New onoceranoid xyloside from Lansium parasiticum

Article abstract of DOI:10.1080/14786419.2018.1510395

A novel onoceranoid triterpene xyloside named methyl lansioside C (1) together with two known glycosides (2 and 3) were isolated from polar fraction of the fruit peels of Lansium parasiticum. The structure and absolute configuration of the new compound we

Full text of DOI:10.1080/14786419.2018.1510395

Natural Product Research
Formerly Natural Product Letters
ISSN: 1478-6419 (Print) 1478-6427 (Online) Journal homepage: http://www.tandfonline.com/loi/gnpl20
New onoceranoid xyloside from Lansium
parasiticum
Rico Ramadhan, Wisuttaya Worawalai & Preecha Phuwapraisirisan
To cite this article: Rico Ramadhan, Wisuttaya Worawalai & Preecha Phuwapraisirisan
(2018): New onoceranoid xyloside from Lansiumꢀparasiticum, Natural Product Research, DOI:
10.1080/14786419.2018.1510395
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NATURAL PRODUCT RESEARCH
https://doi.org/10.1080/14786419.2018.1510395
New onoceranoid xyloside from Lansium parasiticum
a,b
a
a
Rico Ramadhan , Wisuttaya Worawalai and Preecha Phuwapraisirisan
a
Department of Chemistry, Faculty of Science, Center of Excellence in Natural Products,
b
Chulalongkorn University, Bangkok, Thailand; Department of Chemistry, Faculty of Science and
Technology, Airlangga University, Surabaya, Indonesia
ABSTRACT
ARTICLE HISTORY
A novel onoceranoid triterpene xyloside named methyl lansio-
side C (1) together with two known glycosides (2 and 3) were
isolated from polar fraction of the fruit peels of Lansium para-
siticum. The structure and absolute configuration of the new
compound were established using extensive spectroscopic
techniques as well as Mosher’s method. The antioxidant activity
and a-glucosidase inhibitory effect of the isolated compounds
were evaluated. Compounds 1 and 3 displayed moderate rad-
ical scavenging activity with SC50 values of 14.5 and 13.7 mM,
respectively. However, all isolated compounds exhibited no
inhibition against a-glucosidase.
Received 30 April 2018
Accepted 6 August 2018
KEYWORDS
Onoceranoid; triterpene;
glycoside; Lansium
parasiticum; Lansium
domesticum; Meliaceae;
antioxidant
1. Introduction
The plant of Lansium parasiticum (syn L. domesticum) (Meliaceae) is a fruit-bearing
tree and cultivated widely in Thailand and surrounding countries in the Southeast
Asia (Saewan et al. 2006; Dong et al. 2011). The fruit is known locally (in Thai) as
langsat, long-kong, lang-sook or langsat-khao. The seeds have been traditionally
used to treat malaria (Rudiyansyah et al. 2018), and the fruit peels are known to be
toxic to domestic animals (Leaman et al. 1995). Previous chemical studies on its fruit
peels have led to the isolation of onoceranoid triterpenes (Kiang et al. 1967; Tanaka
et al. 2002; Potipiranun et al. 2017). More interestingly, onoceranoid triterpene
glycosides containing rare sugars such as N-acetylglucosamine and xylose were also
reported (Nishizawa et al. 1982, 1983). To date, there has been no additional
CONTACT Preecha Phuwapraisirisan
preecha.p@chula.ac.th
Supplemental data for this article can be accessed at https://doi.org/10.1080/14786419.2018.1510395.
ß 2018 Informa UK Limited, trading as Taylor & Francis Group

2
R. RAMADHAN ET AL.
Figure 1. Structures of isolated compounds.
phytochemical investigation on onoceranoid triterpene glycosides from
L. parasiticum or other related species.
Herein, we described the isolation, structure identification and absolute configur-
ation determination of a new triterpene glycoside, named a methyl lansioside C (1)
together with two known compounds (Figure 1) from the fruit peels of L. parasiticum
collected from Yala, the Southern part of Thailand.
2. Results and discussion
Methyl lansioside C (1) was obtained as a yellow amorphous solid. The positive-ion
þ
observed in HRESIMS spectrum (Figure S1) showed a peak of [M þ Na] ion at m/z
1
6
25.4086, which was accounted for the molecular formula C H NaO . The H NMR
36
58
7
spectrum (Figure S2) displayed the presence of signals due to six singlet methyls and
a methoxy proton (d 3.68 s). In addition, the anomeric proton appeared at d 4.30 as
H
H
a doublet with a large coupling constant of 7.5 Hz, indicating the presence of one
13
sugar unit in this molecule. The C NMR spectrum (Figure S3) revealed the presence
of six methyls (d 15.2, 16.8, 16.9, 23.3 (2ꢀ) and 28.6), trisubstitued olefin (d 137.2
C
C
and 122.7), an oxygenated methine (d 90.4), two exomethylenes (d 149.7, 149.1,
C
C
13
1
07.3 and 114.5) and a methoxy group (d 52.1). Moreover, the C NMR spectrum
C
also contained characteristic signals of pentose residue at d 107.4, 78.0, 75.4, 71.2
C
and 66.7. The above data suggested that 1 was likely to be an onoceranoid triterpene
glycoside featuring a 21,22-seco skeleton, which was inferred to have three cyclic
moieties (A–C) (Nishizawa et al. 1983).
The core structure of 1 was further elucidated by analysis of 2 D NMR, especially
COSY, HSQC and HMBC (Figures S4, S5 and S6, respectively). The oxygenated methine
at d 90.4 was assigned to C-3 of ring A by HMBC correlations (Figure S7) of Me-23,
C
Me-24, CH -2 and CH -1 to C-3. The exomethylene terminal was located to C-8 of ring
2
2
B, which was assigned by HBMC correlations of CH -26 (dH 4.87 and 4.60) to C-7
2

NATURAL PRODUCT RESEARCH
3
(
d 39.2), C-8 (d 149.7) and C-9 (d 59.6). The singlet methyl (d 0.73 and d 15.7) at
C C C H C
C-10 was placed by the correlations of Me-25 to C-1 (d 38.5), C-5 (d 56.3) and C-9
C
C
(dC 59.6). Therefore, the presence of bicylic A–B system was confirmed.
The remaining ring C, was established based mainly on HMBC correlation analysis.
2
2(29)
The terminal D
double bond was located from the observed HMBC crosspeaks of
14
CH -29 to C-17, C-22 and C-30. The trisubtituted D double bond (d 5.40; d 137.2
2
H
C
and 122.7) was placed between C-14 and C-15 by the HMBC correlations of Me-27
(d 1.77) to C-15 (d 122.7), H-15 (d 5.40) to C-13 (d 49.4) and H-15 (d 5.40) to C-16
H C H C H
(dC 30.7). In addition, the presence methoxycarbonyl group was attached to C-20 by
HMBC correlations from CH -20 and OCH to C-21 (d 176.1). Therefore, ring C of 1
2
3
C
was established.
The bicyclic A–B and ring C was connected through the CH -11 and CH -12
2
2
dimethylene bridge. The HMBC crosspeaks revealed critical evidences of H-11 to C-12
and C-13 to support this connection. Futhermore, the attachment of the sugar moiety
to ring A was determined by HMBC correlations (Figure S7) between the anomeric
proton H-1’ (d 4.30, d, J ¼ 7.5 Hz) and C-3 (d 90.4) through O-glycoside bonding. The
H
C
occurrence of pyranose moiety was confirmed by the correlation networks of H-1’
(
(
(
(
dH 4.30)/C-3’ (d 78.0), H-3’ (d 3.32)/C-2’ (d 75.4), H-3’ (d 3.32)/C-5’ (d 66.7), H-5’
C H C H C
d 3.84, dd, J ¼ 11.4, 5.3 Hz)/C-4’ (d 71.2) and H-5’ (d 3.84, dd, J ¼ 11.4, 5.3 Hz)/C-1’
H
C
H
d 107.4). The identify of sugar component was verified, after acid hydrolysis of 1
C
Scheme 1), as D-xylose (1d) by TLC in multiple mobile phase systems together with
positive specific rotation compared with authentic D-xylose . Furthermore, the larger
proton spin-coupling constant (J ¼ 7.5 Hz) of anomeric proton (H-1’) indicated the
b-D-xylose linkage to aglycon. Thus, the overall structure of methyl lansioside C (1)
was deduced as shown.
The relative configuration of 1 was defined by analysis of NOESY spectrum
(Figure S8). For bicyclic A–B system, NOESY experiment revealed the crosspeaks of
CH -23/H-5, H-5/H-1 and H-5/H-9 for a-orientation, while the correlations of Me-24/
3
Me-25 and Me-25/H-6b suggested the b-orientation. In ring C, H-13 and H-17 were
occupied b-plane as indicated by the correlations of H-13/H-17 and H-17/H-29, thus
inevitably Me-28 on the a-plane. With relative configuration in hand, we subsequent
deduced absolute configuration by applying a-methoxyphenylacetic acids (MPAs) as
chiral derivatizing agents (Trost et al. 1986). Prior to introducing chiral MPAs, removal
Scheme 1. Reagents and conditions: (i) TFA/ACN, reflux; (ii) R-(ꢁ)-MPA acid, EDC, DMAP, CH Cl ;
2
2
(
iii) S-(þ)-MPA acid, EDC, DMAP, CH Cl .
2
2

4
R. RAMADHAN ET AL.
Figure 2. DdSR values (in ppm) for the MPA esters (1b and 1c) of 1b.
Table 1. Free radical scavenging activities effect of 1–3 and 1a.
Compounds
SC50 (mM)
Methyl lansioside C (1)
Lansioside C (2)
Lansioside B (3)
14.5
23.6
13.7
21.3
Methyl lansiolate (1a)
Ascorbic acid
2.45
of glucose moiety from 1 was required to avoid unexpectedly anisotropic effects of
multiple phenylacetic acid derivatives (Freire et al. 2005). Acid hydrolysis of 1 afforded
metyl lansiolate (1a) and xylose residue (1d). The obtained aglycon (1a) was
subsequently reacted with (R)- or (S)-MPA acids (Scheme 1) in the presence of
N-ethyl-N’-(3-dimethylaminopropyl) carbodiimide (EDC) as a coupling reagent, yielding
the corresponding MPA esters 1 b and 1c, respectively. The differences in the proton
chemical shifts (DdH ) between (S)- and (R)-MPA esters indicated R configuration at
SR
C-3 (Figure 2), and the absolute configuration of other chiral centers (5 R, 9S and 10R)
in the bicyclic A–B system can also be addressed.
All isolated compounds (1–3) and aglycon (1a) were evaluated for their a-glucosi-
dase inhibition and free radical scavenging activity (Table 1). Compounds 1 and 3 dis-
played moderate radical scavenging activity with SC50 values of 14.5 and 13.7 mM,
respectively, while compounds 2 and 1a exhibited weaker inhibition (SC50 23.6
and 21.3 mM). Unfortunately, all isolated compounds (1–3) and aglycon (1a) exhibited
no inhibition against a-glucosidase. To our knowledge, this is the first report of
report radical scavenging and a-glucosidase inhibition of onoceranoid triterpene
glycosides.
3. Experimental
3.1. Plant material
The fruits of L. parasiticum were collected from Yala, Thailand, in September, 2016).
The voucher specimen (NPRU 105-2016) has been deposited at the Natural Products
Research Unit, Chulalongkorn University, Bangkok, Thailand.

NATURAL PRODUCT RESEARCH
5
3.2. Extraction and isolation
The air-dried and finely ground fruit peels of L. parasiticum (2.1 kg) were extracted
three times with MeOH at room temperature to give a crude extract. The resulting
MeOH extract was suspended in water and partitioned with n-hexane and EtOAc,
respectively. The EtOAc extract (228 g) was subjected to silica gel column chromatog-
raphy (Merck Art 7730) and eluted in stepwise fashion with n-hexane, 1.5:8.5 EtOAc-n-
hexane, 4:6 EtOAc-n-hexane, 8:2 EtOAc-n-hexane, EtOAc, 1:1 MeOH-EtOAc and MeOH
to yield six fractions (fractions 1–6). Fraction 4 was chromatographed on Sephadex
LH-20 using 1:4 MeOH-CH Cl to yield twelve sub-fractions. Sub-faction 1 was sepa-
2
2
rated on silica gel CC using 1:9 MeOH-CH Cl to afford methyl lansioside C (1, 98 mg).
2
2
Sub-fraction 3 was chromatographed on silica gel CC using 1:4 MeOH-CH Cl to yield
2
2
lansioside C (2, 195 mg). Moreover, fraction 5 was subjected to Sephadex LH-20 and
eluted with 1:4 MeOH-CH Cl to afford five sub-fractions (sub-fractions 1-5). Sub-
2
2
fraction 3 was subjected to silica gel column chromatography and eluted with 3:7
MeOH-CH Cl to yield lansioside B (3, 30 mg).
2
2
24
1
Methyl lansioside C (1): colorless amorphous solid; [a]D ¼ þ9.6 (c 1.34, EtOH); H
NMR (400 MHz, CD OD) d : 5.40 (1 H, brs, H-15), 4.87 and 4.60 (each 1 H, brs, H-26),
3
H
0
0
4
3
.85 (2 H, brs, H-29), 4.30 (d, J ¼ 7.5 Hz, 1 H, H-1 ), 3.84 (dd, J ¼ 11.4, 5.3 Hz, 1 H, H-5 ),
0
0
0
.68 (3 H, s, O-Me), 3.49 (1 H, m, H-4 ), 3.32 (m, 1 H, H-3 ), 3.21 (1 H, m, H-2 ), 3.20 (1 H,
m, H-3), 2.44 and 2.34 (each 1 H, m, H-12), 2.43 and 2.02 (each 1 H, m, H-7), 2.26 (1 H,
m, H-17), 2.24 and 1.84 (each 1 H, m, H-16), 1.92 and 1.69 (each 1 H, m, H-19), 1.88
(1 H, m, H-13), 1.81 (s, 3 H, H-30), 1.80 and 1.20 (each 1 H, m, H-1), 1.79 (1 H, m, H-6a)
1
1
.41 (1 H, m, H-6b), 1.77 (3 H, s, H-27), 1.68 (2 H, m, H-20), 1.61 (1 H, m, H-9), 1.44 and
.69 (each 1 H, m, H-11), 1.43 and 1.25 (each 1 H, m, H-2), 1.17 (1 H, m, H-5), 1.08 (3 H,
13
s, H-23), 0.86 (3 H, s, H-24), 0.85 (3 H, s, H-28), 0.73 (3 H, s, H-25). C NMR (100 MHz,
CD OD) d : 176.1 (C-21), 149.7 (C-8), 149.1 (C-22), 137.2 (C-14), 122.7 (C-15), 114.5 (C-
3
C
0
0
0
0
0
2
5
9), 107.3 (C-26), 107.4 (C-1 ), 90.4 (C-3), 78.0 (C-3 ), 75.4 (C-2 ), 71.2 (C-4 ), 66.7 (C-5 ),
6.3 (C-5), 59.6 (C-9), 52.1 (OMe), 50.4 (C-17), 49.4 (C-13), 40.5 (C-18), 40.2 (C-4), 39.7
(C-10), 38.5 (C-1), 39.2 (C-7), 34.0 (C-20), 30.7 (C-16), 30.0 (C-12), 28.6 (C-23), 28.4 (C-2),
2
7.9 (C-19), 25.0 (C-6), 23.3 (C-27), 23.2 (C-30), 16.9 (C-24), 16.8 (C-28) and 15.2 (C-25);
þ
HRESIMS m/z 625.4086 [M þ Na] (calcd for C H NaO , 625.4080).
3
6
58
7
3.3. Sugar moiety analysis
Methyl lansioside C (1, 10 mg) dissolved in acetonitrile (1 mL) was added trifluoroacetic
acid (TFA, 1 mL) and refluxed for 4 h. The resulting mixture was evaporated to dryness,
dissolved in ethyl acetate and extracted with H O. The triterpenoid aglycone 1a was
2
obtained in organic phase while the sugar residue 1d was dissolved in aqueous phase.
The identity of furanose in aqueous phase was determined by silica gel TLC using
5
:3:2 BuOH-EtOH-H O as mobile phase (Harborne 1998). After TLC development fol-
2
lowed by dipping in 5% anisaldehyde reagent, the hydrolysate 1d showed dark blue
spot identical to that of authentic xylose (R 0.62), while authentic arabinose showed
f
the spot with R value of 0.52. The large remaining aqueous layer was concentrated
f
25
and lyophilized to yield colorless solid. The positive specific rotation, [a]D ¼ þ20.1
c 0.86, H O), indicated the identity of D-(þ)-xylose.
(
2

6
R. RAMADHAN ET AL.
3.4. Absolute configuration determination
The absolute configuration of C-3 in 1a was addressed by applying MPA derivatiz-
ing agent with slight modification (Trost et al. 1986). A solution of 1a (9 mg,
0
.021 mmol) in anhydrous CH Cl2 (1 mL) was added R-(-)-a-methoxyphenylacetic
2
acid (R-MPA) (6 mg, 0.032 mmol), EDC (16 mg, 0.053 mmol) and DMAP (catalytic
quantity). After stirred at room temperature overnight, the reaction mixture was
quenched with water and extracted twice with CH Cl . The combined organic layer
2
2
was dried over anhydrous Na SO , and the solvent was removed under reduced
2
4
pressure. The residue was purified by small silica gel column chromatography
eluted with 1:9 EtOAc-hexane to yield R-MPA ester (1 b, 7 mg). In a similar manner,
the S-(þ)-a-methoxyphenylacetic acid (S-MPA) ester (1c, 7 mg) was also prepared.
1
H NMR spectra of R-MPA ester (1b) and S-MPA ester (1c) are showed in Figures
S10 and S11, respectively.
3.5. a-Glucosidase inhibitory activity
Rat intestinal a-glucosidase inhibitory activity was determined according to our pre-
vious report (Ramadhan and Phuwapraisirisan 2015). This assay was carried out
based on enzymatic hydrolysis of maltase and sucrase to form glucose residue. The
concentration of glucose released was detected by the glucose oxidase method
using a glu-kit. A 10 lL of buffer (pH 6.9, 30 lL), 20 lL of the substrate solution (mal-
tose: 10 mM; sucrose: 100 mM) in 0.1 M phosphate buffer, glucose kit (80 lL) and the
ꢂ
crude enzyme solution (20 lL). The reaction mixture was then incubated at 37 C for
either 10 min (for maltose) or 40 min (for sucrose). The concentration of glucose
released from the action mixture was detected by the glucose oxidase method
using a glu-kit (Human, Germany). Enzymatic activity was quantified by measuring
absorbance at 503 nm. The percentage inhibition was calculated by [(A0-A1)/
A0] ꢀ 100, where A0 is the absorbance without the sample, and A1 is the absorb-
ance with the sample. The IC50 value was determined from a plot of percentage
V
R
inhibition versus sample concentration. Acarbose was used as standard control and
the experiment was performed in duplicate. The Baker’s yeast a-glucosidase inhib-
ition assay were determined according to our previous method (Worawalai
et al. 2015).
3.6. DPPH scavenging activity
The antioxidant activity was evaluated through the free radical scavenging effect on
DPPH radical using previous reports (Clarke et al. 2013; Badral et al. 2017) with slight
modifications. DPPH methanolic solution (0.06 mM, 100 lL) was added to 20 lL of the
sample extracts with various concentrations. The mixture was thoroughly mixed and
kept in the dark for 30 min. The absorbance was measured at 517 nm using a TECAN
Infinite 50 microplate reader spectrophotometer. The IC50 value was determined from
a plot of % inhibition versus final concentration of reaction.

NATURAL PRODUCT RESEARCH
7
4. Conclusions
A new onoceranoid-triterpene glycoside named methyl lansioside C (1) was isolated
along with its related congeners 2 and 3 from polar fraction of Lansium parasiticum
fruit peels. The onoceranoid-triterpene glycosides have been few reported so far. In
addition, the absolute configuration of chiral centers in bicyclic A–B system was also
herein first addressed. Of isolated compound, 1 and 3 showed moderate inhibition
againt free radical, while 2 and 1a showed weak inhibition. However, all isolated com-
pounds (1–3) and aglycon (1a) exhibited no inhibition against a-glucosidases.
Acknowledgement
RR is grateful to the Graduate School of Chulalongkorn University for a Postdoctoral Fellowship
(Ratchadaphisek Sompot Fund). This project was supported by the Thailand Research Fund via
the Directed Basic Research Grant (DBG 5980001). The Center of Excellence in Natural Products
was subsidized by Chulalongkorn University.
Disclosure statement
No potential conflict of interest was reported by the authors.
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