To a cooled solution of acetonitrile (5 ml) in a round bottom flask was added trifluoroacetic acid
(
5 ml) and glacial acetic acid (5 ml). Sodium borohydride (1.0 g, 20 mmol, 12 mol eq,) was
4
added to the stirring solution at 0 °C and left to stir for 2 minutes. The 3-keto-Δ sterol substrate
2
3 (1.07 g, 2.08 mmol, 1 mol eq) was dissolved in dichloromethane (2 ml) and added to the
stirring solution. The reaction was further stirred for 2 h and then quenched by the addition of
deionized water (5 ml). The resulting aqueous solution was extracted with dichloromethane (3
×
20 ml). The dichloromethane extract was concentrated under reduced pressure to give crude
colorless oil. Purification through silica gel column chromatography (isocratic 5% ethyl acetate
in hexanes, v/v) afforded colorless oil as product 24 (0.7 g 1.39 mmol, 66 %). R : 0.94 (100%
; IR (ATR) 2930.04, 2864.59, 1658.91, 1462.52, 1374.64,
) δ 5.20 (s, 1H), 3.77 (s, 1H), 2.28 (apparent d, J = 17.53
Hz, 1H), 2.01 (dd, J = 14, 4 Hz, 1H), 1.96 – 1.88 (m, 3H), 1.83 – 1.75 (m, 1H), 1.69 (m, 1H), 1.63 –
.55 (m, 2H), 1.51 – 1.48 (m, 3H), 1.44 – 1.36 (m, 3H), 1.26 – 1.18 (m, 4H), 1.16 – 1.04 (m, 6H), 0.99
s, 3H), 1.04 -0.93 (m, 3H), 0.90 (d, J = 6.8 Hz, 3H ), 0.86 (dd, J = 6, 2.3 Hz, 6H), 0.86 (s, 9H), 0.65
f
2
0
hexanes); [α]
1
D
- 19° [c = 0.8 mg/ml in CHCl
3
-
1 1
250.80 cm ; H NMR (500 MHz, CDCl
3
1
(
(
1
3
s, 3H), 0.02 (d, 21.82 Hz, 6H); C NMR (125 MHz, CDCl
3
) δ 140.80, 122.07, 69.59, 56.48, 50.36,
4
2
5.07, 42.42, 41.23, 41.03, 39.83, 39.61, 37.60, 36.86, 36.37, 36.17, 28.30, 28.13, 26.04, 25.94, 24.27,
4.00, 22.98, 22.69, 22.12, 19.40, 19.30, 18.84, 18.45, 12.04, -3.37, -4.83. HRMS (m/z, ESI+)
+
+
calculated for: [M+H] , C33
H
61OSi , 501.4486; found 501.4396 ( -17 ppm).
Cholest-4-en-7α-ol (Compound 25)
Toluene sulfonic acid (0.37 g, 2.14 mmol, 2.44 mol eq) was added to a solution of cholesterol-7α-
tert-butyldimethylsilyl ether 24 (0.44 g, 0.87 mmol, 1 mol eq) in methanol and dichloromethane
(
20 ml, 1:1, v/v mixture). The reaction was refluxed for 2 h and carefully monitored by TLC and
NMR. The reaction was cooled to room temperature and then quenched by the addition of
saturated sodium bicarbonate (20 ml). The resulting solution was extracted with
dichloromethane (3 × 20 ml) using a separatory funnel. The dichloromethane extract was
concentrated under reduced pressure to afford crude white solids which was then purified by
silica gel column chromatography (10 % ethyl acetate in hexanes) to give the product as a white
2
0
solid 25 (0.27 g, 0.698 mmol, 80%): R
.08 mg/ml in CHCl
; IR (ATR) 3472.38, 2926.00, 2864.77, 1656.94, 1466.92, 1372.77, 1259.61 cm-1 1H
NMR (500 MHz, CDCl ) δ 5.43 (s, 1H), 3.74 (apparent s, 1H), 2.51 (apparent d, J = 17.47 Hz, 1H),
.08 (dd, J = 13.47, 4.49 Hz, 1H), 1.98 -1.92 (m, 3H), 1.89 – 1.82 (m, 1H), 1.75 – 1.67 (m, 2H), 1.64 –
.58 (m, 1H), 1.53 – 1.47 (m, 2H), 1.46 – 1.40 (m, 2H), 1.38 – 1.05 (m, 11H), 1.01 (s, 3H), 1.04 – 0.96
f
: 0.43 (9:1, hexanes:ethyl acetate, v/v); ); [α]
D
- 180° [c =
0
3
3
2
1
1
3
(
m, 1H), 0.90 (d, J = 5.76 Hz, 3H ), 0.86 (dd, J = 6.99, 2.15, 6H), 0.67 (s, 6H); C NMR (125 MHz,
CDCl ) δ 140.17, 124.43, 68.65, 56.18, 50.90, 46.62, 42.66, 40.64, 40.46, 39.69, 39.65, 37.62, 37.24,
6.28, 35.93, 28.36, 28.15, 26.03, 23.88, 23.83, 22.94, 22.71, 21.41, 19.34, 19.07, 18.80, 12.00. HRMS
3
3
+
+
(m/z, ESI+) calculated for: [M+H] , C27
H47O , 387.3621; found 387.3621 ( 0 ppm).
7
α-Formyloxy-4-cholestene (Compound 9)
To the 7α-hydroxy-Δ4-cholesterol 25 (0.15 g, 0.388 mmol, 1 mol eq) in ethyl formate (25 ml, 310
mmol, 798 mol eq) in a 100 ml round bottom flask was added toluene sulfonic acid (0.01 g, 0.058
mmol, 0.14 mol eq). The reaction was refluxed for 2 h and cooled to room temperature. The
resulting solution concentrated under reduced pressure to afford a crude colorless oil. The
crude oil was purified via silica gel column chromatography (isocratic 10% ethyl acetate in
hexanes, v/v) to give colorless oil as product 9 (0.16 g, 3.73 mmol, 96%). R
hexanes:ethyl acetate, v/v); IR (ATR) 2929.35, 2866.84, 1714.13, 1465.80, 1375.54, 1182.46 cm ; H
NMR (300 MHz, CDCl ) δ 8.12 (s, 1H), 5.27 (apparent s, 1H), 5.00 (apparent s, 1H), 2.42 (m, 1H),
.26 (m, 1H), 2.01 – 1.88 (m, 3H), 1.88 – 0.94 (m, 23H) 1.03 (s, 3H), 0.90 (d, J = 7 Hz, 3H), 0.85 (dd,
f
: 0.83 (17:3,
-1 1
3
2
1
3
J = 6.7, 1.5 Hz, 6H), 0.68 (s. 3H); C NMR (125 MHz, CDCl
3
) δ 161.10, 139.43, 122.91, 72.49, 56.20,
5
2
4
0.37, 46.98, 39.63, 39.56, 38.68, 37.47, 37.19, 36.89, 36.25, 35.87, 28.19, 28.16, 25.85, 23.91, 23.72,
+
O
+,
2.96, 22.70, 21.36, 19.24, 19.03, 18.79, 11.85; HRMS (m/z, ESI+) calculated for: [M+H] , C28
H
47
2
15.3571; found 415.3576 ( 1.2 ppm).
1
2