An improved and efficient synthesis for IPL576,092 and its analogues

Article abstract of DOI:10.1007/s00706-012-0920-4

An improved and efficient preparation of IPL576,092 was developed. The synthetic route involves selective allylic oxidation of a? ⁵-sterols and subsequent hydroboration-oxidation as the key steps. In addition, two analogues were readily synthesized from commercially available steroidal compounds in two steps in the same way.

Full text of DOI:10.1007/s00706-012-0920-4

Monatsh Chem (2013) 144:1081–1085
DOI 10.1007/s00706-012-0920-4
ORIGINAL PAPER
An improved and efficient synthesis for IPL576,092
and its analogues
Jin Liu
•
Rong Huang Hongyou Zhu
•
Received: 4 June 2012 / Accepted: 31 December 2012 / Published online: 28 February 2013
Ó Springer-Verlag Wien 2013
Abstract An improved and efficient preparation of
IPL576,092 was developed. The synthetic route involves
in 22 % overall yield. Almost the only route available for
the preparation of these trihydroxysteroids (e.g., 5a-an-
drostan-17-one-3b,6a,7b-triol 4) starts from DHEA. First
the 3b-hydroxyl group of 5 has to be protected (usually as
the acetate or TBDMS ether) otherwise it would be oxi-
dized to a ketone group during the subsequent reaction. In
the second and third step, allylic oxidation at C7 afforded
the a,b-unsaturated steroid 7, which was reduced under
Luche conditions to give the 7b-alcohol 8 as a single
detectable isomer. In the fourth step, a highly stereoselec-
tive hydroboration–oxidation gave the 6a,7b-diol 9.
Finally, 4 was obtained by protection group removal with
aqueous AcOH (Fig. 2a). Preparation of IPL576,092 (1)
from 4 needs another three-step reaction (Scheme 1).
In 2004, Burgoyne et al. [6] studied synthesis and bio-
logical activities of analogues of IPL576,092. Compound 2
was synthesized from cholesterol acetate in four steps by a
traditional method and compound 3 was obtained by cat-
alytic hydrogenation of the C17–C20 double bond of
compound 1. The study showed that 5a-cholestane-
3b,6a,7b-triol (2) and 5a-pregnane-3b,6a,7b-triol (3) have
good anti-inflammatory activity (Scheme 2).
5
selective allylic oxidation of D -sterols and subsequent
hydroboration–oxidation as the key steps. In addition, two
analogues were readily synthesized from commercially
available steroidal compounds in two steps in the same
way.
Keywords IPL576,092 Á Allylic oxidation Á
Hydroborations Á a,b-unsaturated ketones Á Steroids
Introduction
IPL576,092 (1), a potent anti-inflammatory agent, was
identified from a novel group of polyhydroxylated sterols
based on the marine natural product contignasterol [1].
Currently in phase II human clinical trials, IPL576,092
displays a biological activity profile which justifies the
continuation of its evaluation as a potential new treatment
for asthma (Fig. 1) [2–4].
However, to the best of our knowledge, there have been
only a few reports concerning the synthesis of IPL576,092
We wish to report herein an improved and efficient route
for the synthesis of structural analogues of IPL576,092 (1).
The synthetic route developed involves selective allylic
(
1) and its analogues. In 2002, Burgoyne et al. [2] first
reported the structure and preparation of IPL576,092 from
dehydroepiandrosterone (DHEA) in nine steps in 25 %
overall yield. In 2003, Filippo et al. [5] also accomplished
the synthesis of IPL576,092 used for the research of a
transmembrane ionophore by a similar method in 11 steps
5
oxidation of D -sterols and subsequent hydroboration–
oxidation as the key steps (Fig. 2b).
Results and discussion
5
J. Liu (&) Á R. Huang Á H. Zhu
The procedures for the successful synthesis of 7-keto-D -
cholesterol from cholesterol 12 in acceptable yields by using
Key Laboratory of Medicinal Chemistry for Natural Resources
(
Ministry of Education), Yunnan University, Kunming, Yunnan,
People’s Republic of China
e-mail: liujin@ynu.edu.cn
CrO /N-hydroxyphthalimide (NHPI)-activated clay oxidiz-
3
ing system, in which the 3b-hydroxyl group remained
123

1
082
J. Liu et al.
Fig. 1 IPL576,092 and its
analogues
OH
HO
OH
H
HO
OH
HO
H
OH
H
OH
OH
IPL 576,092 (1)
2
3
A
O
O
O
Protection
for 3-OH
O
Allylic
oxidation
O
O
RO
HO
RO
O
5
6
7
Luche
reduction
O
O
O
O
H+
O
Hydroboration-
oxidation
RO
OH
OH
RO
OH
HO
OH
OH
4
9
8
R = protecting group
B
O
O
O
Selective
allylic
oxidation
O
O
O
Hydroboration-
oxidation
HO
OH
HO
HO
O
OH
5
10
11
Fig. 2 Preparation of trihydroxysteroids. a Traditional route; b improved route
1
unaffected, are described in our previous work [7]. Con-
5
sidering that 7-keto-D -cholesterol 13 possesses a flat and
rigid molecular structure, we explored the hydroboration of
the H NMR spectrum of compound 2 assigned to H6
(d = 3.25 ppm, dd, J = 8.9, 10.4 Hz) and H7 (3.11 ppm,
dd, J = 9.1, 8.8 Hz) are consistent with trans diaxial rela-
tionships between H5 and H6, H6 and H7, and H7 and H8.
Thus, the configuration of the hydroxyl groups at C6 and C7
can be assigned as a and b, respectively.
Therefore, we have found an efficient and short route
for the preparation of structural analogues of IPL576,092.
The synthesis of compounds 2 and 3 share a common
route, as detailed in Scheme 2. Cholesterol 12 and
the a,b-unsaturated ketone of ring B of this compound and
subsequent oxidation with NaBO . In this way, compound 5
3
was obtained directly in a one-step process (Scheme 2).
Structural identification revealed that the complex reso-
1
nance at d = 3.58 ppm in the H NMR spectrum assigned
to the hydrogen attached to C3 is consistent with the 3b-OH
configuration. The coupling constants for the resonances in
1
23

An improved and efficient synthesis for IPL576,092
1083
Scheme 1
O
(
i), (ii), (iii)
(iv)
1
OH
OH
HO
HO
H
H
OH
OH
4
3
(
i) 2,2-Dimethoxypropane, TsOH, RT ; (ii) EtPPh Br, t-BuOK, toluene; (iii) HOAc, H O;
3 2
(
iv) Pd/C
Scheme 2
R
R
R
(ii)
(i)
HO
OH
HO
O
HO
OH
2
3
1
2 R =
13
15
1
4 R= C H
2
5
.
(
i) CrO /activated clay/CH Cl , RT; (ii) NaBH /BF OEt -NaBO , 0 °C
3 2 2 4 3 2 3
5
-pregnene-3b-ol (14, prepared from pregnenolone)
underwent selective allylic oxidation with the CrO /NHPI-
was synthesized according to literature from 12 in three
steps (Fig. 2b; Scheme 1).
3
activated clay system [7] to afford compound 13 (45 %
yield) and 15 (52 % yield), respectively (it is noteworthy
that oxidation of compound 6 under these conditions
cleaved the acetal protecting group). Hydroboration of the
cyclic a,b-unsaturated ketone of compound 13 and sub-
sequent oxidation with NaBO3 yielded 5a-cholestane-
In summary, we described an improved and efficient
route for the synthesis of structural analogues of
IPL576,092. The synthetic route developed involves
5
selective allylic oxidation of D -sterols and subsequent
hydroboration–oxidation as the key steps. 5-Cholestane-
3b,6a,7b-triol (2) was synthesized from cholesterol in two
steps in 40 % overall yield, 5a-pregnane-3b,6a,7b-triol (3)
was synthesized from 5-pregnene-3b-ol in two steps in
39 % overall yield, and IPL576,092 (1) was synthesized
from DHEA in seven steps in 27 % overall yields. This
protocol provides an alternative method for application in
combinatorial and parallel syntheses in drug discovery. In
3
b,6a,7b-triol (2, 69 % yield). 5a-Pregnane-3b,6a,7b-triol
3, 71 % yield) was synthesized in the same way from
(
compound 15. The coupling constant between H-6 and
1
H-7 in the H NMR spectrum of 3 also indicated that these
hydrogens have a trans diaxal relationship and compound
3 has a 6a,7b-diol configuration which is consistent with
that in compound 2.
1
13
addition, to the best of our knowledge, H and C NMR
IPL576,092 (1) was also prepared by the improved
method. 5-Androsten-3b-ol-17-one ethyleneketal (5) was
easily obtained by treating DHEA with ethylene glycol in
the presence of p-toluenesulfonic acid. Selective allylic
oxidation of compound 5, i.e., in the presence of the sen-
sitive 3b-hydroxyl group, by the NHPI/O /Bz O -CuCl
data for compounds 2 and 3 have not been reported before.
Experimental
1
13
H NMR and C NMR spectra were recorded on a Bruker
2
2
2
2
5
system [8] afforded the corresponding 7-keto-D -steroid 10
in 67 % yield. Hydroboration–oxidation of 10 with
BF ÁOEt /NaBH -NaBO system resulted in 11 and then
DRX-500 spectrometer. IR spectra were recorded on
Thermo Nicolet Avatar 360 FTIR. MS data were recorded
on a Finnigan MAT 90 spectrometer at an ionization
potential of 70 eV. Field-desorption (FD) mass spectra
were recorded on a VG ZAB 2-SE-FPD spectrometer.
3
2
4
3
treatment with 80 % acetic acid over 3 h gave key inter-
mediate 4 in 67 % yield over two steps. IPL576,092 (1)
123

1
084
J. Liu et al.
3
100 cm dry THF at RT under N
Analytical thin-layer chromatography was performed on
Qingdao Haiyang silica gel GF254 plates, and flash chro-
matography was performed on 200–300 mesh silica gel.
THF and toluene were dried by distillation over
Na/benzophenone under a nitrogen atmosphere. Dehydro-
epiandrosterone and pregnenolone were obtained from
Yongsheng Yinghua Phytochemical Industry Group Co,
Ltd. Activated clay was obtained from Yunnan Jianshan
Runtu Co, Ltd. Unless otherwise noted, all other starting
materials and solvents were obtained from commercial
suppliers and used without further purification.
2
. The slurry was cooled to
3
3
(36 mmol) in 10 cm dry THF
0 °C, and 4.6 cm BF
ÁOEt
3
2
was slowly added, maintaining the temperature of the
mixture below 0 °C for 1 h, then the mixture was warmed
3
to RT. After 5 h 40 cm H
O was slowly added, then
2
2.80 g NaBO
Á4H
O (18 mmol) was added portionwise.
Cl
3
2
The mixture was stirred at RT overnight. CH
3
(100 cm ) was added, the organic layer was separated
2
2
and washed with saturated aqueous NaCl solution
3
(3 9 100 cm ), dried over MgSO
, and the solvent was
4
removed in vacuo. The obtained crude 11 (2.94 g) was
used directly for the next step without further purification.
5
-Androsten-7,17-dione-3b-ol 17-ethyleneketal
10, C H O )
(
2
1
30
4
5a-Androstan-17-one-3b,6a,7b-triol (4, C H O )
1
9 30 4
3
Crude 11 (2.90 g) was treated with 120 cm 80 % acetic
acid over 3 h at RT. The mixture was then concentrated
Compound 10 was prepared by a method based on a patent
by Foricher et al. [8]. NHPI (3.0 g, 18.4 mmol) and 6.0 g
5
-androsten-3b-ol-17-one ethyleneketal (5, 18.1 mmol;
in vacuo and azeotroped to dryness with methanol (2 9
3
0 cm ). Purification of the product was done by column
3
prepared from DHEA) were added to 200 cm of a mixture
of acetone and ethyl acetate (1:1). The mixture was stirred
and warmed to 55 °C, and then 15 mg dibenzoyl peroxide
2
chromatography (eluent ethyl acetate) to give triol 4 as a
white solid (1.82 g). The yield for the conversion of 11 to 4
1
(
Bz O ) was added and air was vigorously bubbled into the
2 2
was 67 %. H NMR (500 MHz, CDCl ): d = 3.54 (m, 1H,
3
mixture at 55 °C for 48 h. After completion of the reaction
3
-H), 3.38 (dd, J = 8.6, 10.6 Hz, 1H, 6-H), 3.20
dd, J = 9.7, 9.2 Hz, 1H, 7-H), 2.47 (m, 1H), 0.97
3
TLC control), 100 cm cyclohexane was added, the
(
(
(
1
s, 3H, 19-H), 0.95 (s, 3H, 18-H) ppm; C NMR
3
mixture was cooled to RT, NHPI was filtered off, and the
2
filtrate was washed with saturated aqueous Na CO3
(125 MHz, CDCl ): d = 224.7 (C-17), 81.5 (C-7), 76.3
3
solution repeatedly until no orange color was observed.
(C-6), 72.2 (C-3), 54.0, 53.2, 49.3, 48.9 (C-13), 42.4, 39.0
The organic layer was washed with saturated aqueous NaCl
3
solution (3 9 100 cm ), dried over MgSO , and the solvent
(
C-16), 37.3, 37.2 (C-10), 33.6, 33.2, 32.3, 26.2, 22.3, 14.9
4
(C-19), 14.3 (C-18) ppm.
was evaporated in vacuo. The resulting residue was added
3
5a-Progest-17(20)-ene-3b,6a,7b-triol (1)
This compound was prepared according to the literature
to 150 cm pyridine, cooled to 0 °C, and CuCl was added
2
under stirring. Stirring was continued overnight and the
procedure [2]; the overall yield for the conversion of 4 to 1
1
mixture was then warmed to RT. The solvent was
was 61 %. M.p.: 182–183 °C (Ref. [2] 183–184 °C). H
NMR and C NMR spectra were found to be identical to
evaporated in vacuo and the residue was poured into
3
50 cm CH Cl and washed with saturated aqueous NaCl
1
3
1
2
2
3
solution (3 9 100 cm ). The organic layer was dried over
those in the literature [2].
MgSO and the solvent was evaporated in vacuo. Purifi-
4
5
-Pregnene-7-one-3b-ol (15, C H O )
2
1 32 2
cation of the product was done by column chromatography
To a solution of 1.50 g 5a-pregnene-3b-ol (14, 5 mmol;
prepared from pregnenolone [9]) in 120 cm CH Cl ,
(
eluent petroleum/ethyl acetate 3:1) to give enone 10 as a
1
3
2
2
white solid (4.2 g, 67 % yield). M.p.: 198–200 °C; H
5
.80 g of the CrO /NHPI-activated clay supported oxidant
3
NMR (500 MHz, CDCl ): d = 5.69 (s, 1H, 6-H), 3.94–
3
[
7] (CrO content 8 mmol) was added at RT under stirring.
3
3
.86 (m, 4H, –OCH CH O–), 3.52 (m, 1H, 3-H), 0.95 (s,
2 2
After 10–24 h, an additional amount of 5.80 g CrO /NHPI-
3
1
H, 19-H), 0.86 (s, 3H, 18-H) ppm; C NMR (125 MHz,
3
3
activated clay supported oxidant (CrO content 8 mmol)
3
CDCl ): d = 201.6 (C-7), 165.6 (C-17), 126.0 (C-6), 118.6
3
was added portionwise during a period of 10 h and stirring
was continued until the reaction was completed (TLC
control, about 24 h). The mixture was filtered through a
bed of activated clay and washed with dichloromethane.
The combined filtrate was washed repeatedly with satu-
rated aqueous Na CO solution until no orange color
(
C-5), 70.4 (C-3), 65.2, 64.5 (–OCH CH O–), 50.0, 46.2
2 2
(
C-13), 45.4, 44.4, 41.9 (C-4), 38.3 (C-10), 36.4, 34.2, 31.2,
9.7, 25.1, 20.7, 17.4 (C-19), 14.4 (C-18) ppm; IR (KBr):
2
-
v = 3,448, 1,666, 1,058 cm ; EI–MS (70 eV): m/z
1
?
%) = 346 (M , 5), 331 (7), 247 (6), 161 (4), 100 (52),
(
2
3
9
9 (100), 86 (15), 79 (5), 55 (4).
was observed in the organic layer. The organic layers were
then washed with saturated aqueous NaCl solution
5
-Androsten-17-one-3b,6a,7b-triol ethyleneketal
11, C H O )
3
3
(
(3 9 100 cm ) and water (3 9 100 cm ) and dried over
MgSO ; the solvent was removed in vacuo. Purification of
the product was done by column chromatography (eluent
2
1 34 5
5
9
-Androsten-7,17-dione-3b-ol 17-ethyleneketal (10, 3.00 g,
mmol) and 2.40 g NaBH (63 mmol) were dissolved in
4
4
1
23

An improved and efficient synthesis for IPL576,092
1085
petroleum/ethyl acetate 3:1) to give 15 (0.87 g, 55 %).
1
5a-Cholestane-3b,6a,7b-triol (2, C H O )
2
7 48 3
M.p.: 192–194 °C; H NMR (500 MHz, CDCl ): d = 5.70
This compound was prepared from 13 according to the
procedure as described for the synthesis of compound 11,
3
(
(
(
(
(
s, 1H, 6-H), 3.68 (m, 1H, 3-H), 1.20 (s, 3H, 19-H), 0.88
1
3
m, 3H, 21-H), 0.57 (s, 3H, 18-H) ppm; C NMR
1
yield 69 %. M.p.: 224–225 °C; H NMR (500 MHz,
125 MHz, CDCl ): d = 203.2 (C-7), 166.3 (C-5), 127.0
CDCl ): d = 3.58 (m, 1H,3-H), 3.25 (dd, J = 8.9,
3
3
C-6), 71.4 (C-3), 52.7, 51.3, 50.4, 46.4 (C-17), 43.6
10.4 Hz, 1H,6-H), 3.11 (dd, J = 9.1, 8.8 Hz, 1H, 7-H),
2.18 (m, 1H), 2.02 (m, 1H), 0.96 (d, 3H, 21-H), 0.90 (m,
C-13), 42.8, 39.3 (C-10), 37.8, 37.3, 32.1, 29.2, 27.6, 23.8,
2
2.0, 18.2 (C-21), 14.1 (C-19), 13.3 (C-18) ppm; IR (KBr):
6H, 26-H, 27-H), 0.82 (s, 3H, 19-H), 0.71 (s, 3H, 18-H)
13
-
1
?
v = 3,430, 1,673, 1,069 cm ; MS (TOF ): m/z = 339
ppm; C NMR (125 MHz, CDCl ): d = 81.9 (C-7), 75.6
3
?
[M ? Na] ).
(
(C-6), 72.0 (C-3), 56.8, 56.3, 53.2, 48.7, 44.5 (C-13), 42.2,
4
2
0.8, 40.4, 38.3, 37.2, 36.6, 36.5 (C-10), 33.3, 31.9, 29.4,
5
Compound 3 was prepared from 15 according to the
a-Pregnane-3b,6a,7b-triol (3, C H O )
2
1 36 3
8.8, 27.7, 24.8, 23.5 (C-27), 23.3 (C-26), 22.2 (C-11), 19.7
?
C-21), 14.5 (C-19), 13.0 (C-18); MS (TOF ): m/z = 443
(
(
procedure as described for 11, yield 71 %. M.p.: 228–
?
[M ? Na] ).
1
2
3
9
3
30 °C; H NMR (500 MHz, CDCl ): d = 3.50 (m, 1H,
3
-H), 3.14 (dd, J = 9.45, 10.0 Hz,1H,6-H),2.99(dd, J = 9.3,
.1 Hz, 1H, 7-H), 2.18 (m, 1H), 0.93 (m, 3H, 21-H), 0.90 (s,
Acknowledgments Thanks are due to Prof Fu-Chu Liu (Yunnan
University) for helpful criticism of the manuscript. This work was
supported by the National Natural Science Foundation of China (No.
13
H, 19-H), 0.63 (s, 3H, 18-H) ppm; C NMR (125 MHz,
20472070) and State University College of Innovative Experimental
Projects (No. 101067319).
CDCl ): d = 82.1 (C-7), 76.4 (C-6), 72.3 (C-3), 57.4, 54.4,
3
54.2, 49.4, 44.5 (C-13), 42.7, 39.7, 39.1, 37.2 (C-10), 33.7,
3
3.3, 29.9, 28.6, 24.6, 22.8, 14.4 (C-21), 14.2 (C-19), 13.6
?
C-18) ppm; MS (TOF ): m/z = 359 ([M ? Na] ).
?
(
References
5
Compound 13 was prepared from cholesterol 12 according
-Cholesten-7-one-3b-ol (13, C H O )
2
7 44 2
1
2
3
. Burgoyne DL, Andersen RJ (1992) J Org Chem 57:525
. Shen Y, Burgoyne DL (2002) J Org Chem 67:3908
. Izzo I, Avallone E, Monica CD, Casapullo A, Amigo M, Riccardis
FD (2004) Tetrahedron 60:5587
to the procedure as described for 15, yield 58 %. M.p.:
1
1
1
3
66–167 °C; H NMR (500 MHz, CDCl ): d = 5.69 (s,
3
4
5
. Kasserra CE, Harris P, Stenton GR, Abraham W, Langlands JM
(
H, 6-H), 3.68 (m, 1H, 3-H), 1.23 (s, 3H, 18-H), 0.88 (d,
2004) Pulm Pharmacol Ther 17:309
. Filippo MD, Izzo I, Savignano L, Tecilla P, Riccardis FD (2003)
Tetrahedron 59:1711
H, 21-H), 0.85 (m, 6H, 26-H, 27-H), 0.68 (s, 3H, 18-H)
1
ppm; C NMR (125 MHz, CDCl ): d = 202.6 (C-7),
3
3
1
67.2 (C-5), 125.8 (C-6), 70.2 (C-3), 54.8, 50.0, 45.4, 43.1
C-13), 41.9 (C-4), 39.5, 38.7, 38.3 (C-10), 36.4, 36.2, 35.7,
1.0, 28.5, 28.0, 26.3, 23.9, 22.8 (C-26), 22.6 (C-27), 21.2
C-11), 18.9 (C-21), 17.3 (C-19), 12.0 (C-18) ppm; IR
6. Burgoyne DL, Shen Y, Langlands JM, Rogers C, Chau JH-L, Piers
E, Salari H (2004) Preparation of 6,7-oxygenated steroids and uses
related thereto. US Patent 6,706,701, 16 Mar 2004
(
3
7
8
. Liu J, Zhu HY, Cheng XH (2009) Synth Commun 39:1076
. Foricher J, Furbringer C, Pfoertner K (1991) Process for the
catalytic oxidation of isoprenoids having allylic groups. US Patent
(
(
-
1
KBr): v = 3,519, 1,664, 1,061 cm ; EI–MS (70 eV):
?
5,030,739, 9 Jul 1991
. Huang M, Chen Z, Zhou W (1965) Acta Chim Sin 31:165
m/z (%) = 400 (M , 59), 367 (30), 287 (25), 245 (16), 205
9
(
(
31), 192 (86), 161 (100), 135 (80), 107 (48), 91 (42), 81
32), 67 (19), 55 (20).
123