Novel approach to the synthesis of istaroxime

Article abstract of DOI:10.1134/S1070363217110196

Istaroxime 1, a novel cardiotonic agent with high efficiency and low toxicity was synthesized from dehydroepiandrosterone 2 using a novel approach that included epoxidation, ring-opening, substitution, and oximation. The new protocol without gas protection was milder than the reported approaches. The overall yield of the method was 24.1%.

Full text of DOI:10.1134/S1070363217110196

ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 11, pp. 2643–2647. © Pleiades Publishing, Ltd., 2017.
Novel Approach to the Synthesis of Istaroxime1
G.-P. Liang, J.-H. Guo, and R.-W. Jiang*
Guangdong Province Key Laboratory of Pharmacodynamic Constituents of TCM and New Drugs Research,
College of Pharmacy, Jinan University, Guangzhou, Guangdong, 510632 China
*e-mail: trwjiang@jnu.edu.cn
Received January 22, 2017
Abstract—Istaroxime 1, a novel cardiotonic agent with high efficiency and low toxicity was synthesized from
dehydroepiandrosterone 2 using a novel approach that included epoxidation, ring-opening, substitution, and
oximation. The new protocol without gas protection was milder than the reported approaches. The overall yield
of the method was 24.1%.
Keywords istaroxime, cardiotonic agents, synthesis
DOI: 10.1134/S1070363217110196
INTRODUCTION
6 was synthesized by several oxidation and reduction
reactions. Meanwhile, the side chain compound 10 was
obtained by substitution and hydrolysis reactions.
Finally, compound 6 was condensed with compound
10 to give the target istaroxime.
Cardiac glycosides, such as digoxin and digitoxin,
are still important drugs for treating heart failure
clinically [1, 2]. Such drugs are known for some side
effects, such as arrhythmia and sinus premature beat
[3].
The synthetic process for the key intermediate 6
was optimized. Initially, the compound 2 reacted with
oxidants to give compound 6. We investigated the
influence of different oxidants and oxidation condi-
tions on the product structure (Table 1). The result
demonstrated that compound 5 could be directly
obtained with the yield 54–65% by using pyridinium
chlorochromate (PCC) as the oxidizing agent. Forma-
tion of 4-alkenyl-androstane-3,17-diketone (12–19%)
as the by-product could be avoided by using peracetic
acid or m-chloroperbenzoic acid (m-CPBA) as the
oxidant for obtaining compound 3. The total yield of
compound 6 was 60%. Because of low stability of
peracetic acid, m-CPBA, might be the optimal oxidant
in the synthesis of compound 6.
Istaroxime (Scheme 1) is a new class of compounds
used for treatment of heart failure. It can inhibit both
sodium-potassium adenosine triphosphatase (ATPase)
and sarcoplasmic calcium ATPase activities [4–7].
Compared with the current inotropic agents, such as
digoxin, istaroxime demonstrated high tolerability in a
phase I/II safety study and currently it is upon
development for treatment of multiple types of acute
heart failure, including systolic, diastolic, and mixed
types [8, 9], coursing low side effects [9–11].
Due to the mentioned above applications,
istaroxime synthesis was considered of high priority
[12–14]. The prior developed methods for it were
many steps, complicated, time consuming, and expensive
processes.
Synthetic approach to the key intermediate 10 was
also optimized. Synthesis of compound 9 from
benzohydroxamic acid (7) and 2-chloroethylamine
Herein we report a novel strategy for the synthesis
of istaroxime using dehydroepiandrosterone (DHEA)
as the starting material. All intermediates and final
products could be purified by filtration and recrystalliza
-tion without column chromatography involved.
Scheme 1. The chemical structure of istaroxime.
18
O
12
17
16
11
9
19
13
14
H
1
4
RESULTS AND DISCUSSION
2
15
10
5
8
The developed synthetic approach to istaroxime is
presented in Scheme 2. Briefly, the steroid compound
H
H
21
O
7
3
H2N
N
6
20
H
1 The text was submitted by the authors in English.
O
2643

2644
LIANG et al.
Scheme 2. Synthetic approach to istaroxime.
O
O
O
H
H
H
H2SO4
96%
m-CPBA
H
H
H
H
H
O
H
HO
HO
HO
OH
O
OH
2
3
O
O
(1) NaBH4, Ni2+
(2) PCC
H
H
H
H2SO4
89%
PCC
91%
78%
H
H
H
O
H
H
O
H
O
O
O
OH
H
O
4
6
5
+
O
O
.
NH2 HCl
OH
O
HCl
56%
KOH
NH2
N
H
N
H
.
HCl H2N O
(two steps)
7
10
9
+
Cl
.
NH2
HCl
8
THF−H2O
O
71%
H
H
O
H
O
H2N
N
H
Istaroxime
hydrochloride (8) at suitable conditions was the
important step of obtaining the key intermediate 10.
That process affected the total yield of the final
product istaroxime. Therefore, we have studied
influence of the alkaline reagents involved, solvents
and temperature upon the yield of compound 9. It was
low upon using TEA or sodium bicarbonate as the
alkaline reagent probably due to inadequate alkalinity
of the reagent [15, 16]. In our experiments, we have
chosen reagents with stronger alkalinity such as
sodium hydroxide, sodium hydride, potassium
hydroxide, and DBU that led to higher yield of com-
pound 9. When the reaction was carried out at 50°C
with KOH in DMSO the compound 9 was formed with
the yield of 67%. In DMF or MeOH-H2O media the
yield reached 58% and 62%, respectively. So, using
KOH in MeOH–H2O was determined to be the most
efficient.
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NOVEL APPROACH TO THE SYNTHESIS OF ISTAROXIME
2645
Table 1. Oxidation conditions of compound 2
n(Oxidant) : Timea, Yield,
EXPERIMENTAL
Reagents and solvents were purchased from
Aladdin, J&K or Fluka and used without further puri-
fication. NMR spectra were measured on a BRUKER
300 MHz or 400 MHz spectrometer in CDCl3 or
DMSO-d6. High-resolution mass spectrometry (HR-
MS) data were measured on an Agilent 1200 Q-TOF
mass spectrometer. Reaction progress was monitored
by TLC on silica gel GF254 plates (Qingdao Ocean
Chemical Factory, P. R. China).
Product Oxidant Solvent
n(2)
2 : 1
5 : 1
1 : 1
2 : 1
1 : 1
1.5 : 1
2 : 1
h
%
54
65
83
94
72
85
96
59
5
5
3
3
3
3
3
5
PCC
PCC
CH2Cl2
CH2Cl2
41
28
5
AcOOH CHCl3
AcOOH CHCl3
m-CPBA CH2Cl2
m-CPBA CH2Cl2
m-CPBA CH2Cl2
4
18
16
15
32
Androstan-3,5,6-trihydroxy-17-one (3). A solu-
tion of compound 2 (5.77 g, 20.0 mmol) with m-CPBA
(6.90 g, 40.0 mmol) in DCM was stirred for 14 h at
ambient temperature. Sodium sulfite solution was
added to the mixture for quenching reaction slowly.
After 5 min, 20 % aqueous solution of H2SO4 (4 mL)
was added and the mixture was stirred for 12 h at room
temperature. Then the reaction solution was poured
into ice water, filtered and washed with distilled water.
Compound 3 was obtained as white solid after drying
Jones
Acetone Excessively
a The reaction was carried out under room temperature.
(6.02 g, 27.91 mmol), and the mixture was stirred at
room temperature for 40 min. The reaction mixture
was filtered and washed with DCM. The solution was
extracted with water, washed with saturated sodium
bicarbonate solution and brine, concentrated in vacuo
and recrystallized from petroleum ether-ethyl acetate
1
the filter cakes. Yield 96 %. H NMR spectrum, δ,
ppm: 0.77 s (3H, 19CH3), 1.05 s (3H, 18CH3), 1.12–1.29
m (5H), 1.33–1.49 m (7H), 1.54–1.74 m (4H), 1.77–1.93
m (3H), 1.97–2.06 m (1H, H3), 2.37 d.d (1H, J = 8.6,
18.9 Hz, H6), 3.74 s (1H, OH), 3.78–3.84 m (1H, OH),
4.51 s (1H, OH). 13C NMR spectrum, δC, ppm: 13.9
(CH3), 16.7 (CH3), 20.5, 21.9, 30.1, 31.5, 32.0, 32.5,
33.8, 35.8, 38.4 (C10), 41.3, 45.3, 47.7 (C13), 51.0, 66.1
(C3), 74.4 (C6), 74.8 (C5), 220.5 (C17). HR-MS, m/z
[M – H]–: 321.2072 (321.2071). C19H29O4.
1
to afford 4 as white solid. Yield 91%. H NMR
spectrum, δ, ppm: 0.79 s (3H, 19CH3), 0.93 s (3H,
18CH3), 1.19–1.40 m (2H), 1.44–1.59 m (3H), 1.66–
1.73 m (2H), 1.90–1.99 m (4H), 2.03–2.13 m (4H),
2.35–2.46 m (2H), 2.72 d (1H, J = 12.2 Hz, H4b), 2.78
d (1H, J = 3.1 Hz, H4a), 3.45 s (1H, OH), 6.00 s (1H,
OH). 13C NMR spectrum, δC, ppm: 13.7 (C18), 13.9
(C19), 20.8 (CH2), 21.6 (CH2), 31.5, 31.6, 35.7, 36.8,
37.2, 40.7, 43.1, 44.5, 44.8, 48.0, 51.0, 82.0 (C5), 210.5
(C6), 211.1 (C3), 219.6 (C17). HR-MS, m/z [M + H2O]+:
336.1929 (336.1931). C19H28O5.
Androstane-5α-hydroxy-3,6,17-trione (4). To a
suspension of compound 3 (3.0 g, 9.30 mmol) and
silica gel (9.0 g) in DCM (100 mL) was added PCC
Table 2. Yields of compound 9 under different reaction conditions
Base
Et3N
Solvent
Me2CO
Temperature
Reflux
Time, h
15.0
20.0
13.0
25.0
12.0
23.0
25.0
20.0
20.0
Yield, %
7
NaHCO3
NaOH
DBU
MeOH–H2O
EtOH–H2O
DMF
50°C
5
Reflux
43
14
62
67
58
17
25
Room temperature
KOH
KOH
KOH
NaH
MeOH–H2O
DMSO
reflux
50°C
DMF
50°C
THF
0 °C to ~room temperature
60°C
NaH
DMF
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

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LIANG et al.
+
+
Androst-4-ene-3,6,17-trione (5). To a solution of
NH3 ), 11.27 br.s (3H, ONH3 ). 13C NMR spectrum,
compound 4 (1.59 g, 5.0 mmol) in ethanol (50 mL)
was added 15% aqueous H2SO4 (4 mL) and the
mixture was stirred upon refluxing for 3.5 h. Then the
solution was concentrated in vacuo and poured into
cold water, filtered and washed with water. The filter
cake was recrystallized from ethyl acetate to afford 5
as white solid. Yield 89%. 1H NMR spectrum, δ, ppm:
0.93 s (3H, 18CH3), 1.20 s (3H, 19CH3), 1.65–1.32 m
(5H), 1.79–2.04 m (4H), 2.09–2.21 m (4H), 2.45–2.62
m (3H, H2,7b), 2.75–2.86 m (1H, H7a), 6.20 s (1H, H4).
13C NMR spectrum, δC, ppm: 13.7 (C18), 17.6 (C19),
20.2 (CH2), 21.6 (CH2), 30.9 (CH2), 33.7 (CH), 33.9
(CH2), 35.6 (CH2), 39.7 (C10), 45.4 (CH2), 47.6 (C13),
50.9 (CH), 51.5 (CH), 125.9 (C4), 160.2 (C5), 199.1
(C3), 201.2 (C6), 219.3 (C17). HR-MS, m/z [M + H]+:
301.1796 (301.1798). C19H25O3.
δC, ppm: 37.2 (CH2N), 71.1 (-CH2ON).
Istaroxime (1). To a stirred solution of compound
6 (0.10 g, 0.33 mmol) in THF (4 mL), a solution of
compound 10 (49.5 mg, 0.33 mmol) in H2O (2 mL)
was rapidly added dropwise. After 1 h, NaCl (200 mg)
was added and the mixture was stirred for 5 min. The
phases were separated and evaporated to give an oily
residue. The residue was dissolved in water (5 mL) and
neutralized with 0.1 mol/L sodium bicarbonate solution
to pH 7. The mixture was extracted with DCM, dried
over Na2SO4, filtered, and evaporated to give the target
compound istaroxime as a pale yellow solid. Yield
1
71%. H NMR spectrum, δ, ppm: 0.88 s (2H), 0.90 s
(2H), 0.92 s (3H, 19CH3), 1.01 s (3H, 18CH3), 1.24–
1.27 m (1H), 1.33–1.49 m (7H), 1.51–1.63 m (4H),
1.64–1.72 m (1H), 1.74–1.98 m (8H), 2.02–2.23 m
(12H), 2.25–2.69 m (12H), 3.01–3.13 m (2H,
CH2NH2), 4.02–4.12 m (2H, NOCH2). 13C NMR spec-
trum, δC, ppm: 12.5 (C18), 12.6 (C18), 13.9 (2C, C19),
20.6, 20.8, 21.7, 31.2, 35.7, 37.0, 37.1, 37.5 (2C), 37.6,
37.7, 38.1, 41.5 (2C, z,e-CH2NH2), 41.8, 41.9, 45.5
(2C), 48.1, 53.7, 51.7, 53.8, 58.1 (C5), 75.4 (NOCH2),
158.4 (C3), 209.3 (C6), 219.7 (C17). HR-MS, m/z [M +
H]+: 361.2488 (361.2486). C21H33N2O3.
(5α)-Androstane-3,6,17-trione (6). The compound
6 was synthesized from compound 5 (1.0 g, 3.33 mmol)
1
following the prior methods [17, 18]. Yield 78 %. H
NMR spectrum, δ, ppm: 0.90 s (3H, 19CH3), 0.99 s
(3H, 18CH3), 1.31–1.47 m (3H), 1.50–1.70 m (4H),
1.80–1.97 m (3H), 1.99–2.19 m (4H), 2.30–2.58 m
(6H). 13C NMR spectrum, δ, ppm: 12.6 (C18), 13.8
(C19), 20.9 (CH2), 21.6 (CH2), 31.1, 35.6, 36.9, 37.3,
37.4, 38.0, 41.2, 45.3, 48.1, 51.5, 53.4, 57.5 (C5), 208.2
(C3), 210.8 (C6), 219.5 (C17). HR-MS, m/z [M + H]+:
303.1957 (303.1955). C19H27O3.
CONCLUSIONS
In summary, the more efficient procedure for the
synthesis of istaroxime was developed. The processes
conditions for the key intermediates 6 and 10 were
optimized. The present study led to superior results as
compared with previously reported methods due to
mild reaction conditions, simpler experimental proce-
dure and no inert gas protection and column chromato-
graphy purification involved at lower temperature. The
overall yield of istaroxime reached 24.1%. In addition,
we have provided the more convenient method for
synthesis of the side chain intermediate 10 by using 2-
chloroethylamine hydrochloride and benzohydroxamic
acid as starting materials, which reduced cost of the
synthesis of istaroxime.
N-(2-Aminoethoxy)-benzamide (9). A solution of
compound 8 (3.0 g, 25.86 mmol) in DMSO was added
dropwise to a stirred solution of compound 7 (5.32 g,
38.80 mmol) and KOH (10.16 g, 181.05 mmol) at
room temperature. After stirring for 25 h, the reaction
solution was poured into cold water, extracted with
ethyl acetate, washed with saturated sodium bicar-
bonate solution and brine, dried over sodium sulfate,
and concentrated in vacuo to afford compound 9 as
light yellow oil. HR-MS, m/z [M + H]+: 181.0973
(181.0972). C9H13N2O2.
2-(Aminooxy)ethanamine dihydrochloride (10).
Compound 9 was dissolved in 30 mL of hydrochloric
acid (6.0 mol/L). The mixture was refluxed gently
upon stirring for 4 h, concentrated in vacuo to 10 mL,
filtered and washed with ice water. The resulted filtrate
was concentrated and recrystallized from methanol to
ACKNOWLEDGMENTS
This study was supported by the National Natural
Science Foundation of China (81573315), Guangdong
Natural Science Fund (2015A030313313) and
Guangzhou Industry-University Collaborative Innova-
tion Major Projects (201508030016).
1
give compound 10 as white solid. Yield 56%. H
NMR spectrum, δ, ppm: 3.14 t (2H, J = 5.4 Hz,
CH2N), 4.28 t (2H, J = 5.4 Hz, CH2ON), 8.35 br.s (3H,
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MCC.0b013e32833e10fb
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