1,1′-Disubstituted ferrocenes as molecular hinges in mono- and bivalent dopamine receptor ligands

Article abstract of DOI:10.1021/jm901120h

On the basis of previous work on dopaminergic partial agonists of type 1 and 2, disubstituted ferrocenes are presented as valuable arene bioisosteres. Because substituents at the distal cyclopentadienyl ring are able to adjust the relative disposition tha

Full text of DOI:10.1021/jm901120h

6860 J. Med. Chem. 2009, 52, 6860–6870
DOI: 10.1021/jm901120h
1,10-Disubstituted Ferrocenes as Molecular Hinges in Mono- and Bivalent Dopamine Receptor Ligands
Daniela Huber, Harald Hubner, and Peter Gmeiner*
Department of Chemistry and Pharmacy, Emil Fischer Center, Friedrich Alexander University, Schuhstrasse 19, 91052 Erlangen, Germany
Received July 28, 2009
On the basis of previous work on dopaminergic partial agonists of type 1 and 2, disubstituted ferrocenes
are presented as valuable arene bioisosteres. Because substituents at the distal cyclopentadienyl ring are
able to adjust the relative disposition that is required for ligand binding, disubstituted ferrocenes can act
as molecular hinges. Taking advantage of click chemistry, the regioselective construction and functio-
nalization of the target molecules is reported. Thus triazole derived appendages were used for the fine-
tuning of biological activity and for the attachment of linker units generating bivalent GPCR ligands.
Receptor binding was evaluated by radioligand displacement experiments, revealing superaffinity with
sub- to single-digit nanomolar Ki values for particular test compounds. As a neutral antagonist at the
dopamine receptors D3 and D4 and a potent partial agonist at the D2 subtype (intrinsic activity=57%,
EC50=2.5 nM), the bifunctional ferrocene 10b revealed a novel and unique activity profile.
Introduction
Chart 1. General Approach
Bioisosteric replacement is an efficient concept for lead opti-
mization, significantly extending the chemical space of bioactive
ligands.1 Evaluating atypical bioactive arene surrogates, metallo-
cene-based compounds were reported, including the novel che-
motherapeutic agent ferroquine.2,3 Starting from dopamine D3
receptor selective lead structures of type 1 and heterocyclic analo-
gues thereof,4,5 we have recently shown that metallocene-derived
benzamide bioisosteres of type 2 can serve as highly potent
G-protein coupled receptor (GPCRa) ligands preferentially inter-
acting with the subtypes of the dopamine D2 receptor family, the
serotonergic 5-HT1A and the adrenergic R1 receptor (Chart 1).6
The biological activity of benzamides of type 1 can be tuned
by the introduction of substituents into ortho-, meta-, and
para-positions of the aromatic system.7-10 As an extension of
our studies on GPCR ligands of type 2, we envisaged to
discover the ferrocene derived bifunctional analogues 3.
According to earlier studies of arene carboxamides, we antici-
pated a putative control of subtype selectivity by a careful
selection of the spacer that links the ferrocene moiety and the
phenylpiperazine substructure.11,12 Thus, linker units of type
A, B, and C should be employed. Bioisosteric displacement of
the arene moiety and beneficial substituents of the lead
compound 1 by a conformational flexible, 1,10-disubstituted
ferrocenyl subunit should lead to novel mono- and bivalent
scaffolds when the substituents at the distal cyclopentadienyl
rings should be able to adopt the relative disposition that is
required for ligand binding and thus act as molecular hinges
(Chart 2). The enhanced conformational flexibility of the
ferrocene derivatives could accelerate lead optimization.
Taking advantage of click chemistry, we herein report on
the construction of disubstituted ferrocenes when triazole
derived appendages were used as affinity generating groups
and for the attachment of linker units generating monovalent
and the corresponding bivalent GPCR ligands (Chart 2).13-15
Receptor binding was evaluated by radioligand displacement
experiments, revealing superaffinity with subnanomolar Ki
values for some of the ferrocene derived test compounds.
Finally, intrinsic activity was investigated in vitro.
*To whom correspondence should be addressed. Phone: þ49 9131 85-
29383. Fax: þ49 9131 85-22585. E-mail: peter.gmeiner@medchem.
uni-erlangen.de.
a Abbreviations: GPCR, G-protein coupled receptor; CHO, Chinese
hamster ovary; HR-EIMS, high resolution electron ionization mass
spectrometry; EI-MS, electron ionization mass spectrometry, APCI-
MS, atmospheric pressure chemical ionization mass spectrometry, ESI-
MS, electrospray ionization mass spectrometry.
Results and Discussion
Chemical Synthesis. Our initial investigations were direc-
ted to the elaboration of a practical synthesis of the
r
pubs.acs.org/jmc
Published on Web 10/06/2009
2009 American Chemical Society

Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 21 6861
Scheme 2a
Chart 2. Conformational Flexibility of the Ferrocene Moiety
Can Be Exploited to Efficiently Generate Monovalent and
Bivalent GPCR Ligands
10-ethynylferrocene-1-carboxylic acid 7, which should serve
as a key intermediate for the synthesis of bioactive carbox-
amides of type 3. On the basis of a recently described
preparation of 10-ethynylferrocene-1-carbaldehyde,16 we in-
tended to work out a reaction sequence involving Friedel-
Crafts acylation followed by a Vilsmeier type formylation
and a final elimination step. In detail, methyl ferrocene
carboxylate (4)17 was reacted with acetyl chloride in the
presence of aluminum chloride to afford the acylation pro-
duct 5 almost quantitatively (Scheme 1). Subsequent activa-
tion of DMF with phosphorus oxychloride and treatment of
the resulting Vilsmeier reagent with the ferrocene 5 led to
formation of the chloroacrolein derivative 6. Elimination
was initiated by subsequent heating in dioxane and sodium
hydroxide, leading to the bifunctional ethynylferrocene 7 in
57% overall yield.
a Reagents and conditions: (a) TBTU, DIPEA, DMF, CH2Cl2, 8a,b,
0 °C to RT, 4 h (96-99%); (b) sodium ascorbate, CuSO4, H2O:tBuOH:
CH2Cl2 2:1:1, RT, 16 h (72-98%).
Scheme 3a
The orthogonal reactivity of the ferrocene derived build-
ing block 7 was used for a selective functionalization. Upon
activation with TBTU and addition of the aminopropyl and
aminobutyl substituted phenylpiperazines 8a and 8b,9 re-
spectively, the carboxamides 9a,b could be prepared when
complete conversion was observed (Scheme 2). Choosing
1,2,3-triazole derivatives as affinity generating appendages,
the advantages of click chemistry should be exploited. Fol-
lowing slightly modified recently described protocols for the
CuSO4/sodium ascorbate promoted variant of copper(I)-
catalyzed azide-alkyne cycloaddition (CuAAC),18 benzyla-
zide19 as well as pentyl- and hexylazide20 were reacted with
the ferrocenylethynes 9a,b to give rise to the target com-
pounds 10a-f in excellent yield. According to our computa-
tional docking and mutagenesis studies on classical arene
carboxamides, the triazole substituent should direct to the
entrance of the binding pocket and thus should be in a highly
a Reagentsandconditions:(a) sodium ascorbate, CuSO4, H2O:tBuOH:
CH2Cl2 2:1:1, RT, 16 h (72-94%); (b) 2-methoxyphenylpiperazine,
Na(OAc)3BH, CH2Cl2, RT, 16 h (75-99%).
Scheme 1a
critical region. Further modifications, however, will be done
within future studies for the optimization of the respective
dimeric ligands when this moiety will determine the linker
length and thus will be highly crucial.
Benzyl piperazines and heterocyclic analogues thereof
have been described as dopamine D4 receptor antagonists
and partial agonists.21-23 To approach to metallocene de-
rived analogues, triazolyl substituted ferrocene carbalde-
hydes should be prepared and coupled to ortho-
methoxyphenyl piperazine via reductive amination. Again,
orthogonal functionalization was envisaged renouncing the
use of protecting groups. Thus, triazole formation was done
by reacting benzyl-, pentyl-, and hexylazide with the ethynyl
substituted building block 11 (Scheme 3).16 The synthetic
a Reagents and conditions: (a) acetyl chloride, AlCl3, CH2Cl2, 0 °C,
4 h (99%); (b) POCl3, DMF, 0 °C (15 min) to RT (2 h) (71%); (c) (1) dry
dioxane, reflux, 5 min; (2) 0.5 N NaOH, reflux, 25 min (81%).

6862 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 21
Huber et al.
Scheme 4a
a Reagents and conditions: (a) sodium ascorbate, CuSO4, H2O:tBuOH:CH2Cl2 2:1:1, RT, 16 h (61-99%); (b) 2-methoxyphenylpiperazine,
Na(OAc)3BH, CH2Cl2, RT, 16 h (48-84%).
intermediates 12a-c were reductively aminated with ortho-
methoxyphenylpiperazine, resulting in formation of the test
compounds 13a-c.
In fact, the binding data depicted in Table 1 clearly indicate
that the benzyl, pentyl, and hexyl substituted triazole units
significantly extending the volume of the ferrocene moiety
are tolerated by the binding sites of the D2 receptor family.
Significant radioligand displacement was observed, leading
to Ki values in the nanomolar range. Whereas D4 preference
was determined for our core structure 2, the substituted
derivatives 10b,d,f revealed superaffinity at D3 resulting in
Ki values of 0.34, 1.3, and 0.63 nM, respectively. Competi-
tion experiments at D2long, D2short, and D4.4 led to Ki values
between 3.7 and 25 nM, indicating only moderately lower
target recognition than for D3. Compared to the aminobutyl
substituted ferrocenylcarboxamides 10b,d,f, the aminopro-
Taking advantage of the high impact and efficiency of
click chemistry, copper promoted 1,3-dipolar cycloaddition
should be used for the construction of dimeric dopamine
receptor ligands that putatively act as bivalent receptor
modulators (Scheme 4).24 According to previous investiga-
tions on bivalent ligands containing μ-opioid agonist and
type 2 cholecystokinin antagonist receptor pharmaco-
phores,25 spacers with 16-18 atoms were chosen in confor-
mationally flexible and rigidized form. For the synthesis of
bivalent carboxamides of type 14a-f, the monomeric ethy-
nyl substituted precursors 9a,b were coupled with aliphatic
diazides and biphenyl derivatives26 to afford the reaction
products 14a-f in good to excellent yield (61-99%). For a
preparation of the respective methylene bridged analogues
16a-c, the building block 11 was reacted with the diazides
mentioned above. Reductive amination of the thus formed
intermediates 15a-c furnished the dimeric final products
16a-c in 48-84% yield.
pyl analogues 10a,c,e displayed lower affinity toward D2long
,
D2short, and D3 but comparable D4 binding, resulting in a
significant D4 preference. On the other hand, only weak to
moderate D1 affinity was observed for all test compounds.
Because of the observation that the lead compounds of type 1
reveal serotonergic and adrenergic properties,32 all ferrocene
derived test compounds were investigated for their potency
to displace [3H]WAY100635, [3H]ketanserin, and [3H]pra-
zosin. Employing porcine R1, 5-HT1A and 5-HT2 receptors,
10b displayed substantial affinity with Ki values in the
nanomolar range (R1: Ki = 2.5 nM, 5-HT1A: Ki = 14 nM,
5-HT2: Ki=260 nM; data for all test compounds, see Sup-
porting Information).
Because benzyl piperazines and heterocyclic analogues
thereof have been described as dopamine D4 receptor
ligands,21-23 significant D4 recognition was expected for
the ferrocene derived analogues 13a-c. Surprisingly, the
displacement studies gave disappointing Ki values (82-130 nM)
for D4 and weak preference for D2, indicating that a
successful bioisosteric replacement was not possible in this
case. This might be due to different binding modes of the
ferrocene entity depending on the lengths of the spacer units.
Over the past decade, evidence has accumulated to suggest
that GPCRs may function as dimers or large oligomers.33
Very recently, communication between protomers of
Receptor Binding. Radioligand binding assays were
employed to analyze affinity and selectivity profiles of the
monomeric target compounds 10a-f and 13a-c and its
dimeric congeners 14a-f and 16a-c. The Ki values of the
test compounds were compared to the properties of the lead
structure 2 and the reference agent quinpirole,27 which is
known to activate D2, D3, and D4 receptors. The binding
data were generated by measuring their ability to compete
with [3H]spiperone for the cloned human dopamine receptor
subtypes D2long, D2short,
28 D3,29 and D4.430 stably expressed
in Chinese hamster ovary cells (CHO).31 D1 receptor affi-
nities were determined utilizing porcine striatal membranes
and the D1 selective radioligand [3H]SCH 23390.31
The characterization of the test compounds was initiated
by investigating the ferrocenylcarboxamides 10b,d,f incor-
porating a butylene spacer and thus displaying the highest
degree of similarity with the lead compounds of type 1 and 2.

Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 21 6863
Table 1. Receptor Binding Data for the Monomeric Ferrocene Compounds 2, 10a-f, and 13a-c and the Reference Quinpirole Employing Porcine D1
Receptor and the Human Subtypes D2long, D2short, D3, and D4.4 Receptors
Ki values (nM) ( SDa
[3H]spiperone
[3H]SCH 23390
D1
compd
n
R
hD2long
hD2short
hD3
hD4.4
2
10a
1900 ( 250
780 ( 300
370 ( 7.1
690 ( 200
1200 ( 210
510 ( 260
240 ( 71
110 ( 10
140 ( 91
3.7 ( 0.21
44 ( 14
25 ( 7.8
33 ( 8.5
4.7 ( 0.85
25 ( 12
78 ( 1.5
170 ( 14
4.0 ( 0.50
100 ( 0
15 ( 7.4
81 ( 0.71
4.4 ( 1.1
49 ( 2.8
49 ( 9.9
70 ( 8.1b
870 ( 0
6.5 ( 0.54 b
73 ( 36
0.34 ( 0.064
58 ( 23
1.3 ( 0.35
43 ( 21
0.52 ( 0.086 b
2.8 ( 0.14
5.4 ( 0.071
4.6 ( 0.14
16 ( 5.0
3.5 ( 0.21
5.4 ( 1.7
82 ( 23
2
3
2
3
2
3
benzyl
benzyl
pentyl
pentyl
hexyl
10b
10c
10d
10e
10f
13a
hexyl
0.63 ( 0.042
370 ( 7.1
260 ( 57
benzyl
pentyl
hexyl
260 ( 85
13b
13c
250 ( 35
32 ( 5.7
39 ( 9.9b
950 ( 340b
87 ( 19
360 ( 19b
72000 ( 0
390 ( 110b
130 ( 13b
quinpirole
49 ( 8.6b
16 ( 4.7b
a Derived from two individual experiments each done in triplicate. b Ki values ( SEM derived from 3-6 experiments each done in triplicate
Chart 3. Structure and Mode of a Mono- (Black) and a Bivalent Ligand Binding (Black and Grey)
Table 2. Receptor Binding Data for the Dimeric Ferrocene Compounds 14a-f, 16a-c, and the Benzamide Analogues 17,18 Employing Porcine D1
Receptor and the Human Subtypes D2long, D2short, D3, and D4.4 receptors
Ki values (nM) ( SDa
[3H]spiperone
[3H]SCH 23390
D1
compd
n
R
hD2long
hD2short
hD3
hD4.4
14a
14b
14c
14d
14e
14f
16a
16b
16c
17
2
3
2
3
2
3
bis-CH2-p-biphenyl
bis-CH2-p-biphenyl
(CH2)10
100 ( 52
87 ( 19
210 ( 64
430 ( 99
130 ( 7.1
76 ( 62
15 ( 4.2
45 ( 13
54 ( 18
64 ( 22
54 ( 32
14 ( 3.5
43 ( 17
55 ( 15
33 ( 21
22 ( 16
1.1 ( 0.21
9.0 ( 2.8
8.4 ( 2.3
7.0 ( 4.2
14 ( 7.2
300 ( 92
86 ( 13
27 ( 6.4
22 ( 6.4
30 ( 0.71
63 ( 25
35 ( 13
58 ( 1.4
480 ( 200
190 ( 21
360 ( 85 b
3400 ( 710
850 ( 640
(CH2)10
(CH2)12
(CH2)12
1100 ( 0
240 ( 28
64 ( 41
170 ( 21
48 ( 46
bis-CH2-p-biphenyl
(CH2)10
(CH2)12
20000 ( 2100
400 ( 14
65 ( 4.2
64 ( 30
33 ( 11
2000 ( 860 b
3400 ( 1300
9500 ( 6400
100 ( 46 b
10000 ( 2100 b
770 ( 200
110 ( 70
230 ( 86 b
70 ( 57
3
3
15000 ( 6200 b
2000 ( 140
18
a Derived from two individual experiments each done in triplicate. b Ki values ( SEM derived from 3-4 experiments each done in triplicate
dopamine D2 receptors has been proved to modulate GPCR
activation.34
In the course of our investigations of bivalent GPCR
ligands putatively binding two binding sites of interacting
receptor oligomers, we tried to evaluate the scope of our click
chemistry based strategy (Chart 3).
Dopamine receptor binding studies of the dimeric ferro-
cenylcarboxamides 14a-f and its methylene analogues
16a-c clearly revealed significant GPCR recognition with
Ki values between 1.1 and 480 nm at the D2-like subtypes
(Table 2).
As observed for the monomers, combination of a butylene
spacer and a benzyltriazolyl substituent was superior for
dopamine receptor binding. Thus, a binding pattern was
observed for the dimer 14b, which closely resembles the
affinity profile of the respective monomer 10b when the
affinities to D2long, D2short, D3, and D4 proved to be only
three- to 4-fold lower. Comparing the excellent binding data
of 14b (Ki=15, 14, 1.1, and 22 nM for D2short, D2long, D3,
and D4, respectively) with those of the meta- and para-
substituted benzamides as reference dimers 17 and 18
(Chart 4) with poor dopamine receptor binding clearly
displayed a highly beneficial effect of the ferrocene-based
molecular hinge that obviously allows the conformationally
restricted bis-methyl-p-biphenyl linker to adopt an optimal
orientation.
Functional Experiments. Evaluation of the binding data
indicating particular high D2, D3, and D4 affinity for test
compound 10b (FAUC 552) suggested further in vitro
studies. As a measure of functional activity, ligand efficacy
of the ferrocenylcarboxamide 10b was determined by
a mitogenesis assay measuring the rate of [3H]thymidine

6864 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 21
Huber et al.
Figure 1. Measurement of [3H]thymidine incorporation as an assay for functional activity of the test compound 10b at the dopamine receptor
subtypes D2long (A), D3 (B), and D4 (C) in comparison to the effect of the reference quinpirole.
Chart 4. Structures of the Reference Dimers 17 and 18
Experimental Section
Chemistry. Dry solvents and reagents were of commercial
quality and were used as purchased. MS were run on a JEOL
JMS-GC Mate II spectrometer by EI (70 eV) with solid inlet or a
Bruker Esquire 2000 by APC or ES ionization. HR-EIMS were
run on a JEOL JMS-GC Mate II using peak-matching (M/
ΔM > 5000). NMR spectra were obtained on a Bruker Avance
360 or a Bruker Avance 600 spectrometer relative to TMS in the
solvents indicated (J value in Hz). Melting points were deter-
mined with
a MEL-TEMP II melting point apparatus
(Laboratory Devices, USA) in open capillaries and given un-
corrected. IR spectra were performed on a Jasco FT/IR 410
spectrometer. Purification by flash chromatography was per-
formed using Silica Gel 60; TLC analyses were performed
using Merck 60 F254 aluminum sheets and analyzed by UV
light (254 nm). Analytical HPLC was performed on Agilent
1100 HPLC systems employing a VWL detector. The purity
of all test compounds and key intermediates was determined
to be >95%. As a column, a ZORBAX ECLIPSE XDB-C8
(4.6 mm ꢀ 150 mm, 5 μm) was used. HPLC purity was measured
using several elution systems. System A, eluent: methanol/
water/0.1 N formic acid, 10% methanol for 3 min to 100%
methanol in 15 min, 100% for 6 min; flow rate, 0.5 mL/min; λ,
254 nm. System B, eluent: methanol/water/0.1 N formic acid,
30% methanol for 1 min to 100% methanol in 11 min, 100% for
4 min; flow rate, 0.5 mL/min; λ, 254 nm. System C, eluent:
methanol/water/0.1 N trifluoroacetic acid, 10-100% methanol
in 21 min, 100% for 3 min; flow rate, 1.0 mL/min; λ, 254 nm.
System D, eluent: acetonitrile/water/0.1 N trifluoroacetic acid,
10% acetonitrile for 2 min to 50% acetonitrile in 13 min to 100%
acetonitrile in 9 min, 100% for 1 min; flow rate, 1.0 mL/min; λ,
254 nm.
Methyl 10-Acetylferrocene-1-carboxylate (5). Acetyl chloride
(1.32 mL, 18.5 mmol) was added at 0 °C to a suspension of
anhydrous aluminum chloride (2.46 g, 18.5 mmol) in CH2Cl2
(12 mL) and stirred for 15 min. The mixture was then added at
0 °C to a solution of methyl ferrocene-1-carboxylate (4, 1.50 g,
6.15 mmol) in CH2Cl2 (23 mL) over a period of 15 min upon
stirring under nitrogen atmosphere. To prevent light induced
degradation, the flask was covered with aluminum foil during
the reaction. After 4 h, the reaction mixture was poured into ice
water and the resulting precipitate was solubilized by addition of
concentrated HCl. The organic layer was separated, and the
aqueous layer was extracted with CH2Cl2. The combined or-
ganic layers were dried (MgSO4) and evaporated under reduced
pressure to give 5 as an orange solid (1.75 g, 99% yield); mp
incorporation into growing CHO10001 cells and a CHO
dhfr- cell line stably expressing the human D2long, D4.2, and
D3 receptor, respectively (Figure 1).29,35,36
Interestingly, test compound 10b displayed to act as a
partial agonist at D2long with an intrinsic activity of 57% and
an EC50 value of 2.6 nM (Figure 1A), which is very similar to
the Ki value of the binding experiments (3.7 nM). This effect
could be reversed by the neutral antagonist haloperidol in a
concentration dependent manner (see Supporting Inform-
ation). On the other hand, the ferrocene 10b did not show any
ligand efficacy at the D3 subtype. Because the reference
compounds of type 1 and 2 are known as D3 partial agonists,
the neutral antagonist properties of 10b are obviously due to
the steric demand of the benzyltriazolyl substituent
(Figure 1B). Measuring the rate of [3H]thymidine incorpora-
tion at D4 indicated only a very low effect (<20%) at high
concentration of 10b (Figure 1C). Thus the bifunctional
ferrocene 10b revealed a particularly interesting activity
profile, with neutral antagonist properties for D3 and D4
behaving as a potent partial agonist at the D2 subtype.
In conclusion, 1,10-disubstituted ferrocenes can serve as
valuable arene bioisosteres when click chemistry allowed a
regioselective construction and functionalization as well as
the formation of GPCR binding dimers. Receptor recogni-
tion was evaluated by radioligand displacement experiments
revealing superaffinity with sub- and single-digit nanomolar
Ki values for some of the ferrocene derived test compounds.
Aiming to better treat schizophrenia in future, the bifunc-
tional ferrocene 10b revealed a particularly interesting activ-
ity profile when neutral antagonist properties for D3 and D4
combined with a potent partial agonist behavior at the D2
subtype (intrinsic activity=57%, EC50=2.5 nM) could pot-
entially lead to an atypical neuroleptic profile.
99-101 °C. IR 1712, 1666, 1465, 1281, 1146, 671 cm-1
.
1H NMR (600 MHz, CDCl3) δ 2.38 (s, 3 H), 3.83 (s, 3 H),
4.42 (m, 2 H), 4.51 (m, 2 H), 4.78 (m, 2 H), 4.82 (m, 2 H). 13C
NMR (150 MHz, CDCl3) δ 27.53, 51.71, 70.94, 71.59, 72.62,
72.99, 73.45, 80.51, 170.67, 201.23. EI-MS calcd m/z for
C14H14FeO3: 286.1, found 286 (Mþ).
Methyl 10-(1-Chloro-3-oxoprop-1-enyl)ferrocene-1-carboxy-
late (6). POCl3 (1.42 mL, 15.5 mmol) was added dropwise to
anhydrous DMF (1.42 mL) at 0 °C. After stirring for 15 min, the

Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 21 6865
resulting Vilsmeier reagent was added to an ice-cold mixture of 5
(1.64 g, 5.73 mmol) and anhydrous DMF (1 mL) over a period of
15 min. The reaction mixture was warmed to room temperature
and stirred for 2 h. The Vilsmeier complex was quenched with
sodium acetate trihydrate (6.60 g, 48.7 mmol). Saturated aqueous
NaHCO3 was added until the aqueous phase was neutralized.
Extraction with CH2Cl2, drying (MgSO4), and evaporation gave
the crude product, which was purified by flash chromatography
(n-hexane:ethylacetate 6:1) to yield 6 as a red oil (1.36 g, 71%
yield): IR 1716, 1666, 1601, 1465, 1281, 1138, 833 cm-1. 1H NMR
(360 MHz, CDCl3) δ3.79 (s, 3 H), 4.44 (m, 2 H), 4.56 (m, 2 H), 4.75
(m, 2 H), 4.84 (m, 2 H), 6.35 (d, 1 H, J=7.04 Hz), 10.10 (d, 1 H, J=
7.04 Hz). 13C NMR: (90 MHz, CDCl3) δ51.75, 69.98, 72.45, 73.43,
73.90, 81.55, 121.45, 152.97, 170.20, 190.62. EI-MS calcd m/z for
C15H13ClFeO3: 332.6, found 332 (Mþ).
10-Ethynylferrocene-1-carboxylic Acid (7). A solution of 6
(1.36 g, 4.09 mmol) in anhydrous dioxane (26 mL) was heated
at reflux temperature for 5 min and subsequently treated with a
boiling solution of 0.5 N NaOH (49.2 mL). The reaction mixture
was refluxed for 25 min and subsequently cooled by addition of
ice water. Neutralization with diluted HCl was followed by
extraction with CH2Cl2. The organic layer was dried (Na2SO4),
and the solvent was removed by reduced pressure. The residue
was purified by flash chromatography (n-hexane:Et2O 1:1) to
give 7 as a red-orange solid (846 mg, 81% yield); mp 144-
145 °C. IR 2110, 1674, 1477, 1296, 1165, 1029, 829, 744 cm-1. 1H
NMR (600 MHz, CDCl3) δ 2.80 (s, 1 H), 4.29 (m, 2 H), 4.45 (m, 2
H), 4.50 (m, 2 H), 4.52 (m, 2 H). 13C NMR (150 MHz, CDCl3) δ
66.41, 70.72, 71.87, 72.11, 73.25, 73.96, 74.92, 80.18, 176.65.
HPLC system A (245 nm) purity 96% (tR=20.5 min). EI-MS
calcd m/z for C13H10FeO2: 254.1, found 254 (Mþ).
APCI-MS calcd m/z for C28H33FeN3O2: 499.4, found 500
(M þ H)þ.
10-(1-Benzyl-1H-1,2,3-triazole-4-yl)-N-{3-[4-(2-methoxyphe-
nyl)piperazin-1-yl]propyl}ferrocene-1-carboxamide (10a). A sus-
pension of 9a (26 mg, 54 μmol), benzyl azide (21 mg, 0.16 mmol),
sodium ascorbate (2.2 mg, 11 μmol), and copper sulfate penta-
hydrate (0.7 mg, 2.8 μmol) in H2O (1 mL), tBuOH (0.5 mL), and
CH2Cl2 (0.5 mL) was stirred at room temperature overnight.
The reaction was quenched with saturated aqueous NaHCO3,
extracted with CH2Cl2, dried (Na2SO4), and evaporated. The
residue was purified by flash chromatography (CH2Cl2:MeOH
98:2-95:5) to give 10a as an orange solid (32 mg, 96% yield); mp
102-105 °C. IR 3325, 2939, 2819, 1635, 1539, 1500, 1454, 1300,
1242, 1026, 752 cm-1 1H NMR (360 MHz, CDCl3) δ 1.79
.
(m, 2 H), 2.59 (br t, 2 H, J=6.58 Hz), 2.74 (m, 4 H), 3.16 (m, 4 H),
3.28 (dt, 2 H, J1 =6.13 Hz, J2 =6.02 Hz), 3.87 (s, 3 H), 4.25
(m, 2 H), 4.31 (m, 2 H), 4.53 (m, 2 H), 4.60 (m, 2 H), 5.53 (s, 2 H),
6.84-6.90 (m, 1 H), 6.91-6.98 (m, 2 H), 6.99-7.05 (m, 1 H),
7.29-7.44 (m, 5 H), 7.48 (s, 1 H), 7.55 (m, 1 H). 13C NMR
(90 MHz, CDCl3) δ 25.42, 39.17, 50.55, 53.57, 54.14, 55.40,
57.45, 68.62, 69.76, 69.98, 70.85, 76.88, 78.75, 111.30, 118.25,
120.07, 121.07, 123.01, 128.11, 128.74, 129.13, 134.70, 141.22,
145.48, 152.34, 169.12. HPLC system D (245 nm) purity >99%
(tR = 15.8 min). HR-EIMS calcd m/z for C34H38FeN6O2:
618.2406, found 618.2408.
10-(1-Benzyl-1H-1,2,3-triazole-4-yl)-N-{4-[4-(2-methoxyphe-
nyl)piperazin-1-yl]butyl}ferrocene-1-carboxamide (10b). Com-
pound 10b was prepared according to the protocol of 10a
using a suspension of 9b (25.5 mg, 51.1 μmol), benzylazide
(20.4 mg, 0.153 mmol), sodium ascorbate (2.0 mg, 10.1 μmol),
and copper sulfate pentahydrate (0.7 mg, 2.80 μmol) in H2O
(1 mL), tBuOH (0.5 mL), and CH2Cl2 (0.5 mL) to give 10b as an
orange solid (27.0 mg, 83% yield); mp 98-101 °C. IR 3317,
10-Ethynyl-N-{3-[4-(2-methoxyphenyl)piperazin-1-yl]propyl}-
ferrocene-1-carboxamide (9a). DIPEA (0.52 mL, 3.2 mmol) was
added to a solution of 7 (0.20 g, 0.79 mmol) in anhydrous
CH2Cl2 (65 mL). The solution was cooled to 0 °C, and subse-
quently TBTU (0.31 g, 0.97 mmol) in anhydrous DMF (16 mL)
was added. After stirring for 15 min, 8a (0.35 g, 1.4 mmol) in
anhydrous CH2Cl2 (82 mL) was added dropwise. The reaction
mixture was warmed to room temperature and stirred for 4 h.
The reaction was quenched with saturated aqueous NaHCO3
and extracted with CH2Cl2. The combined organic layers were
dried (Na2SO4) and evaporated. The residue was purified by
flash chromatography (CH2Cl2:MeOH 98:2) to give 9a as an
orange solid (0.38 g, 99% yield); mp 156-158 °C. IR 3290, 2939,
2939, 2819, 1635, 1539, 1500, 1454, 1300, 1242, 1026, 752 cm-1
.
1H NMR: (360 MHz, CDCl3) δ 1.62-1.76 (m, 4 H), 2.51
(m, 2 H), 2.71 (m, 4 H), 3.12 (m, 4 H), 3.32 (m, 2 H), 3.85
(s, 3 H), 4.26 (m, 2 H), 4.33 (m, 2 H), 4.45 (m, 2 H), 4.54 (m, 2 H),
5.54 (s, 2 H), 6.82-6.87 (m, 1 H), 6.88-6.95 (m, 2 H), 6.96-7.02
(m, 1 H), 7.15 (m, 1 H), 7.28-7.45 (m, 6 H). 13C NMR (90 MHz,
CDCl3) δ 24.26, 27.66, 39.41, 50.44, 53.41, 54.21, 55.38, 58.27,
69.18, 69.79, 70.44, 70.68, 76.46, 78.77, 111.25, 118.28, 119.99,
121.02, 122.94, 128.09, 128.82, 129.18, 134.59, 141.28, 145.95,
152.30, 169.72. HPLC system D (245 nm) purity 98% (tR=15.7
min). HR-EIMS calcd m/z for C35H40FeN6O2: 632.2562, found
632.2558.
2816, 2110, 1635, 1539, 1500, 1454, 1300, 1242, 1030, 749 cm-1
.
N-{3-[4-(2-Methoxyphenyl)piperazin-1-yl]propyl}-10-(1-pentyl-
1H-1,2,3-triazole-4-yl)ferrocene-1-carboxamide (10c). Sodium
azide (1.73 g, 26.6 mmol) was added to a solution of 1-bromo-
pentane (830 μL, 6.65 mmol) in CH3CN (9 mL) and H2O (1 mL)
and heated at reflux temperature overnight. The reaction was
quenched with saturated aqueous NaHCO3, extracted with n-
hexane, dried (Na2SO4), and evaporated to 3.1 mL to obtain a
concentration of 1-azidopentane of 2.15 mmol/mL.
1H NMR (360 MHz, CDCl3) δ 1.83 (m, 2 H), 2.63 (br t, 2 H, J=
6.36 Hz), 2.69-2.84 (m, 5 H), 3.18 (m, 4 H), 3.52 (dt, 2 H, J1=
5.98 Hz, J2=5.98 Hz), 3.87 (s, 3 H), 4.24 (m, 2 H), 4.36 (m, 2 H),
4.45 (m, 2 H), 4.71 (m, 2 H), 6.84-7.07 (m, 4 H), 7.12 (m, 1 H).
13C NMR (150 MHz, CDCl3) δ 25.35, 39.49, 50.54, 53.64, 55.41,
57.68, 65.20, 70.15, 70.52, 72.24, 73.26, 74.62, 78.07, 81.58,
111.29, 118.23, 121.04, 123.15, 141.02, 152.31, 169.28. HPLC
system A (245 nm) purity 98% (tR=16.3 min). APCI-MS calcd
m/z for C27H31FeN3O2: 485.4, found 486 (M þ H)þ.
Compound 10c was prepared according to the protocol of 10a
using a suspension of 9a (26.2 mg, 54.0 μmol), a 2.15 M solution
of 1-azidopentane in n-hexane (75.3 μL, 0.162 mmol), sodium
ascorbate (2.10 mg, 10.8 μmol), and copper sulfate pentahydrate
10-Ethynyl-N-{4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl}-
ferrocene-1-carboxamide (9b). Compound 9b was prepared
according to the protocol of 9a using a solution of 7 (0.20 g,
0.79 mmol) in anhydrous CH2Cl2 (65 mL) as well as DIPEA
(0.52 mL, 3.2 mmol) and TBTU (0.31 g, 0.97 mmol) in anhy-
drous DMF (16 mL) and 8b (0.37 g, 1.4 mmol) in anhydrous
CH2Cl2 (82 mL) to give 9b as a brown oil (0.38 g, 96% yield): IR
3298, 2939, 2819, 2110, 1631, 1539, 1500, 1450, 1300, 1242, 1026,
795, 752 cm-1. 1H NMR (360 MHz, CDCl3) δ 1.62-1.76 (m, 4 H),
2.58 (m, 2 H), 2.78 (m, 4 H), 2.82 (s, 1 H), 3.15 (m, 4 H), 3.44 (dt,
2 H, J1=6.28 Hz, J2=6.19 Hz), 3.86 (s, 3 H), 4.26 (m, 2 H), 4.38
(m, 2 H), 4.44 (m, 2 H), 4.65 (m, 2 H), 6.16 (m, 1 H), 6.83-7.05
(m, 4 H). 13C NMR (90 MHz, CDCl3) δ 23.89, 27.69, 39.33,
50.18, 53.43, 55.40, 58.04, 64.98, 70.50, 72.12, 73.48, 74.72,
77.89, 81.75, 111.30, 118.34, 121.06, 123.17, 140.98, 152.30,
169.44. HPLC system A (245 nm) purity 98% (tR=16.2 min).
t
(0.7 mg, 2.80 μmol) in H2O (1 mL), BuOH (0.5 mL), and
CH2Cl2 (0.5 mL). Purification by flash chromatography
(CH2Cl2:MeOH 98:2-97:3) gave 10c as an orange solid
(24.6 mg, 76% yield); mp 108-111 °C. IR 3309, 2931, 2819,
1635, 1539, 1500, 1450, 1300, 1242, 1026, 748 cm-1. 1H NMR
(360 MHz, CDCl3) δ 0.92 (t, 3 H, J = 6.93 Hz), 1.30-1.44
(m, 4 H), 1.81 (m, 2 H), 1.94 (m, 2 H), 2.59 (br t, 2 H, J=6.47 Hz),
2.73 (m, 4 H), 3.16 (m, 4 H), 3.32 (dt, 2 H, J1=6.21 Hz, J2=
6.07 Hz), 3.87 (s, 3 H), 4.26 (m, 2 H), 4.30-4.38 (m, 4 H), 4.53
(m, 2 H), 4.63 (m, 2 H), 6.84-7.05 (m, 4 H), 7.55 (s, 1 H), 7.57
(m, 1 H). 13C NMR (90 MHz, CDCl3) δ 13.87, 22.12, 25.44,
28.68, 29.98, 39.27, 50.36, 50.60, 53.59, 55.40, 57.52, 68.67,
69.69, 70.02, 70.80, 77.24, 78.77, 111.30, 118.23, 119.97,

6866 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 21
Huber et al.
121.06, 123.00, 141.26, 144.96, 152.35, 169.17. HPLC system A
(245 nm) purity 97% (tR = 17.5 min); system D (245 nm)
purity >99% (tR=16.6 min). HR-EIMS calcd m/z for C32H42-
FeN6O2: 598.2719, found 598.2719.
J2=6.13 Hz), 3.86 (s, 3 H), 4.27 (m, 2 H), 4.31-4.39 (m, 4 H),
4.46 (m, 2 H), 4.57 (m, 2 H), 6.81-7.03 (m, 4 H), 7.18 (m, 1 H),
7.51 (s, 1 H). 13C NMR (90 MHz, CDCl3) δ 13.94, 22.43, 24.24,
26.22, 27.65, 30.25, 31.16, 39.41, 50.44, 53.41, 55.38, 58.26,
69.19, 69.74, 70.46, 70.66, 78.76, 111.27, 118.28, 119.90,
121.03, 122.95, 141.28, 145.39, 152.31, 169.76. HPLC system
A (245 nm) purity 98% (tR = 18.0 min); system D (245 nm)
purity >99% (tR=17.7 min). HR-EIMS calcd m/z for C34H46-
FeN6O2: 626.3032, found 626.3038.
N-{4-[4-(2-Methoxyphenyl)piperazin-1-yl]butyl}-10-(1-pentyl-
1H-1,2,3-triazole-4-yl)ferrocene-1-carboxamide (10d). Com-
pound 10d was prepared according to the protocol of 10a using
a suspension of 9b (19.5 mg, 39.0 μmol), a 2.15 M solution of 1-
azidopentane in n-hexane (54.0 μL, 0.117 mmol), sodium ascor-
bate (1.50 mg, 7.57 μmol), and copper sulfate pentahydrate
(0.5 mg, 1.95 μmol) in H2O (1 mL), tBuOH (0.5 mL) and CH2Cl2
(0.5 mL) to give 10d as a red-orange solid (19.5 mg, 81% yield);
mp 82-85 °C. IR 3324, 2934, 2816, 1635, 1540, 1500, 1451, 1297,
10-(1-Benzyl-1H-1,2,3-triazole-4-yl)ferrocene-1-carbaldehyde
(12a). A suspension of 10-ethynylferrocene-1-carbaldehyde (11,
66.4 mg, 0.279 mmol), benzylazide (111 mg, 0.837 mmol),
sodium ascorbate (11.1 mg, 56.0 μmol), and copper sulfate
t
1241, 1026, 750 cm-1 1H NMR (600 MHz, CDCl3) δ 0.92
.
pentahydrate (3.50 mg, 14.0 μmol) in H2O (4 mL), BuOH
(2 mL), and CH2Cl2 (2 mL) was stirred at room temperature
overnight. Afterward, the reaction was quenched with saturated
aqueous NaHCO3 and extracted with CH2Cl2. The combined
organic layers were dried (Na2SO4), and the solvent was
removed under reduced pressure. The residue was purified by
flash chromatography (n-hexane:Et2O 1:1) to give 12a as an
orange solid (97.9 mg, 94% yield); mp 128-131 °C. IR 3113,
(t, 3 H, J=6.99 Hz), 1.32-1.42 (m, 4 H), 1.62-1.72 (m, 4 H),
1.95 (m, 2 H), 2.50 (br t, 2 H, J=6.61 Hz), 2.70 (m, 4 H), 3.12
(m, 4 H), 3.34 (dt, 2 H, J1=6.04 Hz, J2=5.95 Hz), 3.86 (s, 3 H),
4.28 (m, 2 H), 4.33-4.39 (m, 4 H), 4.45 (m, 2 H), 4.57 (m, 2 H),
6.83-6.88 (m, 1 H), 6.89-6.96 (m, 2 H), 6.97-7.02 (m, 1 H),
7.20 (m, 1 H), 7.51 (s, 1 H). 13C NMR (150 MHz, CDCl3)
δ 13.88, 22.12, 24.29, 27.66, 28.67, 29.99, 39.42, 50.42,
50.47, 53.41, 55.36, 58.28, 69.20, 69.73, 70.46, 70.64, 76.68,
78.76, 111.20, 118.26, 119.90, 121.00, 122.94, 141.27, 145.38
152.29, 169.76. HPLC system B (245 nm) purity 96% (tR=
8.5 min); system D (245 nm) purity >99% (tR=16.4 min).
HR-EIMS calcd m/z for C33H44FeN6O2: 612.2875, found
612.2875.
10-(1-Hexyl-1H-1,2,3-triazole-4-yl)-N-{3-[4-(2-methoxyphe-
nyl)piperazin-1-yl]propyl}ferrocene-1-carboxamide (10e). So-
dium azide (793 mg, 12.2 mmol) was added to a solution of 1-
bromohexane (0.430 mL, 3.05 mmol) in CH3CN (9 mL) and
H2O (1 mL) and heated at reflux temperature overnight. The
reaction was quenched with saturated aqueous NaHCO3,
extracted with n-hexane, dried (Na2SO4), and evaporated
to 7.80 mL to obtain a concentration of 1-azidohexane of
0.391 mmol/mL.
2924, 1678, 1454, 1246, 1045, 825, 721 cm-1 1H NMR
.
(360 MHz, CDCl3) δ 4.36 (m, 2 H), 4.50 (m, 2 H), 4.66
(m, 2 H), 4.79 (m, 2 H), 5.55 (s, 2 H), 7.28-7.33 (m, 2 H),
7.35-7.45 (m, 4 H), 9.70 (s, 1 H). 13C NMR (90 MHz, CDCl3,)
δ 54.19, 68.00, 70.03, 70.96, 74.53, 77.71, 79.97, 119.52, 128.00,
128.77, 129.15, 134.71, 145.10, 193.57. HPLC system A (245 nm)
purity 96% (tR=18.9 min). APCI-MS calcd m/z for C20H17Fe-
N3O: 371.2, found 372 (M þ H)þ.
10-(1-Pentyl-1H-1,2,3-triazole-4-yl)ferrocene-1-carbaldehyde
(12b). Compound 12b was prepared according to the protocol of
12a using a suspension of 11 (63.2 mg, 0.265 mmol), a 2.15 M
solution of 1-azidopentane in n-hexane (372 μL, 800 μmol),
sodium ascorbate (10.5 mg, 53.0 μmol), and copper sulfate
t
pentahydrate (3.3 mg, 13.2 μmol) in H2O (4 mL), BuOH
(2 mL), and CH2Cl2 (2 mL) to give 12b as an orange brown
solid (87.5 mg, 93% yield); mp 68-70 °C. IR 3498, 3120,
2954, 2931, 1682, 1454, 1246, 1049, 825, 744 cm-1. 1H NMR
(360 MHz, CDCl3) δ 0.92 (t, 3 H, J = 6.93 Hz), 1.30-1.42
(m, 4 H), 1.95 (m, 2 H), 4.33-4.40 (m, 4 H), 4.53 (m, 2 H), 4.67
(m, 2 H), 4.83 (m, 2 H), 7.47 (s, 1 H), 9.71 (s, 1 H). 13C NMR
(90 MHz, CDCl3) δ 13.87, 22.10, 28.63, 29.95, 50.40, 68.02,
69.97, 71.00, 74.48, 77.99, 80.00, 119.42, 144.48, 193.57.
HPLC system A (245 nm) purity 99% (tR = 19.7 min).
APCI-MS calcd m/z for C18H21FeN3O: 351.2, found 352
(M þ H)þ.
Compound 10e was prepared according to the protocol of 10a
using a suspension of 9a (23.1 mg, 47.6 μmol), a 0.391 M
solution of 1-azidohexane in n-hexane (366 μL, 0.143 mmol),
sodium ascorbate (1.90 mg, 9.60 μmol), and copper sulfate
t
pentahydrate (0.6 mg, 2.40 μmol) in H2O (1 mL), BuOH
(0.5 mL) and CH2Cl2 (0.5 mL) to give 10e as an orange solid
(28.6 mg, 98% yield); mp 87-89 °C. IR 3336, 2931, 2819, 1635,
1
1539, 1500, 1450, 1300, 1242, 1026, 795, 748 cm-1. H NMR
(600 MHz, CDCl3) δ 0.89 (t, 3 H, J = 6.99 Hz), 1.28-1.40
(m, 6 H), 1.81 (m, 2 H), 1.94 (m, 2 H), 2.59 (br t, 2 H, J=6.61 Hz),
2.74 (m, 4 H), 3.16 (m, 4 H), 3.32 (dt, 2 H, J1=6.29 Hz, J2=
6.14 Hz), 3.87 (s, 3 H), 4.26 (m, 2 H), 4.33 (m, 2 H), 4.35 (t, 2 H,
J=7.37 Hz), 4.53 (m, 2 H), 4.63 (m, 2 H), 6.85-6.89 (m, 1 H),
6.91-6.97 (m, 2 H), 6.99-7.04 (m, 1 H), 7.55 (s, 1 H), 7.60
(m, 1 H). 13C NMR (90 MHz, CDCl3) δ 13.90, 22.39, 25.39,
26.19, 30.21, 31.13, 39.21, 50.34, 50.54, 53.54, 55.36, 57.47,
68.63, 69.65, 69.99, 70.77, 77.08, 78.71, 111.26, 118.19, 119.92,
121.01, 122.96, 141.21, 144.92, 152.30, 169.14. HPLC system
C (245 nm) purity 99% (tR = 18.3 min); system D (245 nm)
purity >99% (tR=17.8 min). HR-EIMS calcd m/z for C33H44-
FeN6O2: 612.2875, found 612.2875.
10-(1-Hexyl-1H-1,2,3-triazole-4-yl)ferrocene-1-carbaldehyde
(12c). Compound 12c was prepared according to the protocol of
12a using a suspension of 11 (34.5 mg, 145 μmol), a 0.391 M
solution of 1-azidohexane in n-hexane (111 μL, 0.435 mmol),
sodium ascorbate (5.80 mg, 29.3 μmol), and copper sulfate
t
pentahydrate (1.8 mg, 7.21 μmol) in H2O (2 mL), BuOH
(1 mL), and CH2Cl2 (1 mL) to give 12c as an orange-brown
solid (38.3 mg, 72% yield); mp 79-80 °C. IR 3118, 2927, 2856,
1
1682, 1456, 1244, 1047, 822, 742 cm-1. H NMR (360 MHz,
CDCl3) δ 0.89 (t, 3 H, J=7.04 Hz), 1.27-1.41 (m, 6 H), 1.95
(m, 2 H), 4.33-4.40 (m, 4 H), 4.53 (m, 2 H), 4.67 (m, 2 H), 4.83
(m, 2 H), 7.46 (s, 1 H), 9.71 (s, 1 H). 13C NMR (150 MHz,
CDCl3,) δ 13.96, 22.45, 26.18, 30.24, 31.18, 50.42, 68.03, 69.99,
71.02, 74.50, 77.96, 79.98, 119.42, 144.49, 193.63. HPLC system
A (245 nm) purity 99% (tR=20.5 min). APCI-MS calcd m/z for
C19H23FeN3O: 365.3 found 366 (M þ H)þ.
10-(1-Hexyl-1H-1,2,3-triazole-4-yl)-N-{4-[4-(2-methoxyphe-
nyl)piperazin-1-yl]butyl}ferrocene-1-carboxamide (10f). Com-
pound 10f was prepared according to the protocol of 10a
using a suspension of 9b (25.2 mg, 50.5 μmol), a 0.391 M
solution of 1-azidohexane in n-hexane (390 μL, 0.152 mmol),
sodium ascorbate (2.0 mg, 10.1 μmol), and copper sulfate
1-{[10-(1-Benzyl-1H-1,2,3-triazole-4-yl)ferrocene-1-yl]methyl}-
4-(2-methoxyphenyl)piperazine (13a). A solution of 12a (21.1
mg, 56.8 μmol), 1-(2-methoxyphenyl)piperazine (16.4 mg,
85.2 μmol), and Na(OAc)3BH (25.3 mg, 114 μmol) in anhydrous
CH2Cl2 (13 mL) was stirred at room temperature overnight. The
reaction mixture was quenched with saturated aqueous NaH-
CO3 and extracted with CH2Cl2. The combined organic layers
were dried (Na2SO4) and evaporated. The residue was purified
t
pentahydrate (0.6 mg, 2.40 μmol) in H2O (1 mL), BuOH
(0.5 mL) and CH2Cl2 (0.5 mL) to give 10f as an orange solid
(23.0 mg, 72% yield); mp 68-72 °C. IR 3317, 2931, 1635, 1539,
1
1500, 1454, 1300, 1242, 1026, 667 cm-1. H NMR (360 MHz,
CDCl3) δ 0.89 (t, 3 H, J = 7.15 Hz), 1.28-1.45 (m, 6 H),
1.61-1.76 (m, 4 H) 1.94 (m, 2 H), 2.52 (br t, 2 H, J=7.04 Hz),
2.71 (m, 4 H), 3.14 (m, 4 H), 3.34 (dt, 2 H, J1 = 6.28 Hz,

Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 21 6867
by flash chromatography (CH2Cl2:MeOH 98:2) to give 13a as a
yellow-orange solid (27.3 mg, 87% yield); mp 121-125 °C. IR
69.97, 70.88, 76.86, 78.73, 111.33, 118.26, 120.17, 121.07,
123.09, 127.77, 128.66, 134.11, 140.73, 141.12, 145.54, 152.33,
169.10. HPLC system A (245 nm) purity 95% (tR=16.7 min);
system D (245 nm) purity 98% (tR=17.4 min). APCI-MS calcd
m/z for C68H74Fe2N12O4: 1235.1 found 1236 (M þ H)þ.
2939, 2816, 1500, 1454, 1238, 1026, 752 cm-1 1H NMR
.
(600 MHz, CDCl3) δ 2.50 (m, 4 H), 3.01 (m, 4 H), 3.16 (s, 2 H),
3.84 (s, 3 H), 4.03 (m, 2 H), 4.07 (m, 2 H), 4.25 (m, 2 H), 4.65 (m, 2 H),
5.54 (s, 2 H), 6.81-6.85 (m, 1 H), 6.86-6.91 (m, 2 H), 6.94-7.00
(m, 1 H), 7.28-7.32 (m, 2 H), 7.34-7.42 (m, 4 H). 13C NMR
(150 MHz, CDCl3) δ 50.39, 52.70, 54.10, 55.33, 57.59, 66.98,
69.17, 69.65, 71.79, 75.75, 82.97, 111.15, 118.21, 118.66, 120.97,
122.83, 127.96, 128.71, 129.16, 134.93, 141.35, 146.73, 152.24.
HPLC system A (245 nm) purity 98% (tR=16.5 min); system D
(245 nm) purity >99% (tR=16.7 min). HR-EIMS calcd m/z for
C31H33FeN5O: 547.2035, found 547.2035.
10,100-[Biphenyl-4,40-diylbis(methylene-1H-1,2,3-triazole-1,4-
diyl)]bis(N-{4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl}ferroc-
ene-1-carboxamide) (14b). Compound 14b was prepared accord-
ing to the protocol of 14a using a suspension of 9b (39 mg,
78 μmol), 4,40-bis(azidomethyl)biphenyl (6.9 mg, 26 μmol),
sodium ascorbate (1.0 mg, 5.0 μmol), and copper sulfate penta-
hydrate (0.3 mg, 1.2 μmol) in H2O (2 mL), tBuOH (1 mL), and
CH2Cl2 (1 mL) to give 14b as an orange solid (32 mg, 96% yield);
mp 147-150 °C. IR 3402, 2939, 2819, 1631, 1539, 1500, 1450,
1-(2-Methoxyphenyl)-4-{[10-(1-pentyl-1H-1,2,3-triazole-4-
yl)ferrocene-1-yl]methyl}piperazine (13b). Compound 13b was
prepared according to the protocol of 13a using a solution of 12b
(20.4 mg, 58.1 μmol), 1-(2-methoxyphenyl)piperazine (16.8 mg,
87.2 μmol), and Na(OAc)3BH (25.7 mg, 116 μmol) in CH2Cl2
(13 mL) to give 13b as an orange-brown solid (30.4 mg, 99%
1300, 1242, 1026, 752 cm-1 1H NMR (360 MHz, CDCl3)
.
δ 1.61-1.76 (m, 8 H), 2.53 (m, 4 H), 2.73 (m, 8 H), 3.13 (m,
8 H), 3.32 (m, 4 H), 3.84 (s, 6 H), 4.26 (m, 4 H), 4.33 (m, 4 H), 4.47
(m, 4 H), 4.55 (m, 4 H), 5.58 (s, 4 H), 6.81-7.04 (m, 8 H), 7.11 (m,
2 H), 7.34-7.44 (m, 4 H), 7.49 (s, 2 H), 7.55-7.67 (m, 4 H). 13
C
yield); mp 92-94 °C. IR 2931, 2816, 1500, 1454, 1238, 1025, 748 cm-1
.
NMR (150 MHz, CDCl3,) δ 24.07, 27.57, 39.30, 50.29, 53.34,
53.83, 55.37, 58.17, 69.12, 69.83, 70.40, 70.74, 76.44, 78.72,
111.23, 118.29, 120.09, 121.02, 123.05, 127.80, 128.64, 134.02,
140.72, 141.12, 145.98, 152.27, 169.71. HPLC system C (245 nm)
purity 95% (tR=18.0 min); system D (245 nm) purity 97% (tR=
17.1 min). APCI-MS calcd m/z for C70H78Fe2N12O4: 1263.1,
found 1264 (M þ H)þ.
1H NMR (600 MHz, CDCl3,) δ 0.92 (t, 3 H, J = 6.99 Hz),
1.30-1.43 (m, 4 H), 1.94 (m, 2 H), 2.55 (m, 4 H), 3.02 (m, 4 H),
3.23 (s, 2 H), 3.83 (s, 3 H), 4.05 (m, 2 H), 4.10 (m, 2 H), 4.27 (m,
2 H), 4.35 (t, 2 H, J=7.18 Hz), 4.68 (m, 2 H), 6.81-6.84 (m, 1 H),
6.86-6.90 (m, 2 H), 6.94-6.99 (m, 1 H), 7.44 (s, 1 H). 13C NMR
(150 MHz, CDCl3,) δ 13.90, 22.12, 28.66, 30.08, 50.29, 50.38,
52.74, 55.32, 57.65, 66.98, 69.14, 69.69, 71.80, 76.01, 82.97,
111.14, 118.21, 118.58, 120.96, 122.84, 141.32, 146.10, 152.24.
HPLC system A (245 nm) purity 97% (tR=16.9 min); system D
(245 nm) purity >99% (tR=17.5 min). HR-EIMS calcd m/z for
C29H37FeN5O: 527.2348, found 527.2348.
10,100-[Decane-1,10-diylbis(1H-1,2,3-triazole-1,4-diyl)]bis-
(N-{3-[4-(2-methoxyphenyl)piperazin-1-yl]propyl}ferrocene-1-
carboxamide) (14c). Compound 14c was prepared according to
the protocol of 14a using a suspension of 9a (38 mg, 78 μmol),
1,10-diazidodecane (5.9 mg, 26 μmol), sodium ascorbate
(1.0 mg, 5.0 μmol), and copper sulfate pentahydrate (0.3 mg,
1.2 μmol) in H2O (2 mL), tBuOH (1 mL), and CH2Cl2 (1 mL).
Purification by flash chromatography (CH2Cl2:MeOH
98:2-9:1) gave 14c as an orange-brown solid (21 mg, 69%
yield); mp 61-62 °C. IR 3313, 2931, 2819, 1635, 1539, 1500,
1454, 1242, 1026, 910, 733 cm-1. 1H NMR (360 MHz, CDCl3) δ
1.20-1.41 (m, 12 H), 1.82 (m, 4 H), 1.92 (m, 4 H), 2.61 (br t, 4 H,
J=6.47 Hz), 2.76 (m, 8 H), 3.17 (m, 8 H), 3.32 (dt, 4 H, J1=6.06
Hz, J2=5.96 Hz), 3.86 (s, 6 H), 4.26 (m, 4 H), 4.30-4.37 (m, 8 H),
4.53 (m, 4 H), 4.63 (m, 4 H), 6.84-6.89 (m, 2 H), 6.90-6.98 (m, 4
H), 6.99-7.05 (m, 2 H), 7.55 (s, 2 H), 7.58 (m, 2 H). 13C NMR
(150 MHz, CDCl3) δ 25.30, 26.50, 28.93, 29.23, 30.26, 39.17,
50.34, 50.46, 53.53, 55.40, 57.45, 68.63, 69.72, 70.01, 70.85,
77.09, 78.67, 111.25, 118.23, 119.99, 121.04, 123.06, 141.11,
144.95, 152.30, 169.19. HPLC system C (245 nm) purity 96%
(tR = 18.7 min). APCI-MS calcd m/z for C64H82Fe2N12O4:
1195.1, found 1196 (M þ H)þ.
1-{[10-(1-Hexyl-1H-1,2,3-triazole-4-yl)ferrocene-1-yl]methyl}-4-(2-
methoxyphenyl)piperazine (13c). Compound 13c was prepared
according to the protocol of 13a using a solution of 12c (29.2 mg,
80.0 μmol), 1-(2-methoxyphenyl)piperazine (23.1 mg, 120 μmol),
and Na(OAc)3BH (35.5 mg, 160 μmol) in CH2Cl2 (19 mL).
Purification by flash chromatography (CH2Cl2:MeOH
98:2-95:5) gave 13c as a yellow-orange solid (32.7 mg, 75%
yield); mp 91-93 °C. IR 2931, 2816, 1500, 1454, 1238, 1026, 748 cm-1
.
1H NMR (360 MHz, CDCl3) δ 0.89 (t, 3 H, J = 7.15 Hz),
1.21-1.42 (m, 6 H), 1.93 (m, 2 H), 2.56 (m, 4 H), 3.02 (m, 4 H),
3.24 (s, 2 H), 3.83 (s, 3 H), 4.05 (m, 2 H), 4.10 (m, 2 H), 4.27
(m, 2 H), 4.35 (t, 2 H, J=7.27 Hz), 4.68 (m, 2 H), 6.80-6.84 (m, 1
H), 6.86-6.90 (m, 2 H), 6.92-7.00 (m, 1 H), 7.44 (s, 1 H).
13C NMR (150 MHz, CDCl3) δ 13.96, 22.45, 26.20, 30.34,
31.17, 50.30, 50.35, 52.70, 55.32, 57.62, 66.98, 69.14, 69.72,
71.80, 76.00, 82.82, 111.13, 118.21, 118.58, 120.96, 122.86,
141.29, 146.09, 152.23. HPLC system A (245 nm) purity 99%
(tR=18.0 min); system D (245 nm) purity >99% (tR=18.7 min).
HR-EIMS calcd m/z for C30H39FeN5O: 541.2504, found
541.2505.
10,100-[Decane-1,10-diylbis(1H-1,2,3-triazole-1,4-diyl)]bis-
(N-{4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl}ferrocene-1-
carboxamide) (14d). Compound 14d was prepared according to
the protocol of 14a using a suspension of 9b (39 mg, 78 μmol),
1,10-diazidodecane (5.9 mg, 26 μmol), sodium ascorbate
(1.0 mg, 5.0 μmol), and copper sulfate pentahydrate (0.3 mg,
1.2 μmol) in H2O (2 mL), tBuOH (1 mL), and CH2Cl2 (1 mL).
Purification by flash chromatography (CH2Cl2:MeOH 98:2-
9:1) gave 14d as an orange solid (20 mg, 61% yield); mp 63-
64 °C. IR 3332, 2931, 2819, 1635, 1539, 1500, 1454, 1242, 1026,
752 cm-1. 1H NMR (600 MHz, CDCl3) δ 1.18-1.39 (m, 12 H),
1.63-1.73 (m, 8 H), 1.92 (m, 4 H), 2.52 (m, 4 H), 2.73 (m, 8 H),
3.13 (m, 8 H), 3.33 (m, 4 H), 3.85 (s, 6 H), 4.27 (m, 4 H),
4.30-4.37 (m, 8 H), 4.45 (m, 4 H), 4.57 (m, 4 H), 6.83-6.87 (m,
2 H), 6.89-6.96 (m, 4 H), 6.97-7.02 (m, 2 H), 7.16 (m, 2 H), 7.51
(s, 2 H). 13C NMR (150 MHz, CDCl3) δ 24.15, 26.50, 27.62,
28.94, 29.24, 30.27, 39.36, 50.36, 50.39, 53.38, 55.38, 58.22,
69.15, 69.77, 70.43, 70.71, 76.68, 78.71, 111.22, 118.27, 119.92,
121.02, 123.01, 141.17, 145.38, 152.27, 169.75. HPLC system A
(245 nm) purity 96% (tR=17.2 min); system D (245 nm) purity
96% (tR=17.7 min). APCI-MS calcd m/z for C66H86Fe2N12O4:
1223.2 found 1224 (M þ H)þ.
10,100-[Biphenyl-4,40-diylbis(methylene-1H-1,2,3-triazole-1,4-
diyl)]bis(N-{3-[4-(2-methoxyphenyl)piperazin-1-yl]propyl}ferro-
cene-1-carboxamide) (14a). A suspension of 9a (36 mg, 75 μmol),
4,40-bis(azidomethyl)biphenyl (6.7 mg, 25 μmol), sodium ascor-
bate (1.0 mg, 5.0 μmol), and copper sulfate pentahydrate
(0.3 mg, 1.2 μmol) in H2O (2 mL), tBuOH (1 mL), and CH2Cl2
(1 mL) was stirred at room temperature overnight. The reaction
was quenched with saturated aqueous NaHCO3, extracted with
CH2Cl2, dried (Na2SO4), and evaporated. The residue was
purified by flash chromatography (CH2Cl2:MeOH 95:5-9:1)
to give 14a as an orange solid (27 mg, 88% yield); mp 147-
148 °C. IR 3328, 2943, 2823, 1635, 1539, 1500, 1450, 1300, 1242,
1026, 752 cm-1. 1H NMR (360 MHz, CDCl3) δ 1.80 (m, 4 H),
2.61 (br t, 4 H, J=6.58 Hz), 2.76 (m, 8 H), 3.17 (m, 8 H), 3.28 (dt,
4 H, J1=5.98 Hz, J2=5.85 Hz), 3.86 (s, 6 H), 4.25 (m, 4 H), 4.31
(m, 4 H), 4.55 (m, 4H), 4.61 (m, 4 H), 5.57 (s, 4 H), 6.84-6.89
(m, 2 H), 6.90-6.96 (m, 4 H), 6.98-7.04 (m, 2 H), 7.36-7.42
(m, 4 H), 7.51-7.62 (m, 8 H). 13C NMR (90 MHz, CDCl3) δ
25.28, 39.15, 50.44, 50.54, 53.79, 55.41, 57.43, 68.59, 69.78,

6868 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 21
Huber et al.
1,100-[Dodecane-1,12-diylbis(1H-1,2,3-triazole-1,4-diyl)]bis-
(N-{3-[4-(2-methoxyphenyl)piperazin-1-yl]propyl}ferrocene-1-
carboxamide) (14e). Compound 14e was prepared according to
the protocol of 14a using a suspension of 9a (58 mg, 0.12 mmol),
1,12-diazidododecane (9.9 mg, 39 μmol), sodium ascorbate
(1.5 mg, 7.8 μmol), and copper sulfate pentahydrate (0.5 mg,
2.0 μmol) in H2O (2 mL), tBuOH (1 mL), and CH2Cl2 (1 mL) to
give 14e as an orange solid (42 mg, 87% yield); mp 116-118 °C.
IR 3332, 2927, 1635, 1539, 1500, 1454, 1242, 1026, 752 cm-1. 1H
NMR (600 MHz, CDCl3) δ 1.21-1.40 (m, 16 H), 1.81 (m, 4 H),
1.92 (m, 4 H), 2.59 (br t, 4 H, J=6.42 Hz), 2.74 (m, 8 H), 3.16 (m, 8
H), 3.32 (dt, 4 H, J1=5.92 Hz, J2=5.76 Hz), 3.87 (s, 6 H), 4.26 (m,
4 H), 4.30-4.36 (m, 8 H), 4.53 (m, 4 H), 4.62 (m, 4 H), 6.85-6.90
(m, 2 H), 6.92-6.97 (m, 4 H), 6.99-7.04 (m, 2 H), 7.55 (s, 2 H),
7.59 (m, 2 H). 13C NMR (150 MHz, CDCl3) δ 25.37, 26.53, 28.99,
29.35, 29.41, 30.28, 39.25, 50.36, 50.56, 53.56, 55.38, 57.51, 68.63,
69.70, 70.01, 70.82, 77.09, 78.71, 111.24, 118.20, 119.98, 121.03,
123.02, 141.19, 144.93, 152.30, 169.17. HPLC system D (245 nm)
purity >99% (tR=19.2 min). APCI-MS calcd m/z for C66H86-
Fe2N12O4: 1223.2 found 1224 (M þ H)þ.
4.53 (m, 4 H), 4.66 (m, 4 H), 4.82 (m, 4 H), 7.46 (s, 2 H), 9.70 (s, 2
H). 13C NMR (150 MHz, CDCl3) δ 26.40, 28.86, 29.17, 30.19,
50.34, 67.98, 69.95, 70.97, 74.45, 77.93, 79.95, 119.42, 144.45,
193.56. HPLC system A (245 nm) purity 96% (tR=20.8 min).
APCI-MS calcd m/z for C36H40Fe2N6O2: 700.4, found 701
(M þ H)þ.
10,100-[Dodecane-1,12-diylbis(1H-1,2,3-triazole-1,4-diyl)]dife-
rrocene-1-carbaldehyde (15c). Compound 15c was prepared
according to the protocol of 15a using a suspension of 11 (31.0
mg, 130 μmol), 1,12-diazidododecane (10.9 mg, 43.2 μmol),
sodium ascorbate (1.70 mg, 8.58 μmol), and copper sulfate
t
pentahydrate (0.6 mg, 2.40 μmol) in H2O (2 mL), BuOH (1
mL), and CH2Cl2 (1 mL) to give 15c as an orange solid (30.0 mg,
95% yield); mp 112-114 °C. IR 3116, 2927, 2854 1678, 1454,
1242, 1045, 825, 744 cm-1 1H NMR (600 MHz, CDCl3) δ
.
1.20-1.40 (m, 16 H), 1.93 (m, 4 H), 4.35 (t, 4 H, J=7.37 Hz), 4.38
(m, 4 H), 4.53 (m, 4 H), 4.67 (m, 4 H), 4.83 (m, 4 H), 7.47 (s, 2 H),
9.71 (s, 2 H). 13C NMR (90 MHz, CDCl3) δ 26.46, 28.94, 29.32,
29.37, 30.23, 50.40, 68.02, 69.98, 71.00, 74.48, 77.96, 79.98,
119.43, 144.46, 193.57. APCI-MS calcd m/z for C38H44Fe2-
N6O2: 728.5 found 729 (M þ H)þ.
1,100-[Dodecane-1,12-diylbis(1H-1,2,3-triazole-1,4-diyl)]bis-
(N-{4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl}ferrocene-1-
carboxamide) (14f). Compound 14f was prepared according to
the protocol of 14a using a suspension of 9b (72.4 mg, 145 μmol),
1,12-diazidododecane (12.2 mg, 48.3 μmol), sodium ascorbate
(1.90 mg, 9.60 μmol), and copper sulfate pentahydrate (0.6 mg,
2.40 μmol) in H2O (2 mL), tBuOH (1 mL), and CH2Cl2 (1 mL) to
give 14f as an orange solid (59.9 mg, 99% yield); mp 141-143
°C. IR 3317, 2931, 1635, 1539, 1500, 1454, 1300, 1242, 1026, 752
1,10-[Biphenyl-4,40-diylbis(methylene-1H-1,2,3-triazole-1,4-
diylferrocene-1,10-diylmethylene)]bis[4-(2-methoxyphenyl)piper-
azine] (16a). A solution of 15a (20 mg, 27 μmol), 1-(2-methox-
yphenyl)piperazine (16 mg, 83 μmol), and Na(OAc)3BH (24 mg,
0.11 mmol) in anhydrous CH2Cl2 (6 mL) was stirred at room
temperature overnight. The reaction mixture was quenched with
saturated aqueous NaHCO3 and extracted with CH2Cl2. The
combined organic layers were dried (Na2SO4) and evaporated.
The residue was purified by flash chromatography (CH2Cl2:
MeOH 98:2-95:5) to give 16a as an orange solid (21.9 mg, 74%
yield); mp 238-240 °C (decomposition). IR 2925, 1591, 1498,
1450, 1240, 1024, 910, 802, 733, 663 cm-1. 1H NMR (360 MHz,
CDCl3 þ 0.5% HCOOH) δ 2.80 (m, 4 H), 3.05 (m, 4 H),
3.18-3.41 (m, 8 H), 3.64 (s, 4 H), 3.80 (s, 6 H), 4.23 (m, 8 H),
4.32 (m, 4 H), 4.73 (m, 4 H), 5.60 (s, 4 H), 6.75-6.96 (m, 6 H),
1
cm-1. H NMR (360 MHz, CDCl3) δ 1.17-1.45 (m, 16 H),
1.60-1.78 (m, 8 H), 1.92 (m, 4 H), 2.51 (m, 4 H), 2.70 (m, 8 H),
3.12 (m, 8 H), 3.34 (m, 4 H), 3.85 (s, 6 H), 4.27 (m, 4 H),
4.30-4.39 (m, 8 H), 4.45 (m, 4 H), 4.57 (m, 4 H), 6.82-7.03 (m, 8
H), 7.14 (m, 2 H), 7.51 (s, 2 H). 13C NMR (150 MHz, CDCl3) δ
24.25, 26.54, 27.66, 29.00, 29.37, 29.43, 30.29, 39.40, 50.43,
53.40, 55.37, 58.26, 69.17, 69.76, 70.45, 70.69, 76.69, 78.73,
111.21, 118.25, 119.91, 121.00, 122.97, 141.24, 145.38, 152.28,
169.75. HPLC system D (245 nm) purity 99% (tR=19.1 min).
APCI-MS calcd m/z for C68H90Fe2N12O4: 1251.2, found 1252
(M þ H)þ.
6.99-7.09 (m, 2 H), 7.37-7.47 (m, 4 H), 7.51-7.66 (m, 6 H). 13
C
NMR (150 MHz, CDCl3) δ (ppm): 49.28, 51.72, 53.77, 55.34,
56.71, 67.16, 69.35, 70.18, 72.14, 76.02, 79.77, 111.18, 118.37,
119.07, 121.01, 123.32, 127.76, 128.62, 134.33, 140.55, 140.58,
146.39, 152.15. HPLC system A (245 nm) purity 95% (tR=16.4
min). APCI-MS calcd m/z for C62H64Fe2N10O2: 1092.9, found
1094 (M þ H)þ.
1,100-[Biphenyl-4,40-diylbis(methylene-1H-1,2,3-triazole-1,4-
diyl)]diferrocene-1-carbaldehyde (15a). A suspension of 10-ethy-
nylferrocene-1-carbaldehyde (11, 58.3 mg, 245 μmol), 4,40-bis-
(azidomethyl)biphenyl (21.6 mg, 81.7 μmol), sodium ascorbate
(3.20 mg, 16.2 μmol), and copper sulfate pentahydrate (1.0 mg,
4.00 μmol) in H2O (4 mL), tBuOH (2 mL), and CH2Cl2 (2 mL)
was stirred at room temperature overnight. Afterward, the
reaction was quenched with saturated aqueous NaHCO3 and
extracted with CH2Cl2. The combined organic layers were dried
(Na2SO4) and the solvent was removed under reduced pressure.
The residue was purified by flash chromatography (CH2Cl2:
MeOH 98:2) to give 15a as a brown solid (60.2 mg, 99% yield);
mp > 200 °C (decomposition). IR 3120, 1678, 1454, 1246, 1045,
822, 760 cm-1. 1H NMR (360 MHz, C6D6/CD3CN) δ 4.20 (m, 4
H), 4.30 (m, 4 H), 4.56 (m, 4H), 4.77 (m, 4 H), 5.37 (s, 4 H),
7.26-7.32 (m, 4 H), 7.43-7.54 (m, 6 H), 9.69 (s, 2 H). 13C NMR
(90 MHz, C6D6/CD3CN) δ 53.35, 68.11, 70.10, 70.96, 74.45,
78.51, 80.72, 120.47, 135.32, 140.52, 144.99, 150.90, 170.47,
192.99. APCI-MS calcd m/z for C40H32Fe2N6O2: 740.4, found
741 (M þ H)þ.
1,10-[Decane-1,10-diylbis(1H-1,2,3-triazole-1,4-diylferrocene-
1,10-diylmethylene)]bis[4-(2-methoxyphenyl)piperazine] (16b).
Compound 16b was prepared according to the protocol of 16a
using a solution of 15b (20.3 mg, 29.0 μmol), 1-(2-methoxyphe-
nyl)piperazine (16.7 mg, 87.0 μmol), and Na(OAc)3BH (25.7
mg, 116 μmol) in CH2Cl2 (7 mL). Purification by flash chroma-
tography (CH2Cl2:MeOH 98:2) gave 16b as an orange-brown
solid (14.8 mg, 48% yield); mp 148-151 °C. IR 2931, 2819, 1500,
1
1454, 1238, 1026, 748 cm-1. H NMR (360 MHz, CDCl3) δ
1.20-1.41 (m, 12 H), 1.91 (m, 4 H), 2.56 (m, 8 H), 3.03 (m, 8 H),
3.24 (s, 4 H), 3.82 (s, 6 H), 4.05 (m, 4 H), 4.10 (m, 4 H), 4.27 (m, 4
H), 4.33 (t, 4 H, J=7.27 Hz), 4.68 (m, 4 H), 6.80-6.85 (m, 2 H),
6.86-6.92 (m, 4 H), 6.93-7.01 (m, 2 H), 7.45 (s, 2 H). 13C NMR
(150 MHz, CDCl3) δ 26.47, 28.91, 29.23, 30.33, 50.26, 50.31,
52.68, 55.33, 57.61, 66.99, 69.17, 69.76, 71.82, 76.02, 82.70,
111.15, 118.21, 118.62, 120.97, 122.89, 141.25, 146.07, 152.23.
HPLC system A (245 nm) purity 96% (tR=17.0 min). APCI-MS
calcd m/z for C58H72Fe2N10O2: 1053.0, found 1054 (M þ H)þ.
1,10-[Dodecane-1,12-diylbis(1H-1,2,3-triazole-1,4-diylferro-
cene-1,10-diylmethylene)]bis[4-(2-methoxyphenyl)piperazine] (16c).
Compound 16c was prepared according to the protocol of 16a
using a solution of 15c (23.4 mg, 32.1 μmol), 1-(2-methoxyphe-
nyl)piperazine (18.5 mg, 96.3 μmol), and Na(OAc)3BH (28.4
mg, 128 μmol) in CH2Cl2 (7 mL) to give 16c as a yellow-orange
oil (29.4 mg, 84% yield). IR 2927, 2854, 1593, 1500, 1454, 1242,
1026, 752 cm-1. 1H NMR (360 MHz, CDCl3 þ 0.5% HCOOH)
δ 1.18-1.40 (m, 16 H), 1.93 (m, 4 H), 3.03 (m, 8 H), 3.22 (m, 8 H),
1,100-[Decane-1,10-diylbis(1H-1,2,3-triazole-1,4-diyl)]diferro-
cene-1-carbaldehyde (15b). Compound 15b was prepared ac-
cording to the protocol of 15a using a suspension of 11 (45.2 mg,
190 μmol), 1,10-diazidodecane (14.2 mg, 63.3 μmol), sodium
ascorbate (2.50 mg, 12.6 μmol), and copper sulfate pentahydrate
(0.8 mg, 3.20 μmol) in H2O (2 mL), tBuOH (1 mL), and CH2Cl2
(1 mL) to give 15b as an orange-brown solid (43.5 mg, 98%
yield); mp 153-156 °C. IR 3116, 2924, 2854 1678, 1454, 1246,
1038, 822, 744 cm-1. 1H NMR (360 MHz, CDCl3) δ 1.20-1.42
(m, 12 H), 1.93 (m, 4 H), 4.35 (t, 4 H J=7.27 Hz), 4.38 (m, 4 H),

Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 21 6869
3.67 (s, 4 H), 3.82 (s, 6 H), 4.20 (m, 4 H), 4.24 (m, 4 H), 4.32 (m, 4
H), 4.33 (t, 4 H, J=7.38 Hz), 4.75 (m, 4 H), 6.81-6.96 (m, 6 H),
6.98-7.06 (m, 2 H), 7.59 (s, 2 H). 13C NMR (150 MHz, CDCl3 þ
0.5% HCOOH) δ 26.51, 28.98, 29.36, 29.42, 30.32, 47.81, 50.42,
50.56, 55.40, 55.66, 67.34, 69.51, 70.97, 72.47, 75.32, 76.76,
111.24, 118.66, 119.52, 121.14, 124.03, 139.43, 145.07, 152.03.
HPLC system A (245 nm) purity 97% (tR=17.8 min). APCI-MS
calcd m/z for C60H76Fe2N10O2: 1081.0, found 1082 (M þ H)þ.
Dopamine Receptor Binding Studies. Receptor binding studies
were carried out as described.31 In brief, the dopamine D1
receptor assay was done with porcine striatal membranes at a
final protein concentration of 40 μg/assay tube and the radi-
Selective Dopamine D3 Receptor Antagonists and Partial Ago-
nists. J. Med. Chem. 2002, 45, 4594–4597.
(5) Newman, A. H.; Grundt, P.; Nader, M. A. Dopamine D3 Receptor
Partial Agonists and Antagonists as Potential Drug Abuse Ther-
apeutic Agents. J. Med. Chem. 2005, 48, 3663–3679.
(6) Schlotter, K.; Boeckler, F.; Hubner, H.; Gmeiner, P. Fancy
Bioisosters: Metallocene-Derived G-Protein-Coupled Receptor
Ligands with Subnanomolar Binding Affinity and Novel Selectiv-
ity Profiles. J. Med. Chem. 2005, 48, 3696–3699.
(7) Boeckler, F.; Gmeiner, P. Dopamine D3 receptor ligands;recent
advances in the control of subtype selectivity and intrinsic activity.
Biochim. Biophys. Acta 2007, 1768, 871–887.
(8) Leopoldo, M.; Berardi, F.; Colabufo, N. A.; De Giorgio, P.;
Lacivita, E.; Perrone, R.; Tortorella, V. Structure-Affinity Rela-
tionship Study on N-[4-(4-Arylpiperazin-1-yl)butyl]arylcarboxa-
mides as Potent and Selective Dopamine D3 Receptor Ligands.
J. Med. Chem. 2002, 45, 5727–5735.
(9) Hackling, A.; Ghosh, R.; Perachon, S.; Mann, A.; Holtje, H.-D.;
Wermuth, C. G.; Schwartz, J.-C.; Sippl, W.; Sokoloff, P.; Stark, H.
N-(ω-(4-(2-Methoxyphenyl)piperazin-1-yl)alkyl)carboxamides as
Dopamine D2 and D3 Receptor Ligands. J. Med. Chem. 2003,
46, 3883–3899.
(10) Murray, P. J.; Harrison, L. A.; Johnson, M. R.; Robertson, G. M.;
Scopes, D. I. C.; Bull, D. R.; Graham, E. A.; Hayes, A. G.;
Kilpatrick, G. J.; Daas, I. D.; Large, C.; Sheehan, M. J.; Stubbs,
C. M.; Turpin, M. P. A novel series of arylpiperazines with high
affinity and selectivity for the dopamine D3 receptor. Biorg. Med.
Chem. Lett. 1995, 5, 219–222.
(11) Boeckler, F.; Gmeiner, P. The Structural Evolution of Dopamine
D3 Receptor Ligands;Structure-Activity Relationships and Se-
lected Neuropharmacological Aspects. Pharmacol. Ther. 2006,
112, 281–333.
oligand [3H]SCH 23390 at 0.3 nM (Kd = 0.41-0.58 nM).
28
Competition experiments with human D2long, D2short
,
D3,29
and D4.430 receptors were run with preparations of membranes
from CHO cells stably expressing the corresponding receptor
and [3H]spiperone at a final concentration of 0.1-0.2 nM. The
assays were carried out at a protein concentration of 5-20 μg/
assay tube and Kd values of 0.07-0.15, 0.05-0.13, 0.11-0.19,
and 0.17-0.35 nM for the D2long, D2short, D3, and D4.4
receptors, respectively. Protein concentration was established
by the method of Lowry using bovine serum albumin as
standard.37
Data Analysis. The resulting competition curves of the re-
ceptor binding experiments were analyzed by nonlinear regres-
sion using the algorithms in PRISM 3.0 (GraphPad Software,
San Diego, CA). The data were initially fit using a sigmoid
model to provide an IC50 value, representing the concentration
corresponding to 50% of maximal inhibition. IC50 values were
transformed to Ki values according to the equation of Cheng
and Prusoff.38 In the fact of two individual measurements Ki
was calculated as mean value in nM with the standard deviation
(SD), while analyzing more than two single values the stand-
ard error of mean (SEM) was calculated as manner of con-
fidence.
Mitogenesis Experiments. Determination of the intrinsic ac-
tivity of the representative compound was carried out by
measuring the incorporation of [3H]thymidine into growing
cells after stimulation with the test compound as described in
the literature.4,36 For this assay, D3 expressing CHO dhfr- cells
as well as D2long and D4.2 expressing CHO100001 cells have
been incubated with 0.02 μCi [3H]thymidine per well (specific
activity 25 μCi/mmol). Dose-response curves of 6-10 experi-
ments have been normalized and pooled to get a mean curve
from which the EC50 value and the maximum intrinsic activity of
each compound could be compared to the effects of the full
agonist quinpirole.
(12) Ehrlich, K.; Gotz, A.; Bollinger, S.; Tschammer, N.; Bettinetti, L.;
Harterich, S.; Hubner, H.; Lanig, H.; Gmeiner, P. Dopamine D2,
D3, and D4 Selective Phenylpiperazines as Molecular Probes To
Explore the Origins of Subtype Specific Receptor Binding. J. Med.
Chem. 2009, 52, 4923–4935.
ꢀ
(13) Badeche, S.; Daran, J.-C.; Ruiz, J.; Astruc, D. Synthesis and
Coordination Chemistry of Ferrocenyl-1,2,3-triazolyl Ligands.
Inorg. Chem. 2008, 47, 4903–4908.
(14) Koster, S. D.; Dittrich, J.; Gasser, G.; Husken, N.; Henao Cas-
~
ꢁ
taneda, I. C.; Jios, J. L.; Della Vedova, C. O.; Metzler-Nolte, N.
Spectroscopic and Electrochemical Studies of Ferrocenyl Triazole
Amino Acid and Peptide Bioconjugates Synthesized by Click
Chemistry. Organometallics 2008, 27, 6326–6332.
(15) Siemeling, U.; Rother, D. Evaluation of heterocumulenic ferrocene
derivatives for ‘‘click” chemistry type reactions. J. Organomet.
Chem. 2009, 694, 1055–1058.
(16) Schottenberger, H.; Lukassser, J.; Reichel, E.; Muller, A. G.;
Steiner, G.; Kopacka, H.; Wurst, K.; Ongania, K. H.; Kirchner,
K. Semimasked 1,10-diethynylferrocenes: synthetic concepts, pre-
parations and reactions. J. Organomet. Chem. 2001, 637-639, 558–
576.
ꢂ ꢁ
ꢁ
ꢁ
(17) Barisic, L.; Rapic, C.; Pritzkow, H.; Pavlovic, G.; Nemet, I.
Ferrocene compounds. Part XXXIII. Synthesis and characteriza-
tion of amino acids containing skeletal 1,10-ferrocenylene unit. J.
Organomet. Chem. 2003, 682, 131–142.
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft (DFG: Gm 13/8).
(18) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. A
Stepwise Huisgen Cycloaddition Process: Copper(I)-Catalyzed
Regioselective “Ligation” of Azides and Terminal Alkynes. Angew.
Chem., Int. Ed. 2002, 41, 2596–2599.
(19) Alvarez, S. G.; Alvarez, M. T. A Practical Procedure for the
Synthesis of Alkyl Azides at Ambient Temperature in Dimethyl
Sulfoxide in High Purity and Yield. Synthesis 1997, 413.
(20) Lieber, E.; Chao, T. S.; Ramachandra Rao, C. N. Improved
Method for the Synthesis of Alkyl Azides. J. Org. Chem. 1957,
22, 238–240.
(21) Lober, S.; Hubner, H.; Utz, W.; Gmeiner, P. Rationally Based
Efficacy Tuning of Selective Dopamine D4 Receptor Ligands
Leading to the Complete Antagonist 2-[4-(4-Chlorophe-
nyl)piperazin-1-ylmethyl]pyrazolo[1,5-a]pyridine (FAUC 213). J.
Med. Chem. 2001, 44, 2691–2694.
(22) Tietze, R.; Lober, S.; Hubner, H.; Gmeiner, P.; Kuwerta, T.;
Prante, O. Discovery of a dopamine D4 selective PET ligand
candidate taking advantage of a click chemistry based REM linker.
Bioorg. Med. Chem. Lett. 2008, 18, 983–988.
Supporting Information Available: Synthesis of compounds
17-20, analytical data (1H NMR, 13C NMR, LC-MS, or HPLC
spectra), receptor binding data employing porcine 5-HT1A, 5-
HT2, and R1 receptors of all target compounds and further
mitogenesis experiments with 10b at D2long, and reference
agents. This material is available free of charge via the Internet
at http://pubs.acs.org.
References
(1) Chen, X.; Wang, W. The use of bioisosteric groups in lead
optimization. Annu. Rep. Med. Chem. 2003, 38, 333–346.
(2) Biot, C.; Glorian, G.; Maciejewski, L. A.; Brocard, J. S. Synthe-
sis and Antimalarial Activity in Vitro and in Vivo of a New
Ferrocene-Chloroquine Analogue. J. Med. Chem. 1997, 40,
3715–3718.
(3) Dubar, F.; Khalife, J.; Brocard, J.; Dive, D.; Biot, C. Ferroquine,
an Ingenious Antimalarial Drug;Thoughts on the Mechanism of
Action. Molecules 2008, 13, 2900–2907.
(23) Enguehard-Gueiffier, C.; Hubner, H.; El Hakmaoui, A.; Allouchi,
H.; Gmeiner, P.; Argiolas, A.; Melis, M. R.; Gueiffier, A. 2-[(4-
Phenylpiperazin-1-yl)methyl]imidazo(di)azines as Selective D4-Li-
gands. Induction of Penile Erection by 2-[4-(2-Methoxyphe-
nyl)piperazin-1-ylmethyl]imidazo[1,2-a]pyridine (PIP3EA), a Potent
and Selective D4 Partial Agonist. J. Med. Chem. 2006, 49, 3938–3947.
(4) Bettinetti, L.; Schlotter, K.; Hubner, H.; Gmeiner, P. Interactive
SAR Studies: Rational Discovery of Super-Potent and Highly

6870 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 21
Huber et al.
(24) Weiss, S.; Keller, M.; Bernhardt, G.; Buschauer, A.; Konig, B.
Modular synthesis of non-peptidic bivalent NPY Y1 receptor
antagonists. Bioorg. Med. Chem. 2008, 16, 9858–9866.
(25) Zheng, Y.; Akgun, E.; Harikumar, K. G.; Hopson, J.; Powers, M.
D.; Lunzer, M. M.; Miller, L. J.; Portoghese, P. S. Induced
Association of μ Opioid (MOP) and Type 2 Cholecystokinin
(CCK2) Receptors by Novel Bivalent Ligands. J. Med. Chem.
2009, 52, 247–258.
(26) Thomas, J. R.; Liu, X.; Hergenrother, P. J. Size-Specific Ligands for
RNA Hairpin Loops. J. Am. Chem. Soc. 2005, 127, 12434–12435.
(27) Wilcox, R. E.; Huang, W. H.; Brusniak, M. Y.; Wilcox, D. M.;
Pearlman, R. S.; Teeter, M.; DuRand, C. J.; Wiens, B. L.; Neve, K.
A. CoMFA-based prediction of agonist affinities at recombinant
wild type versus serine to alanine point mutated D2 dopamine
receptors. J. Med. Chem. 2000, 43, 3005–3019.
(28) Hayes, G.; Biden, T. J.; Selbie, L. A.; Shine, J. Structural subtypes
of the dopamine D2 receptor are functionally distinct: expression
of the cloned D2A and D2B subtypes in a heterologous cell line.
Mol. Endocrinol. 1992, 6, 920–926.
(29) Sokoloff, P.; Andrieux, M.; Besanc-on, R.; Pilon, C.; Martres, M.-
P.; Giros, B.; Schwartz, J.-C. Pharmacology of human dopamine
D3 receptor expressed in a mammalian cell line: comparison with
D2 receptor. Eur. J. Pharmacol. 1992, 225, 331–337.
(30) Asghari, V.; Sanyal, S.; Buchwaldt, S.; Paterson, A.; Jovanovic, V.;
Van Tol, H. H. M. Modulation of intracellular cyclic AMP levels
by different human dopamine D4 receptor variants. J. Neurochem.
1995, 65, 1157–1165.
experiments, and computational studies of novel dopamine recep-
tor agonists recognizing preferentially the D3 subtype. J. Med.
Chem. 2000, 43, 756–762.
(32) Pilla, M.; Perachon, S.; Sautel, F.; Garrido, F.; Mann, A.; Wer-
muth, C. G.; Schwartz, J.-C.; Everitt, B. J.; Sokoloff, P. Selective
inhibition of cocaine-seeking behaviour by a partial dopamine D3
receptor agonist. Nature 1999, 400, 371–375.
(33) George, S. R.; O’Dowd, B. F.; Lee, S. P. G-protein-coupled
receptor oligomerization and its potential for drug discovery.
Nat. Rev. Drug Discovery 2002, 1, 808–820.
(34) Han, Y.; Moreira, I. S.; Urizar, E.; Weinstein, H.; Javitch, J. A.
Allosteric communication between protomers of dopamine class A
GPCR dimers modulates activation. Nat. Chem. Biol. 2009, 5, 688–
695.
(35) Mierau, J.; Schneider, F. J.; Ensinger, H. A.; Chio, C. L.; Lajiness,
M. E.; Huff, R. M. Pramipexole binding and activation of cloned
and expressed dopamine D2, D3 and D4 receptors. Eur. J. Phar-
macol. 1995, 290, 29–36.
(36) Hubner, H.; Kraxner, J.; Gmeiner, P. Cyanoindole derivatives as
highly selective dopamine D4 receptor partial agonists: solid-phase
synthesis, binding assays, and functional experiments. J. Med.
Chem. 2000, 43, 4563–4569.
(37) Lowry, O. H.; Rosebrough, N. J.; Farr, A. L.; Randall, R. J.
Protein measurement with the Folin phenol reagent. J. Biol. Chem.
1951, 193, 265–275.
(38) Cheng, Y.; Prusoff, W. H. Relationship between the inhibition
constant (Ki) and the concentration of inhibitor which causes 50%
inhibition (I50) of an enzymatic reaction. Biochem. Pharmacol.
1973, 22, 3099–3108.
(31) Hubner, H.; Haubmann, C.; Utz, W.; Gmeiner, P. Conjugated
enynes as nonaromatic catechol bioisosteres: synthesis, binding