Cleidbrevoids A-C, new clerodane diterpenoids from Cleidion brevipetiolatum.

Abstract

Three new clerodane-type diterpenoids with a rare sulfoxide group, cleidbrevoids A-C (1-3), were isolated from the twigs and leaves of Cleidion brevipetiolatum. Their structures were elucidated on the basis of spectroscopic methods and the absolute configuration of compounds 1 and 3 was determined by X-ray analysis. Compound 3 showed weak inhibitory against HIV-1.

Full text

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Cleidbrevoids A–C, new clerodane diterpenoids from Cleidion brevipetiolatum
Yuan-Yuan Chenga,b, Shi-Fei Lia,b, Yu Zhanga, Gui-Hua Tanga,b, Ying-Tong Dia, Xiao-Jiang Haoa,
Shun-Lin Lia,⁎, Hong-Ping Hea,⁎
aState Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201,
People's Republic of China
bGraduate University of Chinese Academy of Sciences, Beijing 100039, People's Republic of China
a r t i c l ei n f o a b s t r a c t
Article history:
Received 11 March 2012
Accepted in revised form 25 April 2012
Available online 3 May 2012
Three new clerodane-type diterpenoids with a rare sulfoxide group, cleidbrevoids A–C (1–3),
were isolated from the twigs and leaves of Cleidion brevipetiolatum. Their structures were
elucidated on the basis of spectroscopic methods and the absolute configuration of compounds
1 and 3 was determined by X-ray analysis. Compound 3 showed weak inhibitory against HIV-1.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Cleidion brevipetiolatum
Clerodane-type diterpenoids
Sulfoxide
Cleidbrevoids A–C
1. Introduction
The genus Cleidion (Euphorbiaceae) comprising 25 species
distributes mainly in the tropical southeast regions of Asia. In
the southwest of China, three species, Cleidion brevipetiolatum,
C. javanicum and C. bracteosum growing at an altitude of
200–1500 m, are used as folk medicine to treat inflammation,
diuresis, and acute and chronic hepatitis [1,2]. Up to date, a
series of chemical constituents, such as ellagitannins, phenyl-
propanoids, triterpenoids and diterpenoids have been reported
from the genus Cleidion [3]. As a part of our continuous search
for novel and potentially bioactive secondary metabolites from
Euphorbiaceae family [4], three new clerodane-type diterpe-
noids, cleidbrevoids A–C (1–3), with a rare sulfoxide moiety,
were isolated from C. brevipetiolatum. The chiral centers of
sulfoxide in cleidbrevoids A (1) and C (3) were determined by
X-ray analysis. Sulfur-containing diterpenoids were reported
previously, for example, clerodane diterpenoid cordifolide A
with immunomodulatory activity [5], and atisine diterpenoid
serofendic acid A with potent neuroprotective activity [6].
2. Experimental
2.1. General experimental procedure
X-ray data were collected using a Bruker APEX DUO
instrument. Optical rotations were determined on a Jasco
P-1020 polarimeter.UVdata were measured usinga Shimadzu
UV2401PC spectrometer, and IR spectra were recorded on a
BRUKER TENSOR27 spectrometer with KBr pellets. ESIMS was
carried out on an API QSTAR Pulsar mass spectrometer. 1D and
2D NMR spectra were measured on a Bruker AM-400, DRX-
500 spectrometer. Column chromatography was performed
on Silica gel H (10–40 m; Qingdao Marine Chemical Factory),
MCI gel (75–150 m, Mitsubishi Chemical Corporation, Tokyo,
Japan) and Sephadex LH-20 (40–70 m, Amersham Pharmacia
Biotech AB, Uppsala, Sweden). MPLC was performed on Büchi
Sepacore System (Büchi Labortechnik AG, Switzerland), and
columns were packed with Chromatorex C-18 (40–75 m, Fuji
Silysia Chemical Ltd., Japan). Preparative HPLC was performed
byusingan Agilent1200 series system equipped witha Zorbax
XDB-C18, 9.4 mm×150 mm column. Precoated silica gel GF254
Fitoterapia 83 (2012) 1100–1104
⁎ Corresponding authors. Tel.: +86 871 5223263; fax: +86 871 5223070.
E-mail addresses: lisl@mail.kib.ac.cn (S-L. Li), hehongping@mail.kib.ac.cn
(H-P. He).
0367-326X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.fitote.2012.04.028
Contents lists available at SciVerse ScienceDirect
Fitoterapia
journal homepage: www.elsevier.com/locate/fitote

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and HF254 plates (Qingdao Haiyang Chemical Plant, Qingdao,
People's Republic of China) were used for TLC.
2.2. Plant material
The twigs and leaves of C. brevipetiolatum were collected in
XishuangbannaofYunnanProvince,People'sRepublicofChina,
in October 2010, and identified by Mr. Chen Yu, Kunming
Institute of Botany, Chinese Academy of Sciences. A voucher
specimen (H20101008) was deposited in the Herbarium of
Kunming Institute of Botany.
2.3. Extraction and isolation
The air-dried, powdered twigs and leaves (14.0 kg) of C.
brevipetiolatum were extracted three times with MeOH under
reflux. After removal of the solvent by evaporation in vacuum,
the residue was suspended in water and then partitioned with
EtOAc. One twentieth (9.0 g) of the EtOAc portion (180.0 g)
was fractionated with petroleum ether/acetone in a silica gel
column to give seven fractions (A–G). Fraction D (1.5 g) was
subjected to MCI gel, Sephadex LH-20 and repeatedly silica
gel CC to yield compound 1 (6.0 mg). Fraction E (2.5 g) was
repeatedly chromatographed on silica gel, MPLC, Sephadex
LH-20 and finally purified by semi-preparative HPLC to afford
compounds 2 (3.5 mg) and 3 (5.0 mg) (Fig. 1).
2.4. Cleidbrevoid A (1)
Colorless prism crystals, mp 190.0–191.0 °C; [a]D
(c 0.20, CH3COCH3); UV (MeOH) λmax(log ε) 204 (4.03) nm;
IR (KBr) νmax3543, 3423, 2944, 1720, 1705, 1631, 1436, 1227,
1211, 1107, 1032, 989, 875, 780, 601 cm−1;1H and13C NMR
data see Table 1; ESIMS m/z 437 [M+H]+; HRESIMS m/z
459.1450 [M+Na]+(calcd for C22H28O7SNa, 459.1453).
26+23.5
2.5. Cleidbrevoid B (2)
White amorphous power, [a]D
UV (MeOH) λmax(log ε) 204 (4.00) nm; IR (KBr) νmax3509,
3433, 2920, 1795, 1708, 1639, 1459, 1227, 1269, 1209, 1107,
1032, 989, 875, 780, 601 cm−1;
Table1;ESIMSm/z437[M+H]+,459[M+Na]+;HRESIMSm/z
459.1460 [M+Na]+(calcd for C22H28O7SNa, 459.1453).
26−32.1. (c 0.20, CH3COCH3);
1H and
13C NMR data see
2.6. Cleidbrevoid C (3)
Colorless block crystals, mp 191.0–192.0 °C; [a]D
(c 0.20, CH3COCH3); UV (MeOH) λmax(log ε) 275 (2.27), 204
(3.83) nm; IR (KBr) νmax3543, 3423, 2944, 1720, 1705, 1631,
1436, 1227, 1211, 1129, 1094, 1021, 987, 874, 783, 686,
601 cm−1;
439 [M+H]+; HRESIMS m/z 461.1602 [M+Na]+(calcd for
C22H30O7SNa,461.1609).
26+12.8
1H and
13C NMR data see Table 1; ESIMS m/z
2.7. X-ray structure determination of compound 1
The compound 1 was recrystallized from methanol.
C22H28O7S·CH3OH, Mr468.55, colorless prism crystals, ortho-
rhombic system, space group P212121, with a=7.5599 (4) Å,
b=14.0258 (7) Å, c=22.3956 (11) Å, α=β=γ=90°, V=
2374.7 (2) Å3, Dcald=1.311 g/cm3for Z=4, F (000)=1000,
μ = 1.599 mm−1. Crystal dimensions: 0.64 × 0.23 ×0.23 mm.
18162 reflections measured (θ max=68.12°), 4018 were
unique (Rint=0.0388) and of these 3994 had |F|2≥2σ|F|2
for which final R1, wR2(w=1/σ|F|2), and S (goodness-of-fit)
values were 0.0353, 0.0957 and 1.065, respectively, for 297
parameters, remaining difference electron density 0.374 and
−0.247 e-Å−3.
2.8. X-ray structure determination of compound 3
The compound 3 was recrystallized from methanol.
C22H30O7S, Mr438.52, colorless block crystals orthorhombic
system, space group P212121, with a=11.3573 (4) Å, b=
13.2349 (4)Å,c=13.7885(5)Å,α=β=γ=90°,V=2072.59
(12) Å3, Dcald=1.405 g/cm3for Z=4, F (000)=936, μ=
1.755 mm−1. Crystaldimensions: 0.60×0.48×0.36 mm.15273
reflections measured (θ max=68.18°), 3628 were unique
(Rint=0.0386) and of these 3614 had |F|2≥2σ|F|2for which
final R1, wR2(w=1/σ|F|2), and S (goodness-of-fit) values were
0.0302, 0.0783 and 1.067, respectively, for 277 parameters,
remaining difference electron density 0.240 and −0.225 e-Å−3.
Data were collected using a Bruker APEX DUO diffrac-
tometer using Cu-Kα radiation. Crystal structure solution and
refinement were achieved using direct methods as imple-
mented in SHELXL-97 (Sheldrick, University of Gottingen
(Germany), 2000) and visualized using the XP program.
Crystallographic data (excluding structure factor tables)
for 1 and 3 have been deposited with the Cambridge Crystal-
lographic Data Center as supplementary publication NO.CCDC
845970 and NO.CCDC 845971 respectively. Copies of the data
Fig. 1. Molecular structures of 1–3 (1 and 1a stand for a same compound).
1101
Y-Y. Cheng et al. / Fitoterapia 83 (2012) 1100–1104

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can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB 1EZ, UK [fax: Int. +44 (0) (1223)
336 033; e-mail: deposit@ccdc.cam.ac.uk].
2.9. Anti-HIV-1 assay
Compounds 1–3 were tested for inhibitory activity against
HIV-1 by MTT method [7] and the results were summarized
in Table 2. Compound 3 showed weak activity to prevent
the cytopathic effects of HIV-1 in C8166 cells with an EC50of
16.27 μg/mL, and the TI value of more than 11.39.
3. Results and discussion
Cleidbrevoid A (1), was obtained as colorless prism crystals
(methanol). The molecular formula C22H28O7S, was deduced
from its positive HRESIMS at m/z 459.1450 [M+Na]+(calcd
for C22H28O7SNa, 459.1453) with 9 degrees of unsaturation. Its
IR spectrum displayed the absorption bands of hydroxyl
(3543 cm−1), ester carbonyl (1720 cm−1), and δ-lactone
(1705 cm−1) functionalities. The1H NMR spectrum (Table 1)
showed two tertiary methyl signals (δH1.17 and δH1.31), one
carboxymethylsignal(δH3.68)andonemethylsignal(δH2.52).
Inaddition,thesignalsatδH7.65(1H,br.s),7.59(1H,t,1.6),and
6.60 (1H, d, 1.6) were assigned to two α- and one β-position
protons of a β-substituted furan moiety. The13C NMR (Table 1)
showed22carbonresonancescomprisingfourmethyls(includ-
ing one methoxy), four methylenes, seven methines (one
oxygenated and four olefinic ones), and seven quaternary
carbons (two ester, two olefinic, and one oxygenated ones), as
classified by DEPT and HSQC spectra. The aforementioned
evidence indicated that it was a clerodane-type diterpenoid [8].
The1H–1H COSY spectrum revealed that 1 possessed four
fragments, a (C-1 to C-3), b (C-6 to C-8), c (C-11 to C-12), and
d (C-14 to C-15) as shown in Fig. 2. The HMBC correlations of
H3-19 to C-4, C-5, C-6, and C-10, H3-20 to C-8, C-9, C-10, and
C-11, and H-1 to C-5 established the connectivity of rings A
and B. The three rings, two ester groups, and three olefinic
bonds accounted for the eight degrees of unsaturation, in-
dicative of the formation of one extra ring (ring C). The furan
ring (ring D) was located at C-12 by the HMBC correlations
of H-12/C-14 and C-16. The OH proton signal resonance at
δH4.67 (s, 1H) was assigned at C-4 by the HMBC correlation
of OH-4 to C-4. In addition, a methoxy group attached to
C-18 by HMBC correlations of the methoxyl proton to C-18.
The remaining atoms were linked into a methylsulfoxyl
group that was supported by IR absorption at 1032 cm−1[9]
Table 1
1H and13C NMR data for cleidbrevoids A (1), B (2) and C (3).a
Position
123
δH, mult, (J in Hz)
δC, type
δH, mult, (J in Hz)
δC, type
δH, mult, (J in Hz)
δC, type
1a
1b
2β
2α
3
4
5
6β
6α
7β
7α
8
9
10
11β
11α
12
13
14
15
16
17
18
19
20
SOMe
OMe
OH-4
5.92, t (3.7) 120.7, CH5.73, t (3.8) 119.7, CH2.11, m
1.68, m
1.58, dt (9.6, 3.6)
2.17, m
3.04, t (6.4)
21.9, CH2
2.85, ddd (18.4, 10.0, 3.7)
2.50, m
3.28, dd (10.0, 8.4)
19.6, CH2
2.54, ddd (13.8, 9.0, 3.8)
2.13, m
3.55, t (9.1)
25.2, CH2
28.0, CH2
60.5, CH
78.9, C
43.7, C
26.3, CH2
61.1, CH2
82.0, C
43.4, C
26.3, CH2
65.9, CH
81.4, C
44.0, C
21.2, CH2
1.71, ddd (12.8, 7.6, 0.8)
1.36, dd (12.8, 8.4)
2.47, m
2.08, dt (4.0, 2.0)
2.54, dd (7.6, 4.0)
1.74, ddd (13.4, 7.6, 2.2)
1.52, m
2.42, m
2.04, m
2.50, m
1.85, m
1.76, m
2.33, m
2.03, m
2.42, dd (8.8, 5.6)
19.3, CH2
19.6, CH2
19.4, CH2
45.5, CH
37.9, C
142.6, C
42.9, CH2
45.7, CH
37.8, C
143.4, C
42.8, CH2
47.5, CH
36.3, C
44.5, CH
43.0, CH2
2.04, m
1.81, dd (15.2, 12.4)
2.35, dd (15.2, 4.4)
5.73, dd (12.4, 4.4)
2.03, dd (14.6, 11.8)
2.60, dd (14.6, 2.8)
5.53, dd (11.8, 2.8)
2.00, dd (14.6, 11.9)
2.52, m
5.46, dd (11.9, 2.9) 71.6, CH
126.7, C
109.6, CH
144.5, CH
140.7, CH
174.6, C
174.7, C
23.2, CH3
34.3, CH3
36.8, CH3
52.7, CH3
71.6, CH
126.7, C
109.6, CH
144.5, CH
140.7, CH
173.4, C
174.5, C
23.9, CH3
34.1, CH3
38.3, CH3
51.9, CH3
70.8, CH
126.8, C
109.6, CH
144.5, CH
140.9, CH
173.8, C
174.5, C
26.5, CH3
31.2, CH3
41.3, CH3
52.6, CH3
6.60, d (1.6)
7.59, t (1.6)
7.65, s
6.56, d (1.6)
7.56, t (1.6)
7.61, s
6.56, dd (2.0, 0.8)
7.55, t (2.0)
7.63, m
1.17, s
1.31, s
2.52, s
3.68, s
4.67, s
1.20, s
1.26, s
2.73, s
3.71, s
5.43, s
1.29, s
1.11, s
2.50, s
3.78, s
4.79, s
aNMR data were recorded in CD3COCD3,δ in ppm,1H NMR at 400 MHz,13C NMR at 100 MHz.
Table 2
Anti-HIV-1 activities of compounds 1–3.
CompoundsAnti-HIV-1 activity Cytotoxicity Therapy index (TI)
EC50(μg/mL) CC50(μg/mL)CC50/EC50
1
2
3
AZT
84.88
39.28
16.27
0.0032
>200
>200
>200
1139.47
>2.10
>3.62
>11.39
351688.27
1102
Y-Y. Cheng et al. / Fitoterapia 83 (2012) 1100–1104

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and was located at C-3 from the HMBC correlation of the
methylsulfoxyl protons (δH2.52) to C-3 (δC60.5) [10]. There-
fore, the planar structure of 1 was established.
The relative configuration of 1 was subsequently defined
by analysis of its ROESY correlations. In ROESY spectrum
(Fig. 3), the correlations of H-12/H3-19, H3-19/4-OH, and
H3-19/H-3 indicated that H-12, H-3, 4-OH, and H3-19 were
co-facial and were assigned as α-oriented, while H-8 and
H3-20 were β-oriented based on the ROESY cross-peaks of
H-8/H3-20. Finally, the single-crystal X-ray structure of 1
(Fig. 4) by using Flack parameter [0.064(19)] [11] con-
firmed the supposed structure and determined unambigu-
ously the absolute configuration of 1 as (3S, 4R, 5R, 8R, 9S,
12S), with the (S)-sulfoxide.
Cleidbrevoid B (2), had the same molecular formula,
C22H28O7S, as 1, based on the HRESIMS spectrum at m/z
459.1460 [M+Na]+(calcd for C22H28O7SNa, 459.1453). The
1H-NMR and13C-NMR data (Table 1) of 2 was closely similar
to those of 1 except that C-2 and C-4 were downfield shifted
(ΔδC+5.6, and +3.1) and C-3 was upfield shifted (ΔδC−0.6),
Fig. 3. Key ROESY (arrow) correlations for 1 and 2.
Fig. 4. X-ray crystal structures of compounds 1 and 3.
Fig. 2. Selected COSY (bold) and HMBC (arrow) correlations for 1 and 3.
1103
Y-Y. Cheng et al. / Fitoterapia 83 (2012) 1100–1104

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respectively. The H-3 proton signal of 2 (δH3.55, t, J=9.1 Hz)
was different from that of 1 (δH3.28, dd, J=10.0, 8.4 Hz). The
above data indicated 2 and 3 could be a pair of epimers
differing at C-3. The ROESY correlation between H-3 and H-2β
(δH2.54, ddd) and the absence of the correlation of H3-19 and
H-3 implied that H-3 in 2 took a β-orientation (Fig. 3). There-
fore, the structure of compound 2 was determined as shown,
and the stereochemistry elucidated as 3R, 4R, 5R, 8R, 9S, 10S,
and 12S, with the (S)-sulfoxide.
Cleidbrevoid C (3), colorless block crystals, had a molec-
ular formula of C22H30O7S, as determined by the HRESIMS at
m/z 461.1602 [M+Na]+(calcd for C22H30O7SNa, 461.1609)
with one unsaturation degree less and 2 mass units higher
than those of 1 suggested that the Δ1(10)double bond was
hydrogenated. Comparison of the NMR data of 3 with those
of 1 (Table 1) indicated that both shared the same basic
skeleton. This assignment was confirmed by the presence of a
methylene and a methine signal (δC 21.9 and 44.5) in 3,
which was further confirmed by the 2D NMR (HSQC,1H–1H
COSY, and HMBC) (Fig. 2). In the ROESY spectrum, the cor-
relation of H-10/H3-19 showed that they were α-orientation,
and the others were identical with those of 1. In order to
confirm the relative and absolute structure of compound 3,
the single-crystal X-ray structure of 3 by using Flack param-
eter [0.089(14)] [9] (Fig. 4) revealed its stereochemistry to be
3S, 4R, 5R, 8R, 9S, 10S, and 12S, as well as the configuration of
sulfoxide to be S.
Acknowledgments
This work was financially supported by the National
Natural Science Foundation of China (21072199), the Minis-
try of Science and Technology of China (2009CB522300 and
2009CB940900), the Natural Science Foundation of Yunnan
Province (2009CD112), the Foundation of Chinese Academy
of Sciences to H. P. He, and the Young Academic and Technical
Leader Raising Foundation of Yunnan Province (2010CI047).
The authors thank Yu Chen, for the collection and identifica-
tion of the plant material and Prof. Zheng Yongtang of
Kunming Institute of Zoology for his pioneering work on
bioactive natural products.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
http://dx.doi.org/10.1016/j.fitote.2012.04.028.
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