Silicon analogues of the nonpeptidic GnRH antagonist AG-045572: Syntheses, crystal structure analyses, and pharmacological characterization

Article abstract of DOI:10.1002/cmdc.201100318

AG-045572 (CMPD1, 1a) is a nonpeptidic gonadotropin-releasing hormone (GnRH) antagonist that has been investigated for the treatment of sex hormone-related diseases. In the context of systematic studies on sila-substituted drugs, the silicon analogue disila-AG-045572 (1b) and its derivative 2 were prepared in multi-step syntheses and characterized by elemental analyses (C, H, N), NMR spectroscopic studies (¹H, ¹³C, ²⁹Si), and single-crystal X-ray diffraction. The pharmacological properties of compounds 1a, 1b, and 2 were compared in terms of their in vitro potency at cloned human and rat GnRH receptors. Compounds 1a and 2 were also examined in regard to their pharmacokinetics and in vivo efficacy in both castrated rat (luteinizing hormone (LH) suppression) and intact rat (testosterone suppression) models. The efficacy and pharmacokinetic profiles of 1a and its silicon-containing analogue 2 appear similar, indicating that replacement of the 5,6,7,8-tetrahydronaphthalene ring system by the 1,3-disilaindane skeleton led to retention of efficacy. Therefore, the silicon compound 2 represents a novel drug prototype for the design of potent, orally available GnRH antagonists suitable for once-daily dosing.

Full text of DOI:10.1002/cmdc.201100318

MED
DOI: 10.1002/cmdc.201100318
Silicon Analogues of the Nonpeptidic GnRH Antagonist
AG-045572: Syntheses, Crystal Structure Analyses, and
Pharmacological Characterization
[
a]
[b]
[b]
[a]
Matthew J. Barnes, Christian Burschka, Matthias W. Bꢀttner, Richard Conroy,
[b]
[c]
[a]
[c]
[a]
Jꢀrgen O. Daiss, Ian C. Gray, Alan G. Hendrick, L. H. Tam, Diana Kuehn,
David J. Miller,* John S. Mills, Philip Mitchell, John G. Montana,
Parameswary A. Muniandy, Helen Rapley, Graham A. Showell, David Tebbe,
Reinhold Tacke,* Julie B. H. Warneck, and Bin Zhu
[a]
[a]
[a]
[a]
[c]
[a]
[a]
[b]
[b]
[a]
[c]
AG-045572 (CMPD1, 1a) is a nonpeptidic gonadotropin-releas-
ing hormone (GnRH) antagonist that has been investigated for
the treatment of sex hormone-related diseases. In the context
of systematic studies on sila-substituted drugs, the silicon ana-
logue disila-AG-045572 (1b) and its derivative 2 were prepared
in multi-step syntheses and characterized by elemental analy-
Compounds 1a and 2 were also examined in regard to their
pharmacokinetics and in vivo efficacy in both castrated rat (lu-
teinizing hormone (LH) suppression) and intact rat (testoster-
one suppression) models. The efficacy and pharmacokinetic
profiles of 1a and its silicon-containing analogue 2 appear sim-
ilar, indicating that replacement of the 5,6,7,8-tetrahydronaph-
thalene ring system by the 1,3-disilaindane skeleton led to re-
tention of efficacy. Therefore, the silicon compound 2 repre-
sents a novel drug prototype for the design of potent, orally
available GnRH antagonists suitable for once-daily dosing.
1
13
29
ses (C, H, N), NMR spectroscopic studies ( H, C, Si), and
single-crystal X-ray diffraction. The pharmacological properties
of compounds 1a, 1b, and 2 were compared in terms of their
in vitro potency at cloned human and rat GnRH receptors.
Introduction
While peptidic GnRH antagonists and agonists are currently in
clinical use for the treatment of reproductive disorders and ste-
roid hormone-dependent tumors, nonpeptidic GnRH antago-
nists have only recently appeared in the literature, and poten-
tial advantages over peptidic GnRH agonists and antagonists
change. It should also be noted that the 5,6,7,8-tetrahydro-
[2b]
naphthalene skeleton of 1a is a major site of metabolism.
We report the syntheses of the silicon compounds disila-AG-
045572 (1b) and 2, the crystal structure analyses of 1b and
2·n-C H , and the pharmacological characterizations of 1a, 1b,
5
12
[8]
[
1]
have been discussed. These nonpeptidic inhibitors include
elagolix (NBI-56418, Neurocrine Biosciences, Inc.) and TAK-385
and 2.
(Takeda Pharmaceutical Company), both of which have been
evaluated in clinical studies. AG-045572 (CMPD1, 1a) is another
[2,3]
Results and Discussion
such potent, orally active nonpeptidic GnRH antagonist.
It
has been shown to act as an allosteric modulator of the GnRH
Syntheses
[
4]
receptor and is highly efficacious in in vivo models of hor-
mone suppression. Replacement of a carbon atom with a sili-
5-[(3,5,5,8,8-Pentamethyl-5,8-disila-5,6,7,8-tetrahydro-2-naph-
[5,6]
thyl)methyl]-N-(2,4,6-trimethoxyphenyl)furan-2-carboxamide
con atom (sila-substitution) is a novel tool for drug design
that has already been used in the design of GnRH antagonists.
It has been demonstrated that the carefully targeted introduc-
tion of silicon into a GnRH antagonist, in this case a peptide,
can lead to enhanced bioactivity as a result of improved phar-
[
a] Dr. M. J. Barnes, R. Conroy, Dr. A. G. Hendrick, D. Kuehn, Dr. D. J. Miller,
Dr. J. S. Mills, Dr. P. Mitchell, Dr. J. G. Montana, H. Rapley, G. A. Showell,
J. B. H. Warneck
Paradigm Therapeutics Ltd. (now Takeda Cambridge Ltd.)
418 Cambridge Science Park, Milton Road
Cambridge CB4 0PZ (UK)
[
7]
macokinetics. Herein, we describe our approach to optimize
the pharmacodynamic and pharmacokinetic properties of the
small-molecule GnRH antagonist 1a by two-fold carbon/silicon
exchange within the 5,6,7,8-tetrahydronaphthalene skeleton,
resulting in disila-AG-045572 (1b) and leading to an enlarge-
ment of the ring system. We further propose the silicon-con-
taining analogue 2 to combine the advantages of an overall
molecule size comparable to that of 1a (in this context, see
Ref. [6g]) with the effects of a two-fold carbon/silicon ex-
E-mail: dmiller@takedacam.com
[
b] Dr. C. Burschka, Dr. M. W. Bꢀttner, Dr. J. O. Daiss, Dr. D. Tebbe,
Prof. Dr. R. Tacke
Universitꢁt Wꢀrzburg, Institut fꢀr Anorganische Chemie, Am Hubland
9
7074 Wꢀrzburg (Germany)
E-mail: r.tacke@uni-wuerzburg.de
[
c] Dr. I. C. Gray, L. H. Tam, Dr. P. A. Muniandy, Dr. B. Zhu
Paradigm Therapeutics (S) Pte Ltd. (now Takeda Singapore (S) Pte Ltd.)
10 Biopolis Road, #03-01/02 Chromos, Singapore 138670 (Singapore)
2
070
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2011, 6, 2070 – 2080

Silicon Analogues of a GnRH Antagonist
acid, gave the corresponding acid 8. Treatment of 8 with thio-
nyl chloride and pyridine, in the presence of 4-(dimethylami-
no)pyridine (DMAP), and subsequent reaction with 2,4,6-trime-
thoxyaniline (10) gave the desired compound 1b (Method A in
the Experimental Section). Treatment of 8 with dicyclohexylcar-
bodiimide (DCC) and pyridine, in the presence of DMAP, and
subsequent reaction with 10 also afforded 1b (Method B in
the Experimental Section). Alternatively, compound 1b was
synthesized by treatment of 7 with a reagent obtained from
trimethylaluminum and 10·HCl (Method C in the Experimental
Section). Compounds 10 and 10·HCl were obtained from 2,4,6-
trimethoxybenzamide–methanol (9·MeOH) (Scheme 2). Treat-
ment of 9·MeOH with an aqueous potassium hypochlorite so-
lution gave 10, which upon reaction with hydrogen chloride in
diethyl ether afforded 10·HCl.
(
disila-AG-045572, 1b) was prepared by various methods in
multi-step syntheses, starting from 1,2-bis(ethynyldimethyl-
[
6a]
silyl)ethane (3) and 5-bromo-2-furoic acid (4) (Scheme 1). Re-
action of 4 with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and
iodomethane gave methyl 5-bromo-2-furoate (5), which was
treated with isopropylmagnesium bromide and then 1-bromo-
2
5
-butyne in the presence of copper(I) cyanide to afford methyl
-(but-2-ynyl)-2-furoate (6) (method based on the work of Kno-
[
9]
chel et al. ). Compounds 3 and 6 were then allowed to react
2
Scheme 2. Synthesis of compound 10·HCl. Reagents: a) KOCl/H O; b) HCl.
in a cobalt-catalyzed [CpCo(CO) ] Vollhardt cyclization to afford
2
methyl 5-[(3,5,5,8,8-pentamethyl-5,8-disila-5,6,7,8-tetrahydro-2-
naphthyl)methyl]-2-furoate (7). Reaction of 7 with aqueous po-
tassium hydroxide, followed by treatment with hydrochloric
5-[(1,1,3,3,6-Pentamethyl-1,3-disila-2,3-dihydro-1H-inden-5-
yl)methyl]-N-(2,4,6-trimethoxyphenyl)furan-2-carboxamide (2)
was prepared in a manner analogous to compound 1a, using
[10]
bis(ethynyldimethylsilyl)methane (11) instead of the diyne 3.
Thus, treatment of 11 with 6 in the presence of CpCo(CO) pro-
2
vided methyl 5-[(1,1,3,3,6-pentamethyl-1,3-disila-2,3-dihydro-
1
H-inden-5-yl)methyl]-2-furoate (12), which upon reaction with
the reagent obtained from trimethylaluminum and 10·HCl af-
forded 2 (Scheme 3).
Scheme 3. Synthesis of compound 2. Reagents: a) [CpCo(CO)
0·HCl.
2 3
]; b) AlMe ,
1
Scheme 1. Syntheses of compound 1b. Reagents: a) DBU, MeI; b) 1. i-
PrMgBr; 2. BrCH
e) 1. SOCl , pyridine [DMAP], or DCC, pyridine [DMAP]; 2. 10; f) AlMe
0·HCl.
2
CꢀCMe [CuCN]; c) [CpCo(CO)
2 2 2
]; d) 1. KOH/H O; 2. HCl/H O;
Compounds 1b, 2, 5–8, 9·MeOH, 10, 10·HCl, and 12 were
isolated as crystalline solids. The identities of all compounds
2
3
,
1
ChemMedChem 2011, 6, 2070 – 2080
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
2071

MED
D. J. Miller, R. Tacke et al.
were confirmed by elemental analyses and NMR spectroscopic
studies in solution. In addition, 1b, 2·n-C H , 8, and 12 were
5
12
characterized by crystal structure analyses.
Crystal structure analyses
Compounds 1b, 2·n-C H , 8, and 12 were structurally charac-
5
12
terized by single-crystal X-ray diffraction. Crystal data and ex-
perimental parameters used for these studies are given in
Table 1. The molecular structures of 1b and 2 are depicted in
Figure 1; for further details of the crystal structure analyses,
see the Supporting Information. Bond distances and angles of
the compounds studied are within the expected ranges and
therefore are not discussed further.
In vitro assessment of the interactions of compounds 1a,
1
b, and 2 with human and rat GnRH receptors
In vitro functional assays were developed in order to deter-
mine the potency of the GnRH receptor antagonists 1a, 1b,
and 2 at human and rat GnRH receptors, as shown in Table 2.
Binding affinities for compounds 1a and 2 were also deter-
mined (Table 2). The data obtained suggest that these com-
pounds are potent functional GnRH antagonists and that activ-
Figure 1. Molecular structures of 1b (top) and 2 (molecule I; bottom) in the
crystal. Compound 2 was studied as the solvate 2·n-C
5
H
12, which contains
two molecules in the asymmetric unit.
5
Table 1. Crystal data and experimental parameters for the crystal structure analyses of 1b, 2·n-C H12, 8, and 12.
1
b
2·n-C
5
H
12
8
12
empirical formula
formula mass [gmol
collection T [K]
l(MoKa) [ꢂ]
crystal system
space group (no.)
a [ꢂ]
b [ꢂ]
c [ꢂ]
a [8]
b [8]
C
28
H
37NO
5
Si
2
C
32
H
47NO
5
Si
2
C
19
H
26
O
3
Si
2
19 26 3 2
C H O Si
358.58
173(2)
ꢁ
1
]
523.77
243(2)
0.71073
monoclinic
C2/c (15)
46.264(5)
9.5779(7)
13.6161(17)
90
91.347(14)
90
6031.7(11)
8
1.154
0.152
581.89
173(2)
0.71073
358.58
173(2)
0.71073
monoclinic
C2/c (15)
29.567(2)
5.9168(4)
24.3353(19)
90
110.810(8)
90
3979.6(5)
8
1.197
0.191
0.71073
monoclinic
P2 /c (14)
triclinic
ꢀ
P1(2)
1
11.4487(11)
14.0727(13)
21.182(2)
84.457(12)
81.509(13)
89.833(12)
3359.3(6)
4
8.4069(7)
14.1233(10)
16.6865(14)
90
91.139(10)
90
1980.8(3)
4
1.202
g [8]
3
V [ꢂ ]
Z
D
ꢁ
3
calcd [gcm
]
1.151
0.143
1256
ꢁ
1
m [mm
F(000)
]
0.192
768
2240
1536
crystal dimensions [mm]
q range [8]
index ranges
0.5ꢃ0.3ꢃ0.1
5.00–55.94
0.5ꢃ0.25ꢃ0.1
4.60–46.76
ꢁ12ꢂhꢂ12,
ꢁ15ꢂkꢂ15,
ꢁ23ꢂlꢂ23
16910
0.5ꢃ0.3ꢃ0.1
5.70–55.96
ꢁ38ꢂhꢂ38,
ꢁ7ꢂkꢂ7,
ꢁ31ꢂlꢂ31
12731
0.5ꢃ0.4ꢃ0.3
4.84–55.90
ꢁ11 ꢂhꢂ11,
ꢁ18ꢂkꢂ18,
ꢁ21ꢂlꢂ22
20849
2
ꢁ60ꢂhꢂ60,
ꢁ
ꢁ
11 ꢂkꢂ11,
17ꢂlꢂ17
no. of collected reflections
28091
no. of independent reflections
6789
9163
4718
4496
R
int
0.0706
0.0535
0.0314
0.0277
no. of reflections used
no. of parameters
S
6789
336
0.918
0.0589/0.0000
0.0448
0.1146
+0.236/ꢁ0.243
9163
747
0.847
0.0542/0.0000
0.0475
4718
225
0.959
0.0612/0.0000
0.0348
0.0920
+0.267/ꢁ0.299
4496
223
1.084
0.0543/0.4383
0.0348
0.0970
+0.310/ꢁ0.211
[
a]
[
b]
weight parameters a/b
[
c]
R
1
[I>2s(I)]
(all data)
[
d]
wR
2
0.1113
ꢁ
3
max/min residual electron density [eꢂ
]
+0.356/ꢁ0.352
2
2
2
0.5
ꢁ1
2
2
2
2
2
c
[
/
a] S={S[w(F
o
ꢁF
c
) ]/(nꢁp)} ; n=no. of reflections; p=no. of parameters. [b] w =s (F
ꢁF ) ]/S[w(F ) ]}
o
)+(aP) +bP, with P=[max(F
o
,0)+2F
]/3. [c] R
1
=Sj jF
o
jꢁjF j j
c
2
2
c
2
2 2 0.5
SjF j. [d] wR
o
2
={S[w(F
o
o
.
2
072
www.chemmedchem.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2011, 6, 2070 – 2080

Silicon Analogues of a GnRH Antagonist
levels with similar half-lives. The introduction of silicon (with
concomitant size reduction from a six- to a five-membered
ring) appears to maintain the pharmacokinetic profile of 2
when compared to 1a.
Table 2. Functional activity and in vitro binding of compounds 1a, 1b,
and 2.
[
a]
[a]
Compd
Functional IC50 [nm]
i
Binding K [nm]
[
b]
Human
Rat
Human
Rat
1
1
2
a
b
16ꢃ29
50ꢃ47
11 ꢃ18
34ꢃ24
51ꢃ49
12ꢃ11
27ꢃ10
n.d.
13 ꢃ5
72ꢃ55
n.d.
69ꢃ31
In vivo efficacy of compounds 1a and 2
Numerous groups who have investigated GnRH receptor an-
tagonists have relied on two key in vivo paradigms to deter-
mine efficacy. The evaluation of luteinizing hormone (LH) levels
in the castrated rat is a robust model, which provides predic-
tive data as to the likely impact on testosterone and other sex
hormones. On the other hand, the evaluation of testosterone
suppression in the intact rat, while producing data which may
be more physiologically relevant, is a less robust model due to
variation in basal levels of the hormone caused by circadian
and/or domination effects.
[
a] Data represent meanꢃSD for a minimum of n=3 data points; n.d.=
not determined. [b] Binding of cetrorelix at human GnRH receptor: K
.1 nm (see Ref. [11]).
D
=
0
ity is retained when changing the 5,6,7,8-tetrahydronaphtha-
lene ring system of 1a to the analogous 5,8-disila-5,6,7,8-tetra-
hydronaphthalene (1b) or 1,3-disilaindane skeleton (2). Fur-
thermore, all of these compounds have similar potency at the
rat GnRH receptor as compared with the human GnRH recep-
tor, suggesting the potential advantage of a streamlined devel-
opment process over other compound series, which do not
Compound 2 was studied in castrated rats, and LH levels
were measured following oral administration as shown in
Figure 3. This study indicated that all doses tested significantly
reduce plasma LH levels when compared to vehicle, but that
[
12]
have similar activity in the rat. Based on the recent work of
Sullivan et al., it is likely that the silicon compounds act as allo-
ꢁ
1
ꢁ1
30 and 100 mgkg doses are more effective than 10 mgkg .
Maximal inhibition of LH occurred approximately 12 h after
dosing, at which point LH levels were reduced by approxi-
[
4]
steric modulators of the receptor-peptide interaction.
ꢁ
1
mately 90% at both 30 and 100 mgkg doses. The compound
exerted a significant effect after 4 h at all doses, with the 30
Pharmacokinetic analysis of compounds 1a and 2
ꢁ
1
and 100 mgkg doses showing sustained efficacy at the
Compounds 1a and 2 were subjected to pharmacokinetic ex-
amination in male Wistar rats as shown in Table 3 and Figure 2.
24 hour time point.
ꢁ
1
The effect on testosterone levels in intact rats following ad-
Animals were dosed at 100 mgkg by oral gavage, and the
plasma levels of the compounds were measured over a period
of 24 h. Both 1a and 2 exhibit respectable and similar plasma
ministration of compounds 1a and 2 has also been studied,
which is believed to be more physiologically relevant to diseas-
es such as prostate cancer. The efficacy of test compounds was
[
13]
directly compared to cetrorelix
(Cetrotide, Asta Medica;
ꢁ
1
0
.1 mgkg , s.c.), a potent peptidic GnRH antagonist currently
Table 3. Pharmacokinetic parameters of compounds 1a and 2 in intact
male Wistar rats orally dosed with 100 mgkg of compound.
ꢁ
1
indicated for assisted reproduction (data shown in Figures 4a
and 4b). In Figure 4a, the actual levels of plasma testosterone
[
a]
[a]
Parameter
1a
2
ꢁ
1
are shown in ngmL , whereas in Figure 4b, the changes in
testosterone levels are shown in terms of percentage values
relative to baseline (pre-dose levels at t=ꢁ2 and 0 h, averaged
and set to 100% at t=0). The latter is a better statistical
method to compare differences between treatments in this
model, as the natural fluctuation of daily testosterone levels is
clearly seen in the vehicle-treated animals. According to these
data, all three compounds were able to effectively reduce tes-
ꢁ
1
C
max [ngmL
]
2279ꢃ533
8.0ꢃ1.5
2683ꢃ347
7.7ꢃ1.7
tmax [h]
ꢁ
1
AUC0–inf [nghmL
[h]
]
26531ꢃ7219
3.8ꢃ0.9
35622ꢃ6783
4.7ꢃ0.8
t1
=
2
[a] Data represent meanꢃSD for a minimum of n=5 animals per group.
ꢁ
1
tosterone levels to “castrate” level (ꢂ0.5 ngmL ), and statisti-
cal significance was achieved 8 h and 10 h after dosing (Fig-
ure 4b). At 24 h after dosing, rats treated with either cetrorelix
or compound 2 maintained lower testosterone levels, while
rats treated with compound 1a had higher levels of testoster-
one as compared to the vehicle-treated rats (Figure 4b), sug-
gesting that compound 2 may have an advantage over com-
pound 1a.
Conclusions
Figure 2. Comparison of plasma concentrations of compounds 1a (~) and 2
ꢁ
1
Disila-AG-045572 (1b), a silicon analogue of the nonpeptidic
GnRH antagonist AG-045572 (1a) with a 5,8-disila-5,6,7,8-tetra-
(
^) in intact male rats over 24 h (100 mgkg , p.o.). Data represent the
meanꢃSD for a minimum of n=5 animals per group.
ChemMedChem 2011, 6, 2070 – 2080
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
2073

MED
D. J. Miller, R. Tacke et al.
CDCl , CD Cl , C D , or [D ]DMSO were used as solvents.
3
2
2
6
6
6
Chemical shifts (d , ppm) were determined relative to in-
1
13
ternal CHCl3 ( H, d=7.24 ppm; CDCl ), CDCl ( C, d=
3
3
1
7
7.0 ppm; CDCl ), CHDCl ( H, d=5.32 ppm; CD Cl ),
3 2 2 2
CD Cl2 ( C, d=53.8 ppm; CD Cl ), C6HD5 ( H, d=
13
1
2
2
2
13
7
[
.28 ppm; C D ), C6D6 ( C, d=128.0 ppm; C D ),
6 6 6 6
1
13
D ]DMSO ( H, d=2.49 ppm; [D ]DMSO), [D ]DMSO ( C,
5
6
6
1
5
d=39.5 ppm; [D ]DMSO), external formamide ( N, d=
268.0 ppm; C D ), or external TMS ( Si, d=0 ppm;
6 6
C D ). Assignment of the H NMR data was supported by
H– H, C– H, and Si– H correlation experiments, and
6
29
ꢁ
1
6
6
1
1
13
1
29
1
13
assignment of the C NMR data was supported by DEPT
13
1
1
35 and C– H correlation experiments. Chromatogra-
phy was carried out using either 15–40 mm (Merck
1
.15111) silica gel (stationary phase A) or 32–63 mm (ICN
0
2826) silica gel (stationary phase B). 1,2-Bis(ethynyldi-
methylsilyl)ethane (3) was synthesized according to
Ref. [6a] (method B), and bis(ethynyl-
dimethylsilyl)methane (11) was synthesized according to
Ref. [10]. 5-Bromo-2-furoic acid (4) was obtained from a
commercial source (Sigma–Aldrich).
Figure 3. Effects of compound 2 on plasma luteinizing hormone (LH) levels in castrated
male rats following oral dosing at 100, 30, and 10 mgkg ; **p <0.01 and ***p <0.001,
ꢁ
5-[(3,5,5,8,8-Pentamethyl-5,8-disila-5,6,7,8-tetrahydro-
2-naphthyl)methyl]-N-(2,4,6-trimethoxyphenyl)furan-2-
carboxamide (disila-AG-045572, 1b):
based on a two-way ANOVA followed by Bonferroni post-tests as compared to vehicle
ꢁ
1
ꢁ1
group. *: vehicle (n=9);
: 2 at 10 mgkg (n=9); *: 2 at 30 mgkg (n=8); ~: 2 at
&
ꢁ1
100 mgkg (n=8).
Method A: Solution I. A solution of 8 (1.00 g, 2.79 mmol)
and thionyl chloride (6.85 g, 57.6 mmol) in CH Cl (9 mL)
2
2
was heated under reflux for 5 h. All volatile components
were removed in vacuo (0.001 mbar, 208C, 1 h), and the oily resi-
hydronaphthalene skeleton, and analogue 2, with a 1,3-disilain-
dane skeleton, were prepared in multi-step syntheses, starting
from 5-bromo-2-furoic acid and using the silicon-containing
building blocks ClMe SiCH CH SiMe Cl and ClMe SiCH SiMe Cl,
due was redissolved in CH Cl2 (4 mL). Solution II. Compound 10
2
(
572 mg, 3.12 mmol; with bulb-to-bulb distillation directly before
use), pyridine (245 mg, 3.10 mmol), and 4-(dimethylamino)pyridine
(DMAP; 7.0 mg, 57 mmol) were dissolved in CH Cl (5 mL). Solution I
was added dropwise at 08C over 10 min to the stirred solution II
formation of a precipitate was observed, which redissolved, as
2
2
2
2
2
2
2
respectively. The silicon compounds 1b and 2 were character-
ized by elemental analyses, NMR spectroscopic studies, and
crystal structure analyses. Introduction of silicon into the
parent compound 1a (resulting in 1b and 2) maintains in vitro
binding and functional activity at human and rat GnRH recep-
tors. The pharmacokinetic and efficacy profiles of 1a and the
silicon-containing analogue 2 appear similar, indicating that
the two-fold carbon/silicon exchange and removal of one of
the two methylene groups in the saturated six-membered ring
of 1a led to retained efficacy. The silicon compound 2 repre-
sents an interesting chemical prototype for the design of
potent, orally available GnRH antagonists suitable for once-
daily dosing. This study emphasizes organosilicon chemistry as
a powerful source of chemical diversity in drug design.
2
2
(
well as a color change from colorless to orange). The mixture was
stirred at 08C for 10 min and then at 208C for 16 h, followed by
addition of CH Cl (20 mL). The resulting solution was washed suc-
2
2
cessively with a 5 vol% aqueous AcOH solution (solution A, 20 mL),
a half-saturated aqueous NaHCO solution (solution B, 20 mL), and
3
water (solution C, 20 mL). The AcOH wash solution (A) was extract-
ed with CH Cl (20 mL), and the resulting organic extract was used
2 2
to extract the NaHCO wash solution (B). The resulting organic ex-
3
tract was used to extract the third aqueous wash solution (C), and
the organic phase was separated, followed by a second extraction
of the aqueous wash solutions A, B, and C with a fresh portion of
CH Cl (20 mL), using the same protocol as described for the first
2
2
extraction sequence. The combined organic extracts were dried
over anhydrous Na SO , the solvent was removed under reduced
2
4
pressure, and the residue was dried in vacuo (10 mbar, 208C,
0 min) and purified by column chromatography on silica gel (sta-
tionary phase A, 235 g; column dimensions, 66ꢃ3.5 cm; eluent,
3
Experimental Section
EtOAc/n-hexane 55:45 (v/v)). The residue was dried in vacuo
Chemistry
(0.01 mbar, 208C, 1 h) to give an oil (548 mg), which was dissolved
General procedures: Except for the transformation of 7 to 8, all
syntheses were carried out under an inert atmosphere of dry nitro-
gen. Organic solvents were dried and purified according to stan-
dard procedures and stored under dry nitrogen. A Bꢀchi GKR 50
apparatus was used for bulb-to-bulb distillations. Melting points
were determined with a Bꢀchi Melting Point B-540 apparatus using
in Et O (5 mL). The product crystallized from the resulting solution
at 48C within 7 days, and the precipitate was isolated by decanta-
tion, washed with n-pentane (2 mL), and dried in vacuo (0.01 mbar,
2
208C, 4 h) to give 1b as a colorless crystalline solid (318 mg,
1
607 mmol; 22% yield); mp: 139–1408C; H NMR (C
D
): d=0.38 (s,
C), 2.14 (s, 3H,
, Tri (=2,4,6-trimethoxyphenyl)), 3.51 (s,
6
6
6H, SiCH
CCH ), 3.45 (s, 6H, o-OCH
H, p-OCH , Tri), 3.70 (br s, 2H, CCH C), 5.61 (d, J =3.4 Hz, 1H, H-
), 0.39 (s, 6H, SiCH ), 1.15 (“s”, 4H, SiCH
3
3
2
1
13
15
29
samples in open glass capillaries. H, C, N, and Si NMR spectra
3
3
3
3
4
were recorded at 238C on a Bruker DRX-300 NMR spectrometer
3
2
HH
3
1
13
15
29
, Fu (=furan-2-carbonyl), 6.23 (s, 2H, H-3/H-5, Tri), 7.14 (d, J =
HH
(
H, 300.1 MHz; C, 75.5 MHz; N, 30.4 MHz; Si, 59.6 MHz).
2
074
www.chemmedchem.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2011, 6, 2070 – 2080

Silicon Analogues of a GnRH Antagonist
1
5
1
(
(
60.4 ppm (C-4, Tri);
N NMR
2
9
C D ): d=ꢁ281.8 ppm; Si NMR
6
6
C D ): d=ꢁ7.34, ꢁ7.30 ppm; Anal.
6
6
calcd for C H NO Si (523.78): C
28
37
5
2
6
6
4.21, H 7.12, N 2.67; found: C
4.6, H 7.1, N 2.7.
Method B:
A
solution of
8
(
(
2
584 mg, 1.63 mmol) in CH Cl
2
2
10 mL) was added dropwise at
08C over 10 min to a stirred solu-
tion of dicyclohexylcarbodiimide
DCC; 370 mg, 1.79 mmol) and pyr-
(
idine (265 mg, 3.35 mmol) in
CH Cl2 (10 mL). The mixture was
2
stirred at 208C for 24 h, followed
by addition of DMAP (4.0 mg,
3
3 mmol) in a single portion. Sub-
sequently, solution of 10
358 mg, 1.95 mmol; with bulb-to-
a
(
bulb distillation directly before
use) in CH Cl (5 mL) was added to
2
2
the stirred mixture at 208C over
0 min, and stirring was continued
1
at 208C for a further 3 days (forma-
tion of a precipitate). The mixture
was washed with water (2ꢃ
2
5 mL), and the organic layer was
separated. The first aqueous wash
solution (A) was extracted with
CH Cl2 (20 mL), and the resulting
2
organic extract was used to extract
the second aqueous wash solution
(B), and the organic extract was
separated, followed by a second
extraction of the aqueous was sol-
utions A and B with a fresh portion
of CH Cl (20 mL), using the same
2
2
protocol as described for the first
extraction sequence. All organic
extracts were combined and dried
over anhydrous Na SO4 (the re-
2
maining Na SO and solids that did
2
4
not dissolve in either phase were
removed by filtration). The solvent
was removed under reduced pres-
sure, and the residue was dried in
vacuo (10 mbar, 208C, 30 min) and
then purified by column chroma-
tography on silica gel (stationary
phase A, 250 g; column dimen-
sions, 70ꢃ3.5 cm; eluent, EtOAc/
n-hexane 55:45 (v/v)). The residue
was dried in vacuo (0.01 mbar,
ꢁ
1
Figure 4. a) Effect of a single 100 mgkg oral dose of compounds 1a and 2 on plasma testosterone time course
ꢁ
1
in intact male rats. Cetrorelix was dosed subcutaneously at 0.1 mgkg . Data represent absolute values of testos-
ꢁ1
terone in ngmL ; meanꢃSD of n=5 rats per group. Ftime =8.456, p <0.0001 and Ftreatment =0.6811, p=0.5651,
ꢁ
1
ꢁ1
based on a two-way ANOVA.
&
: vehicle (p.o.); ^: 1a at 100 mgkg (p.o.); ~: 2 at 100 mgkg (p.o.); ^: cetrorelix
ꢁ
1
ꢁ1
at 0.1 mgkg (s.c.); b) Effect of a single 100 mgkg oral dose of compounds 1a and 2 on plasma testosterone
time course in intact male rats. Data represent percentage of baseline testosterone at t=0 h; meanꢃSD of n=5
rats per group. *p <0.05, **p <0.01, ***p <0.001, based on a two-way ANOVA followed by Bonferroni post-tests
ꢁ
1
ꢁ1
as compared to the vehicle group.
: vehicle (p.o.); ^: 1a at 100 mgkg (p.o.); ~: 2 at 100 mgkg (p.o.); ^:
&
ꢁ
1
cetrorelix at 0.1 mgkg (s.c.).
2
08C, 1 h) to give an oil (454 mg),
which was dissolved in Et O
2
3
.4 Hz, 1H, H-3, Fu), 7.41 (s, 1H, H-1, Naph (=5,8-disila-5,6,7,8-tetra-
(8 mL). The resulting solution was then left undisturbed at 48C for
2 days and at ꢁ208C for a further 4 days (formation of a precipi-
tate). The precipitate was isolated by decantation, washed with
n-pentane (3 mL), and dried in vacuo (0.01 mbar, 208C, 4 h) to give
1b as a colorless crystalline solid (318 mg, 607 mmol; 37% yield);
hydro-2-naphthyl)), 7.46 (s, 1H, H-4, Naph), 7.5 ppm (br s, 1H, NH);
1
3
C NMR (C D ): d=ꢁ1.31 (2C, SiCH ), ꢁ1.28 (2C, SiCH ), 8.00
6
6
3
3
(
SiCH C), 8.01 (SiCH C), 19.3 (CCH ), 32.6 (CCH C), 55.0 (p-OCH , Tri),
2 2 3 2 3
5
5.5 (o-OCH , Tri), 91.5 (C-3/C-5, Tri), 108.0 (C-1, Tri), 109.1 (C-4, Fu),
3
1
13
29
1
15.4 (C-3, Fu), 135.2 (C-1, Naph), 135.7 (C-2, Naph), 135.9 (C-4,
Naph), 136.7 (C-3, Naph), 143.3 (C-4a, Naph), 144.3 (C-8a, Naph),
48.4 (C-2, Fu), 156.1 (C-5, Fu), 156.6 (C(O)N), 157.3 (C-2/C-6, Tri),
mp: 1398C; H, C, and Si NMR data for the product were identi-
cal with those obtained for the product prepared according to
1
ChemMedChem 2011, 6, 2070 – 2080
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
2075

MED
D. J. Miller, R. Tacke et al.
Method A (see above); Anal. calcd for C H NO Si (523.78): C
EtOAc (20 mL), the resulting organic extract was used to extract
the second aqueous wash solution (B), and the organic extract was
separated, followed by a second and third extraction of the aque-
ous wash solutions A and B with a fresh portion of EtOAc (20 mL),
using the same protocol as described for the first extraction se-
quence. The combined organic extracts were dried over anhydrous
Na SO , the solvent was removed under reduced pressure, and the
residue was purified by column chromatography on silica gel (sta-
tionary phase B, 300 g; column dimensions, 60ꢃ3.5 cm; eluent,
EtOAc/n-hexane 55:45 (v/v)). The residue was dried in vacuo
28
37
5
2
6
4.21, H 7.12, N 2.67; found: C 64.2, H 7.1, N 2.7.
Method C: A 2.0m solution of trimethylaluminum (AlMe ) in tolu-
3
ene (5.00 mL, 10.0 mmol of AlMe ) was added dropwise at ꢁ308C
3
over 8 min to a stirred suspension of 10·HCl (2.20 g, 10.0 mmol) in
toluene (20 mL) (dissolution of 10·HCl was followed by the forma-
tion of a precipitate). The stirred mixture was warmed to ꢁ208C
over 25 min and then to 208C over a further 1 h (dissolution of the
precipitate). The resulting solution was then added dropwise at
2
4
0
8C over 10 min to a stirred solution of 7 (1.86 g, 4.99 mmol) in
(0.001 mbar, 208C, 1 h), and the resulting product was crystallized
CH Cl (20 mL). The resulting mixture was stirred at 08C for 1 h and
2
2
and then recrystallized from Et O (10 mL for each crystallization
2
then at 208C for 3 days (color change from colorless to black), fol-
step) at 208C by vapor diffusion of n-pentane into the etheral solu-
tion over a period of 7 days. The precipitate was isolated by de-
cantation, washed with n-pentane (5 mL), and dried in vacuo
lowed by addition of a half-saturated aqueous NH OAc solution
4
(
solution A, 100 mL). The resulting precipitate was separated by fil-
tration and washed with EtOAc (5ꢃ20 mL), then the filtrate and
wash solutions were combined, and the organic layer was separat-
ed and washed with water (solution B, 100 mL). The first aqueous
wash solution (A) was extracted with EtOAc (50 mL), the resulting
organic extract was used to extract the second aqueous wash solu-
tion (B), and the organic extract was separated, followed by a
second and third extraction of the aqueous wash solutions A and
B with fresh portions of EtOAc (2ꢃ50 mL), using the same protocol
as described for the first extraction sequence. The combined or-
ganic extracts were dried over anhydrous Na SO , the solvent was
(
0.001 mbar, 208C, 2 h) to give 2 as a colorless crystalline solid
1
(357 mg, 700 mmol; 70% yield); mp: 1058C; H NMR (C D ): d=
6
6
0
2
.08 (s, 2H, SiCH Si), 0.44 (s, 6H, SiCH ), 0.45 (s, 6H, SiCH ), 2.16–
2
3
3
.18 (m, 3H, CCH ), 3.43 (s, 6H, o-OCH , Tri), 3.49 (s, 3H, p-OCH ,
3
3
3
Tri), 3.74 (br s, 2H, CCH C), 5.56–5.60 (m, 1H, H-4, Fu), 6.22 (s, 2H,
H-3/H-5, Tri), 7.14 (d, J =3.4 Hz, 1H, H-3, Fu), 7.45 (br s, 1H, H-4,
Ind (=1,1,3,3,6-pentamethyl-1,3-disila-2,3-dihydro-1H-inden-5-yl)),
7
(
(
C-5, Tri), 108.0 (C-1, Tri), 109.1 (C-4, Fu), 115.5 (C-3, Fu), 133.5 (C-4,
Ind), 134.1 (C-7, Ind), 136.2 (C-5, Ind), 137.4 (C-6, Ind), 148.2 (C-7a,
Ind), 148.4 (C-2, Fu), 149.3 (C-3a, Ind), 156.2 (C-5, Fu), 156.6 (C(O)N),
2
3
HH
13
.48 (br s, 1H, NH), 7.49–7.51 ppm (m, 1H, H-7, Ind); C NMR
C D ): d=ꢁ2.2 (SiCH Si), 0.7 (2C, SiCH ), 0.8 (2C, SiCH ), 19.4
6
6
2
3
3
2
4
CCH ), 32.8 (CCH C), 54.9 (p-OCH , Tri), 55.5 (o-OCH , Tri), 91.4 (C-3/
3
2
3
3
removed under reduced pressure, and the residue (4.00 g of a dark
brown, viscous oil) was purified by column chromatography on
silica gel (stationary phase B, 230 g; column dimensions, 80ꢃ
3
.0 cm; eluent, EtOAc/n-hexane 55:45 (v/v)). The residue was dried
in vacuo (0.001 mbar, 208C, 1 h) to give a brown oily product
2.77 g), which was crystallized and recrystallized from Et O (54 mL
15
1
ꢁ
57.3 (C-2/C-6, Tri), 160.4 ppm (C-4, Tri); N NMR (C D ): d=
6 6
29
281.2 ppm; Si NMR (C D ): d=8.6 ppm (2Si); Anal. calcd for
6 6
(
2
C H NO Si (509.75): C 63.62, H 6.92, N 2.75; found: C 63.6, H 6.9,
27
35
5
2
for each crystallization step, with sonication required to achieve
complete dissolution) at 48C over a period of 1 day and then at
N 2.8.
ꢁ
208C over a period of 3 days). The crystalline solid was isolated
by decantation, washed with n-pentane (5 mL), and dried in vacuo
0.001 mbar, 208C, 4 h) to give 1b (1.58 g). The solvent of the com-
bined mother liquors was removed in vacuo to yield a brown oil
Methyl 5-bromo-2-furoate (5): A mixture of CH Cl2 (700 mL), 4
2
(146 g, 764 mmol), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU; 122 g,
801 mmol), and iodomethane (130 g, 916 mmol) was heated under
reflux for 22 h. The mixture was cooled to 208C and was then suc-
(
(
1.06 g), which was crystallized and then recrystallized from Et O
cessively washed with a saturated aqueous NH Cl solution (solu-
2
4
(
19 mL for each crystallization step) to yield a further quantity of
tion A, 300 mL), a saturated aqueous NaHCO solution (solution B,
3
1
b (580 mg). Compound 1b was obtained as a colorless crystalline
300 mL), and water (solution C, 300 mL). The first aqueous wash so-
lution (A) was extracted with EtOAc (200 mL) and the resulting or-
ganic extract was used to extract the second aqueous wash solu-
tion (B). The resulting organic extract was used to extract the third
aqueous wash solution (C), and the organic extract was separated,
followed by a second extraction of the aqueous wash solutions A,
B, and C with a fresh portion of EtOAc (200 mL), using the same
protocol as described for the first extraction sequence. The com-
bined organic extracts were dried over anhydrous Na SO , the sol-
1
13
solid (2.16 g, 4.12 mmol; 83% total yield); mp: 1398C; H, C, and
2
9
Si NMR data for the product were identical with those obtained
for the product prepared according to Method A (see above); Anal.
calcd for C H NO Si (523.78): C 64.21, H 7.12, N 2.67; found: C
2
8
37
5
2
6
4.2, H 7.1, N 2.7.
5
-[(1,1,3,3,6-Pentamethyl-1,3-disila-2,3-dihydro-1H-inden-5-yl)-
methyl]-N-(2,4,6-trimethoxyphenyl)furan-2-carboxamide (2):
solution of AlMe3 (115 mg, 1.60 mmol) in toluene (5 mL) was
A
2
4
vent was removed under reduced pressure, and the residue was
dried in vacuo (10 mbar, 208C, 30 min). n-Hexane (1.1 L) was
added, and the resulting mixture was heated under reflux for
added dropwise at ꢁ308C over 10 min to a stirred suspension of
1
1
0·HCl (351 mg, 1.60 mmol) in toluene (5 mL) (dissolution of
0·HCl was followed by formation of a precipitate). The stirred mix-
5
min, followed by filtration of the hot mixture. The filter cake was
ture was warmed to 08C over 1 h and then to 208C over a further
h during which the precipitate dissolved. The resulting solution
washed with boiling n-hexane (160 mL), the filtrate and wash solu-
tion were combined, and the resulting solution was cooled to
1
was then added dropwise at 08C over 10 min to a stirred solution
of 12 (359 mg, 1.00 mmol) in CH Cl (10 mL). The resulting mixture
was stirred at 08C for 30 min and then at 208C for 3 days (quanti-
tative conversion evaluated by HPLC analysis, with color change
from colorless to black), followed by addition of a half-saturated
2
08C over 2 h and was left undisturbed at 48C for 2 days. The re-
2
2
sulting precipitate was separated by decantation and recrystallized
from boiling n-hexane (720 mL) at 48C over a period of 4 days. The
product was isolated again by decantation and dried in vacuo
(0.01 mbar, 208C, 4 h) to give a yellowish crystalline solid (112 g).
aqueous NH OAc solution (solution A, 20 mL). The resulting precip-
4
The mother liquors of the crystallization steps were combined and
concentrated under reduced pressure to a volume of 250 mL, and
a further 17 g of the product were obtained by crystallization,
using the same method as described above. Compound 5 was ob-
tained as a yellowish crystalline solid (129 g, 629 mmol; 82% total
itate was separated by filtration and washed with EtOAc (10 mL),
then the filtrate and wash solutions were combined, and the or-
ganic layer was separated and washed with water (solution B,
2
0 mL). The first aqueous wash solution (A) was extracted with
2
076
www.chemmedchem.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2011, 6, 2070 – 2080

Silicon Analogues of a GnRH Antagonist
1
yield); mp: 64–658C; H NMR (CDCl ): d=3.87 (s, 3H, OCH ), 6.43
period of 7 days, and the resulting precipitate was isolated by de-
cantation, washed with cold (ꢁ208C) n-hexane (70 mL), and dried
in vacuo (0.001 mbar, 208C, 2 h) to give a colorless crystalline solid
(6.83 g). The mother liquor was concentrated under reduced pres-
sure to a volume of 25 mL, and a further quantity of the product
(1.28 g) was obtained by crystallization, using the same method as
described above. Compound 7 was obtained as a colorless crystal-
line solid (8.11 g, 21.8 mmol; 39% total yield); mp: 75–768C;
3
3
3
3
(
d, J =3.5 Hz, 1H, H-4, Fu), 7.10 ppm (d, J =3.5 Hz, 1H, H-3,
H
H
H
H
1
3
Fu); C NMR (CDCl ): d=52.1 (OCH ), 113.9 (C-4, Fu), 120.1 (C-3,
Fu), 127.5 (C-5, Fu), 146.2 (C-2, Fu), 158.0 ppm (C(O)O); Anal. calcd
for C H BrO (205.01): C 35.15, H 2.46, Br 38.98; found: C 35.4, H
3
3
6
5
3
2
.7, Br 38.8.
Methyl 5-(but-2-ynyl)-2-furoate (6): A 0.68m solution of isopropyl-
magnesium bromide in THF (552 mL, 375 mmol of i-PrMgBr) was
added dropwise at ꢁ408C (ꢃ58C, temperature measured within
the flask) over 110 min to a solution of 5 (70.0 g, 341 mmol) in THF
1
H NMR (C D ): d=0.359 (s, 6H, SiCH ), 0.361 (s, 6H, SiCH ), 1.13 (s,
6
6
3
3
4
H, SiCH C), 2.16 (br s, 3H, CCH ), 3.55 (s, 3H, OCH ), 3.77 (br s, 2H,
2
3
4
3
3
CCH C), 5.66 (dt, J =3.4 Hz, J =1.0 Hz, 1H, H-4, Fu), 7.03 (d,
2
HH
HH
(
1.0 L). The resulting mixture was stirred at ꢁ408C (ꢃ58C) for 3 h,
3
JHH =3.4 Hz, 1H, H-3, Fu), 7.42 (s, 1H, H-1, Naph), 7.43 ppm (br s,
followed by sequential addition of copper(I) cyanide (7.70 g,
13
1
H, H-4, Naph); C NMR (C D ): d=ꢁ1.34 (2 C, SiCH ), ꢁ1.31 (2 C,
6
6
3
8
4
6.0 mmol) in a single portion and 1-bromo-2-butyne (64.8 g,
SiCH ), 7.94 (SiCH C), 7.95 (SiCH C), 19.3 (CCH ), 32.7 (CCH C), 51.0
3
2
2
3
2
87 mmol) dropwise over 5 min (temperature increase to ꢁ208C).
(
OCH ), 108.7 (C-4, Fu), 119.0 (C-3, Fu), 135.3 (C-1, Naph), 135.5 (C-2,
3
The mixture was stirred at ꢁ358C for 2 h and then left undisturbed
at ꢁ208C for 16 h. The mixture (at ꢁ208C) was then added to a
cold (08C) and vigorously stirred emulsion consisting of a saturated
Naph), 135.9 (C-4, Naph), 136.7 (C-3, Naph), 143.4 (C-4a, Naph),
44.1 (C-2, Fu), 144.5 (C-8a, Naph), 158.9 (C(O)O), 159.2 ppm (C-5,
1
29
Fu); Si NMR (C D ): d=ꢁ7.32, ꢁ7.28 ppm; Anal. calcd for
6
6
aqueous NH Cl solution (400 mL) and EtOAc (200 mL). The result-
ing mixture was stirred at 08C for 30 min, followed by filtration at
4
C H O Si (372.61): C 64.47, H 7.57; found: C 64.2, H 5.7.
20
28
3
2
0
8C. The filter cake was washed with EtOAc (2ꢃ100 mL), and the
5-[(3,5,5,8,8-Pentamethyl-5,8-disila-5,6,7,8-tetrahydro-2-naph-
thyl)methyl]-2-furoic acid (8): A mixture of water (48 mL), MeOH
(143 mL), KOH (6.90 g, 123 mmol), and 7 (4.34 g, 11.6 mmol) was
heated under reflux for 20 min (slow dissolution of 7) and was
then stirred at 08C for 1 min, followed by addition of CH Cl
two-phase filtrate and wash solutions were combined. The organic
layer was separated, the aqueous phase was extracted with EtOAc
(
3ꢃ100 mL), and the organic extracts were combined and dried
over anhydrous Na SO . The solvent was removed under reduced
2
4
2
2
pressure, and the residue was purified by bulb-to-bulb distillation
Kugelrohr apparatus; first fraction (<1008C, 1.03 g) discarded;
(50 mL) and 1m hydrochloric acid to obtain pH 1. The resulting
two-phase mixture was stirred at 08C for 5 min and then at 208C
for a further 15 min. The organic phase was separated, the aque-
ous layer was extracted with CH Cl (3ꢃ50 mL), and the organic ex-
(
second fraction (100–1308C, 51.7 g) contained crude product). The
second fraction (yellowish oil) was crystallized from boiling
n-hexane (265 mL) at 48C over a period of 4 days, and the crystal-
line solid was separated by decantation and recrystallized from
boiling n-hexane (190 mL) at 48C over a period of 2 days. The
product was reisolated by decantation and dried in vacuo
2
2
tracts were combined and dried over anhydrous Na SO . The sol-
2
4
vent was removed under reduced pressure, and the solid residue
was dried in vacuo (0.01 mbar, 208C, 1 h) and dissolved in Et O
2
(140 mL). The product was crystallized by vapor diffusion of n-pen-
tane into this solution at 208C over 14 days and was isolated by
decantation, washed with n-pentane (20 mL), and dried in vacuo
(0.01 mbar, 208C, 4 h) to give a colorless crystalline solid (3.42 g).
The solvent of the mother liquor was removed under reduced
(
0.01 mbar, 208C, 4 h) to give a colorless crystalline solid (34.2 g).
The mother liquors of the crystallization steps were combined, the
solvent was removed under reduced pressure, and a further quan-
tity of the product (3.40 g) was obtained by crystallization of the
residual oil, using the same method as described above. Com-
pressure, the residue was redissolved in Et O (30 mL), and a further
2
pound 6 was obtained as a colorless crystalline solid (37.6 g,
quantity of the product (420 mg) was obtained by crystallization,
using the same method as described above. Compound 8 was ob-
tained as a colorless crystalline solid (3.84 g, 10.7 mmol; 92% total
1
2
1
3
11 mmol; 62% total yield); mp: 448C; H NMR (CD Cl ): d=1.81–
2
2
.84 (m, 3H, CH CꢀCCH ), 3.57–3.62 (m, 2H, CH CꢀCCH ), 3.83 (s,
3
2
3
2
1
H, OCH ), 6.33–6.36 (m, 1H, H-4, Fu), 7.08–7.11 ppm (m, 1H, H-3,
yield); mp: 1718C; H NMR (C D ): d=0.36 (s, 6H, SiCH ), 0.37 (s,
3
6
6
3
13
Fu); C NMR (CD Cl ): d=3.5 (CH CꢀCCH ), 19.4 (CH CꢀCCH ), 52.0
6H, SiCH ), 1.13 (s, 4H, SiCH C), 2.14 (s, 3H, CCH ), 3.72 (s, 2H,
2
2
3
2
3
2
3
2
3
3
4
(
(
OCH ), 72.7 (CH CꢀCCH ), 78.4 (CH CꢀCCH ), 108.8 (C-4, Fu), 119.3
CCH C), 5.58 (dt, J =3.5 Hz, J =0.8 Hz, 1H, H-4, Fu), 7.04 (d,
2 HH HH
3
3
2
3
2
3
C-3, Fu), 144.0 (C-2, Fu), 156.5 (C-5, Fu), 159.2 ppm (C(O)O); Anal.
JHH =3.5 Hz, 1H, H-3, Fu), 7.40 (s, 1H, H-1, Naph), 7.44 (s, 1H, H-4,
13
calcd for C H O (178.19): C 67.41, H 5.66; found: C 67.3, H 5.7.
Naph), 10.1 ppm (br s, 1H, CO(O)H); C NMR (C D ): d=ꢁ1.4 (2C,
1
0
10
3
6
6
SiCH ), ꢁ1.3 (2C, SiCH ), 7.92 (SiCH C), 7.94 (SiCH C), 19.2 (CCH ),
3
3
2
2
3
Methyl 5-[(3,5,5,8,8-pentamethyl-5,8-disila-5,6,7,8-tetrahydro-2-
naphthyl)methyl]-2-furoate (7): A solution of cyclopentadienyl-
3
2.7 (CCH C), 109.1 (C-4, Fu), 121.5 (C-3, Fu), 135.2 (C-2, Naph),
2
1
35.3 (C-1, Naph), 135.9 (C-4, Naph), 136.7 (C-3, Naph), 143.1 (C-2,
cobalt dicarbonyl (CpCo(CO) ) (1.53 g, 8.50 mmol) in m-xylene
2
Fu), 143.5 (C-4a, Naph), 144.6 (C-8a, Naph), 160.6 (C-5, Fu),
(
(
90 mL) was added dropwise over 14 h to a boiling solution of 3
10.9 g, 56.1 mmol) and 6 (10.0 g, 56.1 mmol) in m-xylene (100 mL).
29
1
63.9 ppm (C(O)O); Si NMR (C D ): d=ꢁ7.30, ꢁ7.25 ppm; Anal.
6
6
calcd for C H O Si (358.58): C 63.64, H 7.31; found: C 63.8, H 7.3.
19
26
3
2
This was followed by addition of 3 (5.47 g, 28.1 mmol) in a single
portion at 208C and then by dropwise addition of a solution of
CpCo(CO)2 (1.03 g, 5.72 mmol) in m-xylene (60 mL) under reflux
2,4,6-Trimethoxybenzamide–methanol (9·MeOH): Compound 9
was prepared according to Ref. [14] and isolated, after recrystalliza-
tion from MeOH at 48C, as the solvate 9·MeOH; mp: 187–1888C;
over 12 h. To avoid heating of the CpCo(CO) solution prior to ad-
2
1
3
dition, the dropping funnel containing this catalyst was separated
from the refluxing reaction mixture by a glass tube (length, 20 cm).
The solvent was removed under reduced pressure, and the residue
was purified by column chromatography on silica gel (stationary
phase A, 425 g; column dimensions, 65ꢃ4.5 cm; eluent, n-hexane/
EtOAc 95:5 (v/v)). The residue was dried in vacuo (0.01 mbar, 208C,
H NMR ([D ]DMSO): d=3.16 (d, J =5.2 Hz, 3H, CH OH), 3.71 (s,
6 HH 3
3
6H, o-OCH , Tri), 3.77 (s, 3H, p-OCH , Tri), 4.10 (q, J =5.2 Hz, 1H,
3
3
HH
CH OH), 6.20 (s, 2H, H-3/H-5, Tri), 7.1 (br s, 1H, NH), 7.3 ppm (br s,
3
13
1H, NH); C NMR ([D ]DMSO): d=48.6 (CH OH), 55.4 (p-OCH , Tri),
6
3
3
55.6 (o-OCH , Tri), 90.8 (C-3/C-5, Tri), 110.3 (C-1, Tri), 157.3 (C-2/C-6,
3
Tri), 160.9 (C-4, Tri), 166.6 ppm (C(O)N); Anal. calcd for C H NO
5
11
17
1
h) to give a yellowish oil (11.1 g), which was redissolved in
(243.26): C 54.31, H 7.04, N 5.76; found: C 54.2, H 6.9, N 5.8.
n-hexane (95 mL). The resulting solution was left at ꢁ208C over a
ChemMedChem 2011, 6, 2070 – 2080
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
2077

MED
D. J. Miller, R. Tacke et al.
3
2
,4,6-Trimethoxyaniline (10): 12m Hydrochloric acid (84.0 mL,
JHH =3.4 Hz, 1H, H-3, Fu), 7.45 (br s, 1H, H-4, Ind), 7.47–7.49 ppm
13
1
.01 mol of HCl) was added dropwise at 208C over 40 min to
(m, 1H, H-7, Ind); C NMR (C D ): d=ꢁ2.2 (SiCH Si), 0.70 (2C,
6
6
2
KMnO4 (12.8 g, 81.0 mmol), with an increase in temperature ob-
served, and the resulting chlorine gas was passed through a stirred
solution of KOH (50.5 g, 900 mmol) in water (300 mL) at 08C. After
completing the addition of hydrochloric acid, the residual chlorine
gas was passed into the aqueous KOH solution by a nitrogen gas
stream for 45 min, followed by addition of 9·MeOH (48.7 g,
SiCH ), 0.74 (2C, SiCH ), 19.4 (CCH ), 32.9 (CCH C), 51.0 (OCH ),
3 3 3 2 3
108.7 (C-4, Fu), 119.1 (C-3, Fu), 133.6 (C-4, Ind), 134.2 (C-7, Ind),
136.0 (C-5, Ind), 137.3 (C-6, Ind), 144.1 (C-2, Fu),148.3 (C-7a, Ind),
149.5 (C-3a, Ind), 158.9 (C(O)O), 159.4 ppm (C-5, Fu); Si NMR
(C D ): d=8.55, 8.57 ppm; Anal. calcd for C H O Si (358.59): C
2
9
6
6
19 26
3
2
63.64, H 7.31; found: C 63.7, H 7.2.
2
00 mmol) at 08C in a single portion. The resulting mixture was
stirred at 08C for 6 h and then at 208C for 12 h, during which the
colorless solution became dark brown, followed by addition of
Na SO (12.7 g, 101 mmol) at 208C in a single portion. The mixture
Crystal structure analyses
2
3
was stirred at 208C for 15 min, the resulting precipitate was sepa-
rated by suction filtration, and the filter cake was washed succes-
Suitable single crystals of 1b were obtained by vapor diffusion of
n-pentane into a solution of 1b (100 mg) in Et O (30 mL) (colorless
plates; mp: 1588C), while suitable single crystals of 2·n-C
2
sively with water (100 mL) and Et O (200 mL). The filtrate and wash
H12, 8,
5
2
solutions were combined, the two-phase mixture was shaken thor-
oughly, the organic layer was separated, and the aqueous phase
and 12 were obtained directly from the preparation of these com-
pounds (see above). The crystals were mounted in inert oil (per-
fluoropolyalkyl ether, ABCR) on a glass fiber and then transferred
to the cold nitrogen gas stream of a diffractometer (Stoe IPDS;
was extracted with Et O (2ꢃ200 mL). The combined organic ex-
2
tracts were dried over anhydrous Na SO , the solvent was removed
2
4
under reduced pressure, and the dark-brown residue was purified
by bulb-to-bulb distillation (Kugelrohr apparatus, 110–1408C/
graphite-monochromated Mo K
structures were solved by direct methods.
atoms were refined anisotropically. The OH and NH hydrogen
atoms were localized in difference Fourier syntheses and refined
freely. A riding model was employed in the refinement of the CH
hydrogen atoms.
radiation (l=0.71073 ꢂ)). The
a
[15]
All non-hydrogen
[15]
0
.1 mbar) to give 10 as a colorless liquid, which crystallized at 48C
1
(
13.9 g, 75.9 mmol; 38% yield); mp: 29–318C; H NMR (C D ): d=
6 6
3
6
5
.47 (s, 6H, o-OCH , Tri), 3.58 (s, 3H, p-OCH , Tri), 3.6 (br s, 2H, NH ),
3
3
2
13
.32 ppm (s, 2H, H-3/H-5, Tri); C NMR (C D ): d=55.3 (o-OCH , Tri),
6
6
3
5.4 (p-OCH , Tri), 92.1 (C-3/C-5, Tri), 120.3 (C-1, Tri), 148.1 (C-2/C-6,
3
CCDC-838198 (1b), CCDC-838199 (2·n-C H ), CCDC-838200 (8),
5
12
Tri), 152.7 ppm (C-4, Tri); Anal. calcd for C H NO (183.21): C 59.00,
9
13
3
and CCDC-838201 (12) contain the supplementary data of this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
H 7.15, N 7.65; found: C 58.9, H 7.1, N 7.5.
2
,4,6-Trimethoxyanilinium chloride (10·HCl): A 2m ethereal HCl
solution (15.5 mL, 31.0 mmol of HCl) was added dropwise at 208C
to a stirred solution of 10 (5.34 g, 29.1 mmol) in CH Cl (110 mL).
2
2
The mixture was shaken briefly and then left undisturbed at 208C
for 1 h and then at 48C for a further 16 h. The resulting precipitate
In vitro functional data
was isolated by suction filtration, washed with Et O (20 mL), and
2
dried in vacuo (0.01 mbar, 208C, 4 h) to give 10·HCl as a colorless
Construction of human and rat GnRH receptor expression vector: The
human GnRH receptor (hGnRHR) open reading frame (ORF) was
amplified from human pituitary cDNA (AMS Biotechnology Ltd)
using Expand HiFi polymerase (Roche) and the primers hGnRHR
5’+NheI: 5’-AAATAAGCTAGCACCACCATGGCAAACAGTGCCTCTCCT-
G-3’ and hGnRHR 3’+XhoI: 5’-AATAAACTCGAGTCACAGAGAAAA-
ATATCCATAG-3’. The 1 kb amplified product was gel purified and
restriction digested with NheI and XhoI. Following gel purification,
the digested product was subcloned into the NheI and XhoI sites
of pCDNA5 (Invitrogen). The rat GnRH receptor (rGnRHR) ORF was
generated by amplifying the three coding exons from rat genomic
DNA sourced from Geneservice (WGA—Whole Genome Amplifica-
tion) using pfu Turbo (Stratagene). The amplified exons were ligat-
ed and further amplified using the primers rGnRHR 5’+NheI: 5’-
AATAAAGCTAGCAATATGGCTAACAATGCGTCTC-3’ and rGnRHR 3’+
XhoI: 5’-AAATAACTCGAGTTACAAAGAGAAATACCC-3’. The 1 kb prod-
uct was gel purified and restriction digested with NheI and XhoI.
Following gel purification, the digested product was subcloned
into the NheI and XhoI sites of pCDNA5. Integrity of the amplified
human and rat GnRH receptor ORFs was confirmed by DNA se-
quencing.
crystalline solid (6.28 g, 28.6 mmol; 98% yield); mp: 241–2428C
1
(
dec); H NMR ([D ]DMSO): d=3.79 (s, 3H, p-OCH , Tri), 3.85 (s, 6H,
6
3
o-OCH , Tri), 6.38 (s, 2H, H-3/H-5, Tri), 9.6 ppm (br s, 3H, NH );
3
3
1
3
C NMR ([D ]DMSO): d=55.7 (p-OCH , Tri), 56.4 (o-OCH , Tri), 91.5
6
3
3
(C-3/C-5, Tri), 101.4 (C-1, Tri), 153.7 (C-2/C-6, Tri), 160.3 ppm (C-4,
Tri); Anal. calcd for C H ClNO (219.67): C 49.21, H 6.42, N 6.38;
9
14
3
found: C 49.2, H 6.3, N 6.3.
Methyl 5-[(1,1,3,3,6-pentamethyl-1,3-disila-2,3-dihydro-1H-
inden-5-yl)methyl]-2-furoate (12): solution of CpCo(CO)2
A
(
328 mg, 1.82 mmol) in m-xylene (90 mL) was added dropwise over
1
4 h to a boiling solution of 6 (2.00 g, 11.2 mmol) and 11 (2.02 g,
11.2 mmol) in m-xylene (20 mL). To avoid heating of the CpCo(CO)2
solution prior to addition, the dropping funnel containing this cat-
alyst was separated from the refluxing reaction mixture by a glass
tube (length, 20 cm). The solvent was removed under reduced
pressure, and the residue was purified by column chromatography
on silica gel (stationary phase B, 300 g; column dimensions, 60ꢃ
3
.5 cm; eluent, n-hexane/EtOAc 95:5 (v/v)). The residue was dried
in vacuo (15 mbar, 208C, 30 min) to give a yellowish oil (2.62 g),
which was dissolved in boiling n-hexane (17 mL). The resulting so-
lution was left at ꢁ208C over a period of 3 days, and the resulting
precipitate was isolated by decantation, washed with cold (ꢁ208C)
n-hexane (8 mL), and dried in vacuo (0.001 mbar, 208C, 2 h) to give
Human and rat GnRH receptor cell line generation: Flp-In-CHO (Invi-
trogen) cells were co-transfected with 150 ng of either human or
rat GnRHR pCDNA5 together with 1.4 mg of pOG44 (Invitrogen)
using Polyfect (Qiagen). Transfected cells were selected with
500 mg Hygromycin in DMEM supplemented with 10% fetal clone
III (Hyclone) two days post-transfection and were maintained in
the same media. Cell clones were generated by dilution cloning in
1
2 as a colorless crystalline solid (1.78 g, 4.96 mmol; 44% yield);
1
mp: 1118C; H NMR (C D ): d=0.06 (s, 2H, SiCH Si), 0.41 (s, 6H,
6
6
2
SiCH ), 0.42 (s, 6H, SiCH ), 2.18–2.20 (m, 3H, CCH ), 3.54 (s, 3H,
3
3
3
OCH ), 3.82 (br s, 2H, CCH C), 5.63–5.66 (m, 1H, H-4, Fu), 7.02 (d,
3
2
9
6-well plates (Nunc).
2
078
www.chemmedchem.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2011, 6, 2070 – 2080

Silicon Analogues of a GnRH Antagonist
Human and rat GnRH receptor calcium flux assay: For both human
and rat GnRH functional assays, 25000 cells per well (384-well
plate, Corning) were seeded in normal culture medium. 24 h after
seeding, the cells were loaded with a calcium-sensitive fluorescent
dye by replacing the culture medium with assay buffer (1X Hanks
buffered saline, 25 mm HEPES, 0.1% (w/v) fatty acid free BSA
to dosing and individually housed after castration. At least three
days prior to dosing, rats were cannulated with silicone tubing via
[18]
the right jugular vein as previously described. Prior to initial sam-
pling, the animals were connected to a counterbalanced system
and tubing to enable blood sampling in the freely moving rat. Test
ꢁ1
compounds were administered at 10, 30, or 100 mgkg by oral
ꢁ1
(
bovine serum albumin), pH 7.4) containing 2.5 mm probenecid
gavage in 50% (v/v) labrasol in water (dose volume 5 mLkg ) be-
ꢁ1
and 1X Calcium 3 Reagent (Molecular Devices). Cells were incubat-
ed at 378C for 1 h to allow dye uptake. To test for antagonist activ-
ity, test compounds at a final concentration range between 0.1 nm
and 3.2 mm (diluted in assay buffer) were added to the assay wells
and allowed to incubate 20 min prior to stimulation with GnRH.
After incubation with the test compounds, the assay plate was
placed in a Flexstation II (Molecular Devices), and GnRH (diluted in
assay buffer) was added at the determined EC80 concentration
tween 10:00 and 11:00 am. Vehicle (5 mLkg ) was administered to
a control group by oral gavage. Blood samples were withdrawn at
specific times, collected in lithium heparin tubes, centrifuged
(3000 g, 10 min, 48C), plasma harvested, and split into two samples
for hormone analysis. Samples were stored at ꢁ208C prior to anal-
ysis.
Intact male rat model and pharmacokinetic studies: Male Wistar rats
(
250–300 g; Harlan Winkelmann) were housed in a temperature-
controlled room (20–228C) with a 12 h light/12 h dark cycle. Food
Teklad Global 18% Protein Rodent Diet, Harlan) and water were
(
final). Ligand-dependent changes in intracellular calcium levels
were determined by measuring changes in fluorescence of the dye
at 525 nm following excitation at 485 nm. Readings from wells that
did not contain antagonists enabled percentage inhibition curves
to be plotted using a four-parameter fit algorithm to calculate IC50
values for each compound.
(
available ad libitum. At least two days prior to dosing, rats were
cannulated with silicone tubing via the right jugular vein as previ-
[19]
ously described
and then individually housed. Prior to initial
sampling, the animals were connected to a counterbalanced
system and tubing to enable blood sampling in the freely moving
[19]
rat. To take into account the circadian rhythm of testosterone,
In vitro binding data
baseline testosterone levels were established by two blood sam-
ples taken prior to dosing (ꢁ2 and 0 h). Test compounds were ad-
Crude membranes prepared from rat pituitary glands were used as
ꢁ
1
[16]
ministered at 100 mgkg by oral gavage in 50% (v/v) labrasol in
a source of rat GnRH receptors. Rat receptor binding was per-
ꢁ1
[
17]
125
6
water (dose volume 5 mLkg ) between 10:00 and 11:00 am. Vehi-
formed as previously reported, using 0.05 nm [ I][d-Trp ]-LH-RH
ꢁ1
6
cle (5 mLkg ) was administered to a control group by oral
gavage. Blood samples were withdrawn at specific times, collected
in lithium heparin tubes, centrifuged (3000 g, 10 min, 48C), plasma
harvested, and split into two samples for hormone and drug level
analysis. Samples were stored at ꢁ208C prior to analysis.
as the radiolabelled ligand and 1 mm [d-Trp ]-LH-RH as the non-
specific binding ligand. ES-600 A cell lines (Euroscreen) expressing
the human GnRH recombinant receptor were used as a source of
human GnRH receptors. Human receptor binding was performed
in 96-well plates, with separation of the bound radioactivity on 96-
well filter plates. The binding buffer (25 mm HEPES, pH 7.4, 5 mm
Hormone analysis: Plasma concentrations of testosterone were de-
termined by ELISA (EIA-1559, DRG Instruments). For each rat, the
pre-treatment time points (ꢁ2 and 0 h) were averaged and set to
ꢁ
1
MgCl , 1 mm CaCl , 10 mgmL Saponin, 0.2% protease-free BSA),
[
2
2
1
25
6
6
I]-[d-Trp ]-LH-RH (final concentration 0.2 nm), [d-Trp ]-LH-RH at
various concentrations, and GnRH membranes (10 mg of protein/
well) were added successively in a 96-well plate (Master Block,
Greiner). After 60 min incubation at 258C, the reaction was
stopped by rapid filtration on a GF/C Unifilter plate (PerkinElmer),
saturated with 0.5% polyethyleneimine, using a Filtermate cell har-
vester (PerkinElmer). Filters were washed four times with ice-cold
wash buffer (25 mm HEPES, pH 7.4, 5 mm MgCl , 1 mm CaCl ) and
1
00%, and post-dose samples were calculated as the relative con-
centration compared to pre-treatment values. A paired t-test (Sig-
maStat software, SPSS, Erkrath) was conducted to compare pre-
and post-treatment hormone levels.
Drug analysis: Plasma drug levels were measured by LC-MS/MS.
The LC-MS/MS system consisted of a Surveyor HPLC system
2
2
(
Thermo Finnigan) connected to a TSQ Quantum Classic mass
dried. After addition of 50 mL of Microscint 20 (Packard), the plate
was read in a TopCount (PerkinElmer). IC50 values were determined
by non-linear regression using a single-site model. The binding ac-
tivity is expressed as K calculated from the IC using the Cheng–
spectrometer equipped with an electrospray interface (ESI)
TM
(Thermo Finnigan). Compounds were separated on an XTerra MS
TM
C18 (5 mm, 50ꢃ2.1 mm) analytical column, with an XTerra MS C18
5 mm, 10ꢃ2.1 mm) pre-column (Waters). A linear gradient of
0 mm ammonium acetate in 2% (v/v) MeOH (A) in CH CN (B) was
i
50
(
1
Prusoff equation (K =IC /(1+(L/K )).
i
50
D
3
ꢁ
1
used at a flow rate of 0.35 mLmin . The gradient applied was (%B
min)): 20 (0), 90 (6–7), 20 (8–12). Mass spectra were acquired in
(
In vivo models
positive mode, using the conditions shown in Table 4. Plasma sam-
The procedures used for animal studies described within this
paper were approved by the Institutional Animal Care and Use
Committees of A*STAR (Biopolis, Singapore) for the castrated rat
studies, or performed according to German National Animal Wel-
fare Guidelines with the support of an officer for animal welfare
ples (100 mL) were prepared by addition of internal standard
ꢁ
1
(600 ngmL in CH CN, 200 mL) at room temperature to precipitate
3
(
Pharmacelsus GmbH, Saarbrꢀcken, Germany) for intact pharmaco-
Table 4. Overview of mass spectrometry conditions used in the pharma-
kinetic and testosterone studies.
cokinetic experiments.
Castrated male rat model: Male Wistar rats (250–300 g; Biopolis Bio-
logical Resources Center) were housed in a temperature-controlled
room (20–228C) with a 12 h light/12 h dark cycle. Food (Teklad
Global 18% Protein Rodent Diet, Harlan) and water were available
ad libitum. The rats were surgically castrated at least 14 days prior
+
Compd
[M+H]
m/z]
Monitoring ion
Qualifier ion
Collision energy
[
[m/z]
[m/z]
[V]
1
2
a
492.2
510.1
287.1
305.0
470.1
488.1
35/20
35/20
ChemMedChem 2011, 6, 2070 – 2080
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
2079

MED
D. J. Miller, R. Tacke et al.
protein. Protein was removed by centrifugation (6000 g, 5 min,
Curr. Opin. Drug Discov. Devel. 2003, 6, 526–543; c) G. A. Showell, J. S.
Mills, Drug Discovery Today 2003, 8, 551–556; d) J. S. Mills, G. A. Show-
ell, Expert Opin. Invest. Drugs 2004, 13, 1149–1157; e) P. K. Pooni, G. A.
Showell, Mini-Rev. Med. Chem. 2006, 6, 1169–1177; f) S. Gately, R. West,
Drug Dev. Res. 2007, 68, 156–163; g) A. K. Franz, Curr. Opin. Drug Discov.
Devel. 2007, 10, 654–671.
6] Recent original publications dealing with sila-substituted drugs: a) J. O.
Daiss, C. Burschka, J. S. Mills, J. G. Montana, G. A. Showell, I. Fleming, C.
Gaudon, D. Ivanova, H. Gronemeyer, R. Tacke, Organometallics 2005, 24,
2
08C), and the supernatant was analyzed by LC-MS/MS.
Pharmacokinetic data analysis: Pharmacokinetic parameters were
calculated using WinNonlin Professional 5.0.1 software (Pharsight
Corporation).
[
Acknowledgements
3
192–3199; b) J. O. Daiss, C. Burschka, J. S. Mills, J. G. Montana, G. A.
Showell, J. B. H. Warneck, R. Tacke, Organometallics 2006, 25, 1188–
198; c) G. A. Showell, M. J. Barnes, J. O. Daiss, J. S. Mills, J. G. Montana,
Skillful technical assistance in the synthetic work by Beate E.
Wende (Universitꢁt Wꢀrzburg, Germany) is gratefully acknowl-
edged. Binding affinities were generated by Euroscreen (Gosselies,
Belgium). Pharmacokinetic and intact rat testosterone studies
were performed at Pharmacelsus GmbH (Saarbrꢀcken, Germany).
1
R. Tacke, J. B. H. Warneck, Bioorg. Med. Chem. Lett. 2006, 16, 2555–2558;
d) R. Ilg, C. Burschka, D. Schepmann, B. Wꢀnsch, R. Tacke, Organometal-
lics 2006, 25, 5396–5408; e) R. Tacke, F. Popp, B. Mꢀller, B. Theis, C.
Burschka, A. Hamacher, M. U. Kassack, D. Schepmann, B. Wꢀnsch, U.
Jurva, E. Wellner, ChemMedChem 2008, 3, 152–164; f) J. B. Warneck,
F. H. M. Cheng, M. J. Barnes, J. S. Mills, J. G. Montana, R. J. Naylor, M.-P.
Ngan, M.-K. Wai, J. O. Daiss, R. Tacke, J. A. Rudd, Toxicol. Appl. Pharma-
col. 2008, 232, 369–375; g) W. P. Lippert, C. Burschka, K. Gçtz, M.
Kaupp, D. Ivanova, C. Gaudon, Y. Sato, P. Antony, N. Rochel, D. Moras, H.
Gronemeyer, R. Tacke, ChemMedChem 2009, 4, 1143–1152; h) T. Johans-
son, L. Weidolf, F. Popp, R. Tacke, U. Jurva, Drug Metab. Dispos. 2010, 38,
Keywords: antagonists · drug design · gonadotropin-releasing
hormone (GnRH) · hormone-related diseases · silicon (or sila-
substitution)
7
3–83; i) R. Tacke, B. Nguyen, C. Burschka, W. P. Lippert, A. Hamacher, C.
[
1] a) S. C. Sealfon, H. Weinstein, R. P. Millar, Endocr. Rev. 1997, 18, 180–205;
b) N. H. Petousis, Curr. Opin. Drug Discov. Devel. 2000, 3, 244–249;
c) R. P. Millar, Y.-F. Zhu, C. Chen, R. S. Struthers, Br. Med. Bull. 2000, 56,
Urban, M. U. Kassack, Organometallics 2010, 29, 1652–1660; j) J. B.
Bauer, W. P. Lippert, S. Dçrrich, D. Tebbe, C. Burschka, V. B. Christie, D. M.
Tams, A. P. Henderson, B. A. Murray, T. B. Marder, S. A. Przyborski, R.
Tacke, ChemMedChem 2011, 6, 1509–1517.
7] R. Tacke, M. Merget, R. Bertermann, M. Bernd, T. Beckers, T. Reissmann,
Organometallics 2000, 19, 3486–3497.
761–772; d) K. L. Herbst, Curr. Opin. Pharmacol. 2003, 3, 660–666;
e) M. V. Chengalvala, J. C. Pelletier, G. S. Kopf, Curr. Med. Chem.: Anti-
Cancer Agents 2003, 3, 399–410; f) R. E. Armer, K. H. Smelt, Curr. Med.
Chem. 2004, 11, 3017–3028; g) Y.-F. Zhu, C. Chen, Expert Opin. Ther. Pat.
[
[
8] J. G. Montana, I. Fleming, R. Tacke, J. Daiss, (Amedis Pharmaceuticals
Ltd., Cambridge, UK), PCT Int. Pat. Appl. WO 2004/045625, 2004;
2004, 14, 187–199; h) S. F. Betz, Y.-F. Zhu, C. Chen, R. S. Struthers, J.
Med. Chem. 2008, 51, 3331–3348; i) N. Cho, T. Imada, T. Hitaka, K. Miwa,
M. Kusaka, N. Suzuki, (Takeda Pharmaceutical Company Ltd, Osaka,
Japan), PCT Int. Pat. Appl. WO 2004/067535, 2004; [Chem. Abstr. 2004,
[
Chem. Abstr. 2004, 141, 7278k].
9] M. Abarbri, F. Dehmel, P. Knochel, Tetrahedron Lett. 1999, 40, 7449–
453.
[
7
1
41, 190797r]; j) K. Kamikawa, T. Okabe, M. Nakamura, (Takeda Pharma-
ceutical Company Ltd, Osaka, Japan), PCT Int. Pat. Appl. WO 2010/
26993, 2010; [Chem. Abstr. 2010, 152, 343736].
[
[
10] T. Kusumoto, T. Hiyama, Chem. Lett. 1988, 1149–1152.
11] T. Beckers, K. Marheineke, H. Reilꢄnder, P. Hilgard, Eur. J. Biochem. 1995,
0
2
31, 535–543.
[
2] a) M. B. Anderson, H. N. Vazir, D. R. Luthin, G. D. Paderes, V. P. Pathak,
L. C. Christie, Y. Hong, E. V. Tompkins, H. Li, J. Faust, (Agouron Pharma-
ceuticals, Inc., La Jolla, CA, USA), PCT Int. Pat. Appl. WO 2000/020358,
[
12] See for example: a) S. Sasaki, N. Cho, Y. Nara, M. Harada, S. Endo, N.
Suzuki, S. Furuya, M. Fujino, J. Med. Chem. 2003, 46, 113–124; b) Z.
Guo, Y.-F. Zhu, T. D. Gross, F. C. Tucci, Y. Gao, M. Moorjani, P. J. Con-
ners, Jr., M. W. Rowbottom, Y. Chen, R. S. Struthers, Q. Xie, J. Saunders,
G. Reinhart, T. K. Chen, A. L. Killam Bonneville, C. Chen, J. Med. Chem.
2000; [Chem. Abstr. 2000, 132, 279106b]; b) E. A. Iatsimirskaia, M. L.
Gregory, K. L. Anderes, R. Castillo, K. E. Milgram, D. R. Luthin, V. P.
Pathak, L. C. Christie, H. Vazir, M. B. Anderson, J. M. May, Pharm. Res.
2
004, 47, 1259–1271.
2002, 19, 202–208; c) K. L. Anderes, D. R. Luthin, R. Castillo, E. A. Kray-
[
13] Review dealing with cetrorelix: T. Reissmann, A. V. Schally, P. Bouchard,
H. Riethmꢀller, J. Engel, Human Reproduction Update 2000, 6, 322–331.
14] F. Effenberger, R. Gleiter, L. Heider, R. Niess, Chem. Ber. 1968, 101, 502–
nov, M. Castro, K. Nared-Hood, M. L. Gregory, V. P. Pathak, L. C. Christie,
G. Paderes, H. Vazir, Q. Ye, M. B. Anderson, J. M. May, J. Pharmacol. Exp.
Ther. 2003, 305, 688–695; d) J. Engel, (Aeterna Zentaris GmbH, Frank-
furt, Germany), PCT Int. Pat. Appl. WO 2009/106597, 2009; [Chem. Abstr.
[
511.
[
[
15] G. M. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112–122.
16] G. Halmos, A. V. Schally, J. Pinski, M. Vadillo-Buenfil, K. Groot, Proc. Natl.
Acad. Sci. USA 1996, 93, 2398–2402.
17] B. Szçke, J. Horvꢅth, G. Halmos, Z. Rꢆkꢅsi, K. Groot, A. Nagy, A. V. Schally,
Peptides 1994, 15, 359–366.
2009, 151, 305249q].
[
3] AG-045572 derivatives: a) D. R. Luthin, Y. Hong, V. P. Pathak, G. Paderes,
K. D. Nared-Hood, M. A. Castro, H. Vazir, H. Li, E. Tompkins, L. Christie,
J. M. May, M. B. Anderson, Bioorg. Med. Chem. Lett. 2002, 12, 3467–
[
3470; b) H. Li, K. L. Anderes, E. A. Kraynov, D. R. Luthin, Q.-Q. Do, Y.
[
[
18] A. B. Steffens, Physiol. Behav. 1969, 4, 833–836.
19] E. J. Mock, H. W. Norton, A. I. Frankel, Endocrinology 1978, 103, 1111 –
Hong, E. Tompkins, E. T. Sun, R. Rajapakse, V. P. Pathak, L. C. Christie, H.
Vazir, R. Castillo, M. L. Gregory, M. Castro, K. Nared-Hood, G. Paderes,
M. B. Anderson, J. Med. Chem. 2006, 49, 3362–3367.
1121.
[
[
4] S. K. Sullivan, M. S. Brown, Y. Gao, C. J. Loweth, M. F. Lio, P. D. Crowe,
R. S. Struthers, S. F. Betz, Biochemistry 2006, 45, 15327–15337.
5] Reviews dealing with sila-substituted drugs: a) R. Tacke, H. Linoh in The
Chemistry of Organic Silicon Compounds, Part 2 (Eds.: S. Patai, Z. Rappo-
port), Wiley, Chichester, 1989, pp. 1143–1206; b) W. Bains, R. Tacke,
Received: June 29, 2011
Published online on September 27, 2011
2
080
www.chemmedchem.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2011, 6, 2070 – 2080