Synthesis and SAR of 5-amino- and 5-(aminomethyl)benzofuran histamine H3 receptor antagonists with improved potency

Article abstract of DOI:10.1021/jm0504398

A new series of H₃ receptor antagonists was discovered with nanomolar and subnanomolar affinities at human and rat H₃ receptors. Starting from an earlier, more structurally limited series of benzofurans, the present series of compounds demonstrated increased structural variety and flexibility with greater in vitro potency. One compound in particular, {2-[2-(2-(R)-methylpyrrolidin-1-yl)ethyl]benzofuran-5-yl}(5-nitropyridin-2-yl) amine (7h), gave the best binding potency (human K_i of 0.05 nM, rat K_i of 0.11 nM), which represented a 9-fold (in human) and an 11-fold (in rat) improvement over ABT-239 (compound 5), a compound previously reported to have excellent in vitro potency and in vivo efficacy. The synthesis, SAR of the H₃ binding affinities, in vitro assay for phospholipidosis, and pharmacokinetic properties of the new compounds are described.

Full text of DOI:10.1021/jm0504398

6482
J. Med. Chem. 2005, 48, 6482-6490
Synthesis and SAR of 5-Amino- and 5-(Aminomethyl)benzofuran Histamine H3
Receptor Antagonists with Improved Potency
Minghua Sun,* Chen Zhao, Gregory A. Gfesser, Christine Thiffault, Thomas R. Miller, Kennan Marsh,
Jill Wetter, Michael Curtis, Ramin Faghih, Timothy A. Esbenshade, Arthur A. Hancock, and Marlon Cowart*
Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories, 100 Abbott Park Road,
Abbott Park, Illinois 60064-6123
Received May 9, 2005
A new series of H3 receptor antagonists was discovered with nanomolar and subnanomolar
affinities at human and rat H3 receptors. Starting from an earlier, more structurally limited
series of benzofurans, the present series of compounds demonstrated increased structural
variety and flexibility with greater in vitro potency. One compound in particular, {2-[2-(2-(R)-
methylpyrrolidin-1-yl)ethyl]benzofuran-5-yl}(5-nitropyridin-2-yl)amine (7h), gave the best
binding potency (human Ki of 0.05 nM, rat Ki of 0.11 nM), which represented a 9-fold (in human)
and an 11-fold (in rat) improvement over ABT-239 (compound 5), a compound previously
reported to have excellent in vitro potency and in vivo efficacy. The synthesis, SAR of the H3
binding affinities, in vitro assay for phospholipidosis, and pharmacokinetic properties of the
new compounds are described.
Introduction
The effects of histamine are mediated in the central
nervous system (CNS) and the periphery through four
known receptors, H1, H2, H3, and H4.1 Histamine H1 and
H2 receptors have been successfully targeted, and
therapeutic agents have been developed to treat condi-
tions such as allergies (H1 receptor antagonists) and
gastric ulcers (H2 receptor antagonists). The newly
discovered H4 receptor is found in immune cells, sug-
gesting a role in regulating inflammatory responses.2
Figure 1. Structures of representative H3 antagonists.
The H3 receptor, primarily located on nerve terminals
and in the CNS, modulates the production and release
of histamine.3 Pharmacological blockade of H3 receptors
enhances the release of histamine and other neu-
rotransmitters1 and has been shown to enhance vigi-
lance or alertness.4 Consequently, H3 receptor antago-
nists are thought to have potential as drug therapies
for ADHD, Alzheimer’s disease, Parkinson’s disease,
epilepsy, and sleep disorders.5 Early generations of H3
antagonists were based on structures containing the
imidazole moiety found in histamine; some of these
compounds, most prominently ciproxifan (1), have be-
come reference standards for H3 pharmacological re-
search. However, the imidazole moiety has been asso-
ciated with CYP450 inhibition,6 leading to potential
drug-drug interactions through inhibition of the me-
tabolism of coadministered drugs. For this reason,
recent efforts have been directed toward the discovery
of H3 antagonists without an imidazole moiety. Several
recently disclosed classes of nonimidazoles, such as 2,7a
3,7b and 48 (Figure 1), share common structural features
of the amine-alkoxy-phenyl pharmacophore.
scribed alkoxy-phenyl moiety was reported, as exem-
plified by ABT-239 (5).9 The 2-aminoethylbenzofuran-
based H3 antagonist 5 had nanomolar potency at H3
receptors and was efficacious in different rodent models
of cognition and attention at doses of 0.01-0.1 mg/kg.
With the goal of extending the SAR of the series,
improving binding potency, and possibly increasing
efficacy in behavioral models, two new subclasses of H3
antagonists were investigated. In the new series, the
2-(2R)-methylpyrrolidinylethylbenzofuran moiety was
retained, but 5-aminomethyl or 5-amino linkers were
inserted between the benzofuran nucleus and the lipo-
philic aromatic ring to increase the overall flexibility,
as exemplified by 6 and 7. The precursor (compound 11,
Scheme 1) to compound 6 was a dibasic amine, a feature
associated with a propensity to induce phospholipidosis.
Recently, a series of compounds that have a more rigid
ethylbenzofuran moiety to replace the previously de-
* To whom correspondence should be addressed. M.S.: Phone, (847)
938-6716; Fax, (847) 937-9195; e-mail, sun.minghua@abbott.com.
M.C.: Phone, (847) 938-8170, Fax, (847) 937-9195; e-mail,
marlon.d.cowart@abbott.com.
10.1021/jm0504398 CCC: $30.25 © 2005 American Chemical Society
Published on Web 09/13/2005

H3 Receptor Antagonists with Improved Potency
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20 6483
Scheme 1. Preparation of 5-Arylaminomethylbenzofuran Derivativesa
a Reagents and conditions: (i) KI, I2, in NH4OH; (ii) Pd(OAc)2, Cy2P(biphenylyl), CuI, Et3N, CH3CN; (iii) H2, Ra/Ni, 20% NH3/CH3OH;
(iv) method A, 1.2 equiv ArX, Et3N, ethanol, 75 °C; method B, 1.2 equiv ArX, DIPEA, dioxane, 100 °C; method C, 1.5 equiv ArX, Pd2(dba)3,
BINAP, Cs2CO3, toluene, 100 °C.
Scheme 2. Preparation of 5-Arylaminobenzofuran Derivativesa
a Reagents and conditions: (i) KI, I2, in NH4OH; (ii) 9, Pd(OAc)2, Cy2P(biphenylyl), CuI, Et3N, CH3CN; (iii) 60 psi H2, 10% Pd/C, methanol;
(iv) method A, 1.2 equiv ArX, Et3N, ethanol, 75 °C; method B, 1.2 equiv ArX, DIPEA, dioxane, 100 °C; method C, 1.5 equiv ArX, Pd2(dba)3,
BINAP, Cs2CO3, toluene, 100 °C; (v) LiHMDS, Pd2(dba)3, Cy2P(biphenylyl), aq HCl quench and then 2 N NaOH.
This propensity was reduced when the primary amine
was arylated to give series 6 compounds, a change that
served to reduce the basicity of one of the amines.
could be removed at this step. 5-Nitrobenzofuran 13 was
reduced to 5-aminobenzofuran 14 under 60 psi of
hydrogen in the presence of 10% palladium on carbon.
Alternatively, 5-aminobenzofuran 14 could also be
synthesized from 5-bromobenzofuran 15,9a,20 using
lithium bis(trimethylsilyl)amide as the nitrogen source,
under palladium catalysis.21 The target compounds
(7a-7k) were made by arylation at the amino group of
14 with aryl halides, using the same conditions as for
the preparation of 6a-6r.
Chemistry
As shown in Scheme 1, commercially available 4-cy-
anophenol was treated with potassium iodide and iodine
(1.0 equiv) in aqueous ammonium hydroxide to give
2-iodo-4-cyanophenol (8).10,11 The reaction mixture con-
tained trace amounts of unreacted starting material and
the diiodo phenol, neither of which affected the next step
of the sequence. Iodide 8 was coupled with alkyne 9
under Sonogashira conditions12-14 and subsequently
cyclized to form benzofuran 10. 5-Cyanobenzofuran 10
was cleanly hydrogenated to benzylic amine 11 in the
presence of Raney nickel. This intermediate was used
to prepare the target compounds (6a-6r) by reacting
with a variety of aryl halides. Depending on the nature
of the aryl halides, this coupling could be accomplished
either by simple displacement of electron-deficient het-
eroaryl halides or, in the case of more resistant sub-
strates, the Pd-catalyzed coupling.15-17
As outlined in Scheme 2, the iodination of com-
mercially available 4-nitrophenol with KI/I2/NH4OH
afforded iodide 12. Compared to 4-cyanophenol, the
iodination of 4-nitrophenol was much more sluggish,
proceeding to only about 50% completion, even after 5
days at room temperature. It should be noted that
attempts to iodinate the 4-nitrophenol by alternative
conditions, such as sodium hypochlorite and sodium
iodide18 or iodine/silver (I) triflate,19 were unsuccessful.
Purification of the crude reaction mixture, which con-
tained 12 and unreacted starting material, was un-
necessary, as the subsequent reaction with 9 proceeded
cleanly to form the benzofuran 13 and the 4-nitrophenol
Results and Discussion
The compounds described here were tested in in vitro
binding assays22 in membranes isolated from cells
transfected with both cloned rat H3 receptors and cloned
human H3 receptors. The binding affinities with differ-
ent aromatic substitution on the 5-aminomethylbenzo-
furan system are summarized in Table 1. The primary
amine intermediate, compound 11, was also tested in
the binding assay and was found to be very potent, with
Ki values of 0.1 and 0.27 nM for human and rat
receptors, respectively. But as a compound of potential
interest, compound 11 suffered from a propensity to
slow oxidation in air to the corresponding aldehyde.
Derivatization of the primary amine 11 with aromatic
and heteroaromatic halides resulted in compounds 6a-
6r. With the goal of improving potency over 5 in mind,
it was not clear if the flexible linker with carbon and
nitrogen atoms would be tolerated. 2-Nitro (6a) and
3-cyano (6d) analogues showed slightly better binding
potencies than compound 5, while 4-nitro and 4-trifluo-
roacetyl analogues (6b, 6c) were less potent at both
human and rat receptors. Substituted pyridines as the
aromatic moiety resulted in substantial improvement
in potencies, with the 2,6-dicyanopyridine analogue (6o)

6484 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20
Sun et al.
Table 1. Binding Affinities (pKi and Ki) of 5-Arylaminomethylbenzofurans at Human H3 and Rat H3 Receptorsa
b
b
human H3
rat H3
pKi ( SEM
Ki
(nM)
Ki
(nM)
compd
Ar substituent
pKi ( SEM
5
9.35 ( 0.04
9.50 ( 0.17
9.13 ( 0.13
9.13 ( 0.08
9.40 ( 0.14
9.51 ( 0.08
8.98 ( 0.09
9.53 ( 0.04
8.91 ( 0.09
9.16 ( 0.06
9.48 ( 0.03
9.07 ( 0.11
9.72 ( 0.17
9.36 ( 0.10
9.15 ( 0.03
9.88 ( 0.04
9.13 ( 0.14
9.46 ( 0.12
9.52 ( 0.12
0.45
0.31
0.74
0.74
0.40
0.31
1.04
0.29
1.22
0.69
0.33
0.84
0.19
0.43
0.71
0.13
0.74
0.34
0.30
8.91 ( 0.05
9.06 ( 0.22
8.67 ( 0.19
8.63 ( 0.19
8.93 ( 0.21
8.80 ( 0.10
8.40 ( 0.18
9.09 ( 0.07
8.40 ( 0.16
8.60 ( 0.14
9.24 ( 0.18
8.48 ( 0.11
9.17 ( 0.01
8.57 ( 0.13
8.54 ( 0.07
9.40 ( 0.14
8.72 ( 0.26
8.85 ( 0.17
8.93 ( 0.14
1.23
0.87
2.12
2.36
1.18
1.58
3.96
0.80
4.02
2.51
0.58
3.27
0.68
2.71
2.88
0.40
1.92
1.42
1.19
6a
6b
6c
6d
6e
6f
2-nitrophenyl
4-nitrophenyl
4-(2,2,2-trifluoroacetyl)phenyl
3-cyanophenyl
6-chloropyridazin-3-yl
3-cyanopyrazin-2-yl
pyrazin-2-yl
5-bromopyrimidin-2-yl
pyrimidin-5-yl
5-ethylpyrimidin-2-yl
pyrimidin-2-yl
5-nitrothiazol-2-yl
3-nitropyridin-2-yl
3,5-dinitropyridin-2-y l
2,6-dicyanopyridin-4-yl
3-cyanopyridin-2-yl
5-cyanopyridin-2-yl
5-nitropyridin-2-yl
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
6q
6r
a Binding potencies were assessed by displacement of [3H]-N-R-methylhistamine, using cloned human H3 receptors and cloned rat H3
receptors. pKi ) -logKi. b The values are reported as average of n g 3 independent measurements for all compounds.
Table 2. Binding Affinities (pKi and Ki) of 5-Arylaminobenzofurans at Human H3 and Rat H3 Receptorsa
b
b
human H3
pKi ( SEM
rat H3
pKi ( SEM
Ki
(nM)
Ki
(nM)
compd
Ar substituent
5
9.35 ( 0.04
9.66 ( 0.07
9.57 ( 0.06
9.53 ( 0.07
9.21 ( 0.10
9.51 ( 0.12
10.12 ( 0.09
9.98 ( 0.04
10.32 ( 0.14
9.87 ( 0.17
8.53 ( 0.06
9.27 ( 0.11
0.45
0.22
0.27
0.29
0.62
0.31
0.08
0.11
0.05
0.14
2.98
0.54
8.91 ( 0.05
9.06 ( 0.13
8.87 ( 0.14
8.83 ( 0.15
8.60 ( 0.09
8.70 ( 0.13
9.57 ( 0.18
9.42 ( 0.13
9.98 ( 0.12
9.45 ( 0.13
7.75 ( 0.17
8.56 ( 0.14
1.23
0.87
1.35
1.47
2.51
2.01
0.27
0.38
0.11
0.35
17.90
2.76
7a
7b
7c
7d
7e
7f
2-nitrophenyl
4-cyanophenyl
3-cyanophenyl
5-ethyl-pyrimidin-2-yl
pyrimidin-2-yl
pyrimidin-5-yl
pyrazin-2-yl
5-nitropyridin-2-yl
3-nitropyridin-2-yl
3-cyano-6-methylpyridin-2-yl
5-trifluoromethyl-pyridin-2-yl
7g
7h
7i
7j
7k
a Binding potencies were assessed by displacement of [3H]-N-R-methylhistamine, using cloned human H3 receptors and cloned rat H3
receptors. pKi ) -logKi. b The values are reported as average of n g 3 independent measurements for all compounds.
having a Ki of 0.13 nM at cloned human receptor and
0.40 nM at cloned rat receptor. Substitution at the
5-position of the pyridyl ring (6q, 6r) is clearly more
effective in boosting potency than 3-substitution (6m,
6p) or 3,5-disubstitutions (6n). Other heterocycles such
as substituted pyrimidines (6h-6k) were also investi-
gated. Compound 6j (human Ki of 0.33 nM, rat Ki of 0.58
nM), which has a 5-ethyl group, showed slightly better
binding potency than 5, whereas other pyrimidines (6h,
6i, 6k) were 2-3 times less potent than compound 5 at
both receptors. Similar results were observed with the
homologous pyrazines and pyridazines (6e-6g). 6e and
6g were about equipotent to compound 5 at both human
and rat receptors, and 6f was half as potent in human
and one-third as potent in rat compared with compound
5. One particularly advantageous heterocycle was the
5-nitrothiazol-2-yl group found in 6l, which had twice
the potency of compound 5. Overall, the incremental
increase in flexibility induced by interspersing the
additional carbon and nitrogen atoms between the
benzofuran and lipophilic ring was well tolerated, with
the best compounds showing a 2-3-fold improvement
of potency over compound 5.
The SAR of the 5-aminobenzofurans is summarized
in Table 2. This series of compounds is also more flexible
than compound 5, but compared to compounds 6a-6r,
which have carbon and nitrogen atoms between benzo-
furan and the aromatic ring, compounds 7a-7k have
only one nitrogen linking the benzofuran to the aromatic
ring. This imparts some flexibility to the benzofuran-

H3 Receptor Antagonists with Improved Potency
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20 6485
Table 3. Comparison of Substituent SAR for Series 6 and Series 7 Compounds
aromatic ring moiety, but less than in the series of
compounds 6a-6r. When the aromatic moiety was a
substituted phenyl ring (7a-7c, Table 2), the human
H3 binding potencies for all three compounds were
slightly better than that of compound 5 (1.5-2.0-fold),
whereas the rat potencies were about the same as that
of compound 5. Again, as in the previous series (6a-
6r), 2-nitro substitution (7a) of the phenyl ring induced
the highest potency. When substituted pyridines were
used as the aromatic moiety, compounds showed a wide
range of potencies. The 5-nitropyridyl-2-yl analogue (7h)
gave the best binding potency (human Ki of 0.05 nM,
rat Ki of 0.11 nM), about 10-fold improvement on both
human and rat receptors over compound 5. The 3-ni-
tropyridyl-2-yl analogue (7i) also showed a 3-fold im-
provement in potency over compound 5. The 5-trifluo-
romethylpyridyl-2-yl analogue (7k) was slightly less
potent than compound 5 (human Ki of 0.54 nM, rat Ki
of 2.76 nM), whereas the 3-cyano-6-methylpyridyl-2-yl
analogue (7j) was significantly less potent than 5 (7-
fold for human and 15-fold for rat). In this series of
compounds, the disubstituted analogue reduced the
binding potency, even more so than in the compound 6
series. Among the pyrimidines and pyrazines investi-
gated as aromatic substituents, unlike the compound 6
series, where 5-ethylpyrimidin-2-yl (6j) was slightly
better than others, the unsubstituted pyrimidin-5-yl
analogue (7f) (human Ki of 0.08 nM, rat Ki of 0.27 nM)
was clearly superior, showing about a 6-fold improve-
ment in potency at human H3 receptor and a 5-fold
potency improvement in rat, compared to compound 5.
The pyrazin-2-yl analogue (7g) was also a more potent
compound than 5.
in series 7 (7f, 7h) were clearly more potent than their
corresponding series 6 counterparts (6i, 6r), leaving 7f
and 7h the most active compounds among either series
and representing an advance of 6- and 9-fold in human
potency and 5- and 11-fold in rat potency over the parent
compound 5.
The dibasic compound 11 is highly potent at H3
receptors, a finding that has also been noted with other
chemical classes of H3 antagonists that bear at least two
basic amino groups.5b,23 A potential drawback of this
class of compounds is that they may have the propensity
to potently induce phospholipidosis. Lipophilic com-
pounds incorporating basic amines have reportedly been
associated with the ability to increase concentrations
of phospholipids due to their ability to bind to negatively
charged phospholipid bilayers and to inhibit the activi-
ties of lysosomal phospholipases by neutralizing the
surface negative charges required by these enzymes for
optimal activity.24 Although lipophilic monoamines can
also exhibit this propensity to an extent, the presence
of a second amine greatly exacerbates the potential
toxicity.25 For this reason, and because of the aforemen-
tioned chemical instability seen in 11, this compound
and similar dibasic compounds were deemed to have
characteristics detrimental to their suitability as drugs.
This was one of the motivations behind the strategy of
making aromatic- and heteroaromatic-substituted ana-
logues of 11, a process that served to reduce the basicity
of the second amine and produce monocationic com-
pounds, therefore reducing the propensity to induce
phospholipidosis.
To test this hypothesis, compounds 11, 6j, and 6k
were evaluated in an in vitro assay for phospholipido-
sis.26 The results are expressed as a “phospholipidosis
index” (Chart 1), which was normalized to amiodarone,
a compound with a known propensity to induce phos-
pholipidosis27 that served as a positive control and
reference standard. By this measure, a value of 1.0
indicated that the compound induces phospholipidosis
to the same extend as amiodarone (at 5 µM). The
In general, comparing compounds with the same
substituents (Table 3), analogues in the arylamino series
(7) were more potent than those in the arylaminomethyl
series (6) at both human and rat H3 receptors. The only
exception to this finding was the 5-ethylpyrimidin-2-yl
substituted pair (6j, 7d), where 6j was more potent than
7d, especially in rat binding. The two best compounds

6486 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20
Sun et al.
Chart 1. Normalized Phospholipidosis Index for
aromatic substituent improved potency considerably,
while also providing some analogues with acceptable PK
properties.
Selected Compoundsa
Experimental Section
Chemistry Methods. Unless otherwise noted, all com-
mercially available solvents, chemicals, and reagents were
used without purification. Mass spectra were obtained on a
Kratos MS-50 instrument, and unless otherwise indicated, all
MS instruments were operated in the +APCI or +DCI mode
to detect positively charged ions. Elemental analysis was
performed by Robertson Microlit Laboratories, Inc., Madison,
NJ. 1H NMR spectra were recorded on Bruker 300 MHz
spectrometer. Chemical shifts (δ, ppm) are determined using
TMS as internal standard. Abbreviations used in description
of NMR spectra: s ) singlet, d ) doublet, t ) triplet, dd )
double doublet, dt ) double triplet, m ) multiplet, br ) broad
singlet. Flash column chromatography was performed with
prepacked Biotage cartridges. Thin-layer chromatography was
performed on 250 µM SG-60F TLC plates from Merck. All
reactions were carried out under a nitrogen atmosphere. Basic
methanol was prepared by mixing 10% ammonium hydroxide
in methanol.
a Results were normalized to amiodarone (at 5 µM). Other
compounds were tested at 18.75 µM, in primary cultures of rat
hepatocytes.
Table 4. Rat Pharmacokinetic Properties of Selected H3
Antagonistsa
1 mg/kg iv dose
1 mg/kg po dose
4-Hydroxy-3-iodobenzonitrile (8). In a 1-L round-bottom
flask equipped with a magnetic stirring bar, 4-cyanophenol
(10.0 g, 83.95 mmol) was dissolved in 450 mL of concentrated
ammonium hydroxide. To this solution was added a mixture
of potassium iodide (68.3 g, 411.3 mmol) and iodine (21.3 g,
83.95 mmol) in 100 mL of water quickly. The reaction mixture
darkened immediately. The mixture was stirred at room
temperature overnight during which it became a white sus-
pension. The precipitate was removed by filtration, and the
filtrate was concentrated. The solid was then dissolved in 500
mL of dichloromethane and washed with water (2 × 350 mL).
The organic layer was dried over sodium sulfate, filtered, and
concentrated to dryness under reduced pressure to give the
crude product 8 (14.2 g, 69%), which was used in the next step
without further purification. 1H NMR (CDCl3): δ 7.97 (d, J )
2.03 Hz, 1H), 7.55 (dd, J ) 8.48, 2.03 Hz, 1H), 7.05 (d, J )
8.48 Hz, 1H), 5.80 (s, 1H).
compd
t1/2
AUC
CLb
t1/2
Cmax
AUC
F
5
5.7
1.7
1.0
0.3
3.7
666.8
210.7
350.5
35.9
1.54
4.79
2.86
28.50
2.82
6.7
UC
1.7
UC
4.8
39.6
7.1
34.5
0.0
16.2
426.2
18.9
72.1
0.0
61.8
9.0
20.6
0.0
29.0
6j
6k
7f
7d
355.4
103.2
a 1 mg/kg dose of each compound simultaneously in each rat.
Units: t1/2 (h); Cmax (ng/mL); AUC (ng‚h r/mL); F (%); CLb (L/h‚kg);
ng 2. UC: uncalculated.
phospholipidosis index for compound 11 was 1.22 at a
concentration of 18.75 µM, whereas the phospholipidosis
index for compounds 6j and 6k were 0.57 and 0.42 at
the same concentration. This provides experimental
support for the original hypothesis: by removing one
of the basic amines, the potential of inducing phospho-
lipidosis may be greatly reduced.
2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
carbonitrile (10). The above iodophenol 8 (10.0 g, 40.8 mmol),
palladium(II) acetate (460 mg, 2.05 mmol), dicyclohexylbiphe-
nylylphosphine (1.075 g, 3.07 mmol), and 510 mL of a 0.1 M
solution of 1-but-3-ynyl-2-methylpyrrolidine 9 in acetonitrile
were mixed to give a clear yellow solution. Triethylamine (57
mL, 408 mmol) was added and the mixture stirred for 15 min
before copper(I) iodide (390 mg, 2.05 mmol) was added. The
reaction mixture was heated to and kept at 65 °C overnight.
It was then cooled to room temperature and filtered through
Celite to remove the insoluble material. The filtrate was
concentrated under reduced pressure, and the resulting oil was
redissolved in 800 mL of dichloromethane, washed with 10%
ammonium hydroxide (2 × 500 mL), followed by brine, and
then dried over sodium sulfate. The organic solution was
filtered and evaporated to dryness to give the crude product.
Purification by flash chromatography (1-5% basic methanol
in dichloromethane) gave the title compound as a yellow oil
The rat pharmacokinetic properties of selected com-
pounds were also investigated, and the data are sum-
marized in Table 4. While compound 5 displayed a
favorable PK profile in rats, with an oral bioavailability
of 61.8% and t1/2 of 6.7 h, none of the newly discovered
compounds tested could match this profile. The new
series 6 and 7 compounds all had shorter t1/2, lower
AUC, higher clearance rates, and lower oral bioavail-
ability. It was suspected that the presence of a hetero-
atom (nitrogen) between the two aromatic moieties
increased the polarity of the structure and provided an
extra site for metabolism. It is possible that this change
affected protein binding and blood PK, resulting in
poorer PK properties and faster clearance when com-
pared with the parent compound 5. On the other hand,
in the case of 6k and 7d, which have an oral bioavail-
ability of 21% and 29%, the PK profiles were considered
adequate to support further studies.
1
(5.84 g, 56%). H NMR (CDCl3): δ 7.82 (s, 1 H), 7.49 (d, J )
1.70 Hz, 2 H), 6.54 (s, 1 H), 3.18-3.33 (m, 2 H), 2.98-3.13 (m,
2 H), 2.39-2.63 (m, 2 H) 2.17-2.35 (m, 1 H), 1.91-2.06 (m, 1
H) 1.68-1.89 (m, 2 H) 1.40-1.58 (m, 1 H) 1.17 (d, J ) 6.10
Hz, 3 H).
In summary, highly potent (subnanomolar) H3 an-
tagonists with balanced affinity at human and rat H3
receptors were discovered and several compounds showed
significant improvements (5-11-fold) in binding potency
compared with the benchmark compound (5). A wide
variety of heterocycles were tolerated in both series,
with compound 7h being 9-fold and 11-fold more potent
than compound 5 at human and rat receptors, respec-
tively. Therefore, it was concluded that incorporation
of flexible linker atoms between the benzofuran ring and
C-{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-
5-yl}methylamine (11). The above nitrile 10 (5.80 g, 22.8
mmol) was hydrogenated at 60 psi of H2 in 280 mL of 20%
ammonium in methanol in the presence of 58.6 g of Raney
nickel at room temperature for 2 h. The catalyst was removed
by filtration through Celite. The filtrate was concentrated
under reduced pressure, and the resulting oil was purified by
flash chromatography (5% basic methanol in dichloromethane)
1
to give the desired product as a yellow oil (3.65 g, 63%). H
NMR (CDCl3): δ 7.41 (d, J ) 1.23 Hz, 1 H), 7.36 (d, J ) 8.29
Hz, 1 H), 7.15 (dd, J ) 8.29, 1.84 Hz, 1 H), 6.40 (s, 1 H), 3.92

H3 Receptor Antagonists with Improved Potency
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20 6487
(s, 2 H), 3.15-3.25 (m, 2 H), 2.94-3.02 (m, 2 H), 2.44-2.52
(m, 1 H), 2.33-2.42 (m, 1 H), 2.21 (q, J ) 8.90 Hz, 1 H), 1.88-
1.99 (m, 1 H), 1.66-1.86 (m, 2 H), 1.58 (Br, NH2, 2 H), 1.38-
1.50 (m, 1 H), 1.13 (d, J ) 6.14 Hz, 3 H). Anal. (C16H22N2O·
0.3CH3OH) C, H, N.
General Procedures for the Coupling of Amine 11
with Aromatic Halides To Prepare Compounds 6. Method
A. Compound 11 (50 mg, 0.194 mmol), aromatic halide (0.232
mmol), and triethylamine (81 µL, 0.582 mmol) were mixed in
1 mL of ethanol. The mixture was stirred at 75 °C for 1-3
days. The reaction was quenched with water and extracted
with dichloromethane (3×). The combined organic layers were
dried over sodium sulfate and concentrated to give the crude
product, which was then purified by flash chromatography.
Method B. Compound 11 (50 mg, 0.194 mmol), aromatic
halide (0.232 mmol), and diisopropylethylamine (101 µL, 0.582
mmol) were mixed in 1 mL of dioxane. The mixture was stirred
at 100 °C for 1-3 days. The reaction was quenched with water
and extracted with dichloromethane (3×). The combined
organic layers were dried over sodium sulfate and concentrated
to give the crude product, which was then purified by flash
chromatography.
J ) 6.10 Hz, 3H). Anal. (C23H25N3O) H. C: calcd, 76.85; found,
76.26. N: calcd, 11.69; found, 7.76.
(6-Chloropyridazin-3-yl){2-[2-(2-methylpyrrolidin-1-yl)-
ethyl]benzofuran-5-ylmethyl}amine (6e). Compound 6e
was prepared according to method A (29%). 1H NMR (CDCl3):
δ 7.47 (d, J ) 1.36 Hz, 1H), 7.38 (d, J ) 8.48 Hz, 1H), 7.20
(dd, J ) 8.31, 1.86 Hz, 1H), 7.14 (d, J ) 9.15 Hz, 1H), 6.60 (d,
J ) 9.49 Hz, 1H), 6.42 (s, 1H), 5.11 (br, 1H), 4.65 (d, J ) 5.76
Hz, 2H), 3.15-3.29 (m, 2 H), 2.93-3.07 (m, 2 H), 2.33-2.58
(m, 2 H), 2.15-2.29 (m, 1 H), 1.90-2.03 (m, 1 H), 1.68-1.86
(m, 1 H), 1.39-1.63 (m, 2 H), 1.15 (d, J ) 5.76 Hz, 3 H). Anal.
(C20H23N4OCl·0.2H2O) C, H, N.
3-({2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-
5-ylmethyl}amino)pyrazine-2-carbonitrile (6f). Compound
6f was prepared according to method A (63%). 1H NMR
(CDCl3): δ 8.25 (d, J ) 2.37 Hz, 1H), 7.93 (d, J ) 2.37 Hz,
1H), 7.46 (s, 1H), 7.39 (d, J ) 8.48 Hz, 1H), 7.20 (dd, J ) 8.31,
1.86 Hz, 1H), 6.44 (s, 1H), 5.57 (br, 1H), 4.75 (d, J ) 5.43 Hz,
2H), 3.15-3.33 (m, 2 H), 2.95-3.10 (m, 2 H), 2.35-2.60 (m, 2
H), 2.15-2.31 (m, 1 H), 1.90-2.03 (m, 1 H), 1.69-1.85 (m, 1
H), 1.39-1.62 (m, 2 H), 1.16 (s, 3H). Anal. (C21H25N5O) C, H,
N.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
ylmethyl}pyrazin-2-ylamine (6g). Compound 6g was pre-
pared according to method A (14%). 1H NMR (CDCl3): δ 8.02
(dd, J ) 2.71, 1.36 Hz, 1H), 7.90 (d, J ) 1.36 Hz, 1H), 7.83 (d,
J ) 3.05 Hz, 1H), 7.47 (d, J ) 1.36 Hz, 1H), 7.38 (d, J ) 8.48
Hz, 1H), 7.20 (dd, J ) 8.31, 1.87 Hz, 1H), 6.42 (s, 1H), 4.89
(br, 1H), 4.61 (d, J ) 5.43 Hz, 2H), 3.15-3.29 (m, 2 H), 2.93-
3.10 (m, 2 H), 2.33-2.60 (m, 2 H), 2.13-2.29 (m, 1 H), 1.89-
2.05 (m, 1 H), 1.63-1.87 (m, 2 H), 1.38-1.53 (m, 1 H), 1.15 (d,
J ) 6.10 Hz, 3H). Anal. (C20H24N4O) C, H, N.
(5-Bromopyrimidin-2-yl){2-[2-(2-(R)-methylpyrrolidin-
1-yl)ethyl]benzofuran-5-ylmethyl}amine (6h). Compound
6h was prepared according to method B (66%). 1H NMR
(CDCl3): δ 7.41 (s, 2H), 7.13 (dd, J ) 8.48, 1.70 Hz, 1H), 6.97
(s, 2H), 6.45 (s, 1H), 5.30 (br, 1H), 4.46 (d, J ) 5.43 Hz, 2H),
3.17-3.30 (m, 2 H), 2.97-3.09 (m, 2 H), 2.37-2.59 (m, 2 H),
2.18-2.31 (m, 1 H), 1.90-2.04 (m, 1 H), 1.66-1.89 (m, 2 H),
1.40-1.56 (m, 1 H), 1.16 (d, J ) 6.10 Hz, 3H). Anal. (C20H23N4-
OBr) C, H, N.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
ylmethyl}pyrimidin-5-ylamine (6i). Compound 6i was pre-
pared according to method C (15%). 1H NMR (CDCl3): δ 8.60
(s, 1H), 8.15 (s, 2H), 7.46 (s, 1H), 7.40 (d, J ) 8.48 Hz, 1H),
7.16-7.22 (m, 1H), 6.42 (s, 1H), 4.42 (d, J ) 5.43 Hz, 2H),
4.13 (br, 1H), 3.15-3.31 (m, 2 H), 2.91-3.06 (m, 2 H), 2.33-
2.57 (m, 2 H), 2.14-2.29 (m, 1 H), 1.88-2.04 (m, 1 H), 1.64-
1.87 (m, 2 H), 1.37-1.53 (m, 1 H), 1.14 (d, J ) 5.76 Hz, 3H).
Anal. (C20H24N4O·0.15H2O) C, H, N.
Method C. Compound 11 (50 mg, 0.194 mmol), aromatic
halide (0.233 mmol), tris(dibenzylideneacetone)dipalladium-
(0) (Pd2(dba)3) (9.0 mg, 0.0097 mmol), racemic-2,2′-bis(diphe-
nylphosphino)-1,1′-binaphthyl (BINAP) (9.0 mg, 0.0145 mmol),
and cesium carbonate (95 mg, 0.291 mmol) were placed in a
reaction vessel and dried under vacuum for 2 h. Toluene (1
mL) was added and the mixture was heated at 100 °C
overnight. The reaction was cooled to room temperature,
quenched with water, and then extracted with dichloromethane
(3×). The combined organic layers were dried over sodium
sulfate and concentrated to give the crude product, which was
then purified by flash chromatography.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
ylmethyl}(2-nitrophenyl)amine (6a). Compound 6a was
1
prepared according to method A (74%). H NMR (CDCl3): δ
8.42 (br, 1H), 8.19 (d, J ) 8.59 Hz, 1H), 7.46 (s, 1H), 7.38 (m,
2H), 7.19 (d, J ) 8.59 Hz, 1H), 6.85 (d, J ) 8.59 Hz, 1H), 6.65
(t, J ) 7.67 Hz, 1H), 6.42 (s, 1H), 4.60 (d, J ) 5.52 Hz, 2 H),
3.14-3.31 (m, 2 H), 3.01 (s, 2 H), 2.33-2.59 (m, 2 H), 2.15-
2.30 (m, 1 H), 1.90-2.02 (m, 1 H), 1.65-1.88 (m, 2 H), 1.36-
1.54 (m, 1 H), 1.15 (d, J ) 4.91 Hz, 3H). Anal. (C22H25N3O3) C,
H, N.
{2-[2-(2-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-yl-
methyl}(4-nitrophenyl)amine (6b). Compound 6b was pre-
pared according to method A (22%). 1H NMR (CDCl3): δ 8.05
(d, J ) 8.90 Hz, 2H), 7.43 (s, 1H), 7.38 (d, J ) 8.29 Hz, 1H),
7.17 (dd, J ) 8.29, 1.84 Hz, 1H), 6.57 (d, J ) 9.21 Hz, 2H),
6.42 (s, 1H), 5.05 (br, 1H), 4.46 (d, J ) 5.52 Hz, 2H), 3.17-
3.31 (m, 2 H), 3.02 (t, J ) 7.67 Hz, 2 H), 2.39-2.59 (m, 2 H),
2.18-2.33 (m, 1 H), 1.89-2.02 (m, 1 H), 1.67-1.88 (m, 2 H),
1.41-1.55 (m, 1 H), 1.16 (d, J ) 5.83 Hz, 3H). Anal.
(C22H25N3O3) C, H, N.
2,2,2-Trifluoro-1-[4-({2-[2-(2-methylpyrrolidin-1-yl)eth-
yl]benzofuran-5-ylmethyl}amino)phenyl]ethanone (6c).
Compound 6c was prepared according to method A (55%). 1H
NMR (CDCl3): δ 7.92 (d, J ) 8.14 Hz, 2H), 7.45 (s, 1H), 7.40
(d, J ) 8.48 Hz, 1H), 7.18 (dd, J ) 8.48, 1.70 Hz, 1H), 6.65 (d,
J ) 9.16 Hz, 2H), 6.43 (s, 1H), 4.87 (br, 1H), 4.49 (d, J ) 5.43
Hz, 2H), 3.15-3.30 (m, 2 H), 2.93-3.10 (m, 2 H), 2.33-2.57
(m, 2 H), 2.15-2.29 (m, 1 H), 1.90-2.03 (m, 1 H), 1.67-1.88
(m, 2 H), 1.48-1.62 (m, 1 H), 1.14 (m, 3 H). Anal. (C24H25N2O2F3)
C, H, N.
(5-Ethylpyrimidin-2-yl){2-[2-(2-(R)-methylpyrrolidin-
1-yl)ethyl]benzofuran-5-ylmethyl}amine (6j). Compound
6j was prepared according to method B (13%). 1H NMR
(CDCl3): δ 8.16 (s, 2H), 7.46 (d, J ) 1.36 Hz, 1H), 7.35 (d, J )
8.14 Hz, 1H), 7.20 (dd, J ) 8.48, 1.70 Hz, 1H), 6.40 (s, 1H),
5.29 (br, 1H), 4.67 (d, J ) 6.10 Hz, 2H), 3.14-3.28 (m, 2 H),
2.93-3.05 (m, 2 H), 2.47 (q, J ) 7.80 Hz, 2H), 2.32-2.42 (m,
2 H), 2.15-2.28 (m, 1 H), 1.88-2.03 (m, 1 H), 1.65-1.85 (m, 2
H), 1.37-1.53 (m, 1 H), 1.20 (t, J ) 7.63 Hz, 3H), 1.14 (d, J )
6.10 Hz, 3H). Anal. (C22H28N4O·0.15dioxane) C, H, N.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
ylmethyl}pyrimidin-2-ylamine (6k). Compound 6k was
1
prepared according to method B (55%). H NMR (CDCl3): δ
8.30 (d, J ) 4.75 Hz, 2H), 7.46 (s, 1H), 7.36 (d, J ) 8.14 Hz,
1H), 7.20 (dd, J ) 8.31, 1.86 Hz, 1H), 6.55 (t, J ) 4.75 Hz,
1H), 6.40 (s, 1H), 5.37 (br, 1H), 4.69 (d, J ) 5.76 Hz, 2H), 3.14-
3.28 (m, 2 H), 2.93-3.05 (m, 2 H), 2.32-2.54 (m, 2 H), 2.13-
2.27 (m, 1 H), 1.89-2.01 (m, 1 H), 1.64-1.86 (m, 2 H), 1.37-
1.51 (m, 1 H), 1.14 (d, J ) 5.76 Hz, 3H). Anal. (C20H24N4O·
0.16H2O) C, H, N.
3-({2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-
5-ylmethyl}amino)benzonitrile (6d). Compound 6d was
1
prepared according to method C (13%). H NMR (CDCl3): δ
8.03 (d, J ) 1.36 Hz, 1H), 7.79 (dd, J ) 8.48, 1.70 Hz, 1H),
7.52 (d, J ) 8.48 Hz, 1H), 7.36-7.40 (m, 1H), 7.17-7.20 (m,
1H), 6.96 (d, J ) 7.46 Hz, 1H), 6.83 (s, 1H), 6.57 (s, 1H), 4.34-
4.42 (m, 2 H), 4.25-4.32 (br, 1 H), 3.14-3.30 (m, 2 H), 2.93-
3.09 (m, 2 H), 2.33-2.58 (m, 2 H), 2.15-2.29 (m, 1 H), 1.89-
2.02 (m, 1 H), 1.66-1.88 (m, 2 H), 1.39-1.53 (m, 1 H), 1.14 (d,
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
ylmethyl}(5-nitrothiazol-2-yl)amine (6l). Compound 6l was
1
prepared according to method C (11%). H NMR (CDCl3): δ
7.95 (s, 1H), 7.46 (d, J ) 1.36 Hz, 1H), 7.42 (d, J ) 8.48 Hz,

6488 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20
Sun et al.
1H), 7.18 (dd, J ) 8.48, 1.70 Hz, 1H), 6.90 (br, 1H), 6.44 (s,
1H), 4.54 (s, 2H), 3.16-3.30 (m, 2 H), 2.95-3.07 (m, 2 H), 2.34-
2.57 (m, 2 H), 2.16-2.30 (m, 1 H), 1.89-2.02 (m, 1 H), 1.66-
1.86 (m, 2 H), 1.39-1.54 (m, 1 H), 1.14 (d, J ) 6.10 Hz, 3H).
LC/MS (AA method): m/z 386.7 (M + H). LC/MS (TFA
method): m/z 386.7 (M + H).
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
ylmethyl}(3-nitropyridin-2-yl)amine (6m). Compound 6m
was prepared according to method B (77%). 1H NMR (CDCl3):
δ 8.52 (br, 1H), 8.40-8.49 (m, 2 H), 7.49 (d, J ) 1.36 Hz, 1H),
7.38 (d, J ) 8.48 Hz, 1H), 7.17-7.30 (m, 1 H), 6.68 (dd, J )
8.14, 4.75 Hz, 1H), 6.43 (s, 1H), 4.91 (d, J ) 5.43 Hz, 2H),
3.14-3.34 (m, 2 H), 2.93-3.10 (m, 2 H), 2.35-2.60 (m, 2 H),
2.15-2.31 (m, 1 H), 1.68-2.03 (m, 3 H), 1.40-1.61 (m, 1 H),
1.17 (s, 3H). Anal. (C21H24N4O3) C, H, N.
(3,5-Dinitropyridin-2-yl){2-[2-(2-(R)-methylpyrrolidin-
1-yl)ethyl]benzofuran-5-ylmethyl}amine (6n). Compound
6n was prepared according to method B (77%). 1H NMR
(CDCl3): δ 9.30 (d, J ) 2.37 Hz, 1H), 9.24 (d, J ) 2.71 Hz,
1H), 9.00 (br, 1H), 7.49 (d, J ) 1.36 Hz, 1H), 7.41 (d, J ) 8.14
Hz, 1H), 7.22 (dd, J ) 8.48, 1.70 Hz, 1H), 6.46 (s, 1H), 5.00 (d,
J ) 5.76 Hz, 2H), 3.19-3.35 (m, 2 H), 2.96-3.16 (m, 2 H),
2.41-2.67 (m, 2 H), 2.16-2.36 (m, 1 H), 1.70-2.08 (m, 3 H),
1.47-1.65 (m, 1 H), 1.19 (s, 3H). Anal. (C21H23N5O5·0.4H2O)
C, N. H: calcd, 5.54; found, 5.03.
2-(R)-Methyl-1-[2-(5-nitrobenzofuran-2-yl)ethyl]pyrro-
lidine (13). Compound 13 was synthesized the same way as
compound 10, using compound 12 as the starting material
instead of compound 8. Since compound 12 is about a 1:1
mixture of 4-nitrophenol and 2-iodo-4-nitrophenol, the yield
was not calculated. From 2.97 g of crude 12, 450 mg of pure
product 13 was obtained. 1H NMR (CDCl3): δ 8.42 (d, J ) 2.03
Hz, 1H), 8.16 (dd, J ) 8.82, 2.37 Hz, 1H), 7.48 (d, J ) 9.15
Hz, 1H), 6.61 (s, 1H), 3.16-3.39 (m, 2H), 2.95-3.17 (m, 2H),
2.37-2.67 (m, 2H), 2.16-2.39 (m, 1H), 1.88-2.09 (m, 1H),
1.62-1.90 (m, 2H), 1.38-1.58 (m, 1H), 1.17 (d, J ) 6.10 Hz,
3H).
2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
ylamine (14). Compound 13 (2.15 g, 7.84 mmol) was dissolved
in 55 mL of methanol, and 215 mg of 10% Pd/C was added.
The compound was hydrogenated under 60 psi hydrogen
atmosphere at room temperature for 16 h. After filtration, the
crude product was purified by flash chromatography (3% basic
methanol in dichloromethane) to give the desired product as
a yellow oil (1.41 g, 74%). 1H NMR (CDCl3): δ 7.19 (d, J )
8.82 Hz, 1H), 6.77 (d, J ) 2.37 Hz, 1H), 6.59 (dd, J ) 8.65,
2.54 Hz, 1H), 6.29 (s, 1H), 3.53 (br, 2 H), 3.12-3.29 (m, 2H),
2.89-3.01 (m, 2H), 2.31-2.55 (m, 2H), 2.13-2.28 (m, 1H),
1.87-2.01 (m, 1H), 1.64-1.85 (m, 2H), 1.37-1.55 (m, 1H), 1.14
(d, J ) 6.10 Hz, 3H).
2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
ylamine (14). Compound 14 can be made alternatively from
compound 15. Compound 159a,20 (308 mg, 1.0 mmol, 1 equiv),
tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3) (36 mg,
0.05 mmol, 5%), and dicyclohexylbiphenylylphosphine (42 mg,
0.12 mmol, 12%) were charged into a pressure tube which was
evacuated and refilled with nitrogen. To this system was added
LiHMDS (1.0M in THF, 1.2 mL, 1.2 mmol, 1.2 equiv) and the
mixture was heated at 65 °C for 16 h. It was quenched with 4
mL of 2 N HCl, basified with 6 mL of 2 N NaOH, and extracted
with dichloromethane. The organic layer was dried over
sodium sulfate and concentrated to give the crude product,
which was then purified by flash chromatography using 5%
basic methanol in dichloromethane to give the desired product
(294 mg, 80%).
General Procedures for the Coupling of Compound
14 with Aromatic Halides To Prepare Compounds 7.
Compounds 7a-7k were prepared analogously to 6a-6r,
except using compound 14 as starting material instead of
compound 11.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
yl}(2-nitrophenyl)amine (7a). Compound 7a was prepared
according to method B (31%). 1H NMR (CDCl3): δ 9.52 (s, 1H),
8.21 (dd, J ) 8.65, 1.53 Hz, 1H), 7.45 (d, J ) 8.81 Hz, 1H),
7.40 (d, J ) 2.37 Hz, 1H), 7.31 (t, J ) 7.80 Hz, 1H), 7.12 (dd,
J ) 8.65, 2.20 Hz, 1H), 7.03 (d, J ) 7.80 Hz, 1H), 6.68-6.76
(m, 1H), 6.49 (s, 1H), 3.20-3.39 (m, 2H), 3.00-3.19 (m, 2H),
2.20-2.71 (m, 3H), 1.75-2.05 (m, 4H), 1.27 (d, J ) 5.42 Hz,
3H). Anal. (C21H23N3O3) C, H, N.
4-({2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-
5-ylmethyl}amino)pyridine-2,6-dicarbonitrile (6o). Com-
pound 6o was prepared according to method B (34%). 1H NMR
(CDCl3): δ 8.29 (s, 2H), 7.44 (d, J ) 1.36 Hz, 1H), 7.36 (d, J )
8.48 Hz, 1H), 7.18 (dd, J ) 8.48, 2.03 Hz, 1H), 6.41 (s, 1H),
5.47 (br, 1H), 4.64 (d, J ) 5.76 Hz, 2H), 3.14-3.29 (m, 2 H),
2.94-3.06 (m, 2 H), 2.34-2.56 (m, 2 H), 2.14-2.29 (m, 1 H),
1.88-2.00 (m, 1 H), 1.65-1.87 (m, 2 H), 1.39-1.51 (m, 1 H),
1.15 (d, J ) 5.42 Hz, 3H). Anal. (C23H23N5O·0.1CDCl3) C, H.
N: calcd, 17.47; found, 16.80.
2-({2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-
5-ylmethyl}amino)nicotinonitrile (6p). Compound 6p was
1
prepared according to method B (37%). H NMR (CDCl3): δ
8.32 (dd, J ) 4.92, 1.86 Hz, 1H), 7.67 (dd, J ) 7.63, 1.86 Hz,
1H), 7.47 (d, J ) 1.36 Hz, 1H), 7.38 (d, J ) 8.48 Hz, 1H), 7.21
(dd, J ) 8.48, 1.70 Hz, 1H), 6.63 (dd, J ) 7.63, 4.92 Hz, 1H),
6.43 (s, 1H), 5.43 (br, 1H), 4.76 (d, J ) 5.42 Hz, 2H), 3.14-
3.30 (m, 2 H), 2.94-3.08 (m, 2 H), 2.32-2.57 (m, 2 H), 2.12-
2.29 (m, 1 H), 1.88-2.01 (m, 1 H), 1.65-1.86 (m, 2 H), 1.38-
1.51 (m, 1 H), 1.14 (d, J ) 5.42 Hz, 3H). Anal. (C22H24N4O·
0.12H2O) C, H, N.
6-({2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-
5-ylmethyl}amino)nicotinonitrile (6q). Compound 6q was
1
prepared according to method B (39%). H NMR (CDCl3): δ
8.39 (d, J ) 1.70 Hz, 1H), 7.56 (dd, J ) 8.81, 2.37 Hz, 1H),
7.43 (d, J ) 1.36 Hz, 1H), 7.38 (d, J ) 8.48 Hz, 1H), 7.17 (dd,
J ) 8.48, 2.03 Hz, 1H), 6.42 (d, J ) 0.68 Hz, 1H), 6.38 (dd, J
) 8.81, 0.68 Hz, 1H), 5.37 (br, 1H), 4.61 (d, J ) 5.76 Hz, 2H),
3.14-3.29 (m, 2 H), 2.93-3.06 (m, 2 H), 2.32-2.55 (m, 2 H),
2.13-2.27 (m, 1 H), 1.87-2.02 (m, 1 H), 1.66-1.86 (m, 2 H),
1.37-1.51 (m, 1 H), 1.14 (d, J ) 6.10 Hz, 3H). Anal. (C22H24N4O)
C, H, N.
4-{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-
5-ylamino}benzonitrile (7b). Compound 7b was prepared
1
according to Method C (50%). H NMR (CDCl3): δ 7.35-7.50
(m, 3H), 7.31 (d, J ) 2.03 Hz, 1H), 7.03 (dd, J ) 8.65, 2.20 Hz,
1H), 6.80-6.87 (m, 2H), 6.45 (s, 1H), 6.00 (s, 1H), 3.19-3.38
(m, 2H), 3.06 (s, 2H), 2.41-2.67 (m, 2H), 2.17-2.38 (m, 1H),
1.69-2.09 (m, 4H), 1.20 (s, 3H). Anal. (C22H23N3O·0.22SiO2)
C, H, N.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
ylmethyl}(5-nitropyridin-2-yl)amine (6r). Compound 6r
was prepared according to method B (45%). 1H NMR (CDCl3):
δ 9.05 (d, J ) 2.71 Hz, 1H), 8.18 (dd, J ) 9.15, 2.71 Hz, 1H),
7.45 (s, 1H), 7.39 (d, J ) 8.14 Hz, 1H), 7.18 (dd, J ) 8.48, 1.70
Hz, 1H), 6.42 (s, 1H), 6.37 (d, J ) 9.15 Hz, 1H), 5.64 (br, 1H),
4.68 (d, J ) 5.76 Hz, 2H), 3.13-3.28 (m, 2 H), 2.92-3.07 (m,
2 H), 2.31-2.56 (m, 2 H), 2.13-2.27 (m, 1 H), 1.87-2.02 (m, 1
H), 1.65-1.86 (m, 2 H), 1.36-1.52 (m, 1 H), 1.14 (d, J ) 5.76
Hz, 3H). Anal. (C21H24N4O3) C, H, N.
2-Iodo-4-nitrophenol (12). Compound 12 was prepared
analogously to compound 8. The reaction was run for 5 days
at room temperature and was still not complete. Crude product
was used in the next step without further purification. 1H
NMR (MeOD-d4): δ 8.56 (d, J ) 2.71 Hz, 1H), 8.08 (dd, J )
9.16, 2.71 Hz, 1H), 6.80 (d, J ) 9.16 Hz, 1H).
3-{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-
5-ylamino}benzonitrile (7c). Compound 7c was prepared
1
according to Method C (43%). H NMR (CDCl3): δ 7.38 (d, J
) 8.82 Hz, 1H), 7.22-7.29 (m, 2H), 7.10-7.12 (m, 1H), 7.06-
7.09 (m, 1H), 7.05 (d, J ) 2.03 Hz, 1H), 7.00 (dd, J ) 8.65,
2.20 Hz, 1H), 6.44 (s, 1H), 5.75 (s, 1H), 3.19-3.36 (m, 2H),
3.01-3.15 (m, 2H), 2.41-2.65 (m, 2H), 2.20-2.36 (m, 1H),
1.67-2.07 (m, 4H), 1.20 (s, 3H). Anal. (C22H23N3O) C, H, N.
(5-Ethylpyrimidin-2-yl){2-[2-(2-(R)-methylpyrrolidin-
1-yl)ethyl]benzofuran-5-yl}amine (7d). Compound 7d was
1
prepared according to method C (43%). H NMR (CDCl3): δ
8.26 (s, 2H), 7.79 (d, J ) 2.03 Hz, 1H), 7.31-7.41 (m, 1H),

H3 Receptor Antagonists with Improved Potency
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20 6489
7.22-7.31 (m, 1H), 6.99 (s, 1H), 6.43 (s, 1H), 3.12-3.32 (m,
2H), 2.89-3.08 (m, 2H), 2.53 (q, J ) 7.80 Hz, 2H), 2.32-2.46
(m, 2H), 2.24 (m, 1H), 1.88-2.02 (m, 1H), 1.66-1.88 (m, 2H),
1.40-1.55 (m, 1H), 1.23 (t, J ) 7.63 Hz, 3H), 1.15 (d, J ) 6.10
Hz, 3H). Anal. (C21H26N4O) C, H, N.
were plated at a density of 60 000 cells/mL onto collagen-coated
culture slide chambers (Becton Dickinson Labware, Bedford,
MA) and incubated overnight at 37 °C and 5% CO2 until use
in the phospholipidosis measurement.
Phospholipidosis Assay. Accumulation of phospholipids
was assessed by quantitating the accumulation of a fluorescent
probe N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)dipalmitoylphos-
phatidylethanolamine (NBD-PE, Molecular Probes Inc., Eu-
gene, OR) into lamellar bodies.26 NBD-PE was suspended in
ethanol and diluted to a concentration of 50 µM in Phenol-
Red serum-free modified DMEM media containing 2 mM
L-glutamine, 0.3 mM of nonessential amino acids solution, 22
µg/L gentamicin, 2 mM NaHCO3, 10 mM Hepes, and 2 mM
D-fructose adjusted to pH 7.4 with a final ethanol concentration
of 0.46%. The mixture was placed into a sonicating water bath
for 30 min and then filtered through a 0.22 µm filter.
Compounds were dissolved in DMSO and then diluted into the
above culture medium to a final concentration of 18.8, 37.5,
75, or 150 µM with a 0.1% final DMSO concentration. Hepa-
tocytes were treated for 24 h with the test compounds or
vehicle (0.1% DMSO) and 50 µM NBD-PE in at 37 °C and 5%
CO2. Cells were washed three times with the above media
(without NBD-PE), and then fixed with 3.5% paraformalde-
hyde in phosphate-buffered saline (PBS), pH 7.4, and stored
at 4 °C. Brightfield and fluorescence (NBD-PE, excitation 463/
emission 536) images were acquired using a Leica DMIRE
inverted fluorescence microscope (Wetzlar, Germany) and
Optronics DEI 750 videocamera (Goleta, CA). Quantitation of
the cell area percent occupied by fluorescent granules in
hepatocytes exposed to various concentrations of test com-
pound (n ) 2 wells per dose) was performed using Leica QWIN
image analysis software. An increase in the area percent of
fluorescence is used as a surrogate for phospholipidosis.29
Results were normalized to amiodarone,27 a known inducer of
phospholipidosis used as a positive control, and expressed as
a “phospholipidosis index”. A value g0.9 indicated that the
compound induces phospholipidosis to the same extent as
amiodarone and is considered to be a potent inducer of
phospholopidosis. Moderate inducers have a phopholipidosis
index in the range of 0.50-0.90, and a value e0.5 is inter-
preted as a compound with minimal effect.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
yl}pyrimidin-2-ylamine (7e). Compound 7e was prepared
1
according to method C (59%). H NMR (CDCl3): δ 8.39 (d, J
) 4.75 Hz, 2H), 7.79 (d, J ) 2.03 Hz, 1H), 7.34-7.40 (m, 1H),
7.29 (d, J ) 2.37 Hz, 1H), 7.09 (s, 1H), 6.68 (t, J ) 4.92 Hz,
1H), 6.44 (s, 1H), 3.16-3.31 (m, 2H), 2.94-3.08 (m, 2H), 2.35-
2.59 (m, 2H), 2.17-2.32 (m, 1H), 1.89-2.04 (m, 1H), 1.60-
1.87 (m, 2H), 1.43-1.55 (m, 1H), 1.17 (d, J ) 5.76 Hz, 3H).
Anal. (C19H22N4O·0.12H2O) C, H, N.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
yl}pyrimidin-5-ylamine (7f). Compound 7f was prepared
according to method C (59%). 1H NMR (CDCl3): δ 8.70 (s, 1H),
8.40 (s, 2H), 7.39 (d, J ) 8.48 Hz, 1H), 7.22-7.33 (m, 1H),
7.01 (dd, J ) 8.65, 2.20 Hz, 1H), 6.43 (s, 1H), 5.60 (s, 1H),
3.16-3.37 (m, 2H), 2.97-3.12 (m, 2H), 2.38-2.63 (m, 2H),
2.19-2.35 (m, 1H), 1.92-2.05 (m, 1H), 1.66-1.88 (m, 3H), 1.19
(d, J ) 5.76 Hz, 3H). Anal. (C19H22N4O) C, H, N.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
yl}pyrazin-2-ylamine (7g). Compound 7g was prepared
1
according method A (12%). H NMR (CDCl3): δ 8.15 (d, J )
1.36 Hz, 1H), 8.04-8.10 (m, 1H), 7.94 (d, J ) 2.71 Hz, 1H),
7.55 (d, J ) 2.03 Hz, 1H), 7.40 (d, J ) 8.81 Hz, 1H), 7.16 (dd,
J ) 8.65, 2.20 Hz, 1H), 6.50 (s, 1H), 6.44 (s, 1H), 3.17-3.30
(m, 2H), 2.94-3.09 (m, 2H), 2.33-2.61 (m, 2H), 2.17-2.30 (m,
1H), 1.90-2.05 (m, 1H), 1.63-1.88 (m, 2H), 1.39-1.57 (m, 1H),
1.16 (d, J ) 5.76 Hz, 3H). Anal. (C19H22N4O·0.12H2O) C, H, N.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
yl}(5-nitropyridin-2-yl)amine (7h). Compound 7h was pre-
pared according to method C (42%). 1H NMR (CDCl3): δ 9.08
(d, J ) 2.71 Hz, 1H), 8.20 (dd, J ) 9.16, 2.71 Hz, 1H), 7.40-
7.50 (m, 2H), 7.20 (s, 1H), 7.13 (dd, J ) 8.48, 2.37 Hz, 1H),
6.64 (d, J ) 9.49 Hz, 1H), 6.48 (s, 1H), 3.16-3.32 (m, 2H),
2.95-3.10 (m, 2H), 2.35-2.62 (m, 2H), 2.15-2.31 (m, 1H),
1.89-2.05 (m, 1H), 1.68-1.88 (m, 2H), 1.35-1.58 (m, 1H), 1.16
(d, J ) 5.76 Hz, 3H). Anal. (C20H22N4O3) C, H, N.
{2-[2-(2-(R)-Methylpyrrolidin-1-yl)ethyl]benzofuran-5-
yl}(3-nitropyridin-2-yl)amine (7i). Compound 7i was pre-
pared according to method C (75%). 1H NMR (CDCl3): δ 10.08
(s, 1H), 8.52 (dd, J ) 8.48, 1.69 Hz, 1H), 8.45 (dd, J ) 4.41,
1.70 Hz, 1H), 7.75 (d, J ) 2.03 Hz, 1H), 7.37-7.49 (m, 1H),
7.29-7.37 (m, 1H), 6.79 (dd, J ) 8.31, 4.58 Hz, 1H), 6.48 (s,
1H), 3.16-3.35 (m, 2H), 2.93-3.14 (m, 2H), 2.39-2.64 (m, 2H),
2.14-2.35 (m, 1H), 1.90-2.07 (m, 1H), 1.62-1.87 (m, 3H), 1.18
(s, 3H). Anal. (C20H22N4O3) C, H, N.
Supporting Information Available: Results from com-
bustion analysis. This material is available free of charge via
the Internet at http://pubs.acs.org.
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