Investigation on the synthesis of 25-hydroxycholesterol

Article abstract of DOI:10.1016/j.steroids.2014.02.002

A very efficient and environmentally benign method has been developed for the synthesis of 25-hydroxycholesterol. The reaction was performed in THF-water (4:1, v/v) using NBS as the brominating agent, followed by the easy reduction of C-Br with lithium aluminum hydride in THF, to yield the final product corresponding to a Markovnikov's rule. Excellent yields and regioselectivity have been obtained.

Full text of DOI:10.1016/j.steroids.2014.02.002

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Contents lists available at ScienceDirect
Steroids
journal homepage: www.elsevier.com/locate/steroids
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Investigation on the synthesis of 25-hydroxycholesterol
3
Qian Zhao a, Li Ji a, Guo-Ping Qian b, Jian-Gang Liu b, Zi-Qiang Wang b, Wan-Feng Yu a, Xin-Zhi Chen a,
⇑
6 Q1
a Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Zhejiang University, Hangzhou 310027, PR China
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b Zhejiang Garden Biochemical High-tech. Co., Ltd, Hangzhou 310018, PR China
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a r t i c l e i n f o
a b s t r a c t
1 3
2 5
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Article history:
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A
very efficient and environmentally benign method has been developed for the synthesis of
Received 18 October 2013
Received in revised form 22 January 2014
Accepted 17 February 2014
Available online xxxx
25-hydroxycholesterol. The reaction was performed in THF–water (4:1, v/v) using NBS as the brominat-
ing agent, followed by the easy reduction of C–Br with lithium aluminum hydride in THF, to yield the final
product corresponding to a Markovnikov’s rule. Excellent yields and regioselectivity have been obtained.
Ó 2014 Published by Elsevier Inc.
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Keywords:
25-Hydroxycholesterol
Desmosterol
Reduction
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Bromohydrin
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1. Introduction
The reaction of mercuric acetate with desmosterol leads to the
addition on the double bond of the groups –OH on one side, and –
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Vitamin D3 is an important biological regulator of calcium and
phosphorus metabolism [1]. It is now established that the parent
vitamin D3 is sequentially metabolized in various tissues to the
steroid hormone 1,25-(OH)2-D3 which exerts the highest biological
activity of all vitamin D3 metabolites. This hormonal derivative
stimulates the intestinal absorption of calcium and phosphorus,
and the mobilization of bone calcium through a target organ recep-
tor mediated mechanism [2]. A common characteristic feature of
these metabolites is the C-25 hydroxy group. Thus, the introduc-
tion of 25-hydroxy group into an appropriate substrate would be
a key step in the synthesis of these compounds.
HgOAc on the other. It can be followed by the easy reduction of the
C–Hg bond with sodium borohydride in sodium hydroxide/water,
to yield the 25-hydroxycholesterol corresponding to a Markovni-
kov addition of water on the double bond. The nuclear D5 double
bond, which is quite reactive towards most electrophilic reagents,
was left untouched. This remarkable selectivity has been con-
firmed in 1992, but this study has not been extended. Mercuric
acetate is an environmental problem, obviously because of the poi-
sonous nature of the reagent and of the products of the reaction.
Care must be taken, even when working with small amounts, dur-
ing the reaction and for the disposal of the residues [6].
The vicinal functionalization of carbon–carbon double bond is a
powerful synthetic tool for organic chemists. In particular, selec-
tive introduction of two different functional groups, such as hydro-
xyl and halogen, has attracted sustained attention in organic
synthesis [7]. Halohydrins are usually prepared via the ring open-
ing of epoxides using hydrogen halides or metal halides. These pro-
cedures are associated with the formation of byproducts such as
vic-dihalides and 1,2-diols. Meanwhile, these procedures require
prior synthesis of epoxide. Apart from this, there are two general
approaches for heterolytic addition of water and halogen to an ole-
finic bond. One involves the usage of molecular halogen, TsNBr2,
[8] N-halosaccharin [9] or N-halosuccinimide [10–23] for haloge-
nation, and the other employs metal halide along with an oxidizing
agent [24,25]. Cheap and available N-halosuccinimide, in particular
N-bromosuccinimide (NBS) and N-chlorosuccinimide (NCS), are
the better choice of halogen sources over other hazardous reagents
for such transformations.
Using in situ generated ethyl(trifluoromethyl)dioxirane (ETDO),
a facile synthesis was developed by Ogawa et al. [3] for 25-hydrox-
ycholesterol, as well as its 3-sulfate (overall yield of the sulfate,
24%) and 24-oxocholesterol (16%), starting from cholesterol. How-
ever, long linear synthetic route and low yields are major hitches.
Unlike cholesterol, the conventional starting material for preparing
certain steroids (for example 25-hydroxycholesterol), desmosterol
already contains a reactive side chain (D
24). Desmosterol plays an
important role, as a labile intermediate, in the biosynthesis of cho-
lesterol in animals. It was included in a filtrate of recrystallization
of crude lanolin which was made from lanolin alcohol obtained by
saponification of wool grease, a washing waste of wool, and the
content of desmosterol reached 10–25% [4,5].
⇑
Q2
Corresponding author. Tel.: +86 57187151615.
E-mail address: chemtec@163.com (X.-Z. Chen).
http://dx.doi.org/10.1016/j.steroids.2014.02.002
0039-128X/Ó 2014 Published by Elsevier Inc.
Please cite this article in press as: Zhao Q et al. Investigation on the synthesis of 25-hydroxycholesterol. Steroids (2014), http://dx.doi.org/10.1016/
j.steroids.2014.02.002

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From these points of view we have undertaken the syntheses of
32.52 (C-7 and C-8), 36.27 (C-20), 36.70 (C-22), 37.23 (C-10),
37.64 (C-1), 38.77 (C-12), 40.36 (C-4), 42.98 (C-13), 50.66 (C-9),
56.69 (C-17), 57.31 (C-14), 74.64 (C-3), 123.31 (C-6), 125.88
(C-24), 131.59 (C-25), 140.29 (C-5), 171.23 (–COCH3).
the 25-hydroxycholesterol using inexpensive reagents and avail-
able steroid starting compound. We were able to develop a facile
synthesis of naturally occurring oxysterols, 25-hydroxycholesterol
(1), from desmosterol (2) by using N-halosuccinimide via halohy-
drin reaction. Then, the reductive of halides is achieved by lithium
aluminum hydride (LiAlH4) in THF (Scheme 1). To the best of our
knowledge, there are no examples describing the formation of
25-hydroxycholesterol via halohydrin reaction.
133
2.2. General procedure for the synthesis of bromohydrins 4
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To a well-stirred solution of desmosterol acetate 3 (0.427 g,
1 mmol) in THF–water (4:1) (50 mL), NBS (0.213 g, 1.2 mmol)
was added, and the reaction mixture was allowed to stir at ꢀ10
°C. Progress of the reaction was monitored by TLC (TLC solvents:
n-hexane/EtOAc (8:1, v/v)). After 2 h, 10% aqueous sodium thiosul-
fate was added to destroy the excess NBS. The reaction mixture
was extracted with dichloromethane (3 ꢁ 20 mL) and successively
washed with saturated NaHCO3 solution (20 mL ꢁ 2) and saturated
NaCl solution (20 mL). The extract was dried over anhydrous
sodium sulfate and then concentrated under reduced pressure.
Purification of the crude product by column chromatography on
silica gel (200–300 mesh) with a mixture of n-hexane/EtOAc (8:1,
v/v) as an eluent to give bromohydrins 4 (0.44 g, 85%).
In a large scale, to a well-stirred solution of desmosterol acetate
3 (4.27 g, 10 mmol) in THF–water (4:1) (300 mL), NBS (2.13 g,
12 mmol) was added, and the reaction mixture was allowed to stir
at ꢀ10 °C. Progress of the reaction was monitored by TLC (TLC sol-
vents: n-hexane/EtOAc (8:1, v/v)). After 4 h, 10% aqueous sodium
thiosulfate was added to destroy the excess NBS. The reaction mix-
ture was extracted with dichloromethane (3 ꢁ 300 mL) and succes-
sively washed with saturated NaHCO3 solution (200 mL ꢁ 2) and
saturated NaCl solution (200 mL). The extract was dried over anhy-
drous sodium sulfate and then concentrated under reduced
pressure. Purification of the crude product by column chromatogra-
phy on silica gel (200–300 mesh) with a mixture of n-hexane/EtOAc
(8:1, v/v) as an eluent to give bromohydrins 4 (4.2 g, 80.8%).
4: mp: 148.7–149.9 °C. 1H NMR (CDCl3, 400 MHz): d 5.38
(d, J = 4.0 Hz, 1H, 6-CH), 4.60 (m, 1H, 25-OH), 2.68 (m. 1H,
24-CH), 1.31 (s, 3H, 26-CH3), 1.27 (s, 3H, 27-CH3), 1.01 (s, 3H, 19-
CH3), 0.94 (d, J = 6.5 Hz, 3H, 21-CH3), 0.69 (s, 3H, 18-CH3). 13C
98
2. Experimental
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Melting points were determined using WRR melting point
apparatus. 1H and 13C NMR spectra were recorded on Bruker AV-
400 spectrometer (Bruker Corporation, America) at working fre-
quencies 400 and 100 MHz. respectively in CDCl3 And with TMS
as the internal standard. Chemical shifts are expressed in ppm
downfield from TMS and observed coupling constants (J) are given
in Hertz (Hz). Starting materials and reagents were commercially
purchased and used without further purification. The progress of
the reactions was monitored by thin-layer chromatography (TLC)
Analytical thin-layer chromatography (TLC) was conducted using
silica gel plates (200 lm) containing a fluorescent indicator (silica
gel 60 F254). Detection was performed by spraying with molybdo-
phosphoric acid (5%) at 120 °C Column chromatography was per-
formed using silica gel, 200–300 mesh, and elution was
performed with n-hexane/ethyl acetate.
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2.1. General procedure for the synthesis of desmosterol acetate 3
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To a solution of the desmosterol (20 g, 0.05 mol) in hexane
(150 mL), DMAP (200 mg) and acetic anhydride (10 g, 0.1 mol)
were added, after stirring at 50 °C in 3 h (TLC control, TLC solvents:
n-hexane/EtOAc (8:1, v/v)), the reaction mixture was successively
washed with water, HCl solution (5%wt.) and saturated NaHCO3
solution. Desmosterol acetate (18.85 g, 85.0%) was obtained by
evaporating in a vacuum and recrystallization in EtOH.
3 [26]: mp: 89.1–90.1 °C (lit. Mp: 91–92 °C) 1H NMR (CDCl3,
400 MHz): d 5.38 (d, J = 4.0 Hz, 1H, 6-CH), 5.10 (t, J = 6.4 Hz, 1H,
24-CH), 4.60 (m, 1H, 3-CH), 1.61 (s, 3H, 26-CH3), 1.53 (s, 3H, 27-
CH3), 1.01 (s, 3H, 19-CH3), 0.86 (d, J = 6.5 Hz, 3H, 21-CH3), 0.69 (s,
3H, 18-CH3). 13C NMR (CDCl3, 100 MHz): d 12.52 (C-18), 18.31
(C-21), 19.29 (C-19), 19.97 (C-23), 21.68 (C-11), 22.12 (–COCH3),
24.95 (C-27 and C-28), 25.37 (C-15), 26.40 (C-16), 28.42 (C-2),
NMR (CDCl3, 100 MHz): d 11.76 (C-18), 18.56 (C-21), 19.20
(C-19), 20.90 (C-11), 21.34 (–COCH3), 25.30 (C-27 and C-28),
25.58 (C-15), 27.65 (C-16), 28.12 (C-2), 31.73 (C-23), 32.25 (C-7
and C-8), 35.55 (C-20), 36.47 (C-22), 36.87 (C-10), 38.00 (C-1),
39.60 (C-12), 42.23 (C-4), 49.87 (C-13), 55.80 (C-9), 56.56 (C-17),
58.05 (C-14), 64.71 (C-24), 64.84 (C-25), 73.87 (C-3), 122.50
(C-6), 139.53 (C-5), 171.23 (–COCH3).
N-halosuccinimide
Ac2O
H2O
AcO
HO
2
3
Br
OH
OH
LiAlH4
THF
HO
AcO
1
4
Scheme 1. Synthesis of 25-hydroxycholesterol (1) with desmosterol (2) as starting compound.
Please cite this article in press as: Zhao Q et al. Investigation on the synthesis of 25-hydroxycholesterol. Steroids (2014), http://dx.doi.org/10.1016/
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Table 2
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2.3. General procedure for the synthesis of 25-hydroxycholesterol 1
Bromohydrination of 3 with different solvents.a
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A solution of bromohydrins 4 (0.523 g, 1 mmol) in THF (30 mL)
under a nitrogen atmosphere was treated with LiAlH4 (0.15 g,
4 mmol) at 5 °C. Then the reaction mixture was stirred at 70 °C
for 3 h (TLC control, TLC solvents: n-hexane/EtOAc (2:1, v/v)).
Again cooled, the reaction mixture was added dropwise to a HCl
solution (5%wt.). Then the mixture extracted with dichlorometh-
ane (3 ꢁ 20 mL) and successively washed with saturated NaHCO3
solution (20 mL ꢁ 2) and saturated NaCl solution (20 mL). The ex-
tract was dried over anhydrous sodium sulfate and then concen-
trated under reduced pressure. 25-hydroxycholesterol (0.38 g,
95%) was thus obtained after recrystallization in toluene.
In a large scale, A solution of bromohydrins 4 (5.23 g, 10 mmol)
in THF (100 mL) under a nitrogen atmosphere was treated with
LiAlH4 (1.5 g, 40 mmol) at 5 °C. Then the reaction mixture was stir-
red at 70 °C for 3 h (TLC control, TLC solvents: n-hexane/EtOAc
(2:1, v/v)). Again cooled, the reaction mixture was added dropwise
to a HCl solution (5%wt.). Then the mixture extracted with dichlo-
romethane (3 ꢁ 300 mL) and successively washed with saturated
NaHCO3 solution (200 mL ꢁ 2) and saturated NaCl solution
(200 mL). The extract was dried over anhydrous sodium sulfate
and then concentrated under reduced pressure. 25-hydroxycholes-
terol (3.9 g, 97%) was thus obtained after recrystallization in
toluene.
Entry
Solvent
Time (h)
Yieldb (%)
1
2
3
4
5
CH2Cl2:H2O(4:1)
EtOAc: H2O(4:1)
Toluene:H2O(4:1)
Butanone:H2O(4:1)
t-Butanol:H2O(4:1)
Glyme:H2O(5:1)
Acetone:H2O(10:1)
THF:H2O(4:1)
24
24
24
2
2
2
5
2
4
10
19.8
21.1
15.0
68.8
60.0
70.0
72.3
85.0
78.8
56.6
6c
7c
8
9
10
THF:H2O(10:1)
THF:H2O(30:1)
a
The substrate 3 was treated with NBS (1.2 equiv.) at ꢀ10 °C in different solvents
(40 mL).
Isolated yield.
b
c
The ratio was determined by solubility of the substrate 3.
Table 3
Effect of different amount of NBS.a
Entry
NBS (eq.)
Yieldb/%
1
2
3
4
1.0
1.2
1.5
2.0
77.8
85.0
80.3
65.1
1 [3]: mp: 176.4–177.1 °C (lit. Mp: 178–180 °C). 1H NMR (CDCl3,
400 MHz): d 5.37 (d, J = 3.4 Hz, 1H, 6-CH), 3.50 (m, 1H, 3-CH), 1.23
(s, 6H, 26- and 27-CH3), 1.03 (s, 3H, 19-CH3), 0.94 (d, J = 6.5 Hz, 3H,
21-CH3), 0.70 (s, 3H, 18-CH3). 13C NMR (CDCl3, 100 MHz): d 11.76
(C-18), 18.58 (C-21), 19.30 (C-19), 20.66 (C-23), 20.97 (C-11),
24.18 (C-15), 28.15 (C-16), 29.09 (C-26), 29.25 (C-27), 31.54 (C-
2), 31.79 (C-7 and C-8), 35.64 (C-20), 36.36 (C-22 and C-10),
37.15 (C-1), 39.67 (C-12), 42.21 (C-4 and C-13), 44.31 (C-24),
50.01 (C-9), 55.96 (C-17), 56.65 (C-14), 71.03 (C-25), 71.67 (C-3),
121.58 (C-6), 140.67 (C-5).
a
The substrate 3 was treated with NBS in 20% aqueous THF at ꢀ10 °C.
b
Isolated yield.
Br
+
H2O
NBS
AcO
AcO
3
5
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3. Results and discussion
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Desmosterol (2), obtained from crude lanolin by extraction, was
chosen as a suitable starting material. Initially, the desmosterol 2
was transformed into the 3-protected ester 3 by treating with
acetic anhydride in the presence of DMAP at 50 °C via the usual
acetylation to avoid the side reaction of the nuclear D5 double
bond.
In the next sequence of reactions, 3-protected ester 3 was trans-
formed into the halohydrins derivative 4 (Scheme 1). As mentioned
above, N-halosuccinimide was powerful and versatile. In search for
an effective halogenation reagent for the halohydrin reaction, we
first studied the reaction of 3-protected ester 3 with NBS or NCS
in aqueous THF at different reaction temperature, and the results
was presented in Table 1.
Br
OH
AcO
4
Scheme 2. Probable mechanism of bromination.
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230
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234
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The bromohydrin reaction of 3 proceeded smoothly at ꢀ10 °C
within 2 h, it afforded the desired bromohydroxylation product 4
in 85.0% yield (Table 1, entry 4). Then, the reaction temperature
was varied from ꢀ20 to 20 °C using NBS as the halogenation re-
agent. Unfortunately, the decrease of the yield was observed as
the temperature was increased (Table 1, entries 1–3), which could
be ascribed to the selectivity of the nuclear D5 double bond and
side chain D24 double bond. Lower reaction temperature ꢀ20 °C
has little effect on the yield (Table 1, entry 5). Therefore, ꢀ10 °C
was chosen for the further experiments.
In search for an appropriate solvent for the bromohydrin reac-
tion, the reactions of 3 and NBS in different solvents (Table 2) were
scanned.
Various solvents, such as CH2Cl2, EtOAc, toluene, butanone,
t-butanol, glyme, acetone and THF, in combination with water
were studied for this purpose. CH2Cl2, EtOAc and toluene gave very
Compared with the NCS (Table 1, entry 6), NBS worked much
better as the halogenation reagent under the same conditions.
Table 1
Effect of different halogenation reagent.a
Entry
Reagent
Temp (°C)
Yieldb (%)
1
2
3
4
5
6
NBS
NBS
NBS
NBS
NBS
NCS
20
10
0
ꢀ10
ꢀ20
ꢀ10
58.1
63.7
72.3
85.0
84.8
65.6
a
The substrate 3 was treated with NBS/NCS (1.2 equiv.) in 20% aqueous THF.
Isolated yield.
b
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Br
O
OH
OH
LiAlH4
THF
K2CO3
methanol
HO
AcO
AcO
1
4
6
Scheme 3. The synthetic application of bromohydrins.
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poor results due to the part conversion of 3-protected ester 3
during the long reaction time in two-phase system (Table 2, entries
1–3), except in the case of butanone (Table 2, entry 4). t-Butanol,
glyme and acetone gave 60.0–72.3% yield of the desired product
(Table 2, entries 5–7). It is interesting to observe that when
reaction was carried out in a mixture of tert-butyl alcohol and
water (4:1 volume ratio) a mixture of bromohydrin and tert-
butoxybromide was obtained due to the competitive nucleophilic-
ity of tert-butyl alcohol and water. A mixture of THF and water in a
4:1 ratio was found to be the best solvent for halohydrin formation
(Table 2, entry 8). The reaction takes a relatively longer time in a
lower yield when the THF–water ratio was decreased, especially
the THF and water in a 30:1 ratio (Table 2, entries 9–10). It pro-
vided us the clue that water played an important role to increase
the desired product 4 in this process. The nucleophilic solvent
water could compete with halide ion leading to incorporation of
the latter. An excess of water was employed as nucleophilic re-
agent to increase the yield of 4. Therefore, a mixture of THF and
water in a 4:1 ratio was selected as solvent because of its solubility
of the substrate 3, highest yield.
Having identified the optimized solvent, we next evaluated the
influence of different amount of NBS, as shown in Table 3.
The amount of NBS was varied from 1.0 to 2.0 eq. to study its
effect on the bromohydrin of 3 in 20% aqueous THF. The yield of
4 was measured after 2 h of stirring the reaction mixture at
ꢀ10 °C. It was observed that the yield increases as the amount of
NBS was increased (up to 1.2 eq.) and then slowed down (Table 3,
entries 1–4). Use of a 2.0 eq. amount of the NBS resulted in a lowest
yield. It provided us the clue that the nuclear D5 double bond of
compound 4 may react with the NBS further. Therefore, we decided
to use 1.2 eq. of NBS for further experiments.
289
4. Conclusion
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293
294
295
296
In conclusion, we have developed an efficient and general
method for the synthesis of 25-hydroxycholesterol via hydrobro-
mination of desmosterol acetate by using NBS as a bromine source
with excellent regioselectivity. The procedure is rapid, easy to per-
form at ꢀ10 °C to give bromohydrins product in good yield. Com-
pared to the method of oxymercuration and hydrodemercuration,
the usage of NBS makes it environmentally friendly.
297
5. Uncited reference
Q3 298
[27].
299
Acknowledgments
300
301
302
303
304
The authors are grateful for the support from Research
Fund for the National Natural Science Foundation of China (2137
6213), Doctoral Program of Higher Education of China (20120101
110062) and Zhejiang Low Carbon Fatty Amine Engineering
Technology Research Centre (2012E10033).
305
References
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[1] Dauben WG, Kohler B, Roesle A. Synthesis of 6-fluorovitamin D3. J Org Chem
2007;1985:50.
[2] Norman AW, Roth J, Orci L. The vitamin
metabolism, hormone receptors, and biological response (calcium binding
proteins). Endocr Rev 1982;3:331.
[3] Ogawa S, Kakiyama G, Muto A, Hosoda A, Mitamura K, Ikegawa S, Hofmann AF,
Iida T. A facile synthesis of C-24 and C-25 oxysterols by in situ generated
ethyl(trifluromomethyl) dioxirane. Steroid 2009;74:81–7.
[4] Fagarlund, Idler. Marine sterols. IV. 24-Dehydrocholesterol: isolation from a
barnacle and synthesis by the witting reaction. J Am Chem Soc 1957;79:6473.
[5] Idler DR, Saito A, Wiseman P. Sterols in red algae (Rhodophyceae). Steroids
1968;11:465.
D endocrine system: steroid
The best result was obtained when substrate 3 was treated with
1.2 equiv. of NBS in 20% aqueous THF at ꢀ10 °C within 2 h in the
bromohydrin reaction.
A probable mechanistic pathway to explain the regioselectivity
of the bromohydrins 4 is depicted in Scheme 2. The mechanism of
bromohydrins formation occurs in two steps. A three-membered
cyclic bromonium ion intermediate 5 is formed at the initial stage
of the reaction due to electrophilic addition of the Br+ ion (gener-
ated from NBS) onto the 3. Nucleophilic addition of water to inter-
mediate 5 results in bromohydrins formation. The regioselectivity
can be explained by Markovnikov’s rule, which stated that in the
addition of an unsymmetrical reagent to a multiple bond, the posi-
tive portion of the reagent is introduced at the less-substituted
carbon.
In the next sequence of reaction, the bromohydrins products 4
was transformed into 25-hydroxycholesterol 1 by directly subject-
ing to the reduction with lithium aluminum hydride in THF, a
slight excess of lithium aluminum hydride is generally used. Mean-
while, by action of powdered K2CO3 on the bromohydrins products
4 in methanol at room temperature, 24,25-monoepoxide 6 was ob-
tained in good yield (Scheme 3).
[6] Elkihel L, Charles G, Letourneux Y, Ourisson G. Highly selective Markovnikov
hydration
of
D
24-sterols
and
triterpenes
by
oxymercuration–
hydrodemercuration. C. R. Chimie 2003;6:79–82.
[7] Tenaglia A, Pardigon O, Buono G. Regio- and stereoselective functionalization
of deltacyclenes: a route to the synthesis of optically active (+)-deltacyclan-8-
one. J Org Chem 1996;61:1129–32.
[8] Phukan P, Chakraborty P, Kataki D.
A simple and efficient method for
regioselective and stereoselective synthesis of vicinal bromohydrins and
alkoxybromides from an olefin. J Org Chem 2006;71:7533.
[9] Urankar D, Rutarm B, Modec B, Dolenc D. Synthesis of bromo- and iodohydrins
from deactivated alkenes by use of N-bromo- and N-iodosaccharin. Eur J Org
Chem 2005;2005:2349.
[10] Winstein S, Ingraham LL. The role of neighboring groups in replacement
reactions. XVIII. Migration of the methoxyl group.
1952;74:1160–4.
[11] Bar S. Organocatalysis in the stereoselective bromohydrin reaction of alkenes.
Can J Chem 2010;88:605–12.
J
Org Chem
[12] Barkley LB, Farrar MW, Knowles WS, Raffelson H. Studies in steroid total
synthesis. III. Preparation of cortisone and compound F.
1954;76:5018.
J Org Chem
[13] Raghavan S, Badu VS. Total synthesis of (+)-(20,30R)-zoapatanol exploiting the
B-alkyl Suzuki reaction and the nucleophilic potential of the sulfinyl group.
Chem Eur J 2011;17:8487–94.
Please cite this article in press as: Zhao Q et al. Investigation on the synthesis of 25-hydroxycholesterol. Steroids (2014), http://dx.doi.org/10.1016/
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366
367
368
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370
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372
373
374
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[14] Porter DJ, Stewart AT, Wigal CT. Synthesis of a bromohydrin. J Chem Educ
1995;1039:72.
[15] Lysek R, Lipkowska UZ, Chmielewski M. Transformation of the 7-
[22] White LV, Schwarta BD, Banwell MG, Willis AC. A chemoenzymatic total
synthesis of (+)-clividine. J Org Chem 2011;76:6250–7.
[23] Corey EJ, Lee J. Enantioselective total synthesis of oleanolic acid, erythrodiol,
beta.-amyrin, and other pentacyclic triterpenes from a common intermediate.
J Am Chem Soc 1993;115:8873–4.
[24] Rolston JH, Yates K. Polar additions to the styrene and 2-butene systems. I.
Distribution stereochemistry of bromination products in acetic acid. J Am
Chem Soc 1969;91:1469–76.
[25] Dewkar GK, Narina SV, Sudalai A. NaIO4-mediated selective oxidative
halogenation of alkenes and aromatic using alkali metal halides. Org Lett
2003;5:4501–4.
isopropylidene
group
in
5-dethia-5-oxacephams.
Tetrahedron
2001;57:1301–9.
[16] Bellucci G, Chiappe C, Moro GL. Facial stereoselctivity of two-step additions
initiated by electrophilic halogens to methylenecyclohexanes. A comparison
with epoxidation. J Org Chem 1995;60:6214–7.
[17] Lashley MR, Nantz MH. Synthesis of lipidic tamoxifen. Tetrahedron Lett
2000;41:3295–8.
[18] Dalton DR, Dutta VP, Jones DC. Bromohydrin formation in dimethyl sulfoxide. J
Am Chem Soc 1968;90:5498–501.
[19] Hart DJ, Patterson S, Unch JP. Lasonolide A: synthesis of A and B rings via a
cycloetherification strategy. Synlett 2003;9:1334–8.
[20] Corey EJ, Katzenellenbogen JA, Gliman NW, Roman SA, Erickson BW.
Stereospecific total synthesis of the dl-C18 cecropia juvenile hormone. J Am
Chem Soc 1968;90:5619.
[21] Sisti AJ. A new ring enlargement procedure. IV. The decomposition of the
magnesium salts of various 1-(1-bromoethyl)-1-cycloalkanols. J Org Chem
1970;35:2671–2.
[26] Nicholas CO, Tomkinson MW, Timothy MW. Efficient, stereoselective synthesis
of 24(S), 25-epoxycholesterol. J Org Chem 1998;63:9919–23.
[27] Dauben WG, Bradlow HL. The preparation of cholesterol from D5
norcholestene-3b-o1-25-one. J Am Chem Soc 1950;72:4248–50.
-
376
Please cite this article in press as: Zhao Q et al. Investigation on the synthesis of 25-hydroxycholesterol. Steroids (2014), http://dx.doi.org/10.1016/
j.steroids.2014.02.002