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Iridoid glucosides from Wendlandia ligustroides (Boiss. &Hohen.) Blakelock
Çal, hsan; Weas, Ayham; Soliman Yusufolu, Hasan; Dönmez, Ali A.; Jensen, Søren Rosendal
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Saudi Pharmaceutical Journal
Link to article, DOI:
10.1016/j.jsps.2020.05.009
Publication date:
2020
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Citation (APA):
Çal, ., Weas, A., Soliman Yusufolu, H., Dönmez, A. A., & Jensen, S. R. (2020). Iridoid glucosides from
Wendlandia ligustroides (Boiss. &Hohen.) Blakelock. Saudi Pharmaceutical Journal, 28, 814-818.
https://doi.org/10.1016/j.jsps.2020.05.009
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Saudi Pharmaceutical Journal 28 (2020) 814–818
Contents lists available at ScienceDirect
Saudi Pharmaceutical Journal
journal homepage: www.sciencedirect.com
Original article
Iridoid glucosides from Wendlandia ligustroides (Boiss. &Hohen.)
Blakelock
_
Ihsan
Çalısß a,⇑, Ayham Weas a, Hasan Soliman Yusufoğlu b, Ali A. Dönmez c, Søren R. Jensen d
a
Near East University, Faculty of Pharmacy, Department of Pharmacognosy, Lefkosßa (Nicosia), Cyprus
Prince Sattam Bin Abdulaziz University, Department of Pharmacognosy, Al-Kharj 11942, Saudi Arabia
c
Hacettepe University, Faculty of Science, Department of Biology, Beytepe, 06532 Ankara, Turkey
d
The Technical University of Denmark, Department of Chemistry, DK-2800 Lyngby, Denmark
b
a r t i c l e
i n f o
Article history:
Received 13 June 2019
Accepted 29 May 2020
Available online 3 June 2020
Keywords:
Wendlandia ligustroides
Rubiaceae
Iridoid glucosides
Medicinal chemistry
Natural products chemistry
a b s t r a c t
Eight iridoid glucosides were reported from the aerial parts of Wendlandia ligustroides. 10deoxygeniposidic acid (1), 7-deoxygardoside (2), geniposidic acid (3), 7-deoxy-8-epi-loganic acid (4),
deacetyl-daphylloside (5), scandoside methyl ester (6), 6-O-methyl-deacetyl-daphylloside (7), 6O-methyl-scandoside methyl ester (8). Compounds 3 – 8 were isolated as a pure form while 1 and 2
as a mixture. The structures of the compounds 1 – 8 were established by spectroscopic methods including
1D-NMR (1H NMR, 13C NMR, DEPT-135), 2D-NMR (COSY, NOESY, HSQC, HMBC) and HRMS.
Ó 2020 The Authors. Published by Elsevier B.V. on behalf of King Saud University. This is an open access
article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Wendlandia Bartl. ex DC. (Rubiaceae) is a genus distributed in
paleotropical region with about 70 species. Wendlandia ligustroides
(Boiss. &Hohen.) Blakelock is naturally grows at North Iraq and it
was reported fort he first time in flora of Turkey by one of us
(Dönmez, 2002). The species is closely allied to W. arabica Deflers
which is South Arabian species. The plant is a small chasmophytic
bush with fragrant smelling and is growing on rocky limestone
cliffs at Hakkari in Zap George. W. ligustroides is a small erect shrub
(30 – 40 cm) with puberulent branches. Leaves deciduous and coriaceous with stipules. Inflorescence terminal thyrses with many
smaller. Calyx teeth as long as ovary. Petals white and fragrant.
Fruit globose.
Prevous studies performed on Wendlandia species have focused
on the isolation of iridoids. 10-O-veratroyleranthemoside, 5dehydro-8-epi-adoxosidic acid, 5-dehydro-8-epimussaenoside,
10-O-dihydroferuloyldeacetyldaphylloside, wendoside, 8-epi⇑ Corresponding author.
_ Çalısß).
E-mail address: ihsan.calis@neu.edu.tr (I.
Peer review under responsibility of King Saud University.
Production and hosting by Elsevier
mussaenoside, 8-O-caffeoylmussaenosidic acid, ixoside have been
reported from the roots of Wendlandia tinctoria (Dinda et al.,
2006, 2011a, 2011b). Tarennoside, gardenoside, geniposidic acid,
10-O-caffeoylscandoside methyl ester, scandoside methyl ester,
6-O-methylscandoside methyl ester, methyl deacetylasperulosidate, 10-O-caffeoyldaphylloside have been reported from the
leaves of Wendlandia formosana (Raju et al., 2004), and scandoside
methyl ester from the wood of Wendlandia bicuspidata (De Silva
et al., 1987). Among the Wendlandia species studied, W. tinctoria
has been reported to use as an antidote of snake-bite by local people living in the sub-Himalayan region of India (Dinda et al., 2006).
As a part of our studies on the iridoid containing plants, Wendlandia ligustroides was selected for this study as one of the member
of Rubiaceae recently recorded for Flora of Turkey. No previous
phytochemical and pharmacological and ethnopharmacological
studies have been carried out before on it.
2. Material and methods
2.1. General experimental procedures
Classical column chromatography and a gradient Medium
Pressure Liquid Chromatography (Büchi MPLC equipped by Pump
Modules C-601 & C-605 with a pump Controller C-610 and pump
manager C-605) and Büchi Fraction Collector C-615 were used
for the isolation process. Silica gel (0.063 – 200 ml, Merck),
https://doi.org/10.1016/j.jsps.2020.05.009
1319-0164/Ó 2020 The Authors. Published by Elsevier B.V. on behalf of King Saud University.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
_ Çalısß et al. / Saudi Pharmaceutical Journal 28 (2020) 814–818
I.
LiChroprep C-18 (0.063 – 200 mm, Merck) and Sephadex LH-20
were used as stationary phases throughout chromatographical
studies. Silica gel alumina plates (Silica Gel 60 F254, Merck) were
used for Thin Layer Chromatography. Optical rotations were measured on a Schmidt + Haensch Polartronic MHZ-8 polarimeter.
NMR measurements in CD3OD were performed on Bruker DRX 500
spectrometers operating at 500 MHz for 1H and 125 MHz for 13C,
respectively, using the XWIN NMR software package for the data
acquisition and processing. Negative- and positive-mode HRMS
were recorded on a Finnigan TSQ 7000 and HR-Mass Spectrometer
and an UPLC-Quadrupole Orbitrap instruments. For lyophlization
a CHRIST Alpha 1–4 LD Plus was used. Throughout the study Büchi
R-210 and Heidolph 4001 rotary evaporators were used.
2.2. Plant material
Wendlandia ligustroides (Boiss. & Hohen.) Blakelock was collected from Hakkari: 5.4 km from Sßırnak-Çukurca road junction
to Hakkari, Geçimli village, limestone rock crevicies, 908 m,
37°210 18600 N, 038°300 37500 E, 29.06.2009. Voucher specimen (Ali
A. Dönmez 15,490 is deposited at the HUB (Herbarium of Hacettepe University).
2.3. Extraction and isolation (Aerial Parts)
The air-dried, ground, aerial parts (stems, leaves, and flowers,
290 g) of W. ligustroides were extracted with MeOH (4 L 2) at
50 °C. The combined methanolic extracts were concentrated in
vacuo at 40 °C, diluted with 200 mL of water and extracted with
dichloromethane (200 mL 5). The water phase was concentrated
and then lyophilized to give 47.13 g crude extract (yield 16.25%).
An aliquot (45 g) of the crude extract was dissolved in water
(70 mL) and subjected to vacuum liquid chromatography
(VLC) using reversed-phase material (LiChroprep C18, 100 g)
employing H2O (500 mL), H2O – MeOH (95:5, 200 mL; 90:10,
200 mL) and increasing amount of 5% MeOH at each 100 mL of
H2O – MeOH mixture. The volume of the fractions was 100 mL.
This stepwise gradient elution yielded 22 fractions. TLC was used
to monitor to content of the fractions and combined into the eleven
fractions (frs.: A – K; A. 3.94 g; B, 26.2 g; C, 2.52 g; D, 947 mg; E,
723 mg; F, 3.2 g; G, 709 mg; H, 829 mg; I, 1,23 g; J, 1.57 g; and
K, 460 mg).
An aliquot of fraction B (13 g) was reapplied to vacuum liquid
chromatography (VLC) using reversed-phase material (LiChroprep
C18, 100 g) employing H2O (100 mL), and increasing amount of
3% MeOH in H2O at each 100 mL as eluent until 30% of MeOH in
H2O. 22 fractions were collected (fraction volume 50 mL). The column was then eluted using same mixture with increasing amount
of 10% MeOH at each of 100 mL of eluent. Additional 8 fractions
were collected. By the help of TLC monitoring, these 30 fractions
were combined into thirteen fractions (Frs. B1 – B14: B1,
930 mg; B2, 1070 mg; B3, 1038 mg; B4, 459 mg; B5, 146 mg; B6,
334 mg; B7, 189 mg; B8, 145 mg; B9, 46 mg; B10, 98 mg; B11,
146 mg; B12, 480 mg; B13, 223 mg).
Fraction B2 (1070 mg) was subjected to a Si gel (55 g) column
using DCM-MeOH-H2O
mixtures (80:20:2, 250 mL, 75:25:2.5, 200 mL; 70:30:3,
200 mL; 60:40:4,200 mL) to give geniposidic acid (3, 90 mg) and
deacetyl-daphylloside (5, 48 mg).
Fraction B6 (334 mg) was subjected to a Si gel (70 g) column
using DCM-MeOH-H2O
mixtures (80:20:2, 350 mL, 75:25:2.5, 100 mL; 70:30:3,
200 mL; 50:50:5,600 mL) to give 6-O-methyl-scandoside methyl
ester (8, 25 mg) and scandoside methyl ester (6, 65 mg).
Fraction B8 (145 mg) was subjected to a Si gel (25 g) column
using DCM-MeOH-H2O
815
mixtures (80:20:2, 250 mL, and 70:30:3, 100 mL) to give 6-Omethyl-deacetyl-daphylloside (7, 22 mg).
Fraction G (709 mg) was subjected to a Si gel (70 g) column
eluting with DCM-MeOH-H2O
mixtures (80:20:2, 600 mL, 75:25:2.5, 100 mL; 70:30:3,
200 mL; 60:40:4, 200 mL) to give a mixture of 7deoxygeniposidic acid (1) and 7-deoxygardoside (2).
Fraction I (1.145 g of 1.23 g) rich in colored material was subjected to a polyamide column (50 g). Water has been used in the
column preparation and also for the first elutions. Subsequent elutions have been performed using H2O-EtOH mixtures with increasing amount of EtOH. Fractions eluted with 60% EtOH yielded pure
7-deoxy-8-epi-loganic acid (4, 30 mg).
Further separations performed on the fraction F (3.2 g) resulted
in the isolation of geniposidic acid (3, 172 mg) and additional 7deoxy-8-epi-loganic acid (4, 32 mg).
10-Deoxygeniposidic acid (1): 1H NMR (400 MHz, CD3OD): d
7.45 s (H-3), 5.47 br s (H-7), 5.25 d (J = 8.0 Hz, H-1), 4.71 d
(J = 8.0 Hz, H-1ʹ), 3.88 dd (J = 2.0 and 12.0 Hz, H-6ʹa), 3.66 dd
(J = 6.0 and 12.0 Hz, H-6ʹb), 3.37 t (J = 9.0 Hz, H-3ʹ), 3.30 m (H5ʹ), 3.28 t (J = 9.0 Hz, H-4ʹ); 3.22 dd (J = 8.0 and 9.0 Hz, H-2ʹ),
3.14 dq like (J = 8.0 and 0.5 Hz, H-5), 2.73 m (H-6a), 2.61 t
(J = Hz, H-9), 2.08 m (H-6b), 1.81 br s (H3-10) (Inoue et al. 1992,
Takeda et al., 1996).
7-Deoxygardoside (2): 1H NMR (400 MHz, CD3OD): d 7.42 s (H3), 5.45 d (J = 4.0 Hz, H-1), 5.12 and 5.07 (each 1H, br d, J = 2.0 Hz,
H2-10), 4.68 d (J = 8.0 Hz, H-1ʹ), 3.88 dd (J = 2.0 and 12.0 Hz, H-6ʹa),
3.66 dd (J = 6.0 and 12.0 Hz, H-6ʹb), 3.34 t (J = 9.0 Hz, H-3ʹ), 3.30 m
(H-5ʹ), 3.28 t (J = 9.0 Hz, H-4ʹ); 3.22 dd (J = 8.0 and 9.0 Hz, H-2ʹ),
3.02 m (H-9), 2.86 m (H-5), 2.30 – 1.95 (4H, H2-6 and H2-7)
(Bianco et al. 1986).
1
Geniposidic acid (3): [a]20
D + 13.3° (c 0.5, MeOH); H NMR
(500 MHz, CD3OD): d 7.40 s (H-3), 5.81 br s (H-7), 5.13 d
(J = 7.6 Hz, H-1), 4.74 d (J = 7.9 Hz, H-1ʹ), 4.33 d and 4.21 d (AB system, JAB = 14.1 Hz, H2-10), 3.88 dd (J = 2.0 and 12.0 Hz, H-6ʹa), 3.66
dd (J = 6.0 and 12.0 Hz, H-6ʹb), 3.37 t (J = 9.0 Hz, H-3ʹ), 3.40–3.30
(2H, H-4ʹ and H-5ʹ); 3.20 dd (J = 8.0 and 9.0 Hz, H-2ʹ), 3.17 m (H5), 2.86 m (H-9), 2.72 t (J = 7.6 Hz, H-9), 2.10 m (H-6b); 13C NMR
(125 MHz, CD3OD): d 172.0 (C, C-11), 151.2 (CH, C-3), 144.7 (C,
C-8), 128.5 (CH, C-7), 115.7 (C, C-4), 99.3 (CH, C-1ʹ), 98.1 (CH, C1), 78.3 (CH, C-5ʹ), 77.8 (CH, C-3ʹ), 74.9 (CH, C-2ʹ), 71.2 (CH, C-4ʹ),
62.7 (CH2, C-6ʹ), 61.6 (CH2, C-10), 47.2 (CH, C-9), 39.9 (CH2, C-6),
37.2 (CH, C-5); Negative-ion HRMS m/z 373.1127 [MH], (calc.
for C16H22O10, Mol. Wt. 374.12 (Akdemir & Çalısß, 1991; Tzakou
et al., 2007).
1
8-epi-deoxyloganic acid (4): [a]20
D 76.7° (c 0.5, MeOH); H
NMR and 13C NMR (500 and 125 MHz, resp., CD3OD): d 7.44 s
(H-3), 5.48 d (J = 4.5 Hz, H-1), 4.71 d (J = 8.0 Hz, H-1ʹ), 3.93 dd
(J = 12.0 and 2.0 Hz, H-6ʹa), 3.67 dd (J = 12.0 and 6.0 Hz, H-6ʹb),
3.40 t (J = 9.0 Hz, H-3ʹ), 3.32 m (H-5ʹ), 3.27 t (J = 9.0 Hz, H-4ʹ),
3.22 dd (J = 8.0 and 9.0 Hz, H-2ʹ), 2.92 dd (J = 14.2 and 7.6 Hz, H5), 2.28 m (H-8), 2.27 m (H-9), 2.09 m (H-6a), 1.81 m (H-7a),
1.61 m (H-6b), 1.38 m (H-7b), 1.11 d (J = 6.7 Hz, H3-10); 13C
NMR (125 MHz, CD3OD): d 171.0 (C, C-11), 152.7 (CH, C-3), 113.4
(C, C-4), 99.8 (CH, C-1ʹ), 96.2 (CH, C-1), 78.4 (CH, C-5ʹ), 77.0 (CH,
C-3ʹ), 74.8 (CH, C-2ʹ), 71.8 (CH, C-4ʹ), 63.0 (CH2, C-6ʹ), 44.4 (CH,
C-9), 37.6 (CH, C-8), 34.6 (CH, C-5), 33.3 (CH2, C-7), 32.4 (CH2, C6), 16.8 (CH3, C-10); Positive-ion HRMS: m/z 383.1279 [M+Na]+,
Negative-ion HRMS m/z 359.1336 [MH], (calc. for C16H24O9,
Mol. Wt. 360.14) (Nakamura et al., 2000: Murai et al., 1984: Teng
et al., 2005).
1
Deacetyl-daphylloside (5): [a]20
D 14.4° (c 0.5, MeOH); H NMR
and 13C NMR (500 and 125 MHz, resp., CD3OD): Table 1; Positiveion HRMS: m/z 427.1175 [M+Na]+ (calc. for C17H24O11, Mol. Wt.
404.13) (Tzakou et al. 2007).
_ Çalısß et al. / Saudi Pharmaceutical Journal 28 (2020) 814–818
I.
816
Table 1
H and 13C NMR data of Compounds deacetyl-daphylloside (5) and scandoside methyl ester (6) (CDCl3; dH 500 MHz; dC 125 MHz).
1
C/H
DEPT
dC ppm
dH ppm, J (Hz)
dC ppm
dH ppm, J (Hz)
1
3
4
5
6
7
8
9
10
CH
CH
C
CH
CH
CH
C
CH
CH2
100.5
155.5
108.3
45.9
75.4
129.8
151.5
42.7
62.8
d (9.0)
d (1.2)
98.3
153.9
110.8
45.6
82.3
130.1
147.6
47.1
62.7
11
C
CH3
169.1
51.9
5.06
7.66
–
3.02
4.80
6.03
–
2.57
4.46
4.21
–
3.75
5.22
7.53
–
3.02
4.57
5.83
–
3.06
4.36
4.21
–
3.78
CH
CH
CH
CH
CH
CH2
101.6
75.0
77.8
71.6
78.5
61.7
4.72
3.25
3.40
3.30
3.30
3.85
3.63
d (8.0)
dd (8.0, 9.0)
t (9.0)
– 3.26y
* 3.26y
dd (12.0, 1.2)
dd (11.7, 6.0)
COOCH3
Glucosyl
1ʹ
2ʹ
3ʹ
4ʹ
5ʹ
6ʹ
y
5
6
ddd (7.3, 5.8, 1.2)
dd (1.7, 5.8)
d (1.7)
t (9.0, 7.3)
d (16.0)
d (16.0)
170.4
52.2
s
100.3
74.8
77.9
71.5
78.4
61.1
d (6.3)
s
ddd (7.2, 4.5, 0.8)
br s
br s
dd (6.3, 7.2)
d (15.3)
d (15.3)
s
4.70 d (8.0)
3.24 dd (8.0, 9.0)
3.40 t (9.0)
3.30y
3.32y
3.89 dd (11.7, 1.2)
3.66 dd (11.7, 5.3)
Signal pattern unclear due to overlapping.
1
Scandoside methyl ester (6): [a]20
D 42.7° (c 0.5, MeOH); H
NMR and 13C NMR (500 and 125 MHz, resp., CD3OD): Table 1;
Positive-ion HRMS: m/z 427.1174 [M+Na]+, Negative-ion HRMS
m/z 403.1234 [MH], (calc. for C17H24O11, Mol. Wt. 404.13
(Moreira et al. 2010).
84° (c 0.5,
6-O-methyl-deacetyl-daphylloside (7): [a]20
D
MeOH);
1
H NMR and 13C NMR (500 and 125 MHz, resp., CD3OD): Table 2;
Positive-ion HRMS: m/z 441.1324 [M+Na]+, Negative-ion HRMS m/
z 417.1387 [MH], (calc. for C18H26O11, Mol. Wt. 418.15)
(Machida et al. 2003).
6-O-methyl-scandoside methyl ester (8): [a]20
D + 32° (c 0.5,
MeOH); 1H NMR and 13C NMR (500 and 125 MHz, resp., CD3OD):
Table 2; Positive-ion HRMS: m/z 441.1334 [M+Na]+, Negative-ion
HRMS m/z 417.1391 [MH], (calc. for C18H26O11, Mol. Wt.
418.15) (Machida et al. 2003).
3. Results and discussion
The methanolic extract of overground parts of W. ligustroides
resulted in the isolation of eight iridoid glucosides (1 – 8). The
one proton singlet observed between 7.40 and 7.66 assigned to
H-3 for the compounds in the 1H NMR spectra showed that all isolated compounds were C-4 substitued carboxylic iridoids. The proton signals observed as doublets between 4.62 and 4.74 ppm with
8.0 Hz coupling constants arising from a trans-diaxial interaction
were indicative for their mono glycosidic structures. The other protons found in the same spin system of the anomeric protons and
the corresponding carbon resonances were established by COSY
and HSQC experiments, respectively. The coupling constants
(J1,2 = 8 Hz, J2,3 = J3,4 = J4,5 = 9 Hz, J5,6a = 2 Hz, J5,6b = 6 Hz, and
J6a,6b = 12 Hz) of the sugar protons and the chemical shift values
observed at ca. d 100.0, 74.0, 78.0, 71.0, 79.0 and 62.0 assigned to
Table 2
H and 13C NMR data of 6-O-methyl-deacetyl-daphylloside (7), 6-O-methyl-scandoside methyl ester (8) (CDCl3; dH 500 MHz; dC 125 MHz).
1
C/H
7
8
dC ppm
dH ppm, J (Hz)
dC ppm
dH ppm, J (Hz)
95.20
153.65
110.48
39.08
90.05
127.37
149.71
47.50
60.45
169.18
51.82
5.64 d (2.8)
7.43 s
–
3.25y
4.19 br s
5.85 br s
–
3.30y
4.30 d (15.0)
4.21 d (15.0)
–
3.74 s
1
3
4
5
6
7
8
9
10
CH
CH
C
CH
CH
CH
C
CH
CH2
101.84
155.15
108.16
42.08
84.99
127.61
152.87
46.00
61.74
11
C
CH3
169.50
51.93
4.98
7.64
–
3.11
4.39
6.20
–
2.56
4.50
4.22
–
3.77
CH3
57.45
3.25 s
57.12
3.45 s
CH
CH
CH
CH
CH
CH2
100.78
74.93
77.81
71.37
78.26
62.51
4.74 d (7.9)
3.27y
3.43 t (9.0)
3.37 t (9.0)
3.29y
3.84 brd (12,1, 2.0)
3.70 br d (12,1, 5.3)
99.98
74.64
77.92
71.56
78.35
62.76
4.62 d (7.9)
3.21 dd (7,9, 9.0)
3.38 t (9.0)
3.30y
3.33y
3.91 dd (11.9, 1.2)
3.68 dd (11.0, 5.9)
COOCH3
OCH3
Glucosyl
1ʹ
2ʹ
3ʹ
4ʹ
5ʹ
6ʹ
y
DEPT
Signal pattern unclear due to overlapping.
d (8.8)
br s
t (6.3)
br d (6.0)
s
t (8.0)
d (15.0)
d (15.0)
s
_ Çalısß et al. / Saudi Pharmaceutical Journal 28 (2020) 814–818
I.
the carbon resonances of the sugar units proved the presence of a
b-glucopyranosyl moiety for 1 – 8 (see Experimental).
The 1H NMR spectrum of 1 exhibited a methyl resonance at d
1.81 as a broad singlet which was assigned as H3-10. The downfield
shift of the methyl signal was consistent with the presence of a
double bond between C-7 and C-8. An olefinic proton signal at d
5.47 (br s, H-7) was further evidence for this proposal. In addition
to the protons assigned to H-5 (d 3.14) and H-9 (d 2.61), a set of
methylene protons at d 2.73 (H-6a) and 2.08 (H-6b) were observed.
Based upon these observations the structure of the compound 1
was identified as 10-deoxygeniposidic acid. The 1H NMR data of
1 suggested the presence of a structure similar to those of nepetanudoside B isolated from a Nepeta nuda ssp. albiflora (Takeda et al.
1996). As shown by these authors, the characteristic H-10 shift of
the Nepeta-compounds is dC 104.5, while the ‘normal’ shift for this
carbon is dC 99–100. Thus, the aglycone of nepetanudoside B is an
enantiomer of 10-deoxy-geniposidic acid (1) (Inoue et al., 1992).
Compound 2 was isolated in admixture with compound 1 due
to their similar polarities. Compound 1 was the major one in the
mixture. The major differences were arising in their cyclopentane
rings. In the 1H NMR spectrum of the mixture, the methyl resonance and the olefinic H-7 proton were missing for the minor compound, 2. Instead of a methyl resonance and olefinic H-7 proton,
the two protons of the isolated exocyclic methylene protons are
found at d 5.12 and 5.07 as broadened singlets due to allylic coupling (each 1H, br d, J = 2.0 Hz, H2-10). The remaining signals
between 2.30 and 1.95 ppm were evident for the presence of two
methylene protons for cyclopentane ring (see Experimental). Based
upon these observations the structure of compound 2 was determined as 10-deoxygardoside. The assignments of all protons were
in good agreement with those of reported for 7-deoxygardoside
confirming this deduction (Bianco et al., 1986).
Compound 3 was obtained as an amorphous colourless powder.
The molecular formula was found as C16H22O10 by negative-ion
HRMS (m/z 373.1127 [MH] and NMR data: Molecular weight:
374,12). The 1H NMR spectrum was characteristic for C-4 substituted iridoids (loganin-type). H-3 was observed at 7.40 ppm as a
singlet. Additionaly, an olefinic proton signal at 5.81 assigned as
H-7 indicated a structure similar to that of 10-deoxygeniposidic
acid (1). However, a pair of protons observed at d 4.33 and 4.21
as an AB system (JAB = 14.1 Hz) showed the presence of a hydoxymethylene functionality instead of a methyl gruoup at C-8. Thus
the structure of compound 3 was determined as geniposidic acid
(Akdemir&Çalısß, 1991; Tzaoku et al., 2007). All proton and carbon
resonances were in good accordance with those of reported for
geniposidic acid confirming the proposed structure (see
Experimental).
Compound 4 was obtained as an amorphous powder. The
molecular weight was established as 360,14 indicating a molecular
formula of C16H24O9 by negative-ion HRMS (m/z 373.1127
[MH]) and NMR data (see Experimental). The 1H NMR spectrum
of 4 showed the signals at highfield region arising three methines
(H-5, H-9 and H-8), two methylene groups (H2-6 and H2-7) for
cyclopentane moiety in addition to H-1 and olefinic H-3 protons
of pyrane moiety. Except H-3, all of these protons were observed
as a part of a single spin system in COSY experiment which clearly
assigned all protons including the locations of two methylene protons to be at C-6 and C-7. The stereochemistry of the secondary
methyl resonance was based on a NOESY experiment which shows
a NOE correlation between H-1 (d 5.48 d, J = 4.5 Hz) and Me-10 (d
1.11 d, J = 6.7 Hz). Furthermore, the protons on the a- and b-sites of
the cyclopentan-pyrane ring system were also established by the
help of NOESY experiment (see Experimental). Especially, NOE correlations observed between H-5, H-9 and H-8 supported this argument. The stereochemistry at C-8 for 4 was determined by the 13C
NMR spectrum. Thus, the shift for C-9 and C-10 (dC 44.4 and 16.8,
817
respectively) is characteristic for 7-deoxy-8-epi-loganic acid, as
opposed to the other epimer which would be found at dC 48.5
and 20, respectively (Damtoft et al., 1981). Based on these observations together with the comparison of the NMR data with those of
reported, the structure of compound 4 was determined as 8-epideoxyloganic acid (Murai et al., 1984; Tasdemir et al., 1999; Teng
et al., 2005).
The molecular formula of the compounds 5 and 6 were established by HRMS (m/z 403.3549 [MH] and m/z 427.3519 [M
+Na]+ for both). These results supported the molecular weight for
both compounds to be 404,3629 calculated for C17H24O11. Their
1
H and 13C NMR data (Table 2) showed the presence of an iridoid
mono-glucoside having loganin-type skeletons with similar substitutients and functionalities in the two compounds. These were a
COOCH3, an OH group, an olefinic proton and a CH2OH group.
The 13C NMR resonances (d 129.8 and 151.5 and 130.1 and 147,6,
respectively) assigned for carbons C-7 and C-8 showed the location
of double bond. The major differences between 5 and 6 were
observed for chemical shifts and the coupling constants of the H1 and C-1 as well as H-6 and C-6. Therefore, the structural difference between 5 and 6 was arising the stereochemistry of OH group
located at C-6. The 1H and 13C NMR data of 5 and 6 were in accordance to those of 6a-hydroxy-geniposide (=deacetylasperulosidic
acid methyl ester, deacetyldaphylloside; Tzakou et al., 2007) and
6b-hydroxy-geniposide (=scandoside methyl ester; Moreira et al.,
2010), respectively.
The molecular weights of the compounds 7 and 8 were also
found to be the same and 14 Da bigger than those of 5 and 6 by
HRMS. The negative ion HRMS od 7 and 8 showed the quasi molecular ion peaks at m/z 417.3583 [MH] while positive ion HRMS at
m/z 441.3557 [M+Na]+ showing the molecular weight of both compounds to be 418,3896 giving the molecular composition
C18H26O11. These observation was supported by the presence of
an additional methoxyl signals in the 1H NMR spectra of 7 and 8.
(dH: 3.25 s and 3.45 s, resp., OCH3) as well as in
13
H NMR spectra
(dC: 57.45 and 57.12, resp., OCH3) (Table 2). All protons and carbon
resonances of the compounds 7 and 8 were assigned based on the
2D-NMR experiments (COSY, HSQC and HMBC). Moreover, the
same similarities were observed between 5 and 7 and between 6
and 8 for the chemical shifts of all proton and carbon resonances
as well as for the coupling constants strongly supporting that the
7 and 8 were the 6-O-methoxy derivatives of 5 and 6. These deductions were supported by the long-range 13C, 1H correlations
between C-6 [dC 84.99 and 90.05; C-6 of 7 and 8, resp.)and methoxy signals (dH 3.25 and 3.45; C(6)OCH3 of 7 and 8, resp.] for both
compounds. Consequently, based on the NMR data presented in
Table 3 the structures of 7 and 8 were established as 6-O-methyl
deacetylasperulosidic acid methyl ester and 6-O-methyl deacetylscandoside methyl ester, resp. (Machida et al., 2003). Furthermore,
20
the optical rotations of 7 ([a]20
D 84°) and 8 ([a]D + 32°) were in
good agreement to those of reported in the same study confirming
this deduction.
The coupling constants (J1-9) observed for H-1 of the aglycone
moieties in compounds 5 – 8 (J = 9.0 and 8.8 Hz for 5 and 7;
J = 6.3 and 2.8 Hz for 6 and 8) are caused by a change in the conformations of cyclopentan-pyrane ring junctions. These effects
are best explained by the O-substitution at C-6 as reported
(Damtoft et al.,1981).
4. Conclusion
Wendlandia ligustroides (Rubiaceae) have been investigated
chemically for the first time. The iridoid glucosides isolated in
the present work are common in parts of the Rubiaceae family.
None of them have to our knowledge any particular reported phar-
818
_ Çalısß et al. / Saudi Pharmaceutical Journal 28 (2020) 814–818
I.
macological activities. However, ester derivatives of scandoside
and daphylloside from Wendlandia formosana are known to show
strong radical scavenging activity (Dinda, 2019).
Acknowledgements
Authors kindly thank to Anzarul Haque for 1D and 2D NMR
measurements and Ayman Salkini for HRMS (Prince Sattam Bin
Abdulaziz University).
References
_ 1991. Iridoid and Phenylpropanoid Glycosides from Pedicularis
Akdemir, Z., Çalısß, I.,
pontica Boiss. J. Pharmacy 1, 65–75.
Bianco, A., Passacantilli, P., Righi, G., Nicoletti, M., Serafino, M., Garbarino, J.A.,
Gambaro, V., 1986. 7-deoxygardoside, a new acid iridoid from Argylia radiata.
Gazz. Chim. Ital. 116, 67.
Damtoft, S., Jensen, S.R., Nielsen, B.J., 1981. Carbon-13 and proton NMR
spectroscopy as a tool in the configurational analysis of iridoid glucosides.
Phytochemistry 20, 2717–2732.
Dinda, B., 2019. Pharmacology and Applications of Naturally Occurring Iridoids.
Springer Nature Switzerland AG, Cham, Switzerland.
Dinda, B., Debnath, S., Majumder, S., Sato, N., Harigaya, Y., 2011a. New iridoid
glucoside from Wendlandia tinctoria roots. Chin. Chem. Lett. 22, 1233–1236.
Dinda, B., Debnath, S., Arima, S., Sato, N., Harigaya, Y., 2006. Iridoid Glucosides from
Wendlandia tinctoria Roots. Chem. Pharm. Bull. 54 (7), 1030–1033.
Dinda, B., Debnath, S., Banik, R., Sato, N., Harigaya, Y., 2011b. Iridoid Glucosides from
Wendlandia tinctoria roots. Nat. Prod. Commun. 6, 747–748.
De Silva, L.B., Herath, W.H.M.W., Navaratne, K.M., Ahmad, V.U., Alvi, K.A., 1987. An
iridoid glycoside from Wendlandia bicuspidata. J. Nat. Prod. 50, 1184.
Dönmez, A.A., 2002. Wendlandia ligustroides (Rubiaceae): A New Genus fort he Flora
of Turkey. The Karaca Arboretum Magazine 6 (4), 147–154.
Inoue, K., Ono, M., Nakajima, H., Fujia, I., Inouye, H., Fujita, T., 1992.
Radioimmunoassay of iridoid Glucosides: Part 1. General Method for
Preparations of the Haptens and the Conjugates with a Protein of This Series
of Glucosides. Heterocycles 33, 673–695.
Machida, K., Takehara, E., Kobayashi, H., Kikuchi, M., 2003. Studies on the
Constituents of Gardenia Species. III. New Iridoid Glycosides from the Leaves
of Gardenia jasminoides cv. fortunea HARA. Chem. Pharm. Bull. 2003 (51),
1417–1419.
Moreira, V.F., Oliveira, R.R., Mathias, L., Braz-Filho, R., Vieira, I.J.C., 2010. New
Chemical Constituents from Borreria verticillata (Rubiaceae). Helv. Chim. Acta
93, 1751–1757.
Murai, F., Tagawa, M., Damptof, S., Jensen, S.R., Nielsen, B.J., 1984. (1R,5R,8S,9S)Deoxyloganic Acid from Nepeta cataria. Chem. Pharm. Bull. 32, 2809–2814.
Nakamura, M., Kido, K., Kinjo, J., Nohara, T., 2000. Antinociceptive substances from
Incarvillea delayavi. Phytochemistry 53, 353–1256.
Raju, B.L., Lin, S.-J., Hou, W.-C., Lai, Z.-Y., Liu, P.-C., Hsu, F.-L., 2004. Antioxidant
Iridoid Glucosides from Wendlandia formosana. Nat. Prod. Res. 18, 357–364.
Takeda, Y., Yagi, T., Matsumoto, T., Honda, G., Tabata, M., Fujita, T., Shingu, T.,
Otsuka, H., Sezik, E., Yesßilada, E., 1996. Nepetanudosides and Iridoid Glucosides
Having Novel Stereochemistry from Nepeta nuda ssp. albiflora. Phytochemistry
42 (4), 1085–1088.
_ Sticher, O., 1999. Iridoid
Tasdemir, D., Scapozza, L., Zerbe, O., Linden, A., Çalısß, I.,
Gylycosides of Leonurus persicus. J. Nat. Prod. 62, 811–818.
Teng, R.W., Wang, D.Z., Wu, Y.S., Lu, Y., Zheng, Q.T., Yang, C.R., 2005. Spectral
Assignments and Reference Data. NMR assignments and single-crystal X-ray
diffraction analysis of deoxyloganic acid. Magn. Reson. Chem. 43, 92–96.
Tzakou, O., Mylonas, P., Vagias, C., Petrakis, P.V., 2007. Iridoid Glucosides wth
Insecticidal Activity from Galium melanantherum. Z. Naturforsch. 62c, 597–602.