Preparation and pharmacological profile of 7-(α-azolylbenzyl)-1H-indoles and indolines as new aromatase inhibitors

Article abstract of DOI:10.1016/S0960-894X(03)00182-3

Aromatase (P450 arom) is a target of pharmacological interest for the treatment of breast cancer. New series of 7-(α-azolylbenzyl)-1H-indoles and indolines were synthesized as non-steroidal inhibitors of P450 arom. Selectivity was studied towards P450 17α enzyme. The most active compound, 1-ethyl-7-[(imidazol-1-yl)(4-chlorophenyl)methyl]-1H-indole 12c exhibited promising relative potency (rp) of 336 (rp of aminoglutethimide=1) and most of the described azoles were active and selective towards P450 arom.

Full text of DOI:10.1016/S0960-894X(03)00182-3

Bioorganic & Medicinal Chemistry Letters 13 (2003) 1553–1555
Preparation and Pharmacological Profile of 7-(ꢀ-Azolylbenzyl)-
1H-indoles and Indolines as New Aromatase Inhibitors
Pascal Marchand,a,* Marc Le Borgne,a Martina Palzer,b
Guillaume Le Bauta and Rolf W. Hartmannb
a
´
Laboratoires de Chimie Organique et de Chimie Therapeutique, UFR des Sciences Pharmaceutiques,
1 rue Gaston Veil, 44035 Nantes Cedex, France
bFachrichtung 12.1 Pharmazeutische und Medizinische Chemie, Universitat des Saarlandes,
¨
PO Box 15 11 50, D-66041 Saarbrucken, Germany
¨
Received 18September 2002; revised 24 January 2003; accepted 12 February 2003
Abstract—Aromatase (P450 arom) is a target of pharmacological interest for the treatment of breast cancer. New series of 7-(a-
azolylbenzyl)-1H-indoles and indolines were synthesized as non-steroidal inhibitors of P450 arom. Selectivity was studied towards
P450 17a enzyme. The most active compound, 1-ethyl-7-[(imidazol-1-yl)(4-chlorophenyl)methyl]-1H-indole 12c exhibited promising
relative potency (rp) of 336 (rp of aminoglutethimide=1) and most of the described azoles were active and selective towards P450
arom.
# 2003 Elsevier Science Ltd. All rights reserved.
Introduction
(Fig. 1), the first non-steroidal marketed drug, was
measured at 18.5 mM. Our molecules also exhibited a
good selectivity profile toward the P450 17a which con-
verts progestins to androgens.
Aromatase (P450 arom) is a microsomal enzyme com-
plex consisting of a cytochrome P450 hemoprotein and
a NADPH cytochrome reductase.1 It catalyses the con-
version of androgens into estrogens by aromatization of
the steroid A ring. Inhibitors of this enzyme are poten-
tial therapeutics for the treatment of estrogen dependent
diseases, such as breast cancer.2 Among the non-ster-
oidal compounds, azoles appeared to be very potent and
some of them have already been marketed (fadrozole,3
anastrozole,3 letrozole4) or are in phase III clinical trial
(vorozole5) (Fig. 1).
With the aim to check the relationships between phar-
macological activity and position of the azolylbenzyl
chain on the benzene part of the indole ring we have
developed a new series of 7-(a-azolylbenzyl)-1H-indoles.
Moreover, the indoline analogues were also tested for
inhibitory activity towards P450 arom and P450 17a
enzymes.
During our investigation towards the synthesis of new
non-steroidal aromatase inhibitors, we synthesized a
series of 3-(azolylmethyl)-1H-indoles6,7 and 2-, 3- and
5-(a-azolylbenzyl)-1H-indoles.8,9 Thus, we demon-
strated that most of our compounds display a high level
of estrogen biosynthesis inhibitory activity. Among
them, the 1-ethyl-5-[(imidazol-1-yl)(4-fluorophenyl)-
methyl]-1H-indole I is the most active with IC50 of
0.041 mM while the IC50 of aminoglutethimide (AG)
Chemistry
The compounds synthesized for this study were prepared
by two general routes (Scheme 1). By modification of the
method of Sugasawa et al.,10 ortho-benzoylation of
indoline 1, with suitable benzonitriles as acylating
agents in the presence of boron trichloride and aluminum
trichloride, gave the desired 7-benzoylindolines 1a–d as
starting materials for both indoline and indole series. In
the first series, halogenation in the 5-position of indoline
ring was achieved using either N-bromosuccinimide or
N-chlorosuccinimide in methylene choride.11 N-alkyl-
ation was carried out with ethyl iodide in dry dimethyl
*Corresponding author. Tel.: +33-240-412-874; fax: +33-240-412-
876; e-mail: pascal.marchand@sante.univ-nantes.fr
0960-894X/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0960-894X(03)00182-3

1554
P. Marchand et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1553–1555
Table 1. In vitro activity of 7-(a-azolylbenzyl)-1H-indoles and
indolines
Compd
R1
R2
P450 arom
IC50, mMa
P450 17a
rpc
% Inhibitione
Figure 1. Non-steroidal aromatase inhibitors.
5a
5b
4-F
3-Cl
4-F
4-F
4-F
H
H
Br
Cl
H
H
H
H
H
Br
0.0615
0.11
0.09
0.063
2.90b
0.062
0.17
0.055
0.070
0.20
300.837
164
205.6
293.6
10d
298.4
108.8
336
38
8
sulfoxide in the presence of sodium hydride. The reduc-
tion of the ketones was performed with sodium boro-
hydride in methanol and the crude alcohols, so
obtained, were treated with 1,10-carbonyldiimidazole
(CDI)12 in tetrahydrofuran to afford imidazole deriva-
tives 5a–b, 6a and 60a. A triazole analogue 7a was pre-
pared by reaction of the corresponding carbinol with
1,10-sulfinylditriazole (SDT)13 in acetonitrile. In the first
step of the second series, the 7-benzoylindolines 1a–d
and 2a were converted to the indole analogues 8a–d and
9a by dehydrogenation with activated manganese diox-
ide11 in high yields. As described before, subsequent
N-alkylation, reduction and fixation of the imidazole
moiety led to the corresponding 7-(a-imidazolylbenzyl)-
1H-indoles 12a–d and 13a.
6a
60a
7a
23
NDf
37
43
29
29
9
12a
12b
12c
12d
13a
4-F
3-Cl
4-Cl
4-Br
4-F
264
92.5
aIC50 is the concentration of inhibitor required to give 50% inhibition.
Concentration of testosterone: 2.5 mM. The given values are mean
values of at least three experiments. The deviations were within ꢀ5%.
bConcentration of androstenedione: 0.5 mM.
cRelative potency, calculated from IC50 values and related to AG (IC50
of AG: 18.5 mM).
dIC50 of AG: 29.5 mM.
eConcentration of progesterone: 25mM. Concentration of inhibitor:
2.5 mM. Under identical experimental conditions ketoconazole caused an
inhibition of 70%. All values are the mean of at least two determinations.
fNot determined.
Results and Discussion
potencies of the compounds relative to AG (rp values).
The assay of P450 17a inhibition was performed
according to the literature procedure15 using rat testi-
cular microsomes as source of the enzyme and non-
labeled progesterone as substrate.
The method of Thompson and Siiteri,14 that is human
placental microsomes and [1b,2b-3H]testosterone, was
used for the determination of P450 arom inhibitory activ-
ities. Table 1 shows the IC50 values and the inhibitory
Scheme 1. Reaction conditions and yields: (a) R1-benzonitrile, BCl3/AlCl3, toluene, reflux, 61–73%; (b) NBS or NCS, CH2Cl2, rt, 69–75%; (c) NaH,
EtI, DMF, rt, 52–91%; (d) (1) NaBH4, MeOH, reflux; (2) CDI, THF, reflux, 20–70%; (e) (1) NaBH4, MeOH, reflux; (2) SDT, CH3CN, reflux, 17%;
(f) MnO2, CH2Cl2, reflux, 86–96%.

P. Marchand et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1553–1555
1555
Considering the aromatase inhibitors carrying the imi-
dazolyl substituent, it is evident that the oxidation of
the indoline to indole had no pharmacological effect
and both compounds 5a, 12a and 5b, 12b exhibited the
same range of activity (Table 1). The most active com-
pound was the 1-ethyl-7-[(imidazol-1-yl)(4-chlorophenyl)
methyl]-1H-indole 12c with IC50: 0.055 mM and rp: 336
but all compounds bearing halogen atom in the 4-posi-
tion of phenyl nucleus also remained potent aromatase
inhibitors, except 13a. Moreover, the nature of the
halogen did not appear to be an essential requirement
for inhibitory activity as showed the close and high rp
values of 12a (R1=4-F, rp: 298.4), 12c (R1=4-Cl, rp:
336) and 12d (R1=Br, rp: 264).
activity of our imidazoles by testing enantiomerically
pure compounds as vorozole, for instance.
The triazole analogue 7a was prepared with the aim of
exploring the effects of the variation of the aza-hetero-
cycle. It has been reported that the replacement of the
imidazole moiety with a triazole one can lead to higher
in vivo activity.18
Further experiments on the in vivo inhibitory activity
and on the selectivity towards other steroidogenic P450
enzymes such as P450 scc will be performed.
References and Notes
On the one hand, in the indole series, the introduction
of a bromine into the 5-position led to markedly
decrease the P450 arom inhibition (compound 13a, rp:
92.5). On the other hand, in the indoline series, the
replacement of an hydrogen by a bromine (6a, rp: 205.6)
had a negative effect on inhibitory aromatase activity
and the presence of a chlorine (60a, rp: 293.6) influenced
only moderately this activity by comparison with 5a
showing a relative potency of 300.8.
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For the triazole compound 7a, the aromatase assay was
performed according to described methods,16,17 mon-
itoring enzyme activity by measuring 3H2O formed from
[1b-3H]androstenedione during aromatization. The
replacement of the imidazolyl group of compound 5a by
7. Marchand, P.; Le Borgne, M.; Duflos, M.; Robert-Pies-
sard, S.; Le Baut, G.; Ahmadi, M.; Hartmann, R. W.; Palzer,
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J. Med. Chem. 1984, 27, 1379.
a triazolyl substituent (compound 7a) strongly
decreased the inhibition of P450 arom.
Percent inhibition values of P450 17a indicate that all
compounds do not significantly inhibit the enzyme or
show only marginal inhibitory activity at 2.5 mM.
12. Jones, C. D.; Winter, M. A.; Hirsch, K. S.; Stamm, N.;
Taylor, H. M.; Holden, H. E.; Davenport, J. D.; Krumkalns,
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Conclusion
We have discovered new 7-(a-azolylbenzyl)-1H-indoles
and indolines as potent and selective aromatase inhibi-
tors but less active than an analogue in the 5-position
previously synthesized and tested by us9 (compound I,
rp: 451.2).
The next step of the work will be the separation of the
most active racemic compounds 5a, 60a, 12a and 12c, by
chiral HPLC, so as to enhance the P450 arom inhibitory
17. Graves, P. E.; Salhanick, H. A. Endocrinology 1979, 105, 52.
18. Lang, M.; Batzl, C.; Furet, P.; Bowman, R.; Hausher, A.;
¨
Bhatnagar, A. S. J. Steroid Biochem. Mol. Biol. 1993, 44, 421.