Conversion of epiandrosterone into 17β-amino-5α-androstane

Article abstract of DOI:10.1023/B:CONC.0000033931.36367.0d

A new method for synthesizing 17β-amino-5α-androstane was developed based on tigogenin. The configuration at C-17 was proved by PMR.

Full text of DOI:10.1023/B:CONC.0000033931.36367.0d

Chemistry of Natural Compounds, Vol. 40, No. 2, 2004
CONVERSION OF EPIANDROSTERONE INTO 17β-AMINO-5α-ANDROSTANE
1
1
1
M. I. Merlani, M. G. Davitishvili, N. Sh. Nadaraia,
UDC 547.92
1
2
M. I. Sikharulidze, and K. Papadopulos
A new method for synthesizing 17β-amino-5α-androstane was developed based on tigogenin. The
configuration at C-17 was proved by PMR.
Key words: aminosteroids, synthesis, 5α-androstane.
Aminosteroids of the 5α-androstane series typically have a broad spectrum of pharmacologic action, in particular,
antiarhythmic, hypotensive, anti-inflammatory, and fungicidal activity [1-3].
1
7β-Amino-5α-androstane (1) was first synthesized as the hydrochloride from cholesterol [4]. Amine 1 is usually
prepared by reduction of 17-hydroxyimino-5α-androstane by various reductants [5, 6]. Spectral proof of the configuration at
C-17 in compound 1 has not been reported.
We developed a new scheme for synthesizing 17β-amino-5α-androstane (1) from epiandrosterone (2) (Scheme 1).
Epiandrosterone was prepared from pregn-16-en-3β-ol-20-one acetate, a conversion product of tigogenin, which has been
proposed as an available steroidal raw material by the I. G. Kutateladze Institute of Pharmaceutical Chemistry of the Academy
of Sciences of Georgia [7].
O
O
O
HO
TsO
H
H
H
2
3
4
NOH
R
NH2
R
1
H
H
6
R
R
1
H
H
1
5
7
: R = NH , R = H;
2 1
: R = H, R1 = NH2
H
8
9
: R = NHCHO, R = H;
1
: R = H, R = NHCHO
1
Scheme 1.
) I. G. Kutateladze Institute of Pharmaceutical Chemistry, Academy of Sciences of Georgia, Tbilisi, 0159, ul.
1
Saradzhishvili 36, fax (99532)25 00 26, e-mail: maiamer@hotmail.com; 2)InstituteofPhysical Chemistry, National Scientific-
Research Center DEMOKRITOS, Athens, Greece. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 123-125,
March-April, 2004. Original article submitted March 5, 2004.
©
0
009-3130/04/4002-0144 2004 Plenum Publishing Corporation
1
44

In the first step, C-3 of epiandrosterone (2) was defunctionalized using the literature method [8, 9] for synthesizing
O-sulfonyl derivative 3 from p-toluenesulfonyl chloride in anhydrous pyridine followed by dehydrotosylation of 3 by LiBr in
DMF. The yield of 5α-androst-2-en-17-one (4) was 65%.
In the second step, stereoselective addition of a N-containing substituent to the C-17 position of ketone 4 was studied.
For this, amine 5 was synthesized by two methods: a known one consisting of formation of the oxime from the ketone followed
by reduction of the oxime to the amine and reductive amination by the Leuckart—Wallach reaction that was used previously
for epiandrosterone [10].
Formation of the oxime of 4 using hydroxylamine hydrochloride in pyridine gives 17-hydroximino-5α-androst-2-ene
(
6). Reduction of oxime 6 by metallic sodium in anhydrous propan-1-ol forms a mixture of the 17β- (5) and 17α-amino-5α-
androst-2-ene(7)(in ~10:1ratioaccordingtoPMRspectroscopy). Subsequent crystallization from benzene:hexane(1:2)isolates
the pure 17β-epimer (5) in 60% yield. Amination of ketone 4 by a mixture of ammonium sulfate, formamide, and formic acid
at 180°C gives a mixture offormyl derivatives 8 and 9. The raw product is suitable for further transformation without additional
purification. The mixture of 8 and 9 was hydrolyzed byboiling in HCl (20%) in CH OH into a mixture of 5 and 7 in ~10:1 ratio
3
according to PMR. The 17β-amine was isolated in 59% yield by crystallization from benzene:hexane (1:2). Hydrogenation of
5
2
over Pd/C in EtOH gives saturated aminosteroid 1 in 75% yield. The yields of amine 1 calculated based on starting ketone
by the Leuckart—Wallach reaction and through formation of oxime 6 are 22 and 25%, respectively.
Thus, 2 can be stereoselectively converted to 1 through formation of 6 or the Leuckart—Wallach reaction.
The structures of the synthesized compounds were confirmed by NMR, IR, and mass spectrometry. Mass spectra
exhibit peaks for molecular ions corresponding to the molecular weights of the studied compounds. IR spectra contain
-1
characteristic absorption bands of the functional groups. A strong absorption in 6 at 1651 cm belongs to C=N stretching
-1
vibrations; a weak one at 1634 cm , to the C=C bond. The presence of a hydroxyl (CN–OH) was confirmed by an absorption
-1
-1
band at 3283 cm . Stretching vibrations of the primary amino in 1 and 5 are found at 3439-3459 cm .
PMR spectra of 1, 5, and 6 have signals for the C-18 angular methyls as singlets with chemical shifts in the range
δ 0.61-0.73 ppm; for C-19 methyls, δ 0.77-0.86 ppm. A triplet at δ 2.64 ppm with SSCC J = 8.8 and 8.5 Hz corresponds to the
1
7α-proton of 1 and 5. Signals from vicinal protons of the C-2=C-3 double bond in 6 and 5 appear as a distorted triplet at
δ 5.54 and 5.59 ppm, respectively. The signal with chemical shift δ 8.01 ppm corresponds to the hydroxyl H of 6. Geminal
protons on C-16 of 6 are observed as two doublets with chemical shifts δ 2.45 and 2.47 ppm.
13C NMR spectra of 1, 5, and 6 have signals from C-18 and C-19 at δ 11.66-12.18 and 17.01-20.5 ppm, respectively;
the oxime C=N of 6, at δ 171.5 ppm; the C=C of 6 and 5, at δ 125.86 and 126.8 ppm; and the C–NH of 5 and 1, at δ 62.0 and
2
6
2.89 ppm, respectively.
EXPERIMENTAL
Melting points were determined on a Kofler block. IR spectra were recorded on a Magna-IR Spectrometer 550
instrument in KBr disks. Mass spectra were recorded in a Micromass Platform II instrument (EI, 70 eV). NMR spectra were
obtained on an AC 250 instrument (Bruker, working frequency 250 MHz for H and 62.5 MHz for 13C). Chemical shifts of
1
protons are given on the δ scale with TMS internal standard and CDCl solvent. The course of the reactions and the purity of
3
theproductsweremonitoredbyTLCon Silufol 254 plates (Kavalier, Czech Rep.) using benzene:acetone (10:1) or butanol:acetic
acid:water (4:1:1). Spots weredetectedbysprayingwith phosphomolybdicacidsolution in EtOH(10%) and subsequent heating.
3
β-(4-Methylphenylsulfonyloxy)-5α-androstan-17-one (3). A solution of 2 (2.5 g, 8.60 mmol) in freshly distilled
pyridine (25 mL) at 0°C was treated with p-toluenesulfonylchloride (3.2 g, 16.9 mmol), held at 20°C for 20 h, and poured into
icewater (100 mL). The precipitate was filtered off and washed with water to isolate the product (3.5 g). Crystallization from
benzene:hexane (1:4) afforded 3 (3.36 g, 88%), mp 163-164°C, which corresponds to the literature value [8].
5
α-Androst-2-en-17-one (4). A solution of 3 (2.9 g, 6.58 mmol) in DMF (10 mL) was treated with LiBr (1.4 g,
1
6.09 mmol), boiled for 3 h, cooled, and treated with water. The precipitate was filtered off, washed with water, and dried.
Chromatography over a column (silica gel L 100/160, eluent benzene:acetone, 10:1) isolated 4 (1.15 g, 65%), mp 100-102°C,
lit. [8] mp 103-105°C.
1
7-Hydroximino-5α-androst-2-ene (6). A mixture of 4 (2 g, 7.34 mmol) and hydroxylamine hydrochloride (0.5 g,
7
.35 mmol) in pyridine (15 mL) was heated to 65-67°C for 3 h, cooled to room temperature, and poured into icewater (50 mL).
145

The precipitate was filtered off, washed with water, and dried. Crystallization from CH OH afforded 6 (2.0 g, 95%), mp 141-
3
-1
+
+
1
[
43°C. IR spectrum (ν, cm ): 3283 (OH), 1651 (C=N), 1634 (C=C). Mass spectrum (m/z): 287 [M] , 270 [M - OH] , 256
M - N - OH]+.
PMR spectrum (δ, ppm, J/Hz): 0.73 (3H, s, CH -18), 0.86 (3H, s, CH -19), 2.45 (1H, d, syn-H-16, J = 3.17), 2.47 (1H,
3
3
d, anti-H-16, J = 8.6), 5.54 (2H, distorted t, H-2, H-3, J = 6.8), 8.01 (1H, s, C=NOH). 13C NMR spectrum (δ, ppm): 11.66
(C-18), 17.09 (C-19), 34.96 (C-16), 126.8 (C-2, C-3), 171.5 (C-17).
1
7β-Formamido-5α-androst-2-ene (8). A mixture of 4 (0.37 g, 1.4 mmol), anhydrous ammonium sulfate (0.04 g,
0
1
.3 mmol), and formic acid (0.14 mL, 3.7 mmol, 99.7%), and formamide (1.3 mL, 38.4 mmol) was heated at 150-160°C for
h and at 180-190°C for 3.5 h, cooled to 20°C, and treated with water (10 mL). After 12 h the precipitate was filtered off,
washed with water, and dried to isolate the product (0.39 g). Chromatography over a column (silica gel L 100/160, eluent
-1
benzene:acetone, 20:1 and 10:1) isolated 8 (0.35 g, 85%), mp 149-151°C. IR spectrum (ν, cm ): 3250 (NH), 1655, 1560
CONH), 1635 (C=C).
7β-Amino-5α-androst-2-ene (5). a) A boiling solution of 6 (3 g, 10.43 mmol) in propan-1-ol (100 mL) was treated
(
1
with portions of metallic sodium (3 g) over 3 h, boiled for 1 h, cooled, and treated with saturated NaCl solution. The organic
layer was evaporated in vacuum to dryness. The solid was dissolved in ether and washed with water until the pH was 7. The
ether extracts were dried (MgSO ). The solvent was evaporated to give the product (2 g). Crystallization from benzene:hexane
4
(1:2) afforded 5 (1.73 g, 60%), mp 145-147°C.
b) A mixture of crude reaction product containing 8 and 9 (0.35 g, 1.2 mmol), aqueous HCl (0.9 mL, 20%), and
CH OH (20 mL) was boiled for 10 h and evaporated in vacuum. The CH OH and solid were heated to dissolve them in water
3
3
(
150 mL). The insoluble precipitate was filtered off. The filtrate was made basic with NaOH until the pH was 8. The resulting
precipitate was filtered off, washed with water, and dried to isolate the product (0.22 g). Crystallization from benzene:hexane
1:2) gave 5 (0.19 g, 59%).
(
-1
+
+
IR spectrum (ν, cm ): 3439 (NH ), 1634 (C C). Mass spectrum (m/z): 273 [M] , 258 [M - NH] .
2
PMR spectrum (δ, ppm, J/Hz): 0.64 (3H, s, CH -18), 0.77 (3H, s, CH -19), 2.64 (1H, t, H-17α, J
= 8.5,
17a /16e
3
3
J17a /16a = 8.8), 5.59 (2H, distorted t, H-2, H-3, J = 6.8). 13C NMR spectrum (δ, ppm): 17.2 (C-18), 20.57 (C-19), 47.9 (C-16),
6
2.0 (C-17), 125.86 (C-2, C-3).
7β-Amino-5α-androstane (1). A solution of 5 (2 g, 7.31 mmol) in absolute EtOH (100 mL) was treated with a
suspension of Pd/C (0.5 g) in EtOH (100 mL) and stirred on a magnetic stirrer under a H atmosphere at 20-25°C until H
1
2
2
absorption stopped. The catalyst was filtered off and washed with hot EtOH. The filtrate was evaporated to dryness. The
resulting oil was triturated in ether and filtered off. Crystallization from benzene:hexane (1:2) isolated 1 (1.51 g, 75%),
mp 89-91°C, lit. [3] mp 86-90°C.
-1
+
+
IR spectrum (ν, cm ): 3439 (NH ). Mass spectrum (m/z): 275 [M] , 260 [M - NH] .
2
PMR spectrum (δ, ppm, J/Hz): 0.61 (3H, s, CH -18), 0.77 (3H, s, CH -19), 2.64 (1H, t, H-17α, J
= 8.5,
17a /16e
3
3
J17a /16a = 8.8).
13C NMR spectrum (δ, ppm): 12.18 (C-18), 20.40 (C-19), 47.08 (C-16), 62.89 (C-17).
REFERENCES
1
2
.
.
T. J. Campbell and E. M. V. Williams, Brit. J. Pharmacol., 76, 337 (1982).
R. A. Lucas, D. F. Dickel, R. L. Dziemian, M. J. Ceglowski, B. L. Hensle, and H. B. McPhillamy, J. Am. Chem.
Soc., 82, No. 21, 5688 (1960).
3
4
5
6
7
8
9
.
.
.
.
.
.
.
J. C. Babcock, U.S. Pat. No. 3,009,925 (1961); Chem. Abstr., 56, P10234f (1962).
R. E. Marker, J. Am. Chem. Soc., 58, 480 (1936).
C. W. Choppe and J. C. P. Sly, J. Chem. Soc., 345 (1959).
J. C. Babcock, U.S. Pat. No. 2,863,885 (1958); Chem. Abstr., 54, P2440f (1960).
E. P. Kemertelidze and T. A. Pkheidze, Khim.-Farm. Zh., 6, No. 12, 44 (1972).
W. H. Kruizinga, B. Strijtveen, and R. M. Kellogg, J. Org. Chem., 46, 4321 (1981).
S. Takasuto and N. Ikekawa, Chem. Pharm. Bull., 23, No. 12, 1431 (1989).
N. Sh. Nadaraia, V. I. Sladkov, L. N. Kuleshova, and N. N. Suvorov, Zh. Org. Khim., 23, No. 3, 533 (1987).
1
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