Parallel Synthesis and Biological Evaluation of Destruxin E Analogs Modified with a Side Chain in the α-Hydroxycarboxylic Acid Moiety

Article abstract of DOI:10.1002/ejoc.201801826

This study demonstrates the synthesis and biological evaluation of destruxin E analogs possessing various functional groups in the α-hydroxycarboxylic acid moiety. Parallel synthesis of eleven analogs was successfully achieved through solution-phase peptide synthesis and macrolactonization. Biological evaluation of the synthetic analogs using osteoclast-like multi nuclear cells (OCLs) revealed that the epoxide group in the side chain of α-hydroxycarboxylic acid and the orientation of the oxygen atom are essential factors in the desired potent activity that induces morphological changes in OCLs for the inhibition of bone-resorbing activity.

Full text of DOI:10.1002/ejoc.201801826

A Journal of
Accepted Article
Title: Parallel Synthesis and Biological Evaluation of Destruxin E
Analogs Modified with a Side Chain in the α-Hydroxycarboxylic
Acid Moiety
Authors: Masahito Yoshida, Kenta Adachi, Hayato Murase, Hiroshi
Nakagawa, and Takayuki Doi
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201801826
Link to VoR: http://dx.doi.org/10.1002/ejoc.201801826
Supported by

European Journal of Organic Chemistry
10.1002/ejoc.201801826
FULL PAPER
Parallel Synthesis and Biological Evaluation of Destruxin E
Analogs Modified with a Side Chain in the α-Hydroxycarboxylic
Acid Moiety
[
a, §]
[a]
[b]
[b]
[a]
Masahito Yoshida,
Kenta Adachi, Hayato Murase, Hiroshi Nakagawa, and Takayuki Doi*
Abstract: This study demonstrates the synthesis and biological
evaluation of destruxin E analogs possessing various functional
groups in the α-hydroxycarboxylic acid moiety. Parallel synthesis of
eleven analogs was successfully achieved through solution-phase
peptide synthesis and macrolactonization. Biological evaluation of
the synthetic analogs using osteoclast-like multi nuclear cells (OCLs)
revealed that the epoxide group in the side chain of α-
hydroxycarboxylic acid and the orientation of the oxygen atom are
essential factors in the desired potent activity that induces
morphological changes in OCLs for the inhibition of bone-resorbing
activity.
hydroxycarboxylic acid moiety has not yet been carried out,
except for a study on the hydrophobic allyl and isobutyl groups
shown in destruxins A (3a) and B (3b), which exhibit a potent
activity that is 20-fold less than that found in destruxin E (1). In
addition, destruxin
E diol (3c) is inactive against OCLs,
indicating that a hydrophilic moiety such as a hydroxy group
6
could be prohibited for the biological activity (Figure 1). In this
study, we achieved the synthesis of destruxin E analogs with
modification of the epoxide side chain on the α-
hydroxycarboxylic acid and evaluated their biological activity to
elucidate the effect of the epoxide moiety.
O
Destruxin E (1): R =
H
Introduction
N
O
N
epi-Destruxin E (2): R =
Destruxin A (3a): R =
O
O
O
R
O
O
O
1
9-Membered cyclodepsipeptide destruxin E (1) was isolated
N
O
from Metarhidium anisopliae by Päis et al. in 1981 and is
composed of five amino acids (β-Ala, MeAla, MeVal, Ile, and
Pro), and an α-hydroxycarboxylic acid with a terminal epoxide-
Destruxin B (3b): R =
N
N
H
OH
Destruxin E diol (3c): R =
OH
1
containing a C3 side chain. Thus far, various natural and
2
synthetic analogs have been reported ; in particular, 1 exhibits
Figure 1. Destruxin E (1), epi-destruxin E (2), destruxin A (3a), B (3b), and
diol derivative 3c.
+
the most potent vacuolar (H )-ATPase (V-ATPase) inhibitory
3
activity. We recently achieved the total synthesis of 1 and have
determined that the (S)-epoxide moiety is important for inducing
the potent V-ATPase inhibitory activity, whereas the presence of
Results and Discussion
4
(
R)-epoxide significantly decreases the activity of analog 2. In
addition, destruxin E (1) reversibly inhibits the bone-resorbing
activity by inducing morphological changes in osteoclasts-like
multinuclear cells (OCLs) at an even lower dose level without
To explain the structure–activity relationship of the α-
hydroxycarboxylic acid moiety, we designed various analogs
possessing different functional groups on the side chain, such as
a methyl ether 4a, methyl ketone 4b, difluoromethylene 4c,
cyclopropanes 4d–4f, and oxetanes 4g–4i. In addition, we also
designed the synthesis of epoxide homologs 4j–4k to determine
the role of the epoxide moiety in the biological activity.
Retrosynthesis of the analogs is shown in Scheme 1. According
5
affecting cell viability, indicating that 1 and its analogs could be
promising candidates for the development of novel anti-
resorptive agents for therapeutics used to treat osteoporosis.
Although the structure-activity relationships (SARs) have been
studied by altering the amino acid moieties, a SAR study
focusing on the epoxide-containing C3 side chain in the α-
4, 7
to the total synthesis of destruxin E (1), the desired analogs 4
would be afforded through macrolactonization of the linear
precursors 5, this can be prepared by amidation of acid 6,
containing various functional groups in the side chain and the
known tetrapeptide 7 that we reported previously.
[
a]
b]
Prof.Dr. M. Yoshida, K. Adachi, Prof.Dr. T. Doi
Graduate School of Pharmaceutical Sciences, Tohoku University
6-3 Aza-Aoba, Aramaki, Sendai 980-8578 (Japan)
E-mail: doi_taka@mail.pharm.tohoku.ac.jp
Homepage: http://www.pharm.tohoku.ac.jp/~hannou/index.html
H. Murase, Prof.Dr. H. Nakagawa
[
Department of Applied Biological Chemistry, Chubu University
1200 Matsumoto-cho, Kasugai, Aichi 487-8501 (Japan)
§
Current address:
Faculty of Pure and Applied Sciences, University of Tsukuba
1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571 (Japan)
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Organic Chemistry
10.1002/ejoc.201801826
FULL PAPER
F
F
After hydrolysis of the methyl ester in 11, amidation of the
H
N
F
F
resulting acid with H-Pro-OBn was performed using
N
O
10
O
O
O
R
F
F
PyBrop /DIEA, gave the less polar 9e (27% yield) and polar 9f
O
O
O
O
N
O
a
b
c
d
e
f
(29% yield), respectively, isolated by silica gel column
chromatography. The absolute configurations of the newly
formed stereocenters in 9e and 9f are not determined.
N
O
O
N
H
O
O
O
g
h
i
j
k
4
Oxetane derivatives of 9g–9i were prepared from commercially
available (±)-glycidol (12), and the details of the reaction are
illustrated in Schemes 3 and 4. A hydrolytic kinetic resolution of
the racemic epoxide 13 was carried out using the (S, S)-Salen-
Co complex as a catalyst, and an enantio-enriched epoxide (R)-
O
OTMSE
O
OTMSE
H
N
H
N
N
N
O
O
O
O
TBSO
O
O
O
TBSO
N
R
13 was afforded in 47% yield concomitantly with diol (S)-14,
N
O
R
O
O
11,12
N
obtained in 48% yield.
Alkenylation of (R)-13 using
N
NH
2
HO
N
H
vinylcuprate provided alkene 15 that was converted to a 1:1
diastereomeric mixture of epoxide 16 in 97% yield via
epoxidation with m-CPBA and by protecting the resulting alcohol
with a TBS group. A hydrolytic kinetic resolution of the epoxide
moiety in 16 using the (S, S)-Salen-Co complex resulted in the
5
7
6
Scheme 1. Retrosynthesis of destruxin E analogs.
1
3
formation of the diol (2R, 4S)-17 (48% yield) and the remaining
epoxide (2S, 4S)-16a (41% yield) as a single diastereomer. The
obtained diol (2R, 4S)-17 was converted via two steps into the
corresponding epoxide (2S, 4R)-16b in 72% yield.
As detailed in the retrosynthesis described above, we initially
attempted the preparation of the methyl ether 9a and the
cyclopropyl derivatives 9d–9f (Scheme 2). The oxidative
7
cleavage of the alkene moiety in 8 afforded aldehyde and
reduction of the resulting aldehyde followed by O-methylation
DHP, p-TsOH
O
O
HO
THPO
13
using Me
yield. The cyclopropyl derivatives 9d–9f were prepared as
follows: the Simmons–Smith reaction of 8 using CH /Et Zn
3
OBF
4
provided the desired methyl ether 9a in 82%
CH Cl2
2
rt, 10 min, 80%
(±)-Glycidol (12)
2
I
2
2
afforded 9d in 83% yield. However, the preparation of
difluorocyclopropane moiety in dipeptide 8 using difluorocarbene
(S,S)-Salen-Co Complex
AcOH, H
OH
2
O
O
THPO
(R)-13
THPO
OH
+
THF, 0 °C, 9 h
generated from trimethylsilyl fluorosulfonyldifluoroacetate
(S)-14 (48%)
(
47%, 98%ee)
8
(
TFDA)/NaF failed, and
a
complex mixture including
a
the
VinylMgBr
1) m-CPBA, CH Cl2
2
desilylated
product
was
of
obtained.
the
Fortunately,
CuBr•Me
2
S
rt, 20 h
OH
7
difluoromethylenation
alkene
10
using
(R)-13
THPO
THF
2) TBSCl, imidazole
DMF, rt, 5 h
2 steps 97%
(
bromodifluoromethyl)trimethylsilane/tetrabutylammonium
0 °C, 30 min
97%
15
9
bromide
(TBAB)
proceeded
smoothly
to
afford
difluorocyclopropane 11 in 59% yield as a 1:1 diastereomer
TBSO
O
THPO
mixture.
2
4
(S,S)-Salen-Co Complex
AcOH, H
2
O
(2S, 4S)-16a (41%)
TBSO
THPO
O
1
) OsO
dioxane-H
) NaBH , MeOH, 0 °C, 30 min
4
, NaIO
4
, 2,6-lutidine
THF, rt, 9 h
TBSO
THPO
OH
2
TBSO
2
O, rt ,10 h, 78%
TBSO
OH
2
4
16
O
O
4
O
O
O
N
, Proton-sponge®
3 4
OBF
N
(2R, 4S)-17 (48%)
3
) Me
MS4Å, CH
steps 82%
BnO
BnO
2
2
Cl , rt, 18 h
1
) TsCl, NEt
3
, DMAP
2
CH Cl , rt, 9 h
2
2
8
9a
TBSO
(2R, 4S)-17
O
THPO
2) K
0
2
CO
3
, MeOH
2
4
°C, 2 h
TBSO
O
2 steps 72%
(2S, 4R)-16b
2 2 2
CH I , Et Zn
O
N
CH
rt, 46 h, 83%
2
Cl
2
Scheme 3. Preparation of epoxides (2S, 4S)-16a and (2S, 4R)-16b.
BnO
9d
1
) LiOH•H
THF-MeOH-H
2
O
After synthesizing the desired epoxides, 16a and 16b, formation
TMSCF
TBAB
2
Br
F
2
O
TBSO
TBSO
F
rt, 2 h
of oxetane was carried out by treatment with trimethylsulfonium
9e (27%)
9f (29%)
O
O
14
*
iodide under basic conditions to afford (2S, 4R)-18a and (2S,
toluene
110 °C, 24 h MeO
2) H-Pro-OBn•HCl
PyBroP, DIEA
CH Cl , rt, 20 h
2 2
MeO
4S)-18b, respectively (Scheme 4). THP group was removed,
and the resulting alcohol was oxidized to acid, followed by
amidation with H-Pro-OBn to produce the oxetane-containing
59%
11
1
0
Scheme 2. Synthesis of methyl ester 9a and cyclopropyl derivatives 9d–9f.
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European Journal of Organic Chemistry
10.1002/ejoc.201801826
FULL PAPER
acylproline derivatives 9g and 9h in moderate yields. In addition,
we also attempted to prepare the oxetane derivative 9i from (S)-
26 proceeded smoothly, leading to methyl ketone 27, which was
treated with diethylaminosulfur trifluoride (DAST) at room
temperature to afford 28 in 34% yield. To achieve the synthesis
of epoxide-containing analogs 4j and 4k, diol-containing
1
4. Protection of the diol in (S)-14 with TBS groups, followed by
removal of the THP group using Et AlCl afforded alcohol 19 in
2
1
2
9
2% yield. After conversion of the resulting alcohol to mesylate, acylprolines 9l and 9m were prepared from methyl hexenoate
substitution with dimethyl malonate under basic conditions
derivative 26. Dihydroxylation of the terminal alkene 26 was
performed by treatment with OsO /N-methylmorpholine N-oxide
afforded dimethyl ester 20 in 90% yield. Treatment of dimethyl
4
ester 20 with LiAlH
4
afforded diol 21, and formation of an
(NMO) to provide diols as a 1:1 mixture of diastereomers. The
resulting mixture was subsequently subjected to basic conditions,
and the primary alcohol in the resulting lactone was acylated
with benzoyl chloride to afford benzoates (2S, 5S)-29a and (2S,
1
5
oxetane moiety was achieved smoothly using TsCl/BuLi to
provide 22 in 81% yield. Finally, the selective removal of the
TBS group on the primary alcohol lead to 23, this was then
followed by coupling with H-Pro-OBn via three steps to produce
1
6
5R)-29b, respectively.
After separation of the above
9
i, which possessed a symmetrical oxetane moiety.
diastereomers by column chromatography, solvolysis was
carried out under basic conditions, followed by protection of the
resulting diol that provided methyl esters (2S, 5S)-30a and (2S,
5R)-30b. Finally, acylprolines 9 were synthesized as follows;
hydrolysis of the methyl esters in 27, 28, and 30 using LiOH in
the mixed solvents afforded the corresponding acids that were
subsequently amidated with H-Pro-OBn using PyBroP/DIEA to
provide the desired 9b, 9c, 9l, and 9m in moderate yields.
[
Me
BuOK
3
S(O)]I
1) Mg, (CH
Et O, rt, 4 h
2
2 2
Br)
t
TBSO
THPO
TBSO
THPO
O
O
tBuOH
0 °C, 16 h
2) (COCl) , DMSO
NEt , CH Cl
2
*
*
2
6
3
2
(
(
2S, 4S)-16a
2S, 4R)-16b
(2S, 4R)-18a (58%)
(2S, 4S)-18b (46%)
–78 °C, 1 h
3
) NaClO
2 2 4
, NaH PO
TBSO
O
2
-methyl-2-butene
t
O
BuOH-H
2
O, rt, 1 h
O
*
AllyllMgBr
1) TBSCl, imidazole
4
) H-Pro-OBn•HCl, PyBroP
N
CuBr•Me2S
OH
DMF, rt, 3 h, 88%
BnO
O
DIEA, CH Cl , rt, 15 h
2
2
THPO
(R)-13
THPO
THF-Et2O
2) Et2AlCl, CH2Cl2
rt, 1 h, 87%
0
°C, 2 h
2%
(
(
2S, 4R)-9g (51%)
2S, 4S)-9h (41%)
24
6
1
) MsCl, NEt
3
1) (COCl)2, DMSO, NEt3
CH Cl , –78 °C, 1 h
2 2
1
) TBSCl, imidazole
DMF, rt, 5 h, 96%
OTBS
CH
2
Cl
2
, rt, 1 h
TBSO
OTBS
O
(S)-14
TBSO
OH
HO
2) Et
2
AlCl, CH
2
Cl
2
2) dimethyl malonate
NaH, KI, DMF-THF
2) NaClO2, NaH2PO4
MeO
rt, 1 h, 92%
2-methyl-2-butene
19
rt, 22 h, 2 steps 90%
25
t
BuOH-H2O, rt, 1 h
26
3) MeI, K2CO3, DMF
rt, 15 h, 3 steps 60%
1
) cat. OsO4, NMO
THF-H2O
O
OMe
OMe
OH
TBSO
TBSO
LiAlH
4
rt, 3 h, quant
2) DBU, MS3Å, MeCN
rt, 2 h, 74%
) BzCl, NEt3, CH2Cl2
TBSO
TBSO
OH
THF
PdCl2, CuCl
O2 (balloon)
DMF-H2O
O
0 °C, 20 min, 78%
20
21
3
rt, 2 h
rt, 15 h, 92%
TsCl, BuLi
THF, 0 °C;
TBSO
TBSO
TBSO
HO
O
HF•Py.
O
O
OTBS
OTBS
2
O
BuLi
0 °C, 20 h, 81%
THF
0 °C, 6 h, 64%
O
6
BzO
22
23
*
MeO
O
(2S, 5S)-29a (38%)
27
(2S, 5R)-29b (43%)
1
) (COCl)
CH Cl
) NaClO
-methyl-2-butene
2
, DMSO, NEt
, –78 °C, 1 h
, NaH PO
3
2
2
1) K2CO3, MeOH
2
2
2
4
TBSO
DAST, CH2Cl2
rt, 16 h, 34%
0 °C, 2 h
2) 2,2-DMP, p-TsOH
CH Cl , rt, 10 min
2
2
t
O
O
2
BuOH-H O, rt, 1 h
O
2
N
3
) H-Pro-OBn•HCl, PyBroP
BnO
DIEA, CH Cl , rt, 15 h
2
2
OTBS
OTBS
2
O
O
*
9i
O
F
F
MeO
MeO
O
Scheme 4. Synthesis of oxetane derivatives 9g–9i.
28
(
(
2S, 5S)-30a (86%)
2S, 5R)-30b (87%)
Next, we investigated the synthesis of acylproline derivatives 9b,
c, 9l, and 9m, side-chains of which were elongated with one-
1) LiOH•H2O
THF-MeOH-H2O
rt ,3 h
TBSO
F
F
O
9
O
R
O
9b (68%)
9c (55%)
2
7, 28
R=
carbon unit when compared with natural product 1 (Scheme 5).
Nucleophilic addition of allyl copper reagent to epoxide (R)-13
provided 24, which was converted via two steps to afford
primary alcohol 25. Methyl ester 26 was prepared from 25 via
three steps in 60% yield. Wacker oxidation of terminal alkene in
N
30
3) H-Pro-OBn•HCl
PyBroP, DIEA
CH2Cl2, rt, 11 h
BnO
O
O
O
O
9b, 9c, 9l, 9m
9
l (77%)
9m (75%)
Scheme 5. Preparation of the acylprolines 9b, 9c, 9l, and 9m.
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European Journal of Organic Chemistry
10.1002/ejoc.201801826
FULL PAPER
O
OTMSE
H
N
H
N
N
TBSO
1) H
2
, Pd/C, EtOAc/EtOH, rt, 2 h
O, rt, 3 h
N
or NaOH, THF-MeOH-H
2
O
O
O
R
O
R
1) TBAF, THF, rt, 9 h
2) MNBA, DMAPO
O
O
O
O
O
O
O
O
TBSO
N
O
N
2) H-Ile-MeVal-MeAla-β-Ala-OTMSE (7)
EDCI, HOAt, DIEA, CH Cl
rt, 11 h, 2 steps 75%-quant.
N
O
R
BnO
2
2
2 2
CH Cl , 30 °C, 48 h
N
N
N
H
N
H
9
a-9i, 9l, 9m
4a: 73%, 4b: 64%, 4c: 78%
5a-5i, 5l, 5m
4d: 70%, 4e: 72%, 4f: 85%
4
4
g: 34%, 4h: 35%, 4i: 66%
l: 58%, 4m: 75%
1
) 1 M aq. HCl, dioxane
0
7
°C, 1 h
2% (for 4l), 88% (for 4m)
F
F
H
N
F
F
2
) TsCl, NEt
CH Cl , rt, 3 h
5% (for 4l), 70% (for 4m)
3
, DMAP
2
2
N
O
*
*
6
O
O
O
F
F
R=
O
O
O
O
4l–4m
N
O
*
a
b
c
d
e (less polar)
f (polar)
3) K
2
CO
PrOH/(CH
0 °C, 7 h
j: 87%, 4k: 90%
3
i
O
2
Cl)
2
N
O
O
6
4
N
H
O
O
O
O
O
4
j: (S)-epoxide
g
h
i
l
m
4k: (R)-epoxide
Scheme 6. Total synthesis of destruxin E analogs 4
Successfully having the desired 9, we synthesized destruxin E
analogs 4, details of which are illustrated in Scheme 6.
Hydrogenolysis or hydrolysis of benzyl ester in 9a–9i, 9l, and
morphological changes at a lower concentration, and a target for
destruxins in OCLs would recognize the orientation of the
epoxide moiety to exhibit the desired biological activity.
9
m were performed leading to the corresponding acids, which
7
were subsequently amidated with the tetrapeptide 7 using N-(3-
dimethylaminopropyl)-N'-ethylcarbodiimide (EDCI)/1-hydroxy-7-
azabenzotriazole (HOAt) to afford hexapeptides 5a–5i, 5l, and
Table 1. Biological Evaluation of Destruxin E Analogs for Morphological
Changes in OCLs
5
m in good to excellent yields. After removal of the protecting
[
a]
Entry
Analog
R
Activity [µM]
groups at the N- and C-terminus, macrolactonization of the
resulting precursors was successfully achieved using 2-methyl-
[
b]
O
1
2
3
4
5
6
7
8
9
1
1
0.04
6
-nitrobenzoic anhydride (MNBA)/4-(dimethylamino)pyridine N-
1
7
oxide (DMAPO) to provide the desired analogs 4a–4i, 4l, and
m in moderate yields (34–85%). In addition, the formation of
epoxide from 4l and 4m, as well as the previously reported
4
[b]
O
2
5.0
4
,7
procedure, furnished 4j and 4k, respectively.
[
c]
3a
1.6
The synthetic analogs were then evaluated for the morphological
1
8
changes in OCLs, and the results are summarized in Table 1.
As we have previously reported, destruxin E (1), epi-2, and
destruxin A (3a) and B (3b) induce morphological changes at
minimum concentrations of 0.04, 5.0, 1.6, and 0.80 µM,
[c]
3b
0.80
0.80
1.6
4a
O
O
respectively (entries 1–4). Biological activities of methyl ether 4a,
methyl ketone 4b, difluoromethylene 4c, and cyclopropyl analog
4b
4
d were found to be similar to destruxin B (3b) (entries 5–8). In
contrast, the biological activity of difluorocyclopropyl analogs 4e
and 4f significantly decreased to 3.1 µM (entries 9 and 10),
indicating that gem-difluorocyclopropane is not a bioisostere of
the corresponding epoxide. Notably, the activity was not retained
after the substitution of the epoxide by an oxetane moiety
4c
0.80
0.80
3.1
F
F
4d
F
F
(
entries 11–13). In addition, the (S)-epoxide homolog 4j
F
∗
∗
4e (less polar)
4f (polar)
exhibited 10-fold less activity than destruxin E (1) and the (R)-
epoxide homolog 4k further diminished the activity (entries 14
and 15), although 4j was found to be the most potent among the
analogs 4a–4k. Therefore, the epoxide moiety in the side chain
of the α-hydroxy acid could play a crucial role in inducing the
F
0
3.1
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European Journal of Organic Chemistry
10.1002/ejoc.201801826
FULL PAPER
O
or JEOL JNM-ECA600 spectrometers in the indicated solvent. Chemical
1
1
1
1
1
2
3
4
5
4g
4h
4i
6.3
13
shifts (δ) are reported in units parts per million (ppm), relative to the
1
signal for the internal standard tetramethylsilane (0 ppm for H) for
O
solutions in CDCl
3
. NMR spectral data are reported as follows:
1
13
chloroform (7.26 ppm for H) or chloroform-d (77.0 ppm for C), DMSO
1
13
(
6
2.49 ppm for H), DMSO-d (39.5 ppm for C) when the internal
standard is not indicated. Multiplicities are reported by the following
abbreviations: s (singlet), d (doublet), t (triplet), q (quartet), quin (quintet),
m (multiplet) dd (double doublet), dt (double triplet), ddd (double double
doublet), br (broad singlet), and J (coupling constants in Herts). IR
spectra were recorded on a JASCO FT/IR-4100. Only the strongest
and/or structurally important absorption are recorded as the IR data
O
25
4j
0.40
3.1
O
−
1
afforded in cm . Optical rotations were measured on a JASCO P-1000
polarimeter. Melting points were recorded on a Round Science RFS-10
instrument and are uncorrected. Mass spectra and high-resolution mass
1
4k
O
a
b
c
TM
TM
Minimum concentration for morphological changes. See ref 5b. See ref
spectra were measured on ThermoScienific Exactive Plus Orbitrap
Mass Spectrometer (for ESI), JEOL JMS-DX303 (for EI) and JMS-700
6
.
(
for FAB).
General procedure I: Macrolactonization Using MNBA/DMAPO
Conclusions
To a solution of hexapeptide 5 (1.00 equiv) in THF (5 mL/mmol) was
slowly added a solution of TBAF (1 M in THF solution, 3 equiv) in THF at
0 ºC under an argon atmosphere. After the mixture was stirred at room
temperature for 9 h, DOWEX 80WX8-400 (1 mg/µmol) was added at 0 ºC.
In conclusion, we investigated the synthesis and biological
evaluation of destruxin E analogs that were replaced with
various α-hydroxycarboxylic acid derivatives. Acylproline
derivatives 9, key components for the synthesis of the analog,
were successfully prepared, and amidation of the resulting 9
with tetrapeptide, followed by macrolactonization in parallel
furnished eleven analogs 4a–4k, each possessed different
functional groups in the side chain of α-hydroxycarboxylic acid
moiety. Biological evaluation of the synthetic analogs against
OCLs indicated that the modification of the side chain did not
allow the biological activity of the parent destruxin E to be
retained. Although, (S)-epoxide homolog 4j was the most potent
among the synthetic analogs, meaning that the (S)-epoxide
moiety in the side chain of α-hydroxycarboxylic acid could be an
essential factor for the induction of morphological changes of
OCLs at a lower concentration. Destruxin E reversibly inhibits
the bone-resorbing activity of OCLs, therefore elucidation of the
mode of action could be interesting, in particular, to determine
whether destruxin E binds to a target molecule in OCLs by a
covalent linkage or not. Further investigation of the mode of
action is underway by a chemical biology approach using a
molecular probe of the destruxin E analogs.
®
The reaction mixture was filtered through a pad of Celite , and the filtrate
was concentrated in vacuo. The crude cyclization precursor was used for
next reaction after short pass silica gel column chromatography.
To a solution of the crude cyclization precursor and DMAPO (2.00 equiv)
2 2
in dry CH Cl (330 mL/mmol) was added MNBA (3.00 equiv) at 0 ºC
under an argon atmosphere. After being stirred 30 ºC for 48 h, the
reaction mixture was poured into saturated aqueous NaHCO3 and the
aqueous layer was extracted with CHCl
with brine, dried over MgSO and filtered. The filtrate was concentrated in
vacuo, and the resulting residue was purified by silica gel column
3
. The organic layer was washed
4
chromatography (eluted with CHCl
3
/MeOH
=
100/1) to afford
macrolactone 4 as a yellow oil.
1
4
a: Yield (2 steps): 73% (19.3 mg, 0.0324 mmol); H NMR (600 MHz,
3
CDCl ) δ 8.21 (1H, d, J = 8.5 Hz), 7.18 (1H, d, J = 9.2 Hz), 5.18 (1H, q, J
=
6.7 Hz), 5.05 (1H, dd, J = 5.1, 8.5 Hz). 4.96 (1H, d, J = 10.9 Hz), 4.89
(
1H, dd, J = 6.7, 9.2 Hz), 4.68 (1H, d, J = 7.5 Hz), 4.02–4.08 (1H, m),
3.90 (1H, brt, J = 9.2 Hz), 3.52–3.58 (2H, m), 3.42–3.46 (1H, m), 3.33
(3H, s), 3.23 (3H, s, j), 3.08 (1H, brt, J = 12.1 Hz), 2.73 (3H, s), 2.67 (1H,
ddd, J = 1.9, 11.5, 18.4 Hz), 2.57 (1H, dd, J = 4.3, 18.4 Hz), 2.44–2.49
(
1H, m), 2.28–2.35 (1H, m), 1.88–2.14 (6H, m), 1.39–1.45 (1H, m), 1.27–
.35 (4H, m), 0.93 (3H, d, J = 6.5 Hz), 0.89 (3H, d, J = 6.5 Hz), 0.84–0.87
1
1
3
(
6H, m); C NMR (150 MHz, CDCl
3
) δ 173.6, 173.5, 171.1, 170.9, 169.7,
69.4, 70.6, 67.6, 60.7, 58.7, 58.0, 55.5, 53.6, 46.4, 37.5, 34.4, 33.2,
0.9, 30.8, 29.1, 28.1, 27.2, 24.4, 24.0, 20.0, 19.6, 15.4, 15.2, 11.4; IR
Experimental Section
1
3
−
1
24
General
(neat) 2965, 1731, 1668, 1631, 1517, 1444, 1180, 1120, 752 cm ; [α]
D
+
–
211 (c 0.634, CHCl
3
); HRMS [ESI] calcd for C29
H
49
N
5
O
8
Na [M+Na]
All commercially available reagents were used as received. Dry THF and
618.3473, found 618.3466.
2 2
CH Cl (Kanto Chemical Co.) were obtained through commercially
1
available pre-dried, oxygen-free formulations, and through activated
alumina columns. MeOH was distilled from iodide and magnesium
turnings. DMF was purchased from Wako (for peptide synthesis, grade:
4b: Yield (2 steps): 64% (23.1 mg, 0.0378 mmol); H NMR (600 MHz,
CDCl ) δ 8.17 (1H, d, J = 8.2 Hz), 7.16 (1H, d, J = 9.2 Hz), 5.20 (1H, q, J
3
= 6.8 Hz), 4.93–4.95 (2H, m), 4.86 (1H, dd, J = 6.7, 9.2 Hz), 4.63 (1H, d,
9
9.5%). All reactions in the solution-phase were monitored by thin-layer
chromatography carried out on 0.2 mm E. Merck silica gel plates (60F-
54) with UV light, and visualized with anisaldehyde, or 10% ethanolic
J = 7.2 Hz), 4.03–4.08 (1H, m), 3.85 (1H, dd, J = 1.8, 9.3 Hz), 3.65–3.70
(1H, m), 3.22 (3H, s), 3.04–3.09 (1H, m), 2.64–2.78 (6H, m), 2.56 (1H, m),
2.47–2.50 (1H, m), 2.28–2.36 (1H, m), 2.16 (3H, s), 1.89–2.11 (6H, m),
1.39–1.44 (1H, m), 1.26–1.32 (4H, m), 0.93 (3H, d, J = 6.5 Hz), 0.89 (3H,
2
phosphomolybdic acid. Silica gel 60N (Kanto Chemical Co. 100–210 µm)
1
13
was used for column chromatography. H NMR spectra (400 or 600 MHz)
d, J = 6.5 Hz), 0.83–0.86 (6H, m); C NMR (150 MHz, CDCl ) δ 207.7,
3
1
3
and C spectra (100 or 150 MHz) were recorded on JEOL JNM-AL400
173.7, 173.5, 171.1, 171.0, 169.8, 169.0, 72.0, 60.7, 58.1, 55.5, 53.7,
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201801826
FULL PAPER
4
2
1
6.6, 37.7, 37.5, 34.4, 33.2, 30.9, 30.1, 28.9, 28.1, 27.3, 24.5, 24.1, 23.5,
0.1, 19.6, 15.4, 15.3, 11.4; IR (neat) 3385, 3296, 2966, 1731, 1667,
170.8, 169.7, 168.5, 113.7 (t, J = 284 Hz), 72.9, 60.8, 58.1, 55.5, 53.7,
46.6, 37.5, 34.4, 33.2, 30.8, 28.9, 28.6, 28.1, 27.2, 24.4, 24.0, 20.0, 19.6,
18.5 (t, J = 10.0 Hz), 16.5 (t, J = 10.8 Hz), 15.4, 15.2, 11.4; IR (neat)
−
1
28
630, 1519, 1443 cm ; [α]
D 3
–191 (c 0.426, CHCl ); HRMS [ESI] calcd
+
−1
31
for C30
H
49
N
5
O
8
Na [M+Na] 630.3473, found 630.3468.
D
2966, 1732, 1668, 1632, 1474, 1447, 1180, 754 cm ; [α] –177 (c
+
0
.287, CHCl
3
); HRMS [ESI] calcd for C30
H
47
F
2
N
5
O
7
Na [M+Na] 650.3336,
1
found 650.3320.
4
c: Yield (2 steps): 78% (13.6 mg, 0.0216 mmol); H NMR (600 MHz,
3
CDCl ) δ 8.18 (1H, d, J = 8.2 Hz), 7.16 (1H, d, J = 9.2 Hz), 5.19 (1H, q, J
1
=
6.8 Hz), 4.94–4.96 (2H, m), 4.87 (1H, dd, J = 6.7, 9.2 Hz), 4.67 (1H, d,
4g: Yield (2 steps): 34% (6.5 mg, 0.0107 mmol); H NMR (600 MHz,
J = 7.9 Hz), 4.03–4.08 (1H, m), 3.90 (1H, brt, J = 8.2 Hz), 3.44–3.49 (1H,
m), 3.25 (3H, s), 3.08 (1H, brt, J = 13.0 Hz), 2.73 (3H, s), 2.67 (1H, ddd, J
3
CDCl ) δ 8.21 (1H, d, J = 7.9 Hz), 7.13 Hz, d, J = 9.2 Hz), 5.15 (1H, q, J =
6.8 Hz), 5.03 (1H, dd, J = 5.6, 8.4 Hz), 4.97 (1H, d, J = 10.9 Hz), 4.90
(1H, dd, J = 6.2, 9.2 Hz), 4.80–4.85 (1H, m), 4.66–4.71 (2H, m), 4.55 (1H,
dt, J = 4.5, 11.2 Hz), 4.01–4.07 (1H, m), 3.88 (1H, brt, J = 8.4 Hz), 3.57–
3.62 (1H, m), 3.22 (3H, s), 3.08 (1H, brt, J =13.3 Hz), 2.74–2.79 (1H, m),
2.72 (3H, s), 2.67 (1H, ddd, J = 1.7, 11.3, 18.4 Hz), 2.56 (1H, dd, J = 3.9,
18.4 Hz), 2.38–2.47 (3H, m), 2.29–2.35 (1H, m), 2.21 (1H, ddd, J = 4.1,
8.4, 14.0 Hz), 1.87–2.07 (4H, m), 1.39–1.43 (1H, m), 1.28–1.31 (4H, m),
=
2
1
=
1
5
2
2.0, 11.5, 18.5 Hz), 2.58 (1H, dd, J = 3.8, 18.5 Hz), 2.49–2.52 (1H, m),
.29–2.35 (1H, m), 1.90–2.14 (8H, m), 1.63 (3H, t, J = 18.5 Hz), 1.40–
.44 (1H, m), 1.27–1.31 (4H, m), 0.93 (3H, d, J = 6.5 Hz), 0.89 (3H, d, J
1
3
3
6.5 Hz), 0.84–0.88 (6H, m); C NMR (150 MHz, CDCl ) δ 173.6, 173.5,
71.1, 170.8, 169.7, 168.8, 123.8 (t, J = 238.1 Hz), 72.3, 60.8, 58.1, 55.5,
3.7, 46.6, 37.5, 34.4, 33.2, 32.9 (t, J = 25.1 Hz), 30.9, 28.9, 28.1, 27.2,
4.5, 24.1, 23.8 (t, J = 28.0 Hz), 23.2, 20.0, 19.6, 15.4, 15.2, 11.4; IR
1
3
0.93 (3H, d, J = 6.8 Hz), 0.89 (3H, d, J = 6.8 Hz), 0.84–0.87 (6H, m);
C
−
1
(
neat) 3385, 3297, 2964, 2931, 1732, 1668, 1630, 1441, 1181 cm
;
NMR (150 MHz, CDCl ) δ 173.57, 173.55, 171.1, 170.9, 169.7, 169.0,
3
2
9
[
[
α]
D
–184 (c 0.381, CHCl
+
3
); HRMS [ESI] calcd for C30
H
49
F
2
N
5
O
7
Na
78.1, 69.0, 68.6, 60.9, 58.0, 55.5, 53.6, 46.5, 38.7, 37.4, 34.5, 33.2, 30.8,
29.3, 28.1, 27.4, 27.2, 24.3, 24.0, 20.0, 19.6, 15.4, 15.2, 11.4; IR (neat)
M+Na] 652.3492, found 652.3468.
−
1
31
2
0
963, 2926, 1732, 1667, 1632, 1519, 1446, 1180 cm ; [α]
D
–171 (c
+
1
.344, CHCl ); HRMS [ESI] calcd for C30H N O Na [M+Na] 630.3473,
3
4
9
5
8
4
d: Yield (2 steps): 70% (17.6 mg, 0.0297 mmol); H NMR (600 MHz,
CDCl ) δ 8.21 (1H, d, J = 8.5 Hz), 7.19 (1H, d, J = 9.2 Hz), 5.17 (1H, q, J
6.8 Hz), 4.96 (1H, d, J = 10.9 Hz), 4.92 (1H, t, J = 7.2 Hz), 4.89 (1H, dd,
found 630.3458.
3
4h: Yield (2 steps) : 35% (3.2 mg, 5.27 µmol); H NMR (600 MHz, CDCl )
3
=
1
J = 6.7, 9.2 Hz), 4.67 (1H, d, J = 6.8 Hz), 4.02–4.06 (1H, m), 3.96 (1H, t,
J =8.4 Hz), 3.55–3.39 (1H, m), 3.22 (3H, s), 3.09 (1H, m), 2.73 (3H, s),
δ 8.18 (1H, d, J = 8.5 Hz), 7.17 (1H, d, J = 9.2 Hz), 5.18 (1H, q, J = 6.8
Hz), 5.00–5.05 (1H, m), 4.94–4.97 (2H, m), 4.87 (1H, dd, J = 6.7, 9.2 Hz),
4.67–4.72 (2H, m), 4.55 (1H, dt, J = 4.6, 11.1 Hz), 4.01–4.06 (1H, m),
3.89 (1H, brt, J = 8.2 Hz), 3.52–3.56 (1H, m), 3.22 (3H, s), 3.06 (1H, brt,
J = 13.0 Hz), 2.77–2.83 (1H, m), 2.72 (3H, s), 2.65 (1H, ddd, J = 2.0,
11.5, 18.4 Hz), 2.55 (1H, dd, J = 3.9, 18.4 Hz), 2.47–2.50 (1H, m), 2.28–
2.40 (2H, m), 2.22 (1H, ddd, J = 3.1, 10.7, 14.4 Hz), 2.14 (1H, ddd, J =
2.4, 9.7, 14.4 Hz), 2.05–2.09 (1H, m), 1.89–2.02 (3H, m), 1.38–1.45 (1H,
2
2
1
.67 (1H, ddd, J = 1.7, 11.8, 18.2 Hz), 2.56 (1H, dd, J = 4.8, 18.2 Hz),
.48 (1H, d, J = 6.5 Hz), 2.29–2.34 (1H, m), 1.89–2.07 (5H, m), 1.53–
.58 (1H, m), 1.40–1.46 (1H, m), 1.28–1.34 (4H, m), 0.93 (3H, d, J = 6.5
Hz), 0.89 (3H, d, J = 6.5 Hz), 0.85–0.87 (6H, m), 0.75–0.81 (1H, m),
.51–0.56 (1H, m), 0.44–0.48 (1H, m), 0.16–0.20 (1H, m), 0.08–0.12 (1H,
0
1
3
m); C NMR (150 MHz, CDCl
3
) δ 173.64, 173.56, 171.1, 171.0, 169.7,
69.6, 73.6, 60.9, 58.1, 55.5, 53.7, 46.6, 37.5, 35.8, 34.5, 33.3, 30.9,
9.1, 28.1, 27.3, 24.4, 24.1, 20.0, 19.7, 15.4, 15.2, 11.4, 6.7, 4.8, 4.3; IR
1
2
m), 1.27–1.31 (4H, m), 0.93 (3H, d, J = 6.5 Hz), 0.89 (3H, d, J = 6.5 Hz),
−
1
26
13
(
(
neat) 2965, 1730, 1668, 1631, 1516, 1447, 1181, 753 cm ; [α]
D
–216
3
0.83–0.86 (6H, m; C NMR (150 MHz, CDCl ) δ 173.6, 173.4, 171.1,
+
c 0.712, CHCl
3
); HRMS [ESI] calcd for C30
H
49
N
5
O
7
Na [M+Na] 614.3524,
170.9, 169.8, 169.1, 78.2, 69.5, 68.4, 60.8, 58.1, 55.5, 53.7, 46.6, 38.8,
37.5, 34.4, 33.2, 30.9, 29.0, 28.1, 27.5, 27.3, 24.5, 24.0, 20.1, 19.7, 15.4,
found 614.3518.
1
5.3, 11.4; IR (neat) 2964, 2932, 1732, 1669, 1632, 1519, 1443, 1178
−
1
27
1
cm ; [α]
D
–174 (c 0.163, CHCl
3 49 5 8
); HRMS [ESI] calcd for C30H N O Na
4
e: Yield (2 steps): 72% (7.8 mg, 0.0124 mmol); H NMR (600 MHz,
+
[
M+Na] 630.3473, found 630.3456.
3
CDCl ) δ 8.18 (1H, d, J = 8.2 Hz), 7.15 (1H, d, J = 8.9 Hz), 5.17 (1H, q, J
=
7
3
1
1
6.8 Hz), 4.96 (1H, d, J = 10.9 Hz), 4.88–4.93 (2H, m), 4.68 (1H, d, J =
.2 Hz), 4.03–4.08 (1H, m), 3.95 (1H, t, J = 8.2 Hz), 3.47–3.51 (1H, m),
.23 (3H, s), 3.06–3.11 (1H, m), 2.66–2.72 (4H, m), 2.57 (1H, dd, J = 3.8,
8.5 Hz), 2.50 (1H, d, J = 6.5 Hz), 2.29–2.35 (1H, m), 1.88–2.01 (5H, m),
.60–1.68 (1H, m), 1.43–1.46 (1H, m), 1.48–1.42 (1H, m), 1.27–1.33 (4H,
1
3
4i: Yield (2 steps): 66% (5.3 mg, 8.72 µmol); H NMR (600 MHz, CDCl )
δ 8.14 (1H, d, J = 7.9 Hz), 7.13 (1H, d, J = 9.2 Hz), 5.19 (1H, q, J = 6.8
Hz), 4.95 (1H, d, J = 10.9 Hz), 4.87 (1H, dd, J = 6.7, 9.2 Hz), 4.80–4.83
(3H, m), 4.65 (1H, d, J = 7.5 Hz), 4.39–4.42 (2H, m), 4.02–4.07 (1H, m),
3.89 (1H, brt, J = 8.0 Hz), 3.42 (1H, m), 3.24–3.30 (1H, m), 3.22 (3H, s),
3.60 (1H, brt, J = 12.5 Hz), 2.72 (3H, s), 2.64 (1H, ddd, J = 1.9, 11.5,
18.6 Hz), 2.52–2.56 (2H, m), 2.27–2.34 (2H, m), 2.17 (1H, ddd, J = 4.0,
7.8, 14.4 Hz), 1.89–2.09 (4H, m), 1.38–1.42 (1H, m), 1.27–1.31 (4H, m),
m), 0.99–1.14 (1H, m), 0.93 (3H, d, J = 6.5 Hz), 0.89 (3H, d, J = 6.8 Hz),
1
3
0
1
4
1
3
.84–0.87 (6H, m); C NMR (150 MHz, CDCl ) δ 173.5, 173.4, 171.0,
70.7, 169.7, 168.4, 113.4 (t, J = 284 Hz), 71.8, 60.9, 58.1, 55.5, 53.6,
6.6, 37.5, 34.4, 33.2, 30.8, 29.0, 28.10, 28.07, 27.2, 24.3, 24.0, 20.0,
9.6, 18.0 (t, J = 11.5 Hz), 16.0 (t, J = 10.8 Hz), 15.4, 15.2, 11.3; IR
1
3
0.93 (3H, d, J = 6.5 Hz), 0,89 (3H, d, J = 6.5 Hz), 0.83–0.85 (6H, m);
C
−
1
32
(
(
neat) 2965, 1732, 1668, 1632, 1475, 1446, 1179, 754 cm ; [α]
0.451, CHCl ); HRMS [ESI] calcd for Na [M+Na]
50.3336, found 650.3317.
D
–183
NMR (150 MHz, CDCl ) δ 173.6, 173.5, 171.1, 170.7, 169.8, 168.6, 77.5,
3
+
c
3
C
30
H
47
F
2
N
5
O
7
76.8, 71.8, 60.9, 58.1, 55.5, 53.8, 46.6, .37.5, 34.4, 33.9, 33.2, 31.7, 30.9,
28.9, 28.1, 27.3, 24.5, 24.1, 20.1, 19.6, 15.4, 15.2, 11.4; IR (neat) 2964,
6
−
1
28
2
D 3
931, 1731, 1667, 1631, 1445, 1180 cm ; [α] –210 (c 0.137, CHCl );
+
1
HRMS [ESI] calcd for C30
H
49
N
5
O
8
Na [M+Na] 630.3473, found 630.3455.
4
3
f: Yield (2 steps): 85% (5.6 mg, 8.92 µmol); H NMR (600 MHz, CDCl )
δ 8.19 (1H, d, J = 8.2 Hz), 7.15 (1H, d, J = 9.2 Hz), 5.18 (1H, q, J = 6.8
Hz), 4.95 (1H, d, J = 10.9 Hz), 4.91 (1H, dd, J = 3.8, 9.2 Hz), 4.88 (1H,
dd, J = 6.7, 9.2 Hz), 4.66 (1H, d, J = 7.5 Hz), 4.04–4.09 (1H, m), 3.92 (1H,
t, J = 8.9 Hz), 3.44–3.48 (1H, m), 3.23 (3H, s), 3.09 (1H, m), 2.67–2.73
1
4l: Yield (2 steps): 58% (29.0 mg, 0.0436 mmol); H NMR (600 MHz,
3
CDCl ) δ 8.19 (1H, d, J = 8.2 Hz), 7.17 (1H, d, J = 9.2 Hz), 5.19 (1H, q, J
= 6.7 Hz), 4.95 (1H, d, J = 10.9 Hz), 4.92 (1H, dd, J = 4.3, 8.7 Hz), 4.87
(1H, dd, J = 6.8, 9.2 Hz), 4.65 (1H, d, J = 7.5 Hz), 4.03–4.12 (3H, m),
3.91 (1H, brt, J = 8.9 Hz), 3.54 (1H, t, J = 7.2 Hz), 3.45–3.50 (1H, m),
3.22 (3H, s), 3.08 (1H, brt, J = 12.1 Hz), 2.73 (3H, s), 2.67 (1H, ddd, J =
1.9, 11.5, 18.4 Hz), 2.56 (1H, dd, J = 4.4, 18.4 Hz), 2.49–2.51 (1H, m),
2.29–2.36 (1H, m), 2.04–2.08 (1H, m), 1.87–2.00 (6H, m), 1.79–1.84 (1H,
(
4H, m), 2.60 (1H, dd, J = 4.4, 17.8 Hz), 2.49–2.52 (1H, m), 2.26–2.35
(
2H, m), 2.04–2.08 (1H, m), 1.90–2.00 (3H, m), 1.75–1.83 (1H, m), 1.64–
1
1
0
.69 (1H, m), 1.51–1.57 (1H, m), 1.38–1.46 (1H, m), 1.26–1.32 (4H, m),
.03–1.08 (1H, m), 0.93 (3H, d, J = 6.5 Hz), 0.89 (3H, d, J = 6.8 Hz),
1
3
3
.85–0.87 (6H, m); C NMR (150 MHz, CDCl ) δ 173.6, 173.5, 171.1,
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European Journal of Organic Chemistry
10.1002/ejoc.201801826
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m), 1.60–1.68 (1H, m), 1.27–1.45 (11H, m), 0.93 (3H, d, J = 6.5 Hz), 0.89
4.4 Hz), 2.72 (3H, s), 2.66 (1H, ddd, J = 2.1, 11.6, 18.5 Hz), 2.56 (1H, d,
J = 4.1, 18.5 Hz), 2.46–2.51 (2H, m), 2.29–2.35 (1H, m), 1.90–2.10 (7H,
m), 1.39–1.51 (2H, m), 1.27–1.36 (4H, m), 0.93 (3H, d, J = 6.5 Hz), 0.89
1
3
(
3H, d, J = 6.5 Hz), 0.84–0.87 (6H, m); C NMR (150 MHz, CDCl
3
) δ
1
5
2
2
73.6, 173.5, 171.0, 170.9, 169.7, 169.2, 109.0, 75.8, 73.1, 69.2, 60.8,
1
3
8.1, 55.4, 53.6, 46.6, 37.5, 34.4, 33.2, 30.8, 29.1, 28.9, 28.1, 27.2, 27.0,
6.9, 25.6, 24.4, 24.1, 20.0, 19.6, 15.4, 15.2, 11.3; IR (neat) 3384, 3298,
3
(3H, d, J = 6.5 Hz), 0.84–0.86 (6H, m); C NMR (150 MHz, CDCl ) δ
173.60, 173.58, 171.1, 170.9, 169.7, 169.1, 72.9, 60.8, 58.1, 55.5, 53.7,
51.9, 46.7, 46.6, 37.5, 34.4, 33.2, 30.8, 29.0, 28.2, 28.1, 27.24, 27.22,
24.4, 24.1, 20.0, 19.6, 15.3, 15.2, 11.4; IR (neat) 2965, 2935, 1732, 1668,
−
1
19
966, 1730, 1670, 1630, 1442, 1181 cm ; [α]
D 3
–184 (c 1.00, CHCl );
+
HRMS [ESI] calcd for C33
H
55
N
5
O
9
Na [M+Na] 688.3892, found 688.3882.
−
1
25
1
D 3
634, 1520, 1441, 1180, 752 cm ; [α] –193 (c 0.456, CHCl ); HRMS
+
1
[
ESI] calcd for C30
H
49
N
5
O
8
Na [M+Na] 630.3473, found 630.3468.
4
m: Yield (2 steps): 75% (47.0 mg, 0.0706 mmol); H NMR (600 MHz,
3
CDCl ) δ 8.19 (1H, d, J = 9.9 Hz), 7.17 (1H, d, J = 6.8 Hz), 5.18 (1H, q, J
1
=
6.8 Hz), 4,95 (1H, d, J = 11.3 Hz), 4.90 (1H, dd, J = 5.0, 8.4 Hz), 4.88
1H, dd, J = 6.8, 9.2 Hz), 4.67 (1H, d, J = 7.2 Hz), 4.11–4.15 (1H, m),
.03–4.07 (2H, m), 3.90 (1H, brt, J = 8.4 Hz), 3.49–3.55 (2H, m), 3.22
3H, s), 3.08 (1H, brt, J = 12.6 Hz), 2.72 (3H, s), 2.67 (1H, ddd, J = 1.7,
4k: Yield 90% (18.1 mg, 0.0298 mmol); H NMR (600 MHz, CDCl
3
) δ
(
8.19 (1H, d, J = 8.2 Hz), 7.16 (1H, d, J = 9.0 Hz), 5.19 (1H, q, J = 6.8 Hz),
4.96 (1H, d, J = 10.9 Hz), 4.93 (1H, dd, J = 4.1, 8.5 Hz), 4.87 (1H, dd, J =
6.7, 9.0 Hz), 4.66 (1H, d, J = 7.5 Hz), 4.03–4.08 (1H, m), 3.91 (1H, brt, J
= 9.1 Hz), 3.48–3.52 (1H, m), 3.22 (3H, s), 3.08 (1H, brt, J = 13.1 Hz),
2.98–3.00 (1H, m), 2.79 (1H, dd, J = 4.1, 4.8 Hz), 2.72 (3H, s), 3.08 (1H,
ddd, J = 1.9, 11.5, 18.0 Hz), 2.58 (1H, dd, J = 4.8, 18.0 Hz), 2.47–2.52
(2H, m), 2.29–2.35 (1H, m), 1.87–2.07 (7H, m), 1.61–1.66 (1H, m), 1.39–
1.46 (1H, m), 1.27–1.36 (4H, m), 0.93 (3H, d, J = 6.5 Hz), 0.89 (3H, d, J
4
(
1
2
0
1.5, 18.0 Hz), 2.56 (1H, dd. J = 4.6, 18.0 Hz), 2.49–2.51 (1H, m), 2.29–
.36 (1H, m), 1.84–2.06 (6H, m), 1.66–1.79 (2H, m), 1.27–1.44 (11H, m),
1
3
.93 (3H, d, J = 6.5 Hz), 0.89 (3H, d, J = 6.5 Hz), 0.84–0.87 (6H, m);
) δ 173.61, 173.60, 171.1, 170.9, 169.7, 169.1,
09.0, 74.9, 72.7, 69.1, 60.8, 58.1, 55.5, 53.7, 46.6, 37.5, 34.5, 33.2,
C
NMR (150 MHz, CDCl
3
1
3
1
1
3
0.9, 29.0, 28.5, 28.1, 27.3, 27.0, 26.3, 25.6, 24.5, 24.1, 20.1, 19.7, 15.4,
5.3, 11.4; IR (neat) 3384, 3299, 2966, 1730, 1670, 1629, 1442, 1180
3
= 6.8 Hz), 0.84–0.86 (6H, m); C NMR (150 MHz, CDCl ) δ 173.6, 171.0,
170.9, 169.7, 168.9, 72.6, 60.8, 58.1, 55.5, 53.7, 51.2, 46.8, 46.6, 37.5,
−
1
25
cm ; [α]
D
–176 (c 0.969, CHCl
3
); HRMS [ESI] calcd for C33
H
55
N
5
O
9
Na
34.4, 33.2, 30.8, 28.9, 28.1, 27.3 27.2, 26.2, 24.4, 24.1, 20.0, 19.6, 15.4,
+
−1
[
M+Na] 688.3892, found 688.3883.
15.2, 11.3; IR (neat) 2966, 1732, 1668, 1631, 1441, 1179, 752 cm
;
2
6
[
[
α]
D
–193 (c 0.905, CHCl
3
); HRMS [ESI] calcd for C30
H
49
N
5
O
8
Na
+
M+Na] 630.3473, found 630.3464.
General procedure II: Formation of the Epoxide
To a solution of the macrolactones 4l and 4m (1.00 equiv) in dioxane (1.0
mL) was added 1 M aqueous HCl (2.00 mL) at 0 °C. After being stirred at
the same temperature for 1 h, the reaction mixture was poured into
Acknowledgments
saturated aqueous NaHCO
3
and the aqueous layer was extracted with
This work was supported by JSPS KAKENHI, Grant no.
JP15H05837 (Grant-in-Aid for Scientific Research on Innovative
Areas: Middle Molecular Strategy), the Uehara Memorial
Foundation, and Takeda Science Foundation. This work was
partially supported by the Platform Project for Supporting Drug
Discovery and Life Science Research from AMED under Grant
Number JP18am0101095 and JP18am0101100.
EtOAc. The organic layer was washed with brine, and dried over MgSO
4
and filtered. The filtrate was concentrated in vacuo, and the resulting
residue was purified by silica gel flash column chromatography (eluted
3
with CHCl /MeOH = 30:1) to afford the diols S6 as a colorless oil. (Data
for S6 are shown in the Supporting Information.)
To a solution of the diol S6 (1.00 equiv), triethylamine (1.50 equiv) and
2 2
DMAP (0.100 equiv) in dry CH Cl (15 mL/mmol) was added p-
toluenesulfonyl chloride (1.20 equiv) at 0 °C under argon. After being
stirred at room temperature for 3 h, the reaction mixture was poured into
Keywords: Cyclodepsipeptide • Natural Product • Total
Synthesis • Osteoclasts
saturated aqueous NH
CHCl . The organic layer was washed with saturated aqueous NaHCO
and brine, and dried over MgSO and filtered. The filtrate was
concentrated in vacuo, and the resulting residue was purified by silica gel
flash column chromatography (eluted with CHCl /MeOH = 50:1) to afford
4
Cl and the aqueous layer was extracted with
3
3
4
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tosylate S7 as a colorless oil. (Data for S7 are shown in the Supporting
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To a solution of tosylate S7 (1.00 equiv) in i-PrOH (100 mL/mmol) and
1
,2-DCE (10 mL/mmol) was added K
argon. After being stirred at 60 °C for 7 h, the reaction mixture was
poured into saturated aqueous NH Cl and the aqueous layer was
extracted with CHCl . The organic layer was washed with saturated
aqueous NaHCO and brine, dried over MgSO and filtered. The filtrate
was concentrated in vacuo, and the resulting residue was purified by
2 3
CO (4.00 equiv) at 0 °C under
4
3
3
4
3
silica gel flash column chromatography (eluted with CHCl /MeOH = 70:1)
to afford destruxin E derivative 4j-k as a colorless oil.
[3]
[4]
1
M. Yoshida, H. Takeuchi, Y. Ishida, Y. Yashiroda, M. Yoshida, M.
Takagi, K. Shin-ya, T. Doi, Org. Lett. 2010, 12, 3792–3795.
4
j: Yield 87% (8.1 mg, 0.0133 mmol); H NMR (600 MHz, CDCl
3
) δ 8.19
(
1H, d, J = 8.2 Hz), 7.17 (1H, d, J = 9.0 Hz), 5.19 (1H, q, J = 6.8 Hz),
[
5]
a) H. Nakagawa, M. Takami, N. Udagawa, Y. Sawae, K. Suda, T.
Sasaki, N. Takahashi, M. Wachi, K. Nagai, J. T. Woo, Bone 2003, 33,
4
4
.92–4.96 (2H, m), 4.88 (1H, dd, J = 6.5, 9.0 Hz), 4.68 (1H, d, J = 7.5 Hz),
.02–4.07 (1H, m), 3.92 (1H, brt, J = 9.1 Hz), 3.46–3.51 (1H, m), 3.22
4
43–455. b) M. Yoshida, Y. Ishida, K. Adachi, H. Murase, H. Nakagawa,
(
3H, s), 3.07 (1H, brt, J = 12.7 Hz), 2.93–2.96 (1H, m), 2.78 (1H, t, J =
T. Doi, Chem. Eur. J. 2015, 21, 18417–18430.
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European Journal of Organic Chemistry
10.1002/ejoc.201801826
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[
[
[
[
[
6]
7]
8]
9]
H. Sato, M. Yoshida, H. Murase, H. Nakagawa, T. Doi, ACS Combi. Sci.
016, 18, 590–595.
M. Yoshida, H. Sato, Y. Ishida, H. Nakagawa, T. Doi, J. Org. Chem.
014, 79, 296–306.
[13] Removal of the protecting groups in 17 afforded the corresponding
tetraol, whose analytical data including specific optical rotation were in
good agreement with the reported one; A. J. Boydell, M. J. Jeffery, E.
Bürkstümmer, B. Linclau, J. Org. Chem. 2003, 68, 8252–8255.
2
2
F. Tian, V. Kruger, O. Bautista, J.–X. Duan, A.–R. Li, W. R. Dolbier Jr,
Q.–Y. Chen, Org. Lett. 2000, 2, 563–564.
[14] A. O. Fitton, J. Hill, D. E. Jane, R. Millar, Synthesis 1987, 1140–1142.
[15] R. N. Loy, E. N. Jacobsen, J. Am. Chem. Soc. 2009, 131, 2786–2787.
[16] Stereochemistry of 29a and 29b was determined through conversion to
the known compound, see supporting information.
L. Li, F. Wang, C. Ni, J. Hu, Angew. Chem. Int. Ed. 2013, 52, 12390–
1
2394.
10] PyBroP (Bromotripyrrolidinophosphonium hexafluorophosphate); E.
[17] a) I. Shiina, R. Ibuka, M. Kubota, Chem. Lett. 2002, 286−287. b) I.
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4
7, 259–270.
[
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[18] Biological Evaluation of the synthetic analogs was performed as
previously reported. See refs 5 and 6. This experimental animal study
was approved by and conducted in accordance with the guidelines of
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European Journal of Organic Chemistry
10.1002/ejoc.201801826
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Layout 2:
FULL PAPER
Structure-Activity Relationships
F
H
N
F
O
*
N
O
M. Yoshida, K. Adachi, H. Murase, H.
Nakagawa, and T. Doi*
O
O
O
R
F
F
O
O
O
O
0
.04 µM
0
.78 µM 1.56 µM 0.78 µM 0.78 µM 3.13 µM
N
O
Destruxin E
N
O
O
N
H
O
O
O
O
Page No.–Page No.
5.00 µM
6.25 µM 12.5 µM 25.0 µM 0.39 µM
3.1 µM
Parallel Synthesis and Biological
Evaluation of Destruxin E Analogs
Modified with a Side Chain in the α-
Hydroxycarboxylic Acid Moiety
Synthesis and biological evaluation of destruxin E analogs possessing various
functional groups in the α-hydroxycarboxylic acid moiety have been achieved. The
(
S)-epoxide moiety in the side chain of α-hydroxycarboxylic acid could be an
essential factor for the induction of morphological changes in OCLs at a lower
concentration.
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