steroids 7 1 ( 2 0 0 6 ) 12–17
13
(1H, 13C, DEPT, HETCOR, COSY and HMBC) were determined
with a JEOL eclipse +400, chemical shifts are stated in ppm
(ı), and are referred to the residual 1H signal (ı = 7.27) or to
the central 13C triplet signal (ı = 77.0) for CDCl3. Mass spectra
were obtained at 70 eV with a Hewlett Packard 5989A mass
spectrometer. Optical rotations [˛]2D5 were obtained at room
temperature using chloroform solutions on a Perkin-Elmer 241
polarimeter. HRMS of 7 was obtained on a Jeol JMS-SX102A
using polyethylene glycol (6 0 0) as internal reference. Ele-
mental composition was calculated within an error of 10 ppb
using the program installed in the system. Melting points were
obtained on an Electrothermal 9200 apparatus and are not
corrected. Elemental analyses were performed on a Thermo
Finnigan Flash EA 1112 series apparatus. The products were
separated by chromatography over (70–230 mesh) silica gel.
(1H, br, OH), 3.35 (1H, t, J = 8.2, H-26), 3.13 (1H, br, OH), 2.65 (1H,
m, H-20), 2.37 (1H, m, H-25), 2.01 (3H, s, 3-OCOCH3), 1.04 (3H,
d, J = 7.0 Hz, CH3-27), 1.02 (3H, d, J = 6.2 Hz, CH3-21), 0.95 (3H, s,
CH3-19), 0.76 (3H, s, CH3-18); 13C NMR (CDCl3, 100 MHz) ı: 170.8
(3-OCOCH3), 109.5 (C-22), 107.1 (C-23), 82.1 (C-16), 75.5 (C-26),
70.8 (C-3), 63.6 (C-17), 56.4 (C-14), 41.3 (C-13), 40.3 (C-12), 40.1
(C-15), 40.0 (C-9), 37.3 (C-5), 36.3 (C-25), 35.3 (C-8), 35.1 (C-10),
32.5 (C-20), 31.9 (C-4), 30.8 and 30.7 (C-1, C-2), 26.5 (C-6, C-7),
25.0 (C-24), 23.9 (C-19), 21.6 (3-OCOCH3), 20.9 (C-11), 17.1 (C-
21), 16.5 (C-18), 16.0 (C-27). Anal. calcd. for C29
H 9.45, O 19.56; found: C 70.71, H 9.81, O 19.48.
H46O6: C 70.99,
2.3.
(23R,25S)-3-Acetoxy-16,23:23,26-diepoxy-5-
cholestan-22-one (6)
To a solution of (22S,23S)-22,23-dihydroxy-23,26-epoxyfuro-
stane (5) (13 mg, 0.03 mmol) in dry dichlorometane (4 ml),
TiCl4 was added (0.02 ml, 8 eq.). The reaction was stirred
at room temperature overnight, poured over water and the
organic layer extracted with dichlorometane (2 × 5 ml), dried
over anhydrous MgSO4 and evaporated under vacuum. The 22-
oxo-23-spiroketal was obtained in quantitative yield (rf = 2.2,
hexane/EtOAc, 7:3), mp = 168 ◦C (literature [19], 169–171 ◦C).
2.2.
Oxidation of sarsasapogenin acetate with
NaNO2/BF3·Et2O
2.2.1. Experiment 1
Treatment of sarsasapogenin acetate 1 with NaNO2/BF3 in
glacial acetic acid, as previously described [9–13], afforded
(25S)-3-acetoxy-5-spirostan-23-nitroimino
(2),
which
hydrolyzes upon treatment with neutral Al2O3 (grade III) to
give (25S)-3-acetoxy-5-spirostan-23-one (3) and a small
quantity of (20S)-3-acetoxy-5-pregnan-20,16-carbolactone
(4).
2.4.
nitramine (7)
(25S)-3-Hydroxy-5-spirostan-23-ene-23-
To a solution of (25S)-3-acetoxy-5-spirostan-23-nitroimino
(2) (562 mg, 1.08 mmol) in ethylene glycol were added 17 ml of
a 10% aqueous solution of NaOH. The reaction mixture was
heated 22 h under reflux at 110–120 ◦C, cooled to room tem-
perature and poured over water. The organic layer extracted
with ethyl acetate (3 × 10 ml), dried over anhydrous MgSO4 and
evaporated under vacuum. The crude reaction product (0.56 g)
was chromatographed over silica gel (hexane/EtOAc, 8:2) to
give 350 mg (68% yield) (rf = 0.9, hexane/EtOAc, 7:3) of 7.
Compound 7: white powder, mp 154–156 ◦C; [˛]D25 −30◦ (c,
1.0, CHCl3); IRmax: 3561, 2929 (CH), 1584, 1314 (NNO2), 910
(N–O) cm−1; MS, m/z (%): 474 (M+, 3), 443 (6), 429 (28), 388 (6),
347 (41), 329 (40), 287 (42), 273 (84), 215 (15), 147 (46), 107 (61),
41 (100); 1H NMR (CDCl3, 400 MHz) ı: 9.26 (1H, br, NH), 6.44
(1H, d, J = 7.0 Hz, H-24), 4.53 (1H, q, J = 8.0 Hz, H-16), 4.11 (1H,
br, H-3), 3.91 (1H, dd, J = 3.3 and 11.4 Hz, H-26), 3.51 (1H, d,
J = 11.4 Hz, H-26), 2.27 (1H, m, H-25), 2.10 (1H, m, H-20), 1.20
(3H, d, J = 7.0 Hz, CH3-27), 0.98 (3H, d, J = 6.2 Hz, CH3-21), 0.97
(3H, s, CH3-19), 0.82 (3H, s, CH3-18); 13C NMR (CDCl3, 100 MHz)
ı: 135.9 (C-24), 129.5 (C-23), 107.8 (C-22), 82.5 (C-16), 67.2 (C-3),
63.8 (C-26), 61.4 (C-17). 56.5 (C-14), 41.2 (C-13), 40.1 (C-12), 39.9
(C-9), 38.5 (C-20), 36.6 (C-5), 35.4 (C-10), 35.3 (C-8), 33.6 (C-4), 31.7
(C-15), 30.0 (C-1), 29.9 (C-25), 27.9 (C-2), 26.6 (C-6, C-7), 23.9 (C-
19), 20.9 (C-11), 17.5 (C-27), 16.5 (C-18), 14.5 (C-21). HRMS calcd.
m/z for C27H43O5N2 (M+ + 1): 475.3172; found: 475.3159 error
2.6 ppm.
2.2.2. Experiment 2
Treatment of sarsasapogenin acetate 1 (10.00 g, 21.83 mmol)
with NaNO2/BF3 in acetic acid (100 ml, 5% aqueous solu-
tion) provided
ucts were chromatographed over silica gel with mixtures
of hexane/EtOAc of increasing solvent polarity to give:
2.80 g (27% yield) of (25S)-3-acetoxy-5-spirostan-23-one (3),
mp = 171–172 ◦C (literature [13], 171–173 ◦C) (hexane/EtOAc,
9:1); 3.10 g (37% yield) of (20S)-3-acetoxy-5-pregnan-20,16-
carbolactone (4), mp = 188 ◦C (literature [14], 184.5–185.5 ◦C)
(hexane/EtOAc, 8:2); 0.70 g (7% yield) (rf = 1.3 hexane/EtOAc,
7:3) of (22S,23S)-22,23-dihydroxy-23,26-epoxyfurostane (5),
mp = 178–179 ◦C (hexane/EtOAc, 7:3).
2.2.3. Experiment 3
with NaNO2/BF3 in 80 ml glacial acetic acid provided
and 4. The products were chromatographed over silica gel
to give 3.30 g (37% yield) of (25S)-3-acetoxy-5-spirostan-
23-nitroimino intermediate (2) [11,13] (hexane/EtOAc, 9:1)
and 2.20 g (32% yield) of (20S)-3-acetoxy-5-pregnan-20,16-
carbolactone (4), mp = 188 ◦C (literature [14], 184.5–185.5 ◦C)
(hexane/EtOAc, 8:2).
2
2.2.4. (22S,23S)-22,23-Dihydroxy-23,26-epoxy-
furostane (5)
Compound 5: white crystals, mp 178–179 ◦C (hexane/AcOEt);
[˛]2D5 −60◦ (c, 1.0, CHCl3); IRmax: 3538 (OH), 3475 (OH), 2950 (CH),
1727 (OAc), 1452, 1377, 1252, 1145 cm−1; MS, m/z (%): 490 (M+,
1), 472 (M+ − 18, 4), 444 (4), 389 (37), 329 (100), 315 (26), 255 (85),
130 (43); 1H NMR (CDCl3, 400 MHz) ı: 5.03 (1H, br, H-3), 4.60
(1H, td, J = 7.7 and 7.3 Hz, H-16), 4.18 (1H, t, J = 8.2 Hz, H-26), 3.39
2.5.
Crystal structure determination
Crystals of 2 and 5 suitable for X-ray analysis were obtained
from a mixture of hexane–ethyl acetate (9:1) and (7:3), respec-
tively, by slow evaporation of the solvent at room tem-
perature. The X-ray measurement of (25S)-3-acetoxy-5-