Scalable solution-phase synthesis of the biologically active cyclodepsipeptide destruxin E, a potent negative regulator of osteoclast morphology

Article abstract of DOI:10.1021/jo402437z

The scalable solution-phase synthesis of the cyclodepsipeptide destruxin E (1) has been achieved. Diastereoselective dihydroxylation of the terminal alkene in a 2-alkoxy-4-pentenoic amide, 7, was successfully accomplished utilizing (DHQD)₂PHAL

Full text of DOI:10.1021/jo402437z

Article
pubs.acs.org/joc
Scalable Solution-Phase Synthesis of the Biologically Active
Cyclodepsipeptide Destruxin E, a Potent Negative Regulator of
Osteoclast Morphology
Masahito Yoshida,† Hiroshi Sato,†,‡ Yoshitaka Ishida,† Hiroshi Nakagawa,§ and Takayuki Doi*,†
†Graduate School of Pharmaceutical Sciences, Tohoku University 6-3 Aza-Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan
‡Mitsubishi Tanabe Pharma Corporation 1000 Kamoshida-cho, Aoba-ku, Yokohama 227-0033, Japan
§Department of Applied Biological Chemistry, Chubu University 1200 Matsumoto-cho, Kasugai, Aichi 487-8501, Japan
S
* Supporting Information
ABSTRACT: The scalable solution-phase synthesis of the
cyclodepsipeptide destruxin E (1) has been achieved.
Diastereoselective dihydroxylation of the terminal alkene in a
2-alkoxy-4-pentenoic amide, 7, was successfully accomplished
utilizing (DHQD)2PHAL as the chiral ligand, and it was found
that the use of the L-proline moiety in the substrate as a chiral
auxiliary was essential for the induction of high diastereose-
lectivity to afford the key compound 4 on a gram scale.
MNBA-mediated macrolactonization of 3 was also performed without formation of the dimerized product even under higher-
dilution conditions, and it is noteworthy that the internal hydrogen bonds and s-cis configuration of the amide bond between N-
methylalanine and N-methylvaline in the cyclization precursor 3 would assist in the macrolactonization to provide the
macrolactone 2 without forming a dimerized product. Finally, epoxide formation in the side chain afforded destruxin E (1) on a
gram scale in high purity (>98%).
destruxin derivatives exhibit potent V-ATPase inhibitory
activity, and 1 in particular strongly inhibits the activity of V-
ATPase.5 To date, the synthesis of destruxin and its derivatives
has been reported by several research groups.6 We have
recently achieved the first total synthesis and structural
determination of 1 and also reported that the stereochemistry
of the epoxide is crucial for potent V-ATPase inhibitory
activity.7 In addition, destruxin E (1) intriguingly induces
morphological changes in osteoclast-like multinuclear cells
(OCLs) at low concentration without affecting the V-ATPase
activity of the OCLs.8 Therefore, 1 is consequently considered
as a new type of antiresorptive agent. We are thus interested in
the elucidation of the mode of action of destruxin E (1) in
OCLs and its effect on bone metabolism in vivo. However, the
limited production of 1 from fungi such as M. anisopliae has
prevented a detailed study of its in vivo mechanism. Hence, the
development of an efficient synthetic route to 1 is essential for
obtaining sufficient quantities of 1 for in vivo studies. We
herein report the scalable solution-phase synthesis of the
naturally occurring cyclodepsipeptide destruxin E (1) via a 2-
methyl-6-nitrobenzoic anhydride (MNBA)-mediated macro-
lactonization9 and a diastereoselective dihydroxylation10 of the
terminal alkene in a 2-alkoxy-4-pentenoic amide using
(DHQD)2PHAL as the chiral ligand and the L-proline moiety
in the substrate as a chiral auxiliary.
INTRODUCTION
■
Osteoporosis, characterized by the loss of bone mass and bone
mineral density, is a worldwide health problem, particularly
among postmenopausal women and elderly people.1 Osteopo-
rosis is caused by disorders of bone homeostasis including
excessive bone resorption by osteoclasts, and thus, several
antiresorptive agents such as bisphosphonate and denosumab
have been developed and are widely used for osteoporosis
treatment.2 The antiresorptive agents currently in use efficiently
inhibit osteoclastic bone resorption by reducing the number of
osteoclasts. However, it is difficult for patients to completely
recover their bone health because bone remodeling is regulated
by a balance between osteoblasts and osteoclasts and is
occasionally hampered during treatment with antiresorptive
agents. Thus, a therapy for osteoporosis that inhibits bone
resorption without affecting osteoclast viability is desired.
Recently, a vacuolar-type H+-ATPase (V-ATPase) in osteo-
clasts was postulated as an attractive and a potential drug target
for osteoporosis therapeutics.3 The pumping of protons by the
osteoclastic V-ATPase is a prerequisite for promoting bone
resorption; therefore, specific inhibition of the osteoclastic V-
ATPase without affecting the viability of osteoclasts would be a
desirable mode of action in the treatment of osteolytic diseases.
̈
Destruxin E (1), isolated from Metarhidium anisopliae by Paıs
et al. in 1981, is a 19-membered cyclodepsipeptide consisting of
five amino acids (L-proline, L-isoleucine, N-methyl-L-valine, N-
methyl-L-alanine, and β-alanine) and an epoxide-containing
hydroxy acid derivative.4 It has recently been reported that
Received: November 1, 2013
Published: November 19, 2013
© 2013 American Chemical Society
296
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306

The Journal of Organic Chemistry
Article
Figure 1. Retrosynthesis of destruxin E (1).
RESULTS AND DISCUSSION
■
To achieve the preparation of destruxin E (1) on a gram scale,
we planned a solution-phase synthesis of 1, and the synthetic
outline is illustrated in Figure 1. The unstable epoxide side
chain would be synthesized from macrolactone 2 in the final
step. The selection of the cyclization site was important for
obtaining the desired macrolactone 2, and thus, the macro-
lactonization at the β-Ala−α-hydroxy acid site was chosen in
accordance with our previous sysnthesis.6a,b,7 The cyclization
precursor 3 would be obtained via coupling of acid 4 and
tetrapeptide 5 followed by simultaneous deprotection of the N-
and C-termini. A TBS group was chosen to protect the
hydroxyl group at the N-terminus of 3 and a 2-(trimethylsilyl)-
ethyl (TMSEt) group was selected as the protecting group at
the C-terminus of 5 because both the TBS and TMSEt groups
can be readily removed by treatment with TBAF under ambient
conditions without decomposition of the peptide sequence.11
The efficient preparation of 4 is a key issue for achieving the
gram-scale synthesis of destruxin E (1). The secondary alcohol
at the 1γ position should be diastereoselectively prepared
because the stereochemistry at the 1γ position is important for
the inhibition of V-ATPase activity.7 We previously reported
the synthesis of compound 4 from 8 through lactone 6;
however, the total yield of 4 was not reproducible on a gram
scale because of the high polarity of the resulting acid after
hydrolysis of lactone 6a (Figure 2). Moreover, the overall yield
of the desired lactone 6a was less than 50% because of the non-
stereoselective dihydroxylation of alkene 8, which was utilized
to prepare both lactones 6a and 6b for structural determination
of destruxin E (1). Therefore, preparation of the key compound
4 utilizing lactone 6a is problematic on a gram scale. Thus, an
alternative route to 4 involving diastereoselective dihydrox-
ylation of alkene 7 followed by acetal formation and removal of
the benzyl group was anticipated to provide a higher yield. In
general, it is known that dihydroxylation of terminal alkenes
proceeds with lower enantioselectivity than that of internal
alkenes.12 Therefore, we expected that the proline moiety in 7
might act as a chiral auxiliary in the diastereoselective
dihydroxylation of the terminal alkene moiety. Compound 7
Figure 2. Retrosynthesis of key compound 4.
can be readily synthesized via the coupling of L-proline benzyl
ester and the acid obtained by hydrolysis of the previously
synthesized compound 8.
Compound 7 was initially synthesized from the previously
reported7 TBS ether 9 (Scheme 1). In our previous report, the
asymmetric allylation of 9 was performed using allyl bromide/
lithium hexamethyldisilazide (LiHMDS) at −30 °C for 16 h to
achieve reproducible yield and diastereoselectivity. To improve
on these results, highly reactive allyl iodide was used as the
electrophile.13 Expectedly, the allylation with NaHMDS at −45
°C was smoothly completed within 1.5 h, affording the desired
product 8 in 94% yield with >95% diastereoselectivity.
However, acid 11 was not formed by direct hydrolysis of 8
under basic conditions because the cyclic carbamate was readily
hydrolyzed under the reaction conditions. The stepwise
modification to give 11 through methyl ester 10 was then
attempted via methanolysis of 8 utilizing samarium trifluor-
omethanesulfonate.14 However, this reaction took over 48 h to
go to completion, and the TBS group in 11 was easily removed
under the acidic workup. Thus, the nucleophilic cleavage of 8
with MeOMgBr was investigated;15 this reaction proceeded
successfully at room temperature to provide 10 in 94% yield
without removal of the TBS group. Hydrolysis of the methyl
ester followed by amidation of the resulting acid 11 with L-Pro-
OBn using bromotripyrrolidinophosphonium hexafluorophos-
297
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306

The Journal of Organic Chemistry
Article
Scheme 1. Synthesis of 7
Table 1. Investigation of the Reaction Conditions for Diastereoselective Dihydroxylation of 7
a
b
c
entry
conditions
AD-mix-β (1.4 g/mmol)
S:R ratio
yield (%)
1
2
3
4
5
6
7
67:33
50:50
77:23
86:14
86:14
84:16
51
AD-mix α (1.4 g/mmol)
43
OsO4 (1.0 mol %), (DHQD)2PHAL (5.0 mol %)
K2OsO2(OH)4 (1.0 mol %), (DHQD)2PHAL (5.0 mol %)
K2OsO2(OH)4 (0.5 mol %), (DHQD)2PHAL (5.0 mol %)
K2OsO2(OH)4 (1.0 mol %), (DHQD)2AQN (5.0 mol %)
K2OsO2(OH)4 (1.0 mol %), (DHQD)2PYR (5.0 mol %)
71
97
quant
90
31:69
92
a
b
1
K3[Fe(CN)6] (300 mol %), K2CO3 (300 mol %), tBuOH−H2O (1:1), rt, 18−24 h. Determined by H NMR analysis of the crude mixtures.
c
Combined yields.
Scheme 2. Attempts at Diastereoselective Dihydroxylation of 8
phate (PyBroP)16 then afforded the desired product 7 in 56%
yield.
high enantioselectivity.12 As an initial attempt at the synthesis
of the desired diol 12a, the dihydroxylation of 7 utilizing AD-
mix-β was examined (Table 1). This reaction provided the
desired diol 12a and its diastereomer 12b in a ratio of 67:33
(entry 1).17 By contrast, dihydroxylation utilizing AD-mix-α
provided a 50:50 mixture of diastereomers (entry 2). Thus, the
dihydroxylation was further investigated using cinchonidine-
based chiral ligands. When the reaction was performed using
(DHQD)2PHAL (5 mol %) in the presence of OsO4 (1 mol
%), the diols 12 were formed in a 77:23 ratio (entry 3). After
extensive investigations, it was found that the dihydroxylation
Once the gram-scale synthesis of the desired 7 was achieved,
we next investigated the diastereoselective dihydroxylation of
the terminal alkene in 7. It is known that the asymmetric
dihydroxylation of terminal alkenes generally proceeds with
poor enantioselectivity. Thus, extensive studies of the
asymmetric dihydroxylation of terminal alkenes have been
conducted, and bis(cinchona alkaloid) ligands with 1,4-
phthalazine (PHAL) or pyrimidine (PYR) spacers have been
shown to be effective for obtaining the corresponding diols with
298
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306

The Journal of Organic Chemistry
Article
of 7 utilizing K2OsO2(OH)4−(DHQD)2PHAL quantitatively
afforded 12a with 86% diastereoselectivity and that reduction of
the osmium catalyst loading to 0.5 mol % did not affect the
diastereoselectivity (entry 5). On the other hand, it was found
that with other chiral ligands, such as (DHQD)2AQN18 or
(DHQD)2PYR,12a the yield or diastereoselectivity was
decreased (entries 6 and 7). Therefore, (DHQD)2PHAL was
selected as the chiral ligand for the diastereoselective
dihydroxylation of the terminal alkene in 7. In contrast to the
dihydroxylation of 7, the dihydroxylation of 8 under the
optimized conditions utilizing (DHQD)2PHAL and
(DHQ)2PHAL resulted in poor stereoselectivity (6a:6b =
51:49 and 39:61, respectively; Scheme 2). In addition, the
dihydroxylation of methyl ester 10 in the presence of
K2OsO2(OH)4−(DHQD)2PHAL afforded a mixture of lac-
tones 6a and 6b in a 41:59 ratio. Thus, it seemed that the
chirality at the α-position in the hydroxyl acid derivative was
mismatched in the dihydroxylation utilizing (DHQD)2PHAL
for the induction of the desired stereochemistry at the 1γ
position. Therefore, the chirality of the proline moiety in 7 also
would assist in the induction of the high diastereoselectivity
obtained for 12a.
(trimethylsilyl)ethanol. Hydrogenolysis of 15 in isopropanol
provided amine 16 without transesterification at the C-
terminus. The resulting amine 16 was then coupled with
Cbz-NMeAla-OH using EDCI−HOBt, and dipeptide 17 was
obtained in 86% yield. However, when the preparation of 18
from 17 and Cbz-NMeVal-OH was carried out in the same
manner as for the preparation of 17, the yield of 18 was
moderate (56%). After several attempts at the tripeptide
synthesis, it was found that the use of HOAt instead of HOBt
enabled efficient amidation to provide the desired product 18 in
90% yield without formation of the diketopiperazine through
displacement of the C-terminal β-Ala residue.6e,21 Next,
tetrapeptide 5 was prepared through 19 in the same manner
as used for 18, and then hexapeptide 20 was obtained via
coupling of 5 with 4 using EDCI−HOAt. Concomitant removal
of the TBS and TMSEt groups with TBAF furnished the
desired cyclization precursor 3 on a multigram scale (Scheme
4).
Next, we investigated the MNBA-mediated macrolactoniza-
tion of 3 (Scheme 5).8 Previously, we performed the
macrolactonization of 3 at 3 mM. However, in the present
study it was found that the macrocyclization of 3 could be
achieved at 6 mM on a gram scale, providing the corresponding
product 2 in 81% yield without formation of the dimerized
byproduct (Scheme 5). On the other hand, we also attempted
the macrolactamization of L-Pro and L-Ile residues of 21 based
on the previous reports.6c,f,g Although the macrolactamization
of 2122 at 1 mM utilizing EDCI−HOAt proceeded smoothly at
room temperature, a mixture of 2 and its dimer 22 in a 53:47
ratio was obtained (Scheme 6). On the basis of previously
reported conformational studies of destruxin A and roseotoxin
B using NMR and X-ray crystallographic analyses, it has been
suggested that the amido bond between N-MeAla and N-MeVal
adopts the s-cis configuration, leading to a β-turn-shaped
structure stabilized by two internal hydrogen bonds.23 There-
fore, we believe that the cyclization precursor 3 forms a similar
conformation as A, which is proper for the macrolactonization
(Figure 3). Wang et al.24 recently reported that the destruxins
are produced via nonribosomal peptide synthesis of a linear
peptide, which undergoes macrolactonization in the biosysn-
thesis. Thus, the macrolactonization between β-Ala and the
hydroxy acid would be structurally suitable for the ring
construction of destruxins, rather than the macrolactamization
between the proline and isoleucine residues.
Because it was difficult to separate the resulting diols 12
using conventional column chromatography, acetal formation
with 2,2-dimethoxypropane was performed on the mixture of
diastereomers 12, and this was followed by isolation of the
resulting acetal 13a via flash column chromatography in 66%
overall yield. Finally, removal of the benzyl group by
hydrogenolysis furnished the desired compound 4 in 86%
yield (Scheme 3).
Scheme 3. Synthesis of Compound 4
With the desired macrolactone 2 on a gram scale, removal of
the acetonide in 2 was performed [3 M aqueous HCl/dioxane
(1:2), 10 °C, 10 min] in accordance with our previous report.
However, the yield of 26 was moderate because the N-
methylamide bond was partially cleaved under the acidic
conditions. After further investigation, it was found that the
ratio of water and dioxane was crucial for removal of the
acetonide without cleavage of the peptide bond. The reaction
was complete under milder conditions [1.5 M aqueous HCl/
dioxane (2:1), 0 °C, 2 h], providing diol 26 in 87% yield. For
completion of the scalable synthesis of 1, selective tosylation of
the primary alcohol in 26 was carefully performed via treatment
with 2 equiv of TsCl at room temperature to afford the desired
tosylate 27 in 81% yield. Finally, formation of the epoxide
under basic conditions furnished destruxin E (1) in several
hundred milligram yield with high purity (>98%) after silica gel
column chromatography (Scheme 7).
With the desired 4 in hand, the gram-scale synthesis of the
cyclization precursor 3 was then investigated. Although we have
reported the solid-phase synthesis of cyclization precursor 3
using an Fmoc method, we considered performing the gram-
scale synthesis of 3 in solution because of facile scale-up and
yield. As it is well-known that peptide sequences including N-
methylamide are readily hydrolyzed at the N-methylamide
bond under acidic conditions,19 peptide elongation utilizing the
Boc strategy had to be avoided for the synthesis of 5. Instead,
the benzyloxycarbonyl (Cbz) group was selected as the
protecting group.6a,c−h The Cbz group can be removed by
hydrogenolysis under ambient conditions without cleavage of
N-methylamide bonds, and Cbz-protected N-methylamino
acids can be readily prepared in one step from the
corresponding amino acids on a large scale.20 The starting
material Cbz-β-Ala-OH (14) was thus converted to the
corresponding TMSEt ester 1511b via condensation with 2-
299
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306

The Journal of Organic Chemistry
Article
Scheme 4. Synthesis of Cyclization Precursor 3
Scheme 5. Synthesis of Macrolactone 2 via Macrolactonization
experiments on 1 to study its effect on bone metabolism are
currently underway in our laboratories.
CONCLUSION
■
In conclusion, we have accomplished the improved solution-
phase synthesis of destruxin E (1) and established an efficient
synthetic process for the production of a sufficient quantity of 1
in high purity for use in vivo experiments. Diastereoselective
dihydroxylation of the terminal alkene in 7 was successfully
performed utilizing (DHQD)2PHAL, and the L-proline moiety
in the substrate was essential for inducing the high
diastereoselectivity in this reaction. It is also noteworthy that
the β-turn-shaped structure stabilized by internal hydrogen
bonds and the s-cis configuration of the NMe amido bonds
assisted in the efficient macrolactonization of 3 without high-
dilution conditions, leading to macrolactone 2 without
formation of the dimerized byproduct. These improved
synthetic processes made it possible to access a sufficient
quantity of destruxin E (1) in high purity (>98%), and in vivo
EXPERIMENTAL SECTION
■
General Techniques. Chemicals and solvents were all purchased
from commercial suppliers and used without further purification. All
reactions in the solution phase were monitored by thin-layer
chromatography carried out on glass-packed silica gel plates (60F-
254) with UV light and visualized by p-anisaldehyde H2SO4−ethanol
solution or phosphomolybdic acid ethanol solution. Flash column
chromatography was carried out with silica gel (40−100 μm) with the
indicated solvent system. 1H NMR spectra (400 MHz, 600 MHz) and
13C NMR spectra (100 MHz) were recorded in the indicated solvents.
Chemical shifts (δ) are reported in units of parts per million (ppm)
1
relative to the signal for internal tetramethylsilane (0.00 ppm for H)
for solutions in chloroform-d. NMR spectral data are reported as
follows: chloroform-d (77.0 ppm for 13C), methanol-d3 (3.30 ppm for
300
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306

The Journal of Organic Chemistry
Article
Scheme 6. Alternative Synthesis of Macrolactone 2 via Macrolactamization
centimeters (cm−1). Melting points were measured on a melting point
apparatus and are not corrected. Optical rotations were measured with
a polarimeter at 589 nm. HPLC analysis was performed on an HPLC
system with a photodiode array detector and an analytical C18 column
(3.5 mm, 4.6 × 100 mm i.d.) at a flow rate of 1.1 mL/min with a
gradient solvent (0 min, 10% MeOH/H2O; 4 min, 95% MeOH/H2O;
11 min, 95% MeOH/H2O; 11.1 min, 10% MeOH/H2O; 15 min, 10%
MeOH/H2O). HPLC solvents (MeOH and H2O) were buffered with
0.1% LC−MS-grade formic acid. Purity was measured with the peak
area at UV (214 nm).
Figure 3. Plausible conformation of cyclization precursor 3.
Syntheses. (R)-2-(tert-Butyldimethylsilyloxy)pentenoyl Oxazoli-
dinone (8). To a solution of TBS ether 97 (17.5 g, 58.1 mmol, 1 equiv)
in dry THF (200 mL, 3.4 mL/mmol) was added a solution of
NaHMDS in THF (1.00 M, 116 mL, 116 mmol, 2 equiv) dropwise at
−78 °C under an argon atmosphere. After the reaction mixture was
stirred at −78 °C for 30 min, a solution of allyl iodide (15.9 mL, 174
mmol, 3 equiv) in dry THF (50 mL, 0.29 mL/mmol) was added
dropwise at −78 °C. After being stirred at −45 °C for 1 h, the reaction
mixture was poured into saturated aqueous NH4Cl, and then the
aqueous layer was extracted with ethyl acetate. The organic layer was
washed with saturated aqueous NaHCO3 and brine, dried over
MgSO4, and filtered. The filtrate was concentrated in vacuo, and the
resulting residue was purified by silica gel column chromatography
(eluted with hexane/AcOEt = 20:1) to afford the allylated product 8
Scheme 7. Achievement of the Scalable Synthesis of 1
1
(18.7 g, 54.8 mmol, 94%, >95% ds) as a yellow oil. H NMR (400
MHz, CDCl3) δ 5.84−5.95 (1H, ddt, J = 6.4, 8.4, 16.0 Hz), 5.41 (1H,
dd, J = 4.0, 7.2 Hz), 5.13 (1H, d, J = 16.0 Hz), 5.10 (1H, d, J = 8.4
Hz), 4.51 (1H, dt, J = 3.6, 8.4 Hz), 4.34 (1H, t, J = 8.8 Hz), 4.23 (1H,
dd, J = 3.6, 8.8 Hz), 2.56−2.63 (1H, m), 2.38−2.46 (1H, m), 2.31
(1H, dq, J = 3.6, 7.2 Hz), 0.90 (9H, s), 0.90 (3H, d, J = 6.8 Hz), 0.87
(3H, d, J = 6.8 Hz), 0.07 (3H, s), 0.05 (3H, s); 13C NMR (100 MHz,
CDCl3) δ 173.5, 153.6, 133.4, 118.1, 71.0, 63.9, 58.2, 40.0, 28.2, 25.7,
18.3, 17.8, 14.7, −4.9, −5.2; IR (CHCl3) 2958, 2931, 1781, 1717,
1389, 1249, 1209, 1116, 837 cm−1; [α]D26 +63.5 (c 1.03, CHCl3);
HRFABMS calcd for C17H31NO4Si [M + H]+ 342.2101, found
342.2086.
1
1H), dimethyl sulfoxide-d4 (2.49 ppm for H and 39.5 ppm for 13C)
when an internal standard is not indicated. Multiplicities are reported
using the following abbreviations: s (singlet), d (doublet), t (triplet),
m (multiplet), dd (doublet of doublets), dt (doublet of triplets), dq
(doublet of quartets), ddd (doublet of doublets of doublets), ddt
(doublet of doublets of triplets). Coupling constants (J) are reported
in hertz (Hz). High-resolution mass spectra were measured on TOF-
MS with ESI or FAB probe. Infrared spectra are reported in reciprocal
(R)-2-(tert-Butyldimethylsilyloxy)pent-4-enoic Acid Methyl Ester
(10). Dry MeOH (30 mL, 0.83 mL/mmol) was added to a solution of
301
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306

The Journal of Organic Chemistry
Article
methylmagnesium bromide in THF (0.97 M, 74 mL, 72 mmol, 2
equiv) dropwise at 0 °C under an argon atmosphere. After the reaction
mixture was stirred at 0 °C for 15 min, a solution of 8 (12.3 g, 36.0
mmol, 1 equiv) in dry MeOH (90 mL, 2.5 mL/mmol) was added
dropwise at 0 °C. After being stirred at room temperature for 16 h, the
reaction mixture was poured into saturated aqueous NH4Cl, and then
the aqueous layer was extracted with ether. The organic layer was
washed with brine, and its organic layer was dried over MgSO4 and
filtered. The filtrate was concentrated in vacuo, and the resulting
residue was purified by silica gel column chromatography (eluted with
hexane/AcOEt = 20:1) to afford methyl ester 10 (8.26 g, 33.8 mmol,
94%) as a colorless oil. 1H NMR (400 MHz, CDCl3) δ 5.82 (1H, ddt,
J = 7.2, 10.4, 17.0 Hz), 5.06−5.15 (2H, m), 4.26 (1H, dd, J = 4.8, 7.2
Hz), 3.72 (3H, s), 2.40−2.53 (2H, m), 0.90 (9H, s), 0.08 (3H, s), 0.06
(3H, s); 13C NMR (100 MHz, CDCl3) δ 173.4, 133.4, 117.9, 72.2,
51.8, 39.8, 25.8, 18.4, −4.9, −5.2; IR (CHCl3) 2953, 2935, 1760, 1473,
1257, 1143, 837, 779 cm−1; [α]D26 +11.6 (c 0.900, CHCl3); HRFABMS
calcd for C12H24O3Si [M + H]+ 245.1573, found 245.1587.
N-[(2R)-tert-Butyldimethylsiloxypent-4-enoyl]-L-proline Benzyl
Ester (7). To a solution of methyl ester 10 (8.02 g, 32.8 mmol, 1
equiv) in THF (126 mL, 3.8 mL/mmol) and H2O (126 mL, 3.8 mL/
mmol) was added lithium hydroxide monohydrate (2.75 g, 65.6 mmol,
2 equiv) at 0 °C. After the reaction mixture was stirred at room
temperature for 4 h, 2 M sodium dihydrogen phosphate (pH 3, 70 mL,
140 mmol, 4.3 equiv) was added at 0 °C, and the aqueous layer was
extracted with ether. The organic layer was washed with brine, and its
organic layer was dried over MgSO4 and filtered. The filtrate was
concentrated in vacuo, and the resulting residue was used for the next
reaction without further purification.
trated in vacuo, and the resulting residue was purified by silica gel
column chromatography (eluted with hexane/AcOEt = 6:1) to afford
13a (5.82 g, 11.8 mmol, 66% over two steps) as a colorless oil. H
1
NMR (400 MHz, CDCl3) δ 7.25−7.37 (5H, m), 5.18 (1H, d, J = 12.0
Hz), 5.13 (1H, d, J = 12.0 Hz), 4.52 (1H, dd, J = 3.6, 8.4 Hz), 4.45
(1H, t, J = 6.4 Hz), 4.11 (1H, q, J = 6.4 Hz), 4.04 (1H, dd, app. dt, J =
6.8 Hz), 3.81−3.88 (1H, m), 3.63−3.70 (1H, m), 3.57 (1H, dd, app.
dt, J = 7.2 Hz), 1.88−2.20 (6H, m), 1.40 (3H, s), 1.32 (3H, s) 0.89
(9H, s), 0.08 (3H, s), 0.07 (3H, s); 13C NMR (100 MHz, CDCl3) δ
172.0, 170.9, 135.8, 128.5, 128.1, 128.0, 108.5, 72.8, 71.4, 69.5, 66.6,
59.4, 46.6, 38.7, 28.4, 27.0, 25.7, 25.6, 25.1, 18.1, −4.8, −5.3; IR
(CHCl3) 2956, 2934, 1755, 1666, 1643, 1442, 1256, 1157, 835 cm−1;
[α]2D8 −32.9 (c 1.00, CHCl3); HRFABMS calcd for C26H41NO6Si [M +
H]+ 492.2781, found 492.2787.
Acid 4. To a solution of benzyl ester 13a (5.82 g, 11.8 mmol, 1
equiv) in AcOEt (23.6 mL, 2.00 mL/mmol) and EtOH (23.6 mL, 2.00
mL/mmol) was added 10% Pd/C (580 mg, 10 wt %) at room
temperature under an argon atmosphere, and the flask was purged
with hydrogen three times. After being stirred at room temperature for
1 h, the reaction mixture was filtered through a pad of Celite, and the
filtrate was concentrated in vacuo. The resulting residue was
recrystallized from hexane to afford carboxylic acid 4 (4.06 g, 10.1
1
mmol, 86%) as a white solid. H NMR (400 MHz, CDCl3) δ 4.62
(1H, dd, J = 2.4, 8.4 Hz), 4.55 (1H, dd, app. dt, J = 6.0 Hz), 4.10−4.18
(1H, m), 4.07 (1H, dd, app. dt, J = 6.8 Hz), 3.80−3.90 (1H, m), 3.60−
3.68 (1H, m), 3.58 (1H, dd, app. dt, J = 7.6 Hz), 2.43−2.53 (1H, m),
1.85−2.10, (5H, m), 1.40 (3H, s), 1.32 (3H, s), 0.90 (9H, s), 0.09
(3H, s), 0.08 (3H, s); 13C NMR (100 MHz, CDCl3) δ 173.6, 173.1,
109.0, 72.3, 71.2, 69.4, 60.4, 47.2, 38.8, 27.2, 26.9, 25.7, 25.6, 25.1,
18.1, −4.8, −5.2; IR (CHCl3) 2928, 2857, 1741, 1616, 1462, 1369,
1255, 1159, 1063 cm−1; mp 84−87 °C; [α]D26 −75.9 (c 1.03, CHCl3);
HRFABMS calcd for C19H35NO6Si [M + H]+ 402.2312, found
402.2325.
To a solution of the crude carboxylic acid 11, L-proline benzyl ester
hydrochloride (8.73 g, 36.1 mmol, 1.1 equiv), and N,N-diisopropy-
lethylamine (17.1 mL, 98.4 mmol, 3 equiv) in dry CH2Cl2 (164 mL,
5.00 mL/mmol) was added PyBroP (23.0 g, 49.2 mmol, 1.5 equiv) at
0 °C under an argon atmosphere. After the reaction mixture was
stirred at room temperature for 16 h, H2O was added, and the aqueous
layer was extracted with CH2Cl2. The organic layer was washed with
brine, and its organic layer was dried over MgSO4 and filtered. The
filtrate was concentrated in vacuo, and the resulting residue was
purified by silica gel column chromatography (eluted with hexane/
AcOEt = 7:1) to afford amide 7 (7.67 g, 18.4 mmol, 56%) as a pale-
Cbz-β-Ala-OTMSEt (15). To a solution of Cbz-β-Ala-OH (14)
(3.00 g, 13.4 mmol, 1 equiv), 2-(trimethylsilyl)ethanol (2.12 mL, 14.8
mmol, 1.1 equiv), and DMAP (164 mg, 1.34 mmol, 0.1 equiv) in dry
CH2Cl2 (54 mL, 4 mL/mmol) was added EDCI (2.84 g, 14.8 mmol,
1.1 equiv) at 0 °C under an argon atmosphere. After being stirred at
room temperature for 5 h, the reaction mixture was quenched with 3
M HCl at 0 °C. The aqueous layer was extracted with ethyl acetate.
The organic layer was washed with saturated aqueous NaHCO3 and
brine. The organic layer was dried over MgSO4 and filtered. The
filtrate was concentrated in vacuo to afford TMSEt ester 15 (4.34 g,
1
yellow oil. H NMR (400 MHz, CDCl3) δ 7.26−7.40 (5H, m), 5.81
(1H, ddt, J = 7.2, 10.0, 17.2 Hz), 5.16 (2H, s), 5.10 (1H, d, J = 17.2
Hz), 5.06 (1H, d, J = 10.0 Hz), 4.52 (1H, dd, J = 3.6, 8.8 Hz), 4.32,
(1H, t, J = 6.8 Hz), 3.87 (1H, dt, J = 6.8, 10.4 Hz), 3.68−3.74 (1H, m),
2.39−2.48 (2H, m), 2.10−2.17 (1H, m), 1.99−2.05 (1H, m), 1.88−
1.94 (2H, m), 0.89 (9H, s), 0.07 (3H, s), 0.05 (3H, s); 13C NMR (100
MHz, CDCl3) δ 172.0, 171.3, 135.8, 133.7, 128.4, 128.1, 128.0, 117.8,
74.9, 66.6, 59.6, 46.7, 39.2, 28.4, 25.9, 25.3, 18.3, −4.7, −5.1; IR
(CHCl3) 2954, 2928, 2856, 1746, 1641, 1430, 1258, 1169, 837, 779
cm−1; [α]D25 −34.4 (c 0.450, CHCl3); HRFABMS calcd for
C23H35NO4Si [M + H]+ 418.2414, found 418.2412.
1
13.4 mmol, quant) as a colorless oil. H NMR (400 MHz, CDCl3) δ
7.26−7.36 (5H, m), 5.29 (1H, br s), 5.09 (2H, s), 4.18 (2H, t, J = 8.6
Hz), 3.46 (2H, dt, J = 5.6, 6.0 Hz), 2.52 (2H, t, J = 6.0 Hz), 0.98 (2H,
t, J = 8.6 Hz), 0.04 (9H, s); 13C NMR (100 MHz, CDCl3) δ 172.5,
156.2, 136.5, 128.5, 128.08, 128.05, 66.7, 63.0, 36.6, 34.6, 17.3, −1.52;
IR (CHCl3) 3353, 2954, 1729, 1523, 1250, 1175, 860, 837, 697 cm−1;
HRFABMS calcd for C16H26NO4Si [M + H]+ 324.1631, found
324.1641; HPLC retention time 8.73 min, purity >97%.
Benzyl Ester 13a. To a solution of alkene 7 (7.67 g, 18.4 mmol, 1
equiv) in t-BuOH (90 mL, 4.89 mL/mmol) and H2O (90 mL, 4.89
mL/mmol) were added (DHQD)2PHAL (717 mg, 0.92 mmol, 5.0
mol %), K2CO3 (7.63 g, 55.2 mmol, 3 equiv), K3[Fe(CN)6] (18.2 g,
55.2 mmol, 3 equiv), and a solution of K2OsO2(OH)4 in H2O (0.05
M, 1.84 mL, 0.092 mmol, 0.5 mol %) at 0 °C. After the reaction
mixture was stirred at room temperature for 8 h, saturated aqueous
Na2S2O3 was added, and the aqueous layer was extracted with ethyl
acetate. The organic layer was washed with brine, and its organic layer
was dried over MgSO4 and filtered. The filtrate was concentrated in
vacuo, and the resulting residue was filtered through a short pad of
silica gel (eluted with AcOEt/MeOH = 10:1) to afford diol 12 (86:14
diastereomeric mixture, 8.26 g, 18.4 mmol, quant) as a colorless oil.
To a solution of diol 12 (8.26 g, 18.4 mmol, 1 equiv) and 2,2-
dimethoxypropane (12.1 mL, 92.0 mmol, 5.00 equiv) in dry CH2Cl2
(123 mL, 6.7 mL/mmol) was added p-TsOH (317 mg, 1.78 mmol,
0.10 equiv) at 0 °C under an argon atmosphere. After being stirred at
the same temperature for 10 min, the reaction mixture was quenched
with N,N-diisopropylethylamine. The reaction mixture was concen-
Cbz-MeAla-β-Ala-OTMSEt (17). To a solution of 15 (1.36 g, 4.21
mmol, 1 equiv) in i-PrOH (14 mL, 3.3 mL/mmol) was added 10%
Pd/C (140 mg, 10 wt %) at room temperature under an argon
atmosphere, and the flask was purged with hydrogen three times. After
being stirred at room temperature for 6 h, the reaction mixture was
filtered through a pad of Celite, and the filtrate was concentrated in
vacuo. The crude residue was used for the next reaction without
further purification.
To a solution of the crude amine 16 (0.781 g, 4.13 mmol, 1 equiv),
Cbz-MeAla-OH (1.00 g, 4.21 mmol, 1.0 equiv), HOBt (0.670 g, 4.96
mmol, 1.2 equiv), and DIEA (1.08 mL, 6.20 mmol, 1.5 equiv) in dry
CH2Cl2 (16.5 mL, 4 mL/mmol) was added EDCI (0.951 g, 4.96
mmol, 1.2 equiv) at 0 °C under an argon atmosphere. After being
stirred at room temperature for 12 h, the reaction mixture was
quenched with saturated aqueous NH4Cl at 0 °C. The aqueous layer
was extracted with CHCl3. The organic layer was washed with
saturated aqueous NaHCO3 and brine. The organic layer was dried
over MgSO4 and filtered. The filtrate was concentrated in vacuo, and
the resulting residue was purified by silica gel column chromatography
302
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306

The Journal of Organic Chemistry
Article
(eluted with hexane/AcOEt = 1:1) to afford dipeptide 17 (1.46 g, 3.57
mmol, 86%) as a colorless oil. H NMR (400 MHz, CDCl3) δ 7.33−
(3H, s), 2.39 (2H, t), 2.10−2.26 (1H, m), 1.68−1.75 (1H, m), 1.40−
1.52 (1H, m), 1.05−1.25 (1H, m), 1.13 (3H, d, J = 7.2 Hz), 0.92 (2H,
t, J = 8.4 Hz), 0.83 (3H, d, J = 6.8 Hz), 0.79 (3H, t, J = 7.6 Hz), 0.78
(3H, d, J = 6.8 Hz), 0.68 (3H, d, J = 6.8 Hz), 0.00 (9H, s); 13C NMR
(100 MHz, DMSO-d6, mixture of rotamers) δ 172.4, 171.3, 170.3,
169.6, 156.2, 137.2, 128.3, 127.7, 127.5, 79.2, 65.3, 61.9, 57.4, 54.9,
51.8, 35.6, 34.9, 33.8, 30.4, 30.0, 26.6, 24.2, 19.5, 17.9, 16.8, 15.4, 14.7,
14.3, 10.6, −1.51; IR (CHCl3) 3314, 2961, 2876, 1720, 1685, 1629,
1527, 1467, 1455, 1408, 1388, 1293, 1250, 1226, 1173, 1038, 860, 838
cm−1; [α]D28 −100 (c 1.01, CHCl3); HRFABMS calcd for
C32H55N4O7Si [M + H]+ 635.3840, found 635.3810; HPLC retention
time 9.25 min, purity >97%.
TBS-HA-Pro-Ile-MeVal-MeAla-β-Ala-OTMSEt (20). To a solution of
19 (5.00 g, 7.88 mmol, 1 equiv) in EtOH (50 mL, 6.3 mL/mmol) was
added 10% Pd/C (500 mg, 10 wt %) at room temperature under an
argon atmosphere, and the flask was purged with hydrogen three
times. After being stirred at room temperature for 40 h, the reaction
mixture was filtered through a pad of Celite, and the filtrate was
concentrated in vacuo. The crude residue was used for the next
reaction without further purification.
1
7.23 (5H, m), 6.50 (1H, br s), 5.13 (2H, s), 4.72 (1H, br s), 4.13 (2H,
t, J = 8.6 Hz), 3.46 (2H, dt, J = 5.2, 6.4 Hz), 2.81 (3H, s), 2.44 (2H, t, J
= 5.2 Hz), 1.32 (3H, d, J = 7.2 Hz), 0.94 (2H, t, J = 8.6 Hz), 0.03 (9H,
s); 13C NMR (100 MHz, CDCl3) δ 172.4, 171.0, 136.4, 128.5, 128.1,
127.9, 67.6, 63.0, 35.0, 34.1, 17.3, −1.54; IR (CHCl3) 3340, 2953,
2898, 1732, 1703, 1683, 1527, 1455, 1400, 1313, 1250, 1218, 1172,
1061, 860, 838 cm−1; [α]D26 −44 (c 0.66, CHCl3); HRFABMS calcd for
C20H33N2O5Si [M + H]+ 409.2159, found 409.2158; HPLC retention
time 8.75 min, purity 94%.
Cbz-MeVal-MeAla-β-Ala-OTMSEt (18). To a solution of 17 (1.45 g,
3.55 mmol, 1 equiv) in i-PrOH (14 mL, 3.9 mL/mmol) was added
10% Pd/C (145 mg, 10 wt %) at room temperature under an argon
atmosphere, and the flask was purged with hydrogen three times. After
being stirred at room temperature for 12 h, the reaction mixture was
filtered through a pad of Celite, and the filtrate was concentrated in
vacuo. The crude residue was used for the next reaction without
further purification.
To a solution of the crude amine (0.931 g, 3.39 mmol, 1 equiv),
Cbz-MeVal-OH (1.08 g, 4.07 mmol, 1.2 equiv), HOAt (0.693 g, 5.09
mmol, 1.5 equiv), and DIEA (1.78 mL, 10.2 mmol, 3 equiv) in dry
CH2Cl2 (14 mL, 4 mL/mmol) was added EDCI (0.975 g, 5.09 mmol,
1.5 equiv) at 0 °C under an argon atmosphere. After being stirred at
room temperature for 12 h, the reaction mixture was quenched with
saturated aqueous NH4Cl at 0 °C. The aqueous layer was extracted
with ethyl acetate. The organic layer was washed with saturated
aqueous NaHCO3 and brine. The organic layer was dried over MgSO4
and filtered. The filtrate was concentrated in vacuo, and the resulting
residue was purified by silica gel column chromatography (eluted with
hexane/AcOEt = 1:1) to afford tripeptide 18 (1.67 g, 3.21 mmol, 90%)
as a colorless oil. 1H NMR (600 MHz, DMSO-d6, 80 °C) δ 7.15−7.50
(6H, m), 5.00−5.14 (2H, m), 4.86 (1H, d, J = 6.6 Hz), 4.48−4.58
(1H, m), 4.09 (2H, t, J = 7.8 Hz), 3.20−3.30 (2H, m), 2.66−2.83 (6H,
m), 2.38 (2H, t, J = 7.2 Hz), 2.15−2.25 (1H, m), 1.13−1.30 (3H, m),
0.76−0.91 (8H, m), 0.00 (9H, s); 13C NMR (100 MHz, DMSO-d6,
mixture of rotamers) δ 171.23, 171.19, 170.5, 169.7, 169.6, 169.5,
156.2, 156.0, 155.2, 136.9, 136.7, 136.5, 128.37, 128.34, 128.0, 127.8,
127.6, 127.25, 127.23, 79.1, 66.8, 66.7, 66.5, 61.9, 60.0, 59.3, 54.6, 52.0,
51.9, 35.0, 34.84, 34.81, 33.8, 33.7, 30.5, 30.3, 29.3, 29.0, 28.9, 28.8,
27.1, 26.96, 26.92, 19.42, 19.35, 19.32, 18.3, 18.09, 18.05, 16.75, 16.73,
15.7, 14.4, −1.55, −1.58; IR (CHCl3) 3334, 2958, 2898, 1731, 1692,
1646, 1522, 1498, 1472, 1456, 1396, 1370, 1303, 1250, 1224, 1174,
1133, 1111, 860, 838 cm−1; [α]D27 −117 (c 1.00, CHCl3); HRFABMS
calcd for C26H44N3O6Si [M + H]+ 522.2999, found 522.3011; HPLC
retention time 9.18 min, purity >98%
To a solution of the crude amine 5 (3.73 g, 7.45 mmol, 1 equiv),
acid 4 (2.99 g, 7.45 mmol, 1 equiv), HOAt (1.52 g, 11.2 mmol, 1.5
equiv), and DIEA (3.89 mL, 22.4 mmol, 3 equiv) in dry DMF−
CH2Cl2 (1:1, 30 mL, 4 mL/mmol) was added EDCI (2.15 g, 11.2
mmol, 1.5 equiv) at 0 °C under an argon atmosphere. After being
stirred at room temperature for 12 h, the reaction mixture was
quenched with saturated aqueous NH4Cl at 0 °C. The aqueous layer
was extracted with ethyl acetate. The organic layer was washed with
saturated aqueous NaHCO3 and brine. The organic layer was dried
over MgSO4 and filtered. The filtrate was concentrated in vacuo, and
the resulting residue was purified by silica gel column chromatography
(eluted with CHCl3/MeOH = 50:1) to afford hexapeptide 20 (5.71 g,
6.46 mmol, 87%) as a colorless oil. 1H NMR (400 MHz, DMSO-d6, 80
°C) δ 7.75−7.85 (1H, br), 7.43 (1H, br t, J = 5.2 Hz), 5.09 (1H, d, J =
10.4 Hz), 4.91 (1H, q, J = 7.2 Hz), 4.52−4.62 (1H, m), 4.30−4.50
(2H, m), 4.12 (2H, t, J = 8.4 Hz), 4.00−4.15 (1H, m), 3.97 (1H, dd,
app. dt, J = 7.0 Hz), 3.40−3.75 (3H, m), 3.25−3.35 (2H, m), 2.94
(3H, s), 2.88 (3H, s), 2.42 (2H, t, J = 6.6 Hz), 2.15−2.30 (1H, m),
1.65−2.00 (7H, m), 1.50−1.58 (1H, m), 1.31 (3H, s), 1.24 (3H, s),
1.16 (3H, d, J = 7.2 Hz), 1.05−1.15 (1H, m), 0.95 (2H, t, J = 8.4 Hz),
0.86 (9H, s), 0.75−0.90 (9H, m), 0.72 (3H, d, J = 6.4 Hz), 0.04 (3H,
s), 0.038 (3H, s), 0.03 (9H, s); 13C NMR (100 MHz, DMSO-d6,
mixture of rotamers) δ 172.0, 171.4, 171.3, 170.4, 169.6, 169.5, 107.6,
79.2, 72.5, 72.4, 70.1, 68.9, 68.7, 61.9, 59.2, 57.5, 55.0, 52.5, 51.9, 46.3,
38.0, 35.9, 34.9, 33.8, 30.4, 29.9, 28.6, 26.83, 26.80, 26.6, 25.7, 25.57,
25.55, 24.4, 23.8, 19.6, 17.9, 17.7, 16.8, 14.9, 14.3, 10.7, −1.52, −4.78,
−5.49; IR (CHCl3) 3320, 2958, 2931, 2877, 2858, 1733, 1683, 1634,
1538, 1471, 1463, 1446, 1410, 1379, 1369, 1314, 1251, 1174, 1118,
1098, 860, 838 cm−1; [α]D27 −101 (c 1.00, CHCl3); HRFABMS calcd
for C43H82O10N5Si2 [M + H]+ 884.5595, found 884.5569; HPLC
retention time 10.23 min, purity >98%.
Cbz-Ile-MeVal-MeAla-β-Ala-OTMSEt (19). To a solution of 18
(1.67 g, 3.21 mmol, 1 equiv) in i-PrOH (17 mL, 5.3 mL/mmol) was
added 10% Pd/C (167 mg, 10 wt %) at room temperature under an
argon atmosphere, and the flask was purged with hydrogen three
times. After being stirred at room temperature for 12 h, the reaction
mixture was filtered through a pad of Celite, and the filtrate was
concentrated in vacuo. The crude residue was used for the next
reaction without further purification.
Cyclization Precursor 3. To a solution of 20 (5.71 g, 6.46 mmol, 1
equiv) in dry THF (32 mL, 5 mL/mmol) was slowly added TBAF (1.0
M solution in THF, 19.4 mL, 19.4 mmol, 3 equiv) at 0 °C under an
argon atmosphere. After the reaction mixture was stirred at room
temperature for 9 h, TBAF (1.0 M solution in THF, 6.5 mL, 6.5 mmol,
1 equiv) was added at 0 °C. After the resulting mixture was stirred at
room temperature for 12 h, DOWEX 50WX8-400 (7.0 g) was added
at 0 °C, and the reaction mixture was filtered through a pad of Celite.
The filtrate was concentrated in vacuo, and the resulting residue was
purified by silica gel column chromatography (eluted with CHCl3/
MeOH = 30:1) to afford cyclization precursor 3 (4.2 g, 6.40 mmol,
To a solution of the crude amine (1.24 g, 3.21 mmol, 1 equiv), Cbz-
Ile-OH (1.30 g, 4.91 mmol, 1.5 equiv), HOAt (0.668 g, 4.91 mmol, 1.5
equiv), and DIEA (1.71 mL, 9.84 mmol, 3 equiv) in dry CH2Cl2 (13
mL, 4 mL/mmol) was added EDCI (0.941 g, 4.91 mmol, 1.5 equiv) at
0 °C under an argon atmosphere. After being stirred at room
temperature for 12 h, the reaction mixture was quenched with
saturated aqueous NH4Cl at 0 °C. The aqueous layer was extracted
with ethyl acetate. The organic layer was washed with saturated
aqueous NaHCO3 and brine. The organic layer was dried over MgSO4
and filtered. The filtrate was concentrated in vacuo, and the resulting
residue was purified by silica gel column chromatography (eluted with
hexane/AcOEt = 1:1) to afford tetrapeptide 19 (1.99 g, 3.13 mmol,
1
94%) as a colorless oil. H NMR (600 MHz, DMSO-d6, 80 °C) δ
7.75−7.90 (1H, br), 7.35−7.45 (1H, br), 5.10 (1H, d, J = 9.6 Hz), 4.93
(1H, q, J = 6.6 Hz), 4.48−4.58 (1H, m), 4.35−4.45 (1H, m), 4.18−
4.30 (1H, m), 4.02−4.13 (1H, m), 3.88−4.00 (1H, m), 3.35−3.70
(3H, m), 3.20−3.35 (2H, m), 2.95 (3H, s), 2.88 (3H, s), 2.33−2.41
(2H, m), 2.18−2.40 (1H, m), 1.60−2.00 (7H, m), 1.50−1.60 (1H, m),
1.31 (3H, s), 1.24 (3H, s), 1.16 (3H, d, J = 7.2 Hz), 1.05−1.15 (1H,
m), 0.75−0.90 (9H, m), 0.72 (3H, d, J = 6.0 Hz); 13C NMR (100
1
98%) as a colorless oil. H NMR (400 MHz, DMSO-d6, 80 °C) δ
7.35−7.45 (1H, br), 7.23−7.33 (5H, m), 6.95−7.15 (1H, br), 4.93−
5.10 (3H, m), 4.89 (1H, q, J = 7.2 Hz), 4.30 (1H, dd, app. dt, J = 8.4
Hz), 4.09 (2H, t, J = 8.2 Hz), 3.23−3.35 (1H, m), 2.93 (3H, s), 2.85
303
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306

The Journal of Organic Chemistry
Article
MHz, DMSO-d6, mixture of rotamers) δ 172.9, 172.4, 172.2, 171.9,
171.4, 171.0, 170.8, 170.3, 169.58, 169.55, 169.1, 107.6, 107.4, 79.1,
72.7, 72.6, 68.7, 68.5, 66.8, 66.7, 59.0, 58.5, 57.4, 57.4, 56.8, 54.9, 53.1,
52.9, 51.8, 51.8, 46.6, 46.3, 37.6, 37.3, 35.9, 35.7, 35.2, 34.9, 33.7, 33.6,
31.7, 30.4, 30.1, 29.94, 29.90, 28.96, 28.93, 28.8, 27.0, 26.79, 26.77,
26.60, 26.56, 25.7, 25.6, 24.3, 24.2, 24.12, 24.07, 24.04, 21.4, 19.5, 19.4,
17.7, 15.4, 15.0, 14.86, 14.68, 14.3, 10.9, 10.7; IR (neat) 3311, 2966,
2938, 2877, 1725, 1624, 1540, 1457, 1409, 1380, 1241, 1221, 1159,
1098, 1065, 754 cm−1; [α]D27 −158 (c 0.80, CHCl3); HRFABMS calcd
for C32H55N5O10Na [M + Na]+ 692.3841, found 692.3808; HPLC
retention time 7.18 min, purity 94%.
chromatography (eluted with hexane/AcOEt = 1:1) to afford alcohol
24 (0.281 g, 0.745 mmol, 73%) as a colorless solid. H NMR (400
1
MHz, CDCl3) δ 7.30−7.45 (5H, m), 5.18 (2H, d, J = 11.2 Hz), 4.53
(1H, dd, J = 2.8, 8.8 Hz), 4.41 (1H, dd, J = 6.4, 10.8 Hz), 4.18−4.25
(1H, m), 4.10 (1H, dd, J = 5.8, 8.2 Hz), 3.70 (1H, dd, J = 7.2, 8.2 Hz),
3.60−3.70 (1H, m), 3.58 (1H, d, J = 6.4 Hz), 1.80−2.25 (6H, m), 1.39
(3H, s), 1.34 (3H, s); 13C NMR (100 MHz, CDCl3) δ 172.4, 171.6,
135.6, 128.5, 128.3, 128.1, 108.6, 72.7, 69.2, 67.2, 66.9, 59.6, 46.5, 37.5,
28.8, 26.8, 25.6, 24.6; IR (neat) 3422, 2983, 2956, 2935, 2880, 1744,
1645, 1456, 1380, 1212, 1170, 1051 cm−1; mp 105−106 °C; [α]2D7
−54.5 (c 1.03, CHCl3); HRESIMS calcd for C20H27NO6Na [M + Na]+
400.1731, found 400.1717.
Macrolactone 2. To a solution of cyclization precursor 3 (4.20 g,
6.40 mmol, 1 equiv) and DMAPO (1.77 g, 12.8 mmol, 2 equiv) in dry
CH2Cl2 (1060 mL, 166 mL/mmol) was added MNBA (6.61 g, 19.2
mmol, 3 equiv) at room temperature under an argon atmosphere.
After the reaction mixture was stirred at 30 °C for 48 h, saturated
aqueous NaHCO3 was added at 0 °C, and the aqueous layer was
extracted with CHCl3. The organic layer was washed with brine, dried
over MgSO4, and filtered. The filtrate was concentrated in vacuo, and
the resulting residue was purified by silica gel column chromatography
(eluted with CHCl3/MeOH = 30:1) to afford macrolactone 2 (3.32 g,
5.21 mmol, 81%) as a colorless amorphous solid. 1H NMR (400 MHz,
CDCl3) δ 8.19 (1H, d, J = 8.0 Hz), 7.15 (1H, d, J = 9.2 Hz), 5.15 (1H,
q, J = 6.8 Hz), 5.06 (1H, dd, J = 5.8, 7.6 Hz), 4.97 (1H, d, J = 11.2
Hz), 4.90 (1H, dd, J = 6.8, 9.0 Hz), 4.69 (1H, d, J = 6.8 Hz), 4.00−
4.15 (3H, m), 3.86−3.94 (1H, m), 3.73−3.80 (1H, m), 3.62 (1H, dd,
app. dt, J = 6.8 Hz), 3.23 (3H, s), 3.08 (1H, dd, J = 11.6, 13.4 Hz),
2.72 (3H, s), 2.45−2.75 (3H, m), 2.26−2.39 (1H, m), 1.83−2.20 (6H,
m), 1.24−1.46 (2H, m), 1.49 (3H, s), 1.33 (3H, s), 1.29 (3H, d, J = 6.8
Hz), 0.93 (3H, d, J = 6.8 Hz), 0.89 (3H, d, J = 6.8 Hz), 0.87 (3H, d, J
= 7.2 Hz), 0.86 (3H, t, J = 7.2 Hz); 13C NMR (100 MHz, CDCl3) δ
173.5, 173.4, 171.0, 170.8, 169.6, 168.8, 109.2, 71.5, 70.8, 69.1, 60.8,
58.0, 55.5, 53.5, 46.4, 37.4, 34.5, 34.4, 33.2, 30.8, 29.2, 28.1, 27.2, 26.8,
25.5, 24.3, 23.9, 20.0, 19.6, 15.4, 15.1, 11.3; IR (CHCl3) 3853, 3744,
3385, 3308, 2965, 2928, 2879, 2360, 2341, 1733, 1683, 1669, 1653,
1635, 1628, 1539, 1521, 1441, 1381, 1183, 1101 cm−1; [α]D28 −199 (c
1.00, CHCl3); HRESIMS calcd for C32H53N5O9Na [M + Na]+
674.3735, found 674.3714.
Cbz-Ile-MeVal-MeAla-β-Ala-HA-Pro-OBn (25). To a solution of
acid 23 (20.7 mg, 0.0346 mmol, 1 equiv) in CH2Cl2/DMF (1:1, 1 mL,
23 mL/mmol) were added alcohol 24 (17.0 mg, 0.0450 mmol, 1.3
equiv), DMAP (1.3 mg, 0.0104 mmol, 0.3 equiv), and EDCI (9.9 mg,
0.0519 mmol, 1.5 equiv) at 0 °C under an argon atmosphere. 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 ethyl acetate. The organic layer was washed with
saturated aqueous NaHCO3 and brine, dried over MgSO4, and filtered.
The filtrate was concentrated in vacuo, and the resulting residue was
purified by silica gel column chromatography (eluted with hexane/
AcOEt = 1:3) to afford amide 25 (28.8 mg, 0.0322 mmol, 73%) as an
amorphous solid. 1H NMR (600 MHz, DMSO-d6, mixture of
rotamers) δ 7.60−7.85 (2H, m), 7.31−7.50 (10H, m), 4.80−5.42
(7H, m), 3.80−4.45 (4H, m), 3.60−3.75 (2H, m), 3.30−3.65 (2H, m),
2.80−3.14 (6H, m), 2.50−2.65 (2H, m), 1.70−2.30 (8H, m), 1.10−
1.60 (11H, m), 0.60−1.00 (12H, m); 13C NMR (100 MHz, DMSO-d6,
mixture of rotamers) δ 172.4, 171.2, 170.4, 170.2, 169.7, 166.99,
166.95, 156.2, 137.2, 136.0, 128.5, 128.4, 128.3, 127.9, 127.7, 127.6,
127.5, 108.1, 108.1, 79.2, 72.0, 69.0, 68.5, 68.1, 66.7, 65.7, 65.3, 59.7,
59.1, 58.9, 58.7, 57.4, 54.9, 51.8, 46.3, 35.6, 34.7, 34.2, 33.5, 30.5, 30.0,
28.4, 26.71, 26.66, 26.62, 25.5, 24.4, 24.1, 20.7, 19.4, 17.9, 14.7, 14.31,
14.27, 14.1, 10.6, 10.5; IR (neat) 3309, 2963, 2936, 2877, 1740, 1721,
1639, 1527, 1455, 1407, 1380, 1341, 1249, 1226, 1170, 1095, 1040,
751 cm−1; [α]D27 −120 (c 1.00, CHCl3); HRESIMS calcd for
C47H67N5O12Na [M + Na]+ 916.4678, found 916.4650; HPLC
retention time 8.95 min, purity 97%.
Dimer 22. To a solution of benzyl ester 25 (20.0 mg, 0.0224 mmol,
1 equiv) in AcOEt/EtOH (1:1, 1.0 mL, 45 mL/mmol) was added 20%
Pd(OH)2/C (3.1 mg, 4.48 μmol, 0.2 equiv) under an argon
atmosphere, and the flask was purged with hydrogen three times.
After being stirred at room temperature for 2 h, the reaction mixture
was filtered through a pad of Celite. The filtrate was concentrared in
vacuo, and the resulting residue was used without further purification.
To a solution of amino acid 21 (10.5 mg, 0.0157 mmol, 1 equiv) in
CH2Cl2 (15.7 mL, 1 mM) were added DIEA (13.7 μL, 0.0785 mmol,
5.0 equiv), HOAt (8.5 mg, 0.0628 mmol, 4.0 equiv), and EDCI (9.0
mg, 0.0471 mmol, 3 equiv) at 0 °C under an argon atmosphere. 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 organic layer was washed with saturated
aqueous NaHCO3 and brine, dried over MgSO4, and filtered. The
filtrate was concentrated in vacuo, and the resulting residue was
purified by reversed-phase HPLC (eluted with CH3CN/H2O) to
afford macrolactone 2 (1.4 mg, 0.00215 mmol, 14%) and dimer 22
(1.3 mg, 0.997 μmol, 6%). 1H NMR (400 MHz, CDCl3) δ 7.00−7.80
(4H, m), 1.80−5.50 (54H, m), 0.70−1.55 (46H, m); 13C NMR (100
MHz, CDCl3, mixture of rotamers) δ 173.4, 170.85, 170.83, 170.2,
168.7, 109.3, 71.5, 70.7, 69.2, 60.4, 57.3, 56.0, 53.6, 46.5, 36.4, 36.0,
34.5, 33.7, 31.9, 31.0, 29.7, 29.5, 29.4, 28.9, 27.8, 26.9, 25.6, 25.2, 23.9,
22.7, 19.7, 18.7, 15.1, 14.9, 14.1, 10.5; HRESIMS calcd for
C64H106N10O18Na [M + Na]+ 1325.7579, found 1325.7548; HPLC
retention time 8.65 min, purity >98%.
Cbz-Ile-MeVal-MeAla-β-Ala-OH (23). To a solution of ester 19
(0.100 g, 0.158 mmol, 1 equiv) in dry THF (1.2 mL, 7.6 mL/mmol)
was slowly added TBAF (0.237 mL, 0.237 mmol, 1.5 equiv) at 0 °C
under an argon atmosphere. After the reaction mixture was stirred at
room temperature for 9 h, DOWEX 50WX8-400 (0.200 g) was added
at 0 °C, and the resulting mixture was filtered through a pad of Celite.
The filtrate was concentrated in vacuo, and the resulting residue was
purified by silica gel column chromatography (eluted with CHCl3/
MeOH = 30:1) to afford carboxylic acid 23 (0.0779 g, 0.146 mmol,
1
92%) as a colorless oil. H NMR (600 MHz, DMSO-d6, 80 °C) δ
7.35−7.45 (1H, br), 7.20−7.35 (5H, m), 7.00−7.25 (1H, br), 5.10
(1H, d, J = 10.2 Hz), 4.95−5.18 (2H, m), 4.92 (1H, q, J = 6.6 Hz),
4.33 (1H, dd, app. dt, J = 8.7 Hz), 3.20−3.35 (2H, m), 2.96 (3H, s),
2.88 (3H, s), 2.37 (2H, t, J = 6.6 Hz), 2.15−2.26 (1H, m), 1.74−1.82
(1H, m), 1.45−1.54 (1H, m), 1.15 (3H, d, J = 6.6 Hz), 1.10−1.20
(1H, m), 0.86 (3H, d, J = 6.6 Hz), 0.82 (3H, d, J = 7.8 Hz), 0.80 (3H,
t, J = 7.8 Hz), 0.71 (3H, d, J = 6.6 Hz); 13C NMR (100 MHz, DMSO-
d6) δ 172.9, 172.4, 170.3, 169.7, 156.2, 137.1, 128.3, 127.7, 127.5, 65.3,
57.4, 54.9, 51.8, 35.6, 34.9, 33.7, 30.4, 30.0, 26.6, 24.2, 19.4, 17.9, 14.7,
14.3, 10.6; IR (CHCl3) 3310, 2965, 2938, 2876, 1716, 1681, 1628,
1530, 1456, 1408, 1344, 1293, 1251, 1123, 1099, 1027, 755, 698 cm−1;
[α]2D5 −152 (c 1.04, CHCl3); HRESIMS calcd for C27H42N4O7Na [M
+ Na]+ 557.2946, found 557.2927; HPLC retention time 8.05 min,
purity >98%.
Alcohol 24. To a solution of TBS ether 13a (0.500 g, 1.02 mmol, 1
equiv) in THF (4.0 mL, 3.9 mL/mmol) was added HF−pyridine
(∼70% HF, 1.0 mL) at 0 °C under an argon atmosphere. After being
stirred at same temperature for 6 h, the reaction mixture was poured
into saturated aqueous NaHCO3 at 0 °C. The aqueous layer was
extracted with ethyl acetate, and the organic layer was washed with
brine, dried over MgSO4, and filtered. The filtrate was concentrated in
vacuo, and the resulting residue was purified by silica gel column
Diol 26. To a solution of macrolactone 2 (1.33 g, 2.04 mmol, 1
equiv) in 1,4-dioxane (6.7 mL, 3.3 mL/mmol) was slowly added 1.5 M
HCl(aq) (13.3 mL, 6.5 mmol) at 0 °C. After the reaction mixture was
stirred at 0 °C for 2 h, saturated aqueous NaHCO3 was added, and the
aqueous layer was extracted with ethyl acetate. The organic layer was
304
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306

The Journal of Organic Chemistry
Article
washed with brine, dried over MgSO4, and filtered. The filtrate was
concentrated in vacuo, and the resulting residue was purified by silica
gel column chromatography (eluted with CHCl3/MeOH = 30:1) to
afford diol 26 (1.08 g, 1.77 mmol, 87%) as a colorless amorphous
solid. 1H NMR (400 MHz, CDCl3) δ 8.15 (1H, d, J = 10.4 Hz), 7.13
(1H, d, J = 9.2 Hz), 5.19 (1H, q, J = 6.8 Hz), 5.12 (1H, dd, J = 5.2, 6.4
Hz), 4.98 (1H, d, J = 11.2 Hz), 4.89 (1H, dd, J = 6.4, 9.2 Hz), 4.68
(1H, d, J = 6.0 Hz), 3.96−4.10 (2H, m), 3.85−3.95 (1H, m), 3.63−
3.73 (2H, m), 3.45−3.55 (1H, m), 3.23 (3H, s), 3.05−3.15 (1H, m),
2.73 (3H, s), 2.45−2.70 (3H, m), 2.28−2.38 (1H, m), 1.85−2.10 (5H,
m), 1.25−1.45 (2H, m), 1.31 (3H, d, J = 6.8 Hz), 0.93 (3H, d, J = 6.8
Hz), 0.89 (3H, d, J = 6.8 Hz), 0.86 (3H, d, J = 6.8 Hz), 0.86 (3H, t, J =
7.6 Hz); 13C NMR (100 MHz, CDCl3) δ 173.6, 173.5, 171.1, 171.0,
169.9, 70.8, 67.7, 66.4, 60.9, 58.1, 55.5, 53.7, 46.7, 37.3, 34.5, 33.9,
33.3, 30.8, 29.3, 28.1, 27.2, 24.4, 23.9, 19.9, 19.5, 15.4, 15.1, 11.3; IR
(CHCl3) 3345, 3301, 2961, 2886, 2360, 1734, 1720, 1652, 1634, 1630,
1622, 1538, 1455, 1414, 1262, 1179, 1025 cm−1; [α]D28 −230.4 (c 1.00,
CHCl3); HRESIMS calcd for C29H49N5O9Na [M + Na]+ 634.3422,
found 634.3397.
13C NMR (100 MHz, CDCl3) δ 173.5 173.4, 171.0, 170.8, 169.7,
168.6, 70.6, 60.9, 58.0, 55.5, 53.6, 47.8, 47.1, 46.6, 37.5, 34.5, 33.6,
33.2, 30.8, 29.2, 28.1, 27.2, 24.4, 24.0, 20.0, 19.6, 15.4, 15.2, 11.4; IR
(CHCl3) 3385, 3298, 2960, 2923, 2851, 1731, 1673, 1670, 1636, 1631,
1622, 1519, 1445, 1413, 1378, 1278, 1178, 1100 cm−1; [α]D28 −247 (c
1.00, CHCl3) {lit4b [α]D25 −253 (c 1.00, CHCl3)}; HRESIMS calcd for
C29H47N5O8Na [M + Na]+ 616.3317, found 616.3297.
ASSOCIATED CONTENT
■
S
* Supporting Information
Copies of 1H and 13C NMR spectra for 1−4, 7, 8, 13a, 15, 17−
1
20, 22−27; copy of the H spectrum for 21; and HPLC
chromatograms for 1, 3, 15, 17−23, and 25. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
Tosylate 27. To a solution of diol 26 (1.08 g, 1.77 mmol, 1 equiv),
triethylamine (0.371 mL, 2.12 mmol, 1.5 equiv), and DMAP (21.6 mg,
0.177 mmol, 0.1 equiv) in dry CH2Cl2 (18 mL, 10 mL/mmol) was
added p-toluenesulfonyl chloride (0.405 g, 2.12 mmol, 1.2 equiv) at 0
°C under an argon atmosphere. After the reaction mixture was stirred
at room temperature for 6 h, additional triethylamine (0.246 mL, 1.77
mmol, 1.0 equiv) and p-toluenesulfonyl chloride (0.270 g, 1.416 mmol,
0.8 equiv) were added at 0 °C. After the reaction mixture was stirred at
room temperature for 6 h, saturated aqueous NH4Cl was added, and
the aqueous layer was extracted with CHCl3. The organic layer was
washed with brine, dried over MgSO4, and filtered. The filtrate was
concentrated in vacuo, and the resulting residue was purified by silica
gel flash column chromatography (eluted with CHCl3/MeOH = 30:1)
to afford tosylate 27 (1.10 g, 1.44 mmol, 81%) as a colorless
amorphous solid. 1H NMR (400 MHz, CDCl3) δ 8.12 (1H, d, J = 8.4
Hz), 7.79 (2H, d, J = 8.2 Hz), 7.37 (2H, d, J = 8.2 Hz), 7.09 (1H, d, J
= 9.2 Hz), 5.16 (1H, q, J = 6.8 Hz), 5.10 (1H, dd, app. dt, J = 5.8 Hz),
4.96 (1H, d, J = 11.2 Hz), 4.89 (1H, dd, J = 6.2, 9.4 Hz), 4.65 (1H, d, J
= 6.8 Hz), 4.10−4.16 (1H, m), 3.95−4.09 (3H, m), 3.87−3.94 (1H,
m), 3.57−3.67 (1H, m), 3.22 (3H, s), 3.00−3.10 (1H, m), 2.72 (3H,
s), 2.48−2.68 (2H, m), 2.47 (3H, s), 2.28−2.38 (1H, m), 1.85−2.15
(5H, m), 1.23−1.48 (2H, m), 1.30 (3H, d, J = 6.8 Hz), 1.28−1.33
(1H, m), 0.92 (3H, d, J = 6.8 Hz), 0.88 (3H, d, J = 6.8 Hz), 0.86 (3H,
d, J = 7.2 Hz), 0.85 (3H, t, J = 7.2 Hz); 13C NMR (100 MHz, CDCl3)
δ 173.6, 173.3, 171.0, 170.7, 169.7, 169.5, 145.3, 132.3, 130.0, 127.9,
73.2, 70.0, 65.2, 60.9, 58.0, 55.4, 53.6, 46.7, 37.3, 34.4, 33.6, 33.1, 30.8,
29.1, 28.1, 27.2, 24.3, 23.9, 21.6, 19.9, 19.5, 15.4, 15.1, 11.3; IR
(CHCl3) 3387, 3301, 2962, 2922, 2852, 1733, 1673, 1632, 1630, 1627,
1622, 1520, 1464, 1362, 1265, 1177, 1098 cm−1; [α]D28 −202 (c 1.00,
CHCl3); HRESIMS calcd for C36H55N5O11SNa [M + Na]+ 788.3511,
found 788.3485.
*E-mail: doi_taka@mail.pharm.tohoku.ac.jp.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by a Grant-in-Aid for Young
Scientists (B) (M.Y.) from JSPS and the Japan Science and
Technology Agency (A-STEP, AS242Z00980Q). We thank Mr.
Hisayuki Takeuchi for initial investigations on the synthesis of
destruxin E.
REFERENCES
■
(1) (a) Seeman, E. J. Appl. Physiol. 2003, 95, 2142−2151.
(b) Sambrook, P.; Cooper, C. Lancet 2006, 367, 2010−2018.
́
(2) (a) Karsdal, M. A.; Qvist, P.; Christiansen, C.; Tanko, L. B. Drugs
2006, 66, 1909−1918. (b) Rachner, T. D.; Khosla, S.; Hofbauer, L. C.
Lancet 2011, 377, 1276−1287. (c) Henriksen, K.; Bollerslev, J.; Everts,
V.; Karsdal, M. A. Endocr. Rev. 2011, 32, 31−63.
(3) (a) Farina, C.; Gagliardi, S. Drug Discovery Today 1999, 4, 163−
172. (b) Farina, C.; Gagliardi, S. Curr. Pharm. Des. 2002, 8, 2033−
2048. (c) Bowman, E. J.; Bowman, B. J. J. Bioenerg. Biomembr. 2005,
37, 431−435. (d) Yuan, F.-L.; Li, X.; Lu, W.-G.; Li, C.-W.; Li, J.-P.;
Wang, Y. Mol. Biol. Rep. 2010, 37, 3561−3566. (e) Katner, N.; Yao, Y.;
Crasto, G. J.; Datti, A.; Manolson, M. F. J. Biol. Chem. 2010, 285,
37476−37490. (f) Thudium, C. S.; Jensen, V. K.; Karsdal, M. A.;
Henriksen, K. Curr. Protein Pept. Sci. 2012, 13, 141−151.
(4) (a) Païs, M.; Das, B. C.; Ferron, P. Phytochemisty 1981, 20, 715−
723. (b) Gupta, S.; Roberts, D. W.; Renwick, J. A. A. J. Chem. Soc.,
Perkin Trans. 1 1989, 2347−2357.
Destruxin E (1). To a solution of tosylate 27 (1.10 g, 1.44 mmol, 1
equiv) in i-PrOH/(CH2Cl)2 (10:1, 15 mL, 10 mL/mmol) was added
K2CO3 (0.793 g, 5.74 mmol, 4 equiv) at 0 °C under an argon
atmosphere. After the reaction mixture was stirred at 50 °C for 4 h,
saturated aqueous NH4Cl was added at 0 °C, and the aqueous layer
was extracted with CHCl3. The organic layer was washed with brine,
dried over MgSO4, and filtered. The filtrate was concentrated in vacuo,
and the resulting residue was purified by silica gel flash column
chromatography twice (eluted with CHCl3/MeOH = 50:1, ethyl
acetate/MeOH = 20:1) to afford destruxin E (1) (0.547 g, 0.921
́ ́
(5) Vazquez, M. J.; Albarran, M. I.; Espada, A.; Rivera-Sagredo, A.;
Díaz, E.; Hueso-Rodríguez, J. A. Chem. Biodiversity 2005, 2, 123−130.
(6) (a) Kuyama, S.; Tamura, S. Agric. Biol. Chem. 1965, 29, 168−190.
(b) Lee, S.; Izumiya, N.; Suzuki, A.; Tamura, S. Tetrahedron Lett. 1975,
16, 883−886. (c) Calmes, M.; Cavelier-Frontin, F.; Jacquier, R.;
Mercadier, J.-L.; Sabil, S.; Verducci, J.; Qciot, J.-M.; Vey, A. Int. J. Pept.
Protein Res. 1993, 41, 528−535. (d) Cavelier, F.; Jacquier, R.;
Mercadier, J.-L.; Verducci, J. Tetrahedron 1996, 52, 6173−6186.
(e) Ward, D. E.; Lazny, R.; Pedras, M. S. C. Tetrahedron Lett. 1997, 38,
339−342. (f) Cavelier, F.; Jacquier, R.; Mercadier, J.-L.; Verducci, J.;
Traris, M.; Vey, A. J. Pept. Res. 1997, 50, 94−101. (g) Cavelier, F.;
1
mmol, 64%) as a colorless amorphous solid. H NMR (400 MHz,
CDCl3) δ 8.21 (1H, d, J = 10.0 Hz), 7.16 (1H, d, J = 9.2 Hz), 5.16
(1H, q, J = 6.8 Hz), 4.99 (1H, dd, app. dt, J = 7.2 Hz), 4.97 (1H, d, J =
10.8 Hz), 4.89 (1H, dd, J = 6.8, 9.2 Hz), 4.70 (1H, d, J = 7.2 Hz),
4.00−4.10 (1H, m), 3.92−3.99 (1H, m), 3.23 (3H, s), 3.08 (1H, br t, J
= 12.0 Hz), 2.95−3.00 (1H, m), 2.83 (1H, dd, app. dt, J = 4.4 Hz),
2.72 (3H, s), 2.62−2.72 (1H, m), 2.45−2.59 (3H, m), 2.24−2.40 (2H,
m), 2.02−2.12 (1H, m), 1.85−2.01 (4H, m), 1.38−1.46 (1H, m), 1.31
(3H, d, J = 6.8 Hz), 1.28−1.33 (1H, m), 0.93 (3H, d, J = 6.8 Hz), 0.89
(3H, d, J = 6.8 Hz), 0.87 (3H, d, J = 7.2 Hz), 0.86 (3H, t, J = 7.6 Hz);
́
Verducci, J.; Andre, F.; Haraux, F.; Sigalat, C.; Traris, M.; Vey, A.
Pestic. Sci. 1998, 52, 81−89. (h) Ward, D. E.; Gai, Y.; Lazny, R.;
Pedras, M. S. C. J. Org. Chem. 2001, 66, 7832−7840. (i) Ast, T.;
Barron, E.; Kinne, L.; Schmidt, M.; Germeroth, L.; Simmons, K.;
Wenschuh, H. J. Pept. Res. 2001, 58, 1−11.
(7) Yoshida, M.; Takeuchi, H.; Ishida, Y.; Yashiroda, M.; Takagi, M.;
Shin-ya, K.; Doi, T. Org. Lett. 2010, 12, 3792−3795.
305
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306

The Journal of Organic Chemistry
Article
(8) Nakagawa, H.; Takami, M.; Udagawa, N.; Sawae, Y.; Suda, K.;
Sasaki, T.; Takahashi, N.; Wachi, M.; Nagai, K.; Woo, J. T. Bone 2003,
33, 443−455.
(9) (a) Shiina, I.; Ibuka, R.; Kubota, M. Chem. Lett. 2002, 286−287.
(b) Shiina, I.; Kubota, M.; Ibuka, R. Tetrahedron Lett. 2002, 43, 7535−
7539. (c) Shiina, I.; Kubota, M.; Oshiumi, H.; Hashizume, M. J. Org.
Chem. 2004, 69, 1822−1830. (d) Shiina, I.; Hashizume, M.; Yamai, Y.;
Oshiumi, H.; Shimazaki, T.; Takasuna, Y.; Ibuka, R. Chem.Eur. J.
2005, 11, 6601−6608.
(10) (a) Jacobsen, E. N.; Marko, I.; Mungall, W. S.; Schroder, G.;
Sharpless, K. B. J. Am. Chem. Soc. 1988, 110, 1968−1970. (b) Kolb, H.
C.; VanNieuwenhze, M. S.; Sharpless, K. B. Chem. Rev. 1994, 94,
2483−2547.
(11) (a) Roth, G. A. J. Org. Chem. 1995, 60, 8105−8109.
(b) Kobayashi, M.; Kurosu, M.; Wang, W.; Kitagawa, I. Chem.
Pharm. Bull. 1994, 42, 2394−2396.
(12) (a) Crispino, G. A.; Jeong, K.-S.; Kolb, H.-C.; Wang, Z.-M.; Xu,
D.; Sharpless, K. B. J. Org. Chem. 1993, 58, 3785−3786. (b) Arrington,
M. P.; Bennani, Y. L.; Gobel, T.; Walsh, P.; Zhao, S.-H.; Sharpless, K.
̈
B. Tetrahedron Lett. 1993, 34, 7375−7378. (c) Becker, H.; King, S. B.;
Taniguchi, M.; Vanhessche, K. P. M.; Sharpless, K. B. J. Org. Chem.
1995, 60, 3940−3941. (d) Corey, E. J.; Guzman-Perez, A.; Noe, M. C.
J. Am. Chem. Soc. 1995, 117, 10806−10816.
(13) Crimmins et al. have reported that allyl iodide is effective for the
alkylation of glycolate derivatives. See: Crimmins, M. T.; Emmitte, K.
A.; Katz, J. D. Org. Lett. 2000, 2, 2165−2167.
̂ ́
(14) Evans, D. A.; Trotter, B. W.; Cate, B.; Colman, P. J.; Dias, L. C.;
Tyler, A. N. Angew. Chem., Int. Ed. Engl. 1997, 36, 2744−2748.
(15) Evans, D. A.; Morrissey, M. M.; Dorow, R. L. J. Am. Chem. Soc.
1985, 107, 4346−4348.
́
(16) Frerot, E.; Coste, J.; Pantaloni, A.; Dufour, M.-N.; Jouin, P.
Tetrahedron 1991, 47, 259−270.
(17) Structure determinations of 12a and 12b were carried out after
partial separation by column chromatography. Acetal formation of the
partially obtained 12a and 12b led to 13a and its diastereomer, whose
spectra were identical to those of the corresponding isomers of 13
prepared from optically active known 6S and 6R, respectively.
(18) Becker, H.; Sharpless, K. B. Angew. Chem., Int. Ed. Engl. 1996,
35, 448−451.
(19) Anteunis, M. J. O.; Van Der Auwera, C. Int. J. Pept. Protein Res.
1988, 31, 301−310.
(20) Hughes, A. B.; Sleebs, B. E. Helv. Chim. Acta 2006, 89, 2611−
2637.
(21) Mauger, A. B.; Desai, R. B.; Rittner, I.; Rzeszotarski, W. J. J.
Chem. Soc., Perkin Trans. 1 1972, 2146−2148.
(22) The cyclization precursor 21 was immediately used for next
macrolactamization because of decomposition during the purification
by silica gel column chromatography.
(23) Conformational studies of destruxin and related molecules have
been performed. See: (a) Springer, J. P.; Cole, R. J.; Dorner, J. W.;
Cox, R. H.; Richard, J. L.; Barnes, C. L.; van der Helm, D. J. Am. Chem.
Soc. 1984, 106, 2388−2392. (b) Snyder, J. P. J. Am. Chem. Soc. 1984,
106, 2393−2400. (c) Gupta, S.; Roberts, D. W.; Renwick, J. A. A.; Ni,
C.-Z.; Clardy, J. Tetrahedron Lett. 1989, 30, 4189−4192.
(24) Wang, B.; Kang, Q.; Lu, Y.; Bai, L.; Wang, C. Proc. Natl. Acad.
Sci. U.S.A. 2012, 109, 1287−1292.
306
dx.doi.org/10.1021/jo402437z | J. Org. Chem. 2014, 79, 296−306