Four New Diterpene Glucosides from Perovskia atriplicifolia

Article abstract of DOI:10.1002/cbdv.201700071

Four new diterpene glucosides, namely perovskiaditerpenosides A?–?D (1?–?4), were isolated from the BuOH extract of Perovskia atriplicifolia. Their structures were well elucidated by chemical methods and comprehensive spectroscopic analyses including MS, IR, and NMR (1D and 2D). The newly isolated compounds were screened for their cytotoxic activity against HepG2, NB4, HeLa, K562, MCF7, PC3, and HL60. The obtained results indicated that the new compounds possessed considerable cytotoxic activity.

Full text of DOI:10.1002/cbdv.201700071

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Article Type: Full Paper
Four new diterpene glucosides from Perovskia atriplicifolia
Lu Gao,a,b Jun Zhou,b Le-Yu Zhu,b Juan-Rong Zhang,b Yu-Xing Jing,b Jia-Wen Zhao,b
Xiang-Zhong Huang,b Gan-Peng Li,b Zhi-Yong Jiang,*b Da-Yuan Xue*a
aColledge of Life & Environmental Sciences, Minzu University of China, Beijing, China
100081
bKey Laboratory of Chemistry in Ethnic Medicinal Resources, State Ethnic Affairs Commission &
Ministry of Education, Yunnan Minzu University, Kunming, China 650500
Corresponding authors:
Prof. Dr. Zhi-Yong Jiang.
Tel: +86 871 65926040; E-mail: jiangzy2010@163.com
Prof. Da-Yuan Xue
Tel:+86 10 68931632; E-mail: xuedayuan@hotmail.com
Abstract:
Four new diterpene glucosides, namely perovskiaditerpenosides A-D (1-4), were isolated from the
butanol extract of Perovskia atriplicifolia. Their structures were well elucidated by chemical
methods and comprehensive spectroscopic analyses including MS, IR, and NMR (1D and 2D). The
newly isolated compounds were screened for their cytotoxic activity against HepG2, NB4 Hela, K562,
HL60, MCF7 and HL60. The obtained results indicated that the new compounds possessed
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considerable cytotoxic activity.
Keywords:
Perovskia atriplicifolia, diterpene glucosides, perovskiaditerpenosides A-D, cytotoxic activity
Introduction. - The Perovskia is a small genus from Labiatae family, and had been reported
to possess leishmanicidal, antiplasmodial, and cytotoxic activity [1]. In China, there are
only two species (P. atriplicifolia and P. abrotanoides), distributed mainly in Tibet and
Xinjiang [2]. These two species are used in folk medicine for the treatment of
leishmaniasis by local people. It was also been reported to possess antibacterial and
anti-inflammatory activities [3,4]. Some investigation on this plant had been conducted and
many compounds had been isolated [5-7]. Our previous investigation suggested the petroleum
ether extract of P. atriplicifolia showed anti-HBV (Hepatitis B virus) activity and some
bioactive chemicals had been isolated from the petroleum ether extract [8-12]. But the butanol
extract showed none anti-HBV activity during the preceding investigation. In consideration
that no investigation on the butanol fraction was reported, a subsequent bioassay screening
was conducted and the butanol extract was found to exhibit moderate cytotoxic activity.
Further investigation of the butanol extract of P. atriplicifolia led to the isolation of four new
diterpene glucosides. By chemical methods and comprehensive analyses of their MS, IR, 1D-and
2D-NMR data, the structures of the four new diterpene glucosides were determined (Fig 1). The
cytotoxic activity of the newly isolated compounds was investigated against HepG 2, NB4, Hela,
K562, MCF7, PC3 and HL60 cell lines. Results suggested that compounds 1-4 possessed noticeable
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cytotoxicities. Described herein were the isolation, structural elucidation and cytotoxic
activities of compounds 1-4.
Results and Discussion. - Compound 1 was obtained as a white amorphous powder from Fraction C2.
The positive ESI-MS gave a quasi-molecular ion peak at m/z 649, in agreement with the molecular
formula C32H50O12 revealed by the HR-ESI-MS at m/z 649.3192 [M+Na]+ (calc. for C32H50O12Na+
649.3199). The IR spectrum displayed absorptions attributable to OH (3443 cm-1) and aromatic ring
(1606, 1497, 1448 cm-1) functions. After the hydrolysis of 1 with 10% HCl in MeOH, D-glucose was
identified by
a
comparison with the authentic sugar sample on TLC (developed by
1
n-BuOH/AcOH/H2O 4:1:5, upper layer; and PhOH/H2O 4:1). The H-NMR spectrum (CD3OD, 400
MHz) (Table 1) displayed two aromatic proton signals at δH 7.03 (1H, s, H-11), 6.84 (1H, s, H-14),
three singlet methyls (δH 1.19, 1.05, 0.88), in addition to signals that indicated the presence of
one isopropyl group at δH 3.49 (1H, sept. J = 6.8 Hz, H-15), 1.18 (3H, d, J = 6.8 Hz, H-16),
and 1.13 (3H, d, J = 6.8 Hz, H-17). The two anomeric proton signals at δH 4.93 (1H, d, J = 7.6
Hz, H-1") and 4.79 (1H, d, J = 7.6 Hz, H-1') suggested there were two β- orientation sugar moieties in
the molecule. The 13C-NMR spectrum (CD3OD, 100 MHz) (Table 2) revealed 32 carbon signals,
1
indicating the presence of a diterpene skeleton and two sugar moities. The H and 13C-NMR spectral
data were in total agreement with those of hinokiol [8], suggesting that compound 1 might be a
glucoside derivative of hinokiol. The position of the additional two β-D-glucose units was deduced as
1→2 linkage by comparing the NMR data with those of lucihirtin A [13], and was further confirmed by
the HMBC correlations between H- 1" and C-2'. The obvious HMBC cross peak H- 1' /C-12
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established the location of the inner glucose at C-12 of hinokiol. The absolute configuration of
D-glucose was finally verified by GC analysis of the trimethylsilyl L-cysteine derivative. The other
1
HSQC, HMBC, H-1H COSY (Fig. 2) and ROESY (Fig. 3) correlations allowed the full proton and
carbon assignments of compound 1. Consequently, the structure of compound 1 was determined as
shown in Fig. 1 and named as perovskiaditerpenoside A (1).
Compound 2 was obtained as a white amorphous powder from Fraction C2. The molecular formula
was deduced as C32H50O13 based on its HR-ESI-MS which showed a molecular ion peak at m/z
665.3141 [M+Na]+ (cald. for C32H50O13Na+ 665.3149). The IR spectrum of compound 2 showed
absorption peaks that indicated the presence of OH (3442 cm-1) and aromatic ring (1603, 1498, 1449
cm-1). The presence of D-glucose in compound 2 was corroborated by TLC and GC analyes of the acid
hydrolysate. In the 1H-NMR spectrum (C5D5N, 400 MHz), an aromatic proton signal at δH 6.75 (1H, s,
H-14), three singlet methyls at δH 1.47, 1.29, 1.08, one isopropyl group atδH 4.18 (1H, sept. J =
6.8 Hz, H-15), 1.44 (3H, d, J = 6.4 Hz, H-16), and 1.10 (3H, d, J = 6.8 Hz, H-17), and two
anomeric proton signals ascribable to two β-linked sugar units at δH 5.64 (1H, d, J = 7.8 Hz, H-1")
and 5.21 (1H, d, J = 8.0 Hz, H-1') were displayed. Detailed analysis of the NMR data suggested
compound 2 was also a diterpene glucoside, with a similar sugar chain at C-12. A comparison of the
MS and NMR spectrum indicated that compound 2 contained one more OH than 1. The additional OH
was determined at C-11 by the HMBC correlations observed between H-14 (δH 6.75, δC 117.7) and
each of C-7 (δC 33.4), C-8 (δC 134.4) and C-9 (δC 133.8) in addition to the correlations observed
between H-15 (δH 4.18) and C-12 (δc 141.7). Accordingly, the structure of compound 2 was deduced as
depicted in Fig.1 and named as perovskiaditerpenoside B (2).
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