Ipobscurines C and D: Macrolactam-type indole alkaloids from the seeds of Ipomoea obscura

Article abstract of DOI:10.1016/S0031-9422(02)00756-2

Separation of the methanolic seed extract of Ipomoea obscura afforded five indole alkaloids, three of them (ipobscurines B-D) being new natural products of a unique structural type characterized as serotonin hydroxycinnamic acid amide-type conjugates with a second phenylpropanoid moiety forming an ether with the 5-OH position of the indole nucleus. Due to an oxidative phenolic coupling between the two phenylpropanoid moieties of the supposed precursor ipobscurine B two 21-membered macrolactams with a phenol ether partial structure are formed: the trans-cis isomers ipobscurines C and D. Their structures were established on the basis of spectral data. Moreover, total synthesis of the racemic erythro- and threo-ipobscurine B 4′,4″-dimethyl ethers and the comparison with the corresponding derivative of natural (-)-ipobscurine B proved an erythro configuration of the latter.

Full text of DOI:10.1016/S0031-9422(02)00756-2

Phytochemistry 62 (2003) 1257–1263
www.elsevier.com/locate/phytochem
Ipobscurines C and D: macrolactam-type indole alkaloids from
the seeds of Ipomoea obscura§
Kristina Jenett-Siems, Robert Weigl, Macki Kaloga, Jutta Schulz, Eckart Eich*
Institut fur Pharmazie (Pharmazeutische Biologie), Freie Universitat Berlin, Konigin-Luise-Str. 2-4, D-14195 Berlin, Germany
¨
¨ ¨
Received 22 July 2002; received in revised form 16 December 2002
Abstract
Separation of the methanolic seed extract of Ipomoea obscura afforded five indole alkaloids, three of them (ipobscurines B-D)
being new natural products of a unique structural type characterized as serotonin hydroxycinnamic acid amide-type conjugates with
a second phenylpropanoid moiety forming an ether with the 5-OH position of the indole nucleus. Due to an oxidative phenolic
coupling between the two phenylpropanoid moieties of the supposed precursor ipobscurine B two 21-membered macrolactams with
a phenol ether partial structure are formed: the trans–cis isomers ipobscurines C and D. Their structures were established on the
basis of spectral data. Moreover, total synthesis of the racemic erythro- and threo-ipobscurine B 40,400-dimethyl ethers and the
comparison with the corresponding derivative of natural (ꢀ)-ipobscurine B proved an erythro configuration of the latter.
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Ipomoea obscura; Convolvulaceae; Indole alkaloids; Serotonin; Hydroxycinnamic acid amide-type conjugates; Ipobscurines; Neolignans
1. Introduction
In both cases the special structures are unique in the
plant kingdom.
The largest convolvulaceous genus Ipomoea comprises
species which are phytochemically characterised by the
occurrence of different types of alkaloids in the seeds.
The accumulation of ergoline alkaloids in a remarkable
amount of species is well-known since they were dis-
covered 40 years ago at the same time in Turbina cor-
ymbosa (L.) Raf. [syn.: Rivea corymbosa (L.) H. Hall.]
as well as in I. tricolor Cav. (syn.: I. violacea auct., non
L.) (Hofmann and Tscherter, 1960; Hofmann, 1961;
Amor-Prats and Harborne, 1993). However, species of
the subgenus Quamoclit show other structural types:
members of the section Calonyction accumulate indoli-
zidine alkaloids (Gourley et al., 1969; Dawidar et al.,
1977), whereas members of the section Mina show
pyrrolizidine alkaloids (Jenett-Siems et al., 1993, 1998).
We now report on the isolation and structure deter-
mination of a novel type of Ipomoea seed alkaloids from
I. obscura (L.) Ker-Gawl., a very common and wide-
spread paleotropic perennial herb, belonging to the
subgenus Eriospermum, section Erpipomoea. Five
serotonin hydroxycinnamic acid amide (HCA)-type con-
jugates could be characterized; three of them represent
novel natural compounds of a unique structural type.
2. Results and discussion
TLC examination of the methanolic seed extract of
I. obscura revealed the presence of several compounds
giving a positive reaction with van Urk’s reagent with
typical blue spots indicating a C-3-substituted indole
moiety (Mayer and Eich, 1975). Separation by column
chromatography led to the isolation of five compounds.
On the basis of spectroscopic analyses two of them
turned out to be Nb-(p-coumaroyl)serotonin (ipobscurine
A) and its 5-O-b-d-glucopyranoside, simple serotonin
hydroxycinnamic acid amides already known as con-
stituents of safflower seeds (Carthamus tinctorius L.,
§
Part 15 in the series ‘‘Phytochemistry and chemotaxonomy of the
Convolvulaceae’’. For part 14 see Kraft et al. [Phytochemistry 60
(2002) 167–173].
* Corresponding author. Tel.: +49-30-838-53724; fax: +49-30-
838-53729.
E-mail address: eckeich@zedat.fu-berlin.de (E. Eich).
0031-9422/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0031-9422(02)00756-2

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K. Jenett-Siems et al. / Phytochemistry 62 (2003) 1257–1263
Asteraceae) (Sakamura et al., 1978, 1980). Compounds
1–3 were found to be new natural products of a more
complex structure and named, respectively, ipobscurines
B–D.
Hz) as well as one hydroxymethylene group (ꢀ 3.58, 1H,
m and ꢀ 3.90, 1H, dd, J=11.5, 4.5 Hz). These data hinted
to the presence of a second phenylpropanoid moiety,
namely 7,8-dihydroxy-dihydroconiferyl alcohol. The
positions of the methoxy group as well as the linkage of
the additional phenylpropane residue were determined
by NOE experiments. Irradiation in the methoxy signal
led to an enhancement of the signal of H-200, whereas
irradiation in the hydroxymethine signal at ꢀ 4.43
caused positive NOEs at H-4 and H-6. The small
coupling constant of 4.0 Hz between the two hydroxy-
methine protons indicated that 1 existed as the erythro
isomer (Barata et al., 1978; Zacchino and Badano,
1988). This was confirmed by synthesis of both forms—
Using FAB MS measurements, the molecular mass of
1
1 could be determined as 518. In combination with H
and 13C NMR spectra a molecular composition of
C29H30N2O7 could be assumed. The 1H NMR spectrum
displayed characteristic signals of a serotonin and a
p-coumaroyl moiety as in ipobscurine A but in addition
a
1,2,4-tri-substituted aromatic system could be
observed. Furthermore, the spectrum showed one
methoxy group, two hydroxymethine groups at ꢀ 5.06
(1H, dd, J=4.0, 4.5 Hz) and ꢀ 4.43 (1H, dt, J=4.0, 4.5

K. Jenett-Siems et al. / Phytochemistry 62 (2003) 1257–1263
1259
erythro (6a) and threo (6b)— of the dimethyl ether of 1
(Fig. 1). The spectroscopic data of synthetic rac.
N-[2-[5-erythro-[2-[(3,4-dimethoxyphenyl)-2-hydroxy-1-
hydroxymethyl]ethoxy]indol-3-yl]ethyl]-4-methoxycinna-
moyl amide (6a) were identical with those of the di-
methyl ether of natural 1. In conclusion 1 represents the
(ꢀ)-erythro isomer; we propose ipobscurine B as trivial
name for this novel serotonin–HCA conjugate.
protons of a trans-double bond at ꢀ 7.09 (d, J=15.5 Hz,
H-70) and ꢀ 5.68 (d, J=15.5 Hz, H-80), revealing the
presence of a p-substituted cinnamic acid derivative.
Finally, correlations between H-600 and the hydroxy
group at C-700 as well as between the hydroxy groups at
C-700 and C-900 were also detected. Thus 2, which we
named ipobscurine C, represents a macrocyclic sero-
tonin–HCA conjugate.
Compound 2 displayed a molecular ion peak at m/z
516 in the EIMS spectrum, corresponding to a mole-
Compound 3 showed the same molecular ion peak as
1
2 in the EIMS spectrum. Regarding the H NMR spec-
1
cular formula of C29H28N2O7 (HREIMS). H and 13C
trum, the only striking difference compared to 2 was the
coupling constant J=12.5 Hz between H-70 and H-80
instead of J=15.5 Hz. This pointed to a cis-configur-
ation of the 7,8-double bond. Thus, 3, which we named
ipobscurine D, had to be the Z-isomer of 2.
The ipobscurines A–D are only present in mature
or—in smaller concentrations—in almost mature seeds.
Neither flowers and undeveloped fruits (diameter 3–7
mm) nor epigeal vegetative material and roots show any
ipobscurine. These compounds are synthesized appar-
ently in the late phase of the seed development since the
first small concentrations can be detected in elder
NMR spectra were quite similar to those of 1 revealing
the presence of a 1,2,3,5-tetra-substituted instead of a
1,2,4-tri-substituted aromatic system. These data sug-
gested the existence of an ether bridge between C-40 and
C-500, formed by an oxidative phenolic coupling. In the
NOESY spectrum of 2, cross-peaks between H-6 and
H-800 revealed the attachment of the arylglycerol moiety
at position 5 of the indole ring. The position of the
methoxy group could be deduced from NOESY corre-
lations to H-200 (ꢀ 6.79 d, J=1.5 Hz). Further corre-
lations were observed between H-20/60 and the olefinic
Fig. 1. Synthesis of rac. N-[2-[5-erythro- and threo-[2-[(3,4-dimethoxyphenyl)-2-hydroxy-1-hydroxymethyl]ethoxy]indol-3-yl]ethyl]-4-methoxy-
cinnamoyl amide (6a/6b) from 4-methoxycinnamic acid.

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K. Jenett-Siems et al. / Phytochemistry 62 (2003) 1257–1263
though immature fruits (diameter: 10 mm). The ipob-
scurines A and B were found in any of the provenances
collected in the Asian wild (Sri Lanka/6 prov.; Bali/Java
(Indonesia)/2 prov.) with 0.054–0.104% (dry wt.) for
ipobscurine A and up to 0.062% for B, respectively. The
Asian provenances belong to the cream or white
blooming form of I. obscura var. obscura with or with-
out purple, red or brown centre.
Ipobscurine C in seeds from the wild was only deter-
minable in one provenance of Sri Lanka (0.047%).
However, mature seeds obtained by cultivation in the
greenhouse from seeds originally collected on Java also
contained this macrocyclic lactam. In this latter case the
A:B:C relation was 0.136:0.011:0.079%. Ipobscurine D
was only present as a minor component.
Seeds harvested in the greenhouse originating from
three different locations of Tanzania contained only
very low concentrations of ipobscurine B. Ipobscurine C
was not detectable. Their content of ipobscurine A has
been 0.043, 0.057, and 0.061%, respectively. These
African provenances represented the orange-yellow
blooming form of I. obscura var. obscura. The main
components of the seeds (Asian and African origin) are
caffeic acid derivatives of the chlorogenic acid type (0.8–
1.6%).
Since no threo-configurated compound could be
detected and 1 is present together with 2/3, we assume
that ipobscurine B (1) is the precursor of the macro-
lactams (Fig. 2). Comparison of the coupling constants
between H-700 and H-800 of 1, 2, and 3 (J=4.0 Hz, J <3.0
Hz, and J=3.0 Hz, respectively) clearly demonstrates
that all isolated ipobscurines belong to the erythro series
(Barata et al., 1978; Zacchino and Badano, 1988).
Determination of the absolute configuration by using
the method of Mosher failed (Ohtani et al., 1991), thus
further investigations concerning this problem are
necessary. The fact that compound 2 was only present
in two provenances analyzed, is a strong indicator that 2
cannot be an artefact of 1 since all samples were treated
in the same manner.
Though our group has investigated numerous con-
volvulaceous species from many genera over the years
ipobscurines were not detected in any other case. Com-
pounds arising from the amide formation between
serotonin and a hydroxycinnamic acid (e.g. p-coumaric
acid, ferulic acid) have been observed beside Carthamus
tinctorius (see Introduction) in two other asteraceous
species: Centaurea moschata L. (Sarker et al., 1997) and
C. cyanus L. (Sarker et al., 2001). Moreover, a cycli-
zation of such a conjugate between the side-chain of the
hydroxycinnamic acid moiety and the indole nucleus in
the positions 4 and 5 of the latter could be observed in
safflower seeds forming the phenol ether serotobenine
(Sato et al., 1985).
However, none of these asteraceous species contains
serotonin hydroxycinnamic acid amides with a second
phenylpropanoid moiety like the ipobscurines B–D. The
phenol ether partial structure between the 5-hydroxy-
indole nucleus of ipobscurine A and the second phenyl-
propanoid moiety forming ipobscurine B is somehow
comparable with certain dimeric phenylpropanoid par-
tial structures of lignin (Nimz, 1975) or 8.O.40-neo-
lignans (Zacchino and Badano, 1988; Wang et al.,
1998). Ipobscurine C should be the cyclic derivative of
its supposed precursor B formed by oxidative phenol
coupling between the arylglycerol and the p-coumaroyl
moieties originating a diaryl ether substructure (C-500–
O–C-40) with the result of a unique 21-membered
macrolactam.
Macrocyclic alkaloids with similar neolignan sub-
structures are known based on spermine as the amine
component, e.g. chaenorhine from Chaenorhinum
origanifolium (L.) Willk. et Lge., Scrophulariaceae
(Bernhard et al., 1973). However, in contrast to the
polyamine spermine presenting two amino groups for
the amide type conjugation with two phenylpropanoid
acids or a corresponding neolignan, serotonin shows
only one amino group. But in this case the phenolic
hydroxy group at C-5 of the indole nucleus presents the
possibility of another conjugation with a second phe-
nylpropanoid moiety thus forming a phenol ether link-
age with an arylglycerol.
3. Experimental
3.1. General
For fractionation silica gel 60 (230–400 mesh) or
Sephadex LH-20 were utilized. Preparative high perfor-
mance liquid chromatography (HPLC) was performed
on a Pharmacia LKB instrument on a Superpac Pep-S
C-2/C-18 (5 mm) reversed-phase column. Melting points
(uncorrected) were obtained on a Kofler apparatus and
Fig. 2. Proposed biosynthesis of the ipobscurines.

K. Jenett-Siems et al. / Phytochemistry 62 (2003) 1257–1263
1261
Table 1
1H NMR and 13C NMR data of 1–3a (biogenetic numbering according to formula 2)
1b
2c
3d
ꢀH
ꢀC
ꢀH
ꢀC
ꢀH
1
9.70 br s
7.09 d (2.5)
10.74 s
7.12 d (2.0)
2
124.1
113.2
127.7
105.6
153.7
114.5
112.5
133.3
26.5
125.3
111.5
127.2
105.8
152.4
112.0
111.7
130.7
27.7
7.12 br s
3
3a
4
7.26 d (2.5)
6.92 d (2.0)
6.99 d (2.0)
5
6
6.82 dd (8.5, 2.5)
7.22 d (8.5)
6.37 dd (9.0, 2.0)
7.28 d (9.0)
6.54 dd (8.5, 2.0)
7.04 d (8.5)
7
7a
8
2.90 t (7.5)
3.58 m
7.54 t (5.5)
2.65 m 2.85 m
3.25 m 3.44 m
7.46 br t (7.5)
2.86 m
3.48 m 3.70 m
9
10
40.9
41.8
10
129.0
130.2
116.6
159.8
140.5
119.6
167.2
133.7
127.8
118.4
158.7
138.6
122.2
167.5
20/60
30/50
40
7.39 d (9.0)
6.84 d (9.0)
6.53 d (8.5)
6.70 d (8.5)
6.94 d (8.5)
6.40 d (8.5)
70
7.51 d (15.5)
6.52 d (15.5)
7.09 d (15.5)
5.68 d (15.5)
6.63 d (12.5)
5.89 d (12.5)
80
90
100
134.6
111.7
148.1e
146.6e
115.3
120.4
73.2
132.4
110.3e
148.5
136.7
144.6
106.9e
70.8
200
7.13 d (2.0)
6.79 d (1.5)
7.10 d (1.5)
300
400
500
6.78 d (8.5)
600
6.92 dd (8.5, 2.0)
5.06 dd (4.0, 4.5)
4.43 td (4.0, 4.5)
3.58 m 3.90 dd (11.5, 4.5)
3.77 s
6.55 br s
6.56 br s
4.91 d (3.0)
700
4.79 br d (5.5)
4.06 br t (5.5)
3.40 m 3.65 m
3.89 s
800
85.7
61.8
85.1
59.7
4.32 ddd (6.0, 5.5, 3.0)
3.79 m 3.90 m
3.94 s
900
OCH3
4000-OH
4 -OH
700-OH
900-OH
56.3
56.0
8.80 br s
7.60 s
8.78 s
5.26 d (5.5)
4.68 t (5.5)
4.65 d (4.5)
4.12 t (4.5)
a
Chemical shifts are reported in ppm relative to TMS. J-Values are given in parentheses in Hz.
Acetone-d6.
b
c
DMSO-d6.
CD3OD.
Values within the same column may be interchanged.
d
e
optical rotations were measured with a Perkin Elmer
3.3. Extraction and isolation
241 MC. EIMS and HR-EIMS were recorded on a
Varian MAT 711 (80 eV), FAB MS on a Varian MAT
CH5DF. 1H NM R,13C NM R,1H–1H COSY, and
NOESY spectra were obtained on a Bruker AC 300
MHz or a Bruker AMX 400 MHz spectrometer (TMS
as int. standard).
Ground seeds (500 g) were first defatted for 8 h with
petrol in a Soxhlet apparatus. The dried material was
then extracted with 3 ꢁ 2 l MeOH at room temp. The
solvent was evaporated under reduced pressure at 40 ꢂC,
the residue (50 g) redissolved in 2% aq. tartaric acid and
extracted with EtOAc (5 ꢁ 800 ml). After evaporation
of the organic solvent, the residue was subjected to CC
over Sephadex LH-20 and eluted with MeOH. Frac-
tions containing van Urk positive compounds were
combined and further separated by CC on silica gel with
Me2CO–cyclohexane (60:40). Fractions 31–57 contained
pure 1 (150 mg). Fractions 58–109 were further purified
by preparative reversed-phase HPLC MeOH–H2O
(30:70, flow rate=5.0 ml/min) to afford 3 (5 mg). Frac-
3.2. Plant material
For the isolation of the compounds 1 – 3 plant mate-
rial of I. obscura var. obscura grown from seeds col-
lected in the wild near Surabaya, Java, was harvested in
the greenhouse of the Institut fur Pharmazie, Freie
¨
Universitat Berlin. Herbarium specimens are deposited
¨
there.

1262
K. Jenett-Siems et al. / Phytochemistry 62 (2003) 1257–1263
tions 110–200 were purified by CC on silica gel CHCl3–
MeOH (85:15) and yielded pure 2 (100 mg).
H-70), 7.69 (1H, s, 5-OH), 9.76 (1H, br s, N1-H); EIMS
(80 eV): m/z (rel. int.): 336 [M]+ (2), 178 (3), 161 (20),
159 (100), 146 (30).
3.3.1. N-[2-[5-[2-[(4-Hydroxy-3-methoxyphenyl)-2-
hydroxy-1-hydroxymethyl]ethoxy]indol-3-yl]ethyl]-4-
hydroxycinnamoyl amide (ipobscurine B) (1)
Yellow solid. [ꢁ]2d0ꢀ35ꢂ (MeOH; c 0.28); 1H NM R
(400 MHz, CDCl3): see Table 1; 13C NMR (100 MHz,
Me2CO-d6): see Table 1; (+)-FAB MS (80 eV): m/z 519
[M+H]+; (ꢀ)-FAB MS (80 eV): m/z 517 [MꢀH]ꢀ.
3.4.2. Ethyl 2-[5-[3-[2-[2-(4-methoxyphenyl)-
ethenyl]carbonylamino]ethyl]indolyloxy]-3-(3,4-di-
methoxyphenyl)-3-oxo-propanate (5)
One gram of 4 was dissolved in 50 ml acetonitrile and
boiled with 2.0 g K2CO3 and 0.2 g dibenzo-18-crown-6
for 30 min. After cooling to room temp. a soln. of 1.5 g
ethyl 2-bromo-3-(3,4-dimethoxyphenyl)-3-oxo-propa-
nate (Pearl and Gratzl, 1962) in 20 ml acetonitrile was
added dropwise within 1 h. After 3 h the filtered soln.
was evaporated and the residue purified by means of CC
on silica gel with cyclohexane–EtOAc (7:3) to yield 1.3 g
of 5.
3.3.2. 4,500-Epoxy-N-[2-[5-[2-[(4-hydroxy-3-methoxy-
phenyl)-2-hydroxy-1-hydroxymethyl]ethoxy]indol-3-yl]-
ethyl]-cinnamoyl amide (ipobscurine C) (2)
White crystals. [ꢁ]d20ꢀ44ꢂ (CHCl3; c 0.16); mp 193–195
ꢂ
1
C; H NMR (300 MHz, DMSO-d6) see Table 1; 13C
NMR (75 MHz, DMSO-d6) see Table 1; EIMS (80 eV):
m/z (rel. int.) 516 [M]+ (4), 498 (61), 482 (28), 468 (100),
439 (24), 422 (20), 411 (26), 185 (47), 159 (78), 147 (21),
146 (45); HREIMS: m/z 516.1896 (calc. for C29H28N2O7
516.1897).
1
White solid. H NMR (300 MHz, Me2CO-d6): ꢀ 1.24
(3H, t, J=7.0 Hz, H-2000), 2.95 (2H, t, J=7.0 Hz, H-8),
3.62 (2H, t, J=7.0 Hz, H-9), 3.83 (3H, s, OCH3), 3.85
(3H, s, OCH3), 3.92 (3H, s, OCH3), 4.27 (2H, q, J=7.0
Hz, H-1000), 6.11 (1H, s, H-800), 6.58 (1H, d, J=16.0 Hz,
H-80), 6.87 (1H, dd, J=2.0, 9.0 Hz, H-6), 6.94 (2H, d,
J=9.0 Hz, H-30/H-50), 7.24 (2H, m, H-2/H-4), 7.34 (5H,
m, H-7, H-20/H-60, H-300, N10-H), 7.55 (1H, d, J=16.0
Hz, H-70), 7.83 (2H, m, H-200/H-600), 10.39 (1H, br s, N1-
H); EIMS (80 eV): m/z (rel. int.): 586 [M]+ (1), 568 (2),
409 (6), 391 (11), 252 (11), 165 (100), 161 (37), 159 (43),
146 (16).
3.3.3. 4,500-Epoxy-N-[2-[5-[2-[(4-hydroxy-3-methoxy-
phenyl)-2-hydroxy-1-hydroxymethyl]ethoxy]indol-3-yl]-
ethyl]-(Z)-cinnamoyl amide (ipobscurine D) (3)
Yellow solid. Mp 245–247ꢂ C; H NMR (400 MHz,
1
CD3OD) see Table 1; EIMS (80 eV): m/z (rel. int.): 516
[M]+ (2), 498 (100), 482 (10), 468 (91), 451 (15), 439 (4),
422 (8), 411 (2), 185 (26), 159 (33), 147 (12), 146 (18);
HREIMS: m/z 516.1901 (calc. for C29H28N2O7
516.1897).
3.4.3. Rac. N-[2-[5-erythro- and threo-[2-[(3,4-Di-
methoxyphenyl)-2-hydroxy-1-hydroxymethyl]ethoxy]-
indol-3-yl]ethyl]-4-methoxycinnamoyl amide (rac.
erythro- and threo-ipobscurine B 40,400-dimethyl ether)
(6a/6b)
3.4. Synthesis of rac. N-[2-[5-erythro- and threo-[2-
[(3,4-dimethoxyphenyl)-2-hydroxy-1-hydroxy-methyl]-
ethoxy]indol-3-yl]ethyl]-4-methoxycinnamoyl amide
(rac. erythro- and threo-ipobscurine B 40,400-dimethyl
ether) (6a/6b)
One gram of 5 was dissolved in 100 ml THF and stir-
red with 200 mg LiBH4 for 2 h. Then, H2O was added
and the aq. phase extracted with EtOAc. After evap-
oration of the organic solvent, the residue was purified
by CC on silica gel with CHCl3–MeOH (98:2) to yield
140 mg of the rac. erythro- 6a and 90 mg of the rac.
threo- 6b.
3.4.1. Nb-(4-Methoxycinnamoyl)-serotonin (4)
A soln. of 3.5 g of 4-methoxycinnamic acid in 200 ml
THF was stirred with 6 ml of ethyl chloroformate and 6
ml triethylamine for 10 min. After addition of 8.1 g
serotonin creatinine sulfate monohydrate and 18 ml
triethylamine, the mixture was again stirred for 24 h at
room temp. Then, H2O was added and the aq. phase
extracted with EtOAc. After evaporation of the organic
solvent, the residue was purified by CC on silica gel with
EtOAc–cyclohexane (9:1) to yield 2.9 g of 4.
1
6a: White solid. H NMR (300 MHz, Me2CO-d6): ꢀ
2.92 (2H, t, J=7.5 Hz, H-8), 3.58 (3H, m, H-9/H-900a),
3.77 (3H, s, OCH3), 3.78 (3H, s, OCH3), 3.83 (3H, s,
OCH3), 3.88 (1H, dd, J=5.0, 11.5 Hz, H-900b), 4.45 (1H,
m, H-800), 5.09 (1H, d, J=4.0 Hz, H-700), 6.55 (1H, d,
J=16.0 Hz, H-80), 6.84 (1H, dd, J=2.5, 9.0 Hz, H-6),
6.94 (2H, d, J=9.0 Hz, H-30/H-50), 7.02 (1H, dd, J=2.0,
8.5 Hz, H-600), 7.13 (1H, d, J=2.0 Hz, H-200), 7.15 (1H,
d, J=2.0 Hz, H-2), 7.24 (1H, d, J=9.0 Hz, H-7), 7.35
(1H, d, J=2.5 Hz, H-4), 7.45 (1H, br s, N10-H), 7.51
(1H, d, J=16.0 Hz, H-70), 7.52 (2H, d, J=9.0 Hz, H-20/
H-60), 9.86 (1H, br s, N1-H); 13C NMR (75 MHz, ace-
tone-d6): ꢀ 26.7 (t, C-8), 40.8 (t, C-9), 55.6 (q, 40-OCH3),
56.0 (q, 400-OCH3), 56.1 (q, 300-OCH3), 61.6 (t, C-900), 72.8
(d, C-700), 85.4 (d, C-800), 105.3 (d, C-4), 111.9 (d, C-200),
ꢂ
1
Colourless crystals. Mp 160–162 C. H NMR (300
MHz, Me2CO-d6): ꢀ 2.91 (2H, t, J=7.5 Hz, H-8), 3.58
(2H, dt, J=6.0, 7.5 Hz, H-9), 3.83 (3H, s, OCH3), 6.54
(1H, d, J=15.5 Hz, H-80), 6.70 (1H, dd, J=2.5, 8.5 Hz,
H-6), 6.95 (2H, d, J=9.0 Hz, H-30/H-50), 7.02 (1H, d,
J=2.5 Hz, H-4), 7.10 (1H, d, J=2.0 Hz, H-2), 7.20 (1H,
d, J=8.5 Hz, H-7), 7.29 (1H, t, J=6.0 Hz, N10-H), 7.50
(2H, d, J=9.0 Hz, H-20/H-60), 7.51 (1H, d, J=15.5 Hz,

K. Jenett-Siems et al. / Phytochemistry 62 (2003) 1257–1263
1263
112.6 (d, C-7), 113.1 (s, C-3), 114.3 (d, C-6), 115.0 (d, C-
References
30/C-50), 119.9 (d, C-600), 120.4 (d, C-80), 124.0 (d, C-2),
128.7 (s, C-3a), 129.0 (d, C-500), 130.0 (s, C-10), 130.0 (d,
C-20/C-60), 133.2 (s, C-7a), 135.8 (s, C-100), 139.9 (d, C-
70), 149.4 (s, C-400), 149.9 (s, C-300), 153.5 (s, C-5), 161.7
(s, C-40), 166.7 (s, C-90); EIMS (80 eV): m/z (rel. int.):
528 [MꢀH2O]+ (2), 498 (25), 408 (2), 321 (40), 165 (16),
161 (50), 159 (100), 146 (26); HREIMS: m/z 528.2263
(calc. for C31H32N2O6 528.2260).
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1
6b: White solid. H NMR (300 MHz, Me2CO-d6): ꢀ
2.92 (2H, t, J=7.5 Hz, H-8), 3.58 (3H, m, H-9/H-900a),
3.77 (3H, s, OCH3), 3.78 (3H, s, OCH3), 3.83 (3H, s,
OCH3), 3.94 (1H, dd, J=5.0, 10.5 Hz, H-900b), 4.38 (1H,
m, H-800), 4.99 (1H, d, J=5.5 Hz, H-700), 6.55 (1H, d,
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6.94 (2H, d, J=9.0 Hz, H-30/H-50), 7.02 (1H, dd, J=2.0,
8.5 Hz, H-600), 7.13 (1H, d, J=2.0 Hz, H-200), 7.17 (1H,
d, J=2.0 Hz, H-2), 7.21 (1H, d, J=9.0 Hz, H-7), 7.35
(1H, d, J=2.5 Hz, H-4), 7.46 (1H, br s, N10-H), 7.50
(1H, d, J=16.0 Hz, H-70), 7.51 (2H, d, J=9.0 Hz, H-20/
H-60), 9.85 (1H, br s, N1-H); 13C NMR (75 MHz, ace-
tone-d6): ꢀ 26.5 (t, C-8), 40.7 (t, C-9), 55.6 (q, 40-OCH3),
56.0 (q, 400-OCH3), 56.1 (q, 300-OCH3), 62.1 (t, C-900),
74.2 (d, C-700), 85.5 (d, C-800), 106.1 (d, C-4), 111.9 (d, C-
200), 112.5 (d, C-7), 113.1 (s, C-3), 114.7 (d, C-6), 115.0
(d, C-30/C-50), 120.2 (d, C-600), 120.5 (d, C-80), 124.1 (d,
C-2), 128.9 (s, C-3a), 128.8 (d, C-500), 130.0 (s, C-10),
130.0 (d, C-20/C-60), 133.3 (s, C-7a), 136.1 (s, C-100),
139.8 (d, C-70), 149.5 (s, C-400), 150.0 (s, C-300), 153.3 (s,
C-5), 161.7 (s, C-40), 166.5 (s, C-90); EIMS (80 eV): m/z
(rel. int.): 546 [M]+ (0.5), 528 [MꢀH2O]+ (2), 498 (25),
408 (2), 321 (40), 165 (16), 161 (50), 159 (100), 146 (26);
HREIMS: m/z 528.2266 (calc. for C31H32N2O6
528.2260).
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3.5. Semisynthesis of (ꢀ)-erythro-ipobscurine B 40,400-
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Forty milligrams of 1 were dissolved in 25 ml
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dimethyl sulfate for 1 h to yield 28 mg (ꢀ)-ipobscurine
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Acknowledgements
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The authors are indebted to Mrs. E. Baumel-Eich for
¨
essential support in exploring and collecting the plant
material in the wild and Professor Dr. Klaus Rehse,
Zacchino, S.A., Badano, H., 1988. Enantioselective synthesis and
absolute configuration assignment of erythro-(3,4,5-trimethoxy-7-
hydroxy-10-allyl-20,60-dimethoxy)-8.O.40-neolignan, isolated from
mace (Myristica fragrans). J. Nat. Prod. 51, 1261–1265.
Institut fur Pharmazie, Freie Universitat Berlin, for
¨
¨
establishing systematic names according to IUPAC
nomenclature.