Antioxidant Activity of Lignan
2983
and 20% Pd(OH)2/C (0.20 g) in THF (10 ml) was stirred
under H2 gas at ambient temperature for 4 h before
filtration. Concentration of the filtrate, followed by silica
gel column chromatography (EtOAc/hexane = 2/1)
ane = 1/1) gave diol 7 (0.57 g, 1.05 mmol, 88%) as
colorless crystals, mp 120–121 ꢁC ((iso-Pr)2O/
20
MeOH = 3/1), ½ꢀꢂ
¼ þ37 (c 1.0, CHCl3). NMR
D
ꢁH (CDCl3): 0.57 (3H, d, J ¼ 7:1 Hz), 1.04 (3H, d, J ¼
7:0 Hz), 1.66 (1H, m), 2.07 (1H, br. s), 2.29 (1H, m),
2.31 (1H, br. s), 3.81 (3H, s), 3.86 (3H, s), 4.33 (1H, d,
J ¼ 8:9 Hz), 4.54 (1H, d, J ¼ 7:1 Hz), 5.11 (2H, s), 5.13
(2H, s), 6.64 (1H, dd, J ¼ 8:1, 1.9 Hz), 6.75 (1H, dd,
J ¼ 8:3, 1.8 Hz), 6.76 (1H, d, J ¼ 1:8 Hz), 6.77 (1H, d,
J ¼ 8:3 Hz), 6.82 (1H, d, J ¼ 8:1 Hz), 6.90 (1H, d,
J ¼ 1:9 Hz), 7.27–7.30 (2H, m), 7.33–7.37 (4H, m),
7.41–7.44 (4H, m). NMR ꢁC (CDCl3): 10.7, 12.5, 40.4,
41.1, 55.9, 56.0, 70.99, 71.0, 77.5, 110.1, 110.2, 113.6,
113.7, 118.8, 118.9, 127.18, 127.21, 127.8, 128.5, 137.0,
137.1, 137.2, 147.4, 147.5, 149.56, 149.62. Anal. Found:
gave (ꢀ)-DGA (46 mg, 0.14 mmol, 100%) as colorless
20
crystals, mp 86–87 ꢁC, ½ꢀꢂ
¼ ꢀ27 (c 0.9, CHCl3)
D
20
(mp 87–88 ꢁC, ½ꢀꢂ
¼ ꢀ46 (1%, CHCl3) in litera-
D
ture10)). The NMR data agree with those in the
literature.11) 99% ee (HPLC, iso-PrOH/hexane = 1/4,
16 min, DAICEL AD-H chiral column (1 ml minꢀ1),
20
detected at 280 nm. (+)-DGA, ½ꢀꢂ
¼ þ25 (c 1.0,
D
CHCl3), 99% ee (HPLC, iso-PrOH/hexane = 1/4,
13 min, DAICEL AD-H chiral column (1 ml minꢀ1),
detected at 280 nm.
(7R,70S,8R,80R)-4,40-Dibenzyloxy-3,30-dimethoxy-7,70-
bis(triisopropylsilyloxy)lignane (6). To an ice-cooled
solution of diol 53) (2.16 g, 2.43 mmol) and Et3N
(1.02 ml, 7.32 mmol) in CH2Cl2 (5 ml) was added MsCl
(0.75 ml, 9.69 mmol) at 0 ꢁC. The reaction mixture was
stirred at room temperature for 1.5 h before additions of
H2O and CH2Cl2. The organic solution was separated,
washed with brine, and dried (Na2SO4). After concen-
tration, the residue was dissolved in HMPA (1 ml). To
this solution was added NaBH4 (1.25 g, 33.0 mmol) at
0 ꢁC, and then the resulting reaction mixture was stirred
at 60 ꢁC for 8 h. The reaction mixture was acidified with
1 M aq. HCl solution and neutralized with sat. aq.
NaHCO3 solution, and then extracted with EtOAc. The
organic solution was separated, washed with H2O and
brine, and dried (Na2SO4). Concentration followed by
silica gel column chromatography (5% EtOAc/hexane)
C, 74.92; H, 6.97. Calcd. for C34H38O6: C, 75.24; H,
20
7.06%. (7S,70R,8S,80S)-7, ½ꢀꢂ
¼ ꢀ37 (c 1.2, CHCl3).
D
(8R,80R)-4,40-Dibenzyloxy-3,30-dimethoxylignane-7,70-
dione (8). To a solution of (COCl)2 (60 ml, 0.71 mmol) in
CH2Cl2 (2 ml) was added a solution of DMSO (70 ml,
0.99 mmol) in CH2Cl2 (1 ml) at ꢀ70 ꢁC, and then a
solution of diol 7 (95 mg, 0.18 mmol) in CH2Cl2 (2 ml)
was added. The reaction solution was stirred at ꢀ70 ꢁC
for 2 h before addition of Et3N (0.36 ml, 2.58 mmol), and
then the resulting reaction mixture was stirred at 0 ꢁC for
30 min before additions of sat. aq. NH4Cl solution and
CH2Cl2. The organic solution was separated, washed
with brine, and dried (Na2SO4). Concentration followed
by silica gel column chromatography (EtOAc/hex-
ane = 1/3) gave diketone 8 (89 mg, 0.17 mmol, 94%)
20
as a colorless oil, ½ꢀꢂ
¼ þ135 (c 1.1, CHCl3). NMR
D
gave 6 (1.02 g, 1.19 mmol, 49%) as a colorless oil,
20
ꢁH (CDCl3): 1.27 (6H, d, J ¼ 6:7 Hz), 3.88–3.90 (2H,
overlapped), 3.89 (6H, s), 5.22 (4H, s), 6.90 (2H, d,
J ¼ 8:5 Hz), 7.29–7.32 (2H, m), 7.35–7.38 (4H, m),
7.42–7.43 (4H, m), 7.50 (2H, d, J ¼ 2:0 Hz), 7.61 (2H,
dd, J ¼ 8:5, 2.0 Hz). NMR ꢁC (CDCl3): 15.9, 43.2, 55.9,
70.7, 111.1, 112.2, 122.8, 127.1, 128.0, 128.6, 129.4,
136.4, 149.5, 152.3, 202.9. EIMS m=z: 538 (Mþ, 56),
½ꢀꢂ
¼ þ16 (c 1.4, CHCl3). NMR ꢁH (CDCl3): 0.48
D
(3H, d, J ¼ 7:0 Hz), 0.86 (3H, d, J ¼ 6:9 Hz), 0.90–0.98
(42H, m), 1.60 (1H, m), 2.28 (1H, m), 3.76 (3H, s), 3.83
(3H, s), 4.38 (1H, d, J ¼ 7:1 Hz), 4.40 (1H, d,
J ¼ 8:1 Hz), 5.10 (2H, s), 5.12 (2H, s), 6.54 (1H, d,
J ¼ 8:1 Hz), 6.62 (1H, d, J ¼ 6:4 Hz), 6.69 (1H, d,
J ¼ 6:4 Hz), 6.72 (1H, s), 6.73 (1H, d, J ¼ 8:1 Hz),
6.87 (1H, s), 7.28–7.30 (2H, m), 7.32–7.37 (4H, m),
7.41–7.44 (4H, m). NMR ꢁC (CDCl3): 10.2, 11.6, 12.56,
12.58, 17.99, 18.02, 18.07, 18.14, 40.66, 40.77, 55.70,
55.73, 71.0, 71.1, 78.6, 79.6, 110.5, 110.8, 113.1, 119.4,
119.6, 127.31, 127.34, 127.7, 128.4, 137.27, 137.30,
137.8, 138.0, 147.0, 147.1, 149.1, 149.4. Anal. Found:
522 (99), 241 (99), 91 (100). HREIMS m=z: 538.2353
20
(calcd. for C34H34O6, 538.2355). (8S,80S)-8, ½ꢀꢂ
¼
D
ꢀ135 (c 1.1, CHCl3).
(8R,80R)-4,40-Dihydroxy-3,30-dimethoxylignane-7,70-
dione ((+)-ODGA). A reaction mixture of benzyl ether 8
(0.17 g, 0.32 mmol) and 5% Pd/C (0.2 g) in EtOAc
(10 ml) was stirred under H2 gas at ambient temperature
for 44 h before filtration. Concentration of the filtrate,
followed by silica gel column chromatography (EtOAc/
C, 72.89; H, 9.26. Calcd. for C52H78O6Si2: C, 73.00; H,
20
9.20%. (7S,70R,8S,80S)-6, ½ꢀꢂ
¼ ꢀ16 (c 0.8, CHCl3).
D
(7R,70S,8R,80R)-4,40-Dibenzyloxy-3,30-dimethoxylignane-
7,70-diol (7). A reaction solution of silyl ether 6 (1.02 g,
1.19 mmol) and n-Bu4NF (3.90 ml, 1 M in THF, 3.90
mmol) in THF (10 ml) was stirred at room temperature
for 2 h before additions of sat. aq. NH4Cl solution and
EtOAc. The organic solution was separated, washed
with sat. aq. CuSO4 solution, sat. aq. NaHCO3 solution,
and brine, and dried (Na2SO4). Concentration followed
by silica gel column chromatography (EtOAc/hex-
hexane = 2/1) gave (+)-ODGA (65 mg, 0.18 mmol,
20
56%) as a colorless oil, ½ꢀꢂ
¼ þ102 (c 0.6, CHCl3).
D
NMR ꢁH (CDCl3): 1.29 (6H, d, J ¼ 6:8 Hz), 3.85 (6H,
s), 3.92 (2H, m), 6.33 (2H, br. s), 6.94 (2H, d,
J ¼ 8:3 Hz), 7.47 (2H, d, J ¼ 1:9 Hz), 7.65 (2H, dd,
J ¼ 8:3, 1.9 Hz). NMR ꢁC (CDCl3): 16.0, 43.2, 55.9,
110.4, 113.9, 123.7, 128.8, 146.6, 150.4, 203.0. EIMS
m=z: 358 (Mþ, 99), 151 (100). HREIMS m=z: 358.1417
(calcd. for C20H22O6, 358.1416).