Excavatoids O and P, new 12-hydroxybriaranes from the octocoral Briareum excavatum.

Abstract

Two new 12-hydroxybriarane diterpenoids, designated as excavatoids O (1) and P (2), were isolated from the octocoral Briareum excavatum. The structures of briaranes 1 and 2 were established on the basis of extensive spectral data analysis. Excavatoid P (2) is the first metabolite which possesses a 6β -chlorine atom in briarane analogues.

Full text

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Mar. Drugs 2010, 8, 2639-2646; doi:10.3390/md8102639

Marine Drugs
ISSN 1660-3397
www.mdpi.com/journal/marinedrugs
Article
Excavatoids O and P, New 12-Hydroxybriaranes from the
Octocoral Briareum excavatum
Ping-Jyun Sung 1,2,3,4,5,*, Gung-Ying Li 1,2, Yin-Di Su 2,4, Mei-Ru Lin 2, Yu-Chia Chang 2,6,
Ting-Hsuan Kung 2, Chan-Shing Lin 4,5,6, Yung-Husan Chen 2, Jui-Hsin Su 1,2, Mei-Chin Lu 1,2,
Jimmy Kuo 1,2, Ching-Feng Weng 3 and Tsong-Long Hwang 7
1 Graduate Institute of Marine Biotechnology, National Dong Hwa University, Pingtung 944, Taiwan;
E-Mails: johnny9210014@hotmail.com (G.-Y.L.); x2219@nmmba.gov.tw (J.-H.S.);
jinx6609@yahoo.com.tw (M.-C.L.); jimmy@nmmba.gov.tw (J.K.)
2 National Museum of Marine Biology & Aquarium, Pingtung 944, Taiwan;
E-Mails: gobetter04@yahoo.com.tw (Y.-D.S.); linmeiru@hotmail.com (M.-R.L.);
jay0404@gmail.com (Y.-C.C.); sevenapril@nmmba.gov.tw (T.-H.K.);
tony_chen72001@yahoo.com.tw (Y.-H.C.)
3 Department of Life Science and the Institute of Biotechnology, National Dong Hwa University,
Hualien 974, Taiwan; E-Mail: cfweng@mail.ndhu.edu.tw (C.-F.W.)
4 Department of Marine Biotechnology and Resources, National Sun Yat-sen University,
Kaohsiung 804, Taiwan; E-Mail: shinlin@mail.nsysu.edu.tw (C.-S.L.)
5 Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung 804, Taiwan
6 Doctoral Degree Program in Marine Biotechnology, National Sun Yat-sen University,
Kaohsiung 804, Taiwan
7 Graduate Institute of Natural Products, Chang Gung University, Taoyuan 333, Taiwan;
E-Mail: htl@mail.cgu.edu.tw (T.-L.H.)
* Author to whom correspondence should be addressed; E-Mail: pjsung@nmmba.gov.tw;
Tel.: +886-8-882-5037; Fax: +886-8-882-5087.
Received: 7 September 2010; in revised form: 23 September 2010 / Accepted: 9 October 2010 /
Published: 12 October 2010

Abstract: Two new 12-hydroxybriarane diterpenoids, designated as excavatoids O (1) and
P (2), were isolated from the octocoral Briareum excavatum. The structures of briaranes 1
and 2 were established on the basis of extensive spectral data analysis. Excavatoid P (2) is
the first metabolite which possesses a 6-chlorine atom in briarane analogues.
Keywords: excavatoid; briarane; octocoral; Briareum excavatum

OPEN ACCESS

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1. Introduction
In our research on the chemical constituents of the marine invertebrates collected in Taiwan waters,
a series of briarane-type diterpenoid derivatives had been isolated from various octocorals belonging to
the genus Briareum (family Briareidae), Ellisella, and Junceella (family Ellisellidae), and the
compounds of this type were proven to possess various interesting bioactivities [1–3]. Recently, our
further chemical examination of Briareum excavatum has resulted in the isolation of two new highly
oxidized briarane-type diterpenoids, excavatoids O (1) and P (2) (Scheme 1). The structures of
compounds 1 and 2 were established by spectroscopic methods.
Scheme 1. The Structures of Excavatoids O (1) and P (2).
O
AcO
O
H
AcO
AcO
OC(O)(CH2)2CH3
O
19
HO
O
5
1
2
3
4
6
7
8
9
10
11
12
13
14
15
16
17
18
20
H

O
AcO
O
H
AcO
AcO
OH
O
HO
OH
OC(O)(CH2)2CH3
Cl

1 2
2. Results and Discussion
Excavatoid O (1) was obtained as a white powder and had a molecular formula C30H42O13, as
determined by HRESIMS (C30H42O13 + Na, m/z found 633.2519; calculated 633.2523) indicating
10 degrees of unsaturation. The presence of hydroxy, lactone, and ester groups in 1 were evidenced by
the IR absorptions at 3512, 1793, and 1741 cm−1. It was found that the 1H and 13C spectra of 1 in
CDCl3 revealed mostly broad peaks when measured at 25 °C. In order to make more reliable
assignments of NMR signals of the stabilized conformers, the 1H and 13C NMR spectra of 1 were
measured at 0 °C in CDCl3. In the 13C spectrum of 1, five ester carbonyl resonances appeared at
C 173.6, 170.8, 170.1, 169.5, and 169.3 (5 × s) (Table 1). In the above carbonyl carbons, three were
identified as acetate carbonyls by the presence of three methyl resonances in the 1H NMR spectrum at
H 2.18, 2.12, and 1.96 (each 3H × s) and one was identified as n-butyrate carbonyl by the presence of
seven contiguous protons at H 0.95 (3H, t, J = 7.2 Hz), 1.64 (2H, m), and 2.23 (2H, m) (Table 1). On
the basis of the unsaturation data overall, 1 was concluded to be a briarane diterpenoid molecule
possessing five rings. A tetra-substituted epoxide containing a methyl substituent was elucidated from
the signals of two oxygenated quaternary carbons at C 72.6 (s, C-8) and 63.3 (s, C-17); and further
confirmed by the proton signal of a methyl singlet at H 1.57 (3H, s, H3-18). In addition, a
tri-substituted epoxide containing a methyl substituent was deduced from the signals of an
oxymethine (H 3.11, 1H, d, J = 8.8 Hz, H-6; C 63.0, d, C-6), a quaternary oxygen-bearing carbon
(C 62.1, s, C-5), and a methyl singlet at H 1.35 (3H, s, H3-16).

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Table 1. 1H and 13C NMR data for diterpenoids 1 and 2.
1

2
Position
1
2
3
4
5
6
7
8
9
10
11
12
13
1H a
13C b
43.3 (s) f
69.3 (d) 4.62 s
69.9 (d) 5.07 d (11.6)
33.7 (t) 5.82 s
62.1 (s)
63.0 (d) 4.29 s
78.3 (d) 5.26 s
72.6 (s)
68.5 (d) 5.36 d (8.4)
45.3 (d) 3.52 dd (8.4, 4.4)
34.5 (d) 2.54 m
69.3 (d) 4.13 m
34.8 (t) 1.83 m ()
1.96 m ()
73.0 (d) 4.84 br s
18.2 (q) 0.86 s
21.1 (q) 1.55 s
63.3 (s)
11.1 (q) 1.63 s
170.8 (s)
16.3 (q) 1.11 d (7.6)
3.18 d (11.6)
2.36 s
2.17 br s
169.5
21.1 (q) 2.03 s
169.3
21.2 (q) 2.43 s
170.1
21.1 (q) 2.17 s
173.6
35.6
17.8
13.6 (q)

2.33 t (7.6) (2H)
1.66 m (2H)
0.98 t (7.6)
1H c
13C d
44.0 (s)
88.2 (d)
68.8 (d)
70.9 (d)
77.8 (s)
65.9 (d)
75.7 (d)
67.5 (s)
66.0 (d)
39.5 (d)
37.3 (d)
66.9 (d)
30.3 (t)

5.81 d (2.0) e
5.13 br s
2.25 m (2H)

3.11 d (8.8)
4.69 d (8.8)

5.76 s
2.18 br s
2.32 br s
3.96 br s
1.92 m (2H)
14
15
16
17
18
19
20
OH-3
OH-5
OH-12
2-OAc
5.16 br s
1.52 s
1.35 s

1.57 s

1.19 d (7.2)


n.o. g

2.12 s

2.18 s

1.96 s
80.8 (d)
18.2 (q)
22.3 (q)
60.6 (s)
10.0 (q)
170.0 (s)
9.0 (q)



(s) 172.0
21.1
170.4
21.4
170.3
21.3
(s)
(q)
(s)
(q)
(s)
(q)

9-OAc (s)
14-OAc (s)
3-OCOPr
2.23 m (2H)
1.64 m (2H)
0.95 t (7.2)
(s)
(t)
(t)


4-OCOPr

173.9
36.3
18.4
13.7
(s)
(t)
(t)
(q)
a: Spectra were recorded at 400 MHz at 0 °C; b: Spectra were recorded at 100 MHz at 0 °C;
c: Spectra were recorded at 400 MHz at 25 °C; d: Spectra were recorded at 100 MHz at 25 °C;
e: J values (in Hz) in parentheses; f: Multiplicity deduced by DEPT and HMQC spectra and
indicated by usual symbols; g: n.o. = not observed.

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From the 1H-1H COSY experiment of 1 (Table 2), it was possible to establish the separate spin
systems that map out the proton sequences from H-2/H-3/H2-4, H-6/H-7, and H-9/H-10. These data,
together with the HMBC correlations between H-2/C-1, -4; H-3/C-4; H2-4/C-3, -5, -6; H-7/C-5, -6;
H-9/C-1, -7, -8, -10; and H-10/C-1, -2, established the connectivity from C-1 to C-10 in the
10-membered ring (Table 2). The methyl group at C-5 was confirmed by the HMBC correlations
between H3-16/C-4, -5, -6. The methylcyclohexane ring, which is fused to the 10-membered ring at
C-1 and C-10, was elucidated by the 1H-1H COSY correlations between H-10/H-11/H-12/H2-13/H-14
and H-11/H3-20 and by the HMBC correlations between H-2/C-14; H-9/C-11; H-10/C-11, -12, -14;
H-11/C-10, -20; H2-13/C-1; H-14/C-1, -2; and H3-20/C-10, -11, -12. The ring junction C-15 methyl
group was positioned at C-1 from the HMBC correlations between H-2/C-15; and H3-15/C-1, -2, -10, -14.
In addition, the HMBC correlations also revealed that three acetates should be attached at C-2,
C-9, and C-14, respectively. The remaining n-butyrate ester and hydroxy groups were positioned at
C-3 and C-12 as indicated by analysis of 1H-1H COSY correlations and characteristic NMR signals
analysis (H 5.13, 1H, br s, H-3; C 69.9, d, C-3; H 3.96, 1H, br s, H-12; C 69.3, d, C-12). These data,
together with the HMBC correlations between H-7/C-17, -19 and H3-18/C-8, -17, -19, were used to
establish the molecular framework of 1.
Table 2. The 1H-1H COSY and HMBC (H→C) correlations for diterpenoids 1 and 2.

Position 1H-1H COSY
H-2
H-3
1
HMBC
C-1, -4, -14, -15,
acetate carbonyl
C-4
C-3, -5, -6


H-3
2
HMBC
C-1, -3, -4, -10, -14,
acetate carbonyl
C-1, -5
C-2, -5, -16,
n-butyrate carbonyl
C-4, -5, -7, -8, -16
C-5, -6, -9, -19
C-7, -8, -10, -11, -17,
acetate carbonyl
C-1, -8, -9, -11, -12, -15, -20
1H-1H COSY
H-3
H-4
H-2, H2-4
H-3
H-2, H-4, OH-3
H-3
H-6
H-7
H-9
H-7
H-6
H-10
n.o.
C-5, -6, -17, -19
C-1, -7, -8, -10, -11,
acetate carbonyl
C-1, -2, -11, -12, -14 H-9, H-11
H-7
H-6
H-10
H-10
H-11
H-12
H-13
H-14
H-9, H-11
H-10, H-12, H3-20 C-10, -20
H-11, H2-13
H-12, H-14
H2-13
H-10, H-12, H3-20 C-1, -10, -12, -20
H-11, H2-13
H-12, H-14
H2-13
n.o.
C-1, -14
C-1, -2, -12, -13,
acetate carbonyl
C-1, -2, -10, -14
C-4, -5, -6
C-8, -17, -19
C-10, -11, -12


n.o.
C-20
C-12
C-10, -12
H-15
H-16
H-18
H-20
OH-3
OH-5
OH-12



H-11


n.o. a



H-11
H-3

H-12
C-1, -2, -10, -14
C-4, -5, -6
C-8, -17, -19
C-10, -11, -12
C-3
C-4, -5, -16
C-11
a: n.o. = not observed.

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Based on previous studies, all naturally occurring briarane-type diterpenoids have the C-15 methyl
group as trans to H-10, and these two groups are assigned as - and -oriented, respectively, as shown
in most briarane derivatives [1–3]. The relative stereochemistry of 1 was established from a NOESY
experiment (Figure 1). In the NOESY experiment of 1, the correlations of H-10 with H-2, H-3, H-6, H-9,
and H-11; and H-11 correlated with H-12, indicated that these protons are situated on the same face
and were assigned as  protons since the C-15 methyl is the -substituent at C-1. H-14 was found to
exhibit a correlation with H3-15, revealing the -orientation of this proton. The correlations between
H3-16 and H-3, H-6, reflected the -orientation of H3-16. H-7 correlated with H3-15, indicating this
proton should be -oriented. Furthermore, H3-18 showed a correlation with H-9. By detailed analysis
of molecular models, H3-18 was found to be reasonably close to H-9 when H3-18 was placed on the
 face in the -lactone moiety. Based on the above findings, the structure of 1 was
elucidated unambiguously.
Figure 1. Selective NOESY correlations of 1.
O
O
H
H
O
OAc
H
AcO
H
H
HO
H
: NOESY
H
OAc
H
OC(O)CH2CH2CH3
O
H

The molecular formula of excavatoid P (2) was determined as C30H43ClO14 by its HRESIMS
(m/z 685.2235, calculated for C30H43ClO14 + Na, 685.2239). The IR spectrum showed bands at 3472,
1784, and 1734 cm−1, consistent with the presence of hydroxy, -lactone, and ester groups in 2. From
the 13C NMR data of 2 (Table 1), five carbonyl resonances appeared at C 173.9, 172.0, 170.4, 170.3,
and 170.0 (5 × s), confirming the presence of a -lactone and four esters in 2; three acetyl methyls
(H 2.43, 2.17, 2.03, each 3H × s) and an n-butyryl group (H 0.98, 3H, t, J = 7.6 Hz; 1.66, 2H, m;
2.33, 2H, t, J = 7.6 Hz) were also observed. According to the above data, briarane 2 was found to be a
tetracyclic compound with a -lactone, as no other unsaturated functional group could be found.
1H NMR coupling information in the 1H-1H COSY spectrum of 2 enabled identification of the
C-2/-3/-4, C-6/-7, C-9/-10/-11/-12/-13/-14, and C-11/-20 units (Table 2), which were assembled with
the assistance of an HMBC experiment (Table 2). The HMBC correlations between protons and
quaternary carbons, such as H-2, H-3, H-10, H-11, H3-15/C-1; H-3, H-4, H-6, H-7, H3-16, OH-5/C-5;
H-6, H-9, H-10, H3-18/C-8; H-9, H3-18/C-17; and H-7, H3-18/C-19, permitted elucidation of the
carbon skeleton. A methyl at C-5 was established by the HMBC correlations between H3-16/C-4, -5,
-6 and H-4, H-6, OH-5/C-16. The ring junction C-15 methyl group was positioned at C-1 from the
HMBC correlations between H3-15/C-1, -2, -10, -14; and H-10/C-15. The acetate esters at C-2 and C-9
were established by correlations between H-2 (H 4.62), H-9 (H 5.36) and the acetate carbonyls

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observed in the HMBC spectrum of 2. The n-butyrate ester positioned at C-4 was confirmed from the
HMBC correlation between H-4 (H 5.82) and the carbonyl carbon (C 173.9) of n-butyrate ester. Thus,
the remaining acetoxy group was positioned at C-14 as indicated by analysis of 1H-1H COSY
correlations and characteristic NMR signals (H 4.84, 1H, br s, H-14; C 80.8, d, C-14). The presence
of hydroxy groups at C-3 and C-12 was deduced from the 1H-1H COSY correlations between the
hydroxy protons (H 3.18, OH-3 and H 2.17, OH-12) and H-3 (H 5.07) and H-12 (H 4.13),
respectively. The C-5 hydroxy group was also confirmed by the HMBC correlations between the
hydroxy proton (H 2.36, OH-5) and C-4, -5, -16. Thus, the remaining chlorine atom in 2 should be
attached C-6 by the 1H-1H COSY correlation between H-6 (H 4.29) and H-7 (H 5.26) and further
supported by the HMBC correlations between H-6/C-4, -5, -7, -8, -16 and H-7, H3-16/C-6.
The relative configuration of 2 was elucidated from the interactions observed in a NOESY
experiment and from vicinal proton coupling constant analysis. In the NOESY experiment of 2
(Figure 2), the correlations of H-10 with H-3, H-11, and H-12, indicated that these protons were
situated on the same face and were assigned as  protons since the C-15 and C-20 methyls are
-substituents at C-1 and C-11, respectively. H-2 exhibited an interaction with H-3, and no coupling
was found between H-2 and H-3, indicating that the dihedral angle between H-2/H-3 is approximately
90° and the acetoxy group at C-2 should be -oriented. H-14 was found to exhibit a response with
H3-15, showing that H-14 has a -orientation. H-9 was found to show responses with H-11, H3-18, and
H3-20. From modeling analysis, H-9 was found to be close to H-11, H3-18, and H3-20 when H-9 was
-oriented. Moreover, H3-16 exhibited correlations with H-3 and H-6, and no coupling constant was
detected between H-6 and H-7, suggesting the -orientation of H3-16 and H-6; and -orientation of H-7.
H-7 exhibited a correlation with H-4, and no coupling was found between H-3 and H-4, indicating that
the dihedral angle between H-3 and H-4 is also approximately 90° and the n-butyrate ester group at
C-4 was -oriented. On the basis of the above results, the structure of 2 was elucidated. To the best of
our knowledge, briarane 2 is the first briarane which possesses a 6-chlorine atom.
Figure 2. Selective NOESY correlations of 2.
O
O
H
H
O
OAc
H
AcO
H
H
HO
H
OAc
H
OH
OH
H
OC(O)CH2CH2CH3
Cl
H
: NOESY
H

In the biological activity testing, briaranes 1 and 2 displayed 16.9 and 16.1% inhibitory effects on
elastase release by human neutrophils at 10 g/mL, resepectively [4].

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3. Experimental
3.1. General Experimental Procedures
Melting points were determined on a FARGO apparatus and were uncorrected. Optical rotation
values were measured with a JASCO P-1010 digital polarimeter at 25 °C. Infrared spectra were
obtained on a VARIAN DIGLAB FTS 1000 FT-IR spectrometer. The NMR spectra were recorded on a
VARIAN MERCURY PLUS 400 FT-NMR at 400 MHz for 1H and 100 MHz for 13C, in CDCl3, at 25 or
0 °C, respectively. Proton chemical shifts were referenced to the residual CHCl3 signal ( 7.26 ppm).
13C NMR spectra were referenced to the center peak of CDCl3 at C 77.1 ppm. ESIMS and HRESIMS
data were recorded on a BRUKER APEX II mass spectrometer. Column chromatography was
performed on silica gel (230–400 mesh, Merck, Darmstadt, Germany). TLC was carried out on
precoated Kieselgel 60 F254 (0.25 mm, Merck) and spots were visualized by spraying with 10% H2SO4
solution followed by heating. HPLC was performed using a system comprised of a HITACHI L-7100
pump, a HITACHI photodiode array detector L-7455, and a RHEODYNE 7725 injection port. A
normal phase column (Hibar 250 × 10 mm, Merck, silica gel 60, 5 m,) was used for HPLC.
3.2. Animal Material
Specimens of the octocoral Briareum excavatum were collected and transplanted in 0.6-ton
cultivating tanks located in the NMMBA, Taiwan, in December 2003. This organism was identified by
comparison with previous descriptions [5–7]. A voucher specimen was deposited in the National
Museum of Marine Biology and Aquarium, Taiwan.
3.3. Extraction and Isolation
The organism (wet weight 1.0 kg) was collected and freeze-dried. The freeze-dried material was
minced and extracted with EtOAc. The extract was separated by silica gel column chromatography,
using hexane and hexane/EtOAc mixtures of increased polarity to yield 12 fractions. Fraction 3 was
separated by normal phase HPLC, using a mixture of dichloromethane and acetone to afford briarane 2
(0.9 mg, 9/1). Fraction 2 was separated by normal phase HPLC, using a mixture of hexane and EtOAc
to afford briarane 1 (13.2 mg, 1/1).
Excavatoid O (1): white powder; mp 137–138 °C; []
1793, 1741 cm−1; 13C NMR (CDCl3, 100 MHz) and 1H NMR (CDCl3, 400 MHz) data, see Table 1;
ESIMS m/z 633 (M + Na)+; HRESIMS m/z 633.2519 (Calcd for C30H42O13Na, 633.2523).
Excavatoid P (2): white powder; mp 154–155 °C; []
1784, 1734 cm−1; 13C NMR (CDCl3, 100 MHz) and 1H NMR (CDCl3, 400 MHz) data, see Table 1;
ESIMS m/z 685 (M + Na)+; HRESIMS m/z 685.2235 (Calcd for C30H43ClO14Na, 685.2239).
25
D − 39 (c 0.4, CHCl3); IR (neat) max 3512,
25
D + 14 (c 0.05, CHCl3); IR (neat) max 3472,
3.4. Human Neutrophil Elastase Release
Human neutrophils were obtained by means of dextran sedimentation and Ficoll centrifugation.
Elastase release experiments were performed using MeO-Suc-Ala-Ala-Pro-Valp-nitroanilide as the
elastase substrate [8,9].

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Acknowledgements
This study was supported by grants from the National Museum of Marine Biology and Aquarium
(Grant No. 99200321 and 99200322); National Dong Hwa University; Asia-Pacific Ocean Research
Center, National Sun Yat-sen University (Grant No. 97C031702); and the National Science and
Technology Program for Biotechnology and Pharmaceuticals, National Science Council
(Grant No. NSC 98-2323-B-291-001, 99-2323-B-291-001, and 98-2320-B-291-001-MY3), Taiwan,
awarded to P.-J.S.
References and Notes
1. Sung, P.-J.; Sheu, J.-H.; Xu, J.-P. Survey of briarane-type diterpenoids of marine origin.
Heterocycles 2002, 57, 535–579.
Sung, P.-J.; Chang, P.-C.; Fang, L.-S.; Sheu, J.-H.; Chen, W.-C.; Chen, Y.-P.; Lin, M.-R. Survey
of briarane-type diterpenoids-Part II. Heterocycles 2005, 65, 195–204.
Sung, P.-J.; Chang, P.-C.; Fang, L.-S.; Sheu, J.-H.; Chen, W.-C.; Chen, Y.-P.; Lin, M.-R. Survey
of briarane-type diterpenoids-Part III. Heterocycles 2008, 75, 2627–2648.
Elastatinal was used as a positive control in anti-inflammatory activity testing. This compound
displayed inhibitory effects on elastase release by human neutrophils (IC50 = 31.0 M).
Bayer, F.M. Key to the genera of octocorallia exclusive of Pennatulacea (Coelenterata: anthozoa),
with diagnoses of new taxa. Proc. Biol. Soc. Wash. 1981, 94, 902–947.
Benayahu, Y.; Jeng, M.-S.; Perkol-Finkel, S.; Dai, C.-F. Soft corals (Octocorallia: Alcyonacea)
from southern Taiwan. II. Species diversity and distribution patterns. Zool. Stud. 2004, 43, 548–560.
Fabricius, K.; Alderslade, P. Soft Corals and Sea Fans—A Comprehensive Guide to the Tropical
Shallow-Water Genera of the Central-West Pacific, the Indian Ocean and the Red Sea, 1st ed.;
Australian Institute of Marine Science: Queensland, Australia, 2001; pp. 55, 154–157.
Hwang, T.-L.; Li, G.-L.; Lan, Y.-H.; Chia, Y.-C.; Hsieh, P.-W.; Wu, Y.-H.; Wu, Y.-C. Potent
inhibitors of superoxide anion production in activated human neutrophils by isopedicin, a
bioactive component of the Chinese medicinal herb Fissistigma oldhamii. Free Radic. Biol. Med.
2009, 46, 520–528.
Hwang, T.-L.; Su, Y.-C.; Chang, H.-L.; Leu, Y.-L.; Chung, P.-J.; Kuo, L.-M.; Chang, Y.-J.
Suppression of superoxide anion and elastase release by C18 unsaturated fatty acids in human
neutrophils. J. Lipid Res. 2009, 50, 1395–1408.
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6.
7.
8.
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