Total synthesis of (-)-apratoxin A, 34-epimer, and its oxazoline analogue

Article abstract of DOI:10.1002/asia.200800365

A concise and convergent total synthesis of the highly cytotoxic marine natural product apratoxin A is accomplished by an 18-step linear sequence. The high sensitivity of the thiazoline, bearing an adjacent β-hydroxyl group at the C35-position, results in

Full text of DOI:10.1002/asia.200800365

DOI: 10.1002/asia.200800365
Total Synthesis of (ꢀ)-Apratoxin A, 34-Epimer, and Its Oxazoline Analogue
Yoshitaka Numajiri,[a] Takashi Takahashi,*[a] and Takayuki Doi*[a, b]
Abstract: A concise and convergent
total synthesis of the highly cytotoxic
marine natural product apratoxin A is
accomplished by an 18-step linear se-
quence. The high sensitivity of the thia-
zoline, bearing an adjacent b-hydroxyl
group at the C35-position, results in
the assembly process requiring the in-
clusion of appropriate protecting
groups and the careful optimization of
all individual transformations. In the
synthesis of 3,7-dihydroxy-2,5,8,8-tetra-
methylnonanoic acid (Dtena), the
three reagent-controlled asymmetric
reactions enables us to introduce four
chiral carbon centers in a dihydroxylat-
ed fatty acid moiety. Formation of the
hindered ester and sterically-unfavora-
ble N-methylamide bonds were suc-
cessfully demonstrated. The thiazoline
in apratoxin A was constructed by
Tf2O and Ph3PO-mediated dehydrative
cyclization, and final macrocyclization
was achieved between N-methylisoleu-
cine and proline residues. Moreover,
an oxazoline analogue and
a C34
epimer of apratoxin A have also been
elaborated in a similar approach. This
synthetic route would enable assembly
of other analogues differing in stereo-
centers of Dtena and their amino acids.
Keywords: apratoxin
A
·
cyclic
depsipeptide · natural products ·
thiazoline · total synthesis
Introduction
Luesch et al. recently revealed the mode of action of 1
through a functional genomics approach.[5] According to the
report, its biological activity is developed through the induc-
tion of G1 cell cycle arrest and an apoptotic cascade, which
is at least partially initiated through antagonism of FGF sig-
naling by STAT3. For further biological evaluation and iden-
tification of the molecular target or signal cascade, a chemi-
cal–biological approach using a labelled compound could
also be effective. Having described the design and solid-
phase synthesis[6] of effective fluorescent-labelled aerugino-
sin derivatives based on the information from structure–ac-
tivity relationships, we became interested in the efficient
synthesis of apratoxin A analogues. Apratoxin A is a 25-
membered cyclic depsipeptide consisting of proline, three
methylated amino acids (N-methylisoleucine, N-methylala-
nine, O-methyltyrosine), a,b-unsaturated modified cysteine
residue (moCys), and dihydroxylated fatty acid moiety, 3,7-
Marine cyanobacteria are emerging as a valuable source of
natural products possessing interesting molecular architec-
tures and biological properties.[1] Among these metabolites
are the fascinating family of cyclic peptides and depsipepti-
des, which offer unique scaffolds and nonribosomal amino
acids.[2] Although novel structure and unusual amino acid
units attract considerable interest for organic chemists, they
often complicate structural determination and chemical syn-
thesis.[3]
Apratoxin A (1), isolated from the marine cyanobacteri-
um Lyngbya majuscula, exhibits potent cytotoxic activity.[4]
The unique structural features of 1 are accompanied by high
levels of cytotoxicity against KB and LoVo cancer cells, with
in vitro IC50 values of 0.52 nm and 0.36 nm, respectively.
[a] Y. Numajiri, Prof. Dr. T. Takahashi, Prof. Dr. T. Doi
Department of Applied Chemistry
dihydroxy-2,5,8,8-tetramethylnonanoic
acid
(Dtena)
(Figure 1). The total synthesis of 1 has been achieved by
three groups, including ours.[7–9] The formation of the thiazo-
line ring is a crucial step in this synthesis. The stereogenic
center at C34 has a risk of epimerization,[10] furthermore the
hydroxyl group at C35 is sensitive toward acid-induced de-
hydration leading to (E)-34,35-dehydroapratoxin A (3).[11]
Forsyth and Chen prepared a thiazoline moiety using a
unique intramolecular Staudinger reduction-aza-Wittig pro-
cess of an a-azido thioester.[7] We recently disclosed the
total synthesis of apratoxin A through Ph3PO/Tf2O-mediat-
Tokyo Institute of Technology
2-12-1 Ookayama, Meguro, Tokyo 152-8552 (Japan)
E-mail: ttaka@apc.titech.ac.jp
[b] Prof. Dr. T. Doi
Graduate School of Pharmaceutical Sciences
Tohoku University
Aza-Aoba, Aramaki, Aoba, Sendai 980-8578 (Japan)
Fax : (+81)22-795-6864
E-mail: doi_taka@mail.pharm.tohoku.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.200800365.
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FULL PAPERS
Figure 1. Structures of apratoxin A and its analogues.
ed thiazoline formation.[8] A similar approach of the thiazo-
line formation has been independently reported by Ma
et al.[9] They also reported the synthesis of its oxazoline ana-
logue 2[12] and their biological evaluation in consideration of
facile preparation of oxazolines compared with thiazolines.[9]
In this paper, the details of an improved synthesis of the
fatty acid moiety and a challenging approach to thiazoline
formation towards the total synthesis of apratoxin A (1) and
its oxazoline analogue 2 are described.
Results and Discussion
Retro Synthetic Analysis
Our synthetic strategy is illustrated in Scheme 1. Apratoxin
A (1) can be synthesized by the coupling of 4 with tripeptide
5, followed by macrolactamization between the proline
amine and the N-methylisoleucine carboxylic acid. We se-
lected this precursor to avoid the predictable side reactions,
such as diketopiperadine formation, which are observed
with other precursors for macrolactamization. The thiazoline
formation of 4 is a crucial step as the thiazoline ring is labile
for acid hydrolysis, and there is a risk of epimerization at
the chiral center attached to the 2-position. We planned
thiazoline formation by both routes A and B. In route A,
nucleophilic attack of the cysteine thiol group on the amide
carbonyl group of the residue, followed by dehydration, in-
duces a thiazoline ring. In route B, in contrast, the side
chain is transformed into an electrophile, which is attacked
by the thioamide group of the residue. Both of the thiazo-
Scheme 1. Retrosynthetic analysis of apratoxin A
line precursors can be prepared from 6 (moCys or moSer
residue) with the Dtena moiety 7.
Stereoselective Syntheses of Dtena 20a and C34-epimer 20b
The synthesis of the Dtena 20a was carried out by three
asymmetric reactions for the construction of four chiral cen-
ters (Schemes 2 and 3 and Table 1). First, isomerization of
allylic alcohol 9[8] prepared by 2-step conversion from pro-
line-catalyzed aldol product 8[13] was conducted (Scheme 2).
Rhenium-catalyzed isomerisation[14] of 9 and in situ silyla-
tion of the less-hindered primary alcohol with N,O-bis(tri-
methylsilyl)acetamide (BSA), followed by one-pot removal
of the TMS group, afforded primary allylic alcohols 10a and
10b in 42% and 44% yields, respectively. The E geometry
of the alkene (C36=C37) in 10a was confirmed by the NOE
observation between the proton of the vinylic methyl group
and Ha (Scheme 2). Both isomers were independently used
for the next asymmetric hydrogenation after separation by
column chromatography.
Abstract in Japanese:
Asymmetric hydrogenation[15] of allylic alcohol 10 was
performed to introduce the chiral center at C37 (Table 1).
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Total Synthesis of (ꢀ)-Apratoxin A
yield (>95% ds) (Table 1, Entry 1). (Z)-10b was also con-
verted into 12a in quantitative yield (90% ds) under similar
conditions. Here, RuACHTNUGTRNEUNG(OAc)2[(R)-binap] (11b) was used as a
catalyst (entry 2). The appropriate combination of geome-
tries of the alkene and chirality of the catalysts enabled the
control of the stereogenic center at the C37-position with
(R)-configuration. Furthermore, the diastereomer 12b that
has (S)-configuration at the C37-position was provided from
10a by using catalyst 11b, and from 10b with catalyst 11a in
a similar manner without any affect from the C39 stereogen-
ic center (entries 3 and 4). Therefore, 37-epi apratoxin A
can be also prepared from 12b.
Scheme 2. Preparation of allylic alcohol (E)-10a and (Z)-10b. Reagents
and conditions: a) Ph3SiOReO3, BSA, ether, 08C; b) Et3N, K2CO3,
MeOH, 42% (for 10a) and 44% (for 1b). MPM=4-methoxyphenyl-
methyl, BSA=N,O-bis(trimethylsilyl)acetamide.
Swern oxidation of primary alcohol 12a gave aldehyde 13
in 96% yield according to
a
reported procedure
(Scheme 3).[8] To confirm the stereochemistry at the C37-po-
sition, 13 was converted into lactone 14, which was in good
accordance with that reported previously.[7,12] NOE observa-
tion in 14 also confirmed (R)-configuration at C37. In our
advanced synthesis, Roushꢁs crotylation[16] was utilized for
the preparation of Dtena 20a, and the produced olefin was
used as a masked carboxylic acid. Crotylation of aldehyde
13 with (E)-crotylborate 15a afforded 16a in 95% yield
(>95% ds).[17] Protection of the free hydroxy group with a
Troc group, removal of the MPM group, and esterification
with Fmoc-protected proline by the Yamaguchi method[18]
provided prolyl ester 18a in 92% overall yield. Ozonolysis
of 18a failed, thus we employed a modified oxidation of the
double bond utilizing the OsO4/oxone system[19] followed by
a one-pot treatment with NaIO4 to obtain 20a in 79% yield.
In this reaction, partially-produced b-hydroxy ketone 19 was
also converted into the desired carboxylic acid 20a by treat-
ment with NaIO4.
Table 1. Asymmetric hydrogenation of allylic alcohols 10a and 10b.
binap=2,2’-bis(diphenylphosphino)-1,1’-binaphthyl.
Entry
Substrate
Catalyst
Yield [%]
12a:12b
1
2
3
4
10a
10b
10a
10b
11a
11b
11b
11a
quant.
quant.
quant.
quant.
>95:5
90:10
5:>95
10:90
Ru
(OAc)2[(S)-binap] (11a) (2 mol%)-catalyzed asymmetric
We confirmed the configuration at the C34-position after
construction of the thiazoline ring because it has been re-
ported that the a-position of thiazolines easily isomerizes
hydrogenation of (E)-10a was carried out at 508C for 48 h
under 100 atm of hydrogen to afford 12a in quantitative
Scheme 3. Preparation of the carboxylic acid 20a. Reagents and conditions: a) NaClO2, 2-methyl-2-butene, NaH2PO4 aq., tBuOH, 08C; b) TFA, CH2Cl2,
56% in 2 steps; c) (E)-15a, MS 4ꢂ, toluene, ꢀ788C, 95% (>95% ds); d) TrocCl, DMAP, pyridine, CH2Cl2, 08C, quant.; e) DDQ, H2O, CH2Cl2;
f) FmocPro-OH, C6H2Cl3COCl, DIEA, DMAP, toluene, 92% in 2 steps; g) OsO4, oxone, NaHCO3, DMF then NaIO4, H2O, tBuOH, 79%. TFA=tri-
fluoroacetic acid, Troc=2,2,2-trichloroethoxycarbonyl, DMAP=4-(dimethylamino)pyridine, DDQ=2,3-dichloro-4,5-dicyanobenzoquinone, Fmoc=9-flu-
orenylmethoxycarbonyl.
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113

Y. Numajiri, T. Takahashi, and T. Doi.
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under relatively mild conditions.[10,11] Therefore, we decided
to synthesize the 34-epimer to confirm that there is no epi-
merization at the C34-position during the synthesis. Addi-
tionally, we were also interested in the bioactivity of 34-epi-
apratoxin A.[20] The 34-epi carboxylic acid 20b was prepared
using the same synthetic procedure as 20a. Crotylation of al-
dehyde 13 utilizing (Z)-crotylborate 15b afforded 16b and
16c in 90% yield as
a 10:1 diastereomer mixture
(Scheme 4). Isolation of 16b was carefully achieved by silica
gel column chromatography. Further transformations for the
synthesis of carboxylic acid 20b were conducted in good
yields.
Scheme 4. Synthetic route of C34-epimer 20b. Reagents and conditions:
a) (Z)-15b, MS 4ꢂ, toluene, 90% (16b:16c=10:1); b) TrocCl, DMAP,
pyridine, CH2Cl2, quant.; c) DDQ, H2O, CH2Cl2; d) FmocPro-OH,
C6H2Cl3COCl, DIEA, DMAP, toluene, 81% in 2 steps; e) OsO4, oxone,
NaHCO3, DMF then NaIO4, H2O, tBuOH, 83%.
Synthesis of Oxazoline Analogue
Achieving rapid access to carboxylic acid 20a as a single
diastereomer, we attempted the elongation of peptide seg-
ments in the course of the synthesis of oxazoline analogue 2
for estimation of a site for macrolactamization (Schemes 5
and 6). Furthermore, we initially planned the thiazoline for-
mation by conversion of the corresponding oxazoline deriva-
tive as reported by Wipf et al. in the synthesis of lissoclin-
d-serine in 3 steps (Scheme 5). Reduction of methyl ester 21
by DIBAL-H and treatment of the resulting aldehyde with
22 provided a,b-unsaturated ethyl ester 23 as a single
isomer. Saponification afforded carboxylic acid 24. For the
preparation of tetrapeptide 31, a convergent strategy using
amides.[21] Boc-d-Ser
ACTHNUTRGNEU(GN O-TBS)-OMe (21) was prepared from
Scheme 5. Preparation of the tetrapeptide 31. Reagents and conditions: a) DIBAL-H, toluene, ꢀ788C; b) 22, toluene, 82% in 2 steps; c) LiOH, H2O,
THF, tBuOH, 85%; d) 25, EDCI/HCl, HOBt, CH2Cl2, 82% (based on 24); e) LiOH, THF, H2O, 79%; f) HCl (4m)/EtOAc; g) 29, HATU, DIEA,
CH2Cl2, quant; h) HCl (4m)/EtOAc; i) 27, HATU, DIEA, CH2Cl2, 21%; j) HCl (4m)/EtOAc; k) 33, HATU, DIEA, CH2Cl2, 79%; l) Et2NH, CH3CN;
m) 24, HATU, DIEA, CH2Cl2, 92%. Boc=tert-butoxycarbonyl, DIBAL-H=diisobutylaluminium hydride, EDCI=1-[3-(dimethylamino)propyl]-3-ethyl-
carbodiimide, HOBt=1-hydroxybenzotriazole, HATU=7-azabenzotriazole-1-yl-1,1,3,3-tetramethyluronium hexafluorophosphate.
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Total Synthesis of (ꢀ)-Apratoxin A
dipeptides 27 and 30 was initially conducted. Coupling of
carboxylic acid 24 with amine 25 under EDCI/HOBt condi-
tions afforded dipeptide segment 26 in 82% yield. Then, hy-
drolysis of 26 provided 27. HATU mediated coupling[22] of
Boc-MeAla-OH (29) with HCl·MeIle-OAllyl afforded di-
peptide 30. Despite several efforts for condensation of 27
and 30, tetrapeptide 31 was obtained in low yield arising
from an undesired reaction, which occurred on the activated
ester producing azalactone 32. Therefore, we employed step-
wise elongation from the C-terminal. Removal of the Boc
group in 30 and subsequent amidation of the resulting
fragmentation, and cleavage of the TBS ether with TBAF to
provide the free amino alcohol. Condensation of the result-
ing amine with carboxylic acid 35[8] followed by desilylation
of the C35 hydroxyl group in 36 afforded 37 in 93% yield
(Scheme 6). The oxazoline formation of 37 was performed
by using 3 equivalents of DAST[25] at ꢀ788C to provide 38.
Removal of the Boc group in 38 using TMSOTf/2,6-lutidine
afforded ester 39, which was converted to the carboxylic
acid by treatment with Pd0 catalyst and morpholine. Final
macrolactamization of the resulting amino acid was ach-
ieved using HATU/DIEA in 1 mm CH2Cl2 solution to pro-
vide apratoxin A oxazoline analogue 2 in 56% yield over
2 steps.[12]
amine with Fmoc-TyrACTHNUTRGNE(NUG OMe)-OH (33) provided tripeptide 34
in 79% yield. Subsequently, removal of the Fmoc group of
34 with Et2NH,[23] followed by the coupling with 24 using
HATU/DIEA furnished the tetrapeptide fragment 31 in
92% yield based on 24.
Thiazoline Formation
Treatment of tetrapeptide 31 with 4m HCl/EtOAc for the
removal of the Boc group did not give a satisfactory result.
Therefore, we employed a two-step fashion to avoid strongly
acidic conditions. This procedure involved conversion of the
Boc group into the corresponding tert-butyldimethylsilyl car-
bamate with TBSOTf/2,6-lutidine,[24] desilylative carbamate
The key challenge towards the synthesis of 1 is the construc-
tion of the 2,4-substituted thiazoline ring, which is connected
directly to the macrocycle in the presence of the b-hydroxyl
group at the C35-position. For this purpose, we investigated
two synthetic strategies. First, a modified serine-containing
moiety was chosen as a thiazoline precursor because many
kinds of thiazoline formations utilizing serine moieties have
been reported, and the hydroxyl groups in serines can be
transformed more easily compared with thiol groups in cys-
teines (Scheme 7).[26] Wipfꢁs thiolysis[21] of oxazoline 38 with
H2S/Et3N failed, resulting in complex mixtures (Scheme 7).
To solve this problem, introduction of a sulfur atom by se-
lective thiocarbonylation of amide 42 was carried out. Cou-
pling of carboxylic acid 35 with moSer 41, which is easily
prepared from 24 afforded 42 in 90% yield. Although the
attempt for thioamide formation from amide 42 using Law-
essonꢁs reagent[27] gave 43, intramolecular Michael addition
of the generated thioamide to a,b-unsaturated ester pro-
ceeded, leading to undesired thiazoline 44.[28]
In the second strategy, we employed Kellyꢁs method,[29]
which was reported as dehydrative thiazoline formation in-
volving deprotection of the S-Trt group from a protected
cysteinamide moiety. The key intermediates 46a and 46b
were prepared by coupling of amine 45[8] with 20a and 20b
(Scheme 8). In the thiazoline formation and further transfor-
mation, both intermediates of the natural isomer and its
epimer were synthesized independently, and their NMR
spectra and retention time measured in HPLC analysis were
compared for the detection of epimerization at C34. Treat-
ment of 46a with Ph3PO/Tf2O in CH2Cl2 at 08C induced
thiazoline formation. The reaction proceeded smoothly lead-
ing to desired thiazoline 47a. Since b-elimination of the O-
Troc group in 47a was observed during silica gel column
chromatography, crude 47a was immediately treated with
Zn/NH4OAc to remove the Troc group and 48a was ob-
tained in 90% yield in 2 steps. In the same manner, thiazo-
line formation of 46b, followed by removal of the Troc
group, provided 48b. HPLC analysis and comparison of
spectra data of 48a (tR =24.7 min) and 48b (tR =24.1 min)
confirmed that no epimerization was observed at C34
during the reactions. Removal of the allyl ester in 48a and
Scheme 6. Synthesis of oxazoline analogue 2. Reagents and conditions:
a) TBSOTf, 2,6-lutidine, CH2Cl2; b) TBAF, THF; c) 35, HATU, DIEA,
CH2Cl2; d) TBAF, THF, 93% in 2 steps; e) DAST, CH2Cl2, ꢀ788C, 70%;
f) TMSOTf, 2,6-lutidine, CH2Cl2; g) TBAF, THF, 93% in 2 steps; h) Pd-
ACHTUNGTRENNUNG(PPh3)4, morpholine, THF i) HATU, DIEA, CH2Cl2 (1.0 mm), 56% in
2 steps. TBAF=tetrabutylammonium fluoride, DAST=diethylaminosul-
fur trifluoride.
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Y. Numajiri, T. Takahashi, and T. Doi.
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Scheme 8. Thiazoline formation using moCys moiety 46a and 46b. Re-
agents and conditions: a) 45, EDCI·HCl, HOAt, DIEA, CH2Cl2, 08C to
RT., 81% (for 46a from 20a), and 84% (for 46b from 20b). b) Tf2O,
Ph3PO, CH2Cl2, 08C; c) Zn, NH4OAc, THF, 90% (for 48a), and 95%
(for 48b) in 2 steps; d) PdACHTNUGTRNEG(UN PPh3)4, N-methylaniline, THF, 95% (for 49a),
and 95% (for 49b). Trt=triphenylmethyl, HOAt=1-hydroxy-7-azaben-
zotiazole.
Scheme 7. Attempts to construction of thiazoline using 38 and 42. Re-
agents and conditions: a) H2S, NEt3, MeOH; b) allyl bromide, K2CO3,
DMF, 95%; c) TMSOTf, 2,6-lutidine, CH2Cl2, then MeOH; d) 35,
HATU, DIEA, CH2Cl2, 90%; e) Lawessonꢁs reagent, toluene, 808C, 1 h,
91%.
apratoxin A was provided in lower yield, probably because
it could be disadvantageous in the conformation for macro-
cyclization of 51b rather than in 51a.
48b using PdACHTUNGTRENNUNG
(PPh3)4/N-methylaniline[30] provided 49a and
49b, respectively.
Conclusions
Completion of the Syntheses of Apratoxin A and 34-epi
Analogue
In conclusion, the total synthesis of apratoxin A has been
accomplished in 18 steps (longest linear sequence form hy-
droxyketone 8) and 18% overall yield. The preparation of
the Dtena fragment was performed through a stereoselec-
tive synthetic route based on three asymmetric reactions,
which also enables the preparation of the other stereoiso-
mers under similar conditions. Thiazoline formation in 1 was
successfully accomplished from the moCys amide 46a using
Ph3PO/Tf2O. Furthermore, comparing the spectra of thiazo-
line 48a with that of 34-epi 48b, we conclude that no epime-
rization at C34, the a-position of the thiazoline ring, oc-
curred. Finally, we have demonstrated a convergent total
synthesis of apratoxin A by connection of tripeptide 34 and
thiazoline–Dtena 49a, followed by macrolactamization be-
tween N-methylisoleucine and proline residues using
HATU. Moreover, the oxazoline analogue and 34-epi apra-
49a and 34-epimer 49b were used for the further transfor-
mation (Scheme 9). After removal of the Fmoc group in 34
(Et2NH/CH3CN), coupling of the resulting amine with acids
49a and 49b provided 50a (tR =24.8 min) and 50b (tR =
24.1 min). Cleavage of the O-allyl esters mediated by Pd-
ACHTUNGTRENNUNG(PPh3)4/N-methylaniline, followed by removal of the Fmoc
groups with Et2NH/CH3CN, afforded cyclization precursors
51a and 51b. Finally, the macrolactamization of 51a and
51b was performed with HATU/DIEA at high dilution con-
ditions (1 mm). After purification by silica gel column chro-
matography, apratoxin A (1) and 34-epi apratoxin A (epi-1)
were isolated in 72% and 25% yields, respectively. The
spectral data of synthetic 1 were identical to those of the
natural product reported previously.[4] Interestingly, 34-epi
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Total Synthesis of (ꢀ)-Apratoxin A
Scheme 9. Synthesis of apratoxin A (1) and C(34)-epimer epi-1. Reagents and conditions: a) Et2NH, CH3CN; b) 49a or 49b, HATU, DIEA, CH2Cl2,
75% (for 50a), and 81% (for 50b); c) Pd
(for epi-1) in 3 steps.
ACTHGNUNERTN(UNG PPh3)4, N-methylaniline, THF d) Et2NH, CH3CN; e) HATU, DIEA, CH2Cl2 (1.0 mm), 72% (for 1), and 25%
08C for 30 min, and concentrated in vacuo. The residue was diluted with
MeOH (100 mL) and treated with K2CO3 (5.3 g, 38.4 mmol) at 08C for
1 h. The reaction mixture was filtered through a pad of Celite, concen-
trated in vacuo, and quenched with HCl (1m). The aqueous layer was ex-
tracted with diethyl ether. The combined organic layers were washed
with saturated aqueous NaHCO3, brine, dried over MgSO4, and concen-
trated in vacuo. The residue was purified by column chromatography on
silica gel (20% to 25% ethyl acetate/hexane) to give 10a (2.06 g,
7.04 mmol, 42%) and 10b (2.15 g, 7.35 mmol, 44%) as a colorless oil.
toxin A were synthesized. The information from the synthet-
ic analogues of apratoxin A should enable us to rationally
design functional analogues well-adjusted for both biological
activity and physical properties, which may be used as a new
anticancer drug or probes for identification of the molecular
target of apratoxin A.
10a: Rf =0.45 (hexane/ethyl acetate=1:1); ½aꢁ2D8 =+1.40 (c=0.990,
CHCl3); IR (neat): n˜ =3391, 2870, 1614, 1515, 1248, 1078, 1037, 822 cmꢀ1
;
Experimental Section
1H NMR (400 MHz, CDCl3): d=7.24 (d, J=8.8 Hz, 2H), 6.85 (d, J=
8.8 Hz, 2H), 5.54 (m, 1H), 4.45 (d, J=11.1 Hz, 1H), 4.42 (d, J=11.1 Hz,
1H), 4.15 (dd, J=16.1, 7.3 Hz, 1H), 4.13 (dd, J=16.1, 6.8 Hz, 1H), 3.79
(s, 3H), 3.16 (dd, J=9.3, 3.0 Hz, 1H), 2.10–2.27 (m, 2H), 1.75 (s, 3H),
0.94 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=159.0, 137.8, 131.4,
129.1, 126.0, 113.7, 85.9, 74.4, 59.5, 55.3, 41.6, 36.2, 26.5, 16.9 ppm; HRMS
(ESI-TOF): m/z (%) calcd for [C18H28O3+Na]+: 315.1931; found:
315.1930.
General Techniques
NMR spectra were recorded on a JEOL Model ECP-400 (400 MHz for
1H, 100 MHz for 13C) instrument in the indicated solvent. Chemical shifts
are reported in units parts per million (ppm) relative to the signal for in-
ternal tetramethylsilane (0.00 ppm for 1H) for solutions in CDCl3.
1H NMR spectral data are reported as follows: chloroform (7.26 ppm)
and dichloromethane (5.3 ppm). 13C NMR spectral data are reported as
chloroform-d (77.1 ppm). Multiplicities are reported by the following ab-
breviations: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br,
broad; J, coupling constants in Hertz. IR spectra were recorded on a
Perkin–Elmer Spectrum One FTIR spectrophotometer. Only the stron-
gest and/or structurally important absorption is reported as the IR data
given in cmꢀ1. Optical rotations were measured with a JASCO P-1020 po-
larimeter. All reactions were monitored by thin-layer chromatography
carried out on 0.2 mm silica gel plates (60F-254, E. Merck) with UV
light, visualized by p-anisaldehyde solution, ceric sulfate, or 10% etha-
nolic phosphomolybdic acid. Merck silica gel was used for column chro-
matography. ESI-TOF mass spectra were measured with Applied Biosys-
tems TK-3500 Biospectrometry Workstation or Waters LCT Premier XE.
HRMS (ESI-TOF) were calibrated with angiotensin I (SIGMA), brady-
kinin (SIGMA), and neurotensin (SIGMA) as an internal standard or
with leucine enkephalin (SIGMA) as an external standard. High perfor-
mance liquid chromatography (HPLC) for qualitative and quantitative
analyses, were performed on a Nihon Seimitsu Kagaku apparatus with a
Japan Analytical Industry Model R1–3H refractive detector or Waters
2695 Separation Module with Waters 2996 Photodiode Array detector.
10b: Rf =0.50 (hexane/ethyl acetate=1:1); ½aꢁ2D0 =+44.9 (c=2.44,
CHCl3); IR (neat): n˜ =3341, 2959, 2870, 1614, 1514, 1249, 1077, 1036,
822 cmꢀ1 1H NMR (400 MHz, CDCl3): d=7.24 (d, J=8.8 Hz, 2H), 6.85
;
(d, J=8.8 Hz, 2H), 5.71 (dd, J=7.8, 6.8 Hz, 1H), 4.47 (d, J=10.2 Hz,
1H), 4.42 (d, J=10.2 Hz, 1H), 4.12 (dd, J=12.2, 7.8 Hz, 1H), 3.87 (dd,
J=12.2, 6.8 Hz, 1H), 3.79 (s, 3H), 3.21 (dd, J=11.2, 2.4 Hz, 1H), 2.63
(dd, J=13.7, 11.2 Hz, 1H), 1.96 (dd, J=13.7, 2.4 Hz, 1H), 1.84 (s, 3H),
0.98 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=159.2, 138.2, 130.3,
129.4, 127.2, 113.7, 85.0, 75.2, 58.3, 55.2, 36.4, 33.4, 26.4, 23.8 ppm; HRMS
(ESI-TOF): m/z (%) calcd for [C18H28O3+Na]+: 315.1931; found:
315.1921.
12a: (3S,5S)-5-(4-methoxybenzyloxy)-3,6,6-trimethylheptan-1-ol. In a 50-
mL autoclave, containing a glass tube, was placed RuACTHNUGTRENUNG(OAc)2[(S)-binap]
(11a) (89.0 mg, 106 mmol), (E)-(S)-5-(4-methoxybenzyloxy)-3,6,6-trime-
thylhept-2-en-1-ol (10a) (1.55 g, 5.30 mmol), and degassed methanol
(10 mL). The autoclave was filled with hydrogen (100 atm) after repeated
(3 times) filling and purging of hydrogen. The reaction was carried out
under an appropriate hydrogen pressure at 508C for 24 h. The reaction
mixture was diluted with hexane. This solution was stirred with Florisil at
room temperature for 10 min, then filtered through a pad of Celite, and
the filtrate was concentrated in vacuo. The residue was purified by
column chromatography on silica gel (20% ethyl acetate in hexane) to
give 12a (1.54 g, 5.23 mmol, quant.) as a colorless oil. Rf =0.48 (hexane/
ethyl acetate=1:1); ½aꢁ2D8 =ꢀ29.3 (c=0.990, CHCl3); IR (neat): n˜ =3392,
Rhenium-Catalyzed Isomerization of Allylic Alcohol 9 to 10a and 10b
To a solution of allylic alcohol 9 (4.84 g, 16.6 mmol) and Ph3SiOReO3
(250 mg, 0.497 mmol) in diethyl ether (83 mL) was added N,O-bis(trime-
thylsilyl)acetamide (4.94 mL, 19.9 mmol) at 08C dropwise over 1 h by
using a syringe pump. After being stirred at the same temperature for
1.5 h, the reaction mixture was quenched with Et3N (1.0 mL), stirred at
2955, 1615, 1587, 1515, 1464, 1302, 1249, 1039, 821 cmꢀ1 1H NMR
;
(400 MHz, CDCl3): d=7.28 (d, J=8.2 Hz, 2H), 6.87 (d, J=8.2 Hz, 2H),
Chem. Asian J. 2009, 4, 111 – 125
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
117

Y. Numajiri, T. Takahashi, and T. Doi.
FULL PAPERS
4.54 (s, 2H), 3.80 (s, 3H), 3.72 (m, 1H), 3.62 (m, 1H), 3.10 (dd, J=6.8,
4.8 Hz, 1H), 1.72–1.83 (m, 2H), 1.39–1.42 (m, 2H), 1.29 (m, 1H), 0.95 (d,
J=6.8 Hz, 3H), 0.93 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=
159.0, 131.6, 129.1, 113.8, 85.5, 74.3, 61.2, 55.3, 39.4, 39.0, 36.2, 27.0, 26.6,
21.1 ppm; HRMS (ESI-TOF): m/z (%) calcd for [C18H30O3+Na]+:
317.2087; found: 317.2085.
HCl (1m) and the aqueous layer was extracted with ethyl acetate. The
combined organic layers were washed with saturated aqueous NaHCO3
and brine, dried over MgSO4, and concentrated in vacuo. The residue
was purified by column chromatography on silica gel (5% ethyl acetate
in hexane) to give carbonate 17a (2.26 g, 4.31 mmol, quant.) as a color-
less oil. Rf =0.75 (hexane/ethyl acetate=3/1); ½aꢁ2D4 =ꢀ34.1 (c=1.53,
CHCl3); IR (neat): n˜ =2958, 2872, 1758, 1514, 1380, 1249, 1095, 1039,
12b: (3R,5S)-5-(4-methoxybenzyloxy)-3,6,6-trimethylheptan-1-ol. Follow-
ing a similar procedure from 10a to 12a, 12b was obtained from 10a
945, 820, 734 cmꢀ1 1H NMR (400 MHz, CDCl3): d=7.28 (d, J=8.8 Hz,
;
2H), 6.85 (d, J=8.8 Hz, 2H), 5.57 (m, 1H), 5.06–5.13 (m, 2H), 4.89 (m,
1H), 4.78 (d, J=12.2 Hz, 1H), 4.58 (d, J=10.8 Hz, 1H), 4.50 (d, J=
10.8 Hz, 1H), 4.50 (d, J=12.2 Hz, 1H), 3.79 (s, 3H), 3.06 (dd, J=9.3,
2.4 Hz, 1H), 2.48 (m, 1H), 1.91 (ddd, J=14.2, 11.2, 2.4 Hz, 1H), 1.78 (m,
1H), 1.47 (ddd, J=14.2, 9.3, 3.9 Hz, 1H), 1.34 (ddd, J=14.2, 9.8, 2.4 Hz,
1H), 1.16 (ddd, J=14.2, 9.3, 2.0 Hz, 1H), 1.07 (d, J=6.8 Hz, 3H), 0.99
(d, J=6.3 Hz, 3H), 0.92 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=
159.0, 154.3, 138.9, 131.6, 129.0, 116.4, 113.8, 94.8, 85.2, 80.8, 76.6, 74.5,
55.4, 42.8, 39.8, 37.7, 36.2, 26.6, 26.4, 21.0, 15.7 ppm; HRMS (ESI-TOF):
m/z (%) calcd for [C25H37Cl3O5+Na]+: 545.1604; found: 545.1595.
using RuACHTUNGTRENNUNG(OAc)2[(R)-binap] (11b) instead of RuHCATUNGTRNEN(GUN OAc)2[(S)-binap] (11a).
Rf =0.45 (hexane/ethyl acetate=1:1); ½aꢁ1D8 =ꢀ24.8 (c=1.23, CHCl3); IR
(neat): n˜ =3394, 2955, 2871, 1514, 1249, 1077, 1038, 820 cmꢀ1 1H NMR
;
(400 MHz, CDCl3): d=7.28 (d, J=8.8 Hz, 2H), 6.87 (d, J=8.8 Hz, 2H),
4.58 (d, J=10.8 Hz, 1H), 4.51 (d, J=10.8 Hz, 1H), 3.80 (s, 3H), 3.61–3.72
(m, 2H), 3.11 (dd, J=10.2, 1.5 Hz, 1H), 1.75 (m, 1H), 1.43–1.57 (m, 3H),
1.21 (ddd, J=14.2, 10.2, 1.5 Hz, 1H), 0.95 (d, J=7.3 Hz, 3H), 0.94 ppm
(s, 9H); 13C NMR (100 MHz, CDCl3): d=159.1, 131.5, 129.2, 113.8, 85.9,
75.0, 60.9, 55.3, 41.2, 38.7, 36.2, 26.6, 26.6, 19.9 ppm.
14: (3R,5S)-5-tert-Butyl-3-methyl-d-valerolactone. To a solution of alde-
hyde 13 (58.8 mg, 0.200 mmol) in 2-methyl-2-propanol (2.0 mL) and 0.5m
NaH2PO4 (1.0 mL) was added 2-methyl-2-butene (0.3 mL) and NaClO2
(27.1 mg, 0.300 mmol) at 08C. After being stirred at the same tempera-
ture for 40 min, the reaction mixture was diluted with brine and the
aqueous layer was extracted with CHCl3. The combined organic layers
were washed with brine, dried over Na2SO4, and concentrated in vacuo.
The residue was used for the next reaction without further purification.
To a solution of the crude carboxylic acid in CH2Cl2 (4.0 mL) was added
trifluoroacetic acid (2.0 mL) at 08C. After being stirred at 08C for
20 min, the reaction mixture was concentrated in vacuo. The residue was
purified by column chromatography on silica gel (15% ethyl acetate in
hexane) to give 14 (21.7 mg, 0.112 mmol, 56% in 2 steps) as a colorless
oil. Rf =0.53 (hexane/ethyl acetate=3:2); ½aꢁ2D3 =+46.0 (c=1.49, CHCl3);
Prolyl ester 18a: To a solution of 17a (2.26 g, 4.31 mmol) in CH2Cl2
(20 mL) and H2O (2.0 mL) was added 2,3-dichloro-5,6-dicyano-benzoqui-
none (1.19 g, 5.23 mmol) at 08C. After being stirred at the same tempera-
ture for 1 h, the reaction mixture was quenched with saturated aqueous
NaHCO3, and the aqueous layer was extracted with CH2Cl2. The com-
bined organic layers were washed with brine, dried over MgSO4, and con-
centrated in vacuo. The residue was used for the next reaction without
further purification. To
a solution of N-Fmoc-l-proline (2.94 g,
8.72 mmol) in toluene (25 mL) was added N,N-diisopropylethylamine
(2.25 mL, 13.1 mmol) and 2,4,6-trichlorobenzoyl chloride (2.05 mL,
13.1 mmol) at room temperature under argon. The solution was stirred at
the same temperature for 10 min. To the resultant mixture was added a
solution of the crude alcohol in toluene (25 mL) and 4-dimethylamino-
pyridine (1.87 g, 15.3 mmol) at 108C under argon. After being stirred at
room temperature for 5 h, the reaction mixture was quenched with H2O
and the aqueous layer was extracted with diethyl ether. The combined or-
ganic layers were washed with saturated aqueous NH4Cl, saturated aque-
ous NaHCO3, brine, dried over Na2SO4, and concentrated in vacuo. The
residue was purified by column chromatography on silica gel (10% to
IR (neat): n˜ =2960, 2875, 1747, 1242, 1073, 1002 cmꢀ1
;
1H NMR
(400 MHz, CDCl3): d=3.98 (dd, J=11.7, 3.9 Hz, 1H), 2.51 (dd, J=10.2,
10.2 Hz, 1H), 2.16–2.24 (m, 2H), 1.83 (ddd, J=14.2, 11.7, 7.3 Hz, 1H),
1.51 (ddd, J=14.2, 5.0, 3.9 Hz, 1H), 1.11 (d, J=6.8 Hz, 3H), 0.97 ppm (s,
9H); 13C NMR (100 MHz, CDCl3): d=173.3, 83.8, 37.0, 34.0, 29.9, 25.5,
24.1, 21.3 ppm; HRMS (ESI-TOF): m/z (%) calcd for [C10H18O2+Na]+:
193.1199; found: 193.1196.
15% ethyl acetate in hexane) to give 18a (2.91 g, 4.02 mmol, 92% in
23
2 steps) as a colorless oil. Rf =0.60 (hexane/ethyl acetate=3:1); ½aꢁD
=
16a: (3R,4S,6S,8S)-8-(4-methoxybenzyloxy)-3,6,9,9-tetramethyldec-1-en-
4-ol. To a suspension of crotyl borane (E)-15a (5.27 mL, ca. 1.0m solution
in toluene, ca. 5.3 mmol) and molecular sieves 4 A (320 mg) in toluene
(10.6 mL) was added a solution of aldehyde 13 (617 mg, 2.11 mmol) at
ꢀ788C dropwise over 15 min. After being stirred at the same tempera-
ture for 7 h, the reaction mixture was quenched with NaOH (7.0 mL,
2m), stirred at 08C for 30 min, and filtered through a pad of Celite. The
aqueous layer was extracted with diethyl ether. The combined organic
layers were washed with HCl (1m), saturated aqueous NaHCO3, brine,
dried over MgSO4, and concentrated in vacuo. The residue was purified
by column chromatography on silica gel (5% ethyl acetate/hexane) to
give 16a (699 mg, 2.00 mmol, 95%) as colorless oil. Rf =0.68 (hexane/
ethyl acetate=3:1); ½aꢁ2D4 =ꢀ50.9 (c=1.09, CHCl3); IR (neat): n˜ =3478,
ꢀ65.7 (c=1.66, CHCl3); IR (neat): n˜ =2963, 1753, 1708, 1416, 1250,
739 cmꢀ1; H NMR (400 MHz, CDCl3, mixture of rotamers): d=7.72–7.77
1
(m, 2H), 7.57–7.64 (m, 2H), 7.38–7.42 (m, 2H), 7.29–7.33ACTHNUTRGENUG(N m, 2H), 5.65–
5.77 (m, 1H), 5.00–5.12 (m, 2H), 4.68–4.85 (m, 4H), 4.51 (dd, J=8.8,
2.9 Hz, 0.5H), 4.46 (dd, J=5.8, 2.9 Hz, 0.5H), 4.15–4.45 (m, 3H), 3.48–
3.67 (m, 2H), 2.47 (m, 0.5H), 2.41 (m, 0.5H), 2.05–2.34 (m, 2H), 1.91–
2.01 (m, 2H), 1.78–1.85 (m, 1H), 1.35–1.60 (m, 3H), 1.26 (ddd, J=14.2,
9.8, 2.4 Hz, 0.5H), 1.12 (ddd, J=14.7, 10.3, 2.0 Hz, 0.5H), 1.04 (d, J=
6.8 Hz, 1.5H), 1.02 (d, J=6.8 Hz, 1.5H), 0.95 (d, J=6.8 Hz, 1.5H), 0.88
(s, 4.5H), 0.86 (s, 4.5H), 0.74 ppm (d, J=6.4 Hz, 1.5H); 13C NMR
(100 MHz, CDCl3, mixture of rotamers): d=172.5, 172.4, 154.7, 154.4,
154.2, 154.1, 144.3, 144.0, 143.9, 141.4, 141.4, 141.3, 141.3, 138.9, 138.8,
127.8, 127.7, 127.2, 127.1, 127.1, 80.6, 80.4, 79.6, 79.4, 67.8, 67.5, 59.9, 59.5,
47.3, 47.3, 47.1, 46.5, 42.7, 42.4, 38.0, 37.8, 37.2, 37.0, 35.0, 34.8, 31.3, 30.1,
26.6, 26.5, 25.9, 24.5, 23.4, 20.4, 20.4, 15.6, 15.6 ppm; HRMS (ESI-TOF):
m/z (%) calcd for [C37H46NO7Cl3+H]+: 722.2418; found: 722.2418.
2956, 2870, 1614, 1514, 1465, 1248, 1091, 1039, 915, 821 cmꢀ1 1H NMR
;
(400 MHz, CDCl3): d=7.30 (d, J=8.8 Hz, 2H), 6.85 (d, J=8.8 Hz, 2H),
5.75 (m, 1H), 5.10–5.14 (m, 2H), 4.63 (d, J=10.8 Hz, 1H), 4.51 (d, J=
10.8 Hz, 1H), 3.79 (s, 3H), 3.50 (m, 1H), 3.11 (dd, J=9.3, 2.9 Hz, 1H),
2.17 (m, 1H), 1.96 (m, 1H), 1.57 (ddd, J=13.7, 10.7, 2.9 Hz, 1H), 1.47
(ddd, J=14.2, 8.8, 3.9 Hz, 1H), 1.35 (ddd, J=14.2, 9.3, 2.4 Hz, 1H), 1.12
(ddd, J=13.7, 9.3, 2.4 Hz, 1H), 1.03 (d, J=7.3 Hz, 3H), 0.96 (d, J=
6.8 Hz, 3H), 0.93 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=159.0,
140.7, 131.7, 129.3, 116.4, 113.7, 85.3, 74.2, 72.4, 55.3, 45.3, 40.9, 39.9, 36.2,
26.7, 26.6, 21.0, 16.3 ppm; HRMS (ESI-TOF): m/z (%) calcd for
[C22H36O3+H]+: 349.2743; found: 349.2747.
Carboxylic acid 20a: To a solution of 18a (363 mg, 502 mmol) in DMF
(5.0 mL) was added OsO4 (63 mL, 2.5 wt% solution in 2-methyl-2-propa-
nol, 5.0 mmol), oxone (1.24 g, 2.01 mmol), and NaHCO3 (169 mg,
2.01 mmol) at room temperature. After being stirred at the same temper-
ature for 12 h, the reaction mixture was diluted with H2O (3.0 mL) and
2-methyl-2-propanol (6.0 mL). To the mixture was added NaIO4 (214 mg,
1.0 mmol) at room temperature. The resulting mixture was stirred at the
same temperature for 5 h and poured into HCl (1m) and CH2Cl2. The
aqueous layer was extracted with CH2Cl2. The combined organic layers
were washed with aqueous solution of Na2S2O3 (10 wt%), brine, dried
over Na2SO4, and concentrated in vacuo. The residue was purified by
column chromatography on silica gel (40% ethyl acetate in hexane) to
give 20a (296 mg, 399 mmol, 79%) as a white amorphous solid. Rf =0.40
(hexane/ethyl acetate=1:1); ½aꢁ2D2 =ꢀ45.3 (c=0.99, CHCl3); IR (neat):
17a: (3R,4S,6S,8S)-8-(4-methoxybenzyloxy)-3,6,9,9-tetramethyldec-1-en-
4-yl 2,2,2-trichloroethyl carbonate. To
a solution of 16a (1.52 g,
4.36 mmol) and pyridine (1.06 mL, 13.1 mmol) in CH2Cl2 (20 mL) was
added 2,2,2-trichloroethoxycarbonyl chloride (0.70 mL, 5.23 mmol) and
4-dimethylaminopyridine (27 mg, 0.22 mmol) at 08C. After being stirred
at the same temperature for 1 h, the reaction mixture was quenched with
118
www.chemasianj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2009, 4, 111 – 125

Total Synthesis of (ꢀ)-Apratoxin A
n˜ =2962, 1756, 1742, 1708, 1451, 1419, 1248, 758, 740 cmꢀ1
;
1H NMR
acetate=3:1); ½aꢁ2D2 =ꢀ67.6 (c=1.41, CHCl3); IR (neat): n˜ =2963, 1754,
(400 MHz, CDCl3, mixture of rotamers): d=7.75–7.78 (m, 2H), 7.57–7.67
(m, 2H), 7.36–7.42 (m, 2H), 7.28–7.34 (m, 2H), 5.08–5.16 (m, 1H), 4.69–
4.89 (m, 3H), 4.47–4.50 (m, 1H), 4.15–4.45 (m, 3H), 3.46–3.65 (m, 2H),
2.95 (dq, J=7.3, 7.3 Hz, 0.7H), 2.87 (dq, J=7.3, 7.3 Hz, 0.3H), 2.09–2.36
(m, 2H), 1.81–2.00 (m, 3H), 1.69 (m, 0.7H), 1.49–1.58 (m, 1.3H), 1.21–
1.43 (m, 2H), 1.21 (d, J=7.3 Hz, 0.9H), 1.19 (d, J=7.3 Hz, 2.1H), 0.99
(d, J=6.8 Hz, 2.1H), 0.88 (s, 2.7H), 0.87 (s, 6.3H), 0.76 ppm (d, J=
6.4 Hz, 0.9H); 13C NMR (100 MHz, CDCl3, mixture of rotamers): d=
172.7, 172.1, 155.1, 154.4, 153.8, 153.7, 144.3, 144.1, 143.9, 143.8, 141.4,
141.4, 141.3, 141.3, 127.8, 127.1, 125.4, 125.2, 120.1, 94.7, 79.1, 76.8, 67.9,
67.7, 59.8, 59.5, 47.3, 47.1, 46.5, 43.4, 37.3, 36.7, 36.4, 35.1, 34.8, 31.4, 30.1,
26.2, 26.0, 26.0, 25.9, 24.3, 23.5, 20.4, 20.0, 12.2, 12.1 ppm; HRMS (ESI-
TOF): m/z (%) calcd for [C36H43NO9Cl3+H]+: 740.2160; found: 740.2139.
1708, 1417, 1250, 1118, 758, 740 cmꢀ1 1H NMR (400 MHz, CDCl3, mix-
;
ture of rotamers): d=7.74–7.77 (m, 2H), 7.58–7.66 (m, 2H), 7.38–7.43
(m, 2H), 7.28–7.34 (m, 2H), 5.66–5.81 (m, 1H), 5.04–5.10 (m, 2H), 4.68–
4.89 (m, 4H), 4.51 (dd, J=8.8, 2.9 Hz, 0.5H), 4.46 (dd, J=8.8, 2.9 Hz,
0.5H), 4.15–4.44 (m, 3H), 3.48–3.67 (m, 2H), 2.49 (m, 0.5H), 2.42 (m,
0.5H), 2.09–2.36 (m, 2H), 1.91–2.03 (m, 2H), 1.77–1.85 (m, 1H), 1.53–
1.64 (m, 1H), 1.36–1.51 (m, 2H), 1.31 (ddd, J=14.6, 10.2, 2.4 Hz, 0.5H),
1.18 (ddd, J=14.6, 10.2, 2.0 Hz, 0.5H), 1.04 (d, J=6.8 Hz, 1.5H), 1.02 (d,
J=6.8 Hz, 1.5H), 0.95 (d, J=6.8 Hz, 1.5H), 0.88 (s, 4.5H), 0.86 (s, 4.5H),
0.73 ppm (d, J=6.8 Hz, 1.5H); 13C NMR (100 MHz, CDCl3, mixture of
rotamers): d=172.5, 172.3, 154.7, 154.4, 154.3, 154.1, 144.3, 144.0, 143.9,
141.4, 141.4, 141.3, 141.3, 139.1, 127.8, 127.7, 127.2, 127.1, 127.1, 127.1,
125.5, 125.3, 125.3, 125.2, 120.0, 120.0, 116.2, 116.1, 94.9, 94.9, 80.8, 80.6,
79.6, 79.5, 67.8, 67.5, 59.9, 59.5, 47.3, 47.3, 47.1, 46.4, 42.5, 42.2, 38.0, 37.8,
37.7, 37.4, 35.0, 34.8, 31.3, 30.1, 26.7, 26.5, 25.9, 24.5, 23.4, 20.4, 20.3, 15.5,
15.3 ppm; HRMS (ESI-TOF): m/z (%) calcd for [C37H46NO7Cl3+H]+:
722.2418; found: 722.2421.
Syn-selective crotylation of 13. To a suspension of crotyl borane (Z)-15b
(3.53 mL, ca. 1.0m solution in toluene, ca. 3.5 mmol) and molecular
sieves 4 A (230 mg) in toluene (8.0 mL) was added a solution of aldehyde
13 (343 mg, 1.17 mmol) at ꢀ788C dropwise over 15 min. After being
stirred at the same temperature for 7 h, the reaction mixture was
quenched with NaOH (4.0 mL, 2m), stirred at 08C for 30 min, and fil-
tered through a pad of Celite. The aqueous layer was extracted with di-
ethyl ether. The combined organic layers were washed with HCl (1m), sa-
turated aqueous NaHCO3, brine, dried over MgSO4, and concentrated in
vacuo. The residue was purified by column chromatography on silica gel
(10% ethyl acetate/hexane) to give a mixture of 16b and 16c (367 mg,
1.50 mmol, 90%, dr=10:1) as colorless oil. The diastereomers were ana-
lyzed by HPLC (Senshu Pack Silica-3301-N 8ꢃ300 mm, 10% ethyl ace-
tate in hexane, 2.0 mLminꢀ1, refractive index detection, tR =28.0 min
(16b), 33.5 min (16c)).
Carboxylic acid 20b. Following a similar procedure from 18a to 20a, 20b
was obtained from 18b in 83% yield. Rf =0.40 (hexane/ethyl acetate=
1:1); ½aꢁ2D2 =ꢀ49.7 (c=1.01, CHCl3); IR (neat): n˜ =2957, 1752, 1741, 1707,
1420, 1249, 1183, 1121, 823 cmꢀ1 1H NMR (400 MHz, CDCl3, mixture of
;
rotamers): d=7.75–7.77 (m, 2H), 7.60–7.66 (m, 2H), 7.38–7.42 (m, 2H),
7.29–7.33 (m, 2H), 5.03–5.10 (m, 1H), 4.88 (dd, J=11.2, 2.0 Hz, 0.7H),
4.88 (d, J=12.2 Hz, 0.3H), 4.79 (m, 0.3H), 4.78 (s, 1.4H), 4.70 (d, J=
12.2 Hz, 0.3H), 4.60 (dd, J=7.3, 3.4 Hz, 0.7H), 4.49 (dd, J=8.8, 3.4 Hz,
0.3H), 4.15–4.49 (m, 3H), 3.45–3.67 (m, 2H), 2.79 (dq, J=8.3, 6.8 Hz,
0.7H), 2.71 (dq, J=7.4, 6.8 Hz, 0.3H), 2.10–2.34 (m, 2H), 1.86–2.02 (m,
3H), 1.77 (m, 0.7H), 1.59 (ddd, J=14.6, 11.2, 3.9 Hz, 0.7H), 1.52 (m,
0.3H), 1.11–1.49 (m, 2.3H), 1.26 (d, J=6.8 Hz, 2.1H), 1.24 (d, J=6.8 Hz,
0.9H), 1.00 (d, J=6.8 Hz, 2.1H), 0.88 (s, 2.7H), 0.87 (s, 6.3H), 0.75 ppm
(d, J=6.8 Hz, 0.9H); 13C NMR (100 MHz, CDCl3, mixture of rotamers):
d=177.3, 176.0, 172.8, 171.6, 155.4, 154.4, 154.1, 153.9, 144.3, 144.2, 143.8,
141.4, 141.4, 141.3, 127.8, 127.2, 127.1, 125.5, 125.3, 125.3, 125.2, 120.1,
94.8, 79.8, 79.1, 79.0, 77.8, 68.0, 67.9, 59.7, 59.5, 47.3, 47.2, 47.1, 46.5, 44.1,
43.6, 38.9, 37.9, 37.7, 37.4, 35.3, 34.8, 31.3, 29.9, 29.8, 26.5, 26.1, 25.9, 25.8,
24.2 ppm; HRMS (ESI-TOF): m/z (%) calcd for [C36H43NO9Cl3+H]+:
740.2160; found: 740.2156.
16b: Rf =0.66 (hexane/ethyl acetate=3:1); ½aꢁ2D1 =ꢀ65.3 (c=1.18,
CHCl3); IR (neat): n˜ =3471, 2956, 2870, 1613, 1514, 1248, 1089, 1038,
820 cmꢀ1 1H NMR (400 MHz, CDCl3): d=7.30 (d, J=8.3 Hz, 2H), 6.86
;
(d, J=8.3 Hz, 2H), 5.79 (m, 1H), 5.11 (dd, J=4.4, 1.0 Hz, 1H), 5.07 (brs,
1H), 4.61 (d, J=10.2 Hz, 1H), 4.51 (d, J=10.2 Hz, 1H), 3.76 (s, 3H),
3.60 (m, 1H), 3.10 (dd, J=8.8, 2.4 Hz, 1H), 2.24 (m, 1H), 1.92 (m, 1H),
1.55 (ddd, J=14.2, 7.8, 2.9 Hz, 1H), 1.47 (ddd, J=14.6, 8.8, 4.4 Hz, 1H),
1.35 (ddd, J=14.6, 9.3, 2.4 Hz, 1H), 1.11 (ddd, J=14.2, 10.7, 2.0 Hz, 1H)
1.04 (d, J=6.8 Hz, 3H), 0.96 (d, J=6.8 Hz, 3H), 0.93 ppm (s, 9H);
13C NMR (100 MHz, CDCl3): d=159.0, 141.0, 131.7, 129.2, 115.4, 113.8,
85.3, 74.2, 72.5, 55.4, 44.6, 40.6, 39.8, 36.2, 26.8, 26.6, 21.0, 14.8 ppm;
HRMS (ESI-TOF): m/z (%) calcd for [C22H36O3+H]+: 349.2743; found:
349.2727.
16c: Rf =0.66 (hexane/ethyl acetate=3:1); ½aꢁ2D5 =ꢀ15 (c=0.050, CHCl3);
1H NMR (400 MHz, CDCl3): d=7.29 (d, J=8.8 Hz, 2H), 6.87 (d, J=
8.8 Hz, 2H), 5.82 (m, 1H), 5.12 (m, 1H), 5.08 (m, 1H), 4.55 (d, J=
11.2 Hz, 1H), 4.49 (d, J=11.2 Hz, 1H), 3.80 (s, 3H), 3.65 (m, 1H), 3.08
(dd, J=7.8, 3.4 Hz, 1H), 2.26 (m, 1H), 1.75 (m, 1H), 1.52–1.61 (m, 2H),
1.32 (ddd, J=14.6, 7.8, 5.9 Hz, 1H), 1.23 (m, 1H), 1.02 (d, J=6.3 Hz,
3H), 1.02 (d, J=6.8 Hz, 3H), 0.93 ppm (s, 9H); 13C NMR (100 MHz,
CDCl3): d=159.0, 141.3, 131.6, 128.9, 115.5, 113.8, 86.2, 73.8, 73.0, 55.4,
43.2, 41.3, 39.1, 36.4, 28.4, 26.6, 22.2, 13.6 ppm.
21: (R)-2-N-tert-Butoxycarbonylamino-3-(tert-butyldimethylsilyloxy)pro-
pionic acid methyl ester. To
a solution of Boc-Ser-OMe (6.94 g,
31.7 mmol) and imidazole (4.36 g, 63.4 mmol) in CH2Cl2 (120 mL) was
added tert-butyldimethylsilyl chloride (6.21 g, 41.2 mmol) at 08C. After
being stirred at room temperature for 1.5 h, the reaction mixture was
quenched with methanol, then partitioned between H2O and ethyl ace-
tate. The aqueous layer was extracted with ethyl acetate. The combined
organic layers were washed with saturated aqueous NH4Cl, saturated
aqueous NaHCO3, brine, dried over MgSO4, and concentrated in vacuo.
The residue was purified by column chromatography on silica gel (7%
ethyl acetate in hexane) to give silyl ether 21 (10.0 g, 30.1 mmol, 95%) as
a colorless oil. Rf =0.60 (hexane/ethyl acetate=3:1); ½aꢁ2D3 =ꢀ19.2 (c=
1.34, CHCl3); IR (neat): n˜ =3452, 2956, 2887, 1750, 1723, 1505, 1367,
1351, 1115, 836, 779 cmꢀ1 1H NMR (400 MHz, CDCl3): d=5.34 (d, J=
;
Carbonate 17b. Following a similar procedure from 16a to 17a, 17b was
obtained from 16b in quantitative yield. Rf =0.75 (hexane/ethyl acetate=
3:1); ½aꢁ2D2 =ꢀ33.4 (c=1.15, CHCl3); IR (neat): n˜ =2958, 1758, 1514, 1380,
8.7 Hz, 1H), 4.35 (m, 1H), 4.04 (dd , J=9.7, 2.4 Hz, 1H), 3.82 (dd, J=
9.7, 2.7 Hz, 1H), 3.74 (s, 3H), 1.46 (s, 9H), 0.86 (s, 9H), 0.03 (s, 3H),
0.02 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=171.3, 155.5, 79.9,
63.9, 55.7, 52.3, 28.4, 25.8, 18.2, ꢀ5.5, ꢀ5.6 ppm; HRMS (ESI-TOF): m/z
(%) calcd for [C15H31NO5Si+H]+:334.2050; found: 334.2050.
1
1249, 1038, 820 cmꢀ1; H NMR (400 MHz, CDCl3): d=7.28 (d, J=8.8 Hz,
2H), 6.85 (d, J=8.8 Hz, 2H), 5.77 (m, 1H), 5.08–5.13 (m, 2H), 4.86 (ddd,
J=11.2, 10.3, 2.0 Hz, 1H), 4.81 (d, J=12.2 Hz, 1H), 4.58 (d, J=10.7 Hz,
1H), 4.50 (d, J=10.7 Hz, 1H), 4.47 (d, J=12.2 Hz, 1H), 3.79 (s, 3H),
3.06 (dd, J=9.3, 2.4 Hz, 1H), 2.50 (m, 1H), 1.88 (ddd, J=14.6, 11.2,
2.4 Hz, 1H), 1.78 (m, 1H), 1.47 (ddd, J=14.6, 9.3, 3.9 Hz, 1H), 1.34 (ddd,
J=14.6, 9.8, 2.4 Hz, 1H), 1.23 (ddd, J=14.6, 10.3, 2.0 Hz, 1H), 1.08 (d,
J=6.8 Hz, 3H), 0.99 (d, J=6.4 Hz, 3H), 0.92 ppm (s, 9H); 13C NMR
(100 MHz, CDCl3): d=159.0, 154.4, 139.1, 131.6, 128.9, 116.2, 113.8, 94.8,
85.2, 81.1, 76.6, 74.5, 55.4, 42.5, 39.8, 38.0, 36.2, 26.6, 26.4, 20.9, 15.6 ppm;
HRMS (ESI-TOF): m/z (%) calcd for [C25H37Cl3O5+Na]+: 545.1604;
found: 545.1613.
23: (E)-(S)-4-N-tert-Butoxycarbonylamino-5-(tert-butyldimethylsilyloxy)-
2-methylpent-2-enoic acid ethyl ester. To
a solution of 21 (3.86 g,
11.6 mmol) in toluene (60 mL) was added dropwise DIBAL-H (25.5 mL,
1.0m in toluene, 25.5 mmol) at ꢀ788C over 15 min under argon. After
being stirred at the same temperature for 15 min, the reaction mixture
was poured into aqueous potassium sodium tartrate (10%) at 08C,
stirred at room temperature for 1 h, and the aqueous layer was extracted
with diethyl ether. The combined organic layers were washed with brine,
dried over Na2SO4, and concentrated in vacuo. The residue was used for
the next reaction without further purification. To a solution of the crude
aldehyde in toluene (60 mL) was added (carbethoxyethylidene) triphe-
Prolyl ester 18b. Following a similar procedure from 17a to 18a, 18b
was obtained from 17b in 81% yield over 2 steps. Rf =0.62 (hexane/ethyl
Chem. Asian J. 2009, 4, 111 – 125
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
119

Y. Numajiri, T. Takahashi, and T. Doi.
FULL PAPERS
nylphosphorane (22) (5.45 g, 14.7 mmol) at 08C under argon. After being
at room temperature for 3 h, the reaction mixture was concentrated in
vacuo. The residue was purified by column chromatography on silica gel
1H NMR (400 MHz, CDCl3): d=7.07 (d, J=8.7 Hz, 2H), 6.81 (d, J=
8.7 Hz, 2H), 6.18–6.28 (m, 2H), 4.94 (m, 1H), 4.83 (m, 1H), 4.40 (m,
1H), 3.76 (s, 3H), 3.55–3.64 (m, 2H), 3.19 (dd, J=14.0, 5.8 Hz, 1H), 3.08
(dd, J=14.0, 5.8 Hz, 1H), 1.87 (brs, 3H), 1.44 (s, 9H), 0.87 (s, 9H),
0.04 ppm (s, 6H); 13C NMR (100 MHz, CDCl3): d=174.7, 168.8, 158.8,
134.5, 132.7, 130.5, 127.9, 114.1, 80.6, 64.9, 55.2, 53.7, 50.6, 36.5, 28.5, 25.9,
18.3, 13.3, ꢀ5.4 ppm; HRMS (ESI-TOF): m/z (%) calcd for
[C27H44N2O7Si+H]+: 537.2996; found: 537.2997.
(5% ethyl acetate in hexane) to give 23 (3.70 g, 9.55 mmol, 82% in
27
2 steps) as a colorless oil. Rf =0.58 (hexane/ethyl acetate=2/1); ½aꢁD
=
ꢀ6.71 (c=1.36, CHCl3); IR (neat): n˜ =3373, 2957, 2932, 1717, 1515, 1367,
1254, 1173, 1112, 838, 778 cmꢀ1 1H NMR (400 MHz, CDCl3): d=6.64
;
(dq, J=9.2, 1.0 Hz, 1H), 4.93 (m, 1H), 4.47 (m, 1H), 4.13–4.25 (m, 2H),
3.71 (dd, J=10.3, 3.4 Hz, 1H), 3.61 (dd, J=10.3, 3.9 Hz, 1H) 1.93 (d, J=
1.0 Hz, 3H), 1.44 (s, 9H), 1.28 (t, J=7.2 Hz, 3H), 0.89 (s, 9H), 0.05 ppm
(s, 6H); 13C NMR (100 MHz, CDCl3): d=167.9, 155.3, 139.2, 129.9, 79.7,
65.0, 60.7, 50.6, 28.4, 25.9, 18.4, 14.3, 13.0, ꢀ5.4, ꢀ5.5 ppm; HRMS (ESI-
TOF): m/z (%) calcd for [C19H37NO5Si+H]+: 388.2519; found: 388.2522.
30: Boc-MeAla-MeIle-OAllyl. To Boc-MeIle-OAllyl (28) (2.30 g,
8.07 mmol) was added HCl (4m) in ethyl acetate (10 mL) at 08C. After
being stirred at the same temperature for 1 h, the reaction mixture was
concentrated in vacuo. The residue was azeotropically dried with toluene
and CH2Cl2 twice, then dissolved in CH2Cl2 (34 mL). To this solution was
added Boc-MeAla-OH (29) (1.37 g, 6.72 mmol), N,N-diisopropylethyl-
amine (2.93 mL, 16.8 mmol), and HATU (3.58 g, 9.41 mmol) at room
temperature. After being stirred at the same temperature for 1.5 h, the
reaction mixture was concentrated in vacuo. The residue was purified by
column chromatography on silica gel (25% ethyl acetate in hexane) to
give Boc-MeAla-MeIle-OAllyl (30) (2.47 g, 6.68 mmol, quant.) as a color-
less oil. Rf =0.50 (hexane/ethyl acetate=2:1); ½aꢁ2D9 =ꢀ145 (c=1.09,
CHCl3); IR (neat): n˜ =3525, 2937, 1739, 1694, 1661, 1456, 1392, 1183,
24: (E)-(S)-4-N-tert-Butoxycarbonylamino-5-(tert-butyldimethylsilyloxy)-
2-methylpent-2-enoic acid. To a solution of 23 (1.09 g, 2.81 mmol) in 2-
methyl-2-propanol (23 mL), H2O (6.0 mL), and THF (6.0 mL) was added
LiOH·H2O (589 mg, 14.1 mmol) at 08C. After being stirred at room tem-
perature for 12 h, the reaction mixture was quenched with saturated
aqueous NH4Cl, and the aqueous layer was extracted with CHCl3. The
combined organic layers were washed with brine, dried over MgSO4, and
concentrated in vacuo. The residue was purified by column chromatogra-
phy on silica gel (40% ethyl acetate in hexane) to give 24 (859 mg,
2.39 mmol, 85%) as a colorless oil. Rf =0.42 (hexane/ethyl acetate=1:1);
½aꢁ2D4 =+5.21 (c=1.17, CHCl3); IR (neat): n˜ =3245, 2931, 1692, 1500,
1077, 989, 772 cmꢀ1 1H NMR (400 MHz, CDCl3, major rotamer): d=
;
5.82–5.96 (m, 1H), 5.21–5.33 (m, 2H); 5.12 (q, J=6.8 Hz, 1H), 4.97 (d,
J=10.6 Hz, 1H), 4.52–4.69 (m, 2H), 3.02 (s, 3H), 2.76 (s, 3H), 1.92–2.18
(m, 1H), 1.46 (s, 9H), 1.33–1.40 (m, 1H), 1.28 (d, J=6.8 Hz, 3H), 1.01–
1.10 (m, 1H), 0.85–0.99 ppm (m, 6H); 13C NMR (100 MHz, CDCl3, mix-
ture of rotamers): d=172.6, 172.1, 171.9, 171.2, 171.1, 170.9, 170.2, 170.1,
155.5, 155.1, 154.8, 153.9, 131.8, 119.6, 119.4, 118.7, 118.6, 80.4, 80.1, 66.1,
65.9, 65.3, 63.9, 63.7, 60.6, 52.4, 52.2, 50.7, 50.6, 34.5, 34.3, 33.6, 33.3, 31.1,
30.8, 29.7, 29.5, 29.2, 29.0, 28.7, 28.5, 28.4, 25.5, 25.3, 25.0, 24.8, 16.0, 15.8,
14.8, 14.7, 14.6 ppm; HRMS (ESI-TOF): m/z (%) calcd for
[C19H34N2O5+Na]+: 393.2360; found: 393.2360.
1473, 1393, 1254, 1168, 1116, 837, 778 cmꢀ1 1H NMR (400 MHz, CDCl3):
;
d=6.76 (dq, J=8.7, 1.0 Hz, 1H), 4.98 (m, 1H), 4.49 (m, 1H), 3.71 (dd,
J=10.1, 4.3 Hz, 1H), 3.62 (dd, J=10.1, 4.3 Hz, 1H), 1.94 (d, J=1.0 Hz,
3H), 1.44 (s, 9H), 0.89 (s, 9H), 0.04 ppm (s, 6H); 13C NMR (100 MHz,
CDCl3): d=172.9, 155.4, 141.5, 129.3, 79.8, 64.8, 50.6, 28.4, 25.9, 18.3,
12.6, ꢀ5.4, ꢀ5.5 ppm; HRMS (ESI-TOF): m/z (%) calcd for
[C17H33NO5Si+H]+: 360.2206; found: 360.2206.
26: Boc-moSerACHTUNGTRENNUNG(O-TBS)-TyrACHTUNRTGENN(GUN O-Me)-OMe. To Boc-TyrACTHNUGTREN(NUNG O-Me)-OMe (25)
Coupling of 30 and 27. To Boc-MeAla-MeIle-OAllyl (30) (102 mg,
0.282 mmol) was added HCl (4m) in ethyl acetate (10 mL) at 08C. After
being stirred at the same temperature for 1 h, the reaction mixture was
concentrated in vacuo. The residue was azeotropically dried with toluene
and CH2Cl2 twice, then dissolved in CH2Cl2 (1.0 mL). To this solution
was added a solution of 27 (94.6 mg, 0.176 mmol) and N,N-diisopropyl-
ethylamine (0.153 mL, 0.880 mmol) in CH2Cl2 (3.0 mL), and HATU
(200 mg, 0.528 mmol) at room temperature. After being stirred at the
same temperature for 24 h, the reaction mixture was concentrated in
vacuo. The residue was purified by column chromatography on silica gel
(20% to 60% ethyl acetate in hexane) to give azalactone 32 (45.0 mg,
(118 mg, 0.381 mmol) was added HCl (4m) in ethyl acetate (3.0 mL) at
08C. After being stirred at the same temperature for 1 h, the reaction
mixture was concentrated in vacuo. The residue was azeotropically dried
with toluene and CH2Cl2 twice, then dissolved in CH2Cl2 (2.0 mL) and
DMF (0.8 mL). To this solution was added a solution of Boc-moSerACTHNUTRGNE(UNG O-
TBS)-OH 24 (93.7 mg, 0.293 mmol) in CH2Cl2 (2.0 mL), N,N-diisopropyl-
ethylamine (0.153 mL, 0.878 mmol), HOBt (59.5 mg, 0.439 mmol), and
EDCI·HCl (84.3 mg, 0.439 mmol) at room temperature. After being
stirred at the same temperature for 12 h, the reaction mixture was added
with HCl (1m) at 08C. The aqueous layer was extracted with ethyl ace-
tate. The combined organic layers were washed with saturated aqueous
NaHCO3, brine, dried over MgSO4, and concentrated in vacuo. The resi-
due was purified by column chromatography on silica gel (30% ethyl
acetate in hexane) to give 26 (132 mg, 0.239 mmol, 82%) as a colorless
oil. Rf =0.45 (hexane/ethyl acetate=1:1); ½aꢁ2D4 =+50.7 (c=1.40, CHCl3);
IR (neat): n˜ =3340, 2955, 2932, 1742, 1714, 1634, 1514, 1251, 1176, 838,
86.7 mmol, 49%) as
a colorless oil and tetrapeptide 31 (23.0 mg,
37.6 mmol, 21%) as a white amorphous solid.
Azalactone 32: IR (neat): n˜ =2958, 1717, 1614, 1515, 1248, 1074,
823 cmꢀ1 1H NMR (400 MHz, CDCl3): d=7.21 (d, J=8.8 Hz, 2H), 6.87
;
(d, J=8.8 Hz, 2H), 6.26 (brd, J=6.8 Hz, 1H), 4.93 (m, 1H), 4.45 (m,
1H), 4.12 (s, 2H), 3.79 (s, 3H), 3.69 (dd, J=10.2, 4.4 Hz, 1H), 3.60 (dd,
J=10.2, 4.4 Hz, 1H), 1.96 (d, J=1.0 Hz, 3H), 1.44 (s, 9H), 0.89 (s, 9H),
0.06 (s, 3H), 0.05 ppm (s, 3H); 13C NMR (67.8 MHz, CDCl3): d=173.6,
166.7, 158.9, 155.3, 137.2, 132.9, 130.8, 130.7, 125.7, 114.2, 80.0, 64.7, 55.3,
50.6, 42.9, 28.5, 25.9, 18.4, 13.2, ꢀ5.3 ppm; HRMS (ESI-TOF): m/z (%)
calcd for [C16H24O3+Na]+: 287.1618; found: 287.1617.
779 cmꢀ1 1H NMR (400 MHz, CDCl3): d=6.99 (d, J=8.2 Hz, 2H), 6.81
;
(d, J=8.2 Hz, 2H), 6.19 (m, 1H), 6.16 (d, J=7.8 Hz, 1H), 4.88 (m, 1H),
4.84 (m, 1H), 4.43 (m, 1H), 3.78 (s, 3H), 3.73 (s, 3H), 3.67 (dd, J=10.1,
4.3 Hz, 1H), 3.58 (dd, J=10.1, 4.3 Hz, 1H), 3.13 (dd, J=14.0, 5.8 Hz,
1H), 3.07 (dd, J=14.0, 5.3 Hz, 1H), 1.91 (d, J=1.4 Hz, 3H), 1.44 (s, 9H),
0.88 (s, 9H), 0.04 ppm (s, 6H); 13C NMR (100 MHz, CDCl3): d=172.2,
168.2, 158.8, 155.3, 134.0, 132.8, 130.3, 127.8, 114.1, 79.7, 65.0, 55.2, 53.5,
52.4, 50.3, 37.0, 28.5, 25.9, 18.3, 13.3, ꢀ5.4 ppm; HRMS (ESI-TOF): m/z
(%) calcd for [C28H46N2O7Si+H]+: 551.3153; found: 551.3134.
Tetrapeptide 31: Rf =0.52 (hexane/ethyl acetate=1:2); ½aꢁ2D2 =ꢀ69.7 (c=
1.06, CHCl3); IR (neat): n˜ =3335, 2932, 1737, 1712, 1635, 1513, 1406,
1249, 1177, 1107, 837, 782 cmꢀ1 1H NMR (400 MHz, CDCl3, major rota-
;
27: Boc-moSerACHTUNGTRENNUNG(O-TBS)-TyrACHTUTGNREN(NUGN O-Me)-OH. To a solution of methyl ester 26
mer): d=7.09 (d, J=8.7 Hz, 2H), 6.78 (d, J=8.7 Hz, 2H), 6.38 (d, J=
8.7 Hz, 1H), 6.18 (brd, J=7.7 Hz, 1H), 5.78–5.93 (m, 1H), 5.40 (q, J=
6.8 Hz, 1H), 5.30 (dd, J=16.9, 1.4 Hz, 1H), 5.23 (dd, J=9.2, 1.4 Hz, 1H),
5.21 (m, 1H), 4.94 (d, J=10.6 Hz, 1H), 4.84 (m, 1H), 4.55–4.63 (m, 2H),
4.42 (m, 1H), 3.76 (s, 3H), 3.66 (dd, J=10.1, 4.3 Hz, 1H), 3.57 (dd, J=
10.1, 4.3 Hz, 1H), 3.07 (dd, J=14.0, 7.2 Hz, 1H), 2.97 (s, 3H), 2.85 (dd,
J=14.0, 3.4 Hz, 1H), 2.74 (s, 3H), 1.96 (m, 1H), 1.90 (d, J=1.0 Hz, 3H),
1.43 (s, 9H), 1.24 (d, J=6.7 Hz, 3H), 1.23 (m, 1H), 0.98 (m, 1H), 0.94 (d,
J=6.8 Hz, 3H), 0.88 (s, 9H), 0.86 (t, J=7.2 Hz, 3H), 0.04 ppm (s, 6H);
13C NMR (100 MHz, CDCl3, major rotamer): d=171.8, 171.4, 170.7,
169.6, 168.1, 158.7, 155.3, 133.9, 132.8, 131.7, 130.5, 128.0, 118.7, 113.9,
(188 mg, 0.341 mmol) in 2-methyl-2-propanol (3.0 mL), H2O (1.0 mL),
and THF (2.0 mL) was added LiOH·H2O (51.0 mg, 1.02 mmol) at 08C.
After being stirred at room temperature for 12 h, the reaction mixture
was quenched with saturated aqueous NH4Cl, and the aqueous layer was
extracted with CHCl3. The combined organic layers were washed with
brine, dried over MgSO4, and concentrated in vacuo. The residue was pu-
rified by column chromatography on silica gel (5% methanol in CHCl3)
to give carboxylic acid 27 (145 mg, 0.270 mmol, 79%) as a colorless oil.
Rf =0.40 (CHCl3/methanol=4:1); ½aꢁ2D4 =+43.3 (c=1.53, CHCl3); IR
(neat): n˜ =3324, 2930, 1715, 1669, 1614, 1463, 1366, 1247, 834 cmꢀ1
;
120
www.chemasianj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2009, 4, 111 – 125

Total Synthesis of (ꢀ)-Apratoxin A
79.6, 65.4, 65.0, 60.5, 55.2, 50.5, 49.7, 37.8, 33.3, 31.0, 30.6, 28.4, 25.9, 25.1,
18.3, 15.8, 14.9, 13.3, 10.6, ꢀ5.4 ppm; HRMS (ESI-TOF): m/z (%) calcd
for [C41H68N4O9Si+H]+: 789.4834; found: 789.4837.
saturated aqueous NaHCO3, and the aqueous layer was extracted with
ethyl acetate. The combined organic layers were washed with brine, dried
over Na2SO4, and concentrated in vacuo. The residue was purified by
column chromatography on silica gel (3% methanol in CHCl3) to give 37
(60.2 mg, 60.2 mmol, 93% in 2 steps) as a white amorphous solid. Rf =
0.45 (CHCl3/methanol=9:1); ½aꢁ1D7 =ꢀ62.9 (c=1.34, CHCl3); IR (solid):
34: FmocTyrACHTUNGTRENNUNG(O-Me)-MeAla-MeIle-OAllyl. To a dipeptide 30 (2.43 g,
5.83 mmol) was added HCl (4m) in ethyl acetate (10 mL) at 08C. After
being stirred at the same temperature for 1 h, the reaction mixture was
concentrated in vacuo. The residue was azeotropically dried with toluene
and CH2Cl2 twice, then dissolved in CH2Cl2 (25 mL). To this solution was
added Fmoc-(O-Me)Tyr-OH (33) (2.21 g, 5.30 mmol), N,N-diisopropyl-
ethylamine (2.77 mL, 15.9 mmol), and HATU (3.02 g, 7.95 mmol) at
room temperature. After being stirred at the same temperature for 12 h,
the reaction mixture was concentrated in vacuo. The residue was purified
by column chromatography on silica gel (40% ethyl acetate in hexane)
n˜ =3321, 2967, 2937, 1738, 1695, 1644, 1514, 1404, 1249, 755 cmꢀ1
;
1H NMR (400 MHz, CDCl3, major rotamer): d=7.08 (d, J=8.8 Hz, 2H),
6.78 (d, J=8.8 Hz, 2H), 6.62 (d, J=7.8 Hz, 1H) 6.43 (d, J=8.3 Hz, 1H),
6.23 (dq, J=8.8, 1.0 Hz, 1H), 5.88 (m, 1H), 5.40 (q, J=6.8 Hz, 1H), 5.31
(dd, J=17.1, 1.4 Hz, 1H), 5.23 (dd, J=10.2, 1.4 Hz, 1H), 5.20 (m, 1H),
4.94 (d, J=10.2 Hz, 1H), 4.86 (dd, J=11.7, 2.0 Hz, 1H), 4.83 (m, 1H),
4.59 (m, 2H), 4.30 (dd, J=8.8, 3.4 Hz, 1H), 3.76 (s, 3H), 3.71 (dd, J=
11.2, 3.4 Hz, 1H), 3.61 (m, 1H), 3.48–3.55 (m, 2H), 3.38 (m, 1H), 3.05
(dd, J=13.7, 7.8 Hz, 1H), 2.96 (s, 3H), 2.85 (dd, J=13.7, 5.4 Hz, 1H),
2.74 (s, 3H), 2.21 (dq, J=6.8, 6.4 Hz, 1H), 2.19 (m, 1H), 1.92–2.05 (m,
3H), 1.19 (d, J=1.0 Hz, 3H), 1.85–1.89 (m, 2H), 1.64 (m, 1H), 1.54 (m,
1H), 1.43 (s, 9H), 1.35 (m, 1H), 1.27 (m, 1H), 1.26 (d, J=6.8 Hz, 3H),
1.14 (d, J=6.8 Hz, 3H), 1.12 (m, 1H), 0.94 (brd, J=6.8 Hz, 3Hꢃ2), 0.92
(m, 1H), 0.88 (s, 9H), 0.88 ppm (t, J=8.3 Hz, 3H); 13C NMR (100 MHz,
CDCl3, major rotamer): d=172.8, 171.9, 171.5, 170.7, 158.8, 154.9, 132.5,
131.8, 130.5, 130.4, 128.0, 118.8, 114.0, 80.3, 78.6, 71.8, 65.5, 64.7, 60.6,
59.1, 55.3, 50.6, 49.7, 46.8, 40.2, 37.8, 37.7, 37.3, 34.8, 33.4, 31.0, 30.6, 30.1,
29.8, 28.6, 28.4, 26.1, 26.0, 26.0, 25.9, 25.3, 24.2, 20.3, 15.9, 14.5, 13.4,
10.7 ppm; HRMS (ESI-TOF): m/z (%) calcd for [C53H85N5O13+H]+:
1000.6222; found: 1000.6221.
to give the N-Fmoc-protected tripeptide 34 (2.80 g, 4.18 mmol, 79%) as a
29
white amorphous solid. Rf =0.40 (hexane/ethyl acetate=1:1); ½aꢁD
=
ꢀ87.1 (c=1.08, CHCl3); IR (solid): n˜ =3296, 2965, 1718, 1636, 1512, 1243,
990, 741, 540 cmꢀ1; H NMR (400 MHz, CDCl3, mixture of rotamers): d=
1
7.75 (m, 2H), 7.55 (m, 2H), 7.39 (m, 2H), 7.27–7.32 (m, 2H), 7.11 (d, J=
7.4 Hz, 2H), 6.80 (d, J=7.4 Hz, 2H), 6.70–6.74 (m, 1H), 5.72–5.92 (m,
1H), 5.58 (d, J=9.3 Hz, 1H), 5.42 (q, J=7.4 Hz, 1H), 5.20–5.33 (m, 2H),
4.85–4.96 (m, 1H), 4.53–4.66 (m, 2H), 4.11–4.50 (m, 3H), 3.74 (s, 3H),
2.99–3.05 (m, 1H), 2.98 (s, 3H), 2.81–2.87 (m, 1H), 2.76 (s, 3H), 1.96 (m,
1H), 1.28 (d, J=7.4 Hz, 3H), 1.23–1.27 (m, 1H), 1.00 (m, 1H), 0.95 (d,
J=6.4 Hz, 3H), 0.84–0.90 ppm (m, 3H); 13C NMR (100 MHz, CDCl3,
mixture of rotamers): d=171.9, 171.7, 170.7, 158.7, 155.8, 143.8, 141.3,
131.8, 130.5, 130.4, 128.0, 127.8, 127.1, 125.2, 125.1, 120.0, 118.7, 114.0,
67.1, 65.4, 60.5, 55.2, 52.3, 49.8, 47.2, 38.1, 33.3, 31.0, 30.6, 25.1, 15.8, 14.4,
10.6 ppm; HRMS (ESI-TOF): m/z (%) calcd for [C39H47N3O7+Na]+:
692.3306; found: 692.3314; elemental analysis: calcd (%) for C39H47N3O7:
C 69.93, H 7.07, N 6.27; found: C 69.57, H 7.39, N 6.19.
Oxazoline 38. To
a solution of 37 (25.1 mg, 25.1 mmol) in CH2Cl2
(1.5 mL) was added DAST (3.3 mL, 25 mmol) at ꢀ788C. The solution was
stirred at the same temperature for 1 h, and DAST (3.3 mL, 25 mmol) was
added. After being stirred for another 1 h, the reaction mixture was
quenched with saturated aqueous NaHCO3 at ꢀ788C, and the aqueous
layer was extracted with ethyl acetate. The combined organic layers were
washed with brine, dried over Na2SO4, and concentrated in vacuo. The
residue was purified by column chromatography on silica gel (1.5%
methanol in CHCl3) to give oxazoline 38 (17.2 mg, 17.5 mmol, 70%) as a
colorless oil. Rf =0.48 (CHCl3/methanol=9:1); ½aꢁ1D7 =ꢀ121 (c=0.860,
CHCl3); IR (neat): n˜ =3331, 2968, 1739, 1696, 1650, 1514, 1403, 1249,
Coupling of 24 and 34. To a solution of the N-Fmoc-protected tripeptide
34 (134 mg, 0.200 mmol) in CH3CN (2.0 mL) was added diethylamine
(1.0 mL) at room temperature. After being stirred at the same tempera-
ture for 20 min, the reaction mixture was concentrated in vacuo. The resi-
due was azeotropically dried with toluene and CH2Cl2 twice, then dis-
solved in CH2Cl2 (0.5 mL). To this solution was added a solution of acid
24 (60.0 mg, 0.167 mmol) in CH2Cl2 (1.5 mL), N,N-diisopropylethylamine
(87.0 mL, 0.502 mmol), and HATU (95.0 mg, 0.251 mmol) at room tem-
perature. After being stirred at the same temperature for 7 h, the reac-
tion mixture was concentrated in vacuo. The residue was purified by
column chromatography on silica gel (60% ethyl acetate in hexane) to
give 31 (121 mg, 0.153 mmol, 92%) as a white amorphous solid.
1180, 754 cmꢀ1 1H NMR (400 MHz, CDCl3, major rotamer): d=7.09 (d,
;
J=8.8 Hz, 2H), 6.78 (d, J=8.8 Hz, 2H), 6.49 (m, 1H), 6.16 (m, 1H),
5.84–5.94 (m, 1H), 5.41 (q, J=6.8 Hz, 1H), 5.30 (dd, J=17.6, 1.5 Hz,
1H), 5.17–5.25 (m, 2H), 4.95 (m, 1H), 4.94 (d, J=10.2 Hz, 1H), 4.87 (dd,
J=11.7, 2.0 Hz, 1H), 4.60 (m, 2H), 4.31 (dd, J=8.3, 3.9 Hz, 1H), 3.77 (s,
3H), 3.76 (m, 1H), 3.35–3.52 (m, 3H), 3.00–3.10 (m, 2H), 2.97 (s, 3H),
2.86 (m, 1H), 2.76 (s, 3H), 1.90–2.21 (m, 6H), 1.89 (brs, 3H), 1.87 (m,
1H), 1.57–1.69 (m, 3H), 1.45 (s, 9H), 1.21–1.40 (m, 8H), 0.81–1.01 ppm
(m, 19H); HRMS (ESI-TOF): m/z (%) calcd for [C53H83N5O12+H]+:
982.6116; found: 982.6115.
Coupling product 37. To a solution of the N-Boc protected tetrapeptide
31 (76.4 mg, 96.8 mmol) and 2,6-lutidine (68.0 mL, 0.580 mmol) in CH2Cl2
(1.0 mL) was added dropwise tert-butyldimethylsilyl trifluoromethanesul-
fonate (51.0 mL, 0.290 mmol) at room temperature under argon. After
being stirred at the same temperature for 2 h, the reaction mixture was
quenched with methanol and saturated aqueous NaHCO3 at 08C. The
aqueous layer was extracted with CHCl3. The combined organic layers
were washed with brine, dried over Na2SO4, and concentrated in vacuo.
The residue was used for the next reaction without further purification.
To a solution of the silylcarbamate in tetrahydrofuran (3.0 mL) was
added TBAF (0.323 mL, 1.0m solution in tetrahydrofuran, 0.323 mmol)
at 08C under argon. After being stirred at the same temperature for
30 min, the reaction mixture was quenched with saturated aqueous
NaHCO3, and the aqueous layer was extracted with CHCl3. The com-
bined organic layers were washed with brine, dried over Na2SO4, and
concentrated in vacuo. The residue was azeotropically dried with toluene
and CH2Cl2 twice, then dissolved in CH2Cl2 (0.5 mL). To this solution
was added a solution of acid 35 (36.0 mg, 64.5 mmol) in CH2Cl2 (1.5 mL),
N,N-diisopropylethylamine (34.0 mL, 0.194 mmol), and HATU (31.0 mg,
96.8 mmol) at room temperature. After being stirred at the same temper-
ature for 10 h, the reaction mixture was concentrated in vacuo. The resi-
due was purified by column chromatography on silica gel (2.5% metha-
nol in CHCl3) to give amide 36 as a colorless oil. To a solution of amide
36 in tetrahydrofuran (1.5 mL) was added TBAF (96.8 mL, 1.0m solution
in tetrahydrofuran, 96.8 mmol) at 08C under argon. After being stirred at
room temperature for 1.5 min, the reaction mixture was quenched with
Amine 39. To a solution of the N-Boc-protected precursor 38 (8.0 mg,
8.1 mmol) and 2,6-lutidine (14.0 mL, 122 mmol) in CH2Cl2 (0.6 mL) was
added dropwise trimethylsilyl trifluoromethanesulfonate (7.3 mL,
41 mmol) at room temperature under argon. After being stirred at the
same temperature for 2 h, the reaction mixture was quenched with meth-
anol and saturated aqueous NaHCO3 at 08C. The aqueous layer was ex-
tracted with CHCl3. The combined organic layer was washed with brine,
dried over Na2SO4, and concentrated in vacuo. The residue was used for
the next reaction without further purification. To a solution of the result-
ing silyl ether in tetrahydrofuran (1.0 mL) was added TBAF (24 mL, 1.0m
solution in tetrahydrofuran, 24 mmol) at 08C under argon. After being
stirred at the same temperature for 30 min, the reaction mixture was
quenched with saturated aqueous NaHCO3, and the aqueous layer was
extracted with CHCl3. The combined organic layers were washed with
brine, dried over Na2SO4, and concentrated in vacuo. The residue was pu-
rified by column chromatography on silica gel (5.0% methanol in
CHCl3) to give amine 39 (6.6 mg, 7.5 mmol, 93% in 2 steps) as a white
amorphous solid. Rf =0.50 (CHCl3/methanol=9:1); ½aꢁ2D5 =ꢀ32.4 (c=
0.150, MeOH); IR (neat): n˜ =3315, 2966, 2935, 2876, 1736, 1644, 1513,
1247, 1182 cmꢀ1 1H NMR (400 MHz, CD2Cl2): d=7.10 (d, J=8.8 Hz,
;
2H), 6.79 (d, J=8.8 Hz, 2H), 6.58 (d, J=8.3 Hz, 1H), 6.15 (dq, J=8.8,
1.4 Hz, 1H), 5.91 (m, 1H), 5.37 (q, J=6.8 Hz, 1H), 5.21–5.29 (m, 2H),
Chem. Asian J. 2009, 4, 111 – 125
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
121

Y. Numajiri, T. Takahashi, and T. Doi.
FULL PAPERS
5.16 (m, 1H), 4.95 (ddd, J=9.8, 8.8, 8.8 Hz, 1H), 4.88 (dd, J=11.2,
2.4 Hz, 1H), 4.87 (d, J=10.2 Hz, 1H), 4.58 (m, 2H), 4.43 (dd, J=9.8,
8.3 Hz, 1H), 3.90 (dd, J=8.8, 8.3 Hz, 1H), 3.85 (dd, J=8.3, 5.9 Hz, 1H),
3.76 (s, 3H), 3.66 (ddd, J=10.8, 5.8, 2.0 Hz, 1H), 3.01–3.08 (m, 2H), 2.96
(s, 3H), 2.94 (m, 1H), 2.84 (dd, J=13.6, 6.3 Hz, 1H), 2.71 (s, 3H), 2.42
(dq, J=6.8, 5.8 Hz, 1H), 2.14 (m, 1H), 1.97 (m, 1H), 1.90 (m, 1H), 1.87
(d, J=1.4 Hz, 3H), 1.75–1.82 (m, 3H), 1.53–1.63 (m, 2H), 1.37 (ddd, J=
14.6, 10.8, 2.4 Hz, 1H), 1.23–1.29 (m, 2H), 1.22 (d, J=6.8 Hz, 3H), 1.19
(d, J=6.8 Hz, 3H), 1.02 (ddd, J=14.2, 10.8, 2.4 Hz, 1H), 0.93 (d, J=
6.8 Hz, 3H), 0.92 (d, J=6.8 Hz, 3H), 0.89 (s, 9H), 0.85 ppm (t, J=7.3 Hz,
3H); HRMS (ESI-TOF): m/z (%) calcd for [C45H69N5O9+H]+: 882.5592;
found: 882.5571.
tracted with CHCl3. The combined organic layers were washed with
brine, dried over Na2SO4, and concentrated in vacuo. The residue was
azeotropically dried with toluene and CH2Cl2 twice, then dissolved in
CH2Cl2 (0.5 mL). To this solution was added a solution of acid 35
(68.0 mg, 122 mmol) in CH2Cl2 (2.0 mL), N,N-diisopropylethylamine
(98.0 mL, 0.564 mmol), and HATU (107 mg, 282 mmol) at room tempera-
ture. After being stirred at the same temperature for 10 h, the reaction
mixture was concentrated in vacuo. The residue was purified by column
chromatography on silica gel (20% ethyl acetate in hexane) to give 42
(92.3 mg, 110 mmol, 90%) as a colorless oil. Rf =0.44 (hexane/ethyl ace-
tate=2:1); ½aꢁ1D9 =ꢀ26.8 (c=0.960, CHCl3); IR (neat): n˜ =3357, 2957,
2931, 1718, 1702, 1674, 1399, 1257, 1119, 837, 776 cmꢀ1
;
1H NMR
(400 MHz, CDCl3, mixture of rotamers): d=6.84 (d, J=7.8 Hz, 0.5H),
6.77 (d, J=7.8 Hz, 0.5H), 6.71 (dq, J=8.8, 1.4 Hz, 1H), 5.88–5.98 (m,
1H), 5.21–5.34 (m, 2H), 4.78 (m, 1H), 4.71–4.73 (m, 1H), 4.58–4.68 (m,
2H), 4.35 (dd, J=5.4, 2.9 Hz, 0.5H), 4.32 (dd, J=5.4, 2.9 Hz, 0.5H),
3.77–3.82 (m, 1H), 3.61–3.70 (m, 2H), 3.35–3.53 (m, 2H), 2.42 (m, 1H),
2.17 (m, 1H), 1.96–2.04 (m, 1H), 1.95 (d, J=1.4 Hz, 3H), 1.86–1.92 (m,
2H), 1.48–1.60 (m, 1H), 1.44 (s, 4.5H), 1.42 (s, 4.5H), 1.20–1.38 (m, 4H),
1.19 (d, J=7.3 Hz, 3H), 0.86–0.92 (m, 30H), 0.03–0.13 ppm (m, 12H);
HRMS (ESI-TOF): m/z (%) calcd for [C44H82N2O9Si2+H]+: 839.5637;
found: 839.5652.
Apratoxin A oxazoline analogue 2. To a solution of amine 39 (6.6 mg,
7.5 mmol) and morpholine (7.1 mL, 81 mmol) in tetrahydrofuran (0.7 mL)
was added tetrakis(triphenylphosphine)palladium (1.0 mg, 1.0 mmol) at
room temperature under argon. After being stirred at the same tempera-
ture for 3 h, the reaction mixture was concentrated in vacuo. The residue
was azeotropically dried with toluene and CH2Cl2 twice, then dissolved in
CH2Cl2 (7.5 mL). To this solution was added N,N-diisopropylethylamine
(8.3 mL, 48 mmol) and HATU (5.1 mg, 16 mmol) at room temperature
under argon. After being stirred at the same temperature for 48 h, the re-
action mixture was concentrated in vacuo. The residue was purified by
column chromatography on silica gel (1% to 3% methanol in CH2Cl2) to
give apratoxin A oxazoline analogue 2 (3.5 mg, 4.2 mmol, 56% in 2 steps)
as a white amorphous solid. Rf =0.5 (CHCl3/methanol=9:1); ½aꢁ2D2 =ꢀ167
(c=0.100, MeOH), lit.[12] ½aꢁD25 =ꢀ117.5 (c=0.2, CHCl3); IR (neat): n˜ =
Thioamide 43. To a solution of 42 (9.8 mg, 11.7 mmol) in toluene (1.0 mL)
was added Lawessonꢁs reagent (7.1 mg, 17.5 mmol) at room temperature.
After being stirred at 808C for 1 h, the reaction mixture was poured into
saturated aqueous NaHCO3 at 08C, and the aqueous layer was extracted
with diethyl ether. The combined organic layers were washed with brine,
dried over Na2SO4, and concentrated in vacuo. The residue was purified
by column chromatography on silica gel (15% ethyl acetate in hexane)
to give thioamide 43 (9.1 mg, 10.6 mmol, 91%) as a colorless oil. Rf =0.56
(hexane/ethyl acetate=2:1); IR (neat): n˜ =3291, 2956, 2931, 1720, 1702,
3426, 2966, 2935, 1742, 1624, 1513, 1461, 1178, 754 cmꢀ1 1H NMR
;
(400 MHz, CD2Cl2): d=7.15 (d, J=8.8 Hz, 2H), 6.81 (d, J=8.8 Hz, 2H),
6.07 (dq, J=9.3, 1.0 Hz, 1H), 5.97 (d, J=9.3 Hz, 1H), 5.17 (d, J=
11.7 Hz), 5.03 (ddd, J=10.8, 9.3, 4.9 Hz, 1H), 4.95 (dd, J=12.7, 2.4 Hz,
1H), 4.75 (ddd, J=9.3, 9.3, 5.8 Hz, 1H), 4.52 (d, J=11.2 Hz, 1H), 4.31
(dd, J=9.3, 8.3 Hz, 1H), 4.13–4.18 (m, 2H), 4.07 (dd, J=8.3, 5.8 Hz,
1H), 3.76 (s, 3H), 3.63 (m, 1H), 3.55 (m, 1H), 3.29 (m, 1H), 3.06 (dd, J=
12.7, 4.9 Hz, 1H), 2.87 (dd, J=8.3, 5.8 Hz, 1H), 2.81 (s, 3H), 2.67 (s,
3H), 2.35 (dq, J=10.2, 6.8 Hz, 1H), 2.22–2.33 (m, 2H), 2.04–2.12 (m,
2H), 1.85–1.93 (m, 2H), 1.88 (d, J=1.0 Hz, 3H), 1.77 (m, 1H), 1.50 (m,
1H), 1.24–1.36 (m, 2H), 1.14 (d, J=6.8 Hz, 3H), 1.11 (m, 1H), 1.03 (d,
J=6.8 Hz, 3H), 0.96 (m, 1H), 0.94 (d, J=6.8 Hz, 3H), 0.90 (d, J=6.8 Hz,
3H), 0.89 (t, J=6.8 Hz, 3H), 0.87 ppm (s, 9H); HRMS (ESI-TOF): m/z
(%) calcd for [C45H69N5O9+H]+: 824.5174; found: 824.5199.
1399, 1257, 1160, 1116, 837, 778 cmꢀ1 1H NMR (400 MHz, CDCl3, mix-
;
ture of rotamers): d=9.02 (d, J=7.8 Hz, 0.5H), 8.93 (d, J=7.8 Hz,
0.5H), 6.83 (m, 1H), 5.88–5.98 (m, 1H), 5.42 (m, 1H), 5.21–5.34 (m, 2H),
4.56–4.72 (m, 3H), 4.34 (m, 1H) 3.67–3.91 (m, 3H), 3.35–3.53 (m, 2H),
3.11 (m, 1H), 2.00–2.25 (m, 2H), 1.96 (d, J=1.4 Hz, 3H), 1.86–1.92 (m,
2H), 1.59 (m, 1H), 1.44 (s, 4.5H), 1.43 (s, 4.5H), 1.16–1.42 (m, 7H),
0.85–0.98 (m, 30H), 0.03–0.14 ppm (m, 12H); HRMS (ESI-TOF): m/z
(%) calcd for [C44H82N2O8SSi2+H]+: 855.5409; found: 855.5410.
Coupling of 20a and 45. To a solution of 45 (147 mmol) in CH2Cl2
(0.5 mL) was added a solution of 20a (83.8 mg, 113 mmol) in CH2Cl2
(1.0 mL), N,N-diisopropylethylamine (79.0 mL, 452 mmol), HOAt
(18.0 mg, 136 mmol), and EDCI·HCl (26.0 mg, 136 mmol) at 08C under
argon. After being stirred at the same temperature for 12 h, the reaction
mixture was diluted with ethyl acetate and poured into ice-cooled HCl
(1m). The organic layer was separated and the aqueous layer was extract-
ed with ethyl acetate. The combined organic layers were washed with sa-
turated aqueous NaHCO3, brine, dried over MgSO4, and concentrated in
vacuo. The residue was purified by column chromatography on silica gel
41: (E)-(S)-4-N-tert-Butoxycarbonylamino-5-(tert-butyldimethylsilyloxy)-
2-methylpent-2-enoic acid allyl ester. To a solution of carboxylic acid 24
(543 mg, 1.51 mmol) in DMF (7.5 mL) was added potassium carbonate
(270 mg, 1.97 mmol) and allyl bromide (0.160 mL, 1.81 mmol) at room
temperature. After being stirred at room temperature for 3 h, the reac-
tion mixture was diluted with diethyl ether, filtered through a pad of
Celite, and the filtrate was acidified with saturated aqueous NH4Cl at
08C. The aqueous layer was extracted with diethyl ether. The combined
organic layers were washed with aqueous Na2S2O3 (10%), saturated
aqueous NaHCO3, brine, dried over MgSO4, and concentrated in vacuo.
The residue was purified by column chromatography on silica gel (7%
ethyl acetate in hexane) to give 41 (571 mg, 1.43 mmol, 95%) as a color-
less oil. Rf =0.58 (hexane/ethyl acetate=2:1); ½aꢁ2D0 =+10.0 (c=1.14,
CHCl3); IR (neat): n˜ =3375, 2956, 2931, 1717, 1515, 1254, 1171, 1113,
(25% ethyl acetate in hexane) to give 46a (107 mg, 91.7 mmol, 81%) as
26
white amorphous solid. Rf =0.56 (hexane/ethyl acetate=1:1); ½aꢁD
=
ꢀ34.6 (c=1.35, CHCl3); IR (solid): n˜ =3329, 2962, 1755, 1709, 1523, 1449,
1420, 1248, 1119, 946, 741 cmꢀ1 1H NMR (400 MHz, CDCl3, mixture of
;
rotamers): d=7.74–7.78 (m, 2H), 7.57–7.62 (m, 2H), 7.18–7.42 (m, 19H),
6.35–6.41 (m, 1.6H), 5.80–5.99 (m, 1H), 5.44 (d, J=7.8 Hz, 0.4H), 5.32
(dd, J=17.6, 1.4 Hz, 0.4H), 5.25 (dd, J=17.6, 1.5 Hz, 0.6H), 5.23 (dd, J=
10.2, 1.4 Hz, 0.4H), 5.17 (dd, J=10.7, 1.5 Hz, 0.6H), 4.97 (m, 1H), 4.84
(dd, J=8.2, 3.9 Hz, 0.6H), 4.81 (d, J=12.2 Hz, 0.6H), 4.80 (dd, J=10.2,
5.8 Hz, 0.4H), 4.71 (d, J=12.2 Hz, 0.4H), 4.48–4.67 (m, 5H), 4.36–4.42
(m, 1H), 4.19–4.30 (m, 2H), 3.46–3.66 (m, 2H), 2.09–2.54 (m, 5H), 1.89–
2.02 (m, 3H), 1.73 (brs, 3H), 1.58–1.62 (m, 1H), 1.22–1.49 (m, 3H), 1.09
(d, J=6.8 Hz, 1.8H), 1.06 (d, J=7.3 Hz, 1.2H), 0.92 (d, J=6.8 Hz, 1.8H),
0.87 (s, 3.6H), 0.85 (s, 5.4H), 0.73 ppm (d, J=6.4 Hz, 1.2H); 13C NMR
(100 MHz, CDCl3, mixture of rotamers): d=172.6, 172.2, 171.9, 167.2,
154.9, 154.5, 153.9, 153.8, 144.6, 144.5, 144.1, 143.9, 143.8, 141.4, 141.2,
139.6, 139.4, 132.3, 130.4, 130.2, 129.7, 128.1, 128.0, 127.8, 127.2, 127.0,
126.9, 125.6, 125.3, 125.2, 120.0, 118.3, 118.1, 94.9, 79.3, 79.1, 78.8, 78.5,
67.9, 67.5, 67.2, 67.1, 65.6, 65.5, 59.8, 59.5, 47.3, 47.2, 47.1, 46.4, 45.3, 44.7,
38.1, 37.5, 36.8, 36.4, 35.8, 35.1, 34.8, 31.3, 30.1, 26.1, 25.9, 25.8, 24.3, 23.5,
838, 778 cmꢀ1 1H NMR (400 MHz, CDCl3): d=6.68 (dq, J=9.2, 1.4 Hz,
;
1H), 5.89–5.99 (m, 1H), 5.32 (m, 1H), 5.23 (m, 1H), 4.93 (m, 1H), 4.59–
4.69 (m, 2H), 4.48 (m, 1H), 3.71 (dd, J=9.7, 3.9 Hz, 1H), 3.61 (dd, J=
9.7, 3.9 Hz, 1H), 1.95 (d, J=1.4 Hz, 3H), 1.44 (s, 9H), 0.89 (s, 9H),
0.05 ppm (s, 6H); 13C NMR (100 MHz, CDCl3): d=167.5, 155.3, 139.7,
132.4, 129.6, 118.0, 79.7, 65.4, 65.0, 50.6, 28.4, 25.9, 18.4, 13.0, ꢀ5.4,
ꢀ5.5 ppm; HRMS (ESI-TOF): m/z (%) calcd for [C20H37NO5Si+H]+:
400.2519; found: 400.2520.
42: Boc-Pro-Dtena-moSer-OAllyl. To
188 mmol) and 2,6-lutidine (171 mL, 1.69 mmol) in CH2Cl2 (2.0 mL) was
added slowly trimethylsilyl trifluoromethanesulfonate (102 mL,
a solution of 41 (75.0 mg,
0.563 mmol) at room temperature under argon. After being stirred at the
same temperature for 2 h, the reaction mixture was quenched with meth-
anol and saturated aqueous NaHCO3 at 08C. The aqueous layer was ex-
122
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ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2009, 4, 111 – 125

Total Synthesis of (ꢀ)-Apratoxin A
20.4, 19.9, 13.5, 13.0, 12.9 ppm; HRMS (ESI-TOF): m/z (%) calcd for
[C64H71Cl3N2O10S+Na]+: 1187.3787; found: 1187.3796; elemental analy-
sis: calcd (%) for C64H71Cl3N2O10S: C 65.81, H 6.48. N 2.25; found:
C 65.8, H 6.13. N 2.40.
7.30 (m, 2H), 6.78 (m, 1H), 5.92 (m, 1H), 5.32 (dd, J=17.6, 1.5 Hz, 1H),
5.22 (dd, J=10.8, 1.5 Hz, 1H), 5.18 (m, 1H, e), 5.91 (dd, J=11.7, 1.9 Hz,
1H), 4.64 (m, 2H), 4.43 (m, 1H), 4.37 (dd, J=8.3, 3.4 Hz, 1H), 4.18–4.35
(m, 2H), 3.82 (m, 1H), 3.66 (m, 1H), 3.54 (m, 1H), 3.37 (dd, J=10.8,
8.8 Hz, 1H), 2.94 (dd, J=11.2, 8.8 Hz, 1H), 2.17–2.31 (m, 2H), 2.00–2.08
(m, 3H), 1.97 (d, J=1.4 Hz, 3H), 1.72–1.84 (m, 2H), 1.63 (m, 1H), 1.30
(m, 1H), 1.19–1.26 (m, 3H), 0.96 (d, J=6.8 Hz, 3H), 0.92 (m, 1H),
0.88 ppm (s, 9H); 13C NMR (100 MHz, CDCl3, mixture of rotamers): d=
172.5, 167.4, 155.1, 144.3, 144.0, 141.4, 141.4, 141.3, 140.6, 132.4, 127.7,
127.1, 125.4, 125.3, 120.0, 118.3, 118.2, 79.8, 78.6, 70.9, 70.6, 67.9, 67.8,
65.5, 59.7, 47.3, 47.0, 46.6, 46.1, 39.9, 39.7, 37.9, 37.8, 37.7, 37.6, 34.8, 34.6,
31.3, 30.0, 26.1, 26.0, 25.2, 23.4, 20.7, 20.6, 14.6, 14.2, 13.2 ppm; HRMS
(ESI-TOF): m/z (%) calcd for [C42H54N2O7S+H]+: 731.3730; found:
731.3744.
Amide 46b. Following a similar procedure from 20a to 46a, 46b was ob-
tained from 20b in 84% yield. Rf =0.55 (hexane/ethyl acetate=1:1);
½aꢁ1D9 =ꢀ45.8 (c=1.21, CHCl3); IR (solid): n˜ =3338, 2961, 1758, 1712,
1
1675, 1420, 1249, 757, 742, 701 cmꢀ1; H NMR (400 MHz, CDCl3, mixture
of rotamers): d=7.73–7.77 (m, 2H), 7.56–7.59 (m, 2H), 7.15–7.41 (m,
19H), 6.48 (dq, J=9.3, 1.5 Hz, 0.5H), 6.40 (dq, J=8.8, 1.5 Hz, 0.5H),
6.20 (d, J=7.8 Hz, 0.5H), 5.85–5.95 (m, 1H), 5.59 (d, J=7.8 Hz, 0.5H),
5.18–5.31 (m, 2H), 5.00 (ddd, J=8.3, 8.3, 3.4 Hz, 0.5H), 4.93 (m, 0.5H),
4.68–4.82 (m, 3H), 4.53–4.63 (m, 3H), 4.49 (dd, J=8.8, 2.9 Hz, 0.5H),
4.38–4.43 (m, 1.5H), 4.15–4.31 (m, 2H), 3.48–3.64 (m, 2H), 2.07–2.58 (m,
5H), 1.93–2.01 (m, 2H), 1.67–1.80 (m, 4H), 1.22–1.60 (m, 3H), 1.14 (d,
J=6.8 Hz, 1.5H), 1.11 (d, J=7.3 Hz, 1.5H), 1.00–1.07 (m, 1H), 0.90 (d,
J=6.3 Hz, 1.5H), 0.85 (s, 4.5H), 0.83 (s, 4.5H), 0.66 ppm (d, J=6.8 Hz,
1.5H); 13C NMR (100 MHz, CDCl3, mixture of rotamers): d=172.8,
172.5, 172.4, 172.1, 167.2, 167.1, 154.9, 154.4, 154.0, 153.9, 144.6, 144.4,
144.3, 144.1, 144.0, 143.8, 141.4, 141.3, 139.4, 139.1, 132.4, 132.3, 130.5,
130.3, 129.6, 129.6, 128.1, 128.0, 127.7, 127.2, 127.1, 127.0, 126.9, 125.5,
125.3, 125.2, 120.0, 118.2, 118.1, 94.9, 94.8, 79.8, 79.6, 79.4, 78.7, 67.9, 67.6,
67.2, 67.2, 65.5, 65.4, 59.9, 59.4, 47.6, 47.3, 47.3, 47.1, 47.1, 46.5, 45.9, 44.9,
38.5, 38.2, 38.0, 35.9, 35.7, 35.0, 34.7, 31.4, 30.1, 26.2, 25.9, 25.8, 24.5, 23.4,
20.9, 20.6, 14.2, 13.9, 13.0 ppm; HRMS (ESI-TOF): m/z (%) calcd for
[C64H71Cl3N2O10S+H]+: 1165.3973; found: 1165.3995.
HPLC analysis of 48a and 48b. The 48a and 48b were analyzed by re-
versed-phase HPLC (Inertsil C18 ODS-3, 3 mm, 4.6ꢃ250 mm,
1.0 mLminꢀ1, UV detection at 254 nm) using a CH3CN–H2O linear gradi-
ent (75% for 4 min, 75–95% over 21 min, 95–100% over 5 min and then
100% CH3CN 5 min). 48a and 48b were eluted at tR =24.7 min and tR =
24.1 min, respectively.
Carboxylic acid 49a. To a solution of 48a (28.2 mg, 38.6 mmol) and N-
methylaniline (10.3 mL, 96.5 mmol) in tetrahydrofuran (2.5 mL) was
added tetrakis(triphenylphosphine)palladium (4.5 mg, 3.9 mmol) at room
temperature under argon. After being stirred at the same temperature
for 40 min, the reaction mixture was concentrated in vacuo. The residue
was purified by column chromatography on silica gel (3.0% methanol in
CHCl3) to give acid 49a (25.4 mg, 36.7 mmol, 95%) as a white amorphous
solid. Rf =0.40 (CHCl3/methanol=9:1); ½aꢁ2D6 =ꢀ76.3 (c=1.11, CHCl3);
IR (solid): n˜ =3464, 2957, 1962, 1607, 1419, 1359, 1178, 1124, 988,
Thiazoline 48a. To
a solution of triphenylphosphineoxide (72.0 mg,
257 mmol) in CH2Cl2 (1.0 mL) was added dropwise Tf2O (22.0 mL,
129 mmol) at 08C under argon. The solution was stirred at the same tem-
perature for 10 min. To the resultant mixture was added 46a (50.9 mg,
42.9 mmol) at 08C. After being stirred at the same temperature for
30 min, the reaction mixture was quenched with saturated aqueous
NaHCO3 at 08C, and the aqueous layer was extracted with ethyl acetate.
The combined organic layers were washed with brine, dried over Na2SO4,
and concentrated in vacuo. The residue was used for the next reaction
without further purification. To a solution of the crude thiazoline 47a in
tetrahydrofuran (2.0 mL) and aqueous NH4OAc (0.50 mL, 1.0m) was
added Zn dust (28.0 mg, 429 mmol) at room temperature. After being
stirred at the same temperature for 30 min, the reaction mixture was par-
titioned between ethyl acetate and brine. The solution was extracted five
times with ethyl acetate. The combined organic layers were dried over
Na2SO4 and concentrated in vacuo. The residue was purified by column
chromatography on silica gel (30% ethyl acetate in hexane) to give 48a
(28.2 mg, 38.6 mmol, 90% in 2 steps) as a white amorphous solid. Rf =
0.37 (hexane/ethyl acetate=2:1); ½aꢁ2D6 =ꢀ62.4 (c=0.900, CHCl3); IR
(solid): n˜ =3475, 2960, 2874, 1712, 1610, 1451, 1419, 1362, 1245, 1089,
758 cmꢀ1 1H NMR (400 MHz, CDCl3, mixture of rotamers): d=7.63 (d,
;
J=7.3 Hz, 2H), 7.63 (m, 2H), 7.38 (m, 2H), 7.30 (m, 2H), 6.84–6.89 (m,
1H), 5.14–5.28 (m, 1H), 4.90 (dd, J=11.7, 1.5 Hz, 0.7H), 4.82 (brd, J=
10.3 Hz, 0.3H), 4.18–4.53 (m, 4H), 3.39–3.81 (m, 3H), 3.36 (dd, J=10.8,
7.8 Hz, 0.3H), 3.30 (dd, J=10.8, 8.8 Hz, 0.7H), 2.97 (m, 1H), 2.72 (m,
1H), 2.23 (m, 1H), 1.94–2.07 (m, 3H), 1.94 (brs, 0.9H), 1.92 (d, J=
1.0 Hz, 2.1H), 1.84 (m, 1H), 1.29–1.78 (m, 4H), 1.24 (d, J=7.3 Hz,
0.9H), 1.21 (d, J=7.3 Hz, 2.1H), 0.96 (d, J=6.4 Hz, 2.1H), 0.89 (s,
2.7H), 0.87 (s, 6.3H), 0.78 ppm (d, J=6.8 Hz, 0.9H); 13C NMR
(100 MHz, CDCl3, mixture of rotamers): d=173.0, 172.5, 172.0, 155.1,
155.0, 154.4, 144.3, 144.2, 144.1, 144.0, 143.8, 142.3, 141.4, 141.3, 141.2,
127.7, 127.6, 127.1, 125.5, 125.3, 119.9, 79.5, 78.6, 78.4, 71.5, 70.9, 67.9,
67.8, 59.6, 47.3, 47.2, 47.1, 47.0, 46.5, 46.0, 45.3, 40.1, 39.4, 39.0, 37.9, 37.6,
37.4, 34.8, 34.6, 31.2, 30.0, 26.0, 25.5, 25.1, 24.9, 24.6, 23.4, 20.5, 20.3, 16.2,
14.5, 12.9, 12.8 ppm; HRMS (ESI-TOF): m/z (%) calcd for
[C39H50N2O7S+Na]+: 713.3231; found: 713.3234.
Cyclic precursor 50a. To a solution of tripeptide 34 (36.9 mg, 55.1 mmol)
in CH3CN (2.0 mL) was added diethylamine (1.0 mL) at room tempera-
ture. After being stirred at the same temperature for 20 min, the reaction
mixture was concentrated in vacuo. The residue was azeotropically dried
with toluene and CH2Cl2 twice, then dissolved in CH2Cl2 (0.5 mL). To
this solution was added a solution of acid 49a (25.4 mg, 36.7 mmol) in
CH2Cl2 (1.5 mL), N,N-diisopropylethylamine (19.2 mL, 110 mmol), and
HATU (17.6 mg, 55.1 mmol) at room temperature. After being stirred at
the same temperature for 8.0 h, the reaction mixture was concentrated in
vacuo. The residue was purified by column chromatography on silica gel
(17% acetone in toluene) to give 50a (30.7 mg, 27.4 mmol, 75%) as a
white amorphous solid. Rf =0.60 (CHCl3/methanol=9:1); ½aꢁ2D6 =ꢀ89.0
(c=1.28, CHCl3); IR (solid): n˜ =3465, 3328, 2960, 2876, 1735, 1707, 1625,
740 cmꢀ1 1H NMR (400 MHz, CDCl3, mixture of rotamers): d=7.75 (d,
;
J=7.3 Hz, 2H), 7.63 (dd, J=6.8, 7.3 Hz, 2H), 7.39 (dd, J=7.3, 7.3 Hz,
2H), 7.28–7.32 (m, 2H), 6.78–6.82 (m, 1H), 5.84–6.00 (m, 1H), 5.16–5.35
(m, 3H), 4.90 (dd, J=11.6, 1.9 Hz, 0.8H), 4.82 (dd, J=10.6, 1.4 Hz,
0.2H), 4.59–4.66 (m, 2H), 4.33–4.53 (m, 3H), 4.19–4.31 (m, 1H), 3.80 (m,
0.8H), 3.69 (m, 0.2H), 3.62 (m, 1H), 3.52 (m, 1H), 3.43 (dd, J=11.1,
8.7 Hz, 0.2H), 3.31 (dd, J=11.2, 8.8 Hz, 0.8H), 2.92–3.02 (m, 1H), 2.65–
2.72 (m, 1H), 2.25 (m, 1H), 1.98–2.10 (m, 3H), 1.97 (d, J=1.5 Hz, 0.6H),
1.95 (d, J=1.0 Hz, 2.4H), 1.38–1.74 (m, 4H), 1.25 (d, J=7.3 Hz, 0.6H),
1.21 (d, J=6.8 Hz, 2.4H), 0.99 (m, 1H), 0.95 (d, J=6.8 Hz, 2.4H), 0.88 (s,
9H), 0.79 ppm (d, J=6.4 Hz, 0.6H); 13C NMR (100 MHz, CDCl3, mixture
of rotamers): d=172.5, 167.3, 154.9, 154.4, 144.3, 144.1, 143.9, 141.4,
141.3, 140.3, 132.3, 127.7, 127.0, 125.5, 125.4, 125.3, 119.9, 118.3, 118.1,
79.4, 78.4, 74.1, 71.4, 67.9, 67.8, 65.6, 65.5, 59.6, 47.3, 47.2, 47.0, 46.5, 45.9,
45.3, 40.2, 39.1, 37.9, 37.6, 37.5, 34.8, 34.6, 31.6, 31.2, 30.0, 29.8, 26.1, 25.6,
25.0, 24.6, 23.3, 22.7, 20.6, 20.4, 16.2, 15.6, 14.2, 13.1 ppm; HRMS (ESI-
TOF): m/z (%) calcd for [C42H54N2O7S+Na]+: 753.3544; found: 753.3542.
1513, 1478, 1416, 1299, 1179, 1087, 988, 741, 545 cmꢀ1
;
1H NMR
(400 MHz, CDCl3, mixture of rotamers): d=7.75 (d, J=7.3 Hz, 2H), 7.63
(d, J=7.3 Hz, 2H), 7.39 (dd, J=7.7, 7.3 Hz, 2H), 7.31 (dd, J=7.7, 7.3 Hz,
2H), 7.09 (d, J=6.8 Hz, 2H), 6.76–6.79 (m, 3H), 6.30 (d, J=8.3 Hz, 1H),
5.87 (m, 1H), 5.37 (brd, J=6.8 Hz, 1H), 5.19–5.32 (m, 2H), 5.18 (m,
1H), 5.11 (m, 1H), 4.80–4.94 (m, 2H), 4.59 (brd, J=5.8 Hz, 2H), 4.15–
4.20 (m, 3H), 3.77 (m, 1H), 3.75 (s, 3H), 3.64 (m, 1H), 3.53 (m, 1H),
3.24 (m, 1H), 2.98–3.06 (m, 2H), 2.95 (s, 3H), 2.78–2.93 (m, 2H), 2.73 (s,
3H), 2.66 (m, 1H), 2.23 (m, 1H), 1.91–2.20 (m, 4H), 1.92 (brs, 3H), 1.81
(m, 1H), 1.60–1.74 (m, 2H), 1.20–1.50 (m, 9H), 0.89–1.07 (m, 7H), 0.88
Thiazoline 48b. Following a similar procedure from 46a to 48a, 48b was
obtained from 46b in 95% yield. Rf =0.37 (hexane/ethyl acetate=2:1);
½aꢁ1D6 =ꢀ79.3 (c=0.660, CHCl3); IR (solid): n˜ =3477, 2961, 1740, 1713,
1452, 1423, 1264, 1124, 758, 741 cmꢀ1 1H NMR (400 MHz, CDCl3, major
;
rotamer): d=7.76 (d, J=7.8 Hz, 2H), 7.61–7.67 (m, 2H), 7.39 (m, 2H),
Chem. Asian J. 2009, 4, 111 – 125
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
123

Y. Numajiri, T. Takahashi, and T. Doi.
FULL PAPERS
(s, 9H), 0.76–0.84 ppm (m, 3H); 13C NMR (100 MHz, CDCl3, mixture of
rotamers): d=172.6, 171.9, 171.5, 170.7, 168.1, 158.7, 155.0, 144.1, 144.0,
142.9, 141.4, 141.3, 131.8, 127.7, 130.5, 127.7, 127.1, 125.4, 120.0, 118.7,
114.0, 78.4, 71.5, 67.9, 65.4, 60.5, 59.7, 59.6, 55.2, 49.7, 47.2, 46.6, 45.9,
39.1, 37.7, 37.6, 34.8, 39.1, 37.7, 37.6, 34.8, 33.3, 32.0, 31.0, 30.7, 30.6, 30.1,
30.0, 29.8, 29.7, 26.1, 25.1, 25.0, 23.4, 22.8, 20.4, 15.8, 14.5, 13.6, 10.7 ppm;
HRMS (ESI-TOF): m/z (%) calcd for [C63H85N5O11S+Na]+: 1142.5859;
found: 1142.5858.
13.4,
9.1 ppm;
HRMS
(ESI-TOF):
m/z
(%)
calcd
for
[C45H69N5O8S+Na]+: 862.4759; found: 862.4749.
epi-1: 34-epi apratoxin A. Using the same procedure with 50b, 34-epi
apratoxin A epi-1 was obtained as a white amorphous solid in 25% over
3 steps. Rf =0.35 (ethyl acetate); ½aꢁ2D4 =ꢀ197 (c=0.115, methanol); IR
(neat): n˜ =3438, 2964, 2934, 1744, 1628, 1512, 1453, 1248, 1177, 754 cmꢀ1
;
1H NMR (400 MHz, CD2Cl2, mixture of rotamers): d=7.13 (d, J=8.8 Hz,
1.4H), 7.12 (d, J=8.8 Hz, 0.6H), 6.79 (d, J=8.8 Hz, 2H), 6.29 (d, J=
9.8 Hz, 0.7H), 6.24 (dq, J=10.2, 1.0 Hz, 0.7H), 6.17 (dq, J=9.8, 1.0 Hz,
0.3H), 5.97 (d, J=9.3 Hz, 0.3H), 5.29–5.34 (m, 1.7H), 5.12 (d, J=
11.7 Hz, 0.3H), 5.01 (m, 0.3H), 4.95 (dd, J=12.7, 2.0 Hz, 0.3H), 4.88 (dd,
J=12.7, 3.4 Hz, 0.7H), 4.82 (d, J=11.2 Hz, 0.7H), 4.75 (q, J=6.8 Hz,
0.7H), 4.35 (dd, J=8.3, 5.9 Hz, 0.7H), 3.99–4.14 (m, 2.3H), 3.74 (s,
0.9H), 3.74 (s, 2.1H), 3.54–3.60 (m, 1H), 3.48 (dd, J=11.2, 8.8 Hz, 0.3H),
3.43 (dd, J=11.2, 8.3 Hz, 0.7H), 3.27 (brs, 0.3H), 3.04–3.17 (m, 2H), 2.89
(dd, J=13.2, 5.4 Hz, 0.7H), 2.87 (s, 0.9H), 2.83 (dd, J=13.2, 5.4 Hz,
0.3H), 2.67 (s, 2.1H), 2.66 (s, 0.9H), 2.55 (s, 2.1H), 2.48–2.54 (m, 1H),
2.21–2.29 (m, 1H), 1.68–2.08 (m, 7H), 1.94 (d, J=1.0 Hz, 2.1H), 1.91 (d,
J=1.0 Hz, 0.9H), 1.21–1.30 (m, 2H), 1.12 (d, J=6.8 Hz, 0.9H), 1.10 (d,
J=6.8 Hz, 2.1H), 1.07 (d, J=6.8 Hz, 0.9H), 1.04 (d, J=6.8 Hz, 2.1H),
0.97 (d, J=6.8 Hz, 2.1H), 0.96 (d, J=6.8 Hz, 0.9H), 0.90 (d, J=6.8 Hz,
0.9H), 0.84–0.89 (m, 2H), 0.86 (s, 6.3H), 0.85 (s, 2.7H), 0.81 (t, J=
7.3 Hz, 2.1H), 0.77 (t, J=7.3 Hz, 0.9H), 0.61 ppm (d, J=6.8 Hz, 2.1H);
HRMS (ESI-TOF): m/z (%) calcd for [C45H69N5O8S+H]+: 840.4945;
found: 840.4968.
50b. Following a similar procedure from 48a to 50a, 50b was obtained
from 48b in 77% yield over 2 steps. Rf =0.60 (CHCl3/methanol=9:1);
½aꢁ2D2 =ꢀ84.8 (c=0.780, CHCl3); IR (solid): n˜ =3474, 3329, 2965, 2934,
1738, 1693, 1636, 1452, 1180 cmꢀ1 1H NMR (400 MHz, CDCl3, major
;
rotamer): d=7.74–7.77 (m, 2H), 7.60–7.66 (m, 2H), 7.37–7.42 (m, 2H),
7.28–7.32 (m, 2H), 7.08 (d, J=8.8 Hz, 2H), 6.78 (d, J=8.8 Hz, 2H), 6.42
(d, J=8.8 Hz, 1H), 6.27 (dq, J=8.8, 1.5 Hz, 1H), 5.84–5.93 (m, 1H), 5.41
(q, J=6.8 Hz, 1H), 5.30 (dd, J=17.1, 1.5 Hz, 1H), 5.23 (dd, J=10.3,
1.5 Hz, 1H), 5.20 (m, 1H), 5.11 (m, 1H), 4.94 (d, J=10.2 Hz, 1H), 4.91
(m, 1H), 4.60 (m, 2H), 4.16–4.47 (m, 4H), 3.78 (m, 1H), 3.76 (s, 3H),
3.48–3.69 (m, 2H), 3.34 (dd, J=11.2, 8.8 Hz, 1H), 3.30 (m, 1H), 2.97 (s,
3H), 2.90 (dd, J=11.2, 9.3 Hz, 1H), 2.84 (m, 1H), 2.75 (s, 3H), 2.67 (m,
1H), 1.93–2.30 (m, 6H), 1.92 (d, J=1.5 Hz, 3H), 1.75 (m, 1H), 1.62 (m,
1H), 1.27–1.34 (m, 2H), 1.26 (d, J=6.8 Hz, 3H), 1.21 (d, J=6.8 Hz, 3H),
1.00 (m, 1H), 0.96 (d, J=6.8 Hz, 3H), 0.95 (d, J=6.4 Hz, 3H), 0.90 (m,
1H), 0.88 (s, 9H), 0.96 ppm (t, J=7.3 Hz, 3H); HRMS (ESI-TOF): m/z
(%) calcd for [C63H85N5O11S+H]+: 1120.6045; found: 1120.6042.
HPLC analysis of 1 and epi-1. Apratoxin A (1) and epi-1 were analyzed
by reversed-phase HPLC (Inertsil C18 ODS, 5 mm, 7.6ꢃ250 mm,
2.5 mLminꢀ1, UV detection at 220 nm) using an isocratic system of aque-
ous CH3CN (80%). 1 and epi-1 were eluted at tR =11.1 min and tR =
13.6 min, respectively.
HPLC analysis of 50a and 50b. The 50a and 50b were analyzed by re-
versed-phase HPLC (Inertsil C18 ODS-3, 3 mm, 4.6ꢃ250 mm,
1.0 mLminꢀ1, UV detection at 254 nm) using a CH3CN–H2O linear gradi-
ent (75% for 4 min, 75–95% over 21 min, 95–100% over 5 min and then
100% CH3CN 5 min). 50a and 50b were eluted at tR =24.8 min and tR =
24.1 min, respectively.
1: Apratoxin A. To a solution of 50a (44.9 mg, 40.0 mmol) and N-methyl-
aniline (13.0 mL, 120 mmol) in tetrahydrofuran (1.5 mL) was added tetra-
kis(triphenylphosphine)palladium (2.3 mg, 2.0 mmol) at room tempera-
ture under argon. After being stirred at the same temperature for 45 min,
the reaction mixture was concentrated in vacuo. The residue was purified
by column chromatography on silica gel (5.0% methanol in CHCl3) to
give the N-Fmoc-protected acid as a white amorphous solid. To a solu-
tion of the N-Fmoc-protected acid in CH3CN (4.0 mL) was added dieth-
ylamine (2.0 mL) at room temperature. After being stirred at the same
temperature for 20 min, the reaction mixture was concentrated in vacuo.
The residue was azeotropically dried with toluene and CH2Cl2 twice, then
dissolved in CH2Cl2 (40 mL). To this solution was added N,N-diisopropy-
lethylamine (62.7 mL, 360 mmol) and HATU (38.4 mg, 120 mmol) at 08C
under argon. After being stirred at 08C to room temperature for 20 h,
the reaction mixture was concentrated in vacuo. The residue was purified
by column chromatography on silica gel (3.0% to 6.0% 2-propanol in
CH2Cl2) and solid phase extraction (VARIAN Bond ELUT C18, eluting
with 85% MeOH in H2O to 100% MeOH) to give apratoxin A (1)
(24.0 mg, 28.6 mmol, 72% in 3 steps) as a white amorphous solid. Rf =
0.33 (ethyl acetate); ½aꢁD23 =ꢀ161 (c=0.625, methanol), lit.[4] ½aꢁD25 =ꢀ161
(c=1.33, methanol); IR (solid): n˜ =3420, 2933, 2958, 2874, 1740, 1622,
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research on
Priority Areas (No. 17035026, T.D.) from MEXT. We thank the JSPS Re-
search Fellowships for Young Scientists (Y. N.).
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1511, 1455, 1371, 1246, 1177, 1078 cmꢀ1; H NMR (400 MHz, CDCl3): d=
7.15 (d, J=8.8 Hz, 2H), 6.80 (d, J=8.8 Hz, 2H), 6.35 (d, J=9.8 Hz, 1H),
6.05 (d, J=9.3 Hz, 1H), 5.25 (ddd, J=9.8, 8.7, 4.3 Hz, 1H), 5.20 (d, J=
11.6 Hz, 1H), 5.05 (ddd, J=10.7, 9.3, 4.9 Hz, 1H), 4.97 (dd, J=12.6,
1.9 Hz, 1H), 4.70 (d, J=10.6 Hz, 1H), 4.24 (m, 1H), 4.19 (t, J=7.7 Hz,
1H), 3.78 (s, 3H), 3.66 (m, 1H), 3.54 (m, 1H), 3.46 (dd, J=11.1, 8.7 Hz,
1H), 3.28 (brq, J=6.8 Hz, 1H), 3.14 (dd, J=11.1, 4.3 Hz, 1H), 3.11 (dd,
J=12.2, 10.7 Hz, 1H), 2.86 (dd, J=12.2, 4.9 Hz, 1H), 2.81 (s, 3H), 2.71
(s, 3H), 2.64 (m, 1H), 2.15–2.30 (m, 3H), 2.05 (m, 1H), 1.97 (s, 3H),
1.85–1.90 (m, 2H), 1.79 (m, 1H), 1.57 (m, 1H), 1.31 (m, 1H), 1.25 (m,
1H), 1.21 (d, J=6.8 Hz, 3H), 1.07 (d, J=6.8 Hz, 3H), 1.06 (m, 1H), 0.99
(d, J=6.8 Hz, 3H), 0.95 (d, J=6.8 Hz, 3H), 0.91 (m, 1H), 0.90 (t, J=
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Chem. Asian J. 2009, 4, 111 – 125

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Received: September 18, 2008
Published online: November 25, 2008
Chem. Asian J. 2009, 4, 111 – 125
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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