Peloruside B, a potent antitumor macrolide from the New Zealand marine sponge Mycale hentscheli: Isolation, structure, total synthesis, and bioactivity

Article abstract of DOI:10.1021/jo9021265

(Chemical Equation Presented) Peloruside B(2), a natural congener of pelorusideA(1), was isolated in sub-milligram quantities from the New Zealand marine sponge Mycale hentscheli. Peloruside B promotes microtubule polymerization and arrests cells in the G₂/M phase of mitosis similar to paclitaxel, and its bioactivity was comparable to that of peloruside A. NMR-directed isolation, structure elucidation, structure confirmation by total synthesis, and bioactivity of peloruside B are described in this article. The synthesis features Sharpless dihydroxylation, Brown's asymmetric allylboration reaction, reductive aldol coupling, Yamaguchi macrolactonization, and selective methylation.

Full text of DOI:10.1021/jo9021265

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Peloruside B, A Potent Antitumor Macrolide from the New Zealand
Marine Sponge Mycale hentscheli: Isolation, Structure, Total Synthesis,
and Bioactivity
A. Jonathan Singh,† Chun-Xiao Xu,‡ Xiaoming Xu,‡ Lyndon M. West,^
Anja Wilmes,† Ariane Chan,† Ernest Hamel,§ John H. Miller,†
Peter T. Northcote,*,† and Arun K. Ghosh*,‡
†Centre for Biodiscovery, Victoria University of Wellington, Wellington, New Zealand, ‡Departments of
Chemistry and Medicinal Chemistry, Purdue University, West Lafayette, Indiana 47907, §Toxicology and
Pharmacology Branch, Developmental Therapeutics Program, Division of Cancer Treatment and Diagnosis,
National Cancer Institute, Frederick, National Institutes of Health, Frederick, Maryland 21702, and
^Department of Chemistry & Biochemistry, Florida Atlantic University, Boca Raton, Florida 33431
akghosh@purdue.edu; peter.northcote@vuw.ac.nz
Received October 6, 2009
Peloruside B (2), a natural congener of peloruside A (1), was isolated in sub-milligram quantities from
the New Zealand marine sponge Mycale hentscheli. Peloruside B promotes microtubule polymeri-
zation and arrests cells in the G2/M phase of mitosis similar to paclitaxel, and its bioactivity was
comparable to that of peloruside A. NMR-directed isolation, structure elucidation, structure
confirmation by total synthesis, and bioactivity of peloruside B are described in this article. The
synthesis features Sharpless dihydroxylation, Brown’s asymmetric allylboration reaction, reductive
aldol coupling, Yamaguchi macrolactonization, and selective methylation.
Introduction
mycalamides A, B, and D and the macrodiolide pateamine
are protein synthesis inhibitors acting at different stages of
translation.1-6 In 2000, the polyoxygenated, 16-membered
macrolide peloruside A (1, Figure 1) was reported from a
Pelorus Sound collection of M. hentscheli.7 Peloruside A has
shown potent cytotoxic activity against P388 murine leuke-
mia cells, with an IC50 value of 10 ng/mL (18 nM). Further-
more, it causes cells to accumulate in the G2/M phase of
mitosis by promoting microtubule polymerization.8 This
activity is similar to the highly successful antitumor drug
paclitaxel (Taxol), and thus peloruside A has become a
promising pharmaceutical candidate and a popular synthetic
The New Zealand marine sponge Mycale hentscheli
(Poecilosclerida, Demospongiae) is the source of three
classes of biologically active secondary metabolites,
each with a different activity profile. Heterocyclic amides
*To whom correspondence should be addressed. Phone: 765-494-5323.
Fax: 765-496-1612 (A.K.G). Phone: þ64-4-463-5960. Fax: þ64-4-463-5237
(P.T.N.).
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Chem. 1990, 55, 223–227.
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J. Org. Chem. 2010, 75, 2–10
Published on Web 12/03/2009
DOI: 10.1021/jo9021265
r
2009 American Chemical Society

Singh et al.
JOCFeatured Article
quantities from a wild M. hentscheli specimen collected from
Kapiti Island off the southwestern coast of the North Island
of New Zealand. Its bioactivity was comparable to peloru-
side A, and it promotes microtubule polymerization and
arrests cells in the G2/M phase of mitosis as does paclitaxel.
The structure of peloruside B was confirmed unequivocally
through an enantioselective total synthesis and comparison
of bioactivity with the natural product. Herein, we report the
isolation of peloruside B, structure elucidation, structure
confirmation by total synthesis, and evaluation of its bioac-
tivity.
FIGURE 1. Structures of peloruside A (1) and peloruside B (2).
target. To date, a number of total syntheses9-13 as well
as synthetic studies14 of peloruside A have been reported.
Recently, a review on the synthesis and biological activity
of peloruside A has appeared.15 Currently, quantities
required for biological studies are still presently achieved
mainly by collection from the wild and aquaculture of the
sponge.16,17 Recently, it was shown that, like laulimalide,
peloruside A occupies a different tubulin binding site
than paclitaxel18-21 and acts synergistically with taxoid
site drugs (e.g., paclitaxel, discodermolide, epothilones)
in an in vitro assay using isolated tubulin as well as in
cultured cells.22 Further studies have shown that peloru-
side A does not, in contrast to paclitaxel, induce the
production of pro-inflammatory mediators in murine
macrophages.23
Results and Discussion
Isolation and Structure. Methanolic extracts of a 230 g
wild Kapiti Island M. hentscheli specimen were fractionated
using reversed- (PSDVB, Me2CO/H2O and MeOH/H2O
gradients) and normal-phase (DIOL, MeCN/CH2Cl2 and
i-PrOH/n-hexane) column chromatography, yielding
the known compounds mycalamides A (7.0 mg) and D
(3.0 mg), peloruside A (1) (1.1 mg), and the new compound
peloruside B (2) (327 μg). Positive-ion HRESIMS of 2
afforded
a molecular formula of C26H46O11 (m/z
557.2935, [M þ Na]þ, calcd 557.2932), which, like 1,
required four degrees of unsaturation. The 1H NMR spec-
trum of 2 contained several resonances similar to the parent
structure 1, except for the observation of two methyl ether
resonances (δH 3.38 and 3.48) rather than three, which was
consistent with the difference of 14 mass units between 1
and 2. Detailed inspection of the 1D and 2D NMR spectra
(COSY, HSQC, HMBC) for 1 and 2 revealed the very
similar nature of the two compounds, which allowed most
13C and 1H NMR resonances to be assigned by direct
comparison (Table 1), resulting in the same pelorusane
carbon skeleton as represented by 1. HMBC correlations
(Figure 2) from 7-OMe (δH 3.38) to C-7 (δC 75.9) and 13-
OMe (δH 3.48) to C-13 (δC 77.9) established the connection
Our continuing interest in M. hentscheli and NMR-direc-
ted isolation has resulted in the isolation of a new compound,
peloruside B (2), possessing the 3-des-O-methyl variant of
peloruside A. Peloruside B was isolated in submilligram
(10) Jin, M.; Taylor, R. E. Org. Lett. 2005, 7, 1303–1305.
(11) Ghosh, A. K.; Xu, X.; Kim, J.-H.; Xu, C.-X. Org. Lett. 2008, 10,
1001–1004.
(12) Evans, D. A.; Welch, D. S.; Speed, A. W. H.; Moniz, G. A.; Reichelt,
A.; Ho, S. J. Am. Chem. Soc. 2009, 131, 3840–3841.
(13) Smith, A. B.; Cox, J. M.; Furuichi, N.; Kenesky, C. S.; Zheng, J.;
Atasoylu, O.; Wuest, W. M. Org. Lett. 2008, 10, 5501–5504.
(14) For the studies toward total syntheses of peloruside A, see: (a) Prantz,
K.; Mulzer, J. Angew. Chem., Int. Ed. 2009, 48, 5030–5033. (b) Williams, D.;
Walsh, M. J.; Claeboe, C. D.; Zorn, N. Pure Appl. Chem. 2009, 81, 181–194.
(c) Casey, E. M.; Teesdale-Spittle, P.; Harvey, J. E. Tetrahedron Lett. 2008, 49,
7021–7023. (d)Chen, Z.-L.; Zhou, W.-S. TetrahedronLett. 2006, 47, 5289–5292.
(e) Owen, R. M.; Roush, W. R. Org. Lett. 2005, 7, 3941–3944. (f) Roulland, E.;
Ermolenko, M. S. Org. Lett. 2005, 7, 2225–2228. (g) Engers, D. W.; Bassindale,
M. J.; Pagenkopf, B. L. Org. Lett. 2004, 6, 663–666. (h) Gurjar, M. K.; Pedduri,
Y.; Ramana, C. V.; Puranik, V. G.; Gonnade, R. G. Tetrahedron Lett. 2004, 45,
387–390. (i) Liu, B.; Zhou, W. S. Org. Lett. 2004, 6, 71–74. (j) Taylor, R. E.; Jin,
M. Org. Lett. 2003, 5, 4959–4961. (k) Ghosh, A. K.; Kim, J.-H. Tetrahedron
Lett. 2003, 44, 7659–7661. (l) Ghosh, A. K.; Kim, J.-H. Tetrahedron Lett. 2003,
44, 3967–3969. (m) Paterson, I.; Di Francesco, M. E.; Kuehn, T.Org. Lett. 2003,
5, 599–602.
of the two oxymethyls. Changes in chemical shift (Δδ2-1
)
for the CH-3 oxymethine (ΔδC-3 þ 8.5 ppm; ΔδH-3
þ
0.35 ppm) clearly showed a change in substitution at this
center, confirming the absence of an oxymethyl at this
1
position. Near identical chemical shifts, H-1H coupling
constants, and diagnostic NOESY correlations (all within
experimental error) between 1 and 2 strongly suggested the
retention of relative configuration. Hence, peloruside B (2)
is established here as the 3-des-O-methyl congener of
peloruside A (1).
(15) Williams, D. R.; Nag, P. P.; Zorn, N. Curr. Opin. Drug Discovery
Dev. 2008, 11, 251–271.
(16) Page, M. J.; Northcote, P. T.; Webb, V. L.; Mackey, S.; Handley, S. J.
Aquaculture 2005, 250, 256–269.
(17) Page, M.; West, L.; Northcote, P.; Battershill, C.; Kelly, M. J. Chem.
Ecol. 2005, 31, 1161–1174.
Enantioselective Synthesis of Peloruside B. Peloruside B
has been isolated in miniscule quantity, and to confirm
relative and absolute configuration of peloruside B, as
well as to compare its bioactivity, we have undertaken an
enantioselective synthesis of the proposed structure of
peloruside B. Our retrosynthetic analysis of peloruside B is
shown in Figure 3. Strategic bond disconnection of the
macrolactone bond provided acyclic intermediate 3. We
envisioned that the presence of a gem-dimethyl at C-10 and
the resulting lactol formed between C-5 and C-9 makes the
16-membered ring very sterically hindered for macrolacto-
nization. Therefore, we planned to protect the hydroxyl
group at C-5 and carry out a 16-membered ring macrocycli-
zation. Further disconnection of the C-10 to C-11 bond
provided segments 4 and 5, which can be assembled by a
´
(18) Gaitanos, T. N.; Buey, R. M.; Dıaz, J. F.; Northcote, P. T.; Teesdale-
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ꢀ
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´
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Taylor, R. E.; Sackett, D. L.; Schriemer, D. C. J. Mol. Biol. 2008, 378, 1016–1030.
(21) Huzil, J. T.; Chik, J. K.; Slysz, G. W.; Freedman, H.; Tuszynski, J.;
Taylor, R. E.; Sackett, D. L.; Schriemer, D. C. J. Mol. Biol. 2008, 378, 1016–1030.
(22) (a) Hamel, E.; Day, B. W.; Miller, J. H.; Jung, M. K.; Northcote, P.
T.; Ghosh, A. K.; Curran, D. P.; Cushman, M.; Nicolaou, K. C.; Paterson, I.;
Sorensen, E. J. Mol. Pharmacol. 2006, 70, 1555–1564. (b) Wilmes, A.; Bargh,
K.; Kelly, C.; Northcote, P. T.; Miller, J. H. Mol. Pharmaceutics 2007, 4, 269–
280.
(23) Crume, K. P.; Miller, J. H.; La Flamme, A. C. Exp. Biol. Med. 2007,
232, 607–613.
J. Org. Chem. Vol. 75, No. 1, 2010
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Singh et al.
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TABLE 1. 13C (150 MHz) and 1H (600 MHz) NMR Data for Natural Peloruside B (2) in CDCl3
13C
1H
position
δC
mult.
δ
H (mult., J, Hz)
COSY
HMBC
NOESY
1
2
174.5
69.8
-
C
CH
-
-
4.49 (s)
6.74 (br s)
4.57 (br s)
1.82 (td, 11.7, 3.8)
1.98 (m)
4.15 (tdd, 14.5, 4.4, 2.4)
1.51 (q, 12.0)
1.75 (ddd, 12.6, 5.0, 2.4)
3.79 (ddd, 11.4, 5.0, 3.2)
3.38 (s)
4.00 (d, 3.0)
-
-
4.91 (br d, 12.0)
1.42 (m)
2.07 (m)
3.98 (m)
3.48 (s)
2.05 (dd, 15.0, 10.8)
2.15 (dd, 15.0, 10.2)
5.69 (d, 11.2)
-
5.02 (d, 10.6)
2.56 (m)
1.14 (m)
-
-
2-OH, 4a (w), 5, 11, 15
2, 5, 7, 8, 11, 21
4b, 11, 15 (w), 23
2 (w), 4b, 5
-
1
2-OH
3
4a
4b
5
6a
6b
7
7-OMe
8
9
10
11
12a
12b
13
13-OMe
14a
14b
15
16
17
18
19a
19b
20
21
22
23
24a
24b
-
4a, 4b
-
69.9
38.4
CH
CH2
-
3, 4b, 5
3, 4a, 5
4a, 4b, 6a
5, 6b, 7
6a, 7
6a, 6b, 8
-
3
3, 4a, 6a
3
-
7
7, 8
2, 2-OH, 4a, 6b, 7
4b, 6b, 7
5, 6a, 7
2-OH, 5, 6a, 6b, 7-OMe, 8
7, 8
2-OH, 7, 7-OMe, 21
-
-
2, 2-OH, 3, 12a, 14a, 22
11, 12b, 13, 22
12a, 21
12a, 12b, 13-OMe, 14b
13, 15
11, 14b, 15, 23
14a, 15, 20
2, 3 (w), 13-OMe, 14a, 14b, 17, 18, 20, 23
-
15, 18, 19a, 19b, 20, 23, 24a
15, 17, 19b, 20, 24b
17, 19b, 20
17 (w), 18, 19a, 20, 24b
14b, 15, 17, 18, 19a, 19b, 24b
8, 12b
11, 12a
3, 15, 17
17, 19a, 19b, 24b
18, 19b, 20, 24a
63.7
31.4
CH
CH2
75.9
55.7
66.9
101.9
43.6
73.8
33.9
CH
CH3
CH
C
C
CH
CH2
7-OMe
7, 7-OMe
6, 7, 9
-
7
-
-
12b
-
-
12b, 13
11, 12a, 13
12a, 12b, 14a, 14b
-
13, 14b, 15
13, 14a, 15
14a, 14b, 17, 23
-
-
77.9
59.1
35.6
CH
CH3
CH2
-
13, 13-OMe
12, 13, 15, 16
12, 13
71.7
136.7
130.9
43.3
CH
C
CH
CH
CH2
1, 13, 14, 16, 17, 23
-
15, 18, 19, 23, 24
16, 17, 19, 20, 24
17, 18, 20, 24
17, 18, 20, 24
18, 19, 20
9, 10, 11, 21, 22
9, 10, 11, 21, 22
15, 16, 17, 23
17, 18, 19
15, 18, 23
17, 19a, 19b, 24a, 24b
18, 19b, 20
18, 19a, 20
19a, 19b
-
24.6
1.42 (m)
12.3
15.7
20.8
17.6
67.0
CH3
CH3
CH3
CH3
CH2
0.85 (t, 7.5)
1.08 (s)
1.10 (s)
1.71 (d, 1.2)
3.34 (t, 10.3)
3.62 (br d, 10.3)
-
15, 17
18, 24b
18, 24a
17, 18, 19
diol with NaH and PMBCl gave monoprotected PMB ether
8 (83% yield over three steps). It was converted to alkene 9 by
transformation of the alcohol into an iodide, using iodine
and triphenylphosphine in THF at 0 ꢀC, followed by sub-
stitution of the corresponding iodide with vinyl cuprate
(63% yield for two steps).25 The terminal olefin was con-
verted to an aldehyde using oxidative cleavage. This was
accomplished by dihydroxylation with OsO4 followed by
treatment of the resulting diol with NaIO4.26 The aldehyde
was subjected to Brown’s asymmetric allylboration27 to
afford the corresponding homoallylic alcohol. The resulting
alcohol was protected as TBS ether 10. The allylboration
proceeded with high diastereoselectivity (95:5 dr), and the
diastereomers were separated at this step (53% over four
steps, 95:5 dr). Conversion of terminal alkene to the corre-
sponding aldehyde, using the above oxidative cleavage fol-
lowed by Ando’s modified Horner-Emmons reaction,28
provided the Z-olefin 11 (Z:E 7:1, 81% yield over three
steps). Sharpless asymmetric dihydroxylation of the pure
Z-olefin 11 furnished the corresponding diol in 77% yield
(9:1 dr).29 The resulting diol was protected as an isopropyli-
dene derivative 12 in near quantitative yield. Reduction of
FIGURE 2. Key COSY, 2D TOCSY, and HMBC correlations for
peloruside B (2).
stereoselective aldol reaction to provide 3. Due to the steric
hindrance of the gem-dimethyl group adjacent to the C-9
ketone, selective enolization may be problematic. We
planned the same reductive aldol coupling protocol that
was utilized during the synthesis of (þ)-peloruside A.11
Segment 4 has been synthesized by us previously,11 which
features asymmetric alkylation of oxazolidinone 6, Hor-
ner-Emmons olefination, and Brown’s asymmetric allyl-
boration. The synthesis of segment 5 can be derived from
diethyl tartrate 7.
The synthesis of C-1 to C-10 fragment 5 commenced with
commercially available diethyl D-tartrate as shown in
Scheme 1. Both hydroxyl groups were protected with
MOM ether, and the resulting diester was reduced by LAH
reduction to give the corresponding diol.24 Treatment of the
(25) Lipshutz, B. H.; Sengupta, S. Org. React. 1992, 41, 135–631.
(26) Yu, W.; Mei, Y.; Kang, Y.; Hua, Z.; Jin, Z. Org. Lett. 2004, 6, 3217–
3219.
(27) Jadhav, P. K.; Bhat, K. S.; Perumal, T.; Brown, H. C. J. Org. Chem.
1986, 51, 432–439.
(28) Ando, K. J. Org. Chem. 1998, 63, 8411–8416.
(29) Kolb, H.; VanNieuwenhze, M. S.; Sharpless, K. B. Chem. Rev. 1994,
94, 2483–2547.
(24) Iida, H.; Yamazaki, N.; Kibayashi, C. J. Org. Chem. 1986, 51,
1069–1073.
4
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Singh et al.
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SCHEME 1. Synthesis of Fragment 5
(15%). The reason for the low yield is possibly due to the
presence of the C-15 allylic alcohol, which gets readily
oxidized. Attempts with other oxidizing reagents were
unsuccessful.
FIGURE 3. Retrosynthetic analysis of peloruside B (2).
ester 12 to the aldehyde, followed by reaction with isopro-
penylmagnesium bromide and Dess-Martin oxidation, pro-
vided the enone 5 in 76% yield over three steps. The other
coupling fragment 4 was synthesized following the reaction
schemes reported by us in the context of the synthesis of (þ)-
peloruside A.11
We then envisaged that selective oxidation of the pri-
mary alcohol in the presence of two other hydroxyl groups
would be very difficult due to the C-15 allylic alcohol.
While we achieved the selective oxidation during the
synthesis of (þ)-peloruside A, for peloruside B synthesis,
it was difficult to selectively oxidize the primary alcohol in
good yield. We decided to protect both C-11 and C-15
secondary hydroxyl groups as TES-ethers before oxidizing
the primary alcohol. Reductive aldol product 3 was trea-
ted with TESOTf and pyridine, as shown in Scheme 3.
Subsequent removal of the PMB protecting group with
DDQ gave the corresponding primary alcohol 15 in 65%
yield for two steps. The primary alcohol 15 was oxidized to
the corresponding aldehyde and, without purification,
further oxidized to the corresponding acid in 88% yield
over two steps. Both TES protecting groups at the C-11
and C-15 positions were selectively removed with dilute
HF/pyridine in 80% yield to afford the corresponding
seco-acid 14. The seco-acid 14 was subjected to the Yama-
guchi protocol31 using 2,4,6-trichlorobenzoyl chloride in
the presence of DMAP to generate macrolactone 16 in
77% yield.
With segments 4 and 5 in hand, our subsequent plan was
to use a reductive aldol reaction to couple these segments
and set the C-11 hydroxyl stereocenter. As shown in
Scheme 2, enone 5 was treated with L-selectride to gen-
erate the corresponding enolate, which was reacted with
aldehyde 4 to afford the aldol product 3 as the major
1
desired isomer (66% yield, 6.5:1 dr by H NMR). This
reductive coupling reaction provided a lower yield and
slightly improved diastereoselectivity compared to the C3-
OMe derivative during the synthesis of peloruside A.11
The stereochemical outcome and diastereomeric ratios
were consistent with our previous observation.11,30 The
TES protecting group was selectively removed by treat-
ment with dilute TBAF at -30 ꢀC. DDQ oxidation
effected the removal of the PMB group to provide alcohol
13 in 85% yield. Conversion of the primary alcohol to the
seco-acid 14 was carried out in a two-step sequence invol-
ving (1) TPAP oxidation of the alcohol to the correspond-
ing aldehyde and (2) oxidation of the aldehyde to the acid
with NaClO2. However, the yield was extremely low
The synthesis of the proposed structure of peloruside
B is shown in Scheme 4. We initially attempted the
(30) Ghosh, A. K.; Kass, J.; Anderson, D. D.; Xu, X.; Marian, C. Org.
Lett. 2008, 10, 4811–4814.
(31) Inanaga, J.; Hirata, K.; Saeki, H.; Katsuki, T.; Yamaguchi, M. Bull.
Chem. Soc. Jpn. 1979, 52, 1989–1993.
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Singh et al.
JOCFeatured Article
SCHEME 2. Reductive Aldol Reaction and Synthesis of seco-
Acid 14
SCHEME 3. Revised Route to Macrolactone 16
gave an IC50 of 33 ( 10 nM, a value approximately one-
third of that obtained with peloruside A (1) tested at the
same time (10 ( 4 nM) (n = 3 independent experiments,
Figure 4). Natural peloruside B was also slightly less active
than peloruside A against arresting cells in the G2/M phase
of the cell cycle, with 56 ( 1% of cells in G2/M for 2 (n = 6
replicates from three experiments) compared to 67 ( 3% in
G2/M for 1 (200 nM concentration of 1 or 2; n = 5 rep-
licates in three experiments). Control, untreated HL-60
cells had 23 ( 2% of the cells in the G2/M phase of the cell
cycle.
Synthetic 2 and natural 2 were compared in paired MTT
cell proliferation assays in human ovarian carcinoma 1A9
cells. 1A9 cells were treated for 72 h with drug. The
synthetic 2 (48 ( 11 nM IC50) was slightly more potent
than the natural 2 (71 ( 6 nM) in this cell line (n = 3 exper-
iments). The G2/M arrest results for the synthetic product
were also slightly higher than those obtained with the
natural congener. Synthetic 2 gave 28, 27, 43, and 70%
of cells in G2/M at concentrations of 0, 40, 100, and 140
nM, respectively (Figure 5). Natural 2 gave 25, 28, 31, and
47% at concentrations of 0, 32, 79, and 119 nM, respec-
tively. The slight differences in biological activity between
natural and synthetic 2 are well within the normal uncer-
tainties of the assays performed. Considering the fact that
the synthetic enantiomer of peloruside A has no bioactiv-
ity, the observed potent activity of synthetic peloruside B
further confirms the absolute configuration of natural
peloruside B.9
deprotection of both TBS ethers and acetonide groups by
treatment of 16 with 1 N HCl. However, the reaction was
not very satisfactory, yielding a number of undesired
products. We then planned to remove the TBS ethers of
macrolactone 16 by treatment with HF/pyridine. This
resulted in a mixture (6:1) of hemiketal 17a and the
corresponding hydroxyketone 17b in 86% combined
yield. The isopropylidene group from both hemiketal
17a and hydroxyketone 17b was deprotected with 80%
aqueous acetic acid at 50 ꢀC for 3 h to afford the
corresponding diol 18 in 52% isolated yield. Selective
methylation of the diol was carried out with Meerwein’s
reagent at -5 ꢀC to afford the corresponding C-7 mono-
methylated product. The product was then exposed to
4 N HCl in THF, and this effected the removal of both
MOM groups. Catalytic transfer hydrogenation with Pd/
C in the presence of formic acid selectively removed the
benzyl group in the presence of the C-17-trisubstituted
olefin to generate the synthetic peloruside B in 24% yield
over three steps. The 1D and 2D NMR data of synthetic
peloruside B are in complete agreement with that of
natural peloruside B.
Furthermore, using synthetic and natural peloruside B,
we have performed MTT cell proliferation assays (96 h
incubation) and flow cytometric measurements (16 h
incubation) as previously described with human myeloid
leukemic cells (HL-60 cells).23 Natural peloruside B (2)
6
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Singh et al.
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SCHEME 4. Completion of Total Synthesis of Peloruside B (2)
and arrests cells in the G2/M phase of the cell cycle, as does
paclitaxel. The bioactivity of natural peloruside B was
comparable to that of peloruside A. We have accomplished
an enantioselective and convergent synthesis of peloruside B.
The synthesis involved Sharpless dihydroxylation, Brown’s
asymmetric allylboration reaction, reductive aldol coupling,
and Yamaguchi macrolactonization as the key reactions.
The relative and absolute configuration of 2 was confirmed
by total synthesis and comparison of its bioactivity with
natural peloruside B. Synthesis and biological evaluation
of structural variants of peloruside B are the subjects of
ongoing research in our laboratories.
Experimental Section
Natural Peloruside B. General: The 600 MHz NMR spectra
for both natural and synthetic peloruside B (2) were obtained
using the same spectrometer equipped with a triple resonance
HCN cryogenic probe, operating at 600 or 150 MHz for 1H and
13C nuclei, respectively. Chemical shifts δ (ppm) were refer-
enced to the residual solvent peak (δH 7.26 ppm, δC 77.16 ppm
for CDCl3). Catalytic amounts (1-2 μL) of pyridine-d5 were
added to each NMR sample performed in CDCl3 to prevent
compound degradation due to trace acidity associated with the
solvent. High-resolution positive-ion mass spectra were
recorded on a TOF electrospray mass spectrometer. Normal-
phase column chromatography was carried out using
2,3-dihydroxypropoxypropyl-derivatized silica (DIOL). Re-
versed-phase column chromatography was achieved using
HP20 or Amberchrom poly(styrene divinylbenzene) (PSDVB)
chromatographic resin. HPLC was performed using a solvent
delivery module equipped with 25 mL pump heads. Solvents
used for flash normal- and reversed-phase column chromatog-
raphy were of HPLC or analytical grade quality. All other
solvents were purified by glass distillation. Solvent mixtures
are reported as % v/v unless otherwise stated. Specimens were
stored at -20 ꢀC until required.
Isolation of Natural Peloruside B: Mycale hentscheli (230 g,
NIWA no. MNP 0026), collected at a depth of 23 m from Kapiti
Island, New Zealand, was cut into small segments and extracted
with MeOH (2 ꢀ 700 mL) for 24 h. The combined extracts were
loaded on to HP20 PSDVB beads, washed with H2O, and eluted
with (i) 20% Me2CO/H2O, (ii) 55% Me2CO/H2O, (iii) 55%
Me2CO/0.2 M NH4OH, and (iv) 55% Me2CO/0.2 M NH4OH
adjusted to pH 4 with AcOH. Fraction (ii) was concentrated to
dryness to yield 82.0 mg of a viscous brown oil. The resulting oil
was dissolved in MeOH, loaded onto Amberchrom PSDVB,
and eluted with increasing concentrations of MeOH in H2O
(10-100%). The 48-54% MeOH/H2O fractions were concen-
trated to dryness to yield mycalamide D (3 mg). The 56-60%
MeOH/H2O fractions were concentrated to dryness to yield
peloruside A (1) (1.1 mg), and concentration of the 68-72%
MeOH/H2O fractions gave mycalamide A (7.0 mg). The
54-56% MeOH/H2O fractions were concentrated to dryness
to yield 5.0 mg of brown oil. A portion of this oil (3.0 mg) was
recycled twice on DIOL with increasing concentrations of
MeCN in CH2Cl2 (1-10%) and 50% MeOH/CH2Cl2. The
10% MeCN/CH2Cl2 and 50% MeOH/CH2Cl2 fractions were
concentrated to dryness to yield a pale yellow oil (1.5 mg). This
oil was then purified using HPLC (DIOL, 5 μm, 4 mm ꢀ 250 mm),
with 20% i-PrOH/n-hexane as the mobile phase, collecting
fractions at 1 min intervals to give 13.9 μg of mycalamide D,
9.4 μg of peloruside A (1), and 327 μg of peloruside B (2).
Peloruside A (1): Colorless film; all other data as previously
published.7
FIGURE 4. Typical MTT cell proliferation assay for pelorusides A
(1) and B (2). HL-60 cells were treated for 96 h (n = 3 replicates from
a single preparation).
Conclusion
We have isolated a sub-milligram amount of a new natural
product, peloruside B (2), a natural congener of peloruside
A (1), from the New Zealand marine sponge Mycale
hentscheli. The structure of peloruside B was elucidated
based upon extensive 1D and 2D NMR studies. Like peloru-
side A, peloruside B promotes microtubule polymerization
Peloruside B (2): Colorless film; [R]25 could not be deter-
D
mined accurately because of very small quantity of natural
J. Org. Chem. Vol. 75, No. 1, 2010
7

Singh et al.
JOCFeatured Article
FIGURE 5. G2/M arrest of 1A9 cells by natural and synthetic peloruside B (2).
sample and magnitude of rotation was very small; NMR data
see Table 1; HRESIMS, [M þ Na]þ, observed m/z 557.29356,
calculated 557.29323 for C26H46O11Na, Δ = 0.58 ppm.
Synthetic Peloruside B. General experimental details are
provided as Supporting Information.
chromatography on silica gel (hexanes/ethyl acetate 90/10) to
afford the TES protected product (425 mg, 88% yield): 1H
NMR (400 MHz, CDCl3) δ 0.06 (s, 3H), 0.08 (s, 3H), 0.58 (q,
J = 7.9 Hz, 6H), 0.68 (q, J = 7.9 Hz, 6H), 0.82 (t, J = 7.4 Hz,
3H), 0.88 (s, 9H), 0.91 (t, J = 7.9 Hz, 9H), 1.00 (t, J = 7.9 Hz,
9H), 1.09 (s, 3H), 1.13 (s, 3H), 1.23-1.38 (m, 2H), 1.49 (s, 3H),
1.51-1.73 (m, 4H), 1.70 (s, 3H), 1.98 (m, 1H), 2.58 (m, 1H), 3.21
(s, 3H), 3.27-3.40 (m, 2H), 3.34 (s, 3H), 3.37 (s, 3H), 3.47 (m, 1H),
3.53 (dd, J = 10.0, 6.9 Hz, 1H), 3.64 (dd, J = 10.0, 3.7 Hz, 1H),
3.68 (m, 1H), 3.80 (s, 3H), 3.81 (m, 1H), 3.97 (m, 1H), 4.07 (d,
J = 9.2 Hz, 1H), 4.46 (s, 2H), 4.50 (s, 2H), 4.51 (m, 1H), 4.57
(m, 1H), 4.62 (s, 2H), 4.65 (d, J = 6.8 Hz, 1H), 4.78 (d, J =
6.8 Hz, 1H), 4.97 (d, J = 10.2 Hz, 1H), 5.09 (d, J = 6.7 Hz, 1H),
6.86 (d, J = 8.6 Hz, 2H), 7.24 (d, J = 8.6 Hz, 2H), 7.32 (m, 5H);
13C NMR (100 MHz, CDCl3) δ -4.9, -4.3, 4.8, 5.5, 6.9, 7.1,
11.4, 17.89, 17.93, 19.7, 21.7, 25.2, 25.5, 25.8, 27.7, 38.4, 38.9,
39.4, 39.8, 52.7, 55.1, 55.7, 55.8, 66.3, 67.1, 69.7, 72.90, 72.93,
73.0, 73.2, 74.1, 74.4, 74.9, 77.6, 80.7, 96.9, 108.7, 113.6, 127.3,
127.5, 127.6, 128.2, 129.2, 130.3, 138.5, 138.6, 159.0, 209.2; FT-
IR (film, NaCl) 1039.8, 1100.9, 1248.5, 1379.2, 1462.3, 1513.8,
Aldol Product 3: To the enone 5 (521 mg, 0.81 mmol) dissolved
in anhydrous ethyl ether (132 mL) was added L-selectride (1 M
in THF, 0.85 mL, 0.85 mmol) slowly at -78 ꢀC. The solution
was stirred at -78 ꢀC for 0.5 h to form the corresponding
enolate. The formation of the enolate was monitored by TLC.
Then the aldehyde 4 (500 mg, 1.12 mmol) dissolved in Et2O
(10 mL) was added dropwise over 15 min at -78 ꢀC. The
solution was stirred at -78 ꢀC for 1 h and quenched with
saturated ammonium chloride solution. The aqueous layer
was washed and extracted with ethyl ether. The organic extracts
were washed with brine and dried over anhydrous sodium
sulfate. The solvent was removed under vacuum, and the residue
was purified by flash chromatography on silica gel (hexane/ethyl
acetate, 85/15) to afford the alcohol 3 (503.3 mg, 57% yield) and
the other C-11 diastereomer (77 mg, 9% yield; total yield 66%,
6.5:1 dr). Alcohol 3: 1H NMR (400 MHz, CDCl3) δ 0.06 (s, 3H),
0.07 (s, 3H), 0.55 (q, J = 7.9 Hz, 6H), 0.83 (t, J = 7.5 Hz, 3H),
0.87 (s, 9H), 0.89 (t, J = 8.9 Hz, 9H), 1.10 (s, 3H), 1.17 (s, 3H),
1.17-1.26 (m, 3H), 1.33 (s, 3H), 1.42-1.49 (m, 2H), 1.52 (s, 3H),
1.59-1.74 (m, 6H), 1.70 (s, 3H), 2.06 (m, 1H), 2.54 (m, 1H),
3.26-3.39 (m, 3H), 3.29 (s, 3H), 3.35 (s, 3H), 3.36 (s, 3H), 3.52
(dd, J = 10.0, 7.1 Hz, 1H), 3.57 (m, 1H), 3.63 (dd, J = 10.0, 3.6
Hz, 1H), 3.71 (m, 1H), 3.79 (s, 3H), 3.79 (m, 1H), 3.98 (m, 1H),
4.06 (d, J = 10.5 Hz, 1H), 4.45 (s, 2H), 4.48 (s, 2H), 4.55 (m, 1H),
4.62 (s, 2H), 4.65 (d, J = 6.8 Hz, 1H), 4.77 (d, J = 6.8 Hz, 1H),
4.93 (d, J = 10.2 Hz, 1H), 5.09 (d, J = 6.8 Hz, 1H), 6.86 (d, J =
8.6 Hz, 2H), 7.24 (d, J = 8.6 Hz, 2H), 7.26 (m, 5H); 13C NMR
(100 MHz, CDCl3) δ -4.8, -4.3, 4.7, 6.9, 11.6, 17.9, 18.0, 20.9,
25.3, 25.6, 25.8, 27.4, 33.5, 38.9, 39.1, 39.3, 51.5, 55.1, 55.7, 55.9,
56.2, 66.4, 67.3, 69.8, 72.7, 72.9, 73.0, 73.2, 74.2, 74.8, 76.4, 77.6,
79.2, 96.8, 109.2, 113.6, 127.2, 127.37, 127.45, 128.2, 129.2,
130.3, 138.5, 138.9, 159.0, 210.5; FT-IR (film, NaCl) 1039.5,
1612.4, 1718.3 cm-1; [R]20 -10.1 (c 1.1, CHCl3); MS, m/z
D
(ESI), 1228 [M þ Na]þ.
The TES protected product from above (360 mg, 0.3 mmol)
was dissolved in CH2Cl2 (60 mL), and pH 7 buffer (12 mL) was
added. DDQ (136 mg, 0.6 mmol) was added while the mixture
was vigorously stirred. The mixture was stirred for 4 h before
another portion of DDQ (136 mg, 0.6 mmol) and pH 7 buffer
(12 mL) was added. The mixture was further stirred for 4 h.
Then, a saturated aqueous NaHCO3 solution was added, the
aqueous layer was extracted with CH2Cl2 (3 ꢀ 50 mL), and the
combined extracts were washed with saturated NaHCO3 solu-
tion and brine and dried over anhydrous Na2SO4. The solvent
was evaporated under vacuum, and the residue was purified by
column chromatography on silica gel (hexanes/ethyl acetate 2/1)
to afford the primary alcohol 15 (240 mg, 74% yield) as a
colorless oil: 1H NMR (400 MHz, CDCl3) δ 0.10 (s, 3H), 0.11
(s, 3H), 0.58 (q, J = 7.9 Hz, 6H), 0.70 (q, J = 7.9 Hz, 6H), 0.84
(t, J = 7.4 Hz, 3H), 0.91 (s, 9 H), 1.01 (t, J = 7.9 Hz, 9H), 1.11
(s, 3H), 1.15 (S, 3H), 1.27-1.41 (m, 3H), 1.32 (s, 3H), 1.51
(s, 3H), 1.53-1.65 (m, 2H), 1.69 (s, 3H), 1.75 (m, 2H), 2.02
(m, 1H), 2.59 (m, 1H), 3.17 (m,1H), 3.24 (s, 3H), 3.31 (dd, J =
16.0, 5.6 Hz, 1H), 3.38 (dd, J = 9.3, 5.6 Hz, 1H), 3.41 (s, 3H),
3.43 (s, 3H), 3.49 (m, 1H), 3.65 (m, 2H), 3.75 (m, 2H), 3.97 (m,
1H), 4.09 (d, J = 9.3 Hz, 1H), 4.49 (m, 1H), 4.50 (s, 2H), 4.60
(dd, J = 8.0, 4.7 Hz, 1H), 4.64 (d, J = 6.8 Hz, 1H), 4.68 (d, J =
7.9 Hz, 2H), 4.73 (d, J = 6.8 Hz, 1H), 4.98 (d, J = 10.2 Hz, 1H),
5.12 (d, J = 6.7 Hz, 1H), 7.28 (m, 5H); 13C NMR (125 MHz,
CDCl3) δ -4.9, -4.3, 4.8, 5.5, 6.9, 7.0, 11.4, 17.88, 17.93, 19.7,
21.6, 25.2, 25.5, 25.7, 27.7, 38.4, 39.0, 39.1, 39.5, 39.8, 52.7, 52.8,
1082.5, 1249.4, 1379.1, 1463.4, 1514.0, 1613.3, 1715.8 cm-1
;
[R]20 -7.7 (c 1.37, CHCl3); MS, m/z (MALDI), 1113 [M þ
D
Na]þ.
Primary Alcohol 15: To the alcohol 3 (435 mg, 0.4 mmol)
dissolved in CH2Cl2 (8 mL) were added anhydrous pyridine
(0.32 mL, 4 mmol) and triethylsilyl trifluoromethanesulfonate
(0.18 mL, 0.8 mmol) sequentially at 0 ꢀC. The mixture was
stirred at 0 ꢀC for 2 h and quenched with a saturated NaHCO3
solution. The aqueous layer was extracted with CH2Cl2 (3 ꢀ
10 mL). The combined organic extracts were washed with
brine and dried over anhydrous Na2SO4. The solvent was
evaporated under vacuum, and the residue was purified by flash
8
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Singh et al.
JOCFeatured Article
127.5, 128.2, 130.7, 133.8, 139.0, 169.2, 215.5; FT-IR (film,
55.8, 55.9, 62.1, 66.2, 67.1, 73.0, 73.2, 74.1, 74.4, 75.4, 80.5, 82.4,
97.1, 97.6, 108.7, 127.3, 127.5, 127.6, 128.2, 138.5, 138.6, 209.2;
FT-IR (film, NaCl) 1037.5, 1082.4, 1249.1, 1379.4, 1462.8,
1716.7 cm-1; [R]20D -3.5 (c 1.02, CHCl3); MS, m/z (MALDI),
1108 [M þ Na]þ.
NaCl) 1024.8, 1102.2, 1257.9, 1378.4, 1456.7, 1733.0 cm-1
;
[R]20D -12 (c, 0.8, CHCl3); HRMS (ESI) [M þ Na]þ calcd for
C45H76O13SiNa 875.4953, found 875.4951.
Peloruside B (2): To the macrolactone 16 (64.7 mg, 0.08 mmol)
dissolved in THF (0.5 mL) in a small plastic vial was added
Macrolactone 16: To the primary alcohol 15 from above (245 mg,
0.226 mmol) dissolved in CH2Cl2 (12 mL) were added NaHCO3
(38 mg, 0.45 mmol) and Dess-Martin periodinane (144 mg,
0.34 mmol). The mixture was stirred at 23 ꢀC for 1 h and quenched
with a saturated aqueous NaHCO3 solution (10 mL) and a saturated
aqueous sodium thiosulfate solution (10 mL). The mixture was
stirred until the two layers became clear. The aqueous layer was
extracted with CH2Cl2 (3 ꢀ 10 mL), and the combined extracts were
washed with brine and dried over anhydrous Na2SO4. The solvent
was evaporated under vacuum, and the crude aldehyde was used for
the next step without purification.
HF Py complex (HF Py/Py/THF = 1:2:4, 2 mL) at 0 ꢀC. The
3
3
mixture was allowed to warm to 23 ꢀC and stirred overnight.
Then, THF (10 mL) was added and the solution was cooled to
0 ꢀC. The diluted solution was added to a chilled saturated
NaHCO3 solution dropwise. The aqueous layer was extracted
with ethyl acetate (3 ꢀ 15 mL). The combined extracts were
washed with brine and dried over anhydrous Na2SO4. The
solvent was evaporated under vacuum, and the crude product
was purified by flash column chromatography on silica gel
(hexanes/ethyl acetate 8/2 to 3/2 to 1/1 to 2/8) to afford hemiketal
17a (41.2 mg) and a hydroxyl ketone 17b (7 mg, total 48.2 mg,
86% yield).
The crude aldehyde from above was dissolved in t-BuOH
(8 mL) and H2O (2 mL). To this solution were added 2-methyl-2-
butene (2 mL) followed by sodium chlorite (213 mg) and sodium
phosphate monobasic monohydrate (213 mg) in H2O (2.2 mL)
dropwise. The mixture was stirred at 23 ꢀC for 25 min. Then,
ethyl acetate was added, and the organic layer was washed with
brine and dried over anhydrous Na2SO4. The solvent was
removed under vacuum. The crude acid was passed through a
short column to afford the crude acid (219 mg, 88% yield, over
two steps).
The hemiketal 17a (31 mg, 0.042 mmol) was dissolved in
acetic acid (8/2 v/v, 2 mL) and heated to 50 ꢀC for 3 h. After
cooling to 23 ꢀC, the solvent was removed under vacuum. The
crude product was purified by column chromatography on silica
gel (CHCl3/MeOH 95/5) to afford the diol (15.7 mg, 52% yield)
along with the recovered starting material (10 mg).
To the diol from above (15.7 mg, 0.02 mmol) dissolved in
CH2Cl2 (6 mL) were added molecular sieves (400 mg), 2,6-di-
tert-butylpyridine (100 μL, 0.45 mmol), and Me3OþBF4
-
To the acid from above dissolved in THF (15 mL) was added
10% HF Py in THF solution (1 mL of HF Py complex
(33.3 mg, 0.22 mmol) at -5 ꢀC. The mixture was stirred at
-5 ꢀC for 18 h. The molecular sieves were filtered and washed
with CH2Cl2. The filtrate was washed with saturated NaHCO3
solution and brine and dried over anhydrous Na2SO4. The
solvent was evaporated under vacuum, and the crude product
was purified by flash column chromatography on silica gel
(CHCl3/MeOH 98/2) to afford the crude monomethylated
product (6.1 mg) along with the recovered starting material
(8.7 mg).
The crude monomethylated product was dissolved in THF
(1.5 mL) and cooled to 0 ꢀC, followed by dropwise addition of 4
N HCl (1.5 mL). The solution was warmed to 23 ꢀC and stirred
at this temperature for 4 h. The solution was cooled to 0 ꢀC, and
ethyl acetate was added. Solid NaHCO3 was added to quench
the reaction until no bubbles evolved. Then anhydrous Na2SO4
was added, and the solid was filtered and washed with ethyl
acetate. The solvent was removed under vacuum, and the crude
product was purified by flash chromatography on silica gel
(CHCl3/CH3OH 95/5) to afford the tetraol (2.1 mg).
The crude product (2.1 mg) was dissolved in ethyl acetate
(1 mL) and methanol (1 mL) followed by addition of 10% Pd/C
(7 mg) and formic acid (50 μL). The mixture was stirred at 23 ꢀC
for 1 h. Then Pd/C was filtered with Celite, washed with ethyl
acetate, and concentrated under vacuum. The crude product
was purified by flash column chromatography on silica gel
(CHCl3/MeOH 93/7 to 9/1) to afford peloruside B (2) (1.3 mg,
24% yield over three steps). The synthetic peloruside B was
3
3
dissolved in 9 mL of THF, 3 mL) at 0 ꢀC. The solution was
allowed to warm to 23 ꢀC for 2 h. Then, more 10% HF Py
3
(3 mL) was added at 23 ꢀC. The mixture was kept stirring at
23 ꢀC for another 9 h. TLC evidence showed that the two TES
groups were removed. The mixture was cooled to 0 ꢀC, and 1 mL
of H2O was added. Lithium carbonate was used to quench the
reaction, and the mixture was dried over anhydrous Na2SO4.
The solid was filtered and washed with ethyl ether. The solvent
was evaporated under vacuum, and the crude product was
passed through a short silica gel column to afford the crude
acid 14 (138 mg, 80% yield) as a white solid.
To the seco-acid 14 (115 mg, 0.132 mmol) from above
dissolved in THF (4 mL) were added diisopropylethyl amine
(172 μL, 1 mmol) and 2,4,6-trichlorobenzoyl chloride (103 μL,
0.66 mmol). The mixture was stirred at 23 ꢀC for 4 h. Then most
solvent was removed under vacuum followed by addition of dry
toluene (25 mL). The mixed anhydride toluene solution was
added to the DMAP (403 mg, 3.3 mmol) solution in toluene (200 mL)
via a syringe pump over 13 h at 23 ꢀC. White precipitate was
formed during the addition. The mixture was stirred for an
additional 36 h at 23 ꢀC. Then, 0.1 N HCl was added to quench
the reaction at 0 ꢀC, the aqueous layer was extracted with ethyl
acetate, and the combined extracts were washed with saturated
NaHCO3 solution and brine and dried over Na2SO4. The
solvent was evaporated under vacuum, and the crude product
was purified by column chromatography on silica gel (hexanes/
ethyl acetate 85/15) to afford macrolactone 16 (87 mg, 77%
identical to the natural peloruside B by comparison of 1D
1
1
yield) as a colorless oil: H NMR (500 MHz, CDCl3) δ 0.09
and 2D NMR data: [R]25 = 0 (c 0.09, CH2Cl2); H NMR
D
(s, 3H), 0.10 (s, 3H), 0.86 (t, J = 7.5 Hz, 3H), 0.89 (s, 9H), 1.20
(s, 3H), 1.23-1.33 (m, 2H), 1.36 (s, 3H), 1.43 (s, 3H), 1.59
(s, 3H), 1.59-1.71 (m, 4H), 1.70 (s, 3H), 1.91 (m, 1H), 2.04
(m, 2H), 2.81 (m, 1H), 3.24 (d, J = 11.4 Hz, 1H), 3.31 (s, 3H),
3.34 (s, 3H), 3.36 (s, 3H), 3.55 (dd, J = 9.2, 4.2 Hz, 1H),
3.73-3.79 (m, 2H), 3.99 (d, J = 6.4 Hz, 1H), 4.09 (s, 1H),
4.51 (dd, J = 25.2, 12.2 Hz, 2H), 4.61-4.68 (m, 4H), 4.79 (d, J =
6.9 Hz, 1H), 4.92 (d, J = 7.3 Hz, 1H), 5.10 (d, J = 10.0 Hz, 1H),
5.89 (dd, J = 6.8, 3.1 Hz, 1H), 7.33 (m, 5H); 13C NMR (125
MHz, CDCl3) δ -5.0, -4.2, 11.7, 18.0, 18.2, 21.1, 24.9, 25.2,
25.4, 25.9, 26.7, 29.7, 35.9, 38.1, 38.2, 39.3, 41.4, 50.4, 56.2, 57.5,
65.7, 70.4, 72.8, 72.9, 73.9, 75.6, 80.2, 96.2, 97.3, 110.2, 127.2,
(600 MHz, CDCl3) δ 0.86 (t, J = 7.5 Hz, 3H, H3-20), 1.09 (s, 3H,
H3-21), 1.11 (s, 3H, H3-22), 1.17 (m, 1H, H-19a), 1.40-1.46 (m,
2H,H-12a, H-19b), 1.53 (m, 1H, H-6a), 1.72 (s, 3H, H3-23), 1.77
(ddd, J = 2.4, 5.1, 12.5 Hz, 1H, H-6b), 1.84 (m, 1H, H-4a),
1.98-2.22 (m, 3H, H-4b, H-12b, H-14a), 2.56 (m, 1H, H-18),
2.93 (br s, 1H, OH), 3.13 (br s, 1H, OH), 3.35 (m, 1H, H-24a),
3.38 (s, 3H, 7-OMe), 3.48 (s, 3H, 13-OMe), 3.63 (dd, J = 3.6,
10.8 Hz,1H, H-24b), 3.79 (ddd, J = 3.0, 5.0, 11.5 Hz, 1H, H-7),
3.97-4.01 (m, 2H, H-8, H-13), 4.15 (m, 1H, H-5), 4.41 (br s, 1H,
OH), 4.50 (br s, 1H, H-2), 4.58 (br s, 1H, H-3), 4.91 (br d, J =
10.6 Hz, 1H, H-11), 5.02 (d, J = 10.3 Hz, 1H, H-17), 5.70 (d, J =
10.6 Hz, 1H, H-15), 6.76 (br s, 1H, 2-OH); 13C NMR (150 MHz,
J. Org. Chem. Vol. 75, No. 1, 2010
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Singh et al.
JOCFeatured Article
CDCl3) δ 12.4 (C-20), 15.8 (C-21), 17.8 (C-23), 21.0 (C-22), 24.7
(C-19), 31.6 (C-6), 33.9 (C-12), 35.7 (C-14), 38.6 (C-4), 43.6 (C-
18), 43.8 (C-10), 55.8 (C-7-OMe), 59.3 (C-13-OMe), 63.8 (C-5),
67.0 (C-8), 67.1 (C-24), 69.91 (C-2), 69.94 (C-3), 71.8 (C-15),
74.0 (C-11), 76.1 (C-7), 78.1 (C-13), 102.1 (C-9), 131.0 (C-17),
136.9 (C-16), 174.7 (C-1); see Supporting Information for 2D NMR
Chemistry (VUW) are acknowledged for funding (A.J.S.).
We also thank the Wellington Medical Research Foundation
and a NZ Genesis Oncology Postgraduate Scholarship
(A.C.). The authors thank Dr. John Ryan (VUW), and
Dr. John Harwood (Purdue University) for assistance with
the NMR structure analysis.
spectra; FT-IR (film, NaCl) 1084, 1462, 1736, 2850, 2919 cm-1
.
Supporting Information Available: Full experimental details
for compounds 5 and 9-12 and characterization of selected
compounds; copies of 1H and 13C NMR spectra of selected
Acknowledgment. Financial support of this work was
provided in part by the National Institutes of Health and
Purdue University. The NZ Foundation for Research,
1
compounds; comparison of H and 13C NMR spectra of syn-
Science & Technology (FRST), Cancer Society of
New Zealand and Curtis-Gordon Research Scholarship in
thetic and natural peloruside B. This material is available free of
charge via the Internet at http://pubs.acs.org.
10 J. Org. Chem. Vol. 75, No. 1, 2010