Two acetophenone glucosides, cynanonesides A and B, from Cynanchum taiwanianum and revision of the structure for cynandione A

Article abstract of DOI:10.1021/np960256b

β-Sitosterol, β-amyrin, 4-hydroxyacetophenone, 3,4- dihydroxyacetophenone, sitosteryl 3-O-β-D-glucopyranoside, cynandione A, and cynanonesides A (3) and B (4) were isolated from the roots of Cynanchum taiwanianum. The latter two compounds are new acetophenone glucosides, and their structures were elucidated on the basis of spectral and chemical evidence. Meanwhile, the structure of cynandione A, previously designated as 3',4-diacetyl-2,2',3,6'-tetrahydroxybiphenyl, has been revised as 2,3'- diacetyl-2',3,6,6'-tetrahydroxybiphenyl (9).

Full text of DOI:10.1021/np960256b

368
J . Nat. Prod. 1997, 60, 368-370
Tw o Acetop h en on e Glu cosid es, Cyn a n on esid es A a n d B, fr om Cyn a n ch u m
ta iwa n ia n u m a n d Revision of th e Str u ctu r e for Cyn a n d ion e A
Yun-Lian Lin* and Tung-Chich Lin
National Research Institute of Chinese Medicine, Taipei, Taiwan, Republic of China
Yueh-Hsiung Kuo*
Department of Chemistry, National Taiwan University, Taipei, Taiwan, Republic of China
Received February 21, 1996X
â-Sitosterol, â-amyrin, 4-hydroxyacetophenone, 3,4-dihydroxyacetophenone, sitosteryl 3-O-â-
D-glucopyranoside, cynandione A, and cynanonesides A (3) and B (4) were isolated from the
roots of Cynanchum taiwanianum. The latter two compounds are new acetophenone glucosides,
and their structures were elucidated on the basis of spectral and chemical evidence. Meanwhile,
the structure of cynandione A, previously designated as 3′,4-diacetyl-2,2′,3,6′-tetrahydroxybi-
phenyl, has been revised as 2,3′-diacetyl-2′,3,6,6′-tetrahydroxybiphenyl (9).
Ta ble 1. 1H- and 13C-NMR Data for 3 and 4 (300 MHz, 75
Species of the genus Cynanchum (Asclepiadaceae)
MHz in DMSO-d6)
have been used in folk medicine for the treatment of
H
3
4
C
3
4
chronic tracheitis and as antifebrile, diuretic, antitus-
sive, expectorant, anodyne, and tonic drugs.1-7 Chemi-
cal studies of Cynanchum species have shown the pres-
ence of disecopregnanes, 2,6-dideoxy-3-O-methyl sugars,
and C/D-cis-polyoxypregnanes and their glycosides.9-14
Previous investigation on C. formosanum and C. tai-
wanianum led to the isolation of pregnane glycosides
and flavonoids.15-18
2
3
5
6.95d (3.0)
1
2
3
4
5
6
7
8
1′
2′
3′
4′
5′
6′
129.3
117.6
149.4
151.8
114.4
120.2
198.9
31.7
101.7
73.3
76.7
69.7
77.0
119.4
162.9
102.0
159.2
109.2
131.5
196.3
32.0
100.6
73.2
76.7
69.4
77.1
6.59d (2.0)
6.47 dd
(8.7, 2.0)
7.57d (8.7)
7.10d (8.8)
6
6.88 dd
(8.8, 3.0)
2.57s
4.81d (7.2)
3.44 dd
(10.9, 2.7)
3.69 dd
8
1′
6′
2.52s
4.91d(7.1)
3.51dd
(11.5, 4.2)
3.70 br d
(11.5)
In the present study, we reinvestigated the root ex-
tract of C. taiwanianum and the known â-sitosterol,19
sitosteryl 3-O-â-D-glucopyranoside,19 â-amyrin,20 4-hy-
droxyacetophenone,21 3,4-dihydroxyacetophenone (1),22
cynandione A (2),23 and two new compounds, cynanon-
esides A (3) and B (4). This paper also deals with the
structural elucidation of the compounds 3 and 4, and
the revision of the cynandione A (2) structure.23
(10.9, 4.7)
60.7
60.5
The comparison of 1H- and 13C-NMR data of 3 with
those of 1 indicated that the former was the glucoside
of the latter. Acidic hydrolysis of compound 3 yielded
3,4-dihydroxyacetophenone (1) and glucose. The ano-
meric proton of 3 at δ 4.81 showed a NOESY correlation
with the phenyl proton at δ 7.10 (d, J ) 8.8 Hz),
indicating that compound 3 was 3,4-dihydroxyacetophe-
none 4-O-â-D-glucopyranoside.
Cynanoneside B (4) was an isomer of cynanoneside
A (3) (the molecular formula C14H18O8 was derived from
its negative ion FABMS spectrum and elemental analy-
sis). It had hydroxyl, aromatic, and conjugated ketone
absorption bands in its IR spectrum, and its UV
spectrum showed maxima similar to that of 2,4-dihy-
droxyacetophenone. Compound 4 contained an acetyl
group, an ABX system of phenyl protons, and a sugar
Cynanoneside A (3), an amorphous solid was deter-
mined to have a molecular formula of C14H18O8 on the
basis of its molecular ion peak in the FABMS spectrum
(negative) at m/ z 313 (M+ - 1) and elemental analysis.
UV spectrum showed similar maxima to that of 3,4-
dihydroxyacetophenone (1).24 The IR spectrum indi-
cated the presence of a hydroxyl group (3400 cm-1), a
conjugated ketone (1660 cm-1), and an aromatic ring
1
(1600 and 1500 cm-1). The H-NMR spectrum (Table
1) of 3 showed the presence of an acetyl group at δ 2.57
(3H, s), an ABX system of phenyl protons at δ 6.88 (1H,
dd, J ) 8.8, 3.0 Hz), 6.95 (1H, d, J ) 3.0 Hz), and 7.10
(1H, d, J ) 8.8 Hz), a phenolic proton at δ 9.29 (1H, s),
which disappeared on D2O exchange, and a sugar
moiety at δ 3.44 (1H, dd, J ) 10.9, 2.7 Hz), 3.69 (1H,
dd, J ) 10.9, 4.7 Hz), and 4.81 (1H, d, J ) 7.2 Hz).
Among the 14 13C-NMR signals (Table 1) of 3, two
acetyl, six phenyl, and six sugar signals were observed.
The signals at δ 149.3 and 151.7 suggested two ortho
oxygenated phenyl carbons, while the six sugar 13C
signals indicated that the sugar moiety was a glucose.
Acetylation of 3 with Ac2O and pyridine afforded a
pentaacetate product 5 [amorphous solid; 1755 and 1740
cm-1; δ 2.01, 2.03, 2.05, 2.06, and 2.26 (each 3H, s)].
1
moiety as revealed from its H-NMR spectrum (Table
1). Two signals of phenyl carbons at δ 159.2 and 162.9
showed that the two oxygenated groups were not ortho-
related. The signal of the phenyl carbon at δ 102.0
indicated that this carbon was linked to two oxygenated
carbons. The 13C-NMR chemical shifts of the sugar
moiety of 4 suggested that the sugar moiety was a
glucose. The acetylation of 4 yielded a tetraacetate
product 6 [amorphous solid; 3350 and 1735 cm-1; δ 2.01,
2.02, 2.03, and 2.05 (each 3H, s)] instead of a pentaac-
etate product. Two products, glucose and 2,4-dihy-
droxyacetophenone (7),25 were isolated from the acidic
hydrolysis of 4. Two substituents, consisting of a
X Abstract published in Advance ACS Abstracts, February 15, 1997.
S0163-3864(96)00256-X CCC: $14.00
© 1997 American Chemical Society and American Society of Pharmacognogy

Notes
J ournal of Natural Products, 1997, Vol. 60, No. 4 369
hydroxy and a glycosyl groups, were located at C-4 and
C-2 or reversed positions from the above evidence. The
signal at δ 4.91 (anomeric proton) showed a NOESY
correlation with the phenyl proton at δ 6.59 (d, J ) 2.0
Hz); therefore, the correct structure of 4 is 2,4-dihy-
droxyacetophenone 2-O-â-D-glucopyranoside.
Recently, Huang et al. isolated three new acetophe-
nones, cynandiones A, B, and C,23 from the same source,
and the structure of cynandione A was designated as
3′,4-diacetyl 2,2′,3,6′-tetrahydroxybiphenyl (2). This
designated structure appears to be incorrect for the
following reasons. Two acetyl groups are involved in a
similar chemical environment, but their chemical shifts
are quite different (δ 2.18 and 2.56 as in structure 2
and δ 2.07 and 2.59 as in structure 8).23 The great
difference in the chemical shift for H-4′ and H-5′ of
compounds 2 (δ 7.79 and 6.94) and 8 (δ 7.59 and 7.37)
was deduced from the effect of an acetyl group, but this
difference was not observed between H-5 and H-6 (δ 6.94
and 6.77 in 2, and 7.37 and 7.25 in 8). The NOESY
correlation between H-4′ and H-8′, but not between H-5
and H-8, is unexpected. We also isolated cynandione
A from the same source and revised its structure to be
9 (2,3′-diacetyl-2′,3,6,6′-tetrahydroxybiphenyl) based on
the following evidence.
Cynandione A revealed only one intramolecular hy-
drogen bonding signal at δ 12.80 as it was dissolved in
DMSO-d6 solvent. This finding ruled out the designated
structure 2 for cynandione A. The acetyl group situated
on the B-ring was conjugated to an aryl ring and gave
strong intramolecular hydrogen bonding with C-2′ hy-
droxy group. Due to the steric effect, the acetyl group
located at ring A was not coplanar with ring A, therefore
it failed to form hydrogen bonding and resonated at
higher field (δ 2.18). The IR absorption bands at 1705
(isolated ketone) and 1670 cm-1 (conjugated ketone) in
10 and the NOE experiment of its tetrametyl product
10 provide further evidence, so that the structure of
cynandione A must be revised as structure 9.
fractions were evaporated under reduced pressure to
dryness, and repeated separation and purification on
Si gel and C18 reversed-phase column chromatography
afforded nine pregnane oligoglycosides,18 â-sitosterol,
â-amyrin, 4-hydroxyacetophenone, 3,4-dihydroxyace-
tophenone, sitosteryl-3-O-â-D-glucopyranoside, cynanon-
eside A (325 mg), cynanoneside B (160 mg), and
cynandione A (3.65 g).
Exp er im en ta l Section
Cyn a n on esid e A (3): amorphous solid; [R]20 -5.0
Gen er al Exper im en tal P r ocedu r es. Melting points
were determined with Yanagimoto micromelting point
apparatus and are uncorrected. IR spectra were re-
corded on a Perkin-Elmer 781 spectrophotometer. UV
spectra were measured on a Hitachi U-3200 spectro-
photometer. Optical rotations were measured on a
J ASCO DIP-370 instrument. FABMS spectra were
obtained on a J EOL SX-102A spectrometer. 1H- and
13C-NMR, NOESY, and HMBC spectra were run on a
Bruker AC-300 spectrometer. Elementary analyses
were run on a Perkin-Elmer 2400, EA instrument.
P la n t Ma ter ia l. The root of Cynanchum taiwan-
ianum Yamazaki was bought from Cha-Yi, Taiwan, in
May 1993. The plant material was identified by Dr. Ih-
Sheng Chen, School of Pharmacy, Kaohsiung Medical
College, and a voucher specimen has been deposited at
the Herbarium of the Department of Botany of the
National Taiwan University, Taipei, Taiwan.
D
(c 1.0, EtOH); UV (MeOH) λmax (log ꢀ) 220 (4.14), 327
(3.66) nm; IR (dry film) νmax 3400 (OH), 1660 (CdO,
ketone), 1600, 1500 (aromatic), 1200, 1080, 1000 cm-1
;
1H and 13C NMR (DMSO-d6, 300 MHz, 75 MHz) Table
1; FABMS (negative) m/ z [M - 1]- 313 (16), 199 (30),
168 (27), 153 (100), 152(66), 151 (61), 122 (21); anal. C
53.49%, H 5.80%, calcd for C14H18O8, C 53.50%, H
5.73%.
Cyn a n on esid e B (4): amorphous solid; [R]20D -11.0
(c 1.0, EtOH); UV (MeOH) λmax (log ꢀ) 227 (3.75), 269
(3.64), 296 (3.48) nm; IR (dry film) νmax 3400 (OH), 1665
(CdO, ketone), 1604, 1497 (aromatic), 1203, 1085, 1000
1
cm-1; H and 13C NMR (DMSO-d6, 300MHz, 75 MHz)
Table 1; FABMS (negative) m/ z (M - 1)- 313 (15), 199
(36), 168 (30), 153 (100), 152 (68), 151 (62), 122 (19);
anal. C 53.56%, H 5.78%, calcd for C14H18O8, C 53.50%,
H 5.73%.
Extr a ction a n d Isola tion . The roots of C. taiwan-
ianum (5 kg) were extracted twice with EtOH (30 L) at
50 °C. The EtOH extract was evaporated in vacuo,
yielding a black residue, which was suspended in H2O
(1 L). The aqueous solution was extracted with EtOAc
and n-BuOH, successively. The EtOAc and BuOH
Acetyla tion of 3 a n d 4. A solution of cynanoneside
A (3) (10 mg) or cynanoneside B (4) (10 mg) in pyridine
(0.5 mL) and Ac2O (0.5 mL) was left at room tempera-
ture overnight. The reaction mixture was poured into
iced H2O and then extracted with EtOAc (30 mL × 3).
The EtOAc layer was treated in the usual manner and

370 J ournal of Natural Products, 1997, Vol. 60, No. 4
Notes
purified by Si gel to yield pentaacetate (5) (12 mg) or
tetraacetate (6) (11 mg). Pentaacetate 5: mp 123-124
°C; IR (dry film) νmax 1755, 1740, 1595, 1492, 1230, 1070,
1032, 945 cm-1; 1H NMR (CDCl3, 300 MHz) δ 2.01, 2.03,
2.05, 2.06, 2.26 and 2.52, (each 3H, s), 3.84 (1H, m, H-5′),
4.13 (1H, dd, J ) 12.1, 2.5 Hz, Ha-6′), 4.26 (1H, dd, J )
12.1, 5.2 Hz, Hb-6′), 5.12 (1H, d, J ) 7.6 Hz, H-1′), 5.17
(1H, dd, J ) 9.1, 7.6 Hz, H-2′), 5.28 (1H, t, J ) 9.1 Hz,
H-3′), 5.31 (1H, t, J ) 9.1 Hz, H-4′), 7.06 (1H, d, J ) 9.0
Hz), 7.16 (1H, dd, J ) 9.0, 3.0 Hz), 7.36 (1H, d, J ) 3.0
Hz). Tetraacetate 6: mp 115-116 °C; IR (dry film) νmax
3350, 1735, 1605, 1494, 1248, 1130, 1045, 955 cm-1; 1H
NMR (CDCl3, 300 MHz) δ 2.01, 2.02, 2.03, 2.05 and 2.47
(each 3H, s), 3.88(1H, m, H-5′), 4.17 (1H, dd, J ) 12.4,
2.1 Hz, Ha-6′), 4.25 (1H, dd, J ) 12.4, 5.2 Hz, Hb-6′),
5.15 (1H, dd, J ) 9.1, 7.6 Hz, H-2′), 5.28 (1H, t, J ) 9.1
Hz, H3′), 5.31 (1H, t, J ) 9.1 Hz, H-4′), 7.06 (1H, d, J )
9.0 Hz, H-5), 7.16 (1H, dd, J ) 9.0, 3.0 Hz, H-6), 7.36
(1H, d, J ) 3.0 Hz, H-2).
Acid ic Hyd r olysis 3 a n d 4. A mixture of cynanone-
side A (3) (30 mg) and TsOH (10 mg) in H2O (5 mL)
was heated at 60 °C for 3 h. Then the reaction mixture
was extracted with EtOAc (10 mL × 3). After purifica-
tion, the organic layer gave 3,4-dihydroxyacetophenone
(1) (11 mg) [mp, 114-116 °C (lit.22; mp, 116 °C)] and
glucose was detected from the aqueous layer. The same
treatment of cynanoneside B (4) gave 2,4-dihydroxy-
acetophenone (7) [mp, 145-147 °C (lit25; mp 147 °C)]
and glucose.
(s, C-2), 150.2 (s, C-6), 151.7 (s, C-3), 159.4 (s, C-6′),
161.0 (s, C-2′), 198.7 (s, C-7′), 203.1 (s, C-7).
Ack n ow led gm en t. This research was supported by
the National Science Council and the National Health
Research Institute of the Republic of China.
Refer en ces a n d Notes
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heated under reflux. After 4 h, the solvent was evapo-
rated in vacuo; 30 mL of H2O was poured into the
residue, then extracted with ether (30 mL × 3). After
purification, the organic layer yielded tetramethoxy
ether derivative 10 (28 mg): colorless needles (MeOH);
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1
1280, 1090, 1038, 810, 710 cm-1; H NMR (CDCl3, 300
MHz) δ 2.32, 2.56 (each 3H, s), 3.47, 3.67, 3.73, 3.81
(each 3H, s), 6.69, 7.73 (each 1H, d, J ) 8.8 Hz, H-5′,
H-4′), 6.92, 6.94 (each 1H, d, J ) 9.0 Hz, H-4, H-5); 13
C
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NMR (CDCl3) δ 30.5 (q, C-8′), 30.9 (q, C-8), 55.9 (q, 6′-
OMe), 56.0 (q, 3-OMe), 56.6 (q, 6-OMe), 61.3 (q, 2′-OMe),
106.4 (d, C-5′), 111.3 (d, C-4), 112.7 (d, C-5), 118.7(s,
C-3′), 121.5 (s, C-1′), 125.7 (s, C-1), 131.5 (d, C-4′), 133.1
NP960256B