Ipangulines and minalobines, chemotaxonomic markers of the infrageneric Ipomoea taxon subgenus Quamoclit, section Mina

Article abstract of DOI:10.1016/j.phytochem.2004.11.019

A comprehensive GC-MS analysis of 8 Ipomoea species belonging to the subgenus Quamoclit, section Mina revealed that the members of this taxon form combinations of two necine bases with rare necic acids resulting in unique pyrrolizidine alkaloids. The occurrence and diversity of these metabolites show remarkable variations: Some species, especially Ipomoea hederifolia and Ipomoea lobata, are able to synthesize a large number of alkaloids whereas others, especially Ipomoea coccinea and Ipomoea quamoclit, are poor synthesizers with only a few compounds. However, these metabolites are apparently chemotaxonomic markers of this infrageneric taxon in general. They represent either esters of (-)-platynecine (altogether 48 ipangulines and 4 further esters including results of a previous study) or esters of (-)-trachelanthamidine, an additional novel structural type called minalobines (altogether 21 alkaloids). Both types are characterized by section-specific rare necic acids, e.g., ipangulinic/isoipangulinic acid, phenylacetic acid. The alkaloids of Ipomoea cholulensis, I. coccinea, I. hederifolia, Ipomoea neei, and Ipomoea quamoclit were mono and diesters of platynecine. Minalobines turned out to be metabolites of I. lobata (Cerv.) Thell. (syn.: Mina lobata Cerv.) lacking ipangulines. The major alkaloid of this species, minalobine R, has been isolated and identified as 9-O-(threo-2-hydroxy-2-methyl-3-phenylacetoxy-butyryl)-(-)-trachelanthamidine on the basis of spectral data. Apparently only two of the species included in this study, Ipomoea cristulata and Ipomoea sloteri, are able to synthesize both, ipangulines as well as minalobines. Minalobine O could be isolated as a major alkaloid of I. cristulata, its structure has been established as 9-O-(erythro-2-hydroxy-2-methyl-3-tigloyloxy-butyryl)-(-)-trachelanthamidine on the basis of spectral data.

Full text of DOI:10.1016/j.phytochem.2004.11.019

PHYTOCHEMISTRY
Phytochemistry 66 (2005) 223–231
www.elsevier.com/locate/phytochem
Ipangulines and minalobines, chemotaxonomic markers of the
q
infrageneric Ipomoea taxon subgenus Quamoclit, section Mina
a
Kristina Jenett-Siems , Sonja C. Ott , Thomas Schimming , Karsten Siems ,
a
a
b
c
c
d
Frank Muller , Monika Hilker , Ludger Witte d,z, Thomas Hartmann ,
¨
e
Daniel F. Austin , Eckart Eich
a,
*
a
Institut fu¨r Pharmazie (Pharmazeutische Biologie), Freie Universita¨t Berlin, Ko¨nigin-Luise-Strasse 2+4, D-l4195 Berlin, Germany
b
AnalytiCon Discovery, Hermannswerder Haus 17, D-l4473 Potsdam, Germany
c
¨
Institut fu¨r Biologie (Angewandte Zoologie/Okologie der Tiere), Freie Universita¨t Berlin, Haderslebener Str. 9, D-12163 Berlin, Germany
d
Institut fu¨r Pharmazeutische Biologie, Technische Universita¨t Braunschweig, Mendelssohnstrasse 1, D-38106 Braunschweig, Germany
e
Conservation and Science Department, Arizona-Sonora Desert Museum, 2001 N. Kinney Road, Tucson, AZ 85743, USA
Received 26 July 2004; received in revised form 22 November 2004
Available online 24 December 2004
Abstract
A comprehensive GC–MS analysis of 8 Ipomoea species belonging to the subgenus Quamoclit, section Mina revealed that the
members of this taxon form combinations of two necine bases with rare necic acids resulting in unique pyrrolizidine alkaloids.
The occurrence and diversity of these metabolites show remarkable variations: Some species, especially Ipomoea hederifolia and Ipo-
moea lobata, are able to synthesize a large number of alkaloids whereas others, especially Ipomoea coccinea and Ipomoea quamoclit,
are poor synthesizers with only a few compounds. However, these metabolites are apparently chemotaxonomic markers of this
infrageneric taxon in general. They represent either esters of (ꢀ)-platynecine (altogether 48 ipangulines and 4 further esters including
results of a previous study) or esters of (ꢀ)-trachelanthamidine, an additional novel structural type called minalobines (altogether 21
alkaloids). Both types are characterized by section-specific rare necic acids, e.g., ipangulinic/isoipangulinic acid, phenylacetic acid.
The alkaloids of Ipomoea cholulensis, I. coccinea, I. hederifolia, Ipomoea neei, and Ipomoea quamoclit were mono and diesters of
platynecine. Minalobines turned out to be metabolites of I. lobata (Cerv.) Thell. (syn.: Mina lobata Cerv.) lacking ipangulines.
The major alkaloid of this species, minalobine R, has been isolated and identified as 9-O-(threo-2-hydroxy-2-methyl-3-phenylacet-
oxy-butyryl)-(ꢀ)-trachelanthamidine on the basis of spectral data. Apparently only two of the species included in this study, Ipo-
moea cristulata and Ipomoea sloteri, are able to synthesize both, ipangulines as well as minalobines. Minalobine O could be
isolated as a major alkaloid of I. cristulata, its structure has been established as 9-O-(erythro-2-hydroxy-2-methyl-3-tigloyloxy-
butyryl)-(ꢀ)-trachelanthamidine on the basis of spectral data.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Ipomoea; Subgenus Quamoclit; Section Mina; Convolvulaceae; Pyrrolizidine alkaloids; Platynecine esters; Trachelanthamidine esters;
Ipangulines; Minalobines
q
1. Introduction
Part 16 in the series ‘‘Phytochemistry and Chemotaxonomy of the
Convolvulaceae’’. For part 15 see Jenett-Siems et al. [Phytochemistry
62 (2003) 1257–1263].
Attempts to delimit species-groups of the largest con-
volvulaceous genus Ipomoea comprising at least 600 spp.
*
Corresponding author. Tel.: +49 30 83853720; fax: +49 30
83853729.
´
(Austin and Huaman, 1996; Judd et al., 1999), however
probably much more, have been made since shortly after
E-mail address: eckeich@zedat.fu-berlin.de (E. Eich).
Deceased author.
z
0031-9422/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.phytochem.2004.11.019

224
K. Jenett-Siems et al. / Phytochemistry 66 (2005) 223–231
the time of LinnaeusÕ Species Plantarum (1753). Some of
the more recent arrangements were begun by Verdcourt
the first compound of this new type, minalobine R, has
been isolated from I. lobata (Cerv.) Thell. (syn.: Mina
lobata Cerv.). The necine base of the latter type is repre-
sented by (ꢀ)-trachelanthamidine instead of (ꢀ)-platy-
necine; however, the necic acids are identical or closely
related to those of the ipangulines although only esteri-
fication at O-9 of the necine base is possible due to the
lack of a second hydroxyl (at C-7). Furthermore, the iso-
lation and characterisation of one further minalobine
from Ipomoea cristulata Hall. f. are reported.
´
(1957, 1963), and continued by Austin and Huaman
(1996); Austin (1998); and Austin et al. (2001). The lat-
est morphological classification of infrageneric taxa rec-
ognizes the three subgenera Eriospermum, Ipomoea,
and Quamoclit, (Austin, 1980, 1997). OÕDonell (1959)
made a systematic study of what is now called subgenus
Quamoclit (Moench) Clarke section Mina (Cervantes)
Grisebach. He recognized 13 species within the section
later being considered to comprise 18 species (Austin
´
and Huaman, 1996). They are exclusively native to the
New World; most of them are Mexican, however they
range from the United States to Argentina. In contrast
to all other Ipomoea spp. they are characterized inter alia
by salverformed corollas, red and/or yellow, rarely with
purple patches, the stamens exserted.
Although some authors segregate the group as the
separate genus Quamoclit, the species closest affinities
are clearly within Ipomoea. Usually, people who main-
tain Quamoclit as a genus are familiar only with Ipomoea
hederifolia and Ipomoea quamoclit, and not with the
morphological range within this section. Because those
two species were introduced into the Old World in the
early 1500s, people there have a mistaken view of them.
As OÕDonell (1953) and Wilkin (1999) have pointed out,
Ipomoea decemcornuta OÕDonell is one species that
bridges the morphological gap with Ipomoea.
In two previous papers we reported on the discovery
of ipangulines, a novel, unique type of pyrrolizidine
alkaloids as constituents of I. hederifolia L. (syn.: Ipo-
moea angulata Lam.) (Jenett-Siems et al., 1993, 1998).
These compounds are characterized by the novel combi-
nation of the saturated necine base (ꢀ)-platynecine with
aliphatic and/or an aromatic moiety containing carbox-
ylic acids. In the report of 1998 we already noted the
presence of these metabolites in the related species Ipo-
moea neei (Spreng.) OÕDonell and Ipomoea sloteri
(House) van Ooststr. In this former report the latter spe-
cies was called I. x perigrenium cv. Cardinal. However,
this is only one of different horticultural terms for the
ornamental Cardinal Climber which is not itself a hybrid
but the allotetraploid species Ipomoea sloteri derived
from the hybrids between Ipomoea coccinea L. and I.
quamoclit L. (Eckenwalder, 1986). We were able to har-
vest seeds in our greenhouse which unambiguously be-
long to I. sloteri.
The present communication describes the results of a
comprehensive GC–MS analysis of five additional mem-
bers of the section Mina in comparison with the three
species previously checked. The aim of this study has
been to figure out if the ipangulines are chemotaxo-
nomic markers of this section in general. Moreover, this
study led to the discovery of an additional novel type of
pyrrolizidine alkaloids structurally related to the ipan-
gulines for which we propose the term minalobines since
2. Results
2.1. GC–MS analysis
The study revealed that pyrrolizidine alkaloids with
a saturated necine base are a common feature of all
species investigated. They were detected in all plant or-
gans with a large variety in roots and shoots and a
smaller range also in the seeds. Therefore, only the re-
sults for the vegetative plant parts are given in Table 1.
In contrast to species from other pyrrolizidine alkaloid
containing families, e.g., Asteraceae or Boraginaceae,
no reduction of N-oxides was necessary prior to GC–
MS analysis, since pyrrolizidines are present as free
bases in the Convolvulaceae. Altogether 52 platynecine
esters (48 ipangulines and 4 further esters, Table 1) and
21 trachelanthamidine esters (minalobines, Table 1)
were identified. The ipangulines are divided up accord-
ing to the classification already chosen previously (Je-
nett-Siems et al., 1998; Fig. 1): ipangulines
A
(diesters containing one phenylacetyl moiety), ipangu-
lines B (diesters with one salicyloyl moiety), ipangulines
C (diesters with two aliphatic acyl moieties), ipangu-
lines D (either 7- or 9-monoesters), and ipangulines
X (ambiguous acyl moieties). However, a classification
of the minalobines seems to be of no use; therefore
their individual terms are just chosen alphabetically
(Table 1; Fig. 1). At least 11 diesters out of 21 minalo-
bines could be detected; without exception they show
erythro- or threo-2,3-dihydroxy-2-methylbutyric acid
(ipangulinic/isoipangulinic acid; Roeder, 1995), respec-
tively, as the acyl component directly conjugated with
the necine base. The second, individual ester moiety
is formed by the free 3-hydroxyl group of the first acyl
residue and differential acids. At least six minalobines
represent monoesters. The acyl component of four
compounds could not be determined.
Anhydroplatynecine (1), a compound detected in all
eight species, may be an artefact formed by the GC–
MS procedure from platynecine (3) and/ or its esters,
respectively. Compounds 5, 10, 12, and 16 are not clas-
sified as ipangulines though belonging to group D since
they are already known from plants out of the family
Convolvulaceae (see Section 3).

Table 1
GC–MS analysis of the pyrrolizidine alkaloids (relative abundance in %) from eight species of the section Mina (r, roots; s, shoots; t, trace; e-HMBA, erythro-2,3-dihydroxy-2-methylbutyryl moiety; t-HMBA, threo-2,3-dihydroxy-2-methylbutyryl; Ac-HMBA, 3-
acetoxy-2-hydroxy-2-methylbutyryl; DiAc-HMBA, 2,3-diacetoxy-2-methylbutyryl; MeBu-HMBA, 2-hydroxy-3-(2-methylbutyryloxy)-2-methylbutyryl; MeBu, 2-methylbutyryl; PAA, phenylacetyl; Sal, salicyloyl; Tigl, tigloyl)
Alkaloid
R1 (at O7)
R2 (at O9)
RI
[M]+,
I. hederifoliaa
I. cholulensis
I. coccinea
I. cristulata
I. lobata
I. neei
I. quamoclit
I. sloteri
m/z
s
t
r
t
s
t
s
t
r
t
s
t
r
s
t
r
t
s
t
r
t
s
r
t
s
t
1
2
Anhydroplatynecineb
Trachelanthamidine
Platynecine
–
–
1130
1252
1442
1540
1557
1703
1705
1720
1760
1778
139
141
157
213
199
227
223
239
241
241
t
t
–
H
3
H
H
t
t
4
Minalobine A
9-Acetylplatynecine
Ipanguline D1
Minalobine B
–
COC2H5O
Ac
t
5
H
6
H
COC3H7
Tigl
t
7
–
t
t
t
8
Minalobine C
–
COC4H7O
COC4H9O
H
9
Minalobine D
7-(2-Methylbutyryl)-
platynecine
–
t
t
10
MeBu
t
t
t
t
t
t
11
12
Minalobine E
–
COC4H9O
MeBu
1795
1803
241
241
t
9-(2-Methylbutyryl)-
platynecine
H
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Minalobine F
–
?
1825
1847
1886
1898
1922
2022
2037
2049
2085
2095
2100
2108
2125
2142
2157
2168
2183
2200
2212
2217
2223
2226
2236
2246
2283
2290
2302
2308
2311
2312
2318
2327
2349
2358
2375
2376
2387
2391
313
241
257
239
299
273
273
327
299
327
315
315
315
341
315
275
341
339
275
315
357
343
339
357
357
357
385
357
357
357
355
357
357
355
355
355
355
399
t
t
Minalobine G
Ipanguline D2
9-Tigloylplatynecine
Minalobine H
Isoipanguline D3
Ipanguline D3
Minalobine I
–
COC4H9O
COC4H9O
Tigl
H
t
t
H
–
COC6H11O3
t-HMBA
t
H
t
t
H
e-HMBA
t
–
COC3H7-HMBA
COC6H11O2
COC3H7-HMBA
?
t
t
Ipanguline D4
Minalobine J
H
t
t
–
c
Ipanguline X6
?
30
t
Isoipanguline D5
Ipanguline D12
Minalobine K
Ipanguline D5
Ipanguline D6
Minalobine L
Minalobine M
Ipanguline D7
H
Ac-t-HMBA
H
t
t
Ac-HMBA
–
MeBu-HMBA
Ac-e-HMBA
H
25
t
H
1
t
t
3
PAA
–
MeBu-HMBA
Tigl-t-HMBA
PAA
t
t
t
–
1
H
t
t
t
c
Ipanguline X7
?
?
t
t
12
8
Minalobine N
Ipanguline D8
Minalobine O
Isoipanguline D9
Ipanguline D9
Minalobine P
–
COC4H9O-HMBA
COC8H15O3
Tigl-e-HMBA
DiAc-t-HMBA
DiAc-e-HMBA
COC4H9O-HMBA
?
t
t
H
t
–
10
92
t
H
5
t
t
t
H
–
c
Ipanguline X1
?
t
Isoipanguline C1
Ipanguline C1
Minalobine Q
Ipanguline C6
MeBu
t-HMBA
8
t
50
t
40
t
90
t
97
t
MeBu
e-HMBA
30
20
–
COC4H9O-HMBA
HMBA
t
Tigl
t
d
Isoipanguline D10
H
MeBu-HMBA
MeBu-HMBA
H
1
t
t
t
Ipanguline D10
Ipanguline D13
Ipanguline D14
H
5
Tigl-HMBA
t
H
Tigl-HMBA
?
4
c
Ipanguline X2
?
t
28
t
t
Ipanguline D15
H
Tigl-HMBA
Ac-t-HMBA
87
t
3
Isoipanguline C2
MeBu
5
24
(continued on next page)

Table 1 (continued)
Alkaloid
R1 (at O7)
R2 (at O9)
RI
[M]+,
I. hederifoliaa
I. cholulensis
I. coccinea
I. cristulata
I. lobata
I. neei
I. quamoclit
I. sloteri
m/z
s
r
s
s
r
s
r
s
r
s
r
s
r
t
s
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
Ipanguline D6
Tigl-HMBA
MeBu
H
H
2395
2426
2480
2494
2506
2526
2606
2630
2634
2645
2645
2667
2702
2707
2770
2772
2782
2810
2837
2873
2886
2891
2927
2985
3055
3083
355
399
355
355
441
375
441
375
375
391
439
439
391
391
393
393
433
433
435
435
475
475
477
475
497
499
Ipanguline C2
Ipanguline D18
Ipanguline C7
Ipanguline C3
Minalobine R
Ipanguline C4
Minalobine S
Minalobine T
Minalobine U
Ipanguline C5
Ac-e-HMBA
Tigl-HMBA
HMBA
1
t
23
4
t
t
Tigl
MeBu
–
DiAc-HMBA
PAA-HMBA
MeBu-HMBA
?
5
1
72
97
MeBu
–
t
t
t
–
?
–
?
MeBu
?
Tigl-HMBA
?
t
t
c
Ipanguline X3
t
Isoipanguline A1
Ipanguline A1
Isoipanguline B1
Ipanguline B1
Isoipanguline A2
Ipanguline A2
Isoipanguline B2
Ipanguline B2
Isoipanguline A3
Ipanguline A3
Ipanguline B3
Ipanguline A4
PAA
PAA
Sal
t-HMBA
e-HMBA
t-HMBA
e-HMBA
Ac-t-HMBA
Ac-e-HMBA
Ac-t-HMBA
Ac-e-HMBA
DiAc-t-HMBA
DiAc-e-HMBA
DiAc-HMBA
MeBu-HMBA
?
12
2
7
70
6
t
3
18
3
t
Sal
29
t
PAA
PAA
Sal
8
1
t
t
Sal
t
PAA
PAA
Sal
13
2
4
PAA
?
5
c
Ipanguline X4
t
c
Ipanguline X5
?
?
1
a
b
c
Data of the shoots of I. hederifolia given for comparison, already published in Jenett-Siems et al. (1998).
Anhydroplatynecine might be an artefact due to GC–MS analysis.
According to GC–MS a platynecine ester but identity of necic acids uncertain.
d
This compound was formerly called ipanguline D10 (Jenett-Siems et al., 1998) but detection of 45 in I. cristulata unambiguously proved that 44 had to be the iso-derivative.

K. Jenett-Siems et al. / Phytochemistry 66 (2005) 223–231
227
Fig. 1. The four structural types of ipangulines (necine base: platynecine) and general structure of minalobines (necine base: trachelanthamidine);
R,R0 = aliphatic necic acid.
2.1.1. I. cholulensis Kunth.
2.1.6. I. quamoclit L.
The main alkaloids in shoots and roots were isoipan-
guline/ipanguline A1 (63/64) and ipanguline C1 (41).
Several further congeners, including isoipanguline/ipan-
guline B1 (65/66), were detected, altogether 19 com-
pounds, but no trachelanthamidine esters.
In the shoots and seeds of I. quamoclit no alkaloids
were detected. Only the roots contained small amounts
of PAs, namely anhydroplatynecine (1), ipanguline D10
(44) and ipanguline X2 (48).
2.1.7. I. sloteri (House) van Ooststr. cv. Cardinal
The shoots contained isoipanguline C1 (40) as main
constituent. In the roots, again 40, ipanguline D14 (47)
and D15 (49) represented the major alkaloids. Besides
further minor ipangulines, the trachelanthamidine ester
minalobine O (35) was detected.
2.1.2. I. coccinea L.
The shoots contained only small amounts of anhy-
droplatynecine (1) but no esters, while traces of ipangu-
line D13 (46) and D14 (47) were present in the seeds.
Unfortunately, roots could not be analyzed, due to lack
of plant material.
2.2. Isolation and structure elucidation of novel
pyrrolizidine alkaloids
2.1.3. I. cristulata Hallier f.
Main PAs were minalobine O (35), minalobine M
(30), and ipanguline D10 (45) in the leaves and again
35 and ipanguline D15 (49) in the roots. Additionally,
minalobines L (29) and Q (42) and the ipangulines D18
(53), C6 (43), and C7 (54) were detected as minor
constituents.
2.2.1. Minalobine R
The crude alkaloid fraction of the epigeal parts of I.
lobata yielded one compound giving a positive reaction
with DragendorffÕs reagent. From the HRMS a molecu-
lar formula of C21H29NO5 could be deduced. Character-
istic fragments at m/z 124 (base peak), 96 and 83 in the
EIMS suggested the compound to be a derivative of a
saturated 1-hydroxymethyl-pyrrolizidine. The ester resi-
2.1.4. I. lobata (Cerv.) Thell.
Besides anhydroplatynecine (1) only trachelanthami-
dine derivatives were present in I. Iobata, altogether 19
alkaloids. The dominating PA in leaves and roots was
minalobine R (56), with minalobine K (26) occurring
also in higher amounts only in the roots.
1
due could be identified by comparison of the H NMR
with the corresponding isoipanguline A1 (Jenett-Siems
et al., 1993). The NMR spectrum displayed signals for
a threo-2,3-dihydroxy-2-methylbutyric acid moiety as
well as a phenylacetic acid residue. The downfield shift
of H-3 of the threo-2,3-dihydroxy-2-methylbutyric acid
moiety at d 5.05 (1H, q, J = 6.5 Hz) revealed the attach-
ment of phenylacetic acid at this position. After hydro-
lysis of the alkaloid, GC–MS comparison of the necine
base with authentic isoretronecanol and trachelanthami-
dine together with determination of the optical rotation
2.1.5. I. neei (Spreng.) OÕDonell
Altogether 15 ipangulines were detected in different
parts of I. neei. Major alkaloids in the leaves were ipan-
guline X6 (23) and isoipanguline C1 (40), whereas again
40 and isoipanguline/ipanguline C2 (50/52) were domi-
nating in the roots.

228
K. Jenett-Siems et al. / Phytochemistry 66 (2005) 223–231
Fig. 2. Structures of minalobine R (56) from I. lobata and minalobine O (35) from I. cristulata (2,3-dihydroxy-2-methylbutyric acid residue: rel.
config.).
suggested the isolated compound to be a derivative of
(ꢀ)-trachelanthamidine (Robins and Sakdarat, 1981).
We named this new alkaloid minalobine R (56, Fig. 2).
or similar necic acids. However, (ꢀ)-trachelanthamidine
(2) instead of (ꢀ)-platynecine (3) enables only an esteri-
fication at O-9.
Thus, the structural comparison of minalobine R (56)
with isoipanguline A1 (63) shows that just the same two
necic acids are included in different combinations: both
alkaloids have in common isoipangulinic acid (threo-
2,3-dihydroxy-2-methylbutyric acid; Roeder, 1995) as
the acid component at C-1; however, the second necic
acid, phenylacetic acid, is conjugated with (1) the C-3
hydroxyl of isoipangulinic acid in the case of 56 forming
one diester center and (2) the C-7 hydroxyl of platyne-
cine like in 63 forming a diester with two monoester cen-
ters, respectively. Both acids are very rare as necic acids:
Isoipangulinic acid has been found only in one retrone-
cine type pyrrolizidine alkaloid of two Cryptantha spp.
(Boraginaceae); furthermore, this acid or its erythro-
isomer is conjugated with another retronecine type com-
pound of Senecio caudatus (Asteraceae) (Hartmann
and Witte, 1995). On the other hand, the necine base
platynecine is also rare: The occurrence of its esters out-
side the genus Ipomoea is restricted to certain Senecio
spp. (Asteraceae). However, trachelanthamidine esters
are more frequent, e.g., in different genera of the Orchid-
aceae which are able to synthesize alkaloids of the pha-
laenopsine type.
2.2.2. Minalobine O
The crude alkaloid fraction of the epigeal parts of I.
cristulata again yielded one compound giving a positive
reaction with DragendorffÕs reagent. From the HRMS a
molecular formula of C18H29NO5 could be deduced.
The same characteristic fragments at m/z 124 (base
peak), 96 and 83 in the EIMS again hinted to a deriva-
tive of a saturated 1-hydroxymethyl-pyrrolizidine. The
1H NMR spectrum displayed signals for a erythro-2,3-
dihydroxy-2-methylbutyric acid (Jenett-Siems et al.,
1993) moiety as well as typical resonances for a tiglate
residue (Logie et al., 1994). The downfield shift of H-3
of the erythro-2,3-dihydroxy-2-methylbutyric acid moi-
ety at d 5.09 (1H, q, J = 6.3 Hz) revealed the attachment
of tiglic acid at this position. Thus, the new alkaloid had
to be 9-O-(erythro-2-hydroxy-2-methyl-3-tigloyloxy-bu-
tyryl)-(ꢀ)-trachelanthamidine, which we named minalo-
bine O (35, Fig. 2).
3. Discussion
The occurrence of three different structural types of
pyrrolizidine alkaloids in the family Convolvulaceae
has been documented in previous studies: (1) loline alka-
loids (1-aminopyrrolizidines) as constituents of Argyreia
mollis (Burm. f.) Choisy (Tofern et al., 1999), (2) retro-
necine esters of the lycopsamine type (Mann et al.,
1996; Mann, 1997) as constituents of Merremia quinque-
folia (L.) Hall. f. and M. cissoides (Lam.) Hall. f., and (3)
platynecine esters of the ipanguline type (Jenett-Siems
et al., 1993, 1998). Whereas the first two types are also
present in other angiosperm families the latter is unique
in the plant kingdom. The present report includes an-
other novel structural type of pyrrolizidine alkaloids
which has been named minalobines. They share with
the ipangulines a saturated necine base and identical
Five of the Mina species investigated in this study, I.
cholulensis, I. coccinea, I. hederifolia, I. neei, and I. qua-
moclit, showed platynecine mono- and diesters (one or
two aliphatic necic acyl moieties; ipangulines C and
D). Only two of them, I. cholulensis and I. hederifolia,
are characterized by the additional occurrence of esters
with one aliphatic acyl moiety and one phenylacetyl
(ipangulines A) or one salicyloyl residue (ipangulines
B). These two species represent the members with the
most complex alkaloid spectrum from the qualitative
point of view as well as the species with the highest total
alkaloid content. This is of special interest since I. cho-
lulensis is considered as a neotropical plant of the high-
lands with I. hederifolia as its corresponding tropical
lowland relative. On the other hand I. coccinea, which

K. Jenett-Siems et al. / Phytochemistry 66 (2005) 223–231
229
is considered to be the corresponding temperate relative
of I. hederifolia, and also I. quamoclit show only very
few ipangulines in low concentrations. Furthermore, it
is interesting to notice that I. neei is a fairly good pro-
ducer of these metabolites since it is considered to be
perhaps a primitive member of the section (Austin,
1975).
Only, I. lobata turned out to synthesize 18 minalo-
bines but no ipangulines (left aside anhydroplatynecine
(1)). The two remaining species, I. cristulata and I. slo-
teri are characterized by the occurrence of both, minalo-
bines and ipangulines. The latter species only contains
minalobine O (35) as a minor component together with
several ipangulines already known from I. hederifolia.
Thus, surprisingly the horticultural hybrid I. sloteri is
a much more efficient alkaloid producer than its parents
(I. quamoclit and I. coccinea). I. cristulata is the only spe-
cies which revealed both alkaloid types side by side as
major constituents.
13C NMR spectra were obtained on a Bruker AMX
400 MHz spectrometer (TMS as int. standard).
4.2. Plant material
Seeds of I. quamoclit were collected near San Lore-
nzo, Panama, and of I. neei near Boquete, Panama.
Seeds of I. cristulata were kindly supplied by the Conser-
vation and Science Department, Arizona Sonora Desert
Museum, Tucson, AZ, and of I. cholulensis by J.L.T.
Mun˜oz, Centro de Investigation Cientifica de Yucatan
´
A. C. (CICY), Merida, Yucatan, Mexico. Seeds of I.
coccinea were kindly supplied by the Jardin Botanique,
Museum National dÕHistoire Naturelle, Paris. Seeds of
I. sloteri cv. Cardinal and young plants of I. lobata were
purchased from Gartencenter Pluta, Berlin-Dahlem.
Plants were grown from seeds in the greenhouse and
provided roots and shoots for alkaloid extraction. Vou-
cher specimens are deposited at the Institut fur Pharma-
¨
zie (Pharmazeutische Biologie), Freie Universita¨t Berlin.
From the biosynthetic point of view, the co-occur-
rence of platynecine derivatives and trachelanthamidine
derivatives is conspicuous. The difference between these
two necine bases is not only caused by the presence or
absence of an additional hydroxyl at C-7 but also by
the stereochemistry at C-1. It is unknown if the forma-
tion of platynecine (3) in plants is based on isoretronec-
anol, the lb-epimer of trachelanthamidine (2), or on a
configurative reversal at C-l of trachelanthamidine
(hydroxylation at C-7 left aside). Such a reversal might
take place by the formation of a 1,9-dehydro intermedi-
ate. In case of the section Mina the analyses of certain
members revealed both the presence of minalobines,
the potential precursors, and ipangulines, their potential
final products, e.g., the common occurrence of ipangu-
line D15 (49) and its 7-deoxy derivative minalobine O
(35) in the roots of I. sloteri.
Anyhow, the occurrence of unique pyrrolizidine alka-
loids formed by the combination of a saturated necine
base with section-specific rare necic acids can be consid-
ered as a common chemotaxonomic marker of Mina.
We could neither find this type of alkaloids in any other
Ipomoea species beyond this section nor in any other
convolvulaceous species of numerous genera (total num-
ber of investigated species: >120).
4.3. Extraction and isolation
Ground epigeal parts of I. lobata (450 g) were ex-
tracted with 10 l of MeOH (80%). After evaporation
the extract was acidified and partitioned between water
and organic solvents. The aqueous layer was then alka-
linized and extracted with CHCl3. The crude alkaloid
fraction was reduced with Zn/HCl and purified by pre-
parative HPLC (Rp-18, H2O (+0.5% H3PO4)/MeOH
60:40) to give minalobine R (30 mg).
Ground epigeal parts of I. cristulata (50 g) were ex-
tracted with 0.5 l of MeOH. After evaporation the ex-
tract was acidified and partitioned between water and
organic solvents. The aqueous layer was then alkalinized
and extracted with CHCl3. The crude alkaloid fraction
consisted of one major compound, minalobine O (5 mg).
4.4. Minalobine R (56)
20
Yellow oil. ½aꢁ ꢀ35ꢁ (MeOH; c 0.15); 1H NMR (400
D
MHz, CDCl3): 1.26(3H, d, J = 6.5 Hz, H-40); 1.29 (3 H,
s, H-50); 1.36–1.47 (2 H, m, H-2a, H-6a); 1.63–1.89 (5 H,
m, H-1, H-2b, H-6b, H-7); 2.43 (1H, ddd, J = 6.0, 10.0,
10.0 Hz, H-3a/H-5a); 2.49 (1H, ddd, J = 6.0, 6.0, 12.0
Hz, H-3a/H-5a); 2.90 (1H, ddd, J = 6.0, 12.0, 12.0 Hz,
H-3b/H-5b); 3.07 (2H, m, H-3b/H-5b, H-8); 3.51 (2H,
s, H-700); 3.64 (1H, dd, J = 6.5, 11.0 Hz, H-9a); 3.86 (1
H, dd, J = 7.0, 11.0, H-9b); 3.94 (1H, br s, OH); 5.05
(1H, q, J = 6.5 Hz, H-30); 7.19–7.31 (5H, m, H-200-H-
4. Experimental
4.1. General
13
Preparative high performance liquid chromatography
(HPLC) was performed on a Pharmacia LKB instru-
ment on a Superpac Pep-S C-2/C-18 (5 lm) reversed-
phase column. Optical rotations were measured with a
Perkin–Elmer 241 MC. EIMS and HR-EIMS were re-
600); C NMR (100 MHz, CDCl3): 13.2 (q, C-40), 21.9
(q, C-50), 25.8 (t, C-7), 30.4 (t, C-2/C-6), 31.6 (t, C-2/
C-6), 41.4 (t, C-700), 44.6 (d, C-1), 54.2 (t, C-3/C-5),
54.7 (t, C-3/C-5), 67.8 (d, C-8), 68.2 (t, C-9), 74.5 (d,
C-30), 75.8 (s, C-20), 127.0 (d, C-400), 128.5 (d, C-300/C-
500), 129.2 (d, C-200/C-600), 133.7 (s, C-100), 170.2 (s,
1
corded on a Varian MAT 711 (80 eV). H NMR and

230
K. Jenett-Siems et al. / Phytochemistry 66 (2005) 223–231
Table 2
GC–MS (70 eV) fragmentation patterns of pyrrolizidine alkaloids newly described in this study, for all other compounds compare Jenett-Siems et al.
(1998)
Compound
m/z (rel. int. %)
Trachelanthamidine (2)
Minalobine A (4)
Minalobine B (7)
Minalobine C (8)
Minalobine D (9)
141 [M]+ (37); 124 (12); 110 (10); 83 (100); 82 (52)
213 [M]+ (20); 140 (2); 124 (100); 110 (7); 95 (15); 83 (71); 82 (24)
223 [M]+ (10); 124 (100); 110 (5); 95 (10); 83 (45); 82 (18); 55 (29)
239 [M]+ (11); 168 (2); 124 (100); 95 (5); 83 (28); 82 (18)
241 [M]+ (5); 197(3); 140(12); 124(100); 110(5); 95 (8); 83 (31);
82 (17)
Minalobine E (11)
Minalobine F (13)
Minalobine G (14)
Minalobine H (17)
Minalobine I (20)
Minalobine J (22)
Minalobine K (26)
Minalobine L (29)
Minalobine M (30)
Minalobine N (33)
Minalobine P (38)
Minalobine Q (42)
Ipanguline C6 (43)
Ipanguline D17 (45)
Ipanguline D18 (53)
Ipanguline C7 (54)
Minalobine S (58)
Minalobine T (59)
Minalobine U (60)
241 [M]+ (5); 197 (2); 140 (7); 124 (85); 110 (5); 95 (8); 83 (32); 82
(20)
313 [M]+ (2); 239 (7); 145 (12); 142 (19); 124 (100); 110 (4); 96
(7); 83 (20); 82 (14)
241 [M]+ (2); 157 (5); 140 (7); 124 (85); 110 (5); 96 (7); 83 (67); 82
(38)
299 [M]+ (7); 212 (10); 239 (2); 142 (12); 124 (100); 110 (4); 95
(7); 83 (18); 82 (11)
327 [M]+ (8); 256 (1); 212 (15); 142(11); 124 (100); 110 (3); 96
(7); 83 (20); 82 (10); 71 (20)
327 [M]+ (6); 256 (5); 212 (13); 142 (17); 124 (100); 110 (4); 96
(6); 83 (18); 82 (10); 71 (22)
341 [M]+ (9); 256(3); 212 (11); 142 (13); 124 (100); 110 (3); 96
(5); 83 (18); 82 (9); 57 (22)
341 [M]+ (5); 256 (3); 212 (8); 142 (8); 124 (100); 110 (3); 96 (4);
83 (16); 82 (9); 57 (22)
339 [M]+ (4); 256 (1); 212 (10); 142 (8); 124 (100); 110 (3); 96 (8);
83 (52); 82 (9); 55 (38)
357 [M]+ (2); 212 (2); 142 (10); 124 (100); 110 (3); 96 (5); 83 (18);
82 (9)
357 [M]+ (2); 256 (12); 212 (8); 142 (19); 124 (100); 110 (3); 96
(21); 83 (20); 82 (27)
357 [M]+ (1); 256 (2); 212 (5); 140 (5); 124 (100); 110 (5); 96 (8);
83 (81)
355 [M]+ (2); 242 (8); 224 (7); 196 (8); 140 (29); 138 (31); 122
(30); 95 (33); 83 (78); 82 (100)
357 [M]+ (5); 242 (12); 228 (14); 140 (34); 122 (19); 96 (72); 95
(53); 82 (100); 57 (48)
355 [M]+ (3); 296 (1); 240 (5); 228 (10); 196 (23); 140 (17); 139
(22); 122 (12); 96 (32); 95 (38); 83 (64); 82 (100)
355 [M]+ (2); 254 (21); 240 (8); 222 (14); 196 (12); 140 (17); 138
(54); 122 (48); 95 (51); 83 (62); 82 (100)
375 [M]+ (1); 242 (50); 140 (10); 124 (100); 110 (3); 96 (5); 83
(25); 82 (11)
375 [M]+ (1); 242 (48); 140 (4); 124 (100); 110 (3); 96 (5); 83 (23);
82(10)
391 [M]+ (12); 258 (45); 212 (2); 142 (8); 124 (100); 110 (3); 96
(5); 83 (19); 82 (10)
C-800), 174.7 (s, C-10); EIMS (80 eV) m/z (rel. int.): 375
[M]+ (14); 256 (3); 213 (4); 142 (8); 140 (3); 124 (100);
96 (7); 91 (24); 83 (24); HREIMS m/z: 375.2044
(C21H29NOþ5 , calc. 375.2046); 256.1549 (C13H22NOþ4 ,
calc. 256.1549); 124.1126 (C8H14N+, calc. 124.1126).
4.6. Minalobine O (35)
1
Yellow oil. H NMR (400 MHz, acetone-d6): 1.25 (3
H, d, J = 6.3 Hz, H-40); 1.20–1.28 (2H, m, H-2a, H-6a);
1.38 (3H, s, H-50); 1.36–1.44 (5H, m, H-1, H-2b, H-6b,
H-7); 1.77 (3H, d, J = 5.5 Hz, H-400); 1.78 (3H, s, H-
500); 2.20 (2 H, m, H-3a, H-5a); 2.49 (1H, m, H-3b/H-
5b); 2.80–2.90 (2H, m, H-3b/H-5b, H-8); 4.21 (1H, dd,
J = 9.0 Hz, 11.4 Hz, H-9a); 4.35 (1 H, dd, J = 5.6, 11.4
Hz, H-9b); 5.09 (1 H, q, J = 6.3 Hz, H-30); 8.87 (1H,
q, J = 5.5 Hz, H-300); 13C NMR (100 MHz, acetone-
d6): 12.2 (q, C-400), 13.9 (q, C-40), 14.4 (q, C-500), 22.6
(q, C-50), 25.8 (t, C-7), 30.9 (t, C-2/C-6), 31.4 (t, C-2/
4.5. Hydrolysis of minalobine R
10 mg of minalobine R (56) were refluxed with 200
mg Ba(OH)2 in water for 2 h. Extraction of the aqueous
layer with CHCl3/isopropanol 3:1 yielded 2 mg of
20
D
(ꢀ)-trachelanthamidine. ½aꢁ ¼ ꢀ3 (c 0.1, EtOH); lit.:
ꢀ13.5 (c 2, EtOH) (Robins and Sakdarat, 1981).

K. Jenett-Siems et al. / Phytochemistry 66 (2005) 223–231
231
Austin, D.F., 1998. Parallel and convergent evolution in the Convol-
vulaceae. In: Mathew, P.M.S. (Ed.), Diversity and Taxonomy of
Tropical Flowering Plants. Mentor Books, Calicut, India, pp. 201–
234.
C-6), 40.4 (d, C-1), 52.0 (t, C-3/C-5), 53.1 (t, C-3/C-5),
65.3 (d, C-8), 67.9 (t, C-9), 75.2 (d, C-30), 77.1 (s, C-
20), 129.4 (d, C-200), 138.3 (d, C-300), 169.2 (s, C-100),
174.7 (s, C-10); EIMS (80 eV) m/z (rel. int.): 339 [M]+
(6); 256 (2); 212 (7); 196 (6); 140 (10); 124 (100); 96
(18); 83 (75); 55 (65); HREIMS m/z: 339.2044
(C18H29NOþ5 , calc. 339.2046); 256.1548 (C13H22NOþ4
calc. 256.1549); 212.1286 (C11H18NOþ3 , calc. 212.1287);
124.1127 (C8H14N+, calc. 124.1126).
´
Austin, D.F., Huaman, Z., 1996. A synopsis of Ipomoea (Convolvul-
aceae) in the Americas. Taxon 45, 3–38.
Austin, D.F., Kitajima, K., Yoneda, Y., Qian, L., 2001. A putative
tropical American plant, Ipomoea nil (Convolvulaceae) in Pre-
Columbian Japanese art. Econ. Bot. 55, 515–527.
Eckenwalder, J.E., 1986. Nomenclature of the Cardinal Climber
(Convolvulaceae) reconsidered. Taxon 35, 169–170.
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of the pyrrolizidine alkaloids. In: Pelletier, S.W. (Ed.), Alkaloids:
Chemical and Biological Perspectives, vol. 9. Pergamon Press,
Trowbridge, pp. 155–233.
4.7. GC–MS-analysis
Ground plant parts (50 g) were extracted three times
with 500 ml MeOH (80%). After evaporation the ex-
tract was acidified and partitioned between water and
organic solvents. The aqueous layer was then alkalin-
ized and extracted with CHCl3. The crude alkaloids
were subjected to GC–MS analysis. The GC–MS sys-
tem consisted of a Carlo Erba 5160/Fisons 8060 GC
equipped with a 30 m · 0.32 mm fused silica capillary
column coated with the methyl silicone stationary
phase DB 1 (J&W Scientific, California). Helium was
used as carrier gas. Conditions during split injection:
injector 250 ꢁC, split 1:20, temperature program 70–
300 ꢁC, 6 ꢁC/min. The capillary column was directly
coupled to the quadrupole mass spectrometer Finnigan
MAT 4515/MD800. Retention indices (RI): Kovats
indices (Kovats, 1958; Hartmann and Witte, 1995)
were calculated in respect to a set of co-injected hydro-
carbons. For EIMS fragmentation patterns of pyrro-
lizidine alkaloids newly described in this study see
Table 2.
Jenett-Siems, K., Kaloga, M., Eich, E., 1993. Ipangulines, the first
pyrrolizidine alkaloids from the Convolvulaceae. Phytochemistry
34, 437–440.
Jenett-Siems, K., Schimming, T., Kaloga, M., Eich, E., Siems, K.,
Gupta, M.P., Witte, L., Hartmann, T., 1998. Pyrrolizidine alka-
loids of Ipomoea hederifolia and related species. Phytochemistry 47,
1551–1560.
Judd, W.S., Campbell, C.S., Kellogg, E.A., Stevens, P.F., 1999. Plant
Systematics – A Phylogenetic Approach. Sinauer Associates Inc.,
Sunderland, MA, USA.
Kovats, E., 1958. Gas chromatographic characterization of organic
compounds. I. Retention indexes of aliphatic halides, alcohols,
aldehydes, and ketones. Helv. Chim. Acta 41, 1915–1932.
Linnaeus, C., 1753. Species Plantarum. Facsimile edition with intro-
duction by W.T. Stearn 1957. Ray Society, London.
Logie, C.G., Grue, M.R., Liddell, J.R., 1994. Proton NMR spectros-
copy of pyrrolizidine alkaloids. Phytochemistry 37, 43–109.
Mann, P., 1997. Zur Phytochemie und Chemotaxonomie tropischer
und mediterraner Convolvulaceen unter besonderer Berucksichti-
¨
gung des Alkaloid-Vorkommens. Dissertation Fachbereich Phar-
mazie, Freie Universitat Berlin, pp. 81–85.
Mann, P., Eich, E., Witte, L., Hartmann, T., 1996. GC–MS study on
the alkaloid pattern of Merremia quinquefolia (L.) H. Hall.: first
occurrence of retronecine esters, simple phenylethylamine deriva-
tives and pyrrolidinyl-heptadecanamide in the Convolvulaceae. In:
Abstract Book, 44th Annual Congress of the Society for Medicinal
Plant Research and a Joint Meeting with the Czech Biotechnology
Society, Prague, p. 128.
Acknowledgements
´
OÕDonell, C.A., 1953. Convolvulaceas americanas nuevas o criticas IV.
Lilloa 26, 353–400.
The authors are indebted to Mrs. E. Ba¨umel-Eich
(Berlin) for essential support in exploring and collecting
the plant material in the wild and to J.L.T. Mun˜oz, Cen-
tro de Investigation Cientifica de Yucatan A.C. (CICY),
´
Merida, Yucatan, Mexico, who kindly supplied the
seeds of I. cholulensis.
OÕDonell, C.A., 1959. Las especias americanas de Ipomoea L. sect.
Quamoclit (Moench.) Griseb. Lilloa 29, 19–86.
Robins, D.J., Sakdarat, S., 1981. Synthesis of optically active
pyrrolizidine bases. J. Chem. Soc., Perkin Trans. I, 909–915.
Roeder, E., 1995. Medicinal plants in Europe containing pyrrolizidine
alkaloids. Pharmazie 50, 83–98.
Tofern, B., Kaloga, M., Witte, L., Hartmann, T., Eich, E., 1999.
Occurrence of loline alkaloids in Argyreia mollis (Convolvulaceae).
Phytochemistry 51, 1177–1180.
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