A convenient synthesis of oxandrolone through a regioselective Candida antarctica lipase-catalyzed transformation

Article abstract of DOI:10.1016/S0957-4166(03)00593-7

The use of a regioselective CAL-catalyzed transformation of a suitable intermediate allowed a convenient synthesis of oxandrolone, an anabolic hormone actually employed to improve the quality of life for patients with HIV-infections.

Full text of DOI:10.1016/S0957-4166(03)00593-7

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 14 (2003) 2781–2785
A convenient synthesis of oxandrolone through a regioselective
Candida antarctica lipase-catalyzed transformation
Patrizia Ferraboschi,* Diego Colombo and Paolo Prestileo
Department of Medical Chemistry, Biochemistry and Biotechnology, Universita` degli Studi di Milano, Via Saldini 50,
20133 Milan, Italy
Received 30 June 2003; accepted 23 July 2003
Abstract—The use of a regioselective CAL-catalyzed transformation of a suitable intermediate allowed a convenient synthesis of
oxandrolone, an anabolic hormone actually employed to improve the quality of life for patients with HIV-infections.
© 2003 Elsevier Ltd. All rights reserved.
1. Introduction
different approach, planning to open the 1,2-double
bond of compound 2 with potassium permanganate
and sodium periodate,5 delaying to a later step the
discrimination of C-1 and C-3 of the obtained 1,3-
diacid 4.
Oxandrolone
1
(17b-hydroxy-17a-methyl-2-oxa-5a-
androst-3-one) is a clinically useful, synthetic, anabolic
steroid administered in conditions which included
weight loss due to extensive surgery, chronic infections,
trauma, etc. Actually,1,2 for the activity in increasing
skeletal muscle protein synthesis, oxandrolone is
employed to mitigate weight loss associated with dis-
ease progression, reduced quality of life and increased
mortality, in patients with HIV (human immunodefi-
ciency virus)-infection.
2. Results and discussion
Derivative 2 was prepared starting from 3b-hydroxy-
5a-androstan-17-one 5 in 65% overall yield: in the first
step the 17a-methyl group was introduced by reaction
with methylmagnesium bromide;3 then oxidation of
3-hydroxy group and selective halogenation with pyri-
dinium tribromide6 afforded the 2-bromo-3-keto
derivative that, by elimination (lithium bromide and
lithium carbonate in dimethylformamide4) furnished
compound 2. The best results for oxidative cleavage of
ring A were achieved carrying out the reaction with
potassium permanganate and sodium periodate in the
presence of potassium carbonate in tert-butanol, at
reflux;7 the 17b-hydroxy-17a-methyl -1,3-seco-2-nor-5a-
In 1963 Pappo and Jung3 prepared the appropriate
intermediate, 17b-hydroxy-17a-methyl-1-oxo-1,3-seco-
2-nor-5a-androstan-3-oic acid 3, for the synthesis of
lactone 1, opening the A-ring of 17b-hydroxy-17a-
methyl-1-androsten-3-one 24 with osmium tetroxide and
lead tetraacetate. The choice of these oxidants,
although toxic and expensive, provided the advantage
of a different functionalization of C-1 and C-3, neces-
sary in the next steps of the synthesis. We followed a
* Corresponding author. Tel.: +39 02 50316052; fax: +39 02 50316040; e-mail: patrizia.ferraboschi@unimi.it
0957-4166/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0957-4166(03)00593-7

2782
P. Ferraboschi et al. / Tetrahedron: Asymmetry 14 (2003) 2781–2785
androstane-1,3-diacid 4 was treated with diazomethane
and the obtained dimethylester 6 reduced to 1,3-seco-2-
nor-1,3-diol 78 with lithium aluminum hydride in tetra-
hydrofuran (78% yields from 2) (Scheme 1).
acylation of 7 and alcoholysis of diacetate 8 the two
different regioisomers were obtained: under irreversible
transesterification conditions13,14 (vinyl acetate in tetra-
hydrofuran, 3 h) 1,3-diol 7 was completely converted into
3-monoacetate 9, whereas diacetate 8, on treatment with
1-octanol in tetrahydrofuran15 (24 h, 70% conversion),
afforded only 1-monoacetate 10† (Scheme 2).
The well documented hydrolytic enzymes regio- and
stereoselectivity prompted us to investigate a biocatalytic
method for a different functionalization of 1- and 3-
hydroxy group of 7. Considering the lypophylicity of
substrate we tested some commercially available lipases,
known for their activity in organic solvents and selective
transformations of steroids.9 Whereas 1,3-diol 7 was not
substrate for the lipases from Pseudomonas cepacia and
Candida rugosa, good results were observed with lipase
from Candida antarctica (Novozym 435, type-B lipase
from C. antarctica immobilized on an acrylic resin),
already successfully applied with steroidal compounds,
by others10,11 as well as in our laboratory.12 In fact by
The identity of the novel monoacetates 9 and 10 was
1
ascertained through H NMR analyses. In particular,
lower field shifts of the methylenic C-1 or C-3 protons
with respect to the 1,3-diol 7, accounted for the struc-
ture of compounds 10 or 9, respectively. Complete
1H and 13C NMR characterisation of these new steroids
was also obtained using a combination of 1D and 2D
(COSY, HSQC) experiments recorded in pyridine at 338
K, as this solvent gave the best spread of proton
resonances.
Scheme 1. Reagents: (i) CH3MgBr; (ii) CrO3/H2SO4; (iii) Py·HBr·Br2; (iv) Li2CO3, LiBr; (v) KMnO4, NaIO4; (vi) CH2N2; (vii)
LiAlH4.
Scheme 2.
† The enzyme in both cases acts on the less hindered position 3.

P. Ferraboschi et al. / Tetrahedron: Asymmetry 14 (2003) 2781–2785
2783
Since compound 10 is a suitable intermediate for oxan-
drolone synthesis we tested different CAL-catalyzed
alcoholysis conditions of 8 with the aim of optimizing the
results in terms of conversion and reaction times. Carry-
ing out the transformation in pure 1-octanol a 90%
conversion after 24 h was observed and similar results
(80% conversion after 20 h) were furnished by 1-butanol.
Best results were obtained in pure ethanol: in fact, a 95%
conversion of 1,3-diacetate 8 was reached after only 3 h‡
and the obtained 10, after crystallization, could be
transformed into oxandrolone 1 (70% yields) by oxida-
tion (Jones conditions), hydrolysis of acetate 11 and
acidic treatment of the intermediate hydroxyacid
(Scheme 3).
and 13C, respectively. Chemical shifts are reported as l
(ppm) relative to TMS as internal reference. Analytical
samples were dissolved in CDCl3, unless otherwise stated,
and their spectra recorded at 298 or 338 K (compounds
9 and 10). The assignments for compounds 9 and 10 were
given by a combination of 1D and 2D COSY and HSQC
experiments, using standard Bruker pulse programs. MS
analyses were performed on a Varian Saturn Spectrom-
eter (EI 70 eV).
4.1. 17b-Hydroxy-17a-methyl-5a-androst-1-en-3-one 2
To a solution of methylmagnesium bromide (1.4 M in
toluene/tetrahydrofuran 75/25, 84 mL), at room temper-
ature, 3b-hydroxy-5a-androstan-17-one 5 (3 g, 10.33
mmol) in toluene (84 mL) was added. The reaction
mixture was kept, under stirring, at 80°C for 5 h and at
room temperature overnight. A solution of ammonium
chloride (8.4 g) in water (60 mL) was added dropwise.
The aqueous phase was further extracted with ethyl
acetate (75 mL) and chloroform (75 mL). The combined
organic fractions were washed with water and dried over
sodium sulphate. After evaporation of the solvents at
reduced pressure crude 17a-methyl-5a-androstan-
3b,17b-diol (2.84 g, 90%) was recovered and used in the
3. Conclusion
In summary, a regioselective CAL-catalyzed transforma-
tion, avoiding use of highly toxic and very expensive
reagents, allowed a simple and safe preparation of the
anabolic steroid oxandrolone, actually the object of a
renewed interest for its therapeutic application in AIDS
patients; moreover chemoenzymatically prepared
monoacetates 9 and 10 can be useful intermediates for
the synthesis of other 2-etherosteroids.
1
next step without any further purification. H NMR
(selected signals) l 0.75 (3H, s, CH3-18), 0.76 (3H, s,
CH3-19), 1.12 (3H, s, CH3-20), 3.50 (1H, m, H-3). Jones
reagent was added to the above 3b,17b-diol solution in
acetone (60 mL) until orange colour persisted. Addition
of 2-propanol, filtration through a Celite pad and evap-
oration of the solvent afforded 17b-hydroxy-17a-methyl-
4. Experimental
All solvents and reagents were purchased from Sigma–
Aldrich. All reactions were monitored by TLC on silica
gel 60 F254 plates (Merck) with detection by spraying with
10% phosphomolybdic acid in ethanol solution and
heating at 110°C. Column chromatographies were per-
formed on silica gel 60 (0.063–0.200 mm) (Merck).
Uncorrected melting points were determined on a Bu¨chi
apparatus. Differential scanning calorimetry (DSC) were
performed on a Perkin Elmer DSC-7 instrument. GLC
analysis were performed on a Hewlett Packard HP5890
instrument at 260°C oven temperature, with an HP5-WB
capillary column (25 m×0.32 mm i.d., 0.52 mm film
thickness). Optical rotations were determined on a Perkin
Elmer model 241 polarimeter in a 1 dm cell at 25°C. The
NMR spectra were recorded with a Bruker AM-500
spectrometer operating at 500.13 and 125.76 MHz for 1H
1
5a-androstan-3-one (2.55 g, 90%). H NMR (selected
signals) l 0.85 (3H, s, CH3-18), 1.01 (3H, s, CH3-19), 1.19
(3H, s, CH3-20). To the 3-ketone (2.53 g, 8.38 mmol),
dissolved in a mixture of ethanol (40 mL) and methylene
chloride (20 mL), pyridinium tribromide (2.69 g, 8.41
mmol) was added and the reaction mixture was kept
under stirring at 40°C (2 h). Complete transformation of
starting material (monitored by TLC, toluene/ethyl ace-
tate, 7/3) was achieved by an additional amount of
pyridinium tribromide (0.9 g) keeping the reaction mix-
ture at 40°C (1 h). A saturated sodium hydrogen carbon-
ate aqueous solution (15 mL) was added and, after
removal of the organic solvents at reduced pressure and
addition of water (30 mL), 2a-bromo-17b-hydroxy-17a-
methyl-5a-androstan-3-one (3.0 g) was recovered by
1
filtration and directly used in the next step. H NMR
(selected signals) l 0.84 (3H, s, CH3-18), 1.08 (3H, s,
CH3-19), 1.18 (s, CH3-20) 1.79 (1H, dd, J1a,1b 13.0 Hz,
J1a,213.6 Hz, H-1a), 2.38 (1H, dd, J4a,4b 14.7 Hz, J4a,5 5.0
Hz, H-4a), 2.41 (1H, dd, J4b,5 12.0 Hz, H-4b), 2.62 (1H,
dd, J1b,2 6.4 Hz, H-1b), 4.72 (1H, dd, H-2). Mp 193–
195°C (acetone/hexane).
Dehydrobromination was achieved by treatment of 2-
bromo derivative (3.0 g, 7.85 mmol) with lithium bro-
mide (4.5 g, 51.8 mmol) and lithium carbonate (3.9 g,
52.8 mmol) in dimethylformamide (70 mL) at reflux (2
h). The reaction progress was monitored by TLC (tolu-
ene/ethyl acetate, 7/3). The mixture was poured into
cool water (200 mL) and the precipitate recovered by
filtration. The crude D1-derivative 2 was purified by
Scheme 3. Reagents: (i) CrO3/H2SO4; (ii) NaOH; (iii) HCl.
‡ The enzyme, in these conditions, can be recycled showing an almost
unaltered activity, whereas longer reaction times are required, if it is
re-used after transesterification with vinyl acetate.

2784
P. Ferraboschi et al. / Tetrahedron: Asymmetry 14 (2003) 2781–2785
crystallization from acetone/hexane (2.04 g, 65% yields
from 5). 1H NMR (selected signals) l 0.86 (3H, s,
CH3-18, 1.00 (3H, s, CH3-19), 1.20 (s, CH3-20), 2.20
(1H, dd, J4a,4b 17.5 Hz, J4a,5 4.0 Hz, H-4a), 2.35 (1H,
dd, J4b,5 14.0 Hz, H-4b), 5.83 (1H, d, J2,1 10.0 Hz, H-2),
7.12 (1H, d, H-1). Mp 140–142°C (acetone/hexane).
[h]2D5 +25.6 (c 1, CHCl3) (lit.4 +25.8).
poured into water (15 mL); after extraction with
dichloromethane (3×10 mL), the collected organic
phase was washed with 1 M hydrochloric acid and
water. Usual work-up afforded crude diacetate that was
purified by crystallization (acetone/water) (0.56 g, 90%).
1H NMR (selected signals) l 0.66 (3H, s, CH3-18), 0.80
(3H, s, CH3-19), 1.16 (3H, s, CH3-20), 1.96 (3H, s,
CH3CO), 2.02 (3H, s, CH3CO), 3.84–3.94 (3H, m,
H-1a, H-1b and H-3a), 4.04 (1H, ddd, J3a,3b 10.0 Hz,
J3b,4 5.0 Hz, J3b,4 8.0 Hz, H-3b). Mp 89°C (lit.16 90–
91°C from benzene). [h]2D5 −36.7 (c 1, CHCl3).
4.2. 17b-Hydroxy-17a-methyl-1,3-seco-2-nor-5a-
androstane-1,3-diacid, 1,3-dimethylester 6
Compound 2 (1.5 g, 4.97 mmol) was dissolved in
t-butanol (22 mL) and sodium carbonate (0.77 g, 7.27
mmol) in water (3 mL) was added. To the mixture, kept
under vigorous stirring at reflux, a solution of sodium
metaperiodate (6.0 g, 28 mmol) and potassium perman-
ganate (0.045 g, 0.28 mmol) in warm water (50 mL) was
added. The reaction progress was monitored by TLC
(chloroform/methanol, 8/2) and additional amounts of
permanganate were added after 5 and 15 h (0.020 and
0.040 g, respectively). When starting material disap-
peared, the precipitate was removed by filtration; the
filtrate was concentrated at reduced pressure, acidified
at pH 3 (1 M hydrochloric acid) and extracted with
ethyl acetate (4×40 mL). Collected organic phase was
dried over sodium sulphate and solvent removed at
reduced pressure. The crude diacid (1.5 g, 90%), dis-
solved in methanol, was treated with an ethereal solu-
tion of diazomethane, affording the diester 6 (1.5 g,
92%). An analytical sample was purified by column
chromatography (silica gel 1/10, elution by hexane/
ethylacetate, 6/4). 1H NMR (selected signals) l 0.79
(3H, s, CH3-18), 1.00 (3H, s, CH3-19), 1.16 (s, CH3-20),
3.60 (3H, s, CH3O), 3.63 (3H, s, CH3O). Mp 112–115°C
(acetone/hexane).
4.5. CAL-catalyzed transesterification of 1,3-diol 7
To a solution of 7 (0.15 g, 0.48 mmol) in tetra-
hydrofuran (30 mL) CAL B (Novozym 435, 0.53 g) and
vinyl acetate (0.19 mL, 2.05 mmol) were sequentially
added. The mixture was kept under stirring at 30°C,
monitoring the reaction progress by TLC (chloroform/
methanol, 9/1) until starting material disappearance (1
h). The enzyme was removed by filtration; evaporation
at reduced pressure afforded a crude product (GLC TR
16.99) that was purified by column chromatography
(silica gel 1/10, elution with hexane/ethyl acetate, 6/4).
To the obtained product (0.14 g, 82.5%) was assigned
the structure of 3-monoacetate 9 in agreement with the
observed chemico-physical data. 1H NMR (Py-d5) l
0.70 (s, 3H, CH3-18), 0.91 (m, 1H, H-7a), 1.1 (s, 3H,
CH3-19), 1.29 (m, 1H, H-14), 1.30 (m, 2H, H-4a and
H-6b), 1.33 (m, 1H, H-15a), 1.34 (s, 3H, CH3-20), 1.36
(m, 1H, H-12a), 1.45 (m, 1H, H-8), 1.41 (m, 1H,
H-11a), 1.56 (m, 1H, H-9), 1.61 (m, 1H, H-15b), 1.63
(m, 1H, H-12b), 1.73 (m, 1H, H-7b), 1.77 (m, 1H,
H-6b), 1.78 (m, 1H, H-16a), 1.84 (m, 1H, H-11b), 2.01
(m, 1H, H-5), 2.02 (s, 3H, CH3CꢀO), 2.13 (m, 1H,
H-4b), 2.13 (m, 1H, H-16b), 3.66 (dd, 1H, J1a,OH 4.2
Hz, J1a,1b 11.2 Hz, H-1a), 3.70 (dd, J1b,OH 3.5 Hz, 1H,
H-1b), 4.24 (ddd, 1H, J3a,3b 10.5 Hz, J3a,4a 7.7 Hz, J3a,4b
7.7 Hz, H-3a), 4.31 (ddd, 1H, J3b,4b 8.4 Hz, J3b,4a 5.6
Hz, H-3b), 4.63 (br s, 1H, OH), 5.25 (br dd, 1H, OH).
13C NMR (Py-d5) l 11.80 (C-18 or C-19), 14.60 (C-18
or C-19), 20.80 (CH3CꢀO), 21.63 (C-11), 23.86 (C-15),
26.57 (C-20), 27.96 (C-6), 29.81 (C-4), 32.08 (C-7),
32.34 (C-12), 36.57 (C-8), 37.87 (C-5), 39.64 (C-16),
41.05 (C-10 or C-13), 45.98 (C-10 or C-13), 46.41 (C-9),
51.52 (C-14), 64.35 (C-1 and C-3), 80.72 (C-17), 170.67
(CꢀO). Mp 140–141°C. [h]2D5 −37.7 (c 1, CHCl3).
Endothermic peak fusion (DSC) at 140.17°C. EI-MS
317 (18%), 301 (7.8%), 275 (64%), 257 (100%), 243
(66%), 231 (12.5%), 217 (41). Found C, 71.42; H, 10.27;
C21H36O4 requires C, 71.55; H, 10.29.
4.3. 17a-Methyl-1,3-seco-2-nor-5a-androstane-1,3,17a-
triol 7
A solution of 6 (1.5 g, 4.09 mmol) in anhydrous tetra-
hydrofuran (20 mL) was added dropwise to a suspen-
sion of lithium aluminium hydride (1.9 g, 5.1 mmol) in
tetrahydrofuran (15 mL). The mixture was kept under
stirring at room temperature (2 h). Then water (2 mL),
15% sodium hydroxide (2 mL) and water (6 mL) were
added dropwise. The precipitate was removed by filtra-
tion through a Celite pad and the solvent evaporated at
reduced pressure. Crude product was purified by crys-
tallization (diisopropylether/hexane) affording pure diol
7 (1.21 g, 95%). 1H NMR (selected signals, CDCl3/
CD3OD) l 0.68 (3H, s, CH3-18), 0.80 (3H, s, CH3-19),
1.15 (s, CH3-20), 3.37 (1H, d, J1a,1b 12.0 Hz, H-1a), 3.39
(1H, d, H-1b), 3.51 (1H, ddd, J3a,3b 10.0 Hz, J3a,4 10.0
Hz, J3a,4 4.0 Hz, H-3a), 3.66 (1H, ddd, J3b,4 3.0 Hz, J3b,4
6.0 Hz, H-3b). Mp 146°C (lit.8 139–140°C). [h]D25 −45.6
(c 1, CHCl3).
4.6. CAL-catalyzed alcoholysis of 1,3-diacetate 8
Compound 8 (0.15 g, 0.38 mmol) was dissolved in
ethanol (9 mL) and CAL B was added (0.72 g); the
reaction mixture was kept at 30°C under stirring, mon-
itoring the progress by GLC. After 3 h a 95% conver-
sion of the starting material (GLC TR 17.73) to a
product with TR 14.63 was observed. The oil recovered
after filtration and evaporation of the solvents at
reduced pressure was purified by column chromatogra-
phy (silica gel 1/10); elution by hexane/ethyl acetate 6/4
4.4. 17a-Methyl-1,3-seco-2-nor-5a-androstane-1,3,17a-
triol, 1,3-diacetate 8
A solution of 7 (0.5 g, 1.6 mmol) in pyridine (4 mL)
was treated overnight with acetic anhydride (0.9 mL,
9.5 mmol) at room temperature. The mixture was

P. Ferraboschi et al. / Tetrahedron: Asymmetry 14 (2003) 2781–2785
2785
d, 1b). Other chemico-physical properties are in agree-
ment with the reported data.4
afforded a product (0.114 g, 85%) that was identified as
1-monoacetate 10. 1H NMR (Py-d5) l 0.77 (s, 3H,
CH3-18), 0.88 (m, 1H, H-7a), 1.09 (s, 3H, CH3-19), 1.28
(m, 1H, H-6a), 1.29 (m, 1H, H-14 or H-9), 1.31 (m, 1H,
H-4a), 1.31 (m, 1H, H-15a), 1.33 (m, 1H, H-9 or H-14),
1.35 (s, 3H, 17a-CH3), 1.42 (m, 2H, H-11a and H-12a),
1.43 (m, 1H, H-8), 1.61 (m, 1H, H-15b), 1.67 (m, 2H,
H-11b and H-12b), 1.72 (m, 1H, H-7b), 1.77 (m, 1H,
H-16a), 1.86 (m, 1H, H-5), 1.87 (m, 1H, H-6b), 2.03 (m,
4H, CH3CꢀO and H-4b), 2.12 (m, 1H, H-16b), 3.84 (br
ddd, 1H, J3a,3b 10.5 Hz, J3a,4a 7.7 Hz, J3a,4b 7.7 Hz,
H-3a), 3.91 (br ddd, 1H, J3b,4b 7.7 Hz, J3b,4a 5.0 Hz,
H-3b), 4.11 (d, 1H, J1a,1b 11.9 Hz, H-1a), 4.27 (d, 1H,
H-1b), 4.70 (br s, 1H, OH), 5.22 (br s, 1H, OH). 13C
NMR (Py-d5) l 11.51 (C-18 or C-19), 14.57 (C-18 or
C-19), 20.66 (CH3CꢀO), 21.78 (C-11 or C-12), 23.82
(C-15), 26.56 (C-20), 27.90 (C-6), 31.93 (C-7), 32.17
(C-11 or C-12), 34.34 (C-4), 36.56 (C-8), 38.51 (C-5),
39.59 (C-16), 41.05 (C-10 or C-13), 45.98 (C-10 or
C-13), 47.57 (C-9 or C-14), 51.37 (C-9 or C-14), 61.19
(C-3), 66.51 (C-1), 80.67 (C-17), 170.73 (CꢀO). Mp
123–125°C. [h]2D5 −26.2 (c 1, CHCl3). Endothermic peak
fusion (DSC) at 122.67°C. EI-MS 317 (12%), 289
(11%), 275 (36%), 257 (58%), 243 (100%), 231 (12%),
217 (57%). Found C, 71.45; H, 10.25; C21H36O4
requires C, 71.55; H, 10.29.
Acknowledgements
This work was financially supported by the Universita`
degli Studi di Milano. We thank Professor Fiamma
Ronchetti for helpful discussions.
References
1. Mulligan, K.; Tai, V. W.; Schambelan, M. J. Parenter.
Enter. Nutr. 1999, 23 (6 Suppl), S202–9.
2. Earthman, C. P.; Reid, P. M.; Harper, I. T.; Ravussin,
E.; Howell, W. H. J. Parenter. Enter. Nutr. 2002, 26,
357–365.
3. Pappo, R.; Jung, C. 1963, USP 3101349.
4. Counsell, R. E.; Klimstra, P. D.; Colton, F. B. J. Org.
Chem. 1962, 27, 248–253.
5. Lemieux, R. U.; von Rudloff, E. Can. J. Chem. 1955, 33,
1701–1709.
6. Djerassi, C.; Scholz, C. R. J. Am. Chem. Soc. 1948, 70,
417–418.
7. Rasmusson, G. H.; Reynolds, G. F.; Utne, T.; Jobson, R.
B.; Primka, R. L.; Berman, C.; Brooks, J. R. J. Med.
Chem. 1984, 27, 1690–1701.
8. Koco´r, M.; Kurek, A.; Dabrowski, J. Tetrahedron 1969,
25, 4257–4264.
4.7. Oxandrolone 1
1-Monoacetate 10 (0.1 g, 0.28 mmol) was dissolved in
acetone and Jones reagent was added until orange
colour persistent. 2-Propanol was added to destroy
reagent excess and precipitated salts removed by filtra-
tion through a Celite pad. Crude product 11, recovered
after evaporation of solvents at reduced pressure, was
dissolved in a 5% potassium hydroxide methanol/water
(95/5) solution (2 mL). The mixture was heated at 50°C
(3 h); after cooling at room temperature, 1 M hydro-
chloric acid was added to neutral pH; methanol was
removed at reduced pressure and pH of the remaining
mixture brought to 3. Extraction with ethyl acetate
(3×5 mL) and usual work-up afforded pure 1 (0.06 g,
70%). 1H NMR (selected signals) l 0.84 (3H, s, CH3-18,
0.98 (3H, s, CH3-19 (3H, s, CH3-20), 2.23 (1H, dd,
J4a,4b 19.0 Hz, J4a,5 13.0 Hz, H-4a), 2.50 (1H, dd, J4b,5
6.0 Hz, H-4b), 3.90 (1H, d, J1a,1b 10.0 Hz, 1a), 4.2 (1H,
9. Ferrero, M.; Gotor, V. In Stereoselective Biocatalysis;
Patel, R. N., Ed. Biocatalytic Synthesis of Steroids; M.
Dekker: New York, 2000; pp. 579–631.
10. Bertinotti, A.; Carrea, G.; Ottolina, G.; Riva, S. Tetra-
hedron 1994, 50, 13165–13172.
11. Baldessari, A.; Bruttomesso, A. C.; Gros, E. G. Helv.
Chim. Acta 1996, 79, 999–1004.
12. Ferraboschi, P.; Colombo, D.; Reza-Elahi, S. Tetra-
hedron: Asymmetry 2002, 13, 2583–2586.
13. Degueil-Castaing, M.; De Jeso, B.; Drouillard, S.; Mail-
lard, B. Tetrahedron Lett. 1987, 28, 953–954.
14. Wang, Y. F.; Lalonde, J. J.; Momongan, M.; Bergbreiter,
D. E.; Wong, C. H. J. Am. Chem. Soc. 1988, 110,
7200–7205.
15. Njar, V. C. O.; Caspi, E. Tetrahedron Lett. 1987, 28,
6549–6552.
16. Searle G. D. and Co. 1965, BP 1041089.