18
Q. Zhao et al. / Steroids 109 (2016) 16–21
1733 (CH3CO2), 1654 (C@CH2) 904 (C@CH2). 1H NMR (CDCl3,
400 MHz):d5.30 (d, J = 3.9 Hz, 1H), 5.05 (m, 1H), 4.86 (s, 1H), 4.80
(s, 1H), 4.53(m, 1H), 1.99 (s, 3H), 1.96 (s, 3H), 1.65 (s, 3H), 0.95
(s, 3H), 0.86 (d, J = 6.5 Hz, 3H), 0.60 (s, 3H). 13C NMR (CDCl3,
100 MHz):d169.50, 169.36, 142.41, 138.65, 121.58, 111.46, 76.59,
72.95, 55.66, 54.73, 48.99, 41.30, 37.10 (X2), 35.98, 35.57, 34.32,
30.85, 30.83, 30.28, 28.02, 27.08, 26.76, 23.22, 20.41, 20.21,
20.00, 18.29, 17.63, 17.17, 10.83.
20 mmol) was stirred at room temperature for 4 d. The reaction
mixture was successively washed with 10% HCl, an aq. saturated
solution of NaHCO3, brine, dried over anhydrous sodium sulfate,
and evaporated. The final products (4.20 g, 95%) were isolated
using column chromatography (absorbent: silica gel, mobile
phase: n-hexane/EtOAc (8:1, v/v)). 6 [13]: mp: 128 °C (lit. mp:
130–141 °C). MS-EI (m/z): 467 (M++Na), 385 (M+-CH3COOH). IR
(cmÀ1): 3348 (OH), 1737(COCH3). 1H NMR (CDCl3, 400 MHz):
d5.30 (d, J = 4.4 Hz, 1H), 4.53 (m, 1H), 3.25 (d, J = 4.0 Hz, 1H), 2.25
(d, J = 7.3 Hz, 2H), 1.96 (s, 3H), 0.95 (s, 3H), 0.85 (m, 9H), 0.61 (s,
3H). 13C NMR (CDCl3, 100 MHz):d169.55, 138.64, 121.61, 76.06,
72.99, 55.66, 55.02, 49.01, 41.33, 38.72, 37.11 (X2), 35.98, 35.58,
34.69, 32.54, 31.04, 30.85, 29.58, 27.25, 26.76, 23.26, 20.41,
20.01, 18.29, 17.89, 17.65, 16.22, 10.86.
2.6.
D
5,25-3b,24(S)-Dihydroxycholestadiene-3,24-diacetate (epi-4)
D
5,25-3b,24(S)-dihydroxycholestadiene-3,24-diacetate (epi-4)
was obtained from
5-3b,24(S),25-trihydroxycholestene-3,24-
D
diacetate (epi-3) in 88% yield according to the procedure described
above for 4; epi-4 [10]: mp: 100 °C (lit. mp: 95–95 °C).
20 = À43.5 (c, 0.13, CHCl3). MS-EI (m/z): 424 (M+-CH3COOH),
2.10.
D
5-3b-Hydroxycholestene-24-one-3-acetate (7a)
[
a
]
D
364 (M+-2CH3COOH). IR (cmÀ1): 3080 (C@CH2), 1733 (CH3CO2),
1654 (C@CH2) 904 (C = CH2). 1H NMR (CDCl3, 400 MHz):d5.30 (d,
J = 4.2 Hz, 1H), 5.05 (m 1H), 4.87 (s, 1H), 4.82 (s, 1H), 4.53 (m,
1H), 1.98 (s, 3H), 1.96 (s, 3H), 1.64 (s, 3H), 0.95 (s, 3H), 0.86 (d,
J = 6.4 Hz, 3H), 0.60 (s, 3H). 13C NMR (CDCl3, 100 MHz):d169.52,
169.36, 142.02, 138.64, 121.58, 112.09, 77.06, 72.95, 55.64, 54.78,
48.97, 41.30, 37.09 (X2), 35.97, 35.56, 34.39, 30.85, 30.83, 30.29,
27.79, 27.09, 26.75, 23.22, 20.42, 20.25, 19.99, 18.28, 17.62,
16.87, 10.83
To a stainless steel autoclave was added 6 (2.22 g, 5 mmol),
TEMPO (0.04 g, 0.25 mmol), t-Butyl nitrite (0.02 g, 0.2 mmol), FeCl3
(0.04 g, 0.25 mmol) and dichloroethane (20 mL). Then the auto-
clave was closed and charged with oxygen to 0.4 MPa. The reaction
mixture was then vigorously stirred at room temperature for 8 h.
The barometer dropped to 0.38 MPa, which indicated that the reac-
tion was finished. Carefully depressurized, the reaction mixture
was rotary-evaporated. The final products (1.88 g, 86.2%) were iso-
lated using column chromatography (absorbent: silica gel, mobile
phase: n-hexane/EtOAc (8:1, v/v)). 7a [1]: mp: 126–128 °C (lit.
mp: 128–130 °C). MS-EI (m/z): 465 (M++Na), 383 (M+-CH3COOH).
IR (cmÀ1): 1730(COCH3), 1703(C@O). 1H NMR (CDCl3, 400 MHz):
d5.30 (d, J = 4.2 Hz, 1H), 4.53 (m, 1H), 1.96 (s, 3H), 1.03 (s, 3H),
1.01 (s, 3H), 0.95 (s, 3H), 0.85 (d, J = 6.5 Hz, 3H), 0.61 (s, 3H). 13C
NMR (CDCl3, 100 MHz):d214.41, 169.51, 138.63, 121.59, 72.95,
55.65, 54.87, 48.99, 41.35, 39.82, 38.70, 37.10 (X2), 36.19, 35.98,
35.57, 34.35, 30.85, 28.83, 27.10, 26.76, 23.24, 20.41, 20.01,
18.29, 17.50, 17.36, 17.29, 10.86.
2.7.
D
5-3b,24(R)-Dihydroxycholestene (5)
A solution of 4 (4.84 g, 10 mmol) in ethyl acetate (100 mL) was
stirred at room temperature in the presence of 10% Pd-C (0.5 g)
under an atmospheric pressure of hydrogen. After 48 h, the reac-
tion mixture was filtered, and the filtrate was concentrated in
vacuo. The crude product was dissolved in methanol (200 mL)
and 10% KOH and refluxed for 3 h. The reaction mixture was
rotary-evaporated. The residue was dissolved in dichloromethane
(80 mL) and successively washed with 10% HCl, an aq. saturated
solution of NaHCO3, brine, dried over anhydrous sodium sulfate,
and evaporated. The final products (3.40 g, 85%) were isolated
using column chromatography (absorbent: silica gel, mobile
phase: n-hexane/EtOAc (4:1, v/v)). 5 [6]: mp: 175–176 °C (lit.
2.11.
D
5-3b-Hydroxycholestene-24-one (7)
Alkaline hydrolysis of 7a with 10% methanolic KOH, as
described for the preparation of 5, gave
5-3b-hydroxyc-
D
mp: 177–180 °C). [
a
]
20 = À27.0 (c, 0.7, CHCl3). MS-EI (m/z): 402
D
holestene-24-one (7), which recrystallized from methanol as color-
less prisms. 7 [1]: mp: 129–130 °C (lit. mp: 131–133 °C). MS-EI
(m/z): 400 (M+), 385 (M+-CH3), 382(M+-H2O), 367(M+-CH3-H2O).
IR (cmÀ1): 3381(OH), 1714(C@O). 1H NMR (CDCl3, 400 MHz):
d5.28 (d, J = 4.7 Hz, 1H), 3.45 (m, 1H), 1.03 (s, 3H), 1.01 (s, 3H),
0.94 (s, 3H), 0.85 (d, J = 6.5 Hz, 3H), 0.61 (s, 3H). 13C NMR (CDCl3,
100 MHz):d214.52, 139.73, 120.67, 70.78, 55.72, 54.89, 49.09,
41.35, 41.27, 39.82, 38.75, 36.24 (X2), 35.48, 34.38, 30.88 (X2),
30.63, 28.84, 27.12, 23.25, 20.06, 18.37, 17.49, 17.36, 17.29, 10.86.
(M+), 384 (M+-H2O), 369 (M+-H2O-Me), 351 (M+-2H2O-Me). IR
(cmÀ1): 3369 (OH). 1H NMR (CDCl3, 400 MHz):d5.28 (d, J = 4.8 Hz,
1H), 3.47 (m, 1H), 3.25 (m, 1H), 0.94 (s, 3H), 0.85 (m, 9H), 0.62
(s, 3H). 13C NMR (CDCl3, 100 MHz):d139.76, 120.68, 76.08, 70.78,
55.75, 55.03, 49.12, 41.34, 41.28, 38.77, 36.25, 35.49, 34.69,
32.55, 31.05 (X2), 30.89, 30.64, 29.57, 27.26, 23.27, 20.07, 18.38,
17.89, 17.65, 16.21, 10.87.
2.8. Cerebrosterol (epi-5)
Cerebrosterol (epi-5) was obtained from epi-4 in 85% yield
according to the procedure described above for 5; epi-5 [10]:
3. Results and discussion
mp: 178–179 °C (lit. mp: 181–182 °C). [
a
]
D
20 = À49.0 (c, 0.03,
Our initial step of the synthesis was focused on establishing a
reliable method to generate a specific chiral center on the 24-posi-
tion of the cholesterol side chain. In the past, the synthesis of
24-functionalized oxysterols was performed by benzoylation of a
mixture of 24R- and 24S-hydroxycholesterol, followed by either
resolution via recrystallization or chromatography and hydrolysis
[10]. Recently, it is reported that the fundamental strategy adopted
for stereoselective generation of the 24-functionalized oxysterols
was to apply Sharpless asymmetric dihydroxylation to an appro-
priate derivative of desmosterol, such as acetate 1, to produce 24
(R)-hydroxycholesterol and it epimer [epi’s]. The starting material,
desmosterol acetate 1, was prepared according to the literature
[11]. As depicted in Scheme 1, with adequate quantities of starting
CHCl3). MS-EI (m/z): 402 (M+), 384 (M+-H2O), 369 (M+-H2O-Me),
351 (M+-2H2O-Me). IR (cmÀ1): 3369 (OH). 1H NMR (CDCl3,
400 MHz):d5.28 (d, J = 5.0 Hz, 1H), 3.45 (m, 1H), 3.25 (m, 1H),
0.94 (s, 3H), 0.85 (m, 9H), 0.61 (s, 3H). 13C NMR (CDCl3,
100 MHz):d139.76, 120.67, 76.42, 70.77, 55.73, 54.94, 49.11,
41.33, 41.28, 38.76, 36.25, 35.49, 34.93, 32.12, 31.19 (X2), 30.89,
30.64, 29.71, 27.19, 23.27, 20.07, 18.38, 18.05, 17.81, 15.69, 10.86.
2.9.
D
5-3b,24-Dihydroxycholestene-3-acetate (6)
A solution of 5 (4.02 g, 10 mmol) in acetic anhydride (2.04 g,
20 mmol), dichloromethane (80 mL) and triethylamine (50.60 g,