Synthesis of 3α-hydroxy-21-(1′-imidazolyl)-3β-methoxyl- methyl-5α-pregnan-20-one via lithium imidazole with 17α- acetylbromopregnanone

Article abstract of DOI:10.1016/j.steroids.2005.08.006

The synthesis of biologically active 3α-hydroxyl-21-(1′- imidazolyl)-3β-methoxymethyl-5α-pregnan-20-one (11) was accomplished in six steps. The key steps were the improvement of stereoselectivity for acetyl isomers in C-17 and the introduction of imidazole into the core structure by use of lithium imidazole. This latter key step provided the desired product 11 in 82% yield without the formation of 1,3-disubstituted imidazolium salt as impurity, which is generally observed in traditional method.

Full text of DOI:10.1016/j.steroids.2005.08.006

steroids 7 1 ( 2 0 0 6 ) 77–82
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/steroids
Synthesis of 3␣-hydroxy-21-(1ꢀ-imidazolyl)-3␤-methoxyl-
methyl-5␣-pregnan-20-one via lithium imidazole with
17␣-acetylbromopregnanone
Fung Fuh Wonga,∗, Chun-Yen Chenb, Tse-Hsin Chenb, Jiann-Jyh Huangc,
Hsiao-Ping Fangd, Mou-Yung Yehb,e
a
Environmental Resource Management Research Center, National Cheng Kung University, No. 500, Sec. 3, An-Ming Rd., Tainan City,
Taiwan 709, ROC
b
Department of Chemistry, National Cheng Kung University, No. 1, Ta Hsueh Rd., Tainan, Taiwan 70101, ROC
Development Center for Biotechnology, No. 101, Lane 169, Kangning St., Xizhi City, Taipei County, Taiwan 221, ROC
ScinoPharm Taiwan, Ltd., No. 1, Nan-Ke 8th Rd., Tainan Science-Based Industrial Park, Shan-Hua, Tainan County, Taiwan 741, ROC
Nan Jeon Institute of Technology, No.178, Chaocin Rd., Yanshuei Township, Tainan County 737, Taiwan, ROC
c
d
e
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of biologically active 3␣-hydroxyl-21-(1ꢀ-imidazolyl)-3␤-methoxymethyl-5␣-
pregnan-20-one (11) was accomplished in six steps. The key steps were the improvement of
stereoselectivity for acetyl isomers in C-17 and the introduction of imidazole into the core
structure by use of lithium imidazole. This latter key step provided the desired product 11
in 82% yield without the formation of 1,3-disubstituted imidazolium salt as impurity, which
is generally observed in traditional method.
Received 13 January 2005
Received in revised form 15 June
2005
Accepted 17 August 2005
Available online 24 October 2005
© 2005 Elsevier Inc. All rights reserved.
Keywords:
Hydrogenation
Oxidation
Epoxidation
Ring opening reaction
Bromination
1,3-Disubstituted imidazolium salt
1.
Introduction
synthetic compounds prepared by connecting a special func-
tionality to the core structure of a steroid [4].
Steroid compounds attract much attention because of their
special biological activity [1]. They can regulate a variety
of biological processes and thus be developed as drugs for
the treatment of disease including autoimmune diseases,
brain tumors, breast cancer, cardiovascular, prostate can-
cer, osteoarthritis [2,3]. Except for the naturally-occuring
substances, most of steroidal pharmaceuticals were semi-
The azole moiety often shows some special biological activ-
ity when it is introduced to some biological active compounds
[5]. However, it is unusual that a steroid contains an azole
moiety at C-21 position [6]. The basicity and hydrophilic-
ity of an azole in theory might alter the biological func-
tion of a steroid. Moreover, the azole might interact with
some enzymes, e.g. cytochrome P. 450, as a part of the whole
∗
Corresponding author. Tel.: +886 6 384 0136x212; fax: +886 6 384 0960.
E-mail address: wong99@mail.ncku.edu.tw (F.F. Wong).
0039-128X/$ – see front matter © 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.steroids.2005.08.006

78
steroids 7 1 ( 2 0 0 6 ) 77–82
pharmaceutical [7–10]. The naturally-occurring neuroactive
steroid 3␣-hydroxyl-5␣-pregnan-20-one (1), its 5␤-epimer (2)
and 3␤-substituted derivatives of 1 and 2 (3) are potent
allosteric modulators of the GABA-A receptor [11,12]. As a
result, we designed a new steroidal derivative, 3␣-hydroxyl-21-
(1ꢀ-imidazolyl)-3␤-methoxymethyl-5␣-pregnan-20-one (11). It
possesses an imidazole group in C-21 [12] and was found in
preliminary studies to enhance the ability of the inhibitory
neurotransmitter, gamma aminobutyric acid (GABA) to acti-
vate a type of receptors known as GABA-A receptors. There-
fore, we planned to develop a process for the synthesis of
compound for future investigation of its detailed biological
activity and toxicity.
2.2.
Hydrogenation reaction
3␤-Hydroxy-5␣-pregnan-20-one (5) [13]: To a THF solution
(800 mL) containing 3␤-hydroxypregn-5-en-20-one (4, preg-
nenolone, 100 g, 315 mmol, 1.0 equiv.) and 10% Pd/C (8.0 g)
was added glacial acetic acid (28 mL). The reaction mixture
was hydrogenated under a constant H2 pressure of 60 psi at
50–60 ◦C for 8.0 h. The solution was filtered through Celite and
the Celite bed was washed with hot THF. The filtrate was
concentrated under reduced pressure and the residue was
washed with hexanes (800 mL×2) to give 5 (90 g, 283 mmol) as a
white solid in 90%: m.p. (recrystallized from toluene/hexanes)
194–196 ◦C; 1H NMR (CDCl3, 400 MHz) ı 0.62 (s, 3 H, 19-CH3),
0.83 (s, 3 H, 18-CH3), 0.63–1.09 (m, 3 H), 1.19–1.49 (m, 10 H),
1.60–2.16 (m, 9 H), 2.51 (s, 3 H, 21-CH3), 2.24 (t, 3 H, J = 8.8 Hz,
17␣-CH), 3.61 (m, 1 H, 3␣-CH); MS m/z (relative intensity) 319
(M+, 31), 301 (43), 154 (100), 149 (43), 137 (84), 107 (40), 95 (26), 91
(37), 89 (27), 77 (33); HRMS calcd for C21H34O2 318.2559, found
318.2554.
2.3.
Oxidation reaction
The key features for the synthesis of 11 involved the
improvement of the ratio for acetyl isomers in C-17 in the ring
opening reaction and the introduction of an imidazole moiety
into the core structure. The usual method of direct heating
of ␣-bromoketone with imidazole, however, always provides a
di-alkylated product as major impurity and is not suitable for
scale up. In this work, we report the reaction of lithium imida-
zole with 21-bromo-3␣-hydroxy-3␤-methoxymethyl-5␣-pre-
gnan-20-one (10) to provide 3␣-hydroxyl-21-(1ꢀ-imidazolyl)-
3␤-methoxymethyl-5␣-pregnan-20-one (11) in high yield
without the formation of the 1,3-disubstituted imidazolium
salt dimer.
5␣-Pregnane-3,20-dione (6) [14,15]: To 3␤-hydroxy-5␣-
pregnan-20-one (5, 100 g, 318 mmol, 1.0 equiv.) in glacial
acetic acid (1.5 L) was added dropwise an aqueous NaOCl
solution (12%, 510 mmol, 317 mL) containing sodium bromide
(3.27 g, 3.18 mmol, 0.10 equiv.) under 38 ◦C. The biphasic
reaction mixture was stirred vigorously at room temperature
for 2.0 h. The reaction mixture was quenched with water
(850 mL) and the resultant solids were collected by filtration
and washed with water (100 mL×2). The solids were dried
under vacuum for 12 h and purified by recrystallization from
ethyl acetate to give pure 6 (79.6 g, 252 mmol) as a white solid
in 79% yield: m.p. 200–202 ◦C; 1H NMR (CDCl3, 400 MHz) ı
0.64 (s, 3 H, 19-CH3), 1.01 (s, 3 H, 18-CH3), 0.95–1.00 (m, 2 H),
1.10–1.79 (m, 13 H), 2.02–2.46 (m, 7 H), 2.23 (s, 3 H, 21-CH3),
2.53 (t, 3 H, J = 8.8 Hz, 17␣-CH); IR (diffuse reflectance) 3380 (m),
2937 (s), 1708 (m, C O), 1434 (m), 1385 (m), 1354 (m), 1231 (m),
1206 (m), 1147 (m), 1040 (m), 1004 (m), 947 (m), 866 (m), 804
(m), 722 (m), 569 (m), 502 (m) cm−1; MS m/z (relative intensity)
317 (M+, 100), 176 (42), 154 (80), 149 (55), 137 (75), 107 (30), 95 91
(29), 89 (20), 81 (21), 77 (29), HRMS calcd for C21H32O2 316.2402,
found 316.2408.
2.
Experimental
2.1.
General procedure
Analytical thin-layer chromatography (TLC) was performed on
precoated plates (silica gel 60 F-254), purchased from Merck
Inc. Purification by gravity column chromatography was car-
ried out by use of Merck Reagents Silica Gel 60 (particle
size 0.063–0.200 mm, 70–230 mesh ASTM). Infrared (IR) spectra
were measured on a Bomem Michelson Series FT-IR spec-
trometer. The wavenumbers reported are referenced to the
polystyrene 1601 cm−1 absorption. Absorption intensities are
recorded by the following abbreviations: s, strong; m, medium;
w, weak. Proton NMR spectra were obtained on a Varian Unity-
400 (400 MHz) or a Bruker-300 (400 MHz) spectrometer by use of
CDCl3 and d6-DMSO as solvent. Carbon-13 NMR spectra were
obtained on a Varian Unity-400 (100 MHz) spectrometer or a
Bruker-400 (100 MHz) spectrometer by used of CDCl3 as sol-
vent. Carbon-13 chemical shifts are referenced to the center
of the CDCl3 triplet (ı 77.0 ppm). Multiplicities are recorded
by the following abbreviations: s, singlet; d, doublet; t, triplet;
q, quartet; m, multiplet; J, coupling constant (Hz). Elemental
analyses were carried out on a Heraeus CHN–O RAPID element
analyzer. Purity of all products was >99% from the results of
HPLC analysis.
2.4.
Epoxidation reactions
(3R)-Spiro[oxirane-2ꢀ,5␣-pregnan]-20-one (7) [11]: A stirred
solution of trimethylsulfoxonium iodide (32.0 g, 144 mmol,
1.5 equiv.) and potassium tert-butoxide (17.2 g, 154 mmol,
1.6 equiv.) in DMSO (500 mL) was heated at 55–60 ◦C for
1.0 h under N2. 5␣-Pregnane-3,20-dione (6, 30.4 g, 96.1 mmol,
1.0 equiv.) was added to the reaction mixture and stirred at
room temperature for 5.0 h. After the reaction was completed,
the reaction mixture was quenched and precipitated by water
(500 mL) in ice-bath. The resultant precipitate was collected by
filtration, washed with water (200 mL×2), and dried in vacuum
oven at below 50 ◦C for 12 h. The residue was purified by recrys-
tallization from MeOH/acetone (4/1) to give pure 7 (23.8 g,
72.1 mmol) as a white powder in 75% yield: m.p. 204–206 ◦C;
1H NMR (CDCl3, 400 MHz) ı 0.62 (s, 3 H, 19–CH3), 0.85 (s, 3 H,

steroids 7 1 ( 2 0 0 6 ) 77–82
79
18-CH3), 0.83–1.08 (m, 2 H), 1.10–1.56 (m, 10 H), 1.57–1.83 (m, 7
H), 1.84–2.28 (m, 3 H), 2.16 (s, 3 H, 21–CH3), 2.53 (t, 3 H, J = 8.8 Hz,
17␣-CH), 2.62 (s, 2 H, –OCH2); IR (diffuse reflectance) 3375 (m),
2930 (s), 1702 (m, C O), 1440 (m), 1381 (m), 1358 (m), 1280 (m),
1211 (m), 1166 (m), 958 (m), 916 (m), 901 (m), 835 (m), 792 (m),
700 (m), 594 (m) cm−1; MS m/z (relative intensity) 331 (M+, 57),
149 (100), 137 (82), 107 (64), 95 (79), 91 (91), 81 (70), 77 (63), 55
ous HBr solution (48%). Bromine (13.5 g, 83.9 mmol, 1.05 equiv.)
was dissolved in MeOH solution (200 mL) and added dropwise
to the reaction mixture over 1.0 h in the dark. After the
reaction was completed, the reaction mixture was quenched
and precipitated by water (600 mL). The resultant precipitate
was collected by filtration, washed with water (100 mL×2),
and dried in vacuum oven at below 40 ◦C for 12 h. The residue
was purified by recrystallization from EtOAc/n-hexane (5/95)
to give pure 10 (27.4 g, 62.2 mmol) as white powder in 78%
yield: m.p. 116–118 ◦C; 1H NMR (CDCl3, 400 MHz) ı 0.65 (s, 3 H,
19-CH3), 077 (s, 3 H, 18-CH3), 0.78–1.10 (m, 2 H), 1.20–2.01 (m,
19 H), 2.15–2.29 (m, 1 H), 2.83 (t, 3 H, J = 8.8 Hz, 17␣-CH), 3.20 (s,
2 H, –OCH2), 3.40 (s, 3 H, –OCH3), 3.91 (d, 1 H, J = 13.2 Hz, –CHBr),
3.93 (d, 1 H, J = 13.2 Hz, –CHBr); 13C NMR (CDCl3, 100 MHz) ı
11.20, 13.72, 20.97, 23.71, 24.48, 28.38, 30.23, 31.89, 33.33, 35.58,
36.04, 37.10, 38.98, 40.19, 45.08, 53.93, 56.71, 59.42, 60.55, 71.02,
81.94, 202.12; IR (diffuse reflectance) 3566 (s), 2934 (s), 1709
(s, C O), 1442 (m), 1384 (m), 1312 (m), 1189 (m), 960 (m), 897
(m), 808 (m), 624 (m), 595 (m), 551 (m), 503 (m) cm−1; MS m/z
(relative intensity) 441 (M+, 8), 423 (89), 391 (95), 175 (24), 161
(25), 159 (27), 154 (29), 147 (32), 145 (30), 137 (51), 133 (35), 121
(46), 105 (71), 95 (100), 91 (82), 81 (65), 79 (62), 77 (43), 71 (29),
67 (36), 45 (36); HRMS calcd for C23H37BrO3 440.1926, found
440.1931.
(73), 43 (93); HRMS calcd for C22
H34O2 330.2559, found 330.2565.
2.5. Ring opening reactions
3␣-Hydroxy-3␤-methoxymethyl-5␣,17␣-pregnan-20-one (8)
and 3␣-hydroxy-3␤-methoxymethyl-5␣,17␤-pregnan-20-one
(9) [11]: Sodium hydroxide (7.70 g, 192 mmol, 2.0 equiv.) was
dissolved in MeOH (300 mL) and heated at reflux for 30 min
under N2. Compound 7 (31.7 g, 96.0 mmol, 1.0 equiv.) was
slowly added to the methanolic solution at room tempera-
ture under N2 and the solution was heated at 35–40 ◦C for
8.0–10 h. The reaction mixture was quenched and precipitated
by water (500 mL) in ice-bath. The resultant precipitate was
filtrated, washed with water (100 mL×2), and dried in vac-
uum oven at below 50 ◦C for 12 h to give diastereomers 8
and 9 (34.1 g, 94.1 mmol) as light yellow solids in 98% total
yield. The mixture was purified by recrystallization from ethyl
acetate/hexanes (1/1) to give pure 8 (23.8 g, 75.3 mmol) as a
white powder in 80% yield. The residual solution was concen-
trated under reduced pressure and purified by column chro-
matography on silica gel (30% EtOAc in hexanes as eluant) to
give a pure 9 as a light yellow powder.
For compound 8: m.p. 167–169 ◦C; TLC Rf 0.35 (30% EtOAc in
hexanes as eluant); 1H NMR (CDCl3, 400 MHz) ı 0.62 (s, 3 H, 19-
CH3), 0.77 (s, 3 H, 18-CH3), 0.75–1.08 (m, 3 H), 1.12–1.80 (m, 17 H),
1.91–2.13 (m, 2 H), 2.16 (s, 3 H, 21-CH3), 2.54 (t, 3 H, J = 8.8 Hz,
17␣-CH), 3.12 (s, 2 H, –OCH3), 3.39 (s, 3 H, –OCH3); 13C NMR
(CDCl3, 100 MHz) ı 11.21, 13.46, 20.80, 22.80, 24.40, 28.43, 30.24,
31.51, 31.93, 33.35, .5.54, 36.04, 37.13, 39.13, 40.23, 44.27, 54.03,
56.78, 59.42, 63.85, 71.05, 81.96, 209.69; IR (diffuse reflectance)
3515 (s), 3385 (s), 2910 (s), 1708 (m, C O), 1435 (m), 1385 (m),
1352 (m), 1235 (m), 1207 (m), 1070 (m), 968 (m), 946 (m), 860 (m),
804 (m), 602 (m), 514 (m) cm−1; MS m/z (relative intensity) 363
(M+, 28), 345 (100), 313 (51), 154 (77), 137 (82), 119 (44), 107 (62),
95 (86), 93 (55), 91 (77), 81 (70), 77 (50), 71 (50), 67 (47), 55 (60),
2.7.
Substitution reactions
3␣-Hydroxy-21-(1ꢀ-imidazolyl)-3␤-methoxymethyl-5␣-preg-
nan-20-one (11). Method A: To a solution of imidazole (23.1 g,
217 mmol, 3.0 equiv.) in THF (200 mL) was added lithium
hydride (1.79 g, 224 mmol, 3.1 equiv.). The solution was heated
at reflux for 30 min under N2. Compound 10 (31.2 g, 72.8 mmol,
1.0 equiv.) in THF (200 mL) was slowly added to the reaction
mixture at −5 to 0 ◦C over a period of 5 min under N2. After
being stirred at −5 to 0 ◦C for 30 min, the reaction mixture was
quenched by saturated NH4Cl aqueous solution (500 mL) in
ice-bath. The organic layer was separated and concentrated
under reduced pressure to give pure 11 (25.3 g, 59.1 mmol)
as white powder in 81% isolated yield: m.p. 196–198 ◦C; 1H
NMR (CDCl3, 400 MHz) ı 0.66 (s, 3 H, 19-CH3), 076 (s, 3 H,
18-CH3), 0.78–1.05 (m, 2 H), 1.16–1.71 (m, 18 H), 1.92–1.97 (m,
1 H), 2.14–2.29 (m, 1 H), 2.57 (t, 3 H, J = 9.0 Hz, 17␣-CH), 3.18
(s, 2 H, –OCH2), 3.39 (s, 3 H, –OCH3), 4.50 (d, 1 H, J = 18.0 Hz,
–CHBr), 4.71 (d, 1 H, J = 18.0 Hz, –CHBr), 6.85 (s, 1 H), 7.09 (s, 1
H), 7.41 (s, 1 H); 13C NMR (CDCl3, 100 MHz) ı 12.31, 13.88, 21.27,
23.25, 24.49, 28.54, 31.46, 31.98, 35.52, 35.54, 37.03, 38.12, 39.28,
44.84, 45.11, 54.14, 56.49, 56.78, 60.47, 71.06, 119.95, 129.41,
137.79, 203.19; IR (diffuse reflectance) 3483 (s), 2905 (s), 1754
(m, C O), 1531 (m), 1446 (m), 1372 (m), 1265 (m), 1050 (m), 988
(m), 887 (m), 824 (m), 722 (m), 634 (m), 502 (m) cm−1; MS m/z
(relative intensity) 429 (M+, 100), 427 (31), 413 (15), 411 (22), 383
(22), 137 (28), 105 (13), 93 (12), 82 (37), 69 (39); HRMS calcd for
43 (64); HRMS calcd for C23H38O3 362.2821, found 362.2827.
For compound 9: m.p. 154–156 ◦C; TLC Rf 0.30 (30% EtOAc
in hexanes as eluant); 1H NMR (CDCl3, 400 MHz) ␦ 0.74 (s, 3 H,
19-CH3), 091 (s, 3 H, 18-CH3), 0.98–2.12 (m, 21 H), 2.12 (s, 3 H,
21-CH3), 2.78 (t, 3 H, J = 6.0 Hz, 17␤-CH), 3.17 (s, 2 H, –OCH2), 3.38
(s, 3 H, –OCH3); 13C NMR (CDCl3 100 MHz) ı 11.15, 20.92, 20.95,
24.27, 25.89, 28.50, 30.21, 32.20, 32.70, 35.39, 35.77, 35.99, 37.13,
40.07, 45.79, 50.36, 53.41, 59.41, 61.44, 70.97, 82.00, 212.59; MS
m/z (relative intensity) 363 (M+, 9), 345 (100), 327 (45), 313 (60),
311 (19), 154 (21), 147 (24), 143 (10), 137 (28), 133 (19), 119 (29),
107 (35), 95 (41), 93 (33), 91 (42), 85 (19), 81 (32), 77 (23), 71 (27), 55
(19), 43 (30); HRMS calcd for C23H38O3 362.2821, found 362.2818.
C
26H40N2O3 428.3039, found 428.3037.
Method B: A solution containing compound 10 (35.3 g,
80.0 mmol, 1.0 equiv.) and imidazole (10.9 g, 160 mmol,
2.0 equiv.) in THF (400 mL) was heated at reflux for 8.0–10 h
under N2. The reaction mixture was concentrated under
reduced pressure and the resultant oil was re-dissolved in
CH2Cl2 (600 mL). The solution was washed with 5% aque-
ous NaHCO3 solution (200 mL×2), brine (200 mL×2), and
2.6.
Bromination reactions
21-Bromo-3␣-hydroxy-3␤-methoxymethyl-5␣-pregnan-20-
one (10): To a solution of compound 8 (29.0 g, 80.0 mmol,
1.0 equiv.) in MeOH (300 mL) was added three drops of aque-

80
steroids 7 1 ( 2 0 0 6 ) 77–82
concentrated under reduced pressure. The residue was puri-
fied by column chromatography on silica gel (5.0% MeOH in
CH2Cl2 as eluant) to give 11 (15.5 g, 36.2 mmol) as white solids
in 45% yield and 12 (22.4 g, 28.3 mmol) as light yellow solids
in 35% yield.
For compound 12: 1H NMR (CDCl3 + CD3OD, 400 MHz) ı 0.66
(s, 6 H, 19-CH3), 0.73 (s, 6 H, 18-CH3), 0.75–1.09 (m, 4 H), 1.12–1.92
(m, 36 H), 2.01–2.23 (m, 4 H), 2.71 (t, 2 H, J = 8.8 Hz, 17-CH), 3.36
(s, 4 H, –OCH2), 3.36 (s, 6 H, –OCH3), 5.19 (d, 2 H, J = 18.4 Hz,
–CHBr), 5.49 (d, 2 H, J = 18.4 Hz, –CHBr), 7.28 (s, 1 H), 7.32 (s, 1
H), 9.30 (s, 1 H); IR (diffuse reflectance) 3426 (s), 2931 (s), 1731
(m, C O), 1632 (m), 1569 (m), 1449 (m), 1385 (m), 1352 (m), 1294
(m), 1172 (m), 1119 (m), 1040 (m), 961 (m), 926 (m), 900 (m), 845
(m), 809 (m), 745 (m), 720 (m), 690 (m), 624 (m) cm−1; MS m/z
(relative intensity) 789 (M+, 100), 773 (14), 744 (12), 497 (17), 429
(31), 442 (20), 149 (14), 81 (11), 73 (23), 69 (12); HRMS calcd for
nenolone was subjected to hydrogenation in accordance with
a reported procedure [13] to give compound 5 in 90% yield.
Following the method developed by Kaya et al. [16], the C3-OH
in 5 was oxidized to its corresponding ketone 6 in 79% by use
of NaOCl and NaBr in glacial acetic acid. This conversion pos-
sesses the advantage of higher reaction rate when compared
with traditional methods [17]. The structures of 5 and 6 were
characterized by comparison with the data reported in litera-
ture [13,14] and their purities were >99% from HPLC analysis.
We then treated compound 6 with trimethylsulfoxonium
iodide and potassium tert-butoxide in DMSO [18–20]. The cor-
responding oxiranes 7 was obtained in 75% yield. In this
conversion, the selective epoxidation took place only at C-3
carbonyl moiety in 6. No product containing oxirane function-
ality at C-17 position was found. When we used trimethylsul-
fonium ioide under basic conditions instead [21], the reaction
gave a mixture of C-3 and C-17 oxiranes.
C49H77N2O6 789.5776, found 789.5771.
For the introduction of CH3OCH2-group in the steroid skele-
ton, we tried to use methoxide in methanol to open the oxirane
functionality in 7. The nucleophile would attack the less-
hindered exocyclic CH2 than C-3 in 7 according to the Krasuskii
rule [22]. However, it is also reported that the C-17 acetyl group
would undergo racemization under strong basic condition [23].
3.
Result and discussion
The synthetic pathway of the target pharmacological active
steroid 11 is depicted in Scheme 1. In the first step, preg-
Scheme 1 – The synthetically route of 3␣-hydroxyl-21-(1ꢀ-imidazolyl)-3␤-methoxymethyl-5␣-pregnan-20-one.

steroids 7 1 ( 2 0 0 6 ) 77–82
81
Table 1 – Ring opening reaction of oxirane 7 in the presence of different equivalent of NaOMe at different temperature in
MeOH
Entry
Equivalent of NaOMe
Temperature
Reaction time (h)
Ratioa of 8/9
1
2
3
4
5
1.0
2.5
5.0
2.5
2.5
Reflux (∼68 ◦C)
Reflux (∼68 ◦C)
Reflux (∼68 ◦C)
35–40 ◦C
4.0–6.0
4.0–6.0
4.0–6.0
8.0–10
>50
78/22
79/21
79/21
88/12
90/10
20–30 ◦C
a
The ratios of 8/9 (C-17␤/C17␣) were determined by HPLC on a Hewlett-Packard 1100 Series instrument equipped with Columns (Phenomenex,
Luna C18(2), 3 ␮m particle size, 15 cm (L) × 4.6 mm (i.d.) and mobile phase: MeOH/water (80:20, v/v), flow rate = 0.80 mL/min).
We then investigated the reaction of different equivalent of
methoxide in MeOH with 7 under various temperature and
time (see Table 1). Under refluxing conditions, the ratios of
C-17␤/C17␣ (8/9) were similar (∼80/20) when different equiva-
lents of methoxide were used. When the reaction temperature
was 35–40 ◦C and the reaction time was 8.0–10 h, the ratio of
C-17␤/C17␣ was 88/12 (entry 4 in Table 1). Although the reac-
tion conditions in entry 5 provided the best C-17␤/C17␣ ratio,
the reaction time was >50 h and therefore not suitable for syn-
thetic purposes.
For the optimization of the C-17␤/C17␣ (8/9) ratio, we tried
different soft methoxides including LiOMe, Mg(OMe)2 and
Ca(OMe)2; however, they gave poorer C-17␤/C17␣ ratios than
using NaOMe (see entries 1–3 in Table 2). When we used LiOH
or NaOH in methanol, the reaction provided better C-17␤/C17␣
ratios (see entries 4 and 5 in Table 2). The best result was
accomplished by using NaOH in MeOH at reflux for 8.0–10 h.
The isomeric ratio of C-17␤/C17␣ (8/9) was 91/9 and the yield
was 98%. After recrystallization from ethyl acetate/hexanes,
compound 8 was obtained as white powder in 80% yield with
99.5% purity. Accordingly, bromoketone 10 was synthesized
from the reaction of compound 8 with Br2 in MeOH in the
presence of catalytic amount of HBr [24,25] in 86% yield.
The final step was the key in this synthesis because the
usual introduction of imidazole functionality in the ␣-position
of a ketone often provided dimeric products [10]. Supporting
evidence comes from our direct treatment of bromoketone 10
with imidazole under reflux. The reaction gave a mixture of
the final product 11 in 45% yield and a significant amount
of dimeric product 12 in 35% yield. When bromoketone 10
was allowed to react with 1-trimethylsilylimidazole [10] or 1-
benzylimidazole at reflux [26], no diminishment of dimeric 12
was found and subsequent latter deprotection procedure was
troublesome.
To overcome the low-yield and selectivity of the reaction,
we developed lithium imidazole as a new alkylation agent
for ␣-bromoketone. We treated bromoketone 10 with lithium
imidazole at −5 to 0 ◦C for 10 min under N2 atmosphere.
After worked-up, the crude 11 was obtained as a light yel-
low solid in 91% yield. The crude product was crystallized
from MeOH/diisopropyl ether to provide the pure 11 as white
solid in 82% yield. In this method, the yield of dimeric 12
was very low and could be easily removed by recrystallization.
We believe, this new method would be useful for the future
production of compound 11 to study its in vivo activity and
toxicology.
In conclusion, we developed a new and more efficient
route for the synthesis of 3␣-hydroxyl-21-(1ꢀ-imidazolyl)-3␤-
methoxymethyl-5␣-pregnan-20-one (11). It consisted with six
steps and the overall yield was 28%. For the ring opening reac-
tion of oxirane 7, we found the best reaction condition was the
use of NaOH in methanol at reflux. The ratio of 8/9 was 91/9
and the yield was 98%. In the key step of introduction of imida-
zole group, we developed lithium imidazole as new alkylation
agent. The formation of dimeric by-product was very low and
it can be easily removed by recrystallization. In this conver-
sion, the yield is high (82%). Consequently, a convenient and
efficient method for the introduction of imidazole moiety to
␣-bromoketone was developed via lithium imidazole with the
advantage of high yield and low amount of by-product.
Acknowledgments
Table 2 – The ring opening reaction of oxirane 7 in the
presence of different bases (2.5 equiv.) at 35–40 ◦C in
MeOH
We are grateful to ScinoPharm Taiwan Ltd. and the National
Science Council of Republic of China for financial support.
Entry
Base
Reaction time (h) The ratioa of 8/9
1
2
3
4
5
LiOMe
8.0–10
>30
>50
8.0–10
8.0–10
82/18
76/14b
72/18b
85/15
91/9
r e f e r e n c e s
Mg(OMe)2
Ca(OMe)2
LiOHc
NaOHc
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