Nonsteroidal benzophenone-containing analogues of cholesterol

Article abstract of DOI:10.1021/jo060481q

The four benzophenones, 10-13, containing the natural side chain of cholesterol (1) have been synthesized to explore whether the tetracyclic nucleus of 1 is essential for its biochemical properties. The syntheses of analogues 10, 11, and 13 feature efficient introduction of the alkyl side chain by Suzuki coupling. Preliminary biochemical evaluation of 10 and 12 suggests that the sterol tetracyclic nucleus is not required for biological compatibility with 1.

Full text of DOI:10.1021/jo060481q

Nonsteroidal Benzophenone-Containing Analogues of Cholesterol
Yonghong Gan, David H. Blank, Joshua E. Ney, and Thomas A. Spencer*
Department of Chemistry, Dartmouth College, HanoVer, New Hampshire 03755
taspen@dartmouth.edu
ReceiVed March 6, 2006
The four benzophenones, 10-13, containing the natural side chain of cholesterol (1) have been synthesized
to explore whether the tetracyclic nucleus of 1 is essential for its biochemical properties. The syntheses
of analogues 10, 11, and 13 feature efficient introduction of the alkyl side chain by Suzuki coupling.
Preliminary biochemical evaluation of 10 and 12 suggests that the sterol tetracyclic nucleus is not required
for biological compatibility with 1.
Introduction
As part of a study of cellular cholesterol efflux and HDL
formation, we have been synthesizing benzophenone-containing
analogues of cholesterol (1) for use as photoaffinity labels. One
of these analogues, compound 2, designated FCBP, has already
been used to substitute successfully for 47% of cellular 1 without
perturbing smooth muscle cell function,1 to photolabel caveolin,
a key protein involved in cholesterol efflux, to obtain evidence
that the 1 transferred to apolipoprotein A-I (apo A-I) was
mainly derived from caveolin-rich domains,1 and to help
elucidate the mechanism of platelet-derived growth-factor-
dependent caveolin phosphorylation.2 Seven additional ben-
zophenone-containing analogues of 1, compounds 3-9, have
also been synthesized and have been shown, along with 2, to
substitute effectively for 1 in apo A-I-dependent cellular sterol
efflux.3 These eight compounds are the first demonstrated to
replace cholesterol successfully in a complex pathway of
multiple intracellular steps.
Analogues 2-7 have the benzophenone moiety extending or
replacing part of the sterol alkyl side chain. In analogues 8 and
9, the photophore is attached at the other end of the structure
* To whom correspondence should be addressed: Phone: 603-646-2805.
Fax: 603-646-3946.
via an amide linkage. The success of these compounds as
cholesterol surrogates led naturally to consideration of whether
analogues in which a benzophenone group replaced a major
portion of the tetracycle would also be accepted intracellularly.
To test this idea, we have prepared compounds 10-13 as
prospective cholesterol surrogates, and these syntheses and the
preliminary biochemical evaluation of 10 and 12 are described
(1) Fielding, P. E.; Russel, J. S.; Spencer, T. A.; Hakamata, H.; Nagao,
K.; Fielding, C. J. Biochemistry 2002, 41, 4929-4937.
(2) Fielding, P. E.; Chau, P.; Liu, D.; Spencer, T. A.; Fielding, C. J.
Biochemistry 2004, 43, 2578-2586.
(3) Spencer, T. A.; Wang, P.; Li, D.; Russel, J. S.; Blank, D. H.;
Huuskonen, J.; Fielding, P. E.; Fielding, C. J. J. Lipid Res. 2004, 45, 1510-
1518.
10.1021/jo060481q CCC: $33.50 © 2006 American Chemical Society
Published on Web 07/08/2006
5864
J. Org. Chem. 2006, 71, 5864-5869

Nonsteroidal Benzophenone-Containing Cholesterol Analogues
FIGURE 1. Spartan molecular modeling structures of cholesterol (1), analogue 10, and 1 superimposed on 10 in top and side views. The structure
of 1 was energy minimized and that of 10 was conformationally manipulated for most effective overlap using Dreiding models as a guide.
SCHEME 1. Synthesis of rac-10a
in this paper. Compounds with similarly placed hydroxyben-
zophenone groups have previously shown biological activity
as ligands for steroid 5R-reductase4 and the estrogen receptor.5
Comparison of structures 10-13 with cholesterol (1) by use of
the Spartan molecular modeling program indicated a reasonable
overall correspondence of size and shape, as illustrated for
compound 10 in Figure 1.
a Reagents and conditions: (a) Mg, Et2O, rt; (b) THF, 15 in Et2O, rt,
3 h; (c) Ph3SiH, tBuOOtBu, 140 °C, 5 h; (d) ClCOCOCl, PhH, ∆, 1 h; (e)
MeOPh, AlCl3, 140 °C, 4 h; (f) 57% HI, HOAc, ∆, 3.5 h.
catalyst,11 and trimethylsilyl iodide12 followed by NaBH4,13 all
failed to afford the desired product. Formation of 18 from 17
Results and Discussion
was finally achieved in a modest 36% yield by the use of
Syntheses of 10. The first successful approach to 10,
conducted initially to afford racemic product, involved reaction
triphenylsilane and tert-butyl peroxide.14 The (R,S)-18 thus
obtained was converted via Friedel-Crafts reaction of its acyl
chloride with anisole to afford (R,S)-19 in 79% yield, followed
by methyl ether cleavage with HI to afford (R,S)-10.
Since the overall yield of 10 by this approach was poor, an
alternate strategy was adopted for synthesis of enantiomerically
pure 10. As shown in Scheme 2, iodomethoxybenzophenone
2115 was prepared in 86% yield by Friedel-Crafts acylation of
anisole with the acid chloride of 20 and then combined with
the known (R)-3,7-dimethyloctene (22)16 by the Suzuki coupling
of Grignard reagent 15, derived from (R,S)-iodide 14,6 with
o-carboxybenzaldehyde (16) to afford 17, a diastereomeric
mixture, in a disappointing 50% yield (Scheme 1). It had been
anticipated that reduction of 17 to acid 18 would be facile, but
catalytic hydrogenation, without7 or with added HClO4,8 dis-
solving metal reduction,9,10 triethylsilane and Wilkinson’s
(4) Holt, D. A.; Yamashita, D. S.; Konialian-Beck, A. L.; Luengo, J. I.;
Abell, A. D.; Bergsma, D. J.; Brandt, M.; Levy, M. A. J. Med. Chem. 1995,
38, 13-15.
(5) Schultz, T. W.; Sinks, G. D.; Cronin, M. T. D. EnViron. Toxicol.
2002, 17, 14-23.
(6) Huo, S.; Negishi, E. Org. Lett. 2001, 3, 3253-3256 report preparation
of the R enantiomer of 14. In the present work, (R,S)-14 was prepared via
the corresponding (R,S)-bromide as described in Supporting Information.
(7) Shirasaka, T.; Takuma, Y.; Shimpuku, T.; Imaki, N. J. Org. Chem.
1990, 55, 3767-3771.
(8) Sinhabubu, A. K.; Borchardt, R. T. Synth. Commun. 1982, 12, 983-
988.
(9) Markgraf, J. H.; Hensley, W. M.; Shoer, L. I. J. Org. Chem. 1974,
39, 3168-3170.
(10) Nishizawa, M.; Yamada, H.; Hayashi, Y. J. Org. Chem. 1987, 52,
4878-4884.
(11) Liu, H.-J.; Zhu, B.-Y. Synth. Commun. 1990, 20, 557-562.
(12) Jung, M. E.; Lyster, M. A. J. Am. Chem. Soc. 1977, 99, 968-969.
(13) Clark, R. D.; Heathcock, C. H. Tetrahedron Lett. 1974, 1713-1715.
(14) Sano, H.; Ogata, M.; Migita, T. Chem. Lett. 1986, 77-80.
(15) Ma, Y.; Wang, Q. L.; Jiang, W.; Zuo, B. Appl. Catal., A 1997,
165, 199-206.
(16) Mori, K.; Kuwahara, S.; Levinson, H. Z.; Levinson, A. R.
Tetrahedron 1982, 38, 2291-2297.
J. Org. Chem, Vol. 71, No. 16, 2006 5865

Gan et al.
SCHEME 2. Synthesis of 10a
SCHEME 4. Synthesis of 12a
a Reagents and conditions: (a) ClCOCOCl, PhH, ∆, 1 h; (b) MeOPh,
AlCl3, 140 °C, 4 h; (c) Pd(dppf)Cl2, Cs2CO3, AsPh3, THF, DMF, H2O; (d)
product from 22 + 9-BBN, 4 h, rt; (e) ∆, overnight; (f) 57% HI, HOAc, ∆,
5 h.
SCHEME 3. Synthesis of 11a
a Reagents and conditions: (a) NaH, PhMe, 20 h, rt; (b) 55 psi H2, 10%
Pd/C, 95% EtOH, 4 days; (c) AlCl3, CS2, ∆, 5 h; MeOPh, AlCl3, 0 °C, 12
h; (d) 57% HI, HOAc, ∆, 5 h.
SCHEME 5. Synthesis of 13a
a Reagents and conditions: (a) SOCl2, PhH, ∆, 16 h; (b) MeOPh, AlCl3,
0 °C, 12 h; (c) Ph3PCH2, THF; (d) Pd(dppf)Cl2, Cs2CO3, AsPh3, THF, DMF,
H2O; (e) product from 26 + 9-BBN, 4 h, rt; (f) ∆, overnight; (g) 57% HI,
HOAc, ∆, 5 h.
procedure of Johnson and Braun17 to produce 65% of 19.
Hydriodic acid cleavage of 19 then gave 84% yield of (R)-10.
Synthesis of 11. The second 4-hydroxybenzophenone ana-
logue 11 was prepared via a Suzuki coupling route analogous
to that used to prepare 10 (Scheme 3). 3-Iodobenzoic acid (23)
was converted in 65% yield to benzophenone 24, and this was
coupled with (R)-4,8-dimethylnonene (26),18 prepared by Wittig
methylenation of 25, to afford 72% of 27, which was demeth-
ylated in 81% yield to 11.
Synthesis of 12. Synthesis of the isomeric cholesterol
analogue candidate 12 took advantage of the fact that Wittig
condensation of (R)-citronellal (28) with diethyl benzylphos-
phonate (29) to produce 30 (Scheme 4) had been reported.19
Hydrogenation of 30 thus prepared afforded 31 quantitatively.
Friedel-Crafts acylation of 31 with 32 afforded 94% of
benzophenone 33, which was converted to 12 in 81% yield by
treatment with hydriodic acid.
a Reagents and conditions: (a) 34, PBu3, THF, 20 min, rt, then 35, THF,
10 min, rt; (b) Pd(dppf)Cl2, Cs2CO3, AsPh3, THF, DMF, H2O; (c) product
from 22 + 9-BBN, 4 h, rt; (d) ∆, overnight; (e) 57% HI, HOAc, ∆, 5 h; (f)
NaOH, EtOH, H2O, rt, overnight; (g) 40, PPh3, Pd(OAc)2, pivalic anhydride,
THF, 60 °C, 15 h.
of Maeda et al.,20 3-bromobenzoyl chloride (34) and 3-meth-
oxyphenylmagnesium bromide (35) afforded 98% of benzophe-
none 36, which was subjected to Suzuki coupling with 22 to
afford 37 in 69% yield. Methyl ether cleavage as usual gave
74% of 13. Alternatively, Suzuki coupling of ethyl 3-iodobenzo-
ate (38) with 22 followed directly by ester hydrolysis gave 42%
of 39, which was coupled with 3-methoxyphenylboronic acid
(40) in the presence of pivalic anhydride21 to give 91% of 37.
Syntheses of 13. Compound 13 was prepared by two
comparably efficient routes (Scheme 5). Following the procedure
(17) Johnson, C. R.; Braun, M. P. J. Am. Chem. Soc. 1993, 115, 11014-
11015.
(18) Huo, S.; Shi, J.; Negishi, E. Angew. Chem., Int. Ed. 2002, 41, 2141-
2143.
(19) Staykova, P.; Malakov, P. Bulg. Nauchni TrudoVe-PloVdiVski
UniVersitet “Paisii Khilendarski” 1992, 28, 81-90.
(20) Maeda, H.; Okamoto, J.; Ohmori, H. Tetrahedron Lett. 1996, 37,
5381-5384.
5866 J. Org. Chem., Vol. 71, No. 16, 2006

Nonsteroidal Benzophenone-Containing Cholesterol Analogues
lular membrane compartments. In one recent study, Zhang et
al.32 showed that dehydroergosterol can replace 1 in living
fibroblasts. Very recently, we showed by fluorescence micros-
copy that an analogue of 1 in which the benzophenone moiety
of FCBP (2) had been replaced by a fluorenone group adopts a
distribution similar to 1 in smooth muscle cells.33 Another recent
study34 reports that palmitoyl ceramides also can displace 1 from
membrane bilayers. All these results suggest that there is a much
greater biochemical tolerance for variations in the “cholesterol”
structure than had been previously believed.35 The present results
with 10 and 12, which also indicate that the sterol tetracyclic
nucleus is not an essential part of a successful cholesterol
surrogate, add further support to this idea of structural tolerance
in analogues of cholesterol, at least with respect to its bulk roles
in cells, as in membranes.
FIGURE 2. The dilution of [3H]cholesterol ([3H]1) label in fibroblast
monolayers by 1, 10, or 12. The dilution ratio is the reduction in [3H]1
efflux, induced by apolipoprotein A-I, to the cellular medium after
fibroblast monolayers were equilibrated (48 h, 37 °C) with 10 µCi [3H]1
plus unlabeled 1 or analogue equal to the total sterol content of cells
and medium compared with cells labeled with the same level of tracer
[3H]1 only. Complete equilibration between sterol pools is indicated
by a dilution ratio of 0.5. Values shown represent means (1 standard
deviation of three independent experiments, each including triplicate
dishes of fibroblasts incubated as described in detail in ref 3 and in the
Supporting Information.
Experimental Section
3-(2,6-Dimethylheptyl)phthalide (17). To 1.52 g (62.5 mmol)
of magnesium in 20 mL of ether was added a solution of 15.38 g
(60.5 mmol) of 14 in 80 mL of ether. Formation of Grignard reagent
15 was evidenced by boiling and clouding of the ethereal solution.
To the stirred 15 was added a solution of 3.66 g (24.4 mmol) of
o-carboxybenzaldehyde (16) in 30 mL of THF, and the resulting
mixture was stirred at rt under N2 pressure for 3 h, then quenched
with 100 mL of 1 M aqueous HCl and stirred at rt for 2 h. The
aqueous layer was extracted with ether, and the combined organic
layers were washed with 5% aqueous Na2S2O3 and brine, dried,
filtered, and evaporated to afford 8.9 g of residue which was
chromatographed with EtOAc:hexane to afford 3.2 g (50%) of 17
as a viscous, pale yellow oil. Rechromatography with 1:6 ether:
hexane gave analytically pure 17: 1H NMR (300 MHz) δ 7.90 (d,
J ) 7.5 Hz, 1H), 7.69-7.66 (m, 2H), 7.54-7.51 (m, 2H), 7.45-
7.42 (m, 2H), 5.56-5.52 (m, 2H), 1.93-1.86 (m, 4H), 1.73-1.69
(m, 2H), 1.64-1.49 (m, 4H), 1.41-1.14 (m, 10H), 1.08 (d, J )
7.0 Hz, 3H), 1.01 (d, J ) 6.5 Hz, 3H), 0.88 (d, J ) 6.5 Hz, 6H),
0.86 (d, J ) 6.5 Hz, 6H); 13C NMR (75 MHz) δ 170.9, 170.9,
151.0, 150.9, 134.1, 134.1, 129.2, 129.2, 126.1, 125.9, 125.9, 122.0,
121.9, 80.3, 79.9, 43.0, 42.8, 39.4, 39.3, 38.0, 36.7, 30.2, 29.9, 28.1,
24.7, 22.9, 22.8, 22.8, 22.7, 20.4, 19.3. Anal. Calcd for C17H24O2:
C, 78.42; H, 9.29. Found: C, 78.58; H, 9.38.
(R,S)-2-(3,7-Dimethyloctyl)benzoic acid ((R,S)-18). According
to the procedure of Sano et al.,14 a mixture of 1.58 g (6.0 mmol) of
17, 0.88 g (6.0 mmol) of di-tert-butylperoxide, and 7.7 g (30 mmol)
of triphenylsilane was heated at 140 °C for 5 h, then cooled to rt,
diluted with 40 mL of ether, treated with 40 mL of 1 M hydrochloric
acid, and stirred for 70 h. The phases were separated, and the
organic layer was extracted with 0.5 M NaOH solution. The basic
extracts were acidified and extracted with ether, and these ethereal
extracts were washed with H2O, dried, filtered, and evaporated to
afford 1.3 g of pale yellow oil. Chromatography with EtOAc:hexane
afforded 0.561 g (36%) of (R,S)-18 as a yellow oil. Rechromatog-
Preliminary Biochemical Evaluation. To determine whether
steroidal benzophenone-containing analogues 2-9 had the
potential to serve as substitutes for cholesterol (1) in intact cells,
an isotope dilution assay of apolipoprotein A-I-induced cellular
efflux of 1 was developed.3 To compete successfully with 1 in
this assay, an analogue must enter the cells, equilibrate with 1
in major cellular pools, including membranes, and undergo
efflux from the cells at a rate comparable to that of 1. Thus,
this assay sets a high standard for success as a cholesterol
surrogate, and it was gratifying, albeit unexpected, that each of
2-9 met this demanding criterion.
In the present work, analogues 10-13, having the sterol
tetracyclic framework replaced by a benzophenone with the
photoactivatable cross-linking atom at the top (10 and 11) or
the bottom (12 and 13) of the ring B region of 1, have been
synthesized as described above, and a representative of each
type, 10 and 12, has been evaluated in the same isotope dilution
assay. As shown in Figure 2, both 10 and 12 can also
successfully replace 1 through the entire process of apolipo-
protein A-I-induced cellular efflux of 1.
Previous evaluations of compounds as cholesterol surrogates
have, when conducted at all, almost always tested the ability
either to bind proteins that have 1 as a ligand22-25 or to replace
1 in model membrane bilayers.24,26-30 7,7-Azocholestanol has
been reported31 to mimic 1 in its distribution between intracel-
(28) Mintzer, E. A.; Waarts, B.-L.; Wilschut, J.; Bittman, R. FEBS Lett.
2002, 510, 181-184.
(29) Wenz, J. J.; Barrantes, F. J. Biochemistry 2003, 42, 14267-14276.
(30) Li, Z.; Mintzer, E.; Bittman, R. J. Org. Chem. 2006, 71, 1718-
1721.
(21) Goossen, L. J.; Ghosh, K. Angew. Chem., Int. Ed. 2001, 40, 3458-
3460.
(22) Thurnhofer, H.; Hauser, H. Biochemistry 1990, 29, 2142-2148.
(23) Li, H.; Yao, Z.; Degenhardt, B.; Teper, G.; Papadopoulos, V. Proc.
Natl. Acad. Sci. U.S.A. 2001, 98, 1267-1272.
(31) Cruz, J. C.; Thomas, M.; Wong, E.; Ohgami, N.; Sugii, S.; Curphey,
T.; Chang, C. C. Y.; Chang, T.-Y. J. Lipid Res. 2002, 43, 1341-1347.
(32) Zhang, W.; McIntosh, A. L.; Xu, H.; Wu, D.; Gruninger, T.;
Atshaves, B.; Liu, J. C. S.; Schroeder, F. Biochemistry 2005, 44, 2864-
2884.
(33) Spencer, T. A.; Wang, P.; Popovici-Mu¨ller, J. V.; Peltan, I. D.;
Fielding, P. E.; Fielding, C. F. Bioorg. Med. Chem. Lett. 2006, 16, 3000-
3004.
(24) Scheidt, H. A.; Mu¨ller, P.; Herrmann, A.; Huster, D. J. Biol. Chem.
2003, 278, 45563-45569.
(25) Zheng, Y.-H.; Plemenitas, A.; Fielding, C. J.; Peterlin, B.; Matija,
B. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 8460-8465.
(26) Schroeder, F.; Nemecz, G.; Gratton, E.; Barenholtz, Y.; Thompson,
T. E. Biophys. Chem. 1988, 32, 57-72.
(27) Xu, X.; Bittman, R.; Duportail, G.; Heissler, D.; Vilcheze, C.;
London, E. J. Biol. Chem. 2001, 276, 33540-33546.
(34) Alanko, S. M. K.; Halling, K. K.; Mannula, S.; Slotte, J. P.;
Ramstedt, B. Biochim. Biophys. Acta 2005, 1715, 111-121.
(35) Wilson, M. D.; Rudel, L. L. J. Lipid Res. 1994, 35, 943-955.
J. Org. Chem, Vol. 71, No. 16, 2006 5867

Gan et al.
raphy with 1:2 ether:hexane gave analytically pure (R,S)-18: 1H
NMR (300 MHz) δ 8.06-8.03 (m, 1H), 7.51-7.45 (m, 1H), 7.31-
7.26 (m, 2H), 3.14-2.93 (m, 2H), 1.67-1.15 (m, 10H), 0.97 (d,
J ) 6.3 Hz, 3H), 0.87 (d, J ) 6.9 Hz, 6H); 13C NMR (75 MHz) δ
173.0, 146.7, 133.1, 131.8, 131.4, 128.2, 126.0, 39.5, 37.3, 33.4,
32.6, 28.2, 25.0, 22.9, 22.9, 19.8. Anal. Calcd for C17H26O2: C,
77.82; H, 9.99. Found: C, 77.80; H, 9.86.
of residue which was chromatographed to give 145 mg (81%) of
colorless oily 11: 1H NMR δ 7.81-7.79 (m, 2H), 7.70 (br s, 1H),
7.61-7.57 (m, 2H), 7.43-7.38 (m, 2H), 6.98-6.95 (m, 2H), 2.71-
2.64 (m, 2H), 1.71-1.56 (m, 2H), 1.52 (hept, J ) 6.5 Hz, 1H),
1.46-1.07 (m, 9H), 0.88-0.86 (m, 9H); 13C NMR δ 197.5, 161.1,
143.4, 138.2, 133.3, 132.6, 130.0, 129.8, 128.3, 127.6, 115.6, 39.5,
37.4, 36.9, 36.3, 32.8, 29.1, 28.1, 25.0, 22.9, 22.8, 19.8. Anal. Calcd
for C24H32O2: C, 81.77; H, 9.15. Found: C, 81.55; H, 9.25.
(R)-4,8-Dimethylnonyl-3′-methoxybenzophenone (33). Ac-
cording to the method of Kumar et al.,37 to a stirred solution of
1.71 g (1.00 mmol) of m-anisoyl chloride (32) in 30 mL of CS2
under N2 at rt were added 2.32 g (1.00 mmol) of 31 and 1.60 g
(1.00 mmol) of AlCl3. The mixture was heated at reflux for 5 h,
cooled to rt, treated with 200 g of ice and 5 mL of concentrated
HCl, and extracted with dichloromethane. The organic layer was
washed with brine, dried, filtered, and evaporated to give 4.10 g
of oil which was chromatographed with 1:50 EtOAc:hexane to give
3.4 g (94%) of golden oily 33: 1H NMR δ 7.78-7.76 (m, 2H),
7.40-7.27 (m, 5H), 7.14 (m, 1H), 3.88 (s, 3H), 2.72-2.67 (m,
2H), 1.75-1.60 (m, 2H), 1.54 (hept, J ) 6.5 Hz, 1H), 1.47-1.08
(m, 9H), 0.89-0.88 (m, 9H); 13C NMR δ 196.4, 159.7, 148.4, 139.4,
135.2, 130.5, 129.3, 128.5, 128.5, 122.9, 118.7, 114.4, 55.6, 39.5,
37.4, 36.9, 36.5, 32.8, 28.9, 28.1, 25.0, 22.9, 22.8, 19.8. Anal. Calcd
for C25H34O2: C, 81.92; H, 9.35. Found: C, 82.06; H, 9.51.
(R)-4-(4,8-Dimethylnonyl)-3′-hydroxybenzophenone (12). As
in the preparation of 10, 182 mg (0.50 mmol) of 33 gave 145 mg
(81%) of oily 12: 1H NMR δ 7.78-7.76 (m, 2H), 7.46 (m, 1H),
7.32-7.28 (m, 4H), 7.16-7.14 (m, 1H), 2.71-2.64 (m, 2H), 1.72-
1.60 (m, 2H), 1.56 (hept, J ) 6.5 Hz, 1H), 1.47-1.10 (m, 9H),
0.91-0.90 (m, 9H); 13C NMR δ 197.9, 156.5, 148.9, 138.9, 134.8,
130.8, 129.5, 128.5, 122.6, 120.3, 116.9, 39.5, 37.3, 36.9, 36.5,
32.8, 28.1, 24.9, 22.9, 22.8, 19.8. Anal. Calcd for C24H32O2: C,
81.77; H, 9.15. Found: C, 81.55; H, 9.25.
3-Bromo-4-methoxybenzophenone (36). According to the
procedure of Maeda et al.,20 to a solution of 1.00 g (0.60 mL, 4.56
mmol) of 3-bromobenzoyl chloride (34) in 10 mL of THF was
added 0.97 g (1.2 mL, 4.6 mmol) of PBu3 dropwise at -22 °C
(dry ice/CCl4). The resulting mixture was stirred for 20 min, treated
rapidly with 4.6 mL of 1.0 M 3-methoxyphenylmagnesium bromide
(35) in THF, stirred for 10 min, diluted with 10 mL of 1 M HCl,
and extracted with ether. The combined organic layers were washed
with brine, dried, filtered, and evaporated to give 2.60 g of yellow
oil which was chromatographed with 1:15 ether:hexane to give 1.31
g (98%) of colorless oily 36: 1H NMR δ 7.96-7.95 (m, 1H), 7.74-
7.72 (m, 2H), 7.43-7.32 (m, 4H), 7.19-7.16 (m, 1H), 3.89 (s,
3H); 13C NMR δ 194.9, 159.9, 139.7, 138.4, 135.5, 133.0, 130.1,
129.7, 128.8, 123.0, 122.8, 119.4, 114.6, 55.7. Anal. Calcd for
C14H11BrO2: C, 57.76; H, 3.81. Found: C, 57.99; H, 3.78.
(R)-(3,7-Dimethyloctyl)benzoic acid (39). As in the preparation
of 19, 415 mg (2.96 mmol) of 22 was combined with 9-BBN and
then with 851 mg (3.08 mmol) of ethyl 3-iodobenzoate (38) to give
812 mg of brown oil, which was chromatographed with 1:10 ether:
hexane to give 428 mg of colorless oil, which was then treated
with 843 mg (21.1 mmol) of NaOH in a mixture of 2 mL of EtOH
and 2 mL of H2O at rt overnight. The mixture was then evaporated,
and the residue was acidified with concentrated HCl to pH ) 1
and extracted with ether. The combined organic layers were washed,
dried, filtered, and evaporated to give 534 mg of colorless oil which
was chromatographed with 1:1 ether:hexane to give 321 mg (42%)
of colorless oily 39: 1H NMR δ 8.00-7.98 (m, 2H), 7.48-7.40
(m, 2H), 2.79-2.64 (m, 2H), 1.72-1.67 (m, 1H), 1.57 (hept, J )
6.8 Hz, 1H), 1.54-1.48 (m, 2H), 1.41-1.16 (m, 6H), 0.99 (d, J )
6.0 Hz, 3H), 0.91 (d, J ) 6.5 Hz, 6H); 13C NMR δ 173.1, 143.9,
134.2, 130.3, 129.5, 128.7, 127.8, 39.6, 39.1, 37.4, 33.5, 32.7, 28.2,
25.0, 23.0, 22.9, 19.8. Anal. Calcd for C17H26O2: C, 77.82; H, 9.99.
Found: C, 77.91; H, 10.15.
(R,S)-2-(3,7-Dimethyloctyl)-4′-hydroxybenzophenone ((R,S)-
10). According to a procedure reported by Bhatt and Kulkarni,36
a
mixture of 44 mg (0.12 mmol) of (R,S)-19, prepared as described
in Supporting Information, 2 mL of 57% HI solution, and 0.4 mL
of glacial acetic acid was heated at reflux for 3.5 h. The reaction
mixture was then poured over ice and extracted with ethyl acetate.
The combined organic extracts were washed with 5% sodium
Na2S2O3 solution, saturated Na2CO3 solution and brine, dried,
filtered, and evaporated to afford 57 mg of yellow solid, which
was chromatographed with EtOAc:hexane to afford 21 mg (50%)
1
of 10 as a clear oil, which had H and 13C NMR spectra identical
with those of 10 described below.
(R)-2-(3,6-Dimethyloctyl)-4′-methoxybenzophenone (19). Ac-
cording to the procedure of Johnson and Braun,17 to a solution of
0.90 g (6.4 mmol) of 22 in 8 mL of anhydrous THF was added
14.5 mL of 0.5 M 9-BBN (7.25 mmol) in THF dropwise. The
resulting mixture was stirred at rt for 4 h, then transferred via
syringe to a mixture of 1.31 g (1.60 mmol) of Pd(dppf)Cl2, 7.85 g
(24.1 mmol) of Cs2CO3, 0.49 g (1.61 mmol) of AsPh3, and 2.72 g
(8.03 mmol) of 21 in a mixture of 16 mL of THF, 16 mL of DMF,
and 4 mL of H2O. The resulting mixture was heated at reflux under
N2 overnight, then passed through a short Celite pad. The filtrate
was evaporated, diluted with 50 mL of water, and extracted with
ether. The combined organic layers were washed with brine, dried,
filtered, and evaporated to give 4.6 g of brown oil, which was
chromatographed with 1:10 ether:hexane to give 1.5 g (65%) of
colorless oily 19: 1H NMR δ 7.83-7.80 (m, 2H), 7.41-7.22 (m,
4H), 6.95-6.92 (m, 2H), 3.88 (s, 3H), 2.71-2.56 (m, 2H), 1.57-
1.52 (m, 1H), 1.48 (hept, J ) 6.5 Hz, 1H), 1.39-1.33 (m, 2H),
1.12-1.02 (m, 6H), 0.85 (d, J ) 6.4 Hz, 6H), 0.81 (d, J ) 6.5 Hz,
3H); 13C NMR δ 197.7, 163.9, 141.8, 139.4, 132.8, 131.1, 130.2,
130.0, 128.1, 125.3, 113.9, 55.7, 39.5, 39.3, 37.2, 33.0, 31.1, 28.2,
24.9, 23.0, 22.9, 19.8; [R]D28 ) -5.03° (c 1.63, CHCl3). Anal. Calcd
for C24H32O2: C, 81.77; H, 9.15. Found: C, 81.93; H, 9.17.
2-(3,7-Dimethyloctyl)-4′-hydroxybenzophenone (10). As in the
preparation of (R,S)-10, except that the reaction mixture was heated
for 5 h, 260 mg (0.71 mmol) of 19 gave 210 mg (84%) of colorless
oily 10: 1H NMR δ 7.77-7.74 (m, 2H), 7.42-7.38 (m, 1H), 7.32-
7.31 (m, 1H), 7.28-7.23 (m, 2H), 6.90-6.87 (m, 2H), 6.51 (br s,
1H), 2.69-2.54 (m, 2H), 1.55-1.50 (m, 1H), 1.47 (hept, J ) 6.5
Hz, 1H), 1.37-1.29 (m, 2H), 1.23-1.00 (m, 6H), 0.83 (d, J ) 6.5
Hz, 6H), 0.76 (d, J ) 6.0 Hz, 3H); 13C NMR δ 198.5, 161.0, 141.7,
139.0, 133.2, 130.7, 130.2, 130.1, 128.1, 125.3, 115.6, 39.4, 39.2,
28
37.1, 32.9, 31.0, 28.1, 24.8, 22.9, 22.8, 19.6; [R]D ) -5.29° (c
0.68, CHCl3). Anal. Calcd for C23H30O2: C, 81.61; H, 8.93.
Found: C, 81.60; H, 9.09.
3-(4,8-Dimethylnonyl)-4′-methoxybenzophenone (27). As in
the preparation of 19, 324 mg (2.10 mmol) of 26 was combined
with 9-BBN and then with 887 mg (2.63 mmol) of 24 to give 1.36
g of brown oil which was chromatographed with 1:10 ether:hexane
to give 551 mg (72%) of colorless oily 27: 1H NMR δ 7.87-7.84
(m, 2H), 7.60 (br s, 1H), 7.58-7.56 (m, 1H), 7.41-7.37 (m, 2H),
7.00-6.97 (m, 2H), 3.91 (s, 3H), 2.70-2.65 (m, 2H), 1.73-1.60
(m, 12H), 1.53 (hept, J ) 6.5 Hz, 1H), 1.45-1.06 (m, 9H), 0.88-
0.87 (m, 9H); 13C NMR δ 196.1, 163.3, 143.3, 138.5, 132.8, 132.3,
130.6, 129.8, 128.2, 127.5, 113.7, 55.7, 39.5, 37.4, 36.9, 36.4, 32.9,
29.2, 28.2, 25.0, 22.9, 22.8, 19.9. Anal. Calcd for C25H34O2: C,
81.92; H, 9.35. Found: C, 82.04; H, 9.35.
(R)-3-(4,8-Dimethylnonyl)-4′-hydroxybenzophenone (11). As
in the preparation of 10, 182 mg (0.50 mmol) of 27 gave 580 mg
(37) Kumar, S.; Seth, M.; Bhaduri, A. P.; Agnihotri, A.; Srivastava, A.
K. Indian J. Chem. 1984, 23B, 154-157.
(36) Bhatt, M. V.; Kulkarni, S. U. Synthesis 1983, 249-282.
5868 J. Org. Chem., Vol. 71, No. 16, 2006

Nonsteroidal Benzophenone-Containing Cholesterol Analogues
(R)-3-(3,7-Dimethyloctyl)-4′-methoxybenzophenone (37). Meth-
od A: From 36. As in the preparation of 19, 110 mg (0.79 mmol)
of 22 was combined with 9-BBN and then with 191 mg (0.66 mmol)
of 36 to give 341 mg of brown oil, which was chromatographed
with 1:10 ether:hexane to give 161 mg (69%) of colorless oily 37:
1H NMR δ 7.67 (br s, 1H), 7.62-7.60 (m, 1H), 7.44-7.35 (m,
5H), 7.16-7.14 (m, 1H), 3.89 (s, 3H), 2.77-2.63 (m, 2H), 1.70-
1.65 (m, 1H), 1.54 (hept, J ) 6.5 Hz, 1H), 1.50-1.45 (m, 2H),
1.38-1.13 (m, 6H), 0.95 (d, J ) 6.5 Hz, 3H), 0.88 (d, J ) 7 Hz,
6H); 13C NMR δ 197.0, 159.8, 143.7, 139.3, 137.8, 132.8, 130.0,
129.4, 128.3, 127.8, 123.1, 119.1, 114.5, 55.7, 39.5, 39.1, 37.3,
33.6, 32.7, 28.2, 24.9, 22.9, 22.9, 19.8. Anal. Calcd for C24H32O2:
C, 81.77; H, 9.15. Found: C, 81.54; H, 9.18. Method B. From
39. According to the procedure of Goossen and Ghosh,21 to a
solution of 67 mg (0.26 mmol) of 39 in 1 mL of THF were added
3 mg (0.011 mmol) of PPh3, 2 mg (0.009 mmol) of Pd(OAc)2, 47
mg (0.31 mmol) of 3-methoxyphenylboronic acid (40), and 73 mg
(0.39 mmol) of pivalic anhydride. The resulting mixture was heated
overnight at 60 °C and passed through a short pad of Celite. The
pad was washed with EtOAc, and the combined organic layers were
evaporated to give 212 mg of brown oil which was chromato-
graphed with 1:6 ethyl acetate:hexane to give 84 mg (91%) of
colorless oily 37, which had 1H and 13C NMR spectra identical to
those of 37 from 36.
7.28 (m, 5H), 7.14-7.12 (m, 1H), 2.76-2.61 (m, 2H), 1.68-1.63
(m, 1H), 1.54 (hept, J ) 6.5 Hz, 1H), 1.50-1.44 (m, 2H), 1.36-
1.13 (m, 6H), 0.95 (d, J ) 6.5 Hz, 3H), 0.88 (d, J ) 7 Hz, 6H);
13C NMR δ 198.1, 156.5, 143.8, 139.1, 137.5, 133.2, 130.2, 129.6,
128.4, 128.0, 123.1, 120.4, 116.9, 39.5, 39.1, 37.3, 33.6, 32.7, 28.2,
24.9, 22.9, 22.8, 19.8. Anal. Calcd for C23H30O2: C, 81.61; H, 8.93.
Found: C, 81.40; H, 8.82.
Acknowledgment. We thank Drs. C. J. Fielding and P. E.
Fielding of the University of California, San Francisco, for
generously performing the biochemical assays described herein.
Professor Robert Ditchfield provided helpful computational
advice. Dr. Pingzhen Wang assisted valuably with manuscript
preparation. This research was supported by NIH Grant 67294.
Supporting Information Available: General experimental
methods, descriptions of preparation of compounds 14, (R,S)-19,
21, 22, 24, 25, 26, 30, and 31, details of the isotope dilution assay,
1H and 13C NMR spectra of all new compounds and some known
intermediates, atom coordinates for molecular modeling of com-
pounds 1 and 10. This material is available free of charge via the
Internet at http://pubs.acs.org.
(R)-3-(3,7-Dimethyloctyl)-4′-hydroxybenzophenone (13). As
in the preparation of 10, 161 mg (0.46 mmol) of 37 gave 114 mg
(74%) of colorless oily 13: 1H NMR δ 7.67-7.60 (m, 2H), 7.45-
JO060481Q
J. Org. Chem, Vol. 71, No. 16, 2006 5869