An E-ring γ-lactone pentacyclic triterpene from Myrianthus serratus

Article abstract of DOI:10.1016/S0031-9422(98)00292-1

A novel γ-lactone triterpenoid has been isolated from the methylated ethyl acetate extract of the trunk wood of Myrianthus serratus, as well as friedelin and four known pentacyclic triterpenoid acids, all as their methyl esters. Their structures were elucidated by 2D NMR experiments.

Full text of DOI:10.1016/S0031-9422(98)00292-1

Phytochemistry Vol. 49, No. 8, pp. 2473±2476, 1998
# 1998 Elsevier Science Ltd. All rights reserved
Printed in Great Britain
0031-9422/98/$ - see front matter
PII: S0031-9422(98)00292-1
AN E-RING g-LACTONE PENTACYCLIC TRITERPENE
FROM MYRIANTHUS SERRATUS
DAVID LONTSI,* NGNINZEKO FERNANDE NGOUNOU, AZEFACK LEON TAPONDJOU,
BEIBAM LUCAS SONDENGAM, BERNARD BODO and MARIE-THERESE MARTIN
Department of Organic Chemistry, Faculty of Sciences, University of Yaounde I, BP 812,
Yaounde, Cameroon; Museum National d'Histoire Naturelle, Laboratoire de Chimie, 63 Rue Bu€on,
75005 Paris, France; Institut de Chimie des Substances Naturelles, 27, Avenue de la Terrasse,
91198 Gif-sur-Yvette, France
(Received in revised form 17 March 1998)
Key Word IndexÐMyrianthus serratus; Cecropiaceae; phytochemistry; pentacyclic triter-
penes; g-lactone; serratolide; tormentic acid.
AbstractÐA novel g-lactone triterpenoid has been isolated from the methylated ethyl acetate extract of the
trunk wood of Myrianthus serratus, as well as friedelin and four known pentacyclic triterpenoid acids, all
as their methyl esters. Their structures were elucidated by 2D NMR experiments. # 1998 Elsevier Science
Ltd. All rights reserved
INTRODUCTION
(VLC) and crystallization four methyl esters of pen-
tacyclic triterpenoid acids: methyl tormentate (2) [4],
methyl euscaphate (3) [5], methyl benthamate (4) [6],
methyl 2a-hydroxyoleanolate (5) [7] and a new E-
ring containing g-lactone derivative, serratolide (1).
In our systematic study of the chemical constituents
of the Cameroonian members of the family
Cecropiaceae, we investigated the trunk wood of
Myrianthus serratus Trecul, a minor species of this
taxon which grows in littoral zones [1] and for
which no phytochemical study has yet been pub-
lished. Previous studies on this family led to the iso-
lation of many pentacyclic triterpenes among which
were showing 2,3 oxidative cleavage and A-ring
contraction [2, 3]. The present study deals with the
same structure elucidation of a new pentacyclic tri-
terpene (1) with a g-lactone system in ring E,
obtained together with ®ve known pentacyclic tri-
terpenes including friedelin, methyl tormentate (2),
methyl euscaphate (3), methyl benthamate (4) and
methyl 2a-hydroxyoleanolate (5), which were
characterized by comparison of their spectral data
with those of authentic samples. The original spec-
tral data of known compounds are obtainable from
the author of correspondence.
Compound
1 gave a positive Liebermann±
Burchard test. The EIMS showed the [M]+ at m/z
512 corresponding to the molecular formula
C32H48O5. Its IR spectrum exhibited absorption
bands at 1390 and 1375 (gem-dimethyl), 1765 (g-lac-
1
tone) and 1724 (ester), 3430 (OH) and 1605 cm
(trisubstituted double bond). Interpretation of the
1H and 13C NMR spectral data by means of 1H±
1H-COSY, H±13C COSY and HMBC led to struc-
1
ture 1. The 1H NMR spectrum of 1 showed singlet
resonances of six tertiary methyl groups at d 0.72
(Me-29), 0.80 (Me-24), 1.10 (Me-24), 1.18 (Me-25),
1.27 (Me-27) and 1.42 ppm (Me-29) and a second-
ary methyl signal at d 1.11 (d, J = 7.5 Hz) corre-
sponding to Me-30, as well as an acetyl group
resonance at d 2.07 attributed to 3-OAc. This was
con®rmed by the H-2 signal which appeared at d
4.93 as ddd, with two large (J1=14.5 and
J2=10.5 Hz) and one small (J = 4.5 Hz) coupling
constants. This chemical shift as well as the coup-
ling pattern were almost identical with those of
methyl cecropate (6) in which H-2 appeared at d
4.95 [8], and therefore established an identical sub-
stitution of ring A in both compounds and conse-
quently proved H-2 to be b-axial. Accordingly, the
RESULTS AND DISCUSSION
The ethyl acetate extract of the defatted trunk
wood of M. serratus was methylated and a€orded
after repeated vacuum liquid chromatography
*Author to whom correspondence should be addressed.
2473

2474
D. LONTSI et al.
acetoxyl group at that position was a-equatorial [7]. droxylated derivative) and in compound 1. The
This was con®rmed by the presence of the signal at above carbons resonated at d 73.0 and 178.3, re-
d 3.21 which appeared as a doublet (J = 10.5 Hz) spectively, in methyl tormentate (2); however, these
attributed to H-3 at an a-axial position geminal to carbon atoms appeared at d 79.1 and 183.7 in com-
a hydroxyl group. Similarly, H-3 resonates at d 3.21 pound 1, thus con®rming the presence of the lac-
in compound 6. Close inspection of the 1H NMR tone system in ring E. Furthermore, the down®eld
revealed the presence of the singlet signal at d 2.52 e€ect on the Me-29 protons (d, s 1.42) observed on
attributed to H-18, compatible with the absence of the 1H NMR of compound 1 could be seen as
a proton at the C-19 position, thus con®rming the resulting from the magnetic anisotropy generated
tertiary nature of that carbon atom. Finally, the by the carbonyl function of the lactone system. The
vinylic proton at d 5.32 appeared as a triplet con®guration of the lactone ring was envisaged to
(J = 3.5 Hz) compatible with the existence of the be b, as the result of the epimerization at C-19 con-
allylic methylene group at C-11. The presence of comitant to the change in the junction between
the secondary methyl group in the 1H and 13C rings D and E from trans as in methyl tormentate
NMR spectra further suggested that compound 1 (2) to cis in serratolide (1) (Fig. 1). This was corro-
belonged to the D12 ursene-type pentacyclic triter- borated by molecular model building which showed
penes. In fact C-12 and C-14 in compound 1 reso- the inversed boat conformation to be the most
nated at d 129.0 and 138.0 in good agreement with plausible for the formation of the lactone ring. As a
urs-12-en derivatives [8]. The down®eld e€ect on consequence of the above epimerization, the Me-29
Me-29 (d, 1.42 ppm) is rather unusual compared to group had to be a. According to the Me-20 group,
the chemical shift of that group in other 19a-hy- it has the same orientation as in other similar de-
droxylated urs-12-en derivatives [9]. In fact, the Me- rivatives (Fig. 1). Structure 1 was further supported
29 group in methyl tormentate (2) appeared at d by the results from the HMBC experiment, opti-
1.19, where it was geminal to a hydroxyl group. mized for a coupling constant value of 7 Hz: cross-
The Dd = 0.23 suggested the presence of a lactone peaks were observed between H-18 (d 2.52) and C-
system between the 19-hydroxyl and 28-carboxyl 19 (d 79.1), C-17 (d 47.1) and C-13 (d 138.0). Cross-
groups. This was corroborated by the resonances of peaks were also observed between H-2 and C-3 (d
C-19 and C-28 both in methyl tormentate (19a-hy- 80.9) and C-4 (d 40.0). The EIMS of 1 corroborated

An E-ring g-lactone pentacyclic triterpene from Myrianthus serratus?
2475
Fig. 1. Perspective drawing indicating the conformation change of ring E leading to g-lactone
formation.
the above structure with important fragments at with an Et2O solution of CH2N2. The solid
m/z 43 (acetoxyl group), 246 (RDA) and 266
(M RDA), 485 (M+1 CO). This structure was
also con®rmed by alkaline hydrolysis of 1 which led
to tormentic acid (3) and the methyl ester of which
was identical in all respects (1H, 13C NMR and
m.p.) to methyl tormentate (2). In the light of the
obtained after evaporation of the solvent (50 g) was
repeatedly chromatographed over silica gel (VLC)
columns (1.5 kg) eluted with hexane±EtOAc mix-
tures with increasing polarity. Hexane±EtOAc (9:1)
a€orded friedelin. Elution with hexane±EtOAc
(17:3) gave Me pomolate and 2a-hydroxyoleanolate
(5), whereas 4:1 mixture furnished Me tormentate
(2), Me euscaphate (3) and the new compound
serratolide (1).
above evidence, compound
1 is 2a-acetoxy,3b-
hydroxyurs-12-en-19, 28-olide and has been given
the name serratolide.
EXPERIMENTAL
Table 1. 13C NMR spectral data of serratolide (1), methyl
tormentate (2) and methyl cecropate (6)
General
1H- and 13C-NMR (1D or 2D experiments): 300
and 75 MHz, respectively, with TMS as int. stan-
dard; EIMS: 70 eV; CI-MS: NH3; IR: KBr; CC:
silica gel (70±230 mesh ASTM) (Riedel-de-Haen);
C
1
2
6
1
2
3
4
5
6
7
8
46.7
73.3
80.9
40.0
55.0
18.3
37.4
39.7
47.7
38.3
23.7
129.0
138.0
41.1
28.1
24.5
47.1
52.8
79.1
39.7
32.5
37.4
28.5
17.0
16.3
16.6
183.7
16.9
21.4
171.4
52.8
46.3
68.5
83.3
39.1
55.1
18.3
32.4
39.7
47.0
37.9
23.5
128.6
138.0
41.0
28.0
25.2
47.7
53.0
72.8
41.0
25.8
37.2
28.6
16.7
16.4
16.4
178.3
27.2
15.2
44.2
73.5
81.2
39.9
55.4
18.4
33.1
39.8
47.8
38.5
23.6
125.5
138.6
42.3
28.2
24.4
48.3
53.1
39.4
39.1
30.8
36.8
28.7
17.0
16.5
16.7
178.1
17.0
21.1
171.6
51.4
TlC: silica gel GF254
.
Plant material
The trunk wood of Myrianthus serratus Trecul
was collected in March 1994 at Dizangue
(Cameroon
Achoundong
Herbarium, where a voucher specimen (No. 32440/
SRF/CAM) is deposited.
9
Littoral
of
Province)
by
Gaston
National
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
28
29
30
COCH3
the
Cameroon
Extraction and isolation of compounds
The plant material was cut into pieces, air-dried
and pulverized. The resulting powder (3.5 kg) was
continuously extracted by maceration with MeOH
(15 l) at room temperature for 3 days and the oper-
ation repeated 2 more times. The combined MeOH
extracts were concentrated under red. pres. to yield
a precipitate which was ®ltered and dried (38 g).
The ®ltrate was further diluted with H2O and frac-
tionated successively with hexane and EtOAc. The
EtOAc fraction (16 g) had qualitatively the same
composition as the above precipitate, and therefore
was combined with it and the mixture methylated
OCH3
51.5

2476
D. LONTSI et al.
Saponi®cation of compound 1
``Ministere de la Cooperation'' are also acknowl-
edged for their ®nancial support.
Compound 1 (20 mg) was re¯uxed overnight in
10% MeOH±KOH (10 ml). The reaction medium
was further diluted with H2O (10 ml) and neutral-
ized with 0.1 N HCl. Extraction of the reaction
medium with EtOAc and evaporation to dryness
a€orded tormentic acid.
REFERENCES
1. Berg, C. C, Hijman, M. E. E. and
Weerdenburg, J. C. A., Flore du Cameroun,
Vol. 28, ed. B. Satabie. MESRES, Yaounde,
Cameroon, 1985, pp. 262±270.
2. Lontsi, D., Sondengam, B. L., Martin, M. T.
and Bodo, B., Phytochemistry, 1991, 30, 1621.
3. Lontsi, D., Sondengam, B. L., Martin, M. T.
and Bodo, B., Phytochemistry, 1991, 30, 2361.
4. Ojinnaka, C. M., Okogun, J. I. and Okorie, D.
A., Phytochemistry, 1980, 19, 2482.
5. Lontsi, D., Sondengam, B. L., Martin, M. T.
and Bodo, B., Phytochemistry, 1992, 31, 4285.
6. Barmejio, J., Breton, J. L., De la Fuente, G.
and Gonzales, A. G., Tetrahedron Letters,
1967, 47, 4649.
7. Glen, A. T., Lawrie, W., McLean, J. and
Younes, G., Journal of the Chemical Society,
1967, 510.
2a-Acetoxy,3b-hydroxyurs-12-en-19,28-olide
Amorphous powder (hexane±EtOAc). IR, nmax
cm 1: 3430 (br OH), 1765 (g-lactone), 1725 (ester),
1605 (>C.CH±), 1390±1375 (gem-dimethyl), 1200
1
(C±O), 1030, 920, 860, 795 and 765 cm
;
1H
NMR: d 0.72 (3H, s, CH3-26), 0.80 (3H, s, CH3-
24), 1.10 (3H, s, CH3-23), 1.11 (3H, d, J = 7.5 Hz,
CH3-30), 1.18 (3H, s, CH3-25), 1.27 (3H, s, CH3-
27), 1.42 (3H, s, CH3-29), 0.94 (1H, m, H-1ax), 1.90
(1H, m, H-1eq), 2.00 (1H, m, H2-11), 2.07 (3H, s,
2-COCH3), 2.52 (1H, s, H-18), 3.21 (1H, d, H-3),
4.93 (1H, ddd, J1=14.5, J2=10.5, J3=4.5 Hz). 13C
NMR: Table 1.
8. Lontsi, D., Sondengam, B. L., Ayafor, J. F.,
Tsoupras, M. G. and Tabacchi, R., Planta
Medica, 1990, 56, 287.
9. Seo, S., Tomita, Y. and Tori, K., Tetrahedron
Letters, 1975, 1, 7.
AcknowledgementsÐThe authors express their grati-
tude to Dr G. Achoundong for the identi®cation
and collection of plant material. The International
Foundation for Science (IFS) and the French