Methoxy- and fluorine-substituted analogs of O-1302: Synthesis and in vitro binding affinity for the CB1 cannabinoid receptor

Article abstract of DOI:10.1248/cpb.55.1213

Methoxy and fluorine analogs substituted on the terminal carbon of the pentyl chain of N-(piperidinyl)-1-(2,4-dichlorophenyl)-4-methyl-5-(4- pentylphenyl)-1H-pyrazole-3-carboxamide (O-1302) were synthesized in a multi-step process from 5-phenyl-1-pentanol, which was based on the 1,5-diarylpyrazole core template of N-(piperidinyl)-5-(4-chlorophenyl)-1-(2,4- dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716) through condensation of the respective amine with pyrazole carboxylic acid, in order to develop tracers for medical imaging. Their potency for inhibiting the binding of the CB1 antagonist [³H]SR141716 was evaluated with the aim of developing positron emission tomography (PET) ligands for the cerebral cannabinoid CB1 receptor. These analogs bearing a piperidinyl carboxamide at the C₃ of the pyrazole ring exhibited affinities comparable to those of the CB1 reference antagonist SR141716, which warrants further investigation using the radiolabeled form for biological imaging studies. A morpholine ring substituted at the C₃ of the pyrazole ring resulted in a reduction of the CB1 affinity.

Full text of DOI:10.1248/cpb.55.1213

August 2007
Chem. Pharm. Bull. 55(8) 1213—1217 (2007)
1213
Methoxy- and Fluorine-Substituted Analogs of O-1302: Synthesis and
in Vitro Binding Affinity for the CB1 Cannabinoid Receptor
Shintaro TOBIISHI,a Toru SASADA,a Yumiko NOJIRI,a Fumihiko YAMAMOTO,a Takahiro MUKAI,a
Kiichi ISHIWATA,b and Minoru MAEDA*,a
a Graduate School of Pharmaceutical Sciences, Kyushu University; 3–1–1 Maidashi, Higashi-ku, Fukuoka 812–8582,
Japan: and b Positron Medical Center, Tokyo Metropolitan Institute of Gerontology; 1–1 Naka-cho, Itabashi-ku, Tokyo
173–0022, Japan. Received April 11, 2007; accepted May 17, 2007; published online May 21, 2007
Methoxy and fluorine analogs substituted on the terminal carbon of the pentyl chain of N-(piperidinyl)-
1-(2,4-dichlorophenyl)-4-methyl-5-(4-pentylphenyl)-1H-pyrazole-3-carboxamide (O-1302) were synthesized in
a multi-step process from 5-phenyl-1-pentanol, which was based on the 1,5-diarylpyrazole core template
of N-(piperidinyl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716)
through condensation of the respective amine with pyrazole carboxylic acid, in order to develop tracers for med-
ical imaging. Their potency for inhibiting the binding of the CB1 antagonist [3H]SR141716 was evaluated with
the aim of developing positron emission tomography (PET) ligands for the cerebral cannabinoid CB1 receptor.
These analogs bearing a piperidinyl carboxamide at the C3 of the pyrazole ring exhibited affinities comparable to
those of the CB1 reference antagonist SR141716, which warrants further investigation using the radiolabeled
form for biological imaging studies. A morpholine ring substituted at the C3 of the pyrazole ring resulted in a re-
duction of the CB1 affinity.
Key words cannabinoid CB1 receptor; 1,5-diarylpyrazoles; O-1302; binding
Radiotracers, labeled with a short-lived positron emitter appeared that O-1302 may serve as a useful lead structure for
such as 11C or 18F, are being used increasingly as useful the development of high affinity CB1 imaging agents. We
probes for diagnosis and for monitoring the course of thera- have designed and developed a synthetic route to O-1302
peutic intervention using positron emission tomography analogs with methoxy and fluorine substituents on the termi-
(PET).1) In terms of creating new PET imaging tools, we nal carbon of the pentyl chain, for radiolabeling with 11C or
have been interested in the progress of characterizing cere- 18F of the O-1302 molecule. The in vitro binding affinities of
bral cannabinoid ligands and exploring the possibility of these O-1302 derivatives for the CB1 receptor and lipophilic-
using them as tracers.
ity are also evaluated in this study.
The cannabinoid CB1 receptor is the most abundant
cannabinoid receptor subtype found in the central nervous Results and Discussion
system, and is responsible for inhibitory modulation of
Currently, the general route to construct a pyrazole skele-
synaptic transmission by presynaptic actions on a range of ton includes procedures based on the cyclocondensation of
transmitters. The brain CB1 receptor has been recognized as diketone ester enolates with appropriate hydrazine com-
an interesting therapeutic target for the treatment of several pounds.17,18) In the first stage of this approach, our attempts
psychotropic and neurodegenerative disorders,2,3) although to perform Claisen condensation of 4ꢁ-pentylpropiophenone
the role of the CB1 receptor in the cause and treatment of or 4ꢁ-chloropropiophenone as a model with diethyl oxalate in
these disorders is not fully understood.
the presence of a strong base such as lithium bis(trimethylsi-
Diarylpyrazoles are well known ligands for the central lyl)amide for the preparation of the corresponding diketo
cannabinoid receptor, although cannabinoid ligands are cur- ester were not successful. While our study was in progress,
rently classified into several different structural groups.2,3) Alekseeva et al. reported the synthesis of 5-substituted pyra-
The most widely studied N-(piperidinyl)-5-(4-chlorophenyl)- zole derivatives of O-1302, using a Suzuki-type coupling
1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxam- with an alkene.16) We pursued an alternative approach, ac-
ide (SR141716), a highly potent and selective CB1 receptor cording to a method reported by Dutta et al.,19) in which
antagonist/agonist, has served as a unique pharmacological
and biochemical tool for the characterization of the CB1 re-
ceptor.4—7) Thus, various types of analogs of SR141716 have
been extensively studied as candidate molecules to develop
useful PET ligands for nuclear imaging.8—13) However, the
PET imaging of the cerebral CB1 receptor in vivo is still
problematic, due to high nonspecific binding and insufficient
brain uptake of the radiotracers, although a very recent publi-
cation shows that [11C]JHU75528 appears to hold potential
as a PET agent for imaging the CB1 receptor in human stud-
ies.14) Recently it has been reported that a SR141716 analog
with p-pentylphenyl substituted at the C5 position of the
pyrazole ring (O-1302) has high affinity (Kiꢀ2.1 nM for CB1
Fig. 1. Structure of SR141716 and O-1302, CB1 Cannabinoid Receptor
Antagonist
receptor) with potent antagonistic properties (Fig. 1).15,16) It
∗ To whom correspondence should be addressed. e-mail: maeda@phar.kyushu-u.ac.jp
© 2007 Pharmaceutical Society of Japan

1214
Vol. 55, No. 8
the synthesis was carried out from 4ꢁ-(5-acetoxypentyl)-
propiophenone (2), as outlined in Chart 1, for the preparation
of the fluorine analog (8) of O-1302. This compound (2) was
prepared in good yield under Friedel–Crafts acylation with
AlCl3 and propionyl chloride after being protected by acety-
lation of the hydroxy group of 5-phenyl-1-pentanol;
the use of t-butyldimethylsilyl, t-butyldiphenylsilyl or me-
thoxymethyl group as the protecting group of the hydroxy
group gave either poor yield or was mostly unreacted under
conditions for Friedel–Crafts acylation. The synthesis of ace-
toacetate (4) was achieved by the treatment of ethyl acetoac-
etate with the bromo ketone intermediate (3), prepared by
bromination of 2. The sodium salt of 4 was allowed to react
with a solution of 2,4-dichlorobenzenediazonium chloride,
followed by base hydrolysis to give the 5ꢁ-hydroxy pyrazole
carboxylic acid (5). Acid-amine coupling of 5 with 1-ami-
nopiperidine in the presence of 1-hydroxybenzotriazole
(HOBT), O-(1,2-dihydro-2-oxo-1-pyridyl)-N,N,Nꢁ,Nꢁ-tetra-
methyluronium tetrafluoroborate (TPTU), and diisopropyl-
ethylamine in CH3CN gave the desired carboxamide (6) in
73% yield. The primary alcohol of 6 was tosylated with
toluene-p-sulfonyl chloride in pyridine and subsequent treat-
ment of the tosyl derivative (7) with tetrabutylammonium
fluoride in THF afforded the target fluorine-substituted ana-
log (8) of O-1302 in 59% yield.
The methoxy-substituted analog bearing an N-piperidinyl
ring (16) or N-morpholine ring (17) was accessible by a simi-
lar reaction sequence described for the fluorine analog (8) of
O-1302, starting from acetyl pentylpropiophenone (2). The
acetyl group of 2 was converted to the corresponding O-
methoxy compound (9) via the four-step procedure illus-
trated in Chart 1. This procedure involved ketalization of 2
with ethylene glycol, followed by basic hydrolysis and O-
methylation with CH3I, and deprotection of the 1,3-dioxolane
group to give the methoxy-propiophenone (9). The methoxy-
substituted propiophenone (9) was then transformed into
the corresponding pyrazole carboxylic acid (15) via the
bromoketone (13) and acetoacetate intermediate (14), analo-
gously to the procedure described above.
Reagents: (a) Ac2O, pyridine; (b) AlCl3, CH2CH2COCl; (c) Br2, AcOH for (3) and
(13); (d) ethylene glycol, pyridinium p-toluensulfonate, benzene; (e) NaOH, MeOH; (f)
CH3I, NaH, DMF; (g) HCl, MeOH; (h) NaH, ethyl acetoacetate, THF for (4) and (14);
(i) (1) NaOEt, EtOH, (2) 2,4-dichlorobenzenediazonium chloride, (3) NaOH, EtOH for
(5) and (15); (j) (1) 1-aminopiperidine, HOBT, TPTU, DIPEA, CH3CN for (6), (2) oxa-
lyl chloride, DMF, CH2Cl2, Et3N, 1-aminopiperidine, CH2Cl2 for (16), (3) HOBT,
TPTU, DIPEA, 4-aminomorpholine, CH3CN for (17), and (18); (k) TsCl, pyridine; (l)
TBAF, THF; (m) MeOTf, 2.6-di-tert-butyl-4-methylpyridine, DMF.
Chart 1
The pyrazole carboxylic acid (15) was then converted to though the overall yield is low and the long synthetic steps
the acid chloride intermediate by use of oxalyl chloride, fol- required are undesirable.
lowed by coupling with 1-aminopiperidine to give the target
The affinities of 8, 16 and 17 for binding to the CB1 re-
N-piperidinylamide (16) in a reasonable yield. On the other ceptor site were determined by measuring the ability of each
hand, the synthesis of the N-morpholinylamide (17) was ligand to compete with [3H]SR141716 binding in rat cerebel-
achieved by treatment of the carboxylic acid (15) with 4- lar membrane preparations, and were expressed as Ki values.
aminomorpholine in the presence of HOBT, TPTU, and di- The results are summarized in Table 1, including the Ki val-
isopropylethylamine.
ues of the reference pyrazole SR141716 and O-1302 for
Access to the target compound (17) was also envisaged by comparison. In this study the Ki value of SR141716, chosen
use of O-methylation of the hydroxyl pyrazole carboxamide as a reference ligand, was found to be in agreement with pre-
(18). The O-methylation of 18, which was prepared by cou- vious literature values.21) The fluorine and methoxy analogs
pling of 5 with 4-amino-morpholine, which occurred with (8, 16) of O-1302 were found to have nanomolar affinity (Ki
the use of MeOTf in the presence of 2,6-di-tert-butyl-4- value of 0.91 nM for 8; 0.70 nM for 16) for the sites labeled by
methylpyridine,20) but resulting in isolation of the desired [3H]SR141716, comparable to that of SR141716 and lead
compound (17) in only 16% yield.
compound O-1302, thus confirming the suitability of our ini-
The IR, 1H-NMR and MS spectra for all intermediates and tial design of the molecule. The replacement of the piperi-
final target compounds were consistent with the assigned dine ring of 16 by the more polar morpholine ring resulted in
structures. Moreover, the purity of the final compounds was less than seven-fold affinity, in agreement with the findings
checked by HPLC analysis. Thus, the synthetic route via the in other studies to the effect that the affinity is quite sensitive
acetoacetate intermediate provided access to useable quanti- to carboxamide group modifications.9,10,18)
ties of the target compounds and also is acceptable for fur-
It is well understood that an optimally high lipophilicity (a
ther preparation of experimental radiolabeled material, al- partition coefficient of logP of about 2 of a compound) is re-

August 2007
1215
Table 1. Inhibition of [3H]SR141716 Binding to Rat Cerebellar Mem-
branes and Lipophilicity
formed under an argon atmosphere. HPLC was done using a HITACHI L-
2000 series HPLC system fitted with a nacalai tesque COSMOSIL 5 C18-
AR-II (4.6ꢂ250 mm) with monitoring of UV absorption (at 254 nm).
Synthesis. (5-Acetoxypentyl)benzene (1) Acetic anhydride (2.25 ml,
24 mmol) was added dropwise to a stirred and ice-cold solution of 5-phenyl-
1-pentanol (1.0 g, 6 mmol) in pyridine (50 ml) and stirring was continued at
room temperature for 3 h. EtOAc (10 ml) was then slowly added to the mix-
ture, the resulting solution was washed with water and brine, and then dried
and evaporated in vacuo. The residue was purified by chromatography on a
silica gel column (hexane : EtOAcꢀ10 : 1) to give 1 as a colorless oil (1.2 g,
Ligand
Ki (nM)a)
logP (measured)c)
8
16
17
0.91ꢅ0.24
0.70ꢅ0.26
4.60ꢅ2.16
0.57ꢅ0.14
2b)
2.9
4.5
3.6
3.8
—
SR141716
O-1302
1
97%). H-NMR (CDCl3) d: 1.36—1.43 (2H, m), 1.62—1.65 (4H, m), 2.03
a) The binding assay was performed with [3H]SR141716 and the results are ex-
pressed as KiꢀIC50/(1+L/Kd). The data correspond to mean valuesꢅS.E.M obtained
from at least three independent experiments. b) Taken from ref. 15. c) Lipophilic-
ity (logP) was determined in an octanol/phosphate buffer (pHꢀ7.4) system using the
conventional flask-shake technique. The results were presented as mean values (nꢀ3)
with a maximum range of ꢅ5%.
(3H, s), 2.62 (2H, t, Jꢀ7.7 Hz), 4.05 (2H, t, Jꢀ6.7 Hz), 7.16—7.19 (3H, m),
7.25—7.34 (2H, m); IR (KBr) cmꢃ1: 2935, 1739; FAB-MS (m/z): 207
(MꢄH)ꢄ.
4ꢀ-(5-Acetoxypentyl)propiophenone (2) Anhydrous AlCl3 (3.0 g,
22 mmol) was added with stirring to an ice-cold solution of 5-(ace-
toxypentyl)benzene (1) (1.5 g, 7.3 mmol) and propionyl chloride (1.0 ml,
11 mmol). The mixture was allowed to stir at room temperature for 30 min
under argon, poured into ice-cold water and then extracted with ether. The
ether was successively washed with 1 M HCl, 1 M NaOH, brine, dried and
evaporated in vacuo. The crude product was purified with silica gel chro-
matography (hexane : EtOAcꢀ10 : 1) to give 2 as a light yellow oil (1.66 g,
88 %). 1H-NMR (CDCl3) d: 1.22 (3H, t, Jꢀ7.3 Hz), 1.36—1.44 (2H, m),
1.63—1.70 (4H, m), 2.04 (3H, s), 2.68 (2H, t, Jꢀ7.6 Hz), 2.98 (2H, q,
Jꢀ7.1 Hz), 4.05 (2H, t, Jꢀ6.7 Hz), 7.25 (2H, d, Jꢀ8.6 Hz), 7.88 (2H, d,
Jꢀ8.4 Hz); IR (KBr) cmꢃ1: 2937, 1739, 1683, 1608; FAB-MS (m/z): 263
(MꢄH)ꢄ.
quired for good blood–brain barrier permeability,22) although
there are some exceptions. Currently, there is no sufficiently
general understanding of the relationship between lipophilic-
ity and in vivo imaging characteristics for radioligands inves-
tigated for neuroimaging of the CB1 receptor. Katoch-Rouse
et al. found a correlation between the CB1 receptor binding
affinities and the calculated lipophilicity values for 1,5-diaryl
ligand compounds, and lipophilicity is thought to be an im-
4ꢀ-(5-Acetoxypentyl)-a-bromopropiophenone (3) Under argon, to a
portant factor for explaining the inhibitory potency towards stirred solution of 2 (140 mg, 0.53 mmol) in glacial acetic acid (0.5 ml) was
added dropwise bromine (42 ml, 0.79 mmol) at 0 °C using a syringe. The
mixture was kept at room temperature for 3 h with stirring, was then diluted
by the addition of water, and extracted with ether. The ether was washed
with water, saturated aqueous Na2CO3 and brine, dried and evaporated in
vacuo. The residue was purified by chromatography on silica gel
the receptor, presumably due to the hydrophobic nature of the
binding site region.23) However, factors other than lipophilic-
ity have also been reported to be key determinants of brain
uptake of this class of compounds.12) The lipophilic proper-
ties were determined experimentally as shown in Table 1.
The obtained logP values of compounds 8, 16 and 17 seem to
be above the optimal range of lipophilicity for imaging
agents targeted at the central nervous system, in which 8 dis-
played somewhat lower lipophilicity compared to three other
compounds. Nevertheless, it is suggested that the high bind-
ing affinity and high density of the CB1 receptor in the mam-
malian brain24) warrant further investigation in vivo using
positron-labeled forms of 8 and 16.
1
(hexane : EtOAcꢀ15 : 1) to give 3 as a light yellow oil (127 mg, 70 %). H-
NMR (CDCl3) d: 1.30—1.37 (3H, m), 1.52—1.65 (4H, m), 1.82 (2H, d,
Jꢀ6.7 Hz), 1.95 (3H, m), 2.60—2.64 (2H, m), 3.94—4.00 (2H, m), 5.20
(1H, q, Jꢀ6.7 Hz), 7.21 (2H, d, Jꢀ8.2 Hz), 7.88 (2H, d, Jꢀ8.2 Hz); IR
(KBr) cmꢃ1: 2935, 1735, 1606; FAB-MS (m/z): 341 (MꢄH)ꢄ.
4ꢁ-(5-Acetoxypentyl)-a,aꢁ-dibromopropiophenone was also obtained as a
1
side product: a colorless oily material (55 mg, 24%). H-NMR (CDCl3) d:
1.31—1.37 (2H, m), 1.58—1.64 (4H, m), 1.96 (3H, s), 2.60—2.68 (5H, m),
3.97—4.00 (2H, m), 7.20 (2H, d, Jꢀ8.21 Hz), 8.26 (2H, d, Jꢀ8.2 Hz); IR
(KBr) cmꢃ1: 2935, 1735, 1605; FAB-MS (m/z): 420 (M)ꢄ.
Ethyl [2-Acetyl-4-{4ꢀ-(5-acetoxypentyl)phenyl}-3-methyl-4-oxo]buty-
rate (4) To a suspension of 60% NaH oil (470 mg, 11.7 mmol) in dry THF
(10 ml) was added dropwise ethyl acetoacetate (1.1 ml, 8.6 mmol) with stir-
ring under argon. After stirring at room temperature for 0.5 h, bromoketone
(3) (2.38 g, 6.97 mmol) was added dropwise. The mixture was kept at room
temperature for 30 min and then refluxed for 2 h. After cooling, excess NaH
was decomposed by the addition of water and the THF was removed in
In summary, the present study describes the synthesis of
the methoxy and fluorine analogs of O-1302 in a multi-step
reaction, and their potency for inhibiting the binding of CB1
receptor antagonist [3H]SR141716 was also evaluated in
vitro. These analogs displayed desirably high binding affinity
at the CB1 receptor and one of these, the fluorine analog of vacuo. The residue was extracted with ether. The ether was washed with
water and brine, dried and evaporated in vacuo. The residue was purified by
O-1302 (8), appears to possess a somewhat lower lipophilic-
ity value compared to that of 16, 17 and SR141716. Studies
using positron-labeled analogs are proceeding to assess the
suitability for the imaging of the CB1 receptor in vivo.
silica gel chromatography using hexane : EtOAcꢀ5 : 1 as the eluent to give 4
as a yellow oil (0.998 g, 36%). 1H-NMR (CDCl3) d: 1.13—1.19 (4H, m),
1.32 (2H, t, Jꢀ7.0 Hz), 1.38—1.46 (2H, m), 1.62—1.69 (6H, m), 2.04 (3H,
s), 2.29 (2H, s), 2.39 (1H, s), 2.68 (2H, t, Jꢀ7.6 Hz), 4.14—4.28 (4H, m),
7.27 (2H, d, Jꢀ8.6 Hz), 7.90 (2H, d, Jꢀ8.0 Hz); IR (KBr) cmꢃ1: 2937, 1739,
1716, 1680; FAB-MS (m/z): 391 (MꢄH)ꢄ.
Experimental
1-(2,4-Dichlorophenyl)-5-{4ꢀ-(5-hydroxypentyl)phenyl}-4-methyl-1H-
pyrazole-3-carboxylic Acid (5) To a solution of sodium ethoxide (1.5 ml,
21% wt in absolute ethanol) in absolute ethanol (3.5 ml) was added a solu-
tion of 4 (990 mg, 2.53 mmol) in absolute ethanol (3 ml). After stirring for
30 min at room temperature under argon, the mixture was cooled in an ice-
bath. To this solution with stirring was added a solution of 2,4-dichloro-
benzenediazonium chloride [prepared from 2,4-dichloroaniline (820 mg,
5.07 mmol) in 35% HCl (1.3 ml) and diazotized at 0 °C with the slow addi-
tion (0.5 h) of a solution of NaNO2 (350 mg, 5.07 mmol) in water (20 ml)].
After stirring under argon for 5 h at 0 °C, the reaction mixture was diluted
with water (20 ml) and was allowed to stand in the refrigerator (4 °C) for
16 h. The ethanol was evaporated in vacuo and the residue was redissolved
in EtOAc, which was washed with water and brine. The EtOAc was removed
in vacuo and the residue was redissolved in ethanol (20 ml), followed by the
addition of a solution of NaOH (338 mg, 8.42 mmol) in water (1.5 ml). The
In general, chemical reagents and solvents were of commercial quality
and were used without further purification unless otherwise noted.
SR141716 was prepared according to that described in previous literature.19)
All melting points are uncorrected. 1H-NMR spectra were obtained on a
JOEL GX-270 spectrometer (270 MHz) or Varian Inova 400 (400 MHz), and
the chemical shifts are reported in parts per million downfield from tetra-
methylsilane. Infrared (IR) spectra were recorded with a Shimadzu FTIR-
8400 spectrometer. Mass spectra were obtained with a JOEL JMS DX-300
(FAB-MS), or an Applied Biosystems Mariner System 5299 spectrometer
(ESI-MS). Column chromatography was performed on Kieselgel 60 (70—
230 mesh, Merck), the progress of the reaction was monitored by TLC on
Silica gel 60F 254 plates (Merck), and spots were visualized with UV light.
In the synthetic procedures, organic extracts were routinely dried over anhy-
drous Na2SO4 and evaporated with a rotary evaporator under reduced pres-
sure. All reactions involving air- or moisture-sensitive compounds were per-

1216
Vol. 55, No. 8
mixture was refluxed for 9 h. The EtOH was evaporated in vacuo after fur-
t, Jꢀ6.3 Hz), 4.00 (2H, t, Jꢀ6.5 Hz), 7.13 (2H, d, Jꢀ7.8 Hz), 7.34 (2H, d,
ther addition of water. The residue was again extracted with EtOAc. The Jꢀ8.0 Hz); IR (KBr) cmꢃ1: 3363.
EtOAc was washed with brine, dried and evaporated in vacuo. The crude
4ꢀ-(5-Methoxypentyl)propiophenone (9) Under argon, to a solution of
product was purified by silica gel chromatography (hexane : EtOAcꢀ hydroxyl acetal (11) (2.17 g, 8.20 mmol) in dry DMF (18 ml) was added
2 : 1ꢄ2% acetic acid→hexane : EtOAcꢀ1 : 1ꢄ2% acetic acid) to give 5
NaH (1.64 g, 41.0 mmol) at room temperature. After cooling to 0 °C, methyl
(369 mg, 34%) as an orange solid, mp 95—97 °C. 1H-NMR (CDCl3) d: iodide (2.55 ml, 40.9 mmol) was added to the mixture with stirring. The so-
1.39—1.45 (2H, m), 1.59—1.66 (4H, m), 2.35 (3H, s), 2.60—2.67 (2H, m), lution was kept at 0 °C for 1 h, poured onto ice and extracted with ether. The
3.62—3.67 (2H, m), 7.06 (2H, d, Jꢀ8.0 Hz), 7.11 (2H, d, Jꢀ8.0 Hz), 7.27
(1H, s), 7.38—7.42 (1H, m), 7.48—7.52 (1H, m); IR (KBr) cmꢃ1: 1705;
ESI-MS (m/z): 433 (M)ꢄ.
N-(Piperidin-1-yl)-1-(2,4-dichlorophenyl)-5-{4ꢀ-(5-hydroxypentyl)- yellow oil (1.99 g, 87%). H-NMR (CDCl3) d: 0.87 (3H, t, Jꢀ7.5 Hz), 1.40
phenyl}-4-methyl-1H-pyrazole-3-carboxamide (6) N,N-Diisopropyleth- (2H, m), 1.59—1.64 (4H, m), 1.90 (2H, q, Jꢀ7.5 Hz), 2.60 (2H, t,
ether was washed with brine, dried and evaporated to dryness. The crude
product was purified by silica gel chromatography using hexane :
EtOAcꢀ5 : 1 as the eluent to give the O-methylated product (12) as a pale
1
ylamine (124 ml, 694 mmol) was added to
a
suspension of
5
(105
Jꢀ7.6 Hz), 3.31 (3H, s), 3.36 (2H, t, Jꢀ6.5 Hz), 3.77 (2H, t, Jꢀ4.8 Hz),
mg, 242 mmol), 1-aminopiperidine (34 ml, 314 mmol), 1-hydroxybenzotria- 3.99 (2H, t, Jꢀ4.9 Hz), 7.13 (2H, d, Jꢀ7.8 Hz), 7.33 (2H, d, Jꢀ8.2 Hz); IR
zole (HOBT) (63 mg, 465 mmol), and O-(1,2-dihydro-2-oxo-1-pyridyl)- (KBr) cmꢃ1: 3363.
N,N,Nꢁ,Nꢁ-tetramethyluronium tetrafluoroborate (TPTU) (94 mg, 316 mmol)
To a solution of the O-methylated product (12) (1.98 g, 7.11 mmol) in
methanol (13 ml) was added hydrochloric acid (3 M; 5.0 ml) at room temper-
in dry CH3CN (3 ml). The reaction mixture was stirred at room temperature
for 74 h under argon and then evaporated to dryness. The residue was parti- ature with stirring. The mixture was kept at room temperature for 4 h, then
tioned between EtOAc and 0.2 M aqueous NaHSO3. The organic layer was
diluted with water and the methanol was removed in vacuo. The residue was
washed with saturated aqueous Na2CO3 and brine, dried and evaporated to extracted with ether and the ether was washed with brine, dried and evapo-
dryness. The crude product was purified by silica gel chromatography using
rated to dryness. The crude product was purified by silica gel chromatogra-
hexane : EtOAcꢀ1 : 1ꢄ2% acetic acid as the eluent to give 6 (94 mg, 73%)
phy using hexane : EtOAcꢀ5 : 1 as the eluent to give 9 (1.44 g, 87%) as col-
1
as a yellow solid, mp 93—95 °C. H-NMR (CDCl3) d: 1.40—1.43 (2H, m), erless oil. 1H-NMR (CDCl3) d: 1.19 (3H, t, Jꢀ7.1 Hz), 1.37 (2H, m), 1.54—
1.57—1.65 (6H, m), 1.72—1.77 (4H, m), 2.37 (3H, s), 2.59 (2H, t, 1.66 (4H, m), 2.65 (2H, t, Jꢀ7.7 Hz), 2.95 (2H, q, Jꢀ7.7 Hz), 3.30 (3H, s),
Jꢀ7.7 Hz), 2.86—2.88 (4H, m), 3.62—3.65 (2H, m), 7.01 (2H, d, 3.34 (2H, t, Jꢀ6.3 Hz), 7.30 (2H, d, Jꢀ6.7 Hz), 7.86 (2H, d, Jꢀ8.0 Hz); IR
Jꢀ8.0 Hz), 7.11 (2H, d, Jꢀ8.0 Hz), 7.25 (1H, s), 7.41 (1H, s), 7.63 (1H, s);
(KBr) cmꢃ1: 1670; FAB-MS (m/z): 235 (MꢄH)ꢄ.
IR (KBr) cmꢃ1: 1674; FAB-MS (m/z): 515 (MꢄH)ꢄ.
4ꢀ-(5-Methoxypentyl)-a-bromopropiophenone (13) Compound (13)
was obtained from 9 according to the procedure described for 3 and was iso-
N-(Piperidin-1-yl)-1-(2,4-dichlorophenyl)-4-methyl-5-{4ꢀ-(5-p-toluene-
sulfonyloxypentyl)phenyl}-4-methyl-1H-pyrazole-3-carboxamide (7) p-
Toluenesulfoyl chloride (300 mg, 1.56 mmol) was added to a solution of 6
(200 mg, 0.38 mmol) in dry pyridine (4 ml) at 0 °C. The reaction mixture
was stirred at 0 °C for 1 h, and then a solution of saturated aqueous Na2CO3
1
lated as a pale yellow oil in 64% yield. H-NMR (CDCl3) d: 1.39 (2H, m),
1.55—1.66 (4H, m), 1.87 (3H, d, Jꢀ6.7 Hz), 2.66 (2H, t, Jꢀ7.7 Hz), 3.30
(3H, s), 3.34 (2H, t, Jꢀ6.4 Hz), 5.25 (1H, quintet, Jꢀ6.6 Hz), 7.26 (2H, d,
Jꢀ8.2 Hz), 7.92 (2H, d, Jꢀ8.2 Hz); IR (KBr) cmꢃ1: 1685; FAB-MS (m/z):
was added. The resulting solution was extracted with EtOAc. The separated 313 (MꢄH)ꢄ. 4ꢁ-(5-Acetoxypentyl)-a-bromopropiophenone (3) was also
organic layers were washed with brine, dried and evaporated in vacuo. The
residue was purified by silica gel chromatography using hexane : EtOAcꢀ
2 : 1→hexane : EtOAcꢀ1 : 1→hexane : EtOAcꢀ1 : 2) as the eluent to give 7
obtained in 27% yield as a side product.
Ethyl [2-Acetyl-4-{4ꢀ-(5-methoxypentyl)phenyl}-3-methyl-4-oxo]buty-
rate (14) Compound (14) was obtained from 13 according to the proce-
as a light yellow solid (145 mg, 57%), mp 88 °C. 1H-NMR (CDCl3) d: dure described for 4 and was isolated as a pale yellow oil in 37% yield. 1H-
1.24—1.43 (2H, m), 1.53—1.68 (6H, m), 1.73—1.76 (4H, m), 2.36 (3H, s), NMR (CDCl3) d: 1.16 (3H, d, Jꢀ6.9 Hz), 1.31 (3H, t, Jꢀ7.1 Hz), 1.39 (2H,
2.43 (3H, s), 2.53 (2H, t, Jꢀ7.7 Hz), 4.01 (2H, t, Jꢀ6.3 Hz), 7.00 (2H, d,
Jꢀ8.2 Hz), 7.06 (2H, d, Jꢀ8.2 Hz), 7.25 (1H, s), 7.32 (2H, d, Jꢀ8.0 Hz),
7.41 (1H, s), 7.64 (1H, s), 7.77 (2H, d, Jꢀ8.0 Hz); IR (KBr) cmꢃ1: 1683;
FAB-MS (m/z): 669 (M)ꢄ.
m), 1.55—1.65 (4H, m), 2.27 (3H, s), 2.65 (2H, t, Jꢀ7.7 Hz), 3.30 (3H, s),
3.34 (2H, t, Jꢀ6.5 Hz), 4.05—4.15 (2H, m), 4.18—4.27 (2H, m), 7.25 (2H,
d, Jꢀ8.2 Hz), 7.88 (2H, d, Jꢀ8.0 Hz); IR (KBr) cmꢃ1: 1743, 1716, 1679;
FAB-MS (m/z): 363 (MꢄH)ꢄ.
N-(Piperidin-1-yl)-1-(2,4-dichlorophenyl)-5-{4ꢀ-(5-fluoropentyl)-
1-(2,4-Dichlorophenyl)-5-{4ꢀ-(5-methoxypentyl)phenyl}-4-methyl-1H-
pyrazole-3-carboxylic Acid (15) Compound (15) was obtained from 14
according to the procedure described for 5 and isolated as a brown oil in
phenyl}-4-methyl-1H-pyrazole-3-carboxamide (8) Under argon,
7
(46 mg, 75.4 mmol) was added dropwise to solution of n-Bu4NF (400 ml; 1 M
solution in THF). The mixture was heated under reflux for 15 min and evap- 44% yield. 1H-NMR (CDCl3) d: 1.36 (2H, m), 1.55—1.62 (4H, m), 2.34
orated to dryness. The residue was purified by chromatography on silica gel (3H, s), 2.57 (2H, t, Jꢀ8.0 Hz), 3.30 (3H, s), 3.34 (2H, t, Jꢀ6.5 Hz), 7.00
1
(hexane : EtOAcꢀ1 : 2) to give 8 (23 mg, 59%) as a yellow gum. H-NMR (2H, d, Jꢀ8.0 Hz), 7.11 (2H, d, Jꢀ8.2 Hz), 7.25 (2H, d, Jꢀ3.5 Hz), 7.40
(CDCl3) d: 1.36—1.42 (2H, m), 1.55—1.68 (6H, m), 1.70—1.78 (4H, m), (1H, s); IR (KBr) cmꢃ1: 1716; ESI-MS (m/z): 445 (MꢃH)ꢄ.
2.37 (3H, s), 2.59 (2H, t, Jꢀ7.7 Hz), 2.87 (4H, m), 4.43 (2H, dt, Jꢀ47,
N-(Piperidin-1-yl)-1-(2,4-dichlorophenyl)-5-{4ꢀ-(5-methoxypentyl)-
5.9 Hz), 7.01 (2H, d, Jꢀ8.2 Hz), 7.10 (2H, d, Jꢀ8.2 Hz), 7.26 (1H, s), 7.42 phenyl}-4-methyl-1H-pyrazole-3-carboxamide (16) Under argon, one
(1H, s), 7.64 (1H, s); IR (KBr) cmꢃ1: 1681; ESI-HR-MS (m/z): 517.1937. drop of dry DMF was added to a solution of 15 (61 mg, 0.13 mmol) in dry
Calcd for C27H3235Cl2FN4O (MꢄH): 517.1932.
4ꢀ-(5-Hydroxypentyl)propiophenone Ethylene Acetal (11) Ethylene
glycol (35 ml, 630 mmol) and pyridinium p-toluensulfonate (130 mg,
0.52 mmol) were added to a solution of ketone (2) (3.00 g, 11.4 mmol) in
dichloromethane (2 ml) and to this solution was added dropwise a solution
of oxalyl chloride (0.12 ml, 0.24 mmol; 2.0 M solution in dichloromethane).
The mixture was kept at room temperature for 3 h with stirring, and concen-
trated in vacuo. The residue was then redissolved in dry dichloromethane
benzene (130 ml) and the mixture was refluxed for 27 h by water separation (2 ml). To this solution was added dry triethylamine (32 ml, 0.23 mmol) fol-
with a Dean–Stark trap. After cooling to room temperature, the solvent was lowed by 1-aminopiperidine (21 ml, 0.22 mmol). After stirring at room tem-
concentrated and ether was added. The mixture was washed with saturated perature for 16 h, the reaction mixture was quenched by the addition of
aqueous NaHCO3 and brine, then dried and evaporated in vacuo. The crude
product was chromatographed on silica gel using hexane : EtOAcꢀ10 : 1 as
water (1 ml) and extracted with EtOAc. The EtOAc was then washed with
water, dried and evaporated to dryness. The crude product was purified by
the eluent to give ketal (10) (2.77 g, 93%) as a colorless oil. 1H-NMR silica gel chromatography using hexane : EtOAcꢀ2 : 1 as the eluent to give
(CDCl3) d: 0.84 (3H, t, Jꢀ7.5 Hz), 1.36 (2H, m), 1.59—1.64 (4H, m), 2.00 16 (59 mg, 86%) as a pale yellow solid, mp 97—99 °C. 1H-NMR (CDCl3) d:
(2H, q, Jꢀ7.0 Hz), 2.57 (2H, t, Jꢀ7.8 Hz), 3.31 (3H, s), 3.75 (2H, t,
Jꢀ6.2 Hz), 3.97 (2H, t, Jꢀ6.5 Hz), 4.02 (2H, t, Jꢀ6.7 Hz), 7.10 (2H, d, (4H, br), 2.34 (3H, s), 2.57 (2H, t, Jꢀ7.8 Hz), 2.85–3.00 (3H, br), 3.30 (3H,
Jꢀ8.0 Hz), 7.31 (2H, d, Jꢀ8.0 Hz); IR (KBr) cmꢃ1: 1739.
s), 3.33 (2H, t, Jꢀ6.5 Hz), 6.98 (2H, d, Jꢀ8.2 Hz), 7.08 (2H, d, Jꢀ8.2 Hz),
To a solution of the above (10) (2.77 g, 9.04 mmol) in methanol (8 ml) was 7.23 (2H, d, Jꢀ1.3 Hz), 7.40 (1H, dd, Jꢀ0.56, 1.88 Hz); IR (KBr) cmꢃ1
added a solution of NaOH in water (2 ml). The mixture was stirred at room
1670; ESI-HR-MS (m/z): 529.2162. Calcd for C28H3535Cl2N4O2 (MꢄH):
temperature for 5 min and diluted by the addition of water (2 ml). The mix- 529.2132.
1.31—1.40 (2H, m), 1.40—1.47 (3H, br), 1.53—1.61 (4H, m), 1.72—1.81
:
ture was evaporated in vacuo and the residue was extracted with ether. The
ether was washed with water and brine, dried and evaporated in vacuo to
leave hydroxyl acetal (11) (2.17 g, 91%) as a pale yellow oil. 1H-NMR
(CDCl3) d: 0.87 (3H, t, Jꢀ7.5 Hz), 1.41 (2H, m), 1.56—1.67 (4H, m), 1.90 114 mmol), 1-hydroxybenzotriazole (23 mg, 170 mmol), TPTU (34 mg,
(2H, q, Jꢀ7.5 Hz), 2.61 (2H, t, Jꢀ7.5 Hz), 3.64 (2H, t, Jꢀ6.5 Hz), 3.78 (2H,
114 mmol) and N,N-diisopropylethylamine (45 ml, 252 mmol) according to
N-(Morphorin-1-yl)-1-(2,4-dichlorophenyl)-5-{4ꢀ-(5-methoxypentyl)-
phenyl}-4-methyl-1H-pyrazole-3-carboxamide (17) (a) Compound (17)
was obtained from 15 (39 mg, 87 mmol), 4-aminomorpholine (11 ml,

August 2007
1217
the procedure described for 6 and was isolated as a pale yellow gum in 67% shake flask method. The sample was shaken well with a mixture of a 1-oc-
yield. 1H-NMR (DMSO-d6) d: 1.22—1.27 (2H, m), 1.45—1.55 (4H, m),
2.20 (3H, s), 2.53 (2H, t, Jꢀ7.8 Hz), 2.83 (4H, t, Jꢀ4.8 Hz), 3.18 (3H, s),
3.26 (2H, t, Jꢀ6.5 Hz), 3.63 (4H, t, Jꢀ5.1 Hz), 7.08 (2H, d, Jꢀ8.0 Hz), 7.17
tanol (2.5 ml) and 0.05 M phosphate buffer (2.5 ml, pH 7.4) for 20 min at
25 °C, after which aliquots of both phases were taken for analysis by HPLC
quantitation. The reported logP value represents the mean of three experi-
(2H, d, Jꢀ8.0 Hz), 7.54 (1H, dd, Jꢀ2.2, 8.4 Hz), 7.69—7.73 (2H, m), 9.25 ments.
(1H, s); IR (KBr) cmꢃ1: 1683; ESI-HR-MS (m/z): 531.1933. Calcd for
C27H3335Cl2N4O3 (MꢄH): 531.1924.
References
(b) N-(Morphorin-1-yl)-1-(2,4-dichlorophenyl)-5-{4ꢁ-(5-hydroxypentyl)-
phenyl}-4-methyl-1H-pyrazole-3-carboxamide (18) was prepared from 5
(71 mg, 163 mmol), 4-aminomorpholine (20 ml, 207 mmol), 1-hydroxybenzo-
triazole (43 mg, 318 mmol), TPTU (62 mg, 209 mmol), and N,N-diisopropyl-
amine (84 ml, 694 mmol) according to the procedure described for 6 and was
isolated as an orange gum in 57% yield. 1H-NMR (CDCl3) d: 1.37—1.42
(2H, m), 1.55—1.65 (4H, m), 2.37 (3H, s), 2.59 (2H, t, Jꢀ8.2 Hz), 2.96 (3H,
s), 3.64 (2H, t, Jꢀ6.7 Hz), 3.86 (4H, m), 7.01 (2H, d, Jꢀ8.0 Hz), 7.11 (2H,
d, Jꢀ7.8 Hz), 7.26 (2H, br), 7.43 (1H, d, Jꢀ1.8 Hz), 7.73 (1H, br) ; IR (KBr)
cmꢃ1: 3446; FAB-MS (m/z): 517 (MꢄH)ꢄ. This material was used for the
O-methylation.
To a solution of 18 (11 mg, 20 mmol) in dry DMF (500 ml) was added 2,6-
di-tert-butyl-4-methylpyridine (15 ml, 110 mmol) in one portion. The solu-
tion was cooled to 0 °C, followed by the addition of methyl triflate (3 ml,
27 mmol). After being stirred at room temperature for 15 h, the mixture was
poured into a saturated NaHCO3 solution and extracted with EtOAc. The ex-
tracts were washed with brine, dried and evaporated to dryness, and chro-
matographed on silica gel. Elution with hexane : EtOAcꢀ1 : 1→1 : 2 gave 17
(2 mg, 17%) as a pale yellow gum, which was identical to the sample ob-
tained from 15.
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(1973).