8-O-Methyldioncophyllinol B and revised structures of other 7,6'-coupled naphthylisoquinoline alkaloids from Triphyophyllum peltatum (Dioncophyllaceae)

Article abstract of DOI:10.1016/S0031-9422(00)00107-2

The isolation and structural elucidation of a new naphthylisoquinoline alkaloid, 8-O-methyldioncophyllinol B, from Triphyophyllum peltatum (Hutch. et Dalz.) Airy Shaw (Dioncophyllaceae) is described, together with the revised structures of other 'B-type' compounds previously misidentified as dioncophylline D, dioncophyllinol D, and 8-O-methyldioncophylline D. All of the presently described structures are 7,6'-coupled and thus have to be addressed as 'B-type' naphthylisoquinoline alkaloids. This is in contrast to the initially defined 'D-type' structures, which are 7,8'-coupled as confirmed by a total synthesis of dioncophylline D. Some of these natural and synthetic naphthylisoquinolines were found to display good in vitro antiplasmodial activities. (C) 2000 Published by Elsevier Science Ltd.

Full text of DOI:10.1016/S0031-9422(00)00107-2

Phytochemistry 54 (2000) 337±346
www.elsevier.com/locate/phytochem
8-O-Methyldioncophyllinol B and revised structures of other
7,6'-coupled naphthylisoquinoline alkaloids from Triphyophyllum
peltatum (Dioncophyllaceae)p
Gerhard Bringmanna,*, Christian Gunthera, Wael Saeba, Jan Miesa, Reto Brunb,
Laurent Ake Assic
aInstitut fur Organische Chemie, Universitat Wurzburg, Am Hubland, D-97074 Wurzburg, Germany
È
È
È
È
bSchweizerisches Tropeninstitut, Socinstrasse 57, CH-4002 Basel, Switzerland
cCentre National de Floristique, Universite d'Abidjan, 08 B.P. 172, Abidjan 08, Ivory Coast
Received 1 March 2000; received in revised form 13 March 2000
Abstract
The isolation and structural elucidation of a new naphthylisoquinoline alkaloid, 8-O-methyldioncophyllinol B, from
Triphyophyllum peltatum (Hutch. et Dalz.) Airy Shaw (Dioncophyllaceae) is described, together with the revised structures of
other `B-type' compounds previously misidenti®ed as dioncophylline D, dioncophyllinol D, and 8-O-methyldioncophylline D. All
of the presently described structures are 7,6'-coupled and thus have to be addressed as `B-type' naphthylisoquinoline alkaloids.
This is in contrast to the initially de®ned `D-type' structures, which are 7,8'-coupled as con®rmed by a total synthesis of
dioncophylline D. Some of these natural and synthetic naphthylisoquinolines were found to display good in vitro antiplasmodial
activities. 7 2000 Published by Elsevier Science Ltd. All rights reserved.
Keywords: Triphyophyllum peltatum; Dioncophyllaceae; Structural elucidation; Naphthylisoquinoline alkaloids; 8-O-Methyldioncophyllinol B;
Dioncophyllinol B; 1-epi-Dioncophylline B; 8-O-Methyl-1-epi-dioncophylline B; Dioncophyllinol D; Dioncophylline D; 8-O-Methyldioncophylline
D; Antimalarial activity
1. Introduction
tution pattern, and the stereocenters in the tetrahydro-
isoquinoline part, lead to a great variability, as illus-
trated by dioncophyllines A (1, 7,1'-coupled), B (2,
7,6'-coupled) (Bringmann et al., 1991a), and C (3, 5,1'-
coupled) (Fig. 1). In most of these secondary metab-
olites, e.g. in 1 and 3, the biaryl axis is con®guration-
ally stable due to the high rotational barrier and is
thus an additional stereoelement, whereas e.g. in 2 the
axial con®guration is unstable because of the presence
of only two ortho-substituents. Dioncophyllacine B (4),
the only other known 7,6'-coupled naphthylisoquino-
line alkaloid till date, is characterized by a dehydroge-
nated heterocyclic part and thus by the lack of any
stereogenic centers and is, therefore, even achiral at
room temperature (Bringmann et al., 1992).
The West African liana Triphyophyllum peltatum
(Dioncophyllaceae) is a versatile producer of structu-
rally, pharmacologically, and biosynthetically interest-
ing naphthylisoquinoline alkaloids (Bringmann and
Pokorny, 1995; Bringmann et al., 1998b). The mani-
fold structural features of these natural products, es-
pecially the di€erent positions of the biaryl axis
between the two molecular `halves', the oxygen substi-
p Part 136 in the series `Acetogenic isoquinoline alkaloids'. For
part 135, see Bringmann et al. (2000a).
* Corresponding author. Tel.: +49-931-888-5323; fax: +49-931-
888-4755.
In this paper, we report on the isolation and struc-
tural elucidation of a new, minor alkaloid 5, with a
E-mail address: bringman@chemie.uni-wuerzburg.de (G. Bring-
mann).
0031-9422/00/$ - see front matter 7 2000 Published by Elsevier Science Ltd. All rights reserved.
PII: S0031-9422(00)00107-2

338
G. Bringmann et al. / Phytochemistry 54 (2000) 337±346
Fig. 1. Naphthylisoquinoline alkaloids from T. peltatum.
hydroxy function at C-4. Its spectral similarity to com-
pounds previously isolated from this plant that had
been assigned structures corresponding to the 7,8'-
coupled compounds dioncophyllinol D, dioncophylline
D and 8-O-methyldioncophylline D (Bringmann et al.,
1998c, 1998d), necessitated the re-isolation and
renewed structural investigation of these three further
alkaloids from T. peltatum. Accordingly, these three
naturally occurring alkaloids have been reassigned the
revised structures 6, 8, and 7, i.e. all with 7,6' coupling
sites (`B-type'), not 7,8' (`D-type') as initially supposed
and have thus been renamed as dioncophyllinol B, 1-
epi-dioncophylline B, and 8-O-methyl-1-epi-dionco-
phylline B, respectively. The new compound 8-O-
methyldioncophyllinol B (5), the alkaloids 6, 7, and 8,
as well as authentic dioncophylline D, which has been
synthesized for the ®rst time, were found to exhibit
good antiplasmodial activities.
mula C24H27NO4. The 1H NMR spectrum exhibited
the typical signals of naphthyl-4-hydroxy-1,3-
a
dimethyltetrahydroisoquinoline alkaloid. The singlets
at 3.36 and 4.03 ppm (see Fig. 2), each corresponding
to three protons, indicated the presence of two meth-
oxy groups. One of them (3.36 ppm) is connected to
C-8 of the isoquinoline part as deduced from Hetero-
nuclear Multiple Bond Correlation (HMBC) and
Rotating Frame Overhauser Enhancement Spec-
troscopy (ROESY) measurements (see Fig. 2). The
high-®eld shifted position of this methoxy group must
result from the anisotropic e€ect caused by the
naphthalene substituent, thus providing evidence for a
coupling position ortho to this methoxy group and
hence at C-7. This assumption is supported by HMBC
interactions from H-5 and H-7' to the quaternary C-7
(see Fig. 2).
In the naphthalene part, the biaryl axis cannot be
positioned in the methyl-substituted ring, as can clearly
be deduced from the `normal', i.e. not high-®eld shifted
2'-methyl group signal (2.46 ppm) and must thus be
located at C-6' as in 5A Ð or at C-8' as in the likewise
imaginable structure 5B. The di€erentiation between
these two possibilities Ð and therefore the decision
whether the signal at 7.24 ppm has to be attributed to
H-8' (for 5A) or H-6' (for 5B) Ð turned out to be
quite dicult since neither the chemical shifts nor
H,H-COSY measurements are indicative of the coup-
2. Results and discussion
The MeOH/HCl extract of the leaves of T. peltatum
was perforated with chloroform. The organic layer was
then resolved by CC, yielding the alkaloid previously
identi®ed as `dioncophyllinol D' and a slightly less
polar minor compound, the mass peak of which,
together with HREIMS, hinted at the molecular for-

G. Bringmann et al. / Phytochemistry 54 (2000) 337±346
339
This assumption is further con®rmed by examin-
ation of the coupling constants of the aromatic pro-
tons in the non-methyl substituted ring, i.e. of H-7'
with H-8' (in 7,6'-coupled naphthylisoquinolines) or
H-7' with H-6' (in 7,8'-coupled ones), thus indicating
whether the coupling partner of H-7' is H-6' or H-8'.
The lower double bond character of the C-6'±C-7'
bond as compared to the C-7'±C-8' bond (Hesse et al.,
1991) leads to coupling constants of ca. 7.7±8.0 Hz for
H-7' in 7,8'-coupled alkaloids (see, e.g., Bringmann et
al., 1996b), whilst in 7,6'-coupled ones such as 2 the
coupling constant of H-7' is signi®cantly higher (8.4±
8.6 Hz) (Bringmann et al., 1991a). The present alkaloid
shows a J value of ca. 8.3 Hz for these protons, typical
of a 7,6' coupling, thus again supporting the structure
5A.
The relative con®guration of these three stereocen-
ters of the isoquinoline was found to be as depicted in
Scheme 1(a) by virtue of ROESY measurements and
by analysis of the coupling constants. The absolute
con®guration was elucidated by oxidative degradation
(Bringmann et al., 1996a), now leading to D-alanine
(D-9), exclusively. With the relative con®guration
established above, a 1R,3R,4R-array of the substitu-
Fig. 2. The two initially possible constitutions 5A and 5B of the new
alkaloid together with selected chemical shifts and the HMBC inter-
actions as well as the coupling constants indicative of the coupling
type; the interaction from H-8' to C-1' in 5A, which would, for 5B,
correspond to an (impossible) interaction between H-6' and C-1'
(dotted line), proves 5A to be the correct constitution.
ling site. In the present molecule, only HMBC corre-
lations of H-1' and H-8' (for 5A) or H-6' (for 5B)
allow for an unambiguous attribution of the coupling
type (see Fig. 2): in 5'-hydroxy-4'-methoxy-2'-methyl-
naphthalenes with an isoquinoline residue at C-6' as
given for 5A, HMBC interactions between H-1' and
C-8' (which has to be tertiary) and from H-8' to C-1'
are to be expected, the latter of which should not be
observable in 8'-coupled ones. In the present alkaloid,
both correlations are observed, unambiguously proving
C-6' to be the coupling position in the naphthalene
part, as in 5A. This is supported by an HMBC inter-
action between the hydrogen-bridged 5'-hydroxy pro-
ton and C-6', which is quaternary (not tertiary as
would have been in 5B) and must, therefore, bear the
biaryl axis. A confusion of C-6' with the likewise qua-
ternary C-10' is excluded by HMBC interactions from
H-1' and H-3' to that same carbon. Further evidence
of the presence of structure 5A is given by the fact
that the carbon atom identi®ed by the described
HMBC interaction of H-1' (i.e. C-8'), is observed to
be tertiary, while it would be quarternary in 5B. Like
dioncophylline B (2), hence, the new alkaloid is 7,6',
not 7,8'-coupled, and thus must have the constitution
5A.
Scheme 1. Relative con®guration (and further proof of constitution)
of the new alkaloid: (a) by selected ROESY correlations (double-
headed arrows) and an HMBC interaction; absolute con®guration of
the compound (b) by oxidative degradation and analysis by Gas
Chromatography with Mass Sensitive Detection (GC-MSD). (i)
RuCl3, NaIO4; (ii) esteri®cation with MeOH; (iii) `R-MTPA-Cl'
(`Mosher's chloride') (b).

340
G. Bringmann et al. / Phytochemistry 54 (2000) 337±346
ents at the isoquinoline moiety becomes evident
(Scheme 1(b)).
The new alkaloid from T. peltatum consequently
must have structure 5 (see Fig. 1), it is thus the ®rst
7,6'-coupled naphthylisoquinoline alkaloid containing
three stereocenters in the tetrahydroisoquinoline part
and hence resembles likewise the 7,6'-coupled and 4-
oxygenated, but dehydrogenated alkaloid dioncophyl-
lacine B (4), of which it might be the biogenetic pre-
cursor.
The unexpected similarity of the spectra of 5 to
those of the previously isolated compound identi®ed
initially as `dioncophyllinol D', the only other known
4-hydroxylated naphthylisoquinoline alkaloid, necessi-
tated a structural analysis of that alkaloid, in order to
check whether that compound is really 7,8'-coupled as
assumed before (Bringmann et al., 1998d) Ð or poss-
ibly likewise 7,6'. The isolation of larger amounts of
the compound from T. peltatum and its structural re-
elucidation indeed led to the ®nding that its coupling
type is 7,6' instead of 7,8', as now proven by the pre-
sence of all those diagnostically signi®cant HMBC in-
teractions described above for 5A (see Fig. 2) and by
the NMR coupling constant of H-7' with its vicinal
aromatic proton (J = 8.6 Hz). Therefore, the com-
pound previously misidenti®ed as the 7,8'-coupled
dioncophyllinol D (10, Fig. 3) actually has the 7,6'-
coupled structure 6 (see Fig. 1), characteristic of a `B-
type' rather than a `D-type' coupling. The initial erro-
neous attribution of the 7,8' coupling type to 6 might
have been possibly due to a misinterpretation of the
2D NMR spectra and a partial decomposition of the
alkaloid samples during the HMQC and the HMBC
measurements. The new alkaloid, 5, is thus the 8-O-
methylated analog of 6, hence to be named 8-O-
methyldioncophylline B.
Fig. 3. Structures 10, 11, and 12 previously attributed to the natural
products 6, 8, and 7, respectively. For the correct structures see
Fig. 1.
and 14, both of which had already been used for other
naphthylisoquinoline alkaloid syntheses (Bringmann et
al., 1996c; Bringmann and Gunther, 1999), a Stille
reaction yielded the desired product 15 in a good
coupling yield of 63%. Final deprotection of 15 gave
11 as the ®rst synthetic 7,8'-coupled naphthylisoquino-
line. The compound was found to be a mixture of two
rapidly interconverting atropisomers, which, already
by TLC, proved not to be identical with the compound
previously isolated from T. peltatum now identi®ed as
1-epi-dioncophylline B. While the latter natural com-
pound thus clearly does not have the initially assumed
structure 11, but rather is 8, compound 11 still is a po-
tential Ð but not yet identi®ed Ð natural product: T.
peltatum does produce alkaloids with the two molecu-
lar moieties of 11 (e.g. 2 and 3), and naphthylisoquino-
line alkaloids, with an accurately established 7,8'
coupling type, do indeed occur in related plants, e.g.
ancistroheynine A and yaoundamine A (Scheme 2).
The last problem to be solved was the con®guration
in the isoquinoline parts of 7 and 8. The oxidative
degradation had resulted in an unambiguous attribu-
tion of a 3R-con®guration (Bringmann et al., 1998c).
From NOE interactions between H-1 and H-3, a cis-
This, in turn, gave rise to the revision of the pre-
viously assigned 7,8'-coupled structures 11 and 12 of
the two other alkaloids from T. peltatum, now cor-
rectly represented by 8 and 7 (see Fig. 1), i.e. likewise
with a 7,6' coupling.
The above-described revised structure assignments
raised the question whether 7,8'-coupled alkaloids are
present in this plant at all. To help address this ques-
tion, as well as to further probe structural require-
ments
for
antiparasitic
activity,
authentic
dioncophylline D was ®rst prepared by an unambigu-
ous total synthesis of this structure. Availability of this
material by synthesis also seemed especially desirable
in light of the antimalarial activity of other 7,8'-
coupled alkaloids such as ancistroheynine A from
Ancistrocladus heyneanus (Ancistrocladaceae) (Bring-
mann et al., 1996b) and yaoundamine A from A. koru-
pensis (Hallock et al., 1997), and, in particular, of
some closely related but 7,6'- and 5,1'-coupled alka-
loids such as 2 and 3. Starting from the precursors 13

G. Bringmann et al. / Phytochemistry 54 (2000) 337±346
341
con®gured, which leads to the full absolute stereostruc-
tures 8 and 7 for the two 4-hydroxylated alkaloids of
T. peltatum, hence to be named 1-epi-dioncophylline B
and 8-O-methyl-1-epi-dioncophylline B, respectively.
That 8 is the cis-con®gured 1-epimer of dioncophylline
B (2), is further corroborated by the chromatographic
behaviour of 8 as compared with that of 2 (slightly
more rapid elution on silica gel for cis- as compared to
trans-isomers within the series) (Govindachari et al.,
1974).
The initially wrong attribution of a trans-con®gur-
ation in 7 and 8 had resulted from the unfortunate
fact that the alanine formed in the degradation reac-
tion was likewise D-con®gured. This amino acid had
erroneously been attributed as originating from C-1,
but can indeed also Ð but here for the ®rst time exclu-
sively! Ð be generated from C-3, due to the ease of
oxidation at C-1 in 1,3-cis epimers (Bringmann et al.,
1991b) and thus quantitative destruction of that stereo-
center and hence of the entire source of L-alanine
(Scheme 4). Thus, this example shows that for cis-con-
®gured naphthylisoquinoline alkaloids reliable results
can be obtained only for the C-3 con®guration,
whereas the con®guration at C-1 (relative to the hence
secure absolute con®guration at C-3) must be deduced
from ROESY and NOE measurements.
In conclusion, besides isolating and structurally elu-
cidating the new alkaloid 8-O-methyldioncophyllinol B
(5), we have now achieved an unambiguous structural
revision of compounds 6, 8, and 7 from T. peltatum
previously misidenti®ed as of the old (erroneous) struc-
tures of `dioncophyllinol D' (10), `dioncophylline D'
(11), and `8-O-methyldioncophylline D' (12), respect-
ively. With now six representatives, the 7,6' coupling
type, once seemingly very rare, has been shown to
occur more frequently than hitherto assumed, and the
same applies for the 1,3-cis con®guration in this class
of alkaloids. Of biogenetic interest, dioncophyllacine B
(4), with its additional, apparently not acetate-derived
oxygen at C-4, might ultimately arise from 8, possible
intermediates being the 4-oxygenated alkaloids 6 and
Scheme 2. Synthesis of dioncophylline D (11): (i) Pd(PPh3)2Cl2,
PPh3, CuBr, LiCl, DMF, 1358C, 63%; (ii) BCl3, CH2Cl2, 94%; (iii)
Pd black, HCOOH, MeOH, 65%.
arrangement of the two methyl groups was now
deduced for both 7 and 8 (Scheme 3).
This cis-array is in agreement with the chemical shift
of H-3 around 3.0 ppm (Scheme 3), which lies in the
typical range for cis-substituted 1,3-dimethyl-tetrahy-
droisoquinolines (Bringmann et al., 1990, 1998a), while
the trans-epimers usually give d values around 3.2±3.4.
From this relative cis-con®guration and an absolute R-
con®guration at C-3 as deduced from our oxidative
degradation procedure, C-1 can be established to be S-
Scheme 3. Relative cis-con®guration of 7 and 8, as deduced from
NOE interactions between H-1 and H-3, and con®rmed by the
chemical shifts ꢀd in ppm) for 3-H; absolute con®gurations as eluci-
dated by oxidative degradation; for the reaction conditions see
Scheme 1.

342
G. Bringmann et al. / Phytochemistry 54 (2000) 337±346
Scheme 4. Oxidative degradation of cis-con®gured tetrahydroisoquinolines.
5 Ð or from dioncophylline B (2) via 7 and related
(not yet detected) cis-con®gured 4-oxygenated alka-
loids.
lationship investigations (Bringmann and Feineis,
2000b).
The now achieved synthetic availability of 11, i.e.
authentic dioncophylline D, made it rewarding to test
this and all the other compounds described or structu-
rally revised in this paper, for their antimalarial activi-
ties and to compare them with structurally closely
related, in part very active naphthylisoquinolines of re-
lated structures such as dioncophyllines B (2) and C
(3), in contrast to dioncophylline A (1), which is only
moderately active. IC50 values of the naphthylisoqui-
nolines 5, 6, 7, and 8 against Plasmodium falciparum
are given in Table 1. The most active of these com-
pounds, besides the known highly active dioncophyl-
line C (3), are dioncophyllinol B (6) and the authentic
dioncophylline D (11). These values underline the high
pharmacological potential of 7,6' and 7,8'-coupled
naphthylisoquinolines and can be seen as useful data
points for ongoing quantitative structure±activity re-
3. Experimental
3.1. General
1
Optical rotations: 10 cm cell, CHCl3. IR: KBr. H
NMR (600 MHz, Bruker) and 13C NMR (150 MHz,
Bruker) were recorded in CDCl3 (solvent as internal
standard, d 7.26 and d 77.01, resp.). Proton-detected,
heteronuclear correlations were measured using
1
HMQC (optimized for JHC = 145 Hz) and HMBC
n
(optimized for JHC = 7 Hz). EIMS: 70 eV. CC: silica
gel (60±200 mesh, Merck). TLC: precoated silica gel
60 F254 plates (Merck). Spots were detected under UV
light. HPLC: symmetry RP-18 (7.8 Â 300 mm, Waters),
¯ow 3 ml min 1; UV detection 200±400 nm (photo-
diode array detector). HSCCC: CHCl3±EtOAc±
MeOH±0.1 N HCl (28:17:28:17), mobile phase: lower
phase, (H) 4 T, Tripple1 coil, 1.7 Â 106, 500 mm
(large coil) and 1.7 Â 37, 000 mm (middle coil), elution
mode: forward, TLC detection (see above); ¯ow 4 ml
Table 1
min 1, 850 min
.
1
Activities of the naphthylisoquinolines discussed in this paper on
chloroquine resistant (K1-strain) and susceptible (NF54-strain)
strains of Plasmodium falciparum and of chloroquine for comparison
3.2. Plant material
Compound
K1 strain IC50
1
NF54 strain IC50
1
MIC
1
Leaves of T. peltatum were collected and identi®ed
by L. Ake Assi and G. Bringmann in the Parc de Tai,
West Ivory Coast, in March 1996. Herbarium speci-
mens are deposited at the Centre National de Floris-
tique, Abidjan, and at the Institut fur Organische
Chemie, Herbarium Bringmann (no. 2).
(ng ml
)
(ng ml
)
(mg ml )
1
144 (44a)
84b (44a)
654 (60a)
34 (44a)
402 (69a)
155 (44a)
58 (95a)
237 (3.1a)
119b (3.1a)
245 (3.3a)
43 (3.1a)
1007 (4.2a)
273 (3.1a)
70 (4.3a)
37
67
2
5
90
> 200
33
6
7
8
11
> 200
67
3.3. 8-O-Methyldioncophyllinol B (5)
a Respective value for chloroquine in the same test series.
b For the isolation of 2, see Bringmann et al. (1991a). For previous
results on 2 with a similar test system, see Francois et al. (1994).
Dried leaves of T. peltatum (400 g) were powdered
and macerated for 7 days with 4 l MeOH±1 N HCl

G. Bringmann et al. / Phytochemistry 54 (2000) 337±346
343
(1:1) at room temp. with ultrasonic assistance. After
removal of MeOH, the aqueous solution was re-
extracted with CHCl3 (1.5 l) to yield 2 g of a brownish
crude extract, which was chromatographed over silica
gel (200 g, deactivated with 7.5% NH3) using CH2Cl2±
MeOH (93:7) as the eluent. Further puri®cation on
CC (CH2Cl2±MeOH, 95:5) gave 5 (1.2 mg) as a yellow
solid. [a]2D5 12.88 (CHCl3 c 0.7). CD: De200 2:67,
De220 1:74, De241 0:08, De285 1.49, De328 0.34 (EtOH,
c 0.02). IR nmax cm 1: 2920, 2840, 1660, 1570, 1440,
OCH3-4'), 4.55 (1H, q, J = 6.4 Hz, H-1), 6.71 (1H, d,
J = 1.0 Hz, H-3'), 6.78 (1H, d, J = 7.8 Hz, H-5),
7.14 (1H, d, J = 7.8 Hz, H-6), 7.24 (1H, s, H-1'), 7.33
(1H, d, J = 8.6 Hz, H-8'), 7.37 (1H, d, J = 8.4 Hz,
H-7'). 13C NMR (150 MHz, CDCl3): d 21.71 (CH3-3),
21.93 (CH3-2'), 22.10 (CH3-1), 38.49 (C-4), 48.85 (C-
3), 50.47 (C-1), 56.37 (OCH3-4'), 107.29 (C-3'), 112.93
(C-10'), 118.99 (C-6'), 119.75 (C-8'), 120.97 (C-1'),
121.37 (C-5), 124.56 (C-7), 124.80 (C-9), 128.98 (C-6),
131.03 (C-7'), 136.29, 136.36, 136.41 (C-2', C-9', C-
10), 149.22 (C-5'), 151.23 (C-8), 155.74 (C-4').
1
1250, 1085, 790. H NMR (600 MHz, CDCl3): d 1.38
(3H, d, J = 6.0 Hz, CH3-3), 1.55 (3H, d, J = 6.7 Hz,
CH3-1), 2.46 (3H, s, CH3-2'), 3.36 (3H, s, OCH3-8),
3.47 (1H, mc, H-3), 4.03 (3H, s, OCH3-4'), 4.33 (1H, d,
J = 1.2 Hz, H-4), 4.51 (1H, m, H-1), 6.64 (1H, d, J =
1.1 Hz, H-3'), 7.17 (1H, d, J = 7.9 Hz, H-5), 7.21
(1H, s, H-1'), 7.24 (1H, d, J = 8.4 Hz, H-8'), 7.32
(1H, d, J = 7.77 Hz, H-6), 7.33 (1H, d, J = 8.3 Hz,
H-7'), 9.59 (1H, s, OH-5').13C NMR (150 MHz,
CDCl3): d 17.32 (CH3-3), 20.45 (CH3-1), 21.91 (CH3-
2'), 46.96 (C-3), 48.37 (C-1), 56.11 (OCH3-4'), 60.41
(OCH3-8), 68.64 (C-4), 106.68 (C-3'), 113.31 (C-10'),
118.05 (C-8'), 119.30 (C-6'), 120.91 (C-1'), 125.03 (C-
5), 130.24 (C-7'), 131.06 (C-7), 131.42 (C-6), 131.74
(C-9), 136.0 (C-10, C-9', and C-2'), 150.93 (C-5'),
154.9 (C-8), 156.2 (C-4'). The 13C attributions were
achieved by HMQC and HMBC experiments. EIMS
3.6. 8-O-Methyl-1-epi-dioncophylline B (7)
The CH2Cl2 extract of the leaves of T. peltatum was
resolved by HSCCC under the conditions described
above. One of these frs. was puri®ed by HPLC using
1
MeOH±H2O 52.5:47.5 as eluent. Free base: H NMR
(600 MHz, CDCl3): d 1.31 (3H, d, J 1 6.4 Hz, CH3-3),
1.63 (3H, d, J = 6.3 Hz, CH3-1), 2.47 (3H, s, CH3-2'),
2.64 (1H, m, Hax-4), 2.76 (1H, dd, J = 15.8, 2.8 Hz,
Heq-4), 3.02 (1H, m, H-3), 3.35 (3H, s, OCH3-8), 4.03
(3H, s, OCH3-4'), 4.46 (1H, m, H-1), 6.64 (1H, s, H-
3'), 6.90 (1H, d, J = 7.8 Hz, H-5), 7.21 (1H, d, J not
measurable due to signal overlap, H-6), 7.23 (1H, s,
H-1'), 7.25 (1H, d, J not measurable due to signal
overlap, H-8'), 7.36 (1H, d, J = 8.3 Hz, H-7'), 9.60
m/z (rel. int.): 393 [M]+ (19), 378 [M
CH3]+ (78),
(1H, s, OH-5'). 7 Á CF3COOH: H NMR (600 MHz,
1
373 (86), 358 (41), 350 [M
C2H5N]+ (100), 189 [M
CDCl3): d 1:57 (3H, d, J = 6.4 Hz, CH3-3), 1.82 (3H,
d, J = 6.6 Hz, CH3-1), 2.48 (3H, s, CH3-2'), 2.86 (1H,
dd, J = 17.0, 2.7 Hz, Heq-4), 3.20 (1H, dd, J = 12.0,
16.4 Hz, Hax-4), 3.35 (3H, s, OCH3-8), 3.39 (1H, m,
H-3), 4.05 (3H, s, OCH3-4'), 4.83 (1H, m, H-1), 6.66
(1H, s, H-3'), 6.95 (1H, d, J = 7.8 Hz, H-5), 7.24 (1H,
s, H-1'), 7.27 (1H, d, J 1 8.5 Hz, H-8'), 7.32 (2H, d, J
= 8.2 Hz, H-6 and H-7'), 9.65 (1H, s, OH-5'). 13C
NMR (150 MHz, CDCl3): d 18:37 (CH3-3), 20.29
(CH3-1), 21.91 (CH3-2'), 34.55 (C-4), 50.24 (C-3),
51.23 (C-1), 56.13 (OCH3-4'), 60.22 (OCH3-8), 106.70
(C-3'), 113.29 (C-10'), 118.17 (C-8'), 118.40 (C-6'),
120.88 (C-1'), 123.42 (C-5), 126.25 (C-9), 130.02 (C-7
and C-7'), 132.15 (C-6), 132.95 (C-10), 136.11 (C-2'),
136.58 (C-9'), 150.93 (C-5'), 155.80 (C-8), 156.20 (C-
4'). The 13C attributions were achieved by HMQC and
HMBC experiments using the tri¯uoroacetate of 7.
CH3]2+ (15). HREIMS m/z 393.1934 [M]+
(C24H27NO4 requires 393.1940).
3.4. Dioncophyllinol B (6)
1H NMR (600 MHz, CDCl3): d 1.29 (3H, d, J =
6.5 Hz, CH3-3), 1.51 (3H, d, J = 6.7 Hz, CH3-1), 2.48
(3H, s, CH3-2'), 3.41 (1H, dq, J = 6.5, 2.0 Hz, 3-H),
4.08 (3H, s, OCH3-4'), 4.28 (1H, d, J = 2.1 Hz, H-4),
4.48 (1H, q, J = 6.6 Hz, H-1), 6.71 (1H, s, H-3'), 7.04
(1H, d, J = 7.9 Hz, H-5), 7.24 (1H, d, J = 7.6 Hz, H-
6), 7.25 (1H, s, H-1'), 7.33 (1H, d, J = 9.5 Hz, H-8'),
7.37 (1H, d, J = 8.4 Hz, H-7'). 13C NMR (150 MHz,
CDCl3): d 17.97 (CH3-3), 19.90 (CH3-1), 21.93 (CH3-
2'), 46.46 (C-3), 48.15 (C-1), 56.37 (OCH3-4'), 69.07
(C-4), 107.34 (C-3'), 112.92 (C-10'), 118.89 (C-6'),
119.80 (C-8'), 121.00 (C-1'), 122.28 (C-5), 126.05 (C-
7), 128.30 (C-9), 129.62 (C-6), 130.94 (C-7'), 136.41
(C-2' and C-9'), 137.88 (C-10), 149.26 (C-5'), 150.27
(C-8), 155.76 (C-4').
3.7. (1R,3R )-N-Benzyl-7-(5'-isopropoxy-4'-methoxy-
2'-methyl-8'-naphthyl)-8-methoxymethoxy-1,3-dimethyl-
1,2,3,4-tetrahydroisoquinoline (15)
3.5. 1-epi-Dioncophylline B (8)
A mixture of 14 (45.5 mg, 117 mmol), Pd(PPh3)2Cl2
(16.2 mg, 23.0 mmol), PPh3 (18.3 mg, 69.7 mmol), LiCl
(40.7 mg, 960 mmol), and CuBr (1.5 mg, 10.4 mmol)
was dried in vacuo, dissolved in freshly distilled abs.
DMF (5 ml), and heated to 1358C. After 5 min, a sol-
ution of 13 (197 mg, 379 mmol) in 2 ml of dry DMF
1H NMR (600 MHz, CDCl3): d 1.37 (3H, d, J =
6.3 Hz, CH3-3), 1.68 (3H, d, J = 6.5 Hz, CH3-1), 2.49
(3H, s, CH3-2'), 2.69 (1H, m, Hax-4), 2.75 (1H, dd, J
= 15.6, 2.9 Hz, Heq-4), 3.04 (1H, m, H-3), 4.08 (3H, s,

344
G. Bringmann et al. / Phytochemistry 54 (2000) 337±346
was added in two portions over 1 h. Upon completion
of the reaction (2 h), the solvent was removed by dis-
tillation. CC on deactivated (7.5% NH3) silica gel
using CH2Cl2 as the eluent yielded 15 (39.6 mg, 73.3
mmol, 63%). ‰a]2D5 55.68 (CHCl3, c 0.25). IR nmax
cm 1: 2930 (C±H), 1560, 1350, 1255, 1135, 1095. Iso-
10)1, 135.98 (C-2'), 153.82 (C-8), 154.34 (C-5'), 157.04
(C-4').
The 13C attributions were achieved by HMQC and
HMBC experiments. EIMS m/z (rel. int.): 539 [M]+
(0.4), 524 [M-CH3]+ (6), 360 (16), 296 (11), 91
[CH2Ph]+ (100). HREIMS m/z 524.2806 [M-CH3]+
(C34H38NO4 requires 524.2801).
1
mer 1: H NMR (600 MHz, CDCl3): d 1:35 (3H, d, J
= 6.5 Hz, CH3-3)1, 1.40±1.44 [6H, m, (CH3)2CH]1,
1.48 (3H, d, J = 6.9 Hz, CH3-1), 2.32 (3H, s, CH3-2'),
2.55 (3H, s, CH2OCH3), 2.70±2.80 (2H, m, CH2-4)1,
3.45 (1H, d, J = 14.3 Hz, NCHHPh), 3.61 (1H, mc,
H-3)1, 3.91 (1H, d, J = 14.5 Hz, NCHHPh)1, 3.93
(3H, s, OCH3-4'), 4.04 (1H, d, J = 5.8 Hz, OCHHO),
4.07 (1H, q, J = 6.8 Hz, H-1), 4.35 (1H, d, J = 5.8
3.8. (1R,3R)-N-Benzyl-7-(5'-hydroxy-4'-methoxy-2'-
methyl-8'-naphthyl)-8-hydroxy-1,3-dimethyl-1,2,3,4-
tetrahydroisoquinoline (16)
To a cooled ( 10 8C) solution of 15 (39.6 mg, 73.3
mmol) in dry CH2Cl2 (3 ml) a 1 M solution of BCl3 in
n-hexane (147 ml, 147 mmol) was added dropwise over
10 min. After further 15 min, the reaction was
quenched with dry MeOH (2 ml). CC on deactivated
silica gel with CH2Cl2±MeOH (99:1) as the eluent
yielded 16 (31.4 mg, 69.2 mmol, 94%). ‰a]2D0 71.98
(CHCl3, c 0.29). IR nmax cm 1: 2360 (C-H), 1614,
1584, 1431, 1262. 1H NMR (200 MHz, CDCl3): d
1.32/1.33 (3H, d, J = 6.9/6.7 Hz, CH3-3), 1.38/1.42
(3H, d, J = 6.7/6.6 Hz, CH3 1), 2.35/2.40 (3H, d, J
= 0.7/0.7 Hz, CH3-2'), 2.73 (2H, m, CH2-4), 3.40/3.44
(1H, d, J = 14.4/14.0 Hz, NCHHPh), 3.58 (1H, mc,
H-3), 3.89/3.91 (1H, d, J = 14.1/14.0 Hz, NCH HPh),
4.07/4.08 (3H, s, OCH3-4'), 4.75/4.76 (1H, s, 1-H),
6.66 (1H, br. s, H-3'), 6.78 (1H, d, J = 7.9 Hz, H-5),
6.88 (1H, d, J = 7.9 Hz, H-6'), 6.95/6.98 (1H, br. s,
H-1'), 7.01 (1H, d, J = 8.1 Hz, H-6), 7.20±7.40 (6H,
m, Ph and H-7'), 9.50 (1H, s, OH-5'). 13C NMR (50
MHz, CDCl3): d 19.25/19.42 (CH3-1), 19.54 (CH3-3),
22.19 (CH3-2'), 32.30 (C-4), 45.84 (C-3), 50.05
(CH2Ph), 51.69/51.90 (C-1), 56.25 (OCH3-4'), 106.79
(C-3'), 109.76 (C-6'), 113.73 (C-10'), 118.63 (C-1'),
120.48 (C-5), 123.63 (Ph), 123.93 (Ph), 126.40 (Ph and
C-9), 128.12 (Ph), 128.44 (Ph and C-8'), 130. 81 (C-6
and C-7), 136.65 (C-2', C-9', and C-10), 150.77 (C-8),
155.08 (C-5'), 156.40 (C-4'). Probably due to more
rapid rotation around the axis, the two isomers are
not separately observable in the NMR spectra. The
13C attributions were achieved from analogy to the
data of compound 15. The signal of C-7' is overlayed.
EIMS m/z (rel. int.): 453 [M]+ (1), 438 [M
Hz, OCHHO), 4.56 [1H, sept,
J
=
6.1 Hz,
CH(CH3)2]1,2, 6.65 (1H, s, H-3'), 6.84 (1H, s, H-1'),
6.90 (1H, d, J = 7.9 Hz, H-6'), 6.98 (1H, d, J = 7.7
Hz, H-5), 7.09 (1H, d, J = 7.8 Hz, H-6)1, 2, 7.24±7.32
(4H, m, Ph and H-7')2, 7.36±7.45 (2H, m, Ph)1,2 13C
.
NMR (150 MHz, CDCl3): d 19:82 (CH3-3), 19.90
(CH3-1), 22.06, 22.10, 22.13 [CH(CH3)2 and CH3-2]1,
32.21 (C-4), 45.71 (C-3), 49.87 (CH2Ph), 51.91 (C-1),
56.22
(CH2OCH3),
56.37
(OCH3-4')2,
72.96
[CH(CH3)2], 98.38 (OCH2O), 108.82 (C-3'), 111.77 (C-
6'), 117.49 (C-10'), 118.95 (C-1'), 124.66 (C-5), 126.44
(Ph)2, 128.08 (Ph)2, 128.35 (Ph)2, 128.47 (Ph)2, 129.00
(C-7')2, 129.53 (C-6), 130.38 (C-8'), 131.88 (C-7),
132.94 (C-9), 135.31 (C-10)1, 135.71 (C-2'), 136.11 (C-
9')1, 153.49 (C-8), 154.53 (C-5'), 156.73 (C-4').
1
Isomer 2: H NMR (600 MHz, CDCl3): d 1.36 (3H,
d,
J
=
6.4 Hz, CH3-3)1, 1.40±1.44 [6H, m,
(CH3)2CH]1, 1.46 (3H, d, J = 6.9 Hz, CH3-1), 2.40
(3H, s, CH3-2'), 2.66 (3H, s, CH2OCH3), 2.70 ± 2.80
(2H, m, CH2-4)1, 3.52 (1H, d,
J = 14.1 Hz,
NCHHPh), 3.61 (1H, mc, H-3)1, 3.92 (1H, d, J = 14.5
Hz, NCHHPh)1, 3.95 (3H, s, OCH3-4'), 4.12 (1H, q, J
= 6.6 Hz, H-1), 4.14 (1H, d, J = 5.9 Hz, OCHHO),
4.17 (1H, d, J = 5.7 Hz, OCHHO), 4.56 [1H, sept, J
= 6.1 Hz, CH(CH3)2]1,2, 6.67 (1H, s, H-3'), 6.88 (1H,
d, J = 8.0 Hz, H-6'), 6.95 (1H, d, J = 7.8 Hz, H-5),
7.09 (1H, d, J = 7.8 Hz, H-6)1,2, 7.16 (1H, s, H-1'),
7.24±7.32 (4H, m, Ph and H-7')2, 7.36±7.45 (2H, m,
Ph)1,2 13C NMR (150 MHz, CDCl3): d 19.70 (CH3-1),
.
CH3]+(100), 423 [M
2CH3]+ (7), 347 [M
CH3-
20.02 (CH3-3), 22.14, 22.14, 22.18 [CH(CH3)2 and
CH3-2']1, 32.53 (C-4), 45.68 (C-3), 49.98 (CH2Ph),
51.82 (C-1), 56.37 (OCH3-4')2, 56.40 (CH2OCH3),
72.84 [CH(CH3)2], 98.74 (OCH2O), 108.65 (C-3'),
111.63 (C-6'), 117.97 (C-10'), 118.03 (C-1'), 123.90 (C-
5), 126.44 (Ph)2, 128.08 (Ph)2, 128.35 (Ph)2, 128.47
(Ph)2, 128.61 (C-8'), 129.00 (C-7')2, 130.25 (C-6),
131.29 (C-7), 133.49 (C-9), 135.25 (C-9')1, 135.59 (C-
CH2Ph]+ (14), 219 [M]2+ (5), 188 [C12H12O2]+ (9), 91
[CH2Ph]+ (76). HREIMS m/z 438.2070 [M CH3]+
(C29H28NO3 requires 438.2069).
3.9. Dioncophylline D (11)
To a solution of 16 (31.4 mg, 69.2 mmol) in dry
MeOH (1 ml) Pd black (3.5 mg, 32.8 mmol) and
HCO2H (100 ml, 2.65 mmol) were added. The suspen-
sion was stirred for 1 h and then partitioned between
H2O and CH2Cl2. The combined organic layers were
1 Attributions interchangeable in pairs for two isomers.
2 Superposition of the signals of the two isomers.

G. Bringmann et al. / Phytochemistry 54 (2000) 337±346
345
evaporated and subjected to CC on deactivated silica
gel (7.5% NH3) with CH2Cl2±MeOH (95:5) as the elu-
ent gave 11 (16.4 mg, 45.1 mmol, 65%). ‰a]2D0 -54.38
(CHCl3, c 0.14). IR nmax cm 1: 3380 (O±H), 2890 (C-
similar to the one developed for trypanosomes (Raez
et al., 1997) using ¯uorometric reading to quantify the
change in color.
1
H), 1595, 1415, 1245, 1115. Isomer 1: H NMR (600
MHz, CDCl3): d 1.25 (3H, d, J = 5.6 Hz, CH3-3),
1.47 (3H, d, J = 6.7 Hz, CH3-1), 2.35 (3H, s, CH3-2'),
2.55 (1H, dd, J = 16.6, 10.9 Hz, Hax-4), 2.84 (1H, dd,
J = 16.6, 4.0 Hz, Heq-4)2, 3.37 (1H, mc, H-3)2, 4.08
(3H, s, OCH3-4'), 4.45 (1H, q, J = 7.0 Hz, H-1), 6.66
(1H, br. s, H-3'), 6.74 (1H, d, J = 7.7 Hz, H-5), 6.88
(1H, d, J = 7.9 Hz, H-6')2, 6.92 (1H, br. s, H-1'), 6.99
(1H, d, J = 7.7 Hz, H-6)1, 2, 7.31 (1H, d, J = 7.9 Hz,
H-7'), 9.49 (1H, s, OH-5')1.
Acknowledgements
This work was supported by the Deutsche For-
schungsgemeinschaft (SFB 251 ``Okologie, Physiologie
und Biochemie p¯anzlicher und tierischer Leistung
unter Stress'') and by the Fonds der Chemischen
Industrie (fellowship to C.G. and research funds). This
investigation also received ®nancial support from the
UNDP/World Bank/WHO Special Programme for
Research and Training in Tropical Diseases (to R.B.).
We are indebted to J. Kraus for CD measurements,
Dr. M. Boyd for valuable suggestions on the manu-
script, Dr. M. Ruckert, Dr. M. Wenzel, M. Wohlfarth,
and Dr. M. Ochse for fruitful discussions as well as to
M. Michel and M. Munchbach for performing the
degradation experiments. Furthermore, we thank E.
Ruckdeschel, Dr. K. Grune, and Dr. M. Heubes for
the NMR spectra, as well as Dr. G. Lange and F.
Dadrich for the mass spectra.
1
Isomer 2: H NMR (600 MHz, CDCl3): d 1.24 3H,
d, J = 5.6 Hz, CH3-3), 1.49 (3H, d, J = 6.7 Hz, CH3-
1), 2.37 (3H, s, CH3-2'), 2.50 (1H, dd, J = 16.6, 11.0
Hz, Hax-4), 2.84 (1H, dd, J = 16.6, 4.0 Hz, Heq-4)2,
3.37 (1H, mc, H-3)2, 4.09 (3H, s, OCH3-4'), 4.39 (1H,
q, J = 6.7 Hz, H-1), 6.68 (1H, br. s, H-3'), 6.75 (1H,
d, J = 7.7 Hz, H-5) 6.68 (1H, d, j = 7.9 Hz, H-6')2,
6.97 (1H, br. s, H-1'), 6.98 (1H, d, J = 7.7 Hz, H-
6)1,2, 7.28 (1H, d, J = 7.8 Hz, H-7'), 9.49 (1H, s, 5'-
OH)1. 13C NMR (150 MHz, CDCl3): d 21.04 (CH3-1),
22.16 (CH3-2'), 22.83/22.91 (CH3-3), 37.58 (C-4),
41.81/42.01 (C-3), 47.71/47.80 (C-1), 56.23 (OCH3-4'),
106.78/106.82 (C-3'), 109.68/109.77 (C-6'), 113.65 (C-
10'), 118.61 (C-1'), 120.66 (C-5), 123.64/123.83 (C-7),
126.83/127.19 (C-9), 128.63/128.73 (C-6), 130.76/130.83
(C-7'), 135.12/153.33 (C-8'), 135.58 (C-10), 136.66/
136.77 (C-9'), 149.62/149.71 (C-8), 155.07 (C-5'),
156.33 (C-4'). Due to low resolution of the two
isomers in the HMBC spectrum, these data are not
given separately for the two compounds. EIMS m/z
(rel. int.): 363 [M]+ (12), 348 [M CH3]+ (100), 333
References
Bringmann, G., Rubenacker, M., Jansen, J.R., Scheutzow, D., Ake,
Assi, L., 1990. On the structure of the dioncophyllaceae alkaloids
dioncophylline A (``triphyophylline'') and ``O-methyl-triphyophyl-
line''. Tetrahedron Lett. 31, 639±642.
Bringmann, G., Rubenacker, M., Geuder, T., Ake, Assi, L., 1991a.
Dioncophylline B, a naphthylisoquinoline alkaloid with a new
coupling type from Triphyophyllum peltatum. Phytochemistry 30,
3845±3847.
[M
2CH3]+ (22), 174 [M CH3]2+ (14). HREIMS
Bringmann, G., Geuder, T., Rubenacker, M., Zagst, R., 1991b. A
facile degradation procedure for determination of absolute con-
®guration in 1,3-dimethyltetra- and dihydroisoquinolines.
Phytochemistry 30, 2067±2070.
m/z 363.1825 [M CH3]+ (C22H22NO3 requires
363.1834).
Bringmann, G., Ortmann, T., Rubenacker, M., Ake, Assi, L., 1992.
Dioncophyllacine B: a new 4-methoxylated naphthylisoquinoline
alkaloid from the leaves of Triphyophyllum peltatum. Planta Med.
58 (Suppl. 1), 701±702.
3.10. Biological experiments
The activity against P. falciparum was tested by
the semiautomated microdilution assay against
intraerythrocytic forms derived from asynchronous
stock cultures as previously described (Desjardins et
al., 1979) with minor modi®cations (Ridley et al.,
1996). Antimalarial activities were determined using
two parasite strains: K1 (Thailand; resistant to chlor-
oquine and pyrimethamine) and NF54 (an airport
strain of unknown origin; susceptible to standard
antimalarials). The activities are given as IC50 values
(ng ml 1). Chloroquine was used as the standard All
data are the mean values from three measurements.
Cytotoxicity was tested against rat skeletal muscle
myoblast (L-6) cells using Alamar Blue to assess cell
viability (Page et al., 1993). The assay procedure was
Bringmann, G., Pokorny, F., 1995. The naphthylisoquinoline alka-
loids. In: Cordell, G.A. (Ed.), The Alkaloids, vol. 46. Academic
Press, New York, pp. 127±271.
Bringmann, G., God, R., Scha€er, M., 1996a. An improved degra-
dation procedure for determination of the absolute con®guration
in chiral isoquinoline and b-carboline derivatives. Phytochemistry
43, 1393±1403.
Bringmann, G., Koppler, D., Wiesen, B., Francois, G., Sankara,
Narayanan, A.S., Almeida, M.R, Schneider, H., Zimmermann,
U., 1996b. Ancistroheynine A, the ®rst 7,8'-coupled naphthyliso-
quinoline alkaloid from Ancistrocladus heyneanus. Phytochemistry
43, 1405±1410.
Bringmann, G., Gotz, R., Harmsen, S., Holenz J., Walter, R.
(1996c). Biomimetic total synthesis of michellamines A±C.
Liebigs Ann. 2045±2048.
Bringmann, G., Gunther, C., Busemann, S., Scha€er, M.,
Olowokudejo, J.D., Alo, B., 1998a. Ancistroguineines A and B as

346
G. Bringmann et al. / Phytochemistry 54 (2000) 337±346
well as ancistrotectorine ± naphthylisoquinoline alkaloids from
Ancistrocladus guineensis. Phytochemistry 47, 37±43.
Dochez, C., Rubenacker, M., Schneider, C., Wery, M., Warhurst,
D.C., Kirby, G.C., 1994. Activity of Extracts and
Naphthylisoquinoline Alkaloids from Triphyophyllum peltatum,
Ancistrocladus abbreviatus and A. barteri against Plasmodium fal-
ciparum in vitro. Phytochemistry 35, 1461±1464.
È
Bringmann, G., Francois, G., Ake Assi, L., Schlauer, J., 1998b. The
alkaloids of Triphyophyllum peltatum (Dioncophyllaceae). Chimia
52, 18±28.
Bringmann, G., Wenzel, M., Rubenacker, M., Scha€er, M., Ruckert,
M., Ake, Assi, L., 1998c. Dioncophylline D and 8-O-methyldion-
cophylline D, 7,8'-coupled naphthylisoquinoline alkaloids from
Triphyophyllum peltatum. Phytochemistry 49, 1151±1155.
Bringmann, G., Wenzel, M., Ruckert, M., Wolf, K., Busemann, S.,
Scha€er, M., Ake, Assi, L., 1998d. Dioncophyllinol D, the ®rst 4-
hydroxylated naphthylisoquinoline alkaloid from the leaves of
Triphyophyllum peltatum. Heterocycles 47, 985±990.
Bringmann, G., Gunther, C., 1999. First total synthesis of dionco-
phylline B, a 7,6'-coupled naphthylisoquinoline alkaloid. Synlett,
216±218.
Govindachari, T.R., Nagarajan, K., Parthasarathy, P.C.,
Rajagopalan, T.G., Desai, H.K., Kartha, G., Chen, S.-M.L.,
Nakanishi, K., 1974. Absolute stereochemistry of ancistrocladine
and ancistrocladinine. J. Chem. Soc. Perkin Trans. 1, 1413±1417.
Hallock, Y.F., Cardellina, II, J.H., Scha€er, M., Stahl, M.,
Bringmann, G., Francois, G., Boyd, M.R., 1997. Yaoundamines
A and B, new antimalarial naphthylisoquinoline alkaloids from
Ancistrocladus korupensis. Tetrahedron 53, 8121±8128.
Hesse, M., Meier, H., Zeeh, M., 1991. Spektroskopische Methoden
in der organischen Chemie, 4th ed. Stuttgart, New York: Thieme.
Page, B., Page, M., Noel, C., 1993. A new ¯uorometric assay for
cytotoxicity measurements in vitro. Int. J. Oncol. 3, 473±476.
Raz, B., Iten, M., Grether-Buhler, Y., Kaminsky, R., Brun, R.,
1997. The Alamar Blue assay to determine drug sensitivity of
African trypanosomes (T. b. rhodesiense and T. b. gambiense) in
vitro. Acta Trop. 68, 139±147.
Bringmann, G., Ochse, M., Michel, M., 2000a. Gentrymine B, an N-
quaternary Ancistrocladus alkaloid: stereoanalysis, synthesis, and
biomimetic formation from gentrymine A. Tetrahedron 56, 581±
585.
Bringmann, G., Feineis, D., 2000b. Novel antiparasitic biaryl alka-
loids from West african Dioncophyllaceae plants. Act. Chim.
Therapeut. 26, 151±172.
Ridley, R.G., Hofheinz, W., Matile, H., Jacquet, C., Dorn, A.,
Masciadri, R., Jolidon, S., Richter, W.F., Guenzi, A.,
Girometta, M.A., Urwyler, H., Huber, W., Thaitong, S., Peters,
W., 1996. 4-Aminoquinoline analogs of chloroquine with shor-
tened side chains retain activity against chloroquine-resistant
Plasmodium falciparum. Antimicrob. Agents Chemother. 40,
1846±1854.
Desjardins, R.E., Can®eld, C.J., Haynes, D., Chulay, J., 1979.
Quantitative assessment of antimalarial activity in vitro by a semi-
automated microdilution assay. Antimicrob. Agents Chemother.
16, 710±718.
Francois, G., Bringmann, G., Phillipson, J.D., Ake, Assi, L.,