Total Synthesis and Complete Stereostructure of a Marine Macrolide Glycoside, (-)-Lyngbyaloside B

Article abstract of DOI:10.1002/chem.201600341

We have described in detail the total synthesis of both the proposed and correct structures of (-)-lyngbyaloside B, which facilitated the elucidation of the complete stereostructure of this natural product. Our study began with the total synthesis of 13-demethyllyngbyaloside B, in which an esterification/ring-closing metathesis (RCM) strategy was successfully used for the efficient construction of the macrocycle. We also established reliable methods for the introduction of the conjugated diene side chain and the l-rhamnose residue onto the macrocyclic framework. However, the esterification/RCM strategy proved ineffective for the parent natural product because of the difficulties in acylating the sterically encumbered C-13 tertiary alcohol; macrolactionization of a seco-acid was also extensively investigated under various conditions without success. We finally completed the total synthesis of the proposed structure of (-)-lyngbyaloside B by means of a macrolactonization that involves an acyl ketene as the reactive species. However, the NMR spectroscopic data of our synthetic material did not match those of the authentic material, which indicated that the proposed structure must be re-examined. Inspection of the NMR spectroscopic data of the natural product and molecular mechanics calculations led us to postulate that the configuration of the C-10, C-11, and C-13 stereogenic centers had been incorrectly assigned in the proposed structure. Finally, our revised structure of (-)-lyngbyaloside B was unambiguously verified through total synthesis.

Full text of DOI:10.1002/chem.201600341

DOI: 10.1002/chem.201600341
Full Paper
&
Structure Elucidation |Hot Paper|
Total Synthesis and Complete Stereostructure of a Marine
Macrolide Glycoside, (À)-Lyngbyaloside B
Haruhiko Fuwa,* Naoya Yamagata, Yuta Okuaki, Yuya Ogata, Asami Saito, and
Makoto Sasaki[a]
Abstract: We have described in detail the total synthesis of
both the proposed and correct structures of (À)-lyngbyalosi-
de B, which facilitated the elucidation of the complete ste-
reostructure of this natural product. Our study began with
the total synthesis of 13-demethyllyngbyaloside B, in which
an esterification/ring-closing metathesis (RCM) strategy was
successfully used for the efficient construction of the macro-
cycle. We also established reliable methods for the introduc-
tion of the conjugated diene side chain and the l-rhamnose
residue onto the macrocyclic framework. However, the
esterification/RCM strategy proved ineffective for the parent
natural product because of the difficulties in acylating the
sterically encumbered C-13 tertiary alcohol; macrolactioniza-
tion of a seco-acid was also extensively investigated under
various conditions without success. We finally completed the
total synthesis of the proposed structure of (À)-lyngbyalosi-
de B by means of a macrolactonization that involves an acyl
ketene as the reactive species. However, the NMR spectro-
scopic data of our synthetic material did not match those of
the authentic material, which indicated that the proposed
structure must be re-examined. Inspection of the NMR spec-
troscopic data of the natural product and molecular me-
chanics calculations led us to postulate that the configura-
tion of the C-10, C-11, and C-13 stereogenic centers had
been incorrectly assigned in the proposed structure. Finally,
our revised structure of (À)-lyngbyaloside B was unambigu-
ously verified through total synthesis.
Introduction
the natural product. Moore et al. reported that lyngbyaloside B
displayed moderate cytotoxic activity against human oral epi-
dermoid carcinoma KB cells (IC50 =4.3 mm) and considerably
weaker effects on human colon adenocarcinoma LoVo cells
(IC50 ꢀ15 mm). Almost simultaneously, Gerwick et al. identified
a moderately cytotoxic macrolide glycoside, (À)-lyngbouillo-
side (2), from the marine cyanobacterium L. bouillonii, which
was collected off the north coast of Papua New Guinea.[6] Re-
cently, Luesch and co-workers reported the isolation and struc-
ture characterization of (À)-18E-lyngbyaloside C (3) and
(À)-18Z-lyngbyaloside C (4), the former of which showed mod-
erate cytotoxic activity against human cervical adenocarcinoma
HeLa cells.[7]
Marine natural products continue to attract the interest of the
chemical and biological communities because they provide
unique opportunities to develop therapeutics for intractable
diseases as well as chemical probes for deciphering important
biological questions.[1] Macrolide glycosides constitute a grow-
ing family of marine natural products with moderate to potent
cytotoxic activity against human cancer cell lines. As exempli-
fied by aurisides,[2] callipeltosides,[3] and dolastatin 19
(Figure 1),[4] these natural products were initially discovered
from marine invertebrates, such as sea hares and sponges, but
it is now speculated that these macrolide glycosides are actual-
ly the secondary metabolites of symbiotic microorganisms.
In 2002, Moore and co-workers described the isolation of
(À)-lyngbyaloside B (proposed structure 1) from the Palauan
cyanobacterium Lyngbya sp., which closely resembled Lyngbya
bouillonii.[5] The gross structure was determined on the basis of
extensive 2D NMR analyses, and the relative configuration was
assigned on the basis of conformational analyses by using J
values and ROESY correlations. The absolute configuration
could not be determined because of the limited availability of
Considerable interest has been aroused in the total synthesis
of these macrolide glycosides of cyanobacteria origin because
of their structural complexity and cytotoxic activity.[8] Hoye and
co-workers reported the synthesis of a model compound of
lyngbyaloside B (1) through a macrocyclization that involved
an acyl ketene as the reactive species (hereafter referred to as
“acyl ketene macrocyclization”).[8a,9] The Ley group described
the synthesis of a protected aglycon of the proposed (À)-lyng-
bouilloside (2) by using an anion coupling and a ring-closing
metathesis (RCM)[10] for the construction of the macrocycle.[8c]
Importantly, Ley et al. noticed that the 1H NMR spectrum of
their synthetic material showed significant line broadening,
whereas that of the authentic sample displayed a single set of
sharp signals. Later, Cossy and co-workers successfully synthe-
sized the aglycon of the proposed (À)-lyngbouilloside (2) by
[a] Prof. Dr. H. Fuwa, N. Yamagata, Y. Okuaki, Y. Ogata, A. Saito,
Prof. Dr. M. Sasaki
Graduate School of Life Sciences, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)
Supporting information and ORCID(s) for the author(s) for this article can
be found under http://dx.doi.org/10.1002/chem.201600341.
Chem. Eur. J. 2016, 22, 6815 – 6829
6815
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Figure 1. Structures of auriside A, callipeltoside A, and dolastatin 19, and the proposed structures of lyngbyaloside B (1), lyngbouilloside (2), 18E- and 18Z-
lyngbyaloside C (3 and 4, respectively). 13-Demethyllyngbyaloside B (5) is a non-natural analogue of 1.
using an olefin cross-metathesis reaction[11] and an acyl ketene
macrocyclization as the key transformations.[8d] The Cossy
group reported that the NMR spectroscopic data of their syn-
thetic aglycon were also not in agreement with those of the
corresponding domain of natural lyngbouilloside. These stud-
ies highlighted the possibility that the proposed structure of
lyngbouilloside (2) might have been erroneously determined;
Cossy et al. speculated that the configuration of the C-11 ste-
reogenic center of structure 2, which is opposite to that of the
proposed structure 1, might have been incorrectly assigned. In
any case, it is clear that total synthesis of these macrolide gly-
cosides is required for the determination of their complete ste-
reostructures. Herein, we describe in detail the first total syn-
thesis of both the proposed and correct structures of (À)-lyng-
byaloside B, which established the complete stereostructure of
this natural product in an unambiguous manner.[12]
Our synthetic plan towards target 5 is summarized in
Scheme 1. We envisaged that the 3,4-di-O-methyl-l-rhamno-
pyranoside moiety could be introduced to the aglycon at
a late stage of the total synthesis by means of stereoselective
glycosylation by using trichloroacetimidate 6 under Schmidt
Results and Discussion
Total synthesis of (À)-13-demethyllyngbyaloside B
The initial target of this study was 13-demethyllyngbyaloside B
(Figure 1, 5) because this non-natural analogue represented
a suitable target for preliminary investigations.[13] It was also
anticipated that compound 5 would be useful for evaluating
the impact of the C-13 methyl group on the solution-state
conformation and biological activity of this compound.
Scheme 1. Synthetic plan towards 5. MPM=p-methoxyphenylmethyl,
RCM=ring-closing metathesis, TBDPS=tert-butyldiphenylsilyl, TBS=tert-bu-
tyldimethylsilyl.
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6816
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
conditions.[14] Construction of the conjugated diene side chain
would be achieved through sequential Takai olefination[15] and
Stille reaction.[16] These considerations led us to identify the
macrolactone 7 as a precursor of target compound 5. Based
on our previous work on related macrolide natural products,[17]
we envisioned that macrocycle 7 would be synthesized from
the carboxylic acid 8a or 8b and the alcohol 9 by an esterifica-
tion/RCM sequence.
methylenation of the resultant aldehyde under Takai condi-
tions (CrCl2, CH2I2, THF/DMF),[25] and hydrolysis of the methyl
ester moiety.
The synthesis of the alcohol 9 began with known homoallyl-
ic alcohol 17 (Scheme 3),[26] which was prepared in three steps
from 1,4-butanediol. Protection of the alcohol 17 as its MPM
ether followed by cleavage of the double bond gave the alde-
hyde 18 (65% yield over the two steps). Roush crotylation[27] of
The synthesis of the carboxylic acids 8a,b started with the
silylation of the known alcohol 10[18] to give the silyl ether 11
in 89% yield (Scheme 2). DIBALH reduction of the silyl ether 11
cleanly removed the chiral auxiliary to deliver the aldehyde 12
(93% yield), which was reacted with the dienol silyl ether 13[19]
Scheme 3. Synthesis of alcohol 9. DDQ=2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone, DEAD=diethyl azodicarboxylayte, MS=molecular sieves.
Scheme 2. Synthesis of carboxylic acids 8a and 8b. DIBALH=diisobutylalu-
minum hydride, NMO=N-methylmorpholine N-oxide, OTf=trifluorometha-
nesulfonate, PPTS=pyridinium p-toluenesulfonate, TES=triethylsilyl.
the aldehyde 18 by using chiral crotylboronate reagent 19 (4 Š
MS, toluene, À788C) provided the alcohol 20 in 84% yield
(d.r. 10:1); its absolute configuration was established by NMR
analyses of suitable acetonide derivatives.[23] Silylation of the al-
cohol 20 (quant. yield) followed by removal of the MPM group
(99% yield) led to the alcohol 21. Finally, Mitsunobu inver-
sion[28] of the alcohol 21 under standard conditions
(pNO2C6H4CO2H, DEAD, Ph3P) and DIBALH reduction of the re-
sultant p-nitrobenzoate furnished the alcohol 9 (86% yield
over two steps). Here, we note that we intentionally selected
the alcohol 17 with “incorrect” configuration at the C-13 ste-
reogenic center as the starting material. This was because
Roush crotylation of aldehyde ent-18 with crotylboronate 19
provided the corresponding crotylated product 22 as a 1:1
mixture of diastereoisomers, which suggests that these reac-
tants are “mismatched”.
under Mukaiyama conditions (BF3·OEt2, CH2Cl2, À788C)[20,21] to
afford the alcohol 14 in 95% yield (d.r. 10:1). The high diaste-
reoselectivity that was observed for the vinylogous Mukaiyama
aldol reaction could be ascribed to 1,2- and 1,3-asymmetric in-
ductions that were brought about by the a-methyl and b-silyl-
oxy groups.[22] Exposure of the alcohol 14 to PPTS in methanol
resulted in the loss of the silyl group and concomitant methyl
acetalization to provide the alcohol 15 in 93% yield. The rela-
tive configuration of the alcohol 15 was established on the
basis of J values and an NOE enhancement.[23] Protection of
the alcohol 15 by using MPMOC(=NH)CCl3 (MPM imidate) and
[24]
La(OTf)3 led to the MPM ether 16 in 85% yield; subsequent
hydrolysis under alkaline conditions furnished the carboxylic
acid 8a in 95% yield. Meanwhile, we also prepared the carbox-
ylic acid 8b from 16 by oxidative cleavage of the styryl group,
With the requisite fragments in hand, we proceeded to the
construction of the macrocyclic backbone of compound 5
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6817
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
the diene 23b relative to its phenyl-substituted derivative 23a
was underscored by comparison of the results shown in en-
tries 3 and 7. In all cases, macrocycle 24 was isolated as
a single stereoisomer (E/Z >20:1, JHÀ8,HÀ9 =15.5 Hz) after purifi-
cation by flash column chromatography on silica gel.
Our next task was the construction of the conjugated bro-
modiene side chain (Scheme 5). Hydrogenation of the unsatu-
rated macrocycle 24 followed by selective deprotection of the
TBDPS group[33] gave the alcohol 25 (86% yield over two
steps). Dess–Martin oxidation[34] of the alcohol 25 (97% yield)
Scheme 4. Synthesis of macrocycle 24. DMAP=N,N-dimethylaminopyridine.
(Scheme 4). Esterification of the carboxylic acids 8a and 8b
with the alcohol 9 under Yamaguchi conditions[29] afforded the
dienes 23a and 23b, respectively. Our initial RCM experiments
of 23a by using the second-generation Grubbs (G-II)[30] or Hov-
eyda–Grubbs (HG-II)[31] catalyst turned out to be unproductive
(Table 1, entries 1–3). These results could be ascribed to the
low reactivity of the styryl group in olefin metathesis reac-
tions;[17a,b] therefore, RCM of diene 23b was next investigated
under a series of reaction conditions (entries 4–6). By elevating
the reaction temperature from 1008C to 1408C (bath tempera-
ture), we were able to improve the yield of the desired macro-
cycle 24 to 59% (entry 6). We completed the optimization of
the reaction conditions by increasing the molar amount of 1,4-
benzoquinone[32] (entries 7 and 8). The superior reactivity of
Scheme 5. Construction of the diene side chain. CuTC=copper thiophene-
2-carboxylate, DMP=Dess–Martin periodinane, NBS=N-bromosuccinimide,
NMP=N-methylpyrrolidone, TBAF=tetra-n-butylammonium fluoride,
TMS=trimethylsilyl.
Table 1. RCM of dienes 23a and 23b.[a]
and ensuing Takai olefination (CrCl2, CHI3, 1,4-dioxane/THF)
provided the vinyl iodide 26 in 81% yield (E/Z 13:1). The minor
Z-isomer could be removed at this stage by flash column chro-
matography on silica gel. The Stille reaction of the vinyl iodide
26 with (2-trimethylsilylethenyl)tributylstannane (27)[35] proved
more difficult than anticipated, possibly because of the low re-
activity of the vinylstannane 27. We screened a variety of reac-
tion conditions by using the vinyl iodide 28 as a model com-
pound and found the beneficial effect of CuTC[36] in this partic-
ular case (Table 2). Gratifyingly, CuTC-mediated coupling of the
vinyl iodide 26 with the vinylstannane 27 in degassed NMP at
room temperature afforded the conjugated diene 30 in 99%
yield. Bromodesilylation of the diene 30 with NBS[37] gave the
bromodiene 31, which had undergone partial isomerization of
the C-18=C-19 double bond geometry (E/Z ꢀ15:1),[37] in 89%
yield. Removal of the MPM group of the diene 31 by using
DDQ did not proceed cleanly and gave the corresponding al-
Entry
Diene
Catalyst (equiv)
BQ[b] [equiv]
Temp. [8C]
Yield
1
2
3
4
5
6
7
8[c]
23a
23a
23a
23b
23b
23b
23b
23b
G-II (0.3)
0.6
0.6
1.5
0.4
0.2
0.2
1.5
1.5
100
100
140
100
120
140
140
140
<5%
<5%
<5%
22%
33%
59%
81%
78%
HG-II (0.3)
HG-II (0.1)
HG-II (0.2)
HG-II (0.1)
HG-II (0.1)
HG-II (0.1)
HG-II (0.1)
[a] All the reactions were performed in degassed toluene (3 mm) over-
night, unless otherwise noted. [b] BQ=1,4-benzoquinone. [c] The reaction
was performed in degassed toluene (1 mm).
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6818
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
cohol 32 in only moderate yield; furthermore, treatment of the
protected alcohol 31 with CAN resulted in decomposition of
the material.
Table 2. Stille-type reaction of vinyl iodide 28[a] and vinylstannane 27.[b]
Therefore, we decided to remove the MPM group before
construction of the sensitive conjugated diene side chain
(Scheme 6). Treatment of the vinyl iodide 26 with DDQ led to
the alcohol 33 (96% yield) without incident, which was cou-
pled with the vinylstannane 27 under the influence of CuTC to
provide the vinylsilane 34 (74% yield). Exposure of the vinylsi-
lane 34 to NBS in acetonitrile afforded the aglycon 32 in 84%
yield. As expected, the desilylation of intermediate 34 caused
partial erosion of the geometry of the C-18=C-19 double
Entry
Pd catalyst (equiv)
Cu salt (equiv)
27 [equiv]
Yield
1
2
3[c]
4
5
6
7
[PdCl2(PPh3)2] (0.1)
[PdCl2(CH3CN)2] (0.1)
[PdCl2(CH3CN)2] (0.1)
[PdCl2(CH3CN)2] (0.1)
[PdCl2(CH3CN)2] (0.1)
[PdCl2(CH3CN)2] (0.1)
–
–
–
–
1.5
1.5
1.5
1.5
1.5
3.0
3.0
29%
34%
35%
38%
38%
70%
83%
CuI (1.0)
CuTC (3.8)
CuTC (7.6)
CuTC (7.6)
1
bond,[37] as judged by H NMR analysis. The minor impurities
were removed by preparative reverse-phase HPLC after com-
pletion of the total synthesis.
[a] Vinyl iodide 28 was used as a 10:1 mixture of E/Z isomers. [b] The re-
actions were performed in degassed DMF (entries 1–6) or NMP (entry 7)
at room temperature. [c] iPr2NEt (1.5 equiv) was used as additive.
Completion of the total synthesis of 13-demethyllyngbyalosi-
de B (5) is shown in Scheme 7. Stereoselective glycosylation of
the alcohol 32 with the 2-O-acetylated rhamnopyranosyl tri-
chloroacetimidate derivative 6[23] (10 mol% BF3·OEt2, 4 Š MS,
CH2Cl2, À78 to À408C) delivered, after treatment with K2CO3 in
methanol, the desired glycosylated product 35 (16% yield over
two steps) and the orthoester 36 (55% yield over two steps),
the latter being the major product. The structure of the or-
thoester 36 was characterized on the basis of 2D NMR analy-
ses.[23] It is known that 2-O-acetylated glycosyl donors are
useful for controlling the stereochemical outcome of glycosyla-
tion through anchimeric assistance, although in some instan-
ces such donors potentially complicate the reaction by produc-
ing the corresponding orthoesters.[10,38] To circumvent the or-
thoester formation, we chose the 2-O-benzoylated rhamnopy-
Scheme 6. Synthesis of aglycon 32.
Scheme 7. Completion of the total synthesis of 13-demethyllyngbyaloside B (5). Bz=benzoyl.
Chem. Eur. J. 2016, 22, 6815 – 6829 www.chemeurj.org
6819
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
ranosyl trichloroacetimidate derivative 37[23] as an alternative
donor. Thus, glycosylation of the alcohol 32 with the glycosyl
donor 37 (10 mol% TMSOTf, 4 Š MS, CH2Cl2, À78 to À408C)
cleanly furnished the desired glycosylated product 38 in 85%
yield with greater than 20:1 d.r. The use of BF3·OEt2 as a Lewis
acid gave a slightly lower yield of product 38 (68% yield). The
stereochemical outcome of the glycosylation was confirmed
by NOE experiments and the data were in accordance with
those that were reported for the authentic material.[5] Finally,
the benzoyl group was removed with NaOMe (86% yield), and
the silyl ether and methyl acetal were cleaved with aqueous
hydrofluoric acid in acetonitrile (82% yield), which afforded
(À)-13-demethyllyngbyaloside B (5) ([a]2D4 =À46.1 (c=0.5 in
CHCl3)).
result: first, the C-13 methyl group of the natural product has
significant influence on the overall conformational property of
the macrocycle, and second, the proposed structure 1 has
been incorrectly assigned. Considering the caveats that had
been independently described by Ley[8c] and Cossy[8d] on the
proposed structure 2 of (À)-lyngbouilloside, the non-resem-
blance of the NMR spectroscopic data between derivative 5
and natural (À)-lyngbyaloside B implied possible misassign-
ment of the proposed structure 1 and justified our efforts to-
wards its total synthesis for structure validation.
The first-generation approach toward the proposed struc-
ture 1 of (À)-lyngbyaloside B
1
The H and 13C NMR signals of the non-natural derivative 5
Having completed the total synthesis of 13-demethyllyngbya-
loside B (5), we were in a position to undertake the total syn-
thesis of the proposed structure 1 of (À)-lyngbyaloside B,
which we based on the esterification/RCM strategy. To this
end, the tertiary alcohol 39 was synthesized from known ester
40,[39] which was prepared in four steps from 3-methyl-2-
buten-1-ol (Scheme 8). Reduction of the ester 40 with LiAlH4,
silylation of the resultant alcohol with TBDPSCl/imidazole, and
deprotection of the MPM group by using DDQ gave the alco-
hol 41 in 79% yield over three steps. Sharpless asymmetric ep-
oxidation of the alcohol 41 (e.r. 96:4)[40] followed by reduction
of the derived epoxy alcohol with Red-Al[41] delivered the 1,3-
diol 42 in 82% yield over the two steps. Acetalization of the
diol 42 with pMeOC6H4CH(OMe)2 and PPTS provided the corre-
sponding p-methoxybenzylidene acetal (93% yield), which was
treated with DIBALH[42] to give the alcohol 43 (93% yield). Oxi-
dation of the alcohol 43 under Parikh–Doering conditions[43]
led to the aldehyde 44 (97%). Evans syn-aldol reaction[44] of
the aldehyde 44 with a boron enolate of 45 (Bu2BOTf, Et3N,
CH2Cl2, À78–08C) afforded the alcohol 46 in 98% yield with
greater than 20:1 diastereoselectivity. The absolute configura-
tion of the alcohol 46 was confirmed by using a modified
Mosher analysis[45] and NMR analyses on a suitable acetonide
derivative.[23] After the alcohol 46 was silylated (94% yield), the
resultant silyl ether was reduced with LiBH4 in the presence of
methanol to remove the chiral auxiliary, which gave rise to the
alcohol 47 (82% yield). Oxidation of the alcohol 47 followed
by Wittig methylenation and subsequent cleavage of the MPM
ether delivered the alcohol 39 in 87% yield over the three
steps. The synthesis of the alcohol 39 was somewhat circuitous
because our attempts at asymmetric crotylation of the alde-
hyde 44 to directly obtain the alcohol 48 by using a Brown[46]
or Roush[27] chiral crotylborane reagent only gave an insepara-
ble mixture of diastereoisomers with essentially no diastereose-
lectivity, as judged by 1H NMR spectroscopic analysis.
were assigned on the basis of 2D NMR analyses and were com-
pared with those of natural (À)-lyngbyaloside B; the 13C NMR
data are summarized in Table 3.[23] We were intrigued to find
that significant chemical shift deviations were found not
merely around the C-13 position but all over the macrocycle,
whereas the NMR chemical shift values of the conjugated
diene and l-rhamnopyranoside moieties of compound 5 were
in good accordance with those of natural (À)-lyngbyaloside B.
At this point, two possibilities arose from this unexpected
Table 3. Comparison of the 13C NMR spectroscopic data for (À)-13-deme-
thyllyngbyaloside B (5) and the natural (À)-lyngbyaloside B.[a]
Position
dN [ppm]
dS [ppm]
Dd [ppm]
1
2
3
4
5
6
7
8
172.5
46.8
96.1
42.1
79.1
41.5
75.6
28.1
32.8
36.9
65.7
44.1
86.4
38.6
26.7
135.6
127.7
137.5
106.5
13.6
13.6
23.4
101.1
67.9
81.2
57.4
81.8
61.0
67.4
17.6
169.1
48.9
96.8
39.4
79.1
38.5
74.3
26.2
28.0
32.0
67.3
38.2
70.9
34.6
28.4
134.6
128.3
137.4
106.9
12.7
13.5
N/A[b]
101.2
68.0
81.2
57.5
81.8
60.8
67.5
17.6
+3.4
À1.9
À0.7
+2.7
0
+3.0
+1.3
+1.9
+4.8
+4.9
À1.6
+5.9
+15.5
+4.0
À1.7
+1.0
À0.6
+0.1
À0.4
+0.9
+0.1
N/A[b]
À0.1
À0.1
0
9
10
11
12
13
14
15
16
17
18
19
20
21
22
1’
2’
3’
Unfortunately, we were unable to esterify the tertiary alcohol
39 with the carboxylic acid 8a or its synthetic equivalent 49
(Scheme 9). Esterification under Yamaguchi, Shiina,[47] Kita,[48] or
Steglich[49] conditions did not give the desired ester 50 at all;
in all cases, unreacted alcohol 39 was recovered almost quanti-
tatively. The use of the thioester 49 as an electrophile under
3’ÀOMe
À0.1
4’
0
4’-OMe
5’
6’
+0.2
À0.1
0
[a] The 13C NMR spectra of natural (À)-lyngbyaloside B and synthetic (À)-
13-demethyllyngbyaloside B (5) were collected in CDCl3 at 125 MHz and
150 MHz, respectively. dN and dS are chemical shifts of the natural prod-
uct and synthetic 5. [b] N/A=not applicable.
[50]
the influence of Ag(OCOCF3) or Cu(OTf)2 was also ineffective
in this case. These unproductive results could be ascribed to
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6820
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Scheme 8. Synthesis of alcohol 39. DIPT=diisopropyl tartrate, HMDS=hexamethyldisilazide, py=pyridine, Red-Al=sodium bis(2-methoxyethoxy)aluminum
hydride.
razole-5-thiol (DEAD, Ph3P) and subsequent oxidation afforded
the sulfone 53 (67% yield over two steps). Deprotonation of
the sulfone 53 with LDA followed by addition of the aldehyde
54 (THF, À78 to 08C) led to the olefin 55 in 70% yield as an in-
consequential mixture of E/Z isomers (E/Z 1:5).[52] Hydrogena-
tion of the double bond within 55 (83% yield), cleavage of the
MPM ether (98% yield), and alkaline hydrolysis of the methyl
ester (95% yield) furnished the desired seco-acid 51. However,
in spite of our extensive efforts, macrolactonization of the
seco-acid 51 was found to be completely unproductive;
indeed, under Yamaguchi, Shiina, Keck,[53] Kita–Trost,[48,54] or
Corey-Nicolaou[55] conditions, we did not observe any trace of
Scheme 9. Unproductive attempts at the acylation of tertiary alcohol 39.
the desired macrolactone 57.
Owing to our inability to acylate the C-13 tertiary hydroxy
the extremely low reactivity of the sterically encumbered alco-
hol 39, which surprisingly, proved to be completely unreactive
even under standard acetylation conditions (Ac2O, Et3N, DMAP
or AcCl, pyridine, DMAP).
group with activated anhydrides/esters, we were forced to re-
consider our synthetic strategy for the macrolactone skeleton
of target compound 1. Hoye and co-workers[8a] have described
the synthesis of a model derivative of compound 1 by means
of an acyl ketene macrolactonization.[9] To test the feasibility of
acyl ketene macrocyclization in the real system, we undertook
the synthesis of the cyclization precursor, dioxinone 58
(Scheme 11). While this work was in progress, Cossy et al. re-
ported the total synthesis of the nominal lyngbouilloside agly-
con, in which acyl ketene macrocyclization was exploited for
the construction of the macrolactone skeleton.[8d]
At this stage, we hypothesized that macrolactonization of
the seco-acid 51 might overcome the inherent low reactivity
of the C-13 tertiary hydroxy group if the precursor 51 adopts
a conformation in which the reaction sites, i.e., C-1 and C-13
positions, are brought into close proximity (Scheme 10).[51] To
test this idea, the seco-acid 51 was synthesized from the alco-
hol 46: Protection of 46 as its MOM ether (95% yield) followed
by reductive removal of the chiral auxiliary (87% yield) gave
the alcohol 52. Mitsunobu reaction of 52 with 1-phenyl-1H-tet-
The synthesis of compound 58 started with oxidation of the
alcohol 52 followed by Wittig reaction of the resultant alde-
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6821
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Scheme 10. Unproductive attempts at the macrocyclization of seco-acid 51. LDA=lithium diisopropylamide, mCPBA=m-chloroperoxybenzoic acid,
MOM=methoxymethyl, MW=microwave.
Scheme 11. Synthesis of dioxinone 58 and its macrocyclization. Ts=p-toluenesulfonyl.
hyde to give the a,b-unsaturated ester 59 (71% yield over two
steps). After hydrogenation of the double bond, the ester
moiety was reduced with DIBALH to provide the alcohol 60
(85% yield over the two steps). Oxidation of the alcohol 60
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6822
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
and subsequent Roush crotylation by using chiral crotyl boro-
nate 61 (4 Š MS, toluene, À788C) delivered the alcohol 62
(80% yield over the two steps, d.r.>10:1). At this stage, the
configuration of the newly generated stereogenic centers was
established by using NMR analyses of suitable derivatives.[23] Si-
lylation of the alcohol 62 (TESCl, imidazole, 98% yield) was fol-
lowed by oxidative cleavage of the terminal double bond to
give the aldehyde 63 (93% yield), and its subsequent vinylo-
gous Mukaiyama aldol reaction with the dienol silyl ether 64[56]
(BF3·OEt2, CH2Cl2, À788C) led to the alcohol 65 and its C-5
epimer (76 and 17% yield, respectively). These diastereoiso-
mers were separated by flash column chromatography on
silica gel. After silylation of the alcohol 65 (TESCl, imidazole,
89% yield), the MPM group was cleaved with DDQ to afford
the desired dioxinone 58 (93% yield).
Gratifyingly, when a solution of compound 58 in toluene
(0.3 mm) was heated to reflux, the cyclization proceeded to
give the b-keto lactone 66; this was treated with TsOH in THF/
H2O to cleave the TES groups and initiate simultaneous forma-
tion of the six-membered hemiacetal ring, which gave rise to
the targeted macrolactone 67 in 81% yield over the two steps.
The configuration of the C-5 stereogenic center was deter-
mined on the basis of J values at this stage.[23]
Scheme 12. Synthetic plan towards 68.
Thus, we have demonstrated that the 14-membered macro-
cyclic backbone of the proposed structure of lyngbyaloside B
(1) could actually be synthesized by using acyl ketene macro-
cyclization. However, the synthesis of the cyclization precursor
58 required a number of transformations, and the overall syn-
thetic efficiency was far from satisfactory. At this point, we de-
cided to reconsider our synthetic plan towards target com-
pound 1.
The second-generation approach towards the proposed
structure 1 of (À)-lyngbyaloside B
Our second-generation synthetic plan is summarized in
Scheme 12. The aglycon 68 would be accessible through an
acyl ketene macrocyclization of the dioxinone 69, which was
to be synthesized in a convergent manner from three readily
available fragments, the aldehyde 44, the ester 70, and the
dienol silyl ether 64,[56] by an Abiko–Masamune anti-aldol reac-
tion[57] and a vinylogous Mukaiyama aldol reaction. Although
the Abiko–Masamune anti-aldol reaction has been used to
construct anti-propionate aldol motifs, we envisioned that it
would also be useful as a means to assemble complex frag-
ments with the simultaneous creation of two contiguous ste-
reogenic centers.[58]
Scheme 13. Synthesis of ester 70. DCC=dicyclohexylcarbodiimide.
alcohol 75[56] by using DCC/DMAP afforded the ester 70 (68%
yield).
The synthesis of the ester 70 started with the Brown asym-
metric crotylation of the known aldehyde 71,[59] which gave
the alcohol 72 in 77% yield (e.r. 96:4, d.r.>20:1) (Scheme 13).
The stereostructure of the alcohol 72 was corroborated by
a modified Mosher analysis and NMR analyses of an acetonide
derivative.[23] Silylation of the alcohol 72 with TESCl/imidazole
(94% yield) followed by deprotection of the MPM group (94%
yield) led to the alcohol 73. A two-stage oxidation[60] of the al-
cohol 73 gave the corresponding carboxylic acid 74 (89% yield
over the two steps), and subsequent esterification with known
The synthesis of the cyclization precursor 69 and completion
of the total synthesis of target compound 1 are summarized in
Scheme 14. Abiko–Masamune anti-aldol reaction of the ester
70 and the aldehyde 44 was carried out under standard condi-
tions (Cy2BOTf, Et3N, CH2Cl2, À78 to 08C) to provide the alcohol
76 in 87% yield with 10:1 d.r. The configurations of the newly
generated C-10 and C-11 stereogenic centers of alcohol 76
were unambiguously determined on the basis of NMR analyses
of suitable derivatives.[23] Silylation of the alcohol 76 with
TBSCl in the presence of AgNO3 and pyridine[61] (91% yield) fol-
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6823
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Scheme 14. Synthesis of the cyclization precursor 69 and completion of the total synthesis of 1. Cy=cyclohexyl, TEMPO=2,2,6,6-tetramethylpiperidin-1-oxyl.
lowed by reductive removal of the superfluous chiral auxiliary
gave rise to the alcohol 77 (79% yield). The alcohol 77 was de-
oxygenated by tosylation (85% yield) and LiEt3BH reduction[62]
(92% yield) to deliver the olefin 78. Dihydroxylation of the
olefin 78 and subsequent cleavage of the resultant 1,2-diol
with Pb(OAc)4 gave the aldehyde 79 in 92% yield over the two
steps, which was then reacted with the dienol silyl ether 64
under Mukaiyama conditions (BF3·OEt2, CH2Cl2, À958C) to
afford the alcohol 80 in 87% yield, along with its C-5 epimer in
8% yield. These diastereoisomers were separated by flash
column chromatography on silica gel. Silylation of the alcohol
80 with TESCl/imidazole (96% yield) followed by removal of
the MPM group (93% yield) led to the cyclization precursor 69.
Macrocyclization of the alcohol 69 was carried out in reflux-
ing toluene (1 mm) and gave rise to the b-keto lactone 81,[63]
which was treated with PPTS in MeOH/(CH2Cl)2 to remove the
TES groups and induce a spontaneous acetalization to afford
the methyl acetal 82 in 88% yield over the two steps. At this
stage, the minor stereoisomer that originated from the Abiko–
Masamune reaction was removed, and the configuration of the
C-5 stereogenic center was determined on the basis of NOE ex-
periments.[23]
Having constructed the macrocyclic backbone, we proceed-
ed to complete the total synthesis of target compound 1. The
TBDPS group of compound 82 was selectively removed by
using buffered TBAF to give a diol in 98% yield. The liberated
primary hydroxy group was selectively oxidized with TEMPO/
[64]
PhI(OAc)2 (96% yield), and Takai olefination of the derived al-
dehyde afforded the vinyl iodide 68 in 54% yield as an insepa-
rable mixture of E/Z isomers (E/Z 7:1). Stille-type reaction of
the vinyl iodide 68 with the vinylstannane 27 by the action of
CuTC in degassed NMP provided the vinylsilane 83 in 73%
yield; its exposure to NBS in acetonitrile delivered the bromo-
diene 84 in 91% yield. As aforementioned, the bromodesilyla-
tion of compound 83 was accompanied by partial isomeriza-
tion of the C-18=C-19 double bond; these minor stereoisomers
were removed by preparative reverse-phase HPLC after com-
pletion of the total synthesis. Stereoselective glycosylation of
the alcohol 84 with the trichloroacetimidate 37 under previ-
ously optimized conditions (10 mol% TMSOTf, 4 Š MS, CH2Cl2,
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6824
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
À78 to À408C) afforded the glycosylated product 85 in 71%
yield (d.r.>20:1). The a-glycosidic linkage of the rhamnopyra-
noside moiety of compound 85 was confirmed by NOE experi-
ments.[23] Methanolysis of the benzoyl group of 85 (NaOMe,
MeOH/THF, 88% yield) followed by removal of the TBS group
and simultaneous cleavage of the methyl acetal (aq. HF,
CH3CN, 85% yield) furnished the proposed structure 1 of
(À)-lyngbyaloside B. The synthetic material was purified by re-
verse-phase HPLC to remove minor stereoisomers prior to de-
tailed spectroscopic characterization.
and C-13 stereogenic centers and/or substituents would be
the important structural elements that together determine the
conformational behavior of compound 1.
After screening several deuterated solvents, we found that
1
CD3CN was the solvent of choice; the H and 13C NMR spectra
of compound 1 measured in CD3CN at room temperature dis-
played well-resolved, sharp signals. The gross structure of our
synthetic analogue 1 was ascertained on the basis of 2D NMR
analyses; the relative configuration has already been estab-
lished by detailed NMR analyses of appropriate intermediates
and their derivatives. Thus, it was evident that we have actually
synthesized the proposed structure 1 of (À)-lyngbyaloside B
and that the original stereochemical assignment made by
Moore and co-workers requires reconsideration.
Revision of the original stereochemical assignment and es-
tablishment of the complete stereostructure
Unfortunately, the 1H and 13C NMR spectra of our synthetic
compound 1 were obviously different from those of natural
(À)-lyngyaloside B. The 1H NMR spectrum of the authentic
sample recorded in CDCl3 showed a set of sharp signals,
whereas the 1H NMR spectrum of our sample 1 collected in
CDCl3 at room temperature displayed significant line broaden-
ing for the signals that correspond to the C-8–C-12 domain.
Moreover, the 13C NMR spectrum of compound 1 under the
same conditions did not show any clear signals that account
for the C-8–C-12 domain. These observations strongly suggest-
ed that, in solution, compound 1 actually exists as an ensem-
ble of multiple conformers, which interconvert slowly within
the NMR timescale, at least in CDCl3 at room temperature.[65]
Ley and co-workers have made a similar observation of their
protected aglycon of (À)-lyngbouilloside (2), as noted above.[8c]
In contrast to compound 1, (À)-13-demethyllyngbyaloside B
(5) did not show any broadening of signals in its 1H and
13C NMR spectra measured in CDCl3 at room temperature.
Therefore, it was reasonable to assume that the C-10, C-11,
Moore et al. assigned the relative configuration of the six-
membered hemiacetal and the l-rhamnopyranoside moieties
in a solid manner on the basis of J values and ROE enhance-
ments, but the relative configuration of the stereogenic cen-
ters along the macrocyclic backbone was deduced predomi-
nantly on the basis of ROE correlations. In fact, there was some
ambiguity in the relative configurational assignment of the
C-7/C-10 stereogenic centers because of signal overlap; there-
fore, we opted to further scrutinize the relative configuration
of the C-7/C-10, C-10/C-11, and C-11/C-13 stereogenic centers
with the aid of molecular mechanics (MM) calculations.
The relative configuration of the C-11/C-13 stereogenic cen-
ters could be assigned on the basis of the ROE correlations ob-
served between the H-11 methine proton and the H2-14 meth-
ylene protons of the natural product, which strongly suggests
that the C-11 hydroxy group and the C-13 methyl group
occupy the same face of the macrocycle.[5] Based on this prem-
ise, the correct configuration of the C-11 and C-13 stereogenic
centers should be either (11R,13R) or (11S,13S). As the pro-
Figure 2. Two representative stable conformers of the (10S,11S,13S) isomer of (À)-lyngbyaloside B. The conformers were generated by MM calculations
(MMFF94 s) and geometrically optimized at RB3LYP/6-31G* level of theory.
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6825
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
posed structure 1 has (10R,11R,13R) configuration, the possible
stereoisomers for the correct structure of (À)-lyngbyaloside B
could be narrowed down to the following three: (10S,11R,13R),
(10R,11S,13S), or (10S,11S,13S).
stants of H-8b (dq, J=14.6, ꢀ2 Hz), the weak coupling be-
tween H-10/H-11, and the ROESY correlation between Me-22/
H-12b. Moreover, both of these conformers accommodate an
H-bond between the C-1 carbonyl oxygen atom and the C-3
hemiacetal hydrogen atom, which likely accounts for the char-
acteristic long-range “W-coupling” that is observed between
the C-3ÀOH proton and the H-4 axial proton of the authentic
material (4JH,H =2.4 Hz).
Next, extensive conformational searches (MMFF94 s) were
performed on the candidate stereoisomers. Not unexpectedly,
MM calculations indicated that these stereoisomers show vary-
ing degrees of conformational flexibility with respect to the
macrocyclic backbone, so that it would be difficult to draw de-
finitive conclusions on the correct structure merely from MM-
based conformational analyses. Nevertheless, it was deduced
that the (10S,11S,13S) isomer most likely represents the correct
structure of the natural product. As shown in Figure 2, confor-
mational searches on the (10S,11S,13S) isomer found two rep-
resentative conformers A and B.[66] It appears that the confor-
mer A better fits the NMR characteristics of the authentic ma-
terial, which included the splitting pattern and coupling con-
Accordingly, we proceeded to verify the correct structure 86
of (À)-lyngbyaloside B through its total synthesis, as shown in
Scheme 15. The synthesis started with the Abiko–Masamune
anti-aldol reaction of the aldehyde ent-44[23] and the ester
87,[23] which proceeded in essentially the same way as that de-
1
scribed for compound 1. Gratifyingly, it was found that the H
and 13C NMR spectra of our synthetic analogue 86 were identi-
cal with those of natural lyngbyaloside B. Moreover, the specif-
ic rotation value of our synthetic 86 ([a]2D5 =À16.9 (c=0.20 in
Scheme 15. Total synthesis of the correct structure 86 of (À)-lyngbyaloside B.
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6826
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
CHCl3)) was in close agreement with that of the authentic
sample ([a]2D5 =À20 (c=0.10 in CHCl3)). Thus, the complete
stereostructure of (À)-lyngbyaloside B was undoubtedly estab-
lished to be that shown by structure 86.
Biological evaluation of synthetic (À)-lyngbyaloside B and
related compounds
Scheme 16. Synthesis of aglycon 102.
Evaluation of the antiproliferative activity of the proposed
structure 1, the correct structure 86 and its aglycon 102, and
(À)-13-demethyllyngbyaloside B (5) against a small panel of
human cancer cell lines was carried out by using WST-8 assay
(Figure 3).[67,68] The aglycon 102 was prepared from 99 by hy-
drolysis of the silyl ether and methyl acetal (Scheme 16). In
contrast to what was reported by Moore et al., we were sur-
prised to find that the correct structure 86 was almost inactive
against KB cells and the proposed structure 1 was also essen-
tially inactive. These compounds also did not show appreciable
activity in human non-small cell lung adenocarcinoma A549
cells; however, moderate antiproliferative activity was observed
in human promyelocytic leukemia HL-60 cells and human Bur-
kitt lymphoma DAUDI cells. Interestingly, 13-demethyllyngbyal-
soide B (5) showed somewhat more potent activity than com-
pounds 1 and 86. Meanwhile, the aglycon 102 was considera-
bly less active than the parent compound 86.
At present, we are unable to address why the antiprolifera-
tive potency of our synthetic compound 86 was significantly
lower than that which was reported in the isolation paper.
However, our own data have implications in the structure–ac-
tivity relationships of (À)-lyngbyaloside B: i) The absolute con-
figuration of the stereogenic centers along the macrocyclic
framework (C-10, C-11, and C-13) does not have appreciable
impact on the antiproliferative potency (the proposed struc-
ture 1 versus the correct structure 86), although it certainly af-
fects the conformational behavior in solution; ii) omission of
the C-13 methyl group was rather beneficial for improving the
antiproliferative potency, at least in the case of the proposed
structure 1; iii) the l-rhamnopyranoside moiety plays an impor-
tant role in exerting antiproliferative activity (the correct struc-
ture 86 versus the aglycon 102).
Conclusion
We have described in detail our synthetic and structural stud-
ies on (À)-lyngbyaloside B, a marine macrolide glycoside,
which culminated in the first total syntheses of the proposed
and correct structures of this natural product (compounds
1 and 86, respectively). Our initial investigations into the syn-
thesis of (À)-13-demethyllyngbyaloside B (5), a non-natural an-
alogue, exploited an RCM reaction for the construction of the
macrocyclic skeleton. The bromodiene side chain was stereose-
lectively introduced by a Stille-type reaction that was mediated
by CuTC. Stereoselective glycosylation was efficiently achieved
under Schmidt conditions by using a 2-O-benzoylated l-rham-
nopyranosyl trichloroacetimidate derivative. Thus, our total
synthesis of compound 5 was achieved in 22 steps (longest
linear sequence from 1,4-butanediol). Even though we have
successfully established our synthetic path towards compound
5, we soon realized that the synthesis of the proposed struc-
ture 1 of (À)-lyngbyaloside B was non-trivial because of our in-
ability to acylate the sterically encumbered C-13 tertiary hy-
droxy group under standard esterification conditions. After ex-
tensive investigations, we were finally able to complete the
total synthesis of target compound 1, in which an Abiko–Masa-
mune anti-aldol reaction and a vinylogous Mukaiyama aldol re-
action were utilized to couple readily available fragments (44,
Figure 3. Antiproliferative activity of compounds 1, 5, 86, and 102 against
a small panel of human cancer cell lines (n=3).
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6827
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[9] R. K. Boeckman, Jr. , J. R. Pruitt, J. Am. Chem. Soc. 1989, 111, 8286–8288.
For a review, see: K. P. Reber, S. D. Tilley, E. J. Sorensen, Chem. Soc. Rev.
2009, 38, 3022–3034.
64, and 70) and an acyl ketene macrolactonization was exploit-
ed to forge the macrocyclic backbone (32 linear steps from 3-
methyl-2-buten-1-ol). However, comparison of the 1H and
13C NMR spectra of synthetic compound 1 with those of the
authentic material indicated that the proposed structure 1 of
(À)-lyngbyaloside B required correction. Re-investigation into
the NMR spectroscopic data of the natural product, with the
aid of molecular mechanics calculations, led us to determine
that the configuration of the C-10, C-11, and C-13 stereogenic
centers was incorrectly assigned in the initially proposed struc-
ture 1. The correct structure 86 of (À)-lyngbyaloside B was fi-
nally verified in an unambiguous manner through total synthe-
sis. In line with our conclusion, Taylor and co-workers very re-
cently reported the total synthesis of (À)-18Z-lyngbyaloside C
and revised the original stereochemical assignment of the pro-
posed structure 4 at the same positions as 1 (C-10, C-11, and
C-13).[8i] Therefore, we suggest that the originally assigned
structure 2 of lyngbouilloside should also be reconsidered
carefully. This work illuminates the importance of total synthe-
sis in the establishment of the complete stereostructure of
complex natural products.[69,70]
[10] For reviews, see: a) A. Fürstner, Angew. Chem. Int. Ed. 2000, 39, 3012–
3043; Angew. Chem. 2000, 112, 3140–3172; b) A. Deiters, S. F. Martin,
Chem. Rev. 2004, 104, 2199–2238; c) K. C. Nicolaou, P. G. Bulger, D.
Sarlah, Angew. Chem. Int. Ed. 2005, 44, 4490–4527; Angew. Chem. 2005,
117, 4564–4601; d) A. Gradillas, J. PØrez-Castells, Angew. Chem. Int. Ed.
2006, 45, 6086–6101; Angew. Chem. 2006, 118, 6232–6247; e) A. H.
Hoveyda, A. R. Zhugralin, Nature 2007, 450, 243–251; f) A. Gradillas, J.
PØrez-Castells in Metathesis in Natural Product Synthesis: Strategies, Sub-
strates and Catalysts, (Eds.: J. Cossy, S. Arseniyadis, C. Meyer), Wiley-
VCH, Weinheim, 2010, pp. 149–182.
[11] For a review of olefin cross-metathesis reaction, see: S. J. Connon, S.
Blechert, Angew. Chem. Int. Ed. 2003, 42, 1900–1923; Angew. Chem.
2003, 115, 1944–1968.
[12] a) H. Fuwa, N. Yamagata, A. Saito, M. Sasaki, Org. Lett. 2013, 15, 1630–
1633; b) H. Fuwa, Y. Okuaki, N. Yamagata, M. Sasaki, Angew. Chem. Int.
Ed. 2015, 54, 868–873; Angew. Chem. 2015, 127, 882–887.
[13] In this paper, we designated the 13-demethyl counterpart of the pro-
posed structure 1 of lyngbyaloside B as 13-demethyllyngbyaloside B (5).
The configuration of the C10, C11, and C13 stereogenic centers of com-
pound 5 is same as that of the proposed structure 1, i.e., 10R,11R,13R.
[14] For reviews, see: a) X. Zhu, R. R. Schmidt, Angew. Chem. Int. Ed. 2009,
48, 1900–1934; Angew. Chem. 2009, 121, 1932–1967; b) R. R. Schmidt,
J. Michel, Angew. Chem. Int. Ed. Engl. 1980, 19, 731–732; Angew. Chem.
1980, 92, 763–764.
[15] a) K. Takai, K. Nitta, K. Utimoto, J. Am. Chem. Soc. 1986, 108, 7408–
7410; b) D. A. Evans, W. C. Black, J. Am. Chem. Soc. 1993, 115, 4497–
4513.
Acknowledgements
[16] For reviews, see: a) J. K. Stille, Angew. Chem. Int. Ed. Engl. 1986, 25, 508–
524; Angew. Chem. 1986, 98, 504–519; b) V. Farina, V. Krishnamurthy,
W. J. Scott, Orgnic Reactions, Vol. 50: The Stille Reaction, Wiley 2004,
pp. 1–652.
[17] a) H. Fuwa, M. Kawakami, K. Noto, T. Muto, Y. Suga, K. Konoki, M. Yotsu-
Yamashita, M. Sasaki, Chem. Eur. J. 2013, 19, 8100–8110; b) H. Fuwa, A.
Saito, M. Sasaki, Angew. Chem. Int. Ed. 2010, 49, 3041–3044; Angew.
Chem. 2010, 122, 3105–3108; c) H. Fuwa, K. Noto, M. Kawakami, M.
Sasaki, Chem. Lett. 2013, 42, 1020–1022; d) H. Fuwa, H. Yamaguchi, M.
Sasaki, Tetrahedron 2010, 66, 7492–7503.
This work was financially supported by JSPS KAKENHI (Grant
No. 23681045) and by MEXT KAKENHI (Grant Nos. 24102507
and 26102708).
Keywords: glycosides
· macrocycles · natural products ·
structure elucidation · total synthesis
[18] D. A. Evans, C. W. Downey, J. T. Shaw, J. S. Tedrow, Org. Lett. 2002, 4,
1127–1130.
[19] a) T.-H. Chan, P. Brownbridge, J. Am. Chem. Soc. 1980, 102, 3534–3538;
b) M. Kimura, A. Esoe, M. Mori, K. Iwata, Y. Tamaru, J. Am. Chem. Soc.
2006, 128, 8559–8568.
[20] T. Mukaiyama, A. Ishida, Chem. Lett. 1975, 319–322.
[21] For reviews, see: a) G. Casiraghi, L. Battistini, C. Curti, G. Rassu, F. Zanar-
di, Chem. Rev. 2011, 111, 3076–3154; b) M. Kalesse, M. Cordes, G. Sym-
kenberg, H.-H. Lu, Nat. Prod. Rep. 2014, 31, 563–594.
[22] D. A. Evans, M. J. Dart, J. L. Duffy, M. G. Yang, J. Am. Chem. Soc. 1996,
118, 4322–4343.
[1] For recent reviews, see: a) M. Kita, H. Kigoshi, Nat. Prod. Rep. 2015, 32,
534–542; b) L. A. Salvador-Reyes, H. Luesch, Nat. Prod. Rep. 2015, 32,
478–503; c) J. W. Blunt, B. R. Copp, R. A. Keyzers, M. H. G. Munro, M. R.
Prinsep, Nat. Prod. Rep. 2015, 32, 116–211; d) M. F. Mehbub, J. Lei, C.
Franco, W. Zhang, Mar. Drugs 2014, 12, 4539–4577; e) A. Martins, H.
Vieira, H. Gaspar, S. Santos, Mar. Drugs 2014, 12, 1066–1101; f) D. Skro-
peta, L. Wei, Nat. Prod. Rep. 2014, 31, 999–1025.
[2] H. Sone, H. Kigoshi, K. Yamada, J. Org. Chem. 1996, 61, 8956–8960.
[3] a) A. Zampella, M. V. D’Auria, L. Minale, C. Debitus, C. Roussakis, J. Am.
Chem. Soc. 1996, 118, 11085–11088; b) A. Zampella, M. V. D’Auria, L.
Minale, Tetrahedron 1997, 53, 3243–3248.
[23] See the Supporting Information for details.
[4] G. R. Pettit, J.-P. Xu, D. L. Doubek, J.-C. Chapius, J. M. Schimidt, J. Nat.
Prod. 2004, 67, 1252–1255.
[5] H. Luesch, W. Y. Yoshida, G. G. Harrigan, J. P. Doom, R. E. Moore, V. J.
Paul, J. Nat. Prod. 2002, 65, 1945–1948.
[6] L. T. Tan, B. L. Mµrquez, W. H. Gerwick, J. Nat. Prod. 2002, 65, 925–928.
[7] S. Matthew, L. A. Salvador, P. J. Schupp, V. J. Paul, H. Luesch, J. Nat. Prod.
2010, 73, 1544–1552.
[8] a) T. R. Hoye, M. E. Danielson, A. E. May, H. Zhao, Angew. Chem. Int. Ed.
2008, 47, 9743–9746; Angew. Chem. 2008, 120, 9889–9892; b) J. Ge-
bauer, S. Arseniyadis, J. Cossy, Synlett 2008, 712–714; c) D. Webb, A.
van den Heuvel, M. Kçgl, S. V. Ley, Synlett 2009, 2320–2324; d) A. ElMar-
rouni, R. Lebeuf, J. Gebauer, M. Herras, S. Arseniyadis, J. Cossy, Org. Lett.
2012, 14, 314–317; e) E. Stefan, R. E. Taylor, Org. Lett. 2012, 14, 3490–
3493; f) J. S. Yadav, A. Haldar, T. Maity, Eur. J. Org. Chem. 2013, 3076–
3085; g) G. Sabitha, T. R. Reddy, J. S. Yadav, K. Sirisha, RSC Adv. 2014, 4,
3149–3152; h) R. Chegondi, P. R. Hanson, Tetrahedron Lett. 2015, 56,
3330–3333; i) C.-F. Chang, E. Stefan, R. E. Taylor, Chem. Eur. J. 2015, 21,
10681–10686. See also: A. ElMarrouni, A. Kolleth, R. Lebeuf, J. Gebauer,
S. Prevost, M. Heras, S. Arseniyadis, J. Cossy, Nat. Prod. Commun. 2013,
8, 965–972.
[24] A. N. Rai, A. Basu, Tetrahedron Lett. 2003, 44, 2267–2269.
[25] a) T. Okazoe, K. Takai, K. Utimoto, J. Am. Chem. Soc. 1987, 109, 951–953;
b) O. Su, L. A. Dakin, J. S. Panek, J. Org. Chem. 2007, 72, 2–24.
[26] Y. Yuasa, J. Ando, S. Shibuya, J. Chem. Soc. Perkin Trans. 1 1996, 793–
802.
[27] W. R. Roush, K. Ando, D. B. Powers, A. D. Palkowitz, R. L. Halterman, J.
Am. Chem. Soc. 1990, 112, 6339–6348.
[28] For reviews, see: a) O. Mitsunobu, Synthesis 1980, 1–28; b) K. C. K.
Swamy, N. N. B. Kumar, E. Balaraman, K. V. P. P. Kumar, Chem. Rev. 2009,
109, 2551–2651.
[29] J. Inanaga, K. Hirata, H. Saeki, T. Katsuki, M. Yamaguchi, Bull. Chem. Soc.
Jpn. 1979, 52, 1989–1993.
[30] M. Scholl, S. Ding, C. W. Lee, R. H. Grubbs, Org. Lett. 1999, 1, 953–956.
[31] S. B. Garber, J. S. Kingsbury, B. L. Gray, A. H. Hoveyda, J. Am. Chem. Soc.
2000, 122, 8168–8179.
[32] S. H. Hong, H. P. Sanders, C. W. Lee, R. H. Grubbs, J. Am. Chem. Soc.
2005, 127, 17160–17161.
[33] S. Higashibayashi, K. Shinko, T. Ishizu, K. Hashimoto, M. Nakata, Synlett
2000, 1306–1308.
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6828
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[34] a) D. B. Dess, J. C. Martin, J. Org. Chem. 1983, 48, 4155–4156; b) D. B.
Dess, J. C. Martin, J. Am. Chem. Soc. 1991, 113, 7277–7287.
[35] R. F. Cunico, F. J. Clayton, J. Org. Chem. 1976, 41, 1480–1482.
[36] G. D. Allred, L. S. Liebeskind, J. Am. Chem. Soc. 1996, 118, 2748–2749.
For a review, see: H. Prokopcovµ, C. O. Kappe, Angew. Chem. Int. Ed.
2009, 48, 2276–2286; Angew. Chem. 2009, 121, 2312–2322.
[37] D. P. Stamos, A. G. Taylor, Y. Kishi, Tetrahedron Lett. 1996, 37, 8647–
8650.
dron Lett. 1996, 37, 6885–6888; b) K. C. Nicolaou, A. D. Piscopio, P. Berti-
nato, T. K. Chakraborty, N. Minowa, K. Koide, Chem. Eur. J. 1995, 1, 318–
333; c) T. Nakata, T. Komatsu, K. Nagasawa, Chem. Pharm. Bull. 1994, 42,
2403–2405; d) M. J. Kiefel, J. Maddock, G. Pattenden, Tetrahedron Lett.
1992, 33, 3227–3230.
[59] Y. Morimoto, M. Iwahashi, T. Kinoshita, K. Nishida, Chem. Eur. J. 2001, 7,
4107–4116.
[60] B. S. Bal, W. E. Childers, Jr., H. W. Pinnick, Tetrahedron 1981, 37, 2091–
2096.
[61] K. K. Ogilvie, G. H. Hakimelahi, Z. A. Proba, D. P. C. McGee, Tetrahedron
Lett. 1982, 23, 1997–2000.
[38] X. Zhu, B. Yu, Y. Hui, R. R. Schmidt, Eur. J. Org. Chem. 2004, 965–973.
[39] D. A. Evans, J. D. Burch, E. Hu, G. Jaeschke, Tetrahedron 2008, 64, 4671–
4699.
[40] Estimated by chiral HPLC analysis. For details of stereochemical assign-
ment, see the Supporting Information.
[41] J. Finan, Y. Kishi, Tetrahedron Lett. 1982, 23, 2719–2722.
[42] a) R. Johansson, B. Samuelsson, J. Chem. Soc. Chem. Commun. 1984,
201–202; b) S. Takano, M. Akiyama, S. Sato, K. Ogasawara, Chem. Lett.
1983, 1593–1596.
[43] J. R. Parikh, W. von E. Doering, J. Am. Chem. Soc. 1967, 89, 5505–5507.
[44] D. A. Evans, J. Bartroli, T. L. Shih, J. Am. Chem. Soc. 1981, 103, 2127–
2129.
[45] I. Ohtani, T. Kusumi, Y. Kashman, H. Kakisawa, J. Am. Chem. Soc. 1991,
113, 4092–4096.
[62] S. Krishnamurthy, H. C. Brown, J. Org. Chem. 1976, 41, 3064–3066.
[63] Removing traces of water from the reaction medium by using a Dean–
Stark apparatus immediately before the reaction and minimizing the re-
action time were found to be essential for securing reproducibility of
the acyl ketene macrocyclization; otherwise, a significant amount (40–
62%) of an undesired decarboxylated byproduct was isolated alongside
the desired product. For a relevant discussion, see: T. R. Hoye, M. E.
Danielson, A. E. May, H. Zhao, J. Org. Chem. 2010, 75, 7052–7060.
[64] a) A. De Mico, R. Margarita, L. Parlanti, A. Vescovi, G. Piancatelli, J. Org.
Chem. 1997, 62, 6974–6977; b) M. F. Semmelhack, C. S. Chou, D. A.
Cortes, J. Am. Chem. Soc. 1983, 105, 4492–4494.
[46] H. C. Brown, K. S. Bhat, J. Am. Chem. Soc. 1986, 108, 5919–5923.
[47] I. Shiina, M. Kubota, H. Oshiumi, M. Hashizume, J. Org. Chem. 2004, 69,
1822–1830.
[48] Y. Kita, H. Maeda, K. Omori, T. Okuno, Y. Tamura, Synlett 1993, 273–274.
[49] B. Neises, W. Steglich, Angew. Chem. Int. Ed. Engl. 1978, 17, 522–524;
Angew. Chem. 1978, 90, 556–557.
[50] a) S. Masamune, S. Kamata, W. Schilling, J. Am. Chem. Soc. 1975, 97,
3515–3516; b) S. Masamune, Y. Hayase, W. Schilling, W. K. Chan, G. S.
Bates, J. Am. Chem. Soc. 1977, 99, 6756–6758.
[51] For a review of macrolactonization in natural product synthesis, see: A.
Parenty, X. Moreau, J.-M. Campagne, Chem. Rev. 2006, 106, 911 –939.
[52] a) P. R. Blakemore, W. J. Cole, P. J. Kocienski, A. Morley, Synlett 1998, 26–
28; b) P. R. Blakemore, J. Chem. Soc. Perkin Trans. 1 2002, 2563–2585;
c) C. A¨ıssa, Eur. J. Org. Chem. 2009, 1831–1844.
[53] E. P. Boden, G. E. Keck, J. Org. Chem. 1985, 50, 2394–2395.
[54] B. M. Trost, J. D. Chisholm, Org. Lett. 2002, 4, 3743–3745.
[55] E. J. Corey, K. C. Nicolaou, J. Am. Chem. Soc. 1974, 96, 5614–5616.
[56] J. R. Grunwell, A. Karipides, C. T. Wigal, S. W. Heinzman, J. Parlow, J. A.
Surso, L. Clayton, F. J. Fleitz, M. Daffner, J. E. Stevens, J. Org. Chem. 1991,
56, 91–95.
[57] a) A. Abiko, J.-F. Liu, S. Masamune, J. Am. Chem. Soc. 1997, 119, 2586–
2587; b) T. Inoue, J.-F. Liu, D. C. Buske, A. Abiko, J. Org. Chem. 2002, 67,
5250–5256; c) A. Abiko, Acc. Chem. Res. 2004, 37, 387–395. See also: A.
Abiko, Org. Synth. 2002, 79, 116–124.
[65] Conformational searches (MMFF94s) found multiple stable conformers
of distinct macrocyclic shape within 5 kcalmolÀ1 of the global mini-
mum, which supported the considerable conformational flexibility of
compound 1.
[66] The energy difference between these conformers was within 0.5 kcal
molÀ1 according to energy calculations at B3LYP/6–31G* level.
[67] H. Tominaga, M. Ishiyama, F. Ohseto, K. Sasamoto, T. Hamamoto, K.
Suzuki, M. Watanabe, Anal. Commun. 1999, 36, 47–50.
[68] The growth inhibitory activity of compounds 1, 5, 86, and 102 was
evaluated according to the previously described procedure: H. Fuwa, A.
Saito, S. Naito, K. Konoki, M. Yotsu-Yamashita, M. Sasaki, Chem. Eur. J.
2009, 15, 12807–12818.
[69] For reviews of structural reassignment of natural products by means of
total synthesis, see: a) K. C. Nicolaou, S. A. Snyder, Angew. Chem. Int. Ed.
2005, 44, 1012–1044; Angew. Chem. 2005, 117, 1036–1069; b) M. E.
Maier, Nat. Prod. Rep. 2009, 26, 1105–1124; c) Y. Usami, Mar. Drugs
2009, 7, 314–330; d) T. L. Suyama, W. H. Gerwick, K. L. McPhail, Bioorg.
Med. Chem. 2011, 19, 6675–6701.
[70] a) H. Fuwa, M. Ebine, A. J. Bourdelais, D. G. Baden, M. Sasaki, J. Am.
Chem. Soc. 2006, 128, 16989–16999; b) H. Fuwa, K. Ishigai, K. Hashi-
zume, M. Sasaki, J. Am. Chem. Soc. 2012, 134, 11984–11987; c) H. Fuwa,
T. Muto, K. Sekine, M. Sasaki, Chem. Eur. J. 2014, 20, 1848–1860.
[58] For examples of the application of Evans asymmetric syn-aldol reaction
to fragment assembly, see: a) K. Nagasawa, I. Shimizu, T. Nakata, Tetrahe-
Received: January 25, 2016
Published online on April 26, 2016
Chem. Eur. J. 2016, 22, 6815 – 6829
www.chemeurj.org
6829
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim