924
Chem. Pharm. Bull. 64, 924–929 (2016)
Vol. 64, No. 7
Special Collection of Papers
This article is dedicated to Professor Satoshi Ōmura in celebration of his 2015 Nobel Prize.
Note
Acylated Triterpene Saponins from the Stem Bark of Acer nikoense
(Aceraceae)
,a
Shin-ichiro Kurimoto,* Yu F. Sasaki,a,b Yoshihiro Suyama,c Naonobu Tanaka,c
Yoshiki Kashiwada,c and Takanori Nakamuraa
a Faculty of Pharmaceutical Sciences, Himeji Dokkyo University; 7–2–1 Kamiohno, Himeji, Hyogo,
b
670–8524, Japan: Laboratory of Genotoxicity, Faculty of Chemical and Biological Engineering,
Hachinohe National College of Technology; 16–1 Tamonoki Uwanotai, Hachinohe, Aomori, 039–1192,
c
Japan: and Graduate School of Pharmaceutical Sciences, Tokushima University; 1–78 Shomachi,
Tokushima 770–8505, Japan.
Received February 15, 2016; accepted March 16, 2016
Three new acylated triterpene saponins, acernikoenosides A–C (1–3), were isolated from the stem bark
of Acer nikoense, together with a known sterol glucoside. Their structures were elucidated on the basis of ex-
tensive spectroscopic analyses. This study provided the first example of triterpene saponins isolated from this
plant. The anti-genotoxic activity of 1, 3 and 4 against ultraviolet irradiation was evaluated by comet assay.
Key words Acer nikoense; triterpene saponin; Aceraceae
Acer nikoense MAXIM. (Japanese name: Megusurino-ki) is 4 (45mg). Compound 4 was identified as β-sitosterol-3-O-β-
an Aceraceous plant native to Japan, of which the stem bark D-glucopyranoside22) by comparison of its spectroscopic data
has been used traditionally for the treatment of eye disor- with those reported in the literature.
ders and hepatic disease.1) A variety of phenolic compounds
Compound 1 was obtained as an optically active amor-
including diarylheptanoids,2–11) phenylbutanoids,4,12) couma- phous powder. The molecular formula of 1 was determined
rinolignans,13) neolignans,14) tannins15) and flavonoids12) have as C51H80O21 (m/z 1051.5087 [M+Na]+) by the high-resolution
been reported as the constituents of A. nikoense. Some of electrospray ionization (HR-ESI)-MS. The H-NMR spectrum
1
these compounds show various biological activities such as exhibited the signals due to seven tertiary methyls (δH 0.77,
anti-oxidant,16) anti-inflammatory,9) hepatoprotective,17) osteo- 0.85, 0.89, 0.94, 1.08, 1.08, 1.19), two acetyl groups (δH 1.96,
genic,18) vasorelaxant,19) melanogenesis inhibitory,11,16) nitric 2.00), one trisubstituted olefin [δH 5.32 (brt, 3.2)], two oxygen-
oxide (NO) production inhibitory8,20) and sodium glucose co- ated methines [δH 4.95 (d, 10.5), 5.28 (d, 10.5)], along with
transporter (SGLT) inhibitory activities.10)
signals ascribable to three anomeric protons [δH 4.30 (d, 7.2),
We have been investigating edible and medicinal plants 4.47 (d, 7.8), 4.70 (d, 7.7)]. The 13C-NMR and distortionless
effective for the suppression of genotoxicity to discover new enhancement by polarization transfer (DEPT) spectra showed
chemopreventive agents. Since the n-BuOH-soluble fraction the presence of nine methyl carbons (δC 15.9, 16.9, 17.7, 19.8,
from the MeOH extract of the stem bark of A. nikoense exhib- 20.7, 20.7, 26.6, 28.5, 29.3), eight sp3 methylene carbons (δC
ited an anti-genotoxic effect against UV-irradiation in screen- 19.3, 19.3, 24.6, 27.1, 28.2, 33.9, 39.8, 46.8), three sp3 methine
ing, we explored the chemical constituents of this fraction, carbons (δC 43.0, 48.9, 57.0), six sp3 quaternary carbons (δC
resulting in the isolation of three new acylated olean-type tri- 36.9, 37.8, 40.4, 40.6, 42.9, 53.2), three oxygen-bearing sp3
terpene saponins (1–3), together with a known sterol glucoside methines (δC 74.9, 77.3, 91.5), one sp2 methine (δC 125.1),
(4). Herein, we describe the isolation, structure elucidation one sp2 quaternary carbon (δC 142.9), and three carbonyl car-
and biological activity evaluation of the isolated compounds bons (δC 171.8, 172.3, 177.5). Furthermore, it represented 17
(Fig. 1).
carbon resonances assignable to a pentose and two hexoses.
The stem bark of A. nikoense was extracted with MeOH Acid hydrolysis of 1 with 5% H2SO4 provided D-glucose and
at room temperature. After removal of the solvent, the L-arabinose, which were identified by HPLC analysis.23) These
MeOH extract was partitioned successively between EtOAc, data were similar to those of dipterosides A–D, acylated
n-BuOH and H2O. These fractions were evaluated for their olean-type triterpene saponins previously isolated from
anti-genotoxic activity by comet assay.21) The n-BuOH-soluble Dipteronia dyeriana (Aceraceae),24) implying 1 was also an
fraction exhibited significant activity in a dose-dependent acylated olean-type triterpene saponin. This was further con-
manner (data not shown). Therefore, repeated column chroma- firmed based on the two-dimensional (2D)-NMR correlations
1
tography of this fraction over silica gel, octadecyl silica (ODS) shown in Fig. 2. The H–1H correlation spectroscopy (COSY)
and purification by reversed-phase (RP) HPLC was carried spectrum revealed the connectivity of C-2 to C-3, C-5 to C-6,
out to afford compounds 1 (38mg), 2 (11mg), 3 (7mg) and C-9 to C-12, C-18 to C-19, and C-21 to C-22. The locations of
*To whom correspondence should be addressed. e-mail: kurimoto@gm.himeji-du.ac.jp
© 2016 The Pharmaceutical Society of Japan