Cerebroside and ceramide from the pollen of Brassica napus L.

Article abstract of DOI:10.1016/j.fitote.2010.05.006

The new cerebroside 1-O-(β-d-glucopyranosyl)-(2 S, 3 S, 4R, 8E)-2-[(2′R)-2′-hydroxytetracosenoilamino]-8-octadecene-1,3,4-triol (1) and ceramide (2 S, 3 S, 4R, 8E)-2-[(2′R)-2′- hydroxytetracosenoilamino]-8-octadecene-1,3,4-triol (2) were isolated from the ethyl acetate extract of the pollen of Brassica napus L. The structures of 1 and 2 were elucidated on the basis of chemical and spectroscopic method. Two new compounds were evaluated for activity in vitro assays for the cytotoxic activities against human tongue squamous carcinoma cell line (Tca8113).

Full text of DOI:10.1016/j.fitote.2010.05.006

Fitoterapia 81 (2010) 838–843
Contents lists available at ScienceDirect
Fitoterapia
journal homepage: www.elsevier.com/locate/fitote
Cerebroside and ceramide from the pollen of Brassica napus L.
Dong Pei a,b, Jun-Xi Liu a, Duo-Long Di a,
⁎
a
Key Laboratory of Chemistry of Northwestern Plant Resources and Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics,
Chinese Academy of Sciences, Lanzhou, 730000, PR China
b
Graduate University of the Chinese Academy of Sciences, Beijing, 100049, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The new cerebroside 1-O-(β-D-glucopyranosyl)-(2 S, 3 S, 4R, 8E)-2-[(2′R)-2′-
hydroxytetracosenoilamino]-8-octadecene-1,3,4-triol (1) and ceramide (2 S, 3 S, 4R, 8E)-2-
[(2′R)-2′-hydroxytetracosenoilamino]-8-octadecene-1,3,4-triol (2) were isolated from the
ethyl acetate extract of the pollen of Brassica napus L. The structures of 1 and 2 were elucidated
on the basis of chemical and spectroscopic method. Two new compounds were evaluated for
activity in vitro assays for the cytotoxic activities against human tongue squamous carcinoma
cell line (Tca8113).
Received 21 February 2010
Accepted in revised form 10 May 2010
Available online 17 May 2010
Keywords:
Pollen of Brassica napus L.
Cerebroside
© 2010 Elsevier B.V. All rights reserved.
Ceramide
Cytotoxic activity
1. Introduction
2. Experimental
The pollen of Brassica napus L. has been used in China to treat
benign prostatic hyperplasia (BPH) for over decades. In previous
studies, the ethyl acetate extract of the pollen of Brassica napus
L. showed strong activity on decreasing the secretion of prostate
specific antigen (PSA) in LNCaP cells [1]. Sterols, terpenoids,
flavones, long chain hydrocarbons, and brassinolide have been
reported from the EtOAc-soluble fraction [1–3]. This study deals
with the isolation and characterization of a new cerebroside and
ceramide from the EtOAc-soluble fraction of EtOH extract of this
pollen. The cytotoxic activity of compounds 1 and 2 was tested
in vitro against human tongue squamous carcinoma cell
line Tca8113. Compound 2 was shown to possess significant
cytotoxic activity.
Sphingolipids, e.g. ceramides, cerebrosides, are important
constituents of cellular membranes and are emerging as
important second messengers for various cellular processes
such as cell cycle arrest, differentiation, senescence, apoptosis
[4–6]. Furthermore, some sphingolipids have been reported
to exhibit anti-ulcerogenic [7], antihepatotoxic [8], antitumor
and immunostimulatory activities [9].
2.1. General experimental procedures
Optical rotations were measured using a Rudolph-Re-
search Autopol-III automatic polarimeter. UV spectra were
measured on a T6 UV–vis spectrophotometer (Beijing
Purkinje General Instrument Co., Ltd, Beijing, China). IR
spectra were obtained on a Nicolet-170SX FT-IR spectrometer
(Madison, WI, USA) using KBr pellets in cm−1. NMR spectra
were recorded on a Varian Inova-400 FT-NMR spectrometer
(Palo Alto, CA, USA) with TMS as an internal standard, δ in
ppm, J in Hz. HR-ESI-MS were measured on Bruker APEXII
mass spectrometer in m/z. EI-MS were measured on a VG
ZABHS mass spectrometer at 70 eV. Silica gel (200–300 mesh,
Qingdao Mar. Chem. Ind. Co. Ltd.).
2.2. Plant material
The pollen of Brassica napus L. was collected in September
2007 in Gansu, China. The material was identified by Prof.
Huan-Yang Qi of Lanzhou Institute of Chemical Physics,
Chinese Academy of Sciences, Lanzhou, China. A voucher
specimen (ZY200701) has been deposited at the Key
Laboratory of Chemistry of Northwestern Plant Resources,
⁎
Corresponding author. Tel.: +86 931 4968248; fax: +86 931 8277088.
E-mail address: didl@licp.cas.cn (D.-L. Di).
0367-326X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.fitote.2010.05.006

D. Pei et al. / Fitoterapia 81 (2010) 838–843
839
Lanzhou Institute of Chemical Physics, Chinese Academy of
Sciences, China.
(0.24)nm; IR (KBr) νmax cm−1: 3332 (hydroxyl), 1624, 1545
1
(amide); H and 13C NMR data: see Table 2; HR–ESI–MS: m/z
680.6173 [M+H]+(calcd for C42H82NO5: 680.6188). The struc-
ture of 2 was determined to be (2 S, 3 S, 4R, 8E)-2-[(2′R)-2′-
hydroxytetracosenoilamino]-8-octadecene-1,3,4-triol (Fig. 1).
2.3. Extraction and isolation
The air-dried pollen of B. napus L. (5000 g) was extracted
with 70% EtOH (3×20 L, 7 days each) at room temperature
and the EtOH was removed under reduced pressure to give a
residue (1750 g), which was suspended in distilled water and
extracted with n-hexane and EtOAc, respectively. The EtOAc
extract (80 g) was subjected to column chromatography over
silica gel (200–300 mesh, 2500 g) and eluted with CHCl3,
CHCl3–MeOH (95/5), (90/10), (85/15), (80/20), (70/30), (50/
50), (30/70), (10/90) and MeOH to yield 10 fractions (Fr.1–
Fr.10) . Fr.2 was subjected to a silica gel column eluting with
CHCl3–MeOH (19/1) to give compound 2 (55 mg). Fr.3 was
subjected to a silica gel column eluting with CHCl3–MeOH
(10/1 and 8/2) to give 10 subfractions. Subfraction 4 was
recrystallized from MeOH to give compound 1 (125 mg).
2.4. Methanolysis of compounds 1 and 2
After each compound (15 mg) was refluxed with 0.9 M
HCl in 82% aq. MeOH (10 mL) for 18 h, the reaction mixture
was extracted with n-hexane. The concentrated n-hexane
layer was subjected to silica gel column chromatography
(hexane/EtOAc, 20:1) to yield fatty acid methyl ester (FAM).
The aq. MeOH layer was neutralized with NH3·H2O and
extracted with EtOAc. The combined EtOAc extract was
washed with H2O, dried over Na2SO4 and evaporated to
give the long chain base (LCB). Methanolysis of compounds 1
20
and 2 afforded Methyl 2-hydroxy-tetracosenoate. [α]
D
−2.0 (c=0.1, CHCl3). 1H NMR (400 MHz, CDCl3) δH: 5.33 (2H,
m, H-15, H-16), 4.17 (1H, m, H-2), 3.77 (3H, s, OCH3), 1.99
(4H, m, H-14, 17), 0.86 (3H, t, J=7.2 Hz, H-24). EI-MS: m/z:
396 [M] +, 337[M-59]+. The data were identical to those
published earlier [10,11].
Compound 1 : colorless solid; m.p. 104–106 °C; [α]20
+
D
10.2 (c=0.1, MeOH); UV (MeOH) λmax (log ε): 224.0 (0.49)
nm; IR (KBr) νmax cm−1: 3387 (hydroxyl), 1632, 1541
(amide); 1H and 13C NMR data: see Table 1; HR-ESI-MS: m/z
864.6529 [M+Na]+ (calcd for C48H91NO10Na: 864.6535). The
structure of 1 was determined to be 1-O-(β-D-glucopyrano-
syl)-(2 S,3 S,4R,8E)-2-[(2′R)-2′-hydroxytetracosenoilami-
no]-8-octadecene-1,3,4-triol (Fig. 1).
2.5. Dimethyl disulfide derivative of FAMs from compounds 1
and 2
Compound 2 : white amorphous powder; m.p. 138–139 °C;
FAM-1 and FAM-2 (5 mg) were dissolved respectively in
carbon disulfide (0.5 mL), and then dimethyl disulfide
(0.5 mL) and iodine (10 mg) were added, successively. The
reaction mixture was then kept at 60 °C for 48 h in a small
sealed vial, which was subsequently quenched with 5% aq.
Na2S2O3. And then the mixture was extracted with n-hexane.
The n-hexane layer was dried over Na2SO4, filtered and
concentrated to give the dimethyl disulfide (DMDS) deriva-
tive of FAMs. Finally, the DMDS derivatives were analyzed by
EI-MS. FAM-1 DMDS derivative, EI-MS: m/z=317 [M-
[α]20D+11.0 (c=0.1, MeOH); UV (MeOH) λmax (log ε): 212.0
Table 1
1H NMR (400 MHz) and 13C NMR (100 MHz) spectral data of 1 in DMSO-d6
(TMS, δ in ppm, J in Hz).
No.
1H (m, J, Hz)
13C
68.9
1H–1H COSY
HMBC (H–C)
1″, 2
1a
1b
2
3.61(m)
3.78(m)
4.08(m)
3.39(m)
3.36(m)
1.47(m)
1.57(m)
1.49(m)
1.95(m)
5.34(m)
5.34(m)
1.95(m)
1.30(m)
1.22(m)
1.22(m)
0.83(t)
1b, 2
1a, 2
3, 1a, 1b
2, 4
5a, 5b, 3
5b, 4, 6
5a, 4, 6
5a, 5b, 7
6, 8
49.9
74.1
70.5
31.7
1, 3, 1′
2, 4
3, 5
3
4
C
10H21S]+, 173 [C10H21S]+. FAM-2 DMDS derivative, EI-MS:
m/z=317 [M-C10H21S]+, 173 [C10H21S]+ (Fig. 2).
5a
5b
6
4, 6
25.7
32.1
130.2
129.8
32.4
28.6–29.1
31.3
22.1
5, 7
6, 8
7, 9
8, 10
9
2.6. MS analysis of LCB from compounds 1 and 2
7
8
9
7, 9
8, 10
9
The LCBs of compounds 1 and 2 were subjected to ESI-MS
analysis. The results were as follows: LCB-1, ESI-MS: m/z=
10
11-15
16
17
18
1′
316 [M+H]+. LCB-2, ESI-MS: m/z=316 [M+H]+
.
2.7. Dimethyl disulfide derivatives of LCB from compounds 1
and 2
13.9
173.8
70.9
2′
3.82(m)
1.47(m)
1.57(m)
1.96(m)
5.29(m)
5.29(m)
1.22-1.30(m)
0.83(t)
4.12(d,7.6)
2.92(m)
3.15(m)
3.04(m)
3.10(m)
3.44(d,11.2)
3.65(d,11.2)
3′a, 3′b
3′b
3′a
1′, 3′
2′
3′a
3′b
14′,17′
15′
16′
CH2
24′
1″
2″
3″
4″
5″
34.4
LCBs DMDS derivatives from compounds 1 and 2 were
synthesized according to the procedure described above.
Finally, the DMDS derivatives were analyzed by EI-MS, both
showed a characteristic fragment-ion peak at m/z=187
[C11H23S]+ (Fig. 2).
26.7
129.5
129.3
22.1–31.3
13.9
103.5
73.4
76.5
14′,16′
15′,17′
14′,16′
15′,17′
2″
1″, 3″
2″, 4″
3″, 5″
4″, 6″a, 6″b
6″b, 5″
6″a, 5″
2″, 1
1″, 3″
2″, 4″
3″, 5″
4″, 6″
5″
2.8. Acid hydrolysis of compound 1
Compound 1 (10 mg) was dissolved in MeOH–H2O (1:1,
10 mL) and then 5% HCl (5 mL) solution was added. After the
solution was refluxed for 8 h at 70 °C and cooled to room
temperature, MeOH in the reaction mixture was evaporated
69.9
76.9
61.0
6″a
6″b
5″

840
D. Pei et al. / Fitoterapia 81 (2010) 838–843
Fig. 1. Chemical structures of compounds 1, 1a, 1b and 2.
in vacuo. The residue mixture was extracted twice with
CHCl3. The combined extract was evaporated to yield a
residue, which was compared with standard sugar units on
silica gel plates [12] using n-BuOH-EtOAc-iso-PrOH-HOAc-
H2O (7:20:12:7:6) solvent system and the sugar was found to
be D-glucose.
mycin, 100 IU/mL penicillin, and 0.03% L-glutamineand and
maintained at 37 °C with 5% CO2 in a humidified atmosphere.
2.9.2. Cytotoxity assay
Tca8113 cells were cultured at 5×104 cells/well in 96-well
plates (Corning Costar, Milano, Italy) precultured under the
same conditions. Twenty-four hours later, the medium was
replaced by the 10% fetal bovine serum (FBS) RPMI-1640
containing 0.1% DMSO or samples. After incubating cells with
1 and 2 (2.5, 5, 10, and 20 μg/mL) for 72 h, the cell viability
was assayed by MTT method [13]. Briefly, 4h before the end
of incubation, 20 μL of MTT solutions (5.0 mg/L) was added to
each well. Then, 150 μL of DMSO was added to the culture
system to dissolve formazan crystal. Finally, formazan absor-
bance was assessed at 490 nm by an automated microplate
2.9. Cells and cytotoxic assays
2.9.1. Cell cultures
Human tongue squamous carcinoma cell line (Tca8113)
was obtained from the Institute of Cell Biology, Chinese
Academy of Sciences (Shanghai, China). Tca8113 cells were
cultured in RPMI-1640 medium (Hyclone) supplemented
with 10% fetal bovine serum (Hyclone), 100 μg/mL strepto-

D. Pei et al. / Fitoterapia 81 (2010) 838–843
841
Table 2
showed absorption bands typical for a secondary amide
(1632 cm−1, 1541 cm−1), and hydroxyl (3387 cm−1) func-
tionalities. The NMR data of 1 indicated the presence of a
sugar (δH 4.12, 1H, d, J=7.6 Hz, anomeric H; δC 103.5), an
amide linkage (δH 7.53, 1H, d, J=9.6 Hz, N–H; δC 173.8), and
two long chain aliphatic moieties and olefinic functions (δH
0.83, 6H, t, J=7.0 Hz, CH3; δH 1.22, brs, CH2; δH 5.29 and 5.34,
4H; δC 130.2, 129.8, 129.5, 129.3). Compared the 1H and 13C
NMR spectras of 1 with those of cerebrosides [14–16], the
compound 1 was a cerebroside analogue, obviously. Metha-
nolysis of 1 yielded three parts (Fig. 3): methyl glucoside,
a fatty acid methyl ester (FAM-1) and a long-chain base
(LCB-1).
1H NMR (400 MHz) and 13C NMR (100 MHz) spectral data of 2 in DMSO-d6
(TMS, δ in ppm, J in Hz).
No.
1H (m, J, Hz)
13C
60.4
1H–1H COSY HMBC (H–C)
1a
1b
2
3
4
5a
5b
6
7
8
3.64(dd, 10.8, 4.4)
3.57(dd, 10.8, 4.4)
3.98(m)
3.43(m)
3.40(m)
1.54(m)
1.65(m)
1.56(m)
1.94(m)
1b, 2
2
1a, 2
51.0
74.7
71.1
31.8
3, 1a, 1b
2, 4
1, 3, 1′
2, 4
5a, 5b, 3
5b, 4, 6
5a, 4, 6
5a, 5b, 7
6, 8
7, 9
8, 10
9
3, 5
4, 6
25.6
32.1
130.0
129.6
32.3
5, 7
6, 8
7, 9
8, 10
9
5.35(m)
5.35(m)
1.94(m)
9
10
The FAM-1 was identified as methyl 2-hydroxy-tetraco-
senoate through EI-MS and NMR experiments. The EI-MS of
the FAM-1 exhibited a base peak at m/z 396 [M]+ and an ion
at m/z 337 [M-COOCH3]+, which determined the number of
carbons in the fatty acid (FAM-1) to be 24 and a double bond
in it. The presence of an α-hydroxy fatty acid side chain could
be supported by the HMBC correlation from H-2′ to the
carbonyl carbon, and the proton OH-2′ to C-2′. The absolute
configuration at C-2′ of the 2′-hydroxy fatty acid was
11–15 1.35(m)
28.6–29.1
31.3
22.1
16
17
18
1′
2′
3′a
3′b
1.25(m)
1.25(m)
0.87(t)
13.8
173.7
71.1
34.3
3.89(m)
1.54(m)
1.65(m)
3′a, 3′b
3′b
3′a
1′, 3′
2′
14′,17′ 1.99(m)
26.6
129.3
129.3
22.1-31.3
13.8
15′
16′
CH2
24′
5.30 (m)
5.30 (m)
1.25-1.35(m)
0.87(t)
14′,16′
15′,17′
14′,16′
15′,17′
presumed to be R from the specific rotation value, [α]20
D
-2.0° (c=0.1, CHCl3) [17]. The position of the double bond at
C-15 in the FAM-1 was determined by the characteristic
fragment ions (m/z 317 and 173) due to cleavage between the
carbons bearing the methylthio group in the EI-MS analysis of
the corresponding dimethyl disulfide derivative. The cis (Z)
configuration of the double bond was evidenced by the
chemical shifts of the carbons next to the double bond at δ
26.7 (C-14′ and C-17′) in 1 [8,17]. The FAM-1 part was
determined to be methyl 2-hydroxy-tetracosenoate, which
was also proved by the NMR data.
reader EL311s spectrophotometer (BIO-TEK Instruments, INC.
Winooski, Vermount, USA).
3. Results and discussion
Compound 1 was obtained as a colorless solid. Its
molecular formula was determined as C48H91NO10 on the
basis of the HR-ESI-MS [M+Na]+, m/z 864.6529 (calcd for
The presence of a 1,3,4-trihydroxy unsaturated C18 long
chain base (LCB-1) was deduced from the gCOSY, NMR and
MS experiments. The location of three hydroxy groups at C-1,
C
48H91NO10Na: 864.6535). The IR (KBr) spectrum of 1
Fig. 2. FAM-DMDS derivatives and LCB-DMDS derivatives of 1 and 2.

842
D. Pei et al. / Fitoterapia 81 (2010) 838–843
Fig. 3. The structural parts of 1.
C-3 and C-4 could be confirmed by the gCOSY correlations
between N–H (δ 7.53) and H-2, H-1, H-3 and H-2, H-3 and H-4,
which could be supported by HMBC correlations (Fig. 4).
Furthermore, The proton signal at δ 4.08 (H-2) and the carbon
signals at δ 68.9 (C-1), 49.9 (C-2), 74.1 (C-3), 70.5 (C-4) in 1H,
13C NMR spectra of 1 were in good agreement with those of a
reported cerebroside(1a) (Fig. 1), possessing a 1,3,4-trihy-
droxy unsaturated C18 long chain base, which had been
isolated from the pollen of Typha angustifolia [14]. The ESI-MS
of the LCB-1 exhibited a base peak at m/z 316 [M+H]+, which
determined the number of carbons in the long chain base to be
18 and a double bond in it. The position of the double bond
was determined by EI-MS analysis of the corresponding
dimethyl disulfide derivative of LCB-1. Characteristic frag-
ment ion at m/z 187, from cleavage between the carbons
bearing the methylthio group, indicated that the double bond
was at C-8. The cis (E) configuration of the double bond which
is different from the known compound (1b, δC-7/C-10 =27.8)
(Fig. 1) was confirmed by the chemical shifts at δ 32.1 (C-7/C-
10) and δ 32.4 (C-7/C-10), the special carbons next to the
double bond group [8,16,17].
Additionally, the anomeric proton at δ 4.12 (1H, H-1″) and
the J value (7.6 Hz) suggested the sugar group was a β-D-
glucospyranoyl moiety which also supported by the acidic
hydrolysis experiment. The linkage of three parts of 1 was
determined by HMBC experiment (Fig. 4). The HMBC
correlation from H-2 to C-1′ determined the linkage of
FAM-1 part with C-2 of LCB-1; Furthermore, the HMBC
correlation from the anomeric proton to C-1 (δ 68.9) of the
long chain base determined the linkage of sugar part with
LCB-1.
The chemical shifts of the carbon signals of C2–C4 of
glucosphingolipids are especially suitable for determination
of the absolute stereochemistry of the phytosphingosine
moiety [14,18]. Based on the literature and the 13C NMR
spectral data, the relative stereochemistries of C-2 (δ 49.9),
Fig. 4. Key correlations of 1.

D. Pei et al. / Fitoterapia 81 (2010) 838–843
843
compound 2 (2.5, 5, 10, and 20 μg/mL) significantly inhibited
Tca8113 cells viability in a dose-dependent manner com-
pared with the control cell treat with FBS only. However
compound 1 did not show significant anti-proliferation effect
on Tca8113 cells. Compound 2 shows higher cytotoxic
activity than 1, which also demonstrated that the polarity of
the molecule plays an important role in the neuritogenic
activity of sphingolipids [19].
Acknowledgements
This work was supported by the “Hundred Talents
Program” of Chinese Academy of Sciences and the National
Natural Sciences Foundation of China (NSFC No. 20775083) as
well as the Science and Technology Key Project of Gansu
Province (2GS64-A43-019-06).
Fig. 5. Cytotoxicity of compounds 1 and 2 against Tca8113 cells by MTT
analysis. Tca8113 cells were treated with compound 1 and 2 (2.5, 5, 10, and
20 μg/mL) for 72 h, and cell growth inhibition rate was measured by MTT
assay. The data points are presented as mean S.E.M. of four experiments.
*pb0.05, significance from control (the cells with 10% FBS RPMI-1640
containing 0.1% DMSO).
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C-3 (δ 74.1) and C-4 (δ 70.5) were determined as 2S, 3S, and
4R. Thus, the structure of 1 was concluded as 1-O-(β-D-
glucopyranosyl)-(2S, 3S, 4R, 8E)-2-[(2′R)-2′-hydroxytetra-
cosenoilamino]-8-octadecene-1,3,4-triol.
Compound 2 was obtained as an amorphous white powder.
Its molecular formula was determined as C42H81NO5 by HR-ESI-
MS [M+H]+, m/z 680.6173 (calcd for C42H82NO5: 680.6188).
Compared the IR, 1D, 2D NMR and the HR-ESI-MS data of 2 with
compound 1, it was found that both structures were almost
identical except for the absent glucose of 2 (Table 2). The
similar chemical degradation of 2 further confirmed that the
length of the chain and the location of the double bond were the
same as in 1. Thus, the structure of 2 was determined to be (2S,
3S, 4R, 8E)-2-[(2′R)-2′-hydroxytetracosenoilamino]-8-octade-
cene-1,3,4-triol.
The cytotoxic activity of compounds 1 and 2 was tested in
vitro against human tumor cell line Tca8113. Fig. 5 showed
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