Squalene-derived triterpene polyethers from the red alga Laurencia omaezakiana

Article abstract of DOI:10.1002/hlca.200890137

In our continuing search on halogenated metabolites from species of the red algal genus Laurencia, a novel squalene-derived triterpene polyether, named omaezakianol (2), was isolated from Laurencia omaezakiana Masuda along with 15,16-anhydrothyrsiferol (3). Their structures were determined by spectral and chemical methods.

Full text of DOI:10.1002/hlca.200890137

Helvetica Chimica Acta – Vol. 91 (2008)
1261
Squalene-Derived Triterpene Polyethers from the Red Alga
Laurencia omaezakiana
by Yoshihide Matsuoa)1), Minoru Suzukia)2), Michio Masudab), Toshiyuki Iwaic), and
Yoshiki Morimoto*c)
a) Division of Material Science, Graduate School of Environmental Earth Science, Hokkaido University,
Kita-ku, Sapporo 060-0810, Japan
b) Division of Biological Sciences, Graduate School of Science, Hokkaido University, Kita-ku, Sapporo
060-0810, Japan
c) Department of Chemistry, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka
558-8585, Japan
(fax: þ 81-6-6605-2522; e-mail: morimoto@sci.osaka-cu.ac.jp)
In our continuing search on halogenated metabolites from species of the red algal genus Laurencia, a
novel squalene-derived triterpene polyether, named omaezakianol (2), was isolated from Laurencia
omaezakiana Masuda along with 15,16-anhydrothyrsiferol (3). Their structures were determined by
spectral and chemical methods.
Introduction. – Species of the red algal genus Laurencia (Rhodomelaceae,
Ceramiales) are known to be prolific sources of a variety of halogenated secondary
metabolites, particularly sesquiterpenoids, diterpenoids, triterpenoids, and C15 aceto-
genins [1][2]. Some of these halogenated compounds showed antimicrobial, insecti-
cidal, cytotoxic, and feeding-deterrent activities.
In connection with our chemotaxonomic studies on Laurencia species from
Japanese waters, we previously reported the isolation and structure elucidation of a
pentacyclic triterpene alcohol, enshuol (1), which has a 2,8-dioxabicyclo[5.4.0]unde-
cane molecular skeleton, from Laurencia omaezakiana Masuda (ꢀEnshu-sozoꢁ in
Japanese), collected at Omaezaki, Shizuoka Prefecture [3]. Although the absolute
configurations at C(3), C(6), and C(7) of the 2,8-dioxabicyclo[5.4.0]undecane moiety
were determined, the configurations at C(10) to C(22) remained unsettled3). Recently,
the structure of enshuol, including the absolute configuration, was established as
formula 1 by the asymmetric total synthesis [4]. Further investigation of this species
collected at Enoshima, Kanagawa Prefecture, led to the isolation of a novel tetracyclic
polyether triterpene alcohol 2, which we named omaezakianol3), along with 15,16-
anhydrothyrsiferol3) (3). Herein, we describe the isolation and structure determination
of these metabolites.
1
)
)
Present address: R&D Planning Division, Suntory Limited, Mishima-gun, Osaka 618-8503, Japan.
Present address: Institute for Tropical Biology and Conservation, University Malaysia Sabah,
Locked Bag 2073, 88999 Kota Kinabalu, Sabah, Malaysia.
2
3
)
Trivial atom numbering; for systematic names of 2, 3, and 5 – 7, see Exper. Part.
ꢂ 2008 Verlag Helvetica Chimica Acta AG, Zürich

1262
Helvetica Chimica Acta – Vol. 91 (2008)
Results and Discussion. – A combination of column and thin-layer chromatography
of the MeOH extract from the sample collected at Enoshima, Kanagawa Prefecture,
gave omaezakianol (2) and 15,16-anhydrothyrsiferol (3) in 15 and 3% yield,
respectively, based on the extract.
Omaezakianol (2) was analyzed for C30H52O6 by its HR-FAB-MS. Its IR spectrum
showed absorption at ˜nmax 3455 cmÀ1 due to OH group(s).
1
1
The H-and 13C-NMR data (Table), together with the H,1H-COSY, HOHAHA,
and HMBC data (Fig.) and the FD-and FABM- S led to the assignment of a planar
formula 2, consisting of four tetrahydrofuran units, for omaezakianol.
The 1H-NMR spectrum showed the presence of eight tertiary Me groups, five CH H-atoms adjacent
1
to an O-atom, and an olefinic H-atom. As shown in the Figure, the H,1H-COSY and HOHAHA data
indicated the presence of a 4-methylpent-3-enyl group, three ÀCH2ÀCH2ÀCHÀOÀ moieties, and a
ÀOÀCHÀCH2ÀCH2ÀCHÀOÀ moiety. Since 2 has five degrees of unsaturation, 2 must be composed
of four O-containing rings. The chemical shift values (d(C) 84 – 86) of the corresponding ring C-atoms in
the 13C-NMR spectrum suggested that these O-containing rings are tetrahydrofuran moieties. This was
confirmed by the mass spectra (FD-and FAB-MS), which showed fragment ions at m/z 143, 227, and 211
(Fig.). The same fragment ions were also observed in the MS of a degradation product 4 derived from
enshuol (1) by treatment with zinc and AcOH in MeOH [3].

Helvetica Chimica Acta – Vol. 91 (2008)
1263
Table. 13C- (DEPT) and 1H-NMR Data (100 and 400 MHz, resp.; CDCl3) of Omaezakianol3) (2).
1
Assignments were corroborated by H,1H-COSY, HSQC, and HMBC experiments. d in ppm, J in Hz.
d(H)
d(C)
d(H)
d(C)
Me(1)
C(2)
1.66 (s)
–
25.7 CH2(16)
131.3 CH2(17)
1.70 – 1.95 (m), 1.95 – 2.18 (m) 35.8
1.38 – 1.60 (m), 1.70 – 1.95 (m) 28.6
HÀC(3)
CH2(4)
CH2(5)
C(6)
5.04 – 5.12 (m)
1.95 – 2.18 (m)
1.25 – 1.36 (m), 1.38 – 1.60 (m)
–
124.8 HÀC(18) 4.01 (dd, J ¼ 10.3, 5.9)
84.1
85.5
22.4 C(19)
–
38.5 CH2(20)
73.1 CH2(21)
1.38 – 1.60 (m), 1.95 – 2.18 (m) 31.0
1.70 – 1.95 (m), 1.95 – 2.18 (m) 26.5
HÀC(7)
CH2(8)
CH2(9)
C(10)
3.87 (dd, J ¼ 7.1, 7.1)
1.70 – 1.95 (m), 1.95 – 2.18 (m)
1.38 – 1.60 (m), 1.95 – 2.18 (m)
–
84.6 HÀC(22) 3.82 (dd, J ¼ 7.3, 5.8)
85.5
71.6
25.2
17.6
24.7
24.7
21.0
25.0
28.1
26.2 C(23)
–
32.0 Me(24)
84.8 Me(25)
85.0 Me(26)
27.9 Me(27)
26.5 Me(28)
83.7 Me(29)
84.2 Me(30)
1.05 (s)
1.59 (s)
1.21 (s)
1.14 (s)
1.15 (s)
1.13 (s)
1.22 (s)
HÀC(11) 3.82 (dd, J ¼ 9.5, 6.1)
CH2(12)
CH2(13)
1.38 – 1.60 (m), 1.70 – 1.95 (m)
1.70 – 1.95 (m)
HÀC(14) 3.75 (dd, J ¼ 7.3, 7.3)
C(15)
–
Figure. a) Selected fragment ions (m/z) in the FD-MS and FAB-MS and correlations from COSY and
HOHAHA; b) long-range correlations from HMBC
Confirmation of the planar structure and determination of the relative config-
uration of 2 were made as follows. Treatment of omaezakianol (2) with 3-
chloroperbenzoic acid and Na2HPO4 in CH2Cl2 followed by treatment with a trace of
p-toluenesulfonic acid gave two isomeric pentacyclic compounds, 5 and 6, having the
molecular formula C30H52O7, in 41 and 44% yield, respectively. Compound 5 showed 15
C-signals in the 13C-NMR spectrum, while the isomeric compound 6 showed more than
15 C-signals, thus indicating that 5 and 6 have a symmetrical and unsymmetrical
structure, respectively. Fortunately, the symmetrical compound 5 was found to be
identical with a synthetic meso compound [5], the structure of which was incorrectly

1264
Helvetica Chimica Acta – Vol. 91 (2008)
proposed for glabrescol that has been isolated from the branches and wood of Spathelia
glabrescens [6], by comparison of the spectral properties. The weak optical rotation of
5 must be ascribed to a small amount of concomitant impurity. Hence, compound 6 is an
epimer at C(3) of 5. Thus omaezakianol is represented by formula 2 with a
(6R*,7S*,10R*,11S*,14R*,15S*,18R*,19S*,22R*) configuration. The asymmetric total
synthesis of (þ)-omaezakianol is in progress.
1
Compound 3 having a molecular formula C30H51BrO6, revealed in its H-and
13C-NMR spectra signals very similar to those of 15,16-anhydrothyrsiferyl diactate (7),
which has previously been isolated from Laurencia saitoi Perestenko (as Laurencia
obtusa (Hudson) Lamouroux) [7][8]. Extensive spectral analysis by 2D-NMR
(1H,1H-COSY, HOHAHA, HSQC, HMBC, and NOESY data) strongly suggested 3 to
be 15,16-anhydrothyrsiferol (thyrsiferol ¼ (a2S,2R,5R)-a2-{(3S)-3-{(2R,4aR,6R,8aS)-6-
[(2S,5R)-5-bromotetrahydro-2,6,6-trimethyl-2H-pyran-2-yl]octahydro-8a-methylpyra-
no[3,2-b]pyran-2-yl}-3-hydroxybutyl}tetrahydro-a5,a5,2-trimethylfuran-2,5-dimetha-
nol). Treatment of 3 with Ac2O and N,N-dimethylpyridin-4-amine (DMAP) in CH2Cl2
gave the corresponding diacetate, which was identical with 15,16-anhydrothyrsiferyl
diactate (7) in all respects.
To the best of our knowledge, 15,16-anhydrothyrsiferol (3) has first been found in
the present study. Closely related triterpenoids have previously been isolated from
other Laurencia species: 15,28-anhydrothyrsiferol (as dehydrothyrsiferol) from
Laurencia pinnatifida (Gmal. Lamour) [9] and 10-epi-15,28- and 10-epi-15,16-
anhydrothyrsiferol from Laurencia viridis sp. nov [10].
Omaezakianol (2) and 15,16-anhydrothyrsiferol (3) were also isolated from the
Omaezaki sample [3] in 7 and 3% yield, respectively; however, enshuol (1) was not
found in the Enoshima sample (see Introduction). Within the Japanese species of the
genus Laurencia [2], L. omaezakiana was found to produce only triterpenoids as
characteristic metabolites. The present study strongly suggests that L. omaezakiana
may include chemical races as in the case of Laurencia nipponica Ya m a da [11][12].
Experimental Part
General. Normal-phase high-performance liquid chromatography (HPLC): Shim-Pack Prep-Sil
(4.6 mm ꢀ 250 mm; Shimadzu). Column chromatography (CC): silica gel (Kieselgel 60, 70 – 230 mesh;
Merck). Prep. TLC: precoated silica gel plate (Kieselgel 60254S, 20 cm ꢀ 20 cm, Merck). Optical rotation:
Jasco-DIP-140 polarimeter; in CHCl3. IR Spectra: Jasco-A-102 spectrophotometer; ˜nmax in cmÀ1. 1H-and
13C-NMR Spectra: Jeol-JNM-FX-400 spectrometer (at 400 and 100 MHz, resp.); referencing to SiMe4 as
int. standard; d in ppm, J in Hz. Low-and high-resolution MS: Jeol-JMS-DX303 spectrometer for EI and
Jeol-JMS-HX110 spectrometer for FAB and FD; in m/z (rel. intensity).
Plant Material. A specimen of Laurencia omaezakiana Masuda was collected at Enoshima,
Kanagawa Prefecture, on 18th August, 1994. A voucher specimen was deposited with the Herbarium of
Graduate School of Science, Hokkaido University (SAP 062279).
Extraction and Isolation. Partially dried alga (22.7 g) was immersed in MeOH (300 ml). The MeOH
soln. was concentrated, and the residue partitioned between Et2O and H2O. The Et2O soln. was washed
with H2O, dried (Na2SO4), and concentrated to give a dark green oil (496 mg). This extract (292 mg) was
then fractionated by CC (SiO2, step gradient hexane/AcOEt). The fraction eluted with AcOEt was
further subjected to CC (CHCl3/MeOH 98 :2) followed by prep. TLC (toluene/AcOEt 7:3): 15,16-
anhydrothyrsiferol (3; 8.8 mg, 3.0% based on the extract). The CC fractions eluted with hexane/AcOEt
3 :1 and hexane/AcOEt 1:1 were further subjected to CC (step gradient toluene/AcOEt). The fraction

Helvetica Chimica Acta – Vol. 91 (2008)
1265
eluted with toluene/AcOEt 1:1 was then separated by prep. TLC (CHCl3/MeOH 98 :2): omaezakianol
(2; 43.8 mg, 15%).
Omaezakianol (¼ rel-(a5R,2R,2’S,2’’S,2’’’S,5S,5’R,5’’R,5’’’R)-Hexadecahydro-a5,a5’’’,a5’’’,2,2’’,2’’’-hexa-
methyl-a5-(4-methylpent-3-en-1-yl)-[2,2’:5’,2’’:5’’,2’’’-quaterfuran]-5,5’’’-dimethanol; 2). Colorless oil.
1
[a]2D0 ¼ þ15.8 (c ¼ 0.59, CHCl3). IR (neat): 3455, 1340, 1318, 1302, 1183, 1078, 955, 925, 901, 755. H-
and 13C-NMR: Table. FD-MS: 509 (100, [M þ H]þ), 365 (8, [M À C8H15O2]þ), 227 (16, [M À C17H29O3]þ),
211 (5, [M À C17H29O4]þ), 143 (10, [M À C22H37O4]þ). FAB-MS (pos.): 509 (100, [M þ H]þ), 491 (64,
[M À H2O]þ), 227 (84, [M À C17H29O3]þ), 211 (40, [M À C17H29O4]þ), 143 (83, [M À C22H37O4]þ). HR-
FAB-MS (pos.): 509.3831 ([M þ H]þ, C30H53O6þ ; calc. 509.3842).
15,16-Anhydrothyrsiferol (¼(a2S,2R,5R)-a2-{(2E)-3-{(2R,4aR,6R,8aS)-6-[(2S,5R)-5-Bromotetra-
hydro-2,6,6-trimethyl-2H-pyran-2-yl]octahydro-8a-methylpyrano[3,2-b]pyran-2-yl}but-2-en-1-yl}tetrahy-
dro-a5,a5,2-trimethylfuran-2,5-dimethanol; 3). Amorphous solid. [a]D22 ¼ þ13.1 (c ¼ 0.53, CHCl3). IR
1
(CHCl3): 3650, 3520, 1159, 1147, 1125, 1105, 1078, 1045, 978, 915. H-NMR: 1.13 (s, Me(24)); 1.16 (s,
Me(29)); 1.20 (s, Me(26)); 1.21 (br. s, Me(27), Me(30)); 1.27 (s, Me(25)); 1.40 (s, Me(1)); 1.66 (s,
Me(28)); 1.50 – 1.93 (m, CH2(5), CH2(8), CH2(9), CH2(12), HaÀC(13), HaÀC(20), CH2(21)); 2.10 – 2.16
(m, HaÀC(4), HbÀC(13), HaÀC(17), HbÀC(20)); 2.18 – 2.30 (m, HbÀC(4), HbÀC(17)); 3.08 (dd, J ¼
11.5, 2.2, HÀC(7)); 3.47 (dd, J ¼ 11.2, 6.4, HÀC(11)); 3.56 (dd, J ¼ 9.8, 2.9, HÀC(18)); 3.76 (dd, J ¼
10.0, 6.1, HÀC(22)); 3.89 (dd, J ¼ 12.2, 3.9, HÀC(3)); 4.24 (dd, J ¼ 8.8, 3.9, HÀC(14)); 5.56 (dd, J ¼
7.3, 6.8, HÀC(16)). 13C-NMR: 13.04 (Me(28)); 19.90 (Me(27)); 20.12 (Me(26)); 23.67 (Me(1),
Me(29)); 24.03 (Me(24)); 27.71 (Me(30)); 31.04 (Me(25)); 21.82 (CH2(9)); 23.01 (CH2(8)); 25.82
(CH2(13)); 26.57 (CH2(21)); 28.29 (CH2(4)); 30.43 (CH2(17)); 32.01 (CH2(20)); 37.09 (CH2(5)); 38.77
(CH2(12)); 59.05 (CH(3)); 75.20 (CH(14)); 76.72 (CH(18)); 78.38 (CH(11)); 86.63 (CH(7)); 87.60
(CH(22)); 122.3 (CH(16)); 70.48 (C(23)); 72.46 (C(10)); 74.43 (C(6)); 74.69 (C(2)); 85.83 (C(19)); 138.9
(C(15)). FD-MS: 589 and 587 (30 and 32, [M þ H]þ), 445 and 443 (15 and 17, [M À C8H15O2]þ), 207 and
205 (20 and 19, [M À C22H37O5]þ), 143 (29, [M À C22H36BrO4]þ). EI-MS: 588 and 586 (0.3 and 0.3, Mþ),
570 and 568 (0.5 and 0.5, [M À H2O]þ), 529 and 527 (0.2 and 0.2, [M À C3H7O]þ), 445 and 443 (0.5 and
0.4, [M À C8H15O2]þ), 291 and 289 (2.9 and 2.8, [M À C17H29O4]þ), 143 (100, [M À C22H36BrO4]þ). HR-
EI-MS: 586.2852 (Mþ, C30H5719BrOþ6 ; calc. 586.2869).
Transformation of 2 into 5 and 6. To a soln. of 2 (10 mg) in CH2Cl2 (2 ml) were added 3-
chloroperbenzoic acid (9 mg) and Na2HPO4 · 12 H2O (5 mg), and the mixture was stirred for 3 h at 0 –
208. Then a trace of p-toluenesulfonic acid was added, and the mixture was further stirred for 1 h. The
mixture was extracted with CHCl3, and the CHCl3 soln. was successively shaken with sat. Na2S2O3/
Na2CO3 soln. 1:2 and sat. brine, dried (Na2SO4), and concentrated. The resulting material (13.5 mg) was
subjected to HPLC (hexane/CHCl3/MeOH 625 :370 :5, flow rate 1 ml/min, RI detector: 5 (4.2 mg, 41%;
tR 26 min) and 6 (4.5 mg, 44%; tR 38 min).
rel-(2R,2’S,2’’S,2’’’S,2’’’’S,5S,5’R,5’’R,5’’’R,5’’’’R)-Eicosahydrooctamethyl-a5,a5,a5’’’’,a5’’’’,2,2’’’,2’’’’,5’-
[2,2’:5’,2’’:5’’,2’’’:5’’’,2’’’’-quinquefuran]-5,5’’’’-dimethanol (5): Colorless oil. [a]1D7 ¼ þ0.59 (c ¼ 1.00,
CHCl3). IR (neat): 3455, 1338, 1319, 1302, 1260, 1183, 1080, 998, 955, 923, 900, 803, 755. 1H-NMR:
1.06 (s, Me(1), Me(30)); 1.14 (s, Me(26), Me(29)); 1.15 (s, Me(27), Me(28)); 1.24 (s, Me(24), Me(25));
1.45 (ddd, J ¼ 12.1, 8.7, 5.9, HaÀC(5), HaÀC(20)); 1.52 – 1.66 (m, HaÀC(8), HaÀC(9), HaÀC(12),
HaÀC(13), HaÀC(16), HaÀC(17)); 1.79 – 1.94 (m, HaÀC(4), HbÀC(8), HbÀC(12), HbÀC(13),
HbÀC(17), HaÀC(21)); 2.03 – 2.13 (m, HbÀC(4), HbÀC(9), HbÀC(16), HbÀC(21)); 2.25 (ddd, J ¼
12.0, 9.3, 7.3, HbÀC(5), HbÀC(20)); 3.73 (br. dd, J ¼ 5.4, 5.4, HÀC(3), HÀC(22)); 3.84 (dd, J ¼ 7.8,
5.9, HÀC(11), HÀC(14)); 4.02 (dd, J ¼ 10.3, 5.4, HÀC(7), HÀC(18)). 13C-NMR: 22.57 (Me(27),
Me(28)); 25.02 (Me(26), Me(29)); 25.29 (Me(1), Me(30)); 28.09 (Me(24), Me(25)); 26.56 (CH2(4),
CH2(21)); 27.09 (CH2(12), CH2(13)); 29.08 (CH2(8), CH2(17)); 31.00 (CH2(5), CH2(20)); 34.64 (CH2(9),
CH2(16)); 84.24 (CH(7), CH(18)); 84.60 (CH(11), CH(14)); 85.68 (CH(3), CH(22)); 71.67 (C(2),
C(23)); 83.98 (C(10), C(15)); 85.61 (C(6), C(19)). FD-MS: 525 (100, [M þ H]þ), 381 (25), 227 (29), 143
(27). FAB-MS (pos.): 525 (27, [M þ H]þ), 507 (20, [M þ HÀH2O]þ), 391 (23), 227 (31, [M À
C17H29O3]þ), 154 (100), 143 (54, [M À C22H37O4]þ). HR-FAB-MS (pos.): 525.3782 ([M þ H]þ,
C30H53Oþ7 ; calc. 525.3792). Spectral data in agreement with those of the synthetic meso compound
with a Cs symmetry [5].

1266
Helvetica Chimica Acta – Vol. 91 (2008)
rel-(2R,2’S,2’’S,2’’’S,2’’’’S,5S,5’R,5’’R,5’’’R,5’’’’S)-Eicosahydrooctamethyl-a5,a5,a5’’’’,a5’’’’[2,2’:5’,2’’:5’’,
2’’’:5’’’,2’’’’-quinquefuran]-5,5’’’’-dimethanol (6): Amorphous solids. [a]2D6 ¼ þ8.55 (c ¼ 0.45, CHCl3). IR
(CHCl3): 3425, 1340, 1321, 1302, 1261, 1080, 1035, 958, 925, 901. 1H-NMR: 1.07 (s, 3 H); 1.11 (s, 3 H); 1.14
(br. s, 6 H); 1.15 (s, 3 H); 1.16 (s, 3 H); 1.20 (s, 3 H); 1.25 (s, 3 H); 1.42 – 1.50 (m, 1 H); 1.54 – 2.18 (m,
18 H); 2.24 – 2.40 (m, 1 H); 3.73 – 3.81 (m, 3 H); 3.85 (dd, J ¼ 7.8, 5.6, 1 H); 3.92 (dd, J ¼ 8.8, 6.1, 1 H);
4.03 (dd, J ¼ 9.8, 5.9, 1 H). 13C-NMR: 22.40, 22.79, 23.83, 24.05, 25.09, 25.29, 27.67, 28.07 (8 Me); 26.46,
26.59, 27.38, 27.49, 29.23, 30.87, 34.07, 34.16, 34.27, 34.82 (10 CH2); 83.96, 84.20, 84.27, 84.33, 85.72, 86.91
(6 CH); 70.63, 71.84, 84.66, 84.93, 85.72 (ꢀ2) (6 C). FAB-MS (pos.): 525 (44, [M þ H]þ), 507 (22, [M þ
H À H2O]þ), 307 (63), 289 (34), 227 (21, [M À C17H29O3]þ), 154 (100), 143 (37, [M À C22H37O4]þ). HR-
FAB-MS (pos.): 525.3786 ([M þ H]þ, C30H53O7þ ; calc. 525.3791).
Acetylation of 3 into 7. To a soln. of 3 (7.0 mg) in CH2Cl2 (500 ml) were added Ac2O (200 ml) and
DMAP (10.5 mg), and the mixture was stirred at r.t. for 3 days and then worked up as usual. The product
obtained was subjected to TLC (hexane/AcOEt 9 :1): (a2S,2R,5R)-a2-{(2E)-3-{(2R,4aR,6R,8aS)-6-
[(2S,5R)-5-bromotetrahydro-2,6,6-trimethyl-2H-pyran-2-yl]octahydro-8a-methylpyrano[3,2-b]pyran-2-
yl}but-2-en-1-yl}-tetrahydro-a5,a5,2-trimethylfuran-2,5-dimethanol diacetate (7; 2.2 mg). Amorphous
solid. [a]2D1 ¼ þ3.4 (c ¼ 0.22, CHCl3). HR-FAB-MS (pos.): 671.3149 ([M þ H]þ, C34H5769BrOþ8 ; calc.
671.3159). Further spectral data (1H-and 13C-NMR): in agreement with those of the authentic sample of
15,16-anhydrothyrsiferyl diacetate.
REFERENCES
[1] K. L. Erickson, in ꢀMarine Natural Products: Chemical and Biological Perspectivesꢁ, Ed. P. J.
Scheuer, Academic Press, New York, 1983, Vol. 5, p. 131.
[2] M. Suzuki, C. S. Vairappan, Curr. Top. Phytochem. 2005, 7, 1.
[3] Y. Matsuo, M. Suzuki, M. Masuda, Chem. Lett. 1995, 1043.
[4] Y. Morimoto, H. Yata, Y. Nishikawa, Angew. Chem., Int. Ed. 2007, 46, 6481.
[5] Y. Morimoto, T. Iwai, T. Kinoshita, J. Am. Chem. Soc. 2000, 122, 7124.
[6] W. W. Harding, P. A. Lewis, H. Jacobs, S. McLean, W. F. Reynolds, L.-L. Tay, J.-P. Yang, Tetrahedron
Lett. 1995, 36, 9137.
[7] T. Suzuki, S. Takeda, M. Suzuki, E. Kurosawa, A. Kato, Y. Imanaka, Chem. Lett. 1987, 361.
[8] M. Masuda, T. Abe, Jpn. J. Phycol. 1993, 41, 7.
´
´
[9] A. G. Gonzalez, J. M. Arteaga, J. J. Fernandez, J. D. Martꢃn, M. Norte, J. Z. Ruano, Tetrahedron
1984, 40, 2751.
´
[10] M. Norte, J. J. Fernandez, M. L. Souto, Tetrahedron 1997, 53, 4649.
[11] M. Masuda, T. Abe, S. Sato, T. Suzuki, M. Suzuki, J. Phycol. 1997, 33, 196.
[12] T. Abe, M. Masuda, T. Suzuki, M. Suzuki, Phycol. Res. 1999, 47, 87.
Received November 22, 2007