Total Synthesis of the Naturally Occurring Glycosylflavone Aciculatin

Article abstract of DOI:10.1021/acs.jnatprod.5b01051

The new flavone-glycoside aciculatin (1), from Chrysopogon aciculatus, has been shown to have cytotoxic, anti-inflammatory, and antiarthritis activity. Further biological studies have been limited because of the limited availability of 1 from natural sources. Herein the first total synthesis of 1 in an overall yield of 8.3% is described. The synthesis involved the regio- and stereoselective glycosylation-Fries-type O-to-C rearrangement to construct the C-aryl glycosidic linkage, followed by a Baker-Venkataraman rearrangement and cyclodehydration to form the flavone scaffold.

Full text of DOI:10.1021/acs.jnatprod.5b01051

Article
pubs.acs.org/jnp
Total Synthesis of the Naturally Occurring Glycosylflavone Aciculatin
Chun-Hsu Yao, Chi-Hui Tsai, and Jinq-Chyi Lee*
Institute of Biotechnology and Pharmaceutical Research, National Health Research Institutes, 35 Keyan Road, Zhunan, Miaoli County
35053, Taiwan
*
S Supporting Information
ABSTRACT: The new flavone-glycoside aciculatin (1), from
Chrysopogon aciculatus, has been shown to have cytotoxic, anti-
inflammatory, and antiarthritis activity. Further biological studies have
been limited because of the limited availability of 1 from natural
sources. Herein the first total synthesis of 1 in an overall yield of 8.3%
is described. The synthesis involved the regio- and stereoselective
glycosylation−Fries-type O-to-C rearrangement to construct the C-aryl
glycosidic linkage, followed by a Baker−Venkataraman rearrangement
and cyclodehydration to form the flavone scaffold.
Chrysopogon aciculatus is a traditional herbal medicine in
widespread use for the treatment of swelling, the common cold,
fever, and diarrhea. Some of the naturally occurring C-
glycosylflavone extracts isolated from C. aciculatus were found
1
−3
to show cytotoxic activity against human cancer cell lines.
Aciculatin (1), a β-D-digitoxopyranosyl flavone, is a constituent
of these extracts. Aciculatin itself was first reported to exhibit
1
cytotoxic activity in 1991. It also exerts a potent anti-
inflammatory effect by inhibiting lipopolysaccharide-mediated
inducible nitric oxide synthetase (iNOS) and cyclooxygenase-2
(
COX-2) expression through regulation of the universal
transcription factor NF-κB and c-Jun N-terminal kinase
JNK)/p38 mitogen-activated protein kinase (MAPK) path-
β-C-digitoxosyl derivative (3) with the correct regio- and
stereoselectivity via a Fries-type O-to-C rearrangement. This
process is well precedented in the construction of α-
hydroxyaryl C-glycosyl linkages under acidic conditions,
(
4
ways. The effects of aciculatin on anti-inflammatory arthritis
via decreasing interleukin (IL)-1β-induced granulocyte-colony-
stimulating factor (G-CSF) expression have been correlated
7
,8
where electron-rich phenolic systems are used as acceptors.
Esterification of β-D-digitoxopyranosyl phenol (3) followed by a
Baker−Venkataraman rearrangement and cyclodehydration
5
with G-CSF-associated neutrophil maturation. A recent study
9
,10
indicated that aciculatin (1) is a potent p53 inducer and a
should yield flavone (2).
The digitoxosyl donor (4), the
6
promising anticancer agent with low genotoxicity. However,
key precursor of the synthesis, would be synthesized from
methyl 2,3,4,6-tetra-O-trimethylsilyl-α-D-glucopyranoside (6)
through one-pot protection and functional group conversions.
As shown in Scheme 2, thiodigitoxoside (4) was synthesized
starting from methyl 2,3,4,6-tetra-O-trimethylsilyl-α-D-glucopyr-
anoside (6), from which methyl 4,6-O-benzylidene-2,3-di-O-
tosyl-α-D-glucopyranoside (7) was prepared via a one-pot
such studies are limited since aciculatin is available in only
1
0
.26% (dry wt) yield from natural sources, and hence an
efficient, stereoselective total synthesis is urgently required.
Herein, the first total synthesis of aciculatin is described. The
key steps involve regio- and stereoselective digitoxosylation of
the electron-rich phenol with thiodigitoxoside to construct the
C-aryl glycosidic linkage via the Fries-type O-to-C rearrange-
1
1,12
reaction in 71% yield.
Treatment of glucoside (7) with
) in THF gave 8 in 95%
7
,8
ment and the formation of the flavone scaffold using the
Baker−Venkataraman rearrangement, followed by cyclodehy-
lithium triethylborohydride (LiHBEt
3
13
yield. The proposed mechanism for this conversion is via the
α-D-allo-2,3-epoxide intermediate followed by selective reduc-
tive ring opening. Alternatively, reductive cleavage was
accomplished using methyl 4,6-O-benzylidene-2,3-di-O-mesyl-
α-D-glucopyranoside as the substrate, but the yield was much
lower (52%). Benzoylation of the resulting 3-axial hydroxy
9
,10
dration.
RESULTS AND DISCUSSION
The retrosynthetic analysis, in which the target molecule
aciculatin (1) is obtained from β-D-digitoxopyranosylflavone
■
(
2) via a series of functional-group transformations, is depicted
in Scheme 1. Glycosylation of the electron-rich phenol acceptor
5) with the digitoxosyl donor (4) was anticipated to afford the
Received: November 25, 2015
(
©
XXXX American Chemical Society and
American Society of Pharmacognosy
A
DOI: 10.1021/acs.jnatprod.5b01051
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Article
Scheme 1. Retrosynthetic Analysis of Aciculatin (1)
O-benzoylthiodigitoxoside (4) using p-thiocresol in the
18
presence of SnCl in 85% yield (α/β ≈ 1/1).
4
With the key intermediate 4 in hand, the synthesis of
aciculatin (1) was pursued as outlined in Scheme 3.
Glycosylation of the electron-rich phenol 5 with the digitoxosyl
derivative 4 activated by NIS/TfOH afforded the β-D-
digitoxopyranoside (3) in 81% yield, with good regio- and
19
stereoselectivity. An in situ O → C Fries-type rearrangement
has been proposed to account for the formation of the hydroxy-
7
,8
C-glycosyl product. Alternatively, compound 3 was isolated
in slightly lower yield (63%) when the 3,4-di-O-benzoyldigi-
toxosyl imidate was used as the donor in the presence of a
catalytic amount of TMSOTf. β-C-Digitoxoside (3) was
susceptible to a 1-ethyl-3-(3-(dimethylamino)propyl)-
carbodiimide (EDC)-mediated esterification with 4-benzylox-
ybenzoic acid to give the corresponding ester 12 in 98% yield.
The 1,3-diketo intermediate was formed via Baker−Venkatara-
man rearrangement using NaH, in which enolate formation
9
,10
t
results in intramolecular acyl transfer.
When BuOK or
KOH was used as the base, the 1,3-diketo intermediate was
accompanied by two major byproducts, as detected by thin-
layer chromatography (TLC). The crude 1,3-diketone was
converted into the flavone 2 in 59% over two steps using
camphorsulfonic acid (CSA)-mediated cyclodehydration, sig-
nificantly better than using p-toluenesulfonic acid (pTSA).
Subsequently, the BBr -mediated selective de-O-methylation/
3
de-O-benzylation of flavone 2 afforded the monomethoxy C-
Scheme 2. Synthesis of 3,4-Di-O-Benzoylthiodigitoxoside
20,21
glycosyl compound 13 in 50% yield.
The BBr and the
3
(
4)
selective nature of de-O-methylation result from the formation
of a complex involving oxygen atoms of the 4-carbonyl and 5-
2
1
methoxy groups. Using the boron tribromide/dimethyl
22
sulfide complex (BBr ·SMe ) resulted in a lower isolated
3
2
yield of 42%. Finally, the benzoyl groups were removed by
treatment with NaOMe to give aciculatin (1) in 88% yield. The
spectroscopic data of synthetic 1 are in good agreement with
1
those of natural aciculatin.
In conclusion, the first total synthesis of aciculatin (1) has
been accomplished in 12 steps with an overall yield of 8.3%
starting from methyl 2,3,4,6-tetra-O-trimethylsilyl-α-D-glucopyr-
anoside (6). The formation of the β-C-aryl glycosidic linkage by
regio- and stereoselective glycosylation of the electron-rich
phenol with thiodigitoxoside via a Fries-type O-to-C rearrange-
ment and the use of a Baker−Venkataraman rearrangement/
cyclodehydration to form the flavone are the key steps in the
construction of the requisite skeleton. The efficient nature of
this synthesis may provide sufficient quantities of aciculatin (1)
for further biological studies.
EXPERIMENTAL SECTION
■
General Experimental Procedures. Unless otherwise stated, all
reagents were purchased from commercial sources and used as
supplied without further purification. Optical rotations were measured
on a JASCO P-1020 digital polarimeter at 25 °C with a PTC-102T
temperature controller; a sodium lamp with a wavelength of 589 nm
1
13
group of 8 with BzCl in pyridine afforded methyl 3-O-benzoyl-
,6-O-benzylidene-2-deoxy-α-ribohexopyranoside (9) in 94%
was used as the light source. H and C NMR spectra were recorded
on a Mercury-400 spectrometer, and chemical shifts are reported
4
1
13
relative to the CDCl3 signal ( H, δ = 7.24; C, δ = 77.00) or
yield. The NBS-mediated fragmentation of the 4,6-benzylidene
acetal via the Hanessian−Hullar reaction gave 3,4-di-O-
benzoyl-6-bromo-2,6-deoxy-α-ribohexopyranoside (10) (86%)
1
13
methanol-d ( H, δ = 3.31; C, δ = 49.00). Splitting patterns are
4
recorded as s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; and
ABq, AB quartet. HRFABMS data were obtained with a JEOL JMS-
14−16
via a highly regioselective ring opening.
Compound 10
7
00 mass spectrometer, recorded as m/z values. Reactions were
was then subjected to reductive debromination with AIBN and
monitored by analytic TLC carried out on silica gel 60 F254 precoated
glass-backed plates (Merck). The chromatograms were detected under
UV irradiation (λ = 254 nm) followed by staining with a solution of
Bu SnH in toluene to afford the fully protected digitoxoside
3
1
7
(11) (87%). This was converted into the target donor 3,4-di-
B
DOI: 10.1021/acs.jnatprod.5b01051
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Article
Scheme 3. Synthesis of Aciculatin (1)
Ce(NH ) (NO ) , (NH4) Mo O , and H SO in water. Column
MgSO , filtered, and concentrated under reduced pressure. The
4
2
3
6
6
7
24
2
4
4
chromatography was performed using SiliaFlash P60 silica gel of 230−
00 mesh size. Purity of synthesized aciculatin (1) was determined by
a Hitachi 2000 series HPLC system using a C18 reversed-phase column
Agilent ZORBAX Eclipse XDB-C18 5 μm, 4.6 mm × 150 mm). The
residue was purified by column chromatography (EtOAc/n-hexane =
1/2) to provide 8 (24.1 mg, 95%) as a white solid. The spectroscopic
data of compound 8 were in agreement with literature data.
Methyl 3-O-Benzoyl-4,6-O-benzylidene-2-deoxy-α-D-ribo-
hexopyranoside (9). Benzoyl chloride (2.2 mL, 18.94 mmol) was
added to a stirred solution of 8 (4.8 g, 18.01 mmol) in pyridine (60
mL) at 0 °C under Ar(g). The reaction mixture was gradually warmed
to room temperature and stirred overnight (22 h). Water was added,
4
13b
(
elution system consisted of a MeCN (mobile phase A) and 10 mM
NH OAc aqueous solution containing 0.1% formic acid (mobile phase
4
B). The analysis was carried out in gradient conditions starting from
A/B = 10/90% to A/B = 90/10% in 45 min at a flow rate of 0.5 mL/
min.
and the mixture was extracted with CH
Cl
2
(3 × 100 mL). The
2
Methyl 4,6-O-Benzylidene-2,3-di-O-(p-tolylsulfonyl)-α-D-glu-
copyranoside (7). TMSOTf (18 μL, 0.097 mmol) was added to a
solution of 6 (315 mg, 0.651 mmol), PhCHO (80 μL, 0.782 mmol),
and 3 Å molecular sieves (470 mg) in CH Cl (3 mL) at −78 °C
organic layer was washed with 1 N HCl, dried over MgSO
, filtered,
4
and concentrated under reduced pressure. The residue was purified by
column chromatography (EtOAc/n-hexane = 1/8) to provide 9 (6.3 g,
94%) as a white solid. The spectroscopic data of compound 9 were in
2
2
1
6
under Ar . After 2.5 h stirring, the reaction mixture was warmed to 0
agreement with literature data.
(
g)
°
C, and TBAF (1 M solution in THF, 2.6 mL, 2.6 mmol) was added.
Methyl 3,4-Di-O-benzoyl-6-bromo-2,6-dideoxy-α-D-ribo-
The mixture was gradually warmed to room temperature, and stirring
was maintained. After 2.5 h, the solution was cooled to 0 °C and
diluted with DMF (2.0 mL). A solution of p-toluenesulfonyl chloride
hexopyranoside (10). N-Bromosuccinimide (2.5 g, 14.05 mmol)
and BaCO
(4.9 g, 13.22 mmol) in CCl
reaction mixture was heated under reflux for 5 h and then cooled to
room temperature. The mixture was filtered, and H O was added to
the filtrate. The aqueous layer was extracted with CH Cl (3 × 100
mL), and the organic layer was washed with saturated aqueous
NaHCO , dried over MgSO , filtered, and concentrated under reduced
(3.9 g, 19.76 mmol) were added to a stirred solution of 9
3
(95 mL) at 90 °C under Ar(g). The
4
(
994 mg, 5.213 mmol) in DMF (2.0 mL) and NaH (365 mg, 9.123
mmol) were sequentially added. The reaction mixture was allowed to
warm to room temperature and stirred overnight. The reaction was
quenched with H O at 0 °C, and the resulting mixture was extracted
2
2
2
2
with CH Cl (3 × 25 mL). The organic layer was dried over MgSO ,
3
4
2
2
4
filtered, concentrated under reduced pressure, and purified by column
chromatography (EtOAc/n-hexane = 1/3) to provide 7 (272 mg,
pressure. The residue was purified by column chromatography
(EtOAc/n-hexane = 1/5) to provide 10 (5.1 g, 86%) as a white
solid. The spectroscopic data of compound 10 were in agreement with
7
1%) as a white solid. The spectroscopic data of compound 7 were in
13b
16
agreement with literature data.
literature data.
Methyl 4,6-O-Benzylidene-2-deoxy-α-D-ribohexopyranoside
8). To a stirred solution of compound 7 (57 mg, 0.097 mmol) in
Methyl 3,4-Di-O-benzoyl-2,6-dideoxy-α-D -ribo-
hexopyranoside (11). Azobis(isobutyronitrile) (1.9 g, 11.57
(
THF (1.0 mL) was added LiHBEt (1 M solution in THF, 0.6 mL, 0.6
mmol) and Bu SnH (5.6 mL, 20.71 mmol) were added to a stirred
3
3
mmol) at 0 °C under Ar . The reaction mixture was heated under
reflux for 1 h, and the excess reducing agent was quenched with
solution of 10 (5.2 g, 11.57 mmol) in toluene (50 mL) at room
temperature under Ar . The reaction mixture was heated at 95 °C for
24 h and then concentrated under reduced pressure to remove the
(g)
(g)
EtOAc. The mixture was diluted with saturated aqueous NH Cl and
4
extracted with CH Cl (3 × 15 mL). The organic layer was dried over
solvent. The residue was purified by column chromatography (n-
2
2
C
DOI: 10.1021/acs.jnatprod.5b01051
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Article
hexane → toluene/Et O = 9/1) to give 11 (3.72 g, 87%) as a white
2.08 (ddd, J = 14.4, 2.8, 2.4 Hz, 1H), 0.86 (d, J = 6.4 Hz, 3H); 13C
2
solid. The spectroscopic data of compound 11 were in agreement with
NMR (100 MHz, CDCl ) δ 200.1 (C), 165.5 (C), 165.3 (C), 164.6
3
16
literature data.
-Methylphenyl 3,4-Di-O-benzoyl-2,6-dideoxy-1-thio-D-ri-
bohexopyranoside (4). A solution of SnCl (0.19 mL, 1.607
(C), 163.0 (C), 159.6 (C), 158.2 (C), 147.8 (C), 136.3 (C), 133.0
(CH), 132.9 (CH), 132.3 (CH), 130.3 (C), 129.7 (C), 129.6 (CH),
129.5 (CH), 128.7 (CH), 128.4 (CH), 128.23 (CH), 128.16 (CH),
127.5 (CH), 121.8 (C), 118.9 (C), 114.9 (CH), 114.2 (C), 93.2
4
4
mmol) in CH Cl (2.0 mL) was added dropwise to a mixture of 11
2
2
(
3
541 mg, 1.461 mmol), p-thiocresol (218 mg, 1.755 mmol), and AW-
00 MS (540 mg) in CH Cl (7.0 mL) at −78 °C under Ar . The
(
CH), 73.4 (CH), 71.1 (CH), 70.2 (CH ), 68.7 (CH), 67.4 (CH),
2
2
2
(g)
56.0 (CH ), 55.9 (CH ), 34.2 (CH ), 31.7 (CH ), 17.8 (CH );
3 3 2 3 3
reaction mixture was stirred at −78 °C for 2 h; then CH Cl (150
mL), saturated aqueous NaHCO (25 mL), and saturated aqueous
+
2
2
HRFABMS m/z 744.2576 [M] (calcd for C H O , 744.2571).
44 40 11
3
(1R)-1,5-Anhydro-3,4-di-O-benzoyl-1-{2-[4-(benzyloxy)-
phenyl]-5,7-dimethoxy-4-oxo-4H-chromen-8-yl}-2,6-dideoxy-
D-ribohexitol (2). To a stirred solution of 12 (72 mg, 0.097 mmol) in
THF (1.5 mL) was added 60% NaH (8 mg, 0.193 mmol) at 0 °C.
After stirring for 10 min at this temperature, the mixture was stirred at
potassium sodium tartrate solution (25 mL) were added sequentially
to the solution at 0 °C and stirred for another 1 h at room
temperature. The organic layer was separated, and the aqueous layer
was extracted with CH Cl (3 × 30 mL). The organic layer was dried
2
2
over MgSO , filtered, and concentrated under reduced pressure. The
80 °C for 1 h. The reaction was quenched with H O, and the mixture
4
2
residue was purified by column chromatography (EtOAc/n-hexane =
was extracted with EtOAc (3 × 10 mL). The organic layer was dried
1
/10) to afford 4 (577 mg, 85%, α/β ≈ 1/1) as a colorless solid. 4α:
over MgSO , filtered, and concentrated under reduced pressure to
4
1
H NMR (400 MHz, CDCl ) δ 8.24−8.21 (m, 2H), 7.88−7.86 (m,
2
7
3
afford a crude extract of the 1,3-diketone, which was used for the next
reaction without further purification.
H), 7.60−7.56 (m, 1H), 7.52−7.40 (m, 5H), 7.35−7.31 (m, 2H),
.14 (d, J = 7.6 Hz, 2H), 5.80 (q, J = 3.2 Hz, 1H), 5.49 (dd, J = 6.4, 1.2
A mixture of the crude extract of the 1,3-diketone (72 mg, 0.097
mmol) and CSA (6 mg, 0.024 mmol) in toluene (1.0 mL) was stirred
at 130 °C under Ar . After 5 h, a further portion of CSA (12 mg,
Hz, 1H), 5.04 (dd, J = 9.6, 3.2 Hz, 1H), 4.97−4.90 (m, 1H), 2.63
(
ddd, J = 15.2, 6.4, 3.2 Hz, 1H), 2.48 (ddd, J = 15.2, 3.2, 1.2 Hz, 1H),
(g)
13
2
1
1
.33 (s, 3H), 1.31 (d, J = 6.0 Hz, 3H); C NMR (100 MHz, CDCl ) δ
3
0.048 mmol) was added, and the resulting mixture was stirred at 130
C for another 1 h. The reaction mixture was cooled to 0 °C and
65.8 (C), 165.5 (C), 137.4 (C), 133.2 (CH), 132.7 (C), 131.8 (CH),
30.1 (CH), 129.8 (C), 129.7 (CH), 129.5 (C), 128.4 (CH), 128.3
°
neutralized with saturated aqueous NaHCO . The aqueous layer was
3
(
2
CH), 83.2 (CH), 72.9 (CH), 66.9 (CH), 63.4 (CH), 35.3 (CH ),
2
extracted with EtOAc (3 × 10 mL), and the organic layer was dried
+
1.1 (CH ), 17.5 (CH ); 4: HRFABMS m/z 462.1507 [M] (calcd for
3 3
over MgSO , filtered, and concentrated under reduced pressure. The
4
C H O S, 462.1501).
27
26
5
residue was purified by column chromatography (EtOAc/n-hexane =
(
1R)-1-(3-Acetyl-2-hydroxy-4,6-dimethoxyphenyl)-1,5-anhy-
3
/1 → EtOAc/CH Cl /THF = 1/6/1) to afford 2 (41.2 mg, 59%) as
2 2
dro-3,4-di-O-benzoyl-2,6-dideoxy-D-ribohexitol (3). NIS (260
25
1
a yellowish solid: [α] −25 (c 0.2, CHCl ); H NMR (400 MHz,
CDCl ) δ 8.15 (dd, J = 8.4, 1.2 Hz, 2H), 7.96 (d, J = 8.8 Hz, 2H), 7.93
D
3
mg, 1.155 mmol) and TfOH (0.5 M solution in Et O, 0.30 mL, 0.150
2
3
mmol) were added sequentially to a mixture of 4 (492 mg, 1.064
(dd, J = 8.4, 1.2 Hz, 2H), 7.64−7.60 (m, 1H), 7.53−7.32 (m, 10H),
mmol), 5 (180 mg, 0.917 mmol), and AW-300 MS (1 g) in CH Cl2
2
7
2
2
2
3
.07 (d, J = 8.4 Hz, 2H), 6.60 (s, 1H), 6.39 (s, 1H), 5.85−5.82 (m,
H), 5.34 (dd, J = 10.0, 2.8 Hz, 1H), 5.14, 5.12 (ABq, J = 11.6 Hz,
H), 4.45 (dq, J = 10.0, 6.4 Hz, 1H), 3.98 (s, 3H), 3.93 (s, 3H), 3.01−
(
11 mL) at −40 °C. After stirring for 1 h, the reaction mixture was
warmed to room temperature gradually and stirred overnight. The
reaction was quenched with Et N at 0 °C and filtered through a pad of
3
.94 (m, 1H), 2.09 (ddd, J = 14.8, 2.8, 2.8 Hz, 1H), 1.37 (J = 6.4 Hz,
Celite. The filtrate was washed with an aqueous solution of Na S O ,
13
2
2
3
H); C NMR (100 MHz, CDCl ) δ 177.9 (C), 165.6 (C), 161.4
3
dried over MgSO , filtered, and concentrated under reduced pressure.
4
(
(
C), 161.3 (C), 161.0 (C), 160.9 (C), 157.4 (C), 136.3 (C), 133.2
CH), 130.4 (C), 129.7 (CH), 129.6 (C), 128.64 (CH), 128.57 (CH),
The residue was purified by column chromatography (EtOAc/n-
hexane = 1/5 → 1/3) to provide 3 (395 mg, 81%) as a white solid:
2
5
1
128.4 (CH), 128.2 (CH), 127.9 (CH), 127.6 (CH), 124.3 (C), 115.3
[
(
7
=
α] +20 (c 0.3, CHCl ); H NMR (400 MHz, CDCl ) δ 8.12−8.09
D
3
3
(
(
3
CH), 109.2 (C), 107.8 (C), 107.1 (CH), 91.6 (CH), 73.3 (CH), 71.8
m, 2H), 7.91−7.88 (m, 2H), 7.61−7.57 (m, 1H), 7.51−7.46 (m, 3H),
.34−7.30 (m, 2H), 5.94 (s, 1H), 5.84 (q, J = 3.2 Hz, 1H), 5.63 (dd, J
12.0, 2.4 Hz, 1H), 5.11 (dd, J = 10.0, 3.2 Hz, 1H), 4.34 (dq, J = 10.0,
.0 Hz, 1H), 3.90 (s, 3H), 3.89 (s, 3H), 3.13 (ddd, J = 14.4, 12.0, 3.2
Hz, 1H), 2.58 (s, 3H), 1.93 (ddd, J = 14.4, 3.2, 2.4 Hz, 1H), 1.28 (d, J
CH), 70.2 (CH ), 69.2 (CH), 66.9 (CH), 56.4 (CH ), 56.1 (CH ),
2
3
3
+
4.0 (CH ), 18.4 (CH ); HRFABMS m/z 727.2547 [M + H] (calcd
2
3
for C H O , 727.2543).
44
39 10
6
(
1R)-1,5-Anhydro-3,4-di-O-benzoyl-2,6-dideoxy-1-[5-hy-
6.0 Hz, 3H); 13C NMR (100 MHz, CDCl ) δ 203.4 (C),165.69 (C),
droxy-2-(4-hydroxyphenyl)-7-methoxy-4-oxo-4H-chromen-8-
yl]-D-ribohexitol (13). To a stirred solution of 2 (26.4 mg, 0.036
mmol) in CH Cl (1.0 mL) was added BBr (1 M solution in CH Cl ,
=
3
165.66 (C), 164.8 (C), 164.7 (C), 163.3 (C), 133.01 (CH), 132.98
2
2
3
2
2
(
CH), 130.5 (C), 129.8 (C), 129.69 (CH), 129.65 (CH), 128.5 (CH),
7
5 μL, 0.072 mmol) at −78 °C under Ar . The reaction mixture was
(g)
1
6
28.3 (CH), 107.4 (C), 106.0 (C), 86.4 (CH), 73.9 (CH), 71.2 (CH),
9.3 (CH), 66.3 (CH), 55.7 (CH ), 55.4 (CH ), 33.2 (CH ), 33.1
gradually warmed to 0 °C and stirred for 5 h. Ice water was added to
quench the reaction, and the mixture was extracted with EtOAc (3 × 5
mL). The organic layer was washed with brine, dried over MgSO4,
filtered, and concentrated under reduced pressure. The residue was
purified by column chromatography (MeOH/CH Cl = 1/100) to
3
3
3
+
(
CH ), 18.4 (CH ); HRFABMS m/z 535.1968 [M + H] (calcd for
2 3
C H O , 535.1968).
30
31
9
(
1R)-1-(3-Acetyl-2-{[4-(benzyloxy)benzoyl]oxy}-4,6-dime-
2
2
thoxyphenyl)-1,5-anhydro-3,4-di-O-benzoyl-2,6-dideoxy-D-ri-
bohexitol (12). A mixture of 3 (41 mg, 0.077 mmol), 4-
benzyloxybenzoic acid (35 mg, 0.153 mmol), EDC (44 mg, 0.230
mmol), and DMAP (19 mg, 0.156 mmol) in DMF (1.0 mL) was
2
5
give 13 (11.3 mg, 50%) as a yellowish solid: [α]
−61 (c 0.1,
D
1
CHCl ); H NMR (400 MHz, CDCl ) δ 8.14 (dd, J = 8.0, 1.2 Hz,
3
3
2
H), 7.96 (d, J = 8.8 Hz, 2H), 7.91 (dd, J = 8.0, 1.2 Hz, 2H), 7.66−
7
.62 (m, 1H), 7.54−7.49 (m, 3H), 7.36 (d, J = 8.0 Hz, 1H), 7.34 (d, J
stirred at 60 °C for 16 h. After completion, H O was added to the
2
=
7.6 Hz, 1H), 7.01 (d, J = 8.4 Hz, 2H), 6.58 (s, 1H), 6.38 (s, 1H),
mixture, and the aqueous layer was extracted with EtOAc (3 × 10
mL). The organic layer was washed with an aqueous solution of NaCl,
5.83 (q, J = 2.8 Hz, 1H), 5.76 (dd, J = 12.0, 2.4 Hz, 1H), 5.34 (dd, J =
10.0, 2.8, 1H), 4.44 (dq, J = 10.0, 6.0 Hz, 1H), 3.87 (s, 3H), 2.89 (ddd,
dried over MgSO , filtered, and concentrated under reduced pressure.
4
The residue was purified by column chromatography (EtOAc/n-
J = 14.8, 12.0, 2.8 Hz, 1H), 2.09 (ddd, J = 14.8, 2.8, 2.4 Hz, 1H), 1.36
25
D
13
hexane = 1/1) to provide 12 (56 mg, 98%) as a white solid. [α] +24
(d, J = 6.0 Hz, 3H); C NMR (100 MHz, CDCl
3
) δ 182.9 (C), 165.9
1
(
c 0.3, CHCl ); H NMR (400 MHz, CDCl ) δ 8.12−8.07 (m, 2H),
(C), 165.6 (C), 164.3 (C), 162.5 (C), 159.3 (C), 155.5 (C), 133.31
(CH), 133.29 (CH), 130.3 (C), 129.7 (CH), 129.5 (C), 128.61 (CH),
128.58 (CH), 128.4 (CH), 123.9 (C), 116.3 (CH), 106.0 (C), 105.5
(C), 103.7 (CH), 95.3 (CH), 73.4 (CH), 71.7 (CH), 69.1 (CH), 66.8
(CH), 56.3 (CH ), 34.3 (CH ), 18.4 (CH ); HRFABMS m/z
3
3
7.93 (dd, J = 8.4, 1.2 Hz, 2H), 7.79 (dd, J = 8.4, 1.6 Hz, 2H), 7.54−
7.23 (m, 11H), 7.04−7.01 (m, 2H), 6.37 (s, 1H), 5.77 (q, J = 2.8 Hz,
1H), 5.39 (dd, J = 12.0, 2.4, 1H), 5.16, 5.14 (ABq, J = 12.0 Hz, 2H),
4.65 (dd, J = 10.0, 2.8, 1H), 4.09 (dq, J = 10.0, 6.4 Hz, 1H), 3.87 (s,
3H), 3.83 (s, 3H), 2.77 (ddd, J = 14.4, 12.0, 2.8 Hz, 1H), 2.45 (s, 3H),
3
2
3
+
623.1915 [M + H] (calcd for C H O , 623.1917).
36
31 10
D
DOI: 10.1021/acs.jnatprod.5b01051
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Article
Aciculatin (1). To a stirred solution of 13 (20 mg, 0.032 mmol) in
(13) (a) Baer, H. H.; Hanna, H. R. Carbohydr. Res. 1982, 110, 19−41.
(b) Miller, V. P.; Yang, D.-y.; Weigel, T. M.; Han, O.; Liu, H.-w. J. Org.
Chem. 1989, 54, 4175−4188.
MeOH/CH Cl (1/1, 1.0 mL) was added NaOMe (30% in MeOH,
2
2
2
0 μL, 0.096 mmol) at −20 °C under Ar . The reaction mixture was
(g)
warmed to 0 °C gradually and stirred for 18 h. After completion of the
reaction, the mixture was diluted with MeOH, neutralized by the
addition of acidic Dowex 50W2-200, and filtered. The filtrate was
concentrated under reduced pressure, and the residue was purified by
column chromatography (MeOH/CH Cl = 1/20 → 1/10) to afford
(14) Hannesian, S. Carbohydr. Res. 1966, 2, 86−88.
(15) Failla, D. L.; Hullar, T. L.; Siskin, S. B. Chem. Commun. 1966,
716−717.
(16) Cheung, T. M.; Horton, D.; Weckerle, W. Carbohydr. Res. 1977,
58, 139−151.
2
2
aciculatin (1) (11.7 mg, 88%) as a yellowish solid. The spectroscopic
(17) Robins, M. J.; Nowak, I.; Wnuk, S. F.; Hansske, F.; Madej, D. J.
Org. Chem. 2007, 72, 8216−8221.
1
25
data of the synthetic 1 were in agreement with literature data. [α]
D
1
+
52 (c 0.4, MeOH); lit. [α]25 +51 (c 0.5, MeOH); H NMR (400
(18) Magauer, T.; Myers, A. G. Org. Lett. 2011, 13, 5584−5587.
(19) Konradsson, P.; Udodong, U. E.; Reid, B. F. Tetrahedron Lett.
1990, 31, 4313−4316.
D
MHz, CDCl /methanol-d = 1/1) δ 7.95−7.92 (m, 2H), 6.94−6.91
3
4
(
m, 2H), 6.55 (s, 1H), 6.40 (s, 1H), 5.61 (dd, J = 12.0, 2.0 Hz, 1H),
4
9
1
.13−4.11 (m, 1H), 3.96−3.90 (m, 1H), 3.90 (s, 3H), 3.45 (dd, J =
(20) Wu, Z.; Wei, G.; Lian, G.; Yu, B. J. Org. Chem. 2010, 75, 5725−
5728.
.6, 3.2 Hz, 1H), 2.57 (ddd, J = 14.4, 12.0, 2.4 Hz, 1H), 1.82 (ddd, J =
13
4.4, 2.4, 2.0 Hz, 1H), 1.35 (d, J = 6.0 Hz, 3H); C NMR (100 MHz,
(21) Lee, J. I.; Park, S. B. Bull. Korean Chem. Soc. 2012, 33, 1379−
1382.
CDCl /methanol-d = 1/1) δ 182.6 (C), 164.8 (C), 162.4 (C), 161.1
3
4
(
(
(
C), 160.8 (C), 155.2 (C), 128.2 (CH), 121.8 (C), 115.3 (CH), 106.8
C), 104.6 (C), 102.1 (CH), 94.6 (CH), 72.9 (CH), 72.4 (CH), 67.1
CH), 65.2 (CH), 55.4 (CH ), 35.7 (CH ), 17.6 (CH ); HRFABMS
(22) Mahling, J.-A.; Jung, K.-H.; Schmidt, R. R. Liebigs Ann. 1995,
1
995, 461−466.
3
2
3
+
m/z 415.1389 [M + H] (calcd for C H O , 415.1393); HPLC
22
23
8
purity = 99.28%, t = 22.16 min.
R
ASSOCIATED CONTENT
Supporting Information
■
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jnat-
prod.5b01051.
1
H NMR spectra for all previously reported compounds;
1
13
H and C NMR spectra for all new compounds and
aciculatin (1) (PDF)
AUTHOR INFORMATION
Corresponding Author
E-mail (J.-C. Lee): jinqchyi@nhri.org.tw.
■
*
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We are grateful for the financial support from National Health
Research Institutes.
■
REFERENCES
■
(
1) Carte,
́
B. K.; Carr, S.; DeBrosse, C.; Hemling, M. E.; MacKenzie,
L.; Offen, P.; Berry, D. E. Tetrahedron 1991, 47, 1815−1822.
(
2) Krause, J. A.; Eggleston, D. S. Acta Crystallogr., Sect. C: Cryst.
Struct. Commun. 1991, 47, 2595−2598.
3) Shen, C.-C.; Cheng, J.-J.; Lay, H.-L.; Wu, S.-Y.; Ni, C.-L.; Teng,
C.-M.; Chen, C.-C. J. Nat. Prod. 2012, 75, 198−201.
4) Hsieh, I.-N.; Chang, A. S.-Y.; Teng, C.-M.; Chen, C.-C.; Yang, C.-
R. J. Biomed. Sci. 2011, 18, 28−38.
5) Shih, K.-S.; Wang, J.-H.; Wu, Y.-W.; Teng, C.-M.; Chen, C.-C.;
Yang, C.-R. PLoS One 2012, 7, e42389.
6) Lai, C.-Y.; Tsai, A.-C.; Chen, M.-C.; Chang, L.-H.; Sun, H.-L.;
(
(
(
(
Chang, Y.-L.; Chen, C.-C.; Teng, C.-M.; Pan, S.-L. PLoS One 2012, 7,
e42192.
(
7
(
7) Matsumoto, T.; Hosoya, T.; Suzuki, K. Synlett 1991, 1991, 709−
11.
8) Dos Santos, R. G.; Jesus, A. R.; Caio, J. M.; Rauter, A. P. Curr.
Org. Chem. 2011, 15, 128−148.
(
(
(
9) Baker, W. J. Chem. Soc. 1933, 1381−1389.
10) Mahal, H. S.; Venkataraman, K. J. Chem. Soc. 1934, 1767−1769.
11) Wang, C.-C.; Lee, J.-C.; Luo, S.-Y.; Kulkarni, S. S.; Huang, Y.-
W.; Lee, C.-C.; Chang, K.-L.; Hung, S.-C. Nature 2007, 446, 896−899.
12) Wang, C.-C.; Kulkarni, S. S.; Lee, J.-C.; Luo, S.-Y.; Hung, S.-C.
Nat. Protoc. 2008, 3, 97−113.
(
E
DOI: 10.1021/acs.jnatprod.5b01051
J. Nat. Prod. XXXX, XXX, XXX−XXX