Brianodins A-D, briarane-type diterpenoids from soft coral Pachyclavularia sp

Article abstract of DOI:10.1021/np070684p

Four new briarane-type diterpenoids, brianodins A-D (1-4), were isolated from a soft coral, Pachyclavularia sp., and the structures and relative stereochemistry of 1-4 were elucidated on the basis of spectroscopic data. The absolute configurations of 3 and 4 were assigned by the MTPA method. Brianodin A (1) showed a modest cytotoxicity.

Full text of DOI:10.1021/np070684p

J. Nat. Prod. 2008, 71, 633–636
633
Brianodins A-D, Briarane-Type Diterpenoids from Soft Coral PachyclaWularia sp.
Haruaki Ishiyama,† Taro Okubo,† Tetsuro Yasuda,† Yohei Takahashi,† Kazuo Iguchi,‡ and Jun’ichi Kobayashi*,†
Graduate School of Pharmaceutical Sciences, Hokkaido UniVersity, Sapporo 060-0812, Japan, and School of Life Sciences, Tokyo UniVersity of
Pharmacy and Life Sciences, Horinouchi, Hachioji, Tokyo 192-0392, Japan
ReceiVed NoVember 29, 2007
Four new briarane-type diterpenoids, brianodins A-D (1-4), were isolated from a soft coral, PachyclaVularia sp., and
the structures and relative stereochemistry of 1-4 were elucidated on the basis of spectroscopic data. The absolute
configurations of 3 and 4 were assigned by the MTPA method. Brianodin A (1) showed a modest cytotoxicity.
A characteristic feature of briarane-type diterpenoids is the
presence of a highly substituted bicyclo[8.4.0]tetradecane skeleton,
and most briarane diterpenoids possess a γ-lactone moiety.1 More
than 300 briarane diterpenoids have been isolated from soft corals
so far,2 and some of them show interesting biological properties
such as cytotoxic,3 anti-inflammatory,4–6 antiviral,6,7 insecticidal,8
immunomodulation,9 and multidrug resistance reversing activities.10
Chemical modifications of natural products such as taxane
diterpenoids11 have led to many unprecedented compounds useful
for studies of structure–activity relationships. In order to obtain
briarane diterpenoids for such a study, the terpenoid fractions of a
soft coral PachyclaVularia sp. were purified. As a result, four new
briarane-type diterpenoids, brianodins A-D (1-4), were isolated
together with 10 known briarane diterpenoids. Herein, we describe
the isolation and structure elucidation of 1-4.
(Figure 1). The presence of an 8,17-epoxide was indicated by the
molecular formula and 13C NMR chemical shifts of C-8 (δC 71.5)
and C-17 (δC 64.8). Geometry of the trisubstituted olefin at C-5
and C-6 was assigned as Z from NOESY correlations of H3-16 to
H-6.
The relative stereochemistry of 1 was elucidated by 1H coupling
constants and NOESY correlations. NOESY correlations of H3-20
to H-9 (δH 5.96, d, J ) 3.9 Hz), H-12, and H3-15, H-9 to H3-18,
and H3-15 to H-3 indicated that H-3, H-12, Me-15, Me-18, and
Me-20 had ꢀ-orientations and H-9 possessed an R-orientation.
NOESY correlations of H-2 (δH 3.31, s) to H-10 and H3-16, H3-16
to H-4a and H-6, and H-4b to H-7 suggested that H-2, H-10, and
8,17-epoxide had R-orientations and H-7 and H-9 possessed
ꢀ-orientations (Figure 2). Thus, the relative stereochemistry of
brianodin A was elucidated to be 1.
Brianodin B (2) was revealed to have the molecular formula
C28H38O14 by HRFABMS (m/z 599.2336 [M + H]+, ∆ -0.3 mmu).
The IR spectrum of 2 suggested the presence of an ester (1740
1
cm-1) functionality. From the H and 13C NMR analyses, 2 was
indicated to possess four acetoxy groups, a γ-lactone moiety [δH
2.10 (3H, s), 2.15 (3H, s), 2.15 (3H, s), 2.21 (3H, s), δC 169.9,
170.9, 171.3, 172.7, 176.4] and two olefins [δH 5.55 (1H, d, J )
4.5 Hz), 5.68 (1H, m), 5.75 (1H, br d, J ) 10.0 Hz), δC 121.1,
126.5, 139.4, 141.7] (Tables 1 and 2). The gross structure of 2 was
elucidated from 1H-1H COSY and HMBC correlations (Figure 3).
1
The relative stereochemistry of 2 was assigned by H coupling
Results and Discussion
constants and NOESY correlations. NOESY correlations of H3-20
to H3-15, H-12 (δH 5.04, d, J ) 3.3 Hz) and H-9 (δH 6.07, d, J )
4.8 Hz) indicated that H-12, Me-15, and Me-20 had ꢀ-orientations
and H-9 possessed an R-orientation. NOESY correlations of H-2
(δH 4.66, br s) to H-10 (δH 2.96, d, J ) 4.8 Hz) and H3-16, H3-16
to H-4 and H-6, and H-3 to H-7 suggested that H-2, H-4, and H-10
were R-orientated and H-3, H-7, and H-9 were ꢀ-orientated (Figure
4). The relative configuration at C-8 and C-17 was elucidated by
comparison of 13C NMR chemical shifts of brianodin B (2) with
those of violide J,16 whose structure was determined by X-ray
analysis. Thus, the relative stereochemistry of brianodin B was
elucidated to be 2.
The soft coral PachyclaVularia sp. (SC-114) collected in Oki-
nawa was extracted with MeOH, and the extract was partitioned
between EtOAc and water. The EtOAc-soluble materials were
subjected to passage over a silica gel column (CHCl3/MeOH,
95:5, and then n-hexane/EtOAc, 1:3) followed by C18 HPLC
(MeOH/H2O, 40:60 f 70:30) to afford brianodins A-D (1-4) (1,
0.0032%, wet wt; 2, 0.0006%; 3, 0.0007%; 4, 0.0013%) together
with 10 known briarane-type diterpenoids, briarlides A,12 G,12 H,12
and J13 and violides B,14 G,15 J,16 M,16 O,17 and P.17
Brianodin A (1) was obtained as a colorless solid, and the
molecular formula, C26H34O11, was established by HRFABMS (m/z
523.2178 [M + H]+, ∆ -0.1 mmu). The IR spectrum of 1 implied
The molecular formula, C26H36O13, of brianodin C (3) was
1
the presence of an ester (1740 cm-1) functionality. The H NMR
established by HRFABMS (m/z 557.2247 [M + H]+, ∆ +1.3 mmu).
spectrum of 1 revealed signals due to three acetyl methyls (δH 2.09,
2.14, and 2.21), an olefinic methyl (δH 1.94), and three tertiary
methyls (δH 1.08, 1.24, and 1.72), and the 13C NMR spectrum of
1 disclosed the presence of four carbonyl carbons (δC 168.4, 168.8,
169.3, and 170.1) and four olefinic carbons (δC 120.7, 121.1, 138.9,
and 141.5) (Tables 1 and 2). The gross structure of 1 was elucidated
by analysis of 2D NMR data (1H-1H COSY, HMQC, and HMBC)
The IR spectrum of 3 indicated the presence of ester (1730 cm-1
)
and γ-lactone (1650 cm-1) functionalities. The 1H NMR spectrum
of 3 was similar to that of brianodin B (2), except that H-12 (δH
3.71, d, J ) 6.2 Hz) was shifted upfield by 1.33 ppm (Table 1) as
compared with that of 2, indicating that an acetyl group at C-12 in
2 was absent for 3. The relative stereochemistry of 3 was elucidated
1
by H coupling constants and NOESY correlations. The relative
configuration at C-8 and C-17 was elucidated by comparison of
13C NMR chemical shifts of brianodin C (3) with those of violide
J.16 The absolute configuration of 3 was elucidated by a modified
Mosher’s method18 for the 2-methoxy-2-trifluoromethylphenylacetic
* To whom correspondence should be addressed. Tel: +81-11-706-3239.
Fax: +81-11-706-4989. E-mail: jkobay@pharm.hokudai.ac.jp.
† Hokkaido University.
‡ Tokyo University of Pharmacy and Life Sciences.
10.1021/np070684p CCC: $40.75
2008 American Chemical Society and American Society of Pharmacognosy
Published on Web 03/18/2008

634 Journal of Natural Products, 2008, Vol. 71, No. 4
Table 1. 1H NMR Data of Brianodins A-D (1-4) (J in Hz)
Ishiyama et al.
position
1a
2a
3b
4b
2
3.31 br s
4.66 br s
4.57 br s
3.26 br s
3
5.59 dd (12.2, 5.8)
2.11 m
5.07 d (11.2)
4.86 br dd (11.0, 0.8)
4.90 d (10.6)
5.17 d (11.3)
5.61 dd (12.2, 5.7)
1.88 m
4a
4b
6
7
9
10
12
13
14
15
16
18
20
MeCO
3.04 br dd (13.8, 3.9)
5.46 br d (9.3)
5.70 d (9.6)
5.96 d (3.9)c
2.52 d (3.9)
4.79 d (5.9)
5.95 dd (10.3, 5,9)c
6.05 d (10.3)
1.08 s
2.92 br dd (13.8, 5.3)
5.45 br d (9.6)
5.81 d (9.8)
6.07 d (4.3)
2.67 d (4.3)
3.58 d (6.0)
5.65 br dd (10.3, 6.0)
5.78 d (10.3)
0.92 s
1.78 br s
1.25 s
1.27 s
1.85 (s), 2.00 (s)
5.75 br d (10.0)
5.93 d (10.0)
6.07 d (4.8)
2.96 d (4.8)
5.04 d (3.3)
5.68 m
5.55 d (4.5)
1.29 s
2.13 br d (1.6)
1.45 s
5.72 br d (10.0)
6.04 d (9.9)
6.20 d (4.7)
3.01 d (4.7)
3.71 d (6.2)
5.79 dd (10.4, 6.3)
5.56 d (10.6)
1.32 s
1.94 s
1.72 s
1.24 s
2.17 br d (1.1)
1.41 s
1.43 s
1.49 s
2.09 (s), 2.14 (s), 2.21 (s)
2.10 (s), 2.15 (s), 2.15 (s), 2.21 (s)
2.14, 2.18, 2.19
a In CDCl3. b In CD3OD. c Overlapping with other signals in the same column.
Table 2. 13C NMR Data of Brianodins A-D (1-4)
position
1a
2a
3b
4b
1
2
3
4
5
6
7
8
48.0
77.7
71.7
33.9
138.9
120.7
74.0
71.5
65.0
44.1
72.0
47.0
78.4
70.8
77.1
139.4
126.5
79.3d
79.3d
65.6
39.6
75.8
72.2
121.1
141.7
16.8
25.9
80.2
15.6
176.4
23.6
49.0
79.8
72.8
80.5
141.8
128.2
80.1
81.2
68.4
40.8
77.1
49.9
79.6
75.0
35.6
139.8
124.9c
81.8
81.7d
68.8
9
10
11
12
13
14
15
16
17
18
19
20
MeCO
41.4
77.0
73.0
72.3
73.2
121.1
141.5
13.4
27.4
64.8
9.5
170.1
21.0
20.6, 20.8,
20.8
126.4
140.9
17.1
26.9
81.7
16.8
179.4
23.8
21.5, 21.8,
23.1
124.6c
142.7
15.8
35.6
81.7d
17.0
Figure 2. Selected NOESY correlations for brianodin A (1).
179.6
23.6
23.1, 22.0
21.0, 21.2,
21.4, 22.3
MeCO
168.4, 168.8, 169.9, 170.9,
169.3 171.3, 172.7
173.1, 173.1, 173.0, 173.5
173.4
a In CDCl3. b In CD3OD. c Data interchangeable. d Overlapping with
other signals in the same column.
Figure 3. Selected 2D NMR correlations for brianodin B (2).
Brianodin D (4) had the molecular formula C24H34O11 by
HRFABMS (m/z 499.2187 [M + H]+, ∆ +0.6 mmu). The IR
spectrum of 4 suggested the presence of an ester (1730 cm-1
)
1
functionality. The H NMR spectrum of 4 showed signals due to
two acetyl methyls (δH 1.85, 2.00), an olefinic methyl (δH 1.78),
and three tertiary methyls (δH 0.92, 1.25, and 1.27). The 13C NMR
spectrum of 4 indicated the presence of three carbonyl carbons (δC
173.0, 173.5, and 179.6) and four olefinic carbons (δC 124.6, 124.9,
139.8, and 142.7) (Table 2). The gross structure of 4 was elucidated
from 1H-1H COSY and HMBC correlations (Figure 6). The relative
stereochemistry of 4 was elucidated by 1H coupling constants and
NOESY correlations. NOESY correlations from H3-20 to H3-15,
H-12 (δH 3.58, d, J ) 6.0 Hz) and H-9 (δH 6.07, d, J ) 4.3 Hz)
indicated ꢀ-orientations for H-12, Me-15, and Me-20 and an
R-orientation for H-9. NOESY correlations of H-2 (δH 3.26, s) to
Figure 1. Selected 2D NMR correlations for brianodin A (1).
acid (MTPA) esters at C-12 of 3, due to steric hindrance at C-2.
The values of ∆δ [δ(S-MTPA ester) - δ(R-MTPA ester)] for H-2,
H-3, H-4, H-13, and H-14 were positive, while the values of ∆δ
for H-6, H-7, H-9, and H-10 were negative, suggesting that the
absolute configuration at C-12 was R. Thus, the absolute config-
uration of 3 was assigned as shown in Figure 5.

Briarane-Type Diterpenoids from PachyclaVularia sp.
Journal of Natural Products, 2008, Vol. 71, No. 4 635
Figure 4. Selected NOESY correlations for brianodin B (2).
Figure 7. Selected NOESY correlations for brianodin D (4).
Figure 5. ∆δ values [∆δ (in ppm) ) δS - δR] obtained for (S)-
and (R)-MTPA esters at C-12 of brianodin C (3).
Figure 8. ∆δ values [∆δ (in ppm) ) δS - δR] obtained for (S)-
and (R)-MTPA esters at C-12 of brianodin D (4).
not show such activity (IC50, >10 µg/mL). Chemical modifications
of briarane diterpenoids and SAR studies5 are currently underway.
Experimental Section
General Experimental Procedures. Optical rotations were recorded
on a JASCO DIP-1000 polarimeter. IR spectra were taken on a JASCO
FT/IR-5300 IR spectrometer. 1H and 13C NMR spectra were recorded
on a Bruker AMX-600 NMR spectrometer and a JEOL ECA500 NMR
spectorometer. The 7.26 and 77.0 ppm resonances of residual CDCl3
were used as internal references for 1H and 13C NMR spectra,
respectively, while the 3.35 and 49.8 ppm resonances of residual
MeOH-d4 were used as internal references for 1H and 13C NMR spectra,
respectively. FAB mass spectra were obtained on a JEOL HX110
spectrometer. ESI mass spectra were obtained on a JEOL JMS-T100LP
spectrometer.
Figure 6. Selected 2D NMR correlations for brianodin D (4).
H-10 and H3-16, H3-16 to H-6, and H-4a to H-3 and H-7 suggested
that H-2 and H-10 were R-orientated and H-3, H-7 and H-9 were
ꢀ-orientated (Figure 7). The relative configuration at C-8 and C-17
was elucidated by comparison of 13C NMR chemical shifts of
brianodin D (4) with those of violide J.16 Thus, the relative
stereochemistry of brianodin D was elucidated to be 4. The absolute
stereochemistry of 4 was assigned as follows. Compound 4 was
converted into its (S)- and (R)-MTPA esters of a hydroxy group at
C-12, due to steric hindrance at C-2. The ∆δ [δ(S-MTPA ester) -
Animal Material. The soft coral PachyclaVularia sp. (SC-114) was
collected from Okinawa, Japan, and kept frozen until used. A voucher
specimen was deposited at the Graduate School of Pharmaceutical
Sciences, Hokkaido University.
Extraction and Isolation. The soft coral (0.8 kg, wet weight) was
extracted with methanol (1.1 L × 1 and 0.8 L × 1). The extract (44.3
g) was partitioned between EtOAc (500 mL × 3) and water (500 mL).
A part (1.0 g) of the EtOAc-soluble materials (12.6 g) was subjected
to passage over a silica gel column (CHCl3/MeOH, 95:5) to give
fractions I (59.9 mg) and II (56.8 mg). Fraction I was separated by
silica gel column chromatography (n-hexane/EtOAc, 1:3) to afford
brianodin A (1, 26.0 mg, 0.0032%, wet wt). Fraction II in the first
silica gel column was chromatographed on C18 HPLC (Luna 5u C18(2),
Phenomenax Co., Ltd., 10 × 300 mm; flow rate, 2.5 mL/min; eluent,
MeOH/H2O, 40:60 to 70:30; UV detection at 220 nm) to yield
brianodins B (2, tR 38.0 min, 4.4 mg, 0.0006%), C (3, tR 28.0 min, 5.7
mg, 0.0007%), and D (4, tR 25.5 min, 10.4 mg, 0.0013%).
1
δ(R-MTPA ester)] values obtained from the H NMR spectra of
the MTPA esters suggested that the absolute configuration at C-12
in 4 was R (Figure 8).
In this study, four new briarane diterpenoids, brianodins A-D
(1-4), were isolated from a soft coral PachyclaVularia sp., in which
compounds 2-4 are rare examples16 of briarane diterpenoids with
a 1,2-diol moiety at C-8 and C-17. The absolute configurations for
brianodins C (3) and D (4) were assigned, although absolute
configurations of many briarane diterpenoids remain to be defined.
Brianodin A (1) showed cytotoxicity19 against L1210 murine
leukemia (IC50, 1.8 µg/mL) and KB human epidermoid carcinoma
cells (IC50, 4.3 µg/mL) in Vitro, while brianodins B-D (2-4) did
25
Brianodin A (1): colorless solid; mp 255–258 °C; [R]D -129 (c
1
1.0, CHCl3); IR (NaCl) νmax 3550, 1780, and 1740 cm-1; H and 13C
NMR (Tables 1 and 2); FABMS (3-nitrobenzylalcohol) m/z 523 [M +
H]+; HRFABMS m/z 523.2178 [M + H]+, calcd for C26H35O11,
523.2179.

636 Journal of Natural Products, 2008, Vol. 71, No. 4
Ishiyama et al.
Brianodin B (2): colorless solid; mp 170–172 °C; [R]D25 -6 (c 1.0,
CHCl3); IR (NaCl) νmax 3270, and 1740 cm-1; 1H and 13C NMR (Tables
1 and 2); FABMS (glycerol) m/z 599 [M + H]+; HRFABMS m/z
599.2336 [M + H]+, calcd for C28H39O14, 599.2339.
was partly supported by a Grant-in-Aid from the Uehara Memorial
Foundation and a Grant-in-Aid for Scientific Research from the Ministry
of Education, Culture, Sports, Science and Technology of Japan.
25
References and Notes
Brianodin C (3): colorless solid; mp 286–288 °C; [R]D +20
1
(c 0.5, CHCl3); IR (NaCl) νmax 3420, 1730, and 1650 cm-1; H and
(1) Burks, J. E.; van der Helm, D.; Chang, C. Y.; Ciereszko, L. S. Acta
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M. H. G.; Northcote, P. T.; Prinsep, M. R. Nat. Prod. Rep. 2007, 24,
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13C NMR (Tables 1 and 2); FABMS (glycerol) m/z 557 [M + H]+;
HRFABMS m/z 557.2247 [M + H]+, calcd for C26H37O13, 557.2234.
25
Brianodin D (4): colorless solid; mp 181–183 °C; [R]D -79
(c 0.5, CHCl3); IR (NaCl) νmax 3270, and 1730 cm-1; 1H and 13C NMR
(Tables 1 and 2); FABMS (glycerol) m/z 499 [M + H]+; HRFABMS
m/z 499.2187 [M + H]+, calcd for C24H35O11, 499.2181.
(S)- and (R)-MTPA Esters of Brianodin C (3). To a solution of 3
(0.3 mg) in pyridine (50 µL) were added N,N-dimethylaminopyridine
(50 µg) and (R)-MTPACl (6 µL). The mixture was allowed to stand at
room temperature for 30 min. After addition of N,N-dimethyl-1,3-
propanedioamine (6 µL), the residue was concentrated and applied to
a silica gel column to give the (S)-MTPA ester of 3. The (R)-MTPA
ester of 3 was prepared according to the same procedure as described
above.
1
(S)-MTPA ester of 3: H NMR (CD3OD) δ 6.13 (1H, H-9), 5.93
(1H, H-7), 5.90 (1H, H-13), 5.77 (1H, H-14), 5.43 (1H, H-6), 5.21
(1H, H-12), 5.09 (1H, H-4), 4.79 (1H, H-3), 4.62 (1H, H-2), 2.85 (1H,
H-10); ESIMS m/z 795 [M + Na]+; HRESIMS m/z 795.2445 [M +
Na]+, calcd for C36H43F3NaO15, 795.2452.
1
(R)-MTPA ester of 3: H NMR (CD3OD) δ 6.17 (1H, H-9), 5.96
(1H, H-7), 5.87 (1H, H-13), 5.72 (1H, H-14), 5.49 (1H, H-6), 5.13
(1H, H-12), 5.05 (1H, H-4), 4.78 (1H, H-3), 4.41 (1H, H-2), 2.87 (1H,
H-10); ESIMS m/z 795 [M + Na]+; HRESIMS m/z 795.2431 [M +
Na]+, calcd for C36H43F3NaO15, 795.2452.
(S)- and (R)-MTPA Esters of Brianodin D (4). The (S)- and (R)-
MTPA esters of 4 were prepared according to the same procedure as
described above.
1
(S)-MTPA ester of 4: H NMR (CD3OD) δ 6.20 (1H, H-14), 6.15
(1H, H-9), 5.92 (1H, H-13), 5.87 (1H, H-7), 5.69 (1H, H-3), 5.35 (1H,
H-6), 5.27 (1H, H-12), 3.02 (1H, H-4), 2.71 (1H, H-10); ESIMS m/z
737 [M + Na]+; HRESIMS m/z 737.2388 [M + Na]+, calcd for
C34H41F3NaO13, 737.2397.
1
(R)-MTPA ester of 4: H NMR (CD3OD) δ 6.22 (1H, H-9), 6.13
(1H, H-14), 5.92 (1H, H-7), 5.88 (1H, H-13), 5.67 (1H, H-3), 5.43
(1H, H-6), 5.22 (1H, H-12), 3.01 (1H, H-4), 2.76 (1H, H-10); ESIMS
m/z 737 [M + Na]+; HRESIMS m/z 737.2369 [M + Na]+, calcd for
C34H41F3NaO13, 737.2397.
(19) Komatsu, K.; Tsuda, M.; Shiro, M.; Tanaka, Y.; Mikami, Y.;
Kobayashi, J. Bioorg. Med. Chem. 2004, 12, 5545–5551.
Acknowledgment. We thank S. Oka, Center for Instrumental
Analysis, Hokkaido University, for FABMS and ESIMS measurements,
and Z. Nagahama for his help with the soft coral collection. This work
NP070684P