Chemical methods for the conversion of Prednisolone to 11-β-hydroxy-1,4-androstadiene-3,17-dione

Article abstract of DOI:10.1007/s12039-015-0950-7

Several microbial transformations of steroids to 17-keto cortisones through side chain cleavage have been presented in the literature; however, yields and product selectivity in these methods were low. In the present study, some new methods have been identified for the side chain cleavage of prednisolone (1) to form 11- β-hydroxy-1,4-androstadiene-3,17-dione (11- β-hydroxy ADD). Prednisolone upon reaction with zinc chloride in dry THF results in the formation of cleavage product in good yield (76%). 11- β-hydroxy ADD (2) has been formed in moderate yield (60%) under the Reformatsky reaction conditions by reacting with zincate. While performing the Wittig reaction using stable ylides, again results in the formation of compound 2 in good yield (56%). Side chain cleavage of prednisolone was confirmed from the physical and analytical data and similar when compared with the literature reports.

Full text of DOI:10.1007/s12039-015-0950-7

c
J. Chem. Sci. Vol. 127, No. 10, October 2015, pp. 1827–1830. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-015-0950-7
Chemical methods for the conversion of Prednisolone
to 11-β-hydroxy-1,4-androstadiene-3,17-dione
PINNAMA REDDY SURYA PRATAPa, SYED SHAFIb,∗, FATIMA NAAZc
and NAYAKANTI DEVANNAa
aDepartment of Industrial Chemistry, Jawaharlal Nehru Technological University, Anantapur, India
bDepartment of Chemistry, Faculty of Science, Jamia Hamdard, Hamdard Nagar, New Delhi 110 062, India
cDepartment of Pharmaceutical Chemistry, Faculty of Pharmacy, Jamia Hamdard, Hamdard Nagar, New
Delhi 110 062, India
e-mail: syedshafi@jamiahamdard.ac.in; shafirrl@gmail.com
MS received 21 May 2015; revised 14 July 2015; accepted 22 July 2015
Abstract. Several microbial transformations of steroids to 17-keto cortisones through side chain cleavage
have been presented in the literature; however, yields and product selectivity in these methods were low. In
the present study, some new methods have been identified for the side chain cleavage of prednisolone (1) to
form 11-β-hydroxy-1,4-androstadiene-3,17-dione (11-β-hydroxy ADD). Prednisolone upon reaction with zinc
chloride in dry THF results in the formation of cleavage product in good yield (76%). 11-β-hydroxy ADD (2)
has been formed in moderate yield (60%) under the Reformatsky reaction conditions by reacting with zincate.
While performing the Wittig reaction using stable ylides, again results in the formation of compound 2 in good
yield (56%). Side chain cleavage of prednisolone was confirmed from the physical and analytical data and
similar when compared with the literature reports.
Keywords. Prednisolone; 11-β-hydroxy-1,4-androstadiene-3,17-dione; Chemical methods; ZnCl2; Stable
Wittig ylide; Reformatsky reaction
1. Introduction
of bioactive molecules. Androstadienedione (ADD)
is one of that important 17-keto cortisones that has
served as a key synthon for the development of several
bioactive molecules. ADD is an important precursor for
the production of sex hormones such as testosterone,
estrogen, estrone and ethinyl estradiol.3,5,6
Androstadienedione (1,4-androstadiene-3,17-dione)
is a next generation orally active prohormone. It is
a direct precursor to the anabolic steroid boldenone.
Boldenone is an anabolic steroid most often found in
injectable form as a veterinary medicine (boldenone
undecylenate). It is chemically a derivative of testoster-
one. Androstadienedione is used as a pharmaceutical
intermediate for further synthesis of female sex hor-
mones, in hormone replacement therapies and oral con-
traceptives.
Steroids like progesterone, testosteronedianabol, preg-
nenolone, cholesterol, sitosterol, stigmasterol, ergos-
terol, etc. have been reported to produce ADD through
bio-transformations.5–7 Progesterone is widely used as
an important precursor of androstadienedione (ADD).
Progesterone was biotransformed to ADD by Bacillus
sphaericus with the maximum yield of 22%.8 A major
problem in the biotransformation of steroid is the poor
solubility of substrates in aqueous solutions, which
Steroids play an important role in the hormonal balances.
Steroids are widely used as therapeutic agents and since
their inception in the market and research efforts have
been made to improve production processes as well
as to develop novel synthetic molecules with enhanced
efficiency and reduced side effects.
Microorganisms have been widely applied for the
biotransformation of steroids to generate functionalized
steroids over the years.1 These biotransformations lead
to the production of steroidal contraceptive hormones
and anti-inflammatory drugs from various precursors
such as steroids, phytosterols, sapogenins, etc.2 Bio-
transformations of steroids result in the formation of
variety of synthons which can be readily used for fur-
ther drug development.3 A number of microorganisms
have been utilized for steroid transformation including
varieties of bacteria, fungi, yeast and algae.4
Amongthese biotransformations and microbial trans-
formation, enzyme catalysed side chain cleavage of
steroids result in the formation of 17-keto cortisones.5,6
17-keto cortisones have a wide range of applications
including the semi-synthetic modifications for the synthesis
∗For correspondence
1827

1828
Pinnama Reddy Surya Pratap et al.
leads to extremely low productivity. Identifying the added and refluxed under inert atmosphere for 8 h. After
suitable microorganism is also a difficult aspect.3b,9 the completion of the reaction, monitored by TLC, the
Keeping in view the worldwide market for the ADD and reaction mixture was quenched with excess of water
its derivatives, several efforts were made in identifying and extracted with ethyl acetate. The organic layer was
suitable microorganisms for side chain cleavage with dried over anhydrous sodium sulfate and evaporated
greater yields which remain a challenging aspect.10–13
under vacuum to get the crude product which was puri-
To overcome these problems, several chemical meth- fied on column to obtain the side chain cleavage product
ods have been developed to obtain 17-ketosteroids from (2) as a colourless solid (0.63 g, 76%).
the corresponding corticosteroids by cleaving the hy-
droxy ketone bond between C-17 and C-20.14–16 Both
2.2 General procedure for side chain cleavage of pred-
the base and acid induced side chain cleavage methods
have been identified. In 1981, Simons et al. reported the
side chain cleavage of prednesolone by ethanolic KOH
to afford 23% of 11-β-hydroxy-1,4-androstadiene-3,
17-dione.14 In 2003, Pera et al. reported a straightfor-
ward chemical synthesis of 17-ketosteroids by cleavage
of the C-17-dihydroxy acetone side chain in corticoste-
roids15 by using NaOMe. However very few reports are
present in the literature for the side chain cleavage of
prednesolone. In 2009, Pinto et al. reported Bismuth
(III) Triflate-Catalyzed side chain cleavage of pred-
nesolone to 11-hydroxy ADD with 78% yield.16
Keeping in view the demand for ADD derivatives,
alternate methods have to be explored for the bulk pro-
duction of ADD derivatives. In this regard we have
explored the chemical methods for the generation of
ADD derivatives. During our semi-synthetic modifica-
tions on prednisolone, some chemical methods were
observed for the side chain cleavage of prednisolone.
In the present manuscript, we are reporting our findings
nisolone by Reformatsky Reaction
To THF (10 mL) solution of 2-bromoethylacetate
(0.33 mmol), freshly activated zinc (0.42 mmol) was
added under inert atmosphere and the reaction mixture
was stirred for 15 h at room temperature. Reaction mix-
ture turns viscous along the walls indicating the genera-
tion of Reformatsky reagent. Then prednisolone (0.1 g,
0.28 mmol) was added at once to the reaction mixture
under inert atmosphere. Reaction mixture was contin-
ued to stir for further 24 h at room temperature. Even
after 24 h the starting material remains in the reaction
mixture. Reaction mixture was quenched with saturated
ammonium chloride solution and extracted with ethyl
acetate. Combined organic layers were dried over anhy-
drous sodium sulphate and evaporated under vacuum
to get the crude product which was purified on col-
umn to obtain the side chain cleavage product (2) as a
colourless solid (0.050 g, 60%).
for the generation of 11-hydroxy ADD through side 2.3 General procedure for side chain cleavage of pred-
chain cleavage by chemical methods (figure 1).
nisolone by Wittig reaction with stable ylide
To dry THF solution of prednisolone (0.1 g, 0.28 mmol)
stable Wittig ylide (0.33 mmol) was added and the reac-
tion mixture was refluxed for 6 h. After the completion
of the reaction, monitored by TLC, reaction mixture
was cooled to room temperature and evaporated under
2. Experimental
2.1 General procedure for side chain cleavage of pred-
nesolone by ZnCl2
To the solution of prednisilone (0.1 g, 0.28 mmol) in vaccum to get the impure mixture which was sub-
dry THF (5 mL), dry zinc chloride (0.33 mmol) was jected to column chromatography to obtain the pure
ZnCl2, Dry THF, Reflux
OH
O
(or)
O
ZnCl2, Dry THF, Anisaldehyde, Reflux
HO
HO
OH
(or)
H
H
O
H
H
H
H
BrZn
Ph3P
Dry THF/DMF
OEt
O
O
1
2
(or)
11-β-hydroxy-ADD
Prednisolone
Dry THF/DMF
C
COOEt
H
26-76%
(or)
H2
C
EtOOC
P+Ph3Br-
NaOH, CHCl3
Figure 1. Chemical methods for side chain cleavage of prednisolone.

Prednisolone to 11-β-hydroxy-1,4-androstadiene-3,17-dione
1829
side chain cleavage product (2) as a colourless solid formation of 11-β-hydroxy-1,4-androstadiene-3,17-dione
(0.047 g, 56%).
has been observed through the side chain cleavage.
ll-β-Hydroxy-l,4-androstadiene-3,l7-dione: (M.p 184– Then, Wittig reaction with a stable ylide was tried under
1
186◦C), H NMR (400 MHz, CDCl3) δ 1.06-1.09 (dd neutral conditions to generate betenolide, again side
J = 11.20 and 2.80 Hz, 1H), 1.13–1.24 (m, 5H), 1.45–1.50 chain cleavage was observed and the formation of 11-β-
(m, 4H), 1.62-1.70 (m, 2H), 1.91-2.09 (m, 3H), 2.19-2.29 hydroxy ADD was identified (compound 2). By using
(m, 2H), 2.36-2.39 (m, 1H), 2.47–2.54 (m, 1H), 2.54– Wittig salt under basic conditions as well as under neu-
2.63 (m, 1H), 4.48 (m, 1H), 6.03 (s, 1H), 6.27 (d, J = tral conditions (stable ylide) same product formation
10.00 Hz, 1H), ), 7.25 (d, J = 8.40 Hz, 1H). 13C NMR was observed (figure 2).
(100 MHz, CDCl3) δ 15.80, 21.22, 21.89, 30.87, 31.76,
While attempting the 1,3-diol protection of the side
32.70, 35.16, 41.00, 44.00, 46.87, 51.75, 55.90, 69.90, chain of prednisolone using anisaldehyde in presence
122.71, 128.10, 155.67, 169.31, 186.39, 218.56. IR of ZnCl2, side chain cleavage product was observed in
(Bruker alpha-FT IR spectrophotometer, Liquid, CHCl3, good yield instead of acetal. When prednisolone was
cm−1): 3010, 2964, 2940, 2916, 1736, 1660, 1622, 1447, treated with ZnCl2 alone, again side chain cleavage hap-
1407, 1162, 1051, 890, 827. MS (EI) m/z (rel intensity): pened with improved yield. Among all the methods
301 (M++1), 323 (M++23). Anal. Calcd for (C19H24 observed, Lewis acid catalysed reaction was found to
O3): C, 75.97; H, 8.05%; Found: C, 75.95; H, 8.09%.
be better with 76% yield (scheme 1).
Side chain cleavage by Lewis acids can be explained
by the following plausible mechanism. Addition of
Lewis acid on the carbonyl oxygen followed by the con-
comitant cleavage of C18-C19 bond will result in the
formation of compound 2 as shown in scheme 2.
3. Results and Discussion
When Reformatskii reaction was performed on prednis-
olone in order to synthesize betenolide, a serendipitous
O
OH
O
O
O
O
BrZn
O
BrZn
Ph3P
OEt
OEt
HO
HO
OH
HO
OH
H
H
H
H
H
H
H
H
H
O
O
2
1
C
COOEt
C
COOEt
O
Ph3P
11-β-hydroxy-ADD
Prednisolone
3
H
H
26-76%
Figure 2. Attempts towards the construction of butenolide ring on prednisolone.
OH
O
O
O
HO
HO
HO
OH
COOEt
Ph3P
C
H
ZnCl2
H
H
H
H
Dry THF
H
Dry THF/DMF
H
H
H
H
1
O
O
O
2
2
56%
76%
Prednisolone
P+Ph3Br-
H2C
EtOOC
A
n
Z
h
n
C
D
i
s
l 3
r
l
al
y
C
2
d
H
T
H
O
e
C
ZnBr
F
y
H,
de
HO
O
a
N
O
O
H
HO
EtO
H
H
H
O
O
H
H
26%
2
HO
H
O
2
54%
H
H
2
O
60%
Scheme 1. Chemical methods for the side chain cleavage of prednisolone.

1830
Pinnama Reddy Surya Pratap et al.
OH
OH
OH
O
O+
LA
O
HO
HO
HO
O
H
ZnCl2
Dry THF
1
2
O
O
O
Scheme 2. Plausible mechanism for the Lewis acid catalysed side chain cleavage of prednisolone.
Cruz A, Angelova B, Pinheiro H M and Cabral J M S
2003 Enzyme Microb. Technol. 32 688; (d) Mahato S B
and Garai S 1997 Steroids 62 332
4. Conclusion
In conclusion, we have reported the chemical methods
for the side chain cleavage of prednisolone in moderate
to good yield which can be used for the further chemical
transformations.
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Supplementary Information
Supplementary information is available at www.ias.ac.
in/chemsci.
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6725
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The authors thank Dr. G. N. Qazi, Hon’ble Vice
Chancellor, Jamia Hamdard- New Delhi for providing
the facilities. SS thanks Hamdard National Foundation
for providing Hamdard Centenary Research Fellowship.
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