.0
3376 J. Org. Chem. Vol. 74, No. 9, 2009

Total Synthesis of Haterumalides NA and B
mg, 230 µmol) at 0 °C. The mixture was stirred at room temperature
for 11 h, and MnO2 (9.4 mg, 108 µmol) was added. The mixture
was stirred at room temperature for 6.5 h and filtrated through a
pad of Celite. The filtrate was concentrated, and the residual oil
was purified by column chromatography on silica gel (0.6 g,
hexane-EtOAc 1:1 f 1:2) to give haterumalide B (1) (2.2 mg,
73%) as a colorless oil. This sample contained a small amount of
byproduct, maybe the C-15 epimer. An attempt to separate this
sample by HPLC (Develosil ODS-HG-5 250 × 20 mm, flow rate
5 mL/min; detection, UV 215 nm; solvent 63% MeOH) resulted
in the decomposition of product: CD (MeOH) λext 218 nm, ∆ε
17.4; HRMS (ESI) m/z 575.2024, calcd for C28H3735ClNaO9 [M +
Na]+ 575.2024.
Acknowledgment. We thank Professor Katsuhiro Ueda
(University of the Ryukyus) for providing spectra of hateru-
malide B. This work was supported in part by Grants-in-Aid
for Young Scientists (B), Scientific Research on Priority Area
“Creation of Biologically Functional Molecules”, Grants-in-Aid
for Scientific Research (B), and by the 21st COE program from
the Ministry of Education, Culture, Sports, Science and Tech-
nology (MEXT), Japan. We also thank Nippon Kayaku Co.,
Ltd., for its financial support. We would like to thank Professors
Akira Sekiguchi, Tatsuya Nabeshima, Masaaki Ichinohe, and
Shigehisa Akine (University of Tsukuba) for APCI mass
analysis and CD spectrum analysis.
1
+0.31; H NMR (600 MHz, CDCl3) δ 6.19 (s, 1H), 6.03 (t, J )
1.5 Hz, 1H), 5.78 (dd, J ) 11.1, 4.8 Hz, 1H), 5.68 (m, 1H), 5.46
(dd, J ) 8.3, 1.1 Hz, 1H), 5.34 (t, J ) 3.4 Hz, 1H), 5.21 (m, 1H),
4.81 (br s, 2H), 4.61 (t, J ) 8.1 Hz, 1H), 3.96 (m, 1H), 3.96 (dd,
J ) 8.1, 3.8 Hz, 1H), 3.54 (m, 1H), 3.11 (br s, 2H), 2.80 (dd, J )
11.3, 11.3 Hz, 1H), 2.77 (dd, J ) 11.3, 4.8 Hz, 1H), 2.56-2.49
(m, 2H), 2.38 (m, 1H), 2.37 (s, 3H), 2.18 (dd, J ) 12.7, 5.5 Hz,
1H), 2.13 (dd, J ) 13.0, 3.0 Hz, 1H), 2.05 (s, 3H), 1.89 (br s, 3H),
1.86 (d, J ) 1.3 Hz, 3H), 1.48 (ddd, J ) 12.5, 12.5, 3.2 Hz, 1H),
1.41 (m, 1H), a signal due to one proton (OH) was not observed;
13C NMR (150 MHz, CDCl3) δ 198.1, 170.7, 169.5, 168.0, 143.2,
134.3, 133.2, 132.0, 129.8, 129.6, 126.9, 125.6, 82.7, 76.5, 75.8,
67.4, 66.4, 62.3, 44.9, 38.0, 37.8, 34.8, 28.0, 26.7, 25.9, 21.1, 18.3,
Supporting Information Available: Experimental proce-
dures and copies of the 1H and 13C NMR spectra for compounds
2, 13, 17-18, 22-26, 28, 31, 34-36, 39-43, 46, 48, 55-59,
1
and 61-63, and copies of the H and 13C NMR spectra for 1,
15, and 52-54. This material is available free of charge via
the Internet at http://pubs.acs.org.
JO802806Z
J. Org. Chem. Vol. 74, No. 9, 2009 3377