Furanoid and furofuranoid lignans from Daphne oleoides

Article abstract of DOI:10.1515/znb-2000-1217

Furofuranoid lignan (1) and (2) and furanoid lignan (3) have been isolated from Daphne oleoides and their structures elucidated through chemical and spectroscopic studies as 2-(3′-methoxy-4′-O-α-D-galactopyranosylphenyl)-6-(3″- methoxy-4″-hydroxyphenyl)-3,7-dioxabicyclo[3.3.0]octane (1), 2-(3′,5′-dimethoxy-4′-O-α-D-galactopyranosylphenyl)-6- (3″-methoxy-4″-hydroxyphenyl)-3,7-dioxabicyclo[3.3.0]octane (2), and 4,9′-dihydroxy-3,3′-dimethoxy-4′-O-ss-D-glucopyranosyl- 7′,9-epoxylignan (3). Two known lignans (4) and (5) have also been reported for the first time from this species.

Full text of DOI:10.1515/znb-2000-1217

Furanoid and Furofuranoid Lignans from Daphne oleoides
Muhammad Riaz3, Nisar Ullah3, Arshad M ehm ood3, Hafiz Rab Nawaz3,
Abdul M alik3, and Nighat Afzab
a International Centre for Chemical Sciences, H. E. J. Research Institute of Chemistry,
University of Karachi, Karachi-75270, Pakistan
b Pharmaceutical and Fine Chemical Division, PCSIR Karachi Complex, Karachi-75280,
Pakistan
Reprint requests to Prof. Dr. A. Malik
Z. Naturforsch. 55 b, 1216-1220 (2000); received July 1, 2000
Daphne oleoides, Thymeleceae, Furanoid and Furofuranoid Lignans
Furofuranoid lignan (1) and (2) and furanoid lignan (3) have been isolated from Daphne
oleoides and their structures elucidated through chemical and spectroscopic studies as 2-(3'-
methoxy-4'-0-a-D-galactopyranosylphenyl)-6-(3"-methoxy-4"-hydroxyphenyl)-3,7-dioxabi-
cyclo[3.3.0]octane (1), 2-(3',5'-dimethoxy-4'-0-a-D-galactopyranosylphenyl)-6-(3"-methoxy-
4"-hydroxyphenyl)-3,7-dioxabicyclo[3.3.0]octane (2), and 4,9'-dihydroxy-3,3'-dimethoxy-4'-
0-ß-D-glucopyranosyl-7',9-epoxylignan (3). Two known lignans (4) and (5) have also been
reported for the first time from this species.
Introduction
of naturally occurring furofuranoid lignans is char-
acteristically in the cis configuration, and the LH
NM R spectrum (Table I) indicated that this was
true for 1. The aryl substituents of C-2 and C-6
can be either axial or equatorial, allowing for three
types of stereoisomers. Compound 1 was con-
cluded to be an equatorial-equatorial isomer on
Daphne oleoides L. (Thymeleceae) is a xero-
phytic shrub found in northern hilly regions of Pa-
kistan. It finds a variety of uses in folk medicines
[1]. A num ber of compounds have previously been
reported from the chloroform soluble extract of
this plant. Following further studies on the ethyl
acetate soluble fraction of D. oleoides, it has been
possible to isolate two new furofuranoid lignans 1
and 2, a furanoid lignan 3 and two known lignans
4 [2] and 5 [3] reported for the first time from
this species.
the basis of the following features of its
NM R
spectrum [4,5]: (1) similar environment for m eth-
ine protons 1-H and 5-H and hence the similar
chemical shift at d 3.08 (2H, m); (2) similar chemi-
cal shift of benzylic protons at d 4.70 (2H, J = 5.0
Hz); (3) the presence of two equatorial methylene
protons at C-4 and C-8, respectively, found at d
4.18-4.28 due to the deshielding by the equatorial
Results and Discussion
Com pound 1: The IR spectrum showed absorp- aromatic rings.
tions at 3510, 1645 and 1470 cm -1 characteristic
for hydroxyl and aromatic moieties, respectively.
The molecular formula of 1 was assigned as
C26H 32O n through HR-MS (neg., FAB) showing
the [M+-H] peak at m /z 519.1920 (calcd. for
C ^ j O n : 519.1919). The 13C NM R experiment
revealed signals for four methylene, fourteen
methine, two methyl and six quaternary carbons.
The presence of a carbohydrate moiety was evi-
dent from the !H NM R (anomeric equatorial pro-
ton at (5 4.72, d, / = 2.0 Hz) and 13C NMR
spectrum (anomeric carbon at d 100.98 and other
oxygen bearing carbons at (3 61.94, 68.41, 71.10,
71.80, and 72.60). A comparison of the signals for
these carbons with those reported in the literature
[6] revealed its identity as a-D-galactopyranoside,
The
NM R spectrum indicated the presence of which was further confirmed by the comparative
two methoxy groups ((3 3.81 and 3.83) and the sig- TLC of the sugar moiety with an authentic sample
nals between d 3.08 and 4.70 indicated the pres- after the acid hydrolysis of compound 1.
ence of a furofuranoid moiety [4]. The compound
1 was, therefore, clearly a derivative of 2,6-diaryl-
3,7-dioxabicyclo[3.3.0]octane. The C-l-C-5 bond
The remaining problem was to locate the rela-
tive positions of various substituents in the two
aromatic rings. The peak at m /z 151 in EI-MS was
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M. Riaz et al. • Furanoid and Furofuranoid Lignans from Daphne oleoides
Table I.
and 13 NMR data for compounds 1 and 2.
Compound 1
Compound 2
Carbon
atom
Connectivity 13C NMR JH NMR (HMQC)
Carbon
atom
Connectivity
13C NMR !H NMR (HMQC)
[6/ppm]
[<Vppm]
[(3/ppm]
[ö/ppm]
1
2
4
CH
CH
c h 2
-
CH
CH
CH
-
C
CH
C
C
CH
CH
-
C
CH
54.7
85.5
72.0
-
3.08 (m)
1
2
4
-
5
6
8
-
1'
2'
3'
4'
5'
6'
1"
2"
3''
4"
5"
6"
-
CH
CH
CH2
-
CH
CH
c h 2
-
c
CH
C
C
C
54.4
85.4
73.0
-
54.3
85.7
72.8
-
136.4
103.1
148.9
140.0
149.9
103.1
132.9
110.4
147.6
145.5
116.1
121.0
-
3.08 (m)
4.70 (d, J = 5.0 Hz)
3.81-3.96 (m ,/3-H ),
4.61-4.32 (m, a -H )
3.08 (m)
4.70 (d. J = 5.0 Hz)
3.8-3.9 (m, /3-H)
4.18-4.28 (m, a -H )
-
6.96 (d,7 = 1.7 Hz)
-
-
4.79 (d, J = 4.8 Hz)
3.78-3.92 (m, a -H )
4.22-4.30 (m, /3-H)
3.08 (m)
4.71 (d, J = 5.0 Hz)
3.8-3.92, (m, a -H )
4.2-4.29, (m, /3-H)
-
5
6
8
54.9
85.49
71.98
-
136.2
110.9
149.2
146.6
117.9
122.7
-
132.8
110.2
147.2
145.4
115.2
120.1
100.98
68.41
71.80
71.10
72.60
61.94
1'
2'
3'
4'
5'
6'
6.54 (s)
-
-
-
7.07 (d, J = 8.23, Hz)
6.86 (dd, J = 1.7,
8.23 Hz)
-
6.54 (s)
-
6.79 (d, J = 2.0 Hz)
-
CH
C
CH
C
-
1''
2"
3"
4"
5"
6"
V"
2"'
6.90 (d, J = 1.8 Hz)
-
-
C
C
C
-
CH
CH
-
7.00 (d, J - 8.4 Hz)
6.87 (dd, J = 2.0, 8.4. Hz)
-
CH
CH
C
CH
CH
CH
CH
CH,
c h 3
7.00 (d, J = 8.1 Hz)
6.81 (dd, J = 1.6,8.1 Hz)
4.72 (d, J = 2.0 Hz)
3.33 (m)
3.40 (m)
3.32 (m)
4.73 (d, J = 2.0 Hz)
3.36 (m)
3.41 (m)
3.34 (m)
3.31 (m)
3.30 (m)
3.82 (6H. s)
3.83 (3H, s)
1'"
CH
CH
CH
CH
CH
c h 2
2 x OMe
101.1
68.5
71.62
71.20
71.99
62.3
2
3
„,
" ,
3"'
4„,
4'"
5"'
6'"
2 x
OMe
3.30 (m)
3.28 (m)
5"'
6"'
56.1, 55.9 3.83 (3H, s), 3.81
(3H, s)
56.4,
55.9
due to known fragmentation of furofuranoid lig- to the proposed structure of 1 as 2-(3'-methoxy-
nans [7], allowing us to assign one of the two m e- 4'-0-a-D-galactopyanosylphenyl)-6-(3"-methoxy-
thoxy and a hydroxy group to one of the aromatic
ring and the remaining methoxy group to the
other. The signals in the aromatic region of the *H
NM R spectrum at d 7.07 (1H, d, J = 8.23 Hz), 7.00
(1H, d, J = 8.10 Hz), 6.96 (1H, d, J = 1.7 Hz), 6.90
(1H, d, J = 1.8 Hz), 6.86 (1H, dd, J = 1.7, 8.23 Hz)
and 6.81 (1H, dd, J = 1.8, 8.10 Hz) were due to 5'-
H, 5"-H, 2'-H, 2"-H, 6'-H , and 6"-H, respectively,
revealing the 3', 4' and 3", 4" substitution pattern
in the aryl groups. The positions of various groups
in the aromatic rings were further confirmed by
an HM BC experiment. The anomeric proton of
4"-hydroxyphenyl)-3,7-dioxabicyclo[3.3.0]octane.
Com pound 2: The molecular formula of 2 was
assigned as C27H340 12 through HR-MS (neg.,
FAB) showing the [M+-H] peak at m /z 549.1997
(calcd. for C z t ^ O ^ : 549.1988.) The IR, lH and
13C NM R spectra were very similar to 1. The m o-
lecular formula of 2 indicated the presence of an
additional methoxy group. This group was as-
signed to C-5' as protons at C-2' and C-6' were
observed together at
d 6.54 in the !H NM R
spectrum. Further confirmation was obtained by
an HM BC experiment which showed 3J interac-
the sugar moiety at <5 4.72 showed the 3J interac- tions of C-5' (d 149.9) with protons 2'-H and 6'-
tions with C-4' at d 146.6, while another 3J interac-
tion was observed between methoxy protons at <5
3.83 and C-3' at d 149.2. The protons at <5 3.81
showed 3J- interaction with C-3" at d 147.2 and of
C-4" at 6 145.4 with 2"-H (Ö 6.90) and 6"-H (d
H. The structure of 2 was, therefore, assigned as
2-(3',5'-dimethoxy-4'-O-a-D-galactopyranosyl-
phenyl)-6-(3"-methoxy-4"-hydroxyphenyl)-3,7-di-
oxabicyclo[3.3.0]octane. The JH, 13C and HM QC
data are given in Table I to reveal the close sim-
6.81), confirming the presence of methoxy and hy- ilarities between 1 and 2.
droxy groups at C-3" and C-4", respectively. O ther
HM BC interactions were in complete agreem ent
Com pound 3: The molecular formula of 3 was
assigned as C26H340n by HR-MS (neg., FAB),
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1218
M. Riaz et al. • Furanoid and Furofuranoid Lignans from Daphne oleoides
showing the molecular ion peak [M+-H] at m /z
521.2088 (calcd. for Q ^ O n : 521.2079). The IR
spectrum of compound 3 showed absorptions at
nelignan and allowed us to assign the methoxy and
hydroxy moieties at C-3' and C-4', respectively.
The presence of the remaining methoxy group
3510, 1640 and 1470 cm “1, characteristic for a hy- and the sugar moiety at C-3" and C-4", respectively,
droxyl and aromatic moieties, respectively. M eth-
ylation of 3 with diazomethane yielded 3a with an
additional methoxy group, indicating the presence
of a phenolic group in 3.
was confirmed on the basis of an HMBC experi-
ment. The proton at d 7.1 (5'-H ) showed cross
peaks to carbons at <3 148.9 (C-4'), 137.7 (C -l') and
110.3 (C-2'). Likewise proton 6'-H (<3 6.77)
The 'H NM R spectrum of 3 displayed the pres- showed connectivities to carbons at d 148.9 (C-4')
ence of six aromatic protons in a complicated
pattern at <3 7.10, 6.88, 6.77, 6.73, 6.65, and 6.56,
respectively, two methoxy groups at d 3.73 and 3.74
and 137.7 (C -l'). O ther im portant cross peaks
were found between proton 5-H ((3 6.65) and car-
bons at <3 145.6 (C-5), 144.6 (C-4) and 131.1 (C-l),
(each 3H, s). The remaining protons were found be- proton 7-H ((3 2.80) and carbons at d 131.1 (C -l),
tween <3 2.41 and 4.96. The D EPT experiment re- 41.9 (C-8) and proton d 4.96 (7'-H ) with carbons
vealed the signals of fourteen methine, four m ethy- at (3 52.4 (C-8') and 137.7 (C -l'). The configura-
lene and two methyl carbon atoms. The quaternary
atoms were determined by subtracting these from
broad band spectrum. Both !H and 13C NM R
spectra indicated the presence of a sugar moiety
(anomeric proton at d 4.84, J = 7.4 Hz, and anom-
eric carbon at d 100.42 in addition to other oxygen
bearing carbons at d 60.8, 69.6, 71.9, 76.9 and 77.0).
tions of the chiral centres were confirmed by NOE
difference measurements. Irradiation of a proton
at (3 2.80 (8-H) caused an enhancement of the sig-
nal at (3 2.56 (8'-H ) and similarly 7'-H showed
N O E interactions with 7-H and 9'-H. Irradiation
of the signal at (3 4.84 (anomeric proton) caused an
enhancem ent of the peak coupled with an ortho
Acid hydrolysis of 3 provided 3b and sugar m oi- proton at d 7.1 (5'-H ), confirming the position of
ety; the latter was identified as /3-D-glucose by re- glucose linkage at C-4' which was further con-
tention time of its trimethylsilyl ether in gas chro- firmed by HM BC interactions. Biogenetic evi-
matography [8]. The ß configuration was further
dence was provided by co-occurrence of lariciresi-
confirmed by the coupling constant of the anom - nol, in the same plant. The structure of 3 was,
eric proton (J = 7.4 Hz).
Acetylation of 3 with acetic anhydride and pyri-
therefore, assigned as the tetrahydrofuran deriva-
tive 4,9'-dihydroxy-3',3-dimethoxy-4'-0-ß-D-glu-
dine gave a hexaacetate 3c revealing the six hy- copyranosyl-7',9-epoxylignan.
droxy groups. Five of these have already been ac-
counted by sugar and phenolic moieties, the
remaining one was shown to be a primary hydroxy
Experimental Section
General experimental procedures: IR spectra of
group through !H NMR (dd at d 4.20 and 3.74, 1H
each). It was confirmed by comparing the *H
NM R data of 3 and 3c, the latter showing a down-
field shift of these protons at 6 = 4.55 and 4.02,
respectively.
Treatment of aglycone 3b with diazomethane
gave the tetram ethyl ether 3d. As only one pheno-
lic group has been inferred in 3, the additional
phenolic group in 3d must arise by loss of a glu-
cose moiety confirming the phenolic O-linkage.
The 13C NM R spectrum was very similar to
those of laracinol and daphnelignan, respectively,
showing similarities in stereochemistry of these
compounds. It was also confirmed by similarities
in fragmentation pattern in EI-MS spectrum show-
ing characteristic fragments at m /z 137 and 123.
The fragment at m /z 137 was also found for daph-
all the compounds were measured on a Schimadzu
Infrared spectrophotom eter IR 460. E l mass
spectra were recorded on a Varian MAT 311,
FAB-MS m easurements were done on a JEOL-
HX 110 mass spectrom eter using glycerol as in-
ternal standard. NM R experiments were carried
out on a Bruker AMX-400 instrum ent (‘H: 400.1
MHz; 13C: 100.61 MHz). D EPT experiments were
carried out with pulse angles 6 = 45°, 90°, 135°.
Chemical shifts are in d with TMS as internal stan-
dard and coupling constants are in Hz. Pyridine-
d5 was used as solvent in all NM R experiments of
compounds 3, 4 and 5 whereas CDC13 with a few
drops of CD3OD was used as solvent in case of
compound 1 and 2. 2D experiments were done an
a Bruker AMX-500 instrument. Silica gel 60 (35-
70 mesh) was used for column chromatography.
TLC was carried out on a precoated Kieselgel 60,
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M. Riaz et al. • Furanoid and Furofuranoid Lignans from Daphne oleoides
1219
F254 aluminum sheet (Merck) using
a CHC13/
(calcd. for C27H 3 3 0 12: 549.1997). - MS (E l, 70 eV):
m /z (% ) = 388 (100 ) [M+-sugar moiety], 210 (11),
193 (12), 183 (15), 180 (14), 163 (18), 155 (23), 154
(68), 153 (47), 151 (45), 124 (24), 123 (30).
M eOH mixture 89:11 for compounds 4, 5 and
85:15 in case of 1,2 and 3); spots were visualized
by spraying with a solution of eerie sulphate in
10% h 2s o 4.
Acid hydrolysis and the identification of the
Collection o f plant material, extraction and isola- sugar part were done by the procedure described
tion: W hole plant m aterial of D. oleoides was col- for 1, and the sugar was identified as D-galactose.
lected from M ansehra district of N orth West Fron-
tier Province, Pakistan, and was identified by Prof.
Iftikhar Hussain Shah of Faculty of Pharmacy, Go-
mal University, D. I. Khan, Pakistan, in Feb. 1995
where a voucher specimen (DIU-2119x) has been
deposited in the Herbarium .
Com pound 3: IR (KBr): v = 3510,1640 and 1470
cm -1. - *H NM R and 13C NM R data is given in
Table II. - HR-M S (neg., FAB): m /z = 521.2088
[M+-H] (calcd. for C26H 3 3 0 n : 521.2079). - MS
(El, 70 eV): m /z (% ) = 360 (100) [M+-sugar moi-
ety], 236 (17), 194 (27), 137 (80), 123 (8), 66 (24).
Com pound 3a: To an ethereal solution of 3
Shade dried ground whole plant material (15
kg) of D. oleoides was extracted thrice with metha- (12 mg), freshly prepared C H 2N2 was added in ex-
nol. The combined methanolic extract was evapo- cess and the solution was kept at rt overnight.
rated under reduced pressure and to the resulting
gummy residue was added H20 and the mixture
Usual workup of the reaction mixture afforded 3a,
which precipitated as an am orphous powder on
was successively extracted with hexane, chloro- keeping its concentrated methanolic solution in
form, ethyl acetate and n-butanol. The ethyl ace- the cold. The XH NM R (500 MHz, pyridine-d5)
tate extract was subjected to column chrom atogra- showed an additional resonance at d 3.69 (3H, s,
phy using hexane-chloroform and chloroform-
m ethanol gradient systems to obtain fractions (A-
O CH 3). - HR-M S (neg., FAB): m /z = 535.2248
[M+-H] (calcd. for C ^ g O n : 535.2239).
M). The fraction
m ethanol (98:2) was subjected to column chroma- M eOH (5 ml) containing 1 N HC1 (4 ml) was re-
tography eluting with chloroform-methanol (96:4)
fluxed for 4 h, concentrated under reduced pres-
E obtained from chloroform-
Com pound 3b:
A solution of 3 (16 mg) in
to afford com pound 4 (40 mg) and 5 (30 mg) as sure and diluted with H 20 (5 ml). It was extracted
colourless am orphous powder. The column chro- with ethyl acetate and the residue recovered from
m atography of fraction G eluting with chloroform-
m ethanol (94:6) afforded the compounds
(50 mg), 2 (18 mg) and 3 (28 mg) as colourless
am orphous powders.
1
Table II. 'H and 13C NMR data of compound 3.
Carbon
atom
Connectivity
13C NMR ‘H NMR (HMQC)
[ö/ppm]
C om pound (1): IR (KBr): v = 3510, 1645 and
1470 cm -1. - JH and 13C NMR are given in Ta-
ble I. - HR-M S (neg., FAB), m /z = 519.1920 [M+-
H], (calcd. for C26H 31O n : 519.1919). - MS (El, 70
eV): m /z (% ) = 358 (48.2) [M+-sugar moiety], 205
(22.3), 196 (10.2), 190 (11.2), 180 (11.6), 163 (30.6),
162 (9.5), 152 (23.5), 151 (100) 150 (30.5), 137
(46.67), 133 (9.6), 131 (8.29).
_
1
2
3
4
5
6
7
-
C
CH
C
C
CH
CH
CH2
-
131.1
120.6
145.6
144.6
115.4
112.3
32.1
-
6.88 (d ,J = 1.9 Hz)
-
-
6.65 (d, J = 7.9 Hz)
6.56 (dd, J = 7.9, 1.9 Hz)
2.80 (dd, J = 13.2, 5.0 Hz)
2.41 (dd, J = 13.2, 10.5 Hz)
2.80 (m)
3.88 (d, J = 8.5, 6.9 Hz)
3.65 (dd, J = 8.5, 4.5 Hz)
-
41.9
71.9
-
8
9
-
CH
CH2
-
Hydrolysis of 1: A solution of compound
1
(8 mg) in m ethanol (1 ml) and IN HCl (1 ml) was
refluxed for 4h. The solution was concentrated un-
der reduced pressure and diluted with H 20 (5 ml).
It was extracted with ethyl acetate. The sugar in
the aqueous phase was identified as galactose by
comparative TLC with an authentic sample using
solvent system «-BuOH/EtOAc/Z-PrOH/HOAc/
H 20 (7:20:12:7:6). The TLC was run thrice in the
same direction and spots were visualized with ani-
line phosphate reagent. The sugar was found to be
D-galactose.
1'
2'
3'
4'
5'
6'
7'
8'
9'
-
C
CH
C
C
CH
CH
CH
CH
CH2
-
137.7
110.3
147.4
148.9
112.8
115.2
81.6
52.4
58.6
-
6.73 (d, J = 1.8 Hz)
-
-
7.1 (d, J = 8.4 Hz)
6.77 (dd, J = 8.4, 1.8 Hz)
4.96 (d, J = 7.0 Hz)
2.56 (m)
4.20 (dd, J = 11.5, 7.1 Hz)
3.74 (dd, 11.5, 4.2 Hz)
4.84 (d, J = 7.4 Hz)
3.15 (m)
3.22 (m)
3.54 (m)
3.45 (m)
3.81 (m)
1"
2"
3''
4"
5"
6"
CH
CH
CH
CH
CH
CH
100.42
71.9
76.9
69.6
77.0
C om pound 2: IR (KBr): v = 3520, 1650 and 1478
cm -1. - !H and 13C NMR data are given in Ta-
ble I. - HR-M S (neg., FAB), m /z = 549.1998 [M+],
60.8
55.6, 55.8
3.73, 3.74 (each for 3H, s)
OMe x 2 CH3
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1220
M. Riaz et al. • Furanoid and Furofuranoid Lignans from Daphne oleoides
the organic phase was subjected to preparative
TLC to obtain compound 3b which was identified
as the corresponding aglycone of 3. The *H NM R
(500 MHz, pyridine-d5) of compound 3b showed
similar resonances as 3, except for the now absent
signals of the sugar moiety. - HR-M S (neg., FAB):
R3
m /z
= 359.1542 [M+-H] (calcd. for C2oH23 0 6:
359.1494).
Com pound 3c: A mixture of 3 (4 mg), Ac20
(6 ml) and pyridine (7 ml) was stirred overnight at
rt and worked up in the usual way to afford 3c.
The !H NMR spectrum (500 MHz, pyridine-d5)
showed, in relation to 3, additional resonances at
(3 2.21 (3H, s, 4-OOCM e), 2.15 (3H, s, 9'-
OOCM e), 2.02 (12H, s, 4 xOOCMe, sugar). - HR-
MS (neg., FAB): m /z = 773.2742 [M+-H] (calcd.
for C38H 450 17: 773.2734).
1: R1 = R4 = CH3, R2 = a-D-galactopyranosyl; R3 = R5 = H.
2 R1 = R4 = CH3, R2 = a-D-galactopyranosyl; R3 = OCH3, R5 = H.
Com pound 3d: M ethylation of 3b as described
for
3 afforded compound 3d. The XH NM R
spectrum (500 MHz, pyridine-d5) showed in rela-
tion to 3b, an additional resonance at c3 3.75 (6H,
s, 2xOMe). - HR-MS (neg., FAB): m /z = 387.1863
[M+-H] (calcd. for C22H 270 6: 387.1854).
3: R1 = ß-D-glucopyranosyl; R2 = R3 = H.
3a: R1 = ß-D-glucopyranosyl; R2 = H, =R3 =CH3
3b: R1 = R2 = R3 = H
3c: R1 = Tetra-O-acetyl-ß-D-glucopyranosyl; R2 =R3 = COCH3
3d: R1 = R3 = CH3, R2 = H
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(1989).
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Chem. Soc. 101, 1265 (1979).
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(1973).
[8] K. R. Markham, Techniques of Flavonoids Identifi-
[4] W. D. Macrae, G. H. N. Towers, Phytochemistry 24,
561 (1985).
cation, p.52. Academic Press, London (1982).
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