Synthesis and biological evaluation of 5-[(aryl)(1H-imidazol-1-yl)methyl]- 1H-indoles: Potent and selective aromatase inhibitors

Article abstract of DOI:10.1016/j.bmcl.2005.11.099

The synthesis and the aromatase (CYP19) inhibitory activity of 5-[(aryl)(imidazol-1-yl)methyl]-1H-indoles were reported. Among the tested racemate compounds, 5-[(4-chlorophenyl)(1H-imidazol-1-yl)methyl]-1H-indole 8b emerged as a potent CYP19 inhibitor (IC

Full text of DOI:10.1016/j.bmcl.2005.11.099

Bioorganic & Medicinal Chemistry Letters 16 (2006) 1134–1137
Synthesis and biological evaluation of
5-[(aryl)(1H-imidazol-1-yl)methyl]-1H-indoles: Potent
and selective aromatase inhibitors
a,
a
a
b
a
Marie-Pierre Leze, * Marc Le Borgne, Patricia Pinson, Anja Palusczak, Muriel Duflos,
´ ´
Guillaume Le Bauta and Rolf W. Hartmannb
aDepartment of Pharmacochemistry, BioCiT UPRES EA1155, Faculty of Pharmacy, Nantes University,
1 rue Gaston Veil, F-44035 Nantes Cedex, France
bFachrichtung 8.5 Pharmaceutische und Medizinische Chemie, Universita¨t des Saarlandes,
PO Box 151150, D-66041 Saarbru¨cken, Germany
Received 2 November 2005; revised 25 November 2005; accepted 28 November 2005
Available online 27 December 2005
Abstract—The synthesis and the aromatase (CYP19) inhibitory activity of 5-[(aryl)(imidazol-1-yl)methyl]-1H-indoles were reported.
Among the tested racemate compounds, 5-[(4-chlorophenyl)(1H-imidazol-1-yl)methyl]-1H-indole 8b emerged as a potent CYP19
inhibitor (IC50 = 15.3 nM). Chiral chromatography allowed isolation of the (+) enantiomer 8b2, which was about twice as active
as the racemate (IC50 = 9 nM).
Ó 2005 Elsevier Ltd. All rights reserved.
N
Breast cancer is the most common cancer in women and
it causes 70,000 deaths per year in Europe.1
N
N
N
NH2
N
N
NC
Estrogens are known to play a pivotal role in the prolif-
eration of cancer cells.2 In endocrine therapy, the two
major approaches consist in: (i) blocking estrogen recep-
tors using selective estrogen receptor modulators such as
tamoxifen,3 (ii) blocking estrogen biosynthesis using
aromatase (CYP19) inhibitors such as aminoglutethi-
mide (Fig. 1). Among the nonsteroidal aromatase
inhibitors (NSAIs), more specific compounds than the
well-established inhibitor aminoglutethimide have been
marketed for the treatment of hormone-dependent
breast cancer in postmenopausal women; letrozole4
and anastrozole5 are potent inhibitors exerting less
severe side effects and are used in second-line therapy.
However, several reports6 showed advantages of NSAIs
over tamoxifen in adjuvant treatment. Therefore, aro-
matase inhibitors represent an interesting alternative in
the first-line therapy.
O
N
O
CN
NC
CN
Letrozole
N
Aminoglutethimide
N
Anastrozole
N
N
N
N
N
Cl
N
N
N
N
N
F
N
H
Cl
1
Vorozole
Liarozole
Figure 1. P450 enzyme inhibitors.
In our effort to design more potent and selective aroma-
tase inhibitors, we have developed a novel class of
NSAI-based 2-, 3-, 5- or 7-[(aryl)(azolyl)methyl]-1H-
indoles.7,8
Considering the structure of reference drugs such as
vorozole and liarozole (Fig. 1), we carried out pharma-
comodulations in the imidazole series starting from
compound 1 which exhibits a promising activity
(IC50 = 0.040 lM). We present here the first data result-
ing from modifications at the level of indolic nitrogen
Keywords: Breast cancer; Aromatase inhibitors; 5-[(Aryl)-
(imidazolyl)methyl]indoles.
*
Corresponding author. Tel.: +33 2 40 41 11 14; fax: +33 2 40 41 28
76; e-mail: mpl_leze@yahoo.fr
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.11.099

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M.-P. Leze et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1134–1137
1135
(R1 = H, CH3) and phenyl substitution (X = halogens,
cyano).
microwave dielectric heating.11 The key intermediates,
aroylindoles 6a–d, were prepared by oxidation using
activated manganese oxide.12,13 Alkylation of com-
pound 6b was achieved using methyl iodide in the pres-
ence of sodium hydride in dimethylsulfoxide to provide
7b. The synthesis of target compounds 8a–c, 9b, and 11
(Scheme 1) was carried out by reduction of the ketone
in the presence of sodium borohydride in methanol,
followed by the fixation of imidazole moiety using
1,10-carbonyldiimidazole (CDI) in dry acetonitrile.14,15
Taking into account that the biosynthesis of androgens
(androstenedione, testosterone) is also regulated by
monooxygenase belonging to the cytochrome P450 en-
zyme family, 17a-hydroxylase-C17,20-lyase (CYP17),
the studied compounds were also considered in order
to determine their selectivity.
The synthetic pathway to provide 5-[(aryl)(1H-imidazo-
lyl)methyl]-1H-indoles 8a–c, 9b is described in Scheme 1.
It required three main steps: acylation of indoline pre-
cursor 3, followed by oxidation into the indole counter-
parts and fixation of imidazole moiety.
The compound 6d was used as a precursor to afford the
nitrile derivative 10 by a bromine/cyano exchange reac-
tion in the presence of zinc cyanide and Pd(PPh3)4 as
catalyst under microwave irradiation (Scheme 2).16,17
1-Benzenesulfonyl-1H-indoline 3 was synthesized by sul-
fonation of the commercially available indoline 2 in the
presence of triethylamine. The N-protected haloge-
nobenzoylindolines 4a–d were prepared by a Friedel–
Crafts acylation with aluminum chloride as Lewis
acid.9,10 Compounds 5a–d were obtained by deprotec-
tion of indolic nitrogen with sulfuric acid under
The in vitro antiaromatase activity of the compounds
8a–c, 9b, and 11 was evaluated using microsomal frac-
tion of human placental tissue,18 according to a previ-
ously described procedure.19 [1b-3H]Androstenedione
(0.08 lCi,
15 nM),
unlabeled
androstenedione
(485 nM), NADPH-generating system, and inhibitor
(0–100 lM, DMSO as solvent) in phosphate buffer
(pH 7.4) were preincubated for 5 min at 30 °C in a shak-
ing water bath. Microsomal protein was added to start
the enzymatic reaction. After incubation for 14 min at
30 °C, a cold HgCl2 1 mM solution and a Norit A 2%
suspension were added. After shaking and centrifuga-
tions, aliquots of the supernatant were assayed for
3H2O by counting in a scintillation mixture using
LKB-Wallac b-counter. The IC50 values were deter-
mined by plotting the percent inhibition versus the
concentration of inhibitor on a semilog plot.
O
ii
i
X
N
N
N
SO2
SO2
H
4a-d
3
2
O
O
iii
iv
X
X
N
N
The CYP17 assay was performed in vitro using mem-
brane fractions of recombinant Escherichia coli pJL17/
OR coexpressing human CYP17/rat NADPH-P450
reductase and progesterone as a substrate.20 Results
are summarized in Table 1.
H
H
6a-d
5a-d
v
vi, vii
N
O
All the studied target racemate compounds showed
a higher activity toward CYP19 than our previously
described derivatives7 or aminoglutethimide (AG,
IC50 = 29.75 lM). Moreover, they were inactive on the
inhibition of CYP17 (% inhibition <52).
N
vi, vii
X
X
N
N
7b
8a-c R1 = H
9b R1 = CH3
R1
a, X = 4-F; b, X = 4-Cl; c, X = 3-Cl; d, X = 4-Br
Replacement of ethyl chain on indolic nitrogen in com-
pound 1 by hydrogen (8a) increased 1.5-fold the activity
(IC50 = 40 and 26 nM, respectively) and the decrease of
activity by N-methylation of 8b, leading to 9b (IC50 = 15
and 24 nM, respectively), tend to confirm the detrimen-
tal effect of N-alkylation.
Scheme 1. Reagents and conditions: (i) PhSO2Cl, Et3N, ClCH2CH2Cl,
0 °C to rt, 1 h, quantitative; (ii) X-C6H4COCl, AlCl3, CH2Cl2, reflux,
rt, 4 h 1-week; (iii) H2SO4 80%, microwave, 40 W, 90 °C, 5 min, 85%-
quantitative; (iv) MnO2, CH2Cl2, reflux, 16 h, 73% quantitative; (v)
NaH, CH3I, DMSO, rt, 1 h, 95%; (vi) NaBH4, CH3OH, rt; (vii) CDI,
CH3CN, rt, 21–96 h, 30–53%.
N
N
O
O
i
ii, iii
N
N
N
NC
NC
Br
H
H
H
6d
10
11
Scheme 2. Reagents and conditions: (i) Zn(CN)2, Pd(PPh3)4, DMF, microwave, 60 W, 153 °C, 3 min, 68%; (ii) NaBH4, CH3OH, rt; (iii) CDI,
CH3CN, rt, 23 h, 54%.

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M.-P. Leze et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1134–1137
1136
Table 1. In vitro CYP19 and CYP17 inhibitions by 5-[(aryl)(1H-
imidazolyl)methyl]-1H-indoles
2. Clemons, M.; Goss, P. N. Engl. J. Med. 2001, 276.
3. Osborne, C. K.; Yochmowitz, M. G.; Knight, W. A.; Mc
Guire, W. L. Cancer 1980, 46, 189.
4. Simpson, D.; Curran, M. P.; Perry, C. M. Drugs 2004, 64,
1213.
Compound R1
X
CYP19
CYP17
IC50 (lM) RPb
% inhibitionc
a
5. Howell, A.; Robertson, J. F. R.; Vergote, I. Breast Cancer
Res. Treat. 2003, 82, 215.
6. (a) Nabholtz, J. M.; Buzdar, A.; Pollak, M.; Harwin,
W.; Burton, G.; Mangalik, A.; Steinberg, M.; Webster,
A.; von Euler, M. J. Clin. Oncol. 2000, 18, 3758; (b)
8a
8b
H
H
H
H
H
4-F
0.0263
0.0153
0.045
1129 25
1144 28
4-Cl
4-Cl
4-Cl
3-Cl
(ꢀ)-8b1
(+)-8b2
8c
661 26
3305 37
1000 52
1255 24
1541 31
0.009
0.0297
0.0237
0.0193
29.75
´
Mouridsen, H.; Gershanovich, M.; Sun, Y.; Perez-
Carrion, R.; Boni, C.; Monnier, A.; Apffelstaedt, J.;
9b
11
Me 4-Cl
´
H
—
4-CN
—
Smith, R.; Sleeboom, H. P.; Ja¨nicke, F.; Pluzanska, A.;
Dank, M.; Becquart, D.; Bapsy, P. P.; Salminen, E.;
Snyder, R.; Lassus, M.; Verbeek, J. A.; Staffler, B.;
Chaudri-Ross, H. A.; Dugan, M. J. Clin. Oncol. 2001,
19, 2596; (c) Howell, A.; Buzdar, A. J. Steroid Biochem.
Mol. Biol. 2005, 93, 237.
AG
1
—
a Values are the mean of at least two experiments performed in
duplicate.
b Relative potency RP = IC50(AG)/IC50 (tested compound).
c Progesterone (25 lM), inhibitor: 2.5 lM. Values are the mean of two
experiments performed in duplicate.
7. Le Borgne, M.; Marchand, P.; Delevoye-Seiller, B.;
Robert, J.-M.; Le Baut, G.; Hartmann, R. W.; Palzer,
M. Bioorg. Med. Chem. Lett. 1999, 9, 333.
8. Marchand, P.; Le Borgne, M.; Palzer, M.; Le Baut, G.;
Hartmann, R. W. Bioorg. Med. Chem. Lett. 2003, 13, 1553.
9. Ketcha, D. M.; Lieurance, B. A.; Homan, D. F. J. J. Org.
Chem. 1989, 54, 4350.
10. Synthesis of (1-benzenesulfonyl-2,3-dihydro-1H-indol-5-
yl)(4-chlorophenyl)methanone 4b. To a suspension of
aluminum chloride (3.29 g, 1.6 equiv) in 80 mL CH2Cl2
was added 4-chlorobenzoylchloride (4.32 mL, 1.6 equiv).
After the mixture was stirred for 1 h at rt, a solution of 1-
benzenesulfonyl-1H-indoline 3 (4 g, 15.42 mmol) in 30 mL
CH2Cl2 was added dropwise. The reaction mixture was
stirred overnight at rt prior to pouring onto crushed ice
and CH2Cl2. The layers were separated and the aqueous
layer was extracted with CH2Cl2. The combined organic
fractions were washed with brine and dried over Na2SO4.
The solvent was evaporated and the residue was recrys-
tallized from diisopropylic ether to afford compound 4b in
95% overall yield.
The nature and position of halogen on phenyl moiety
provided significant difference in aromatase inhibitory
activity (compounds 8a–c). Thus, a chlorine atom at
the C-4 position of the phenyl ring (8b) showed the high-
est antiaromatase activity with an IC50 of 15 nM. Its
replacement by a cyano group (11), present in different
reference drugs, allowed a comparable level of activity.
The liarozole analogue 8c, with a chlorine atom fixed
at carbon 3 of the phenyl ring, was the less active tested
derivative.
To investigate the influence of stereochemistry on bio-
logical activity, the most active compound 8b was sepa-
rated into its enantiomers (ꢀ)-8b1 and (+)-8b2 using
chiral HPLC.21,22 The slower eluting enantiomer 8b2
was found to be highly potent, with an IC50 of 9 nM,
in comparison with its racemate and its enantiomer
which exhibited IC50 values of 15 and 45 nM, respective-
ly. This result confirms that the configuration of the
chiral center plays a key role in biological activity, as
previously observed with the (+) enantiomer of vorozole
(Fig. 1).23
Beige powder; mp 111–112 °C; IR (KBr): 3060 (CHarom),
1
2937 (CHalkane), 1648 (C@O), 1168 (SO2) cmꢀ1; H NMR
(DMSO-d6): d 3.09 (t, J = 8.55 Hz, 2H, CH2), 4.05 (t,
J = 8.55 Hz, 2H, NCH2), 7.61–7.76 (m, 10H, indolyl H-4,
H-6, H-7, 4-chlorophenyl H-2, H-3, H-5, H-6, benze-
nesulfonyl H-3, H-4, H-5), 7.95 (d, J = 7.3 Hz, 2H,
benzenesulfonyl H-2, H-6).
In conclusion, we described some 5-[(aryl)(imidazol-1-
yl)methyl]-1H-indoles acting as potent and selective
CYP19 inhibitors. We showed the importance of a chlo-
rine or cyano group on the C-4 position of the phenyl
ring as well as a free indolic nitrogen. Moreover, we
underlined the importance to separate the racemic com-
pounds in order to enhance by far the IC50 values. X-ray
crystallographic and molecular modeling studies of
these enantiomers are now in progress. Although an
imidazole is more efficient than a triazole moiety, the lat-
ter may be more selective and also more stable metabol-
ically. So, it would be of interest to carry out future
synthesis and evaluation works in the subseries of the
corresponding triazole derivatives. In parallel, the inhib-
itory activity of 4 and 6-[(aryl)(azolyl)methyl]-1H-in-
doles will be investigated.
11. Synthesis of (2,3-dihydro-1H-indol-5-yl)(4-chloro-phen-
yl)methanone 5b. A solution of 4b (1 g, 2.51 mmol) in
2 mL of sulfuric acid (80%) was stirred for 5 min at 90 °C
under MW irradiation (40 W). After cooling, H2O and
aqueous NaOH solution (25%) were added up to pH 9.
The aqueous layer was extracted with Et2O. The organic
layer was washed with brine and dried over Na2SO4. The
solvent was evaporated to give compound 5b in 85%
overall yield.
Ochre powder; mp 146–147 °C; IR (KBr): 3305 (NH),
3050 (CHarom), 2937 (CHalkane), 1579 (C@O) cmꢀ1 1H
;
NMR (DMSO-d6): d 3.03 (t, J = 8.55 Hz, 2H, CH2),
3.61 (t, J = 8.55 Hz, 2H, NCH2), 6.51 (d, J = 8.1 Hz,
1H, indolyl H-7), 6.73 (s, 1H, NH), 7.44 (dd,
J = 8.1 Hz, J = 1.8 Hz, 1H, indolyl H-6), 7.50 (s, 1H,
indolyl H-4), 7.60 (d, J = 8.55 Hz, 2H, 4-chlorophenyl
H-3, H-5), 7.65 (d, J = 8.55 Hz, 2H, 4-chlorophenyl H-
2, H-6).
12. Lo, Y. S.; Walsh, D. A.; Welstead, W. J., Jr.; Mays, R. P.;
Rose, E. K.; Causey, D. H.; Duncan, R. L. J. Heterocycl.
Chem. 1980, 17, 1663.
References and notes
13. Synthesis of (4-chlorophenyl)(1H-indol-5-yl)methanone
6b. A solution of 5b (303 mg, 1.18 mmol), manganese
`
1. Jougla, E.; Salem, G.; Rican, S.; Pavillon, G.; Lefevre, H.
Bull. Epidemiol. Hebdo. 2003, 41–42, 198.

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M.-P. Leze et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1134–1137
1137
oxide (1.23 g, 12 equiv) in 20 mL CH2Cl2 was stirred
overnight at 40 °C. After cooling, the reaction mixture was
filtered through Celite. The solvent was removed to afford
compound 6b in 99% overall yield.
C-4), 135.6 (C-7a), 137.4 (imidazolyl C), 140.3 (4-chlor-
ophenyl C-1).
16. Tschaen, D. M.; Desmond, R.; King, A. O.; Fortin, M. C.;
Pipik, B.; King, S.; Verhoeven, T. R. Synth. Commun.
1994, 24, 887.
17. Synthesis of 4-(1H-indol-5-ylcarbonyl)benzonitrile 10. A
solution of 6d (500 mg, 1.66 mmol), Zn(CN)2 (195 mg,
1 equiv), and Pd(PPh3)4 (57 mg, 3% equiv) in 2 mL of DMF
was stirred for 4 min at 153 °C in a sealed vial under MW
irradiation (60 W). After cooling, AcOEt was added. The
organic layer was washed with brine and dried over Na2SO4.
The solvent was removed and the residue was purified on
silica gel (CH2Cl2) to afford compound 10 in 68% overall
yield.
Gray powder; mp 159–160 °C; IR (KBr): 3397 (NH), 3060
(CHarom), 1646 (C@O) cmꢀ1
;
1H NMR (DMSO-d6): d
6.65 (d, J = 2.75 Hz, 1H, indolyl H-3), 7.54 (d,
J = 2.75 Hz, 1H, indolyl H-2), 7.60 (d, J = 8.2 Hz, 1H,
indolyl H-7), 7.64 (dd, J = 8.2 Hz, J = 1.8 Hz, 1H, indolyl
H-6), 7.66 (d, J = 8.55 Hz, 2H, 4-chlorophenyl H-3, H-5),
7.77 (d, J = 8.55 Hz, 2H, 4-chlorophenyl H-2, H-6), 8.03
(s, 1H, indolyl H-4), 11.60 (s, 1H, NH).
14. Njar, V. C. O. Synthesis 2000, 14, 2019.
15. Synthesis of 5-[(4-chlorophenyl)(1H-imidazol-1-yl)meth-
yl]-1H-indole 8b. Sodium borohydride (107 mg, 2 equiv)
was added portionwise to a stirred solution of 6b
(360 mg, 1.41 mmol) in 20 mL methanol. The reaction
mixture was stirred for 1 h at rt prior to quenching with
H2O. The aqueous layer was extracted with Et2O. The
organic layer was dried over Na2SO4 and the solvent was
evaporated to give a light yellow oil. The corresponding
alcohol (363 mg, 1.41 mmol) and CDI (342 mg, 1.5 equiv)
in CH3CN were stirred for 40 h at rt. The solvent was
removed and the residue was dissolved in H2O and
CH2Cl2. The layers were separated, the organic layer was
washed with H2O, and dried over Na2SO4. The solvent
was evaporated and the residue was purified on silica gel
(CH2Cl2–EtOH, 19:1 v/v) to give compound 8b in 53%
overall yield.
Beige powder; mp 185–186 °C; IR (KBr): 3380 (NH), 2223
1
(C„N), 1644 (C@O) cmꢀ1; H NMR (DMSO-d6): d 6.66
(d, J = 2.7 Hz, 1H, indolyl H-3), 7.55 (dd, J = 2.7 Hz, 1H,
indolyl H-2), 7.58 (d, J = 8.6 Hz, 1H, indolyl H-7), 7.66 (dd,
J = 8.6 Hz, J = 1.7 Hz, 1H, indolyl H-6), 7.88 (d,
J = 8.5 Hz, 2H, 4-CN-phenyl H-3, H-5), 8.02 (s, 1H, indolyl
H-4), 8.08 (d, J = 8.5 Hz, 2H, 4-CN-phenyl H-2, H-6), 11.61
(s, 1H, NH).
18. Thompson, E. A.; Siiteri, P. K. J. Biol. Chem. 1974, 249,
5364.
19. (a) Graves, P. E.; Salhanick, H. A. Endocrinology 1979, 105,
52; (b) Foster, A. B.; Jarman, M.; Leung, C.-S.; Rowlands,
M. G.; Taylor, G. N. J. Med. Chem. 1983, 26, 50.
20. (a) Ehmer, P. B.; Jose, J.; Hartmann, R. W. J. Steroid
Biochem. Mol. Biol. 2000, 75, 57; (b) Hutschenreuter, T.
U.; Ehmer, P. B.; Hartmann, R. W. J. Enzyme Inhib. Med.
Chem. 2004, 19, 17.
Beige powder; mp 172–173 °C; IR (KBr): 3449 (NH),
3120 (CHarom), 1490 (C@Carom) cmꢀ1; 1H NMR (DMSO-
d6): d 6.44 (s, 1H, indolyl H-3), 6.96–6.98 (m, 3H, indolyl
H-6, CH, imidazolyl H), 7.13 (s, 1H, imidazolyl H), 7.15
(d, J = 8.8 Hz, 2H, 4-chlorophenyl H-2, H-6), 7.32 (s, 1H,
indolyl H-4), 7.43 (d, J = 8.8 Hz, 2H, 4-chlorophenyl H-3,
H-5), 7.46 (dd, J = 2.9 Hz, 1H, indolyl H-2), 7.47 (d,
J = 8.8 Hz, 1H, indolyl H-7), 7.65 (s, 1H, imidazolyl H),
11.20 (s, 1H, NH); 13C NMR (DMSO-d6): d 63.5 (CH),
101.6 (C-3), 112.0 (C-7), 119.5 (imidazolyl C), 119.9 (C-
4), 121.5 (C-6), 126.5 (C-2), 127.8 (C-4a), 128.8 (3C,
imidazolyl C, 4-chlorophenyl C-3, C-5), 129.6 (2C, 4-
chlorophenyl C-2, C-6), 130 (C-5), 132.4 (4-chlorophenyl
21. The HPLC separation used a ChiracelÒ OD-H (5 lm)
semi-preparative column, a mixture of acetonitrile-meth-
anol (95:5, v/v) as eluent, a flow rate of 5 mL/min, and a
sample concentration of 1.33 mg/mL. 8b1: tR = 16.05 min;
8b2: tR = 21.62 min.
22. Polarimeter Schmidt-Haensch Polartronic NH8; sample
concentration: 10 mg/mL (CHCl3 as solvent). 8b1:
[a]D = ꢀ77; 8b2: [a]D = +58.
23. Wouters, W.; Van Ginckel, R.; Krekels, M.; Bowden,
C.; De Coster, R. J. Steroid Biochem. Mol. Biol. 1993,
44, 617.