An effective synthesis of ursodeoxycholic acid from dehydroepiandrosterone

Article abstract of DOI:10.1016/j.steroids.2021.108870

A novel synthetic route of producing ursodeoxycholic acid (UDCA) was developed through multiple reactions from plant-source dehydroepiandrosterone (DHEA), with a Mistunobu reaction and regioselective allyl oxidationat as the key steps. The reaction conditions of the key allyl oxidation reaction were also investigated and optimized, including solvent, oxidant and reaction temperature. In this novel route for the preparation of UDCA, most of the reaction steps have high conversions and overall yield up to 35% for 8 steps. Since all starting materials are cost-effective, commercially available and effectively avoided the risk of animal derived raw materials, this promising synthetic route offers economical and efficient strategies for potential production of UDCA.

Full text of DOI:10.1016/j.steroids.2021.108870

Steroids 172 (2021) 108870
Contents lists available at ScienceDirect
Steroids
journal homepage: www.elsevier.com/locate/steroids
An effective synthesis of ursodeoxycholic acid
from dehydroepiandrosterone
,
Wang Chena *, Daihua Hua, Zili Fenga, Zhaopeng Liub
a School of Biological Science and Engineering, Shaanxi University of Technology, Hanzhong 723000, China
b Key Lab. of Chemical Biology(Ministry of Education), Institute of Medicinal Chemistry, School of Pharmaceutical Sciences, Shandong University, Jinan 250012, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
A novel synthetic route of producing ursodeoxycholic acid (UDCA) was developed through multiple reactions
from plant-source dehydroepiandrosterone (DHEA), with a Mistunobu reaction and regioselective allyl oxida-
tionat as the key steps. The reaction conditions of the key allyl oxidation reaction were also investigated and
optimized, including solvent, oxidant and reaction temperature. In this novel route for the preparation of UDCA,
most of the reaction steps have high conversions and overall yield up to 35% for 8 steps. Since all starting
materials are cost-effective, commercially available and effectively avoided the risk of animal derived raw
materials, this promising synthetic route offers economical and efficient strategies for potential production of
UDCA.
Ursodeoxycholic acid
Dehydroepiandrosterone
Synthesis
1. Introduction
abundant and least expensive bile acid, it is commonly used as the raw
material to produce UDCA through the dihydroxylation at C12 and the
Ursodeoxycholic acid (UDCA) (Fig. 1) is the main component of the
bile of black bears which has been widely used in clinics for the treat-
ment of hepatobiliary diseases [1]. As reported [2], UDCA solubilizes
cholesterol gallstones, improves the liver function in cholestatic diseases
and significantly decreases cholesterol saturation in the bile. Becuase of
possessing high efficacy and no side effects, UDCA is the only bile acid
drug approved by FDA for the non-surgical treatment of cholesterol
gallstone disease [3]. Additionally, UDCA was approved by FDA for the
treatment of primary biliary cholangitis [4,5], which is a chronic,
autoimmune disease of the liver characterized by destruction of intra-
hepatic bile ducts, resulting in fibrosis and eventually cirrhosis. UDCA
was also reported to exhibit other biological activities such as treatment
of cholestasis [6], anti-inflammatory [7], anticancer [8], enhance of
insulin sensitivity [9], and improvement mitochondrial function in fi-
broblasts [10].
epimerization of the 7-OH group. Firstly, the Wolff-Kishner reduction
[12–14] and Mozingo reduction [15] methods were applied in the
dihydroxylation at C12 of CA. The second step is the epimerization of the
7-OH group as described below. Qiu et al. developed a new route by
elimination of C12-mesylate ester group of CA with high yield of 94%,
and overall yield up to 65% (7 steps) for preparation of UDCA [16].
CDCA is the most convenient material for the synthesis of UDCA and
related steroid compounds, due to the simple steps and high conversion
rate. CDCA was first oxidized by NBS [17] (yield 86%), or sodium hy-
pochlorite [18] (yield 89.5%) or IBX [13] (yield 90%) to obtain lith-
ocholic acid. Subsequently, 7-oxo was reduced to 7β-OH to yield UDCA
at high yield [11,19] (yield 70%). The enzymatic transformation of
CDCA into UDCA can be obtained using 7α-HSDH and 7β-HSDH [20].
Several enzymatic routes for the synthesis of UDCA from bile acids were
reported [21]. HDCA is a less expensive and more easily obtained ma-
terial compared to CDCA, but HDCA was not frequently used because a
few extra steps would be required for the conversion between 6-OH and
7-OH. Zhou et al. described a 7-step sequence to synthesize UDCA from
HDCA in 15% total yield [22]. More recently, Dou et al. developed a
facile route to synthesize UDCA from HDCA with a Shapiro reaction as
the key step and in 26% overall yield [23].
UDCA was mainly extracted from natural bear bile. However, the
resources of living bears are very limited and the measure violates the
animal protection law. With the increase in the need of clinical appli-
cations, it is necessary to develop efficient and economical synthetic
methods to produce UDCA. At present, UDCA can be commonly pro-
duced by transformation of cholic acid(CA), chenodeoxycholic acid
(CDCA) or hyodeoxycholic acid(HDCA) [11]. Because CA is the most
However, no matter the CA, CDCA or HDCA, they are all extracted
* Corresponding author at: School of Biological Science and Engineering, Shaanxi University of Technology, Hanzhong 723000, China.
E-mail addresses: chenwang@snut.edu.cn (W. Chen), hudaihua007@163.com (D. Hu), fengzili@snut.edu.cn (Z. Feng), liuzhaop@sdu.edu.cn (Z. Liu).
https://doi.org/10.1016/j.steroids.2021.108870
Received 7 February 2021; Received in revised form 25 April 2021; Accepted 16 May 2021
Available online 24 May 2021
0039-128X/© 2021 Elsevier Inc. All rights reserved.

W. Chen et al.
Steroids 172 (2021) 108870
O
COOMe
a
b
c
H
H
H
H
H
H
H
H
H
HO
HO
HO
DHEA
1
2
COOMe
d
COOMe
e
COOMe
f
H
H
H
H
H
H
H
H
H
HO
PNBO
PNBO
O
3
4
5
COOMe
h
COOH
COOMe
g
H
H
H
H
H
H
H
H
H
PNBO
OH
HO
OH
PNBO
OH
H
H
6
7
UCDA
Fig. 1. Structures of bile acids.
from the bile acid and belongs to animal origin. Therefore, developing a
plant source compound as the starting material is very valuable. There is
only one reliable synthetic route to UDCA based on a plant-source
commercial starting material. Qiu et al. reported a novel synthetic
route of UDCA from the plant-source bisnoralcohol, with overall yield
up to 59% (6 steps) [24]. In this paper, we report an efficiency synthetic
route of UDCA from commercial plant-source dehydroepiandrosterone
(DHEA).
0 ◦C, and a solution of the DHEA (16.78 g, 58.2 mmol) in THF (200 mL)
was added. The reaction mixture was stirred at 80℃ under argon for 4 h.
After cooling to 0 ◦C, water (300 mL) was added slowly, and the product
was extracted with EtOAc (150 mL × 3). The combined organic layers
were washed with brine, dried over Na2SO4, and evaporated under
reduced pressure. Hexane/EtOAc (v/v = 5:1) (500 mL) was added to the
residue to precipitate the byproduct, triphenylphosphine oxide, which
was filtered out. The filtrated organic phase was evaporated under
reduced pressure to dryness, affording the crude product, which was
purified by recrystallization with methanol to give 1 (16.09 g, 92%) as
2. Experimental
1
◦
◦
white needles; mp: 119–121 C [lit. [25] 118–120 C]. H NMR (600
MHz, CDCl3) δ 5.39–5.34 (m, 1H), 5.18 – 5.10 (m, 1H), 3.57–3.49 (m,
1H), 2.41–2.34 (m, 1H), 2.34–2.28 (m, 2H), 2.27–2.23 (m, 1H),
2.22–2.15 (m, 1H), 2.06–1.99 (m, 1H), 1.89–1.81 (m, 2H), 1.66 (dt, J =
7.2, 1.9 Hz, 3H), 1.64–1.62 (m, 1H), 1.62–1.60 (m, 1H), 1.60–1.56 (m,
1H), 1.55–1.53 (m, 3H), 1.53–1.47 (m, 2H), 1.26–1.15 (m, 1H),
1.17–1.13 (m, 1H), 1.12–1.06 (m, 1H), 1.02 (s, 3H), 1.00–0.95 (td, J =
11.5, 4.8 Hz, 1H), 0.90 (s, 3H); 13C NMR (150 MHz, CDCl3) δ 150.25,
140.80, 121.58, 113.50, 71.76, 56.54, 50.16, 44.05, 42.30, 37.21,
36.99, 36.57, 31.73, 31.66, 31.46, 31.42, 24.49, 21.24, 19.38, 16.63,
13.14. ESI-MS m/z: 301.2 [M + H]+.
2.1. General procedures
All chemicals, unless otherwise noted, were purchased from Energy-
Chemical (Shanghai, China) and were used as received without further
purification. When needed, the reactions were carried out in oven-dried
glassware under a positive pressure of dry nitrogen. Solvents were re-
agent grade and, when necessary, they were purified and dried by
standard methods. All water employed was ultrapure (>18.2 MΩcmꢀ 1 at
25℃, Milli-Q, Millipore, Billerica, MA). All melting points were deter-
mined on a micro melting point apparatus (SGW X4) and were uncor-
rected. 1H NMR and 13C NMR spectra were recorded on a Brucker
Avance-600 NMR-spectrometer in the indicated solvents. Chemical
shifts are expressed in ppm (δ units) relative to TMS signal as internal
reference. The electrospray ionization mass spectrometry (ESI-MS) was
carried out on a Thermo Finnigan MSQ 10275. TLC was carried out on
Silica Gel GF254 plates (Qingdao Haiyang Chemical Co., Ltd) and spots
were visualized by iodine vapors or by irradiation with UV light (254
nm). Flash column chromatography was performed on column packed
with Silica Gel 60 (Qingdao Haiyang Chemical Co., Ltd, 200–300 mesh)
using the indicated eluents. Concentration of the reaction solutions
involved the use of rotary evaporator at reduced pressure.
2.2.2. (22E)-3β-hydroxy-Chola-5,16,22-trien-24-oic acid methyl ester (2)
[26]
To a solution of 1 (16.0 g, 53.2 mmol) and methyl propiolate (5.37 g,
63.8 mmol) in anhydrous benzene (150 mL) at 0 ◦C was added dropwise
a solution of Et2AlCl (13 mL, 106 mmol, 1 M in toluene) under nitrogen
atmosphere. After being warmed to room temperature and stirred for 24
h, the mixture was quenched with saturated aqueous NaHCO3 solution
(150 mL) and extracted with ether (100 mL × 2). The combined organic
solution was dried over Na2SO4 and concentrated under reduced pres-
sure to dryness, affording the crude product. The crude product was
recrystallized in ether yield 2 (19.03 g, 93%) as white powder; no sharp
melting point [lit. [26] 80–90 ◦C]. 1H NMR (600 MHz, CDCl3) δ 6.94 (dd,
J = 15.6, 7.8 Hz, 1H), 5.82 (dd, J = 15.7, 1.0 Hz, 1H), 5.43–5.39 (m,
1H), 5.38–5.34 (m, 1H), 3.73 (s, 3H), 3.56–3.49 (m, 1H), 3.05–2.98 (m,
1H), 2.33–2.28 (m, 1H), 2.27–2.20 (m, 1H), 2.08 (ddd, J = 14.9, 6.4, 3.1
Hz, 1H), 2.04–1.97 (m, 1H), 1.88–1.84 (m, 2H), 1.84–1.80 (m, 3H),
1.80–1.76 (m, 1H), 1.72–1.64 (m, 1H), 1.64–1.59 (m, 2H), 1.56–1.46
(m, 2H), 1.41–1.29 (m, 2H), 1.19 (d, J = 6.9 Hz, 3H), 1.12–1.05 (m, 1H),
2.2. Chemical synthesis
2.2.1. (3β, 17Z)-pregna-5,17(20) -dien-3-ol (1)
A flask was charged with EtPPh3Br (64.82 g, 174.6 mmol), t-BuOK
(19.59 g, 174.6 mmol), and a stir bar under nitrogen atmosphere.
Anhydrous THF (300 mL) was added via syringe, and the suspension was
stirred for 1 h at room temperature. The reaction mixture was cooled to
2

W. Chen et al.
Steroids 172 (2021) 108870
1.04 (s, 3H), 1.03–0.98 (m, 1H), 0.79 (s, 3H); 13C NMR (150 MHz,
CDCl3) δ 167.41, 156.97, 153.84, 141.07, 124.03, 121.45, 118.76,
71.69, 57.31, 51.47, 50.66, 47.08, 42.29, 37.20, 36.73, 35.42, 34.82,
31.61, 31.53, 31.15, 30.46, 20.74, 19.58, 19.31, 16.34. ESI-MS m/z:
385.3 [M + H]+.
(m, 1H), 1.20–1.14 (m, 1H), 1.11 (q, J = 9.4 Hz, 1H), 0.94 (d, J = 6.5 Hz,
3H), 0.71 (s, 3H); 13C NMR (150 MHz, CDCl3) δ 201.67, 174.67, 163.82,
163.26, 150.59, 135.64, 130.64, 127.17, 123.65, 71.61, 54.49, 51.52,
49.99, 49.91, 45.49, 43.18, 38.84, 38.57, 36.43, 35.26, 33.34, 31.06,
31.01, 28.41, 26.28, 25.75, 20.90, 18.47, 16.96, 11.98. ESI-MS m/z:
552.5 [M + H]+.
2.2.3. Methyl 3β-hydroxy-5-cholen-24-oate (3)
A flask was charged with 2 (19.0 g, 49.4 mmol), 5% Pd/CaCO3 (1.0
g), ethyl acetate (200 mL) and a magnetic stir bar. The suspension was
hydrogenated at room temperature. The hydrogen uptake ceased after
consumption of approximate 2.3 L. The catalyst was filtered off, the
solvents evaporated under reduced pressure and the residue was puri-
fied by recrystallization with aqueous methanol to give 3 (16.09 g, 96%)
as white needles; mp: 140–142 ◦C [lit. [27] 139–141 ◦C]. 1H NMR (600
MHz, CDCl3) δ 5.38–5.33 (m, 1H), 3.66 (s, 3H), 3.56–3.48 (m, 1H),
2.39–2.33 (m, 1H), 2.32–2.27 (m, 1H), 2.26–2.19 (m, 2H), 2.02–1.94
(m, 2H), 1.88–1.81 (m, 3H), 1.81–1.76 (m, 1H), 1.66–1.54 (m, 3H),
1.54–1.48 (m, 3H), 1.46–1.39 (m, 3H), 1.36–1.26 (m, 2H), 1.16 (td, J =
12.8, 4.4 Hz, 1H), 1.12–1.04 (m, 3H), 1.01 (s, 3H), 0.95–0.90 (m, 1H),
0.92 (d, J = 6.6 Hz, 3H), 0.68 (s, 3H); 13C NMR (150 MHz, CDCl3) δ
174.80, 140.75, 121.65, 71.76, 56.70, 55.74, 51.50, 50.05, 42.35,
42.27, 39.72, 37.23, 36.48, 35.36, 31.86, 31.84, 31.62, 31.04, 31.00,
28.10, 24.25, 21.05, 19.39, 18.30, 11.86. ESI-MS m/z: 389.3 [M + H]+.
2.2.6. (3α,7β)-7-hydroxy-3-[(4-nitrobenzoyl)oxy]-5-cholen-24-oic acid
methyl ester (6)
Sodium borohydride (0.78 g, 20.6 mmol) was added in small por-
tions to a clear solution of 5 (9.5 g, 17.2 mmol) and CeCl3⋅7H2O (7.69 g,
20.6 mmol) in a mixture of methanol (20 mL) and tetrahydrofuran (80
mL). The reaction mixture was stirred for 4 h at room temperature and
then treated with acetone (20 mL). The mixture was filtered to remove
the insoluble solids, then the solvents were evaporated under reduced
pressure and the residue was purified by flash column chromatography
on silica gel elution with hexane/EtOAc (v/v = 4:1) to give 6 (7.62 g,
80%) as white powder; mp: 175–177 ◦C [lit. [28] 174–177 ◦C]. 1H NMR
(600 MHz, CDCl3) δ 8.29 (d, J = 8.8 Hz, 2H), 8.15 (d, J = 8.8 Hz, 2H),
5.33 (brs, 1H), 5.29 (brs, 1H), 3.90 (dd, J = 7.3, 6.1 Hz, 1H), 3.67 (s,
3H), 2.64 (dd, J = 15.3, 1.8 Hz, 1H), 2.44–2.32 (m, 2H), 2.27–2.20 (m,
2H), 2.06–1.97 (m, 2H), 1.96–1.87 (m, 2H), 1.86–1.80 (m, 2H),
1.78–1.72 (m, 2H), 1.60–1.55 (m, 1H), 1.51–1.42 (m, 6H), 1.36–1.20
(m, 4H), 1.12 (s, 3H), 0.94 (d, J = 6.5 Hz, 3H), 0.72 (s, 3H); 13C NMR
(150 MHz, CDCl3) δ 174.71, 163.95, 150.46, 141.03, 136.28, 130.59,
126.52, 123.55, 73.06, 72.12, 55.90, 55.16, 51.51, 48.43, 42.97, 40.74,
39.48, 37.04, 36.08, 35.31, 33.61, 31.06, 31.02, 28.40, 26.28, 26.16,
20.82, 18.71, 18.38, 11.84. ESI-MS m/z: 554.5 [M + H]+.
2.2.4. (3α)-3-[(4-nitrobenzoyl)oxy]-5-cholen-24-oic acid methyl ester (4)
To a solution of 3 (16.0 g, 41.2 mmol), triphenylphosphine (11.93 g,
45.5 mmol) and p-nitrobenzoic acid (7.6 g, 45.5 mmol) in anhydrous
THF (100 mL), a solution of diisopropyl azodicarboxylate (9.58 g, 47.4
◦
mmol) in anhydrous THF (50 mL) was added dropwise at 0 C under
nitrogen atmosphere. The mixture was warmed up to room temperature
and stirred 12 h. The reaction mixture was evaporated to dryness and re-
dissolved in EtOAc (200 mL), washed with saturated sodium bicarbon-
ate solution, and brine, then dried over Na2SO4 and evaporated to
dryness. The residue was purified by flash column chromatography on
silica gel elution with hexane/EtOAc (v/v = 20:1) to give 4 (19.05 g,
86%) as light yellow oil. 1H NMR (600 MHz, CDCl3) δ 8.29 (d, J = 8.8
Hz, 1H), 8.15 (d, J = 8.8 Hz, 1H), 5.34–5.31 (m, 1H), 5.30–5.27 (s, 1H),
3.67 (s, 3H), 2.66–2.61 (m, 1H), 2.40–2.32 (m, 2H), 2.26–2.20 (m, 1H),
2.04–1.93 (m, 2H), 1.92–1.87 (m, 1H), 1.82–1.73 (m, 1H), 1.62–1.55
(m, 3H), 1.51–1.43 (m, 3H), 1.36–1.27 (m, 2H), 1.23–1.17 (m, 1H),
1.14–1.10 (m, 2H), 1.10–1.04 (m, 1H), 1.07 (s, 3H), 0.94 (d, J = 6.5 Hz,
3H), 0.87–0.83 (m, 1H), 0.70 (s, 3H); 13C NMR (150 MHz, CDCl3) δ
174.77, 164.05, 150.39, 138.11, 136.50, 130.60, 123.53, 122.63, 72.50,
56.68, 55.80, 51.51, 50.35, 42.36, 39.69, 37.12, 36.48, 35.38, 33.99,
31.90, 31.81, 31.05, 31.01, 28.11, 26.27, 24.22, 20.80, 18.92, 18.32,
11.87. HRMS(ESI): calcd for C32H43NO6 [M + H]+, 538.3207, found
538.3202.
2.2.7. (3α,5β,7β)-7-hydroxy-3-[(4-nitrobenzoyl)oxy]-5-cholen-24-acid
methyl ester (7)
A flask was charged with 6 (7.2 g, 13 mmol), [Ir(cod)pyr(PCy3)]PF6
(Crabtree’s catalyst, 0.5 g), anhydrous DCM (100 mL) and a magnetic
stir bar. The reaction mixture was hydrogenated at room temperature.
The hydrogen uptake ceased after consumption of approximate 0.3 L.
The solvent was evaporated to dryness and re-dissolved in ether (200
mL). The catalyst was filtered off, the solvents evaporated under reduced
pressure and the residue was purified by recrystallization with aqueous
methanol to give 7 (6.86 g, 95%) as white powder; mp: 181–183 ◦C. 1H
NMR (600 MHz, CDCl3) δ 8.28 (d, J = 8.9 Hz, 2H), 8.20 (d, J = 8.9 Hz,
2H), 5.00–4.93 (m, 1H), 3.67 (s, 3H), 3.65–3.59 (m, 1H), 2.40–2.33 (m,
1H), 2.27–2.19 (m, 1H), 2.05–2.00 (m, 1H), 1.95–1.88 (m, 2H),
1.87–1.78 (m, 6H), 1.69–1.61 (m, 2H), 1.56–1.41 (m, 7H), 1.38–1.28
(m, 4H), 1.24–1.14 (m, 2H), 1.09 (q, J = 9.6 Hz, 1H), 1.00 (s, 3H), 0.94
(d, J = 6.5 Hz, 3H), 0.70 (s, 3H); 13C NMR (150 MHz, CDCl3) δ 174.68,
164.13, 150.47, 136.16, 130.66, 123.47, 75.66, 71.23, 55.76, 54.98,
51.52, 43.79, 43.78, 42.35, 40.11, 39.29, 36.62, 35.25, 34.60, 34.17,
33.18, 31.06, 31.04, 28.59, 26.86, 26.55, 23.36, 21.27, 18.41, 12.15.
HRMS(ESI): calcd for C32H45NO7 [M + H]+, 556.3205, found 556.3201.
2.2.5. (3
α)-3-[(4-nitrobenzoyl)oxy]-7-oxo-5-cholen-24-oic acid methyl
ester (5)
To a mechanically stirred suspension of 4 (14.0 g, 26 mmol), pyr-
idinium dichromate (PDC; 29.34 g, 78 mmol) and celite (30 g) in
anhydrous benzene (200 mL), 70% tert-butylhydroperoxide (t-BuOOH;
22.8 mL, 156 mmol) were added gradually at 0 ◦C. The whole reaction
mixture was stirred at 25 ◦C for 24 h. After filtration on celite, the
organic layer was evaporated under reduced pressure to give a dark
brown residue. The crude product was purified by flash column chro-
matography on silica gel elution with hexane/EtOAc (v/v = 8:1) to give
5 (10.04 g, 70%) as white powder; mp: 157–159 ◦C [lit. [28]
157–160 ◦C]. 1H NMR (600 MHz, CDCl3) δ 8.28 (d, J = 8.8 Hz, 2H), 8.12
(d, J = 8.8 Hz, 2H), 5.73 (d, J = 1.2 Hz, 1H), 5.44 (s, 1H), 3.67 (s, 3H),
2.82–2.74 (m, 1H), 2.64–2.56 (m, 1H), 2.47–2.40 (m, 1H), 2.39–2.35
(m, 1H), 2.29 (t, J = 11.6 Hz, 1H), 2.26–2.20 (m, 1H), 2.12–2.07 (m,
1H), 2.06–2.02 (m, 1H), 1.98–1.92 (m, 1H), 1.90–1.85 (m, 1H),
1.84–1.79 (m, 1H), 1.69–1.57 (m, 5H), 1.46–1.42 (m, 1H), 1.41–1.37
(m, 1H), 1.37–1.34 (m, 1H), 1.33–1.30 (m, 1H), 1.27 (s, 3H), 1.29–1.24
2.2.8. Ursodeoxycholic acid (UDCA)
To a solution of 7 (6.8 g, 12.2 mmol) in MeOH (100 mL), a solution of
10% NaOH (2.78 mol/L; 11 mL, 30 mmol) was added. The reaction
mixture was stirred at room temperature for 6 h, then added 5% HCl
(0.13 mol / L) solution, adjust to pH = 3, and remove methanol under
reduced pressure. The residues were extracted with EtOAc (100 mL × 2),
washed with brine, then dried over Na2SO4 and evaporated to dryness.
The crude product was purified by recrystallization with aqueous
methanol to give UDCA (4.52 g, 94%) as white powder; mp: 198–200 ◦C
[lit. [24] 200–202 ◦C]. [
α]25 D + 60.1 (c 1.0, Ethanol). [lit. [24] [α]25
D + 60.9 (c 1.0, Ethanol]. 1H NMR (600 MHz, DMSO‑d6) δ 11.93 (s, 1H),
4.44 (s, 1H), 3.86 (s, 1H), 3.34–3.24 (m, 2H), 2.26–2.20 (m, 1H),
2.13–2.06 (m, 1H), 1.96–1.91 (m, 1H), 1.88–1.81 (m, 1H), 1.77–1.72
(m, 1H), 1.69–1.63 (m, 3H), 1.50–1.44 (m, 3H), 1.42–1.38 (m, 1H),
1.37–1.32 (m, 5H), 1.31–1.27 (m, 1H), 1.23–1.16 (m, 3H), 1.15–1.08
(m, 3H), 1.01 (q, J = 9.6 Hz, 1H), 0.95–0.90 (m, 1H), 0.88 (d, J = 8.5 Hz,
3

W. Chen et al.
Steroids 172 (2021) 108870
and 13C NMR spectra. Compound 3 was obtained by stereo-selective
introduction of side chains at C (17) and C (20) in 93% yield. This
approach could set the stereochemistry of the C-20 carbon in the natural
configuration [26]. The triene intermediate 2 was selectively hydroge-
nated with palladium on calcium carbonate in ethyl acetate to 3 in 96%
OH
H
COOH
COOH
H
H
H
H
H
HO
H
OH
HO
OH
H
yield. The 3β-OH of 3 was converted to 3α-(4-nitrobenzoyl)oxyl group
by Mitsunobu reaction. The inversion of stereochemistry from the 3β-OH
could up to 100% configuration reversal and give 4 in 86% yield. The
yield of oxidation at the C-7 position of 4 to afford compound 5 was
relatively low. Therefore, a model system was employed to find an ideal
solvent and optimal reaction conditions (Table 1). After screening
various oxidants, we found that the oxidant of PDC/ TBHP was the
optimal oxidant for this reaction. Then we examined several different
solvents, and the results showed that benzene is the optimal solvent. We
Ursodeoxycholic acid
(UDCA)
Cholic acid
(CA)
COOH
COOH
H
H
H
H
H
H
HO
HO
OH
H
H
OH
◦
also investigated the reaction temperature, and discovered that 25 C
Hyodeoxycholic acid
(HDCA)
Chenodeoxycholic acid
(CDCA)
was the most suitable temperature, and the yield was up to 70% for the
oxidation reaction. Increasing the temperature was beneficial to the
rapid completion of the reaction. But, the oxidation of compound 4
under higher temperature produced more by-products. Regioselective
reduction of compound 5 was performed following the Luche reduction
procedure with sodium borohydride in THF/MeOH to obtain 7β epimer
6 after isolation by column chromatography in 80% yield. Selective
hydrogen addition of 6 in the presence of Crabtree’s catalyst given 5β
epimer 7 in 95% yield. The addition of hydrogen on one face of a cyclic
molecule can be directed by the presence of a hydroxyl group on that
face using Crabtree’s catalyst[29], however using Pd/C as catalyst given
Scheme 1. Synthesis of ursodeoxycholic acid from DHEA. Reagents and con-
ditions: (a) EtPPh3Br, t-BuOK, anhydrous THF, 80℃, 4 h, under nitrogen at-
mosphere, 92%; (b) methyl propiolate, Et2AlCl 1 M in toluene, anhydrous
benzene, 0℃ to r.t., 24 h, under nitrogen atmosphere, 93%; (c) 5% Pd/CaCO3,
H2, EtOAc, r.t., 96%; (d) DIAD, PPh3, p-nitrobenzoic acid, anhydrous THF, 0℃
to r.t., 12 h, under nitrogen atmosphere, 86%; (e) PDC, 70% t-BuOOH, celite,
anhydrous benzene, r.t., 24 h, 70%; (f) NaBH4, CeCl3⋅7H2O, THF, MeOH, r.t., 4
h, 80%; (g) Crabtree’s catalyst, H2, anhydrous DCM, r.t., 95%; (h) NaOH,
MeOH, then HCl, r.t., 6 h, 94%.
5α epimer [28]. Lastly, hydrolysis of the C-24 methyl ester of 7 under
NaOH in MeOH provided ursodeoxycholic acid in 94% yield. In this
novel route for the preparation of UDCA from DHEA, most of the con-
versions are very efficient in 8 steps and overall yield up to 35%.
Table 1
Allyl oxidation of compound 4a.
Entry
Solvent
Oxidant
RTb
Yieldc
(%)
Nd
Nd
Nd
Nd
4. Conclusion
1
2
3
4
DCM
PDC(3 eq)
reflux
reflux
reflux
1,2-Dichloroethane
Acetone
PDC(3 eq)
PDC(3 eq)
In summary, we designed an efficient and economical method for the
synthesis of UDCA from plant-source DHEA with the Mistunobu reaction
and regioselective oxidationat C7 as the key steps. The final product was
obtained through the 7β-OH and 5β-H inversion employing Luche
reduction and Crabtree’s catalyst. Since all starting materials are cost-
effective, commercially available and most of the conversions are effi-
ciently and the overall yield is high, this synthetic route can effectively
avoid the risk of animal derived raw materials. The key reaction con-
ditions were investigated and the optimal solvent, oxidant and reaction
temperature were determined. However, the yield of intermediate 5 and
6 are low, which is 70% and 80% respectively, and the conditions of
allylic oxidation need further optimization. Further studies on improved
routes and higher yield are underway in our laboratory.
Acetone/H2O (9:1,
v/v)
PDC(1.1 eq)/ NHPI(1.1 eq)
25 ◦
C
5
6
7
8
Acetone
Na2Cr2O7(3 eq)
25 ◦
25 ◦
25 ◦
25 ◦
C
C
C
C
26
35
42
48
Acetone
K2Cr2O7(3 eq)
Acetone
K2Cr2O7(3 eq)/NHPI(1.1 eq)
K2Cr2O7(3 eq)/NHPI(1.1
eq)/AcOH(1.1 eq)
Acetone
9
Acetone
Pyridine
t-BuOH
BPO(1.1 eq)/NHPI(1.1 eq)
CrO3(3 eq)
25 ◦
25 ◦
25 ◦
25 ◦
25 ◦
25 ◦
25 ◦
25 ◦
25 ◦
50 ◦
C
C
C
C
C
C
C
C
C
C
Nd
51
Nd
56
58
65
53
55
70
62
58
10
11
12
13
14
15
16
17
18
19
PDC(3 eq)/TBHP(70%, 6 eq)
PDC(3 eq)/TBHP(70%, 6 eq)
PDC(3 eq)/TBHP(70%, 6 eq)
PDC(3 eq)/TBHP(70%, 6 eq)
PDC(3 eq)/TBHP(70%, 6 eq)
PDC(3 eq)/TBHP(70%, 6 eq)
PDC(3 eq)/TBHP(70%, 6 eq)
PDC(3 eq)/TBHP(70%, 6 eq)
PDC(3 eq)/TBHP(70%, 6 eq)
Acetone
MeCN
Toluene
DCM
1,2-Dichloroethane
Benzene
Benzene
Benzene
Acknowledgments
reflux
a
All the reactions were performed for 24 h, and the ratio of oxidant/com-
This work was supported by Key laboratory project of Shaanxi Pro-
vincial Department of Education (20JS023) and Key projects of science
and Technology Department of Shaanxi Province (2018ZDXM-SF-083).
pound 4 was showed.
b
Reaction temperature.
c
Isolated yield.
d
No reaction.
Appendix A. Supplementary data
3H), 0.87 (s, 3H), 0.62 (s, 3H); 13C NMR (150 MHz, DMSO‑d6) δ 175.35,
70.19, 69.92, 56.31, 55.15, 43.56, 43.48, 42.65, 39.19, 38.20, 37.74,
35.31, 34.23, 31.24, 30.72, 28.63, 27.18, 23.78, 21.32, 18.78, 12.50.
ESI-MS m/z: 393.5 [M + H]+.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.steroids.2021.108870.
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