Long-chain alkanoic acid esters of lupeol from Dorstenia harmsiana Engl. (Moraceae)

Article abstract of DOI:10.1080/14786419.2010.551769

In addition to lupeol (1a), three long-chain alkanoic acid esters of lupeol, in which two were new, were isolated from the hexane and ethyl acetate twigs extract of Dorstenia harmsiana Engl. (Moraceae). The structures of the new compounds were elucidated

Full text of DOI:10.1080/14786419.2010.551769

Natural Product Research
Vol. 26, No. 8, April 2012, 749–755
Long-chain alkanoic acid esters of lupeol from Dorstenia harmsiana
Engl. (Moraceae)
ab
a
Herve Martial P. Poumale *, Kenzo Patrice Awoussong ,
c
a
Rivoarison Randrianasolo , Christophe Colombe F. Simo ,
a
Bonaventure Tchaleu Ngadjui and Yoshihito Shiono
b
a
Department of Organic Chemistry, Faculty of Science, University of Yaounde´ I, PO Box
8
Yamagata University, Tsuruoka, Yamagata 997-8555, Japan; Department of Organic
b
12, Yaounde´, Cameroon; Department of Bioresource Engineering, Faculty of Agriculture,
c
Chemistry, Faculty of Science, University of Antananarivo, PO Box 906,
Antananarivo 101, Madagascar
(
Received 20 September 2010; final version received 30 December 2010)
In addition to lupeol (1a), three long-chain alkanoic acid esters of lupeol, in
which two were new, were isolated from the hexane and ethyl acetate twigs
extract of Dorstenia harmsiana Engl. (Moraceae). The structures of the new
compounds were elucidated on the basis of 1D and 2D NMR experiments.
Some isolated compounds were evaluated for their antimicrobial activities.
The lupeol and its three long-chain alkanoic acid esters showed antifungal
and antibacterial activities.
Keywords: Dorstenia harmsiana; Moraceae; lupeol; antimicrobial
1
. Introduction
There are about 170 species of the genus Dorstenia worldwide (Mabberly, 1987). It is
largely made up of undergrowth and herbaceous perennials with succulent and
scrambling rhizomes (Berg, Human, & Weerdenburg, 1989). In many parts of Africa,
Dorstenia species are commonly used for the treatment of an array of human
disorders, including arthritis, rheumatism, gout, stomach disorders, cough, headache
and skin diseases (Omisore et al., 2004).
To the best of our knowledge, no previous phytochemical study has been
reported on Dorstenia harmsiana Engl. so far. However, the widespread use of
Dorstenia in indigenous medicine for different ailments, as well as the antimicrobial
activity exhibited by this genus (Mbaveng et al., 2008), justified further attempts to
isolate and identify active compounds. This article deals with the isolation and the
structural elucidation of two new long-chain alkanoic acid esters of lupeol, and their
biological activities.
*Corresponding author. Email: poumale@yahoo.fr
ISSN 1478–6419 print/ISSN 1478–6427 online
ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/14786419.2010.551769
http://www.tandfonline.com

7
50
H.M.P. Poumale et al.
2
. Results and discussion
The powdered twig of D. harmsiana was successively extracted with n-hexane (extract
A) and ethyl acetate (extract B) in soxhlet apparatus. The extracts were submitted to
repeated column chromatography and preparative TLC to afford fatty acid, lupeol
(
1a) and three long-chain alkanoic acid esters of lupeol (1b–1d) in which two were
1
13
isolated and described here for the first time. The H and C NMR as well as the MS
of the known compounds were consistent with those reported in the literature.
Compound 1b was obtained as a white powder from extract A. The (þ)-HR-ESI
mass spectrum exhibited a pseudo-molecular ion of compound 1b at m/z 567.5138
þ
[
MþH] , corresponding to a molecular formula C H O . The IR spectrum showed
3
9
67
1
2
ꢀ
an ester signals at ꢀ 1713 (C¼O) and 1241 (C–O) cm . Three absorption bands at ꢀ
ꢀ
1
2
930, 1633 and 878 cm indicated a vinylidene group (¼CH ), characteristic of lup-
2
2
0(29)-ene (Roitman & Jurd, 1978).
1
The H NMR data indicated that compound 1b (Figure 1) is a pentacyclic
triterpenoid (Mbaze et al., 2007) with six methyl groups between ꢁ 0.68 and 1.15 (s,
H each), an olefinic methyl at ꢁ 1.63 (s, 3H), a methylene at ꢁ 2.18 (t, 2H,
3
J ¼ 6.7 Hz), six methine and 16 methylene groups between ꢁ 1.12 and 1.90. A methine
signal at ꢁ 2.28 (ddd, J ¼ 11.8, 9.7, 4.7 Hz) was attributed to the proton at C-19
position and one proton signal at ꢁ 4.41 (dd, 1H, J ¼ 4.1, 10.6 Hz) down field due to
the nonanoxy moiety was attributed to the proton at C-3 position, and its
characteristic of an equatorial (ꢂ) orientation. Two olefinic signals at ꢁ 4.46 (brd, 1H,
J ¼ 1.1 Hz, Hb-29) and 4.62 (brd, 1H, J ¼ 1.1 Hz, Ha-29) indicated an exomethylene
group.
1
3
The C NMR and DEPT spectra (Section 3) of compound 1b revealed the
presence of 39 carbon atoms, which were in accordance with the HR-ESI-MS and
the proton data. The carbonyl was found at ꢁ 174.0. The carbon atoms at ꢁ 151.3 and
1
2
09.7 are characteristic for the carbons 20 and 29 of lup-20(29)-ene (Mbaze et al.,
007), respectively. These data indicated that compound 1b might be a lupan-type
triterpene. The fragment at m/z 189 supported the presence of lup-20(29)-ene
Kumar, Muthukuda, & Wazeer, 1985).
(
(
a)
Hb
(
b)
2
9
Ha
2
9
3
0
20
3
0
1
9
1
2
22
19
17
1
2
22
2
5
26
17
2
5
26
2
8
2
8
1
14
1
1
4
9
6
9
O
3
3
27
27
9
„
RO
1„
O
6
2
4
2
23
24
1
a: R=H; 1b: R=C H17CO;
8
1
c: R=C10H21CO;1d: R=C15H31CO
Figure 1. (a) Structures of compounds 1a–1d. (b) Selected HMBC correlation in
compound 1b. Respective correlations were found also in compound 1c and 1d.

Natural Product Research
751
In the HMBC spectrum (Figure 1), correlations between the H-3 signal and
0
carbons 1, 2, 4, 5, 23, 24 and 1 , and the correlation of H-19 with C-17, 18, 20, 21, 22,
2
9 and 30 as well as the similarity with the shifts of lupeol (1a) indicated that
compound 1b has a long-chain ester moiety at the position C-3 (Figure 1) (Razdan,
Kachroo, Qurishi, Kalla, & Waight, 1996). Thus compound 1b was characterised as
lup-20(29)-en-3-nonanoate, which is described here for the first time.
1
D and 2D NMR spectra of compounds 1b and 1c were super-imposable,
suggesting that they belonged to a homologous series of lupeol with a long side chain
at C-3 position. The only differences between compounds 1b and 1c were in their
mass spectra and physical properties (Section 3). The positive HR-ESI mass
þ
spectrum of 1c exhibited a pseudo-molecular ion at m/z 595.5451 [MþH] , C H O
4
1
71
2
(
1c), thus compounds 1c was characterised as lup-20(29)-en-3-undecanoate.
Compound 1d identified as lup-20(29)-en-3-hexadecanoate was also isolated in
Koelpinia linearis (Compositeae) (Razdan et al., 1996).
The chemical constituents of the genus Dorstenia have been reported to be
coumarins/furanocoumarins (Abegaz et al., 2004; Caceres et al., 2001; Franke,
ˆ
Porzel, Masaoud, Adam, & Schmidt, 2001; Rojas-Lima, Santillan, DomoAnguez, &
˜
ˆ
GutieArrez, 1999; Swain, Quirke, Winkle, & Downum, 1991), flavonoids (Abegaz
et al., 2002, 2004; Ngadjui, Dongo, Abegaz, Fotso, & Tamboue, 2002; Ngadjui,
Dongo, Tamboue, Kouam, & Abegaz, 1999; Ngadjui, Kapche, Tamboue, Abegaz, &
Connolly, 1999; Ngadjui, Kouam, Dongo, Kapche, & Abegaz, 2000; Ngadjui,
Tabopda, et al., 1999; Ngadjui et al., 2005; Ngameni, Ngadui, Folefoc, Watchueng,
&
&
Abegaz, 2004; Ngameni et al., 2006) and triterpenoids (Uchiyama, Hara, Makino,
Fujimoto, 2002; Vouffo et al., 2008). This is the first time that long-chain alkanoic
acid ester has been isolated from Dorstenia genus.
Hydrolysis of 1b and 1c gave 1a, nonanoic acid and undecanoic acid (Section 3).
The structures of nonanoic acid and undecanoic acid were confirmed by HR-EI-MS
1
and H NMR spectra.
Since some of these genus are known to show some antimicrobial activity
(
Mbaveng et al., 2008), we investigated whether isolated compounds (1a–1d) would
also exhibit antimicrobial activity. The antifungal and antibacterial activities of
a–1d were determined using the agar diffusion method with 8 mm paper disks
loaded with 40 mg of each compound while nystatin (Staphylococcus aureus ¼ 12,
1
Bacillus subtilis ¼ 16, Streptomyces viridochromogenes (Tu 57) ¼ 14, Escherichia
¨
coli ¼ 14) was used as the reference. Compounds 1a, 1b, 1c and 1d showed activities
against Staphylococcus aureus (9, 12, 12, and 13 mm inhibition diameter), Bacillus
¨
subtilis (9, 10, 10 and 10 mm), Streptomyces viridochromogenes (Tu 57) (11, 12, 12
and 13 mm) and Escherichia coli (12, 11, 12 and 12 mm), respectively.
3
3
. Experimental section
.1. General
Melting point is uncorrected and was obtained with a micro melting point apparatus
Yanaco, Tokyo-Japan). Optical rotation values were measured with a Horiba
SEPA-300 polarimeter, and IR spectra were recorded with JASCO J-20A
(
1
13
spectrophotometer. The H and C NMR spectra were acquired with a Jeol
EX-400 spectrometer. Chemical shifts are given on a ꢁ (ppm) scale with TMS as an

7
52
H.M.P. Poumale et al.
internal standard. Mass spectra were obtained with a Jeol JMS-700 instrument.
Column chromatography was conducted on silica gel 60 (Kanto Chemical Co., Inc.,
Japan), Sephadex LH-20 (Pharmacia, Sweden) and ODS (Fuji Silysia, Japan). TLC
analysis was carried out by using precoated silica gel plates (Merck), and the spots
were detected by spraying with H SO /10% vanillin and then heating. Flash
2
4
chromatography was carried out on silica gel (230–400 mesh). R values were
f
measured on PolyGram SIL G/UV254 (Macherey-Nagel & Co.).
3
.2. Extraction and isolation
The twigs of D. harmsiana were collected in July 2008 at Kribi, South Cameroon.
A specimen has been deposited in the National Herbarium, Yaounde, Cameroon
Ref. No. 21642/SRF).
Powdered twigs (500 g) of D. harmsiana were successively extracted with
´
(
n-hexane and ethyl acetate in soxhlet apparatus. The solvent was removed under
reduced pressure to yield 12 and 9 g extract of n-hexane (extract A) and ethyl acetate
(extract B), respectively.
Extract A (12 g) was chromatographed over silica gel using hexane–acetone of
increasing polarity, which yielded two main fractions. Fraction I (2.2 g) was purified
by a small column chromatography using Sephadex LH-20 and CHCl : MeOH
3
(
7 : 2) as eluent, followed by preparative TLC to afford lupeol (1a, 85.1 mg)
Poumale, 2007) and lup-20(29)-en-3-nonanoate (1b, 28.0 mg). Fraction II (0.9 g)
(
was purified by a silica gel column chromatography eluted with hexane:ethyl acetate
(4 : 1) to yield lup-20(29)-en-3-undecanoate (1c, 24.3 mg).
Extract B (9.0 g) was passed through a Sephadex LH-20 column and subjected to
silica gel column chromatography and preparative TLC to afford lupeol (1a, 14.9
mg) and lup-20(29)-en-3-hexadecanoate (1d, 31.0 mg) (Razdan et al., 1996).
3
.2.1. Lup-20(29)-en-3-nonanoate (1b)
ꢁ
ꢁ
White powder; m.p.: 78–79 C; R ¼ 0.53 (CHCl ); [ꢃ] þ 26.7 (c 0.1, CHCl ); IR
f
3
D
3
(film) ꢀ : 2947, 2873, 1724, 1641, 1451, 1375, 1247, 1183, 1040, 1020, 975, 888
max
ꢀ
1 1
cm ; H NMR (400 MHz, CDCl ): ꢁ 4.62 (brd, 1H, J ¼ 1.1 Hz, Ha-29), 4.46 (brd,
3
1
9
H, J ¼ 1.1 Hz, Hb-29), 4.41 (dd, 1H, J ¼ 10.6, 4.1 Hz, H-3), 2.28 (ddd, 1H, J ¼ 11.8,
.7, 4.7 Hz, H-19), 2.18 (t, 2H, J ¼ 6.7 Hz, H-2’), 1.63 (s, 3H, H-30), 1.11-1.90
(overlapping multiplets, 39H, H-1, H-2, H-5, H-6, H-7, H-9, H-11, H-12, H-13, H-
0
0
0
0
0
0
0
1
2
5, H-16, H-18, H-21, H-22, H-3 , H-4 , H-5 , H-6 ; H-7 , H-8 , H-9 ), 1.12 (s, 3H, H-
3), 0.90 (s, 3H, H-24), 0.80 (s, 3H, H-27), 0.78 (s, 3H, H-26), 0.77 (s, 3H, H-25), 0.69
1
s, 3H, H-28); C NMR (100 MHz, CDCl ): ꢁ 174.0 (s, C-1 ), 151.3 (s, C-20), 109.7
3
0
(
(
(
(
(
3
t, C-29), 80.9 (d, C-3), 55.7 (d, C-5), 50.6 (d, C-9), 48.6 (d, C-18), 48.3 (d, C-19), 43.3
s, C-17), 43.1 (s, C-14), 41.2 (s, C-8), 40.3 (t, C-22), 38.7 (t, C-1) 38.7 (d, C-13), 38.6
0
t, C-15), 38.1 (s, C-4), 37.4 (s, C-10), 35.9 (t, C-16), 35.2 (t, C-7), 34.5 (t, C-2 ), 32.2
0
0
0
0
0
0
t, C-21), 30.1-27.7 (overlapping triplets, C-3 , C-4 , C-5 , C-6 , C-7 , C-8 ), 25.5 (t, C-
1
C-28), 16.9 (q, C-25), 16.4 (q, C-26), 16.3 (q, C-27), 14.8 (q, C-24), 14.4 (q, C-9 ); EI-
2), 25.4 (t, C-2), 21.2 (t, C-11), 24.1 (q, C-23), 18.5 (t, C-6), 19.6 (q, C-30), 18.2 (q,
0
þ
MS (70 eV): m/z (%) 566 (M , 9), 538(16), 530 (8), 513 (12), 460 (6), 425 ([M ꢀ
þ
C H CO] ,18), 409 (90), 407 (9), 367 (8), 365 (10), 307 (42), 289 (34), 229 (12), 203
8 17

Natural Product Research
753
(
40), 189 (21), 154 (100) 143 (90), 136 (94), 107 (7), 81 (10), 55 (13), 43 (40); (þ)-HR-
þ
ESI-MS: m/z 567.5138 ([MþH] , Calcd 567.5141 for C H O ).
3
9
67
2
3
.2.2. Lup-20(29)-en-3-undecanoate (1c)
ꢁ
ꢁ
White powder; m.p. ¼ 83–84 C; R ¼ 0.61 (CHCl ); [ꢃ] þ 38.6 (c 0.5, CHCl ); IR
f
3
D
3
1
(
4
film) (See 1b); H NMR (400 MHz, CDCl ): ꢁ 4.62 (brd, 1H, J ¼ 1.1 Hz, Ha-29),
3
.46 (brd, 1H, J ¼ 1.1 Hz, Hb-29), 4.41 (dd, 1H, J ¼ 10.6, 4.1 Hz, H-3), 2.28 (ddd, 1H,
0
J ¼ 11.8, 9.7, 4.7 Hz, H-19), 2.18 (t, 2H, J ¼ 6.7 Hz, H-2 ), 1.63 (s, 3H, H-30), 1.11-
1
H-15, H-16, H-18, H-21, H-22, H-3 , H-4 , H-5 , H-6 ; H-7 , H-8 , H-9 , H-10 , C-11 ),
.90 (overlapping multiplets, 43H, H-1, H-2, H-5, H-6, H-7, H-9, H-11, H-12, H-13,
0
0
0
0
0
0
0
0
0
1
3
.12 (s, 3H, H-23), 0.90 (s, 3H, H-24), 0.80 (s, 3H, H-27), 0.78 (s, 3H, H-26), 0.77 (s,
1
H, H-25), 0.69 (s, 3H, H-28); C NMR (100 MHz, CDCl ): ꢁ 174.0 (s, C-1 ), 151.3
3
0
3
(s, C-20), 109.7 (t, C-29), 80.9 (d, C-3), 55.7 (d, C-5), 50.6 (d, C-9), 48.6 (d, C-18),
4
3
3
7
8.3 (d, C-19), 43.3 (s, C-17), 43.1 (s, C-14), 41.2 (s, C-8), 40.3 (t, C-22), 38.7 (t, C-1)
8.7 (d, C-13), 38.6 (t, C-15), 38.1 (s, C-4), 37.4 (s, C-10), 35.9 (t, C-16), 35.2 (t, C-7),
0
0
0
0
0
4.5 (t, C-2 ), 32.2 (t, C-21), 30.1-27.7 (overlapping triplets, C-3 , C-4 , C-5 , C-6 , C-
0
0
0
0
, C-8 , C-9 , C-10 ), 25.5 (t, C-12), 25.4 (t, C-2), 21.2 (t, C-11), 24.1 (q, C-23), 18.5 (t,
C-6), 19.6 (q, C-30), 18.2 (q, C-28), 16.9 (q, C-25), 16.4 (q, C-26), 16.3 (q, C-27), 14.8
þ
0
(
q, C-24), 14.4 (q, C-11 ); EI-MS (70 eV): m/z (%) 594 (M , 10); (þ)-HR-ESI-MS:
þ
m/z 595.5451 ([MþH] , calcd 595.5454 for C H O ).
4
1
71
2
3
.2.3. Hydrolysis of 1b and 1c
Compounds 1b and 1c (4.0 mg each) were dissolved separately in MeOH (1 mL)/
distilled H O (1 mL). Then 7% HCl (1 mL) solution was added and the solution was
2
ꢁ
refluxed at 39 C for 4 h. Usual work up gave lupeol 1a, nonanoic acid (1.7 mg) and
undecanoic acid (1.3 mg).
1
Nonanoic acid. Amorphous solid, H NMR (400 MHz, CDCl ): ꢁ 2.24 (t, 2H), 1.20
3
(brs, 12H), 0.88 (t, 3H); HR-EI-MS m/z 158.1306 (Calcd 158.1307 for C H O ).
9 18 2
1
Undecanoic acid. Amorphous solid, H NMR (400 MHz, CDCl ): ꢁ 2.24 (t, 2H), 1.20
3
(brs, 16H), 0.88 (t, 3H); HR-EI-MS m/z 186.1618 (Calcd 186.1620 for C H O ).
11 22 2
3
.3. Antimicrobial assay
Agar diffusion tests were performed in the usual manner (Poumale et al., 2008) with
B. subtilis and E. coli (on peptone agar), S. aureus (Bacto nutrient broth),
S. viridochromogenes (M Test agar), the fungi Mucor miehei and Candida albicans
(Sabouraud agar), and three microalgae (Chlorella vulgaris, Chlorella sorokiniana
and Scenedesmus subspicatus).
Compounds were dissolved in an azeotrope chloroform:MeOH (87 : 13) and
4
dried for 1 h under sterile conditions and placed on the pre-made agar test plates.
0 mg pro paper disks (Ø8 mm) were impregnated with each using a 100 mL syringe,
ꢁ
Bacteria and fungi plates were kept in an incubator at 37 C for 12 h and micro algae
plates were kept for 3 days at room temperature in a day light incubator.
The diameter of inhibition zones was measured.

7
54
H.M.P. Poumale et al.
4
. Conclusion
Lupeol and three long-chain alkanoic acid esters of lupeol were isolated form the
twigs extract of D. harmsiana. Hydrolysis of the new compounds was carried out for
the confirmation of their structures. The isolated compounds showed some
antimicrobial activity at 40 mg pro paper disks. Flavonoids and coumarins which
are common in this genus were not isolated.
Acknowledgements
The authors are grateful to the Japan Society for the Promotion of Science (JSPS) for the
fellowship (No. P08430) awarded to Dr H.M.P. Poumale at the University of Yamagata,
Japan.
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