Leptolyngbyolides, Cytotoxic Macrolides from the Marine Cyanobacterium Leptolyngbya sp.: Isolation, Biological Activity, and Catalytic Asymmetric Total Synthesis

Article abstract of DOI:10.1002/chem.201701183

Four new macrolactones, leptolyngbyolides A–D, were isolated from the cyanobacterium Leptolyngbya sp. collected in Okinawa, Japan. The planar structures of leptolyngbyolides were determined by extensive NMR studies, although complete assignment of the abs

Full text of DOI:10.1002/chem.201701183

A Journal of
Accepted Article
Title: Leptolyngbyolides, Cytotoxic Macrolides from the Marine
Cyanobacterium Leptolyngbya sp.: Isolation, Biological Activity,
and Catalytic Asymmetric Total Synthesis
Authors: Jin Cui, Maho Morita, Osamu Ohno, Tomoyuki Kimura,
Toshiaki Teruya, Takumi Watanabe, Kiyotake Suenaga, and
Masakatsu Shibasaki
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: Chem. Eur. J. 10.1002/chem.201701183
Link to VoR: http://dx.doi.org/10.1002/chem.201701183
Supported by

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
Leptolyngbyolides, Cytotoxic Macrolides from the Marine
Cyanobacterium Leptolyngbya sp.: Isolation, Biological Activity,
and Catalytic Asymmetric Total Synthesis
[
a]
[b]
[b]
[a]
[c]
[a]
Jin Cui, Maho Morita, Osamu Ohno, Tomoyuki Kimura, Toshiaki Teruya, Takumi Watanabe,*
[b]
[a]
Kiyotake Suenaga,* Masakatsu Shibasaki*
Abstract: Four new macrolactones, leptolyngbyolides A–D, were
isolated from the cyanobacterium Leptolyngbya sp. collected in
Okinawa, Japan. The planar structure of leptolyngbyolides were
determined by extensive NMR studies, although complete
assignment of the absolute configuration awaited the catalytic
asymmetric total synthesis of leptolyngbyolide C. The synthesis took
advantage of the catalytic asymmetric thioamide-aldol reaction using
copper (I) complexed with a chiral bidentate phosphine ligand to
regulate two key stereochemistries of the molecule at the outset. The
present total synthesis demonstrates the utility of this reaction for the
construction of complex chemical entities. In addition to the total
synthesis, this work reports that leptolyngbyolides depolymerize
filamentous actin (F-actin) both in vitro and in cells. Detailed biological
studies suggest the probable order of F-actin depolymerization and
apoptosis caused by leptolyngbyolides.
Madagascan seas that also affect the actin cytoskeleton.[6]
Swinholide A (1) was also mentioned in their report as a
secondary metabolite of this cyanobacteria. The fact that
swinholide A was already isolated from several taxonomically
different species of sponge suggests that macrolides of this class
are products of symbiotic microorganisms. The presence of a
related
“monomeric”
22-membered
cytotoxic
marine
[7]
macrolactone, scytophycins (3), biosynthesized by another
genus of cyanobacteria, corroborates this hypothesis.
Accordingly, it is widely recognized that marine cyanobacteria are
a promising source of pharmaceutical lead compounds belonging
to relatively unexplored chemical entities.
In this report, we describe the chemistry and biology of novel 22-
membered marine lactones, leptolyngbyolides A–D (5a – 5d).
Leptolyngbyolides were isolated from the extracts of
cyanobacterium Leptolyngbya sp. collected in Okinawa, Japan;
the structure is closely related to lobophorolide (4), which is also
a 22-membered lactone isolated from the sea alga Lobophora
variegata.[8] The gross structures of leptolyngbyolides were
Introduction
elucidated based on the extensive application of 2D NMR
techniques; the stereochemistry, however, has remained
uncharacterized. The absolute configuration of leptolyngbyolide C
was unequivocally elucidated by total synthesis using catalytic
asymmetric reactions developed in this laboratory as key stereo-
defining transformations. Based on the structure similarity with
related macrolides and observed changes in cell morphology
caused by leptolyngbyolide A, we examined the actin-
depolymerizing activities of leptolyngbyolides. In addition, we
evaluated the effects of leptolyngbyolides on cancer-cell growth
and apoptosis. This work sheds light on the biological
mechanisms of leptolyngbyolides and suggests the probable
order of F-actin depolymerization and apoptosis caused by this
class of macrolactones.
Marine natural products have attracted extraordinary attention
from the scientific community due to their unusual and diverse
structures, and intriguing biological activities. For example,
swinholide A (1) was first reported by Kashman and Carmely as
a constituent of extracts from the marine sponge Theonella
swinhoei,[1] and later Kitagawa and co-workers unveiled its
structure as a 44-membered macrolactone comprising two seco
acids connected in a head-to-tail manner. [2] Swinholide A exhibits
potent cytotoxicity against some cancer cell lines, which is
believed to be due to its actin-binding activity.[3] Curiously, related
natural products with a similar structure but clear differences in
the ring substructure do not necessarily exhibit the same extent
of activity.[4] The precise mode of interaction of this molecule with
actin is now well understood at the atomic level based on their co-
crystal structures.[ In 2005, Gerwick and co-workers isolated
related 44-membered marine macrolactones, ankaraholides
produced by cyanobacteria samples collected in the Fijian and
5]
[
[
a]
b]
Dr. J. Cui, Dr. T. Kimura, Dr. T. Watanabe, Prof. Dr. M. Shibasaki
Institute of Microbial Chemistry (BIKAKEN), Tokyo
3-14-23 Kamiosaki, Shinagawa-ku, Tokyo, 141-0021 (Japan)
E-mail: twatanabe@bikaken.or.jp; mshibasa@bikaken.or.jp
Dr. M. Morita, Dr. O. Ohno, Prof. Dr. K. Suenaga
Department of Chemistry
Keio University
3-14-1 Hiyoshi Kohoku-ku, Yokohama, Kanagawa 223-8522 (Japan)
E-mail: suenaga@chem.keio.ac.jp;
Prof. Dr. T. Teruya
[c]
Faculty of Education
University of the Ryukyus
1
Senbaru, Nishihara, Okinawa 993-0213 (Japan)
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
Figure 1. Structure of cytotoxic marine macrolactones structurally related to leptolyngbyolides.
Figure 2. Structure of leptolyngbyolides (highly probable stereochemistry is shown for A, B, and D).
Results and Discussion
MeOH/H
2
O mixed solvent systems with varying ratios; 80%
and absolute MeOH fractions potently inhibited the cell growth
of HeLa S cells. The fraction eluted with 80% methanol was
Isolation
of
leptolyngbyolides:
Bioassay-guided
3
fractionation of the extract of Leptolyngbya sp. led to isolation
of four new macrolactones, leptolyngbyolides A–D (5a-5d).
First, the marine cyanobacterium Leptolyngbya sp. was
manually collected on the coast of Itoman City, Okinawa
Prefecture, Japan, and stored at −30 ˚C until use.
Approximately 2.1 kg (wet weight) of the frozen Leptolyngbya
sp. was extracted with MeOH at room temperature for 2
months. The methanolic extract was filtered, and the filtrate
was evaporated in vacuo. The residue was partitioned
subjected to HPLC [Cosmosil Cholester; 70% MeOH] to give
leptolyngbyolide A (5a) (183 mg), leptolyngbyolide B (5b) (34.5
mg), and leptolyngbyolide D (5d) (2.6 mg), and [Cosmosil 5C18
-
MS-II; 75% MeCN] to give leptolyngbyolide C (5c) (12.1 mg).
Elucidation of the planar structures of leptolyngbyolides:
The molecular formula of 5a was deduced to be C46
high-resolution mass measurement (m/z 891.5096 calculated
76
H O15 by
+
1
76
for C46H O15Na [M+Na] 891.5082). Subsequently, H NMR,
between AcOEt and H
2
O. The material obtained from the
DEPT, and HMQC spectra showed that leptolyngbyolide A has
four methyl groups substituted at the methine carbon, a vinylic
methyl group, four O-methyl groups, three aliphatic methines,
fifteen methine carbons adjacent to oxygen atoms, five
methine carbons within olefin, and eleven methylene carbons.
organic layer was partitioned between 90% MeOH and hexane.
Among these four fractions, the 90% MeOH fraction showed
the most potent growth-inhibitory activity (IC50 < 0.1 g/mL)
against HeLa S
3
cells. Then, the aqueous MeOH fraction was
1
3
applied to ODS column chromatography eluted with a series of
C NMR revealed that this molecule consists of 46 carbons,
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
1
including a carbonyl carbon (δ
C
= 170.7 ppm) and six olefinic
overlapped H NMR spectra of leptolyngbyolides, neither the
NOESY experiments nor crystal structure analysis of
leptolyngbyolides was successful in determining their relative
structures. It is assumed that leptolyngbyolides have a relative
stereochemistry identical to that of lobophorolide: the NOESY
data for the present study did not contradict this assumption
(Figure S1).
C
carbons (δ = 152.7, 139.8, 136.2, 131.4, 125.6, 116.7 ppm).
Additionally, the 13C NMR spectrum of 5a showed resonances
at  103.1 (CH), 74.1 (CH), 75.3 (CH), 71.9 (CH), and 63.8
(
2
CH ), which indicated the presence of a sugar moiety.
Analysis of the COSY spectrum demonstrated the structures
of four fragments as shown in Figure 3 as bold bonds. Detailed
analysis of the HMBC spectrum allowed us to establish the
connectivities of the four fragments and the locations of the O-
methyl groups at C15, C17, C19, and C29. A 22-membered
macrolactone ring of 5a was identified based on an HMBC
correlation between C1-O-C21 and supported by a deshielded
chemical shift of an oxymethine proton at δ 5.23 (H21).
Furthermore, the shielded oxymethylene carbon at δ 49.2
(
C35) suggested the presence of an epoxide at C16, which
was strongly supported by an unsaturation of 5a and HMBC
correlations between H35/C16 and H35/C17. The geometries
of the two disubstituted olefins were determined to be 2E and
1
0Z based on their 3JH-H coupling constants, 15.8 Hz and 10.3
Hz, respectively. Additionally, the NOESY correlations
between H2/H3, H3/H5, H6a/H33, and H6b/H33 led us to
assign the geometry of the trisubstituted olefin at C4 as 4E
Figure 4. Stereochemistry of the sugar moiety of leptolyngbyolide A.
1
3
(
Figure 4), which was confirmed by the resonance in C NMR
at  12.7 (C33).[ Overall, leptolyngbyolide A was found to be
a glycosylated 22-membered macrolactone with an epoxide
moiety within it.
9]
The NOESY spectrum of an acylated derivative 6, which was
originally prepared for the purpose of crystal structure analysis,
enabled us to identify the sugar as a xylose (Figure 4). The
relative stereochemistry of the xylose and aglycon was
established by the NOESY correlations between H1’/H7 and
H1’/H9. The stereochemistry of the THP ring system at the side
chain moiety was examined by analyzing the 1H NMR and
NOESY spectra; the spectral data of leptolyngbyolide C (5c)
1
were used due to the spectral complexity of 5a in H NMR. The
NOESY correlation between H28b/H29, H29/H30b, and
H30b/H31, together with the characteristic coupling constants
between H29/H30a (12.6 Hz), H30a/H31 (10.3 Hz), and
H30b/H31 (2.8 Hz), revealed the relative configuration of the
THP ring shown in Figure 5.
Figure 3. Planar structure of leptolyngbyolides (bold: COSY correlation,
arrow: HMBC correlation ( H to C), dash: JH-H coupling constant of olefinic
protons).
1
13
3
The structure of 5b, 5c, and 5d was determined in a manner
similar to the case of 5a, which is described in Supporting
Information. The high similarities of the 1H and C NMR
spectra of 5d with those of 5b suggested that 5d was an
aglycon of 5b; this assignment was confirmed by the analyses
of COSY and HMBC spectra. To the best of our knowledge,
most of the related swinholide-like macrolides have no sugar
moiety except for ankaraholides including 2. These structural
features, together with the recent study on biosynthesis of this
compound class,[7d] suggests that leptolyngbyolide C (5c), a
methyl-branched analog, can be a biosynthetic precursor for
13
Figure 5. NOESY correlations observed for the THP moiety of
leptolyngbyolide C.
Comparison of the 1H and 13C NMR spectral data of 5a with
those of 1, 2, and 4 strongly suggested that the side chain of
5a had the same relative chemistry as that of the related
leptolyngbyolides A (5a) and B (5b). Table S1 in Supporting
swinholide-based compounds. As above, the spectral
experiments gave us information on the relatively rigid and
partial structures in leptolyngbyolides; however, their
stereochemistries were not completely characterized before
the total synthesis of 5c was accomplished in this work (vide
infra).
Information summarizes the chemical shift data of H and 13
1
C
NMR for leptolyngbyolides A-D (5a-5d).
Relative stereochemistry of leptolyngbyolides: Due to the
flexibility of the 22-membered macrocyclic ring and the highly
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
Figure 6. Effects of leptolyngbyolide A (5a) on F-actin of HeLa S
3
cells. HeLa S
3
cells were preincubated or not with 50 M Z-VAD-FMK for 30 min, and then treated
with 5a or mycalolide B at various concentrations for 24 h. Cells were fixed and exposed to the microfilament-staining rhodamine-phalloidin (actin filaments are
visualized as red) and to the DNA-reactive compound Hoechst33258 (cell nuclei are visualized as blue).
Biological activity of leptolyngbyolide: The related
compounds, including 1-4, exhibit potent growth-inhibitory
activities against several cancer cell lines. The results of the
MTT assay showed that 5a-5d inhibited the cell growth of HeLa
5a on cellular morphology, however, was not blocked in the
presence of Z-VAD-FMK. Thus, it was likely that the observed
changes in cell morphology were not caused by apoptosis, but
rather by the effect of 5a on the cytoskeleton. In addition,
previous studies reported that swinholide-based compounds,
including 1-4, targeted actin, a cytoskeleton protein that plays
central roles in cell morphology, movement, and cytokinesis.[
S
3
cells with IC50 values 0.099 to 0.64 M (Table 1 and Figure
S2). Comparison of the IC50 value of 5b (0.16 M) with that of
d (0.15 M), which is an aglycon of 5b, revealed that the
12]
5
xylose moiety is not essential for the growth-inhibitory activity
of leptolyngbyolides. Furthermore, the results of the trypan
blue dye exclusion assay and DNA ladder analyses showed
These actin-binding macrolides form a 1:1 or 2:1 of
complex[12,13] with globular (G-) actin by binding to the barbed
end of filamentous (F-) actin. Based on our observation and
previous studies, we examined the effect of 5a-5d in vitro.
Fluorescent attenuation of the pyrenyl actin demonstrated that
5a depolymerized F-actin over time in a concentration-
3
that 5a-5d induced apoptosis in HeLa S cells (Figure S3).
Table 1. Growth inhibition against HeLaS
3
cells (IC50) and depolymerization
of F-actin (EC50).
dependent
manner
(Figure
S6).
Likewise,
actin-
compound
growth-inhibitory
activity (M)
0.099
actin-depolymerizing
depolymerizing activities of 5b-5d were examined to evaluate
the influences of the sugar moiety and substituent at C16
(Table 2 and Figure S7). Comparison of the IC50 value of 5b
activity (M) [
12.6
a]
5a
5b
0.16
0.64
0.15
11.6
26.9
21.5
5c
(
11.6 M) with that of 5d (12.6 M) showed that the sugar
5d
moiety did not affect the actin-depolymerizing activity in the
same way as the growth-inhibitory activity (Table 1). Among
the four leptolyngbyolides, 5c showed the weakest actin-
depolymerizing activity with an IC50 value of 26.9 M;
interestingly, its growth-inhibitory potency was 5-fold weaker
than that of the other analogs (Table 1). A previous study on
Measurements were conducted in triplicate. Appendix Figures S2 and S7
present growth curves (for growth-inhibitory activities) and progress curves
(for actin-depolymerizing activities), respectively.
[
a]
EC50 indicates the concentration required to depolymerize F-actin (3.0 M)
to 50% of its control amplitude.
Leptolyngbyolide A (5a) caused morphological changes in
synthetic analogs of aplyronine A,
a
potent actin-
HeLa S cells at 0.1 M (Figures S4 and S5). As shown in
3
depolymerizing macrolide, indicated that there were strong
correlations between actin-depolymerizing activity and growth-
inhibitory activity.[14] Taken together, it is plausible that
leptolyngbyolides 5a-5d exhibited growth-inhibitory activities
Figure S4, the cell death induced by 5a was completely
blocked by Z-VAD-FMK, an irreversible and cell-permeable
inhibitor of caspases. Caspases[10] are a group of death
proteases that cause most of the visible morphological
changes characteristic of apoptotic cell death.[11] The effect of
by targeting F-actin in HeLa S
3
cells. The effect of 5a on F-actin
in HeLa cells was then analyzed by fluorescence
S
3
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
microscopy. As shown in Figure 6, 5a led to the disruption and
aggregation of F-actin in HeLa S cells in a concentration-
3
dependent manner. The F-actin disruption caused by 5a was
not suppressed by the presence of Z-VAD-FMK, which blocks
apoptosis. This result suggests the probable order of action of
leptolyngbyolides. Leptolyngbyolides are likely to target F-actin,
disrupt the cytoskeleton in HeLa S
apoptotic cell death.
3
cells, and then induce
Catalytic asymmetric total synthesis of leptolyngbyolide
C: To evaluate the predicted stereochemistry, we performed a
catalytic asymmetric total synthesis of leptolyngbyolide C. It
should be also noted that macrocyclic compounds currently
draw considerable attention of the medicinal chemistry
community,[ and so much efforts are being made for the
synthetic studies on the molecules of this class.[16] Among the
related natural products, swinholide A and its monomeric
precursor preswinholide A have been extensively studied
toward the total synthesis; monumental achievements by
15]
Paterson[ and Nicolaou
17]
[18]
for swinholide A as well as by
Nakata for preswinholide A were disclosed in the 1990s.[19]
Very recently, Krische and co-workers reported the concise
total synthesis of swinholide A in almost half the steps of the
precedents.[ In the present total synthesis, a distinct strategy
was used to install the appropriate stereochemistry at the initial
stage of the fragment-synthesis; the catalytic asymmetric
direct aldol reaction effected by Cu(I)-chiral bidentate
phosphine ligand complex using thioamide as the
prenucleophile developed by us was the key transformation.[21]
In this process, a copper complex chemoselectively activates
the thioamide by soft-soft interaction to facilitate deprotonation
at the -position in the presence of the more acidic enolizable
aldehyde. The whole process of the reaction accompanies only
the transfer of the -proton to the hydroxy group of the aldol
adduct wherein perfect atom economy is achieved;
preactivation of the prenucleophile by derivatization, such as
transformation into silylenolether, is not necessary to avoid
emission of waste. The resultant thioamide moiety of the aldol
products is a versatile functionality from which diverse
substructures, including aldehydes, methylketones, primary
20]
Scheme 1. Retrosynthesis of leptolyngbyolide C.
alcohols, carboxylic acids, -ketoester, amines, and amides,
21b]
are accessible in
a
single operation.[
This catalytic
Scheme 1 illustrates our retrosynthetic plan: the macrocyclic
core should be cyclized at the final stage of the synthesis,
expecting regioselectivity between two unprotected hydroxy
groups at C21 and C23 of 7, which is preceded by the
assembly of two segments (segment A, 8 and segment B, 9)
by aldol chemistry. The synthetic route to segment A (8) is
similar to the scheme developed in the course of our formal
total synthesis of scytophycin C.[ The methyl ketone should
be furnished by the oxidation of the corresponding secondary
alcohol, and the diene part of this intermediate could be
installed by the Horner-Wadsworth-Emmons reaction and
vinylogous Mukaiyama aldol reaction from the aldehyde with
the DHP ring system 10. The cyclic ether structure should be
formed via allylative cyclization[26] of -hydroxy enal 11, which
was expected to be prepared from cross metathesis with
homoallylic alcohol 12, a product of Krische allylation.[ The
asymmetric process was incorporated into the reaction
schemes toward the total synthesis of biologically relevant
compounds such as thuggacin B,[22] membrenones,[23]
caprazamycin B,[24] and atorvastatin.[21c,d] Moreover, iterated
use of this reaction facilitates the construction of the
polypropionate backbone of natural products; propionate-
derived thioamide gave the corresponding aldol adducts in
good to excellent enantio- (up to > 99% ee) and syn-selectivity
25]
(
up to > 20:1), after which the thioamide substructure was
converted to a formyl group to serve in the subsequent
thioamide-aldol reaction.
27]
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
primary alcohol 13 should be readily obtained by sequential
manipulation of the functional group from the product (14) of
the initial catalytic asymmetric thioamide-aldol reaction of 15
and 16, which we already optimized in our synthetic studies of
thuggacin B[22] and scytophycin C.[25] Segment B (9) should be
readily available by the hydrogenation of 17, which can be
steps. Then, selective deprotection of the primary silyl ether
was successfully achieved in 73% yield using NH F under
4
gentle warming to lead to the substrate of the following Krische
allylation (13).[
26]
prepared by cross metathesis between the two olefins 18 and
9; the latter is reported in the literature.[ The terminal double
28]
1
bond was furnished by partial reduction of the alkyne 20, a
product of the diastereoselective addition of allenylmetal
species to aldehyde (21) generated from enantioenriched
propargylic mesylate (22) catalyzed by Pd(0).[29] The aldehyde,
2
1, was easily transformed from thioamide-aldol adduct 23
from -chiral aldehyde (24) and propionate-derived thioamide,
6.
1
Scheme 2. Catalytic asymmetric thioamide-aldol reaction.
The synthetic route of segment A was elaborated from the
endeavor toward our formal total synthesis of the related
marine natural product scytophycin C,[25] which also provided
indispensable information during the synthesis of the
substances of this class. The synthesis commenced with
thioamide 26 in Scheme 3, which was prepared by silylation of
1
4. It has already been reported that 14 could be obtained with
excellent diastereo- (syn/anti = >20/1) and enantioselectivity
95% ee) by the catalytic asymmetric thioamide-aldol reaction
(
developed in this laboratory using a second-generation
catalyst system comprising a Cu(I)-bidentate chiral phosphine
complex prepared from mesitylcopper and (R,R)-Ph-BPE, and
2,2,5,7,8-pentamethylchromanol (25) as an additive, as
demonstrated in Scheme 2.
The thioamide moiety of 26 was readily transformed into
methylketone in a one-pot protocol by way of an iminothioether
intermediate, which accepts MeLi, followed by the hydrolysis
upon work up. The resultant carbonyl group of the methyl
ketone was converted to secondary alcohol 27 in 84% yield
over 2 steps, followed by protection as PMB ether (28) under
Lewis acidic conditions (86% yield). The reduction proceeded
with reasonable diastereoselectivity (5:1) to a predominant
Felkin-Anh product. In fact, the stereochemistry should not be
meaningful as it is to be lost at the later stage. In reality, the
major isomer was isolated for use during further synthetic study
to simplify the characterization of the studies of the subsequent
Scheme 3. Synthesis of the segment A.
A previous study on scytophycin C[25] revealed that Ir catalyst
ligated with (S)-SEGPHOS and 4-cyano-3-nitrobenzoate (S3,
Figure S8), which is commercially available, was not the
correct choice for our case: the starting material S2 (Figure S8)
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
was mostly unchanged with 5 mol% of catalyst at 100 °C after
either 24 h or 36 h to reach to a conversion as low as 16%-
The subsequent Horner-Wadsworth-Emmons reaction
proceeded uneventfully to add another olefin moiety with E-
geometry exclusively (33 in 90% yield). Finally, protecting
group manipulations (silylation to give 33 in 82%, and removal
of the PMB group to afford 35 in 79%) and Dess-Martin
oxidation of the resulting secondary alcohol to the
methylketone completed the synthesis of segment A, 8, in 94%.
20%. Gratifyingly, the alternative system using Ir(III) and a
chiral Cl, MeO-BIPHEP as the bidentate phosphine ligand, and
the benzoic acid derivative with finely tuned substituents as
depicted in Scheme 3 remarkably enhanced the reaction rate.
Although 5 mol % of catalyst loading based on Ir produced an
unsatisfactory yield of allylated product even after 48 h, 7.5
mol% was revealed to be enough to attain a 74% yield, even
after a 24-h reaction. The optimized condition was applied to
the present study using 13 as the substrate to give the desired
hydrogenative allylated product 12 in good yield (82%) as well
as excellent diastereoselectivity (>15:1). The succeeding cross
metathesis with acrolein under 8 mol% of Hoveyda-Grubbs
2nd generation catalyst afforded the expected trans-enal 11 in
90% yield.
Scheme 4. Asymmetric thioamide-aldol reaction for the synthesis of
segment B.
Next, we performed allylative cyclization following the
procedure of Yadav and co-workers.[26,30] The cyclization
condition employing InBr
transformations such as trimerization and dimerization when
,3-diol was used as the substrate (Figure S9). Changing the
catalyst to ZnBr and I , which are reported to be reliable
alternatives,[31] had no beneficial effect. Even with a catalytic
amount of ZnBr decomposition followed after full
consumption of the substrate. For these reasons, the present
synthetic protocol requires TBS-protection at one of the
secondary alcohols of 11. In fact, the allylative cyclization
3
suffered from undesired
The synthesis of segment B was set out again with the
1
asymmetric thioamide-aldol reaction demonstrated in Scheme
2
2
4. During the previous synthetic study to membrenones,[
23]
-
methylaldehydes were confirmed to be good substrates for
diastereoselective thioamide-aldol reaction, which is also the
case for 24, an appropriate starting material for the present
purpose to afford 10 times the desired diastereomer in
amounts comparable to that of the minor undesired product.
The thioamide-aldol adduct 23 was protected as a TBS ether
2
,
easily proceeded with a catalytic amount of I
2
(25 mol%) and 3
equiv of allyltrimethylsilane in CH Cl to afford 29 in a
2
2
3
6 (86%), which was reduced to the corresponding aldehyde
by treatment with LiAlH(OtBu) to intermediary
reasonable yield (60%) after pouring MeOH onto the reaction
mixture and stirring for an additional 3 h, which favorably
promoted the removal of the TBS group by HI that was
generated during the course of the catalytic cycle. Use of
21
3
iminothioether in 76% yield (Scheme 5). For the first trial, the
aldehyde was further reduced to an alcohol to which Krische
allylation was applied.[27c] Even after thorough optimization of
the reaction conditions, the desired product was obtained in no
more than 15% yield, which led us to switch our strategy to
diastereoselective allylation of aldehyde.
2 2
CH Cl in the first cyclization process was indispensable; the
originally reported THF ended up with an unsatisfactory yield
of less than 40%. Then, the unveiled hydroxy group was
methylated to give 30 in 74% yield under standard conditions,
which was followed by oxidative cleavage of the terminal olefin.
A previous report on the synthesis of scytophycin C by
In the beginning, Roush crotylation was tested, but the
undesired diastereoisomer predominated.[ Disappointingly,
the change in the protecting groups of the substrate never
switched the selectivity, which led us to investigate alternative
34]
[
32]
Miyashita’s group, utilized the stepwise operation of osmium
dihydroxylation and glycol cleavage mediated by NaIO . For
the present synthesis, this condition afforded 57% of the diol
4
2
Roush’s condition using (Ipc) BH and allenylstannane
reagent[
35]
to give the desired diastereomer as the major
4
with concomitant over-oxidation product, tetraol. OsO reagent
supported on PEM-polystyrene[33] slowed the reaction rate
although the regioselectivity improved. Gratifyingly, AD-mix-
was found to be the reagent of choice to convert 30 to 31 in
adduct although the selectivity was moderate (3.7:1).
Unfortunately, the tedious purification procedure hampered its
use for further reaction sequences. Finally, we found that the
Marshall-Tamaru reaction[
28]
employing enantio-enriched
70% yield with perfect regioselection, which preceded the
propargylic mesylate 22 as the allenylindium source worked
well; the nucleophilic species could be generated via an
allenylpalladium intermediate. In the present case for aldehyde
oxidative cleavage of the diol to give aldehyde 10 (80%). Then,
another key transformation in the synthesis of segment A, a
vinylogous Mukaiyama aldol reaction between 10 and a
21, the homopropargylic alcohol product 20 was accessible in
silyldienol ether as used in Paterson’s and Miyashita’s
syntheses[
17c,32]
75% yield with reasonable selectivity (5:1). Then, partial
hydrogenation with poisoned palladium catalyst gave rise to
the terminal olefin 37 (78%). Precision of the configuration was
smoothly (80%) afforded the corresponding
adduct 32 together with no trace amounts of the undesired
diastereomer (dr >15:1). Interestingly, the remote methyl group
at the tip of the substrate highly influenced the
diastereoselectivity; the lack of the methyl group substantially
reduced the diastereomeric ratio to 9.3:1 (Scheme S1).
1
verified by analysis of the coupling constant of H NMR of S10
(
Scheme S2), which was readily derived from 37 in a 3-step
procedure.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
From here on, interconversion of the protective group to
dimethylacetal (desilylation, 38 in 74%, acetalization in 95%)
afforded the substrate of cross metathesis 18 to install the
terminal THP part. Subsequently, metathesis effected by Zhan
catalyst-1B with 19 as the counterpart olefin prepared
according to the reported protocol[28] was carried out to
construct the whole framework of segment B (17 in 64% yield).
A successive diimide reduction to afford 39 (90%) was followed
by unmasking the PMB ether (40 in 90%) and oxidation of the
primary alcohol to the corresponding aldehyde achieved the
asymmetric synthesis of segment B (9, 82%).
NMR chemical shift value of the corresponding bis-
dimethylacetal derivative S11 (Scheme S2).[37]
The diol system was methylated to give 43 (70%), which
proceeded to the subsequent deacetalyzation (44, 65%) and
hydrolysis of the methylester moiety to afford the substrate of
macrolactonization (7, 86%). Then, the Yamaguchi protocol
was applicable to this reaction (0.005 M) to result in the mixture
of 22- and 24-membered isomers in good combined yield
(85%);[38] 22-membered lactone slightly predominated (45:46
= 55:45). Exposure of the undesired isomer 46 to Lewis acidic
media (Ti(Oi-Pr)
5:46). Then, the final removal of the TBS group of 45
4
)[38,39] equilibrate 46 to 45 up to 80:20 (=
4
processed uneventfully (78%) to accomplish the catalytic
asymmetric total synthesis of leptolyngbyolide C (5c). All the
physicochemical data of the synthetic sample were identical to
those of the naturally occurring compound to determine the
absolute configuration of leptolyngbyolide C as shown in
Figure 2.
Conclusions
Cyanobacteria are a reliable source of natural biological
products. Here, we report the isolation of four cytotoxic
macrolactones, leptolyngbyolides, that exhibit cytotoxicity
against cancer cell lines and actin-depolymerizing activity.
Detailed biological studies clarified that leptolyngbyolides
depolymerize filamentous actin (F-actin) both in vitro and in
cells, and suggested the probable order of F-actin
depolymerization and apoptosis caused by leptolyngbyolides.
Extensive NMR studies together with HRMS data revealed the
planar structure of leptolyngbyolides. Characteristic coupling
constants and NOESY experiments deciphered the relative
stereochemistry of these natural products, and the catalytic
asymmetric total synthesis of leptolyngbyolide C completely
elucidated the absolute configuration of this molecule. The
synthesis took advantage of the catalytic asymmetric
thioamide-aldol reaction developed by our group using copper
(
I) complexed with chiral bidentate phosphine ligand; the
catalyst selectively activates the thioamide substrate by soft-
soft interaction to facilitate deprotonation of the -proton, even
in the presence of an aldehyde substrate with higher acidic
protons. The whole process proceeds only with the migration
of protons: perfect atom economy is fulfilled. We have already
incorporated this method into several schemes of the total
synthesis of biologically active compounds, including natural
products, demonstrating the practicality of this reaction to
produce chemical entities with complex structures. The
present synthesis expands the repertoire of products produced
by this reaction. Structure-activity relationship studies of
substances that interfere with the behavior of actins as well as
further synthetic endeavors toward the other three congeners,
leptolyngbyolides A, B, and D, are underway, and will be
reported in due course.
Scheme 5. Synthesis of segment B.
A key reaction in the endgame of the synthesis should be a
coupling of the two segments by the aldol-approach; the
Mukaiyama aldol reaction after the conversion of segment A to
the silylenol ether, which was subjected to Lewis acidic
3 2
conditions effected by BF ·OEt to give the product 41 as a
single isomer in 78% yield (Scheme 6). Then, the Narasaka-
Prasad reduction,[36]
a
syn-selective protocol using -
hydroxyketone as the substrate, was successfully adopted to
lead to the syn-diol 42 in 73% yield. The stereochemistry
around this polyol portion was confirmed by analysis of the 13C
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
Scheme 6. Endgame of the catalytic asymmetric total synthesis of leptolyngbyolide C (5c).
partitioned between 90% MeOH (3 × 3 L) and n-hexane. The aqueous
MeOH fraction was partially purified by column chromatography on ODS
using 40% MeOH, 60% MeOH, 80% MeOH, absolute MeOH, and
Experimental Section
General: For isolation, purification, and structure determination of natural
CHCl
were subjected to HPLC (Cosmosil Cholester (φ 20 × 250 mm); flow rate
5 mL/min; detection at UV 269 nm; eluent 70% MeOH) to give
leptolyngbyolide A (5a, 183 mg, t = 70.1 min), leptolyngbyolide B (5b,
4.5 mg, t = 60.7 min), and leptolyngbyolide D (5d, 2.4 mg, t = 83.8 min).
Likewise, the fractions eluted with absolute MeOH were subjected to HPLC
Cosmosil 5C18-MS-II (φ 20 × 250 mm); flow rate = 5 mL/min; detection
at UV 269 nm; eluent 75% CH CN) to give leptolyngbyolide C (5c, 12.1
mg, t = 34.0 min).
3
/MeOH (1:1), successively. The fractions eluted with 80% MeOH
leptolyngbyolides, chemicals, and solvents except for the CH
reactions, which was distilled over P , were the best grade available and
were used as received from commercial sources. Optical rotation was
2 2
Cl used for
2 5
O
=
R
measured with
a
JASCO DIP-1000 polarimeter. CD spectra were
3
R
R
1
measured with a JASCO J-720 W spectropolarimeter. H NMR spectra
were recorded on a JEOL JNM-ECA800 (800 MHz) or a JEOL JNM-
ECX400 (400 MHz) instrument. Chemical shifts are reported as δ values
(
3
in parts per million relative to the solvent signal (CHD
3
OD: δ = 3.31 ppm,
1
R
C HD
6
5
: δ = 7.16 ppm for H) and coupling constants are reported in hertz
(
Hz). The following abbreviations are used for spin multiplicity: s = singlet,
d = doublet, t = triplet, q = quartet, m = multiplet, and brd = broad. 13C NMR
Cell growth analysis: HeLa S
in minimal essential medium (Nissui, Tokyo, Japan) supplemented with
0% heat-inactivated fetal bovine serum, 100 units/mL penicillin, 100
3 2
cells were cultured at 37 °C with 5% CO
spectra were recorded on a JEOL JNM-ECA800 (200 MHz), or JEOL JNM-
ECA400 (100 MHz) instrument. Chemical shifts are reported as δ values
in parts per million relative to the residual solvent signal (CD OD: δ = 49.0
ppm, C
1
μg/mL streptomycin, 0.25 μg/mL amphotericin, 300 μg/mL L-glutamine,
3
3
: δ = 128.06 ppm for 1 C). Assignments of the H NMR and
3
1
13
and 2.25 mg/mL NaHCO
3
. HeLa S
3
cells were seeded at 4 × 10 cells/well
D
6 6
C
in 96-well plates (Iwaki, Tokyo, Japan) and cultured overnight. Then,
various concentrations of test compounds were added, and after
incubation for 72 h, cell proliferation was measured with an MTT assay.
NMR spectra were determined by H-H COSY, HMQC, HMBC, and DEPT
experiments. ESI mass spectra were recorded on an LTC premier EX
spectrometer (Waters). Both TLC analysis and preparative TLC were
conducted on E. Merck precoated silica gel 60 F254. Nacalai Tesque ODS
silica gel 75C18-OPN was used for column chromatography.
Actin-depolymerizing activity: The actin-depolymerizing activity of
leptolyngbyolides were measured based on their ability to attenuate the
fluorescence of pyrene-labeled (pyrenyl) actin, as previously described.[
To the 3.0 μM solution of actin [2.7 M of actin (Cytoskeleton, AKL95), 0.3
40]
Extraction and isolation of leptolyngbyolides: Approximately 2.1 kg
(
wet weight) of cyanobacterium Leptolyngbya sp. was extracted with

8
M of pyrenyl-actin (Cytoskeleton, AP05)] in G-buffer [2 mM Tris-HCl (pH
.0), 0.2 mM CaCl , 0.5 mM 2-mercaptoethanol, 0.2 mM ATP] was added
(1 mM of total). The mixture was then stirred at
MeOH (5 L) over 2 months. The extract was filtered, the filtrate was
concentrated, and the resultant residue was partitioned between AcOEt (3
2
a 0.15 M solution of MgCl
2
×
2
3 L) and H O (0.3 L). The material obtained from the organic layers was
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
Gugger, H. Takeyama, S. Matsunaga, J. Piel, Nat. Chem. Biol. 2015, 11,
rt for 1 h to polymerize the G-actin to F-actin. To a solution of F-actin was
added various concentrations of test compounds with stirring. The time
course of the depolymerization was continuously monitored by measuring
the fluorescence of pyrenyl-actin with a JASCO CAF-110 intracellular ion
analyzer at 25 °C at 365 nm excitation and 405 nm emission wavelengths.
The IC50 values were the concentrations required to depolymerize F-actin
to 50% of its control amplitude.
705−712.
[
8]
9]
a) J. Kubanek, P. R. Jensen, P. A. Keifer, M. C. Sulldards, D. W. Collins,
W. Fenical, Proc. Natl. Acad. Sci. USA 2003, 100, 6916−6921; b) C. J.
Blain, Y.-F. Mok, J. Kubanek, J. S. Allingham, Chem. & Biol. 2010, 17,
802−807.
[
[
L. Carey, J. M. Clough, G. Pattenden, J. Chem. Soc., Perkin Trans 1
1983, 3005−3009.
10] E. S. Alnemri, D. J. Livingston, D. W. Nicholson, G. Salvesen, N. A.
Thornberry, W. W. Wong, J. Yuan, Cell 1996, 87, 171.
[
[
11] J. F. Kerr, A. H. Wyllie, A. R. Currie, Br. J. Cancer 1972, 26, 239−257.
12] a) T. D. Pollard, J. A. Cooper, Science, 2009, 326, 1208; b) V.A.
Klenchin, J.S. Allingham, R. King, J. Tanaka, G. Marriott, I. Rayment,
Nat. Struct. Biol. 2003, 10, 1058.
3
Fluorescence imaging: HeLa S cells were treated with leptolyngbyolide
A and a control compound, mycalolide B, for 24 h, then washed with PBS,
and fixed with 4% formaldehyde solution at rt for 10 min. The cells were
washed with PBS, then permeabilized with 0.1% Triton X-100 in PBS for
[13] a) K. Hirata, S. Muraoka, K. Suenaga, T. Kuroda, K. Kato, H. Tanaka, M.
Yamamoto, M. Takata, K. Yamada, H. Kigoshi, J. Mol. Biol. 2006, 356,
10 min. The cells were washed again with PBS and stained with 165 nM
945; b) J. S. Allingham, A. Zampella, M. V. D’Auria, I. Rayment, Proc.
rhodamine-phalloidin at rt for 30 min. The cells were washed with PBS
followed by treatment with 2.0 μg/mL of Hoechst 33258 in PBS at rt for 10
min. After washing with PBS, coverslips were mounted with aqueous
glycerol (1:1), covered with glass coverslips, and sealed with nail polish.
Fluorescence images were captured with an Eclipse E600 microscope.
The cells were photographed through a UV filter at a magnification of ×
Natl. Acad. Sci. USA 2005, 102, 14527−14532; c) J. C. Blain, Y.-F. Mok,
J. Kubanek, J. S. Allingham, Chem. Biol. 2010, 17, 802−807.
[14] O. Ohno, M. Morita, K. Kitamura, T. Teruya, K. Yoneda, M. Kita, H.
Kigoshi, K. Suenaga, Bioor. Med. Chem. Lett. 2013, 23, 1467−1471.
[
15] a) E. M. Diggers, S. P. Hale, J. Lee, N. K. Terret, Nat. Rev. Drug
Discovery 2008, 7, 608−624; b) E. Marsault, M. L. Peterson, J. Med.
Chem. 2011, 54, 1961−2004; c) F. Giordanetto, J. Kihlverg, J. Med.
Chem. 2014, 57, 278−295; d) A. K. Yudin, Chem. Sci. 2015, 6, 30−49.
16] a) I. B. Seiple, Z. Zhang, P. Jakubec, A. Langlois-Mercier, P. M. Wright,
D. T. Hog, K. Yabu, S. R. Allu, T. Fukuzaki, P. N. Carlsen, Y. Kitamura,
X. Zhou, M. T. Condakes, F. T. Szczypiński, W. D. Green, A. G. Myers,
Nature, 533, 338−345; b) C. Kitsiou, J. J. Hindes, P. I’Anson, P. Jackson,
T. C. Wilson, E. K. Daly, H. R. Felstead, P. Hearnshaw, W. P. Unsworth,
Angew. Chem. Int. Ed. 2015, 54, 15794−15798; Angew. Chem. 2015,
400.
[
Catalytic asymmetric total synthesis of leptolyngbyolide C: See
details in Supporting Information.
127, 16020−16024.
[
[
17] a) I. Paterson, K.-S. Yeung, R. A. Ward, J. G. Cumming, J. D. Smith, J.
Am. Chem. Soc. 1994, 116, 9391−9392; b) I. Paterson, J. G. Cumming,
R. A. Ward, S. Lamboley, Tetrahedron 1995, 51, 9393−9412; c) I.
Paterson, J. D. Smith, R. A. Ward, Tetrahedron 1995, 51, 9413−9436; d)
I. Paterson, R. A. Ward, J. D. Smith, J. G. Cumming, K.-S. Yeung,
Tetrahedron 1995, 51, 9437−9466; e) I. Paterson, K.-S. Yeung, R. A.
Ward, J. D. Smith, J. G. Cumming, S. Lamboley, Tetrahedron 1995, 51,
Acknowledgements
M.S. is grateful to the JST and ACT-C, and J. C. is grateful for
financial support from a Grant-in-Aid for JSPS fellows. The
authors also thank Dr. Ryuichi Sawa, Ms. Yumiko Kubota, Dr.
Kiyoko Iijima, and Ms. Yuko Takahashi (BIKAKEN) for the
spectroscopic analysis, Dr. Yoji Umezawa for generation of
artwork of crystal structure of lobophorolide, and professors
Takeshi Nakayama and Isao Inoue (Univ. of Tsukuba) for
identifying the cyanobacterium.
9467−9486.
18] a) K. C. Nicolaou, K. Ajito, A. P. Patron, H. Khatuya, P. K. Richter, P.
Bertinato, J. Am. Chem. Soc. 1996, 118, 3059−3060: b) K. C. Nicolaou,
A. P. Patron, K. Ajito, P. K. Richter, H. Khatuya, P. Bertinato, R. A. Miller,
M. J. Tomaszewski, Chem. Eur. J. 1996, 2, 847−868.
[19] a) T. Nakata, T. Komatsu, K. Nagasawa, Chem. Pharm. Bull. 1994, 42,
2403; b) T. Nakata, T. Komatsu, K. Nagasawa, H. Yamada, T.
Takahashi, Tetrahedron Lett. 1994, 35, 8225−8228; c) K. Nagasawa, I.
Shimizu, T. Nakata, Tetrahedron Lett. 1996, 37, 6881−6884; d) K.
Nagasawa, I. Shimizu, T. Nakata, Tetrahedron Lett. 1996, 37,
Keywords: Natural products • Macrocycles • Cytotoxicity •
Asymmetric catalysis • Total synthesis
6
885−6888.
[20] I. Shin, S. Hong, M. J. Krische, J. Am. Chem. Soc. 2016, 138,
4246−14249.
1
[
21] a) M. Iwata, R. Yazaki, Y. Suzuki, N. Kumagai, M. Shibasaki, J. Am.
Chem. Soc. 2009, 131, 18244−18245; b) M. Iwata, R. Yazaki, I.-H. Chen,
D. Sureshkumar, N. Kumagai, M. Shibasaki, J. Am. Chem. Soc. 2011,
[
[
1]
2]
S. Carmely, Y. Kashman, Tetrahedron Lett. 1985, 26, 511−514.
a) M. Kobayashi, J. Tanaka, T. Katori, M. Matsuura, I. Kitagawa,
Tetrahedron Lett. 1989, 30, 2963−2966; b) I. Kitagawa, M. Kobayashi, T.
Katori, M. Yamashita, J. Tanaka, M. Doi, T. Ishida, J. Am. Chem. Soc.
133, 5554−5560; c) Y. Kawato, M. Iwata, R. Yazaki, N. Kumagai, M.
Shibasaki, Tetrahedron 2011, 67, 6539−6546; d) Y. Kawato, C.
Sandeep, N. Kumagai, M. Shibasaki, Chem. Eur. J. 2013, 19,
1
990, 112, 3710−3712; c) M. Kobayashi, J. Tanaka, M. Katori, M.
Matsuura, I. Yamashita, I. Kitagawa, Chem. Pharm. Bull. 1990, 38,
409−2418; d) M. Kobayashi, J. Tanaka, T. Katori, I. Kitagawa, Chem.
3
802−3806.
22] A. Matsuzawa, C. R. Opie, N. Kumagai, M. Shibasaki, Chem. Eur. J.
014, 20, 68−71.
23] K. Alagiri, S. Lin, N. Kumagai, M. Shibasaki, Org Lett. 2014, 16,
301−5303.
24] a) P. Gopinath, T. Watanabe, M. Shibasaki, J. Org. Chem. 2012, 77,
260−9267; b) H. Abe, P. Gopinath, G. Ravi, L. Wang, T. Watanabe, M.
2
[
[
[
Pharm. Bull. 1990, 38, 2960−2966; e) M. Doi, T. Ishida, M. Kobayashi, I.
Kitagawa, J. Org. Chem. 1991, 56, 3629−3632.
a) M. R. Bubb, I. Spector, A. D. Bershadsky, E. D. Korn, J. Biol. Chem.
2
[
[
3]
4]
5
1
1
995, 270, 3463; b) Saito, S-y. Karaki, H. Clin. Exp. Pharmacol. Physiol.
996, 23, 743−746.
9
a) J. S. Todd, K. A. Alvi, P. Crews, Tetrahedron Lett. 1992, 33, 441−442.
b) Tanaka, J. Higa, T. Kobayashi, M. Kitagawa, I. Chem. Pharm. Bull.
Shibasaki, Tetrahedron Lett. 2015, 56, 3782−3785.
[
[
25] J. Cui, T. Watanabe, M. Shibasaki, Tetrahedron Lett. 2016, 57, 446−448.
26] D. K. Mohapatra, P. O. Das, M. R. Pattanayak, J. S. Yadav, Chem. Eur.
J. 2010, 16, 2072−2078.
27] a) A. Hassan, Y. Lu, M. J. Krische, Org. Lett. 2009, 11, 3112−3115. See
also: b) A.-M. R. Dechert-Schmitt, D. C. Schmitt, M. J. Krische, Angew.
Chem. Int. Ed. 2013, 52, 3195−3198; Angew. Chem. 2013, 125,
1
990, 38, 2967−2970.
V. A. Klenchin, R. King, J. Tanaka, G. Marriott, I. Rayment, Chem. Biol.
005, 12, 287−291.
[
[
5]
6]
2
[
E. H. Andrianasolo, H. Gross, D. Goeger, M. Musafija-Girt, K. McPhail,
R. N. Leal, S. L. Mooberry, W. H. Gerwick, Org. Lett. 2005, 7,
1375−1378.
3
277−3280; c) I. Shin, M. J. Krische, Org Lett. 2015, 17, 4686−4689; d)
X. Gao, H. Han, M. J. Krische, J. Am. Chem. Soc. 2011, 133,
2795−12800.
[
7]
a) M. Ishibashi, R. E. Moore, G. M. L. Patterson, C. Xu, J. Clardy, J. Org.
Chem. 1986, 51, 5300−5306; b) R. E. Moore, G. M. L. Patterson, J. S.
Mynderse, J. Barchi Jr., T. R. Norton, E. Furusawa, S. Furusawa, Pure
Appl. Chem. 1986, 58, 263−271; c) R. E. Moore, S. Banarjee, V.
Bornemann, F. R. Caplan, J. L. Chen, D. E. Corley, L. K. Larsen, B. S.
Moore, G. M. L. Patterson, V. J. Paul, J. B. Stewart, D. E. Williams, Pure
Appl. Chem. 1989, 61, 521−524; d) R. Ueoka, A. R. Uria, S. Reiter, T.
Mori, P. Karbaum, E. E. Peters, E. J. N. Helfrich, B. I. Morinaka, M.
1
[
[
[
28] I. Shin, G. Wang, M. Krische, Chem. Eur. J. 2014, 20, 13382−13389.
29] J. A. Marshall, C. M. Grant, J. Org Chem. 1999, 64, 8214−8219.
30] a) J. S. Yadav, V. Sunitha, B. V. S. Reddy, E. Gyanchander, Synthesis
2008, 2933−2938; b) J. S. Yadav, V. Sunitha, B. V. S. Reddy, P. P. Das,
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
E. Gyanchander, Tetrahedron Lett. 2008, 49, 855−857. See also: c) J. S.
Yadav, A. K. Raju, V. Sunitha, Tetrahedron Lett. 2006, 47, 5269−5272.
[39] a) H. Kigoshi, M. Ojika, T. Ishigaki, K. Suenaga, T. Mutou, A. Sakakura,
T. Ogawa, K. Yamada, J. Am. Chem. Soc. 1994, 116, 7443−7444; b) H.
Kigoshi, K. Suenaga, T. Mutou, T. Ishigaki, T. Atsumi, H. Ishiwata, A.
Sakakura, T. Ogawa, M. Ojika, K. Yamada, J. Org. Chem. 1996, 61,
5326−5351.
[40] a) S. Saito, S. Watabe, H. Ozaki, H. Kigoshi, K. Yamada, N. Fusetani, H.
Karaki, J. Biochem. 1996, 120, 552−555; b) T. Kuroda, K. Suenaga, A.
Sakakura, T. Handa, K. Okamoto, H. Kigoshi, Bioconjugate Chem. 2006,
17, 524−529; c) K. Suenaga, T. Kimura, T. Kuroda, K. Matsui, S. Miya,
S. Kuribayashi, A. Sakakura, H. Kigoshi, Tetrahedron 2006, 62,
8278−8290.
[
31] D. S. Reddy, B. Padhi. D. K. Mohapatra, J. Org Chem. 2015, 80,
365−1374.
1
[
[
[
32] R. Nakamura, K. Tanino, M. Miyashita, Org. Lett. 2003, 5, 3579−3582.
33] S. Kobayashi, T. Ishida, R. Akiyama, Org. Lett. 2001, 3, 2649−2652.
34] W. R. Roush, K. Ando, D. B. Powers, A. D. Palkowitz, R. L. Halterman,
J. Am. Chem. Soc. 1990, 112, 6339−6348.
35] M. Chen, W. R. Roush, J. Am. Chem. Soc. 2012, 134, 3925−3931.
36] a) K.-M. Chen, G. E. Hardtmann, K. Prasad, O. Repič, M. J. Shapiro,
Tetrahedron Lett. 1987, 28, 155−158; b) K. Narasaka, F.-C. Pai,
Tetrahedron 1984, 40, 2233−2238.
[
[
[
[
37] a) S. D. Rychnovsky, D. J. Skalitzky, Tetrahedron Lett. 1990, 31,
945−948. See also: b) D. A. Evans D. L. Rieger, J. R. Gage, Tetrahedron
Lett. 1990, 31, 7099−7100.
38] R. Nakamura, K. Tanino, M. Miyashita, Org. Lett. 2003, 5, 3583−3586.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701183
FULL PAPER
Entry for the Table of Contents (Please choose one layout)
Layout 1:
FULL PAPER
Four
new
macrolactones,
Author(s), Corresponding Author(s)*
leptolyngbyolides A–D, were isolated
from the cyanobacterium Leptolyngbya
sp. collected in Okinawa, Japan.
Page No. – Page No.
Title
Absolute
stereochemistry
of
leptolyngbyolide C was elucidated by
catalytic asymmetric total synthesis.
Layout 2:
FULL PAPER
Author(s), Corresponding Author(s)*
Page No. – Page No.
Title
Text for Table of Contents
This article is protected by copyright. All rights reserved.