Cholane derivatives with potential ligating groups at the 3- and 24-positions

Article abstract of DOI:10.1080/00397910500521803

Starting from readily available lithocholic acid, a number of new cholane derivatives have been prepared consisting of the same or different electron-donor groups at the 3- and 24-positions. Yields ranged from good to excellent. The donor groups were chos

Full text of DOI:10.1080/00397910500521803

Synthetic Communicationsw, 36: 1317–1331, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500521803
Cholane Derivatives with Potential Ligating
Groups at the 3- and 24-Positions
Sudershan Reddy Gondi and David Y. Son
Department of Chemistry, Southern Methodist University,
Dallas, Texas, USA
Abstract: Starting from readily available lithocholic acid, a number of new cholane
derivatives have been prepared consisting of the same or different electron-donor
groups at the 3- and 24-positions. Yields ranged from good to excellent. The donor
groups were chosen on the basis of their known ability to coordinate to transition-
metal ions and include pyridyl, 1,3-dithiolanyl, phenylthioether, and oxime ether groups.
Keywords: Ligand, lithocholic acid, pyridyl, steroid, thioether
INTRODUCTION
The widespread use of steroids in applications such as radiotracing,[1–10]
gelation,[11–13] and molecular recognition[14] is now well known. Bile acids
have been employed in these applications[15–18] in addition to being used as
DNA transfection agents[19–22] and as drug carriers with specificity to the
enterohepatic circuit.[23–28] For the majority of these applications it is
necessary to chemically modify the natural steroid, normally by attaching
electron-donor groups to enable binding to transition-metal ions or other
electron-deficient moieties. In this regard, considerable research has been
carried out in the synthesis of steroids modified with various nitrogen- or
sulfur-containing moieties.[1–3,7,9,10,18,23,24,26,27,29–35]
Keeping these applications in mind, we have investigated the synthesis
and characterization of a series of cholane derivatives with various
Received in the USA October 25, 2005
Address correspondence to David Y. Son, Department of Chemistry, Southern
Methodist University, P.O. Box 750314, Dallas, TX 75275-0314, USA. E-mail:
dson@smu.edu
1317

1318
S. R. Gondi and D. Y. Son
electron-donor groups at the 3- and 24-positions. Lithocholic acid was chosen
as a starting material because of its ready availability and because it can be
easily converted to cholane-3,24-diol (3a,5b), a compound that can be
selectively functionalized at the alcohol positions.[36] The electron-donor
groups chosen for this study were pyridyl, 1,3-dithiolanyl, oxime ether, and
phenylthioether, all known for their Lewis basicity and ligating potential.
This investigation is a reflection of our ongoing interest in synthesizing new
organic ligands for supramolecular design.[37–41]
RESULTS AND DISCUSSION
The initial step in all the functionalizations described herein was the conver-
sion of lithocholic acid to cholane-3,24-diol (3a,5b) (1) via reduction of the
methyl ester[42,43] (Equation 1).
Identical Substitution at the 3- and 24-Positions
Derivatives 2–4 were each synthesized in straightforward one-step procedures
from 1 as summarized in Scheme 1. Attempts to prepare bis(nicotinate),
compound 2, by reaction of 1 with nicotinoyl chloride hydrochloride
(prepared from nicotinic acid) in the presence of triethylamine were unsuccess-
ful and resulted in the isolation of unreacted 1. A direct esterification reaction
between 1 and nicotinic acid with 1-(3-dimethylaminopropyl)-3-ethylcarbo-
diimide hydrochloride (EDCI) and 1-hydroxybenzotriazole (HOBt) proved
quite effective and resulted in the formation of 2 as an oil in 80% yield after
chromatographic purification. Reaction of 1 with 1,3-dithiolane-2-carbonyl
chloride in the presence of sodium hydride led to the isolation of the 3,24-
bis(1,3-dithiolanyl) product 3 as an oil in 59% yield after repeated purifications
using column chromatography. In a similar procedure, compound 1 was
reacted with 2.2 equivalents of a-benzyloximino acid chloride. After chroma-
tographic separation, compound 4 was isolated in 40% yield along with the
mono-24-substituted product 5 in 23% yield. Both compounds were isolated
as oils. Compounds 1–5 are air- and moisture-stable and are freely soluble
1
in common organic solvents. Product identities were confirmed with H and
13C NMR spectroscopy and high-resolution mass spectrometry.

Cholane Derivatives
1319
Scheme 1.
We also attempted to synthesize the (bis)phenylthioether derivative 6
from direct nucleophilic substitution reactions of thiophenol with either of
previously unreported steroid derivatives 7 and 8 (Scheme 2). In both cases,
our attempts were unsuccessful and resulted in either the isolation of
starting materials or unidentified mixtures of products. We include this
negative result because we believe 7 and 8 to be of potential value as
synthetic intermediates for other cholane derivatizations.

1320
S. R. Gondi and D. Y. Son
Scheme 2.
Different Substitution at the 3- and 24-Positions
As mentioned previously, the synthesis of bis(oxime ether) 4 was
accompanied by the isolation of the mono-substituted oxime ether 5. Recog-
nizing that 5 could lead to mono(oxime ether) cholane derivatives with a
different substituent at the 3-position, we sought to increase the yield of 5.
Accordingly, diol 1 was reacted with 1.2 equivalents of a-benzyloximino
acid chloride. Column chromatographic purification resulted in the isolation
of the desired monosubstituted product 5 in 55% yield along with bis(oxime
ether) 4 in 15% yield. Subsequent reaction of 5 with 1,3-dithiolane-2-
carbonyl chloride led to new ditopic derivative 9 as an oil in 78% yield
after column chromatographic purification (Equation 2).
Although we were unsuccessful in synthesizing (bis)phenylthioether 6,
we were successful in synthesizing the 24-substituted phenylthioether 10

Cholane Derivatives
1321
Scheme 3.
from diol 1 in three steps (Scheme 3). As was the case with 5, the secondary
alcohol in 10 allowed us to attach different substituents at the 3-position for
the synthesis of new ditopic derivatives. Thus, reaction of 10 with a-benzylox-
imino acid chloride gave 11 as a white solid in 55% yield, and reaction with
1,3-dithiolane-2-carbonyl chloride gave 12 as an oil in 50% yield after chro-
matographic purification (Scheme 3).
As was the case with compounds 1–5, compounds 9–12 are air- and
moisture-stable and are freely soluble in common organic solvents. Character-
1
ization was accomplished with H and 13C NMR spectroscopy.
CONCLUSION
In conclusion, we describe the synthesis of new cholane derivatives with
various electron-donor substituent patterns at the 3- and 24-positions. The
chemistry is straightforward, and the products are obtained in good to
excellent yields after chromatographic purification. Derivatives with noniden-
tical substitution can be obtained by an initial functionalization at the more
reactive 24-position, followed by modification at the 3-position. Excellent
solubility properties and the presence of electron-donor groups in the
modified steroids described herein may be advantageous in applications
such as steroid-metal conjugate synthesis, for example.

1322
S. R. Gondi and D. Y. Son
EXPERIMENTAL
All reactions were carried out in a dry nitrogen atmosphere. 1H and 13C NMR
spectra were obtained on a 400-MHz Bruker Avance NMR spectrometer. All
starting materials were obtained commercially and used as received. Mass spec-
trometry was provided by the Washington University Mass Spectrometry
Resource with support from the National Institutes of Health (NIH) National
Center for Research Resources (Grant No. P41RR0954). Elemental analyses
were obtained with a CE Elantech Thermo-Finnigan Flash 1112 CHN
elemental analyzer. Cholane-3,24-diol (3a,5b) (1) was prepared by esterification
of lithocholic acid[42] followed by LAH reduction in THF.[43] a-Benzyloximino
acid chloride[44] and 1,3-dithiolane-2-carbonyl chloride[41] were prepared as
described previously.
Synthesis of Bis(nicotinate) Ester 2
Nicotinic acid (740 mg, 0.006 mol) was dissolved in dichloromethane (20 mL)
and cooled in a water/ice bath. 1-Hydroxybenzotriazole (HOBt, 0.820 g,
0.006 mol) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochlo-
ride (EDCI, 1.16 g, 0.006 mol) were added, and the resulting mixture was
stirred in the ice bath for 30 min to give a white precipitate. A solution of 1
(1.0 g, 0.0027 mol) in dichloromethane (10 mL) was added; the resulting
mixture was allowed to warm to room temperature and was stirred for 48 h.
The reaction mixture was then poured into 10% aqueous sodium bicarbonate
solution (100 mL) and stirred for 30 min. The aqueous layer was extracted with
dichloromethane (2 ꢀ 100 mL), and the combined organic layers were washed
with 10% aqueous sodium bicarbonate solution (100 mL), water (100 mL),
and brine (100 mL). The organic layer was then dried over anhydrous
MgSO4 and filtered. Removal of volatiles using a rotary evaporator gave a
residue, which was purified by column chromatography (SiO2, 1 : 1 EtOAc–
1
hex) to give 2 as an oil (1.26 g, 80%). Rf 0.2 (1 : 1 EtOAc–hex). H NMR
(CDCl3): 9.16 (s, 2H), 8.71–8.69 (t, 2H, J ¼ 4.8 Hz), 8.25–8.23 (d, 2H,
J ¼ 6.8 Hz), 7.35–7.31 (m, 2H), 4.96–4.91 (m, 1H), 4.27–4.25 (m, 2H),
1.94–1.03 (m, 28H), 0.90 (s, 6H), 0.60 (s, 3H). 13C NMR (CDCl3): 164.9,
164.4, 152.9, 152.8, 150.5, 150.4, 136.9, 136.8, 126.5, 126.2, 123.1, 123.0,
75.4, 65.8, 56.2, 55.8, 42.5, 41.7, 40.3, 39.9, 35.6, 35.1, 34.8, 34.4, 32.0,
31.8, 28.0, 26.8, 26.5, 26.1, 25.0, 23.9, 23.1, 20.6, 18.4, 11.8. IR (neat):
2940, 2866, 1720, 1591 (strong), 1459, 1342, 979 cm21 (medium). HRMS:
calcd. for C36H48N2O4 (M þ Li): 579.3774. Found: 579.3754.
Synthesis of Bis(1,3-dithiolanyl) 3
Diol 1 (1.0 g, 0.0027 mol) was dissolved in THF (15 mL) and cooled in a
water/ice bath. Sodium hydride (160 mg, 0.0066 mol) was then added, and

Cholane Derivatives
1323
the resulting suspension was stirred for 15 min. A solution of 1,3-dithialone-2-
carbonyl chloride (1.02 g, 0.006 mol) in THF (15 mL) was added dropwise
over a period of 15 min; the resulting mixture was allowed to warm to room
temperature and was stirred for 6 h. The THF was removed using a rotary
evaporator, and the residue was quenched by the addition of water
(100 mL). The aqueous solution was extracted with ethyl acetate (100 mL),
and the organic layer was washed with water (100 mL), saturated aqueous
sodium bicarbonate solution (100 mL), water again (100 mL), and brine
(100 mL). The organic solution was then dried over anhydrous MgSO4 and
filtered. Removal of volatiles using a rotary evaporator gave a residue,
which was purified using column chromatography (SiO2, 10 : 90 EtOAc–
hex, then 15 : 85 EtOAc–hex) to give slightly impure 3 (1.1 g). Repeated
column chromatography gave pure 3 as an oil (1.0 g, 59%). Rf 0.6 (20 : 80
EtOAc–hex). 1H NMR (CDCl3): 4.77 (s, 1H), 4.73 (s, 1H), 4.64–4.63
(m, 1H), 4.04–4.00 (m, 2H), 3.39–3.36 (m, 4H), 3.27–3.24 (m, 4H), 1.77–
0.95 (m, 24H), 0.86–0.81 (m, 6H), 0.58 (s, 3H). 13C NMR (CDCl3): 171.2,
170.6, 75.9, 66.5, 56.4, 56.0, 50.7, 50.5, 42.6, 41.8, 40.4, 40.0, 38.7, 35.7,
35.2, 34.9, 34.5, 31.9, 31.8, 28.2, 26.9, 26.3, 26.2, 25.0, 24.1, 23.2, 20.8,
18.5, 12.0. IR (neat): 2932, 2865, 1732, 1160 (strong), 1621, 1450,
986 cm21 (medium). HRMS: calcd. for C32H50O4S4 (M þ Li): 633.2752.
Found: 633.2756.
Synthesis of Bis(oxime Ether) 4 and Mono(oxime Ether) 5
Diol 1 (0.80 g, 0.0022 mol) was dissolved in THF (15 mL) and cooled in a
water/ice bath. Sodium hydride (130 mg, 0.0052 mol) was added, and the
resulting suspension was stirred for 15 min. A solution of a-benzyloximino
acid chloride (0.96 g, 0.0048 mol) dissolved in THF (15 mL) was added
dropwise over a period of 15 min. The mixture was then allowed to warm
to room temperature and was stirred for 6 h. The THF was removed using
rotary evaporation, and the residue was quenched by the addition of water
(100 mL). The aqueous solution was extracted with ethyl acetate (100 mL),
and the organic layer was washed with water (100 mL), saturated aqueous
sodium bicarbonate solution (100 mL), water again (100 mL), and brine
(100 mL). The organic solution was dried over anhydrous MgSO4, and all
volatiles were removed using a rotary evaporator. The residue was purified
using column chromatography (SiO2, 10 : 90 EtOAc–hex, 15 : 85 EtOAc–
hex, then 30 : 70 EtOAc–hex) to give bis(oxime ether) 4 (600 mg, 40%) and
mono(oxime ether) 5 (270 mg, 23%) as colorless oils. Rf(4) 0.6, Rf(5)
0.4 (20 : 80 EtOAc–hex). Compound 4: 1H NMR (CDCl3): 7.46–7.45
(d, 2H, J ¼ 5.6 Hz), 7.28–7.26 (d, 10H, J ¼ 8.8 Hz), 5.22–5.21 (d, 4H,
J ¼ 3.0 Hz), 4.85–4.79 (m, 1H), 4.16–4.08 (m, 2H), 1.98–0.97 (m, 24H),
0.86–0.83 (m, 6H), 0.56 (s, 3H). 13C NMR (CDCl3): 161.9, 161.4, 141.6,
141.1, 136.0, 135.9, 128.8, 128.3, 128.2, 78.0, 77.9, 76.0, 66.1, 56.4, 56.0,

1324
S. R. Gondi and D. Y. Son
42.6, 41.9, 40.3, 40.1, 35.7, 35.3, 34.9, 34.5, 32.0, 31.7, 28.2, 26.9, 26.4,
26.2, 25.0, 24.1, 23.2, 20.8, 18.5, 12.0. IR (neat): 2941, 2868, 1735, 1600,
1455 (strong), 1332, 910 cm21 (medium). HRMS: calcd. for C42H56N2O6
(M þ Li): 691.4298. Found: 691.4323. Compound 5: 1H NMR (CDCl3):
7.55 (s, 1H), 7.37–7.35 (d, 5H, J ¼ 8.8 Hz), 5.30 (s, 2H), 4.24–4.20
(m, 2H), 3.65–3.60 (m, 1H), 1.93–0.97 (m, 24H), 0.94–0.93 (m, 6H), 0.65
(s, 3H). 13C NMR (CDCl3): 161.8, 141.0, 135.9, 128.5, 128.4, 128.3, 77.9,
71.6, 66.0, 56.0, 55.9, 42.6, 42.0, 40.3, 40.0, 36.3, 35.7, 35.3, 35.2, 34.4,
31.6, 30.4, 28.1, 27.1, 26.3, 24.9, 24.1, 23.2, 20.7, 18.4, 11.9. IR (neat):
3401 (broad peak-OH), 2936, 2869, 1720 (strong), 1600, 1453, 1196 cm21
(medium). HRMS: calcd. for C33H49NO4 (M þ Li): 530.3822. Found:
530.3816. Repeating these procedure using only 1.2 equiv of a-benzyloxi-
mino acid chloride gave a 55% yield of 5 and a 15% yield of 4 after chromato-
graphic purification.
Synthesis of Cholane-3-methanesulfonyl-24-iodo (3a,5b) 7
Cholane-3,24-bis(methanesulfonyl) (3a,5b) was first prepared in the
following manner. Diol 1 (1.0 g, 0.0027 mol) was dissolved in THF (15 mL)
and cooled in a water/ice bath. Triethylamine (0.93 mL, 0.0066 mol) was
added, and the mixture was stirred for 15 min. Methanesulfonyl chloride
(695 mg, 0.006 mol) was added; the mixture was allowed to warm to room
temperature and was stirred for 4 h. Solvent was removed using a rotary evap-
orator, and the residue was extracted with ethyl acetate (2 ꢀ 100 mL). The
organic solution was washed with 10% aqueous sodium bicarbonate
solution and brine and dried over anhydrous MgSO4. Filtration and removal
of volatiles using a rotary evaporator gave a residue, which was purified
using column chromatography (SiO2, 30 : 70 EtOAc–hex) to give cholane-
3,24-bis(methanesulfonyl) (3a,5b) as a white solid (1.30 g, 91%). Mp
1
1588C (lit. mp 138.9–141.28C[45]). H NMR (CDCl3): 4.68–4.63 (m, 1H),
4.21–4.19 (t, 2H, J ¼ 3.4 Hz), 3.01 (s, 6H), 2.07–1.83 (m, 2H), 1.65–1.03
(m, 26H), 0.94 (s, 6H), 0.65 (s, 3H). 13C NMR (CDCl3): 82.9, 70.2, 56.3,
55.9, 42.6, 42.0, 40.3, 39.9, 38.7, 37.3, 35.6, 35.2, 34.9, 34.3, 33.3, 31.4,
28.1, 27.7, 26.8, 26.1, 25.7, 24.0, 23.0, 20.7, 18.4, 11.9. IR (neat): 2937,
2866, 1449, 1352, 1173, 926 (strong), 867 cm21 (medium). Elemental
analysis: calcd.: C, 60.20; H, 8.94. Found: C, 60.18; H, 9.30.
Cholane-3,24-bis(methanesulfonyl) (3a,5b) (3.0 g, 0.0057 mol) was
dissolved in acetone (75 mL), and then sodium iodide (1.90 g, 0.0127 mol)
was added. The resulting mixture was heated at reflux for 4 h and then
cooled to room temperature. Removal of volatiles using rotary evaporation
gave
a solid residue, which was extracted with dichloromethane
(2 ꢀ 100 mL). The organic solution was washed with 10% aqueous sodium
bicarbonate solution and brine, and then dried over anhydrous magnesium
sulfate and filtered. Removal of volatiles using a rotary evaporator gave a

Cholane Derivatives
1325
residue, which was purified using column chromatography (SiO2, 10 : 90
EtOAc–hex) to give 7 as a white solid (2.75 g, 87%). Rf 0.7 (40 : 60
1
EtOAc–hex). Mp 1248C. H NMR (CDCl3): 4.69–4.63 (m, 1H), 3.23–3.01
(m, 2H), 3.01 (s, 3H), 2.08–1.90 (m, 2H), 1.89–1.04 (m, 26H), 0.94–0.92
(m, 6H), 0.65 (s, 3H). 13C NMR (CDCl3): 82.9, 56.4, 56.0, 42.7, 42.1, 40.4,
40.0, 38.8, 36.8, 35.7, 35.0, 34.9, 34.3, 33.3, 30.3, 28.2, 27.8, 26.8, 26.2,
24.1, 23.1 20.7, 18.6, 12.0, 7.8. IR (neat): 2941, 2868, 1450, 1354, 926
(strong), 868 cm21 (medium). Elemental analysis: calcd.: C, 54.54; H, 7.87.
Found: C, 54.79; H, 7.93.
Synthesis of Cholane-3,24-diiodo (3a,5b) 8
Compound 7 (2.0 g, 0.0038 mol) was dissolved in acetone (75 mL). Sodium
iodide (1.15 g, 0.0078 mol) was added, and the mixture was heated at reflux
for 48 h and then cooled to room temperature. Removal of volatiles using a
rotary evaporator gave a solid residue, which was extracted with dichloro-
methane (2 ꢀ 100 mL). The organic layer was washed with 10% aqueous
sodium bicarbonate solution and brine, and then dried over anhydrous
magnesium sulfate and filtered. Volatiles were removed using a rotary evap-
orator, and the residue was purified using column chromatography (SiO2,
10 : 90 EtOAc–hex) to give 8 as a white solid (2.1 g, 81%). Rf 0.6 (10 : 90
EtOAc–hex). Mp 1018C. NMR spectroscopy indicated that the product
consisted of a mixture of C3 epimers. IR (KBr): 2935, 2858, 1454, 1376
(strong), 949 cm21 (medium). Elemental analysis: calcd.: C, 49.50; H, 6.92.
Found: C, 49.45; H, 6.83.
Synthesis of 9
Mono(oxime ether) 5 (1.0 g, 0.0019 mol) was dissolved in THF (15 mL) and
cooled in a water/ice bath. Sodium hydride (55 mg, 0.0019 mol) was added,
and the mixture was stirred for 15 min to give a clear solution. A solution
of 1,3-dithiolane-2-carbonyl chloride (1.02 g, 0.006 mol) in THF (10 mL)
was added dropwise over a period of 15 min, and the mixture was stirred at
room temperature for 6 h. Volatiles were removed under reduced pressure,
and the residue was quenched by the addition water (10 mL). The mixture
was then extracted with ethyl acetate (100 mL); the organic layer was
washed with saturated aqueous sodium bicarbonate solution (100 mL),
water (100 mL), and brine (100 mL), dried over anhydrous MgSO4, and
filtered. Removal of volatiles using a rotary evaporator gave an oil, which
was purified using column chromatography (SiO2, 10 : 90 EtOAc–hex) to
give 9 as an oil (975 mg, 78%). Rf 0.6 (20 : 80 EtOAc–hex). 1H NMR
(CDCl3): 7.46 (s, 1H), 7.28 (s, 5H), 5.21 (s, 2H), 4.72 (s, 1H), 4.63–4.62
(m, 1H), 4.14–4.12 (d, 2H, J ¼ 6.0 Hz), 3.39–3.33 (m, 2H), 3.23–3.20

1326
S. R. Gondi and D. Y. Son
(m, 2H), 1.90–1.03 (m, 28H), 1.01–0.85 (m, 6H), 0.56 (s, 3H). 13C NMR
(CDCl3): 170.8, 161.8, 141.0, 135.9, 128.4, 128.3, 77.9, 76.1, 66.0, 56.3,
55.9, 50.7, 42.6, 41.8, 40.3, 40.0, 38.7, 35.6, 35.2, 34.8, 34.4, 31.8, 31.6,
28.1, 26.9, 26.3, 26.2, 24.9, 24.0, 23.2, 20.7, 18.4, 11.9. IR (neat): 2938,
2867, 1731, 1600, 1453 (strong), 925 cm21 (medium).
Synthesis of 10
Diol 1 (4.0 g, 0.011 mol) was dissolved in THF (80 mL) and cooled in a water/
ice bath. Triethylamine (3.1 mL, 0.022 mol) was added, and the solution was
stirred for 15 min. p-Toluenesulfonyl chloride (4.2 g, 0.022 mol) was added,
and the resulting mixture was stirred at room temperature for 72 h. Volatiles
were removed using a rotary evaporator, and the residue was extracted with
ethyl acetate (2 ꢀ 100 mL). The organic layers were washed with 10%
aqueous sodium bicarbonate solution and brine, then dried over anhydrous
MgSO4 and filtered. Removal of volatiles using a rotary evaporator gave a
residue, which was purified using column chromatography (SiO2, 30 : 70
EtOAc–hex) to give cholane-3-ol-24-(p-toluenesulfonyl) (3a,5b) as a white
solid (3.75 g, 65%). Rf 0.7 (50 : 50 EtOAc–hex). Mp 2078C (lit. reported as
an oil).[46] 1H NMR (CDCl3): 7.77–7.73 (d, 2H, J ¼ 8.0 Hz), 7.35–7.33
(d, 2H, J ¼ 8.0 Hz), 4.01–3.97 (m, 2H), 3.64–3.58 (m, 1H), 2.44 (s, 3H),
1.93–0.95 (m, 28H), 0.90 (s, 3H), 0.85–0.83 (d, 3H, J ¼ 6.2 Hz), 0.59
(s, 3H). 13C NMR (CDCl3): 144.5, 133.2, 129.7, 127.7, 71.7, 71.2, 56.4,
55.9, 42.5, 42.0, 40.3, 40.0, 36.3, 35.7, 35.3, 35.1, 34.4, 31.3, 30.4, 28.1,
27.1, 26.3, 25.4, 24.1, 23.2, 21.5, 20.7, 18.3, 11.9. IR (neat): 2931, 1176
(strong), 1598, 1448, 1176 cm21 (medium). Elemental analysis: calcd.: C,
72.05; H, 9.36. Found: C, 71.60; H, 9.25.
Cholane-3-ol-24-(p-toluenesulfonyl) (3a,5b) (2.0 g, 0.0038 mol) was
dissolved in acetone (60 mL), and sodium iodide (1.15 g, 0.0078 mol) was
added. The resulting mixture was refluxed for 4 h, and then volatiles were
removed using a rotary evaporator. The residue was extracted with ethyl
acetate (2 ꢀ 100 mL); the combined organic layers were washed with 10%
aqueous sodium bicarbonate solution and brine, and then dried over
anhydrous MgSO4 and filtered. Removal of volatiles using a rotary evaporator
gave a residue, which was purified using column chromatography (SiO2,
10 : 90 EtOAc–hex) to give cholane-3-ol-24-iodo (3a,5b) as a white solid
(1.65 g, 92%). Rf 0.8 (50 : 50 EtOAc–hex). Mp 1438C (lit. mp 131–
1348C[46]). 1H NMR (CDCl3): 3.64–3.62 (m, 1H), 3.20–3.12 (m, 2H),
1.94–1.04 (m, 28H), 0.92-0.91 (d, 6H, J ¼ 4.8 Hz), 0.64 (s, 3H). 13C NMR
(CDCl3): 71.8, 56.4, 56.0, 42.6, 42.0, 40.4, 40.1, 36.8, 36.4, 35.8, 35.4,
35.0, 34.5, 30.5, 30.3, 28.2, 27.1, 26.4, 24.1, 23.3, 20.8, 18.6, 12.0, 7.8. IR
(KBr): 3332 (broad peak-OH), 2927, 2863, 1449, 1360, 1176 (strong),
917 cm21 (medium). Elemental analysis: calcd.: C, 61.01; H, 8.75. Found:
C, 60.95; H, 8.75.

Cholane Derivatives
1327
Sodium hydride (56 mg, 0.0023 mol) was suspended in THF (5 mL) and
cooled in a water/ice bath. A solution of thiophenol (280 mg, 0.0025 mol)
in THF (10 mL) was added, and the suspension was stirred for 15 min. A
solution of cholane-3-ol-24-iodo (3a,5b) (1.0 g, 0.0021 mol) in THF
(10 mL) was added dropwise over a period of 15 min. The resulting mixture
was stirred at room temperature for 12 h, and then poured into a beaker con-
taining 100 mL of water. The aqueous solution was extracted with ethyl
acetate (100 mL). The organic layer was washed with water (100 mL) and
brine (100 mL), followed by drying over anhydrous MgSO4 and filtration.
Removal of volatiles using a rotary evaporator gave a solid residue, which
was purified using column chromatography (SiO2, 10 : 90 EtOAc–hex, then
20 : 80 EtOAc–hex) to give 10 as a white solid (820 mg, 85%). Rf 0.6
(20 : 80 EtOAc–hex). Mp 106–1088C. 1H NMR (CDCl3): 7.24–7.16
(m, 4H), 7.08–7.05 (t, 1H, 6.9 Hz), 3.54–3.52 (m, 1H), 2.83–2.78 (m, 2H),
1.89–0.99 (m, 28H), 0.96–0.80 (m, 6H), 0.55 (s, 3H). 13C NMR (CDCl3):
137.0, 128.7, 128.6, 125.4, 71.6, 56.3, 56.0, 42.6, 42.0, 40.3, 40.0 36.3,
35.7, 35.3, 35.2, 35.0, 34.4, 33.9, 30.4, 28.1, 27.1, 26.3, 25.7, 24.1, 23.2,
20.7, 18.5, 11.9. IR (neat): 2930, 2862, 1479, 1375 (strong), 1031 cm21
(medium).
Synthesis of 11
Sodium hydride (58 mg, 0.0024 mol) was suspended in THF (5 mL) and
cooled in a water/ice bath. A solution of 10 (1.0 g, 0.0022 mol) in THF
(10 mL) was added, and the resulting suspension was stirred for 15 min. A
solution of a-benzyloximino acid chloride (520 mg, 0.0026 mol) in THF
(10 mL) was added dropwise over a period of 15 min. The resulting
mixture was stirred at room temperature for 18 h, and then poured into a
beaker containing 100 mL of water. The aqueous solution was extracted
with ethyl acetate (100 mL), and the organic layer was washed with
aqueous sodium bicarbonate solution (100 mL), water (100 mL), and brine
(100 mL). The solution was dried over anhydrous MgSO4 and filtered.
Removal of volatiles using a rotary evaporator gave a residual oil, which
was purified using column chromatography (SiO2, 5 : 95 EtOAc–hex) to
give 11 as a white solid (740 mg, 55%). Rf 0.8 (30 : 70 EtOAc–hex). Mp
1
144–1468C. H NMR (CDCl3): 7.45 (s, 1H), 7.30–7.18 (m, 9H), 7.10–
7.06 (t, 1H, J ¼ 7.2 Hz), 5.23 (s, 1H), 4.85–4.80 (m, 1H), 2.85–2.78
(m, 2H), 1.90–0.97 (m, 28H), 0.86–0.82 (d, 3H, J ¼ 13.8 Hz), 0.81
(s, 3H), 0.56 (3H). 13C NMR (CDCl3): 161.5, 141.6, 137.0, 136.0, 128.8,
128.7, 128.6, 128.5, 128.4, 125.6, 77.9, 76.0, 56.4, 56.1, 42.7, 41.9, 40.4,
40.1, 35.8, 35.5, 35.1, 35.0, 34.6, 34.1, 32.0, 28.2, 27.0, 26.4, 26.3, 25.8,
24.1, 23.2, 20.8, 18.6, 12.0. IR (neat): 2938, 2867, 1733 (strong), 1599,
1480, 1331 cm21 (medium).

1328
S. R. Gondi and D. Y. Son
Synthesis of 12
Sodium hydride (30 mg, 0.0023 mol) was suspended in THF (5 mL) and
cooled in a water/ice bath. A solution of 10 (0.5 g, 0.0011 mol) dissolved in
THF (10 mL) was added, and the resulting suspension was stirred for
15 min. A solution of 1,3-dithiolane-2-carbonyl chloride (1.02 g, 0.006 mol)
in THF (10 mL) was added dropwise over a period of 15 min. The mixture
was stirred for 12 h at room temperature and then poured into a beaker contain-
ing 100 mL of water. The aqueous solution was extracted with ethyl acetate
(100 mL), and the organic layer was washed with aqueous sodium bicarbonate
solution (100 mL), water (100 mL), and brine (100 mL). The solution was then
dried over anhydrous MgSO4 and filtered. Removal of volatiles using a rotary
evaporator gave a residual oil, which was purified using column chromato-
graphy (SiO2, 5 : 95 EtOAc–hex, then 10 : 90 EtOAc–hex) to give 12 as an
1
oil (320 mg, 50%). Rf 0.6 (30 : 70 EtOAc–hex). H NMR (CDCl3): 7.26–
7.19 (m, 4H), 7.10–7.07 (t, 1H, J ¼ 7.0 Hz), 4.73, (s, 1H), 4.67–4.62
(m, 1H), 3.39–3.34 (m, 2H), 3.26–3.23 (m, 2H), 2.81–2.78 (m, 2H), 1.76–
0.98 (m, 28H), 0.85–0.81 (m, 6H), 0.56 (s, 3H). 13C NMR (CDCl3): 170.9,
137.0, 128.8, 128.7, 125.6, 76.2, 56.4, 56.1, 50.8, 42.7, 41.9, 40.4, 40.1,
38.8, 35.7, 35.4, 35.1, 34.9, 34.5, 34.1, 31.9, 28.2, 26.9, 26.4, 26.3, 25.8,
24.1, 23.2, 20.8, 18.6, 12.0. IR (neat): 2925, 1731, 1584, 1480 (strong),
1223 cm21 (medium).
ACKNOWLEDGMENTS
The authors thank the National Science Foundation (Grant No. 0092495) and
the Welch Foundation (Grant N-1375) for support of this work.
REFERENCES
1. DiZio, J. P.; Flaschi, R.; Davison, A.; Jones, A. G.; Katzenellenbogen, J. A.
Progestin–rhenium complexes: Metal-labeled steroids with high receptor binding
affinity, potential receptor-directed agents for diagnostic imaging or therapy.
Bioconjugate Chem. 1991, 2, 353–366.
2. O’Neil, J. P.; Carlson, K. E.; Anderson, C. J.; Welch, M. J.;
Katzenellenbogen, J. A. Progestin radiopharmaceuticals labeled with technetium
and rhenium: Synthesis, binding affinity, and in vivo distribution of a new
progestin n2s2-metal conjugate. Bioconjugate Chem. 1994, 5, 182–193.
3. Spies, H.; Johannsen, B. Functionalization of technetium complexes to make them
active in vivo. Analyst 1995, 120, 775–777.
4. Top, S.; El Hafa, H.; Vessieres, A.; Quivy, J.; Vaissermann, J.; Hughes, D. W.;
McGlinchey, M. J.; Mornon, J.-P.; Thoreau, E.; Jaouen, G. Rhenium carbonyl
complexes of b-estradiol derivatives with high affinity for the estradiol receptor:

Cholane Derivatives
1329
An approach to selective organometallic radiopharmaceuticals. J. Am. Chem. Soc.
1995, 117, 8372–8380.
5. Katzenellenbogen, J. A. Designing steroid receptor-based radiotracers to image
breast and prostate tumors. J. Nucl. Med. 1995, 36, 8S–13S.
6. Katzenellenbogen, J. A.; Welch, M. J.; Dehdashti, F. The development of estrogen
and progestin radiopharmaceuticals for imaging breast cancer. Anticanc. Res.
1997, 17, 1573–1576.
7. Hom, R. K.; Katzenellenbogen, J. A. Technetium-99 m-labeled receptor-specific
small-molecule radiopharmaceuticals: Recent developments and encouraging
results. Nucl. Med. Biol. 1997, 24, 485–498.
8. Jurisson, S. S.; Lydon, J. D. Potential technetium small molecule radiopharmaceu-
ticals. Chem. Rev. 1999, 99, 2205–2218.
9. Skaddan, M. B.; Wust, F. R.; Katzenellenbogen, J. A. Synthesis and binding affi-
nities of novel re-containing 7a-substituted estradiol complexes: Models for breast
cancer imaging agents. J. Org. Chem. 1999, 64, 8108–8121.
10. Luyt, L. G.; Bigott, H. M.; Welch, M. J.; Katzenellenbogen, J. A. 7a- and 17a-sub-
stituted estrogens containing tridentate tricarbonyl rhenium/technetium
complexes: Synthesis of estrogen receptor imaging agents and evaluation using
micropet with technetium-94m. Bioorg. Med. Chem. 2003, 11, 4977–4989.
11. Kawano, S.-I.; Fujita, N.; Bommel, K. J. C. V.; Shinkai, S. Pyridine-containing
cholesterols as versatile gelators of organic solvents and the subtle influence of
ag(i) on the gel stability. Chem. Lett. 2003, 32, 12–13.
12. Xue, P.; Lu, R.; Huang, Y.; Jin, M.; Tan, C.; Bao, C.; Wang, Z.; Zhao, Y. Novel
pearl-necklace porous CdS nanofiber templated by organogel. Langmuir 2004, 20,
6470–6475.
13. Sugiyasu, K.; Fujita, N.; Shinkai, S. Visible-light-harvesting organogel composed
of cholesterol-based perylene derivatives. Angew. Chem., Int. Ed. Engl. 2004, 43,
1229–1233.
14. Wallimann, P.; Marti, T.; Furer, A.; Diederich, F. Steroids in molecular recog-
nition. Chem. Rev. 1997, 97, 1567–1608.
15. Tamminen, J.; Kolehmainen, E. Bile acids as building blocks of supramolecular
hosts. Molecules 2001, 6, 21–46.
´
ˆ
16. Dukh, M.; Draesar, P.; Cerny, I.; Pouzar, V.; Shriver, J. A.; Kraal, V.; Sessler, J. L.
Novel deep cavity calix[4]pyrroles derived from steroidal ketones. Supramol.
Chem. 2002, 14, 237–244.
17. Virtanen, E.; Kolehmainen, E. Use of bile acids in pharmacological and supramo-
lecular applications. Eur. J. Org. Chem. 2004, 3385–3399.
18. Campazzi, E.; Cattabriga, M.; Marvelli, L.; Marchi, A.; Rossi, R.;
Pieragnoli, M. R.; Fogagnolo, M. Organometallic radiopharmaceuticals:
Rhenium(i) carbonyl complexes of natural bile acids and derivatives. Inorg.
Chim. Acta 1999, 286, 46–54.
19. Walker, S.; Sofia, M. J.; Kakarla, R.; Kogan, N. A.; Wierichs, L.; Longley, C. B.;
Bruker, K.; Axelrod, H. R.; Midha, S.; Babu, S.; Kahne, D. Cationic facial amphi-
philes: A promising class of transfection agents. Proc. Natl. Acad. Sci. USA 1996,
93, 1585–1590.
20. Geall, A. J.; Al-Hadithi, D.; Blagbrough, I. S. Spermine and thermine conjugates of
cholic acid condense DNA, but lithocholic acid polyamine conjugates do so more
efficiently. Chem. Commun. 1998, 2035–2036.
21. Walker, S.; Sofia, M. J.; Axelrod, H. R. Chemistry and cellular aspects of cationic
facial amphiphiles. Adv. Drug Deliv. Rev. 1998, 30, 61–71.

1330
S. R. Gondi and D. Y. Son
22. Blagbrough, I. S.; Geall, A. J.; Neal, A. P. Polyamines and novel polyamine con-
jugates interact with DNA in ways that can be exploited in non-viral gene therapy.
Biochem. Soc. Trans. 2003, 31, 397–406.
23. Criado, J. J.; Herrera, M. C.; Palomero, M. F.; Medarde, M.; Rodriguez, E.;
Marin, J. J.G. Synthesis and characterization of a new bile acid and platinum(ii)-
complex with cytostatic activity. J. Lipid Res. 1997, 38, 1022–1032.
24. Paschke, R.; Kalbitz, J.; Paetz, C. Novel spacer linked bile acid-cisplatin
compounds as a model for specific drug delivery, synthesis and characterization.
Inorg. Chim. Acta 2000, 304, 241–249.
25. Larena, M. G.; Martinez-Diez, M. C.; Macias, R. I. R.; Dominguez, M. F.;
Serrano, M. A.; Marin, J. J. G. Relationship between tumor cell load and sensitivity
to the cytostatic effect of two novel platinum–bile acid complexes, bamet-d3 and
bamet-ud2. J. Drug Targ. 2002, 10, 397–404.
26. Paschke, R.; Paetz, C.; Mueller, T.; Schmoll, H.-J.; Mueller, H.; Sorkau, E.;
Sinn, E. Biomolecules linked to transition metal complexes—new chances for che-
motherapy. Curr. Medicinal Chem. 2003, 10, 2033–2044.
27. Paschke, R.; Kalbitz, J.; Paetz, C.; Luckner, M.; Mueller, T.; Schmoll, H.-J.;
Mueller, H.; Sorkau, E.; Sinn, E. Cholic acid–carboplatin compounds (carbochapt)
as models for specific drug delivery: Synthesis of novel carboplatin analogous
derivatives and comparison of the cytotoxic properties with corresponding
cisplatin compounds. J. Inorg. Biochem. 2003, 94, 335–342.
28. Marin, J. J.G.; Romero, M. R.; Vallejo, M.; Monte, M. J. Targeting of cytostatic
bile acid derivatives toward tumours of the enterohepatic circuit. Cancer Ther.
2005, 3, 57–64.
29. Wu¨st, F.; Spies, H.; Johannsen, B. Synthesis of “3 þ 1” mixed-ligand oxorhe-
nium(V) complexes containing modified 3,17b-estradiol. Bioorg. Med. Chem.
Lett. 1996, 6, 2729–2734.
30. Reisgys, M.; Wuest, F.; Alberto, R.; Schibli, R. Synthesis of rhenium(I) and tech-
netium(I) carbonyl/dithioether ligand complexes bearing 3,17a-estradiol. Bioorg.
Med. Chem. Lett. 1997, 7, 2243–2246.
31. Wu¨st, F.; Spies, H.; Johannsen, B. Synthesis of 17a-substituted mercaptoalkynyl
derivatives of 3,17a-estradiol. Tetrahedron Lett. 1997, 38, 2931–2932.
32. Wu¨st, F.; Scheller, D.; Spies, H.; Johannsen, B. Synthesis of oxorhenium(V)
complexes derived from 7a-functionalized testosterone: First rhenium-containing
testosterone derivatives. Eur. J. Inorg. Chem. 1998, 789–793.
33. Wu¨st, F.; Carlson, K. E.; Katzenellenbogen, J. A.; Spies, H.; Johannsen, B.
Synthesis and binding affinities of new 17a-substituted estradiol-rhenium
“n þ 1” mixed-ligand and thioether-carbonyl complexes. Steroids 1998, 63,
665–671.
34. Wu¨st, F.; Skaddan, M. B.; Leibnitz, P.; Spies, H.; Katzenellenbogen, J. A.;
Johannsen, B. Synthesis of novel progestin–rhenium conjugates as potential
ligands for the progesterone receptor. Bioorg. Med. Chem. 1999, 7, 1827–1835.
35. Spera, D.; Cabrera, G.; Fiaschi, R.; Carlson, K. E.; Katzenellenbogen, J. A.;
Napolitano, E. Estradiol derivatives bearing sulfur-containing substituents at the
11b or 7a positions: Versatile reagents for the preparation of estrogen conjugates.
Bioorg. Med. Chem. 2004, 12, 4393–4401.
36. Kim, S. J.; Bang, E.-K.; Kwon, H. J.; Shim, J. S.; Kim, B. H. Modified oligonucleo-
tides containing lithocholic acid in their backbones: Their enhanced cellular uptake
and their mimicking of hairpin structures. Chem. Bio. Chem. 2004, 5, 1517–1522.

Cholane Derivatives
1331
37. Sengupta, P.; Zhang, H.; Son, D. Y. Spacer flexibility in bis(pyridyl) ligands:
Chelating organosilicon pyridylethynyl ligands. Inorg. Chem. 2004, 43,
1828–1830.
38. Siaw-Lattey, C.; Zhang, H.; Son, D. Y. Synthesis and characterization of a
versatile bis(pyridylether) ligand and its complexes with ag(I), cu(II) and co(II).
Polyhedron 2005, 24, 785–790.
39. Kalra, M. K.; Zhang, H.; Son, D. Y. Helical metallopolymers from the coordi-
nation of new bis(pyridyl)terephthalate ligands with silver(I). Inorg. Chem.
Commun. 2004, 7, 1019–1022.
40. Gondi, S. R.; Son, D. Y. Synthesis of n,n-bis(2-thiazolinyl)-, n,n-bis(2-thiazolyl)-,
and n,n-bis(2-pyrimidinyl)-benzene dicarboxamides. Synth. Commun. 2004, 34,
3061–3072.
41. Gondi, S. R.; Son, D. Y. Mono-, bis-, and tris-1,3-dithiolane aromatic derivatives
by esterification and amidation reactions. J. Sulfur Chem. 2005, 26, 13–19.
42. Dayal, B.; Speck, J.; Bagan, E.; Tint, G. S.; Salen, G. P-toluenesulfonic acid/
methanol: Mild reagent for the preparation of bile acid methyl esters. Steroids
1981, 37, 239–242.
43. Kano, K.; Tatemoto, S.; Hashimoto, S. Specific interactions between sodium deox-
ycholate and its water-insoluble analogues: Mechanisms for premicelle and
micelle formation of sodium deoxycholate. J. Phys. Chem. 1991, 95, 966–970.
44. Herscheid, J. D. M.; Colstee, J. H.; Ottenheijm, H. C. J. 1,4-Dihydroxy-2,5-dioxo-
piperazines from activated n-hydroxy amino acids. J. Org. Chem. 1981, 46,
3346–3348.
45. Chang, F. C. Methanesulfonate esters of cholane alcohols. J. Pharm. Sci. 1964, 53,
1014–1016.
46. Kihira, K.; Mikami, T.; Ikawa, S.; Okamoto, A.; Yoshii, M.; Miki, S.;
Mosbach, E. H.; Hoshita, T. Synthesis of sulfonate analogs of bile acids.
Steroids 1992, 57, 193–198.