Regio- and stereoselectivity in the coupling reaction of secologanin with dopamine derivatives

Article abstract of DOI:10.1021/np000326l

The coupling reaction of tetraacetylsecologanin with dopamine and its N-benzyl derivative was investigated. In both series, stereoisomers at C-1, as well as regioisomer normal and neo compounds, were formed. Moreover, the N-unsubstituted products were partially lactamized, and the N-benzyl derivatives epimerized at C-1. In the products, the R configuration of C-1 over the S and the formation of the normal structure over the neo one predominated: The epimerization of both epimers gave an equilibrium of R and S in a ratio of 7:3 and was interpreted by cleavage of the C-1-N-2 bond. The fact that lactamization was much faster in the R than in the S series was explained on the basis of the supposed transition states. The structure, the configuration of C-1, and in several cases the conformations were established by detailed NMR studies and supported by chemical correlations.

Full text of DOI:10.1021/np000326l

332
J . Nat. Prod. 2001, 64, 332-340
Regio- a n d Ster eoselectivity in th e Cou p lin g Rea ction of Secologa n in w ith
Dop a m in e Der iva tives†
Gyula Beke,‡ La´szlo´ F. Szabo´,*,‡ and Benjamin Poda´nyi§
Institute of Organic Chemistry, Semmelweis University, Ho¨gyes u. 7, H-1092 Budapest, Hungary, and Chinoin Pharmaceutical
and Chemical Works, Ltd., To´ u. 1-5, H-1045, Budapest, Hungary
Received J une 30, 2000
The coupling reaction of tetraacetylsecologanin with dopamine and its N-benzyl derivative was
investigated. In both series, stereoisomers at C-1, as well as regioisomer normal and neo compounds,
were formed. Moreover, the N-unsubstituted products were partially lactamized, and the N-benzyl
derivatives epimerized at C-1. In the products, the R configuration of C-1 over the S and the formation
of the normal structure over the neo one predominated. The epimerization of both epimers gave an
equilibrium of R and S in a ratio of 7:3 and was interpreted by cleavage of the C-1-N-2 bond. The fact
that lactamization was much faster in the R than in the S series was explained on the basis of the supposed
transition states. The structure, the configuration of C-1, and in several cases the conformations were
established by detailed NMR studies and supported by chemical correlations.
In tr od u ction
Now, it seems to be firmly established that labeled
2-deacetylipecoside (with 1R) was incorporated into alangi-
side (1R) and ipecoside (1R), whereas 2-deacetylisoipecoside
(1S) is a precursor of the emetine alkaloids (1S).9 De-
Eknamkul and co-workers described the enzymatic con-
densation of secologanin and dopamine under cell-free
conditions.10 It was found that compounds of both the series
R and S were formed. However, after purification of the
crude enzyme preparation, only the activity of the enzyme
catalyzing the formation of the compounds of the R series
could be demonstrated. No mention was made concerning
the formation of neo isomers or the possible isomerization
of C-1 in the products obtained. Therefore, as an extension
of our work on the chemistry of secologanin, the coupling
reaction of secologanin and dopamine under chemical
conditions was investigated.
A special class of isoquinoline alkaloids can be derived,
formed, and prepared by coupling secologanin (1) with
dopamine (2) and related compounds.2 Typical representa-
tives of these alkaloids are emetine and ipecoside from
Cephaelis ipecacuanha A. Rich. (Rubiaceae). A. R. Bat-
tersby and co-workers were the first to demonstrate the
terpenoid origin of the non-dopamine part of these alka-
loids.3 It was found that secologanin with dopamine at pH
5 gave 2-deacetylisoipecoside (deacetyl-3c) and 2-deacetyl-
ipecoside (deacetyl-3d ) in approximately a 1:4 ratio. The
structure and configurations of the products were prede-
termined by those of the coupling partners, except for the
configuration of the newly formed center of chirality at C-1.
However, regarding this point, there was some confusion
because in the matrix of the reactions used in the chemical
and stereochemical correlations, a hidden epimerization
gave incorrect results. Finally, X-ray diffraction analysis
of 7-O,8-O-dimethylipecoside (3e) proved unequivocally the
R configuration at C-1.4 In this way, the configurations of
the compounds derived from ipecoside, i.e., representatives
of the R series, were experimentally established. Later,
from NMR measurements presented by Zenk and co-
workers, the assignment of the configuration at C-1 was
extended to the lactams of the R series [i.e., the alangiside
(7d ) derivatives, e.g., 8-O-methylalangiside] as well.5 How-
ever, no direct determination was carried out in compounds
having the 1S configuration, i.e., in the S series. Moreover,
since in dopamine the C-2′ and C-6′ are chemically non-
equivalent, it was expected that the coupling reaction
might give normal (cyclization at C-6′) and neo (cyclization
at C-2′) regioisomers. Although neo derivatives were
isolated from Cephaelis ipecacuanha and Alangium lama-
rckii Thw. (Alangiaceae) by Nagakura and co-workers,6-8
their formation in the coupling reaction of secologanin and
dopamine was not described. Previously, there was some
confusion about the biogenesis of these alkaloids as well.
Resu lts a n d Discu ssion
Previous experiments on analogous reactions of the
â-carboline series showed that the stereoselectivity of the
coupling reaction could be strongly influenced by the
substituent on the N atom (H, methyl, or benzyl group)
and by the solvent (protic, dipolar-aprotic, or apolar).11
However, in the dopamine series these conditions did not
give dramatic changes in the stereoselectivity. Finally, to
have mild conditions under which the reactions would be
complete in a relatively short time, the reactions were
carried out in acetonitrile or methanol with O,O,O,O-
tetraacetylsecologanin (1a ) and dopamine (2) or N-benzyl-
dopamine (2a ) prepared from homoveratrylamine (2b).
Under such conditions, the coupling reaction was complete
under reflux in less than 1 h. The thin-layer chromatogram
showed several spots, which indicated that in both series
(N-unsubstituted and N-alkylated) not only stereoisomers
at C-1 but also normal and neo regioisomers were formed.
Moreover, the N-unsubstituted products were partially
cyclized to lactams, which were separated by preliminary
column chromatography into sample A (amide fraction, 7a ,
7b, 8b) and sample B (ester fraction, 3a , 4a ) according to
the tetracyclic lactams and the tricyclic esters.12 (See Chart
1 for structures.)
† Part
8 in the series Chemistry of Secologanin. For Part 7, see:
Ka´rolyha´zy, L. et al.1
* To whom correspondence should be addressed. Tel: 36 12 17 12 95.
E-mail: szalasz@szerves.sote.hu.
The relative amounts of the different components of the
crude product mixtures (3-4, 5-6, 7-8) were estimated
‡ Semmelweis University.
§ Chinoin Pharmaceutical and Chemical Works, Ltd.
10.1021/np000326l CCC: $20.00
© 2001 American Chemical Society and American Society of Pharmacognosy
Published on Web 03/07/2001

Coupling Reaction of Secologanin
J ournal of Natural Products, 2001, Vol. 64, No. 3 333
Ch a r t 1
1
by the intensity and multiplicity of the aromatic protons
of the dopamine subunit in the 1H NMR spectrum and
expressed in percentage of the total amount of the products.
The normal derivatives were easily distinguished from the
neo ones, as the former had two singlet peaks and the latter
two doublet peaks in the aromatic region of the H NMR
spectrum (Table 1). Lactamization was followed by a
decrease of the intensity of the singlet of the methoxycar-
bonyl group at ∼3.5 ppm. Likewise, the presence of the
vinyl and benzyl groups was established by the appropriate

334 J ournal of Natural Products, 2001, Vol. 64, No. 3
Beke et al.
Ta ble 1. Chemical Shift of Aromatic Protons in the Products
With respect to stereochemical analysis, the lactam
derivatives will be discussed first. Since the most detailed
spectroscopic information was obtained for 7c, this com-
pound also served as a reference for the analysis of the
other lactam derivatives. Compound 7c was prepared by
the direct coupling of secologanin (1) and dopamine (2). The
rotation around the bonds C-1-C-11 and C-11-C-12
defines nine possible staggered conformers, which were
characterized by the relative orientations (antiperiplanar
or synclinal) of the hydrogens of C-11 to H-1 and H-12
(Table 3). As in the lactams in the tryptamine derivatives,
in both the R and S series only two of the C-11 conformers
have the nitrogen and the methoxycarbonyl group in an
appropriate orientation for cyclization. According to our
previous notation,11 these are R12 and R33, as well as S13
and S31. In 7c, one of the H-11 protons displayed large
coupling constants to H-1 (11.5 Hz) and H-12 (13.3 Hz),
which involve antiperiplanar orientation. This pattern
corresponds to only one (R12) of the four preselected
conformers. As the configuration at C-12 of the secologanin
subunit was established to be S by X-ray diffraction
analysis of 7-O,8-O-dimethylipecoside (7-O,8-O-dimethyl-
3d ),4 and this involves the â axial orientation of H-12 to
the lactam ring in the usual representation, the coupling
constants mentioned previously established the â axial
orientation of H-1 and the negative dihedral angle of the
lactam ring along the C-11-C-12 bond, as well as the R
configuration of C-1 in 7c. The conformation of the tet-
rahydropyridine ring in 7c is partially predetermined by
the lactam ring. As the dihedral angle C-11-C-1-N-2-C-
19 is necessarily negative, the orientation of C-10 and C-3
may be either R-equatorial-R-axial (cis) or R-equatorial-
â-equatorial (trans). One of the H-3 protons displayed a
high paramagnetic shift (4.65 ppm), which was caused by
the magnetic anisotropy of the carbonyl group; conse-
quently, it should be in the N-C-O plane. This is possible
only for the H-3R in a negative conformation of the
tetrahydropyridine ring. In a positive conformation, both
H-3 atoms (R and â orientations) would be outside of this
plane. This conformation is also in agreement with the
coupling constant pattern of H-3 and H-4 atoms. In
summary, the stereostructure of 7c is described as R12NN.14
These stereochemical results were also considered to be
correct for the other derivatives, where not all these NMR
parameters could be determined. The identities of the
stereostructures were based on the similarity of the key
parameters.
of the Coupling Reactionsa
compound
%
H-6
H-7
H-9
6.34
3a
3b
4a
4b
7a
7b
8a
8b
5a
5b
6a
6b
12
<2
12
<2
8
40
<2
28
16
70
<2
14
6.49
6.73
s
s
d 8.1
6.39
d 8.1
6.72
6.66
s
s
6.66
6.62
s
s
6.72
6.69
6.58
d 8.0
s
s
6.49
6.58
d 8.0
d 8.2
6.45
6.35
s
s
6.72
d 8.2
a
In ppm, % ) relative amount of isomers formed in the coupling
reaction, s ) singlet, d ) doublet.
proton signals. Determination of the configuration of C-1
required stereochemical analysis (see later).
The chromatograms combined with NMR data provided
the product distribution of the reaction cascade (Table 2).
These data reflected a “cross section” of the reactions at 1
h, rather than in the final state. At a longer reaction time
(about 6 h) the lactamization was nearly complete, and
epimerization was observed at C-1. Finally, the major
components or isomeric pairs were isolated by repeated
column chromatography, and their structures determined
by NMR spectroscopy.
The epimerization of C-1 was investigated in detail for
compounds 5a and 5b. The reaction was followed by the
change of the intensity of the aromatic protons of the
dopamine subunit in the 1H NMR spectrum. The half-time
of the reaction is about 36 h at room temperature in
chloroform, i.e., definitely slower than that of the coupling
reaction, but comparable to the half-time for the lactam-
ization in the S series. In methanol or acetonitrile the
epimerization was not observed. The equilibrium state
could be approached from both sides, and the ratio of the
1S and 1R epimers was found to be 3:7 in the equilibrium
mixture. No epimerization was observed after methylation
of the phenolic hydroxyl groups or in the phenolic lactams,
indicating the assistance of both the phenolic group(s) and
the basic nitrogen in the process. During epimerization,
the formation of the neo isomer from the normal one was
not observed. Therefore, it was concluded that in the
epimerization the C-1-N-2 bond was cleaved, rather than
the C-1-C-10 bond. On the basis of these experimental
facts, the isomerization was interpreted as proceeding
through 9 according to the curved arrows. A similar
isomerization was not observed in the analogous tryptamine
derivatives.
The following conclusions were drawn about the selectiv-
ity of the coupling reaction based on the data of Table 2.
(1) The stereoselectivity at C-1 is favored for the R series
over the S series and further increased in the N-benzyl
derivatives. (2) The lactamization is definitely faster in the
R series than in the S series. Therefore with a short
reaction time, derivatives of the S series could be obtained
as esters, and those of the R series as lactams. (3)
Formation of the normal isomers is slightly favored over
the neo isomers and was slightly increased by N-benzyla-
tion.
The amide fraction from the coupling reaction of O,O,O,O-
tetraacetylsecologanin (1a ) with dopamine (2) afforded 7b
and 8b as pure products, but 7a could be demonstrated
only as an accompanying component. The presence of 8a
could not be established reliably because of its low concen-
tration. As in 7c, in 7b and 8b one of the hydrogens of the
C-11 displayed large coupling constants with both vicinal
hydrogens H-1 and H-12, and one of the H-3 atoms gave a
signal at high chemical shift. According to these data, in
both compounds, the configuration of C-1 is R, H-1 has a â
axial orientation, the conformation around C-11 is R12, and
the dihedral angle of the tetrahydropyridine ring has a
negative value. Thus, they could be described likewise as
R12NN.
In the S series, the normal lactam 7a was found only as
a minor product in a sample containing 7a and 7b in a 1:5
ratio. Although only a few spectroscopic characteristics of
7a could be measured, its presence was clearly demon-
strated in the H NMR spectrum of the epimer mixture by
an “anomalous” chemical shift (δ 1.51 instead of ∼δ 2.0)
The structural investigation of the compounds was
assisted by previous results obtained in the â-carboline
series.11 In all derivatives (except 3a and 4a , see later) the
3J H17,H18 coupling constant had a small value (1.7-2.8 Hz),
which indicated the negative conformation of the dihydro-
pyran ring.
1

Coupling Reaction of Secologanin
J ournal of Natural Products, 2001, Vol. 64, No. 3 335
Ta ble 2. Product Distribution in the Coupling Reaction in Percent
Ta ble 3. Relative Orientation of H-1 and H-12 to H-11proR
The investigation of the stereochemistry of the tricyclic
esters was more complicated because the conformations
around C-11 were not fixed by ring formation.
and H-11proSa
In the N-unsubstituted series, the lactamization already
started in the coupling reaction mixture. This subsequent
reaction was so fast in the R series that the presence of
3b and 4b could not be demonstrated in the crude sample
B. As in the S series, the lactamization was slower, and
the appropriate normal 3a and neo 4a esters were obtained,
but in a moderate yield. Because of their very similar
chromatographic properties, the two regioisomers could not
be separated. According to the proton signals in the
aromatic region (Table 1), 3a and 4a were formed in a 1:1
ratio in the coupling reaction. Although most of their other
signals (at least partially) overlapped, in the 13C NMR
spectrum two complete series of signals were noted, and
the differences of the chemical shifts of the two compounds
were in most cases less than 1 ppm. The highest difference
(3.5 ppm) was observed in the chemical shift of C-1, which
is sterically close to C-9, where the ligand is different in
the two isomers (H in 3a vs OH in 4a ). This shift difference
might be ascribed to the γ-steric effect of the OH group in
the neo isomer. To establish the configuration at C-1, the
sample containing 3a and 4a was refluxed in acetonitrile
in the presence of triethylamine and triethylammonium
a
ap and sc indicate antiperiplanar and synclinal position of the
appropriate H’s, respectively.
for the proton singlet of one of the acetyl groups. This signal
is well known in all tetraacetyl lactam derivatives of the
strictosidine (10a ) (3S) and isoipecoside (3c) (1S), but not
of the vincoside (10b) (3R) and ipecoside (3d ) (1R) se-
ries.5,11,15,16 The signal may be used for identification on
the basis of the following arguments.
In the detailed analysis of the analogous â-carboline
(tryptamine) derivative (O′,O′,O′,O′-tetraacetyl-18,19-di-
hydrostrictosamide 11a , numbering according to the â-car-
boline derivatives), it was demonstrated by a selective
INEPT experiment that the “anomalous” diamagnetic shift
came from the hydrogens of the 2′-acetoxy group of the â-D-
glucopyranosyl unit.11 The same result was established by
Aimi and co-workers in 7-O-methylisoalangiside tetra-
acetate (7-O,8-O-dimethyl-7a ) on the basis of HMBC
measurements.17 The steric proximity of these hydrogens
to H-9 and H-11 of the indole ring in 11a was likewise
established by cross-peaks in the NOESY spectrum. As the
pentacyclic aglucon subunit is rigid, the distance between
the interacting groups depends principally on the confor-
mation around the glucosidic oxygen. Conformational
analysis showed that the 2′-acetoxy group, independently
of its rotation, can be proximate to the aromatic ring only
in the G11 conformation of the nine possible conformations
around the glucosidic O bridge. Previously,18 it was dem-
onstrated that in this conformation one of the nonbonding
orbitals of the O-21 atom is antiperiplanar to the O-17-
C-21 bond, the other to the C-1′-O-5′ bond (stabilization
by double σ-conjugation; this interaction is shown by curved
arrows in Figure 2 at the appropriate sites of the three-
dimensional picture of the tetrahedral intermediate toward
the analogous 7a ). Therefore, it was clear that the aniso-
tropic effect of the aromatic indole ring was responsible
for the “anomalous” shift (∼1.2 ppm instead of ∼2.0 ppm)
in 11a . The presence of the same (although less diamag-
netic) “anomalous” chemical shift in the spectrum of 7a
suggested the same steric arrangement in the dopamine
derivative (the S configuration of C-1, conformation S31
around C-11, a negative conformation of the dihydropyran
and tetrahydropyridine rings, i.e., S31NN, and a G11
conformation around the glucosidic O). The “anomalous”
shift could not be observed either in 11b or in 7b.
1
chloride. In the H NMR spectrum of the isolated nonbasic
product, the signal of the methoxycarbonyl protons disap-
peared, and an “anomalous” chemical shift was measured
at 1.54 ppm, in the expected position. The appearance of
this shift was a clear indication of the presence of the
lactams having a 1S configuration (7a and 8a ). Control
experiments established that the lactams could not be
epimerized. Consequently, lactams 7a and 8a should be
formed from 3a and 4a , respectively, also having a 1S
configuration. A further analogy should be mentioned at
3
this point. The value of J H17,H18 in the epimeric pair 3a
and 4a is relatively large (7 Hz) and close to the analogous
value (8.8 Hz) in strictosidine (10a ), which also suggested
the positive conformation of the dihydropyran ring in these
compounds. Conformational analysis of 10a showed that
the negative conformation is strongly disfavored. These
observations were sufficient to establish the formation of
the normal-neo isomer pair 3a and 4a in the coupling
reaction and the S configuration at C-1, but further
information about the conformation around C-11 and in
the tetrahydropyridine ring could not be obtained. There-
fore, the stereostructure should be given as SXXP Y, where
X and Y indicate unknown conformations.
From the coupling reaction with N-benzyldopamine (2a ),
compounds 5b and 6b of the R series were isolated in the
pure state. The stereochemistry of 5b was established by
detailed NMR studies. The proton H-1 displayed a large
coupling constant with one of the H-11 protons, and H-12

336 J ournal of Natural Products, 2001, Vol. 64, No. 3
Beke et al.
F igu r e 1. Transition states in the formation of the precursor conformers for the lactamization.
F igu r e 2. Three-dimensional structure of the tetrahedral intermediates giving the lactams 7a and 7b.
with the other H-11 proton. These data were in agreement
only with the conformers (R or S)11 and (R or S)22 (Table
4). The actual stereostructure, out of the eight possibilities
(conformer 11 or 22 in the R or S series with negative or
positive dihedral angle in the tetrahydropyridine ring), was
established by comparison of three pairs of through-space
interatomic distances calculated from experimental NOE
data (“calculated” values) and measured on computer-
generated molecular models (“measured” values).19 As
shown in Table 4, there are large differences in the

Coupling Reaction of Secologanin
J ournal of Natural Products, 2001, Vol. 64, No. 3 337
Ta ble 4. Comparison of Selected Through-Space Interatomic Distances in Å Derived from NOE Enhancements and Measured on
Computer-Generated Modelsa
measured on model
calculated
from NOE
R11NN
R11NP
R22NN
R22NP
S11NN
S11NP
S22NN
S22NP
H-1-H-9
2.46
2.41
2.55
2.61
2.89
1.88
4.54
2.02
2.51
1.87
2.12
2.44
2.88
4.71
4.58
3.57
2.60
4.71
1.96
3.86
2.51
4.78
2.05
2.50
2.88
4.72
4.58
2.08
2.52
1.87
2.11
3.87
2.88
1.88
4.55
3.66
H-1-H-17
H-3ax-H-11ab
H-9-H-11bc
a
Identical values for each of the structures indicated in the table (the first values were derived from NOEs, the second from molecular
models): H-1-H-11a: 3.1, 3.0; H-3ax-H-3eq: 2.1, 1.8; H-4ax-H-4eq: 2.1, 1.7; H-11a-H-11b: 2.1, 1.7; H-12-H-17: 2.2, 2.4; H-12-H-
18: 3.4, 3.7; H-17-H-18: 2.3, 2.5; H-16-H-15Z: 3.1, 3.1; H-16-H-15E: 2.4, 2.4; H-15Z-H-15E: 1.9, 1.9; H-4ax-H-6: 3.1, 2.9; H-4eq-
b
H-6: 2.6, 2.5. H-11a is ap to H-1. c H-11b is ap to H-12.
measured alternative values (“measured” values in bold fit
well the calculated values; those in plain do not). Therefore,
the short distance of H-1-H-17 justified the conformation
(R)11 around C-11, that of H-3ax-H-11a confirmed the R
configuration of C-1, and that of H-9-H-11b supported the
positive conformation of the tetrahydropyridine ring; that
is, the stereochemical description of 5b is R11NP . Further
1H NMR data and analysis, not detailed here, indicated
the trans diaxial orientation of the two large ligands C-11
and the benzyl group, at C-1 and N-2, respectively.
In 6b, the 1H NMR chemical shifts and the H,H coupling
constants which were relevant for the conformation around
C-11 and in the tetrahydropyridine ring showed values
close to those found in 5b. In the 13C NMR spectrum of 5b
and 6b the difference of the chemical shifts in the signal
pairs of the secologanin subunit of the molecules was
smaller than 1 ppm, except for the signal of C-1. The
chemical shift difference at C-1 (3.5 ppm) was interpreted
again as due to the γ-steric effect of the O-9 atom. These
observations suggested the same stereochemistry for 6b
as in 5b, i.e., R11NP .
At this point, it should be noted that the epimerization
observed was not restricted to the N-benzyl derivatives.
In the lactamization experiment of 3a and 4a described
above, the 1H NMR spectrum of the product mixture
showed signals that should be assigned to the lactams
having the 1R configuration (7b and 8b). Therefore, the
epimerization of C-1 should be considered as a general
phenomenon in the dopamine derivatives of secologanin,
and it may have some significance in the biogenesis. It is
known that in the tryptamine series the coupling reaction
is catalyzed by strictosidine synthase with complete ste-
reoselectivity and that most of the alkaloids that contain
the unrearranged carbon skeleton of the secologanin
subunit have the 3S configuration (if it is present at all).
The coupling reaction in the dopamine series in the
presence of an enzyme is not completely clear yet.10
However, compounds of both the 1S and 1R series were
isolated from plants.8 In the interpretation of the biosyn-
thetic results (described mainly in refs 9, 10) this fact
should be taken into consideration.
According to previous observations,11,20 the lactamization
took place under milder reaction conditions in the vincoside
(R) series (e.g., 10b) than in the strictosidine (S) series (e.g.,
10a ). The same was found in the ipecoside and isoipecoside
series (e.g., 3b and 3a , respectively). The phenomenon
should be attributed to two factors. The first concerns the
formation of the tetrahedral intermediate (cyclization), and
the second that of the final product (lactam).
Of the 2-benzyl derivatives in the S series, only the
normal 5a could be isolated from the coupling reaction in
sufficient amount; the formation of the neo isomer 6a could
not be detected. The configuration of C-1 in 5a was derived
from the epimerization experiment. Unfortunately, 5a
1
could be purified only to 80% purity. According to the H
NMR spectrum, the minor component was the epimer 5b.
During epimerization, the intensity of the main signals
decreased, and that of the minor ones increased. In the
epimerization of 5b, parallel to the decrease of the original
signals, new resonances appeared which were identical to
those of 5a . So the changes in the intensities of the signals
were mutually opposite and complementary in the spectra
of the two samples. Finally, in the equilibrium state, the
spectra of the two samples became identical. Comparison
of the 1H and 13C NMR parameters of 5a and 5b with those
of the analogous derivatives in the â-carboline series (10c
and 10d ) also afforded reasonable correlations. As in 5b,
also in 5a the two bulky ligands at C-1 and N-2 should be
in a trans diaxial orientation, which involves a necessarily
negative conformation of the tetrahydropyridine ring.
Therefore, the epimerization of 5b to 5a (and vice versa)
was accompanied by the inversion of the tetrahydropyri-
dine ring. These conformational changes were supported
by the values of the appropriate coupling constants of H-3
and H-4. Unfortunately, the experimental data were not
sufficient to establish the conformation around C-11.
Therefore, the stereochemistry of 5a may be summarized
as SXXNN. The fact that the equilibrium mixture contains
the two epimers in a 3:7 ratio indicates a difference of ∼2
kJ /mol in the free enthalpy of formation between them. It
would be inappropriate to interpret this small difference
in structural terms.
The rate of cyclization depends on the structure of the
transition state between tricyclic educts and the tetrahe-
dral intermediate and involves rotation along the appropri-
ate bond(s). While the conformations around C-11 of the
tetrahedral intermediates could be predicted to be close to
that of the lactams, i.e., R12 and S31, respectively, the
analogous conformations of the tricyclic educts were un-
known. However, in each series (R and S), five of the
possible nine staggered conformers (Table 3) have H-1 (in
R/S31, R/S32, R/S33) and/or H-12 (in R/S13, R/S23,
R /S33) in a synclinal position to both H atoms of C-11.
Consequently, large (non-H) ligands of C-1 and C-12 are
definitely closer than the sum of the van der Waals radii
of the appropriate atoms (measured on computer generated
models) and therefore are less probable. The same is true
for R/S21. Therefore all these conformers are less probable
(although not improbable or even not impossible) in the
equilibrium mixture. The remaining conformers (R/S11,
R/S12, and R/S22, shown in Figure 1) can be mutually
transformed by rotation along C-1-C-11 and/or C-11-C-
12 without passing an eclipsed conformer in which two,
non-hydrogen ligands are in a syn periplanar (eclipsed)
orientation. Because in the R series the precursor for
lactamization has the conformation R12, which is one of
the favored conformers, it could be easily formed through
R12t1 or R12t2 from any of the others. However, in the S

338 J ournal of Natural Products, 2001, Vol. 64, No. 3
Beke et al.
1:5. Rechromatography once more gave pure 7b. Fraction B,
a beige amorphous powder, contained two components in
approximatively a 1:1 ratio which could not be separated and,
according to the subsequent analysis, were established to be
O′,O′,O′,O′-tetraacetyl-2-deacetylisoipecoside(3a)and O′,O′,O′,O′-
tetraacetyl-2-deacetylneoisoipecoside (4a ).
series, the precursor for lactamization having the less-
favored conformation S31 can be formed only through such
an eclipsed S31t conformer in which two non-hydrogen
ligands (N-2 and C-12, indicated by arrow) are in a syn
periplanar orientation. Consequently, the lactamization
requires higher activation energy and proceeds slowly.
In the second step, the elimination of methanol from the
tetrahedral intermediate can take place easily if the leaving
methoxy group has an axial orientation in which the
elimination is facilitated by the double stereoelectronic
effect owing to the nonbonding electron pairs of both the
N-2 atom and the O of the geminal hydroxy group (see
curved arrows at the reaction sites in Figure 2). However,
this intermediate is rather crowded in the S31 conformer
because, as in the final lactam, the aromatic ring is in an
axial orientation. The tetrahedral intermediate of R12 has
an uncrowded flat shape and is therefore lactamized more
easily.
In summary, it can be established that the coupling
reaction between the derivatives of secologanin and dopa-
mine gave both the tricyclic esters and the tetracyclic
lactam glucosides in the R and S, as well as the normal
and neo series, and was accompanied by epimerization at
C-1 at the ester level. The stereochemistry of the reactions
may help to interpret the analogous biogenetic reactions
as well.
O′,O′,O′,O′-Tetr a a cetyl-2-d ea cetylisoip ecosid e (3a ) a n d
O′,O′,O′,O′-Tetr a a cetyl-2-d ea cetyln eoisoip ecosid e (4a ). 1H
NMR (CDCl3, 400 MHz): δ 7.55, 7.51 (each 1H, s, H-14), 6.73
3
(1 H, d, J 6,7 ) 8.1 Hz, H-6 in 4a ) 6.49 (1H s, H-6 in 3a ), 6.39
3
(1H, d, J 6,7 ) 8.1 Hz, H-7 in 4a ), 6.34 (1H, s, H-9 in 3a ), 5.6
3
(2H, m, H-16), 5.4, 5.5 (each 1H, d, J 17,18 ) 7 Hz, H-18), 4.4,
3.95 (each 1H, m, H-1), 3.79, 3.75 (each 3H, s, OCH3), 1.83
(each 1H, m, H-11proR). 13C NMR (CDCl3, 100 MHz): δ 170.6-
169.1 (C-19, four O′-CH3CO), 154.3, 154.0 (C-14), 144.4, 143.5,
142.7, 140.8 (C-7 in 3a , C-8 in 3a and 4a , C-9 in 4a ), 132.6,
132.1 (C-16), 122.9, 122.8, 122.3, 120.0 (C-5, C-10), 120.4, 119.5
(C-15), 120.0, 116.1, 115.2, 112.9 (C-6 in 3a and 4a , C-7 in 4a ,
C-9 in 3a ), 108.3, 108.2 (C-13), 97.0, 96.9, 96.8, 96.6 (C-18,
C-1′), 72.4 (C-3′), 71.7 (C-5′), 70.6 (C-2′), 67.9 (C-4′), 61.4 (C-
6′), 52.8 (C-1 in 3a ), 52.3 (OCH3), 49.3 (C-1 in 4a ), 43.1, 43.0
(C-17), 39.9, 38.0 (C-3), 34.7, 31.9 (C-11), 29.5, 29.1 (C-12), 24.4
(C-4), 20.5-20.4 (CH3CO).
La cta m iza tion Exp er im en t of 3a a n d 4a . The mixture
ofO′,O′,O′,O′-tetraacetyl-2-deacetylisoipecoside(3a)andO′,O′,O′,O′-
tetraacetyl-2-deacetylneoisoipecoside (4a) (0.092 g, 0.133 mmol)
was dissolved in MeCN (1 mL), Et3N (0.019 mL, 0.133 mmol)
and Et3NHCl (0.018 g, 0.133 mmol) were added, and the
reaction mixture was refluxed for 6 h. After evaporation of the
solvent, the residue gave on TLC (MeCOOEt:C6H6, 2:1) the
following spots: 8a and 8b (Rf 0.25), 7a and 7b (Rf 0.38). The
crude total product was taken up in CHCl3 (10 mL) and
consecutively washed with 2 M aqueous HCl (2 × 5 mL) and
water (4 × 5 mL), dried, and evaporated, affording a beige
amorphous solid (0.037 g), which proved to be a mixture of
the following products: 7-O-demethyl-O′,O′,O′,O′-tetraacetyl-
neoisoalangiside (8a , 20%), 7-O-demethyl-O′,O′,O′,O′-tet-
raacetylneoalangiside (8b, 13%), 7-O-demethyl-O′,O′,O′,O′-
tetraacetylisoalangiside (7a, 48%), and 7-O-demethyl-O′,O′,O′,O′-
tetraacetylalangiside (7b, 19%). 1H NMR signals used in
identification of the products (CDCl3): in 7a δ 7.35 (1H, d,
4J 12,14 ) 2.3 Hz, H-14), 1.55, 1.94 (3H×2, both s, CH3CO); in
Exp er im en ta l Section
Gen er a l Exp er im en ta l P r oced u r es. NMR spectra were
recorded on a Bruker AM-200 spectrometer at 200 MHz (1H)
and 50 MHz (13C) or on a Bruker DRX-400 spectrometer at
400 MHz (1H) and 100 MHz (13C). Internal TMS was used for
chemical shift reference. NOESY spectra of 5b were measured
with 0.3, 0.6, and 0.9 s mixing times using the standard Bruker
microprogram of the XWINNMR software. The cross-peak
intensities were determined by volumetric integration in the
XWINNMR program. The hydrogen-hydrogen distances were
calculated on the basis of the known 1.9 Å distance of the
geminal H2-15 hydrogens using the isolated two-spin ap-
proximation. Similar distances were calculated for the same
atomic pairs in all three experiments; the values obtained with
0.9 s mixing time are reported. Selective INEPT spectra were
measured with 10 ms selective rectangular 90° 1H pulses; the
delays were optimized for 7 Hz couplings.
4
7b δ 7.44 (1H, d, J 12,14 ) 2.3 Hz, H-14); in 8a δ 7.17 (1H, d,
4J 12,14 ) 2.6 Hz, H-14), 1.55, 1.94 (3H×2, both s, CH3CO); in
4
8b δ 7.48 (1H, d, J 12,14 ) 2.4 Hz, H-14).
7-O-Dem eth yl-O′,O′,O′,O′-tetr a a cetyla la n gisid e (7b). 1H
4
NMR (C6D6, 400 MHz): δ 7.82 (1H, d, J 12,14 ) 2.1 Hz, H-14),
6.62 (2H, s, H-6, H-9), 5.48-5.32 (3H, m, H-2′, H-3′, H-4), 5.28
3
The organic solutions were dried with anhydrous sodium
sulfate. Thin-layer chromatography (TLC) was carried out on
Si gel plates.
(1H, d, J 17,18 ) 1.6 Hz, H-18), 5.24 (1H, m, H-16), 4.9-4.83
3
(3H, m, H2-15, H-3R), 4.78 (1H, d, J 1′,2′ ) 7.8 Hz, H-1′), 4.33
3
3
2
(1H, dd, J 1,11S ) 12.5, J 1,11R ) 3.5, H-1), 4.30 (1H, dd, J 6′a,6′b
3
2
Secologanin (1) was isolated from Lonicera xylosteum L.
) 12.5, J 5′,6′a ) 3.8 Hz, H-6′a), 3.98 (1H, dd, J 6′a,6′b ) 12.5,
3J 5′,6′b ) 2.0 Hz, H-6′b), 3.17 (1H, m, H-5′), 2.89 (1H, m, H-12),
2.70-2.56 (2H, m, H-3â, 4-HR), 2.34 (1H, ddd, J 16,17 ) 9.9, J 12,17
) 5.9, J 17,18 ) 1.6 Hz, H-17), 2.22 (1H, m, H-4â), 1.80 (1H, dt,
according to a method elaborated in our Institute.21
R ea ct ion of O,O,O,O-Tet r a a cet ylsecologa n in w it h
Dop a m in e. Dopamine hydrobromide (2‚HBr, 0.18 g, 0.5
mmol) was refluxed in a mixture of acetonitrile (2.0 mL) and
triethylamine (0.07 mL, 0.5 mmol) until partial dissolution,
then O,O,O,O-tetraacetylsecologanin (1a , 0.28 g, 0.5 mmol)
was added, and the mixture was refluxed for 10 min. After
evaporation of the solvent, the residue showed the following
spots on TLC with CHCl3-MeOH (4:1): 8b (Rf 0.77), 7a and
7b (Rf 0.72), 3a and 4a (Rf 0.41). The crude total product was
chromatographed on Si gel (35 g) with CHCl3-MeOH (4:1)
(each fraction 3 mL). The combined fractions 13-25 gave, after
removal of the solvent in vacuo, fraction A (“amide” fraction,
0.196 g, 59%). Fractions 27-36, treated likewise, gave fraction
B (“ester” fraction, 0.109 g, 32%). Fraction A was rechromato-
graphed on Si gel (20 g) with CHCl3-Me2CO (5:1) (each
fraction 4 mL). Fractions 22-38 were combined and after
evaporation of the solvent gave O′,O′,O′,O′-tetraacetyl-neoa-
langiside (8b) (0.056 g, 21%), and fractions 47-76, treated
likewise, gave a beige amorphous solid [0.10 g, 37%, Rf 0.17
in CHCl3-Me2CO (5:1)], which proved to be a mixture 7-O-
demethyl-O′,O′,O′,O′-tetraacetylisoalangiside (7a ) and 7-O-
demethyl-O′,O′,O′,O′-tetraacetylalangiside (7b) in a ratio of
2J 11R,11S ) 12.5, 3J 1,11R ) 3J 11R,12 ) 3.5 Hz, H-11proR), 2.01 (3H,
2
s, CH3-CO), 1.70 (9H, s, CH3-CO), 1.29 (1H, q, J 11R,11S
)
3J 11S,12
)
3J 1,11S ) 12.5 Hz, H-11proS). 13C NMR (CDCl3, 50
MHz): δ 170.8, 170.1, 169.9, 169.6 (each CH3CO), 163.9 (C-
19), 147.2 (C-14), 143.4a (C-7), 143.2a (C-8), 131.6 (C-16), 128.0b
(C-5), 126.7b (C-10), 120.7 (C-15), 115.2c (C-6), 112.3c (C-9),
108.3 (C-13), 96.3d (C-18), 96.1d (C-1′), 72.3e (C-5′), 72.3e (C-
3′), 70.6 (C-2′), 68.2 (C-4′), 61.8 (C-6′), 55.7 (C-1), 42.6 (C-17),
40.1 (C-3), 33.4 (C-11), 28.3 (C-4), 26.5 (C-12), 20.8, 20.6, 20.6,
20.6 (each CH3CO); a-erevised assignment is also possible.
7-O-Dem eth yl-O′,O′,O′,O′-tetr a a cetylisoa la n gisid e (7a )
a n d 7-O-Dem eth yl-O′,O′,O′,O′-tetr a a cetyla la n gisid e (7b)-
(a mixture in 1:5 ratio). 1H NMR (CDCl3, 200 MHz): δ 7.43
4
4
(1H, d, J 12,14 ) 2.4 Hz, H-14), 7.34 (0.2H, d, J 12,14 ) 2.5 Hz,
H-14, in 7a ), 6.72 (0.2H, s, H-6, in 7a ), 6.66 (1H, s, H-6), 6.66
(0.2H, s, H-9, in 7a ), 6.62 (1H, s, H-9), 5.42 (1H, dt, J 15Z,16
3
)
3
3
3
17.1, J 15E,16 ) 9.4, J 16,17 ) 9.4 Hz, H-16), 5.28 (1H, d, J 17,18
) 1.9 Hz, H-18), 4.8-5.3 (6H, m, H-1′, H-2′, H-3′, H-4′, H-15Z,
H-15E), 4.65 (1H, dd, 3J 1,11R ) 2.5, 3J 1,11S ) 11.9 Hz, H-1), 4.74
2
(1H, m, H-3R), 4.33 (1H, dd, J 6′a,6′b ) 12.4, H-6′a), 4.14 (1H,

Coupling Reaction of Secologanin
J ournal of Natural Products, 2001, Vol. 64, No. 3 339
2
3
3
2
dd, J 6′a,6′b ) 12.4, J 5′,6′b ) 2.1 Hz, H-6′b), 3.77 (1H, ddd, J 4′,5′
) 2.2 Hz, H-5′), 3.71 (1H, d, J NCHa,NCHb ) 12.9 Hz, H-benzyl-
) 9.7, 3J 5′,6′a ) 4.5, 3J 5′,6′b ) 2.1 Hz, H-5′), 2.5-3.0 (5H, m, H-3â,
H-4R, H-4â, H-12, H-17), 2.17 (1H, ddd, J 11S,11R ) 13, J 1,11R
) 2.5, 3J 11R,12 ) 3.3 Hz, H-11proR), 2.11, 2.04, 2.02, 1.97 (each
3H, s, CH3CO), 2.09, 2.03, 1.94, 1.51 (each 0.6H, s, CH3CO, in
7a ), 1.41 (1H, td, J 11S,11R ) 13, J 1,11S ) 11.9, J 11S,12 ) 13.0
Hz, H-11proS).
CHa), 3.63 (1H, d, 2J NCHa,NCHb ) 12.9 Hz, H-benzyl-CHb), 3.57
(3H, s, OCH3), 3.43 (1H, dd, 3J 1,11S ) 3.2, 3J 1,11R ) 9.8 Hz, H-1),
3.18 (1H, td, 2J 3R,3â ) 12.0, 3J 3â,4â ) 5.2, 3J 3â,4R ) 12.0 Hz, H-3â),
2.96-2.75 (4H, m, H-3R, Η-4R, H-12, H-17), 2.44 (1H, dd, 2J 4R,4â
) 16.7, 3J 3â,4â ) 5.2 Hz, H-4â), 2.20 (1H, m, H-11S), 2.13, 2.05,
2.04, 1.87 (each 3H, s, CH3CO), 1.68 (1H, ddd, 2J 11R,11S ) 13.5,
2
3
2
3
3
3
7-O-Dem eth yl-O′,O′,O′,O′-tetr aacetyln eoalan giside (8b).
A beige amorphous solid [Rf 0.28 in CHCl3-Me2CO (5:1)]):
anal. C 58.02%, H 5.45%, N 2.03%, calcd for C32H37NO14, C
58.27%, H 5.65%, N 2.12%; UV (EtOH) λmax (log ꢀ) 208 (4.35),
232 (4.19), 280 (3.55) nm; IR (KBr) νmax 3600-3300, 1745, 1657
3J 1,11R ) 9.8, J 11R,12 )3.3 Hz, H-11R); 13C NMR (CD3OD, 100
MHz) δ 172.2, 170.7, 170.1, 169.5 (each CH3CO), 166.9 (C-19),
149.3 (C-14), 143.7a (C-7), 140.8a (C-8), 139.6 (C-1′′), 132.6 (C-
16), 129.5b (C-5), 129.3 (C-3′′, C-5′′), 128.2 (C-2′′, C-6′′), 127.0
(C-4′′), 126.3b (C-10), 120.7 (C-15), 115.4c (C-9), 115.0c (C-6),
112.3 (C-13), 95.3d (C-18), 94.5d (C-1′), 72.4e (C-5′), 71.9e (C-
3′), 70.9 (C-2′), 68.3 (C-4′), 61.5 (C-6′), 57.4 (CH2-benzyl), 56.9
(C-1), 51.2 (OCH3), 42.8 (C-17), 42.6 (C-3), 34.6 (C-11), 26.8
cm-1; H NMR (CDCl3, 400 MHz) δ 7.47 (1H, d, J 12,14 ) 2.5
1
4
3
3
Hz, H-14), 6.72 (1H, d, J 6,7 ) 8.0 Hz, H-6), 6.49 (1H, d, J 6,7
) 8.0 Hz, H-7), 5.44 (1H, dt, J 15Z,16 ) 17.1, J 15E,16 ) 3J 16,17
)
3
3
3
a-e
10 Hz, H-16), 5.29 (1H, d, J 17,18 ) 1.9 Hz, H-18), 5.27 (1H, t,
(C-12), 23.0 (C-4), 20.8, 20.6, 20.2, 20.1 (each CH3CO);
revised assignment is also possible. The sample contains the
signals of 5b with 20% intensity.
3J 2′,3′ ) 9.7, J 3′,4′ ) 9.7 Hz, H-3′), 5.21 (1H, dd, J 15Z,15E ) 1.8,
3J 15Z,16 ) 17.1 Hz, H-15Z), 5.14 (1H, dd, 2J 15Z,15E ) 1.8, 3J 15E,16
) 10 Hz, H-15E), 5.13 (1H, t, 3J 3′,4′ ) 9.7, 3J 4′,5′ ) 9.7 Hz, H-4′),
5.06 (1H, dd, 3J 1′,2′ ) 8, 3J 2′,3′ ) 9.7 Hz, H-2′), 4.95 (1H, d, 3J 1′,2′
3
2
O′,O′,O′,O′-Tet r a a cet yl-2-d ea cet yl-2-b en zylip ecosid e
(5b): white amorphous solid [Rf 0.34 in CHCl3-Me2CO (5:1)]);
anal. C 61.12%, H 5.95%, N 1.74%, calcd for C40H47NO15, C
61.45%, H 6.06%, N 1.79%; UV (EtOH) λmax (log ꢀ) 212 (4.48),
3
3
) 8 Hz, H-1′), 4.91 (1H, dd, J 1,11R ) 11.0, J 1,11â ) 2.2 Hz,
H-1), 4.86 (1H, m, H-3R), 4.30 (1H, dd, 2J 6′a.6′b ) 12.4, 3J 5′,6′a
)
2
3
4.5 Hz, H-6′a), 4.16 (1H, dd, J 6′a.6′b ) 12.4, J 5′,6′b ) 2.2 Hz,
228 (4.20), 291 (3.69) nm; IR (KBr) νmax 3600-3300, 1750 cm-1
;
3
3
3
H-6′b), 3.77 (1H, ddd, J 4′,5′ ) 9.7, J 5′,6′a ) 4.5, J 5′,6′b ) 2.2
Hz, H-5′), 2.99 (1H, m, H-12), 2.65-2.75 (3H, m, H-4R, H-11â,
1H NMR (CDCl3, 400 MHz) δ 7.39-7.32 (4H, m, H-2′′, H-3′′,
4
H-5′′, H-6′′), 7.25 (1H, d, J 12,14 ) 2.1 Hz, H-14), 7.23 (1H, m,
2
3
3
H-17), 2.55 (1H, dt, J 4R,4â ) 15.7, J 3R,4â ) 2.4, J 3â,4â ) 2.4
H-4′′), 6.58 (1H, s, H-6), 6.35 (1H, s, H-9), 5.43 (1H, td, 3J 15E,16
2
3
3
3
3
Hz, H-4â), 2.38 (1H, td, J 3R,3â ) 12.6, J 3â,4R ) 12.6, J 3â,4â
)
) 10.1, J 15Z,16 ) 17.1, J 16,17 ) 10.1 Hz, H-16), 5.28-5.1 (3H,
m, H-2′,-3′,-4′), 5.12 (1H, dd, 2J 15E,15Z ) 2.1, 3J 15E,16 ) 10.1 Hz,
H-15E), 5.03 (1H, d, 3J 17,18 ) 3.1 Hz, H-18), 4.84 (1H, d, 3J 1′,2′
) 8.2 Hz, H-1′), 4.73 (1H, dd, 2J 15E,15Z ) 2.1, 3J 15Z,16 ) 17.1 Hz,
2.4 Hz, H-3â), 2.10, 2.04, 2.02, 2.01 (each 3H, s, CH3CO), 1.19
2
3
3
(1H, td, J 11R,11â ) 13, J 1,11R ) 11.0, J
) 13 Hz, H-11R);
11R,12
13C NMR (CD3OD, 50 MHz) 171.0, 170.0, 169.0, 169.5 (each
CH3CO), 163.9 (C-19), 147.0 (C-14), 141.9a (C-8), 141.8a (C-9),
131.9 (C-16), 128.5b (C-5), 123.1b (C-10), 120.3 (C-15), 119.7c
(C-6), 114.0c (C-7), 108.8 (C-13), 96.8d (C-1′), 96.4d (C-18), 72.3e
(C-5′), 72.2e (C-3′), 70.7 (C-2′), 68.2 (C-4′), 61.8 (C-6′), 54.1 (C-
1), 42.6 (C-17), 39.2 (C-3), 31.0 (C-11), 29.4 (C-4), 27.4 (C-12),
20.8, 20.6, 20.6, 20.6 (each CH3CO); a-erevised assignment is
also possible.
2
3
H-15Z), 4.33 (1H, dd, J 6′a,6′b )12.6 Hz, J 5′,6′a ) 4 Hz, H-6′a),
2
3
4.27 (1H, dd, J 6′a,6′b )12.6 Hz, J 5′,6′b ) 2.7 Hz, H-6′b), 3.79
2
(1H, d, J NCHa,NCHb ) 12.8 Hz, H-benzyl-CHa), 3.73 (1H, m,
2
H-5′), 3.63 (3H, s, OCH3), 3.54 (1H, d, J NCHa,NCHb ) 12.8 Hz,
H-benzyl-CHb), 3.42 (1H, ddd, 2J 3R,3â ) 14.1, 3J 3R,4R ) 5.2, 3J 3R,4â
3
3
) 12.6 Hz, H-3R), 3.33 (1H, dd, J 1,11S ) 11.7, J 1,11R )3.2 Hz,
2
3
H-1), 3.05 (1H, m, H-12), 3.03 (1H, dd, J 3R,3â ) 14.1, J 3â,4â
)
Rea ction of O,O,O,O-Tetr a a cetylsecologa n in w ith N-
Ben zyld op a m in e. N-Benzyldopamine hydrobromide (2a ‚
HBr, 0.114 g, 0.35 mmol) was dissolved in a mixture of H2O
(1.00 mL) and CHCl3 (4.0 mL), and 1 M aqueous solution of
NaOH (0.35 mL, 0.35 mmol) was added dropwise and with
stirring. After separation of the phases, the aqueous phase was
extracted with CHCl3 (3 times, 4.0 mL), the combined organic
phase was washed with H2O and dried, and the solvent was
evaporated. The residue (N-benzyldopamine, 0.071 g, 0.3
mmol, 2b) was dissolved in CH3OH (1.00 mL), O,O,O,O
-tetraacetylsecologanin (1a , 0.163 g, 0.30 mmol) was added,
and the reaction mixture was stirred at 50 °C for 30 min. After
evaporation of the solvent, the residue gave the following spots
on TLC [CHCl3-Me2CO (5:1)]: 6b (Rf 0.46), 5b (Rf 0.35), and
5a (Rf 0.21). The crude product was purified and separated
by column chromatography on Si gel (30 g) with CHCl3-Me2-
CO (5:1) (each fraction 3 mL). Fractions containing single
compounds were combined, and the eluent was evaporated.
Fractions 25-28 gave O′,O′,O′,O′-tetraacetyl-2-deacetyl-2-ben-
zylneoipecoside (6b) (0.026 g, 11.6%), fractions 29-40 gave
O′,O′,O′,O′-tetraacetyl-2-deacetyl-2-benzylipecoside (5b) (0.115
g, 50.2%), and fractions 46-61 gave O′,O′,O′,O′-tetraacetyl-2-
deacetyl-2-benzylisoipecoside (5a ) and O′,O′,O′,O′-tetraacetyl-
2-deacetyl-2-benzylipecoside (5b) in a 4:1 ratio as a colorless,
amorphous solid [0.015 g, 6.5%; Rf 0.19 in CHCl3-Me2CO (5:
1)].
6.5 Hz, H-3â), 2.91 (1H, ddd, 2J 4R,4â ) 16.9, 3J 3R,4â ) 12.6, 3J 3â,4â
2 3
) 6.5 Hz, H-4â), 2.37 (1H, ddd, J 11R,11S ) 14.3, J 1,11S ) 11.7,
3J 11S,12 ) 2.7 Hz, H-11S), 2.34 (1H, m, H-4R), 2.13, 2.06, 2.04,
3
3
1.95 (each 3H, s, CH3CO), 1.92 (1H, ddd, J 12,17 ) 6, J 16,17
)
3
2
10.1, J 17,18 ) 3.1 Hz, H-17), 1.11 (1H, ddd, J 11R,11S ) 14.3,
3J 1,11R ) 3.2, J 11R,12,) 11.0 Hz, H-11R); 13C NMR (CDCl3, 50
3
MHz) δ 171.0, 170.4, 169.6, 169.3 (each CH3CO), 167.6 (C-19),
149.7 (C-14), 142.3 (C-7), 142.3 (C-8), 139.8 (C-1′′), 133.4 (C-
16), 130.4a (C-5), 129.9 (C-3′′), 129.9 (C-5′′), 128.4 (C-2′′), 128.4
(C-6′′), 127.0 (C-4′′), 125.8a (C-10), 119.8 (C-15), 115.3b (C-6),
114.0b (C-9), 112.4 (C-13), 96.3c (C-18), 95.3c (C-1′), 72.6d (C-
3′), 72.0d (C-5′), 70.8 (C-2′), 68.3 (C-4′), 61.7 (C-6′), 56.9 (CH2-
benzyl), 53.9 (C-1), 51.2 (OCH3), 43.0 (C-3), 41.6 (C-17), 34.4
(C-11), 24.9 (C-12), 21.6 (C-4), 20.7, 20.6, 20.6, 20.1 (each CH3-
CO); a-drevised assignment is also possible.
O′,O′,O′,O′-Tet r a a cet yl-2-d ea cet yl-2-b en zyln eoip eco-
sid e (6b): white amorphous solid [Rf 0.45 in CHCl3-Me2CO
(5:1)]); anal. C 61.15%, H 5.91%, N 1.69%, calcd for C40H47
-
NO15, C 61.45%, H 6.06%, N 1.79%; UV (EtOH) λmax (log ꢀ)
210 (4.54), 228 (4.23), 282 (3.53) nm; IR (KBr) νmax 3600-3300,
1751 cm-1; H NMR (CDCl3, 200 MHz) δ 7.42-7.35 (4H, m,
1
4
H-2′′, H-3′′, H-5′′, H-6′′), 7.27 (1H, d, J 12,14 ) 2.1 Hz, H-14),
3
7.25 (1H, m, H-4′′), 6.72 (1H, d, J 6,7 ) 8.2 Hz, H-6), 6.58 (1H,
3
3
3
d, J 6,7 ) 8.2 Hz, H-7), 5.64 (1H, dt, J 15Z,16 ) 17.1, J 15E,16
)
3J 16,17 ) 10.1 Hz, H-16), 5.3-5.1 (4H, m, H-15E, H-2′, H-3′,
3
3
H-4′), 5.05 (1H, d, J 17,18 ) 2.8 Hz, H-18), 4.84 (1H, d, J 1′,2′
)
2
3
O′,O′,O′,O′-Tet r a a cet yl-2-d ea cet yl-2-b en zylisoip eco-
7.6 Hz, H-1′), 4.80 (1H, dd, J 15E,15Z ) 1.9, J 15Z,16 ) 17.1 Hz,
2 3
sid e (5a ): anal. C 61.11%, H 5.92%, N 1.72%, calcd for C40H47
-
H-15Z), 4.33 (1H, dd, J 6′a,6′b ) 12.4, J 5′,6′a ) 3.9 Hz, H-6′a),
2 3
NO15, C 61.45%, H 6.06%, N 1.79%; 1H NMR (CDCl3, 400 MHz)
7.40-7.20 (5H, m, H-2′′, H-3′′, H-4′′, H-5′′, H-6′′), 7.26 (1H, d,
4J 12,14 ) 2 Hz, H-14), 6.69 (1H, s, H-6), 6.45 (1H, s, H-9), 5.52
4.23 (1H, dd, J 6′a,6′b ) 12.4, J 5′,6′b ) 2.5 Hz, H-6′b), 3.79 (1H
2
d, J NCHa,NCHb ) 12.7 Hz, H-benzyl-CHb), 3.73 (1H, m, H-5′),
3.63 (3H, s, OCH3), 3.6-3.4 (2H m, H-1, H-3R), 3.52 (1H, d,
2J NCHa,NCHb ) 12.7 Hz, H-benzyl-CHa), 3.17 (1H, m, H-12),
3.08 (1H, ddd, 2J 3R,3â ) 14.0, 3J 3â,4â ) 6.6, 3J 3â,4R < 1 Hz, H-3â),
3
3
3
(1H, td, J 16,17 ) 10.0, J 15E,16 )10.0, J 15Z,16 ) 17.0 Hz, H-16),
3
5.32 (1H, d, J 17,18 ) 2.4 Hz, H-18), 5.30-5.12 (3H, m, H-2′,
2
3
2
3
3
H-3′, H-4′), 5.16 (1H, dd, J 15E,15Z ) 1.2, J 15E,16 ) 10.0 Hz,
2.96 (1H, ddd, J 4R,4â ) 17.4, J 3R,4â ) 12.1, J 3â,4â ) 6.6 Hz,
2 3 3
H-15E), 4.90 (1H, dd, 2J 15E,15Z ) 1.2, 3J 15Z,16 ) 17.0 Hz, H-15Z),
H-4â), 2.43 (1H, dd, J 4R,4â ) 17.4, J 3R,4R ) 3.4, J 3â,4R < 1 Hz,
3
2
2
3
3
4.81 (1H, d, J 1′,2′ ) 7.9 Hz, H-1′), 4.35 (1H, dd, J 6′a,6′b ) 12.5,
H-4R), 2.39 (1H, ddd, J 11R,11S ) 15.1, J 1,11R ) 3.2, J 11R,12
)
3J 5′,6′a ) 4.3 Hz, H-6′a), 4.16 (1H, dd, J 6′a,6′b ) 12.5, J 5′,6′b
)
9.8 Hz, H-11R), 2.12, 2.06, 2.04, 1.95 (each 3H, s, CH3-CO),
2
3
3
3
3
2
3
2.2 Hz, H-6′b), 3.77 (1H, ddd, J 4′,5′ ) 10.1, J 5′,6′a ) 4.3, J 5′,6′b
2.1-1.9 (1H, m, H-17), 1.29 (1H, ddd, J 11R,11S ) 15.1, J 1,11S

340 J ournal of Natural Products, 2001, Vol. 64, No. 3
Beke et al.
3
) 11.9, J 11S,12 ) 3.9, Hz, H-11S); 13C NMR (CDCl3, 50 MHz)
(C-8), 133.8 (C-16), 129.1a (C-5), 127.4a (C-10), 120.4 (C-15),
116.1b (C-9), 113.4b (C-6), 109.2 (C-13), 99.6 (C-18), 97.5 (C-
1′), 78.1c (C-5′), 77.9c (C-3′), 74.7 (C-2′), 71.5 (C-4′), 62.6 (C-6′),
56.7 (C-1), 44.3 (C-17), 41.1 (C-3), 34.7 (C-11), 29.2 (C-4), 27.5
(C-12); a-crevised assignment is also possible.
δ 170.9, 170.8, 169.5, 169.1 (each CH3CO), 167.4 (C-19), 149.9
(C-14), 141.3 (C-8), 141.3 (C-9), 139.8 (C-1′′), 134.7 (C-16), 129.9
(C-3′′), 129.9 (C-5′′), 128.4 (C-2′′), 128.4 (C-6′′), 127.0 (C-4′′),
126.4, 124.5 (C-5, C-10), 120.8 (C-6), 113.2 (C-7), 119.9 (C-15),
112 (C-13), 96.2, 95.4 (C-18, C-1′), 72.6, 72.2 (C-3′, C-5′), 70.7
(C-2′), 68.2 (C-4′), 61.6 (C-6′), 57.0 (CH2-benzyl), 51.2 (OCH3),
50.4 (C-1), 42.4 (C-3), 41.6 (C-17), 34.8 (C-11), 25.7 (C-12), 21.4
(C-4), 20.8, 20.7, 20.6, 20.2 (each CH3CO).
Ack n ow led gm en t. Financial support of this work by the
National Scientific Research Foundation, Budapest, Hungary,
is gratefully acknowledged.
Ep im er iza tion Exp er im en ts. The epimerizations were
carried out with 5b or a mixture of 80% 5a and 20% 5b (0.16.
g, 2 mmol), in dry and acid-free CDCl3 (0.70 mL) at 20 or 60
°C. In each case the equilibrium was set in at 31:69 ratio of
1S:1R. The changes were checked by measuring the intensity
of the signals of H-6 and H-9 in 5a (6.67 and 6.42 ppm) and
5b (6.55 and 6.33 ppm). No isomerization was observed in
acetonitrile or methanol. Epimerizations using 6b, 11, or 7b
gave likewise negative results.
Refer en ces a n d Notes
(1) Part 7 of this series: Ka´rolyha´zy, L.; Patthy-Luka´ts, AÄ .; Szabo´, L.
F.; Poda´nyi, B. Tetrahedron Lett. 2000, 41, 1575-1578.
(2) Fujii, T.; Ohba, M. In The Alkaloids; Brossi, A., Ed.; Academic
Press: New York, 1983; Vol. 22, pp 1-50.
(3) Battersby, A. R.; Burnett, A. R.; Parsons, P. G. J . Chem. Soc. (C)
1969, 1187-1192.
(4) Kennard, O.; Roberts, P. J .; Isaacs, N. W.; Allen, F. H.; Motherwell,
W. D. S.; Gibson, K. H.; Battersby, A. R. Chem. Commun. 1971, 899-
900.
7-O-Dem eth yla la n gisid e (7c). To the solution of dopamine
hydrobromide (2‚HBr, 0.140 g, 0.59 mmol) in H2O (0.40 mL)
was added dropwise 1 M aqueous NaOH solution (0.60 mL,
0.60 mmol), followed by secologanin (1, 0.23 g, 0.59 mmol).
The reaction mixture was stirred at 50 °C for 15 min. After
evaporation of the solvent, the crude product was chromato-
graphed on Si gel (37 g) with MeCOOEt-i-PrOH-H2O (8:2:
1) (each fraction 2.3 mL). Fractions 45-63 were combined and,
after evaporation of the solvent, gave O-demethylalangiside
as an amorphous beige solid (7c) [0.189 g, 65%, Rf 0.54 in
MeCOOEt-i-PrOH-H2O (8:2:1)]: anal. C 58.12%, H 5.88%,
N 2.85%, calcd for C24H29NO10, C 58.65%, H 5.95%, N 2.85%;
UV (EtOH) λmax (log ꢀ) nm 208 (4.41), 234 (4.29), 288 (3.74);
(5) Hoefle, G.; Nagakura, N.; Zenk, M. H. Chem. Ber. 1980, 113, 566-
576.
(6) Itoh, A.; Tanahashi, T.; Nakagura, N. Chem. Pharm. Bull. 1989, 37,
1137-1139.
(7) Itoh, A.; Tanahashi, T.; Nagakura, N. Phytochemistry 1991, 30, 3117-
3124.
(8) Itoh, A.; Tanahashi, T.; Nagakura, N. J . Nat. Prod. 1995, 58, 1228-
1239.
(9) Nagakura, N.; Hofle, G.; Coggiola, D.; Zenk, M. H. Planta Med. 1978,
34, 381-389.
(10) De-Eknamkul, W.; Ounaroon, A.; Tanahashi, T.; Kutchan, T. M.;
Zenk, M. H. Phytochemistry 1997, 45, 477-484.
(11) Luka´ts-Patthy, AÄ .; Kocsis, AÄ .; Szabo´, L. F.; Poda´nyi, B. J . Nat. Prod.
1999, 62, 1492-1499.
(12) In the formulas, a biogenetic numbering system analogous to that
used in the tryptamine series13 was applied.
(13) Le Men, J .; Taylor, W. I. Experientia 1965, 21, 508-510.
(14) The stereostructures were characterized by descriptors given in the
following order: configuration of C-1 (R or S); type of conformation
around bonds C-1-C-11 and C-11-C-12 (11, ..., 33); conformation of
the dihydropyran ring (N or P ); conformation of the tetrahydropyri-
dine ring (N or P ).
(15) De Silva, K. T. D.; Smith, G. N.; Warren, K. E. H. Chem. Commun.
1971, 905-907.
(16) Hutchinson, C. R.; Heckendorf, A. H.; Straugh, J . L.; Daddona, P.
E.; Cane, D. E. J . Am. Chem. Soc. 1979, 101, 3358-3369.
(17) Takayama, H.; Ohmori, O.; Subhadhirasakul, S.; Kitajima, M.; Aimi,
N. Chem. Pharm. Bull. 1997, 45, 1231-1233.
(18) Patthy-Luka´ts, AÄ .; Ka´rolyha´zy, L.; Szabo´, L. F.; Poda´nyi, B. J . Nat.
Prod. 1997, 60, 69-75.
(19) ALCHEMY II molecular modeling system for the IBM PC; Tripos
Associates, Inc.: St. Louis, MO.
(20) Battersby, A. R.; Burnett, A. R.; Parsons, P. G. J . Chem. Soc. (C)
1969, 1193-1200.
(21) Dabi-Lengyel E.; Kocsis, AÄ .; Bo¨jthe-Horva´th, K.; Szabo´, L.; Ma´the´,
I.; Te´te´nyi, P.; Za´mbo´, I.; Varga-Bala´zs, M. Hung. Teljes HU 28,415,
28 Dec 1983; Chem. Abstr. 1984, 100, 180105q.
1
IR (KBr) νmax cm-1 3600-3200, 1624; H NMR (CD3OD, 400
MHz) δ 7.40 (1H, d, 4J 12,14 ) 2.4, H-14), 6.65 (1H, s, H-6), 6.54
3
3
3
(1H, s, H-9), 5.53 (1H, dt, J 15Z,16 ) 17, J 15E,16 ) 10, J 16,17
)
3
10 Hz, H-16), 5.49 (1H, d, J 17,18 ) 2 Hz, H-18), 5.28 (1H, dd,
2J 15Z,15R ) 2, J 15Z,16 ) 17 Hz, H-15Z), 5.19 (1H, dd, J 15Z,15R
)
3
2
3
3
3
2, J 15E,16 ) 10 Hz, H-15E), 4.70 (1H, dd, J 1,11S ) 11.5, J 1,11R
3
) 3.8 Hz, H-1), 4.69 (1H, d, J 1′,2′ ) 7.9, H-1′), 4.65 (1H, ddd,
2J 3R,3â ) 12.5, J 3R,4R ) 4.3, J 3R,4â ) 3.5 Hz, H-3R), 3.90 (1H,
dd, 2J 6′a,6′b ) 11.9, 3J 5′,6′b ) 1.9 Hz, H-6′b), 3.67 (1H, dd, 2J 6′a,6′b
) 11.9, 3J 5′,6a ) 5.5 Hz, H-6′a), 3.25-3.41 (3H, m, H-3′,-4′,-5′),
3
3
3
3
3.15-3.23 (1H, m, H-12), 3.20 (1H, dd, J 1′,2′ ) 7.9, J 2′,3′
)
)
2
3
3
9.1, H-2′), 2.89 (1H, ddd, J 3R,3â ) 12.5, J 3â,4R ) 11.3, J 3â,4â
3
3.5 Hz, H-3â), 2.7 (1H, m, H-4R), 2.70 (1H, ddd, J 12,17 ) 5.7,
3J 16,17 ) 10, J 17,18 ) 2 Hz, H-17), 2.58 (1H, dt, J 4R,4â ) 15.5,
3
2
3J 3R,4â ) 3.5, J 3â,4â ) 3.5 Hz, H-4â), 2.29 (1H, dt, J 11R,11S
)
3
2
3
3
13.3, J 1,11R ) 3.8, J 11R,12 ) 3.8 Hz, H-11R), 1.36 (1H, td,
2J 11R,11S ) 13.3, 3J 1,11S ) 11.5, 3J 11S,12 ) 13.3, H-11S); 13C NMR
(CD3OD, 50 MHz) 165.9 (C-19), 148.7 (C-14), 145.1 (C-7), 145.1
NP000326L