F.K. Yoshimoto et al.
Steroids128(2017)50–57
ABSPACK [27], respectively. The structure, using Olex2 [28], was
solved with the ShelXT [29] structure solution program using direct
methods and refined (on F2) with the ShelXL [30] refinement package
using full-matrix, least-squares techniques. All non-hydrogen atoms
were refined with anisotropic displacement parameters. All hydrogen
atom positions were determined by geometry and refined by a riding
model, except for the hydrogen atom on atom O3 which was de-
termined by electron density map. The data was deposited in the
Cambridge structural database with the deposition number CCDC
1559616.
reflux for 20 h. The reaction mixture was cooled to room temperature,
diluted with H2O (100 ml), and extracted with ethyl acetate (200 ml). The
organic layer was concentrated by reduced pressure and purified by
column chromatography (100% hexanes to 20% ethyl acetate in hexanes,
v/v) to afford the silyl ether 11 as a clear oil (6.7 g, 14 mmol, 88%); IR
(neat) 2933, 2854, 1732, 1471, 1462, 1438, 1371, 1239, 1119, 1092,
1048, 1029, 980, 956, 939, 918, 887, 834, 810, 773, 733 cm−1; Rf: 0.90
(Hexanes:ethyl acetate, 4:1, v/v); 1H NMR (500 MHz, CDCl3)δ 5.39–5.33
(m, 1H), 4.64–4.54 (m, 1H), 3.77–3.68 (m, 1H), 2.33–2.27 (m, 2H),
2.18–2.12 (m, 1H), 2.02 (s, 3H), 1.99–1.91 (m, 1H), 1.89–1.81 (m, 2H),
1.78–1.74 (m, 1H), 1.66–1.52 (m, 4H), 1.52–1.34 (m, 5H), 1.19–1.08 (m,
3H), 1.07 (d, J = 5.84 Hz, 3H), 1.01 (s, 3H), 1.00–0.91 (m, 2H), 0.90 (s,
3H), 0.87 (s, 9H), 0.69 (s, 3H), 0.058 (s, 3H), 0.055 (s, 3H); 13C NMR
(125 MHz, CDCl3) δ 170.7, 139.8, 122.7, 74.1, 71.2, 58.4, 56.5, 50.2, 42.2,
39.3, 38.2, 37.1, 36.7, 32.1, 31.9, 27.9, 26.2, 25.9, 25.8, 24.5, 23.9, 21.6,
20.9, 19.5, 18.2, 12.2, -3.3, -3.5, -3.9; HRMS (m/z) calculated for
4.4. Chemical syntheses
Pregnenolone-3-acetate (Compound 9). Triethylamine (20 ml,
143 mmol, 2.3 mol eq) and acetic anhydride (10 ml, 106 mmol,
1.7 mol eq) were added to a solution of pregnenolone (20 g, 63.3 mmol,
1.0 mol eq) in CH2Cl2 (200 ml, 0.3 M). To the mixture was added 4-
dimethylaminopyridine (0.4 g, 3.3 mmol, 0.05 mol eq). The reaction
was stirred for 24 h. The resulting mixture was concentrated by reduced
pressure and purified by flash column chromatography (100% hexanes
to 30% ethyl acetate in hexanes) to afford pregnenolone-3-acetate as a
white solid (15 g, 41.9 mmol, 66%); mp: 142.7–146.0 °C; IR (neat)
2942, 2914, 2891, 2873, 2847, 1727, 1701, 1467, 1454, 1434, 1387,
1372, 1357, 1290, 1268, 1246, 1232, 1193, 1170, 1152, 1135, 1114,
1085, 1028, 1019, 993, 979, 953, 940, 922, 912, 900, 883, 874, 854,
C
29H51O3Si [M + H]+, 497.3421; found, 497.3422 (Δ 0.20 ppm).
7-Oxo-pregn-5-ene-3β-acetoxy-20-tert-butyldimethylsilyl
ether
(Compound 8). CrO3 (9.7 g, 97 mmol, 13 mol eq) was stirred in CH2Cl2
(350 ml) at −78 °C for 10 min. 3,5-Dimethylpyrazole (9.9 g, 100 mmol,
14 mol eq) was added to the reaction as a solid and the reaction was
stirred for 20 min at -78 °C. The TBDMS ether 11 (3.4 g, 7.2 mmol,
1.0 mol eq) in CH2Cl2 (20 ml) was added and the reaction was stirred
for 20 h. The resulting mixture was directly loaded on a silica gel
column and purified by column chromatography (100% hexanes to
20% ethyl acetate in hexanes, v/v, to 40% ethyl acetate in hexanes, v/
v) to afford ketone 8 as a clear oil (2.3 g, 4.7 mmol, 68%); IR (neat)
2949, 2930, 2878, 2855, 2708, 1733, 1673, 1633, 1471, 1463, 1387,
1372, 1297, 1245, 1186, 1116, 1097, 1083, 1052, 1032, 980, 930, 906,
869, 834 cm−1; Rf: 0.56 (Hexanes:ethyl acetate, 4:1, v/v); 1H NMR
(500 MHz, CDCl3)δ 5.70–5.68 (m, 1H), 4.74–4.66 (m, 1H), 3.77–3.69
(m, 1H), 2.57–2.50 (m, 1H), 2.49–2.44 (m, 1H), 2.44–2.36 (m, 1H),
2.26–2.18 (m, 2H), 2.03 (s, 3H), 2.00–1.93 (m, 2H), 1.73–1.62 (m, 3H),
1.58–1.48 (m, 3H), 1.42–1.22 (m, 5H), 1.20 (s, 3H), 1.19–1.09 (m, 2H),
1.08 (d, J = 5.71 Hz, 3H), 0.90 (s, 3H), 0.87 (s, 9H), 0.70 (s, 3H), 0.06
(s, 3H), 0.05 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 202.09, 170.4,
164.2, 126.7, 72.4, 71.4, 57.1, 50.1, 49.8, 45.5, 43.0, 38.5, 38.4, 37.9,
36.2, 27.5, 26.6, 26.3, 26.2, 25.8, 24.0, 21.4, 21.1, 18.2, 17.4, 12.2,
-3.30, -3.45, -3.89; [α]D20 + 948° [0.4% in CH2Cl2]; HRMS (m/z) cal-
culated for C29H49O4Si [M + H]+, 489.3395; found, 489.3398 (Δ
0.61 ppm).
;
836 cm−1 Rf: 0.74 (Hexanes:ethyl acetate, 4:1, v/v); 1H NMR
(500 MHz, CDCl3)δ 5.38–5.35 (m, 1H), 4.63–4.55 (m, 1H), 2.53 (ap-
parent t, J = 9.2 Hz, 1H), 2.35–2.25 (m, 2H), 2.21–2.13 (m, 1H), 2.12
(s, 3H), 2.03–2.01 (m, 1H), 2.03 (s, 3H), 2.02–1.95 (m, 1H), 1.90–1.82
(m, 2H), 1.72–1.52 (m, 5H), 1.52–1.40 (m, 3H), 1.27–1.18 (m, 1H),
1.18–1.10 (m, 2H), 1.01 (s, 3H, H-19), 1.04–0.96 (m, 1H, H-9), 0.62 (s,
3H, H-18); 13C NMR (125 MHz, CDCl3) δ 209.8 (C-20), 170.7, 139.7 (C-
4), 122.5 (C-5), 73.9, 63.8, 56.9, 50.0 (C-9), 44.1, 38.9, 38.2, 37.1,
36.7, 31.91, 31.86, 31.7, 27.8, 24.6, 22.9, 21.6, 21.1, 19.4 (C-19), 13.4
(C-18); HRMS (m/z) calculated for C23H34O3Na [M + Na]+, 381.2400;
found, 381.2399 (Δ −0.26 ppm).
Pregn-5-ene-3β-acetoxy-20β-ol (Compound 10). NaBH4 (0.38 g,
10.0 mmol, 0.3 mol eq) was added to a solution of pregnenolone-3-
acetate (10.7 g, 29.9 mmol, 1 mol eq) in CH3OH (100 ml, 0.3 M). The
reaction was stirred for 24 h at room temperature. The mixture was
diluted with water (100 ml) and extracted with ethyl acetate (200 ml).
The organic extract was concentrated under reduced pressure and
purified by flash column chromatography (100% hexanes to 50%
hexanes in ethyl acetate, v/v) to afford the alcohol 10 as a white solid
(3.0 g, 8.27 mmol, 28%). The solid (∼200 mg) was dissolved in ethyl
acetate/hexanes (3 ml, 1:1, v/v), and left at rt to crystallize over a
period of 5 days to form crystals to determine the stereochemistry at
C20 as the R-configuration (Fig. 3); mp: 165.9–168.2 °C; IR (neat) 3555,
2969, 2948, 2939, 2909, 2889, 2866, 2854, 2823, 1720, 1681, 1464,
1450, 1425, 1399, 1367, 1334, 1277, 1255, 1197, 1147, 1129, 1108,
1079, 1048, 1029, 1012, 989, 968, 957, 943, 936, 917, 905, 896, 882,
871, 849, 839 cm−1; Rf: 0.44 (Hexanes:ethyl acetate, 4:1, v/v); 1H NMR
(500 MHz, CDCl3)δ 5.39–5.33 (m, 1H), 4.64–4.54 (m, 1H), 3.75–3.66
(m, 1H), 2.35–2.24 (m, 2H), 2.10–2.04 (m, 1H), 2.02 (s, 3H), 1.99–1.92
(m, 1H), 1.90–1.79 (m, 2H), 1.70–1.40 (m, 7H), 1.36–1.18 (m, 3H),
1.20–1.06 (m, 3H), 1.12 (d, J = 5.82 Hz, 1H), 1.06–0.99 (m, 1H), 1.01
(s, 3H), 0.99–0.92 (m, 1H), 0.75 (s, 3H); 13C NMR (125 MHz, CDCl3) δ
170.7, 139.8, 122.6, 74.0, 70.6, 58.5, 56.2, 50.1, 42.3, 39.9, 38.2, 37.1,
36.7, 32.0, 31.8, 27.8, 25.7, 24.6, 23.8, 21.6, 21.0, 19.4, 12.5; HRMS
(m/z) calculated for C23H37O3 [M + H]+, 383.2557; found, 383.2557
(Δ 0.00 ppm).
7α-Hydroxy-pregn-5-ene-3β-acetoxy-20-tert-butyldimethylsilyl
ether (Compound 7). L-selectride (2.93 ml of a 1 M solution in THF,
2.9 mmol, 1.1 mol eq) was added to a solution of ketone 8 (1.3 g,
2.7 mmol, 1.0 mol eq) in tetrahydrofuran (50 ml) at −78 °C. The reac-
tion was stirred for 30 min at −78 °C. The reaction was quenched with
the addition of water (50 ml) and the resulting reaction mixture was
extracted with ethyl acetate (100 ml). The organic layer was con-
centrated by reduced pressure and purified by column chromatography
(100% hexanes to 50% hexanes in ethyl acetate, v/v) to afford 7α-hy-
droxy compound 7 as a transparent white solid (290 mg, 0.59 mmol,
22%); mp: 140.6–144.7 °C; IR (neat) 3495, 2962, 2935, 2905, 2891,
2870, 2855, 1712, 1668, 1470, 1442, 1414, 1373, 1366, 1333, 1314,
1257, 1200, 1155, 1135, 1082, 1041, 1019, 978, 957, 9445, 938, 920,
905, 893, 873 cm−1; Rf: 0.31 (Hexanes:ethyl acetate, 4:1, v/v); 1H NMR
(500 MHz, CDCl3)δ 5.62 (d, J = 5.2 Hz, 1H), 4.69–4.60 (m, 1H),
3.85–3.80 (m, 1H), 3.78–3.71 (m, 1H), 2.41–2.30 (m, 2H), 2.21–2.13
(m, 1H), 2.03 (s, 3H), 1.93–1.83 (m, 2H), 1.79–1.64 (m, 2H), 1.64–1.57
(m, 1H), 1.57–1.40 (m, 6H), 1.33–1.11 (m, 6H), 1.09 (d, J = 6.02 Hz,
3H), 1.01 (s, 3H), 0.88 (s, 9H), 0.71 (s, 3H), 0.07 (s, 6H); 13C NMR
(125 MHz, CDCl3) δ 170.5, 145.4, 124.9, 73.6, 73.1, 65.5, 58.2, 49.2,
42.5, 42.1, 38.8, 38.1, 37.7, 37.6, 36.9, 27.7, 26.3, 26.0, 24.5, 24.0,
21.5, 20.6, 18.4, 18.3, 12.0, 1.16, -3.27, -3.89; HRMS (m/z) calculated
Pregn-5-ene-3β-acetoxy-20-tert-butyldimethylsilyl ether (Compound
11). tert-Butyldimethylsilyl chloride (8.0 g, 53 mmol, 3.3 mol eq) and
imidazole (8.0 g, 118 mmol, 7.4 mol eq) were added to a solution of al-
cohol 10 (5.8 g, 16 mmol, 1.0 mol eq) in acetonitrile (200 ml, 0.08 M). The
reaction flask was equipped with a Dean-Stark trap and heated under
for
C
29H50O5SiNa [M + Na]+
,
513.3371; found, 513.3372 (Δ
0.19 ppm). ∗At a larger scale (∼5 g scale of ketone 8, it was necessary
to add 2 mol equivalents of L-selectride for the reaction to proceed).
55