1162
Vol. 53, No. 9
1H-NMR (CDCl3) d ppm: 1.01 (3H, s), 1.25 (3H, s), 1.34 (3H, s), 1.43 (3H,
s), 1.47 (1H, m), 1.59 (3H, s), 1.60 (3H, s), 1.63 (1H, m), 1.76 (3H, s), 2.00
(3H, m), 2.08 (4H, m), 2.12 (2H, m), 2.18 (3H, br s), 2.20 (1H, m), 3.29 (2H,
d, Jꢀ7.3 Hz), 3.68 (1H, dd, Jꢀ3.4, 9.0 Hz), 4.76 (1H, s), 5.08 (1H, dt,
Jꢀ0.9, 6.8 Hz), 5.11 (1H, s), 5.14 (1H, dt, Jꢀ0.8, 6.8 Hz), 5.27 (1H, dt,
Jꢀ0.8, 7.3 Hz), 6.46 (1H, d, Jꢀ3.0 Hz), 6.50 (1H, d, Jꢀ3.0 Hz). 13C-NMR
(CDCl3) d ppm: 15.95, 16.00, 16.07, 16.15, 22.9, 26.0, 26.30, 26.39, 26.8,
27.6, 28.5, 30.0, 36.6, 39.51, 39.66, 80.3, 82.7, 106.6, 113.9, 115.4, 121.5,
123.7, 124.8, 125.6, 127.5, 134.1, 135.4, 138.5, 146.3, 148.9. EI-MS m/z:
470 (M)ꢁ.
Conversion to 7 Compound 6 (93 mg, 198 mmol) was treated with pyri-
dine (2 ml) and acetic anhydride (1.5 ml) at room temperature under N2 at-
mosphere. After standing over 12 h at r.t., the mixture was concentrated
under reduced pressure. The residue was purified with silica gel column
chromatography [hexane–acetone (3 : 1)] to provide diacetate (96 mg, 87%
yield). The obtained diacetate (45 mg, 82 mmol) was dissolved into MeOH
(3 ml), and then TsOH·H2O (8 mg) was added to the mixture at r.t. under
N2. After stirring for 2 h, triethylamine (1 drop) was added, and the mixture
was concentrated. The residue was purified with silica gel column chro-
matography [hexane–ethyl acetate (3 : 1)] to provide compound 7 (21 mg,
50% yield), and starting acetonide was also recovered (18 mg).
2—5 m. A voucher specimen (No. SM-0109) has been deposited at Lead
Chemical Co., Ltd., Himata, Toyama, Japan.
Extraction and Isolation Wet specimens (2.3 kg) were immersed in
methanol (3ꢅ3 l). After filtration, the combined extracts were concentrated
under reduced pressure. The methanol extract (442 g) was dissolved into a
mixture of chloroform–methanol (3 : 1, 0.8 l), and then the precipitate was
filtered with a sintered glass filter to remove highly polar compounds and
salts. The precipitate on the glass filter was rinsed with a small amount of a
3 : 1 mixture of chloroform–methanol. The combined filtrate was concen-
trated under reduced pressure to give a chloroform–methanol (3 : 1) soluble
portion (203 g). An aliquot of this portion (10.0 g) was chromatographed on
a silica gel column (300 g). Stepwise elution with chloroform–methanol
(99 : 1, 9 : 1 and 1 : 1, 400 ml of each) gave three fractions. The second frac-
tion (2.2 g) eluted with chloroform–methanol (9 : 1), contained terpenoids
and glycerides along with color pigments like chlorophylls from the 1H-
NMR analysis. Most of this fraction (2.15 g out of 2.2 g) was subjected to
ODS silica gel flash column chromatography [H2O–methanol (1 : 19) and
methanol] to obtain a mixture of plastoquinones. The former fraction eluted
with H2O–methanol (1 : 19) was purified with MPLC [hexane–acetone
(5 : 1)], followed by HPLC separation [hexane–ethyl acetate (4 : 1)] to afford
new compounds 1 (10.7 mg), 2 (8.0 mg), and a mixture (29.8 mg) of 3 and 4,
which was separated by recycled HPLC to obtain 3 (11.2 mg) and 4
(2.3 mg). The latter fraction, obtained by the separation using ODS silica gel
flash column chromatography eluted with methanol, was also separated by
MPLC [hexane–ethyl acetate (5 : 2)] and HPLC [hexane–ethyl acetate (7 : 3)]
to give 5 (1.28 g),1,3) which was used for chemical conversions to determine
the structures of the new compounds and their absolute configuration of the
secondary alcohol on the side chain terminal in 3 and 4.
Compound 7: Colorless oil. IR (dry film) cmꢂ1: 1739, 1585, 1210. 1H-
NMR (CDCl3) d ppm: 1.14 (3H, s), 1.18 (3H, s), 1.41 (1H, m), 1.58 (1H,
m), 1.59 (3H, s), 1.61 (3H, s), 1.66 (1H, m), 1.96—2.16 (9H, m), 2.14 (3H,
s), 2.21 (1H, m), 2.18 (3H, br s), 2.27 (3H, s), 2.32 (3H, s), 3.18 (2H, d,
Jꢀ7.2 Hz), 3.33 (1H, dd, Jꢀ2.1, 10.7 Hz), 5.11 (1H, dt, Jꢀ1.3, 6.9 Hz), 5.17
(1H, dt, Jꢀ1.2, 7.0 Hz), 5.21 (1H, dt, Jꢀ1.3, 7.2 Hz), 6.77 (1H, d,
Jꢀ2.8 Hz), 6.82 (1H, d, Jꢀ2.8 Hz).
Compound 1: Colorless oil. UV lmax (EtOH) nm (log e): 230 (4.0), 265
Conversion to 2 To a solution of oxalyl chloride (30 mg, 236 mmol) in
dichloromethane (1 ml) was added dimethylsulfoxide (DMSO, 30 mg,
384 mmol) at ꢂ60 °C under N2 atmosphere. After stirring for 15 min at this
temperature, compound 7 (18 mg, 35 mmol) in dichloromethane (0.2 ml) was
added, and the mixture was stirred for 20 min at ꢂ60 °C, followed by addi-
tion of triethylamine (40 mg, 395 mmol). The mixture was gradually warmed
to r.t. for 1 h, diluted with a hexane–ethyl acetate (1 : 1, 30 ml) mixture, and
washed with water and brine. The organic phase was dried over Na2SO4, fil-
tered, and concentrated under reduced pressure. The oily residue was puri-
fied with silica gel column chromatography [hexane–acetone (3 : 1)] to pro-
vide hydroxyketone (14 mg, 78% yield) as a colorless oil. Basic hydrolysis
of phenolic diacetate for the above compound (14 mg, 27 mmol) was carried
out with potassium carbonate (14 mg, 100 mmol) in MeOH (2 ml) at r.t.
under N2. After the reaction mixture was stirred for 30 min, saturated ammo-
nium chloride solution (3 drops) was added. Most of the solvent was re-
moved under reduced pressure, and then the residue was diluted with ethyl
acetate (20 ml). The organic phase was washed with water and brine, dried
over Na2SO4, filtered, and concentrated. The residue was purified with silica
gel column chromatography [hexane–acetone (2 : 1)] to provide 2 (10 mg,
86% yield) as a colorless oil. The spectral data of synthetic 2 were identical
to those of the isolated compound from the alga.
Oxidation of 2 to 1 To a solution of 2 (4 mg, 10 mmol) in acetonitrile
(0.6 ml) at 0 °C under N2 was added a water solution of ammonium cerium
(IV) nitrate (CAN, 10 mg, 18 mmol). The reaction mixture was stirred for
30 min at 0 °C, a Na2S2O3 solution (3 drops) was added to quench active
CAN, and the mixture was concentrated under reduced pressure. The residue
was extracted twice with ethyl acetate (each 10 ml) and the combined ex-
tracts were washed with a saturated NaCl solution, dried over MgSO4, fil-
tered, and concentrated under reduced pressure. The oily residue was puri-
fied by passing over a small plug of silica gel [hexane–ethyl acetate (2 : 1)],
followed by MPLC separation [normal phase, hexane–acetone (3 : 1)] to af-
ford 2 (1.3 mg, 32% yield) as a pale yellowish oil. The spectral data obtained
by the above procedure were identical to those of isolated 1.
1
(3.6), 334 (3.4). IR (dry film) cmꢂ1: 3485 (br), 1709, 1653, 1614. H- and
13C-NMR, see Table 1. HR-EI-MS m/z: 426.2752 [Calcd for C27H38O4:
426.2770 (M)ꢁ].
Compound 2: Pale yellowish oil. UV lmax (EtOH) nm (log e): 234 (3.3),
1
285 (5.2), 310 (3.9). IR (dry film) cmꢂ1: 3445 (br), 1758, 1713, 1667. H-
and 13C-NMR, see Table 1. HMBC (H→C): H-3→C-2, C-4; H-5→C-4, C-6;
6-Me→C-1; H-1ꢃ→C-1, C-2, C-3; H-2ꢃ→C-4ꢃ; 3ꢃ-Me→C-2ꢃ, C-3ꢃ; H-
4ꢃ→C-2ꢃ; H-6ꢃ→C-8ꢃ; 7ꢃ-Me→C-6ꢃ, C-7ꢃ; H-8ꢃ→C-6ꢃ; H-10ꢃ→C-12ꢃ; 11ꢃ-
Me→C-10ꢃ, C-11ꢃ; H-12ꢃ→C-10ꢃ; H-13ꢃ→C-14ꢃ; 15ꢃa-Me→C-14ꢃ, C-15ꢃ;
15ꢃb-Me→C-14ꢃ, C-15ꢃ. HR-EI-MS m/z: 428.2884 [Calcd for C27H40O4:
428.2927 (M)ꢁ].
Compound 3: Colorless oil. [a]D25 ꢁ6.2° (cꢀ0.56, CHCl3). UV lmax
(EtOH) nm (log e): 234 (3.3), 285 (5.2), 310 (3.9). IR (dry film) cmꢂ1: 3460
1
(br), 1740, 1655. H- and 13C-NMR, see Table 2. HR-EI-MS m/z: 694.5547
[Calcd for C45H74O5: 694.5536 (M)ꢁ].
Compound 4: Colorless oil. [a]D25 ꢁ6.0° (cꢀ0.33, CHCl3). UV lmax
(EtOH) nm (log e): 234 (3.3), 285 (5.2), 310 (3.9). IR (dry film) cmꢂ1: 3460
1
(br), 1739, 1655. H- and 13C-NMR, see Table 2. HR-EI-MS m/z: 696.5679
[Calcd for C45H76O5: 696.5693 (M)ꢁ].
Compound 5:1) 1H-NMR (500 MHz, CDCl3) d ppm: 1.16 (3H, s, one of
15ꢃ-Me), 1.19 (3H, s, one of 15ꢃ-Me), 1.42 (1H, m, one of H-13ꢃ), 1.53 (1H,
m, one of H-13ꢃ), 1.57 (3H, s, 7ꢃ-Me), 1.59 (3H, s, 11ꢃ-Me), 1.74 (3H, s, 3ꢃ-
Me), 1.98 (1H, m, one of H-8ꢃ), 2.00 (1H, m, one of H-4ꢃ), 2.04 (1H, m, one
of H-12ꢃ), 2,05 (1H, m, one of H-5ꢃ), 2.05 (1H, m, one of H-9ꢃ), 2.06 (1H,
m, one of H-6ꢃ), 2.08 (1H, m, one of H-8ꢃ), 2.10 (1H, m, one of H-5ꢃ), 2.10
(1H, m, one of H-9ꢃ), 2.17 (3H, s, 6-Me), 2.23 (1H, m, one of H-12ꢃ), 3.27
(2H, br d, Jꢀ7.3 Hz, H-1ꢃ), 3.37 (1H, dd, Jꢀ1.7, 9.7 Hz, H-14ꢃ), 5.07 (1H,
br t, Jꢀ6.9 Hz, H-6ꢃ), 5.12 (1H, br t, Jꢀ7.3 Hz, H-2ꢃ), 5.15 (1H, dt, Jꢀ0.9,
7.3 Hz, H-10ꢃ), 6.44 (1H, d, Jꢀ3.8 Hz, H-3), 6.52 (1H, d, Jꢀ3.8 Hz, H-5).
13C-NMR (125 MHz, CDCl3) d ppm: 15.7 (q, 7ꢃ-Me), 15.9 (q, 11ꢃ-Me),
16.05 (q, 3ꢃ-Me), 16.09 (q, 6-Me), 23.1 (q, 15ꢃ-Me), 26.13 (q, 15ꢃ-Me),
26.19 (t, C-5ꢃ), 26.21 (t, C-9ꢃ), 29.4 (t, C-13ꢃ), 29.7 (t, C-1ꢃ), 36.8 (t, C-12ꢃ),
39.4 (t, C-8ꢃ), 39.6 (t, C-4ꢃ), 73.3 (s, C-15ꢃ), 78.2 (s, C-14ꢃ), 113.8 (d, C-3),
115.3 (d, C-5), 121.7 (s, C-2ꢃ), 123.9 (d, C-6ꢃ), 125.3 (d, C-10ꢃ), 125.5 (s, C-
6), 127.6 (s, C-2), 134.7 (s, C-11ꢃ), 135.2 (s, C-7ꢃ), 138.6 (s, C-3ꢃ), 149.08
(s, C-4), 149.10 (s, C-1).
Preparation of
8 N,Nꢃ-Dicyclohexylcarbodiimide (DCC, 55 mg,
266 mmol) was added to a solution of compound 6 (33 mg, 69 mmol), stearic
acid (30 mg, 105 mmol) and a catalytic amount of DMAP in chloroform
(2 ml) at r.t. The mixture was stirred for 4 h at r.t., which was then diluted
with hexane (2 ml), followed by filtration through a small plug of silica gel
column. After eluted with hexane–ethyl acetate (3 : 1, 10 ml), the combined
filtrate was concentrated under reduced pressure. The residue was purified
with silica gel column chromatography [hexane–acetone (9 : 1)] to give 8
(47 mg, 92% yield).
Preparation of Acetonide 6 To a solution of 5 (219 mg, 509 mmol) in
MeOH (1 ml) and 2,2-dimethoxypropane (3 ml) was added p-toluenesulfonic
acid monohydrate (TsOH·H2O, 10 mg) at room temperature. The reaction
mixture was stirred for 30 min, triethylamine (1 drop) was added to neutral-
ize it, and the mixture was concentrated under reduced pressure. The residue
was purified by passing over a small plug of silica gel [hexane–ethyl acetate
(5 : 1)] to afford 6 (236 mg, 99% yield).
1
Compound 8: H-NMR (CDCl3) d: 0.87 (3H, t, Jꢀ7.1 Hz), 1.19 (3H, s),
1.23—1.42 (28H, m), 1.24 (3H, s), 1.32 (3H, s), 1.42 (3H, s), 1.42—1.49
Compound 6: Colorless oil. IR (dry film) cmꢂ1: 3410 (br), 1592, 1243.
(2H, m), 1.60 (3H, s), 1.61 (3H, br s), 1.73 (2H, quint, Jꢀ7.7 Hz), 1.78 (3H,