Synthesis, biological evaluation, and molecular modeling of abiraterone analogues: Novel CYP17 inhibitors for the treatment of prostate cancer

Article abstract of DOI:10.1021/jm800355c

Abiraterone, a steroidal cytochrome P450 17α-hydroxylase-17,20-lyase inhibitor (CYP17), is currently undergoing phase II clinical trials as a potential drug for the treatment of androgen-dependent prostate cancer. Since steroidal compounds often show side

Full text of DOI:10.1021/jm800355c

J. Med. Chem. 2008, 51, 5009–5018
5009
Synthesis, Biological Evaluation, and Molecular Modeling of Abiraterone Analogues: Novel
CYP17 Inhibitors for the Treatment of Prostate Cancer
Mariano A. E. Pinto-Bazurco Mendieta,† Matthias Negri,† Carsten Jagusch,† Ursula Mu¨ller-Vieira,‡ Thomas Lauterbach,§ and
Rolf W. Hartmann*,†
Pharmaceutical and Medicinal Chemistry, Saarland UniVersity, P.O. Box 151150, D-66041 Saarbru¨cken, Germany, Pharmacelsus CRO,
Science Park 2, D-66123 Saarbru¨cken, Germany, and Schwarz Pharma, Alfred-Nobel-Strasse 10, D-40789 Monheim, Germany
ReceiVed March 29, 2008
Abiraterone, a steroidal cytochrome P450 17R-hydroxylase-17,20-lyase inhibitor (CYP17), is currently
undergoing phase II clinical trials as a potential drug for the treatment of androgen-dependent prostate
cancer. Since steroidal compounds often show side effects attributable to their structure, we have tried to
replace the sterane scaffold by nonsteroidal core structures. The design and synthesis of 20 new abiraterone
mimetics are described. Their activities have been tested with recombinant human CYP17 expressed in E.
coli. Promising compounds were further evaluated for selectivity against CYP11B1, CYP11B2, and the
hepatic CYP3A4. Compounds 19 and 20 showed comparable activity to abiraterone (IC50 values of 144 and
64 nM vs 72 nM) and similar or even better selectivity against the other CYP enzymes. Selected compounds
were also docked into our homology model, and the same binding modes as for abiraterone were found.
Introduction
ation of antiandrogen administration. This led to the hypothesis
that under antiandrogen treatment androgen receptor mutations
occur causing PC cells to recognize antagonists as agonists.7
An alternative target proposed in the recent past is the
cytochrome P450 enzyme 17R-hydroxylase-17,20-lyase (CYP17).
This enzyme is localized in the endoplasmic reticulum in the
testes as well as in the adrenals and is the key enzyme for
androgen biosynthesis. Its inhibition should stop the production
of androgens both in the testes and in the adrenals, and therefore,
inhibitors of CYP17 should be more effective for treating
androgen-dependent PC than GnRH analogues. Proof of prin-
ciple was achieved by the unspecific CYP inhibitor ketocona-
zole, which clinically turned out to be a good adjuvant
therapeutic capable of reducing testosterone levels.8 Neverthe-
less, the side effects shown by this antimycotic compound are
the reason that it is not used anymore.9
Prostate cancer (PCa) is the most common tumor and age-
related cause of death in elder men worldwide.1 Because of the
advanced age of the patients, less invasive approaches are
needed. Accordingly, the treatment of choice is “watchful
waiting”,2 followed by radiation therapy only when it is
necessary. Since PC is androgen dependent in over 80% of the
cases, another current standard treatment is orchiectomy, the
surgical removal of the testes, usually applied to patients under
70 years old. The reduction of testicular androgen production
by gonadotropin-releasing hormone (GnRH) analogues,3
a
“medical castration”, is often preferred over the surgical one
and can also be used for treating older patients. Nevertheless,
castration whether surgical or medical reduces maximally
90-95% of the daily testosterone production, which is often
not enough to stop the tumor from growing, since prostate levels
of testosterone and dihydrotestosterone are still about 25% and
10%, respectively, even after three months of treatment with a
GnRH agonist.4
The remaining 5-10% of the androgens are produced in the
adrenals. In the 1980s, Labrie5 hypothesized that additionally
counteracting adrenal androgens by application of antiandrogens
would further inhibit tumor growth. This approach, known as
“combined androgen blockade” (CAB), has been widely used
in the past. The results have been partially positive, especially
in patients with minimal disease and good performance status.
However, it must be mentioned that antiandrogen therapy is
associated with notable side effects.6 Another drawback of CAB
is that in refractory PC regression is observed after discontinu-
CYP17 catalyzes two reactions, the 17R-hydroxylation of
pregnenolone and progesterone to the corresponding 17R-
alcohols and the subsequent 17,20-lyase reaction cleaving the
C17-C20 bond. This yields the 17-keto androgens androsten-
dione and dehydroepiandrosterone, precursors of all other
androgens, including testosterone (Chart 1).
The side effects of ketoconazole caused others10 and our
group to develop steroidal11 and nonsteroidal12,13 inhibitors. One
compound, the steroidal CYP17 inhibitor abiraterone (Chart 2),
is currently undergoing phase II clinical trials showing high
activity in postdocetaxel castration refractory PC patients. In
contrast to ketoconazole, it seems to have no dose-limiting
toxicity.14
Because steroidal compounds often show side effects due to
interactions with steroid receptors,15 it is our aim to develop
nonsteroidal compounds. In this work, we present the design,
synthesis, in vitro evaluation regarding activity and selectivity
and modeling studies of nonsteroidal analogues of abiraterone
(Chart 3).
* To whom correspondence should be addressed. Phone: +49 (681) 302-
2424. Fax: +49 (681) 302-4386. E-mail: rwh@mx.uni-saarland.de. Website:
http://www.PharmMedChem.de.
†
Saarland University.
Pharmacelsus CRO.
Schwarz Pharma.
‡
§
a Abbreviations: CYP, cytochrome P450; CYP17, cytochrome P450 17R-
hydroxylase-17,20-lyase; PC, prostate cancer; CYP11B1, cytochrome P450
steroid-11-ꢀ-hydroxylase; CYP11B2, cytochrome P450 18-hydroxylase;
GnRH, gonadotropin-releasing hormone; CAB, combined androgen block-
ade; PDB, Protein Data Bank; TMS, trimethylsilane; ESI, electrospray
ionization; ATR, attenuated total reflection; GA, genetic algorithm.
Design
The three most important structural features of abiraterone
are the aromatic nitrogen-containing heterocycle, the hydro-
10.1021/jm800355c CCC: $40.75
2008 American Chemical Society
Published on Web 08/02/2008

5010 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16
Chart 1. Role of CYP17 in Androgen Biosynthesis
Pinto-Bazurco Mendieta et al.
Chart 2. Substrate, Abiraterone, and Synthesized Mimetics
Chart 3. List of Synthesized Compounds 1-20
enzymes have the particularity of bearing a heme moiety in their
binding site. The complexation of the Fe2+ of the heme with
an sp2 hybridized nitrogen as in pyridyl and imidazolyl is widely
described.16 In recent studies13 we showed that a biphenyl
moiety can replace the steroidal core AC-rings and that a
biphenyl moiety furnished with an imidazolyl-methylene group
ensures high CYP17 inhibitory activity (Chart 2). Introduction
of alkyl substituents at the methylene bridge13b,f (for example,
compound A13f) and first attempts to rigidify the structures
resulting in indane compounds (like compound B13b) increased
activity. Interestingly, 4-fluoro substituted compounds in general
showed very high inhibitory activity. Compound A, the indane
ring opened analogue to compound B, was more active in the
rat and showed a longer plasma half-life and higher bioavail-
ability compared to abiraterone, while its in vitro activity with
regard to potency and selectivity was not as outstanding as that
of the steroidal compound. In this work we want to elucidate
whether it is possible to further increase activity and especially
selectivity by additional attempts to rigidify the biphenyl struc-
ture and to exchange the heterocycle. The resulting compounds
are mimics of the steroidal compound abiraterone. For the design
of the synthesized compounds, the steroidal core was replaced
by an indane (mimicking the steroidal C- and D-rings) or
tetrahydronaphthalene scaffold (for expansion of the D-ring)
connected to an A-ring mimicking phenyl moiety. Electron
donating and withdrawing substituents (including hydroxy and
fluoro) were introduced in different positions at the phenyl ring.
The iron-complexing aromatic nitrogen was represented by a
3- or 4-pyridine moiety.
phobic steroidal core, and the hydroxy group mimicking the
oxygen at the 3-position of the substrates. All of them are
similarly important for a high affinity to the enzyme. CYP

Abiraterone Analogues
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16 5011
Scheme 1. Synthesis of Indane Derivativesa
was carried out with Pearlman’s catalyst (Pd(OH)2), resulting
in compounds 15-20 (method D).
Results
Biological Results. Inhibition of human CYP17 was deter-
mined by performing our previously described assay.13d For the
source of human CYP17, E. coli19 coexpressing human CYP17
and NADPH-P450 reductase were used. After homogenization,
the 50 000 g sediment was incubated with progesterone (25 µM)
and the inhibitor.12a Separation of the product was performed
by HPLC using UV detection. The IC50 values determined for
compounds 1-20 are shown in Table 1.
The compounds can be divided into two classes according
to the CD-ring mimicking moiety, namely in indane and
hydronaphthalene derivatives, and also into three classes regard-
ing the pyridyl bearing C atom, that is in alcohols, alkenes, and
alkanes. Most of the indane derivatives, either bearing a
3-pyridyl or a 4-pyridyl substituent, showed no or little CYP17
inhibition. Only compound 2, with a moderate inhibition of 333
nM, and compound 16 (IC50 ) 233 nM) were active. Interest-
ingly, both compounds contain a 4-pyridyl group as iron-com-
plexing heterocycle and a fluorine at R1.
a Reagents and conditions. (a) Method A: Na2CO3, R1R2C6H3B(OH)2,
Pd(PPh3)4, toluene, H2O, reflux, 8 h. (b) Method B: 3-iodopyridine or
4-bromopyridine, n-BuLi, THF, Et2O, -78 °C to room temp, 3 h. (c) Method
C: HCl in isopropanol, 80 °C, 2 h. (d) Method D: Pd(OH)2, ethanol, THF,
H2, room temp, 3 h.
The hydronaphthalenes were more potent than the indanes,
showing a broad range of activity. The alkenes (11-14) were
weaker inhibitors than the corresponding compounds with a
single bond, the alcohols (5-7) and tetrahydronaphthalenes
(17-20). The inhibition values range from about 200 to over
5000 nM, while for the single bond compounds the values range
mostly from around 100 to 500 nM. An important condition
for inhibitory activity in the class of the alkanes is a 4-pyridyl
substituent. In the 4-position of the phenyl ring (R1) a F or OH
group and in 3-position (R2) H, F, or OH led to highly active
compounds. Interestingly, the 3,4-di-F-substituted compound 18
only showed moderate activity. One explanation for this finding
might be the electron withdrawing effect of the two F atoms at
the phenyl ring. The most potent compounds were the 4-OH
compounds 19 and 20 (IC50 ) 144 and 64 nM). A hydroxy
substituent in 4-position of the phenyl ring also makes the
alkenes from the 4-pyridyl substituted dihydronaphthalene type
potent inhibitors (compounds 13 and 14). In the class of the in-
denes, 3-pyridyl substitution, as in abiraterone, led to an active
compound (8) whereas 4-pyridyl substitution does not (9). It is
striking, that 11 out of the 20 synthesized compounds were more
active than ketoconazole. The most potent compound 20 showed
a slightly higher inhibition compared to abiraterone (IC50 ) 72
nM). Our seven most potent compounds from this work were
more active than compound A (345 nM), and regarding
compound B (670 nM), nine showed significantly higher
inhibitory activities for CYP17. In the whole cell assay, i.e., E.
coli coexpressing human CYP17 and NADPH-P450 reduc-
tase,12f the most active compound of this series, 20, was also
highly active (IC50 < 200 nM).
Since the target enzyme contains a heme in its binding site,
hence CYP/P450 enzyme, which is crucial for the enzymatic
reaction and for binding the iron-complexing nitrogen containing
inhibitors, the latter compounds were tested for selectivity
against other CYP enzymes. Accordingly, selected compounds
were tested for inhibitory activity on the steroidogenic CYP
enzymes CYP11B1 and CYP11B2, key enzymes in glucocor-
ticoid and mineralocorticoid biosynthesis. For the assay,20
V79MZh11B1cellsexpressinghumanCYP11B1andV79MZh11B2
cells expressing human CYP11B2 were used. The IC50 values
determined for selected compounds are shown in Table 2.
With the exception of compounds 4 and 7 showing IC50
values of 291 and 686 nM toward CYP11B1, respectively, the
Three classes of mimetically relevant compounds were
synthesized. Compounds 1-7, hydroxylated at the C17 mimick-
ing position, are analogues of the steroidal substrates for the
second enzymatic step (lyase reaction). Compounds 7-14
bearing a double bond are structurally analogous to abiraterone.
The saturated alkanes 15-20 show the highest similarity to the
first-step (hydroxylase reaction) substrates.
In the following, the synthesis, determination of activity, and
selectivity and molecular modeling studies of the synthesized
abiraterone analogues are presented. Besides CYP17 inhibitory
activity, inhibition of other CYP enzymes was examined to
exclude possible side effects due to unspecific heme iron
complexation. Thus, selectivity toward CYP11B1 and CYP11B2
was determined, since their biological relevance relies on the
fact that CYP11B1 is involved in glucocorticoid biosynthesis
while CYP11B2 catalyzes the last step in mineralocorticoid
formation. Special attention was given to the most crucial
hepatic enzyme CYP3A4, since it is involved in the metabolism
of over 50% of all prescription drugs.17 The most interesting
compounds were docked into our homology-approach derived
protein model and the binding modes in the active site discussed.
Chemistry
The syntheses of compounds 1-20 are shown in Schemes 1
and 2. In our aim to rigidify our biphenylic core structure by
connecting the methylene bridge with the C-ring mimicking
phenyl moiety, we synthesized indane derivatives (Scheme 1),
which can be considered abiraterone analogues, and expanded
the nonaromatic ring by one methylene group yielding tetrahy-
dronaphthalene derivatives (Scheme 2). Different substitution
patterns at the A-ring mimicking phenyl substituent were used.
Suzuki coupling18 (method A) using 5-bromoindanone for the
abiraterone analogues and 1-tetralon-6-yl trifluoromethanesul-
fonate, synthesized from the respective alcohol, for the tetrahy-
dronaphthalenes yielded the indanones 1a-4a and the tetralones
5a-7a. The pyridine moiety was introduced by means of a
nucleophilic addition (method B) with the corresponding lithium
pyridinyl salt to yield the tertiary alcohols 1-7 and 13a. The
condensation to the corresponding alkenes was performed in
HCl/isopropanol (8-12, method C) or in HBr/H2O (13 and 14,
method E). The latter method was applied when a simultaneous
ether cleavage was desired. The hydration to the saturated rings

5012 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16
Scheme 2. Synthesis of Tetrahydronaphthalene Derivativesa
Pinto-Bazurco Mendieta et al.
a Reagents and conditions. (a) Method E: HBr, reflux, 16 h. (b) Pyridine, Tf2O, DCM, 0 °C to room temp, 3 h. (c) Method A: Na2CO3, R1R2C6H3B(OH)2,
Pd(PPh3)4, toluene, H2O, reflux, 8 h. (d) Method B: 3-iodopyridine or 4-bromopyridine, n-BuLi, THF, Et2O, -78 °C to room temp, 3 h. (e) Method C: HCl
in isopropanol, 80 °C, 2 h. (f) Method D: Pd(OH)2, ethanol, THF, H2, room temp, 3 h.
Table 1. Inhibition of CYP17 by Alcohols 1-7, Alkenes 8-4, and Alkanes 15-20
structuresa
R1
R2
n
N
compda
alcohol, CYP17 IC50 (nM)b
compda
alkene, CYP17 IC50 (nM)b
compda
alkane, CYP17 IC50 (nM)b
indanes
F
F
OMe
OMe
H
1
1
1
1
3
4
4
4
1
2
3
4
>20000
333
>20000
>10000
8
9
10
2346
>20000
>5000
15
16
>20000
H
H
F
233
hydronaphthalenes
F
F
OMe
OH
OH
H
F
F
OH
F
2
2
2
2
2
4
4
4
4
4
5
6
7
587
423
>5000
11
12
>5000
>5000
17
18
163
1222
13
14
307
188
19
20
144
64
KTZc
ABTd
2780
72
a Compounds 8-12 and 15-18 were tested as HCl salts and 13, 14, 19 and 20 as HBr salts. b Data shown were obtained by performing the tests in
duplicate. The deviations were within (5%. Concentration of progesterone (substrate) was 25 µM. c KTZ: ketoconazole. d ABT: abiraterone.
other tested compounds exhibited IC50 values above 1 µM. Most
of the compounds (2, 6, 11-14, 17-19) turned out to be more
selective than abiraterone (IC50 ) 1608 nM), and all compounds
were more selective compared to ketoconazole (127 nM)
regarding the cortisol forming enzyme. Concerning compound
A (66% inhibition at 0.2 µM), all compounds from this study
showed much higher selectivity.
(72 nM) and compound A (88% at 1 µM). Most of the
compounds were even more selective than abiraterone (IC50
2704 nM).
)
Molecular Modeling. Since there is no crystal structure of
CYP17 available, we recently built a homology model using
the X-ray structure of human CYP2C9 (PDB ID 1r9o) as
template.13e Docking simulations with energy minimized com-
pounds were carried out by means of the GOLD 3.2 software
running Linux CentOS 5.1 on an Intel P4 CPU 3.00 GHz
computer, using a slightly modified GOLDSCORE function with
goldscore.P450_pdb.parameters, for a better evaluation of
hydrophobic interactions. From every class, the most potent
compounds were docked into this protein model, and in the case
of chiral compounds, both enantiomers were docked.
In Figure 1 two binding modes of the substrate pregnenolone
are shown: one already described by others21 (SM1 mode) and
an additional one (SM2). Poses in SM1 occur more often
(approximately 7:3) with an overall better scoring with respect
to those in SM2. Furthermore, pregnenolone was also docked
with CHEMSCORE, a scoring function with a higher assessment
of the hydrophobic interactions, showing poses mostly in SM1
(>9:1). Interestingly, great similarities between SM2 and the
The inhibition of CYP11B2 observed with the evaluated
compounds was a little higher showing IC50 values between
121 and 2324 nM. Compared to abiraterone (IC50 ) 1751 nM),
compounds 6 and 13 exhibited a similar selectivity whereas
compound 19 (IC50 ) 2324 nM) was more selective than the
reference. Compared to ketoconazole (IC50 ) 67 nM) and
compound A (66% inhibition at 0.2 µM), all compounds were
more selective with the exception of compound 11 (IC50 ) 121
nM).
The synthesized compounds were also evaluated for inhibition
of the most crucial hepatic CYP enzyme CYP3A4 in regard to
its important role in drug metabolism. Except for compound 9
(IC50 ) 159 nM) and compound 13 (IC50 ) 357 nM), the IC50
values for compounds 1-20 were between 632 and >20000
nM. These compounds were more selective than ketoconazole

Abiraterone Analogues
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16 5013
Table 2. Inhibition of CYP11B1, CYP11B2, and CYP3A4 by Compounds 1-20
structures
IC50 (nM)
compda
R1
R2
n
N
CYP11B1b
CYP11B2b
CYP3A4b
1
2
3
4
5
6
7
8
F
F
OMe
OMe
F
F
OMe
F
F
OMe
F
H
1
1
1
1
2
2
2
1
1
1
2
2
2
2
1
1
2
2
2
2
3
4
4
4
4
4
4
3
4
4
4
4
4
4
3
4
4
4
4
4
ndc
ndc
>20000
3231
3291
3364
8757
13841
15190
6947
159
2394
4199
3643
357
2114
1697
1093
2173
2300
632
H
H
F
H
F
>10000
816
ndc
ndc
291
436
840
1676
945
ndc
1159
3109
686
F
H
H
H
H
F
OH
F
H
H
H
F
ndc
9
ndc
ndc
10
11
12
13
14
15
16
17
18
19
20
ndc
ndc
>10000
>20000
>10000
2748
ndc
1076
>5000
>20000
2135
1370
127
121
311
1492
991
ndc
543
518
567
2324
587
67
F
OH
OH
F
F
F
F
OH
OH
OH
F
3386
72
2704
KTZd
ABTe
1608
1751
a Compounds 8- 12 and 15-18 were tested as HCl salts and 13, 14, 19 and 20 as HBr salts. b Data shown were obtained by performing the tests in
duplicate. The deviations were within (5%. Concentration of progesterone (substrate) was 25 µM. c nd: not determined. d KTZ: ketoconazole. e ABT:
abiraterone.
Figure 1. Both binding modes of the substrate pregnenolone (SM1, cyan, and SM2, yellow; the red arrow indicates the position of the C17 atoms,
rendered as red spheres) are shown as docking complex with CYP17. For comparison, the two orientations of compound A (in the formerly
described binding modes BM1, blue, and BM2, green13f) and abiraterone (magenta) are given. Heme, interacting residues, and ribbon rendered
tertiary structure of the active site are also presented. Figures were generated with Pymol (http://www.pymol.org).
orientation of our previously described biphenyl compound A
can be observed (there are actually two very similar modes
described as BM1 and BM213e). Like the substrate, the steroidal
inhibitor abiraterone is also able to bind in both modes but

5014 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16
Pinto-Bazurco Mendieta et al.
Figure 2. Docking complexes of CYP17 and compounds 5 (R enantiomer in SM1, blue-green; S enantiomer in SM2, violet) and 20 (S enantiomer
in SM1, magenta; R enantiomer in SM2, green). A dashed yellow line is representing the H-bond between the OH in C17 and Gly301.
showing a good complexation with the heme iron only in SM1
(Figure 1). The same is true for compound B, the ring-closed
analogue of compound A (not shown).
inhibitory activity in contrast to the respective alcohols and
alkanes. In the case of the corresponding 4-pyridyl substituted
compounds, it is the other way around: the alcohols and the
alkanes were active, while the unsaturated compounds did not
show activity. However, it became apparent that the five-
membered ring, though analogous to the substrate and abirater-
one, is not favorable for CYP17 inhibition. On the other hand,
the expansion of this ring by one methylene group resulting in
the hydronaphthalenes led to very potent and selective com-
pounds. Summarizing, we have discovered nine very potent
abiraterone analogues, four of them (14, 17, 19, and 20) showing
an IC50 value below 200 nM and one of them (20, IC50 ) 64
nM) being slightly more active than abiraterone. These com-
pounds showed low inhibition of the CYP enzymes considered
for selectivity issues CYP11B1, CYP11B2 and the hepatic
CYP3A4. Owing to their promising in vitro profile, presently
compounds 20 and 19 are separated into their enantiomers and
extensively evaluated for their in vivo activities and pharma-
cokinetics in the rat.
The R and S configurated abiraterone analogues of the alcohol
and alkane class also bind in both modes. Interestingly, a
correlation between the inhibitory activities of the compounds
of each class and the score values could be observed. In the
case of highly active compounds, the percentage of poses
presenting a good iron-nitrogen coordination is higher than for
weak inhibitors. For enantiomers of a given racemic compound,
one enantiomer always shows a preference for poses in one
binding mode while the other enantiomer prefers to dock in
the alternative one. In the case of the alcohols, in Figure 2
exemplified by compound 5, the R enantiomer binds predomi-
nantly in the SM1 mode (9:1) while the S enantiomer binds in
SM2 (8:2). The opposite relation can be seen for the alkanes
(Figure 2).
The most important interactions in SM1, besides heme iron
complexation, are hydrophobic interactions with Ala113, Phe114,
Ile371, Pro372, and Val482 and, depending on substituents R1
and R2, polar ones with the backbone of Glu98 and Met99 and
the carboxyl group of Asp103. Furthermore, an H-bond forma-
tion between the OH group of R-alkohols and the backbone
carbonile of Gly301 was observed, which could act as an
additional stabilizing factor. Regarding SM2, the same interac-
tions as described in refs 13e and 13f were found.
Experimental Section
Chemistry. IR spectra were recorded neat on a Bruker Vector
33FT-infrared spectrometer. 1H NMR spectra were measured on a
Bruker DRX-500 (500 MHz). Chemical shifts are given in parts
per million (ppm), and TMS was used as an internal standard for
spectra obtained in CDCl3. All coupling constants (J) are given in
Hz. ESI (electrospray ionization) mass spectra were determined on
a TSQ quantum (Thermo Electron Corporation) instrument. Column
chromatography was performed using silica gel 60 (50-200 µm),
and reaction progress was determined by TLC analysis on Alugram
SIL G/UV254 (Macherey-Nagel). The purities of the final compounds
were determined with the Surveyor LC system and were always
greater than 98%. Boronic acids and bromoaryls used as starting
materials were commercially obtained (CombiBlocks, Chempur,
Aldrich, Acros).
Low activity compounds did not show a real clustering in
SM1 mode and were characterized by an unsuitable binding
angle between the N lone electron pair and the heme plane
(compound 12, Figure 3). On the other hand, the highly active
alkenes 13 and 14 bind preferentially in SM2 mode and present
a good complexation of the heme iron and a strong binding
due to their 3,4-di-OH or 3-F,4-OH substitution.
Discussion and Conclusion
Method A: Suzuki-Coupling. See Supporting Information.
Method B: Nucleophilic Addition of the Heterocycle. 3-Io-
dopyridine (4 mmol), or 4-bromopyridine (4 mmol) for the 4-pyridyl
In the class of the indanes the 3-pyridyl substituted unsatur-
ated compound 8, which is analogous to abiraterone, showed

Abiraterone Analogues
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16 5015
Figure 3. Docking complexes of CYP17 and compounds 11 (yellow; its lone electron pair at the nitrogen and the axis of the octahedral heme iron
atom are shown), 13 (cyan), and 14 (magenta).
compounds, after basic extraction of its hydrochloride salt with Et2O
(20 mL) and NaHCO3 (saturated, aqueous), followed by drying over
Na2SO4 and concentration under reduced pressure, was prepared
in Et2O and THF (3:2, 50 mL) at -78 °C. Then n-BuLi in hexane
(1.6 N, 4.4 mmol) was added, and after 5 s the corresponding ketone
(4 mmol) in THF (20 mL) was added at once and the mixture was
left stirring for an additional 3 h at room temperature. After
neutralization with NH4Cl (saturated, aqueous), the phases were
separated, the aqueous layer was extracted two times with EtOAc,
and the combined organic extracts were dried over Na2SO4 and
concentrated under reduced pressure. The purification was per-
formed by silica gel flash chromatography.
MHz) 1.75-1.82 (m, 1H), 2.00-2.08 (m, 2H), 2.09-2.16 (m, 1H),
2.86-3.00 (m, 2H), 6.98 (d, J ) 8.1 Hz, 1H), 7.07 (t, J ) 8.8 Hz,
2H), 7.27 (dd, J ) 2.0 Hz, J ) 8.1 Hz, 1H), 7.33-7.34 (m, 3H),
7.51 (dd, J ) 5.4 Hz, J ) 8.6 Hz, 2H), 8.40 (d, J ) 6.3 Hz, 2H);
m/z ) 320.06 [M+ + H].
6-(3,4-Difluorophenyl)-1-(pyridin-4-yl)-1,2,3,4-tetrahydronaph-
thalen-1-ol (6). 6 was synthesized from 6a and 4-bromopyridine
according to method B: yield ) 40%; δH (CDCl3 + CD3OD, 500
MHz) 1.81-1.89 (m, 1H), 1.99-2.07 (m, 2H), 2.12-2.18 (m, 1H),
2.89-3.00 (m, 2H), 6.99 (d, J ) 8.1 Hz, 1H), 7.19 (q, J ) 8.4 Hz,
1H), 7.24-7.26 (m, 2H), 7.30-7.37 (m, 4H), 8.48 (d, J ) 6.0 Hz,
2H); m/z ) 338.13 [M+ + H].
5-(4-Fluorophenyl)-1-(pyridin-3-yl)-2,3-dihydro-1H-inden-1-
ol (1). 1 was synthesized from 1a and 3-iodopyridine according to
method B: yield ) 55%; δH (CDCl3, 500 MHz) 2.36-2.47 (m,
2H), 2.85-2.89 (m, 1H), 3.08-3.14 (m, 1H), 6.98-7.04 (m, 3H),
7.14-7.16 (m, 1H), 7.24-7.26 (d, J ) 7.9 Hz, 1H), 7.36 (s, 1H),
7.41-7.44 (m, 2H), 7.69 (d, J ) 7.9 Hz, 1H), 8.29 (s, 1H), 8.48
(s, 1H); m/z ) 305.17 [M+ + H].
5-(4-Fluorophenyl)-1-(pyridin-4-yl)-2,3-dihydro-1H-inden-1-
ol (2). 2 was synthesized from 2a and 4-bromopyridine according
to method B: yield ) 50%; δH (CDCl3 + CD3OD, 500 MHz)
2.37-2.47 (m, 2H), 2.92-2.98 (m, 1H), 3.15-3.21 (m, 1H), 7.00
(d, J ) 7.9 Hz, 1H), 7.04 (t, J ) 8.6 Hz, 2H), 7.29-7.31 (m, 3H),
7.41 (s, 1H), 7.41-7.47 (m, 2H), 8.38 (d, J ) 4.8 Hz, 2H); m/z )
306.21 [M+ + H].
5-(4-Methoxyphenyl)-1-(pyridin-4-yl)-2,3-dihydro-1H-inden-
1-ol (3). 3 was synthesized from 3a and 4-bromopyridine according
to method B: yield ) 45%; δH (CDCl3 + CD3OD, 500 MHz)
2.34-2.46 (m, 2H), 2.91-2.97 (m, 1H), 3.12-3.20 (m, 1H), 3.77
(s, 3H), 6.90 (d, J ) 8.8 Hz, 2H), 6.98 (d, J ) 7.9 Hz, 1H),
7.30-7.32 (m, 3H), 7.42 (s, 1H), 7.44 (d, J ) 8.8 Hz, 2H), 8.38
(d, J ) 6.2 Hz, 2H); m/z ) 318.18 [M+ + H].
5-(3-Fluoro-4-methoxyphenyl)-1-(pyridin-4-yl)-2,3-dihydro-
1H-inden-1-ol (4). 4 was synthesized from 4a and 4-bromopyridine
according to method B: yield ) 56%; δH (CDCl3, 500 MHz)
2.39-2.48 (m, 2H), 2.93-2.98 (m, 1H), 3.14-3.19 (m, 1H), 3.85
(s, 3H), 6.93-6.98 (m, 2H), 7.21-7.30 (m, 5H), 7.40 (s, 1H), 8.40
(d, J ) 6.2 Hz, 2H); m/z ) 336.11 [M+ + H].
6-(3-Fluoro-4-methoxyphenyl)-1-(pyridin-4-yl)-1,2,3,4-tet-
rahydronaphthalen-1-ol (7). 7 was synthesized from 7a and
4-bromopyridine according to method B: yield ) 64%; δH (CDCl3
+ CD3OD, 500 MHz) 1.70-1.77 (m, 1H), 1.94-2.03 (m, 2H),
2.03-2.10 (m, 1H), 2.82-2.93 (m, 2H), 3.84 (s, 3H), 6.92 (dd, J
) 2.7 Hz, J ) 8.1 Hz, 2H), 6.96 (dt, J ) 2.4 Hz, J ) 8.4 Hz, 1H),
7.19-7.28 (m, 6H), 8.35-8.36 (m, 2H); m/z ) 350.13 [M+ + H].
Method C: Condensation with HCl. The corresponding alcohol
(1 mmol) was refluxed in HCl in i-PrOH (10 mL, 3 N) for 2 h.
Afterward, the resulting solution was concentrated under reduced
pressure and washed three times with Et2O. No further purification
was necessary.
3-(5-(4-Fluorophenyl)-3H-inden-1-yl)pyridine Hydrochloride
(8). 8 was synthesized from 1 according to method C: yield ) 96%;
δH (CDCl3, 500 MHz) 3.53 (s, 2H), 6.61-6.62 (m, 1H), 7.06 (t, J
) 8.7 Hz, 2H), 7.32 (dd, J ) 4.8 Hz, J ) 7.8 Hz, 1H), 7.44 (dd,
J ) 1.4 Hz, J ) 7.8, 1H), 7.49-7.52 (m, 3H), 7.65 (s, 1H),
7.83-7.85 (m, 1H), 8.55-8.56 (d, J ) 4.0 Hz, 1H), 8.81 (s, 1H);
MS (ESI): m/z ) 288.13 [M+ + H].
4-(5-(4-Fluorophenyl)-3H-inden-1-yl)pyridine Hydrochloride
(9). 9 was synthesized from 2 according to method C: yield )
100%; δH (CDCl3, 500 MHz) 3.20-3.22 (m, 2H), 7.08 (t, J ) 8.8
Hz, 2H), 7.30 (s, 1H), 7.54 (dd, J ) 1.7 Hz, J ) 8.1 Hz, 1H), 7.58
(dd, J ) 5.4 Hz, J ) 8.8 Hz, 2H), 7.69 (d, J ) 8.1 Hz, 1H), 7.76
(d, J ) 1.4 Hz, 1H), 8.30 (d, J ) 6.8 Hz, 2H), 8.81 (d, J ) 6.8 Hz,
2H); m/z ) 287.96 [M+ + H].
6-(4-Fluorophenyl)-1-(pyridin-4-yl)-1,2,3,4-tetrahydronaph-
thalen-1-ol (5). 5 was synthesized from 5a and 4-bromopyridine
according to method B: yield ) 44%; δH (CDCl3 + CD3OD, 500
4-(5-(4-Methoxyphenyl)-3H-inden-1-yl)pyridine Hydrochlo-
ride (10). 10 was synthesized from 3 according to method C: yield
) 99%; δH (CDCl3 + CD3OD, 500 MHz) 3.24-3.27 (m, 2H), 3.78

5016 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16
Pinto-Bazurco Mendieta et al.
(s, 3H), 6.92 (d, J ) 8.8 Hz, 2H), 7.43 (s, 1H), 7.50 (d, J ) 8.8
Hz, 2H), 7.53 (dd, J ) 1.7 Hz, J ) 8.1 Hz, 1H), 7.60 (d, J ) 8.1
Hz, 1H), 7.73 (d, J ) 1.7 Hz, 1H), 8.23 (d, J ) 6.7 Hz, 2H), 8.80
(d, J ) 6.7 Hz, 2H); m/z ) 301.16 [M+ + H].
4-(6-(4-Fluorophenyl)-3,4-dihydronaphthalen-1-yl)pyridine Hy-
drochloride (11). 11 was synthesized from 4 according to method
C: yield ) 100%; δH (CDCl3, 500 MHz) 2.58-2.61 (m, 2H), 2.94
(t, J ) 7.8 Hz, 2H), 6.55 (t, J ) 4.7 Hz, 1H), 6.95 (d, J ) 7.9 Hz,
1H), 7.14 (t, J ) 8.7 Hz, 2H), 7.38 (d, J ) 7.9 Hz, 1H), 7.46 (s,
1H), 7.56 (dd, J ) 5.3 Hz, J ) 8.7 Hz, 2H), 7.93 (d, J ) 5.6 Hz,
2H), 8.79 (d, J ) 5.6 Hz, 2H); m/z ) 302.10 [M+ + H].
4-(6-(3,4-Difluorophenyl)-3,4-dihydronaphthalen-1-yl)pyri-
dine Hydrochloride (12). 12 was synthesized from 5 according to
method C: yield ) 98%; δH (CDCl3, 500 MHz) 2.57-2.61 (m,
2H), 2.94 (t, J ) 8.0 Hz, 2H), 6.57 (t, J ) 4.8 Hz, 1H), 6.96 (d, J
) 8.0 Hz, 2H), 7.23 (q, J ) 8.5 Hz, 1H), 7.29-7.31 (m, 1H), 7.36
(d, J ) 8.5 Hz, 1H), 7.37-7.41 (m, 1H), 7.44 (s, 1H), 7.92
(s, 1H), 7.93 (s, 1H), 8.81 (s, 1H), 8.82 (s, 1H); m/z ) 320.11 [M+
+ H].
Method D: Hydration with Pearlman’s Catalyst. Pearlman’s
catalyst (10 mass %) and the corresponding alkene were prepared
in EtOH and THF (2:1, 5 mL) under H2 atmosphere. The mixture
was left stirring for 3 h. Then the catalyst was filtered off three
times and the solution concentrated under reduced pressure. The
obtained solid was washed three times with Et2O. No further
purification was necessary.
3-(5-(4-Fluorophenyl)-2,3-dihydro-1H-inden-1-yl)pyridine Hy-
drochloride (15). 15 was synthesized from 8 according to method
D: yield ) 99%; δH (CDCl3, 500 MHz) 1.92-1.98 (m, 1H),
2.65-2.71 (m, 1H), 2.95-3.06 (m, 2H), 4.51 (s, 1H), 6.84 (d, J )
6.9 Hz, 1H), 7.00 (t, J ) 8.6 Hz, 2H), 7.24 (d, J ) 6.9 Hz, 1H),
7.38-7.41 (m, 3H), 7.76 (s, 1H), 8.13 (d, J ) 5.0 Hz, 1H), 8.49
(s, 1H), 8.55 (s, 1H); m/z ) 290.10 [M+ + H].
4-(5-(4-Fluorophenyl)-2,3-dihydro-1H-inden-1-yl)pyridine Hy-
drochloride (16). 16 was synthesized from 9 according to method
D: yield ) 100%; δH (CDCl3, 500 MHz) 2.03-2.09 (m, 1H),
2.72-2.78 (m, 1H), 3.03-3.13 (m, 2H), 4.60 (s, 1H), 6.93 (d, J )
7.1 Hz, 1H), 7.06 (t, J ) 8.6 Hz, 2H), 7.32 (d, J ) 6.7 Hz, 1H),
7.45-7.47 (m, 3H), 7.68 (s, 2H), 8.71 (s, 2H); m/z ) 290.17 [M+
+ H].
4-(6-(4-Fluorophenyl)-1,2,3,4-tetrahydronaphthalen-1-yl)py-
ridine Hydrochloride (17). 17 was synthesized from 11 according
to method D: yield ) 97%; δH (CDCl3, 500 MHz) 1.82-1.90 (m,
3H), 2.33-2.37 (m, 1H), 2.94-3.00 (m, 2H), 4.46 (s, 1H), 6.78
(d, J ) 7.5 Hz, 1H), 7.12 (t, J ) 8.6 Hz, 2H), 7.30 (d, J ) 6.8 Hz,
1H), 7.39 (s, 1H), 7.53 (dd, J ) 5.3 Hz, J ) 8.6 Hz, 2H), 7.67 (s,
2H), 8.71 (s, 2H); m/z ) 304.10 [M+ + H].
4-(6-(3,4-Difluorophenyl)-1,2,3,4-tetrahydronaphthalen-1-
yl)pyridine Hydrochloride (18). 18 was synthesized from 12
according to method D: yield ) 98%; δH (CDCl3, 500 MHz)
1.82-1.90 (m, 3H), 2.33-2.37 (m, 1H), 2.94-3.00 (m, 2H), 4.46
(s, 1H), 6.79 (d, J ) 6.2 Hz, 1H), 7.22 (q, J ) 8.4 Hz, 2H),
7.26-7.28 (m, 2H), 7.34-7.38 (m, 2H), 7.66 (s, 2H), 8.72 (s, 2H);
m/z ) 322.11 [M+ + H].
Method E: Ether Cleavage and Condensation with HBr. The
corresponding ether was refluxed overnight in 48% HBraq (100 mL
for compound 5c, 3 mL for compounds 13 and 14). For compound
5c, after reaction completion water (100 mL) was added and the
mixture was cooled and filtered. The solid was washed three times
with water, and no further purification was needed. For compounds
13 and 14, after reaction completion the mixture was neutralized
with solid NaHCO3 and extracted three times with EtOAc. The
combined organic extracts were dried over Na2SO4, concentrated
underreducedpressure,andpurifiedbysilicagelflashchromatography.
4-(5-(Pyridin-4-yl)-7,8-dihydronaphthalen-2-yl)benzene-1,2-
diol Hydrobromide (13). 13 was synthesized from 13a according
to method E: yield ) 65%; δH (CDCl3 + CD3OD, 500 MHz)
2.53-2.55 (m, 2H), 2.87 (t, J ) 7.8 Hz, 2H), 6.53-6.55 (m, 1H),
6.83-6.89 (m, 2H), 6.94-6.96 (m, 1H), 7.28-7.31 (m, 1H),
7.40-7.41 (m, 1H), 7.94-7.96 (m, 2H), 8.77-8.79 (m, 2H); m/z
) 316.18 [M+ + H].
2-Fluoro-4-(5-(pyridin-4-yl)-7,8-dihydronaphthalen-2-yl)phe-
nol Hydrobromide (14). 14 was synthesized from 7 according to
method E: yield ) 28%; δH (CDCl3 + CD3OD, 500 MHz)
2.49-2.53 (m, 2H), 2.94 (t, J ) 7.9 Hz, 2H), 6.25-6.27 (m, 1H),
7.02 (q, J ) 8.4 Hz, 2H), 7.26 (d, J ) 8.1 Hz, 1H), 7.31 (s, 1H),
7.34 (d, J ) 5.8 Hz, 1H), 7.39-7.42 (m, 3H), 8.58 (d, J ) 5.7 Hz,
2H); m/z ) 318.08 [M+ + H].
Biological Assays. CYP17 Preparation and Assay. For the
source of human CYP17, our E. coli system19 (coexpressing human
CYP17 and NADPH-P450 reductase) was used, and the assay was
performed as previously described12a using unlabeled progesterone
as substrate and applying HPLC with UV detection for separation.
Inhibition of CYP11B1 and CYP11B2. V79MZh11B1 or
V79MZh11B222 cells expressing the respective human enzyme were
used, and our assay procedure using [4-14C]-11-deoxycorticosterone
was performed.20
Inhibition of CYP3A4. The recombinantly expressed enzymes
from baculovirus-infected insect microsomes and cytochrome b5
(BD supersomes) were used, and the manufacturer’s instructions
(www.gentest.com) were followed.
Molecular Modeling. Various inhibitors of Table 1 were docked
into our CYP17 homology model by means of the GOLD 3.2
software23 using GOLDSCORE and CHEMSCORE. Since the
GOLD docking program allows flexible docking of the compounds,
no conformational search was employed to the ligand structures.
GOLD gave the best poses by a genetic algorithm (GA) search
strategy, and then various molecular features were encoded as a
chromosome.
The structures of the inhibitors were built with SYBYL 7.3.2
(Sybyl, Tripos Inc., St. Louis, MO) and energy-minimized in
MMFF94s force-field24 as implemented in Sybyl.
Ligands were docked in 50 independent GA runs using GOLD.
Heme iron was chosen as active site origin, while its radius was
set equal to 19 Å. The automatic active site detection was switched
on. Furthermore, a distance constraint of a minimum of 1.9 Å and
a maximum of 2.5 Å between the sp2-hybridized nitrogen of the
pyridine and the iron of the heme was set. Additionally, the
goldscore.p450_pdb parameters were used and some of the GOLD-
SCORE parameters were modified to improve the weight of
hydrophobic interaction and of the coordination between iron and
nitrogen. The genetic algorithm default parameters were set as
suggested by the GOLD authors.23 On the other hand, the annealing
parameters of fitness function were set at 3.5 Å for hydrogen
bonding and 6.5 Å for van der Waals interactions.
4-(5-(Pyridin-4-yl)-5,6,7,8-tetrahydronaphthalen-2-yl)benzene-
1,2-diol Hydrobromide (19). 19 was synthesized from 13 accord-
ing to method D: yield ) 98%; δH (CDCl3 + CD3OD, 500 MHz)
1.73-1.80 (m, 3H), 2.19-2.24 (m, 1H), 2.81-2.89 (m, 2H),
4.27-4.32 (m, 1H), 6.63-6.65 (m, 1H), 6.81 (d, J ) 8.2 Hz, 1H),
6.88-6.90 (m, 1H), 7.00 (s, 1H), 7.17 (d, J ) 8.0 Hz, 1H), 7.28
(s, 1H), 7.45-7.51 (m, 2H), 8.59 (s, 2H); m/z ) 318.65 [M+
H].
+
All 50 poses for each compound were clustered with ACIAP,25
and the representative structure of each significant cluster was
selected. After the docking simulations and cluster analysis were
performed, the quality of the docked representative poses was
evaluated on the basis of visual inspection of the putative binding
modes of the ligands. The latter compounds were further evaluated
by means of Silver, version 3.1.1, the postprocessing tool of GOLD,
and last by GOLDSCORE.
2-Fluoro-4-(5-(pyridin-4-yl)-5,6,7,8-tetrahydronaphthalen-2-
yl)phenol Hydrobromide (20). 20 was synthesized from 14
according to method D: yield ) 96%; δH (CDCl3 + CD3OD, 500
MHz) 1.84-1.92 (m, 3H), 2.34-2.40 (m, 1H), 2.92-3.00 (m, 2H),
4.48-4.50 (m, 1H), 6.76 (d, J ) 8.0 Hz, 1H), 7.02 (t, J ) 8.8 Hz,
1H), 7.22 (d, J ) 8.4 Hz, 1H), 7.26-7.28 (m, 2H), 7.38 (s, 1H),
7.73 (s, 1H), 7.74 (s, 1H), 8.79 (s, 1H), 8.80 (s, 1H); m/z ) 320.08
[M+ + H].

Abiraterone Analogues
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16 5017
complex 17alpha-hydroxylase/17,20-lyase (P45017R). Bioorg. Med.
Chem. Lett. 2006, 16, 4011–4015.
Acknowledgment. We thank Professor J. Hermans, Car-
diovascular Research Institute (University of Maastricht, The
Netherlands), for providing us with V79MZh11B1 cells ex-
pressing human CYP11B1 and Professor R. Bernhardt (Saarland
University, Germany) for making the V79MZh11B2 cells
expressing human CYP11B2 available to us. We also thank
U. E. Hille and G. Schmitt for performing the CYP11B1 and
CYP11B2 tests and Dr. K. Hansen and his group for the
CYP3A4 data.
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