Fancy bioisosteres: Synthesis and dopaminergic properties of the endiyne FAUC 88 as a novel non-aromatic D3 agonist

Article abstract of DOI:10.1016/j.bmc.2004.09.044

Enlargement of the π-electronic system of the non-aromatic D3 agonist FAUC 73 led to dopaminergic endiynes of type 1 being synthesized via the bromovinyl triflate 7a as a key intermediate when palladium catalyzed coupling reactions were exploited for the

Full text of DOI:10.1016/j.bmc.2004.09.044

Bioorganic & Medicinal Chemistry 13 (2005) 185–191
Fancy bioisosteres: synthesis and dopaminergic properties of the
endiyne FAUC 88 as a novel non-aromatic D3 agonist
Carola Lenz, Christian Haubmann, Harald Hubner, Frank Boeckler and Peter Gmeiner*
¨
Department of Medicinal Chemistry, Emil Fischer Center, Friedrich Alexander University, Schuhstraße 19,
D-91052 Erlangen, Germany
Received 4 May 2004; accepted 24 September 2004
Abstract—Enlargement of the p-electronic system of the non-aromatic D3 agonist FAUC 73 led to dopaminergic endiynes of type 1
being synthesized via the bromovinyl triflate 7a as a key intermediate when palladium catalyzed coupling reactions were exploited
for the introduction of the (aza)alkyne substituents. As the first neuroreceptor active endiyne, FAUC 88 (1c) displayed high and
selective dopamine D3 receptor affinity (Ki high = 3.2nM) and substantial ligand efficacy (72%, EC50 = 2.5nM). Similarities between
molecular electrostatic potentials induced by the catechol subunit of the genuine neurotransmitter and those of its non-aromatic
endiyne bioisostere are discussed.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
In order to investigate scope and limitations of these
fancy aryl bioisostere and to develop a D3 selective anti-
psychotic drug candidate, we regarded further lead
structure modifications as a highly interesting project.
Our main focus lay on the enlargement of the p-elec-
tronic system in order to mimic the aromatic shape more
closely. For this reason we envisioned to introduce a fur-
ther conjugated triple bond leading to conjugated
(aza)endiynes of type 1.5
Bioisosteric replacement of benzene derived structural
moieties by heteroarenes has proven to be a valuable
methodology in drug discovery providing access to drug
candidates with excellent pharmacodynamic or pharma-
cokinetic properties.1 As an extension of this means, we
recently disclosed that 2,2-dicyanovinyl as a non-aro-
matic p-substituent as well as [2.2]paracyclophanes can
serve as competitive aryl bioisosteres.2,3 Moreover, we
could show that a conjugated enyne system can simulate
the catechol moiety of dopamine exerting agonist effects
and D3 subtype selectivity. Thus, the dopaminergic
FAUC 73 was evaluated as the first non-aromatic bio-
genic amine surrogate activating type 1 GPCRs.4
2. Results and discussion
To build up the endiyne moiety, we intended to use a
cyclohexenediyl-1,2-bis-triflate of type 4 as a central
intermediate (Scheme 1). Aside from aryl bis-triflates,
this structural element was only known in diarylvinyl-
enes.6,7 We planned to synthesize the functionalized
cyclohexene precursor via a Ru¨hlmann-type acyloin con-
densation.8 To find suitable conditions for the reaction
sequence, we started first from the commercially availa-
ble dimethyl adipate (2a) as a representative model
building block, which was reacted with disperse sodium
in the presence of chlorotrimethylsilane to furnish 3a in
82% yield. Subsequent removal of the trimethylsilyl
groups followed by sulfonylation turned out to be diffi-
cult when fluoride induced desilylation and subsequent
reaction with trifluoromethanesulfonic anhydride5 or
N-phenyltrifluoromethane sulfonimide did not result in
NH2
NPr2
NPr2
X
HO
OH
H
R
dopamine
FAUC 73
1
*
Corresponding author. Tel.: +49 (9131) 8529383; fax: +49 (9131)
8522585; e-mail: gmeiner@pharmazie.uni-erlangen.de
0968-0896/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.09.044

186
R1
C. Lenz et al. / Bioorg. Med. Chem. 13 (2005) 185–191
R1
approached. Thus, Pd-catalyzed cross-coupling of the
bromoenyne 8 with CuCN12 led to the cyano substituted
enyne 1b that was transformed into the final product 1a
by fluoride induced desilylation.
CO2CH3
b
a
R1=H
OSi(CH3)3
CO2CH3
OSO2CF3
OSO2CF3
OSi(CH3)3
2a: R1 = H
3a: R1 = H
Receptor binding experiments were established to evalu-
ate the binding properties of the target compounds 1a–d
and the intermediate 8 in comparison to the references
FAUC 73 and dopamine (Table 1). D1 receptor affini-
ties were determined utilizing porcine striatal mem-
branes and the D1 selective radioligand [3H]SCH
23390. D2, D3 and D4 affinities were investigated
employing the cloned human dopamine receptors
D2long, D2short,13 D314 and D4.415 stably expressed
in Chinese hamster ovary cells (CHO) and the radiolig-
and [3H]spiperone. The competition data were analyzed
according to a sigmoid model by non-linear regression.
If the dose–response curves showed biphasic properties
and the calculated Hill coefficients (nH) were between
À0.50 and À0.75 with a better fit of equation indicating
a two-site model and if the amount of calculated high
affinity binding sites was greater than 15% of the total
receptor population, Ki values for the high and low
affinity binding sites of the receptor were derived. The
Ki high values representing the ternary complex of ligand,
4
2b: R1 = NPr2
3b: R1 = NPr2
c
R2
R2
5a: R2 = Si(CH3)3
5b: R2 = Ph
Scheme 1. Reagents and conditions: (a) Na, chlorotrimethylsilane,
toluene, for 2a: rf, 1.5h, 82%; for 2b: rt, 5h, rf, 30min, 61%; (b) (1)
MeLi, DME, À60ꢁC to À20ꢁC, 2h; (2) Tf2O, À78ꢁC to 10ꢁC, 15h,
15%; (c) trimethylsilylacetylene for 5a, phenylacetylene for 5b,
Pd(PPh3)4, CuI, EtMe2N, THF, rt, for 5a: 3h, 50%; for 5b: 10h, 65%.
formation of the vicinal bistriflate 4. However, one-pot
desilylation with MeLi and reaction with trifluorometh-
anesulfonic anhydride furnished the desired bistriflate 4.
Transition-metal catalyzed cross-coupling reactions
employing trimethylsilylacetylene or phenylacetylene in
the presence of Pd(PPh3)4, CuI and EtMe2N9,10 led to
formation of the endiynes 5a,b in 50–65% yield, respec-
tively. Unfortunately, we could not successfully apply
this methodology for the synthesis of our target com-
pounds of type 1 since the silyl sulfonyl exchange reac-
tion of the dipropylamine substituted intermediate 3b,
being readily available from the aminoadipate 2b, led
to complete decomposition when we added MeLi and
trifluoromethanesulfonic anhydride.
NPr2
NPr2
NPr2
NPr2
a
b
+
Br
Br
Br
O
O
OSO2CF3
OSO2CF3
6
7a
7b
c or d
NPr2
NPr2
NPr2
f
e
To develop an alternative synthetic pathway, we decided
to utilize a 2-bromo substituted vinyltriflate11 as a cen-
tral intermediate that should be available from the
respective a-bromoketone. Bromination of the 4-dipro-
pylaminocyclohexanone4 by deprotonation with LDA
and subsequent reaction with dibromotetrachloroethane
furnished the a-bromoketone 6 in 66% yield (Scheme 2).
Further deprotonation with LiHMDS and sulfonylation
by 2-[N,N-bis-(trifluoromethylsulfonyl)-amino]-5-chlor-
opyridine afforded the bromovinyltriflate 7a in 36%
yield besides 15% of the regioisomer 7b being separated
by flash chromatography. It is interesting to note that
both reactive positions could be reacted consecutively.
Thus, treatment of the key intermediate 7a with trimeth-
ylsilylacetylene in the presence of Pd(PPh3)4, CuI and
piperidine at 40ꢁC resulted in monosubstitution of the
triflate group affording bromoenyne 8 in 67% yield, be-
sides 7% of the endiyne 1d. On the other hand, treatment
of the bromovinyltriflate 7a at 95ꢁC with the same mix-
ture of reagents afforded the endiyne 1d as the main
product. Cleavage of the trimethylsilyl groups with
Bu4NF led to the terminal endiyne 1c. To investigate
the biological effect of the introduction of a nitrogen
atom into the pharmacophore, the aza-analog 1a was
Br
N
N
H
Si(CH3)3
Si(CH3)3
1a
1b
8
+
NPr2
NPr2
g
H
Si(CH3)3
H
Si(CH3)3
1c
1d
Scheme 2. Reagents and conditions: (a) (1) LDA, THF, À78ꢁC, 1h;
(2) dibromotetrachloroethane, THF, À90ꢁC, 30min, 66%; (b): (1)
LiHMDS, THF, À78ꢁC, 1.75h; (2) 2-[N,N-bis-(trifluoromethylsulfon-
yl)amino]-5-chloropyridine, THF, À78ꢁC to À20ꢁC, 2.25h, rt, 1h,
36% 7a, 15% 7b; (c) trimethylsilylacetylene, Pd(PPh3)4, CuI, piperidine,
THF, 40ꢁC, 3.5h, 67% 8; 7% 1d; (d) trimethylsilylacetylene, Pd(PPh3)4,
CuI, piperidine, THF, 95ꢁC, 1h, 24% 8, 42% 1d; (e) CuCN, Pd2(dba)3,
dppf, dioxane, reflux, 2.75h, 54%; (f) Bu 4NF, THF, À20ꢁC, 45min,
60%; (g) Bu4NF, THF, À20ꢁC, 20min, 82%.

C. Lenz et al. / Bioorg. Med. Chem. 13 (2005) 185–191
187
Table 1. Receptor binding data for 1a–d, 8, FAUC 73 and dopamine employing porcine D1 as well as human D2long, D2short, D3 and D4.4
receptorsa
Compound
Ki values (nM)
[3H]spiperone
[3H]SCH23390
pD1
hD2long
hD2short
hD3
hD4.4
8
19,000
21,000
21,000
4400
520 + 18,000b
49 + 9700b
42 + 5300b
5200
94 + 10000b
270 + 14,000b
20 + 1900
260 + 8800b
96 + 13,000b
72 + 6500b
8600
54 + 2600b
250 + 12,000b
17 + 1100
110 + 1200b
38 + 950b
26 + 910b
23 + 720b
3.2 + 49b
5.2 + 590b
50 + 1600
3100
120 + 5500b
77 + 5600b
3600
6.3 + 420b
22 + 380b
1.2 + 62
1b (R = TMS, X = N)
1a (R = H, X = N)
1d (R = TMS, X = CH)
1c (R = H, X = CH)
FAUC 73
12,000
49,000
7.0 + 650
Dopamine
a Ki values are the means of two to six experiments each done in triplicate.
b Ki high and Ki low values derived from a biphasic curve, if data analysis fits better with the equations for a two-site binding mode.
receptor and G-protein thus indicating agonist proper-
ties were chosen for the comparison of agonist affinities.
Table 2. Ki values [nM] of 1c and FAUC 73 for the porcine 5-HT1A
and 5-HT2 receptora
Compound
5-HT1A
5-HT2
After a D1 binding assay, indicating only weak affinities
of the non-aromatic test compounds, our initial SAR
investigations were directed to a comparison of the
4-trimethylsilylethynyl substituted cyclohexenylamines
involving the 3-bromo, 3-cyano and 3-trimethylsilyl-
ethynyl derivatives 8, 1b and 1d. In fact, substantial
binding affinities were determined for the D3 subtype
leading to Ki values between 23 and 110nM. Strong
subtype selectivity over D2long, D2short and D4 was
observed, especially for the bis-trimethylsilyl protected
endiyne 1d combining high D3 affinity (Ki = 23nM)
and selectivity ratios greater 150. At least for the D3
subtype, the binding data corroborate earlier observa-
tions that an H-bond donor activity of the terminal
sp-hybridized CH proton is not essential for the receptor
recognition.4,16 However, desilylation led to a significant
increase of affinity when the terminal alkyne 1c and its
aza-analog 1a revealed Ki values of 3.2 and 26nM,
respectively, at the D3 receptor. Whereas deprotection
of the nitrile 1b caused a similar increase of binding
for all subtypes of the D2 family, the bis-desilylation
of the endiyne 1d had much higher influence onto the
D2long, D2short and D4 affinity. In detail, a 55-, 160-
and 570-fold increase of affinities was observed for the
D2long, D2short and D4 subtypes whereas the Ki values
for the D3 subtype improved only by a factor of 7. Nev-
ertheless, the cis-hexendiyne functionality of the test
compound 1c (FAUC 88) was superior to the butenyne
moiety of the lead compound FAUC 73 and, thus,
proved to be the most potent non-aromatic dopamine
[3H]8-OH-DPAT
[3H]ketanserin
1c
FAUC 73
150
1000
3100
9000
a Ki values are the means of two to four experiments each done in
triplicate.
receptor ligand investigated, yet. In order to further
characterize the binding properties of FAUC 88 (1c)
and the reference agent FAUC 73, 5-HT1A and 5-
HT2 receptor recognition was evaluated (Table 2).
Employing porcine brain homogenates and the radiolig-
ands [3H]8-OH-DPAT and [3H]ketanserin, respectively,
the resulting Ki values indicated only moderate 5-
HT1A (150–1000nM) and 5-HT2 affinities (3100–
9000nM).
To investigate the intrinsic effects of FAUC 88 (1c) com-
pared to the lead compound FAUC 73 and the full
agonist quinpirole, a mitogenesis assay was performed
employing CHO 10001 cells stably expressing human
D2long, D2short and D4.2 receptors as well as D3
expressing CHO dhfrÀ cells.19 Agonist activation of
dopamine receptors can be determined by measuring
the rate of [3H]thymidine incorporation into growing
heterologously transfected cell lines.20 Intrinsic activities
and EC50 values are depicted in Table 3 clearly indicat-
ing substantial ligand efficacy for all subtypes investi-
gated and significant D3 preference. In consistence to
Table 3. Intrinsic activity of 1c, FAUC 73 and the reference quinpirole at the D2long, D2short, D3 and D4.4 receptor determined by measuring the
stimulation of mitogenesisa
Compound
D2long
D2short
D3
D4.2
Effc
EC50
Effc
EC50
Effc
EC50
Effc
b
b
b
b
EC50
1c
FAUC 73
quinpirole
4.2
6.5
2.4
87
85
12
25
12
86
76
3.2
4.4
2.7
72
74
180
280
14
60
67
100
100
100
100
a Incorporation of [3H]thymidine in CHO10001 cells expressing the rat D2long, D2short and the human D4.2 receptor or in CHO dhfrÀ cells
expressing the human D3 receptor.
b EC50 values in [nM] derived from the mean curves of 6–11 experiments each done in quadruplicate.
c Ligand efficacy in [%] compared to the full agonist qunipirole.

188
C. Lenz et al. / Bioorg. Med. Chem. 13 (2005) 185–191
the Ki high values of the binding experiments, the EC50
data of the endiyne FAUC 88 (1c) indicated a superior
activity profile compared to the enyne FAUC 73.
for the receptor recognition of the novel bioisostere
are currently in progress.
In order to understand the molecular necessities for the
receptor recognition of dopamine receptor agonists,
we investigated the molecular electrostatic potentials
(MEPs) of the catechol moiety (A) of dopamine and
the cis-hexene-1,5-diyne fragment (B) of the non-
aromatic agonist FAUC 88 (1c) both being calculated
quantum chemically. In detail, the pharmacophoric ele-
ments A and B were pre-optimized with B3LYP/3-21G
and subsequently optimized with B3LYP/6-311G(d).
3. Experimental
Reactions were performed under dry N2. Solvents were
purified and dried under standard procedures. All rea-
gents were of commercial quality and used as purchased.
Flash chromatography was carried out with silica gel 60
(4.0–6.3lm) eluting with appropriate solution in the sta-
1
ted v:v proportions. H and 13C NMR spectra were ob-
tained in CDCl3 on Bruker AM 360 (360MHz) and
Bruker AC 250 (90MHz) spectrometers, respectively.
MS and HRMS were run on Finnigan MAT TSQ 70
and 8200 spectrometers, respectively, by EI (70eV). IR
The charges used to contour the MEPs were calculated
on the resulting structures applying BrenemanÕs
CHelpG charge distribution scheme. The negative iso-
potential surfaces were contoured with MOLCAD
implemented in Sybyl 6.9.118 at À1.0kcal/mol. Interest-
ingly, shape and size of the MEP of the catechol unit (A)
in dopamine revealed strong similarity to the respective
isopotentials of the non-aromatic bioisostere (B) (Fig.
1). Obviously the endiyne B efficiently mimics the aro-
matic moiety of dopamine. According to the receptor
binding profile of FAUC 88, the non-covalent inter-
molecular p-interactions19 will best stabilize the protein–
ligand association at the dopamine D3 receptor binding
site crevice.
spectra were recorded on
spectrometer.
a
Jasco FT/IR 410
3.1. [Cyclohexene-1,2-diyl-bisoxy]-bis(trimethylsilane)
(3a)
Sodium (4.06g, 175mmol) was stirred vigorously in
refluxing toluene (100mL) until sodium sand was
obtained. After being cooled to room temperature,
chlorotrimethylsilane (22.7mL, 179mmol) and dimethyl
adipate (2a) (7.29mL, 44mmol) were added to the mix-
ture. After being refluxed for 1.5h, the mixture was fil-
trated immediately and evaporated. The residue was
purified by flash chromatography (petroleum ether–
CH2Cl2 6:4) to give 3a as a colourless liquid (9.33g,
82%): IR (film) 2956, 2841, 1694, 1446, 1265, 1213,
In conclusion, we were able to demonstrate that the p-
electronic system of the non-aromatic endiyne FAUC
88 can be used as an efficient bioisostere for the catechol
fragment of dopamine. Combined with conformational
rigidization, the approach led to dopamine receptor
agonists with high affinity for the subtypes of the D2-
family, especially for D3. Further investigations giving
mechanistic insights into the p-interactions responsible
1122, 951cmÀ1; H NMR d 0.00 (s, 18H, 2·Si(CH3)3),
1.40–1.44 (m, 4H, 4-H, 5-H), 1.88–1.90 (m, 4H, 3-H,
6-H); EIMS 258 (M+).
1
3.2. Dipropyl-[3,4-bis(trimethylsilyloxy)cyclohex-3-en-1-
yl]amine (3b)
(a) After treatment of sodium (1.22g, 53mmol), having
reacted in MeOH (300mL) at 0ꢁC, with a solution of
dipropylamine (200mL) and dimethyl trans-3-hexene-
dioate (52.8g, 307mmol) in MeOH (100mL), the mix-
ture was being stirred at room temperature for 15h
and evaporated. HCl (2N) was added to the residue
at 0ꢁC and the mixture was extracted with Et2O. The
aqueous layer was then alkalized with 2N NaOH and
extracted with Et2O. The organic layer was dried
(MgSO4) and evaporated and the residue was purified
by flash chromatography (petroleum ether–EtOAc 8:2)
to give 2b as a colourless oil (5.84g, 7%); (b) Sodium
(703mg, 30.5mmol) was stirred vigorously in refluxing
toluene (50mL) until sodium sand was obtained. After
being cooled to room temperature chlorotrimethylsilane
(3.9mL, 30.8mmol) and 2b (2.09g, 7.64mmol) were
added to the mixture, stirred at room temperature for
5h, then refluxed for 1.5h and then immediately filtrated
and evaporated. The residue was purified by bulb-to-
bulb distillation to give 3b as a colourless oil (1.68g,
61%): IR (film) 2958, 2865, 2807, 1690, 1250, 1210,
Figure 1. Isopotential surfaces of the catechol fragment (A) of
dopamine and the endiyne core unit (B) of the non-aromatic dopamine
receptor agonist FAUC 88 contouring negative electrostatic potentials
(À1kcal/mol) viewed from the front side (top) and from the bottom
side (below).
1
1125cmÀ1; H NMR d 0.18 (s, 18H, 2·Si(CH3)3), 0.83
(t, J = 7.3Hz, 6H, 2·NCH2CH2CH3), 1.32–1.56 (m,
5H, 2·NCH2CH2CH3, 6-H), 1.69–1.85 (m, 1H, 6-H),

C. Lenz et al. / Bioorg. Med. Chem. 13 (2005) 185–191
189
1.96–2.17 (m, 4H, 2-H; 5-H), 2.31–2.45 (m, 4H,
2·NCH2CH2CH3), 2.67–2.84 (m, 1H, 1-H).
ture was cooled to À90ꢁC and dibromotetrachlorethane
(2.13g, 6.5mmol) was added. After 30min at À90ꢁC sat-
urated aqueous NaHCO3 solution was added and the
mixture was allowed to warm to room temperature.
After extraction with EtOAc the combined organic lay-
ers were dried (MgSO4) and evaporated. The residue
was purified by flash chromatography (petroleum
ether–EtOAc 1:1) to give 6 as a colourless oil (1.11g,
66%): IR (film) 2958, 2871, 2810, 1721, 1462, 1190,
3.3. Cyclohexene-1,2-diyl bis(trifluoromethanesulfonate)
(4)
To a solution of 3a (3.1g, 12mmol) in DME (30mL) at
À60ꢁC was added MeLi (16mL, 1.6M in Et2O) and the
solution was allowed to warm up to À20ꢁC during 2h.
After being recooled to À78ꢁC trifluoromethanesulfonic
anhydride (4mL, 24.3mmol) was added drop by drop
and the mixture was warmed to 10ꢁC slowly. After
15h aqueous NaHCO3 solution (5%) was added and
the mixture was extracted with Et2O. The combined org-
anic layers were dried (MgSO4) and evaporated. The
residue was purified by flash chromatography (neutral
Al2O3, petroleum ether–CH2Cl2 9:1) to give 4 as a col-
ourless liquid (675mg, 15%): IR (film) 2960, 2870,
1076cmÀ1
;
1H NMR d 0.87 (t, J = 7.3Hz, 6H, 2·
NCH2CH2CH3), 0.88 (t, J = 7.3Hz, 6H, 2·NCH2CH2-
CH3), 1.37–1.51 (m, 8H, 4·NCH2CH2CH3), 1.67–1.82
(m, 2H, 2·5-Hax), 1.98–2.48 (m, 15H, 4·NCH2CH2-
CH3, 2·5-Heq, 2·6-H, 3-H), 2.63–2.73 (m, 2H, 2·4-
Hax), 3.03–3.16 (m, 2H, 3-H2), 3.35 (dd, J = 10.6,
3.4Hz, 1H, 3-H), 4.43–4.47 (m, 1H, 2-Heq), 4.65 (dd,
J = 13.1, 6.4Hz, 1H, 2-Hax); EIMS 276 (M+); HREIMS
calcd for C12H2281BrNO: 277.0864; Found: 277.0866
(M+); HREIMS calcd for C12H2279BrNO: 275.0885;
Found: 275.0887 (M+).
1
1712, 1425, 1260, 1220, 1050, 920, 875cmÀ1; H NMR
d 1.68–1.79 (m, 4H, 4-H, 5-H), 2.41–2.50 (m, 4H, 3-H,
6-H); 13C NMR d 21.8 (C-4, C-5), 27.3 (C-3, C-6),
113.4, 116.6, 119.8, 122.9 (CF3), 140.2 (C@C); EIMS
378 (M+).
3.7. 2-Bromo-4-(dipropylamino)cyclohex-1-en-1-yl tri-
fluoromethanesulfonate (7a). 6-Bromo-4-(dipropylamino)-
cyclohex-1-en-1-yl trifluoromethanesulfonate (7b)
3.4. (Cyclohexene-1,2-diyl-bisethynyl)-bis(trimethylsilane)
(5a)
To a solution of 6 (660mg, 2.4mmol) in THF (60mL)
was added LiHMDS (2.99mL, 1.06M in hexane) at
À78ꢁC. After being stirred at À78ꢁC for 1.75h, 2-
[N,N-di-(trifluoromethylsulfonyl)amino]-5-chloropyridine
(1.01g, 2.56mmol) in THF (6mL) was added and the
mixture was allowed to warm to À20ꢁC during 2.25h
and then stirred at room temperature for 1h. Then sat-
urated aqueous NaHCO3 solution was added and the
mixture was extracted with Et2O. The combined organic
layers were dried (MgSO4) and evaporated. The residue
was purified by flash chromatography (petroleum ether–
EtOAc 95:5) to give 7a as a slightly yellowish oil
(348mg, 36%) as well as 7b as a slightly yellowish oil
(146mg, 15%): 7a: IR (film) 2960, 2813, 1677, 1422,
To a solution of 4 (52mg, 0.13mmol) in THF (4mL)
were added EtMe2N (130lL, 1.2mmol), trimethylsilyl-
acetylene (75lL, 0.53mmol), Pd(PPh3)4 (10mg,
6mol%) and CuI (5mg, 20mol%). After being stirred
at room temperature for 3h, aqueous NaHCO3 (5%)
was added and the mixture was extracted with Et2O.
The combined organic layers were dried (MgSO4) and
evaporated. The residue was purified by flash chroma-
tography (petroleum ether–CH2Cl2 9:1) to give 5a as
colourless crystals (18mg, 50%): 1H NMR d 0.19
(s, 18H, 2·Si(CH3)3), 1.50–1.63 (m, 4H, 4-H, 5-H),
2.13–2.27 (m, 4H, 3-H, 6-H); EIMS 274 (M+); Anal.
Calcd for C16H26Si2: C, 69.99; H, 9.54. Found: C,
69.88; H, 9.64.
1
1212, 1140, 860cmÀ1; H NMR d 0.86 (t, J = 7.3Hz,
6H, 2·NCH2CH2CH3), 1.42 (m, 4H, 2·NCH2CH2-
CH3), 1.70 (dddd, J = 12.6, 12.4, 10.1, 6.7Hz, 1H, 5-
Hax), 1.95 (dddd, J = 12.6, 6.2, 3.0, 1.5Hz, 1H, 5-Heq),
2.35–2.41 (m, 4H, 2·NCH2CH2CH3), 2.44–2.69 (m,
4H, 3-H, 6-H), 2.95 (dddd, J = 12.4, 9.5, 5.6, 3.0Hz,
1H, 4-Hax); EIMS 409, 407 (M+); HREIMS calcd for
C13H2181BrF3O3S: 409.0357; Found: 409.0356 (M+);
HREIMS calcd for C13H2179BrF3NO3S: 407.0378;
Found: 407.037 (M+). 7b: IR (film) 2961, 2813, 1671,
3.5. (Cyclohexene-1,2-diyl-bisethynyl)-bisbenzene (5b)
To a solution of 4 (52mg, 0.13mmol) in THF (4mL)
were added EtMe2N (130lL, 1.2mmol), phenylacetyl-
ene (57lL, 0.51mmol), (Ph3P)4Pd (10mg, 6mol%) and
CuI (5mg, 20mol%). After being stirred at room tem-
perature for 10h, aqueous NaHCO3 (5%) was added
and the mixture was extracted with Et2O. The combined
organic layers were dried (MgSO4) and evaporated. The
residue was purified by flash chromatography (petro-
leum ether) to give 5b as a slightly yellowish oil
1464, 1420, 1246, 1222, 1141, 862cmÀ1 1H NMR d
;
0.88 (t, J = 7.4Hz, 6H, 2·NCH2CH2CH3), 1.38–1.51
(m, 4H, 2·NCH2CH2CH3), 2.14 (ddd, J = 14.4, 12.1,
4.1Hz, 1H, 5-Hax), 2.28–2.47 (m, 7H, 2·NCH2CH2-
CH3, 3-H, 5-Heq), 3.37 (dddd, J = 12.1, 9.7, 6.7,
2.8Hz, 1H, 4-Hax), 4.82–4.86 (m, 1H, 6-H), 5.94 (dd,
J = 5.1, 3.3Hz, 1H, 2-H); EIMS 407, 409 (M+).
1
(24mg, 65%): H NMR d 1.62–1.74 (m, 4H, 4-H, 5-
H), 2.30–2.43 (m, 4H, 3-H, 6-H), 7.21–7.54 (m, 10H,
Ph); EIMS 282 (M+).
3.6. 2-Bromo-4-(dipropylamino)cyclohexanone (6)
3.8. Dipropyl-[3-bromo-4-(trimethylsilylethynyl)cyclohex-
3-en-1-yl]amine (8)
To
a
solution of 4-dipropylaminocyclohexanone4
(1.18g, 6.0mmol) in THF (60mL), was added a freshly
prepared solution of LDA (17.4mL, 0.40M in THF)
at À78ꢁC. After being stirred at À78ꢁC for 1h, the mix-
To suspension of 7a (24mg, 0.059mmol), Pd(PPh3)4
(10mg, 0.009mmol) and CuI (2mg, 0.01mmol) in
THF (2.5mL) were added trimethylsilylacetylene

190
C. Lenz et al. / Bioorg. Med. Chem. 13 (2005) 185–191
(37lL, 0.26mmol) and piperidine (75lL, 0.76mmol)
and the reaction mixture was heated at 40ꢁC for 3.5h.
After being cooled to room temperature saturated aque-
ous NaHCO3 solution was added and the mixture was
extracted with Et2O. The combined organic layers were
dried (MgSO4) and evaporated. The residue was purified
by flash chromatography (petroleum ether–EtOAc 95:5)
to give 1d (1.5mg, 7%) (see below) and 8 as a colourless
oil (14mg, 67%): IR (film) 2958, 2810, 2147, 1249,
229 (M+); HREIMS calcd for C16H23N: 229.1830;
Found: 229.1834 (M+).
3.11. 5-(Dipropylamino)-2-(trimethylsilylethynyl)cyclo-
hex-1-ene-1-carbonitrile (1b)
To a solution of 8 (31mg, 0.09mmol) in dioxane (4mL)
were added CuCN (35mg, 0.4mmol), Pd2(dba)3 (7.3mg,
0.008mmol) and dppf (18mg, 0.03mmol) and the reac-
tion mixture was refluxed for 2.75h. After being cooled
to room temperature the mixture was filtrated over Cel-
ite, saturated aqueous NaHCO3 solution was added and
the mixture was extracted with EtOAc. The combined
organic layers were dried (MgSO4) and evaporated.
The residue was purified by flash chromatography
(petroleum ether–EtOAc 9:1) to give 1b as a colourless
oil (14mg, 54%): IR (film) 2958, 2811, 2214, 2148,
1461, 1249, 845cmÀ1; 1H NMR d 0.23 (s, 9H, Si(CH3)3),
0.86 (t, J = 7.3Hz, 6H, 2·NCH2CH2CH3), 1.36–1.55
(m, 5H, 2·NCH2CH2CH3, 4-Hax), 1.84 (dddd,
J = 10.4, 7.6, 5.0, 2.6Hz, 1H, 4-Heq), 2.19–2.49 (m,
8H, 2·NCH2CH2CH3, 3-H, 6-H), 2.86 (dddd,
J = 12.0, 10.4, 5.0, 2.8Hz, 1H, 5-H); EIMS 302 (M+);
HREIMS calcd for C18H30N2Si: 302.2178; Found:
302.2177 (M+).
1
859cmÀ1; H NMR d 0.20 (s, 9H, Si(CH3)3), 0.85 (t,
J = 7.2Hz, 6H, 2·NCH2CH2CH3), 1.34–1.55 (m, 5H,
2·NCH2CH2CH3, 6-Hax), 1.81–1.89 (m, 1H, 6-Heq),
2.20–2.44 (m, 6H, 2·NCH2CH2CH3, 5-H), 2.45–2.58
(m, 1H, 2-H), 2.59–2.69 (m, 1H, 2-H), 2.88 (dddd,
J = 12.2, 10.4, 5.2, 2.9Hz, 1H, 1-H); EIMS 355,
357 (M+); HREIMS calcd for C17H3079BrNSi:
355.1331; Found: 355.1331 (M+); HREIMS calcd for
C17H3081BrNSi: 357.1310; Found: 357.1323 (M+).
3.9. Dipropyl-[3,4-di(trimethylsilylethynyl)cyclohex-3-en-
1-yl]amine (1d)
To a suspension of Pd(PPh3)4 (20mg, 0.018mmol) and
CuI (5mg, 0.02mmol) in THF (9mL) were added 7a
(72mg, 0.18mmol) in THF (1mL), trimethylsilylacetyl-
ene (150lL, 1.06mmol) and piperidine (170lL,
1.72mmol). After being stirred at 95ꢁC for 1h, the mix-
ture was allowed to cool to room temperature, saturated
aqueous NaHCO3 solution was added and the mixture
was extracted with Et2O. The combined organic layers
were dried (MgSO4) and evaporated. The residue was
purified by flash chromatography (petroleum ether–
EtOAc 95:5) to give 8 (15mg, 24%) and 1d as a slightly
yellowish oil (28mg, 42%): IR (film) 2958, 2900, 2871,
3.12. 5-(Dipropylamino)-2-ethynylcyclohex-1-ene-1-carbo-
nitrile (1a)
To a solution of 1b (7mg, 0.023mmol) in THF (1mL)
was added Bu4NF (28lL, 1M solution in THF) at
À20ꢁC. After being stirred at this temperature for
45min saturated aqueous NaHCO3 solution was added
and the mixture was extracted with EtOAc. The
combined organic layers were dried (MgSO4) and
evaporated. The residue was purified by flash chroma-
tography (petroleum ether–EtOAc 8:2) to give 1a as
a slightly yellowish oil (3mg, 60%): IR (film) 3297,
1
2809, 2142, 1249, 842cmÀ1; H NMR d 0.20 (s, 9H,
Si(CH3)3), 0.21 (s, 9H, Si(CH3)3), 0.85 (t, J = 7.4Hz,
6H, 2·NCH2CH2CH3), 1.33–1.47 (m, 5H, 2·NCH2-
CH2CH3, 6-Hax), 1.76–1.86 (m, 1H, 6-Heq), 2.08–2.45
(m, 8H, 2·NCH2CH2CH3, 5-H, 2-H), 2.66–2.78 (m,
1H, 1-H); EIMS 373 (M+); HREIMS calcd for
C22H39NSi2: 373.2621; Found: 373.2622 (M+).
2816, 2214, 2098, 1605, 1462, 1249, 1099cmÀ1 1H
;
NMR d 0.87 (t, J = 7.4Hz, 6H, 2·NCH2CH2CH3),
1.37–1.54 (m, 5H, 2·NCH2CH2CH3, 4-Hax), 1.90–1.94
(m, 1H, 4-Heq), 2.21–2.52 (m, 8H, 2·NCH2CH2CH3,
3-H, 6-H), 2.85 (dddd, J = 12.0, 10.4, 5.0, 2.8Hz,
1H, 5-H), 3.43 (s, 1H, C„CH); EIMS 230 (M+);
HREIMS calcd for C15H22N2: 230.1783; Found:
230.1780 (M+).
3.10. Dipropyl(3,4-diethynylcyclohex-3-en-1-yl)amine
(1c)
To a solution of 1d (12mg, 0.032mmol) in THF (3mL)
was added Bu4NF (70lL, 1M solution in THF) at
À20ꢁC. After being stirred for 20min saturated aqueous
NaHCO3 solution was added and the mixture was
extracted with Et2O. The combined organic layers were
dried (MgSO4) and evaporated. The residue was purified
by flash chromatography (petroleum ether–EtOAc 2:1)
to give 1c as a slightly yellowish oil (6mg, 82%): IR
(film) 3291, 2958, 2933, 2871, 2809, 2096, 1463,
3.13. Receptor binding experiments and data analysis
Receptor binding studies utilizing dopamine receptors
were carried out as described in Ref. 4. In brief, the dop-
amine D1 receptor assay was done with porcine striatal
membranes at a final protein concentration of 40lg/
assay tube and the radioligand [3H]SCH 23390 at
0.3nM (Kd = 0.35–0.70nM). Competition experiments
with the human D2long, D2short, D3 and D4.4 recep-
tors were run with preparations of membranes from
CHO cells expressing the corresponding receptor and
[3H]spiperone at a final concentration of 0.5nM. The
assays were carried out at a protein concentration of
6–20lg/assay tube and Kd values of 0.10–0.12nM for
D2long, 0.10nM for D2short, 0.10–0.30nM for D3
and 0.10–0.50nM for D4.4.
1380cmÀ1
; d 0.86 (t, J = 7.3Hz, 6H,
1H NMR
2·NCH2CH2CH3), 1.36–1.51 (m, 5H, 2·NCH2CH2-
CH3, 6-Hax), 1.85 (dddd, J = 12.6, 5.0, 5.0, 2.3Hz, 1H,
6-Heq), 2.15–2.45 (m, 8H, 2·NCH2CH2CH3, 5-H,
2-H), 2.78 (dddd, J = 12.1, 10.5, 5.0, 2.8Hz, 1H, 1-H),
3.24 (s, 2H, 2·CꢀCH); 13C NMR d 11.8 (NCH2CH2-
CH3), 22.2 (NCH2CH2CH3), 24.8, 30.9, 32.4 (C-2,
C-5, C-6), 52.5 (NCH2CH2CH3), 55.2 (C-1), 80.9, 81.4
(2·CꢀCH), 83.4, 83.6 (2·CCH), 126.4 (C@C); EIMS

C. Lenz et al. / Bioorg. Med. Chem. 13 (2005) 185–191
191
Receptor binding experiments with 5-HT1A and 5-HT2
receptors were done according to literature with porcine
cortical membranes (at 330lg/tube and 150lg/tube for
5-HT1A and 5-HT2, respectively) and the radioligand
[3H]8-OH-DPAT (for 5-HT1A; Kd = 1.4nM) or
[3H]ketanserin (for 5-HT2; Kd = 1.6nM) both at
0.5nM.17
D4, D3 and D2 receptor expressing cell lines, respec-
tively, as well as Dr. R. Huff (Pharmacia) for providing
dopamine D2 and D4 receptor expressing cell lines
transfected in CHO10001.
References and notes
1. Progress in Drug Research; Jucker, E., Ed.; Birkha¨user:
Basel, Boston, Berlin, 1991; Vol. 37.
2. Haubmann, C.; Huebner, H.; Gmeiner, P. Bioorg. Med.
Chem. Lett. 1999, 9, 1969.
3. (a) Ortner, B.; Waibel, R.; Gmeiner, P. Angew. Chem., Int.
Ed. 2001, 40, 1283; (b) Ortner, B.; Huebner, H.; Gmeiner,
P. Tetrahedron: Asymmetry 2001, 12, 3205.
4. Huebner, H.; Haubmann, C.; Utz, W.; Gmeiner, P. J.
Med. Chem. 2000, 43, 756.
5. Rigby, J. H.; Cavezza, A.; Heeg, M. J. J. Am. Chem. Soc.
1998, 120, 3664.
6. Maas, G.; Lorenz, W. J. Org. Chem. 1984, 49, 2273.
7. Sonoda, T.; Garcia Martinez, A.; Hanack, M.; Subrama-
nian, L. R. Croat. Chem. Acta 1992, 65, 585.
8. Ruehlmann, K. Synthesis 1971, 236.
The resulting competition curves were analyzed by non-
linear regression using the algorithms in PRISM
(GraphPad Software, San Diego, USA). The data were
initially fit using a sigmoid model to provide a slope
coefficient (nH) and an IC50 value, representing the con-
centration corresponding to 50% of maximal inhibition.
Data were then calculated for a one-site (nH ꢁ 1) or a
two-site model (nH < 1) depending on the slope factor.
Calculating a two-site model IC50 values for a high
and low affinity binding site and the amount of both
receptor populations could be obtained. Finally, IC50
values were transformed to Ki values according to the
equation of Cheng and Prusoff.20
9. Cacchi, S.; Morera, E.; Ortar, G. Synthesis 1986, 320.
10. Thorand, S.; Krause, N. J. Org. Chem. 1998, 63, 8551.
11. Voigt, K.; Von Zezschwitz, P.; Rosauer, K.; Lansky, A.;
Adams, A.; Reiser, O.; De Meijere, A. Eur. J. Org. Chem.
1998, 1521.
12. Aboul-Fadl, T.; Lober, S.; Gmeiner, P. Synthesis 2000,
1727.
13. Hayes, G.; Biden, T. J.; Selbie, L. A.; Shine, J. Mol.
Endocrinol. 1992, 6, 920.
14. Sokoloff, P.; Andrieux, M.; Besancon, R.; Pilon, C.;
Martres, M.-P.; Giros, B.; Schwartz, J.-C. Eur. J. Phar-
macol. 1992, 225, 331.
15. Asghari, V.; Sanyal, S.; Buchwaldt, S.; Paterson, A.;
Jovanovic, V.; Van Tol, H. H. M. J. Neurochem. 1995, 65,
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16. Lenz, C.; Boeckler, F.; Huebner, H.; Gmeiner, P. Bioorg.
Med. Chem. 2004, 12, 113.
17. Heindl, C.; Huebner, H.; Gmeiner, P. Tetrahedron:
Asymmetry 2003, 14, 3141.
3.14. Mitogenesis experiments
Determination of the ligand efficacy of representative
compounds was carried out by measuring the incorpora-
tion of [3H]thymidine into growing cells after stimula-
tion with the test compound as described in
literature.21,22 For this assay CHO10001 cells stably
expressing the ratD2long, ratD2short and humanD4.2
receptor and D3 expressing CHO dhfrÀ cells have been
incubated with 0.02lCi [3H]thymidine per well (specific
activity 25Ci/mmol). Dose–response curves of 6–11
experiments have been normalized and summarized to
get a mean curve from which the EC50 value and the
maximum intrinsic activity of each compound could
be derived compared to the effects of the full agonist
quinpirole.
18. SYBYLꢂ 6.9.1, Tripos: 1699 South Hanley Rd., St. Louis,
Missouri, 63144, USA.
19. Meyer, E. A.; Castellano, R. K.; Dietrich, F. Angew.
Chem., Int. Ed. 2003, 42, 1210.
Acknowledgements
The Deutsche Forschungsgemeinschaft (DFG) is
acknowledged for financial support. The authors wish
to thank Dr. H. H. M. Van Tol (Clarke Institute of Psy-
chiatry, Toronto), Dr. J.-C. Schwartz, Dr. P. Sokoloff
(INSERM, Paris) and J. Shine (The Garvan Institute
of Medical Research, Sydney) for providing dopamine
20. Cheng, Y. C.; Prusoff, W. H. Biochem. Pharmacol. 1973,
22, 3099.
21. Huebner, H.; Kraxner, J.; Gmeiner, P. J. Med. Chem.
2000, 43, 4563.
22. Bettinetti, L.; Schlotter, K.; Huebner, H.; Gmeiner, P. J.
Med. Chem. 2002, 45, 4594.