Lp-PLA2 inhibitory activities of fatty acid glycerols isolated from Saururus chinensis roots

Article abstract of DOI:10.1016/j.bmcl.2005.05.056

(R)-Glycerol-monolinoleate 4 and (R)-glycerol-monostearate 5 were isolated from the ethyl acetate extracts of Saururus chinensis roots and (R)- or (S)-fatty acid glycerols 4 and 5 were synthesized for confirming their structures and evaluating their inhibitory activities against Lp-PLA ₂. The (R)-4 and (S)-4 exhibited Lp-PLA₂ inhibitory activities with IC₅₀ values of 45.0 and 52.0 μM, respectively.

Full text of DOI:10.1016/j.bmcl.2005.05.056

Bioorganic & Medicinal Chemistry Letters 15 (2005) 3573–3575
Lp-PLA inhibitory activities of fatty acid glycerols isolated
2
from Saururus chinensis roots
a,b
Woo Song Lee, Mi Jeong Kim, Young-Il Beck,
a
a
a,b
Yong-Dae Park and Tae-Sook Jeong
a,b,
*
a
National Research Laboratory of Lipid Metabolism and Atherosclerosis, Korea Research Institute of Bioscience and Biotechnology,
2 Oun, Yusong, Daejeon 305-333, Republic of Korea
5
University of Science and Technology, 52 Oun, Yusong, Daejeon 305-333, Republic of Korea
b
Received 7 February 2005; revised 3 May 2005; accepted 16 May 2005
Available online 14 June 2005
Abstract—(R)-Glycerol-monolinoleate 4 and (R)-glycerol-monostearate 5 were isolated from the ethyl acetate extracts of Saururus
chinensis roots and (R)- or (S)-fatty acid glycerols 4 and 5 were synthesized for confirming their structures and evaluating their inhib-
itory activities against Lp-PLA
respectively.
2 2
. The (R)-4 and (S)-4 exhibited Lp-PLA inhibitory activities with IC50 values of 45.0 and 52.0 lM,
ꢀ
2005 Elsevier Ltd. All rights reserved.
Lipoprotein-associated phospholipase A2 (Lp-PLA2),
platelet-activating factor acetylhydrolase (PAF-AH,
EC 3.1.1.47), is a secreted calcium-independent member
Although various synthetic compounds have been devel-
6
oped as potent Lp-PLA inhibitors, thus far, however,
2
naturally occurring Lp-PLA inhibitors have not been
2
of the phospholipase A superfamily produced mainly
2
described, except for SB-253514 and analogues isolated
7
by cells of the monocyte–macrophage series, T-lympho-
1
from Pseudomonas fluorescens DMS 11579. In our
8
cytes, and mast cells. The plasma isoform of Lp-PLA2
is about 80% bound to LDL, with the remaining frac-
tion bound to high-density lipoprotein (HDL) and very
search for naturally occurring Lp-PLA2 inhibitors,
ethyl acetate extracts of S. chinensis roots exhibited
Lp-PLA inhibitory activities. Two known (R)-glycerol-
2
2
low-density lipoprotein (VLDL). Especially, accumula-
tion of oxidized LDL in artery wall is known as early
monolinoleate 4 and -monostearate 5 were isolated by
9
bioassay-guided fractionation and identified by their
spectroscopic analysis, synthesis, and comparison with
3
stage of atherosclerosis. Lp-PLA hydrolyzes the sn-2
2
1
0,11
fatty acid of oxidatively modified LDL to release two
lipid products, oxidized free fatty acid (oxFFA) and
the reported data (Fig. 1).
Additionally, (S)-glycer-
ol-monolinoleate 4 and -monostearate 5 were synthe-
4
lysophosphatidylcholine (lyso-PC). These two products
are highly effective inflammatory mediators capable of
attracting monocytes and driving the atherogenic pro-
sized for evaluating their Lp-PLA inhibitory activities
2
(Scheme 1).
4
5
25
Compound 4, colorless oil, exhibited a value of ½aꢀ +5.0ꢁ
cess. Leach et al. reported that Lp-PLA inhibitor
2
D
1
0
reduced atherosclerotic plaque development in the
Watanabe heritable hyperlipidemic (WHHL) rabbit
study. Therefore, a number of studies have focused
on the development of Lp-PLA2 inhibitors to treat
atherosclerosis.
(c 0.2, MeOH) (lit. [a]D +3.0ꢁ (c 0.36, MeOH)). The
OH
2'
4'
6'
8'
HO
O
1'
O
2
9'
3
1
3'
5'
7'
10'
1
12'
1'
18'
16'
14'
17'
15'
13'
Keywords: Lp-PLA
*
2
inhibitor; Fatty acid glycerols; Saururus chinensis.
Corresponding author. Tel.: +82 42 860 4558; fax: +82 42 861
675; e-mail: tsjeong@kribb.re.kr
Figure 1. Chemical structures (R)-4 and -5 of isolated from
S. chinensis.
2
0
960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.05.056

3574
W. S. Lee et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3573–3575
+
mass spectrum showed molecular ions of m/z 354 [M]
and characteristic fragment ions of m/z 262 [Mꢁ2],
from S. chinensis. Therefore, the structures of
compounds 4 and 5 were elucidated to be (R)-(+)-glycer-
ol 1-9(Z),12(Z)-octadecadienate (4) and (R)-(ꢁ)-glycerol
1-octadecanate (5). Also, stereochemistry of the glycerol
group in isolated compounds 4 and 5 was determined by
comparing the optical activities of the synthetic com-
1
followed by loss of glycerol in the EI MS data. The H
NMR (CDCl , 500 MHz) showed four olefinic methines
3
at dH 5.37 (4H, m, H-9, -10, -12, and -13), a-methylene
protons of linoleate at d 2.36 (2H, t, J = 7.5 Hz, H-2 ),
0
H
25
methylene protons between two olefinic bonds at dH
pounds (R)-4 and -5 with ½aꢀ +3.7ꢁ (c 0.2, MeOH) and
25
D
0
25
D
2
.77 (2H, t like, J = 5.9 Hz, H-11 ), and methyl protons
0
½aꢀ ꢁ32.0ꢁ (c 0.25, CHCl ), respectively, to those of iso-
3
at d 0.89 (3H, t, J = 6.6 Hz, H-18 ), respectively. The
lated compounds 4 and 5 with ½aꢀ +5.0ꢁ (c 0.2, MeOH)
H
D
1
3
25
D
C NMR data indicated ester carbonyl carbon at dC
74.3 (C-1 ), glycerol group at d 63.3 (C-3), 65.2 (C-1),
and 70.3 (C-2), and four olefinic carbons at d 127.9
C-10 or 12 ), 128.1 (C-12 or 10 ), 130.0 (C-9 or 13 ),
and 130.3 (C-13 or 9 ), respectively. Additionally, the
stereochemistry of the (2R)-glycerol moiety in 4 was
determined by comparison of its optical activity to the
and ½aꢀ ꢁ35.0ꢁ (c 0.25, CHCl ), respectively.
3
0
1
C
1
0
Although 1-fatty acid glycerols and 2-fatty acid glycer-
12
C
0
0
0
0
0
0
(
ols have been reported to show various biological
activities, the potential of compounds 4 and 5 as inhib-
0
0
itors of Lp-PLA (LDL-PLA ) was evaluated for the
2
2
1
3
first time according to a previous testing method.
Compound (2R)-4 exhibited moderate Lp-PLA inhibi-
1
0
reported data of (R)-glycerol monolinoleate.
2
tory activity with an IC50 value of 45.0 lM, whereas
(2R)-5 showed a very weak inhibitory activity (20% inhi-
bition at 25 lM). Their enantiomers (2S)-4 and -5 were
assessed for structural specificity against Lp-PLA2,
resulting in a very similar degree of inhibitory activity
with an IC50 value of 52.0 lM and inhibition of 21%
at 25 lM, respectively. These results suggested that the
fatty acid group is concerned with biological activity,
regardless of the stereochemistry of the glycerol moiety
in compounds 4 and 5. In general, polyunsaturated fatty
acid analogues have been known to exhibit anti-inflam-
Compound 5, white powder, showed a base peak at m/z
3
+
58 [M] and characteristic fragment ions of m/z 270
[
M+2], followed by loss of glycerol in the EI MS data
1
1
and has mp 71–72 ꢁC (CH Cl ) (lit. mp 70–72 ꢁC).
The signals at d 3.60 (1H, dd, J = 5.7, 11.4 Hz, H-3),
2
2
H
3
.70 (1H, dd, J = 3.9, 11.4 Hz, H-3), 3.94 (1H, m,
H-2), 4.15 (1H, dd, J = 6.6, 11.6 Hz, H-1), and 4.22
1H, dd, J = 4.7, 11.7 Hz, H-1) indicated the presence
of a glycerol group, which was confirmed by its spectro-
(
1
3
scopic analysis (e.g., EI MS and C NMR) and by com-
1
1
14
paring with reported data. The stereochemistry of the
2R)-glycerol moiety in 5 was considered by comparison
matory activity, in vitro or in vivo antioxidant activ-
5
1
(
ity, and beneficial effects on the risk factors of
16
coronary heart disease (CHD). Based on these results,
25
of its optical activity, ½aꢀ ꢁ35.0ꢁ (c 0.25, CHCl ), to the
D
3
reported data of (R)-glycerol stearate, [a] ꢁ36.36ꢁ
D
linoleic and stearic acids (1 and 2) and methyl linoleate
3, purchased from Sigma–Aldrich Co., were tested ten-
tatively for their Lp-PLA inhibitory activities, resulting
11
(
c 0.055, CHCl3).
2
Fatty acid derivatives 4 and 5 were prepared to confirm
more exact structures and structural specificity against
in being inactive against Lp-PLA2.
Lp-PLA . The results are summarized in Scheme 1.
2
(R)- or (S)-Fatty acid glycerol 4, isolated first from the
EtOAc extracts of S. chinensis or synthesized from
fatty acid 1, exhibited moderated Lp-PLA inhibitory
The reaction of linoleic acid 1 (or stearic acid 2) with
(
S)-(+)-2,2-dimethyl-1,3-dioxolane-4-methanol
and
2
EDC in THF at 0 ꢁC gave the corresponding (R)-isopro-
pylidene glycerol-monolinoleate (or -stearate), which
was then deprotected with Dowex 50W · 2 to produce
activities. Furthermore, the in vivo efficacy tests of
cholesterol lowering and antiatherogenic activity of 4
are underway.
(
R)-glycerol-monolinoleate 4 (or -stearate 5) in good
1
1
yield. To obtain their enantiomers 4 and 5, linoleic
acid 1 (or -stearic acid 2) was treated with (R)-(ꢁ)-2,
Acknowledgment
2
-dimethyl-1,3-dioxolane-4-methanol under similar
reaction conditions to give the corresponding (S)-(+)-
glycerol-monolinoleate 4 (or -stearate 5). The synthetic
compounds (2R)-4 and -5 were identical with the spec-
troscopic data of compounds 4 and 5 that were isolated
This work is supported by a grant (BioGreen 21 Project)
from the Rural Development Administration, Korea.
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R
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4
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(
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