Synthesis of (25R)-5α-Cholestane-3β,6β,15α,16β,26-pentol, a Cytostatic Starfish Steroid1

Article abstract of DOI:10.1021/jo980266c

The synthesis of (25R)-5αa-cholestane-3β,6β 15α,16β,26-pentol (1a), a marine cytostatic steroid, has been achieved in 13 steps (7.8% overall yield) starting from commercially available diosgenin (2). A key step in the synthesis was the dimethyldioxirane oxidation of the enolsilane 16 to introduce the 15α-hydroxy group in the D ring.

Full text of DOI:10.1021/jo980266c

4438
J . Org. Chem. 1998, 63, 4438-4443
Syn th esis of (25R)-5r-Ch olesta n e-3â,6â,15r,16â,26-p en tol, a
Cytosta tic Sta r fish Ster oid †
Irene Izzo, Francesco De Riccardis,* and Guido Sodano*
Dipartimento di Chimica, University of Salerno, Via S. Allende, 84081 Baronissi (SA), Italy
Received February 13, 1998
The synthesis of (25R)-5R-cholestane-3â,6â,15R,16â,26-pentol (1a ), a marine cytostatic steroid, has
been achieved in 13 steps (7.8% overall yield) starting from commercially available diosgenin (2).
A key step in the synthesis was the dimethyldioxirane oxidation of the enolsilane 16 to introduce
the 15R-hydroxy group in the D ring.
In tr od u ction
oligoglycosides, some of them displaying cytotoxic or
cytostatic activity. In particular three of them (1a -c),
having a 5R-cholestane-3â,6â,15R,16â,26-pentol frame-
work, showed a cytostatic effect upon human bronchop-
ulmunary non-small-cell lung carcinoma cells (NSCLC-
N6), by blocking the cell cycle in phase G1 (period prior
the DNA synthesis).
Polyhydroxysteroids are naturally occurring steroids
present in a wide variety of marine organisms.1 They
have been isolated from soft corals, gorgonians, nudi-
branchs, sponges, and ophiuroids, but starfishes appear
to be the richest source of new polyhydroxysteroids.
Although polyhydroxysteroids do not contain stuctural
features commonly associated with cytotoxicity, such as
alkylation sites, Michael’s acceptors, intercalators, or
redox-active quinones, some of them show interesting
antiproliferative activity in several tumor cell lines.2
Few hypotheses have been made for the activity of
steroidal cytotoxins:3,4 they may interfere with the eu-
cariotic cell membrane,5 they may be enzyme inhibitors,6
they may disrupt the cascade of signal transduction.7
Despite the interesting bioactivities showed by polyhy-
droxysteroids, few syntheses of these compounds have
been reported.8
The fact that insufficient amounts of these compounds
were available for further pharmacological studies, coupled
with the need to evaluate the mechanism of action,
prompted us to undertake the synthesis of one of them:
(25R)-5R-cholestane-3â,6â,15R,16â,26-pentol (1a ).
We envisaged diosgenin (2) as an useful starting
material both for its commercial availability and for the
presence of functional groups in position suitable for
conversion to 1a .
Recently2a an investigation of an Antarctic starfish
belonging to the Echinasteridae family has led to the
isolation of several polyhydroxysteroids and steroidal
* Authors to whom correspondence should be addressed. Tel.: +39-
89-965230. Fax: +39-89-965296. E-mail: guiso@vaxsa.csied.unisa.it.
† Dedicated to the memory of Professor Luigi Minale, deceased May
11, 1997.
(1) (a) Minale, L.; Riccio, R.; Zollo, F. In Progress in the Chemistry
of Organic Natural Products; Herz, W., Kirby, G. W., Moore, R. E.,
Steglich, W., Tamm, Ch., Eds.; Spinger-Verlag: New York, 1993; Vol.
62, pp 75-308. (b) D’Auria, M. V.; Minale, L.; Riccio, R. Chem. Rev.
1993, 93, 1839. (c) Minale, L.; Riccio, R.; Zollo, F. In Studies in Natural
Products Chemistry. Structure and Chemistry (Part C); Atta Ur-
Rahman, Ed.; Elsevier Science B. V.: Amsterdam, 1995; Vol. 15, pp
43-110.
(2) (a) Iorizzi, M.; De Marino, S.; Minale, L.; Zollo, F.; Le Bert, V.;
Roussakis, C. Tetrahedron 1996, 52, 10997. (b) Andersson, L.; Bohlin,
L.; Iorizzi, M.; Riccio, R.; Minale, L.; Moreno-Lopez, W. Toxicon 1989,
27, 179. (c) Higuchi, R.; Noguchi, Y.; Komori, T.; Sasaki, T. Liebigs
Ann. Chem. 1988, 1185. (d) Ganesan, A. Angew. Chem., Int. Ed. Engl.
1996, 35, 611.
(3) (a) Pettit, G. R.; Inoue, M.; Kamano, Y.; Herald, D. L.; Arm, C.;
Dufresne, C.; Christie, N. D.; Schmidt, J . M.; Doubek, D. L.; Krupa, T.
S. J . Am. Chem. Soc. 1988, 110, 2006. (b) Fukuzawa, S.; Matsunaga,
S.; Fusetani, N. J . Org. Chem. 1994, 59, 6164.
(4) Mimaki, Y.; Kuroda, M.. Kameyama, A.; Sashida, Y.; Hirano,
T.; Oka, K.; Maekawa, R.; Wada, T.; Sugita, K.; Beutler, J . A. Bioorg.
Med. Chem. Lett. 1997, 7, 633.
Resu lts a n d Discu ssion
The synthesis began with the protection of diosgenin
(2) to give the benzyl ether 3 in 90% yield (eq 1).
Treatment of compound 3 with BH3‚SMe2, followed by
oxidation with alkaline hydrogen peroxide,9 afforded a
mixture of two diasteromeric alcohols (4 and 5) in good
overall yield (82%) and with a predominance of the trans-
fused 6R-alcohol 4 (OH-6R (4)/OH-6â (5), 10.7/1).
The two diastereomers were separated by flash chro-
matography on silica gel, and the unambiguous assign-
ment of the stereochemistry of the A/B ring junction was
determined by comparison of their CH3-19 1H and 13C
1
NMR resonances (4, trans-A/B ring junction, H NMR δ
0.79 ppm, 13C NMR δ 13.3 ppm; 5, cis-A/B ring junction,
1H NMR δ 1.15 ppm, 13C NMR δ 26.0 ppm).10
(5) Ganesan, A.; Heathcock, C. H. Chemtracts: Org. Chem. 1988,
1, 311.
(6) Pan, Y.; Merriman, R. L.; Tanzer, R. L.; Fuchs, P. L. Bioorg. Med.
Chem. Lett. 1992, 2, 967.
(7) Marx, J . Science 1995, 270, 232.
(8) (a) Izzo, I.; De Riccardis, F.; Massa, A.; Sodano G. Tetrahedron
Lett. 1996, 37, 4775. (b) Mitome, H.; Miyaoka, H.; Nakano, M.;
Yamada, Y. Tetrahedron Lett. 1995, 36, 8231. (c) Harney, D. W.;
Macrides T. A. J . Chem. Soc., Perkin Trans. 1 1997, 1353.
(9) (a) Tavares, R.; Randoux, T.; Braekman, J .-C.; Daloze, D.
Tetrahedron 1993, 49, 5079. (b) Danishefsky, S. J .; Masters, J . J .;
Young, W. B., Link, J . T.; Snyder, L. B.; Magee T. V.; J ung D. K.; Isaacs
R. C. A.; Bornmann W. G.; Alaimo C. A.; Coburn C. A., Di Grandi M.
J . J . Am. Chem. Soc. 1996, 118, 2843.
(10) Dolle, F.; Hetru, C.; Luu, B. Tetrahedron 1991, 47, 7059.
S0022-3263(98)00266-7 CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/05/1998

(25R)-5R-Cholestane-3â,6â,15R,16â,26-pentol
J . Org. Chem., Vol. 63, No. 13, 1998 4439
Since the target molecule has a 1,2-trans-diol in the D
ring, we considered that this moiety could be introduced
by opening of a 15,16-epoxide (eq 4). Thus, kinetic
enolization of 11 with lithium bis(trimethylsilyl)amide
(LiN(TMS)2) and quenching of the enolate with N-
phenyltrifluoromethanesulfonimide14 (PhN(SO2CF3)2) gave
the stable enoltriflate 12. Deoxygenation of the latter
with tributyltin hydride (Bu3SnH) and tetrakis(triphen-
ylphosphine)palladium(0)15 afforded (25R)-26-[(tert-bu-
tyldimethylsilyl)oxy]-3â,6â-bis(benzyloxy)-5R-cholest-15-
ene (13) in 47% yield (two steps). Desilylation at C-26
with tetra-n-butylammonium fluoride (TBAF) and sub-
sequent epoxidation with m-chloroperbenzoic acid (MCP-
BA) furnished compound 15 (31%, two steps). The
Inversion of the configuration at C-6 of 4 with a two-
step procedure (oxidation11 to ketone 6 and subsequent
highly diasteroselective reduction with LiAlH4, eq 2)8a
furnished alcohol 7 in 95% overall yield. Compound 7
was first protected as benzyl ether (8, 75% yield) and then
subjected to Clemmensen reduction following Seo’s pro-
cedure12 to afford (25R)-3â,6â-bis(benzyloxy)-5R-choles-
tane-16â,26-diol (9, 52%).
oxirane stereochemistry was indicated by the CH3-18 1,3-
syn deshielding effect compared to that reported for
cholesterol (δH-18 cholesterol, 0.68 ppm; δH-18 15, 0.92
ppm)16 and supported by a ROESY17 experiment which
showed dipolar coupling between the signals at δH 3.06
(H-15) and δH 3.20 (H-16) with the resonance at δH 1.05
(H-14R). Unfortunately, attempts to open the oxirane
ring in acidic conditions resulted in the formation of an
uncharacterized mixture of compounds.
Chemoselective silylation of diol 9 with tert-butyldi-
methylsilyl chloride (TBDMSCl) and 1,8-diazabicyclo-
[5.4.0]undec-7-ene (DBU)13 produced the monoprotected
derivative 10 (eq 3). The secondary alcohol at C-16 was
then easily oxidated with pyridinium dicromate (PDC)
to afford ketone 11 in 78% yield (two steps).
We then decided to hydroxylate the ketone 11. At-
tempts to obtain the R-hydroxy ketone by treatment of
the kinetic enolate of 11 with oxodiperoxymolybdenum-
(11) Herscovici, J .; Antonakis, K. J . Chem. Soc., Chem. Commun.
1980, 561.
(12) Seo, S.; Yoshimura, Y.; Satoh, T.; Uomori, A.; Takeda, K. J .
Chem. Soc., Perkin Trans. 1 1986, 411.
(14) McMurry, J . E.; Scott, W. J . Tetrahedron Lett. 1983, 24, 979.
(15) Scott, W. J .; Stille, J . K. J . Am. Chem. Soc. 1986, 108, 3033.
(16) Dictionary of Steroids; Hill, R. A., Kirk, D. N., Makin, H. L. J .,
Murphy, G. M., Eds.; Chapman and Hall: London, 1991; p 169.
(17) Bax, A.; Davis, D. G. J . Magn. Reson. 1985, 63, 207.
(13) Aizpurua, J . M.; Palomo, C. Tetrahedron Lett. 1985, 26, 475.

4440 J . Org. Chem., Vol. 63, No. 13, 1998
Izzo et al.
(pyridine)(hexamethylphosphoric triamide) (MoOPH)18
were also unsuccessful since the unreacted ketone was
always recovered. However highly stereoselective hy-
droxylation at C-15 was accomplished by a three-step
sequence involving the preparation of a hydrolitically
labile silyloxy epoxide (eq 5). The applied method19
started from ketone 11 which was selectively enolized
under kinetic control (-78 °C) using the bulky base
lithium bis(trimethylsilyl)amide. The regioisomeric eno-
late was then quenched with chorotrimethylsilane (TM-
SCl), giving the silylenol ether 16. Dimethyldioxirane20
epoxidation and opening of the silyloxy epoxide 17 with
camphorsulfonic acid (CSA), gave the C-26 desilylated
R-hydroxy ketone 18 in good overall yield (71%).
Work is in progress to evaluate the cytostatic activity
of 1a in vivo.
Exp er im en ta l Section
Gen er a l P r oced u r es. Analytical instrumentation and
spectral formats are the same as previously described.22 All
reactions were carried out under a dry argon atmosphere using
freshly distilled solvents unless otherwise noted. Tetrahydro-
furan was distilled from sodium and benzophenone. Toluene,
methylene chloride, and diethyl ether were distilled from
calcium hydride. Glassware was flame dried (0.05 Torr) prior
to use. When necessary, compounds were dried in vacuo over
P2O5 or by azeotropic removal of water with toluene under
reduced pressure. Starting materials and reagents purchased
from commercial suppliers were generally used without puri-
fication. Dimethyldioxirane was prepared according ref 20.
Reactions were monitored by thin-layer chromatography (TLC)
on Merck silica gel plates (0.25 mm) and visualized using UV
light, spraying with H2SO4-Ce(SO4)2 solution and drying.
Reaction temperatures were measured externally. Flash
chromatography was performed on Merck silica gel (60,
particle size 0.040-0.063 mm). Yields refer to chromato-
graphically and spectroscopically (1H and 13C NMR) pure
materials. High-resolution mass spectra (electron impact,
EIMS; fast ion bombardment, FIBMS) were obtained at 70 eV
and 4 kV (Cs+ ion), respectively, on a Fisons VG Prospec mass
spectrometer. The NMR spectra were recorded on a Bruker
AM-250, Bruker DRX-400, and Bruker DRX-600 spectrom-
eters. Assignments of 1H and 13C NMR resonances were based
on DEPT, COSY, HETCOR, and ROESY17 experiments.
(25R)-3â-(Ben zyloxy)sp ir ost-5-en e (3). To a suspension
of NaH (0.43 g, 18 mmol) in THF (5 mL) at 0 °C was slowly
added a solution of diosgenin (2, 5.00 g, 12.0 mmol) in THF
(35 mL). After the solution was stirred for 0.5 h at 0 °C, benzyl
bromide (BnBr, 2.6 mL, 22.0 mmol) and tetrabutylammonium
iodide (TBAI, 0.31 g, 0.84 mmol) were added. The resulting
mixture was refluxed for 16 h and then quenched with a
saturated solution of NH4Cl (10 mL), concentrated in vacuo
to remove the excess THF, and extracted with diethyl ether.
The organic phase was dried (Na2SO4) and concentrated in
vacuo. Crystallization from CHCl3/MeOH gave 3 (5.45 g, 90%)
as white crystals.
Assignment of the configuration at C-15 was made on
the basis of a ROESY17 experiment which showed a
strong cross peak between the â-axial CH3-18 (δ 0.88
ppm) and the C-15 proton (δ 3.59 ppm), establishing an
R stereochemistry for the C-15 hydroxy group.
The penultimate step of the synthesis was the reduc-
tion of the C-16 oxo group (eq 6). This seemingly
straightforward reaction was unexpectedly difficult to
perform with acceptable stereoselectivity. Several hy-
dride based reagents were used in this step. NaBH4 and
DIBAL-H gave exclusively the undesired cis isomer 19
in 90% and 86% yields, respectively, while NaBH3CN and
LiAlH4 afforded both 19 and 20 in 1.6/1 (75%) and 1/1.25
(90%) ratio. The BH3‚SMe2 reduction procedure, accord-
ing to Brown and Vogel,21 afforded exclusively 20 in 58%
yield.
1
3: mp 134-135 °C; [R]D -90.5 (c ) 1.0, CHCl3); H NMR
(250 MHz, CDCl3) δ 0.79 (3 H, s, Me-18), 0.79 (3 H, d, J ) 6.7
Hz, Me-27), 0.98 (3 H, d, J ) 6.0 Hz, Me-21), 1.04 (3 H, s,
Me-19), 3.28 (1 H, m, H-3), 3.37 (1 H, dd, J ) 10.6, 10.6 Hz,
H-26), 3.48 (1 H, dd, J ) 10.6, 2.9 Hz, H′-26), 4.43 (1 H, bdd,
J ) 14.6, 6.9 Hz, H-16), 4.56 (2 H, s, CH2Ph), 5.35 (1 H, m,
H-6), 7.31 (5 H, m, C6H5); 13C NMR (62.5 MHz, CDCl3) δ 14.5,
16.2, 17.1, 19.4, 20.8, 28.4, 28.7, 30.2, 31.4 (× 2), 31.8, 32.0,
37.0, 37.1, 39.1, 39.7, 40.2, 41.5, 50.0, 56.5, 62.0, 66.8, 69.9,
78.4, 80.7, 109.2, 121.0, 127.3, 127.5 (× 2), 128.3 (× 2), 139.0,
140.9; HR EIMS m/z 504.3633 (calcd 504.3603 for C34H48O3).
(25R)-3â-(Ben zyloxy)-5r-sp ir osta n -6r-ol (4) a n d (25R)-
3â-(Ben zyloxy)-5â-sp ir osta n -6â-ol (5). To a solution of 3
(0.70 g, 1.4 mmol) in THF (10 mL) at 0 °C was slowly added
BH3‚SMe2 (2.8 mL, 2.0 M in THF, 5.6 mmol). After 0.1 h the
solution was warmed to room temperature and stirred for a
further 20 h. The solution was then cooled at 0 °C, and
Hydrogenolysis (Pd/C) of triol 20 resulted in removal
of the benzyl protecting groups to provide (25R)-5R-
cholestane-3â,6â,15R,16â,26-pentol (1a ) in quantitative
yield. The target compound was identified by comparison
of the NMR data with those reported for the natural
product.2a
(18) Vedejs, E.; Engler, D. A.; Telschow, J . E. J . Org. Chem. 1978,
43, 188.
(19) Adam, W.; Prechtl, F. Chem. Ber. 1991, 124, 2369.
(20) Adam, W.; Chan, Y. Y.; Cremer, D.; Gauss, J .; Scheutzow, D.;
Schindler, M. J . Org. Chem. 1987, 52, 2800.
(22) De Riccardis, F.; Izzo, I.; Di Filippo, M.; Sodano, G.; D’Acquisto,
(21) Brown, H. C.; Vogel, F. G. M. Liebigs Ann. Chem. 1978, 695.
F.; Carnuccio, R. Tetrahedron 1997, 53, 10871.

(25R)-5R-Cholestane-3â,6â,15R,16â,26-pentol
J . Org. Chem., Vol. 63, No. 13, 1998 4441
absolute ethanol (2.5 mL), a solution of NaOH (3.5 mL, 3.0
M), and H2O2 (0.7 mL, 30% in water) were added in succession.
The mixture was refluxed for 1 h, concentrated in vacuo to
remove the excess of THF, and extracted with ethyl acetate.
The organic phase was dried (Na2SO4), filtered, and concen-
trated in vacuo. The residue was flash chromatographed
(silica gel, 5-40% diethyl ether in petroleum ether) to give 4
(0.54 g, 75%) as a white solid and 5 (0.05 g, 7%) as a colorless
oil.
resulting mixture was heated at reflux for 16 h, quenched with
a saturated solution of NH4Cl (2 mL), concentrated in vacuo
to remove the excess of THF, and extracted with diethyl ether.
The organic phase was dried (Na2SO4), filtered, and concen-
trated in vacuo. The residue was flash chromatographed
(silica gel, 5-15% diethyl ether in petroleum ether) to give 8
as a white solid (1.55 g, 75%).
8: mp 54-56 °C; [R]D -69.5 (c ) 1.8, CHCl3); 1H NMR (250
MHz, CDCl3) δ 0.81 (3 H, s, Me-18), 0.82 (3H, d, J ) 6.7 Hz,
Me-27), 1.00 (3 H, d, J ) 6.0 Hz, Me-21), 1.10 (3 H, s, Me-19),
3.35 (1 H, dd, J ) 10.6, 10.6 Hz, H-26), 3.39 (1 H, m, H-3),
3.45 (1 H, dd, J ) 10.6, 2.9 Hz, H′-26), 3.46 (1 H, m, H-6),
4.34 (1 H, d, J ) 12.2 Hz, CHPh), 4.43 (1 H, bdd, J ) 14.6, 6.9
Hz, H-16), 4.58 (2 H, bs, CH2Ph), 4.60 (1 H, d, J ) 12.2 Hz,
CH′Ph), 7.34 (10 H, m, C6H5); 13C NMR (62.5 MHz, CDCl3) δ
14.5, 15.7, 16.4, 17.1, 20.8, 28.2, 28.7, 30.2, 30.4, 31.3, 31.7,
32.4, 35.1, 36.0, 38.3, 39.9, 40.6, 41.6, 47.7, 54.4, 55.9, 62.2,
66.8, 69.7, 71.1, 78.4, 79.1, 80.7, 109.1, 126.9 (× 3), 127.3, 127.5
(× 2), 128.1 (× 2), 128.2 (× 2), 139.1, 139.6; HR EIMS m/z
612.4137 (calcd 612.4179 for C41H56O4).
1
4: mp 228-231 °C; [R]D -48.8 (c ) 1.3, CHCl3); H NMR
(250 MHz, CDCl3) δ 0.74 (3 H, s, Me-18), 0.77 (3 H, d, J ) 6.7
Hz, Me-27), 0.79 (3 H, s, Me-19), 0.94 (3 H, d, J ) 6.0 Hz,
Me-21), 3.30 (1 H, m, H-3), 3.34 (1 H, m, H-6), 3.35 (1 H, dd,
J ) 10.6, 10.6 Hz, H-26), 3.45 (1 H, dd, J ) 10.6, 2.9 Hz, H′-
26), 4.38 (1 H, bdd, J ) 14.6, 6.9 Hz, H-16), 4.50 (1 H, d, J )
11.8 Hz, CHPh), 4.58 (1 H, d, J ) 11.8 Hz, CH′Ph), 7.30 (5 H,
m, C6H5); 13C NMR (62.5 MHz, CDCl3) δ 13.3, 14.4, 16.3, 17.0,
20.8, 27.9, 28.6 (× 2), 30.1, 31.2, 31.6, 33.7, 36.4, 37.1, 39.6,
40.4, 41.4, 41.6, 51.3, 53.6, 55.8, 61.9, 66.6, 68.9, 69.7, 77.8,
80.5, 109.1, 127.2, 127.4 (× 2), 128.2 (× 2), 138.8; HR EIMS
m/z 522.3683 (calcd 522.3709 for C34H50O4).
(25R)-3â,6â-Bis(ben zyloxy)-5r-ch olestan e-16â,26-diol (9).
To a suspension of zinc amalgam, freshly prepared from HgCl2
(0.30 g, 1.10 mmol), and zinc powder (3.20 g, 48.9 mmol) were
added 8 (0.094 g, 0.186 mmol), dissolved in absolute ethanol
(12 mL), and concentrated hydrochloric acid (3 mL, 37%,
aqueous solution). The mixture was heated at reflux for 1.6
h, cooled to room temperature, filtered, and concentrated under
reduced pressure. The crude material was diluted with
chloroform, washed with water, dried (Na2SO4), and evapo-
rated. Flash chromatography of the residue on silica gel (0-
1% MeOH in CHCl3) gave 9 (0.049 g, 52%) as a white solid.
9: mp 94-96 °C; [R]D -12.1 (c ) 1.6, CHCl3); 1H NMR (250
MHz, CDCl3) δ 0.87 (3 H, s, Me-18), 0.90 (3 H, d, J ) 6.7 Hz,
Me-27), 0.97 (3 H, d, J ) 6.0 Hz, Me-21), 1.06 (3 H, s, Me-19),
3.36 (1 H, m, H-3), 3.44 (3 H, m, H-6, H2-26), 4.32 (1 H, m,
H-16), 4.33 (1 H, d, J ) 12.2 Hz, CHPh), 4.56 (2 H, s, CH2Ph),
5: [R]D -27.9 (c ) 2.5, CHCl3); 1H NMR (250 MHz, CDCl3)
δ 0.78 (3 H, s, Me-18), 0.78 (3 H, d, J ) 6.7 Hz, Me-27), 0.96
(3 H, d, J ) 6.0 Hz, Me-21), 1.15 (3 H, s, Me-19), 3.35 (1 H,
dd, J ) 10.6, 10.6 Hz, H-26), 3.45 (1 H, dd, J ) 10.6, 2.9 Hz,
H′-26), 3.64 (1 H, m, H-3), 3.69 (1 H, bs, H-6), 4.40 (1 H, bdd,
J ) 14.6, 6.9 Hz, H-16), 4.45 (1 H, d, J ) 11.8 Hz, CHPh),
4.55 (1 H, d, J ) 11.8 Hz, CH′Ph), 7.32 (5 H, m, C6H5); 13C
NMR (62.5 MHz, CDCl3) δ 14.5, 16.5, 17.1, 20.6, 24.1, 26.0,
28.7, 30.2, 30.6, 31.3, 31.7, 34.5, 34.8, 40.0, 40.2, 40.4, 40.7,
41.6, 44.2, 56.3, 62.2, 66.8, 68.9, 69.5, 72.8, 73.2, 77.2, 80.8,
109.2, 127.3 (× 2), 128.3 (× 2), 139.2; HR EIMS m/z 522.3745
(calcd 522.3709 for C34H50O4).
(25R)-3â-(Ben zyloxy)-5r-sp ir osta n -6-on e (6). To a solu-
tion of 4 (0.18 g, 0.34 mmol) in CH2Cl2 (2 mL) were added 4 Å
molecular sieves (m.s., 0.34 g) and PDC (0.26 g, 0.69 mmol).
After 2 h the reaction mixture was diluted with diethyl ether
(10 mL). Filtration through a short pad of Celite and CaSO4
(10% in weight) afforded a solution which was concentrated
in vacuo to give 6 as a white solid (0.17 g, 95%).
4.59 (1 H, d, J ) 12.2 Hz, -CH′Ph), 7.34 (10 H, m, C6H5); 13
C
NMR (62.5 MHz, CDCl3) δ 13.3, 15.7, 16.6, 18.1, 20.6, 23.7,
28.2, 29.6, 30.4, 32.4, 33.3, 34.9, 35.6, 35.9, 36.0, 36.6, 38.3,
40.0, 42.5, 47.8, 53.8, 54.5, 61.6, 68.4, 69.7, 71.1, 72.4, 78.4,
79.2, 126.9 (× 3), 127.3, 127.5 (× 2), 128.1 (× 2), 128.3 (× 2),
139.1, 139.7; HR EIMS m/z 616.4461 (calcd 616.4492 for
1
6: mp 178-180 °C; [R]D -82.6 (c ) 1.0, CHCl3); H NMR
(250 MHz, CDCl3) δ 0.77 (6 H, s, Me-18, Me-19), 0.78 (3H, d,
J ) 6.7 Hz, Me-27), 0.97 (3 H, d, J ) 6.0 Hz, Me-21), 3.29 (1
H, m, H-3), 3.35 (1 H, dd, J ) 10.6, 10.6 Hz, H-26), 3.45 (1 H,
dd, J ) 10.6, 2.9 Hz, H′-26), 4.40 (1 H, bdd, J ) 14.6, 6.9 Hz,
H-16), 4.50 (1 H, d, J ) 11.8 Hz, CHPh), 4.58 (1 H, d, J ) 11.8
Hz, CH′Ph), 7.32 (5 H, m, C6H5); 13C NMR (62.5 MHz, CDCl3)
δ 13.1, 14.4, 16.4, 17.1, 21.3, 26.3, 27.9, 28.7, 30.2, 31.5, 36.6,
37.2, 39.5, 40.9, 41.2, 41.5, 46.7, 53.8, 56.4, 56.7, 61.9, 66.8,
69.7, 76.9, 80.4, 109.3, 127.4, 127.5 (× 2), 128.3 (× 2), 138.7,
210. 7; HR EIMS m/z 520.3544 (calcd 520.3553 for C34H48O4).
(25R)-3â-(Ben zyloxy)-5r-sp ir osta n -6â-ol (7). To a solu-
tion of 6 (0.15 g, 0.29 mmol) in diethyl ether (15 mL) was added
LiAlH4 (0.43 mL, 1.0 M in THF, 0.43 mmol). The reaction
mixture was stirred for 0.2 h and quenched with ethyl acetate
(1 mL) and NH4OH (0.5 mL, 30% aqueous solution). Filtration
through a short pad of Celite and concentration in vacuo gave
7 (0.15 g, 100%) as a white solid.
C
41H60O4).
(25R)-26-[(ter t-Bu tyld im eth ylsilyl)oxy]-3â,6â-bis(ben -
zyloxy)-5r-ch olesta n -16â-ol (10). To a solution of 9 (0.640
g, 1.04 mmol) in CH2Cl2 (5 mL) were added 1,8-diazabicyclo-
[5.4.0]undec-7-ene (DBU, 0.28 mL, 1.9 mmol) and TBDMSCl
(0.250 g, 1.66 mmol). The reaction was stirred for 1.5 h before
being diluted with CH2Cl2 (15 mL), sequentially washed with
0.1 M HCl (10 mL) and with a saturated solution of NaHCO3
(10 mL) and water, dried (Na2SO4), and concentrated in vacuo.
The residue (0.760 g), a colorless oil, was used in the next step
without purification.
10: [R]D -11.8 (c ) 1.5, CHCl3); 1H NMR (250 MHz, CDCl3)
δ 0.04 (6 H, s, (CH3)2-Si), 0.86 (3 H, s, Me-18), 0.89 (9 H, s,
(CH3)3-C), 0.90 (3 H, d, J ) 6.7 Hz, Me-27), 0.97 (3 H, d, J )
6.0 Hz, Me-21), 1.06 (3 H, s, Me-19), 3.40-350 (4 H, m, H-3,
H-6 and H2-26), 4.32 (1 H, m, H-16), 4.32 (1 H, d, J ) 12.2 Hz,
CHPh), 4.55 (2 H, s, CH2Ph), 4.57 (1 H, d, J ) 12.2 Hz, CH′Ph),
7.32 (10 H, m, C6H5); 13C NMR (62.5 MHz, CDCl3) δ -5.3 (×
2) 13.3, 15.7, 16.7, 18.1, 18.4, 20.6, 23.7, 25.6, 26.0 (× 3), 28.2,
29.8, 30.4, 32.4, 33.6, 34.9, 35.8, 36.0, 36.2, 36.5, 38.4, 40.0,
42.5, 47.8, 54.5, 61.5, 68.5, 69.7, 71.1, 72.5, 78.4, 79.2, 126.9
(× 3), 127.3, 127.6 (× 2), 128.1 (× 2), 128.3 (× 2), 139.1, 139.8;
EIMS m/z 730 (M+).
(25R)-26-[(ter t-Bu tyld im eth ylsilyl)oxy]-3â,6â-bis(ben -
zyloxy)-5r-ch olesta n -16-on e (11). To a solution of 10 (0.760
g, 1.04 mmol) in CH2Cl2 (5 mL) were added 4 Å molecular
sieves (1.40 g) and PDC (0.782 g, 2.18 mmol). After 2 h the
reaction mixture was diluted with diethyl ether (10 mL).
Filtration through a short pad of Celite and CaSO4 (10% in
weight) afforded a solution which was concentrated in vacuo
and purified by flash chromatography (silica gel, 5-10%
diethyl ether in petroleum ether) to give 11 as a colorless oil
(0.59 g, 78% two steps).
1
7: mp 194-196 °C; [R]D -62.3 (c ) 1.2, CHCl3); H NMR
(250 MHz, CDCl3) δ 0.77 (3 H, d, J ) 6.7 Hz, Me-27), 0.78 (3
H, s, Me-18), 0.95 (3 H, d, J ) 6.0 Hz, Me-21), 1.03 (3 H, s,
Me-19), 3.35 (1 H, m, H-3), 3.35 (1 H, dd, J ) 10.6, 10.6 Hz,
H-26), 3.45 (1 H, dd, J ) 10.6, 2.9 Hz, H′-26), 3.75 (1 H, bs,
H-6) 4.38 (1 H, bdd, J ) 14.6, 6.9 Hz, H-16), 4.52 (1 H, d, J )
11.8 Hz, CHPh), 4.57 (1 H, d, J ) 11.8 Hz, CH′Ph), 7.32 (5 H,
m, C6H5); 13C NMR (62.5 MHz) δ 14.4, 15.6, 16.4, 17.0, 20.7,
28.1, 28.6, 29.8, 30.1, 31.2, 31.6, 31.9, 35.6, 38.3, 39.6, 39.9,
40.4, 41.4, 47.2, 54.1, 55.9, 62.0, 66.7, 69.7, 71.6, 78.1, 80.6,
109.2, 127.3, 127.4 (× 2), 128.2 (× 2), 138.8; HR EIMS m/z
522.3734 (calcd 522.3709 for C34H50O4).
(25R)-3â,6â-Bis(ben zyloxy)-5r-sp ir osta n e (8). To a sus-
pension of NaH (0.20 g, 8.52 mmol) in THF (1 mL) at 0 °C
was added a solution of 7 (1.75 g, 3.35 mmol) in THF (9 mL).
After the solution was stirred for 0.5 h, BnBr (1.2 mL, 10.2
mmol) and TBAI (0.09 g, 0.24 mmol) were added. The

4442 J . Org. Chem., Vol. 63, No. 13, 1998
Izzo et al.
11: [R]D -55.5 (c ) 2.6, CHCl3); 1H NMR (250 MHz, CDCl3)
δ 0.04 (6 H, s, (CH3)2-Si), 0.81 (3 H, s, Me-18), 0.87 (3H, d, J
) 6.7 Hz, Me-27), 0.89 (9 H, s, (CH3)3-C), 0.96 (3 H, d, J )
6.0 Hz, Me-21), 1.09 (3 H, s, Me-19), 3.34 (1 H, dd, J ) 10.9,
6.5 Hz, H-26), 3.36 (1 H, m, H-3), 3.45 (1 H, dd, J ) 10.9, 5.8
Hz, H′-26), 3.46 (1 H, bs, H-6), 4.37 (1 H, d, J ) 12.2 Hz,
CHPh), 4.54 (1 H, d, J ) 12.2, CH′Ph), 4.56 (2 H, s, CH2Ph),
7.32 (10 H, m, C6H5); 13C NMR (62.5 MHz, CDCl3) δ -5.4 (×
2) 13.8, 15.7, 16.7, 18.6, 20.4, 24.6, 25.9 (× 3), 28.2, 29.7, 31.2,
32.3, 33.3, 35.2, 35.7, 35.9, 36.0, 38.1, 38.9, 39.1, 43.3, 47.7,
50.4, 54.3, 68.2, 68.5, 69.8, 71.4, 78.3, 79.2, 126.9 (× 3), 127.1,
127.3, 127.5 (× 2), 128.1 (× 2), 128.3 (× 2), 139.1, 139.6, 218.7;
EIMS m/z 728 (M+).
(25R)-26-[(ter t-Bu tyld im eth ylsilyl)oxy]-3â,6â-bis(ben -
zyloxy)-5r-ch olest-15-en -16-yl Tr ifla te (12). To a solution
of 11 (0.250 g, 0.340 mmol) in THF (4 mL) at -78 °C was added
LiN(TMS)2 (0.77 mL, 1.0 M in THF, 0.77 mmol). After 1 h
N-phenyltrifluoromethanesulfonimide (0.235 g, 0.660 mmol)
was added, and after an additional 0.3 h, the reaction mixture
was warmed to room temperature. The reaction was then
quenched by addition of water, concentrated in vacuo to
remove the excess of THF, and extracted with diethyl ether.
The organic layer was washed with a saturated solution of
NH4Cl, dried (Na2SO4), and concentrated in vacuo. The
residue was flash chromatographed (silica gel, 0-10% diethyl
ether in petroleum ether) to give 12 as a colorless oil (0.274 g,
94%).
graphed (silica gel, 5-20% ethyl acetate in petroleum ether)
to give 14 as a colorless oil (0.017 g, 54%).
14: [R]D -27.1 (c ) 1.0, CHCl3); 1H NMR (400 MHz, CDCl3)
δ 0.75 (3 H, s, Me-18), 0.90 (3 H, d, J ) 6.7 Hz, Me-27), 0.92
(3 H, d, J ) 6.0 Hz, Me-21), 1.08 (3 H, s, Me-19), 2.20 (1 H,
bd, J ) 13.7 Hz, H-7â), 3.39 (1 H, m, H-3), 3.42 (1 H, dd, J )
9.7, 6.7 Hz, H-26), 3.47 (1 H, bs, H-6), 3.49 (1 H, J ) 9.7, 5.9
Hz, H′-26), 4.35 (1 H, d, J ) 12.2 Hz, CHPh), 4.56 (2 H, s,
CH2Ph), 4.64 (1 H, d, J ) 12.2 Hz, CH′Ph), 5.74 (1 H, bd, J )
6.2 Hz, H-15 or H-16), 5.81 (1 H, bd, J ) 5.8 Hz, H-15 or H-16),
7.29 (10 H, m, C6H5); 13C NMR δ (100 MHz, CDCl3) 12.8, 15.6,
16.5, 18.4, 20.7, 23.8, 28.0, 28.2, 32.1, 32.4, 33.5, 35.1, 35.8,
36.1, 36.4, 37.7, 38.2, 48.0, 49.6, 55.0, 61.5, 62.3, 68.5, 69.7,
71.2, 78.4, 79.2, 126.8 (× 2), 127.0, 127.3, 127.6 (× 2), 128.1
(× 2), 128.3 (× 2), 130.9, 133.7, 139.1, 139.7; HR EIMS m/z
598.4377 (calcd 598.4386 for C41H58O3).
(25R)-3â,6â-Bis(ben zyloxy)-15â,16â-epoxy-5r-ch olestan -
26-ol (15). To a solution of 14 (0.007 g, 0.012 mmol) in
methylene chloride (0.5 mL) at 0 °C was added MCPBA (0.004
g, 0.024 mmol). After 5 h the reaction mixture was quenched
with a saturated solution of Na2SO3 (1 mL), extracted with
methylene chloride, dried (Na2SO4), and concentrated in vacuo.
The residue was flash chromatographed (silica gel, 0-2%
methanol in methylene chloride) to give 15 as a colorless oil
(0.004 g, 57%).
15: [R]D -19.7 (c ) 0.5, CHCl3); 1H NMR (400 MHz, CDCl3)
δ 0.92 (3 H, s, Me-18), 0.93 (6 H, d, J ) 7.0 Hz, Me-27 and
Me-21), 1.05 (1 H, d, J ) 11.6 Hz, H-14), 1.08 (3 H, s, Me-19),
2.26 (1 H, bd, J ) 13.7 Hz, H-7â), 3.06 (1 H, bs, H-15 or H-16),
3.20 (1 H, d, J ) 3.2 Hz, H-15 or H-16), 3.36 (1 H, m, H-3),
3.44 (1 H, dd, J ) 10.4, 6.7 Hz, H-26), 3.50 (1 H, bs, H-6), 3.51
(1 H, J ) 10.4, 6.0 Hz, H′-26), 4.43 (1 H, d, J ) 12.2 Hz, CHPh),
4.55 (2 H, s, CH2Ph), 4.59 (1 H, d, J ) 12.2 Hz, CH′Ph), 7.29
(10 H, m, C6H5); 13C NMR δ (100 MHz, CDCl3) 15.2, 16.4, 18.5,
20.3, 23.9, 27.2, 28.2, 29.6, 32.3 (× 2), 33.3, 35.3, 35.7, 36.1,
36.9, 37.2, 38.1, 48.0, 53.7, 54.7, 58.8, 59.3 (× 2), 64.1, 68.4,
69.8, 71.6, 78.3, 79.4, 126.9 (× 2), 127.0, 127.3, 127.5 (× 2),
128.1 (× 2), 128.3 (× 2), 139.1, 139.8; HR EIMS m/z 614.4306
(calcd 614.4335 for C41H58O4).
(25R)-26-[(ter t-Bu tyld im eth ylsilyl)oxy]-3â,6â-bis(ben -
zyloxy)-16-[(tr im eth ylsilyl)oxy]-5r-ch olest-15-en e (16). To
a solution of 11 (0.200 g, 0.275 mmol) in THF (2 mL) at -78
°C was added LiN(SiMe3)2 (0.55 mL, 1.0 M in THF, 0.55 mmol).
After 1 h Me3SiCl (0.10 mL, 0.83 mmol) was added, and after
additional 0.3 h, the mixture was allowed to warm to room
temperature. The reaction was then quenched by addition of
water, concentrated in vacuo to remove the excess of THF, and
extracted with petroleum ether. The organic phase was dried
(Na2SO4) and concentrated in vacuo to give crude 16 as a
colorless oil (0.240 g). 16 was used in the next step without
further purification.
16: 1H NMR (250 MHz, CDCl3) δ 0.07 (6 H, s, (CH3)2-Si),
0.24 (9 H, s, (CH3)3-Si), 0.91 (3 H, s, Me-18), 0.92 (3 H, d, J )
6.7 Hz, Me-27), 0.95 (9 H, s, (CH3)3-C), 1.09 (3 H, d, J ) 6.0
Hz, Me-21), 1.18 (3 H, s, Me-19), 3.37 (1 H, m, H-3), 3.38 (1 H,
dd, J ) 9.8, 6.7 Hz, H-26), 3.48 (1 H, dd, 9.8, 5.9 Hz, H′-26),
3.49 (1 H, bs, H-6), 4.39 (1 H, d, J ) 12.2 Hz, CHPh), 4.58 (1
H, s, CH2Ph), 4.61 (1 H, bs, H-15), 4.66 (1 H, d, J ) 12.2 Hz,
CH′Ph), 7.33 (10 H, m, C6H5); 13C NMR (62.5 MHz, CDCl3) δ
-5.3 (× 2), -5.4 (× 3), 13.6, 15.6, 16.7, 18.3, 19.4, 20.4, 22.6,
25.2, 26.0 (× 3), 28.1, 28.3, 32.1, 32.4, 33.7, 35.3, 35.9, 36.1,
36.7, 36.9 38.1, 48.1, 49.1, 54.8, 56.6, 61.3, 68.6, 69.8, 71.4,
78.5, 79.5, 101.2, 126.9 (× 2), 127.0, 127.3, 127.5 (× 2), 128.1
(× 2), 128.3 (× 2), 139.1, 139.8, 158.7.
12: [R]D -8.22 (c ) 2.0, CHCl3); 1H NMR (250 MHz, CDCl3)
δ 0.08 (6 H, s, (CH3)2-Si), 0.91 (3 H, d, J ) 6.7 Hz, Me-27),
0.94 (9 H, s, (CH3)3-C), 0.96 (3 H, s, Me-18), 1.04 (3 H, d, J )
6.0 Hz, Me-21), 1.12 (3 H, s, Me-19), 3.39 (1 H, m, H-3), 3.40
(1 H, dd, J ) 9.7, 6.5 Hz, H-26), 3.44 (1 H, J ) 9.7, 5.9 Hz,
H′-26), 3.51 (1 H, bs, H-6), 4.41 (1 H, d, J ) 12.2 Hz, CHPh),
4.59 (2 H, s, CH2Ph), 4.63 (1 H, d, J ) 12.2 Hz, CH′Ph), 5.72
(1 H, bs, H-15), 7.33 (10 H, m, C6H5); 13C NMR (62.5 MHz,
CDCl3) δ -5.4 (× 2), 13.6, 15.5, 16.6, 19.2, 20.2, 25.0, 25.9 (×
3), 27.3, 28.1, 31.5, 32.3, 33.3, 35.0, 35.7, 36.0, 36.1, 36.1, 36.4,
38.0, 47.9, 50.5, 54.5, 56.4, 60.4, 68.4, 69.8, 71.6, 78.2, 79.0,
116.2, 118.4 (q), 126.9 (× 2), 127.1, 127.3, 127.5 (× 2), 128.1
(× 2), 128.3 (× 2), 139.0, 139.5, 153.1; HR EIMS m/z 860.4648
(calcd 860.4693 for C48H71F3O6SSi).
(25R)-26-[(ter t-Bu tyld im eth ylsilyl)oxy]-3â,6â-bis(ben -
zyloxy)-5r-ch olest-15-en e (13). To a solution of 12 (0.038
g, 0.045 mmol) in THF (2 mL) were added LiCl (0.008 g, 0.200
mmol), Pd(PPh3)4 (0.002 g, 0.002 mmol), and Bu3SnH (0.018
mL, 0.062 mmol). The reaction mixture was refluxed for 16
h, then quenched with water (1 mL), concentrated in vacuo to
remove the excess of THF, and extracted with petroleum ether.
The organic layer was washed with a solution of NH4OH (10%
in water), and then with brine and finally dried (Na2SO4) and
concentrated in vacuo. The residue was flash chromato-
graphed (silica gel, 0-1% diethyl ether in petroleum ether) to
give 13 as a colorless oil (0.016 g, 50%).
13: [R]D -6.5 (c ) 1.8, CHCl3); 1H NMR (250 MHz, CDCl3)
δ 0.07 (6 H, s, (CH3)2-Si), 0.77 (3 H, s, Me-18), 0.88 (3 H, d, J
) 6.7 Hz, Me-27), 0.91 (9 H, s, (CH3)3-C), 0.92 (3 H, d, J )
6.0 Hz, Me-21), 1.10 (3 H, s, Me-19), 3.36 (1 H, m, H-3), 3.37
(1 H, dd, J ) 9.7, 6.5 Hz, H-26), 3.47 (1 H, J ) 9.7, 5.9 Hz,
H′-26), 3.49 (1 H, bs, H-6), 4.35 (1 H, d, J ) 12.2 Hz, CHPh),
4.57 (2 H, s, CH2Ph), 4.65 (1 H, d, J ) 12.2 Hz, CH′Ph), 5.79
(1 H, bd, J ) 6.2 Hz, H-15 or H-16), 5.83 (1 H, bd, J ) 5.8 Hz,
H-15 or H-16), 7.35 (10 H, m, C6H5); 13C NMR (62.5 MHz,
CDCl3) δ -5.3 (× 2), 12.8, 15.6, 16.7, 18.3, 18.5, 20.8, 23.8,
26.0 (× 3), 28.0, 28.3, 32.2, 32.5, 33.5, 35.2, 35.7, 36.1, 36.5,
37.7, 38.3, 48.1, 49.6, 55.1, 61.5, 62.4, 68.5, 69.8, 71.3, 78.5,
79.3, 126.9 (× 2), 127.1, 127.3, 127.5 (× 2), 128.1 (× 2), 128.3
(× 2), 130.8, 133.8, 139.2, 139.7; HR EIMS m/z 712.5238 (calcd
712.5251 for C47H72O3Si).
(25R)-3â,6â-Bis(ben zyloxy)-5r-ch olest-15-en -26-ol (14).
To a solution of 13 (0.037 g, 0.052 mmol) in THF (0.5 mL) was
added Bu4NF (0.1 mL, 1 M in THF, 0.1 mmol). After 16 h the
reaction mixture was quenched with water (1 mL), concen-
trated in vacuo to remove the excess of THF, and extracted
with ethyl acetate. The organic layer was dried (Na2SO4) and
concentrated in vacuo, and the residue was flash chromato-
(25R)-3â,6â-Bis(ben zyloxy)-5r-ch olesta n e-15r,26-d iol-
16-on e (18). To a solution of 16 (0.220 g 0.275 mmol) in CH2-
Cl2 at 0 °C was added dimethyldioxirane (3.3 mL 0.1 M in
acetone, 0.33 mmol). After 1 h the mixture was concentrated
in vacuo, and the residue was dissolved in acetone (4 mL).
Camphorsulfonic acid (0.01 g, 0.04 mmol) was added, and the
mixture was left at 4 °C for 16 h. The reaction mixture was
then diluted with water (2 mL), concentrated in vacuo to
remove the excess of acetone, extracted with chloroform, dried
(Na2SO4), and concentrated in vacuo. The crude residue was

(25R)-5R-Cholestane-3â,6â,15R,16â,26-pentol
J . Org. Chem., Vol. 63, No. 13, 1998 4443
purified by flash chromatography (0-1% methanol in chloro-
form) to give 18 (0.123 g, 71%, overall yield) as a white solid.
18: mp 53-55 °C; [R]D -31.2 (c ) 1.0, CHCl3); 1H NMR
(250 MHz, CDCl3) δ 0.88 (3 H, s, Me-18), 0.92 (3 H, d, J ) 6.7
Hz, Me-27), 1.01 (3 H, d, J ) 6.0 Hz, Me-21), 1.12 (3 H, s,
Me-19), 3.37 (1 H, m, H-3), 3.39 (1 H, dd, J ) 9.8, 6.7 Hz, H-26),
3.49 (1 H, dd, J ) 9.8, 5.9 Hz, H′-26), 3.50 (1 H, bs, H-6), 3.59
(1 H, d, J ) 11.5 Hz, H-15), 4.39 (1 H, d, J ) 12.2 Hz, CHPh),
4.57 (2 H, bs, CH2Ph), 4.63 (1 H, d, J ) 12.2 Hz, CH′Ph), 7.33
(10 H, m, C6H5); 13C NMR (62.5 MHz) δ 15.7, 15.8, 16.5, 19.3,
20.3, 24.4, 28.1, 29.8, 31.2, 32.2, 33.1, 34.9, 35.1, 35.5, 36.0,
38.1, 39.1, 39.7, 47.4, 53.9, 56.1, 64.5, 68.1, 69.7, 71.3, 76.6,
77.2, 78.2, 79.1, 126.8 (× 2), 127.2, 127.4 (× 2), 128.0 (× 2),
128.2 (× 2), 139.0, 139.8, 213.1; HR EIMS m/z 630.4256 (calcd
630.4284 for C41H58O5).
(25R)-3â,6â-Bis(b en zyloxy)-5r-ch olest a n e-15r,16r,26-
tr iol (19) a n d (25R)-3â,6â-Bis(ben zyloxy)-5r-ch olesta n e-
15r,16â,26-tr iol (20). (a ) Red u ction w ith LiAlH 4. To a
solution of 18 (0.042 g, 0.67 mmol) in diethyl ether (2 mL) at
0 °C was added LiAlH4 (0.2 mL, 1.0 M in THF, 0.2 mmol).
The reaction mixture was stirred for 0.2 h and quenched with
ethyl acetate (0.5 mL) and NH4OH (0.2 mL, 30% aqueous
4.06 (1 H, dd, J ) 7.4, 1.6 Hz, H-16), 4.37 (1 H, d, J ) 12.2
Hz, CHPh), 4.55 (2 H, bs, CH2Ph), 4.60 (1 H, d, J ) 12.2 Hz,
CH′Ph), 7.33 (10 H, m, C6H5); 13C NMR (100 MHz, CDCl3) δ
14.6, 15.8, 16.7, 17.9, 20.6, 23.5, 28.2, 29.3, 30.2, 32.3, 33.2,
35.1, 35.4, 35.8, 35.9, 38.4, 40.2, 43.8, 47.5, 54.2, 58.6, 59.9,
68.3, 69.7, 71.4, 78.3, 79.3, 82.4, 83.9, 126.9 (× 2), 127.0, 127.3,
127.5 (× 2), 128.1 (× 2), 128.3 (× 2), 139.1, 139.9; HR FABMS
m/z 633.4487 (calcd 633.4519 for C41H61O5, [M + H]+).
(25R)-5r-Ch olesta n e-3â,6â,15r,16â,26-p en tol (1a ). To a
solution of 20 (0.068 g, 0.107 mmol) in absolute ethanol (2.5
mL) was added palladium on activated carbon (7 mg). The
flask was evacuated (20 Torr) and flushed with hydrogen three
times. The reaction mixture was then stirred vigorously under
an atmosphere of hydrogen for 5 h. The reaction mixture was
filtered through a pad of silica gel and concentrated to give
1a (0.048 g, 0.104 mmol, 100%).
1
1a : mp 133-135 °C; [R]D +29.5 (c ) 2.3, MeOH); H NMR
(400 MHz, CD3OD3) δ 0.93 (3 H, d, J ) 6.9 Hz, Me-27), 0.95 (3
H, s, Me-18), 0.99 (3 H, d, J ) 6.6 Hz, Me-21), 1.07 (3 H, s,
Me-19), 2.18 (1 H, bd, J ) 14.3 Hz, H-7â), 3.36 (1 H, dd, J )
10.5, 6.8 Hz H-26), 3.44 (1 H, J ) 10.5, 5.9 Hz H′-26), 3.57 (1
H, m, H-3), 3.77 (1 H, bs, H-6), 3.78 (1 H, dd, overlapped with
H-6, H-15), 4.00 (1 H, dd, J ) 7.6, 2.0 Hz, H-16), 4.37 (1 H, d,
J ) 12.2 Hz, CHPh), 4.55 (1 H, bs, CH2Ph), 4.60 (1 H, d, J )
12.2 Hz, CH′Ph), 7.33 (10 H, m, C6H5); 13C NMR (100 MHz,
CD3OD3) δ 15.0 (C-18), 16.3 (C-19), 17.1 (C-27), 18.6 (C-21),
21.9 (C-11), 24.8 (C-23), 30.9 (C-20), 31.2 (C-8), 32.2 (C-2), 34.7
(C-24), 36.3 (C-4), 36.6 (C-10), 36.9 (C-25), 37.3 (C-22), 39.8
(C-1), 40.6 (C-7), 41.8 (C-12), 44.7 (C-13), 48.8 (C-5), 55.7 (C-
9), 60.0 (C-17), 61.1 (C-14), 68.6 (C-26), 72.4 (C-3), 72.5 (C-6),
82.9 (C-16), 85.0 (C-15); HR FIBMS m/z 453.3577 (calcd
453.3580 for C27H49O5, [M + 1]+).
solution). Filtration through
a short pad of Celite and
concentration in vacuo gave a crude residue which was purified
by flash chromatography (0-1% methanol in chloroform) to
give 19 as colorless oil (0.017 g, 40%) and 20 (0.021 g, 50%) as
white solid.
(b) Red u ction w ith BH3‚SMe2. To a solution of 18 (0.022
g, 0.35 mmol) in THF (3 mL) at 0 °C was added BH3‚SMe2
(0.055 mL, 2 M in THF, 0.11 mmol). After 2 h the mixture
was quenched with 0.1 M HCl, concentrated in vacuo to
remove the excess of THF, extracted with chloroform (6 mL),
and washed with a saturated solution of NaCl. The organic
phase was then dried (Na2SO4) and concentrated to give a
crude residue which was purified by flash chromatography (0-
1% methanol in chloroform) to give 20 (0.013 g, 58%).
19: [R]D -6.3 (c ) 1.1, CHCl3); 1H NMR (400 MHz, CDCl3)
δ 0.70 (3 H, s, Me-18), 0.91 (3 H, d, J ) 7.0 Hz, Me-27), 0.95
(3 H, d, J ) 6.6 Hz, Me-21), 1.07 (3 H, s, Me-19), 2.43 (1 H,
bd, J ) 14.3 Hz, H-7â), 3.36 (1 H, m, H-3), 3.47 (3 H, m, H-6
and H2-26), 3.64 (1 H, dd, J ) 8.2, 8.0 Hz, H-15), 3.80 (1 H,
dd, J ) 7.2, 7.0 Hz, H-16), 4.37 (1 H, d, J ) 12.2 Hz, CHPh),
4.56 (2 H, m, CH2Ph), 4.60 (1 H, d, J ) 12.2 Hz, CH′Ph), 7.33
(10 H, m, C6H5); 13C NMR (100 MHz, CDCl3) δ 15.3, 15.8, 16.6,
19.2, 20.5, 23.8, 28.3, 30.2, 32.4, 33.5, 33.9, 35.2, 35.6, 35.7,
36.0, 38.5, 39.8, 40.3, 47.5, 54.2, 59.8, 63.6, 68.4, 69.8, 71.4,
72.8, 74.8, 78.4, 79.4, 126.9 (× 3), 127.4, 127.6 (× 2), 128.1 (×
2), 128.3 (× 2), 139.1, 139.9; HR FABMS m/z 633.4492 (calcd
633.4519 for C41H61O5, [M + H]+).
Ack n ow led gm en t. This work has been supported
by the European Commission, MAST-III program (con-
tract no. MAS3-CT95-0032), by MURST (40%), and by
CNR (Rome). The mass spectra were obtained from the
“Servizio di Spettrometria di Massa del CNR e dell′Uni-
versita` di Napoli” and from the CRIAS (Centro Inter-
dipartimentale di Analisi Strumentale) dell’Universita`
di Napoli “Federico II”; the staffs are gratefully acknowl-
edged.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
compounds 1a and 3-20, 13C NMR spectra of compounds 1a ,
3-11, 13-15, and 18-20, and two-dimensional spectra of
compounds 15, 18, and 19 (42 pages). This material is
contained in libraries on microfiche, immediately follows this
article in the microfilm version of the journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
20: mp 61-63 °C; [R]D -1.5 (c ) 2.0, CHCl3); 1H NMR (400
MHz, CDCl3) δ 0.88 (3 H, s, Me-18), 0.89 (3 H, d, J ) 7.0 Hz,
Me-27), 0.95 (3 H, d, J ) 6.6 Hz, Me-21), 1.07 (3 H, s, Me-19),
2.29 (1 H, bd, J ) 14.3 Hz, H-7â), 3.36 (1 H, m, H-3), 3.45 (3
H, m, H-6 and H2-26), 3.75 (1 H, dd, J ) 10.0, 1.6 Hz, H-15),
J O980266C