Cytotoxic dehydromonacolins from red yeast rice

Article abstract of DOI:10.1021/jf203579f

Two new dehydromonacolins (1 and 3), together with nine known monacolins (4-12), were isolated from red yeast rice. Compounds 4-6 were isolated from a natural resource for the first time. Their structures were elucidated by means of NMR and mass spectroscopic analyses. The structure of dehydromonacolin N (1) was further confirmed by its semisynthesis from monacolin K (lovastatin) (11). Dehydromonacolin J (2), an intermediate in the semisynthesis of 1, was obtained as a new dehydromonacolin. The structure of dehydromonacolin L (3) was also confirmed by an elimination reaction of monacolin L (12). Compound 1, possessing a C2 side chain, is unprecedented in the natural monacolin family and exhibited moderate cytotoxic activity against Hep G2, Caco-2, and MCF-7 cancer cell lines. Dehydromonacolin K (8) demonstrated the most potent cytotoxicity to all three of these cell lines. The structure-activity relationship of natural and synthesized monacolins was discussed. This is the first report on the cytotoxic effects of dehydromonacolins.

Full text of DOI:10.1021/jf203579f

Article
pubs.acs.org/JAFC
Cytotoxic Dehydromonacolins from Red Yeast Rice
Lin Zhu,† Lee-Fong Yau,† Jing-Guang Lu,† Guo-Yuan Zhu,† Jing-Rong Wang,† Quan-Bin Han,†
Wen-Luan Hsiao,† and Zhi-Hong Jiang*,†,‡
†School of Chinese Medicine, Hong Kong Baptist University, Kowloon Tong, Hong Kong, People's Republic of China
‡State Key Lab of Quality Research in Chinese Medicine, Macau Institute for Applied Research in Medicine and Health, Macau
University of Science and Technology, Taipa, Macau, People's Republic of China
S
* Supporting Information
ABSTRACT: Two new dehydromonacolins (1 and 3), together with nine known monacolins (4−12), were isolated from red
yeast rice. Compounds 4−6 were isolated from a natural resource for the first time. Their structures were elucidated by means of
NMR and mass spectroscopic analyses. The structure of dehydromonacolin N (1) was further confirmed by its semisynthesis
from monacolin K (lovastatin) (11). Dehydromonacolin J (2), an intermediate in the semisynthesis of 1, was obtained as a new
dehydromonacolin. The structure of dehydromonacolin L (3) was also confirmed by an elimination reaction of monacolin L
(12). Compound 1, possessing a C2 side chain, is unprecedented in the natural monacolin family and exhibited moderate
cytotoxic activity against Hep G2, Caco-2, and MCF-7 cancer cell lines. Dehydromonacolin K (8) demonstrated the most potent
cytotoxicity to all three of these cell lines. The structure−activity relationship of natural and synthesized monacolins was
discussed. This is the first report on the cytotoxic effects of dehydromonacolins.
KEYWORDS: Monascus, red yeast rice, monacolins, cytotoxicity
INTRODUCTION
MATERIALS AND METHODS
■
■
General Experimental Procedures. Optical rotations were
obtained on a JASCO P-1010 polarimeter. UV spectra were obtained
on a JASCO V-530 UV−vis spectrophotometer. NMR spectroscopy
was performed on a Bruker Avance-III NMR spectrometer with
tetramethylsilane (TMS) as an internal standard; chemical shifts (δ)
are reported in parts per million and coupling constants (J) in hertz.
Ultraperformance liquid chromatography (UPLC)-HRESIMS was
performed on Waters Acquity ultraperformance liquid chromatog-
raphy (UPLC) system (Waters Corp., Milford, MA) with a
photodiode array (PDA) detector, hyphenated to a Bruker MicrO-
TOFQ system with an electrospray ionization (ESI) interface (Bruker
Daltonics, Bremen, Germany). Column chromatography (CC) was
performed with silica gel (40−63 μm, Grace, USA) and Bondapak C18
(37−55 μm, Waters). TLC was performed on precoated Kieselgel 60
F254 plates (0.2 mm thick, Merk KGaA); detection was by ultraviolet
(UV) illumination and by heating after spraying with 10% H2SO4
reagent. Semipreparative HPLC was carried out on a PerkinElmer
series 200 separation system, with an Alltima C18 (250 × 22 mm, 10
μm) semipreparative column.
Reagents. Analytical grade EtOAc, petroleum ether, CHCl3,
MeOH, and HPLC grade MeCN were purchased from Anaqua
Chemicals Supply (USA). HCl, NaHCO3, and Na2SO4 were obtained
from BDH (Auckland, New Zealand). Triethylamine and methane-
sulfonyl chloride were purchased from International Laboratory
(USA). Toluene was obtained from Labscan Asia (Bangkok,
Thailand). LiOH, acetic anhydride, and 4-dimethylaminopyridine
(DMAP) were purchased from Sigma-Aldrich (St. Louis, MO).
Material. Red yeast rice powder was purchased from Zhejiang
Sanhe Bio-Tech Co. Ltd. (Quzhou, China) in March 2010. This
commercial material was made by fermenting the fungus M. purpureus
Red yeast rice, produced from the fermentation of steamed rice
using the fungus Monascus purpureus,1 has been applied as food
and medicine for improving digestion and blood circulation in
China for thousands of years.2 Recently, much attention has
been focused on the family of bioactive substances named
monacolins in red yeast rice, because they are inhibitors of
HMG-CoA reductase, have therapeutic effects on lipid profiles
of hypercholesterolemic patients,3 and showed anticancer
activities against colorectal cancer,4 prostate cancer,5 and breast
cancer6 etc. Since monacolin K was first reported from
Monascus ruber by Endo in 19797 and, independently, by
Alberts from Aspergillus terreus,8 a series of monacolin
compounds have been found. Monacolin J and monacolin L
were isolated and reported in 1985,9 and then dihydromona-
colin L and monacolin X were found.10 After that, monacolin M
was disclosed from M. ruber.11 Seven monacolins were isolated
from red yeast rice.1 Although the content of monacolins in red
yeast rice is low (ca. 0.4%),1 it is still a potential resource for
discovering new natural monacolins.
In the course of our investigation on monacolins in red yeast
rice, two new dehydromonacolins (1 and 3), together with nine
known monacolins (4−12), were isolated from red yeast rice.
Compounds 4−6 were isolated from a natural resource for the
first time. Semisynthesis from monacolin K (lovastatin) (11)
confirmed the structure of dehydromonacolin N (1) and
generated a new compound, dehydromonacolin J (2), as an
intermediate. The structure of dehydromonacolin L (3) was
also confirmed by an elimination reaction of monacolin L (12).
Some of the isolates were evaluated for their cytotoxicity
against Hep G2, Caco-2, and MCF-7 cancer cell lines. Herein
we report the isolation, structural elucidation, and cytotoxic
activities of these monacolins.
Received: September 5, 2011
Revised: January 3, 2012
Accepted: January 3, 2012
Published: January 3, 2012
© 2012 American Chemical Society
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SW1008 on steamed rice. A voucher specimen was deposited in the
Monacolin K was used as the positive control. Cytotoxicity was
evaluated with the colorimetric MTT assay. Briefly, MTT solution (10
μL per well, 5 mg/mL solution) was added to each well and incubated
for 4 h at 37 °C. One hundred microliters of stop solution (10% SDS
in 0.01 N HCl) was then added to each well, and they were kept
overnight at room temperature. The optical densities of the resulting
solutions were colorimetrically determined at 570 nm using a
microplate reader. Dose−response curves were generated, and results
were expressed as IC50 values in micromolar. Tests were performed in
triplicate and all experiments repeated three times (n = 3).
Dehydromonacolin N (1). 1 was obtained as a colorless oil:
[α]22D= +30.7 (c 0.30, MeOH); UV (MeOH) λmax (log ε) 230 (3.86),
238 (3.82), 246 (3.72) nm; 1H and 13C NMR, see Tables 1 and 2 and
the Supporting Information; HR-ESI-MS, 345.2063 ([M + H]+,
C21H29O4, calcd 345.2060).
School of Chinese Medicine, Hong Kong Baptist University.
Extraction and Isolation. Red yeast rice powder (2.0 kg) was
extracted with EtOAc (20 L × 3) at room temperature under
sonication. The extract was combined and evaporated under reduced
pressure to afford a brownish residue (ca. 150 g). The residue was
subjected to a silica gel CC eluted with petroleum ether/CHCl3
(100:0→0:100) and then CHCl3/MeOH (100:0→65:35) to obtain 16
major fractions (fractions 1−16). Fraction 6 (42 g) was chromato-
graphed on silica gel eluted with petroleum ether/EtOAc (100:0→
0:100) to give 13 fractions (fraction 6-1−6-13). Fraction 6-7 (4 g) was
subjected to a silica gel CC eluted with petroleum ether/EtOAc
(95:5→50:50) and then ODS eluted with MeOH/H2O (50:50→
80:20) to give compounds 3 (1 mg) and 4 (12 mg). Fraction 6-8 (300
mg) was subjected to CC on ODS eluted with MeOH/H2O (60:40→
90:10) to give compound 7 (10 mg). Fraction 6-12 (1.5 g) was
subjected to a silica gel CC with CHCl3/EtOAc (100:0→80:20) and
then ODS eluted with MeOH/H2O (50:50→90:10) to give
compounds 1 (1 mg), 5 (20 mg), and 8 (3 mg). Fraction 6-13 (700
mg) was subjected to CC on ODS eluted with MeOH/H2O (50:50→
80:20) and finally isolated on semipreparative HPLC eluted with
CH3CN/H2O (70:30) to give compounds 6 (5 mg), 10 (4 mg), and 9
(3 mg). Fraction 8 (23 g) was chromatographed on silica gel eluted
with CHCl3/MeOH (100:0→90:10) to give compound 11 (6 g).
Fraction 9 (10 g) was subjected to CC on silica gel eluted with
petroleum ether/EtOAc (100:0→20:80) and then purified on
semipreparative HPLC eluted with CH3CN/H2O (70:30) to give
compound 12 (70 mg).
Synthesis of Compound 1. Monacolin K (11) (500 mg, 1.238
mmol) was dissolved in 45 mL of CH2Cl2. To this solution was added
525.7 μL (378 mg, 3.77 mmol, 3 equiv) of triethylamine, followed by
145.4 μL (212 mg, 1.863 mmol, 1.5 equiv) of methanesulfonyl
chloride, and the reaction was stirred at room temperature for 1 h. The
reaction was diluted with CH2Cl2 and extracted with 0.1 M HCl (1 ×
150 mL) and saturated NaHCO3 (1 × 150 mL), washed with H2O (3
× 150 mL), dried with anhydrous Na2SO4, and filtered to give
dehydromonacolin K (8) (460 mg).
Compound 8 (300 mg) was suspended in 10 mL of aqueous LiOH
(1 M) and refluxed overnight. The reaction was cooled to room
temperature, acidified with 2 M HCl, and extracted with CH2Cl2 (3 ×
10 mL). The combined organic extracts were dried with anhydrous
Na2SO4, filtered, and evaporated to give 343 mg of crude residue,
which was refluxed in 10 mL of toluene for 4 h. After cooling to room
temperature, the solvent was evaporated and the residue (308 mg) was
purified by silica gel CC (1% MeOH in CHCl3) to give compound 2
(20 mg).
1
Table 1. H NMR (400 MHz, CDCl3) Data for Compounds
a
1−3 (δ in Parts per Million)
position
1
2
3
1
2
3
1.73 (m)
2.39
1.82
2.37
1.41
2.30
5.79 (dd,
J = 9.6, 6.1 Hz)
5.79 (dd,
J = 9.6, 6.0 Hz)
5.72 (dd,
J = 9.6, 6.4 Hz)
4
5.99 (d, J = 9.6 Hz)
5.99 (d,
J = 9.6 Hz)
5.91 (d,
J = 9.6 Hz)
5
6
7
5.53 (m)
2.45
5.55 (m)
2.46
5.43 (m)
2.33
1.97
1.88
1.71
1.91
1.88
1.59
8
5.37 (dd,
J = 5.9, 3.4 Hz)
4.24 (dd,
J = 6.4, 3.2 Hz)
1.17 (d,
J = 12.4 Hz)
1.77
2.03
8a
9
2.24
2.16
0.90 (d, J = 7.0 Hz)
0.91 (d,
J = 7.0 Hz)
0.89 (d,
J = 7.0 Hz)
10
1.07 (d, J = 7.0 Hz)
1.19 (d,
J = 7.0 Hz)
0.99 (d,
J = 7.0 Hz)
2′
6.01 (ddd,
J = 9.6, 2.6, 0.9 Hz)
6.02 (dt,
J = 9.6, 1.6 Hz)
6.03 (dt,
J = 9.6, 1.6 Hz)
3′
4′
6.87 (m)
2.34
6.89 (m)
2.36
6.89 (m)
2.35
2.28
2.36
2.35
5′
6′
4.38 (m)
1.89
4.43 (m)
1.92
4.43 (m)
1.88
Compound 2 (5 mg, 0.016 mmol) was dissolved in 500 μL of
pyridine. To this solution was added 200 μL (200 mg, 1.96 mmol, 100
equiv) of acetic anhydride, followed by 1 mg (0.008 mmol, 0.5 equiv)
of 4-dimethylaminopyridine (DMAP). After the reaction was stirred at
room temperature overnight, the reaction was diluted with 10 mL of
H2O and extracted with EtOAc (3 × 10 mL). The organic layer was
evaporated to give compound 1 (6 mg).
Synthesis of Compound 3. Monacolin L (12) (10 mg, 0.033
mmol) was dissolved in 1.2 mL of CH2Cl2. To this solution was added
14.0 μL (10 mg, 0.010 mmol, 3 equiv) of triethylamine, followed by
3.9 μL (5.7 mg, 0.050 mmol, 1.5 equiv) of methanesulfonyl chloride,
and the reaction was stirred at room temperature for 1 h. The reaction
was diluted with CH2Cl2 and extracted with 0.1 M HCl (1 × 5 mL)
and saturated NaHCO3 (1 × 5 mL), washed with H2O (3 × 5 mL),
dried with anhydrous Na2SO4, and filtered to give dehydromonacolin
L (3) (6 mg).
Cell Culture and Cytotoxicity Assay of Compounds 1−3, 8,
and 11. Exponentially growing cells were plated in a 96-well
microplate (Becton, Dickinson and Co.) at densities of 8000 cells
(Hep G2), 5000 cells (Caco-2), and 2000 cells (MCF-7) per well in
100 μL of culture medium, which were allowed to adhere overnight
before treatment. Compounds of different concentrations were then
added, and the cells were incubated for another 48 h (Hep G2) or 72 h
(Caco-2 and MCF-7) at 37 °C in a humidified incubator with 5% CO2.
1.41
1.56
1.52
7′
1.53
1.80
1.76
1.38
1.52
1.40
2″
2.03 (s)
a
Overlapped signals are reported without designating multiplicity.
Dehydromonacolin J (2). 2 was obtained as a colorless oil:
[α]22D= +82.7 (c 0.75, MeOH); UV (MeOH) λmax (log ε) 230 (3.89),
238 (3.89), 246 (3.77) nm; 1H and 13C NMR, see Tables 1 and 2 and
the Supporting Information; HR-ESI-MS, 303.1959 ([M + H]+,
C19H27O3, calcd 303.1954).
Dehydromonacolin L (3). 3 was obtained as a colorless oil:
[α]22D= +3.5 (c 0.05, MeOH); UV (MeOH) λmax (log ε) 230 (2.76),
238 (2.60), 246 (2.52) nm; 1H and 13C NMR, see Tables 1 and 2 and
the Supporting Information; HR-ESI-MS, 287.2011 ([M + H]+,
C19H27O2, calcd 287.2005).
RESULTS AND DISCUSSION
■
Repeated column chromatography of the ethyl acetate extract
of red yeast rice afforded two new dehydromonacolins (1 and
3), as well as nine known monacolins (4−12). The known
compounds were identified as α,β-dehydrodihydromonacolin L
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Table 2. 13C NMR (100 MHz, CDCl3) Data for Compounds
1−3
elucidated to be the dehydration derivative of the known
compound and named dehydromonacolin N. This elucidation
was supported by the molecular weight difference of 18 (H2O)
mass units between 1 and the known compound. Assignment
of all the proton signals (Table 1) and CH−CH linkage of 1
position
1
2
3
1
32.6
29.9
36.5
30.9
41.9
31.4
1
was confirmed by the H−1H COSY spectrum (Figure 1).
2
3
133.3
128.5
131.8
129.8
27.6
133.7
128.6
131.4
130.2
27.5
132.9
128.3
136.5
130.5
28.7
A transformation from monacolin K (11) to compound 1
was undertaken as described in Scheme 1 to confirm the
chemical structure of compound 1.
4
4a
5
Elimination from the methanesulfonates of monacolin K
(11) gave dehydromonacolin K (8). Basic hydrolysis of 8 by
reflux overnight with lithium hydroxide solution and then
relactonization by reflux in toluene afforded dehydromonacolin
6
7
32.4
36.0
29.3
8
68.2
65.4
22.5
1
J (2). The H (Table 1) and 13C (Table 2) NMR spectra of 2
8a
9
37.3
38.9
34.9
showed a close relationship with those of 8,1 except for the
difference at the ester-linked side chain. The disappearance of
an ester carbonyl signal at δC 176.9 (C-1″), as well as the signals
for a sec-butyl group at the side chain in 2, indicated the loss of
the side chain. It was supported by its molecular weight
(C19H26O3), which is 84 (C5H8O) mass units less than that of 8
(C24H34O4). The upfield shift of H-8 from δH 5.39 to δH 4.24
and of C-8 from δC 67.8 to δC 65.4 also confirmed that the
ester-linked side chain at C-8 in 8 was replaced by the hydroxyl
in 2. Therefore, compound 2 was elucidated as a new
dehydromonacolin and named dehydromonacolin J, bearing
the structure as illustrated in Figure 1.
14.1
14.1
13.8
10
1′
2′
3′
4′
5′
6′
7′
1″
2″
22.8
24.0
21.2
164.5
121.6
145.0
29.7
164.8
121.5
145.3
29.9
164.5
121.4
144.9
29.6
78.1
78.6
28.2
30.9
32.3
32.4
23.8
24.2
24.4
171.3
21.5
(4),12 the ethyl ester of monacolin K (5),13 (1S,2S,4aR,6S,8-
S,8aS,3′S,5′R,2″S)-methyl 1,2,4a,5,6,7,8,8a-octahydro-3′,5′-dihy-
droxy-2,6-dimethyl-8-[(2-methyl-1-oxobutyl)oxy]-1-naphthale-
neheptanoate (6),14 α,β-dehydrodihydromonacolin K (7),1
dehydromonacolin K (8),1 the methyl ester of the hydroxyl
acid form of monacolin K (9),1 dihydromonacolin K (10),1
monacolin K (11),1 and monacolin L (12)9 on the basis of
comparison of their NMR and HR-ESI-MS data with those
reported in the literature. It is worthwhile to point out that
compounds 4−6 were isolated from a natural resource for the
first time.
Finally, acetylation of 2 yielded a new compound, which was
identified to be 1 after comparison of the retention time (9.2
min) in UPLC with mobile phase using A (0.1% formic acid in
H2O; 0→12 min, 80%→20%) and B (0.1% formic acid in
CH3CN; 0→12 min, 20%→80%), accurate molecular mass,
1
and H NMR data with that isolated from red yeast rice. The
13C NMR (Table 2) spectrum of synthesized 1 showed 21
carbon signals, including 3 methyl, 4 methylene, 11 methane,
and 3 quaternary carbons. It also closely resembled that of
dehydromonacolin K (8),1 with the exception of a difference at
the ester-linked side chain. A methyl signal at δC 21.5 (C-2″)
appeared in 1 instead of signals for the sec-butyl group in 8,
further confirming the structural elucidation of 1.
Dehydromonacolin N (1), obtained as a colorless oil,
exhibited the molecular ion at m/z 345.2063 [M + H]+ in
the HR-ESI-MS spectrum, which was consistent with the
molecular formula C21H28O4. The UV absorptions of 1 at λmax
230 (3.86), 238 (3.82), and 246 (3.72) nm, indicating the
presence of a conjugated double bond at the naphthalene
moiety, are typical triplet absorptions in the UV spectra of
On the basis of the above evidence, the structure of 1 was
confirmed as demonstrated in Figure 1. This is the first example
bearing the acetyl group in the natural monacolin family.
Dehydromonacolin L (3) was obtained as a colorless oil and
exhibited the molecular ion at m/z 287.2011 [M + H]+ in the
HR-ESI-MS spectrum, which was consistent with the molecular
formula C19H26O2. The UV absorbance at λmax 230 (2.76), 238
(2.60), and 246 (2.52) nm is identical to that of 2, suggesting
monacolins.1 The H NMR spectrum of 1 displayed three
1
methyl signals at δH 0.90 (3H, d, J = 7.0 Hz, H-9), 1.07 (3H, d,
J = 7.0 Hz, H-10), and 2.03 (3H, s, H-2″) and five olefin signals
at δH 5.79 (1H, dd, J = 9.6, 6.1 Hz, H-3), 5.99 (1H, d, J = 9.6
Hz, H-4), 5.53 (1H, m, H-5), 6.01 (1H, ddd, J = 9.6, 2.6, 0.9
Hz, H-2′), and 6.87 (1H, m, H-3′). Comparison of the overall
1H NMR data revealed high similarities between 1 and
dehydromonacolin K (8).1 The only difference was that the
methyl signal at δH 2.03 (3H, s, H-2″) in the side chain of 1 was
replaced with signals for a sec-butyl group in 8, in agreement
with the molecular weight of 1 (C21H28O4) that was 42 (C3H6)
mass units less than that of 8 (C24H34O4). Furthermore, the 1H
NMR data of 1 closely resembled those of the synthesized
monacolin possessing a C2 side chain,15 with the exception that
signals of the oxygenated methine [ δH 4.39 (1H, m, H-3′)] and
the vicinal methylene [δH 2.67 (2H, d, J = 4.0 Hz, H-2′)] in the
known compound disappeared, and a pair of olefinic proton
signals at δH 6.87 (1H, m, H-3′) and δH 6.01 (1H, ddd, J = 9.6,
2.6, 0.9 Hz, H-2′) were observed in 1. Therefore, it was
1
they have the same skeleton. The H NMR spectroscopic data
of 3 were almost identical to those of 2, except that H-8
observed at δH 5.37 in 2 shifted to the upfield region (δH 1.17)
in 3, suggesting that the hydroxyl at C-8 in 2 was absent in 3.
This change was consistent with the observed molecular weight
difference of 16 mass units between 2 and 3. Furthermore, the
1H NMR data of 3 were closely related to those of monacolin L
(12),9 except that signals of the oxygenated methine [ δH 4.38
(1H, m, H-3′)] and the vicinal methylene [δH 1.75 (1H, m, H-
2′a), δ 1.98 (1H, m, H-2′b)] in monacolin L disappeared, and a
pair of olefinic proton signals at δ 6.89 (m, H-3′) and δ 6.03
(dt, J = 9.6, 1.6 Hz, H-2′) were observed in 3. Therefore, it was
elucidated to be the dehydration derivative of monacolin L
(12) and named dehydromonacolin L. This elucidation was
supported by the molecular weight difference of 18 (H2O)
mass units between 3 and monacolin L. Assignment of all the
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1
Figure 1. H−1H COSY correlations in compound 1.
proton signals (Table 1) and CH−CH linkage of 3 was
absence of hydroxyl at the C-8 position of 3. On the basis of the
above evidence, the structure of 3 was identified as
demonstrated in Figure 2.
1
confirmed by the H−1H COSY spectrum (Figure 2).
A transformation from monacolin L (12) to compound 3
was undertaken as described in Scheme 2 to confirm the
chemical structure of compound 3. Elimination from the
methanesulfonates of monacolin L (12) yielded a compound
that was identified to be 3 after comparison of the retention
time (11.0 min) in UPLC with mobile phase using A (0.1%
formic acid in H2O; 0→12 min, 80%→20%) and B (0.1%
formic acid in CH3CN; 0→12 min, 20%→80%), accurate
molecular mass, and 1H NMR data with those isolated from red
yeast rice. The 13C NMR (Table 2) spectrum of synthesized 3
showed 19 carbon signals, including 2 methyl, 5 methylene, 10
methane, and 2 quaternary carbons, which closely resemble
those of dehydromonacolin J (2), except that a methylene
signal at δC 22.5 (C-8) appeared in 3 instead of an oxygenated
methane signal [δC 65.4 (C-8)] in 2. This further confirmed the
Monacolins are gaining popularity as anticancer agents
against various cancers including colorectal cancer, skin cancer
(melanoma), prostate cancer, and breast cancer. Their
antitumor effects maybe due to inhibition of cell proliferation,
promotion of apoptosis, inhibition of angiogenesis, prevention
of metastasis, improvement of immunity, or possibly the
targeting of the CSC population.16 However, the cytotoxicity of
dehydromonacolins remains unknown.
In this study, we focused on the preliminary screening of
dehydromonacolins for their cytotoxicity. All four of these
dehydromonacolins (1−3 and 8) obtained in our research
share the same structure with only difference in the length of
side chains, so we wish to see the relationship between the
cytotoxity and the side chain. Monacolin K (11), the
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Scheme 1. Semisynthesis of 1 from Monacolin K (11)
Table 3. IC50 Values (n = 3) of Compounds 1−3, 8, and 11
for Three Cancer Cell Lines
a
IC50 values (μM SD) for cell line
compound
Hep G2
Caco-2
MCF-7
dehydromonacolin N
(1)
51.84 4.44
56.98 8.41
11.78 0.65
dehydromonacolin J (2)
>100
>100
51.95 1.68
>100
1
Figure 2. H−1H COSY correlations in compound 3.
dehydromonacolin L (3) >100
>100
dehydromonacolin K (8)
Mmonacolin K (11)
7.62 0.97
57.62 2.22
10.83 0.14
48.55 3.18
3.95 0.48
27.82 1.67
Scheme 2. Semisynthesis of 3 from Monacolin L (12)
a
Cell lines: Hep G2, human liver cancer; Caco-2, human colon cancer;
MCF-7, human breast cancer.
Caco-2 cancer cell lines, with IC50 > 100 μM. Compound 3,
without a side chain, exhibited weak cytotoxicity toward all
three cell lines used, with IC50 > 100 μM. The MCF-7 cell line
seems to be more sensitive than the Hep G2 and Caco-2 cell
lines for all of the compounds tested. From a structure−activity
point of view, the cytotoxicity increased as the side chain
lengthened (compare 8 with 1−3), thus suggesting that
extension of the alkyl function group, which in turn resulted
in the increased lipophilicity, may contribute to the activity.
Besides, it was found that dehydromonacolin K (8) had much
stronger cytotoxicity than monacolin K (11) toward the cancer
cell lines, which was in agreement with the studies revealing
that more lipophilic monacolins could exert direct anticancer
activity in vitro because their lipophilicity allowed them to
directly permeate the cell membrane and affect cell
proliferation, survival, and motility.20
cytotoxicity17 and anticancer effects18,19 of which have been
reported in many papers, was used as a positive control in the
cytotoxicity evaluation. They were evaluated for their
cytotoxicity against Hep G2, Caco-2, and MCF-7 cancer cell
lines using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra-
zolium bromide (MTT) assay.
Among the four dehydromonacolins (1−3 and 8),
compound 8 with a C5 side chain at C-8 exhibited the most
potent cytotoxic activity, with IC50 values ranging from 3.95
0.48 to 10.83 0.14 μM (Table 3). Compound 1, possessing a
C2 side chain, was less cytotoxic than 8, showing moderate
cytotoxicity. Compound 2, with a hydroxyl group at the side
chain, showed weak cytotoxicity against both Hep G2 and
This study demonstrated that dehydromonacolins with
extended alkyl side chain exerted more potent cytotoxic effects
toward cancer cells. This is the first report on the cytotoxic
effects of dehydromonacolins.
938
dx.doi.org/10.1021/jf203579f | J. Agric.Food Chem. 2012, 60, 934−939

Journal of Agricultural and Food Chemistry
Article
(20) Campbell, M. J.; Esserman, L. J.; Zhou, Y.; Shoemaker, M.;
Lobo, M.; Borman, E.; Baehner, F.; Kumar, A. S.; Adduci, K.; Marx, C.;
Petricoin, E. F.; Liotta, L. A.; Winters, M.; Benz, S.; Benz, C. C. Breast
cancer growth prevention by statins. Cancer Res. 2006, 66, 8707−8714.
ASSOCIATED CONTENT
■
S
* Supporting Information
1D and 2D NMR spectra of compounds 1−3. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Phone: +853-88972777. Fax: + 853-28825886. E-mail:
zhjiang@must.edu.mo..
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