A facile synthesis of ursodeoxycholic acid and obeticholic acid from cholic acid

Article abstract of DOI:10.1016/j.steroids.2018.10.009

A novel synthetic route of producing ursodeoxycholic acid (UDCA) and obeticholic acid (OCA) was developed through multiple reactions from cheap and readily-available cholic acid. The reaction conditions of the key elimination reaction of mesylate ester group were also investigated and optimized, including solvent, base and reaction temperature. In the straightforward synthetic route for preparation of UDCA and OCA, most of the reaction steps have high conversions with average yields of 94% and 92%, and overall yield up to 65% (7 steps) and 36% (11 steps) from cholic acid, respectively. This promising route offers economical and efficient strategies for potential large-scale production of UDCA and OCA.

Full text of DOI:10.1016/j.steroids.2018.10.009

Steroids140(2018)173–178
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Steroids
journal homepage: www.elsevier.com/locate/steroids
A facile synthesis of ursodeoxycholic acid and obeticholic acid from cholic
acid
⁎
Xiao-Long Hea, Li-Ting Wanga, Xiang-Zhong Gub, Jie-Xin Xiaoa, Wen-Wei Qiua,
a Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, School of Chemistry and Chemical Engineering, East China Normal
University, Shanghai 200241, China
b Department of Research and Development, Jiangsu Jiaerke Pharmaceuticals Group Co., Ltd., Zhenglu Town, Changzhou 213111, 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) and obeticholic acid (OCA) was developed
through multiple reactions from cheap and readily-available cholic acid. The reaction conditions of the key
elimination reaction of mesylate ester group were also investigated and optimized, including solvent, base and
reaction temperature. In the straightforward synthetic route for preparation of UDCA and OCA, most of the
reaction steps have high conversions with average yields of 94% and 92%, and overall yield up to 65% (7 steps)
and 36% (11 steps) from cholic acid, respectively. This promising route offers economical and efficient strategies
for potential large-scale production of UDCA and OCA.
Ursodeoxycholic acid
Obeticholic acid
Cholic acid
Synthesis
1. Introduction
resistance, obesity, dyslipidemia and hypertension [17,18]. Nonalcoholic
steatohepatitis (NASH) is the most extreme form of NAFLD and the leading
Primary biliary cholangitis (PBC), previously termed primary biliary
cirrhosis, is a rare autoimmune inflammatory liver disease, which pro-
duces bile duct injury, fibrosis, cholestasis and eventual cirrhosis. PBC
mainly affects middle-aged women, with a sex ratio of at least 9:1 female
to male [1,2]. Ursodeoxycholic acid (UDCA) (Fig. 1), one of the secondary
bile acids, is the only drug approved by the US Food and Drug Adminis-
tration (FDA) for the treatment of PBC since the year 1988 [3,4]. UDCA in
patients has been shown to improve serum biochemistries, liver trans-
plantation-free, and ameliorate the overall morbidity and mortality asso-
ciated with PBC [5–7]. In addition, the clinical properties of UDCA include
non-surgical treatment of cholesterol gallstones, anti-apoptotic effects,
decreasing serum TNF-α concentrations and improving muscle and he-
patic insulin sensitivity [8–11]. UDCA was the recommended first-line
drug for treatment of PBC until 2016 when obeticholic acid (OCA, also
known as 6-ECDCA or INT-747) (Fig. 1) was approved by US FDA and
European Medicines Agency [12]. OCA is a farnesoid X receptor (FXR)
agonist, which has been evaluated as a second-line therapy in PBC [13]. It
is used in patients who show an inadequate response to UDCA or who are
unable to tolerate UDCA [14].
cause of hepatic morbidity and mortality [19]. It is also regarded as a
major cause of cirrhosis, which ultimately lead to hepatocellular carci-
noma and has become the second leading indication for liver transplan-
tation in United States [20]. NASH affects 2–5% of adults in United States
and other Western countries [21]. Despite the significant burden to the
public health system, there are no current FDA-approved therapies for this
disease [22]. It is gratifying that there are several drugs in the phase III
trial in NASH patients. For instance, elafibranor (GFT505), a dual per-
oxisome proliferator-activated receptor alpha/delta (PPARα/δ) agonist, is
being studied by Genfit; Liraglutide, a glucagon-like peptide-1 (GLP-1)
agonist, is being studied by Novo Nordisk; OCA, a bile acid derivative that
acts as an agonist of the FXR, is being studied by Intercept Pharmaceuticals
[23]. Among these novel agents, the OCA is a very promising medication
and gets FDA breakthrough therapy designation for NASH with liver fi-
brosis [22]. Accordingly, exploitation of economical and efficient synthetic
methods of UDCA and OCA will not only benefit PBC patients, but also
promote the further development of NASH medications.
UDCA is usually synthesized from its relatively expensive epimer
chenodeoxycholic acid (CDCA) (Fig. 1) by regioselective oxidation of
7α-OH to 7-oxo and then reduction to 7β-OH [24–26]. Recently other
chemical methods for the preparation of UDCA have also been devel-
oped. Zhou et al. synthesized of UDCA from low cost hyodeoxycholic
acid (HDCA) (Fig. 1) with a 15% poor total yield [27]. Subsequently
Nonalcoholic fatty liver disease (NAFLD) is the most common liver
disorder in developed countries, which is defined as the presence of he-
patic steatosis in patients due to causes other than excessive alcohol use
[15,16]. NAFLD is a metabolic syndrome and associated with insulin
⁎ Corresponding author.
E-mail address: wwqiu@chem.ecnu.edu.cn (W.-W. Qiu).
https://doi.org/10.1016/j.steroids.2018.10.009
Received 19 June 2018; Received in revised form 27 September 2018; Accepted 20 October 2018
Availableonline31October2018
0039-128X/©2018ElsevierInc.Allrightsreserved.

X.-L. He et al.
Steroids140(2018)173–178
Fig. 1. Structures of obeticholic acid, 7-keto-lithocholic acid and bile acids.
Dou et al. developed a route from HDCA with an improved 26% overall
yield via a key Shapiro reaction [28]. UDCA can also be synthesized
from cholic acid (Fig. 1). For instance, Ferrari et al. provided a 10% low
overall yield method by a crucial high-temperatured Wolff–Kishner
reduction [29]; Dangate et al. also exploited an optimized protection-
free route (53% overall yield) with o-iodoxybenzoic acid (IBX) as key
regioselective oxygenant and hydrazine hydrate as key Wolff–Kishner
reducing agent from cholic acid [30]. Cholic acid is a bile acid and
relatively much cheap than CDCA, which can be commercially and
abundantly available. Thus, it is rather valuable to develop an improved
synthetic route for large scale production of UDCA using the cost-ef-
fective and readily-available starting material cholic acid.
as solvent and tetramethylsilane (TMS) as the internal standard. All
chemical shift values were reported in units of δ (ppm). The following
abbreviations were used to indicate the peak multiplicity: s = singlet;
d = doublet; t = triplet; m = multiplet; br = broad. High-resolution
mass data were obtained on a BrukermicroOTOF-Q II spectrometer.
2.2. Chemical synthesis
2.2.1. 3α,12α-Dihydroxy-7-keto-5β-cholan-24-oic acid (1)
To a solution of cholic acid (18 g, 44.1 mmol) in a mixed solvent
(400 mL) of acetone-H2O (3:1, v/v) was added NBS (11.4 g, 64.0 mmol) at
room temperature. The flask was covered with aluminum foil to keep the
reaction in the dark. The reaction mixture was stirred at room temperature
for 2 h and then added a saturated solution of NaHSO3 (50 mL). The
mixture was evaporated under reduced pressure to remove acetone, and
then poured into H2O (100 mL) and extracted with CH2Cl2 (100 mL × 3).
The organic layer was washed with brine, dried over anhydrous Na2SO4
and then concentrated. The residue was purified by silica gel chromato-
graphy (CH2Cl2/MeOH, 20/1, v/v) to give 1 [35] (16.5 g, 92%) as a white
solid. 1H NMR (400 MHz, CDCl3) δ 4.00 (s, 1H), 3.64–3.58 (m, 1H), 1.17
(s, 3H), 0.99 (d, J = 6.0 Hz, 3H), 0.68 (s, 3H).
OCA is generally synthesized from CDCA. For examples, Yu et al.
reported a 5 steps approach (20% overall yield), and the key reactions
are regioselective oxidation of the 7α-OH with PCC, enolate formation
with LDA/HMPA and alkylation with iodoethane [31]; Valentina et al.
also used the CDCA as the starting material for preparation of OCA with
an improved synthetic strategy (32% overall yield), and the crucial
steps are aldol addition with acetaldehyde, selective reduction of the
C7-ketone with NaBH4 and CeCl3, and stereoselective hydrogenation of
exocyclic double bond [32]. Alexander et al. exploited a synthetic route
to OCA with a 3% poor overall yield from the cheap deoxycholic acid
[33] (Fig. 1). In addition, a procedure provided by Pellicciari et al.
starts with the expensive 7-keto-lithocholic acid (Fig. 1) and gives a
very low overall yield (2–3%) [34]. However, there is no efficient
procedure available for preparation of OCA that begins with cholic acid.
Herein, we report an efficient and economical synthetic route of
UDCA and OCA from cost-effective cholic acid.
2.2.2. Methyl 3α,12α-dihydroxy-7-keto-5β-cholan-24-oate (2)
To a solution of 1 (8.5 g, 20.9 mmol) in MeOH (100 mL) was added
concentrated H2SO4 (2 mL) at room temperature. The reaction mixture
was refluxed for 2 h, and then concentrated. The residue was dissolved
in DCM (100 mL). Organic layer was washed with 5% aqueous NaOH
and brine, dried over anhydrous Na2SO4 and concentrated to give
compound 2 [36] (8.7 g, 99%) as a white solid. 1H NMR (400 MHz,
CDCl3) δ 4.00 (s, 1H), 3.66 (s, 3H), 3.58 (s, 1H), 1.18 (s, 3H), 0.97 (d,
J = 5.2 Hz, 3H), 0.68 (s, 3H).
2. Experimental
2.1. General procedures
2.2.3. Methyl 3α-acetoxy-12α-hydroxy-7-keto-5β-cholan-24-oate (3)
To a solution of 2 (8.7 g, 20.7 mmol) in dry CH2Cl2 (80 mL), Ac2O
(2.5 mL, 26.8 mmol), pyridine (3.3 mL, 41.2 mmol) and DMAP (122 mg,
1 mmol) were added at room temperature. The reaction mixture was
stirred for 2 h under nitrogen atmosphere at room temperature and
concentrated. The residue was poured into H2O (30 mL) and extracted
with AcOEt (30 mL × 3). The organic layer was washed with aqueous
2 M HCl and brine, dried with anhydrous Na2SO4 and concentrated. The
residue was purified by silica gel chromatography (petroleum ether/
AcOEt, 3/1, v/v) to give 3 [37] (8.6 g, 90%) as a white solid. 1H NMR
(400 MHz, CDCl3) δ 4.71–4.63 (m, 1H), 4.00 (s, 1H), 3.66 (s, 3H), 1.99
All reagents and chemicals were purchased from commercial sup-
pliers and used without further purification unless otherwise stated.
When needed, the reactions were carried out in oven-dried glassware
under a positive pressure of dry N2. Column chromatography was
performed on silica gel (QinDao, 200–300 mesh) using the indicated
eluents. Thin-layer chromatography was carried out on silica gel plates
(QinDao) with a layer thickness of 0.25 mm. Melting points were de-
termined using the MEL-TEMP 3.0 apparatus and uncorrected. 1H
(400 MHz or 500 MHz) and 13C (100 MHz) NMR spectra were recorded
on Bruker 400 MHz or 500 MHz spectrometer with CDCl3 or DMSO‑d6
174

X.-L. He et al.
Steroids140(2018)173–178
(s, 3H), 1.18 (s, 3H), 0.97 (d, J = 6.0 Hz, 3H), 0.68 (s, 3H).
silica gel chromatography (CH2Cl2/MeOH, 20/1, v/v) to give UDCA
(3.8 g, 93%) as a white solid; mp: 198–200 °C [lit. [17] 195–197 °C].
25
2.2.4. Methyl 3α-acetoxy-12α-methanesulfonate-7-keto-5β-cholan-24-oate
(4)
[α]D
+59.7 (c 1.0, CH3CH2OH). 1H NMR (400 MHz, CDCl3) δ
3.63–3.57 (m, 2H), 0.94 (d, J = 6.0 Hz, 6H), 0.68 (s, 3H). 13C NMR
(100 MHz, DMSO‑d6) δ 174.8, 69.7, 69.4, 55.8, 54.7, 43.1, 43.0, 42.2,
39.9, 39.8, 39.7, 38.7, 37.7, 37.2, 34.8, 33.7, 30.7, 30.2, 28.2, 26.7,
To a solution of 3 (8.6 g, 18.6 mmol) in dry pyridine (80 mL), MsCl
(2.9 mL, 37.2 mmol) was added at room temperature. The reaction
mixture was stirred for 8 h under nitrogen atmosphere at room tem-
perature and then concentrated. The residue was poured into aqueous
2 M HCl (50 mL) and extracted with AcOEt (50 mL × 3). The organic
layer was washed with brine, dried with anhydrous Na2SO4 and con-
centrated. The residue was purified by silica gel chromatography
(petroleum ether/AcOEt, 5/1, v/v) to give 4 (9.9 g, 99%) as a white
solid; mp: 75–77 °C. IR (ATR) cm−1: 1730, 1710, 1244, 1171, 905. 1H
NMR (400 MHz, CDCl3) δ 5.12 (s, 1H), 4.70–4.62 (m, 1H), 3.66 (s, 3H),
3.06 (s, 3H), 1.99 (s, 3H), 1.20 (s, 3H), 0.98 (d, J = 6.4 Hz, 3H), 0.76 (s,
3H). 13C NMR (100 MHz, CDCl3) δ 210.7, 174.4, 170.6, 82.9, 72.8,
51.5, 49.0, 46.4, 45.9 (2C), 45.1, 41.4, 39.4, 36.4, 35.0, 34.8, 33.7,
33.3, 30.9 (2C), 27.8, 27.6, 25.7, 24.0, 22.8, 21.3, 17.8, 12.5. HRMS
(ESI): calcd for C28H44NaO8S [M+Na]+: 563.2675, found 563.2649.
23.3, 20.8, 18.3, 12.0. HRMS (ESI): calcd for C24H40O4 [M+H]+
393.2984, found 393.3005.
,
2.2.8. Methyl 3α-hydroxy-7-keto-5β-chol-11-enoate (7)
To a solution of 5 (7.0 g, 15.7 mmol) in MeOH (50 mL), NaOH (690 mg,
17.3 mmol) was added at room temperature. The reaction mixture was
stirred for 1.5 h under nitrogen atmosphere at room temperature. The re-
action mixture was acidified to pH 5 with aqueous 1 M HCl and evaporated
under reduced pressure to remove MeOH. The residue was poured into H2O
(80 mL) and extracted with AcOEt (50 mL × 3). The organic layer was
washed with brine, dried with anhydrous Na2SO4 and concentrated. The
residue was purified by silica gel chromatography (petroleum ether/AcOEt,
2/1, v/v) to give 7 (6.3 g, 99%) as a white solid; mp: 94–96 °C. IR (ATR)
cm−1: 3362, 3240, 1732, 1710, 1265, 1064. 1H NMR (400 MHz, CDCl3) δ
6.20 (d, J = 10.0 Hz, 1H), 5.35 (d, J = 10.0 Hz, 1H), 3.66 (s, 3H), 3.62 (s,
1H), 1.13 (s, 3H), 1.01 (d, J = 6.0 Hz, 3H), 0.74 (s, 3H). 13C NMR
(100 MHz, CDCl3) δ 211.8, 174.5, 139.5, 124.0, 70.6, 51.5, 50.6, 47.5, 47.3,
45.7, 45.2, 44.9, 44.5, 38.0, 35.9, 35.4, 34.1, 31.1, 30.9, 29.8, 28.7, 23.5,
23.1, 18.3, 17.0. HRMS (ESI): calcd for C25H38NaO4 [M+Na]+: 425.2663,
found 425.2662.
2.2.5. Methyl 3α-acetoxy-7-keto-5β-chol-11-enoate (5)
To a solution of 4 (9.5 g, 17.6 mmol) in NMP (80 mL), CH3COOK
(17.2 g, 176 mmol) was added at room temperature. The reaction
mixture was stirred for 12 h under nitrogen atmosphere at 135 °C. After
cooling, the residue was poured into H2O (150 mL) and extracted with
AcOEt (60 mL × 3). The organic layer was washed with brine, dried
with anhydrous Na2SO4 and concentrated. The residue was purified by
silica gel chromatography (petroleum ether/AcOEt, 10/1, v/v) to give 5
(7.2 g, 92%) as a white solid; mp: 138–140 °C. IR (ATR) cm−1: 1731,
1712, 1244, 1038. 1H NMR (500 MHz, CDCl3) δ 6.21 (dd, J = 10.5 Hz,
3.0 Hz, 1H), 5.33 (dd, J = 10.5 Hz, 2.0 Hz, 1H), 4.74–4.67 (m, 1H),
3.66 (s, 3H), 1.99 (s, 3H), 1.14 (s, 3H), 1.01 (d, J = 6.5 Hz, 3H), 0.74 (s,
3H). 13C NMR (100 MHz, CDCl3) δ 210.9, 174.4, 170.4, 139.7, 123.8,
72.7, 51.4, 50.6, 47.4, 47.2, 45.4, 44.9, 44.7, 44.5, 35.8, 35.4, 33.7,
33.6, 31.0, 30.8, 28.6, 25.9, 23.5, 23.0, 21.2, 18.3, 17.0. HRMS (ESI):
calcd for C27H40NaO5 [M+Na] +: 467.2776, found 467.2768.
2.2.9. Methyl 3α,7-trimethylsilyloxy-5β-chol-11-enoate (8)
To a solution of LDA (100 mL, 100 mmol) in dry THF (100 mL),
TMSCl (12.7 mL, 100 mmol) was added under nitrogen atmosphere at
−78 °C. The reaction mixture was stirred for 20 min, then a solution of
7 (4.0 g, 10.0 mmol) in dry THF (50 mL) was added dropwise in 10 min.
The reaction mixture was stirred at −78 °C for an additional 1 h, and
then triethylamine (16.6 mL, 120 mmol) was added. After 1 h, the re-
action mixture was allowed to warm to room temperature, treated with
aqueous saturated solution of NaHCO3 (30 mL). The organic phase was
separated, and the aqueous phase was extracted with AcOEt
(50 mL × 3). The organic layer was washed with brine, dried with
anhydrous Na2SO4 and concentrated to give 8 as a yellow residue,
which was subjected to next step without any purification.
2.2.6. 3α-Hydroxy-7-keto-5β-chol-11-en-24-oic acid (6)
To a solution of 5 (7.0 g, 15.7 mmol) in a mixed solvent (60 mL) of
MeOH-THF (4:1, v/v), NaOH (6.3 g, 157 mmol) and H2O (5 mL) were
added at room temperature. The reaction mixture was refluxed for 4 h
under nitrogen atmosphere. After cooling, the reaction mixture was
acidified to pH 5 with aqueous 1 M HCl and evaporated under reduced
pressure to remove MeOH and THF. The residue was poured into H2O
(80 mL) and extracted with CH2Cl2 (50 mL × 3). The organic layer was
washed with brine, dried with anhydrous Na2SO4 and concentrated.
The residue was purified by silica gel chromatography (CH2Cl2/MeOH,
10/1, v/v) to give 6 (5.7 g, 93%) as a white solid; mp: 214–216 °C. IR
(ATR) cm−1: 3275, 2920, 2863, 1728, 1698, 1278, 1052. 1H NMR
(400 MHz, CDCl3) δ 6.20 (d, J = 10.4 Hz, 1H), 5.35 (d, J = 10.0 Hz,
1H), 3.62 (s, 1H), 1.13 (s, 3H), 1.02 (d, J = 6.0 Hz, 3H), 0.74 (s, 3H).
13C NMR (100 MHz, DMSO‑d6) δ 210.7, 174.7, 138.7, 124.5, 69.0, 50.1,
47.4, 46.4, 45.3, 44.5, 44.4, 44.0, 38.1, 35.3, 35.0, 33.6, 30.7, 30.6,
29.8 28.2, 23.1, 22.8, 18.2, 16.8. HRMS (ESI): calcd for C24H36NaO4 [M
+Na]+: 411.2493, found 411.2506.
2.2.10. Methyl 3α-hydroxy-6-ethyliden-7-keto-5β-chol-11-enoate (9).
To a solution of 8 in CH2Cl2 (100 mL), was added acetaldehyde (1.1 mL,
20.0 mmol) under nitrogen atmosphere at −60 °C. The reaction mixture
was added dropwise BF3·OEt2 (12.6 mL, 100 mmol). The reaction mixture
was stirred for 2 h at −60 °C and allowed to warm to 35 °C and stirred for
2 h at this temperature. The reaction mixture was quenched with saturated
aqueous solution of NaHCO3 and extracted with AcOEt (50 mL × 3). The
combined organic phases were washed with brine, dried with anhydrous
Na2SO4 and concentrated. The residue was purified by silica gel chroma-
tography (CH2Cl2/MeOH, 40/1, v/v) to give 9 (3.0 g, 70%, over two steps)
as a white solid; mp: 74–76 °C. IR (ATR) cm−1: 3418, 1734, 1688, 1264,
1168, 1061, 1020. 1H NMR (400 MHz, CDCl3) δ 6.23 (d, J = 10.0 Hz, 1H),
6.16 (q, J = 6.0 Hz, 1H), 5.41 (d, J = 10.4 Hz, 1H), 3.66 (br, 4H), 1.69 (d,
J = 6.4 Hz, 3H), 1.01 (d, J = 6.0 Hz, 3H), 0.98 (s, 3H), 0.73 (s, 3H). 13C
NMR (100 MHz, CDCl3) δ 204.5, 174.5, 143.7, 140.0, 129.5, 123.7, 70.4,
51.5, 50.4, 48.7 46.6, 45.7, 45.5, 41.4, 38.3, 36.0, 35.0, 34.5, 31.1, 30.9,
29.7, 29.0, 24.5, 23.7, 18.4, 17.0, 12.6. HRMS (ESI): calcd for C27H40NaO4
[M+Na]+: 451.2834, found 451.2819.
2.2.7. Ursodeoxycholic acid (UDCA)
To a solution of 6 (4.0 g, 10.3 mmol) in i-PrOH (100 mL) in auto-
clave, was added Raney-Ni (4.0 g), t-BuOK (1.2 g, 10.8 mmol) and KBH4
(1.6 g, 29.4 mmol), then flushed with H2 (4.0 MPa). The reaction mix-
ture was stirred for 24 h at 40 °C. After cooling, the reaction mixture
was acidified to pH 5 with AcOH and the catalyst was removed by
filtration through celite, then the filtrate was evaporated under reduced
pressure. The residue was poured into H2O (200 mL) and extracted with
CH2Cl2 (50 mL × 3). The organic layer was washed with brine, dried
with anhydrous Na2SO4 and concentrated. The residue was purified by
2.2.11. 3α-Hydroxy-6-ethyliden-7-keto-5β-chol-11-en-24-oic acid (10)
To a solution of 9 (2.0 g, 4.7 mmol) in MeOH (100 mL), NaOH (560 mg,
14.0 mmol) and H2O (6 mL) were added at room temperature. The reaction
mixture was stirred for 3 h under nitrogen atmosphere at 50 °C. After
cooling, the reaction mixture was acidified to pH 5 with aqueous 1 M HCl
and evaporated under reduced pressure to remove MeOH. The residue was
175

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Steroids140(2018)173–178
Scheme 1. Synthesis of ursodeoxycholic acid and obeticholic acid from cholic acid. Reagents and conditions: (a) NBS, acetone, H2O, rt, 92%; (b) MeOH, H2SO4,
reflux, 99%; (c) Ac2O, pyridine, DMAP, CH2Cl2, rt, 90%; (d) MsCl, pyridine, 99%; (e) CH3COOK, NMP, 135 °C, 92%; (f) NaOH, H2O, MeOH, THF, reflux, 93%; (g)
Raney-Ni, KBH4, H2 (4 MPa), t-BuOK, i-PrOH, 40 °C, 93%; (h) NaOH, MeOH, rt, 99%; (i) TMSCl, LDA, Et3N, THF, −78 °C; (j) MeCHO, BF3·OEt2, CH2Cl2, −60 °C, 70%
(over two steps); (k) NaOH, H2O, MeOH, 50 °C, 95%; (l) (1)H2 (4 MPa), Pd/C, MeOH, 70 °C; (2) NaOH (30%), reflux, 81%; (m) NaOH (50%), NaBH4, reflux, 91%.
poured into H2O (60 mL) and extracted with CH2Cl2 (30 mL × 3). The or-
ganic layer was washed with brine, dried with anhydrous Na2SO4 and
concentrated. The residue was purified by silica gel chromatography
(CH2Cl2/MeOH, 20/1, v/v) to give 10 (1.8 g, 95%) as a white solid; mp:
103–104 °C. IR (ATR) cm−1: 3405, 2918, 2882, 1264, 1060, 1021. 1H NMR
(400 MHz, CDCl3) δ 6.24 (dd, J = 10.4, 2.4 Hz, 1H), 6.16 (q, J = 6.8 Hz,
1H), 5.42 (d, J = 10.4 Hz, 1H), 3.71–3.63 (m, 1H), 1.70 (d, J = 7.2 Hz, 3H),
1.03 (d, J = 6.4 Hz, 3H), 0.99 (s, 3H), 0.74 (s, 3H). 13C NMR (100 MHz,
CDCl3) δ 204.6, 179.2, 143.6, 140.1, 129.7, 123.7, 70.5, 50.4, 48.7, 46.6,
45.7, 45.5, 41.4, 38.2, 36.0, 35.0, 34.5, 31.1, 30.7, 29.6, 29.0, 24.5, 23.7,
18.4, 17.0, 12.6. HRMS (ESI): calcd for C26H38NaO4 [M+Na]+: 437.2661,
found437.2662.
(30 mL × 3). The organic layer was washed with brine, dried with anhy-
drous Na2SO4 and concentrated. The residue was purified by silica gel
chromatography (CH2Cl2/MeOH, 20/1, v/v) to give 11 (1.4 g, 81%) as a
white solid. 1H NMR (400 MHz, CDCl3) δ 3.56–3.51 (m, 1H), 1.22 (s, 3H),
0.93 (d, J = 6.4 Hz, 3H), 0.80 (t, J = 7.2 Hz, 3H), 0.65 (s, 3H). 13C NMR
(100 MHz, CDCl3) δ 213.0, 179.5, 71.2, 54.8, 52.0, 50.7, 50.0, 49.0, 43.7,
42.7, 39.0, 35.7, 35.2, 34.3, 31.6, 31.1, 30.8, 29.7, 28.3, 24.6, 23.5, 21.9,
18.8, 18.3, 12.1, 12.0.
2.2.13. Obeticholic acid (OCA)
To a solution of 11 (1.3 g, 3.1 mmol) in H2O (100 mL), was added
NaOH (1.0 g, 32.5 mmol) and the reaction mixture was heated to reflux.
Then a solution of NaBH4 (130 mg, 3.4 mmol) in H2O (30 mL) was
added in 10 min. The reaction mixture was reflux for 4 h. After cooling,
the reaction mixture was acidified to pH 5 with aqueous 1 M HCl and
extracted with CH2Cl2 (30 mL × 3). The organic layer was washed with
brine, dried with anhydrous Na2SO4 and concentrated. The residue was
purified by silica gel chromatography (CH2Cl2/MeOH, 10/1, v/v) to
give OCA (1.2 g, 91%) as a white solid; mp: 120–122 °C [lit. [38]
120–124 °C]. [α]D25 +5.20 (c 1.8, CH3OH). 1H NMR (400 MHz, CDCl3)
δ 3.70 (s, 1H), 3.45–3.37 (m, 1H), 0.93 (d, J = 6.4 Hz, 3H), 0.92–0.88
(m, 6H), 0.66 (s, 3H). 13C NMR (100 MHz, DMSO‑d6) δ 174.9, 70.6,
2.2.12. 3α-Hydroxy-6α-ethyl-7-keto-5β-cholan-24-oic acid (11)
To a solution of 10 (1.7 g, 4.1 mmol) in MeOH (120 mL), 10% palla-
dium on carbon (170 mg) was added under nitrogen atmosphere at room
temperature in autoclave. Then the autoclave was flushed with H2
(4.0 MPa) and stirred for 24 h at 70 °C. After cooling, the catalyst was re-
moved by filtration through Celite, and the filtrate was evaporated under
reduced. The residue was poured into 30% aqueous solution of NaOH
(140 mL) and refluxed for 5 h under nitrogen atmosphere. Then the reaction
mixture was acidified to pH 5 with H3PO4 (85%) and extracted with CH2Cl2
176

X.-L. He et al.
Table 1
Steroids140(2018)173–178
Optimization of the elimination reactions of mesylate ester group of compound 4.a
Entry
Solvent
Base
RTb (°C)
Yieldc (%)
1
DMPU
NMP
DMF
CH3COOK
CH3COOK
CH3COOK
CH3COOK
CH3COOK
MeONa
125
125
125
125
reflux
125
125
125
125
125
125
115
135
145
90
90
56
82
Nd
Ce
C
2
3
4
DMSO
Toluene
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
5
6
7
NaOH
8
K2CO3
84
C
9
t-BuOK
10
11
12
13
14
Na2CO3
75
70
80
92
81
Cs2CO3
CH3COOK
CH3COOK
CH3COOK
a
b
c
d
e
All the reactions were performed for 12 h, and the ratio of base/compound 4 was 10:1 (mol: mol).
Reaction temperature.
Isolated yield.
No reaction.
Complex.
68.4, 55.5, 50.1, 45.3, 42.0, 41.2, 39.9, 39.3, 35.5, 35.2, 34.9, 33.5,
stereoisomer? We think maybe both the chiral inducement of com-
pound 6 itself and the stereoselectivity of potassium tert-butoxide
contribute to the stereoselective reduction [40]. In this straightforward
methodology for preparation of UDCA, most of the conversions are very
efficient with an average yield of 94% in 7 steps and overall yield up to
65%.
32.6, 30.7 (2C), 30.4, 27.8, 23.1 (2C), 22.1, 20.4, 18.1, 11.7 (2C).
HRMS (ESI): calcd for C26H44O4 [M+Na]+, 443.3135, found 443.3137.
3. Results and discussion
OCA was also synthesized according to the pathway described in
Scheme 1. Compound 7 was furnished by regioselective hydrolysis of
the 3-acetate group of the key intermediate 5 under NaOH in 99% yield.
The silyl enol ether 8 was obtained by reaction of 7 with TMSCl, and
subsequent aldol addition with acetaldehyde in the presence of boron
trifluoride etherate gave the desired compound 9 (70% yield, over two
steps). Hydrolysis of the C-24 methyl ester of 9 under NaOH in MeOH
and H2O provided compound 10 in 95% yield. Reduction of two double
bonds of 10 under H2 (4 MPa) and palladium in carbon in autoclave
(the ratio of 6α-ethyl/6β-ethyl is 1/3 based on 1H NMR spectrum), and
then transformation of the 6β-ethyl to 6α-ethyl in NaOH aqueous so-
lution gave compound 11 in 81% yield. The product OCA was afforded
by stereoselective reduction of 7-ketone group to 7α-OH with NaBH4 in
NaOH aqueous solution in 91% yield. In this novel methodology for
preparation of OCA, most of the conversions are very efficient with an
average yield of 91% in 11 steps (from cholic acid) and overall yield up
to 36%.
The synthesis of UDCA is shown in Scheme 1. Compound 1 was
obtained by regioselective oxidation of the 7α-OH to 7-ketone group
with NBS in 92% yield. Protection of the C-24 carboxyl group in the
presence of H2SO4 and MeOH gave ester 2 in 99% yield, then selective
esterification of the 3α-OH with Ac2O in the presence of pyridine and
DMAP provided ester 3 in 90% yield. Compound 4 was prepared by
protection of 12α-OH with MsCl under pyridine in 99% yield. The key
intermediate 5 was afforded by reaction of 4 under CH3COOK in N-
methyl-2-pyrrolidone (NMP) with 92% yield. For this elimination re-
action of mesylate ester group of 4, the efficient solvent is 1,3-dimethyl-
3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU) according to our pre-
viously reported procedure [39]. However, the DMPU is expensive and
searching for an inexpensive solvent is important for industrialization.
Therefore, a model system was employed to find an ideal solvent and
optimal reaction conditions (Table 1). After examining several different
solvents, we found the economical NMP was as efficient as DMPU, and
the yield was up to 90% (Table 1, entry 1–5). Then we screened various
bases, and the results showed that the CH3COOK was the optimal base
for this reaction (entry 2 and 6–11). Finally, we also investigated the
reaction temperature, and discovered that 135 °C was the most suitable
temperature, and the yield reached 92% for the elimination reaction
(entry 2 and 12–14). Compound 6 was produced by hydrolysis of 5 with
NaOH and H2O in a mixed solvent of MeOH-THF in 93% yield. Finally,
UDCA was afforded by reduction of C11-C12 double bond and stereo-
selective reduction of 7-ketone group to 7β-OH (no 7α-OH isomer was
detected based on 1H NMR spectrum) of 6 under H2 (4 MPa), KBH4,
Raney-Ni, t-BuOK and isopropanol in autoclave with 93% yield. In this
step, we combined the reduction of double bond and carbonyl group in
a one-pot synthesis and made the process high yield and efficient. Why
4. Conclusion
In summary, we have successfully developed an efficient and eco-
nomical synthetic route of UDCA and OCA from cost-effective and
readily-available cholic acid. Simultaneously, the reaction conditions of
the key elimination reaction of mesylate ester group of compound 4
were also investigated and the optimal solvent, base and reaction
temperature were determined. In our novel methodologies for pre-
paration of UDCA and OCA, most of the conversions are efficiently and
overall yields are very high. We wish this work may not only suitable
for industrialization but also facilitate the research and development of
novel UDCA and OCA derivatives for PBC or NASH disease.
the reduction of 7-ketone group offered
a dominant 7β-OH
177

X.-L. He et al.
Steroids140(2018)173–178
Acknowledgments
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