Synthesis of 1α-Hydroxyvitamin D5 using a modified two wavelength photolysis for vitamin D formation

Article abstract of DOI:10.1021/jo050853f

1α-Hydroxyvitamin D₅ (1) is a promising chemopreventive agent for breast cancer and is being developed as a drug. We report a synthesis for this vitamin D analogue which uses a photochemical method for the B-ring opening, leading to the conjugated triene system. The precursor 7-dehydrositosteryl acetate (4) obtained through a one-pot, five-step procedure, was completely free of the 4,6-diene isomer that usually forms in the 5,7-diene synthesis. The pre-vitamin isomer (11) was generated using a modified two-wavelength photolysis procedure that increases the yield for this step more than 3-fold compared to classically used photolysis. The 1α-hydroxylation step was performed on the 3-triethylsilyl-trans-vitamin D₅ (17) obtained via the sulfur dioxide adduct of cis-vitamin D₅, in an overall yield of 48%. Photoisomerization and deprotection completed the synthesis.

Full text of DOI:10.1021/jo050853f

Synthesis of 1r-Hydroxyvitamin D5 Using a Modified Two
Wavelength Photolysis for Vitamin D Formation
Robert M. Moriarty* and Dragos Albinescu
Department of Chemistry (M/C 111), University of Illinois at Chicago, Chicago, Illinois 60607
moriarty@uic.edu
Received April 27, 2005
1R-Hydroxyvitamin D5 (1) is a promising chemopreventive agent for breast cancer and is being
developed as a drug. We report a synthesis for this vitamin D analogue which uses a photochemical
method for the B-ring opening, leading to the conjugated triene system. The precursor 7-dehy-
drositosteryl acetate (4) obtained through a one-pot, five-step procedure, was completely free of
the 4,6-diene isomer that usually forms in the 5,7-diene synthesis. The pre-vitamin isomer (11)
was generated using a modified two-wavelength photolysis procedure that increases the yield for
this step more than 3-fold compared to classically used photolysis. The 1R-hydroxylation step was
performed on the 3-triethylsilyl-trans-vitamin D5 (17) obtained via the sulfur dioxide adduct of
cis-vitamin D5, in an overall yield of 48%. Photoisomerization and deprotection completed the
synthesis.
Introduction
of a sufficient amount of 1 for extensive biological activity
investigations.
1R-Hydroxyvitamin D5 1 was first synthesized in
19971a in our group, and preliminary biological studies
showed that this novel vitamin D analogue not only
possessed lower calcemic activity than the metabolically
activated form of vitamin D3, calcitriol 2, but also
inhibited the development of preneoplastic lesions in
mouse mammary glands in organ culture.1b Since then,
several biological studies have shown the potential of this
vitamin D analogue as a breast cancer chemopreventive
agent.1c-g The original synthetic route used to synthesize
1R-hydroxyvitamin D5 did not allow for the production
One drawback of the original synthesis was the low
purity of the starting material, sitosterol.
* To whom correspondence should be addressed.
(1) (a) Mehta, R. G.; Moriarty, R. M.; Mehta; R. R.; Penmasta, R.;
Lazzaro, G.; Constantinou, A. et al. J. Natl. Cancer Inst. 1997, 89, 212-
218. (b) Mehta, R. G.; Hawthorne, M.; Albinescu, D.; Moriarty, R. M.;
Christov, K.; Mehta, R. J. Natl. Cancer Inst. 2000, 92, 1836-1840. (c)
Mehta, G. R.; Mehta, R. R. J. Nutr. Biochem. 2002, 13, 252-264. (d)
Lazzaro, G.; Agadir, A.; Poria, M.; Mehta, R. M.; Moriarty, R. M.; Das
Gupta, T. K.; Zhang, X.-K.; Mehta, R. G. Eur. J. Cancer 2000, 36, 780-
786. (e) Mehta, R. G.; Hussain, E. A.; Mehta, R. R.; Das Gupta, T. K.
Mutat. Res. 2003, 523-524, 253-264. (f) Guyton, K. Z.; Kensler, T.
W.; Posner, G. H. Nutr. Rev. 2003, 61, 230-234. (g) Mehta, R. G. Intl.
J. Cancer Prev. 2004, 1, 77-87. (h) Albinescu, D. Synthesis and
biological activity of 1R-hydroxyvitamin D5 and derivatives. Thesis,
University of Illinois at Chicago, 2001; Available UMI, Order No.
DA3032778, 158 pp. From: Diss. Abstr., Int., B 2002, 62 (11), 5116.
Difficulties in removal of the contaminants campesterol
and dihydrobrassicasterol detracted from the efficiency
of the entire synthesis. In the original synthesis (Scheme
1), sitosterol 3 was converted to the corresponding acetate
and further to 7-dehydrositosteryl acetate 4, using di-
bromantin for the allylic bromination step, followed by
dehydrobromination, with Bu4NF and s-collidine (50%,
for two steps). Removal of the acetate group by reduction
10.1021/jo050853f CCC: $30.25 © 2005 American Chemical Society
Published on Web 08/12/2005
7624
J. Org. Chem. 2005, 70, 7624-7628

Synthesis of 1R-Hydroxyvitamin D5
SCHEME 1
medium-pressure mercury lamp. Formation of the lumi-
isomer 12 is circumvented by filtering out the 300-315
nm light, using 20% ethyl 4-(dimethylamino)benzoate,
with respect to the amount of 4 in the reaction mixture,
which has a strong, relatively sharp absorption at 305
nm. This prevents ring closure of the pre-isomer 11 to
the lumi-isomer. Tachy-isomer 13 is converted back to
pre-isomer 11 by filtering out the light domain below 340
nm, using a uranium glass filter and 9-acetylanthracene
as a sensitizer.5
1R-Hydroxylation of the trans-vitamin D5 derivative 17
obtained via extrusion of the sulfur dioxide from its
adduct with cis-vitamin D5 15 followed by photoisomer-
ization of the trans-derivative 18 to the cis-configuration
19 completes the sequence, leading to the desired 1R-
hydroxyvitamin D5 1 (Scheme 4).
Results and Discussion
The commercially available â-stigmasterol 6 was con-
verted to p-toluenesulfonate 7 by treatment with p-
toluenesulfonyl chloride in pyridine/methylene chloride,
in the presence of 4-(dimethylamino)pyridine as catalyst
(95%) (Scheme 2). The p-toluenesulfonate 7 underwent
solvolysis7 in refluxing methanol, in the presence of
anhydrous potassium acetate, to afford the isostigmas-
teryl methyl ether 8 (80%). Catalytic hydrogenation7 of
8 with 10% palladium on charcoal led to 9. The ether 9
was refluxed in glacial acetic acid7 in the presence of
anhydrous zinc acetate to yield the acetate 10 (80%),
which was converted into the corresponding 7-dehydroac-
etate 4 through a one-pot five-step process8 as follows:
10 was refluxed with dibromantin in hexanes, and the
resulting mixture of 7R- and 7â-bromo derivatives (1:1
ratio) was equilibrated with anhydrous lithium bromide
in acetone/toluene at 0 °C to enrich the ratio of the
R-bromo isomer to about 4R:1â. Subsequent treatment
of the 7-bromo derivatives with benzenethiol and Et3N
afforded the corresponding phenyl sulfides (4â:1R), which
were oxidized to the corresponding sulfoxides using
m-CPBA at 0 °C. Only the â-sulfoxide isomer underwent
cis-elimination of sulfenic acid at 70 °C, in the presence
of triethylamine in toluene, leading to the desired 7-de-
hydroacetate 4, free of 4,6-diene contaminant (40% for
five steps). Irradiation of a solution of diene acetate 4
(Scheme 4) in tert-butyl methyl ether at -20 to 0 °C with
a 450 W Hanovia medium-pressure mercury lamp in the
presence of 20% ethyl 4-(dimethylamino)benzoate fol-
lowed by irradiation through a uranium glass filter in
the presence of 9-acetylanthracene as a photosensitizer
is equivalent to using two wavelength light and practi-
cally eliminates the formation of 12 and 13. The resulting
crude pre-vitamin 11 underwent thermal isomerization
in refluxing ethyl acetate to afford the vitamin D5 acetate
14. Hydrolysis of 14 with 10 M sodium hydroxide in
methanol afforded vitamin D5 5 (50% from 4).
with lithium aluminum hydride was followed by classical
photolysis and by thermal isomerization in refluxing
ethanol to give 5 (15% from 4). The resulting vitamin D5
5 underwent 1R-hydroxylation using the Paaren-DeLuca
sequence2 (27% for this sequence), leading to the title
compound 1. We sought to improve the synthesis in order
to obtain amounts of 1R-hydroxyvitamin D5 1 sufficient
for additional biological data.
In summary, the present synthetic route1h proceeds
from â-stigmasterol 6 which was converted into 7-dehy-
drositosteryl acetate 4 (Scheme 2).
The next step in the synthesis is the photolysis.In the
classical photolysis, simple exposure of 7-dehydroprecur-
sor 8 to UV light using a high-pressure mercury lamp
and solvents such as ether, ethanol, or benzene generates
a mixture of photoisomers3 4, 11, 12, and 13 (Scheme 3)
out of which only the pre-isomer 11 can undergo thermal
isomerization4 to vitamin D 14 in an overall yield of about
15%. A more efficient photolytic method, leading to
higher overall yields of 14 (about 55% versus 15% in
classical photolysis), is known as “the two wavelength
photolysis”.5
In the two wavelength photolysis method, higher yields
of preisomer 11 can be obtained by irradiating 4 with a
narrow band of 250 nm UV light generated by a low-
pressure mercury lamp or by a laser,3 and then selective
isomerization of the tachy-isomer 13 to 11 can be effected
by irradiation with light at 350 nm or by use of a
sensitizer.6 In the present case, we used a modification5
of the two wavelength photolysis method that employs
one broad UV light spectrum generated by a 450 W
Direct 1-hydroxylation of vitamins D is feasible, but
because of difficulty in controlling the site, extent, and
stereochemistry of the hydroxylation, it has not yet
(2) Paaren, H. E.; DeLuca, F.; Schnoes, H. K. J. Org. Chem. 1980,
45, 3253-3258.
(3) (a) Malatesta, V.; Willis, C.; Hackett, P. A. J. Am. Chem. Soc.
1981, 103, 6781-6783. (b) Dauben, W. G.; Phillips, R. B. J. Am. Chem.
Soc. 1982, 104, 355-356. (c) Dauben, W. G.; Phillips, R. B. J. Am.
Chem. Soc. 1982, 104, 5780-5781.
(4) Hoeger, C. A.; Okamura; W. H.J. Am. Chem. Soc. 1985, 107,
268-270.
(5) Okabe, M.; Sun, R. C.; Scalone, M.; Jibilian, C. H.; Hutchings,
S. D. J. Org. Chem. 1995, 60, 767-771.
(6) (a) Stevens, R. D. S. US 4,686,023 (Cl. 204-157.67; C07J), 1987,
5 pp. (b) Eyley, S. C.; Williams, D. H. J. Chem Soc., Chem. Commun.
1975, 858.
(7) Steele, J. A.; Mosettig, E. J. Org. Chem. 1963, 28, 571-572.
(8) Confalone, P. N.; Kulesha, I. D.; Uskokovic, M. R. J. Org. Chem.
1981, 46, 1030-1032.
J. Org. Chem, Vol. 70, No. 19, 2005 7625

Moriarty and Albinescu
SCHEME 2a
a Reagents and conditions: (a) TsCl, DMAP, Py, CH2Cl2, room temperature, 95%; (b) AcOK, MeOH reflux, 80%; (c) H2, 10% Pd/C,
AcOEt, room temperature, 100%; (d) (AcO)2Zn, AcOH, reflux, 80%; (e) (i) dibromantin, hexanes, NaHCO3, reflux, (ii) LiBr, Me2CO, PhMe,
0 °C, (iii) PhSH, Et3N, room temperature; (iv) m-CPBA, AcOEt, 0 °C; (v) PhMe, Et3N, 70 °C, 40%.
SCHEME 3
emerged as an efficient process. A much more efficient
approach, leading to 1R-hydroxy vitamin D derivatives,
is the direct 1R-hydroxylation of a 5,6-trans-geometric
isomer of vitamin D, protected as a triethylsilyl or tert-
butyldimethylsilyl derivative at C-3. The process involves
the conversion of vitamin D into its sulfur dioxide adduct
through addition of sulfur dioxide to the vitamin D.
Thermal elimination of sulfur dioxide from its adduct
leads to the 5,6-trans-vitamin D.9,10 According to this
procedure, vitamin D5 5 was converted into the sulfur
dioxide adduct 15, which underwent extrusion of sulfur
dioxide, at 90 °C in dimethylformamide and sodium
bicarbonate,10 to yield the trans-vitamin D5 16 (80%). The
hydroxyl group in 16 was protected as the triethylsilyl
ether, and the resulting derivative 17 underwent 1R-
hydroxylation with selenium dioxide and NMO (N-
methylmorpholine N-oxide)11 to yield the 1R-hydroxylated
derivative 18 (60%). Photo-isomerization of 18, back to
the cis-configuration using phenazine as photosensi-
tizer,12 afforded derivative 19 (80%). Removal of the TES
(triethylsilyl) group with Bu4NF yielded the desired final
product, 1R-hydroxyvitamin D5 1 (95%). The product was
recrystallized three times from methyl formate in order
to remove the C-1 epimer, 1â-hydroxyvitamin D5, formed
during the 1R-hydroxylation step, and other impurities.
A total amount of 0.2 g of pure 1R-hydroxyvitamin D5
was obtained. The overall yield for 18 steps and three
recrystallizations of the final product 1 was 1.2%.
A convergent approach to the synthesis of 1R-hydrox-
yvitamin D5 has been recently reported.13 The convergent
synthetic approach was described as an 11-step total
synthesis of 1R-hydroxyvitamin D5 in high overall yield
(46%) from commercially available vitamin D2. However,
the 11-step and 46% yield refer exclusively to the
(9) (a) Yamada, S.; Takayama, H. Chem. Lett. 1975, 83-586. (b)
Reischl, W.; Zbiral, Helv. Chem. Acta 1979, 62, 1763-1769.
(10) (a) Ray, R.; Vicchio, D.; Yergey, A.; Holick, M. Steroids 1992,
57, 142-146. (b) Yamada, S.; Suzuki, T.; Takayama, H.; Miyamoto,
K.; Matsunaga, I.; Nawata, Y. J. Org. Chem. 1983, 48, 3483-3488. (c)
Andrews, D. R.; Barton, D. H. R.; Hesse, H.; Pechet, M. M. J. Org.
Chem. 1986, 51, 4819-4828. (d) Ando, K.; Kondo, F.; Koike, F.;
Takayama, H. Chem. Pharm. Bull. 1992, 40, 1662-1664. (e) Calverley,
M. J. Tetrahedron 1987, 43, 4609-4619.
(11) Hesse, R. H. U.S. 4,554,105 (Cl. 260-397.2; C07J), 1985, 10 pp.
(12) Tachibana, Y. Bull. Chem. Soc. Jpn. 1989, 62, 2090-209.
(13) Gao, L.-J.; Zhao, X.-Y.; Vandewalle, M.; De Clercq, P. Eur. J.
Org. Chem. 2000, 2755-2759.
7626 J. Org. Chem., Vol. 70, No. 19, 2005

Synthesis of 1R-Hydroxyvitamin D5
SCHEME 4a
a Reagents and conditions: (a) (i) hν, t-BuOMe, ethyl 4-(dimethylamino)benzoate, -20 °C to 0 °C, (ii) uranium glass filter,
9-acetylanthracene, -20 to 0 °C, (iii) AcOEt, reflux; (b) 10 M NaOH, MeOH, room temperature, 50% from 8; (c) SO2, -10 °C, 100%; (d)
NaHCO3, DMF, 90 °C, 80%; (e) Et3SiCl, DMF, CH2Cl2, i-Pr2EtN, 95%; (f) SeO2, NMO, MeOH, CH2Cl2, reflux, 60%; (g) hν, uranium glass
filter, phenazine, C6H6, room temperature, 80%; (h) Bu4NF, THF, 95%.
anhydrous lithium bromide (6.05 g, 69.7 mmol) in dry acetone
(80 mL). The mixture was stirred at 0 °C for 2 h, removed
from the ice bath, and treated with triethylamine (6.5 mL, 46.9
mmol) and thiophenol (4.8 mL, 46.9 mmol). After being stirred
for 1.25 h at room temperature, the reaction mixture was
diluted with ethyl acetate (400 mL) and washed with 1 N
hydrochloric acid (50 mL) and then with water (200 mL), twice.
The organic phase was dried over anhydrous sodium sulfate
and evaporated to dryness under vacuum. The residue was
dissolved in ethyl acetate (200 mL), cooled to 0 °C, and treated
with m-chloroperoxybenzoic acid (11.59 g, 38.29 mmol) for 2
h. The reaction mixture was washed with 10% sodium bicar-
bonate and water. The organic phase was dried over anhydrous
sodium sulfate and evaporated. The residue was dissolved in
toluene (200 mL), treated with triethylamine (10.7 mL, 76.58
mmol), heated at 70 °C for 28 h, cooled, and washed twice with
water (300 mL). The organic phase was dried over anhydrous
sodium sulfate, and the solvent was evaporated under reduced
pressure. The residue was chromatographed over silica gel
using dichloromethane as the eluent. The fractions containing
the desired product were concentrated, and the solid residue
was recrystallized from diethyl ether/methanol to afford the
desired diene (5.97 g, 40%) as a white, crystalline solid. Mp:
130-132 (lit.14 126 °C). IR (neat): 2941, 2823, 1729, 1468,
synthesis of the side chain. Moreover, the total synthesis
of 1R-hydroxyvitamin D5 from commercially available
vitamin D2, as it is described in the paper, requires no
less than 40 steps and the overall yield barely exceeds
3%. Therefore, we believe that the present 18-step
synthesis in 1.2% yield compares favorably with the
convergent method for the synthesis of 1R-hydroxyvita-
min D5.
Experimental Section
General Experimental Details. 1H and 13C NMR spectra
were recorded on a 300 MHz spectrometer in CDCl3 and are
referenced to 77.23 (13C) and 7.27 (1H) chloroform peaks. The
IR spectra were recorded on a FTIR spectrometer. Melting
points were determined on a capillary melting point apparatus
and are uncorrected. The reactions were performed under
argon using anhydrous solvents.
3â-Acetoxystigmast-5-ene (10). A mixture of 9 (17.1 g,
0.040 mol) and zinc acetate (25 g, 0.136 mol) in glacial acidic
acid (300 mL) was stirred under reflux for 3 h. The reaction
mixture was cooled to room temperature, and water (200 mL)
was added. The resulting precipitate was filtered, washed with
water, and dissolved in diethyl ether (100 mL). The ethereal
solution was washed with 5% sodium bicarbonate, water, and
brine and dried over anhydrous sodium sulfate. The solvent
was evaporated under reduced pressure, and the solid was
recrystallized from diethyl ether-methanol to afford the
acetate 10 (15.25 g, 84%) as a white, crystalline solid: mp 121-
122 °C (lit.7 mp 121-122 °C).
1
1373, 1235, 1030 cm-1. H NMR (CDCl3), δ (ppm): 0.62 (1H,
s, 18-H), 0.84 & 0.81 (2H each, d’s, J ) 6.5 Hz), 0.96 (3H, s),
2.02 (3H, s, MeCO), 4.72 (1H, m), 5.37 (1H, m), 5.57 (1H, m).
13C NMR (CDCl3), δ (ppm): 170.7, 141.7, 138.7, 120.4, 116.5,
73.0, 56.0, 54.6, 46.2, 46.0, 43.1, 39.3, 38.1, 37.3, 36.8, 36.7,
36.8, 34.1, 29.3, 28.3, 26.3, 23.25, 23.2, 21.6, 21.2, 20.0, 19.2,
19.1, 16.3, 12.5, 12.0. Anal. Calcd for C31H50O2: C, 81.88; H,
11.08. Found: C, 81.92; H, 11.15.
3â-Acetoxystigmasta-5,7-diene (4). A mixture of 10 (15
g, 35 mmol), dibromantin (7 g, 24.5 mmol), and sodium
bicarbonate (15.8 g, 189 mmol), in hexanes (310 mL), was
heated under reflux for 0.5 h. The reaction mixture was cooled
and filtered to remove 5,5-dimethylhydantoin and inorganic
salts, and the filtrate was evaporated in vacuo to dryness. The
residue was taken up in toluene (110 mL) and treated with
9,10-seco-Stigmasta-5(Z),7(E),10(19)-trien-3â-ol (5). A
solution of 4 (3 g, 6.6 mmol) and ethyl 4-(dimethylamino)-
(14) Karmakar, T.; Chakraborty, D. P. Phytochemistry 1983, 22,
608-609.
J. Org. Chem, Vol. 70, No. 19, 2005 7627

Moriarty and Albinescu
benzoate (0.3 g) in tert-butyl methyl ether (250 mL) at -20 °C
was irradiated with a 450 W medium-pressure mercury lamp
through a quartz immersion well. After 8 h of irradiation at
-20 to 0 °C, a uranium glass filter was inserted in the arc
housing and then 9-acetylanthracene (12 mg, 0.055 mmol) was
added to the solution. After 1 h 45 min of irradiation through
the filter at -20 to 0 °C, the lamp was turned off, and the
solution was allowed to warm to room temperature , washed
four times with a total of 50 mL of 3 N hydrochloric acid and
then with saturated sodium bicarbonate, and dried over
anhydrous sodium sulfate. The solvent was evaporated under
vacuum. A second experiment involving 2.7 g of compound 4
gave a second crop of crude photolysis product. The two
combined photolysis products were purified by column chro-
matography (hexanes/ethyl acetate 96:4) to yield pre-vitamin
D5 acetate 11 (3.7 g, 65%). Compound 11 (3.7 g, 8.2 mmol)
was dissolved in ethyl acetate (100 mL) and refluxed overnight.
The solvent was evaporated under low pressure, the residue
was dissolved in methanol (100 mL), and the solution was
treated with 10 M aqueous sodium hydroxide (4 mL, 40 mmol)
for 3 h at room temperature. The excess sodium hydroxide was
neutralized with acetic acid, and the solution was diluted with
water (50 mL) and extracted three times with diethyl ether.
The organic phase was dried over anhydrous sodium sulfate,
the solvent was evaporated, and the crude product was
chromatographed on silica gel using hexanes/ethyl acetate 9:1
as the eluent to afford vitamin D5 5 (2.6 g, 50%). Mp: 105-
106 °C (lit.15 mp 106 °C). [R]20D: +45 (c 0.5, CHCl3). IR (neat):
3361, 2940, 2865, 1590, 1456, 1378, 1291, 1045, 890 cm-1. 1H
NMR (CDCl3), δ (ppm): 0.56 (3H, s), 3.90 (1H, br m), 4.68 and
4.98 (2H, s), 5.88 (1H, d, J ) 12 Hz), 6.54 (1H, d, J ) 12 Hz).
13C NMR (CDCl3), δ (ppm): 145.3, 142.6, 135.2, 122.7, 117.7,
112.6, 69.4, 56.7, 56.6, 46.1, 46.1, 46.0, 40.7, 36.7, 35.4, 34.1,
32.1, 29.3, 29.2, 27.9, 26.3, 23.8, 23.3, 22.5, 20.0, 19.2, 19.1,
12.2, 12.2. Anal. Calc. for C29H48O2: C, 84.40; H, 11.72.
Found: C, 84.20; H, 11.92.
SO2 Adduct of 9,10-seco-Stigmasta-5(Z),7(E),10(19)-
trien-3â-ol (15). The vitamin D5 5 (2.6 g, 6.3 mmol) was
dissolved in liquid sulfur dioxide (about 10 mL) at -20 to -10
°C and maintained under stirring at -10 °C for 1 h. The excess
sulfur dioxide was evaporated, and the adduct was chromato-
graphed on silica gel using hexanes/ethyl acetate 4:6 as the
eluent. Evaporation of the solvent gave the sulfur dioxide
adduct (3 g, 100%) as a white foamy solid. The product was
used in the next step without purification. IR (neat): 3427,
2930, 2867, 1453, 1303, 1103, 1090, 1025, 950 cm-1. 1H NMR
(CDCl3), δ (ppm): 0.56 (3H, s), 0.65 (3H, s), 3.37 (4H, s), 4.11
(2H, m), 4.59 (1H, d, J ) 9 Hz), 4.68 (1H, d, J ) 9 Hz), 4.75
(2H, d, J ) 9 Hz).
9,10-seco-Stigmasta-5(E),7(E),10(19)-trien-3â-ol (16). A
mixture of 15 (3 g, 6.3 mmol) and sodium bicarbonate (3 g, 35
mmol) in dimethylformamide (30 mL) was stirred at 90 °C for
1.5 h while argon was passed through the reaction mixture.
The reaction mixture was cooled to 0 °C, and water (30 mL)
was added. The aqueous layer was extracted three times with
ethyl acetate, and the organic layer was washed with water
and brine and dried over anhydrous sodium sulfate. The
solvent was evaporated under reduced pressure, and the
residue was chromatographed on silica gel using hexanes/ethyl
acetate 8:2 as the eluent to yield the trans-derivative (2.24 g,
86%) as a viscous liquid. IR (neat): 3325, 2926, 2861, 1717
1r-Hydroxy-3â-triethylsilyloxy-9,10-seco-stigmasta-
5(E),7(E),10(19)-triene (18). A solution of N-methylmorpho-
line N-oxide monohydrate (2.8 g, 23.9 mmol) in dichlo-
romethane (30 mL) was dried over anhydrous sodium sulfate
for 30 min then transferred into a solution of 17 (2.8 g, 5.3
mmol) in 1,2-dichloroethane (30 mL). The reaction mixture was
heated to reflux for 15 min, and a solution of selenium dioxide
(0.59 g, 5.3 mmol) in dry methanol (30 mL), which was stirred
at room temperature for 45 min, was added. The reflux was
continued for an additional 2 h. The orange reaction mixture
was cooled, diluted with dichloromethane (100 mL), washed
with saturated sodium bicarbonate and brine, and dried over
anhydrous sodium sulfate. The solvent was evaporated under
reduced pressure and chromatographed on silica gel using
hexanes/ethyl acetate 9:1 as the eluent to give the desired
product (1.81 g, 63%). IR (neat): 3421, 2950, 2875, 1597 (vw),
1458, 1373 (vw), 1234 (vw), 1072, 1007, 733 cm-1 1H NMR
.
(CDCl3), δ (ppm): 0.56 (3H, s), 4.20 (1H, m), 4.50 (1H, m), 4.95
and 5.09 (2H, s), 5.88 (1H, d, J ) 11.4 Hz), 6.53 (1H, d, J )
11.4 Hz). 13C NMR (CDCl3), δ (ppm): 152.6, 144.8, 134.1, 122.7,
116.3, 108.9, 71.4, 66.5, 56.7, 56.7, 46.2, 46.0, 42.9, 40.7, 37.5,
36.7, 34.1, 29.3, 29.3, 27.9, 26.2, 23.8, 23.3, 22.4, 20.0, 19.2,
19.1, 12.2, 12.2, 7.1, 5.0. MS m/z: 542 (M+) for C35H62O2Si.
HRMS: found 542.451592, calcd 542.451910.
1r-Hydroxy-3â-triethylsilyloxy-9,10-seco-stigmasta-
5(Z),7(E),10(19)-triene (19). A solution of 18 (1.6 g, 29 mmol)
and phenazine (20% with respect to the substrate) in dry
benzene (150 mL) was irradiated for 30 min with a Hanovia
medium-pressure mercury lamp fitted with an uranium glass
filter. The solvent was evaporated under reduced pressure, and
the residue was chromatographed on silica gel using hexanes/
ethyl acetate 90:1 as the eluent to afford the cis-derivative
(1.33 g, 83%). IR (neat): 3421, 2950, 2875, 1597 (vw), 1458,
1373 (vw), 1234 (vw), 1072, 1007, 733 cm-1. 1H NMR (CDCl3),
δ (ppm): 0.56 (3H, s), 4.20 (1H, m), 4.96 and 5.27 (2H, m),
6.02 (1H, d, J ) 11.4 Hz), 6.33 (1H, d, J ) 11.4 Hz). 13C NMR
(CDCl3), δ (ppm): 147.7, 142.6, 133.7, 124.5, 117.4, 112.7, 72.1,
67.1, 56.6, 56.5, 46.4, 45.98, 45.96, 43.6, 40.7, 36.6, 34.0, 29.3,
29.2, 27.8, 26.2, 23.7, 23.2, 22.4, 20.9, 19.2, 19.1, 12.2, 12.1,
7.0, 5.0. MS m/z: 542 (M+) for C35H62O2Si. HRMS: found
542.451436, calcd 542.451910.
1r,3â-Dihydroxy-9,10-seco-stigmasta-5(Z),7(E),10(19)-
triene (1).1a A solution of triethylsilyl ether derivative 19 (1.2
g, 2.21 mmol) in tetrahydrofuran (20 mL) was treated with 1
M tetrabutylamonium fluoride in tetrahydrofuran (5.5 mL, 5.5
mmol) at room temperature for 45 min. The reaction mixture
was quenched with water and extracted three times with ethyl
acetate. The organic phase was washed with water and brine
and dried over anhydrous sodium sulfate. After solvent
evaporation under reduced pressure, the residue was chro-
matographed on silica gel using hexanes/ethyl acetate 6:4 to
4:6 as the eluent to give the deprotected derivative (0.7 g, 75%)
as a solid. The solid (a mixture of 1R-hydroxy- and 1â-
hydroxyvitamin D5 4:1) was crystallized three times from
anhydrous methyl formate to afford pure 1R-hydroxyvitamin
D5 (0.200 g, 28%). Mp: 153-154 °C. [R]20
: +29.3, (c 0.5,
D
CHCl3). IR (neat): 3386, 2947, 2866, 1697 (vw), 1457, 1373,
1043, 891 cm-1. 1H NMR (CDCl3), δ (ppm): 0.54 (3H, s), 4.23
(1H, m), 4.43 (1H, m), 5.0 and 5.33 (2H, s), 6.02 (1H, d, J )
11.4 Hz), 6.38 (1H, d, J ) 11.4 Hz). 13C NMR (CDCl3), δ
(ppm): 147.8, 143.5, 133, 125.2, 117.2, 112.0, 70.9, 67.0, 56.7,
56.5, 46.2, 46.0, 45.4, 43.0, 40.7, 36.7, 34.0, 29.3, 29.3, 27.8,
26.2, 23.2, 23.2, 22.5, 20.0, 19.2, 19.1, 12.19, 12.18. Anal. Calcd
for C29H48O2: C, 81.25; H, 11.29. Found: C, 81.14; H, 11.30.
(vw), 1621 (vw), 1447, 1369 (vw), 1136 (vw), 1029, 780 cm-1
.
1H NMR (CDCl3), δ (ppm): 0.53 (3H, s), 3.80 (1H, m), 4.64
and 4.93 (2H, s), 5.83 (1H, d, J ) 11.4 Hz), 6.46 (1H, d, J )
11.4 Hz). 13C NMR (CDCl3), δ (ppm): 149.3, 145.0, 135.0, 121.2,
116.0, 108.5, 69.2, 56.8, 56.7, 46.1, 46.0, 40.7, 37.3, 36.7, 34.9,
34.1, 31.4, 29.3, 29.2, 27.9, 26.2, 23.8, 23.2, 22.5, 20.0, 19.2,
19.1, 12.3, 12.2. Anal. Calcd for C29H48O: C, 84.40; H, 11.72.
Found: C, 84.33; H, 12.10.
Supporting Information Available: Listing of the 1H
spectrum of compound 1 and 13C spectra of compounds 1, 8,
and 13-18, as well as the experimental details for the
synthesis of compounds 7-9 and 17. This material is available
free of charge via the Internet at http://pubs.acs.org.
(15) Wunderlich, W. Hoppe-Seylers Z. Physiol. Chem. 1936, 241
116-124.
JO050853F
7628 J. Org. Chem., Vol. 70, No. 19, 2005