The first total synthesis of cytopiloyne, an anti-diabetic, polyacetylenic glucoside

Article abstract of DOI:10.1002/chem.201100986

The first total synthesis of cytopiloyne 1, a novel bioactive polyacetylenic glucoside isolated from the extract of Bidens pilosa, is described. The structure of cytopiloyne was determined to be 2-β-D-glucopyranosyloxy-1-hydroxytrideca-5,7,9,11-tetrayne by using various spectroscopic methods, but the chirality of the polyyne moiety was unknown. Herein, the convergent synthesis of two diastereomers of cytopiloyne by starting from commercially available 4-(2-hydroxyethyl)-2,2-dimethyl-1,3-diozolane is described. The synthetic sequence involved two key steps: stereoselective glycosylation of the glucosyl trichloroacetimidate with 1-[(4-methoxybenzyl)oxy] hex-5-yn-2-ol to give the desired β-glycoside and the construction of the glucosyl tetrayne skeleton by using a palladium/silver-catalyzed cross-coupling reaction to form the alkyne-alkyne bond, the first such use of this reaction. Comparison between the observed and published characterization data showed the 2R isomer to be the natural product cytopiloyne.

Full text of DOI:10.1002/chem.201100986

DOI: 10.1002/chem.201100986
The First Total Synthesis of Cytopiloyne, an Anti-Diabetic, Polyacetylenic
Glucoside
Chidambaram Ramesh Kumar, Chi-Hui Tsai, Yu-Sheng Chao, and Jinq-Chyi Lee*[a]
Abstract: The first total synthesis of cy-
topiloyne 1, a novel bioactive polyace-
tylenic glucoside isolated from the ex-
tract of Bidens pilosa, is described. The
structure of cytopiloyne was deter-
mined to be 2-b-d-glucopyranosyloxy-
1-hydroxytrideca-5,7,9,11-tetrayne by
using various spectroscopic methods,
but the chirality of the polyyne moiety
was unknown. Herein, the convergent
synthesis of two diastereomers of cyto-
piloyne by starting from commercially
available 4-(2-hydroxyethyl)-2,2-di-
methyl-1,3-diozolane is described. The
synthetic sequence involved two key
steps: stereoselective glycosylation of
the glucosyl trichloroacetimidate with
1-[(4-methoxybenzyl)oxy]hex-5-yn-2-ol
to give the desired b-glycoside and the
construction of the glucosyl tetrayne
skeleton by using a palladium/silver-
catalyzed cross-coupling reaction to
form the alkyne–alkyne bond, the first
such use of this reaction. Comparison
between the observed and published
characterization data showed the 2R
isomer to be the natural product cyto-
piloyne.
Keywords: chirality
·
cross-cou-
pling · glycosylation · natural prod-
ucts · total synthesis
Introduction
Diabetes mellitus is a metabolic disorder characterized by
high blood glucose levels, which result from the deficiency
or diminished effectiveness of endogenous insulin. Blood
glucose levels are controlled by a complex interaction of
multiple chemicals and hormones in the body, including the
hormone insulin made in the b cells of the pancreas. There
are two main types of diabetes mellitus, type 1 and type 2.
Type 1 diabetes is an autoimmune disease resulting from the
destruction of insulin-producing pancreatic b cells, leading
to a deficiency of insulin.[1] Type 2 diabetes is characterized
by insulin resistance and b-cell dysfunction; it is a very
costly disease because of its chronic nature and its frequent
association with heart disease, stroke, kidney disease, blind-
ness and lower limb amputations.[2] To date, several oral
drugs and insulin have been developed for the treatment of
diabetes; however, these agents are insufficient for the great
diversity of patients. Recently, the search for novel anti-dia-
betic drugs has focused on herbal medicines, due to efficacy
in human clinical trials and minimal side effects. Some of
the naturally occurring polyacetylenic extracts isolated from
Bidens pilosa are effective in treating both type 1 and 2 dia-
betes,[3–7] and cytopiloyne 1, a b-O-glucopyranoside that con-
tains a glucose moiety and a tetrayne aglycone unit, is one
of these extracts. Cytopiloyne has been reported to effec-
tively control and prevent type 1 diabetes in non-obese dia-
betic mice and be effective in controlling type 2 diabetes in
db/db mice, a leptin receptor-deficient mouse model for the
study of type 2 diabetes.[7–9] This paper describes the first
total synthesis of two diastereomers of cytopiloyne (1a and
1b) from commercially available isomers of 4-(2-hydrox-
yethyl)-2-2-dimethyl-1,3-diozolane and identifies the abso-
lute stereochemistry (C2) of the natural product.
Results and Discussion
Synthetic plan: Our retrosynthetic analysis of cytopiloyne 1
is shown in Scheme 1. Two approaches were designed and
performed simultaneously in our laboratory to expedite the
synthesis of the target molecule. The first strategy specifies
an alkyne–alkyne coupling to prepare the tetra-acetylenic
moiety followed by glycosylation to complete the synthesis.
Coupling of the glycosyl donor 2 with the alcohol 3 was ex-
pected to furnish the b-glucosyl tetrayne skeleton with the
correct stereochemistry by participation of a neighbouring
acetate group. The b-glucoside could be subjected to a
series of functional-group transformations to yield the target
molecule 1. The key precursor 3 would be obtained by the
[a] Dr. C. R. Kumar, C.-H. Tsai, Dr. Y.-S. Chao, Dr. J.-C. Lee
Institute of Biotechnology and Pharmaceutical Research
National Health Research Institutes, 35, Keyan Road
Zhunan Town, Miaoli County 35053 (Taiwan, ROC)
Fax : (+886)37-586456
E-mail: jinqchyi@nhri.org.tw
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100986.
8696
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FULL PAPER
Scheme 1. Retrosynthetic analysis of cytopiloyne 1. L=leaving group, PG=protecting group, R=TMS (trimethylsilane) or H.
hydrolysis and then selective protection of the isopropyl tet-
rayne, made by Sonogashira coupling of iodo-heptatriyne 5
with chiral alkyne 4.[10] The chiral intermediate 4 would
arise from the commercially available alcohol 6 through io-
dination followed by alkynylation, and the palladium-cata-
lyzed cross-coupling partner 5 would be made from commer-
cially available 1,4-bis(trimethylsilanyl)buta-1,3-diyne (7).
The second strategy introduces the b-glycosidic bond be-
tween glucose and the monoalkyne unit 10, prior to comple-
tion of the glucosyl tetrayne skeleton, proposed to be
Scheme 2. Synthesis of (4S)-alkyne 4a: a) PPh3, I2, imidazole, CH3CN,
Et2O, À108C to RT, 17 h, 86%; b) trimethylsilyl acetylene, nBuLi, THF,
À788C to RT, 17 h, 68%; c) TBAF, THF, 08C, 1.5 h, 74%.
formed by using a Pd/Ag-catalyzed coupling reaction[11]
—
the first time this reaction has been used. The b-glucosyl in-
termediate 8 could be prepared by the neighbouring-group-
assisted glycosylation of glucosyl donor 2 with acceptor 10.
Iodination of the alcohol 6 followed by alkynylation, hydrol-
ysis and selective protection would give the key precursor
10. The heptatriyne 9, the substrate of Pd/Ag-catalyzed cou-
pling, would be obtained from commercially available 7.
Strategy I: Synthesis of alkyne 4a commenced from com-
mercially available (4S)-(+)-4-(2-hydroxyethyl)-2,2-dimeth-
yl-1,3-dioxolane (6a), which was iodinated with PPh3/I2/imi-
dazole in CH3CN/Et2O to give iodide 11a, followed by alky-
nylation with trimethylsilyl acetylene in the presence of
nBuLi (Scheme 2) to give 12a.[12] (4S)-Alkyne 4a was ob-
tained after desilylation by using tetrabutylammonium fluo-
ride (TBAF). The (4S)-isomer 6a was chosen over its enan-
tiomer, (4R)-isomer 6b, for cost reasons.
Iodoalkyne 5 was prepared from commercially available
1,4-bis(trimethylsilanyl)-buta-1,3-diyne (7). Friedel–Crafts
acylation of 7 in the presence of aluminium chloride (AlCl3)
gave ketone 13 in good yield (Scheme 3).[13] Subsequent
Scheme 3. Synthesis of (2S)-tetraalkyne 3a: a) CH3COCl, AlCl3, CH2Cl2,
08C, 1.5 h; b) CBr4, PPh3, CH2Cl2, 458C, 16 h, 58% in 2 steps; c) dry
hexane, nBuLi, À78 to À408C, 1 h, 88%; d) K2CO3, MeOH, acetone,
08C to RT, 2 h; then NIS, AgNO3, RT, 16 h, 66%; e) 4a, [PdCl
CuI, THF, iPr2NH, RT, 2 h, <5%.
2ACHTUNGTRENNUNG(PPh3)2],
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J.-C. Lee et al.
Corey–Fuchs reaction yielded dibromoolefin 14, which was
converted into the desired trialkyne 9 by dropwise addition
of nBuLi as a solution in hexanes.[14,15] Desilylation of 9 was
carried out by using potassium carbonate (K2CO3) and
methanol in acetone. Silver nitrate (AgNO3)-catalyzed iodi-
nation by using N-iodosuccinimide (NIS) afforded iodoal-
kyne 5.[16]
ride (PMBCl) to furnish acceptor 19a.[20] Further desilyla-
tion of 19a yielded the acceptor 20a.
Next, optimization of glycosylation by coupling of the
well-known donors 21–23 with 17a–20a was studied and the
results are summarized in Table 1. Coupling of peracetylated
Table 1. Optimization of glycosylation conditions.
With both compounds 4a and 5 in hand, the bis(triphenyl-
phosphine)palladium(II) chloride [PdCl2ACHTNUGTRENUNG(PPh3)2] and cop-
per(I) iodide (CuI)-mediated Sonogashira coupling[10] was
studied. Unfortunately, tetraalkyne 15a was obtained in
poor yield (<5%) under standard conditions. Alternatively,
other well-known conditions for alkyne–alkyne coupling,
such as copper-catalyzed Cadiot–Chodkiewicz coupling[17] or
Negishi coupling[18] were also carried out; however, no de-
sired product was obtained. Further hydrolysis of tetrayne
15a was performed, but the insoluble byproduct was gener-
ated. In our observation, tetrayne 15a was decomposed
easily when it was left to stand at room temperature, per-
haps due to the inherently unstable nature of the longer
polyynes.[19] This unsatisfactory result caused us to suspend
development of this strategy.
Entry Donor Acceptor Activator
T
t
Glycoside Yield
[%]
[8C] [h]
1
2
3
4
5
6
7
8
9
21
21
22
22
22
23
23
23
23
17a
17a
17a
17a
19a
17a
18a
19a
20a
BSP/Tf2O
À60 0.5
–
–
–
–
–
–
NIS/TfOH À40 16
Ag2O
25
64
Ag2CO3/I2 25
Ag2CO3/I2 25
TMSOTf
TMSOTf
TMSOTf
TMSOTf
64 24a
64 26a
22[a]
5
À60 16 24a
À60 16 25a
À60 16 26a
À60 16 27a
22[b]
27
35
65
Strategy II: Four acceptors (17a–20a) were prepared to
study construction of the required glycosidic linkage. As
shown in Scheme 4, hydrolysis of the isopropylidene acetal
[a] The yield of the desired product 24a and the inseparable byproduct in
a 18:1 ratio determined by 1H NMR spectroscopic analysis. [b] The yield
of the desired product 24a and the inseparable byproduct in a 7:1 ratio
1
determined by H NMR spectroscopic analysis.
glucosyl thioglycoside 21 with acceptor 17a activated by
benzenesulfinyl piperidine/trifluoromethanesulfonic anhy-
dride (BSP/Tf2O)[21] or NIS/trifluoromethanesulfonic acid
(TfOH)[22] failed to afford the desired b-linked glucoside
(Table 1, entries 1 and 2). In entry 3, coupling of the glucosyl
bromide 22 and acceptor 17a with activation by silver oxide
(Ag2O) led to complicated mixtures.[23] When Ag2CO3/I2
were used as activators, the mixture of glycoside 24a and an
inseparable byproduct was obtained in 22% yield with a
ratio of 18:1 (entry 4).[24] By using donor 22 and acceptor
19a under the same conditions, b-glycoside 26a was pro-
duced in lower yield (entry 5). Glycosyl trichloroacetimidate
23[25] reacted with acceptor 17a in the presence of trimethyl-
silyl trifluoromethanesulfonate (TMSOTf), with the same
result as described in entry 4 with a ratio of 7:1 (entry 6).
The coupling of 23 with OAc-desilylated compound 18a was
also performed under the same conditions; however, insig-
nificant improvement in the yield was observed (entry 7). In
contrast, glycosylation of 23 with 19a furnished compound
26a in 35% yield (entry 8). Although the TMSOTf-cata-
lyzed glycosylation provided b-glycoside 26a in moderate
yield, the acetylated product 28a was identified as a major
side product in 29% yield. Replacement of the acceptor 19a
with its desilylated compound 20a was found to significantly
decrease the acetylated product 29a formation (8%) and
give glycoside 27a in 65% yield (entry 9).
Scheme 4. Synthesis of acceptors 17a–20a: a) HOAc, H2O, RT, 16 h,
85%; b) Ac2O, Et3N, DMAP, CH2Cl2, À608C, 16 h, 75%; c) TBAF, THF,
08C, 1 h, 74%; d) Bu2SnO, toluene, reflux, 2 h; then CsF, tetrabutyl-
ACHTUNGTRENNUNGammonium iodide (Bu4NI), PMBCl, DMF, reflux, 5 h, 67%; e) TBAF,
THF, 08C, 1 h, 83%.
in 80% acetic acid (HOAc) solution converted compound
12a into diol 16a. Two functional groups were chosen for in-
stallation at the primary alcohol position: the electron-with-
drawing acetyl group, and the electron-donating p-methoxy-
benzyl group (PMB). Regioselective acetylation of com-
pound 16a at the primary alcohol with acetic anhydride
(Ac2O) in triethylamine furnished acceptor 17a, which was
then subjected to desilylation with TBAF to give the corre-
sponding alkyne 18a. The PMB group was introduced by
using dibutyltin oxide (Bu2SnO) and p-methoxybenzyl chlo-
8698
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Chem. Eur. J. 2011, 17, 8696 – 8703

The First Total Synthesis of Cytopiloyne
FULL PAPER
fluoride (AgF) and tetrakis(triphenylphosphine)palladium
[PdACHTNUTGRNEUNG
(PPh3)4] as catalysts to give the desired tetrayne.[11] De-
protection of the PMB and acetyl groups was achieved by
using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)
and sodium methoxide (NaOMe), respectively, to afford
(2S)-cytopiloyne 1a as a colourless solid, the spectroscopic
and optical rotation data for which did not match that of the
natural product.
Synthesis of naturally occurring cytopiloyne 1b: The (2R)-
cytopiloyne detailed in this account was synthesized accord-
ing to the established method of (2S)-cytopiloyne. The syn-
thesis of (2R)-cytopiloyne began with iodination of (4R)-4-
(2-hydroxyethyl)-2,2-dimethyl-1,3-dioxolane (6b) with PPh3/
I2/imidazole to give iodide 11b, which was then alkylated
with trimethylsilyl acetylene in the presence of nBuLi to
afford monoalkynyl TMS compound 12b as the major prod-
uct and desilylated compound 4b as the minor product
(Scheme 6). Without purification, the mixture was treated
with TBAF to furnish 4b in good yield (62% in two steps),
which on hydrolysis of the isopropylidene group of 4b by
using 80% HOAc gave 1,2-diol 32b. Regioselective benzyla-
tion of the primary alcohol was performed to afford 20b as
the desired acceptor, which was coupled with the glucosyl
trichloroacetimidate 23 by using TMSOTf as an activator to
give the b-linked O-glycoside 27b in 86% yield. Iodination
of alkyne 27b with NIS gave the important precursor alkyn-
yl iodide 31b for the tetralkyne skeleton development. The
key step, the Pd/Ag-catalyzed cross-coupling, was then car-
ried out to construct the alkyne–alkyne bond between 31b
and the trialkynyl silane 9. Finally, deprotection of the fully
protected b-glucosyl tetrayne was performed to furnish the
target molecule 1b as a colourless solid. The (2R)-cytopi-
loyne 1b was finally obtained in 1.6% overall yield over 10
steps from (4R)-4-(2-hydroxyethyl)-2,2-dimethyl-1,3-dioxo-
Scheme 5. Synthesis of (2S)-cytopiloyne 1a: a) 5, [PdCl2ACHTUNTRGENUNG(PPh3)2], CuI,
THF, iPr2NH, RT, 2 h; b) NIS, AgNO3, acetone, RT, 2 h, 86%; c) i) 9,
[Pd(PPh3)4], AgF, K2CO3, MeOH, DMF, RT, 16 h; ii) DDQ, CH2Cl2,
ACHTUNGTRENNUNG
H2O, RT, 2 h; iii) NaOMe, MeOH, CH2Cl2, 08C, 2 h, 36% over 3 steps.
With iodoalkyne 5 and b-glucosyl alkyne 27a in hand,
their Sonogashira coupling was investigated, as outlined in
Scheme 5. After much experimentation, reaction of 27a
with 5 by using [PdCl2ACHTNUTRGNEUNG(PPh3)2] and CuI furnished the fully
protected cytopiloyne 30a in trace amounts. Because the
Cadiot–Chodkiewicz coupling and Negishi coupling failed to
give tetrayne 15a, alternative conditions were sought and
the Pd/Ag-catalyzed coupling[11] was investigated. The Pd/
Ag-catalyzed cross-coupling is commonly used in the cou-
pling of vinyl triflate or aryl iodides with either free alkynes
or 1-(trialkylsilyl)alkynes to construct the functionalized
enynes; no alkyne–alkyne coupling, to the best of our
knowledge, has ever been reported. Iodination of glycoside
27a by using NIS afforded iodoalkyne 31a, which was cou-
pled with silyl-protected triyne 9 in the presence of potassi-
um carbonate (K2CO3), methanol (MeOH) and with silver
Scheme 6. Synthesis of (2R)-cytopiloyne 1b: a) PPh3, I2, imidazole, CH3CN, Et2O, À108C to RT, 17 h, 91%; b) trimethylsilyl acetylene, nBuLi, À788C to
RT, 18 h; c) TBAF, THF, 08C, 1 h, 62% in 2 steps; d) HOAc, H2O, RT, 16 h, 71 %; e) Bu2SnO, toluene, reflux, 2 h; then CsF, Bu4NI, PMBCl, DMF,
reflux, 5 h, 82%; f) 23, TMSOTf, CH2Cl2, MS 3 ꢁ, À608C, 16 h, 86%; g) NIS, AgNO3, acetone, RT, 2 h, 93%; h) i) 9, [Pd
ACHTNUGTNERN(NUG PPh3)4], AgF, K2CO3, DMF,
MeOH, 08C to RT, 16 h; ii) DDQ, CH2Cl2, H2O, RT, 2 h; iii) NaOMe, MeOH, CH2Cl2, 08C, 2 h, 6% over 3 steps.
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J.-C. Lee et al.
and concentrated under reduced pressure. The residue was purified by
column chromatography (hexanes/EtOAc 10:1) to give 11a (2.21 g, 86%)
as a colourless oil. [a]D25 =À23.99 (c=1 in CHCl3); 1H NMR (400 MHz,
CDCl3): d=4.19–4.12 (m, 1H), 4.06 (dd, J=8.0, 6.0 Hz, 1H), 3.55 (dd,
J=8.0, 6.8 Hz, 1H), 3.28–3.17 (m, 2H), 2.11–1.98 (m, 2H), 1.38 (s, 3H),
1.33 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=109.0, 75.6, 68.5, 37.8,
26.9, 25.5, 1.2 ppm; the characterization data of compound 11a were in
agreement with the literature.[26]
lane (6b). The characterization data of 1b were found to be
identical in all respects to the natural product, confirming
the configuration at the 1b stereocenter to be R.
The low overall yield was attributed to the unexpected in-
stability of the final product upon purification. An unidenti-
fied byproduct, insoluble in MeOH and H2O, was generated
during concentration of 1b under reduced pressure. A water
suspension of 1b and this byproduct was filtered to remove
the insoluble byproduct and the filtrate lyophilized to give
1b in low yield. The same byproduct was quickly regenerat-
ed when 1b was left to stand at room temperature, although
samples of 1b were found to be more stable in solution.
{4-[(4S)-2,2-Dimethyl-1,3-dioxolan-4-yl]but-1-yn-1-yl}(trimethyl)silane
(12a): Compound 12a was prepared according to the literature proce-
dure.[27] To
a stirred solution of trimethylsilylacetylene (786 mg,
8.00 mmol) in THF (15 mL) was added an 1.6m solution of nBuLi in hex-
anes (5.0 mL, 8.00 mmol) dropwise at À788C. After stirring at À788C for
40 min, a solution of 11a (1.02 g, 4.0 mmol) in hexamethylphosphoramide
(HMPA) (1.5 mL) and THF (1.5 mL) was added dropwise and the result-
ing mixture was then allowed to warm to room temperature slowly. The
reaction was quenched with 50% NH4Cl solution after overnight stirring
(ca. 16 h) and the mixture was extracted with Et2O. The organic phase
was washed with brine, dried over MgSO4, filtered and concentrated
under reduced pressure. The residue was purified by column chromatog-
raphy (hexanes/EtOAc 10:1) to give 12a (0.61 g, 68%) and 4a (68 mg,
11%) as colourless oils. [a]2D5 =À7.8 (c=1 in CHCl3); 1H NMR
(400 MHz, CDCl3): d=4.17–4.12 (m, 1H), 4.06 (dd, J=8.0, 6.0 Hz, 1H),
3.56 (dd, J=8.0, 6.8 Hz, 1H), 2.37–2.24 (m, 2H), 1.85–1.66 (m, 2H), 1.37
(s, 3H), 1.33 (s, 3H), 0.12 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=
108.7, 106.2, 85.1, 74.9, 69.2, 32.7, 26.9, 25.6, 16.4, À0.1 ppm; HRMS
(FAB): m/z: calcd for C12H22O2Si: 226.1389 [M]+; found: 226.1390.
Conclusion
The first total synthesis of two diastereomers of cytopiloyne
1 was accomplished by starting from (4S)-6a or (4R)-(2-hy-
droxyethyl)-2,2-dimethyl-1,3-dioxolane (6b), confirming the
absolute configuration at the C2-position of cytopiloyne.
Key steps in the synthesis were formation of the b-linked
glucoside by anomeric stereocontrol of glycosylation with
neighbouring-group participation and the first application of
Pd/Ag-catalyzed cross-coupling in the formation of the
alkyne–alkyne bond. The 2R isomer 1b was definitively
identified as the natural product by comparison of the ob-
served and reported characterization data. The properties of
1b will be investigated in future studies.
(4S)-4-(But-3-yn-1-yl)-2,2-dimethyl-1,3-dioxolane (4a): A 1m solution of
TBAF in THF (2.7 mL, 2.70 mmol) was added to a stirred solution of
12a (410 mg, 1.81 mmol) in THF (14 mL) at 08C. After stirring at 08C
for 1.5 h, the reaction was quenched with saturated NH4Cl solution. The
reaction mixture was extracted with Et2O and the organic phase was
dried over MgSO4, filtered and concentrated under reduced pressure.
The residue was purified by flash column chromatography (hexanes/
EtOAc 10:1) to furnish alkyne 4a (206 mg, 74%) as a yellowish oil.
[a]2D5 =À8.3 (c=1.1 in CHCl3); 1H NMR (400 MHz, CDCl3): d=4.21–
4.15 (m, 1H), 4.05 (dd, J=8.0, 6.0 Hz, 1H), 3.55 (dd, J=8.0, 6.8 Hz, 1H),
2.31–2.26 (m, 2H), 1.94 (t, J=2.8 Hz, 1H), 1.84–1.68 (m, 2H), 1.38 (s,
3H), 1.33 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=108.7, 83.4,
74.6, 69.0, 68.7, 32.5, 26.8, 25.5, 14.9 ppm.
Experimental Section
General: All chemicals were purchased as reagent grade and used with-
out further purification unless otherwise stated. Column chromatography
was performed with silica gel (Merck Kieselgel 60, 230–400 mesh). Reac-
tions were monitored with TLC by using Merck 60 F254 silica gel glass-
backed plates and visualized under UV (254 nm) and/or by staining with
either acidic ceric ammonium molybdate or basic potassium permanga-
nate solution. 1H NMR spectra were recorded on a Varian Mercury-300
(300 MHz) or Mercury-400 (400 MHz) spectrometer. Chemical shifts (in
ppm) are reported relative to the internal standard signal of CDCl3 (d=
7.24 ppm) or CD3OD (d=3.30 ppm). 13C NMR spectra were obtained
with a Varian Mercury-300 (75 MHz) or Mercury-400 (100 MHz) spec-
trometer and reported relative to CDCl3 (d=77.00 ppm) or CD3OD (d=
49.15 ppm). Coupling constants (J) are reported in Hertz (Hz). Splitting
patterns are described by using the following abbreviations: s, singlet; d,
doublet; t, triplet; q, quartet; m, multiplet. LCMS data was obtained on
an Agilent MSD-1100 ESI-MS/MS system. High-resolution mass spectra
were measured with MAT-95XL or JEOL JMS-700 high-resolution mass
spectrometers in electron impact (EI) or fast atom bombardment (FAB)
ionization modes. Specific optical rotations were recorded on JASCO P-
1020 digital polarimeter by using a temperature controller (PTC-102T)
and sodium lamp (589 nm) as the light source.
6-(Trimethylsilyl)hexa-3,5-diyn-2-one (13): Acetyl chloride (0.71 mL,
9.95 mmol) and AlCl3 (1.46 g, 10.95 mmol) were added to a stirred solu-
tion of 1,4-bis(trimethylsily)-1,3-butadiyne (1.94 g, 9.98 mmol) in CH2Cl2
(40 mL) at 08C. After stirring at 08C for 1.5 h, the reaction was quenched
by the addition of iced 1n aqueous hydrochloric acid. The aqueous phase
was extracted with CH2Cl2 (3ꢂ50 mL) and the combined organic extracts
were washed with saturated NaHCO3 solution, dried over MgSO4, fil-
tered and concentrated under reduced pressure. The residue was purified
by flash column chromatography (hexanes/EtOAc 15:1 to 10:1) to furnish
ketone 13 as a pale-yellow oil. 1H NMR (400 MHz, CDCl3): d=2.32 (s,
3H), 0.20 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=183.1, 97.3,
85.6, 74.6, 73.4, 32.5, À0.9 ppm; the characterization data of compound
13 were in agreement with the literature.[12]
(6,6-Dibromo-5-methylhex-5-ene-1,3-diyn-1-yl)(trimethyl)silane (14): Tri-
phenylphosphine (10.29 g, 39.23 mmol) was added to a stirred solution of
carbon tetrabromide (8.13 g, 24.52 mmol) in CH2Cl2 (35 mL) at 08C.
After stirring at 08C for 15 min, the reaction was removed to room tem-
perature and a solution of ketone 13 (1.61 g, 9.80 mmol) in CH2Cl2
(35 mL) was added. The mixture was warmed to 458C and stirred for an-
other 16 h. The reaction mixture was cooled to room temperature and
concentrated under reduced pressure. The residue was purified by flash
column chromatography (100% hexanes) to give dibromoolefin 14
(4S)-4-(2-Iodoethyl)-2,2-dimethyl-1,3-dioxolane (11a): Imidazole (1.50 g,
22.04 mmol), PPh3 (5.25 g, 20.02 mmol) and I2 (6.09 g, 23.99 mmol) were
added to a stirred solution of (4S)-(+)-4-(2-hydroxyethyl)-2,2-dimethyl-
1,3-dioxolane (6a) (1.46 g, 10.00 mmol) in CH3CN (40 mL) and Et2O
(60 mL) at À108C. After being stirred at this temperature for 1 h, the
mixture was warmed to room temperature gradually and stirred for an-
other 16 h. The reaction was quenched with 10% Na2S2O3 solution and
saturated NH4Cl solution. The resulting mixture was extracted with Et2O.
The organic phase was washed with brine, dried over MgSO4, filtered
1
(1.84 g, 58% in 2 steps) as a yellow oil. H NMR (400 MHz, CDCl3): d=
1.96 (s, 3H), 0.20 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=124.7,
100.8, 94.3, 87.3, 80.7, 75.0, 23.3, À0.5 ppm; HRMS (FAB): m/z: calcd for
C10H12Br2Si: 317.9075 [M]+; found: 317.9071.
Hepta-1,3,5-triyn-1-yl(trimethyl)silane (9): nBuLi (7.2 mL, 11.50 mmol,
1.6m in hexanes) was added dropwise to a stirred solution of dibromoole-
8700
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 8696 – 8703

The First Total Synthesis of Cytopiloyne
FULL PAPER
fin 14 (1.84 g, 5.75 mmol) in dry hexanes (30 mL) at À788C under argon
over 10 min. The mixture was warmed to À408C gradually and then
quenched with saturated NH4Cl solution. Et2O was added (5 mL) and
the organic layer was separated, washed with saturated NH4Cl solution,
dried over MgSO4, filtered and concentrated under reduced pressure.
The residue was purified by flash column chromatography (100% hex-
anes) to give 9 as a yellow oil (0.81 g, 88%). 1H NMR (400 MHz,
CDCl3): d=1.95 (s, 3H), 0.17 ppm (s, 9H); 13C NMR (100 MHz, CDCl3):
d=88.3, 85.2, 76.6, 64.7, 62.5, 59.3, 4.5, À0.5 ppm; the characterization
data of compound 9 were in agreement with the literature.[28]
10 min. The solution was then treated with PMBCl (169 mL, 1.25 mmol)
and TBAI (111 mg, 0.30 mmol) and the resulting mixture was refluxed
for 5 h. The solvent was removed under reduced pressure and the residue
was purified by column chromatography (hexanes/EtOAc 5:1) to yield
19a (248 mg, 67%) as a colourless oil. [a]2D5 =À3.8 (c=0.5 in CHCl3);
1H NMR (400 MHz, CDCl3): d=7.24 (d, J=8.4 Hz, 2H), 6.87 (d, J=
8.4 Hz, 2H), 4.47 (s, 2H), 3.92–3.89 (m, 1H), 3.79 (s, 3H), 3.48 (dd, J=
9.6, 3.6 Hz, 1H), 3.32 (dd, J=9.6, 7.6 Hz, 1H), 2.39 (d, J=3.6 Hz, 1H),
2.35 (t, J=7.2 Hz, 2H), 1.66–1.61 (m, 2H), 0.12 ppm (s, 9H); 13C NMR
(100 MHz, CDCl3): d=159.3, 130.0, 129.4, 113.9, 106.8, 85.0, 73.9, 73.0,
69.4, 55.3, 32.0, 16.2, 0.1 ppm; HRMS (FAB): m/z: calcd for
C17H26O3SiNa: 329.1549 [M+Na]+; found: 329.1547.
1-Iodohepta-1,3,5-triyne (5): K2CO3 (95 mg, 0.69 mmol) was added to a
stirred solution of 9 (50 mg, 0.31 mmol) in acetone (2 mL) and methanol
(30 mL) at 08C. The reaction was warmed up to room temperature and
stirred for 2 h. The mixture was filtered and then NIS (77 mg, 0.34 mmol)
and AgNO3 (5.3 mg, 0.03 mmol) were added to the filtrate. After over-
night stirring, the reaction mixture was filtered through a pad of Celite.
The filtrate was concentrated under reduced pressure and the residue
was purified by flash column chromatography (100% hexanes) to give 5
(2S)-1-[(4-Methoxybenzyl)oxy]hex-5-yn-2-ol (20a):
A 1m solution of
TBAF in THF (0.6 mL, 0.60 mmol) was added to a stirred solution of
19a (153 mg, 0.50 mmol) in THF (5 mL) at 08C under nitrogen. The re-
action was stirred at 08C for 1 h and quenched with saturated NH4Cl so-
lution. The resulting mixture was diluted with EtOAc and the organic
phase was separated. The aqueous was extracted with EtOAc and the
combined organic layers were dried over MgSO4, filtered and concentrat-
ed under reduced pressure. The residue was purified by column chroma-
tography (hexanes/EtOAc 2:1) to give alkyne 20a (97 mg, 83%) as a col-
ourless oil. [a]2D5 =À4.9 (c=1 in CHCl3); 1H NMR (400 MHz, CDCl3):
d=7.24 (d, J=8.8 Hz, 2H), 6.87 (d, J=8.8 Hz, 2H), 4.47 (s, 2H), 3.94–
3.91 (m, 1H), 3.79 (s, 3H), 3.48 (dd, J=9.6, 3.2 Hz, 1H), 3.31 (dd, J=9.6,
7.6 Hz, 1H), 2.38 (d, J=3.2 Hz, 1H), 2.34–2.30 (m, 2H), 1.93 (t, J=
2.8 Hz, 1H), 1.66–1.61 ppm (m, 2H); 13C NMR (100 MHz, CDCl3): d=
159.3, 129.9, 129.4, 113.8, 83.9, 73.9, 73.0, 69.1, 68.6, 55.3, 31.8, 14.7 ppm;
HRMS (FAB): m/z: calcd for C14H18O3: 234.1256 [M]+; found: 234.1257.
as
a
yellow solid (44 mg, 66%). 1H NMR (400 MHz, CDCl3): d=
1.97 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=79.1, 75.9, 64.2, 60.1,
59.6, 4.5 ppm.
(2S)-6-(Trimethylsilyl)hex-5-yne-1,2-diol (16a):
A
solution of 12a
(498 mg, 2.20 mmol) in HOAc (15 mL) and H2O (8 mL) was stirred at
room temperature overnight (ca. 16 h). The solvent was then removed by
coevaporation with toluene under reduced pressure and the residue was
purified by flash column chromatography (hexanes/EtOAc 1:1) to give
16a (348 mg, 85%) as a colourless solid. [a]2D5 =À15.4 (c=1 in CHCl3);
1H NMR (400 MHz, CDCl3): d=3.85–3.80 (m, 1H), 3.64 (dd, J=11.2,
3.2 Hz, 1H), 3.46 (dd, J=11.2, 7.2 Hz, 1H), 2.35 (t, J=6.8 Hz, 2H), 1.62
(q, J=6.8 Hz, 2H), 0.12 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=
106.6, 85.5, 71.3, 66.4, 31.6, 16.3, 0.0 ppm; HRMS (FAB): m/z: calcd for
C9H18O2SiNa: 209.0974 [M+Na]+; found: 209.0980.
(2S)-2-[(2,3,4,6-Tetra-O-acetyl-b-d-glucopyranosyl)oxy]-6-(trimethylsilyl)-
hex-5-yn-1-yl acetate (24a): A mixture of 17a (50 mg, 0.22 mmol), 50%
Ag2CO3 in Celite (165 mg, 0.30 mmol), I2 (17 mg, 0.07 mmol) and freshly
activated powdered molecular sieves 3 ꢁ (160 mg) in anhydrous CH2Cl2
(1 mL) was stirred at room temperature under argon for 30 min. A solu-
tion of glycosyl donor 22 (82 mg, 0.20 mmol) in anhydrous CH2Cl2
(1 mL) was added to the mixture dropwise and stirred for 3 d. The mix-
ture was filtered through a pad of Celite and the filtrate was washed with
aqueous Na2S2O3 solution. The solvent was removed under reduced pres-
sure and the residue was purified by column chromatography (hexanes/
EtOAc 2:1) to afford 24a and an inseparable byproduct in a 18:1 ratio
(24 mg, 22%) as a colourless solid. 1H NMR (400 MHz, CDCl3): d=5.17
(t, J=10.0 Hz, 1H), 5.05 (t, J=10.0 Hz, 1H), 4.93 (dd, J=10.0, 8.0 Hz,
1H), 4.58 (d, J=8.0 Hz, 1H), 4.23 (dd, J=12.4, 4.4 Hz, 1H), 4.13 (dd, J=
12.4, 2.4 Hz, 1H), 4.10–3.99 (m, 2H),
(2S)-2-Hydroxy-6-(trimethylsilyl)hex-5-yn-1-yl acetate (17a): Ac2O
(145 mL, 1.54 mmol) was added to a stirred solution of diol 16a (261 mg,
1.40 mmol) and Et3N (215 mL, 1.54 mmol) in anhydrous CH2Cl2 (20 mL)
under argon at À608C in the presence of a catalytic amount of 4-dime-
thylaminopyridine (DMAP) (17 mg, 0.14 mmol). The reaction was
quenched with 1n HCl solution (10 mL) after stirring at À608C for 16 h
and the resulting mixture was extracted with CH2Cl2. The organic layer
was dried over MgSO4, filtered and concentrated under reduced pressure.
The residue was purified by flash column chromatography (hexanes/
EtOAc 5:1) to afford 17a (239 mg, 75%) as a colourless oil. [a]2D5 =À3.7
(c=1 in CHCl3); 1H NMR (400 MHz, CDCl3): d=4.14–4.11 (m, 1H),
4.01–3.97 (m, 2H), 2.38 (t, J=7.2 Hz, 2H), 2.32 (brs, 1H), 2.08 (s, 3H),
1.69–1.64 (m, 2H), 0.12 ppm (s, 9H); 13C NMR (400 MHz, CDCl3): d=
171.1, 106.2, 85.7, 69.0, 68.3, 31.9, 20.9, 16.2, 0.0 ppm; HRMS (FAB): m/
z: calcd for C11H20O3SiNa: 251.1080 [M+Na]+; found: 251.1079.
, 3.90–3.87 (m, 1H), 3.67–3.63 (m, 1H), 2.37–2.31 (m, 2H), 2.07 (s, 3H),
2.06 (s, 3H), 2.01 (s, 1H), 2.00 (s, 3H), 1.98 (s, 3H), 1.78–1.67 (m, 2H),
0.11 ppm (s, 9H); 13C NMR (400 MHz, CDCl3): d=170.64, 170.56, 170.3,
169.4, 169.3, 106.6, 100.5, 84.9, 76.9, 72.8, 71.7, 71.3, 68.4, 66.1, 61.9, 31.0,
20.8, 20.7, 20.60, 20.58, 20.5, 16.0, 0.1 ppm; HRMS (FAB): m/z: calcd for
C25H38O12SiNa: 581.2031 [M+Na]+; found: 581.2026.
(2S)-2-Hydroxyhex-5-yn-1-yl acetate (18a): A 1m solution of TBAF in
THF (0.6 mL, 0.60 mmol) was added to a stirred solution of 17a (114 mg,
0.50 mmol) in THF (5 mL) at 08C under nitrogen. After stirring at 08C
for 1 h, the reaction was quenched with saturated NH4Cl solution. The
reaction mixture was extracted with EtOAc and the organic phase was
dried over MgSO4, filtered and concentrated under reduced pressure.
The residue was purified by flash column chromatography (hexanes/
EtOAc 2:1) to furnish alkyne 18a (58 mg, 74%) as a colourless oil.
(2S)-2-[(2,3,4,6-Tetra-O-acetyl-b-d-glucopyranosyl)oxy]hex-5-yn-1-yl ace-
tate (25a): A mixture of alcohol 18a (47 mg, 0.30 mmol), glucosyl tri-
chloroacetimidate 23 (246 mg, 0.50 mmol) and freshly activated pow-
dered molecular sieves AW-300 (500 mg) in anhydrous CH2Cl2 (20 mL)
was stirred at room temperature under argon for 10 min. The reaction
mixture was cooled to À608C and TMSOTf (5 mL, 0.03 mmol) was
added. After stirring at À608C overnight (ca. 16 h), the reaction mixture
was quenched with Et3N (10 mL) and filtered through a pad of Celite.
The filtrate was concentrated under reduced pressure and the residue
was purified by column chromatography (hexanes/EtOAc 2:1) to give b-
glucoside 25a (40 mg, 27%) as a colourless solid. [a]2D5 =À33.6 (c=0.8 in
1
[a]2D5 =À10.7 (c=1 in CHCl3); H NMR (400 MHz, CDCl3): d=4.14–4.12
(m, 1H), 4.01–3.96 (m, 2H), 2.35 (td, J=7.2, 2.4 Hz, 2H), 2.23 (d, J=
4.4 Hz, 1H), 2.08 (s, 3H), 1.96 (t, J=2.4 Hz, 1H), 1.70–1.63 ppm (m,
2H); 13C NMR (400 MHz, CDCl3): d=171.2, 83.4, 69.0, 68.3, 68.2, 31.7,
20.7, 14.5 ppm; HRMS (FAB): m/z: calcd for C8H12O3Na: 179.0684
[M+Na]+; found: 179.0684.
1
CHCl3); H NMR (400 MHz, CDCl3): d=5.15 (t, J=9.6 Hz, 1H), 5.03 (t,
(2S)-1-[(4-Methoxybenzyl)oxy]-6-(trimethylsilyl)hex-5-yn-2-ol (19a):
A
J=9.6 Hz, 1H), 4.92 (dd, J=9.6, 8.0 Hz, 1H), 4.58 (d, J=8.0 Hz, 1H),
4.19 (dd, J=12.4, 4.4 Hz, 1H), 4.12 (dd, J=12.4, 2.8 Hz, 1H), 4.08–3.97
(m, 2H), 3.95–3.93 (m, 1H), 3.67–3.62 (m, 1H), 2.31–2.27 (m, 2H), 2.04
(s, 6H), 1.982 (s, 3H), 1.977 (s, 3H), 1.96 (s, 3H), 1.88 (t, J=2.8 Hz, 1H),
1.71–1.64 ppm (m, 2H); 13C NMR (400 MHz, CDCl3): d=170.6, 170.5,
170.2, 169.3, 169.2, 100.4, 83.8, 76.4, 72.7, 71.6, 71.3, 68.6, 68.4, 66.1, 61.9,
stirred solution of diol 16a (224 mg, 1.20 mmol) and Bu2SnO (448 mg,
1.80 mmol) in toluene (5 mL) was refluxed for 2 h in a flask equipped
with a Dean–Stark separator. The solvent was evaporated under reduced
pressure to leave the crude dibutylstannylene, which was combined with
CsF (365 mg, 2.40 mmol) and dried in vacuum for 2 h. The reaction flask
was charged with DMF (5 mL) and stirred at room temperature for
Chem. Eur. J. 2011, 17, 8696 – 8703
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8701

J.-C. Lee et al.
30.7, 20.8, 20.7, 20.54, 20.53, 20.48, 14.4 ppm; HRMS (FAB): m/z: calcd
for C22H30O12Na: 509.1635 [M+Na]+; found: 509.1641.
7.8 Hz, 1H), 4.43, 4.39 (ABq, J=14.8 Hz, 2H), 4.21 (dd, J=12.0, 4.8 Hz,
1H), 4.10 (dd, J=12.0, 2.4 Hz, 1H), 3.92–3.87 (m, 1H), 3.79 (s, 3H),
3.64–3.59 (m, 1H), 3.40 (d, J=5.7 Hz, 1H), 2.50–2.44 (m, 2H), 2.07 (s,
3H), 2.01 (s, 3H), 1.98 (s, 3H), 1.95 (s, 3H), 1.70–1.62 ppm (m, 2H);
13C NMR (100 MHz, CDCl3): d=170.7, 170.3, 169.5, 169.4, 159.3, 129.9,
129.2, 113.9, 100.4, 94.2, 77.5, 77.2, 73.2, 72.9, 71.6, 71.5, 68.5, 62.0, 55.3,
31.0, 20.8, 20.7, 20.6, 16.9 ppm; HRMS (FAB): m/z: calcd for
C28H35O12NaI: 713.1071 [M+Na]+; found: 713.1069.
(2S)-1-[(4-Methoxybenzyl)oxy]-6-(trimethylsilyl)hex-5-yn-2-yl
2,3,4,6-
tetra-O-acetyl-b-d-glucopyranoside (26a): mixture of alcohol 19a
A
(116 mg, 0.38 mmol), glucosyl trichloroacetimidate 23 (278 mg,
0.56 mmol) and molecular sieves AW-300 (100 mg) in anhydrous CH2Cl2
(20 mL) was stirred at room temperature for 10 min. The reaction mix-
ture was cooled to À608C and TMSOTf (6 mL, 0.04 mmol) was added.
After stirring at À608C overnight (ca. 16 h), the reaction was quenched
by the addition of Et3N (12 mL) and the resulting mixture was filtered
through a pad of Celite. The filtrate was concentrated under reduced
pressure and the residue was purified by column chromatography (hex-
anes/EtOAc 3:1) to give b-glucoside 26a (85 mg, 35%) as a colourless
solid. [a]2D5 =À25.0 (c=1.4 in CHCl3); 1H NMR (400 MHz, CDCl3): d=
7.23 (d, J=8.4 Hz, 2H), 6.87 (d, J=8.4 Hz, 2H), 5.16 (t, J=9.6 Hz, 1H),
5.03 (t, J=9.6 Hz, 1H), 4.92 (dd, J=9.6, 8.0 Hz, 1H), 4.69 (d, J=8.0 Hz,
1H), 4.42, 4.38 (ABq, J=11.2 Hz, 1H), 4.20 (dd, J=12.0, 4.8 Hz, 1H),
4.09 (dd, J=12.0, 2.4 Hz, 1H), 3.88–3.85 (m, 1H), 3.78 (s, 3H), 3.62–3.58
(m, 1H), 3.41–3.40 (m, 2H), 2.33–2.28 (m, 2H), 2.05 (s, 3H), 1.99 (s, 3H),
1.97 (s, 3H), 1.94 (s, 3H), 1.70–1.65 (m, 2H), 0.10 ppm (s, 9H); 13C NMR
(100 MHz, CDCl3): d=170.6, 170.2, 169.4, 169.3, 159.2, 129.9, 129.1,
113.8, 107.1, 100.4, 84.4, 77.9, 73.1, 72.9, 72.8, 71.5, 71.4, 68.5, 62.0, 55.2,
31.2, 20.7, 20.6, 20.5, 16.0, 0.1 ppm; HRMS (FAB): m/z: calcd for
C31H44O12Si: 636.2602 [M]+; found: 636.2594.
Cytopiloyne 1a: A mixture of 31a (169 mg, 0.24 mmol), 9 (118 mg,
0.74 mmol), [PdACHTNUTRGNEUNG(PPh3)4] (14 mg, 12.12 mmol), AgF (6 mg, 47.2 mmol) and
K2CO3 (271 mg, 1.96 mmol) in DMF (5 mL) was stirred at room tempera-
ture under nitrogen for 10 min. MeOH (79 mL, 1.98 mmol) was added
and the mixture was stirred at room temperature for 16 h. The reaction
was diluted with Et2O and quenched by the addition of H2O. The result-
ing mixture was filtered through a pad of Celite. The organic phase was
separated and the aqueous phase was extracted with Et2O. The combined
organic layers were dried over MgSO4, filtered and concentrated under
reduced pressure. The residue was purified by column chromatography
(hexanes/EtOAc 2:1) to give the desired tetrayne and the inseparable by-
product as a colourless solid (137 mg).
DDQ (72 mg, 0.32 mmol) was added to a stirred solution of the desired
tetrayne and the byproduct (137 mg) in CH2Cl2/H2O (20:1, 10.5 mL) at
room temperature. The resulting mixture was stirred for 2 h and the mix-
ture was poured into saturated NaHCO3 solution. The mixture was dilut-
ed with CH2Cl2 and the organic layer was separated. The aqueous layer
was extracted with CH2Cl2. The combined organic layers were dried over
MgSO4, filtered and concentrated under reduced pressure. The residue
was purified by column chromatography (hexanes/EtOAc 2:1 to 1:2) to
give the fully protected (2S)-cytopiloyne and the inseparable byproduct
as a colourless solid (114 mg).
(2S)-1-[(4-Methoxybenzyl)oxy]hex-5-yn-2-yl
2,3,4,6-tetra-O-acetyl-b-d-
glucopyranoside (27a): A mixture of alcohol 20a (457 mg, 1.95 mmol),
glucosyl trichloroacetimidate 23 (1.92 g, 3.90 mmol) and molecular sieves
AW-300 (1 g) in anhydrous CH2Cl2 (40 mL) was stirred at room tempera-
ture for 10 min. The reaction mixture was cooled to À608C and TMSOTf
(35 mL, 0.20 mmol) was added. After stirring at À608C overnight (ca.
16 h), the reaction was quenched by the addition of Et3N (70 mL) and the
resulting mixture was filtered through a pad of Celite. The filtrate was
concentrated under reduced pressure and the residue was purified by
column chromatography (hexanes/EtOAc 2:1) to give b-glucoside 27a
(713 mg, 65%) as a colourless solid. [a]2D5 =À27.4 (c=2.06 in CHCl3);
1H NMR (400 MHz, CDCl3): d=7.24 (d, J=8.4 Hz, 2H), 6.88 (d, J=
8.4 Hz, 2H), 5.18 (t, J=9.6 Hz, 1H), 5.04 (t, J=9.6 Hz, 1H), 4.94 (dd, J=
9.6, 8.0 Hz, 1H), 4.70 (d, J=8.0 Hz, 1H), 4.43, 4.39 (ABq, J=11.6 Hz,
2H), 4.19 (dd, J=12.0, 4.8 Hz, 1H), 4.12 (dd, J=12.0, 2.4 Hz, 1H), 3.94–
3.91 (m, 1H), 3.79 (s, 3H), 3.64–3.60 (m, 1H), 3.40 (d, J=5.2 Hz, 2H),
2.30–2.26 (m, 2H), 2.06 (s, 3H), 2.00 (s, 3H), 1.98 (s, 3H), 1.95 (s, 3H),
1.87 (t, J=2.4 Hz, 1H), 1.69–1.64 ppm (m, 2H); 13C NMR (100 MHz,
CDCl3): d=170.7, 170.3, 169.5, 169.4, 159.3, 129.9, 129.2, 113.9, 100.4,
84.2, 77.6, 73.2, 72.9, 71.54, 71.52, 68.6, 68.3, 62.1, 55.3, 31.0, 20.7, 20.64,
20.61, 14.5 ppm; HRMS (FAB): m/z: calcd for C28H36O12Na: 587.2105
[M+Na]+; found: 587.2093.
A 30% solution of NaOMe in MeOH (46 mL) was added to a stirred so-
lution of the above residue (114 mg) in MeOH/CH2Cl2 (2:1, 6.0 mL) at
08C under argon. After stirring at 08C for 2 h, the reaction was diluted
with MeOH and neutralized with acidic resin. The mixture was filtered
and the filtrate was concentrated under reduced pressure. The residue
was purified by column chromatography (CH2Cl2/MeOH 20:1 to 10:1) to
furnish the desired (2S)-cytopiloyne 1a (32 mg, 36% over 3 steps) as a
white solid. [a]2D2 =À81.6 (c=0.32 in MeOH); 1H NMR (400 MHz,
CD3OD): d=4.37 (d, J=7.6 Hz, 1H), 3.85 (dd, J=12.0, 2.4 Hz, 1H), 3.78
(quint, J=5.6 Hz, 1H), 3.69 (dd, J=12.0, 5.2 Hz, 1H), 3.63 (dd, J=12.0,
4.0 Hz, 1H), 3.53 (dd, J=12.0, 5.6 Hz, 1H), 3.38–3.32 (m, 2H), 3.26–3.22
(m, 1H), 3.20–3.16 (m, 1H), 2.57–2.53 (m, 2H), 1.98 (s, 3H), 1.75 ppm
(q, J=6.8 Hz, 2H); 13C NMR (100 MHz, CD3OD): d=104.2, 82.2, 80.7,
78.2, 78.0, 77.97, 75.5, 71.6, 66.0, 65.12, 65.11, 62.8, 62.4, 62.0, 60.9, 60.2,
31.5, 16.6, 4.0 ppm; HRMS (FAB): m/z: calcd for C19H22O7: 362.1366
[M]+; found: 362.1365.
2(S)-1-[(4-Methoxybenzyl)oxy]-6-(trimethylsilyl)hex-5-yn-2-yl
acetate
(4R)-4-(2-Iodoethyl)-2,2-dimethyl-1,3-dioxolane (11b): The title com-
pound was obtained from (4R)-(+)-4-(2-hydroxyethyl)-2,2-dimethyl-1,3-
dioxolane (6b) (2.09 g, 14.30 mmol) as a colourless oil in 91% yield by
following the procedure described for 11a. [a]2D5 =+23.46 (c=1 in
CHCl3); 1H NMR (400 MHz, CDCl3): d=4.17–4.11 (m, 1H), 4.05 (dd,
J=8.0, 6.4 Hz, 1H), 3.54 (dd, J=8.0, 6.4 Hz, 1H), 3.27–3.16 (m, 2H),
2.11–1.96 (m, 2H), 1.38 (s, 3H), 1.33 ppm (s, 3H); 13C NMR (100 MHz,
CDCl3): d=109.1, 75.6, 68.6, 37.8, 26.9, 25.5, 1.2 ppm; HRMS (FAB): m/
z: calcd for C7H13IO2: 255.9960 [M]+; found: 255.9963.
(28a): 1H NMR (400 MHz, CDCl3): d=7.24 (d, J=8.4 Hz, 2H), 6.87 (d,
J=8.4 Hz, 2H), 5.10–5.07 (m, 1H), 4.49, 4.42 (ABq, J=11.6 Hz, 2H),
3.79 (s, 3H), 3.50 (d, J=5.2 Hz, 2H), 2.25 (t, J=7.2 Hz, 2H), 2.05 (s,
3H), 1.85 (q, J=7.2 Hz, 2H), 0.12 ppm (s, 9H); LCMS (ESI): m/z: 349.1
[M+H]+, 371.1 [M+Na]+.
2(S)-1-[(4-Methoxybenzyl)oxy]hex-5-yn-2-yl acetate (29a): 1H NMR
(400 MHz, CDCl3): d=7.24 (d, J=8.8 Hz, 2H), 6.88 (d, J=8.8 Hz, 2H),
5.16–5.10 (m, 1H), 4.51, 4.43 (ABq, J=11.6 Hz, 2H), 3.80 (s, 3H), 3.51
(d, J=4.8 Hz, 2H), 2.25–2.20 (m, 2H), 2.08 (s, 3H), 1.95 (t, J=2.8 Hz,
1H), 1.90–1.84 ppm (m, 2H); LCMS (ESI): m/z: 299.1 [M+Na]+.
(4R)-4-(But-3-yn-1-yl)-2,2-dimethyl-1,3-dioxolane (4b): A 1.6m solution
of nBuLi in hexanes (7.8 mL, 12.50 mmol) was added dropwise to a
stirred solution of trimethylsilylacetylene (1.28 g, 13.03 mmol) in THF
(20 mL) at À788C. After stirring at À788C for 40 min, a solution of 11b
(1.28 g, 5.00 mmol) in HMPA (2 mL) and THF (2 mL) was added drop-
wise and the resulting mixture was then allowed to warm to room tem-
perature slowly. The reaction was quenched with 50% NH4Cl solution
after overnight stirring (ca. 16 h) and the mixture was extracted with
Et2O. The organic phase was washed with brine, dried over MgSO4, fil-
tered and concentrated under reduced pressure. The residue was used for
the next step without further purification. A 1m solution of TBAF in
THF (6.0 mL, 6.0 mmol) was added to a stirred solution of crude 12b
(1.13 g) in THF (40 mL) at 08C. After stirring at 08C for 1.5 h, the reac-
(2S)-6-Iodo-1-[(4-methoxybenzyl)oxy]hex-5-yn-2-yl
acetyl-b-d-glucopyranoside (31a): NIS (96 mg, 0.43 mmol) and AgNO3
(5 mg, 0.03 mmol) were added to stirred solution of alkyne 27a
2,3,4,6-tetra-O-
a
(161 mg, 0.29 mmol) in acetone (10 mL) in the dark at room temperature.
After stirring at same temperature for 2 h, the reaction mixture was fil-
tered through a pad of Celite and the filtrate was concentrated under re-
duced pressure. The residue was purified by column chromatography
(hexanes/EtOAc 2:1) to furnish iodoalkyne 31a (169 mg, 86%) as a col-
ourless solid. [a]2D5À27.4 (c=1.1 in CHCl3); 1H NMR (300 MHz, CDCl3):
d=7.24 (d, J=8.4 Hz, 2H), 6.89 (d, J=8.4 Hz, 2H), 5.18 (t, J=9.6 Hz,
1H), 5.04 (t, J=9.6 Hz, 1H), 4.93 (dd, J=9.6, 7.8 Hz, 1H), 4.69 (d, J=
8702
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 8696 – 8703

The First Total Synthesis of Cytopiloyne
FULL PAPER
tion was quenched with saturated NH4Cl solution. The reaction mixture
was extracted with Et2O and the organic phase was dried over MgSO4,
filtered and concentrated under reduced pressure. The residue was puri-
fied by flash column chromatography (hexanes/EtOAc 10:1) to furnish
alkyne 4b (478 mg, 62% in 2 steps) as a yellowish oil. [a]2D4 =+8.04 (c=1
in CHCl3); 1H NMR (400 MHz, CDCl3): d=4.20–4.15 (m, 1H), 4.05 (dd,
J=8.0, 6.0 Hz, 1H), 3.55 (dd, J=8.0, 6.8 Hz, 1H), 2.31–2.26 (m, 2H),
1.94 (t, J=2.8 Hz, 1H), 1.83–1.70 (m, 2H), 1.38 (s, 3H), 1.33 ppm (s,
3H); 13C NMR (100 MHz, CDCl3): d=108.8, 83.5, 74.7, 69.1, 68.7, 32.6,
26.9, 25.6, 15.0 ppm; HRMS (FAB): m/z: calcd for C9H15O2: 155.1067
[M+H]+; found: 155.1073; the characterization data of compound 4b
were in agreement with the literature.[29]
62.5, 61.9, 61.1, 60.2, 31.5, 16.2, 4.0 ppm; HRMS (FAB): m/z: calcd for
C19H22O7: 362.1366 [M]+; found: 362.1351.
Acknowledgements
We are grateful to the National Health Research Institutes for financial
support.
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(2R)-Hex-5-yne-1,2-diol (32b): The title compound was obtained from
4b (478 mg, 3.10 mmol) as a colourless solid in 71% yield by following
the procedure described for 16a. [a]2D5 =+43.39 (c=1 in MeOH);
1H NMR (400 MHz, CD3OD): d=3.74–3.68 (m, 1H), 3.50–3.42 (m, 2H),
2.33–2.25 (m, 2H), 2.21 (t, J=2.8 Hz, 1H), 1.76–1.68 (m, 1H), 1.60–
1.52 ppm (m, 1H); 13C NMR (100 MHz, CD3OD): d=84.9, 71.9, 69.8,
67.2, 33.5, 15.6 ppm; HRMS (FAB): m/z: calcd for C6H10O2Na: 137.0578
[M+Na]+; found: 137.0576.
(2R)-1-[(4-Methoxybenzyl)oxy]hex-5-yn-2-ol (20b): The title compound
was obtained from 32b (298 mg, 2.07 mmol) as a colourless oil in 82%
yield by following the procedure described for 19a. [a]2D5 =+3.1 (c=1 in
CHCl3); 1H NMR (400 MHz, CDCl3): d=7.23 (d, J=8.8 Hz, 2H), 6.86
(d, J=8.8 Hz, 2H), 4.46 (s, 2H), 3.93–3.90 (m, 1H), 3.78 (s, 3H), 3.47
(dd, J=9.6, 3.2 Hz, 1H), 3.30 (dd, J=9.6, 7.6 Hz, 1H), 2.38 (d, J=3.6 Hz,
1H), 2.33–2.29 (m, 2H), 1.92 (t, J=2.8 Hz, 1H), 1.66–1.60 ppm (m, 2H);
13C NMR (100 MHz, CDCl3): d=159.1, 129.8, 129.3, 113.7, 83.9, 73.8,
72.8, 68.9, 68.5, 55.1, 31.7, 14.6 ppm; HRMS (FAB): m/z: calcd for
C14H18O3: 234.1256 [M]+; found: 234.1255.
(2R)-1-[(4-Methoxybenzyl)oxy]hex-5-yn-2-yl 2,3,4,6-tetra-O-acetyl-b-d-
glucopyranoside (27b): The title compound was obtained from 20b
(703 mg, 3.00 mmol) and glucosyl trichloroacetimidate 23 (2.76 g,
5.60 mmol) as a white solid in 86% yield by following the procedure de-
scribed for 27a. [a]2D5 =+17.00 (c=1 in CHCl3); 1H NMR (400 MHz,
CDCl3): d=7.24 (d, J=8.8 Hz, 2H), 6.87 (d, J=8.8 Hz, 2H), 5.19 (t, J=
9.6 Hz, 1H), 5.05 (t, J=9.6 Hz, 1H), 4.99 (dd, J=9.6, 8.0 Hz, 1H), 4.66
(d, J=8.0 Hz, 1H), 4.48 (s, 2H), 4.20 (dd, J=12.4, 5.2 Hz, 1H), 4.09 (dd,
J=12.4, 2.4 Hz, 1H), 3.93–3.90 (m, 1H), 3.80 (s, 3H), 3.67–3.62 (m, 2H),
3.47 (dd, J=10.0, 5.6 Hz, 1H), 2.26–2.21 (m, 2H), 2.07 (s, 3H), 2.06 (s,
3H), 2.02 (s, 3H), 2.00 (s, 3H), 1.97 (t, J=2.8 Hz, 1H), 1.81–1.74 ppm
(m, 2H); 13C NMR (100 MHz, CDCl3): d=170.4, 170.1, 169.3, 159.1,
130.0, 129.1, 113.6, 101.2, 83.4, 78.8, 72.84, 72.76, 72.0, 71.5, 71.4, 69.0,
68.2, 61.9, 55.1, 30.7, 20.6, 20.52, 20.46, 14.0 ppm; HRMS (FAB): m/z:
calcd for C28H36O12Na: 587.2105 [M+Na]+; found: 587.2100.
(2R)-6-Iodo-1-[(4-methoxybenzyl)oxy]hex-5-yn-2-yl
2,3,4,6-tetra-O-
acetyl-b-d-glucopyranoside (31b): The title compound was obtained from
27b (425 mg, 0.75 mmol) as a yellowish solid in 93% by following the
procedure described for 31a. [a]2D0 =+17.05 (c=1 in CHCl3); 1H NMR
(400 MHz, CDCl3): d=7.22 (d, J=8.8 Hz, 2H), 6.85 (d, J=8.8 Hz, 2H),
5.17 (t, J=9.6 Hz, 1H), 5.04 (t, J=9.6 Hz, 1H), 4.96 (dd, J=9.6, 8.0 Hz,
1H), 4.61 (d, J=8.0 Hz, 1H), 4.43 (s, 2H), 4.18 (dd, J=12.4, 4.8 Hz, 1H),
4.07 (dd, J=12.0, 2.4 Hz, 1H), 3.87–3.84 (m, 1H), 3.78 (s, 3H), 3.64–3.59
(m, 2H), 3.43 (dd, J=10.0, 5.6 Hz, 1H), 2.40–2.37 (m, 2H), 2.040 (s, 3H),
2.037 (s, 3H), 2.00 (s, 3H), 1.98 (s, 3H), 1.75–1.70 ppm (m, 2H);
13C NMR (100 MHz, CDCl3): d=170.6, 170.3, 169.4, 159.2, 130.0, 129.2,
113.7, 101.2, 93.5, 78.8, 73.0, 72.9, 72.1, 71.6, 71.5, 68.3, 61.9, 55.2, 30.8,
20.70, 20.65, 20.56, 16.4 ppm; HRMS (FAB): m/z: calcd for
C28H35O12NaI: 713.1071 [M+Na]+; found: 713.1059.
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Cytopiloyne 1b: The title compound was obtained from 31b (450 mg,
0.65 mmol) and 9 (313 mg, 1.95 mmol) as a white solid in 6% yield over
3 steps by following the procedure described for 1a. [a]2D2 =+52.1 (c=
0.286 in MeOH); 1H NMR (400 MHz, CD3OD): d=4.31 (d, J=8.0 Hz,
1H), 3.85 (dd, J=12.0, 1.6 Hz, 1H), 3.77–3.72 (m, 1H), 3.67–3.55 (m,
3H), 3.37–3.27 (m, 3H), 3.19 (dd, J=9.2, 8.0 Hz, 1H), 2.58 (t, J=6.8 Hz,
2H), 1.98 (s, 3H), 1.78 ppm (q, J=6.8 Hz, 2H); 13C NMR (100 MHz,
CD3OD): d=104.9, 81.8, 81.7, 78.1, 78.0, 75.3, 71.6, 66.4, 65.9, 65.1, 62.7,
[29] U. Emde, U. Koert, Eur. J. Org. Chem. 2000, 1889–1904.
Received: March 31, 2011
Published online: June 16, 2011
Chem. Eur. J. 2011, 17, 8696 – 8703
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8703