New megastigmane glucosides from Excoecaria cochinchinensis Lour. var. cochinchinensis

Article abstract of DOI:10.1248/cpb.53.1600

Two new megastigmane glucosides, called excoecariosides A and B were isolated from the leaves of a medicinal Vietnamese plant, Excoecaria cochinchinensis Lour. var. cochinchinensis (Euphorbiaceae) together with seven known compounds. Their structures were

Full text of DOI:10.1248/cpb.53.1600

1600
Notes
Chem. Pharm. Bull. 53(12) 1600—1603 (2005)
Vol. 53, No. 12
New Megastigmane Glucosides from Excoecaria cochinchinensis LOUR.
var. cochinchinensis
a
b
,b
Phan Minh GIANG,a,b Phan Tong SON, Katsuyoshi MATSUNAMI, and Hideaki OTSUKA
*
a Faculty of Chemistry, College of Natural Science, Vietnam National University; 19 Le Thanh Tong, Hanoi, Vietnam; and
b Graduate School of Biomedical Sciences, Hiroshima University; 1–2–3 Kasumi, Minami-ku, Hiroshima 734–8551, Japan.
Received August 4, 2005; accepted August 24, 2005.
Two new megastigmane glucosides, called excoecariosides A and B were isolated from the leaves of a medici-
nal Vietnamese plant, Excoecaria cochinchinensis LOUR. var. cochinchinensis (Euphorbiaceae) together with
seven known compounds. Their structures were elucidated by spectroscopic analyses and chemical reactions in-
cluding the modified Mosher’s method.
Key words Excoecaria cochinchinensis; Euphorbiaceae; megastigmane glucoside; excoecarioside
Excoecaria cochinchinensis LOUR. var. cochinchinensis MeOH extract between H2O and organic solvents of increas-
(Euphorbiaceae) (Vietnamese name: Don mat troi) is a small ing polarity, n-hexane, EtOAc, and 1-BuOH, gave three cor-
plant, about 1 m high and endemic to eastern Indochina.1—3) responding soluble fractions. The 1-BuOH-soluble fraction
Growing wild and also being cultivated as a medicinal and was subjected to a general separation procedure (see Experi-
ornamental plant, the plant is characterized by the features mental) to give compounds 1—9.
that its leaves are nearly opposite, deep green above, and pur-
Excoecarioside A (3), an amorphous powder, gave a mole-
ple red beneath, and the margins denticulate.1,2) Its leaves are cular formula of C19H32O8 at m/z 387.2028 ([MꢀH]ꢀ) in the
usually used in a Vietnamese folk medicine to treat furun- negative-ion high-resolution (HR)-FAB-MS. The IR spec-
cles, pruritus, prolonged diarrhoea, urethrorrhagia, and trum indicated the presence of hydroxy (3368 cmꢀ1) and an
dysentery.2) Until now, there has been no information on gly- a,b-unsaturated ketone (1643 cmꢀ1) group. The H-, 13C-
1
cosidic compounds from E. cochinchinensis var. cochinchi- NMR (Table 1), distortionless enhancement by polarization
nensis. This paper describes the isolation and structure eluci- transfer (DEPT), and heteronuclear single quantum correla-
dation of two new megastigmane glucosides (3, 4), together tion (HSQC) spectra of 3 showed the presence of 13 carbons
with seven known compounds (1, 2, 5—9) from the leaves of of a megastigmane skeleton and six carbons of b-glucopyra-
the title plant.
nose [dC 104.3 (d), 77.8 (d), 77.6 (d), 74.8 (d), 71.3 (d), and
The air-dried and powdered leaves of E. cochinchinensis 62.2 (t); anomeric proton: dH 4.15 (d, Jꢁ7.8 Hz)]. A similar
var. cochinchinensis were extracted with MeOH at room tem-
perature, and the successive partition of the concentrated
Table 1. 1H- and 13C-NMR Spectroscopic Data of 3 and 4 (d in ppm, J in
Hz, CD3OD)
3
4
C/H
C
H
C
H
1
2a
b
41.3
44.1
42.7
50.6
2.33 d (16.8)
2.33 d (16.8)
2.18 d (16.8)
2.49 d (16.8)
3
4
5
6
7a
b
8a
b
201.4
125.5
169.1
46.1
201.3
124.4
165.1
79.1
5.82 s
6.29 s
2.35 m
1.65 m
1.75 m
1.56 m
1.56 m
3.70 m
1.15 d (6.1)
3.70 m
1.12 s
26.2
130.0
5.83 s
39.2
137.1
5.82 d (4.4)
9
68.5
24.3
76.4
23.1
21.9
68.7
23.8
23.4
24.1
67.8
4.31 m
1.23 d (6.6)
0.99 s
1.04 s
4.29 m
10
11
12
13a
b
2.04 s
4.66 dd (17.6, 2.0)
4.27d (7.8)
3.27 m
3.30 m
3.28 m
3.30 m
3.65 dd (12.0, 5.4)
3.85 dd (12.0, 2.2)
1ꢂ
2ꢂ
3ꢂ
4ꢂ
5ꢂ
6ꢂa
b
104.3
74.8
77.8
71.3
77.6
62.2
4.15 d (7.8)
3.15 m
3.30 m
3.30 m
3.30 m
103.7
75.0
78.0
71.6
77.9
62.7
3.70 m
3.86 br d (11.2)
Fig. 1. Chemical Structures of Compounds 3, 3a—c, 4, 4a, 6, 6a—c, 10,
and 11
∗ To whom correspondence should be addressed. e-mail: hotsuka@hiroshima-u.ac.jp
© 2005 Pharmaceutical Society of Japan

December 2005
1601
Fig. 2. DdS–R Values (in ppm) Obtained for (S)- and (R)-MTPA Esters (3b,
c) of 3a
Fig. 3. HMBC Correlations of 4
structure to blumenol C (10) was deduced by comparing the
13C-NMR data of 3 with those of 10,4) except for a glucose-
bearing hydroxymethylene group [dC 76.4 (t), dH 3.70 (2H,
m)], which was positioned at either C-11 or C-12. The 6S
configuration of 3 was determined by the extremes at 223 nm
(De ꢃ1.39) and 244 nm (De ꢃ1.08) in the circular dichroism
(CD) spectrum.5) Enzymatic hydrolysis yielded D-glucose
and the aglycone 3a, called excoecariol A, whose structure
1
was in agreement with the H- and 13C-NMR spectroscopic
data (see Experimental). The nuclear Overhauser enhance-
ment and exchange spectroscopy (NOESY) of 3a showed a
NOE between H3-12 (dH 1.12) and Ha-6 (dH 2.15), hence
the hydroxymethylene group was assigned in a b-orientation.
Since stereoisomers of (9R) and (9S)-alcohols of megastig-
Fig. 4. Phase-Sensitive NOESY Correlations of 4a
mane structures show essentially indistinguishable 13C val- relative stereochemistry of 4 was determined using the
ues,5) the absolute configuration at C-9 of 3a was determined phase-sensitive NOESY spectrum of 4a (Fig. 4). NOEs from
to be S by the modified Mosher’s method,6) using the DdS–R H-7 (dH 5.71) to H3-11 (dH 0.91) and Ha-13 (dH 4.08), and
values obtained for (S)- and (R)-MTPA esters (3b, c) of 3a from H3-10 (dH 1.14) to H3-12 (dH 0.95) are indicative of the
(Fig. 2). Therefore, the structure of 3 was determined to be 6a,9a stereochemistry of the epoxy ring and a-orientation
(6S,9S)-megastigman-3-on-4-ene-9,11-diol 11-O-b-D-glu- of the methyl group at C-10. Therefore, the structure of 4
copyranoside.
was determined to be 6a,9a-epoxymegastigman-3-on-4-ene
Excoecarioside B (4) was obtained as a syrup with a mole- 13-O-b-D-glucopyranoside. Since the first report on thea-
cular formula of C19H28O8 at m/z 383.1729 ([MꢀH]ꢀ) in the spirones from black tea essential oil in 1968,9) this work is
negative-ion high-resolution (HR)-FAB-MS. The IR spec- the first isolation of a theaspirone glucopyranoside from Na-
trum indicated the presence of hydroxy (3372 cmꢀ1) and an ture.
1
1
a,b-unsaturated ketone (1650 cmꢀ1) group. The H-, 13C-
Compound 6 showed identical H- and 13C-NMR spectro-
NMR (Table 1), and DEPT spectra characterized 4 as a scopic data and HR-FAB-MS as those of glochidionionoside
megastigmane glucoside. Two tertiary methyl groups [dH B, previously isolated from Glodichion zeylanicum.5) Of two
0.99 (s), 1.04 (s)], a glucose-bearing hydroxymethylene chiral centers at C-6 and C-9, the configuration at C-6 was
group [dH 4.29 (m) and 4.66 (dd, Jꢁ17.6, 2.0 Hz)], and an determined to be R by the same extremes as those of glochid-
a,b-unsaturated ketone group [dC 201.3 (s), 165.1 (s), and ionionoside B in the CD spectrum. Due to the ambiguity
124.4 (d); dH 6.29 (s)] and b-glucopyranose [dC 103.7 (d), caused by the small values of the optical rotations of 6
78.0 (d), 77.9 (d), 75.0 (d), 71.6 (d), and 62.7 (t), anomeric {[a]2D5 ꢃ7.5° (cꢁ0.53, MeOH)} and glochidionionoside B
proton: dH 4.27 (d, Jꢁ7.8 Hz)] were assigned for the struc- {[a]2D8 ꢃ7.4° (cꢁ1.22, MeOH)} we verified the configuration
ture of 4. Enzymatic hydrolysis released the aglycone 4a, at C-9. The modified Mosher’s method was applied for the
which showed a chemical shift of H-4 [dH 6.07 (s)] charac- aglycone (6a) of 6,6) indicating the same distribution of posi-
teristic of the presence of the hydroxymethylene at C-13,7) tive and negative DdS–R values of (S)- and (R)-MTPA esters
1
and D-glucose. Full H- and 13C-NMR assignments of 4a, of 6a (data not shown) as those reported for (S)- and (R)-
named excoecariol B, are listed in Experimental. The posi- MTPA esters of the aglycone of glochidionionoside B. Thus
tion of the sugar moiety was determined at C-13 on the basis the 9R stereochemistry and the identity of 6 with glochodion-
of the heteronuclear multiple bond correlations (HMBC) of 4 ionoside B were proved.
between H-1ꢂ (dH 4.27) and C-13 (dC 67.8), between H2-13
Gallic acid (1) and (ꢀ)-shikimic acid (2) were determined
(dH 4.29, 4.66) and C-4 (dC 124.4), C-5 (dC 165.1) and C-1ꢂ by direct comparison ([a]D and NMR) with the authentic
(dC 103.7), and between H-4 (dH 6.29) and C-13 (Fig. 3). samples. Comparison of H- and 13C- NMR spectroscopic
1
The C-6 side chain formed an epoxy ring between C-6 and data with those reported in the literature determined p-hy-
C-9 in accordance with the number of double bond equiva- droxybenzoic acid (5),10) kaempferol 3-O-b-D-glucopyra-
lence (6) and remarkable small coupling constants of H-7 noside (7),11) kaempferol 3-O-b-D-galactopyranoside (8),12)
and H-8 [dH 5.83 (s), 5.82 (d, Jꢁ4.4 Hz)]. Thus 4 was de- and kaempferol 3-O-a-L-rhamnopyranoside (9).13)
duced to have a spirocyclic structure of a theaspirone.8) The

1602
Vol. 53, No. 12
Experimental
(C-9), 69.4 (C-11), 125.9 (C-4), 169.0 (C-5), 201.6 (C-3). Negative-ion HR-
General Procedure Optical rotations were measured on a Union Giken FAB-MS: m/z 225.1469 [MꢀH]ꢀ (Calcd for C13H21O3: 225.1491).
PM-101 digital polarimeter at 25 °C. FT-IR spectra were recorded on a
Preparation of (R)- and (S)-MTPA Esters (3b, c) from Excoecarinol A
Horiba FT-710 spectrophotometer. 1H-NMR (400 MHz) and 13C-NMR (3a) A solution of 3 (2.0 mg) in 1 ml of dehydrated CH2Cl2 was reacted
(100 MHz) spectra were obtained on a JEOL JNM a-400 NMR spectrome- with (R)-MTPA (50 mg) in the presence of EDC (28.8 mg) and 4-DMAP
ter. Negative-ion and positive-ion HR-FAB-MS were measured on a JEOL (31.5 mg) and the resulting mixture was occasionally stirred at 25 °C for
SX-102 mass spectrometer with PEG-400 and PEG-600, respectively, as the
calibration matrix. HPLC was carried out with a JASCO PU-1580 pump and
24 h. After the addition of 1 ml of each of H2O and CH2Cl2, the solution was
washed successively with 5% HCl, NaHCO3-saturated H2O and brine. The
UV-2075 Plus detector (set at 254 nm) on YMC ODS columns (150ꢄ organic layer was dried over Na2SO4 and then evaporated under reduced
4.6 mm i.d. in analytical and 150ꢄ20 mm i.d. in preparative scales) at the
corresponding flow rates of 0.5 and 5 ml/min. Diaion HP-20 (Mitsubishi),
silica gel 60 (0.063—0.200 mm, Merck) and reversed-phased octadecyl sil-
ica (ODS) gel (YMC) were used for open column chromatography (CC).
TLC was carried out on Merck TLC glass plates (silica gel 60 F254), and de-
pressure. The residue was purified by silica gel CC (CHCl3 and
CHCl3–(CH3)2CO, 19:1) to give the ester, 3b (2.0 mg). Using a similar pro-
cedure, 3c (1.0 mg) was prepared from 3a (0.91 mg) with (S)-MTPA
(25.3 mg), EDC (23.2 mg), and 4-DMAP (12.2 mg).
Excoecariol A (R)-MTPA Ester (3b): Amorphous powder. 1H-NMR
tected by spraying with 10% H2SO4 in 50% EtOH, followed by heating on a (CDCl3) d: 0.93 (3H, s, Me-12), 1.32 (3H, d, Jꢁ6.3 Hz, Me-10), 1.46—1.70
hot plate at 200 °C. b-Glucosidase from almond, (R)-(ꢃ)- and (S)-(ꢀ)-a- (4H, m, 2H-7, 2H-8), 2.02 (1H, d, Jꢁ17.3 Hz, H-2a), 2.09 (1H, m, H-6),
methoxy-a-trifluoromethylphenylacetic acids (MTPA) were from Nacalai 2.10 (3H, s, Me-13), 2.20 (1H, d, Jꢁ17.3 Hz, H-2b), 3.42—3.53 (2H, m,
Tesque (Japan). 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochlo- 2H-11), 3.47 (3H, s, –OMe), 3.50 (3H, s, –OMe), 5.08 (1H, m, H-9), 5.74
ride (EDC) was from Cica (Japan). 4-Dimethylaminopyridine (4-DMAP) (1H, br s, H-4), 7.19—7.48 (10H, m, aromatic protons). Positive-ion HR-
was from Wako (Japan).
FAB-MS: m/z 681.2302 [MꢃNa]ꢃ (Calcd for C33H36O7F6Na: 681.2263).
Excoecariol A (S)-MTPA Ester (3c): Amorphous powder. 1H-NMR
(CDCl3) d: 0.96 (3H, s, Me-12), 1.26 (3H, d, Jꢁ6.4 Hz, Me-10), 1.53—1.77
(4H, m, 2H-7, 2H-8), 2.14 (1H, d, Jꢁ17.6 Hz, H-2a), 2.16 (1H, m, H-6),
2.17 (3H, s, Me-13), 2.26 (1H, d, Jꢁ17.6 Hz, H-2b), 3.42 (6H, s, –OMeꢄ2),
3.49 (1H, d, Jꢁ8.0, 2.0 Hz, H-11a), 3.55 (1H, d, Jꢁ8.0 Hz, H-11b), 5.08
(1H, qui, Jꢁ6.4 Hz, H-9), 5.78 (1H, br s, H-4), 7.19—7.45 (10H, m, aro-
matic protons). Positive-ion HR-FAB-MS: m/z 681.2288 [MꢃNa]ꢃ (Calcd
Plant Material Leaves of E. cochinchinensis var. cochinchinensis were
collected in September 2003 in Hanoi, Vietnam. Identification was carried
out by Dr. Tran Ngoc Ninh of the Institute of Ecology and Biological Re-
sources, Vietnam Academy of Science and Technology Hanoi, Vietnam. A
voucher specimen (HCTN No. 903) is deposited in the Herbarium of the In-
stitute of Ecology and Biological Resources.
Extraction and Isolation The air-dried and powdered leaves of E.
cochinchinensis var. cochinchinensis (2.5 kg) were extracted three times with for C33H36O7F6Na: 681.2263).
MeOH by percolation at room temperature. The combined extracts were
concentrated under reduced pressure and the obtained MeOH extract was
suspended in H2O and extracted with n-hexane, EtOAc, and 1-BuOH, suc-
Enzymatic Hydrolysis of Excoecarioside B (4) Excoecarioside B (4)
(20 mg) was hydrolyzed with b-glucosidase (24 mg) in 2 ml of H2O at 37 °C
for 30 h. The reaction mixture was concentrated and then workup in a simi-
cessively. Three corresponding soluble fractions were obtained with the re- lar manner to that for 3a gave an aglycone, 4a (3.1 mg) and D-glucose
spective weights of 179 g, 49 g, and 57 g. The 1-BuOH-soluble fraction was
divided into fractions I—VI by Diaion HP-20 CC by eluting with H2O,
MeOH–H2O (20%, 40%, 60%, 80%, and 100%). The separation procedure
for fractions II—IV is as follows: 1) CC on silica gel using CHCl3–MeOH
solvent systems; 2) CC on ODS gel using MeOH–H2O, from 20 to 40%, as
(3.7 mg). D-Glucose: [a]2D5ꢃ49.3° (cꢁ0.37, H2O, 24 h after being dissolved
in H2O).
Excoecariol B (4a): Colorless syrup, [a]2D5 ꢃ48.4° (cꢁ0.31, MeOH). IR
1
nmax (film) cmꢀ1: 3367, 2966, 2931, 2875, 1656, 1070. H-NMR (CD3OD)
d: 0.91 (3H, s, Me-11), 0.95 (3H, s, Me-12), 1.14 (3H, d, Jꢁ6.4 Hz, Me-10),
solvent systems, and 3) preparative ODS HPLC using CH3CN–H2O, 15% 2.09 (1H, d, Jꢁ16.8 Hz, H-2a), 2.40 (1H, d, Jꢁ16.8 Hz, H-2b), 4.08 (1H, dd,
(HPLC solvent system I) or MeOH–H2O, 40% (HPLC solvent system II).
Jꢁ18.6, 1.7 Hz, H-13a), 4.20 (1H, m, H-9), 4.23 (1H, d, Jꢁ18.6, 1.7 Hz, H-
Compounds 1 (240 mg), 2 (744 mg), 3 (13.6 mg), and 4 (60 mg) were iso- 13b), 5.70 (1H, d, Jꢁ3.4 Hz, H-8), 5.71 (1H, s, H-7), 6.07 (1H, s, H-4). 13C-
lated from fraction II (31.9 g), 5 (3.4 mg) and 6 (5.3 mg) from fraction III NMR (CD3OD) d: 23.4 (C-12), 23.8 (C-10), 42.8 (C-1), 50.7 (C-2), 61.4 (C-
(4.8 g) using HPLC solvent system 1. Compounds 7 (44.5 mg), 8 (22.1 mg),
13), 68.7 (C-9), 79.3 (C-6), 123.1 (C-4), 130.3 (C-7), 136.9 (C-8), 166.8 (C-
and 9 (55.6 mg) were isolated from fraction IV (6.3 g) using HPLC solvent 5), 201.5 (C-3). Negative-ion HR-FAB-MS: m/z 221.1201 [MꢀH]ꢀ (Calcd
system 2.
Excoecarioside
for C13H17O3: 221.1178).
Enzymatic Hydrolysis of 6 Compound 6 (5.8 mg) was hydrolyzed with
A
(3): Amorphous powder. [a]2D5 ꢀ10.3° (cꢁ1.36,
MeOH). IR nmax (film) cmꢀ1: 3368, 2966, 2931, 2884, 1643, 1377, 1077, b-glucosidase (15 mg) in 2 ml of H2O at 37 °C for 30 h. The usual workup
1044. CD (MeOH): De (nm): ꢃ1.39 (223), ꢃ1.08 (244), ꢀ0.83 (292), gave an aglycone, 6a (3.5 mg) and D-glucose (2.2 mg). D-Glucose: [a]2D5
ꢀ0.03 (328) (cꢁ4.25ꢄ10ꢀ3 M). 1H- and 13C-NMR: see Table 1. Negative- ꢃ40.8° (cꢁ0.22, H2O, 24 h after being dissolved in H2O). The 1H-NMR
ion HR-FAB-MS: m/z 387.2028 [MꢀH]ꢀ (Calcd for C19H31O8: 387.2019).
Excoecarioside B (4): Syrup, [a]2D5 ꢃ29.3° (cꢁ0.82, MeOH). IR nmax
(CD3OD) of 6a was compatible with that of glochidionionol B.5)
Preparation of (R)- and (S)-MTPA Esters (6b, c) from 6a Usual es-
(film) cmꢀ1: 3372, 2965, 2931, 2878, 1650, 1077, 1041. CD (MeOH): De terification procedure gave 6b (2.8 mg) from 6a (1.7 mg), (R)-MTPA
(nm): +7.53 (234), ꢀ0.61 (328) (cꢁ5.18ꢄ10ꢀ4 M). H- and 13C-NMR: see (37.3 mg), EDC (36.6 mg), and 4-DMAP (19.2 mg), and 6c (1.6 mg) from 6a
1
Table 1. Negative-ion HR-FAB-MS: m/z 383.1729 [MꢀH]ꢀ (Calcd for (1.8 mg), (S)-MTPA (54.8 mg), EDC (36.6 mg), and 4-DMAP (15.9 mg).
C19H27O8: 383.1706).
The 1H- and 13C-NMR (CDCl3) of 6b, c were compatible with those of (R)-
Glochidionionoside B (6): Amorphous powder, [a]2D5 ꢃ7.5° (cꢁ0.53, MTPA and (S)-MTPA esters of glochidionionol B.5)
MeOH). IR nmax (film) cmꢀ1: 3367, 2962, 2931, 2877, 1649, 1371, 1076,
1044. CD (MeOH): De (nm): ꢃ0.77 (218), ꢃ1.32 (242), ꢀ0.24 (290),
Acknowledgments This work was supported by a Grant-in-Aid from
ꢃ0.07 (328) (cꢁ1.30ꢄ10ꢀ4 M). H- and 13C-NMR: see ref. 5. Negative-ion the Japan Society for the Promotion of Science (JSPS). One of the authors
1
HR-FAB-MS: m/z 387.2061 [MꢀH]ꢀ (Calcd for C19H31O8: 387.2019).
(P.M.G.) is grateful to the JSPS for a Postdoctoral Research Fellowship and
Enzymatic Hydrolysis of Excoecarioside A (3) Excoecarioside A (3) to the International Foundation for Science (Stockholm, Sweden) for a Re-
(12.6 mg) was hydrolyzed with b-glucosidase (20 mg) in 2 ml of H2O at
37 °C for 30 h. The reaction mixture was concentrated and then subjected to
silica gel CC eluting with CHCl3 (50 ml), CHCl3–MeOH (19:1, 100 ml;
9:1, 100 ml; 17:3, 100 ml; and 7:3, 100 ml) to give an aglycone, 3a
(2.7 mg) and D-glucose (3.2 mg). D-Glucose: [a]2D5ꢃ50.8° (cꢁ0.32, H2O,
24 h after being dissolved in H2O).
search Grant. We wish to thank the Research Center of Molecular Medicine
of the Hiroshima University Faculty of Medicine, Japan, for access to the
400 MHz NMR instrument.
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n
max (film) cmꢀ1: 3420, 2965, 2930, 2871, 1658, 1378, 1122, 1019. 1H-NMR
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1603
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