Four new pentasaccharide resin glycosides from Ipomoea cairica with strong α-glucosidase inhibitory activity

Article abstract of DOI:10.3390/molecules20046601

Six pentasaccharide resin glycosides from Ipomoea cairica, including four new acylated pentasaccharide resin glycosides, namely cairicoside I-IV (1-4) and the two known compounds cairicoside A (5) and cairicoside C (6), were isolated from the aerial parts of Ipomoea cairica. Their structures were established by a combination of spectroscopic, including two dimensional (2D) NMR and chemical methods. The core of the six compounds was simonic acid A, and they were esterfied the same sites, just differing in the substituent groups. The lactonization site of the aglycone was bonded to the second saccharide moiety at C-2 in 1-4, and at C-3 in 5-6. Compounds 1 and 5, 4 and 6 were two pairs of isomers. The absolute configuration of the aglycone in 1-6 which was (11S)-hydroxyhexadecanoic acid (jalapinolic acid) was established by Mosher's method. Compounds 1-4 have been evaluated for inhibitory activity against α-glucosidase, which all showed inhibitory activities.

Full text of DOI:10.3390/molecules20046601

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Molecules 2015, 20, 6601-6610; doi:10.3390/molecules20046601
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Four New Pentasaccharide Resin Glycosides from Ipomoea cairica
with Strong α-Glucosidase Inhibitory Activity
Jie-Tao Pan †, Bang-Wei Yu †, Yong-Qin Yin *, Jie-Hong Li, Li Wang, Li-Bing Guo
and Zhi-Bin Shen
School of Traditional Chinese Medicinal Chemistry, Guangdong Pharmaceutical University,
Guangzhou 510006, China; E-Mails: panjietao123@126.com (J.-T.P.); bondbeth@126.com (B.-W.Y.);
lijiehongivy@163.com (J.-H.L.); wangli182646@163.com (L.W.);
guolibing512@126.com (L.-B.G.); szb8113@126.com (Z.-B.S.)
†
These authors contributed equally to this work.
* Author to whom correspondence should be addressed; E-Mail: yongqinyin@gdpu.edu.cn;
Tel.: +86-20-39352179; Fax: +86-20-39352174.
Academic Editor: Derek J. McPhee
Received: 22 January 2015 / Accepted: 7 April 2015 / Published: 14 April 2015
Abstract: Six pentasaccharide resin glycosides from Ipomoea cairica, including four new
acylated pentasaccharide resin glycosides, namely cairicoside I–IV (1–4) and the two known
compounds cairicoside A (5) and cairicoside C (6), were isolated from the aerial parts of
Ipomoea cairica. Their structures were established by a combination of spectroscopic,
including two dimensional (2D) NMR and chemical methods. The core of the six
compounds was simonic acid A, and they were esterfied the same sites, just differing in the
substituent groups. The lactonization site of the aglycone was bonded to the second
saccharide moiety at C-2 in 1–4, and at C-3 in 5–6. Compounds 1 and 5, 4 and 6 were two
pairs of isomers. The absolute configuration of the aglycone in 1–6 which was
(11S)-hydroxyhexadecanoic acid (jalapinolic acid) was established by Mosher’s method.
Compounds 1–4 have been evaluated for inhibitory activity against α-glucosidase, which all
showed inhibitory activities.
Keywords: Ipomoea cairica; resin glycoside; simonic acid A; α-glucosidase

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1. Introduction
Ipomoea cairica (L.) Sweet (Convolvulaceae) is widely distributed in the tropical and subtropical
regions and is an invasive species in Southern China. I. cairica grows quickly and can then climb up
the nearby trees and thus block the light, killing these trees, and damaging small ecological
environments [1–3]. I. cairica was used in folk medicine to treat sores and so on [4]. Many different
compounds have been found in the plant, including resin glycosdes, lignans, benzenoids, coumarins,
flavonoids, steroids, and fatty acids [5,6]. There were five reported resin glycosides from I. cairica, in
which the lactone was attached at C-3 of Rha. In this paper six compounds were found, including two
pairs of isomers, which were 1 and 5, and 4 and 6. The lactone attachment sites in four new resin
glycosides 1–4 were assigned to C-2 of Rha and the lactone attachment sites of the two known resin
glycosides 5–6 were assigned to C-3 of Rha. Some plants from the Convolvulaceae family showed
strengthened inhibition against α-glucosidase or anti-diabetes activity [7,8], so this paper will elaborate
on the structures and α-glucosidase inhibitory activities of compounds 1–4.
2. Results and Discussion
Cairicoside I (1) obtained as a white, amorphous powder, which gave a quasi-molecular ion at m/z
1321.7212 [M+Na]+ in HR-TOF-MS, which suggested the molecular formula C65H102O26 (calcd. for
C65H102O26Na, 1321.6557). Its IR spectrum gave a hydroxyl group absorption band at 3442 cm−1,
carbonyl group at 1724 cm−1, and aromatic group at 1641 cm−1. Alkaline hydrolysis of 1 afforded a
glycosidic acid (compound 7) and organic acids. The organic acids were identified as 2-methylbutyric,
and Cna (trans-cinnamic acids), with a ratio of 2:1 by GC-MS. Mbaa (2-Methylbutyric acid) was found
to have the S-configuration by comparison of its optical rotation value with that of an authentic
sample [3]. Acid hydrolysis the glycosidic acid afforded Rha (L-rhamnose) and Glu (D-glucose), with a
ratio of 4:1. The monosaccharides was derivatized and identified as Rha and Glu by GC-MS by
comparison with authentic samples. Taken together the hydrolysis information and NMR data identified
the glycosidic acid as simonic acid A (7).
The 1H-NMR spectrum of 1 (Figure 1) exhibited two trans-coupled olefinic protons at δH 6.53 (1H,
d) and 7.81 (1H, d), a multiplet due to five protons at δH 7.27–7.45 (m) suggesting the presence of a Cna.
The protons at δH 0.82 (1H, t), 1.13 (1H, d), and 2.38 (m) were assignable to another Mba group. The
13C-NMR spectrum data of 1 (Table 1) exhibited four ester carbonyl carbons at δC 175.7, 175.2, 173.7,
and 166.1 and five anomeric carbon signals at δC 104.6, 104.3, 103.6, 99.2 and 98.3. The anomeric
protons were assigned to the peaks at 5.66 (1H, br s), 4.91 (1H, d), 5.94 (1H, br s), 6.08 (1H, br s) and
5.58 (1H, br s), respectively, by the HSQC data. All protons in each saccharide system and carbon
1
signals were assigned by H-, 13C-NMR, TOCSY, HMBC and HSQC experiments, leading to the
identification of one glucopyranosyl unit and four rhamnopyranosyl units as the monosaccharides
present in 1. The anomeric configuration for the sugar moieties were defined as β for the glucopyranosyl
moieties from their coupling constants of 7.2 Hz, and α for the rhamnopyranosyl from the C-5 chemical
shift [9].

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HO
HO
HO
O
HO
HO
11S
O
O
11S
O
O
HO
O
O
O
O
O
HO
O
O
O
O
OH
O
O
O
O
OR1
R3O
O
O
O
OR1
R3O
O
R2O
HO
OH
O
R1
Mba
Bu
R2
R3
R2O
HO
OH
O
R1
Mba
Deca Cna Mba
R2
R3
1
2
3
4
Cna Mba
Cna Mba
5
6
Cna Mba
HO
OH
Octq Cna Mba
Deca Cna Mba
HO
OH
Figure 1. The structures of compounds 1–6.
Table 1. NMR Data for Compounds 1–4 in pyridine-d5.
1 a
2 a
3 a
4 a
Position b
13C
1H
13C
104.3
81.8
76.1
71.7
77.8
62.6
1H
13C
102.7
80.3
74.8
70.2
76.3
61.1
1H
13C
104.3
81.8
76.3
71.7
77.8
62.6
1H
Glc-1
104.3
81.8
76.3
71.7
77.8
62.6
4.91 d (7.2)
3.87 *
4.97 d (7.2)
3.95 *
4.95 d (7.2)
3.92 *
4.91 d (7.2)
3.89 *
2
3
4.17 dd (9.0, 9.0)
4.12 dd (9.0, 9.0)
3.83 *
4.24 dd (9.0, 9.0)
4.12 dd (9.0, 9.0)
4.18 *
4.21 dd (9.0, 9.0)
4.15 dd (9.0, 9.0)
3.90 *
4.21 dd (9.0, 9.0)
4.12 dd (9.0, 9.0)
3.84 *
4
5
6a
4.44–4.46 *
4.29 *
4.52 *
4.48 *
4.48 *
6b
4.34 *
4.30 *
4.30 *
Rha-1
98.3
71.2
69.6
79.8
68.2
19.2
99.2
72.8
79.4
80.2
68.1
18.4
103.6
72.4
73.2
73.5
68.4
17.6
104.6
69.8
72.3
73.2
70.4
18.6
173.7
33.0
5.58 br s
98.5
71.2
69.6
79.4
68.1
18.6
99.3
72.9
79.9
79.4
68.1
18.3
103.1
72.4
73.1
73.5
68.4
19.2
104.3
69.8
72.3
73.4
70.6
18.5
173.5
34.2
5.64 br s
6.16 br s
97.0
69.7
67.9
77.8
66.6
18.6
97.6
71.3
78.3
78.8
66.6
16.1
101.8
70.9
71.4
71.8
66.9
17.7
102.7
68.3
70.9
71.8
69.1
16.9
171.6
32.6
5.61 br s
98.6
71.2
69.5
79.3
68.1
18.6
99.0
73.0
79.8
80.2
68.0
17.6
103.4
72.4
73.1
73.4
68.4
19.2
104.3
69.8
72.3
73.4
70.6
18.4
173.1
33.0
5.58 br s
2
6.04 br s
6.15 br s
6.15 br s
3
5.05 dd (9.6, 3.0)
4.18 dd (9.6, 9.6)
4.24 *
5.12 dd (9.6, 2.0)
4.24 dd (9.6, 9.6)
4.27 *
5.10 dd (9.6, 3.0)
4.23 dd (9.6, 9.6)
4.28 *
5.08 dd (9.6, 2.0)
4.20 dd (9.6, 9.6)
4.30 *
4
5
6
1.56 d (6.0)
6.08 br s
1.60 d (6.0)
6.12 br s
1.59 d (6.0)
6.08 br s
1.59 d (6.0)
6.05 br s
Rha'-1
2
5.98 br s
6.06 br s
6.05 br s
6.02 br s
3
4.56 dd (9.0, 2.4)
4.29 dd (9.0, 9.0)
4.34 dd (9.0, 6.0)
1.64 d (6.0)
5.94 br s
4.56 dd (9.0, 2.4)
4.20 dd (9.0, 9.0)
4.54 *
4.66 dd (10.0, 2.4)
4.20 dd (10.0, 10.0)
4.53 *
4.64 dd (9.0, 2.4)
4.20 dd (9.0, 9.0)
4.50 *
4
5
6
1.67 d (5.5)
5.94 br s
1.64 d (5.4)
5.99 br s
1.64 d (5.4)
5.96 br s
Rha"-1
2
4.78 br s
4.84 br s
4.81 br s
4.77 br s
3
5.91 dd (3.0, 10.0)
6.06 t (10.0)
4.49 dd (10.0, 6.5)
1.36 d (6.5)
5.66 br s
5.96 dd (3.0, 10.0)
6.11 t (10.0)
4.30 *
5.93 dd (2.9, 10.2)
6.10 dd (10.2, 10.2)
4.30 *
5.90 dd (3.0, 10.0)
6.05 dd (10.0, 10.0)
4.21 *
4
5
6
1.46 d (6.0)
5.69 br s
1.43 d (6.0)
5.65 br s
1.42 d (5.5)
5.62 br s
Rha"'-1
2
4.97 br s
4.97 br s
4.98 br s
4.94 br s
3
4.39 *
4.37 *
4.38 *
4.35 *
4
5
4.23 *
4.24 *
4.23 *
4.21 *
4.41 *
4.45 *
4.43 *
4.40 *
6
1.58 d (6.0)
1.58 d (6.0)
1.61 d (6.0)
1.59 d (6.0)
Ag-1
2
2.40 m, 2.24 m
2.30 m, 2.24 m
2.40 m, 2.29 m
2.40 m 2.26 m

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Table 1. Cont.
1
2
3
4
Position b
13C
173.7
33.0
1H
13C
1H
13C
1H
13C
1H
Ag-1
173.5
34.2
171.6
32.6
173.1
33.0
2
2.40 m, 2.24 m
3.89 *
2.30 m, 2.24 m
3.96 *
2.40 m, 2.29 m
3.90 *
2.40 m 2.26 m
3.90 *
11
82.5
82.6
81.1
82.6
16
14.0
0.84 t (7.0)
14.0
0.85 t (7.0)
12.6
0.82 t (7.0)
14.1
0.84 t (7.0)
Cna-1
166.1
118.1
145.4
134.3
128.4
129.0
130.7
175.2
41.2
166.0
118.0
145.3
134.4
128.3
129.1
130.4
175.6
41.3
164.8
116.8
143.9
133.0
126.8
127.6
129.0
175.7
39.8
166.2
118.1
145.3
134.4
128.3
129.1
130.5
175.7
41.3
2
6.53 d (16.0)
7.81 d (16.0)
6.60 d (16.0)
7.86 d (16.0)
6.57 d (16.0)
7.84 d (16.0)
6.54 d (16.0)
7.75 (16.0)
3
1'
2' and 6'
7.43 m
7.34 m
7.34 m
7.49 m
7.38 m
7.38 m
7.46 m
7.36 m
7.36 m
7.44 m
7.34 m
7.34 m
3' and 5'
4'
Mba-1
2
2.38 m
1.06 d (7.0)
1.41 m *
2.45 m
1.17 d (7.0)
1.41 m *
2.49 m
2.47 m
2-CH3
16.6
16.7
15.2
1.13 d (7.0)
1.38 m *
16.7
1.13 d (7.0)
1.44 m *
3
27.5
27.5
27.4
27.1
4
11.6
0.81 t (7.0)
11.7
0.79 t (7.0)
10.1
0.79 t (7.0)
11.6
0.79 t (7.0)
Mba'-1
175.7
41.3
2
2.47 m
1.13 d (7.0)
1.22 m *
2-CH3
16.7
3
27.0
4
11.6
0.82 t (7.0)
Bu-1
172.5
17.6
13.4
2
2.50 tq (7.0, 7.0)
0.84 t (7.0)
4
Oct-1
171.3
32.6
12.5
2
2.30 m
8
Deca-1
2
0.81 t (7.0)
172.7
34.2
14.0
2.32 tq (7.0, 7.0)
0.83 t (7.0)
10
a Chemical shifts (δ) are in ppm relative to TMS. The spin coupling (J) is given in parentheses (Hz). Chemical
shifts marked with an asterisk (*) indicate overlapped signals. Spin-coupled patterns are designated as follows:
s = singlet, br s = broad singlet, d = doublet, t = triplet, m = multiplet, q = quartet. All assignments are based on
1H-1H TOCSY experiments. b Abbreviations:Glc = glucose; Rha = rhamnose; Ag = 11-hydroxyhexadecanoyl;
Mba = 2S-methylbutanoyl; CA = trans-cinnamoyl; Deca = n-decanoyl; Octa = n-octanoyl; Bu = butytyl.
The interglycosidic connectivities were determined from the following HMBC (Figure 2)
correlations from Rha-H-1 (δH 5.58) to Glu-C-2 (δC 81.8), Rha'-H-1 (6.08) to Rha-C-4 (79.8), Rha''-H-1
(δH 5.94) to Rha'-C-4 (80.2), Rha'''-H-1 (δH 5.66) to Rha'-C-3 (79.4). Esterification positions were also
determined by HMBC data, between Rha''-H-4 (δH 6.06) to Mba-C-1(δC 175.7); Rha''-H-3 of rhamnose''
(δH 5.91) to Cna-C-1 (δC 166.1); Rha'-H-2 (δH 5.98) to Mba-C-1 (δC 175.2); and Rha-H-2 (δH 6.04) and
aglycone-C-1 (δC 173.7), respectively. The position of the jalapinolic acid unit was finally determined
by HMBC to be between aglycone-H-11 (δH 3.89) to Glu-C-1 (δC 104.3), which correlations established
the structure of 1 as (S)-jalapinolic acid 11-O-α-L-rhamnopyranosyl-(1→3)-O-[3-O-trans-cinnamoyl-
4-O-(S)-2-methyl-butyryl-α-L-rhamnopyranosyl-(1→4)]-O-[2-O-(S)-2-methylbutyryl]-α-L-rhamnopyra