Synthesis and characterization of new phenyl esters derived from 16-dehydropregnenolone acetate (16-DPA)

Article abstract of DOI:10.1007/s11164-012-0890-5

A series of new phenyl esters based on a 5,16-pregnadiene-20-one skeleton, namely 3β-benzoyloxy-5,16-pregnadiene-20-ones, which may be good inhibitors of 17α-hydroxylase and 5α-reductase enzyme or useful intermediates for producing steroidal drugs, were synthesized starting from diosgenin. The structures of the steroids were characterized by ¹H nuclear magnetic resonance (NMR), ¹³C NMR, infrared (IR), and mass spectra.

Full text of DOI:10.1007/s11164-012-0890-5

Res Chem Intermed
DOI 10.1007/s11164-012-0890-5
Synthesis and characterization of new phenyl esters
derived from 16-dehydropregnenolone acetate
(16-DPA)
•
Hongqi Li Jueshu Fang Juan Li Yulong Wang
•
•
•
•
Xiujuan Tian Yuanhui Xiang
Received: 9 October 2012 / Accepted: 26 October 2012
Ó Springer Science+Business Media Dordrecht 2012
Abstract A series of new phenyl esters based on a 5,16-pregnadiene-20-one
skeleton, namely 3b-benzoyloxy-5,16-pregnadiene-20-ones, which may be good
inhibitors of 17a-hydroxylase and 5a-reductase enzyme or useful intermediates for
producing steroidal drugs, were synthesized starting from diosgenin. The structures
1
of the steroids were characterized by H nuclear magnetic resonance (NMR), 13C
NMR, infrared (IR), and mass spectra.
Keywords Steroid Á Pregnadiene Á Phenyl ester Á 16-DPA
Introduction
Among numerous steroidal compounds that have been reported, 16-dehydropregn-
enolone (16-DHP) and 16-dehydropregnenolone acetate (16-DPA) and their
analogs, as useful drugs and intermediates for producing steroid drugs, have
received much attention. It is estimated that more than 65 % of steroid drugs are
derived from 16-DPA and its analogs [1]. Recent years have witnessed increasing
application of 16-DPA as a versatile scaffold and building block for different
steroidal drugs, as it is an ideal platform for preparation of dexamethasone, b-
methasone, 5a-reductase inhibitor, c-aminobutyric acid type A (GABAA) receptor,
inhibitor of steroid C17(20) lyase, dipeptidyl peptidase (DPP)-IV, and other related
steroidal pharmacophores [2–6]. 16-DHP is an efficient inhibitor of 17a-hydrox-
ylase and 15a-reductase [7]. In continuation of our study on steroids [8–10] and to
explore an improved way for synthesis of new steroidal compounds from the cheap
H. Li (&) Á J. Fang Á J. Li Á Y. Wang Á X. Tian Á Y. Xiang
Key Laboratory of Science and Technology of Eco-Textile, Ministry of Education, College
of Chemistry, Chemical Engineering and Biotechnology, Donghua University,
2999 North Renmin Road, Shanghai 201620, People’s Republic of China
e-mail: hongqili@dhu.edu.cn
123

H. Li et al.
starting material diosgenin, herein we report synthesis and structural characteriza-
tion of a series of new phenyl esters derived from 16-DPA.
Experimental
All chemical reagents were purchased from commercial sources and used as
received unless otherwise stated. Melting points were determined on a XT-4 melting
apparatus, and the quoted temperatures are uncorrected. Elemental analysis was
1
carried out on an Elmentar Vario EL III system. H NMR and 13C NMR spectra
were recorded on a Bruker AM 400 spectrometer. CDCl3 was used as solvent, and
recorded chemical shifts were internally referenced to Me4Si (0 ppm). IR spectra
were obtained on a Thermo Electron Corporation Nicolet 380 FT-IR spectropho-
tometer. Mass spectra were recorded on a Shimadzu QP-2010 instrument using
electron impact ionization (EI) at 70 eV.
Pseudodiosgenin diacetate (2) and 3b-acetoxy-5,16-pregnadiene-20-one (16-
dehydropregnenolone acetate, 16-DPA, 3) were prepared from diosgenin (1) as
described in literature [10].
3b-Hydroxypregna-5,16-diene-20-one (16-dehydropregnenolone, 16-DHP, 4)
To a flask were added 16-DPA (0.1 g, 0.28 mmol), methanol (15 mL), and 2 %
aqueous sodium hydroxide (1 mL, 0.50 mmol). The mixture was stirred at room
temperature for 12 h. The resulting solution was poured into water (100 mL) then
extracted with ethyl acetate (39 30 mL). The organic phase was dried over
anhydrous magnesium sulfate, and the solvent was removed in vacuum to afford
16-DHP (85 mg, 97 %) as white powder. M.p. 210.5–212 °C (literature [11] value:
211–212 °C). IR (KBr): m (cm-1) 3,431 (s), 2,982 (s), 2,878 (m), 2,864 (w), 1,657
(s), 1,588 (m), 1,432 (m), 1,306 (s), 1,252 (s), 1,233 (m), 874 (m).
To a flask were added 16-DPA (0.1 g, 0.28 mmol), t-BuOH (15 mL), and potassium
hydroxide (0.08 g, 1.43 mmol). The mixture was stirred at room temperature for 10 h.
Theresultingsolutionwaspouredintowater(100 mL)thenextractedwithethylacetate
(39 30 mL). The organic phase was dried over anhydrous magnesium sulfate, and the
solvent was removed in vacuum to afford 16-DHP (81 mg, 92 %) as white powder.
3b-(p-Nitrobenzoyloxy)pregna-5,16-diene-20-one (5a)
A solution containing 16-DHP (0.20 g, 0.64 mmol), p-nitrobenzoic acid (0.285 g,
1.7 mmol), 1,3-dicyclohexylcarbodiimide (DCC, 0.22 g, 1.1 mmol), and 4-dimeth-
ylaminopyridine (DMAP, 0.126 g, 1.0 mmol) in methylene dichloride (10.5 mL)
was stirred for 2 h at room temperature. After reaction, the resulting pale-yellow
solution was poured into ice-water (150 mL), then extracted with chloroform (39
30 mL). The organic phase was washed with water and dried over anhydrous
magnesium sulfate. Crude product was obtained after the solvent was removed in
vacuum. The crude product was dissolved in ethyl acetate and filtered through a
123

Synthesis and characterization of new phenyl esters
column containing neutral alumina. The organic solvent was removed in vacuum to
1
give a white crystalline solid 5a (0.14 g, 50 %). H NMR (CDCl3): 0.94 (s, 3H);
1.11 (s, 3H); 2.29 (s, 3H); 4.89 (m, 1H); 5.45 (t, 1H, J = 5.0 Hz); 6.72 (t, 1H,
J = 1.7 Hz); 8.20 (m, 2H), 8.23 (m, 2H). 13C NMR (CDCl3): 15.7 (C(18)); 20.7
(C(19)); 22.7 (C(21)); 38.1; 56.4; 75.7 (C(3)); 122.5 (C(6)); 123.5; 130.7; 136.2;
139.8 (C(16)); 144.5 (C(17)); 150.5; 155.3 (C(5)); 164.0 (ester C=O); 196.8 (C(20)).
IR (KBr): m (cm-1) 1,700 (s), 1,609 (s), 1,525 (m), 1,349 (m), 1,278 (s), 841 (m).
MS: m/z (%) 296 (59), 145 (41), 105 (55), 91 (69), 79 (32), 43 (100).
16-DHP (1.0 g, 3.2 mmol) and p-nitrobenzoyl chloride (2.4 g, 12.9 mmol) were
added to a flask containing anhydrous pyridine (12 mL) at 0 °C. The mixture was
heated to 90 °C and stirred for 6 h. After reaction, the resulting mixture was allowed
to cool to room temperature and filtered. The precipitate was washed with water and
dried, then dissolved in ethyl acetate and purified by column chromatography to
give a white crystalline solid 5a (0.89 g, 61 %).
Other steroidal compounds 5b–h were prepared from 16-DHP and corresponding
substituted benzoic acids in a similar procedure, and the physical data of the new
steroids were as follows:
3b-(o-Nitrobenzoyloxy)pregna-5,16-diene-20-one (5b)
White powder. Yield 51 %. M.p. 142–144 °C. Rf 0.54 (petroleum ether/ethyl
acetate, 6:1, v/v). H NMR (CDCl3): 0.93 (s, 3H); 1.07 (s, 3H); 2.27 (s, 3H); 4.89
1
(m, 1H); 5.48 (t, 1H, J = 5.2 Hz); 6.75 (t, 1H, J = 1.8 Hz); 7.68 (m, 2H); 7.76 (m,
1H); 7.95 (m, 1H). 13C NMR (CDCl3): 15.7 (C(18)); 20.7 (C(19)); 22.7 (C(21));
76.3 (C(3)); 122.5 (C(6)); 139.9 (C(16)); 144.4 (C(17)); 155.4 (C(5)), 164.9 (ester
C=O); 196.9 (C(20)).
3b-(m-Nitrobenzoyloxy)pregna-5,16-diene-20-one (5c)
White powder. Yield 47 %. M.p. 164–166 °C. Rf 0.68 (petroleum ether/ethyl
acetate, 5:1, v/v). H NMR (CDCl3): 0.94 (s, 3H); 1.08 (s, 3H); 2.28 (s, 3H); 4.94
1
(m, 1H); 5.48 (t, 1H, J = 5.0 Hz); 6.75 (t, 1H, J = 1.9 Hz); 7.68 (m, 1H); 8.43 (m,
2H); 8.88 (m, 1H). 13C NMR (CDCl3): 14.1 (C(18)); 20.7 (C(19)); 22.7 (C(21));
75.7 (C(3)); 122.5 (C(6)); 139.9 (C(16)); 144.4 (C(17)); 155.4 (C(5)); 163.9 (ester
C=O); 196.9 (C(20)).
3b-(3,5-Dinitrobenzoyloxy)pregna-5,16-diene-20-one (5d)
White powder. Yield 40 %. M.p. 148–150 °C. Rf 0.62 (petroleum ether/ethyl
acetate, 6:1, v/v). H NMR (CDCl3): 0.95 (s, 3H); 1.11 (s, 3H); 2.27 (s, 3H); 4.99
1
(m, 1H); 5.50 (t, 1H, J = 5.2 Hz); 6.75 (t, 1H, J = 2.0 Hz); 9.18 (m, 2H); 9.25 (m,
1H). 13C NMR (CDCl3): 16.4 (C(18)); 18.0 (C(19)); 21.6 (C(21)); 74.7 (C(3));
124.5 (C(6)); 141.9 (C(16)); 146.7 (C(17)); 164.2 (C(5)); 175.6 (ester C=O); 199.2
(C(20)).
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H. Li et al.
3b-(p-Methoxybenzoyloxy)pregna-5,16-diene-20-one (5e)
White powder. Yield 64 %. M.p. 118–120 °C. Rf 0.71 (petroleum ether/ethyl
acetate, 10:1, v/v). 1H NMR (CDCl3): 0.95 (s, 3H); 1.12 (s, 3H); 2.28 (s, 3H); 4.86
(m, 1H); 5.47 (t, 1H, J = 5.1 Hz); 6.75 (t, 1H, J = 1.6 Hz); 6.97 (m, 2H); 8.08 (m,
2H). 13C NMR (CDCl3): 14.1 (C(18)); 19.3 (C(19)); 22.7 (C(21)); 74.1 (C(3));
122.0 (C(6)); 140.4 (C(16)); 144.4 (C(17)); 155.4 (C(5)); 163.2 (ester C=O); 196.9
(C(20)).
3b-(o-Methoxybenzoyloxy)pregna-5,16-diene-20-one (5f)
White powder. Yield 43 %. M.p. 102–106 °C. Rf 0.57 (petroleum ether/ethyl
acetate, 5:1, v/v). H NMR (CDCl3): 0.92 (s, 3H); 1.05 (s, 3H); 2.27 (s, 3H); 4.90
1
(m, 1H); 5.46 (t, 1H, J = 5.2 Hz); 6.75 (t, 1H, J = 1.9 Hz); 7.02 (m, 2H); 7.49 (m,
1H); 7.81 (m, 1H). 13C NMR (CDCl3): 15.7 (C(18)); 20.7 (C(19)); 22.7 (C(21));
74.2 (C(3)); 121.9 (C(6)); 140.4 (C(16)); 144.4 (C(17)); 155.4 (C(5)); 165.6 (ester
C=O); 196.9 (C(20)).
3b-(o-Methylbenzoyloxy)pregna-5,16-diene-20-one (5g)
White powder. Yield 69 %. M.p. 122–124 °C. Rf 0.44 (petroleum ether/ethyl
acetate, 30:1, v/v). 1H NMR (CDCl3): 0.94 (s, 3H); 1.12 (s, 3H); 2.27 (s, 3H); 4.85
(m, 1H); 5.44 (t, 1H, J = 5.0 Hz); 6.72 (t, 1H, J = 1.9 Hz); 7.24 (m, 2H); 7.37 (m,
1H); 7.88 (m, 1H). 13C NMR (CDCl3): 15.7 (C(18)); 20.7 (C(19)); 21.7 (C(21));
74.4 (C(3)); 122.1 (C(6)); 139.8 (C(16)); 144.4 (C(17)); 155.4 (C(5)); 167.2 (ester
C=O); 196.9 (C(20)).
3b-(m-Methylbenzoyloxy)pregna-5,16-diene-20-one (5h)
White powder. Yield 75 %. M.p. 158–160 °C. Rf 0.40 (petroleum ether/ethyl
acetate, 20:1, v/v). 1H NMR (CDCl3): 0.95 (s, 3H); 1.15 (s, 3H); 2.29 (s, 3H); 4.85
(m, 1H); 5.44 (t, 1H, J = 5.0 Hz); 6.72 (t, 1H, J = 1.8 Hz); 7.35 (m, 2H); 7.83 (m,
2H). 13C NMR (CDCl3): 14.1 (C(18)); 19.3 (C(19)); 22.7 (C(21)); 74.4 (C(3));
122.1 (C(6)); 140.3 (C(16)); 144.5 (C(17)); 155.4 (C(5)); 166.2 (ester C=O); 196.9
(C(20)).
Results and discussion
The synthetic route of the target 3b-benzoyloxypregna-5,16-diene-20-one steroids
(5a–h) is shown in Fig. 1. The starting material diosgenin was transformed by
acetylation and oxidation to 3b-acetoxy-5,16-pregnadiene-20-one (16-DPA, 3) in
35 % yield as reported previously [10]. Hydrolysis of 16-DPA under basic
conditions afforded 16-DHP in high yield. If the hydrolysis was carried out in t-
BuOH/H2O with potassium hydroxide as base, 16-DHP (4) was obtained in 92 %
yield. Hydrolysis by using NaOH in MeOH/H2O afforded 16-DHP in 97 % yield.
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Synthesis and characterization of new phenyl esters
O
OAc
NH4Cl/Py
Ac2O, reflux
O
H
O
H
H
H
86%
H
H
HO
AcO
2
1
O
O
KOH, t-BuOH
H2O
ArCO2H
DCC
DMAP
H
H
92%
CrO3/HOAc
41%
H
H
H
NaOH, MeOH
H2O
97%
H
3
HO
AcO
4
O
H
O
H
H
NO2
NO2
Ar
O
Ar =
5a-h
NO2
NO2
NO2
5a: 50%
5b: 51%
5c: 47%
5d: 40%
Me
OMe
OMe
Me
5h: 75%
5f: 43%
5g: 69%
5e: 64%
Fig. 1 Synthetic route to target steroids 5a–h
Esterification of 16-DHP to synthesize phenyl esters 5a–h could be achieved in
two ways. In the case of 5a, reaction between 16-DHP and p-nitrobenzoyl chloride
in pyridine produced the targeted ester in 61 % yield. Pyridine was necessary as
both solvent and deacid reagent in the reaction [12]. The other method for
preparation of 5a involved Steglich reaction by using 16-DHP, p-nitrobenzoic acid,
and DCC catalyzed by DMAP in 50 % yield. In this case substituted benzoic acids
did not need to be transformed into the corresponding acyl chlorides and could be
used directly for preparation of the targeted phenyl esters. Therefore, phenyl esters
5b–h were synthesized by Steglich reaction from 16-DHP, substituted benzoic acid,
and DCC catalyzed by DMAP in fair to good yields (40–75 %).
1
The chemical structures of steroids 5a–h were characterized by H NMR, 13C
NMR, IR, and mass spectra and melting point measurements. Characteristic
chemical shifts in 1H NMR and 13C NMR spectra of steroids 5a–h are summarized
in Tables 1 and 2, respectively. All of the chemical shifts of protons in methyl
groups, OCH moieties, C=CH moieties, and aryl rings were in reasonable ranges, as
shown in Table 1, and the spectral data were in good accordance with the structures.
The chemical shifts of carbons in methyl groups, OCH moieties, C=CH moieties,
and C=O groups were also in reasonable ranges, as shown in Table 2, and the
spectral data were in good accordance with the structures.
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H. Li et al.
Table 1 Characteristic chemical shifts in 1H NMR spectra of steroids 5a–h
No.
d (ppm)
H–C(18)
H–C(19)
H–C(21)
H–C(3)
H–C(6)
H–C(16)
H-phenyl
5a
5b
5c
5d
5e
5f
0.94
0.93
0.94
0.95
0.95
0.92
0.94
0.95
1.11
1.07
1.08
1.11
1.12
1.05
1.12
1.15
2.29
2.27
2.28
2.27
2.28
2.27
2.27
2.29
4.89
4.89
4.94
4.99
4.86
4.90
4.85
4.85
5.45
5.48
5.48
5.50
5.47
5.46
5.44
5.44
6.72
6.75
6.75
6.75
6.75
6.75
6.72
6.72
8.20, 8.23
7.68, 7.76, 7.95
7.68, 8.43, 8.88
9.18, 9.25
6.97, 8.08
7.02, 7.49, 7.81
7.24, 7.37, 7.88
7.35, 7.83
5g
5h
Table 2 Characteristic chemical shifts in 13C NMR spectra of steroids 5a–h
No.
d (ppm)
C(18)
C(19)
C(21)
C(3)
C(6)
C(16)
C(17)
C(5)
Ester C=O
C(20)
5a
5b
5c
5d
5e
5f
15.7
15.7
14.1
16.4
14.1
15.7
15.7
14.1
20.6
20.7
20.7
18.0
19.3
20.7
20.7
19.3
22.3
22.7
22.7
21.6
22.7
22.7
21.7
22.7
75.7
76.3
75.7
74.7
74.1
74.2
74.4
74.4
122.5
122.5
122.5
124.5
122.0
121.9
122.1
122.1
139.8
139.9
139.9
141.9
140.4
140.4
139.8
140.3
144.5
144.4
144.4
146.7
144.4
144.4
144.4
144.5
155.3
155.4
155.4
164.2
155.4
155.4
155.4
155.4
164.0
164.9
163.9
175.6
163.2
165.6
167.2
166.2
196.8
196.9
196.9
199.2
196.9
196.9
196.9
196.9
5g
5h
Conclusions
In summary, eight new phenyl esters based on a 5,16-pregnadiene-20-one skeleton,
namely 3b-benzoyloxy-5,16-pregnadiene-20-ones, were synthesized starting from
diosgenin. The structures of the steroids were characterized by 1H NMR, 13C NMR,
IR, and mass spectra. These new steroids may serve as good inhibitors for 17a-
hydroxylase and 5a-reductase enzyme or as useful intermediates for producing
steroidal drugs. Investigation of the biological activity of the new steroids will be
conducted in the near future.
Acknowledgments The authors acknowledge the financial support of the project by Shanghai Natural
Science Foundation (No. 06ZR14001).
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