Calcitriol derivatives with two different side chains at C-20. II. Diastereoselective syntheses of the metabolically produced 24(R)-hydroxygemini

Article abstract of DOI:10.1021/jm049340b

Vitamin D derivatives containing two side chains emanating at C-20 are known as gemini. We have recently synthesized two gemini which are related to calcitriol and 19-norcalcitriol containing two identical side chains. The metabolism of these species invo

Full text of DOI:10.1021/jm049340b

6476
J. Med. Chem. 2004, 47, 6476-6484
Calcitriol Derivatives with Two Different Side Chains at C-20. II.
Diastereoselective Syntheses of the Metabolically Produced
24(R)-Hydroxygemini1
Hubert Maehr,* Milan R. Uskokovic, Luciano Adorini, and G. Satyanarayana Reddy†
Bioxell, Inc., Nutley, New Jersey 07110
Received August 10, 2004
Vitamin D derivatives containing two side chains emanating at C-20 are known as gemini.
We have recently synthesized two gemini which are related to calcitriol and 19-norcalcitriol
containing two identical side chains. The metabolism of these species involves 24(R)-
hydroxylation on one of the side chains. To determine the outcome of this diastereospecific
transformation, we synthesized both C-20 epimeric pairs containing the 24(R)-hydroxy group
in the gemini and 19-norgemini series. On the basis of the availability of these reference
compounds, it was shown that the metabolic hydroxylation occurred at the pro-R side chain in
both gemini compounds. In comparison to the parent compounds, the 24-hydroxygemini required
higher doses to increase blood calcium levels in mice and to suppress INF-γ release in MLR.
1. Introduction
The calcitriol derivatives 1a and 1b featuring two
identical side chains emanating at C-20 exert the full
spectrum of calcitriol activities such as binding to the
VDR, suppression of increased parathyroid hormone
levels in nephrectomized rats, INF-γ release in MLR
cells, stimulation of HL-60 leukemia cell differentiation,
and inhibition of solid-tumor cell proliferation.2-4 The
major metabolic conversion of calcitriol (1R,25(OH)2D3)
proceeds through a series of side-chain modifications to
the biologically inactive calcitroic acid. This cascade
is initiated by the 24R-hydroxylase leading to
1R,24(R),25(OH)3D3, followed by 24-oxidation, 23-
hydroxylation, and oxidative chain cleavage at C23/24
leading to calcitroic acid.5-8 Similar to the introduction
of a double bond at C-16, epimerization at C-20 can
arrest the degradative sequence at the 24-oxo level.7
This phenomenon moved gemini 1a and 1b to the focal
point of interest by raising several questions as the two
calcitriol side chains at C-20 in gemini mimic the
presence of both calcitriol C-20 epimers in one molecule.
Would gemini, similar to calcitriol, also be monohy-
droxylated? In other words, would the inherent presence
of the “20-epi-feature” also arrest the metabolic degra-
dation at the 24-oxo stage followed by initial 24-
hydroxylation? Would the hydroxylation produce a
24(R)-metabolite? Most importantly, which of the two
side chains would be subject to metabolism as indicated
by initial hydroxylation? And, would the regio- and
stereospecificity of the hydroxylation remain invariant
to changes in the A-ring?
2. Metabolic Studies and Preliminary
Pharmacological Results
Metabolism in bone cells and in perfused rat kidney
converted 1a and 1b each to a single 24-hydroxy species.
A 24(R)-hydroxylation creates a new stereocenter at
C-20 and thus the possibility of two side-chain hydroxyl-
ated epimers of the 24(R),20(R)- and 24(R),20(S)-
configurations as shown in 2a, 2b and 3a, 3b, respec-
tively. Synthetic access to these species, as described
herein, allowed the determination as to which of the two
side chains in 1a and 1b are the preferred metabolic
substrates, and the evaluation of their potential as
pharmaceutically useful entities.
* Author to whom correspondence should be addressed. Mailing
address: Bioxell Inc., 340 Kingsland Street, Nutley, NJ 07110.
Phone: 973-235-3224: Fax: 973-235-4056: E-mail: Hubert.maehr@
roche.com.
† Department of Chemistry, Brown University, 324 Brook St., Box
H, Providence, RI 02912. The contribution of G.S.R. was supported by
US Public Health Service Grant DK 52488.
Calcitriol (1R,25(OH)2D3) was shown by rat kidney
perfusion9-11 to be rapidly metabolized to calcitroic acid.
10.1021/jm049340b CCC: $27.50 © 2004 American Chemical Society
Published on Web 11/20/2004

Diastereoselective Syntheses of 24(R)-Hydroxygemini
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 26 6477
Table 1. Calcium Levels (mg/dL) with Standard Errors (SE) after Four Diurnal Drug Administrations
drug concentrations (mg/kg)
vehicle
MTD
(mg/kg)
drug
(miglyol)
0.3
1
3
10
30
100
1a
2a
3a
1b
2b
3b
9.33 (0.08)
10.00 (0.19)
9.37 (0.08)
9.90 (0.19)
12.30 (0.44)
9.73 (0.11)
9.63 (0.15)
12.50 (0.72)
9.57 (0.15)
9.43 0.08)
16.50 (0.07)
9.77 (0.22)
9.43 (0.16)
3
30
9.63 (0.08)
9.53 (0.23)
11.07 (0.25)
9.70 (0.07)
9.73 (0.11)
10.77 (0.08)
9.57 (0.15)
>100
<1
3
9.80 (0.07)
16.73 (0.80)
9.60 (0.12)
9.80 (0.07)
3
More than 50% of the substrate disappeared from the
kidney perfusate due to its rapid metabolism mediated
by the C-24-oxidation pathway. The gemini compounds
1a and 1b, on the other hand, were metabolically more
stable as only about 20% of the substrate disappeared
from the kidney perfusate. Moreover, only one polar
metabolite each was detected in the perfusates, appar-
ently resisting further degradation. The chemospecific-
ity to produce a single metabolite from each gemini was
confirmed by chromatography and mass spectrometry
and the regiospecificity at the C24 site by periodate-
mediated glycol cleavage. The same 24-hydroxy metabo-
lites were also produced in rat osteosarcoma cells (UMR
106). Considering the heterotopic environment of the
two identical side chains in 1a and 1b, metabolic mono-
24-hydroxylation can potentially occur either on their
pro-R or pro-S side chain. More specifically, hydroxyl-
ation of the pro-R chain in 1b, as shown in 2b, is
tantamount to hydroxylation of the chain with the
natural configuration. At first glance, one could there-
fore speculate that the pro-R chain should be the
preferred substrate, thus identifying 2a and 2b as the
more likely metabolic products of 1a and 1b. On the
other hand, the observation that 20-epicalcitriol is
hydroxylated at a higher rate than its natural 20(R)
counterpart might suggest selective hydroxylation at the
unnatural side chain thus rendering 3a and 3b as the
more likely metabolic prospects. A comparison of each
epimeric pair with the corresponding metabolic products
has now indeed revealed the natural pro-R side chain
as the exclusive metabolic substrate. Figure 1 illustrates
the identification of the major metabolic product of 1b
as 2b by comparison of its HPLC profile with those of
the synthetic specimens 2b and 3b. These studies were
repeated with 1a as substrate. The major metabolite
was again compared with 2a and 3a and unambiguously
identified as 2a. More specifically, the substrates 1a and
1b were eluted from the HPLC column at 21.4 and 18.6
min, respectively, and produced but one major metabo-
lite each upon incubation with osteosarcoma sells (UMR
106) that eluted at 37.5 and 30.9 min, respectively.
These elution times are congruent with the ones exhib-
ited by the 20R isomers 2a and 2b and deviant from
the times of 32.9 and 27.7 min, characteristic of the 20S
isomers 3a and 3b, respectively.
Figure 1. HPLC comparisons of the metabolite derived from
1b with the 20(R) and 20(S) epimers 2b and 3b, respectively.
Table 2. IC50 Values for INF-γ Release in MLR
MLR IFN-γ IC50 (pM)
drug characteristic
drug
drug (D)a
drug/calcitriol
19-nor
1a
2a
3a
1b
2b
3b
44 (8)
781 (254)
3856 (2800)
4 (1)
1.8
31
160
0.1
2.5
18
20(R)
20(S)
natural A-ring
20(R)
20(S)
80 (17)
579 (4)
a D = average error, N = 3.
taining the 19-nor feature.12 Concomitant with this
improved tolerance, correspondingly higher doses were
required to inhibit INF-γ release in MLR as shown in
Table 2. Regardless of the A-ring constitution, hydroxyl-
ation at the pro-R side chain increases the required dose
for INF-γ release inhibition by a factor of ca. 20; an
equivalent change at the pro-S side chain, however,
necessitates a ca. 100-fold increase. A comparison with
calcitriol confirms that 24-hydroxylation in the series
of compounds containing the natural A-ring increases
the required dose for INF-γ release inhibition less
drastically than those in the 19-nor category.
Table 1 shows the minimum tolerated dose (µg/kg) in
mice based on calcium levels (mg/dL) after 4 diurnal
drug administrations. In general, the 19-norgemini 1a,
2a, and 3a were better tolerated than the counterparts
containing the “natural” A-ring (i.e., the 3,5-dihydroxy-
2-methylenecyclohexylidene ring of calcitriol). No in-
crease in calcium levels was observed when 3a was
administered to mice at a dose as high as 100 µg/kg.
These comparisons corroborate DeLuca’s discovery of
diminished hypercalcemic activity of compounds con-

6478 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 26
Maehr et al.
Scheme 1
Scheme 2
3. Synthetic Methods13
For the synthesis of the two epimeric pairs 2a, 3a and
2b, 3b we chose the convergent and established Wittig-
Horner reaction employing the Lythgoe phosphine oxide
coupling protocol14-16 in which the two elaborated
ketones 19 and 28 are each linked to 20a and 20b as
illustrated in Scheme 1. A single step removed all five
silyl protecting groups in each member of the pairs 21a,
21b and 29a, 29b and led to the target compounds 2a,
2b and 3a, 3b. The different protective groups in 19 and
28 are the result of two dissimilar pathways investi-
gated for their synthesis.
We have previously described two different desym-
metrization processes of the gemini side chains.17,18 One
of them, pertinent to the current synthetic task, and
diagrammatically represented in Scheme 2, provides the
pair of epimeric iodoalkenes 8 and 9. Their synthesis
commenced with the 4-O-(tert-butyldimethylsilyl)-Lyth-
goe diol 4 that was first converted to alkenol 5. A
subsequent hydroboration furnished the epimeric pair
of diols 6 and 7, easily separated by chromatography
and transformed to the iodides 8 and 9, respectively.
The assignment of absolute configuration of 6 and 7
rests on a crystallographic analysis of a derivative of
7.18 Consequently, diol 7 with the “natural” side chain,
corresponding to the 20(R) designation in the vitamin
D nomenclature, exhibits the shorter retention time on
a silica gel column than its epimeric counterpart 6.
The syntheses of the pairs 2a, 2b and 3a, 3b were
achieved by two different routes as indicated in Scheme
1. The sequence of steps leading to 2a and 2b involves
an elaborate functional-group protection strategy, previ-
ously established,19 with the aim to ensure the integrity
of the trans-octahydroindene ring juncture. This se-
quence, illustrated in Scheme 3 for the synthesis of 2a
and 2b, commenced with the conversion of diol 618 to
the iodo alcohol 8 followed by iodide displacement with
sodium benzenesulfinate. The resulting alcohol 10a was
silylated to afford 10b and then lithiated and treated
with the 2-oxiranyl-2-propanol, prepared in situ from
11, leading to the epimeric diol mixture 12.
A subsequent reductive desulfonylation gave 13a but
also some partially desilylated 13b. Rather than com-
pletely desilylating this mixture to obtain the tetraol
13c directly, we opted for the selective removal of the
trimethylsilyl group providing 13b as a crystalline
intermediate and hence the opportunity for additional
purification and characterization. A subsequent treat-
ment with fluorosilicic acid then produced the tetraol
13c. Treatment of 13c with acetone and 2,2-dimethoxy-
propane with pyridinium tosylate as catalyst gave a
mixture of 15a and a more polar material, assumed to
be the acetal 14. Somewhat surprisingly, it was a brief
aqueous treatment of this mixture that converted this
more polar substance quantitatively to 15a. A subse-
quent reaction with acetic anhydride in pyridine led to
the O-acetyl compound 15b, and 80% aqueous acetic
acid at 68 °C hydrolyzed the acetal moiety within 2.5 h
to produce 16. In an attempt to balance product stability
with the ease of final removal of the five silyl ethers, as
present in the projected condensation product 21b, we
introduced just one bulky silyl ether moiety and em-
ployed trimethylsilyl ether protection for the two ter-
tiary hydroxyl groups. Indeed, O-silylation with thexyl-
dimethylsilyl chloride proceeded regioselectively to 17a,
and a following treatment with 1-(trimethylsilyl)imid-
azole gave 17b. The 4-acetoxy group was then removed
by treatment with lithium aluminum hydride, and the
resulting alcohol 18 was oxidized to the ketone 19 using
pyridinium dichromate. The standard coupling protocol,
employing 20a and 20b as Wittig-Horner components,
gave 21a and 21b, respectively, and single treatments
with tetrabutylammonium fluoride furnished the target
compounds 2a and 2b.

Diastereoselective Syntheses of 24(R)-Hydroxygemini
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 26 6479
Scheme 3
For the syntheses of 3a and 3b we designed shorter
routes as shown in Scheme 4. The conversion of diol 7
to 23a via the iodo alcohol 9, phenyl sulfone 22a,
trimethylsilyl derivative 22b, and subsequent conden-
sation of 22b with 11 was conducted in a fashion very
similar to the corresponding steps described previously
for the other epimer. The trimethylsilyl group in the
epimeric pair 23a, however, was now removed prior to
reductive desulfonylation thereby avoiding a mixture of
mono- and disilylated species as observed in the form
of 13a and 13b in the course of synthesis of the other
epimer. Thus, treating 23a with methanolic oxalic acid
gave 23b, and stirring of this triol with sodium amalgam
led to 24a. A subsequent treatment with fluorosilicic
acid in acetonitrile served for the generation of the
tetraol 24b. In a major deviation from the former
synthetic pathway, 24b was treated with 4-methoxy-
benzylidene dimethyl acetal and pyridinium tosylate to
produce the oxolane 25, which was oxidized with pyri-
dinium dichromate to ketone 26. A considerable syn-
thetic improvement was thus realized as the 4-methoxy-
benzylidene acetal proved to be sufficiently acid labile
to permit its hydrolysis under conditions that did not
compromise the trans ring juncture of the 7a-methyl-
octahydro-4-indenone system. A subsequent treatment
with either 80% acetic acid or 1 N methanolic oxalic
acid, the latter previously employed for the selective
hydrolysis of the tertiary trimethylsilyl ether function
in both 13a and 23a, converted 26 to the ketotriol 27,
which was treated with chlorotriethylsilane in N,N-
dimethylformamide and imidazole to produce rapidly
the disilyl ether. Further reaction of the second tertiary
alcohol proceeded smoothly overnight, leading to 28,
which was condensed with 20a and 20b leading to 29a
and 29b, respectively. One deprotection step with tetra-
butylammonium fluoride liberated all five protected
hydroxyl groups in each of the two pentasilyl ethers to
furnish, after chromatographic purification, compounds
3a and 3b.
4. Experimental Section
All operations involving vitamin D analogues were con-
ducted in amber-colored glassware in a nitrogen atmosphere.
Tetrahydrofuran was distilled from sodium-benzophenone
ketyl just prior to its use, and solutions of solutes were dried
with sodium sulfate. Melting points were determined on a
Thomas-Hoover capillary apparatus and are uncorrected.
1
Optical rotations were measured at 25 °C. H NMR spectra
were recorded at 400 MHz in CDCl3 unless indicated other-
wise. UV spectra were recorded using methanol as solvent.
TLC was carried out on silica gel plates (Merck F-254) with
visualization under short-wavelength UV light or by spraying
the plates with 5% phosphomolybdic acid in methanol followed

6480 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 26
Maehr et al.
Scheme 4
by heating. Flash chromatography was carried out on 40-65
µm mesh silica gel. Preparative HPLC was performed on a 5
× 50 cm column and 15-30 µm mesh silica gel at a flow rate
of 100 mL/min. HPLC for metabolic studies was carried out
on a Zorbax Sil column, 9.4 × 250 mm using 15% 2-propanol
in hexane as isocratic mobile phase at a flow rate of 2 mL/
min. Quoted retention times refer to this system.
6(S)-7-Benzenesulfonyl-[(1R,3aR,4S,7aR)-4-(tert-butyl-
dimethylsilanyloxy)-7a-methyloctahydroinden-1-yl]-2-
methylheptan-2-ol (10a). A mixture of 8 (0.94 g, 1.8 mmol),
sodium benzenesulfinate (2.18 g, 13 mmol), and N,N-dimethyl-
formamide (31.8 g) was stirred at room temperature for 12 h
and then in a 40 °C bath for ca. 6 h until all educt was
converted as shown by TLC (1:4 ethyl acetate-hexane). The
solution was equilibrated with 1:1 ethyl acetate-hexane (120
mL) and 1:1 brine-water (45 mL). The organic layer was
washed with water (4 × 25 mL) and brine (10 mL), then dried,
and evaporated to leave a colorless oil, 1.0317 g. This material
was flash chromatographed using a stepwise gradient (1:9, 1:6,
and 1:3 ethyl acetate-hexane) to give 10a as a colorless oil,
0.930 g, 96%: 300 MHz 1H NMR δ -0.02 (3H, s), 0.00 (3H, s),
0.87 (9H, s), 0.88 (3H, s), 1.12 (1H, m), 1.20 (6H, s), 1.2-1.8
(18H, m), 1.81 (1H, m), 3.09 (2H, m), 3.97 (1H, brs), 7.59 (3H,
m), 7.91 2H, m). Anal. (C30H52O4SSi) C, H.
hexane (2.75 mL) was added dropwise. The temperature was
allowed to rise to -20 °C and maintained at that temperature
for 6 h. Reaction progress was monitored by TLC (1:4 ethyl
acetate-hexane) exhibiting the educt (Rf 0.71) and the two
epimeric diols 12 (Rf 0.09 and 0.12). Toward the end of the
reaction period the temperature was increased briefly to 0 °C
and lowered again to -10 °C, and then saturated ammonium
chloride (25 mL) was added followed by ethyl acetate (50 mL)
and enough water to dissolve the precipitated salts. The
resulting aqueous phase was extracted with ethyl acetate (15
mL). The combined extracts were washed with brine (15 mL),
dried, and evaporated. The resulting syrup was flash chro-
matographed using a stepwise gradient of 1:9, 1:6, 1:4, and
1:1 ethyl acetate-hexane to give 12 as a colorless syrup, 0.8586
g. This material was dissolved in a mixture of tetrahydrofuran
(30 mL) and methanol (18 mL), then 5% sodium amalgam (20
g) was added. The reductive desulfonylation was complete after
stirring of the mixture for 14 h. Progress of the reaction was
monitored by TLC (1:1 ethyl acetate-hexane), which showed
the disappearance of the epimeric 12 (Rf 0.63 and 0.74) and
the generation of 13a (Rf 0.79) and the partially desilylated
analogue 13b (Rf 0.16). The mixture was diluted with methanol
(20 mL) and stirred for 3 min, then ice (20 g) was added, the
mixture was stirred for 2 min, and the supernatant was
decanted into a mixture containing saturated ammonium
chloride (50 mL). The residue was repeatedly washed with
small amounts of tetrahydrofuran, which was also added to
the salt solution, which was then equilibrated with ethyl
acetate (80 mL). The aqueous layer was re-extracted once with
ethyl acetate (20 mL), and the combined extracts were washed
with brine (10 mL), then dried, and evaporated. The resulting
colorless oil, containing both 13a and 13b, was dissolved in
10 mL of a 1 N oxalic acid solution in methanol (prepared from
oxalic acid dihydrate), effecting the selective hydrolysis of the
trimethylsilyl ether within minutes. Calcium carbonate (1 g)
was added and the suspension stirred overnight and then
filtered. The filtrate was evaporated and the resulting residue
flash chromatographed using a stepwise gradient of 1:4, 1:2,
1:1, and 2:1 ethyl acetate-hexane, giving a residue of the triol
13b that crystallized in very fine branching needles from
acetonitrile, 0.45 g: mp 94-95 °C; [R]D +44.1° (methanol, c )
(1R,3aR,4S,7aR)-1-((S)-1-Benzenesulfonylmethyl-5-
methyl-5-trimethylsilanyloxyhexyl)-4-(tert-butyldimeth-
ylsilanyloxy)-7a-methyloctahydroindene (10b). 1-(Tri-
methylsilyl)imidazole (1 mL) was added to a solution of 10a
(0.800 g) in cyclohexane (10 mL), stirred overnight, and then
flash chromatographed using a stepwise gradient of hexane
and 1:39 and 1:19 ethyl acetate-hexane. The elution was
monitored by TLC (1:4 ethyl acetate-hexane) leading to 10b
1
as a colorless syrup, 0.792 g, 87%: 300 MHz H NMR δ 0.00
(3H, s), 0.02 (3H, s), 0.12 (9H, s), 0.90 (9 + 3H, s), 1.16 (1H,
m), 1.20 (6H, s), 1.2-1.6 (15H, m), 1.66-1.86 (3H, m), 3.10
(2H, m), 4.00 (1H, brs), 7.56-7.70 (3H, m), 7.93 (2H, m).
(1R,3R,6R)-6-[(3aR,4S,7aR)-4-(tert-Butyldimethylsilan-
yloxy)-7a-methyloctahydroinden-1-yl]-2,10-dimethyl-
undecane-2,3,10-triol (13b). A solution of 10b (0.7513 g, 1.23
mmol) and diol 11 (0.508 g, 1.85 mmol) in tetrahydrofuran (28
mL) was cooled to -35 °C, and then 2.5 M butyllithium in

Diastereoselective Syntheses of 24(R)-Hydroxygemini
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 26 6481
1
0.37); H NMR δ -0.005 (3H, s), 0.007 (3H, s), 0.89 (9H, s),
with a small amount of toluene to leave 16 as a colorless film
(0.303 g), which was used directly in the next step: 300 MHz
1H NMR δ 0.89 (3H, s), 1.17 (3H, s), 1.22 (6H, s), 1.56 (3H, s),
1.1-1.6 (21H, m), 1.6-2.0 (5H, m), 2.04 (3H, s), 3.32 (1H, brd,
J ) 10 Hz), 5.15 (1H, brs). A small amount was further purified
by flash chromatography (2:1 ethyl acetate-hexane). Anal.
(C25H46O5) C, H.
0.92 (3H, s), 1.15 (1H, m), 1.16 (3H, s), 1.21 (9H, s), 1.2-1.6
(19H, m), 1.67 (1H, m), 1.79 (2H, m), 1.90 (2H, m), 2.06 (1H,
m), 3.31 (1H, brd, J ) 10 Hz), 4.00 (1H, brs); LR-ES(-) m/z
533 (M + Cl), 497 (M - H); HR-ES(+) calcd for C29H58O4Si +
Na 521.3996, found 521.4003. Anal. (C29H58O4Si) C, H.
(1R,3R,6R)-6-((3aR,4S,7aR)-4-Hydroxy-7a-methylocta-
hydroinden-1-yl)-2,10-dimethylundecane-2,3,10-triol (13c).
A stirred solution of the triol 13b (0.4626 g, 0.927 mmol) in
acetonitrile (10 mL) and dioxane (0.7 mL) was cooled to 10
°C, and a fluorosilicic acid solution18 (2 mL) was added
dropwise. The cooling bath was removed and the 2-phase
system further diluted with acetonitrile (2 mL) and then
stirred at room temperature for 31/4 h. The disappearance of
educt was monitored by TLC (ethyl acetate). The mixture was
equilibrated with water (10 mL) and ethyl acetate (30 mL).
The aqueous phase was re-extracted with ethyl acetate (2 ×
20 mL), and the combined extracts were washed consecutively
with water (5 mL), brine (10 mL), and 1:1 brine-saturated
sodium hydrogen carbonate solution and then dried. The
residue was purified by flash chromatography using a stepwise
gradient from 1:1 to 2:1 ethyl acetate-hexane and neat ethyl
acetate to give a residue, which was taken up in 1:1 dichloro-
methane-hexane, filtered, and evaporated to furnish 13c as
amorphous solids, 0.3039 g (85%): [R]D +42.6° (methanol, c )
0.48); 1H NMR (DMSO-d6) δ 0.87 (3H, s), 0.97 (3H, s), 1.02
(3H, s), 1.04 (6H, s), 1.1-1.4 (18H, m), 1.5-1.8 (4H, m), 1.84
(1H, m), 2.99 (1H, dd, J ) 6 and 10 Hz), 3.87 (1H, brs), 4.02
(1H, s, OH), 4.05 (1H, s, OH), 4.16 (1H, d, OH, J ) 3.6 Hz),
4.20 (1H, d, OH, J ) 6.4 Hz); LR-ES(+) m/z 384 (M), 383 (M
- H); HR-ES(+) calcd for (M + Na) 407.3132, found 407.3134.
Acetic Acid (1R,3aR,4S,7aR)-1-[(1R,4R)-4-[Dimethyl-
(1,1,2-trimethyl-propyl)silanyloxy]-5-hydroxy-1-(4-hy-
droxy-4-methylpentyl)-5-methylhexyl]-7a-methyloctahy-
droinden-4-yl Ester (17a). A solution of the triol 16 (0.30
g), imidazole (0.68 g, 10 mmol) and dimethylthexylsilyl chloride
(1.34 g, 7.5 mmol) in N,N-dimethylformamide (6 g) was kept
at room temperature. After 48 h 4-(N,N-dimethylamino)-
pyridine (15 mg) was added and the mixture stirred for an
additional 24 h. Reaction progress was monitored by TLC
(ethyl acetate; 16, Rf 0.83; 17a, Rf 0.38). The mixture was
diluted with water (2 mL), stirred for 10 min, and then
distributed between ethyl acetate (45 mL) and water (20 mL).
The aqueous layer was extracted once with ethyl acetate (10
mL). The combined organic phases were washed with water
(4 × 12 mL) and brine (8 mL), then dried, and evaporated.
The residual oil was purified by flash chromatography using
a stepwise gradient of 1:9 and 1:4 ethyl acetate-hexane to give
17a as colorless syrup. A small amount of unreacted educt (80
mg) was eluted with ethyl acetate. The syrupy 17a was used
directly in the next step: 1H NMR δ 0.13 (3H, s), 0.14 (3H, s),
0.87 (6H, s), 0.91 (9H, m), 1.10 (1H, m), 1.14 (3H, s), 1.15 (3H,
s), 1.21 (6H, s), 1.1-1.6 (19H, m), 1.6-1.9 (5H, m), 1.94 (1H,
brd, J ) 12.8 Hz), 2.05 (3H, s), 3.38 (1H, brs), 5.15 (1H, brs).
Acetic Acid (1R,3aR,4S,7aR)-1-[(1R,4R)-4-[Dimethyl-
(1,1,2-trimethylpropyl)silanyloxy]-5-methyl-1-(4-methyl-
4-(trimethylsilanyloxy)pentyl)-5-(trimethylsilanyloxy)-
hexyl]-7a-methyloctahydroinden-4-yl Ester (17b). 1-(Tri-
methylsilyl)imidazole (0.90 mL, 6.1 mmol) was added to a
solution of 17a (0.2929 mg) in cyclohexane (6 mL), and the
mixture was stirred for 12 h and then flash chromatographed
(1:79 ethyl acetate-hexane) to yield 17b as a colorless syrup
(0.3372 g): 1H NMR δ 0.074 (3H, s), 0.096 (3H, s), 0.103 (9H,
s), 0.106 (9H, s), 0.82 (1H, m), 0.83 (6H, s), 0.88 (6 + 3H, m),
1.32 (3H, s), 1.20 (12H, s), 1.15-1.6 (14H, m), 1.6-1.9 (5H,
m), 1.97 (1H, brd, J ) 12.8 Hz), 2.05 (3H, s), 3.27 (1H, m),
5.15 (1H, brs); LR-FAB(+) m/z 712 (M), 711 (M - H), 697 (M
- Me), 653 (M - AcO), 627 (M - C6H13).
(1R,3aR,4S,7aR)-1-[(1R,4R)-4-[Dimethyl-(1,1,2-trimeth-
ylpropyl) silanyloxy]-5-methyl-1-(4-methyl-4-(trimethyl-
silanyloxy)pentyl)-5-(trimethylsilanyloxy)hexyl]-7a-
methyloctahydroinden-4-ol (18). A stirred solution of 17b
(0.335 mg, 0.47 mmol) in tetrahydrofuran (15 mL) was cooled
in an ice bath, and a 1 M solution of lithium aluminum hydride
in tetrahydrofuran (2 mL) was added dropwise. TLC (1:9 ethyl
acetate-hexane) showed complete conversion of 17b (Rf 0.61)
to 18 (Rf 0.29) after 1.5 h. A 2 M sodium hydroxide solution
(14 drops) was added, followed by water (0.5 mL) and ethyl
acetate (30 mL). A small amount of Celite was added, and,
after stirring for 15 min, the liquid layer was decanted off.
The solid residue was rinsed repeatedly with ethyl acetate,
and the combined liquid phases were evaporated to leave a
colorless syrup, which was taken up in hexane, filtered, and
evaporated to yield 18 (0.335 g), which was used without
further purification: 1H NMR δ 0.075 (3H, s), 0.10 (21H, brs),
0.82 (1H, m), 0.84 (6H, s), 0.89 (6H, m), 0.93 (3H, s), 1.13 (3H,
s), 1.20 (9H, s), 1.2-1.6 (16H, m), 1.6-1.7 (2H, m), 1.82 (3H,
m), 1.95 (1H, brd, J ) 12.4 Hz), 3.27 (1H, m), 4.08 (1H, brs);
LR-FAB(+) m/z 585 (M - C6H13), 481 (M - TMSO); HR-ES(+)
calcd for C37H78O4Si3 + Na 693.5100, found 693.5100.
(1R,3aR,4S,7aR)-1-{(R)-5-Hydroxy-5-methyl-1-[2-((R)-
2,2,5,5-tetramethyl-[1,3]dioxolan-4-yl)ethyl]hexyl}-7a-
methyloctahydroinden-4-ol (15a). A solution of the tetraol
13c (0.2966 g, 0.771 mmol) and pyridinium tosylate (100 mg)
in acetone (8 mL) and 2,2-dimethoxypropane (8 mL) was kept
at room temperature for 12 h. TLC analysis (ethyl acetate)
showed the absence of educt (Rf 0.21) and two new spots with
Rf 0.82 and 0.71, the former the expected 15a and the latter
assumed to be the methyl acetal 14. The reaction mixture was
diluted with water (5 mL) and stirred for 10 min. At that time
only the spot with the higher Rf value was observed. The
mixture was neutralized with sodium hydrogen carbonate (0.5
g) and then equilibrated with ethyl acetate (50 mL) and brine
(5 mL). The organic layer was washed with water (5 mL) and
brine (5 mL), then dried, and evaporated to leave 15a as a
sticky residue (0.324 g), which was used directly in the next
1
step; 300 MHz H NMR δ 0.94 (3H, s), 1.10 (3H, s), 1.20 (1H,
m), 1.22 (6H, s), 1.25 (3H, s), 1.34 (3H, s), 1.41 (3H, s), 1.2-
1.65 (20H, m), 1.78-1.86 (3H, m), 1.93 (1H, m), 3.62 (1H, dd,
J ) 4.6 and 8.3 Hz), 4.08 (1H, brs).
Acetic Acid (1R,3aR,4S,7aR)-1-{(R)-5-Hydroxy-5-meth-
yl-1-[2-((R)-2,2,5,5-tetramethyl-[1,3]dioxolan-4-yl)ethyl]-
hexyl}-7a-methyloctahydroinden-4-yl Ester (15b). The
residue obtained above was dissolved in pyridine (6.9 g) and
further diluted with acetic anhydride (3.41 g). The mixture
was allowed to stand at room temperature for 24 h and then
in a 35 °C bath for ca. 10 h until the educt was no longer
detectable (TLC, ethyl acetate). The mixture was diluted with
toluene and evaporated. The residue was purified by flash
chromatography (1:4 ethyl acetate-hexane) to give 15b as
colorless syrup, 0.3452 g, 97%: 1H NMR δ 0.89 (3H, s), 1.10
(3H, s), 1.20 (1H, m), 1.22 (6H, s), 1.25 (3H, s), 1.33 (3H, s),
1.41 (3H, s), 1.25-1.6 (19H, m), 1.72 (1H, m), 1.82 (2H, m),
1.95 (1H, m), 2.05 (3H, s), 3.63 (1H, dd, J ) 4.4 and 8.4 Hz),
5.15 (1H, brs); LR-FAB(+) m/z 467 (M + H), 465 (M - H), 451
(M - Me).
Acetic Acid (1R,3aR,4S,7aR)-1-[(1R,4R)-4,5-Dihy-
droxy-1-(4-hydroxy-4-methylpentyl)-5-methylhexyl]-
7a-methyloctahydroinden-4-yl Ester (16). A solution of
15b (0.334 g, 0.716 mmol) in 80% acetic acid (2 mL) was kept
in a 68 °C bath. TLC (ethyl acetate, Rf 0.33) monitored the
progress of the hydrolysis. The educt was no longer detectable
after 2.5 h. The mixture was evaporated and then coevaporated
(1R,3aR,7aR)-1-[(1R,4R)-4-[Dimethyl-(1,1,2-trimethyl-
propyl)silanyloxy]-5-methyl-1-(4-methyl-4-(trimethyl-
silanyloxy)pentyl)-5-(trimethylsilanyloxy)hexyl]-7a-
methyloctahydroinden-4-one (19). Celite (0.6 g) was added
to a stirred solution of 18 (0.310 g, 0.462 mmol) in dichloro-
methane (14 mL) followed by pyridinium dichromate (0.700
g, 1.86 mmol). TLC (1:4 ethyl acetate-hexane) monitored the
conversion of 18 (Rf 0.54) to the ketone 19 (Rf 0.76). The

6482 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 26
Maehr et al.
mixture was diluted with cyclohexane after 4.5 h and then
filtered through a layer of silica gel. Filtrate and ether washes
were combined and evaporated. The residue was flash chro-
matographed (1:39 ethyl acetate-hexane) to give 19 as a
colorless syrup, 0.2988 g, 96.6%: 1H NMR δ 0.078 (3H, s),
0.097 (3H, s), 0.107 (18H, s), 0.64 (3H, s), 0.81 (1H, m), 0.84
(6H, s), 0.89 (6H, m), 1.134 (3H, s), 1.201 (3H, s), 1.207 (3H,
s), 1.211 (3H, s), 1.3-1.6 (14H, m), 1.6-1.7 (3H, m), 1.88 (1H,
m), 2.04 (2H, m), 2.2-2.32 (2H, m), 2.46 (1H, dd, J ) 7.5 and
11.5 Hz), 3.28 (1H, m); LR-FAB(+) m/z 583 (M - C6H13), 479
(M - OTMS); HR-ES(+) calcd for C37H76O4Si3 + Na 691.4943,
found 691.4949.
acetate, and ethyl acetate containing 1.5% methanol, and
obtained as a colorless, microcrystalline material from methyl
formate-pentane, 38.4 mg (93%): HPLC 37.5 min; TLC Rf
0.05 (ethyl acetate); [R]D +66.5° (methanol, c ) 0.37); UVmax
(ꢀ) 243 (32317), 251 (38040), 261 (25777) nm; 1H NMR δ 0.55
(3H, s), 1.17 (3H, s), 1.22 (9H, s), 1.24-1.60 (23H, m), 1.60-
1.70 (1H, m), 1.71-2.08 (5H, m), 2.18-2.24 (2H, m), 2.46-
2.50 (1H, m), 2.72-2.83 (2H, m), 3.32 (1H, brd), 4.05 (1H, brs),
4.12 (1H, brs), 5.86 (1H, d, J ) 11.2 Hz), 6.31 (1H, d, J ) 11.2
Hz); LR-ES(+) m/z 529 (M + Na); LR-ES(-) m/z 541 (M + Cl);
HR-ES(+) calcd for C31H54O5 + Na 529.3863, found 529.3869.
Anal. (C31H54O5) C, H.
(R)-7-Benzenesulfonyl-6-[(1R,3aR,4S,7aR)-4-(tert-butyl-
dimethylsilanyloxy)-7a-methyloctahydroinden-1-yl]-2-
methylheptan-2-ol (22a). A solution of 918 and sodium
benzenesulfinate (0.263 g, 1.6 mmol) in N,N-dimethylform-
amide (5 mL) was stirred in a 77 °C bath for 3 h. The solution
was equilibrated with 1:1 ethyl acetate-hexane (25 mL) and
the organic layer washed with water (5 × 10 mL), dried, and
evaporated. The residue was flash chromatographed with a
stepwise gradient of 1:9, 1:4, and 1:3 ethyl acetate-hexane to
furnish the sulfone as a colorless syrup: 1H NMR δ -0.02 (3H,
s), 0.005 (3H, s), 0.79 (3H, s), 0.87 (9H, s), 1.12 (1H, m), 1.19
(6H, s), 1.12 (1H, m), 1.20 (6H, s), 1.2-1.8 (18H, m), 2.08 (1H,
m), 3.09 (1H, dd, J ) 9.3 and 14.5 Hz), 3.31 (1H, dd, J ) 3
and 14.5 Hz), 3.97 (1H, brs), 7.58 (3H, m), 7.66 (1H, m), 7.91
2H, m); LR-ES(+) m/z 600 (M + Na + MeCN), 559 (M + Na);
LR-ES(-) m/z 536 (M), 535 (M - H); HR-ES(+) calcd for
C30H52O4SSi + Na 559.3248, found 559.3253.
(1R,3aS,7aR)-4-[2-[(3S,5R)-3,5-Bis(tert-butyldimethyl-
silanyloxy)-2-methylenecyclohex-(Z)-ylidene]-eth-(E)-
ylidene]-7a-methyl-1-[5-methyl-1(R)-[4-methyl-4-(tri-
methylsilanyloxy)pentyl]-4(R)-[dimethyl(1,1,2-trimethyl-
propyl)silanyloxy]-5-trimethylsilanyloxyhexyl]octahydro-
indene (21b). A solution of 2.5 M butyllithium in hexane (0.17
mL) was added dropwise to a solution of (1S,5R)-1,5-bis-((tert-
butyldimethyl)silanyloxy)-3-[2-(diphenylphosphinoyl)-eth-(Z)-
ylidene]-2-methylene-cyclohexane (20b, 0.1415 g, 0.396 mmol)
in tetrahydrofuran (2 mL) at -70 °C. After 10 min a solution
of ketone 19 (0.1415 g, 0.211 mmol) in tetrahydrofuran (2 mL)
was added dropwise over a 15 min period. The reaction was
quenched after 4 h by the addition of pH 7 phosphate buffer
(1 M, 2 mL). The temperature was allowed to increase to 0
°C, and then hexane (30 mL) was added. The aqueous layer
was re-extracted with hexane (15 mL). The combined extracts
were washed with brine (5 mL), dried, and evaporated to give
a colorless oil, which was purified by flash chromatography
(1:100 ethyl acetate-hexane) to yield 21b as colorless syrup,
0.173 g, 79%: 1H NMR δ 0.068 (15H, m), 0.103 (12H, s), 0.107
(9H, s), 0.53 (3H, s), 0.82 (1H, m), 0.84 (6H, s), 0.88 (18H, m),
0.89 (6H, m), 1.14 (3H, m), 1.20 (9H, s), 1.2-1.9 (22H, m), 1.97
(2H, m), 2.22 (1H, dd, J ) 7.5 an 13 Hz), 2.45 (1H, brd, J ) 13
Hz), 2.83 (1H, brd, J ) 13 Hz), 3.28 (1H, m), 4.20 (1H, m),
4.38 (1H, m), 4.87 (1H, d, J ) 2 Hz), 5.18 (1H, d, J ) 2 Hz),
6.02 (1H, d, J ) 11.4 Hz, 6.24 (1H, d, J ) 11.4 Hz); LR-FAB(+)
m/z 1033 (M + H), 1032 (M), 1031 (M - H), 901 (M - TBDMS).
(3R,6R)-6-{(1R,3aS,7aR)-4-[2-((R)-3-(S)-Hydroxy-5-hy-
droxy-2-methylene-cyclohexylidene)-(E)-ethylidene]-7a-
methyloctahydroinden-1-yl}-2,10-dimethylundecane-2,3,-
10-triol (2b). The pentasilyl ether 21b (0.153 g, 0.148 mmol),
as obtained in the previous experiment, was dissolved in a 1
M solution of tetrabutylammonium fluoride in tetrahydrofuran
(3.5 mL). TLC (ethyl acetate) monitored reaction progress. The
solution was diluted with brine (5 mL) after 24 h, stirred for
5 min, and then equilibrated with ethyl acetate (35 mL) and
water (15 mL). The aqueous layer was re-extracted once with
ethyl acetate (15 mL). The combined organic layers were
washed with water (5 × 10 mL) and once with brine (5 mL),
then dried, and evaporated. The residue was purified by flash
chromatography using a stepwise gradient of ethyl acetate and
1:100 methanol-ethyl acetate, furnishing 2b as colorless,
microcrystalline material from methyl formate-pentane, 70
mg, 91%, HPLC 30.9 min: [R]D +34.4° (methanol, c ) 0.51);
UVmax (ꢀ) 213 (13554), 265 (16029), 241 (s, 12801) nm; 1H NMR
δ 0.55 (3H, s), 1.17 (3H, s), 1.22 (9H, s), 1.15-1.8 (22H, m),
1.8-2.1 (7H, m), 2.32 (1H, dd, J ) 6.6 and 13.6 Hz), 2.61 (1H,
d), 2.84 (1H, brd), 3.32 (1H, brs), 4.23 (1H, brs), 4.43 (1H, brs),
5.01 (1H, s), 5.33 (1H, s), 6.03 (1H, d, J ) 11.4 Hz), 6.38 (1H,
d, J ) 11.4 Hz); LR-ES(+) m/z 519 (M + H), 501 (M - H);
HR-ES(+) calcd for C32H54O5 + Na 541.3863, found 541.3870.
Anal. (C32H54O5) C, H.
(1R,3aR,4S,7aR)-1-((R)-1-Benzenesulfonylmethyl-5-
methyl-5-(trimethylsilanyloxy)hexyl)-4-(tert-butyldi-
methylsilanyloxy)-7a-methyloctahydroindene (22b). 1-
(Trimethylsilyl)imidazole (0.146 mL) was added to a solution
of 22a (0.145 g, 0.27 mmol) in cyclohexane (2 mL). After 17 h
the product was purified by flash chromatography using a
stepwise gradient of 1:79 and 1:39 ethyl acetate-hexane to
give 22b as a colorless residue, 0.157 g: TLC (1:9 ethyl
1
acetate-hexane) Rf 0.14; 300 MHz H NMR δ -0.02 (3H, s),
0.00 (3H, s), 0.87 (12H, s), 1.12 (1H, m), 1.17 (6H, s), 1.2-1.6
(15H, m), 1.6-1.9 (3H, m), 3.08 (2H, m), 3.97 (1H, brs), 7.53-
7.70 (3H, m), 7.90 (2H, d, J ) 7 Hz).
(6R,5ê,3R)-5-Benzenesulfonyl-6-[(1R,3aR,4S,7aR)-4-(tert-
butyldimethylsilanyloxy)-7a-methyloctahydroinden-1-
yl]-2,10-dimethyl-10-(trimethylsilanyloxy)undecane-2,3-
diol (23a). A solution of 22b (0.2589, 0.425 mmol) and diol 11
(0.176 g, 0.638 mmol) in tetrahydrofuran (9 mL) was cooled
to -25 °C, and 1.6 M butyllithium in hexane (1.4 mL) was
added. The temperature was raised to -20 °C, maintained at
that temperature for 3 h, and then maintained at -10 °C for
2.5 h and at 0 °C for 10 min. The mixture was cooled again to
-10 °C, saturated ammonium chloride solution (5 mL) was
added, and then the mixture was equilibrated with ethyl
acetate (50 mL) and enough water to dissolve precipitated
salts. The aqueous layer was re-extracted with ethyl acetate
(15 mL), the combined extracts were dried and evaporated,
and the residue was purified by flash chromatography using
a stepwise gradient of 1:6, 1:4, and 1:1 ethyl acetate-hexane
to produce the diastereomeric mixture 23a as a colorless syrup,
0.212 g, 70%: 300 MHz 1H NMR δ 0.00 (3H, s), 0.017 (3H, s),
0.12 (9H, s), 0.81 (3H, s), 0.89 (9H, s), 1.16 (1H, m), 1.19 (12H,
m), 1.1-1.6 (20H, m), 1.6-1.8 (2H, m), 3.10 (1H, dd, J ) 8.4
and 14.7 Hz), 3.30 (1H, m), 3.99 (1H, brs), 7.61 (2H, m), 7.67
(1H, m), 7.93 (2H, m).
(3R,6S)-6-[(1R,3aR,4S,7aR)-4-(tert-Butyldimethylsilan-
yloxy)-7a-methyloctahydroinden-1-yl]-2,10-(dimethyl)-
undecane-2,3,10-triol (24a). The mixture represented by 23a
(0.186 mg, 0.262 mmol) was dissolved in 0.5 M oxalic acid
dihydrate in methanol (2.5 mL). The solution was stirred for
15 min, then calcium carbonate was added (0.5 g), and the
suspension was stirred overnight and then filtered. The filtrate
was evaporated to give the diastereomeric mixture 23b as a
white foam, 0.188 g, 98%: TLC Rf 0.06 (1:1 ethyl acetate-
hexane). This material was combined with a second lot (0.426
g, 0.667 mmol) and dissolved in a mixture of tetrahydrofuran
(3R,6R)-6-{(1R,3aS,7aR)-4-[2-((R)-3-(R)-Hydroxy-5-hy-
droxy-cyclohexylidene)-(E)-ethylidene]-7a-methyloctahy-
droinden-1-yl}-2,10-dimethylundecane-2,3,10-triol (2a).
The condensation of ketone 19 with (1R,3R)-1,3-bis-((tert-
butyldimethyl)silanyloxy)-5-[2-(diphenylphosphinoyl)ethylidene]-
cyclohexane (20a) and the deprotection of the resulting 21a
(83 mg) was conducted as described for 21b, with the exception
that the exposure to tetrabutylammonium fluoride was ex-
tended to 48 h, to furnish 2a, purified by flash chromatography
with a stepwise gradient using 4:1 ethyl acetate-hexane, ethyl

Diastereoselective Syntheses of 24(R)-Hydroxygemini
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 26 6483
(15 mL) and methanol (9 mL). Then sodium amalgam (5%
sodium, 10.8 g) was added, and the suspension was stirred
for 24 h. The reaction progress was monitored by TLC (1:1
ethyl acetate-hexane) to observe the production of 24a (Rf
0.17). The mixture was diluted with methanol (3 mL), stirred
for 5 min, then further diluted with water (10 mL), stirred for
2 min, and decanted into a saturated ammonium chloride
solution (25 mL). The aqueous layer was extracted with ethyl
acetate (2 × 20 mL). The combined extracts were washed with
pH 7 phosphate buffer (5 mL) and then brine (10 mL), dried,
and evaporated. The residue was purified by flash chroma-
tography using a stepwise gradient of 1:1 and 2:1 ethyl
acetate-hexane to provide 24a as a colorless syrup, 0.244 g,
73%: 1H NMR δ -0.006 (3H, s), 0.006 (3H, s), 0.86 (9H, s),
0.92 (3H, s), 1.11 (1H, m), 1.15 (3H, s), 1.21 (9H, s), 1.2-1.75
(21H, m), 1.7-1.85 (3H, m), 1.90 (1H, m), 3.29 (1H, brd), 3.99
(1H, brs); LR-ES(+) m/z 521 (M + Na), 481 (M - OH); LR-
ES(-) m/z 544 (M + CH2O2), 543 (M - H + CH2O2), 533 (M -
Cl); HR-ES(+) m/z calcd for C29H58O4Si + Na 521.3996, found
521.3999.
(3R,6S)-6-((1R,3aR,4S,7aR)-4-Hydroxy-7a-methyloctahy-
droinden-1-yl)-2,10-(dimethyl)undecane-2,3,10-triol (24b).
An aqueous fluorosilicic acid solution (3 mL) was added to a
stirred solution of 24a (0.240 g, 0.481 mmol) in acetonitrile
(12 mL). TLC (ethyl acetate) monitored the reaction. After 2.5
h compound 24b (Rf 0.37) was the predominating species,
produced at the expense of less polar 24a. The mixture was
equilibrated with ethyl acetate and water (10 mL), the aqueous
layer was re-extracted with water (2 × 10 mL), and the
combined extracts were washed with water (6 mL) and brine
(2 × 10 mL) and then dried and evaporated. The colorless
residue was flash chromatographed using a stepwise gradient
of 1:2, 1:1, and 2:1 ethyl acetate-hexane to elute some
unreacted 24a, followed by 24b, obtained as a colorless syrup,
0.147 g, 79%: 1H NMR δ 0.94 (3H, s), 1.12 (1H, m), 1.15 (3H,
s), 1.21 (9H, s), 1.15-1.7 (20H, m), 1.7-1.9 (5H, m), 1.96 (1H,
brd), 3.29 (1H, d, J ) 9.6 Hz), 4.08 (1H, brs); LR-ES(+) m/z
448 (M + Na + MeCN), 407 (M + Na); LR-ES(-) m/z 419 (M
+ Cl); HR-ES(+) calcd for C23H44O4 + Na 407.3132, found
407.3135.
(1R,3aR,4S,7aR)-1-((S)-5-Hydroxy-1-{2-[(R)-2-(4-meth-
oxyphenyl)-5,5-dimethyl-[1,3]dioxolan-4-yl]ethyl}-5-
methylhexyl)-7a-methyloctahydroinden-4-ol (25). 4-Meth-
oxybenzaldehyde dimethyl acetal (60 µL, 0.35 mmol) was
added to a solution of 24b (81.2 mg, 0.211 mmol) in dichloro-
methane (2 mL), followed by a solution (0.2 mL) containing
pyridinium tosylate (200 mg) in dichloromethane (10 mL).
Reaction progress was followed by TLC (1:2 ethyl acetate-
hexane), which showed 4-methoxybenzaldehyde dimethyl ace-
tal (Rf 0.80), 4-methoxybenzaldehyde (Rf 0.65), educt 24b (Rf
0.42), and product 25 (Rf 0.26). After 53/4 h the mixture was
stirred for 15 min with saturated sodium hydrogencarbonate
solution (5 mL) and then equilibrated with ethyl acetate (25
mL). The organic layer was washed with brine (5 mL), dried,
and evaporated. The residue was flash chromatographed using
a stepwise gradient of 1:3 and 1:2 ethyl acetate-hexane to
yield 25 as a colorless syrup, 0.106 mg (100%): 1H NMR δ
0.94 (3H, s), 1.19 (3H, s), 1.21 (3H, s), 1.23, 1.35 and 1.24, 1.37
(6H, s each, major and minor 5,5-dimethyloxolane diastereo-
mer), 1.1-1.7 (18H, m), 1.7-1.9 (5H, m), 1.9-2.0 (2H, m), 3.65
(1H, m), 3.81 (3H, s), 4.08 (1H, brs), 5.78 and 5.96 (1H, s each,
major and minor acetal diastereomer), 6.89 (2H, m), 7.41 (2H,
m).
(1R,3aR,7aR)-1-((S)-5-Hydroxy-1-{2-[(R)-2-(4-methoxy-
phenyl)-5,5-dimethyl-[1,3]dioxolan-4-yl]ethyl}-5-methylhexyl)-
7a-methyloctahydroinden-4-one (26). Pyridinium dichro-
mate (230 mg, 0.61 mmol) was added to a stirred mixture
containing 25 (0.0838, 0.167 mmol), Celite (185 mg), and
dichloromethane (4 mL). The conversion of 25 (Rf 0.31) to 26
(Rf 0.42) was monitored by TLC (1:25 methanol-chloroform).
The mixture was diluted with dichloromethane (10 mL) after
2.5 h and then filtered through a layer of silica gel. Filtrate
and washings (1:1 dichloromethane-ethyl acetate) were evapo-
rated, and the residue was chromatographed (1:4 ethyl acetate-
hexane) to give ketone 26, 0.0763 g, 91%: 1H NMR δ 0.63 (3H,
s), 1.19, 1.21 and 1.23 (6H, s each, Me2COH), 1.25, 1.36, 1.38
(6H, m,s,s, 5,5-dimethyloxolane diastereomer), 1.1-1.9 (18H,
m), 1.9-2.1 (3H, m), 2.1-2.4 (2H, m), 2.45 (1H, m), 3.66 (1H,
m), 3.802 and 3.805 (3H, s each), 5.78 and 5.95 (1H, s each,
major and minor acetal diastereomer), 6.89 (2H, m), 7.39 (2H,
m).
(1R,3aR,7aR)-1-[(1S,4R)-4,5-Dihydroxy-1-(4-hydroxy-4-
methylpentyl)-5-methylhexyl]-7a-methyloctahydroinden-
4-one (27). The ketone 26 was stirred in a 1 N oxalic acid
solution in 90% methanol. The mixture became homogeneous
after a few minutes. TLC (ethyl acetate) suggested complete
reaction after 75 min (Rf 0.24 for 27). Thus, calcium carbonate
(0.60 g) was added and the suspension stirred overnight and
then filtered. The filtrate was evaporated and flash chromato-
graphed using a stepwise gradient of 4:1:5 dichloromethane-
ethyl acetate-hexane, 1:1 ethyl acetate-hexane, and neat
ethyl acetate, to produce 27 as a colorless residue, 0.060 mg,
94%: 1H NMR δ 0.5 (3H, s), 1.17 (3H, s), 1.22 (6H, s), 1.23
(3H, s), 1.2-1.21 (23H, m), 2.15-2.35 (2H, m), 2.45 (1H, dd, J
) 7 and 11 Hz), 3.30, 1H, brd); LR-ES(+) m/z 424.5 (M + H +
MeCN), 406.4 (M + H + Na); 383.5 (M + H); HR-ES(+) calcd
for C23H42O4 + Na 405.2975, found 405.2979.
(1R,3aR,7aR)-7a-Methyl-1-[(1S,4R)-5-methyl-1-(4-meth-
yl-4-(triethylsilanyloxy)pentyl)-4,5-bis-(triethylsilanyl-
oxy)hexyl]octahydroinden-4-one (28). A mixture of 27
(0.055 g, 0.143 mmol), imidazole, (14.9 mg, 1.69 mmol), N,N-
dimethylpyridine (6 mg), triethylchlorosilane (0.168 mL, 1
mmol), and N,N-dimethylformamide (1.5 mL) was stirred for
17 h. The reaction was followed by TLC (1:4 ethyl acetate-
hexane) and showed rapid conversion to the disilyl intermedi-
ate (Rf 0.47). Further reaction proceeded smoothly overnight
to give the fully silylated 28 (Rf 0.90). The solution was
equilibrated with water (3 mL), and ethyl acetate (20 mL). The
ethyl acetate layer was washed with water (3 × 4 mL), dried,
and evaporated. The residue was flash chromatographed using
a stepwise gradient of hexane and 1:100 ethyl acetate-hexane
to yield 28 as a colorless syrup, 0.0813 g, 78.4%: 1H NMR δ
0.55-0.64 (21H, m), 0.92-0.97 (27H, m), 1.12 (3H, s), 1.18 (3H,
s), 1.19 (3H, s), 1.21 (3H, s), 1.1-1.7 (18H, m), 1.9-2.15 (2H,
m), 2.15-2.35 (2H, m), 2.43 (1H, dd, J ) 7.7 and 11 Hz), 3.30
(1H, dd, J ) 3 and 8.4 Hz).
(1R,3aS,7aR)-4(E)-{2-[(R)-3-((R)-(tert-Butyldimethyl-
silanyloxy))-5-(tert-butyldimethylsilanyloxy)-cyclohex-
ylidene]ethylidene}-7a-methyl-1-[(1S,4R)-5-methyl-1-(4-methyl-
4-(triethylsilanyloxy)pentyl)-4,5-bis-(triethylsilanyloxy)-
hexyl]octahydroindene (29b). A solution of 1.6 M butyl-
lithium in hexane (0.14 mL) was added to a solution of 20b
(0.1308 g, 0.224 mmol) in tetrahydrofuran (1.5 mL) at -70
°C. After 10 min a solution of ketone 28 (0.0813 g, 0.112 mmol)
in tetrahydrofuran (1.5 mL) was added dropwise over a 15 min
period. The ylide color had faded after 3 h, thus pH 7 phos-
phate buffer (2 mL) was added and the temperature allowed
to increase to 0 °C. The mixture was equilibrated with hexane
(30 mL), and the organic layer was washed with brine (5 mL),
dried, and evaporated to give a colorless oil, which was purified
by flash chromatography (1:100 ethyl acetate-hexane). No
attempt was made to recover unreacted 28 as only the band
with Rf 0.33 (TLC 1:39 ethyl acetate-hexane) was collected.
Evaporation of those fractions gave 29b as a colorless syrup,
0.070 g, 57%: 1H NMR δ 0.06 (12H, brs), 0.53-0.64 (21H, m),
0.88 (18H, s), 0.92-0.97 (27H, m), 1.11 (3H, s), 1.177 (3H, s),
1.184 (3H, s), 1.195 (3H, s), 1-1.9 (22H, m), 1.98 (2H, m), 2.22
(1H, m), 2.45 (1H, m), 2.83 (1H, brd, J ) 13 Hz, 3.27 (1H, d,
J ) 6 Hz), 4.19 (1H, m), 4.38 (1H, m), 4.87 (1H, brs), 5.18 (1H,
brs), 6.02 (1H, d, J ) 11 Hz), 6.24 (1H, d, J ) 11 Hz).
(3R,6S)-6-{(1R,3aS,7aR)-4(E)-[2-((R)-3-(R)-Hydroxy-5-
hydroxy-cyclohexylidene)-(E)-ethylidene]-7a-methyl-
octahydroinden-1-yl}-2,10-dimethylundecane-2,3,10-triol
(3b). The deprotection reaction of 29b (0.068 g, 0.062 mmol)
in a 1 M solution of tetrabutylammonium fluoride in tetra-
hydrofuran (1.5 mL), monitored by TLC (Rf 0.18, ethyl acetate),
gradually proceeded over a 24 h period to give 3b. The mixture
was diluted with brine (5 mL), stirred for 5 min, and then

6484 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 26
Maehr et al.
(5) Rao, S.; Balkundi, D.; Uskokovic, M. R.; Tserng, K.-Y.; Clark, J.
W.; Horst, R. L.; Reddy, G. S. Double bond in the side chain of
1R,25-dihydroxy-22-ene-vitamin D3 is reduced during its me-
tabolism: Studies in chronic myeloid leukemia (RWLeu-4) cells
and rat kidney. J. Steroid Biochem. Mol. Biol. 2001, 78, 167-
176.
(6) Siu-Caldera, M. L.; Sekimoto, H.; Peleg, S.; Nguyen, C.; Kiss-
mayer, A.-M.; Binderup, L.; Weiskopf, A.; Vouros, P.; Uskokovic,
M. R.; Reddy, G. S. Enhanced biological activity of 1R,25-
dihydroxy-20-epi-vitamin D3, the C-20 epimer of 1R,25-dihydroxy-
vitamin D3, is in part due to its metabolism into stable
intermediary metabolites with significant biological activity J.
Steroid Biochem. Mol. Biol. 1999, 71, 111-121.
(7) Uskokovic, M. R.; Norman, A. W.; Manchand, P. S.; Studzinski,
G. P.; Campbell, M. J.; Koeffler, H. P.; Takeuchi, A.; Siu-Caldera,
M.-L.; Rao, D. S.; Reddy, G. S. Highly active analogs of 1R,25-
dihydroxy-vitamin D3 that resist metabolism through C-24
oxidation and C3 epimerization pathways. Steroids 2001, 66,
463-471.
(8) Weinstein, E. A.; Rao, D. S.; Siu-Caldera, M.-L.; Tserng, K.-Y.;
Uskokovic, M. R.; Ishizuka, S.; Reddy, G. S. Isolation and
identification of 1R-hydroxy-24-oxovitamin D3 and 1R,23-di-
hydroxy-24-oxovitamin D3: Metabolites of 1R,24(R)-dihydroxy-
vitamin D3 produced in rat kidney. Biochem. Pharmacol. 1999,
58, 1965-1973.
(9) Reddy, G. S.; Tserng, K.-Y. Isolation and identification of 1,24,25-
trihydroxyvitamin D2, 1,24,25,28-tetrahydroxyvitamin D2, and
1,24,25,26-tetrahydroxyvitamin D2: New metabolites of 1,25-
dihydroxyvitamin D2 produced in rat kidney. Biochemistry 1986,
25, 5328-5336.
(10) Reddy, G. S.; Tserng, K.-Y.; Thomas, B. R.; Dayal, R.; Norman,
A. W. Isolation and identification of 1,23-dihydroxy-24,25,26,-
27-tetranorvitamin D3. Biochemistry 1987, 26, 324-331.
(11) Reddy, G. S.; Tserng, K.-Y. Calcitroic acid, end product of renal
metabolism of 1,25-dihydroxyvitamin D3 through C-24 oxidation
pathway. Biochemistry 1989, 28, 1763-1769.
(12) (a) Perlman, K. L.; Sicinski, R. R.; Schnoes, H. K.; DeLuca, H.
F.; 1R,25 dihydroxy-19-nor-vitamin D3, a novel synthetic vitamin
D3 related compound with potential therapeutic activity. Tet-
rahedron Lett. 1990, 31, 1823-1824. (b) DeLuca, H. F.; Schnoes,
H. K.; Perlman, K. L. Preparation of intermediates for the
synthesis of 19-nor-vitamin D compounds. US 5086191, 1992.
(c) Deluca, H. F.; Schnoes, H. K.; Perlman, K. L.; Swenson, R.
E. Novel synthesis of 19-nor-vitamin D compounds. EP 516410,
1992.
(13) Chemical structures are drawn according to a proposed conven-
tion: Maehr, H. Graphic representation of configuration in two-
dimensional space. Current conventions, clarifications, and
proposed extensions. J. Chem. Inf. Comput. Sci. 2002, 42, 894-
902.
(14) Lythgoe, B. Synthetic approaches to vitamin D and its relatives.
Chem. Soc. Rev. 1981, 10, 449-475.
(15) Zhu, G.-D.; Okamura, W. H. Synthesis of vitamin D (calciferol).
Chem. Rev. 1995, 95, 1877-1952.
(16) Baggiolini, E. G.; Iacobelli, J. A.; Hennessy, B. M.; Batcho, A.
D.; Sereno, J. F.; Uskokovic, M. R. Stereocontrolled total
synthesis of 1R,25-dihydroxycholecalciferol and 1R,25-dihydroxy-
ergocalciferol. J. Org. Chem. 1986, 51, 3098-3108.
(17) Maehr, H.; Uskokovic, M. R.; Norman, A.; Bishop, J.; Reddy, G.
S.; Koeffler, P.; Studzinski, G. DeLuca Symposium on Vitamin
D, Taos, New Mexico, June 15-19, 2002, Abstract p 42.
(18) Maehr, H.; Uskokovic, M. R. Formal desymmetrization of the
diastereomeric chains in gemini calcitriol derivatives with two
different side chains at C-20. Eur. J. Org. Chem. 2004, 1703-
1713.
equilibrated with ethyl acetate (35 mL) and water (15 mL).
The aqueous layer was re-extracted once with ethyl acetate
(35 mL), and the combined extracts were washed with water
(5 × 10 mL) and brine (5 mL), then dried, and evaporated.
The residue was flash chromatographed using a linear gradi-
ent of 1:1 and 2:1 ethyl acetate-hexane and 2:98 methanol-
ethyl acetate to give a residue, which was taken up in methyl
formate and evaporated to give 3b as a white foam, 30 mg,
93%; HPLC 27.7 min; [R]D +29.3° (methanol, c ) 0.34); UVmax
(ꢀ) 211 (15017), 265 (15850), 204 (s, 14127), 245 (s, 13747) nm;
1H NMR δ 0.55 (3H, s), 1.16 (3H, s), 1.21 (9H, s), 1.2-1.75
(22H, m), 1.75-188 (2H, m), 188.-2.05 (5H, m), 2.31 (1H, dd,
J ) 6.8 and 13.4 Hz), 2.60 (1H, d), 2.84 (1H, brd), 3.30 (1H,
brd), 4.42 (1H, m), 4.31 (1H, brs), 5.00 (1H, s), 5.33 (1H, s),
6.01 (1H, d, J ) 11.2 Hz), 6.37 (1H, d, J ) 11.2 Hz); LR-ES(+)
m/z 564 (M + H2CO2); 563 (M - H + H2CO2); HR-ES(+) calcd
for C32H54O5 + Na 541.3863, found 541.3854. Anal. (C32H54O5)
C, H.
(3R,6S)-6-{(1R,3aS,7aR)-4(E)-[2-((R)-3-(S)-Hydroxy-5-
hydroxy-2-methylene-cyclohexylidene)-(E)-ethylidene]-
7a-methyloctahydroinden-1-yl}-2,10-dimethylundecane-
2,3,10-triol (3a). The condensation of ketone 28 (0.109 g, 0.15
mmol) was repeated with 20a (0.1729 g, 0.30 mmol), to give
29a (0.142 g, 88%). This pentasilyl ether (0.118 g) was
deprotected as described for 29b, but extending the contact
time with the tetrabutylammonium fluoride solution to 48 h,
to furnish 3a in microcrystalline form (0.0479 g, 86%): HPLC
32.9 min; [R]D +71.3° (methanol, c ) 0.32); UVmax (ꢀ) 243
(32679), 251(38564), 261(26095), 225 (s, 12097), 235 (s, 22062)
1
nm, H NMR δ 0.55 (3H, s), 1.17 (3H, s), 1.22 (9H, s), 1.10-
1.75 (22H, m), 1.75-1.9 (4H, m), 1.9-2.1 (3H, m), 2.18-2.25
(2H, m), 2.47-2.49 (1H, m), 2.73-2.83 (2H, m), 3.32 (1H, m),
4.04 (1H, brs), 4.12 (1H, brs), 5.86 (1H, d, J ) 11.4 Hz), 6.31
(1H, d, J ) 11.4 Hz; LR-ES(-) m/z 552 (M + H2CO2), 551 (M
- H + H2CO2), HR-ES(+) calcd for C31H54O5 + Na 529.3863,
found 529.3865. Anal. (C31H54O5), C, H.
Supporting Information Available: Elemental analysis
data for 2a,b, 3a,b, 10a, 13b, and 16. This material is
available free of charge via the Internet at http://pubs.acs.org.
References
(1) This paper was presented in part at the 12th Workshop on
Vitamin D, July 6-10, 2003, Maastricht, The Netherlands,
Abstracts, p 41. Part I: Reference 18.
(2) Uskokovic, M. R.; Manchand, P. S.; Peleg, S.; Norman, A. W.
Synthesis and preliminary evaluation of the biological properties
of a 1R,25-dihydroxyvitamin D3 analogue with two side chains.
In Vitamin D: Chemistry, Biology and Clinical Applications of
the Steroid Hormone; Norman, A. W., Bouillon, R., Thomasset,
M., Eds.; University of California: Riverside, 1997; pp 19-21.
(3) (a) Manchand, P. S.; Uskokovic, M. R. Method of using vitamin
D3 analogs with bis-C-20 side chains for treating or preventing
neoplastic diseases, US 6008209, 1999, 13 pp. (b) Manchand, P.
S.; Uskokovic, M. R. Preparation of vitamin D3 analogs with bis-
C-20 side chains as therapeutic agents, WO 9849138 1998, 35
pp.
(4) Norman, A. W.; Manchand, P. S.; Uskokovic, M. R.; Okamura,
W. H.; Takeuchi, J. A.; Bishop, J. E.; Hisatake, J.-I.; Koeffler,
(19) Hatakeyama, S.; Kawase, A.; Uchiyama, Y.; Maeyama, J.;
Iwabuchi, Y.; Kubodera, N. Synthesis and biological character-
ization of 1R,24,25-trihydroxy-2â-(3-hydroxypropoxy)vitamin D3
(24-hydroxylated ED-71). Steroids 2000, 66, 267-276.
H. P.; Peleg, S. Characterization of
a novel analogue of
1R,25(OH)2-vitamin D3 with two side chains: Interaction with
its nuclear receptor and cellular actions. J. Med. Chem. 2000,
43, 2719-2730.
JM049340B