New iridoid glucoside from Wendlandia tinctoria roots

Article abstract of DOI:10.1016/j.cclet.2011.05.018

A new iridoid glucoside, 10-O-veratroyleranthemoside (1) was isolated from the roots of Wendlandia tinctoria. The structure was established by spectroscopic (including 2D NMR) and chemical methods.

Full text of DOI:10.1016/j.cclet.2011.05.018

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 1233–1236
www.elsevier.com/locate/cclet
New iridoid glucoside from Wendlandia tinctoria roots
b
c
Biswanath Dinda a, , Sudhan Debnath , Santanu Majumder ,
*
Noriko Sato d, Yoshihiro Harigaya d
a Department of Chemistry, Tripura University, Suryamaninagar 799130, Agartala, India
b Department of Chemistry, MBB College 799004, Agartala, India
c Department of Chemistry, Iswarchandra Vidyasagar College, Belonia 799155, South Tripura, India
d School of Pharmaceutical Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108 8641, Japan
Received 22 February 2011
Available online 18 July 2011
Abstract
A new iridoid glucoside, 10-O-veratroyleranthemoside (1) was isolated from the roots of Wendlandia tinctoria. The structure
was established by spectroscopic (including 2D NMR) and chemical methods.
# 2011 Biswanath Dinda. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Wendlandia tinctoria; Rubiaceae; Iridoid glucoside; 10-O-Veratroyleranthemoside
Wendlandia tinctoria (Roxb) DC var. normalis Hook (Rubiaceae) is a small tree found scatterly in the semi-forest
hills of the north eastern states of India. The root juice of the plant has been used by the native communities in
traditional medicines including antidote of snake-bite [1]. Our previous studies on roots and stem have resulted in the
isolation of some iridoids and steroids [2]. Our continued studies on the roots of the same plant have resulted in the
isolation of one new iridoid glucoside (1).
1. Experimental
IR, Shimadzu FIIR-8100 spectrometer; NMR, Varian XL-400 spectrometer; FAB-MS, JEOL JMS-AX 505 HA
spectrometer; Diaion HP-20 (Mitsubishi Chemical, Japan) and silica gel (60–120 mesh, Merck) were used for CC and
silica gel G (Merck) for TLC.
Fresh roots of the plant, at the flowering stage, were collected from hilly area of South Tripura in April, 2003. The
plant was identified by Dr. B.K. Datta, Tripura University. A voucher specimen (#BD-2/05) has been deposited at the
Herbarium of Botanical Survey of India, Shibpur, Howrah.
Fresh dried semi-powdered roots (6 kg) were extracted with MeOH (10 L ꢀ2). The concentrated semisolid extract
(385 g) was suspended in H2O (Ca. 50 mL) and successively partitioned with hexane, chloroform and n-butanol. The
butanol extract (55 g) was column chromatographed over Diaion HP-20 using H2O and H2O with increasing MeOH
* Corresponding author.
E-mail address: dindabtu@gmail.com (B. Dinda).
1001-8417/$ – see front matter # 2011 Biswanath Dinda. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.05.018

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B. Dinda et al. / Chinese Chemical Letters 22 (2011) 1233–1236
(25–100%) to get five fractions. Fractions of H2O–MeOH (1:1 and 1:3) exhibiting identical TLC pattern were mixed
and concentrated to a semisolid mass. A part of this mass (8.5 g) was subjected to column chromatography (CC) over
silica gel using CHCl3, CHCl3 with increasing MeOH (5–80%). The fractions from CHCl3–MeOH (60:40 and 50:50)
were almost similar in composition on TLC. These fractions were mixed and were further purified through silica gel
CC to get compound 1 (70 mg) in yellow amorphous powder.
10-O-Veratroyleranthemoside (1): yellow amorphous powder; [a]D25 – 41.28 (c 0.15, MeOH); UV lmax (MeOH)
nm: 275.8, 300 sh, 330 sh; IR (KBr): 3400, 1710, 1641, 1605, 1508, 1373, 1270, 1080, 648 cmꢁ1; 1H and 13C NMR
(CD3OD) are listed in Table 1; FAB-MS: (rel.int.%): 533 [M+Na]+ (7), 511 [M+H]+ (10), 347 [Mꢁveratroyl+2H]+
(13), 183 [veratric acid+H]+ (100); HR-FAB-MS: m/z [M+H]+ calcd. for C24H31O12: 511.1810; found 511.1808.
Acetylation of 1: compound 1 (20 mg) was suspended in a mixture of pyridine (4 drops), and acetic anhydride
(3 mL) and was kept at room temperature (20 8C) for overnight. Usual workup gave light yellow amorphous solid of
1a (15 mg).
10-O-Veratroyleranthemoside tetraacetate (1a): light yellow amorphous solid. IR (KBr): 3429, 1743, 1710, 1636,
1609, 1508, 1235, 1055 cmꢁ1; 1H and 13C NMR (CDCl3) are shown in Table 1. FAB-MS m/z (rel.int.%): 701 [M+Na]+
(4), 331 (13), 183 (21), 169 (79), 109 (36), 43 (100).
Alkaline hydrolysis of 1: compound 1 (5 mg) was stirred with 1 mol/L NaOH (2 mL) for 2 h under N2 at room
temperature. The reaction mixture was extracted with ether (ꢀ2) after acidification by 2 mol/L HCl. From the ether
extract, veratric acid was detected by co-TLC and super imposable IR spectra with an authentic sample.
Acid hydrolysis of 1: compound 1 (5 mg) was stirred with 2 mol/L aq-methanolic HCl for 1 h. After neutralization
with Amberlite IRA-400 (OHꢁ form), the reaction mixture was concentrated. D-Glucose was detected by co-TLC with
Table 1
NMR spectral data of 1 (CD3OD) and 1a (CDCl3) (400 MHz for 1H NMR and 100 MHz for 13C NMR).
Position
1
1a
dC
dH
dC
dH
1
95.0 d
5.35 d (2.0)
93.3 d
138.8 d
107.2 d
34.7 d
138.3 d
133.9 d
85.8 s
5.33 d (2.0)
3
139.6 d
106.5 d
38.6 d
138.0 d
133.1 d
85.8 s
6.11 dd (6.0, 2.0)
4.93 dd (6.0, 3.0)
3.07 br m
6.33 dd (6.0, 2.0)
4.98 dd (6.0, 2.0)
3.42a
4
5
6
6.01 dd (5.5, 2.5)
5.86 dd (5.5, 1.0)
–
5.95 dd (5.5, 2.5)
5.86 dd (5.5, 2.5)
–
7
8
9
45.9 s
2.53 dd (8.5, 2.0)
4.23 d (11.5), 4.12 d (11.5)
46.0 d
70.5 t
2.51 dd (8.5, 2.0)
4.22 d (11.5), 4.11 d (11.5)
10
Gln
10
20
30
40
50
60
71.2 t
100.8 d
74.2 d
76.4 d
71.2 d
78.6 d
62.3 t
4.72 d (7.0)
3.21–3.34a
101.3 d
71.1 d
72.5 d
68.4 d
72.6 d
61.9 t
4.98 d (8.0)
4.95 dd (8.0, 9.0)
5.26 dd (9.0, 9.5)
5.05 dd (9.5, 9.5)
3.76 m
3.83 dd (12.5, 4.5)
3.68 dd (12.5, 2.0)
4.28a 4.12 dd (12.5, 2.0)
Veratroyl moiety
100
200
300
400
500
600
700
123.3 s
113.6 d
150.2 s
153.2 s
112.0 d
125.9 d
168.2 s
56.4 q
–
123.2 s
–
7.53 d (2.0)
113.4 d
7.51 d (2.0)
–
152.8 s
–
–
153.3 s
–
7.00 d (8.5)
110.3 d
7.02 d (8.5)
7.63 dd (8.5, 2.0)
126.6 d
7.62 dd (8.5, 2.0)
–
166.8 s
–
300-OMe
400-OMe
Ac
3.87 s
3.82 s
56.2 q
3.85 s
56.1 q
56.0 q
3.82 s
169.4, 170.2, 170.5, 170.6 (each s),
20.5, 20.6, 20.7, 21.0 (each q)
2.02, 2.04, 2.10, 2.12
a
Signal pattern is unclear due to overlapping.

B. Dinda et al. / Chinese Chemical Letters 22 (2011) 1233–1236
1235
MeO
3''
MeO
H
4
6
H
3
1''
5
7
7''
9
8
O
O
1
OR
OR
'
'
6
O
1
RO
H
10
O
O
H
O
OH
OH
2 R = H
OGlc
RO
OR
1
R = H
1a R = Ac
3 R = trans-p-coumaroyl
Fig. 1.
an authentic sample as well as GLC analysis of its TMS derivative obtained on treatment of the dry residue with 5
drops of TMS-imidazole for 15 min at 60 8C followed extraction with hexane and analysis in OV-1 column at 180 8C.
2. Results and discussion
The positive ion FAB-MS of compound 1 (Fig. 1) displayed quasi-molecular ions [M+H]+ and [M+Na]+ at m/z
511 and 533 compatible with molecular formula C24H30O12. It exhibited UV spectrum in MeOH at lmax 275.8,
300 sh and 330 sh nm, characteristic of aromatic chromophore. The IR spectrum showed absorptions at 3400
1
(OH), 1710 (ester), 1641 and 1270 (enol ether) and 1605 and 1508 (aromatic) cmꢁ1. The H NMR spectrum
(Table 1) revealed the presence of an C-4-unsubstituted iridoid moiety [d 6.11 (dd, J = 6.0, 2.0 Hz, H-3) and 4.93
(dd, J = 6.0, 3.0 Hz, H-4), 5.35 (d, J = 2.0 Hz, H-1)] along with a glucose moiety [d 4.72 (d, J = 7.0 Hz, H-10),
3.68 (dd, J = 12.5, 2.0 Hz, H-60) and 3.83 (dd, J = 12.5, 4.5 Hz, H-60)] and veratroyl moiety [d 7.53 (d, J = 2.0 Hz,
H-200), 7.00 (d, J = 8.5 Hz, H-500), 7.63 (dd, J = 8.5, 2.0 Hz, H-600), 3.87 (s, MeO-300) and 3.82 (s, MeO-400)] [3a].
Both the 1H and 13C NMR (including DEPT) data (Table 1) also suggested the presence of one olefine group (dH
6.01, dC 138.0 and dH 5.86, dC 133.1), one tertiary hydroxyl group (dC 85.8) and one oxymethylene group (dH 4.12
and 4.23, dC 71.2). The point of attachment of a b-glucopyranosyl unit at C-1 was confirmed by long range
HMBC correlations between H-1 (dH 5.35) and C-10 (dC 100.8) and between H-10 (dH 4.72) and C-1 (dC 95.0). The
C-10 side chain was linked to veratroyl moiety forming an ester linkage, based on the downfield shift value of C-
10 (dC 85.8) and the existence of HMBC coupling between C-10 protons with C-700 carbonyl (dC 168.2). The
stereochemistry of the C-8 CH2O-group was determined to be b on the basis of the shielding chemical shifts of C-
9 and C-7 (dC 45.9 and 133.1, respectively) as well as from ROESY cross peaks between H-600 and H-5 and
between H-200 and H-10. The small coupling of J1,9 (2.0 Hz) indicated their dihedral angle of nearly 908. The
coupling (8.5 Hz) between H-5 and H-9 indicated a small dihedral angle demonstrating the cis-configuration at
the ring fusion. ROSEY correlations between H-600 and H-5 and between H-200 and H-10 confirmed the attachment
of veratroyl unit at C-10 CH2O-group. Moreover, ROSEY cross peaks between H-10, H-9 and H-5 revealed their
cis-orientations. The compound on mild acid hydrolysis with 2 mol/L-methanolic HCl afforded D-glucose and on
alkaline hydrolysis with 1 mol/L-methanolic NaOH gave veratric acid. The compound on acetylation with Ac2O
and pyridine at room temperature (20 8C) for 24 h afforded tetraacetate (1a), C32H38O16 (MW 678) (FAB-MS, m/z
701 [M+Na]+). The EI-MS of the tetraacetate showed a strong mass peak at m/z 331 supporting no ester linkage at
the glucose moiety. The NMR data of the compound 1 were very similar to that of eranthemoside (2) isolated
from Eranthemum pulchellum (Acanthaceae) and 10-O-trans-coumaroyleranthemoside (3) isolated from Barleria
strigosa (Acanthaceae) except of aryl moiety [3b] and [3c]. Based on these evidence the structure of compound 1
(Fig. 1) was elucidated as 10-O-veratroyl-eranthemoside. Isolation of this compound from the family Rubiaceae
may be interesting from biogenetic and chemotaxonomic point for study of phylogeny of the angiosperms.
Acknowledgments
The work was supported by a grant (No. SR/S1-OC-75/2009) from DST, New Delhi. The authors are thankful to Dr.
B.K. Datta, Tripura University for authentication of the plant material.

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B. Dinda et al. / Chinese Chemical Letters 22 (2011) 1233–1236
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