4
96
B. Wungsintaweekul et al. / Phytochemistry 72 (2011) 495–502
0
0
00
00
et al., 1993), rhinchoin Ia (31) (Foo, 1987), cinchonain Id (32) (Chen
et al., 1993), (4S,8R,9S)-4,8-bis(3,4-dihydroxyphenyl)-3,4,9,10-tet-
rahydro-5,9-dihydroxy-2H,8H-benzo[1,2-b:3,4-b ]dipyran-2-one
172.7 (MeCO-3 ), 3: 172.6 (MeCO-4 ), 5: 172.6 (MeCO-4 )]. The
absolute configurations of the C-2 of 2, 3, and 5 were determined
to be 2R due to the detection of a positive Cotton effect at
330 nm and a negative Cotton effect at 295 nm in their CD spectra.
0
(33) (Chen et al., 1993), cinchonain Ic (34) (Chen et al., 1993),
0
0
00
(
4R,8R,9S)-4,8-bis(3,4-dihydroxyphenyl)-3,4,9,10-tetrahydro-5,9-
From these results, the structures of 3 -acetyl astilbin (2), 4 -acetyl
astilbin (3), and 4 -acetyl isoastilbin (5) were determined to be
(2R,3R)-5,7,3 ,4 -tetrahydroxyflavanonol 3 -acetyl rhamnoside or
(2R,3R)-3 -acetyl astilbin (2), (2R,3R)-5,7,3 ,4 -tetrahydroxyflava-
nonol 4 -acetyl rhamnoside or (2R,3R)-4 -acetyl astilbin (3), and
(2R,3S)-5,7,3 ,4 -tetrahydroxyflavanonol 4 -acetyl rhamnoside or
(2R,3S)-4 -acetyl isoastilbin (5), respectively.
3 -Acetyl engeletin (4) was assigned the molecular formula
23 24
C H O11, as determined from its molecular ion [M + Na] peak
at 499.1237 in HRFABMS. The H NMR spectrum of 4 indicated
the structure to be a flavanonol rhamnoside like 2 from the similar-
ity between the two spectra, and 4 was recognized to have a 1,4-
0
00
dihydroxy-2H,8H-benzo[1,2-b:3,4-b ]dipyran-2-one (35) (Chen
et al., 1993), phyllocoumarin (36) (Foo, 1989), epiphyllocoumarin
0
0
00
0
0
0
0
(37) (Foo, 1989), trans-resveratrol (38) (Nakajima et al., 1978),
0
0
00
piceatannol (39) (Yao et al., 2005), isorhapontigenin (40) (Silayo
et al., 1999), eucryphin (41) (Tschesche et al., 1979), (ꢀ) syring-
aresinol (42) (Deyama, 1983), 5-O-caffeoylshikimic acid (43)
0
0
00
0
0
0
0
(Silayo et al., 1999), caffeic acid (44) (Flamini et al., 2001), and pro-
+
tocatechuic acid (45) (Wu et al., 2007) (Fig. 1).
1
The spectroscopic features of the new compounds (1–5) were
very similar to one another, suggesting they were flavonoid glyco-
00
sides and 2 -acetyl astilbin (1) was assigned the molecular for-
+
mula, C23
H
24
O
12, as determined from its molecular ion [M + H]
2 2
disubstituted B-ring from its A B -type aromatic proton signals [d
1
peak at m/z 493.1355 in HRFABMS. The H NMR spectrum of 1
showed a pair of doublet aromatic proton signals [d 5.90 (d,
J = 2 Hz) and 5.92 (d, J = 2 Hz)] and ABX-type aromatic proton sig-
nals [d 6.76 (d, J = 8 Hz), 6.79 (dd, J = 8, 2 Hz) and 6.93 (d, J = 2 Hz)],
and it was suggested that the aglycone moiety was a 2,3-trans fla-
6.82 (d, J = 8 Hz), 7.36 (d, J = 8 Hz)] while ABX-type aromatic pro-
ton signals were observed in 2. That is the only difference between
these two compounds. Acid hydrolysis of 4 gave (+)-dihydroka-
empferol (19) as an aglycone and a sugar moiety, which was iden-
tified as L-rhamnose by GC analysis. In the HMBC spectrum of 4,
vanonol from the characteristic signals for H-2 and 3 observed at d
correlations were observed (i) from the anomeric proton of rham-
nose [d 4.08 (d, J = 1.5 Hz) to C-3 (d 79.2) and (ii) from H-3 [d 4.91
1
00
5
.11 (d, J = 10.5 Hz) and 4.53 (d, J = 10.5 Hz), respectively. The
H
NMR spectrum also indicated the presence of a rhamnose moiety
(dd, J = 10, 3 Hz)] to the carbonyl carbon (d 172.6), which suggested
0
00
from the following signals: [d 3.97 (d, J = 2 Hz), 1.18 (d, J = 6 Hz)],
its structure to be (2R,3R)-5,7,4 -trihydroxyflavanonol 3 -acetyl
00
00
00
which are unique for the H-1 and Me-6 of the sugar, respectively.
rhamnoside or (2R,3R)-3 -acetyl engeletin (4).
Acid hydrolysis of 1 gave (+)-taxifolin (18) as an aglycone and a su-
Corbulain Ia (6) and Ib (7) were assigned the molecular formula
+
gar moiety, which was identified by GC analysis as
HMBC spectrum of 1 indicated the bonding position of
to be C-3 according to the H–C long-range connectivity of H-1 [d
.97 (d, J = 2 Hz)] to C-3 (d 78.3). The spectrum supported the
L-rhamnose. The
C
24
H
20
O
8
, as determined from their molecular ion [M + H] peak at
+
L
-rhamnose
m/z 437.1242 and the [M] peak at m/z 436.1187 in HRFABMS,
respectively. The H and C NMR spectroscopic data of 6 and 7
were similar to those of cinchonain Ia (28) and Ib (30), respectively.
0
0
1
13
3
1
NMR assignments since the aromatic proton signals at d 6.79 (dd,
J = 8, 2 Hz) and 6.93 (d, J = 2 Hz) showed correlations with C-2 (d
However, the H NMR spectra showed the presence of a 1,4-disub-
stituted phenyl group [6: d 7.09 (2H, d, J = 8.5 Hz), 6.68 (2H, d,
J = 8.5 Hz); 7: d 7.28 (2H, d, J = 8.5 Hz), 6.77 (2H, d, J = 8.5 Hz)]
and a 1,3,4-trisubstituted phenyl group [6: d 6.60 (1H, d,
8
3.7). Furthermore, a correlation of the proton resonance of rham-
00
nose at d 4.87 (H-2 ) with the carbonyl carbon signal at d 171.5
00
(
MeCO-2 ) suggested that the bonding position of the acetyl moi-
J = 2 Hz), 6.69 (1H, d, J = 8 Hz), 6.51 (1H, dd, J = 8, 2 Hz); 7: d 6.52
(1H, d, J = 2 Hz), 6.60 (1H, d, J = 8 Hz), 6.42 (1H, dd, J = 8, 2 Hz)], in-
stead of the two 1,3,4-trisubstituted phenyl groups found in the
cinchonain I series. In the HMBC spectra of 6 and 7, correlations
00
ety was C-2 . The absolute configuration of the C-2 of 1 was deter-
mined as 2R due to the detection of a positive Cotton effect
(
1
[h]328 + 6900, [h]295 – 39,400) in the CD spectrum (Gaffield et al.,
975). On the basis of the above spectroscopic evidence, 1 was
0
0
were observed from the H-7 [6: d 4.44 (dd, J = 7,1.5); 7: d4.52
0
0
00
00
00
00
found to be a new compound with the structure (2R,3R)-5,7,3 ,4 -
tetrahydroxyflavanonol 2 -acetyl rhamnoside or (2R,3R)-2 -acetyl
(dd, J = 7.5,1.5)] to C-2 and 6 [6: d115.3 (C-2 ), 119.4 (C-6 ); 7:
00
00
00
00
d115.0 (C-2 ), 119.2 (C-6 )], which suggested the bonding position
of the catechol group to be C-7 . The NOE spectrum of 7 indicated
the configuration of C-7 from enhancement of the H-2 and H-6
proton signals of its B-ring (d 7.28) when H-7 (d 4.52) was irradi-
ated, and no NOE enhancement was observed in the case of 6. The
CD spectra of 6 and 7 also showed good accordance to the corre-
sponding compounds (28 and 30) (Chen et al., 1993). From these
results, corbulain Ia (6) and Ib (7) were defined as 2-(4-hydroxy-
phenyl)-3,4,9,10-tetrahydro-3,5-dihydroxy-10-(3,4-dihydroxy-
0
0
astilbin.
0
0
00
00
00
0
0
3
-Acetyl astilbin (2), 4 -acetyl astilbin (3), and 4 -acetyl isoa-
0
0
stilbin (5) were assigned the molecular formula C23 12, which
H
24
O
is same as that of 1, as determined from their molecular ion
[
M + Na]+ peaks at m/z 515.1174, 515.1146, and 515.1188 in
1
HRFABMS, respectively. Their H NMR spectra indicated that they
shared a pair of doublet aromatic proton signals around the d
5
.9, ABX-type aromatic proton signal at d 6.8–7.0 and rhamnose
1
0
sugar moieties. From their H NMR spectra, 2 and 3 were deduced
to be as 2,3-trans flavanonol rhamnosides from their H-2 coupling
constants [2: d 5.09 (d, J = 11 Hz), 3: 5.06 (d, J = 11 Hz)], whereas 5
was found to be a 2,3-cis flavanonol rhamnoside [5: d 5.42 (d,
J = 2 Hz)]. Acid hydrolysis of these compounds (2,3, and 5) gave
phenyl)-(2R,3R,10R)-2H,8H-benzo [1,2-b:3,4-b ] dipyran-8-one (6)
and 2-(4-hydroxyphenyl)-3,4,9,10-tetrahydro-3,5-dihydroxy-10-
0
(3,4-dihydroxy phenyl)-(2R,3R,10S)-2H,8H-benzo [1,2-b:3,4-b ]
dipyran-8-one (7).
Gnetumontanin E (8), F (9), and G (10) were assigned the molec-
(
+)-taxifolin (18) as an aglycone with a common sugar moiety,
which was identified by GC analysis as -rhamnose. The HMBC
spectra indicated that these compounds commonly bore an
rhamnose moiety at their C-3 position, as determined by the H–C
ular formula C23
18 6 18 7 20 6
H O , C23H O , and C24H O , respectively, as
+
L
determined from their molecular ion peaks at m/z 390.1111 [M] ,
+
+
L
-
406.1071 [M] , and 404.1288 [M] in HRFABMS, respectively. The
spectroscopic features of these compounds were very similar to
one another and shared many features with those of gnetumonta-
00
long range correlations of H-1 [2: d 4.01 (d, J = 1.5 Hz), 3: 4.05
d, J = 1.5 Hz), 5: 4.96 (d, J = 1.5 Hz)] to C-3 (2: d 75.7, 3: 78.7, 5:
4.7). Additionally, the bonding positions of their acetyl moieties
were confirmed from the correlations between their rhamnose
1
(
7
nin C, a stilbene analogue (Li et al., 2004). The H NMR spectrum
of 8 showed a pair of meta-coupled aromatic proton signals [d
6.48 (d, J = 2.5 Hz) and 6.90 (d, J = 2.5 Hz)], aromatic proton reso-
nances from a 1,3,4-trisubstituted phenyl group [d 6.47 (dd, J = 8,
2 Hz), 6.53 (d, J = 2 Hz), and 6.70 (d, J = 8 Hz)], aromatic proton
00
proton signals [2: d 4.90 (dd, J = 10, 3, H-3 ), 3: 4.85 (t, J = 10, H-
4
0
0
00
), 5: 4.65 (t, J = 10, H-4 )] and carbonyl carbon signals [2: d